1) Strain hardening, is the strengthening of a metal or polymer by plastic deformation.

2) This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material.

3) Increase in the number of dislocations is a quantification of work hardening. Plastic deformation occurs as a consequence of work being done on a material, energy is added to the material. In addition, the energy is almost always applied fast enough and in large enough magnitude to not only move existing dislocations, but also to produce a great number of new dislocations by jarring or working the material sufficiently enough. New dislocations are generated in proximity to a Frank–Read source.

4) However, ductility of a work-hardened material is decreased. Ductility is the extent to which a material can undergo plastic deformation, that is, it is how far a material can be plastically deformed before fracture.

5) Another method to harden the metal is to control grain size, as rain boundary act as barrier to dislocation and results in slip between grains, so if grain size is small , shorter the atoms move along slip plane, and for better strength grain size should be small, and size is controlled by rate of solidification from liquid phase.

6) Basically the principle here is to restrict the mobility of dislocations which increases the hardness of material.

7) Main reason that strain harden material is not heated as they lose their strength and hardness by heating as dislocations disappears during heating.

8) But we can use heat treatment to recover the metal form the hardened state and that process is known as recrystallization hardening.

9) Here the work hardened metal is heated below recrystallization temperature so as to recover the grain size as of initial.