Factors affecting non-propagation of fatigue crack in a low-carbon steel -(Effect of oxide-induced crack closure)

Rotating bending fatigue tests were carried out in air and in pure argon to clarify the effect of oxide-induced crack closure on crack non-propagation . The materials used were Ti added extra-low-carbon steel with no strain ag eing, 0.02% carbon steel with a single ferrite phase, and annealed 0.19% ca rbon steel. The results obtained are as follows. (1) Threshold stress for f atigue crack growth is lower for Ti added extra-low-carbon steel in argon t han for that in air, though the fatigue crack has a tendency to propagate m ore slowly in argon than the air. The above result shows that oxide-induced crack closure plays a significant role in crack non-propagation. (2) It se ems that the influence of oxide-induced crack closure on crack non-propagat ion is smaller than the influence of strain ageing and microstructure. (3) A non-propagating crack is observed in the steel with a single ferrite phas e even when strain ageing and oxide-induced crack closure do not occur.