4340 Alloy Round Metal Bar
AISI 4340 round steel (UNS G43400) is an ultra-high strength medium carbon low alloy steel that combines deep hardenability, high ductility, toughness and strength, and has high fatigue resistance and creep resistance. It is not affected by tempering and embrittlement, shows good strength retention at high temperatures, and is not easy to soften. In thin sections, this steel is air hardened. In practice, it is usually oil quenched.
4340 alloy round bar chemical composition
| Carbon | 0.38-0.43 |
| Manganese | 0.60-0.80 |
| Phosphorus (max) | 0.035 |
| Sulfur (max) | 0.040 |
| Silicon | 0.15-0.35 |
| Nickel | 1.65-2.00 |
| Chromium | 0.70-0.90 |
| Molybdenum | 0.20-0.30 |
4340 round steel mechanical property
| Tensile strength (psi) | 105,000 - 115,000 |
| Yield strength (psi) | 75,000 - 85,000 |
| Elongation in 2" (%) | 20 - 30 |
| Reduction of area (%) | 35 - 45 |
| Brinell Hardness (BHN) | 210 - 240 |
AISI 4340 Welding of Steel
AISI 4340 steel has good weldability. It can be easily gas or arc welded, but electrodes of the same composition should be used. Since 4340 alloy steel is air hardening, welded parts should be annealed or normalized and tempered shortly after welding.
The high hardness of 4340 alloy steel requires the material to be welded in an annealed or tempered state and then heat treated to resist martensite formation and cold cracking. However, as in motor shaft applications, 4340 steel typically uses high preheat in low-hydrogen processes in the quenched and tempered condition. Preheating or interpass heating of the weld metal and heat affected zone is recommended. Hydrogen control is also essential to prevent weld cracking. Extremely clean vacuum-melted steel is the first choice for welding.
aISI 4340 alloy steel round bar product image
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