Fatigue properties of a transformation-induced plasticity-aided martensitic steel subjected to vacuum carburisation under carbon potentials ranging from 0.70 to 0.80 mass% and subsequent fine-particle peening were investigated for the fabrication of precision transmission gears. The fatigue limits of smooth specimens increased by 34–41% with increasing carbon potential, compared with that of heat-treated and fine-particle peened steel. The notched fatigue limits increased to a lesser degree except in case of carbon potential of 0.70 mass%. The increased smooth fatigue limits were associated with the high Vickers hardness and compressive residual stress via severe plastic deformation and the strain-induced martensitic transformation during fine-particle peening, as well as a 50% reduction of retained austenite fraction during fatigue deformation.
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