Inhomogeneous deformation during the hot rolling of sheet steels

Abstract

A technique has been developed whereby MnS inclusions in free-cutting steel are used to delineate conditions existing during hot strip rolling. The MnS inclusions are initially oriented perpendicular to the rolling plane and, after hot rolling, the steel samples are sectioned in the rolling direction through the sheet thickness. Metallographic examination of the MnS inclusions can then be made in order to observe the influence of hot-rolling variables (e.g. percent reduction, entry thickness, and lubrication) on the through-thickness deformation conditions. The observations were concentrated on the mid-width portions of the sample. Here the conditions corresponded to those which would pertain over most of the strip width during production hot rolling ofwide strip, i.e. essentially plane strain. The deformation pattern varied considerably through the strip thickness, and plane vertical sections, normal to the rolling direction, did not remain plane during hot rolling. The surface layers were sheared to varying extents depending upon the lubrication conditions, the amount of reduction, and entry gauge of the material. Lubricating the rollfstrip interface with fluid vitreous enamel completely eliminated the shearing so that the deformation conditions then became virtually uniform through the thickness and essentially equivalent to those found during cold rolling. The possible implications of these findings on metallurgical structures and properties are discussed.