Microstructure-Based Creep Life Assessment of 1CrMoV Turbine Rotor Steels After Long-Term Service

This study evaluates the use of quantitative analytical electron microscopy for microstructure-based creep life assessment of service-exposed 1CrMoV steel turbine rotors. Changes in the microstructure (bainitic laths, carbide phases) were related to creep life exhaustion estimations done using conventional methods based on cavities and hardness. The volume-weighted average size and surface density of bainitic laths correlate with cavity-based estimated creep life exhaustion. However, the heterogeneity of grain structure limits the use of bainitic lath parameters for assessing creep life based on microstructure. The phase proportions of M₃C, M₂C, and M₇C₃ carbides, as determined by TKD-EDS mapping, show a strong correlation (R²: 0.64, 0.61, and 0.86) with creep life exhaustion estimations and could potentially be used as an additional indicator of the material state of the critical failure region in 1CrMoV turbine rotors.