Abstract
The influence of alloy composition and microstructure on fatigue-crack initiation in air and in hot, neutral sodium chloride solution has been investigated. Corrosion-fatigue experiments were carried out with three martensitic chromium steels and two ferritic high-chromium steels. The mechanisms of corrosion-fatigue crack initiation were strongly related to the general corrosion behaviour of these steels. Pitting corrosion led to a drastic decrease in the fatigue lifetime, and a fatigue limit such as that measured in air no longer occurred. In contrast, a fatigue limit was observed under passive corrosion conditions. The decrease in the fatigue strength was less pronounced than in the case of pitting corrosion. The fatigue properties of the hfghest alloyed steel are not influenced by the corrosive medium, and the increase in resistance to corrosion fatigue as the chromium content is increased may be explained by the film-rupture model. An attempt is made to show how to optimize the corrosion-fatigue resistance of ferritic chromium steels.
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