The application of new materials in the power units of new generation, which are able to work at ultra-supercritical parameters of steam (T ≥ 620-650 °С, Р = 25 - 35 MPa), can increase their efficiency up to 41-44 % and decrease the amount of harmful emissions. The aim of the present research was to investigate the major structural changes in new Re-containing steel during ageing at temperature of 650 °C. Structural changes in martensitic 10%Сr-3 %Co-3 %W-0.2 %Re steel during long-term ageing at 650 °C for about 13,600 h were investigated. This steel was solution treated at 1050 °C for 1 h, cooled in air, and subsequently tempered at 770 °C for 3 h. High thermal stability of tempered martensitic/ferritic lath structure is provided by a dispersion of fine M23C6 carbides precipitated during tempering and the Laves phase particles precipitated after 110 h of 650 °C aging. The precipitation of the Laves phase particles is accompanied with depletion of W atoms from the ferritic matrix. Moreover, decreasing W content in the ferritic matrix have a good correlation with increasing volume fraction of the Laves phase particles in the structure of the 10 %Сr-3 %Co-3%W-0.2 %Re steel during long-term ageing at 650 °C. The effect of Re addition on the kinetic of depletion of W from the solid solution and kinetic of precipitation Laves phase will be discussed.Keywords: Martensitic steel, phase transformation, ageing, particles, microstructural evolution, precipitation
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