Effect of Specific Magnetic Susceptibility of AISI 304 and 08Kh18N10 Steels on Their Limiting Potentials in Chloride-Containing Environments

Abstract

The resistance of AISI 304 and 08Kh18N10 steels to crevice corrosion in chloride-containing media was studied using potential-dynamic methods. The preset gap width of 0.3 mm between the sample and the counter body simulates the gap between adjacent plates of plate-like heat exchangers. The area of the hysteresis loop of the constructed anode potential-dynamic curves of the forward and reverse stroke was used to compare the volume of local damage caused by crevice corrosion of the studied steels. The maximum areas of the steel hysteresis loop and the volume of local corrosion damage in the ingots with the lowest (2.23×10^–8 and 2.24×10^–8 m³/kg) and highest (2.31×10^–8 m³/kg) values of the specific paramagnetic susceptibility χ₀ of austenite were established. The free corrosion potential E_corr of steels intensively shifts in the negative direction (from –0.28 up to –0.41), and the repassivation E_rp and crevice corrosion E_crev – in the positive direction from –0.38 up to –0.29 and from –0.1 to 0.1 V, respectively, with an increase in the parameter χ₀ from 2.23×10^–8 up to 2.25×10^–8 m³/kg, which contributes to an increase in their ∆E-criterion from 0.02 up to 0.69 V and resistance to crevice corrosion. This is because, in this range of values, the change in the χ₀ parameter is determined by deviations in the content of C, N, S, P, and Cr in the solid solution of austenite in steels. With an increase in the parameter χ₀ of steels to 2.31×10^–8 m³/kg, their potential E_corr shifts in the positive direction from –0.41 up to –0.32, and E_rp , E_crev – in the negative direction from 0.29 up to 0.15 and from 0.10 up to –0.02 V, respectively, which contributes to a decrease in the ∆E criterion of steels from 0.65 up to 0.14 V and their resistance to crevice corrosion. The χ₀ parameter of steels is an integral characteristic of the paramagnetic state of austenite and can be used to assess their resistance to crevice corrosion in chloride-containing media.