Abstract The mechanical properties of the G115/Sanicro25 dissimilar steel welded joints were characterized by room temperature tensile and microhardness. The microstructures of fine-grain heat affected zone (FGHAZ) and base metal (BM) in the G115 steel side were characterized by optical microscopy, SEM, TEM, and XRD. The results show that as the strain increases, weld beam first yields and hardens, the stress on the specimen is further increased, then Sanicro25 steel yields and hardens, and G115 steel yields finally, the specimen broken in the FGHAZ of G115 steel side. The FGHAZ of G115 steel side softens after post-weld heat treatment (PWHT). The size of the heat-affected zone (HAZ) on the G115 side after welding is 3.7 mm. After PWHT, dynamic recovery occurs in the FGHAZ of the G115 side. The precipitates increase, martensite laths are polygonal, dislocation density is reduced, residual austenite disappears. The FGHAZ with large residual stress after welding undergoes stress relaxation during PWHT. Residual stress in the FGHAZ is reduced, the dislocation density is reduced, which reduces the effect of dislocation strengthening and martensite lath strengthening. The strength of the FGHAZ is lowered than BM.

中文翻译：

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G115/Sanicro25异种钢焊接接头焊后热处理后细晶粒热影响区软化

摘要 用室温拉伸和显微硬度表征G115/Sanicro25异种钢焊接接头的力学性能。通过光学显微镜、SEM、TEM和XRD对G115钢侧细晶粒热影响区（FGHAZ）和母材（BM）的显微组织进行表征。结果表明，随着应变的增加，焊缝首先屈服硬化，试样上的应力进一步增加，然后Sanicro25钢屈服硬化，最后G115钢屈服，试样在G115钢侧的FGHAZ断裂。G115 钢侧面的 FGHAZ 在焊后热处理 (PWHT) 后软化。焊接后G115侧的热影响区（HAZ）尺寸为3.7mm。PWHT 后，G115 侧的 FGHAZ 发生动态恢复。析出物增多，马氏体板条呈多边形，位错密度降低，残余奥氏体消失。焊后残余应力较大的 FGHAZ 在 PWHT 过程中会发生应力松弛。FGHAZ内残余应力降低，位错密度降低，降低了位错强化和马氏体板条强化的效果。FGHAZ 的强度低于 BM。