What is residual stress?

Residual stress is a structural weakness that occurs in the casting process of iron, the main material used in brake discs.

During normal street-use, residual stress does not cause any problems with the discs. When the discs are used at race circuits at high temperature conditions for an extensive of time, the residual stresses within the disc can lead to thermal cracking and deformation. The heat treatment process relieves the residual stresses to prevent thermal cracking and deformation from occurring.