COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF ASTM A194 GRADE 8C NUTS
ASTM A194 Grade 8C specifies premium austenitic stainless steel nuts manufactured from AISI Type 347. This highly specialized grade is alloyed with Columbium (Niobium) and Tantalum, which act as stabilizing agents. This stabilization prevents chromium carbide precipitation (sensitization) when the material is exposed to critical temperature ranges (800°F to 1500°F / 427°C to 816°C) or during welding processes, offering unparalleled resistance to intergranular corrosion in high-heat environments.
Standard Grade 8C nuts are expertly machined from solution-treated bar stock, providing an exceptional balance of high tensile strength and high-temperature oxidation resistance for aggressive petrochemical and power generation piping.
■ Product Overview & Specifications
ASTM A194 Grade 8C represents the industry benchmark for high-temperature, Columbium-stabilized austenitic pressure piping components.
| Material Classification | Columbium-Stabilized Austenitic Stainless Steel (Type 347) |
|---|---|
| UNS Designation | S34700 |
| Microstructure | Austenitic (Stabilized against carbide precipitation) |
| Magnetic State | Non-Magnetic (May show slight magnetism from cold-working) |
| Density | ~8.00 g/cm³ (0.289 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" Custom oversized nuts available upon request. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
| Strengthening Method | Carbide Solution Treated Bar Stock |
■ Proprietary Datasheet Download (GATED)
ASTM A194 Grade 8C — 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 B8C assemblies.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
Material traceability is the backbone of safety in high-temperature 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 Columbium stabilization limits, mechanical test results, hardness, and proof load tests).
- EN 10204 Type 3.2: For critical aerospace, nuclear, or high-temp petrochemical applications, we facilitate third-party witness testing.
■ Chemical Composition
Grade 8C relies on a highly specific Columbium (Niobium) and Tantalum ratio. This addition preferentially bonds with carbon to form highly stable carbides, leaving the Chromium intact to maintain the protective passive oxide layer.
| Carbon (C) | Manganese (Mn) | Chromium (Cr) | Nickel (Ni) | Columbium + Tantalum (Cb+Ta) | Phosphorus (P) | Sulfur (S) | Silicon (Si) |
|---|---|---|---|---|---|---|---|
| 0.08 Max | 2.00 Max | 17.00 – 19.00 | 9.00 – 13.00 | 10 × Carbon content (Min) to 1.00 (Max) | 0.045 Max | 0.030 Max | 1.00 Max |
■ Mechanical Properties
| Mechanical Property | Grade 8C Limits |
|---|---|
| Proof Load Stress (Heavy Hex) | 80 ksi (550 MPa) |
| Proof Load Stress (Standard Hex) | 75 ksi (515 MPa) |
| Hardness Limit (Rockwell) | 60 HRB to 32 HRC |
| Hardness Limit (Brinell) | 126 to 302 HBW |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| ASME Standard | SA194 Grade 8C |
| Common Trade Name | Type 347 Stainless Nuts, Columbium Stabilized Nuts |
| European Equivalent | EN 1.4550 / X6CrNiNb18-10 |
■ Applications & Industries
- Petrochemical Refining: Fasteners for Fluid Catalytic Cracking (FCC) units, high-temperature distillation columns, and flare stack systems.
- Aerospace & Defense: Engine manifolds, exhaust systems, and high-heat aerospace components requiring stabilized metallurgy.
- Power Generation: Heavy-duty bolting for radiant superheaters and boiler tubes operating continuously at elevated temperatures.
■ Compatible Fastener Assemblies
| Internal Threads (A194 Gr 8C) | Mating Bolts (A193 Gr B8C) | Mating Studs (A193 Gr B8C) |
|---|---|---|
| Grade 8C Heavy Hex Nuts | ASTM A193 Grade B8C Hex Bolts | A193 Grade B8C Fully Threaded Studs |
■ Torque & Installation Guidelines
Because austenitic stainless steels are highly prone to thread galling, especially in high-heat applications, premium high-temperature anti-seize lubrication (e.g., nickel-based) is absolutely mandatory.
| 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 |
■ Frequently Asked Questions
1. What is the difference between Grade 8, 8M, and 8C?
Grade 8 (Type 304) is standard 18/8 stainless for general corrosion. Grade 8M (Type 316) adds Molybdenum for superior resistance to chloride pitting. Grade 8C (Type 347) adds Columbium (Niobium) and Tantalum to prevent carbide precipitation, making it the only choice for severe high-temperature environments (800°F–1500°F).
2. What does Columbium (Cb) do in Grade 8C steel?
Columbium (also known universally as Niobium) has a higher affinity for carbon than chromium does. When exposed to high heat, the carbon bonds with the Columbium instead of the Chromium. This keeps the Chromium safely dissolved in the steel matrix, preserving the material's protective oxide layer and preventing intergranular corrosion.
3. What is the exact difference between Grade 8C and Grade 8CA?
A standard Grade 8C nut may retain localized cold-work stresses from being machined. Grade 8CA is an alternate designation where the component is solution-annealed after all machining is completely finished, eliminating all stresses.