Steelmaking

Steelmaking is the process of producing steel from iron ore and/or scrap. Steel has been made for millennia and was commercialized on a massive scale in the 1850s and 1860s, using the Bessemer and Siemens-Martin processes. Currently, two major commercial processes are used. Basic oxygen steelmaking (BOS) uses liquid pig iron from a blast furnace and scrap steel as the main feed materials. Electric arc furnace (EAF) steelmaking uses scrap steel or direct reduced iron (DRI). Oxygen steelmaking has become more popular over time. Steelmaking is one of the most carbon emission-intensive industries. In 2020, the steelmaking industry was reported to be responsible for 7% of energy sector greenhouse gas emissions. The industry is seeking significant emission reductions.

Steel Steel is made from iron and carbon. Cast iron is a hard, brittle material that is difficult to work, whereas steel is malleable, relatively easily formed, and versatile. On its own iron is not strong, but a low concentration of carbon – less than 1 percent, depending on the kind of steel – gives steel strength and other important properties. Impurities such as nitrogen, silicon, phosphorus, sulfur, and excess carbon (the most important impurity) are removed, and alloying elements such as manganese, nickel, chromium, carbon, and vanadium are added to produce different grades of steel.

History

Early history Early processes evolved during the classical era in China, India, Rome and among hunter-foragers in northern Sweden. The earliest means of producing steel was in a bloomery. For much of human history, steel was made only in small quantities. Early modern methods of producing steel were often labor-intensive and highly skilled arts. The Bessemer process and subsequent developments allowed steel to become integral to the global economy. Chahak was a crucible steel making center in medieval Persia, which is also the first known example chromium steel production.

China A system akin to the Bessemer process originated in the 11th century in East Asia. Hartwell writes that the Song dynasty (960–1279 CE) innovated a "partial decarbonization" method of repeated forging of cast iron under a cold blast. Needham and Wertime describe the method as a predecessor to the Bessemer process. This process was first described by government official Shen Kuo in 1075, when he visited Cizhou. Hartwell states that the earliest center where this was practiced was perhaps the great iron-production district along the Henan–Hebei border during the 11th century.

Europe

In the 15th century, the finery process, which shares the air-blowing principle with the Bessemer process, was developed in Europe. High-quality steel was also made by the reverse process of adding carbon to carbon-free wrought iron, usually imported from Sweden. The manufacturing process, called the cementation process, consisted of heating bars of wrought iron together with charcoal for periods of up to a week in a long stone box. This produced blister steel. The blister steel was put in a crucible with wrought iron and melted, producing crucible steel. Up to 3 tons of (then expensive) coke was burnt for each ton of steel produced. When rolled into bars such steel was sold at £50 to £60 (approximately £3,390 to £4,070 in 2008) per long ton. The most difficult and laborious part of the process was the production of wrought iron in finery forges in Sweden. In 1740 Benjamin Huntsman developed the crucible technique for steel manufacture at his workshop in Handsworth, England. This process greatly improved the quantity and quality of steel production. It added three hours firing time and required large quantities of coke. In making crucible steel, the blister steel bars were broken into pieces and melted in small crucibles, each containing 20 kg or so. This produced higher quality metal but increased the cost. The Bessemer process reduced the time needed to make lower-grade steel to about half an hour while requiring only enough coke needed to melt the pig iron. The earliest Bessemer converters produced steel for £7 per long ton, although it initially sold for around £40 per ton.

Japan The Japanese may have made use of a Bessemer-type process, as observed by 17th century European travellers. Adventurer Johan Albrecht de Mandelslo describes the process in a book published in English in 1669. He writes, "They have, among others, particular invention for the melting of iron, without the using of fire, casting it into a tun done about on the inside without about half a foot of earth, where they keep it with continual blowing, take it out by ladles full, to give it what form they please." Wagner states that Mandelslo did not visit Japan, so his description of the process is likely derived from other accounts. Wagner states that the Japanese process may have been similar to the Bessemer process but cautions that alternative explanations are plausible.

By the early 19th century the puddling process was widespread. At the time, process heat was too low to entirely remove slag impurities, but the reverberatory furnace made it possible to heat iron without placing it directly in the fire, offering some protection from impurities in the fuel source. Coal then began to replace charcoal as fuel. By the 1850s the Bessemer process allowed steel to be produced without fuel, using the iron's impurities to create the necessary heat. This drastically reduced costs, but raw materials with the required characteristics were not always easy to find.

Processes

Modern steelmaking consists of three steps: primary, secondary, and tertiary. Primary steelmaking involves melting iron into steel. Secondary steelmaking involves adding or removing other elements such as alloying agents and dissolved gases. Tertiary steelmaking casts molten metal into sheets, rolls or other forms. Multiple techniques are available for each step.

Primary steelmaking

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