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Effect of thermomechanical process on the austenite transformation in Nb-Mo microalloyed steels
1. Titulo de la
Effect of composition and thermomechanical
presentación
process on the austenite transformation in
Nb-Mo microalloyed steels
October 21, 2010 – Houston, Texas
N. Isasti, B. López and P. Uranga
puranga@ceit.es
(CEIT and TECNUN, Univ. Navarra)
A. Leff, E. Toby, M. Hartshorne, C. Wrinkler and M. Taheri (Drexel U.)
M. Grimes (Lehigh U.)
2. 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
4. 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
5. 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
6. 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)
7. Schematics of thermomechanical schedules
Temperature (ºC)
1250ºC, 5min
20ºC/s→ 12s
ε=0.3, ε&& = 1s −−11
1150ºC, ε = 0.3, ε =1s-1
20ºC/s→
5s
ε = 0.4εε = 1s −−11
900ºC, ε =0.4, ,&& =1s-1
Cycle A Cycle B
Time (s)
18. Effect of Retained Strain on CCT
6NbMo31
1000
900
800
A PF
700
Temperature (ºC)
GF
600 GF+QF
500
BF
400 Ms M
300
200 ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
100
6NbMo31
0
0.1 1 10 100 1000 10000
Time (s)
19. Mo Effect on CCT
Cycle B
1000
900
800
A
PF
700
Temperature (ºC)
GF+QF GF
600
500 BF
400 Ms M
300
200 ºC/s 200 100 50 20 10 5 2 1 0.5 0.1
100
Cycle B
0
0.1 1 10 100 1000 10000
Time (s)
29. 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
30. 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
31. Titulo de la
Effect of composition and thermomechanical
presentación
process on the austenite transformation in
Nb-Mo microalloyed steels
October 21, 2010 – Houston, Texas
N. Isasti, B. López and P. Uranga
puranga@ceit.es
(CEIT and TECNUN, Univ. Navarra)
A. Leff, E. Toby, M. Hartshorne, C. Wrinkler and M. Taheri (Drexel U.)
M. Grimes (Lehigh U.)