Development of A New Test Method for Chloride Stress Corrosion Cracking of Stainless Steels and Its Application to That of Type 316 in Dilute NaCl Solutions

Abstract

Tapered Double Cantilever Beam specimen with artificial crevice has been designed to clarify SCC behaviors of Type 316 stainless steel in dilute NaCl solutions. This specimen has two dimensional characteristics, which mean that both mechanical and chemical parameters are independent of the specimen thickness. The former is stress intensity, K_I and the latter is repassivation potential of crevice, E_R. SCC tests have been conducted potentiostatically in 3, 0.3, and 0.03% NaCl solutions at 80°C under K_I constant condition.
Cracking occurs at the crevice bottom only when the bottom surface is dissolving at potentials more noble than E_R and K_i is over K_ISCC, 1314kgf/mm^3/2. Bulk NaCl concentration has no significant influence on K_ISCC and i_II, crack growth rate in the region II where i is independent of K_I. Cracking occurs at potentials between -0.23 and -0.18 V (SCE) in 3% NaCl, and between -0.11 and +0.10 V in 0.03% NaCl solution. The lower limit of the potential range for cracking is the potential just more noble than E_R in each solution and the upper corresponds to the potential where the dissolution rate at the crevice bottom is equal to i_II.