5.13.5 Stress Relief
Stress relief is the heating of steel to a temperature below the transformation temperature, as in
tempering, but it is done primarily to relieve internal stresses and to prevent distortion or cracking
during machining.
When a metal is heated, expansion occurs. Upon cooling, the reverse reaction takes place and
contraction is observed. In welding, when a part is heated more at one point than at another, internal
stresses develop. Internal, or residual stresses, are bad because they can generate warping during
machining. To relieve stresses, steel is heated uniformly and cooled slowly to room temperature.