Stainless steel
Overview
 
In metallurgy
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

 with a minimum of 10.5 or 11% chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

 content by mass.

Stainless steel does not stain, corrode
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

, or rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

 as easily as ordinary steel, but it is not stain-proof. It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry.
Encyclopedia
In metallurgy
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

 with a minimum of 10.5 or 11% chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

 content by mass.

Stainless steel does not stain, corrode
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

, or rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

 as easily as ordinary steel, but it is not stain-proof. It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required.

Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

s readily when exposed to air and moisture. This iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...

 film (the rust) is active and accelerates corrosion by forming more iron oxide. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion and blocks corrosion from spreading into the metal's internal structure.

Passivation
Passivation
Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...

 only occurs if the proportion of chromium is high enough.

History

A few corrosion-resistant iron artifacts survive from antiquity. A famous example is the Iron Pillar of Delhi, erected by order of Kumara Gupta I
Kumara Gupta I
Kumaragupta I ' was a ruler of the Gupta Empire in 415–455 CE. Like his father and predecessor, Chandragupta II, Kumaragupta was an able ruler. He retained, intact, the vast empire, which extended from Bengal to Kathiawar and from the Himalayas to the Narmada. He ruled efficiently for nearly forty...

 around AD 400
400
Year 400 was a leap year starting on Sunday of the Julian calendar. At the time, it was known as the Year of the Consulship of Stilicho and Aurelianus...

. Unlike stainless steel, however, these artifacts owe their durability not to chromium but to their high phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

 content, which, together with favorable local weather conditions, promotes the formation of a solid protective passivation layer of iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...

s and phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

s, rather than the non-protective cracked rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

 layer that develops on most ironwork.

The corrosion resistance of iron-chromium alloys was first recognized in 1821 by French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 metallurgist Pierre Berthier, who noted their resistance against attack by some acids and suggested their use in cutlery
Cutlery
Cutlery refers to any hand implement used in preparing, serving, and especially eating food in the Western world. It is more usually known as silverware or flatware in the United States, where cutlery can have the more specific meaning of knives and other cutting instruments. This is probably the...

. Metallurgists of the 19th century were unable to produce the combination of low carbon and high chromium found in most modern stainless steels, and the high-chromium alloys they could produce were too brittle to be practical.

In the late 1890s Hans Goldschmidt
Hans Goldschmidt
Johannes Wilhelm "Hans" Goldschmidt was a German chemist.Born in Berlin, he was a student of Robert Bunsen. His father, Theodor Goldschmidt, was the founder of the chemical company Chemische Fabrik Th...

 of Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 developed an aluminothermic (thermite
Thermite
Thermite is a pyrotechnic composition of a metal powder and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction...

) process for producing carbon-free chromium. Between 1904 and 1911 several researchers, particularly Leon Guillet
Léon Guillet
Léon B. Guillet was a French metallurgist, known for his work on stainless steels in the early 20th century.-Reference:*...

 of France, prepared alloys that would today be considered stainless steel.

Friedrich Krupp Germaniawerft
Friedrich Krupp Germaniawerft
Friedrich Krupp Germaniawerft was a German shipbuilding company, located in the harbour at Kiel, and one of the largest and most important builders of U-boats for the Kaiserliche Marine in World War I and the Kriegsmarine in World War II.-History:The company was founded in 1867 by Lloyd Foster, as...

built the 366-ton sailing yacht Germania featuring a chrome-nickel steel hull in Germany in 1908. In 1911, Philip Monnartz reported on the relationship between chromium content and corrosion resistance. On October 17, 1912, Krupp
Krupp
The Krupp family , a prominent 400-year-old German dynasty from Essen, have become famous for their steel production and for their manufacture of ammunition and armaments. The family business, known as Friedrich Krupp AG Hoesch-Krupp, was the largest company in Europe at the beginning of the 20th...

 engineers Benno Strauss and Eduard Maurer patented austenitic
Austenite
Austenite, also known as gamma phase iron, is a metallic non-magnetic allotrope of iron or a solid solution of iron, with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of ; other alloys of steel have different eutectoid temperatures...

 stainless steel as ThyssenKrupp Nirosta
ThyssenKrupp Nirosta
ThyssenKrupp Nirosta is a business segment of ThyssenKrupp, headquartered in Krefeld, Germany. It produces flats of stainless steel....

.

Similar developments were taking place contemporaneously in the United States, where Christian Dantsizen and Frederick Becket were industrializing ferritic
Ferrite (iron)
Ferrite or alpha iron is a materials science term for iron, or a solid solution with iron as the main constituent, with a body centred cubic crystal structure. It is the component which gives steel and cast iron their magnetic properties, and is the classic example of a ferromagnetic material...

 stainless steel. In 1912, Elwood Haynes
Elwood Haynes
Elwood P. Haynes was an American inventor, metallurgist, automotive pioneer, entrepreneur and industrialist. He invented the metal alloys stellite and martensitic stainless steel and designed one of the earliest automobiles made in the United States...

 applied for a US patent on a martensitic
Martensite
Martensite, named after the German metallurgist Adolf Martens , most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by displacive transformation. It includes a class of hard minerals occurring as lath- or...

 stainless steel alloy, which was not granted until 1919.

Also in 1912, Harry Brearley
Harry Brearley
Harry Brearley is usually credited with the invention of "rustless steel" in the anglophone world.-Life:...

 of the Brown-Firth
Firth Brown Steels
Firth Brown Steels was initially formed in 1902, when Sheffield steelmakers John Brown and Company exchanged shares and came to a working agreement with neighbouring company Thomas Firth & Sons...

 research laboratory in Sheffield, England, while seeking a corrosion-resistant alloy for gun barrels, discovered and subsequently industrialized a martensitic stainless steel alloy. The discovery was announced two years later in a January 1915 newspaper article in The New York Times
The New York Times
The New York Times is an American daily newspaper founded and continuously published in New York City since 1851. The New York Times has won 106 Pulitzer Prizes, the most of any news organization...

. The metal was later marketed under the 'Staybrite' brand by Firth Vickers
Vickers
Vickers was a famous name in British engineering that existed through many companies from 1828 until 1999.-Early history:Vickers was formed in Sheffield as a steel foundry by the miller Edward Vickers and his father-in-law George Naylor in 1828. Naylor was a partner in the foundry Naylor &...

 in England and was used for the new entrance canopy for the Savoy Hotel
Savoy Hotel
The Savoy Hotel is a hotel located on the Strand, in the City of Westminster in central London. Built by impresario Richard D'Oyly Carte with profits from his Gilbert and Sullivan operas, the hotel opened on 6 August 1889. It was the first in the Savoy group of hotels and restaurants owned by...

 in London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

 in 1929.

Brearley applied for a US patent during 1915 only to find that Haynes had already registered a patent. Brearley and Haynes pooled their funding and with a group of investors formed the American Stainless Steel Corporation, with headquarters in Pittsburgh, Pennsylvania. In the beginning stainless steel was sold in the US under different brand names like 'Allegheny metal
Allegheny Technologies
Allegheny Technologies, Inc. is a specialty metals company headquartered in Pittsburgh, Pennsylvania in the United States. Allegheny Technologies is one of the largest and most diversified specialty metals producers in the world with revenue of $3.0 billion in 2009. ATI's key markets are...

' and 'Nirosta steel'. In 1929 before the Great Depression hit, over 25,000 tons of stainless steel was manufactured and sold in the US.

Properties

High oxidation-resistance in air
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

 at ambient temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments. The chromium forms a passivation
Passivation
Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...

 layer of chromium(III) oxide
Chromium(III) oxide
Chromium oxide is the inorganic compound of the formula Cr2O3. It is one of principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.-Structure and properties:...

 (Cr2O3) when exposed to oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. The layer is too thin to be visible, and the metal remains lustrous. The layer is impervious to water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and air, protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 and titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

. Corrosion-resistance can be adversely affected if the component is used in a non-oxygenated environment, a typical example being underwater keel
Keel
In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...

 bolts buried in timber
Timber
Timber may refer to:* Timber, a term common in the United Kingdom and Australia for wood materials * Timber, Oregon, an unincorporated community in the U.S...

.

When stainless steel parts such as nut
Nut (hardware)
A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...

s and bolts are forced together, the oxide layer can be scraped off, causing the parts to weld
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

 together. When disassembled, the welded material may be torn and pitted, an effect known as galling
Galling
Galling usually refers to the adhesive wear and transfer of material between metallic surfaces in relative converging contact during sheet metal forming and other industrial operations....

. This destructive galling can be best avoided by the use of dissimilar materials for the parts forced together, for example bronze and stainless steel, or even different types of stainless steels (martensitic against austenitic), when metal-to-metal wear is a concern. Nitronic alloys reduce the tendency to gall through selective alloying with manganese and nitrogen. In addition, threaded joints may be lubricated to prevent galling.

Applications

Stainless steel’s resistance to corrosion and staining, low maintenance and familiar lustre
Lustre (mineralogy)
Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning "light", and generally implies radiance, gloss, or brilliance....

 make it an ideal material for many applications. There are over 150 grades of stainless steel, of which fifteen are most commonly used. The alloy is milled
Steel mill
A steel mill or steelworks is an industrial plant for the manufacture of steel.Steel is an alloy of iron and carbon. It is produced in a two-stage process. First, iron ore is reduced or smelted with coke and limestone in a blast furnace, producing molten iron which is either cast into pig iron or...

 into coils, sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, hardware
Hardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....

, surgical instruments
Surgical instruments
A surgical instrument is a specially designed tool or device for performing specific actions of carrying out desired effects during a surgery or operation, such as modifying biological tissue, or to provide access for viewing it. Over time, many different kinds of surgical instruments and tools...

, major appliances, industrial equipment (for example, in sugar refineries
Sugar refinery
A sugar refinery is a factory which refines raw sugar.Many cane sugar mills produce raw sugar, i.e. sugar with more colour and therefore more impurities than the white sugar which is normally consumed in households and used as an ingredient in soft drinks, cookies and so forth...

) and as an automotive and aerospace structural alloy and construction material in large buildings. Storage tanks and tankers used to transport orange juice
Orange juice
Orange juice is a popular beverage made from oranges. It is made by extraction from the fresh fruit, by desiccation and subsequent reconstitution of dried juice, or by concentration of the juice and the subsequent addition of water to the concentrate...

 and other food are often made of stainless steel, because of its corrosion resistance and antibacterial properties. This also influences its use in commercial kitchens and food processing plants, as it can be steam-cleaned and sterilized
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...

 and does not need paint or other surface finishes.

Stainless steel is used for jewellery and watches with 316L being the type commonly used for such applications. It can be re-finished by any jeweler and will not oxidize or turn black.

Some firearms incorporate stainless steel components as an alternative to blued
Bluing (steel)
Bluing is a passivation process in which steel is partially protected against rust, and is named after the blue-black appearance of the resulting protective finish. True gun bluing is an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface...

 or parkerized steel. Some handgun
Handgun
A handgun is a firearm designed to be held and operated by one hand. This characteristic differentiates handguns as a general class of firearms from long guns such as rifles and shotguns ....

 models, such as the Smith & Wesson Model 60
Smith & Wesson Model 60
The Smith & Wesson Model 60 revolver is a 5-shot snubnosed revolver that is chambered in either .38 Special or .357 Magnum calibers. Like nearly all other "J-frame" Smith & Wesson revolvers, it has a swing-out cylinder, and features an exposed hammer...

 and the Colt M1911 pistol, can be made entirely from stainless steel. This gives a high-luster finish similar in appearance to nickel plating. Unlike plating, the finish is not subject to flaking, peeling, wear-off from rubbing (as when repeatedly removed from a holster), or rust when scratched.

Some automotive manufacturers
Automotive industry
The automotive industry designs, develops, manufactures, markets, and sells motor vehicles, and is one of the world's most important economic sectors by revenue....

 use stainless steel as decorative highlights in their vehicles.

Architectural

Stainless steel is used for buildings for both practical and aesthetic reasons. Stainless steel was in vogue during the art deco
Art Deco
Art deco , or deco, is an eclectic artistic and design style that began in Paris in the 1920s and flourished internationally throughout the 1930s, into the World War II era. The style influenced all areas of design, including architecture and interior design, industrial design, fashion and...

 period. The most famous example of this is the upper portion of the Chrysler Building
Chrysler Building
The Chrysler Building is an Art Deco style skyscraper in New York City, located on the east side of Manhattan in the Turtle Bay area at the intersection of 42nd Street and Lexington Avenue. Standing at , it was the world's tallest building for 11 months before it was surpassed by the Empire State...

 (pictured). Some diners and fast-food restaurants use large ornamental panels and stainless fixtures and furniture. Because of the durability of the material, many of these buildings retain their original appearance.

The forging of stainless steel has given rise to a fresh approach to architectural blacksmith
Blacksmith
A blacksmith is a person who creates objects from wrought iron or steel by forging the metal; that is, by using tools to hammer, bend, and cut...

ing in recent years.

Type 316 stainless is used on the exterior of both the Petronas Twin Towers
Petronas Twin Towers
The Petronas Towers are skyscrapers and twin towers in Kuala Lumpur, Malaysia...

 and the Jin Mao Building
Jin Mao Building
The Jin Mao Tower is an 88-story landmark supertall skyscraper in the Lujiazui area of the Pudong district of Shanghai, People's Republic of China. It contains offices and the Shanghai Grand Hyatt hotel. Until 2007 it was the tallest building in the PRC, the fifth tallest in the world by roof...

, two of the world's tallest skyscraper
Skyscraper
A skyscraper is a tall, continuously habitable building of many stories, often designed for office and commercial use. There is no official definition or height above which a building may be classified as a skyscraper...

s.

The Parliament House of Australia in Canberra
Parliament House, Canberra
Parliament House is the meeting facility of the Parliament of Australia located in Canberra, the capital of Australia. The building was designed by Mitchell/Giurgola Architects and opened on 1988 by Elizabeth II, Queen of Australia...

 has a stainless steel flagpole weighing over 220 tons (200 metric tonnes
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

).

The aeration building in the Edmonton Composting Facility
Edmonton Composting Facility
The Edmonton Composting Facility is the site of the City of Edmonton's advanced co-composting system for processing organic waste. Co-composting involves mixing household wastes with biosolids , to create compost. Together with the City's three recycling programs, Edmonton is able to divert 60% of...

, the size of 14 hockey rinks, is the largest stainless steel building in North America.

Bridges

  • Minorca Road Bridge (Spain) is the first stainless steel road bridge.
  • Sant Fruitos Pedestrian Bridge (Catalonia, Spain), arch pedestrian bridge.
  • Padre Arrupe Bridge (Bilbao, Spain) links the Guggenheim museum to the University of Deusto.

Monuments and sculptures

  • The Unisphere
    Unisphere
    The Unisphere is a 12-story high, spherical stainless steel representation of the Earth. Located in Flushing Meadows – Corona Park in the borough of Queens, New York City, the Unisphere is one of the borough's most iconic and enduring symbols....

    , constructed as the theme symbol of the 1964-5 World's Fair in New York City, is the world's largest globe-shaped structure.
  • The Gateway Arch (pictured) is clad entirely in stainless steel: 886 tons (804 metric tonnes) of 0.25 in (6.4 mm) plate, #3 finish, type 304 stainless steel.
  • The United States Air Force Memorial
    United States Air Force Memorial
    The United States Air Force Memorial honors the service of the personnel of the United States Air Force and its predecessors. The Memorial is located in Arlington, Virginia, on the grounds of Fort Myer near The Pentagon and Arlington National Cemetery, at the intersection of Columbia Pike and...

     has an austenitic stainless steel structural skin.
  • The Atomium
    Atomium
    The Atomium is a monument in Brussels, originally built for Expo '58, the 1958 Brussels World's Fair. Designed by André Waterkeyn, it stands 102 metres tall...

     in Brussels
    Brussels
    Brussels , officially the Brussels Region or Brussels-Capital Region , is the capital of Belgium and the de facto capital of the European Union...

    , Belgium
    Belgium
    Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

     was renovated with stainless-steel cladding in a renovation completed in 2006; previously the spheres and tubes of the structure were clad in aluminium.
  • The Cloud Gate
    Cloud Gate
    Cloud Gate, a public sculpture by Indian-born British artist Anish Kapoor, is the centerpiece of the AT&T Plaza in Millennium Park within the Loop community area of Chicago, Illinois, United States. The sculpture and AT&T Plaza are located on top of Park Grill, between the Chase Promenade and...

     sculpture by Anish Kapoor
    Anish Kapoor
    Anish Kapoor CBE RA is a British sculptor of Indian birth. Born in Mumbai , Kapoor has lived and worked in London since the early 1970s when he moved to study art, first at the Hornsey College of Art and later at the Chelsea School of Art and Design.He represented Britain in the XLIV Venice...

    , in Chicago US.
  • The Sibelius monument
    Sibelius monument
    The Sibelius Monument is dedicated to the Finnish composer Jean Sibelius . The monument is located at the Sibelius Park in the district of Töölö in Helsinki, the capital city of Finland....

     in Helsinki, Finland, is made entirely of stainless steel tubes.

Other

  • The DeLorean DMC-12 automobile used stainless steel body panels over a glass-reinforced plastic
    Glass-reinforced plastic
    Fiberglass , is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass. It is also known as GFK ....

     monocoque
    Monocoque
    Monocoque is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork...

    .
  • Passenger rail cars have commonly been manufactured using corrugated stainless steel panels (for additional structural strength). One notable example was the early Pioneer Zephyr
    Pioneer Zephyr
    The Pioneer Zephyr is a diesel-powered railroad train formed of railroad cars permanently articulated together with Jacobs bogies, built by the Budd Company in 1934 for the Chicago, Burlington and Quincy Railroad , commonly known as the Burlington...

    .

Recycling and reuse

Stainless steel is 100% recyclable. An average stainless steel object is composed of about 60% recycled material of which approximately 40% originates from end-of-life products and about 60% comes from manufacturing processes. According to the International Resource Panel
International Resource Panel
The International Resource Panel is a scientific panel of experts that aims to help nations use natural resources sustainably without compromising economic growth and human needs...

's Metal Stocks in Society report
Metal Stocks in Society report
The report Metal Stocks in Society: Scientific Synthesis was the first of six scientific assessments on global metals to be published by the International Resource Panel of the United Nations Environment Programme...

, the per capita stock of stainless steel in use in society is 80–180kg in more developed countries and 15kg 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.

Types of stainless steel

There are different types of stainless steels: when nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

 is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels virtually non-magnetic and less brittle
Brittle
A material is brittle if, when subjected to stress, it breaks without significant deformation . Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses ...

 at low temperatures. For greater hardness and strength, more carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 is added. With proper heat treatment
Heat treatment
Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass...

, these steels are used for such things as razor
Razor
A razor is a bladed tool primarily used in the removal of unwanted body hair through the act of shaving. Kinds of razors include straight razors, disposable razors and electric razors....

 blades, cutlery, and tool
Tool
A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

s.

Significant quantities of manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

 have been used in many stainless steel compositions. Manganese preserves an austenitic structure in the steel as does nickel, but at a lower cost
Cost
In production, research, retail, and accounting, a cost is the value of money that has been used up to produce something, and hence is not available for use anymore. In business, the cost may be one of acquisition, in which case the amount of money expended to acquire it is counted as cost. In this...

.

Stainless steels are also classified by their crystalline structure:
  • Austenitic
    Austenite
    Austenite, also known as gamma phase iron, is a metallic non-magnetic allotrope of iron or a solid solution of iron, with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of ; other alloys of steel have different eutectoid temperatures...

    , or 300 series, stainless steels make up over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy. A typical composition of 18% chromium and 10% nickel, commonly known as 18/10 stainless, is often used in flatware. 18/0 and 18/8 are also available. Superaustenitic stainless steels, such as alloy AL-6XN
    AL-6XN
    The AL-6XN alloy is a superaustenitic stainless steel which was developed by . It exhibits far greater resistance to chloride pitting, crevice corrosion and stress corrosion cracking than exhibited by the standard 300 series stainless steels, and is less costly than the traditional nickel-base...

     and 254SMO, exhibit great resistance to chloride pitting and crevice corrosion because of high molybdenum
    Molybdenum
    Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...

     content (>6%) and nitrogen additions, and the higher nickel content ensures better resistance to stress-corrosion cracking versus the 300 series. The higher alloy content of superaustenitic steels makes them more expensive. Other steels can offer similar performance at lower cost and are preferred in certain applications, for example ASTM A387 is used in pressure vessels but is a low alloy carbon steel with a chromium content of 0.5% to 9%. Low-carbon versions, for example 316L or 304L, are used to avoid corrosion problems caused by welding. Grade 316LVM is preferred where biocompatibility
    Biocompatibility
    Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used , or to more empirical clinical success of a whole device in...

     is required (such as body implants and piercings). The "L" means that the carbon content of the alloy is below 0.03%, which reduces the sensitization effect (precipitation of chromium carbides at grain boundaries) caused by the high temperatures involved in welding.

  • Ferritic
    Ferrite (iron)
    Ferrite or alpha iron is a materials science term for iron, or a solid solution with iron as the main constituent, with a body centred cubic crystal structure. It is the component which gives steel and cast iron their magnetic properties, and is the classic example of a ferromagnetic material...

    stainless steels generally have better engineering properties than austenitic grades, but have reduced corrosion resistance, because of the lower chromium and nickel content. They are also usually less expensive. They contain between 10.5% and 27% chromium and very little nickel, if any, but some types can contain lead. Most compositions include molybdenum; some, aluminium or titanium. Common ferritic grades include 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2Ni. These alloys can be degraded by the presence of chromium, an intermetallic phase which can precipitate upon welding.

  • Martensitic
    Martensitic stainless steel
    Martensitic stainless steel is a specific type of stainless steel alloy.Stainless steels may be classified by their crystalline structure into three main types: Austenitic, Ferritic and Martensitic. Martensitic steels are low carbon steels built around the Type 410 composition of iron, 12%...

    stainless steels are not as corrosion-resistant as the other two classes but are extremely strong and tough, as well as highly machinable
    Machinability
    The term machinability refers to the ease with which a metal can be machined to an acceptable surface finish. Materials with good machinability require little power to cut, can be cut quickly, easily obtain a good finish, and do not wear the tooling much; such materials are said to be free machining...

    , and can be hardened by heat treatment. Martensitic stainless steel contains chromium (12–14%), molybdenum (0.2–1%), nickel (less than 2%), and carbon (about 0.1–1%) (giving it more hardness but making the material a bit more brittle). It is quenched and magnetic.

  • Precipitation-hardening martensitic stainless steels have corrosion resistance comparable to austenitic varieties, but can be precipitation hardened to even higher strengths than the other martensitic grades. The most common, 17-4PH, uses about 17% chromium and 4% nickel. The Lockheed-Martin Joint Strike Fighter is the first aircraft to use a precipitation-hardenable stainless steel—Carpenter Custom 465—in its airframe.

  • Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim usually being to produce a 50/50 mix, although in commercial alloys the ratio may be 40/60. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels and also improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterized by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. Duplex grades are characterized into groups based on their alloy content and corrosion resistance. Lean duplex refers to grades such as UNS
    Unified numbering system
    The unified numbering system is an alloy designation system widely accepted in North America. It consists of a prefix letter and five digits designating a material composition. A prefix of S indicates stainless steel alloys, C for copper, brass, or bronze alloys, T for tool steels, etc...

     S32101 (LDX 2101), S32304, and S32003. The standard duplex is 22% chromium with UNS S31803/S32205 known as 2205 being the most widely used. Super duplex is by definition a duplex stainless steel with a pitting corrosion equivalent (PRE) > 40, where PRE = %Cr + 3.3x(%Mo + 0.5x%W) + 16x%N. Usually super duplex grades have 25% chromium or more and some common examples are S32760 (Zeron 100
    Zeron 100
    Zeron 100 is a superduplex stainless steel developed by Rolled Alloys . The alloy has excellent corrosion resistance combined with high strength. It typically contains 25% chromium and 7% nickel and 3.6% molybdenum along with copper and tungsten additions. Zeron 100 has a 50–50 austenitic-ferritic...

    ), S32750 (2507) and S32550 (Ferralium), although not all Ferralium grades are super duplex grades. Hyper duplex refers to duplex grades with a PRE > 48 and at the moment only UNS S32707 and S33207 are available on the market. 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.

Comparison of standardized steels

EN-standard
Steel no. k.h.s
DIN
EN-standard
Steel name
SAE grade UNS
Unified numbering system
The unified numbering system is an alloy designation system widely accepted in North America. It consists of a prefix letter and five digits designating a material composition. A prefix of S indicates stainless steel alloys, C for copper, brass, or bronze alloys, T for tool steels, etc...

440A S44002
1.4112 X90CrMoV18 440B S44003
1.4125 440C S44004
440F S44020
1.4016 X6Cr17 430 S43000
1.4408 G-X 6 CrNiMo 18-10 316
1.4512 X6CrTi12 409 S40900
410 S41000
1.4310 X10CrNi18-8 301 S30100
1.4318 X2CrNiN18-7 301LN N/A
1.4307 X2CrNi18-9 304L S30403
1.4306 X2CrNi19-11 304L S30403
1.4311 X2CrNiN18-10 304LN S30453
1.4301 X5CrNi18-10 304 S30400
1.4948 X6CrNi18-11 304H S30409
1.4303 X5CrNi18-12 305 S30500
X5CrNi30-9 312
1.4541 X6CrNiTi18-10 321 S32100
1.4878 X12CrNiTi18-9 321H S32109
1.4404 X2CrNiMo17-12-2 316L S31603
1.4401 X5CrNiMo17-12-2 316 S31600
1.4406 X2CrNiMoN17-12-2 316LN S31653
1.4432 X2CrNiMo17-12-3 316L S31603
1.4435 X2CrNiMo18-14-3 316L S31603
1.4436 X3CrNiMo17-13-3 316 S31600
1.4571 X6CrNiMoTi17-12-2 316Ti S31635
1.4429 X2CrNiMoN17-13-3 316LN S31653
1.4438 X2CrNiMo18-15-4 317L S31703
1.4362 X2CrNi23-4 2304 S32304
1.4462 X2CrNiMoN22-5-3 2205 S31803/S32205
1.4539 X1NiCrMoCu25-20-5 904L N08904
1.4529 X1NiCrMoCuN25-20-7 1925hMo/6MO N08926
1.4547 X1CrNiMoCuN20-18-7 254SMO S31254

Stainless steel grades

There are a number of different systems for grading stainless and other steels
Steel grades
Steel grades to classify various steels by their composition and physical properties have been developed by a number of standards organizations.*SAE steel grades*British Standards*International Organization for Standardization ISO/TS 4949:2003...

. The article on US SAE steel grades details a large number of grades with their properties.

Stainless steel in 3D printing

Some 3D printing
3D printing
3D printing is a form of additive manufacturing technology where a three dimensional object is created by laying down successive layers of material. 3D printers are generally faster, more affordable, and easier to use than other additive manufacturing technologies. However, the term 3D printing is...

 providers have developed proprietary stainless steel sintering
Sintering
Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...

 blends for use in rapid prototyping. Currently available grades do not vary significantly in their properties.

Stainless steel finishes

Standard mill finishes
Surface finishing
Surface finishing is a broad range of industrial processes that alter the surface of a manufactured item to achieve a certain property. Finishing processes may be employed to: improve appearance, adhesion or wettability, solderability, corrosion resistance, tarnish resistance, chemical resistance,...

 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 annealed
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...

 to change the properties of the final material. Any oxidation that forms on the surface (mill scale
Mill scale
Mill scale, often shortened to just scale, is the flaky surface of hot rolled steel, iron oxides consisting of Iron oxide, hematite, and magnetite....

) is removed by pickling
Pickling (metal)
Tarnision is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale from ferrous metals, copper, and aluminum alloys. A solution called Tarnision liquor, which contains strong acids, is used to remove the surface impurities...

, and a passivation layer is created on the surface. A final finish can then be applied to achieve the desired aesthetic appearance.
  • No. 0: Hot rolled, annealed, thicker plates
  • No. 1: Hot rolled, annealed and passivated
  • No. 2D: Cold rolled, annealed, pickled and passivated
  • No. 2B: Same as above with additional pass-through highly polished rollers
  • No. 2BA: Bright annealed (BA or 2R) same as above then bright annealed under oxygen-free atmospheric condition
  • No. 3: Coarse abrasive finish applied mechanically
  • No. 4: Brushed finish
  • No. 5: Satin finish
  • No. 6: Matte finish
  • No. 7: Reflective finish
  • No. 8: Mirror finish
  • No. 9: Bead blast finish
  • No. 10: Heat colored finish-wide range of electropolished
    Electropolishing
    Electropolishing, also known as electrochemical polishing or electrolytic polishing , is an electrochemical process that removes material from a metallic workpiece. It is used to polish, passivate, and deburr metal parts. It is often described as the reverse of electroplating...

     and heat colored surfaces

See also

  • Architectural steel
  • Argon oxygen decarburization
    Argon Oxygen Decarburization
    Argon oxygen decarburization is a process primarily used in stainless steel making and other high grade alloys with oxidizable elements such as chromium and aluminum. After initial melting the metal is then transferred to an AOD vessel where it will be subjected to three steps of refining;...

  • Budd Company
    Budd Company
    The Budd Company is a metal fabricator and major supplier of body components to the automobile industry, and was formerly a manufacturer of stainless steel passenger rail cars during the 20th century....

     — Historically notable user of stainless steel
  • Knife metal
    Knife metal
    A knife metal is a metal, usually consisting of steel or stainless steel, that is used to construct a knife blade. Below is a list of various steel types for knives and their characteristics.-References:*http://sogknives.com/...

  • Panel edge staining
    Panel Edge Staining
    Panel edge staining is a naturally occurring problem that occurs to anodized aluminium and stainless steel paneling and facades. It is semi-permanent staining that dulls the panel or facades surface , reducing the natural luster and shine produced by the anodizing processes used on the aluminium...


  • Marine grade stainless
    Marine grade stainless
    Marine grade stainless is a stainless steel preferred for use in marine environments to avoid pitting corrosion. The AISI number grade is 316 and refers to the chromium content....

     steel
  • Razor blade steel
    Razor blade steel
    Razor blade steel, also known as razor steel, is special type of stainless steel designed specifically to be used as a razor blade. Its defining characteristics are its chemical composition and shape.-Chemical composition:...

  • Rouging
    Rouging
    Rouging refers to a form of corrosion found in stainless steel. It can be due to iron contamination of the stainless steel surface due to welding of ferrous steel for support columns, or other temporary means, which when welded off, leaving a low chromium area....

  • Stainless steel soap
    Stainless steel soap
    A stainless steel soap is a piece of stainless steel, usually in the shape of a soap bar. Its advertised purpose is to neutralize or reduce strong odors from the hands, present from handling odorous ingredients such as garlic, onion or fish....

     — used to remove strong odors

  • SAE steel grades - List of grades and their respective properties.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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