COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF NITRONIC 60 (UNS S21800) FASTENING SYSTEMS
Nitronic 60, officially designated as UNS S21800 or Alloy 218, is a fully austenitic stainless steel engineered to solve one of the most persistent problems in mechanical engineering: thread galling and cold-welding. By precisely balancing high levels of Silicon and Manganese, this nitrogen-strengthened alloy creates a highly tenacious surface oxide layer that actively resists metal-to-metal tearing and wear.
Offering a yield strength significantly higher than standard 304 or 316 stainless steels, Nitronic 60 provides outstanding corrosion resistance alongside unmatched unlubricated wear resistance. It has become the global industry standard for premium fastening nuts, valve stems, and dynamic joint assemblies that require frequent assembly and disassembly without the reliance on messy or contaminating anti-seize lubricants.
■ Product Overview & Specifications
While available as bolts and studs, Nitronic 60 is most frequently specified as the ultimate "anti-galling nut material," designed to be mated with almost any other stainless or alloy steel fastener to ensure seamless installation and removal.
| Material Classification | Galling-Resistant Austenitic Stainless Steel |
|---|---|
| UNS Designation | S21800 (Alloy 218) |
| Microstructure | Fully Austenitic |
| Magnetic State | Consistently Non-Magnetic (Maintains low permeability even when cold-worked) |
| Density | ~7.62 g/cm³ (0.275 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" Specializing in heavy hex nuts and custom machined bushings. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
| Strengthening Method | Solid Solution Strengthening (Nitrogen) & Strain Hardening |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for Nitronic 60, including unlubricated galling threshold stress charts (tested against 17-4, 316, and A286), wear loss data, and high-temperature oxidation thresholds.
Nitronic 60 (S21800) — Complete Technical Datasheet
Contains comprehensive button-on-block galling test results, cyclic friction coefficients, and specific mating torque parameters for unlubricated clean-room and high-vacuum applications.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
Because Nitronic 60 relies on a very specific chemical balance to achieve its anti-galling properties, strict compositional verification is mandatory.
- EN 10204 Type 3.1: Mandatory reporting of Silicon (Si), Manganese (Mn), and Nitrogen (N) levels to guarantee the alloy's wear-resistant properties, alongside verified yield and tensile strengths.
- EN 10204 Type 3.2: Third-party witness testing facilitated for critical infrastructure, pharmaceutical clean-rooms, and naval deployments.
■ Chemical Composition (UNS S21800)
The magic of Nitronic 60 lies in the extraordinarily high additions of Manganese and Silicon. When these elements interact at the surface under pressure, they prevent the microscopic cold-welding (galling) that plagues other stainless steels.
| Chromium (Cr) | Nickel (Ni) | Manganese (Mn) | Silicon (Si) | Nitrogen (N) | Carbon (C) | Phosphorus (P) |
|---|---|---|---|---|---|---|
| 16.0 – 18.0 | 8.00 – 8.50 | 7.00 – 9.00 | 3.50 – 4.50 | 0.08 – 0.18 | 0.10 Max | 0.060 Max |
*Sulfur is restricted to 0.030 Max to maintain high toughness and cleanliness.
■ Mechanical Properties (Annealed Condition)
While generally supplied in the Annealed condition for nuts and hardware, Nitronic 60 still provides a yield strength vastly superior to annealed 304 or 316 stainless.
| Property | Standard Annealed Condition | Cold-Worked Fasteners (Approximate) |
|---|---|---|
| Tensile Strength (Min) | 95 ksi (655 MPa) | 105 - 125+ ksi |
| Yield Strength (0.2% Offset, Min) | 50 ksi (345 MPa) | 90 - 105+ ksi |
| Elongation in 2" (Min) | 35% | 15% - 20% |
| Reduction of Area (Min) | 55% | 45% |
| Hardness | 95 HRB (Max) | 25 to 30 HRC |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| UNS Designation | S21800 |
| Common Trade Name | Nitronic 60®, Alloy 218 |
| ASTM Specifications | ASTM A193 / A194, ASTM A276, ASTM A479 |
| European Equivalent | EN 1.4369 (Approximate/Nearest Match) |
■ Applications & Industries
Nitronic 60 is strictly necessary in environments where lubricants are prohibited, or where extreme wear and dynamic friction destroy standard alloys.
- Food & Pharmaceutical: Clean-room assemblies, sanitary valve stems, and processing equipment where anti-seize paste would contaminate the product.
- Infrastructure & Bridges: Expansion joint pins and heavy structural bolting requiring decades of corrosion-free, unseized service.
- Oil & Gas / Chemical: High-pressure pump shafts, wear rings, and mating nuts for precipitation-hardened (17-4/15-5) reactor studs.
- Aerospace & Space Systems: High-vacuum fastening where liquid or paste lubricants would instantly off-gas or freeze.
■ Compatible Fastener Assemblies (The Ultimate Nut)
The most common and effective use of Nitronic 60 is as a highly specialized nut. By pairing a standard high-strength stud with a Nitronic 60 nut, the entire assembly becomes completely immune to thread galling.
| External Threads (Studs/Bolts) | Nitronic 60 Nuts Application | Galling Risk |
|---|---|---|
| ASTM A193 Grade B8M (316 SS) | Nitronic 60 Heavy Hex Nuts | Eliminated (Replaces 316-on-316 seizing) |
| 17-4 PH / 15-5 PH (Any Condition) | Nitronic 60 Heavy Hex Nuts | Eliminated (Allows unlubricated high-torque assembly) |
| Nitronic 50 (XM-19) | Nitronic 60 Heavy Hex Nuts | Eliminated (Optimal high-strength marine package) |
■ Torque & Installation Guidelines (Unlubricated Potential)
Unlike almost every other stainless steel, Nitronic 60 can be successfully torqued dry. However, calculating torque without lubrication significantly alters the K-Factor (friction coefficient). The values below are estimates for annealed Nitronic 60 bolts installed dry into standard steel.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — DRY / Unlubricated (ft-lbs) |
|---|---|---|
| 3/8" | 16 | 20 - 25 |
| 1/2" | 13 | 45 - 55 |
| 5/8" | 11 | 90 - 110 |
| 3/4" | 10 | 150 - 180 |
■ Why Choose Ananka Group?
Ananka Group understands that a seized fastener on a critical offshore platform or sterile reactor can cost millions in downtime. We supply Nitronic 60 solutions to prevent these catastrophic failures.
- Dedicated Nut Production: We stock and manufacture massive quantities of Nitronic 60 heavy hex nuts specifically to pair with our high-strength 17-4 and A286 stud packages.
- CNC Wear Components: Precision machining of custom Nitronic 60 wear rings, bushings, and dynamic valve pins.
- Absolute Traceability: Heat numbers permanently stamped on every fastener, mapped back directly to mill certificates.
- Rolled Internal Threads: Whenever possible, internal nut threads are formed/rolled to maximize surface hardness and further enhance wear resistance.
■ Frequently Asked Questions
1. What exactly is "Galling"?
Galling (or cold-welding) occurs when two metal surfaces—especially stainless steels—slide against each other under heavy pressure (like tightening a nut on a bolt). The friction strips away the protective oxide layer, causing the raw metals to fuse together at a microscopic level. The fastener seizes completely and must usually be cut off.
2. How does Nitronic 60 prevent this?
The high levels of Silicon and Manganese in Nitronic 60 form a much tougher, more resilient oxide film on the surface. Instead of stripping away under pressure, this film acts as a built-in solid lubricant, preventing the raw metals from ever touching and fusing.
3. Is Nitronic 60 as corrosion-resistant as 316 Stainless?
Yes. Nitronic 60 offers general corrosion resistance that falls perfectly between 304 and 316 stainless steel. In most chloride pitting, crevice corrosion, and general oxidation tests, it performs on par with or slightly better than standard 316.
4. Should I use Nitronic 60 for both the bolt AND the nut?
You can, but it's usually unnecessary and expensive. The most cost-effective engineering solution is to use a high-strength, lower-cost bolt (like 17-4 PH or 316 SS) and pair it with a Nitronic 60 nut. Having just ONE of the mating surfaces made of Nitronic 60 is usually enough to completely eliminate galling.