ASTM A 265, B 366, B 463
B 464, B 471, B 472, B 473
B 474, B 475
UNS N08020
NACE MR0175
Other common names: Carpenter 20, 20Cb-3®, Incoloy® alloy 20

Alloy 20, also known as Carpenter 20, is a nickel-iron-chromium austenitic alloy that was developed for maximum resistance to acid attack, specifically sulfuric acid. Thissuperalloy has excellent resistance to general corrosion, pitting, and crevice corrosion in chemicals containing chlorides and sulfuric, phosphoric, and nitric acids. It also contains niobium for stabilization against sensitization and resultant intergranular corrosion. Carpenter 20 combines excellent corrosion resistance with elevated mechanical properties and relatively easy fabrication. Although originally designed for use in sulfuric acid related industries, Alloy 20 is now a popular choice for a wide variety of industries including the chemical, food, pharmaceutical, and plastics industries. In addition, this superalloy is used in heat exchangers, mixing tanks, metal cleaning and pickling equipment, and piping.

There has long been a debate on whether Carpenter 20 is a stainless steel or a nickel alloy because the nickel content is right on the border of defining it as one way or the other. So, depending on who you talk to this alloy may be referred to as alloy 20 Stainless Steel or as a nickel alloy. Either way it is still great for corrosion resistance.

In what forms is Alloy 20 Available?
• Sheet
• Plate
• Bar
• Pipe & Tube (welded & seamless)
• Fittings (i.e. flanges, slip-ons, blinds, weld-necks, lapjoints, long welding necks, socket welds, elbows, tees, stub-ends, returns, caps, crosses, reducers, and pipe nipples)
• Wire

What are the characteristics of Alloy 20?
• Excellent general corrosion resistance to sulfuric acid
• Excellent resistance to chloride stress corrosion cracking
• Excellent mechanical properties and fabricability
• Minimal carbide precipitation during welding
• Excels in resisting corrosion to hot sulfuric acids
Chemical Composition, %

Ni	Fe	Cr	Cu	Mo	Nb
32.00-38.00	Balance	19.0-21.0	3.0-4.0	2.0-3.0	8xC-1.0max

C	Mn	P	S	Si
.07max	2.0max	.045max	.035max	1.0max

In what applications is Alloy 20 used?
• Synthetic rubber manufacturing equipment
• Processing of pharmaceuticals, plastics and organic and heavy chemicals
• Tanks, piping, heat exchangers, pumps, valves, and other process equipment
• Acid cleaning and pickling equipment
• Chemical process piping, reactor vessels
• Bubble caps
• Petrochemical process equipment
• Food and dye production
ASTM Specifications

Pipe Smls	Pipe Welded	Tube Smls	Tube Welded	Sheet/Plate	Bar	Forging	Fitting
B729	B464	B729	B468	B463	B473	B462	B366

Mechanical Properties
Annealed Material

Form	Tensile Min.	Yield Min. (.2% offset)	Elongation Min.	Reduction of Area Min.
Bar (hot or cold finished)	80 ksi	35 ksi	30%	50%
Sheet/Plate	80 ksi	35 ksi	30%	-

*Incoloy® is a registered trademark of Special Metals Corporation group of Companies.