1988 Volume 74 Issue 2 Pages 380-387
Creep tests of Ni-base heat resistant alloys (Hastelloy XR and XR-II) were conducted at 950°C in four kinds of helium environments with different impurity compositions in order to examine the effect of decarburizing environment.
Both alloys were decarburized in a helium environment with low partial pressure of oxygen and carbon activity. The decarburization induced degradation of creep properties such as lower creep rupture strength, higher creep rate and earlier start of accelerating creep. Whether the decarburization of the Hastelloy XR and XR-II might occur or not in the primary helium coolant of high temperature gas-cooled reactor (HTGR) could be predicted by using a corrosion map of a stability diagram for chromium. Controlling impurities to maintain higher partial pressure of oxygen and carbon activity in primary helium coolant of HTGR is proposed in order to prevent degradation of creep properties of the materials caused by decarburization.
