Speaker
Description
Martensitic steels such as modified 9% Cr steels (P91 & P92) were developed and widely utilized in industry due to their low price and acceptable creep strength among martensitic steels. The martensitic 12% Cr steels were proposed to improve corrosion resistance of components at higher temperature to improve efficiency of power plants and reduce CO2 emission. However, all attempts to develop 12% Cr steels failed due to the microstructure instability of martensite during service.
Addition of 13-16% chromium with different Nickel and Carbon contents, can change the martensitic microstructure to the more stable ferritic structure. Both, microstructure and mechanical properties of ferritic steels strongly depend on the chemical composition and the performed heat treatment. In this study, first, the equilibrium phases of ferritic steels with different Nickel and Carbon contents were simulated by MatCalc software in order to predict the phase fraction of the stable phases. Afterwards, chemical composition was modified to improve the stability of the microstructure.
The experimental results reveal that ferritic steels have a better creep strength than the martensitic steels such as MarBN due to the lower dislocation density and lack of lath structure. In addition, ferritic steels reveal the lowest coefficient of thermal expansion among superalloys, martensitic and austenitic steels, which makes them suitable for future cyclic operating power plants. Finally, the microstructure of a ferritic steel was investigated by means of SEM, XRD and TEM to determine phase fraction, shape and distribution of precipitates such as MX phases, carbides and Laves-phase during creep.
| Speaker Country | Austria |
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