Metal treatment – Stock – Ferrous
Patent
1996-07-18
1998-03-10
Yee, Deborah
Metal treatment
Stock
Ferrous
148328, 148330, 148333, 148334, 148335, 148906, C22C 3802, C22C 3806
Patent
active
057256900
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a long-life induction-hardened bearing steel. More particularly, the present invention relates to a steel which is produced through a step of controlling oxide inclusions and a induction hardening step, and which will be suitable for bearing parts such as outer rings, inner rings, rollers, etc, used under high load conditions.
BACKGROUND OF THE INVENTION
An improvement in rolling fatigue life of bearing parts has been strongly required due to the higher power of automobile engines and the stricter environmental regulations introduced in recent years. To cope with such a demand, longer service life has been sought by attaining higher cleanness of a steel because it was believed that rolling fatigue failure of the bearing parts originates from non-metallic inclusions as the starting points. For example, the Japan Institute of Metals, Vol. 32, No. 6, pp. 411-443 reports that quantities of oxide type inclusions can be reduced by the combination of an eccentric furnace bottom tapping technique, an RH vacuum degassing method, etc, and rolling fatigue life can be thus improved. However, longer life by this method is not always sufficient, and particularly when the bearing is used under a high load condition, the development of a steel having longer service life has been strongly required.
As a kind of steel in this field, SUJ 2 (according to JIS), for example, has been widely used as a steel which has improved rolling fatigue life. Since the C and Cr contents are high in this steel kind, large eutectic carbides are formed, so that a long annealing time is necessary for these eutectic carbides. To improve the cuttability of this bearing steel, Japanese Unexamined Patent Publication (Kokai) No. 55-145158 discloses a Te-containing bearing steel and Japanese Unexamined Patent Publication (Kokai) No. 1-255651 discloses a bearing steel to which REM is added. However, a strong demand for higher life of these steels under a high load condition still exists.
In contrast, the inventors of the present invention proposed in Japanese Patent Application No. 6-134535 a high carbon chromium type bearing steel containing suitable amounts of Mg and Mo. Excellent rolling fatigue characteristics can be obtained by using this steel. In order to produce the bearing parts by the high carbon chromium type bearing steel, a spheroidization annealing step and a hardening/tempering step are necessary, and the production cost becomes high. Therefore, the total production cost of the bearing parts using the Mg- and Mo-containing high carbon chromium type bearing steel involving the increase of the material cost becomes remarkably high. For this reason, there is also a strong requirement for low cost during the production of the bearing parts.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a induction-hardened bearing steel which can be used to produce bearing parts at low cost, and which exhibits excellent rolling fatigue characteristics in the bearing parts.
The inventors of the present invention have paid specific attention to induction hardening which will replace the hardening/temperating step of the conventional high carbon chromium type bearing steel, or a carburizing step of a medium carbon steel. Because great compression residual stress occurs in the surface layer of the induction hardened material, longer service life can be effectively obtained. To accomplish a induction hardened bearing steel capable of obtaining excellent rolling fatigue characteristics even under a high load, the present inventors have furthered their studies and have made the following observation.
(1) In rolling fatigue failure under a high load condition, a rolling fatigue failure starts from a nonmetallic inclusion accompanying a white structure with a carbide structure on the periphery thereof. The white structure and the carbide structure involve hardness lowering. The formation of the white structure and the carbide structure is inhibited by making the nonmetallic inc
REFERENCES:
patent: 4642219 (1987-02-01), Takata et al.
patent: 5013525 (1991-05-01), Hamada et al.
Bulletin of Japan Institute of Metals, vol. 68, No. 6, pp. 441-443 (1993).
Kawauchi Yuji
Ochi Tatsuro
Nippon Steel Corporation
Yee Deborah
LandOfFree
Long-life induction-hardened bearing steel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Long-life induction-hardened bearing steel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Long-life induction-hardened bearing steel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-135943