ASTM A320 B8M Class 1 specifcation for Stud bolt
ASTM A320 is a standard material specification for alloy steel bolting materials for pressure vessels, valves, flanges, and fittings for low temperature services. ASTM A320 Grade B8M is heat treated stainless steel (AISI 316L) with notch toughness properties. We would like to introduce the chemical composition, mechanical properties, impact test requirement, and reference standards for product dimensions, threads, coatings and recommended nuts and washers.
| Grade | A320 B8M Class 1 |
|---|---|
| USA UNS | S31600 |
| Other Names | |
| Corresponding Standard | ASTM A320 Alloy-steel and stainless steel bolting for low-temperature service |
| Classification | Stainless steel |
A320 B8M Class 1 Chemical Element Composition Content (%)
| Component | C | Si | Mn | P | S | Cr | Ni | Mo |
|---|---|---|---|---|---|---|---|---|
| Minimum Value | – | – | – | – | – | 16 | 10 | 2 |
| Maximum Value | 0.08 | 1 | 2 | 0.045 | 0.03 | 18 | 14 | 3 |
A320 B8M Class 1 Mechanical Properties
A320 B8M Class 1 Heat Treatment: Carbide Solution Treated in the Finished Condition
| Heat Treatment or Condition | Tensile Strength σb Mpa |
Yield Point σs Mpa |
Elongation or Extension Rate δ % |
Reduction of Area ψ % |
Hardness HBW |
|---|---|---|---|---|---|
| Carbide Solid Solution Treatment | ≥515 | ≥205 | ≥30 | ≥50 | ≤223 |
ASTM A320 B8M Class 1 Equivalent grade
| China | Japan | United States | International Organization for Standardization | European Standard | ||||
| GB | ISC | JIS | ASTM/AISI | UNS | ISO | Numerical Grade | EN | Numerical Grade |
| 06Cr17Ni12Mo2 (0Cr17Ni12Mo2) |
S31608 | SUS316 | 316 | S31600 | X5CrNiMo17-12-2 | 4401-316-00-I | X5CrNiMo17-12-2 | 1.4401 |
ASTM A320 Impact Test Requirements (Notch Toughness)
| Size of Specimen, mm | Test Temperature | Minimum impact value required for average of each set of three specimens, ft-lbf [J] | Minimum impact value permitted for one specimen only of a set, ft-lbf [J] | |
|---|---|---|---|---|
| °F | °C | |||
| 10 X 10 | 20 [27] | 15 [20] | ||
| 10 X 7.5 | 16 [22] | 12 [16] | ||
ASTM A320 B8M Class 1 Stud Bolt – Specification & FAQ
1. What is ASTM A320 B8M Class 1?
ASTM A320 B8M Class 1 stud bolts are low-temperature stainless steel fasteners made from AISI 316 / 316L stainless steel. These bolts offer excellent corrosion resistance, particularly in marine, chemical, and cryogenic environments.
🔹 Common Applications:
✔ Cryogenic & Low-Temperature Services
✔ Marine & Offshore Structures
✔ Chemical & Petrochemical Processing
✔ Food & Pharmaceutical Industries
2,What coatings are available for ASTM A320 B8M Class 1 Stud Bolts?
B8M is naturally corrosion-resistant, coatings are generally not required, but optional finishes include:
PTFE (Teflon) Xylan Coating – Provides low friction and chemical resistance
3. What are the standard sizes for ASTM A320 B8M Class 1 Stud Bolts?
Diameter Range: ¼” to 2½” (M6 to M64)
Thread Type: UNC, UNF, 8UN, Metric
Length: As per ASME B18.31.2 (studs) and ASME B18.2.1 (hex bolts)
4 .The difference between ASTM A320 B8M Class 1 and Class 2 Stud Bolt
| Property | A320 B8M Class 1 | A320 B8M Class 2 |
|---|---|---|
| Tensile Strength | 75 ksi (515 MPa) min | 125 ksi (860 MPa) min |
| Yield Strength (0.2% offset) | 30 ksi (205 MPa) min | 100 ksi (690 MPa) min |
| Elongation | 30% min | 15% min |
| Hardness | 223 HB max (96 HRB max) | 321 HB max (35 HRC max) |
🔹 Class 2 has significantly higher strength and hardness due to cold working.
🔹 Class 1 is softer but offers better corrosion resistance.
5. How to order ASTM A320 B8M Class 1 Stud Bolts?
To get the right B8M Class 1 stud bolts, provide the following details:
Size & Diameter – Example: M24 x 200mm
Thread Type – UNC, UNF, 8UN, Metric
Length & Finish – Plain, passivated, PTFE-coated
