ASTM A320 Grades L7A, L7B and L7C
The three alternative-chemistry versions of L7 — carbon-moly 4037, chrome-moly 4137 and nickel-chrome-moly 8740 — all to L7 strength and −150 °F toughness.
What A320 L7A/B/C is.
ASTM A320 provides three alternatives to Grade L7 that use different alloy steels but meet identical mechanical and impact requirements: L7A is AISI 4037 (carbon-molybdenum), L7B is AISI 4137 (chromium-molybdenum) and L7C is AISI 8740 (nickel-chromium-molybdenum). All three are quenched and tempered to 125 ksi minimum tensile in diameters up to 2½ inches and Charpy tested at −150 °F.
The grades exist so that a manufacturer can meet A320 with the bar stock available; performance in service is equivalent to L7. We supply them to order from certified bar of the specified analysis, with the same heat treat and impact test regime as L7.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.35 | 0.40 |
| Manganese | Mn | 0.70 | 0.90 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Molybdenum | Mo | 0.20 | 0.30 |
Values per ASTM A320/A320M-26, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation in 2 in., min (%) | Reduction of area, min (%) | Hardness, max |
|---|---|---|---|---|---|
| L7A, L7B, L7C — 2½ and under | 125 | 105 | 16 | 50 | 321 HBW / 35 HRC |
Values per ASTM A320/A320M-26, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.35 | 0.40 |
| Manganese | Mn | 0.70 | 0.90 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Chromium | Cr | 0.80 | 1.10 |
| Molybdenum | Mo | 0.15 | 0.25 |
Values per ASTM A320/A320M-26, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.38 | 0.43 |
| Manganese | Mn | 0.75 | 1.00 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Nickel | Ni | 0.40 | 0.70 |
| Chromium | Cr | 0.40 | 0.60 |
| Molybdenum | Mo | 0.20 | 0.30 |
Values per ASTM A320/A320M-26, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
| Grade | Test temperature | Specimen | Energy, average of three (ft·lbf) | Energy, single specimen min (ft·lbf) |
|---|---|---|---|---|
| L7A / L7B / L7C | −150 °F (−101 °C) | 10 × 10 mm | 20 | 15 |
| L7A / L7B / L7C | −150 °F (−101 °C) | 10 × 7.5 mm | 16 | 12 |
Values per ASTM A320/A320M-26, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How A320 L7A/B/C ships from Houston.
- Full-thread studs and stud bolts
- Double-end and tap-end studs
- Hex and heavy hex bolts
- Socket head cap screws
- Threaded rod (cut and rolled thread)
- Machined components from certified bar
A320 L7A/B/C fasteners we make.
Every item is manufactured to your drawing or standard in A320 L7A/B/C, imperial or metric, with an EN 10204 3.1 certificate.
What are L7A, L7B and L7C?
Grade L7 is defined around the 4140 family. A320 recognises that other medium-carbon alloy steels can be heat treated to the same properties and lists three of them as separate grades with their own chemistry tables: 4037, a plain carbon-molybdenum steel (L7A); 4137, a chromium-molybdenum steel with slightly less carbon than 4140 (L7B); and 8740, a triple-alloy nickel-chromium-molybdenum steel (L7C). All three carry the same strength, hardness cap, tempering minimum and −150 °F Charpy requirement as L7, and all are listed to 2½ inches diameter in Table 1, a limit the specification notes is not absolute.
Does the letter matter to the buyer?
Rarely. The grades are interchangeable in service and are marked with their own symbol so the material is traceable. Most purchase orders simply call for L7; a manufacturer can offer L7A, L7B or L7C when that is what is available, provided the order or the piping specification allows it. If a drawing names one of the letters specifically, we supply that analysis.
Testing, certification and marking
- Tensile and hardness tested per heat-treat lot on the finished product
- Grade symbol L7A, L7B or L7C and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Charpy V-notch impact tested per heat-treat lot at −150 °F
ASTM A320 Grade L7
The low-temperature twin of B7 — same 4140 Cr-Mo steel, same 125 ksi strength, but impact tested at −150 °F for cryogenic and cold-climate service.
ASTM A320 / ASME SA-320ASTM A320 Grade L43
4340 low-temperature bolting — L7 strength in diameters up to 4 in., thanks to the deep hardenability of a nickel-chrome-moly steel.
ASTM A194 / ASME SA-194ASTM A194 Grade 7
The Cr-Mo heavy hex nut — same 4140 steel as a B7 stud, rated for elevated temperature and the usual match for B16 and L7.