Effect of thermomechanical process on the austenite transformation in Nb-Mo microalloyed steels
31
Titulo de la presentación Effect of composition and thermomechanical process on the austenite transformation in Nb-Mo microalloyed steels October 21, 2010 – Houston, Texas N. Isasti, B. López and P. Uranga [email protected] (CEIT and TECNUN, Univ. Navarra) A. Leff, E. Toby, M. Hartshorne, C. Wrinkler and M. Taheri (Drexel U.) M. Grimes (Lehigh U.)
-
Upload
pello-uranga -
Category
Technology
-
view
126 -
download
9
description
Presentation made at Materials Science and Technology 2010 held in Houston
Transcript of Effect of thermomechanical process on the austenite transformation in Nb-Mo microalloyed steels
Titulo de la presentaciónEffect of composition and thermomechanical
process on the austenite transformation in Nb-Mo microalloyed steels
October 21, 2010 – Houston, Texas
N. Isasti, B. López and P. Uranga
(CEIT and TECNUN, Univ. Navarra)
A. Leff, E. Toby, M. Hartshorne, C. Wrinkler and M. Taheri (Drexel U.)
M. Grimes (Lehigh U.)
Introduction
• Multiple microalloying for high performance grades:– High strength and low-T toughness
• Combined effect – synergies Nb-Mo• Effect of thermomechanical route:
– Recrystallized austenite– Deformed austenite
• Reducing grain size (unit size) in transformed phases:– strength and toughness improved
EXPERIMENTALSteel compositions and Techniques
Chemical compositions of steels (wt%)
Steel C Mn Si Nb Mo Al N
CMn 0.05 1.58 0.05 - 0.01 0.03 0.005
3NbMo0 0.05 1.6 0.06 0.029 0.01 0.028 0.005
3NbMo16 0.05 1.58 0.04 0.03 0.16 0.027 0.005
3NbMo31 0.05 1.57 0.05 0.028 0.31 0.028 0.005
6NbMo0 0.05 1.56 0.05 0.06 0.01 0.028 0.004
6NbMo16 0.05 1.6 0.05 0.061 0.16 0.03 0.005
6NbMo31 0.05 1.57 0.05 0.059 0.31 0.031 0.005
Chemical compositions of steels (wt%)
Steel C Mn Si Nb Mo Al N
6NbMo0 0.05 1.56 0.05 0.06 0.01 0.028 0.004
6NbMo16 0.05 1.6 0.05 0.061 0.16 0.03 0.005
6NbMo31 0.05 1.57 0.05 0.059 0.31 0.031 0.005
Experimental Procedure
• Bähr DIL805D deformation dilatometer
• Optical Microscopy
• Philips XL30cp Scanning Electron Microscope (SEM), using TSL (TexSEM laboratories) MSC 2002 equipment.
• Field Emission Scanning Electron Microscope (FEG-SEM) Jeol JSM-7000F, using HKL Channel5 EBSD
• Vickers hardness (HV 1 kg)
1250ºC, 5min
1150ºC, ε=0.3, =1s-1
900ºC, ε=0.4, =1s-1
Cycle A Cycle BTem
pera
ture
(ºC
)
Time (s)
12s
20ºC/s5s
20ºC/sε&
ε& 11,4.0 −== sεε &
11,3.0 −== sεε &→
→
11,3.0 −== sεε &
11,4.0 −== sεε &
Schematics of thermomechanical schedules
RESULTSMicrostructural Characterization and Dilatometry Curves
0.1 ºC/s
0.5 ºC/s
PF+GF(+P)
PF+QF+GF
Optical Micrographs 6NbMo0Cycle BCycle A
10 ºC/s
100 ºC/s
QF+GF
QF+GF+BF+M
Optical Micrographs 6NbMo0Cycle BCycle A
Dilatometry curves
ΔL/L0 vs Temperature (ºC) Transformed Fraction vs Temperature (ºC)
6NbMo31
Cycle B
-0.012
-0.008
-0.004
0
0.004
0 200 400 600 800
ΔL/
Lo
Temperature (ºC)
0.1ºC/s 0.5ºC/s 10ºC/s 100ºC/s
0
20
40
60
80
100
0 200 400 600 800
Tran
sfor
med
fra
ctio
n (%
)Temperature (ºC)
0.1ºC/s 0.5ºC/s 10ºC/s 100ºC/s
Dilatometry curves – Transfomation Rates6NbMo31 Cycle B
0
20
40
60
0 200 400 600 800
Tran
sfor
mat
ion
Rat
e
Temperature (ºC)
10ºC/s 100ºC/s
0
0.2
0.4
0.6
0 200 400 600 800
Tran
sfor
mat
ion
Rat
e
Temperature (ºC)
0.1ºC/s 0.5ºC/s
CCT DIAGRAMSPhase Stability Regions
0
100
200
300
400
500
600
700
800
900
1000
0.1 1 10 100 1000 10000
Tem
pera
ture
(ºC
)
Time (s)
A PF
GF+QF
BF
GF
M
15% 88%
Ms
ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
HV 279 275 272 240 220 207 204 202 197 1916NbMo0 Cycle A
0
100
200
300
400
500
600
700
800
900
1000
0.1 1 10 100 1000 10000Te
mpe
ratu
re (º
C)
Time (s)
PF
GF+QF
92%
45% 65%
25%
BF
25%
Ms
P
M
A
6NbMo0Cycle B
GF
ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
HV 268 265 257 227 215 210 209 197 185 160
CCT Diagrams 6NbMo0
Cycle BCycle A
0
100
200
300
400
500
600
700
800
900
1000
0.1 1 10 100 1000 10000
Tem
pera
ture
(ºC
)
Time (s)
PF
GF+QF
BF
Ms
6NbMo16Cycle A
M
87%
15%
A
GF
ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
HV 292 280 271 240 229 219 217 211 203 199
0
100
200
300
400
500
600
700
800
900
1000
0.1 1 10 100 1000 10000Te
mpe
ratu
re (º
C)
Time (s)
PF
GF+QF
BF
Ms
85%
6NbMo16Cycle B
85%
55%
M
GF
A
ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
HV 270 268 264 248 234 219 213 212 204 157
CCT Diagrams 6NbMo16
Cycle BCycle A
0
100
200
300
400
500
600
700
800
900
1000
0.1 1 10 100 1000 10000
Tem
pera
ture
(ºC
)
Time (s)
70%PF
GF+QF
BF
GF
MMs
A
6NbMo31Cycle A
ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
HV 311 298 292 260 236 220 214 213 212 210
0
100
200
300
400
500
600
700
800
900
1000
0.1 1 10 100 1000 10000Te
mpe
ratu
re (º
C)
Time (s)
A
GF+QF
PF93%
19% 41% 65%
75%
Ms
A
PF93%
19% 41% 65%
75%BF
Ms M
6NbMo31Cycle B
GF
ºC/s 200 100 50 20 10 5 2 1 0,5 0,1
HV 299 292 282 241 232 215 213 201 176 147
CCT Diagrams 6NbMo31
Cycle BCycle A
CCT ANALYSISAlloying and Retained Strain Effects
0
100
200
300
400
500
600
700
800
900
1000
0.1 1 10 100 1000 10000
Tem
pera
ture
(ºC
)
Time (s)
PF
GF+QF
BF
GF
MMs
A
6NbMo31
ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
Effect of Retained Strain on CCT 6NbMo31
0
100
200
300
400
500
600
700
800
900
1000
0.1 1 10 100 1000 10000
Tem
pera
ture
(ºC
)
Time (s)
PF
GF+QF
BF
GF
MMs
A
Cycle B
ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
Mo Effect on CCT Cycle B
LOW COOLING RATE PHASESEBSD / SEM-FEGSEM
Cooling Rate= 0.1 ºC/s
Low CR-EBSD
Effect of Mo addition
Cycle B
6NbMo0 6NbMo16 6NbMo31
Cooling Rate= 0.1 ºC/s
0
0.2
0.4
0.6
0.8
1
1.2
5 15 25 35 45 55 65 75 85 95 105
115
125
135
145
155
Accu
mul
ated
Are
a Fr
actio
n
Grain Size (Diameter µm)
6NbMo0
6NbMo16
6NbMo31
0.1ºC/s
EBSD
Effect of MoCycle B
IDENTIFICATION OF SECONDARY PHASES
EBSD / SEM-FEGSEM
Fe3C-1
MAD 0.538
Degenerated Pearlite
EBSD
Identification of second phases
1 ºC/s0.5 ºC/s
6NbMo16
Cycle B
M/A Islands
HIGH COOLING RATE PHASESBainite + Martensite + (GF+QF)
=50 µm; Map15; Step=0.2 µm; Grid700x700=50 µm; Map15; Step=0.2 µm; Grid700x700
High CR products – FEGSEM EBSD6NbMo16
100 ºC/s20 ºC/s
Image Quality (IQ)
1-15º>15º
=50 µm; Map15; Step=0.2 µm; Grid700x700=50 µm; Map15; Step=0.2 µm; Grid700x700
EBSD (Electron Backscatter Diffraction) 6NbMo16
100 ºC/s20 ºC/s
Misorientation Map
=50 µm; Map15; Step=0.2 µm; Grid700x700=50 µm; Map15; Step=0.2 µm; Grid700x700
EBSD (Electron Backscatter Diffraction) 6NbMo16
100 ºC/s20 ºC/s
Inverse Pole Figure IPF (z)
Final Remarks
• Effect of Mo and retained strain has been evaluated– Slight effect of Mo: increase in ferrite size– Strong effect of strain
• EBSD unit size measurements may be useful for toughness predictions
• The generated data will be the input for modeling
Acknowledgements
• Science and Innovation Ministry of Spain (MAT2009-09250)
• NSF and TMS. Conference Registration Fee Funding
• N . Isasti for all the experimental results and analysis (1st year PhD student)
• D. Jorge-Badiola: help on EBSD
Titulo de la presentaciónEffect of composition and thermomechanical
process on the austenite transformation in Nb-Mo microalloyed steels
October 21, 2010 – Houston, Texas
N. Isasti, B. López and P. Uranga
(CEIT and TECNUN, Univ. Navarra)
A. Leff, E. Toby, M. Hartshorne, C. Wrinkler and M. Taheri (Drexel U.)
M. Grimes (Lehigh U.)
