Detailed analysis of microstructure of intentionally formed built-up edges for improving wear behaviour in dry metal cutting process of steel

Abstract

Tool wear is a very important factor determining tool life and surface quality of a machined workpiece surface. In the range of small cutting geometries the cutting depth can be in the range of the cutting edge radius, hence, it promotes the development of built-up edges (BUE). A systematic and comprehensive examination of built-up edge formation and associated microstructural features is still lacking. In the present study a targeted examination of microstructural features of the built-up edge was carried out with uncoated WC/Co as cutting tool and SAE 1045 steel as workpiece material. The process parameters were chosen so that the built-up edge formation was provoked.The dimensions of the built-up edge were assessed by light-optical microscopy (LOM) and scanning electron microscopy (SEM). The microstructure of the adhering built-up edge was revealed using new nonconventional metallographic methods. The nanocrystalline grain structure of the built-up edges was analysed by means of focused ion beam (FIB) inspection and preparation as well as transmission electron microscopy (TEM) in combination with energy-filtered TEM (EFTEM). The investigated built-up edges showed a highly deformed microstructure and a possible protecting effect could be concluded with respect to the cutting tool for certain cutting speed regimes. The built-up edge can be considered as a protecting surface layer formed in-situ during the metal cutting process with different microstructural states of ferrite and cementite. The developed microstructures show similar properties as microstructures produced by severe plastic deformation processes.In addition to built-up edge and wear examinations, the resulting surface layer states in the machined workpiece were determined using a stylus instrument for surface roughness measurement and by means of X-ray diffraction for residual stress analysis.