Strength improvement of laser beam welded joints in cold worked high-manganese-steel by means of deep rolling

High manganese steels offer a great potential for lightweight and resource efficient design in vehicle manufacturing due to their excellent controllability of the mechanical properties by cold forming based on the TWIP effect. Laser beam welding results in a significant softening and strong loss of hardness and strength in the weld metal and the heat affected zone due re-crystallization. The aim of the current study is to investigate the work hardening effect and strength improvement of welded joints by means of deep rolling. The weld zone of joints made in the ultra-high strength steel X30MnCrN16-14 was characterized before and after deep rolling by an analysis of hardness, microstructure, surface topology and residual stress. Finite Element were performed to quantify penetration of the work hardening effect by deep rolling. Significant increase of hardness as well as the formation of deformation twins indicate a restoration of strength in the weld zone.