No abstract

Electro discharge machining (EDM) technique is widely used in the die and mold industries for its distinct advantages in machining hard metals. Nevertheless, the properties of EDM treated steel, especially its corrosion resistance, have not been well understood or clearly identified. In this paper, electrochemical corrosion behavior of EDM treated AISI H13 steel in NaOH solution was investigated, with the diamond polished being reference specimen. The corrosion resistance of the specimens was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The morphology and microstructure of the machined surface layer were also observed. Electrochemical experimental results revealed that EDM treated specimen has a weaker resistance to corrosion compared with diamond polished one. This weakening is considered to be correlated to differences in surface morphology and subsurface microstructure.

In the field of hard cutting, researches on white layer have become more extensive and in-depth in recent years, because white layer has an important influence on the performances and life of components. Nevertheless, properties of white layer, especially its corrosion properties, have not been well understood or clearly defined. In this study, specimens with different subsurface microstructures (no obvious change, dark layer, and white layer) were produced in the process of tool wear to analyze their electrochemical properties using electrochemical methods. It was found that electrochemical properties were distinct between specimens with and without white layer. A specimen with white layer had obviously lower electrochemical impedance and more anodic steady-state open-circuit potential than that without white layer in 3.5 wt.% NaCl solution. That is to say, specimens with white layer were prone to corrosion in this solution. The results also manifest that electrochemical method can be a reliable, convenient, and nearly nondestructive method to detect white layer.