Mechanism Of Rapid Melting Of Steel Scrap In Electric Arc Furnace Molten Pool

Steel scrap is the main raw materials in traditional electric arc furnace(EAF)steelmaking,and the scrap is heated and melted by the electric arc generated between electrode and charge.Because arc heating belongs to point heat source,the temperature distribution in EAF is uneven,resulting in slow local melting rate of scrap and low energy utilization rate.In modern EAF steelmaking,the large"hot heel" and flat bath smelting are widely used,with the "hot heel" volume of more than 40%,and the scrap is heated and melted by molten steel.Due to the low carbon content of molten steel,the initial melting stage of scrap is mainly controlled by the heat transfer of molten steel.Therefore,if the heat transfer between molten steel and scrap can be accelerated,the scrap will be melted rapidly and the energy consumption of EAF will be reduced.Based on this,the rapid melting mechanism of scrap in the molten pool was studied by using thermal simulation experiment and numerical simulation,and the influencing factors of scrap melting in EAF bath were analyzed by using water model experiment in this paper.On the basis of these,the calculation model of scrap melting time under different bulk density and free stacking conditions was established,which can predict the melting time and energy consumption of scrap.The melting characteristics and melting law of single scrap in molten pool were studied.The results show that the steel shell formed around the scrap is an important reason for the increase of melting time.An increase in the specific surface area and preheating temperature of scrap,and the temperature,carbon content and stirring strength of the molten steel,can effectively reduce the existence time of steel shell around the scrap,and reduce the adverse effect of steel shell on the melting process of scrap,thus increasing the melting rate of scrap.A study on the heating law in the center of the scrap was carried out,and the law of heat transfer between molten steel and scrap under different melting conditions was discovered.The characteristics of oxidation and decarburization,ablation and spalling,and solidification steel shell of scrap during the melting process were also studied,and the melting law of scrap was analyzed.It was found that the oxidation of high carbon scrap is more serious than that of low carbon scrap,while the decarbonization is the opposite.The thickness and existence time of steel shell on the surface of high carbon scrap are less than that of low carbon scrap,and the melting time is lower than that of low carbon scrap by more than 20%.The study of the law of multi scrap melting in the molten pool was carried out,and the effects of spacing,porosity and preheating temperature of scrap on the degree of mutual agglomeration in the melting process of scrap were discovered.The results show that an increase in the spacing up to 6 mm,the porosity up to 0.90,and the preheating temperature up to 800?,can greatly reduced or eliminated the agglomeration phenomenon between the scraps,thus increasing the melting rate of scraps.Based on the similarity theory,the hydraulic model of scrap melting in the EAF bath was established,and the factors affecting the melting of scrap in the EAF bath were analyzed.The results show that an increase in the specific surface area of ice,the flow rate of bottom-blowing and side-blowing gas,and a decrease in the height of top-blowing hot steam,can effectively reduce the melting time of ice and shorten the mixing time of the molten pool.In the actual EAF steelmaking process,it is necessary to increase the proportion of scrap with large specific surface area,optimize the bottom-blowing stirring,and improce the impact stirring strength of oxygen supply to the furnace door and furnace wall,which is conducive to the rapid melting of scrap and the uniform mixing of temperature and composition of molten steel.Based on the studies of the melting mechanism of scrap in the molten pool and the factors affecting the melting of scrap in the molten pool of the EAF,a calculation model for the melting time of scrap under different bulk density and free stacking conditions in the molten pool of the EAF was established.The calculation results of the model are consistent with the actual results of the EAF,which can accurately predict the melting time of the scrap in the EAF.Using the scrap melting time calculation model,combined with the calculation of the material balance and energy balance in EAF smelting process,the energy comsumption of EAF steelmaking can be predicted,thus the measures for rapid melting of scrap and consumption reduction of EAF smelting are proposed.