Excellent Corrosion Resistance of 254 SMO
254 SMO is a high-alloy austenitic stainless steel developed for maximum resistance to pitting and crevice corrosion in halide-rich environments. It offers excellent corrosion resistance in seawater, brackish water, and chloride-containing chemical processes. With high strength and good weldability, it is suitable for a wide range of demanding industrial applications.
This article discusses the composition, characteristics, and applications of 254 SMO to help you make better material selections in engineering.
What is 254 SMO?
254 SMO (UNS S31254) is an austenitic stainless steel developed by Avesta (now part of Outokumpu) for use in aggressive chloride-bearing environments. It is often described as a “super austenitic” alloy due to its exceptional corrosion resistance and high alloy content.
254 SMO contains high levels of molybdenum (~6%), nitrogen, and chromium, giving it superior pitting resistance and excellent mechanical strength compared to conventional stainless steels.
254 SMO Equivalent Grades
| Standard / System | Equivalent Designation |
| UNS | S31254 |
| ASTM / ASME | ASTM A240, A312, A479, B366 |
| EN / DIN | 1.4547 (X1CrNiMoCuN20-18-7) |
| ISO | X1CrNiMoCuN20-18-7 |
| JIS | SUS 312L |
254 SMO Chemical Composition
| Element | Content (%) |
| Chromium (Cr) | 19.5 – 20.5 |
| Nickel (Ni) | 17.5 – 18.5 |
| Molybdenum (Mo) | 6.0 – 6.5 |
| Nitrogen (N) | 0.18 – 0.22 |
| Copper (Cu) | 0.5 – 1.0 |
| Carbon (C) | ≤ 0.020 |
| Manganese (Mn) | ≤ 1.0 |
| Silicon (Si) | ≤ 0.8 |
254 SMO Mechanical Properties
| Property | Typical Value |
| Tensile Strength | 650 – 900 MPa |
| Yield Strength | ≥ 300 MPa |
| Elongation | ≥ 35% |
| Hardness (HBW) | ≤ 300 |
254 SMO Physical Properties
| Property | Value |
| Density | 8.0 g/cm³ |
| Melting Point | ~1350 °C |
| Thermal Conductivity | 12 W/m·K (at 20 °C) |
| Electrical Resistivity | ~0.98 µΩ·m |
| Modulus of Elasticity | ~195 GPa |
| Service Temperature Range | -50 °C to ~300 °C |
Applications of 254 SMO
- Desalination Plants: Ideal for brine handling and reverse osmosis systems.
- Chemical Processing: Used in heat exchangers and pressure vessels handling chlorides and acids.
- Marine Equipment: Excellent resistance to seawater, used in shafts, pumps, and valves.
- Oil & Gas Industry: Effective in offshore environments and sour gas conditions.
- Flue Gas Scrubbers: Resistant to aggressive exhaust gases in pollution control systems.
- Pulp & Paper: Withstands chlorinated chemicals and bleaching agents.
Advantages of 254 SMO
- Outstanding corrosion resistance: Particularly in chloride-rich environments.
- High pitting resistance: PREN > 42, much higher than 316L or 904L.
- High strength: Better mechanical properties than many standard stainless steels.
- Good weldability: Suitable for various welding methods without post-weld heat treatment.
- Excellent fatigue resistance: Performs well under cyclic stress and load.
Limitations of 254 SMO
- High cost: Due to high alloy content, it is more expensive than 316L or duplex steels.
- Challenging machining: Requires specialized tools due to high work hardening rate.
- Limited high-temperature performance: Not ideal for applications above 300 °C.
- Availability: May be less readily available compared to common stainless grades.
254 SMO vs Other Stainless Steels
| Feature | 316L | 904L | 254 SMO |
| PREN (Pitting Index) | ~25 | ~35 | ~43–45 |
| Molybdenum Content | ~2% | ~4.5% | ~6.5% |
| Chloride Resistance | Moderate | High | Very High |
| Strength | Medium | Medium | High |
| Cost | Low | High | Very High |
Summary
This article introduces 254 SMO, its alloy composition, mechanical and physical properties, and key applications. It is a super austenitic stainless steel known for its exceptional resistance to chloride-induced corrosion, making it ideal for marine, chemical, and high-performance industrial systems.
MT.BOLTS offers 254 SMO fasteners and custom-machined components to meet your most demanding application needs. Contact our team or visit our website to learn more or request a quote.
