Introduction

EN8 is an unalloyed medium carbon steel grade as per British Standard BS 970. It is known for its excellent combination of strength, toughness, and good machinability. EN8 is suitable for applications that require better mechanical properties than mild steel but do not require the superior strength of high-carbon steel. It can be heat treated to achieve higher strength and hardness levels.

  • Moderate strength and toughness.
  • Good machinability.
  • Acceptable weldability.
  • Suitable for heat treatment to improve hardness.
  • Reasonable wear resistance.
  • Moderate hardenability.

Properties of EN8 Grade:

  • Medium carbon content offering good strength and wear resistance
  • Excellent machinability in normalized or annealed condition
  • Capable of heat treatment for enhanced mechanical properties
  • Good dimensional stability after machining
  • Moderate weldability with proper preheating

Uses/Applications of EN8 Grade:

  • Shafts, axles, spindles, and studs
  • Automotive components
  • Gears, bolts, keys, and couplings
  • Crankshafts and connecting rods
  • General engineering parts
  • High-strength machine parts
  • Agricultural and construction machinery components

Chemical Composition (Typical):

Element Content (%)
Carbon (C) 0.35 – 0.45
Manganese (Mn) 0.60 – 1.00
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 550 – 700 MPa
Yield Strength 280 MPa min
Elongation (in 50 mm) 16% min
Impact Strength (Charpy V-notch) 28 J min
Hardness (Brinell) 152 – 207 HB
Hardness (After Hardening and Tempering) Up to 225 – 285 HB

Physical Properties:

Property Value
Density 7.85 g/cm³
Modulus of Elasticity ~205 GPa
Thermal Conductivity ~49 W/m·K
Specific Heat Capacity ~486 J/kg·K
Electrical Resistivity ~0.15 µΩ·m

Forging:

  • Forging temperature range: 950°C – 1250°C.
  • Start forging at around 1200°C and do not forge below 850°C.
  • After forging, slow cooling in furnace, sand, or dry ash is recommended to prevent internal stresses.
  • Normalizing after forging improves toughness and refines grain size.

Heat Treatment:

  • Annealing: Heat to 680°C – 700°C, hold, and then cool slowly in the furnace to soften for improved machinability.
  • Normalizing: Heat to 820°C – 860°C, then air cool to enhance toughness and uniformity.
  • Hardening: Heat to 810°C – 830°C, quench in oil or water.
  • Tempering: After hardening, temper at 550°C – 660°C to improve toughness and reduce brittleness.

Dimensional Tolerances:

  • Hot rolled bars: General tolerances as per BS 970 and equivalent standards.
  • Cold drawn or ground bars: Tighter dimensional tolerances achievable.
  • Specific tolerances on size, straightness, and out-of-roundness available based on application requirements.

Machinability:

  • EN8 has good machinability in the annealed or normalized condition.
  • Machining should be carried out using appropriate tooling such as carbide-tipped or high-speed steel tools.
  • Use of cutting fluids improves surface finish and tool life.

Corrosion Resistance:

  • EN8 has limited corrosion resistance under atmospheric or moist environments.
  • It is recommended to use protective coatings such as oiling, painting, or galvanizing when exposed to corrosive environments.
  • Not suitable for marine or chemical exposure without surface protection.

Weldability:

  • Moderate weldability; preheating to 150°C – 300°C is recommended for thick sections.
  • Use low hydrogen welding electrodes.
  • Post-weld stress-relieving heat treatment is advisable to maintain mechanical properties and avoid weld cracking.

Available Form:

  • Hot Rolled Round Bars
  • Hot Rolled Flats and Squares
  • Bright Bars (Cold Drawn or Peeled)
  • Forged Bars and Blanks
  • Precision Ground Bars
  • Custom lengths and shapes available on request
  • Supplied in normalized, annealed, or quenched & tempered condition

Conclusion:

EN8 Carbon Steel is a versatile and cost-effective medium carbon steel offering excellent strength, toughness, and machinability. It is ideal for producing components where moderate strength and wear resistance are required. With proper heat treatment and surface protection, EN8 serves efficiently in a wide range of industrial and engineering applications.

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