Corrosion of mild steel and 316L austenitic stainless steel with different surface roughness in sodium chloride saline solutions

Abstract

The corrosion behaviour of mild steel and 316L austenitic stainless steel was investigated in saline solution containing 1 and 3% NaCl. Specimens with surface roughness of 200, 600 grit emery paper and 1 μm diamond paste were investigated. The anodic polarization measurement technique was performed at a scan rate of 1 mV/s for a fixed period of 1 hour. Experimental results revealed that chloride ions have a significant effect on the corrosion behaviour of both steels as expected. As the surface roughness of 316L stainless steel increased, the breakdown potential (Ebreak), the free corrosion potential (E corr ) and the width of passivity decreased, hence corrosion rate increased. However, in the case of mild steel specimens, improving surface finish led to shifts in corrosion potential to more noble states and increased the corrosion rate. Metallographic examination of corroded specimens after electrochemical corrosion tests confirmed that the breakdown of the passive region was due to pitting corrosion.

Simultaneous effect of surface roughness and passivity on corrosion resistance of metals

“…This can be attributed to the high rate of corrosion propagation after initiation. It is said that localized corrosion is controlled by the diffusion process and in this case once the corrosion started, it propagated at a fast rate due to the continuous diffusion process and the formation of acid media at the bottom of the grooves [8]. The results are in a good agreement with the observations of Alvarez on AE44 magnesium alloy which has similar characteristics as mild steel i.e.…”

“…Alvarez et al [9] showed that the corrosion rate in AE44 from polished coupons (with lower roughness) was notably greater than the corrosion rate from the semi-polished coupons (with higher roughness). Similar behaviour was observed by Abosrra et al [8] on mild steel in saline solution containing 1 and 3% NaCl. In his work Abosrra et al [8] showed that the improvement of the surface finish led to a shift in the corrosion potential to more noble states and to an increase of the corrosion rate.…”

“…Similar behaviour was observed by Abosrra et al [8] on mild steel in saline solution containing 1 and 3% NaCl. In his work Abosrra et al [8] showed that the improvement of the surface finish led to a shift in the corrosion potential to more noble states and to an increase of the corrosion rate. The obvious difference between these two groups of materials is that materials such as aluminium, copper, nickel, stainless steel passivate quickly by developing stable oxide films whereas AE44 magnesium alloy and mild steel, unlike the first group, do not form a stable passive film.…”

“…These results are in agreement with results of previously reported studies which investigated the appearance, oxygen concentration and roughness parameters in SEM, EDS and profilometry tests, respectively. This is a general trend in corrosion of metals with no ability to form a passive layer [8,9]. This trend is exactly the opposite to the one in nickel (Fig.…”

“…Zuo et al [7] investigated the metastable pitting behaviour of 316L stainless steel with various degrees of surface roughness and showed that, as surface roughness increased, the nucleation rate of metastable pits as well as the overall corrosion rate increased. In contrast, a range of materials such as mild steel [8] and AE44 magnesium alloy [9] show the reverse trend namely, as surface roughness increases, the corrosion rate decreases. Alvarez et al [9] showed that the corrosion rate in AE44 from polished coupons (with lower roughness) was notably greater than the corrosion rate from the semi-polished coupons (with higher roughness).…”