Susceptibility to Stress Corrosion Cracking for Low-Carbon Steel Welds in Carbonate-Bicarbonate Solution

The susceptibility to stress corrosion cracking (SCC) of the weld zone of carbon steel overpack, a candidate container for geological disposal of high-level radioactive waste, was studied using the slow strain rate testing (SSRT) technique. Several welding processes were applied to low-carbon steel, and SCC susceptibility of the weld zone, which consists of weld metal, weld interface, and heat-affected zone (HAZ), was compared with that of the base metal. The test results indicated that SCC behavior of low-carbon steel weld was strongly dependent on microstructure, while SCC in the base metal, which consists of ferrite and pearlite, mainly propagated along ferrite-ferrite or ferrite-pearlite boundaries. However, crack morphology in the weld zone, made up of fine-grained microstructure, was more complicated; the average crack growth rate in the weld zone was less than that of the base metal. SCC propagation was thought to be suppressed by the fine grain size and/or redistribution of cementite (iron carbide [Fe₃C]) along the crack path, and welding processes were found to have no significant influence on SCC susceptibility of low-carbon steel.