新型含铝奥氏体耐热合金Fe-20Cr-30Ni-0.6Nb-2Al-Mo的动态再结晶行为

摘要

Isothermal compression tests at a temperature of 950-1 100 ℃ and strain rates ranging from 0.01 to 1 s 1 were performed on alumina-forming austenitic (AFA) alloy Fe-20Cr-30Ni-0.6Nb-2Al-Mo to reveal the hot deformation characteristics.The evolutions of microstructure and nucleation mechanisms of dynamic recrystallization (DRX) were analyzed combined with the technique of OM,EBSD and TEM.The regression method Was adopted to determine the thermal deformation activation energy,apparent stress index,and to construct a thermal deformation constitutive model.The results show that the flow stress is strongly dependent on deformation temperature and strain rate,which increases with decreasing temperature and increasing strain rate.The DRX phenomenon occurred more easily at comparably higher deformation temperatures or lower strain rates.Based on the method for solving the inflection point via cubic polynomial fitting of lnθ-ε curves,the critical strain (εc) during DRX were precisely predicted.The nucleauon mechanisms of DRX during thermal deformation mainly included the strain-induced grain boundary (GB) migration,grain fragmentation,and subgrain coalescence.%在Gleeble-3500热力模拟试验机上对一种新型奥氏体耐热合金(Fe-20Cr-30Ni-0.6Nb-2Al-Mo)进行单道次热压缩实验,结合OM、EBSD及TEM等表征手段,研究了该合金在950～1 100℃和0.01～1 s-1热变形参数下的动态再结晶行为,采用回归法确定了合金的热变形激活能和表观应力指数,并以此构建其高温本构模型.实验结果表明,新型奥氏体耐热合金的应力水平随变形温度的升高而降低,随应变速率的增大而升高;动态再结晶行为更易发生在较高变形温度或较低应变速率下.采用lnθ-ε曲线的三次多项式拟舍求解临界再结晶拐点的方法,较准确地预测了合金的动态再结晶临界点.此外,归纳出该合金在动态再结晶过程中的形核机制,主要包括应变诱导晶界迁移、晶粒碎化以及亚晶的合并.