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{{Steels}} 

'''Steel''' is an [[alloy]] that consists mostly of [[iron]] and has a [[carbon]] content between 0.2% and 2.1% by weight, depending on the [[steel grade|grade]]. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as [[manganese]], [[chromium]], [[vanadium]], and [[tungsten]].<ref name=EM2>{{cite book|last=Ashby |first=Michael F.|coauthors=David R. H. Jones|title=Engineering Materials 2|origyear=1986|edition=with corrections|year=1992|publisher=Pergamon Press |location=Oxford|isbn=0-08-032532-7}}</ref> Carbon and other elements act as a hardening agent, preventing [[dislocation]]s in the iron atom [[crystal lattice]] from sliding past one another. Varying the amount of alloying elements and the form of their presence in the steel (solute elements, precipitated phase) controls qualities such as the [[hardness (materials science)|hardness]], [[ductility]], and [[tensile strength]] of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but such steel is also less [[ductile]] than iron.

Alloys with a higher than 2.1% carbon content are known as [[cast iron]] because of their lower [[melting point]] and [[castability]].<ref name=EM2/> Steel is also distinguishable from [[wrought iron]], which can contain a small amount of carbon, but it is included in the form of [[slag]] [[inclusion (casting)|inclusion]]s. Two distinguishing factors are steel's increased [[rust]] resistance and better [[weldability]].

Though steel had been produced by various inefficient methods long before the [[Renaissance]], its use became more common after more-efficient production methods were devised in the 17th century. With the invention of the [[Bessemer process]] in the mid-19th century, steel became an inexpensive [[mass production|mass-produced]] material. Further refinements in the process, such as [[basic oxygen steelmaking]], further lowered the cost of production while increasing the quality of the metal. Today, steel is one of the most common materials in the world, with more than 1.3 billion tons produced annually. It is a major component in buildings, infrastructure, tools, ships, [[automobile]]s, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted [[standards organizations]].
[[File:Steel wire rope.JPG|thumb|250px|The steel cable of a [[coal mining|colliery]] [[headframe|winding tower]]]]

==Material properties==
[[File:Steel pd.svg|thumb|left|420px|Iron-carbon [[phase diagram]], showing the conditions necessary to form different phases]]

Iron, like most metals, is found in the [[Earth]]'s [[crust (geology)|crust]] only in the form of an ore, i.e., combined with other elements such as [[oxygen]] or [[sulfur]].<ref>{{cite web|last=Winter|first=Mark|title=Periodic Table: Iron|publisher=The University of Sheffield|url=http://www.webelements.com/iron/|accessdate=2007-02-28}}</ref> Typical iron-containing [[minerals]] include Fe<sub>2</sub>O<sub>3</sub>—the form of [[iron oxide]] found as the [[mineral]] [[hematite]], and FeS<sub>2</sub>—[[pyrite]] (fool's gold).<ref>{{cite journal|last=F. Brookins|first=Theo|title=Common Minerals and Valuable Ores|journal=Birds and All Nature|volume=6|issue=4|publisher=A. W. Mumford|month=November|year=1899|url=http://birdnature.com/nov1899/ores.html|accessdate=2007-02-28|ref=harv}}</ref> Iron is extracted from [[ore]] by removing oxygen and combining the ore with a preferred chemical partner such as carbon. This process, known as [[smelting]], was first applied to metals with lower [[melting]] points, such as [[tin]], which melts at approximately {{convert|250|C|F|abbr=on}} and [[copper]], which melts at approximately {{convert|1000|C|F|abbr=on}}. In comparison, cast iron melts at approximately {{convert|1370|C|F|abbr=on}}. All of these temperatures could be reached with ancient methods that have been used since the [[Bronze Age]]. Since the oxidation rate itself increases rapidly beyond 800 °C, it is important that smelting take place in a low-oxygen environment. Unlike copper and tin, liquid iron dissolves carbon quite readily. Smelting results in an alloy ([[pig iron]]) containing too much carbon to be called steel.<ref>{{cite encyclopedia|title=Smelting|encyclopedia=Britannica|publisher=Encyclopedia Britannica|year=2007|accessdate=2007-02-28}}</ref> The excess carbon and other impurities are removed in a subsequent step.

Other materials are often added to the iron/carbon mixture to produce steel with desired properties. [[Nickel]] and manganese in steel add to its tensile strength and make austenite more chemically stable, [[chromium]] increases hardness and melting temperature, and [[vanadium]] also increases hardness while reducing the effects of [[metal fatigue]]. To prevent corrosion, at least 11% chromium is added to steel so that a hard [[passivation|oxide]] forms on the metal surface; this is known as [[stainless steel]]. [[Tungsten]] interferes with the formation of cementite, allowing martensite to form with slower quench rates, resulting in [[high speed steel]]. On the other hand, [[sulfur]], [[nitrogen]], and [[phosphorus]] make steel more brittle, so these commonly found elements must be removed from the ore during processing.<ref name=materialsengineer>{{cite web|title=Alloying of Steels|publisher=Metallurgical Consultants|date=2006-06-28|url=http://materialsengineer.com/E-Alloying-Steels.htm|accessdate=2007-02-28}}</ref>

The [[density]] of steel varies based on the alloying constituents, but usually ranges between 7.75 and 8.05&nbsp;g/cm<sup>3</sup> (0.280–0.291&nbsp;lb/in<sup>3</sup>).<ref>{{cite web|last = Elert|first = Glenn|title = Density of Steel|url = http://hypertextbook.com/facts/2004/KarenSutherland.shtml|accessdate = 2009-04-23}}</ref>

Even in the narrow range of concentrations which make up steel, mixtures of carbon and iron can form a number of different structures, with very different properties. Understanding such properties is essential to making quality steel. At [[room temperature]], the most stable form of iron is the [[body-centered cubic]] (BCC) structure α-[[ferrite (iron)|ferrite]]. It is a fairly soft metallic material that can dissolve only a small concentration of carbon, no more than 0.021 wt% at {{convert|723|C|F|abbr=on}}, and only 0.005% at {{Convert|0|C|F|abbr=on}}. If the steel contains more than 0.021% carbon then it transforms into a [[face-centered cubic]] (FCC) structure, called [[austenite]] or γ-iron. It is also soft and metallic but can dissolve considerably more carbon, as much as 2.1%<ref>Sources differ on this value so it has been rounded to 2.1%, however the exact value is rather academic as plain-carbon steel is very rare made with this level of carbon. See:
*{{harvnb|Smith|Hashemi|2006|p=363}}—2.08%.
*{{harvnb|Degarmo|Black|Kohser|2003|p=75}}.—2.11%.
*{{harvnb|Ashby|Jones|1992}}—2.14%.</ref> carbon at {{convert|1148|C|F|abbr=on}}), which reflects the upper carbon content of steel.<ref>{{harvnb|Smith|Hashemi|2006|p=363}}.</ref>

When steels with less than 0.8% carbon, known as a hypoeutectoid steel, are cooled from an austenitic phase the mixture attempts to revert to the ferrite phase, resulting in an excess of carbon. One way for carbon to leave the austenite is for [[cementite]] to [[precipitate]] out of the mix, leaving behind iron that is pure enough to take the form of ferrite, resulting in a cementite-ferrite mixture. Cementite is a hard and brittle [[intermetallics|intermetallic compound]] with the [[chemical formula]] of Fe<sub>3</sub>C. At the [[eutectoid]], 0.8% carbon, the cooled structure takes the form of [[pearlite]], named after its resemblance to [[mother of pearl]]. For steels that have more than 0.8% carbon the cooled structure takes the form of pearlite and cementite.<ref>{{harvnb|Smith|Hashemi|2006|p=365–372}}.</ref>

Perhaps the most important [[polymorphism (materials science)|polymorphic form]] is [[martensite]], a metastable phase which is significantly stronger than other steel phases. When the steel is in an austenitic phase and then [[quenching|quenched]] it forms into martensite, because the atoms "freeze" in place when the cell structure changes from FCC to BCC. Depending on the carbon content the martensitic phase takes different forms. Below approximately 0.2% carbon it takes an α ferrite BCC crystal form, but higher carbon contents take a [[body-centered tetragonal]] (BCT) structure. There is no thermal [[activation energy]] for the transformation from austenite to martensite. Moreover, there is no compositional change so the atoms generally retain their same neighbors.<ref name="smith&hashemi">{{Harvnb|Smith|Hashemi|2006|pp=373–378}}.</ref>

Martensite has a lower density than austenite does, so that transformation between them results in a change of volume. In this case, expansion occurs. Internal stresses from this expansion generally take the form of [[physical compression|compression]] on the crystals of martensite and [[tension (mechanics)|tension]] on the remaining ferrite, with a fair amount of [[shear stress|shear]] on both constituents. If quenching is done improperly, the internal stresses can cause a part to shatter as it cools. At the very least, they cause internal [[work hardening]] and other microscopic imperfections. It is common for quench cracks to form when water quenched, although they may not always be visible.<ref>{{cite web|title=Quench hardening of steel|url=http://steel.keytometals.com/default.aspx?ID=CheckArticle&NM=12|accessdate=2009-07-19}}</ref>

===Heat treatment===
{{Main|Carbon steel#Heat treatment|l1=Heat treating carbon steel}}

There are many types of [[heat treatment|heat treating]] processes available to steel. The most common are [[annealing (metallurgy)|annealing]] and [[quenching]] and [[tempering]]. Annealing is the process of heating the steel to a sufficiently high temperature to soften it. This process occurs through three phases: [[recovery (metallurgy)|recovery]], [[recrystallization (metallurgy)|recrystallization]], and [[grain growth]]. The temperature required to anneal steel depends on the type of annealing and the constituents of the alloy.<ref>{{harvnb|Smith|Hashemi|2006|p=249}}.</ref>

Quenching and tempering first involves heating the steel to the austenite phase, then quenching it in [[water]] or [[oil]]. This rapid cooling results in a hard and brittle martensitic structure.<ref name="smith&hashemi"/> The steel is then tempered, which is just a specialized type of annealing. In this application the annealing (tempering) process transforms some of the martensite into cementite or [[spheroidite]] to reduce internal stresses and defects, which ultimately results in a more ductile and fracture-resistant metal.<ref>{{harvnb|Smith|Hashemi|2006|p=388}}.</ref>

==Steel production==
[[File:LightningVolt Iron Ore Pellets.jpg|thumb|right|250px|[[Iron ore]] pellets for the production of steel]]
{{Main|Steelmaking}}
{{See also|Steel production by country}}

When iron is smelted from its ore by commercial processes, it contains more carbon than is desirable. To become steel, it must be melted and reprocessed to reduce the carbon to the correct amount, at which point other elements can be added. This liquid is then [[continuous casting|continuously cast]] into long slabs or [[casting (metalworking)|cast]] into [[ingot]]s. Approximately 96% of steel is continuously cast, while only 4% is produced as cast steel ingots.{{Citation needed|date=February 2010}} The ingots are then heated in a [[soaking pit]] and [[hot rolling|hot rolled]] into slabs, [[wikt:bloom|blooms]], or [[billet]]s. Slabs are hot or [[cold rolling|cold rolled]] into [[sheet metal]] or plates. Billets are hot or cold rolled into bars, rods, and wire. Blooms are hot or cold rolled into [[structural steel]], such as [[I-beam]]s and [[rail tracks|rails]]. In modern [[foundries]] these processes often occur in one [[assembly line]], with ore coming in and finished steel coming out.<ref>{{harvnb|Smith|Hashemi|2006|pp=361–362}}.</ref> Sometimes after a steel's final rolling it is heat treated for strength, however this is relatively rare.<ref>{{Harvnb|Bugayev|Konovalov|Bychkov|Tretyakov|Savin|2001|p=225}}</ref>

==History of steelmaking==
[[File:Bas fourneau.png|thumb|left|upright|[[Bloomery]] smelting during the [[Middle Ages]]]]
{{Main|History of ferrous metallurgy}}

===Ancient steel===
<!-- Please show restraint. This is a general article on steel. It is not the right place for a detailed history of the industry. That should appear in separate articles elsewhere. --> 

Steel was known in antiquity, and may have been produced by managing [[bloomery|bloomeries]], iron-smelting facilities, where the bloom contained carbon.<ref>{{cite web|last=Wagner|first=Donald B.|title=Early iron in China, Korea, and Japan|url=http://www.staff.hum.ku.dk/dbwagner/KoreanFe/KoreanFe.html|accessdate=2007-02-28}}</ref> 

The earliest known production of steel is a piece of ironware excavated from an [[archaeological site]] in [[Anatolia]] ([[Kaman-Kalehoyuk ]]) and is about 4,000 years old.<ref>{{cite web|title=Ironware piece unearthed from Turkey found to be oldest steel|url=http://www.hindu.com/thehindu/holnus/001200903261611.htm|accessdate=2009-03-27}}</ref> Other ancient steel comes from [[Eastern Africa|East Africa]], dating back to 1400 BC.<ref>{{cite web |url=http://www.wsu.edu/~dee/CIVAFRCA/IRONAGE.HTM |title=Civilizations in Africa: The Iron Age South of the Sahara |publisher=Washington State University |accessdate=2007-08-14}}</ref> In the 4th century BC steel weapons like the [[Falcata]] were produced in the [[Iberian Peninsula]], while [[Noric steel]] was used by the [[Military of ancient Rome|Roman military]].<ref>"Noricus ensis," [[Horace]], Odes, i. 16.9</ref> The [[ancient China|Chinese]] of the [[Warring States]] (403&ndash;221 BC) had [[quench|quench-hardened steel]],<ref>{{cite book|author=Wagner, Donald B.|year=1993|title=Iron and Steel in Ancient China: Second Impression, With Corrections|publisher=Leiden: E.J. Brill|isbn=9004096329| page=243}}</ref> while Chinese of the [[Han Dynasty]] (202 BC – 220 AD) created steel by melting together [[wrought iron]] with [[cast iron]], gaining an ultimate product of a carbon-intermediate steel by the 1st century AD.<ref name="needham volume 4 part 3 563g">{{cite book|author=Needham, Joseph|year=1986|title=Science and Civilization in China: Volume 4, Part 3, Civil Engineering and Nautics|publisher=Taipei: Caves Books, Ltd. |page=563}}</ref><ref name="gernet 69">Gernet, 69.</ref>

===Wootz steel and Damascus steel===
{{Main|Wootz steel|Damascus steel}}

Evidence of the earliest production of high carbon steel in the [[Indian Subcontinent]] was found in Samanalawewa area in [[Sri Lanka]].<ref>{{cite news| last = Wilford|first = John Noble|title = Ancient Smelter Used Wind To Make High-Grade Steel|work = The New York Times|date = 1996-02-06|url = http://www.nytimes.com/1996/02/06/science/ancient-smelter-used-wind-to-make-high-grade-steel.html?n=Top%2FNews%2FScience%2FTopics%2FArchaeology%20and%20Anthropology}}</ref> Wootz steel was produced in [[India]] by about 300 BC.<ref name=ann>Ann Feuerbach, 'An investigation of the varied technology found in swords, sabres and blades from the Russian Northern Caucasus' [https://www.es.ucl.ac.uk/iams/jour_25/iams25_Feuerbach.pdf IAMS 25 for 2005, 27-43 at 29], apparently ultimately from the writings of [[Zosimos of Panopolis]].</ref> Along with their original methods of forging steel, the Chinese had also adopted the production methods of creating [[Wootz steel]], an idea imported into China from India by the 5th century AD.<ref name="needham volume 4 part 1 282">Needham, Volume 4, Part 1, 282.</ref> In Sri Lanka, this early steel-making method employed the unique use of a wind furnace, blown by the monsoon winds, that was capable of producing high-carbon steel.<ref name="Juleff1">{{cite journal|author=G. Juleff|title=An ancient wind powered iron smelting technology in Sri Lanka|journal=[[Nature (journal)|Nature]]|volume=379|issue=3|pages=60–63|year=1996|doi=10.1038/379060a0|ref=harv}}</ref> Also known as [[Damascus steel]], wootz is famous for its durability and ability to hold an [[Sharpening|edge]]. It was originally created from a number of different materials including various [[trace element]]s. It was essentially a complicated alloy with iron as its main component. Recent studies have suggested that [[carbon nanotubes]] were included in its structure, which might explain some of its legendary qualities, though given the technology available at that time, they were produced by chance rather than by design.<ref>{{cite journal |title = Sharpest cut from nanotube sword|first = Katharine|last = Sanderson|publisher=[[Nature (journal)|Nature]]|date = 2006-11-15|accessdate = 2006-11-17|doi = 10.1038/news061113-11 |journal = News nature |ref = harv}}</ref> Natural wind was used where the soil containing iron was heated up with the use of wood. The ancient Sinhalese managed to extract a ton of steel for every 2 tons of soil{{Citation needed|date=January 2010}}, a remarkable feat at the time. One such furnace was found in Samanalawewa and archaeologists were able to produce steel as the ancients did long ago.<ref name="Juleff1"/><ref>{{cite journal|author=Wayman, M L and Juleff, G|title=Crucible Steelmaking in Sri Lanka|journal=Historical Metallurgy|volume=33|issue=1|year=1999|page=26|ref=harv}}</ref>

[[Crucible steel]], formed by slowly heating and cooling pure iron and carbon (typically in the form of charcoal) in a crucible, was produced in [[Merv]] by the 9th to 10th century AD.<ref name=ann/> In the 11th century, there is evidence of the production of steel in [[Song Dynasty|Song China]] using two techniques: a "berganesque" method that produced inferior, inhomogeneous steel and a precursor to the modern [[Bessemer process]] that utilized partial decarbonization via repeated forging under a [[cold blast]].<ref>{{cite journal|author=Robert Hartwell|title=Markets, Technology and the Structure of Enterprise in the Development of the Eleventh Century Chinese Iron and Steel Industry|journal=Journal of Economic History|volume=26|year=966|pages=53–54|ref=harv}}</ref>

===Modern steelmaking===
[[File:Bessemer Converter Sheffield.jpg|thumb|right|upright|A Bessemer converter in Sheffield, England]]
Since the 17th century the first step in European steel production has been the smelting of iron ore into [[pig iron]] in a [[blast furnace]].<ref name="tyle">R. F. Tylecote, ''A history of metallurgy'' 2 edn, Institute of Materials, London 1992, 95-99 and 102-105.</ref> Originally using charcoal, modern methods use [[coke (fuel)|coke]], which has proven to be a great deal cheaper.<ref>A. Raistrick, ''A Dynasty of Ironfounders'' (1953; York 1989)</ref><ref>C. K. Hyde, ''Technological Change and the British iron industry'' (Princeton 1977)</ref><ref>B. Trinder, ''The Industrial Revolution in Shropshire'' (Chichester 2000)</ref> 

====Processes starting from bar iron====
{{Main|Blister steel|Crucible steel}}

In these processes pig iron was "fined" in a [[finery forge]] to produce [[bar iron]] (wrought iron), which was then used in steel-making.<ref name="tyle"/> 

The production of steel by the [[cementation process]] was described in a treatise published in Prague in 1574 and was in use in [[Nuremberg]] from 1601. A similar process for [[case hardening]] armour and files was described in a book published in [[Naples]] in 1589. The process was introduced to England in about 1614.<ref>K. C. Barraclough, ''Steel before Bessemer: I Blister Steel: the birth of an industry'' (The Metals Society, London, 1984), 48-52.</ref> It was produced by Sir [[Basil Brooke (metallurgist)|Basil Brooke]] at [[Coalbrookdale]] during the 1610s. The raw material for this were bars of wrought iron. During the 17th century it was realised that the best steel came from [[oregrounds iron]] from a region of [[Sweden]], north of [[Stockholm]].  This was still the usual raw material in the 19th century, almost as long as the process was used.<ref>{{cite journal|author=P. W. King|title=The Cartel in Oregrounds Iron: trading in the raw material for steel during the eighteenth century|journal=Journal of Industrial History|volume=6|issue=1|year=2003|pages=25–49|ref=harv}}</ref><ref name="britannicaironandsteel">{{cite encyclopedia|title=Iron and steel industry|encyclopedia=Britannica|publisher=Encyclopaedia Britannica|year=2007|accessdate=2007-03-01}}</ref>

Crucible steel is steel that has been melted in a [[crucible]] rather than being [[forging|forged]], with the result that it is more homogeneous. Most previous furnaces could not reach high enough temperatures to melt the steel. The early modern crucible steel industry resulted from the invention of [[Benjamin Huntsman]] in the 1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast (usually) into ingots.<ref name="britannicaironandsteel"/><ref>K. C. Barraclough, ''Steel before Bessemer: II Crucible Steel: the growth of technology'' (The Metals Society, London, 1984).</ref>

====Processes starting from pig iron====
[[File:Siemens Martin Ofen Brandenburg.jpg|thumb|right|A Siemens-Martin steel oven from the [[Brandenburg]] Museum of Industry]]
[[File:Allegheny Ludlum steel furnace.jpg|thumb|right|White-hot steel pouring out of an electric arc furnace]]

The modern era in [[steelmaking]] began with the introduction of [[Henry Bessemer]]'s [[Bessemer process]] in 1858. His raw material was pig iron.<ref>{{cite book|title=History of the Manufacture of Iron in All Ages|author= James Moore Swank|isbn=0833734636| year=1892}}</ref> This enabled steel to be produced in large quantities cheaply, thus [[mild steel]] is now used for most purposes for which wrought iron was formerly used.<ref>{{cite encyclopedia|title=Bessemer process|encyclopedia=Britannica|volume=2|pages=168|publisher=Encyclopedia Britannica|year=2005|accessdate=2005-08-06}}</ref> The Gilchrist-Thomas process (or ''basic Bessemer process'') was an improvement to the Bessemer process, lining the converter with a [[basic (chemistry)|basic]] material to remove phosphorus. Another improvement in steelmaking was the [[Siemens-Martin process]], which complemented the Bessemer process.<ref name="britannicaironandsteel"/>

These were rendered obsolete by the Linz-Donawitz process of [[basic oxygen steelmaking]] (BOS), developed in the 1950s, and other oxygen steelmaking processes. Basic oxygen steelmaking is superior to previous steelmaking methods because the oxygen pumped into the furnace limits impurities.<ref>{{cite encyclopedia|title = Basic oxygen process|encyclopedia = Britannica|publisher = Encyclopedia Britannica|year = 2007|accessdate = 2007-02-28}}</ref> Now, [[electric arc furnace]]s (EAF) are a common method of reprocessing [[scrap|scrap metal]] to create new steel. They can also be used for converting pig iron to steel, but they use a great deal of electricity (about 440 kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity.<ref>J.A.T. Jones, B. Bowman, P.A. Lefrank, ''Electric Furnace Steelmaking'', in ''The Making, Shaping and Treating of Steel'', 525–660. R.J. Fruehan, Editor. 1998, The AISE Steel Foundation: Pittsburgh.</ref>

==Steel industry==
[[File:Port talbot large.jpg|left|thumb|A [[Corus Group]] plant in the [[United Kingdom]]]]
[[File:Steel production by country map.PNG|thumb|left|Steel production by country in 2007]]
{{See also|History of the modern steel industry|Global steel industry trends|Steel production by country|List of steel producers}}

It is common today to talk about "the iron and steel industry" as if it were a single entity, but historically they were separate products. The steel industry is often considered to be an indicator of economic progress, because of the critical role played by steel in infrastructural and overall [[economic development]].<ref>{{cite web| title = Steel Industry|url = http://bx.businessweek.com/steel-industry/|accessdate = 2009-07-12}}</ref>

The [[boom and bust|economic boom]] in [[China]] and India has caused a massive increase in the demand for steel in recent years. Between 2000 and 2005, world steel demand increased by 6%. Since 2000, several Indian <ref>{{cite web|url=http://csmonitor.com/2007/0212/p07s02-wosc.html|title=India's steel industry steps onto world stage| accessdate = 2009-07-12}}</ref> and Chinese steel firms have risen to prominence like [[Tata Steel]] (which bought [[Corus Group]] in 2007), [[Shanghai Baosteel Group Corporation]] and [[Shagang Group]]. [[ArcelorMittal]] is however the world's [[List of steel producers|largest steel producer]].

In 2005, the [[British Geological Survey]] stated China was the top steel producer with about one-third of the world share; Japan, Russia, and the US followed respectively.<ref>{{cite web| title = Long-term planning needed to meet steel demand|work = The News|date = 2008-03-01|url = http://www.thenews.com.pk/daily_detail.asp?id=98951}}{{dead link|date=April 2010}}</ref>

In 2008, steel started to be [[commodity market|traded as a commodity]] in the [[London Metal Exchange]]. At the end of 2008, the steel industry faced a sharp downturn that led to many cut-backs.<ref>{{cite news| last = Uchitelle|first = Louis|title = Steel Industry, in Slump, Looks to Federal Stimulus|newspaper = The New York Times|date = 2009-01-01|url = http://www.nytimes.com/2009/01/02/business/02steel.html?_r=1&partner=permalink&exprod=permalink|accessdate = 2009-07-19}}</ref>

==Recycling==
[[File:CompactedSteelScraps.jpg|thumb|left|A pile of steel scrap in Brussels, waiting to be recycled]]

Steel is one of the most [[recycling|recycled]] materials in the world,<ref name="encarta">{{cite news| last = Hartman|first = Roy A.|year = 2009|title = Recycling|publisher = [[Encarta]]|url = http://encarta.msn.com/encyclopedia_761556346/Recycling.html|archiveurl = http://web.archive.org/web/20080414215636/http://encarta.msn.com/encyclopedia_761556346/Recycling.html|archivedate = 2008-04-14}}</ref> and, as of 2008, more than 83% of steel was recycled in the United States.<ref name="reservesteel">{{cite web|url=http://www.recycle-steel.org/pdfs/2008Graphs.pdf|title = Steel Recycling Rates at a Glance |accessdate=2010-02-20 | archiveurl = http://www.webcitation.org/5nge7f632 | archivedate = 2010-02-20}}</ref> In the United States, it is the most widely recycled material; in 2000, more than 60 million metric tons were recycled.<ref name="encarta"/><ref>{{cite web|title=2005 Minerals Handbook|date=February 2007|url=http://minerals.usgs.gov/minerals/pubs/commodity/recycle/recycmyb05.pdf|format=PDF|accessdate=2008-06-15}}</ref> 

The most commonly recycled items are containers, automobiles, appliances, and construction materials. For example, in 2008, more than 97% of structural steel and 106% of automobiles were recycled, comparing the current steel consumption for each industry with the amount of recycled steel being produced (the [[late 2000s recession]] and the associated sharp decline in automobile production explains the over-100% calculation).<ref name="reservesteel"/> A typical appliance is about 75% steel by weight<ref>{{cite web|title = Recycling steel appliances|url = http://recycle-steel.org/appliances.html|accessdate = 2009-07-13}}</ref> and automobiles are about 65% steel and iron.<ref>{{cite web| title = Steel: Driving auto recycling success|url = http://recycle-steel.org/cars.html|accessdate = 2009-07-13}}</ref>

The steel industry has been actively recycling for more than 150 years, in large part because it is economically advantageous to do so. It is cheaper to recycle steel than to mine iron ore and manipulate it through the production process to form new steel. Steel does not lose any of its inherent [[physical property|physical properties]] during the recycling process, and has drastically reduced energy and material requirements compared with refinement from iron ore. The energy saved by recycling reduces the annual energy consumption of the industry by about 75%, which is enough to power eighteen million homes for one year.<ref>{{cite web|title = Facts About Steel Recycling|url = http://earth911.com/metal/steel/facts-about-steel-recycling/|accessdate = 2009-07-18}}</ref>

[[File:Steel from WTC for USS New York.jpg|thumb|right|Steel from the [[World Trade Center]] is poured for construction of {{USS|New York|LPD-21}}]]

The BOS steelmaking uses between 25 and 35% recycled steel to make new steel. BOS steel usually has less residual elements in it, such as [[copper]], [[nickel]] and [[molybdenum]] and is therefore more [[malleable]] than EAF steel so it is often used to make [[automotive fender]]s, [[soup can]]s, [[industrial drum]]s or any product with a large degree of cold working. EAF steelmaking uses almost 100% recycled steel. This steel contains more residual elements that cannot be removed through the application of oxygen and [[calcium oxide|lime]] so it is used to make [[structural beam]]s, [[steel plate|plate]]s, [[rebar|reinforcing bar]] and other products that require little cold working.<ref>{{cite web|title = Steel|url = http://www.epa.gov/waste/conserve/materials/steel.htm|accessdate = 2009-07-13}}</ref> Recycling one ton of steel saves 1,100 kilograms of [[iron ore]], 630&nbsp;kilograms of [[coal]], and 55&nbsp;kilograms of [[limestone]].<ref name="wastecap">{{cite web|title=Information on Recycling Steel Products |publisher=WasteCap of Massachusetts|url=http://wastecap.org/wastecap/commodities/steel/steel.htm#Benefitssteel|archiveurl=http://web.archive.org/web/20071011205459/http://wastecap.org/wastecap/commodities/steel/steel.htm#Benefitssteel|archivedate=2007-10-11|accessdate=2007-02-28}}</ref>

Because steel beams are manufactured to standardized dimensions, there is often very little waste produced during [[construction]], and any waste that is produced may be recycled. For a typical {{convert|2000|sqft|m2|-2|sing=on}} two-story house, a [[steel frame]] is equivalent to about six recycled cars, while a comparable wooden [[Light-frame construction|frame house]] may require as many as 40–50 [[tree]]s.<ref>{{cite web|title = Steel: the clear cut alternative for building homes| url = http://recycle-steel.org/PDFs/brochures/residenfram.pdf|accessdate = 2009-07-13}}</ref>

==Contemporary steel==
{{See also|Steel grades}}
Modern steels are made with varying combinations of alloy metals to fulfill many purposes.<ref name="materialsengineer"/> [[Carbon steel]], composed simply of iron and carbon, accounts for 90% of steel production.<ref name=EM2/> [[HSLA steel|High strength low alloy steel]] has small additions (usually < 2% by weight) of other elements, typically 1.5% manganese, to provide additional strength for a modest price increase.<ref>{{cite web|url=http://resources.schoolscience.co.uk/Corus/16plus/steelch3pg1.html|title=High strength low alloy steels|publisher=Schoolscience.co.uk|accessdate=2007-08-14}}</ref> [[Low alloy steel]] is alloyed with other elements, usually [[molybdenum]], manganese, [[chromium]], or [[nickel]], in amounts of up to 10% by weight to improve the hardenability of thick sections.<ref name=EM2/> [[Stainless steel]]s and [[surgical stainless steel]]s contain a minimum of 11% chromium, often combined with nickel, to resist [[corrosion]] ([[rust]]). Some stainless steels are [[magnetic]], while others are [[nonmagnetic]].<ref>{{cite web|url=http://steel.org |title=Steel Glossary |publisher= [[American Iron and Steel Institute]] (AISI)|accessdate=2006-07-30}}</ref>

Some more modern steels include [[tool steel]]s, which are alloyed with large amounts of tungsten and [[cobalt]] or other elements to maximize [[solution hardening]]. This also allows the use of [[precipitation hardening]] and improves the alloy's temperature resistance.<ref name=EM2/> Tool steel is generally used in axes, drills, and other devices that need a sharp, long-lasting cutting edge. Other special-purpose alloys include [[weathering steel]]s such as Cor-ten, which weather by acquiring a stable, rusted surface, and so can be used un-painted.<ref>{{cite web|url=http://aisc.org/MSCTemplate.cfm?Section=Steel_Interchange2&Template=/CustomSource/Faq/SteelInterchange.cfm&FaqID=2311|archiveurl=http://web.archive.org/web/20071222180444/http://aisc.org/MSCTemplate.cfm?Section=Steel_Interchange2&Template=/CustomSource/Faq/SteelInterchange.cfm&FaqID=2311|archivedate=2007-12-22|title=Steel Interchange|publisher= American Institute of Steel Construction Inc. (AISC)|accessdate=2007-02-28}}</ref>

Many other high-strength alloys exist, such as [[dual-phase steel]], which is heat treated to contain both a ferritic and martensitic microstructure for extra strength.<ref>{{cite web|title=Dual-phase steel|publisher=Intota Expert Knowledge Services|url=http://www.intota.com/experts.asp?strSearchType=all&strQuery=dual%2Dphase+steel|accessdate=2007-03-01}}</ref> Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of austentite at room temperature in normally austentite-free low-alloy ferritic steels. By applying strain to the metal, the austentite undergoes a [[phase transition]] to martensite without the addition of heat.<ref>{{cite web|last=Werner|first=Prof. Dr. mont. Ewald|title=Transformation Induced Plasticity in low alloyed TRIP-steels and microstructure response to a complex stress history|url=http://www.wkm.mw.tum.de/Forschung/projekte_html/transtrip.html|accessdate=2007-03-01}}</ref> [[Maraging steel]] is alloyed with nickel and other elements, but unlike most steel contains almost no carbon at all. This creates a very strong but still [[malleability|malleable]] metal.<ref>{{cite web|title = Properties of Maraging Steels|url = http://steel.keytometals.com/default.aspx?ID=CheckArticle&NM=103|accessdate=2009-07-19}}</ref> Twinning Induced Plasticity (TWIP) steel uses a specific type of strain to increase the effectiveness of work hardening on the alloy.<ref>{{cite web|last=Mirko|first=Centi|coauthors=Saliceti Stefano|title=Transformation Induced Plasticity (TRIP), Twinning Induced Plasticity (TWIP) and Dual-Phase (DP) Steels|publisher=Tampere University of Technology |url=http://www.dimet.unige.it/resta/studenti/2002/27839/26/TWIP,TRIPandDualphase%20mirko.doc |archiveurl=http://web.archive.org/web/20080307200557/http://www.dimet.unige.it/resta/studenti/2002/27839/26/TWIP,TRIPandDualphase+mirko.doc |archivedate=2008-03-07|accessdate=2007-03-01}}</ref> [[Eglin Steel]] uses a combination of over a dozen different elements in varying amounts to create a relatively low-cost metal for use in [[bunker buster]] weapons. Hadfield steel (after Sir [[Robert Hadfield]]) or [[manganese]] steel contains 12–14% manganese which when abraded forms an incredibly hard skin which resists wearing. Examples include [[Continuous track|tank tracks]], [[bulldozer#Blade|bulldozer blade]] edges and cutting blades on the [[jaws of life]].<ref>[http://answers.com/topic/hadfield-manganese-steel Hadfield manganese steel.] Answers.com. McGraw-Hill Dictionary of Scientific and Technical Terms, McGraw-Hill Companies, Inc., 2003. Retrieved on 2007-02-28.</ref>

Most of the more commonly used steel alloys are categorized into various grades by standards organizations. For example, the [[Society of Automotive Engineers]] has a series of [[SAE steel grades|grades]] defining many types of steel.<ref name=bringas>{{Cite book|last=Bringas|first=John E.|title=Handbook of Comparative World Steel Standards: Third Edition|publisher=ASTM International|page =14|year=2004|edition=3rd.|url=http://astm.org/BOOKSTORE/PUBS/DS67B_SampleChapter.pdf|archiveurl=http://web.archive.org/web/20070127135646/http://www.astm.org/BOOKSTORE/PUBS/DS67B_SampleChapter.pdf|archivedate=2007-01-27|format=PDF|isbn=0-8031-3362-6}}</ref> The [[ASTM International|American Society for Testing and Materials]] has a separate set of standards, which define alloys such as [[A36 steel]], the most commonly used structural steel in the United States.<ref>Steel Construction Manual, 8th Edition, second revised edition, American Institute of Steel Construction, 1986, ch. 1 page 1-5</ref>

Though not an alloy, [[hot-dip galvanizing|galvanized]] steel is a commonly used variety of steel which has been hot-dipped or electroplated in [[zinc]] for protection against rust.<ref>{{cite encyclopedia|title=Galvanic protection|encyclopedia=Britannica|publisher=Encyclopedia Britannica|year=2007|accessdate=2007-02-28}}</ref>

==Uses==
[[File:Steel-wool.jpg|thumb|right|A roll of [[steel wool]]]]

Iron and steel are used widely in the construction of roads, railways, other infrastructure, applicances, and buildings. Most large modern structures, such as [[stadium#The modern stadium|stadiums]] and [[skyscraper]]s, [[bridge]]s, and [[airports]], are supported by a steel skeleton. Even those with a concrete structure will employ steel for reinforcing. In addition to widespread use in [[major appliances]] and [[cars]]. Despite growth in usage of [[aluminium]], it is still the main material for car bodies. Steel is used in a variety of other [[construction]] materials, such as bolts, [[nail (engineering)|nails]], and [[screw]]s.<ref>{{cite web|last=Ochshorn|first=Jonathan|title=Steel in 20th Century Architecture|publisher=Encyclopedia of Twentieth Century Architecture|date=2002-06-11|url=http://www.ochshorndesign.com/cornell/writings/steel.html|accessdate=2010-04-26}}</ref> Other common applications include [[shipbuilding]], [[pipeline transport]], [[mining]], [[offshore construction]], [[aerospace]], [[white goods]] (e.g. [[washing machine]]s), [[heavy equipment]] such as bulldozers, office furniture, [[steel wool]], [[tool]]s, and [[armour]] in the form of personal vests or [[vehicle armour]] (better known as [[rolled homogeneous armour]] in this role).

===Historical===
[[File:Carbon steel knife.jpg|thumb|right|A carbon steel [[knife]]]]
Before the introduction of the Bessemer process and other modern production techniques, steel was expensive and was only used where no cheaper alternative existed, particularly for the cutting edge of knives, razors, swords, and other items where a hard, sharp edge was needed. It was also used for [[spring (device)|springs]], including those used in [[clock|clocks and watches]].<ref name=britannicaironandsteel/> With the advent of speedier and thriftier production methods, steel has been easier to obtain and much cheaper. It has replaced wrought iron for a multitude of purposes. However, the availability of [[plastic]]s in the latter part of the 20th century allowed these materials to replace steel due to their lower cost and weight.<ref>{{cite encyclopedia|title=Materials science|encyclopedia=Britannica|publisher=Encyclopedia Britannica|year=2007|accessdate=2007-03-01}}</ref>

===Long steel===
[[File:Steel tower.jpg|thumb|right|A steel pylon suspending [[overhead powerline]]s]]
*As reinforcing bars and mesh in [[reinforced concrete]]
*[[Rail tracks|Railroad tracks]]
*[[Structural steel]] in modern [[building]]s and [[bridge]]s
*[[Wire]]s

===Flat carbon steel===
*[[Major appliance]]s
*[[Magnetic core]]s
*The inside and outside body of [[automobile]]s, [[train]]s, and [[ship]]s.

===Stainless steel===
[[File:Sauce boat.jpg|thumb|right|A stainless steel [[sauce boat|gravy boat]]]]
{{Main|Stainless steel}}
*[[Cutlery]]
*[[Rulers]]
*[[Surgery|Surgical]] equipment
*[[Wrist watch]]es
<div style="clear:both"></div>

==See also==
{{col-start}}
{{col-break}}
*[[Cold rolling]]
*[[Global steel industry trends]]
*[[Hot rolling]]
*[[Iron in folklore]]
*[[List of steel producers]]
*[[Machinability]]
{{col-break}}
*[[Maraging steel]]
*[[Pelletizing]]
*[[Rolling (metalworking)|Rolling]]
*[[Rolling mill]]
*[[Rust Belt]]
*[[SAE steel grades]]
*[[Silicon steel]]
{{col-break}}
*[[Steel mill]]
*[[Steel abrasive]]
*[[Tamahagane]], used in Samurai swords.
*[[Tinning|Tinplate]]
{{col-end}}

==References==
{{clear}}
{{Reflist|colwidth=35em}}

===Bibliography===
*{{Cite document | last = Ashby | first = Michael F. | author-link = Michael F. Ashby | last2 = Jones | first2 = David Rayner Hunkin | title = An introduction to microstructures, processing and design | publisher = Butterworth-Heinemann | year = 1992 | ref = harv | postscript =.}}
*{{Cite book|last = Bugayev|first = K.|last2 = Konovalov|first2 = Y.|last3 = Bychkov|first3 = Y.|last4 = Tretyakov|first4 = E.|last5 = Savin|first5 = Ivan V.|title = Iron and Steel Production|publisher = The Minerva Group, Inc.|year = 2001|url = http://books.google.com/?id=MJdIVtmwuUsC|isbn = 9780894991097|accessdate = 2009-07-19}}.
*{{Cite book | last = Degarmo | first = E. Paul | last2 = Black | first2 = J T. | last3 = Kohser | first3 = Ronald A. | title = Materials and Processes in Manufacturing | publisher = Wiley | year = 2003 | edition = 9th | isbn = 0-471-65653-4 | ref = harv | postscript =.}}
*Gernet, Jacques (1982). ''A History of Chinese Civilization''. Cambridge: Cambridge University Press.
*{{Cite book | last = Smith | first = William F. | last2 = Hashemi | first2 = Javad | title = Foundations of Materials Science and Engineering | edition = 4th | year = 2006 | publisher = McGraw-Hill | isbn = 0-07-295358-6 | ref = harv | postscript =.}}

==Further reading==
*Duncan Burn; ''[http://questia.com/PM.qst?a=o&d=3914930 The Economic History of Steelmaking, 1867–1939: A Study in Competition]''. Cambridge University Press, 1961.
*Harukiyu Hasegawa, ''[http://questia.com/PM.qst?a=o&d=108742046 The Steel Industry in Japan: A Comparison with Britain]''. 1996.
*J. C. Carr and W. Taplin, ''[http://questia.com/PM.qst?a=o&d=808791 History of the British Steel Industry]''. Harvard University Press, 1962.
*H. Lee Scamehorn, ''[http://questia.com/PM.qst?a=o&d=94821694 Mill & Mine: The Cf&I in the Twentieth Century]''. University of Nebraska Press, 1992.
*Needham, Joseph (1986). ''Science and Civilization in China'': Volume 4, Part 1 & Part 3. Taipei: Caves Books, Ltd.
*Warren, Kenneth, ''[http://eh.net/bookreviews/library/0558 Big Steel: The First Century of the United States Steel Corporation, 1901–2001]''. University of Pittsburgh Press, 2001.

==External links==
{{commons|Steel}}
{{Wiktionary|steel}}
*[http://www.worldsteel.org/ World Steel Association (worldsteel)]
*[http://steeluniversity.org/ steeluniversity.org: Online steel education resources from worldsteel and the University of Liverpool]
*[http://www.stahlseite.de/ Extensive picture gallery of iron and steel production methods in North America and Europe]
*[http://www.zknives.com/knives/steels/steelchart.php Interactive knife steel composition chart and comparison graph builder]
*[http://www.msm.cam.ac.uk/phase-trans/2005/Fealloys.html Huge archive on steels, Cambridge University]

{{RecyclingByMaterial}}

[[Category:Building materials]]

[[Category:Steel| ]]
[[Category:Steelmaking]]

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