Abstract
In order to investigate the influence of grain size on the resistance to crack growth, fatigue properties of commercial fine-grained carbon steels with grain sizes of 6.5 and 20 μm were investigated based on the crack initiation and propagation behavior through the successive observation of surface state of smooth specimen under rotating bending. A crack initiated at the early stage of stress repetitions and most of fatigue life was occupied by the growth life of a crack smaller than 1〜2 mm. The crack growth rate determined by the term σ_a^nl, uniquely in both steels, where σ_a and l are the stress amplitude and the crack length and n is constant. The fine grained- steel has an excellent resistance to crack growth in comparison with many annealed carbon steels.
