Steel 4340 Plate Prices

About 4340|When 4140 isn't strong enough. The addition of 1.65-2.00% nickel on top of the chromium and molybdenum gives 4340 significantly better toughness, impact resistance, and hardenability, especially in thick cross-sections. This is aircraft landing gear steel, heavy-duty crankshaft steel, drill collar steel. At the same hardness as 4140, the two have similar tensile strength, but 4340 retains far more toughness and fracture resistance. The nickel makes it through-harden more uniformly in large sections where 4140 would go soft in the core. Harder to machine than 4140 (about 55-60% machinability vs 65% for 4140). Costs roughly double. Use 4340 when you need the toughness or the section size demands it. Otherwise 4140 does the job for less money. Compare to 4140 (cheaper, easier to machine, adequate for smaller sections) and 4330V (vacuum-melt aerospace variant).

About Plate|Thick flat stock, generally 3/16" and up, used for machined base plates, fixture plates, wear surfaces, and structural fabrication. Heavier grades get milled, drilled, and tapped directly.