JP2000345296A - Pearlitic rail excellent in wear resistance and resistance to internal fatigue damage, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a hardness difference in the cross section of a railhead and to improve the wear resistance and internal fatigue damage resistance of a high-load railroad rail by adding V and further N to a hyper-eutectoid steel. SOLUTION: The pearlitic rail excellent in resistance to wear and internal fatigue damage is a steel rail which has a composition containing, by mass, >0.85-1.20% C, 0.10-1.00% Si, 0.10-1.50% Mn, 0.01-0.20% V, and further 0.0060-0.0500% N and also containing, if necessary, Cr, Mo, Cu, Ni, Nb, Ti, Mg, Ca, and Co. In this steel rail, the region from the surface of railhead corners and a railhead to the position at a depth of at least 20 mm from the surface has a pearlitic structure. Further, the hardness of the pearlitic structure in the above region is regulated to Hv 360 to 480, and the difference in the hardness is regulated to <= Hv 40. The rail can be manufactured by applying accelerated cooling to the railhead of a high temperature steel rail.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pearlitic rail having improved abrasion resistance and internal fatigue damage resistance required for rails of heavy load railways, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Overseas heavy-load railways have been designed to increase the speed of trains and increase the weight of trains as means for increasing the efficiency of rail transportation. Such an increase in the efficiency of rail transportation implies a severer use environment for rails, and further improvements in rail materials have been required. Specifically, wear on the GC (gauge corner) and head sides of the rails laid in the curved section sharply increases, and this has become a problem in terms of the service life of the rails. Was.

However, with the recent progress in heat treatment technology for increasing the strength, a high-strength (high-hardness) rail having a fine pearlite structure using eutectoid carbon steel as shown below has been invented. The rail life of the section has been dramatically improved. Heat treatment rail for ultra-high load with a sorbite head or a fine pearlite head (Japanese Patent Publication No. 54-254)
No. 90). After rolling, or after reheating the rail head from the austenitic zone temperature to 850-500 ° C, 1-4 ° C / s
A method of manufacturing a high-strength rail of 130 kgf / mm2 or more, which is accelerated and cooled by ec (Patent No. 1597914). The characteristics of these rails are eutectoid carbon-containing steel (carbon content:
(0.7-0.8%), which is a high-strength rail exhibiting a fine pearlite structure according to the object of the present invention, in which the lamellar spacing in the pearlite structure is reduced to improve wear resistance.

[0004] However, in recent years, heavy load railways overseas have been strongly promoting the loading of cargo in order to further increase the efficiency of rail transportation, and particularly in the case of sharply curved rails, using the rails developed above. However, the wear resistance of the GC section and the head side cannot be sufficiently ensured, and the reduction of the rail life due to the wear has become a problem. Against this background, the development of rails having wear resistance higher than that of the current high-strength eutectoid carbon steel rails has been required.

[0005] In order to solve these problems, the present inventors have developed the following rails. Using hypereutectoid steel (C: more than 0.85 to 1.20%) to increase the cementite density in the lamella in the pearlite structure and to provide a rail with excellent wear resistance (JP-A-8-144).
061) Hypereutectoid steel (C: more than 0.85 to 1.20%) is used to increase the density of cementite in the lamella in the pearlite structure, and at the same time, is excellent in wear resistance by controlling hardness. Rails (JP-A-8-246100) These rails are characterized by increasing the carbon content of the steel, increasing the density of the highly wear-resistant semetite phase in the pearlite lamella, and controlling the hardness. Thereby, the wear resistance of the pearlite structure is improved.

Further, the present inventors have developed a rail as shown below using a hypereutectoid steel having a high carbon content and having improved wear resistance and internal fatigue damage resistance of the rail head. A rail improved in wear resistance and internal fatigue damage resistance by adding B to hypereutectoid steel (C: more than 0.85 to 1.20%) (Japanese Patent Application No. 8-527465). The feature of this rail is that by adding a small amount of B to hypereutectoid steel, it promotes pearlite transformation, gives a more uniform hardness distribution from the surface of the rail head to the inside, and has abrasion resistance and internal fatigue resistance of the rail. Damage was greatly improved.

[0007]

The inventive rail shown above is obtained by adding a small amount of B to hypereutectoid steel (C: more than 0.85 to 1.20%) having excellent wear resistance. It has high wear resistance and internal fatigue damage resistance, and is expected to contribute to the longevity of rails for heavy-load railways. However, depending on the composition of the steel, simply add B to the hypereutectoid steel. It was clarified that the effect of promoting pearlite transformation was not sufficiently obtained only by the addition, and that a uniform hardness distribution from the surface to the inside of the rail head could not be obtained.

[0008] In order to solve this problem, the present inventors have experimentally studied an additive element in place of B. As a result of an accelerated cooling test of the rail head using an actual rail, the V-added V-added steel to the hypereutectoid steel showed that the pearlite structure It was confirmed that carbide of V easily precipitated on the ferrite ground in the inside, and the hardness inside the rail head was improved.

Further, the present inventors have studied the elements which further improve the effect of V by the above experiment. As a result, V
In addition to the addition of N, the addition of N causes the V nitride to precipitate in addition to the V carbide precipitated in the ferrite ground in the pearlite structure of the hypereutectoid steel, and the hardness inside the rail head. Has been confirmed to be greatly improved. From the above experimental results, the present inventors have found that, instead of adding B to hypereutectoid steel, V, and further, N in addition to V, improve the hardness inside the rail head. Possible,
It has been confirmed that the wear resistance and the internal fatigue damage resistance can be simultaneously improved.

[0010] In addition, the present inventors have conducted experiments on heat treatment conditions for increasing the strength of steel rails to which V and, in addition, N in addition to V are added. As a result, an abnormal structure such as martensite is not generated in the surface of the rail head, and a pearlite structure having excellent wear resistance is stably generated. At the same time, V carbide and nitride are precipitated in the rail head. In order to improve the hardness, it was confirmed that a certain range exists in the cooling rate of the rail head surface.

From the above results, the present inventors first increased the carbon content of the rail steel and simultaneously improved the abrasion resistance and the internal fatigue damage resistance of the heavy load railway rail.
V, and further, by adding N in addition to V, V
Carbides and nitrides are stably generated, and accelerated cooling heat treatment is performed to provide a uniform high hardness distribution from the surface of the rail head to the inside. It was found that high-strength rails could be manufactured.

That is, an object of the present invention is to improve the abrasion resistance required for rails of heavy load railways, and at the same time, to stably improve the resistance to internal fatigue damage and the production of pearlitic rails. It is about the law.

[0013]

The present invention achieves the above object, and the gist thereof is as follows. (1) In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.02 to 0.20 , Cr: 0.05 to 1.00%, Mo: 0.01 to 0.20%, Cu: 0.05 to 0.50%, Ni: 0.05 1.00%, Nb: 0.002 to 0.050%, Ti: 0.0050 to 0.0300%, Mg: 0.0010 to 0.0100%, Ca: 0.0010 to 0.0150%, A pearlite-based rail excellent in wear resistance and internal fatigue damage resistance, wherein one or more of Co: 0.10 to 2.00% is contained, and the balance is Fe and unavoidable impurities. . (2) In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.02 to 0.20 %, N: 0.0060 to 0.0500%, and if necessary, Cr: 0.05 to 1.00%, Mo: 0.01 to 0.20%, Cu: 0.05 to 0.50%, Ni: 0.05 to 1.00%, Nb: 0.002 to 0.050%, Ti: 0.0050 to 0.0300%, Mg: 0.0010 to 0.0100%, Ca : 0.0010 to 0.0150%, Co: 0.10 to 2.00%, the balance being Fe and unavoidable impurities. A pearlitic rail with excellent internal fatigue damage. (3) A rail having the component according to (1) or (2), wherein the steel rail has a hardness Hv of 360 to 480 in a range of at least 20 mm in depth starting from a head corner portion and a top surface. A pearlitic rail excellent in abrasion resistance and internal fatigue damage resistance characterized by having a pearlite structure within a range and a hardness difference of Hv 40 or less. (4) A steel rail head having a temperature of Ar1 point or more as hot-rolled, or a steel heated to a temperature of Ac1 point + 30 ° C or more for the purpose of heat treatment, comprising the component described in (1) or (2) above. Raise the rail head from austenite temperature to 1
Accelerated cooling was performed at a cooling rate of 15 ° C./sec. When the temperature of the head of the steel rail reached 650 to 450 ° C., accelerated cooling was stopped. At least 20 mm depth starting from the top surface
Is a pearlite structure having a hardness in the range of Hv 360 to 480 and a difference in hardness of Hv 40 or less, the pearlitic rail having excellent wear resistance and internal fatigue damage resistance. Production method.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In Claims 1 to 12, the reasons for limiting the chemical component, or the range and hardness of the chemical component and the pearlite structure, and the difference in hardness of the pearlite structure as described in the above claims will be described in detail.

(1) Chemical Composition of Rail Steel First, the reason for limiting the chemical composition of the rail in the present invention as described above will be described. C is an effective element that promotes pearlite transformation and secures abrasion resistance. As a normal rail steel, the C content is 0.60 to 0.85.
However, if the C content is 0.85% or less, the density of the cementite phase in the pearlite structure for improving the wear resistance cannot be ensured, and furthermore, the starting point of the fatigue damage inside the rail head is reduced. Grain boundary ferrite is likely to be generated, and the rail life is shortened. If the C content exceeds 1.20%, depending on the component system, a pro-eutectoid cementite structure is generated in the pearlite structure, and the toughness and ductility of the rail are greatly reduced, and the density of the cementite phase in the pearlite structure is reduced. Is increased, and the ductility required for the rail cannot be sufficiently secured. Therefore, the C content is limited to more than 0.85 to 1.20%.

Si is an element that increases the hardness (strength) of the rail head by solid solution hardening into the ferrite phase in the pearlite structure, but if its content is less than 0.10%, its effect cannot be expected sufficiently. If it exceeds 1.00%, a large number of surface flaws are generated during hot rolling, and the weldability is reduced due to the formation of oxides.
%.

Mn lowers the pearlite transformation temperature,
It is an element that contributes to high strength by improving hardenability and further suppresses the formation of a proeutectoid cementite structure. However, its effect is small when the content is less than 0.10%,
It is difficult to secure the required hardness of the rail head. If the content exceeds 1.50%, the hardenability is remarkably increased, a martensite structure is easily formed, segregation is promoted, and a pro-eutectoid cementite structure harmful to rail toughness is formed in the segregated portion. Mn amount is 0.10 to 1.5
Limited to 0%.

In the heat treatment of the rail head, V forms carbides and nitrides inside the rail head, which has a lower cooling rate than the rail head surface part, and precipitates on the ferrite ground in the pearlite structure. Although it is an element for improving the hardness inside the portion, if it is less than 0.01%, it becomes difficult to form a nitride or a nitride, and it becomes difficult to precipitate and harden a pearlite structure inside the rail head. Further, even if it is added in excess of 0.20%, no further effect can be expected, and the addition amount of N, which is a chemical equivalent to form V nitride, is 0.05%.
When V exceeds 00%, internal defects such as blowholes, which are the starting points of internal fatigue damage, are likely to occur during the smelting of molten steel. Therefore, the V amount is limited to 0.01 to 0.20%.

In some cases, N is further contained to enhance the effect of V by a synergistic effect. Therefore, it is added as necessary.
N is an element that combines with V to form a nitride of V and precipitates on ferrite ground in the pearlite structure, thereby further improving the hardness inside the rail head having a relatively slow cooling rate. If it is less than 0.0060%, it becomes difficult to form a nitride of V. On the other hand, if the content exceeds 0.0500%, internal defects such as blowholes, which are a starting point of internal fatigue damage, are likely to occur during the smelting of molten steel.
Limited to 60-0.0500%. In order to stably generate nitrides of V and to suppress the occurrence of internal defects such as blowholes in order to increase the hardness inside the rail, the amount of N added should be 0.0100-0. It is desirable to be in the range of 0200%.

The rails manufactured with the above-described composition have strength, ductility, toughness, and Cr, Mo, Cu, Ni, Nb, Ti, M for the purpose of preventing material deterioration during welding.
g, Ca, and Co elements may be used alone or as necessary.
Add seed or more. Here, Cr and Mo are mainly used for enhancing strength and abrasion resistance, Ni, Nb and Ti are mainly used for improving ductility and toughness and strength, Cu and Co are used for improving strength, and Mg and Ca are mainly used for improving ductility and toughness. Add for purpose.

Cr is an element that raises the equilibrium transformation point of pearlite and consequently refines the pearlite structure to contribute to high strength, and at the same time, enhances the wear resistance by strengthening the cementite phase in the pearlite structure. However, when the content is less than 0.05%, the effect is small.
%, The amount of Cr is limited to 0.05 to 1.00% in order to generate a large amount of martensite structure and reduce the toughness of the rail.

Mo is an element which raises the equilibrium transformation point of pearlite like Cr and consequently makes the pearlite structure finer, thereby contributing to higher strength and improving wear resistance, but less than 0.01%. The effect is small.
Excessive addition exceeding 20% promotes segregation,
Further, the pearlite transformation rate decreases, a martensite structure is generated in the segregated part, and the toughness of the rail decreases,
The amount of Mo was limited to 0.01 to 0.20%.

Cu is an element which improves the strength without impairing the toughness of the pearlite steel, and its effect is 0.05 to 0.1.
The largest amount is in the range of 50%, and if it exceeds 0.50%, red heat embrittlement is likely to occur.
Limited to 5 to 0.50%.

Ni is an element that improves the ductility and toughness of the pearlite steel and, at the same time, enhances the strength of the pearlite steel by solid solution strengthening. Even if excessive addition exceeding 0.000% is performed, no further effect can be expected. Therefore, N
The i amount was limited to 0.05 to 1.00%.

Like V, Nb increases the strength by precipitation hardening with Nb carbide and Nb nitride, and further suppresses the growth of crystal grains during heat treatment at a high temperature to reduce austenite grains. The effect of suppressing austenite grain growth acts up to a temperature range higher than V (around 1200 ° C.), and improves the ductility and toughness of the pearlite structure. The effect cannot be expected if it is less than 0.002%, and no further effect can be expected even if an excessive addition exceeding 0.050% is performed. Therefore, the Nb content is set to 0.002
Limited to ~ 0.050%.

In the reheating at the time of rail rolling, Ti
Utilizing the fact that precipitated Ti carbides and Ti nitrides do not dissolve, it is an effective component for refining austenite crystal grains during rolling and heating and improving ductility and toughness of pearlite structure. However, if the content is less than 0.0050%, the effect is small, and if it is added more than 0.0300%, coarse Ti carbides and Ti nitrides are generated, which becomes a starting point of fatigue damage during use of the rail and cracks are generated. Ti
The amount was limited to 0.0050-0.0300%.

Mg combines with O or S or Al to form a fine oxide, and suppresses the growth of crystal grains and refines austenite grains during reheating during rail rolling. Is an element effective for improving the ductility and toughness of the pearlite structure. Further, MgO and MgS are replaced with MnS
Is dispersed finely, and a thin band of Mn is formed around MnS, thereby contributing to the generation of pearlite transformation. As a result, by reducing the size of the pearlite block, it is possible to improve the ductility and toughness of the pearlite structure. It is an effective element. However, if less than 0.0010%, the effect is weak,
When added in excess of 0.0100%, a coarse oxide of Mg is formed to deteriorate the ductility and toughness of the rail. Therefore, the amount of Mg is limited to 0.0010 to 0.0100%.

Ca has a strong bonding force with S and forms a sulfide as CaS. Further, CaS finely disperses MnS, forms a thin band of Mn around MnS, and forms pearlite transformation. It contributes, and as a result, is an element effective for improving the ductility and toughness of the pearlite structure by reducing the pearlite block size. But,
If less than 0.0010%, the effect is weak, and 0.0150
%, A coarse oxide of Ca is formed to deteriorate the ductility and toughness of the rail.
It was limited to ~ 0.0150%.

Co is an element that increases the transformation energy of pearlite to improve the strength by making the pearlite structure finer, but its effect cannot be expected if it is less than 0.10%. %, The effect reaches the saturation region even if an excessive addition exceeds
The amount was limited to 0.10-2.00%.

The rail steel having the above-described composition is melted in a commonly used melting furnace such as a converter or an electric furnace, and the molten steel is subjected to an ingot-bulking method or a continuous casting method.
Further, it is manufactured as a rail through hot rolling. next,
By applying heat treatment to this hot-rolled rail that holds high-temperature heat or to the rail head that has been reheated to a high temperature for the purpose of heat treatment, a pearlite structure with high hardness is generated stably on the rail head. It is possible to do.

(2) Desirable hardness of pearlite structure and its range First, the desired hardness of pearlite structure is defined as Hv360.
The reason for limiting the range to 480 will be described. If the hardness of this component system is less than Hv360, the wear of the rails progresses, making it difficult to secure the wear resistance required for heavy load railways. Fatigue cracks tend to occur from inside the part. Further, if the hardness exceeds Hv480, the conformability of the rail head surface with the wheels is reduced, and surface damage is likely to occur. In addition, bainite, martensite, etc. The hardness was limited to the range of Hv 360 to 480 in order to generate an abnormal structure of No. and reduce the wear resistance and the internal fatigue damage resistance of the rail.

Next, the reason why the desirable range of the pearlite structure in the range of hardness Hv of 360 to 480 is limited to the range of 20 mm in depth starting from the head surface at the head corner and the crown. If less than 20mm,
This is because the wear resistance and the resistance to internal fatigue damage required for the rail head are small, and a sufficient life improvement effect cannot be obtained due to the progress of wear and the occurrence of internal fatigue damage. It is more desirable that the range in which the pearlite structure is present is 30 mm or more in depth starting from the head surface at the corner of the head and the top of the head.

Here, FIG. 1 shows the names of the rails of the present invention, which are excellent in wear resistance and internal fatigue damage resistance, at the surface position of the cross section of the head and the regions where the wear resistance is required. In the rail head, 1 is a crown, 2 is a head corner, and one of the head corners 2 is a gauge corner (GC) that mainly contacts the wheel. Moreover, hardness Hv360-480
If the pearlite structure in the range is arranged at least in the hatched portion in the figure, the service life of the rail can be improved.

(3) Desirable difference in hardness of pearlite structure Lastly, the reason why the maximum value of the difference in hardness between desirable pearlite structures in a depth range of 20 mm is limited to Hv40 or less will be described. In the rail head, since the cooling rate differs depending on each part of the cross section, the hardness generally shows a distribution that decreases from the front of the rail head to the inside of the head. When the hardness difference between the rail head surface and the inside of the head exceeds Hv40,
In the cross section of the rail head, the change in material strength becomes remarkably large, and with this, the strain (plastic deformation region) generated from the external force acting on the rail concentrates on the low hardness (strength) part inside the rail head, As a result, internal fatigue damage occurs and rail life is shortened.
Limited to v40 or less.

(4) Manufacturing Conditions In the manufacturing method of the present invention, the reason why the heating and cooling conditions at the time of manufacturing the rail are limited as described above will be described in detail. First, the temperature condition before cooling the rail head is necessary. At least the rail head must be sufficiently austenitized in order to obtain a predetermined structure and hardness. The temperature is Ar at the head of the rail immediately after rolling.
The temperature range is one or more points, and the temperature of the reheated rail head is higher than the Ac point + 30 ° C. The upper limit of the temperature is not particularly defined, but if the temperature is too high, a liquid phase appears and the austenite phase becomes unstable, so that the upper limit of the temperature is substantially 1350 ° C.

Here, the above-mentioned "rail head" refers to the one shown in FIG.
Are included including the rail top part (reference number: 1) and the head corner part (reference number: 2). The cooling rate and temperature described below are set at the top of the rail shown in FIG.
1) and at a depth of 2 to 5 mm from the head surface of the head corner (reference number: 2), at least a range of the rail head at a depth of 20 mm (shaded portion in FIG. 2) is represented. At least the above-mentioned portions (shaded portions in FIG. 2)
It is possible to control the structure and hardness of the steel.

Next, in the method of accelerated cooling the rail head from the austenitic zone temperature to 650 to 450 ° C. at a cooling rate of 1 to 15 ° C./sec, the reason why the accelerated cooling stop temperature is limited as described above. Will be described. 650 ° C
When accelerated cooling is stopped at a temperature higher than the above, pearlite transformation starts immediately after accelerated cooling, many pearlite structures with low hardness are generated, the hardness of the rail head becomes less than Hv360, and wear resistance and internal fatigue damage resistance Cannot be secured,
It was limited to 650 ° C or lower. Also, if accelerated cooling to less than 450 ° C, sufficient heat regain from the inside of the rail cannot be expected after accelerated cooling, and martensite which is harmful to the toughness of the rail and the resistance to internal fatigue damage at segregated parts inside the rail head, etc. The temperature was limited to 450 ° C. or higher because a site structure was generated.

The acceleration cooling rate of the rail head is 1 ° C. /
When the temperature is less than sec, pearlite transformation starts in a high temperature range during accelerated cooling, a large number of pearlite structures having low hardness are generated, the hardness of the rail head becomes less than Hv360, and the abrasion resistance and resistance of the rail head are reduced. 1 ° C / sec because it is difficult to secure internal fatigue damage and a proeutectoid cementite structure harmful to the toughness and ductility of the rail is generated depending on the component system.
Limited to the above. When the accelerated cooling rate exceeds 15 ° C / sec, abnormal structures such as bainite and martesite are formed on the rail head without accelerated pearlite transformation during accelerated cooling, and the wear resistance and internal fatigue damage resistance are reduced. For this purpose, the accelerated cooling rate was limited to the range of 1 to 15 ° C./sec. In order to stably generate a pearlite structure having a high hardness up to the inside of the rail head, it is most preferable that the accelerated cooling rate be in the range of 5 to 10 ° C./sec.

This accelerated cooling rate range limits the average cooling rate from the start to the end of cooling, but during the accelerated cooling, heat is generated due to pearlite transformation and temporary temperature rise due to spontaneous reheating from inside the rail. May occur. However, as long as the average cooling rate from the start to the end of accelerated cooling is within the above range, the characteristics of the perlite rail are not significantly affected. It also includes a decrease in cooling rate due to a significant temperature rise.

As a method for obtaining a cooling rate of 1 to 15 ° C./sec, it is possible to obtain a predetermined cooling rate by using a cooling medium mainly composed of air, air, and mist, and a combination thereof.

Therefore, in order to manufacture a rail having a pearlite structure of Hv 360 or more and excellent in abrasion resistance and internal fatigue damage resistance, the formation of a pearlite structure having a low hardness at the rail head surface is prevented. To prevent the formation of proeutectoid cementite, martensite, and bainite structures that are harmful to abrasion resistance, ductility, toughness, and internal fatigue damage resistance, use air or a refrigerant mainly containing air and mist etc. Accelerated cooling at a cooling rate of 1 to 15 ° C./sec,
By stopping the accelerated cooling when the temperature of the steel rail top reaches 650 to 450 ° C., it becomes possible to stably generate a pearlite structure having high hardness from the rail head to the inside.

<Subsequent Explanation of Cooling> It is preferable that cooling after accelerated cooling is not performed forcibly, but is allowed to cool until natural pearlite transformation is completed, that is, natural cooling. When the rail is forcibly cooled to improve productivity, it is desirable to perform cooling after the pearlite transformation is completed in order to prevent the formation of a structure such as a martensite structure that reduces the toughness of the rail. . In this component system, the temperature at which the pearlite transformation of the entire rail head is almost completed is a state where the temperature of the rail head surface is cooled to less than 350 ° C.

The metal structure of the rail is preferably a pearlite structure, but depending on the component system, the accelerated cooling rate and the segregation state of the material, a small amount of a proeutectoid ferrite structure or a proeutectoid cementite structure may be formed in the pearlite structure. Sometimes. However, even if these structures are formed in trace amounts in the pearlite structure, they do not significantly affect the wear resistance, ductility, toughness, internal fatigue damage resistance and strength of the rail. Contains a small amount of pro-eutectoid ferrite structure and pro-eutectoid cementite structure.

[0044]

Next, an embodiment of the present invention will be described. Table 1 shows the chemical composition of the rail steel of the present invention, the conditions for accelerated cooling of the head, the hardness of the shaft center of the rail head, and the microstructure of the head. Table 1 also shows the wear amount after 700,000 repetitions of the Nishihara-type wear test under the forced cooling condition shown in FIG. 2 and the rolling fatigue test result shown in FIG.

[0045]

[Table 1]

Table 2 shows the chemical composition of the comparative rail steel, the conditions for accelerated cooling of the head, the hardness of the axial center of the rail head, and the microstructure of the head. Table 1 also shows the wear amount after 700,000 repetitions of the Nishihara-type wear test under the forced cooling condition shown in FIG. 2 and the rolling fatigue test result shown in FIG.

[0047]

[Table 2]

FIG. 4 shows the rail steel of the present invention shown in Table 1 and Table 2.
5 shows a comparison of the wear test results of the comparative rail steel (eutectoid carbon-containing steel) shown in FIG. FIG.
6 and 7 are examples of the head section hardness distribution of the rail steel of the present invention (reference C, reference D, reference E). 8 and 9 show examples of the hardness distribution of the head section of the comparative rail steel (reference R, reference S).

In FIG. 2, 3 is a rail test piece, 4 is a mating material, and 5 is a cooling nozzle. Also, in FIG.
Reference numeral 6 denotes a rail moving slider, on which a rail 7 is mounted.
Is installed. Reference numeral 10 denotes a load-loading device that controls the left-right movement and load of the wheel 8 rotated by the motor 9. In the test, wheels 8 roll on rails 7 moving left and right.

The configuration of the rail is as follows.・ Rail steel of the present invention (12 pieces) Symbols A to L In the above component ranges, at least a range from the rail head surface to a depth of 20 mm from the rail head surface as a starting point exhibits a pearlite structure, and pearlite in the above range. A pearlitic rail having excellent wear resistance and internal fatigue damage resistance, wherein the hardness of the tissue is Hv360 or more and the difference in hardness is Hv40 or less. -Comparative rail steel (11 pieces) Symbols M to O: Comparative rail steels (3 pieces) made of eutectoid carbon-containing steel whose chemical components are out of the above-mentioned claims. Symbols P to S: Comparative rail steels (four) made of hypereutectoid carbon-containing steel whose chemical components are outside the above-mentioned claims. Symbols T to W: Comparative rail steel (four) made of hypereutectoid carbon-containing steel whose production conditions are outside the above-described claims.

The wear test conditions were as follows. Testing machine: Nishihara-type abrasion tester Specimen shape: disk-shaped specimen (outer diameter: 30 mm, thickness: 8 m)
m) Test load: 686N Sliding rate: 20% Counterpart material: Pearlite steel (Hv390) Atmosphere: Air cooling: Forced cooling with compressed air (flow rate: 100N)
1 / min) Number of repetitions: 700,000 times

The conditions for the rolling fatigue test were as follows. Test machine: Rolling fatigue tester Test piece shape Rail: 136 pound rail x 2m Wheel: AAR type (diameter 920mm) Radial load: 147000N Thrust load: 9800N Lubrication: Dry + oil (intermittent lubrication)

As shown in FIG. 5, the rail steel of the present invention has a smaller amount of wear at the same hardness by increasing the carbon content as compared with the comparative rail steel, and the wear resistance is greatly improved.

As shown in FIG. 6, in the rail steel of the present invention (reference C), the addition amount of V is controlled within an appropriate range.
Compared with the comparative rail steel (reference R, reference S) shown in FIGS. 9 and 10, the difference in hardness between the rail head surface and the inside is reduced, and the occurrence of internal fatigue damage can be prevented as shown in Table 1.

Further, by adding N in addition to V, the rail steel of the present invention (reference D) can be obtained as shown in FIG.
Compared with the rail steel of the present invention (symbol C), the hardness difference between the rail surface and the inside is reduced.

Further, the addition amount of N is set to 0.0100 to 0.1.
By controlling within the range of 0200%, the rail steel of the present invention (symbol E) is compared with the rail steel of the present invention (symbol C) as shown in FIG. The difference in hardness between the rail surface and the inside is reduced, and the resistance to internal fatigue damage is further improved.

As shown in Tables 1 and 2, by forming the chemical components within an appropriate range and selecting an appropriate heat treatment condition, a proeutectoid cementite structure and a martensite structure which are harmful to the toughness and wear resistance of the rail are formed. Without this, it is possible to stably generate a pearlite structure having a high hardness up to the inside of the rail head.

[0058]

As described above, according to the present invention, it is possible to provide a rail with excellent wear resistance and internal fatigue damage resistance for heavy load railways.

[Brief description of the drawings]

FIG. 1 is a diagram showing the rail head cross-sectional surface position and Hv37.
The figure which showed the required range of 0 or more perlite structure.

FIG. 2 is a schematic diagram of a Nishihara type abrasion tester.

FIG. 3 is a schematic diagram of a rolling fatigue tester.

FIG. 4 is a diagram comparing the wear test results of the rail steel of the present invention and a comparative rail steel in relation to hardness and wear amount.

FIG. 5 is a diagram showing a head section hardness distribution of the rail steel (symbol C) of the present invention.

FIG. 6 is a diagram showing a head section hardness distribution of the rail steel (symbol D) of the present invention.

FIG. 7 is a diagram showing a head section hardness distribution of the rail steel (symbol E) of the present invention.

FIG. 8 is a diagram showing a head section hardness distribution of a comparative rail steel (symbol R).

FIG. 9 is a diagram showing a head section hardness distribution of a comparative rail steel (symbol S).

[Brief description of reference numerals]

 1: top part, 2: head corner part, 3: rail test piece, 4: mating material, 5: cooling nozzle, 6: rail moving slider, 7: rail, 8: wheel, 9: motor, 10: Loading device

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4K032 AA00 AA06 AA07 AA08 AA09 AA10 AA11 AA14 AA16 AA19 AA21 AA22 AA23 AA31 AA35 AA36 BA00 CD02 CD03 CD05 4K042 AA04 BA03 BA04 CA03 CA04 CA05 CA05 CA05 CA05 CA05 CA05 CA05 CA06 DF01

Claims (12)

[Claims] 1. Mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0 A pearlite-type rail excellent in wear resistance and internal fatigue damage resistance, characterized by containing 20% by weight and the balance being Fe and inevitable impurities. 2. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.02 to 0 20%, Cr: 0.05 to 1.00%, Mo: 0.01 to 0.20%, Cu: 0.05 to 0.50%, Ni: 0.05 to 1 0.000%, Nb: 0.002 to 0.050%, Ti: 0.0050 to 0.0300%, Mg: 0.0010 to 0.0100%, Ca: 0.0010 to 0.0150%, Co: A pearlite-based rail excellent in wear resistance and internal fatigue damage resistance, characterized in that it contains 0.10 to 2.00% of one or more kinds, and the balance consists of Fe and inevitable impurities. 3. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0% 20% with the balance being Fe and unavoidable impurities, wherein at least a range of at least 20 mm in depth starting from the head corner and top surface of the steel rail,
A pearlitic rail excellent in wear resistance and internal fatigue damage resistance, having a pearlite structure having a hardness in the range of Hv 360 to 480 and a difference in hardness of Hv 40 or less. 4. Mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0 .20%, Cr: 0.05-1.00%, Mo: 0.01-0.20%, Cu: 0.05-0.50%, Ni: 0.05-1. 00%, Nb: 0.002 to 0.050%, Ti: 0.0050 to 0.0300%, Mg: 0.0010 to 0.0100%, Ca: 0.0010 to 0.0150%, Co: 0 0.10 to 2.00%, the balance being Fe and unavoidable impurities, wherein the steel rail has at least a depth starting from the top corner and top surface. The range of 20 mm is in the range of hardness Hv360 to 480, and the difference in hardness is Hv4. Abrasion resistance, characterized in that the at which pearlite structure below 耐内 unit fatigue resistance superior pearlitic rails. 5. Mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0% 20%, N: 0.0060 to 0.0500%, the balance being Fe and unavoidable impurities, the pearlite-based rail having excellent wear resistance and internal fatigue damage resistance. 6. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0 .20%, N: 0.0060-0.0500%, Cr: 0.05-1.00%, Mo: 0.01-0.20%, Cu: 0.05-0. 50%, Ni: 0.05 to 1.00%, Nb: 0.002 to 0.050%, Ti: 0.0050 to 0.0300%, Mg: 0.0010 to 0.0100%, Ca: 0 0.10 to 0.0150%, Co: 0.10 to 2.00%, the balance being Fe and unavoidable impurities, the balance being wear resistance and internal fatigue resistance. Pearlitic rail with excellent damageability. 7. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0% .20%, N: 0.0060 to 0.0500%, with the balance being Fe and unavoidable impurities, wherein the steel rail has at least a depth starting from the top corner and top surface. The range of 20mm
A pearlitic rail excellent in wear resistance and internal fatigue damage resistance, having a pearlite structure having a hardness in the range of Hv 360 to 480 and a difference in hardness of Hv 40 or less. 8. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0 .20%, N: 0.0060-0.0500%, Cr: 0.05-1.00%, Mo: 0.01-0.20%, Cu: 0.05-0. 50%, Ni: 0.05 to 1.00%, Nb: 0.002 to 0.050%, Ti: 0.0050 to 0.0300%, Mg: 0.0010 to 0.0100%, Ca: 0 0.0010 to 0.0150%, Co: 0.10 to 2.00%, and a balance comprising Fe and unavoidable impurities, and a head corner of the steel rail. Part and at least a range of a depth of 20 mm starting from the top surface of the head are hardness Hv360-480. A pearlitic rail excellent in abrasion resistance and internal fatigue damage resistance characterized by having a pearlite structure within a range and a hardness difference of Hv 40 or less. 9. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0 .20%, with the balance being Fe and unavoidable impurities,
The steel rail head at the temperature of Ar1 point or more as hot rolled or the steel rail head heated to the temperature of Ac1 point + 30 ° C or more for the purpose of heat treatment is cooled from the austenite region temperature by 1 to 15 ° C / sec. Accelerated cooling at a speed, stop the accelerated cooling when the temperature of the head of the steel rail reaches 650-450 ° C., then allow it to cool down, starting from the head corner and top surface of the steel rail At least depth 2
A pearlite rail excellent in wear resistance and internal fatigue damage resistance characterized by having a pearlite structure having a hardness of Hv 360 to 480 in a range of 0 mm and a hardness difference of Hv 40 or less. Manufacturing method. 10. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.02 to 0% .20%, Cr: 0.05-1.00%, Mo: 0.01-0.20%, Cu: 0.05-0.50%, Ni: 0.05-1. 00%, Nb: 0.002 to 0.050%, Ti: 0.0050 to 0.0300%, Mg: 0.0010 to 0.0100%, Ca: 0.0010 to 0.0150%, Co: 0 0.10 to 2.00%, the balance being Fe and unavoidable impurities, the hot-rolled steel rail head at the temperature of Ar1 point or higher, or Ac1 for heat treatment. The temperature of the steel rail head heated to a temperature of + 30 ° C or higher is increased by 1 to 1 from the austenite region temperature. ° C. / accelerated cooling at a sec cooling rate of the temperature of the head of the steel rail 650-450
° C, accelerated cooling is stopped, and then the steel rail is allowed to cool. At least a range of a depth of 20 mm starting from the head corner and the top surface of the steel rail has a hardness Hv360 to Hv360.
Abrasion resistance characterized by having a pearlite structure in a range of 480 and a hardness difference of Hv 40 or less,
A method for manufacturing pearlitic rails with excellent resistance to internal fatigue damage. 11. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0% .20%, N: 0.0060 to 0.0500%, the balance being Fe and unavoidable impurities,
The steel rail head at the temperature of Ar1 point or more as hot rolled or the steel rail head heated to the temperature of Ac1 point + 30 ° C or more for the purpose of heat treatment is cooled from the austenite region temperature by 1 to 15 ° C / sec. Accelerated cooling at a speed, stop the accelerated cooling when the temperature of the head of the steel rail reaches 650-450 ° C., then allow it to cool down, starting from the head corner and top surface of the steel rail At least depth 2
A pearlite rail excellent in wear resistance and internal fatigue damage resistance characterized by having a pearlite structure having a hardness of Hv 360 to 480 in a range of 0 mm and a hardness difference of Hv 40 or less. Manufacturing method. 12. In mass%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, V: 0.01 to 0 .20%, N: 0.0060-0.0500%, Cr: 0.05-1.00%, Mo: 0.01-0.20%, Cu: 0.05-0. 50%, Ni: 0.05 to 1.00%, Nb: 0.002 to 0.050%, Ti: 0.0050 to 0.0300%, Mg: 0.0010 to 0.0100%, Ca: 0 0.0010 to 0.0150%, Co: 0.10 to 2.00%, the balance being Fe and unavoidable impurities, the balance being at a temperature of one or more Ar as hot-rolled. Steel rail head or steel rail head heated to a temperature of more than Ac1 point + 30 ° C for heat treatment And accelerated cooling at a cooling rate of 1 to 15 ° C. / sec from the austenite zone temperature, the temperature of the head of the steel rail 650-450
° C, accelerated cooling is stopped, and then the steel rail is allowed to cool. At least a range of a depth of 20 mm starting from the head corner and the top surface of the steel rail has a hardness Hv360 to Hv360.
Abrasion resistance characterized by having a pearlite structure in a range of 480 and a hardness difference of Hv 40 or less,
A method for manufacturing pearlitic rails with excellent resistance to internal fatigue damage.