铸态ER8车轮钢的热变形行为及本构模型研究

采用Gleeble-1500D热模拟试验机,在变形温度为900~1250℃、应变速率为0.001~1 s^-1的条件下对铸态ER8车轮钢进行热压缩试验,得到真应力-真应变曲线。结果发现:其真应力-真应变曲线符合动态再结晶型软化机制,变形初始阶段,材料发生硬化,真应力快速增加,随着变形的继续,材料发生动态回复,加工硬化速率减缓;在材料变形过程中,材料畸变的应变储存能增加,动态再结晶激活,真应力迅速降低,后硬化及软化达到动态平衡。并分析了变形温度和应变速率对该材料高温下真应力的影响,发现真应力的大小随着变形温度的升高及应变速率的降低而减小。通过对试验数据的归纳整理得出,铸态ER8车轮钢的热变形激活能为258.4 k J·mol^-1。建立了Arrhenius双曲正弦本构方程,用作图法求解加工硬化速率,找出峰值应变及临界应变,基于此建立动态再结晶体积分数模型。其能精准地预测此材料的高温软化行为,为有限元数值模拟提供了理论基础。

Study on hot deformation behavior and constitutive model of as-cast ER8 wheel steel

The hot compression experiment of as-cast ER8 wheel steel under deformation temperature of 900-1250℃ and strain rate of 0.001-1 s^-1 was conducted by Gleeble-1500 D thermal simulation testing machine,and the true stress-true strain curve was obtained.The results show that the true stress-true strain curve conforms to the dynamic recrystallization softening mechanism.At the initial stage of deformation,the hardening of material occurs,and the true stress increases rapidly.However,as the deformation continues,the dynamic recovery of material occurs,and the work hardening rate slows down.Furthermore,in the material deformation process,the distortion strain storage energy of metarial increases,the dynamic recrystallization is activated,the true stress decreases rapidly,and the post-hardening and softening reach dynamic balance.Finally,the influences of deformation temperature and strain rate on the true stress of material at high temperature were analyzed.The true stress decreases with the increasing of deformation temperature and the decreasing of strain rate.By summarizing the experimental data,the hot deformation activation energy of as-cast ER8 wheel steel is 258.4 k J·mol^-1,and the Arrhenius hyperbolic sine constitutive equation was established.In addition,the work hardening rate was solved by the graphing method to find the peak strain and critical strain,and the dynamic recrystallization volume fraction model was established,which accurately predicted the high-temperature softening behavior of this material and provided the theoretical basis for finite element numerical simulation.