Study On Stress Corrosion Of S32168Stainless Steel In Chloride Environment

Austenitic stainless steel has been widely used in various industries for its excellent performance, superior corrosion resistance and better biocompatibility. But austenitic stainless steel shows higher stress corrosion sensitivity when it is in certain environments which contain chloridion. The existence of chloridion can accelerate the dissolution of surface oxide film of the austenitic stainless steel. In this case, austenitic stainless steel will be exposed in the corrosion environment and then pitting corrosion and stress corrosion will appear.This paper takes the S32168austenitic stainless steel as research object, focuses on the mechanism of stress corrosion of S32168stainless steel in chloridion environment. The mechanism of stress corrosion of S32168austenitic stainless steel in chloridion environment is anodic dissolution. Under the chloridion environment, S32168stainless steel experiences three stages that are rupture of passive film, dissolution, and finally fracture. And chloridion ions take an important role in the process.With S32168stainless steel pipeline applied in virtual environment of FLUENT, the software will simulate the influence of flow to pitting in the case of the discrete phase bubble. The velocity vector of the pipes, turbulence intensity, wall pressure and shear force will be got by FLUENT. The studies show that flow field changes when it flows through pitting corrosion area because of the existence of pitting corrosion. The stress depraves on the surface of the pitting corrosion and the crack extends, and the cracks of material in the case of stress corrosion would occur on the surface of pitting corrosion in priority.Using slow strain rate tensile testing machine through comparing the characteristics of different types of stress corrosion, the research on stress corrosion behavior of austenitic stainless steel in chloridion environment has been done. The tensile rate is1.9×10-6s-1in this test, and the solution is NACE standard liquor. The breakdown time and elongation would be obtained in five environments. Stress corrosion sensitivity index of S32168stainless steel would be obtained by calculating the elongation, reduction, rupture of inner product and obtaining the stress strain curve.S32168stainless steel would occur plastic fracture in normal temperature and pressure. There are many toughening nest in the fracture surface and there are no crack on the lateral surface of fracture. There are quasi cleavage charact-eristicsin150℃,1.6MPa and150℃,11MPa.and there are many cracks on the lateral surface of fracture. However, the stress corrosion sensitivity indexes of S32168stainless steel are similar in both environments. From which, we know that pressure changes have little impact on stress corrosion sensitivity of S32168stainless steel. There is clear quasi cleavage fracture characteristics as well as secondary crack in260℃、4.6MPa and260℃、11MPa.And there are many pits on the lateral surface of fracture with many cracks. From which we get the result that the stress corrosion sensitivity of S32168stainless steel is higher with the increase of temperature and pressure.