S0306-1-2 Mod.9Cr鋼のクリープおよびクリープ疲労損傷過程の微視構造観察([S0306-1]損傷の結晶解析的評価)

概要

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EBSD(Electron BackScattering Diffraction) observation was conducted on creep damaged and creep-fatigue damaged Mod.9Cr steam pipe steel. Creep damage was imposed for the time fraction as 0.1, 0.2, 0.5, 0.8 and 1 at 650℃, 1OOMPa as well as creep-fatigue for the cycle fraction as 0.1, 0.25, 0.5 and 1 at 650℃, l%strainrange and 10min tensile strain hold. The longitudinal mid-section of specimen was observed and IQ(Image Quality) maps, IPF(Inverse Pole Figure) maps and KAM(Kernel Average Misorientation) maps were obtained for the each damage level. Area averaged parameters of KAM: KAM_<ave> showed gradual decrease in creep and initial decrease in creep-fatigue. Boundary spacing obtained from KAM map increased at early stage of damage process. By combining those two parameters and pixel step size, the "Modified misorientation parameter M_ε" was introduced and showed linear correlation with permanent strain. After the initial increase of creep-fatigue plateau stage for M_ε was recognized suggesting the onset of crack propagation dominated process. Thus, EBSD observation was revealed as a powerful tool for analyzing damage process as the quantitative measure of accumulated strains at sub-grain size level.
2010-09-04