ASTM A320 Grade L7B is a standard material specification for alloy steel bolting materials for pressure vessels, valves, flanges, and fittings for low temperature services. ASTM A320 Grade L7B is heat treated chromium molybdenum alloy steel (AISI 4140/AISI 4140H) with 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.
| Element | Composition, % A |
|---|---|
| Chromium - Molybdenum (AISI 4137) |
|
| Carbon, max | 0.35 - 0.40 |
| Manganese | 0.70 - 0.90 |
| Phosphorus, max | 0.035 |
| Sulfur, max | 0.040 |
| Silicon | 0.015 - 0.35 |
| Chromium | 0.80 - 1.10 |
| Molybdenum | 0.15 - 0.25 |
Notes :
A The intentional addition of Bi, Se, Te, and Pb is not permitted except for Grade B8F, in which selenium is specified and required.
B Typical steel compositions used for this grade include 4140, 4142, 4145, 4140H, 4142H, and 4145H.
C For the L7B grade, a minimum carbon content of 0.28 % is permitted provided that the required tensile properties are met in the section sizes involved; the use of
AISI 4130 or 4130H is allowed.
| Diameter, in. [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 | |||||
| 2 1/2 [65] and under A | 125 [860] | 105 [725] | 16 | 50 | 321 | 35 |
Heat Treatment : Quenched and Tempered at 1100°F [593°C] minimum.
| 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 |
|---|---|---|