stainless steel & titanium surface hardening - expanite.de · enter material. challenge #2...

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!

THANK YOU!

web: expanite.comemail: info@expanite.com