Mechanism and kinetics of pcbn tool wear during face milling of hardened steel

This article presents the results of a study on the wear behavior of cutting tools equipped with polycrystalline cubic boron nitride (PCBN) inserts in the machining of 4Kh5MFS hardened steel with a high hardness of 62 HRC. A key property of 4Kh5MFS steel is its ability to be hardened uniformly without losing hardness throughout the depth of the workpiece, and to maintain its strength level under high temperatures and mechanical loading. Laboratory experiments were carried out on vertical milling machines – DMU 80 eVo Deckel Maho and HAAS VF-2SSYT-NG – using a Seco Tools face mill with a built-in inclination angle of −6°, fitted with six cutting inserts at negative angles of −20° and −25°. Four types of Seco Tools inserts were employed: Group BH (CBN200, CH3505, DBS900) and Group BL (DCS500). The study focuses on comparing the performance of PCBN tools in BL and BH groups, which differ in composition, microstructure, and resistance to shock and high temperatures. Group BH inserts exhibit higher fracture toughness and strength, making them generally recommended for operations involving considerable dynamic loading. The wear rate of PCBN tools, especially at high cutting speeds, is largely determined by the mechanical, chemical, and adhesive interactions in the cutting zone, driven by tribological reactions between the cutting and workpiece materials. By means of energy-dispersive X-ray (EDX) microscopy, the worn areas of the cutting inserts were scanned to identify the wear mechanism, measure the width of the worn notch, and detect any chemical element adhesion that occurred as a result of interactions between the workpiece and the cutting insert over time. Based on the research findings and subsequent analysis, characteristic wear stages for each PCBN tool group were established, along with recommended cutting conditions that provide the best balance between machining efficiency and tool life. The practical significance of this study lies in the development of guidelines for selecting the appropriate type of PCBN tool (BL or BH) depending on thermal and mechanical loading conditions and the required surface quality.