Corrosion Resistant Super Alloys

By Richard Batten

What are Corrosion Resistant Super Alloys?

Much like 304, 316, and 316L stainless steels, these alloys contain a face-centered cubic austenitic microstructure. Properties of corrosion resistant super alloys include the ability to retain stability at high temperatures, excellent mechanical strength, resistance to thermal deformation, and resistance to corrosion and oxidation. While there are several super alloys, let’s take a closer look at one of them: Hastelloy C-22.

Hastelloy C-22

This corrosion resistant super alloy is comparable to 316L stainless steel, but its elemental makeup is altered for increased mechanical strength and corrosion resistance. Hastelloy C-22 consists of 56% nickel, 22% chromium, and 13% molybdenum, whereas 316L stainless consists of 14% nickel, 18% chromium, and 3% molybdenum. Hastelloy C-22 is primarily used when traditional 316L stainless is insufficient, and other corrosion resistant super alloys, such as AL-6XN, have reached their material design limit. For example, Hastelloy C-22's critical pitting temperature in acidified 6% iron(III) chloride is >150°C (>300°F), while 316L's is 15°C (59°F). Characteristics of Hastelloy C-22 that make it comparable to 316L are its ductility, weldability, and ease of fabrication into industrial systems (albeit with an increase in price!). For more information, please refer to the reference for Haynes International.

Conclusions

Corrosion resistant super alloys provide an increase in mechanical strength, resistance to thermal deformation, and resistance to corrosion compared to traditional alloys, requiring less maintenance and better withstanding harsh environments. Efforts are underway to make new corrosion resistant super alloys such as aluminum-based super alloys, and to create new methods of manufacturing such as radiolysis which utilizes nano-particle synthesis for polycrystalline formation. There are many stainless steel alloys, and we at N.B.Oler are here to help you choose the best for your application!

References/Further Reading

Bell, Terence. “Properties of Type 316 and 316L Stainless Steels.” ThoughtCo, 2 Mar. 2020, www.thoughtco.com/type-316-and-316l-stainless-steel-2340262.

F.. Paulonis, J. M.. Oblak, et al. “Morphology of y' and y’ Precipitates and Thermal Stability of Inconel 718 Type Alloys.” Metallurgical and Materials Transactions B, Springer New York, 1 Jan. 1969, link.springer.com/article/10.1007/BF02649604.

International, Haynes. “HASTELLOY® C-22® Alloy.” Hastelloy C-22 Alloy, haynesintl.com/docs/default-source/pdfs/new-alloy-brochures/corrosion-resistant-alloys/brochures/c-22-brochure.pdf?sfvrsn=fd7929d4_22.

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