A physical-based yield strength model for the microstructural degradation of G115 steel during long-term creep

The changes occurring in the microstructure and mechanical properties of interrupted G115 steel samples during creep at 650 degrees C and 140 MPa were systematically investigated. M23C6 carbides exhibited a low coarsening rate in the G115 steel upon the addition of boron. Cu-rich phase particles can significantly stabilize the microstructure in the early stages of creep. However, they gradually dissolved after similar to 1000 h. The geometrically necessary dislocation (GND) density decreased significantly during the transient creep stage and was relatively stable after 1045 h. Finally, it decreased rapidly. The mean width of the martensite lath structures increased slightly with an increase in the creep time from 0 h to 302 h, after which it dramatically increased, which is closely related to the evolution of Cu-rich phase particles. On the basis of the obtained experimental results, a microstructural-based yield strength model was developed for establishing the correlation between the microstructure and mechanical properties of G115 steel at different creep stages. The results calculated by the model were in good agreement with the experimental data.