Effects Of Pre-electrochemical Corrosion Electrolyte Type And Concentration,Current And Drawing Pass On Electrochemical Cold Drawing Of Q235 Steel Bar

At present,a new cold drawing technology named electrochemical cold drawing(ECD)based on chemical mechanical effect(CME)has been developed.Compared with traditional drawing in air(DIA),ECD can obviously reduce drawing force and improve plasticity of the surface layer of bar,which provides a new technical route for the cold drawing of tube,bar and wire of hardly deformable metals.Previous researches have shown that pre-electrochemical corrosion can plasticize or soften the surface layer of bar,which can increase the reduction of the drawing force and make the drawing easier.However,the previous researches mainly focused on the pre-electrochemical corrosion,but did not fully quantitative research the additional dislocation flux generated in the surface layer of the bar during ECD under various process parameters(electrolyte type,electrolyte concentration,current and drawing pass)after preelectrochemical corrosion.In this paper,aiming at these problems existing in the previous researches,the annealed Q235 steel bar was used as the research material,and ECD was deeply studied under the most basic process parameters such as electrolyte type,electrolyte concentration,current and drawing pass,and the theory of additional dislocation flux was indirectly and quantitatively proved.The results indicate that an electrolyte with the highest corrosion rate and uniform corrosion is suitable for ECD.That is to say,the concentration of vacancy cluster defects formed in the surface layer of the bar after pre-electrochemical corrosion in the solution with this characteristic is the highest,resulting in the plasticizing(softening)degree of the surface layer of the bar maximally.This kind of vacancy cluster defects with the highest concentration have the greatest relaxation effect on the dislocations in the surface deformation layer during deformation,which makes the dislocations move most easily,thus forming the additional dislocation flux most easily.Resulting in the dislocations in the surface deformation layer overflow the surface of the bar in the form of additional dislocation flux to the maximum extent.As a result,the dislocation density in the surface deformation layer is the lowest,the work hardening degree of the surface layer is smallest,and the reduction rate of the drawing force during drawing is the largest.It is for this reason that among the selected electrolyte types,the dislocation density of surface deformation layer of the ECD bar after pre-electrochemical corrosion in the sulfuric acid solution with the highest corrosion rate is the lowest,the work hardening degree of the surface layer is the smallest,and the reduction rate of the drawing force during drawing is the largest,reaching 27.3%.In the range of sulfuric acid concentration and current studied,the corrosion rate is consistent with the concentration of vacancy cluster defects in the surface layer of the bar after pre-electrochemical corrosion and the plasticizing(softening)degree of the surface layer of the bar,as well as increases with the increase of sulfuric acid concentration and current.Thus,the reduction rate of the drawing force of the corresponding ECD increases gradually,and the work hardening degree of the surface layer of the bar decreases gradually.Among them,the reduction rate of the drawing force of the ECD after pre-electrochemical corrosion with 0.95 M sulfuric acid solution and 0.42 A current is both the highest,which is 32.3% and 36.4% respectively.It is mainly due to the relaxation of dislocations in the surface deformation layer during deformation caused by the vacancy cluster defects formed in the surface layer of the bar after pre-electrochemical corrosion.Under the given ECD process parameters,as the number of drawing pass increases,the work hardening ceaselessly intensifies,which gradually reduces the degree of relaxation of dislocations in the surface deformation layer.This makes the number of dislocations in the surface deformation layer overflowing the surface of the bar in the form of additional dislocation flux gradually reduce.As a result,the reduction rate of ECD to drawing stress is only 13.3% maximally,and the thickness of softened layer is about 80 ?m maximally.That is to say,the plasticizing(softening)degree of the surface layer of the bar constantly decreases.