Investigation on the Microstructure and Mechanical Properties of T23 Steel of Super-Critical Final Boiler Reheater after Long-Term Service

At present, the changes of microstructure and mechanical properties of T23 steel after served for more than 50 000 h have been less studied.In this work, with using the heat-delivery surface tubes of a 600 MW super-critical boiler as research object, the T23 steel final reheater tubes at various positions after about 80 000 h of service time were tested by microstructure analysis, tensile properties tests at room temperature and 525 ℃ temperature, and the deterioration degree and difference in mechanical properties between back and meet smoke side of tubes after long-term service were investigated further.Results showed that the coarse M6C carbide apparently grew and precipitated at grain boundary, and the microstructure of samples presented obvious aging characteristics.As for the mechanism properties, all T23 tube samples showed badly degradation in tensile properties, and they could not meet the usage requirement.Moreover, there was no significant difference in microstructure between the tubes at the front and back of smoke side, but the sample at the front smoke side showed an obvious decline in tensile properties in the comparison of that at the back smoke side, indicating that the long-term high temperature flue gas scour in the furnace had a significant effect on the performance of samples at the front smoke side.