Hard austenitic stainless steel screw and a method for manufacturing the same

摘要

This invention allows to form a nitrided hard layer on the surface of an austenitic stainless steel screw by forming a nitrided layer thereon and to prevent causing rust on some parts such as a screw head portion which is in contact with the outside air by removing the nitrided hard layer to expose austenitic stainless steel base which has sufficient corrosion resistance. On the contrary, in a thread part and the like of the screw, the nitrided hard layer is left and to thereby improves hardness and the like to strengthen tapping functions and the like of the screw. In the method for manufacturing the austenitic stainless steel screw according to the invention, the austenitic stainless steel screw is held in a fluorine- or fluoride-containing gas atmosphere prior to nitriding to form a fluorided film on its surface and then is nitrided in that state. Accordingly, so formed nitrided hard layer becomes uniform and deep to obtain an austenitic stainless steel screw having excellent surface properties.