SAE 4140 steel can be used in a ready-made semi-hardened (quenched + tempered) state. Its hardness is in the range of 28-32 HRc. It is a material known as tempering steel in the industry, which can be used in hydraulic cylinder shafts, gears, and machine parts working under high tensile strength thanks to its high tensile strength.
4140 is a medium-carbon (nominal 0.40%C) chromium-molybdenum alloy steel that is most often oil quenched to attain an as-quenched hardness ranging from about 54-59 HRC (as quenched), depending on the precise carbon content (which affects the hardenability of the material).
Applications of Grade 4140 Quench +Tempered
Medium-high stressed 4140 shafts and components where the use of carbon steel 1045 would not be appropriate. Reasons for using 4140 are the higher yield and fatigue strength, better through hardening of the material and superior impact properties compared to plain carbon steels like 1045. These advantages are only achieved when 4140 is used in the heat-treated condition. Typical components include transmission shafts, cylinder piston rods , spindles and small gears, threaded fasteners such as bolts, nuts and studs.