White layers generated in AISI O1 tool steel by hard turning or by EDM
by Virginia Garcia Navas, Imanol Ferreres, Jose Anged Maranon, Carmen Garcia-Rosales, Javier Gil Sevillano
International Journal of Machining and Machinability of Materials (IJMMM), Vol. 4, No. 4, 2008

Abstract: The structure and origin of White Layers (WL) induced by hard turning and by Electro-Discharge Machining (EDM) have been studied and compared. The WL induced by turning is particularly important when the tool is worn. It is associated with tensile residual stresses, increased hardness and larger amount of retained austenite. Transmission Electron Microscope (TEM) reveals that its structure is nanocrystalline and very different from the tempered martensitic structure of the substrate. The very high plastic strains and plastic gradients measured beyond the WL (that grow exponentially as free surface is approached) justify the conclusion that Severe Plastic Deformation (SPD) is at the origin of this nanocrystalline WL associated with hard turning, without recourse to any phase transformation. In contrast, the WL induced by EDM shows typical signs of thermal origin below a thin melted and resolidified layer, signs of austenitising, quenching and auto-tempering are clearly found.

Online publication date: Sun, 08-Mar-2009

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