CORRELATION OF CURRENT TRANSIENTS TO FILM RUPTURE DURING TENSILE LOADING OF TYPE 304 SS AND ALLOY 22 IN 4 M NaCl SOLUTION AT 60 deg C

摘要

The objective of this study is to investigate the effect of strain hardening on the passive film repassivation kinetics. This helps understand the film breakdown and repair processes occurring at the crack tip of a ductile material. Straining electrode tests were carried out by applying load-unload-reload cycles at different strain rates on 304 SS and alloy 22 tensile specimens in 4 M NaCl solution at 60 deg C at a constant potential of -250 mV (Ag/AgCl). Current transients were measured during straining and the slope of strain rate vs maximum current plot for 304 SS in mill-annealed condition was 0.65 and with strain hardening it decreased to 0.5. The slope of the strain rate vs maximum current plot for alloy 22 in mill-annealed condition was 0.73 and with strain hardening the slope increased marginally. This slope could be directly related to the slope of the current decay during formation of the passive film. Based on this analogy, the experimental results indicated that the strain hardening adversely affected the repassivation kinetics of 304 SS. Strain hardening of alloy 22 did not show any adverse effect on repassivation kinetics.