Study On Manufacturing Process And Nitrogen Increasing Of TIG Arc Additive Composed Of High Nitrogen Steel Wire And Nitride Powder

Aiming at the nitrogen loss of high nitrogen steel wire in the process of arc additive,based on the method of wire and powder composite additive,the nitride powder was synchronously fed into the arc additive molten pool of high nitrogen steel with TIG arc as the heat source.The process method of wire and powder composite additive and the effects of wire and powder composite additive on nitrogen addition,forming,microstructure and properties of high nitrogen steel were studied.The research on TIG arc additive process and forming characteristics of high nitrogen steel shows that the effects on weld bead width from large to small are current,welding speed and wire feeding,and the effects on weld bead height from large to small are current,wire feeding and welding speed respectively.The three droplet transfer modes of TIG arc additive for high nitrogen steel are uninterrupted contact transition,discontinuous contact transition and free transition respectively.When the uninterrupted contact transition changes to free transition,the droplet transition frequency decreased and the spatter increased.The spatter comes from the droplet precipitated gas explosion at the end of the welding wire and the droplet impacting the molten pool.The feasibility of wire and powder composite additive system is designed and verified.The mechanical mixing pretreatment of nitride powder can effectively improve its fluidity.The three tube powder feeding method can effectively inhibit the arc deflection.The powder convergence point is located at the lower part of the arc area,which is most beneficial to the forming and process stability.The research on the optimization of wire and powder composite additive process and the improvement of forming quality determined the optimal and maximum powder feeding air flow and powder feeding speed of chromium nitride mixed powder and manganese nitride powder on the premise of meeting the requirements of weld bead forming,process stability and low porosity.It was determined that the heat input of wire and powder composite additive was 170 A current,and a well formed straight wall of wire and powder composite additive was obtained.The nitrogen content test results showed that the nitrogen increase value of the two kinds of wire and powder composite samples was lower than the theoretical nitrogen increase value.The nitrogen content of the high nitrogen steel and chromium nitride composite sample was lower than that of the pure sample,and the nitrogen increase was not realized.The nitrogen content of the high nitrogen steel and manganese nitride composite sample was 14.5% higher than that of the pure sample.XRD results showed that the characteristic peaks of austenite and ferrite were detected in the three samples,and there were no other precipitates.The microstructure of the three types of wall samples were mainly matrix austenite and a small amount of ferrite dendrite.The bottom was mainly cellular austenite and the middle was mainly columnar austenite dendrite.Secondary austenite precipitated at the edge of ferrite dendrite in the composite sample of high nitrogen steel and chromium nitride,and white manganese oxide particles were produced in the composite sample of high nitrogen steel and manganese nitride.In terms of properties,the hardness of the two kinds of wire and powder composite samples increased by about 20-30 HV compared with the pure samples,and the hardness of wire and powder composite samples fluctuated greatly at different positions.The tensile results showed that the yield strength of pure samples is 625.8 Mpa,the tensile strength is 811.3 Mpa,and the elongation after fracture is 33.3%.The yield strength of high nitrogen steel and chromium nitride composite samples increased by 7.3%,the tensile strength decreased by 5.6%,and the elongation after fracture decreased by 80.8%.The yield strength of high nitrogen steel and manganese nitride composite samples increased by 18.8%,the tensile strength increased by 22.0%,and the elongation after fracture increased by 12.6%.The impact results showed that the impact energy of pure sample is 17.52 J,that of high nitrogen steel and chromium nitride composite sample is 5.94 J,and that of high nitrogen steel and manganese nitride composite sample is 21.26 J.The SEM photos of tensile and impact fracture showed that the pure samples and the composite samples of high nitrogen steel and manganese nitride were ductile fracture characteristics,and the fracture surface was full of dimples.The composite sample of high nitrogen steel and chromium nitride was characterized by brittle cleavage fracture,the cross section was full of crystalline facets,and there were micropores.Chromium nitride mixed powder weakened the properties of the sample,and manganese nitride powder strengthened the sample to a certain extent.