Heat Treatment of EN36 Steel

Heat Treatment of EN36 Steel

EN36 is a versatile alloy steel that offers excellent combination of strength, toughness, and wear resistance. To fully optimize its mechanical properties, a well-executed heat treatment process is essential.

In this blog post, we will explore the heat treatment of EN36, including its chemical composition, mechanical properties, and detailed guidelines for annealing, hardening, tempering, stress relieving, as well as the recommended holding times, temperatures, and heating/cooling rates.

EN36 Chemical Composition

EN36, also known as 655M13 or 3.25% Nickel-Chromium Case Hardening Steel, exhibits the following chemical composition:

  • Carbon (C): 0.14-0.20%
  • Silicon (Si): 0.10-0.35%
  • Manganese (Mn): 0.70-1.00%
  • Phosphorus (P): 0.035% maximum
  • Sulfur (S): 0.040% maximum
  • Nickel (Ni): 3.00-3.75%
  • Chromium (Cr): 0.60-1.00%

Mechanical Properties of EN36

EN36 steel demonstrates impressive mechanical properties after appropriate heat treatment:

  • Tensile Strength: 880-1080 MPa (megapascals)
  • Yield Strength: 630-930 MPa
  • Elongation: 14-18%
  • Hardness: 220-260 HB (Brinell hardness)
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Heat Treatment Process for EN36

  1. Annealing:
    Annealing is performed to relieve internal stresses, refine the microstructure, and improve machinability. The recommended annealing process for EN36 involves heating the steel to around 850-880°C (1562-1616°F) and holding it at that temperature for 2-4 hours. Subsequently, the steel is furnace cooled to room temperature at a rate of approximately 10-20°C (50-68°F) per hour.
  2. Hardening:
    Hardening enhances the hardness and strength of the steel. For EN36, the hardening process consists of heating the steel to a temperature range of 820-860°C (1508-1580°F) and holding it at that temperature for 1-2 hours. Afterward, the steel is rapidly quenched in oil or water to achieve the desired hardness. The recommended quenching medium depends on the specific requirements and properties desired.
  3. Tempering:
    Tempering is crucial to reduce brittleness and attain the desired balance of hardness and toughness. For EN36, the tempering process is carried out by heating the hardened steel to a temperature range of 150-200°C (302-392°F) and holding it at that temperature for 2-4 hours. This allows for the transformation of the microstructure, ensuring improved toughness and ductility.
  4. Stress Relieving:
    Stress relieving helps alleviate residual stresses and stabilize the steel’s properties. The stress relieving process for EN36 involves heating the steel to a temperature range of 550-650°C (1022-1202°F) and holding it at that temperature for 2-4 hours. The steel is then furnace cooled at a rate of approximately 10-20°C (50-68°F) per hour.
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Heating and Cooling Rates

During the heating and cooling stages of the heat treatment process, it is essential to achieve uniform and controlled rates.

Slow and controlled heating rates are generally recommended to avoid thermal shock and potential distortion. Cooling rates should be tailored to the specific heat treatment process (e.g., gradual for stress relieving and rapid for hardening).