ASTM A320 Grade L1
A boron-treated low-carbon steel for small low-temperature bolting — L7 strength in sizes to 1 in. with twice the impact energy requirement.
What A320 L1 is.
ASTM A320 Grade L1 is a low-carbon boron steel, the only grade in the specification that is not a medium-carbon alloy steel. Boron gives the 0.17 to 0.24 percent carbon steel enough hardenability to be quenched and tempered to 125 ksi tensile in diameters up to 1 inch, while the low carbon makes it exceptionally tough: A320 requires 40 ft·lbf average at −100 °F, double the energy asked of the L7 grades.
L1 is used for small bolting on cold service where notch toughness matters more than large-section strength. We supply it to order from certified bar.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.17 | 0.24 |
| Manganese | Mn | 0.70 | 1.40 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.050 |
| Silicon | Si | 0.15 | 0.30 |
| Boron | B | 0.001 | 0.003 |
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 |
|---|---|---|---|---|---|
| 1 and under | 125 | 105 | 16 | 50 | Not specified |
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. No minimum tempering temperature or hardness maximum is specified for L1.
| Grade | Test temperature | Specimen | Energy, average of three (ft·lbf) | Energy, single specimen min (ft·lbf) |
|---|---|---|---|---|
| L1 | −100 °F (−73 °C) | 10 × 10 mm | 40 | 30 |
| L1 | −100 °F (−73 °C) | 10 × 7.5 mm | 32 | 24 |
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 L1 ships from Houston.
- Full-thread studs
- Hex bolts and cap screws
- Socket head cap screws
- Machined components from certified bar
A320 L1 fasteners we make.
Every item is manufactured to your drawing or standard in A320 L1, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A320 L1?
L1 is the boron-steel grade of A320. Boron in the range of 0.001 to 0.003 percent multiplies the hardenability of a low-carbon steel, so a 0.2 percent carbon composition can be quenched and tempered to the same 125 ksi tensile and 105 ksi yield as L7, but only in sections up to 1 inch. The reward for the low carbon is toughness: A320 Table 2 requires 40 ft·lbf average and 30 ft·lbf minimum single specimen at −100 °F, compared with 20 and 15 for the L7 family.
Where it fits
L1 is a niche grade. It suits small bolting on cold service where a specification demands high impact energy, and it is occasionally called out on instrument and valve hardware. For anything over 1 inch, or for −150 °F service, use L7 or L43.
Testing, certification and marking
- Tensile, hardness and Charpy V-notch impact tested per heat-treat lot
- Grade symbol L1 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 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.
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.