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Evaluating the residual life of exposed components in power industry is a very important procedure in routine examination.The microstructures of a series of X20CrMoV12.1martensitic superheater tube samples in a boiler in different service periods were investigated extensively to extract a quantitative relationship.During long-term service from start to rupture,hardness decreased monotonically with life depletion,and the decrease of hardness in prior austenite grain boundary was steeper than that in the matrix.Microstructure observation showed obvious damage characteristics,including carbide coarsening and martensite decomposing,and the martensite structure decomposed completely in rupture state.The morphology,distribution and composition of the main precipitates M_(23)C_6 varied distinctly.The aspect ratio of coarsened carbides along grain boundary increased several fold with respect to their original size.The composition of coarsened M_(23)C_6 carbide shows the most regular trend of Cr enrichment and the statistical result of Cr enrichment in M_(23)C_6 shows a linear correlation between the ratio of Cr to Fe and service time to the power of 3/2,which may be considered as an index of material degradation due to long-term service exposure.
Evaluating the residual life of exposed components in power industry is a very important procedure in routine examination. Microstructures of a series of X20CrMoV12.1martensitic superheater tube samples in a boiler in different service periods were conducted extensively to extract a quantitative relationship. Duration long- term service from start to rupture, hardness decreased monotonically with life depletion, and the decrease of hardness in prior austenite grain boundary was steeper than that in the matrix. Microstructure study showed significant damage characteristics, including carbide coarsening and martensite decomposing, and the martensite structure decomposed completely in rupture state. The morphology, distribution and composition of the main precipitates M_ (23) C_6 varied distinctly. The aspect ratio of coarsened carbides along grain boundary increased several fold with respect to their original size. The composition of coarsened M_ (23 ) C_6 carbide shows the most regular trend of C r enrichment and the statistical result of Cr enrichment in M_ (23) C_6 shows a linear correlation between the ratio of Cr to Fe and service time to the power of 3/2, which may be considered as an index of material degradation due to long -term service exposure.