Converter Production

the production of steel in steel-smelting units, or converters, by blowing air or oxygen through molten pig iron. The conversion of pig iron into steel takes place because of oxidation of the impurities (silica, manganese, carbon, and so on) contained in the pig iron and their subsequent removal from the melt.

The Bessemer process, the first large-scale method for producing molten steel, was discovered in 1856 by the English inventor H. Bessemer. Its main disadvantage is the low quality of the metal produced, which is due to harmful impurities (phosphorus and sulfur) that are not removed during the blow. Extremely pure iron ores (with respect to phosphorus and sulfur content), the natural reserves of which are limited, are required for the smelting of Bessemer pig iron.

In 1878, S. Thomas of England used a basic refractory lining in a Bessemer converter, instead of the acidic Dinas lining, and he proposed the use of lime to bind phosphorus. The Thomas-Gilchrist process made possible the refining of high-phosphorus pig iron and was widely used in countries where the iron ores of most deposits contained large amounts of phosphorus (for example, Belgium and Luxembourg). However, even the Thomas steels were of low quality.

In 1864 the French metallurgist P. Martin developed a process for the production of steel in an open-hearth furnace (also called the Martin furnace). Unlike the converter methods of steel production, the open-hearth process did not have strict requirements concerning the chemical composition of the inital raw material and made possible the smelting of a large quantity of steel scrap; the quality of open-hearth steel was higher than that of converter steel. By the mid-20th century, approximately 80 percent of the world’s steel was produced by the open-hearth process.

In 1936 the Soviet engineer N. I. Mozgovoi was the first to use oxygen for the blasting of cast iron in a converter, thus radically changing the technology of converter production. The metal produced by the oxygen-converter process was equal in quality to open-hearth steel, the cost of the steel was reduced by 2–4 percent, and capacity was increased by 25–30 percent.