Alloys or metallic compositions – Ferrous – Chromium containing – but less than 9 percent
Patent
1996-09-06
1997-12-16
Yee, Deborah
Alloys or metallic compositions
Ferrous
Chromium containing, but less than 9 percent
420105, 420109, C22C 3806, C22C 3818
Patent
active
056981597
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a long-life carburizing bearing steel. Specifically, the present invention relates to a steel which is produced by a step of carburizing-quenching process, and which is suitably used for bearing parts such as outer rings, inner rings, rollers, etc., applied to a condition under high load.
BACKGROUND ART
An improvement in rolling fatigue life of bearing parts has also been strongly required due to the higher power of automobile engines and the severer environmental regulations, enacted in recent years. To cope with these demands, longer service life has been accomplished by increasing the cleanness of steel because it was believed that rolling fatigue failure of the bearing parts occurs from non-metallic inclusions as starting points. For example, the Japan Institute of Metals, Vol. 32, No. 6, pp. 411-443 reports that oxide type inclusions can be reduced by the combination of a tapping technique of an eccentric furnace bottom, an RH vacuum degassing method, etc., and thus the rolling fatigue life can be improved. However, the longer life of this material is not always sufficient, and specifically when the bearing is applied under a high load condition, the development of a steel having an even longer service life is required.
As a steel kind in this field, SUJ 2 (according to JIS), for example, has been commonly used as a steel which has improved in rolling fatigue life. For improvement of the cuttability of this bearing steel, Japanese Unexamined Patent Publication (Kokai) No. 55-145158 discloses a Te-containing bearing steel and Japanese Unexamined Paten Publication (Kokai) No. 1-255651 discloses a bearing steel to which REM is added. However, a strong demand for a longer life of these steels, under a high load condition, still exists.
In contrast, the inventor 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. However, there is a problem in that the high carbon chromium type bearing steel requires a long annealing step, for refining coarse carbides, because the coarse carbides deteriorate the fatigue life, since C and Cr contents are high and large eutectic carbides are formed in the bearing steel. Specifically, in the high carbon chromium type bearing steel the fatigue life in use under a high load is not necessarily sufficient.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a carburizing bearing steel which can exhibit excellent rolling fatigue characteristics in bearing parts. The present invention solves the problems in the above prior arts.
The invention of each of claims 1 to 4 provides a long-life carburizing bearing steel which comprises, in terms of weight: 0.10 to 0.35% of C, 0.3 to 2.0% of Mn, 0.001 to 0.03% of S, 0.4 to 1.50% of Cr, 0.010 to 0.07% of Al, 0.003 to 0.015% of N, 0.0005 to 0.0300% of total Mg; and further 0.35 to 1.70% of Si, or 0.05 to 1.70% of Si and 0.30 to 1.20% of Mo; or further, one or at least two elements selected from the group consisting of the following elements in the following amounts; 0.10 to 2.00% of Ni, 0.03 to 0.7% of V; and further, no more than 0.025% of P, not more than 0.0050% of Ti, not more than 0.0020% of total 0, and the balance consisting of iron and unavoidable impurities.
In the inventions as set forth in claims 1 to 4, the invention of claim 5 relates to the long-life carburizing bearing steel wherein oxides contained in the steel satisfy the following formula in terms of a number ratio: type inclusions.gtoreq.0.80.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention pays specific attention to a carburizing step of a medium carbon steel to realize a production process for bearing parts in which formation of eutectic carbides cannot occur, that is, a long annealing time is not necessary in the process, and the fatigue life is not deteriorated due to coarse carbides,
REFERENCES:
patent: 5407635 (1995-04-01), Iseda et al.
patent: 5518685 (1996-05-01), Sakamoto et al.
Bulletin of The Japan Institute of Metals (1993), vol. 32, No. 5, pp. 441-443.
Kawauchi Yuji
Ochi Tatsuro
Nippon Steel Corporation
Yee Deborah
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