Alloy 20 is an

austenitic stainless steel Austenitic stainless steel is one of the five classes of stainless steel by crystalline structure (along with ''ferritic'', ''martensitic, duplex and precipitation hardened''). Its primary crystalline structure is austenite (face-centered cubic) ...

containing less than 50% iron developed for applications involving

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

. Its corrosion resistance also finds other uses in the

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...

petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sou ...

power generation Electricity generation is the process of generating electric power from sources of primary energy. For utilities in the electric power industry, it is the stage prior to its delivery ( transmission, distribution, etc.) to end users or its stor ...

, and

plastics Plastics are a wide range of synthetic polymers, synthetic or semi-synthetic materials that use polymers as a main ingredient. Their Plasticity (physics), plasticity makes it possible for plastics to be Injection moulding, moulded, Extrusion, e ...

industries. Alloy 20 resists

pitting 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 ...

and

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

corrosion, better than 304 stainless steel and on par with

316L SAE 316L grade stainless steel, sometimes referred to as A4 stainless steel or marine grade stainless steel, is the second most common austenitic stainless steel after 304/A2 stainless steel. Its primary alloying constituents after iron, are c ...

stainless steel. Its copper content protects it from sulfuric acid. Alloy 20 is often chosen to solve

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. SCC ...

problems, which may occur with 316L stainless. Alloy of the same name with the designation "Cb-3" indicates

columbium Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...

stabilized.

Composition

* Nickel, 32–38% *

Chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...

, 19–21% *

Carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

, 0.06% maximum * Copper, 3–4% *

Molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

, 2–3% *

Manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

, 2% maximum *

Silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

, 1.0% maximum *

Niobium Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...

, (8.0 X C), 1% maximum * Iron, 31–44% (balance)

Other names

* UNS N08020 * DIN 2.4660 * CN7M * Carpenter 20 CB-3 * AL 20 * Carlson Alloy C20 * Nickelvac 23 * Nicrofer 3620 Nb, also known as VDM Alloy 20

Specifications

* ASTM B729, B464, B366, B463, B473, B462 * ASME SB729, SB464, SB366, SB473, SB462 * ANSI / ASTM A555-79 * EN 2.4660 * UNS N08020 * Werkstoff 2.4660 * Castings are designated CN7M

References

Steels Chromium alloys Nickel alloys {{alloy-stub