| Stainless steel is widely used in various fields of modern society because of its superior corrosion resistance. However, in many corrosion environments, the corrosion of stainless steel happens still frequently. Especially it is prone to occur tremendous harms of local corrosion. Depth study of the corrosion resistance mechanism of stainless steel is of great significance for guiding the development of high corrosion resistance of new materials of stainless steel and surface modification technology.Nanocrystalline materials have received much attention in many fields for their unique physical, chemical and mechanical properties, and the investigation on the corrosion behavior of nanocrystalline materials is becoming an important issue in the corrosion field. In this work, we made bulk nanocrystalline materials by severe rolling technology and used samples of conventional polycrystalline alloy as a comparative experiment to study the corrosion behavior of nanocrystalline materials in different corrosion environments.The investigation results of pitting corrosion behavior of 304 stainless steels showed that the binding energy of Fe, Cr, Ni elements on the corrosion surface for bulk nanocrystalline 304 stainless steel(BN-SS304) were higher than those of conventional polycrystalline 304 stainless steel(CP-SS304) after nanocrystallization. The oxidation film formed on the surface of BN-SS304 was complete and stable. Meanwhile, the surface activity of chloride ion in the oxidation film decreased significantly, which caused lower dissolution of the membrane and improved the chloride ion corrosion resistance property of BN-SS304. Because of the lower weight of s-s track electron on the surface of BN-SS304, the chemical reaction rate of the corrosion process was decreased, which improved the chemical stability of BN-SS304.The investigation results of oxidation behavior of 304 stainless steel indicated that a protective oxidation scale of Cr2O3 formed on the surface of BN-SS304 after nanocrystallization. Because the grain size had been minimized, by which the Cr2O3 scale could fast form on the BN-SS304. Meanwhile, the positive effect on grain boundary improved the oxidation corrosion resistance of BN-SS304.The investigation results of hot corrosion behavior of 304 stainless steel showed that after nanocrystallization, the amount of grain boundaries for BN-SS304 of the reduction of the grain size had increased, which caused Cr could easily diffuse to the surface and made a protective CrO3 scale fast form on the substrate surface, and the oxidation scale was not cracking and shedding in the whole time. As a result, the hot corrosion resistance of BN-SS304 had been enhanced.The investigation results of electrochemical corrosion behavior of 304 stainless steel indicated that the SO42- and Cl" ions corrosion resistance properties of BN-SS304 were enhanced after nanocrystallization. This was ascribed to the large amount of grain boundaries in BN-SS304 through which Cr element can easily diffuse to the surface with fast diffusion paths. The passive film formed on surface of BN-SS304 was more compact and more protective to chloride ion than that formed on its counterpart alloy. Therefore, the BN-SS304 was more protective against chloride ion attacking and the electrochemical corrosion resistance property had been improved.The experimental results of electrochemical corrosion behavior of ingot iron showed that the corrosion resistance of bulk nanocrystallin ingot iron(BNII) in the hydrochloric acid solution was improved in camparison with conventional polycrystalline ingot iron(CPII). Since the surface uniformity and texture of BNII made its rolling surface of the surface energy lower than the average surface energy of CPII, which reducing the formation of the corrosion micro-cell. As a result, the corrosion resistance of BNII in hydrochloric acid solution had been enhanced. |
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