Study On The Process And Properties Of Phenolic Bonded 316L Stainless Steel By Binder Jet 3D Printing

Compared with traditional additive manufacturing technology,Binder jet 3D printing(BJ3DP)has the advantages of low manufacturing cost and a wide range of applicable materials,and has the development potential in rapid and mass production,which has received widespread attention in recent years.Due to the first-mover advantage,some research achievements have been made in related fields in foreign countries.However,the research on BJ3 DP technology in China is still at the initial stage,and the relevant literature reports are few.Using 316 L stainless steel powder as raw material and phenolic solution as binder,this paper analyzes the influence of printing parameters on the density and size of green billet,summarizes the printing parameters of high density and low size deviation samples,and explores the curing and degreasing process.Then,the effects of sintering temperature and sintering time on the sample density,microstructure and mechanical properties were studied.Finally,the complex structure parts with high density were prepared,and the feasibility of reusing powder after recovery was analyzed.The main results are as follows:The thickness of the powder layer has the greatest effect on the blank density,and the effect of the powder speed is the least.The thickness of coating layer has the greatest influence on the sample size accuracy,while the saturation of binder is the least.The optimal process is as follows: the coating thickness is 150 μm(that is,three times the average particle size),the binder saturation is 35%,and the coating speed is 10 cm/s.Due to the process characteristics,there are morphology differences among different surfaces of the blank,in which the defects of the YOZ plane perpendicular to the paving direction are more concentrated,the defects of the XOZ plane perpendicular to the inkjet direction are scattered point defects,the defects of the XOY plane are the least,and the surface is the most smooth and smooth.The compressive strength of the green sample is 4.54 MPa,which is enough to meet the strength requirements in the subsequent treatment.Increasing sintering temperature can significantly improve the density and mechanical properties of the samples.The carbon content of the sample is the lowest when degreasing at600 ℃,and the carbon content is lower than 0.030% after sintering at 1385 ℃,1410 ℃ and1435 ℃,which meets the requirements of 316 L stainless steel.The samples sintered at different temperatures are dominated by austenite structure and produce a new phase of δ-ferrite.The highest relative density of the sample is 88.7% at 0.99Ts(1435 ℃).The mechanical properties are the best.The yield strength is 160 MPa,close to the level of 170 MPa of commercial 316 L stainless steel,the tensile strength is 355 MPa and the elongation is 26.4%.Prolonging the sintering time can improve the density and mechanical properties of the samples.The relative density of the samples exceeds 92% after the sintering time is extended from 2.5 h to 7.5 h at 1435 ℃.Although the average grain size increased from 46.2 μm to 82.4μm,its comprehensive mechanical properties were greatly improved by the improvement of density and pore morphology.The yield strength was 290 MPa,the tensile strength was 558 MPa,and the elongation was 41.0%,All indicators meet the standard of 316 L commercial stainless steel.The volume fraction of δ-ferrite in the samples held for 2.5 h and 7.5 h is about6%,and the distribution is uniform.During sintering,the friction and adhesion between the sample bottom and the alumina ceramic bottom block the shrinkage of the bottom surface,so that the porosity is more than that of other surfaces.The complex parts,such as rotor,impeller and helical gear,with curved surface,cavity,thin wall and mesh,have been manufactured by using the better technological parameters.The relative density of each part is between 91.3% and 92.6%,which is in good agreement with the results of condition experiment.After the used 316 L stainless steel powder is screened by 150-mesh screen to remove powder aggregates,almost all of it can be recycled as BJ3 DP printing material again.