Hard turning: Chip formation mechanisms and metallurgical aspects

A 100Cr6 (AISI E52100) steel in the hardness range of 180 to 750HV(10) was machined. Quick stop tests were carried our at various hardness values to o bserve the different chip formation mechanisms. A limit was found between t he shearing and cracking chip formation. Experiments on the selected steel at 750HV(10) were carried our at various cutting speeds and feed rates. The ''saw tooth chips'' obtained were examined geometrically and metallurgical ly on longitudinal midsections. A relationship has been established between the chip geometry and the cutting conditions. A theoretical study of the c hip shape was made. in particular its thickness. The friction stick slip ve locities, and the segment apparition frequency were calculated. Each stage of the chip formation could be observed on each micrograph of Q.S.T. especi ally the crack initiation. A discussion on the apparition of the thin white layers is also proposed. [S1087-1357(00)01502-1].