Incoloy® Alloy 20 / UNS N08020 / W.Nr. 2.4660
Alloy 20
Alloy 20, also known as Carpenter 20, is a popular nickel-iron-chromium austenitic alloy that boasts exceptional resistance to acid attack, particularly sulfuric acid. With its unique composition, this superalloy provides superior resistance to general corrosion, crevice corrosion, and pitting in chemical environments containing sulfuric, phosphoric, and nitric acids, as well as chlorides. The addition of niobium makes it highly resistant to sensitization and intergranular corrosion.
Originally developed for use in industries that utilize sulfuric acid, Alloy 20 has become a popular choice for a wide range of industries, including the chemical, food, pharmaceutical, and plastics industries. This versatile superalloy is also used in heat exchangers, mixing tanks, metal cleaning and pickling equipment, and piping. Carpenter 20 offers a unique combination of corrosion resistance, elevated mechanical properties, and ease of fabrication.
One of the intriguing characteristics of Alloy 20 is its classification. Some consider it a stainless steel, while others classify it as a nickel alloy. The nickel content of Alloy 20 is right on the border of defining it as either a stainless steel or a nickel alloy. Regardless of the classification, Alloy 20 provides excellent resistance to corrosion.
Industries and Applications
Alloy 20, also known as Carpenter 20, is a versatile superalloy that offers excellent corrosion resistance in a variety of chemical environments. This nickel-iron-chromium austenitic alloy is specially designed for maximum resistance to acid attack, particularly sulfuric acid, and it is highly resistant to general corrosion, pitting, and crevice corrosion in chemicals containing chlorides, sulfuric, phosphoric, and nitric acids. Alloy 20 also contains niobium, which provides stability against sensitization and resultant intergranular corrosion.
Industries that require superior corrosion resistance turn to Alloy 20 for its unique properties. Originally developed for industries that utilize sulfuric acid, this superalloy is now widely used in various industries such as:
Chemical Industry: The chemical industry is a significant user of Alloy 20. The exceptional corrosion resistance of this superalloy makes it an ideal choice for storage tanks, heat exchangers, process piping, and pumps.
Food and Beverage Industry: The food and beverage industry requires equipment that is hygienic, easy to clean, and has excellent corrosion resistance. Alloy 20 meets all these requirements, making it an ideal choice for food and beverage processing equipment.
Pharmaceutical Industry: The pharmaceutical industry requires high purity materials for their equipment to avoid contamination. Alloy 20 is an excellent choice for pharmaceutical equipment, particularly for the production of drugs that require high-purity materials.
Plastics Industry: The plastics industry requires equipment that can withstand harsh chemicals used in the production process. Alloy 20 is used to make process piping, mixing tanks, and other equipment used in the production of plastic.
Metal Cleaning and Pickling Industry: Alloy 20 is used extensively in the metal cleaning and pickling industry, where it provides excellent resistance to acid attack, making it ideal for pickling tanks, pumps, and process piping.
In addition to these industries, Alloy 20 is used in various other applications such as heat exchangers, piping systems, and metal fabrication. The ease of fabrication and elevated mechanical properties of this superalloy make it a popular choice for various industrial applications.
Resistance to Corrosion
Carpenter 20 is designed for maximum resistance to acid attack, particularly sulfuric acid. It provides superior resistance to general corrosion, pitting, and crevice corrosion in chemicals containing chlorides, sulfuric, phosphoric, and nitric acids. The addition of niobium stabilizes the alloy against sensitization and resultant intergranular corrosion.
Resistance of Alloy 20
Alloy 20 offers exceptional resistance to a wide range of corrosive environments, making it an ideal choice for applications that require superior corrosion resistance. The following are some of the types of resistance provided by Alloy 20:
Acid Resistance: The unique composition of Alloy 20 makes it highly resistant to acid attack, particularly sulfuric acid, which is known to cause severe corrosion. Alloy 20 also provides excellent resistance to other acids, including phosphoric and nitric acid.
Chloride Resistance: Alloy 20 provides superior resistance to corrosion in environments containing chlorides, such as seawater, making it an ideal choice for marine applications.
Crevice Corrosion Resistance: Alloy 20 provides excellent resistance to crevice corrosion, which can occur in tight spaces, such as in fittings and joints, where stagnant corrosive solutions can build up.
Corrosion of Alloy 20
Despite its exceptional corrosion resistance, Alloy 20 can still experience corrosion in certain circumstances. However, the rate of corrosion is significantly lower than other materials, and it does not affect the mechanical properties of the alloy. The following are some of the types of corrosion that can occur in Alloy 20:
General Corrosion: General corrosion occurs when the surface of the alloy corrodes uniformly over time due to exposure to corrosive environments.
Pitting Corrosion: Pitting corrosion occurs when small holes or pits form on the surface of the alloy due to localized corrosion.
Intergranular Corrosion: Intergranular corrosion occurs when the grain boundaries of the alloy are attacked, resulting in a loss of mechanical strength.
Fabrication and Heat Treatment
Alloy 20 is a versatile nickel-iron-chromium austenitic alloy that provides exceptional corrosion resistance in a variety of corrosive environments. In addition to its superior corrosion resistance, Alloy 20 offers ease of fabrication and enhanced mechanical properties, making it a popular choice for various industrial applications.
Fabrication of Alloy 20
Alloy 20 is easy to fabricate using conventional methods such as welding, forming, and machining. The following are some of the fabrication techniques used for Alloy 20:
Welding: Alloy 20 can be welded using common welding techniques such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and shielded metal arc welding (SMAW).
Forming: Alloy 20 can be formed using common techniques such as hot and cold working, bending, and forging.
Machining: Alloy 20 can be machined using standard machining techniques such as drilling, milling, and turning.
Heat Treatment of Alloy 20
Alloy 20 can be heat treated to improve its mechanical properties. The following are some of the heat treatment processes used for Alloy 20:
Annealing: Annealing is the process of heating the alloy to a high temperature and then cooling it slowly. This process helps to improve the ductility and toughness of the alloy.
Stress Relieving: Stress relieving is the process of heating the alloy to a moderate temperature and then cooling it slowly. This process helps to relieve residual stresses in the alloy and improve its dimensional stability.
Solution Annealing: Solution annealing is the process of heating the alloy to a high temperature and then quenching it in water. This process helps to dissolve any precipitates that may have formed during the manufacturing process and improve the corrosion resistance and mechanical properties of the alloy.
Alloy 20 – Applicable Specifications
| Form | ASTM | ASME | Other |
|---|---|---|---|
Alloy 20 Seamless Pipe |
B729 | SB729 | – |
Alloy 20 Welded Pipe |
B464 | SB464 | – |
Alloy 20 Seamless Tube |
B729 | SB729 | – |
Alloy 20 Welded Tube |
B468 | SB468 | – |
Alloy 20 Bars and Shapes |
B473 | SB473 | – |
Alloy 20 Forgings |
B462 | SB462 | – |
Alloy 20 Fittings |
B366 | SB366 | – |
Alloy 20 Plate, Sheet, Strip |
B463 | SB463 | – |
Common Trade Names
Carpenter 20, and 20Cb-3 are the most commonly used trade names for Alloy 20, a highly versatile superalloy with excellent resistance to acid attack and general corrosion, used in a variety of industries including chemical, food, and pharmaceutical.
Key Properties
(in annealed condition)
| Key Properties | Alloy 20 |
|---|---|
| Tensile Strength | 80 ksi (551 MPa) |
| Yield Strength | 35 ksi (241 MPa) |
| Elongation | 30% |
| Hardness | HRB 92-99 |
Chemical Composition (%)
| Element | Alloy 20 |
|---|---|
| Nickel | 32.0 – 38.0 |
| Chromium | 19.0 – 21.0 |
| Molybdenum | 2.0 – 3.0 |
| Copper | 3.0 – 4.0 |
| Manganese | 2.0 max |
| Silicon | 1.0 max |
| Carbon | 0.07 max |
| Phosphorus | 0.045 max |
| Sulfur | 0.035 max |
| Iron | Balance |
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