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

The electropolishing behaviour of P/M high-speed tool steel (ASP 23) has been investigated in HClO₄-CH₃COOH 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 HClO₄ from 20 to 80 vol%. Temper-induced carbides in both MC and M₆C 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 HClO₄ 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 ClO₄^-, and/or its complexes, suggested to the governing species for the acceptor-limited mechanism during anodic dissolution in limiting-current plateau.