Editing Steel (section)

===Origins and production===
[[File:FeC-phase-diagram--multilingual.svg|thumb|upright=1.75|An iron-carbon [[phase diagram]] showing the conditions necessary to form different phases]]
[[File:Blacksmithing at the 2015 Fort Ross Festival - Fort Ross State Historic Park - Jenner, California - Sarah Stierch.jpg|thumb|An [[Incandescence|incandescent]] steel workpiece in a [[blacksmith]]'s art]]
Iron is commonly found in the Earth's [[crust (geology)|crust]] in the form of an [[ore]], usually an iron oxide, such as [[magnetite]] or [[hematite]]. Iron is extracted from [[iron ore]] by removing the oxygen through its combination with a preferred chemical partner such as carbon which is then lost to the atmosphere as carbon dioxide. This process, known as [[smelting]], was first applied to metals with lower [[melting]] points, such as [[tin]], which melts at about {{convert|250|C|F|abbr=on}}, and [[copper]], which melts at about {{convert|1100|C|F|abbr=on}}, and the combination, bronze, which has a melting point lower than {{convert|1083|C|F|abbr=on}}. In comparison, cast iron melts at about {{convert|1375|C|F|abbr=on}}.<ref name="Smelting">{{cite book |chapter=Smelting |title=[[Encyclopædia Britannica]] |edition=online |date=2007 |chapter-url= https://www.britannica.com/technology/smelting}}</ref> Small quantities of iron were smelted in ancient times, in the solid-state, by heating the ore in a [[charcoal]] fire and then [[welding]] the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon content could be controlled by moving it around in the fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily.{{Cn|date=January 2024}}

All of these temperatures could be reached with ancient methods used since the [[Bronze Age]]. Since the oxidation rate of iron increases rapidly beyond {{convert|800|C|F}}, it is important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iron oxides, results in an alloy ([[pig iron]]) that retains too much carbon to be called steel.<ref name="Smelting" /> The excess carbon and other impurities are removed in a subsequent step.{{Cn|date=January 2024}}

Other materials are often added to the iron/carbon mixture to produce steel with the desired properties. [[Nickel]] and [[manganese]] in steel add to its tensile strength and make the [[austenite]] form of the iron-carbon solution more stable, [[chromium]] increases hardness and melting temperature, and [[vanadium]] also increases hardness while making it less prone to [[metal fatigue]].<ref name="materialsengineer">{{cite web |title=Alloying of Steels |publisher=Metallurgical Consultants |date=28 June 2006 |url= http://materialsengineer.com/E-Alloying-Steels.htm |access-date=28 February 2007 |url-status=dead |archive-url= https://web.archive.org/web/20070221070822/http://www.materialsengineer.com/E-Alloying-Steels.htm |archive-date=21 February 2007}}</ref>

To inhibit corrosion, at least 11% chromium can be added to steel so that a hard [[Passivation (chemistry)|oxide]] forms on the metal surface; this is known as [[stainless steel]]. Tungsten slows the formation of [[cementite]], keeping carbon in the iron matrix and allowing [[martensite]] to preferentially form at slower quench rates, resulting in [[high-speed steel]]. The addition of [[lead]] and [[sulphur]] decrease grain size, thereby making the steel easier to [[lathe|turn]], but also more brittle and prone to corrosion. Such alloys are nevertheless frequently used for components such as nuts, bolts, and washers in applications where toughness and corrosion resistance are not paramount. For the most part, however, [[Block (periodic table)|p-block]] elements such as sulphur, [[nitrogen]], [[phosphorus]], and lead are considered contaminants that make steel more brittle and are therefore removed from steel during the melting processing.<ref name="materialsengineer" />