Effect of Cooling Rate on Carbide Characteristics of the High Vanadium High-speed Steel

Abstract

Effect of cooling rate on carbide precipitation, morphology, size, distribution and composition of the high carbon and vanadium high-speed steel (HCVHSS) was investigated by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and electron probe micro analyzer (EPMA). The results illustrated that the as-cast microstructure of HCVHSS mainly included the carbides of primary and eutectic MC, eutectic M₂C, secondary M₂₃C₆ and the matrix of martensite, retained austenite. With the higher CR, the grain size is refined, the size and quantity of both primary MC and eutectic M₂C decreased significantly, while an increase of eutectic clustered MC was obtained. Except for the more uniform distribution of MC and M₂C, the poorer network continuity of M₂C at grain boundary and fewer M₂₃C₆ carbides in the matrix were also found. For the composition of carbides, the weaker effect of selective crystallization and more uniform distribution of carbides composition were obtained in higher CR specimen. In addition, a higher content of V and Mo in MC and M₂C respectively was found. Owing to the excellent microstructure obtained at higher CR, the hardness value of the specimen was higher too which was beneficial to the improvement of its wear resistance.