AISI 4140 Steel (UNS G41400)


4140 alloy steel is a medium carbon, chromium-molybdenum, through-hardening alloy steel that has a good hardenability with high strength and toughness as well as good fatigue and impact resistance after heat treating.  It can be readily nitrided for improved surface wear.  For best machining, it is often used in the annealed condition; however, when the amount of machining necessary is minimal or when the risk of distortion in heat treating a finished part is paramount, it is typically used in the quenched and tempered condition.  Typical applications for 4140 bar are sprockets, bolts, chain pins, drill collars, universal joints, highly stressed parts or parts subject to severe wear.

Chemical Composition

Chemical Composition (wt%) limits of AISI 4140 per ASTM A29*

Carbon 0.38-0.43 Molybdenum 0.15-0.25
Manganese 0.75-1.00 Phosphorus 0.035
Silicon 0.15-0.35 Sulfur 0.040
Chromium 0.80-1.10    

*Maximum, unless range is indicated

Physical Properties

Physical properties for AISI 4140 Steel

Density, lb/in3 0.284
Modulus of Elasticity, psi 29 x 106
Coefficient of Thermal Expansion, 68-212˚F, /˚F 6.83 x 10-6
Thermal Conductivity, Btu/ft hr ˚F 30.0
Specific Heat, Btu/lb ˚F 0.114
Electrical Resistivity, Microhm-in 6.42


Typical standards for AISI 4140 Steel