GB2410281A

GB2410281A - Composite rail

Info

Publication number: GB2410281A
Application number: GB0329865A
Authority: GB
Inventors: Jackman Stuart
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-12-24
Filing date: 2003-12-24
Publication date: 2005-07-27
Also published as: GB0329865D0

Abstract

A railway track rail made of a first metal at least partially covered with a second metal the properties of the respective metals having been selected for the purposes of improving fatigue resistance and the formation of defects. The second metal may be austnitic stainless steel ANS 301 and between one and three millimetres thick. The second metal may cover at least the crown 1, 5 of the rail and extend at least partly down the gauge faces 7 of the rail. The second metal may cover the bottom 9, 8 of the rail and extend partially up the sides of the foot 4 of the rail. The first and second metals may be incorporated into a billet from which the rail is formed by rolling.

Description

COMPOSITE RAIL

This invention relates to a composite rail With the ever increasing tonnages of rail traffic carried each year by the UK railways, the incidence of rail defects brought on by fatigue and associated processes is increasing.

As these defects are potentially catastrophic, the railway industry spends many millions of poundsevery year on controlling and mitigating these effects, such as rail grinding and ultrasonic testing of rails.

Given the statistical nature of failure physics in metallurgy, it is also the case that rails have to be withdrawn from services when they may otherwise have many years of service left in them on account of the increasing incidence of defects, in order to maintain the level of safety There have been a considerable number of studies funded into the causes and processes of fatigue, rolling contact failure, gauge corner cracking and similar.

However, there have been very few attempts if any of developing practical engineering ways of avoiding these defects in the first place.

The present invention seeks to address these issues.

According to the present invention, there is provided a railway track rail made of a first metal at least partially covered with a second metal the properties of the respective metals having been selected for the purposes of improving fatigue resistance and the formation of defects.

. - 1 -...DTD: . . . ^ ë Thus the second metal may be selected to provide a required degree of wear resistance at one or more surfaces of the rail whereas the first metal may be selected to provide improved fatigue resistance, that is to say resistance to cracking.

Preferably said second metal is austenitic stainless steel. More preferably the second metal is austenitic stainless steel ANS 301.

Advantageously the second metal covers at least the crown of the rail. The second metal may cover the crown of the rail and extend partially down the gauge faces of the rail. In the latter case the second metal preferably extends down the gauge faces of the rail by approximately two centimetres.

The second metal may also cover the bottom of the rail. In this case the second metal advantageously covers the bottom of the rail and extends partially up the sides of the foot of the rail.

Preferably the layer of second metal is less than one centimetre in thickness. More preferably the layer of second metal is less than five millimetres in thickness Even more preferably the layer of second metal is between one and three millimetres in thickness.

Preferably the first and second metals are incorporated into a billet from which the rail is formed by rolling. Thus the second metal may be deposited upon a billet of the first metal in the form of one or more weld runs so located on the billet that they form the required layer or layers at appropriate positions on the rail when the billet is rolled to the form of the rail.

In order that the invention may be more clearly understood a specific embodiment will now be described by way of example and with reference to the accompanying drawings of which: Figure 1 is a cross section of a normal rail; and 2 e ae.

. - . Figure 2 is a cross section of a rail according to one embodiment of the invention with a layer of austenitic stainless steel on the rail head.

Referring to Figure 1, the rail comprises a crown (1), having gauge faces 7 and gauge corners 2, a web (10) and a foot (4) The conventional rail shown in Figure 1 is generally formed of a high carbon steel such as BS11 normal grade with a carbon content of 0.45-0.6%, BS11 Grade B steel having a carbon content of 0.55-0.75% or BS11 Grade A steel having a carbon content of 0.65-0.85%. The higher the carbon content, the more wear-resistant is the rail, but increased carbon content has the attendant disadvantage that the body of the rail is more brittle and thus more susceptible to the development of fatigue cracking. Fatigue cracks and other defects causing cracks can originate in the top and/or bottom surfaces of the rail. As a train wheel moves along the length of a normal rail, which structurally forms a continuous beam across the rail supports, any given position along the rail will experience bending moment and/or shear stresses varying in magnitude and the rail may also hog and sag. Fatigue defects such as cracks initiated by flexing and/or shear may then grow in top and bottom surfaces of the rail; i.e. in the top surface of the rail head (3) and the bottom surface of the rail foot (4), where tensile stresses are greatest.

Cracking may also be due to changes in the structure of the steel following temperature fluctuations caused by so-called "wheel burn". There may also have been defects present In the rail and its surfaces arising from, for example, manufacture, installation and maintenance. These defects may induce cracks under cyclic service loading which may then grow and cause either an unsafe rail, or complete failure of the rail The choice of steel for a rail is" thus inevitably a compromise in which fatigue resistance is sacrificed for increased wear resistance or vice-versa.

Referring to Figure 2, the rail of the invention is formed by the rolling of a rail to the form of Figure 1 with layers of austenitic stainless steel (5,8). One layer of austenitic stainless steel ANS 301 is situated on the rail head (3), such that the gauge faces (7) - 3 .e . . :::: : :e age:: . ...

of the rail head, the gauge corners (2) and the crown (1) of the rail head are covered to a depth of one to two and preferably approximately two millimetres. Another layer of austentic stainless steel (8) is provided on the bottom (9) of the rail such that the bottom (9) of the rail and the sides of the rail foot (4) are covered to a depth of approximately two millimetres. Layers (5,8) may be manufactured separately, prior to rolling together with the main body of the rail, or may be incorporated in the billet from which the rail is formed, as already mentioned above Alternatively, explosive bonding may be used to 'weld' the metals together The rolled austenitic stainless steel has a Brinell Hardness of approximately 280 to 350 BNH, which compares favourably to the Hardness of BS11 Grade B steel, which has a Brinell Hardness of approximately 280 to 320 BNH. Austenitic stainless steel has enhanced work hardening characteristics compared to normal rail steel, with ANS 301 (or 17-7) work hardening from about 280 BNH (as rolled) to 450 BNH compared to a work hardening from 280 to 320 BNH from BS11 grade B rail steel.

Also the yield stress of ANS 301 ranges from 860 N/mm2 (25% Work Hardened) , 1030 N/mm2 (50% Work Hardened), 1210 N/mm2 (75% Work Hardened) and 1280 N/mm2 (100% Work Hardened). This compares favourably with the yield stress of VIC 860, Grade 700, Grade 900A and B The provision of layers of austenitic stainless steel (5,8) on the surfaces of the rail of the present invention inhibits initiation and growth of the fatigue cracks and other defects described above. The rail is thus more resistant to the onset of these defects, the development of the defects into cracks and crack growth through this layer.

In the rail of the present invention the wear resistance characteristics of the rail are achieved by the use of austenitic stainless steel covering the head and/or base and sides of the foot of the rail, thus allowing the second metal forming the main body of the rail to have characteristics more optimised for providing strength and resisting fatigue - 4 .e e ë -e ::: :. ::: e e.. e Since the surface layers 5,8 will also provide the appropriate wear resistance the main body of the rail may be formed of a grade of steel of relatively low carbon content, thus providing optimum resistance to fatigue, or of an alternative grade of steel, for example of lower carbon content, that has improved structural characteristics and can be chosen with less regard to wear resistance.

It will be appreciated that the rail could be covered in austentic stainless steel to a greater or lesser extent, that the depth of said steel may vary, and indeed other materials may equally be used.

This invention, in addition to its application to plain lengths of rail, can also be applied to switches and crossings, switch blades and other components of the railway and its junctions The above embodiment is described by way of example only. Many variations are possible without departing from the invention.

ë . . . . ...

Claims

CLAIMS: 1. A railway track rail made of a first metal at least partially

covered with a second metal the properties of the respective metals having been selected for the purposes of improving fatigue resistance and the formation of defects.
2. The rail of Claim I wherein the second metal is austenitic stainless steel.
3. The rail of Claim 2 wherein the second metal is austenitic stainless steel ANS 301.
4. The rail of any previous claim wherein the second metal covers at least the crown of the rail.
5. The rail of any of Claims I to 3 wherein the second metal may cover the crown of the rail and extend partially down the gauge faces of the rail.
6. The rail of Claim 5 wherein the second metal preferably extends down the gauge faces of the rail by approximately two centimetres.
7. The rail of any previous claim wherein the second metal substantially covers the bottom of the rail.
8. The rail of Claim 7 wherein the second metal covers the bottom of the rail and extends partially up the sides of the foot of the rail.
9. The rail of any previous claim wherein the layer of second metal is less than one centimetre in thickness.
10. The rail of any of Claims I to 8 wherein the layer of second metal is between one and three millimetres in thickness.
11. The rail of any of Claims 1 to 8 wherein the layer of second metal is between one and three millimetres in thickness. - 6 -
12. The rail of any previous claim wherein the first and second metals are incorporated into a billet from which the rail is formed by rolling.
13. A rail substantially as described herein with reference to the accompanying drawings. - 7 -