Role of Reversed Austenite Behavior in Determining Microstructure and Toughness of Advanced Medium Mn Steel by Welding Thermal Cycle
Abstract
:1. Introduction
- (1)
- The reversed austenite nucleation characterization on heating.
- (2)
- The reversed austenite growth kinetic.
- (3)
- The effect of different austenite grain size on continuous cooling transformation temperature, and thus martensite transformation and reversed austenite transformation.
- (4)
- The role of microstructure in influencing the cryogenic toughness of heat-affected zone.
2. Experimental
3. Results and Discussion
3.1. Nucleation and Growth of Reversed Austenite
3.2. Effect of Prior Austenite Grain Size on the Continuous Cooling Transformation Temperature and Transformation Rate
3.3. Martensite Transformation and Retained Austenite
3.4. Hardness
3.5. Impact Toughness and the Microstructure Effect
4. Conclusions
- (1)
- The pre-existing retained austenite in the investigated 5Mn steel enhanced the reversed austenite nucleation number during heating of the welding thermal cycle and led to the relatively small grain size in simulated CGHAZ and FGHAZ.
- (2)
- Austenite growth dominantly took place in the heating process and there was almost no austenite growth in the cooling process above peak temperature during the simulated welding thermal cycle. Therefore, the relatively small size was found in CGHAZ.
- (3)
- The higher transformation rate was measured to be a maximum of 0.98 in the simulated FGHAZ and a maximum of 0.60 in the simulated CGHAZ. Thus, a 10~11% austenite was retained in FGHAZ.
- (4)
- Compared to CGHAZ with the larger grain size, the impact toughness in fine grain FGHAZ was not significantly improved. This was due to the transformation of relatively harder martensite and the TRIP effect during the impact test in simulated FGHAZ. Therefore, how to retain austenite will be the future work of how to improve impact toughness of HAZ.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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C | Si | Mn | S | P | Ni | Cr + Cu + Mo | Alt |
---|---|---|---|---|---|---|---|
0.04~0.06 | 0.2~0.25 | 4.9~5.2 | ≤0.0012 | ≤0.009 | 0.27~0.30 | 0.2~0.5 | ≤0.023 |
Rel/MPa | Rm/MPa | A/% | KV2 (−60 °C)/J |
---|---|---|---|
645~650 | 770~775 | 25~27 | 200~205 |
t8/5/s | 5 | 7.5 | 20 | 30 | 60 | Peak Temperature |
---|---|---|---|---|---|---|
Start transformation temperature/°C | 371 | 380 | 383 | 388 | 394 | Tp = 1320 °C |
397 | 403 | 414 | 405 | 423 | Tp = 850 °C | |
Finish transformation temperature/°C | 220 | 235 | 212 | 213 | 200 | Tp = 1320 °C |
251 | 214 | 256 | 261 | 258 | Tp = 850 °C | |
Transformation temperature range/°C | 151 | 145 | 171 | 175 | 194 | Tp = 1320 °C |
146 | 189 | 158 | 144 | 165 | Tp = 850 °C |
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Chen, Y.; Wang, H.; Cai, H.; Li, J.; Chen, Y. Role of Reversed Austenite Behavior in Determining Microstructure and Toughness of Advanced Medium Mn Steel by Welding Thermal Cycle. Materials 2018, 11, 2127. https://doi.org/10.3390/ma11112127
Chen Y, Wang H, Cai H, Li J, Chen Y. Role of Reversed Austenite Behavior in Determining Microstructure and Toughness of Advanced Medium Mn Steel by Welding Thermal Cycle. Materials. 2018; 11(11):2127. https://doi.org/10.3390/ma11112127
Chicago/Turabian StyleChen, Yunxia, Honghong Wang, Huan Cai, Junhui Li, and Yongqing Chen. 2018. "Role of Reversed Austenite Behavior in Determining Microstructure and Toughness of Advanced Medium Mn Steel by Welding Thermal Cycle" Materials 11, no. 11: 2127. https://doi.org/10.3390/ma11112127