The Effect of Molybdenum on Precipitation Behaviour in Austenite of Strip-Cast Steels Containing Niobium
Abstract
:1. Introduction
2. Materials and Methods
3. Results
3.1. Hardness
3.2. Microstructure
3.3. TEM
4. Discussion
4.1. The Effect of Mo on the Thermodynamics of Precipitation
4.2. The Effect of Mo on the Coarsening Kinetics of Precipitation
4.3. Precipitation Hardening
5. Conclusions
- (1)
- The hardness values of both as-cast steels were similar. During isothermal holding at 900 °C, the hardness of the two steels increased and reached the peak at 3000 s, then decreased after 10,000 s isothermal holding. Generally, the Nb-Mo steel had higher hardness than the Nb steel at all isothermal holding times.
- (2)
- The microstructures of both steels after isothermal holding at 900 °C were bainite, only some grain boundary allotriomorph (GBA) were formed in the Nb steels heat treated for 10,000 s at 900 °C.
- (3)
- Nb-carbonitrides precipitated in both steels after isothermal holding for 1000 s at 900 °C, and the size of the particles in the Nb-Mo steel was finer than that in the Nb steel. In the Mo-containing steel, Mo also participated in the precipitation, and the concentration of Mo in Nb-rich carbonitrides decreased with increasing particle size and isothermal holding time.
- (4)
- The enrichment of Mo in the Nb-rich carbonitrides reduces the interfacial energy between precipitates and the matrix, which lowers the nucleation energy barrier and the precipitate coarsening rate.
- (5)
- Strength modelling suggests that precipitation reached maximum volume fraction (0.0605%) after isothermal holding at 900 °C for 3000 s. The precipitates in the Nb-Mo steel imparted an increase in yield strength up to ~140 MPa, which was higher than that in the Nb steel, ~96 MPa. Further strengthening contributions of the precipitates in both steels decreased after 10,000 s isothermal holding at 900 °C due to the coarsening of the particles.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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C | Mn | Si | Al | Nb | Mo | S | N | Fe | |
---|---|---|---|---|---|---|---|---|---|
Nb steel | 0.05 | 1.45 | 0.21 | 0.003 | 0.05 | - | <0.0005 | 0.01 | bal. |
Nb-Mo steel | 0.05 | 1.50 | 0.23 | 0.004 | 0.05 | 0.33 | <0.0005 | 0.01 | bal. |
Ageing Time | Nb Steel | Nb-Mo Steel |
---|---|---|
1000 s | 144 | 171 |
3000 s | 96 | 140 |
10,000 s | 63 | 87 |
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Jiang, L.; Marceau, R.K.W.; Dorin, T.; Yin, H.; Sun, X.; Hodgson, P.D.; Stanford, N. The Effect of Molybdenum on Precipitation Behaviour in Austenite of Strip-Cast Steels Containing Niobium. Metals 2020, 10, 1330. https://doi.org/10.3390/met10101330
Jiang L, Marceau RKW, Dorin T, Yin H, Sun X, Hodgson PD, Stanford N. The Effect of Molybdenum on Precipitation Behaviour in Austenite of Strip-Cast Steels Containing Niobium. Metals. 2020; 10(10):1330. https://doi.org/10.3390/met10101330
Chicago/Turabian StyleJiang, Lu, Ross K. W. Marceau, Thomas Dorin, Huaying Yin, Xinjun Sun, Peter D. Hodgson, and Nicole Stanford. 2020. "The Effect of Molybdenum on Precipitation Behaviour in Austenite of Strip-Cast Steels Containing Niobium" Metals 10, no. 10: 1330. https://doi.org/10.3390/met10101330
APA StyleJiang, L., Marceau, R. K. W., Dorin, T., Yin, H., Sun, X., Hodgson, P. D., & Stanford, N. (2020). The Effect of Molybdenum on Precipitation Behaviour in Austenite of Strip-Cast Steels Containing Niobium. Metals, 10(10), 1330. https://doi.org/10.3390/met10101330