Effect Of Solution Treatment On Microstructure And Properties Of 316l Stainless Steel Arc Prints

Compared with traditional manufacturing technology,additive manufacturing can significantly shorten the manufacturing cycle and reduce production costs,and has obvious advantages in the manufacture of some complex structural parts.However,the additive accumulation of additive manufacturing itself determines the need to undergo cyclic heating and rapid cooling,resulting in the production of non-equilibrium materials by additive metal materials,and more or less accompanied by coarse grain,grain oriented growth and the phenomenon of component segregation,and affecting the performance of the metal produced by the additive to varying degrees.As a long-established material modification method,heat treatment can effectively adjust the microstructure,mechanical properties and corrosion resistance of additive manufacturing metals without affecting the additive manufacturing process itself and without changing the additive manufacturing equipment and process.The performance makes the additive manufacturing products more in line with the performance requirements.In this study,316L welding wire produced by Metrode was used,and arc printing and cold metal transition(CMT)forming block materials were used as printing parts.A portion of the print was subjected to a solution treatment at 1050'C for 0.5 hour and 1 hour.OM,SEM and EBSD were used to analyze the microstructure,and the kind,distribution and content of precipitated phase of the printed parts in different states.The tensile,impact and microhardness tests of the printed parts under different conditions were carried out to study the mechanical properties.Electrochemical potentiodynamic reactivation(EPR),potentiodynamic Tafel curve method and electrochemical impedance spectroscopy(EIS)were used to study and analyze the intergranular corrosion and pitting corrosion sensitivity of the printed materials.The main findings are as follows:(1)The solidification mode of the 316L stainless steel print is the ferrite-austenite(FA)solidification mode.There are differences in the middle and bottom structures of the deposited layer of the deposited state.The middle part is the austenite matrix plus dendritic and strip-shaped ? ferrite,and the bottom is austenite matrix plus strip-like and worm-like S ferrite.And the delta ferrite is finer than the middle.(2)After the solution treatment at 1050? for 0.5 hours,the ? ferrite morphology changed into worm-like,island-like,and the content decreased.After the solution treatment at 1050'C for 1 hour,the ? ferrite almost disappeared.(3)The precipitated phases in the microstructure of the deposited 316L stainless steel are?phase and Cr23C6,distributed in the ferrite and austenite phase boundaries and in the ferrite crystal,and all have aggregation phenomenon.After solution treatment at 1050? for 0.5 hours,the ? phase content decreased significantly.Cr23C6 was mainly distributed in the ferrite and austenite phase boundaries and accumulated more,and a small amount of Cr23C6 was distributed in the ? ferrite and austenite crystals,and the content of Cr23C6 further reduced.After the solution treatment at 1050'C for 1 hour,the ? phase disappeared,and the printed microstructure was austenite with a small amount of uniformly distributed Cr23C6.(4)After the solution treatment at 1050? for 1 hour,the tensile strength and yield strength of the printed article decreased,but the elongation increased and the impact toughness was the best.The tensile properties and impact properties in the Z direction in the same treatment state are superior to that in the Y direction.The microhardness of the prints under different treatment conditions did not change obviously,and the average hardness value of the solution treated state decreased slightly.The microhardness values of the different treatment states along the Y direction showed the highest hardness values in the region between the two weld beads,and the microhardness values along the Z direction showed the highest hardness values in the region between the two deposition layers.There was no significant difference in the average microhardness values along the Z and Y directions,indicating that the print tissue was relatively uniform and had no obvious defects.(5)Compared with the as-deposited state,the precipitated phase Cr23C6 and ? phase are dissolved into the austenite matrix by solution treatment,which increases the intergranular corrosion resistance of the print.The solution treated at 1050? for 1 hour is the most resistant to intergranular corrosion,the as-deposited state is the worst.The appearance of pitting pits was clearly observed in the 3.50%(mass fraction)NaC1 solution of the 316L stainless steel prints.After the solution treatment at 1050? for 1 hour,the pitting corrosion resistance was improved,and no pitting pit was observed in the microstructure.