Patent ID: 6020025
Filing Date: 2000-02-01
Classification: F16C,Y10S

Abstract:
A method of manufacturing a crank shaft made of austenitic stainless steel comprising masking portions other than a journal portion of the crank shaft, holding the journal portion of the crank shaft in a fluorine- or a fluoride-containing gas atmosphere having a concentration of fluorine source component of 1000 to 5000 ppm, wherein at least one fluorine source component is selected from NF.sub.3, BF.sub.3, CF.sub.4, HF, SF.sub.6, and F.sub.2 and is contained in an inactive gas, under a heated condition at a temperature of 250 to 400.degree. C. to form a fluoride layer on the surface of the journal portion, removing said fluorine- or fluoride-containing gas atmosphere from contact with said journal portion, thereafter further holding the journal portion of the crankshaft with said fluoride layer on the surface of the journal portion in a nitrogen-containing atmosphere containing NH.sub.3 under a heated condition at a temperature of 480 to 700.degree. C. to form a nitride layer having a thickness of 10 to 70 .mu.m and a surface hardness of 1000 to 1350 Hv on the surface of the journal portion, and thereafter removing said masking.