ELECTROCHEMICAL COLD DRAWING OF HARD ALLOYS

Existing cold drawing technology for not enough ductile alloys meets serious problems (cracking, surface finish deterioration, etc.). For instance, some brittle alloys like FeSi6.5 with excellent soft magnetic performance are hard to be formed into wires.

In this work a new technique, electrochemical cold drawing, was proposed to produce wires from hard carbon steel 1070 and FeSi6.5. Overcoming mentioned problems can be achieved with the use of special electrochemical conditions capable to plasticize thin surface layer. The reason for such plasticization is chemomechanical effect (CME) that consists in increasing ductility of a solid surface due to exposure to chemical or electrochemical reactions, taking place, e.g., during anodic polarization of the surface. The significant hardness decrease of the metal surface as compared to air was obtained using anodic polarization. For example, the relative Vickers hardness of FeSi6.5 in 0.5 M sulfuric acid decreased by about a factor of two with current density i varying from 1 mA/cm² to ≈ 50 mA/cm². The hardness decay ΔH in solution as compared to air is larger (the CME is more pronounced) for the steel with a higher hardness. For example, Vickers hardness for steels 1020, 1070 and FeSi6.5 amounted to 1.32, 1.72 and 4.05 GPa, respectively. For these steels, studied in 0.5 M H₂SO₄ at current density of 2 mA/cm², ΔH values were found as 24%, 30% and 47%, respectively.

It was found that electrochemical cold drawing as compared to existing technology showed significant decrease in the drawing stress fluctuation. Therefore, good surface quality can be expected. The effect of anodic polarization of 1070 and Fe-6.5Si steels during cold drawing on the surface quality and corrosion resistance of wires was investigated.