Comparison of Pitting and Crevice Corrosion - The Effect of Alloying Elements

摘要

The localized corrosion resistance of stainless steels and nickel alloys is primarily due to alloying elements. The most important elements, as indicated by the Pitting Resistance Equivalent (PRE) are Cr, Mo, N and sometimes W. This paper compares the effect of these elements in pitting and crevice corrosion. Using ASTM G48 Methods C and D, the critical pitting temperature and critical crevice temperature are determined for several superaustenitic stainless steels (UNS N08366, N08367, N08830 and N08031) and a nickel alloy (UNS N06625). The varying effect of the elements on the two forms of corrosion and its relation to localized corrosion mechanisms are discussed. Differences between pitting corrosion and crevice corrosion are discussed. Most notably, the CCT of N06625 was the same as that of N08367 (6Mo) although the CPT of N06625 was at least 25°C greater than that of N08367 (6Mo).