Introduction

EN8D is a high-strength, medium carbon steel grade conforming to BS 970 standard. It is a modified version of EN8 with slightly higher carbon content, offering increased tensile strength and hardness. EN8D is widely used for components subjected to high stress and wear. It is suitable for mechanical engineering applications that require improved mechanical properties over standard EN8.

Properties of EN8D Grade:

  • Higher tensile strength compared to EN8
  • Good impact resistance and toughness
  • Excellent response to heat treatment (hardening and tempering)
  • Good machinability in normalized condition
  • Moderate weldability with correct procedures
  • Good dimensional stability after heat treatment

Uses/Applications of EN8D Grade:

  • High-strength machine components
  • Shafts, axles, and spindles
  • Automotive crankshafts and connecting rods
  • Gears and heavy-duty fasteners
  • Precision components requiring high strength and wear resistance
  • Agricultural and construction machinery parts

Chemical Composition (Typical):

Element Content (%)
Carbon (C) 0.45 – 0.50
Manganese (Mn) 0.60 – 0.90
Silicon (Si) 0.05 – 0.35
Sulfur (S) ≤ 0.05
Phosphorus (P) ≤ 0.05
Iron (Fe) Balance

Mechanical Properties (Typical in Normalized Condition):

Property Value
Tensile Strength 700 – 850 MPa
Yield Strength 450 MPa min
Elongation (in 50 mm) 14% min
Impact Strength (Charpy V-notch) 30 J min
Hardness (Brinell) 201 – 255 HB
Hardness (After Hardening and Tempering) Up to 300 – 400 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 ~0.15 µΩ·m

Forging:

  • Forging temperature range: 950°C – 1250°C.
  • Begin forging at approximately 1200°C and do not forge below 850°C.
  • Slow cooling after forging is recommended to minimize internal stress and cracking.
  • Normalizing post-forging improves toughness and mechanical properties.

Heat Treatment:

  • Annealing: Heat to 680°C – 700°C, hold, and cool slowly in furnace to soften and enhance machinability.
  • Normalizing: Heat to 820°C – 860°C, air cool to refine grain structure and enhance mechanical properties.
  • Hardening: Heat to 820°C – 860°C, quench in oil or water.
  • Tempering: Temper at 550°C – 660°C after hardening to achieve the desired balance of hardness and toughness.

Dimensional Tolerances:

  • Hot Rolled Bars: Standard tolerances according to BS 970 and similar norms.
  • Cold Drawn or Peeled Bars: Closer dimensional accuracy achievable.
  • Specific tolerances on size, straightness, and roundness can be provided upon request.

Machinability:

  • EN8D offers good machinability when normalized or annealed.
  • After hardening, machining becomes more challenging and requires carbide or coated tooling.
  • Application of appropriate cutting fluids ensures better surface finish and tool life.

Corrosion Resistance:

  • EN8D exhibits limited natural corrosion resistance.
  • Protective coatings such as oiling, painting, or electroplating are advised for parts exposed to humid or corrosive environments.
  • Not suitable for use in highly corrosive or marine environments without protection.

Weldability:

  • Moderate weldability; preheating to 150°C – 300°C is recommended to prevent cracking, especially for thick sections.
  • Use of low hydrogen electrodes is recommended.
  • Post-weld heat treatment or stress relieving may be necessary to maintain mechanical properties.

Available Form:

  • Hot Rolled Round Bars
  • Hot Rolled Flats and Squares
  • Forged Bars (Rounds, Flats, Blocks)
  • Bright Bars (Cold Drawn, Peeled, Ground)
  • Precision Ground Bars
  • Custom lengths and shapes available
  • Supplied in normalized, annealed, or quenched and tempered conditions

Conclusion:

EN8D Carbon Steel is a highly versatile and durable grade designed for applications demanding superior mechanical strength, wear resistance, and toughness. Its ability to be heat treated, good machinability, and reliable performance make it ideal for critical mechanical and engineering components. With appropriate processing, EN8D offers a robust solution across a wide range of industries.

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