Effects of Previous Electrochemical and Chemical Corrosions on Surface Layer Softening During Electrochemical Cold Drawing of Q235 Bar

Abstract

Influences of previous electrochemical corrosion and chemical corrosion in H2SO4 aqueous solution on surface layer softening during electrochemical cold drawing (ECD) of Q235 steel bar were investigated. Results indicate that these two corrosions all further soften the steel during the subsequent ECD and make the ECD to easier conduct, and the effect from the former corrosion is larger than that from the latter one. Two modes of corrosion can slightly soften or plasticize the bar surface layer due to the increased vacancy clusters, but the contribution of this softening or plasticizing itself to the further softening during ECD is very limited, and the further softening should be mainly attributed to the relaxation of dislocations through absorbing the vacancy clusters and the resulted weakening of work hardening. The current applied during the electrochemical corrosion can promote more vacancy clusters to form in a deeper region beneath the bar surface, and thus the relaxing degree for the dislocations and the influence region are larger than those from the chemical corrosion respectively, resulting in the greater softening.