4340 Alloy Steel Bar: AMS6415 Certified
Tailwind Aerospace Solutions stocks 4340 alloy steel bar in both air melt and vacuum arc remelt (VAR) forms for aerospace, defense, oil and gas, and high-performance industrial applications. 4340 is a nickel-chromium-molybdenum low-alloy steel recognized as the workhorse of aircraft-quality alloy steels, delivering ultra-high tensile strength, deep hardenability, and good ductility in the heat-treated condition. Our 4340 inventory is fully certified to the specifications aerospace OEMs and MRO providers call for most.
Properties and Performance
4340 achieves its exceptional mechanical properties from a carefully balanced chemistry of nickel, chromium, molybdenum, and a nominal carbon content of approximately 0.40%. Nickel contributes toughness and impact resistance, chromium improves hardenability and wear resistance, and molybdenum increases strength while reducing the risk of temper brittleness. In the quenched and tempered condition, 4340 can reach ultimate tensile strengths exceeding 260 ksi depending on section size and heat treatment.
The alloy offers good machinability in the annealed condition and responds well to both conventional and induction heat treatment processes. 4340 is weldable, though preheating and post-weld stress relief are recommended to maintain mechanical integrity in the heat-affected zone. Its combination of high strength, fatigue resistance, and through-hardening capability makes it the standard alloy for large cross-section aerospace structural parts.
Available Forms and Specifications
Tailwind supplies 4340 alloy steel bar in normalized and tempered as well as vacuum-melt conditions.
Key specifications include:
- AMS6414: Covers 4340 vacuum arc remelted (VAR) bar and forging stock. The VAR process produces an exceptionally clean steel with superior transverse properties, tighter inclusion control, and improved fatigue performance. AMS6414 is the primary specification for flight-critical landing gear and structural components.
- AMS6415: Covers 4340 air melt bar in the normalized and tempered condition. This specification is widely used for general aerospace and high-performance industrial applications where vacuum melt cleanliness is not required.
- AMS6359: Covers 4340 alloy steel sheet and plate for applications requiring the alloy's high-strength properties in flat product form. Tailwind stocks 4340 sheet and plate for airframe skins, brackets, and structural panels. View our Steel Sheet & Plate inventory.
Browse our full Steel Rod & Bar page for all available alloy steel grades and sizes.
Specifications
| Grade | Condition | Shape | Temper | Size Range | Specifications |
|---|---|---|---|---|---|
| 4340 | Plate | Plate | 0.250” – 6.00” | AMS 6359, DMS 1555, MIL-S-5000 | |
| 4340 | Sheet | 0.016” – 0.190” | AMS 6359, DMS 1555, MIL-S-5000 | ||
| 4340 | Round | 0.25” – 8.0” Diameter | AMS 6414, AMS 6415, AMS 6409, AMS 6484, BMS7-28, MIL-S-5000 | ||
| 4340 | Square/Flat | 0.50” × 0.50” – 4.00” × 8.00” | AMS 6414, AMS 6415, AMS 6409, AMS 6484, BMS7-28, MIL-S-5000 | ||
| 4340 | Hexagon | 0.3125” – 2.50” | AMS 6414, AMS 6415, AMS 6409, AMS 6484, BMS7-28, MIL-S-5000 | ||
| 4340 | Tube | Per drawing or custom profile | AMS 6414, AMS 6415, AMS 6409, AMS 6484, BMS7-28, MIL-S-5000 |
Our Quality Management System is certified to ISO 9001 and AS9100
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Common Applications
4340 alloy steel bar is used in landing gear, flap tracks, actuator components, engine bolting, drive shafts, gears, and other highly stressed structural and power transmission parts. Outside of aerospace, the alloy serves oil and gas downhole tools, automotive crankshafts, and power generation turbine components.
Why Source 4340 from Tailwind Aerospace Solutions?
Our Quality Management System is certified to ISO 9001 and AS9100, and every shipment includes complete mill test reports with full traceability. We supply bar cut to size and offer value-added processing to reduce your lead times. Our team can also help source hard-to-find sizes and conditions through our network of approved mill partners.
Request a quick quote on 4340 alloy steel bar or call us at 888-304-7075.
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