Effect of post-weld heat treatment on microstructures and properties of friction stir welded joint of 32Mn–7Cr–1Mo–0·3N steel

In this study, the microstructures and mechanical properties of friction stir welded and post-weld heat treated joints of 32Mn–7Cr–1Mo–0·3N steel were investigated. Significant microstructural and mechanical property gradients were found along the transverse directions of the as welded joint. These gradients led to overmatching characteristic with higher strength but lower ductile than base material. The post-weld heat treatment effectively reduced the gradient characteristics in the as welded joint. Consequently, the mechanical property of the joint was nearly restored to the level of base metals. However, the abnormal grain growth was observed in the heat affected zone of the post-weld heat treated joint. The possible mechanism was discussed in term of the evolution of atom segregation at grain boundaries.