Basic Research On Preparation Of Spherical Ultrafine Metal Powder Using Stainless Steel Dust

As Stainless steel dust is the solid waste collected by the dust removal system during the stainless steel smelting process,accounting for about 3%of the stainless steel furnace capacity.It is roughly estimated that the annual output of stainless steel dust in my country is about 900,000 tons.Stainless steel dust contains a large amount of valuable metals such as Fe,Cr,Ni,Zn and trace amounts of harmful elements such as Pb,Cd and is clearly classified as hazardous solid waste.Due to the high cost of reduction and recovery and large investment,the ratio of reduction and recovery of stainless steel dust at this stage is very low.To this end,this article proposes a new idea of using stainless steel dust to prepare spherical ultra-fine metal powder,aiming to improve the economic benefits of stainless steel dust reduction products to promote the reduction and recovery of stainless steel dust,and also provide low cost for metal 3D printing and other powder metallurgy industries.Spherical ultrafine metal powder consumables.In this paper,stainless steel dust from a domestic steel plant is used as the research object.A various modern analysis and detection methods are used to analyze its composition,morphology,and equivalent properties;the FactSage7.2 thermodynamic software is used to calculate the thermodynamics of carbon thermal reduction of stainless steel dust;and the MoSi2 tube type is used.The resistance furnace studied the effects of reduction processes such as powder particle size,carbon ratio,reduction time,etc.on the morphology and size of the metal particles of the reduction products of stainless steel dust;in view of the irregular morphology of some metal particles,the stainless steel dust was modified and then reduced and screened find the optimal modifier and its added amount.On this basis,the reduction process parameters were further optimized.Get the following results:(1)The content of easily reducible metal oxides Fe2O3,FeO,Cr2O3,NiO,MnO and ZnO in stainless steel dust are 29.17%,20.43%,18.89%,2.92%,2.85%and 0.38%respectively;it is not easy to reduce metal oxide CaO,the contents of SiO2,MgO and Al2O3 are 16.43%,4.54%,3.14%and 1.24%respectively.The quaternary alkalinity of stainless steel dust is as high as 3.39.Stainless steel dust is roughly composed of five phases.Fe and Cr elements mainly form complex oxides with Ca and Si elements.(2)FactSage thermodynamic simulation results show that the order of appearance of carbothermic reduction products of stainless steel dust is FeCr2O4/FeNi204→M2O3→M7C3/M3C→Fe-Cr-Ni-C.(3)The carbothermic reduction product contains spherical metal particles and irregular metal particles,and the two metal particles with different morphologies are distributed regionally.The irregular metal particles contain a large amount of high melting point primary M7C3 carbides,which makes their morphology irregular.The content of MgO in the residue around the irregular metal particles is 4.54%higher than that of the spherical metal particles,resulting in poor sinterability and inclusion of a large amount of free carbon,which ultimately leads to the formation of irregular metal particles.(4)The longer the milling time is,the morphology of the metal particles will not change much,but the size will be smaller.Too high and too low carbon ratio is not conducive to obtain spherical and fine metal particles.The longer the reduction time,the closer to the spherical shape of the metal particles,but the larger the size.(5)SiO2,Al2O3 and MgO modifiers all significantly refine the size of the metal particles,and the refinement effect increases with the increase of the added amount.SiO2 significantly promotes the spheroidization of metal particles,and the addition of 5%SiO2 can eliminate the irregular metal particles in the flakes;Al2O3 promotes the spheroidization of metal particles,but a small amount of Al2O3 has little effect on the morphology of metal particles;MgO deteriorates the shape of metal particles appearance.(6)On the basis of 20%SiO2 modification,The reasonable process parameters are:the carbon ratio is 0.95,the reduction time is 30min,and the reduction temperature is 1350℃.The metal particles obtained by reduction have smooth surface,high sphericity,uniform size,mainly concentrated in 10～30 μm.(7)When adding 20%SiO2 modifier,the stainless steel dust will be severely dusted after reduction,and the residue will be granular and very dense.The Ca,Si,and Al elements in the residue are uniformly distributed,and the Mg element is slightly enriched.Fe,Cr,Ni,Mn and Si in the metal particles are uniformly distributed without significant enrichment.