Research On Microstructures Evolution And Mechanical Properties Of Components Deposited By Hybrid Double-wire CMT Additive Manufacturing Process

Applying the double-wire CMT process with two wires melting into same pool together,a research on depositing high strength steel components by adjusting the ratio of two wires’feeding rate were implemented,and the investigating wires includes ER50-6carbon steel wire,ER316L stainless steel wire and self-developed HNS high-nitrogen austenitic steel wire.Both‘low-carbon steel wire and stainless steel wire’manufacturing mode and‘stainless steel wire and high nitrogen steel wire’manufacturing mode were designed,to deposit high strength steel components.And the influence of the ratio of two wires on the elemental composition,microstructures and mechanical properties of these components,were investigated in details.The high strength and high toughness alloy steel was successfully manufactured with the suitable proportion of two wires by hybrid double-wire CMT additive manufacturing process,and the cost of this process is lower than before.First,the proportion design and additive process tests of ER316L stainless steel and ER50-6 low-carbon steel hybrid wire were carried out.50-layer straight-walled members in seven kinds of wire proportions were stacked to study the changes in the chemical composition of the members and the effects of phases and properties of Fe-Cr-Ni alloy steel additives.The study found that with the increase of Cr and Ni elements,the martensite and ferrite content in the component gradually decreased,and the austenite content gradually increased.When the proportion of stainless steel wire(R_ER316L)is 80%,there are only austenite and a small amount of ferrite in the component.Discovered by XRD,with the decrease of Cr_eq/Nieq,Fe-Cr-Ni alloy steel members in the additive manufacturing components gradually precipitated second phases such asσphase,Cr₂₃C6 and Cr₇C₃.Under the action of martensite strengthening and second-phase strengthening,the additive manufacturing component has obtained greater strength and hardness.Among them,the component has the highest tensile strength when R_ER316Lis 40%,which can reach 1153.53MPa,and the sample with R_ER316L30%has the highest microhardness,which is 394.44HV.Then,taking the proportion of ER316L stainless steel wire and self-developed HNS high nitrogen austenitic steel wire as the control object,we explored the influence of component phase and performance of the change in the composition of Ni and N elements on the arc additive to produce Fe-Cr-Ni-N alloy steel without changing the Cr_eq.With the increase of the proportion of ER316L stainless steel wire,the austenite content in the components has undergone an"up-down-up"trend,and the ferrite content has continued and dispersed.In addition,as the content of the N element increases,chromium nitride precipitation increases and carbide precipitation decreases.With the increase of Ni_eq,the tensile strength of the seven groups of additive components gradually decreased,and the elongation after breaking showed a"W-shaped"fluctuation,and the elongation after breaking was close to or even higher than 40%.Finally,based on the reinforced structure of soft layer and hard layer as the model,multidimensional hybrid double-wire CMT multi-layer additive experiment was carried out.The hard layer is manufactured by mixing stainless steel with low carbon steel when R_ER316Lis 40%,to make a high-strength and high-hardness deposited layer.The soft layer is manufactured by mixing stainless steel with high nitrogen austenite steel when R_ER316Lis40%,to make a high-strength high-plasticity deposited layer.The ratio of hard layer and soft layer is 3:1.Microstructure observation revealed that the main components at the interface between the hard layer and the soft layer were austenite and ferrite.Performance testing shows that the tensile strength is 679 MPa,which is lower than both the hard layer and the soft layer,which is mainly due to the existence of unfused parts between the channels.