An original method was recently developed for an assessment of residual stresses in case-hardened steels based on S-N curves of hardened and virgin samples along with the measurement of location of fish-eye crack centres. This method is applicable only when the surface of virgin specimens is sufficiently smooth to avoid the initiation of fatigue cracks from large surface defects. A systematic study focused on identification of the applicability range was started using specimens with extremely rough surfaces finished by turning. The analysis yielded compressive stresses up to 700 MPa at the hardened surface and high tensile stresses up to 500 MPa in the specimen bulk. The most probable location of fish-eye centres was, however, predicted to be in a significantly higher depth than that found in the real specimens. This could be attributed to the large surface damage induced by turning which, therefore, lies beyond the acceptable range of surface machining.Keywords: Nitrided steel, residual stress, fish-eye crack, S-N curves.
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