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Abstract: Specimens from a series of carburizing steels with constant compositions except for variations in sulfur content, 0.006, 0.015, and 0.029 wt%, were machined from bar stock into cantilever type fatigue specimens. The specimens were carburized at 927° C (1700° F), oil quenched, tempered at 150° C (300° F), and tested in bending fatigue. Endurance limits of 1260 MPa (183 ksi), 1200 MPa (174 ksi), and 1070 MPa (155 ksi) were determined for the 0.006 wt% S, 0.015 wt% S, and 0.029 wt% S specimens, respectively. The major effect of sulfur was to increase the scatter in fatigue performance. All fracture was initiated by intergranular cracking, and elongated sulfides close to or intersecting the fatigue specimen surfaces apparently lowered the applied stresses required to initiate incipient intergranular cracks.