18.7Cr-1.0Ni-5.8Mn-0.2N节Ni型双相不锈钢的大变形热压缩软化行为

在1123~1423 K、0.1~10 s^-1条件下对18.7Cr-1.0Ni-5.8Mn-0.2N节Ni型双相不锈钢进行70%大变形量热压缩研究。利用OM、SEM和EBSD分析热变形组织。结果表明,铁素体动态再结晶(DRX)主要发生在1123 K较低变形温度,随应变速率增大,晶粒细化程度增加,晶粒不均匀程度减小。应变速率对铁素体DRX影响较大,而奥氏体DRX对变形温度更加敏感。在1223 K、10 s^-1条件下,铁素体相发生了以小角度晶界(LAGB)向大角度晶界(HAGB)转变的连续动态再结晶(CDRX),而在1323 K、0.1 s^-1条件下,奥氏体相以不连续动态再结晶(DDRX)为主。低应变速率条件下升高温度易诱发DDRX,而在高应变速率条件下易发生CDRX。在高温低应变条件下,奥氏体相晶粒取向主要为(001)和(111)再结晶织构,而铁素体相在(001)和(111)织构之间存在竞争关系。拟合获得临界应力(应变)并确定了其与峰值应力(应变)的关系。随着应变增加,热加工失稳区缩小,且稳定区逐渐向高温高应变速率方向移动,1323~1423 K、0.01~6.05 s^-1的热参数条件最适合热加工。

Softening Behavior of 18.7Cr-1.0Ni-5.8Mn-0.2N Low Nickel- Type Duplex Stainless Steel During Hot Compression Deformation Under Large Strain

It is difficult to form the precipitated phase of duplex stainless steel(DSS)with low nickel content,and a low Cr content of 18.7%(mass fraction)during hot working.However,the stability of the austenite phase changes by substituting Mn for Ni,which can increase the difference between the softening mechanisms of the two phases under high temperature and deformation conditions.Under a temperature and strain rate of 1123-1423 K and 0.1-10 s^-1,respectively,the large thermal compression deformation behavior(70%)of 18.7 Cr-1.0 Ni-5.8 Mn-0.2 N DSS was investigated.The thermal deformation microstructures were analyzed by OM,SEM,and EBSD.The results show that the dynamic recrystallization(DRX)of the ferrite phase mainly occurred at a lower deformation temperature of 1123 K,and that the degree of grain refinement increased,and the degree of grain inhomogeneity decreased with an increase instrain rate.The strain rate was observed to have a large impact on the ferrite phase DRX,while the austenite phase DRX was more sensitive to deformation temperature.The ferrite phase underwent continuous dynamic recrystallization(CDRX)with the transition from low-angle to high-angle grain boundaries under deformation at 1223 K and 10 s^-1,while the austenite phase was dominated by discontinuous dynamic recrystallization(DDRX)deformed at 1323 K and 0.1 s^-1.DDRX can be easily induced by increasing the temperature at a low strain rate,while CDRX can be induced at a higher strain rate.The crystal orientation of the austenite phase is mainly characterized by the recrystallization texture of the(001)and(111)planes at higher temperatures and lower strain rates.In the ferrite phase,there is a competitive relationship between the recrystallization texture of the(001)and(111)planes.The critical stress(strain)was obtained by data fitting and its relationship with the peak stress(strain)was determined.As the strain increased,the flow instability domain of hot compression decreased,and the stability zone gradually moved toward higher temperature and strain rate.Furthermore,the optimum hot working conditions,1323-1423 K and 0.01-6.05 s^-1,were obtained.