The electrochemical polishing behaviour of P/M high-speed steel (ASP 23) in perchloric–acetic mixed acids

Abstract

The electropolishing behaviour of P/M high-speed tool steel (ASP 23) has been investigated in HClO 4–CH 3COOH mixed acids at a temperature range from −10 to 30 °C. The surface morphologies and roughness of polished samples were examined with field-emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The results show that the steel can be electrochemically polished in the mixed acids with concentrations of HClO 4 from 20 to 80 vol%. Temper-induced carbides in both MC and M 6C forms can be leveled together with the steel matrix when the sample was polished at lower temperatures (<0 °C) in the mixed acids with higher HClO 4 contents (60–80 vol%), and the roughness (Ra) of the polished surface can be achieved to 30–50 nm. The electropolishing behaviour of the steel is under mass-transfer control and the anion ClO 4 −, and/or its complexes, suggested to the governing species for the acceptor-limited mechanism during anodic dissolution in limiting-current plateau.