Primary objective of this work was to determine whether or not a threshold stress and incubation period exists preceeding stress-corrosion cracking of Types 302 and 316 austenitic stainless steel wires.
An investigation of the threshold stress and incubation periods was conducted on as-received (bright-annealed wire) and laboratory-annealed wire. The corrosion environment used was boiling 42 weight percent MgCl2 solution. Stress levels varied from 700 to 35,900 psi; however, most testing was conducted at 5000, 10,000 and 20,000 psi.
Testing to determine threshold stresses was conducted by exposing stressed wires to the corrosive environment and recording the times-to-failure. Incubation times were determined by exposing stressed specimens to the environment for preselected periods of time and subsequently examining the specimens metallographically to determine average crack depths. A correlation between average crack depth and exposure time was obtained.
Results of threshold stress determination testing revealed that no threshold stress was evident for as-received wire, but laboratory annealed wire stressed at 5000 psi did not crack until cross-sectional area had been reduced considerably due to general corrosion. A study of the incubation times revealed that, if there is an incubation period with as-received wire, it is less than ten minutes. For laboratory annealed wires, incubation periods of 35 minutes at 20,000 psi, 100 minutes at 10,000 psi and 500 minutes at 5000 psi were found.
