Introduction

EN24 is a high-quality, high-strength alloy steel known for its excellent combination of toughness, wear resistance, and tensile strength. It is a nickel-chromium-molybdenum alloy steel often supplied hardened and tempered to achieve high mechanical performance. EN24 is widely used in engineering applications requiring superior strength and impact resistance, making it an ideal material for critical components in industries such as aerospace, automotive, and general engineering.

Properties of the Grade:

  • High tensile strength and toughness
  • Excellent fatigue resistance
  • Good ductility and shock resistance
  • High wear resistance
  • Good machinability in the normalized and tempered condition
  • Suitable for nitriding to improve surface hardness
  • Good dimensional stability after heat treatment
  • Moderate corrosion resistance in mild environments

Uses/Applications of the Grade:

  • Gears and shafts
  • Heavy-duty axles
  • Crankshafts
  • High-strength bolts and studs
  • Couplings
  • Aircraft landing gear components
  • Propeller shafts
  • High-strength machine parts
  • Automotive drivetrain components

Chemical Composition:

Element Content (%)
Carbon (C) 0.36 – 0.44
Silicon (Si) 0.10 – 0.35
Manganese (Mn) 0.45 – 0.70
Chromium (Cr) 0.90 – 1.40
Molybdenum (Mo) 0.20 – 0.35
Nickel (Ni) 1.30 – 1.80
Sulfur (S) ≤ 0.035
Phosphorus (P) ≤ 0.035

Mechanical Properties:

(Typical values after heat treatment)

Property Typical Value
Tensile Strength 850 – 1000 MPa
Yield Strength ≥ 680 MPa
Hardness (Annealed) ~ 217 HB
Hardness (Hardened & Tempered) 248 – 302 HB (depends on condition)
Elongation ~ 13%
Impact Energy (Charpy V-notch) Excellent
Fatigue Strength High

Physical Properties:

Property Typical Value
Density ~ 7.85 g/cm³
Modulus of Elasticity (Elastic Modulus) ~ 210 GPa
Thermal Conductivity (at 20°C) ~ 46.6 W/m·K
Specific Heat Capacity ~ 460 J/kg·K
Coefficient of Thermal Expansion (20–100°C) ~ 12.3 × 10⁻⁶ /°C

Forging:

Forging Temperature Range: 850°C – 1200°C

Procedure:

  • Heat slowly and uniformly.
  • Do not forge below 850°C.
  • After forging, cool slowly in the furnace or in dry lime to avoid thermal cracks.

Heat Treatment:

  1. Annealing:
    • Heat to 830°C – 850°C.
    • Hold for an adequate time.
    • Furnace cool slowly.
    • Resultant hardness: ~ 217 HB.
  2. Hardening:
    • Heat to 820°C – 850°C.
    • Oil quench is recommended.
  3. Tempering:
    • Temper immediately after quenching.
    • Typical tempering temperature: 600°C – 660°C.
    • Achieves balance between hardness and toughness depending on the application.
  4. Nitriding (optional):
    • Can be nitrided to achieve surface hardness up to 60–65 HRC.

Dimensional Tolerances:

  • Hot Rolled Bars: As per EN 10060 standards.
  • Bright Bars (Peeled, Drawn, or Ground): Tolerances as per EN 10278 (ISO h9, h11).
  • Plates and Blocks: Machined or flame-cut to close tolerances on request.

Machinability:

  • Good machinability in the normalized or tempered condition.
  • Best results with high-speed steel or carbide cutting tools.
  • Coolant use is recommended to maintain tool life and surface finish.

Corrosion Resistance:

  • Moderate corrosion resistance in dry and mild corrosive environments.
  • Not designed for marine or highly corrosive industrial applications.
  • Surface treatments like nitriding, hard chrome plating, or coating can enhance corrosion resistance.

Weldability:

  • Fair weldability, but preheating to 200°C – 300°C is strongly recommended.
  • Post-weld heat treatment is advisable to avoid stress concentration and cracking.
  • Suitable welding methods include TIG and MIG processes.

Available Form:

EN24 alloy steel is available in:

  • Hot Rolled Bars
  • Forged Bars
  • Peeled and Ground Bright Bars
  • Plates
  • Blocks
  • Cut Pieces (custom sizes)

Material can be supplied in annealed, normalized, or hardened and tempered condition based on customer requirements.

Conclusion:

EN24 alloy steel offers a powerful combination of high tensile strength, excellent toughness, and good wear resistance, making it a preferred material for critical engineering applications across multiple industries. With proper heat treatment and surface enhancement, EN24 can deliver exceptional mechanical performance and extend the life of highly stressed machine components. Its reliable machinability and versatility make it a standard choice for both heavy-duty and precision applications.

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