Characterization of friction stir welded multilayered steel

This study investigates the influence of the welding parameters on the temperature evolution and the mechanical properties of friction stir butt welded multilayered steel consisting of 15 alternating layers of SUS301 austenitic stainless steel and SUS420J2 martensitic stainless steel with a total thickness of 1.2mm. Large temperature asymmetries between the advancing and retreating side were noticed and a temperature increase was observed as the revolution pitch decreased and the down force increased. With optimized welding parameters defect free welds with an ultimate tensile strength (UTS) of 1240MPa (90% joint efficiency) and a fracture elongation of 13% could be produced. In this case, fracture occurred in the heat affected zone as a result of a very pronounced hardness drop in the martensitic layers. By applying a post-weld heat treatment, the mechanical properties could be enhanced to 1310MPa UTS and a fracture elongation of 22%. This corresponds to a joint efficiency of 95%.