Pearlitic steel rail having excellent wear resistance and method of producing the same

Abstract

This invention is directed to improve a wear resistance and a damage resistance required for a rail of a sharply curved zone of a heavy load railway, comprising more than 0.85 to 1.20% of C, 0.10 to 1.00% of Si, 0.40 to 1.50% of Mn and if necessary, at least one member selected from the group consisting of Cr, Mo, V, Nb, Co and B, and retaining high temperature of hot rolling or a steel rail heated to a high temperature for the purpose of heat-treatment, the present invention provides a pearlitic steel rail having a good wear resistance and a good damage resistance, and a method of producing the same, wherein a head portion of the steel rail is acceleratedly cooled at a rate of 1° to 10° C. / sec from an austenite zone temperature to a cooling stop temperature of 700° to 500° C. so that the hardness of the head portion is at least Hv 320 within the range of a 20 mm depth.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)[0001]The present application is a continuation of U.S. patent application Ser. No. 10 / 974,048 filed Oct. 26, 2004, which is a reissue application of U.S. Pat. No. 5,762,723 which issued on Jun. 9, 1998. The entire disclosures of the application and U.S. Patent referenced above are incorporated herein by reference.TECHNICAL FIELD[0002]This invention relates to a pearlitic steel rail which improves the wear resistance and breakage resistance that are required for rails at curved zones of heavy load railways, and drastically improves the service life of the rails, and a method of producing such rails.BACKGROUND ART[0003]Attempts have been made to improve a train speed and loading as one of the means for accomplishing higher efficiency of railway transportation. Such as improvement in efficiency of railway transportation means severe use of the rails, and a further improvement in the rail materials has become necessary. More concretely, wear dra...

AI Technical Summary

Benefits of technology

The present invention relates to a pearlitic steel rail with improved wear resistance and damage resistance. The technical effects of the invention include increasing the hardness of the pearlite structure by increasing the carbon content and the ratio of hard cementite layer, and increasing the cementite density immediately below the rolling surface. The invention also addresses the problem of pro-eutectic cementite formation and promotes the formation of a good wear resistance by reducing the contact surface pressure and the wear of the head top portion. Additionally, the invention addresses the problem of resistance flash butt welding in rail welding and provides a solution to prevent damage to the rails and road bed.

Problems solved by technology

More concretely, wear drastically increases in the rails laid down in a curved zone of a heavy load railway and produces a problem from the aspect of longer service life of the rails.

In the case where the rails are sharply curved, the wear resistance cannot be secured even when the rails developed as described above are used, and the drop of rail life due to the wear has become a serious problem.

The contact state between the wheel and the rail is complicated.

On the head top portion of the inner track rail of the curved zone, on the other hand, the rail receives great slipping contact having large contact surface pressure from the wheel.

Therefore, fatigue damage builds up on the head top surface before it is worn out.

Therefore, if fitting of the rail to the wheel is not quick at the initial wear state immediately after the laying of the rail, a local and excessive contact surface pressure consecutively acts on the rail and surface damage due to fatigue is likely to occur.

In addition, even after fitting is established between the rail and the wheel, a large contact surface pressure always acts on the head top portion and consequently, surface damage similar to so-called “head check”, which generally occurs at the gage corner portion, develops with plastic deformation because the wear is less.

Because the cutting work requires a long time and is expensive, the following rail has been developed.

However, higher axial load of cargos (increase of railway loading) has been vigorously promoted in recent years so as to attain higher efficiency of railway transportation, and even when the rails developed as described above are used, sufficient wear resistance cannot be secured at the gage corner portions of the outer track rail even though they can prevent the surface damage by the periodically grinding of the head top portion in the inner track rail at the sharply curved zone, and the drop of rail life due to wear has been a serious problem.

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