Microstructure–Mechanical Property Correlations and Tensile Elastoplastic Behavior of Similar Rotary Friction Welded 304L/316L Stainless Steel Joints

This work elucidates the relationship between welding parameters, microstructure evolution, and tensile elastoplastic behavior in 304L and 316L stainless steels, contributing to fundamental understanding of strain hardening and grain refinement mechanisms. Welding is performed under varying friction (5, 6, 8, 10 s) and forging (5, 8, 10 s) times. Grain refinement occurs in the welding zone (WZ) due to dynamic recrystallization. In 316L, WZ grain size reduces from 8.38 μm to 3.87 μm with longer friction times, while in 304L, it drops from 8.57 μm to 5.36 μm at 6 s and then stabilizes between 5.60 and 5.65 μm for longer friction times. This grain refinement leads to increased microhardness in the WZ, and the heat‐affected zone of 316L shows further hardness increase due to its molybdenum content. Tensile testing shows continuous yielding in both steels: 316L exhibits higher stiffness and strength, while 304L displays better ductility. The proportional limit ( σ 0 ) follows the Hall–Petch relationship in both materials, and for 316L, microhardness also correlates with grain size. While base metals show three distinct strain hardening stages, rotary friction welding joints exhibit only stages II and III. Notably, at 5 s of friction time, enhanced strain hardening is observed. Fractography reveals ductile fracture characteristics in all joints.