Metal treatment – Stock – Ferrous
Reexamination Certificate
2000-06-01
2002-04-16
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Ferrous
C148S334000, C148S335000, C420S112000
Reexamination Certificate
active
06372057
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to railway wheels, and more particularly, to chemical steel compositions for use in manufacturing railway wheels and rims.
BACKGROUND OF THE INVENTION
Numerous steel compositions are known for use in manufacturing wheels for railway cars. Recently, the volume of railway freight transportation, sometimes referred to in terms of railroad freight revenue ton-miles, is increasing to meet an increasing rail transport demand. As a result, rail cars are hauling increasingly heavier average loads. The load on the wheels of such heavy haul rail cars often approaches permissible limits, leaving little safety margin for wheel loading.
One serious problem with railway wheels is known as shattered-rim fracture. Shattered-rim fracture is a phenomenon whereby a rolling contact fatigue crack initiating at an internal defect in a wheel rim subsurface propagates from the crack ultimately to cause substantial damage to the wheel. Left unchecked, the shattered-rim fracture can cause catastrophic failure of the railway wheel and derailment of the rail car. This problem can be exacerbated as the load on the wheel or the speed of travel increase. The tendency towards shattered-rim fracture in a railway wheel also can be affected by transient effects caused by unbalanced loads, heavy braking, and other circumstances, and is becoming more of a concern with increasing railway transportation.
Shattered-rim fracture is believed to stem from internal defects in the railway wheel, such as inclusions, pores, voids, vacancies, cavities, or pinholes. The driving force of the fracture is believed to be cyclic shear stress caused by contact loading on the rim. Such stress is thought to cause Mode II (in-place shearing) crack propagation from internal defects in the wheel rim, a phenomenon in which cracks propagate from a defect in the rim when the Mode II stress intensity factor range is greater than the threshold Mode II stress intensity factor range for the rim. For this reason, railway wheels should be manufactured such that the size of internal defects is kept as small as possible, particularly in the wheel rim. While the permissible defect size for a given railway wheel may depend on factors such as diameter of the wheel and the wheel loading, in most cases, it is believed that the defect size, i.e., the diameter of the void, inclusion, or the like in the railway wheel rim, should be kept below about 1.5 mm. in size.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a railway car wheel that is resistant to shattered-rim fracture during long term heavy haul usage.
Another object is to provide a steel composition that enables the manufacture of railway wheels that are more resistant to shattered-rim fracture.
A further object is to provide a steel composition as characterized above which is less susceptible than conventional steel compositions to formation of voids, inclusions, or like defects in the finished product.
A related object is to provide a steel composition that can be consistently formed into railway wheels with voids, inclusions, and like defects in the rim that do not exceed 1.5 mm in size.
In carrying out these objects, a steel composition has been discovered, which according to the invention, consists essentially of iron, 0.40 to 0.77 wt. % carbon, 0.25 to 0.60 wt. % silicon, 0.40 to 1.20 wt. % manganese, 0.003 to 0.060 wt. % aluminum, and up to 0.0030 wt. % oxygen, with other alloying ingredients preferably not being present, or being present only in limited quantities as described in more detail hereinbelow. The invention also encompasses a railway wheel that generally comprises a rim, a hub, and a plate that connects the rim to the hub, with at least the rim, and preferably the entire wheel, being composed of the steel composition of the invention. Surprisingly, a steel alloy composed of the foregoing ingredients may be forged to form a railway wheel in which the size of internal defects, such as inclusions, voids, and the like, may be minimized and maintained within acceptable standards.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:
REFERENCES:
patent: 4042273 (1977-08-01), Heller et al.
patent: 5565044 (1996-10-01), Kim et al.
patent: 5711914 (1998-01-01), Heller
patent: 5899516 (1999-05-01), Fujimura et al.
Sen et al., “Influence of Inclusions and Heat Treatment on Fatigue Strength of Wheel And Axle Steel,” Fatigue Design Symposium (1998).
Danian et al., “The Effects of Cyclic Softening on the Shakedown Limit of Railway Wheel Steel,” International Conference on Mechanical Behaviour of Materials (6th), Kyoto, Japan (1992).
Bo et al., “Railway Wheel Rim Fatigue Break-Down and Relevant Problem,” 12thInternational Wheelset Congress Proceedings, Qingdao, China (Sep. 21-25, 1998).
Qian et al., “Fatigue of Railway Wheel and its Damage,” 12thInternational Wheelset Congress Proceedings, Qingdao, China (Sep. 21-25, 1998).
Marais, “Wheel Failures on Heavy Haul Freight Wheels Due to Subsurface Defects,” 12thInternational Wheelset Congress Proceedings, Qingdao, China (Sep. 21-25, 1998).
Lixian et al., “Study on Rim Fatigue Crack and Prevention,” 12thInternational Wheelset Congress Proceedings, Qingdao, China (Sep. 21-25, 1998).
Catot et al., “Contribution to Improve Steel Grades for Wheels for Heavy Freight Traffic,” International Wheelset Congress, Sydney, Australia (Sep. 27-Oct. 1, 1992).
Sakamoto et al., “Simulation Test on Tread Shelling of Railroad Wheel,”Rail Transportation, 12, pp. 73-78 (1996).
Ekberg et al., “Effects of Imperfections on Fatigue Initiation in Railway Wheels,”Charmec(Oct. 21, 1999).
Gordon et al., “Evaluation of Service-Induced residual Stresses in Railroad Commuter Car Wheels,”Rail Transportation15, pp. 25-31 (1998).
Magel et al., “Controlling Wheel Shelling,”Railway Track&Structures(Nov. 1997).
Snyder, “Shattered Rim Update, ”Lab Noted(Jul. 1998).
Diener et al., “Fracture Toughness of R7 Railroad Wheels,”La Metallurgia Italiana, 85 (3), pp. 161-167 (1993).
Sakamoto et al., “Fracture Toughness of Medium-High Carbon Steel for Railroad Wheels,” NAF-IMM Symposium on Micromechanic Modeling of Industrial Materials: In Honor of Professor T. Mor's 65th Birthday, Seattle, Washington (Jul. 20-22, 1998).
Stone, et al., “Wheel Thermal Damage Limits,”ASME, 1994, pp. 57-63 (1994).
Fujimura Takashi
Makino Taizo
Leydig , Voit & Mayer, Ltd.
Sumitomo Metal Industries, Inc.
Yee Deborah
LandOfFree
Steel alloy railway wheels does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Steel alloy railway wheels, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Steel alloy railway wheels will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2856192