Microstructure characterization and mechanical properties of austenitic Super 304H steel after operation

The paper presents the results of testing the microstructure and mechanical properties of austenitic Super 304H steel after approximately 31,000 h of operation at a temperature of 570 °C. The microstructure analysis showed that the utilization of the tested steel contributed to the precipitation of numerous M23C6 carbides and individual sigma phase particles at grain boundaries, while dispersive ε_Cu and MX particles was observed inside the grains. At the grain boundaries, the precipitates sometimes formed a continuous mesh. The presence of numerous secondary phases resulted in higher than standard strength properties while maintaining the required plastic properties. •Austenitic creep-resistant Super 304h steel after long-term service has been investigated.•Changes in the microstructure after long-term service have been examined.•Precipitation of the secondary carbides M23C6, sigma, MX and ε_Cu was observed after service.