Atmospheric Penetration Depth on Stainless Steels in contact with NaCl, MgCl₂ and Sea Salt under Relative Humidities of 33, 50 and 75% at Room Temperature

Abstract

Atmospheric corrosion behavior of for stainless steels in contact with chlorides was studied in laboratory atmosphere. According to Shoji's method, nine droplets, each of which consist of 5μl of 0.5N Cl^- solution, were put on a stainless steel specimen and were dried up. Thus-prepared specimens were exposed in a humidity-controlled chamber for three to six months. Penetration depth at the deposit strongly depended on RH and the maximum value of penetration depth was obtained at 50% RH for 430 steel and at 33% RH for 304 steel with the deposits of sea salt and MgCl₂, while no penetration was observed with the deposit of NaCl at 33% and 50% RH. Under RH of 75% all the three kinds of salt gave no penetration for 430 and 304 steels. The test was extended to seven other steels, and penetration was summarised in terms of Pitting Resistance Equivalent=[%Cr]+3.3[%Mo]+16[%N].