Numerical Simulation Study On Loss Of Iron Scale In Soaking Process Of CSP Line

The roller hearth reheating furnace is the key thermotechical facility of compact strip production (CSP). The study of iron scale mechanism on high-carbon billet in the soaking process of this technology was carried out. It was propitious to ameliorate the quality of hot rolled steel sheet and reduce the cost.In this thesis, the latest research results on oxidation of steel and the application of numerical simulation on reheating furnace were analyzed. Based on the computation of loss of iron scale in an experimental furnace according to the soaking process of CSP line, the methods of organizing combustion and high temperature gas fluid flow in the roller hearth reheating furnace were studied to optimize the soaking process and reduce loss of iron scale. The principal contents of this thesis are summarized as following:(1) By introducing the oxidation process of pure iron in air, the oxidation mechanism of steel was described. Many important theories about iron scale were summarized, such as, the principal factors of influencing oxidation of billet in reheating furnaces, the empirical computational models of loss of iron scale, etc. What's more, the soaking strategies of high-carbon steel in the roller hearth reheating furnace were analyzed as well.(2) The mathematical theories about modeling fluid flow, heat transfer and combustion in reheating furnaces and the computational model of loss of iron scale were summarized. And the mathematical model of computing loss of iron scale in the roller hearth reheating furnace was established according to both the latest domestic and overseas research results and the characteristics of the soaking process of CSP line. The mathematical model was verified by experimental results of gas temperature and the literature data of loss of iron scale.(3) Based on the latest research results of iron scale mechanism in reheating furnaces, Computational Fluid Dynamics (CFD) software FLUENT 6.2 integrated with computational program of loss of iron scale was used to research the effects of rate of reheating, soaking temperature and soaking atmosphere on the soaking process of 65Mn steel. The numerical simulation results show that the loss of iron scale reduces while increasing the rate of reheating, and it increases with increasing the soaking temperature as well as increasing air consumption ratio.(4) According to the technological characteristics of the soaking process in CSP line, the effects of air consumption ratio, the ratio of the capacity of core air to the capacity of secondary air and air preheating temperature on fluid flow, combustion and the heat transfer between gas and billet were studied experimentally. Some key information, such as, the distribution of oxidizing gas on surface of billet, the temperature of billet, etc, were obtained. Those are important reference data for organizing high temperature gas fluid flow and combustion in the roller hearth reheating furnace.