Abstract:

Investigations madeby the authors and collaborators into the microstructural and fracture aspects of adiabatic shear bands(ASBs) of the hardened steels andTi alloys induced by high speed machining(HSM) are briefly reviewed. The principal findings arethefollowing:(a) the microstructure inside the ASBs varies from the band center to the normal chip material, the gradient microstructures are found; (b) the HSM can produce two types of ASBs with increasing in cutting speed, the deformed shear bands formed at lower cutting speed and the transformed shear bands formed athigher cutting speed;(c) the very small equiaxed recrystallized grains are observed in the center of the ASBs, the dynamic recrystallization and phase transformation may occur simultaneously during the formation of the transformed ASBs; (d) The dynamic rotational recrystallization is the origin of the equiaxed grains in the center of the ASBs. A microstructural evolution model in ASBs produced during HSM for the harden steel is proposed; (e) the microstructural pattern of fracture surfaceis characterised by the elongated dimples. A microcosmic adiabatic shear fracture model during HSM of the hardened steel is built up.

Key words: Adiabatic shear bands (ASBs), High speed machining (HSM), Microstructure, Fracture