Cold Working

Cold working refers to the deliberate, plastic deformation of metals at temperatures notably below the recrystallisation point of the respective material. The unintentionally induced and uncontrollable deformation is known as cold deformation. In cold working, the strength of materials is determined by the increase of dislocations within the crystal structure. Upon movement, they can interfere each other. In some cases, the material is heat treated to achieve better surface properties.  

Results of Cold Working

The result of cold working is called work hardening. This process describes the alternation and increase of dislocations within the crystal structure. The result of work hardening: tensile strength, yield point, and hardness of the material increase. At the same time, it can also become more brittle and the internal stress can increase.

Other side effects of cold working are the changes in electric conductivity as well as ferromagnetic properties. Electric conductivity can be negatively influenced, while ferromagnetic properties can improve. For instance, permanent magnetisation can occur in steel, such as tool steel.

Work hardening is caused intentionally to increase hardness and strength of the material. In the steel industry however, unintentional cold deforming can occur when materials are exposed to challenging conditions. Work hardening is most widely used for the processing of copper. Due to its ductile nature, copper can be cold worked and then work hardened, to increase hardness. This is often the case with too soft copper wires.

Distinction from Hot Working

Hot working is the intentional deformation of a material at a temperature above recrystallisation point.

The differences between hot and cold working are as follows:

  • Temperature: The most obvious difference between warm and cold working is, of course, the temperature. While cold working operates at temperatures far below recrystallisation temperature, how working operates at temperatures slightly above.
  • Shape change: Due to the high temperature, materials can be made more malleable when it comes to hot working. Cold working, on the other hand, only allows small shape changes. However, the primary intent of cold working is the change of material property, not shape.
  • Size tolerance: Size tolerances are smaller for materials that are cold worked, which is why they can be processed more precisely.
  • Hardening: The main objective of cold working is the hardening of materials. In contrast, hardness is removed when it comes to hot working.