Abstract
Modern (9–12)%Cr steels designated for power plants with higher steam parameters show a pronounced time dependent change in microstructure during purely thermal or creep stress exposure at temperatures around 600°C that determines their properties in service. In addition to other microstructural parameters, the state of the precipitates plays an important role for microstructural stability which is a prerequisite for long term creep strength. In order to support theoretical studies on precipitation growth and coarsening with more reliable experimental data, in this study a method is introduced for the quantification of the state of precipitates in (9–12)%Cr steels which is based on the application of different TEM methods. Therefore up to about 33 000 h aged specimens of the martensitic cast alloy G-X12CrMoWVNbN-10-1-1 were investigated by means of electron microscopy. The application of energy filtering transmission electron microscopy (EFTEM) allowed a reliable quantitative distinction between M23C6, VN, and Laves phases to establish the size distribution of these precipitates in different specimens conditions.
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