Patriot Bolt machines ASTM A320 Grade L43 stud bolts from certified AISI 4340 nickel-chromium-molybdenum bar for large-diameter flanges in low-temperature service. The nickel addition lets 4340 harden deeply, so L43 keeps 125 ksi minimum tensile strength in diameters up to 4 in while passing Charpy impact tests at −150 °F.
We make L43 studs to your purchase order or drawing and supply impact-tested A194 Grade 7 nuts. Every order ships with mill test reports and impact test results traceable to the heat.
A320 L43 Stud Bolts at a Glance
- Specification
- ASTM A320 / ASME SA320 Grade L43
- Material
- AISI 4340 Ni-Cr-Mo steel (UNS G43400), quenched and tempered
- Strength
- 125 ksi min tensile, 105 ksi min yield (4 in and under)
- Hardness
- 321 HBW / 35 HRC max
- Impact test
- Charpy V-notch at −150 °F, 20 ft-lb average
- Matching nut
- A194 Grade 7 (7L) heavy hex
Why Engineers Specify A320 L43 Stud Bolts
In large diameters, 4140 steel cannot harden fully through the core, so L7 is limited to 2-1/2 in. L43 solves that.
- Deep hardening. About 1.65 to 2.00 percent nickel lets 4340 reach full strength through thick sections.
- Full strength to 4 in. 125 ksi minimum tensile and 105 ksi minimum yield in every size up to 4 in.
- Low-temperature toughness. Each lot is Charpy tested at −150 °F.
- Matched nuts. Pair with impact-tested A194 Grade 7 nuts marked 7L.
A320 L43 Stud Bolt Specifications
A320 sets one set of L43 properties up to 4 in diameter.
| Diameter | Tensile, min | Yield (0.2%), min | Elongation, min | Reduction of area, min | Charpy test |
|---|---|---|---|---|---|
| 4 in and under | 125 ksi | 105 ksi | 16% | 50% | −150 °F, 20 ft-lb avg / 15 ft-lb single |
Maximum hardness is 321 HBW (35 HRC).
A320 L43 Chemical Composition
| Element | Weight % |
|---|---|
| Carbon | 0.38–0.43 |
| Manganese | 0.60–0.85 |
| Phosphorus | 0.035 max |
| Sulfur | 0.040 max |
| Silicon | 0.15–0.35 |
| Nickel | 1.65–2.00 |
| Chromium | 0.70–0.90 |
| Molybdenum | 0.20–0.30 |
Limits per the current edition of the specification. The mill test report for your heat is the controlling document.
Stud Configurations
- Fully threaded studs, threaded end to end, for flange bolting where grip length varies.
- Double-end studs, threaded on both ends with an unthreaded center.
- Tap-end studs, with one end made to thread into a tapped hole.
Applications and Industries
- LNG and cryogenic: Large-diameter flanges on liquefaction, storage and export equipment. See Oil & Gas.
- Petrochemical: Cold-box, ethylene and heat exchanger bolting. See Petrochemical & Refining.
- Heavy valves and pumps: Bonnet and casing studs in low-temperature service.
Certification and Traceability
Patriot Bolt is ISO 9001:2015 certified. Each L43 order includes mill test reports traceable to the heat, along with a certificate of conformance to the specification on your purchase order.
Studs are marked with the grade symbol and our identification, as the specification requires.
L43 certifications include the Charpy impact results for the lot.
Compare L43 with other bolting grades in our Fastener Materials Matrix.
A320 L43 Stud Bolts FAQ
When should I use L43 instead of L7?
Use L43 when the stud diameter is over 2-1/2 in, or when the design calls for deeper hardenability. Both grades are impact tested at −150 °F.
Is L43 the same as 4340?
L43 is made from AISI 4340 steel, quenched and tempered and impact tested to the A320 requirements.
Which nut goes with L43?
ASTM A194 Grade 7 nuts impact tested per A320 and marked 7L.
Can you make large-diameter L43 studs?
Yes. We machine L43 studs up to the 4 in limit of the grade, in any length and thread, from your drawing or purchase order.
Request a Quote
Send us the stud configuration, diameter, length, thread, specification and quantity, or upload your drawing. Our team will confirm the material and lead time. Call (281) 581-0176 or request a quote.
Also in L43: A320 L43 fasteners hub · A194 Grade 7 heavy hex nuts · L7 stud bolts · All stud bolts