二相ステンレス鋼の溶接部の耐食性

概要

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Since type 329 J1 duplex alloys have good resistance to pitting, crevice corrosion and stress corrosion cracking in chloride media, they have widely been used in the heat exchangers of chemical plants or seawater condensers. However, it has often been said that type 329 J1 duplex alloys are susceptible to welded joint corrosion. Therefore, this study is aimed at investigating the corrosion behavior of welded joints in duplex alloys in various kinds of corrosive environments compared with base metals. Tests include acid immersion, intergranular and crevice corrosion tests, and also electrochemical measurements. The test results are described as follows : (1) Distribution of principal alloying elements in 25Cr-6Ni-2Mo-N and 25Cr-6Ni-0.4Cu-3Mo-N duplex alloys have been observed, i. e., Cr and Mo concentrate in α phase, and Ni, N, and Cu do in γ phase. (2) Welded joints having a poor area ratio of γ phase in 25Cr-6Ni-0.4Cu-2Mo-low N steel are more severely been attacked than base metal, because chromium depletion at grain boundaries due to chromium carbide or nitride precipitation has induced intergranular attack both in acid and chloride media. (3) Selective dissolution of γ phase in base metal occurs in 25Cr-6Ni-2Mo-N steel at crevice, whereas no selective corrosion does in 25Cr-6Ni-0.4Cu-3Mo-N steel.
社団法人日本鉄鋼協会の論文
1980-07-01