On the basis of the electrochemical characteristic of stress corrosion cracking in aqueous solution system, the effects of various environmental and mechanical parameters, such as organic additives, potential perturbation, temperature and strain rate etc., on the susceptibility of stress corrosion cracking for austenitic stainless steel have been studied. The purpose is to further understand the stress corrosion cracking mechanisms and to control the metallic straining electrochemical processes. From the point of view of concentration and temperature on reaction rate, the effects of concentration and temperature of the acidic chloride solution on the susceptibility of stress corrosion cracking have been studied, and the systems susceptible to stress corrosion cracking were determined. The inhibitors action of a series of organic compounds on the susceptibility has been compared. Two inhibitors which markedly decrease the stress corrosion cracking susceptibility were selected. The SCC susceptibility of 321 austenitic stainless steel in acidic chloride solution and the inhibiting effect of both benzotriazole(BTA) and propargyl alcohol(PA) on stress corrosion and general corrosion were studied by slow strain rate testing(SSRT), combined with transient current measurements during intermediate strain rate testing (ISRT) under potentiostatic condition, scanning electron microscopy(SEM), potentiodynamic polarization measurements and in situ electrochemical impedance spectroscopy(EIS) measurements. The relationships between the mechanical properties and electrochemical parameters which affected the stress corrosion cracking have been established. The results indicated that the inhibiting action of BTA and PA can be attributed to their adsorption and inhibiting the anodic dissolution of the metal by the effect of blocking the active sites on the metal surface. The change of reactivity on the metal surface can be monitored by the impedance measurements during SSRT. The results showed that the reactivity of the surface of tensile specimens increased directly proportional to the strain, while the addition of inhibitors obviously retarded the increase rate. By applying constant potential polarization, potential sweep and step perturbation polarization during SSRT, the SCC susceptibility and fracture characteristic of type 321 austenitic stainless steel in acidic chloride solution have been studie. The results indicated that the anodic polarization promoted the SCC of the stainless steel, whereas cathodic polarization inhibited the initiation and propagation of the cracks. Therefore, the SCC of this metal/environment system seems to follow anodic dissolution mechanism. However, hydrogen played a decisive role in the SCC of this metal/environment system under high frequency cyclic potential step perturbation. When cyclic potential scan or cyclic potential step was applied to the metal specimen during SSRT, the slower the scan rate was(quasi-steady state), or the higher the step frequency, the higher the fracture susceptibility. Within the same polarized potential ranges, fracture elongation in cyclic potential step was lower than that in cyclic potential scan. This work opened up a new field to study the effect of potential factor on the SCC. Based on the model of slip-bare metal dissolution-repassivation and crack-tip strain analysis, a theoretical equation of stress corrosion cracks growth rate as a function of crack-tip strain rate and potential for 304L stainless steel in acidic chloride solution was deduced and proposed. The theoretical prediction showed that there are two regions in the curve of crack growth rate with the crack-tip strain rate. In region 1, the crack growth rate increased with increasing crack-tip strain rate. In region 2, the crack growth rate was independence of the crack-tip strain rate. The crack growth rate of 304L stainless steel in acidic chloride solution has been measured by slow strain rate testing(SSRT) technique. The theoretical calculation was consistent with the experimental SCC growth rate in region 2 when potential was controlled in anodic region. This work provided a theoretical guideline for the experimental study of crack growth rate influenced by strain rate at crack tip and potential. The effect of elastic and plastic strain on the electrochemical behavior of austenitic stainless steel has been studied. Based on the relationships between thermodynamic criteria and electrochemical parameters, the straining electrochemical behaviors of stainless steel have been analyzed. The results showed that the changes of open circuit potential and EIS with time for unstressed specimen were obviously different from those of dynamic slow tensile specimen. The elastic strain only affected the anodic dissolution process of metal and had no effect on the cathodic process. The strengthened deformation and the formation of dislocation block played a key role in the mechanical-chemical effect.
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