Effect of Cavitation on Corrosion Behavior of 20SiMn Low-Alloy Steel in 3% Sodium Chloride Solution

The cavitation corrosion behavior of 20SiMn low-alloy steel in both distilled water and 3% sodium chloride (NaCl) solution was investigated using a magnetostrictive-induced cavitation facility. The micrographs of damaged surfaces were observed with a scanning electron microscope (SEM). The role of corrosion was analyzed using polarization curves, electrochemical impedance spectroscopy (EIS), linear polarization resistance, and the corrosion potential with or without cavitation. Furthermore, the effect of cavitation on corrosion behavior of 20SiMn steel was compared to that of oxygen bubbling. The results showed that a fraction (0.05) of the damage arose from electrochemical corrosion and a fraction (0.59) arose from corrosion-induced erosion. Cavitation shifted the corrosion potential in the positive direction and strongly enhanced the cathodic current density in the polarization curves. Cavitation also reduced the magnitude of impedance. The morphological examination revealed that the ferrite area and grain and ferrite-pearlite boundaries were preferential sites for cavitation attack as a result of the low hardness of ferrite. The mass loss came from the detachment of small pieces in the ferrite area in the early stage and from the removal of massive chunks by the propagation and connection of cracks in the following test period.