熱間圧延HSSロールの黒皮の生成と脱落機構

抄録

To shorten the roll transfer time and improve the surface quality of the hot-rolled products, the black oxide layers formed on the roll surface were analyzed by means of SEM, WDS and X-ray diffraction techniques, for two rolls with different W and Mo contents. The observation of the near-surface region of the HSS roll with more W and Mo additions indicated that microcracks formed in the black oxide layers on the roll surface, and easily propagated along needle-shaped M₂C type primary carbides segregated in the intercellular regions. This led to further crack growth along M₂C carbides, and then to the final falling of the black oxide layers from the roll surface. On the other hand, in the HSS roll with less W and Mo additions, the black oxide layers were hardly evident, since they were fallen off easily from the roll surface. These results were interpreted by the molybdenum addition which affected the amount of M₂C carbides and the black oxide formation, suggesting the existence of a proper molybdenum content to achieve the stable black oxide layers on the HSS roll surface.