Turning of hardened AISI 4340 steel using coated carbide inserts

The machining of hardened steels employing polycrystalline cubic boron nitride and ceramic tooling has been comprehensively investigated over the last 20 years; however, the development of newer cemented carbide grades has extended the use of this group of Materials to the machining of steels hardened up to 45 HRC (Rockwell C). The current paper is therefore concerned with continuous turning of AISI 4340 steel hardened from 250 to 525 HV using coated carbide tools in order to investigate whether this cutting tool grade is capable of providing a satisfactory performance when machining a steel with increasing levels of hardness. Machining forces, tool life, and wear mechanisms were assessed and the results indicated that the relationship between the hardness of the work material and the machining force is not straightforward. In general, the machining force components increased with the work material hardness, however, the cutting force decreased slightly as the work hardness increased from 250 to 345 HV. Tool wear was lower when machining the 345 HV workpiece compared with cutting the 250 HV steel. Finally, abrasion was the principal wear mechanism observed and catastrophic failure took place when attempting to machine the 525 HV steel.