Chemistry "Steel"

Steels with only small amounts of other metals are called carbon steels. These steels are far stronger than pure iron, with properties varying with the composition. Alloy steels contain greater amounts of other metals. Low-alloy steels have less than 5 of the alloying material high-alloy steels have more. Low-alloy steels containing up to 5 silicon with relatively little carbon have a high electrical resistance and are used in power transformers and motor or generator cores, for example.

Steel is produced by increasing the carbon content of wrought iron, or decreasing that of cast iron, produced by a blast furnace. The main industrial process is the basic oxygen process, in which molten pig iron and scrap steel is placed in a container lined with heat-resistant, alkaline (basic) bricks. A pipe or lance is lowered near to the surface of the molten metal and pure oxygen blown through it at high pressure. The surface of the metal is disturbed by the blast and the impurities are burned out. The open-hearth process is an older steel making method in which molten iron and limestone are placed in a shallow bowl or hearth. Burning oil or gas is blown over the surface of the metal, and the impurities are oxidized. High-quality steel is made in an electric furnace. A large electric current flows through electrodes in the furnace, melting a charge of scrap steel and iron. The quality of the steel produced can be controlled precisely because the temperature of the furnace can be maintained exactly and there are no combustion by-products to contaminate the steel. Electric furnaces are also used to refine steel, producing the extra-pure steels used, for example, in the petrochemical industry.

Steel has innumerable uses, including ship and car manufacture, skyscraper frames, and machinery of all kinds.