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Influence Of Process Parameters On The Microstructure Of 316L Stainless Steel Manufacture By Selective Laser Melting

Posted on:2023-04-15Degree:MasterType:Thesis
Country:ChinaCandidate:L WangFull Text:PDF
GTID:2531306845460134Subject:Materials and Chemicals
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Selective laser melting(SLM)technology is currently the most mature metal additive manufacturing technology,used for complex structural parts forming,with short cycle time,high precision,and a variety of available materials.However,the cooling rate of this technology is extremely fast,and the point-by-point and layer-by-layer accumulation and formation can easily lead to metallurgical defects,microstructure heterogeneity,obvious anisotropy and other problems.Process parameters are an important reason for the formation microstructure and mechanical properties of selective laser melting technology.In this thesis,in the range of 135-335 W laser power,400-900 mm/s scanning speed and25-140 J/mm~3laser energy density,taking 316L stainless steel as the research object,the influence of laser power and scanning speed changes on the density,defects,microstructure and mechanical properties of selective laser melting additive manufacturing of 316L stainless steel are studied.Within the range of parameters set in this thesis,the results show that:pores are the main reason for the reduction of the density of 316L stainless steel by selective laser melting,and the main types of pores are unfused pores,keyholes and gas pores.With the increase of laser energy density,the sample density first increased and then decreased.Laser energy input lower than 52.78 J/mm~3will result in insufficient melting and incomplete overlap of melt tracks,resulting in unfused pores.The laser energy input higher than 93.06 J/mm~3will lead to excessive melt pool temperature,excessive melt pool depth,and the formation of significant keyholes.Therefore,when the laser energy density is in the range of 52.78-93.06 J/mm~3,the density is higher than 99%.The microstructure of316L stainless steel by selective laser melting is not uniform,and it is dominated by columnar crystals growing from the edge of the molten pool to the center.And there are more finer cellular structures within the columnar crystals.Increasing the laser energy density can promote the melt track and interlayer remelting,thereby suppressing the columnar crystals and making the grains refined and homogenized.Due to the preferential growth of columnar crystals in the SLM-formed structure,the formed samples mainly have a texture with the<100>crystal orientation deviated from approximately 10°parallel to the build direction.Increased laser energy density can refine grains and suppress columnar grains,thereby weakening preferred orientation.Furthermore,due to the higher oxygen content in the raw material and the faster cooling rate,a large amount of Si,Cr,and Mn oxide-containing secondary phases are present in the additively manufactured samples,and their structure is amorphous.Changes in process parameters have little effect on the distribution of the second phase.The performance study shows that the SLM-formed 316L stainless steel has higher strength than the traditional forging process samples,and the tensile strength can reach up to 785.98 MPa,but the elongation does not exceed 30%.In addition,the yield strength and tensile strength of SLM-formed 316L stainless steel at550°C can reach 360 MPa and 450 MPa,respectively,and have application prospects for high-temperature structural parts.Due to the grain refinement and homogenization caused by the increase of laser energy density,the elongation always shows an increasing trend with the increase of laser power.However,due to the keyhole caused by too high energy input,the strength first increases and then decreases with the increase of energy density.
Keywords/Search Tags:Selective laser melting, 316L stainless steel, Microstructure, Texture, Mechanical properties
PDF Full Text Request
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