压下率对42CrMo钢塑性成形与微结构演化的影响

Effects of deformation degree on plastic formation and microstructure evolution of 42CrMo steel

以热物理模拟试验为基础,得到42CrMo钢发生动态再结晶的数学模型。采用热力耦合的弹塑性有限元法对42CrMo钢圆柱试样在形变温度为1 050℃、应变速率为0.1 s-1的热变形过程进行数值模拟,讨论该热变形过程中压下率对42CrMo钢试样应力/应变分布情况与微结构演化规律的影响。模拟结果表明:在热变形过程中,试样各部位变形不均匀,试样心部的等效应变最大,且变形不均匀性随着压下率增加先增大,然后趋于稳定;试样各部位的等效应力分布不均匀,其最大值一般位于心部大变形区与自由变形区和粘着区的交界处,平均等效应力在压下率约为20%时达到峰值;由于变形的不均匀性导致了动态再结晶的不等时性,动态再结晶首先发生在心部大变形区,然后,向自由变形区和粘着区延伸,而且该条件下动态再结晶临界应变约为20%;试样心部等大变形区的动态再结晶晶粒较细,而粘着区等小变形区的动态再结晶晶粒较粗大,随着压下率的增大,动态再结晶晶粒继续长大。

Based on the results of thermo-simulation experiments, the dynamic recrystallization mathematical models of 42CrMo steel were derived. The effects of the deformation degree on the evolution of the stress/strain and microstructures of 42CrMo steel cylindrical specimen at elevated temperatures were simulated by integrating the thermo-mechanical coupled finite element method with the derived microstructural evolution models. The results show that the deformation of the specimen is uneven, and the effective strain at the center of the specimen is the maximum. The degree of the deformation non-uniformity firstly increases with the increase of the deformation degree, and then one stable phase appears when the deformation degree is more than 50%. The distribution of the effective stress in the specimen is also uneven, and the maximum effective stress is located at the common boundary of the large and small deformation areas. The maximum average effective stress appears when the degree of the deformation is about 20%. The deformation non-uniformity of the specimen results in the asynchronism of the dynamic recrystallization, which occurs at the center of the large deformation area firstly, and then in the small deformation areas. The critical degree of deformation for the dynamic recrystallization is about 20%. The size of the dynamic recrystallization grain of the large deformation areas is finer than that of the small deformation areas. Additionally, the size of the dynamic recrystallization grain increases with the increase of the deformation degree.