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439M铁素体不锈钢广泛应用于汽车排气系统消声器中,其主要失效形式是点蚀破坏。采用点腐蚀试验、去钝化起始p H值试验、微区电化学试验,并结合扫描电镜及能谱分析,观察分析了点腐蚀和夹杂物的形貌,研究了点蚀诱发时夹杂物的变化情况。研究结果表明,439M不锈钢的点蚀主要在复合氧化物夹杂处诱发,而Ti N夹杂物未诱发点蚀;夹杂物诱发点蚀时,复合氧化物夹杂的Ca O优先溶解。最后,建立了在氯离子环境下439M不锈钢中复合氧化物夹杂诱发点蚀的模型。
439M ferritic stainless steel is widely used in the muffler of automobile exhaust system, and the main failure mode is pitting corrosion. Pitting corrosion test, depassivation initial p H value test and micro-region electrochemical test were carried out. Combined with SEM and EDS, the morphology of pitting and inclusions was observed and analyzed. The effects of inclusions Changes in the situation. The results show that the pitting corrosion of 439M stainless steel is mainly induced by composite oxide inclusions, while the TiN inclusions do not induce pitting corrosion. When the inclusions induce pitting corrosion, CaO mixed with mixed oxides is preferentially dissolved. Finally, a model of pitting-induced pitting induced by composite oxide in 439M stainless steel under chloride environment was established.