ASTM A320 Grades B8LN and B8MLN (304LN / 316LN Stainless)
Low-carbon, nitrogen-strengthened 304LN and 316LN bolting certified to A320 — weldable without sensitization and stronger than the plain L grades, Class 1 and 1A only.
What A320 B8LN / B8MLN is.
Everything in this grade is the same steel as ASTM A193 B8LN / B8MLN: identical 304LN and 316LN 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.
The LN grades combine the 0.030 percent carbon ceiling of the L grades, which prevents sensitization at welds, with 0.10 to 0.16 percent nitrogen that restores the strength the low carbon would otherwise cost. The result is a solution-treated bolt that meets the same 75 ksi minimum as B8 while staying weld-safe. A320 lists B8LN and B8MLN in Class 1 and 1A only; there is no strain-hardened class. B8LN takes the −425 °F impact exemption and B8MLN the −325 °F exemption.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.030 |
| 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 |
| Nitrogen | N | 0.10 | 0.16 |
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 (B8LNA / B8MLNA) — 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. A320 lists this grade in Class 1 and 1A only.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.030 |
| Manganese | Mn | — | 2.00 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 16.0 | 18.0 |
| Nickel | Ni | 10.0 | 13.0 |
| Molybdenum | Mo | 2.00 | 3.00 |
| Nitrogen | N | 0.10 | 0.16 |
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.
| 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 B8LN / B8MLN 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 B8LN / B8MLN fasteners we make.
Every item is manufactured to your drawing or standard in A320 B8LN / B8MLN, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A320 B8LN / B8MLN?
A320 B8LN and B8MLN are the nitrogen-bearing low-carbon versions of B8 and B8M, certified for low-temperature service. Nitrogen is an austenite former and a potent solid-solution strengthener, so the LN grades reach the standard 30 ksi yield minimum in the annealed condition despite their low carbon, and in practice sit well above it. B8LN (304LN, UNS S30453) is the general-purpose grade; B8MLN (316LN, UNS S31653) adds molybdenum for chlorides. Both are supplied solution treated as Class 1 or, when specified, solution treated in the finished condition as Class 1A (B8LNA / B8MLNA), with A194 Grade 8LN or 8MLN nuts.
Impact testing under A320
- Class 1 and 1A material of this grade is exempt from impact testing above −425 °F (B8LN) / −325 °F (B8MLN). 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 B8LN or B8MLN 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 8LN / 8MLN, impact tested when the service temperature requires it
ASTM A193 Grades B8LN and B8MLN (304LN / 316LN)
304LN and 316LN bolting — low carbon for weld-zone corrosion resistance, nitrogen to recover the strength that low carbon gives away.
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.