CRYOGENIC PROPERTIES OF SOME CUTTING-TOOL MATERIALS

Cutting tool materials belong to a group of nonductile materials. Chipping and breaking of the cutting edge and fracturing of the tool are common types of tool failure even under conventional machining conditions. This leads to a concern about whether cutting tool materials are able to maintain their strength and toughness and withstand the low-temperature thermal shock during cryogenic machining. The objective of this investigation was to study the behaviors of these kinds of materials at cryogenic temperatures. The results will also serve as a basis in selecting the suitable cutting tool materials for cryogenic machining and in determining the cryogenic strategy and optimum cutting conditions. Several representative cutting tool materials, such as five grades of commercial carbide-cobalt alloys and M46 high-speed steel, are investigated in terms of microstructural observation, impact testing, transverse rupture strength measurement, and indentation testing. It has been shown that carbide tool materials generally retain their strength and toughness as the temperature decreases to liquid nitrogen temperature. The behaviors of carbide tool materials at cryogenic temperatures can be explained in terms of the temperature effects on the binder phase.