| Short process casting is a process in which the molten iron in blast furnace is directly cast into castings through proper composition adjustment,which saves the remelting of bread iron in the traditional process and reduces the energy consumption,time and pollution of the casting industry.However,due to the lack of experience in short process smelting and the lack of research on its technological process,it is difficult to overcome the adverse effects caused by the existence of coarse graphite in molten iron in blast furnace due to high C content,and this process has not been widely used.Therefore,the short process casting of molten iron in blast furnace is studied.Based on the traditional process samples,this paper studies the influence of process parameters such as melting temperature,holding time,residence time in ladle,casting thickness,inoculation and spheroidization on the microstructure of hot metal in short-process blast furnace.By using the experimental comparison of metallographic structure,thermal analysis curve and mechanical properties,the influence laws of each process on the microstructure of short-process hot metal castings in blast furnace are summarized.The results show that:Increasing the melting temperature,properly increasing the holding time and the residence time in the ladle can refine the graphite flake of the short process casting of blast furnace molten iron,reduce the solidification undercooling of molten iron and improve the mechanical properties of the casting,so that the graphite shape,size,distribution,matrix structure and mechanical properties of the short process casting of blast furnace molten iron are closer to those of the traditional casting,and the structural heredity of the short process casting of blast furnace molten iron is basically eliminated.Under the condition that other process parameters are basically unchanged,the solidification process,metallographic structure and mechanical properties of molten iron in the traditional process and the short process of blast furnace molten iron after inoculation are compared.It is found that there are some bad graphite such as C-type and massive graphite in the structure without inoculation,which is basically transformed into A-type flake graphite after inoculation,with higher uniformity of morphology distribution and smaller difference between graphite size,pearlite content and mechanical properties and the state of molten iron.That is to say,reasonable inoculation treatment has a positive effect on eliminating the heredity of the structure of short process castings with direct pouring of blast furnace molten iron.The difference percentage of average size of graphite balls of nodular cast iron in short process and traditional process after spheroidizing inoculation is smaller than that in two processes without spheroidizing treatment with the same process parameters,and the position of eutectic section of molten iron solidification is closer,and the problems of graphite size,uneven distribution and low mechanical properties of short-process cast iron in blast furnace molten iron are obviously improved,so reasonable spheroidizing treatment can strengthen inoculation and further inhibit the heredity of molten iron structure in blast furnace.Increasing the thickness of castings is beneficial to the graphitization ability of blast furnace molten iron.When the thickness of the casting is 4～10 mm,the hardness of the casting is too high because the cooling speed is too fast and the undercooling degree is too high.When the thickness of the casting is 20～30 mm,the A-type flake graphite is mostly in the sample structure of the traditional process and the short process,and the graphite size,distribution,matrix structure and mechanical properties are closer,which is more effective in reducing the microstructure heredity of the short process of hot metal in blast furnace.When the thickness of the casting is more than 30 mm,the graphite length of the two processes is more effective. |
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