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| Carbides Evolution in 12Cr Martensitic Heat-resistant Steel with Life Depletion for Long-term Service |
| Zheng-fei HU,Da-hai HE,Fan MO |
| School of Materials Science and Engineering, Tongji University, Shanghai 201804, China |
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Abstract Evaluating the residual life of exposed components in power industry is a very important procedure in routine examination. The microstructures of a series of X20CrMoV12.1 martensitic 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 M23C6 varied distinctly. The aspect ratio of coarsened carbides along grain boundary increased several fold with respect to their original size. The composition of coarsened M23C6 carbide shows the most regular trend of Cr enrichment and the statistical result of Cr enrichment in M23C6 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.
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Received: 10 December 2013
Published: 06 March 2015
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| Fund:National Natural Science Foundation of China |
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2015, Vol. 22 
