Research on the microstructure and the growth mechanism of oxidation film of T91 steels after service

摘要

The character of structure and the micro-area elements of inner oxidation film were investigated by using metallographic microscope, electron microscopy, energy spectrum analysis and other testing methods based on samples of superheater and reheater tube cutting from three units. The results showed that the inner wall oxide layer of T91 steel superheater tube after running exhibited a double-layer structure, including inner and outer layer, and the interface between the two layers is the original metal surface. There exists a transition zone between the inner oxide film and metal matrix. A concentration gradient of alloy element in transition zone can be observed and the intergranular oxidation is present. The Fe-rich outer oxide layer does not contain Cr, which consists of Fe_3O_4, and the internal oxidation layer is composed of (Fe, Cr)_3O_4.