Abstract
Small Punch Creep (SPC) test has been recognized as a practical procedure to examine creep lives only sampling a very small volume. The size and volume of the SPC specimen is smaller than that of conventional uni-axial creep specimens, i.e., its volume ratio is about 1/300. However any standard cord for the SPC testing has not been established yet, because many configurations and geometry of testing apparatus, and test atmosphere severely affect test results. In order to investigate an effect of atmosphere on creep rupture lives, a series of SPC tests in air and in vacuum were carried out at 600℃ employing 2.25Cr-lMo Steel. It was shown that the rupture lie in vacuum beyond the applied load of 250N was longer than that in air, because the friction between the SPC specimen and a loading ball in vacuum was greater than that in air. On the other hand, there was little differences among the test results less than die applied load of 250N for all atmospheres. This was because the oxide scale grew thick and remained without peeling off in air, and the oxide scale still endured membrane stress in the SPC specimen. Furthermore since the very thin oxide scale formed in vacuum easily peeled off, the net cross-section decreased and the actual stress increased.
