Relationship between Microstructure and Corrosion Behavior in Dual-Phase Steels with Various Si Content

The objective herein is to evaluate the effect of silicon on the corrosion behavior of dual-phase steels. For this purpose, five different steels with various Si content ranging from 0.34 to 2.26 wt% are intercritically annealed at 780 degrees C for 15 min. It is clarified that the mechanism of the effect of Si on the corrosion behavior of dual-phase steels is a mutual mechanism. The increase in Si content (from 0.34% to 0.91%) initially reduces corrosion resistance due to a decrease in the volume fraction of martensite. However, according to microcapillary studies, a further increase in Si content (from 0.91% to 2.26%) reduces the potential difference between ferrite and martensite and, as a result, reduces the galvanic couple between them. Therefore, corrosion resistance improves by increasing Si content in the range of 0.91%-2.26%. It is also shown that in the corroded surface of the low-silicon sample, gamma-FeOOH is mainly formed, whereas with an increase in Si content, this compound reduces and alpha-FeOOH rises. Also, beta-FeOOH, silicon oxide and Fe3O4 are formed in the high-silicon sample. The study of the corroded surface topography depicts that surface roughness in a high-Si sample is less than low-Si sample.