Deformation and Fatigue Damage in 1070 Steel under Thermal Loading

The fatigue lives of 1070 steel (Class U wheel steel) under (1) isothermal loading, (2) thermo-mechanical constant amplitude loading, and (3) thermo-mechanical block loading have been examined. Fatigue lives for these three cases were compared based on the same mechanical strain range and maximum temperature level, with similar strain rates. Predictions of thermo-mechanical block loading cases were nonconservative based on isothermal data, while the predictions improved to within a factor of 1.5 of experimental lives when thermo-mechanical constant amplitude data were utilized.

Oxide scales readily formed at high temperatures (>500°C) and resulted in increased damage due to a localized high strain state and an inherent lack of ductility. Oxides of different composition and morphology form depending on the temperature and type of loading. Stratified and non-stratified oxide layers (predominantly Fe₃O₄) were identified in the experiments.