Factors affecting the development of oxide scales on austenitic stainless steels during hot rolling in Steckel Mills

The hot rolling of austenitic stainless steels in Steckel Mills introduces particular characteristics to the development of oxides scales and surface structures. In this work, the formation of oxide structures during multipass hot rolling of 302 steel was studied under different sets of processing parameters in a laboratory system designed for the simulation of the Steckel process. The resulting surface structures were characterized by a set of complementary techniques involving scanning electron microscopy, energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and glow discharge optical spectroscopy (GDOS). The surface analysis revealed two alternative surface structures: one consisting in a thin protective oxide layer rich in Cr(2)O(3) and the other consisting in thick complex structures containing several successive nonprotective oxide scale and metal layers resulting from a cyclic oxidation pattern involving stages of protective oxidation, chemical breakaway, and duplex oxidation. The critical condition that determined the activation of one mechanism or the other was identified associated with the parabolic rate constant for Cr(2)O(3) growth and the diffusivity of Cr in the alloy. The effects of changes in temperature, deformation, and furnace atmosphere are discussed. Alternatives for controlling scale development are presented.