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Ordet ''stål'' kommer af det [[urgermansk]]e adjektiv ''stakhlijan'' (''lavet af stål''), som er beslægtet med ''stakhla'' (''stå fast'').<ref>{{cite web|url=http://www.etymonline.com/?term=steel|title=steel|work=[[Online Etymology Dictionary]]|author=Harper, Douglas|accessdate=20. november 2016}}</ref>
 
Stål er jern med mellem 0,002% og 2,1% karbon, målt efter vægt, når der er tale om rene jern-karbon-legeringer. Disse værdier varierer alt efter om der indgår andre [[grundstoffer]] såsom [[mangan]], [[chrom]], [[nikkel]], [[tungsten]] og så videre. For lidt kulstofindhold gør jernet forholdsvis blødt, smidigt og svagt. Er kulstofindholdet derimod højere end i stål, giver det en legering der almindeligvis kaldes [[råjern]], som er for sprød og skrøbelig til at den let kan bearbejdes. Der kan også indgå [[molybdæn]], [[bor (grundstof)|bor]], [[titan (grundstof)|titan]], [[vanadium]], [[kobolt]] og [[niobium]].<ref name=EM2>{{cite book|author1=Ashby, Michael F. |author2=Jones, David R. H. |lastauthoramp=yes |title=Engineering Materials 2|origyear=1986|edition=revideret|year=1992|publisher=Pergamon Press |location=Oxford|isbn=0-08-032532-7}}</ref> Andre grundstoffer er også vigtige, såsom [[fosfor]], [[svovl]] og [[silicium]], samt spor af [[oxygen]], [[nitrogen]] og [[kobber]] som oftest betragtes som uønskede.
<!--Alloys with a higher than 2.1% carbon content, depending on other element content and possibly on processing, are known as [[cast iron]]. Cast iron is not malleable even when hot, but it can be formed by [[casting]] as it has a lower [[melting point]] than steel and good [[castability]] properties.<ref name=EM2/> Certain compositions of cast iron, while retaining the economies of melting and casting, can be heat treated after casting to make [[malleable iron]] or [[ductile iron]] objects. Steel is also distinguishable from [[wrought iron]] (now largely obsolete), which may contain a small amount of carbon but large amounts of [[slag]].-->
<!--The carbon content of steel is between 0.002% and 2.1% by weight for plain [[iron]]&ndash;[[carbon]] [[alloy]]s. These values vary depending on [[alloying elements]] such as [[manganese]], [[chromium]], [[nickel]], iron, [[tungsten]], carbon and so on. Basically, steel is an iron-carbon alloy that does not undergo [[eutectic system|eutectic reaction]]. In contrast, [[cast iron]] does undergo eutectic reaction. Too little carbon content leaves (pure) iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy, commonly called [[pig iron]], that is brittle (not malleable). While iron alloyed with carbon is called carbon steel, [[alloy steel]] is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include: manganese, nickel, chromium, [[molybdenum]], [[boron]], [[titanium]], [[vanadium]], tungsten, [[cobalt]], and [[niobium]].<ref name=EM2>{{cite book|author1=Ashby, Michael F. |author2=Jones, David R. H. |lastauthoramp=yes |title=Engineering Materials 2|origyear=1986|edition=with corrections|year=1992|publisher=Pergamon Press |location=Oxford|isbn=0-08-032532-7}}</ref> Additional elements are also important in steel: [[phosphorus]], [[sulfur]], [[silicon]], and traces of [[oxygen]], [[nitrogen]], and [[copper]], that are most frequently considered undesirable.
 
Alloys with a higher than 2.1% carbon content, depending on other element content and possibly on processing, are known as [[cast iron]]. Cast iron is not malleable even when hot, but it can be formed by [[casting]] as it has a lower [[melting point]] than steel and good [[castability]] properties.<ref name=EM2/> Certain compositions of cast iron, while retaining the economies of melting and casting, can be heat treated after casting to make [[malleable iron]] or [[ductile iron]] objects. Steel is also distinguishable from [[wrought iron]] (now largely obsolete), which may contain a small amount of carbon but large amounts of [[slag]].-->
 
== Stålproduktion ==
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