Effect of surface layer softening from previous electrochemical corrosion on electrochemical cold drawing of Q235 steel bar

The effects of H₂SO₄ concentration and current in electrochemical corrosion on surface layer softening or plasticizing of Q235 steel bar and their effects on subsequent electrochemical cold drawing (ECD) were investigated. The results indicate that the electrochemical corrosion can soften or plasticize the surface layer of Q235 steel bar and then make the subsequent ECD be conducted more easily. The softening degree and thickness of the surface layer are continuously enhanced with increasing corrosion rate, i.e., increasing H₂SO₄ concentration or current, due to the generation of more vacancy clusters in deeper regions of surface layer. These vacancy clusters then relax dislocations through being absorbed during ECD, and the formation and movement of additional dislocation flux are thereby enhanced, resulting in the further obvious decrease in the drawing force. It is also due to the enhanced formation and movement of additional dislocation flux that the dislocation density and thus the hardness of the surface layer are decreased, as well as that the texture structure is weakened. These behaviors are enhanced as the corrosion rate increases.