A comparison study on pitting corrosion susceptibility of AISI 201 and AISI 444 stainless steels

• Main Authors: Chia-HsienLi, 李佳憲
• Other Authors: Wen-Ta Tsai
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/54952682363318119749

碩士 === 國立成功大學 === 材料科學及工程學系 === 104 === In this study, we investigated the pitting corrosion susceptibility of AISI 201 and 444 S.S., took 304 S.S. as the control group. The solution used in this research were 25,250, and 2500 ppm Cl- and 0.1 M Na2SO4 + 2500 ppm Cl- aqueous solution. The determination of the critical pitting temperature (CPT), observation of the pit morphology and the comparison of pitting initiation potential (Enp) are the main means to estimate the pitting corrosion susceptibility. In 0.1 M Na2SO4 + 2500 ppm Cl- aqueous solution. The CPT of as-received materials of 201, 304 and 444 S.S. are 36, 35 and 36 oC. The CPT of heat treatment samples are 30, 30 and 28 oC. After the heat treatment, the grain size grew. Because the grain growth influence, the passive film on surface contain less Chromium. That leads to the rise of the pitting corrosion susceptibility. With surface observation, we found that is no pit on sample surface below CPT. With temperature higher than CPT, some pits could be found. The magnitude of it were about 10 μm. In 25, 250, and 2500 ppm chloride solution, the Enp and Epp dropped with chloride content increased. In 2500 ppm chloride content, large pits were found on all three materials. The diameter were about 50 μm. The Enp of 304 S.S. is higher than 444 S.S. In 250 ppm chloride solution, large pits were only found on 201 S.S. The Enp of 304 and 444 S.S were very close. In 25 ppm chloride solution, there are only small and swallow pits on all three materials. The magnitude of them were mostly smaller than 10 μm. From observation of cross section of pit morphology. We found the pits on 201 S.S. and 304 S.S. grew deeper and likely to grow horizontally. While the pits on 444 S.S. are shallow and unlikely to grow horizontally. Over all, in chloride solution, the pitting corrosion resistance 444 S.S.〉 304 S.S.〉201 S.S.