Microstructures and their influences on tensile performance of friction stir welded joints in high aluminum low-density austenite steel

To address weldability challenges and achieve excellent tensile performance of low-density austenitic steel in friction stir welding (FSW), two low heat input parameters were used to join Fe–30Mn–9Al–0.85C steel. The results indicate that low heat input suppresses the dissolution of κ -carbides in the stir zone, while promoting the growth of grains and carbides and increasing annealing twin boundaries (ATBs) in the heat-affected zone (HAZ). The welded joints exhibited a joint efficiency of 103%. This study uncovers a mechanism – during tensile deformation in the HAZ, ATBs transformed into high-angle grain boundaries, leading to grain refinement and giving rise to the dynamic Hall–Petch effect – that enables a strategy for achieving the excellent tensile performance of FSW joints in low-density austenitic steel.