低碳马氏体不锈钢热变形行为及本构方程

Hot deformation behavior and constitutive equation of low-carbon martensitic stainless steel

为研究低碳马氏体不锈钢的热变形行为,利用Gleeble-3800热模拟试验机对该材料进行不同温度的压缩变形试验,利用流变应力曲线构建了基于Arrhenius双曲正弦模型的本构方程,并建立试验材料的热加工图,最后对比分析试验材料在不同变形条件下的显微组织。结果表明,材料在高变形温度与低应变速率下变形时主要发生动态再结晶现象,在低变形温度与高应变速率下变形时主要发生加工硬化现象,流变应力的理论值与实测值的线性相关系数为0.995 5,验证了本构方程的准确性;结合热加工图分析和显微组织观察,得出该材料的失稳工艺窗口区域为变形温度1 020~1 120℃、应变速率0.01~1 s^(-1);材料的最佳工艺窗口区域为变形温度900~1 150℃、应变速率0.003~0.01 s^(-1)。变形温度的提高有利于将粗大变形组织逐渐转变成细小的等轴组织,应变速率的降低同样有利于发生动态再结晶,但过低则会延长变形时间,导致再结晶晶粒逐渐长大与粗化。

In order to study the thermal deformation behavior of low carbon martensitic stainless steel,used Gleeble-3800 thermal simulation testing machine to carry out compression deformation experiments at different temperatures for this material.The constitutive equation was constructed by using Arrhenius hyperbolic sine equation,and the hot working diagram based on dynamic material model was constructed.Finally,the microstructures under different deformation conditions were compared and analyzed to reveal the influence of hot deformation process on the microstructure.The results show that the deformation of the material at high deformation temperature and low strain rate is dominated by dynamic recrystallization,and the deformation at low deformation temperature and high strain rate is dominated by work hardening.The linear correlation coefficient between the theoretical value and the measured value of flow stress is 0.9955,which verifies the accuracy of the constitutive equation.Combined with the analysis of the hot working diagram and the observation of the microstructure,it is concluded that the unstable deformation process window of the material is the deformation temperature 1020-1120℃,the strain rate 0.01-1 s^(-1),and the optimal hot deformation process window of the material is the deformation temperature 900-1150℃,the strain rate 0.003-0.01 s^(-1).The increase of deformation temperature is conducive to the gradual transformation of coarse deformation structure into fine equated structure,and the decrease of strain rate is also conducive to the occurrence of dynamic recrystallization,but the low strain rate prolongs the deformation time,and finally leads to the gradual growth and coarsening of recrystallized grains.