Effect Of Scanning Speed And Heat Treatment On Microstructure And Properties Of 316L Stainless Steel By SLM

Selective laser melting(SLM),due to its repeated thermal cycles and layered manufacturing during the printing process,exhibits a hierarchical microstructure of components that traditional manufacturing processes do not possess.This unique microstructure can provide excellent mechanical properties for SLM-formed 316 L stainless steel(SS).After analyzing and summarizing the literatures,it was found that this structure is more sensitive to forming process parameters,especially the laser scanning speed.Currently,there are still inherent defects in SLM-formed 316 L SS.Researchers usually choose to use heat treatment to eliminate these defects.At the same time,the microstructure will be affected,which leads to changes in the mechanical properties of the part.Therefore,this paper first investigates the effect of different scanning speeds on the microstructure and the relationship between this effect and mechanical performance.Subsequently,the evolution of the microstructure of the sample after heat treatment was analyzed,as well as its impact on hardness,mechanical properties,and corrosion resistance.The main research findings are as follows:(1)The microstructure of all specimens was revealed to be a fully austenitic singlephase structure.The alteration in scanning speed and heat treatment process will not change the phase composition of SLM-formed 316 L SS.As the scanning speed increases,the density shows a trend of first increasing and then decreasing.The as-shaped 316 L SS contains a large number of cellular and columnar substructures,and has <101> texture in the building direction(BD).Holding at 800 ℃ for 2 h and 1100 ℃ for 5 min,grain growth will occur,and new weaker <111> texture will appear in the specimens.(2)Due to the presence of a large number of columnar grains along the BD in SLMformed specimens,stretching perpendicular to the BD can obtain more dislocation and grain boundary strengthening,resulting in higher tensile strength and yield strength of horizontal tensile specimens compared to vertical tensile specimens.The <101> texture of the asshaped 316 L is consistent with the FCC austenite slip direction,resulting in the elongation in the vertical direction is slightly higher than that in the horizontal direction.Heat treatment at temperatures of 800 ℃ and above will reduce the tensile strength and yield strength of SLM-formed 316 L,and improve the elongation.(3)The vickers hardness and relative density of the as-shaped 316 L are closely related.The trend of hardness and relative density changing with scanning speed is consistent.As the heat treatment temperature increases,the hardness of the horizontal and vertical surfaces of specimens gradually decreases.After holding at 1100 ℃ for 5 min,the hardness of the two surfaces of specimens decreased significantly,by 28.6% and 31.7%,respectively.Increasing the holding time at this temperature has little effect on hardness.Heat treatment with different processes will deteriorate the corrosion resistance of SLM-formed 316 L SS to varying degrees.Holding at 1100 ℃ will occur recrystallization,which can slightly improve the corrosion resistance of the specimens,but still has poorer corrosion resistance than the as-shaped 316 L SS.