RAYCHIN LIMITED

Complete Range of 254 SMO Lock Washers

Manufacturing Standards for 254 SMO Lock Washers

RAYCHIN LIMITED manufactures 254 SMO lock washers to the following national and international standards, ensuring full compliance for projects worldwide. Both standard and non-standard custom configurations are available.

International Standards & Global Designations for 254 SMO Lock Washers

To serve clients worldwide, RAYCHIN LIMITED manufactures 254 SMO lock washers from material conforming to the following national and international specifications. This ensures full compliance for projects in the Americas, Europe, Asia, and the Middle East.

UNS S31254 1.4547 X1CrNiMoCuN20-18-7 F44 ASTM A479 NACE MR0175

Chemical Composition (Weight %) – 254 SMO Super Austenitic Stainless Steel

Our 254 SMO lock washers are produced from melts that strictly conform to the limits below per ASTM A479 / UNS S31254. The high levels of chromium, molybdenum, and nitrogen provide exceptional resistance to pitting and crevice corrosion, with a Pitting Resistance Equivalent (PRE) of ≥42.5. The PRE is calculated as %Cr + 3.3 × %Mo + 16 × %N.

Expert note: The high molybdenum (6%) and nitrogen content gives 254 SMO a PRE value ≥42.5, providing resistance to pitting and crevice corrosion in seawater and other chloride environments that is far superior to 316L (PRE≈24) and 317L (PRE≈29). This makes 254 SMO lock washers ideal for offshore, desalination, and FGD applications. The material offers nearly twice the strength of 300-series stainless steels and serves as a cost-effective substitute for nickel-based alloys in many applications.

Complete Mechanical Properties of 254 SMO Lock Washers (Solution Annealed Condition)

254 SMO lock washers are supplied in the solution annealed condition (1150–1200°C followed by water quenching). The data below represent minimum values per ASTM A479 and EN 10088-3. Washers are hardness tested to ensure proper heat treatment.

Mechanical Properties at Room Temperature

High Temperature Performance of 254 SMO Lock Washers

254 SMO maintains good mechanical properties at elevated temperatures, with a suggested operating range from -196°C to 538°C (-320°F to 1000°F). It should not be exposed to temperatures between 600–1000°C for prolonged periods due to the risk of intermetallic phase precipitation. For continuous service, the maximum operating temperature is approximately 400°C. Spring properties are maintained within this temperature range, making 254 SMO lock washers suitable for high-temperature applications in power generation and chemical processing.

Temperature-Dependent Yield Strength (0.2% Offset)

Note: Intermetallic phases precipitate within the temperature range of 600–1000°C. Therefore, 254 SMO should not be exposed to these temperatures for prolonged periods. The material maintains excellent oxidation resistance up to 500°C and retains good impact strength at cryogenic temperatures down to -196°C. The steel passes the Strauss test (ASTM A262, practice E) even after sensitizing for one hour at 600–1000°C.

Thermal Stability Limits

Corrosion Resistance of 254 SMO Lock Washers

254 SMO was specifically developed for use in aggressive chloride-bearing environments. Its high molybdenum (6%) and nitrogen content provide exceptional resistance to localized corrosion, including pitting, crevice corrosion, and stress corrosion cracking. The material is frequently used as a cost-effective substitute for nickel-based alloys and titanium in high-chloride environments. Lock washers made from 254 SMO maintain their spring properties while providing outstanding corrosion resistance.

Pitting and Crevice Corrosion Resistance

The Pitting Resistance Equivalent (PRE) for 254 SMO is ≥42.5. This value is significantly higher than 316L (PRE≈24) and 317L (PRE≈29), indicating superior resistance to pitting and crevice corrosion in chloride environments such as seawater. Even at elevated temperatures, 254 SMO demonstrates exceptional resistance to crevice corrosion in seawater. Tests in natural seawater at 60°C (140°F) have shown that 254 SMO can be exposed for prolonged periods without suffering crevice corrosion. Only a few stainless steel grades possess this property.

Stress Corrosion Cracking (SCC) Resistance

Ordinary austenitic steels (304, 316) are prone to chloride stress corrosion cracking at temperatures above 60°C. 254 SMO, with its high nickel and molybdenum content, exhibits excellent resistance to SCC. In boiling 25% NaCl solution (pH=1.5) U-bend tests, 254 SMO showed no failure after 1000 hours, while AISI 316 failed in less than 150 hours. The material is approved per NACE MR0175/ISO 15156 for sour service applications in oilfield equipment.

Intergranular Corrosion

With its very low carbon content (≤0.020%), 254 SMO has minimal risk of carbide precipitation during heating. The steel passes the Strauss test (ASTM A262, practice E) even after sensitizing for one hour at 600–1000°C, demonstrating excellent resistance to intergranular corrosion. This makes 254 SMO lock washers suitable for applications involving welding or elevated temperature exposure during fabrication.

Critical Corrosion Considerations for Lock Washers

• PRE ≥42.5: The high Pitting Resistance Equivalent ensures outstanding performance in seawater and aggressive chemical environments. With 6% molybdenum content, 254 SMO provides exceptional resistance to chloride-induced pitting.
• NACE MR0175 Compliance: 254 SMO is qualified for sour service (sulfide stress cracking resistance) in oilfield equipment per NACE MR0175/ISO 15156.
• Temperature Limitations: Avoid prolonged exposure to 600–1000°C to prevent intermetallic phase precipitation, which can affect corrosion resistance. Proper solution annealing restores full corrosion resistance.
• Galvanic Corrosion: When paired with lower-grade materials, galvanic corrosion should be considered. 254 SMO is cathodic to most other stainless steels. Proper isolation may be required in mixed-material assemblies.
• Spring Properties: Unlike hardened carbon steel lock washers, 254 SMO lock washers maintain their spring properties while providing exceptional corrosion resistance, making them ideal for marine and chemical applications.

Corrosion Engineering Note: For critical applications in aggressive environments, RAYCHIN LIMITED can provide passivation, specialized coatings (Xylan, PTFE, silver plating), or recommend optimal heat treatment conditions. Third-party corrosion testing per ASTM G31, G48, or G61 available upon request. NACE MR0175 compliant 254 SMO lock washers available for sour service applications. In many applications, 254 SMO serves as a cost-effective substitute for high nickel alloys and titanium alloys in chloride environments.

Why RAYCHIN LIMITED – The 254 SMO Lock Washer Authority