Effect Of Silicon Element On Microstructure And Mechanical Properties Of Austenitic Stainless Steel

Lead-cooled fast reactor is one of the fourth-generation nuclear energy reactor types that are currently focused on in the field of nuclear power.The fuel cladding tube is the core component in the core assembly.The cladding tube needs to withstand high-energy neutron irradiation,steadily export heat,resist coolant erosion,avoid leakage of core radioactive materials,and have poor service conditions.High temperature and other external environmental factors still need to have excellent comprehensive performance.Austenitic stainless steel has the characteristics of excellent mechanical properties,excellent corrosion resistance,low price and easy processing.It is widely used as an alternative material for fast reactor cladding tubes.Silicon element can improve the formation ability of austenitic stainless steel oxide film and the corrosion resistance.However,the additions of Si can significantly affect the microstructure and mechanical properties of the cold-worked material..This topic is based on the austenite stainless steel for lead-cooled fast reactor,this paper designs alloys with three different compositions of 1.0Si,1.5Si and 2.0Si,respectively.In this paper,with the aid of the performance test and material microstructure characterization methods to study the different Si content of austenitic stainless steel properties.The main conclusions of the experiment are as follows:(1)As Si increases from 1.0 wt.% to 2.0 wt.%,,the number of the deformation twins is increased by 3.35%,the yield strength of the alloy is increased by 62 MPa,and the tensile strength is increased by 76 MPa,and the elongation basically remains constant.Si element reduces the alloy’s stacking fault energy,increases dislocation slip resistance,and deformed twins are easy to formed.Si addition increases the quantity of deformation twins in the alloy,improves the strength of the alloy.(2)The alloy aging 1000 h under 4500℃,a lot of fine TiC phases are precipitated in the matrix,but the deformed twin area is more.As the number of the deformation twins increases,the stronger the effect of precipitation strengthening of the second phase,improves the strength of the alloy.(3)The higher the silicon content in the alloy,the worse the durability of the alloy at 650℃;the main reason is that a lot of σ phase precipitates at the grain boundary,and the more silicon element content,the more the σ phase precipitates.It is easy to form tiny voids at the trigeminal grain boundary where σ phase gathers,and then continue to form cracks,reducing the strength of the grain boundary and shortening the longevity of the alloy.(4)The higher the silicon content in the alloy,the stronger the durability of the alloy at 550℃;the main reason is that the number of σ phases precipitated at the changed temperature is small,the size is small,and the precipitated phases are more uniformly distributed at the grain boundaries.Crack propagation has a suppressive effect,a small amount of fine precipitation and uniform distribution along the grain boundary can improve the endurance life of the material.