Alloy 20 / UNS N08020 / W.Nr. 2.4660

Description

Alloy 20 is a nickel-iron-chromium based, austenitic alloy with excellent corrosion resistance in chemical environments containing sulfuric acid and many other aggressive media. This alloy is stabilized with niobium to resist intergranular corrosion. Alloy 20 may provide potential cost savings when carefully compared to higher nickel-based alloys, while out performing standard stainless steels.

Industries and Applications

Alloy 20 is used in a variety of industries, including chemical processing, petrochemical and refining, marine, pharmaceutical and food processing. End use applications include storage tanks, mixing tanks, agitators, pump and valve parts, food processing equipment, fasteners and fittings. Applications are limited to a maximum temperature of 1000°F per ASME. It is also important to determine if the necessary corrosion resistance can be achieved within the given environment.

Resistance to Corrosion

Alloy 20 has very good resistance to sulfuric acid. This alloy also shows suitable resistance in phosphoric acid, nitric acid and aqueous salt solutions. Alloy 20 is an excellent option when chloride stress corrosion cracking is an issue, as it resists pitting and crevice corrosion. Caution should be taken in chloride ion containing environments because the corrosion rate can increase significantly.

Fabrication and Heat Treatment

Alloy 20 can be formed by either hot-working or cold-work using traditional methods. Hot forged material should be heated between 2100°F and 2250°F with careful temperature control insuring that the material not fall below 1800°F prior to forging. After hot working, anneal the material by heating to 1725°F and 1850°F for a minimum of 30 minutes per inch of thickness followed by water quench.

When stress relieving is desired, heat to a temperature below 1000°F followed by water quench after the desired time at temperature has been established. Annealing Alloy 20 should be between 1725°F and 1850°F for 30 minutes at temperature per inch of thickness. A lower hardness can be obtained by heating to 2100°F but his may have a negative effect on the stabilization of the alloy.

Welding Alloy 20 is commonly performed via, TIG, MIG as well as submerged arc welding (SAW) using either the matching filler metal, ER320LR for TIG and MIG and E320LR for SAW. When welding to dissimilar alloys such as 316 or higher alloys such as C276 and Alloy 22, AWS ERNiCrMo-3 can be used for TIG and MIG while using ENiCrMo-3 for SAW.

Common Trade Names

INCOLOY® alloy 20, Carpenter® 20 alloy, 20CB-3®

INCOLOY® is a registered trademark of the Special Metals Corporation group of companies.

Carpenter® and 20CB-3® are registered trademarks of Carpenter.

Download Our Alloy 20 Datasheet

Alloy 20 Available Forms:

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Chemical Composition (%)

(Fe) Iron Remainder
(Ni) Nickel 32.00 to 38.00
(Cr) Chromium 19.00 to 21.00
(Cu) Copper 3.00 to 4.00
(Mo) Molybdenum 2.00 to 3.00
(Mn) Manganese 2.00 max
(Nb+Ta) Niobium* + Tantalum (8 x C) to 1.00
(Si) Silicon 1.00 max
(C) Carbon 0.07 max
(P) Phosphorus 0.045 max
(S) Sulfur 0.035 max

*Niobium (Nb) formerly classified as Columbium (Cb).

Applicable Specifications*

Form ASTM ASME
Bar B473 SB473
Sheet & Plate B463 SB463
Seamless Pipe & Tube B729 SB729
Welded Pipe B464, B4741 SB464, SB474
Welded Tube B468 SB468

* EN10204-3.1 applies to all product forms.
1Electric fusion welded pipe material only.

Alloy 20 Frequently Asked Questions

1. What is Alloy 20 and when should it be used instead of stainless steel?

Alloy 20 is a nickel‑iron‑chromium austenitic alloy stabilized with niobium, developed for service in aggressive chemical environments. It is commonly selected as an upgrade when standard stainless steels such as 304 or 316 lack sufficient corrosion resistance, particularly in sulfuric acid and other harsh process conditions. Read our Alloy Insights blog post on Alloy 20 to learn more.

2. Why is Alloy 20 resistant to intergranular corrosion?

Alloy 20 is stabilized with niobium, which prevents the formation of chromium carbides at grain boundaries. Instead, niobium carbides form, preserving chromium content in the alloy matrix and significantly reducing the risk of intergranular corrosion that can affect unstabilized stainless steels when exposed to elevated temperatures or aggressive media.

3. What acids and environments is Alloy 20 resistant to?

Alloy 20 provides excellent resistance to sulfuric acid and performs well in phosphoric acid, nitric acid, and aqueous salt solutions. This combination of corrosion resistance makes it particularly suitable for chemical processing environments where standard stainless steels may fail prematurely.

4. How does Alloy 20 compare to high‑nickel alloys in terms of cost and performance?

Alloy 20 delivers strong corrosion resistance at a more economical price point than many higher nickel‑based alloys. While it may not replace nickel alloys in the most extreme environments, it offers an attractive balance of performance and cost where aggressive corrosion resistance is required without the expense of premium nickel materials.

5. What industries and applications commonly use Alloy 20?

Alloy 20 is widely used in chemical processing, petrochemical and refining, marine, pharmaceutical, and food processing industries. Typical applications include mixing tanks, agitator shafts, process piping, pickling equipment, pumps, valves, mechanical seals, and fasteners and fittings exposed to corrosive media.

6. What are the temperature limits for Alloy 20 applications?

Under ASME guidelines, Alloy 20 is generally limited to a maximum service temperature of 1000°F. Staying within this temperature range helps ensure the alloy maintains its corrosion resistance and mechanical integrity in demanding process environments.

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The information shown on this page is intended to be used as a guide and may be revised at any time without prior notice. The information is believed to be reliable and accurate, however Corrosion Materials does not make any warranty or assume any legal liability with respect to the accuracy, completeness or usefulness of the information.