Speaker
Description
Tokyo Denkai has supplied over 20000 fine grain (FG) niobium sheets for superconducting cavities for the European XFEL, LCLS-II, LCLS-II HE and SHINE projects. In this study, tensile test data obtained during mass production were statistically evaluated. Tensile strength, 0.2 % proof strength and elongation showed normal distributions. The minimum values estimated as the mean minus three standard deviations were 153 MPa, 48 MPa and 45 %, respectively. According to JIS B 8266, the design-stress strength (allowable stress) of FG niobium was calculated to be 32 MPa based on the 0.2 % proof strength. The differences in tensile strength and 0.2 % proof strength between the rolling and transverse directions were small. On the other hand, elongation showed larger differences, mainly due to the fracture position of the tensile test specimens. In addition, the influence of a change in the final heat-treatment condition was statistically evaluated. The tensile strength and 0.2 % proof strength showed statistically significant changes, but the magnitude of the changes was small compared with the specified values. These results show that statistical evaluation of mass-production data is useful for evaluating the mechanical properties of FG niobium and confirming the validity of manufacturing conditions.