ASTM A320 Grades L70, L71, L72 and L73
Same steels and strength as L7, L7A, L7B and L7C, but Charpy tested at −100 °F — the economical A320 grades when the design temperature does not go all the way to −150 °F.
What A320 L70–L73 is.
ASTM A320 Grades L70, L71, L72 and L73 use the same four alloy steels as L7, L7A, L7B and L7C (chromium-molybdenum 4140, carbon-molybdenum 4037, chromium-molybdenum 4137 and nickel-chromium-molybdenum 8740) and are heat treated to the same 125 ksi minimum tensile strength. The difference is the impact test: 20 ft·lbf average at −100 °F rather than −150 °F.
They give the buyer a spec-compliant low-temperature grade for refrigeration, cold-climate and moderately cryogenic service without paying for the −150 °F qualification. We supply them to order from certified bar of the specified analysis.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.38 | 0.48 |
| Manganese | Mn | 0.75 | 1.00 |
| 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.
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 |
|---|---|---|---|---|---|
| L70, L71, L72, L73 — 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 |
| 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.
| 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) |
|---|---|---|---|---|
| L70 / L71 / L72 / L73 | −100 °F (−73 °C) | 10 × 10 mm | 20 | 15 |
| L70 / L71 / L72 / L73 | −100 °F (−73 °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 L70–L73 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 L70–L73 fasteners we make.
Every item is manufactured to your drawing or standard in A320 L70–L73, imperial or metric, with an EN 10204 3.1 certificate.
What are ASTM A320 L70 through L73?
A320 pairs each of its four L7-family steels with a second grade symbol that carries a −100 °F impact test instead of −150 °F: L70 is the 4140 steel of L7, L71 the 4037 of L7A, L72 the 4137 of L7B and L73 the 8740 of L7C. Chemistry, heat treatment, 125 ksi tensile, 105 ksi yield and the 35 HRC hardness cap are identical to the L7 grades; only Table 2 of the specification differs, with the same 20 ft·lbf average and 15 ft·lbf single-specimen minimum applied at −100 °F.
When to specify them
Use the L70 series when the piping specification or design minimum temperature sits between −20 °F and −100 °F, which covers most refrigeration, LPG and cold-climate services. If the design temperature is lower, or the specification simply says L7, order L7. The L70 grades cannot be substituted for L7 without the purchaser's agreement, because their impact qualification is at a warmer temperature.
Testing, certification and marking
- Tensile, hardness and Charpy V-notch impact tested per heat-treat lot
- Grade symbol L70, L71, L72 or L73 and manufacturer's identification on every piece
- EN 10204 3.1 material test report with impact values and test temperature; 3.2 witness available
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 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.
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.