| Ultra-high-strength dual-phase steel is widely used in various fields due to its excellent performance and good processing.Additive manufacturing technology transforms the computer model into a forming route point,controls the three-dimensional additive system equipment through a series of software,and rapidly forms the work piece cumulatively in a three-dimensional space,so it has more advantages than traditional machining methods for the complex structure.Arc additive manufacturing technology combines welding arc with a processing heat source,to melt wire layer by layer stacking metal and then form components,so it is characterized by high deposition rate,low cost,good feasibility as well as high efficiency.The research on advanced ultra-high-strength steel arc additive manufacturing technology has an important practical significance in meeting the requirements for high efficiency and intelligence and safety of parts manufacturing at the same time.In this paper,the single-layer and singlemulti-layer additive process was investigated by using 1.0mm ER120S-G welding wire of DP980 ultra-high-strength dual-phase steel to carry out additive experiments based on the heat source of cold metal transition welding arc.By focusing on the single multi-layer additive straight wall forming process,microstructures and mechanical properties,orthogonal design experiments were carried out to determine the process parameters when the performance of the additive straight wall was the best.The finite element simulation analysis of the temperature field and stress field in the additive process was carried out.The experimental results indicate that the process parameters have some influence on the formation of the additive sample.For single multi-layer additive samples,the forming size of the additive sample increases with the increase of wire feed speed or interpass temperature,and the forming size of the additive sample decreases with the increase of welding speed.The microstructure of single multi-layer additive straight-wall body sample exists mainly in the form of columnar crystals and equiaxedcrystals,and the microstructureis mainly granular bainite and the grain distribution is uniform.For the additive straight-wall samples,the maximum transverse tensile strength is 976 MPa,the maximum longitudinal tensile strength is 917 MPa,and both of them reach over 90% of DP980 base material tensile strength.The fracture of transverse and longitudinal tensile specimen is plastic fracture and there are a lot of dimples in the fracture.There is little difference between the transverse and longitudinal impact properties of the additive straight-wall samples,and the impact fracture form is the microporous aggregation type fracture.The microhardness of the lower part of the additive straight-wall samples is higher than that of the upper part.The average microhardness value is about 360 HV,which is higher than 320 HV of the DP980 base material.By comparing the finite element simulated temperature field with the experimental measurement results,it is proved that the heat source model established by the DP980 single multi-layer CMT arc additive manufacturing process is correct.After simulation and calculation,the maximum equivalent stress value of the additive straight-wall samples is generated in the middle part of the first layer,and the maximum value is 915 MPa.The maximum residual stress is 184.8MPa.The maximum deformation position of the additive straight-wall samples is at both ends of the top of the straight wall,with a total deformation amount of 2.32 mm.Under the experimental conditions,with the optimal transverse tensile strength as the standard,the optimum process parameters of CMT arc additive manufacturing for DP980 dual-phase steel are as follows: wire feed speed is 3.0m/min,welding speed is550mm/min,interpass temperature is 140℃.The obtained single multi-layer additive straight-wall body has good forming quality and excellent mechanical properties. |
