Electrochemical techniques for estimating the degree of sensitization in austenitic stainless steels

摘要

The thermal exposure of austenitic stainless steels in the temperature range of 500 degrees C-800 degrees C results in the precipitation of chromium-rich M23C6 carbides along the grain boundaries and concomitant chromium depletion. When chromium level falls below 12% at such depleted zones, the material is said to be sensitized. When the sensitized material is exposed to corrosive media, intergranular corrosion (IGC) and intergranular stress corrosion cracking take place. ASTM standard A262-13 is available for detecting the susceptibility to IGC. However, the extent of chromium depletion of shop-fabricated or field-constructed components is required to determine the presence or absence of sensitization for critical applications. In this review, various electrochemical techniques that can be employed to assess the degree of sensitization (DOS) in austenitic stainless steels are critically reviewed. Techniques such as electrochemical potentiokinetic and potentiostatic reactivation with recent modifications for the accurate estimation of the DOS are analyzed. The possibility of using AC impedance technique and electrochemical noise technique for assessing the DOS is also presented. The merits and demerits of each technique and areas where further research should be focused are presented in this review.