Effects of Niobium on Microstructure, Hardness and Wear Behavior for High-Speed Steel Rolls

In order to refine the microstructure and improve the performance of high-speed steel (HSS) roll, the effects of Nb addition on the microstructure, hardness, and wear behavior were evaluated. The results show that adding Nb raises the precipitation temperature of NbC, which is even higher than the liquidus temperature. The NbC precipitates are accompanied by alloying elements such as Mo and V, which decreases the C and alloying element contents in the liquid phase. The variation of the content of C and alloying elements and refined austenite dendrites further refine the microstructure of the eutectic carbides of M6C, M2C, and Cr7C3. The refined as-cast microstructure increases the hardness of cast HSS rolls. However, a decrease in the content of C in austenite weakens the precipitation strengthening effect after heat treatment and results in a slight decrease of the hardness of HSS rolls with the increase of the addition of Nb. The refinement of microstructure, especially primary carbides, improves the continuity and uniformity of oxide film formed on the wear surface, which efficiently retards the wear of the matrix and improves the wear resistance of HSS rolls.