Effect of Long-Term Aging on the Microstructural Evolution in a P91 Steel

The precipitation and growth mechanism of the Laves phase and the coarsening behaviors of Laves phase, M23C6 and MX carbonitrides have been emphatically investigated in P91 steel at 625 degrees C under different aging conditions. After long-term aging at 625 degrees C (>1500 h), it was observed that the Laves phase grew rapidly in the region near the M23C6 carbide once precipitated, and further gradually completed the engulfment process until the M23C6 carbide particles disappeared. Furthermore, a new crystallographic orientation relationship between M23C6 carbides and Laves phase has been observed at 625 degrees C for 5000 h, which is {0001}(Laves)parallel to{111}(M23C6), < 11 (2) over bar1 >(Laves) parallel to < 011 >(M23C6). The coarsening behaviors of Laves phase, M23C6 carbides and MX carbonitrides have been emphatically investigated, conforming to the existing ripening model of multicomponent alloys. The coarsening rates for the Laves phase, M23C6 and MX have values of similar to 32.2 (>= 5000 h), 5.3 and 0.6 nm/h(1/3), respectively.

Automated summary

This study investigated the precipitation and growth mechanism of the Laves phase and the coarsening behaviors of Laves phase, M23C6, and MX carbonitrides in P91 steel at 625 degrees C. It was found that the Laves phase grew rapidly near the M23C6 carbide and exhibited a specific crystallographic orientation relationship. Additionally, the study observed the coarsening rates of these phases.