Effect of Corrosive Factors on Progression of Pitting Corrosion of Welded SUS304 Steel under Freezing and Thawing Corrosive Environment

Abstract

It has been reported that pitting corrosion occurs in stainless steel under the specific conditions which a corrosion factor superimposes. In cold and snowy area, welded structures on the outdoors are exposed to combinational environment of the salt damage and the freezing damage, in which the corrosive solution containing Cl- chlorine ions from the sea breeze and snow melting agents undergo freezing-thawing cycles during the winter. The cause of pitting corrosion phenomenon which occurs in the welded stainless steel under such a combinational environment has not yet been clarified. In the previous report, accelerated pitting corrosion is confirmed to have occurred as a result of concentration cell corrosion due to a local concentration of Cl- chlorine ion around a weld bead during freezing and thawing of the solution. In the present study, it is investigated that the effect of corrosive factors on the progression of pitting corrosion in welded austenitic stainless steel under freezing and thawing corrosive environment. Austenitic stainless steel SUS 304 plates with bead-on-plate welding are used as specimens. The specimens are fully immersed in FeCl3 solution. The freezing-thawing environment is created by temperature cycling form 20°C to -20°C. One cycle of freezing-thawing is 12 hours and 24 hours. As a result, in the austenitic stainless steels under a freezing and thawing corrosive environment, it became evident that sensitive metallographic structures influences an occurrence of large scale pitting corrosion, and a stress level influences an accelerated progression of the pitting corrosion.