Creep Damage Evaluation by Intra-Granular Distortion Analysis

A method of determining the deformation amount by examining the distortion of grains in transmission electron microscope(TEM)called IGD(Intra-granular Distortion)analysis was developed. In this paper, we quantitatively evaluated creep and tensile strain by the shift vector of Kikuchi pattern. Good correlations between average distortion in grains and macro deformation amount were obtained for two heats of 2.25Cr-1Mo steel after tensile and creep deformation. Based on the results, the creep damage of a 2.25Cr-1Mo heat exchanger tube, used for 220 000 hours of service in a fossil power plant, was assessed. Creep strain of the heat exchangeer tube was estimated to be 2% by IGD analysis, which corresponded to life consumption of 70%, reasonable for the material used for 220 000 hours in service.