surface engineering of stainless steels · 2017. 11. 1. · cavitation erosion resistance of duplex...
TRANSCRIPT
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09 a 11 setembro de 2015
SURFACE ENGINEERING OF STAINLESS STEELS
André Paulo Tschiptschin
Metallurgical and Materials Engineering Department University of São Paulo
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• Austenitic (ASS), Martensitic (MSS), Duplex (DSS) and Precipitation Hardening (PH) stainless steels have been used in a variety of applications within the refining and petrochemical industry, where high corrosion resistance and mechanical properties are required.
• Surface properties of these materials may be improved by thermochemical and plasma assisted treatments, to reach better performance in highly stressed tribological systems.
• Thermochemical and plasma assisted surface treatments have been proposed to improve tribological properties of these CRA.
• HTGN High Temperature Gas Nitriding • LTGN Low Temperature Gas Nitriding • LTPN Low Temperature Plasma Nitriding • LTPC Low Temperature Plasma Carburizing • LTPNC Low Temperature Plasma Nitrocarburizing
Surface Engineering of Stainless Steels
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• The common characteristic of these surface treatments is the introduction of nitrogen or carbon in solid solution by diffusional processes, increasing hardness and developing compressive residual stresses, as well.
• Increasing carbon or nitrogen contents in solid solution in austenite, up to and also beyond the solid solubility limit, increases steadily the hardness of these alloys.
• Chromium nitrides or chromium carbides precipitation should be avoided in order to avoid sensitization and preserve corrosion resistance.
• High Temperature Gas Nitriding allows obtaining equilibrium nitrogen contents, up to 1.1 wt.%, in solid solution in austenite, depending on SS chemical composition, N2 potential in the nitriding atmosphere, nitriding temperature and pressure.
High Temperature Gas Nitriding
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Cr23C6 precipitation harms the corrosion resistance due to Chromium depletion (sensitization)
Improve surface hardness without loss of corrosion resistance
Grain boundary
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High Temperature Gas Nitriding
• High Temperature Gas Nitriding equilibrium nitrogen contents, up to 1.1 wt.%, in solid solution in austenite.
• Solid-state nitrogen alloying technique, consisting of exposing SS to a N2-containing gas atmosphere in the range 1000-1200ºC.
• Atomic nitrogen is interstitially absorbed at the surface of the steel and then diffuses into the near surface region, promoting hardening and improving corrosion resistance.
Phase fields and nitrogen iso-concentration lines for a Fe-16.2 wt% Cr alloy
Garzon, C.M.; Tschiptschin, A.P. Materials Science and Engineering: A, volume 441, 2006, pp.230-238
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• Change in pitting potential of 18 wt% Cr austenitic stainless steels in dilute chloride solution [Speidel, 1991]
N effect on Pitting Potential
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High Temperature Gas Nitriding
• Stainless Steels:
– HTGN Duplex SS fully austenitic layer % N
– HTGN Dual phase (a + M) fully martensitic layer % N
– HTGN martensitic SS fully martensitic layer % N
– HTGN austenitic SS fully austenitic layer % N
• Properties:
– High Hardness ( martensitic ) Roller bearings and tools.
– Wear resistance (Cavitation-erosion, Erosion-corrosion) pump rotors slurry environments.
– Corrosion resistance (generalized and localized) surgical implants, biomedical application, retaining rings, etc.
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c,T T, PN2
t
High Temperature Gas Nitriding UNS 31803 SS
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• When UNS S31803 duplex stainless steel is heated at 1200ºC for HTGN the structure becomes completely ferritic.
• During nitriding ferrite transforms to Widmanstätten austenite.
• At the end a fully austenitic case is achieved
Austenite formation during HTGN
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Austenite formation during HTGN
UNS S31803 duplex stainless steel during HTGN treatment at 1150ºC
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Hardening of UNS31803 after HTGN
Hardness of UNS S31803 DSS after HTGN treatment at 1150ºC
HV
mm
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Non isobaric treatment for grain refinement
GARZON, C.G.; TSCHIPTSCHIN, A.P; – PI05048850, "Ciclo de tratamento que inibe o crescimento de grão e a formação de nitretos durante recozimento em alta temperatura de aços inoxidáveis duplex sob atmosfera de nitrogênio" , INPI.
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Non isobaric treatment for grain refinement
GARZON, C.G.; TSCHIPTSCHIN, A.P; – PI05048850, "Ciclo de tratamento que inibe o crescimento de grão e a formação de nitretos durante recozimento em alta temperatura de aços inoxidáveis duplex sob atmosfera de nitrogênio" , INPI.
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Kolsterising
B. H. Kolster, VDI-Berichte, 506 (1983), 107-113
IMPROVEMENT OF SURFACE HARDNESS WITHOUT LOSS OF CORROSION RESISTANCE
Low Temperature Hardening of Stainless Steel
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A “new phase” identified by Ichii et al., the so-called S phase. Peaks of a cubic phase shifted (S) to the left. metastable, precipitate free, interstitial supersaturated, superhard ‘expanded austenite’, form at low temperatures introduction of interstitials (such as N and C, or both) into an FCC
structured substrate K. Ichii, K. Fujimura and T. Takase: Technol. Rep. Kansai Univ.,1986, 27, 135–144
Low Temperature Hardening of Stainless Steel
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Paths A and C avoid Cr23C6 precipitation, that harms the corrosion resistance HTIH and LTIH allows hardening without losing corrosion resistance
Improve surface hardness without loss of corrosion resistance – Interstitial Hardening
HTIH
LTIH
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A = Pure iron B = 316 SS with Cr7C3 formation C = 316 SS without Cr7C3 formation
C solubility in 316L stainless steel
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1) Depassivation by Halide containing atmospheres: NF3 or HCl – Low Temperature Gas Carburizing
(patent by Swagelok). 2) Activation of the surface of the part Ni metal to prevent repassivation catalytic NH3 gas
decomposition – (Patent by Somers US 7431778 B2). 3) Activation of the surface by sputtering in H2, under a high applied voltage and low pressure – Patent
018090023300 INPI – by Tschiptschin .
LTIH with C / N - Surface Activation
Cr2O3 passive layer
SS substrate should be activated
N CO, CxHy NH3
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1) Depassivation by Halide containing atmospheres: NF3 or HCl – Low Temperature Gas Carburizing
(patent by Swagelok). 2) Activation of the surface of the part Ni metal to prevent repassivation catalytic NH3 gas
decomposition – (Patent by Somers US 7431778 B2). 3) Activation of the surface by sputtering in H2, under applied voltage and low pressure – (Patent
018090023300 INPI – by Tschiptschin).
Surface Activation
SS substrate
N CO, CxHy NH3
Expanded austenite
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LTPN LTGC LTGNC metastable, precipitate free, interstitial supersaturated, superhard ‘expanded austenite’, form at low temperatures Introduction of interstitials (such as N and C, or both) into an FCC structured substrate
T. L. Christiansen; M.A.J. Somers – Advanced Materials and Processes, nov-dec (2013),
Low Temperature Nitriding, Carburizing and Nitrocarburizing
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Low Temperature Gas Carburizing
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C Expanded Austenite
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Low Temperature Gas Carburizing
Stainless Steel Fittings
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Swagelok development: • The hardened back-ferrule drives onto the surface of super duplex
tubing • Pressure enough to ensure predictable, leak tight installation and
performance at working.
Low-temperature Gas Carburizing
EXPANDED AUSTENITE
HEAVILY COLD WORKED
AUSTENITIC STAINLESS STEEL
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C Expanded Austenite
Hardening depth ~30 m
Maximum hardness ~900 HV
Compressive residual stresses 2 GPa
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Low Temperature Gas Carburizing
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N / NC Expanded Austenite
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N Expanded Austenite
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N Expanded Austenite
Surface hardening of stainless steel ball valves
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Carbon X Nitrogen Expanded Austenite
(N) (c)
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Carbon X Nitrogen Expanded Austenite
N expanded austenite - hardening depth ~30 m
Maximum hardness ~1200 HV
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Low Temperature Plasma Nitriding
• Depassivation by H2 sputtering
– Ionization of gas molecules and atoms
– Acceleration of ions towards the cathode
– Generation and recombination of chemical compounds or radicals , in particular Fe/N ions
– Condensation of FeN molecules in the cathode surface with release of nitrogen to the surface
– Penetration of ions in the surface of the part
– Plasma nitriding (H2+N2) least affects the surface finish of the product.
– Plasma nitriding has a higher surface hardness and maintains your material's core properties due to the lower processing temperatures associated with plasma nitriding
– Plasma nitriding is environmentally friendly. Plasma nitriding uses non-toxic precisely controlled gas mixtures.
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Kölbel Mechanism of Plasma Nitriding
Anode
Cathode Voltage (V)
electron electron
adsorption
impurities
ion
electron
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Low Temperature Plasma Nitriding
• Disadvantages
– Rings of different colors are formed when stainless steel parts are pulsed DC plasma nitrided.
– Distortions of the electric field around the corners and edges,
– Shape of plasma sheath, which is connected to the shape of samples, determines the ion flux distribution
– Affects the uniformity, hardness and surface phases of coating.
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Kölbel Mechanism Operating in Active Screen
Part to be nitrided at floating potential
N N
N
N N
N
N N
N
N N
N N
N N N
N N
N N
N
N N
N
N N
N
N N
N
N N
N
N N
N
N N
N
N N
N
N N
N
N N
N N
N
Active screen Active screen
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• Plasma nitriding reactions occur directly on the surface of the part
• Higher N potential • Influence of the part geometry on the
nitrogen potential and nitrogen flux • Edge effect
• Plasma nitriding reactions occur on the surface of the screen
• Lower N potential • More homogeneous nitrogen flux
throughout the surface • More even nitrided layer
DC Plasma X Active Screen Plasma Nitriding
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Duplex Treatment (HTGN + LTPN)
(a) HTGN of duplex stainless steel (b) High Nitrogen layer (c) Expanded austenite layer MESA, D.H ; PINEDO, C.E.; TSCHIPTSCHIN, A. P - Improvement of the cavitation erosion resistance of UNS S31803 stainless steel by duplex treatment – Surface and Coatings Technology. Surface and Coatings Technology, 205 (2010)1552-1556
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Cavitation Erosion Resistance of Duplex Treated UNS S31803
MESA, D.H ; PINEDO, C.E.; TSCHIPTSCHIN, A. P - Improvement of the cavitation erosion resistance of UNS S31803 stainless steel by duplex treatment – Surface and Coatings Technology. Surface and Coatings Technology, 205 (2010)1552-1556
The mechanical support given by HTGN, improves the performance of
the LTPN layer
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N Expanded Austenite
The mechanical support given by HTGN, improves the performance of the LTGN layer
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Plasma removed from the parts’ surface Plasma nitriding reactions occur on the surface of the screen
Active Screen Plasma Nitriding
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N Expanded Martensite
• Martensitic stainless steels are used for manufacturing hydraulic components affected by cavitation erosion.
• The introduction of nitrogen atoms using thermochemical treatments has been proved to be an effective way to enhance the cavitation erosion resistance
• Low temperature nitriding of martensitic stainless steel leads to formation of expanded martensite a’N, (BCC expanded phase)
BCC expanded martensite a’N
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N Expanded Martensite
• Low temperature nitriding of martensitic stainless steel leads to formation of expanded martensite a’N, (BCC expanded phase).
DC Plasma Nitriding 400ºC, 20 h ASPN nitriding 400ºC, 20 h Fe4N Nitrides + a’N (BCC expanded phase) a’N, (BCC expanded phase).
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• Low temperature nitriding of martensitic stainless steel leads to formation of expanded martensite a’N, (BCC expanded phase).
DC Plasma Nitriding 400ºC, 20 h ASPN nitriding 400ºC, 20 h Fe4N, Fe3N Nitrides + a’N (BCC expanded phase) a’N, (BCC expanded phase).
N Expanded Martensite
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• Low temperature nitriding of martensitic stainless steel leads to formation of expanded martensite a’N, (BCC expanded phase)
DC Plasma Nitriding 400ºC, 20 h ASPN nitriding 400ºC, 20 h Fe4N Nitrides + a’N (BCC expanded phase) a’N, (BCC expanded phase).
N Expanded Martensite
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• Cavitation erosion resistance
DCPN 400ºC, 20 h ASPN 400ºC, 20 h Fe4N Nitrides + a’N (BCC expanded phase) a’N, (BCC expanded phase) Erosion rates decreased from 1,2 to 0,36 mg/h Erosion rates decreased 27 times
N Expanded Martensite
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Mechanical Properties of Expanded Martensite (ASPN)
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Mechanical Properties of Expanded Martensite (ASPN)
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Mechanical Properties of Expanded Martensite (ASPN)
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Mechanical Properties of Expanded Martensite (ASPN)
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FEM modeling of cavitation damage
50 F. Pohl, S. Mottyll, R. Skoda, S. Huth - Evaluation of cavitation-induced pressure loads applied to material surfaces by finite-element assisted pit analysis and numerical investigation of the elasto-plastic deformation of metallic materials – to be published in Wear, 2015.
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FEM - Calculated plastic strain
51
F. Pohl, S. Mottyll, R. Skoda, S. Huth - Evaluation of cavitation-induced pressure loads applied to material surfaces by finite-element assisted pit analysis and numerical investigation of the elasto-plastic deformation of metallic materials – to be published in Wear, 2015.
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Energia de deformação elástica e plástica
16/12/2014
- PPGEM - TRICORRMAT
52
F. Pohl, S. Mottyll, R. Skoda, S. Huth - Evaluation of cavitation-induced pressure loads applied to material surfaces by finite-element assisted pit analysis and numerical investigation of the elasto-plastic deformation of metallic materials – to be published in Wear, 2015.
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Relationship between b/h, pmax, pl, Wel, Wpl
53
F. Pohl, S. Mottyll, R. Skoda, S. Huth - Evaluation of cavitation-induced pressure loads applied to material surfaces by finite-element assisted pit analysis and numerical investigation of the elasto-plastic deformation of metallic materials – to be published in Wear, 2015.
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Scratch Resistance of Plasma Nitrided Martensitic 410 SS
• Abrasive wear due to scratching using a diamond tip • Measuring COF – Coefficient of friction
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Fric
tio
n c
oef
fici
ent
Fric
tio
n c
oef
fici
ent
Aco
ust
ic e
mis
sio
n (
V)
Aco
ust
ic e
mis
sio
n (
V)
Distance (mm) Distance (mm)
Distance (mm) Distance (mm)
N Expanded Martensite
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Duplex Coating of Martensitic 440B Stainless Steel
PVD coatings has been increasingly employed on piston rings: o Excellent wear resistance o Small wear of cylinder o High scuffing resistance and low friction coefficient.
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Surface Patterning of Stainless Steel
T. Czerwiec, G. Marcos, T. Thiriet, Y. Guo, T. Belmonte - IOP Conf. Series: Materials Science and Engineering 5 (2009) 012012
• Expansion of austenite occurs horizontally and vertically • Vertical expansion is responsible for the patterning
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Surface Patterning of Stainless Steel
• Expansion of austenite occurs horizontally and vertically • Vertical expansion is responsible for the patterning
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Microtexturing SS Tools by Inkjet Printing
T. Katoh , T. Aizawa, T. - Manufacturing Rev. 2 (2015) 2, 2-7
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T. Katoh , T. Aizawa, T. - Manufacturing Rev. 2 (2015) 2, 2-7
Microtexturing SS Tools by Inkjet Printing
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CONCLUSIONS
• The tribological behavior of stainless steels can be improved by using plasma assisted thermochemical treatments.
• Depending on the contact stresses the duplex and combined treatments HTGN, LTPN and PVDTiN may be used to obtain a better combination of surface properties.
• Low temperature plasma treatments lead to the formation of supersaturated metastable phases on the surface (expanded austenite, expanded ferrite and expanded martensite) increasing hardness, wear resistance and cavitation-erosion resistance.
• The expanded phases show very low coefficient of friction when scratched with a diamond tip during instrumented scratch testing.
• Microtexturing and Surface Patterning can be accomplished by plasma assisted surface treatment.
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ACKNOWLEDGEMENTS
• Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
• Prof. Hanshan Dong - University of Birmingham – Surface Engineering Group
• Dr. Xiao-Ying Li - University of Birmingham – Surface Engineering Group
• Carlos Eduardo Pinedo – Heat Tech – Technologies for Heat Treatment and Surface Engineering
• PróReitoria de Pesquisa da USP
• Luis Armando Espitia
• Luis Bernardo Varela
• Fernando Luis Sato
• Dairo Hernan Mesa
• Sharys Varela
• Abel André Cândido Recco
• Diana Maria López
• Carlos Mario Garzón
• Claudia Patrícia Ossa
• Alejandro Toro
• Juan Manuel Vélez
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FEM modeling of cavitation damage
63 F. Pohl, S. Mottyll, R. Skoda, S. Huth - Evaluation of cavitation-induced pressure loads applied to material surfaces by finite-element assisted pit analysis and numerical investigation of the elasto-plastic deformation of metallic materials – to be published in Wear, 2015.
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FEM - Calculated plastic strain
64
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Energia de deformação elástica e plástica
16/12/2014
- PPGEM - TRICORRMAT
65
F. Pohl, S. Mottyll, R. Skoda, S. Huth - Evaluation of cavitation-induced pressure loads applied to material surfaces by finite-element assisted pit analysis and numerical investigation of the elasto-plastic deformation of metallic materials – to be published in Wear, 2015.
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Relationship between b/h, pmax, pl, Wel, Wpl
66
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