EBSD法と硬さ計測による高Cr鍛鋼のクリープ損傷評価(<小特集>結晶回折法および電子線後方散乱法による材料評価)

概要

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10Cr-1Mo-1W-VNbN steel forging was observed through TEM, SEM with EBSD method and tested through nano-indentation tester to investigate the microstructural change during creep damage process. Long term creep rupture and interrupted creep test samples were investigated and effective damage parameters were selected. IPF map showed apparent boundaries within prior austenite grain boundaries, which corresponded to block boundaries. Area averaged KAM value KAM_<ave> was shown to be effective parameter for evaluating dislocation microstructural changes during creep. Nano-indentation tests were conducted at the same point of EBSD measurement, which showed good correlation between hardness value and the square root of KAM_<ave>. The differential equation of dislocation density with creep exposure time was applied to estimate the relationship between mean KAM_<ave> and creep exposure time through the relationship between hardness and dislocation density. The creep damage estimation curves were obtained from the the integrated form of the equation. As the KAM_<ave> showed substantial inclination plotted against time fraction in the primary creep stage, it could be used as the steady state creep characterization of the material and the rupture time. The statistical distribution characteristics of KAM_<ave> during creep damage process were also discussed.
2008-03-25