as the distance below the surface
where the hardness was equal to 550 VHN. Microstructural aspects of case and core zones were examined by
an optical microscope. Mechanical residual stress
measurements were realised by measuring the changes
in length of 10 mm diameter and 100 mm long specimens, after removing surface layers by stepwise cylindrical grinding. The specimens used in residual stress
measurements were carburized in the same manner with
the fatigue specimens, and an LVDT with the accuracy
of 10−6 meters was used to measure dimensional
changes. Therefore, considering the elastic strain relaxation after each grinding, the residual stresses at the surfaces were determined respectively [21].