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
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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
5 World leader in gases, technologies and services for Industry and HealthCryogenic Treatment Of Metals
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
6 World leader in gases, technologies and services for Industry and HealthCryogenic Treatment Of Metals
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
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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
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Overview installation for cryogenic treatment
Liquid nitrogen
(LIN) supply 1-3 bar
or
20/09/2017
Cryogenic chamber
Air ventilation
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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
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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
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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
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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
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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
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Number of TUS elements depends
on the volume of working space
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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
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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
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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
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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
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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
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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
20 World leader in gases, technologies and services for Industry and HealthCryogenic Treatment Of Metals
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
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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)
22 World leader in gases, technologies and services for Industry and HealthCryogenic Treatment Of Metals
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
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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