4140 Steel properties
4140 is a chromium-molybdenum (chromoly) alloy steel known for its strength, toughness, and deep hardenability. It is one of the most popular alloy steels for shafts, axles, gears, and tooling. Values below are for the quenched-and-tempered condition.
Mechanical properties
| Property | Value |
|---|---|
| Yield strength | 115 ksi (795 MPa) |
| Ultimate tensile strength | 156 ksi (1075 MPa) |
| Elongation | 18% |
| Hardness | 311 HB (Brinell) |
| Modulus of elasticity | 29,700 ksi (205 GPa) |
Physical properties
| Property | Value |
|---|---|
| Density | 0.284 lb/in³ (7850 kg/m³) |
| Melting point | about 1416 °C |
Thermal properties
| Property | Value |
|---|---|
| Thermal conductivity | 42.6 W/m·K |
| Thermal expansion | 12.3 µm/m·°C |
| Specific heat | 473 J/kg·K |
Values are typical for the grade and condition shown. Actual properties vary with temper, heat treatment, and product form, so use these for comparison and preliminary design and confirm against material certificates for final work.
Compare with other materials
See the Material Properties Comparison, Yield Strength, and Density charts.
Typical uses
4140 is used for shafts, axles, spindles, gears, collars, tooling, and high-stress machine parts. Its chromium and molybdenum give deep, uniform hardening, so even thick sections reach full strength, and it is often supplied pre-hardened ready to machine.
How it compares
4140 is far stronger and tougher than plain carbon steels and hardens more deeply thanks to its alloy content. It is the go-to general alloy steel, stronger than 1045 but less hardenable and tough than nickel-bearing 4340, at a lower cost.
FAQ
What is 4140 steel used for?
High-strength machine parts: shafts, axles, gears, spindles, collars, and tooling, especially where heat treatment and deep hardening are needed.
Is 4140 stronger than 1045?
Yes. As an alloy steel it reaches higher strength and hardens more deeply than medium-carbon 1045, particularly in thick sections.
Can 4140 be welded?
It can, but its alloy content needs preheat and post-weld tempering to avoid cracking and to restore properties in the weld zone.