General Information about 4340 Steel Round Bar

4340 steel, or AISI 4340 (American Iron and Steel Institute), is a heat treatable, low alloy steel that contains nickel, chromium and molybdenum. As such, is often called AISI 4340 nickel-chromium-molybdenum steel.

4340 steel round bar is known for its toughness and ability to achieve high strength in the heat treated condition. 4340 steel has a good combination of ductility, toughness and strength along with high hardenability. 4340 bar stock is often supplied in a hardened and tempered condition. It offers a good balance of strength and toughness. Machinability of 4340 steel round bar is better in the annealed or normalized condition.  Tempering may be done to restore some of the ductility after heat treatment and quench. As far a forming, 4340 steel has good ductility in the annealed condition and most forming operations are done in that condition.

A typical length for 4340 bar stock is 20′, although many mills have the capacity to roll a variety of lengths depending on the application. 4340 steel round bar is also supplied in a wide range of diameters. 4340 steel may also be supplied in wire rod form, with a typical package weighing around 4,000#.


4340 bar stock may be forged as well as used in hot and cold working applications. Some typical applications for 4340 steel round bar are gears, spindles, pins, studs, bolts, couplings, sprockets, torsion bars and crow bars.


4340 bar stock consists of carbon, .38/.43, manganese, .60/.80, phosphorus, .035 (max.), sulfur, .04 (max.), silicon, .15/.35, nickel, 1.65/2.00, chromium, .70/.90 and molybdenum, .20/.30.