Effect of post-welded heat treatment on the microstructures and mechanical properties of friction stir welded joint of high-nitrogen austenitic stainless steel

Friction stir welding is applied to a high-nitrogen austenitic stainless steel. Loss of nitrogen and other precipitates are not found during the process of friction stir welding. In the as-welded joint, the nugget zone is consisted of fine grains with high fraction of low angle boundaries. Significant differences of microstructure are observed along the transverse direction of as-welded joint. Further, the post-weld heat treatment joint is shown an effectively weaken difference. The differences of microstructure have a significant impact to the mechanical property. In the as-welded, the distribution of different microstructures leads to overmatching characteristic with higher strength but lower ductile. In the post-weld heat treatment joint, the strength matching mode is changed. The elongation of the joint is increased companied with enhanced strength. © 2015 Journal of Mechanical Engineering.