含铬低合金钢在海水中耐蚀性“逆转”原因分析

ANALYSIS FOR THE REASON OF CORROSION RESISTANCE “REVERSION” OF CONTAINING CHROMIUM LOW ALLOY STEELS IN SEAWATER

经 16年实海暴露腐蚀试验 ,在国内首次发现 92 1等含铬低合金钢在榆林和青岛站海水中出现了耐蚀性“逆转”现象 .用金相法、SEM/EDS法、细菌鉴定法、化学分析方法 ,以榆林站的 92 1钢海水锈层为重点研究对象 ,对试验钢的锈层进行了综合性分析研究了“逆转”的原因 .初步查明 ,某些含铬钢耐蚀性“逆转”的主要原因是 ,经较长时间的海水腐蚀 ,由于麻点腐蚀的深入发展 ,产生了比碳钢、无铬钢严重得多的金属小颗粒的“脱落” ,对腐蚀速率作了较大贡献 .并认为 ,在实海腐蚀 1年左右 ,碳钢和低合金钢的腐蚀动力 ,可能由氧扩散控制逐渐变为硫酸盐还原菌 (SRB)

Through exposure corrosion test in seawater for 16 years,the “reversion” phenomena of corrosion resistance of containing chromium low alloy steels such as 921 in Yulin and Qingdao seawater were first found in China,but the reason was not understood at home and abroad.In order to study the reason of “reversion”,several methods including metallography,SEM/EDS,bacteria identification and chemical analysis were used for entirely investigating the rust layer on test steels and the rust layer on 921 steel exposed in Yulin seawater was emphasized on.The reason of corrosion resistance “reversion” of some containing chromium low alloy steels in seawater has been initially found out.As the seawater corroded for a long period,the corrosion pits deeply developed and many small metal granules fell off substrate,that greatly contributed to corrosion rate.“Falling off” containing chromium steels was much serious than carbon steels and non-containing chromium steel.It is considered that the corrosion dynamic of carbon steels and low alloy steels may change from oxygen diffusion control to bacteria such as SRB corrosion control at about one year.