Effect of pH on corrosion mechanism of two austenitic stainless steels in artificial sweat

The sweat is highly corrosive, and its pH fluctuates in the range of 4-7.5 with different physiological conditions. In order to study the effect of sweat pH change on the corrosion behavior of two austenitic stainless steels (304 and 316 L), the failure mechanism was studied by electrochemical experiments and immersion corrosion. Metallographic study results show that the grain size of the two austenitic stainless steels is similar (similar to 16 mu m), but the inclusion content (carbides and sulfides) in 304 stainless steel is higher than that in 316 L stainless steel. The results showed that the corrosion current (I-corr) of 304 and 316 L increased significantly with the decrease of sweat pH from 7.5 to 4.5, and I-corr increased by 10.2 times and 8.9 times, respectively. The results of electrochemical impedance spectroscopy show that the decrease of pH will lead to the decrease of the thickness of the passivation film on the surface of the sample, and the roughness of the passivation film increases and the uniformity decreases. Further, the results of 30-day immersion test showed that the corrosion mechanism of the samples in sweat was mainly pitting corrosion. With the decrease of pH, the loss of Cr, Ni, and Mo on the surface of the samples increased, indicating that low pH could promote the migration and loss of Cr, Ni and Mo, resulting in an increase in the degree of corrosion of the samples. The above research results can provide guidance for the design of anti-sweat corrosion materials.