Heat Treatment of C45 Steel

C45 steel, also known as EN 1.0503 or AISI 1045, is a widely used medium carbon steel known for its excellent mechanical properties and versatility. One of the key factors behind its remarkable performance is the application of heat treatment.

In this blog post, we will explore the heat treatment process for C45 steel and delve into its chemical and mechanical properties.

Chemical Composition of C45 Steel

C45 steel is primarily composed of the following elements:

  • Carbon (C): 0.42-0.50%
  • Silicon (Si): 0.17-0.37%
  • Manganese (Mn): 0.50-0.80%
  • Phosphorus (P): 0.035% maximum
  • Sulfur (S): 0.040% maximum

The carbon content in C45 steel provides it with its characteristic strength and hardness, while the other elements contribute to its overall mechanical properties and machinability.

Heat Treatment Processes for C45 Steel

The heat treatment process for DIN C45 round bar steel grade involves the following temperature ranges:

  1. Forging or hot rolling: The steel is heated to a temperature between 1100 and 850°C.
  2. Normalizing: The steel is heated to a temperature range of 840 to 880°C and then cooled in ambient air.
  3. Soft annealing: The steel is heated to a temperature range of 680 to 710°C and held at this temperature in a furnace.
  4. Hardening: The steel is heated to a temperature range of 820 to 860°C and then rapidly cooled using water or oil.
  5. Tempering: The hardened steel is reheated to a temperature range of 550 to 660°C and cooled in ambient air.
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C45 Hardening Heat Treatment

To achieve hardening of DIN C45 round bar steel grade, the following steps should be followed:

  1. Heating: Heat the steel from a temperature of 820-860°C. The recommended temperature range for heating is 820-850°C or 830-860°C, depending on the specific requirements. Ensure uniform heating throughout the section.
  2. Soaking: Hold the steel at the desired temperature for a sufficient duration to ensure uniformity. The recommended soaking time is 10-15 minutes per 25mm of section thickness. This allows the heat to penetrate the entire section and achieve the desired hardness.
  3. Quenching: After soaking, the steel should be rapidly cooled by quenching it in water, brine, or oil. The choice of quenching medium depends on factors such as the desired hardness and the specific requirements of the application.
  4. Tempering: Once the quenching process is complete, the steel should be tempered immediately while it is still hand warm. Tempering involves reheating the steel to a temperature range of 550-660°C, followed by holding it at this temperature for a specific duration.

The heat treatment process for C45 steel typically involves the following stages:

  1. Annealing:
    • The initial step is the annealing process, which involves heating the steel to a temperature range of 800-900°C (1470-1650°F).
    • This temperature is maintained for a specific period to allow for complete homogenization and softening of the steel’s microstructure.
    • Slow cooling (furnace cooling) is employed to relieve internal stresses and enhance machinability.
  2. Quenching:
    • Quenching is a critical step in the heat treatment of C45 steel, aimed at achieving high hardness and strength.
    • The steel is heated to a temperature above the transformation range (830-870°C or 1520-1598°F) and then rapidly cooled by immersing it in a quenching medium such as water, oil, or polymer.
    • Quenching transforms the steel’s microstructure into a hard and brittle martensitic structure, which imparts increased strength and hardness.
  3. Tempering:
    • Tempering follows the quenching process and involves reheating the steel to a temperature between 450-650°C (842-1202°F).
    • The steel is held at this temperature for a specific duration, which allows for the transformation of some of the brittle martensite into a more ductile structure.
    • Tempering reduces the brittleness of the steel, improves its toughness, and relieves internal stresses.
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Mechanical Properties of C45 Steel

The heat treatment process significantly influences the mechanical properties of C45 steel. Here are the typical mechanical properties achieved through proper heat treatment:

  • Tensile Strength: 600-800 MPa (87,000-116,000 psi)
  • Yield Strength: 370-450 MPa (54,000-65,000 psi)
  • Elongation: 16-20%
  • Reduction in Area: 40-45%
  • Hardness: 170-210 HB (Brinell hardness)

C45 steel exhibits a good balance of strength, toughness, and wear resistance, making it suitable for a wide range of applications. Its mechanical properties make it popular for components such as shafts, gears, bolts, and other machine elements subjected to high stress and load.


The heat treatment of C45 steel unlocks its true potential, transforming it into a robust and reliable material for various industrial applications. By following the annealing, quenching, and tempering stages, manufacturers can achieve the desired mechanical properties, including high strength, hardness, and improved toughness. It is crucial to adhere to proper heat treatment procedures and consult with metallurgical experts to ensure optimal results for specific applications.

C45 steel’s versatility, combined with its excellent mechanical properties, has solidified its position as a preferred choice in industries such as automotive, machinery, and construction. Understanding and harnessing the power of heat treatment is key to unlocking the full potential of C45 steel and maximizing its performance in demanding engineering applications.

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FAQs – C45 Steel and S45C Steel

  1. Is C45 steel the same as S45C steel?
    Although their carbon content is around 0.45%, they are equivalent grades. C45, also known as DIN 1.0503, is the grade of the European standard EN10083, while S45C comes from the JIS G4051 Japanese standard.
  2. Is C45 steel considered high-carbon steel?
    C45 steel has a carbon content ranging from 0.42% to 0.50%. However, compared to the carbon content of high-carbon steel in the carbon steel classification (C > 0.6%), it does not meet the level of high-carbon steel.
  3. Does C45 steel contain alloying elements?
    The main composition of C45 steel does not contain alloying elements, as shown in the chemical composition table. However, C45 may contain residual alloying elements within certain limits during the smelting process.
  4. Can C45 steel be welded?
    C45 steel is a medium-carbon steel, and its welding performance gradually deteriorates compared to low-carbon steels. If C45 steel is welded using the welding process for low-carbon steel, there is a risk of weld cracking and product failure. Strict control of the welding process, including preheating and post-weld heat treatment, is necessary to prevent welding cracks and ensure the safety and reliability of weldments.
  5. Is C45 steel suitable for shafts?
    The suitability of C45 steel for shafts depends on the working conditions and requirements. Different heat treatment methods such as quenching and tempering, normalizing, and quenching should be applied to obtain the desired strength, toughness, and wear resistance based on the specific use of the shaft.