Abstract
The authors studied the oxide films of aluminum diffusion coated stainless steels: SUS 430, SUS 304 and SUS 321, which were formed by oxidation of respective diffusion coated layers in the air at high temperatures. The studies were made by transmission electron diffraction, X-ray diffraction, X-ray microanalysis and scanning electron microscopy. The results obtained were as follows. (1) The oxide film formed on aluminum diffusion coated SUS 430 by oxidation at 1, 050°C for 2min, was mainly composed of α-Al2O3, and the oxide films of the other two kinds of steels were mainly conposed of α-Al2O3. (2) It was found that the oxide films of aluminum diffusion coated stainless steels, formed by oxidation at 1, 050°C for 1hr., contained a small amount of (Cr, Fe)2O3, which seems to be formed in defective parts of oxide films composed of α-Al2O3 or γ-Al2O3. (3) With the decrease of aluminum concentration on the interface, (Cr Fe)2O3 as well as α-Al2O3 was formed followed by the formation of FeO⋅Cr2O3. (4) When each kind of aluminum diffusion coated stainless steels was oxidized at 1, 050°C, the critical aluminum concentration was about 2 wt% on the interface between the matrix (for forming the oxide film mainly composed of α-Al2O3) and the oxide film. (5) The oxide film of aluminum diffusion coated SUS 321 was more resistant to thermal shock than that of diffusion coated SUS 430.
