SUS304HTB鋼におけるクリープ損傷過程のEBSD解析

抄録

Creep damage evaluation by EBSD (Electron BackScatter Diffraction pattern) method was conducted on the austenitic stainless steel SUS304HTB widely used as the boiler tube material. Creep damage was imposed under the condition of 650℃ /130MPa and 700℃ /75MPa for preparing various interruption time samples. The longitudinal mid-section of specimen was observed by EBSD equipment and then IPF (Inverse Pole Figure) maps, KAM (Kernel Average Misorientation) maps, GROD (Grain Reference Orientation Deviation) maps were made for damaged samples. IPF maps showed the increasing inhomogeneity incrystal orientation within each grain as the time fraction increased. Area averaged parameters of KAM and GROD, i.e., KAM_ave and GROD_ave showed monotonically increasing trend with creep time fraction. Compared with KAM_ave, GROD_ave showed better performance for insensitivity of EBSD pixel step size. As GROD_ave showed excellent proportionality with creep strain except for rupture stage, the linear relationship was used as the conversion function into creep strain. Using this relationship, it was suggested that creep void diameter was proportional to the creep strain derived from local GROD_ave measurement method proposed here. Therefore, GROD_ave could be a good measure for estimating the strains around creep voids and the void growth mechanisms of SUS304HTB.