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

Flat

Product typeFinishesThicknessWidth
Black hot band1U4,50-12,701000-1600
Cold rolled coil2B, 2E, 2R0,50-6,3530-2040
Cold rolled sheet2B, 2E, 2R0,50-6,35300-2040
Hot rolled coil, pickled1D4,50-6,0050-1250
Quarto plate1D8,00-20,00400-2700

Long

Product typeFinishesThicknessWidth
Cast billet127,00-180,00127-180
Cast slab165,00-175,001000-1500
Cold drawn bar hex8,00-25,408-25
Cold drawn bar round6,00-25,406-25
Cold drawn bar square8,00-22,008-22
Forged billet round150,00-200,00150-200
Forged billet square150,00-200,00150-200
Hot rolled / Black bar round75,00-180,0075-180
Peeled / turned bar round70,00-130,0070-130
Rolled billet round90,00-150,0090-150
Rolled billet square75,00-150,0075-150
Wire rod (Rod coil) hex9,00-27,009-27
Wire rod (Rod coil) round5,00-27,005-27
Wire rod (Rod coil) square9,00-24,009-24
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.

CMnCrNiMoNOther
Typical 0.0120.018.06.10.20Cu:0.7
ASME II A SA-240 ≤0.020≤1.0019.50-20.5017.50-18.506.00-6.500.18-0.25Cu:0.50-1.00
ASTM A240 ≤0.020≤1.0019.5-20.517.5-18.56.0-6.50.18-0.25Cu:0.50-1.00
EN 10028-7 ≤0.020≤1.0019.5-20.517.5-18.56.0-7.00.18-0.25Cu:0.50-1.00
EN 10088-2 ≤0.020≤1.019.5-20.517.5-18.56.0-7.00.18-0.25Cu:0.5-1.0
EN 10088-3 ≤0.020≤1.0019.5-20.517.5-18.56.0-7.00.18-0.25Cu:0.50-1.00
EN 10088-4 ≤0.020≤1.019.5-20.517.5-18.56.0-7.00.18-0.25Cu:0.5-1.0
EN 10088-4 -5MEK ≤0.020≤1.019.5-20.517.5-18.56.0-7.00.18-0.25Cu:0.5-1.0
IS 6911 ≤0.020≤1.0019.5-20.517.5-18.56.0-6.50.18-0.25Cu:0.50-1.00
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.

StandardRp0.2Rp1.0RmElongationImpact strengthRockwellHBHV
 MPaMPaMPa%J
Product type: Cold rolled coil and sheet
Typical (thickness 1 mm)37541573560
ASME II A SA-240 ≥ 310 ≥ 655 ≤ 223
ASTM A240 ≥ 310 ≥ 655 ≤ 96HRB ≤ 223
EN 10028-7 ≥ 320 ≥ 350650-850 ≥ 35
EN 10088-2 ≥ 320 ≥ 350650-850 ≥ 35
EN 10088-4 ≥ 320 ≥ 350650-850 ≥ 35
IS 6911 ≥ 310 ≥ 690 ≤ 96HRB ≤ 223
Product type: Hot rolled coil and sheet
Typical (thickness 4 mm)
ASME II A SA-240 ≥ 310 ≥ 655 ≤ 223
ASTM A240 ≥ 310 ≥ 655 ≤ 223
EN 10028-7 ≥ 320 ≥ 350650-850 ≥ 35
EN 10088-2 ≥ 320 ≥ 350650-850 ≥ 35
EN 10088-4 ≥ 320 ≥ 350650-850 ≥ 35
IS 6911 ≥ 310 ≥ 690 ≤ 96HRB ≤ 223
Product type: Hot rolled quarto plate
Typical (thickness 15 mm)32035068050160
ASME II A SA-240 ≥ 310 ≥ 655 ≤ 96HRB ≤ 223
ASTM A240 ≥ 310 ≥ 655 ≤ 96HRB ≤ 223
EN 10028-7 ≥ 300 ≥ 340650-850 ≥ 40
EN 10088-2 ≥ 300 ≥ 340650-850 ≥ 40
EN 10088-4 ≥ 300 ≥ 340650-850 ≥ 40
EN 10088-4 -5MEK ≥ 300 ≥ 340650-850 ≥ 40
IS 6911 ≥ 310 ≥ 655 ≤ 96HRB ≤ 223
Product type: Wire rod
Typical34038068050

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
PRECPTCCT
4387±335

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
kg/dm3GPa10-6/°CW/m°CJ/kg°CµΩm
8.019516,5145000.85No
Fabrication

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.

Machining

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

Welding

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.

 

StandardDesignation
ASME SA-240M Code Sect. II. Part AUNS S31254 / 254
ASTM A240/A240MUNS S31254 / 254
EN 10028-7, PED 2014/68/EU1.4547
EN 10088-21.4547
EN 10088-31.4547
EN 10088-41.4547
IS 6911, AMENDMENT NO. 2ISS 312