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254 SMO Stainless Steel

254 SMO (UNS S31254) is a high-alloy austenitic stainless steel developed for its excellent corrosion resistance in highly aggressive environments. 254 SMO is a preferred choice in chemical processing, marine engineering, and desalination plants because of its superior strength, weldability, and resistance to pitting and crevice corrosion.

254-smo-round-bar

254 SMO Round Bar

Specifications

  • UNS Number: S31254
  • EN/DIN: 1.4547
  • Standards: ASTM A240, ASTM A312, ASTM A182, ASME SA240, ASME SA312
  • Forms Available: Plates, sheets, bars, pipes, fittings, flanges, and fasteners

Material Properties

  • Category: Austenitic stainless steel
  • Corrosion Resistance: High resistance to chloride-induced pitting and crevice corrosion
  • Thermal Conductivity: Low, typical of stainless steel
  • Workability: Excellent formability and weldability

254 SMO (UNS S31254) Chemical Composition

ElementComposition (%)
Chromium19.5 – 20.5
Nickel17.5 – 18.5
Molybdenum6.0 – 6.5
Nitrogen0.18 – 0.22
Carbon≤0.020
Manganese≤1.00
Silicon≤0.80
Phosphorus≤0.030
Sulfur≤0.010
IronBalance

254 SMO (UNS S31254) Mechanical Properties

PropertyValue
Tensile Strength (MPa)≥670
Yield Strength (MPa)≥300
Elongation (%)≥40
Hardness (Brinell, max)210

254 SMO (UNS S31254) Physical Properties

PropertyValue
Density (g/cm³)8
Thermal Conductivity14.5 W/m·K
Specific Heat500 J/kg·K
Electrical Resistivity0.85 μΩ·m
Coefficient of Expansion15.0 × 10⁻⁶ /K

Possible Alternative Grades

GradeKey Characteristics
316LLower molybdenum content, less corrosion-resistant
904LComparable corrosion resistance but different alloy composition
Alloy 625High strength, excellent corrosion resistance, and weldability
Super Duplex 2507Higher strength, lower cost, and good resistance in chloride environments

Chemical Formula

Nominal Formula: Fe-Cr-Ni-Mo-N

Grade Specification Comparison Table

SpecificationASTMEN/DINUNS
Plate/SheetASTM A240EN 10088-2S31254
PipeASTM A312EN 10216-5S31254
BarASTM A276EN 10088-3S31254

Corrosion Resistance

254 SMO exhibits outstanding resistance to:

  • Pitting and crevice corrosion, especially in chloride-rich environments
  • Stress corrosion cracking (SCC)
  • General corrosion in acids like sulfuric acid and seawater

Heat Resistance

  • 254 SMO maintains excellent mechanical properties and corrosion resistance at temperatures up to 500°C.
  • Continuous use above 600°C is not recommended due to potential carbide precipitation.

Heat Treatment

  • Solution Annealing: Heat to 1150–1200°C followed by rapid cooling (typically water quenching).
  • Avoid prolonged exposure to high temperatures to prevent carbide precipitation.

Welding

  • Suitable for most welding methods, including TIG, MIG, and manual arc welding.
  • Use filler materials like AWS A5.9 ERNiCrMo-3 for optimal corrosion resistance.
  • Preheating is not required; post-weld heat treatment is typically unnecessary.

Fabrication

  • Machining: It might be difficult due to its high strength and work hardening. Use sharp tools at modest speeds.
  • Forming: Excellent formability but requires higher force compared to standard austenitic stainless steel.
  • Cutting: Plasma or water-jet cutting is recommended for precision.

Applications

  • Oil and Gas Pipelines
  • Water Treatment Plants
  • Petrochemical
  • Construction
  • Pressure Vessels
  • Phosphate Mining

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