Characterisation of the microstructural evolution of aged super 304H (UNS30432) advanced austenitic stainless steel
2019-07-18T10:26:44Z (GMT) by
Advanced austenitic stainless steels, such as Super 304H, have been used in reheater and superheater tubes in supercritical and ultra-supercritical power plants for many years now. It is important to characterise the microstructure of ex-service reheater and superheater tubes as this will help to understand long-term microstructural evolution and degradation of the material which can impact the performance and lifetime of the components that are in service. In this research, the microstructure of an ex-service Super 304H reheater tube that has been in service for 99,000 hours at an approximate metal temperature of 873K (600°C), has been characterised. The characterisation techniques used were electron microscopy based and include imaging and chemical analysis techniques. Seven phases were observed as a result of the characterisation work. The phases observed were, MX carbo-nitrides rich in niobium, copper rich particles, M23C6, sigma, Z phase, a cored phase and a BCC phase.