2000 Fiscal Year Final Research Report Summary
DEVELOPMENT OF ANTI-DARK SPOT RAILWAY RAILS
| Project/Area Number |
10555054
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
設計工学・機械要素・トライボロジー
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| Research Institution | KYUSHU INSTITUTE OF TECHNOLOGY |
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Principal Investigator |
KANETA Motohiro KYUSHU INSTITUTE OF TECHNOLOGY, FACULTY OF ENGINEERING, PROFESSOR, 工学部, 教授 (90039123)
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| Co-Investigator(Kenkyū-buntansha) |
UEDA Masaharu NIPPON STEEL CO., YAHATA R&D LAB., SENIOR RESEARCHER, 八幡技術研究部, 主任研究員
UCHINO Koichi NIPPON STEEL CO., YAHATA R&D LAB., CHIEF RESEARCHER, 八幡技術研究部, 主幹研究員
MATSUDA Kenji KYUSHU INSTITUTE OF TECHNOLOGY, FACULTY OF ENGINEERING, ASSOCIATE PROFESSOR, 工学部, 助教授 (40229480)
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| Project Period (FY) |
1998 – 2000
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| Keywords | Dark spot / Cracking / Pearlitic steel / Bainitic steel / Railroad / Rolling contact fatigue / Vickers hardness / Tribology |
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| Research Abstract |
As traffic speed on railroads increases, various kinds of defects have been produced in rail systems. One of them is the rail dark spot defect or rail shelling. The dark spot defect is characterised by a principal crack, which initiates at the contact surface and propagates at an acute angle to the rail surface in the direction of traffic, and a second crack, which grows more slowly from almost the same point on the surface, in the opposite direction to traffic and at a slightly less shallow angle. The principal crack has many sub-cracks and at some stage one of these may extend transversely across the railhead leading to a catastrophic tensile failure of the rail. Thus, this defect is a very dangerous rail failure. The authors have found the mechanism for the dark spot cracking. Furthermore, they have made a bainitic steel, which seems to be effective for the occurrence of rolling contact fatigue failures. The purpose of this study is to establish the design instruction for the develo
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pment of anti-dark spot defect railway rails on the basis of the mechanism for dark spot cracking. The main results obtained are summarised as follows :
1. Cracking is produced by a high traction force due to a local direct contact. The crack initiated propagates by a hydraulic pressure effect due to water penetrated into the crack in a period of wet running.
2. Under conditions where the mean traction force is rather low, the dark spot resistance of bainitic steel is much higher than that of conventional pearlitic steel.
3. Under conditions where the mean traction force is rather high, surface damages due to the plastic deformation are produced. The increase in hardness of steels is effective for the enhancement of such damages.
4. The bainitic steel is much worse than the pearlitic steel in the wear resistance. However, the wear resistance of bainitic steel can be improved by increasing the hardness and the carbon content.
5. Although a common opinion that the higher wear rate prevents the crack initiation is believed, the fact is somewhat different.
6. The welded parts of bainitic steel rails are almost the same joint performance as those of conventional pearlitic steel rails.
7. Presently, the rolling contact fatigue resistance test of bainitic steel railroads (HB=250-350) is in progress using actual railways. It has been found that the dark spot defect resistance of bainitic steel rails is much higher than that of conventional pearlitic steel rails.
Considering above results, the chemical composition of bainitic steel is under investigation now for application of bainitic steel rails so as to satisfy JIS standard on pearlitic rail steel strength and the electrical resistance standard established by the Japan Rail companies. Less
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[Publications] Satoh, Y., Tatsumi, M., Kasiwaya, K., Ueda, M.and Yokoyama, H.: "Anti-Darkspot Bainitic Steel Rail"Nihon Tetudou Shisetu Kyoukai-Shi, (Journal of Japan Railway Facilities Association). Vol.37, No.4. 258-261 (1999)
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