YOS HI DAI)For the production by medium size

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SynopsisNew process " SMP " (Slag Minimum Refining Process) which consists of hot metal desiliconization stage in hot metal container and dephosphorization and decarburization stage in LD converter has been studied in order to reduce the consumption of refining fluxes and slag volume yield in conventional LD process.After experimental studies which have been carried out in KR equipment and conventional LD converter to estimate the feasibility of this new process, it becomes clear that hot metal desiliconization treatment can be done with simple equipment by using proper desiliconization agent and flux and its proper adding method.By this new process, CaO consumption for dephosphorization in LD converter and slag volume can be reduced drastically with decreasing Si content in hot metal and that CaO consumption and slag volume required is 18 kg/t-s, 42 kg/t-s at Si-0.15 % for low carbon rimmed steel. As a result, lining life of refractory can be extended and the amount of metal and heat losses can be decreased and it makes the LD refining very stable.Based on the results obtained by the above experiments, a practical equipment of hot metal desiliconization treatment has been installed and came in use in October 1979, and now is in a stable operation. I. IntroductionThe LD process is presently the most common steelmaking process. It is characterized by the removal of carbon, silicon, manganese, phosphorus and sulphur in the same refining vessel. Further, this process is known for its excellent productivity. Therefore, in the age of high economic growth with the highest priority given to the securing of output, the principal role of the LD converter was to produce more crude steel from a given amount of hot metal than before by raising the scrap ratio using the carbon and silicon in hot metal as the source of heat. With changes in the situation of natural resources and energy after the oil crisis of 1973, however, it has become necessary to develop steelmaking techniques for effectively producing limited amount of crude steel.With this background behind, the authors re-examined the conventional LD steelmaking process and commenced work on the development of an effective steelmaking process suited to the situation of change of natural resources and energy. As a result, they concluded that in order to increase the refining efficiency in the steelmaking process, it is of importance to limit the slag volume to within a certain range and, at the same time, to refine hot metal with having the slag volume kept constant. In other words, in order to reduce the slag volume, it is vital to save submaterials (especially CaO). Furthermore, with a de-