Effects Of Si Element On The Microstructure Evolution And Corrosion Resistance Of 11.5CrMoWXSi Ferritic/Martensitic Steel

The fourth-generation fast reactor technology is the frontier of nuclear energy development.As an important part of ensuring safety,the selection of fuel cladding materials has always been attached great importance.Ferritic/martensite steel?FM steel?is one of the important candidate materials for high performance fast reactor fuel cladding due to its excellent mechanical properties and resistance to neutron radiation swelling.However,the mechanical properties of traditional FM steel fail to meet the requirements of the fourth-generation fast reactor with elevated working temperature,and its resistance to liquid metal corrosion is insufficient,therefore,it is necessary to research on the high performance FM steel to improve the creep performance and corrosion resistance at high temperature.11.5CrMoXSi ferritic/martensite steels with Si content of 0.6%,0.9%,1.2%and 1.5%were designed to investigate the effect of Si addition on the second phase during the aging.The results demonstrated that Si content would affect the amount and distribution of M₂₃C₆and Laves phase,which would affect the mechanical properties of the material.When Si content was 0.6%,M₂₃C₆ carbides dispersed within the grain,which greatly improved the strength of the material.However,M₂₃C₆ would grow up with the aging process and gradually lose the diffusion strengthening effect.When Si content reached 1.5%,M₂₃C₆ carbides distributed at grain boundaries,and their quantity and distribution remain relatively stable with aging.In addition,Si element would gather at the micrograin boundary near the M₂₃C₆carbide,promoting the formation of Laves phase and phagocytic M₂₃C₆ particles to grow rapidly.The number,size and volume fraction of Laves phase would continuously increase with aging,which enhanced the hardness and tensile strength of the material.Before the aging,the hardness and tensile strength of the materials with lower Si content were higher,and the hardness and tensile strength of the FM steel with lower Si content rapidly decreased within50h at the initial aging stage;the hardness of FM steel with Si content of 1.5%remained stable and its tensile strength was slightly improved.With the increase of Si content,the impact fracture changed from ductile fracture to brittle fracture.The effect of Si on the corrosion resistance of 11.5CrMoWXSi was studied by polarization curves and electrochemical impedance spectroscopy.The results showed that with the increase of Si content in FM steel before aging,the greater the passivation current density was,the shorter the width of the passivation area was,and the smaller the role of the passivation film was,the smaller the value of pitting potential E_p was,and the worse the corrosion resistance of the material was.After 400 h of aging,the corrosion resistance of FM steel with Si content of 1.2%and 1.5%rebounded.The results of Nyquist plots showed that with the increase of Si content,the resistance value R_ct of FM steel gradually decreased,and its corrosion resistance also gradually weakened,which was consistent with the data presented by the polarization curve.The effect of aging time on the corrosion resistance of FM steel was studied.It was found that the corrosion resistance of FM steel became worse with the extension of aging time,and rebounded after 400h of aging.