UNDERSTANDING THE EFFECT OF STRAIN LOCALIZATION ON CORROSION FATIGUE OF TYPE 304 AUSTENITIC STAINLESS STEELS IN HIGH TEMPERATURE WATER

摘要

Austenitic stainless steels are widely used inpressurized water reactors (PWRs) because of their goodcorrosion resistance. However, they are susceptible toenvironmentally-assisted cracking (e.g. stress corrosioncracking and corrosion fatigue) when exposed to hightemperature reactor coolant. In the present paper, twoheats of low sulphur type 304 austenitic stainless steels thatexhibited different corrosion fatigue behaviors insimulated PWR primary coolant have been investigated.Both heats showed enhanced crack growth, with the degreeof enhancement increasing with decreasing loadingfrequency; however, whilst one remained enhanced, thesecond heat retarded to rates close to those observed in airwhen rise time increased to 510 s and 1500 s. Deformationbehaviors of both heats were quantitatively studied atambient temperature and 300 °C via high resolution digitalimage correlation (HRDIC). Particular attention was paidto strain localization and the occurrence of planar slip vs.alternate slip. HRDIC analysis showed that alternate slipwas more prominent on the heat that retarded whilst thesample that was enhanced displayed higher strainlocalization clusters, especially at elevated temperature. Itis therefore postulated that the limited alternate slip andthe enhanced strain localization at elevated temperatureare accountable for the greater environmentalenhancement because alternate slip can act as a crackdeflection mechanism and slow down crack propagationwhen the cracking is crystallographic.