4140 Alloy Steel Bar for Shafts, Gears and Heavy-Duty Mechanical Parts

When buyers choose 4140 steel bar, they are usually looking for more than basic machinability. The main reason for selecting 4140 is its ability to achieve higher strength through heat treatment while maintaining good toughness.

In actual purchasing projects, 4140 is commonly used for transmission shafts, gears, bolts, spindles, hydraulic components, and mining equipment parts. Compared with ordinary carbon steel grades, it offers better wear resistance and higher load-bearing capacity, making it a popular choice for demanding mechanical applications.

Product Specifications

Item	Details
Standard	ASTM A29 / SAE 4140
Equivalent Grades	EN19, 42CrMo4, SCM440
Supply Condition	Hot Rolled, Annealed, QT (Quenched & Tempered)
Diameter Range	20 mm – 800 mm
Length	3 m – 12 m
Surface	Black, Peeled, Turned, Ground
Processing Service	Cutting, Rough Machining, Heat Treatment
Payment Terms	T/T, L/C

Item	Typical Value
Carbon (C)	0.38 – 0.43%
Chromium (Cr)	0.80 – 1.10%
Molybdenum (Mo)	0.15 – 0.25%
Manganese (Mn)	0.75 – 1.00%
Tensile Strength	850 – 1000 MPa
Yield Strength	≥ 655 MPa
Elongation	≥ 12%
Hardness	28 – 32 HRC

Why Many Engineering Buyers Choose 4140

Excellent Response to Heat Treatment

One of the biggest advantages of 4140 is its hardenability. After quenching and tempering, the material can achieve significantly higher strength than standard carbon steels, making it suitable for parts subjected to repeated loading.

Better Wear Resistance for Moving Components

For shafts, gears, couplings, and hydraulic rods, surface wear is often a concern. The chromium and molybdenum content in 4140 helps improve wear resistance compared with low-carbon grades.

Suitable for Large-Diameter Parts

Many machine builders use 4140 for heavy-section components because it maintains mechanical properties more effectively after heat treatment than ordinary carbon steel.

Reduced Risk of Premature Failure

In applications involving torque, impact, or cyclic stress, 4140 provides a good balance of strength and toughness, helping extend component service life.