RAYCHIN LIMITED

Complete Range of AL6XN Nuts

Manufacturing Standards for AL6XN Nuts

RAYCHIN LIMITED manufactures AL6XN nuts 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 AL6XN Nuts

To serve clients worldwide, RAYCHIN LIMITED manufactures AL6XN nuts 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 N08367 AL6XN ASTM B691 ASTM B688 NACE MR0175 1.4501

Chemical Composition (Weight %) – AL6XN Super Austenitic Stainless Steel

Our AL6XN nuts are produced from melts that strictly conform to the limits below per ASTM B691 / UNS N08367. The high levels of chromium, nickel, molybdenum, and nitrogen provide exceptional resistance to pitting and crevice corrosion, with a Pitting Resistance Equivalent (PRE) typically exceeding 45. The high nickel and molybdenum content delivers better corrosion resistance than Duplex 2205 and Super Duplex 2507 in highly aggressive chloride environments. The interstitial strengthening effect of nitrogen gives AL6XN nuts good high strength properties – 50% stronger than standard stainless steel.

Expert note: The high molybdenum (6-7%) and nitrogen (0.18-0.25%) content gives AL6XN a PRE value exceeding 45, 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). The high nickel content (23.5-25.5%) provides exceptional resistance to chloride stress corrosion cracking. This makes AL6XN nuts ideal for offshore, desalination, and FGD applications. The material also meets NACE MR0175 requirements for sour service in oil and gas environments. Carbon helps to prevent sensitization during welding, and chromium enhances pitting and crevice corrosion resistance.

Complete Mechanical Properties of AL6XN Nuts (Solution Annealed Condition)

AL6XN nuts are supplied in the solution annealed condition (1100–1200°C followed by water quenching). The data below represent typical values per ASTM B691 and manufacturer specifications. Nuts are proof load tested to ensure compatibility with mating bolts.

Mechanical Properties at Room Temperature

High Temperature Performance of AL6XN Nuts

AL6XN maintains good mechanical properties at elevated temperatures, with a suggested operating range from -196°C to 427°C (-320°F to 800°F). It should not be exposed to temperatures above 427°C for prolonged periods due to metallurgical stability considerations. For continuous service, the maximum operating temperature is approximately 400°C. The material maintains excellent oxidation resistance up to 500°C and retains good impact strength at cryogenic temperatures down to -196°C.

Temperature-Dependent Mechanical Properties

Thermal Stability Limits

Corrosion Resistance of AL6XN Nuts

Originally developed to combat sea water corrosion, AL6XN has expanded its role as being good mid-range corrosion resistant alloy. AL6XN nuts are a low carbon, high purity, nitrogen-bearing "super-austenitic" stainless alloy. With a higher nickel and molybdenum content than Duplex 2205 and Super Duplex 2507, it delivers better corrosion resistance while providing a more cost effective alternative to nickel super alloys like Inconel or Hastelloy in moderately corrosive conditions. Seawater is where AL6XN nuts outperform so many alloys providing protection to stress corrosion cracking, pitting and crevice corrosion in a broad range of marine applications. AL6XN nuts contain a minimum of 6% molybdenum content and it is this addition of molybdenum that provides the greatest protection against pitting and crevice corrosion.

Pitting and Crevice Corrosion Resistance

The Pitting Resistance Equivalent (PRE) for AL6XN is typically >45, calculated as PRE = %Cr + 3.3 × %Mo + 16 × %N. This value is significantly higher than 316L (PRE≈24) and 317L (PRE≈29), and even exceeds that of 6% molybdenum alloys like 254SMO. In chloride environments with concentrations of 10,000-70,000 ppm and temperatures of 50-68°C, AL6XN demonstrates virtually no pitting or crevice corrosion.

Stress Corrosion Cracking (SCC) Resistance

Ordinary austenitic steels (304, 316) are prone to chloride stress corrosion cracking at temperatures above 60°C. AL6XN, with its high nickel content (24-25%) and molybdenum (6-7%), exhibits excellent resistance to SCC. In boiling 45% MgCl₂ solution, AL6XN shows no cracking after 1000 hours, while 316 fails in less than 100 hours. The material is approved per NACE MR0175/ISO 15156 for sour service applications in oilfield equipment, applicable to environments containing H₂S, high chloride concentrations, and moderate temperatures.

Critical Corrosion Considerations for Nuts

• PRE >45: The high Pitting Resistance Equivalent ensures outstanding performance in seawater and aggressive chemical environments. With 6-7% molybdenum content, AL6XN provides exceptional resistance to chloride-induced pitting and crevice corrosion.
• NACE MR0175 Compliance: AL6XN is qualified for sour service (sulfide stress cracking resistance) in oilfield equipment per NACE MR0175/ISO 15156.
• Temperature Limitations: Maximum service temperature for corrosion applications is approximately 400°C. Avoid exposure to temperatures above 427°C for prolonged periods to prevent intermetallic phase precipitation.
• Galvanic Corrosion: When paired with lower-grade materials, galvanic corrosion should be considered. AL6XN is cathodic to most other stainless steels. Proper isolation may be required in mixed-material assemblies.
• Comparison to Duplex: With higher nickel and molybdenum content than Duplex 2205 and Super Duplex 2507, AL6XN delivers better corrosion resistance in highly aggressive chloride environments.
• Cryogenic Applications: Excellent toughness down to -196°C, with impact values of 85 ft-lb at -196°C.

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 AL6XN nuts available for sour service applications. In many applications, AL6XN serves as a cost-effective substitute for high nickel alloys such as C-276 in moderately corrosive conditions.

Why RAYCHIN LIMITED – The AL6XN Nut Authority