High-Cycle and Impact Fatigue Behavior of Carburized Steels 780771

The influence of residual stress and retained austenite on the fracture behavior of bend test specimens of carburized steels was evaluated. The test results are part of an ongoing research effort intended to compare the relative fracture properties of alternate grades of steel and their respective standard grades having similar hardenability. In general, steels of equal hardenability and core carbon content exhibited similar fracture behavior. Compressive residual stress in the carburized case was found to significantly influence the impact fracture stress which, in turn, was correlated with impact fatigue properties. High levels of retained austenite at the surface caused the peak compressive residual stress to occur further into the case. The occurrence of residual stress peaks further into the case was not necessarily detrimental to impact fracture stress or impact fatigue properties. High-cycle fatigue limits were more dependent on processing variables than on differences in alloy content.