The Effect Of Calcium And Aluminium On Pitting Corrosion Resistance Of 3161 Stainless Steel

摘要

Pitting in chloride containing aqueous solutions occurs on Manganese sulphide, when they are present in the steel. Adding a slight amount of Calcium as an alloying element prevents the MnS formation, since calcium is a stronger sulphide former than Mn. In this work, calcium treated stainless steels have been investigated electrochemically. Staircase polarization measurements were performed in a 3.5% NaCl solution, where the dissolution of inclusions caused a current transit. The results show that calcium addition in Ca/S ratio of 1～2 leads to an increase in the pitting potential of several hundred mV. During staircase polarization, calcium treated steels show low and discontinuous current fluctuation while steel without calcium treatment shows high and continuous current fluctuation. The high pitting corrosion resistance of the former is attributed to the inactive pits.