​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Outokumpu Ultra range

Extremely corrosive 


  • ​​Stainless steels for extremely corrosive environments (PRE >27)
  • The best choice when you know that grades like 304/4307 or 316L/4404 are not sufficient for the wet-corrosion challenges of your application​
  • Includes key products Ultra 904L and Ultra 254 SMO, as well as several alternatives
  • We have decades of experience developing, testing, and using our products in close cooperation with customers​

Ultra 904L
Ultra 254 SMO
Ultra 317L
Ultra 4439
Ultra 725L
Ultra 6XN
Ultra 4565
Ultra 654 SMO
Typical applications
Oil and gas
Petrochemical industry
Bleaching equipment in the pulp and paper industry
Flue gas cleaning
Desalination plants
Seawater processing
Hydrometallurgy processes
Food and beverage industry

​Compa​re product performance​​​​

​​Product properties​​​

 Corrosion resistance

​​In general, a high content of alloying elements gives the Outokumpu Ultra range exceptionally good resistance to uniform corrosion. As an example, Ultra 904L is one of the few stainless steels that at temperatures of up to 35 °C/95 °F provides full resistance in dilute sulfuric acid environments within the entire range of concentration, from 0 to 100%.

For acids and acid solutions containing halide ions – such as hydrochloric acid, hydrofluoric acid, chloride-contaminated sulfuric acid, phosphoric acid produced according to the wet process (WPA) at elevated temperatures, and pickling acid based on nitric acid and hydrofluoric acid mixtures – Ultra 254 SMO and Ultra 4565 are preferable.

For more information

Check Stainless Steel Finder to find corrosion information by products in the Outokumpu Ultra range​

Check the online corrosion table and search by chemical name, formula corrosion rates or alphabetically for stainless steel products.

Find an Outokumpu sales office near you to get the printed version of the Outokumpu Corrosion Handbook​​​​​​​​​



Outokumpu Ultra range products have very good formability and are suitable for the full range of forming processes for stainless steel. The somewhat higher yield strength – and in some cases lower fracture elongation compared to the most common standard austenitic steel grades – can result in small differences in forming behavior depending on the chosen forming process, such as an increased springback.


Austenitic stainless steels work harden quickly. Together with their high toughness, this means that they are often perceived as problematic from a machining perspective, for example in operations such as turning, milling, and drilling. However, with the right choice of tools, tool settings, and cutting speeds, these products can be successfully machined.


​Outokumpu Ultra range steels are well suited for welding, and the methods used for welding conventional austenitic steels can also be used on these products. However, due to their stable austenitic structure, they are somewhat more sensitive to hot cracking in connection with welding, so in general welding should be performed using a low heat input.

More information is available in the Outokumpu Welding Handbook, available from our Outokumpu sales offices

 Forms & dimensions

​​The available forms for Outokumpu Ultra range products can include:
To see the forms available for a specific product or to get information about dimensions, check Stainless Steel Finder​​​​​​​​​​

 Standards and approvals


​European delivery standards

  • ​​EN 10028-7 Flat products for pressure purposes – Stainless steels
  • EN 10088-2 Stainless steels – Corrosion resisting sheet/plate/strip for general and construction purposes
  • EN 10088-3 Stainless steels – Corrosion resisting semi-finished products/bars/rods/wire/sections for general and construction purposes
  • EN 10088-4 Technical delivery conditions for sheet/plate and strip of corrosion resisting steels for construction purposes
  • EN 10088-5 Technical delivery conditions for bars, rods, wire, sections and bright products of corrosion resistant steels for construction purposes
  • EN 10272 Stainless steel bars for pressure purposes
  • EN 10283 Corrosion resistant steel castings

​ASTM/ASME delivery standards

  • ​​ASTM A 193 / ASME SA-193 Alloy and stainless steel bolts and nuts for high pressure and high temperature service
  • ASTM A 240 / ASME SA-240 Heat-resisting Cr and Cr-Ni stainless steel plate/sheet/strip for pressure purposes
  • ASTM A 276 Stainless and heat-resisting steel bars/shapes
  • ASTM A 312 / ASME SA-312 Seamless and welded austenitic stainless steel pipe
  • ASTM A 351 / ASME SA-351 Steel castings, austenitic, duplex for pressure containing parts
  • ASTM A 358 / ASME SA-358 Electric fusion-welded austenitic Cr-Ni alloy steel pipe for high temperature
  • ASTM A 409 / ASME SA-409 Welded large diameter austenitic pipe for corrosive or high-temperature service
  • ASTM A 473 Stainless steel forgings for general use ​
  • ASTM A 479 / ASME SA-479 Stainless steel bars for boilers and other pressure vessels
  • ASTM A 743 Castings, Fe-Cr-Ni, corrosion resistant for general application
  • ASTM A 744 Castings, Fe-Cr-Ni, corrosion resistant for severe service
  • ASTM B 649 / ASME SB-649 Bar and wire

​Other common specification standards

  • ​​NACE MR0175 Sulfide stress cracking resistant material for oil field equipment
  • Norsok M-CR-630 Material data sheets for 6Mo stainless steel
  • VdTÜV WB 473 Austenitischer Stahl X 1 CrNiMoCuN 20 18 7 Werkstoff-Nr. 1.4547
  • VdTÜV WB 537 Stickstofflegierter austenitischer Stahl X2CrNiMnMoN 25-18-6-5 Werkstoff-Nr 1.4565​​

Certificates and approvals

  • ​​AD 2000 Merkblatt
  • Approval of Material Manufacturers
  • Factory Production Control Certificate
  • ISO 9001
  • ISO 14001
  • ISO 50001
  • ISO/TS 16949
  • OHSAS 18001
  • Pressure Equipment Directive (PED)



 Customer views



Outokumpu stainless steel works in the extremes in power plant in Jyväskylä, Finlandhttp://www.outokumpu.com/en/stainless-news/cases/stainless-steel-works-in-the-extremes-in-power-plantOutokumpu stainless steel works in the extremes in power plant in Jyväskylä, FinlandAleksi VuorenmaaProject manager, Jyväskylä Energy GroupWe needed a material that could withstand the conditions in the flue gas duct and chimney, while also being cost-efficient. Stainless steel responded to these expectations well. The main reason for our choice was its high corrosion resistance.
Stainless steel for seawater desalinationhttp://www.outokumpu.com/en/stainless-news/cases/desalinationStainless steel for seawater desalinationOutokumpu 254 SMO offers very high resistance to chloride stress corrosion cracking—50% stronger than 300-series austenitic stainless steels.
Qatar oil platforms use high performance austenitichttp://www.outokumpu.com/en/stainless-news/cases/qatar-oil-platformsQatar oil platforms use high performance austeniticOutokumpu's high-alloyed super-austenitic grade was developed and patented by Outokumpu to withstand the most corrosive environments, including those presented by crude oil.
Italy’s cleaner coal powered plant driven forward by Outokumpu steelhttp://www.outokumpu.com/en/stainless-news/cases/cleaner-coal-plantItaly’s cleaner coal powered plant driven forward by Outokumpu steelAs a result of the new absorber towers, sulfur dioxide and particulate emissions are both down by 88 percent. And nitrogen oxide emissions are down by 61 percent from the previous oil-fired operations.

Stainless steel finder

Stainless Steel Finder is a tool for easily comparing and finding details of all Outokumpu stainless steel grades​​​​

Go to Steel Finder