Alloys or metallic compositions – Ferrous – Chromium containing – but less than 9 percent
Patent
1996-01-31
1998-01-06
Yee, Deborah
Alloys or metallic compositions
Ferrous
Chromium containing, but less than 9 percent
420110, 420111, 148906, 148334, C22C 3822, C22C 3844
Patent
active
057051240
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a bearing steel and, particularly, to a high carbon bearing steel having a long life which is excellent in rolling fatigue characteristics when used, as bearing parts such as outer rings, inner rings, rollers and balls, under a high load.
BACKGROUND OF THE INVENTION
As automotive engines have been made to have a high power and to correspond to environmented regulations in recent years, bearing parts are also required to have an improved rolling fatigue life. Rolling fatigue failures of bearing parts are thought to start from oxide inclusions.
Accordingly, attempts to extend the life of a bearing steel have heretofore included lowering the oxygen content and enhancing the cleanliness of the steel. For example, The Japan Institute of Metals 32, No.6, 441-443 discloses that a combination of tapping from the bottom of an eccentric furnace, RH vacuum degassing, and the like procedure decreases the oxygen content of a bearing steel to 3 to 6 ppm, resulting in fewer large oxide inclusions and an improved rolling fatigue life. However, extending the life of the bearing steel by the procedures as mentioned above is not necessarily satisfactory particularly when the steel is used under a high load. On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 3-644430 discloses that, in contrast to the improvement of the cleanliness of the steel by lowering the oxygen content as mentioned above, when the oxygen content in the steel is instead increased to from 0.002 to 0.005% to make the oxide inclusions an Al.sub.2 O.sub.3 --SiO.sub.2 --CaO (MnO) system, the steel exhibits an improved life.
However, even the bearing steel thus obtained does not necessarily exhibit a sufficiently extended life when used under a high load. As described above, the development of a longer-lived steel is strongly desired particularly when the bearing steel is to be used under a high load.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a high carbon bearing steel for bearing parts, particularly for bearing parts which are used under a high load and which exhibit excellent rolling fatigue characteristics.
The subject matter of the present invention is as described below. terms of weight, 0.70 to 1.20% of C, 0.15 to 1.70% of Si, 0.15 to 1.20% of Mn, 0.50 to 2.00% of Cr, 0.05 to 1.50% of Mo, 0.001 to 0.03% of S, 0.010 to 0.05% of Al, 0.003 to 0.015% of N, 0.0005 to 0.0300% of total Mg, up to 0.025% of P, up to 0.0040% of Ti, up to 0.0015% of total oxygen and the balance Fe and unavoidable impurities. terms of weight, 0.70 to 1.20% of C, 0.15 to 1.70% of Si, 0.15 to 1.20% of Mn, 0.50 to 2.00% of Cr, 0.05 to 1.50% of Mo, 0.001 to 0.03% of S, 0.010 to 0.05% of Al, 0.003 to 0.015% of N, 0.0005 to 0.0300% of total Mg, one or at least two elements selected from the group consisting of the following elements in the following amounts: 0.03 to 0.7% of V, 0.005 to 0.3% of Nb and 0.10 to 2.00% of Ni, up to 0.025% of P, up to 0.0040% of Ti, up to 0.0015% of total oxygen and the balance Fe and unavoidable impurities. (2), wherein the number ratio of oxides contained therein satisfies the formula inclusions).gtoreq.0.80
BEST MODE FOR CARRYING OUT THE INVENTION
In order to realize a high carbon bearing steel which can exhibit excellent rolling fatigue characteristics even under a high load, the present inventors have intensively carried out investigations, and have made the discovery described below. starts from 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 inclusions fine. extending the life of the steel. Making nonmetallic inclusions fine has the following two advantages: (i) reduction of stress concentration which has heretofore been believed to cause crack formation, and (ii) inhibition of the formation of the white stru
REFERENCES:
patent: 4581079 (1986-04-01), Borik
patent: 5268141 (1993-12-01), Ototani et al.
Patent Abstracts of Japan, vol. 14, No. 100 (C-693), Feb. 23, 1990 & JP-A-306542 (Sanyo Special Steel Co., Ltd.), Dec. 11, 1989.
Patent Abstracts of Japan, vol. 18, No. 215 (C-1191), Apr. 18, 1994 & JP-A-06010097 (Sumitomo Metal Ind.), Jan. 18, 1994.
Patent Abstracts of Japan, vol. 18, No. 030 (C-1153), Jan. 17, 1994 & JP-A-05 255809 (Aichi Steel Works Ltd.), Oct. 5, 1993.
Patent Abstracts of Japan, vol. 17, No. 361 (C-1080), Jul. 8, 1993 & JP-A-05 051693 (Sumitomo Metal Ind. Ltd.), Mar. 2, 1993.
Development of a Bearing Steel Having Ultra High Purification (EP Steel), Bulletin of Japan Institute of Metals, vol. 32, No. 6, pp. 441-443 (1993).
Kawauchi Yuji
Ochi Tatsuro
Nippon Steel Corporation
Yee Deborah
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