铸态超级双相不锈钢S32750热加工性能

Investigation on Hot Workability of As-Cast S32750 Super Duplex Stainless Steel

为研究热变形参数对铸态超级双相不锈钢S32750热变形行为和显微组织的影响,运用Gleeble-3800热模拟试验机对S32750进行不同温度和应变速率下的高温拉伸和压缩试验。结果表明,S32750在1 000～1 200℃范围内具有较好的热塑性。在变形温度较低、应变速率较低时,流变曲线表现出不同于单相不锈钢的"类屈服平台"特征;当应变速率较高或变形温度较高、应变速率较低时,流变曲线为典型的动态再结晶特征。微观组织演变显示,铁素体和奥氏体两相都发生动态再结晶,且铁素体的再结晶先于奥氏体。降低应变速率,提高变形温度,可促进动态再结晶发生。基于热变形动力学模型建立了本构方程,表观应力指数为3.99,热变形激活能为393.75kJ/mol。S32750的高温软化机制与Zener-Hollomon(Z)参数有关,随Z参数增加,热变形峰值应力增加。

In order to investigate the hot deformation behavior and microstructure evolution of as-cast S32750 super duplex stainless steel,high temperature tensile tests and compression tests were carried out at different temperatures（900-1 200 ℃） and strain rates（0.1-25 s-1） by Gleeble-3800 thermo-mechanical simulator.High temperature tensile tests show that S32750 has good ductility from 1 000 ℃ to 1 200 ℃.The flow behavior of S32750 was investigated by high temperature compression tests.The flow curves of low temperatures and slow strain rates exhibit a particularly yield-point-elongation-like effect,which is different from single phase stainless steel.The flow curves of high strain rates or high temperatures and slow strain rates were characterized by recrystallization.The microstructure evolution shows that dynamic recrystallization（DRX） can occur in both ferrite and austenite phases,and DRX in ferrite is prior to austenite.By increasing temperature and decreasing strain rate,DRX can be enhanced.Based on this,the hot deformation equation is set up,the apparent stress exponent is 3.99,and the apparent activation energy（Q） is 393.75 kJ/mo1.Its softening mechanism varies with Zener-Hollomon parameter（abbreviated Z） in the above mentioned deformation conditions,and with increasing Z parameter,the peak stress of hot deformation increases.