Selectively hardened self drilling fasteners

摘要

A process for making self-threading screw fasteners wherein only the cutting portions of the tip of the fasteners are hardened. The unhardened portions of the fastener remain ductile and are not subject to hydrogen embrittlement during subsequent plating to improve corrosion resistance. The process preferably comprises applying a radiation curable plastic coating over the drill tip followed by plating of a thin (minimum 0.0005 inch, 0.013 mm) layer of copper. The cured coating is then removed leaving an unplated tip. The screw is then subjected to a hardening process, wherein only the portions of the screw without the copper layer are hardened. The screw may then be plated conventionally with a corrosion resistant metal. The invention is further directed to the product of the process. A second embodiment for making screws suitable for extreme corrosion resistance is also described.