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Alloy 20

Last updated: September 6, 2019

What Does Alloy 20 Mean?

Alloy 20 is a nickel-iron-chromium austenitic alloy with excellent resistance to acid attack, pitting and crevice corrosion in acids and chemicals containing chlorides, general corrosion and intergranular corrosion. The alloy combines excellent resistance to corrosion, ease of fabrication and elevated mechanical characteristics.

Alloy 20 is also known as Carpenter 20, Incoloy and 20Cb-3.


Corrosionpedia Explains Alloy 20

The alloying elements of alloy 20 are: carbon 0.07, chromium 19 – 21, copper 3 – 4, manganese 2, molybdenum 2 – 3, nickel 32 – 38, niobium 8xC-1.0, phosphorus 0.045, silicon 1, sulfur 0.035, iron – balance (all in %).

Alloy 20 contains copper and molybdenum, which enhance the material’s resistance to hostile environments and resistance to pitting and crevice corrosion. Columbium is used stabilize the material and minimize the precipitation of the carbide during welding. This allows welded materials to be used in corrosive environments without subjecting them to post-weld heat treatment. The nickel increases the resistance to chloride-corrosion cracking.

The alloy characteristics include:

  • Excellent resistance to general corrosion, pitting and crevice corrosion in hostile environments such as those with chemicals containing chlorides and sulfuric, nitric and phosphoric acids.
  • Low carbide precipitation during welding
  • Excellent resistance to corrosion in hot sulfuric acid
  • Resistance to chloride-corrosion cracking
  • Resists intergranular corrosion

The characteristics are at the border between stainless steel and nickel due to the high nickel content. The alloy is therefore referred to either as a stainless steel or as a nickel alloy.

The material, which has good mechanical properties both at ambient and elevated temperatures of up to 930°F (500°C), is readily fabricated using the common industrial techniques.

Alloy 20 is usually available in a variety of forms; these includes plates, sheets, bars, welded and seamless tubes and pipes, wires, and fittings such as weld-necks, long welding necks, elbows, returns, reducers, pipe nipples, tees, blinds and socket welds.

The great corrosion resistance of alloy 20 makes it suitable for a wide range of applications and industries. It is used in heat exchangers, metal cleaning and pickling equipment, piping, in mixing tanks, etc. The industries where it is used include chemical, petroleum, food, plastic and pharmaceutical.


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