COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF AL-6XN (UNS N08367) SUPER AUSTENITIC FASTENING SYSTEMS
AL-6XN (officially designated as UNS N08367) is a "Super Austenitic" stainless steel, famously known as a "6 Moly" alloy due to its robust 6% Molybdenum content. Engineered to bridge the performance and cost gap between standard 300-series stainless steels and highly expensive Nickel-based superalloys, AL-6XN provides extraordinary resistance to chloride-induced pitting, crevice corrosion, and stress corrosion cracking (SCC).
The addition of Nitrogen not only stabilizes the austenitic microstructure against phase precipitation during welding and high-temperature exposure but also significantly boosts its mechanical yield strength to levels nearly 50% higher than standard 316L. Boasting a Pitting Resistance Equivalent Number (PREN) exceeding 43, AL-6XN is a primary fastening choice for reverse osmosis desalination, flue gas desulfurization (FGD), and aggressive offshore marine environments where standard stainless alloys rapidly degrade.
■ Product Overview & Specifications
AL-6XN fastening systems are typically deployed in the annealed condition, providing maximum corrosion resistance while maintaining impressive structural strength.
| Material Classification | Super Austenitic Stainless Steel (6% Mo) |
|---|---|
| UNS Designation | N08367 |
| Microstructure | Fully Austenitic |
| Magnetic State | Consistently Non-Magnetic |
| Density | ~8.06 g/cm³ (0.291 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" Custom U-Bolts and threaded rods available for piping systems. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
| Strengthening Method | Solid Solution Strengthening (Nitrogen Alloyed) |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for AL-6XN, including PREN calculations, critical pitting temperature (CPT) charts, and chloride stress-corrosion cracking thresholds.
AL-6XN (N08367) — Complete Technical Datasheet
Contains detailed ferric chloride pitting test results (ASTM G48), elevated temperature degradation limits, and specific flange torque values for desalination plants.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
To guarantee the alloy's survival in lethal and hyper-saline environments, Ananka ensures absolute chemical precision through rigorous testing protocols.
- EN 10204 Type 3.1: Detailed reporting of actual ladle chemical analysis, specifically verifying Molybdenum (min 6.0%) and Nitrogen levels, alongside standard mechanical yield testing.
- EN 10204 Type 3.2: Third-party witness certification (e.g., DNV, TUV, ABS) provided for critical marine scrubber and offshore jacket fastening.
■ Chemical Composition (UNS N08367)
The synergy of high Chromium, high Molybdenum, and Nitrogen gives AL-6XN its "Super" classification, making it vastly superior to conventional 316 and 904L stainless steels.
| Nickel (Ni) | Chromium (Cr) | Molybdenum (Mo) | Nitrogen (N) | Manganese (Mn) | Copper (Cu) | Carbon (C) |
|---|---|---|---|---|---|---|
| 23.5 – 25.5 | 20.0 – 22.0 | 6.00 – 7.00 | 0.18 – 0.25 | 2.00 Max | 0.75 Max | 0.03 Max |
*Silicon is capped at 1.00 Max, and Phosphorus/Sulfur are tightly restricted to ensure weldability and toughness.
■ Mechanical Properties (Annealed Condition)
Thanks to Nitrogen alloying, AL-6XN provides excellent structural strength, allowing engineers to reduce fastener cross-sections and overall weight without sacrificing load capacity.
| Property | Bar / Forged Fasteners (Typical Minimums) |
|---|---|
| Tensile Strength (Min) | 95 - 100 ksi (655 - 690 MPa) |
| Yield Strength (0.2% Offset, Min) | 45 ksi (310 MPa) |
| Elongation in 2" (Min) | 30% |
| Reduction of Area (Min) | 50% |
| Hardness | 88 HRB to 23 HRC |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| UNS Designation | N08367 |
| Common Trade Name | AL-6XN® (Trademark of ATI), 6-Moly |
| ASTM Fastener Specs | ASTM F467 / F468, ASTM B691 (Bar) |
| European Equivalent | Similar to EN 1.4529 / 254 SMO (UNS S31254) |
■ Applications & Industries
AL-6XN is specified where standard stainless steels fail rapidly, but the budget or structural requirements do not justify transitioning to pure Nickel superalloys like Hastelloy C-276.
- Desalination & Reverse Osmosis: High-pressure piping flanges and pump fasteners exposed to concentrated hot brine.
- Power Generation (FGD): Scrubber systems handling highly acidic, chloride-rich flue gases in coal-fired power plants.
- Marine & Offshore: Seawater cooling systems, splash-zone structural fastening, and subsea umbilical anchors.
- Pulp & Paper / Chemical: Bleach plant washers and reactors handling aggressive oxidizing chlorides.
■ Compatible Fastener Assemblies
To prevent galvanic corrosion in seawater systems, AL-6XN bolts must be paired with nuts of identical or superior electrochemical nobility.
| External Threads (AL-6XN Studs/Bolts) | Recommended Mating Component (Nuts) |
|---|---|
| AL-6XN (UNS N08367) | AL-6XN (UNS N08367) Heavy Hex Nuts (Requires heavy lubrication to prevent galling) |
| AL-6XN (UNS N08367) | Hastelloy C-276 / Inconel 625 Nuts (Acceptable upgrade in extreme severe-service) |
■ Torque & Installation Guidelines
Like all highly alloyed austenitic stainless steels, AL-6XN is exceptionally prone to thread galling (cold-welding). High-performance anti-seize compounds (Nickel-based or MoS2) are absolutely mandatory during assembly.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — Lubricated (ft-lbs) |
|---|---|---|
| 1/2" | 13 | 45 - 55 |
| 5/8" | 11 | 90 - 110 |
| 3/4" | 10 | 150 - 175 |
| 1" | 8 | 360 - 410 |
■ Why Choose Ananka Group?
Ananka Group specializes in the complex metallurgy required to manufacture and supply "6-Moly" fastening systems for global mega-projects.
- Precision Machining: Because AL-6XN work-hardens rapidly during machining, we utilize specialized low-speed, high-feed tooling to ensure perfect thread profiles.
- Rolled Threads: Threads are rolled wherever feasible to improve fatigue life and surface finish, drastically reducing the risk of installation galling.
- Absolute Traceability: Heat numbers permanently stamped on every fastener, ensuring your desalination or chemical plant complies with rigorous safety standards.
- Custom Configurations: Fully custom U-bolts, double-end studs, and specialty flange bolting manufactured to exact engineering drawings.
■ Frequently Asked Questions
1. What does "PREN" mean, and why is it important for AL-6XN?
PREN stands for Pitting Resistance Equivalent Number. It is a predictive measurement of a stainless steel's resistance to localized pitting corrosion based on its chemical makeup (Cr + 3.3xMo + 16xN). Standard 316 has a PREN of ~24. AL-6XN has a PREN exceeding 43, making it nearly twice as resistant to seawater pitting.
2. How does AL-6XN compare to SMO 254?
Both are "6-Moly" Super Austenitic stainless steels and perform very similarly in highly corrosive environments. While SMO 254 (UNS S31254) is a European development and AL-6XN is an American development, they are often used interchangeably in piping and fastening systems, provided the engineering specifications allow it.
3. Is AL-6XN magnetic?
No. The alloy remains completely austenitic (and therefore non-magnetic) under all conditions, making it suitable for applications requiring low magnetic permeability.
4. Why is Nitrogen added to this alloy?
In high-Molybdenum alloys, there is a risk of secondary "sigma phase" precipitation during hot working or welding, which makes the metal brittle. Nitrogen acts as a powerful austenite stabilizer, preventing this phase from forming. Additionally, Nitrogen heavily increases the overall yield strength of the steel.