In Japan, the hot metal pretreatment process has been developed to refine hot metal under conditions where each impurity can be removed most efficiently. At Nippon Steel, three types of hot metal pretreatment process, using torpedo car, hot metal ladle, or LD converter, are employed, that make a great contribution to the reduction of slag volume. Recently, Nippon Steel has developed a new hot metal pretreatment called the multirefining converter (MURC) process, in which dephosphorisation and decarburisation are carried out continuously in the same converter. Nevertheless, since the dephosphorisation efficiency of CaO is less than 30%, CaO is now being used in far greater quantities than that stoichiometrically required to make 3CaO.P2O5. As hot metal dephosphorisation is a non-equilibrium reaction, in which hot metal is in contact with slag whose oxygen activity differs greatly from that: of hot metal, it is important to increase the interfacial oxygen activity. From the results of a fundamental experiment, the 2CaO.SiO2 solid phase, in which P2O5 can be dissolved, has a great effect on the dephosphorisation reaction.
