Machinability of Normalized and Stress-Relieved C45 Steel in Dry Internal Turning

This experimental study provides new insights into the dry internal turning behaviour of seamless cold-drawn DIN C45 steel tubes subjected to different heat treatment conditions (normalized and stress-relieved). Unlike conventional studies that focus solely on parameter optimization, this work emphasizes the interaction between cutting parameters and heat treatment on surface integrity and chip morphology. A factorial experimental design was applied to evaluate the combined effects of cutting speed and feed rate on surface roughness parameters arithmetic mean deviation (Ra), total profile height (Rt), and maximum profile height (Rz) while maintaining a constant cutting depth. The results highlight that feed rate and its interaction with cutting speed significantly affect surface roughness (p < 0.05), with normalized steel showing superior chip fragmentation and surface finish compared to the stress-relieved condition. The findings contribute to a better understanding of dry machining behaviour in medium-carbon steels, offering experimentally validated guidelines for selecting cutting parameters that improve surface quality and process efficiency while minimizing empirical testing in industrial applications.