View source for Stainless steel

{{Short description|Steel alloy resistant to corrosion}}
{{Use dmy dates|date=March 2014}}
[[File:Sink and taps in the men's locker room 3 BW.jpg|thumb|Stainless steel taps and sink]]
[[File:Inside detail of DEMACO DTC-1000 Treatment Center for Fresh Pasta Production (October 1995) 002.jpg|thumb|Stainless steel is used for industrial equipment when it is important that the equipment is durable and easy to clean.]]
{{Steels}}

'''Stainless steel''' is an [[iron]]-based [[alloy]] that contains [[chromium]], making it resistant to [[rust]] and [[corrosion]]. Alternatively, it is known as '''inox''' (an abbreviation of the French term ''inoxydable'', meaning non-oxidizable), '''corrosion-resistant steel''' ('''CRES'''),  '''Nirosta''' (an abbreviation of the German term ''nichtrostender Stahl'')<ref>{{cite web | title=Nirosta | date=4 March 2019 | url=https://en.wiktionary.org/wiki/Nirosta }}</ref> or '''rustless steel'''. Stainless steel's [[resistance to corrosion]] comes from its chromium content of 10.5% or more, which forms a [[Passivation (chemistry)|passive film]] that protects the material and can [[self-healing material|self-heal]] when exposed to oxygen.<ref name="Davis1994">{{Cite book |url=https://books.google.com/books?id=OrlG98AHdoAC |title=Stainless Steels |publisher=ASM International |year=1994 |isbn=978-0871705037 |editor-last=Davis |editor-first=Joseph R. |series=ASM Specialty Handbook |location=Materials Park, OH |access-date=8 March 2020 |archive-url=https://web.archive.org/web/20210414012400/https://books.google.com/books?id=OrlG98AHdoAC |archive-date=14 April 2021 |url-status=live}}</ref>{{rp|3}} It can be further alloyed with elements like [[molybdenum]], [[carbon]], [[nickel]] and [[nitrogen]] to enhance specific properties for various applications.

The alloy's properties, such as luster and resistance to corrosion, are useful in many applications. Stainless steel can be rolled into [[Sheet metal|sheets]], plates, bars, wire, and tubing. These can be used in [[cookware]], [[cutlery]], [[surgical instrument]]s, [[major appliance]]s, vehicles, construction material in large buildings, industrial equipment (e.g., in [[paper mill]]s, [[chemical plant]]s, [[water treatment]]), and storage tanks and tankers for chemicals and food products. Some grades are also suitable for [[forging]] and [[casting]].

The biological [[cleanability]] of stainless steel is superior to both copper and [[aluminium]], and comparable to glass.<ref>{{cite journal |last1=Boulané-Petermann |first1=L. |title=Processes of bioadhesion on stainless steel surfaces and cleanability: A review with special reference to the food industry |journal=Biofouling |date=1996 |volume=10 |issue=4 |pages=275–300 |doi=10.1080/08927019609386287 |pmid=22115182 |bibcode=1996Biofo..10..275B |issn=0892-7014}}</ref> Its cleanability, strength, and corrosion resistance have prompted the use of stainless steel in pharmaceutical and food processing plants.<ref>{{cite journal |last1=Zaffora |first1=Andrea |last2=Di Franco |first2=Francesco |last3=Santamaria |first3=Monica |title=Corrosion of stainless steel in food and pharmaceutical industry |journal=Current Opinion in Electrochemistry |date=October 2021 |volume=29 |page=Article 100760 |article-number=100760 |doi=10.1016/j.coelec.2021.100760 |url=https://www.sciencedirect.com/science/article/abs/pii/S2451910321000740 |access-date=21 January 2022|url-access=subscription }}</ref>

Different types of stainless steel are labeled with an [[American Iron and Steel Institute|AISI]] three-digit number.<ref name="asmads">{{cite book |author=ASM International |url=https://www.asminternational.org/documents/10192/1849770/06940G_Chapter_1.pdf/53f29213-5dd6-4499-9959-841477b385b9 |title=Alloy Digest Sourcebook: Stainless Steels |date=2000 |chapter=Introduction to Stainless Steels |access-date=1 October 2021 |archive-url=https://web.archive.org/web/20210701021614/https://www.asminternational.org/documents/10192/1849770/06940G_Chapter_1.pdf/53f29213-5dd6-4499-9959-841477b385b9 |archive-date=1 July 2021 |url-status=live}}</ref> The ISO 15510 standard lists the chemical compositions of stainless steels of the specifications in existing ISO, [[ASTM]], [[European Norm|EN]], [[Japanese Industrial Standards|JIS]], and [[Guobiao standards|GB]] standards in a useful interchange table.<ref name="iso15510">{{cite news |author=International Organization for Standardization |date=May 2014 |title=ISO 15510:2014 Stainless steels – Chemical composition |url=https://www.iso.org/standard/61187.html |url-status=live |access-date=1 October 2021 |archive-url=https://web.archive.org/web/20210602214530/https://www.iso.org/standard/61187.html |archive-date=2 June 2021}}</ref>

== Properties ==

=== Corrosion resistance ===

Although stainless steel does rust, this only affects the outer few layers of atoms, its chromium content shielding deeper layers from oxidation.

The addition of nitrogen also improves resistance to pitting corrosion and increases mechanical strength.<ref name="ISSFstaff_SSFamilyPDF_20200308">{{cite web |author=International Stainless Steel Forum |date=8 March 2020 |title=The Stainless Steel Family |url=http://www.worldstainless.org/Files/issf/non-image-files/PDF/TheStainlessSteelFamily.pdf |url-status=live |archive-url=https://web.archive.org/web/20160324085201/http://www.worldstainless.org/Files/ISSF/non-image-files/PDF/TheStainlessSteelFamily.pdf |archive-date=24 March 2016 |access-date=8 March 2020 |location=Brussels, Belgium}}</ref> Thus, there are numerous grades of stainless steel with varying chromium and molybdenum contents to suit the environment the alloy must endure.<ref>{{cite web |author=International Stainless Steel Forum |date=21 September 2018 |title=Corrosion Resistance of Stainless Steels |url=https://www.imoa.info/download_files/stainless-steel/issf/educational/Module_05_Corrosion_Resistance_of_Stainless_Steels_en.pdf |url-status=live |archive-url=https://web.archive.org/web/20210701021619/https://www.imoa.info/download_files/stainless-steel/issf/educational/Module_05_Corrosion_Resistance_of_Stainless_Steels_en.pdf |archive-date=1 July 2021 |access-date=16 June 2021}}</ref> Corrosion resistance can be increased further by the following means:
* increasing chromium content to more than 11%<ref name="ISSFstaff_SSFamilyPDF_20200308" />
* adding nickel to at least 8%<ref name="ISSFstaff_SSFamilyPDF_20200308" />
* adding molybdenum (which also improves resistance to [[pitting corrosion]])<ref name="ISSFstaff_SSFamilyPDF_20200308" />

=== Strength ===

The most common type of stainless steel, 304,<ref>{{Cite web |last= |date=2025-04-07 |title=Overview of Stainless Steel Grades and Types - Machining Concepts – Erie, PA |url=https://machiningconceptserie.com/overview-of-stainless-steel-grades-and-types/ |access-date=2025-08-20 |website=Machining Concepts |language=en-US}}</ref> has a tensile yield strength around {{cvt|30000|psi|MPa|order=flip}} in the annealed condition. It can be strengthened by cold working to a strength of {{cvt|153000|psi|MPa|order=flip}} in the full-hard condition.

The strongest commonly available stainless steels are precipitation hardening alloys such as [[17-4 stainless steel|17-4 PH]] and Custom 465. These can be heat treated to have tensile yield strengths up to {{cvt|251000|psi|MPa|order=flip}}.<ref>{{cite book
| title = MIL-HDBK-5J
| publisher = United States Department of Defense
| date = 31 January 2003
| page = 2-153, 2-222
}}</ref>

=== Melting point ===

The melting point of stainless steel ranges from {{convert|1325|to|1530|C|F}}, depending on the alloy, which is near that of ordinary steel, and much higher than aluminium or copper.<ref>{{Cite web |title=What is the melting point of stainless steel? |url=https://www.langleyalloys.com/knowledge-advice/what-is-the-melting-point-of-stainless-steel/ |access-date=2022-03-23 |website=Langley Alloys |language=en-US}}</ref><ref>{{Cite web |title=Melting Temperature Range for Stainless Steels – British Stainless Steel Association |url=https://bssa.org.uk/bssa_articles/melting-temperature-range-for-stainless-steels/ |access-date=2025-03-05}}</ref>

=== Conductivity ===

Like [[steel]], stainless steels are relatively poor conductors of electricity, with significantly lower [[Resistivity#Resistivity of various materials|electrical conductivities]] than copper. In particular, the [[Contact resistance|electrical contact resistance]] (ECR) of stainless steel arises as a result of the dense protective oxide layer and limits its functionality in applications as electrical connectors.<ref>{{Cite journal |last1=André |first1=Johan |last2=Antoni |first2=Laurent |last3=Petit |first3=Jean-Pierre |last4=De Vito |first4=Eric |last5=Montani |first5=Alexandre |date=April 2009 |title=Electrical contact resistance between stainless steel bipolar plate and carbon felt in PEFC: A comprehensive study |url=https://linkinghub.elsevier.com/retrieve/pii/S0360319909001475 |journal=International Journal of Hydrogen Energy |language=en |volume=34 |issue=7 |pages=3125–3133 |doi=10.1016/j.ijhydene.2009.01.089|bibcode=2009IJHE...34.3125A |url-access=subscription }}</ref> Copper alloys and nickel-coated connectors tend to exhibit lower ECR values and are preferred materials for such applications. Nevertheless, stainless steel connectors are employed in situations where ECR poses a lower design criterion and corrosion resistance is required, for example in high temperatures and oxidizing environments.<ref>{{Cite journal |last1=Zhu |first1=J.H. |last2=Zhang |first2=Y. |last3=Basu |first3=A. |last4=Lu |first4=Z.G. |last5=Paranthaman |first5=M. |last6=Lee |first6=D.F. |last7=Payzant |first7=E.A. |date=January 2004 |title=LaCrO3-based coatings on ferritic stainless steel for solid oxide fuel cell interconnect applications |url=https://linkinghub.elsevier.com/retrieve/pii/S0257897203009952 |journal=Surface and Coatings Technology |language=en |volume=177-178 |pages=65–72 |doi=10.1016/j.surfcoat.2003.05.003|bibcode=2004SurCT.177...65Z |url-access=subscription }}</ref>

=== Magnetism ===

[[Martensitic stainless steel|Martensitic]], [[Duplex stainless steel|duplex]] and [[ferritic stainless steel]]s are [[Permeability (electromagnetism)#Values for some common materials|magnetic]], while [[austenitic stainless steel]] is usually non-magnetic.<ref>{{Cite web |date=October 2008 |title=Atlas Tech Note: qualitative sorting tests for steels |url=https://www.atlassteels.com.au/documents/TN1-qualitative%20sorting%20tests%20rev%20Oct%202008.pdf |access-date=2022-08-24 |website=Atlas Steels}}</ref> Ferritic steel owes its magnetism to its [[Cubic crystal system|body-centered cubic]] [[crystal structure]], in which iron atoms are arranged in cubes (with one iron atom at each corner) and an additional iron atom in the center. This central iron atom is responsible for ferritic steel's magnetic properties.<ref>{{Cite web |title=Ferritic stainless steels |url=https://bssa.org.uk/bssa_articles/ferritic-stainless-steels/ |access-date=2025-06-11 |website=bssa.org.uk |quote=Body‑centred cubic grains are what give ferritic steel its magnetic properties...}}</ref> This arrangement also limits the amount of carbon the steel can absorb to around 0.025%.<ref>{{Cite web |title=What Is The Difference Between Ferritic, Austenitic & Martensitic Stainless Steels? |url=https://www.accu.co.uk/p/112-what-is-the-difference-between-ferritic-austenitic-martensitic-stainless-steels-accu |access-date=2022-08-24 |website=Accu.co.uk}}</ref> Grades with low coercive field have been developed for electro-valves used in household appliances and for injection systems in internal combustion engines. Some applications require non-magnetic materials, such as [[magnetic resonance imaging]].<ref>{{Cite web |title=MRI Safety Tutorial |url=https://www.biac.duke.edu/research/safety/mri-safety-tutorial |access-date=2025-06-11 |website=biac.duke.edu |quote=Objects that are constructed in part or whole with ferromagnetic materials ... will be strongly attracted to the magnet bore...}}</ref> [[austenitic stainless steel|Austenitic]] stainless steels, which are usually [[Permeability (electromagnetism)#Values for some common materials|non-magnetic]], can be made slightly magnetic through [[work hardening]]. Sometimes, if austenitic steel is bent or cut, magnetism occurs along the edge of the stainless steel because the crystal structure rearranges itself.<ref>{{Cite web |title=Why don't magnets work on some stainless steels? |url=https://www.scientificamerican.com/article/why-dont-magnets-work-on/ |access-date=2022-07-22 |website=Scientific American |language=en}}</ref>
{| class="wikitable"
|+Magnetic permeability of some austenitic stainless steel grades after annealing 2 hours at 1050{{nbsp}}°C<ref>{{Cite news|last1=Fofanov|first1=D.|title=Magnetic properties of Stainless Steels: applications, opportunities, and new developments|date=29 Nov 2011|work=Stainless steel World Conference|last2=Riedner|first2=S.}}</ref>
|-
! EN grade
! 1.4307
! 1.4301
! 1.4404
! 1.4435
|-
| Magnetic permeability, μ
| 1.056
| 1.011
| 1.100
| 1.000
|}

=== Wear ===

[[Galling]], sometimes called cold welding, is a form of severe adhesive wear, which can occur when two metal surfaces are in relative motion to each other and under heavy pressure. Austenitic stainless steel fasteners are particularly susceptible to thread galling, though other alloys that self-generate a protective oxide surface film, such as aluminum and titanium, are also susceptible. Under high contact-force sliding, this oxide can be deformed, broken, and removed from parts of the component, exposing the bare reactive metal. When the two surfaces are of the same material, these exposed surfaces can easily fuse. Separation of the two surfaces can result in surface tearing and even complete seizure of metal components or fasteners.<ref>{{Cite web |last=Committee of Stainless Steel Producers. American Iron and Steel Institute |date=1978 |title=Review of the Wear and Galling Characteristics of Stainless Steels |url=https://nickelinstitute.org/en/library/technical-guides/review-of-wear-and-galling-characteristics-of-stainless-steel-9006/ |url-status=live |archive-url=https://web.archive.org/web/20180612143620/https://nickelinstitute.org/~/media/Files/TechnicalLiterature/ReviewofWearandGallingCharacteristicsofStainlessSteel_9006_.ashx |archive-date=12 June 2018 |access-date=1 October 2021 |website=Nickel Institute}}</ref><ref name="BSSA=2001">{{cite journal |author=British Stainless Steel Association |title=Galling and Galling Resistance of Stainless Steels |year=2001 |journal=SSAS Information Sheet No. 5.60 |url=http://www.bssa.org.uk/publications.php?id=17 |access-date=1 October 2021 |archive-date=24 July 2020 |archive-url=https://web.archive.org/web/20200724062703/https://www.bssa.org.uk/publications.php?id=17 |url-status=live }}</ref> Galling can be mitigated by the use of dissimilar materials (bronze against stainless steel) or using different stainless steels (martensitic against austenitic). Additionally, threaded joints may be [[Lubrication|lubricated]] to provide a film between the two parts and prevent galling. [[Nitronic]] 60, made by selective alloying with [[manganese]], [[silicon]], and nitrogen, has demonstrated a reduced tendency to gall.<ref name="BSSA=2001" />

=== Density ===
The density of stainless steel ranges from {{cvt|7.5|to|8.0|g/cm3|lb/in3}} depending on the alloy.

== History ==
[[File:Stainless steel nyt 1-31-1915.jpg|thumb|An announcement, as it appeared in a 1915 issue of ''The New York Times'', of the development of stainless steel in [[Sheffield]], England<ref name="NYT">{{cite journal |journal=New York Times |title=A non-rusting steel |date=31 January 1915}}</ref>]]

The invention of stainless steel followed a series of scientific developments, starting in 1798 when chromium was first shown to the [[Académie française|French Academy]] by [[Louis Vauquelin]]. In the early 1800s, British scientists James Stoddart, [[Michael Faraday]], and [[Robert Mallet]] observed the resistance of chromium-iron alloys ("chromium steels") to [[oxidizing agents]]. [[Robert Bunsen]] discovered chromium's resistance to strong acids. The corrosion resistance of iron-chromium alloys may have been first recognized in 1821 by [[Pierre Berthier]], who noted their resistance against attack by some acids and suggested their use in cutlery.<ref>{{Cite book|url = https://books.google.com/books?id=E30rCBeM8nkC&q=Stainless+Steel+Berthier&pg=PA10|title = The History of Stainless Steel|isbn = 978-1615030118|last1 = Cobb|first1 = Harold M.|year = 2010| publisher=ASM International |access-date = 1 October 2021|archive-date = 14 April 2021|archive-url = https://web.archive.org/web/20210414012347/https://books.google.com/books?id=E30rCBeM8nkC&q=Stainless+Steel+Berthier&pg=PA10|url-status = live}}</ref>

In the 1840s, both Britain's [[Sheffield]] steelmakers and then [[Krupp]] of Germany were producing chromium steel with the latter employing it for cannons in the 1850s.<ref>{{Cite book|url = https://books.google.com/books?id=CAwyBgAAQBAJ&q=Chrome+Steel+Baur&pg=PA149|title = The Metallurgic Age: The Victorian Flowering of Invention and Industrial Science|isbn = 978-1476611136|last1 = Quentin r. Skrabec|first1 = Jr|date = 24 January 2015| publisher=McFarland |access-date = 1 October 2021|archive-date = 14 April 2021|archive-url = https://web.archive.org/web/20210414012546/https://books.google.com/books?id=CAwyBgAAQBAJ&q=Chrome+Steel+Baur&pg=PA149|url-status = live}}</ref> In 1861, [[Robert Forester Mushet]] took out a patent on chromium steel in Britain.<ref>{{cite magazine |last=Waldo |first=Leonard |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015014665320&view=1up&seq=902 |title=Chrome-Nickel Iron and Steel Products |magazine=Iron Age |volume=98 |date=October 1916 |pages=838–839 |publisher=David Williams Co. |location=New York City |via=Haithi Trust |access-date=1 October 2021 |archive-date=14 April 2021 |archive-url=https://web.archive.org/web/20210414010929/https://babel.hathitrust.org/cgi/pt?id=mdp.39015014665320&view=1up&seq=902 |url-status=live }}</ref>

These events led to the first American production of chromium-containing steel by J. Baur of the Chrome Steel Works of Brooklyn for the construction of bridges. A US patent for the product was issued in 1869.<ref name="CobbHistory2010">{{Cite book |last=Cobb |first=Harold M. |url=https://books.google.com/books?id=E30rCBeM8nkC |title=The History of Stainless Steel |date=2010 |publisher=ASM International |isbn=978-1615030118 |location=Materials Park, OH |access-date=8 March 2020 |archive-url=https://web.archive.org/web/20200729124003/https://books.google.com/books?id=E30rCBeM8nkC |archive-date=29 July 2020 |url-status=live}}</ref>{{rp|2261}}{{efn|{{citation needed span|text=Despite the evidence of the use of Baur's "chrome steel" in bridgeworks, others{{who|date=March 2020}} have argued that metallurgists of the 19th century were unable to produce anything but <!--the combination of low carbon and high chromium found in most modern stainless steels, and the--> high-chromium <!-- they could produce were-->alloys that were "too brittle to be practical".{{quote without source|date=December 2022}}{{according to whom|date=March 2020}}|date=March 2020}} }}<!--IF YOU WANT THESE ORIGINAL STATEMENTS TO APPEAR IN THE MAIN BODY, AS THEY DID EARLIER, FIND SOURCES, AND STATE WHAT THE SOURCES SAY, AND MAKE THE CITATIONS FULL ENOUGH AND CLEAR ENOUGH THAT WE CAN CHECK THEM.--> This was followed with recognition of the corrosion resistance of chromium alloys by Englishmen John T. Woods and John Clark, who noted ranges of chromium from 5–30%, with added tungsten and "medium carbon". They pursued the commercial value of the innovation via a British patent for "Weather-Resistant Alloys".<ref name = CobbHistory2010/>{{rp|261,11}}<ref>{{cite web |url=http://www.airedalesprings.co.uk/its-complicated-the-discovery-of-stainless-steel/ |title=It's Complicated: The Discovery of Stainless Steel |publisher=Airedale Springs |date=September 2015 |access-date=1 October 2021 |archive-date=15 April 2021 |archive-url=https://web.archive.org/web/20210415170555/https://www.airedalesprings.co.uk/its-complicated-the-discovery-of-stainless-steel/ |url-status=live }}{{full citation needed|date=March 2020}}{{verify source|date=March 2020}}</ref>{{full citation needed|date=March 2020}}

Scientists researching steel corrosion in the second half of the 19th century didn't pay attention to the amount of carbon in the alloyed steels they were testing until in 1898 [[Adolphe Carnot]] and E. Goutal noted that chromium steels better resist to oxidation with acids the less carbon they contain.<ref>[[s:fr:Page:Comptes rendus hebdomadaires des séances de l'Académie des sciences, tome 126, 1898.djvu/1243]]</ref><ref>{{Cite book |last=Monypenny |first=J. h g |url=https://archive.org/details/in.ernet.dli.2015.125041/page/n27/mode/1up |title=Stainless Iron And Steel |date=1923}}</ref>

Also in the late 1890s, German chemist [[Hans Goldschmidt]] developed an aluminothermic ([[thermite]]) process for producing carbon-free chromium.<ref name="bssahist" /> Between 1904 and 1911, several researchers, particularly [[Leon Guillet]] of France, prepared alloys that would later be considered stainless steel.<ref name="bssahist">{{cite web |archive-url=https://web.archive.org/web/20120112001630/http://www.bssa.org.uk/about_stainless_steel.php?id=31 |archive-date=12 January 2012 |publisher=British Stainless Steel Association |url=http://www.bssa.org.uk/about_stainless_steel.php?id=31 |title=The Discovery of Stainless Steel }}</ref><ref name="chezeau97">{{cite journal |doi=10.1051/metal/199794050592|title=Léon Alexandre Guillet (1873–1946)|year=1997|last1=Chezeau|first1=N.|journal=Revue de Métallurgie|volume=94|issue=5|pages=592–596}}</ref>

In 1908, the [[Essen]] firm [[Friedrich Krupp Germaniawerft]] built the 366-ton sailing yacht ''[[Germania (yacht)|Germania]]'' featuring a chrome-nickel steel hull, in Germany. In 1911, Philip Monnartz reported on the relationship between chromium content and corrosion resistance.<ref name="outooyj"/> On 17 October 1912, [[Krupp]] engineers Benno Strauss and Eduard Maurer patented as [[Nirosta]] the [[austenitic stainless steel]]<ref name=nirostade>{{cite web |url=http://www.nirosta.de/History.22.0.html?&L=1 |title=ThyssenKrupp Nirosta: History |access-date=13 August 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070902202906/http://www.nirosta.de/History.22.0.html?&L=1 |archive-date=2 September 2007 |df=dmy-all }}</ref><ref name=patnet1>{{cite web |url=https://depatisnet.dpma.de/DepatisNet/depatisnet?action=pdf&docid=DE000000304126A |title=DEPATISnet-Dokument DE000000304126A |access-date=1 October 2021 |archive-date=13 August 2017 |archive-url=https://web.archive.org/web/20170813231441/https://depatisnet.dpma.de/DepatisNet/depatisnet?action=pdf&docid=DE000000304126A |url-status=live }}</ref><ref name=patnet2>{{cite web |url=https://depatisnet.dpma.de/DepatisNet/depatisnet?action=pdf&docid=DE000000304159A |title=DEPATISnet-Dokument DE000000304159A |access-date=1 October 2021 |archive-date=7 August 2020 |archive-url=https://web.archive.org/web/20200807084553/https://depatisnet.dpma.de/DepatisNet/depatisnet?action=pdf&docid=DE000000304159A |url-status=live }}</ref><ref name="outooyj">{{cite news |title=Handbook of Stainless Steel |publisher=Outokumpu Oyj |date=2013 |page=12}}</ref> that became known as '''18/8''' or AISI type 304.<ref name=hmcname/>

Similar developments were taking place in the United States, where Christian Dantsizen of [[General Electric]]<ref name="hmcname">{{cite journal |last1=Cobb |first1=Harold M. |title=The Naming and Numbering of Stainless Steels |url=https://www.asminternational.org/home/-/journal_content/56/10192/AMP16509P039/PERIODICAL-ARTICLE |volume=165 |journal=Advanced Materials & Processes |issue=9 |publisher=ASM International |date=September 2007 |access-date=1 October 2021 |archive-date=27 June 2021 |archive-url=https://web.archive.org/web/20210627164956/https://www.asminternational.org/home/-/journal_content/56/10192/AMP16509P039/PERIODICAL-ARTICLE |url-status=live }}</ref> and Frederick Becket (1875–1942) at [[Union Carbide]] were industrializing ferritic stainless steel.<ref name="ebbecket">{{cite news |title=Frederick Mark Becket American metallurgist |url=https://www.britannica.com/biography/Frederick-Mark-Becket |publisher=Encyclopaedia Britannica |date=7 January 2021 |access-date=1 October 2021 |archive-date=7 June 2021 |archive-url=https://web.archive.org/web/20210607073125/https://www.britannica.com/biography/Frederick-Mark-Becket |url-status=live }}</ref> In 1912, [[Elwood Haynes]] applied for a US patent on a martensitic stainless steel alloy, which was not granted until 1919.<ref>Carlisle, Rodney P. (2004) [https://books.google.com/books?id=pDbQVE3IdTcC&pg=PA380 Scientific American Inventions and Discoveries] {{Webarchive|url=https://web.archive.org/web/20210413225151/https://books.google.com/books?id=pDbQVE3IdTcC&pg=PA380 |date=13 April 2021 }}, p. 380, John Wiley and Sons, {{ISBN|0-471-24410-4}}.</ref>

===Harry Brearley===
[[File:Harry Brearley.jpg|thumb|Monument to [[Harry Brearley]] at the former [[Firth Brown Steels|Brown Firth Research Laboratory]] in [[Sheffield]], England]]
While seeking a corrosion-resistant alloy for gun barrels in 1913, [[Harry Brearley]] of the [[Firth Brown Steels|Brown-Firth]] research laboratory in Sheffield, England, discovered and subsequently industrialized a [[martensitic stainless steel]] alloy, later known as AISI type 420.<ref name=hmcname/> The discovery was announced two years later in a January 1915 newspaper article in ''The New York Times''.<ref name="NYT" />

The metal was later marketed under the "Staybrite" brand by [[Vickers|Firth Vickers]] in England and was used for the new entrance canopy for the [[Savoy Hotel]] in London in 1929.<ref>Howse, Geoffrey (2011) ''A Photographic History of Sheffield Steel'', History Press, {{ISBN|0752459856}}.</ref> Brearley applied for a US patent during 1915 only to find that Haynes had already registered one. Brearley and Haynes pooled their funding and, with a group of investors, formed the American Stainless Steel Corporation, with headquarters in [[Pittsburgh]], Pennsylvania.<ref name="CobbHistory2010" />{{rp|360}}

===Rustless steel===
Brearley initially called his new alloy "rustless steel". The alloy was sold in the US under different brand names like "Allegheny metal" and "Nirosta steel". Even within the metallurgy industry, the name remained unsettled; in 1921, one trade journal called it "unstainable steel".<ref>{{cite news |last=Moneypenny |first=J. H. G. |title=Unstainable Steel |pages=442, 463 |date=2 April 1921 |url=https://archive.org/details/miningscientific122sanfuoft |access-date=17 February 2013 |newspaper=Mining and Scientific Press}}</ref>

Brearley worked with a local cutlery manufacturer, who gave it the name "stainless steel".<ref>{{cite web |title=The development of stainless steel |publisher=Korea Iron & Steel Association |work=Stainless Steel Club |location=[[Seoul, Korea]] |url=http://www.stainlesssteel.or.kr/english/stsinfo/develop.asp  |archive-url=https://web.archive.org/web/20050827005100/http://www.stainlesssteel.or.kr/english/stsinfo/develop.asp |archive-date=27 August 2005 |access-date=22 July 2011}}</ref><ref>{{Cite web |title=Stainless Steel |url=https://yijinsolution.com/services/cnc-machining/stainless-steel/ |access-date=2025-06-11}}</ref> As late as 1932, [[Ford Motor Company]] continued calling the alloy "rustless steel" in automobile promotional materials.<ref>{{cite web |title=1932 – The Invention of the Ford V8 Engine |date=18 November 2015 |publisher=[[YouTube]] |url=https://www.youtube.com/watch?v=3RB3z1er9Sw |accessdate=5 February 2022}}</ref> However, stainless tended to predominate worldwide, and even in modern Japan, Western cutlery is simply referred to as "stainless (without "steel") spoon/fork" etc. [ステンレス: sutenresu].

In 1929, before the Great Depression, over 25,000 tons of stainless steel were manufactured and sold in the US annually.<ref>{{cite magazine |title=New Steel Alloy is Rustproof |magazine=Popular Science |url=https://books.google.com/books?id=sygDAAAAMBAJ&pg=PA31 |date=December 1930 |publisher=Bonnier Corporation |pages=31– |issn=0161-7370 |access-date=1 October 2021 |archive-date=13 April 2021 |archive-url=https://web.archive.org/web/20210413225149/https://books.google.com/books?id=sygDAAAAMBAJ&pg=PA31 |url-status=live }}</ref>

Major technological advances in the 1950s and 1960s allowed the production of large tonnages at an affordable cost:
* AOD process ([[argon oxygen decarburization]]), for the removal of carbon and sulfur
* [[Continuous casting]] and [[Rolling (metalworking)#Hot rolling|hot strip rolling]]<ref>{{Cite book |title=Primer on flat rolling |last=Lenard |first=John G. |date=2014 |publisher=Elsevier Science |isbn=978-0-08-099418-5 }}</ref>
* The [[Z-mill|Z-Mill]], or Sendzimir cold rolling mill<ref>{{Cite web | url=http://www.sendzimir.com/company/history/ | title=Sendzimir {{pipe}} Company Info {{pipe}} Company History | date=23 February 2021 | access-date=1 October 2021 | archive-date=15 April 2021 | archive-url=https://web.archive.org/web/20210415165151/https://www.sendzimir.com/company/history/ | url-status=live }}</ref><ref>{{Cite web |url=https://www.nipponsteel.com/en/tech/report/nsc/pdf/n9902.pdf |title=Technical Progress of Stainless Steel and its future trend |last=Ikeda |first=Satoshi |date=2010 |website= |publisher=Nippon Steel |access-date=1 October 2021 |archive-date=1 July 2021 |archive-url=https://web.archive.org/web/20210701021621/https://www.nipponsteel.com/en/tech/report/nsc/pdf/n9902.pdf |url-status=live }}</ref>
* The Creusot-Loire Uddeholm (CLU) and related processes which use steam instead of some or all of the argon<ref>{{Cite book|last=India: National Institute of Industrial Research|title=The Complete Technology Book on Hot Rolling of Steel|publisher=Asia Pacific|year=2017|isbn=978-8190568586|location=Delhi |page=324|language=English}}</ref>

== Families ==
{{anchor|Types of stainless steel}}<!-- target from [[drug-eluting stent#design]] -->
Stainless steel is classified into five different "families" of alloys, each having a distinct set of attributes. Four of the families are defined by their predominant [[crystalline structure]] - the austenitic, ferritic, martensitic, and duplex alloys. The fifth family, precipitation hardening, is defined by the type of heat treatment used to develop its properties.

=== Austenitic ===
{{main|Austenitic stainless steel}}

Austenitic stainless steel<ref>{{Cite book|title=Stainless steels for design engineers (#05231G)|publisher=ASM International|year=2008|isbn=978-0-87170-717-8|url=https://www.asminternational.org/search/-/journal_content/56/10192/05231G/PUBLICATION|pages=69–78 (Chapter 6)|access-date=1 October 2021|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414010819/https://www.asminternational.org/search/-/journal_content/56/10192/05231G/PUBLICATION|url-status=live}}</ref><ref>{{Cite book|url=https://www.nickelinstitute.org/library/?opt_perpage=20&opt_layout=grid&searchTerm=austenitic%20stainless%20steel&contentTypes=22f540f09ae14cab816ae22ddd6e0bf5,b412a2a14cea4a9cb03684666654b559&page=2|title=Practical Guidelines for the Fabrication of High Performance Austenitic Stainless Steels|isbn=978-0-87170-717-8|last1=McGuire|first1=Michael F.|year=2008|publisher=ASM International |access-date=1 October 2021|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414011308/https://nickelinstitute.org/library/?opt_perpage=20&opt_layout=grid&searchTerm=austenitic%20stainless%20steel&contentTypes=22f540f09ae14cab816ae22ddd6e0bf5,b412a2a14cea4a9cb03684666654b559&page=2|url-status=live}}</ref> is the largest family of stainless steels, making up about two-thirds of all stainless steel production.<ref name="ISSF-2021" /> They have a [[face-centered cubic]] crystal structure.<ref name="totalmateria">{{Cite web|title=Microstructures in Austenitic Stainless Steels :: Total Materia Article|url=https://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=268|access-date=2020-06-23|website=www.totalmateria.com|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414010819/https://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=268|url-status=live}}</ref> This microstructure is achieved by alloying steel with sufficient nickel, manganese, or nitrogen to maintain an austenitic microstructure at all temperatures, ranging from the [[cryogenic]] region to the melting point.<ref name="totalmateria" /> Thus, austenitic stainless steels are not hardenable by heat treatment since they possess the same microstructure at all temperatures.<ref name="totalmateria" />

Austenitic stainless steels consist of two subfamilies:
* 200 series<ref>{{Cite web|url=https://www.bssa.org.uk/publications.php?id=96|title=200 Series Stainless Steels. An overview|last=Bristish Stainless Steel Association|date=August 2006|publisher=Stainless Steel Industry|access-date=1 October 2021|archive-date=7 August 2020|archive-url=https://web.archive.org/web/20200807114612/https://www.bssa.org.uk/publications.php?id=96|url-status=live}}</ref> are chromium-manganese-nickel alloys that maximize the use of manganese and nitrogen to minimize the use of nickel. Due to their nitrogen addition, they possess approximately 50% higher yield strength than 300-series stainless sheets of steel. Representative alloys include Type 201 and Type 202.
* 300 series are chromium-nickel alloys that achieve their austenitic microstructure almost exclusively by nickel alloying; some very highly alloyed grades include some nitrogen to reduce nickel requirements. 300 series is the largest group and the most widely used. Representative alloys include Type [[SAE 304 stainless steel|304]] and Type [[Marine grade stainless|316]].

=== Ferritic ===
{{main|Ferritic stainless steel}}

Ferritic stainless steels have a [[body-centered cubic]] crystal structure, are magnetic, and are hardenable by cold working, but not by heat treating. They contain between 10.5% and 27% chromium with very little or no nickel. Due to the near-absence of nickel, they are less expensive than austenitic stainless steels. Representative alloys include Type 409, Type 429, Type 430, and Type 446. Ferritic stainless steels are present in many products, which include:
* Automobile exhaust pipes<ref>{{Cite book|last1=Santacreu|first1=P-O|title=K4X: A new ferritic stainless steel grade with improved durability for high temperature exhaust manifolds|last2=Faivre|first2=L.|last3=Acher|first3=A.|last4=Leseux|first4=J.|publisher=Proceedings of 7th European Stainless Steel Science & Market (Como, Italy) Paper 25|year=2011}}</ref>
* Architectural and structural applications<ref>{{Cite journal|last1=Cashell|first1=K. A.|last2=Baddoo|first2=N.R.|date=2014|title=Ferritic stainless steels in structural applications|journal=Thin-walled Structures|publisher=Elsevier B.V.|volume=83|pages=169–181|doi=10.1016/j.tws.2014.03.014|url=https://bura.brunel.ac.uk/handle/2438/9834|access-date=1 October 2021|archive-date=24 November 2020|archive-url=https://web.archive.org/web/20201124152713/https://bura.brunel.ac.uk/handle/2438/9834|url-status=live}}</ref>
* Building components, such as slate hooks, roofing, and chimney ducts{{Citation needed|date=January 2025}}
* Power plates in [[solid oxide fuel cell]]s operating at temperatures around {{cvt|700|C|F|sigfig=2}}<ref>{{Cite journal|last1=Shaigan|first1=Nima|last2=Qu|first2=Wei|last3=Ivey|first3=Douglas|last4=Chen|first4=Weixing|date=2010|title=A review of recent progress in coatings, surface modifications and alloy developments for solid oxide fuel cell ferritic stainless steel interconnects|journal=Journal of Power Sources|publisher=Elsevier B.V.|volume=195|issue=6|pages=1529–1542|doi=10.1016/j.jpowsour.2009.09.069|bibcode=2010JPS...195.1529S}}</ref>

=== Martensitic ===
{{main|Martensitic stainless steel}}

Martensitic stainless steels have a body-centered tetragonal crystal structure, are magnetic, and are hardenable by heat treating and by cold working. They offer a wide range of properties and are used as stainless engineering steels, stainless tool steels, and [[Creep (deformation)|creep]]-resistant steels. They are not as corrosion-resistant as ferritic and austenitic stainless steels due to their low chromium content. They fall into four categories (with some overlap):<ref>{{Cite web|url=http://worldstainless.org/news/show/2125|title=Martensitic Stainless Steels|date=21 November 2017|website=worldstainless.org/|access-date=28 January 2019|archive-date=9 July 2018|archive-url=https://web.archive.org/web/20180709154627/http://worldstainless.org/news/show/2125|url-status=live}}</ref>
* Fe-Cr-C grades. These were the first grades used and are still widely used in engineering and wear-resistant applications. Representative grades include Type 410, Type 420, and Type 440C.
* Fe-Cr-Ni-C grades. Some carbon is replaced by nickel. They offer higher toughness and higher corrosion resistance. Representative grades include Type 431.
* Martensitic precipitation hardening grades. 17-4 PH (UNS S17400), the best-known grade, combines martensitic hardening and [[precipitation hardening]] to increase strength and toughness.
* Creep-resisting grades. Small additions of niobium, [[vanadium]], [[boron]], and [[cobalt]] increase the strength and creep resistance up to about {{cvt|650|C|F|sigfig=2}}.

Martensitic stainless steels can be heat treated to provide better mechanical properties. The heat treatment typically involves three steps:<ref>{{Cite book|url=https://www.asminternational.org/web/hts/home/-/journal_content/56/10192/ZASMHBA0005985/BOOK-ARTICLE|title=ASM Handbook Vol 4D Heat treating of irons and steels|editor1=Dossett, J |editor2=Totten, GE |publisher=ASM International|year=2014|pages=382–396|doi=10.31399/asm.hb.v04d.a0005985|access-date=1 October 2021|archive-date=23 June 2018|archive-url=https://web.archive.org/web/20180623221947/https://www.asminternational.org/web/hts/home/-/journal_content/56/10192/ZASMHBA0005985/BOOK-ARTICLE|url-status=live}}</ref>

# Austenitizing, in which the steel is heated to a temperature in the range {{Convert|980-1050|C|F|abbr=}}, depending on grade. The resulting austenite has a face-centered cubic crystal structure.
# [[Quenching]]. The austenite is transformed into martensite, a hard [[body-centered tetragonal]] crystal structure. The quenched martensite is very hard and too brittle for most applications. Some residual austenite may remain.
# Tempering. Martensite is heated to around {{cvt|500|C|F|sigfig=2}}, held at temperature, then air-cooled. Higher tempering temperatures decrease [[yield strength]] and [[ultimate tensile strength]] but increase the elongation and impact resistance.

=== Duplex ===
{{main|Duplex stainless steel}}

Duplex stainless steels have a mixed microstructure of austenite and ferrite, the ideal ratio being a 50:50 mix, though commercial alloys may have ratios of 40:60. They are characterized by higher chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. Duplex stainless steels have roughly twice the [[yield strength]] of austenitic stainless steel.<ref>{{Cite web |last=Grocki |first=John M. |date=2012-03-27 |title=A Primer for DUPLEX Stainless Steel |url=https://www.academia.edu/36652228 |access-date=2025-06-11 |website=academia.edu |quote=Duplex stainless steels have roughly twice the yield strength of their counterpart austenitic grades.}}</ref> Their mixed microstructure provides improved resistance to chloride stress corrosion cracking in comparison to austenitic stainless steel types 304 and 316.<ref>{{Cite web |last=Fritz |first=James |date=2020-04-18 |title=Practical guide to using duplex stainless steels |url=https://nickelinstitute.org/media/8dab1e8a1825480/nickelpub10044_apracticalguidetousingduplex.pdf |access-date=2025-06-11 |website=nickelinstitute.org |quote=They provide better corrosion resistance, particularly chloride stress corrosion ... than standard austenitic stainless steels such as A2/304 or A4/316.}}</ref> Duplex grades are usually divided into three sub-groups based on their corrosion resistance: lean duplex, standard duplex, and super duplex. The properties of duplex stainless steels are achieved with an overall lower alloy content than similar-performing super-austenitic grades, making their use cost-effective for many applications. The pulp and paper industry was one of the first to extensively use duplex stainless steel. The oil and gas industry became the largest user and has pushed for more corrosion resistant grades, leading to the development of super duplex and hyper duplex grades. More recently, the less expensive (and slightly less corrosion-resistant) lean duplex has been developed, chiefly for structural applications in building and construction (concrete reinforcing bars, plates for bridges, coastal works) and in the [[water industry]].{{Citation needed|date=January 2025}}

=== Precipitation hardening ===
[[Precipitation hardening]] stainless steels are characterized by the ability to be precipitation hardened to higher strength. There are three types of precipitation hardening stainless steels which are classified according to their crystalline structure:<ref>{{Cite book|last=De Cooman|first=Bruno Charles|date=April 2016|others=Pohang University of Science and Technology Korea Graduate Institute of Ferrous Technology|title=Lecture on stainless steel_9|url=https://www.researchgate.net/publication/301692427|doi=10.13140/RG.2.1.1950.2488}}</ref>
* Martensitic precipitation hardenable stainless steels are martensitic at room temperature in both the solution annealed and precipitation hardened conditions. Representative alloys include 17-4 PH (UNS S17400), 15-5 PH (UNS S15500), Custom 450 (UNS S45000) and Custom 465 (UNS S46500).
* Semi-austenitic precipitation hardenable stainless steels are initially austenitic in the solution annealed condition for ease of fabrication, but are subsequently transformed to martensite to provide higher strength and to be precipitation hardened. Representative alloys include 17-7 PH (UNS S17700), 15-7 PH (UNS S15700), AM-350 (UNS S35000), and AM-355 (UNS S35500).
* Austenitic precipitation hardenable stainless steels are austenitic at room temperature in both the solution annealed and precipitation hardened conditions. Representative alloys include A-286 (UNS S66286) and Discalloy (UNS S66220).<ref>Precipitation-Hardening Stainless Steels, Stainless Steels for Design Engineers, By Michael F. McGuire, ASM International, 2008, p 137–146, https://doi.org/10.31399/asm.tb.ssde.t52310137</ref>

== Classification systems ==
{{see also|Steel grades|SAE steel grades}}

Several different classification systems have been developed for designating stainless steels. The main system used in the United States has been the [[SAE steel grades]] numbering system. The SAE numbering system designates stainless steels by "Type" followed by a three-digit number and sometimes a letter suffix. A newer system that was jointly developed by [[ASTM]] and SAE in 1974 is The [[Unified Numbering System for Metals and Alloys]] (UNS).<ref>{{cite web |title=Unified Numbering System (UNS) for Metals and Alloys |url=https://www.azom.com/article.aspx?ArticleID=6127 |website=AZO Materials | date=29 June 2012 |access-date=9 January 2025}}</ref> The Unified Numbering System classifies stainless steels using an alpha-numeric identifier consisting of "S" followed by five digits, although some austenitic stainless steels with high nickel content may fall into the nickel-base designation which uses "N" as the alpha identifier. The UNS designations incorporate previously used designations, whether from the SAE numbering system or proprietary alloy designations. Europe has adopted EN 10088 for classification of stainless steels.<ref name=hmcname/>

==Corrosion resistance==
[[File:Corrosion of alloys in NaCl.jpg|thumb|Stainless steel (bottom row) resists [[salt-water]] [[corrosion]] better than [[aluminium-bronze]] (top row) or [[copper-nickel]] alloys (middle row).]]

Unlike [[carbon steel]], stainless steels do not suffer uniform [[corrosion]] when exposed to wet environments. Unprotected carbon steel rusts readily when exposed to a combination of air and moisture. The resulting [[iron oxide]] surface layer is porous and fragile. In addition, as iron oxide occupies a larger volume than the original steel, this layer expands and tends to [[Hammerscale|flake]] and fall away, exposing the underlying steel to further attack. In comparison, stainless steels contain sufficient chromium to undergo [[Passivation (chemistry)|passivation]], spontaneously forming a microscopically thin inert surface film of chromium oxide by reaction with the oxygen in the air and even the small amount of dissolved oxygen in the water. This passive film prevents further corrosion by blocking oxygen diffusion to the steel surface and thus prevents corrosion from spreading into the bulk of the metal.<ref name = nano>{{cite journal|journal= ACOM|issn = 1101-0681|volume= 2|date=2006|title= Passive Films on Stainless Steel: Recent Nano-Range Research|first1= Clas|last1=Olsson |last2=Herting|first2= Gunilla|last3= Odnevall Wallinder |first3= Inger }}</ref> This film is self-repairing, even when scratched or temporarily disturbed by conditions that exceed the inherent corrosion resistance of that grade.<ref name = nano/><ref name="worldstainless">{{Cite web |url=https://www.worldstainless.org/education/education-for-architects-and-engineers/ |title= Chapter 5 corrosion resistance of stainless steels |website=www.worldstainless.org |access-date=1 October 2021 |archive-date= 12 September 2021 |archive-url=https://web.archive.org/web/20210912093829/https://www.worldstainless.org/education/education-for-architects-and-engineers/ |url-status=live }}</ref>

The resistance of this film to corrosion depends upon the chemical composition of the stainless steel, chiefly the chromium content. It is customary to distinguish between four forms of corrosion: uniform, localized (pitting), galvanic, and SCC (stress corrosion cracking). Any of these forms of corrosion can occur when the grade of stainless steel is not suited for the working environment.

=== Uniform ===

Uniform corrosion takes place in very aggressive environments, typically where chemicals are produced or heavily used, such as in the pulp and paper industries. The entire surface of the steel is attacked, and the corrosion is expressed as corrosion rate in mm/year (usually less than 0.1&nbsp;mm/year is acceptable for such cases). Corrosion tables provide guidelines.<ref>{{Cite web |url=https://www.materials.sandvik/fr/materials-center/corrosion-tables/ |title=Corrosion Tables |last=Sandvik |access-date=1 October 2021 |archive-date=13 April 2021 |archive-url=https://web.archive.org/web/20210413223759/https://www.materials.sandvik/fr/materials-center/corrosion-tables/ |url-status=live }}</ref>

This is typically the case when stainless steels are exposed to acidic or basic solutions. Whether stainless steel corrodes depends on the kind and concentration of [[acid]] or [[Base (chemistry)|base]] and the solution temperature. Uniform corrosion is typically easy to avoid because of extensive published corrosion data or easily performed laboratory corrosion testing.[[File:Crevice corrosion of 316 SS tube and tube sheet in a desalination plant.png|thumb|Stainless steel is not completely immune to corrosion, as shown in this [[desalination]] equipment.]]

Acidic solutions can be put into two general categories: reducing acids, such as [[hydrochloric acid]] and dilute [[sulfuric acid]], and [[oxidizing acid]]s, such as [[nitric acid]] and concentrated sulfuric acid. Increasing chromium and molybdenum content provides increased resistance to reducing acids while increasing chromium and silicon content provides increased resistance to oxidizing acids. Sulfuric acid is one of the most-produced industrial chemicals. At room temperature, [[SAE 304 stainless steel|type 304]] stainless steel is only resistant to 3% acid, while [[SAE 316L stainless steel|type 316]] is resistant to 3% acid up to {{Convert|50|C|F|abbr=|sigfig=2}} and 20% acid at room temperature. Thus type 304 SS is rarely used in contact with sulfuric acid. [[SAE 904L stainless steel|Type 904L]] and [[Alloy 20]] are resistant to sulfuric acid at even higher concentrations above room temperature.<ref>{{Cite web |last=International Nickel Company |date=1983 |title=The Corrosion Resistance of Nickel-Containing Alloys in Sulphuric Acid and Related Compounds |url=https://nickelinstitute.org/en/library/technical-guides/the-corrosion-resistance-of-nickel-containing-alloys-in-sulphuric-acid-and-related-compounds-1318/ |url-status=live |archive-url=https://web.archive.org/web/20180108175035/https://nickelinstitute.org/~/media/Files/TechnicalLiterature/TheCorrosionResistanceofNickel_ContainingAlloysinSulphuricAcidandRelatedCompounds_1318_.ashx |archive-date=8 January 2018 |access-date=1 October 2021 |website=Nickel Institute}}</ref><ref>{{Cite web |author=Davies |first=Michael |date=2011 |title=Alloy selection for service in sulphuric acid |url=https://nickelinstitute.org/en/library/technical-guides/alloy-selection-for-service-in-sulphuric-acid-10057/ |access-date=2 November 2023 |series=NiDI Technical Series No. 10 057 |publisher=Nickel Development Institute |location=Toronto, CA}}</ref> Concentrated sulfuric acid possesses oxidizing characteristics like nitric acid, and thus silicon-bearing stainless steels are also useful.<ref>{{Cite web |title=Alloy selection for service in sulphuric acid |url=https://nickelinstitute.org/media/4122/alloy-selection-for-service-in-sulphuric-acid-10057.pdf |access-date=2025-06-11 |website=nickelinstitute.org |quote=Silicon (Si) also plays a role in oxidation resistance, in particular with respect to strongly oxidizing acids (concentrated nitric acid or hot concentrated sulfuric acid).}}</ref> [[Hydrochloric acid]] damages any kind of stainless steel and should be avoided.<ref name=Davis1994/>{{rp|118}}<ref>{{Cite web|author=Davies, Michael|date=2018|editor=Moe, Geir|title=Alloy Selection for Service in Chlorine, Hydrogen Chloride and Hydrochloric Acid: A Guide to the Use of Nickel-Containing Alloys|url=https://nickelinstitute.org/~/media/Files/TechnicalLiterature/AlloystoResistChlorine_HydrogenChlorideandHydrochloricAcid_10020_.ashx|publisher=Nickel Development Institute|location=Toronto, CA|pages=8–10|edition=2nd|access-date=1 October 2021|archive-date=5 December 2017|archive-url=https://web.archive.org/web/20171205093116/https://nickelinstitute.org/~/media/Files/TechnicalLiterature/AlloystoResistChlorine_HydrogenChlorideandHydrochloricAcid_10020_.ashx|url-status=dead}}</ref> All types of stainless steel resist attack from [[phosphoric acid]] and [[nitric acid]] at room temperature. At high concentrations and elevated temperatures, attack will occur, and higher-alloy stainless steels are required.<ref>{{cite web |last1=Schillmoller |first1=C.M. |title=Alloy selection in wet-process phosphoric acid (10015) |url=https://nickelinstitute.org/en/library/technical-guides/alloy-selection-in-wet-process-phosphoric-acid-10015/ |website=Nickel Institute |access-date=2 November 2023}}</ref><ref>{{Cite web |last=International Nickel Company |title=Corrosion Resistance of Nickel-Containing Alloys in Phosphoric Acid |url=https://nickelinstitute.org/en/library/technical-guides/corrosion-resistance-of-nickel-containing-alloys-in-phosphoric-acid-415/ |url-status=live |archive-url=https://web.archive.org/web/20171205093113/https://nickelinstitute.org/~/media/Files/TechnicalLiterature/CorrosionResistanceofNickel_ContainingAlloysinPhosphoricAcid_415_.ashx |archive-date=5 December 2017 |access-date=1 October 2021 |website=Nickel Institute}}</ref><ref>{{Cite web |last=C. M. Schillmoller |title=Alloy Selection for Service in Nitric Acid |url=https://nickelinstitute.org/en/library/technical-guides/alloy-selection-for-service-in-nitric-acid-10075/ |url-status=live |archive-url=https://web.archive.org/web/20171205093123/https://nickelinstitute.org/~/media/Files/TechnicalLiterature/SelectionandUseofStainlessSteelandNiBearingAlloysinNitricAcid_10075_.ashx |archive-date=5 December 2017 |access-date=1 October 2021 |website=Nickel Institute}}</ref> In general, [[organic acid]]s are less corrosive than mineral acids such as hydrochloric and sulfuric acid.

Type 304 and type 316 stainless steels are unaffected by weak bases such as [[ammonium hydroxide]], even in high concentrations and at high temperatures. The same grades exposed to stronger bases such as [[sodium hydroxide]] at high concentrations and high temperatures will likely experience some etching and cracking.<ref>{{Cite web |last=C. M. Schillmoller |date=1988 |title=Alloy Selection for Caustic Soda Service |url=https://nickelinstitute.org/en/library/technical-guides/alloy-selection-for-service-in-caustic-soda-10019/ |access-date=1 October 2021 |website=Nickel Institute}}</ref> Increasing chromium and nickel contents provide increased resistance.

All grades resist damage from [[aldehyde]]s and [[amine]]s, though in the latter case type 316 is preferable to type 304; [[cellulose acetate]] damages type 304 unless the temperature is kept low. Fats and [[fatty acid]]s only affect type 304 at temperatures above {{convert|150|C|F|sigfig=2}} and type 316 SS above {{convert|260|C|F|sigfig=2}}, while type 317 SS is unaffected at all temperatures. Type 316L is required for the processing of [[urea]].<ref name=Davis1994/><ref>{{Cite web |title=Design guidelines for the selection and use of stainless steels (9014) |url=https://nickelinstitute.org/media/1667/designguidelinesfortheselectionanduseofstainlesssteels_9014_.pdf |access-date=2025-06-11 |website=nickelinstitute.org |quote=Type 316L is generally required for urea production.}}</ref>

=== Localized ===

Localized corrosion can occur in several ways, e.g. [[pitting corrosion]] and [[crevice corrosion]]. These localized attacks are most common in the presence of [[Chloride|chloride ions]]. Higher chloride levels require more highly alloyed stainless steels.

Localized corrosion can be difficult to predict because it is dependent on many factors, including:
* Chloride ion concentration. Even when chloride solution concentration is known, it is still possible for localized corrosion to occur unexpectedly. Chloride ions can become unevenly concentrated in certain areas, such as in crevices (e.g. under gaskets) or on surfaces in vapor spaces due to evaporation and condensation.
* Temperature: increasing temperature increases susceptibility.
* Acidity: increasing acidity increases susceptibility.
* Stagnation: stagnant conditions increase susceptibility.
* Oxidizing species: the presence of oxidizing species, such as ferric and cupric ions, increases susceptibility.

Pitting corrosion is considered the most common form of localized corrosion. The corrosion resistance of stainless steels to pitting corrosion is often expressed by the [[Pitting resistance equivalent number|PREN]], obtained through the formula:

:<math>\text{PREN}=%\text{Cr}+3.3\cdot%\text{Mo}+16\cdot%\text{N}</math>,

where the terms correspond to the proportion of the contents by mass of chromium, molybdenum, and nitrogen in the steel. For example, if the steel consisted of 15% chromium %Cr would be equal to 15.

The higher the PREN, the higher the pitting corrosion resistance. Thus, increasing chromium, molybdenum, and nitrogen contents provide better resistance to pitting corrosion.

Though the PREN of certain steel may be theoretically sufficient to resist pitting corrosion, crevice corrosion can still occur when the poor design has created confined areas (overlapping plates, washer-plate interfaces, etc.) or when deposits form on the material. In these select areas, the PREN may not be high enough for the service conditions. Good design, fabrication techniques, alloy selection, proper operating conditions based on the concentration of active compounds present in the solution causing corrosion, pH, etc. can prevent such corrosion.<ref>{{Cite web |title=Resistance of Stainless Steel to Corrosion in Naturally Occurring Waters |url=https://nickelinstitute.org/en/library/technical-guides/resistance-of-stainless-steel-to-corrosion-in-naturally-occuring-waters-1262/ |url-status=live |archive-url=https://web.archive.org/web/20180612141639/https://nickelinstitute.org/NickelUseInSociety/MaterialsSelectionAndUse/Water/AlloySelection.aspx |archive-date=12 June 2018 |access-date=1 October 2021 |website=Nickel Institute}}</ref>

=== Stress ===
[[Stress corrosion cracking]] (SCC) is caused by combination of tensile stress and a corrosive environment and can lead to unexpected and sudden failure of a stainless steel component. It may occur when three conditions are met:
* The part contains either applied or residual tensile stresses.
* The part is in a corrosive environment.
* The stainless steel is susceptible to SCC.

SCC can be prevented by eliminating one of these three conditions.

The SCC mechanism results from the following sequence of events:

# Pitting occurs
# Cracks start from a pit initiation site
# Cracks then propagate through the metal in a transgranular or intergranular mode
# Failure occurs

=== Galvanic ===
[[File:P4150144 cable tyrolienne inox.jpg|thumb|The [[Nut (hardware)|nut]] on the left is not stainless steel and is [[rust]]y, unlike the nut on the right.]]

[[Galvanic corrosion]]<ref>{{Cite web |url=http://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Contact_with_Other_EN.pdf |title=Stainless steels in contact with other materials |last=A Euro Inox publication |date=2009 |access-date=1 October 2021 |archive-date=16 April 2021 |archive-url=https://web.archive.org/web/20210416102705/https://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Contact_with_Other_EN.pdf |url-status=live }}</ref> (also called "dissimilar-metal corrosion") refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte. The most common electrolyte is water, ranging from freshwater to seawater. When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would alone, while the other becomes the cathode and corrodes slower than it would alone. Stainless steel, due to having a more positive electrode potential than for example carbon steel and aluminium, becomes the cathode, accelerating the corrosion of the anodic metal. An example is the corrosion of aluminium rivets fastening stainless steel sheets in contact with water.<ref name="Bauer">{{Cite web |last=Bauer |first=Alfred E. |title=Stainless Steels in Waters; Galvanic Corrosion and its Prevention |url=https://nickelinstitute.org/en/library/technical-guides/stainless-steel-in-waters-galvanic-corrosion-and-its-prevention-bauer-1806/ |url-status=live |archive-url=https://web.archive.org/web/20180612143626/https://nickelinstitute.org/~/media/Files/TechnicalLiterature/StainlessSteelinWatersGalvanicCorrosionandit%20PreventionAEBauer.ashx |archive-date=12 June 2018 |access-date=1 October 2021 |website=Nickel Institute |pages=7–9}}</ref> The relative surface areas of the anode and the cathode are important in determining the rate of corrosion. In the above example, the surface area of the rivets is small compared to that of the stainless steel sheet, resulting in rapid corrosion.<ref name="Bauer" /> However, if stainless steel fasteners are used to assemble aluminium sheets, galvanic corrosion will be much slower because the galvanic current density on the aluminium surface will be many orders of magnitude smaller.<ref name="Bauer" /> A frequent mistake is to assemble stainless steel plates with carbon steel fasteners; whereas using stainless steel to fasten carbon-steel plates is usually acceptable, the reverse is not. Providing electrical insulation between the dissimilar metals, where possible, is effective at preventing this type of corrosion.<ref name="Bauer" />

=== High-temperature ===

At elevated temperatures, all metals react with hot gases. The most common high-temperature gaseous mixture is air, of which oxygen is the most reactive component. To avoid corrosion in air, carbon steel is limited to approximately {{convert|480|C|F|sigfig=2|abbr=}}. Oxidation resistance in stainless steels increases with additions of chromium, silicon, and aluminium. Small additions of [[cerium]] and [[yttrium]] increase the adhesion of the oxide layer on the surface.<ref>{{Cite web |url=https://www.bssa.org.uk/topics.php?article=107 |title=Oxidation resistance of stainless steels |publisher=British Stainless Steel Association |access-date=1 October 2021 |archive-date=7 August 2020 |archive-url=https://web.archive.org/web/20200807084144/https://www.bssa.org.uk/topics.php?article=107 |url-status=live }}</ref> The addition of chromium remains the most common method to increase high-temperature corrosion resistance in stainless steels; chromium reacts with oxygen to form a chromium oxide scale, which reduces oxygen diffusion into the material. The minimum 10.5% chromium in stainless steels provides resistance to approximately {{convert|700|C|F|sigfig=2|abbr=}}, while 16% chromium provides resistance up to approximately {{convert|1200|C|F|sigfig=2|abbr=}}. Type 304, the most common grade of stainless steel with 18% chromium, is resistant to approximately {{convert|870|C|F|sigfig=2|abbr=}}. Other gases, such as [[sulfur dioxide]], [[hydrogen sulfide]], [[carbon monoxide]], [[chlorine]], also attack stainless steel. Resistance to other gases is dependent on the type of gas, the temperature, and the alloying content of the stainless steel.<ref>{{Cite web |last=American Iron and Steel Institute |date=April 1979 |title=High Temperature Characteristics of Stainless Steel |url=https://nickelinstitute.org/en/library/technical-guides/high-temperature-characteristics-of-stainless-steel-9004/ |url-status=live |archive-url=https://web.archive.org/web/20180307082335/https://nickelinstitute.org/~/media/Files/TechnicalLiterature/High_TemperatureCharacteristicsofStainlessSteel_9004_.ashx |archive-date=7 March 2018 |access-date=1 October 2021 |website=Nickel Institute}}</ref><ref>{{Cite web |last=Elliott |first=Peter |date=August 1990 |title=Practical Guide to High Temperature Alloys |url=https://nickelinstitute.org/en/library/technical-guides/practical-guide-to-high-temperature-alloys-10056/ |url-status=live |archive-url=https://web.archive.org/web/20180307150834/https://nickelinstitute.org/~/media/Files/TechnicalLiterature/PracticalGuidetoHigh_TemperatureAlloys_10056_.ashx |archive-date=7 March 2018 |access-date=1 October 2021 |website=Nickel Institute}}</ref> With the addition of up to 5% aluminium, ferritic grades Fe-Cr-Al are designed for electrical resistance and oxidation resistance at elevated temperatures. Such alloys include [[Kanthal (alloy)|Kanthal]], produced in the form of wire or ribbons.<ref name="ISSF-2017">{{Cite book|url=http://worldstainless.org/publications/brochures_and_posters|title=The ferritic solution Properties/advantages/applications|date=April 2017|publisher=ISSF, International Stainless Steel Forum |isbn=978-2-930069-51-7|access-date=15 October 2018|archive-url=https://web.archive.org/web/20181012045555/http://www.worldstainless.org/publications/brochures_and_posters|archive-date=12 October 2018|url-status=dead}}</ref>

==Standard finishes==

[[File:316L Stainless Steel Unpolished.jpg|upright|thumb|right|alt=Matte surface of pipe, with a few horizontal scratches|316L stainless steel, with an unpolished, mill finish]]
Standard [[surface finishing|mill finishes]] can be applied to flat rolled stainless steel directly by the rollers and by mechanical abrasives. Steel is first rolled to size and thickness and then [[Annealing (metallurgy)|annealed]] to change the properties of the final material. Any [[oxidation]] that forms on the surface ([[mill scale]]) is removed by [[Pickling (metal)|pickling]], and a passivation layer is created on the surface. A final finish can then be applied to achieve the desired aesthetic appearance.<ref>{{Cite web|date=21 Dec 2018|title=ASTM A480/A480M-18 Standard Specification for General Requirements for Flat-Rolled Stainless and Heat-Resisting Steel Plate, Sheet, and Strip|url=https://www.astm.org/a0480_a0480m-18.html|access-date=30 Nov 2021|website=ASTM International}}</ref><ref>{{Cite book|last1=Cochrane|first1=David|url=https://www.imoa.info/download_files/stainless-steel/euroinox/Finishes.pdf?m=1454491282&|title=Guide to Stainless Steel Finishes 3rd Ed.|last2=Helzel|first2=Martina|publisher=Euro Inox|year=2005|isbn=287997173X|location=Brussels. Belgium|pages=4–23|language=English}}</ref>

The following designations are used in the U.S. to describe stainless steel finishes by [[ASTM International|ASTM]] A480/A480M-18 (DIN):<ref>{{Cite web|last=Velling|first=Andreas|date=13 Sep 2019|title=Stainless Steel Finishes Explained – EN & ASTM|url=https://fractory.com/stainless-steel-finishes-din-astm/|access-date= |website=Fractory}}</ref>
* No. 0: Hot-rolled, annealed, thicker plates
* No. 1 (1D): Hot-rolled, annealed and passivated
* No. 2D (2D): Cold rolled, annealed, pickled and passivated
* No. 2B (2B): Same as above with additional pass through highly polished rollers
* No. 2BA (2R): Bright annealed (BA or 2R) same as above then bright annealed under oxygen-free atmospheric condition
* No. 3 (G-2G:) Coarse abrasive finish applied mechanically
* No. 4 (1J-2J): Brushed finish
* No. 5: Satin finish
* No. 6 (1K-2K): Matte finish (brushed but smoother than #4)
* No. 7 (1P-2P): Reflective finish
* No. 8: Mirror finish
* No. 9: Bead blast finish
* No. 10: Heat colored finish – offering a wide range of [[Electropolishing|electropolished]] and heat colored surfaces

== Joining ==

A wide range of joining processes are available for stainless steels, though [[welding]] is by far the most common.<ref name="Pierre-Jean-2007">{{Cite book|last=Pierre-Jean|first=Cunat|url=https://www.worldstainless.org/about-stainless/process-and-production/fabrication/|title=The Welding of Stainless Steels|date=2007|isbn=978-2-87997-180-3|access-date=1 October 2021|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414011254/https://www.worldstainless.org/about-stainless/process-and-production/fabrication/|url-status=live}}</ref><ref name="Nickel Institute">{{Cite web |title=Welding of stainless steels and other joining methods |url=https://nickelinstitute.org/en/library/technical-guides/welding-of-stainless-steels-and-other-joining-methods-9002/ |url-status=live |archive-url=https://web.archive.org/web/20210701021829/https://nickelinstitute.org/media/1854/weldingofstainlessssteelandotherjoiningmethods_9002_.pdf |archive-date=1 July 2021 |access-date=1 October 2021 |publisher=Nickel Institute}}</ref>

The ease of welding largely depends on the type of stainless steel used. Austenitic stainless steels are the easiest to weld by [[electric arc]], with weld properties similar to those of the base metal (not cold-worked). Martensitic stainless steels can also be welded by electric-arc but, as the heat-affected zone (HAZ) and the fusion zone (FZ) form martensite upon cooling, precautions must be taken to avoid cracking of the weld. Improper welding practices can additionally cause sugaring (oxide scaling) and heat tint on the backside of the weld. This can be prevented with the use of back-purging gases, backing plates, and fluxes.<ref>{{Cite web|title=Ultimate Guide - Stainless Steel - Fabrication, Grinding, and Finishing with Abrasives|url=https://www.empireabrasives.com/blog/stainless-steel-fabrication-weld-grinding-finishing-abrasives/|access-date=2021-06-28|website=Empire Abrasives|language=en|archive-date=30 June 2021|archive-url=https://web.archive.org/web/20210630034722/https://www.empireabrasives.com/blog/stainless-steel-fabrication-weld-grinding-finishing-abrasives/|url-status=live}}</ref> Post-weld heat treatment is almost always required while preheating before welding is also necessary in some cases.<ref name="Nickel Institute" /> Electric arc welding of type 430 ferritic stainless steel results in grain growth in the HAZ, which leads to brittleness. This has largely been overcome with stabilized ferritic grades, where niobium, titanium, and zirconium form precipitates that prevent grain growth.<ref>{{Cite journal|last1=Gordon|first1=Wayne|last2=van Bennekom|first2=A.|date=1996|title=Review of stabilization of ferritic stainless steels|journal=Materials Science and Technology|volume=12|issue=2|pages=126–131|doi=10.1179/mst.1996.12.2.126|bibcode=1996MatST..12..126G }}</ref><ref>{{Cite journal|last=Singh|first=Ramesh|date=2012|title=Chapter 6 - Welding corrosion resistant Alloys - Stainless Steel|journal=Applied Welding Engineering|pages=191–214|doi=10.1016/B978-0-12-391916-8.00018-2|isbn=9780123919168}}</ref> Duplex stainless steel welding by electric arc is a common practice but requires careful control of the process parameters. Otherwise, the precipitation of unwanted intermetallic phases occurs, which reduces the toughness of the welds.<ref>{{Cite web|title=Duplex stainless steel welding guidelines|url=https://industeel.arcelormittal.com/wp-content/uploads/2019/06/Duplex-Stainless-Steels-Welding-Guidelines-EN-Juin-2019-Web.pdf|date=2019|publisher=Industeel ArcelorMittal|access-date=1 October 2021|archive-date=6 January 2021|archive-url=https://web.archive.org/web/20210106143919/https://industeel.arcelormittal.com/wp-content/uploads/2019/06/Duplex-Stainless-Steels-Welding-Guidelines-EN-Juin-2019-Web.pdf|url-status=live}}</ref>

Electric arc welding processes include:<ref name="Pierre-Jean-2007" />
* [[Gas metal arc welding]], also known as MIG/MAG welding
* [[Gas tungsten arc welding]], also known as tungsten inert gas (TIG) welding
* [[Plasma arc welding]]
* [[Flux-cored arc welding]]
* [[Shielded metal arc welding]] (covered electrode)
* [[Submerged arc welding]]

MIG, MAG and TIG welding are the most common methods.

Other welding processes include:
* [[Stud welding]]
* [[Resistance spot welding]]
* [[Resistance seam welding]]
* [[Flash welding]]
* [[Laser beam welding]]
* [[Oxy-fuel welding and cutting|Oxy-acetylene welding]]

Stainless steel may be bonded with adhesives such as silicone, [[silyl modified polymers]], and [[Epoxy#Adhesivese|epoxies]]. Acrylic and [[List of polyurethane applications#Adhesives|polyurethane]] adhesives are also used in some situations.<ref>{{Cite book|url=https://www.worldstainless.org/about-stainless/process-and-production/fabrication/|title=Adhesive Bonding of Stainless Steels|last=Kosmac|first=Alenka|date=2013|pages=11–13|publisher=Euro Inox |isbn=978-2-87997-388-3|access-date=1 October 2021|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414011254/https://www.worldstainless.org/about-stainless/process-and-production/fabrication/|url-status=live}}</ref>

== Production ==
{{more citations needed section|date=March 2020}}
<!--EVERY PURPORTED FACTUAL STATEMENT SHOULD BE SUPPORTED BY AN INLINE CITATION THAT STATES THE SAME THING THAT WE SAY IN THE SENTENCE. SENTENCES WITHOUT SOURCES ARE, BY DEFINITION, PLAGIARISM AS UNDERSTOOD BY WESTERN, ENGLISH-SPEAKING ACADEMIA. (NO ONE HERE "WROTE THE BOOK" ON STAINLESS STEEL; THE MATERIAL IS BEING TAKEN FROM SOMEONE'S WRITING, SOMEWHERE. IF IT IS NOT CITED, IT IS ACADEMIC DISHONESTY.) See Lipson's small book, "Doing Honest Work in College." PLEASE, NO MORE ADDITIONS WITHOUT SOURCES.-->

Most of the world's stainless steel production is produced by the following processes:
* [[Electric arc furnace]] (EAF): stainless steel scrap, other ferrous scrap, and ferrous alloys (Fe Cr, Fe Ni, Fe Mo, Fe Si) are melted together. The molten metal is then poured into a ladle and transferred into the AOD process (see below).
* [[Argon oxygen decarburization]] (AOD): carbon in the molten steel is removed (by turning it into [[carbon monoxide]] gas) and other compositional adjustments are made to achieve the desired chemical composition.
* [[Continuous casting#Steel|Continuous casting]] (CC): the molten metal is solidified into slabs for flat products (a typical section is {{Convert|20|cm|in|abbr=}} thick and {{Convert|2|m|ft|1|abbr=}} wide) or [[Semi-finished casting products#Bloom|blooms]] (sections vary widely but {{Convert|25 x 25|cm|in|abbr=}} is the average size).
* [[Rolling (metalworking)#Hot rolling|Hot rolling]] (HR): slabs and blooms are reheated in a furnace and hot-rolled. Hot rolling reduces the thickness of the slabs to produce about {{Convert|3|mm|in|abbr=on}}-thick coils. Blooms, on the other hand, are hot-rolled into bars, which are cut into lengths at the exit of the rolling mill, or wire rod, which is coiled.
* Cold finishing (CF) depends on the type of product being finished:
** Hot-rolled coils are pickled in acid solutions to remove the oxide scale on the surface, then subsequently cold rolled in [[Tadeusz Sendzimir|Sendzimir]] rolling mills and annealed in a protective atmosphere until the desired thickness and surface finish is obtained. Further operations such as slitting and tube forming can be performed in downstream facilities.
** Hot-rolled bars are straightened, then machined to the required tolerance and finish.
** Wire rod coils are subsequently processed to produce cold-finished bars on drawing benches, fasteners on boltmaking machines, and wire on single or multipass drawing machines.

World stainless steel production figures are published yearly by the International Stainless Steel Forum. Of the EU production figures, Italy, Belgium, and Spain were notable, while Canada and Mexico produced none. China, Japan, South Korea, Taiwan, India, the US, and Indonesia were large producers while Russia reported little production.<ref name="ISSF-2021">{{Cite web |last=International Stainless Steel Forum |title=Stainless Steel in Figures 2021 |url=https://www.worldstainless.org/files/issf/non-image-files/PDF/ISSF_Stainless_Steel_in_Figures_2021_English_public_version.pdf |url-status=live |access-date=1 October 2021 |archive-date=30 June 2021 |archive-url=https://web.archive.org/web/20210630080307/https://www.worldstainless.org/files/issf/non-image-files/PDF/ISSF_Stainless_Steel_in_Figures_2021_English_public_version.pdf }}</ref>
{| class="wikitable sortable" style="text-align:right;"
|+World stainless steel production in flat and long products (metric tons, '000s)
|-
! Year
! {{verth|va=middle|European Union}}
! {{verth|va=middle|Americas}}
! {{verth|va=middle|China}}
! {{verth|va=middle|Asia excluding China}}
! {{verth|va=middle|Other countries}}
! World
|-
|2021
|{{val|7181}}
|{{val|2368}}
|{{val|32632}}
|{{val|7792}}
|{{val|8316}}
|{{val|58289}}
|-
|2020
| {{val|6323}}
| {{val|2144}}
| {{val|30139}}
| {{val|6429}}
| {{val|5857}}
| {{val|50892}}
|-
|2019
| {{val|6805}}
| {{val|2593}}
| {{val|29400}}
| {{val|7894}}
| {{val|5525}}
| {{val|52218}}
|-
|2018
| {{val|7386}}
| {{val|2808}}
| {{val|26706}}
| {{val|8195}}
| {{val|5635}}
| {{val|50729}}
|-
| 2017
| {{val|7377}}
| {{val|2754}}
| {{val|25774}}
| {{val|8030}}
| {{val|4146}}
| {{val|48081}}
|-
| 2016
| {{val|7280}}
| {{val|2931}}
| {{val|24938}}
| {{val|9956}}
| {{val|672}}
| {{val|45778}}
|-
| 2015
| {{val|7169}}
| {{val|2747}}
| {{val|21562}}
| {{val|9462}}
| {{val|609}}
| {{val|41548}}
|-
| 2014
| {{val|7252}}
| {{val|2813}}
| {{val|21692}}
| {{val|9333}}
| {{val|595}}
| {{val|41686}}
|-
| 2013
| {{val|7147}}
| {{val|2454}}
| {{val|18984}}
| {{val|9276}}
| {{val|644}}
| {{val|38506}}
|}

Breakdown of production by stainless steels families in 2017:
* Austenitic stainless steels Cr-Ni (also called 300-series, see "Grades" section above): 54%
* Austenitic stainless steels Cr-Mn (also called 200-series): 21%
* Ferritic and martensitic stainless steels (also called 400-series): 23%

== Applications ==
{{main|List of applications of stainless steel}}

Stainless steel is used in a multitude of fields including architecture, art, chemical engineering, food and beverage manufacture, vehicles, medicine, energy and firearms.

==Life cycle cost==

[[Whole-life cost|Life cycle cost]] (LCC) calculations are used to select the design and the materials that will lead to the lowest cost over the whole life of a project, such as a building or a bridge.<ref>{{Cite web|url=http://worldstainless.org/about-stainless/life-cycle-costing/|title=Life cycle Costing|website=World Stainless ( www.worldstainless.org )|access-date=1 October 2021|archive-date=17 September 2021|archive-url=https://web.archive.org/web/20210917064903/https://www.worldstainless.org/about-stainless/life-cycle-costing/|url-status=live}}</ref><ref>{{Cite web|url=https://www.wbdg.org/resources/life-cycle-cost-analysis-lcca|title=Life Cycle Cost Analysis|last=Fuller|first=Sieglinde|date=2016|website=WBDG |access-date=1 October 2021|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414011309/https://www.wbdg.org/resources/life-cycle-cost-analysis-lcca|url-status=live}}</ref>

The formula, in a simple form, is the following:<ref>{{Cite web|url=https://highways.dot.gov/public-roads/novemberdecember-2005/applying-lcca-bridges|title=Applying LCCA to Bridges|last1=Al-Wazeer|first1=Adel|last2=Harris|first2=Bobby|date=2005|editor-last=Federal Highway Administration (USA)|series=Publication FHWA-HRT-06-001 Vol. 69 No. 3, Nov-Dec 2005|last3=Nutakor|first3=Christopher|access-date=1 October 2021|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414011043/https://www.fhwa.dot.gov/publications/publicroads/05nov/09.cfm|url-status=dead}}</ref><ref>{{Cite web|url=https://shop.bsigroup.com/en/ProductDetail/?pid=000000000030101720|title=ISO 15686-5 Standard: Buildings and constructed assets. Service life planning. Life cycle costing|date=2008|access-date=1 October 2021|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414010816/https://shop.bsigroup.com/en/ProductDetail/?pid=000000000030101720|url-status=dead}}</ref>{{verify source|date=June 2023}}

: <math> \text{LCC}=\text{AC}+\text{IC}+\sum_{n=1}^N\frac{\text{OC}}{(1+i)^n}+\sum_{n=1}^N\frac{\text{LP}}{(1+i)^n}+\sum_{n=1}^N\frac{\text{RC}}{(1+i)^n} </math>

where LCC is the overall life cycle cost, AC is the acquisition cost, IC the installation cost, OC the operating and maintenance costs, LP the cost of lost production due to downtime, and RC the replacement materials cost.

In addition, ''N'' is the planned life of the project, ''i'' the interest rate, and ''n'' the year in which a particular OC or LP or RC is taking place. The interest rate (''i'') is used to convert expenses from different years to their present value (a method widely used by banks and insurance companies) so they can be added and compared fairly. The usage of the sum formula (<math display="inline">\sum</math>) captures the fact that expenses over the lifetime of a project must be cumulated (added together) after they are corrected for interest rate.<ref>{{Cite web |last=Ozbay |first=Kaan |date=2003-07-20 |title=Guidelines for Life Cycle Cost Analysis |url=https://cait.rutgers.edu/wp-content/uploads/2018/05/fhwa-nj-2003-012.pdf |access-date=2025-06-11 |website=Rutgers CAIT FHWA report |quote=The LCCA process is performed by summing up the discounted monetary equivalency of all benefits and costs that are expected to be incurred in each option.}}</ref>

'''Application of LCC in materials selection'''

Stainless steel used in projects often results in lower LCC values compared to other materials. The higher acquisition cost (AC) of stainless steel components are often offset by improvements in operating and maintenance costs, reduced loss of production (LP) costs, and the higher resale value of stainless steel components.<ref>{{Cite web |date=2019-11-19 |title=Life Cycle Costing |url=https://worldstainless.org/sustainability/economic/life-cycle-costing/ |access-date=2025-06-11 |website=worldstainless.org |quote=Although the initial cost of the stainless steel material may be higher, the whole life cycle cost is often lower than for other materials.}}</ref>

LCC calculations are usually limited to the project itself. However, there may be other costs that a project stakeholder may wish to consider:{{citation needed|date = March 2020}}
* Utilities, such as power plants, water supply & wastewater treatment, and hospitals, cannot be shut down. Any maintenance will require extra costs associated with continuing service.
* Indirect societal costs (with possible political fallout) may be incurred in some situations such as closing or reducing traffic on bridges, creating queues, delays, loss of working hours to the people, and increased pollution by idling vehicles.

== Sustainability – recycling and reuse ==

The average [[carbon footprint]] of stainless steel (all grades, all countries) is estimated to be 2.90&nbsp;kg of CO<sub>2</sub> per kg of stainless steel produced,<ref>{{Cite web|url=http://www.sustainablestainless.org/planet|title=Stainless Steel and CO2: Facts and scientific observations|last=International Stainless Steel Forum|date=2015|access-date=1 October 2021|archive-date=8 May 2020|archive-url=https://web.archive.org/web/20200508090411/http://www.sustainablestainless.org/planet|url-status=live}}</ref> of which 1.92&nbsp;kg are emissions from raw materials (Cr, Ni, Mo); 0.54&nbsp;kg from electricity and steam, and 0.44&nbsp;kg are direct emissions (i.e., by the stainless steel plant). Note that stainless steel produced in countries that use cleaner sources of electricity (such as France, which uses nuclear energy) will have a lower carbon footprint. Ferritics without Ni will have a lower CO<sub>2</sub> footprint than austenitics with 8% Ni or more. Carbon footprint must not be the only sustainability-related factor for deciding the choice of materials:
* Over any product life, maintenance, repairs or early end of life (planned obsolescence) can increase its overall footprint far beyond initial material differences. In addition, loss of service (typically for bridges) may induce large hidden costs, such as queues, wasted fuel, and loss of man-hours.
* How much material is used to provide a given service varies with the performance, particularly the strength level, which allows lighter structures and components.

Stainless steel is 100% [[recyclable]].<ref>{{citation |author1= Johnson, J. |author2=Reck, B.K. |author3=Wang, T. |author4=Graede, T.E. |title=The energy benefit of stainless steel recycling |year=2008 |journal=Energy Policy|volume=36 |issue=1 |pages=181–192 |doi=10.1016/j.enpol.2007.08.028|bibcode=2008EnPol..36..181J }}</ref><ref>{{Cite web |title=Nickel Recycling |url=https://nickelinstitute.org/en/policy/nickel-life-cycle-management/nickel-recycling/ |url-status=live |archive-url=https://web.archive.org/web/20180612142524/https://nickelinstitute.org/Sustainability/LifeCycleManagement/RecyclingofNickel/HowNickelIsRecycled/RecyclingStainlessSteel.aspx |archive-date=12 June 2018 |access-date=1 October 2021 |website=Nickel Institute}}</ref> An average stainless steel object is composed of about 60% recycled material of which approximately 40% originates from end-of-life products, while the remaining 60% comes from manufacturing processes.<ref>{{cite web |url        = http://www.worldstainless.org/ISSF/Files/Recycling08/Flash.html |archive-url = https://web.archive.org/web/20110127075255/http://www.worldstainless.org/ISSF/Files/Recycling08/Flash.html |url-status   = dead |archive-date = 27 January 2011 |title      = The Recycling of Stainless Steel ("Recycled Content" and "Input Composition" slides) |access-date = 19 November 2006 |year       = 2006 |format     = Flash |publisher  = International Stainless Steel Forum }}</ref> What prevents a higher recycling content is the availability of stainless steel scrap, in spite of a very high recycling rate. According to the [[International Resource Panel]]'s [[Metal Stocks in Society report]], the per capita stock of stainless steel in use in society is {{cvt|80|to|180|kg|lb}} in more developed countries and {{cvt|15|kg|lb}} in less-developed countries. There is a secondary market that recycles usable scrap for many stainless steel markets. The product is mostly coil, sheet, and blanks. This material is purchased at a less-than-prime price and sold to commercial quality stampers and sheet metal houses. The material may have scratches, pits, and dents but is made to the current specifications.{{Citation needed|date=May 2020}}

The stainless steel cycle starts with carbon steel scrap, primary metals, and slag. The next step is the production of hot-rolled and cold-finished steel products in steel mills. Some scrap is produced, which is directly reused in the melting shop. The manufacturing of components is the third step. Some scrap is produced and enters the recycling loop. Assembly of final goods and their use does not generate any material loss. The fourth step is the collection of stainless steel for recycling at the end of life of the goods (such as kitchenware, pulp and paper plants, or automotive parts). This is where it is most difficult to get stainless steel to enter the recycling loop, as shown in the table below:

{| class="wikitable"
|+ Estimates of collection for recycling by sector<ref>{{Cite journal|title=Global Stainless Steel Cycle exemplifies China's rise to metal dominance|journal=Environmental Science & Technology|volume=44|issue=10|last1=Reck|first1=Barbara|last2=Chambon|first2=Martine|date=2010|publisher=Environ. Sci. Technol., 44, 10|pages=3940–3946|last3=Hashimoto|first3=Seiji|last4=Graedel|first4=T.E.|doi=10.1021/es903584q|pmid=20426460|bibcode=2010EnST...44.3940R}}</ref>
|-
! rowspan="3" | End-use sector
! colspan="2" | Results
! colspan="2" | Use, global average
! colspan="4" | Estimates
|-
! rowspan="2" | 2000
! rowspan="2" | 2005
! rowspan="2" | Average lifetime <br />(years)
! rowspan="2" | Coefficient <br />of variation
! rowspan="2" | To landfill
! colspan="3" | Collected for recycling
|-
! Total
! Of which as stainless steel
! Of which as carbon steel
|-
|Building and infrastructure
|17%
|18%
|50
|30%
|8%
|92%
|95%
|5%
|-
|Transportation (total)
|21%
|18%
| colspan="2" |
|13%
|87%
|85%
|15%
|-
|''Of which passenger cars''
|''17%''
|''14%''
|''14''
|''15%''
| colspan="4" |
|-
|''Of which others''
|''4%''
|''4%''
|''30''
|''20%''
| colspan="4" |
|-
|Industrial machinery
|29%
|26%
|25
|20%
|8%
|92%
|95%
|5%
|-
|Household appliances & electronics
|10%
|10%
|15
|20%
|30%
|70%
|95%
|5%
|-
|Metal goods
|23%
|27%
|15
|25%
|40%
|60%
|80%
|20%
|}

== Nanoscale stainless steel ==

Stainless steel nanoparticles have been produced in the laboratory.<ref>{{Cite journal|last1=Wu|first1=Wenjie|last2=Maye|first2=Mathew M.|date=2014-01-01|title=Void Coalescence in Core/Alloy Nanoparticles with Stainless Interfaces|journal=Small|volume=10|issue=2|pages=271–276|doi=10.1002/smll.201301420|pmid=23881842 |bibcode=2014Small..10..271W }}</ref><ref>{{cite patent|country=US|status=patent|number=10695831|title=Method to control void formation in nanomaterials using core/alloy nanoparticles with stainless interfaces|inventor-last=Maye|inventor2-last=Wu|inventor-first=Mathew M.|inventor2-first=Wenjie|fdate=2017-04-24}} {{Cite web |url=http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1 |title=Patent Database Search: Error |access-date=24 April 2017 |archive-date=21 November 2005 |archive-url=https://web.archive.org/web/20051121200711/http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1 |url-status=bot: unknown }}</ref> These may have applications as additives for high-performance applications. For example, sulfurization, phosphorization, and nitridation treatments to produce nanoscale stainless steel based catalysts could enhance the electrocatalytic performance of stainless steel for [[water splitting]].<ref>{{cite journal|doi=10.1021/acssuschemeng.7b00182 | volume=5 | issue=6 | title=Facile Surface Modification of Ubiquitous Stainless Steel Led to Competent Electrocatalysts for Overall Water Splitting | journal=ACS Sustainable Chemistry & Engineering | pages=4778–4784 | last1 = Liu | first1 = Xuan| year=2017 | bibcode=2017ASCE....5.4778L }}</ref>

== Health effects ==

There is extensive research indicating some probable increased risk of cancer (particularly lung cancer) from inhaling fumes while welding stainless steel.<ref name="nickel_in_welding_fumes_1984_nih_gov">Langård, S. and R.M. Stern, [https://www.ncbi.nlm.nih.gov/pubmed/6398291 "Nickel in welding fumes--a cancer hazard to welders? A review of epidemiological studies on cancer in welders,"] 1984, ''[[IARC Scientific Publications]]'' 1984;(53):95-103, summarized on website of [[National Institutes of Health]], retrieved 16 March 2020</ref><ref name="nickel_cancer_1994_06_06_sci_total_environ">{{cite journal| pmid=8029707 | doi=10.1016/0048-9697(94)90408-1 | volume=148 | title=Nickel-related cancer in welders | year=1994 | journal=Sci Total Environ | pages=303–9 | last1 = Langård | first1 = S| issue=2–3 | bibcode=1994ScTEn.148..303L }}</ref><ref name="cancer_incidence__1996_10_am_j_ind_med">Lauritsen, J.M., K.S. Hansen, and A. Skytthe: [https://www.ncbi.nlm.nih.gov/pubmed/8892541 "Cancer incidence among mild steel and stainless steel welders and other metal workers,"] {{Webarchive|url=https://web.archive.org/web/20211001031904/https://pubmed.ncbi.nlm.nih.gov/8892541/ |date=1 October 2021 }} October 1996, ''[[American Journal of Industrial Medicine]],'' pp.373-82, summarized on website of [[National Institutes of Health]], retrieved 16 March 2020</ref><ref name="lung_cancer_mortality__1996_10_am_j_ind_med">Lauritsen, J.M. and K.S. Hansen, [https://www.ncbi.nlm.nih.gov/pubmed/8892542 "Lung cancer mortality in stainless steel and mild steel welders: a nested case-referent study,"] {{Webarchive|url=https://web.archive.org/web/20140410082502/http://www.ncbi.nlm.nih.gov/pubmed/8892542 |date=10 April 2014 }}, October 1996, ''[[American Journal of Industrial Medicine]],'' summarized on website of [[National Institutes of Health]], retrieved 16 March 2020</ref><ref name="follow_up_2003_07__14_nih_gov">Knudsen, L.E. and H. Burr, [https://www.ncbi.nlm.nih.gov/pubmed/12908358 "Follow-up examination of Danish stainless steel welders previously examined in 1987"] {{Webarchive|url=https://web.archive.org/web/20211001031904/https://pubmed.ncbi.nlm.nih.gov/12908358/|date=1 October 2021}} (article in Danish) 14 July 2003 ''[[Ugeskr Laeger]],'' 165(29):2882-6, summarized on website of [[National Institutes of Health]], retrieved 16 March 2020</ref><ref name="more_evidence_2019_05_21_reuters">Rapaport, Lisa, [https://www.reuters.com/article/us-health-welding-cancer/more-evidence-welding-fumes-raise-lung-cancer-risk-idUSKCN1SR2IA "More evidence welding fumes raise lung cancer risk"] {{Webarchive|url=https://web.archive.org/web/20210414011043/https://www.reuters.com/article/us-health-welding-cancer/more-evidence-welding-fumes-raise-lung-cancer-risk-idUSKCN1SR2IA |date=14 April 2021 }}, 21 May 2019, [[Reuters News Service]], retrieved 16 March 2020</ref> Stainless steel welding is suspected of producing carcinogenic fumes from cadmium oxides, nickel, and chromium.<ref name="welding_cancer_council_australia">[https://www.cancer.org.au/preventing-cancer/workplace-cancer/welding.html "Welding and cancer,"] {{Webarchive|url=https://web.archive.org/web/20200620083514/https://www.cancer.org.au/preventing-cancer/workplace-cancer/welding.html |date=20 June 2020 }} in "Welding" on the website of the [[Cancer Council Australia]], retrieved 16 March 2020</ref> According to [[Cancer Council Australia]], "In 2017, all types of welding fumes were classified as a [[List of IARC Group 1 Agents - Carcinogenic to humans|Group 1 carcinogen]]."<ref name="welding_cancer_council_australia" />

Stainless steel is generally considered to be biologically inert. However, during cooking, small amounts of nickel and chromium leach out of new stainless steel cookware into highly acidic food.<ref>{{Cite journal|last1=Kamerud|first1=Kristin L.|last2=Hobbie|first2=Kevin A.|last3=Anderson|first3=Kim A.|date=2013-09-19|title=Stainless Steel Leaches Nickel and Chromium into Foods during Cooking|journal=Journal of Agricultural and Food Chemistry|volume=61|issue=39|pages=9495–9501|doi=10.1021/jf402400v|issn=0021-8561|pmc=4284091|pmid=23984718|bibcode=2013JAFC...61.9495K }}</ref> Nickel can contribute to cancer risks—particularly [[lung cancer]] and [[Paranasal sinus and nasal cavity cancer|nasal cancer]].<ref name="safe_cookware">[http://healthybuildingscience.com/2013/11/22/safe-cookware-2/ Safe Cookware: Does Stainless Steel Leach Chemicals?] {{Webarchive|url=https://web.archive.org/web/20210626164708/https://healthybuildingscience.com/2013/11/22/safe-cookware-2/ |date=26 June 2021 }} ''healthybuildingscience.com'', accessed 28 January 2019</ref><ref name="natl_cancaer_inst">[https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/nickel "Nickel Compounds,"] {{Webarchive|url=https://web.archive.org/web/20210815021924/https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/nickel |date=15 August 2021 }} in "Cancer-Causing Substances", in "Risk Factors," in "Cancer Causes and Prevention," in "About Cancer," at the website of the [[National Cancer Institute]], retrieved 16 March 2020</ref> However, no connection between stainless steel cookware and cancer has been established.<ref name="cookware_cancer_2015_02_08_upmc_healtbeat">[https://share.upmc.com/2015/02/can-common-cookware-cause-cancer/ "Can Common Cookware Cause Cancer?"] {{Webarchive|url=https://web.archive.org/web/20210413223844/https://share.upmc.com/2015/02/can-common-cookware-cause-cancer/|date=13 April 2021}} 8 February 2015, ''[[UPMC HealthBeat]],'' UPMC ([[University of Pittsburgh Medical Center]]), retrieved 16 March 2020</ref>

== See also ==
* [[Cobalt-chrome]]
* [[Corrosion engineering]]
* [[Corrugated stainless steel tubing]]
* [[List of blade materials]]
* [[List of steel producers]]
* [[Metallic fiber]]
* [[Pilling–Bedworth ratio]]
* [[Rouging]]
* [[Weathering steel]]

== Notes ==

{{notelist}}

== References ==

{{reflist}}

== Further reading ==
* {{Cite book |last=Honeycombe|first=R. W. K. |date=1981 |title=Steels: microstructure and properties |oclc=7576277 |publisher=E. Arnold |isbn=0-7131-2793-7|location=London}}
* [https://www.iso.org/standard/61187.html International Standard ISO15510:2014] {{Subscription required}}
* {{Cite book | author1 = Lacombe, P. |author2=Baroux, B. |author3=Béranger, G. | year = 1990 | title = Les aciers inoxydables | trans-title = Stainless Steels | language = fr | at = Chapters 14 and 15 | location = Paris | publisher = Ed. de physique | isbn = 978-0868831428 | url = https://books.google.com/books?id=lpgnzQEACAAJ | access-date = 8 March 2020}}
* {{Cite book | author1 = Peckner, D. |author2=Bernstein, I.M. | year = 1977 | title = Handbook of Stainless Steels | location = New York | publisher = McGraw-Hill | series = McGraw-Hill Handbooks | isbn = 978-0070491472 | url = https://books.google.com/books?id=KY1UAAAAMAAJ | access-date = 8 March 2020}}

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