ASTM A320 L7 Specfication for Stud bolt
ASTM A320 Grade L7 is a standard material specification for alloy steel bolting materials for pressure vessels, valves, flanges, and fittings for low temperature services. ASTM A320 Grade L7 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.
| Grade | ASTM A320 L7 |
|---|---|
| Corresponding Standard | ASTM A320 Alloy-steel and stainless steel bolting for low-temperature service |
| Classification | Alloy Steel |
A320 L7 Chemical Element Composition Content (%)
| Component | C | Si | Mn | P | S | Cr | Mo |
|---|---|---|---|---|---|---|---|
| Minimum Value | 0.38 | 0.15 | 0.75 | – | – | 0.8 | 0.15 |
| Maximum Value | 0.48 | 0.35 | 1 | 0.035 | 0.04 | 1.1 | 0.25 |
A320 L7 Mechanical Properties
| Heat Treatment or Condition | Tensile Strength σb Mpa |
Yield Point σs Mpa |
Elongation or Extension Rate δ % |
Reduction of Area ψ % |
Hardness HBW |
|---|---|---|---|---|---|
| Quenching and Tempering, Minimum Tempering Temperature 593℃ | ≥860 | ≥725 | ≥16 | ≥50 | HBW ≤321 or HRC ≤35 |
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 | -150 | -101 | 20 [27] | 15 [20] |
| 10 X 7.5 | 16 [22] | 12 [16] | ||
ASTM A320 Recommended Nuts & Washers
| Bolt Grade | Nut Grade | Washer Grade |
|---|---|---|
| ASTM A320 Grade L7 | ASTM A194 Grade 7 | ASTM F436 Type 1 |
| ASTM A320M Grade L7 | ASTM A194M Grade 7 | ASTM F436M Type 1 |
Applications of ASTM A320 Bolts
Cryogenic Storage Tanks – LNG, Liquid Nitrogen, Liquid Oxygen
Petrochemical & Refining – Cold-weather pipelines, reactors
Power Generation – Boilers, turbines, nuclear power plants
Offshore & Marine – Oil rigs, subsea pipelines
Structural Engineering – Bridges, steel frames in cold environments
Available Sizes & Thread Types of ASTM A320
Diameter Range: ¼” to 4” (M6 to M100)
Thread Types: UNC / UNF / 8UN / Metric
Length Options: Custom sizes available
FAQ – ASTM A320 Grade L7 Stud Bolts
1. What is ASTM A320 Grade L7?
ASTM A320 Grade L7 is a high-strength, low-alloy steel used in stud bolts and fasteners designed for low-temperature and cryogenic applications. These bolts are quenched and tempered to improve tensile strength and impact toughness, making them ideal for petrochemical, power generation, and structural applications.
2.What is the heat treatment process for A320 L7?
Quenched & Tempered: The material is heat-treated to improve strength and toughness while maintaining ductility.
3.What is differene between A320 L7 from A320 L7M?
| Property | A320 L7 | A320 L7M |
|---|---|---|
| Strength | Higher | Lower |
| Hardness | Up to 35 HRC | Up to 22 HRC |
| Toughness | Lower | Higher |
| Applications | Structural, general use | H₂S environments (sour gas service) |
L7M is used in sour gas applications (H₂S environments) where lower hardness prevents stress corrosion cracking (SCC).
