Electrolytic polishing of Stainless Steels

Abstract

A Study has been made of the electro polishing characteristics of sulphuric acid- glycerine-water baths of different compositions for the polishing of (i) Nickel-free Cr-Mn-N, (ii) 18:8, Cr:Ni, and (iii) Ferritic (17% Cr) stainless steels. It has been found that for getting a polish on these steels, at room or higher temperature, the minimum concentrate of sulphuric acid in the bath , should be 30% by volume. At room temperature, acid concentration was inversely related to current density, whereas at higher temperatures, the reserve was the case. Nickel –free Cr-Mn-N stainless steels could be polished at lower current densities than those required for the 18:8 Cr:Ni steels, and the Ferritic stainless steels did not give a comparable bright polish even at very high current densities (of the order of 200 A/dm2). The surface could be improved by treatment first at low current densities, followed by that at the optimum limit. The rate of dissolution of metal in terms of thickness decreased with time.