Ultra 254 SMO
EN 1.4547, ASTM UNS S31254

General characteristics

Ultra 254 SMO is a 6% molybdenum and nitrogen-alloyed austenitic stainless steel with extremely high resistance to both uniform and localized corrosion. This product was developed especially for oil and gas offshore platforms and the pulp and paper industry.

Typical applications

  • Applications requiring resistance to chlorinated seawater
  • Flue gas cleaning
  • Maritime exhaust gas cleaning (EGC)
  • Bleaching equipment in the pulp and paper industry
  • Flanges and valves


Product forms, available sizes and finishes


Product typeFinishesThicknessWidth
Cold rolled coil and sheet2E0,60-6,35≤ 2000
Hot rolled coil and plateHot rolled white6,00-6,35≤ 1524
Quarto plateHot rolled white7,00-40,00≤ 2700
Chemical composition

The typical chemical composition for this grade is given in the table below, together with composition limits given for the product according to different standards. The required standard will be fully met as specified on the order.

The chemical composition is given as % by mass.

TypicalUltra 254 SMO0.0120.
ASTM A240/A240MUNS S31254<0.020<119.5-20.517.5-18.56.0-6.50.18-0.25Si:<0.80 P:<0.030 S:<0.010 Cu:0.50-1
EN 10088-21.4547<0.020<119.5-20.517.5-18.56.0-7.00.18-0.25Si:<0.70 P:<0.030 S:<0.010 Cu:0.50-1
Mechanical properties

The addition of nitrogen to Ultra 254 SMO gives higher proof strength and tensile strength. Despite the greater strength, the possibilities for cold as well as hot forming are very good.

Mechanical properties at room temperature are shown in the table below.

StandardGradeRp0.2Rp1.0RmElongationImpact strengthRockwellHBHV
Product type: Cold rolled coil and sheet
Typical (thickness 1 mm)Ultra 254 SMO3754157356087HRB
Product type: Hot rolled quarto plate
Typical (thickness 15 mm)Ultra 254 SMO32035068050160

1)Elongation according to EN standard:
A80 for thickness below 3 mm.
A for thickness = 3 mm.
Elongation according to ASTM standard A2” or A50.


Corrosion resistance

Uniform corrosion

The high content of alloying elements gives Ultra 254 SMO exceptionally good resistance to uniform corrosion. It can withstand a wide range of acids due to the high alloying content of chromium and molybdenum. For guidance on material selection in a large number of environments, consult the tables and isocorrosion diagrams in the Outokumpu Corrosion Handbook.

Pitting and crevice corrosion

Resistance to pitting and crevice corrosion is determined mainly by the chromium, molybdenum, and nitrogen content. Ultra 254 SMO has high amounts of these elements and is suitable for demanding environments like chlorinated sea water.

Stress corrosion cracking

Resistance to stress corrosion cracking increases with increased content of nickel and molybdenum in particular. This means that Ultra 254 SMO has very good resistance to stress corrosion cracking.

Pitting corrosion resistanceCrevice corrosion resistance

PRE Pitting Resistant Equivalent calculated using the formula: PRE = %Cr + 3.3 x %Mo + 16 x %N
CPT Corrosion Pitting Temperature as measured in the Avesta Cell (ASTM G 150), in a 1M NaCl solution (35,000 ppm or mg/l chloride ions).
CCT Critical Crevice Corrosion Temperature is the critical crevice corrosion temperature which is obtained by laboratory tests according to ASTM G 48 Method F



Physical properties

The typical values of some physical properties are given in the table below.


DensityModulus of elasticityThermal exp. at 100 °CThermal conductivityThermal capacityElectrical resistanceMagnetizable

*) Austenitic stainless steel grades may be magnetizable to a certain degree after cold deformation, e.g. in temper rolled condition.


Ultra 254 SMO cold hardens considerably faster than conventional austenitic grades. This, together with the initial high strength, makes it necessary to apply high forming forces. The springback for Ultra 254 SMO is also greater than for conventional austenitic steels. In complicated cold forming operations, intermediate annealing of the material may sometimes be necessary, especially if the workpiece is welded.


The work hardening behavior together with the toughness means that highly alloyed grades are often perceived as problematic from a machining perspective, e.g. operations such as turning, milling, and drilling. This applies to an even greater extent to most highly alloyed steels, especially those that have a high nitrogen content. However, with the right choice of tools, tool settings, and cutting speeds, these materials can be sucessfully machined. Machining guidelines for Ultra 254 SMO can be found here :Machining guidelines Ultra 254 SMO


Ultra 254 SMO is well suited for welding, and the methods used for welding conventional austenitic steels can be used. However, due to its stable austenitic structure, it is somewhat more sensitive to hot cracking in connection with welding, and generally welding should be performed using a low heat input. On delivery, sheet, plate, and other processed products have a homogeneous austenitic structure with an even distribution of alloying elements in the material. Solidification after partial remelting, e.g. by welding, causes redistribution of elements such as molybdenum, chromium, and nickel. These variations, segregation, remain in the cast structure of the weld and can impair the material’s corrosion resistance in certain environments.

More detailed information concerning welding procedures can be obtained from the Outokumpu Welding Handbook, available from our sales offices.

More detailed information concerning welding procedures can be obtained from the Outokumpu Welding Handbook, available from our sales offices.

Standards & approvals

The most commonly used international product standards are given in the table below.


ASTM A240/A240MUNS S31254
EN 10088-21.4547