Study on the microstructure evolution and effect on mechanical properties of P92 steel during long term service

P92 heat-resistant steel is widely utilized in ultra-supercritical units due to its exceptional properties. This study examines the microstructure evolution and mechanical properties change of P92 during service spanning 0 to 93,000 hours, while also exploring the correlation between microstructure changes and property variations. The results indicate that the matrix of P92 steel retains its characteristic tempered martensite structure, and the large-angle and small-angle grain boundaries in the steel remain nearly unchanged throughout extended service periods. However, the deterioration of P92 steel properties can mainly be attributed to alterations in precipitate size and martensitic lath width. The size of M23C6 and Laves particles increased from their initial dimensions of 150 nm and 0 nm to 260 nm and 370 nm, respectively. Moreover, the width of the martensitic lath increased from 350 nm to 700 nm. The martensitic lath contributes over 60% of the theoretical tensile strength, playing a pivotal role in the exceptional strength of P92 steel during service. The presence of coarse Laves particles at the interface leads to a rapid reduction in impact energy, decreasing from approximately 130J to 50J, negatively affecting the impact energy of P92 steel.