ASTM 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.
What A320 L43 is.
ASTM A320 Grade L43 is the nickel-chromium-molybdenum member of A320, made from AISI 4340. Nickel gives 4340 much deeper hardenability than the 4140 used for L7, so L43 meets the same 125 ksi tensile and 105 ksi yield in diameters up to 4 inches, where L7 stops at 2½.
Every lot is Charpy impact tested at −150 °F. L43 is the grade for large low-temperature flange studs, cryogenic exchanger bolting and heavy valve bonnets in LNG and ethylene plants. We machine it from certified 4340 bar, heat treat after threading and impact test each lot.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.38 | 0.43 |
| Manganese | Mn | 0.60 | 0.85 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Nickel | Ni | 1.65 | 2.00 |
| Chromium | Cr | 0.70 | 0.90 |
| 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 |
|---|---|---|---|---|---|
| 4 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.
| Grade | Test temperature | Specimen | Energy, average of three (ft·lbf) | Energy, single specimen min (ft·lbf) |
|---|---|---|---|---|
| L43 | −150 °F (−101 °C) | 10 × 10 mm | 20 | 15 |
| L43 | −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 L43 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 L43 fasteners we make.
Every item is manufactured to your drawing or standard in A320 L43, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A320 L43?
L43 is A320's 4340 grade. The 1.65 to 2.00 percent nickel in 4340, together with chromium and molybdenum, lets the steel harden through much larger sections than 4140, so a 4 inch L43 stud can be quenched and tempered to the same properties a 2½ inch L7 stud reaches. The specification requires the same 125 ksi tensile, 105 ksi yield, 35 HRC hardness cap and −150 °F Charpy test as L7.
When to use L43 instead of L7
For diameters up to 2½ inches, L7 is the economical choice and is more commonly stocked. Above 2½ inches A320 does not list L7, so L43 is the grade for large low-temperature studs. Some purchasers also specify L43 in smaller sizes where the extra toughness margin of a nickel steel is wanted.
Nuts
A320 lists ASTM A194 Grade 7 nuts, or nuts made from A320 L43 or L73, for L43, impact tested as A320 clauses 1.4 and 10.1 require and marked 7L.
Testing, certification and marking
- Tensile and hardness tested per heat-treat lot on the finished product
- Grade symbol L43 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
Recent A320 L43 jobs.
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 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.