ASTM F593 – Mechanical, Material & Chemical Properties
The ASTM F593 specification establishes the chemical and mechanical requirements for stainless steel fasteners ranging from 0.25 to 1.50 inches in nominal diameter. These fasteners are intended for general-purpose applications requiring corrosion resistance.
Key Classification Groups
The standard categorizes stainless steel alloys into seven distinct groups based on their chemical composition and metallurgical structure:
- Groups 1, 2, and 3: Austenitic alloys (e.g., 304, 316, 321, 347).
- Group 4: Ferritic alloys (e.g., 430).
- Groups 5 and 6: Martensitic alloys (e.g., 410, 431).
- Group 7: Precipitation-hardening alloys (e.g., 630).
Manufacturing and Material Conditions
Fasteners can be produced through cold forming, hot forming, or machining. The mechanical properties are largely determined by the delivery "Condition," which must be specified during the ordering process:
- CW (Cold Worked): The standard condition for Groups 1, 2, 3, and 4; acquired through heading and rolling.
- A (Annealed): Machined from annealed stock or hot-formed and solution-annealed.
- H (Hardened & Tempered): Standard for martensitic alloys (Groups 5 and 6), tempered at $1050^\circ\text{F}$ minimum.
- AH (Age Hardened): Solution-annealed and aged after forming; specific to Group 7.
Testing and Quality Control
Fasteners under ASTM F593 are subject to rigorous testing. Full-size products are typically tested for tensile strength, yield strength, and hardness. For austenitic alloys (Groups 1–3), the standard also includes requirements for intergranular corrosion resistance to ensure the material has not been compromised by carbide precipitation during heat treatment or welding.
Note on Compatibility: Unless otherwise specified, all nuts used with these fasteners must conform to ASTM F594, be of the same alloy group, and possess a minimum proof stress equal to or greater than the bolt's tensile strength.
Mechanical Properties
The ASTM F593 specification defines the mechanical requirements for stainless steel fasteners based on their alloy group and manufacturing condition. These properties—including tensile strength, yield strength, and hardness—are determined by whether the fastener is cold-worked, annealed, or hardened and tempered.
Core Requirements
- Testing Methods: Fasteners are primarily subject to full-size tensile and yield strength tests. Machined specimen tests are permitted for larger diameters or when equipment capacity is exceeded.
- Property Determinants: Strength levels vary significantly across the seven alloy groups, with condition-specific markings such as CW (Cold Worked), H (Hardened), and AF (Annealed after forming).
- Standard Compliance: Finished fasteners must meet the specific minimum and maximum values detailed in the table below to ensure performance in corrosive service applications.
| Mechanical Property Requirements | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Stainless Alloy Group | Condition | Alloy Mechanical Property Marking | Nominal Diameter, in. | Full-Size Tests | Machined Specimen Tests | ||||
| Tensile Strength, ksi | Yield Strength, ksi (0.2% offset) | Rockwell Hardness | Tensile Strength, ksi | Yield Strength, ksi | Elongation in 4 D, % | ||||
| 1 (303, 304, 304L, 305, 384, XM1, 18-9LW, 302HQ, 304J3, 303Se) |
AF | F593A | 1/4 to 1-1/2, incl | 65 to 85 | 20 | B85 max | 60 | 20 | 40 |
| A | F593B | 1/4 to 1-1/2, incl | 75 to 100 | 30 | B65 to 95 | 70 | 30 | 30 | |
| CW1 | F593C | 1/4 to 5/8, incl | 100 to 150 | 65 | B95 to C32 | 95 | 60 | 20 | |
| CW2 | F593D | 3/4 to 1-1/2, incl | 85 to 140 | 45 | B80 to C32 | 80 | 40 | 25 | |
| SH1 | F593A | 1/4 to 5/8, incl | 120 to 160 | 95 | C24 to C36 | 115 | 90 | 12 | |
| SH2 | F593B | 3/4 to 1, incl | 110 to 150 | 75 | C20 to C32 | 105 | 70 | 15 | |
| SH3 | F593C | 1-1/8 to 1-1/4, incl | 100 to 140 | 60 | B95 to C30 | 95 | 55 | 20 | |
| SH4 | F593D | 1-3/8 to 1-1/2, incl | 95 to 130 | 45 | B90 to C28 | 90 | 40 | 28 | |
| 2 (316, 316L) |
AF | F593E | 1/4 to 1-1/2, incl | 65 to 85 | 20 | B85 max | 60 | 20 | 40 |
| A | F593F | 1/4 to 1-1/2, incl | 75 to 100 | 30 | B65 to 95 | 70 | 30 | 30 | |
| CW1 | F593G | 1/4 to 5/8, incl | 100 to 150 | 65 | B95 to C32 | 95 | 60 | 20 | |
| CW2 | F593H | 3/4 to 1-1/2, incl | 85 to 140 | 45 | B80 to C32 | 80 | 40 | 25 | |
| SH1 | F593E | 1/4 to 5/8, incl | 120 to 160 | 95 | C24 to C36 | 115 | 90 | 12 | |
| SH2 | F593F | 3/4 to 1, incl | 110 to 150 | 75 | C20 to C32 | 105 | 70 | 15 | |
| SH3 | F593G | 1-1/8 to 1-1/4, incl | 100 to 140 | 60 | B95 to C30 | 95 | 55 | 20 | |
| SH4 | F593H | 1-3/8 to 1-1/2, incl | 95 to 130 | 45 | B90 to C28 | 90 | 40 | 28 | |
| 3 (321, 347) |
AF | F593J | 1/4 to 1-1/2, incl | 65 to 85 | 20 | B85 max | 60 | 20 | 40 |
| A | F593K | 1/4 to 1-1/2, incl | 75 to 100 | 30 | B65 to 95 | 70 | 30 | 30 | |
| CW1 | F593L | 1/4 to 5/8, incl | 100 to 150 | 65 | B95 to C32 | 95 | 60 | 20 | |
| CW2 | F593M | 3/4 to 1-1/2, incl | 85 to 140 | 45 | B80 to C32 | 80 | 40 | 25 | |
| SH1 | F593J | 1/4 to 5/8, incl | 120 to 160 | 95 | C24 to C36 | 115 | 90 | 12 | |
| SH2 | F593K | 3/4 to 1, incl | 110 to 150 | 75 | C20 to C32 | 105 | 70 | 15 | |
| SH3 | F593L | 1-1/8 to 1-1/4, incl | 100 to 140 | 60 | B95 to C30 | 95 | 55 | 20 | |
| SH4 | F593M | 1-3/8 to 1-1/2, incl | 95 to 130 | 45 | B90 to C28 | 90 | 40 | 28 | |
| 4 (430, 430F) |
AF | F593X | 1/4 to 1-1/2, incl | 55 to 75 | 30 | B85 max | 50 | 25 | - |
| A | F593N | 1/4 to 1-1/2, incl | 55 to 75 | 30 | B85 max | 50 | 25 | - | |
| CW1 | F593V | 1/4 to 5/8, incl | 60 to 105 | 40 | B75 to 98 | 55 | 35 | - | |
| CW2 | F593W | 3/4 to 1-1/2, incl | 55 to 100 | 30 | B65 to 95 | 50 | 25 | - | |
| 5 (410, 416, 416Se) |
H | F593P | 1/4 to 1-1/2, incl | 110 to 140 | 90 | C20 to 30 | 110 | 90 | 18 |
| HT | F593R | 1/4 to 1-1/2, incl | 160 to 190 | 120 | C34 to 45 | 160 | 120 | 12 | |
| 6 (431) |
H | F593S | 1/4 to 1-1/2, incl | 125 to 150 | 100 | C25 to 32 | 125 | 100 | 15 |
| HT | F593T | 1/4 to 1-1/2, incl | 180 to 220 | 140 | C40 to 48 | 180 | 140 | 10 | |
| 7 (630) |
AH | F593U | 1/4 to 1-1/2, incl | 135 to 170 | 105 | C28 to 38 | 135 | 105 | 16 |
Material Properties
ASTM F593 categorizes stainless steel alloys into seven primary groups based on their chemical composition and metallurgical structure, ranging from common austenitic grades to high-strength precipitation-hardening alloys. These groupings allow for a standardized approach to selecting fasteners that provide the necessary level of general corrosion resistance for specific service environments.
To ensure consistent performance, the specification mandates strict chemical composition limits for key elements like Chromium, Nickel, and Molybdenum. While the choice of a specific alloy within a group is generally at the manufacturer's discretion to accommodate fabrication methods, purchasers can specify an exact alloy number to meet precise engineering requirements.
- Austenitic Alloys (Groups 1–3): Provide excellent corrosion resistance and are often cold-worked to enhance strength.
- Ferritic & Martensitic (Groups 4–6): Selected for specific magnetic or high-hardness requirements through thermal hardening.
- Precipitation Hardening (Group 7): Utilizes Alloy 630 (17-4PH) for applications requiring the highest strength levels through age hardening.
| Alloy Groups | |
|---|---|
| Alloy Group | Alloys |
| 1 | 304, 304 L, 305, 384, XM7A |
| 2 | 316, 316 L |
| 3 | 321, 347 |
| 4 | 430B |
| 5 | 410C |
| 6 | 431 |
| 7 | 630 |
| 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 maxA | ||
| 1 | S30323 | 303 Se | 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 | 304 L | 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 | 0.50 maxA | ||
| 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 | 1.75 to 2.25 | ||
| 1 | S30430 | XM7 | 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 | ||
| 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 to 3.00 | ||
| 2 | S31603 | 316 L | 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 16.0 to 18.0 | 10.0 to 14.0 | 2.00 to 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 × 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 × 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 maxA | |||
| 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 maxA | |||
| 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 | |
| A At manufacturer's option, determined only when intentionally added. | ||||||||||||