Introduction

EN9 is a medium-carbon steel that offers a good balance of hardness, strength, and wear resistance. It is widely used in various industrial applications that require moderate strength along with durability and fatigue resistance. With its ability to undergo heat treatment processes like hardening and tempering, EN9 is particularly useful for producing components subjected to wear and stress. EN9 is commonly used for shafts, gears, axles, and other high-strength components in machinery and automotive applications.

Uses/Applications of EN9 Grade:

  • Shafts: EN9 is used to make medium-duty shafts where moderate strength and toughness are essential.
  • Gears: Suitable for gears and pinions that require moderate wear resistance.
  • Axles: Commonly used for automotive axles and other high-stress components.
  • Crankshafts: Ideal for manufacturing crankshafts due to its balance of toughness and strength.
  • Bolts, Nuts, and Fasteners: Used for high-strength fasteners in mechanical applications.

Properties of EN9 Grade:

  • Medium-carbon steel offering a combination of good strength, toughness, and wear resistance.
  • Good machinability when in the annealed or normalized condition.
  • Hardenability improves with heat treatment, making it suitable for components requiring higher strength.
  • Excellent fatigue resistance under cyclical loads.
  • Moderate wear resistance, making it suitable for components in contact with other machine parts.
  • Pins: Used in machinery for manufacturing pins subjected to heavy load.
  • Machine parts: Other general-purpose mechanical components requiring medium to high strength.

Chemical Composition (Typical):

Element Content (%)
Carbon (C) 0.38 – 0.45
Manganese (Mn) 0.60 – 0.90
Silicon (Si) 0.10 – 0.35
Sulfur (S) ≤ 0.05
Phosphorus (P) ≤ 0.05
Iron (Fe) Balance

Mechanical Properties (Typical in Normalized Condition):

Property Value
Tensile Strength 600 – 750 MPa
Yield Strength 350 MPa min
Elongation (in 50 mm) 16% min
Impact Strength (Charpy V-notch) 40 J min
Hardness (Brinell) 170 – 250 HB
Hardness (After Hardening and Tempering) 300 – 330 HB

Physical Properties:

Property Value
Density 7.85 g/cm³
Modulus of Elasticity ~205 GPa
Thermal Conductivity ~50 W/m·K
Specific Heat Capacity ~480 J/kg·K
Electrical Resistivity ~0.16 µΩ·m

Forging:

  • Forging Temperature Range: 950°C – 1200°C.
  • Forge at 1100°C – 1200°C for optimal results and material integrity.
  • Avoid forging below 850°C to prevent embrittlement.
  • Cooling after forging should be done gradually to relieve stresses and avoid cracking.

Heat Treatment:

  • Annealing: Heat to 680°C – 700°C and cool slowly for better machinability and to relieve internal stresses.
  • Normalizing: Heat to 820°C – 880°C and allow air cooling to refine the grain structure, improving toughness.
  • Hardening: Heat to 830°C – 860°C, followed by quenching in oil or water depending on component size and hardness requirements.
  • Tempering: After hardening, temper at 550°C – 650°C to adjust hardness and toughness as needed for the application.

Dimensional Tolerances:

  • Hot Rolled Bars: Tolerances are in accordance with BS 970 or equivalent standards for general applications.
  • Cold Drawn Bars: These bars offer precise tolerances and are suitable for precision engineering applications.
  • Forged Bars: Custom tolerances can be tailored according to specific client requirements.
  • Tolerances for straightness, roundness, and flatness are provided based on the intended application.

Machinability:

  • Good machinability when in normalized or annealed state.
  • EN9 is suitable for turning, milling, drilling, and boring operations with standard tools.
  • Hardening of EN9 requires carbide tools or coated tools to ensure efficient cutting.
  • Cutting fluids should be used for enhanced tool life and better surface finishes.

Corrosion Resistance:

  • Moderate corrosion resistance in untreated form. EN9 is susceptible to rust and corrosion when exposed to moist or aggressive environments.
  • Protective coatings such as galvanizing, painting, or oiling are recommended to enhance the steel’s corrosion resistance.
  • Parts exposed to outdoor environments should be coated or treated for long-term protection.

Weldability:

  • Moderate weldability in the normalized or annealed condition.
  • For welding, preheating to 150°C – 250°C is recommended for thicker sections to reduce the risk of cracking.
  • Use of low-hydrogen electrodes and appropriate filler materials is suggested for high-quality welds.
  • Post-weld heat treatment may be necessary to restore mechanical properties after welding.

Available Form:

  • Hot Rolled Bars
  • Cold Drawn Bars
  • Precision Ground Bars
  • Forged Bars
  • Flat Bars
  • Custom shapes and sizes can be manufactured according to specific customer requirements.
  • Supplied in normalized, annealed, or quenched and tempered conditions as per application demands.

Conclusion:

EN9 Carbon Steel is a reliable and versatile medium-carbon steel that offers an excellent combination of strength, toughness, and machinability. It is widely used in mechanical components like shafts, gears, and axles that require high strength and moderate wear resistance. Although it has moderate corrosion resistance, proper treatment and coating can significantly improve its durability. With good weldability and machinability, EN9 is an ideal choice for many industrial applications, particularly in the automotive and machinery sectors.

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