Thermodynamic calculation and experimental analysis on equilibrium precipitation phase in 2Cr12Ni4Mo3VNbN steel
LIU Shuai1,2, LÜ Zhi-qing1, ZHAO Ji-qing2, YANG Gang2, XIN Rui-shan3, YU Zhan-yang3
1. Key Laboratory of Advanced Forging and Stamping Technology and Science, Ministry of Education, Yanshan University, Qinhuangdao 066004, Hebei, China; 2. Special Steel Research Institute, General Iron and Steel Research Institute Co., Ltd., Beijing 100081, China; 3. Ansteel Beijing Research Institute Co., Ltd., Beijing 102209, China
Abstract：In order to analyze the influence of the main equilibrium precipitated phase and alloying element content in the 2Cr12Ni4Mo3VNbN steel on the precipitation behavior of the precipitated phase, the equilibrium phase diagram of 2Cr12Ni4Mo3VNbN steel was calculated by Thermo-Calc thermodynamic software when all elements in the composition range were median, and the equilibrium phase diagram of steel when the content of C, Cr, Mo, Nb, and N changed was calculated. To verify the reliability of thermodynamic calculations, XRD, SEM and TEM analysis methods were used to identify the types of precipitates in the heat-treated 2Cr12Ni4Mo3VNbN steel. The results show that the equilibrium precipitated phases in steel are MX phase, M23C6, M6C, Z phase and Laves phase. Under thermodynamic equilibrium conditions, MX phase transforms into Z phase at 850 ℃, and M6C transforms to Laves phase at 787 ℃. However, in the heat treatment process, due to the short holding time and the faster cooling rate, the above conversion process will not occur, so the main precipitated phases in the steel are MX phase, M23C6and M6C. The types of equilibrium precipitates are basically consistent with the experimental results of microstructure observation and phase analysis. There are large-scale primary MX phases and nano-level MX phases in the MX phase. MX phase is mainly affected by Nb and N. The precipitation amount increases with the increase of N content, and the precipitation temperature increases with the increase of Nb content. The precipitation temperature of M23C6 phase increases with the increase of C content, and the precipitation amount increases with the increase of C content. The precipitation temperature of M6C decreases with the increase of Cr content, and increases with the increase of Mo content. Within the composition range, the element control principle is to increase the C content to increase the precipitation strengthening effect of M23C6, reduce the Cr content to avoid entering the δ-Fe phase area during hot working, reduce the Mo content to reduce the precipitation tendency of the Laves phase, reduce the Nb content to Lower the precipitation temperature of the primary MX phase, the N content needs to take an intermediate amount to reduce the precipitation of the primary MX phase, and increase the precipitation of the dispersed fine MX phase in the low temperature stage.
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2022, Vol. 57 
