Abstract
High-temperature oxidation behavior of Fe-20Cr-4Al alloys with small amounts of sulfur (1-6 300 ppmS) was studied in oxygen for 18 ks at 1 273, 1 373, 1 473, 1 573 and 1 673 K by mass-change measurements, X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. Spalling of the scales on all of the alloys was not observed after oxidation at 1 273 K. The scales on the 4 and 7 ppmS spalled from the entire surface after oxidation at 1 373 K, however, the scales on the other alloys did not spalled. Intensive spalling of scales was observed for the 4, 7, 35, and 53 ppmS after oxidation at 1 473 K, and that of scales was recognized for the 4, 7, 35, 53 and 104 ppmS after oxidation at 1 573 K. On the other hand, after oxidation at 1 673 K, intensive spalling of scales was observed for the 4, 7, 1 300 and 6 300 ppmS. Spalling of scales on the alloys depends on sulfur content and oxidation temperature. The mass gain of these alloys tended to increase with increasing sulfur content. The scales formed on all the alloys were α-Al2O3. The scale/alloy interface changed from planar to convoluted morphologies with increasing sulfur content after oxidation at 1 673 K. Sulfur in the alloys with more than 7 ppmS existed all over the matrix as chromium-sulfide particles, and then moved to the oxide-alloy interface during oxidation.
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