Sustainable machining of ARMCO pure iron

ARMCO® pure iron is increasingly used in the manufacturing of electrical and magnetic components due to its excellent magnetic properties and high thermal and electrical conductivity. Despite its low mechanical strength and the extreme ductility characteristic of its 100% ferritic microstructure, ARMCO® is considered a difficult-to-cut metal. Its high plasticity promotes indeed the formation of severe built-up edge and continuous chips, which can entangle and damage the machined surface. To overcome the aforementioned drawbacks, the paper introduces an environmentally friendly cooling method for machining ARMCO®, utilizing liquid nitrogen to significantly reduce the material’s plasticity. The study analyzes and compares cutting forces, chip morphology, surface roughness, surface defects, severely plastically deformed layer, and crystallographic orientations of samples machined under dry, flood, and cryogenic cooling conditions at different cutting speeds. Findings indicate that cryogenic machining reduces ARMCO® plasticity, resulting in lower cutting forces, smaller chip sizes, cleaner and less defective surfaces, lower nano-hardness beneath the machined surface, and reduced thickness of the severely plastically deformed layer, compared to the other cooling methods. In addition, magnetic characterization tests on machined rings reveal that the hysteresis loop parameters remain consistent across all cooling conditions. Cryogenic machining thus proves to be an effective approach to enhance the machinability of ARMCO® pure iron. It also provides cleaner machined surfaces, offering a competitive advantage by minimizing the need for additional cleaning steps when producing electrical and magnetic components.