Abstract
Electrochemical localized corrosion tests in substitute ocean water at 40°C and 70°C and ASTM G48 tests in 6% FeCl~3~ solution were performed on three classes of stainless steels: Ni‐austenitic (both traditional and with high nitrogen content ones), high nitrogen Mn‐austenitic nickel free and duplex (both traditional and with high nitrogen content ones).
The Pitting Resistance Equivalent formula, PRE~Mn~ = % Cr + 3.3% Mo + 30% N – 1% Mn, proposed to consider the presence of noticeable amount of manganese in some of the new high nitrogen stainless steels yields good linear correlation with experimental results. The existence of a threshold value of PRE~Mn~ (≥ 45) to attain excellent localized corrosion resistance has been recognized. According to this observation the high nitrogen Ni‐austenitic 21Cr24Ni6MoO.24N, 24Crl8Ni4MoO.48N, 24Cr22Ni7MoO.52N and the duplex 25Cr8Ni4MoO.26N “super” stainless steels are immune to localized attack also in the most severe electrochemical test conditions. This superiority is maintained also in ASTM G48 tests. Due to their values of Critical Crevice Temperature (CCT~ASTM G48~ ≥ 35°C) these steels seem suitable for practical service in seawater environments up to about 30 °C.