Designing new damage tolerant forging steels by ICMPE
Transcript of Designing new damage tolerant forging steels by ICMPE
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Designing new damage tolerant forging steels by ICMPE
Wolfgang Bleck
Werkstoffwoche Dresden 2015
ICMPE: Integrated Computational Materials and Process Design
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Topics
Steels
Trends
Outline
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Topics New processes
Optimal material utilisation
Damage tolerance
Integrated Computational Materials Engineering (ICME) Nano-characterisation
Steels
Trends
Outline
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T
Heating
Austenitisation Forging
Conventional process chain
tconventional t
Hardening Tempering
Straightening
Stress relief
Topics: new processes
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tconventional
T
Heating
Austenitisation Forging
Isothermal
holding
Controlled cooling
Surface treatment
Air cooling
Machining at
medium heat
Conventional process chain
EcoForge process chain
t tEcoForge
Topics: new processes
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T
Heating
Austenitisation Forging Controlled cooling
Conventional process chain
EcoForge process chain
tEcoForge tconventional t
PHFP-Mod. process chain
tPHFP-Mod.
Topics: new processes
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T
Heating
Austenitisation Forging
Hardening
Conventional process chain
EcoForge process chain
t
PHFP-Mod. process chain
High temperature carburising
process chain
tEcoForge tconventional tPHFP-Mod.
tHT-carburising
Carburising
Topics: new processes
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High pressure components
Source: Bosch, Schaeffler
Gear components
Topics: material utilisation
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Conventional 100Cr6 as bainite
m
axim
um
syste
m p
ressu
re [b
ar]
Source: DVM-Bericht 135 "Optimierungspotentiale in der Betriebsfestigkeit", Sindelfingen 2008
High pressure components
Source: Bosch, Schaeffler
Topics: material utilisation
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Year
1994 1989 1976 1966 1952
400
200
0
600
500
300
100
Dynamic load rating C
Nominal life expectancy
Relative capacity:
in %
Cylinder roller bearing NU 1010 Gear components
Source: Bosch, Schaeffler
Topics: material utilisation
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load capacity load
„ppm-failure“
safety
increased damage tolerance
σ2 < σ1
with reduced medium load capacity
with increased load capacity
Source: HiPerComp
Topics: damage tolerance
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* Source: T. Hilditch et al: Metallurgical and Materials
Transactions A, Vol. 40 (2009), pp. 342-353
TRIP 780 EBSD image
red: ferrite, martensite green: retained austenite
with reduced medium load capacity
with increased load capacity
σ2 < σ1
increased damage tolerance
Topics: damage tolerance
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Transformation of retained Austenite into Martensite in front of a fatigue crack :
EBSD picture of a crack tip of a TRIP 780:
Ferrite and Martensite are red, retained
Austenite is green [1]
Volume fraction of retained Austenite
as a function of distance from crack
tip measured by EBSD [2]
Source: [1] T. Hilditch et al.: Cyclic Deformation of Advanced High-Strength Steels: Mechanical Behavior and Microstructural analysis,
Metallurgical and Materials Transactions A, Vol. 40 (2009), pp. 342-353
[2] X. Cheng et al.: Fatigue crack growth in TRIP steel under positive R-ratios, Engineering Fracture Mechanics, Vol. 75 (2008)
No. 3-4, pp. 739–749
Steels: Q&T steels
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Hot rolling Forging FP annealing Machining Carburising
A → F+P precipitation
grain growth F+P → A precipitation,
dissolution
mic
ro
grain growth
carburising cooling forging rolling FP annealing
ma
cro
machining
Topics: ICMPE Integrative Computational Materials and Process Engineering
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Comprehensive, standardised, modular and extendable modeling platform
being efficiently adaptable to a specific material, process-chain and product
ma
cro
m
icro
su
b-µ
Thermodynamic databases
Hot rolling Forging FP annealing Machining Carburising
Topics: ICMPE Integrative Computational Materials and Process Engineering
Designing new forging steels by ICMPE - Wolfgang Bleck 16
Topics: ICMPE
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1 m 10-3 mm 10-6 µm 10-9 nm
Source: Müller Weingarten AG
TMP
UFG
NS Nanostructured steels
Ultra Fine Grain
Thermo Mechanically Processed
conventional steel
Topics: nano-characterisation
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1 m 10-3 mm 10-6 µm
Source: Müller Weingarten AG
10-9 nm
Atom probe
DE-Synchotron
Topics: nano-characterisation
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Topics New processes
Optimal material utilisation
Damage tolerance
Integrated Computational Materials Engineering (ICME)
Nano-characterisation
Steels Case-hardening steels
Quenched and Tempered Steels Bearing steels
High Mn steels
Trends
Outline
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Pro
ce
ss
ch
ain
fo
r g
ea
r c
om
po
ne
nts
Heat
Treatment Rolling
Melting/
Casting Processing
Semi-
Products
cold warm
Deformation
Forging
Heat
Treatment Cutting
Case
Hardening
Final
Product
Post
Treatment
Steels: Case hardening steels
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loading heating vacuum carburising diffusion gas quenching decrease to
hardening temperature
1000
0,1
pressure, mbar
930
20
930 930 890
40
air
time
930 890
20
Temperature, °C
1000
0,1
nitrogen propane vacuum nitrogen
air
1000
0,1
vacuum
Source: ALD
Steels: Case hardening steels
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High temperature carburizing
decreases the production time
and costs of gear components.
Grain size control of austenite is
needed.
Grain growth can be prevented by
microalloying of case hardening
steels.
Prediction and optimization of particle size and amount is
performed by numerical
simulation of particle evolution.
Steels: Case hardening steels
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Steels: Al-free steel
120 ppm N 220 ppm N
We
igh
t fr
actio
n
We
igh
t fr
actio
n
T in ºC T in ºC
1: MLE (C,N)
2: MnS
3: AlN
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r
fPz
2
3 σ=
CASTS carburising
MICRESS Grain growth
Zener pinning pressure, MPa
Abnormal grain growth
No grain growth
Normal grain growth
Hot rolling
Carburising
Forging
FP Annealing
Machining
precipitation
evolution
Casting
Steels: Al-free steel
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Al reduction is requested for cleanliness improvement.
The same pinning force at 1050 °C in Nb modified 25CrMo4 steel can be obtained
by an increase of Nb content to 850 ppm.
Additionally, an increase in solution temperature is needed.
Conclusion: a combined development of alloy and process parameters is needed in order to realize this new steel concept.
Reference
Al-reduced
HT-Carburizing
Temperature, °C
Vo
lum
e fra
ctio
n
Vo
lum
e fra
ctio
n (
Ti,N
b),
(C
,N)
+ (
AL
N)
Temperature, °C
Steels: Al-free steel
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100 µm
C Si Mn Cr Mo Ni V Al Nb Ti N
REF 0.24 0.22 0.89 0.92 0.43 0.18 0.008 0.023 0.034 0.0090 0.0170
Al-free 0.24 0.22 0.90 0.92 0.42 0.18 0.008 0.002 0.082 0.0005 0.0137
chemical composition in mass-% Steels: Al-free steel
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PHFP-M = Precipitation Hardening Ferritic-Pearlitic - Modified
PHFP-M
pearlite lamellae spacing λ
Ti, V, Nb (C,N)
ferrite fraction
Steels: Quenched & Tempered steel
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PHFP-M = Precipitation Hardening Ferritic-Pearlitic - Modified
HDB = High Strength Ductile Bainitic
HDB
bainitic ferrite FB + retained austenite γR
PHFP-M
pearlite lamellae spacing λ
Ti, V, Nb (C,N)
ferrite fraction
Steels: Quenched & Tempered steels
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Bainitic steels: Phase field simulation
Kinetics calculations and microstructure evolution simulations
Phase-field simulated bainitic sheaves
SEM observation of bainitic sheaves
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Bainitic steels: Phase field simulation of precipitates
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Microstructural description of bainite
Form
Polygonal1
Quasi-Polygonal1
Granular
Widmanstätten
Acicular
Lath-like2
Basic structure (LOM) Sub structures (≤LOM)
2nd phase form
Round1
Elongated2
Lath-like2
Film like2
Clustered
Crystal structure
bcc
Location
Boundary
Intragranular
2nd phase
Fe3C-Carbides
ε -carbide
Martensite
Austenite
None
Definitions: 1Roundness (Diff. of enclosing/enclosed ellipse) 2Aspect ratio (Length/width)
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Microstructure characterisation by SEM
Quelle: F. Gerdemann: Bainite in medium carbon steel, Dr.-Ing. Disseration RWTHAachen (2010)
Primärphase Sekundärphase
kristallographische Struktur
Morphologie Entstehungsort kristallographische
Struktur Morphologie
krz (Ferrit) Polygonal Intergranular hex (Karbide) Rund
Quasi-polygonal Intragranular trz (Martensit) Gestreckt
Blockartig
kfz (Austenit) Lattenartig
Widmannstätten Nicht vorhanden Filmartig
Azikular
Inselförmig
Lattenartig Blockartig
F-L Inter-M/A-I
A-L A-B
F-B
TRIP1 Tiso=375°C tiso=30 min 4000-fache Vergrößerung
lattenartiger bainitischer Ferrit
lattenartiger Restaustenit
blockartiger bainitischer Ferrit
blockartiger Restaustenit
Martensit/Austenit
TRIP1 Tiso=375°C tiso=30 min 4000-fache Vergrößerung
15 von 48
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Steels: bearing steels
Source: Schaeffler
ab initio Modelling
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Mechanical properties and microstructures in 100Cr6
Mechanical properties
• High tensile strength (> 2 GPa)
• High hardness (> 700HV)
• Fatigue strength
• Wear resistance
• Ductility
• Toughness
• ……
Microstructure
• Martensitic matrix + precipitates
• Bainitic ferrite matrix + precipitates
• types • vol. fractions
• morphology • strain energy
• bound./matrix
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3-Dimensional Atom Probe approach – Sample preparation
• Electropolishing + FIB sharpening
• FIB Lift-out + TEM + FIB resharpening
(a) (b) (c)
(e) (d) (f)
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Atom Probe Tomography: sample and results
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APT results: Precipitates in lower bainite
Selected box 1
Selected box 2
Carbon atom map and 13 at% isoconcentration surface in lower bainite in 100Cr6 isothermally heat treated at 260 °C for 2500 s
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ε and θ carbides in ferrite have almost identical thermodynamic stability. In austenite, however,
cementite formation is clearly preferred. This indicates that ε carbide is more prone to
precipitation from lower bainite than from upper bainite.
Atom Probe Tomography Ab initio calculation
θ and ε carbide precipitation in lower
Bainite in 100Cr6 isothermally heat-
treated at 260 °C for 2500 s.
Gibbs free reactions energies between ε
(Fe2.4C) and cementite θ (Fe3C) as a function of
temperature in a ferritic and austenitic matrix.
Bearing steel 100Cr6: carbide analysis in bainitic matrix
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Processing of forging steels: cooling strategy
1
2
3
4
Temperature
Time
1: Forging
2: Dependent on component size: acceleration of cooling by fan
3: Isothermal transformation step Tiso=375°C für 15 Minuten
4: Quenching in water
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Industrial tests
• Inhomogeneous cooling in different component areas impedes homogeneous microstructure development. Processing adjustments
dependent on size and geometry are required.
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C Si Mn S Cr Mo B Nb Ti V N
42CrMo4 0.440 0.30 0.80 0.022 1.15 0.190 - - - - -
AFP-M 0.360 0.68 1.44 0.026 0.15 0.030 - 0.029 0.022 0.19 0.0210
HDB 0.226 1.62 1.50 0.019 1.30 0.079 0.0030 0.030 0.024 - 0.0105
TRIP 0.181 0.97 2.50 0.017 0.20 0.096 0.0018 - 0.032 - 0.0069
Automotive applications:
~ 2 kg
Common Rail Axle Leg
~ 5 kg
Steering Link
~ 1 kg
chemical composition in mass-% Steels: Q&T steels
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Forging steels
0
10
20
30
40
50
60
400 500 600 700 800 900 1000 1100 1200 1300
Av
at
RT
in
J
Rp0,2 in MPa
AFP
+ MLE
Q + T
+micro-alloying elements
Q + T
AFP-M
HDB
TRIP TRIP
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Forging steels
0
10
20
30
40
50
60
400 500 600 700 800 900 1000 1100 1200 1300
Av
at
RT
in
J
Rp0,2 in MPa
AFP
+ MLE
Q + T
+micro-alloying elements
Q + T
AFP-M
HDB
+bainitic
microstructure
TRIP TRIP
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Forging steels
0
10
20
30
40
50
60
400 500 600 700 800 900 1000 1100 1200 1300
Av
at
RT
in
J
Rp0,2 in MPa
AFP
+ MLE
Q + T
+micro-alloying elements
Q + T
AFP-M
HDB
+bainitic
microstructure
+retained austenite
in bainitic
microstructure TRIP TRIP
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Forging steels with TRIP - effect
Austenite stability
Intrinsic Parameters:
Chemical Composition
C: increases γ stability
Si: solid solution strengthening; carbide formation retarded
Morphology
film-like austenite parallel to bainite sheaves shows slowlier transformation
Size
Austenite grains <0,01 µm are very stable
Crystallographic Orientation
Extrinsic Parameters:
Location of austenite grains
Different C enrichment dependent on diffusion conditions
Hardness of matrix
High hardness impairs transformation due to
volume change
Stress state
Kinetic of transformation depends on stress state
Residual stresses
Source: Jacques, P.; Furnémont, Q.; Pardoen, T.; Delannay, F.: On the Role of Martensitic Transformation on Damage and Cracking
Resistance in TRIP-Assisted Multiphase Steels, Acta Mat. 49 (2001)p. 139–152
Designing new forging steels by ICMPE - Wolfgang Bleck 46
0,0 0,2 0,4 0,6 0,8 1,0
0
200
400
600
800
1000
Rp0,2
=658MPa
Sp
an
nu
ng
sa
mp
litud
e σ
a [M
Pa
]
Dehnungsamplitude εa,t
[%]
TRIP
zyklisch
zügig
42CrMo4
zyklisch
zügig
Rp0,2
=834MPa
0,0 0,2 0,4 0,6 0,8 1,0
0
200
400
600
800
1000
Rp0,2
=658MPa
R'p0,2
=705MPa
R'p0,2
=602MPa
Sp
an
nu
ng
sa
mp
litud
e σ
a [M
Pa
]
Dehnungsamplitude εa,t
[%]
TRIP
zyklisch
zügig
42CrMo4
zyklisch
zügig
Rp0,2
=834MPa
Static and cyclic properties of Q+T steels and TRIP steels
0,0 0,2 0,4 0,6 0,8 1,0
0
200
400
600
800
1000
42CrMo4
zyklisch
zügig
TRIP1
zyklisch
zügig
Spannungsam
plit
ude σ
a [
MP
a]
Dehnungsamplitude εa,t
[%]
• Static tensile properties Q+T > TRIP
• Cyclic properties Q+T < TRIP (constant loading)
• Cyclic properties Q+T < TRIP (variable loading)
Service fatigue life of TRIP forging steel is improved compared to conventional
Q+T steel
TRIP
zyklisch
zügig
42CrMo4
zyklisch
zügig
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Notch sensitivity
Formzahl Kt = σ1,max
σn
σ1,max
σn
F
A
F
• Smaller notch sensitivity of TRIP steel compared to Q+T steels
• Notch sensitivity of TRIP comparable to mild steels
Advantages for components with complex geometrical shapes
F A
Nennspannung σn =
Designing new forging steels by ICMPE - Wolfgang Bleck 48
Topics New processes
Optimal material utilisation
Damage tolerance
Integrated Computational Materials Engineering (ICME)
Nano-characterisation
Steels Case-hardening steels
Quenched and Tempered Steels Bearing steels
High Mn Steels
Trends
Outline
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High Mn Steels: Mechanical properties and deformation modes
S. Hoffmann; W. Bleck; B. Berme, Steel Research International 2012, 83, 79-384. T. Labudde; T. Ingendahl; M. Wildau; A. Saeed-Akbari; S. Hoffmann; W. Bleck, Materials Testing, 2013, 55, 636-642. .
strain / -
Str
ess, M
Pa
Str
ess, M
Pa
Technical strain / %
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Deformation Mechanisms in High Manganese Steels
γ
κ κ
κ
κ
κ
κκ
T κ T T
T
T T
T
T T
T T T T T T
T
T T
T
T T T
Transformation during
deformation
Twinning during
deformation
Dislocation generation and
reactions
Dislocation channels by
intermetallics
SLIP TRIP TWIP MBIP
SLIP: Dislocation slip TRIP: transfomation induced plasticity TWIP: twinning induced plasticity MBIP: Microband induced plasticity
T T T
T T T
T T T T
T T T
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Material design
Mechanismenorientiertes Werkstoff- und Prozessdesign Christian Haase
O. Bouaziz, C.P. Scott, G. Petitgand: Scripta Mater., 60 (2009) 714-716. H.T. Wang, N.R. Tao, K. Lu: Acta Mater., 60 (2012) 4027-4040.
C. Haase et al.: Met. Mater. Trans. A, 44 (2013) 4445-4449.
Deformation Twins
before cold rolling after cold rolling after recovery annealing
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Material design
50 % + 550 °C/30 min 40 % + 550 °C/1 h
1 µm 1 µm
RX
Twins
Twin boundaries are heat resistant C. Haase et al.: Acta Mater., 80 (2014) 327-340.
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0 10 20 30 40 50 60 700
200
400
600
800
1000
1200
1400
Technische S
pannung (MPa)
T echnis che D ehnung (% )
Material design
Variation of rolling degree and annealing parameters
allows the adjustment of final mechanical properties
CR: cold rolled RC: recovered RX: recrystallized
C. Haase et al.: Acta Mater., 80 (2014) 327-340. C. Haase et al.: Adv. Mater. Res., 922 (2014) 213-218.
0 10 20 30 40 50 60 70
0
200
400
600
800
1000
1200
1400
0 10 20 30 40 50 60 70
0
200
400
600
800
1000
1200
1400
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In situ bending test in large chamber SEM
• Twins and twin intersections are
visible
• Surface roughening
• Fracture occurs on surface at
shear bands
shear
bands
twin
intersections
Crack initiation at characteristic microstructural features
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Damage development
Initial state: polished
WR
30µm
-25µm
0µm
WR -25µm WR
X60Mn23
50% strain
Steel: X60Mn17 60µm
-50µm
0µm
WR
RD RD RD
Tensile strain
Investigation of surface defects by confocal microscopy I
90° to RD 45° to RD 0° to RD
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Damage related to Hydrogen – Identification of hydrogen related mechanisms in steels
grain boundary
diffusion
hydrogen
embrittlement
bulk
diffusion
bulk with
vacancies
HΨ = EΨ
Investigation of H effects in AHHS
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Nanostructured Steels Stähle
γ
κ κ
κ
κ
κ
κκ
T κ T T
T
T T
T
T T
T T T T T T
T
T T
T
T T T
Transformation during
deformation
Twinning during
deformation
Transformation +
precipitation
Dislocation channels by
intermetallics
SLIP TRIP TWIP MBIP
SLIP: Dislocation slip TRIP: transfomation induced plasticity TWIP: twinning induced plasticity MBIP: Microband induced plasticity MMnS: Mittel-Mn-Stähle
T T T
T T T
T T T T
T T T
α‘ retained γ
Bainit MMnS
Interfaces Transfer✓
γ α’
Process
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Topics New processes
Optimal material utilisation
Damage tolerance
Integrated Computational Materials Engineering (ICME)
Nano-characterisation
Steels Case-hardening steels
Quenched and Tempered Steels
Bearing steels
Trends ICMPE
Damage tolerant design Nanostructuring
Outline
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Integrative Computational Material and Process Engineering m
acro
m
icro
su
b-µ
AixViPMaP
Integration of machining
Ex
ten
sio
n t
o
life
tim
e/r
ep
air
Ex
ten
sio
n t
o
desig
n o
pti
mis
ati
on
Standardised data format / data generation ab initio
Hot rolling Forging FP annealing Carburising Machining
Thermodynamic databases
Trends: ICMPE
Designing new forging steels by ICMPE - Wolfgang Bleck 60
Damage prevention approach:
Avoid any damage occurrence by local stress / strain accumulation that results in
local failure
Damage tolerance approach:
Self healing approach:
Allow local metal degradation but limit its impact on the component structural behavior
Allow local metal degradation but enable inherent repair
Avoid critical features
Accept local plasticity
Allow diffusion repair
Trends: damage tolerance
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C
Cr
Mn
Si (Fe,Cr)3C / Fe3C boundary
Fe3C/αB
boundary
Z zone
(Fe,Cr)3C + Fe3C αB
(Fe,Cr)3C + Fe3C
~12nm Cr atoms map
αB
αB
αB (Fe,Cr)3C Fe3C
(Fe,Cr)3C Fe3C
(Fe,Cr)3C
Fe3C αB
Steels: bearing steels
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(Fe,Cr)3C
Fe3C
αB
1-Dimensional concentration profile showing the
distribution of C, Si, Cr, Mn in undissolved
spheroidized carbide (Fe,Cr)3C, newly formed
cementite at 500 °C and bainitic ferrite matrix.
Cr exhibits a gradual
chemical gradient from
surface to the core in
spheroidized carbides.
S i e x h i b i t s a l a r g e
enrichment at the growth
front of cementite, which
hinders the coarsening of
cementite particles.
The spheroidized carbide
may exist as a nucleation
site for the precipitation of
cementite within bainite.
This microstructral feature
might be beneficial for
wear res i s tance and
fatigue properties of the
material.
Trends: Nanostructuring
01.10.15
32
Designing new forging steels by ICMPE - Wolfgang Bleck 63
The authors thank
• Exzellenzcluster - Integrative Production Technology for High-Wage Countries
RWTH Aachen University
• Industrieverband Massivumformung e. V. (IMU)
• Forschungsvereinigung Stahlanwendung e. V. (FOSTA)
• Arbeitsgemeinschaft industrieller Forschungsvereinigungen Otto von Guericke
e.V. (AiF)
• Arbeitsgemeinschaft der eisen- und metallverarbeitenden Industrie e.V (AVIF)
• Deutsche Forschungsgemeinschaft (DFG)
• Partners of the projects „TRIP-Schmiedestahl“, „EcoForge“, „ICMPE“, „HDB-
Schmiedestahl“, „Al-freie Einsatzstähle“, „HiPerComp“ and „SFP 761 – ab
initio“.
Acknowledgement
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