Microstructure And Strength-Toughness Of A Cu-Contained Maraging Stainless Steel

Compared with traditional stainless steel,maraging stainless steel has higher strength,good welding performance and corrosion resistance,so it has been widely used in aerospace,petrochemical,machinery manufacturing and other fields.However,maraging stainless steel still faces the problem that strength and toughness of the material cannot be achieved simultaneously while pursuing ultra-high strength.Some studies found introducing a certain amount of sub-micro/nanometer-sized retained or reverted austenite could break the strength-ductility/toughness trade-off of high-strength maraging stainless steels.In this paper,a new type of Cu-containing maraging stainless steel with a composition of Fe-7.5Ni-3.5Mo-8Co-12.5Cr-1Cu is designed according to the principle that Cu element accelerates the formation of reversed austenite during the aging process.Through the optimization of heat treatment process,the best heat treatment process is determined to be 1050℃solution treatment/1h+cryogenic treatment 8 h+480℃aging treatment 60 h.The mechanical properties show that the tensile strength of the Cu-containing maraging stainless steel under solution treatment and cryogenic treatment is 880 MPa,the impact energy is 263 J,and the fracture toughness is 50 MPa·m^1/2.When the aging time reaches 60 h,the tensile strength increases to 1502 MPa,the impact energy decreases to 55 J,and the fracture toughness reaches 85 MPa·m^1/2.Extend the aging time to 90 h,the tensile strength remains at 1495 MPa,the impact energy rises to 81 J,and the fracture toughness rises to 102 MPa·m^1/2.The microstructure evolution of maraging stainless steel during aging was systematically studied by XRD,EBSD,TEM and APT.The results show that Cu-rich phase and Mo-rich phase are successively precipitated in the matrix during the aging process,and some Mo-rich phases nucleate and grow at the interface of Cu-rich phase,which reduces the nucleation energy of Mo-rich phase and increases its number density.In addition,the reversed austenite and the content of Cu and Ni elements in the matrix gradually increased during the aging process,and most of them were distributed at the interface of the martensitic lath.With the prolongation of aging time,the mechanical stability and toughening effect of reverse transformation austenite are improved.Finally,according to the evolution of precipitates and reversed austenite during aging,the influence of them on mechanical properties is discussed...