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ASTM A320/A320M Grade L7A Carbon-Molybdenum Bolting
Low Temperature Fasteners - AISI 4037 Alloy Steel Specification
ASTM A320/A320M Grade L7A is a carbon-molybdenum alloy steel bolting material specifically developed for low temperature pressure equipment applications. With a carbon content of 0.35-0.40% and molybdenum addition of 0.20-0.30%, L7A achieves optimal balance between strength and weldability. ASTM A320/A320M Grade L7A undergoes mandatory quenching and tempering to deliver 125 ksi tensile and 105 ksi yield strength with excellent notch toughness at -150°F test temperature.
ASTM A320/A320M Grade L7A Stud Bolts Properties
ASTM A320/A320M Grade L7A Stud Bolts Chemical Requirements
Ferritic Steels
| Grade Symbol | Description | C | Mn | P, max | S, max | Si | Mo | |
|---|---|---|---|---|---|---|---|---|
| ASTM A320 L7A | C - Mo (AISI 4037) | Range,% | 0.38 - 0.48 | 0.70 - 0.90 | 0.035 | 0.04 | 0.15 - 0.35 | 0.20- 0.30 |
| Product Variation, % Over or Under | 0.02 | 0.03 | 0.005 over | 0.005 over | 0.02 | 0.02 | ||
ASTM A320/A320M Grade L7A Stud Bolts Mechanical Requirements
Ferritic Steels
| Class and Grade, Diameter, in. [mm] | Heat Treatment | Minimum Tempering Temperature, °F [°C] | Tensile Strength, min, ksi [MPa] | Yield Strength, min, ksi [MPa] (0.2 % offset) | Elongation in 2 in. or 50 mm, min, % | Reduction of Area, min, % | Hardness, max |
|---|---|---|---|---|---|---|---|
| ASTM A320 L7A 21/2 [65] and underA | quenched and tempered | 1100 [593] | 125[860] | 105[725] | 16 | 50 | 321 HBW or 35 HRC |
ASTM A320/A320M Impact Test Requirements
| Grade | Test Temperature | CVN Specimen Section Size, mm | Min Average Impact Toughness of Three Test Specimens, ft-lbf [J] | Min Impact Value of a Single Specimen of Set of Three, ft-lbf [J] | |
|---|---|---|---|---|---|
| °F | °C | ||||
| ASTM A320 L7A | - 150 | - 101 | 10 × 7.5 | 16 [22] | 12 [16] |
| 10 × 10 | 40 [54] | 30 [41] | |||
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