利用TEM, EDS和SAED等分析方法, 研究了11Cr 铁素体不锈钢409L在600 ℃敏化下析出物特性, 并将双环电化学动电位再活化法(DL-EPR)用于评价409L钢的晶间腐蚀敏感性, 通过研究DL-EPR的扫描速率、介质成分、介质温度对测试结果的影响, 对该方法进行了优化, 并用该优化法研究了敏化处理对409L钢晶间腐蚀敏感性的影响. 结果表明, 敏化的409L钢发生晶间腐蚀是由于M₂₃C₆沿晶界析出. 在最优化条件下, DL-EPR法能定量评价409L钢的晶间腐蚀敏感性且具有良好的重复性. 随敏化处理时间延长, 沿晶界析出的M₂₃C₆增多, 晶间腐蚀敏感性也随之增强.

Ferritic stainless steel (FSS) containg (11%~13%)Cr with low C and N has excellent comprehensive performances and thus can be widely applied in extensive fields such as automobile exhaust systems, containers, buses and so on. Among them, 409L steel containing 11%Cr has been increasingly used in applications for tail pipes in the cold end parts of automobile exhaust systems because of its good corrosion resistance and moderate price. During the manufacture process for these tail pipes, improper heat treatments and welding operations cause the precipitation of some detrimental phases such as carbides, nitrides, which leads to a reduction on the resistance to intergranular corrosion (IGC) due to the presence of Cr-depleted zone in the grain boundaries. In this work, the precipitates in grain boundaries of 409L steel aged at 600 ℃ were investigated using TEM, EDS and SAED. The double loop-electrochemical potentiokinetic reactivation (DL-EPR) method was extended for evaluating the IGC susceptibility of 409L steel. The operating conditions of the DL-EPR test for 409L steel were optimized by investigating the influences of the main test parameters, such as scanning rate, solution composition, solution temperature. The experimental results showed that the IGC occurred in aged 409L steel due to the precipitation of M₂₃C₆ along grain boundaries. The optimized DL-EPR test could evaluate the IGC susceptibility of 409L steel quantitatively with high reproducibility. With the increase of aging time, much more M₂₃C₆ precipitated along grain boundaries, which resulted in 409L steel more susceptible to IGC.