4140 Steel

AISI 4140 is a versatile chromium-molybdenum alloy steel known for its exceptional toughness, high fatigue strength, and good abrasion resistance. It is often referred to as "Chromoly" steel. Its primary advantage is its ability to be through-hardened or surface-hardened to achieve a wide range of mechanical properties. At Jucheng Precision, we frequently machine 4140 in its Pre-Hardened (Condition L) state to provide our clients with high-strength components that require no further heat treatment. It is the premier choice for high-stress applications like automotive axles, industrial gears, and oilfield tools where durability and impact resistance are non-negotiable.

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4140 Alloy Steel

4140 Steel Machining Capabilities

Capability Technical Description Jucheng Advantage
Pre-Hardened Machining 4140 is often supplied in a pre-hardened state (28-32 HRC). We use high-performance coated carbide tools to machine finished parts directly. Eliminates the risk of heat-treat distortion, ensuring your high-strength shafts and gears fit perfectly without secondary grinding.
High-Torque 4-Axis Milling Milling complex splines, keyways, and bolt patterns into tough alloy steel billets. Our rigid Haas/Mazak machines handle the high cutting forces of 4140 with ease, maintaining tight tolerances (+/- 0.01mm) on structural hubs.
Surface Nitriding Prep Machining parts with precise surface finishes to prepare for gas or plasma nitriding to achieve 60+ HRC surface hardness. We manage the complete workflow, providing 4140 parts that are tough in the core but extremely wear-resistant on the surface.
Cylindrical Grinding Achieving Ra 0.4μm finishes on 4140 bearing surfaces post-heat treatment. Essential for precision axles and spindles where concentricity and surface smoothness are critical for service life.

Fabrication Guidelines for 4140 Alloy Steel

Condition Selection:
4140 is available in Annealed (easier to machine) or Pre-Hardened (ready to use). Tip: If your part needs extreme strength, machine in annealed state, then quench and temper.

Machinability:
4140 has good machinability for an alloy steel (approx. 65% of 1212). It produces stable chips. Tip: We use high-pressure coolant to manage the heat generated by the Chromium and Molybdenum content.

Weldability:
4140 can be welded, but it requires careful pre-heating and post-weld heat treatment to prevent cracking in the heat-affected zone. Tip: Avoid welding pre-hardened 4140 if possible.

Nitriding Advantage:
This alloy is excellent for nitriding. It allows for a very hard surface without the extreme distortion caused by traditional through-hardening.

Primary Applications

Automotive Drivetrain
Axle shafts, crankshafts, steering knuckles, and transmission gears requiring high fatigue strength.

Oil & Gas Industry
Downhole tool bodies, drill collars, and high-pressure valves that must withstand shock and abrasion.

Industrial Fasteners
Grade 8.8 and 10.9 high-strength bolts, studs, and heavy-duty nuts for infrastructure and machinery.

Tooling Components
Ejector pins, mold bases, and holder blocks that require more toughness than standard carbon steel.

Properties

Density 7.85 g/cm³
Tensile Strength 850 - 1000+ MPa
Yield Strength 650 - 900 MPa
Hardness 28 - 32 HRC
Elongation at Break 12 - 20%
Thermal Conductivity 42.6 W/m-K
Fatigue Strength High
Machinability Rating 65%
Weldability Fair
Corrosion Resistance Poor
Max Part Size 2000 x 800 x 600 mm