Effect of Tool Materials on Surface Machined Roughness and Cutting Force of Low-carbon Resulfurized Free-machining Steels

Abstract

This study examined the effects of ceramic tool materials on the surface roughness and cutting force when low-carbon resulfurized free-machining steels were plunge-machined. The Tool materials used for the study were 9 kinds in total; 7 kinds ceramics-TiN, TiC, HfO₂, ZrN, Al₂O₃, ZrO₂ and La₂O₃-and a high-speed steel (Fe₃C) and a cemented carbide (WC+Co).
(1) Surface roughness and cutting force are the smallest in the ZrO₂ tool, increasing in the order of TiN, ZrN, Al₂O₃, TiC, HfO₂, WC+Co, La₂O₃ and Fe₃C tools.
(2) ZrO₂, TiN, ZrN and Al₂O₃ tend to adhere selectively to manganese sulfide inclusions in steels, resulting in the formation of MnS films over the rake face of tools. On the other hand, HfO₂, WC+Co, Fe₃C and La₂O₃ tend to adhere selectively to the ferrite phase, forming a kind of built-up edge, whereas TiC hardly to manganese sulfide inclusions and ferrite phase.
(3) Surface roughness and cutting force decrease in proportion to the area percentage of MnS films formed over the rake face of tools, because the MnS films play a role as a lubricant.
(4) Adhesion of manganese sulfide inclusions to tools may not only stem from physical properties such as surface roughness of the tools but also from chemical bonding.