What are the mechanical properties of 20CrMo

20CrMo is an alloy steel grade that contains chromium (Cr) and molybdenum (Mo), which provide it with excellent hardenability, strength, and toughness, especially after heat treatment. It is commonly used for components that require high strength, good wear resistance, and toughness, such as gears, shafts, and automotive components.

Here are the mechanical properties of 20CrMo steel:

1. Yield Strength (σ₀.₂):
- The minimum yield strength is typically around 355 MPa to 440 MPa after heat treatment, depending on the specific processing conditions and dimensions.

2. Tensile Strength (σb):
- The tensile strength of 20CrMo is generally in the range of 590 MPa to 750 MPa, depending on the exact heat treatment (quenching and tempering) and composition.

3. Elongation (A):
- The elongation (percentage of deformation before fracture) is typically in the range of 12% to 15% for this grade. It shows good ductility, meaning it can undergo some deformation before failure, which is important for mechanical components under stress.

4. Hardness:
- The hardness of 20CrMo steel after heat treatment is typically around HRC 25 to 32 (Rockwell C scale) for carburized components or HRC 50 and higher after surface hardening.
- The exact hardness can depend on the specific heat treatment process, like quenching or tempering, used on the material.

5. Impact Toughness (Charpy V-notch):
- The impact toughness or Charpy V-notch impact value of 20CrMo is generally greater than 20 J at -40°C, depending on the heat treatment.
- This makes the steel suitable for applications requiring impact resistance at low temperatures.

6. Modulus of Elasticity:
- The modulus of elasticity (also called Young's modulus) of 20CrMo is approximately 210 GPa, which is typical for most steels.

7. Fatigue Strength:
- 20CrMo exhibits good fatigue resistance, particularly after surface hardening processes, making it suitable for cyclic loading applications, such as gears, shafts, and other automotive parts that undergo repeated stress.

8. Weldability and Machinability:
- Weldability: 20CrMo has moderate weldability, but preheating and post-weld heat treatment are usually recommended to avoid cracking and to ensure proper mechanical properties after welding.
- Machinability: 20CrMo is generally considered machinable, though its machinability may decrease after heat treatment, particularly when it is hardened.

9. Composition (Approximate):
- Carbon (C): 0.17% to 0.23%
- Chromium (Cr): 0.90% to 1.10%
- Molybdenum (Mo): 0.15% to 0.30%
- Manganese (Mn): 0.40% to 0.70%
- Silicon (Si): 0.20% to 0.35%
- Phosphorus (P): ≤ 0.035%
- Sulfur (S): ≤ 0.035%

Applications of 20CrMo Steel:
- Automotive industry: Gears, crankshafts, camshafts, and other high-strength components.
- Power generation: Components in turbines, such as shafts and rotors.
- Aerospace: Structural parts and components requiring high strength and toughness.
- Machine components: Shafts, axles, and other parts that undergo high wear and stress.

Summary:
20CrMo is a chromium-molybdenum alloy steel with good tensile strength (590–750 MPa), yield strength (355–440 MPa), and toughness. It performs well under high stress and can be heat-treated to provide high hardness. It is commonly used in automotive and industrial applications that require strength, wear resistance, and the ability to withstand fatigue and impact loading. The alloy's mechanical properties make it ideal for critical components in engines, gears, and shafts.