变形参数对护环用超高氮奥氏体钢组织的影响

Effect of Deformation Parameters on Microstructure of Ultra-high NitrogenAustenitic Steel Used for Retaining Ring

采用Gleeble 3500热模拟试验机对护环用超高氮奥氏体钢进行高温压缩变形。通过金相显微镜、扫描电镜和能谱分析等手段,分析了试验用钢热变形后的显微组织形貌;运用截线法和定量金相法,确定了动态再结晶临界应力和峰值应力与Z参数间的定量关系,得到了动态再结晶晶粒尺寸和体积分数与变形条件之间的关系曲线。结果表明:试验用钢在热变形过程中,当变形程度与变形温度一定时,应变速率越低,越易发生加工状态下的动态再结晶,动态再结晶程度越大;当变形程度与应变速率一定时,变形温度越高,再结晶晶粒尺寸越大;再结晶晶粒所占体积分数越大,动态再结晶程度也越大。在热变形过程中,试验用钢晶内和晶界均有第二相析出,这些析出相为MX型复合析出相(Nb,V)N。

Gleeble 3500 high temperature thermal simulation test machine was used to conduct high temperature compression deformation of ultra-high nitrogen austenitic steel for retaining ring.By metallographic microscope,scanning electron microscope and energy spectrum analysis methods,the microstructure and morphology of the steel after thermal deformation was analyzed.Using transversal method and quantitative metallography,the quantitative relationship between the critical stress and peak stress of dynamic recrystallization and Z parameter was determined.The results show that during the hot deformation of the test steel,when the degree of deformation and the deformation temperature are fixed,the lower the strain rate,the easier dynamic recrystallization occurs and the greater the degree of dynamic recrystallization.When the deformation degree and strain rate are fixed,the higher the deformation temperature,the larger the recrystallized grain size,the larger the volume fraction of recrystallized grains,the greater the dynamic recrystallization degree.During the hot deformation,the second phase precipitates appear in the crystal grains and grain boundaries of the test steel.These precipitates are MX-type composite precipitates(Nb,V)N.