254 SMO Stainless Steel
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
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
| Element | Composition (%) |
|---|---|
| Chromium | 19.5 – 20.5 |
| Nickel | 17.5 – 18.5 |
| Molybdenum | 6.0 – 6.5 |
| Nitrogen | 0.18 – 0.22 |
| Carbon | ≤0.020 |
| Manganese | ≤1.00 |
| Silicon | ≤0.80 |
| Phosphorus | ≤0.030 |
| Sulfur | ≤0.010 |
| Iron | Balance |
254 SMO (UNS S31254) Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength (MPa) | ≥670 |
| Yield Strength (MPa) | ≥300 |
| Elongation (%) | ≥40 |
| Hardness (Brinell, max) | 210 |
254 SMO (UNS S31254) Physical Properties
| Property | Value |
|---|---|
| Density (g/cm³) | 8 |
| Thermal Conductivity | 14.5 W/m·K |
| Specific Heat | 500 J/kg·K |
| Electrical Resistivity | 0.85 μΩ·m |
| Coefficient of Expansion | 15.0 × 10⁻⁶ /K |
Possible Alternative Grades
| Grade | Key Characteristics |
| 316L | Lower molybdenum content, less corrosion-resistant |
| 904L | Comparable corrosion resistance but different alloy composition |
| Alloy 625 | High strength, excellent corrosion resistance, and weldability |
| Super Duplex 2507 | Higher strength, lower cost, and good resistance in chloride environments |
Chemical Formula
Nominal Formula: Fe-Cr-Ni-Mo-N
Grade Specification Comparison Table
| Specification | ASTM | EN/DIN | UNS |
| Plate/Sheet | ASTM A240 | EN 10088-2 | S31254 |
| Pipe | ASTM A312 | EN 10216-5 | S31254 |
| Bar | ASTM A276 | EN 10088-3 | S31254 |
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
