EFFECT OF MARTENSITE ON SCC INITIATION IN AUSTENTITC STAINLESS STEELS IN SIMULATED PWR PRIMARY WATER ENVIRONMENT

摘要

Metastable austenitic stainless steels are susceptibleto martensitic transformations during cold-working;however, their implication on SCC initiation in PWRprimary water is unclear. In this study, cold -rolling andwarm-forging were applied to austenitic stainless steelstype 304L and 316L in order to introduce differentamounts of martensite. Multiple specimens were thenextracted from these rolled/forged materials and testedunder slow strain rate tensile (SSRT) test conditions inPWR primary water to assess their SCC initiationbehaviors. These specimens were characterized prior toand after the tests, using SEM and EBSD. The resultsshowed that a plastic strain of ～3% during SSRT testinginduced extensive intergranular SCC initiation in thesteels which did not contain martensite. However, coldrolled304L, which contained martensite, showed fewSCC cracks even when strained to ～4.5% and only limitedcracking occurred on specimens strained to ～5.8%. Post–test characterization revealed that extensive preferentialoxidation of martensite occurred in the cold-rolled 304Lwhereas only intergranular oxidation was observed forthe steels in which no martensite was detected. Thecorrelation between martensite and oxidationbehavior/SCC initiation is discussed.