Formation of an adherent layer on a cutting tool studied by micro-machining and finite element analysis

In order to clarify further the formation of an adherent layer on a cutting tool when machining a calcium deoxidized low sulphur content austenitic free machining stainless steel, the deformation and crack propagation around inclusions were monitored dynamically using a micro-cutting device in a scanning electron microscope. The temperature distribution field within a cutting tool under conditions of adherent layer formation was determined using the finite element method. It was observed that in the chip secondary shear zone, cracks around inclusions tended to propagate to the edge of the chip which allowed the inclusions to extrude onto the cutting tool surface. These extended inclusions formed an adhered layer on the cutting tool surface which was analysed using energy-dispersive analysis of X-rays. It was found that the temperature gradient in the cutting tool from the tool face at a position 0.25 to 0.5 mm from the major cutting edge is much smaller in the presence of an adhered layer than without an adhered layer. A stable adhered layer formed on the tool was associated with a constant tool face temperature in the region of 850 °C. The results of the present investigation support the mechanism of adherent layer formation proposed previously.