Machinability of metals and machining costs

Abstract

In the present work, a comparative study is reported on tool wear characteristics induced by machining two distinctively different types of materials: Vanadis 10 tool steel containing large amounts of MC and M7C3 carbides, and 316L austenitic stainless steel which is nearly free of hard abrasive phases. Tool life tests were conducted using cemented tungsten carbide tools (WC-Co), both uncoated and TiCN-Al2O3 coated. The subsequent wear characterization included scanning electron microscopy and electron backscatter diffraction (EBSD). Examination of worn WC-Co substrates and coatings revealed significantly different wear characteristics after machining the two workpiece materials. Predominantly abrasion-induced wear was revealed by micro-fragmented tool constituents as well as sub-micron sized grooves and ridges on tool substrates and coatings when machining the tool steel. Moreover, EBSD analysis indicated that the tool substrates exhibited significant superficial strains caused by localized plastic deformation during sliding contact of the tools with the carbides of the tool steel. In contrast, during machining of the stainless steel using uncoated tools, the predominantly dissolution-induced wear resulted in WC-Co substrates with smooth surfaces and absence of significant strain. The worn coatings showed signs of spalling of micro-fragments which indicated the dominant contribution of adhesive wear when machining stainless steel.