Stainless Steel & Titanium Surface Hardening

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

N + C not able to Expanite gas process penetrate oxide layer removes oxide layer N + C is now able to enter material

Expanite patent: eu WO2011009463 Challenge #2 – low temperature

CrN Expanded austenite

Too high temperature Low temperature – corrosion resistance lost! – supersaturated solid solution Challenge #3 – accurate control

ü. ü. ü. X

Changing thermodynamical parameters

Use a gaseous process ! … homogeneous hardening Porosity

Gas penetrates powder samples … 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: 5-35µm

Expanite 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

2 Low-T

1 High-T 2

N + C Even stronger (load bearing) or plus enhanced corrosion C only resistance! 1 duplex

N2 ExpaniteHigh-T Time temperature transformation diagram

Transgranular Nitrogen in solid g solution

Cr2N c

Grain Boundary Cellular ExpaniteHigh-T Time temperature transformation diagram

Critical range!! Transgranular g

Cr2N c

Grain Boundary Cellular Nitrogen still in solid solution after fast quench Traditionel Solution Nitriding N2 cooling gas N2 cooling compromise corrosion resistance

Ar cooling gas N2 cooling gas

Surface decorated with fine surface nitrides

Ar cooling gas Expanite patent: WO 2013/159781 Traditionel Solution Nitriding N2 cooling compromise corrosion resistance

N2 cooling gas Ar cooling gas

ExpaniteHigh-T AISI 904L – high Chromium alloyed Expanite patent pending ExpaniteLow-T Carbon and/or Nitrogen

N C

Especially suite for higher ductility and welding. Challenge #4 – cold worked surfaces

Formation of nitrides or carbides!

Low temperature process applied on cold worked material Work from 2010

Flash annealing – strategy 1 Inter-critical annealing? As machined Flash 700C

270HV 300HV

Flash 800C Full anneal

250HV 170HV

Increasing Flash temperature, reduces precipitation of nitrides/carbides. ExpaniteHigh-T – strategy 2

1mm 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 Surface free from defects

1200 HV

280 HV

High bulk strength – High surface hardness – Superior corrosion resistance Titanium grade 5 ExpaniteHard-Ti 50µm • 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 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 treatment so 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! THANK YOU!

web: expanite.com email: [email protected]