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Stainless steel & Titanium surface hardening
European Conference on Heat Treatment - ECHT 2019 - Bardolino
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Agenda
• Story of Expanite
• Challenges of surface hardening
• Expanite technology
• Automotive case studies
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Who are Expanite?
• Established: yr. 2010 based on ongoing research since yr. 2000
• Founders: Prof. Marcel Somers, Dr. Thomas Christiansen, Dr. Thomas Strabo Hummelshøj
• Company culture: driven by tailoring, cleanliness, on-site, fast turn-around
• Today: +20 employees, sites in Germany, China, US, Denmark
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Stainless steel is corrosion resistant but suffers from poor wear resistance
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Challenges of surface hardening
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Challenge #1 – the passive oxide layer
Expanite patent: eu WO2011009463
N + C not able to penetrate oxide layer
Expanite gas process removes oxide layer
N + C is now able to enter material
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Challenge #2 – low temperature
CrN
Too high temperature– corrosion resistance lost!
Expanded austenite
Low temperature– supersaturated solid
solution
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Challenge #3 – accurate control
ü. ü. ü. X
Use a gaseous process !
Changing thermodynamical parameters
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… homogeneous hardening
Gas penetrates powder samples
Porosity
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… and scalability
University anno 2009 Today
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The ExpaniteLow-T Process
• Low-temperature gas process: 380-470C
• Adds nitrogen & carbon or carbon only in solid solution – Expanded Austenite
• Can be used for:
• Austenitic, Duplex, Martensitic & Ferritic alloys in combination with ExpaniteHigh-T
• Generally not applicable standalone.
• Surface hardness: 1000-1500 HV
• Case depth: 5-35µmExpanite patent: WO 2011/009463
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The ExpaniteHigh-T Process
• High temperature vacuum process: 1000-1200C – fast gas quench with N2 or Ar
• Adds nitrogen during process
• Can be used for:
• Austenitic & Duplex alloys in combination with ExpaniteLow-T
• Martensitic & Ferritic alloys as standalone or in combination with ExpaniteLow-T
• Surface/core hardness: 250-900 HV depending on alloy
• Case depth: 500-1000µm
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SuperExpanite
+
ExpaniteHigh-T ExpaniteLow-T
Expanite patent: WO 2012/146254
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SuperExpanite = ExpaniteHigh-T + ExpaniteLow-T
Low-T
High-T
duplexN2
Even stronger (load bearing) plus enhanced corrosion resistance!
1
21
2
N + Cor
C only
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Transgranular
CellularGrain Boundary
Cr2N
g
c
h
ExpaniteHigh-TNitrogen in solid solution
Time temperature transformation diagram
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Transgranular
CellularGrain Boundary
Cr2N
g
c
h
ExpaniteHigh-TCritical range!!
Nitrogen still in solid solution after fast quench
Time temperature transformation diagram
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Traditionel Solution NitridingN2 cooling compromise corrosion resistance
N2 cooling gas
Expanite patent: WO 2013/159781
Ar cooling gas
N2 cooling gas
Ar cooling gas
Surface decorated with fine surface nitrides
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Traditionel Solution NitridingN2 cooling compromise corrosion resistance
Expanite patent pending
N2 cooling gas Ar cooling gas
AISI 904L – high Chromium alloyed
ExpaniteHigh-T
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ExpaniteLow-T Carbon and/or Nitrogen
NC
C
Especially suite for higher ductility and welding.
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Challenge #4 – cold worked surfaces
Low temperature process applied on cold worked material
Formation of nitrides or carbides!
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Flash annealing – strategy 1As machined Flash 700C
Flash 800C Full anneal
Work from 2010
Increasing Flash temperature, reduces precipitation of nitrides/carbides.
270HV 300HV
250HV 170HV
Inter-critical annealing?
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1mm
ExpaniteHigh-T – strategy 2
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ExpaniteHigh-T – tailoring the core hardness - Washer
Nitrogen content: 0.12wt%- 200 HV
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ExpaniteHigh-T – tailoring the core hardness - Washer
Nitrogen content: 0.45wt%- 250 HV
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ExpaniteHigh-T – tailoring the core hardness - Washer
Nitrogen content: 0.64wt%- 280 HV
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SuperExpanite – mechanical performance & anti-corrosion
High bulk strength – High surface hardness – Superior corrosion resistance
280 HV
1200 HV
Surface free from defects
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• Gas process < 800C
• Adds oxygen• Can be used for: • Alloyed titanium e.g. grade 5
• Pure titanium e.g. grade 2
• Typical for watch industry and medical device
• Surface hardness: approx. 1000HV• Case depth: 10-50µm
ExpaniteHard-Ti
50µm
Titanium grade 5
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Expanite in Automotive – a few examples
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Case no. 1 – bushing• What: Bushing used in the fuel injection system
on marine engines from MAN Energy Solutions
• Part are made in AISI 316 and then hardened by Expanite (SuperExpanite 20µm & 1200HV)
• Expanite solution replaced hard-chrome plating
• Benefits:
• Not a coating (hard-chrome was spalling-off)
• Environmentally better; no hard-chrome
• Better corrosion resistance
• More homogenous hardening
• Simplified logistics
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Case no. 2 – turbocharger• What: assembly with piston and diffuser used in
turbochargers for trucks
• Part are made in AISI 316 and then hardened by Expanite (SuperExpanite 20µm & 1200HV)
• Expanite solution replaced plasma nitriding
• Benefits:
• Significant improvement in corrosion resistance
• More homogeneous hardening – better wear resistance
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Case no. 3 – valve seat/plate• What: valve seat/plates in gasoline high-pressure
(300bar) pump
• Part are made in AISI 420 (X46Cr13) – new solution with ExpaniteHigh-T (core hardness min. 600HV10, surface hardness 750HV1 +/-50HV1)
• Expanite solution replaced conventional heat treatmentso pump pressure could be increased, biofuel and less pure fuels could be allowed
• Benefits:
• Better corrosion resistance
• Better wear resistance
• Simplified logistics; identical hardening process available in Europe and Asia
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Case no. 4 – guide pole• What: guide pole used in Active Cylinder
Technology.
• Part are made in AISI 304 and then hardened by Expanite (SuperExpanite C 24µm)
• Expanite solution on AISI304 replaced Bodycote Kolsterising® K33 on AISI316
• Benefits:
• Significant cost reductions
• Faster lead times
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Summary
• Challenges
#1: By-pass oxide layer#2: Low-temperature process#3: Gaseous process#4: Anti-cold work
• Accurate tailoring the process and properties
• Unique On-site capability!