Anodic Film Studies on Steel in Nitrate-Based Electrolytes for Electrochemical Machining

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Abstract
Steady‐state polarization measurements along with constant‐current film stripping determinations were carried out on steel wires in solutions of , , and mixtures of and from which it was found that ion can efficiently remove the film formed by nitrate by a potential‐dependent mechanism. In a closed system employing an ECM test rig, mass balance studies showed that the film formed by ion is electronically conducting since most of the current is consumed in O2 evolution instead of metal removal. With additions of ion to the nitrate, the current efficiency for metal removal is increased to 100%. The character of the surface finish in the mixed electrolytes is highly dependent on the flow rate of the solution which was confirmed by the machining of fully hardened type 5160H steel bushings in a through‐hole ECM machine. To account for these results, an ion exchange model for metal removal in the transpassive region is suggested.

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