Environmental Effects on Initiation and Propagation of Fatigue Cracks in High Strength Steel

Abstract

Environmentally enhanced fatigue crack initiation and propagation characteristics of a high strength steel have been discussed in regard to the influences of stress cycle frequency and of tempering temperature. A small amount of moisture or an aqueous environment considerably decreases the fatigue strength of the steel tempered at a temperature lower than 400°C due to the increased sensitivity to hydrogen embrittlement (HE). The co-operative action of fatigue and HE due to the occluded hydrogen results in an enhanced crack growth characteristics can be well explained by the occulusion process of hydrogen. The facet area fraction by HE increases with an increase by hydrogen content, though striation-like secondary cracking is observable on almost whole surfaces in argon. A fruitful cathodic protection can not be expected for the corrosion fatigue of a high strength steel having a high hydrogen content.