What is ASTM F593?
ASTM F593 is the standard specification for stainless steel bolts, hex cap screws and stud bolts covering nominal diameters from ¼ inch to 1½ inch. It is the go-to specification for any application requiring general corrosion resistance combined with defined mechanical strength.
The standard covers seven alloy groups — twelve austenitic, two ferritic, four martensitic, and one precipitation-hardening stainless steel each available in multiple supply conditions (cold-worked, annealed, strain-hardened, or age-hardened). Mating nuts are covered under companion specification ASTM F594, and the ASME equivalent designation is ASME SF593, used interchangeably under boiler and pressure vessel codes.
Jade Alloys manufactures ASTM F593 bolts in all seven alloy groups with full EN 10204 Type 3.1 material test reports, chemical and mechanical certification, and PMI testing on request. Stock items ship within 3–5 working days; custom lengths and special conditions are available on lead time.
ASTM F593 Alloy Groups Complete Guide
Understanding the seven alloy groups is essential for correct material selection. Each group has unique chemical composition, corrosion performance, and mechanical properties.
Alloy Group Selection Guide
| Application Requirement | Recommended Group | Alloy(s) | Key Advantage |
|---|---|---|---|
| General corrosion resistance, indoor / mild environment | Group 1 | 304, 304L | Cost-effective, widely available |
| Marine, coastal, chloride exposure, seawater | Group 2 | 316, 316L | Molybdenum for pitting resistance |
| Elevated temperature, sensitisation risk, post-weld | Group 3 | 321, 347 | Stabilised — no carbide precipitation |
| Mildly corrosive, magnetic required, low cost | Group 4 | 430 | Ferritic — lower cost than austenitic |
| High strength, moderate corrosion, hardened joints | Group 5 | 410 | Hardenable, good wear resistance |
| High strength + better corrosion than Group 5 | Group 6 | 431 | Nickel addition improves corrosion |
| Highest strength stainless, aerospace, oil & gas | Group 7 | 630 (17-4 PH) | 150–170 ksi tensile, age-hardened |
Chemical Composition — ASTM F593
Chemical requirements vary by alloy within each group. All values are weight percentages (maximum unless noted).
Austenitic Groups 1, 2 & 3 — Key Alloys
| Group | Alloy | UNS | C max | Cr % | Ni % | Mo % | Si max | Mn max |
|---|---|---|---|---|---|---|---|---|
| 1 | 304 | S30400 | 0.08 | 18.0–20.0 | 8.0–10.5 | — | 1.00 | 2.00 |
| 1 | 304L | S30403 | 0.03 | 18.0–20.0 | 8.0–12.0 | — | 1.00 | 2.00 |
| 1 | 302HQ | S30430 | 0.03 | 17.0–19.0 | 8.0–10.0 | — | 1.00 | 2.00 |
| 2 | 316 | S31600 | 0.08 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | 1.00 | 2.00 |
| 2 | 316L | S31603 | 0.03 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | 1.00 | 2.00 |
| 3 | 321 | S32100 | 0.08 | 17.0–19.0 | 9.0–12.0 | — | 1.00 | 2.00 |
| 3 | 347 | S34700 | 0.08 | 17.0–19.0 | 9.0–13.0 | — | 1.00 | 2.00 |
Ferritic, Martensitic & Precipitation Hardening Groups 4–7
| Group | Alloy | UNS | C max | Cr % | Ni % | Special Element |
|---|---|---|---|---|---|---|
| 4 | 430 | S43000 | 0.12 | 16.0–18.0 | — | — |
| 5 | 410 | S41000 | 0.15 | 11.5–13.5 | — | — |
| 6 | 431 | S43100 | 0.20 | 15.0–17.0 | 1.25–2.50 | — |
| 7 | 630 | S17400 | 0.07 | 15.0–17.5 | 3.0–5.0 | Cb+Ta: 0.15–0.45 |
Mechanical Properties — ASTM F593
Mechanical requirements depend on alloy group, supply condition, and diameter. Values listed are minimums unless a range is shown.
Groups 1, 2 & 3 — Austenitic Alloys
| Condition | Marking | Diameter (in) | Tensile (ksi) | Yield min (ksi) | Hardness |
|---|---|---|---|---|---|
| AF – Annealed & Re-annealed | F593A/E/J | ¼ to 1½ | 65–85 | 20 | B85 max |
| A – Annealed Stock | F593B/F/K | ¼ to 1½ | 75–100 | 30 | B65–95 |
| CW1 – Cold Worked | F593C/G/L | ¼ to 5/8 | 100–150 | 65 | B95–C32 |
| CW2 – Cold Worked | F593D/H/M | ¾ to 1½ | 85–140 | 45 | B80–C32 |
| SH1 – Strain Hardened | F593A/E/J | ¼ to 5/8 | 120–160 | 95 | C24–C36 |
| SH2 – Strain Hardened | F593B/F/K | ¾ to 1 | 110–150 | 75 | C20–C32 |
| SH3 – Strain Hardened | F593C/G/L | 1⅛ to 1¼ | 100–140 | 60 | B95–C30 |
| SH4 – Strain Hardened | F593D/H/M | 1⅜ to 1½ | 95–130 | 45 | B90–C28 |
Groups 5 & 6 — Martensitic
| Group | Condition | Marking | Diameter (in) | Tensile (ksi) | Yield min (ksi) | Hardness |
|---|---|---|---|---|---|---|
| 5 (410) | H – Hardened & Tempered (1050°F min) | F593P | ¼ to 1½ | 85–110 | 60 | B95–C32 |
| 5 (410) | HT – Hardened & Tempered (525°F min) | F593Q | ¼ to 1½ | 140–170 | 120 | C32–C40 |
| 6 (431) | H – Hardened & Tempered (1050°F min) | F593R | ¼ to 1½ | 100–130 | 80 | B96–C33 |
Group 7 — Precipitation Hardening 630 (17-4 PH)
| Condition | Marking | Diameter (in) | Tensile (ksi) | Yield min (ksi) | Elongation (%) |
|---|---|---|---|---|---|
| AH – Age Hardened | F593S | ¼ to ½ | 150–170 | 130 | 14 min |
| AH – Age Hardened | F593S | 9/16 to 1 | 145–165 | 120 | 14 min |
| AH – Age Hardened | F593S | 1⅛ to 1½ | 140–160 | 110 | 16 min |
Supply Conditions Explained
ASTM F593 defines multiple supply conditions, each producing different strength levels from the same base alloy.
ASTM F593 Bolt Marking Codes
Every ASTM F593 bolt must be marked with a manufacturer’s identification symbol and a marking code indicating alloy group and condition.
Some codes (e.g., F593A, F593B) are shared between CW and SH conditions within the same alloy group. The condition must be determined from the material test report. Jade Alloys clearly states the condition on all MTRs.
Specification & Available Product Forms
Jade Alloys supplies ASTM F593 stainless steel fasteners in all standard product forms, dimensioned to ASME B18.2.1, ASME B18.3, and ASME B16.5 / B16.11.
| Parameter | Detail |
|---|---|
| Standard | ASTM F593 / ASME SF593 |
| Diameter Range (ASTM) | ¼ inch to 1½ inch |
| Metric Equivalent | M6 to M39 (ASTM F738M) |
| Thread Types | UNC (coarse), UNF (fine), metric, BSW, BSF on request |
| Dimensional Standards | ASME B18.2.1 (hex bolts), ASME B18.3 (socket screws), ASME B18.31.2 (stud bolts) |
| Certification | EN 10204 Type 3.1 MTC standard; Type 3.2 available |
| Additional Testing | PMI, hardness, IGC, salt spray on request |
| Mating Nuts | ASTM F594 (same alloy group required) |
| Coatings Available | Passivation (ASTM A380), PTFE, black oxide |
Product Forms Available
Dimension Chart of ASTM F593 Hex Bolts & Stud Bolts
Standard dimensions per ASME B18.2.1 for inch-series hex cap screws. All values in inches.
Hex Cap Screw Dimensions — Inch Series (ASME B18.2.1)
| Nominal Size | TPI (UNC) | Width Across Flats (in) | Head Height (in) | Thread Length ≤6″ (in) | Thread Length >6″ (in) |
|---|---|---|---|---|---|
| 1/4 | 20 | 7/16 | 11/64 | 3/4 | 1 |
| 5/16 | 18 | 1/2 | 7/32 | 7/8 | 1-1/8 |
| 3/8 | 16 | 9/16 | 1/4 | 1 | 1-1/4 |
| 7/16 | 14 | 5/8 | 19/64 | 1-1/8 | 1-3/8 |
| 1/2 | 13 | 3/4 | 11/32 | 1-1/4 | 1-1/2 |
| 5/8 | 11 | 15/16 | 27/64 | 1-1/2 | 1-3/4 |
| 3/4 | 10 | 1-1/8 | 1/2 | 1-3/4 | 2 |
| 7/8 | 9 | 1-5/16 | 37/64 | 2 | 2-1/4 |
| 1 | 8 | 1-1/2 | 43/64 | 2-1/4 | 2-1/2 |
| 1-1/4 | 7 | 1-7/8 | 27/32 | 2-3/4 | 3 |
| 1-1/2 | 6 | 2-1/4 | 1 | 3-1/4 | 3-1/2 |
Stud Bolt Dimensions — Common Flange Applications (ASME B16.5)
| Flange Size (NPS) | Class 150 Bolt Dia × Length | Class 300 Bolt Dia × Length | Class 600 Bolt Dia × Length | Qty (150#) |
|---|---|---|---|---|
| 1/2 | ½″ × 2-1/2″ | ½″ × 3″ | ½″ × 3-1/4″ | 4 |
| 1 | ½″ × 3″ | 5/8″ × 3-1/4″ | 3/4″ × 3-3/4″ | 4 |
| 2 | 5/8″ × 3-1/4″ | 3/4″ × 4″ | 7/8″ × 4-3/4″ | 4 |
| 4 | 5/8″ × 3-3/4″ | 7/8″ × 4-3/4″ | 1-1/8″ × 6″ | 8 |
| 6 | 3/4″ × 4″ | 1″ × 5-1/4″ | 1-1/4″ × 7″ | 12 |
| 8 | 3/4″ × 4-1/4″ | 1-1/8″ × 5-3/4″ | 1-3/8″ × 7-3/4″ | 12 |
| 10 | 7/8″ × 4-1/2″ | 1-1/4″ × 6-1/4″ | 1-1/2″ × 8-3/4″ | 16 |
Galling Prevention for ASTM F593 Stainless Bolts
Galling (cold welding / thread seizure) is one of the most common problems with stainless steel fasteners. Austenitic stainless steels (Groups 1–3) are particularly prone because the hard oxide film breaks down under the heat and pressure of assembly.
Recommended Mating Hardware (ASTM F594 Nuts)
The alloy group of the nut must match the bolt group to prevent galvanic corrosion. Mismatched groups are a leading cause of premature joint failure.
| Bolt Group (F593) | Required Nut (F594) | Alloy | Why It Matters |
|---|---|---|---|
| Group 1 (304 family) | F594 Group 1 | 304, 304L | Same family — no galvanic potential |
| Group 2 (316 family) | F594 Group 2 | 316, 316L | Molybdenum match critical in marine |
| Group 3 (321/347) | F594 Group 3 | 321, 347 | Stabilised alloy consistency |
| Group 4 (430) | F594 Group 4 | 430 | Ferritic pairing prevents galling |
| Group 5 (410) | F594 Group 5 | 410 | Hardened nut matches hardened bolt |
| Group 6 (431) | F594 Group 6 | 431 | Consistent strength and corrosion |
| Group 7 (630) | F594 Group 7 | 630 (17-4 PH) | Age-hardened nut required |
Recommended Torque Values — ASTM F593 Bolts
Torque values for ASTM F593 stainless bolts are significantly lower than for alloy steel bolts of the same size. Values below assume clean, dry threads; reduce by 30–40% with lubrication.
| Bolt Size | Thread | Group 1–3 (304/316) CW — Torque (ft-lb) | Group 7 (630) AH — Torque (ft-lb) |
|---|---|---|---|
| 1/4 | 20 UNC | 6–8 | 8–11 |
| 5/16 | 18 UNC | 12–16 | 16–20 |
| 3/8 | 16 UNC | 22–28 | 28–36 |
| 1/2 | 13 UNC | 54–68 | 70–88 |
| 5/8 | 11 UNC | 105–130 | 140–175 |
| 3/4 | 10 UNC | 185–230 | 240–300 |
| 1 | 8 UNC | 435–545 | 565–710 |
| 1-1/4 | 7 UNC | 880–1100 | 1140–1425 |
| 1-1/2 | 6 UNC | 1530–1910 | 1980–2480 |
International Grade Equivalents
ASTM F593 alloys correspond to widely recognised international standards. Specify the exact standard and grade — do not assume equivalence without a chemical cross-check.
Industries & Applications of ASTM F593 Bolts
ASTM F593 stainless steel bolts are the specification of choice wherever corrosion resistance, hygienic surfaces, or aesthetic finish is required alongside defined mechanical strength.
Application-Specific Grade Recommendations
| Industry / Environment | Recommended F593 Group | Reason |
|---|---|---|
| Offshore platforms, seawater cooling | Group 2 (316L) | Mo content resists chloride pitting |
| Food processing, dairy, brewing | Group 2 (316L) | Low carbon, smooth surface, crevice resistance |
| Exhaust systems, hot gas ducting | Group 3 (321/347) | Stabilised — no sensitisation on cycling |
| Gate valves, pumps, mild corrosion | Group 1 (304) | Cost-effective, good general corrosion |
| Structural fasteners, high-strength joints | Group 7 (630 / 17-4 PH) | 150+ ksi tensile with corrosion resistance |
| Decorative architecture, handrails | Group 1 (304) — AF condition | Best surface finish; fully annealed |
Frequently Asked Questions - ASTM F593 Bolts
What is ASTM F593?
ASTM F593 is the standard specification for stainless steel bolts, hex cap screws, and stud bolts covering ¼″ to 1½″ nominal diameter. It defines seven alloy groups, multiple supply conditions, and mechanical requirements. The ASME version is ASME SF593, used for pressure vessel and piping applications.
What are the seven alloy groups in ASTM F593?
Group 1: 304, 304L, 305 (austenitic, general purpose). Group 2: 316, 316L (austenitic, molybdenum-bearing, marine). Group 3: 321, 347 (austenitic, stabilised, high temperature). Group 4: 430 (ferritic). Group 5: 410, 416 (martensitic, hardenable). Group 6: 431 (martensitic, higher nickel). Group 7: 630 / 17-4 PH (precipitation hardening, highest strength).
What does "F593C bolt" mean?
The marking "F593C" identifies a Group 1 austenitic alloy (304 family) bolt in cold-worked CW1 condition, ¼″ to 5/8″ diameter. Full-size tensile strength is 100–150 ksi, minimum yield 65 ksi, hardness B95 to C32. The same code can also indicate SH3 (strain-hardened) condition for larger diameters — the MTR confirms which condition applies.
What is the difference between ASTM F593 and ASTM A193?
ASTM F593 covers stainless steel fasteners for corrosion-resistance applications in smaller diameters (¼″–1½″). ASTM A193 covers high-strength bolting for elevated-temperature and high-pressure service — mainly alloy steel grades (B7, B16) but also stainless grades (B8 = 304, B8M = 316). For sustained temperatures above 500°F or flanges above Class 600, A193 is typically specified.
Why do stainless steel bolts seize (gall) and how can it be prevented?
Austenitic stainless steels are prone to galling because the protective oxide film breaks down under thread engagement friction. Prevention: (1) apply MoS₂ or PTFE anti-seize to threads, (2) specify AF or A condition rather than CW, (3) reduce installation speed, (4) use a martensitic nut (F594 Group 5) on an austenitic bolt when design allows.
What nuts should be used with ASTM F593 bolts?
ASTM F594 nuts are required, from the same alloy group as the bolt. Using nuts from a different alloy group creates a galvanic couple that accelerates corrosion of the less noble metal. The nut must also have a minimum proof stress equal to or greater than the bolt's full-size tensile strength.
Does Jade Alloys supply custom lengths and non-standard configurations?
Yes. Jade Alloys manufactures ASTM F593 bolts to custom lengths, special head configurations, non-standard thread forms (BSPP, BSPT, metric), and special finishes. Custom orders typically carry a 3–6 week lead time. Contact sales@jadealloys.com with your drawings or specifications.
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