Effects Of Electroslag Remelting On Microstructure And Corrosion Properties Of Austenite-based Low Density Steel

Due to its high Mn,high Al and high C characteristics,austenite-based low-density steel is prone to problems such as coarse non-metallic inclusions,developed columnar crystals and composition segregation in vacuum induction melting,which will affect the forging material and the alloy.The mechanical properties,electrochemical corrosion properties and high-temperature oxidation corrosion properties of hot-rolled materials are adversely affected.Based on the above problems,this paper takes vacuum induction melting austenite-based low-density steel Fe-20Mn-10Al-1.5C(Mn20Al10)as the research object,and uses electroslag remelting to remelt the induction melting billet.The cast slabs before and after remelting were forged to obtain induction melting forged plates and electroslag remelting forged plates,respectively.The effects of electroslag remelting on the microstructure,mechanical properties,non-metallic inclusion,electrochemical corrosion and high temperature oxidation corrosion of Mn20Al10 were investigated by OM,SEM,EDS,ASPEX,EBSD,FactSage,electrochemical testing system and thermogrigmetric testing system.The main research conclusions are as follows:(1)The induction melting forged plate is composed of austenite and a small amount ofκ-type carbides,and the average grain size of austenite is about 97.7 μm.The tensile strength is about 1194 MPa,the elongation after fracture is about 11.5%,the hardness is about 423 HV,and the geometrical dislocation density is about 8.9B×1013 m-2.The microstructure did not change after electroslag remelting,but the average austenite grain size decreased to about 40.3 μm.The tensile strength,elongation after fracture,hardness and geometrically necessary dislocation density are increased to about 1413 MPa,14.1%,478 HV and 1.8B×1014 m-2,respectively.Electroslag remelting refines the grains of the Mn20Al10 forging plate and improves the mechanical properties.(2)The non-metallic inclusions in the induction melting forged plate are mainly compound inclusions rich in O and S,among which silicate inclusions are the highest,accounting for about 19.5%,followed by MnS inclusions,accounting for about 14.4%%.The size of non-metallic inclusions is mainly concentrated in the range of 0～2 μm,accounting for about 80%,and the distribution of inclusions is very uneven.One end has a sharp angle and aggregation phenomenon occurs in the matrix,especially the MnS type inclusions are concentrated.After electroslag remelting,the types of non-metallic inclusions did not change,but the proportion of silicate inclusions decreased to about 8.1%,and the proportion of MnS inclusions decreased to about 10%.The size is mainly concentrated in the range of 0～2 μm,accounting for about 78%.At the same time,the aspect ratio of inclusions is mostly concentrated in the range of 0 to 2,accounting for about 70.8%,and their shapes are mostly spherical or ellipsoid,and their distribution in the matrix is relatively uniform.Electroslag remelting reduces the size of non-metallic inclusions and improves their morphology and distribution.(3)The electrochemical test results of induction melting forging plate and electroslag remelting forging plate in NaCl environment at different pH(5,7,9)show that the electrochemical corrosion products on the surface of the two forging plates are β-FeOOH,γ-Fe2O3.The two forged plates showed poor corrosion resistance in a neutral chloride ion environment,and the maximum corrosion current densities before and after electroslag remelting were about 9.9× 10-6 A·cm-2 and 7.8× 10-6 A·cm-2.The two forged plates show good corrosion resistance in the acidic chloride ion environment,and the polarization resistances before and after electroslag remelting are about 3223 Ω·cm2 and 4559 Ω·cm2,respectively.The electroslag remelting improves the polarization resistance and decreases the corrosion current density of the experimental steel,and the electrochemical corrosion performance of the experimental steel is improved compared with that of vacuum induction melting.(4)In the range of oxygen content of 2%～7%,holding temperature of 1050～1150℃,holding time of 75～95 min and heating rate of 5～8℃/min,the iron oxide scale on the surface of induction melting forging plate from inside to outside was They are Al2O3,Fe3O4,Fe2O3,MnO,Mn2O3,Mn3O4,etc.The oxidation weight gain curve conforms to the parabolic law,and a ferrite region with a thickness of about 358μm appears on the substrate side near the scale.Electroslag remelting did not change the phase composition and distribution characteristics of iron oxide scale,but reduced the oxidation weight gain and increased the thickness of the ferrite region near the matrix side of scale to about 416μm.