Alloy Steel 4340

Alloy Steel 4340 belongs to the AISI 4000 series of steels, a heat-treatable, low-alloy steel with high strength and toughness.

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Carbon steel machined ring part isolated on white

G43400
1.6511
36CrNiMo4
EN24
817M40

690-1080 MPa

Ultimate Tensile Strength
470-630 MPa

Yield Strength
205-213 GPa

Young's Modulus(Elasticity)
15-22 %

Elongation at Break

At a Glance

Material Type
Metal
Material Name
Alloy Steel 4340
Alternative Names
G43400 | 1.6511 | 36CrNiMo4 | EN24 | 817M40 | AISI 4340
Process Compatibility
CNC Milling, CNC Turning

Properties Table of Alloy Steel 4340

Properties

Ultimate Tensile Strength 690-1080 MPa
Yield Strength 470-630 MPa
Young's Modulus(Elasticity) 205-213 GPa
Elongation at Break 15-22 %
Physical Properties
Corrosion Resistance Moderate to Poor
Magnetism Semi-Magnetic
UV Resistance Excellent
Weldability Moderate
Thermal Properties
Maximum Service Temperature 613-652°C
Thermal Expansion Coefficient 11.5-13 x 10^-6/°C
Thermal Conductivity 35-50W/(m·K)
Electrical Properties
Electrical Resistivity 18-27 μΩ*cm

Applications of Alloy Steel 4340

Aircraft landing gear components
Automotive crankshafts and connecting rods
Oil and gas drilling equipment
Power generation turbine shafts and gears
Heavy machinery axles and shafts
Automotive transmission gears and axles
Tool and die making molds and dies
Marine propeller shafts

Advantages of Alloy Steel 4340

Exhibits high tensile strength
Good toughness and impact resistance, even at lower temperatures
Good ductility
Good wear resistance
Balanced combination of properties for various applications
Relatively machinable with appropriate tooling and techniques
Responds well to heat treatment for optimizing mechanical properties
Weldable with proper procedures and precautions

Raw Stock

CNC Machined

Finished Parts

Alloy Steel 4340 — Machining Notes

Alloy Steel 4340 in CNC
is Alloy Steel 4340?

Alloy Steel 4340 in CNC Machining

Alloy Steel 4340 belongs to the AISI 4000 series of steels, a heat-treatable, low-alloy steel with high strength and toughness.

The machinability of Alloy Steel 4340 depends on its heat treatment condition. In its annealed state, it machines relatively easily. However, when heat-treated for increased strength, it becomes more challenging to machine. It is common to machine the material in the annealed state and then heat-treat it to achieve the desired mechanical properties. It can achieve high strength through heat treatment while maintaining toughness, wear resistance, fatigue strength, atmospheric corrosion resistance, and overall strength.

Due to its toughness, cutting tools with high-speed steel or carbide inserts are commonly used. We use coolant during machining to dissipate heat and improve tool life. Lubrication helps reduce friction and extend tool life. It cannot be anodized, but we can do other post-processing treatments, such as tempering and annealing. We can also do surface finishing for a smoother surface.

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What is Alloy Steel 4340?

4340 steel is a strong, durable steel with medium carbon and low alloy content. It has exceptional strength, ductility, toughness, creep resistance, and fatigue resistance compared to many other types of steel.

The hardness of 4340 steel can range from 24 to 53 HRC, depending on the applied heat treatment. In terms of chemical composition, it contains a minimum of 95.10% iron, 1.65% nickel, 0.7% chromium, 0.65% manganese, 0.38% carbon, 0.15% silicon, and 0.2% molybdenum, with slight variations within defined maximum limits.

This steel is widely used in various applications, including heavy shafting, fasteners, aircraft, automotive, and hydraulic systems.

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FAQ

Is 4340 steel wear resistant?

Yes, Steel 4340 is wear-resistant and has excellent resistance to abrasion, shock, and impact. It also shows impressive atmospheric corrosion resistance.

Can 4340 steel be hardened?

Yes, 4340 steel is easily hardenable. It can be heat-treated to achieve high levels of hardness and strength. The most common method for hardening 4340 steel involves heating it to a specific temperature range and then quenching it in oil. This process helps enhance its mechanical properties.

What is stronger 4130 or 4340 steel?

4340 steel is stronger than 4130 steel. When normalized, 4340 has a tensile strength of about 110,000 lbs, higher than 4130 or 4140. Additionally, 4340 can be heat-treated in thick sections, a capability that 4130 and 4140 lack.

Is 4340 steel weldable?

Yes, but it requires careful attention during the welding process. Preheating and post-weld heat treatment are often recommended to avoid issues like cracking and to ensure the desired mechanical properties in the welded joints. Proper welding procedures and expertise are essential when working with 4340 steel to maintain its integrity and performance.