Research On Composition Optimization Of Maraging Steel And Its Selective Laser Melting Process

As an ultra-high strength steel,maraging steel plays an increasingly critical role in aerospace,nuclear energy,medical and transportation industries.It is one of the key materials used in the field of 3D printing lightweight design,cost saving and shortening R&D cycle.The strengthening of maraging steel mainly depends on alloying elements such as Co,Mo,Ti and Al.Co element and Mo element have a synergistic strengthening effect.With the shortage of global Co resources,the future development of high-strength steel will gradually reduce the content of metallic Co element.Currently,the research on maraging steel mainly focuses on the evolution law of precipitation phase during aging process.Research on the effect of strengthening elements on the microstructure and mechanical properties is also limited to the single metallic elements(Co,Mo,Ti).If the Ti content is too high the ductility and toughness of maraging steel will decrease sharply.The joint effects of Ti and Al as the main strengthening elements of maraging steels on microstructure and properties need to be studied.In this paper,the 18 Ni maraging steel is used as the research object.First,the content of Ti and Al elements is controled to study the effect of the two elements on the as-cast microstructure.Then,After heat treatment,the mechanical properties are tested.It was found that Ti and Al elements can promote the increasement of the residual ferrite volume fraction in the as-cast structure.When wt(Ti)= 0.7%,the addition of Al element has a promoting effect on the strength and plasticity of steel,but when wt(Ti)= 1.2%,the addition of Al element deteriorates the plasticity.The composition with the best strength-plastic matching after heat treatment is 18Ni9Co5Mo0.9Ti0.3Al.Its as-cast tensile strength is 2050 MPa,and the elongation is 4% at room temperature?For 18Ni9Co5Mo0.9Ti0.3Al new maraging steel,the powder for additive manufacturing was prepared by vacuum gas atomization.The laser selective melting additive manufacturing process of this alloy was optimized.When the powder thickness(t)is 50?m,the scanning distance(h)is 0.11 mm,the laser power is 300-400 W and the laser body energy density is between 58-70J/mm3,and the relative density of the formed sample reaches more than 99.97%.When the horizontal overlap rate is 30-50% and the vertical overlap rate is about 70%,the shape of the molten pool is more stable and the shaping quality is better.Based on optimizing laser selective melting process,the effect of common heat treatment processes on the structure and mechanical properties of the shaped parts was studied.It was found that the new composition maraging steel has a tensile strength of 2182 MPa,an elongation of 4.8%,and a Rockwell hardness of 56 HRC after solution aging heat treatment.The strength and hardness of the new composition maraging steel exceeded the standard forgings of 18Ni300 steel after solution aging heat treatment,and the elongation reached standard forging level.