JPH0790494A - Rail excellent in rolling fatigue damage resistance - Google Patents

Abstract

PURPOSE:To produce a rail excellent in rolling fatigue damage resistance by specifying the compsn. constituted of C, Si, Mn, P, S, Cr, V and iron and regulating the hardness of the uniform bainitic structure and head corner part into specified one. CONSTITUTION:The compsn. of a rail is constituted of the one contg., by weight, 0.15 to 0.45% C, 0.05 to 1.0% Si, 0.30 to 2.5% Mn, <=0.03% P, <=0.03% S, 0.70 to 3. 00% Cr and 0.005 to 0.05% V, and the balance Fe with inevitable impurities. The microstructure of the head is formed into a uniform bainitic one, and the hardness of any position of the head and the head corner part is regulated to 240 to 390 by Hv. The bainitic structure is obtd., after rolling, by subjecting rail stock to air cooling or accelerated cooling. In addition to the same components, prescribed amounts of one or more kinds of Nb and Ti and one or more kinds among Cu, Ni and Mo may be incorporated according to necessary. Thus, the wear amount is increased more than that in the conventional rail to obtain the rail excellent in rolling fatigue resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rail having excellent resistance to rolling fatigue damage that occurs at the crown and head corners that affect the life of the rail in a railway.

[0002]

2. Description of the Related Art Rail transportation has a higher transportation efficiency than other transportation means, and is aimed at speeding up and congestion of timetables year by year, and the load on rails is becoming severer year by year. For this reason, rolling fatigue damage increases on the rail top surface in the straight portion and in the head corner portion in the curved portion.

Therefore, the characteristics required for rails are becoming higher in performance, and there is a demand for rails that are more excellent in damage resistance against rolling fatigue characteristics than ever before. As such a rail, for example, the head as disclosed in Japanese Patent Publication No. 55-2388 is reheated to a high temperature and cooled from a predetermined temperature range, and a temperature range of 700 to 650 ° C. is set to 10.
Heat-treated rails obtained by cooling at a rate of 5 to 15 ° C / sec are known. Since such a heat-treated rail has a particularly high hardness at the head, it is used in railways with a high axial load and exhibits excellent characteristics.

Further, Japanese Patent Laid-Open No. 2-2824848 discloses that
A rail is disclosed in which the amount of C is slightly lower than that of a conventional rail, and a hardness difference is further provided between the crown and the head corner to improve rolling fatigue damage resistance.

[0005]

By the way, in conventional lines whose speed has been recently increased, rail top shelling, which has been observed only in rails laid on Shinkansen trains, has occurred. I have a hard time.

Regarding the cause of the parietal surface shelling,
Although not all have been clarified, one of the causes is the formation of a martensite layer called a white layer on the surface of the rail due to rapid heating / cooling of the rail surface during wheel running and slipping. It has been reported. In this case, it is said that the white layer is so hard that cracks occur at the boundary with the matrix and the cracks propagate to lead to shelling damage.

The hardness of the white layer is generally determined by the amount of C, and the higher the amount of C, the higher the hardness of the white layer. Conventional rails, including those disclosed in Japanese Examined Patent Publication No. 55-2388, have a large amount of C of 0.65 to 0.85%. Therefore, when a white layer is formed, the hardness is high. Has become. In addition, the conventional rail has a pearlite microstructure and is hard to wear because the soft ferrite layer and hard cementite layer are lamellar.
There is also a drawback in that the white layer that has been once generated is not removed even by the abrasion caused by the contact between the wheel and the rail during passage of the train, and is likely to be the starting point of damage.

In order to address this problem, the present inventors have proposed a rail whose white layer has a low hardness and which is removed by abrasion due to contact between the wheel and the rail when the train passes even if the white layer is formed. investigated. Since the hardness of the white layer, that is, martensite, is uniquely determined by the amount of C, it is effective to reduce the amount of C in order to reduce the hardness.

However, in a rail with only a small amount of C, the strength is lowered and a large plastic flow occurs on the rail surface, which causes another kind of damage such as squeak cracking. For this, for example, the above-mentioned Japanese Patent Laid-Open No. 2-2
As disclosed in No. 82448, a rail having a low C content has been developed in which only the head corners have high hardness by heat treatment or the like. However, in the actual running of trains on railways, the contact between the wheels and the rails is not uniform, and the hardened corners of the head may come into contact with the wheels.In this case, contact occurs at the crown. However, since the original purpose of removing the white layer by increasing the amount of wear is not achieved, it is difficult to remove the white layer, and rolling fatigue damage resistance is not necessarily good.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rail having excellent rolling fatigue damage resistance.

[0010]

As a result of considering the drawbacks of the prior art as described above, the inventors of the present application have found that both the crown and the head corner are damaged by the plastic flow without complicated heat treatment. It has a uniform hardness that does not occur, the fatigue strength and hardness are equivalent to those of the conventional rail, and the entire head bainite structure has a microstructure of 1.3-3. It has been found that the white layer can be removed and the damage resistance to rolling fatigue damage is excellent by increasing the wear amount by 0 times. Furthermore, by adding a trace amount of alloying elements, the amount of wear is the same as in the case of a full-scale Bayner toy structure, the formation of a white layer is suppressed, and the head shows the same hardness to the inside, which clearly extends the service life. did.

The present invention has been made on the basis of the above findings, and in% by weight, C: 0.15 to 0.45%, S
i: 0.05 to 1.0%, Mn: 0.30 to 2.5%,
P: 0.03% or less, S: 0.03% or less, Cr: 0.
70 to 3.00%, V: 0.005 to 0.05%, the balance consisting of iron and unavoidable impurities, the head has a uniform bainite structure, and the hardness is either the crown or the head corner. The rail having excellent resistance to rolling contact fatigue damage is also provided at Hv between 240 and 390.

Further, in% by weight, Nb: 0.005 to 0.
Provided is a rail excellent in rolling contact fatigue damage resistance, characterized by further containing one or two of 01% and Ti: 0.001 to 0.01%.

Further, in the above basic composition or in the composition further containing the above element, Cu: 0.05 to 2.0
%, Ni: 0.05 to 2.0, Mo: 0.005 to 0.
Disclosed is a rail excellent in rolling contact fatigue damage resistance, characterized by containing 05% of one kind or two or more kinds.

The present invention will be described in detail below. First, the reasons for limiting the chemical components will be described. In addition, in the following description, all percentages represent% by weight.

C: 0.15 to 0.45% C is an element that has an important influence on the hardness of the white layer and the strength of the rail itself. If the content exceeds 0.45%, the white color at the top of the rail head is white. The hardness of the layer becomes extremely hard and the difference in hardness of the base material becomes too high, which causes the shelling damage. On the other hand, if it is less than 0.15%, the strength of the base material becomes low, the plastic flow is remarkable, and damage originating from this occurs. Therefore, the C content is 0.15 to 0.45%
Prescribed in.

Si: 0.05 to 1.0% Si is an element that is not only effective as a deoxidizing agent but also forms a solid solution in the matrix to increase the strength, but its content is less than 0.05%. Then the effect is not recognized. Also 1.
If it exceeds 0%, the matrix becomes brittle and hard SiO ₂
Are dispersed in the matrix, and this is the starting point of shelling. Therefore, the amount of Si is specified to be 0.05 to 1.0%.

Mn: 0.30 to 2.5% Mn is an element that forms a solid solution in the matrix to enhance hardenability and enhance strength, but if it is less than 0.30%, its effect is not recognized. If it exceeds 5%, martensite is likely to be generated in the segregated portion, which becomes a starting point of damage. Therefore, the Mn content is specified to be 0.30 to 2.5%.

P: 0.03% or less Since P deteriorates the toughness, it is specified to be 0.03% or less. S: 0.03% or less S is mainly present in the steel in the form of inclusions, but 0.03%
If it exceeds 0.1%, the amount of the inclusions remarkably increases to embrittle the matrix, so the content is specified to be 0.03% or less.

Cr: 0.70 to 3.00% Cr is an element that increases the bainite hardenability, and is a very important element for enhancing the strength of the steel of the present invention by using the microstructure as a bainite structure. However, if it is less than 0.70%, the bainite hardenability is low and the bainite structure does not have a uniform microstructure. On the other hand, if it exceeds 3.00%, martensite is likely to be generated, which becomes a starting point of damage.
Therefore, the Cr amount is specified to be 0.70 to 3.00%.

V: 0.005-0.05% V is associated with C in the matrix and precipitates after rolling. Therefore, the hardness is increased by precipitation strengthening to the inside of the head.
It is not only effective for extending the life of the rail, but also forms precipitates with C during the rapid heating of the head surface during running and slipping of the wheels, which does not decompose. It is very effective in reducing the amount of solute C and lowering the hardness of the white layer to suppress shelling damage. However, if the amount is less than 0.005%, the effect cannot be effectively exhibited. Also 0.0
Even if added over 5%, the effect is saturated. Therefore, the V amount is specified to be 0.005 to 0.05%.

Nb: 0.005 to 0.01% Ti: 0.001 to 0.01% Similar to V, Nb and Ti are associated with C in the matrix and precipitate after rolling. Not only is it effective in increasing the hardness by precipitation strengthening and extending the life of the rail, but it also forms a precipitate with C when the head surface is rapidly heated when the wheel is running or slipping, and this does not decompose. As a result, the solid solution C of the rapidly heated portion
It is effective in reducing the amount, and is very effective in suppressing the shelling damage by lowering the hardness of the white layer. The effect is remarkable when combined with V, but is not effective when added with less than 0.005% of Nb and less than 0.001% of Ti.
Further, even if the addition amount of Nb exceeds 0.01% and the addition amount of Ti exceeds 0.01%, not only the effect is saturated, but also the precipitate is likely to be coarsened, which may cause another damage. Therefore, when Nb and Ti are contained, the amount is N
b: 0.005 to 0.01%, Ti: 0.001 to 0.
It is defined as 01%, and one or two of these are added.

Cu: 0.05 to 2.0% Ni: 0.05 to 2.0% Mo: 0.005 to 0.05% Cu, Ni and Mo all form a solid solution in the matrix and are bainite baked. Although it is an element effective for improving the penetrability and increasing the strength, its effect is not recognized when it is less than the above range, and when it exceeds the range, martensite is apt to be generated and becomes a starting point of shelling damage. Therefore, Cu,
When Ni and Mo are contained, the amount is Cu: 0.
05-2.0%, Ni: 0.05-2.0%, Mo:
It is specified to 0.005 to 0.05%, and one or more of these are added.

Next, the microstructure of the rail of the present invention will be described. In the present invention, the rail head has a uniform bainite structure. Since the bainite structure has higher dislocation density and higher strength than the conventional rail pearlite structure, it is possible to make the C content lower than that of pearlite steel. Further, in the pearlite structure, hard carbides (cementite) are oriented in a layered form, which makes it difficult to wear, whereas in the bainite structure, since carbides are dispersed as fine carbides in the matrix, they are simultaneously removed when the matrix wears. Therefore, it has a feature that it is more easily worn as compared with the pearlite structure.

Rolling fatigue damage is considered to occur when a fatigue layer accumulates near the rail surface, or when a crack develops from the boundary between the white layer and the base material and develops. Even in such a case, damage can be suppressed by abrading and removing the accumulated fatigue layer or the generated white layer due to the contact between the rail and the wheel when the train passes. Therefore, as described above, if the rail head is made into a uniform bainite structure having a predetermined hardness so that it is easily worn, rolling fatigue damage is excellent. As described above, in order to effectively remove the white layer by wear, it is necessary that the wear amount is larger than that of a normal rail (JIS, the same applies hereinafter). The wall thickness is significantly reduced, and the required life cannot be secured. In practice, if the amount of wear is 1.3 to 3.0 times that of a normal rail, the rolling fatigue resistance is excellent while ensuring the required life. If the bainite structure is manufactured from the steel having the composition of the present invention and has a hardness in the range shown below, the wear amount is 1.3 to 10% of that of a normal rail.
It is in the range of 3.0 times, and there is no problem in life due to thinning. Such a bainite structure can be obtained by air-cooling or accelerating-cooling the rail material after rolling.

It is most desirable to evaluate the amount of wear of the rail by the amount of wear when actually laid,
A value evaluated by a comparative test using a Nishihara-type abrasion tester that simulates the contact conditions of an actual laying rail is also effective.

Regarding the hardness, it is necessary to have a hardness of 240 to 390 in Hv at any position of the crown and the head corner. If it has a bainite structure and a hardness within this range, the amount of wear is larger than that of a normal rail, and the rolling fatigue damage resistance is good. In this case, it is desirable in terms of cost to make the crown and head corners of the bainite structure substantially uniform in hardness, because complicated heat treatment is unnecessary.

The head corner portion is Hv 240 to 3
If it is 90, the plastic flow is equivalent to that of the conventional rail, and the damage originating from the plastic flow does not occur. If Hv exceeds 390, the amount of wear is reduced, which causes inconvenience. To obtain Hv390 or higher in the bainite structure, it is necessary to increase the amount of alloy addition, and therefore it is not cost effective.

Next, the grounds for the reasons for limiting the above-mentioned requirements of the present invention will be described based on experimental examples. FIG. 1 shows the results of investigating the effects of matrix structure and hardness on the wear reduction ratio. As shown in Table 1, the composition range of the test steel is C, Si, Mn, Cr, Cu, Ni, Mo, V,
Nb and Ti are variously changed components, and each is hot-rolled into a steel plate of 16 mm, and some of the steel plates are air-cooled. Outer diameter 30 mm, width 8 mm from these steel plates
A Nishihara type wear test piece was sampled and a wear test was carried out under a non-lubricated condition with a contact load of 135 kg simulating contact between a conventional rail and wheel, a slip rate of -10%, and the wear reduction after 100,000 rotations. It was measured. In the evaluation, the wear amount of the ordinary rail is measured, the wear reduction ratio of the sample steel to the ordinary rail is obtained, and this value is used. In addition, in the column of the structure of FIG. 1, P shows pearlite and B shows bainite.

[0029]

[Table 1]

As can be seen from FIG. 1, the wear loss decreases as the matrix hardness increases. Ordinary rails have a hardness of Hv240 or higher, and this hardness does not cause serious problems with creaking cracks in the rail head corners. The squeaking cracks are due to plastic deformation of the rail corners. Since it is defined only by the strength (hardness) of the corner portion, it can be understood that there is no problem if the lower limit of hardness is Hv240 or higher. Further, the wear loss of the bainite structure is larger than that of the pearlite structure at the same matrix hardness. From this, it can be understood that the head needs to have a bainite structure in order to increase the amount of wear loss and to improve the damage resistance as compared with a normal rail.

From various studies to date, it is considered that the wear reduction ratio needs to be 1.3 times or more to remove the fatigue layer due to wear. Furthermore, from the viewpoint of the planned life of the rail, if the wear loss exceeds 3.0 times that of a normal rail, the metal loss due to the wear of the rail head will be significant before the planned life is reached, and it will be unusable. The upper limit of the ratio is 3.0 times. The hardness of a normal rail having a pearlite structure currently used is about Hv240 to 260, but the hardness of a bainite structure showing a wear reduction ratio of 1.3 to 3.0 times is higher than Hv240. It can be seen from FIG. 1 that it is 390. Therefore, if the hardness of the bainite structure that is the object of the present invention is Hv240 to 390, from the viewpoint of removal of the fatigue layer due to wear, life due to thinning of the rail head, and squeak cracking of the rail head corners. It is shown from this figure that the rail will be satisfactory.

FIG. 2 shows the effect of the amount of C in the matrix on the hardness and thickness of the white layer formed on the rail crown surface. The sample steel was a steel sheet having a composition in which the C content was changed so as to show the composition range in Table 2, and was made into a steel plate of 16 mm by hot rolling. A cylindrical test piece with a diameter of 3 mm was sampled from these steel plates, and this cylindrical test piece was set on the side where the rail sample of Nishihara-type rolling contact fatigue tester was to be attached, and it was brought into instantaneous contact with the wheel test piece and forced sliding The hardness and thickness of the white layer produced by simulating the white layer formation due to slippage on the actual rail of rapid heating and rapid cooling were evaluated.

[0033]

[Table 2]

As can be seen from FIG. 2, the thickness of the white layer becomes thinner as the C content decreases. It is considered that this is because the white layer is not formed in the inside where the cooling rate is slow because the critical cooling rate in forming the white layer shifts to the high cooling rate side as the amount of C decreases. The hardness of the white layer largely depends on the C content, and the hardness decreases as the C content decreases. It is considered that the hardness of the white layer needs to be 1.75 times or less than the matrix hardness, because if there is an excessive hardness difference between the white layer and the matrix, the resistance of the white layer is removed by abrasion. As shown in FIG. 1, since the upper limit of the matrix hardness is Hv390 from the viewpoint of the wear reduction ratio, the white layer hardness needs to be Hv680 or less. Therefore, the upper limit of the amount of C is 0.45%.

FIG. 3 shows the effect of a trace amount of additive on the thickness of the white layer formed on the rail top surface.
The test steel was a composition in which V, Nb, and Ti were changed based on 0.4% C as shown in the composition range in Table 3, and a 16 mm steel plate was obtained by hot rolling. Similar to the case of Fig. 2, a cylindrical test piece with a diameter of 3 mm was sampled from these steel plates, and the cylindrical test piece was set on the side where the rail sample of the Nishihara-type rolling contact fatigue tester was attached, and the wheel test piece was momentarily attached. Contact them,
The thickness of the white layer was evaluated by simulating the white layer formation due to slip on the actual rail of rapid heating and rapid cooling due to forced sliding.

[0036]

[Table 3]

From FIG. 3 it can be seen that the addition of V, Nb, Ti reduces the white layer thickness. V, N
b and Ti form carbides, and these carbides are not decomposed by rapid heating. As a result, the amount of solid solution C decreases, and the critical cooling rate in the formation of the white layer shifts to the high cooling rate side. As a result, the white layer is not formed, and the thickness of the white layer is reduced. As shown in FIG. 3, this effect has a remarkably large V, and although Nb and Ti have high carbide forming ability, they are not so large when added alone. The effect is 0.05% or more for V and 0.01 for Nb and Ti.
It is confirmed that it is saturated at over%. In addition, as shown by the black mark in FIG. 3, Nb based on the V addition system,
It can be seen that when Ti is added, the white thickness is lower than when V is added alone. And in this case, the hardness of the white layer is also reduced. Therefore, N
It is understood that b and Ti alone have a small effect, but the combined addition with V increases the above-mentioned effect, so that the combined addition with V is desirable.

FIG. 4 shows an inner portion 30 mm from the surface of the rail head.
It shows the effect of the components of the matrix on the hardness distribution up to the position. The test steel is a composition in which Cu, Ni, Mo, V, Nb, and Ti are changed so that the composition range is shown in Table 4. After simulated rolling into the shape of the rail head by hot rolling, the center of the head Vickers hardness was measured from the surface to the position of 30 mm inside.

[0039]

[Table 4]

As can be seen from FIG. 4, the decrease in internal hardness is reduced by the addition of the precipitation hardening elements V, Nb and Ti. In addition, Cu, N which increases bainite hardenability
It can be understood that the combined addition of i and Mo reduces the size. However, even if a large amount of V, Nb, or Ti is added, the suppression of the decrease in hardness inside the rail is saturated, so it is not necessary to add 0.05% or more for V and 0.01% or more for Nb, Ti. . On the other hand, addition of a large amount of Cu, Ni and Mo is not desirable because it forms a martensite layer on the surface layer.

[0041]

EXAMPLES Specific examples of the present invention will be described below. (Example 1) A wear test was conducted on sample steels having the compositions, microstructures and hardnesses shown in Table 5. Wear test for outer diameter 30
mm, width 8 mm test pieces were taken from the test steel, tire test pieces with the same dimensions were taken from the railroad wheel materials, and these were reported as contact conditions on conventional lines using the Nishihara abrasion tester. Contact load 135kg, slip rate -10
%, Contact was made under the condition of no lubricant. Then, the ratio of the amount of wear reduction at that time to the amount of wear reduction of the ordinary rail material obtained as a comparison was taken, and the wearability was evaluated by the ratio of the amount of wear reduction. The results are also shown in Table 5. In addition, Table 5 also shows whether or not accelerated cooling was performed during the production of the sample steel.

[0042]

[Table 5]

As shown in Table 5, with respect to E-4,7,9 having a higher C content than the present invention and showing a pearlite structure, the hardness of E-4,9 is 250,350 at Hv. While satisfying the range of the present invention, the wear reduction ratio is 1.00, 0.9
The wear reduction ratio of E-7 is as low as 5, and the wear reduction ratio is as good as 1.40, but the hardness is 200 at Hv, which is less than the lower limit of the present invention, and is not practical.

E-1,2,3,5,6,8 has a bainite structure, but E-2 has a Cr content of 0.65%, which is below the range of the present invention. The value is as low as 230 and the wear reduction ratio is 3.58, which is too large. E-6 has a Mn of 3.05%, which exceeds the range of the present invention, has a high hardness of 420 as Hv, and has a wear reduction ratio of 1.2.
It cannot be said that the wear resistance is 0, which is sufficient.

E-1, 3, 5, 8 having a bainite structure and having all the components within the scope of the present invention have a hardness within the scope of the present invention and an appropriate wear reduction amount. Was confirmed.

Example 2 With respect to the sample steels having the compositions, microstructures and hardnesses shown in Table 6, the abrasion test was conducted in the same manner as in Example 1. The wear reduction ratio at that time is also shown in Table 6. In addition, Table 6 also shows whether or not accelerated cooling was performed during the production of the sample steel. All the test steels had a bainite structure.

[0047]

[Table 6]

As shown in Table 6, the hardness of F-1, 4, and 7 having the Mn and Cr contents lower than the range of the present invention is low,
The wear reduction ratio shows a high value of 3.0 or more. In addition, Mn,
F-3,6,9 having a Cr content higher than the range of the present invention
Has a significantly high hardness, and the wear reduction ratio is less than 1.3. On the other hand, regarding F-2, 5 and 8 in which the contents of Mn and Cr satisfy the range of the present invention, it is confirmed that the hardness is within the range of the present invention and the wear reduction ratio is within a proper range. It was

Example 3 With respect to the sample steels having the compositions, microstructures and hardnesses shown in Table 7, the abrasion test was conducted in the same manner as in Example 1. The wear reduction ratio at that time is also shown in Table 7. In addition, Table 7 also shows whether or not accelerated cooling was used during the production of the sample steel. Regarding the microstructure of the sample steel, some of the Hv of more than 390 became a mixed structure of bainite and martensite. In the column of microstructure in Table 7, M + B indicates a mixed structure of martensite and bainite.

[0050]

[Table 7]

As shown in Table 7, 1 of Cu, Ni and Mo
G-1,3,5,7,9,11,13 in which the addition amount of one or more kinds satisfies the range of the present invention has a hardness Hv of 271 to 335 and is within the range of the present invention, The wear reduction ratio was in the proper range of 1.43 to 2.84. However, among the alloying elements, the amount of Cu added exceeds the range of the present invention G-2, and the amount of Ni added exceeds the range of the present invention G
-4,8,12,14, the amount of addition of Mo exceeds the range of the present invention G-6,10, and the amount of addition of Ni and Mo of G-14 exceeds the range of the present invention, Both are Hv39
It was confirmed that the hardness was 0 or more and the wear reduction ratio was as small as 1.3 or less.

Example 4 With respect to the sample steels having the compositions, microstructures and hardnesses shown in Table 8, the abrasion test was conducted in the same manner as in Example 1. The wear reduction ratio at that time is also shown in Table 8. In this example, the thickness of the white layer was measured in addition to the wear reduction ratio. For the white layer thickness, collect a cylindrical test piece with a diameter of 3 mm from the sample steel, set this cylindrical test piece on the side to which the rail sample of Nishihara type rolling fatigue tester is attached, and contact it with the wheel test piece momentarily. By doing so, forced slippage is generated to rapidly heat and rapidly cool the test piece, and a test simulating generation of a white layer due to slippage on an actual rail is performed, and the thickness of the generated white layer is measured. The results are also shown in Table 8. Table 8 also shows the presence or absence of accelerated cooling during the production of the sample steel. The components of the test steel are H-1 and H-2, H
-3 and H-4, H-5 and H-6, H-7 and H-8, H-
Between C9 and H-10, C, Si, Mn, and Cr were adjusted so as to have almost the same addition amounts, and V, Nb, and Ti were added in amounts within and above the range of the present invention, respectively. There is.

[0053]

[Table 8]

As is clear from Table 8, the structure is bainite, the hardness is within the range of the present invention, and the wear reduction ratio is an appropriate value. However, the thickness of the white layer is almost unchanged even if V, Nb, or Ti is added beyond the range of the present invention, and therefore addition exceeding the range of the present invention only causes an increase in cost and is effective. It was confirmed that no sex was recognized.

(Embodiment 5) Here, steel having the composition shown in Table 9 is actually rolled into a rail shape, and after the rolling, air cooling or accelerated cooling is performed. Then, the surface hardness of these test steels was measured at Hv 10 kg on the crown surface of each rolled material. Also, the internal hardness is Hv1 at a position 30 mm deep from the parietal surface.
It was measured at 0 kg. The wear reduction ratio is the rolling material head (however,
For the test material having a mixed structure of martensite and bainite, the wear test sample shown in Example 1 was taken from the bainite single layer portion) and evaluated by the same test method as in Example 1. These values are also shown in Table 10. In addition,
The presence or absence of accelerated cooling during the production of the sample steel is also shown in Table 9. Further, Table 10 shows the surface layer structure, and M + B in the column indicates martensite + bainite.

[0056]

[Table 9]

[0057]

[Table 10]

The test steels I-1 and I-2 are C, Si, Nb and M.
The effects of V were compared while making the n and Cr contents substantially the same, but I-2 having a V content within the range of the present invention showed a small decrease in internal hardness, whereas the V content was V content. Is 0.00
The internal hardness of I-1 as low as 2% is remarkably lowered.

I-3 and I-4 are compared in the region where the V content is high, but I-4 is added even though the V content is 0.105%, which exceeds the range of the present invention. , The internal hardness is equivalent to I-3, so a large amount of V
It was confirmed that the addition was not effective.

I-5 and I-6, I-7 and I-8, I-9
And I-10, the contents of C, Si, Mn, Cr, and V are almost the same, and the effects of addition of Nb and Ti alone or in combination are compared. In each of I-6, 8 and 10 in which Nb and Ti were added beyond the range of the present invention, the degree of decrease in internal hardness was the same as that of steels I-5, 7 and 9 in the range of the present invention. It was confirmed that the effect was saturated even if a large amount of Nb, Nb, or Ti was added.

I-11 and I-12, I-13 and I-1
4, I-15 and I-16, I-17 and I-18, I-1
9 and I-20, I-21 and I-22, I-23 and I-2
No. 4 compares the effects of Cu, Ni, and Mo alone or in combination with the contents of C, Si, Mn, Cr, and V being approximately the same. I-12, 14, 16, 18, 20, 2 in which Cu, Ni, Mo are added beyond the scope of the present invention
Nos. 2 and 24 are steels according to the present invention having a decrease in internal hardness of I-1.
1,13,15,17,19,21,23 is almost equivalent and ineffective, and it was confirmed that martensite, which is a starting point of damage on the surface layer, becomes a mixed structure of martensite and bainite. It was

I-25 and 26 are for comparing the effects of Mn, and I-25 whose Mn content is within the range of the present invention has a surface layer hardness of Hv379, which satisfies the claims, and has an internal hardness of Is small and the wear reduction ratio is 1.37, which is an appropriate value, whereas I-26 has a high Mn, so that martensite is generated in the surface layer and the surface layer is significantly hardened.

I-27 and 28 were compared with each other for the influence of C. I-27 in which the amount of C was within the range of the present invention, the surface layer structure and the surface hardness were within the range of the present invention, and the wear loss was reduced. While the ratio is also an appropriate value, I-28 has a high C content, so that martensite is generated in the surface layer and the surface layer hardness is significantly high.

I-29 and 30 compare the effects of Nb and Ti in the case of containing all alloy elements in the present invention. Even if Nb and Ti are added in an amount equal to or more than the amount specified in the present invention, the internal hardness is not different from that of the steel of the present invention, and the effect is saturated with a large addition.

[0065]

As described above, according to the present invention,
The head has a uniform bainite structure with a specific composition, and the hardness is 2 at Hv at both the crown and head corners.
By setting it to 40 to 390, the amount of wear is increased more than that of a normal rail, so that a rail having excellent rolling contact fatigue resistance is provided.

[Brief description of drawings]

FIG. 1 is a diagram showing an influence of a matrix structure and hardness on a wear reduction ratio.

FIG. 2 is a diagram showing the effect of C content on the hardness and thickness of a white layer.

FIG. 3 is a diagram showing the influence of a trace amount additive on the thickness of a white layer.

FIG. 4 is a diagram showing the influence of components on the hardness distribution from the top of the rail to the inside.

Claims (3)

[Claims] 1. C: 0.15 to 0.45% by weight,
Si: 0.05 to 1.0%, Mn: 0.30 to 2.5
%, P: 0.03% or less, S: 0.03% or less, Cr:
0.70 to 3.00%, V: 0.005 to 0.05%, the balance consisting of iron and unavoidable impurities, the head has a uniform bainite structure, and the hardness is the crown and head corners. A rail excellent in rolling contact fatigue damage, characterized in that it is between 240 and 390 in Hv at any position. 2. Nb: 0.005-0.01 by weight%.
%, Ti: 0.001 to 0.01% of one or two types are further contained, and the rail excellent in rolling contact fatigue damage resistance according to claim 1. 3. Cu: 0.05 to 2.0% by weight,
Ni: 0.05-2.0, Mo: 0.005-0.05
%, Further containing 1 type or 2 types or more of%, The rail excellent in rolling contact fatigue damage resistance according to claim 1 or 2.