Rotating
fatigue tests were carried out on a cantilever bending test
machine, at a frequency of 47 Hz (2820 rpm) in laboratory air atmosphere. The fatigue tests were carried out
until complete fracture of specimens occurred. The
fatigue strength is assumed to be the maximum bending
stress at 106 cycles to cause failure for all carburized
and heat treated specimens. The fracture surfaces of
specimens were examined under the scanning electron
microscope in order to evaluate the crack initiation and
growth behaviour of the materials in the core and carburized regions of the specimens.