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Electropolishing Electro-Chemical Cleaning (ECC) Passivation

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Super-Austenitic Steel

Super-austenitic stainless steel alloys are characterized by their high nickel and molybdenum contents plus nitrogen. The most common of the alloys are AL-6XN, 254 SMO, 25-6MO and 1925 hMO.  


These alloys have a face-centered cubic crystal structure similar to other austenitic stainless steels and are non-magnetic and their magnetic permeability remains low even after severe cold forming. The nitrogen addition provides the alloy with improved resistance to pitting and crevice corrosion, a greater resistance to localized corrosion in oxidizing chlorides and reducing solutions plus higher strength. Nitrogen also helps to significantly reduce the potential formation of harmful secondary phases during welding.

 Over the years corrosion resistance in chloride environments have forced the change of the more popular 18%-8% Ni austenitic stainless steels. Corrosion resistance, weld ability and strength of the austenitic alloys were improved by changing the basic chemical composition to meet the more demanding applications.



  • Molybdenum was added to improve corrosion resistance in chloride environments.

  • Carbon was reduced to minimize sensitization during welding.

  • Nitrogen was added to compensate for the reduced strength of the "L" grades, improve phase stability and together with chromium and molybdenum, improve pitting resistance.

  • Chromium was increased to improve oxidation resistance.

  • Nickel was added to stabilize the austenitic crystal structure and, at higher contents, improve stress-corrosion cracking resistance and general corrosion resistance in reducing environments.

The high strength and corrosion resistance of these alloys offer an alternative to more expensive nickel-based alloys in application where excellent form-ability, weld-ability, strength and corrosion resistance are essential.  They also offer exceptional resistance to chloride corrosion, pitting corrosion stress corrosion cracking, and excellent general corrosion resistance to various acid, alkalies and salt solutions.



Considering these alloys were designed for their corrosion resistance and electropolishing is in fact a "controlled" corrosion process of the surface helping to remove free iron and other surface contaminants, they do offer a special challenge to achieve an optimum surface.  Studies have shown however, super-austenitic alloys just as standard 300 series stainless steels, can benefit and further improve it resistance in harsh environments.  Contact us at 877-823-7911 for further details.