Stress Corrosion Cracking Behavior of Carbon Steel in High-Purity Water at 100 to 288°C

Abstract Stress corrosion cracking tests were performed on carbon steels at the strain rate of 10-6 sec-1 in high purity water containing 0.16, 1, and 8 ppm oxygen over the temperature range of 100 to 288°C. In 1 and 8 ppm oxygen water, increasingly severe transgranular cracking was observed from ~135°C. In 0.16 ppm oxygen water, transgranular cracking was first seen at 175°C and became more severe with increasing temperature up to 250°C. At temperatures of 265°C and above, the fracture was ductile. In both high and low oxygen waters, cracks propagate at high stress levels close to the ultimate tensile strength and are probably also initiated at high stresses. In 0.16 ppm oxygen water, cracks initiate at pits which form at active sulfide inclusions at the surface because of crevices created between inclusions and the matrix on straining. Sulfides also play an important role in, but probably are not necessary for, crack propagation at the higher oxygen levels.