Machinability Improvement and Its Mechanism in SUS304 Austenitic Stainless Steel by h-BN Addition

In order to improve the machinability of Type 304 austenitic stainless steels, 0.016 mass % boron and 0.2 mass % nitrogen were added, and hexagonal boron nitride (h-BN) particles (1 similar to 5 mu m diameter) were precipitated. During turning with cemented carbide insert, cutting force and tool wear were reduced by h-BN precipitation, especially at higher cutting speed of more than 40 m/min. The reduction of cutting force seems to be due to the internal lubrication effect of h-BN in chip shear region and deformation flow layer, along with the lubrication between chip and carbide tool. Better disposability of chip and suppression of tool wear were also achieved by h-BN precipitation. Good machinability of h-BN precipitated Type 304 steel was also found in drilling and sawing with high-speed steel tools.