ASTM A320 Grade B8 Class 1 (304 Stainless)
304 stainless bolting certified to the low-temperature specification — the same 75 ksi solution-treated material as A193 B8, with A320 impact rules and matching A194 Grade 8 nuts.
What A320 B8 Class 1 is.
Everything in this grade is the same steel as ASTM A193 B8: identical 304 chemistry, the same heat treatment classes and the same room-temperature strength table. What A320 adds is the framework for cold service — impact testing rules, the requirement that nuts come from the matching austenitic A194 grade, and certification to a specification that piping and vessel codes call out for sub-zero design temperatures.
B8 is the workhorse austenitic grade for cryogenic bolting because 304 keeps its toughness to liquid-helium temperatures. Under A320, Class 1 and 1A B8 is exempt from impact testing above −425 °F, which covers LNG, liquid nitrogen and liquid oxygen service without a test program. We manufacture A320 B8 studs and bolts from certified 304 bar and supply them with A194 Grade 8 nuts, dual-certified to A193 on request.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.08 |
| Manganese | Mn | — | 2.00 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 18.0 | 20.0 |
| Nickel | Ni | 8.0 | 11.0 |
Values per ASTM A320/A320M-26, Tables 1 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation in 2 in., min (%) | Reduction of area, min (%) | Hardness, max |
|---|---|---|---|---|---|
| Class 1 — all diameters | 75 | 30 | 30 | 50 | 223 HBW / 96 HRB |
| Class 1A (B8A) — all diameters | 75 | 30 | 30 | 50 | 192 HBW / 90 HRB |
Values per ASTM A320/A320M-26, Tables 1 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Class 1 sizes ¾ in. and smaller may be 241 HBW / 100 HRB. Strain-hardened Class 2 properties are on the A320 B8 Class 2 page.
| Grade and class | Impact test exempt above | Below that temperature |
|---|---|---|
| B8, B8C, B8P, B8LN — Class 1 and 1A | −425 °F (−254 °C) | Impact tested to agreed criteria |
| B8M, B8T, B8F, B8MLN — Class 1 and 1A | −325 °F (−198 °C) | Impact tested to agreed criteria |
| All austenitic grades — Class 2 | −325 °F (−198 °C) | Impact tested to agreed criteria |
| Any grade ½ in. and smaller | Exempt at all temperatures | Unless S1 is specified |
Per ASTM A320/A320M-26 (verified against the specification). When impact tests are required for austenitic grades, the test temperature and acceptance criteria are agreed between purchaser and supplier; Supplementary Requirement S1 may be ordered.
Specifications that apply.
How A320 B8 Class 1 ships from Houston.
- Full-thread studs and stud bolts
- Double-end and tap-end studs
- Hex and heavy hex bolts
- Socket head cap screws
- Threaded rod (cut and rolled thread)
- Machined components from certified bar
A320 B8 Class 1 fasteners we make.
Every item is manufactured to your drawing or standard in A320 B8 Class 1, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A320 B8?
A320 B8 is 304 austenitic stainless steel bolting, carbide solution treated, certified for service below room temperature. 304 has no ductile-to-brittle transition: its face-centred-cubic structure stays tough at −425 °F and below, which is why the specification exempts B8 Class 1 from impact testing above that temperature. The grade carries the full corrosion resistance of 304 and the modest 75 ksi strength of the annealed condition.
Impact testing under A320
- Class 1 and 1A material of this grade is exempt from impact testing above −425 °F. Below that, the test temperature and acceptance values are agreed between purchaser and supplier, or ordered under Supplementary Requirement S1.
- Class 2 (strain hardened) austenitic bolting is exempt above −325 °F.
- Bolting ½ in. and smaller is exempt at all temperatures unless S1 is specified.
- Nuts follow 10.2: matching A194 austenitic grades, with the same exemption temperatures.
Why order to A320 instead of A193?
The mechanical numbers are the same, so the choice comes down to what the design code and the purchaser's specification ask for. ASME B31.3 and Section VIII list SA-320 for bolting below the A193 minimum temperatures, and an A320 certificate carries the impact-test statement, or the exemption under 6.2.1.1, that a low-temperature package needs. Ordering A320 also brings in 10.2, which requires austenitic A194 nuts of the matching grade and states when those nuts must be impact tested. Dual-certified A193/A320 bolting is available on request when a stock item must serve both.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade symbol B8 or B8A and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Impact test results, or the 6.2.1.1 exemption, stated on the certificate
- Nuts from A194 Grade 8, impact tested when the service temperature requires it
Recent A320 B8 Class 1 jobs.
ASTM A320 Grade B8 Class 2 (304 Strain Hardened)
Strain-hardened 304 bolting certified to A320 — 125 ksi tensile in ¾ in. and under, for cryogenic joints that need more bolt strength than annealed stainless.
ASTM A193 / ASME SA-193ASTM A193 Grade B8 Class 1 (304 Stainless)
304 stainless bolting — Class 1 for corrosion resistance and cryogenic-to-1500 °F service, Class 2 strain hardened to 125 ksi for strength.
ASTM A320 / ASME SA-320ASTM A320 Grade B8M Class 1 (316 Stainless)
316 stainless bolting certified to the low-temperature specification — chloride resistance for LNG terminals and coastal cold service, impact exempt above −325 °F.