| The melting behavior of steel scrap is a key factor controlling the temperature trajectory and scrap ratio of converter steelmaking process,as well as the energy consumption and productivity of electric arc furnace steelmaking.It is of great significance to study the melting behavior of steel scrap to improve the utilization rate of steel scrap in converter,electric arc furnace,and provide theoretical guidance and experimental basis for the process modeling of them.Although predecessors have carried out a lot of research on the melting behavior of steel scrap,the solid-liquid interface during the melting process of steel scrap is still worthy of further discussion.Meanwhile,the variation of temperature field,bath velocity field,heat transfer coefficient between melt and steel scrap,mass transfer coefficient of carbon,interface carbon content and center temperature of steel scrap with time and steel scrap ratio,gas-stirred,scrap shape,size and density on steel scrap melting behavior are worth further study.In this study,the melting mechanism of steel scrap in iron-carbon melt were explored through numerical calculation and simulation,thermal simulation experiment and cold model experiment.The effects of bath temperature,bath carbon content,preheating temperature,shape and characteristic length of steel scrap and gas-stirred on the melting behavior of steel scrap were studied.The main conclusions of this paper are as follows:（1）Steel scrap melting mainly includes the formation and remelting of solidified layer,and carburizing melting of parent steel scrap.The solidified layer is formed when the steel scrap is immersed in iron-carbon melt for a short time.Due to the chilling effect,an air gap is formed between the solidified layer and the parent steel scrap.During the immersion process,the microstructure of the steel scrap changes from pearlite and ferrite to austenite.After water quenching,acicular martensite is formed in the carburized layer,and lath martensite is formed inside the steel scrap.When the steel scrap is immersed in iron-carbon melt for a long time,the ferrite and liquid phases are formed in the outer layers of steel scrap.（2）With the increase of bath temperature,bath carbon content,and the decrease of characteristic length of steel scrap,the maximum thickness of solidified layer gradually decreases,the formation and remelting time of solidified layer gradually decrease,melting time of steel scrap gradually decrease,and the melting rate of steel scrap increases gradually.As the carbon content of steel scrap increases,the maximum thickness of solidified layer,the formation and remelting time of solidified layer are basically unchanged,and the final stable melting rate of steel scrap increases from-0.260×10-4m/s to-0.501×10-4m/s,the complete melting time is shortened from 400 s to 300 s.（3）Through the programming calculation of the steel scrap melting model based on moving boundary layer theory,it can be known that,with the increase of bath temperature,the ultimate steady heat transfer coefficient and mass transfer coefficient between melt and steel scrap first increased and then decreased,and their variation ranges from 1.04×105to 2.86×105W/（m2·K）and 0 to 2.89×10-4m/s,respectively,the final stable interface carbon content gradually decreased.As the bath carbon content increases,the final stable heat transfer coefficient first increases and then decreases,with a range of 7.59×104to 1.01×105W/（m2·K）,the final stable mass transfer coefficient gradually decreases from1.40×10-4m/s to 5.21×10-5m/s,and the final stable interface carbon content increases from 0.69 wt%to 0.73 wt%.With the reduction of scrap size and the increase of preheating temperature of steel scrap,the final stable heat transfer coefficient,mass transfer coefficient and interface carbon content remain essentially unchanged at 8.40×104W/（m2·K）,1.40×10-4m/s and 0.69wt%,respectively.Through the steel scrap melting model based on linear dissipative thermodynamics,it is possible to predict the change of interface carbon content,temperature and carbon activity with time in the steel scrap melting process,and reveal the heat and mass transfer mechanism of scrap melting.（4）Compared with the square ice cubes,the specific surface area of the sphere and the cylinder is relatively large,the heat transfer rate from the melt to ice cube is faster,and the complete melting time of ice cube is shortened,the sphere have the shortest complete melting time at 1227 s.With the increase of ice cube ratio,the decreasing speed of bath temperature gradually accelerated,the final stable bath temperature gradually decreased,the complete melting time of steel scrap and bath mixing time gradually increased.（5）Compared with no gas-stirred,top and bottom blowing can play the role of stirring the bath,which is beneficial to improve the temperature distribution,strengthen the heat and mass transfer process from melt to steel scrap,and promote the melting of steel scrap and mixing of bath.Meanwhile,the oxygen lance’s position has little effect on bath temperature,but as the oxygen lance’s position increased,the complete melting time of ice cube and bath mixing time are gradually extended from548 s and 105 s to 664 s and 142 s,respectively.With the increase of top blowing and bottom blowing,the decreasing rate of bath temperature increased.At the same time,the complete melting time of steel scrap and bath mixing time decreased with the increase of top blowing and bottom blowing.However,when the gas-stirred is too large,that is,the bath mixing energy is too large,the reduction of total melting time of steel scrap and bath mixing time slows down.In this case,increasing the gas flow can not effectively stir the bath,and also cause the waste of energy. |
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