COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF ASTM A194 GRADE 8RA NUTS
ASTM A194 Grade 8RA specifies premium, high-performance austenitic stainless steel nuts manufactured from UNS S20910, widely recognized in the industry by the commercial trade names Nitronic® 50 or XM-19. This highly advanced alloy utilizes a complex matrix of Chromium, Nickel, Molybdenum, and significantly elevated levels of Manganese (4.0% - 6.0%) and Nitrogen to provide a unique combination of exceptional corrosion resistance and mechanical strength.
What sets Grade 8RA apart is the critical "A" designation, which mandates that the fasteners undergo a final Carbide Solution Treatment (full annealing) after all forging, machining, and thread-tapping operations are completed. This vital thermal process eliminates any residual cold-work stresses introduced during manufacturing, ensuring a fully softened matrix. This structural restoration maximizes the alloy's resistance to Stress Corrosion Cracking (SCC) in highly aggressive chemical, subsea, and offshore applications, guaranteeing a strictly non-magnetic fastener.
■ Product Overview & Specifications
| Material Classification | Nitrogen-Strengthened, High-Manganese Austenitic Stainless Steel (XM-19 - Annealed) |
|---|---|
| UNS Designation | S20910 |
| Microstructure | Austenitic (Stabilized by Manganese and Nitrogen, Post-Annealed) |
| Magnetic State | Strictly Non-Magnetic (Annealed post-machining) |
| Density | ~7.88 g/cm³ (0.285 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" |
| Strengthening Method | Nitrogen/Manganese Strengthening & Full Solution Annealing After Machining |
■ Proprietary Datasheet Download (GATED)
ASTM A194 Grade 8RA — Complete Technical Datasheet
Contains detailed proof load thresholds, dimensional tolerances for ASME B18.2.2 standard and heavy hex profiles, and precise galling-prevention torque values for A193 B8RA assemblies.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
Material traceability is the backbone of safety in high-pressure and corrosive environments. Every lot shipped by Ananka is accompanied by fully authenticated documentation mapping back to raw steel mill certificates.
- EN 10204 Type 3.1: Issued by our independent quality department, providing specific heat-traceable test results (actual chemical analysis verifying high manganese levels, mechanical test results, hardness limits, and proof load tests).
- EN 10204 Type 3.2: For critical offshore, marine, or highly corrosive petrochemical applications, we facilitate third-party witness testing.
■ Chemical Composition
The highly elevated Chromium (20.5-23.5%) and Molybdenum (1.50-3.00%) provide an exceptional shield against pitting and general corrosion. The heavy Manganese content (4.0-6.0%) acts alongside Nitrogen to ensure phase stability even under extreme conditions.
| Carbon (C) | Manganese (Mn) | Chromium (Cr) | Nickel (Ni) | Molybdenum (Mo) | Phosphorus (P) | Sulfur (S) | Silicon (Si) |
|---|---|---|---|---|---|---|---|
| 0.06 Max | 4.0 – 6.0 | 20.5 – 23.5 | 11.5 – 13.5 | 1.50 – 3.00 | 0.045 Max | 0.030 Max | 1.00 Max |
*Note: The UNS S20910 specification also inherently includes strict tolerances for Nitrogen, Columbium, and Vanadium to achieve full material stabilization.
■ Mechanical Properties
Because Grade 8RA is explicitly annealed after all machining to remove localized cold-work hardening, ASTM limits the maximum hardness to ensure the material remains fully stress-relieved.
| Mechanical Property | Grade 8RA (Annealed) Limits |
|---|---|
| Hardness Limit (Rockwell) | 25 HRC Maximum |
| Proof Load | Dependent on Size |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| ASME Standard | SA194 Grade 8RA |
| Common Trade Name | Nitronic® 50 (Annealed), XM-19 Stainless, UNS S20910 |
■ Applications & Industries
- Marine & Subsea Engineering: Fasteners deployed in extreme seawater depths, where both severe corrosion resistance and completely stress-free microstructures are required to prevent SCC.
- Offshore Oil & Gas: Fasteners deployed in "sour gas" wells and platforms, offering excellent resistance to sulfide stress cracking.
- Chemical & Fertilizer Production: Fasteners used in urea production facilities and highly corrosive chemical extraction tanks.
■ Compatible Fastener Assemblies
| Internal Threads (A194 Gr 8RA) | Mating Bolts (A193 Gr B8RA) | Mating Studs (A193 Gr B8RA) |
|---|---|---|
| Grade 8RA Heavy Hex Nuts (Annealed) | ASTM A193 Grade B8RA Hex Bolts | A193 Grade B8RA Fully Threaded Studs |
■ Torque & Installation Guidelines
Due to the fully softened, extremely tough austenitic nature of Grade 8RA, thread galling is a prominent risk under clamping loads. Premium, heavy-duty anti-seize lubrication (such as nickel or molybdenum-disulfide pastes) is absolutely mandatory for safe installation.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — Lubricated (ft-lbs) |
|---|---|---|
| 1/2" | 13 | 35 |
| 5/8" | 11 | 70 |
| 3/4" | 10 | 120 |
| 1" | 8 | 280 |
■ Frequently Asked Questions
1. What does the "A" stand for in Grade 8RA?
The "A" indicates that the component has been Annealed after all manufacturing and machining processes are complete. This removes all internal cold-work stresses generated during machining, ensuring the part is fully softened and strictly non-magnetic to maximize resistance against Stress Corrosion Cracking.
2. How does Grade 8RA compare to Grade 8R?
While both share the exact same chemical composition (Nitronic 50 / XM-19), standard Grade 8R may retain residual stress and slight magnetism from the manufacturing process. Grade 8RA guarantees that these stresses are completely removed through post-machining full solution annealing.
3. What is the role of Manganese in this alloy?
Manganese (at a high 4.0% - 6.0%) acts as an austenite stabilizer. Because Nitrogen is heavily added to increase strength, the high Manganese content allows the steel to actually dissolve and absorb that Nitrogen safely into the matrix without causing defects, creating a final product that is incredibly strong yet ductile.