Effects of Cyclic Softening on Fatigue Crack Propagation Properties of Steel

Abstract

In this paper, the effect of cyclic softening properties on fatigue crack propagation behavior was investigated. Ferrite and ferrite-pearlite steels with different cyclic softening properties were produced by cold rolling process. The cold-rolled steels showed cyclic softening, and the cyclic softening rate increased as the cold reduction rate increased. As a result of fatigue crack propagation tests using CT specimens, the fatigue crack growth rate decreased with increasing the cold reduction rate. The crack growth rate and the cyclic softening rate showed a good correlation regardless of the microstructure. The cold-rolled steels showed crack closure/opening behavior, and the crack opening load increased with increasing cold reduction rate. In addition, the difference in the fatigue crack propagation rates of cold-rolled steels was explained by the effective stress intensity factor range. From these results, the decrease of the fatigue crack growth by cold rolling was considered to be mainly due to the suppression of crack opening by cyclic softening near the fatigue crack tip.