The Investigation On Microstructure And Electrochemical Corrosion Performance Of New Austenitic Stainless Steels

The main pipe of the primary circuit of the pressurized water reactor has been serviced in high-temperature and high-pressure water environment for a long time,which is an important channel for nuclear power energy transmission.Austenitic stainless steel is the first material of choice for nuclear power main pipe.Its stable structure and electrochemical corrosion resistance are closely related to the safe operation of PWR nuclear power plants.The manufacturing process of the main pipe is usually casting or forging,so it is of great engineering significance to study the influence of the manufacturing process on the microstructure and electrochemical corrosion resistance of the nitrogen-containing test material,and the alloy element and solution treatment on the microstructure and electrochemical corrosion resistance of the forged test materials.In this paper,six new components of austenitic stainless steel test materials were designed and produced.The casting test test materials and forged test materials has been obtained through casting and forging manufacturing processes,respectively.The differences in microstructure and electrochemical corrosion resistance of nitrogen-containing casting and forged test material,forged test materials with different components and states has been analyzed by contrast.Using optical microscope,scanning electron microscope and electron backscatter diffraction technology to analyse the microstructure of nitrogen-containing casting test material and four kinds of forged test materials with different compositions,found that the structure of the nitrogen-containing as-cast samples are coarse columnar crystals or equiaxed crystals.After solution treatment,columnar crystals and equiaxed crystals grow.The adjacent grains of solid solution state sample in equiaxed crystal region show anisotropy.After forging,the structure of the four forging state samples are uniform and fine equiaxed crystals,due to plastic deformation,there is lattice distortion inside the crystal grains;the adjacent crystal grains show anisotropy.After solution treatment,the crystal grains grow and contain more twins inside.With the addition of alloying elements,the proportion of low-angle boundaries in the forged test material increases,and the proportion of special grain boundaries in the forging state sample decreased.After solution treatment,the proportion of low-angle boundaries in the forged test material decreased,while the proportion of special grain boundaries all increased,and Σ3 grain boundaries increased exponentially.The potentiodynamic polarization curve and electrochemical impedance spectrum of nitrogen-containing casting test material and four kinds of forged test materials with different compositions were measured by an electrochemical workstation,The influence of the manufacturing process on the electrochemical corrosion resistance of nitrogencontaining test material,and alloy element and solution treatment on the electrochemical corrosion resistance of the forged test materials were studied.The results show that among the forged test materials,electrochemical corrosion performance of the niobium-containing test materials is best.After solution treatment,the electrochemical corrosion performance of the forged test material is better.For the nitrogen-containing test material,the electrochemical corrosion performance of the forged test material is better than that of the cast test material.The above research not only enriches the data related to the microstructure and electrochemical corrosion resistance of nuclear power main pipe,but also provides theoretical guidance for the development and production of new components of the main pipe in China,which is of great significance for the safe and efficient development of nuclear power in China.