Research On Microstructure And Mechanical Properties Of High Strength Steel By Arc Additive Manufacturing

Wire Arc Additive Manufacturing(WAAM)has many advantages,like high deposition efficiency,high material utilization ratio,low cost and short period,which makes it suitable for direct preparation of large metal components.And it is beneficial to accumulate the relative data of the forming,micro-structure,and mechanical properties of high-strength steels made by WAAM,which promotes the further application of WAAM.With GHS-90high-strength low-alloy steel welding wire as raw material,this paper makes a detailed study on the changing principles of the forming,micro-structure and mechanical properties of thin-walled parts manufactured by WAAM in various process parameters.And on this basis,this paper also analyses the impact of isothermal heat treatment process on the thin-walled parts’ micro-structure and mechanical properties.In response to the difficulty of real-time temperature data measurement in the high-temperature region during the arc additive manufacturing process,a finite element model of high-strength steel is established so as to deeply analyses the variation law of the number of collapsed layers of high-strength steel forming samples.Besides,the relationship between the parameters of WAAM and the geometric features is modeled by utilizing machine learning algorithm.Through studying the principles of the forming,micro-structure and mechanical properties of thin-walled parts manufactured by WAAM in various process parameters,the research reveals that the samples with an inter-layer temperature of 150 °C have a relatively good usability.And the composition of the deposited layers is made up of ferrite,bainite and M-A group elements.And the difference between the bottom and the top of the sample results in a difference in micro-hardness,with the bottom region being slightly harder than the top region(～16 HV).In addition,when the tensile strength of the sample ranges from886.5 MPa to 1065.5 MPa and the elongation ranges from 6.8% to 16.2%,the tensile strength and elongation in the transverse direction are higher than those in the longitudinal direction.And before fracturing,obvious delamination appears in the longitudinal direction and fractures occur in the fusion region,while no delamination appears in the transverse direction.Explored the effects of different isothermal heat treatments on the forming quality,microstructure,and mechanical properties of high-strength steel thin-walled parts manufactured with arc additive.The results indicate that after the heat treatment at the temperature of 200,the size,orientation and distribution of grains of the sample are similar in diverse regions.And its micro-structure is mainly bainite.The average micro-hardness increases,with the bottom reaching(～38.0 HV),the middle(25.1 HV).Besides,the difference between the maximum transverse and longitudinal elongation of each region decreases,with a maximum decrease from 34% to within 14% and a minimum of 7%.Delamination of the sample in the longitudinal direction is not obvious,and migration of the fracture region occurs from the fusion zone to the non-fusion zone.The temperature field of the collapsed layer in arc additive manufacturing of highstrength steel was studied using finite element method.The results indicate that the deposited layers with long deposition length have a wider heat transfer range and longer cooling time at the end points of the former layer,which means that the number of collapsed layers of the formed sample increases with the deposition length becoming longer.And the stochastic forest model established on this basis can accurately predict the number of collapsed layers.