Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Creep-Fatigue Conditions

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概要

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• EBSD(Electron BackScatter Diffraction) analyses were conducted for studying the quantitative microstructural metrics of creep and creep-fatigue damage for austenitic SUS304HTB boiler tube steel and ferritic Mod.9Cr piping steel. KAM(Kernel Average Misorientation) maps and GOS(Grain Orientation Spread) maps were obtained for these samples and the area averaged values <I>KAM<SUB>ave</SUB></I> and <I>GOS<SUB>ave</SUB></I> were obtained. While the increasing trends of these misorientation metrics were observed for SUS304HTB steel, the decreasing trends were observed for damaged Mod.9Cr steel with extensive recovery of subgrain structure. To establish more universal parameter representing the accumulation of damage to compensate these opposite trends, the EBSD strain parameters were introduced for converting the misorientation changes into the quantities representing accumulated permanent strains during creep and creep-fatigue damage process. As <I>KAM</I> values were dependent on the pixel size (inversely proportional to the observation magnification) and the permanent strain could be expressed as the shear strain which was the product of dislocation density, Burgers vector and dislocation movement distance, two KAM strain parameters <I>M<SUB>εKAMnet</SUB></I> and <I>M<SUB>εδKAMave</SUB></I> were introduced as the sum of product of the noise subtracted <I>KAM<SUB>net</SUB></I> and the absolute change from initial value <I>δKAM<SUB>ave</SUB></I> with dislocation movement distance divided by pixel size. <I>M<SUB>εδKAMave</SUB></I> parameter showed better relationship both with creep strain in creep tests and accumulated creep strain range in creep-fatigue tests. This parameter can be used as the strain-based damage evaluation and detector of final failure.

著者

• FUJIYAMA Kazunari

  Department of Mechanical Engineering, Faculty of Science and Technology, Meijo University

• KIMACHI Hirohisa

  Department of Mechanical Engineering, Nagoya University

• TSUBOI Toshiki

  Graduate School of Mechanical Engineering, Meijo University

• HAGIWARA Hiroyuki

  Graduate School of Mechanical Engineering, Meijo University

• OGINO Shotaro

  Graduate School of Mechanical Engineering, Meijo University

• MIZUTANI Yoshiki

  Graduate School of Mechanical Engineering, Meijo University

• KIMACHI Hirohisa

  Department of Mechanical Engineering, Meijo University

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• Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Creep-Fatigue Conditions

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