American Iron and Steel Institute (AISI 4140) is a member of the low alloy tool steel family characterized by small quantities of trace elements added to an otherwise simple steel. These trace elements, when compared with more simple steel such as 1040, improves the characteristics of 4140 . However, because 4140 remains relatively simple, it is used in a wider range of applications than more specialized tool steels like the D or S series of steel.
AISI 4140 has enough carbon present to allow for adequate heat treatment. Recommended hardening procedures are to bring the steel up to 1,675 degrees Fahrenheit for normalization (removal of stress within the steel). After it cools properly, heat the steel to 1,550 degrees Fahrenheit before quenching it in oil. The toughness of the steel makes machining in its hardened form difficult. However, after annealing the steel at 1,600 degrees followed by a slow cooling, the steel is much softer and far easier to machine. It can then be heat-treated after machining to produce a hard, precise item.
Chemical Composition（%）of AISI 4140
Mechanical Properties of AISI 4140
|Condition||Hardened & Tempered|
|0.2% Proof Stress||80KSI min|
|Reduction of Area||40% min|
The lower cost due to simple chemistry coupled with the physical properties also makes it a good choice for axles, shafts and structural components. However, since the steel has a lower carbon content than other steels, it doesn’t harden to the same degree. This makes hard, sharp edges, such as those found in knives, difficult.
Since AISI 4140 is a moderately simple steel with a high degree of toughness and tensile strength, it is useful for machined applications such as gears, bolts and fasteners.
One of the most popular alloys for Oil Field applications, a high proportion of which is in Tubular form for downhole tools and accessories.