Z phase strengthened steels for ultra-supercritical power plants
The idea is to exploit the Z phase as a thermodynamically stable strengthening agent in martensitic creep resistant steels. Previously the Z phase has been considered as detrimental, since the coarse Z-phase particles that develop during long time service in high-chromium steels hardly contribute to the strength while growing at the expense of the fine, strengthening nitride particles. However, high chromium contents around 12% are needed, since the current 9% chromium steels do not provide sufficient oxidation resistance at 650°C. Hence the challenge is to control the precipitation of the Z phase in 12% Cr steels such that fine Z particles are formed, which are stable for long times. An important aspect is that the beneficial microstructure should be established also by the post-weld heat treatment.
The Z-Ultra project is funded by FP7 under NMP.2012.2.2-3 - Advanced materials for high-temperature power generation call with Grant agreement no: 309916.