High Temperature Oxidation of Stainless Steel Diffusion-coated With Chromium

The oxidation of 18Cr/10 Ni/Ti stainless steel diffusion-coated with chromium was studied regarding the change of chromium concentration with oxidation time in the region near the surface of metal. Samples prepared for the oxidation tests were diffusion-coated at 950 and 1, 050°C for 1, 3 and 5hrs. The oxidation was made in the still atmosphere at temperatures of 950-1, 050°C, and the results were discussed by measurement of weight increase, electron probe microanalysis, X-ray diffraction analysis, and scanning electron microscopy. Breakthrough occurred in a stainless steel as received by oxidation at 1, 050°C in 10-20hrs.; whereas, no breakthrough was observed in any sort of diffusion-coated stainless steels in less than about 130hrs. The thicker diffusion-coated layer could make the time to breakthrough longer. However, any stainless steel as received before breakthrough showed less weight increase than the diffusion-coated one at any temperature of oxidation. It was considered that the breakthrough of the material occured when the chromium concentration on the metal surface dropped to about 10%, which led to the formation of FeCr2O4 by the exposure of metal surface to the air owing to cracking or peeling of oxide scale.