Effect Of Forming Process On Microstructure And Properties Of 316L Stainless Steel Prepared By Selective Laser Melting

The selective laser melting(SLM)forming process is simple,and products with complex internal structures can be directly formed by laser melting metal powder.316 L stainless steel is a metal material widely used in industrial and medical applications.It is an internationally recognized medical implant material.It is also widely used in complex shape components in seawater desalination devices,petroleum pipelines and other fields.In the above practical applications,reliability is a necessary prerequisite,and the integrity,corrosion resistance and mechanical properties of the printed samples are important guarantees for reliability.Due to the characteristics of the selective laser melting technology process principle,the corrosion resistance,tensile properties,impact properties and fatigue properties of the printed parts are significantly different from those of traditional materials.Therefore,it is of practical significance to systematically study the influence of different forming process conditions on the microstructure and properties of 316 L stainless steel formed by laser melting technology in selected areas.In this paper,a four-factor five-level orthogonal experiment is carried out based on the factors of laser power,laser scanning speed,laser hatching space,and printing layer thickness.The results show that the laser scanning speed is the most important factor affecting the relative density of 316 L SLM prints(316L-SLM).The optimization experiment is carried out with the laser scanning speed as a variable.The results show that under the conditions in this paper,the relative density first increases and then decreases to the increase in the scanning speed.The structure and mechanical properties of the prints under different scanning speeds were further studied.In general,in the vertical direction,the crystal grains grow along the direction of increasing layer thickness.The average tensile strength in the vertical direction of the sample of different scanning speeds is about 87% of that of the 316L-R(rolled)sheet,and the elongation is 48%.The impact energy of the specimen is 43% of 316L-R,and the fatigue cycle is 12% of 316 LR.The tensile strength of the sample of the x and y directions in the horizontal section under different speed conditions are higher than that of the 316L-R plate.The impact energy is 47% of 316L-R,and the fatigue cycle is 28% of 316L-R.Its fracture surface presents small honeycomb dimples,which is a typical ductile fracture.Compared with the sample at room temperature,the tensile strength of the sample after the preheating temperature has little change in the tensile strength in all directions.However,in the y and z directions,the elongation of the sample after the preheating temperature is increased by 6.3% compared with the elongation of the sample at room temperature.Compared with the sample under room temperature,the impact energy of the sample after preheating temperature has no obvious change in all directions.Compare with the fatigue cycle of the specimen under the condition of preheating in the x and y directions,the fatigue cycle of the specimen is increased by 62%,and the fatigue cycle of the specimen in the z direction has little change.The corrosion resistance of the 316L-R sample is better than that of the sample of SLM process conditions.The open circuit voltage of the 316L-R sample is-0.474 V,and the open circuit voltage of the SLM sample under different speed conditions is 0.1V?0.4V lower than that of the 316L-R sample.After to heat treatment of 650°C,the open circuit voltage of the SLM sample increased by 0.01V?0.2V,and after heat treatment at 1050°C,the open circuit voltage of the sample increased by 0.05V?0.17 V.According to the polarization curve,the corrosion current density of the 316L-R sample is the smallest,and the corrosion current density of the sample is higher than that of the 316L-R under different speed conditions.After to heat treatment of 650?,the corrosion current density is reduced by 1.2%?5.8% compared with the sample without heat treatment.The corrosion current density of the sample after heat treatment of 1050? is reduced by2.5%?17% compared with the sample after heat treatment of 650?.