Kinetics of steel scrap melting in liquid steel bath in an electric arc furnace.

摘要

Steel scrap melting in liquid steel bath has been studied by many researchers. However, most previous work has been largely limited to single-piece melting experiments and simulations. The present work was undertaken to conduct a comprehensive experimental and modeling study on multi-piece steel scrap melting.; Single-bar, two-bar and multi-bar melting experiments were performed. It was found that solidified shell(s) ("steel icebergs") formed around the original bar(s) immediately after they were immersed in the liquid steel. Interfacial gap(s) were found between the original bar(s) and the solidified shell(s). These gaps buffer heat flow from the solidified shell into original bar(s), hence retarding the growth of the solidified shell(s). The spacing between the bars, the initial solid and liquid steel temperatures and the rate of heat transfer from liquid to solid steel were examined and found to influence the final scrap melting time by altering the "degree" of steel iceberg formation.; A 2D phase field model for melting was developed to simulate the steel scrap melting. The model was validated against the single-bar and two-bar melting experiments. The single-bar simulations revealed that a time-independent heat conduction in the interfacial gap must be incorporated in order to reproduce the melting kinetic observed in the experiments.; The modeling formalism was then extended to model melting of multi-piece, randomly distributed scrap distributions. Two types of simulations were performed. The first type assumed constant heat transfer coefficient and liquid steel temperature. The results revealed that the "steel icebergs" islands formed immediately at the beginning of simulation in the regions where the local scrap porosity was relatively low. The final melting time of the system was determined by the melting of the largest steel icebergs formed in the system. The second type used an effective heat conductivity to simulate convection in the liquid steel, with heat being sourced from the constant-temperature top boundary. The melting proceeded via a melting front that moves down from the top boundary to the bottom. Two regions were distinguished in the system: liquid region and solid-liquid mixture region. These were delineated by the melting front line. The temperature in the mixture region reached approximately the melting temperature at the early stages of melting and stayed near the melting temperature during the rest of melting process. Using these observations, a simple 1D analytical heat transfer model was developed and validated by the phase-field predictions.; In both types of multi-piece simulations, the effects of initial solid and liquid steel temperature, initial solid fraction and convection in the bath on melting were examined.