Microcosmic Observing and Analysing of the Chips Formation from Precision Hard Cutting GCr15 Bearing Steel

The sawtooth chip from hard cutting can influence on the precision of the form and dimension, the machined surface integrity and the tool life. A study on the microcosmic dynamic fracture mechanism of hardened bearing steel carried out by the author, based on the microcosmic observing and analysing of sections of the chips from PCBN tools cutting GCr15 bearing steel. The experiments and analyses indicate that the adiabatic shear loses stabilization in the primary deformation zones due to thermal softening during cutting machining, and shear ductile fracture limitation of the chip forms. The sawtooth chip formation of GCr15 bearing steel hardened cutting results not from the periodical brittleness fracture but from periodical adiabatic shear fracture; being no clear damnification before the adiabatic shear loses stabilization, thermal softening occurs and be controlled by nucleation, growth and coalescence of microvoids in the whole shear fracture tenacity progress.