Influence of Long-Term Annealing on Microstructure and Creep Properties of P92 Steel Welded Joints
Abstract
The study presents an analysis of the relationship between microstructural evolution and creep properties degradation in welded joints made of P92 (X10CrWMoVNb9-2) steel subjected to long-term annealing. The investigated material consisted of butt-welded pipe joints exposed to thermal ageing at 600°C and 650°C for up to 10,000 h. Microstructural observations were performed using scanning electron microscopy (SEM), while creep behaviour was evaluated using both constant-load tests with strain measurement and accelerated creep rupture tests. The results indicate that degradation processes are strongly temperature-dependent and are particularly intensified in the heat-affected zone (HAZ), where fracture initiation consistently occurs. The dominant degradation mechanisms include coarsening of M23C6 carbides, dissolution of MX precipitates and recovery of the tempered martensitic structure. These changes lead to a significant increase in creep rate, reaching up to 25.7 times compared to the initial state, and a reduction in creep rupture strength of up to 34%. A strong correlation between microstructure and creep behaviour was confirmed, indicating that microstructural analysis can be effectively used to assess the residual life of welded joints in high-temperature applications.