The Effects of Dissolved Oxygen, Chloride Ion and Applied Potential on the SCC Behavior of Type 304 Stainless Steel in 290 C Water Available to Purchase

Slow strain rate stress corrosion cracking (SCC) experiments have been performed on annealed and duplex Type 304 stainless steel in 290 C water. Experimental variables included dissolved oxygen concentration (<1 ppb to 28 ppm), chloride ion concentration (0 to 100 ppm as NaCl), and applied potential and current. Rapid, severe transgranular SCC is observed at 100 ppm chloride when the corrosion potential is shifted over the deaerated threshold potential (-0.15 V vs 0.01 N silver/silver chloride) by adding dissolved oxygen. Likewise, this severe cracking persists in aerated, 100 ppm chloride until cathodic potentials active to the threshold value are applied. However, even at these potentials, some slight cracking persists and is similar in nature to SCC in aerated pure water. At sufficiently active potentials (between -0.25 and -0.40 V), fully ductile failure is observed, and this potential is correlated with a critical oxygen concentration for SCC. Applied anodic currents increase the severity of SCC in aerated water at all chloride concentrations, although at currents above approximately 0.25 mA/cm² the presence of dissolved oxygen results in a decreased severity of SCC relative to deaerated solutions. Fracture surfaces are examined, and reveal some distinctive characteristics.