1998 Volume 47 Issue 12 Pages 771-776
Electrochemical behavior and environment-induced degradation in strength for a carbon steel, SM400B, have been investigated in 0.025M Na2CO3+0.075M NaHCO3 solutions containing various concentrations of NaCl at 363K. A slow strain rate test (SSRT) was employed to evaluate the degradation in mechanical properties. It was found from polarization curves that there generated pitting corrosion beyond 0.01M NaCl. The SSRT was carried out applying a potential below the pitting potential to the specimen in the test solutions containing 0.5 and 0.01M NaCl. Under both solution conditions, an increase in the applied potential resulted in a reduction in maximum stress and fracture strain, as well as an increase in current density during SSRT. From observation of the surface of the fracture specimens, however, there was no crack on it. Based on assumption of homogeneous deformation and general dissolution until maximum load, true stress at the maximum load was calculated. It was revealed that the true stress was almost independent of the applied potential, although the maximum load decreased with increase in the applied potential. It means that the homogeneous dissolution is accelerated by applying the stress and/or the dynamic strain. It is concluded from the facts that the degradation in the mechanical properties results from a rapid reduction in the cross section due to homogeneous dissolution, instead of localized corrosion.
