Explain the stages of Recrystallization annealing and Factors affecting it.
1 Answer

Recrystallization annealing is a process in which the grains of the metal get deformed and get reformed into smaller and un-deformed grains at a temperature below recrystallization temperature. There are three stages of recrystallization annealing which includes –

a) Grain Deformation:

  • During the cold working of the metal it is deformed by external applied forces, the low energy grains get deformed and form high energy elongated grains.
  • Here the grains get elongated due to compression of external applied force, and thus store the strain energy within them.
  • Due to this external deformation dislocations are created and due to this dislocations the strength of metal increases and ductility of the metal decreases.

b) Nucleation:

  • After such external deformation, the metal object is heated below its recrystallization temperature.
  • As it is heated below its recrystallization temperature it is known as cold worked metal, so now under the heating conditions the grain tries to relieve the stress and form new grain boundaries, this process of formation of new grain boundaries is known as nucleation.

c) Recrystallized Grain:

  • Due to stress relieving in the elongated grains, the grain structure starts nucleation resulting into formation new grain structure.
  • Show the large elongated grains get reformed into small low energy grain structure, bus decreases the strength and increases the ductility of metals as of initial condition.

Factors affecting the recrystallization annealing:

i. Melting Point: Higher the melting point of metal, higher the recrystallization temperature of metal

ii. Degree Of Cold Work: Higher the degree of cold more the dislocation

iii. Grain Size: Finer the grain size lower the recrystallization temperature

iv. Metal Purity: Impurity increases the recrystallization temperature

v. Heating Time: Longer the heating time more finer the recrystallization of grains

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