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A steel mill or steelworks is an industrial plant for the
manufacture Manufacturing is the creation or Production (economics), production of goods with the help of equipment, Work (human activity), labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary secto ...
of
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
. It may be an integrated steel works carrying out all steps of
steelmaking Steelmaking is the process of producing steel from iron ore and carbon/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon (the most important impurity) are removed from the sourced iron, and alloy ...
from smelting
iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the ...
to rolled product, but may also be a plant where steel
semi-finished casting products Semi-finished casting products are intermediate castings produced in a steel mill that need further processing before being finished goods. There are four types: ''ingots'', ''blooms'', ''billets'', and ''slabs''. Ingot Ingots are large roug ...
are made from molten
pig iron Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with ...
or from
scrap Scrap consists of recyclable materials, usually metals, left over from product manufacturing and consumption, such as parts of vehicles, building supplies, and surplus materials. Unlike waste, scrap has monetary value, especially recovered m ...
.


History

Since the invention of the
Bessemer process The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation ...
, steel mills have replaced
ironworks An ironworks or iron works is an industrial plant where iron is smelted and where heavy iron and steel products are made. The term is both singular and plural, i.e. the singular of ''ironworks'' is ''ironworks''. Ironworks succeeded bloomer ...
, based on puddling or fining methods. New ways to produce steel appeared later: from scrap melted in an
electric arc furnace An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to ...
and, more recently, from
direct reduced iron Direct reduced iron (DRI), also called sponge iron, is produced from the direct reduction of iron ore (in the form of lumps, pellets, or fines) into iron by a reducing gas or elemental carbon produced from natural gas or coal. Many ores are suit ...
processes. In the late 19th and early 20th centuries the world's largest steel mill was the Barrow Hematite Steel Company steelworks located in
Barrow-in-Furness Barrow-in-Furness is a port town in Cumbria, England. Historically in Lancashire, it was incorporated as a municipal borough in 1867 and merged with Dalton-in-Furness Urban District in 1974 to form the Borough of Barrow-in-Furness. In 2023 t ...
,
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
. Today, the world's largest steel mill is in
Gwangyang Gwangyang () is a city in South Jeolla Province, South Korea. Gwangyang city is the home of POSCO's Gwangyang Steel Works, the largest facility of its kind in the world. The city is also home to K League Classic football side Jeonnam Dragons. G ...
,
South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
."POSCO Steel’s Fourth Quarter Executive Board Meeting in India"
New Delhi, October 18, 2007


Integrated mill

An integrated steel mill has all the functions for primary steel production: * iron making (conversion of ore to liquid iron), *
steel making Steelmaking is the process of producing steel from iron ore and carbon/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon (the most important impurity) are removed from the sourced iron, and alloy ...
(conversion of
pig iron Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with ...
to liquid steel), *
casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejecte ...
(solidification of the liquid steel), * roughing rolling/billet rolling (reducing size of blocks) * product rolling (finished shapes). The principal raw materials for an integrated mill are iron ore, limestone, and coal (or coke). These materials are charged in batches into a
blast furnace A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheri ...
where the iron compounds in the ore give up excess oxygen and become liquid iron. At intervals of a few hours, the accumulated liquid iron is tapped from the blast furnace and either cast into
pig iron Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with ...
or directed to other vessels for further steel making operations. Historically the
Bessemer process The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation ...
was a major advancement in the production of economical steel, but it has now been entirely replaced by other processes such as the
basic oxygen furnace Basic oxygen steelmaking (BOS, BOP, BOF, or OSM), also known as Linz-Donawitz steelmaking or the oxygen converter processBrock and Elzinga, p. 50. is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing ...
. Molten steel is cast into large blocks called ''blooms''. During the casting process various methods are used, such as addition of
aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
, so that impurities in the steel float to the surface where they can be cut off the finished bloom. Because of the energy cost and structural stress associated with heating and cooling a blast furnace, typically these primary steel making vessels will operate on a continuous production campaign of several years duration. Even during periods of low steel demand, it may not be feasible to let the blast furnace grow cold, though some adjustment of the production rate is possible. Integrated mills are large facilities that are typically only economical to build in 2,000,000-ton per year annual capacity and up. Final products made by an integrated plant are usually large structural sections, heavy plate, strip, wire rod, railway rails, and occasionally
long products In steel industry terminology long steel products or long products refers to steel products including wire, rod, rail, and bars as well as types of steel structural sections and girders. Overview The term long products may include hot rolled bar, c ...
such as bars and
pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circular ...
. A major
environmental hazard An environmental hazard is a substance, state or event which has the potential to threaten the surrounding natural environment or adversely affect people's health, including pollution and natural disasters such as storms and earthquakes. It can i ...
associated with integrated steel mills is the pollution produced in the manufacture of coke, which is an essential intermediate product in the reduction of iron ore in a blast furnace. Integrated mills may also adopt some of the processes used in mini-mills, such as arc furnaces and direct casting, to reduce production costs.


Minimill

A minimill is traditionally a secondary steel producer; however,
Nucor Nucor Corporation is an American producer of steel and related products based in Charlotte, North Carolina. It is the largest steel producer in the United States, the largest "mini-mill" steelmaker (i.e. it uses electric arc furnaces to melt s ...
(one of the world's largest steel producers) and Commercial Metals Company (CMC) use minimills exclusively. Usually it obtains most of its iron from
scrap Scrap consists of recyclable materials, usually metals, left over from product manufacturing and consumption, such as parts of vehicles, building supplies, and surplus materials. Unlike waste, scrap has monetary value, especially recovered m ...
steel, recycled from used automobiles and equipment or byproducts of manufacturing.
Direct reduced iron Direct reduced iron (DRI), also called sponge iron, is produced from the direct reduction of iron ore (in the form of lumps, pellets, or fines) into iron by a reducing gas or elemental carbon produced from natural gas or coal. Many ores are suit ...
(DRI) is sometimes used with scrap, to help maintain desired chemistry of the steel, though usually DRI is too expensive to use as the primary raw steelmaking material. A typical mini-mill will have an
electric arc furnace An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to ...
for scrap melting, a ladle furnace or vacuum furnace for precision control of chemistry, a strip or billet continuous caster for converting molten steel to solid form, a reheat furnace and a
rolling mill In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simil ...
. Originally the mini mill was adapted to production of bar products only, such as
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
reinforcing bar, flats, angles, channels, pipe, and light rails. Since the late 1980s, successful introduction of the direct strip casting process has made mini mill production of strip feasible. Often a mini mill will be constructed in an area with no other steel production, to take advantage of local markets, resources, or lower-cost labour. Mini mill plants may specialize, for example, in making coils of rod for wire-drawing use, or pipe, or in special sections for transportation and agriculture. Capacities of mini mills vary: some plants may make as much as 3,000,000 tons per year, a typical size is in the range 200,000 to 400,000 tons per year, and some old or specialty plants may make as little as 50,000 tons per year of finished product.
Nucor Corporation Nucor Corporation is an American producer of steel and related products based in Charlotte, North Carolina. It is the largest steel producer in the United States, the largest "mini-mill" steelmaker (i.e. it uses electric arc furnaces to melt sc ...
, for example, annually produces around 9,100,000 tons of sheet steel from its four sheet mills, 6,700,000 tons of bar steel from its 10 bar mills and 2,100,000 tons of plate steel from its two plate mills. Since the electric arc furnace can be easily started and stopped on a regular basis, mini mills can follow the market demand for their products easily, operating on 24-hour schedules when demand is high and cutting back production when sales are lower.


See also

*
Foundry A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals pr ...
*
List of steel producers This is a list of the largest steel-producing companies in the world mostly based on the list by the World Steel Association. This list ranks steelmakers by volume of steel production in millions of tonnes and includes all steelmakers with product ...
* Steel § Steel industry


References


Further reading

* McGannon, Harold E. (editor) (1971). ''The Making, Shaping and Treating of Steel: Ninth Edition''. Pittsburgh, Pennsylvania: United States Steel Corporation.


External links


Travel Channel video 1 of the Homestead Works

An extensive picture gallery of all methods of production in North America and Europe

History of steelworks in Scotland


{{authority control Steelmaking Manufacturing buildings and structures Firing techniques