Abstract
The mechanism of localized corrosion and the initiation of corrosion fatigue cracks were investigated metallographically on HT50-CR steel by testing it with a rotating beam fatigue machine in artificial sea water. Two types of localized corrosion, i.e., pitting and grooving, were observed on the specimen surface. The sites of grooving were restricted to the area which was equivalent to the center region of the received plate. Quantitative metallographic data of pit distribution indicated that the pit growth rate in this area was significantly faster than that in the other area, and many cracks nucleated at the grooving sites. Degenerate or banitic pearlite and elongated inclusions (MnS) were observed in this area. SEM and EPMA examinations showed that the preferential dissolution of ferrite around the degenerate pearlite and MnS resulted in the growth of pitting and grooving corrosion. These inhomogeneous structures in the material had a significant role on the corrosion fatigue life.
