The results of the investigations of fatigue crack behaviour in laser hardened specimens made of medium carbon steel under reversed bending (R=-1) are presented. Characteristic features of crack propagation were selected: various crack source locations, temporary crack arrest at the border of laser tracks and the matrix, discontinuous crack growth in the tracks. In order to explain the sites of primary crack sources in the samples the results of residual stress measurements and analytical description of the stress distributions as a function of sample depth were included. A mechanism of cracking has been established on the basis of fractographic analysis of fracture surfaces.
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