4140 Alloy Steel

4140 is a widely used chromium-molybdenum alloy steel offering high strength, hardness, toughness, and good wear resistance, together with excellent heat-treatability. Compared with 4130, its higher carbon content allows 4140 to achieve greater strength and hardness, making it suitable for precision mechanical components subjected to high loads, impact, and wear.

Appearance & Properties

Color: Silver-gray to dark gray

Density: Approx. 7.85 g/cm³

Tensile Strength: Approx. 650–1,000+ MPa (depending on heat-treatment condition)

Corrosion Resistance: Poor

Machinability: Good

Weldability: Moderate

Wear Resistance: Good

Magnetism: Magnetic

Heat Treatment: Hardening, tempering, normalizing, etc.

Surface Finishes: Black oxide, phosphating, zinc plating, nickel plating, nitriding, painting, etc.

Typical Applications

4140 Alloy Steel is widely used in automotive, oil and gas, industrial machinery, construction equipment, energy systems, and high-load power transmission applications.

Typical parts include drive shafts, gears, sprockets, spindles, couplings, high-strength bolts, pins, sleeves, hydraulic components, and high-load CNC machined parts.

Advantages

• High strength with good toughness

• Good wear and fatigue resistance

• Excellent heat-treatment capability

• Good CNC machinability

• Suitable for high-load and power transmission components

Limitations

• Poor corrosion resistance and usually requires surface protection

• Lower weldability than 4130

• CNC machining becomes more difficult after hardening

• Improper heat treatment may cause distortion or inconsistent properties