JP2000178690A - Pearlitic rail excellent in resistance to wear and internal fatigue damage, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pearlitic rail capable of improving the wear resistance of a high-load railroad rail and capable of stably improving its resistance to internal fatigue damage, and its manufacturing method. SOLUTION: The pearlitic rail, excellent in resistance to wear and internal fatigue damage, has a composition consisting of, by weight, >0.85-1.20% C, 0.10-1.00% Si, 0.10-1.50% Mn, 0.0001-0.0040% B, 0.0050-0.0300% Ti, and the balance Fe with inevitable impurities and further containing, if necessary, one or >=2 elements among Cr, Mo, V, Nb, and Co. The structure of this rail, in the region ranging from railhead surface and railhead corner surface to a position at a depth of at least 20 mm from the surface, has pearlitic structure, and the hardness of the pearlitic structure in the above region is >=Hv 370 and difference in the hardness is <=Hv 30. This rail can be manufactured by applying accelerated cooling from the austenite region after hot rolling.

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 railway transportation means severer use environment of the rail, and further improvement of the rail material is required. Specifically, in the rail laid in the curved section, G. C. (Gauge corner)
The wear of the part and the head side part rapidly increased, and it became a problem in terms of the service life of the rail.

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. A heat treatment rail for a super heavy load having a sorbite structure or a fine pearlite structure in the head (Japanese Patent Publication No. 54-25490). A method of manufacturing a high-strength rail of 130 kgf / mm ² or more in which the rail head after rolling or reheated is accelerated and cooled at a rate of 1 to 4 ° C./sec from 850 to 500 ° C. from the austenite region temperature (Japanese 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, overseas heavy-load railways have been strongly promoting the loading of cargo in order to further increase the efficiency of railway transportation. Even G. C. The abrasion resistance of the part and the head side cannot be sufficiently secured, and the reduction of the rail life due to 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.

In a conventional rail steel exhibiting a pearlite structure of an eutectoid carbon component, a method of reducing the lamella spacing in the pearlite structure and improving hardness is used in order to improve wear resistance. However, in a rail steel exhibiting a pearlite structure of an eutectoid carbon component, the current hardness is an upper limit (H
v420), and when the heat treatment cooling rate or the alloy addition amount is increased in order to improve the hardness, bainite or martensite structure is generated in the pearlite structure, which causes a problem that the wear resistance and toughness of the rail are reduced. there were.

As another solution, a method of using a material having a metal structure more excellent in wear resistance than a pearlite structure as a rail steel can be considered. However, in a rolling wear environment such as a rail and a wheel, it is conceivable. At present, no material has been found which is less expensive than the fine pearlite structure and has excellent wear resistance.

[0007] The pearlite structure of the eutectoid carbon component conventionally used as a high-strength rail steel has a layered structure of a soft ferrite phase and a plate-like hard cementite phase. The present inventors have analyzed the wear mechanism of the pearlite structure, and as a result, first, a soft ferrite phase was squeezed out by passing through the wheel, and thereafter, only a hard cementite phase was laminated just below the rolling surface, thereby ensuring wear resistance. Confirmed that.

Accordingly, the present inventors improved the hardness of the pearlite structure in order to improve the wear resistance,
By increasing the carbon content of the steel, increasing the ratio of the plate-like hard cementite phase in the pearlite structure that secures wear resistance, and increasing the density of the cementite phase immediately below the rolling surface, wear resistance is improved. It was confirmed by experiments that the dramatic improvement was achieved, and the following rail was developed. A rail in which the carbon content is increased to the hypereutectoid region (C content> 0.85%) to increase the cementite density and improve the wear resistance (Japanese Patent Application Laid-Open No. 8-144016). By increasing the carbon content to the hypereutectoid range (C content> 0.85%), the cementite density is increased, and at the same time, a difference in hardness is given in the cross section of the rail head, and not only wear resistance but also surface resistance Rails with improved damageability (JP-A-8-24)
No. 6101).

Further, the present inventors have developed a rail as shown below in which the wear resistance and the internal fatigue damage resistance of the rail head are improved by using hypereutectoid steel having a high carbon content. A rail improved in wear resistance and internal fatigue damage resistance by adding B to hypereutectoid steel (C content> 0.85%) (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.

[0010]

As a result of further experiments, the present inventors have found that depending on the composition of the steel and the cooling conditions during rolling, the addition of B to the hypereutectoid steel is not
It was found that the effect of promoting the pearlite transformation was not sufficiently obtained, and that a uniform hardness distribution was not obtained from the rail head surface to the inside. Then, the present inventors investigated the cause in detail, and as a result, in the steel in which a more uniform hardness distribution was obtained from the surface of the rail head to the inside, the iron was directly above the temperature range (650-700 ° C.) where pearlite transformation starts. (Fe ₂₃ (CB) ₆ ) was formed, and this was used as a transformation nucleus to promote pearlite transformation.

On the other hand, in a steel in which a uniform hardness distribution was not obtained from the surface to the inside of the rail head, the formation of iron boride (Fe ₂₃ (CB) ₆ ) was not observed.
The formation of nitride (BN) was observed. From these experimental results, the present inventors promoted the pearlite transformation, to obtain a uniform hardness distribution from the rail head surface to the inside,
It was considered necessary to suppress the formation of nitrides of B and to stably generate iron borides.

Therefore, the present inventors have studied by experiment the additive element which suppresses the formation of nitride of B and preferentially forms iron boride. As a result, by adding a small amount of Ti, excess nitrogen in the steel is precipitated as TiN, and at the same time, the precipitation of nitride of B is suppressed, and as a result, iron boride is preferentially generated. Was confirmed.

Further, the present inventors have studied a method for producing a rail for stably producing these iron borides and obtaining a pearlite structure having high hardness from the surface of the rail head to the inside of the head. As a result, it was confirmed that stable high strength of the rail head could be achieved by accelerating and cooling the head of the steel rail holding high-temperature heat in a certain temperature range from the austenitic temperature range. .

As a result of these investigations, as shown in FIG. 1, iron borides are stably formed by optimizing the added elements and the cooling rate during the production, and the pearlite nose is formed with the promotion of the pearlite transformation. It was confirmed that the difference in the pearlite transformation temperature with respect to the cooling rate was reduced due to the movement to the higher temperature side, and a more uniform hardness distribution was obtained stably from the rail head surface to the inside.

From the above results, the present inventors first increased the carbon content of the rail steel and simultaneously improved the wear resistance and the internal fatigue damage resistance of the heavy-load railway rail.
Addition of B and Ti to stably generate iron boride, accelerated pearlite transformation by accelerated cooling, uniform wear distribution from rail head surface to inside and wear resistance and internal fatigue damage resistance It was found that a high-strength rail excellent in quality can be manufactured.

That is, an object of the present invention is to provide a pearlitic rail capable of improving the abrasion resistance required for rails of heavy load railways and stably improving the resistance to internal fatigue damage, and a method of manufacturing the same. To provide.

[0017]

Means for Solving the Problems In order to achieve the above object, the present invention has the following features. That is, (1)
By weight%, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, B: 0.0001 to 0.0040%, Ti : 0.0050 to 0.0300%, and if necessary, Cr: 0.05 to 1.00%, Mo: 0.01 to 0.20%, V: 0.01 to 0.20% , Nb: 0.002 to 0.050%, Co: 0.10 to 2.00%, and the balance is Fe and unavoidable impurities. (2) A rail having the above-mentioned components, wherein at least a range of a depth of at least 20 mm starting from the head corner and top surface of the rail exhibits a pearlite structure. Hardness of pearlite structure is H
abrasion resistance characterized by having a pearlite structure having a hardness difference of not less than v370 and a hardness difference of not more than Hv30,
A pearlitic rail with excellent internal fatigue damage resistance,
(3) Furthermore, Ar as hot-rolled comprising the above components
Accelerated cooling of a steel rail head at a temperature of ₁ point or more or a steel rail head heated to a temperature of ₁ point + 30 ° C or more for the purpose of heat treatment at a cooling rate of 1 to 15 ° C / sec from the austenite region temperature And the temperature of the steel rail head is 65
When the temperature reaches 0 to 450 ° C., the accelerated cooling is stopped, and then the steel rail is allowed to cool. At least a range of a depth of 20 mm from the head corner portion and the top surface of the steel rail exhibits a pearlite structure, Hardness of pearlite structure is H
abrasion resistance characterized by having a pearlite structure having a hardness difference of not less than v370 and a hardness difference of not more than Hv30,
This is a method for manufacturing a pearlite-based rail with excellent resistance to internal fatigue damage.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the present invention, the reasons for defining the difference in hardness between the pearlite structure and the chemical component, the range and hardness of the pearlite structure will be described.

(1) Chemical Components of Rail First, the reasons for limiting the chemical components 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 becomes easy to form,
Rail life decreases. If the C content exceeds 1.20%, depending on the component system, a pro-eutectoid cementite structure is formed 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. However, if it is less than 0.10%, its effect cannot be expected sufficiently. , More than 1.00%, since many surface flaws are generated at the time of hot rolling and weldability is reduced due to generation of oxides, the Si content is set to 0.10 to 1.0%.
Limited to 0%.

Mn lowers the pearlite transformation temperature,
It is an element that contributes to high strength by enhancing hardenability and further suppresses the formation of a proeutectoid cementite structure. However, its effect is small at a content of less than 0.10%, and it is required for the rail head. It is difficult to secure sufficient hardness. Further, when the content exceeds 1.50%, the burntability increases remarkably,
Since a martensitic structure is easily generated, segregation is promoted, and a pro-eutectoid cementite structure harmful to rail toughness is easily generated in a segregated portion.
Limited to 1.50%.

B is iron boride (Fe ₂₃ (C
B) Forming ₆ ) and promoting pearlite transformation,
As a result, it is an element that reduces the cooling rate dependence of the pearlite transformation temperature and imparts a more uniform hardness distribution from the rail head surface to the inside, but its effect is not sufficient with a content of less than 0.0001%, Further, if it is added in excess of 0.0040%, coarse iron borides are formed, which leads to a decrease in ductility and toughness.
It was limited to 0.0040%. Since B is easily segregated in steel and easily combined with excessive nitrogen in steel, depending on the composition of the steel, even a small amount of B can stably form iron borides. It may be difficult to do. Therefore, in order to stably generate iron borides, the B content is more preferably in the range of 0.0005 to 0.0040%.

[0023] Ti is formed by converting excess nitrogen in steel into nitride (Ti
N), and at the same time, precipitation of nitride (BN) of B
Outflow, and as a result, the iron boride (Fe_{twenty three}(C
B) ₆) Is preferentially produced, but 0.00
With a content of less than 50%, it is not enough to form nitrides.
And if added in excess of 0.0300%, coarse
Nitrides (TiN) and carbides (TiC)
At the same time as the ductility and toughness of
Since it is likely to be a starting point of labor damage, the Ti content is 0.0050
Limited to ~ 0.0300%.

Further, one or more of the following elements may be added to a rail manufactured with the above-mentioned composition as required for the purpose of improving strength, ductility and toughness. Cr: 0.05 to 1.00%, Mo: 0.01 to 0.20%, V: 0.01 to 0.20%, Nb: 0.002 to 0.050%, Co: 0.10 to 0.10 2.00%

Next, the reasons for defining these chemical components as described above will be described. 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, If it is less than 0.05%, the effect is small, and if it is excessively added exceeding 1.00%, a large amount of martensite structure is generated and the toughness of the rail is reduced. Limited to 00%.

Mo is an element that, like Cr, raises the equilibrium transformation point of pearlite and consequently refines the pearlite structure, thereby contributing to higher strength and improving wear resistance. Below, the effect is small,
If an excessive addition exceeding 0.20% is performed, segregation is promoted, the pearlite transformation rate is reduced, a martensite structure is generated in the segregated portion, and the toughness of the rail is reduced. It was limited to 01 to 0.20%.

V is V generated in a cooling process during hot rolling.
Carbide, increase the strength by precipitation hardening by V-nitride, furthermore, by performing the heat treatment of heating to a high temperature, by suppressing the growth of crystal grains, to refine the austenite grains, the strength of pearlite structure, ductility and Although it is an effective component for improving toughness, if its content is less than 0.01%, its effect cannot be expected sufficiently, and if it is added more than 0.30%, no further effect can be expected. The amount of V was limited to 0.01 to 0.30%.

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, thereby reducing austenite grains. The effect of suppressing austenite grain growth is reduced in a higher temperature range than V (1200
(Approx. ° C) to improve 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 amount of Nb was limited to 0.002 to 0.050%.

Co is an element that improves the strength by increasing the transformation energy of pearlite and making the pearlite structure finer, but its effect cannot be expected if it is less than 0.10%. Even if an excessive addition exceeding 00% is performed, the effect reaches the saturation range.
The amount of Co was limited to 0.10 to 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) Hardness of pearlite structure and its range First, the reason why the hardness of pearlite structure is limited to Hv370 or more will be described. In this component system, the hardness is H
If it is less than v370, the rail wears out, making it difficult to secure the wear resistance required for heavy-load railways. In addition, for rails used in sharply curved sections, fatigue cracks occur from inside the head. Therefore, it is desirable to limit the hardness of the pearlite structure to Hv370 or more.

The upper limit of the hardness is not particularly defined. However, if the hardness is excessively increased, the surface damage resistance of the rail head tends to decrease, and the rail is harmful to the toughness such as martensite structure in the manufacture of the rail. Since a simple structure is easily generated, the upper limit of the hardness is practically about Hv500.

Next, the reason why the range of the pearlite structure having a hardness of Hv 370 or more is limited to the range of a depth of 20 mm starting from the head surface at the corner and the top of the head will be described. If the thickness is less than 20 mm, the wear resistance and internal fatigue damage resistance area required for the rail head is 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 preferable that the area exhibiting the pearlite structure has a depth of 30 mm or more starting from the surface of the head at the corners and crowns of the head as a starting point, because the life improvement effect is further increased.

FIG. 2 shows the nomenclature of the rail of the present invention having excellent wear resistance and internal fatigue damage resistance at the cross-sectional surface of the head, and the area where wear resistance is required. In the rail head shown in the figure, 1 is a crown, 2 is a corner of the head, and one of the corners of the head 2 is a gauge corner (GC) that mainly contacts the wheel. If the pearlite structure of Hv 370 or more is arranged at least in the hatched portion in the drawing, that is, at least 20 mm deep from the surface, the rail service life can be improved.

(3) Difference in hardness of pearlite structure The reason why the maximum value of the difference in hardness of the pearlite structure in a range of a depth of 20 mm is limited to Hv30 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 surface of the rail head and the inside of the head exceeds Hv30, the change in material strength in the cross section of the rail head becomes significantly large,
Along with this, the strain (plastic deformation area) generated from the external force acting on the rail causes low hardness (strength) inside the rail head.
Because of this, internal fatigue damage occurs and the life of the rail is shortened. Therefore, it is desirable to limit the maximum value of the difference in hardness to Hv30 or less.

(4) Manufacturing Conditions The reasons for limiting the temperature conditions and the respective cooling conditions at the time of manufacturing the rails in claims 5 and 6 will be described in detail. First, there is a temperature condition before cooling the rail head. In order to obtain a desired structure and hardness, at least the rail head needs to be sufficiently austenitized. The temperature is A at the rail head immediately after rolling.
The temperature range is r ₁ or more, and the temperature of the reheated rail head is more than 30 ° C. for ₁ point of Ac. The upper limit is not particularly specified, but if the temperature is too high during reheating, a liquid phase appears and the austenite phase becomes unstable, so that the upper limit is substantially 1350 ° C.

Here, the "rail head" refers to the rail top (reference number: 1) and the head corner (reference number: FIG. 2) shown in FIG.
This is the part containing 2). The cooling rate and temperature described below are measured at a depth of 2 to 5 mm from the surface of the head at the top of the rail (symbol: 1) and the corner of the head (symbol: 2) shown in FIG. Then, starting from the head surface of at least the head corner portion and the crown portion of the rail head, a range of at least 20 mm in depth (hatched portion in FIG. 2) can be represented, and at least the portion (FIG. (Shaded area) can be controlled in texture and hardness.

Next, in the method of accelerating cooling the rail head from austenite temperature to 650 to 450 ° C. at a cooling rate of 1 to 15 ° C./sec, the accelerating cooling stop temperature is limited as described above. The reason will be described. 650
When accelerated cooling is stopped at a temperature exceeding ℃, pearlite transformation starts immediately after accelerated cooling, many pearlite structures with low hardness are generated, the hardness of the rail head becomes less than Hv370, and wear resistance and internal fatigue resistance are reduced. Because damage cannot be secured,
It was limited to 650 ° C or lower. In addition, if the cooling is performed to less than 450 ° C., sufficient reheating 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 in segregated portions in the head of the rail. Due to the formation of tissue, the temperature was limited to 450 ° C. or higher.

Further, the accelerated cooling rate of the rail head is 1 ° C./s.
When the temperature is less than ec, 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 Hv 370, and the wear resistance and resistance of the rail head are reduced. Since it is difficult to secure the internal fatigue damage, and depending on the component system, a first-fraction cementite structure harmful to the toughness and ductility of the rail is generated, the temperature is limited to 1 ° C./sec or more. If the accelerated cooling rate exceeds 15 ° C./sec, abnormal structures such as bainite and martesite are formed on the rail head without performing pearlite transformation during accelerated cooling,
To reduce the wear resistance, toughness and internal fatigue damage resistance of the rail head, the accelerated cooling rate was limited to the range of 1 to 15 ° C / sec.

In order to stably generate a pearlite structure with high hardness up to the inside of the rail head, as shown in the pearlite transformation region of the rail steel of the present invention in FIG. 1, the accelerated cooling rate is 5 to 10 ° C./sec. Is most desirable.

This accelerated cooling rate range limits the average cooling rate from the start to the end of cooling. However, during accelerated cooling, heat generated by pearlite transformation and temporary recovery due to spontaneous reheating from inside the rails are obtained. Temperature rise 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 the cooling rate due to a rise in temperature.

As a method of 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 produce a rail having a pearlite structure of Hv 370 or more and excellent in wear resistance and internal fatigue damage resistance, it is necessary to prevent the formation of a pearlite structure having a low hardness at the rail head, and to improve the abrasion resistance, Ductility,
1-15 ° C / sec from austenite zone temperature using air or air-based refrigerant with mist etc. to prevent the formation of first-fraction cementite, martensite, bainite structure harmful to toughness and internal fatigue damage resistance Cooling is accelerated at a cooling rate of 1. When the temperature of the steel rail head reaches 650 to 450 ° C., the accelerated cooling is stopped to stably generate a high-hardness pearlite structure from the surface to the inside of the rail head. It is possible to do.

The metal structure of the rail is preferably a pearlite structure. However, depending on the component system, the accelerated cooling rate, and the segregation state of the material, a trace amount of a first-order ferrite structure or a first-order cementite structure may be included in the pearlite structure. May be generated. However, even if these structures are generated in trace amounts in the pearlite structure, the wear resistance, ductility,
The structure of the present pearlite-based rail includes a slight mixture of a first-fold ferrite structure and a first-fold cementite structure, since it does not significantly affect toughness, internal fatigue damage resistance and strength.

[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 in the Nishihara-type wear test under the forced cooling condition shown in FIG. 3 and the rolling fatigue test result shown in FIG.

In FIG. 3, reference numeral 3 denotes a rail test piece,
Reference numeral 4 denotes a mating member, and reference numeral 5 denotes a cooling nozzle. In FIG. 4, reference numeral 6 denotes a rail moving slider, on which the rail 7 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.

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 2 also shows the wear amount after 700,000 repetitions in the Nishihara-type wear test under the forced cooling conditions shown in FIG. 3 and the rolling fatigue test results shown in FIG.

FIG. 5 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.

FIGS. 6, 7, and 8 show the rail steel of the present invention (reference numeral:
6 is an example of a head section hardness distribution of (C, D, E). Also,
9 and 10 show examples of the hardness distribution of the head section of the comparative rail steel (symbols: R and S).

The configuration of the rail is as follows. -Rails of the present invention (12 rails) Symbols A to L In the above component ranges, at least a range of 20 mm in depth from the rail head surface to the head surface of the steel rail exhibits a pearlite structure. A pearlitic rail excellent in wear resistance and internal fatigue damage resistance, characterized by having a pearlite structure having a hardness of Hv 370 or more and a hardness difference of Hv 30 or less.

Reference rails (11) Reference symbols M to O: Comparative rail steels (3) made of eutectoid carbon-containing steel whose chemical components are outside 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 conditions of the abrasion test were as follows. Test machine: Nishihara type abrasion tester (see Fig. 3) Specimen shape: disc-shaped test piece (outer diameter: 30 mm, thickness: 8 m)
m) Test load: 686N Sliding rate: 20% Partner 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 of the rolling fatigue test were as follows. Test machine: Rolling fatigue test machine (see Fig. 4) Specimen shape Rail: 136 pound rail x 2 m Wheel: AAR type (920 mm in diameter) Radial load: 147000 N Thrust load: 4800 N Lubrication: Dry + oil (intermittent lubrication) )

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

As shown in FIG. 5, the rail steel of the present invention comprises:
By increasing the carbon content as compared with the comparative rail steel, the wear amount is small at the same hardness, and the wear resistance is greatly improved. Further, as shown in FIGS. 6, 7 and 8, the rail steel of the present invention has an added amount of B and Ti in an appropriate range, so that it can be compared with the comparative steel rail shown in FIGS. Thus, the difference in hardness between the rail head surface and the inside is reduced, and as shown in Table 1, the occurrence of internal fatigue damage can be prevented. Further, as shown in Tables 1 and 2, by containing a chemical component in an appropriate range, formation of a proeutectoid cementite or a martensite structure which is harmful to the ductility and toughness of the rail can be prevented. 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 pearlite transformation characteristics of the rail steel of the present invention.

FIG. 2 is a diagram showing the names of rail cross-sectional surface positions and Hv37.
The figure which showed the required range of 0 or more perlite structure.

FIG. 3 is a schematic diagram of a Nishihara-type abrasion tester.

FIG. 4 is a schematic diagram of a rolling fatigue tester.

FIG. 5 is a diagram comparing the wear test results of the rail steel of the present invention and the comparative rail steel in relation to hardness and wear amount.

FIG. 6 is a diagram showing a head section hardness distribution of the rail C of the present invention.

FIG. 7 is a diagram showing a head section hardness distribution of the rail D of the present invention.

FIG. 8 is a diagram showing a head section hardness distribution of the rail E of the present invention.

FIG. 9 is a diagram illustrating a head section hardness distribution of a comparative rail R;

FIG. 10 is a diagram illustrating a head section hardness distribution of a comparative rail S.

[Explanation of symbols]

 1: Top of head 2: Corner of head 3: Rail test piece 4: Counterpart material 5: Cooling nozzle 6: Slider for moving rail 7: Rail 8: Wheel 9: Motor 10: Load loading device

Claims (6)

[Claims] 1. Weight%: C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, B: 0.0001 to 0 A pearlite-based rail excellent in wear resistance and internal fatigue damage resistance, characterized by containing 0.0040% and Ti: 0.0050 to 0.0300%, with the balance being Fe and unavoidable impurities. 2. In% by weight, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, B: 0.0001 to 0% 0.0040%, Ti: 0.0050-0.0300%, Cr: 0.05-1.00%, Mo: 0.01-0.20%, V: 0.01-0. 20%, Nb: 0.002 to 0.050%, Co: 0.10 to 2.00%, and the balance is Fe and unavoidable impurities. A pearlitic rail with excellent wear resistance and internal fatigue damage resistance. 3. In% by weight, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, B: 0.0001 to 0 A rail containing 0.0040% to 0.050% of Ti and 0.0050% to 0.0300% of Ti, with the balance being Fe and unavoidable impurities, having a depth of at least 20 mm starting from the top corner and top surface of the rail. Has a pearlite structure, and the hardness of the pearlite structure in the above range is Hv370 or more, and the difference in hardness is Hv30 or less. A perlite rail with excellent properties. 4. In% by weight, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, B: 0.0001 to 0 0.0040%, Ti: 0.0050-0.0300%, Cr: 0.05-1.00%, Mo: 0.01-0.20%, V: 0.01-0. 20%, Nb: 0.002 to 0.050%, Co: 0.10 to 2.00%, and the balance is Fe and unavoidable impurities. A region having a depth of at least 20 mm from the head corner portion and the top surface of the rail as a starting point exhibits a pearlite structure, and the hardness of the pearlite structure in the above range is Hv370 or more, and the difference in hardness is Hv30 or less. Wear resistance, characterized by having a pearlite structure Excellent pearlitic rail parts fatigue resistance. 5. In% by weight, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, B: 0.0005 to 0% .0040%, Ti: 0.0050-0.0300%, with the balance being Fe and unavoidable impurities,
The hot-rolled steel rail head at the temperature of Ar ₁ point or higher, or the steel rail head heated to the temperature of ₁ point Ac + 30 ° C. or higher for the purpose of heat treatment, is heated from the austenite region temperature to 1 to 15 ° C./sec. Accelerated cooling at a cooling rate of, when the temperature of the head of the steel rail reaches 650 to 450 ° C., stop the accelerated cooling, and then allow the steel rail to cool down, and then the surface of the head corner and the top of the steel rail At least depth 2 starting from
A range of 0 mm shows a pearlite structure, and the hardness of the pearlite structure in the above range is Hv370 or more, and the difference in hardness is Hv30 or less. Manufacturing method of perlite rail with excellent damageability. 6. In% by weight, C: more than 0.85 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.10 to 1.50%, B: 0.0005 to 0 0.0040%, Ti: 0.0050-0.0300%, Cr: 0.05-1.00%, Mo: 0.01-0.20%, V: 0.01-0. 20%, Nb: 0.002 to 0.050%, Co: 0.10 to 2.00%, one or more of the following, the balance being Fe and unavoidable impurities, as hot rolled Accelerate the steel rail head at a temperature of ₁ point or higher or a steel rail head heated to a temperature of ₁ point + 30 ° C. or higher for heat treatment at a cooling rate of 1 to 15 ° C./sec from the austenite region temperature. Cool, the temperature of the head of the steel rail is 650-450 ° C
At the time of reaching, accelerated cooling is stopped, and then allowed to cool, at least a range of a depth of 20 mm from the head corner portion and the top surface of the steel rail as a starting point exhibits a pearlite structure, and the pearlite structure of the range A method for producing a pearlite-based rail having excellent wear resistance and internal fatigue damage resistance, wherein the pearlite structure has a hardness of Hv370 or more and a difference in hardness of Hv30 or less.