Microstructure of Oxide Scale on Hot-Rolled Iron

Abstract

In hot rolling processes, oxide scale shows complicated deformation behavior and may cause surface defects on sheet. It influences the friction and the heat transfer on the interface between the sheet and the rolls. To reveal the mechanism, it is necessary to investigate the scale deformation during the hot rolling. In this study, the microstructure of the scale before / after the hot rolling was preserved by glass coating and analysed by scanning electron microscopy (SEM)/ electron backscatter diffraction (EBSD) technique. Using this technique, the microscopic deformation of oxide scale during hot rolling is discussed. Electrolytic pure iron sheets were rolled at a thickness reduction of 30% at 1273 K after oxidation in air for 0 s to 40 s. The scale consists of columnar grains which cover mostly throughout the thickness. The scale preferentially grows to the thickness direction at the initial stage of oxidation (<10 s). After the initial stage (>10 s), scale grains grow parallel as well as perpendicular in the thickness direction (ND). The scale grains are deformed at a fixed volume during hot rolling. The lower ductility of the thick scale results in the fracture of the scale and extrusion of matrix sheet to the outermost surface.