Transfer layer and friction in cold metal strip rolling processes

Mechanically mixed layers (MMLs) and transfer layers (TLs) are present in the metal forming industry, in rolling processes among others, just as in other fields of Materials and Mechanical science and engineering. Due to the asymmetry of mechanical properties between workpieces and tools, however, TLs are much more frequent - indeed, almost systematic - and the present paper focuses on them. A review is given of experiments performed both on an experimental rolling mill and on a tribological simulation test, the plane strain compression test (PSCT). Various metals and alloys have been investigated under a range of deformation conditions. As in other systems, the origin is abrasive wear followed by adhesion, or adhesive wear. Constant exchanges between the tool surface, the workpiece and the re-circulating lubricant lead to a steady state TL, the characteristics of which (density and size of transferred particles, hardness and roughness of the TL) depend on the tool-workpiece contact conditions. Tribological consequences, in terms of friction and formed piece surface aspect, vary with the TL properties. (C) 2000 Published by Elsevier Science S.A.