Influence of Chloride-Containing Media on the Pitting Resistance of AISI 321 Steel

We develop mathematical models used to describe the dependences of the critical pitting temperatures of AISI 321 steel in model circulating waters with pH 4-8 and a concentration of chlorides varying within the range 350-600 mg/liter on its chemical composition and structure. These models are based on multidimensional linear regressions of the first order and neural networks with forward signal propagation. By using the developed mathematical models, it is established that the critical pitting temperatures of AISI 321 steel become higher as the pH value of the circulating water, the mean distance between oxides in the steel, and the contents of manganese and chromium increase and as the mean grain diameter of austenite and the content of chlorides in the medium decrease. At the same time, it is shown that the influence of the medium is most pronounced but the heterogeneity of steel, which depends on the contents of Cr, Si, Mn, and N, also strongly affects its pitting resistance. It is proposed to use the developed mathematical models for the choice of the optimal heats of AISI 321 steel guaranteeing its highest pitting resistance in model circulating waters.