Corrosion Behavior of Austenitic Stainless Steels on the Cut Edge Surface

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The cut edge surface of the stainless steel sheet is susceptible to corrosion compared with the surface of the sheet. At the cut edge surface, red rust easily tends to occur by the attack of chloride ion. However, there are still a lot of points not clear about the cause of the cut edge corrosion.The salt spray test and the immersion test using NaCl solutions were conducted to evaluate corrosion resistance for the shear cut edge of SUS304 (18Cr-8Ni) and SUSXM7 (18Cr-9Ni-3Cu) cold rolled strips. It was found that transverse section (T section) corroded easier than longitudinal section (L section). In addition, the rust at the machined edge was less than shear cut edge.The difference of the corrosion behavior in each section, L and T, was investigated by the electrochemical method. In anodic polarization curves at T section, the current density rose gradually at the less-noble potential than the L section. By the SEM observation and EPMA elemental mappings after anodic polarization measurement, it was considered that non-metallic inclusions (MnS etc.) extended along the metal flow of rolling direction influenced on the initiation and the growth of pitting corrosion.
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