ASTM A320 Grade B8 Class 1 is a standard material specification for stainless steel bolting materials for pressure vessels, valves, flanges, and fittings for low temperature services. ASTM A320 Grade B8 is heat treated AISI 304 stainless steel with supplementary notch toughness properties. Please find chemical composition, mechanical properties, impact test requirement, and reference standards for product dimensions, threads, coatings and recommended nuts and washers for ASTM A320 Grade B8 Class 1 bolting specification.
Supplementary requirements includes Impact properties and hardness testing of class 2 bolting materials for ASME applications.
| Element | Composition, % A |
|---|---|
| Chromium Molybdenum B | |
| Carbon, max | 0.08 |
| Manganese, max | 2.00 |
| Phosphorus, max | 0.045 |
| Sulfur, max | 0.030 |
| Silicon, max | 1.00 |
| Nickel | 8.00 - 11.00 |
| Chromium | 18.00 - 20.00 |
Note : The intentional addition of Bi, Se, Te, and Pb is not permitted except for Grade B8F, in which selenium is specified and required.
| Diameter, inch [mm] |
Tensile Strength, min, ksi [MPa] | Yield Strength min, ksi [MPa] (0.2% offset) | Elongation in 2 inch or 50mm, min, % | Reduction of Area, min, % | Hardness, max | |
|---|---|---|---|---|---|---|
| HBW | HRC | |||||
| All Diameters | 75 [515] | 30 [205] | 30 | 50 | 223D | 96 |
Heat Treatment : Carbide solution treated.
Notes :
* Class 1 products are made from solution-treated material. Class 1A products are solution treated in the finished condition for corrosion resistance; heat treatment is critical for enhancing this physical property and meeting the mechanical property requirements. Class 2 products are made from solution-treated material that has been strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the cross section, particularly in sizes over 3⁄4 in. [20 mm] in diameter.
* For sizes 3⁄4 in. [20 mm] in diameter and smaller, a maximum hardness of 241 HB (100 HRB) is permitted.
| 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 | -150 | -101 | 20 [27] | 15 [20] |
| 10 X 7.5 | 16 [22] | 12 [16] | ||
| Bolt Grade | Nut Grade | Washer Grade |
|---|---|---|
| ASTM A320 Grade B8 Class 1 | ASTM A194 Grade 8 (S1) | ASTM A240 TP304 |
| ASTM A320M Grade B8 Class 1 | ASTM A194M Grade 8 (S1) | ASTM A240M TP304 |