700℃超超临界锅炉材料GH4700合金热压缩行为

Deformation behaviors during hot compression of GH4700 alloy for 700 ℃ ultra-supercritical boilers

利用变形温度为1120～1210℃、应变速率为0.1～20 s-1以及变形量为15%～60%的等温热压缩实验研究了GH4700合金的热变形行为.通过对低温和高应变速率条件下的形变热效应进行修正,得到准确的流变曲线,推导出描述峰值应力与温度和应变速率等变形参数的本构方程,并得到GH4700合金热变形表观激活能为322 kJ.组织分析表明,动态再结晶是热变形过程中最主要的软化方式,再结晶形核方式为应变诱发晶界迁移,变形温度升高和应变速率增大均有利于再结晶形核.再结晶发展阶段,随着变形量的增大和变形温度的升高,动态再结晶比例增加,在应变速率-温度坐标中,再结晶比例等值线呈反"C"形式.采用分段函数描述了不同应变速率下GH4700合金动态再结晶晶粒尺寸与变形参数的关系.

The hot deformation behavior of nickel-based superalloy GH4700 was investigated by isothermal com pression tests at temperatures of 1120 to 1210 ℃ and strain rates of 0.1 to 20 s^-1 with deformations of 15% to 60%. The flow curves at high strain rate and low temperature were corrected in consideration of the deformation-heating effect. Accurate constitutive equations were established between peak stress and deformation parameters, i.e., temperature and strain rate. The activation energy of the alloy was determined to be 322 kJ. Microstructure analysis results show that dynamic recrystallization （DRX） is the principal softening mechanism during hot working. Strain-induced-grain boundary-migration is the nucleation mechanism, which is promoted by the increase of both temperature and strain rate. The ratio of DRX grains is increased by temperature and strain, while the iso-ratio contour of DRX exhibits an ＂anti C＂ type in the strain rate-temperature coordinate system. The relationship between DRX grain size and deformation parameters was calculated to be a piecewise function which depends on strain rate.