COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF ASTM F594 GRADE 2 (AISI 316 / 316L) NUTS
ASTM F594 Grade 2 is the premier specification for marine-grade and chemically resistant austenitic stainless steel nuts. This grade primarily encompasses the AISI 316 and 316L stainless steel alloys. Building upon the basic 18/8 architecture of Grade 1 (304 SS), Grade 2 incorporates a critical addition of 2.0% to 3.0% Molybdenum. This specific alloying element fundamentally transforms the nut's performance, providing massively enhanced resistance to chloride-induced pitting and crevice corrosion.
Under the ASTM F594 specification, the mechanical proof loads of Grade 2 nuts are determined by their manufactured "Condition"—ranging from fully annealed (Condition A) to severely cold-worked (Condition CW1/CW2) to structurally support the high tensile loads of corresponding cold-worked bolts. Grade 2 nuts are the undisputed global standard for securing coastal construction, offshore oil and gas platforms, wastewater treatment plants, and severe chemical processing equipment.
■ Product Overview & Specifications
Grade 2 nuts are supplied in multiple conditions depending on the required mechanical strength of the mating fastener. Condition CW (Cold Worked) is the most common for structural bolting to ensure the nut threads will not shear under heavy tension.
| Material Classification | Molybdenum-Bearing Austenitic Stainless Steel Nuts |
|---|---|
| ASTM Specification | ASTM F594 Grade 2 (Hex Nuts, Heavy Hex Nuts, Jam Nuts) |
| UNS Designation | S31600 (316), S31603 (316L) |
| Magnetic State | Non-Magnetic (Annealed) / Slightly Magnetic (Cold Worked) |
| Density | ~7.98 g/cm³ (0.288 lb/in³) |
| Temperature Limits | -320°F to +800°F (-196°C to +427°C) |
| Size Range | Metric: M6 to M36 | Imperial: 1/4" to 1-1/2" Standardly supplied as Finished Hex or Heavy Hex Nuts. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for ASTM F594 Grade 2, including specific Pitting Resistance Equivalent Number (PREN) charts, Condition CW proof load stripping charts, and marine environment galling prevention guides.
ASTM F594 Grade 2 (316 Series) — Complete Technical Datasheet
Contains detailed allowable thread shear calculations, precise dimensional tolerances for heavy hex profiles, and comprehensive torque-tension mapping for offshore installations.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
For critical infrastructure and sanitary processing applications, Ananka Group provides absolute material traceability mapping back to the primary melt.
- EN 10204 Type 3.1: Detailed reporting of actual chemical analysis (specifically verifying the critical 2.0-3.0% Molybdenum content), mandatory mechanical proof load testing verifying the specific Condition (A, CW1, or CW2), and dimensional inspection.
- EN 10204 Type 3.2: Third-party witness testing facilitated for large-scale offshore platforms, desalination plants, or municipal water infrastructure.
■ Chemical Composition (Typical AISI 316 / S31600)
The alloy relies on Chromium to form a stable passive oxide layer, Nickel to stabilize the ductile austenitic microstructure, and a crucial addition of Molybdenum to defend the internal threads against penetrating chloride ions.
| Chromium (Cr) | Nickel (Ni) | Moly (Mo) | Carbon (C) | Manganese (Mn) | Phosphorus/Sulfur |
|---|---|---|---|---|---|
| 16.00 – 18.00 | 10.00 – 14.00 | 2.00 – 3.00 | 0.08 Max* | 2.00 Max | P: 0.045 / S: 0.030 Max |
*If the 316L variant is utilized to prevent sensitization during extreme temperature service, Carbon is strictly limited to 0.030% Max.
■ Mechanical Properties & Proof Loads (By Condition)
Unlike bolts which are tested for tensile strength, nuts are tested for Proof Stress. The nut must support this applied load on its threads without stripping or causing dimensional damage.
| Condition / Diameter | Minimum Proof Stress (Hex / Heavy Hex) | Hardness Limits |
|---|---|---|
| Condition A (Annealed) 1/4" to 1-1/2" |
75 ksi (515 MPa) | 85 HRB Max |
| Condition CW1 (Cold Worked) 1/4" to 5/8" |
100 ksi (690 MPa) | 95 HRB to 32 HRC |
| Condition CW2 (Cold Worked) 3/4" to 1-1/2" |
85 ksi (585 MPa) | 80 HRB to 32 HRC |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| ASTM Specification | ASTM F594 Grade 2 (Nuts) |
| UNS Designation | S31600 (316), S31603 (316L) |
| Common Trade Name | Marine Grade Stainless, 316 Stainless Nuts |
| European Equivalent | EN 1.4401 / ISO 3506 A4-70 (Rough equivalent to CW1/CW2) |
■ Corrosion & Environmental Resistance Profile
Grade 2 is explicitly engineered to handle aggressive environments where standard Grade 1 (304) alloys fail:
- Marine & Coastal: Unparalleled resistance to "tea-staining" and saltwater corrosion. It is the absolute minimum requirement for fasteners installed within 5 miles of a coastline or in splash zones.
- Chemical & Chlorides: Highly resistant to localized pitting caused by chloride ions (found in de-icing salts, swimming pool environments, and chemical processing).
- Wastewater & Sanitation: Exceptional resilience against aggressive cleaning agents, sulfurous compounds, and corrosive slurries in municipal water treatment.
■ Applications & Industries
ASTM F594 Grade 2 is deployed heavily in industries requiring a reliable, zero-maintenance fastening solution in harsh environments:
- Offshore & Marine: Nuts for subsea structural bolting, dockside infrastructure, and boat hardware.
- Water & Desalination: Fasteners for RO (Reverse Osmosis) skids, municipal piping, and high-chloride filtration equipment.
- Chemical & Pharmaceutical: Processing vats, sanitary piping lines, and environments utilizing aggressive sterilization wash-downs.
- Coastal Architecture: Structural bolting for bridges, glass facades, and exposed frameworks in salt-air environments.
■ Compatible Fastener Assemblies
To avoid galvanic corrosion and ensure that the nut's proof stress safely exceeds the bolt's yield strength, F594 nuts must be mated with their exact corresponding bolt specification and condition.
| Mating Nut (ASTM F594) | Recommended External Threads (ASTM F593) |
|---|---|
| F594 Grade 2 Condition A | ASTM F593 Grade 2 Condition A (Annealed Bolts) |
| F594 Grade 2 Condition CW1/CW2 | ASTM F593 Grade 2 Condition CW1/CW2 (Cold Worked Bolts) |
■ Torque & Installation Guidelines
Like all austenitic stainless steels, 316 is highly susceptible to severe thread galling (cold-welding). The application of premium anti-seize paste (such as Nickel, PTFE, or Marine-grade lubricants) is strictly mandatory prior to installation to prevent nuts from seizing to the bolt before achieving proper clamp load.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque (When mated w/ CW bolts) — Lubricated (ft-lbs) |
|---|---|---|
| 1/4" | 20 | 5 - 8 |
| 1/2" | 13 | 40 - 55 |
| 3/4" | 10 | 130 - 170 |
| 1" | 8 | 260 - 340 |
■ Why Choose Ananka Group?
Ananka Group specializes in the high-volume precision manufacturing of marine and structural stainless steel fastening systems.
- Cold-Working Expertise (CW1/CW2): We expertly control the cold-forming processes to ensure our nuts meet the elevated proof stress requirements of standard structural designs without thread distortion.
- Chemical Verification: Strict internal auditing ensures that Molybdenum levels never dip below the required 2.0% minimum, guaranteeing the marine-grade pitting resistance you expect from 316 stainless.
- Precision Tapping: Internal threads are meticulously cut to standard 2B or 6H tolerances, ensuring smooth run-down on mating bolts and drastically reducing the likelihood of galling in wet environments.
- 100% Traceability: Every nut is marked with the specific F594 grade identification, backed by a comprehensive EN 10204 3.1 MTC.
■ Frequently Asked Questions
1. What is the difference between Grade 1 (304) nuts and Grade 2 (316) nuts?
Grade 2 contains 2-3% Molybdenum, while Grade 1 contains none. This molybdenum addition acts as a shield against chlorides (salt), making Grade 2 nuts vastly superior for preventing thread-locking corrosion in marine environments, swimming pools, and applications exposed to de-icing salts.
2. What is the difference between Condition A and Condition CW nuts?
Condition A nuts are machined from fully annealed stock. They are highly ductile and completely non-magnetic, but have a lower proof stress. Condition CW (Cold Worked) nuts are mechanically strain-hardened during forming. This massively increases their proof load capacity, allowing them to support the high tension of cold-worked structural bolts without stripping.
3. Is ASTM F594 Grade 2 magnetic?
In the fully annealed state (Condition A), it is completely non-magnetic. However, standard structural nuts (Condition CW) undergo cold working. This mechanical stress transforms a tiny amount of the austenite into martensite, causing the nut to become very slightly magnetic, though typically less so than Grade 1 (304).
4. Why did my F594 Grade 2 nut lock up on the bolt halfway down?
This is called thread galling or cold-welding, a very common issue with austenitic stainless steel. Friction during tightening causes the protective oxide layer to scrape off, and the bare metals weld together. To prevent this, always install stainless hardware at slow speeds and heavily lubricate the threads with an anti-seize compound before assembly.
