The Finite Element Analysis Of The Anodic Dissolution Stress Corrosion Cracking

Stress corrosion cracking (SCC), which is a low stress brittle fracture without warning, always leads to disastrous consequences and a big loss to the economy. According to some statistics, the proportion of the accidents induced by SCC is as high as35%in all the corrosion accidents. More than one century, the study of SCC is still an important research filed.For most anodic dissolution SCC, a corrosion product film (CPF) can be formed at the surface of the metal/the crack tip during SCC. It plays an important role during SCC, there are many researches about the CPF, but there is still a dispute. The effects of the mechanical properties and growth law of the CPF on the anodic dissolution SCC were simulated by finite element method. The emphasis is the role of the CPF on the stress field in front of the crack tip. The cohesive zone model of the anodic dissolution SCC was also built, the CPF rupture and the crack propagation were studied. The relationships of the SCC susceptibility and the normalized threshold stress intensity factor with the CPF mechanical properties (Young’s modulus, CPF rupture strength) were investigated. The SCC of310s austenitic stainless steel in a boiling42%MgCl2solution was also studied. The effect of hydrogen in the anodic dissolution SCC which the cathodic process is hydrogen evolution reaction was quantitatively investigated. The conclusions are listed below:1) The residual stress in the CPF is compressive, a tensile CPF-induced stress can generate in the metal substrate according to the self balance. The CPF-induced stress distribution is not uniform. In the U-shaped edge-notched specimen, the position of the maximum CPF-induced stress appears near the interface on the surface. The value of the maximum CPF-induced stress depends on the CPF thickness, CPF Young’s modulus, notch depth and opening. There are two possible mechanisms of CPF rupture during SCC. The first mechanism involves a large tensile stress that is produced on the surface of the CPF. In the second mechanism, The CPF-induced tensile stress is superimposed on the applied load to enhance localized plastic flow from the crack tip through increasing the resolved shear stress.2) The cohesive zone model of the anodic dissolution was biult, we can conclude that for the flat specimen, the SCC susceptibility increases with an increase in CPF thickness and Young’s modulus while decreases with an increase in the CPF rupture strength. The existence of the CPF-induced stress yields first the specimen and facilitates SCC. For the U-shaped edge-notched specimen, the normalized threshold stress intensity factor decreases with an increase in CPF thickness and notch depth. In both flat and U-shaped edge-notched specimens, the crack initiates in the CPF. The CPF-induced stress intensity factor is superimposed on the applied stress intensity factor. The anodic dissolution SCC crack can initiate and propagation with a constant applied load.3) We utilized the slow strain rate test, the electrochemical method and other methods to study the role of hydrogen in the anodic dissolution SCC. In the SCC of310s austenitic stainless steel in a42%boiling MgCl2solution, the cathodic polarization restrained SCC, and anodic polarization promoted SCC. Under an open circuit potential,ISCC(H)/ISCC=0.035, the cleavage fracture of SCC differs from the quasi-cleavage fracture of HIC in the pre-charged sample. The anodic dissolution controlled the the SCC of310s austenitic stainless steel in a boiling MgCl2solution, hydrogen plays a negligible role.