| It is very difficult to develop ultra-low carbon IF steel products with high cleanliness by using high phosphorus hot metal produced in Bayan Obo mine.Through the research on the coordinated control of smelting process temperature,the cleanliness of liquid steel can be improved,and the special role of rare earth in steel can be brought into full play.The research on the application of rare earth in IF steel is carried out,so as to reduce the inclusion defects of ultra deep stamping IF cold rolled strip and improve the quality of strip,which provides theoretical and practical guidance for deep stamping and corrosion resistance of steel.According to the analysis of the whole process of IF steel-making process,the evolution and distribution characteristics of various inclusions in the whole process,and the corresponding research on the surface defects of cold-rolled plate,it is concluded that the high content of hot metal P leads to the low tapping temperature and large fluctuation of converter,resulting in the increase of RH refining oxygen blowing and aluminum treatment heats and refining aluminum consumption,resulting in a large number of deoxidation products.Meanwhile,statistical data analysis shows that the higher the T.O of molten steel,the higher the probability of surface inclusion defect of strip steel.Through the research on the coordinated control of the temperature in each process of IF steel smelting,the whole process temperature control was optimized,the overall heat utilization efficiency was improved,the prediction model of RH process temperature control was established,the RH oxygen blowing and aluminum consumption were reduced,and the cleanliness control requirements of high grade IF steel were met.The vacuum refining and rolling experiments were carried out by adding different content of rare earth Ce into the steel.The results show that when the content of rare earth in the steel is in the range of 20×10-6?60×10-6wt%,the rare earth oxide sulfide inclusions are formed after the reaction of rare earth in the steel.The rare earth can obviously modify and improve the inclusions in the steel.Moreover,the rare earth can refine the grain in the steel.Further research shows that in order to improve the yield of rare earth,Ce Fe alloy with Ce content of 10%?30%should be used,and the content of T.Fe in slag should be controlled as low as possible before the addition of rare earth alloy,and the protective casting in continuous casting process should be strictly done.The research of adding rare earth Ce into IF steel strengthened by adding phosphorus shows that the Gibbs free energy of rare earth Ce combined with active oxygen and sulfur in steel is much lower than that of Al and O,the influence of rare earth on the evolution of Al2O3 and MnS in steel during the whole process of casting and rolling of automobile plate is clarified,and the large-scale inclusions of Al2O3 and MnS in automobile plate are transformed into CeAlO3?Ce2O3?Ce2O2S.In the whole process of casting rolling,the inclusion size is obviously reduced,and the precipitation of MnS in the solidification process is hindered.The morphology of inclusions is transformed from chain shape and strip shape to spherical shape and dispersed distribution,which improves the surface quality of products and reduces the probability of stamping cracking.The mechanism of increasing the nucleation rate of rare earth compounds with high melting point during solidification is clarified.The grain size of continuous annealing products is improved by 1.5 grades with the addition of rare earth.The mechanism of inhibiting the segregation of P element at grain boundary and the precipitation of Fe(Nb+Ti)P phase by rare earth is revealed,which effectively increases the solid solution amount of P element in steel,improves the solid solution strengthening effect of P element in high strength IF steel,and obtains a large proportion of {111} favorable texture,which is conducive to improving the formability index r90 value of automobile sheets.The weight gain and corrosion depth of IF cold-rolled plate strengthened by adding phosphorus were studied by dry wet alternate test.The results show that adding rare earth Ce into the steel and combining with S in the steel can obviously reduce the size and number of MnS inclusions in each position of the slab,reduce the corrosion active points on the matrix,thus greatly reducing the probability of matrix corrosion induced by inclusions.Meanwhile,rare earth can make the inclusions in the steel evenly distributed,the area of anode is reduced effectively,and then the corrosion reaction rate is reduced. |
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