Alloys or metallic compositions – Ferrous – Chromium containing – but less than 9 percent
Reexamination Certificate
1998-04-29
2001-05-01
Yee, Deborah (Department: 1742)
Alloys or metallic compositions
Ferrous
Chromium containing, but less than 9 percent
C420S109000
Reexamination Certificate
active
06224825
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a case hardening steel with a minimum of grain boundary oxidation, which is suitable for use in the manufacture of mechanical components with high demands on fatigue resistance and wear resistance.
In, for example, gear transmissions, the movable parts are exposed to heavy stresses. In order to obtain a stronger material, the steel is alloyed. It has been found that among other alloying elements, Si, Mn and Cr are deleterious in increasing the depth of grain boundary oxidation. The content of those substances that can be increased first-hand in order to improve this effect are Ni and Mo, but they are very expensive.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of this invention to avoid or alleviate the problems of the prior art.
It is further an object of this invention to provide a case hardening steel with a minimum of grain boundary oxidation which is suitable for use in the manufacture of mechanical components with high demands on fatigue resistance and wear resistance.
It is an aspect of the invention to improve the internal oxidation properties in case hardening steel compared to conventional steels by decreasing the internal grain boundary oxidation.
Another object of the invention is to reduce the demand of expensive alloying components such as Ni and Mo and still obtain very low values of oxidation depth compared to conventional steels.
This is obtained with the steel according to the presently claimed invention, having the following composition, in % by weight:
C
0.12-0.25
Si
≦ 0.30
Mn
0.30-0.80
Cr
0.30-0.80
Ni
0.20-0.80
Mo
0.10-0.50
Ti
0.020-0.080
Al
0.005-0.10
B
0.001-0.006
remainder Fe+normal impurities.
REFERENCES:
patent: 3615370 (1971-10-01), Ridall et al.
patent: 3664830 (1972-05-01), Kambayashi et al.
patent: 5536335 (1996-07-01), Burris
patent: 46-29256 (1971-08-01), None
patent: 02 170944 (1990-07-01), None
patent: 03 028347 (1991-02-01), None
patent: 07 179990 (1995-07-01), None
patent: 09 053150 (1997-02-01), None
Burns Doane Swecker & Mathis L.L.P.
Ovako Steel AB
Yee Deborah
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