Research On The Cavitation Erosion Behavior Of 316L Steel Welded Joints With Different Treatment Processes And Heat Input In Liquid Lead-bismuth Alloy

Energy is the most important factor that can determine the sustainable development of the current society,and the use of nuclear energy helps to alleviate the current energy dilemma.Liquid lead bismuth eutectic alloy（LBE）has strong radiation resistance,good thermal conductivity and safety,and excellent neutron properties.It is widely used in nuclear power accelerator,subcritical drive system（ADS）and coolant lead cooled fast reactor（LFR）,but the liquid lead bismuth flowing in the pipeline could cause the serious corrosion to the materials of the loop in the storage tank and the main pump impeller.The welded joint of structural steel is casting structure,and the coarse grain inside and the residual stress after welding will further aggravate the corrosion in the liquid LBE.316 L stainless steel is a kind of austenitic stainless steel with excellent comprehensive mechanical properties.It is the most widely used structural materials in nuclear reactors.The study of its corrosion resistance is helpful to improve the corrosion resistance and the service life of nuclear reactors.In this paper,a set of cavitation corrosion experimental device is designed,in which the power of ultrasonic horn is 3kW,the frequency is 19.2kHz,and the amplitude is 50μm.Research on the effect of different heat input,pre-corrosion and nickel on the cavitation corrosion of 316 L welded joint in liquid LBE at 550℃ with the cavitation corrosion device.Firstly,316 L welded joints of different heat input was carried out after cavitation corrosion for 80 h and the results show that 316 L welding joint of cavitation erosion resistance is negatively related to the welding heat input.As the welding heat input increases,cavitation erosion resistance of welded joints becomes worse.316 L welding joint cavitation erosion resistance is mainly affected by the grain size of austenite,and when welding heat input increases,the austenite grain in weld zone is fully grown under the effect of welding residual heat,leading to worse cavitation erosion resistance.The parent material is better than the cavitation erosion resistance of weld,the weld zone is due to the solidification mode of F-A type ferrite and austenitic recrystallization;weld internal formation of vermicular ferrite austenite grains and coarse.When the 316 L welded joint is subjected to cavitation corrosion in liquid LBE at 550℃,the double oxide layer will be formed on the surface of the specimen.The outer oxide layer is Fe₃O₄,the inner oxide layer is FeCr2O4,and the density of inner oxide layer is higher than that of the outer oxide layer.With the increase of welding heat input,the outer oxide layer becomes thicker while the inner oxide layer changes little.Secondly,after cavitation corrosion of welded joint of 316 L in liquid LBE at 550 ℃during different time,of SEM and AFM morphology was carried out for the observation and analysis of surface morphology.The results show that the surface roughness and corrosion pit depth of welded joints of 316 L will increase with the increase of cavitation erosion time.In the process of cavitation erosion,cavitation stress of the 316 L welded joints,the surface hardening will occur.Due to the deformation of the rapid accumulation in the grain boundary and the dislocation after delivery,the surface hardness after cavitation is higher than that before cavitation.Thirdly,the effect of nickel on the cavitation corrosion of 316 L welded joint in liquid LBE at 550℃ was studied.The results showed that the Ni particles in the weld joint are dispersed in the grains and bonded with the matrix phase with high intensity,so it can significantly enhance the anticorrosion ability of welded joints.The effect of pre-corrosion on cavitation corrosion resistance of 316 L welded joints was studied.The thin Fe₃O₄ oxide layer is formed on the surface of the 316 L steel welded joint after the pre-corrosion of 80 h at 200 LBE.℃ During the incubation period,the impact of cavitation stress can be effectively resisted,while in the rising phase the cavitation erosion resistance of the matrix material is reduced.