Role of inclusions and carbide bands in corrosion fatigue of pressure vessel steel in high-temperature water

The low-cycle fatigue (LCF) behavior of as-received and thermally aged A533B pressure vessel steels has been investigated in a simulated boiling water reactor (BWR) environment. The inclusions, microstructure, and cyclic cracking behavior were examined carefully. Pronounced carbide bands were found to precipitate along the rolling direction and around inclusions in the thermally aged steel. The aged steel showed a degraded LCF resistance and an enhanced strain-rate dependence of LCF life in simulated BWR water. The inclusions and carbide bands played an important role in the cyclic cracking process. The degradation in fatigue resistance for the thermally aged steel may be attributed to a combined action between the inclusions and the thermal aging-induced material degradation. Possible environmentally assisted cracking mechanisms are also discussed.