AISI 4140 / 4142 chromium-molybdenum alloy steel · Quench-and-tempered
ASTM A320 Grade L7 is a quenched-and-tempered chromium-molybdenum alloy steel bolting grade for low-temperature service; typical compositions include AISI 4140 (UNS G41400), 4142, 4145, 4140H, 4142H, and 4145H. Grade L7 meets a minimum tensile strength of 125 ksi (860 MPa) and yield strength of 105 ksi (725 MPa) for diameters up to 2-1/2 inches. The specification requires Charpy V-notch impact testing at -150°F (-101°C), with a minimum average energy of 20 ft-lbf (27 J), and 15 ft-lbf (20 J) for any single specimen, for full-size 10 × 10 mm specimens. Hardness is limited to 321 HBW or 35 HRC maximum. Grade L7 is equivalent to ASME SA-320 Grade L7 in the ASME Boiler and Pressure Vessel Code, Section II.
| Grade Symbol | Description | C | Mn | P, max | S, max | Si | Cr | Mo | |
|---|---|---|---|---|---|---|---|---|---|
| ASTM A320 L7 | Cr - Mo - B | Range,% | 0.38 - 0.48C | 0.75 - 1.00 | 0.035 | 0.04 | 0.15 - 0.35 | 0.80 - 1.10 | 0.15 - 0.25 |
| Product Variation, % Over or Under | 0.02 | 0.04 | 0.005 over | 0.005 over | 0.02 | 0.05 | 0.02 | ||
| 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 L7 21/2[65] and underA | quenched and tempered | 1100 [593] | 125[860] | 105[725] | 16 | 50 | 321 HBW or 35 HRC |
| 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 L7 | - 150 | - 101 | 10 × 7.5 | 16 [22] | 12 [16] |
| 10 × 10 | 40 [54] | 30 [41] | |||
For low-temperature service consistency, ASTM A320 Grade L7 stud bolts are paired with ASTM A194 Grade 4 or Grade 7 heavy hex nuts (or Grade L43 or L73 nuts, per A320 10.1; all nut material is Charpy tested to A320 and the nuts are marked “L”, per 10.1 and 13.2) and ASTM F436 hardened steel washers. A194 Grade 7 nuts have the same chromium-molybdenum composition limits as A320 Grade L7 and are quenched and tempered at 1100°F [595°C] minimum. TorqBolt supplies kit-matched A320 L7 + A194 Gr 7 + F436 sets with a single EN 10204 3.1 or 3.2 certificate covering all three components.
TorqBolt’s ASTM A320 Grade L7 stud bolt production route is qualified to NORSOK M-650 for North Sea oil & gas offshore service. Each manufacturing record links heat number → melt analysis → quench-and-temper batch → mechanical test → Charpy V-notch curve at -150°F → dimensional inspection → coating → dispatch. Standard certification: EN 10204 Type 3.1 (manufacturer’s test report). On request: Type 3.2 (third-party witnessed by Lloyd’s Register, DNV, BV, ABS, or TUV). The qualification packet covers ASME SA-320 L7 equivalence, NACE MR0175 / ISO 15156-2 for sour-service variants (Grade L7M), API 6A PSL-3/PSL-4, and PED 2014/68/EU for European pressure-equipment buyers.
