Steel Production


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Steel Production

 

the production of steel from pig iron and steel scrap in the furnaces of metallurgical works. Steel production is an important step in the overall production cycle of ferrous metallurgy, the others being the production of pig iron in blast furnaces and the rolling of steel ingots and semifinished shapes. The two main technological processes in steel production are melting and pouring.

In modern metallurgy, the principal methods for the melting of steel are the basic oxygen process, the open-hearth process, and the electric-furnace process. The relative importance of these processes is changing; in the early 1950’s the open-hearth process accounted for approximately 80 percent of world output, but by the mid-1970’s the basic oxygen process had become predominant, accounting for more than half of world production.

The steel produced in a furnace is transferred to a ladle, from which it is then poured either into metal forms, or molds, or into the machines used in continuous casting. Only about 2 percent of all steel produced is used to manufacture shaped castings. Solidification of the metal yields ingots and semifinished shapes, which are then worked mechanically by, for example, rolling or forging. Although continuous casting offers obvious advantages over pouring the steel into molds, most metal is still produced by the latter technique. Pouring is a critical step in steel production, and the process employed determines to a significant extent the quality of the finished metal and the quantity of waste in the subsequent reduction of the steel ingots.

The furnaces used in the basic oxygen process usually have a capacity of 100–350 tons. The range of steel types obtained by this method is increasing continuously, and the quality of alloy steel produced through the basic oxygen process is on a par with that produced through the open-hearth process and electric steel of the same grade. Considerations of both economy and quality recommend the use of basic oxygen furnaces for producing certain low-alloy steels. Thus, steel that is to be cold-worked, especially automotive sheet steel, is produced at metallurgical works the world over mainly in basic oxygen furnaces. High-alloy steels are now also produced in basic oxygen furnaces. Development work on the process now centers on intensifying the melting process, in particular, the blow, increasing the resistance of the furnace lining, using computers to control the process, and working out new variations of the process. The combination of the basic oxygen process with refining methods that are carried out outside the furnace holds promise for the future.

Despite the sharp reduction in the role of the open-hearth process in world production, the process still figures prominently in the ferrous metallurgy of many countries. The use of oxygen, natural gas, and high-quality refractories permits a significant rise in the process’s productivity. However, new open-hearth furnaces are no longer being produced, and what now appears promising is a conversion of existing furnaces into two-bath furnaces.

The second half of the 20th century has seen a marked development of steel production employing electric furnaces, a development encouraged by the numerous advantages of the electric-furnace process over other methods of steel production. In the USSR, 200-ton arc furnaces are currently in operation, and furnaces with a capacity of 400 tons are in the design stage. The world’s largest electric furnace, with a capacity of 360 tons, is currently (1975) in operation in the United States. Work is under way on constructing furnaces with 500–600-ton capacities using six electrodes. An important tendency in the electric-furnace production process is the considerable increase in the power per ton of the furnaces, from 250–300 to 500–600 kilovolt-amperes per ton and more. Some countries have introduced a prior heating of the charge, which permits a reduction in the time required for melting and in the consumption of electric power and electrodes. The performance characteristics of arc furnaces are such that the furnaces can be used efficiently in the production of not only alloy steel but also common steel. Thus, common steel accounts for 70 percent of the output of electric-furnace steel mills in the United States and 50 percent of the output of similar mills in the Federal Republic of Germany. An impetus to the development of the electrometallurgy of steel will result from a widespread use of the direct reduction of iron ore, which permits the production of high-quality raw material for electric furnaces. The use of metallized charges, for example, metallized pellets, in electric melting lowers the capital investment required for the construction of an electric-furnace steel mill and raises the productivity of arc furnaces.

A development in steel production of great promise is the improvement of steel quality through refining processes carried out outside the furnace. The processes with the greatest industrial importance include bubbling inert gases or oxidizing mixtures through the metal in the ladle or in a special apparatus, vacuum processing, and treating the steel with synthetic slags.

The mid-1960’s witnessed the beginning of an intensive development of electrometallurgical processes, which for purposes of refining involve remelting of the semifinished shapes obtained from ordinary steelmaking units, usually arc or induction furnaces. Among the processes are melting in arc vacuum furnaces, vacuum induction melting, electroslag melting, electron-beam melting, and melting in plasma furnaces. As a result of refining remelting, nonmetallic inclusions and other undesirable materials are efficiently removed from the metal, the uniformity of the structure and the density are increased, and many of the properties of steel are improved.

With regard to pouring, there has been an uninterrupted increase in the percentage of metal produced through continuous casting, and by the mid-1970’s there were more than 500 continuous casting machines in operation. The largest such machine, capable of turning out 1.9 million tons of steel a year, is in operation in the United States (1975). The curved-mold type of continuous casting machine is the most common. The yield of finished product for the best continuous casting machines reaches 96–99 percent. In both continuous casting and conventional pouring, good technical and economic results have been obtained by replacing the stoppers with slide valves, which are reliable and safe and which permit a precise regulation of the rate of pouring. The use of exothermic slag-forming mixtures results in improved ingot surfaces, and metal loss may be significantly reduced by using heat-insulating and exothermic hot tops.

The tendency in steel production, as in ferrous metallurgy as a whole, is toward concentration of production and a greater use of continuous production processes. There is also a tendency for individual enterprises to specialize. These developments serve to lower unit costs, improve the quality of the steel, advance the degree of mechanization and automation of the entire metallurgical process, and facilitate the introduction of computers and automatic control systems. Work in progress in a number of countries on developing a continuous steelmaking process and production units for this process holds great promise for steelmaking.

World production of steel in 1974 exceeded 700 million tons, of which 136 million tons were produced in the USSR. The per capita steel production in the industrially developed countries is 400–600 kg; in the USSR, the figure is more than 500 kg. According to some predictions, by the year 2000 world production of this most important metal of the modern era will reach 2 billion tons.

REFERENCES

Staleplavil’noe proizvodslvo: Spravochnik, vols. 1–2. Edited by A. M. Samarin. Moscow, 1964.
Iavoiskii, V. I. Teoriia protsessov proizvodstva stall, 2nd ed. Moscow, 1967.
Lempitskii, V. V., I. N. Golikov, and N. F. Sklokin. Progressivnye sposoby povysheniia kachestva stall. Moscow, 1968.
Perspektivy razvitila tekhnologil chernoi metallurgii. Moscow, 1973.
Elektrometallurgiia stall iferrosplavov. Moscow, 1974.
Kalinnikov, E. S. Chernala metallurgiia: Real’nost’ I tendentsii. Moscow, 1975.
Baptizmanskii, V. I. Teoriia klslorodno-konvertornogo protsessa. Moscow, 1975.

S. I. VENETSKH

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