Transient billet heating model for a steel reheat furnace

A finite difference approximation for the transient thermal response of a steel billet moving through a reheat furnace was developed. The two dimensional model accounted for the insulating properties and the exothermic reaction heat effect of the growing oxide layer, as well as the radiation shadowing of the furnace skidrail structure. The Comini-Hsaio apparent heat capacity method was successfully implemented to account for the phase change behaviour of the steel. The two dimensional model was tuned and validated with actual furnace reheat data. Two factorial designs were carried out to determine the dependency of the responses on various process variables such as: zone temperatures, furnace residence time, initial billet temperature and steel grade. The responses studied included the maximum billet temperature difference (which ranged from 67.70 to 208.64K), the minimum billet temperature (1373.29 to 1563.33K), the weighted average billet temperature (1442.91 to 1573.32K), the billet temperature variance (348.60 to 1504.88K2), and the weighted average oxide scale thickness (0.92 to 1.47mm).;A transient one dimensional model was also developed to assess the impact of various physical phenomena on the billet reheating process. This screening process identified the enhanced heat transfer through decarburised steel as negligible. The phase change behaviour of steel was proven significant to the reheating process, and therefore remained in all ensuing analyses.