Where ASTM fasteners are used
- Pressure and temperature service (flanges, valves, pressure vessels): ASTM A193 studs and bolts with A194 nuts. Low-temperature service: A320.
- Structural steel connections: ASTM F3125 grades A325 and A490 heavy hex bolts, with A563 nuts and F436 washers.
- General purpose: A307 (low carbon), A449 and A354 (quenched and tempered).
- Anchor bolts in foundations: F1554 grades 36, 55 and 105.
ASTM fasteners are in inch sizes; metric versions use an "M" suffix, such as A193M. Strengths are given in ksi (1 ksi = 6.895 MPa).
Raw material and manufacturing process
- Steel bar or wire rodCr-Mo alloy bar (AISI 4140/4142, EN19 type) for B7 and L7; Ni-Cr-Mo (4340) for L43; medium-carbon or boron steel for A325 and A449; alloy steel for A490 and A354 BD; 304 and 316 bar for B8 and B8M.
- Cutting and formingStuds are cut from bar. Heads are hot forged (or cold formed in smaller sizes). Nuts are hot or cold forged, then tapped.
- Heat treatmentAlloy and carbon grades are quenched and tempered above a minimum tempering temperature. Stainless grades are solution treated, and class 2 is then strain hardened.
- ThreadingThreads are rolled or cut to UNC or 8UN (8 threads per inch for studs 1" and up), class 2A/2B.
- TestingHardness on every lot, tensile and proof load, impact tests for A320, PMI for alloy and stainless.
- Coating and markingPlain, hot-dip galvanised (F2329), zinc-nickel or PTFE (Xylan type). Grade and maker's mark stamped on the head or stud end.
Minimum tempering temperatures
| Grade | Steel | Heat treatment | Minimum tempering |
|---|---|---|---|
| A193 B7 | Cr-Mo (4140/4142/4145) | Quench and temper | 1100 °F (593 °C) |
| A193 B7M | Cr-Mo, as B7 | Quench and temper, 100% hardness tested | 1150 °F (620 °C) |
| A193 B16 | Cr-Mo-V | Quench and temper | 1200 °F (650 °C) |
| A320 L7 | Cr-Mo (4140) | Quench and temper, impact tested | 1100 °F (593 °C) |
| A194 2H | Medium carbon | Quench and temper | 1000 °F (538 °C) |
| A194 4, 7 | C-Mo / Cr-Mo alloy | Quench and temper | 1100 °F (593 °C) |
| A194 2HM, 7M | as 2H / 7 | Quench and temper, hardness limited | 1150 °F (620 °C) |
| F3125 A325, A490; A449; A354 | Carbon, boron or alloy | Quench and temper | 800 °F (427 °C) |
| A193 B8, B8M Class 1 | 304, 316 | Carbide solution treated (about 1040 °C, rapid cool) | – |
| A193 B8, B8M Class 2 | 304, 316 | Solution treated, then strain hardened | – |
Chemical composition: A193 and A320 bolting
| Grade | C | Mn | P max | S max | Si | Cr | Ni | Mo | V |
|---|---|---|---|---|---|---|---|---|---|
| B7 / B7M / L7 (4140 type) | 0.37–0.49 | 0.65–1.10 | 0.035 | 0.040 | 0.15–0.35 | 0.75–1.20 | – | 0.15–0.25 | – |
| B16 (Cr-Mo-V) | 0.36–0.47 | 0.45–0.70 | 0.035 | 0.040 | 0.15–0.35 | 0.80–1.15 | – | 0.50–0.65 | 0.25–0.35 |
| L43 (4340 type) | 0.38–0.43 | 0.60–0.85 | 0.035 | 0.040 | 0.15–0.35 | 0.70–0.90 | 1.65–2.00 | 0.20–0.30 | – |
| B8 (304) | 0.08 max | 2.00 max | 0.045 | 0.030 | 1.00 max | 18.0–20.0 | 8.0–11.0 | – | – |
| B8M (316) | 0.08 max | 2.00 max | 0.045 | 0.030 | 1.00 max | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | – |
Product analysis ranges, %. B7M uses the same steel as B7 but is tempered higher and hardness limited for sour (H₂S) service.
Mechanical properties: A193 and A320
| Grade | Size | Tensile min | Yield min | Elongation min | Reduction of area min | Hardness |
|---|---|---|---|---|---|---|
| B7 | up to 2½" | 125 ksi (862 MPa) | 105 ksi (724 MPa) | 16% | 50% | 321 HB / 35 HRC max |
| B7 | over 2½" to 4" | 115 ksi (793 MPa) | 95 ksi (655 MPa) | 16% | 50% | 321 HB max |
| B7 | over 4" to 7" | 100 ksi (690 MPa) | 75 ksi (517 MPa) | 18% | 50% | 321 HB max |
| B7M | up to 4" | 100 ksi (690 MPa) | 80 ksi (552 MPa) | 18% | 50% | 235 HB / 99 HRB max |
| B16 | up to 2½" | 125 ksi (862 MPa) | 105 ksi (724 MPa) | 18% | 50% | 321 HB / 35 HRC max |
| B8 / B8M Class 1 | all sizes | 75 ksi (517 MPa) | 30 ksi (207 MPa) | 30% | 50% | 223 HB / 96 HRB max |
| B8 Class 2 | up to ¾" | 125 ksi (862 MPa) | 100 ksi (690 MPa) | 12% | 35% | 321 HB / 35 HRC max |
| B8M Class 2 | up to ¾" | 110 ksi (758 MPa) | 95 ksi (655 MPa) | 15% | 45% | 321 HB / 35 HRC max |
| L7 | up to 2½" | 125 ksi (862 MPa) | 105 ksi (724 MPa) | 16% | 50% | Charpy 20 ft·lbf (27 J) at −150 °F (−101 °C) |
| L43 | up to 4" | 125 ksi (862 MPa) | 105 ksi (724 MPa) | 16% | 50% | Charpy 20 ft·lbf (27 J) at −150 °F (−101 °C) |
Class 2 strain-hardened strengths fall with increasing diameter; check the size table in the standard for larger studs.
A194 nuts for A193 and A320 bolting
| Grade | Material | Proof stress (heavy hex) | Hardness | Use with |
|---|---|---|---|---|
| 2H | Medium carbon, C 0.40 min, Mn 1.00 max, Q&T | 175 ksi (1207 MPa) | about 248–327 HB (24–35 HRC) | B7, B16 |
| 2HM | as 2H, hardness limited | 150 ksi (1034 MPa) | 159–237 HB | B7M (sour service) |
| 4 | C-Mo steel (C 0.40–0.50, Mo 0.20–0.30), Q&T | 175 ksi | about 248–327 HB | B7, B16, higher temperature |
| 7 | Cr-Mo alloy (4140 type), Q&T | 175 ksi | about 248–327 HB | B7, L7, low temperature |
| 8 | Stainless 304 | 80 ksi (552 MPa) | 126–300 HB | B8 |
| 8M | Stainless 316 | 80 ksi (552 MPa) | 126–300 HB | B8M |
Hardness limits vary slightly by size and edition; take them from the current A194.
Structural bolting: F3125 A325 and A490
ASTM F3125 replaced the separate A325 and A490 standards in 2016. The grade names and head markings stayed the same.
| Grade | Steel (Type 1) | Chemistry (heat, %) | Tensile | Yield min | Elong. / RA min | Hardness |
|---|---|---|---|---|---|---|
| A325 (120 ksi) | Medium carbon, carbon-boron or alloy steel | C 0.30–0.52, Mn 0.60 min, P 0.035, S 0.040, Si 0.15–0.30, B 0.003 max | 120 ksi (827 MPa) min | 92 ksi (634 MPa) | 14% / 35% | 25–34 HRC |
| A490 (150 ksi) | Alloy steel | C 0.30–0.48, P 0.035, S 0.040, B 0.003 max; alloy elements per spec | 150–173 ksi (1034–1193 MPa) | 130 ksi (896 MPa) | 14% / 40% | 33–38 HRC |
Type 3 is a weathering-steel version with added Cu, Cr and Ni (for example A325 Type 3: Cu 0.20–0.60, Ni 0.20 min or Mo 0.10 min, Cr 0.20 min). F1852 and F2280 are the twist-off "tension control" versions of A325 and A490.
- Use A563 grade DH heavy hex nuts (proof 175 ksi, about 24–38 HRC) or A194 2H, and F436 hardened washers (through-hardened, 26–45 HRC).
- A490 must not be hot-dip galvanised or electroplated, because of the hydrogen embrittlement risk at its hardness. A325 may be galvanised, with oversize-tapped galvanised nuts.
General-purpose and anchor bolt grades
| Grade | Steel and treatment | Tensile | Yield / proof | Hardness |
|---|---|---|---|---|
| A307 Gr A | Low carbon (C 0.29 max, Mn 1.20 max), no heat treatment | 60 ksi (414 MPa) min | – | 69–100 HRB |
| A307 Gr B | Low carbon, for cast-iron flanged joints | 60–100 ksi | – | 69–95 HRB |
| A449 | Medium carbon or boron, Q&T, temper ≥800 °F | 120 ksi up to 1"; 105 ksi to 1½"; 90 ksi to 3" | 92 / 81 / 58 ksi yield | 25–34 HRC (to 1") |
| A354 BC | Alloy steel, Q&T | 125 ksi (862 MPa) to 2½" | yield 109 ksi; proof 105 ksi | 26–36 HRC |
| A354 BD | Alloy steel, Q&T | 150 ksi (1034 MPa) to 2½" | yield 130 ksi; proof 120 ksi | 33–39 HRC |
| F1554 Gr 36 | Low carbon, weldable | 58–80 ksi | yield 36 ksi (248 MPa) | – |
| F1554 Gr 55 | Carbon steel (weldable with S1 supplement) | 75–95 ksi | yield 55 ksi (379 MPa) | – |
| F1554 Gr 105 | Alloy steel, Q&T | 125–150 ksi | yield 105 ksi (724 MPa) | – |
Equivalents and substitutions
| ASTM grade | Nearest metric / Indian | Comment |
|---|---|---|
| A193 B7 | ISO 8.8 (strength); EN 10269 42CrMo4 | B7 also guarantees elevated-temperature use and a maximum hardness |
| A194 2H | ISO 898-2 class 10 heavy nut (strength) | Heavy hex pattern, larger across flats than ISO nuts |
| F3125 A325 | ISO 8.8 / IS 3757 8.8S | Different head and thread dimensions; not interchangeable without approval |
| F3125 A490 | ISO 10.9 / IS 3757 10.9S | Same note |
| A193 B8M Class 2 | ISO 3506 A4-70 / A4-80 (approx.) | Strength depends on size |
ASTM bolting in Indian industry
Refineries, petrochemical complexes, fertiliser and power plants across India, including the large refining and chemical belt in Gujarat, use A193 B7 studs with A194 2H nuts as the standard flange bolting. Studs are usually made from 4140 / EN19-type bar, threaded full length, quenched and tempered, and often supplied with PTFE or hot-dip galvanised coating for corrosion protection. Projects normally ask for an EN 10204 3.1 certificate, and often third-party inspection (3.2) and PMI testing. For sour gas service, B7M studs with 2HM nuts (22 HRC maximum) are specified to NACE MR0175 / ISO 15156.
Ordering ASTM bolting. Specify the standard and grade (for example A193 B7 / A194 2H), size and length, thread series (UNC or 8UN), coating and certificate. We supply ASTM studs, bolts and nuts with full test certificates. Send your requirement.
Figures are typical values for guidance. For design, inspection and purchase, always follow the current edition of the standard on your drawing.