Study On Process Optimization Method Of Selective Laser Melting For The Tooling Steel Hhn18Ni300

Additive manufacturing technology is based on the principle of discrete stacking,through the gradual accumulation of materials to achieve material forming technology,this manufacturing technology can break through the limitations of processing molds,to achieve the free manufacturing of complex structures,for the manufacture of mold steel 18Ni300 conformal cooling mold Provide new solutions.Selective zone laser melting(SLM)has the advantages of high product density,superior performance,short processing cycle and high utilization rate of raw materials.It has attracted the attention of the industry and has become one of the mainstream additive manufacturing technologies for large-scale applications.The existing SLM process and application research are based on imported powder as experimental materials.In order to explore the practicality of SLM technology,this paper uses domestic 18Ni300 powder as experimental material to systematically characterize powder,SLM manufacturing process and heat treatment system.the study.First,the characteristics of the powder were characterized.The chemical composition of the powder satisfies the DIN-17350 standard,and the particle size distribution of the powder and the comprehensive properties of the powder(loose density,tap density,angle of repose,and collapse angle)satisfy the EOS standard after sieving.Most of the powder composition phase is martensite,and a small amount of austenite is present.The surface of the powder is smooth and the roundness of the powder is generally at high standard,and satellite powder is present.The inside of the powder has pores to form a hollow powder,but the hollow powder has a small content and has less influence on printing.Due to rapid cooling,the small particle powder is more common in equiaxed grains,and the large particle powder dendrites are more obvious.Through the industrial CT scanning of the printed cavity,it was found that the powdering was relatively uniform,and there were large pores in the cavity wall and the structural corner.The simulation of the properties by the Thermocalc software yields a path of change with temperature.Then the selective melting process of 18Ni300 was studied.The results of the study show: 1)The density of the sample piece increases as the laser power increases,eventually reaching a stable value.When the scanning pitch is appropriate,as the laser power increases,the surface roughness first decreases and then rises.2)Excessive scanning speed reduces the energy obtained by the molten pool,and reduces the density of the sample.Too low scanning speed leads to melt collection spheroidization,reduce the density,and deteriorate the surface quality.3)When the energy supply is insufficient,reducing the scanning pitch can increase the density of the sample,but there are still many voids.When the energy supply is sufficient,the influence of the scanning pitch on the density is not significant,but increasing the scanning pitch causes the surface roughness to rise.4)The hardness of the print gradually rises to a steady state as the density increases,and the density decreases first and then increases as the surface roughness increases.5)Metallographic analysis shows that the microstructure of the sample is a small cell structure and a bundle structure,and the bundle structure can pass through the boundary of the molten pool and face the center of the molten pool.The molded part has a cubic texture,and the grain boundaries are mostly small-angle grain boundaries.Finally,the heat treatment system of laser melting 18Ni300 in selected area was studied.After the solution treatment and aging treatment,the internal sub-grain structure and the molten pool boundary disappear,and the lath martensite and the original austenite grain boundary are replaced,and the alloy elements are reabsorbed into the matrix by solution treatment.Directly aging treatment,the original cell structure was preserved,and the hardness and strength were slightly higher than those of the solution treated with aging,but the elongation was slightly lower than that of the solution with aging.The SEM analysis of the fracture shows that the original print is plastic fracture and the fracture mechanism is micropore aggregation fracture.After solution aging treatment and aging treatment,it becomes brittle fracture,and the fracture form is quasi-cleavage fracture.