尿素对模拟汽车废气环境中不锈钢冷凝液腐蚀行为的影响

采用高温废气氧化-酸性冷凝液浸泡循环法模拟柴油机的排气环境，对比研究废气中引入尿素后排气系统用304和439不锈钢的冷凝液腐蚀行为，并分析了尿素对不锈钢氧化与腐蚀的作用。电化学测试结果表明：经400 ℃氧化后，304不锈钢在冷凝液中的腐蚀处于钝化状态，而439不锈钢的腐蚀趋于活化状态；在有/无尿素条件下，试样表面产物膜在氧化和腐蚀的循环作用下均会发生破坏而形成局部腐蚀坑；废气中引入尿素会增强其对两种不锈钢的氧化作用，进而导致不锈钢的均匀腐蚀量增大而局部腐蚀深度减小。

Effect of Urea on Condensates Corrosion of Stainless Steels in Simulated Automotive Exhaust Environments

The high-temperature exhaust gas oxidation-acidic condensates immersion cyclic test was used to simulate diesel exhaust after-treatment environments. After oxidation at 400 ℃ in simulated exhaust gas environments with or without urea, the corrosion behavior of 304 and 439 stainless steels was investigated in the condensate solutions. The electrochemical test results indicate that 304 stainless steels oxidized in the presence or absence of urea show passive corrosion characteristics in the condensate solutions, whereas 439 stainless steels oxidized under both conditions tend to active corrosion. Corrosion product films on the specimen surfaces may be damaged during the oxidation and immersion cycles, which give rise to the formation of some pits on the specimens. As urea is added into the exhaust gas, it can promote the oxidation processes of both 304 and 439 stainless steel. As a result, the general corrosion processes of both stainless steels are accelerated by the urea addition, but the localized corrosion processes are inhibited to a certain extent.