4340 Alloy Steel Bar Suppliers
102 vetted U.S. suppliers · 24 states
4340 is the high-strength nickel-chromium-molybdenum alloy steel for aerospace structural, large machinery shafting, and any application requiring deep hardenability. Below is our live count of vetted U.S. suppliers with state distribution and a one-click RFQ flow.
Geographic distribution
Where these suppliers are
Top 8 states by vetted-supplier density. 27 more across 16 additional states — listed below the chart.
Also covered
North Carolina (5) · Arizona (3) · New Jersey (3) · Connecticut (2) · Georgia (2) · Washington (2) · Virginia (1) · Mississippi (1) · Maryland (1) · Kansas (1) · Massachusetts (1) · Minnesota (1) · Utah (1) · Indiana (1) · New Hampshire (1) · Oklahoma (1)
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What 4340 alloy steel bar is
4340 is a low-alloy steel with chromium, nickel, and molybdenum — designed for very high tensile strength after heat treatment (180-280 ksi achievable depending on temper) with excellent toughness. The nickel content gives it deep hardenability — cross-sections that 4140 can't through-harden, 4340 can. Bar is supplied per AMS 6415 (aerospace) or ASTM A322 (commercial), annealed or quenched-and-tempered. Common downstream uses: aircraft landing gear, gear shafts, large fasteners, drive shafts.
What to look for in a supplier
Aerospace work calls for AMS 6415 with full mill certs traceable to heat. Commercial buyers can spec ASTM A322. Decide on temper: annealed (~217 BHN) for machining-then-heat-treat workflows, normalized for higher as-shipped strength, or Q&T to a specific Brinell range. Vacuum-arc-remelted (VAR) and electroslag-remelted (ESR) variants are available for the cleanest microstructure — important for high-cycle fatigue and aerospace work. Ask about diameter tolerance, surface finish, and whether the supplier can certify to your specific AMS or military spec.
FAQ
Common questions
Is 4340 better than 4140?
Stronger and tougher, but more expensive. The deciding factor is cross-section: 4340 through-hardens deeper than 4140, so for shafts and parts thicker than ~4", 4340 holds its strength to the core. For smaller cross-sections, 4140 is usually adequate and cheaper.
What's AMS 6415?
The aerospace material spec for 4340 bar in annealed or normalized condition. Buyers in aerospace and high-performance applications spec AMS 6415 to ensure consistent chemistry, cleanliness, and traceability. Not every stocking distributor carries AMS-spec bar — confirm before quoting.
What's the difference between 4340 and 300M?
300M is a modified 4340 with higher silicon and slightly higher carbon — used for ultra-high-strength aerospace parts (landing gear, hooks) where 4340's strength ceiling isn't enough. If your print calls for 300M specifically, you can't substitute 4340.
Can 4340 be welded?
Yes with care — pre-heat (250-400°F) and post-weld heat treatment are essential to prevent cracking. Filler choice matters; most welded 4340 work uses matching low-hydrogen filler. Generally avoided in primary structural welds; usually used in machined-and-bolted assemblies.
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