20CrMnTiH钢唯象本构模型及动态再结晶行为

采用Gleeble-3800热模拟试验机对20CrMnTiH钢进行了等温热压缩试验,研究了该钢在变形温度为850~1 150℃、应变速率为0.01~10 s~(-1)条件下的高温热变形行为,运用数学回归方法和热力学不可逆原理,建立了20CrMnTiH钢应变补偿的唯象本构方程和动态再结晶模型,并对该应变补偿的唯象本构模型进行了有效验证。在真应力-真应变曲线中,变形温度和应变速率对20CrMnTiH钢的流变应力影响显著,表现出正的应变速率敏感性和负的温度敏感性;由本构模型计算得到的流变应力值与试验值两者之间有很好的相关性(R=0.976 64),平均相对误差为5.544 2%;在应变硬化速率与流变应力关系曲线中,利用单一参数法和求解拐点法获得了不同变形条件下动态再结晶的临界应力σ_c和临界应变ε_c值,建立了临界应力、临界应变和Zener-Hollomon参数的数学模型ε≥ε_c=0.007 9 lnZ-0.153 23,且临界应变ε_c随着温度补偿应变速率因子Z的增加而增加。

Phenomenological constitutive model and dynamic recrystallization behavior of 20CrMnTiH steel

The high temperature hot deformation behavior of 20CrMnTiH steel at deformation temperature in the range of 850-1150℃and strain rate in the range of 0.01-10 s-1 was discussed by isothermal compression test on Gleeble-3800 thermal simulation test machine. The phenomenological constitutive equation and dynamic recrystallization model of 20CrMnTiH steel were established by mathematical regression method and thermodynamic irreversible principle,and the constitutive model compensated by strain was verified effectively. The true stress-strain curve showed that the defor-mation temperature and strain rate had significant effects on the deformation temperature and strain rate on 20CrMnTiH steel and exhibited positive strain rate sensitivity and negative temperature sensitivity. There was a good correlation (R=0.97664) between the calculated flow stress values and the experimental values,and the average relative error was 5.5442%. In the hardening rate and flow stress curves,the critical stressσc and the critical strainεc value of dynamic re-crystallization under different deformation conditions by single parameter method and solving the inflection point meth-od have been obtained,and the critical stress and critical strain and Zener-Hollomon parameters of the mathematical model (ε≥εc=0.0079lnZ-0.15323) were established,and the critical strainεc increased with the increase of tempera-ture compensated strain rate factors Z.