Research on the Microstructure and the Growth Mechanism of Oxidation Film of T91 Steels after Service

Abstract

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 Fe3O4, and the internal oxidation layer is composed of (Fe,Cr)3O4.

Study on Initial Oxidation Film Formation Mechanism of T23 Steel at 600°C

“…The creep resistance performance of the material is better in helium gas than in the air, which shows that the influence in different levels of oxidation is led to the creep resistance properties of materials. Shutao Liu et al [9][10][11][12] analyzed the T23 steel reheater tube explosion accident of a certain power plant and found that it is caused by oxidation in the outer wall of the T23 tube.…”

Oxidation Behavior of a TP304H Stainless Steel in the High Temperature and High Pressure Water Vapor

“…With further researches on oxidation behavior in high temperature of iron and ferroalloy by Kofstad [8][9] , the Cr 2 O 3 layer can form in dry atmosphere, but it is difficult to produce or remain stable in wet oxygen environment. In the present, the oxidation researches were mainly focused on long-term service accident analyses in high-temperature and high-pressure water vapor at domestic and overseas [10][11][12] . However, the oxidation behaviors in high temperature and pressure steam conditions still need further study.…”