Abstract
The machinability of a specially deoxidized free-cutting steel both in turning and drilling has been studied in comparison with that of ordinary steels and leaded steels, for the purpose of clarifying the relations between the machinability of steels and their nonmetallic inclusions.
The tool life, for turning the specially deoxidized free-cutting steel with carbide or ceramic tools is definitely longer than that of an oridinary or leaded free-cutting steel, apparently because of the effect of the oxide layer formed on the tool face. The composition of this oxide layer is similar to that of the oxide inclusion in the steel, being comprised of SiO2, CaO and Al2O3. As this layer apparently impedes the physical and chemical reactions that may otherwise take place between the tool and the steel chip, and, furthermore, apparently acting as a kind of lubricant, the tool life is exceedingly improved.
With a high-speed steel tool, however, such difference in tool life has hardly been noticeable in respect of the said three types of steels, and, furthermore no oxide layer has been noted to form on the tool face even when turning the specially deoxidized free-cutting steel.
The drill life was found to be remarkably improved and the work resistance was greatly lowered with increase in the sulfur content of the steel. This favorable effect of sulfur content has been more salient in the specially deoxidized free-cutting steel having an high oxygen content than in the case of ordinary steels.
