微合金化高强钢的热变形行为及物理本构方程

Hot deformation behaviors and physical constitutive equation of microalloyed high-strength steel

采用Gleeble-1500型热模拟机对微合金化高强钢在变形温度为900~1100℃、应变速率为0.01~30 s^(-1)的条件下进行热压缩实验,得到流变应力曲线。分析高强钢的动态再结晶行为,分别采用综合考虑杨氏模量E和奥氏体自扩散系数D对绝对温度依赖性的、包含可变应力指数n的物理本构方程和蠕变应力指数为5的物理本构方程,建立实验钢应变补偿的流变应力预测模型。结果表明:随着变形温度的升高和应变速率的降低,动态再结晶更易于发生。利用应变补偿的物理本构方程预测流变应力的精度较高,其中,包含可变应力指数n的物理本构方程的预测精度(相关系数R=0.991,平均相对误差δ=4.81%)高于蠕变应力指数为5的物理本构方程(相关系数R=0.989,平均相对误差δ=6.49%)。这是由于:当物理本构方程中的蠕变应力指数为5时,材料的变形机制仅有滑移和攀移,而包含可变应力指数n的物理本构方程综合考虑了所有的变形机制,预测精度更高。

The rheological stress curves of microalloyed high-strength steel were obtained by hot compression experiment with thermal simulator Gleeble-1500 under the conditions for deformation temperature of 900-1100℃ and strain rate of 0.01-30 s^(-1),and the dynamic recrystallization behavior of the high-strength steel was analyzed.Then,a rheological stress prediction models for the strain compensation of the experimental steel were established by adapting the physical constitutive equations considering the absolute temperature dependence of Young's modulus E and austenite self-diffusion coefficient D with variable stress exponent n and creep stress exponent of 5,respectively.The results show that with the increasing of deformation temperature and the decreasing of strain rate,the dynamic recrystallization is more likely to occur,and the accuracy of predicting rheological stress using the strain-compensated physical constitutive equation is relatively high.And the prediction accuracy of the physical constitutive equation with the variable stress exponent n(correlation coefficient R=0.991,average relative error δ=4.81%)is higher than that of the physical constitutive equation with the creep stress exponent of 5(correlation coefficient R=0.989,average relative error δ=6.49%).This is because that when the creep stress exponent in the physical constitutive equation is 5,the deformation mechanism of the material is only slip and climb,but the physical constitutive equation with the variable stress exponent n considers all the deformation mechanisms comprehensively,so the prediction accuracy is higher.