High cycle fatigue resistance of AISI E9310 carburized steel with two different levels of surface retained austenite and surface residual stress

Abstract

The high cycle fatigue resistance of carburized AISI E9310 steel has been investigated for two different levels of surface retained austenite and surface residual stress. Fatigue specimens were carburized to a case depth of 1.9 mm with a surface carbon content of 1.0 wt pct carbon. This treatment gave surface retained austenite and surface residual stress levels of 56 vol pct and -595 MPa (-86 ksi), respectively. Half of these specimens were then given a refrigeration treatment which lowered the surface retained austenite level to 31 vol pct and raised the surface residual stress level to —760 MPa (-110 ksi). High cycle fatigue tests showed that the specimens with the higher surface retained austenite level had the best high cycle fatigue resistance. X-ray diffraction studies showed that both treatments of steel exhibited decreasing retained austenite and residual stress levels with cycling. Light microscopy and electron fractography showed that fracture apparently initiated in the carburized case, although the exact initiation site could not be determined. A nalysis of the results suggests that the poorer high cycle fatigue resistance for the steel with the low retained austenite results from a degradation of the fatigue resistance of the case material.