Abstract
A native passive film on 25Cr-7Ni super duplex stainless steel was analyzed using synchrotron hard X-ray photoemission electron microscopy, focusing on variations between individual grains of ferrite and austenite phases. The film consists of an oxide inner layer and an oxyhydroxide outer layer, in total 2.3 nm thick. The Cr content is higher in the outer than the inner layer, ca. 80 % on average. The Cr content is higher on ferrite than austenite, whereas the thickness is rather uniform. The grain orientation has a small but detectable influence, ferrite (111) grains have a lower Cr content than other ferrite grains.
Highlights
Under ambient conditions, oxidation reactions of metals usually lead to spontaneous formation of an oxide film on the surface
The results reported in this paper provide new insights into the native passive film of duplex stainless steel, which cannot be obtained with conventional surface analysis techniques
The results show that the average Cr content of the native passive film is generally higher on the ferrite grains compared to the austenite grains except the (111) orientation, which is similar for the two phases
Summary
Oxidation reactions of metals usually lead to spontaneous formation of an oxide film on the surface. The variations in chemical composition and thickness of the surface layer over individual austenite and ferrite grains were analyzed by using synchrotron hard X-ray photoemission electron microscopy (HAXPEEM), with a lateral resolution down to 1 μm. This allows the comparison between austenite and ferrite phases and between individual grains. We present a comprehensive local chemical analysis of the native passive film formed on a super duplex stainless steel, on the level of the average, individual phases, and individual grain orientations, based on data from 58 single grains. The results reported in this paper provide new insights into the native passive film of duplex stainless steel, which cannot be obtained with conventional surface analysis techniques
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