Iron metallurgy

Article By:

St. Pierre, George R. Department of Metallurgical Engineering, Ohio State University, Columbus, Ohio.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.353400

Extracting iron from ores and preparing the crude iron for conversion to steel. Extraction involves the conversion of naturally occurring iron-bearing minerals into metallic iron. The term ironmaking is commonly used to include all of the industrial processes that convert raw materials into metallic iron. Almost all of the iron that is produced is converted into steel in modern basic oxygen furnaces and electric arc furnaces, as illustrated in Fig. 1. Steel plants vary in size from production capacities of about 0.5 to 15.0 million metric tons of steel products per year (1 metric ton = 1000 kg). In 2010, steel plants around the world produced about 1400 million metric tons of steel, of which about 70% was derived from iron and the balance was derived from recycled steel scrap. The major facility for the production of iron is the iron blast furnace, which varies widely in size and specific features. The largest blast furnaces are capable of producing as much as 20,000 metric tons of molten iron per day and operate continuously for several years without interruption. Figure 2 shows a cross-sectional diagram of a blast furnace, illustrating the continuous countercurrent flow of solids from top to bottom and gases from bottom to top. Some blast furnaces have base diameters of more than 15 m and stand more than 50 m high. Since the 1950s, there has been growth in the use of alternative direct-reduction processes, but the blast furnace still accounts for more than 90% of iron production. The principal differences between the blast-furnace process and direct-reduction processes are the types of fuels and reducing agents used and the temperature of operation. In the blast furnace, high operating temperatures enable the production of molten iron. At the lower operating temperatures of the direct-reduction processes, solid or sponge iron is produced. The small amount of molten iron from the blast furnace that is not immediately refined into steel is converted into iron castings, ferroalloys, iron powder, and “pigs” for subsequent processing.

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