GB622194A - Production of stainless steel - Google Patents

Abstract

A method of making stainless steel directly from chrome ore comprises continuously smelting in a ferro-alloy furnace a charge including chrome ore, a carbonaceous reducing material and iron ore which may be wholly or partly replaced by steel scrap, mill scale or hammer scale, all in such selective proportions as to produce an impure stainless steel of chromium and iron contents approximately the values desired in the finished steel, and subsequently decarburizing the impure steel in a steel-making furnace, thereby incidentally oxidizing some of the chromium of the steel to form a slag component, and thereafter recovering into the steel bath the chromium so oxidized by adding to the slag a non-carbonaceous reducing agent, e.g. ferro-silicon. The ferro-alloy furnace may have a magnetic lining and the steel-making furnace may have a chromite lining. The ore charged into the ferro-alloy furnace may be low-grade chrome ore giving a chromium content in the impure stainless steel of 10 to 35 per cent, the carbon content having a maximum of 2 per cent. The molten metal may be withdrawn from the ferro-alloy furnace in an intermittent manner, a portion being retained on each occasion. The metal may be decarburized in the steel-making furnace by oxidizing the carbon with iron oxide, the metal oxides of the slag being subsequently reduced; and to the charge chromium-containing slag resulting from the first smelting step may be added. Iron ore may be charged into the steel-making furnace to serve as a slag constituent and to decarburize the metal. The steel-making furnace may be an electric arc furnace in which the bath is decarburized by maintaining a thin slag and uniform operation of the furnace electrodes. Additional chrome ore may be charged into said furnace whereby any variations of chromium content in the metal from the desired value may be adjusted. To prevent silicon contamination of the metal burnt lime, which may be pre-dried, may be added to the steel-making furnace. Specifications 282,387, [Class 82(i)], 400,747, and 428,950 are referred to.