Process for the dephosphorising and desulphurisation of molten steel with simultaneous reduction of the iron and manganese in the slag

摘要

In the basic steel manufacturing processes, it is well known from the refining process that silicon burns off before the carbon and that the dephosphorisation is somewhere in between, that is to say reference is occasionally made in the literature to a dephosphorisation even before the start of the carbon combustion, although it is generally true that the dephosphorisation starts only with the onset of carbon combustion. According to statements in the literature, the combustion of silicon has been investigated only to a small extent - not at all in the opinion of the author. Precisely very small contents of burning silicon and the silicates SiO2 resulting from the combustion are capable of binding considerable quantities of ferrous and manganous oxides as metal lower-oxide silicates, so that, on the one hand, considerable quantities of iron and manganese pass into the slag and, on the other hand, the ferrous oxide necessary for the dephosphorisation is virtually absent and is thus available only after the silicon combustion has ended. The destruction of the silicates, when the silicon combustion subsides, due to compounds of fluorine and/or alkalis, thus suppresses the formation of metal lower-oxide silicates, so that fewer lower metal oxides go into the slag, and, on the other hand, the ferrous oxides necessary for the dephosphorisation are already available in the region of the subsiding silicon combustion. When alkalis are used or added, their outstanding desulphurisation properties are utilised at the same time.