Briefly explain with the aid of a quick calculation why some

Briefly explain, with the aid of a quick calculation, why some metals (e.g., lead and tin) do not get stronger when rolled or forged at room temperature.

Solution

Generally all metals get stronger or we can say their tensile strength increases when they are rolled or forged at room temperature. This phenomenon is known as work hardening or strain hardening.

This phenomenon happens due to slip movement of dislocations and piling up of dislocation forest outside crystal or near grain boundaries so that they act as obstacle for further dislocation movement or slip in crystal, Therefore further strain is difficult to produce.

But this phenomenon does not occur during rolling or forging at room temperature of some metals like lead or tin because these metals have thier recrystallisation temperature below room temperature. So, when they are strained even at room temperature, the recrystallization of the grains take place and no piling up of dislocation takes place, hence no strain hardening takes place.