Bridging legacy and innovation: mechanism-resolved reform of creep damage equations of high-Cr steels in long-term service

High-chromium martensitic steels in power plants must endure decades of creep at 500–650 °C under moderate stress. Direct testing is impractical, making extrapolation essential – yet small modelling errors can lead to overdesign or premature maintenance. While Dyson’s multiplicative ordinary differential equation (ODE) model is a benchmark for creep damage modelling, its strain-driven cavitation lacks explicit calibration with a time-temperature-stress (TTS) framework. This study introduces a TTS-calibrated constitutive framework with three specific refinements: (1) micro-to-macro cavitation damage mapping via 𝝎𝒏⁡(𝝈,𝑻)=𝑼′⁡(𝝈,𝑻)⁢𝒕𝒎 𝒂⁢𝐧𝐝 𝑫𝒏⁡(𝝈,𝑻)=𝑼 ′′⁡(𝝈,𝑻)⁢𝒕𝒎, grounded in cavitation kinetics; (2) a modified Sinh law for minimum creep rate: εmin = Asinh(C 𝝈𝒒); and (3) a stress-dependent amplification term for tertiary creep: 1⁄(1–Dn)^P(σ). P91 steel was chosen for its industrial relevance and synchrotron cavitation data at specific temperature. The refined model aligns well with experimental creep curves and cavitation data and enhances lifetime prediction, offering improved physical traceability and extrapolation fidelity.