GB685326A - Improvements in or relating to process for making steel - Google Patents

Abstract

In a process for making low phosphorus low nitrogen steel from pig irons of varying phosphorus content, molten pig iron, lime-containing slag-forming material in sufficient quantity to produce a slag having a lime/silica ratio of at least 1.5, and iron oxide are introduced into a basic-lined vesel and an oxidizing gas containing more than 21 per cent by volume of oxygen is blown in at the metal surface. The turbulent mixing of slag, iron oxide, and metal produces rapid elimination of phosphorus and some of the carbon and the rapid solution of lime so that the lime/silica ratio is developed while the carbon content of the metal is above 1.0 per cent. The carbon content of the metal is then reduced to the desired value by the continued injection of the oxidizing gas, substantially all the heat for the process being obtained by the exothermic reaction and the formation of the slag. A lime/silica ratio of 2 may be developed while the carbon content of the metal is above 2.0 per cent. The slag may be removed and replaced by a new slag at intermediate stages in the process particularly when the original pig-iron has a high phosphorus content. Preheated lime and mill scale may be introduced into the vessel and then the molten pig-iron poured in. The oxidizing gas may be introduced through a lance and, if desired additional ground lime and mill scale may be added to the gas stream. Good elimination of sulphur is also stated to be obtained.