| ||Cold working produces additional dislocations within the metal structure. When two or more dislocations meet, the movement of one tends to interfere with the movement of the other. The more dislocations there are, the more they will hinder each other's movement. |
Initially the dislocations produced by cold working can move through the metal structure and the shape of the material will change. As the working continues, however, the movement of the dislocations becomes more difficult. This increases the strength of the metal and also makes it stiffer. Therefore it becomes less malleable and ductile. That is, it is more difficult to change its shape. We say that the metal has become work hardened.
To make it more malleable and ductile again, the metal can be annealed (see page 9).