Sh. Zhang et al., Crack initiation and propagation of sensitized Type 304 stainless steel inthe mixed solutions of sulfate and borate, CORROS SCI, 41(5), 1999, pp. 853-867
The stress corrosion cracking (SCC) of sensitized Type 304 stainless steel
has been examined in Na2B4O7 + Na2SO4 solutions with a constant solution co
nductivity by using the slow strain rate test (SSRT). The cracking behavior
was observed in-situ by a dynamic observation system with a charge-coupled
device (CCD) camera. It was found that an increase in the k (= [Na2B4O7]/[
Na2SO4]) value, or borate concentration, leads to a decrease in the SCC sus
ceptibility by retarding crack initiation, namely, by delaying crack initia
tion time and reducing crack initiation frequency. By contrast, an increase
in sulfate concentration enhances SCC susceptibility by shortening crack i
nitiation time and accelerating crack initiation frequency. The critical su
lfate concentration to accelerate crack initiation is 10(-5) kmol/m(3) and,
below this concentration, the suppressing effect of berate ions on the SCC
works. In addition, it is the solution conductivity, rather than the anion
type or their concentrations, which control crack propagation. (C) 1999 El
sevier Science Ltd. All rights reserved.