ASTM A194 Grade 8CLNA specifies an exceptionally advanced, high-performance austenitic stainless steel nut, corresponding to AISI Type 347LN. This highly specialized grade combines three distinct metallurgical advantages: Columbium (Niobium) stabilization, an ultra-low carbon profile (0.005% - 0.020%), and Nitrogen strengthening to provide unparalleled resistance to sensitization and intergranular corrosion.
What sets Grade 8CLNA apart is the crucial "A" designation. This 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, strictly non-magnetic state (60-90 HRB). This restoration of the matrix maximizes resistance to Stress Corrosion Cracking (SCC) in highly aggressive applications, making it the ultimate choice for heavy welded assemblies and extreme thermal cycling.
| Material Classification | Columbium-Stabilized, Nitrogen-Strengthened Austenitic Stainless Steel (Type 347LN - Annealed) |
|---|---|
| UNS Designation | S34751 |
| Microstructure | Austenitic (Low-Carbon, Stabilized, Nitrogen-Strengthened, Post-Annealed) |
| Magnetic State | Strictly Non-Magnetic (Annealed post-machining) |
| Density | ~8.00 g/cm³ (0.289 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" |
| Strengthening Method | Nitrogen Strengthening & Full Solution Annealing After Machining |
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 B8CLNA assemblies.
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The highly precise chemistry of Grade 8CLNA provides unparalleled metallurgical stability. The stringent 0.020% maximum carbon limit ensures absolute resistance to intergranular corrosion, while Chromium and Nickel provide an impenetrable baseline austenitic matrix for extreme operational environments.
| Carbon (C) | Manganese (Mn) | Chromium (Cr) | Nickel (Ni) | Phosphorus (P) | Sulfur (S) | Silicon (Si) |
|---|---|---|---|---|---|---|
| 0.005 – 0.020 | 2.00 Max | 17.0 – 19.0 | 9.0 – 13.0 | 0.045 Max | 0.030 Max | 1.00 Max |
Because Grade 8CLNA is explicitly annealed after all machining to remove localized cold-work hardening, ASTM tightly controls the hardness range to guarantee the matrix remains fully softened and stress-free.
| Mechanical Property | Grade 8CLNA (Annealed) Limits |
|---|---|
| Hardness Limit (Rockwell) | 60 - 90 HRB Maximum |
| Proof Load | Dependent on Size |
| Standard / System | Designation |
|---|---|
| ASME Standard | SA194 Grade 8CLNA |
| Common Trade Name | Type 347LN Stainless Nuts (Annealed), Columbium-Stabilized Low-Carbon |
| European Equivalent | EN 1.4546 / X5CrNiNb18-10 (Approximate mapping for 347 family) |
| Internal Threads (A194 Gr 8CLNA) | Mating Bolts (A193 Gr B8CLNA) | Mating Studs (A193 Gr B8CLNA) |
|---|---|---|
| Grade 8CLNA Heavy Hex Nuts | ASTM A193 Grade B8CLNA Hex Bolts | A193 Grade B8CLNA Fully Threaded Studs |
Due to the fully softened and high-nickel austenitic nature of 8CLNA, thread galling is a prominent risk under high clamping loads—especially in high-temperature service applications. Premium, high-temperature anti-seize lubrication (such as nickel-based paste) is absolutely mandatory for installation.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — Lubricated (ft-lbs) |
|---|---|---|
| 1/2" | 13 | 30 |
| 5/8" | 11 | 60 |
| 3/4" | 10 | 100 |
| 1" | 8 | 250 |
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.
While both share the exact same chemical composition (Columbium stabilized, ultra-low carbon, and Nitrogen strengthened), Grade 8CLN may retain residual stress and slight magnetism from the manufacturing process. Grade 8CLNA guarantees that these stresses are removed through post-machining full solution annealing.
Because the "A" specification is designed to eliminate internal stress through annealing, the hardness is restricted between 60 and 90 HRB. If a nut measures harder than 90 HRB, it strongly indicates that residual cold-work stress remains from the machining or threading process, meaning the part is not fully annealed and fails the specification.
