Titulo de la            Effect of composition and thermomechanical                               presentación            p...
Introduction• Multiple microalloying for high performance  grades:  – High strength and low-T toughness• Combined effect –...
Steel compositions and TechniquesEXPERIMENTAL
Chemical compositions of steels (wt%)     Steel    C     Mn      Si     Nb     Mo      Al      N   CMn       0.05   1.58  ...
Chemical compositions of steels (wt%)   Steel    C     Mn      Si     Nb     Mo      Al     N  6NbMo0   0.05   1.56   0.05...
Experimental Procedure• Bähr DIL805D deformation dilatometer• Optical Microscopy• Philips XL30cp Scanning Electron Microsc...
Schematics of thermomechanical schedules         Temperature (ºC)                         1250ºC, 5min                    ...
Microstructural Characterization and Dilatometry CurvesRESULTS
Optical Micrographs                                6NbMo0           Cycle A    Cycle B0.1 ºC/s                          PF...
Optical Micrographs                                6NbMo0           Cycle A    Cycle B10 ºC/s                           QF...
Dilatometry curves                                                                                                        ...
Dilatometry curves – Transfomation Rates                                                                                  ...
Phase Stability RegionsCCT DIAGRAMS
CCT Diagrams                                                                                                              ...
CCT Diagrams                                                                                                              ...
CCT Diagrams                                                                                                              ...
Alloying and Retained Strain EffectsCCT ANALYSIS
Effect of Retained Strain on CCT                                                                                          ...
Mo Effect on CCT                                                                                                       Cyc...
EBSD / SEM-FEGSEMLOW COOLING RATE PHASES
Low CR-EBSD                                            Cycle B    Effect of Mo addition  6NbMo0                6NbMo16    ...
EBSD                                                       Cooling Rate= 0.1 ºC/s                                         ...
EBSD / SEM-FEGSEMIDENTIFICATION OFSECONDARY PHASES
EBSD                                              6NbMo16   Identification of second phases             Cycle B           ...
Bainite + Martensite + (GF+QF)HIGH COOLING RATE PHASES
High CR products – FEGSEM EBSD                                                                 6NbMo16    Image Quality (I...
EBSD (Electron BackscatterDiffraction)                                                                                    ...
EBSD (Electron BackscatterDiffraction)                                                                               6NbMo...
Final Remarks• Effect of Mo and retained strain has been  evaluated  – Slight effect of Mo: increase in ferrite size  – St...
Acknowledgements• Science and Innovation Ministry of Spain  (MAT2009-09250)• NSF and TMS. Conference Registration Fee  Fun...
Titulo de la            Effect of composition and thermomechanical                               presentación            p...
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Effect of thermomechanical process on the austenite transformation in Nb-Mo microalloyed steels

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Effect of thermomechanical process on the austenite transformation in Nb-Mo microalloyed steels

  1. 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. 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
  3. 3. Steel compositions and TechniquesEXPERIMENTAL
  4. 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. 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. 6. Experimental Procedure• Bähr DIL805D deformation dilatometer• Optical Microscopy• Philips XL30cp Scanning Electron Microscope (SEM), usingTSL (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. 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)
  8. 8. Microstructural Characterization and Dilatometry CurvesRESULTS
  9. 9. Optical Micrographs 6NbMo0 Cycle A Cycle B0.1 ºC/s PF+GF(+P)0.5 ºC/s PF+QF+GF
  10. 10. Optical Micrographs 6NbMo0 Cycle A Cycle B10 ºC/s QF+GF QF+GF+100 ºC/s BF+M
  11. 11. Dilatometry curves 6NbMo31 Cycle B 0.004 100 0.1ºC/s 0.1ºC/s 0.5ºC/s 0.5ºC/s Transformed fraction (%) 10ºC/s 80 10ºC/s 0 100ºC/s 100ºC/s 60 ΔL/Lo -0.004 40 -0.008 20 -0.012 0 0 200 400 600 800 0 200 400 600 800 Temperature (ºC) Temperature (ºC) ΔL/L0 vs Temperature (ºC) Transformed Fraction vs Temperature (ºC)
  12. 12. Dilatometry curves – Transfomation Rates 6NbMo31 Cycle B 0.6 60 0.1ºC/s 10ºC/s 0.5ºC/s 100ºC/sTransformation Rate Transformation Rate 0.4 40 0.2 20 0 0 0 200 400 600 800 0 200 400 600 800 Temperature (ºC) Temperature (ºC)
  13. 13. Phase Stability RegionsCCT DIAGRAMS
  14. 14. CCT Diagrams 6NbMo0 Cycle A Cycle B 1000 1000 900 900 800 800 A A PF 700 PF 700Temperature (ºC) Temperature (ºC) 45% 65% 88% 15% 92% GF 25% GF P 600 GF+QF 600 25% GF+QF 500 500 BF BF Ms 400 Ms M 400 M 300 300 ºC/s 200 100 50 20 10 5 2 1 0.5 0.1 200 ºC/s 200 100 50 20 10 5 2 1 0.5 0.1 200 HV 268 265 257 227 215 210 209 197 185 160 100 6NbMo0 HV 279 275 272 240 220 207 204 202 197 191 100 6NbMo0 Cycle A Cycle B 0 0 0.1 1 10 100 1000 10000 0.1 1 10 100 1000 10000 Time (s) Time (s)
  15. 15. CCT Diagrams 6NbMo16 Cycle A Cycle B 1000 1000 900 900 800 800 A PF A PF 700 700Temperature (ºC) Temperature (ºC) 87% 55% 85% 15% GF GF 600 600 GF+QF GF+QF 500 BF 500 BF 400 Ms M 400 85% Ms M 300 300 200 ºC/s 200 100 50 20 10 5 2 1 0.5 0.1 200 ºC/s 200 100 50 20 10 5 2 1 0.5 0.1 100 6NbMo16 HV 292 280 271 240 229 219 217 211 203 199 100 6NbMo16 HV 270 268 264 248 234 219 213 212 204 157 Cycle A Cycle B 0 0 0.1 1 10 100 1000 10000 0.1 1 10 100 1000 10000 Time (s) Time (s)  
  16. 16. CCT Diagrams 6NbMo31 Cycle A Cycle B   1000 1000 900 900 A 800 800 PF A 700 700Temperature (ºC) 93% Temperature (ºC) PF 19% 41% 65% 70% 600 GF+QF GF 600 GF+QF GF 500 500 BF BF 75% 400 Ms M 400 Ms M 300 300 200 ºC/s 200 100 50 20 10 5 2 1 0.5 0.1 200 ºC/s 200 100 50 20 10 5 2 1 0,5 0,1 100 6NbMo31 HV 311 298 292 260 236 220 214 213 212 210 100 6NbMo31 HV 299 292 282 241 232 215 213 201 176 147 Cycle A Cycle B 0 0 0.1 1 10 100 1000 10000 0.1 1 10 100 1000 10000 Time (s) Time (s)    
  17. 17. Alloying and Retained Strain EffectsCCT ANALYSIS
  18. 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. 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)
  20. 20. EBSD / SEM-FEGSEMLOW COOLING RATE PHASES
  21. 21. Low CR-EBSD Cycle B Effect of Mo addition 6NbMo0 6NbMo16 6NbMo31 Cooling Rate= 0.1 ºC/s
  22. 22. EBSD Cooling Rate= 0.1 ºC/s Cycle B Effect of Mo 1.2 1 Accumulated Area Fraction 0.8 0.6 0.4 0.1ºC/s 6NbMo0 0.2 6NbMo16 6NbMo31 0 105 125 135 145 155 5 15 25 35 45 55 65 75 85 95 115 Grain Size (Diameter µm)
  23. 23. EBSD / SEM-FEGSEMIDENTIFICATION OFSECONDARY PHASES
  24. 24. EBSD 6NbMo16 Identification of second phases Cycle B Degenerated 0.5 ºC/s 1 ºC/s M/A Islands Pearlite Fe3C-1 MAD 0.538
  25. 25. Bainite + Martensite + (GF+QF)HIGH COOLING RATE PHASES
  26. 26. High CR products – FEGSEM EBSD 6NbMo16 Image Quality (IQ) 20 ºC/s 100 ºC/s =50 µm; Map15; Step=0.2 µm; Grid700x700 =50 µm; Map15; Step=0.2 µm; Grid700x700
  27. 27. EBSD (Electron BackscatterDiffraction) 6NbMo16 Misorientation Map 20 ºC/s 100 ºC/s =50 µm; Map15; Step=0.2 µm; Grid700x700 =50 µm; Map15; Step=0.2 µm; Grid700x700 1-15º >15º
  28. 28. EBSD (Electron BackscatterDiffraction) 6NbMo16 Inverse Pole Figure IPF (z) 20 ºC/s 100 ºC/s =50 µm; Map15; Step=0.2 µm; Grid700x700 =50 µm; Map15; Step=0.2 µm; Grid700x700
  29. 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. 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. 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.)

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