SA-03-2(040) Non-destructive creep damage evaluation by carbide structure analysis-1 : Carbide structure change of CrMoV turbine rotor steel(Life Assessment of Thermal Power Plant 3)

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This paper describes a unique and brand-new non-destructive creep damage evaluation method using carbide extraction replica film. Quantitative investigation of the extracted carbides structure by X-ray diffraction was carried out using interrupted creep test specimens. During creep deformation, the carbides initially precipitated at grain boundaries of CrMoV steel were mainly Fe_3C, whereas M_<23>C_6 carbides started precipitating and coarsening at grain boundaries. The ratio of M_<23>C_6 carbide to Fe_3C carbide, which tentatively defined as J-parameter here, continuously increased with increasing creep strain and time. Creep interruption tests were conducted for a number of heats, and then the effect of microstructure and chemical composition were surveyed. As a result, it was found that the change in J-parameter during creep was influenced by chemical composition such as Si content and grain size. In the low Si content materials, which showed higher creep rupture strength, the change in J-parameter was relatively small. The large grained material also show small change in J-parameter. The effect of creep test condition such as temperature and stress on carbide structure change was also investigated. Finally, a good correlation between J-parameter and creep damage was found. The master curve based on J-parameter for creep damage evaluation was proposed.
社団法人日本機械学会の論文
2001-06-03