COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF ASTM F593 GRADE 2 (AISI 316 / 316L) FASTENING SYSTEMS
ASTM F593 Grade 2 is the premier specification for marine-grade and chemically resistant austenitic stainless steel fasteners. 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 single alloying element fundamentally transforms the metal's performance, providing massively enhanced resistance to chloride-induced pitting and crevice corrosion.
Under the ASTM F593 specification, the mechanical properties of Grade 2 fasteners are strictly determined by their manufactured "Condition"—ranging from fully annealed (Condition A) for maximum ductility to severely cold-worked (Condition CW1/CW2) for structural yield strength. Grade 2 is the undisputed global standard for coastal construction, offshore oil and gas platforms, wastewater treatment plants, and severe chemical processing environments where standard 304 stainless would quickly succumb to chloride attack.
■ Product Overview & Specifications
Grade 2 fasteners are supplied in multiple conditions depending on the required mechanical strength. Condition CW (Cold Worked) is the most common for standard structural bolting to ensure sufficient load-bearing capacity.
| Material Classification | Molybdenum-Bearing Austenitic Stainless Steel |
|---|---|
| ASTM Specification | ASTM F593 Grade 2 (Bolts, Hex Cap Screws, Studs) |
| 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" Custom U-bolts, marine anchor studs, and socket head caps available. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine (Rolled threads recommended) |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for ASTM F593 Grade 2, including specific Pitting Resistance Equivalent Number (PREN) charts, Condition CW strain-hardening limits, and chloride stress-corrosion cracking thresholds.
ASTM F593 Grade 2 (316 Series) — Complete Technical Datasheet
Contains detailed allowable stress design values, precise thread shear calculations, and comprehensive torque-tension mapping for marine and 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 2.0-3.0% Molybdenum content), mandatory mechanical testing verifying the specific Condition (A, CW1, or CW2), and dimensional inspection reports.
- 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 oxide layer 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 (weld decay) during high-heat operations, Carbon is strictly limited to 0.030% Max.
■ Mechanical Properties (By Condition)
ASTM F593 dictates mechanical properties primarily based on the diameter of the fastener and the degree of cold working applied during manufacturing.
| Condition / Diameter | Tensile Strength | Yield Strength (0.2% Offset) | Elongation (Min) | Hardness |
|---|---|---|---|---|
| Condition A (Annealed) 1/4" to 1-1/2" |
75 to 100 ksi (515 to 690 MPa) |
30 ksi Min (205 MPa) |
30% | ~85 HRB Max |
| Condition CW1 (Cold Worked) 1/4" to 5/8" |
100 to 150 ksi (690 to 1035 MPa) |
65 ksi Min (450 MPa) |
20% | ~95 HRB to 32 HRC |
| Condition CW2 (Cold Worked) 3/4" to 1-1/2" |
85 to 140 ksi (585 to 965 MPa) |
45 ksi Min (310 MPa) |
25% | ~80 HRB to 32 HRC |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| ASTM Specification | ASTM F593 Grade 2 |
| UNS Designation | S31600 (316), S31603 (316L) |
| Common Trade Name | Marine Grade Stainless, 316 Stainless Steel |
| 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 F593 Grade 2 is deployed heavily in industries requiring a reliable, zero-maintenance fastening solution in harsh environments:
- Offshore & Marine: 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 in conductive electrolytes (like seawater) and ensure consistent thread engagement, ASTM F593 bolts must be mated with their exact corresponding nut specification.
| External Threads (ASTM F593) | Recommended Mating Nuts (ASTM F594) |
|---|---|
| F593 Grade 2 (316) Hex Bolts | ASTM F594 Grade 2 (316) Hex Nuts |
| F593 Grade 2 (316) Studs | ASTM F594 Grade 2 (316) Heavy Hex Nuts |
■ 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 or Marine/PTFE based) is strictly mandatory prior to installation to prevent fasteners from seizing before achieving proper clamp load.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque (Condition CW1/CW2) — 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-drawing and heading processes to ensure our bolts meet the elevated yield strength requirements of structural designs without causing strain-induced brittleness.
- Chemical Verification: Strict internal auditing ensures that Molybdenum levels never dip below the required 2.0% minimum, guaranteeing the pitting resistance you expect from 316 stainless.
- Rolled Threads: External threads are rolled rather than cut, drastically increasing fatigue resistance, improving surface finish, and minimizing the risk of galling during installation.
- 100% Traceability: Every fastener is marked with the specific F593 grade identification, backed by a comprehensive EN 10204 3.1 MTC.
■ Frequently Asked Questions
1. What is the difference between Grade 1 (304) and Grade 2 (316) fasteners?
Grade 2 contains 2-3% Molybdenum, while Grade 1 contains none. This molybdenum addition acts as a shield against chlorides (salt), making Grade 2 vastly superior for marine environments, swimming pools, and applications exposed to de-icing salts where Grade 1 would quickly pit and rust.
2. What is the difference between Condition A and Condition CW?
Condition A fasteners are machined from fully annealed stock. They are soft (30 ksi yield), highly ductile, and completely non-magnetic, but generally too weak for heavy structural joints. Condition CW (Cold Worked) fasteners are mechanically strain-hardened during forming. This massively increases their yield strength (up to 65 ksi), making them the standard choice for structural applications.
3. Is ASTM F593 Grade 2 magnetic?
In the fully annealed state (Condition A), it is completely non-magnetic. However, standard structural fasteners (Condition CW) undergo cold working. This mechanical stress transforms a tiny amount of the austenite into martensite, causing the fastener to become very slightly magnetic, though typically less so than Grade 1 (304).
4. Why did my F593 Grade 2 bolt lock up when I tightened the nut?
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.
