Research On Process Of High Nitrogen Steel By Vacuum Brazing And Molecular Dynamics Simulation Of The Diffusion Process

High nitrogen steel has many excellent properties such as high strength,good toughness,good process performance and excellent corrosion resistance,and has been widely used.Compared with traditional stainless steel,high nitrogen steel uses nitrogen instead of nickel to austenitize the structure.Nitrogen can stabilize the austenite structure,expand the austenite phase zone,delay the precipitation of carbides,and improve the strength and corrosion resistance of steel.But nitrogen element exists in the form of supersaturated solid solution in high nitrogen steel,in traditional fusion welding,because of the melting near the joint of base metal,the nitrogen element in the austenite is precipitated in the form of nitrogen,affects the mechanical properties and corrosion resistance of the joint.In this paper,high nitrogen steel was bonded by vcauum brazing,explored the second phase precipitation of high nitrogen steel under brazing process,determined the range of brazing temperature,used AgCuNi filler to bond high nitrogen steel and analyzed the typical interface morphology of the joints,and discuss the influence of different technological parameters on the joint interface structure and mechanical properties.Finally,research the element diffusion process of high nitrogen steel brazing by molecular dynamics simulation.Analyzed the second phase precipitation behavior of high nitrogen steel under brazing process.The phase diagram and cooling transition curve of high nitrogen steel are obtained through thermodynamic calculation,got the conclusion that the sensitive temperature range for the second phase precipitates is 700℃-800℃.Avoided the sensitive temperature,heat treatment of high nitrogen steel base metal by brazing process.We found that the heat treatment of brazing process had little influences on high nitrogen steel.At last,the brazing temperature range was determined to be 850℃-1050℃.High nitrogen steel was bonded by vcauum brazing used of AgCuNi filler.We analyzed the typical interface morphology of the joints and found out that brazing process was mainly diffusion between elements.The typical joint structure is mainly the Ag-Cu eutectic structure of the solder layer and the element diffusion area on the base material side.By analyzing the influence of brazing parameters on the structure and mechanical properties of high nitrogen steel joints,it was found that brazing joints with good interface and mechanical properties can be obtained at temperatures of 850℃ and 950℃.When the process parameters are T=950℃ and t=20min,we got the best mechanical property and the shear strength can reach 228.6MPa.Finally,we researched the element diffusion process of high nitrogen steel brazing by molecular dynamics simulation,simulated the diffusion process of Fe-Cu and Fe-Ni binary systems respectively.We found that in the Fe-Cu diffusion process,only atoms diffuse to each other,while some mesophase were found in the Fe-Ni diffusion process.By the calculation of mean square displacement and diffusion coefficient,we can also find that in the binary system,the diffusion coefficient of Fe is higher than Cu and Ni.