from the conferences organized by TANGER Ltd.
Ferritic-martensitic P91 grade steel is widely used for manufacture pipes and boilers of thermal and nuclear power plants due to its high strength and creep behaviour at high temperatures and the advantage of small thermal stress in cyclic operations. During long-term operation of power plant components under elevated temperatures and steam pressure the changes of steels structure occur, on which those mechanical features and remnant service life depend. Due to diffusion processes at elevated temperatures, alloying elements replace iron within carbides, leading to precipitate and coarsening of more thermodynamically favoured alloy carbides as well as lattices parameters of those changing. Thermal ageing effect on the crystal structure parameters changes of M23C6 carbide during long term thermal exposure at 600, 650 and 700 °C temperatures have been performed. The identification of alloy carbides and calculation of their lattice parameters have been accomplished by XRD analysis using the Powder Cell program based on the Le Bail pattern-decomposition method. X-ray diffraction revealed that carbide M23C6 crystal lattice parameter changes as a function of time at high temperature exposure in laboratory conditions. Johnson-Mehl-Avrami (JMA) law was applied for the calculation changes of carbides activation energy E, lattice transformation rate constant k, lattice parameter a and transformation constant n.
Keywords: steel P91, thermal ageing, XRD analysis, carbides, lattice parameters© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.