Factors Affecting Non-Propagation of Fatigue Crack in a Low-Carbon Steel

(Effect of Oxide-Induced Crack Closure)

Abstract

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 ageing, 0.02% carbon steel with a single ferrite phase, and annealed 0.19% carbon steel. The results obtained are as follows. (1) Threshold stress for fatigue crack growth is lower for Ti added extra-low-carbon steel in argon than for that in air, though the fatigue crack has a tendency to propagate more 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 seems that the influence of oxide-induced crack closure on crack non-propagation is smaller than the influence of strain ageing and microstructure. (3) A non-propagating crack is observed in the steel with a single ferrite phase even when strain ageing and oxide-induced crack closure do not occur.