11 wt% 크롬이 함유된 Ti 첨가 페라이트스테인리스강의 입계부식에 미치는 규소의 영향

Abstract

Ti-stabilized 11 wt% Cr ferritic stainless steels (FSSs) for automotive exhaust systems have been experiencedintergranular corrosion (IC) in some heat-affected zone (HAZ). The effects of sensitizing heat-treatmentand silicon on IC were studied. Time-Temperature-Sensitization (TTS) curves showed that sensitization toIC was observed at the steels heat-treated at the temperature lower than 650oC and that silicon improvedIC resistance. The sensitization was explained by chromium depletion theory, where chromium is depletedby precipitation of chromium carbide during sensitizing heat-treatment. It was confirmed with the resultsfrom the analysis of precipitates as well as the thermodynamical prediction of stable phases. In addition,the role of silicon on IC was explained with the stabilization of grain boundary. In other words, siliconpromoted the formation of the grain boundaries with low energy where precipitation was suppressed andconsequently, the formation of Cr-depleted zone was retarded. The effect of silicon on the formation ofgrain boundaries with low energy was proved by the analysis of coincidence site lattice (CSL) grain boundary,which is a typical grain boundary with low energy.