Heat treatment of forgings

January 26, 2018 | Views: 112 |

After the forging has undergone pre-machining, it is subjected to a final heat treatment. Thanks to special modes of heating and cooling, workpieces acquire specific characteristics: increased strength, wear resistance, ductility, etc.

Types and features of heat treatment of forgings

Rolled metal in general and forged products in particular can be subjected to the following types of heat treatment:

  • annealing;
  • normalization;
  • hardening;
  • vacation.

Annealing – This is the heating of steel to the temperature of the phase transformation, followed by gradual cooling. Annealing can be complete or incomplete. With full annealing, the product is heated to a temperature 30-50 degrees higher than the transition to the austenite phase. Then it is kept at this temperature for some time, after which it is slowly cooled. As a result, the steel becomes more ductile, and its hardness and strength decrease.

In incomplete annealing, the forging is heated to a temperature slightly above 723°C. This eliminates the internal stresses of the material and improves its machinability.

Normalization – this is the process of heating a forging to a temperature 50-60°C above the austenite transformation point with a short exposure and cooling in air. Thanks to normalization, it is possible to obtain steel with a fine-grained structure. Such products are characterized by high surface finish. They also cut well.

Tempering – this is heating the workpiece to a temperature exceeding the austenite transformation point by 30-70°C, followed by holding and rapid cooling. The holding time must be sufficient to complete the phase transition. Cooling is carried out by using water or oil. Hardened steel is characterized by very high strength and hardness, but strong internal stresses occur in it, making it very brittle. Therefore, after hardening, the forging must be tempered.

Vacation is low, medium and high. At low, the forging is heated to a temperature of 150-250°C and kept for some time. This helps to remove internal stresses from the steel, however, in this case, the product will not be able to withstand dynamic (shock) loads. Therefore, such processing is used only to obtain cutting and measuring equipment.

Average tempering is carried out at 350-500°C, as a result, the steel is characterized by high elasticity. Therefore, springs and springs are subjected to medium tempering. High tempering completely removes internal stresses in the material, giving it good plastic properties. Unfortunately, this significantly reduces the strength of the steel. High release temperature – 500-680°C.

Combination of hardening and tempering – the most common type of heat treatment. It is this method that makes it possible to obtain forgings with an optimal combination of mechanical characteristics.


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