The effect of oxide scale of stainless steels on friction and surface roughness in hot rolling
Friction is one of the most significant physical phenomena influencing metal forming. The deformation or fracture of oxide scale significantly affects the roll–strip interface behaviour. Sticking occurs frequently during hot rolling of stainless steels especially ferritic stainless steels, which causes surface defects of both steel products and rolls. It is important to characterize the features of the oxide scale in hot rolling of stainless steel strips, but few studies have been carried out. This paper focuses on the deformation of oxide scale and roll–strip interface characteristics in hot rolling of austenitic stainless steel 304L and ferritic stainless steel 430. Oxidation tests in a short time in humid air with water vapour content of 7.0 vol.% were carried out using Gleeble 3500 thermo-mechanical simulator, and the oxidation characteristics of 304L and 430 steels were obtained. The deformation, surface morphology of oxide scale of the steels, and the friction in hot rolling were studied in hot rolling tests. Thick oxide scale of 304L steel shows high lubricative effect while the breaking of thin oxide scales of 430 steel may make the steel substrate to contact with the roll, which counteracts the lubricative effect of the oxide scale and results in friction coefficient increasing with an increase of reduction. A FEM simulation has been developed to analyse the deformation behaviour of oxide scale and surface roughness transfer during hot rolling of stainless steels and the model describing the rough surface profiles of the scales and steel has been integrated into the simulation.