SA508Gr.4N钢热变形过程微观组织演变及流变应力模型

利用Gleeble-1500D热模拟试验机研究Ni-Cr-Mo系低合金SA508Gr.4N钢在变形温度为850~1200℃,应变速率为0.001~1 s^-1,真应变为0.9条件下的等温热变形行为,建立包含动态回复和动态再结晶的基于物象的流变应力模型与动态再结晶晶粒尺寸模型,并提出避免粗大晶粒组织遗传性的适宜锻造工艺。结果表明:随着变形温度的升高,应变速率的降低,动态再结晶体积分数和晶粒尺寸逐渐增加;SA508Gr.4N钢的真应力-真应变曲线具有明显的不连续动态再结晶现象;通过实验值和模型预测值对比可得流变应力模型的相关系数(R)及平均相对误差(MRE)分别为0.998和4.76%,动态再结晶晶粒尺寸模型的相关系数(R)及平均相对误差(MRE)分别为0.991和8.69%,两个模型均具有较高的准确性。

Microstructure evolution and flow stress modeling of SA508Gr.4N steel during hot deformation process

The isothermal deformation behavior of Ni-Cr-Mo low alloy SA508 Gr.4 N steel at deformation temperature of 850-1200℃,strain rate of 0.001-1 s^-1,and true strain of 0.9 was studied by using Gleeble-1500 D thermal simulation testing machine.The physically based flow stress model including dynamic recovery and dynamic recrystallization and the dynamic recrystallization grain size model were established,and the suitable forging process to avoid the coarse grain structure heredities was put forward.The results show that as the deformation temperature increases and the strain rate decreases,the dynamic recrystallization volume fraction and grain size gradually increase;the true stress-true strain curve of SA508 Gr.4 N steel has an obvious discontinuous dynamic recrystallization phenomenon;by comparing the experimental value with the predicted value of the model,the correlation coefficient(R)and mean relative error(MRE)of the flow stress model are 0.998 and 4.76%,respectively,and the correlation coefficient(R)and mean relative error(MRE)of the dynamic recrystallization grain size model are 0.991 and 8.69%,respectively.The two models have high accuracy.