Study On 18Ni300 Die Steel Powder For Additive Manufacturing

As an emerging molding technology,additive manufacturing technology is widely used in various fields of industry.In an environment where the demand for molds is increasing,traditional manufacturing techniques cannot fully meet current production needs.Selective laser melting is one of the most widely used processes in metal augmentation manufacturing at present.It is mainly used for forming conformal cooling channels in the field of moulds.18Ni300 shows high strength and toughness,it is one of the few die steels that can be directly used by selective laser melting.At present,the domestic research mostly focuses on the optimization of the forming parameters,and the research on the relationship between the process and the properties of powder materials is not common.Therefore,the study on the selective laser melting properties of 18Ni300 powder has great significance for the follow-up industrial development.This article mainly contains three parts.First,the spherical powder prepared by gas atomization is used as the original powder to optimize the parameters of the laser melting forming process.The effects of scanning speed,scanning pitch and laser power on the density of molded parts were investigated.The microscopic pores and molten pool morphology of the molded parts were observed.The highest density forming process was selected by comparison.After that,the influence of the powder's own properties on the molding quality was investigated,and the proportion was re-matched according to the proportion of the original powder.Four groups of mixed powders containing:the mixed powders without coarse powder,the mixed powders have no fine powder,the mixed powders with no coarse powder and fine powder,the mixed powders have both coarse and fine powder.The above-mentioned selected process parameters are used.Molding,compared with the original powder molded parts,analyzed the influence of the median diameter and apparent density on the density of the molded parts,measured the tensile properties and impact properties of the molded parts,and observed the metallographic structure and fracture morphology.Finally,the effects of heat treatment on the tensile properties and impact properties of the selected laser-molded parts were discussed.The molded parts were aged,and then the tensile properties and impact properties were tested.The results were compared with the untreated mechanical properties.Fracture morphology of the samples were observed.The conclusions obtained from the experiment are as follows:the optimum molding process parameters are:laser power 80W,scanning speed 1600mm/s,layer thickness 20?m,scanning pitch 0.03mm,and the density of the original powder molded part is 99.51%.The molded part corresponding to the D50 with the closest layer thickness setting has the highest density of 99.87%.The effect of the particle size of the powder on the density of the molded part is greater than the apparent density.Under the premise of similar D50,the powder molded parts with high apparent density have high relative density.The molded parts of the five groups of powders are lath martensite and retained austenite structure,and the mechanical properties are positively correlated with the density.The tensile strength of the molded part with the best mechanical properties is 1219 MPa,the elongation is 15.5%,and the impact absorption energy KV2 is 59J.After aging treatment at 490? for 6h,the tensile strength increased significantly compared with the untreated state,with the highest increase of 47%;the elongation decreased significantly,the difference decreased by about 4%;the impact absorption energy decreased greatly,with a maximum of 71%.After aging treatment,the strength of the material increases,and the ductility and toughness decrease.