Estimation of Thermal Stresses in Hot-Rolled Steel Coils During Natural Air Cooling

Hot-rolled steel coils are stored upon manufacturing to cool to about 50°C. High temperatures of coiling cause thermal stresses during the cooling stage that result in spot welding between strip layers of coil. Under these conditions, surface defects or strip ruptures may occur during uncoiling. This paper will initially introduce the heat transfer model in the coil based on stress-dependent thermal conductivity in the radial direction of the coil. The two approaches of “solid body” and “thin-walled, concentric cylinders” for thermal stress analysis will then be used to compute the thermal compressive stresses in the coil. Comparison of the results obtained from these two approaches in the mathematical model reveals that the solid body approach overestimates the thermal stresses when compared to the thin-walled concentric cylinders approach, the inequality rising with reduced strip thickness. This difference, however, is found to have no considerable impact on predicting coil temperature.