Effect of the purity of oxygen used for blowing on the nitrogen content of steel made in high-power arc steelmaking furnaces at ural steel

Abstract

Given the high rate of injection of steel with oxygen in modern high-power arc steelmaking furnaces (close to the rate attained in basic oxygen furnaces), the purity of the oxygen becomes the deciding factor in determining the nitrogen content of the steel. An analysis is made of the factors that affect nitrogen content in the production of steel in modern electric-arc furnaces at Ural Steel. In particular, a determination is made of the extent to which the purity of the oxygen that is used affects the steel’s nitrogen content. The injection of steel with oxygen in modern high-power arc steelmaking furnaces ‐ which is done to speed up melting of the scrap and oxidation of the impurities in the charge ‐ is carried out at very high rates. For example, the highest injection rate on arc furnaces Nos. 1 and 2 in the electric steelmaking shop at Ural Steel is 12000 m 3 /h. At rates this high (close to the rates used in basic oxygen furnaces), the purity of the oxygen is of critical importance because its injection can change the nitrogen content of the steel. Thus, basic oxygen furnaces and all large modern arc steelmaking furnaces (ASFs) are operated with the use of commercially pure oxygen (O 2 content no lower than 99.5%). The literature data [1‐10] and experience with the operation of basic oxygen furnaces show that even a slight decrease in the purity of the oxygen (at high rates of injection) has a marked effect on the nickel content of the steel. As regards the effect of the parameters of the injection of steel with oxygen (oxygen consumption, oxygen purity) on furnace performance, the technical literature offers complete information only for converters and less productive arc steelmaking furnaces used earlier. No such investigations have yet been conducted for modern ASFs. Thus, Ural Steel performed an analysis of different heats in order to refine information on the factors that affect nickel content when steel is made in modern electric-arc furnaces. Also, since many metallurgical plants cannot use commercially pure oxygen when making steel in arc furnaces (due to the lack of a modern oxygen plant or a deterioration in the condition of the existing plant), they employ industrial-grade oxygen (with an O 2 content below 95.0%). There may be a significant difference in the nickel contents of steel made using oxygen of commercial and industrial purity. Use of the latter makes it more difficult to produce grades of steel used in critical applications, such as tube steels. The nickel content of such steels cannot be any greater than 0.008%. To determine the extent to which the purity of the oxygen used in the steelmaking operation affects the steel‘s nickel content, we analyzed heats made with the use of oxygen of different degrees of purity. Method of investigation. The trial heats were made in 120-ton arc steelmaking furnaces Nos. 1 and 2 at Ural Steel with the use of up to 45% liquid pig iron in the metallic part of the charge. This part of the charge was introduced into the