Development of new additive for grain refinement of austenitic stainless steel

Recently, a new additive for grain refinement of Ni based superalloys(1,2) has been developed. In those studies, it was considered that niobium carbide in Ni-Nb-C alloy additives would act as nuclei on the solidification of Ni based superalloys. It is known that the crystallographic characteristics of iron are quite similar to those of nickel. Thus, it was expected that niobium carbide would act as a grain refiner for iron base alloys, especially for austenitic steels. In this study, the effect of the additives on the microstructure of SUS316 steel was examined in various experimental conditions. The grain size of SUS316 specimens without inoculation was similar to 2700 mu m. On the other hand, when NbC containing alloy additives were added into the SUS316 melt, fine equiaxed grains were observed and the grain size of the specimen was significantly reduced to similar to 200 mu m.