Question

The main purpose of annealing is

Answer 1

It is very important to heat –treat a metal to give it certain properties. For this purpose various treatments are carried out. One of which is Annealing. The purposes of annealing are
1-To soften the steel so that it may be more easily machined
2-To relieve internal stresses which may have been caused by working the metal or by unequal contraction in casting.

Now how the process of annealing is carried out is also an interesting question. The basic process can be briefly summarized in three steps. The three steps are as follows:

(a)heating slowly to the required temperature
(b)holding as that temperature for long enough to enable the internal changes to take place
(c)Cooling slowly.

The temperature for annealing must be 30 to 50 degree centigrade above the higher critical pointfor steels up to 0-9% carbon and about the same amount above the lower critical point for high carbon and tool steel.
The time taken by the metal to reach the temperature of the furnace and the period for which it should be soaked at annealing temperature vary according to the shape and dimensions of the article, but it must be remembered that the process should not be hurried.