Bao Shun, Feng Han, Song Zhigang, He Jianguo, Wu Xiaohan, Gu Yang
Central Iron & Steel Research Institute Co., Ltd., Beijing 100081, China.
Materials (Basel). 2025 Apr 29;18(9):2030. doi: 10.3390/ma18092030.
In this study, we investigated the two-phase hardening behavior and microstructural evolution of S32750 duplex stainless steel during the tensile deformation process. The analysis was conducted using in situ electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and microhardness testing. It was observed that strain transfer occurred between the two phases in the position away from the fracture. The ferrite phase exhibited softening, while the austenite phase underwent hardening. In the region less than 1 mm from the fracture site, both phases experienced a rapid hardening, with the maximum hardness difference between the two phases near the fracture reaching approximately 45 HV. In situ EBSD results indicate that the kernel average misorientation (KAM) value for the ferrite phase consistently exceeds that of the austenite phase during the initial stages of deformation. Conversely, in the final stages of deformation, the KAM value for austenite surpasses that of ferrite. In the initial stage of deformation, the type of grain boundaries in both phases remains largely unaltered. However, in the later stages of deformation, there is a marked increase in the number of small-angle grain boundaries within ferrite, which become approximately three times that of the large-angle grain boundaries. As deformation progresses, the maximum orientation distribution density of the ferrite phase is reduced by approximately 50%, with the preferred orientation shifting from the {100} plane to the {111} plane. In contrast, the orientation distribution of the austenite remains relatively uniform, with no significant change in the maximum orientation distribution density observed. This indicates that after substantial deformation, the rotation of ferrite grains significantly increases the deformation resistance, whereas the austenite phase continues to harden. This differential behavior leads to the continuous accumulation of strain at the phase boundaries, ultimately causing cracks to form at these boundaries and resulting in the sample's fracture.
在本研究中，我们研究了S32750双相不锈钢在拉伸变形过程中的两相硬化行为和微观结构演变。使用原位电子背散射衍射（EBSD）、扫描电子显微镜（SEM）和显微硬度测试进行了分析。观察到在远离断裂处的位置，两相之间发生了应变传递。铁素体相表现出软化，而奥氏体相则发生硬化。在距断裂部位小于1毫米的区域，两相均经历快速硬化，断裂附近两相之间的最大硬度差达到约45 HV。原位EBSD结果表明，在变形初始阶段，铁素体相的晶粒平均取向差（KAM）值始终超过奥氏体相。相反，在变形的最后阶段，奥氏体的KAM值超过铁素体。在变形初始阶段，两相中的晶界类型基本保持不变。然而，在变形后期，铁素体内小角度晶界的数量显著增加，约为大角度晶界数量的三倍。随着变形的进行，铁素体相的最大取向分布密度降低了约50%，择优取向从{100}面转移到{111}面。相比之下，奥氏体的取向分布保持相对均匀，未观察到最大取向分布密度有显著变化。这表明在大量变形后，铁素体晶粒的旋转显著增加了变形抗力，而奥氏体相继续硬化。这种差异行为导致相界处应变不断积累，最终导致这些边界处形成裂纹并导致样品断裂。
