Characteristics of Microstructure, Microhardness, and Oxidation of FSW and MIG Welded Steels

The SUS 409L stainless steel plates were joined by FSW and MIG welding techniques. The welding electrode used for MIG welding was SUS 430 stainless steel. In the case of the MIG welding, the hardness was the highest in the weld metal, decreased in HAZ, and rose slightly in the base metal. The weld metal had the highest hardness owing to the large residual stress, and its refined microstructure. The weld metal had better oxidation resistance than the HAZ and base metal because of its high Cr content compared with the HAZ and base metal. In the case of the FSW, the microstructure consisted of the stir zone, thermo-mechanically affected zone (TMAZ), and base metal. The stir zone had a relatively high hardness, owing to intense plastic deformation and dynamic recrystallization. It had better oxidation resistance than the base metal.