18Ni-300Powder Characteristics Used In Selective Laser Meltingand Microstructure Of Selective Laser Melted18Ni-300Steel

SLM (Selective Laser Melting) technology is one of the most promising technologyin metal3D printing.3D printing metal products are widely used in the defenceindustry,aerospace, shipbuilding, industry machinery and medical etc. Against the abovebackground, maraging steel powder (Maraging300) as representative was revealed inthis paper, the characteristics of the powder and powder forming mechanisim werein-depth research, mainly completed the following work:①The characteristics of M300metal powder which was made in EOS companyused in SLM were deeply studied and tested in this paper. The result shows as followed:the M300powder specific surface area is0.1082m2/g, microporous covers an area is0.001m2/g. Powder average particle size is28.66μm,90%of the particle sizeisunder60μm,10%of particle sizeis below12.12μm.Mostpowders are spherical or nearlyglobose, large particle surface adsorpted a few of small particles, there is no biggerreunion, the ellipsoid coefficient is1.38. Internal organization structure of the powder isisometric. M300powder melting point is1460℃, TG curves are smooth. M300powder’smain phase is iron-nickel martensiteand less residual austenite. Apparent density is58%,angle of repose is33.86°, the compression degree isabout11%,dispersion differenceangle is14.47%, the flowing of the powder performance meet the needs ofSLM process.②The M300powder was using SLM equipment to carry through the experiment.The process parameter selection was40μm thickness, laser printing speed was400mm/s,laser power was80W, laser printing oxygen levels belowed1.3%, finally forming partsdensity was about99%or more.Bigger macroholes and crackswere not occured in theforming part which proved that the setupprint process parameters were relativereasonable.But metallographic and SEM analysis of the forming part was indicatedthattiny holes and loose were in existence. Fine and clear scaly structure wereobserved.It can be seen that main microstructure is Fe-Ni martensite and a few remnantaustenite.③In this paper, the forming parts were carried through the research of heattreatment. The forming parts without heat treatment had a bad mechanical performance.In200℃-500℃after aging4hours, tensile strength and elongation increased along withthe rise of temperature, Yield strength and elasticity changed little. In500℃-600℃afteraging4hours, tensile strength and elongation reduced along with the rise of temperature. The best temperature for solid solution is about850℃and aging temperatureis around500℃, the ductility was28%, tensile strength reached more than1900MPa, the yieldstrength was800MPa, modulus of elasticity was7.21×104MPa, reached the level ofmechanical forgings.④The SEM examination of the fracture showed cleavage fracture, quasi-cleavagefracture and few dimples on the fracture surface at no heat treatment and annealingtreatment. The sample after solution treatment, cleavage fracture and quasi-cleavagefracture were founded at200℃-400℃aging temperature, quasi-cleavage fracture werefounded at500℃aging temperature, dimple fracture area is very large. Cleavagefracture and quasi-cleavage fracture were founded at600℃aging temperature.