Nb的非平衡晶界偏聚动力学模拟与实验研究

摘要：Nb是现代高性能钢铁材料中重要的微合金化元素，其在晶界有强偏聚特性。采用3种Nb 空位复合体扩散系数分别对非平衡晶界偏聚进行拟合，根据铁 铌二元合金中Nb在晶界偏聚实验的EPMA测量结果筛选出最终的复合体扩散系数，并据此讨论了低温恒温温度，基体Nb含量，原奥氏体晶粒尺寸对非平衡晶界偏聚动力学的影响，得出了最符合实验结果的铌 空位复合体扩散系数公式。结果表明，在1000℃恒温过程，Nb非平衡晶界偏聚的临界时间在15min左右，临界时间常数为6.57×105。从1200℃固溶态冷却至某低温等温时，随着等温温度的升高临界时间迅速减小，Nb在晶界的最大偏聚量逐渐越小；随着基体Nb含量增加晶界Nb的最大偏聚量线性增加；随着原奥晶粒尺寸的增加临界时间逐渐增大。

Kinetic simulation and experimental study on non equilibrium grain boundary segregation of Nb

Niobium is an important microalloying element in modern high performance steels. It has a strong segregation characteristic at the grain boundaries. In this work, three kinds of Nb vacancy complex diffusion coefficients were tested by using non equilibrium grain boundary segregation kinetic model. According to EPMA measurement results of niobium segregation kinetics at the grain boundary in Fe Nb binary alloy, the final Nb vacancy complex diffusion coefficient was selected. The effects of lower isothermal temperature, matrix niobium content and prior austenite grain size on non equilibrium grain boundary segregation kinetics were discussed accordingly. The results show that the diffusion coefficient of the niobium vacancy complex is found. At an isothermal temperature of 1000℃, the critical time for the non equilibrium grain boundary segregation of niobium is about 15min, and the critical time constant is 6.57×105. When isothermal temperature increases, the critical time decreases rapidly and the maximum segregation amount of Nb at the grain boundary decreases gradually. The maximum segregation of niobium at grain boundary increases linearly with the increasing of matrix niobium content. The critical time increases gradually with the prior austenite grain size increasing.