Authors: Virginia Garcia Navas, Imanol Ferreres, Jose Anged Maranon, Carmen Garcia-Rosales, Javier Gil Sevillano
Addresses: Fundacion TEKNIKER-IK4, Avda. Otaola, 20, Eibar, Guipuzcoa 20600, Spain. ' IDEKO S. Coop., Arriaga Kalea, 2, Elgoibar 20870, Guipuzcoa, Spain. ' IDEKO S. Coop., Arriaga Kalea, 2, Elgoibar 20870, Guipuzcoa, Spain. ' CEIT and Tecnun, University of Navarra, Manuel de Lardizabal, 15, San Sebastian 20018, Spain. ' CEIT and Tecnun, University of Navarra, Manuel de Lardizabal, 15, San Sebastian 20018, Spain
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.
Keywords: white layers; hard turning; EDM; electro-discharge machining; electrical discharge machining; tool steel; residual stresses; surface integrity; machining; tensile residual stresses; hardness; retained austenite; nanocrystalline structure; plastic deformation.
International Journal of Machining and Machinability of Materials, 2008 Vol.4 No.4, pp.287 - 301
Published online: 08 Mar 2009 *Full-text access for editors Full-text access for subscribers Purchase this article Comment on this article