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在Gleeble-3800热模拟试验机上通过高温等温压缩试验研究了20MND5钢在应变速率为0.001~10 s~(~(-1))、变形温度为950~1150℃的热变形行为及组织转变,研究了变形工艺对20MND5钢的热变形流动应力的影响规律,建立了其热变形本构方程。结果表明:在应变速率为0.001~0.1 s~(-1)时,20MND5钢的高温流变应力主要以动态再结晶软化机制为特征。在应变速率为1.0~10 s~(-1)时,真应力随应变量的增大而增大,但当应变速率为1.0 s~(~(-1)),变形温度达到1150℃时,发生明显的动态再结晶。综合考虑应变速率和变形温度对材料组织性能的影响,建立了基于本构方程的20MND5钢的热加工图,并确定了该钢的热变形流变失稳区及热变形过程的最佳工艺参数。分析讨论了不同区域的20MND5钢的高温变形特征,确定了20MND5钢在低温、中温及高温变形时,宜控制的应变速率及其应变量。
The hot deformation behavior and microstructure transformation of 20MND5 steel at strain rate of 0.001 ~ 10 s ~ (-1) and deformation temperature of 950 ~ 1150 ℃ were investigated by means of high temperature isothermal compression test on a Gleeble-3800 thermal simulator. The effect of deformation process on the hot deformation flow stress of 20MND5 steel was established and its thermal deformation constitutive equation was established. The results show that the high temperature flow stress of 20MND5 steel is mainly characterized by the dynamic recrystallization softening mechanism when the strain rate is 0.001-0.1 s ~ (-1). When the strain rate is 1.0 ~ 10 s ~ (-1), the true stress increases with the increase of strain, but when the strain rate is 1.0 s ~ (-1) and the deformation temperature reaches 1150 ℃, Significant dynamic recrystallization occurred. Considering the influence of strain rate and deformation temperature on the microstructure and properties of the material, a hot working diagram of 20MND5 steel based on the constitutive equation was established and the optimum technological parameters of the deformation zone and the thermal deformation of the steel were determined . The high temperature deformation characteristics of 20MND5 steel in different regions were analyzed and discussed, and the strain rate and its strain to be controlled in 20MND5 steel at low temperature, medium temperature and high temperature deformation were determined.