Degassing of Steel

the removal of gases from liquid steel.

Gases have a harmful effect on the mechanical and physical properties of steel. It was only in the early 1950’s that the problem of producing steel with minimum gas content was solved through the development of a method of vacuum treatment of liquid steel in the ladle, before pouring. The method was proposed by the Soviet scientists A. M. Samarin and L. M. Novik in 1940. It was first tried industrially in the USSR in 1952 at the Enakievskii metallurgical plant, and in 1954 in the Federal Republic of Germany, at the Bochumer Verein, a method of degassing a flow of metal was tried. The industrial introduction of the ladle method of vacuum treatment was first made in the USSR in 1955. These labors initiated a new trend, vacuum metallurgy outside the furnace. By the end of the 1950’s other kinds of vacuum treatment of steel outside the furnace (the batch and circulation methods) had been developed; along with the ladle method, they came to be extensively applied in many countries.

The theoretical basis of the vacuum processes conducted outside the furnace is an increase of the deoxidation capacity of carbon and a decrease in the solubility of hydrogen and nitrogen by lowering the partial pressures of CO, H₂, and N₂. In the late 1960’s, an important trend in the development of vacuum processes outside the furnace was the vacuum treatment of ordinary rimmed steel, which made it possible to solve the complex problem of the production of low-carbon steel. With vacuum treatment of unscavenged steel outside the furnace, the deoxidizing capacity of the carbon is raised by a factor of 10-20. Under such conditions it is possible to make a low-carbon steel with a very low oxygen content. Metals with such a low carbon and oxygen content have very high plastic properties, and bars and slabs cast in continuous steel casting plants are of dense and homogeneous structure. Vacuum processes that are performed outside the furnace considerably raise the technical and economic indexes of metallurgical production by reducing the length of the smelting process by 10-20 percent, reducing the consumption of deoxidant and alloying additives by up to 30 percent, and increasing the yield and improving the quality of usable steel, with low expenses for the construction and operation of vacuum installations. In addition, the useful life of articles made from vacuum-treated steel is prolonged. In 1970 there were about 400 plants operating with vacuum treatment of steel outside the furnace.