Effects of roll surface deteriorations on scale defect in hot rolling

Roll surface deteriorations and scale deformation behavior in hot rolling a re investigated in order to clarify a mechanism of rolling load increase an d scale defect formation on using high speed steel roll. Several experiment s are conducted; a rolling/sliding friction test at elevated temperature an d model rolling tests for the sheet coil and plate by using high Cr cast ir on and high speed steel as roll material. The results obtained are as follo ws; (1) Worn surface of high Cr cast iron is flat and smooth in hot rolling . On the other hand, fine asperities are formed on worn surface of high spe ed steel. it is found that this peculiar topography of high speed steel con sists of MC carbides which are left by prior wear of matrix in roll microst ructure and black oxide film which prevent MC carbides from removing from w orn surface, which leads higher friction coefficient and higher rolling loa d. (2) Fine asperities cause scale heterogeneous deformation of the steel p roducts in roll bite, resulting in scale defect. (3) Heterogeneous scale de formation is easily occurs under conditions with the large oxide film on th e steel before rolling and the large reduction in thickness and the high ro lling temperature.