efffect of alloy elements on haz mico and toughness_001

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ISSN 1018-5593

European Commission

t e c h n i c l s t e e l r e s e r c h

Properties and service performance

Effect of alloying elements on HAZmicrostructure and toughness

STEEL RESEARCH



LEGAL NOTICE

Neither the European Commission nor any person acting on

behalf of the Commission is responsible for the use which might be made of the

following information

Cataloguing data can be found at the end of this publication

Luxembourg: Office for Official Publications of the European Communities, 1996

ISBN 92-827-7203-9

© ECSC-EC-EAEC, Brussels · Luxembourg, 1996Reproduction is authorized, except for commercial purposes, provided the source is acknowledged

Printed in L uxembourg



LIST OF TABL ES

1. Chem ical Composition of Exp erime ntal Steels

2. Sum ma ry of Bead in Groove Welding Conditions

3 . Summ ary of Parent Plant Tensile Data

4. Par ent Pla te Charpy Impact Data

5. Sum ma ry of Bead in Groove HAZ Ch arpy Data

6. Sum ma ry of Bead in Groove HAZ CTO D Data

7. Sum ma ry of Simulated HAZ Cha rpy Res ults at 0 and -40°C

8. Sum ma ry of Qu antitativ e Optical M etallogra phy for the HAZ of 3.5 kJ /m m Bead in GrooveWelds

9. Sum ma ry of Qu antitive Optical M etallograp hy for the HAZ of 7.5 kJ /m m Bead in GrooveWelds

10. Sum ma ry of SEM Metallography

11 . HAZ Width Me asuremen ts 3.5 kJ/mm Welds

12 . HAZ Width M easuremen ts 7.5 kJ/mm Welds

13 . Sum mary of HAZ Grain Size Me asurem ents

14. Sum mary of HAZ Hard ness Measu rements15. Com parison of HAZ Toughness Data for Bead in Groove and Sim ula ted GCHAZ Regio ns

IV



L I S T O F F I G U R E S

1 . B ead in Groove We ld ing P roc edu r es

2. P ho tom acro g raph s o f Typ ica l B ead in Groove W elds

3 . T h e r m a l C y c le s f or G C H A Z a n d I C G C H A Z S i m u l a t i o n s

4. C las s i f ica t ion o f M ic ros t ruc tu r e to I IW S chem e

5. S u m m a r y o f P a r e n t P l a t e T e n s i l e D a t a

6 . C ha rpy Tran s i t ion C ur ves fo r P a ren t P la t e s

7 . S u m m a r y o f P a r e n t P l a t e C h a r p y 4 0 J T r a n s i t i o n T e m p e r a t u r e s

8 . C ha rpy Tran s i t ion C u rves for B ead in Groove HA Zs

9 . S um m ary o f B ead in Groove HAZ C h arpy 40 J T ra ns i t ion Te m pe ra tu r e s

10. C TO D Tran s i t ion C u rves for B ead in Groove HA Zs

11 . S u m m a r y of B e a d i n G r o o v e H A Z 0 .1 m m C T O D T r a n s i t i o n T e m p e r a t u r e s

12. S u m m a r y o f S i m u l a t e d G r a i n C o a r s e n e d H A Z C h a r p y D a t a ( 3 .5 k J / m m )

13 . S u m m a r y of S i m u l a t e d G r a i n C o a r s e n e d H A Z C h a r p y D a t a ( 7. 5 k J / m m )

14. S u m m a r y o f S i m u l a t e d I n t e r c r i t i c a l l y R e h e a t e d G r a i n C o a r s e n i n g H A Z C h a r p y D a t a(3 .5 kJ /mm)

15. S u m m a r y of S i m u l a t e d I n t e r c r i t i c a l l y R e h e a t e d G r a i n C o a r s e n i n g H A Z C h a r p y D a t a( 7 . 5 k J / m m )

16 . Opt ica l Mic rog raphs I l lu s t r a t ing the HAZ o f 3 .5 k J /m m B ea d in Groove W elds

17. Opt ica l Mic ro g raphs I l lu s t r a t ing the HAZ o f 7 .5 k J /m m B ead in Groove W elds

18. Opt ica l Mic rog raphs o f Gr a in C oa r s ened HA Z R eg ions o f 3 .5 k J /m m B ead in Groove Welds

19. Opt ica l Mic ro g raphs of Gr a in C oa r s ened HA Z R eg ions o f 7 .5 k J / m m B ead in Groove Welds

2 0 . Gr a in C oar s ened HAZ C o lony S ize Ve r s us Weld H ea t I np u t

2 1 . Opt ica l Mic rog raphs I l lu s t r a t in g the L igh t E tc h in g Zone a t t he F us ion B o und ary in S tee l Ga t 7 .5 k J /mm

2 2 . Effec t o f C a rbon on GC H AZ Mic rophas e C o n ten t

2 3 . Effect of Al loying of M-A Fra ct i on in the CG HA Z of Bead in Groove W elds

2 4 . Inf luence of Va nad ium on GC H AZ M ic ros t ruc tu r e and Tou ghn es s o f 7 .5 k J /m m B ead inGroove Welds

2 5. Inf luence of T i t an i um on GC H AZ M ic ros t ruc tu r e and Tou ghne s s o f 7 .5 k J / m m B ead in

Groove Welds

V



26. Influence of Alu min ium on GCHAZ M icrostr uctu re and Tou ghne ss of 7.5 kJ/m m Bead inGroove Welds

27. Influence of Boron on GCHAZ M icrostr uctu re and Toug hness of 7.5 kJ/ m m Bead in GrooveWelds

28. Influence of HAZ Microstructure on Ch arpy 40 J Te m pe ratu re of 7.5 kJ/ m m Bead in GrooveWelds

29. Results of Mult iple Linear Regression Ana lyses between M icrostructural Fe atur es andToughness of 7.5 kJ/m m Bead in Groove HAZ s

30 . Multiple Linea r Regression between M-Α Fra ction Gra in Size and 0.1 mm CTOD Tra nsiti onfor 7.5 kJ/mm Bead in Groove HAZs

31. Effect of HAZ Ha rdne ss on 0.1 mm CTOD Te m pe ratu re for 7.5 kJ/m m Bead in Groove HAZs

32. Resu lts of M ultiple Line ar Regression An alyse s Between Gra in Size, M-Α Frac tion , Ha rdn essand Tough ness of 7.5 kJ/m m Bead in Groove HAZs

VI



TABLE DES MATIERES PAGE

1. INTRODUCTION 1

2. LE CONTEXTE : LA SELECTION DES ACIERS 1

3. LA PROCEDURE EXPERIMENTALE 2

3.1 Coulées 2

3.2 Soudure et simulations thermiques 23.3 Essais Charpy et élargissement de crique 33.4 Propriétés métallographiques et dureté 3

4. RESULTATS 3

4.1 Propriétés : métal de base 34.2 Propriétés : essai Charpy en Z.A.T. 4

4.3 Propriétés : élargissement de crique en Z.A.T. 44.4 Propriétés : Z.A.T. simulées 44.5 Propriétés métallographiques et dureté 4

5. DISCUSSION 5

5.1 L'effet d'éléments d'alliage sur lesmicrostructures Z.A.T. à gros grains 5

5.2 L'effet d'éléments d'alliage sur larésistance Z.A.T. à gros grains 9

5.3 L'effet d'éléments d'alliage sur larésistance Z.A.T. à gros grains inter-critiquement chauffée 12

5.4 Rapports structures/propriétés Z.A.T. 13

6. CONCLUSIONS 15

7. REFERENCES 16

TABLES 18

FIGURES 34

V



LISTE DES TABLES

1. La composition chimique des aciers expérimentaux

2. Résumé des conditions de soudage à cordon-en-rainure

3. Métal de base : essais de traction

4. Métal de base : essais Charpy

5. Soudures à cordon-en-rainure : essais Charpy/Z.A.T.

6. Soudures à cordon-en-rainure : essais d'élargissement decrique/Z.A.T.

7. Z.A.T. simulées : résultats Charpy à 0 et -40°C

8. Propriétés métallographiques optiques quantitatives/Z.A.T.pour soudures à cordon-en-rainure 3.5 kJ/mm

9. Propriétés métallographiques optiques quantitatives/Z.A.T.pour soudures à cordon-en-rainure 7,5 kJ/mm

10. Propriétés métallographiques/balayage électronique desurface

11. Mesure des largeurs Z.A.T. - soudures 3,5 kJ/mm

12. Mesure des largeurs Z.A.T. - soudures 7,5 kJ/mm

13. Mesures granulométriques Z.A.T.

14. Mesures de dureté Z.A.T.

15. Données comparatives : dureté Z.A.T. soudures à cordon-en-rainure et Z.A.T. à gros grains simulées

IX



LISTE DES FIGURES

1. Procédés de soudage à cordon-en-rainure

2. Macrophotographies de soudures à cordon-en-rainure types

3. Cycles thermiques : simulations

4. Classification IIS des microstructures

5. Métaux de base : données de traction

6. Métaux de base : courbes de transition Charpy

7. Métaux de base : températures de transition Charpy 40J

8. Courbes de transition Charpy pour Z.A.T. cordon-en-rainure

9. Températures de transition Charpy 40J/Z.A.T. cordon-en-rainure

10. Courbes de transition/élargissement de crique pour Z.A.T.cordon-en-rainure

11. Températures de transition de soudures à cordon-en-rainure: Z.A.T/élargissement de crique 0,1 mm

12. Données Charpy : Z.A.T. à gros grains simulée (3,5 kJ/mm)

13. Données Charpy : Z.A.T. à gros grains simulée (7,5 kJ/mm)

14. Données Charpy : Z.A.T. simulée à gros grains chaufféeentre points critiques (3,5 kJ/mm)

15. Données Charpy : Z.A.T. simulée à gros grains chaufféeentre points critiques (7,5 kJ/mm)

16. Micrographies optiques : Z.A.T./soudures à cordon-en-rainure (3,5 kJ/mm)

17. Micrographies optiques : Z.A.T./soudures à cordon-en-rainure (7,5 kJ/mm)

18. Micrographies optiques : Z.A.T. à gros grains de souduresà cordon-en-rainure (3,5 kJ/mm)

19. Micrographies optiques : Z.A.T. à gros grains de souduresà cordon-en-rainure (7,5 kJ/mm)

20. Colonie Z.A.T. à gros grains par rapport à la chaleurd entrée

21. Micrographies optiques : zone de corrosion à la limite defusion - acier G à 7,5 kJ/mm

22. L effet du carbone sur le contenu de la microphase de laZ.A.T. à gros grains

23. L effet de l alliage sur une fraction M-Α dans la Z.A.T àgros grains de soudures à cordon-en-rainure



24. L effet du vanadium sur la microstructure et la résistancedans la Z.A.T. à gros grains de soudures à cordon-en-rainure. (7,5 kJ/mm)

25. L effet du titanium sur la microstructure et la résistancedans la Z.A.T. à gros grains de soudures à cordon-en-rainure (7,5 kJ/mm)

26. L effet de l aluminium sur la microstructure et larésistance dans la Z.A.T. à gros grains de soudures àcordon-en-rainure (7,5 kJ/mm)

27. L effet du bore sur la microstructure et la résistance dansla Z.A.T. à gros grains de soudures à cordon-en-rainure(7,5 kJ/mm)

28. L effet de la microstructure Z.A.T. sur la température detransition (Charpy 40 J) de soudures à cordon-en-rainure(7,5 kJ/mm)

29. Résultats d analyses par régression linéaire multiple :grosseur du grain, fraction M-Α, dureté et résistance deZ.A.T. cordon-en-rainure à 7,5 kJ/mm

30. Régression linéaire multiple entre la grosseur du grain dela fraction M-Α et la température de transition 0,1 mm CTODpour des Z.A.T. de soudures à cordon-en-rainure (7,5 kJ/mm)

31. L effet de la dureté Z.A.T. sur une température CTOD 0,1 mmpour des Z.A.T. de soudures à cordon-en-rainure (7,5 kJ/mm)

32. Résultats des analyses par régression linéaire multiple :grosseur du grain, fraction M-Α, dureté et résistance desZ.A.T. de soudures à cordon-en-rainure (7,5 kJ/mm)

XI



Effekt der Legierungselemente auf das Mikrogefüge und auf dieZähigkeit in der wärmebeeinflußten Zone

British Steel pie

EGKS Vertrag Nr. 7210.KA/816

Zusammenfassung

Man hat siebzehn experimentelle Stahlgüsse zur Bewertung der V-,Ti-, Al-, Β-, Ν- und Si-Auswirkungen auf das Mikrogefüge und aufdie Zähigkeit in der WEZ eingesetzt und zwar mit verschiedenenVerbindungen der Legierungselemente. In allen siebzehn Stählenwurden Rillen ins Grobblech gefräst und daran entlang bei 3,5 und7,5 kJ/mm im UP-Lichtbogenverfahren geschweißt, damit Schweiß-raupen in der WEZ erzeugt werden konnten. Die Wärmesimulationensind bei der selben Wärmezufuhr durchgeführt worden. Man hat dieZähigkeit der Schweißraupen anhand der Charpy-, Gleeble-Charpy

und CTOD-Testverfahren bewertet, die für diese Methode vorge-schrieben worden sind. Die mit dieser Methode in der WEZproduzierten Mikrogefüge wurden voll anhand der quantitativoptischen und SEM-Techniken charakterisiert.

Die Ergebnisse haben gezeigt, daß eine Beziehung zwischen derZähigkeit in der WEZ und den Mikrogefügen in der WEZ besteht, unddaß dies eine Funktion der chemischen Zusammensetzung der Stähleund des Wärmeübertragungssystems während des Schweißens ist. Manhat beobachtet, daß die Zähigkeit in der WEZ gegen das Ausmaß derM-A-Bestandteile (Martensit/Austenit), die Härte (bzw.Streckgrenze) und grobkörnigen Koloniegrößen in der WEZ

empfindlich ist. In diesem Falle werden die Charpy-Daten stärkervon der Korngröße beeinflußt, und die CTOD-Daten sindempfindlicher gegen das Ausmaß der M-A-Bestandteile. Man konntezeigen, daß die individuellen Elemente komplizierter sind undhäufig vom betroffenen Legierungssystem abhängig sind. DieErgebnisse haben vorangegangene Abhandlungen in der Literaturbestätigt, d.h., daß kleine Vanadium- und Titanzusätze die Zähig-keit in der WEZ fördern und besonders bei niedriger Wärmezufuhr.Bei einer höheren Wärmezufuhr hat man aber beobachtet, daß dieseElemente nicht immer die Zähigkeit in der WEZ fördern, und hierist der genaue Effekt jedes Elements vom Zusammenspiel derverschiedenen Mikrogefügefaktoren abhängig gewesen. Silizium hateinen merklich nachteiligen Einfluß auf CTOD in der WEZ wegenFörderung der M-A-Bestandteile, aber man konnte keinenkonsistenten Effekt auf die Charpy-Zähigkeit beobachten.Aluminium wirkt sich allgemein vorteilhaft auf die Zähigkeit inder WEZ bei Vanadiumstählen aus, aber es hat die Zähigkeit derTi-B-Stähle stark gehemmt und zwar wegen Zunahme der M-A-Bestand-teilmenge, Steigerung der Härte und Fragmentreduzierung desnadeiförmigen Ferrits. Boron fördert die Zähigkeit in der WEZ beialuminiumarmen Stählen, weil der freie Stickstoff und die M-A-Mengen reduziert und das intergranulare Ferrit verstärkt werden.Der Gesamtstickstoffgehalt hat keinen konsistenten Effekt auf dieZähigkeit in der WEZ bei einen V-Ti-Stahl aufgewiesen, das heißt,manche Versuche zeigen einen vorteilhaften Effekt und manche

einen nachteiligen.

X



Inhaltsverzeichnis Seite

1. Einleitung 1

2. Vorgeschichte zur Wahl der Stähle 1

3. Experimentelles Verfahren 2

3.1 Stahlgüsse 23.2 Schweiß- und Wärmesimulationen 23.3 Charpy- und CTOD-Versuche 33.4 Metallographie und Härte 3

4. Ergebnisse 3

4.1 Eigenschaften der Grundgrobbleche 34.2 Charpy-Eigenschaften in der WEZ 44.3 CTOD-Eigenschaften in der WEZ 4

4.4 Simulierte Eigenschaften in der WEZ 44.5 Metallographie- und Härtedaten 4

5. Diskussion 5

5.1 Effekt der Legierungselemente auf diegrobkörnigen Mikrogefüge in der WEZ 5

5.2 Effekt der Legierungselemente auf diegrobkörnige Zähigkeit in der WEZ 9

5.3 Effekt der Legierungselemente auf dieinterkritische, wiedererwärmte undgrobkörnige Zähigkeit in der WEZ 12

5.4 Gefüge in der WEZ/Beziehungen zwischenden Eigenschaften 13

6. Schlußfolgerungen 15

7. Literaturverzeichnis 16

Tabellen 18

Abbildungen 34

XIV



Aufstellung der Tabellen

1. Chemische Zusammensetzung der experimentellen Stähle

2. Übersicht der Bedingungen für Schweißraupen im Grobblech

3. Übersicht der Zugdaten für Grundgrobbleche

4. Charpy-Kerbschlagzähigkeitsdaten für Grundgrobbleche

5. Übersicht der Charpy-Daten für Schweißraupen in der WEZ

6. Übersicht der CTOD-Daten für Schweißraupen in der WEZ

7. Übersicht der simulierten Charpy-Ergebnisse in der WEZ bei 0und -40°C

8. Übersicht der quantitativ optischen Metallographie für

Schweißraupen in der WEZ bei 3,5 kJ/mm

9. Übersicht der quantitativ optischen Metallographie fürSchweißraupen in der WEZ bei 7,5 kJ/mm

10. Übersicht der SEM-Metallographie

11. Breitenmessung in der WEZ - Schweißungen bei 3,5 kJ/mm

12. Breitenmessung in der WEZ - Schweißungen bei 7,5 kJ/mm

13. Übersicht der Korngrößenmessungen in der WEZ

14. Übersicht der Härtemessungen in der WEZ

15. Vergleich der Zähigkeitsdaten für Schweißraupen und simulierte grobkörnige Bereiche in der WEZ

XV



Aufstellung der Abbildungen

123,

5.6.7.

8.9.

10.

11

12.

13.

14.

15.

16.

17.

18.

19.

20.

21 .

22.

23.

24.

25.

26.

27.

28.

29.

Schweißvorgang für Schweißraupen im GrobblechPhotomakrographe typischer SchweißraupenWärmeübertragung für grobkörnige und interkritische, grobkörnige SimulationenKlassifizierung des Mikrogefüges gemäß dem Schema des IIW-InstitutesÜbersicht der Zugdaten für GrundgrobblecheCharpy-übergangskurven für GrundgrobblecheÜbersicht der Charpy 40J Übergangstemperaturen für GrundgrobblecheCharpy-übergangskurven für Schweißraupen in der WEZÜbersicht der Charpy 40J Übergangstemperaturen für Schweißraupen in der WEZCTOD-Übergangskurven für Schweißraupen in der WEZÜbersicht der CTOD-übergangstemperaturen für Schweißraupen inder WEZ (0,1 mm)

für die simulierte, grobkörnigebersicht derWEZ (3,5 kJ/mm)Übersicht derWEZ (7,5 kJ/mm)Übersicht der

Charpy-Daten

Charpy-Daten für die simulierte, grobkörnige

für dieharpy-Datentische, wiedererwärmte und grobkörnigeÜbersicht der Charpy-Daten für dietische, wiedererwärmte und grobkörnigeOptischeWEZ (3,5OptischeWEZ (7,5

Optische

i 1lustrieren

derkJ/mmderkJ/mm

grobkörnigen

grobkörnigen

MikrographekJ/mm)MikrographekJ/mm)

MikrographeSchweißraupen bei 3,5Optische MikrographeSchweißraupen bei 7,5Grobkörnige Koloniegrößebeim SchweißenOptische Mikrographe illustrieren dieder Verschmelzunggrenze in Stahl G beiEffekt des Kohlenstoffshalt in der WEZEffekt der M-A-FragmentlegierungSchweißraupen in der WEZ

simulierte, interkri-WEZ (3,5 kJ/mm)simulierte, interkri-

WEZ (7,5 kJ/mm)die Schweißraupen in der

illustrieren die Schweißraupen in der

Bereiche in der WEZ,

Bereiche in der WEZ

in der WEZ gegen die Wärmezufuhr

leicht geätzte Zone an7,5 kJ/mm

auf den grobkörnigen Mikrophasenge-

auf die grobkörnigen

derinfluß des Vanadiums auf das grobkörnige Mikrogefüge inWEZ und die Zähigkeit der Schweißraupen bei 7,5 kJ/mmEinfluß des Titans auf das grobkörnige Mikrogefüge in der WEZund die Zähigkeit der Schweißraupen bei 7,5 kJ/mmEinfluß des Aluminiums auf das grobkörnige Mikrogefüge in derWEZ und die Zähigkeit der Schweißraupen bei 7,5 kJ/mmEinfluß des Borons auf das grobkörnige Mikrogefüge in der WEZund die Zähigkeit der Schweißraupen bei 7,5 kJ/mmEinfluß des Mikrogefüges in der WEZ auf die Schweißraupen bei40J Temperaturen und 7,5 kJ/mmErgebnisse der mehrfachlinearen Regressionsanalysen zwischenden Mikrogefügemerkmalen und der Zähigkeit der Schweißraupenin der WEZ bei 7,5 kJ/mm

XVI



3 0 . Meh rfac hl ineare Regressio n z w isc h en der K o rngrö ße des M-A -Fra gm entes und der 0 ,1 m m CT OD - Ü bergan gstem p eratur fürSc h w eiß raup en in der WEZ bei 7,5 k J/ mm

3 1 . Eff ek t der H ä rte in der WEZ auf den 0,1 mm C TO D- Ü berg ang fürSc h we iß raup en in der WEZ bei 7,5 kJ /m m

3 2 . Ergebnis se der me h rfac h 1 inearen Regre ssio nsana ly se z w isc h ender K o rngrö ß e , dem M- A - Fra gm ent, der H ä rte und Z ä hig k eit fürSc h wei ßrau pen bei 7 , 5 k J / m m

XVll



T H E E F F E C T O F A L L O Y IN G E L E M E N T S O N H A Z M I C R O S T R U C T U R E A N D T O U G H N E S S

Bri t ish S tee l p ic

E C S C A g r e e m e n t N u m b e r 7 2 1 0 . K A / 8 1 6

F I N A L T E C H N I C A L R E P O R T

1. I N T R O D U C T I O N

High hea t inpu t we ld ing o ff er s adv an t age s to the f ab r i ca to r in r educed we ld ing cos t s . How ever , hea ta f f ec ted zone (HAZ) toughnes s de te r io r a t e s marked ly in s t ee l s a s hea t inpu t inc r eas es and a t p r e s en t , f o rc r i t i ca l app l i ca t ions , hea t inpu t s t end to be l imi t ed to abo u t 3 to 5 k J / m m . In s ome ind us t r i e s , f or exam ples h ipbu i ld ing and the o f f s ho re indus t ry , l a rge cos t s av ings cou ld be made i f hea t inpu t s cou ld be s a f e lyinc reas ed above cu r r en t l eve l s . HAZ toughnes s i s r e l a t ed to HAZ mic ros t ruc tu r e and th i s i s a f unc t ion o fs t ee l chemica l compos i t ion and we ld the rma l cyc le . I n pa r t i cu la r , i t i s known tha t low HAZ toughnes s i sa s s o c i a t e d w i t h c o a r s e g r a i n e d m i c r o s t r u c t u r e s w h i c h c o n s i s t o f W i d m a n s t ä t t e n s i d e p l a t e s o r u p p e r

b a i n i t e . I n t h e s e m i c r o s t r u c t u r e s , t h e W i d m a n s t ä t t e n o r b a i n i t i c f e r r i t e g r a i n s a r e s e p a r a t e d b y l ow a n g l eboundar i e s and thus the ' e f f ec t ive ' g r a in s i ze , o r the c l eavage f r ac tu r e f ace t s i ze , i s t ha t o f the ba in i t e o rs idep la t e co lony. Moreove r , t he r e i s now a body o f da ta w h ich ind ica te th a t the p r e s enc e of mar ten s i t e -a u s t e n i t e ( M - Α ) m i c r o p h a s e s i n e i t h e r i n t e r o r i n t r a g r a n u l a r l o c a t i o n s a r e a l s o d e t r i m e n t a l t o H A Ztoughnes s .

F rom we ld me ta l s tud ie s i t appea r s tha t ce r t a in a l loy ing combina t ions can d i s cou rage the deve lopmen t o fba in i t e / s ide p la t e s t r uc tu r e s in f avou r o f the f ine g r a ined p has e know n as ac icu la r f e r r i t e a nd the r e byimprove tough nes s . Th i s app ro ach i s now be ing app l i ed by s ome s t ee l man ufa c tu re r s to hea t a f fec tedzones* 1 ' and the r e appea r s to be cons ide ra b le s cope for f u r the r s tu d ie s on s e l ec ted a l loy ing e l e m en tc o m b i n a t i o n s t o i m p r o v e H A Z m i c r o s t r u c t u r e a n d t o u g h n e s s .

The ob jec t ives o f th i s p ro jec t were thus to s tudy a r an ge o f a l loy ing e l e me n t com bina t ion s in o rde r to a s s es sthe i r e f f ec t s on HAZ mic ros t ruc tu r e and toughnes s in h igh hea t inpu t we ld s . The e l emen t s o f pa r t i cu la rin t e r e s t were thos e wh ich a r e know n to in f luence the deve lo pm en t o f tough m ic ro s t ruc tu r e s in C -Mn we ldmeta l s .

2 . B A C K G R O U N D T O S T E E L S E L E C T I O N

I n w e l d m e t a l s a n u m b e r o f e l e m e n t s e n h a n c e a c i c u l a r f e r r i t e d e v e l o p m e n t a n d t h u s i m p r o v e m e c h a n i c a lp rope r t i e s . The s e inc lude V, T i , Β , Al and S i . Th e p r ec i s e am ou n t o f each e l em en t r eq u i r e d to p roduc e theop t imum we ld me ta l mic ro s t ruc tu r e d i f f e r s and i s be l i eved to be dependen t , t o s ome ex ten t , on the ove ra l lha rd ena b i l i ty o f the we ld depos i t and the in f luence o f each e l em en t on ac icu la r f e r r i t e nuc le a t ion .

Vanad ium has been s hown to p romote ac icu la r f e r r i t e in s ome we ld me ta l s * 2 1 . Heat af fec ted zone s tudieshave a l s o iden t i f i ed van ad i um as be ing capa b le of p ro mo t ing ac icu la r f e r r i t e l i ke m ic ro s t ru c tu r e s in theHAZ o f h igh hea t inpu t we ld s * 3 · 4 ' and th i s had gen e ra l ly been a s s oc ia t ed wi th an imp rov em en t in HAZtoughnes s .

T i t an ium i s gene ra l ly accep ted a s be ing one o f the mos t impor tan t e l emen t s in p romot ing ac icu la r f e r r i t ein we ld m e ta l s . On ly s ma l l concen t r a t ion s of t i t a n iu m a r e r equ i r ed to p rom ote ac ic u la r f e r r i t e in we ldmeta ls because the main inf luence of Ti i s be l ieved to be through i ts ef fec t on fer r i te nucleat ion f rom Ticon ta in ing ox ide inc lu s io n^ ) . I n HA Zs , t i t an ium h as u s ua l ly been u s ed in com bina t ion w i th n i t r oge n tofo rm f ine T iN pa r t i c l e d i s t r ibu t ions wh ich r e s t r i c t au s t en i t e g r a in coa r s en ing in the HAZ ( 6 ) . However ,m o r e r e c e n t s t e e l m a k i n g d e v e l o p m e n t s h a v e i n v o lv e d t h e u se of t i t a n i u m t o p r o m o t e i n t r a g r a n u l a r f e r r i tenuc lea t ion ( i . e . ac i cu la r f e r r i t e ) by deve lop ing t i t an ium-bo ron and t i t an ium ox ide s t ee l s s .



Boron is used in combination with titanium in weld metals in order to increase the volume fraction ofacicular ferrite developed. The mech anism is believed to involve protection of boron from nitro gen bytitani um . This allows some 'active' boron to segregate to prior aus teni te grain b ou nda ries w here it re duces

grain boundary energy and hence suppresses the nucleation of proeutectoid ferrite*

91

. In the HAZ s of Ti-Bsteels, boron has been reported to promote intragranular ferrite due to the formation of complex secondphase particles (e.g. TiN + MnS + Fe23(CB)g) which p rom ote a cicu lar ferri te nucleation*7». Boron in theform of BN ha s been reported to prom ote ferrite nu cleation in the HAZ of a recen tly d eveloped low A l-B-Nsteel which is reported to have h igh HAZ toughness over a very wide range of hea t in puts* 1 0 '.

Aluminium is an element which is now recognised to promote acicular ferrite in weld metals when presentat low levels. How ever, at higher levels it inhib its acicula r ferrite developm ent. A m ech anis m whichcould account for this is one in which the aluminium containing spinel ΜηΟΑΐ2θ3 (Galaxite) acts as anactive substrate for acicular ferrite nucleation*11 ' . Acicular ferrite development in weld metal is thereforesensitive to A1:0 ratio and in some systems may be maximised at about stoichiometry for ΜηΟΑΐ2θ3 (1 2 '.In HAZs aluminium has been reported to be beneficial to toughness when present at high levels due toremoval of'free' nitrogen*13 ' . How ever, some of the newly developed steels such a s the T i- 0 an d low Al-B-N types rely on low levels of Al to achieve the necessary p articles for promoting ferrite nuc leatio n.

Silicon has received relatively little attention in terms of its effects on weld metals microstructure.However, at least two stud ies had revealed optimum silicon levels and it is believed th at the op tim um levelis related to other aspects of weld me tal chemistry such as the hard ena bility a nd deoxid ation s tate . InHAZs silicon has generally been observed to have a detrimental effect on toughness due to the promotionofM-Aphases(14,15,16).

3 . E X P E R I M E N T A L P R O C E D U R E

3.1 Stee l Ca sts

A series of 50 kg vacuum melts were produced to investigate the influence of various elements, andelement combinations, on HAZ toughness. The main elements under invest igat ion were those which arebelieved to have a potentially beneficial influence on acicular ferrite development in the grain coarsenedHAZ such as V, Ti, Β, Al and Si. The b ase composition in which the effects of mos t by the se elem ent s wereexam ined w as 0.07 C, 1.40 Mn, 0.50 Ni. Such steels would typically be aimed at a chie ving eith er pipe ors t ruc tura l s tee l proper ty requi rements in the Thermomechanica l ly Cont ro l led Processed (TMCP)conditions. How ever, for the purpose of the presen t investiga tion, which was pri m ari ly conc erned withprop erties of the transforme d HAZ, these steels were produced in the norm alised co ndition. In addition tothese stee ls, a series of me lts with vary ing Si levels were made using a 0.10 C, 1.40 M n, 0.50 N i, 0.25 Cu,0.025 Nb base composition, suitable for normalised structural steel property requirements. All steels werenom inally 30 mm thick and norm alised at 910°C for one hour. The steel comp ositions and t he ir project

identification letters ar e given in Tab le 1.

3.2 W elding and The rm al Simulation

Subm erged-arc bead in groove welds were made in all steels at hea t inputs of 3.5 and 7.5 kJ/m m . De tails ofthe welding para m eters an d weld preparat ions are given in Table 2 and Fig. 1. Typical weld ma crogra phsare pres ented in Fig. 2.

Thermal simulat ion of HAZ microstructure was achieved using a Gleeble 1500 thermal simulator ,simu lat ing the GCHAZ and ICGCHAZ regions of 3.5 and 7.5 kJ/mm welds. Gleeble sim ula t ion wasconducted in vacuum on 1 2 X 1 2 X 1 0 0 mm blanks with a hea t ing ra te of ~450°C/s , a peak tem pera tu re of1350°C and cooling times between 800 and 500°C of 20 s (3.5 kJ/m m) and 90 s (7.5 kJ/m m ). For ICG CHA Z

simulation the second peak temperature was 800°C. Typical simulated HAZ thermal cycles are given inFig. 3.



3 . 3 C h a r p y a n d C T O D T e s t i n g

S ubs ize Cha rpy s pec im ens (7 .5 m m Χ 10 mm ) w ere ma ch in ed f rom a l l bead in g roove w e lds . S pec im ensw ere e t ched and then no tched a t the fu s ion l ine . Tes t s w ere conduc ted ove r a r ange o f t empera tu res top r o d u c e t r a n s i t i o n c u r v e s . S i m u l a t e d H A Z t o u g h n e s s w a s a s s e s s e d u s i n g C h a r p y s p e c i m e n s m a c h i n e d

f rom G leeb le b lank s . Tes t s w ere condu c ted in t r ip l i ca te a t - 40°C (3 .5 k J /m m) and 0°C (7 .5 k J /m m) . Thes ete m pe ra tu re s w ere s e lec ted to ena b le the s imu la ted H A Z toug hne s s o f the s tee l s to be r ank ed . CTO Ds pec imens (10 X 10 mm) w ere a l s o mach ined f rom a l l bead in g roove w e lds . Thes e s pec imens w ere e t chedan d notc hed a t the fusion l ine pr ior to fa t ig ue pre cra ck ing to an a im crac k depth of ~ 3 mm (a/W ~ 0 .3) . Te s tsw ere conduc ted in acco rdance w i th BS 5762 :1979 a t s e l ec ted t empera tu res w i th the a im o f de te rmin ing the0 .1 m m CTO D t r ans i t io n t em pe ra t u re . I n in s t an ces w he re on ly one s pec imen w as t e s t ed a t a g iventempera tu re , pos t t e s t s ec t ion ing w as conduc ted to check no tch loca t ion va l id i ty .

3 .4 M e t a l l o g r a p h y a n d H a r d n e s s

Q u a n t i t a t i v e m e t a l l o g r a p h i c t e c h n i q u e s w e r e u s e d to a s s e s s t h e r e l a t i v e p r o p o r t i o n o f t h e v a r i o u sm ic r os t ruc tu r a l co ns t i tu en t s in the G CH A Z of each bead in g roove w e ld . P o in t coun t ing , u t i l i s in g a S w i ft

po in t coun te r a t a mag n i f i ca t ion o f x78 7 , w as u s ed to quan t i fy the ma jo r t r ans fo rma t ion p rodu c t s , w h i l s tpo in t coun t ing on S EM pho tog r aph s t ak en a t x3000 w as u s ed to quan t i fy th e min or ph as es ( i . e . t hemi c rop has e ) . F o r the op t i ca l ex am ina t io ns , s pec imen s w ere e t ched in 2% n i t a l and 500 po in t s w erecoun ted fo r each H A Z. The po in t coun t ing t r ave r s e w as a l igned w i th the H A Z immed ia te ly ad jacen t to thefus ion l ine and covered a d i s t a nce o f ~ 6 m m of the H A Z. E igh t types of t r ans fo rma t ion p rod uc t w ere cou n tedus ing the In te rna t iona l In s t i tu t e o f Weld ing ( I IW) c la s s i f i ca t ion s cheme* 1 7 ' i l lu s t ra ted in F ig . 4 . For theS E M e x a m i n a t i o n s , s p e c i m e n s w e r e e l e c t ro l y t i c a l l y e t c h e d u s i n g Ik a w a ' s e t c h* 1 5 ' and 1120 points countedp e r H A Z . P o i n t c o u n t i n g w a s c o n d u c t e d on e i g h t r a n d o m l y s e l e c t e d m i c r o g r a p h s f o r e a c h G C H A Zco un t ing for M -Α cons t i t uen t , f e r r i t e and ca rb ide . G ra in coa r s ened H A Z w id th w as m ea s u r ed us ing anop t i ca l mic ros co pe inco rp o ra t ing an eyep ie ce g ra t i cu le and s t age mic rom ete r . Tw o s e r i e s o f m eas u re m en tswere made def in ing the GCHAZ as HAZ with a gra in s ize (colony s ize) > 100 pm and > 50 pm respect ively .M ea s u rem en ts w ere made 5 mm s ub s u r f a ce and a t the bead roo t for the 3 .5 k J /mm w elds . F o r the 7 .5k J / m m w e l d s , m e a s u r e m e n t s w e r e t a k e n i n t h r e e r e g i o n s : b a y , 8 m m s u b s u r f a c e a n d r o o t . G r a i n

coa r s ene d H A Z 'co lony ' s i ze m ea s u re m en ts w ere made on a l l bead in g roov e H A Zs us in g an op t i ca lmic ro s cope and an eyep iece g ra t i cu le . Th e t echn ique invo lved m ea s u r ing the la rges t d ime ns ion s o f theth r ee l a r ge s t co lon ies obs e rved in each f i e ld o f v iew a t a magn i f i ca t ion o f x 2 0 0 . Ten adjacent f ields of vieww e r e a s s e s s e d c o v e r i n g a p p r o x i m a t e l y 8 m m o f G C H A Z . G r a i n c o a r s e n e d H A Z h a r d n e s s w a s m e a s u r e d fo ra l l bead in g roove w e lds . Tes t s w ere conduc ted us in g a 5 kg load , inden ta t ions b e ing s paced a t 1 .5 mmin te rva l s w i th in 0 .4 mm o f the fu s ion boundary and in the r eg ions r e l evan t to the H A Z Charpy and CTO Ds p e c i m e n s .

4. R E S U L T S

4 .1 P a r e n t P l a t e P r o p e r t i e s

The r e s u l t s of the pa re n t p la t e t ens i l e t e s t s a r e g iven in Tab le 3 and p res en ted g ra ph ica l ly in F ig . 5 . Theupper y ie ld s t r eng ths r anged f rom 287 to 448 N /mm 2 . Tens i l e s t r e ng t hs va r i ed from 405 to 526 N /m m 2 .The lowes t y ie ld s t rength was observed in the C-Mn-Ni-V-B-high Al s teel , ( I ) whi ls t the lowes t tens i les t r eng th w as obs e rved in the C-M n-N i -T i -B- low A l s t ee l , (F ) w h ich a l s o had the low es t ca rbon con ten t .The h ighes t y ie ld and t ens i l e s t r eng ths w ere obs e rved in the C-M n-N i -Cu-N b-A l s t ee l w i th the h ighes ts i l icon level (S teel Q) .

T h e r e s u l t s o f t h e p a r e n t p l a t e C h a r p y t e s t s a r e g i v e n in T a b l e 4 a n d C h a r p y t r a n s i t i o n c u r v e s a r ep r e s e n t e d i n F i g . 6 . U p p e r a n d l o w e r b o u n d s h a v e b e e n d r a w n t o t h e d a t a a n d 4 0 J t r a n s i t i o nt e m p e r a t u r e s t a k e n fro m t h e b o u n d s . T h e 4 0 J t e m p e r a t u r e s w h i c h r a n g e d f ro m - 3 6 t o - 11 9CC a res ummar i s ed in F ig . 7 . The low es t t r ans i t ion t empera tu res w ere obs e rved in the C-M n-N i -N b-A l s t ee l s , (O ,Ρ and Q ) w h i l s t the h ighes t t r ans i t ion t empera tu res w ere fo r the C-M n-X i -V - (T i ) -B-h igh A l s t ee l s ( I andK ). The mos t s a t i s f ac to ry comb ina t io n of pa ren t p la t e s t r en g th and tough nes s w as ob ta in ed in the C-M n-X i -Cu-X b-A l s t e e l s , (O , P a nd Q ) w h ich a r e s im i la r to thos e cu r r en t ly u s ed in the o f fs hore indu s t ry .



4.2 HAZ Charp y Pro perties

The HAZ Ch arpy re sults for the 3.5 and 7.5 kJ/mm bea d in groove welds are given in Tab le 5 and plotte d astran sitio n curves in Fig. 8. Upper and lower bounds have been drawn to the tran sitio n cu rves an d lowerbound 40 J transiti on tem pe ratu res have been defined. These are summ arised in Table 15 and Fig . 9. At

3.5 kJ/m m th e 40 J tem pe ratu res rang ed from -17 to -64°C. A t 7.5 kJ/mm the rang e wa s + 23

to -55°C.At both heat inputs , the lowest transitio n tem per atur es we re observed in Steel F (C-Mn-Ti-B-low Al). Thehighest transition temperatures at 3.5 kJ/mm were in Steels A and N (C-Mn-Ni-Al and C-Mn-Ni-Cu-Nb).At 7 .5 kJ/mm the highest t ransi t ion temperatures were in the C-Mn-Ni-Cu-Nb-Al s teels , indicat ing thatthese a re the leas t suitable for high heat input welding.

4.3 HAZ CTOD Propert ies

The resu lts of the HAZ CTOD tests are given in Table 6 and presente d gra phically in Fig. 10. Th e 0.1 m mCTOD temperatures have been determined from lower bound l ines drawn on the data and these aresummarised in Table 15 and Fig. 11. At 3.5 kJ/mm transition temperatures ranged from -107°C (Steel J)to ~-20°C (Steel K). S tee lJ was a C-Mn-Ni-Ti-V-B-low Al compositions and was amo ng st the tou gh est stee lsran ked by the HAZ Cha rpy tests. Steel K was sim ilar to J except for hav ing a high alu m ini um co nte nt. At7.5 kJ/m m the transitio n tem per atu res ranged from -90°C to + 35°C. The toughest steel wa s again Steel J,but at the higher heat input the least tough steel was Steel M which was a C-Mn-Ni-Cu-V-Ti-Nb-high Si-high Al type.

In one weld at 3.5 kJ/mm (Steel N) no valid HAZ CTOD data was obtained due to fracture initiation inweld metal . Subsequent metal lographic examination indicated that s teel of this part icu lar ch em istry hadresu lted in a rat he r poor weld me tal microstructure w ith low fracture tough ness . Th is effect is well kn ownin high di lut ion submerged-arc weld metal and can be at t r ibuted to the high aluminium content of thesteel and the absence of titanium* 19 '.

4.4 Sim ulated HAZ Charpy Properties

The simulated HAZ Charpy results are presented in Table 7 and illustrated graphically in Figs. 12 to 15.The results for the single thermal cycle simulation of grain coarsened HAZ (GCHAZ) regions given inFigs. 12 and 13 show a wide rang e of behaviour with absorbed energie s rang ing from < 40 J to > 2 8 0 J atboth heat inputs. The tough est steels at both hea t inpu ts were Ti-treate d Steels C, D and F . All st eelsshowed quite high scatter in Charpy energy despite the fact that the Charpy notch was sampling uniformGCHAZ microstructure.

The results for the double cycle simulation of intercritically reheated GCHAZ (ICGCHAZ) regions areshown in Fig. 14 and 15. These resu lts also show a wide ran ge of behav iour an d in m any ca ses widescat ter . Again, the toughest s teels appear to be the T i-trea ted Steels C, D and F .

In general i t was noted that the second intercr i t ical thermal cycle tended to reduce HAZ toughness.However, this phenomena was by no means universal and some steels showed an increase in Charpytoughness following intercritical reheating.

4.5 Metal lography and Hardness Data

The res ults of the optical quantification of HAZ microstructure for the 3.5 and 7.5 kJ/mm bead in grooveHAZs are given in Tables 8 and 9 respectively. A wide rang e of mic rostru cture s w ere produced, inc lud ingsome containing qui te large proport ions of intr ag ran ula r polygonal ferr i te and a cicular fe rr i te . Thesetypes of mic rostru ctures were partic ularly no ticeable in the Ti-low Al and Ti-B low Al steels at 7.5 kJ /m m .Two of the Steels (G and K) produced a lighter etching zone in the high temperature HAZ adjacent to thefusion boundary. In these steels, additional quan tification of HAZ mi cros truc ture was conducted ju st

outside the se regions at ~F B + 0.5 mm and this is included at the bottom of Table 9. Th ese FB + 0.5 m mregions contained quite high proportions of AF (51 in Steel G) indicating th at it is possible to produ ce



weld me ta l l ike mic ro s t r uc tu r e s in h igh he a t inpu t HAZs . Op t i ca l mic rog ra phs i l l u s t r a t in g the bead ingroove HAZs of a l l 17 s tee ls a t bo th heat inputs are presented in F igs . 16 to 19 . F igures 16 and 17 show 3 .5kJ /m m an d 7 .5 k J /m m we lds a t xlOO. F igu res 18 and 19 s how 3 .5 k J /m m an d 7 .5 k J /mm HA Zs a t x400 .

Th e r e s u l t s of the S EM quan t i f i ca t ion o f M-Α cons t i tuen t s a r e g iven in Tab le 10 . Th e da ta s h ows acons i s t en t t r en d fo r r educed M-Α leve l s a t h igh e r hea t inpu t s . The h ighe s t obse rved M-Α f r ac t ion was14 .6% in S tee l Q a t 3 .5 kJ /mm and the lowes t f rac t ion was 1 .2% in S teel J a t 7 .5 kJ /mm.

HAZ wid th meas u remen t s fo r the 3 .5 and 7 .5 k J /mm we lds a r e p r e s en ted in Tab le s 11 and 12 r e s pec t ive ly .As expec ted , the na r row es t HAZs were obs e rved in the T i - t r ea ted s t ee l s . A s um m ary o f HAZ g ra in s i zemeasurements based on FS colony s ize is shown in Table 13 . The f ines t co lony s izes were , as expected ,observed in the Ti- t rea ted s tee ls and the coarses t co lony s ize was that of the microal loy-f ree base s tee l .

HA Z ha rd nes s da ta i s p r e s en ted in Tab le 14 . W i th the excep tion of S tee l C, a l l s t ee l s exh i b i t ed theexpec ted t r en d of h ighe r HAZ ha rdne s s a t lower hea t inpu t . The s of t es t HAZ a t bo th hea t inp u t s was tha t

o f S tee l D (T i -low Al ) wh i l s t t he ha rd es t a t bo th he a t inp u t s was S tee l L ( C -M n-N i -C u-N b-Ti -V -S i -h i g h A l ) .

5 . D I S C U S S I O N

5 .1 E f f e c t o f A l l o y i n g E l e m e n t s o n G C H A Z M i c r o s t r u c t u r e

5 . 1. 1 G e n e r a l O b s e r v a t i o n s o f G r a i n S i z e

I n t h e c u r r e n t p r o j e c t , G C H A Z g r a i n s i z e a n d G C H A Z w i d t h h a v e b e e n m e a s u r e d i n t e r m s o f t h e'B a in i t e /Widmans tä t t en f e r r i t e ' co lony s i ze ( i . e . F S co lony s i ze ) wh ich i s the mic ro s t ruc tu r a l pa r ame te rbe l i eved to co r r e l a t e mos t c lo s e ly wi th f r ac tu r e f ace t s i ze . Thes e pa ra m e te r s a r e in f luenced by p r io r

au s te n i t e g r a in s i ze an d the s t ee l ' s γ to α t r an s fo r ma t ion cha rac te r i s t i c s . B o th thes e f ac to r s a r e in f luencedby s t ee l chemis t ry and we ld the rma l cyc le .

F i gu re 20 show s the FS colony s ize of a l l seve nte en s tee ls as a funct ion of weld he at inp ut . Al l s tee ls showthe expec ted t r e nd o f inc r e as ing g r a in s i ze wi t h inc r eas ed w e ld hea t inpu t due to γ g r a in g ro wt h r e s u l t in gf rom h ighe r r e t en t ion t imes a t e l eva ted t empera tu r e in the s upe rc r i t i ca l HAZ. However , s ome s t ee l s , s uchas S tee l F s how ve ry l i t t l e e l eva t ion in co lony si ze wi th inc r ea s ing hea t inpu t . Th i s i s due m a in ly to thes t ee l ' s t r an s fo rma t ion cha rac te r i s t i c s wh ich have r e s u l t ed in a low p ropo r t ion o f s ma l l F S co lon ie s , wh ichhave been l imi t ed in s i ze by o the r t r an s fo rma t ion p roduc t s s uch a s p r imary f e r r i t e , ac i cu la r f e r r i t e andin t r a g r an u l a r po lygona l f e r r i t e . F rom F ig . 20 i t i s c l ea r tha t a l l t he mic roa l loyed s t ee l s exa mi ned in thepresent work had smal ler gra in s izes tha t the base , microal loy-f ree S tee l (A) . I t i s a lso c lear tha t a t 7 .5kJ /m m th e T i -b ea r in g s t ee l s gene ra l ly exh ib i t ed the f ines t co lony s i zes fo llowed by the va na d iu m s t ee l s

; .nd the n the n io biu m s tee ls . I t i s a lso notab le f rom Fig . 10 th at th e s tee ls wi t h the f inest co lony s izes a t 7 .5kJ /mm were Ti-B- low Al s tee ls and the next f ines t were a lso low Al , bu t boron f ree .

5 .1 .2 G e n e r a l O b s e r v a t i o n s o n T r a n s f o r m a t i o n P r o d u c t s

In the p r e s en t work , a wide r ange o f t r an s fo rma t ion p roduc t s were deve loped in the GC HAZs ' o f theva r io us s t ee l s inc lud in g ac icu la r f e r r i t e . Th e h igh es t f r ac t ion of ac i cu la r f e r r i t e obs e rved w as 51 % in a T i -B s t ee l wi th h igh a lum in iu m con ten t .

L i t e r a tu r e on ac icu la r f e r r i t e f o rma t ion in we ld me ta l s has t ended to s ugges t tha t qu i t e h igh ox ideinc lu s ion con ten t s a r e a r equ i r ed fo r ac i cu la r f e r r i t e nuc lea t ion and tha t h igh a lumin ium leve l s p r even tAF deve lopm en t . F rom the p r e s en t work i t s eem s l ike ly th a t h igh ac icu la r f e r r i t e f r ac t i on ca n begene ra ted in HAZs wi th r e l a t ive ly low oxygen con ten t s ( a l l me l t s were vacuum mel t s ) and tha t th i s can bedone in the p r e s e nce of a lu mi n iu m. Th i s imp l i e s tha t t i t a n iu m ox ides a r e no t neces s a ry for ac i cu la r f e r r i t enuc le a t ion a nd s ug ges t s tha t pe rhap s TiX" o r B X m ay be capab le o f nuc lea t in g ac icu la r f e r r i t e a s r epo r t edi n e a r l v l i t e r a t u r e o n w e l d m e t a l s ' 2 0 ' .



Of pa r t i c u la r in t e r e s t i n the cu r r en t work was the occu r r ence o f l i gh t e t ch ing zones in bo th the T i -B -h ighAl s t ee l s a t h igh hea t inpu t . F igu re 21 s hows the GC HA Z o f S tee l G a t 7 .5 k J /m m . Th e ou te r p a r t o f th eG C H A Z w h i c h h a s e x p e r i e n c e d a l o w e r p e a k t e m p e r a t u r e h a s d e v e l o p e d a f i n e a c i c u l a r f e r r i t e

mi c ros t ruc tu r e . The r eg ion ad jacen t to the fu sion bound ary , however , has fa i l ed to deve lop AF an d ha st r ans fo rme d to the mo re u s ua l HAZ t r ans fo rma t ion p roduc t s s uch a s P F and F S . Th e r ea s on fo r th i sbehav iou r r equ i r e s examina t ion , bu t i t i s pos s ib le tha t the n i t r ide pa r t i c l e s r e s pons ib le fo r AF nuc lea t ionwen t in to s o lu t ion in the GC HAZ ad jacen t to the fu sion bound ary , thu s p r e ve n t i ng AF nuc lea t ion . I n theT i -B - low Al s t ee l s , ac i cu la r f e r r i t e was deve loped r igh t up to the fu s ion boundary s ugges t ing tha t thes t ab i l i ty o f the nuc lea t ing pa r t i c l e s in the T i-B s t ee l s was r educed in the p r e s e nce o f a l um in iu m .

5 .1 .3 G e n e r a l O b s e r v a t i o n s o f M i c r o p h a s e s

I n t h e c u r r e n t w o r k , t h e G C H A Z m i c r o p h a s e w e r e q u a n t i f i e d u s i n g a n S E M t e c h n i q u e i n v o l v i n g p o i n tcoun t ing . Un der equ i l ib r iu m coo l ing cond i t ions the vo lum e fr ac t ion o f pe a r l i t e in s t ee l is r e l a t ed to ca rb oncon ten t . Un de r we ld ing cond i t ions , t he coo ling r a t e is non -equ i l ib r ium and the f r ac t ion o f m ic r op ha s edepends on coo l ing r a t e and the t r an s fo rm a t ion c ha r ac t e r i s t i c s of the s t ee l . At h igh he a t inp u t s an d wi ths t e e l s o f l ow h a r d e n a b i l i t y , t r a n s f o r m a t i o n i s o ft en t o p r o e u t e c t o i d f e r r i t e a n d W i d m a n s t ä t t e n f e r r i t e .B o th o f thes e t r an s fo rma t ion p roduc t s g row un t i l t he eu tec to id ca rbon con ten t i s r eac hed in the ca r bonen r i ched aus ten i t e and unde r thes e cond i t ions , t he to t a l mic rophas e f r ac t ion s hou ld be r e l a t ed to s t ee lca rbon con ten t by the l eve l r u l e . The e ff ec t of ca rbon co n ten t on to t a l m ic rop has e f r ac t ion (MA p lu sca rb ides ) o f the 3 .5 k J /m m and 7 .5 k J /m m GC HA Zs a r e s how n in F ig s . 22 (a ) and 22 (b ) . At 7 .5 k J / m m F ig .22(b) s hows tha t fo r m an y of the s t ee l s the r e i s qu i t e c lo se ag re em en t w i th the l eve r ru le s u gg es t ing th a tt h e t r a n s f o r m a t i o n p r o d u c t s a r e e s s e n t i a l ly p r oe u t e c t o id i n n a t u r e ( i .e . t h e ' F S ' i s W i d m a n s t ä t t e n f e r r i t e ) .At 3 .5 k J /m m F ig . 22 (a ) s hows tha t s ome o f the s t ee l s dev ia t e s ign i f i can t ly f rom the l ev e r ru le s u gg es t ingt h a t b a i n i t e t r a n s f o r m a t i o n p r o d u c t s a r e p r e s e n t in t h e s e G C H A Z s .

The na tu re o f the t r an s fo rma t ion p roduc t wi th in the mic rophas e appea r s to have a s ign i f i can t in f luence onthe f r ac t u r e to ugh nes s of the HAZ. Wo rk on dua l pha s e s t ee l s s ugg es t s tha t t r an s fo r m a t i on o f the ca r bo n

e n r i c h e d a u s t e n i t e t o m a r t e n s i t e i s c o n t ro l l ed b y a l l o y i n g c o n t e n t a n d e q u a t i o n s h a v e b e e n p r o p o s e d b a s e do n a m a n g a n e s e e q u i v a l e n t * 2 1 ' . F ew s tud ie s on the ef fec t o f a l loy in g o r M-Α dev e lo pm en t in GC H AZ s ha veb e e n p u b l i s h e d . H o w e v e r , a s t u d y o n t h e e ff ec t o f a l l o y i n g on i n t e r c r i t i c a l l y r e h e a t e d G C H A Zm i c r o s t r u c t u r e s u g g e s t e d t h a t t h e p r o p e n s i t y t o d e v e l o p M - Α c o n s t i t u e n t w a s r e l a t e d t o a l l o y c o n t e n tg iven by the CE V form ula incl udin g a fac tor for s i l icon over s ix '2 2 1 ,i.e.

Si + Mn Cr + Mo + V N i + CuAlloy fac tor = -I- + . . . ( 1 )

6 5 15

The M-Α f r ac t ions obs e rved in the p r e s en t p ro jec t have been p lo t t ed aga in s t t h i s f o rmu la and a r e g iven inFig . 23 . Th e f igure in dic ate s th a t M-Α f rac t ion red uce s ab ru pt ly in the ra ng e 0 .29 to 0 .32 of th e ab ov efo rmu la . Th i s i s s im i l a r to th a t p r ev ious ly obs e rved for IC G C H AZ reg ion s . The a l loy l eve l a t wh ich thes wi tch f rom M-Α to pea r l i t e domina ted mic rophas es occu r s depends on coo l ing r a t e . F o r t r an s fo rma t ion topea r l i t i c mic rophas es a t f a s t e r coo l ing r a t e s , F ig . 23 ind ica te s tha t s l igh t ly lower a l loy l eve l s a r e r equ i r ed .Th i s i s expec ted f rom ha rdenab i l i ty cons ide ra t ions .

Obv ious ly , an accu ra te p r ed ic t ion o f the amoun t o f M-Α cons t i tuen t in the GC HAZ o f a s t ee l r equ i r e sd e t a i l e d k n o w l e d g e o f t h e s t e e l s t r a n s f o r m a t i o n c h a r a c t e r i s t i c s a n d t h e r m a l c y cl e . H o w e v e r , f o r t h ep res en t work i t appea r s tha t f o r h igh hea t inpu t s ( i . e . 7 .5 k J /mm) the to t a l mic rophas e con ten t i s r e l a t ed toca rbon and the t end ency for the thes e r eg ions to fo rm M-Α depen ds on a l loy con te n t g iven by Eq ua t io n (1 ) .

At lower hea t inpu t s , where ba in i t i c s t r uc tu r e s a r e deve loped unde r con t inuous coo l ing cond i t ions , t he Μ-Α f rac t ion wi l l be d i f f icu l t to pred ic t as i t wil l dep end on know ledg e of the v olu m e f rac t ion of th e va r io usp roeu tec to id and ba in i t i c t r an s fo rma t ion p roduc t s f o rmed in add i t ion to the ab i l i t y to p r ed ic t t he ex ten t towh ich the ba in i t e r eac t ion p roceeds .

T h e p r e s e n t w o r k a l s o s u g g e s t s t h a t v a r i o u s m i c r o a l l o y i n g e l e m e n t s m a y h a v e a n ef fe c t o n M - Adevelopment and these too need to be taken in to account i f M-Α f rac t ions are to be predic ted .



5 . 1 . 4 V a n a d i u m

The e f f ec t o f vanad ium on H A Z mic ros t ruc tu re can be s een by compar ing the bas e S tee l (A ) w i th thevan ad i um bea r in g S tee l (B). F rom th i s com par i s on i t i s app are n t tha t 0 .08% van ad i um p rom oted thedeve lopm en t of bo th p r im ary f e r r i t e and M -Α con s t i tu en t in the G CH A Z a t bo th hea t inpu t s inve s t iga te d .

Th i s w as accompan ied by a s ma l l r educ t ion in the f e r r i t e w i th s econd phas e (F S ) in the 3 .5 k J /mm w eldand a l a rge r r edu c t ion in F S in the 7 .5 k J /mm w eld . The am oun t of ac icu la r f e r r i t e w as l i t t l e in f luenced byv a n a d i u m , a l t h o u g h a t 7 . 5 k J / m m s l i g h t ly m o r e i n t r a g r a n u l a r p r i m a r y f e r r i te w a s o b s e r v e d . G r a i n s iz emeas u remen ts ind ica te tha t vanad ium reduced the G CH A Z co lony s i ze and had a s ma l l in f luence onredu c ing the > 100 pm G CH A Z w id th . The ha rd ne s s of the G CH A Z w as inc reas ed by van ad i um a t bo thhea t inpu t s .

Th e ef fect of va na di um in the Ti-B- low Al sys tem c an be seen by com par ing S teels F an d J . At 3 .5 k J / m mv a n a d i u m s l i g h t l y r e d u c e d t h e a m o u n t o f a c i c u l a r f e r r i t e a n d i n t r a g r a n u l a r p o l y g o n a l f e r r i t e b u tinc rea s ed the f r ac t ion o f f e r r i t e w i th s econd pha s e and M -Α cons t i tu en t . A t 7 .5 k J / m m va na d iu m s l igh t lyr e d u c e d p r i m a r y f e r r i te a n d M -Α c o n s t i t u e n t b u t i n c r e a s e d a c i c u l a r fe r r i te a n d i n t r a g r a n u l a r p r i m a r yfe r r i t e . H A Z g ra in s ize w a s no t in f luenced by va na d iu m a t 7 .5 k J / m m bu t w as r educed a t 3 .5 k J / m m . A t

bo th hea t in pu t s H A Z hardn es s inc reas ed . In the T i -B-h igh A l s ys tem , van ad iu m had l i t t l e ef fec t on H A Zm i c r o s t r u c t u r e o t h e r t h a n p r o m o t i n g M - Α c o n s t i t u e n t a t b ot h h e a t i n p u t s . A t b o t h h e a t i n p u t s H A Zh a r d n e s s i n c r e a s e d w i t h v a n a d i u m .

5 .1 . 5 T i t a n i u m

The e ff ec t of t i t a n i um on H A Z mic ro s t ruc tu re ca n be s een by com par ing the bas e S tee l (A ) w i th th et i t a n i u m b e a r i n g S t e e l ( C ). F r o m t h i s c o m p a r i s o n i t i s a p p a r e n t t h a t 0. 01 4 % t i t a n i u m p r o m o t e d t h ed e v e l o p m e n t o f p r i m a r y f e r r i t e , a c i c u l a r f e r r i t e a n d i n t r a g r a n u l a r p o l y g o n a l f e r r i t e a n d t h i s w a saccom pan ied by a r educ t ion in the am oun t o f f e r r i t e w i th second phas e . A t 3 .5 k J /m m , t i t an ium had l i t t l ee ff ec t on M -Α f r ac t ion , bu t a t 7.5 k J /m m , M -Α app ea re d to be s t rong ly p rom oted . T i t an ium reduced thew id th of the G CH A Z and the G CH A Z g ra in s i ze . A t 3 .5 k J / m m t i t an ium reduced H A Z har dn es s bu t a t 7 .5k J / m m , h a r d n e s s w a s s l i g h t l y i n c r e a se d .

Th e ef fect of t i ta n i um in th e V-B-low Al sys tem ca n be see n by com pa r in g S teel H and J . At both he atinpu t s , t i t an ium p romoted p r imary f e r r i t e and in t r ag ranu la r f e r r i t e a t the expens e o f f e r r i t e w i th s econdpha s e . A t 7 .5 k J /m m , t i t a n iu m a l s o p rom oted ac icu la r f e r r i t e . A t bo th hea t inpu t s , M -Α f r ac t ion w a sreduced by t i t a n iu m . The G CH A Z colony s i ze , G CH A Z w id th and H A Z har dne s s w ere a l l r educed byt i t a n i u m .

In the V -B-h igh -A l s ys tem a t 3 .5 k J /mm, T i aga in p romoted p r imary f e r r i t e and in t r ag ranu la r po lygona lf e r r i t e a t the exp ens e o f f e r r i t e w i th s econd ph as e an d r educed G CH A Z co lony s ize and G CH A Z w id th .U n l ike the low A l s ys tem , M -Α w as inc rea s ed and H A Z hardn es s w as no t r educed . A t 7.5 k J /m m a l igh te tc hin g zone (LEZ) wa s produc ed adjacent to th e fus ion bou nda ry . Aw ay from th is region ( i .e . ~ F B + 0 .5m m ) t i t a n i u m p r o m o t e d p r i m a r y f e r ri t e , i n t r a g r a n u l a r p o l yg o n a l f e r r it e a n d a c i c u l a r f e r r i te . H o w e v e r , i n

t h e L E Z m i c r o s t r u c t u r e a p p e a r e d t o b e l i t tl e in f l u e n ce d b y t i t a n i u m . M a r t e n s i t e - a u s t e n i t e f r a c t i o n w a sag a in p romo ted by t i t an iu m and H A Z har dne s s s l igh t ly inc reas ed . G ra in coa r s ened H A Z co lony s i ze andG CH A Z w id th w ere aga in r educed by t i t an ium a t 7 .5 k J /mm.

5 . 1 . 6 A l u m i n i u m

The e ff ec t of inc rea s in g a lu m in i um f rom 0 .005 to 0 .04 3% in t i t an iu m t r e a t ed s t e e l can be s een byc o m p a r i n g S te e l s C a n d D . I n c r e a s i n g a l u m i n i u m d e c r e a s e d t h e p r o p o r t i o n of p r i m a r y f e r r i t e a n dinc re as ed the p rop or t ion o f f e r r i t e w i th second pha s e a t bo th hea t inpu t s . A t 7 .5 k J /m m in c r ea s in ga lu m in i um red uced the deve lopm en t of ac icu la r f e r r i t e and inc reas ed the p ropor t ion of M -Α . A t 3 .5 k J /m mthe p ropo r t ions o f ac icu la r f e r r i t e and M -Α w ere l i t t l e in f luenced by a lu mi n iu m. Inc re as ing a lu m in i um int h e t i t a n i u m s t e e l i n c r e a s e d th e G C H A Z w i d th a n d G C H A Z g r a i n s iz e . G C H A Z h a r d n e s s w a s a l s o

inc reas e d w i th h ighe r a lum in iu m des p i t e the h ighe r ca rbon l evel o f the low a lu mi n iu m s tee l .



The effect of increasing aluminium from 0.004 to 0.047% in a vanadium steel can be seen by comparingSteels Β and E. At 7.5 kJ/mm increasing aluminium had very little influence on GCHAZ microstructure.At 3.5 kJ/mm the low aluminium steel developed slightly more acicular ferrite and some lath martensite.

This was probably a consequence of slightly higher hardenability in the low aluminium steel due tosl ight ly higher carbon, vanadium and ni trogen levels , ra ther than true inf luence of a luminium ontransforma tion behav iour. The GCHAZ width and GCHAZ grain size was slightly sm alle r in the loweralum inium ste el. This may have been a consequence of the slightly high er van adi um nitro gen levelsproviding more VN precipitation to restrict austenite grain coarsening in the outer parts of the GCHAZ.The GCHAZ hardness values were also slightly higher in the low aluminium steel and this is probably areflection of the effects of higher C, V and X on transfo rma tion and precipitation beh avio ur ra th er th an atrue influence of aluminium.

The effect of incre asing a lumin ium in the Ti-B steels can be seen by com paring Stee ls F an d G. At 3.5kJ/mm aluminium promoted primary ferr i te , but reduced intragranular polygonal ferr i te and acicularferri te . At 7.5 kJ/m m primary ferr ite was reduced by high alum iniu m whils t ac icu lar fe rr i te waspromoted at the fusion boundary +0.5 mm location, but reduced in the LEZ immediately adjacent to theFB . M-Α const i tuent was promoted by high alum inium a t both heat inputs . HAZ hard nes s was alsoincreased at both heat inputs. GCHAZ colony size was increased by aluminium at 7.5 kJ/mm but reducedat 3.5 kJ/mm. Grain coarsened HAZ width was little influenced at 3.5 kJ/mm but increased with higheraluminium at 7.5 kJ/mm .

The effect of incre asin g alum inium in the V-Ti-B system c an be seen by com paring Stee ls J an d K. As inthe Ti-B system at 3.5 kJ/mm , alum inium promoted prim ary ferr i te but reduced intr ag ra nu lar polygonalferrite at the FB + 5 mm locat ion. Once again in the LEZ adjacent to the F B, ac icu lar fer r i te andintrag ranu lar polygonal ferr ite were reduced by high alum inium . As before M-Α fract ion and HAZhardness was increased by high aluminium and HAZ width observations were similar to those of the Ti-Bsteels.

5.1.7 Boron

The effect of adding 0.0025% boron to low aluminium Ti-treated steel can be seen by comparing Steels Fand D. A t both he at inputs the proportion of in tra gra nu lar polygonal ferrite was increa sed by boron. At3.5 kJ.mm the proportion of grain boundary nucleated primary ferrite was reduced, but the proportion ofacicular ferrite increased. However, at 7.5 kJ/m m the opposite was observed and the boron steel exh ibitedmore primary ferrite and less acicular ferrite than the boron-free steel. The proportion of M-Α phase wasreduced by boron at both inputs , however, it seem s likely that this m ay be to some exte nt d ue to the lowercarbon content of the boron-treated steel. GCHAZ width was increased by boron at the 3.5 kJ/mm heatinput. GCHAZ grain size was increased by boron in the lower heat input weld, but slig htly reduced in thehigh inpu t weld. This latte r effect was probably an influence of boron on transfo rm atio n ch ara cte rist icsrather than austenite grain size (a lower proportion of Widmanstätten ferrite colonies being present on the

boron steel). GCHAZ hardn ess was not influenced by boron in the high heat inp ut weld. Ho wev er, th elower heat inp ut level, hard ness was increased by boron despite the lower carbon lev el. Th is is su gge stedto be par tly a consequence of a larger prior aus ten ite gra in size leading to lower γ-α tra ns fo rm ati ontemp erature bu t may also be part ly due to the presence of some active boron incre asing hard ena bil i ty andlowering γ-α t ransformation tem perature .

The effect of adding 0.0033% boron to low aluminium vanadium steel can be seen by comparing Steel Ηand E. At both heat inputs the proportion of pri m ary ferrite was reduced and the propor tion off errit e withsecond phase increased by boron. At 3.5 kJ/m m the proportion of M-Α was incre ased by boron b ut at 7.5kJ/mm it was reduced. GCHAZ width tended to be increased by boron and th e GCH AZ colony size w asincreased by boron at both heat inputs (presumably due to the reduction in primary ferrite at the prioraustenite grain boundaries). GCHAZ hardness was increased by boron at both heat inputs probably as a

consequence of active boron on h ardena bility.



5 . 1. 8 N i t r o g e n i n a T i - t r e a t e d V a n a d i u m S t e e l

Th e inf luence of 0 .004% ni t rog en in a V-Ti-Al s teel can be seen by com par ing S tee ls L an d M. At both he atinpu t s , n i t rogen w as obs e rved to inc reas e the p ropor t ion o f p r imary f e r r i t e and r educe the p ropor t ion o ffer r i te wi t h second phas e . At 3 .5 kJ /m m the propor t io n of M-Α was s l ight ly lower in the h igh n i t ro gen

s tee l , pos s ib ly a s a re s u l t o f r educe d F S vo lum e f r ac t ion . The G CH A Z w id th w as r educe d by inc reas edn i t ro gen l eve l a t bo th hea t inpu t s . A t 7 .5 k J / m m G C H A Z co lony s i ze w as l i t t l e in f luenced by n i t rogen bu ta t 3 .5 k J / m m the co lony s i ze w as l a rg e r in the h igh n i t rog en s t ee l . Th i s l a t t e r obs e rva t ion i s con t r a ry toexpec ta t ions becaus e the h ighe r F S f r ac t ions and r e s t r i c t ed H A Z w id th o f the h ighe r n i t rogen s t ee l s hou ldtend to res ul t in lower GC HA Z colony s ize . GCH AZ har dn es s was l i t t le inf luenced by n i t rog en a t 7 .5kJ /mm bu t w as r educed a t 3 .5 k J /mm.

5 .1 .9 S i l i co n in a N i o b i u m S t e e l

Th e ef fect of red uc ing s i l icon in the ran ge 0 .4 to 0 .1 % can be seen by com par ing S te els Ο, Ρ and Q. At 7 .5kJ /mm the G CH A Z mic ros t ruc tu res w ere obs e rved to be p rac t i ca l ly iden t i ca l excep t fo r d i f f e r ences in M -Af rac t ion , h igh s il i con p romo t ing M -Α con s t i tuen t . A t 3 .5 k J /m m deve lopm en t o f M -Α w a s aga in s t rong ly

p rom oted by s i l i con . The p ropo r t ions of o the r mic ros t ru c tu ra l con s t i tuen t s in the 3 .5 k J /m m H A Zs w eres im i la r a l t hou gh the s t eel w i th the low es t s il i con con ten t , s t ee l 'O ' con ta ined m ore ac icu l a r f e r r i t e and l a thm ar t en s i t e . Th i s w as p robab ly a cons equ ence of i t s s l igh t ly h ighe r CEV ra t he r tha n an in f luence o fs i l i con . G r a in coa r sened H A Z w id th w a s s im i la r in a l l t h r e e s t ee l s a t 3. 5 k J /m m. A t 7 .5 k J /m m , theG CH A Z w id th o f S tee l s O and Ρ w ere s im i la r bu t tha t of S tee l Q d i s coun t ing the bay r eg io n , w as l a rge r .Th i s may be in pa r t due to s l igh t ly low er ca rbon con te n t o f th i s s t ee l . G CH A Z g ra in s i ze fol low ed a s imi la rpa t t e rn to G C H A Z w id th . G CH A Z har dn es s fol low ed the expec ted t r end of r educ ing w i th r educe d s i l i conlevel except for th e 3 .5 kJ / m m HAZ in th e lowes t s i l icon s tee l . Th is HAZ was s l ight ly h ar de r due to thedeve lopmen t o f more l a th mar tens i t e d i s cus s ed ea r l i e r .

5 .2 E f f e ct o f A l l o y i n g E l e m e n t s o n G C H A Z T o u g h n e s s

5 . 2 . 1 V a n a d i u m

He at af fected zone s tudies ha ve ident i f ie d sm al l add i t ion s of va na diu m to be benef ic ia l to as -welded HAZtoug hne s s pa r t i cu la r l y a t low er w e ld he a t inp u t s . The benef i c i a l e ff ec t has been r epo r t ed to be r educed , o re l i m i n a t e d , a t h i g h e r w el d h e a t i n p u t s , h i g h e r v a n a d i u m l e v e l s a n d a f t e r P W H T d u e to V Nprec ip i t a t ion* 2 3 ' . I n s om e c i r c u m s t a n c e s v a n a d i u m c a n b e d e t r i m e n t a l t o H A Z t o u g h n e s s . T h e p r e s e n tw ork con f i rms t ha t vana d ium i s bene f i c i a l to G CH A Z toughn es s a t the low er hea t inpu t ( 3 .5 k J /m m) in theC-M n-N i -A l s ys tem . In the T i -B low A l s t ee l s vana d iu m w as obs e rved to be s l igh t ly benef ic i a l to H A ZCTO D bu t de t r im en ta l to H A Z Ch arp y tough nes s a t 3.5 k J /m m , w herea s in the T i -B-h igh A l s ys tem theoppos i t e w as obs e rved .

A t h ighe r hea t inpu t , t he bead in g roove Charpy t e s t s how ed l i t t l e change in toughnes s due to vanad ium inthe C-M n-N i -A l s ys tem bu t a de t r im en ta l e f fect o f va nad ium in the T i -B s ys tem s . Th e bead in g roove

CTO D tes t s how e d a s ligh t ly benef i c ia l e f f ec t o f van ad i um in the T i-B- low A l s ys tem bu t a d e t r im en t a lef fect in the C-Mn-Ni-Al and C-Mn-Ni-Ti-B-high Al sys tems .

The d i f f e r en t r a nk in g of the t e s t ing t ech n iqu es s ugge s t s d i ff e r en t s e ns i t iv i t i e s o f each t e s t to va r i a t ions inm i c r o s t r u c t u r a l f e a t u r e s . F i g u r e 2 4 s u m m a r i s e s t h e o b se r v e d ef fe c ts of v a n a d i u m o n m i c r o s t r u c t u r a l a n dtoug hne s s cha nge s for the 7 .5 k J / m m bead in g roove w e lds . The m a in de t r im en t a l in f luences o f van ad iu ma r e b e l i e v e d t o b e p r e c i p i ta t i o n h a r d e n i n g a n d p r o m o t i o n o f M - Α c o n s t i t u e n t . H A Z h a r d e n i n g w a sobs e rved in a l l vanad ium bea r ing w e lds and M -Α f r ac t ions w ere inc reas ed in a l l s y s tems excep t the T i -B-low A l s ys tem . In th i s l a t t e r s y s tem th e M -Α con ten t of the V -bea r in g s t ee l w as s l igh t ly low er than th e V -f ree s t ee l , bu t th i s ma y have been a cons equ ence o f s l igh t ly low er ca rbon con ten t r a th e r th an vana d ium .The ma in benef i c i a l in f luence o f vanad ium a re be l i eved to be r educ t ion in ' f r ee ' n i t rogen and r educedef fec tive g r a in s i ze . F igu re 24 s how s th a t in mos t s i tua t ions a t 7 .5 k J /m m, V i s de t r i m en ta l to H A Ztoug hnes s . The on ly s i tua t ion in w h ich vana d iu m w a s s l igh t ly benefi c i al w ere the C-M n-X i -A l Cha rpyand C-M n-X i -T i -B-Low A l CTO D tes t s . Th e fo rmer w as p robab ly a cons equence o f the r edu ced G CH A Zcolony s ize and s l ight promotion of in t ragranular polygonal fer r i te , both of which reduce ef fect ive grain



s i z e . The l a t t e r w as p robab ly a consequence o f the s l igh t ly r educed M -Α f r ac t ion an d p rom ot ion o f ac icu la rfer r i te in the C-Mn-Ni-Ti-V-B-low Al s teel .

5 . 2 . 2 T i t a n i u m

Ti tan ium may be added to s t ee l s to improve w e ldab i l i ty by combin ing w i th n i t rogen and fo rming f ine T iXp a r t i c l e d i s t r i b u t i o n s w h i c h r e s t r i c t a u s t e n i t e g r a i n c o a r s e n i n g i n t h e H A Z . T o u g h n e s s b e n e f i t s h a v e b e e nrepo r ted to be due to r educed H A Z g ra in s ize , r educ ed f r ee n i t rogen and r educe d ha rdn es s r e s u l t i ng f romh i g h e r t e m p e r a t u r e t r a n s f o r m a t i o n p ro d u ct s ( b ot h g r a i n b o u n d a r y a n d i n t r a g r a n u l a r l y n u c l e a t e d ) . I n t h ep re s e n t w ork , the t i t a n iu m ad d i t ion 0 .014% has p roved to be ve ry benef i c i a l a t 3 . 5 k J /m m in th e C-M n-N i -A l s t ee l s . I n the V -B- low A l s ys tem a t 3.5 k J /m m t i t an iu m had l i t t l e ef fec t on Char py to ug hn es s , bu timp rove d CTO D toug hne s s due to r educ t ion in M -Α f r ac t ion and r educ t io n in H A Z ha rdn es s . H o w e ver , inthe V -B-h igh A l s ys tem a t 3 .5 k J /mm, T i r educed bo th the CTO D and Charpy toughnes s due to p romot ionof M -Α c ons t i tuen t s .

A t h ighe r hea t inpu t s , t he bead in g roove Charpy da ta s how ed a s l igh t improvemen t in toughnes s in the C-M n-N i -A l and C-M n-N i -V -B- low A l s ys tems due to T i , bu t a dec reas e in toughnes s in the C-M n-N i -V -B-h i g h A l s y s t e m . F i g u r e 2 5 s u m m a r i s e s t h e o b s e r ve d e ff e ct s of t i t a n i u m o n m i c r o s t r u c t u r a l a n d t o u g h n e s scha nge s for the h igh hea t inp u t bead in g roove w e ld s . The ma i n benef i c i a l f ac to r s a r e be l i eve d to bereduc t ion in G CH A Z co lony s i ze , r educ t ion in ' f r ee ' n i t rogen and p romot ion o f in t r ag ranu la r po lygona lf e r r i t e and ac icu la r f e r r i t e , w h ich occu r r ed in a l l T i - s t ee l s excep t for the T i -B-h igh A l s ys te m a t th e fu s ionbou nda ry (The LEZ phe nom ena) . The ma in de t r i m en ta l f ac to rs a r e be l i eved to be p ro mo t ion o f M -Acons t i tuen t and p rec ip i t a t ion ha rden ing w h ich w ere a f ea tu re o f the T i -Α Ι and T i -B-h igh A l s t ee l s .

T h e r e a s o n fo r t h e d e t e r i o r a t i o n i n H A Z C h a r p y t o u g h n e s s w i t h T i in t h e V - B - h i g h A l s y s t e m w a sp robab ly p rec ip i t a t ion ha rden ing and p romot ion o f M -Α cons t i tuen t combined w i th the f a i lu r e to p romoteac ic u la r f e r r i t e a t the fu s ion l ine (due to LEZ fo rm at ion ) . Bead in g roove CT O D toug hn es s im pro ve d w i t hTi in the V -B s t ee l s bu t de te r io r a ted in the C-M n-N i -A l s t e e l . Th e de t r i m en ta l in f luence r eco rde d in the

CT O D te s t i s p robab ly a r e f l ec tion o f the s ign i f i can t ly h ig he r M -Α f r ac t ion dev e loped in the T i s t ee l (4 .4%higher ) and ind ica te s tha t CTO D i s ve ry s ens i t ive to M -Α cons t i tuen t a s s ugges ted in the l i t e r a tu re .

5 . 2 . 3 A l u m i n i u m

A lumin ium has been r epo r ted to be benef i c i a l to G CH A Z toughnes s due to r emova l o f ' f r ee ' n i t rogen inbo th T i - f r ee and T i - t r ea ted s t ee l s * 2 4 ' . H o w e v e r, i n T i - t r e a t e d s t e e l s i t h a s b e e n o b s e r v e d t h a t a l u m i n i u mreduces the e f f i c i ency o f the T iN pa r t i c l e d i s t r ibu t ions , r e s u l t ing in l e s s g ra in boundary p inn ing* 2 5 ' andth is could have a negat ive ef fect on HAZ toughness .

In th e C-M n-N i -T i -A l s t ee l s exa m ine d in the p re s en t w ork , no e ff ec t of a l um in iu m w as obs e rved in bead ing r o o v e C h a r p y t e s t s a t 3. 5 k J / m m . H o w e v er , t h e 0 .1 m m C T O D t e m p e r a t u r e w a s d e p r e s s e d b y a l u m i n i u m

and in abs en ce o f an y mic ro s t ruc tu ra l r eas on w h ich cou ld exp la in th i s dep res s io n , it m us t be a s s u m ed th a t' f r ee ' n i t r o g e n w a s re d u c e d by a l u m i n i u m .

I n t h e T i - B s t e e l s a t 3 .5 k J / m m , a l u m i n i u m w a s c l e a r l y d e t r i m e n t a l t o t o u g h n e s s w i t h a n e l e v a t i o n o f b o t ht h e C h a r p y a n d C T O D t r a n s i t i o n t e m p e r a t u r e s . T h i s w a s a s s o c i a te d w i t h i n c r e a s e d M - Α c o n s t i t u e n t , h i g hH A Z h a r d n e s s a n d re d u c e d f r a c t io n s of i n t r a g r a n u l a r f e r r i t e m o r p h o l o g i e s ( A F a n d P F ( I ) ) . S i m i l a robs e rva t ion s w ere ma de for the T i-V -B s t eel s a t 3 . 5 k J /m m . In the C-M n-X i -V -A l s t ee l s , a l um in iu m w a sobs e rv ed to be benef i c i a l to H A Z toughnes s a t 3 .5 k J /m m . The ma in r eas o n fo r th i s i s be l i ev ed to beredu c t ion in the ' f ree ' n i t rog en l eve l o f the G CH A Z. In the V -B s t ee l s a t 3 .5 k J /m m , a lu m in iu m w a so b s e r v e d t o b e d e t r i m e n t a l to H A Z t o u g h n e s s. T h i s w a s a s s o c i a te d w i t h a r e d u c t i o n i n t h e v o l u m ef rac t ions o f in t r ag ranu la r f e r r i t e morpho log ies (A F and P F ( I ) ) .

A t the h igh e r hea t inpu t of 7 .5 k J / m m , a lum in ium w a s gene ra l ly obs e rved to be de t r i m en ta l to H A Ztoug hne s s . The on ly excep t ions to th i s w ere the Ch arp y and CTO D res u l t s fo r the C-M n-N i -V s t e e l s andthe CT O D res u l t s for the C-M n-X i -T i s t ee ls . F igu re 26 s u m m ar i s e s the ma jo r in f luences o f a lu m in iu m onmi c ro s t ru c tu res and tou ghn es s of the 7.5 k J /mm bead in g roove w e lds . The on ly benef i c i a l f ac to r s o f no tew ere r educ t ion o f ' f ree ' n i t rog en and fo r T i -bea r ing s t ee l s a r educ t ion in p r im ar y f e r r i t e f r a c t ion . Th e

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f ac to r s r educ ing toughnes s w ere p romot ion o f M -Α cons t i tuen t , i nc reas e in H A Z hardnes s , inc reas e inG CH A Z co lony s i ze and r educ t ions in the p ropor t ions o f ac ic u la r f e r r i te and in t r a g r an u la r po ly gon a lf e r r i t e .

Th e ma in r e as on fo r the imp rovem en t in toughn es s o f the van ad i um s tee l s w i th a lu m in iu m w as r educ ed' f r ee ' ni t rogen. No s ignif icant ef fects on micros t ructure were observed in these s teels . The benef ic ia l ef fecto f a lumin ium on CTO D of the t i t an ium s tee l w as though to be due to the r educ t ion in ' f r ee ' n i t rogenou tw e igh ing the de t r imen ta l mic ros t ruc tu ra l e f f ec t s o f inc reas ed g ra in s i ze , M -Α f r ac t ion and H A Zh a r d n e s s .

5.2.4 B o r o n

In w e ld me ta l s and H A Zs bo ron can be u s ed in combina t ion w i th t i t an ium to inc reas e ac icu la r f e r r i t ed e v e l o p m e n t a n d r e d u c e ' fr e e ' n i t r o g e n , t h u s i m p r o v i n g t o u g h n e s s . I n t h e t i t a n i u m t r e a t e d l o wa l u m i n i u m s t e e l s e x a m i n e d i n t h e p r e s e n t w o r k , b o r o n d e p r e s s e d C h a r p y a n d C T O D t r a n s i t i o nt e m p e r a t u r e s a t b o t h h e a t i n p u t s .

In the va na d i um low a lu m in iu m s tee l s , bo ron impro ved toug hne s s s ign if i can t ly in a l l t e s t s and a t bo thhe a t inpu t s . Th i s imp rove me n t occu r r ed des p i t e inc r eas es in G CH A Z hardne s s and co lony s i ze , an d in thecas e of 3 .5 k J /m m H A Zs an inc reas e in M -Α f r ac tion , the im prov em en t i s a s s u me d to be due to r edu c t ion in' f r ee ' n i t rogen by BN p rec ip i t a t ion .

F i g u r e 2 7 s u m m a r i s e s t h e m i c r o s t r u c t u r a l a n d t o u g h n e s s c h a n g e s d u e t o b o r o n i n t h e 7 . 5 k J / m m b e a d i ng roove w e lds . Th e ma jo r benef i c i al f ac to rs w ere r educ t ion in M -Α f r ac tion , p romot ion of in t r a g r an u l a rpo lygon a l f e r r i t e and r educ t ion o f ' f r ee ' n i t rogen w h ich occu r r ed in bo th the T i - low A l and V - low A l s ys tem .The de t r imen ta l e f f ec t s , w h ich w ere ou tw e igh ted by the above f ac to r s , w ere p romot ion o f P F and r educ t ionof AF in the Ti- low Al s teel and incr eas e in HAZ ha rdn es s wi th a n inc reas e in GC HA Z colony size in the V-low Al s teel .

5 .2 .5 N i t r o g e n

N i t rogen i s gene ra l ly r ega rded as be ing de t r imen ta l to H A Z toughnes s due to i t s embr i t t l ing e f f ec t w henin i ts ' f ree ' form. How ever , n i t r i de s such as TiX* ar e reg ar de d as bein g benef ic ia l to HAZ tou gh ne ss i fp re s en t in s u i t a b le vo lume f r ac t ions and s i ze d i s t r i bu t i ons . Th us , the in f luence o f n i t rog en on H A Ztou ghn es s depe nds c r i t i ca l ly on the s t ee l type and w e ld ing cond i t ions be ing cons ide red . In the p res en tinv es t i ga t ion , tw o n i t roge n l eve l s w ere exam ined in h igh s i l i con , h igh a lu m in i um Ti -V -N b s t ee l s . TheG leeb le Ch ar py da ta and the bead in g roove Cha rpy a t 7 .5 k J /m m reco rded an imp rove me n t in tou gh nes sand th i s i s cons i s t en t w i th a r educ t ion in the vo lume f r ac t ion o f F S in the mic ros t ruc tu res a t bo th hea tinpu t s . T he bead in g roove Cha rpy da ta , how ever , r eco rded a de t r im en t a l in f luence o f n i t roge n a t 3 .5kJ / m m a nd th i s i s cons i s t e n t w i th the obs e rva t ion o f h ig he r G CH A Z g ra in si ze in th i s w e ld . The 0 .1 m m

CTO D tempera tu re o f the 3 .5 k J /mm H A Z w as low ered by inc reas ed n i t rogen and th i s i s be l i eved to be dueto the low er obs e rved M -Α f r ac t ion ou tw e igh in g the inc rea s e in 'f r ee ' n i t rogen .

A t 7 .5 k J /m m no d i f fe r ence in M -Α f r ac tion w as obs e rved and t he e l eva t ion o f 0 .1 mm C TO D tem pe ra tu rei s p r e s u m ed to be due to h ighe r ' fr ee ' n i t roge n in the h igh e r n i t rog en s t ee l .

5.2.6 S i l i c o n

In H A Zs s i l i con has s omet imes been obs e rved to have a de t r imen ta l e f f ec t on toughnes s due to p romot iono f M - Α c o n s t i t u e n t s ' 14.15). In the p res en t w ork , a c l ea r dep res s ion o f 0 .1 mm CTO D tem pe ra t u re w asobse rved w ith low er in g s i l icon levels in the bead in groove welds a t both heat inp uts . How ever , bead ingroove Ch ar py t es t s an d Gleeble Ch arp y tes ts fa i led to show a con s is te nt effect of s i l icon . At 3 .5 k J / m m ,low er ing s i l i con f rom 0 .40 to 0 .19% w as benef i c i a l to bead in g roove Charpy toughnes s bu t fu r the rred uct ion in s i l icon to 0 .1% was not benef ic ia l . Th is la t te r effect may hav e been due to the h ig her la thm ar t en s i t e con te n t o f the 0 .1% S i s t ee l caus ed by i t s s ligh t ly h igh CE V compared to the 0 .19% S i s t ee l . A t7 .5 k J /m m no s ign i f i can t e f fect of s i li con w as obs e rved in the Cha rpy t e s t s ( t r ans i t ion t em pe ra t u re s be ingw i th in ~ -8°C o f each o the r ) and th i s i s cons i s t en t w i th the p ra c t i ca l ly ide n t i ca l G CH A Z mi c ro s t ruc tu re s

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obs e rved ( excep t ing M -Α f r ac t ions ) . G leeb le Ch arp y t e s t s a t bo th hea t inp u t s r a nk ed the 0 .1% s tee l abovethe 0 .19% Si s tee l bu t ra nk ed the 0 .40% Si s tee l h igh es t . Th is is bel ieve d to be a ref lect io n of th e lowerca rbon and n i t roge n of the 0 .40% S i s t ee l r a t he r th an a bene f i c ia l in f luenc e o f S i on s im u la ted H A Z Ch arp y

toughnes s . The obs e rva t ions made in the s i l i con s e r i e s s ugges t tha t the Charpy t e s t i s no t ve ry s ens i t ive tova r i a t ion s in M -Α vo lume f r ac t ion and th i s con t r a s t s s t rong ly w i th the obs e rved e f f ec t s of M -Α on CTO D .

5.3 E f f e ct o f A l l o y i n g E l e m e n t s o n I n t e r c r i t i c a l l y R e h e a t e d G C H A Z T o u g h n e s s

In t h e p r e s e n t w o r k , i n t e r c r i t i c a l l y r e h e a t e d G C H A Z m i c r o s t r u c t u r e s w e r e p r o d u c e d b y t h e r m a ls i m u l a t i o n a n d w e r e e v a l u a t e d by t h e C h a r p y t e s t . T h e m a i n a d v a n t a g e s o f t h i s m e t h o d a r e t h a t i t i squ ick , the rmal cyc les a r e r ep roduc ib le and the ICG CH A Z reg ions p roduced a r e r e l a t ive ly l a rge , a l low ingacc u ra t e loca t ion o f the Charp y no tch . The t e s t r e s u l t s , w h ich a r e g iven in Tab le 7 , s how th a t Ch arp ye n e r g i e s fo r e a c h p a r t i c u l a r s t e e l a r e s c a t t e r e d , e v e n t h o u g h p r o b l e m s a s s o c i a t e d w i t h s a m p l i n g , w h i c h a r eo f ten quo ted a s a s ou rce o f s ca t t e r in r ea l w e ld t e s t s , have been e l im ina ted . Th i s ind ica te s th a t s c a t t e r i sa n i n h e r e n t f e a t u r e o f G C H A Z a n d IC G C H A Z t o u g h n e s s a n d i n v ie w of t h i s , t h e a v e r a g e C h a r p y e n e r g i e shave been us ed in the fo l low ing ana l ys i s o f e ff ec ts o f e l em en t s on ICG CH A Z tou gh nes s .

The e ff ec t of va na d iu m on ICG CH A Z toughne s s of A l t r ea te d s t ee l s can be s een by com pa r in g S te e l s A andΒ i n T a b l e 7. A t 3 .5 k J / m m , v a n a d i u m w a s o b s e r v e d t o b e d e t r i m e n t a l t o t o u g h n e s s , p r e s u m a b l y d u e t o ac o m b i n a t i o n of p r o m o t i o n o f M -Α c o n s t i t u e n t s i n t h e I C G C H A Z a n d p r e c i p i t a t i o n h a r d e n i n g . A t 7 . 5k J / m m , v a n a d i u m w a s o b s e r v e d t o b e s l i g h t ly b e n e f ic i a l t o I C G C H A Z C h a r p y t o u g h n e s s . D e t a i l e dm e t a l l o g r a p h i c c h a r a c t e r i s a t i o n w a s n o t c o n d u c t e d o n H A Z s i m u l a t e d s p e c i m e n s a n d t h u s t h e r e a s o n f o rimproved toug hne s s i s no t know n . H ow eve r , bas e d on p rev ious a rg um en ts for the G C H A Z (F ig . 24 ) i ts eem s p robab le tha t the benef i c i a l in f luences of va na d iu m ( r edu c t ion o f e f f ec tive g ra i n s i ze and r ed uc t iono f ' f r ee ' n i t rogen ) ou tw e i gh the de t r im en ta l fac to r s s uch as p rom ot ion of M -Α con s t i t ue n t and p re c ip i t a t ionh a r d e n i n g i n t h e I C G C H A Z a t 7 .5 k J / m m .

The e f f ec t o f t i t an ium on ICG CH A Z toughnes s can be s een by compar ing S tee l s A and C in Tab le 7 .

T i t an ium w as obs e rved to be ve ry benef i c i a l to ICG CH A Z toughnes s a t bo th hea t inpu t s . Th i s i s p r es umedto be due to the com bine d benef ic ia l effects of red uce d ef fect ive g ra in s ize an d redu ce d ' f ree ' n i t r og encon ten t on toughnes s .

A l um in iu m w as obs e rve d to be s l igh t ly benef i c i al to ICG CH A Z tou gh ne s s o f the C-M n-N i -T i s t ee l s (S tee lC ν S tee l D ) a t bo th hea t inp u t s . H ow ever , bo th s e t s of r e s u l t s w ere e f f ec t ive ly on th e upp er s he l f a t thed e s i g n a te d t e s t t e m p e r a t u r e s , m a k i n g i t i m p o s s i b l e t o c o m m e n t o n t h e e f fe c t of A l on t r a n s i t i o ntem pe ra t u re . I n the abs ence o f any mic ro s t ruc tu ra l e ff ec ts , a lu m in iu m w ou ld be expe c ted to be b enef i c i a ldue to s l igh t r edu c t ion in ' f ree ' n i t roge n in the ICG C H A Z .

Boron w as a l s o obs e rved to be s l igh t ly benef i c i a l to ICG CH A Z toughnes s in the C-M n-Ti low A l s t ee l s (Dand F ) a t bo th hea t inpu t s . Th i s cou ld aga in be due to fu r the r r educ t ion in ' f r ee ' n i t rogen con ten t o f the

ICG CH A Z and a l s o the r edu c t ion in M -Α f r ac t ion due to e l eva t ion o f Ae3 by boron*2

*?'.

N i t rog en in the V-Ti-X b s t ee l s un der inv es t iga t io n (S te e l s L an d M ) s ho w e d a bene f i c i a l e f f ec t onICG CH A Z toug hne s s . Th i s i s p robab ly a cons eque nce of r educed e f f ec t ive g ra i n s i ze cau s ed by p r om ot io nof g ra in bound ary f e r r i t e morpho log ies in the G C H A Z o f the h igh n i t r oge n s t ee l .

S i l i con in the C-M n-N i -Cu-N b s t ee l s (S tee l s Ο , Ρ and Q ) s how ed l i t t l e s ys temat i c e f f ec t on ICG CH A Ztough nes s . Th i s obs e rva t io n i s s im i la r to tha t of the bead in g roove Ch arp y t e s t s an d i s tho ug h t to be dueto th e lack of s ignif i cant ef fects of s i l icon on factors w hich inf lu ence the Ch ar py tes t such as ef fect ive gr ai nsize, ' f ree ' n i t roge n l eve l and H A Z ha rdn es s .

In H A Z toughnes s s tud ies o f mu l t ipas s w e lds , the ICG CH A Z i s o f t en quo ted a s be ing the r eg ion o f low es t

f r ac tu re toughnes s *2 7

' . Th i s i s u s ua l ly exp la ined in t e rm s of l a rge h igh ca rbon m ar te ns i t e i s l an ds fo rmeda t p r i o r a u t e n i t e g r a i n b o u n d a r i e s d u r i n g t h e i n t e r c r i t i c a l t h e r m a l c y c le . S t e e l s w h i c h a r e p a r t i c u l a r l yp r o n e t o t h i s t y p e of e m b r i t t l e m e n t a r e t h os e w i t h h i g h a l l o y i n g e l e m e n t c o n c e n t r a t i o n s a n d i n p a r t i c u l a r ,s t e e l s w i t h v a n a d i u m a n d h i g h s i l i c o n c o n t e n t s h a v e b e e n o b s e r v e d t o b e p a r t i c u l a r l y s u s c e p t i b l e t o

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in tercr i t ica l embr i t t lement*2** '. S tee l s w i th low er a l loy e l em en t l eve l s and s ome T i t r ea ted s t ee l s havebeen observed to be f ree f rom low ICGCHAZ toughness .

In the p res en t w ork a t 3 .5 k J /mm i t w as no ted tha t a l l t he T i t r ea ted s t ee l s excep t fo r thos e con ta in ingv a n a d i u m o r v a n a d i u m w i t h h i g h si li c on ( S te e l s K , L a n d M ) h a d h i g h e r C h a r p y t o u g h n e s s i n t h eICG CH A Z co mp ared to the G CH A Z. I t w as a l s o no ted tha t a l l t he s t ee l s w h ich exh ib i t ed low er ICG CH A Ztoug hnes s th an G CH A Z tough nes s w ere e i th e r vana d iu m bea r in g o r had h igh s i li con con ten t s . A t theh igh er hea t inp u t , s imi la r obs e rva t ions w ere ma de conce rn ing the T i t r ea ted s tee l s . H o w e ver , s omeano ma lou s behav iou r w as obs e rved for van ad iu m bea r ing s t ee l s Β and E w h ich unexp ec ted ly s how ed a nimp rove me n t in toug hnes s a f t e r in t e r c r i t i ca l r ehea t ing . W i th the excep t ion o f the abov e an om al i e s ,obs e rva t ions made in the p res en t w ork genera l ly con f i rm p rev ious s tud ies ind ica t ing tha t T i t r ea tmen t ,low V levels and low Si levels are benef ic ia l to ICGCHAZ toughness .

5 .4 H A Z S t r u c t u r e / P r o p e r t y R e l a t i o n s h i p s

S t ru c tu re p rope r ty r e l a t ions h ips fo r h igh hea t inpu t H A Zs a re no t w e l l under s tood . F ac to r s r epo r ted toinf luence toughness are as fo l lows:

( i) Typ e of t ran sfor ma t ion prod uct

(ii) Effe ctive gra in s ize or fra ctu re facet s ize

( i ii ) M i c roph as e type , vo lume f r ac t ion and s i ze d i s t r ib u t ion

( iv ) H A Z har dne s s o r y ie ld s t r e ng th due to t r an s fo rm at ion , p r e c ip i t a t io n an d s o l id s o lu t ion

s t r eng then ing e f f ec t s

(v) F re e n i t rog en

In the p res en t w ork , qu i t e a w ide r ange o f t r ans fo rmat ion p roduc t s have been deve loped in the 7 .5 k J /mmH A Zs , mak ing i t pos s ib le to exam ine the i r e ff ect s. F rom w e ld me ta l s tud ies i t i s w e l l e s t ab l i s he d th a t ah igh p ropor t ion o f ac icu la r f e r r i t e is bene f i c i a l to toug hnes s . I n the p res e n t s tudy s ome o f the H A Zs havedeve loped in exces s of 20% ac icu la r f e r r i t e w i th s imi la r qu an t i t i e s of in t r a g r an u l a r po lyg ona l f e r r i t e .Thes e s t ee l s hav e a l s o t ended to have the h ighes t l eve l s of Ch arpy tou ghn es s . The obs e rved r e l a t ions h ipsbe tw e en H A Z Ch arp y 40 J t r ans i t ion t em pe ra t u re s and mic r os t ru c tu re a r e s how n in F ig . 28 . Th i s f igurei l l u s t r a t e s th e b e n e f i c i a l e ff ec t o f i n c r e a s i n g i n t r a g r a n u l a r f e r r i t e c o n t e n t ( A F + P F ( I) ) a n d t h ede t r im en ta l e f fec t o f h igh f e r r i t e w i th s econd phas e (F S ) con ten t on to ughn es s .

W e l d m e t a l a n d H A Z s t u d i e s h a v e s u g g e s t e d t h a t g r a i n b o u n d a r y n u c l e a t e d f e r r i t e h a s a d e t r i m e n t a lef fect on toughness* 2 9 - 3 0 ' . I t has been pos tu la te d tha t g r a in boun dary f e r r i t e g r a i n s of fe r a p r e f e r r e d s i t e

for in i t i a t ion and p ropag a t ion o f c l eavage and tha t toughne s s i s low ered w i th inc reas ing g ra in boun daryfe r r i t e w id th and inc rea s e g ra in bound ary f e r r i t e vo lum e f r ac t ion . Th i s behav io u r may be r e l a t ed to s t r a inconcentra t ion ef fects in the sof ter pro-eutecto id fer r i te phase and the tendency for gra in boundary fer r i teto ex i s t in con t inu ous bands a long the p r io r aus te n i t e g r a in s t ru c tu re .

M ic ro phas es a r e a l s o r epo r ted to have a de t r im en ta l e f fect on bo th w e ld me ta l and H A Z toughn es s . I nw e ld me ta l s , b locky l a th mar tens i t i c mic rophas es have been r epo r ted to be pa r t i cu la r ly de t r imen ta l toi m p a c t p r o p e r t i e s * 3 1 ' . H ow ever , fo r w e ld me ta l s tw inned mar ten s i t i c mic ropha s es a l s o r educ e imp ac tt o u g h n e s s . I n H A Z s , M -Α c o n s t i t u e n t s c o n t a i n i n g t w i n n e d m a r t e n s i t e a r e r e p o r t e d t o h a v e a v e r ys ign i f i can t e f f ec t in low er ing CTO D leve l s bu t a r e l e s s de t r imen ta l to impac t p roper t i e s * 1 5 ' . M ic rophas escons i s t in g o f f e r r i t e - ca rb id e agg rega tes can a l s o low er to ug hn es s , bu t a r e u s u a l l y cons ide red to bep r e f e r a b le to m a r t e n s i t i c m i c r o p h a s e s . I n s o m e s y s t e m s , d e c o m p o s i t i o n o f M - Α t o f e r r i t e c a r b i d ea g g r e g a t e s c a n b e d e t r i m e n t a l t o t o u g h n e s s b u t t h i s p r o b a b l y d e p e n d s o n t h e o r i g i n a l a u s t e n i t e -mar tens i t e ba lance in the o r ig ina l M -Α cons t i tuen t s : cons t i tuen t s cons i s t ing o f a h igh p ropor t ion o f s t ab ler e ta ined aus ten i t e be ing benef i c i a l .

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In the p re s en t w ork , mu l t ip le l ine a r r eg res s ion ana lys i s w as conduc ted to iden t i fy s t ru c t u r e p rop er tyre la t ions h ips in the 7 .5 k J /mm bead in g roove w e lds . The independen t va r i a t ions u s ed fo r the r eg res s ionsw ere ; g r a in bou nda ry f e r r i t e f r ac t ion (P F + P F (G )) , I n t r a g r an u l a r f e r r i t e f r ac t ion (A F + P F ( I) ) , f e r r i t e

w i th s econd pha s e f r ac t ion (F S ) , mic ro phas e ca rb ide f r ac t ion (C) and m ic rop has e M -Α f r ac t ion (M -Α ) . Thed e p e n d e n t v a r i a b l e s w e r e 0 .1 m m C T O D t e m p e r a t u r e a n d C h a r p y 4 0 J t e m p e r a t u r e .

The r e s u l t ing r eg res s ion equa t ions a r e a s fo l low s :

0 .1 m m CT OD Te mp . , °C = 10 .80 PF + 10 .12 FS + 8 .91 AF + 4 .40 C + 10 .16 MA- 1 1 1 5 . . . ( 2 )

Ch arp y 40 J Te mp . , °C = 4 .06 PF + 3 .64 FS + 2 .05 AF + 5 .53 C + 4 .7 8 MA- 4 0 1 . . . ( 3 )

wh ere P F = (PF + PF (G)) and A F = (AF + PF ( I) )

Cor re la t io n coe f fi c ien t s for the equ a t io ns w ere 0 . 80 and 0 .76 r e s pec t ive ly . G ra ph s of ca l cu la te d ve r s usobs e rved toughnes s a r e g iven in F ig . 29 .

Bo th ana lys es s how tha t max imis ing the ac icu la r f e r r i t e f r ac t ion w h i l s t r educ ing the p ropor t ions o f P Fand F S i s bene f i c i a l to tough nes s . The r eg res s ion equ a t ion s s ugg es t a 10% inc rea s e in ac icu la r f e r r i t e a tthe expe ns e of F S p roduc es a 12°C dep res s ion in 0 .1 mm te m pe ra tu re a nd a 16°C de p re s s io n in Ch arp y 40 Jt em pe ra t u re . F o r bo th Ch arp y and CTO D tes t s , r edu c ing P F in f avour of F S i s s l ig h t ly benef i c i a l .

F o r CTO D tes t s , r ep lac ing M -Α phas e w i th f e r r i t e ca rb ide mic rophas es i s s how n to be h igh ly benef i c i a lr e d u c i n g t h e 0 .1 m m C T O D t r a n s i t i o n t e m p e r a t u r e b y ~ 6 ° C p e r p e r c e n t o f M-Α. H o w e v e r , f o r C h a r p y t e s t sthe re appea r s to be l i t t l e in f luence o f mic rophas e type on toughnes s .

Recen t w ork by F ukada e t a l* 1 5 ' r epo r te d a muc h l a rg e r e ff ec t o f M -Α f r ac t ion on CTO D co mp ared toC h a r p y t r a n s i t i o n t e m p e r a t u r e . T h e r e g r e s s i o n e q u a t i o n de v e l o p e d b y t h e s e a u t h o r s b e t w e e n 0 . 2 5 m mCTO D t r an s i t i on t e m pe ra t u re , M -Α fr ac tion and f r ac tu re f ace t s i ze i s a s fo l low s :

0 .25 m m CT OD Tem p. , °C = -10 .0 d-* + 10 .3 (% M-A) + 23 .4 . . . (4)

Th i s equa t ion s ugges t s a ve ry pow er fu l in f luence o f M -Α on t r ans i t ion t empera tu re (10 .3°C/% M -A ) .

A s i m i l a r m u l t i p l e l i n e a r re g r e s s i o n a n a l y s i s h a s b e e n c o n d u c t e d i n t h e p r e s e n t w o r k u s i n g t h e 7 . 5 k J / m mH A Z da ta . The inde pen den t va r i ab les w ere M -A f r ac t ion and me an F S co lony s i ze (be l i eved to r ep res en tf r a c t u r e f a ce t si ze ) a n d t h e d e p e n d e n t v a r i a b l e w a s 0 .1 m m C T O D t e m p e r a t u r e . T h e r e s u l t o f t h i s a n a l y s i swas as follows:

0 .1 m m CTO D Tem p. , °C = -11 .03 d- i + 9 .58 (% M-A) - 65 .3 . . . ( 5 )

T h e c o r r e l a t i o n c oe ff ic ie n t w a s 0. 6 3 a n d t h e g r a p h of m e a s u r e d v e r s u s c a l c u l a t e d t r a n s i t i o n t e m p e r a t u r e i sg i v e n i n F i g . 3 0 . T h e a b o v e e q u a t i o n s h o w s g o o d a g r e e m e n t w i t h t h e p u b l i s h e d l i t e r a t u r e a n d a g a i nind ic a te s a pow er ful e ff ec t of M -A f r ac t ion on CTO D . H ow ever , i t s hou ld be no t ed th a t the co r r e la t ioncoef f i c i en t w as low and the da ta qu i t e s ca t t e r ed s ugges t ing tha t f ac to r s add i t iona l to thos e o f M -A andf rac tu re f ace t s i ze a r e ac t in g on toug hne s s . O ne o f thes e f ac to r s w h ich w as iden t i f i ed in p rev i ous s ec t io nsis ' f ree ' n i t r oge n. Th is factor is d i f f icult to quan t i fy in the HAZ of mic roal lo yed s t ee ls and ca nn ot be ea s i lyaccoun ted for in the p res en t ana ly s i s . A fu r the r f ac to r w h ich can be cons ide red , how eve r , i s H A Z ha rd ne s sw h ich , in h igh hea t inpu t H A Zs , i s a r e f lec t ion of the con t r ibu t ion s of d i s loc a t ion s t r en g t he n i ng , s o l ids o l u ti o n s t r e n g t h e n i n g a n d p r e c i p i t a t io n s t r e n g t h e n i n g to H A Z y ie l d s t r e n g t h .

A n u m b e r of s t u d i e s h a v e r e p o r t e d th e in f lu e n c e o f y i e ld s t r e n g t h o n t r a n s f o r m a t i o n t e m p e r a t u r e . T h eo b s e r v ed r e l a t i o n s h i p b e t w e e n H A Z h a r d n e s s a n d 0.1 m m C T O D t e m p e r a t u r e i n t h e 7 .5 k J / m m w e l d s i sshown in F ig . 31 .

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Tw o fu r the r mu l t ip le l inea r r eg res s ion ana lys es w ere conduc ted w i th independen t va r i ab le o f g r a in s i ze(me an F S co lony s i ze) , M -A f r ac t ion and H A Z ha rd ne s s and de pen den t va r i ab les o f 0 .1 m m CT O Dt e m p e r a t u r e a n d C h a r p y 4 0 J t r a n s i t i o n t e m p e r a t u r e . T h e r e s u l t i n g r e g r e ss i o n e q u a t i o n s a r e a s fo ll ow s :

0.1 mm CT OD Tem p., °C = 0.057 (pm) + 6.61 (% M-A) + 0.8 55 (HV)-259 . . . (6)

Ch arp y 40 J Te m p. , °C = 0.18 8 (pm ) + 1.48 (% M-A) + 0.738 (HV)-206 . . . (7)

Co r re la t ion coe f fi c ien t s for the equa t ions w ere 0 .76 and 0 .53 r e s pec t ive ly . G ra phs of ca lcu la ted ve r s u sobs e rved tou ghn es s a r e g iven in F ig . 32 . Bo th eq ua t ion s i l lu s t r a t e th a t H A Z toug hne s s i s in f luenced byef f ec t ive g ra in s i ze , M -A f r ac t ion and H A Z ha rdn es s . I n bo th equ a t ion s the con t r ibu t io n f rom ha r dn es swa s s im ila r a t abou t 8°C pe r 10 HV . Th e ef fect of HA Z yie ld s t r en gth on t ran s i t i on can be cal cul a te d f roma know ledge o f the r e l a t ions h ip be tw een H A Z hardnes s and H A Z y ie ld s t r eng th ' 3 2 ' . F rom th is i t has beenes t ima ted tha t the e f f ec t o f H A Z y ie ld s t r eng th on t r ans i t ion i s abou t °C per Newton, which is in goodagreemen t w i th pub l i s hed va lues fo r p r ec ip i t a t ion ha rden ing in con t ro l l ed ro l l ed s t ee l s ' 3 3 ' .

The equa t ions aga in i l lu s t r a t ed tha t CTO D tes t ing i s more s ens i t ive to M -A phas e than the Charpy t e s t .F o r CTO D tes t s equa t ion (6 ) s how s tha t t r ans i t ion t empera tu re i s e l eva ted by 6 .6 °C/% M -A w hich i s ingood ag ree m en t w i th equa t ion (2 ). H ow e ver , the Ch arp y 40 J t r a ns i t i on i s on ly e l eva ted by — 1.5°C/% M -A.E qu at io n (6) a lso indic ates that CTOD is e le vate d by 5 .7°C/100 pm inc rea se in m ea n FS colony s ize (Thisis ab out 11 χ d- i ) an d th is is in ag re em en t wi th equa t io n (5) . In co ntr as t , eq uat ion (7) show s th at theCh arp y 40 J t emp era tu r e i s mu ch mo re s t rong ly in f luenced by g ra in s i ze ; the 40 J t em pe ra tu r e be in ge lev a ted by 18 .8°C/100 pm inc reas e in m ean F S colony s ize .

6 . C O N C L U S I O N S

B e a d i n g r o o v e H A Z C h a r p y a n d C T O D t e s t s , a n d s i m u l a t e d H A Z C h a r p y t e s t s , h a v e b e e n u s e d t oev a lu a te th e H A Z tough nes s of a r ang e o f s t ee l s o f va r i ous compos i t ions . Th e H A Z m ic ro s t ru c tu res o fthe s e s t ee l s hav e been fu l ly cha rac te r i s e d us ing op t i ca l and S EM techn iques . Th e fo l low ing con c lus ionshave been r eached .

1. G r a in coa r s ened H A Z co lony s i zes w e re obs e rved to be r educed by a l l mic ro a l loy ing e lem en t s .The l a rges t r educ t ions w ere obs e rved in the T i -bea r ing s t ee l s .

2. A c ic u la r f e r r i te and in t r ag ran u la r po lygona l f e r r i t e w ere p romoted in h igh hea t inp u t w e ldsm ad e in Ti- low Al an d Ti-B- low Al s tee ls . Aci cula r fer r i te was a lso prom oted in Ti-B-h igh Als teels but th is ef fect was los t c lose to the fus ion boundary where a l ight e tching zone was

formed.

3. G r a in coa r s ened H A Z mic ro phas e con ten t w as obs e rved to be r e l a t e d to ca rbon con ten t inhigh input welds . The volume f ract ion of M-A was noted to be inf luenced by a l loy content .

4. V a na d iu m in h igh hea t inpu t w e lds w a s obs e rved to p romo te M -A con s t i tue n t and e leva teH A Z h a r d n e s s a n d t h i s t e n d e d t o b e d e t r i m e n t a l t o t o u g h n e s s . A t l o w e r h e a t i n p u t s ,how e ver , vanad ium w as o f ten obs e rved to be benef i c ia l to H A Z toug hnes s . Th i s w as be l i evedto be due to reduct ion in GCHAZ colony s ize and ' f ree ' n i t rogen levels .

5. Ti t an ium w as gene ra l ly obs e rved to be benef i c i a l to tough nes s due to r educ t ion in G CH A Zco lony s ize , r educ t ion in ' f ree ' n i t rog en an d p romot ion o f in t r ag ran u la r f e r r i t e morph o log ies .H ow ever , a t h igh hea t inpu t and in the p res ence of a lu mi n iu m, t i t an ium p rom oted M -Acons t i tuen t and e leva ted ha rdnes s and cou ld thus r educe H A Z toughnes s .

15



6. Alu min ium exhibited no significant beneficial influence on HAZ m icro stru ctu re bu t in thepresence of Ti and Β increased GCHAZ colony size, elevated hardness, promoted M-A andreduced the proport ions of intrag ranu lar ferr i te . Alum inium w as thus usu al ly observed to be

det rim en tal to HAZ toughness in these steel s. A bene ficial effect of AI wa s ob serv ed,how ever, for the vana dium steels due to red uct ion in 'free' nitro gen . Th e effect of Al on the Tisteels w as not clear cu t.

7. Boron in high heat input welds made in Ti-low Al and V-low Al steel was observe d to reduceM-A levels and promote intragranular polygonal ferrite. These observations combined with apowerful effect on reducing 'free' nitrogen are believed to be responsible for the largeobserved impro vem ent in HAZ tough ness of the B-low Al steels.

8. Si l icon was observed to have a ma rked de tr im en tal inf luence on HAZ CTOD due toprom otions of M-A constituents but no cons istent effect on Charpy tou gh nes s was observed .

9. Total nitroge n conte nt showed no cons istent effect on HAZ toug hnes s of a V-Ti steel.

10. In te rc r it i ca l rehea t ing of GCHAZ m icros t ruc tu res resu l ted in de te r iora t ion in Cha rpytough ness of some steels, but elevation of toug hne ss in othe rs. In genera l Ti tre ate d steelsimproved after the intercritical cycle, whereas vanadium steels and higher silicon bearingsteels deteriorated.

11. HAZ toughness was observed to increase with increasing fractions of intr ag ran ula r ferr i temorphologies (Acicular ferrite and intragranular polygonal ferrite) and reducing fractions ofpr imary fe r r i t e (a t p r ior aus ten i te g ra in boundar ies ) and fe r r i t e wi th second phase(W idman stät ten s ideplates) . For CTOD tests M-A const i tuents w ere very detr im enta l bu t forCh arpy tests th ere w as little effect of micro phase type on toughne ss.

12. Mult iple l inear regression equat ions have been gen erate d for HAZ Ch arp y and CTO Dtoughness of h igh hea t input welds . Thes e equa t ion s sugges t th a t HAZ tou ghn ess i sinfluenced by grain size, M-A fraction and HAZ hard ness (i .e. HAZ yield stre ng th) . Th eequations indicate that HAZ grain size is the dominant factor for Charpy tests but HAZ M-Afraction is dominant for CTOD.

7 . REFERENCES

1. K. Nish ioka and H. Tam ehiro, 'High Stre ngt h Titanium -Oxid e Be arin g Line Pipe Steel forLow Tem pera ture Service' , Proc. Conf. M icroalloying '88, Chicago, 1988.

2. R.E. Dolby, 'Review of Work on the Influence of Va nad ium on the M icr ost ruc tur e andTou ghne ss of Fer ritic W eld M etal ', IIWDOC J-33-80, IX-1213-81.

3. T.W. Lau, GR . W ang and T.H. North, 'HAZ Frac ture Toughne ss of Ti tan ium Co ntainin gSteels ' , M ateria ls Science and Technology, 5, pp575-583, (1989).

4. P.L. Ha rriso n and P.H.M. Ha rt, 'Influences of Steel Comp osition and W elding Pro cedu re onthe HAZ Toughness of Thick Sect ion Struc tural Steels ', 'Microalloying Inter nat io nal ' , AW SHou ston, Nov. 1990.

5. X. Mor i , H. Homma, S. Oki ta and M. W aka bay ash i , 'Mecha nism of Notch Tou ghne ssImp rovem ent in Ti-B Bearin g Welding Me tals ' , IIW Doc. IX-1196-81 (1981).

6. S . Kanazama, A. Xaka shima , H. M imu ra , K. Yam ato , K. Ok amo to and Y. Ha giw ara ,'Development of New Steels for High Heat Input Welding( IIW Doc IX-952-76 (1976).

16



7. Y. Ohno, K. Uchino, S. Ma t s u d a , T. Satoh, Y. O k a m u r a , K. Y a m a m o t o and K. Ikeda ,'Development of Low-Temperature Steel for Welding with High Heat Input ' , Nippon SteelTechn ical Repo rt No . 36, pp49-59, (1988).

8. H. Homma, S. Ohkita , S. M atsuda and K. Yamamoto, ' Improvement of HAZ Toughness in

HSLA Steel by Finely Dispersed Ti-Oxide', Paper Present at the 67th AWS Convent ionAt lan ta , USA (1986).

9. J. Tsuboi and H. Terashima, 'Review of Strength and Toughness of Ti and Ti-B MicroalloyedDeposits', Welding in the World, 21, No . 11/12, pp304 -316 (1983).

10. K. Arimochi, R. Someya and K. Bessyo, 'Approach of Local Brittle Zone Free Steel Plate for

Offshore Structures' in Internal Conference on Weld Fa i lures , The Welding Ins t i tu te ,London,1988.

11 . G. Thewlis, The influence of Pipe Plate and Consumables Chemistry on the Composition,Microstructure and Toughness of Weld M etal ' in W elding and Performance of Pipelines, P roc.Conf. The Welding Instit ute, London, 1986.

12. P.L. Harrison, 'Factors Influencing the Toughness of Submerged-Arc Weld ing LinepipeWelds - Part 2 Hardenability Cooling Rate, and A1:0 Ratios' , Welding Institute Res. Bull 30,

pp64 -67, (1989).

13 . I. W atanabe , M. Suzuki , K. Tsukada , Y. Yamazaki and T. Tokunaga, 'Development of NK-

HIWEL Steel Suitable for High-Heat-Input Welding ' , J., Materials for Energy Systems, 6,

No. I,ppl4-23(1984) .

14. Y. Ito, M. Ikeda, Y. Ohmori , H. Ohtani and M. Nakanishi , 'Propert ies of Low Silicon High

Strength Steels ' , IIW Doc. IX-10 21-77 .

15. M. Nakan ishi, Y. Komizo and Y. Fukada, 'Study on the Critical CTOD Properties in the HeatAffected Zone of C-Mn Microalloyed Steels', The Sumitomo Search, 33 , pp22-3 4, (1986).

16 . Am ano, Kudo, I takura and Nakiano , in OMAE 1989, The Hague (1989).

17 . R.J. Pargeter and R.E. Dolby, 'Guidelines for Classification of Ferritic Steel Weld MetalMicrostructural Const i tuents Using the Light Microscope', IIW Doc. IX-1377-85,1985.

18. H. Ikawa, H. Oshige and T. Tanoue, 'Effect of Martensi te-Austeni te Const i tuent on HAZ

Toughness of a High Strength Steels ' , Trans . JWS , 1980 ,11 (2).

19. H. Terash ima and P.H.M. Hart, 'Effect of Flu x T i 02 and Wire Ti Content on Tolerance to

High Al Content of Subm erged-Arc W elds Made with Basic Fluxes' , Proc. Conf. The Effect of

Residual Impurity and Micro-Alloying Elements on Weldability and Weld properties, The

Welding Institute, 1983.

20. T.H. North, H .B. Bell, A. Koukabi and I. Craig, Weld, J. Res. Supp. 58, 343-S, 1979.

21 . K. Hashiguch, T. Kato, M, Nishida and T. Tanaka, 'Effect of Alloying Elem ents and CoolingRate after Annealing on Mechanical Properties of Dual Phase Sheet Steel ' Kawasaki SteelTechnical Report No. 1, pp70-78, September 1980.

22 . P.L. Harrison and P.H.M. Hart , 'Relat ionship between HAZ Micros t ruc ture and CTODTransi t ion Behaviour in Mu ltipass C-Mn W elds', 2nd International Conference on T r e n d s in

Welding Research ' ASM Internat iona l Gatl ingurg, T ennessee, May 1989.

17



23 . N.E. Ha nne rz and B.M. Jonsson-Holmquist, ' Inf luence of Van adium on the HAZ Pro per t ies ofMild Steels', Metal Science 8, (7), Ju ly 1974, pp228-234.

24 . I. W atan abe and M. Suzuki, 'New Steels for High He at Inpu t W elding', M etal Co nstru ctio n,May (1984), pp311-315.

25 . J.Str id and K.E. Easter l ing, 'On the Chem istry and Sta bi l i t y of Com plex C arb ide s andNitrid es in Microalloying Steels ', Lule å Un iversity Techn ical Rep ort, 1985:17T.

26. X.P. Shen and R. Prie stne r, 'Effect of Boron on the M icros tructu re and Ten sile Pr op ert ies ofDua l-Phase Steel ' , Metallurgical Tra nsa ctio ns A, 21 A, pp 2547-2 553 , Sept. 1990.

27. T. Haze and S. Aih ara, 'Metallurgical Factors Con trolling HAZ Tou ghn ess in HT 50 Steels,IIW Doc. 1X-1423-86.

28 . P.L. Har r i son and P .H.M. Har t , 'HAZ Toug hness of Thick Sec t ion S t ruc tur a l S tee l s ' ,Internat ion al Conference on Weld Fai lures ' . The Welding Inst i tu te , Londo n, No vem ber1988, Paper 45.

29. E. Levine and D.C. Hill, 'A Review of the Stru cture and Pro per ties of Welds in Co lum bium orVan adium Con taining High Strength Low Alloy Steel ' , WRC B ulleti n, 213 , 20 (1976).

30. R. Ot te rberg , R . Sands t röm and A. Sandberg , ' In fluence of W idm ans tä t te n Fe r r i te onMe chanical P rope rties of Microalloyed Steels ' M etals Technology pp3 97-408 October 1980.

31. J. G Garla nd and P.R. Kirkwood, To wa rds Improved Subm erged-Arc Weld M et al ' M etalCo nstruction pp275-283, May 1975.

32. O.M. Ak selsen , G. Rørvik, M.I. Onsø ien and 0 . Grong, 'Ass essm ent and Pre dic tion s of HAZTensi le Propert ies of High Strength Steels ' , Welding Journ al , pp 356s-359s. Septe mb er 1989.

33 . W.B. M orrison, B. Mintz and R.C. Coc hrane, Proc. Conf. 'Controlled Processing of HSLASteels ' York University, September 1976.

C D .

18



TABLE 1

CHEMICAL COMPOSITION OF EXPERIMENTAL STEELS

io

Comments

Manganese-Nickel Steels

Base (C-Mn-Ni)

Base + V

Base + Ti

Base + Ti + Low Al

Base + V + Low Al

Base + Ti + Β + Low Al

Base + Ti + Β + High Al

Base I V ) B t Low Al

Base + V + B + High Al

Base -1- Ti + V + B + Low Al

Base + Ti + V + B + High Al

Base + Ti + V + High Al + Si + Nb + Low Ν

Base t Ti f- V + High Al + Si + Nb + High Ν

Buse + Ti + High Al + Si + Nb + Low Ν

Manganese-Nickel-Copper-Niobium Steels

Base + V Low Si

Base -f Low Si

Base C Mn-Ni-Cu-Nb)

Ident.

A

Β

C

D

E

F

G

HI

J

K

L

M

Ν

0

Ρ

Q(D*Qui>*

c

0.077

0.077

0.079

0.089

0.082

0.061

0.086

0.085

0.079

0.074

0.086

0.067

0.066

0.066

0.11

0.11

0.095

0.092

Si

0.21

0.21

0.21

0.19

0.19

0.20

0.20

0.21

0.21

0.21

0.20

0.72

0.68

0.70

0.10

0.19

0.40

0.41

Mn

1.42

1.40

1.40

1.40

1.42

1.35

1.47

1.38

1.41

1.37

1.39

1.39

1.39

1.39

1.44

1.42

1.47

1.38

Ρ

0.007

0.008

0.007

0.007

0.007

0.004

0.007

0.005

0.007

0.005

0.007

0.008

0.008

0.008

0.007

0.007

0.007

0.008

S

0.004

0.004

0.003

0.003

0.003

0.004

0.002

0.002

0.002

0.004

0.002

0.004

0.003

0.004

0.002

0.005

0.002

0.003

El

Ni

0.50

0.53

0.51

0.50

0.50

0.49

0.50

0.50

0.51

0.50

0.50

0.20

0.20

0.20

0.50

0.49

0.50

0.52

jinent, Wt. %

Al

0.043

0.047

0.043

0.005

0.004

0.005

0.064

0.007

0.071

0.006

0.072

0.073

0.071

0.073

0.040

0.040

0.038

0.043

Cu

.

-

-

-

-

-

-

-

-

-

-

0.29

0.29

0.29

0.25

0.24

0.24

0.25

Nb

_

-

-

-

-

-

-

-

-

-

-

0.020

0.020

0.021

0.025

0.025

0.025

0.025

Ti

_

-

0.014

0.014

-

0.011

0.014

-

-

0.011

0.014

0.01

0.01

-

.

-

-

-

V

_

0.08

-

-

0.09

-

-

0.10

0.09

0.10

0.10

0.10

0.10

-

.

-

-

-

Β

_

-

-

-

-

0.0025

0.0039

0.0033

0.0038

0.0025

0.0040

-

-

-

-

-

-

Ν

0.006

0.006

0.006

0.006

0.008

0.005

0.006

0.007

0.006

0.008

0.005

0.004

0.008

0.003

0.007

0.006

0.008

0.004

Q ι j used for bead in groove studies

Q ii) used for Gleeble studies



TABLE 2SUMMARY OF BEAD IN GROOVE W ELDING CONDITIONS

Electrode diameter , mm

Voltage, V

Curren t , A

W elding head an gle, °

Travel speed, mm/min

Voltage TypeEnergy Input , kJ/mm

Flux

Wire

3.5 kJ/mmProcedure

3.25

30

900

90

463

DC +ve3.5

OP121TT

SD2 INiCrMo

7.5 kJ/mmProcedure

3.25

30

830

78

200

DC +ve7.5

OP121TT

SD2 INiCrMo

20



TABLE 3SUMMARY O F PARENT PLATE TENSILE DATA

Steel

Idcnt.

A

Β

C

D

Ii

F

G

II

I

J

K

L

M

N

0

Ρ

Lower Yield Stress

N / m m 2

Individual

304,304

321,319

309,313

306,316

369,374

262,266

298,297

308,312

27 8 , 275

316,313

302,302

324,317

366,366

338,341

367,375

368,367

Ave.

304

320

311

311

371

264

297

310

27 6

314

302

320

366

339

371

367

Upper Yield Stress

N / m m 2

Individual

346,357

352,373

355,379

368,373

405,411

309,300

336,325

339,339

296,287

349,337

350,336

337,326

392,416

392,368

411,407

431,407

Ave.

351

362

367

370

408

304

330

339

291

34 3

34 3

331

404

38 0

409

419

Tensile Strength

N / m m 2

Individual

440,439

456,456

441,441

442, 445

494,492

406,405

448,446

452,453

458,458

4 4 8 , 448

460,461

520,520

510,512

484,485

507,507

508,509

Ave.

4 39

456

441

4 4 3

4 93

405

447

452

458

448

460

520

511

484

507

508

Elongation

%

Individual

44,42

3 7 , 4 1

43,40

40,40

40,38

47,45

40,40

39,37

37,37

4 1 , 4 2

38,39

39,38

39,39

38,40

36,36

36,38

Ave.

4 3

39

4 1

40

39

46

4 0

3 8

37

41

38

38

39

39

36

37

Reduction of Area

%

Individual

82,82

80,80

83,82

8 2 , 8 1

8 1 , 8 2

83,83

80,80

80,79

77,78

8 1 , 8 0

78,78

80,80

8 1 , 8 1

83,83

79,79

80,80

Ave.

8 2

8 0

8 2

81

8 1

8 3

8 0

79

77

8 0

7 8

8 0

81

8 3

79

8 0



TABLE 4P A R E N T P L A T E C H A R P Y I M P A C T D A T A

Steel

Λ

Β

C

D

E

F

G

II

I

J

K

L

M

Ν

0

Ρ

Q

RT

208

232

228

0

280

264

289

289

286

280

246

222

185

258

229

220

270

267

238

268

224

-10

160

192

-15

241

168

175

-20

270

260

288

285

264

284

206

239

114

248

164

182

264

269

226

236

233

-40

235

138

150

102

225

266

230

247

229

-45

121

15

-50

207

181

9

13

138

185

Charpy Enei

-55

175

204

-60

261

241

262

225

272

257260

161190

158

20

246

6

5448

22

213

227

232

136

gy.J.at °C

-65

1110

1418

164

-70

242

216

237

218

25820

16

204

63

199

2126

188

-75

226

193

27

171160

-80

196

220183

243

1969

214

19

25

12

8

223186

6

16

109

219

182

183

115

-85

3716

239

910

16

10

18021

33

-90

266

19819

235220

106

16

11

17537

203138

166180

-95

50

215

32

-100

162

4

13

12

10

18

92

18115

192

188

111

-110

8

27

12

70

36

18

-120

7

10

8

8

6

18

14

17

28

38



TABLE 5SUMMARY O F BEAD IN GROOVE H AZ CHARPY DATA

NJUJ

Steel

Ident.

Λ

Β

C

I)

E

V

(ï

II

I

J

K

L

M

Ν

0

Ρ

Q

-80

NA

15,26,38

8, 168,16«

15,23,134

11,126,32

132,5,25

22,7,27

122,103,48

11,9,19

148,130,154

26,7,16

ΝΛ

ΝΛ

ΝΛ

ΝΛ

ΝΛ

ΝΛ

HAZ Cha

-60

48,29,179

15,33,12

169,177,192

13,129,48

27,23,5

177,141,169

10,120,16

108,23,178

11,67,19

160,167,129

39,14,72

43,86,87

74,113,134

23,33,177

NA

ΝΛ

ΝΛ

rpy Energy for 3.5 kJ/mm Weld, J

-40

191,186,191

183,140,195

184,179,69

174,111,171

60,131,60

173,192,139

167,156,20

167,180,181

22,21,130

177,171,105

118,14,165

126,140,144

32,65,122

38,72,174

48,127,173

98,147,191

28,35,54

-20

31,203,192

194,178,179

190,182,183

178,177,159

204,221,208

192,199,187

149,162,151

182,181,150

146,140,126

162,157,174

198,165,169

73,134,143

44,81,133

25,53,191

NA

NA

ΝΛ

0

190,187,193

204,184,197

197,175,186

186,180,172

195,204,190

184,191,180

186,90,171

187,179,182

130,133,143

184,170,178

166,128,148

169,174,176

158,164,164

191,201,211

NA

NA

ΝΛ

+ 20

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

HAZ Charpy Energy for 7.5 kJ/mm Weld, J

-80

NA

NA

NA

NA

NA

6 ,8 ,5

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

-60

7,27,34

22,17,9

21,40,9

11,14,6

7,10,17

19,188,174

70,72,12

39,26,15

30,50,34

64,8,10

9,47,15

N A

NA

ΝΛ

N A

N A

N A

-40

11,21,19

15,49,80

179,140,176

149,174,174

10,21,11

175,180,164

40,32,80

77,91,57

22,39,47

157,171,158

19,30,9

27,40,18

19,30,29

24,28,38

20,19,10

30,24,21

6,9,10

-20

117,28,122

32,128,88

122,35,174

178,191,122

49,16,18

175,172,184

124, 102,136

118,118,114

70,80,87

154,135,155

12,95,41

31,14,27

22,21,39

129,19,76

16,34,28

24,23,48

16,20,10

0

169,168,74

67,145,173

130,183,192

174,180,185

130,25,14

183,185,178

161, 146,155

159,156,161

130,53,116

146, 147, 112

85,86,46

27,41,23

81,60,74

20,55,20

16,113,114

24,37,40

54,29,56

+ 20

NA

NA

ΝΛ

NA

NA

ΝΛ

NA

NA

NA

NA

NA

50,74,97

65,84,96

142,109,120

115,38,112

150,124,55

88,45,88

ΝΛ No t Applicable



TABLE 7SUMMARY O F SIMULATED H AZ CHARPY RESULTS AT 0 AND -40°C

Steel

Ident.

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

Energyat-40°C,J

3.5 kJ/mm

GCHAZ

Individual

30,37,31

118,108,46

2 5 6 , 244, 288

270,229,271

41,46,59

255,286,237

124,23,164

112,76,25

60,47,24

1 4 8 , 1 6 3 , 134

27,26,71

49,23,39

75,80,140

21,92,44

1 7 , 1 3

6, 7, 24

25,28,32

Av e .

3 3

9 1

263

257

4 9

259

104

71

44

148

41

37

9 8

52

15

12

2 8

3.5 kJ/mm

ICGCHAZ

Individual

14,20,88

23,20,57

2 7 5 , 245 , 286

285,243,253

23,47,49

285,286,279

55,132,180

2 3 , 1 5 , 2 7

16,26,18

142,174,171

2 4 , 30, 49

12,10,10

14,32,15

20,12,23

1 9 , 2 0

14,17,21

20,23,17

Av e .

41

3 3

269

260

40

283

122

2 2

2 0

162

3 4

11

20

18

19

17

2 0

Energy at 0°C, J

7.5 kJ/mm

GCHAZ

Individual

2 6 , 1 8 9 , 3 9

184,193,149

2 8 7 , 285 , 286

2 8 5 , 2 8 5 , 2 8 6

59 , 29,46

2 8 6 , 2 8 7 , 2 8 6

2 84 , 285 , 265

169,186,142

146,126,134

196,195,177

206,212,160

97 , 54, 77

118,154,73

164,52,70

29,133

102,22,68

126,143,68

Ave.

8 5

175

286

285

45

286

2 7 8

166

135

189

193

76

115

9 5

8 1

6 4

112

7.5 kJ/mm

ICGCHAZ

Individual

124,41

130,81,121

2 8 6 , 2 8 5 , 286

2 8 5 , 2 8 7 , 2 4 3

230,168,284

2 8 6 , 2 8 7 , 2 8 6

2 8 2 , 28 2 , 284

1 4 2 , 3 5 , 9 2

140,249,107

2 2 5 , 2 6 7 , 2 8 5

186,167,170

25,20,21

22,20,55

125,25,94

45,82

2 8 , 156,102

39,83,55

Av e .

8 2

111

286

272

227

286

2 8 3

9 0

165

259

174

2 2

3 2

8 1

6 3

9 5

59

25



TABLE 8

SUMMARY OF QUANTIT ATIVE O PTI CA L ME TAL LOG RAP HY

FOR THE HAZ OF 3.5 kJ /m m B EAD IN GRO OVE WELDS

Steel

Ident.

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

Microstructural Consti tuent, °Io

PF

4

9

15

32

6

7

13

0

2

8

12

6

12

0

4

1

2

PF(G)

2

1

1

1

1

0

1

0

0

0

0

0

0

0

0

0

0

FS(A)

14

11

7

6

11

8

10

19

13

8

11

10

8

8

15

9

15

FS(NA)

67

68

54

39

48

44

48

50

62

51

49

72

69

85

57

73

66

AF

6

6

14

12

20

18

15

18

16

15

18

4

3

3

12

7

9

PF(I)

3

4

8

7

10

21

11

10

4

17

10

7

7

4

4

5

4

FC

3

0

1

3

1

2

3

0

0

0

0

0

0

0

1

0

0

M

0

0

0

0

3

0

0

3

3

0

0

0

0

0

6

2

3

PF - Prima ry ferrite AF

PF(G) - Grain boundary ferrite PF(I)

FS<A) - Fe rrite with second phase (aligned) FC

FS(N) - Fer rite with second phase (non-aligned) M

Acicular ferrite

Intragranular polygonal ferrite

Ferrite-carbide aggregate

Martensite

26



TABLE 9S U M M A R Y O F Q U A N T I T A T I V E O P T I C A L M E T A L L O G R A P H Y

FOR TH E HAZ OF 7 .5 kJ /m m BEAD IN GRO OVE W ELD S

SteelIden t .

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

G a t F B + 0 . 5 m m

K a t F B + 0 .5 m m

M i c r o s t r u c t u r a l C o n s t i t u e n t ,

P F

10

22

15

2 4

2 5

3 6

7

8

8

2 8

5

2 1

3 6

4

9

9

8

19

2 2

PF(G)

3

5

2

2

3

1

1

0

1

1

3

2

1

1

1

1

1

2

2

FS(A)

22

2 3

8

10

10

4

17

13

14

3

7

6

2

12

19

18

16

4

5

F S (N A )

54

35

56

32

49

22

62

58

65

23

74

63

54

72

59

61

64

18

37

A F

9

10

14

27

11

20

10

11

9

24

6

4

3

6

8

6

7

51

28

PF(I)

3

5

5

5

2

18

2

9

4

2 1

5

4

5

6

4

5

3

6

6

FC

0

0

0

0

3

0

0

3

3

0

0

0

0

0

0

0

0

0

0

P F - P r i m a r y f e r r i t e

PF(G) - Gra in bou ndary f er r i t e

FS ( A) - Fe r r i t e wi th s econd phase ( a l i gned)

FS(N) - Fe r r i t e wi th s econd phase (non-a l igned )

AF - Acicu lar f er r i t e

P F ( I) - I n t r a g r a n u l a r p o l y g o n a l f e r r i te

F C - F e r r i t e - c a r b i d e a g g r e g a t e

27



TABLE 10

SUMMARY OF SEM MET ALLOG RAPHY

SteelIdent .

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

H A Z M icros t ruc tu re

F e r r i t e

94.5

93.4

92 .7

92 .2

92 .3

93.5

92 .2

88 .5

90.4

91.7

84.7

86 .3

89 .3

86 .2

84.5

82 .2

84 .2

Carb ide

1.5

1.2

2.7

3.2

2.2

3.0

1.6

3.4

2 .3

0.6

1.7

1.3

0.4

0.9

10.4

6.5

1.2

- 3.5 k J / m m

M -A P has e

4.0

5.4

4.6

4.6

5.5

3.5

6.2

8.1

7.3

7.7

13.6

12.4

10.3

12.9

4.6

11.3

14.6

H A Z M i c r o s t r u c t u r e

F e r r i t e

93 .4

93 .3

89 .5

92 .2

93.1

94.1

92 .1

92 .9

92 .1

94.4

90.7

90 .3

90.2

89 .9

89 .8

86 .5

88 .5

C a r b i d e

4.1

2.6

3.6

3.0

2.3

4.3

4.6

4.9

4.2

4.4

4.0

0

0.2

0.6

9.5

11.0

4.0

- 7 . 5 k J / m m

M - A P h a s e%

2.5

4.1

6.9

4 .8

4 .6

1.6

3.3

2.2

3.7

1.2

5.3

9.7

9.6

9.5

0 .8

2.5

7.5

28



TABLE 11

HAZ WIDTH MEASUREMENTS - 3.5 kJ/mm WELDS

Steel

Ident.

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

5 m m Subsurface

>50pm

1.05

1.35

0.70

0.25

1.00

0.70

0.70

1.25

1.20

0.25

0.45

0.65

0.30

0.80

0.30

0.45

0.55

>100pm

0.60

0.55

0.30

< 0 . 1

0.40

0.25

0.15

0.50

0.55

0.10

< 0 . 1

0.10

< 0 . 1

0.30

0.15

0.10

0.15

Root

>50pm

0.35

0.40

0.25

0.20

0.35

0.20

0.35

0.50

0.65

0.40

0.30

0.05

0.05

0.50

0.25

0.45

0.20

>100pm

0.25

0.25

< 0 . 1

< 0 . 1

0.15

0.10

0.15

0.30

0.30

0.10

0.10

< 0 . 1

< 0 . 1

0.30

0.10

0.15

< 0 . 1

29



TABLE 12

HAZ WIDTH MEASUREME NTS - 7.5 kJ /m m WELDS

Steel

Ident.

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

Bay

>50pm

3.50

3.80

2.10

2.20

3.50

1.10

2.45

4.50

4.05

2.60

4.10

3.40

3.00

3.90

3.30

3.90

3.60

>100pm

2.65

2.55

1.05

1.15

2.50

0.75

1.05

3.05

1.70

1.50

1.90

1.80

1.60

3.25

2.40

2.30

2.10

8 m m Subsurface

> 50pm

2.35

2.25

1.15

0.80

1.95

0.45

1.45

1.95

3.10

1.20

2.10

1.60

0.95

1.80

1.65

1.35

1.75

>100pm

1.55

1.45

0.45

0.20

1.40

0.25

0.45

1.30

1.40

0.55

0.60

0.85

0.30

1.00

0.60

0.55

1.30

Root

> 50pm

0.95

1.00

0.35

0.30

0.65

0.30

0.40

0.70

1.55

0.50

1.20

0.95

0.45

1.00

2.00

2.30

2.70

> 100pm

0.45

0.35

0.25

0.15

0.35

0.15

0.25

0.35

0.70

0.15

0.30

0.35

0.15

0.40

0.80

0.70

0 .85

30



TABLE 13SUMMARY O F H A Z GRAIN SIZE MEASUREMENTS

SteelIdent.

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

H A Z Colony Grai n Size , pm

Range

Mean

7 .5 kJ/mm

175-490

327

120-350

205

110-400

191

80-270

175

100-230

156

100-240

142

110-310

182

155-395

229130-400

221

75-250

142

110-350

185

110-330

189

95-280

185

110-370

223

130-395

223

125-395

230

160-430

271

3.5 kJ/mm

115-305

173

75-160

106

75-215

124

50-145

8 9

65-165

102

70-215

115

50-125

8 0

80-240

14280-170

120

40-125

8 8

55-110

79

50-175

8 4

75-160

103

95-180

125

70-145

9 7

85-165

113

60-150

9 9

Average H A Z Colony Grain Size

d'*

7.5kJ/mm

1.75

2.21

2.29

2.52

2.53

2.65

2.34

2.09

2.13

2.65

2.32

2.30

2.32

2.12

2.12

2.08

1.92

3.5 kJ/mm

2.40

3.07

2.84

3.35

3.13

2.95

3.54

2.65

2.89

3.37

3.56

3.45

3.12

2 .83

3.21

2.97

3.18

31



TABLE 14SUMMARY OF HAZ HARDNESS MEASUREMENTS

SteelIdent.

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

H A Z Hardness 5 kg Load)

Range

Mean

7 5kJ/mm

169-190

181

190-208

201

167-201

183

160-183

173

195-212

204

167-183

174

164-203

180

204-225

211203-219

209

193-208

200

201-227

212

225-236

229

223-239228

210-227

217

192-214

204

199-214

207

210-219

214

3 5 kJ/mm

191-209

203

204-216

210

169-199

181

164-193

175

213-235

224

193-215

201

192-229

208

235-265

245226-257

239

212-240

224

227-253

240

239-254

245

232-246236

229-251

235

210-237

219

209-225

217

217-227

224

32



TABLE 15C O M P A R I S O N O F H A Z T O U G H N E S S D A T A F O R

B EA D IN G R O O V E A N D S IM U L A T E D G C H A Z R E G I O N S

SteelIdent .

A

Β

C

D

E

F

G

H

I

J

K

L

M

Ν

0

Ρ

Q

B ea d in Groove W elds a t F us ion L ine

0 .1 mm C TODT e m p e r a t u r e , °C

7.5 kJ /mm

-80

-74

-65

-60

-35

-86t

-67

-81

-17

-91t

-40

+ 13

+ 35

-7

-55

-34

-25

3 .5 k J /mm

-58

-79

-94t

-75

-56

-105

-65

-79

-64

-107

-20*

-60

-75

-6Í

-100

-71

-40

Charpy 40 JT e m p e r a t u r e , ° C

7 . 5 k J / m m

-13

-14

-18

-47

+ iot

-55

-36

-46

-16

-50

-2

+ 15

-0

+ 7

+ 23

+ 15

+ 18

3 . 5 k J / m m

-17

-55

-53

-56

-43

-64

-22

-59

-36

-55t

-31

-60

-22

-17

-45

-55*

-30

S i m u l a t e d G C H A Z

C harpy Ene rgy , J a t0°C -40°C

7 .5 k J /mm

85

175

286

285

45

286

278

166

135

189

194

76

115

95

81

64

112

3 .5 k J /mm

33

91

263

257

49

259

104

71

44

148

41

37

98

52

15

12

28

' By extrapo lation* Est imated* Resu lt due to weld metal

33



ΧΠmm

>45

14 mm

ou S i n g l e w i r e s aw a t 3 . 5 k J /m m S i n g l e w i r e s aw a t 7 . 5 k J / t i

B E A I ) I N G R O O V E W E L D I N G P R O C E D U R E S F IG. 1(R 3 / 61 7 6)



χ 3.5 3.5 kJ/mm ΡΗ292 (a)

χ 3.5 7.5 kJ/m m (b)

P H O T O M A C R O G R A P H S O F T Y P I C A L B E A D IN G R O O V E W E L D S F I G . 2

35



Temperature, °C

1350

1050

750.0

450.0

150.0

0.000

Temperature °C

1350

2nd Cycle

60.0 120.0 180.0

Time, s

3.5 kJ/mm Simulation

240.0

2nd Cycle

260 520 780

Time, s

7.5 kJ/mm Simulation

1040

300.0

1300

THERMAL CYCLES FOR GCHAZ AND ICGCHAZ SIMULATIONS FIG. 3R3/7662)

36



" ." S . I

/ 'ν*.:χ*ίίΊ'Γ'& :ί7 / / /

*

W V ./ > ,

'. ' v 'V ?/ /■ < / / V . ί

£ £ k ^"'M- JW

Key

P FPF(G)PF(I)

AFFS(A)

PF(NA)

FC

M

Primary ferr i teGrain boundary ferriteIntragra nular polygonal ferr i te

Acicular ferriteFe rrite with aligned secondphase

Fe rrite w ith non-aligned secondphase

Fer ri te carbide ag gregateincludes pearlite

Martensi te

20 pmI

«_*«T·

- t i*

%

s e

CLASSIFICATION OF MICROSTRUCTURE TO IIW SCH EME FIG. 4

37



S t r e n g t h , N / m m2

500

4 6 0

420

380

340

300

260

200

Δ Δ

-

oo

Δ Δ

O

0

Δ Δ

O

O

O U p p e r Y i e l d

Δ UTS

ΔΔ

O

o

Δ Δ

OO

Δ Δ

OO

Δ Δ

O

o

Δ *

oo

Δ Δ

oo

Δ Δ

O

O

Δ Δ

O

O

Δ Δ

O

O

Δ Δ

O

O

Δ Δ

O

O

Δ Δ

S

Δ Δ

o

o

Δ Δ

O

o

A B C D E F G H I J ΚSteel Identity

L M Ν 0 Ρ Q

SUMMARY OF PARENT PLATE TENSILE DATA FIG. 5(R3/5790)

38



Energy, J

280

Steel A

200

120

40

Steel Β

ff

••-¿-L

Steel C Steel D

280

200

120

40

-120 -80-L

-40 0 -120

Temperature, °C

· » - ·

CHARPY TRANSITION CURVES FOR PARENT PLATES FIG. 6(R3/7663)(Cont...)

39



Energy, J

280

200

120

40

Steel E

• ·'

S t e e 1 F

-

i

•<

Λ I

= Α = - ·

•

280

200

120

40

-

-

— I

S t e e l G

ι

/

· ' · *: J : _ L _

^^.9

— · —

i

120 -80 -40

Steel Η

0 -120

Temperature, °C

· ;

•

-80 -40

CHARPY TRANSITION CURVES FOR PARENT PLATES FIG. 6R3/7664)Cont...)

40



E n e r g y , J

280

200

120

4 0

β

_ J

S te e l I

•

/

/ /

t-* /

/•

/

I

S t e e l J

/ ·

(s

/ • I

t=¿: ■

280 r S t e e l Κ S t e e l L

- 1 2 0 0 -120Temperature, °C

CHARPY TRANSITION CURVES FOR PARENT PLATES FIG. 6(R3/7665)(Cont )

41



280

200

120

4 0

* " " S t e e

•

//

•

I

1 M

•

J•

r

+ ·

Steel N

■ I

280 r

200

120

40

Steel 0 Steel Ρ

J _ : L

Î0 -80 -40

J

0 120 -80 -40 0Temperature, °C

CHARPY TRANSITION CURVES FOR PARENT PLATES FIG. 6(R3/7666)(Cont )

42



Energy, J

280

200

Steel Q

120

40

-120 -80 -40Temperature, °C

CHARPY TRANSITION CURVES FOR PARENT PLATES

40 J Temperature. °C

-40

-60 -

-80 -

-100

-120 -

FIG. 6R3/7667)

M U Π

l _ l I I I I I I I ■ ι ι ■ ι ι

A B C D E F G H I J K L M N O P Q

S t e e l C o d e

SUMMARY OF PARENT PLATE CHARPY 40 J TRANSITION TEMPERATURES FIG. 7R3/7667)

43



— — — 3.5 kJ/mm

^ — 7.5 kJ/mm

Energy, J

200

120

Steel A

40

L J -

S t e e l

Γ + '/+

ι .i /1 +ι 'ι '»' /»' /

» ' Ζ */ ' /

+ _ _ . I — · 'ι * ■

Β-' " Γ

/ ·/ ·

f

•/

•

yι

Steel C Steel D

200

120

.'-TjrF*

40

-80 -40 -80 -40

Temperature. °C

CHARPY TRANSITION CURVES FOR BEAD IN GROOVE HAZs FIG. 8(R3/7668)(Cont...)

44



_ _ _ 3 . 5 k J/ m ir ,

E n e r g y , J

200

20

40

+

^ ^ — 7 . 5 k J / m m

S t e e l E

/ // /

/ II I

+ I' »

' I

/ ./ »

/ ♦/ /

+ -ι

:te¿>-*

S t e e l F

Si

• J/V

200

120

S t e e l G

40 -

-80 -40

Temperature, °C

-80 -40

CHARPY TRANSITION CURVES FOR BEAD IN GROOVE HAZs FIG. 8(R3/7669)(Cont )

45



3.5 kJ/mm

—~~ 7 . 5 kJ/mm

Energy, J

200 r Steel I

120

40

/V/*·

» +· — ι

Steel J

. - - t r "+- - » " / i ^ f c

' ·

rt

200

120

40 -

Steel K

/ I +/ + »

/+

1

• ·

-80 -40

Steel L

« i - ·-80 -40

Temperature, °C

CHARPY TRANSITION CURVES FOR BEAD IN GROOVE HAZs FIG. 8R3/7670)Cont...)

46



■* 3.5 kJ/mm

— 7.5 kJ/mm

Energy, J

200

120

40

Steel M

î

/+ /

I

%

Steel N

. χ

+ -"* +

• /ƒ

//

t~L..'_¿

Steel O Steel Ρ

200

120

40

-80

U

t t

JU

-40 -80

Temperature, °C

-40

CHARPY TRANSITION CURVES FOR BEAD IN GROOVE HAZs FIG. 8R3/7671)Cont...)

47



Energy, J

200 Γ

120

40

Χ

Steel Q

3.5 kJ/mm

7.5 kJ/mm

j

-80 -40 0

Temperature, °C

CHARPY TRANSITION CURVES FOR BEAD IN GROOVE HAZs FIG. 8R3/7672)

40 J Temperature. °C

+ 20

0 ■

-20

- 40

-60

7 . 5 k J/ m m l o w e r b o u n d

- — 3 . 5 k J /m m l o w e r b o u n d

L_ j

i-J

ι 1ι ιι ι

ι ιι ιb - -I

L_ Jι

ιJ

■ ■ ■ I I I I I I I I I I


Steel Identity

SUMMARY OF BEAD IN GROOVE HAZ CHARPY 40 J TRANSITION TEMPERAT URES FIG. 9R3/7672)

48



CTOD, mm

0.9

0.7

0.5

0.3

0 1

Λ

Steel A

— — — 3.5 kJ/mm

— 7.5 kJ/mm

•

Steel Β

0.9

0.7

0.5

0.3

0 1

Steel C

•

1

■■■

-120 -80 -40 0

-

-

_

Steel D

•

• i

ƒ// // /

/ /

f >-120 -80

Temperature, °C

CTOD TRANSITION CURVES FOR BEAD IN GROOVE HAZs

-40

FIG. 10R3/7673)Cont...)

49



CTOD, mm Steel E Steel F

0.9

0.7

0.5

0.3

0.

3.5 kJ/mm

7.5 kJ/mm

Steel G Steel H

0.9 ι-

Ο.7

0.5

0.3

0.

120

> *

-80 -40

-J

0 -120

Temperature, °C

-80 -40

CTOD TRANSITION CURVES FOR BEAD IN GROOVE HAZs FIG. 10

R3/7674)Cont...)

50



CTOD, mm

0.4 ι-

Ο.3

0.2

Steel I

— — — 3.5 kJ/mm

- — ^ — 7.5 kJ/mm

. : - /

Steel J

/ /+/j l-

Steel Κ Steel L

0.4

0.3

0.2

\

- +JL

120 -80 -40

-L,

0 -120

Temperature, °C

ι+/

-80 -40

•I


R3/7675)Cont...)

51



CTOE

0.4

0.3

, mm

— —

—

Steel M

-3.5 kJ/mm

+'

0.2

L

-80 -40

.y+40 120

Steel Ν

-80 -40

0.4

0.3

0.2

0.1

Steel 0

+

/

/

J. J_

-120 -80 -40

J

0

4.

-120

'C

Steel Ρ

+ι

a.-80 -40

Temperature,

CTOD TRANSITION CURVES FOR BEAD IN GROOVE HAZs FIG. 10R3/7676)Cont...)

52



CTOD

0 . 3

mm

— 3 . 5 k J / m m

— 7 . 5 k J /m m

0.2

120

J

080 -40

Temperature, °C


(R3/7677)

0.1 mm CTODTemperature, °C

+20

-20

-60

100

7.5 kJ/mm lower bound

■- — 3.5 kJ/mm lower bound

ι «

II I I

Ι ι

Γ

·- ·*

J I I i l _ J L. ι ι

' J

J IB C D E F G H I J K L M N O P

Steel Identity

SUMMARY OF BEAD IN GROOVE HAZ 0. I mm CTOD TRANSITION TEMPERATURES FIG. 11

(R3/7677)

53



E n e r g y a t - 4 0 ° C , J

280

240

200

160

120

80

40

r + ·

Γ + η+

ÎÎ3·+·* α

Q Γ + - Ι

+ , L * -

UJ.+-U U-LJ Uct=rf*3

+ -Ι

J » I I I I I I ■ ■ ' ' I ■ JA B C D E F G H I J K L M N O P Q

Steel Identity

SUMMARY OF SIMULATED GRAIN COARSENED HAZ CHARPY DATA (3.5 kJ/mm)

Energy at 0°C°C

280

240

200

160

120

80

40

Β · * * Μ ·*·♦·■♦-

■ + -

· +t i

*1

+

■ + -

■+ -

■ · * ■ -

Γ + Ί

- + -

p+-

Θ-+-

+

- -

Γ *

+

-+-

—f η

-+-

'+-

+

+

- +■ «

1 .1 1 · I I 1 l . . . I 1 - 1 l 1 - 1 1 ï — I

FIG. 12

(R3/7678)


Steel Identity

SUMMARY OF SIMULATED GRAIN COARSENED HAZ CHARPY DATA (7.5 kJ/mm) FIG. 13

(R3/7678)

54



E n e r g y a t - 4 0 ° C , J

28

24

2

160

12

8 0

4

:τ τ rø

4-L J

ρ η

+Ί

a

'.Xi U Bi» y JU:*****«ι ι ι t ■ ι ι ι ■ ι ι


S t e e l I d e n t i t y

SUMMARY OF SIMULATED INTERCRITICALLY REHEATED GRAIN COARSENED HAZCHARPY DATA (3.5 kJ/mm)

Energy at 0°C

280

240

FIG. 14(R3/7679)

-a

i

m *

r+"

» Φ «

ι

Γ + "+

t f**+k+m

r

h -

-+

• 4

I l l i l i

- + -

" +

+-

αΓ + "1

ι 1 1 1 I

■ 4 -

4

- 4 -

1 1

-+-

- + -

1 1

+

·■♦—

1 1

- + -

+

-+-

1 1

200

160

120

80 -

40


S t e e l I d e n t i t y

SUMMARY OF SIMULATED INTERCRITICALLY REHEATED GRAIN COARSENED HAZCHARPY DATA (7.5 kJ/mm)

FIG. 15(R3/7679)

55



' , s .Tfe . ; -s - ' ' . : - Ï

'?»':;

c «

?" -ν-* - W - V · ' ■< ._,-£-■-<: ,i

χ 100 O F 5 4 0

Vf .

S tee l A

t^ìsi;*;¿ f ë - "

ψψΡ-$ι •kM$ï*iχ 100 IF 6 S tee l Β

-■■ν > ΐ - & - ■ : :■

^ V f , - - i t ' * - ™* / - .... 'ν

s&«;2 - * - ' ' ■ .

- * '* >2",ι~' ν .Λ · . ■ . -

r ' > -; v.

x lOO IF 1 S t e e l C

■■■■■ k4'H^'f- --' -

ι

■ Α Α » ' ί ? · > · ' ν - . - Λ . · · ; · . ' ;.«•«'.'."fe·»':

1 ,

v-

x l O O I F 1 3 S t e e l D

xlOO IF 17 Steel E

< ~ ,

' '' Ζ* - ..Cis-: / ^i Γ '

x lO O O F 3 5 2 S t e e l F

O P T I C A L M I C R O G R A P H S I L L U S T R A T I N G T H E H A Z OF 3 .5 k J / m m F I G . 16B E A D IN G R O O V E W E L D S ( C o n t .. .)

56



-S.-i;

.g? .'-•■*?>;':'Ä->.1 ' w ^ ' i A > V

' ν -Λ ι Η ί ï J? -i i · - Λ Λ - » ->?-">"'5

S»—«^:* i

•Α'·^3ί;

Í :V~"_ · . ' V · ': rs-"?.. .*·■■ ~*--t-.

xlOO IFIO Steel G xlOO OF348 Steel H

xlOO IF22 Steel I

' Ï 3 ■¿Λ

ΐ:ΐτ

' V ì g i l i W^ï. ' i----· "."'i»Τ;:,í'v«<<i Ííirr-?- ·—,-.>;-·", -.

^*¿#·: . ¿i?Ci.V*eí>.¿;

χ 100 OF356 Stee lJ

SS&áP

xlOO IF26 Steel K xlOO OF205 SteelL

OPTICAL MIC ROG RAPH S ILLUST RAT ING THE HAZ OF 3.5 kJ/m m FIG. 16BEA D IN GROO VE WELD S (Cont. .. )

57



■ v - ^

:'ίι*ί5·

* * , « ■

' -** -----<&r».

r.¡i¿:--< - ' - ' T ' S i i - , - rV » i ¿ w ; . y v > . . · ;£~;U*->~· - - ' ' · - Α·;;-;ν '.COK* Ϊ^ΤΪΤΛ:;»- .· γ;

i-vrr ' . - C * - . '■& "'■'-' -' ,'· * Ti»

•'><-'-^:C-''Jíf>>>/"'4í

-'·'· ' ¥i'î -i-";-¿'f -r %---%;

tes ;·^;>'·¥ §*. :·? w*mms

i f f ν%' -" .- - - ■ ; =

• * ' 1 .

χ 100 OF209 Steel M χ 100 OF201 Steel Ν

i A"Jpr. C-y -;-'.· ' 3 f e > ^ % : ;• • ' - í ' j »» ■ ff-

Ά

> Λ ^ ΐ '^Æ i•.-ï r.-.-:.; :,.—- fils ..'<^ ;- -,

· -

' i -v

*.< ^

* * « -V :,· · >i > f ¡t* * ΐ ' ?- ;

· > t - ' « A · - • •- '' .- if

.- > . - ο 'V i - -1 ï -

xlOO OF 177 Steel 0 xlOO OF181 Steel Ρ

&

^Ä/-^'..-'i,,<^V-5'·^- i >^ A -

^«^^^S^ v » , c ■ ·ν .■

• ■ . v - v . - f í - - . · > , . . · . - , » .

xlOO OF173 Steel Q

OPTICAL MICROGRAPHS ILLUSTRATING THE HAZ OF 3 .5 kJ/mmBEAD IN GROOVE W ELDS

FIG. 16

58



S í S s S - ' f J v ^ ' S v - ' - V í -; ^-. ' »Γ·····- .:--*5^·^ό».;.

N vrtv- ϋ ΐ -

:^ ο ; ':Ê 3ær

"' 'Vs

* " Γ · ' ·, .^*^ -ν ' v. ' . · . - - - . ^ , L - ' '• r

■ i ¿

í ¿ - 5 V ·

$SS9* C'<

ζ^/ΐ,^' %:

iv:'''-·'^' %

χ 100 IF36 S t e e l A χ 100 IF 40 S tee l Β

■ r-

:' ~í'

<' ,'íy ν*- ' -t - t* * ·'. ·

^4* ϊΚ££ ' . · .. . ; .- , : - - , . ■ - : .

Λ - S ^ . ^ ' · . - . ·· Ν ,:"-ίώΑί?ί-..>,·;;. . . ·_ · . - - · · ' ■ < :

. - j ' ; - r > ¿ . . . y ; · · . - ' - .: 'V :, - ■ :" .

ÍV"·.·?·?«^ - '·

- ■ " , « " ■ · : · ' - ■ " ■ - - - " - t i t-Λ» ·* - · . ' .«,*V--- ■ " —■·'- · . - ' . ·ν-"Α ,~-",">Κ'· V ■'' · > » ' " - " · . Λ» O · ; ."" ^ ^ i P Ä ^ V - i C · ' ^

Α - « · ' * '

*%%&*< *'■■:■:, λ

$Ε&Χ: > ;'■:Γ ^ά**-*. ■ ■■

ν

■ ΐ.- ■: ' ' . , /■ ' ' ■■ ·- - 'ν'

^ - r - > . · . *- ' ' · ' . ' . '- . .- _ - * - < ' . ' · * Λ -ν . - -.'■·.· - ' **'

: ~ ~. ' * - ' - .■ , ' **-

xlOO IF44 S t e e l C χ 100 IF 48 S tee l D

— A i t 'i^5r~ r - - -

•vifAftl ·:-ΐ

ïS^tSr?'-· -■

^ ·.- - : · * * · , y % - . - > r - T T < .

. ' • ^ i . ^ ' 7 4 ' " Ä

■ ^ : ;: - , J , ' W ' ^ : . · >

, - '>- t, t ' : - -. ' ^ Γ · , ^ · Λ > ■ · '·

- 'f ¿í,/a&ér'' i -

·/· . % i ? · — . - - · ; . ' Α ν

• * t " í : 5 # ì ~

" W ^ f

- , -t.

-*:í'·

Sí-1

xlOO IF52 S t e e l Ε χ 100 O F 3 7 1 S tee l F

O P T I C A L M I C R O G R A P H S I L L U S T R A T I N G THE H A Z OF 7.5 k J / m m FIG. 17B E A D IN G R O O V E W E L D S ( C o nt .. .)

59



is·. · β ' ν « ^ ' ' · · ^ ' ν ·

< · - ï ' · ' v i s ? · ist*'S ■·■-■■

-"'j ' >·· .·.· -", <.,%*--.· ' . -Λ , ^ J

— "* . · -> - , · ■ » ^ v ' A V i W f «i '- ν

• ; < v > - ' · * · · ; · « * . · ^ ^ .:■■

'- *>- < · » ' . : ΐ r.V-f,- ■ " ' ' , * . * ' ' • ' - * : . "* ·- J T - v · ^ * ■ > . " ' ' , ' ■ * ' ' * ;

4££ ;ν ·0~ ν^ ^ ? æ

fcMteTl^

•:-'-'¿*vS%

• : * ¿. ·-¥>%»V*Sïîif-v. ■·■■■*¥**:

Í ? A Í '~-

;--^" ^¿ ■£ \_ *

tè-SíV-; ·

't' ^ ¿ - - V

- ; , . . ; · , , &"?: -;, -.-ï, -·V-··. * ¿Ci»·,*ti-

. '* * . ' * * * - \ ... '- C " '*

~ ■ * *;■'.-» · * ' ' " i * ' ,'■-. y.

-i^i^Lthi<-.<; , - * M ^ r . · ^

• .t·"·. "· , '-Ç'·? ' ^ t í ^ - ·)· V " " " ■ s^^^i>¿?.Ü>J

• > , ,ƒ " : , . f " ¿ ^ * ·-'* ·>'-;^ ' ' t ' - ' -> ·* <-.V?V''-^t.

" ^ y cX , r'T^ùL·^^

.-**,f V->¿ ■> V"W%':ä ■-->-*■

i:;«3*i"Æ>-

>.· .'Í,'Í>' ' « 5 : ï 1 t e ^ ■ ■ - s

x lOO IF 56 Steel G x lOO O F 3 7 9 S t e e l H

A --s ■*?,^>ν -, , . - ' T . f - W ' ^ . / > i . · . . ■> *>

·' '-;;. '"· ^-■¿'.ily?.*.. ν >,'; '

t ' , t - ¿ - ; v i ¿ ί , · ; 'f/.-·-:.'';.;»

xlOO IF 60 Steel I x lO O O F 3 7 5 S t e e l J

* 5 * * Ä ; . J :·'4;·■.ΐ·-·;-'',* i* ': - Ϊ ΛC ¿ Í ' 1 ^ » · .

xlOO I F 6 4 Steel K x l O O O F 2 1 7 Steel L

O P T I C A L M I C R O G R A P H S I L L U S T R A T I N G T H E H A Z O F 7 .5 k J m m F I G . 1 7B E A D I N G R O O V E W E L D S C o n t .. .)

60



:*-*-*Sfe?«*;3ñ«ss· 'ta?-

S ä S S ^ - ^ ^ f c ^ i · . jí;

Ér• t í ' .

- ^ ¿ , ,

. V * - ;

·* '.$-<·*· :.< ^ < i*A^ '*ρ^

s·» i'ci-a *»«-' ^tr-'í1"^*. iV - '

;Λ .* >'

i '&*&XiÊ<iL '■- '--T-'J f: ; ; * - ? J ^ ' - : W « í i * · ^ Γ . ν > Λ > Λ ί

t - Λ ί ^ ν

§v .Äs

{ T V Α,νΥΪ

x l O O O F 2 2 1 Steel M

& · ' ^ · • -5·.· ' r ^ ' - ' - v t ó ^ . · - : ¿«i .-

x l O O O F 2 1 3 S t e e l Ν

v ' " ' <*VSSá' : · ··' >" '■ 'Kg· *¿i£**r : ■ t' ' ^ * ν # 3 \ - t Ä v f 3 & · - ^ -'Λ *Μ

t ^ ÄÄ

3&$L...

% 1Ä**· ·: i · . ·.·>·:."- í^ è ^ T -t ^ s s s ^ -,

x l O O O F 2 8 3 Steel O x l O O O F 2 8 7 Steel Ρ

f < à r · ' - * : < X · ' . ' -

S & v TV2SVS>\ · Í. ....?«££*?*■ ■-. ··^ í j * ^ - · ·jSg'V-^iv- ·. ■■

ν * * - ' ■'-■;>-"> - Λ

- ■ % * . ' ■

i^ .&· ' . .-.·« ...r

; t > ^ , ^ A ^ 4 v . ^ ^ ^ o ' ; - i . ^ M . ' t í : í : V

i i - ' v Ä k ^ Ä ^ ' l E ^ ^ f ^ l■vef¥.;j ^ í ^ è ;

- ' - ' · * ■ - . ■ ^ ■ > , - . . - . . - '

t i -Jis«.-V.*:-rS>3?a··«..-■.íf.t . i s- ·1 ' - · - -- JT · 7 . ^ V - . T -

. · ,·,ί?Λ. .-?;=· ' .- ~-^Æ'.-.·>-.">"·">■" % . ^ ' ~ Γ ^ - ^ ν . ; ' , :

> S Ï Ï T * ^

χ 100 O F 2 7 9 Steel Q

O P T I C A L M I C R O G R A P H S I L L U S T R A T I N G T H E H A Z O F 7 . 5 k J / m mB E A D IN G R O O V E W E L D S

FIG . 17

61



.*.. -Γ .. « »j. Ο,·'· V , , . j --νΐ Λ -

? J , * W . ' _ * V - ' V U / - : -tf, . ί.-.,ΤΓ. S ' -7

?v;- : - '^'W'-' .V^v^^

S ? - í ^ \ ^ ^ ^ . ^ :ro> >w,#xS-χ 4 0 0 OF541 Steel Α χ 400 IF7 Steel Β

Λ · 4 v-'5fT..·» <V ν % < t. ; ; -· . ,V,v i t . . *■·,

V ·'

^ - w — ^ £ ¿ & S V '

V , \ i ■» /J.;V.Vv. " , ' ; . . ' " ■"■,>/*- -

, . . * * » Ä·

-í'~¿i; - · * r .- '-*: "i '- '; ', ' · '**t ·> \ -· I - - -' ·> - ~' · ν "^ ^γ/ν Λ' . ^ / ' i ^ v ; : - V , f > ' ; " ' ->--.,>?·,< <:·· ,

V 'yf»> > -^ν~^>·;- {C¡>'.y ir--;* A'.vr:c.¿-s

χ 400 IF2 Steel C

**-v ' ' t -.- *e-«.*>- J > ^ · ., ,<J * ■ .;«. - ■ · 1

■ ^^-y^y η*ψ /V<V*':K''· 3Λ*Α

v , , . - ' « -« .* Κ» νr* : '^ϊ.·^,·* v ■-*> . ' Λ τ ΐ ί . c-i» -""1---Î ' . iS.'H_ . . - - -ra i l■. *■ r * * ·* > v ^ >

h ^¿~* ' *-~ -' Φ* l Ϊ ί * - - ^ ' -% V · 4" 5

χ 400 IF14 Steel D

^ ^ 4 " ■-ÍW -¿^i l ν^Λ fl •^.- -,.->>-'^V- ^ - >r ' î ; «

i - ? ' - ' -^ VN " - / " i . V f " ' · ' ' F - " < ^ ' \ w '' .-O ■ *.

•^\,~^■■ -.'.'.·.*> ^--jT^ \ ' Is

'.¿¿lii. - / · ,. ' i , ·«.■,, - '• - . . - - ν - < V· ^ - ° - >- ',.v.; .^>^'%'. ■ ^-·

' *y,. ν t.- ·-í-*^-■■£/"--· ·*■ « v— 'i?' - / .' , ' i \ ' . '-·· ·· ν» Λ Λ ' ' .*?? ~ , · ; > " . . ' . < } ' · % i . · '<rv'-'- ■

y ' Λ , ' 3 ^

χ 400 IF18 Steel Ε χ 400

" ί· / ■·.

OF353 Steel F

O P T I C A L M I C R O G R A P H S OF G R A I N C O A R S E N E D H A Z R E G I O N S FIG. 18

OF 3.5 kJ /mm BE AD IN G R O O V E W E L D S ( C o n t . . )

62



^^^^^iSv^H^- 'r

' $ ^ *'■" '■ . - 't> < V * - - - ^ V ,. . / ' V i M ' - v ' V - ^ ' · ' · ■*

~^ - ' : ;^ ^•ir'HsA/.v^i'. p.-->;v-,r--.»· -T.- \ ' < - - > ^ ■ -. 1 Λ , ï . ' f l " - i % - < ^ ' r - i - " - ' . ' - · . - ^ , -

'■'¿'■CrÀTte^tJ£^¿^¿-&£*~'''¿ t ¥v",=

-· ' ί-,-,ν-^-'Λ'ϊ-^'.νΐ: ^-η<?· --· t / ' . ν , · £vS?£*¿y'rc> ν - r-.'-.f; * . , 7 ; . . v í ; ; i ^ / : ^ - Ï ' --t\-

* ~ν , '* "■ ■ ■ *- ' - -·'■■» * , . ^ ' „ *-¿f7 -Λ?7 * > .

χ 400 IF11 Steel G x 4 0 0 OF349 Steel H

χ 400 IF23 Steel I x 4 0 0 OF357 Stee lJ

v*,.-

-, ' , J**t-" — V* ι . . - >.

ΐ , - V ; .» - η - ' V . * · :x * >■>·ϊ-,.χ. •^Vr _ t

■ J-v'.V. ." «; * ■£ » ¿ϊκ·' -;"r-" ,tr·'— : .·,, xv : - -.- ~._- -0-= -— - . ; . · » · i , . ->y. * -> ^ i . ¿.--¿-O ·' - ' - - " - " - - ■

, . . v-* . - „, -^- - ^ ^ --VÎT» " ^ «■ ' - - ^ -- s . - " -, -

v- C ·, - — - . . . . - ' ^ t >-. , 1 - ' - . ;> f > . - • ^ . ' V / P ; ; ·- . · ' . - . t ST- , , „*-

mjx^n%tftä&{S$ti •■■•Α--τ X ' U f l C j ¿ .>■ "»

χ 400

to.-. '-%■*> J-.

IF27 Steel Κ

54'·^ \ν v \V-- /-■ ' 2 ·.« "¿¿^ ^. Ή■■'■■

ι" ' % >. * ' - . ' ' - ''■'.- - ' - « ' t ' " ~ ' - · - ' ' ' - — ■*"»-.. ' -

Γ ' - . >- - ' > , t * j r - v . *-> .*·. ^*,"ïJ>', .'■'· - - I S " / - '

V f I '^■? -·■*

V .

x 4 0 0 OF206 Steel L

OPTICAL MICRO GRAPH S OF GRA IN COA RSENE D HAZ REGIONS FIG. 18OF 3.5 kJ/mm BEA D IN GROO VE WELDS (Con t. . )

63



' ' " i _ - ■ · Γ1 » 1 ' ·*0" "-. 5 '-*<

í - T - -'·ί'*ν/· ï^A-V^-.r-.-'î.

χ 400 OF210 Steel M x400 OF202 Steel Ν

x 4 0 0 OF178 Steel 0

•-•il <*J~< t ' •sf&P'*·"' ~-~ ■ ■ t^ -~ - *>s . * „r-r. ?.jz<r*0,

« Ì ¿-J-S"" Ç î , - V ->~<> ï ,">?»*· ,■" " <VV-," 't ," - y X ? , . -i

V x j > ^ t ^ i ^ v ^ ^ r v A . ' ^ - V ' . V . - V V ' V*J%&^*?*&22 w w %&■ :-^??->V ~ V ~ ^

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, ' * / / , - · / , ^ ; ^ -Í.Í--J>>'~- ¡-è -t-t -. .- ', ^ -Γ, -ν - -i. ' ·

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x400 OF 182

x400 0F174 Stee l Q

Steel Ρ

O P T I C A L M I C R O G R A P H S O F G R A I N C O A R S E N E D H A Z R E G I O N SO F 3.5 k J / m m B E A D IN G R O O V E W E L D S

F I G . 18

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χ 400 IF53 Steel E x 400 OF373 Steel F

OPTICAL MICR OGR APHS OF GRAIN COA RSEN ED HAZ REGIONS FIG. 19OF 7.5 k J m m BEA D IN GRO OVE WELD S (Cont. .. )

65



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£ ■ > > :

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::ί /:;,ν-ν-,-ν / , ,. ■¡ϊ\ ^Μκ \\.:

& - ' ·-.·:·:

χ 400 IF57 Stee l G χ 400 OF381 Steel Η

• '-■ Γ' -*ζ? s JN.?s«

■ht*-:* '.? * · *» . : ; - „ y ^ > Í Í V V Y

. ·-ί· .·'γ. - .ν Y^-lr Γ : ^^

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Γ Ut ■· . V f <Α ν*?-· .;.' , . ^.--- - - k--

* · ' : , : / ' - • ^ • - . / ..»ί· > ♦"* -ri. ^ , -" < χ-*"-'Γ-" ï* -'-" '' > Ο l t ^ ->

' ' ί f Jr ti« y' ν.-Λ>Λ- ? '>· V'M » V-

• χ- :' ./', '-Α-νΛ,-ΐ ^*/ Χ--- '--'ti

χ, /. ·

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ι <

;

t ì ι b ri —- S'S -r> s Ky tf Î V ^ S V- 'A.· /-., r« · . ν .· ν■-- -. -?4„ - ^ > V T - > ^ * t·>-A.

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x400 IF61 Stee l Ι χ 400 OF377 SteelJ

i v . ^ ' ; ' , : · ^ ' t , . rC^ - l — V V : ^

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- :■,■.:=■-* ^.--.* «-ν,··/ , ■ ¿■£_y,., ι-' ., ν /·'■" d ,-- ■ - »-«..■ . - ' / ι ' . ' · - * ' . -· i-.'V. · J> - ^rf--.. .'' '· . V·-. . ■

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x400 IF65 Steel Κ χ 400 OF218 Steel L

OPTICAL MICROGRAP HS OF GRA IN COA RSENED HAZ REGIONS FIG. 19

OF 7.5 kJ/mm BEA D IN GROOVE WELDS (Cont. .. )

66



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χ 400 OF 222

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Steel M χ 400 OF 214 Steel N

--—'-Ui.

χ 400 OF 284

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Steel O χ 400 O F 2 8 8 S tee l Ρ

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Λ Λ \ yi -r

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-' ^ 4 .1 - . . -' U Γ- ·* f ?

■ > -'- ' , i l · , ' ' : , · . . ? » . ' · Ί - *, · -.

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. " ■ " ■ " ' · ' ' ■ * ' '

■ ' t l · χ

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\ ' \ .:. ¿ . *..' „-/' ίtr ' t' ',-ν ■ ■ ; * · ·ν' ·- '- - ' . · - . , -, . ,.

V \ . * C - J .<V Τ . , - - ν ' ι

χ 400 O F 280 Steel Q

O P T I C A L M I C R O G R A P H S O F G R A I N C O A R S E N E D H A Z R E G I O N S F I G. 19

O F 7.5 k J m m B E A D IN G R O O V E W E L D S

67



GCHAZ Colony Size, ym

340

300

260

220

180

140

100

Al (A)

Al-Nb(Q)

Al-Nb(P)V-B (H)Al-Nb (N)Al-Nb (0)Al-V-B (I)

Al-V (B)Al-Ti (C)Al-Ti-V (L)Al-V-Ti-B (K)Al-Ti-V (M)Al-Ti-B (G)

Ti (D)V (E)

Ti-B (F)Ti-V-B (J)

3.5 7.5

Heat Input, kJ/mm

GRAIN COARSENED HAZ COLONY SIZE v WELD HEAT INPUT FIG. 20R3/7679A)

68



" Χ Χ <-j-ä"*cY'"~ Y Y '

^ - Ä ^ x ^ ; Y ·

I?YY:

èï^Ji l fe ;^^fe í sr^^ íS'^ í^^

feÄ

XÎKï*'^·

λ^Ρ Υ ^Φ 4 ΧΧ -' ' '

-S

■li '

; -'^-®.VX'·

íY'~ -yj.

χ 50 ΡΗ297 Steel G

ν- ,"w- ' ' s ν- ■ r , .. v v. .

χ Ύ X r· ; Y ; Y Y : Y- . Y - \ N > \ \ ' X ^ Y -Y c :

·· Y X Y Y - Y ·:• Ύ ; Y . . Y X Y x ^

. Y .. \ * · γ γ ^ - , > · . '' ; *· ^ Υ ν, Υ - '-Υ/.- ¿·. /

\

Υ'_ χ_'s 'ν Υ ^ Υ

χ 400 ΡΗ298 Steel G χ 400 ΡΗ299 Steel G

Light Etching Zone Gra in Coarsened HAZ A djacent

to Light Etching Zone

OPTICAL MICROGR APHS ILLUSTRATING THE LIGHT ETCHINGZONE A THE FUSION BOUNDAR Y IN STEEL G AT 7.5 kJ/mm

FIG. 21

69



Microphase Fraction,

20

16

12

8

4

( a ) 3 .

_JL

5 kJ/mm Be

Qκ ·•

N%L

HM ·• I j

• E / GF ,/TD• / • B

/ ·

ad in

Ρ•

0•

L .

G r o o v e H A Z s /

/ Le\

. . .J 1

Lever Rule

20

16

12

(b ) 7. 5 kJ/mm Bead in

-

-

0C ·

¿ · J

L * 1/M */5*ÇH

7 y ·

Α

/

/ ι I

Ρ j

• 0

L .

G r o o v e H A Z s /

/ L e v

1 1J

0.04 0.08 0.12 0.16 0.20

Carbon Content, %

EFFECT OF CARBON ON GCHAZ MICROPHASE CONTENT FIG. 22(R3/7680)

70



+ 7.5 kJ/mm

O 3.5 kJ/mm

Volume Fraction MA,

14

12

10

8

6

4

2

m

1

¡1

ƒ I

ο 'F I

I1

1F +

0

/ Ρ/ °

/ Η

/ °-">/ <P ι // c x ^ J O /

/ + // G // 0 ƒƒ

/ oED c o K / B

6"θ 0 H-Ε0 + B /

G I + '+ /

A /+ P+

H+

»4

oο

Ν

° LO

M

ο— __ _

^ ■ ^ _ — — x " M L. y ^ — ^ <*

χ «·» yΖ . — χ

χ'*

yy

yyy

yy

y

1 i 1 1 1

0.28 0.30 0.32Si + Mn 0.34 0.36Cr + Mo + V+ +

0.38Ni + Cu

15

0.40 0.42

EFFECT OF ALLOYING ON MA FRACTION IN THE GCHAZ OF BEAD IN GROOVE WELDS FIG. 23

(R3/7681)

71



MICROSTRUCTURE

ToughnessIncreased

Promotes AFin Ti-B-lowAl System

Promotes P F (I)in C-Mn-Ni-Al

and C-Mn-Ni-Ti-B-

low Al System

Reduces GCHAZColony Size

in C-Mn-Ni-Al

System

Reduces'free'

Nitrogen

Toughness

Decreased

Promotes PFin C-Mn-Ni-Al

System

Promotes M-A(Excep t in Ti-B-low Al System )

PrecipitationHardens

TOUGHNESS

Transition TempDecreased, °C

20

20

Transition Temp.Increased, °C

HAZ CharpyC-Mn-Ni-Al

HAZ CharpyC-Mn-Ni-Ti-B-high Al

Τ

HAZ CTODC-Mn-Ni-Ti-B-low Al

4

HAZ CTODC-Mn-Ni-Al

HAZ CharpyC-Mn-Ni-Ti-B-low Al

HAZ CTODC-Mn-Ni-Ti-B-high A l

INFLUENCE OF VANADIUM ON GCHAZ MICROSTRUC TURE ANDTOUGHNESS OF 7.5 kJ/mm B EAD IN GROOVE WELDS

FIG. 24

72



MICROSTRUCTURE

ToughnessIncreased

Toughness

Decreased

P r o m o t e s AF P r o m o t e s(Except when PF(I)

P r e s e n t w i t h Β+ high Al at the

F u s i o n B o u n d a r y )

A ▲

▼

P r o m o t e sP F

'

R e d u c e sM - A P h a s ei n P r e s e n c e

o f B + l o w A l

li

"

P r o m o t e s M - Ain Presen ce ofAI and A l + Β

R e d u c e sG C H A ZColony

Size

ι ν

R e d u c e s H A ZH a r d n e s s inP r e s e n c e ofΒ + low Al

i k

▼

P r e c i p i t a t i o nH a r d n e s s in

Presence of A lan d A l + Β

R e d u c e s'free '

N i t r o g e n

a

TOUGHNESS

Transition Temp.Decreased, °C

20 -

20 -


H A Z C h a r p yC-Mn-Ni-Al

HAZC-Mn-Ni

H A Z C h a r p yC-Mn-Ni-V-B-low Al

r ιC h a r p y HAZ-V-B-h igh Al C-Mi

H A ZC - M n - N i -

H A Z C T O D 'C-Mn-Ni-V-B-low AI

Î

rC T O D

l-Ni-Al

C T O DV-B-hig

ι

INFLUENCE OF TITANIUM ON GCHAZ MICROSTRUCTURE ANDTOUGHNESS OF 7.5 kJ/mm BEAD IN GROOVE WELDS

FIG. 25

73



MICROSTRUCTURE

ToughnessIncreased

Reduces PFin Ti and

Ti-(V)-B Stee ls

Reduces'free'

Nitrogen

Toughness

Decreased

Reduces AFin Ti-Steeland Ti-(V)-B Steels atthe FusionBoundary

(LEZ)

ReducesPF(I)inTi-(V)-B

Steels andV-B Steels

IncreasesGCHAZ

Colony Sizein Ti and

Ti-B Steels

PromotesM-A in Ti

andTi-(V)-B Steelsand V-BSteels

IncreasesHAZ Hardness

in Ti andTi-B Steels

TOUGHNESS

Transition Temp,Decreased, °C

20

20

Transition Temp.

Increased, °C

HAZ CTODC-Mn-Ni-V

HAZ CharpyC-Mn-Ni-V

HAZ CTODC-Mn-Ni-Ti

i rHAZ Charpy

C-Mn-Ni-Ti-B

HAZ CharpyC-Mn-Ni-Ti

HAZ CharpyC-Mn-Ni-V-B

HAZ CharpyC-Mn-Ni-Ti-V-B

HAZ CTODC-Mn-Ni-Ti-B

HAZ CTODC-Mn-Ni-Ti-V-B

HAZ CTODC-Mn-Ni-V-B

INFLUENCE OF ALUMINIUM ON GCHAZ MICROSTR UCTU RE AND FIG. 26TOUGHNESS OF 7.5 kJ/mm BE AD IN GROOV E W ELDS

74



MICROSTRUCTURE

ToughnessIncreased

Toughness

Decreased

R e d u c e s P Fin V-low Al

St ee l

P r o m o t e s P F ( I )in Ti-low Al

and V-low AlSt ee l s

Reduces M-APhase in Ti-low Al

and V-low AlSt ee l s

R e d u c e s'free'

N i t r o g e n

ReducesG C H A Z C o l o n ySize in Ti-low Al

St ee l

Promotes PFin Ti-low Al

Steel

Reduces AFin Ti-low Al

Steels

IncreasesHAZ Hardness

in V-low AISteel

IncreasesGCHAZ ColonySize in V-low Al

Steel

TOUGHNESS

HAZ CharpyC-Mn-Ni-V-low Al

Transition Temp.Decreased, °C

20 -

20


k

1

H A Z C h a r p yC-Mn-Ni-Ti-low A l

Î

H A ZC-Mn-N

i

H A ZC-Mn-N

i

C T O Di-Ti-low A l

C T O Di-V-low A l

INFLUENC E OF BORON ON GCHAZ MICROSTRUCTURE ANDTOUG HNESS OF 7.5 kJ/mm BE AD IN GROOVE WELDS

FIG. 27

75



X PF + GBF

O FS(A) + FS(N)

D AF + PF(I)

Microstructural Constituents,

100

80 -

60

40

20

-60

J . ± ± J .

- 4 0 - 2 0 0 20

4 0 J T r a n s i t i o n T e m p e r a t u r e , °C

INFLUENCE OF HAZ MICROSTRUCTURE ON CHARPY 40 J TEMPERATURE F IG . 28

OF 7. 5 kJ/mm BEAD IN GROOVE WELDS (R 3 /7 6 8 1 A )

7 6



Observed 0.1 mm CTODTransition Temperature

°C

+40

+ 20

-40

-80 -40 0 +40

Calculated 0.1 mm CTOD Transition Temperature, °C

Observed Charpy 40 JTransition Temperature

+40

-40

-

-

-

¿-_L_

J+

/ D Η/ + +

/ +

1 ι

M

+ /

1

+ 2σ y '

Μ " 2 σ /■4- /

1

-80

-80 -40 0 +40Calculated Charpy 40 J Transition Temperature, °C

RESULTS OF MULTIPLE LINEAR REGRESSION ANALYSES BETWEEN MICROSTRUCTURAL FIG. 29

FEATURES AND TOUGHNESS OF 7.5 kJ/mm BEAD IN GROOVE HAZs (R3/7681B)

77



Observed 0.1 mm CTODTransition Temperature

°C

+40

-80

-80 -40 0 +40


MULTIPLE LINEAR REGRESSION BETWEEN MA FRACTION GRAIN SIZE AND 0.1 mm FIG. 30CTOD TRANSITION FOR 7.5 kJ/mm BEAD IN GROOVE HAZs R3/7682)

Mean HAZ Hardness HV5

220 -

200

180

-100 -60 -20 +20

0.1 mm CTOD Temperature, °CEFFECT OF HAZ HARDNESS ON 0.1 mm CTOD TEMPERATURE FOR 7.5 kJ/mm

BEAD IN GROOVE HAZsFIG. 31R3/7682)

78



Observed 0.1 mm CTOD

Transition Temperature

°C

+40 -

-80 -40 0 +40


Observed Charpy 40 JTransition Temperature, °C

+ 20 -

-20

-60 -

-60 -20 +20

Calculated Charpy 40 J Transition Temperature, °C

RESULTS OF MULTIPLE LINEAR REGRESSION ANALYSES BETWEEN GRAIN SIZEMA FRACTION, HARDNESS AND TOUGHNESS OF 7.5 kJ/m m

BEAD IN GROOVE HAZs

FIG. 32R3/7682A)

79



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European Commission

EUR 15834 — Properties and service performance

Effect of alloying elements on HAZ microstructure and toughness

P. Harr ison P. Wall

Luxembourg: Office for Official Publications of the European Communities

1 9 9 6 — X V I I , 7 9 p p . — 2 1 . 0 x 2 9 . 7 c m

Technical steel research series

ISBN 92-827-7203-9

Price (excluding VAT) in Luxembourg: ECU 11.50

Seventeen experimental steel casts have been used to evaluate the effectsof V, Ti, ΑΙ, Β, N and Si, in various alloying element combinations, on HAZmicrostructure and toughness. HAZs were produced in all steels usingsubmerged-arc bead in groove welds at 3.5 and 7.5 kJ/mm and thermalsimulations were conducted at the same heat inputs. Toughness wasevaluated using bead-in-groove Charpy, Gleeble Charpy and bead-in-groove CTOD test techniques. HAZ microstructures produced by the bead-in-grove welds were fully cha racterized using quantitative optical and SEMtechniques.



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