Creep damage quantification of 2 center dot 25Cr-1Mo steel using scanning electron microscopy

The material 2.25Cr-1Mo alloy steel has been used extensively for high temp erature applications in power generation plant for over five decades owing to its long term creep resistance. It has been recognised that the lifetime of a high temperature component containing pre-existing defects is depende nt not only upon the material's crack propagation resistance but also upon an incubation period before crack growth during which a damage zone ahead o f the defect tip develops. The extent of the damage occurring during this i ncubation period, before crack propagation, is dependent upon the stress in tensity at the defect tip, the ductility of the material, and the microstru cture in the damage zone. The present paper details a technique for quantif ying the early stages of creep damage using image analysis in the scanning electron microscope, and compares the degree, distribution, and orientation of creep damage occurring in two microstructural variables of 2.25Cr-1Mo a lloy steel, The paper describes the procedures necessary for generating con sistent and reproducible quantitative analysis results, including specimen preparation, defect detection, and measurement criteria. The image analysis process, its accuracy, and application to the study of creep damage mechan isms occurring ahead of defects are discussed.