it is deformation below recrystalization temperature.

Plastic deformation is a permanent change in the shape or size of a material that occurs when it is subjected to stress beyond its elastic limit. During plastic deformation, the material undergoes a restructuring of its internal arrangement of atoms without ultimately breaking. This type of deformation is common in metals and other materials used in engineering applications.

Copper wire will undergo plastic deformation even though it does not break like steel wire.

When a material deforms, it does so in several stages. The first stage, called the elastic region of deformation, is linear in nature and not permanent. A stress can be applied, and once it's removed, the material will regain all of the deformation. The second stage, plastic deformation, is permanent. A material that has been stressed into the plastic region will regain the elastic deformation, but will permanently maintain the plastic.

The proportional strength is the point at which plastic deformation begins.

fracturing, basal slip and plastic deformation or plastic flow :)