Research on Specialty Steels at the Materials and Metallurgy Department at Polytechnic School of University of São Paulo

Metallurgical and Materials Engineering DepartmentP l h i S h lPolytechnique School

University of São Paulo

Prof. Dr. André Paulo Tschiptschin

Outline

Metallurgical and Materials Engineering Department: Historical facts.

Met & Mat Engineering Department’s profileMet & Mat Engineering Department s profile.

Research work on Specialty Steels in the last 30 years.

On going research lines on tool and stainless steels.

Conclusions

Some historical facts

In 1907 a Metallog aph Labo ato as mo nted at theIn 1907 a Metallography Laboratory was mounted at the Materials Office of the Polytechnique School. Pujol brought from Berlin a Carl Zeiss equipment, starting the studies on the relationship between microstructure and properties of steelsproperties of steels.

The Mining and Metallurgical Engineering Department was founded as a separate Department in 1939.

In 1955 the Metallurgical Engineering Department separated from the Mining Engineering becoming a 5 years course.

Moved to the campus of the University of São Paulo campus near the Technological Research Institute in May 8th 1967, 40 years ago.

Physical Metallurgy studies started in the 50´s and became one of the main activities of the Department from the mid 60´s on.

Research work in collaboration in the past years

Professor Ivan Falleiros started working at the Villares Group as Coordinator of the Development and Research Center in 1975 and as Technical Director pin 1984.

Several MSc and PhD research works were conducted under his advise and of other faculty members as wellof other faculty members as well.

Marcos Henrique Carlos de Souza. Effect of the substitution of V by Nb in a comercial high speed steel. Efeito da substituição do vanádio pelo nióbio em um aço rápido comercial. 1983. Ivan Gilberto Sandoval Falleiros.1983. Ivan Gilberto Sandoval Falleiros.

The effect of Nb in the microstructure and creep resistance of an ASTM A-297 – HC steel– Eduardo Augusto Ayroza Galvão Ribeiro, 1984 (Director of Aços Villares – Sidenor)

Marcos Alexandre Stuart Nogueira. Effect of the previous microstructure andMarcos Alexandre Stuart Nogueira. Effect of the previous microstructure and microsegregation on the formation of austenite and isothermic tranformation of an AISI 52100 steel. 1986. Ivan Gilberto Sandoval Falleiros. (Director of Villares Metals)

Marcos de Brito Orsini. Effect of the hogeneizing treatment in the microstructure and t h f f d i 18% Ni t l 1987 I Gilb t S d l F ll itoughness of a forged maraging 18% Ni steel. 1987 - Ivan Gilberto Sandoval Falleiros.

Ricardo Fonseca de Mendonça Lima. Hot workability of an AISI D2 tool steel using the torsion test. 1993. Ivan Gilberto Sandoval Falleiros. (presently at Aços Villares).

Al d S k l ki Eff t f Nb d Ti dditi i th i t t d h i lAlexandre Sokolowski. Effect of Nb and Ti additions in the microstructure and mechanical properties of an ASTM A608 Grau HK40. 1993. Ivan Gilberto Sandoval Falleiros.

Research work in collaboration in the past years

Dionisio Quintino de Abreu. Hot ductility of an AISI 309 stainless steel. 1990. Ivan Gilberto Sandoval FalleirosSandoval Falleiros. Tadeu Carneiro – Effect of W and Mo in the structure and mechanical properties of Nb containing high speed steels – 1981, Renato Papaleo.Martensite formation during wire drawing of an AISI 302 stainless steel, 1992, Ivan FalleirosPaulo Sérgio Correa - Gaseous Nitriding of an H13 tool steel, 1995, Hélio GoldensteinPaulo de Tarso Haddad – Effect of Nb on the recrystallization of fully austenitic 15Cr – 15 Ni stainles steels, 1994 – Angelo fernando Padilhastainles steels, 1994 Angelo fernando PadilhaMiguel Angelo Carvalho – Simulation of Wear of cold rolling mill rolls, 1995, Ivan Falleiros

Department's Profile

7.200 m2 building where many different laboratories are installed.

25 faculty members25 faculty members4 faculty members involved with research on the specialty steels subject

120 undergraduate students:20 Metallurgical Engineering students per year20 Materials Engineering students per year

120 graduate students80 MSc students40 PhD studentsAround 18 students working on the specialty steels subjectg p y j

Characterization Laboratories

Microstructure and Electron Microscopy LaboratoryZeiss Metalographic Microscopes.

Scanning Electron Microscopy Laboratory.Philips XL-30 SEM with EDAX and TSL – EBSD.

Transmission Electron Microscopy (shared with IPEN)Jeol T-400 TEM with EDS characterization.Jeol T 400 TEM with EDS characterization.

SPM - Shimadzu SPM – 9500 – Atomic Force MicroscopyNanoscale Depth Sensing Techniques and Nanoscale Sclerometry (scratch tests) for mechanical characterization of thin filmstests) for mechanical characterization of thin films.Thermal Analysis

DTA, TGATGADilatometry

Mechanical Testing

Processing Laboratories

Heat Treatment FacilitiesPlasma nitriding and PVD – TiN, TiAlN, TiC, TiCN multilayer coating laboratory.Triode Reactive Magnetron Sputtering using N2 and CH4g p g g 2 4

Main research lines on Specialty Steels

High Nitrogen Stainless SteelsMartensiticAusteniticAusteniticDuplex

High Temperature Gas Nitriding of Stainless SteelsWear Resistant MaterialsErosion-CorrosionCavitation-Erosion

Tool SteelsMorphology of Eutectic Carbides in Tool SteelsT h ti i ti f Hi h C b T l St lToughness optimization of High Carbon Tool SteelsPVD – coatings and duplex treatment for increasing lifetime

Modeling

Solidification Processes (Magma)

Computer Aided Thermodynamics L + gasLp y(Thermocalc)

Transport Phenomena (Heat and

δ + gas

L + gasL

δ

Transport Phenomena (Heat and Mass Transfer)

F i d R lli d li

γ + gas

γ

δ+γ

CForging and Rolling modeling (Qform, Abaqus)

γ + Cr2N

High Nitrogen Stainless Steels

AusteniticCorrosion resistant and biocompatible steels for surgical implantsCavitation -Erosion and Erosion-Corrosion Resistant for hydroelectricCavitation Erosion and Erosion Corrosion Resistant for hydroelectric power generation plants.

MartensiticMi iMiningOil prospection, extraction and distribution industries

Duplex and Superduplexp p pOil prospection and extraction

Morphology of Eutectic carbides – Tool Steels

Solidification of High Speed SteelsAs Cast M2As Cast M2 MM C Carbides MorfologyC Carbides MorfologyAs Cast M2 As Cast M2 -- MM22C Carbides MorfologyC Carbides Morfology

The classification was used to design new wear resistant materials: tool steels rolling mill rolls

Solidification of High Speed SteelsAs Cast M2 As Cast M2 -- MM22C Carbides MorfologyC Carbides Morfology

Type 1

Irregular Eutectic

Type 2

Regular complex EutecticIrregular Eutectic(Boccalini & Goldenstein, 2003)

Regular-complex Eutectic(Boccalini & Goldenstein, 2003)

Cast M2 - Decomposition Heat Treatmentp

MM22C Carbide Type MetaestabilityC Carbide Type Metaestabilityin situ decomposition betwen 900 e 1200°C:in situ decomposition betwen 900 e 1200°C:

• M2C + Fe(γ) → M6C + MC (Fredrikson & Nica, 1976)• Simultaneous Precipitation → M6C + MC diffusion controled

MC and M6C Carbide Type Spheroidization and CoarseningMC and M6C Carbide Type Spheroidization and Coarsening• MC Carbide → Controled by V Diffusion in Fe(γ) • M6C Carbide → Controled by W Diffusion in Fe(γ)

1050 °C – 0,2 h 1200 °C – 24 h

Fracture Toughness of tool steels

High Speed Tool SteelsHigh Speed Tool SteelsVM2 (Forged and Rolled)VM2 (Forged and Rolled)

•• Fine Aligned CarbidesFine Aligned Carbides•• Fine Aligned CarbidesFine Aligned Carbides

Sinter 23 (P/M)Sinter 23 (P/M)•• Fine Homogeneous Carbide DistributionFine Homogeneous Carbide Distribution

M2 L S ti F iM2 L S ti F iM2 Large Section ForgingM2 Large Section Forging•• Ledeburitic Carbides Slightly BrokenLedeburitic Carbides Slightly Broken

As Cast, Modified and Heat Treated M2As Cast, Modified and Heat Treated M2•• Slightly Spheroidized Eutectic CarbidesSlightly Spheroidized Eutectic Carbides

HSS Microstructures x Mechanical Properties

M2 ThyssenM2 Thyssen Villares M2Villares M2

Sinter23Sinter23 As Cast Decomposed M2As Cast Decomposed M2Sinter23Sinter23 As Cast Decomposed M2As Cast Decomposed M21200 1200 °°C C –– 24 h24 h

Test Apparatus

Chevron Notched TestApparatus

Three Point Bend TestApparatus

Apparatus

Chevron Methodology – Samples

Chevron Methodology (ASTM E 1304) for measuring KIc• Small Samples• Fast and unexpensive test

Does not need Pre cracking– Does not need Pre-cracking– Maximum Load Test

Transversal Rupture Strenght x Carbide Distribuition

F F

[(L-L0)/L0]

5 Strain

F F

1

Rupture Strengh[MPa]

2000

Yelding1500

Yelding

Carbide Size

Fracture Toughness x Carbides Distribution

Carbides

Notch

25 0

Plastic ZoneCrack Plastic Zone

20,0

25,0

MPa m1/2

15,0

10,025,4 210

Bar Diameter (mm)

Fracture Toughness x Crack Path

Crack Tip

ρ2

ρ1

Crack Tip

nTD ρρρ +++= ...21C k P hCrack Path

LR RLAISI D2

Ø 25,4 mm

25μm 25μm

Ø 70,0 mm

25μm 25μm

Ø 210,0 mm

25μm 25μm

Cold Work Tool Steel - AISI D2

20

25

Ene

rgy

(J)

25 mm70 mm210 mm

30354045

t MPa

25 mm70 mm210 mm

10

15

py A

bsor

ved

E

15202530

Ben

d St

reng

ht

0

5

Cha

rp

LT/ Trat.1 TL/ Trat. 1LT/ Trat. 2 TL/ Trat. 205

10B

LT/ Trat. 1 TL/ Trat. 1LT/ Trat. 2 TL/ Trat. 2

20,0

25,0

MPa

. m

0.5

10,0

15,0

re T

ough

ness

M

25,470,0210,0

0,0

5,0

Frac

tur

TT/Trat.1 LL/ Trat.1 TT/ Trat. 2 LL/ Trat. 2

High Nitrogen Stainless Steels (HNSS)

Nitrogen in solid solution improves the cavitation-erosion resistanceof stainless steels.

Production routes of high nitrogen stainless steels (HNSS) byalloying, pressure metallurgy, powder metallurgy and solid-statediffusion have been studied Recently a chemical solid-statediffusion have been studied. Recently, a chemical solid-statenitrogen alloying technique was developed, consisting of exposing aSS under a N2-containing gas atmosphere in the range 1000-1200ºC.

In this High Temperature Gas Nitriding (HTGN) treatment, atomicnitrogen is interstitially absorbed at the surface of the steel andthen diffuses into the near surface region.

Structure of Fe-Cr-N and Fe-Cr-C solid solutions

In Fe-Cr-C-N solid solutions the substitution (partial or total) ofIn Fe-Cr-C-N solid solutions the substitution (partial or total) ofcarbon by nitrogen promotes ordering of interstitial andsubstitutional elements

Structure of Fe-Cr-N and Fe-Cr-C solid solutions

There are few free electrons in the structure of Fe-C alloys leading to a strongercovalent character of the chemical bonding.

In Fe-N alloys there are more free electrons and the metallic character of thechemical bonding is stronger.chemical bonding is stronger.

Free electron concentration in austenitic stainless steels Cr18Ni16Mn10 and Cr20Ni16Mn6 as a function of the interstitial content [BERNS, 2000]

High Temperature Gas Nitriding

t

c,TT, PN2, 2

Texture of the nitrided case

T t d i t t f th it id d t i l t l l t d bTexture and microtexture of the nitrided stainless steels was evaluated by Electron Backscattered Diffraction – EBSD.Fraction of Coincidence and non-Coincidence Site Lattice (CSL)Boundaries

Nitrogen Content and Hardness of HTGN UNS 30403(Fully austenitic microstructure)(Fully austenitic microstructure)

Nitrogen contents (WDS) and hardness profiles of the HTGN UNS 30403. Nitriding treatment performed at 0.07 MPa N2 partial pressure.

High Nitrogen Stainless Steels (HNSS)

NitrogenNitrogen bearingbearing stainlessstainless steelssteels hashas beenbeen usedused inin applicationsapplications wherewhereaa widewide varietyvariety ofof adverseadverse conditionsconditions areare foundfound::aa widewide varietyvariety ofof adverseadverse conditionsconditions areare foundfound::

I.I. cavitationcavitation--erosion, erosion, IIII erosionerosion--corrosion corrosion II.II. erosionerosion--corrosion, corrosion, III.III. pitting pitting IV.IV. crevice corrosion.crevice corrosion.

TheThe useuse ofof wearwear andand corrosioncorrosion resistantresistant materialsmaterials isis vitalvital inincomponents,components, workingworking inin contactcontact withwith slurryslurry environmentsenvironments andandp ,p , gg yysubmittedsubmitted toto cavitationcavitation damage,damage, suchsuch asas::

II i d t i li d t i l llI.I. industrialindustrial valves,valves,II.II. impellers,impellers,III.III. pumpspumps andand turbinesturbines

Corrosion

NitrogenNitrogen hashas aa beneficialbeneficial effecteffectNitrogenNitrogen hashas aa beneficialbeneficial effecteffectonon localizedlocalized corrosioncorrosion resistanceresistanceofof austeniticaustenitic stainlessstainless steelssteels..

AusteniticAustenitic stainlessstainless steelssteels withwithnitrogennitrogen contentscontents upup toto 00..6060 wtwt--%%havehave beenbeen successfullysuccessfully usedused ininhavehave beenbeen successfullysuccessfully usedused ininapplicationsapplications involvinginvolving pittingpittingcorrosion,corrosion, crevicecrevice corrosioncorrosion andandstressstress corrosioncorrosion crackingcracking inin hothotchloridechloride solutionssolutions

PERN = %Cr + 3.3%Mo + k%N with 13<k<30

Change in pitting potential of 18 wt% Craustenitic stainless steels in dilute chloridesolutions [Speidel]

PERN = %Cr + 3.3%Mo + k%N with 13<k<30

MARC = %Cr + 3.3%Mo+20%N+20%C-0.5%Mn-0.25%Ni

Surgical Steelsg

Ti and Cr-Co alloys are very expensive. A High Nitrogen Nickel Free AusteniticStainless Steel is a potential substitute of the ASTM – F138 and ASTM –1586. We are working on the investigation of the corrosin behavior of thesetwo alloys compared to Böhler’s P 558 and to two experimental alloys ACW1and ACW2.

Element %Cr % Mn %Mo %N %C %Si %Ni ASTM F138 17 5 2 8 0 1 max 0 03 14 6 ASTM-F138 17,5 -- 2,8 0,1 max. 0,03 -- 14,6 ASTM-1586 21,2 3,6 2,4 0,42 max. 0,05 -- 9,5 Böhler P558 17,3 10,5 3,3 0,5 0,2 0,45 max. 0,2 ACW1 18 2 15 1 - 0 39 max 0 03 -- - ACW1 18,2 15,1 0,39 max. 0,03 ACW2 18,6 15,2 2,5 0,39 0,04 -- -

Corrosion Resistance of Surgical Steels

Cyclic Polarization Curves in Ringer Solution [OSSA, 2003]y g [ , ]

1600F138 and F1586 showedvery close and relativelylow Epp values suggesting

800

1200

EC

S) F1586P558

some difficulties inrepassivation of the pit.

The alloy P558 shows thatare no differences between

400E(m

V E are no differences between

the pitting potential and therepassivation potentialindicating that theformation of a new passive

-400

0

1 E 10 1 E 09 1 E 08 1 E 07 1 E 06 1 E 05 1 E 04 1 E 03 1 E 02

F138 formation of a new passivelayer is very easy.

1,E-10 1,E-09 1,E-08 1,E-07 1,E-06 1,E-05 1,E-04 1,E-03 1,E-02

i(A/cm2)Material Pitting Potential

Ep (mVecs) Protection Potential Epp (mVecs)

ASTM F138 571 0 ASTM F1586 1097 -108 Böhler P558 1114 1114

??

Carbon and Nitrogen Synergism

MARC = %Cr + 3,3%Mo + 20%C + 20%N - 0,5%Mn - 0,25%Ni

(Measure of alloying for resistance to corrosion) [Speidel, 2004]

PRE MARC ASTM F138 27,50 20,59

ASTM F1586 35 03 37 19 ASTM F1586 35,03 37,19

Böhler P558 37,19 60,09

The P558 steel shows a synergism between carbon and nitrogen improving thepitting corrosion resistance. [OSSA, 2003]

Corrosion of martensitic stainless steels

ToroToro etet alal.. [[55]] foundfound aa muchmuch[[ ]]betterbetter corrosioncorrosion resistanceresistance ofofhighhigh--temperaturetemperature nitridednitridedAISIAISI 410410SS stainlessstainless steelsteelAISIAISI 410410SS stainlessstainless steelsteelstainlessstainless steelssteels whenwhen testedtestedinin acidacid solutionsolution containingcontainingchloridechloride ionsions..

TheThe superioritysuperiority ofof thethe highhigh

C i b t l i ti

nitrogennitrogen steelsteel prevailedprevailed forfor allallthethe temperingtempering temperaturestemperaturesstudied,studied, 200200,, 400400 andand 600600 Comparison between polarization

curves for AISI 420, and hightemperature nitrided AISI 410Smartensitic stainless steels tested at

,, ,,ºCºC..

25°C, tempered at 200 °C.

Corrosion of martensitic stainless steels

Nitrogen increases also the pitting potential of P\M processed martensiticstainless steels (Fe-Cr-N alloys) when compared to the conventional Fe-( y ) pCr-C alloys.

Variation of Pitting Potential Ep with nitrogen content in P\Md hi h d it t iti t i l t l t t d iprocessed, high-density, martensitic stainless steels, tested in

0.5M H2SO4 +3.5% NaCl.

Erosion and Erosion-Corrosion

AISI 420 AISI 420 410N 410N 410SN 410SN

30

40

(g/m

2 )

410N 410SN 410SN

Tempering 200°CTest temperature 25°C, Impact 90°

20

30ss

Los

s, ( p g

Tempering 450°C

(b) 25°C

0

10

ecifi

c M

a

00 24 48 72 96

Time, h

Sp

Variation of specific mass loss with testing time, as a function of tempering andtesting temperatures. AISI 420 and high-nitrogen 410SN and 410N martensitictesting temperatures. AISI 420 and high nitrogen 410SN and 410N martensiticstainless steels.

Synergism between Erosion and Erosion-Corrosion

2 0 02 2 0

)

1 2 0

1 4 01 6 01 8 0

2 0 0

Loss

(g/m

2

4 06 08 0

1 0 0

ecifi

c M

ass

02 0

410S-90° 410S-45° 420-90° 420-45°

Sp

Eros ion Corros ion Eros ion-Corros ion Synergism

Effect of synergism between corrosion and erosion in AISI 420 and high-temperaturey g g pnitrided AISI 410S martensitic stainless steels, tempered at 200°C for 1 hour.

Distribuition of Cr and Fe in nitrided AISI 410S steel

Cr and Fe distribution in nitrided AISI 410S, tempered at 550°C for 1 hour.EDX windowless Si (Li) detector, STEM-300 kV, probe size 1.5 nm, beamEDX windowless Si (Li) detector, STEM 300 kV, probe size 1.5 nm, beamcurrent 0.5 nA.

Distribuition of Cr and Fe in AISI 420S steel

Cr and Fe distribution around M23C6 precipitates in quenched and200 C d AISI 420 i i i l l200°C-tempered AISI 420 martensitic stainless steel.

CE Resistance of High Nitrogen Austenitic Stainless Steelsg g

High nitrogen austenitic steels have been reported as suitablematerials for applications in which erosive damage caused bycavitation is significantcavitation is significant.

These alloys are higher CE resistant compared to conventionali f i i l d h d h CEnitrogen free austenitic steels and cheaper compared to the CE-

resistant cobalt-based alloys.

No systematic analysis have been carried out studying the effect ofincreasing nitrogen contents, different microstructures or differenttextures on the cavitation erosion resistance of austenitic stainlesssteels.

Cumulative mass loss of CE UNS 30403

Cumulative mass-loss as a function of % N wt% and exposure time.

Cumulative mass loss versus cavitation-erosion testing timeUNS 31803UNS 31803

Cumulative mass-loss as a function of grain size and texture.

Mass loss rate versus cavitation-erosion testing timeMass loss rate versus cavitation erosion testing time

125μm 3TR

+ 92μm 3.5TR

20μm 11TR

40μm 10TR

84μm 5TR

Samples with different grain diameters andSamples with different grain diameters and Samples with increasing nitrogen content.Samples with increasing nitrogen content.Samples with different grain diameters and Samples with different grain diameters and increasing texture intensities.increasing texture intensities.(Nitrogen content c.a. 0.8 wt(Nitrogen content c.a. 0.8 wt--%)%)

Samples with increasing nitrogen content. Samples with increasing nitrogen content. (Mean grain diameter c.a. 40 (Mean grain diameter c.a. 40 μμm and maximum m and maximum texture times random intensity c.a. 10)texture times random intensity c.a. 10)

Nitrided UNS S31803 (0,77 % N – grain diameter 92 μm)The incubation time according mass loss measurements was 57.6 ks.

18 x 103 s 54 x 103 s 75.6 x 103 s

Fraction of CSL and non CSL boundaries damaged by cavitation-erosion in UNS 30403 SScavitation erosion in UNS 30403 SS

F ti f CSL d CSL b d i d d b it tiF ti f CSL d CSL b d i d d b it ti i i Fraction of CSL and non CSL boundaries damaged by cavitationFraction of CSL and non CSL boundaries damaged by cavitation--erosion erosion in a sample with 0.48 wt% N exposed to CE during 7.2 ks in a sample with 0.48 wt% N exposed to CE during 7.2 ks

Relative CE resistance of nitrided stainless steels

CE r

esis

tanc

eRe

lati

ve C

UNS3003 UNS31803 UNS30403 UNS31803 Stellite 6 Ireca UNS3003 UNS31803 UNS30403 UNS31803 Stellite 6 Ireca Solubilized Solubilized Nitrided Nitrided Welding Welding

High nitrogen stainless steels compared to more expensive cobalt alloys

Relative CE resistance of nitrided stainless steelse

30403 Solubilized

31803 Solubilized

d d

resi

stan

ce 30403 Nitrided

31803 Nitrided

tive

CE

rRe

la

HV 300g

PVD Coating and Duplex treatment of tool steels

Controlling the adherence of the deposited ceramic layer to the Controlling the adherence of the deposited ceramic layer to the sample’s surface constitutes one of the main difficulties and object sample’s surface constitutes one of the main difficulties and object of concern of many research groups in the area of surface of concern of many research groups in the area of surface y g py g pengineering and surface science. engineering and surface science. Duplex treatments consisting of an ion nitriding preDuplex treatments consisting of an ion nitriding pre--treatment treatment followed by a PVDfollowed by a PVD –– TiN coating has been used to increase theTiN coating has been used to increase thefollowed by a PVD followed by a PVD –– TiN coating has been used to increase the TiN coating has been used to increase the adherence of PVD coatings.adherence of PVD coatings.When performed in a When performed in a hybrid reactorhybrid reactor (both treatments inside the (both treatments inside the same chamber) it improves the adherence between the ion nitrided same chamber) it improves the adherence between the ion nitrided layer and the TiN film. layer and the TiN film. The adherence of the TiN layer is improved due to a stronger loadThe adherence of the TiN layer is improved due to a stronger loadThe adherence of the TiN layer is improved due to a stronger load The adherence of the TiN layer is improved due to a stronger load bearing capacity of the ion nitrided layer.bearing capacity of the ion nitrided layer.

Complex stressed machineComplex stressed machine components and tools

FunctionalFunctionalStress

AbrasionAdhesion

Contact fatigue Functional Functional properties of properties of

duplex coatings duplex coatings Material Thin surface layers on

Contact fatigue

obtained by obtained by plasma plasma

nitriding andnitriding and

MaterialStructure hardened cases and tough

core material

nitriding and nitriding and PVDPVD--TiNTiNTreatment

technologyCombination of nitriding

and hardcoating

Duplex Surface TreatmentDuplex Surface Treatment

Duplex Surface Treatmentp

2000

HV

TiN layer

1000ness

, H

Nitrided layer 1000

Ha r

dn

Depth mμ

500

SubstractSubstrate

Depth, mμ

The nitrided layer is very hard and induces a high degree of internal compressive The nitrided layer is very hard and induces a high degree of internal compressive stresses stresses Stress gradients between the substrate and the hard coating are reduced Stress gradients between the substrate and the hard coating are reduced increasing the supporting load capacityincreasing the supporting load capacity

TiN and TiC coatings on H13 and D2 tool steels

Assess the adherence of TiNx and TiCy coatings to a H13 tool steel Assess the adherence of TiNx and TiCy coatings to a H13 tool steel substrate in terms of the Hardness to Young Modulus ratio of the substrate in terms of the Hardness to Young Modulus ratio of the coating and the substrate:coating and the substrate:gg

(H(Hcoatingcoating /E/Ecoatingcoating) and (H) and (Hsubstratesubstrate /E/Esubstratesubstrate).).

Treatment conditions used in the hybrid process.

D lD l t t tt t t i di d tt ii hh b iltb ilt h b idh b id ttDuplexDuplex treatmentstreatments carriedcarried outout inin aa homehome builtbuilt hybridhybrid reactorreactor(pulsed(pulsed plasmaplasma nitridingnitriding ++ reactivereactive magnetronmagnetron sputtering)sputtering)..

TwoTwo treatmentstreatments inin thethe samesame chamberchamber withoutwithout exposingexposing thetheTwoTwo treatmentstreatments inin thethe samesame chamber,chamber, withoutwithout exposingexposing thethesurfacesurface ofof thethe samplesample toto atmosphericatmospheric pressurepressure..

N2

Flow

( )

H2

Flow

( )

Ar

Flow

( )

Time

(min)

Pressure

(Torr)

Temperature

(0C)

Power

(W)

Current

(A)

Ton

(μs)

Toff

(μs)

(sccm) (sccm) (sccm)

PVD-A2 2.0 xx 20.0 120.0 3.0x10-3 320 500 xx xx xx

Plasma 200 11.0 xx 60.0 3.5 520 330 1.4 70.0 160,0Plasma

nitriding

200 11.0 xx 60.0 3.5 520 330 1.4 70.0 160,0

Thermocalc and Dictra calculated parameters to avoid white-layer formation

Adherence: modified Daimler test

TheThe adherenceadherence andand thethe failurefailuremodemode ofof thethe coatingscoatings werewerecharacterizedcharacterized usingusing aa RockwellRockwell C,C,conicalconical indenter,indenter, withwith aa 00..33 mmmm tiptipppradius,radius, withwith loadsloads ofof 1010,, 1515,, 3030,,4040,, 6060,, 100100,, 125125,, andand 150150 kgfkgf..

ThTh ii l dl d iiTheThe specimensspecimens werewere analyzedanalyzed ininanan opticaloptical microscopemicroscope afterafter thetheRockwellRockwell CC testtest.. TheThe criticalcritical loadloadtoto promotepromote radialradial crackscracks (LC(LC )) andandtoto promotepromote radialradial crackscracks (LC(LC11)) andandthethe criticalcritical loadload forfor delaminationdelaminationofof thethe filmfilm (LC(LC22)) werewere determineddetermined..

Microstructure of the TiNx coatings .

H/E Ratio for the TiNx and TiCy coatings

A4B2

A3

A4

B3

B2

A1

A2

B1

H/E ratio as a function of the amount of reactive gas.

Duplex treated H13 tool steel

Thicknesses of the diffusion zone (no white layer) and of theThicknesses of the diffusion zone (no white layer) and of the TiNx coating were 20 μm and 2 μm respectively.

Vickers hardness of the nitrided layer, near the surface was 1250 ± 10 HV0.01.

Crack patterns developed during the Daimler adherence test

Lc2 critical loads for delamination for the A1, B3 and Duplex treatment conditions

Conclusions

Th i tifi d t h l i l i t ti b t th M t ll i l dThe scientific and technological interaction between the Metallurgical and Materials Engineering Department and the Villares group led, in the past, to many important specialty steels developments and to the formation of competent professionals who are working today in both Villares Companies.

Tool steels and stainless steels constitute an important subject of investigation in the Metallurgical and Materials Engineering Department. Optimizing the microstructure of these alloys can lead to better mechanicalOptimizing the microstructure of these alloys can lead to better mechanical, corrosion and wear properties. The main concern of the research lines on specialty steels in the Department are focused on the relationship between the microstructure and different properties.

Development of novel compositions and new fabrication techniques should be considered for optimizing mechanical, corrosion and wear properties.

Special coating techniques, like duplex, multi-layers and nanostructured film deposition can improve the performance of tool steels and stainless steels and constitute nowadays an important fiel of investigation.