Estimating the resistance to deformation of the layer of scale during hot rolling of carbon steel strips

Low carbon steel strips were hot rolled at various temperatures, speeds and reductions. The thickness of the layer of scale before and after the rolling pass was carefully controlled. Pre-heated oxygen-free nitrogen was used to purge the heating furnace while the strips to be rolled were brought to the test temperature. As well, after the rolling pass the strips were cooled in a closed box, which was also purged using oxygen-free nitrogen. The roll forces, roll torques, the forward slip and the scale thickness, before and after rolling, were measured. The coefficient of friction, calculated using Geleji’s formula, was found to decrease as the scale thickness increased. The thickness of the oxide layer before and after rolling and the duration of the pass were used to calculate the strains and strain rates it experienced. These, along with the surface temperature, were related to the interfacial pressure and hence, to the resistance of the scale layer to deformation. The strength of the scale increased with increasing contact times and with decreasing temperatures.