Residual stress, fatigue and stress relief

wrote:
This is because residual compression on one side of the bend is
residual tension on the other, (clip)
^^^^^^^^^^^^^^^^
No. You are evidently applying the equations for bending stress, with
symmetry about the neutral axis. If there are tensile stresses present, the
bending stresses add on one side and subtract on the other. Then, if the
higher value (either tensile or compressive) passes the yield point, the
symmetry is gone, and the residual stress could have an effect on fatigue
afterward.