What is 4140 Steel: Definition, Applications, Properties


4140 alloy steel is a chromium-molybdenum alloy steel that is widely used in many industrial applications due to its combination of high strength, toughness, and fatigue resistance. 4140 alloy steel is a versatile high-strength steel with an excellent combination of strength, toughness, and fatigue resistance after heat treatment. This makes it an ideal choice for many critical components and high-stress applications.

What Is 4140 Alloy Steel Used For?

Here are some of the most common uses and applications of 4140 alloy steel:

Typical Heat Treatment Processes Used for 4140 Alloy Steel

-Done by heating the steel to 1650°F (900°C) and then air cooling.

-Refines the grain structure and improves machinability and uniformity.

-Heating to about 1550°F (845°C), soaking, and slow cooling in the furnace.

-Produces a fine pearlitic structure and maximum softness and ductility.

-Heating to 1100-1200°F (595-650°C), soaking, and slow cooling.

-Removes stresses from prior cold working to prevent potential distortion or cracking.

-Austenitizing at 1500-1525°F (815-830°C), followed by quenching in oil or water.

-Produces a martensitic structure with high hardness and strength.

-Reheating quenched steel to 1100-1200°F (595-650°C) and holding for 1-3 hours.

-Decreases brittleness and increases toughness and ductility. Multiple tempering stages may be applied.

What Are the Properties of 4140 Alloy Steel?

Carbon (C)0.38% – 0.43%
Chromium (Cr)0.8% – 1.1%
Molybdenum (Mo)0.15% – 0.25%
Manganese (Mn)0.75% – 1.0%
Silicon (Si)0.15% – 0.30%
Sulfur (S)≤ 0.040%
Phosphorus (P)≤ 0.035%
Tensile Strength830 – 1000 MPa
Yield Strength≥ 655 MPa
Reduction of Area≥ 50%
Hardness217 – 255 HB
Normalizing1650°F (900°C), air cool
Annealing1500°F (650°C), slow furnace cool
Hardening1500-1525°F (815-830°C), oil quench
Tempering1100-1200°F (595-650°C)
WeldabilityWelds well using manual and automatic methods. Preheating may be required.
Machinability65-95% of 1% carbon steel