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The purpose of heat treatment is

The purpose of heat treatment is Correct Answer To change the mechanical properties of steel

Explanation:

Heat Treatment:

  • The heat treatment process is a series of operations involving the heating and cooling of metals in the solid-state.
  • Its purpose is to change a mechanical property or combination of mechanical properties so that the metal will be more useful, serviceable, and safe for a definite purpose.
  • By heat treating, a metal can be made harder, stronger, and more resistant to impact, heat treatment can also make a metal softer and more ductile.
  • Based on the range of temperature, cooling process, and properties enhancement, they can be divided into many types.
  • Some of them are mentioned below.

  • Process

    Function

    Normalizing

    Heat the steel from 30°C to 50°C above its upper critical temperature, held about fifteen minutes and then allowed to cool down in still air.

    The homogeneous structure provides a higher yield point, ultimate tensile strength and impact strength with lower ductility to steels.

    Main objective

    • Refine grain, improve machinability, tensile strength, and structure of weld.
    • Remove cold worked stress.
    • Remove dislocations due to hot working.

    Annealing

    Annealing involves heating the steel to a suitable temperature, holding it at that temperature for some time, and then cooling it slowly. 

    There are different methods of cooling. The main purpose of Annealing is to reduce the hardness of a material.

    Besides this, it is also used –

    • To relieve the internal stress of a material
    • To restore ductility to perform the further operation on the material
    • To induce softness

    Hardening

    Hardening is a heat treatment process in which steel is heated to 30 – 50° above the critical range.

    Soaking time is allowed to enable the steel to obtain a uniform temperature throughout its cross-section. Then the steel is rapidly cooled through a cooling medium. 

    Hardening increase the brittleness in the metal.

    Tempering

    Tempering is a heat treatment process in which the hardness of a hardened alloy is reduced by the appropriate heat-treatment process.

    Tempering is a heat-treatment process consisting of reheating the hardened steel to a temperature below 400°C, followed by cooling.

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