Wear of Coated Hardmetals in Machining Cast Iron

摘要

The wear of CVD-coated hardmetals on clearance and rake face in machining lamellar and globular grey cast iron grades GG20 (EN-GJL-200), GGG40 (EN-GJS-400-15) GGG70 (EN-GJS-800-2) at different cutting speeds was investigated by means of optical and raster electron microscopes and energy-dispersive X-ray analysis (EDX). Tool surfaces and cross-sections were analysed. Furthermore, the cutting forces were measured. Although the wear rate in machining perlitic EN-GJS-800-2 is much higher than for ferritic EN-GJS-400-15 the principal wear mechanisms are similar. In both cases a glassy layer is formed on the tool which separates tool and work piece and, under the conditions of the experiments, tool life is strongly influenced by crater wear. The worn regions of the CVD layers are very smooth like polished by the chip whereas the worn regions of the substrate beneath the layers are very rough as complete WC grains or even agglomerates of WC and Co are removed by the chip.