Carburizing method
A process is disclosed for selectively carburizing (tailored carburizing) a steel gear or similar ferrous metal object. The process of the present invention includes two similar but separate methods. The first method includes the steps of: first, masking the roots of the gear with an appropriate masking material, and conducting a first carburizing operation of the gear. Then, the masking material is removed from the gear roots and a second carburizing operation of the gear is conducted. The resulting carburized gear will have a lighter case with a lower carbon content in the root areas of the gear. The second method includes the steps of: masking the root areas of the gear with a coating material which would inhibit carbon diffusion in the root areas but not completely stop it. Then, carburizing the gear. Finally, the inhibiting agent is removed. The resulting carburized gear will have a lighter case with a lower carbon content in the root areas of the gear.
1 . A method for selectively carburizing a ferrous metal article, said method comprising the steps of:
providing said ferrous metal article having at least one first region and at least one second region;
covering said at least one second region of said ferrous metal article with a layer of masking material provided to substantially isolate said at least one second region of said ferrous metal article from a carburizing atmosphere;
carburizing said ferrous metal article in the carburizing atmosphere with said at least one second region thereof covered with said masking material;
removing said layer of said masking material; and
carburizing said ferrous metal article to form a carburized article in the carburizing atmosphere,
wherein at least one of a case depth and a region carbon content of said at least one first region of said ferrous metal article in a final form is higher than the respective case depth and the region carbon content of said at least one second region of said ferrous metal article.
2 . The method according to claim 1 , wherein said at least one second region is disposed at a root area between gear teeth.
3 . The method according to claim 1 , wherein said at least one first region is disposed at adjacent portions of the gear surrounding the root area of the gear teeth.
4 . The method according to claim 1 , wherein said case depth of said at least one second region is approximately 0.4 mm.
5 . The method according to claim 1 , wherein said region carbon content of said at least one second region is approximately 0.60%.
6 . The method according to claim 1 , wherein said case depth of said at least one first region is approximately 1.2 mm.
7 . The method according to claim 1 , wherein said region carbon content of said at least one first region is approximately 0.90%.
8 . A method for selectively carburizing a ferrous metal article, said method comprising the steps of:
providing said ferrous metal article having at least one first region and at least one second region;
covering said at least one second region of said ferrous metal article with a layer of a coating material provided to partially inhibit carbon diffusion in said at least one second region of said ferrous metal article in a carburizing atmosphere;
carburizing said ferrous metal article with said at least one second region thereof covered with said coating material;
selectively removing said coating material;
wherein at least one of a case depth and a region carbon content of said at least one first region of said ferrous metal article in a final form is higher respectively than the case depth and carbon region content of said at least one second region of said ferrous metal article.
9 . The method according to claim 8 , wherein said at least one second region is disposed at a root area between gear teeth.
10 . The method according to claim 8 , wherein said at least one first region is disposed at adjacent portions of the gear surrounding the root area of the gear teeth.
11 . The method according to claim 8 , wherein said case depth of said at least one second region is approximately 0.4 mm.
12 . The method according to claim 8 , wherein said region carbon content of said at least one second region is approximately 0.60%.
13 . The method according to claim 8 , wherein said case depth of said at least one first region is approximately 1.2 mm.
14 . The method according to claim 8 , wherein said region carbon content of said at least one first region is approximately 0.90%.