Role of Cavity Formation on Crack Growth of Cold-Worked Carbon Steel, TT 690 and MA 600 in High Temperature Water

Abstract

The role of cavity formation on crack growth of intergranular stress corrosion cracking (IGSCC) in high temperature water and creep cracking was examined in quantitatively for cold worked carbon steel (ASTM A106 (UNS K03006, CW carbon steel), Alloy 690 (UNSN06690, CW TT 690), and Alloy 600 (UNSN06600, CW MA 600). Three important patterns were observed: First, cavities were observed at grain boundaries just ahead crack tips and crack wall after tests in gas and high temperature water for all test materials. Second, population of cavities decreased with distance from crack tips and crack wall. This result seems to suggest that cavities will form at high stress region such as crack tips before crack advance as crack embryos. Third, good correlation was observed between the rate of cavity formation and crack growth of IGSCC and intergranular creep cracking not only carbon steel, but also TT690 and MA600. Finally, the formation of crack embryos from the collapse of vacancies induced by cold work and absorbed hydrogen play an important role on the process of crack growth both of SCC and creep for CW carbon steel, CW TT690, and CW MA600 in high temperature water.