ASTM F594 – Specification
The ASTM F594 specification establishes the requirements for stainless steel nuts with nominal diameters ranging from 0.25 to 1.50 inches. Intended for service applications requiring general corrosion resistance, this standard categorizes fasteners into seven distinct alloy groups, encompassing austenitic, ferritic, martensitic, and precipitation-hardening stainless steels.
Practical Application for Professionals
To successfully apply this specification to your procurement or engineering project, you must define several critical parameters during the ordering process:
- Alloy Group Selection: Choose from Group 1 through 7 based on the required environmental resistance and material properties.
- Condition Designation: Specify the metallurgical condition (e.g., Annealed, Cold Worked, or Hardened and Tempered) as this directly dictates the final mechanical performance.
- Dimensional Compliance: Unless otherwise specified, nuts must conform to ASME B18.2.2 dimensions and feature Class 2B threads per ASME B1.1.
- Compatibility: For optimal performance and corrosion integrity, these nuts are designed to be paired with stainless steel bolts, hex cap screws, and studs conforming to ASTM F593 of the same alloy group.
Key Technical Requirements
The specification ensures product quality through rigorous standards for chemical composition and mechanical integrity:
- Mechanical Integrity: Nuts must meet specific proof stress and Rockwell hardness values outlined in Table 2, which vary significantly based on the chosen alloy group and condition.
- Corrosion Resistance: Austenitic alloy groups (1, 2, and 3) must be capable of passing intergranular corrosion tests to ensure long-term durability in corrosive environments.
- Quality Control: Standard manufacturing includes sample inspections for mechanical properties, with optional supplementary requirements available for shipment-specific lot testing or source inspection.
Mechanical Properties
Finished ASTM F594 fasteners must meet specific mechanical requirements for proof stress and Rockwell hardness as defined by their alloy group and metallurgical condition. These properties are strictly categorized across seven alloy groups, ranging from austenitic to precipitation-hardening stainless steels, to ensure performance integrity in corrosive environments. Values are established based on the nominal diameter of the nut and its specific heat treatment or work-hardening state, such as Annealed (A), Cold Worked (CW), or Hardened and Tempered (H).
| Mechanical Properties Requirements | |||||
|---|---|---|---|---|---|
| Stainless Alloy Group | Condition | Alloy Mechanical Property Marking | Nominal Diameter (in.) | Proof Stress (ksi, min) | Rockwell Hardness |
| Austenitic Alloys | |||||
| 1 (303, 304, 304L, 305, 384, XM1, 18-9LW, 302HQ, 303Se) | AF | F594A | 1/4 to 1-1/2, incl | 70 | B85 max |
| A | F594B | 1/4 to 1-1/2, incl | 75 | B65 to 95, incl | |
| CW1 | F594C | 1/4 to 5/8, incl | 100 | B95 to C32, incl | |
| CW2 | F594D | 3/4 to 1-1/2, incl | 85 | B80 to C32, incl | |
| SH1 | F594A | 1/4 to 5/8, incl | 120 | C24 to C36, incl | |
| SH2 / SH3 | F594B / F594C | 3/4 to 1, incl / 1-1/8 to 1-1/4, incl | 110 / 100 | C20 to C32, incl / B95 to C30, incl | |
| SH4 | F594D | 1-3/8 to 1-1/2, incl | 85 | B90 to C28, incl | |
| Austenitic Alloys (Group 2) | |||||
| 2 (316, 316L) | AF | F594E | 1/4 to 1-1/2, incl | 70 | B85 max |
| A | F594F | 1/4 to 1-1/2, incl | 75 | B65 to 95, incl | |
| CW1 | F594G | 1/4 to 5/8, incl | 100 | B95 to C32, incl | |
| CW2 | F594H | 3/4 to 1-1/2, incl | 85 | B80 to C32, incl | |
| SH1 | F594E | 1/4 to 5/8, incl | 120 | C24 to C36, incl | |
| SH2 | F594F | 3/4 to 1, incl | 110 | C20 to C32, incl | |
| SH3 / SH4 | F594G / F594H | 1-1/8 to 1-1/4, incl / 1-3/8 to 1-1/2, incl | 100 / 85 | B95 to C30, incl / B90 to C28, incl | |
| Austenitic Alloys (Group 3) | |||||
| 3 (321, 347) | AF | F594J | 1/4 to 1-1/2, incl | 70 | B85 max |
| A | F594K | 1/4 to 1-1/2, incl | 75 | B65 to 95, incl | |
| CW1 | F594L | 1/4 to 5/8, incl | 100 | B95 to C32, incl | |
| CW2 | F594M | 3/4 to 1-1/2, incl | 85 | B80 to C32, incl | |
| SH1 | F594J | 1/4 to 5/8, incl | 120 | C24 to C36, incl | |
| SH2 | F594K | 3/4 to 1, incl | 110 | C20 to C32, incl | |
| SH3 / SH4 | F594L / F594M | 1-1/8 to 1-1/4, incl / 1-3/8 to 1-1/2, incl | 100 / 85 | B95 to C30, incl / B90 to C28, incl | |
| Ferritic Alloys | |||||
| 4 (430, 430F) | A | F594N | 1/4 to 1-1/2, incl | 55 | B85 max |
| CW1 | F594V | 1/4 to 5/8, incl | 60 | B75 to 98, incl | |
| CW2 | F594W | 3/4 to 1-1/2, incl | 55 | B65 to 95, incl | |
| Martensitic Alloys | |||||
| 5 (410, 416, 416Se) | H | F594P | 1/4 to 1-1/2, incl | 100 | C20 to 30, incl |
| HT | F594R | 1/4 to 1-1/2, incl | 160 | C34 to 45, incl | |
| 6 (431) | H | F594S | 1/4 to 1-1/2, incl | 125 | C25 to 32, incl |
| HT | F594T | 1/4 to 1-1/2, incl | 180 | C40 to 48, incl | |
| Precipitation Hardening Alloys | |||||
| 7 (630) | AH | F594U | 1/4 to 1-1/2, incl | 135 | C28 to 38, incl |
Material Properties
The ASTM F594 specification classifies stainless steel nuts into seven distinct alloy groups based on their metallurgical structure and chemical composition. These groups include austenitic (Groups 1–3), ferritic (Group 4), martensitic (Groups 5–6), and precipitation-hardening (Group 7) alloys. Unless a specific alloy is requested by the purchaser, the manufacturer may choose a suitable grade from within the specified group based on fabrication methods and material availability.
To ensure consistent performance and corrosion resistance, each alloy must adhere to strict chemical composition limits, specifically regarding elements such as Chromium, Nickel, and Molybdenum. Furthermore, the final properties of the nut are dictated by its delivery condition, with standard options including Cold Worked (CW) for austenitic and ferritic grades, Hardened and Tempered (H) for martensitic grades, and Age Hardened (AH) for precipitation-hardening alloys.
| Alloy Groups | ||
|---|---|---|
| Group | Alloys | Condition |
| 1 | 304, 305, 304L, 384, 18-9LW, 302HQ | Cold Worked (CW) |
| 2 | 316, 316L | Cold Worked (CW) |
| 3 | 321, 347 | Cold Worked (CW) |
| 4 | 430 | Cold Worked (CW) |
| 5 | 410 | Hardened and Tempered (H) |
| 6 | 431 | Hardened and Tempered (H) |
| 7 | 630 | Age Hardened (AH) |
| Chemical Requirements | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Alloy Group | UNS Designation | Alloy | Composition, % maximum except as shown | |||||||||
| Carbon | Manganese | Phosphorus | Sulfur | Silicon | Chromium | Nickel | Copper | Molybdenum | Others | |||
| Austenitic Alloys | ||||||||||||
| 1 | S30300 | 303 | 0.15 | 2.00 | 0.20 | 0.15 min | 1.00 | 17.0 to 19.0 | 8.0 to 10.0 | 0.60 max | - | - |
| 1 | S30323 | 303Se | 0.15 | 2.00 | 0.20 | 0.060 | 1.00 | 17.0 to 19.0 | 8.0 to 10.0 | - | - | Se 0.15 min |
| 1 | S30400 | 304 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 18.0 to 20.0 | 8.0 to 10.5 | 1.00 | - | - |
| 1 | S30403 | 304L | 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 18.0 to 20.0 | 8.0 to 12.0 | 1.00 | - | - |
| 1 | S30500 | 305 | 0.12 | 2.00 | 0.045 | 0.030 | 1.00 | 17.0 to 19.0 | 10.5 to 13.0 | 1.00 | - | - |
| 1 | S38400 | 384 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 15.0 to 17.0 | 17.0 to 19.0 | - | - | - |
| 1 | S20300 | XM1 | 0.08 | 5.0 to 6.5 | 0.040 | 0.18 to 0.35 | 1.00 | 16.0 to 18.0 | 5.0 to 6.5 | 0.50 max | - | 1.75 to 2.25 |
| 1 | S30430 | 18-9LW | 0.10 | 2.00 | 0.045 | 0.030 | 1.00 | 17.0 to 19.0 | 8.0 to 10.0 | 3.0 to 4.0 | - | - |
| 1 | S30433 | 302HQ | 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 17.0 to 19.0 | 8.0 to 10.0 | 3.0 to 4.0 | - | - |
| 2 | S31603 | 316L | 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 16.0 to 18.0 | 10.0 to 14.0 | - | 2.00-3.00 | - |
| 2 | S31600 | 316 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 16.0 to 18.0 | 10.0 to 14.0 | - | 2.00-3.00 | - |
| 3 | S32100 | 321 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 17.0 to 19.0 | 9.0 to 12.0 | - | - | Ti 5 x C min |
| 3 | S34700 | 347 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 17.0 to 19.0 | 9.0 to 13.0 | - | - | Cb+Ta 10 x C min |
| Ferritic Alloys | ||||||||||||
| 4 | S43000 | 430 | 0.12 | 1.00 | 0.040 | 0.030 | 1.00 | 16.0 to 18.0 | - | - | - | - |
| 4 | S43020 | 430F | 0.12 | 1.25 | 0.060 | 0.15 min | 1.00 | 16.0 to 18.0 | - | 0.60 max | - | - |
| Martensitic Alloys | ||||||||||||
| 5 | S41000 | 410 | 0.15 | 1.00 | 0.040 | 0.030 | 1.00 | 11.5 to 13.5 | - | - | - | - |
| 5 | S41600 | 416 | 0.15 | 1.25 | 0.060 | 0.15 min | 1.00 | 12.0 to 14.0 | - | 0.60 max | - | - |
| 5 | S41623 | 416Se | 0.15 | 1.25 | 0.060 | 0.060 | 1.00 | 12.0 to 14.0 | - | - | - | Se 0.15 min |
| 6 | S43100 | 431 | 0.20 | 1.00 | 0.040 | 0.030 | 1.00 | 15.0 to 17.0 | 1.25 to 2.50 | - | - | - |
| Precipitation Hardening Alloy | ||||||||||||
| 7 | S17400 | 630 | 0.07 | 1.00 | 0.040 | 0.030 | 1.00 | 15.0 to 17.5 | 3.0 to 5.0 | 3.0 to 5.0 | - | Cb + Ta 0.15-0.45 |