Evolution of corrosion damage to cold rolled grain oriented steel sheets under rainwater followed by ambient atmosphere exposure

Corrosion damage to cold rolled grain oriented (CRGO) steel sheets with inorganic insulation coating was studied. The coating damage and corrosion on the sheets were analyzed via visual as well as stereomicroscopic imaging, and based on the examinations the sheet surfaces were classified into three categories namely coating intact (Type A), coating damaged (Type B), and coating damage followed by corrosion (Type C). The sheets’ surfaces were examined with scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) to establish the extent of the coating damage and corrosion. Furthermore, core loss measurements were carried out to check the quality of the CRGO sheets. To understand the evolution of corrosion under rainwater followed by ambient atmosphere exposure at coastal regions, the sheet samples were kept immersed in simulated rainwater for 4 h followed by placing them in ambient atmosphere for seven consecutive days (atmospheric corrosion test). Corrosion was absent on the sheet samples with the coating intact while other sheet samples with the coating damaged or having corroded spots suffered from selective corrosion.

► CRGO steel sheets with the coating damaged are vulnerable to corrosion under ambient atmosphere.
► Corrosion resistance of the coating damaged CRGO steel is poor under sea water.
► Increased core losses with lengthy exposures of the corroded regions to ambient atmosphere.