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| Effect of Ti/V ratio on thermodynamics and kinetics of MC in γ/α matrices of Ti–V microalloyed steels |
| Ke Zhang1,2, Xin-jun Sun3, Zhao-dong Li3, Kun Xu2, Tao Jia4, Zheng-hai Zhu2, Xiao-yu Ye1,2, Jun-yu Kang3, Qi-long Yong3 |
1 State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization, Panzhihua Group Co., Ltd., Panzhihua 617000, Sichuan, China
2 School of Metallurgical Engineering, Anhui University of Technology, Maanshan 243032, Anhui, China
3 Institute of Structural Steels, Central Iron and Steel Research Institute, Beijing 100081, China
4 State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, Liaoning, China |
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Abstract Through the solubility product theory of the ternary secondary phase, classical nucleation theory, and Ostwald ripening theory, a model was established to describe the thermodynamics and kinetics of (Ti, V)C precipitates in austenite/ferrite (γ/α) matrices. The model was used to calculate the volume fraction, precipitation–temperature–time (PTT) curve, and nucleation rate–temperature (NrT) curve of MC (M = Ti, V) precipitates in γ/α matrices in Ti–V microalloyed steels with various Ti/V ratios, which is verified by hardness tester, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The calculations indicate that, by decreasing Ti/V ratio from Ti4V0 steel to Ti0V4 steel, the completedissolution temperature decreases monotonically from 1226 to 830 °C, and the equilibrium volume fraction of MC precipitated from austenite decreases from 0.333% to 0.091% at 900 °C. Moreover, the maximum nucleation temperature of MC precipitated from α matrix decreases from 748 to 605 °C and the fastest precipitation temperature decreases from 844 to 675 °C as Ti/V ratio decreases. PTT and NrT diagrams of MC precipitated from α matrices in different Ti–V microalloyed steels all exhibit C-shaped and inverse C-shaped curves. In addition, both theoretical calculation and experimental results show that when tempered at 600 °C for 100 h, Ti2V2 steel shows the largest hardness value of 312 HV among the three steels tested because it has a larger volume fraction (0.364%), a larger precipitate density (1689 μm-2), and the smallest average size (8.4 nm) of (Ti, V)C precipitates. The theoretical calculations are consistent with experimental results, which indicates that the thermodynamics and kinetics model for (Ti, V)C precipitates is reliable and accurate.
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Received: 20 May 2020
Published: 25 August 2021
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| Cite this article: |
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Ke Zhang,Xin-jun Sun,Zhao-dong Li, et al. Effect of Ti/V ratio on thermodynamics and kinetics of MC in γ/α matrices of Ti–V microalloyed steels[J]. Journal of Iron and Steel Research International, 2021, 28(8): 1019-1029.
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2021, Vol. 28 
