Analysis of carbides formed during accelerated aging of 2·25Cr–1Mo steel

Power-generating plants require materials that can withstand service conditions up to 100 000 h. It is well established that creep properties are controlled by the microstructure and that the microstructure changes during creep service. Accelerated aging was used to obtain a series of simulated microstructures similar to those observed in specimens after long-time service. Electron microscopy was used to monitor the microstructural changes in the specimens. Energy-dispersive X-ray analysis was performed on carbon extraction replicas in a transmission electron microscope. The analysis was combined with an in situ electron diffraction identification of the crystal structure of the carbides present. The authors concluded that accelerated thermal aging can produce simulated service microstructures and that it is possible to distinguish between the cubic carbide M₆C and M₂₃C₆ using the X-rays generated in these crystals by the electron beam. Thus a comprehensive study of carbide formation and composition could be achieved.