Stress Corrosion Cracking Test Using Notched Round Bar Specimen of Type 304 Steel in H<SUB>2</SUB>SO<SUB>4</SUB>-NaCl Solution

Effects of a mechanical notch on initiation and growth of stress corrosion cracks in Type 304 steel were studied using a round notched bar specimen. Notches were circumferential ones which had a constant tip radius of 0.13 mm and various depths. Surface layers of notches introduced by electrodischarge machining had electrochemical characteristics different from those of bulk metal. They were removed by transpassive treatment in 0.5 kmol/m3 H2SO4 solution followed by mechanical polishing. Cracking occurred in the potential range from −0.52 to −0.35 V (SCE) in 0.5 kmol/m3 H2SO4 solution containing 0.5 kmol/m3 NaCl at 298 K. At potentials more noble than −0.40 V cracked surfaces were rugged and consisted of mixed low index planes. At −0.43 V, lower than −0.40 V, cracked surfaces consisted of smooth {111} planes. The threshold stress intensity, KISCC, below which no cracks issued was 4 MPa·m1⁄2 both at −0.37 V and −0.43 V. Variation of notch depth in the range from 1.4 to 0.4 mm had no significant effect on the KISCC values obtained.