Research On The Microstructure And Mechanical Property Of 304 Stainless Steel Produced By CMT Wire Arc Additive Manufacturing

304 Austenitic stainless steel is widely used in the fields of petrochemical,marine applications and daily life due to its excellent low temperature mechanical property,machining performance and corrosion resistance in aggressive environments.Comparing with traditional manufacturing technology,there is more feasible for complex cavity structure in the additive manufacturing processing.Wire-Arc Additive Manufacturing(WAAM)is an important direction in metal material's 3D printing field.WAAM can manufacture 3-dimensional model by the way of deposition by arc melting wire.The advantages of WAAM comparing with Laser Additive Manufacture are better economy,higher formation efficiency.Based on Austenitic stainless steel additive manufacturing technology using cold metal transfer(CMT),respectively,by using arc as heat source,the research on the forming process and the microstructure and mechanical property were carried out on straight wall structures in the paper.In terms of the influence of wire feeding angle on the macro morphology of single layer during the process of CMT,the forming morphology of single layer under different feeding angle was firstly studied,then selecting the optimal parameters manufactures wall straight parts.And the influence of process parameters on the width uniformity of the forming wall was studied.The microstructures along the height direction are austenite columnar crystals,which are divided into three regions.At the bottom zone,the substrate of austenite contains a small amount of columnar residual ferrite.The central stable forming region contains less ferrite,presenting columnar and secondary dendrites.Because of the change of cooling conditions,the top of straight wall appears the equiaxial crystal structure.The microstructure along the welding direction in the straight wall is equiaxial crystal.With the change of process parameters,the microstructure morphology and dendrite spacing will change,which is actually by different heat input.The Hammar and Svensson Austenitic stainless steel solidification model is used to predict the room temperature microstructures.The component undercooling theory was used to analyze the mechanism of dendritic growth.The tensile strength of the straight wall showed a slight difference in different directions.The tensile strength along the height was between 530-550 MPa,tensile strength reached 550-580 MPa along the welding direction,which were equivalent to annealing condition.Meanwhile,the overall elongation rate of the additive manufacturing samples reached 50 %,which reached 83 % of the annealing condition.The HV hardness along the height of the samples was between 170 to 190 HV.