Lapped friction stir welding between ductile cast irons and stainless steels

Abstract

This study investigated the influence of preheating temperature and welding speed on the microstructure of dissimilar lapped friction stir welding (FSW) of ductile cast iron FCD450 and 304 stainless steel. The stainless steel was placed on FCD450, and then FSW was carried out at a tool rotational speed of 200, 400, and 600 rpm and welding speed between 1 and 10 mm/s. Preheating was conducted at 573 and 773 K. Martensitic structure was formed in HAZ of FCD450 without the preheating, while the preheating resulted in the formation of a pearlite structure. Even when the preheating was employed, however, stir zone (SZ) of FCD450 had the chill structure at a lower welding speed, because the SZ temperature exceeded the eutectic temperature. Formation of the chill structure in the SZ could be prevented at a higher welding speed. This study showed that FSW would be available as a dissimilar welding method between ductile cast iron and stainless steel.