**Chemical Composition and Mechanical Properties of 40CrMnMo Steel**
40CrMnMo is a type of alloy structural steel specified under Chinese national standards. It has the uniform digital code **A34402**. This steel is widely used in heavy-duty mechanical applications due to its excellent mechanical properties and good hardenability.
### **Chemical Composition (in %)**
- Carbon (C): 0.37 – 0.45
- Silicon (Si): 0.17 – 0.37
- Manganese (Mn): 0.90 – 1.20
- Chromium (Cr): 0.90 – 1.20
- Molybdenum (Mo): 0.20 – 0.30
These elements contribute to the steel’s strength, toughness, and resistance to wear and deformation.
### **Mechanical Properties (after heat treatment, sample size: 25mm)**
- **Quenching temperature**: 850°C, cooled with oil
- **Tempering temperature**: 600°C, cooled with water or oil
**Key mechanical properties include:**
- Tensile strength (σb): ≥ 980 MPa
- Yield strength (σs): ≥ 785 MPa
- Elongation (δ5): ≥ 10%
- Reduction of area (ψ): ≥ 45%
- Impact energy (Aku2): ≥ 63 J
- Brinell hardness (HBS 100/3000): ≤ 217 (in annealed or high-temperature tempered condition)
The steel exhibits excellent comprehensive mechanical performance, high hardenability, and good tempering stability when subjected to quenching and tempering treatments. It is typically used in this state for critical engineering components.
### **Main Applications**
40CrMnMo is commonly used to manufacture large-sized, high-load parts such as:
- Gear shafts and gears
- Rear axle shafts for heavy trucks
- Eccentric shafts and connecting rods
- Components for steam turbines
It can also serve as an alternative to 40CrNiMo in certain applications where similar mechanical properties are required.
This steel grade is ideal for parts that require both high strength and good ductility, making it a popular choice in the automotive, aerospace, and industrial machinery sectors.
Source: [http://news.chinawj.com.cn](http://news.chinawj.com.cn)
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