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.