Abstract
A defect called“orange skin” of“rippling” is often found on the surface of work rolls of cold strip mill after 300-500 tons of steel strip have been rolled.
We observed the roll surface by photo-and electron-microscope after these defects had developed.Also, we investigated the effects of hardness, micro-segregation, and microstructure on the wear of roll materials. The results are summarized as follows:
(1) The cause of the defect formation is due to the microsegregation of roll surface.
(2) In this case the segregation index Is, which shows the degree of micro-segregation, is about 1.4from the line analysis of Cr by EPMA.
(3) To obtain higher homogeneity of the is lower than 1.2, the dendrite arm spacing after forging should be kept lower than 200. It is very difficult to obtain this condition.
(4) We could expect that, if the segregation index is 1.1 or 1.2, the defect formed on roll surface will be avoided by homogeneous carbide distribution and higher hardness by adopting suitable heat treatment.
