Steel mill

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Integrated steel mill in the Netherlands. The two large towers are blast furnaces. Hoogovens.JPG
Integrated steel mill in the Netherlands. The two large towers are blast furnaces.

A steel mill or steelworks is an industrial plant for the manufacture of steel. It may be an integrated steel works carrying out all steps of steelmaking from smelting iron ore to rolled product, but may also describe plants where steel semi-finished casting products (blooms, ingots, slabs, billets) are made, from molten pig iron or from scrap.

Contents

History

Since the invention of the Bessemer process, steel mills have replaced ironworks, based on puddling or fining methods. New ways to produce steel appeared later: from scrap melted in an electric arc furnace and, more recently, from direct reduced iron 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, United Kingdom. Today, the world's largest steel mill is in Gwangyang, South Korea. [1] [2]

Integrated mill

Plan of the Lackawanna Steel plant in Buffalo, New York ca. 1903, showing the various elements of an integrated steel mill Lackawanna steel plant 1903.png
Plan of the Lackawanna Steel plant in Buffalo, New York ca. 1903, showing the various elements of an integrated steel mill
Blast furnaces of Trinec Iron and Steel Works VysokePece1.jpg
Blast furnaces of Třinec Iron and Steel Works
Interior of a steel mill SteelMill interior.jpg
Interior of a steel mill

An integrated steel mill has all the functions for primary steel production:

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 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 or directed to other vessels for further steel making operations. Historically the Bessemer process 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.

Molten steel is cast into large blocks called blooms. During the casting process various methods are used, such as addition of aluminum, 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 such as bars and pipe.

A major environmental hazard 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

An ingot of steel entering a rolling mill Block-Grobstrasse Witten.tif
An ingot of steel entering a rolling mill

A minimill is traditionally a secondary steel producer; however, Nucor (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 steel, recycled from used automobiles and equipment or byproducts of manufacturing. Direct reduced iron (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 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.

Originally the mini mill was adapted to production of bar products only, such as concrete 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, 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

Related Research Articles

Pig iron Iron alloy

Pig iron is an intermediate product of the iron industry, also known as crude iron, which is obtained by smelting iron ore in a blast furnace. Pig iron has a very high carbon content, typically 3.8–4.7%, along with silica and other constituents of dross, which makes it very brittle and not useful directly as a material except for limited applications.

Steelmaking process for producing steel from iron ore and scrap

Steelmaking is the process of producing steel from iron ore and/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon are removed from the sourced iron, and alloying elements such as manganese, nickel, chromium, carbon and vanadium are added to produce different grades of steel. Limiting dissolved gases such as nitrogen and oxygen and entrained impurities in the steel is also important to ensure the quality of the products cast from the liquid steel.

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In 2014, the United States was the world’s third-largest producer of raw steel, and the sixth-largest producer of pig iron. The industry produced 29 million metric tons of pig iron and 88 million tons of steel. Most iron and steel in the United States is now made from iron and steel scrap, rather than iron ore. The United States is also a major importer of iron and steel, as well as iron and steel products.

History of the iron and steel industry in the United States aspect of history

The US iron and steel industry has paralleled the industry in other countries in technological developments. In the 1800s, the US switched from charcoal to coke in ore smelting, adopted the Bessemer process, and saw the rise of very large integrated steel mills. In the 20th century, the US industry successively adopted the open hearth furnace, then the basic oxygen steelmaking process. Since the American industry peaked in the 1940s and 1950s, the US industry has shifted to small mini-mills and specialty mills, using iron and steel scrap as feedstock, rather than iron ore.

Lithgow Blast Furnace Former blast furnace in New South Wales

The Lithgow Blast Furnace is a heritage-listed former blast furnace and now park and visitor attraction at Inch Street, Lithgow, City of Lithgow, New South Wales, Australia. It was built from 1906 to 1907 by William Sandford Limited. It is also known as Eskbank Ironworks Blast Furnace site; Industrial Archaeological Site. The property is owned by Lithgow City Council. It was added to the New South Wales State Heritage Register on 2 April 1999.

References

  1. "Barrow". Ironbridge Gorge Museum Trust. Archived from the original on 2007-08-19. Retrieved 2007-08-25.
  2. "POSCO Steel’s Fourth Quarter Executive Board Meeting in India" New Delhi, October 18, 2007

Further reading