SAE 304 stainless steel is the most common

stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...

. It is an alloy of

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

and

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

. It is an

austenitic stainless steel Austenitic stainless steel is one of the five families of stainless steel (along with ferritic, martensitic, duplex and precipitation hardened). Its primary crystalline structure is austenite (face-centered cubic). Such steels are not hardena ...

, and is therefore not magnetic. It is less electrically and thermally

conductive In physics and electrical engineering, a conductor is an object or type of material that allows the flow of Electric charge, charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. The flow ...

than

carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...

. It has a higher

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

resistance than regular steel and is widely used because of the ease in which it is formed into various shapes.Data sheet on SAE 304 stainless steel
. The composition was developed by W. H. Hatfield at Firth Brown in 1924 and was marketed under the trade name "Staybrite 18/8". It is specified by

SAE International SAE International is a global professional association and standards organization based in Warrendale, Pennsylvania, United States. Formerly the Society of Automotive Engineers, the organization adopted its current name in 2006 to reflect bot ...

as part of its

SAE steel grades The SAE steel grades system is a standard alloy numbering system (SAE J1086 – Numbering Metals and Alloys) for steel grades maintained by SAE International. In the 1930s and 1940s, the American Iron and Steel Institute (AISI) and SAE were both ...

. It is also known as: * 4301-304-00-I and X5CrNi18-9, the ISO 15510 name and designation. * UNS S30400 in the

unified numbering system The Unified Numbering System for Metals and Alloys (UNS) is an alloy designation system widely accepted in North America. Each UNS number relates to a specific metal or alloy and defines its specific chemical composition, or in some cases a speci ...

. * A2 stainless steel outside the US, in accordance with ISO 3506 for

fasteners A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or disman ...

. * 18/8 and 18/10 stainless steel (also written 18-8 and 18-10) in the commercial

tableware Tableware items are the dishware and utensils used for setting a table, serving food, and dining. The term includes cutlery, glassware, serving dishes, serving utensils, and other items used for practical as well as decorative purposes. The ...

and fastener industries. * SUS304 the Japanese JIS G4303 equivalent grade. * 1.4301, the EN 10088 equivalent. * 06Cr19Ni10 and ISC S30408, the equivalent in Chinese GB/T 20878 and GB/T 17616 nomenclature. * 08Kh18N10 and 03Kh18N11, the equivalents for 403 and 403L in

GOST GOST () refers to a set of international technical standards maintained by the Euro-Asian Council for Standardization, Metrology and Certification (EASC), a regional standards organization operating under the auspices of the Commonwealth of I ...

nomenclature.

Chemical composition

Corrosion resistance

304 stainless steel has excellent resistance to a wide range of atmospheric environments and many corrosive media. It is subject to pitting and crevice corrosion in warm

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

environments and to

stress corrosion cracking Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It can lead to unexpected and sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. SC ...

above about . It is considered resistant to pitting corrosion in water with up to about 400 mg/L chlorides at ambient temperatures, reducing to about 150 mg/L at 60 °C. 304 stainless steel is also very sensitive at room temperature to the

thiosulfate Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, ...

anions released by the

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

pyrite The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...

(as encountered in

acid mine drainage Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines and coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weatherin ...

) and can undergo severe

pitting corrosion Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the random creation of small holes in metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic (oxidation re ...

problems when in close contact with

- or

sulfide Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families o ...

-rich

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

materials exposed to oxidation. For more severe corrosion conditions, when 304 stainless steel is too sensitive to pitting or crevice corrosion by chlorides or general corrosion in acidic applications, it is commonly replaced by

316 __NOTOC__ Year 316 ( CCCXVI) was a leap year starting on Sunday of the Julian calendar. At the time, it was known as the Year of the Consulship of Sabinus and Rufinus (or, less frequently, year 1069 ''Ab urbe condita''). The denomination 316 f ...

stainless steel. 304 and 302 stainless steels are subject to chloride stress fracture failure when used in tropical salt water conditions such as oil or gas rigs. 316 stainless steel is the preferred alloy for these conditions.

Mechanical properties

304 stainless steel cannot be heat treated—instead it can be strengthened by cold working. It is weakest in the annealed condition, and is strongest in the full-hard condition. The tensile yield strength ranges from . The density is , and its modulus of elasticity ranges from .

Applications

304 stainless steel is used for a variety of household and industrial applications such as food handling and processing equipment, screws, machinery parts, utensils, and exhaust manifolds. 304 stainless steel is also used in the architectural field for exterior accents such as water and fire features. It is also a common coil material for vaporizers. Early

SpaceX Starship Starship is a two-stage fully reusable launch vehicle, reusable super heavy-lift launch vehicle under development by American aerospace company SpaceX. On 20 April 2023, with the Starship flight test 1, first Integrated Flight Test, Starship b ...

s used SAE 301 stainless steel in their construction, before moving over to SAE 304L for the SN7 test tank and Starship SN8 in 2020. 304 stainless steel was used to clad the

Gateway Arch The Gateway Arch is a monument in St. Louis, Missouri, United States. Clad in stainless steel and built in the form of a weighted catenary Catenary arch, arch, it is the world's tallest arch and List of tallest buildings in Missouri, Missouri's ...

in St. Louis, Missouri.

Carbon content

304, 304H, and 304L all possess the same nominal chromium and nickel content and also possess the same corrosion resistance, ease of fabrication, and weldability. The difference between 304, 304H, and 304L is the carbon content, which is < 0.08, < 0.1, and < 0.035% respectively (also see UNS designations S30400, S30409, & S30403 respectively). 304 has both the H=High and the L=Low carbon variants. The carbon content of 304H (UNS S30409) is restricted to 0.04–0.10%, which provides optimal high-temperature strength. The carbon content of 304L (UNS 30403) is restricted to a maximum of 0.035%, which prevents sensitization during welding. Sensitization is the formation of chromium carbides along grain boundaries when stainless steel is exposed to temperatures in the approximate range of . The subsequent formation of chromium carbide results in reduced corrosion resistance along the grain boundary, leaving the stainless steel susceptible to unanticipated corrosion in an environment where 304 would be expected to be corrosion resistant. This grain boundary corrosive attack is known as intergranular corrosion. The carbon content of 304 (UNS 30400) is restricted to a maximum of 0.08% and is not useful for corrosive applications where welding is required, such as tanks and pipes where corrosive solutions are involved, and 304L is preferred. Its lack of a minimum carbon content is not ideal for high-temperature applications where optimal strength is required, thus, 304H is usually preferred. Therefore 304 is typically restricted to bars that will be machined into components where welding is not required or thin sheets that are formed in articles such as kitchen sinks or cookware that are also not welded. Carbon content has a strong influence on room temperature strength and thus the specified minimum tensile properties of 304L are lower than for 304. However, nitrogen also has a strong influence on room temperature strength and a tiny addition of nitrogen produces 304L with the same tensile strength as 304. Thus, practically all 304L is produced as dual certified 304/304L, meaning it meets the minimum carbon content of 304L and also meets the minimum tensile strength of 304.

References