UNS S32050 Forgings: Super Austenitic Stainless Steel

23Cr-22Ni-6Mo-0.25N. Forged bars, hollow bars, seamless rolled rings, discs, shafts and parts to drawing.

1. What UNS S32050 is

UNS S32050 is a corrosion resistant austenitic stainless steel built on a high nickel, high chromium, high molybdenum design. It holds up in severe environments such as high temperature seawater, and depending on the medium it can give corrosion resistance close to that of nickel alloys and commercially pure titanium at a lower material cost. Nippon Yakin Kogyo produces the grade under the designation NAS 224N.

The high nitrogen content makes S32050 a high strength material in the annealed condition, noticeably stronger than Type 304 or 316L. Hot and cold workability are much the same as for standard austenitic stainless steels, but that extra strength has to be allowed for in both. In practice it means open-die forging of S32050 needs more press capacity and tighter temperature control than the common 300 series grades.

2. Chemical composition

Published molybdenum ranges differ a little between sources: both 6.0 to 6.8% and 6.0 to 6.6% appear in print. We work to whichever range the governing purchase specification states, so please confirm the standard on your enquiry.

3. Mechanical properties, solution annealed

Independent sources do not agree exactly. One dataset gives 330 MPa proof, 675 MPa tensile and 40% elongation; another gives 370 MPa, 770 MPa and 46%. The table therefore shows the span rather than one figure. Certified values for your heat and section are stated on the mill test certificate.

4. Corrosion resistance

S32050 has very high pitting and crevice corrosion resistance in concentrated chloride environments, and good resistance to chloride stress corrosion cracking. Reported ASTM G48 results are a critical pitting temperature of about 95 C by Method C and a critical crevice temperature of about 45 C by Method D. Those are laboratory reference points rather than service limits. Final selection should be checked against your actual medium, temperature, chloride level and oxygen content.

5. Heat treatment, welding, machining

Solution annealing

Solution anneal at 1150 C or higher, then water quench or cool rapidly by other means. Conditions are given in ASTM A480/A480M. Rapid cooling through the intermediate range matters: like all 6% Mo super austenitics, S32050 will precipitate sigma and chi phase if cooled slowly, and both toughness and corrosion resistance suffer. Unless an order states otherwise, every forging we ship is re-solution annealed after hot work.

Welding

Shielded metal arc, TIG and plasma welding all work, in the same way as for standard austenitic stainless steels. Use Alloy 276 nickel chromium molybdenum consumables. Matching composition filler is not suitable, because molybdenum segregates in as-deposited weld metal and the weld would end up less corrosion resistant than the base material. Preheating and post-weld heat treatment are not required.

Machining

As with other high nickel stainless steels, machining is harder than for standard austenitic grades but easier than for nickel-base alloys. Use cemented carbide tooling where possible, and favour a slower feed rate with a greater depth of cut. Rigid setups and positive rake geometry help keep the surface from work hardening.

Pickling

Mixed nitric and hydrofluoric acid is used. Descaling is somewhat harder than for Type 304, which follows from the higher alloy content. A short immersion in alkaline solution beforehand, and shot blasting where practical, improves descaling a great deal.

6. Standards and related designations

One point worth stating plainly: we have not found UNS S32050 listed as a grade within ASTM A182, the specification for forged flanges and fittings in high temperature service. Where a project calls for an A182-listed super austenitic forging, the usual route is A182 F44, UNS S31254. For S32050 forgings we work to ASTM A479 bar requirements or to a customer written specification. Tell us the end code you are building to, whether ASME VIII, NORSOK or a client spec, and we will confirm in writing what we can certify before you place the order.

7. Where the grade is used

S32050 gets specified where chloride attack defeats 316L and duplex grades but a full nickel alloy is hard to justify on cost. The main areas are seawater service, including desalination systems, seawater heat exchangers and condenser tubes, and concentrated chloride ion service such as pulp and paper plants and bleaching systems. It also appears in chemical process equipment, storage tanks and reaction vessels handling aggressive media, and in offshore oil and gas work including platform and subsea components.

The forged parts we most often make in this grade are tubesheets and tube plates for seawater heat exchangers, valve bodies and pump casings, rings and flanges for desalination piping, bushings and sleeves, and heavy shafts.

8. Forged product range in UNS S32050

Supply condition: forged, solution annealed and pickled, rough machined or finish machined to drawing. Testing on request covers chemical analysis, tensile and impact, hardness, ultrasonic examination to ASTM A388, PMI, intergranular corrosion testing to ASTM A262 and ASTM G48 pitting tests. EN 10204 3.1 certification is standard and 3.2 third party certification is available.

9. Common questions

10. Related grades

Buyers looking at UNS S32050 usually also price A182 F44, S31254, 904L, Sanicro 28, Alloy 24, A182 F55 super duplex, A182 F53, A182 F51, duplex 2205, Nitronic 50 and Alloy 31. Where chloride temperatures run higher, the next step up is usually Hastelloy C-276 or Inconel 625.

Page reviewed 5 October 2026. Figures are compiled from producer datasheets and published property databases, are indicative only, and do not replace a mill test certificate.