Evaluation of microstructure and properties in friction stir welded superaustenitic stainless steel

A superaustenitic stainless steel was friction stir welded using a polycrystalline cubic boron nitride tool, and then effect of microstructure on properties in the weld was examined. Friction stir welding resulted in a fine equiaxed grain structure in the stir zone, which raised the hardness, but a banded structure with a high density of intermetallic phases was yielded in the bottom of the stir zone. The amount of intermetallic phases in the bottom of the stir zone was significantly large at high rotational speed. The high rotational speed drastically reduced mechanical and corrosion properties of the weld due to the high density of intermetallic phases, while the reduction of the properties was not significant at low rotational speed. Findings of the present study suggest that low heat input friction stir welding is an effective method to produce a weld with relatively good properties in superaustenitic stainless steels.