recent scientific investigations and implementation in ...€¦cryogenic treatment of metals recent...

Cryogenic Treatment of MetalsRecent scientific investigations and implementation in industrial heat treatment processesVästerås, 20/09/2017 Georg Lehmkuhl Air Liquide CWE, Krefeld

2 World leader in gases, technologies and services for Industry and HealthCryogenic Treatment Of Metals

Impact on Lifetime

Construction

operational-

purpose,

requirements

kind of

stressing

Material

steelgrade,

quality,

properties

Production

chipping,

forming,

Heat treatment,

coating,

assembling

Operating

conditons

parameters,

maintenance,

repairs,

reassembly

20/09/2017

3 World leader in gases, technologies and services for Industry and Health20/09/2017 Cryogenic Treatment Of Metals

Martensitic transformation

Hardening means to quench the steel

very quickly after austenitising and

transform the austenit into a martensitic

structure.

Hardness of martensite is mainly driven

by the enforced embedded carbon atoms

and residual stresses.

The critical quenching rate must be

achieved.

Deformation


The formation of retained austenite RA

Hardness

Retained austenite RA

Ms

Mf

99 80 60 40 20 1

Content of martensite [Vol.%]

0,3 0,6 0,9 1,2 1,5 1,8

Carbon content [%]

0

200

400

600

800

1000

1200

Ha

rdn

es

s H

V

0

100

200

300

400

500

600

0

Te

mp

era

ture

[°C

]

Co

nte

nt o

f re

tain

ed

au

ste

nite

RA [V

ol.%

]

100

80

60

40

20

0

Dr. Sommer

Winter-school 2003

If Mf boundary is not reached

during quenching, retained

austenite RA will remain.

Hardness

In many cases, the structure

of hard martensite and soft

retained austenite affects

lifetime of steel

Wearing quality

During operating time,

heating up and cooling down

cycles can cause

uncontrolled transformation

of retained austenite to

martensite

Volume expansion

Dimension stability

Martensite start Ms and martensite finish Mf temperatures

are mainly affected by the carbon content and the alloying

elements of the steel.

20/09/2017


Case hardening combined with cryogenic treatment

0

10

20

30

40

50

60

15 Cr Ni 6 14 Ni Cr 14 14 Ni Cr 18

quenched quenched and tempered

quenched and cooled quenched, cooled and tempered

Nach O. Schwarz u.a.

0

0,2

0,4

0,6

0,8

1

1,2

0

10

20

30

40

50

60

0 0,2 0,4 0,6 0,8 1 1,2

Case hardened layer

Retained austenite

Carbon content

[Vol.-%] [Weight-%]

Distance from surface

[mm]

Contentofretained

austenite

Carb

onContent

During carburising the surface is enriched with RA

Cryogenic treatment reduces RA significantly

Reta

ined

auste

nite

[Vol.-%

]

20/09/2017


Benefits from cryogenic treatment directly after quenching

Quality improvement:

- Significant reduction of RA content

- Homogenisation of RA content

- Prevention of RA stabilisation

- Increase of hardness

- Dimension stability

Costs savings:

- Substitution of 1or 2 following tempering cycles

Aircraft

Precision Gears

15 NiCr 13

Automotive

Diesel injection

nozzles18CrNi 8

Engineering

Precision bolts +

bushings 16MnCr5

Bearing

Bearings

100Cr6

20/09/2017


Implementation of Cryogenic Treatment CT

Cryogenic Treatment CT

- 80°C, > 1hr

Effects on content of retained austenite RA:

- Material and it´s alloying elements

- Carbon potential (too high during carburising)

- Austenitising/carburising temperature (too high)

- Holding time (too long)

- Insufficient quenching velocity

(limitation due to risk of crack formation)

- Quenching not downsized to RT (vacuum)

Austenitising/

Carburising

Quenching

Oil/Gas/Air

Tempering (up to 3 cycles)

> 180°C, 1h/20 mm

Tem

pera

ture

RT

Time0

20/09/2017


Overview installation for cryogenic treatment

Liquid nitrogen

(LIN) supply 1-3 bar

or

20/09/2017

Cryogenic chamber

Air ventilation


Standard cryogenic equipment for cooling

Direct injection of liquide nitrogen (LIN)

Integrated ventilation sytem

Operating temperatures from -180 to +100°C

Uniform temperature distribution (5°C)

Program controller for cooling/heating cycles

Recording function for documentation

User: hardening shops, assembly by shrinkage

automotive, aircraft-, bearing-, tooling-industries etc.

ALNAT Cryo Top-Lid Chamber ACKT 1900 S

20/09/2017


Specific cryogenic equipment for cooling and tempering

Individual design

Batch size is adapted to furnace dimensions

Integration in automatic driven furnace lines (PLC controlled)

Operating temperature from -140°C up to +550°C

Tempering under nitrogen atmosphere

Powerful ventilation turbine(s)

Uniform temperature distribution (<5°C)

Hot/Cold working chamber ACKW 420

Continuous working freezer ACCF 475

20/09/2017


Aerospace Material Specification: AMS 2750E compliance

● AMS 2750 E “Pyrometry” specification:

– Defines pyrometric requirements for thermal processing equipment used for heat treatment

– Covers temperature sensors, instrumentation, system accuracy tests and temperature uniformity survey

● Cryogenic chambers compliance with AMS 2750E

– Definition of MIN/MAX temperature range

– Definition of required tolerance (equipment class)

– Different thermocouples sensors required for:

- Control, Policeman, Min, Max, Load

– Calibration for thermocouples (ISO/IEC17025)

– UKAS calibration of instruments

– SAT: System Accuracy Test

– TUS: Temperature Uniformity Survey

– Documentation/certificates

20/09/2017


Cryogenic chambers: AMS 2750 compliance

UKAS calibration

SAT: System Accuray Test

TUS: Temperature Uniformity Survey

High temperature uniformity:

- Class 2 in standard

- Class 1 possible with custom optimisation

20/09/2017


Continous Quality Improvement: CQI-9 compliance

Self assessment to create a global quality

standard in Automotive Industry

Specific design of cryogenic chambers

Precise temperature control for cooling and heating

Integrated recirculation fans or turbines

Use of calibrated thermocouples

Use of calibrated instruments

Use of tamper resistant recorders/documentation

Safety and Reliability

20/09/2017

Number of TUS elements depends

on the volume of working space


Operating efficiency (exemplary)

14,1128,22

42,3456,45

70,5684,67

98,78112,90

100

100

100

100

100

100

100

100

0,00

0,20

0,40

0,60

0,80

1,00

1,20

0,00

50,00

100,00

150,00

200,00

250,00

100 200 300 400 500 600 700 800

LIN Chamber [kg]

LIN Metal [kg]

LIN specific material [kg LIN/kg Steel]

Specific LIN chamber + metal

Sp

ec

ific

LIN

co

ns

um

pti

on

[kg

LIN

/kg

Ste

el]

LIN

co

ns

um

pti

on

[kg

]]

Weight of load [kg]

Processing: 1.00 h cooling from +20°C to -80°C

1.00 h holding at - 80°C

LIN = f(material+chamber+operating conditions)

20/09/2017


New development: Deep Cryogenic Treatment (DCT)

DCT is preferabely applied to improve wear resistance and lifetime of

tools, considering the enhancement of mechanical properties like hardness,

toughness and fatigue resistance.

Steel Material-No. Application

Cold work tool Steel 1.2379 Machine Cutting tools, stamps,

pressing tools, chisel, cutter

block, etc.

High Speed Steel 1.3202 Drilling bits, reamer, chisel,

milling tools, saw blades etc.

Hot work tool Steel 1.2343 Die shapes, extrusion die

Theories:

Nearly complete transformation of retained austenite to martensite

Optimal conditioning of martensite and precipitation of fine carbides

Reduction of residual stresses

1 Cold work tools steel

2 Hot work tool steel

3 High speed tool steel

Annealing temperature

Hard

ness

Secondary hardening maximum

20/09/2017


How to apply Deep Cryogenic Treatment ?

a) Austenitising

b) Quenching (gas, salt, oil)

c) DCT cycle

Ramp down from RT to -185 °C in 4 to 10 hours

Hold at or below -185°C for 6 up to 40 hours

Ramp up to RT over a period of 4 to10 hours

d) Tempering at SHM (up to 3 cycles)

a) Austenitising

1080°C, 30 minutes

b) Quenching

Oil/Gas/Air

5 bars

d) Tempering (up to 3 cycles)

up to SHM

Te

mp

era

ture

°C

RT

Time0 c) Deep Cryogenic

Treatment

- 185°C

1 2 3

DCT is used within conventional heat treatment processes

500°C

1200°C

20/09/2017


Vacuum isolated vessel for Deep Cryogenic Treatment

- Minimal losses of nitrogen at low temperatures and long holding times

- Processcontroller for regulation and documentation

- Parts are exposed above liquid nitrogen below -185 °C

(no contact with LIN)

20/09/2017


Benefits from Deep Cryogenic Treatment

DCT: - Reduces the content of RA significantly (under quantification limit)

- Homogenises the content of RA caused by downsized quenching velocities

- Replaces 1 or 2 tempering cycles

Dr. Sommer, TFWW

Project 10, 2007

The content of retained austenite (RA)

is increasing when quenching velocity is downsized

1.2379 X153CrVMo12

C Cr V Mo Si Mn

1,53 12,00 0,95 0,80 0,30 0,40

Axles of different diameters Ø 150 -350 mm

Reta

ine

da

us

ten

ite

%

Quenching rate 800°C 500°C [s]

Vacuum hardened 1080°C, 5 bar, 30 min

DCT -185°C, 1 h

Tempered 1 x 530°C

Tempered 2 x 530°C

20/09/2017


DCT - Precipitation of secondary carbides (REM)

DCT with high tempering at SHM:

- Tough tempered martensite

- Fine distribution and high amount of secondary carbides

- Martensite laths of DCT samples are even thinner

1.2379

20/09/2017

Ruhr-Universität Bochum, RUB,

REM study CryoDuran


DCT: Formation of carbides

0 12 24 36 48 60 72 84

Holding time [h] at < - 185 °C)

SSC

LSC

6,5

6,0

5,5

5,0

4,5

4,0

3,5

3,0

2,5

Material: 1,2379 (X155 Cr V Mo 12)

Hardened 1020°C / 30 min

DCT < -185°C; cooling/heating 0,75 K/min

Tempering 1x 2h 500°C

Conventional

Co

nte

nt ofse

co

nd

ary

ca

rbid

es

[Vo

l-%

]

SSC: Small Secondary carbide (0,3-0,4 m)

LSC: Large Secondary carbide (2,0-2,5 m)Optimum

20/09/2017


Deep Cryogenic Treatment: Tempering diagram

Material: 1.2379

- Influence of

austenitising temperature TA

- Tempering behavior is modified

(Displacement of SHM)

- Hardness is increasing by DCT

- DCT is recommended

directly after quenching

(Stabilisation of RA at RT)

20/09/2017

Ruhr-Universität Bochum (RUB),

Abschlussbericht CryoDuran)


Influence of DCT on wear resistance of stamps (test)

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

1,00

30000 50000 100000

1.2379

DCT

Standard

Number of strokes

We

ar

rate

- Angle curve improves with number of strokes

- Cryogenic treated stamps show lower abrasion and disruption

- Significantly enhancement of tool life

Improvement of wear resistance up to 30%

20/09/2017

nach F. Wendl et AL

HTM Mat 66


Cryogenic treatment: New possibilities in heat treatment

Tribological properties of metals will be effected substantially when applying

(deep) cryogenic treatment.

Controlled martensitic formation and the precipitation of well distributed carbides

is the key to form a homogenous microstructure, to improve hardness and wear

resistance.

Further investigations have to be done to determine the best processing parameters

for each material in combination with heat treatment.

Austenitizing

temperature

Result

Position in

processDCT cooling

temperature

Quenching/

cooling rate

Annealing

temperature

DCT holding-

time /-temperature

DCT heating rateNumber of cycles

Steel grade

20/09/2017

Thank you for your attentionGeorg Lehmkuhl

Air Liquide CWE

recent scientific investigations and implementation in ...€¦cryogenic treatment of metals recent...

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