Heat Treatment Response of Nb Alloyed Cast High Speed Tool Steel

Abstract High speed steels (HSS) are iron-based alloys containing Fe-C-X where X represents a group of alloying elements which includes Cr, W, Mo, V, and Co, respectively. A major issue associated with these steels is the formation of a network of eutectic phases at the end of solidification. This network, beside the primary MC, which contains austenite and lamellar M2C or skeleton M6C carbides reduces the toughness and the hardness. In this study a new niobium alloyed HSS is designed that is different from known high speed steels. The objective is to produce cast high speed tool steel without the need for hot working. The microstructure was modified by niobium additions and an optimized heat treatment. Niobium helps to control precipitation of monocarbides from the liquid phase, thus decreasing the formation of brittle interdendritic eutectic carbide films and increasing toughness. Microstructure and mechanical properties of as-cast and heat treated samples of this modified steel were characterized by op...