Tetsuo Shiraga

Improved machinability of nitriding steel (SACM 645)

Abstract Nitriding steel (SACM 645) is a base material which has a high resistivity of wear and high fatigue strength. However the machinability is very low, because the hardness of this steel is relatively high. To improve the machinability of SACM 645, molybdenum and vanadium are added during making this steel. Two kinds of improved machinability steel (Mo 1.3, 2.1%, V 0.48%) and standard steel are made and cutting mechanism is investigated. In chip formation, easy treatment chips are produced in cutting of two kinds of improved steels. But in cutting of standard steel, that length of chip is a little bit long continued type and not easy treatment. In cutting temperature, average temperature of standard steel is about 200C° lower than that of two improved steels. This is an opposite result of tool life experiment. In tool life, improved steels have a long tool life as compared with standard steel in conventional cutting velocity (150–200 m/min). However in high cutting velocity (more than 260 m/min), tool life of three kind of steel is almost the same. The addition of alloying element (Molybdenum and Vanadium) and the resulting different microstructures are responsible for AMV1 and AMV2 having a higher degree of machinability than standard SACM645 nitriding steel.