Environmentally Controlled Fatigue Crack-Growth Rates in SAE 4340 Steel—Temperature Effects

Abstract

The temperature dependence of sustained-loading and corrosion-fatigue crack-propagation behavior of SAE 4340 steel immersed in distilled water was investigated using the fracture mechanics approach. During the load cycle, stress-intensity histories had values higher than the static threshold stress intensity (KIscc ). For a stress-intensity range of 20 ksi in., a factor of 30 increase in the corrosion-fatigue crack-growth rate was noted for a temperature increase of 70 deg C. The mechanical variables were found to have much less influence than the environmental reaction rate. In contrast with dry air results, the fatigue crack-growth rate in a distilled water environment was dependent on the mean stress-intensity for stress-intensity histories above KIscc . This dependence varied with temperature level.