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中国物理学会期刊

高Cr铸铁中M7C3碳化物与奥氏体共生长的元胞自动机模拟

CSTR: 32037.14.aps.70.20210725

Cellular automaton simulation on cooperative growth of M7C3 carbide and austenite in high Cr cast irons

CSTR: 32037.14.aps.70.20210725
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  • 高铬铸铁中M7C3碳化物大小适中、弥散均匀分布, 有利于提高合金的耐磨性. 为分析凝固过程中M7C3碳化物晶粒在基体中的形貌及分布、M7C3碳化物与奥氏体晶粒生长的相互作用、引起的溶质偏聚对最终M7C3碳化物粒径分布的影响, 本文开发了Fe-C-Cr三元合金小面晶M7C3碳化物与奥氏体晶粒共生长的二维微观元胞自动机模型, 模型中加入潜热释放对凝固过程温度场的影响, 由C, Cr两溶质界面扩散共同确定晶体生长速度, 由凝固路径数据表插值获取液相元胞的溶质平衡浓度, 设定M7C3碳化物邻胞结构并优化形状因子来保持M7C3碳化物小面晶形貌, 模拟了Fe-4%C-17%Cr三元合金(C和Cr的质量分数分别为4%和17%)初生M7C3碳化物和共晶奥氏体晶粒的生长演变过程. 研究表明, M7C3碳化物和奥氏体晶粒各自的生长速度随着界面液相中C, Cr溶质的超饱和度和贝克列数的增大而增大; 随着奥氏体的析出和晶粒生长, M7C3碳化物晶粒的生长速度明显增快; 当奥氏体晶粒逐渐接触并包围M7C3碳化物晶粒时, 两相晶粒生长速度逐渐降低. 凝固过程中, 奥氏体晶粒生长向外排出C, Cr溶质, 与吸收C, Cr溶质生长的M7C3碳化物晶粒互补, 致使二者生长互相促进, 最终奥氏体晶粒包围M7C3碳化物晶粒生长. 预测的冷却曲线与实验冷却曲线变化趋势相符; 最终凝固组织形貌和M7C3碳化物体积分数与实验相符; 剩余液相、奥氏体中C, Cr溶质浓度演变也与Gulliver-Scheil, Partial Equilibrium, Lever Rule模型预测结果相符.

     

    M7C3 carbide’s amount, size, morphology and distribution in the microstructure contribute much to the wear resistance of high chromium cast irons. In the present paper, a two-dimensional microscopic cellular automaton model for the growth of the faceted M7C3 carbide together with the austenitic dendrite grains in an Fe-4%C-17%Cr ternary alloy is developed to obtain the evolution of M7C3 carbide grain morphology, the concentration redistribution and their interaction during the growth of M7C3 carbide and austenite grains, and also the total influence on the final M7C3 carbides’ size. The model includes the effect of latent heat release on the temperature drop. The grain growth velocity is determined by both the diffusion of C solute and the diffusion of Cr solute at the S/L interface. The equilibrium concentration in liquid cells is interpolated from the tablulated solidification path which is prescribed by Gulliver-Scheil approximation coupling with the thermodynamic equilibrium calculation. The morphology of the faceted M7C3 carbide is maintained through setting its neighborhood relations and optimizing its shape factor at grain growth. The results show that the individual grain growth velocity for M7C3 carbide and austenite increases with the increase of the supersaturation and Peclet number of solute C and Cr. The austenite precipitation and grain growth obviously speed up the growth velocity of M7C3 carbide grains. While with the austenite grains gradually touching and enveloping the M7C3 carbide grain, the growth velocities for both kinds of grains decrease. The rejection of solute C and Cr during austenite grain growth complements the absorption of solute C and Cr during M7C3 carbide grain growth, thus promoting their growth. The predicted cooling curve fits with the evolution tendency of the experimental one. The predicted final solidification microstructure and M7C3 carbide amount in volume fraction are in agreement with the experimental ones. Furthermore, both C solute concentration distribution and Cr solute concentration distribution in both residual liquid and austenite are consistent with the predictions by the Gulliver-Scheil, partial equilibrium and lever rule model.

     

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