COMPARATIVE STUDY OF ASTM A262 PRACTICES A, E AND G108 TESTS FOR THE EVALUATION OF SENSITIZATION IN AISI TYPE 316 STAINLESS STEEL

摘要

In this paper the results obtained in a comparative study of ASTM A 262 Practices A (metallography), E (immersion test) and G108 (Electrochemical Potentiokinetic Reactivation technique) tests for the evaluation of sensitization in AISI type 316 stainless steel are reported. Different degrees of sensitization (DOS) were obtained by heat treating the material at 948K for durations ranging from 3h to 2000h. Depending upon the thermal history, the material may be either in sensitized, non-sensitized or desensitized condition. ASTM A262 Practices A, E and G108 tests were performed on each specimen. Prolonged aging beyond desensitization resulted in the precipitation of embrittling secondary phases which were separated by electrolytic method and were identified by X ray diffraction technique. The need to carry out both ASTM A262 A and G108 to differentiate between sensitization and desensitization is brought out in this investigation. Both act as complementary to each other and when performed separately yields results which are inconclusive. A method has been suggested to distinguish between various microstructural states possible in a fabricated or service-exposed component.