ASTM A320 Grade B8P (305 Stainless)
305 stainless bolting certified to A320 — the high-nickel 18-8 that stays non-magnetic and ductile after cold forming, impact exempt above −425 °F.
What A320 B8P is.
Everything in this grade is the same steel as ASTM A193 B8P: identical 305 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.
B8P uses 305, an 18-8 with 11 to 13 percent nickel. The extra nickel makes the austenite more stable, so the alloy work-hardens less and stays non-magnetic when cold headed or rolled. It is ordered where fasteners are cold formed in quantity, or where a low magnetic permeability matters in a cold assembly. A320 gives B8P the −425 °F impact exemption of the 304 group.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.12 |
| Manganese | Mn | — | 2.00 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 17.0 | 19.0 |
| Nickel | Ni | 11.0 | 13.0 |
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 (B8PA) — all diameters | 75 | 30 | 30 | 50 | 192 HBW / 90 HRB |
| Class 2 — ¾ and under | 125 | 100 | 12 | 35 | 321 HBW / 35 HRC |
| Class 2 — over ¾ to 1 | 115 | 80 | 15 | 35 | 321 HBW / 35 HRC |
| Class 2 — over 1 to 1¼ | 105 | 65 | 20 | 35 | 321 HBW / 35 HRC |
| Class 2 — over 1¼ to 1½ | 100 | 50 | 28 | 45 | 321 HBW / 35 HRC |
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. Class 2 is limited to 1½ in. Strain-hardened austenitic steel may not show uniform properties through the section, particularly over ¾ in. diameter.
| 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 B8P 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 B8P fasteners we make.
Every item is manufactured to your drawing or standard in A320 B8P, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A320 B8P?
A320 B8P is 305 austenitic stainless bolting certified for low-temperature service. 305 differs from 304 in carrying more nickel and allowing slightly more carbon; the effect is a very stable austenite that resists transformation to martensite under cold work. That makes B8P the preferred grade for cold-headed stainless bolts and for equipment where the bolting must remain non-magnetic, such as instrumentation and MRI-adjacent cold systems. It is available in Class 1, Class 1A (B8PA) and Class 2 (B8PSH), with A194 Grade 8 nuts.
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 B8P (B8PSH for Class 2) 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
ASTM A193 Grade B8P Class 1 (305 Stainless)
305 stainless bolting — the low-work-hardening 18-8 for cold-headed and deep-formed fasteners that must stay non-magnetic.
ASTM A320 / ASME SA-320ASTM 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.
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.