Abstract
A mathematical model to explain quantitatively the existence of the threshold stress intensity factor (KISCC) and the growth rate(da/dt) of stress corrosion cracking (SCC) of 18-8 austenitic stainless steel in a chloride environment at room temperature was investigated using electric circuit theory applied to the closed corrosion path with a metal-electrode (1 anode-2 cathode) -solution system of SCC crack geometry. Several conceptual assumptions and simplifications of the equations were attempted to derive the circuit current and the concentration of the chemical components of solution in SCC crack. It is predicted from the derived equation that the accumulation of solution in SCC crack may arise in the condition of f-CCl-×K×g2>0 holds where f and g2 are parameters due to the circuit resistances etc, CCl- is the free chloride ion concentration inside the crack, and K is the equilibrium constant or stability constant of the crack solution. A relation between da/dt and applied external force was simulated using an anode dissolution parameter relating to stress intensity factor Kl. The SCC growth rate of about 10-8 m/s obtained is reasonable compared with the data in the literatures. A parameter ε(KISCC) corresponding to KISCC was derived and it may predict quanitatively the concentration dependence of KISCC regarding metallic ions and hydrogen ions.
