汽车用超高强度25MnB钢的热变形行为及本构方程

Thermal deformation behavior and constitutive equation ofultra-high strength 25MnB steel for automobile

在MMS-200热模拟试验机上对25MnB钢进行了单轴等温热压缩实验,得到了25MnB钢在温度为850~1150℃,应变速率分别为0.01、 1、 10和30 s^(-1),最大真应变为0.7时的真应力-真应变曲线。结果表明:在低应变速率下,材料主要软化机制为动态再结晶,高应变速率下材料变形机制为加工硬化-动态回复。通过引入Zener-Hollomon参数,利用应力-应变数据建立了修正的Arrhenius型本构方程,峰值应力状态下25MnB钢的热变形激活能为297.376 k J·mol^(-1),在峰值应力本构方程的基础上,将应变对材料常数的影响纳入本构分析中,通过对比实验数据和预测数据,使用相关系数和平均绝对相对误差评估了所建立本构方程的适用性,结果表明考虑应变补偿的本构方程对25MnB钢的流变应力有着良好的预测性。

The uniaxial isothermal compression tests of 25MnB steel were carried out on the MMS-200 thermal simulator,and the true stress-true strain curves of 25MnB steel were obtained at 850-1150℃,with the maximum true strain of 0.7,and the can strain rates of 0.01,1,10 and 30 s^(-1),respectively.The results show that the main softening mechanism of the material is dynamic recrystallization with low strain rate,and the deformation mechanism of the material with high strain rate is work hardening-dynamic recovery.A modified Arrhenius-type constitutive equation was established by introducing the Zener-Hollomon parameter and using the stress-strain data.The thermal deformation activation energy of 25MnB steel under the peak stress state is 297.376 kJ·mol^(-1).Based on the peak stress constitutive equation,the effect of strain on the material constant is included in the constitutive analysis.By comparing the experimental data and predicted data,the applicability of the established constitutive equation was evaluated using the correlation coefficient and the average absolute relative error.The results show that the constitutive equation considering strain compensation has a good prediction for the flow stress of 25MnB steel.