Cracking and deformation of surface scale during hot rolling of steel

Hot rolling tests, using mild steel slabs with thin and thick oxide scales, have been conducted to investigate the cracking and deformation behaviour of the scale during hot rolling to various reductions. The effects of the variables other than temperature on scale cracking have been simulated by cold rolling tests, using lead slabs with brittle lacquer coatings. Using the point counting method, surface fractions of cracks in the scale and in the lacquer layers have been measured. The results indicate that thin scales can undergo a substantial amount of plastic elongation before cracking in the roll gap, while thick scales suffer from severe brittle cracking before entering the roll gap. Based on these comparative studies, the major parameters that control scale cracking and deformation behaviour during the hot rolling of steel are highlighted, and a quantitative relationship between scale crack fraction and rolling reduction is established. MST/5038.