HIGH-TEMPERATURE OXIDATION BEHAVIOR OF HIGH-NITROGEN FERRITIC STEELS

High temperature oxidation behavior of a high nitrogen steel with abou t 0.15 mass% nitrogen was studied, comparing with a base material of 9 Cr-0.5Mo-1.8W-0.2V-0.05Nb-0.04N steel. Weight gains were measured and microstructural observation and analyses were carried out using SEM, X -ray diffraction, EPMA and ESCA for the specimens heated in air at tem peratures of 500 to 900 degrees C and for 10 000 h at maximum. The wei ght gain due to oxidation in the high nitrogen steel was far smaller t han that in the base material, and about one fifth of that in the base material at 10 000 h. In the high nitrogen steel, the depletion of Cr concentration at the metal surface was smaller than in the base mater ial, and this was considered to be a possible cause of the intensified oxidation resistance of high nitrogen steel.