Knowledge

Steel C45 and 40Cr are two commonly used medium carbon steels that are widely applied in mechanical manufacturing. However, there are significant differences in their chemical composition, properties, and applicable scenarios. The following is a detailed comparison:

 

1. Chemical composition comparison

Material	Carbon(C) Content	Main Alloy Elements	Other Elements
C45	0.42 - 0.50 %	None	Si, Mn
40Cr	0.37 - 0.44 %	Cr 0.8 - 1.1 %	Si, Mn & microelements of Ph and Su

 

Key differences:

40Cr, due to the addition of chromium, is an alloy structural steel, while C45 steel is a common carbon steel.

The addition of chromium significantly enhances the hardenability, strength, and corrosion resistance of 40Cr.

 

2. Mechanical property comparison

Index	C45 (Annealing / QT)	40Cr (QT)
Tensile Strength	600 - 800 MPa	800 - 1000 MPa
Yield Strength	355 MPa (Normalizing)	≥785 MPa(QT)
Hardness	HRC 18 - 25 (Normalizing)	HRC 25-32 (QT)
Impact	Low	High (Cr improve toughness)

 

Conclusion:

40Cr has higher strength and hardness, making it particularly suitable for parts that bear heavy loads or impact loads. C45 steel is less costly, but its overall performance is relatively weaker.

 

3. Heat Treatment Processes

C45 Steel:

Normalizing: Improves machinability (hardness HB ≤ 197).

Quenching and tempering (quenching + high-temperature tempering): Hardness HRC 20-30, used for general structural components.

Surface quenching: Enhances wear resistance (e.g., on gear surfaces).

 

40Cr:

Quenching and tempering (quenching + high-temperature tempering) is the core process, achieving a balance between high strength and toughness.

High-frequency quenching: Used for surface hardening (e.g., on shaft parts).

Difference: Due to the better quenchability of chromium in 40Cr, it is suitable for uniform quenching of large cross-section parts.

 

4. Typical Application Scenarios

Material	Application for Spare Parts	Application for Industry
C45	Ordinary Shaft,Gear, Connecting rod,Bolts and the parts with ordinary loading capability	Agriculture Machinery,Ordinary Machine Tool, Ordinary Structure Parts
40Cr	High strength Shaft, Gear, Connecting rod, Bolts and moulds etc.	Drive Shaft, Engine Crankshaft, and Heavy Load Machinery

 

Selection Principles:

C45 Steel: Suitable for scenarios where cost is a concern and the load is moderate.

40Cr: Appropriate for parts that require high strength, wear resistance, or have a larger cross-sectional size.

 

5. Machining and Welding Performance

Machinability: C45 steel is superior (lower hardness, less tool wear).

Weldability: Both require preheating (medium carbon steel is prone to cracking), but 40Cr, due to its chromium content, needs to be annealed after welding to relieve stress.

 

6. Price and Procurement

The price of 40Cr is approximately 20% to 30% higher than that of C45 steel (due to alloy composition).

For critical components, 40Cr is recommended; for non-critical parts, C45 steel can be chosen to reduce costs.

Summary: How to Choose?

Choose C45 steel: for parts with limited budgets, low loads, or no need for high-frequency heat treatment.

Choose 40Cr for parts that require high strength, high fatigue life, or large sizes that need deep quenching.

If there are still doubts, further analysis can be conducted based on specific working conditions (such as load, heat treatment conditions).

 

Vigor team has rich experience in producing die-forged and CNC machined C45 and 40Cr components. If you have question or any parts need to be developed, please feel free to contact us info@castings-forging.com