Technical Report on EN8 Carbon Steel
1. Introduction
EN8 carbon steel is an unalloyed medium carbon steel grade with good tensile strength. It is commonly used in applications that require higher strength than mild steel but do not necessitate the hardness or strength of alloy steels. EN8 is typically supplied in the untreated or normalized condition and can be heat treated to achieve enhanced mechanical properties.
2. Chemical Composition
The typical chemical composition of EN8 carbon steel is as follows:
| Element | Content (%) |
|---|---|
| Carbon (C) | 0.36 – 0.44 |
| Manganese (Mn) | 0.60 – 1.00 |
| Silicon (Si) | 0.10 – 0.40 |
| Sulphur (S) | ≤ 0.050 |
| Phosphorus (P) | ≤ 0.050 |
| Iron (Fe) | Balance |
3. Mechanical Properties
Mechanical properties of EN8 steel vary based on its condition (as supplied, normalized, or heat-treated):
| Property | Typical Value (As Supplied) |
|---|---|
| Tensile Strength | 550 – 700 MPa |
| Yield Strength | 280 – 350 MPa |
| Elongation (in 50 mm) | 16 – 22% |
| Hardness (Brinell) | 152 – 207 HB |
| Impact Value (Charpy V-notch) | 25 – 35 J |
Note: Heat treatment such as quenching and tempering can significantly increase hardness and tensile strength.
4. Heat Treatment
EN8 carbon steel can be heat treated to improve its mechanical properties:
- Normalizing: ~830–860°C followed by air cooling.
- Hardening: ~800–860°C followed by oil or water quenching.
- Tempering: ~550–660°C to relieve stresses and improve toughness.
The hardened and tempered condition enhances wear resistance and strength.
5. Machinability and Weldability
- Machinability: Good, especially in normalized or turned and ground conditions.
- Weldability: Fair. EN8 is not readily weldable in its untreated condition due to its higher carbon content. Preheating and post-weld heat treatment are recommended to reduce the risk of cracking.
6. Applications
EN8 is widely used in industries for medium-strength applications such as:
- Shafts and axles
- Gears and bolts
- Studs and keys
- Automotive components
- General engineering parts
7. Comparison with Other Steels
| Grade | Type | Key Difference |
|---|---|---|
| EN8 | Medium carbon | Balanced strength and machinability |
| EN9 | Higher carbon | Higher hardness but lower ductility |
| EN24 | Alloy steel | Higher tensile strength and toughness due to alloying elements |
8. Standards and Designations
- BS 970-3:1991: 080M40
- AISI Equivalent: 1040/1045
- UNS Number: G10400
- DIN Equivalent: C40 or CK40
9. Conclusion
EN8 carbon steel is a versatile, cost-effective material suited for general engineering applications requiring higher strength than mild steel. With the right heat treatment, it offers a balance of strength, toughness, and wear resistance, making it a popular choice in manufacturing and automotive sectors.
