High Temperature Tensile Properties and Related Microstructural Evolution in Grade 92 Steel

Ferritic-martensitic steels with good high temperature mechanical properties have many promising applications in fossil and nuclear power plants. In this work, a F92 steel was tensile tested from room to elevated temperatures (up to 700 degrees C). This material exhibited higher strength than traditional P92 steels. The reasons for the observed changes in mechanical properties were investigated by studying the microstructural characteristics in undeformed and deformed specimens using transmission electron microscopy. The microstructural evolution accelerated significantly under loading as temperature increased. For instance, the deformed microstructure at 600 degrees C showed early stages of M23C6 precipitate formation under loading. The M23C6 precipitates exhibited more coarsening tendency whereas the MX-type precipitates retained their size. As coarsening of M23C6 precipitates progressed at elevated temperatures, the strength gradually decreased as the solid solution strengthening deteriorated by removing W and Mo from the solid solution matrix.