Characterization And Detection Of Stainless Steel And Aluminum Alloy During Stress Corrosion Cracking In Typical Environment

Austenitic stainless steel and aluminum alloy have been widely applied in nuclear industry, aerospace and ocean transportation fields due to their excellent resistance to corrosion and mechanical properties. However, stress corrosion cracking(SCC) has become to be one of the greatest risks for these metal materials in service. Therefore, The SCC behavior of 304 austenitic stainless steel(304SS), 01570 alloy, 7A60 alloy and 2195 alloy in typical environment were detected and characterized in this paper.Wavelet-based fractal dimension D was proposed to study electrochemical noise(EN) signals of different corrosion types for 304 SS. The results showed that the fractal dimension D can be selected to distinguish corrosion types and evaluate the localized degree of corrosion. The more uniformly the corrosion occurred over the electrode surface, the larger the D value was. The more locally, the smaller the D value was for 304 SS. Then wavelet-based fractal dimension D was used to analyze the corrosion process of Q235 carbon steel in simulated concrete pore solution. The results showed that D was larger than 2 when the surface was under passivation. However, D was decreased to be 1.75 as pitting corrosion occurred. And then D was decreased to be 1.1~1.2 as immersion time further increased.Acoustic emission(AE), EN and the complementary surface analysis techniques such as scanning electron microscopy(SEM) were used to study the SCC behavior of 304 SS. The intergranular corrosion cracking(IGSCC) behavior of sensitized 304 SS in 0.5mol/L Na2S2O3 solution and transgranular corrosion cracking(TGSCC) behavior of solution heat treated 304 SS in 4mol/LNaCl+0.01mol/L Na2S2O3 solution(TGSCC1) and 0.5mol/L NaCl + 1.5mol/L H2SO4 solution(TGSCC2) were studied. The correlation between EN transients, AE hits and the stress rate peaks were studied. The evolution of Rn, SI, cumulative hits and energy with time was analyzed. AE signals were analyzed by K-means cluster analysis, and the AE cluster results were consistent with the fractal dimension D in distinguishing corrosion types.In addition, transmission electron microscopy(TEM), SEM and energy dispersive X-ray spectroscopy energy(EDS) techniques were used to study the SCC behaviors of 01570 alloy which could not be precipitation strengthened, 7A60 alloy and 2195 alloy which could be precipitation strengthened in 3.5% NaCl solution. The results proved that for 01570 alloy the residual stress and internal strain of alloy induced by cold rolling treatment released with the elevated annealing temperature. Consequently, SCC resistance was greatly improved. For 7A60 alloy, the SCC resistance was increased obviously with the retrogression time as the precipitates η(MgZn2) at grain boundary were coarsened and more spaced. However, the SCC susceptibility of 2195 alloy was low and hardly influenced by T1(Al2CuLi) precipitation at grain boundary.