An experimental and analytical analysis on chip morphology, phase transformation, oxidation, and their relationships in finish hard milling

Milling hardened steels has emerged as a key technology in mold and dye manufacturing industry. The effects of cutting parameters on chip morphology, phase transformation and oxidation reaction of the chips during finish milling AISI H13 tool steel (50±1 HRc) with coated inserts were investigated in this paper. The chip morphology and phase transformation were examined using an optical microscope and a scanning electron microscope (SEM). The X-ray photoelectron spectroscopy was used to measure the chemical compositions of oxidation layer on chip surfaces. Shear-induced lamella structures characterized by jagged and rough appearance are the basic features of free surfaces. The microstructural analysis indicated that saw-tooth chips and white layers are produced only under certain combinations of cutting parameters of high cutting speed and feed rate. Based on chip color, chip morphology and X-ray photoelectron spectroscopy (XPS) analysis of the chip oxidation layer, the maximal instantaneous temperature at the tool–chip interface is semi-qualitatively estimated using the analytical method developed. In addition, chip color can be predicted based on the oxidation compositions.