Microstructures and Mechanical Properties of Friction Stir Welded 2.25Cr–1Mo Steel

Abstract

The present study was carried out to evaluate the microstructural and mechanical properties of a friction stir welded 2.25Cr–1Mo steel. For this work, friction stir welding (FSW) was performed at a tool rotation speed of 300 and 700 rpm and a traveling speed was fixed at 40 mm/min. Phase transformation of the microstructure in the joint was investigated by optical microscopy and scanning electron microscopy. Vickers hardness and tensile test were used to evaluate the mechanical properties of the joints. In the Stir Zone (SZ), fine martensite was observed, indicating that phase transformation and dynamic recrystallization occurred during FSW. The microhardness of the SZ was higher than that of the base metal (BM) due to the phase transformation. After the tensile test, the FSW joint was fractured in the BM region and showed the same yield strength (YS) and ultimate tensile strength (UTS) as that of the BM.