Electrochemical Measurement Method of Chromium Depth-profile Near the Surface of SUS 304 Steel
The depth-profile of Cr concentration of Cr depleted zone formed under oxide film of stainless steels during oxidation process plays an important role in the corrosion behavior and oxidation resistance. In order to produce stainless steels with high quality surface, speedy and exact measurement of the depth-profile of Cr is required, through which production process should be properly controlled. In this paper, a new method is presented for measurement of the depth-profile of Cr. This method depends on the relation between the Cr concentration of stainless steel and the current density in transpassive region in H3PO4 solution at 323K. SUS 304 steel which was oxidized in air at 1, 273 K, and then removed oxide film by mechanical polishing, was polarized at +1.40 V (SCE) (transpassive region) in 10% H3PO4 (air open, 323K) in order to measure the it, p (10-3A·cm-2)-Q (C·cm-2) curve. From the it, p-Q curve, the depth-profile of Cr was obtained by converting it, p into Cr concentration and Q into depth. The usefulness of this method was evaluated through the comparison between the depth-profile of Cr measured by this method and the one calculated and measured by evaporation model, AES, EPMA, chemical analysis respectively.