stainless steel & titanium surface hardening - expanite.de · enter material. challenge #2...
TRANSCRIPT
Stainless steel & Titanium surface hardening
European Conference on Heat Treatment - ECHT 2019 - Bardolino
Agenda
• Story of Expanite
• Challenges of surface hardening
• Expanite technology
• Automotive case studies
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
Stainless steel is corrosion resistant but suffers from poor wear resistance
Challenges of surface hardening
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
Challenge #2 – low temperature
CrN
Too high temperature– corrosion resistance lost!
Expanded austenite
Low temperature– supersaturated solid
solution
Challenge #3 – accurate control
ü. ü. ü. X
Use a gaseous process !
Changing thermodynamical parameters
… homogeneous hardening
Gas penetrates powder samples
Porosity
… and scalability
University anno 2009 Today
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
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
SuperExpanite
+
ExpaniteHigh-T ExpaniteLow-T
Expanite patent: WO 2012/146254
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
Transgranular
CellularGrain Boundary
Cr2N
g
c
h
ExpaniteHigh-TNitrogen in solid solution
Time temperature transformation diagram
Transgranular
CellularGrain Boundary
Cr2N
g
c
h
ExpaniteHigh-TCritical range!!
Nitrogen still in solid solution after fast quench
Time temperature transformation diagram
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
Traditionel Solution NitridingN2 cooling compromise corrosion resistance
Expanite patent pending
N2 cooling gas Ar cooling gas
AISI 904L – high Chromium alloyed
ExpaniteHigh-T
ExpaniteLow-T Carbon and/or Nitrogen
NC
C
Especially suite for higher ductility and welding.
Challenge #4 – cold worked surfaces
Low temperature process applied on cold worked material
Formation of nitrides or carbides!
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?
1mm
ExpaniteHigh-T – strategy 2
ExpaniteHigh-T – tailoring the core hardness - Washer
Nitrogen content: 0.12wt%- 200 HV
ExpaniteHigh-T – tailoring the core hardness - Washer
Nitrogen content: 0.45wt%- 250 HV
ExpaniteHigh-T – tailoring the core hardness - Washer
Nitrogen content: 0.64wt%- 280 HV
SuperExpanite – mechanical performance & anti-corrosion
High bulk strength – High surface hardness – Superior corrosion resistance
280 HV
1200 HV
Surface free from defects
• 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
Expanite in Automotive – a few examples
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
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
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
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
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!
