Corrosion Behavior Of Duplex Stainless Steel For PWR Primary Loop Under Simulation Working Condition

Duplex stainless steel Z3CN20.09M is widely used in primary coolant loop of PWR due to its good comprehensive mechanical properties and corrosion resistance. But the operation condition of the primary Loop is very strict, so Materials will occure corrosion during prolonged exposure to high-pressure water vapor, which poses a great threat to the safe operation and service life of PWR. Therefore, exploring the corrosion behavior of Z3CN20.09M has an important theoretical and practical significance to ensure the safe operation of the PWR.Oxidation behavior of Z3CN20.09M in air and water vapor condition are respectively studied at 350 ℃ and 400 ℃ by isothermal oxidation method, non-continuous weighing method was used to explore the oxidation kinetics, microstructure and thickness of the oxided film were observed by scanning electron microscope, the composition and phase structure of the oxided film are analyzed by EDS and XRD, Finally. the influence of thermal aging on corrosion resistance of Z3CN20.09M steel is tested by electrochemical test The conclusions are as follows.The oxidation kinetic curve of Z3CN20.09M duplex stainless steel in 350 ℃ and 400 ℃-air obeys the parabolic law. The difference is that the oxidation rate is higher in 400 ℃ than in 350℃-air. With the gradual increasing of the oxidation time, the granular and rod-like oxidation film becomes flocculent and tumor-like. The thickness of films in two different temperatures are both 7～8 μm after 5000 hours’oxidation. And its main composition is Cr2O3 and Fe3O4.The oxidation kinetic curve of Z3CN20.09M duplex stainless steel in 350 ℃ and 400 ℃ water vapor condition follows the parabolic law and linear regularity, after 2000 hours’, the corresponding morphology of oxidation film in 350 ℃ water vapor condition is octahedral spinel structure and aggregation of lumpy. The compositions of the oxide film is FeCr2O4 The oxidation is about 15 μm. With the gradual increasing of the oxidation time, the microstructure of the oxide film in 400 ℃ static water vapor condition has a 3 stages transformation from needle-like to circular granular and finally octahedral. In this 3-stages transformation. The needle-like oxidation is Cr2O3 and the granular oxidation is FeCr2O4 After 5000 hours of oxidation, the thickness of film is about 26μm.Electrochemical test results show that,after thermal aging, the polarization curve of the sample changes little in the passivation platform width with the increasing of oxidation time. But the passivation current slightly increases. And the curve radius of electrochemical impedance spectroscopy, generally, the resistance value becomes smaller with the gradual increasing aging time.