Effect of niobium and austenitizing temperature on the microstructures and properties of spray-deposited AISI M3:2 high speed steel

The microstructure and properties of niobium-containing AISI M3:2 high speed steels (HSSs) fabricated by spray forming and traditional casting have been investigated. The results show that fine and uniformly-distributed grains without macrosegregation appeared in the as-deposited HSSs that differ from those of as-cast HSSs. Nb mostly appears in primary MC carbides, whereas it contributes less to the formation of M6C carbides. The high stabilization of Nb-rich MC carbides can pin the grain boundaries during high-temperature austenitizing process, thus conferring a fine grains and raising the content of dissolved alloying elements. Enhanced precipitation strengthening and fine dispersion of NbC carbides throughout the matrix contribute to the high hardness and red hardness of Nb-containing HSS.