General Information about 4140 Round Bar and 4140 Steel Bar

4140 round bar is an alloy steel that contains measurable amounts of carbon, molybdenum, silicon, phosphorus, sulfur, chromium and manganese. These elements are added in order to achieve specific properties.

4140 round bar may be supplied in an annealed or prehardened condition. The carbon content helps to make the steel capable of being heat treated. The chromium, manganese and molybdenum add toughness and strength.

By normalizing 4140 round bar, it helps to remove stress within the steel. By annealing 4140 steel bar, it makes the material softer and easier to machine. 4140 round bar may be supplied as hot rolled, cold drawn, rough turned or turned and polished. A typical length for 4140 round bar is 20′, although many mills have the capacity to roll a variety of lengths depending on the diameter and application. It is also available in a wide range of diameters.


4140 steel bar responds well to heat treatment, is relatively easy to machine in the annealed condition, and is used in a wide variety of machined parts.  With its moderately simple composition, strength and toughness, 4140 steel bar is used in a variety of machined applications such as gears, bolts and fasteners.


4140 steel bar consists of carbon, .37/.43, manganese, .75/1.00, phosphorus, .035 (max.), sulfur, .04 (max.), silicon, .15/.35, chromium, .80/1.10 and molybdenum, .15/.25.  Other elements, such as phosphorous and sulfur are found in small amounts and are considered to be impurities.

The overall composition of 4140 round bar makes it difficult to machine.