Abstract
The initiation of corrosion-fatigue cracks has been studied for BS 4360 50D (1·5Mn–0·5Si steel) tested in 3·5% NaCl. Pit and crack depths have been measured, and it has been shown that pits initiate mainly at inclusions, while cracks nucleate at large pits or groups of pits. Quantitative metallographic data were obtained for pit and crack distributions for specimens with cracks nucleating both normal and parallel to the banding direction. Comparative data are presented for an unbanded 50D steel and a low-sulphur steel. This provides a basis of information for future comparative studies. The fact that short cracks grow to lengths of about 100μm at a constant growth rate is interpreted as indicating that anodic dissolution is the initial mechanism of crack extension. For these short cracks the absolute growth rates correspond to only a few atomic dimensions per cycle.
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