Introduction

20C8 carbon steel is a low-carbon, mild steel grade known for its excellent combination of machinability, strength, and weldability. It belongs to the family of plain carbon steels and is mainly utilized where moderate strength and good formability are required. Its structure allows for easy manufacturing processes like forging, welding, and machining, making it ideal for general engineering applications.

Properties of 20C8 Grade

  • Good machinability and weldability
  • Moderate tensile and yield strength
  • Suitable for carburizing for improved surface hardness
  • High ductility and toughness
  • Cost-effective material with good availability
  • Good surface finish after machining and cold finishing

Uses/Applications of 20C8 Grade:

  • Automotive components (gears, shafts, bolts)
  • Machinery parts
  • Agricultural implements
  • Forged components
  • Structural applications
  • Pins and bushes
  • Low-stress fasteners
  • Mild engineering applications requiring surface hardening

Chemical Composition (Typical):

Element Content (%)
Carbon (C) 0.15 – 0.25
Manganese (Mn) 0.50 – 0.80
Phosphorus (P) ≤ 0.05
Sulfur (S) ≤ 0.05
Iron (Fe) Balance

Mechanical Properties (Typical):

Property Value
Tensile Strength 410 – 550 MPa
Yield Strength 250 MPa (min)
Elongation (in 50 mm) 23% – 30%
Brinell Hardness (HB) 120 – 170 HB
Impact Strength Good (Charpy tested)

Physical Properties

Property Value
Density 7.85 g/cm³
Melting Point ~ 1490 °C
Modulus of Elasticity 200 GPa
Thermal Conductivity ~ 50 W/m·K
Specific Heat Capacity ~ 450 J/kg·K

Forging

20C8 steel can be forged at a temperature range of 1100 °C to 1250 °C, with final forging done at around 850 °C.

After forging, slow furnace cooling is recommended to relieve internal stresses and improve the toughness of the material.

Dimensional Tolerances

Manufactured in accordance with international standards:

  • Cold Drawn Bars: Tight tolerances of ±0.01 mm to ±0.03 mm depending on the size.
  • Hot Rolled Bars: Standard rolling tolerances depending on section size.

Special tolerances are available on request for precision applications.

Machinability:

20C8 offers good machinability with conventional cutting tools. It provides good surface finishes and moderate tool life. Its machinability rating is approximately 60% – 70% compared to free-machining steels like AISI 1112.

For optimal results:

  • Use carbide or high-speed steel tools.
  • Moderate cutting speeds are recommended.
  • Proper cooling is essential during machining to enhance tool life.

Heat Treatment:

  • Annealing: Performed at 850 °C – 900 °C followed by slow cooling in the furnace to soften the material and improve machinability.
  • Normalizing: Heating to about 870 °C – 920 °C followed by air cooling to refine the grain structure and enhance strength and toughness.
  • Carburizing: Commonly carburized to increase surface hardness while maintaining a tough and ductile core.
  • Stress Relieving: Typically done at 540 °C – 650 °C to remove internal stresses after heavy machining or welding.

Corrosion Resistance:

20C8 carbon steel does not possess high corrosion resistance and is prone to rust when exposed to humid or corrosive environments.

It is generally protected by applying oil coatings, painting, galvanizing, or other protective coatings where necessary.

Weldability:

20C8 exhibits excellent weldability:

  • Can be welded using conventional processes such as TIG, MIG, and SMAW.
  • Preheating is generally not required for thin sections but may be recommended for thicker sections to avoid weld cracking.
  • Post-weld stress relief can be beneficial for high-reliability applications.

Proper welding practices should be followed to maintain mechanical properties and avoid defects.

Available Form

  • Hot Rolled Round Bars
  • Cold Drawn Round Bars
  • Square Bars
  • Hexagonal Bars
  • Flat Bars
  • Wire Rods
  • Peeled and Polished Bars
  • Coils
  • Custom Cut Lengths

Available in both bright finish (cold drawn) and black finish (hot rolled).

Conclusion

20C8 carbon steel is a versatile, low-carbon engineering steel ideal for applications requiring moderate strength, good ductility, and excellent machinability. Its low cost, good availability, and adaptability for carburizing treatments make it a preferred choice across industries such as automotive, agriculture, construction, and general machinery. However, due to its moderate corrosion resistance, protective measures are recommended for use in aggressive environments.

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