OXIDE SCALES FORMED ON AUSTENITIC Fe-Cr-Ni ALLOYS EXPOSED TO SUPERCRITICAL WATER: ROLE OF ALLOYING ELEMENTS

摘要

A microscopic examination of the oxide scale structure and composition formed on Alloy 800 HT and Alloy 3033 after exposure in supercritical water (SCW) was conducted to better understand the manner in which alloying elements affect the corrosion resistance. Test coupons were exposed in 25 MPa SCW at 625 °C for 500 h for this purpose. Gravimetric measurement in combination with electron microcopy analysis showed that the highest relative corrosion resistance coincides with the formation of a relatively thin, continuous chromia (Cr_2O_3)-rich scale on an alloy substrate within which the Cr content is in excess of 20 wt.%, as observed on Alloy 3033.