The yield strength increases more rapidly than the tensile strength, so that, as the amount of plastic deformation is increased, the gap between the yield and tensile strengths decreases. This is important in certain forming operations where appreciable deformation is required. In drawing, for example, the load must be above the yield point to obtain appreciable deformation but below the tensile strength to avoid failure. If the gap is narrow, very close control of the load is required. Effect of cold working on tensile and yield strength of copper.
Ductility follows a path opposite to that of hardness.
The increase in internal energy, particularly at the grain boundaries, makes the material more susceptible to inter granular corrosion, thereby reducing its corrosion resistance. Known as stress corrosion, this is an acceleration of corrosion in certain environments due to residual stresses resulting from cold working. One of the ways to avoid stress corrosion cracking is to relieve the internal stresses by suitable heat treatment after cold working and before placing the material in service. Effect of cold working on tensile strength, hardness, ductility and grain size.