Abstract:
High-speed steel (HSS) provides superior wear resistance and high surface quality of rolled-steel products. In this study, the
influence of niobium addition on the solidification behavior and microstructure of high-speed steel rolls and their impact on
the roll’s hardness and wear resistance were investigated by a combination of thermodynamic simulations of solidification
using ThermoCalc, optical and scanning microscopy and hardness testing. The study was conducted on two centrifugal-cast
commercial high-vanadium high-speed steel sleeves whose compositions differed in niobium content. Thermodynamic
simulations showed that niobium promotes the precipitation of proeutectic Nb-rich MC carbide during solidification. Microscopic
observations showed that the proeutectic carbide promotes carbide dispersion in the microstructure. This was found
to improve the microhardness of the martensitic matrix and counteract softening during repeated tempering treatment. The
addition of less than 2 wt.% Nb in the HSS roll yielded better hot hardness as a result of the roll’s better microstructural
integrity and response to HT. The conclusion was that Nb-containing HSS rolls can be produced for the hot-rolling stands
that operate at higher rolling force and temperature if the cost-benefit analysis is favorable.
