Effect Of Corrosion On Electrochemical Cold Drawing Of Q235 Steel Bar

In order to overcome the shortcomings of low plasticity of hardly deformable metal material like tubes,bars and wires during drawing,a new processing technology called electrochemical cold drawing?ECD?was proposed by our research group and Gutman et al.,which was based on chemomechanical effect.Previous studies revealed that ECD could significantly reduce drawing force when compared with the traditional drawing in air?DIA?technique.In addition,it was found that pre-electrochemical corrosion could plasticize the surface of the bar,but the detailed plasticization mechanism has not been thoroughly explored.In this paper,the common Q235 steel was used as the model material,and on the basis of previous research,the plasticization mechanism of pre-electrochemical corrosion and the influence of pre-electrochemical corrosion time on ECD were further investigated,which aimed at laying foundation for the ECD study of hardly deformable metal materials in future.The results indicated that:When ECD was applied to Q235 steel bar,the H₂SO₄ solution with high corrosion rate could promote the emigration of dislocation in the bar surface to form dislocation flux,thereby reducing the dislocation density of the surface layer of the bar and weakening the effect of work hardening.Vacancy defects with different concentrations was generated in the surface layer when the Q235 steel bar was pre-electrochemically corrosion in the different electrolytes for 30 min,leading to the formation of plasticized surface layer with thickness of 80?m.As the Q235 steel bar was pre-electrochemically corroded in different electrolytes for 30 min and then subjected to DIA,the drawing force of the corroded part decreased compared with the uncorroded part,and the reduction rate in the 0.35 M H₂SO₄ was the largest by reaching 13%,resulting mainly from the relaxation of dislocations due to vacancy defects that were formed during pre-electrochemical corrosion.After being pre-electrochemical corroded for different times,a layer of l oose corrosion layer adhered to the surface of the Q235 steel bar,and the surface of bar exhibited different degrees of plasticization.The surface plasticization of the bar was the highest at 20 min,due mainly to the highest concentration of vacancy clu sters generated in the bar at this time.The reduction rate of the drawing force reached maximum value of 22%at 10 min when compared with DIA,which was a combined result of the chemomechanical effect,the corrosion layer and the plasticized layer.The drawing force of pre-electrochemical corrosion reduced more greatly than pre-chemical corrosion,and its reaction rate as well as surface plasticization degree was greater and higher than the pre-chemical corrosion.By comparing the hardness,the thickness of the deformed layer and the elongation after drawing,it was further concluded that the pre-electrochemical corrosion had a greater degree of plasticization on the surface layer of the bar.Therefore,the role of current during ECD was quite critical.When ECD was performed after 60 min of pre-electrochemical corrosion,the frictional force generated by the corrosion layer was 1.08 kN.Most of the corrosion layer on the surface of the bar was squeezed by the compression cone of the die and accumulated in the die,a small amount of corrosion products was embedded into the surface of the bar,and the embedded corrosion products exerted relatively small effect on the surface hardness of the bar.After being pre-electrochemical corroded for 60 min,the plasticized layer generated on the surface of the bar during ECD can reduce the drawing force by 0.78 kN.