V. Smanio, T. Sourmail Ascometal CREAS - CENIM - CSIC · 3 Introduction xHow to shorten bainitic...
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1 Bainite Bainite kinetics kinetics of of high high carbon carbon steels steels V. Smanio, T. Sourmail Ascometal CREAS
Transcript of V. Smanio, T. Sourmail Ascometal CREAS - CENIM - CSIC · 3 Introduction xHow to shorten bainitic...
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Bainite Bainite kineticskinetics of of highhigh carboncarbon steelssteels
V. Smanio, T. SourmailAscometal CREAS
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IntroductionIntroduction
x Bainitic treatment– High carbon steel (100Cr6)
• High hardness (>700HV)• Reducing distortions associated with quenching• Low retained austenite content in-service dimensional stability
– “low” temperature (<250°C) of bainitization for hardness requirements• Long transformation times
Time
Tem
pera
ture
Austenitizing
Austempering""Bainitizing /
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IntroductionIntroduction
x How to shorten bainitic treatment ?– Process changes (Dong, Vetters et al, Smanio et al publications)
Time
Tem
pera
ture
Austenitizing
Double stepbainitizing
Time
Tem
pera
ture
Austenitizing
Pre-quenching / bainitization
Time
Tem
pera
ture
Austenitizing
Double stepbainitizing
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A: 100Cr6 (52100)B: 1C-1.5Si-2.5CoC / D: 1C-1.5Si-X
Time
Tem
pera
ture
3°C/s
950°C/15min
50°C/s
20°C/s
400°C
T_end °C30°C/s
T_hold (220-250) / 10-20h
Ms
1°C/s
Time
Tem
pera
ture
3°C/s
950°C/15min
50°C/s
20°C/s
400°C
T_end °C30°C/s
T_hold (220- -20h
1°C/s
ProcessProcess changeschanges
x Martensite formation before bainitizing (Smanio et al, 2010)
5
0,00E+00
1,00E-03
2,00E-03
3,00E-03
4,00E-03
5,00E-03
6,00E-03
0 10000 20000 30000 40000 50000 60000Time / s
Stra
in
Alloy C
Very significant impact on early stages
x Martensite formation before bainitizing– Kinetics
15% Martensite
0% Martensite
30% Martensite
Reduction bainitizing time up to 50%
ProcessProcess changeschanges
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0,00E+00
1,00E-03
2,00E-03
3,00E-03
4,00E-03
5,00E-03
6,00E-03
0 10000 20000 30000 40000 50000 60000 70000Time / s
Stra
in
Alloy C
Bainite formation kinetics appears virtually identical in the remaining austenite
x Martensite formation before bainitizing (Smanio et al, 2010)
ProcessProcess changeschanges
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Hardness is unchanged
600
650
700
750
800
0 5 10 15 20 25 30 35Target martensite %
Har
dnes
s (H
V30)
x Martensite formation before bainitizing (Smanio et al, 2010)– Martensite amount vs hardness
ProcessProcess changeschanges
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ProcessProcess changeschanges
x Modified bainitic treatments– Reduction time up to 25-50% – Added complexity to industrial process
Time
Tem
pera
ture
Austenitizing
Double stepbainitizing
Time
Tem
pera
ture
Austenitizing
Pre-quenching / bainitization
Time
Tem
pera
ture
Austenitizing
Double stepbainitizingSteel chemical
composition design
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MethodMethod
x Development of steels for bainitic treatment– Based on high carbon steel like 100Cr6 and variants– Effect of alloying elements on bainitic kinetics
• Carbon Austenitization temperature and time variations• Manganese• Silicon• Chromium• Molybdenum
x Methods– Dilatometry isothermal treatment on Bähr 805 quenching dilatometer
Lab casts with different chemical compositions
Time
Tem
pera
ture
Austenitizing
Bainitizing
10
100
150
200
250
300
0,1 1 10 100 1000
Austenitization time (min)
Ms
(°C
)
AusteniteAustenite compositioncomposition
x Austenite composition of hypereutectoid steels– Carbon in solid solution in austenite depends on
• Austenitization temperature• Austenitization time (equilibrium)
– Carbon in solid solution in austenite influences properties
T°aust 860°C
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AusteniteAustenite compositioncomposition
x Method for determination of austenite composition– At equilibrium using Matcalc time to reach equilibrium ?
– In defined austenitization conditions using Ms formula • Dilatometry quenching after defined austenitization conditions Ms• Calculation of austenite Carbon content using Ms formula
T°aust 860°C
100
150
200
250
300
0,1 1 10 100 1000
Austenitization time (min)
Ms
(°C
)
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AusteniteAustenite compositioncomposition
x Validation of the method : 100CrMnSi6-4– Austenitization at 890°C– All carbon in solid solution at this temperature (Matcalc + SEM observations)
0
50
100
150
200
250
300
0 20 40 60 80 100 120 140 160 180 200
Austenitization time (min)
Ms
(°C
)
Andrews 2
Andrews 1
Steven Haynes
Nehrenberg
Measurement
1 µm
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Austenitization/C content Austenitization/C content effecteffect
x Austenite composition of 100CrMnSi6-4– Austenite carbon content depending on austenitization temperature and time
0,700
0,750
0,800
0,850
0,900
0,950
1,000
820 830 840 850 860 870 880 890 900Austenitization temperature (°C)
Aus
teni
te c
arbo
n co
nten
t (%
)
60 min
60 min60 min
20 min
2071478261241180596958bulkCuCrMoNiMnSiC
140
20
40
60
80
100
120
0 20000 40000 60000 80000Time (s)
Bai
nitic
tran
sfor
mat
ion
(%)
e
100CrMnSi6-4 830°C/60 min 100CrMnSi6-4 850°C/60 min
100CrMnSi6-4 860°C/60 min 100CrMnSi6-4 890°C/20 min
↓ Austénitisation T°
890°C/20 min860°C/60 min850°C/60 min830°C/60
Austenitization/C content Austenitization/C content effecteffect
x Kinetics– Isothermal transformation at 220°C
740
760
780
800
820
840
860
880
900
0 5000 10000 15000 20000 25000 30000 35000Time (s)
Car
bon
cont
ent (
10-3
%)
10% transformation 50% transformation 90% transformation
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Austenitization/C content Austenitization/C content effecteffect
x Hardness– Isothermal transformation at 220°C
70888220890703842608607098326085071075560830
Hardness(HV30)
C content (10-3 %)
Austenitization time (min)
AustenitizationT (°C)
No difference in hardness
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AlloyingAlloying elementselements effecteffect
x Manganese content– Isothermal transformation at 220°C
860°C/60 min860°C/60 min
Aust
189185Cu
244175612132476864884100CrMo7-3 low Si low Mn261174011871074852873100CrMo7-3 low Si MoCrNiMnSiC austC bulk
0
10
20
30
40
50
60
70
80
90
100
0 10000 20000 30000 40000Time (s)
Bai
nitic
tran
sfor
mat
ion
(%)
100CrMo7-3 low Si low Mn100CrMo7-3 low Si
↓ Mn content
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AlloyingAlloying elementselements effecteffect
x Molybdenum content– Isothermal transformation at 220°C
0
10
20
30
40
50
60
70
80
90
100
0 10000 20000 30000 40000Time (s)
Bai
nitic
tran
sfor
mat
ion
(%) 100CrMo7-3 low Si low Mn
100CrMo7 low Si
189191Cu
860°C/70 min860°C/60 min
Aust
244175612132476864884100CrMo7-3 low Si low Mn151177012230760862908100CrMo7 low Si MoCrNiMnSiC austC bulk
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AlloyingAlloying elementselements effecteffect
x Chromium content– Isothermal transformation at 220°C
860°C/20 min860°C/60 min
Aust
189189Cu
253149212131566845898100CrMo6-3 low Si low Mn244175612132476864873100CrMo7-3 low Si low MnMoCrNiMnSiC austC bulk
0
10
20
30
40
50
60
70
80
90
100
0 10000 20000 30000 40000Time (s)
Bai
nitic
tran
sfor
mat
ion
(%)
100CrMo7-3 low Si low Mn100CrMo6-3 low Si low Mn
↓ Cr content
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AlloyingAlloying elementselements effecteffectx Silicon content
– Determination of austenitization conditions
860°C/60 min860°C/10 min860°C/20 min
Aust
189191189Cu
26517441182951198793899100CrMo7-3 high Si low Mn2301744119321599796889100CrMo7-3 medium Si low Mn244175612132476794884100CrMo7-3 low Si low MnMoCrNiMnSiC austC bulk
0,700
0,720
0,740
0,760
0,780
0,800
0,820
0,840
0,860
0,880
0,900
0 20 40 60 80 100 120 140 160 180 200Austenitization time (min)
Car
bon
cont
ent (
%)
100CrMo7-3 low Si low Mn100CrMo7-3 medium Si low Mn100CrMo7-3 high Si low Mn
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AlloyingAlloying elementselements effecteffectx Silicon content
– Isothermal transformation at 220°C
0
10
20
30
40
50
60
70
80
90
100
0 10000 20000 30000 40000Time (s)
Bai
nitic
tran
sfor
mat
ion
(%)
100CrMo7-3 low Si low Mn100CrMo7-3 medium Si low Mn100CrMo7-3 high Si low Mn
↓ Si content
0
200
400
600
800
1000
1200
1400
0 2000 4000 6000 8000 10000 12000 14000 16000
Time (s)
Si c
onte
nt (1
0-3%
)
10% transformation 50% transformation 90% transformation
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DiscussionDiscussion
x Alloying elements effect on bainitic transformation kinetics in hypereutectoid steels
– No influence : Molybdenum– Small influence : Chromium– Strong influence : Manganese, Silicon and Carbon
Quidort et al, Acta Materialia 2001
↓Chromiumcontent
Quidort et al, Acta ISIJ 2002
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DiscussionDiscussion
x Design of new steels chemical compositions
253149231566898100CrMo6-3 low Si low Mn151177030760908100CrMo7 low Si
2601752639239973100CrMo7-3MoCrMnSiC bulk
Time reduction up to 50%/ standard
100CrMo7 low Si
100CrMo7
100CrMo6-3 low Si low Mn
100CrMo7-3
-60
-50
-40
-30
-20
-10
0700 720 740 760 780 800
Hardness (HV30)
Tim
e re
duct
ion/
100C
rMo7
-3
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ConclusionsConclusions
x Conclusions– Parametric study to evaluate influence of alloying elements on bainitic kinetics
of 100Cr6 and variants
– Main influence of :• Carbon (austenitization conditions)• Manganese• Silicon
– Design of new steels chemical compositions dedicated to bainitic treatment • Time reduction up to 50% / standard steel without loss in hardness
