Stress corrosion cracking of pressure vessel steels in high-temperature caustic aluminate solutions

Abstract

Stress corrosion cracking (SCC) behavior of three kinds of low alloy pressure vessel steels in high-temperature (200 °C to 300 °C) caustic aluminate (AIO-2) solutions has been studied by slow strain rate tests (SSRT). The results indicate that these pressure vessel steels are susceptible to SCC in caustic aluminate solution and that the SCC susceptibility increases with increasing temperature between 200 °C to 300 °C. Sulfide content and stringered sulfide inclusions severely and anisotrop-ically affect the caustic SCC of these low alloy steels. The inclusions in the rare-earth-treated steel are predominantly globular rare-earth sulfides or oxysulfides, resulting in improved transverse prop-erties. The effect of inclusions on SCC behavior correlates with the projected area of inclusions perunit volume at the crack tip,A v , on the plane perpendicular to the tensile direction. The susceptibility to SCC increases with increasingA v .