Mechanism of Oxidation of Austenitic Stainless Steels under Conditions of Hot Rolling in Steckel Mills

The development of oxide scales on hot-rolled austenitic stainless steels under conditions imposed by the industrial Steckel Mill operation introduces particular characteristics that impact downstream on the surface quality of the hot-rolled strip product. In this research, the development of these particular surface structures were studied on 302 austenitic stainless steel by means of laboratory process simulation involving mechanical deformation in a multipass hot rolling schedule and long interpass time inside equalizing furnaces. Surface analysis using a set of complementary techniques that included field emission gun scanning electron microscopy (FEG-SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and glow discharge optical spectroscopy (GDOS) provided a full characterization of the resulting surface structures. These structures consisted in multiple oxide scale and metal layers that were developed after each rolling pass and heavily modified by the following rolling operation establishing a single repetitive mechanism of surface development. The mechanism of formation of these complex multilayer surface structures has been fully determined as being associated with a cyclic oxidation pattern involving successive stages of protective oxidation, chemical breakaway, and the progress of duplex oxidation.