Effects of the stability of austenitic phases worked by shot-peening on the structures and chemical compositions of oxide films formed on 18-8 and 18-18 stainless steels by wet oxidation have been studied mainly by electron diffraction and characteristic X-ray micro-analysis.
The following results are obtained by the present investigation.
The oxide films formed on the surfaces of 18-8 stainless steels worked by shot-peening after mechanical or chemical polishing by oxidizing in high-temperature (300°C) water for 1 hr were the same in structure and chemical composition for both polished surfaces. The oxides were identical with the corundum type oxides consisting of (Cr, Fe)2O3 possibly accompanied by α-Fe2O3, showing characteristic X-rays of Fe and Cr.
On the contrary, the surface of the 18-18 stainless steel worked by shot-peening was covered with an oxide film which gave diffraction patterns showing clearly the existence of spinel type oxides with corundum type oxides of weak intensity under the same oxidizing conditions as in the case of 18-8 stainless steel. Further, besides Fe and Cr, Ni was detected from this oxide film. And the residual strain introduced by the shot-peening did not affect the structures and compositions of the wet oxidized films. From the above, it becomes clear that the stability of austenitic phases affects the structures of oxide films formed by wet oxidation of Fe-Cr-Ni austenitic stainless steels.
(Received January 30, 1971)
* This paper was published in J. Japan Inst. Metals, in Japanese 34 (1970) 1264.
** Department of Metallurgical Engineering, Faculty of Science and Engineering, Waseda University, Tokyo, Japan.
*** Yokohama Ship Ward and Engine Works, Mitsubishi Heavy Industry, Ltd., Yokohama, Japan.
© 2002 The Japan Institute of Metals
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