The effects of elevated testing temperature on the fatigue behavior of carburized steel were evaluated by testing modified Brügger bending fatigue specimens at room temperature, 90 °C and 150 °C. SAE
4023, SAE
4320, and SAE
9310 steel were studied to assess the influence of alloy content and stability of retained austenite. Fatigue samples were gas-carburized and tested in air at 30 Hz with a stress ratio of 0.1. An infrared spot lamp was used to heat samples to 90 °C (150 °F) or 150 °C (302 °F) during testing. S-N curves were developed for the room temperature baseline tests as well as elevated temperature tests. The endurance limits determined are as follows: SAE
4023-RT (1170 MPa), SAE
4023-90°C (1140 MPa), SAE
4320-RT (1210 MPa), SAE
4320-90°C (1280 MPa), SAE
9310-RT (1380 MPa), SAE
9310-90°C (1240 MPa). At 150 °C all samples exhibited permanent plastic deformation under the test conditions examined; therefore, it was not possible to obtain meaningful endurance limits at this temperature. The results showed that for all steels, the high stress/low cycle fatigue performance decreased with increased testing temperature. The endurance limit of SAE
9310 steel was most affected by the elevated testing temperature, resulting in a 140 MPa decrease in endurance limit. The endurance limits of the lower alloyed materials, SAE
4023 and
4320 steels, were essentially unaffected by the elevated testing temperature.