18CrNiMo7-6齿轮钢的热压缩变形行为及显微组织演变

Hot Compression Deformation Behavior and Microstructure Evolution of 18CrNiMo7-6 Gear Steel

采用热模拟方法研究了18CrNiMo7-6齿轮钢在变形温度900~1150℃、应变速率0.01~5 s-1条件下的热压缩变形行为;建立了基于Arrhenius模型的全应变本构方程,采用该方程对流变应力曲线进行预测;根据动态材料模型绘制热加工图,并结合热加工图系统地研究显微组织演变特征。结果表明:试验钢的峰值应力随应变速率的增加或变形温度的降低而增大,动态回复和动态再结晶是热变形过程中的主要软化机制;采用建立的全应变本构方程预测得到流变应力曲线与试验结果基本吻合,预测真应力与试验结果的相对误差小于4.715%,说明该模型可以精确地模拟18CrNiMo7-6齿轮钢的热压缩变形行为。试验钢的适合热加工工艺参数为变形温度1050~1150℃、应变速率0.1~1 s^(-1),此时组织为均匀细小的再结晶晶粒,晶粒尺寸在5~15μm。随着变形温度的升高或应变速率的降低,原始奥氏体晶粒不断被动态再结晶晶粒取代,且动态再结晶程度和再结晶晶粒尺寸增大。

The thermal simulation method was used to study the hot compression deformation behavior of 18CrNiMo7-6 gear steel at temperatures of 900-1150°C and strain rates of 0.01-5 s-1.The full strain constitutive equations based on the Arrhenius model were established,and the flow stress curves were predicted by the equations.The hot working maps were drawn according to the dynamic material model and the microstructure evolution characteristics was systematically studied in conjunction with the hot working maps.The results show that the peak stress of the test steel increased with the increase of strain rate or the decrease of deformation temperature.Dynamic recovery and dynamic recrystallization were the main softening mechanisms in hot deformation.The flow stress curves predicted by the established full-strain constitutive equation were basically consistent with the test results,and the relative error between predicted true stresses and test results was less than 4.715%,indicating that the equation could accurately simulate the hot compression deformation behavior of 18CrNiMo7-6 gear steel.The suitable hot working parameters for the test steel were deformation temperatures of 1050-1150℃and strain rates of 0.1-1 s^(-1),and the microstructure was uniform and fine recrystallized grains with grain size of 5-15μm.With the increase of deformation temperature or the decrease of strain rate,the original austenite grains were replaced by dynamic recrystallization grains,and the degree of dynamic recrystallization and the size of recrystallization grains increased.