RAYCHIN LIMITED

Complete Range of AL6XN Lock Nuts

Manufacturing Standards for AL6XN Lock Nuts

RAYCHIN LIMITED manufactures AL6XN lock 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 Lock Nuts

To serve clients worldwide, RAYCHIN LIMITED manufactures AL6XN lock 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 DIN 980 ISO 7042 1.4501

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

Our AL6XN lock 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 lock nuts good high strength properties.

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 lock 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 Lock Nuts (Solution Annealed Condition)

AL6XN lock 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. Lock nuts are proof load tested to ensure compatibility with mating bolts.

Mechanical Properties at Room Temperature

High Temperature Performance of AL6XN Lock 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 Lock Nuts

Originally developed to combat sea water corrosion, AL6XN has expanded its role as being good mid-range corrosion resistant alloy. AL6XN lock 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 giving a more cost effective alternative to nickel super alloys like Inconel or Hastelloy in moderately corrosive conditions. Seawater is where AL6XN lock nuts outperform so many alloys providing protection to stress corrosion cracking, pitting and crevice corrosion in a broad range of marine applications. AL6XN lock 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). 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.

Chemical Resistance in Specific Environments

In chemical processes which utilize chlorides, such as paper mills and waste water, stress corrosion cracking (SCC) is a common culprit for 316L stainless failures. Duplex alloys will outlast environments that will cause SCC in 316 stainless, but for more severe low PH environments, lock nuts made from higher nickel content alloys like AL6XN will generally work better. For the most extreme situations, alloys with >45% nickel content like Hastelloy are often considered.

Critical Corrosion Considerations for Lock 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, applicable to environments containing H₂S, high chloride concentrations, and moderate temperatures.
• Temperature Limitations: All-metal lock nuts can be used up to 427°C (800°F). Nylon insert lock nuts are limited to 176°C (350°F). For applications above 350°F, all-metal configurations are recommended.
• 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.
• Flexloc Advantage: All-metal flexloc nuts distribute load evenly due to the fact that they are manufactured as one solid piece, making them the most reliable all-metal self-locking nut for high temperature or corrosive applications.
• Polymer Insert Options: Various polymers inserts available (Nylon, Vespel, PVDF, etc.) for higher temperature or corrosive applications, with excellent reusability up to 15 cycles.

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 lock 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 Lock Nut Authority