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What is the purpose of annealing process?

What is the purpose of annealing process? Correct Answer To remove internal stress

Explanation:

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 increase the machinability of the material
    • To induce softness

​There are the following processes in Annealing.

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Diffusion Annealing
  • In this process, hypo-eutectoid, eutectoid, and hyper-eutectoid steel are heated uniformly and the component is held at a temperature between 1000 °C – 1200 °C and then cooled very slowly in the furnace in order to remove the heterogeneity in the composition of heavy castings.
  • During this, a coarse grain structure produced.
  • A homogenous structure appears.
  • To increase material properties, it goes through full annealing after diffusion annealing.

Full Annealing
  • Full annealing consists of heating the steel component to about 50 °C – 70 °C above the critical temperature, holding it for a sufficient length of time, and cooling the same in the furnace.  
  • Adopted for steel casting and ingots.
  • The coarse structure produced during solidification break down to a much smaller size.
  • Machinability and ductility increases.
  • Hardness is reduced.
  • All structural imperfection gets removed.

Spherodise Annealing
  • In this method heating can be done in three ways:
    • Prolonged heating just below the lower critical temperature followed by relatively slow cooling
    • Alternately heating and cooling the work-piece to just above and below the lower critical temperature.
    • Short heating at a high temperature followed by relatively slow cooling.
  • Conversion of hard lamellar or network carbides of high-carbon steels into globular or spherical shapes.
  • Improve machinability and ductility.

Process Annealing
  • This process involves heating of steel to a temperature just below the lower critical temperature (723 °C) of steel.
  • Usually, cold worked steel has high hardness and low ductility making it difficult to work.
  • Deformed grains in cold working get reoriented.
  • Hardness is lowered and ductility also increases.

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