SUS304HTB鋼のクリープ損傷過程における結晶粒内ひずみ分布のEBSDによる評価

Abstract

Creep damage evaluation by EBSD(Electron BackScatter Diffraction pattern) method was conducted on the austenitic stainless steel SUS304HTB as the boiler tube material. Creep damage was imposed under the condition of 650℃/130MPa and 700℃/75MPa with various interruption hours. The longitudinal mid-section of specimen was cut and observed by EBSD equipment and then Phase maps, IPF(Inverse Pole Figure) maps, KAM(Kernel Average Misorientation) maps and GROD(Grain Reference Orientation Deviation) maps were obtained. Phase maps showed the increasing α-phase transformed from γ-phase at the grains oriented with (111) as the normal direction with the increasing time fraction or the accumulated macroscopic creep strain. The misorientation parameters obtained from KAM maps and GROD maps showed increasing trend with increasing time fraction. The distribution function of GROD was regressed on the basis of continuously distributed dislocation theory and its representative coefficient parameter AG showed the good correlation with time fraction or accumulated creep strain. By measuring AG value near creep voids, creep strains were evaluated in the vicinity of creep voids and did not show significant strain concentration compared with the non-voided area. However, the good correlation between the void length and the creep strain evaluated from AG was observed. The AG parameter was considered as an effective quantity obtained from EBSD observation to evaluate creep strain intensity at the grains with and without creep voids irrespectively.