JP2002256393A - Wear-resistant pearlite-based rail with excellent destruction resistance - Google Patents

Abstract

(57) [Problem] To improve toughness in a mixed structure of pearlite and pro-eutectoid cementite by controlling the maximum value of the minor axis and the occupied area ratio of pro-eutectoid cementite in an arbitrary cross section of the mixed structure. In this way, the rail is provided with stable destruction resistance and the life of the rail is extended. SOLUTION: A steel rail containing C: 0.90 to 1.20% by mass, wherein at least a part of the rail exhibits a mixed structure of pearlite and proeutectoid cementite, In any cross section, the maximum value of the minor axis of the proeutectoid cementite is 500 nm or less, and the total area of the proeutectoid cementite is 5% or less of the area of the mixed structure in the arbitrary cross section. Abrasion-resistant pearlite-based rail with excellent destruction resistance.

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 destruction resistance and wear resistance required for rails of heavy load railways.

[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, in the rail laid in the curved section, G. C. (Gauge corners) and head side wear increased sharply, and it became a problem in terms of rail service life.

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 sorbite head or fine pearlite head (Japanese Patent Publication No. 54-2549)
No. 0). After the end of rolling or after reheating, the rail head is heated from 850 to 500 ° C from the austenitic zone temperature to 1 to 4 ° C /
A method for producing a high-strength rail of 130 kgf / mm ² or more that is accelerated and cooled in sec (Japanese Patent Laid-Open No. 57-198216). 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 with the purpose of minimizing the lamellar spacing in the pearlite structure and improving 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. 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.

[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).
016 publication). A hypereutectoid steel (C: more than 0.85 to 1.20%) is used to increase the cementite density in the lamella in the pearlite structure, and at the same time, to control the hardness and to provide a rail with excellent wear resistance (JP-A-Hei. 8-246100). The characteristics of these rails are to increase the carbon content of the steel, increase the density of the highly wear-resistant semetite phase in the pearlite lamella, and improve the wear resistance of the pearlite structure by controlling the hardness. It was to let.

[0006]

The invention rail steel disclosed in the above contributes to prolonging the life of heavy load railway rails by improving the wear resistance. However, due to changes in steel composition and rail manufacturing conditions, the toughness tended to decrease significantly. It was difficult to impart destructibility.

Therefore, it has been a new task to develop a wear-resistant rail having stable destruction resistance when using a rail in a low temperature range. That is, the present invention
An object of the present invention is to provide a rail for the purpose of simultaneously improving fracture resistance and wear resistance required for rails of a heavy load railway.

[0008]

The present invention attains the above-mentioned object, and its gist is as follows. (1) A steel rail containing C: 0.90 to 1.20% by mass, wherein at least a part of the rail has a mixed structure of pearlite and proeutectoid cementite, and the mixed structure is optional. In the cross section, the maximum value of the minor axis of the proeutectoid cementite is 500 nm or less, and the total area of the proeutectoid cementite is 5% or less of the area of the mixed structure in the arbitrary cross section. Abrasion resistant pearlitic rail with excellent destructibility. (2) In mass%, C: 0.90 to 1.20%, S
i: 0.10 to 1.00%, Mn: 0.10 to 1.50
%, The balance being Fe and unavoidable impurities, at least a part of the steel rail has a mixed structure of pearlite and proeutectoid cementite, and in an arbitrary cross section of the mixed structure, proeutectoid The maximum value of the minor axis of the cementite is 500 nm or less, and the total area of the proeutectoid cementite is 5% or less of the area of the mixed structure in the arbitrary cross section. Wear-resistant perlite rail. (3) In mass%, C: 0.90 to 1.20%, S
i: 0.10 to 1.00%, Mn: 0.10 to 1.50
%, The balance being Fe and unavoidable impurities, and a range of at least a depth of 20 mm starting from the steel rail from at least the rail head surface of the steel rail is a mixture of pearlite and proeutectoid cementite. In any cross section of the mixed structure, the maximum value of the minor axis of the proeutectoid cementite is 500 nm or less, and the total area of the proeutectoid cementite is 5% of the area of the mixed structure in the arbitrary cross section. A wear-resistant pearlitic rail with excellent destruction resistance, characterized by the following.

(4) The rails (1) to (3) may further contain the following components in mass%. Cr: 0.05-1.50%, Mo: 0.01
Nb: 0.002 to 0.050%, V: 0.01
One or two kinds of B: 0.0001 to 0.2000%, Co: 0.10 to 2.00%, Cu: 0.05
One or two kinds of Ni: 0.05 to 2.00%. One or more of Ti: 0.0050 to 0.0500%, Mg: 0.0010 to 0.0300%, and Ca: 0.0010 to 0.0150%, with the balance being Fe and inevitable Consists of impurities.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present inventors have conducted detailed fracture surface analysis on a rail having a pearlite structure containing a high carbon content (carbon content of 0.90% or more) having excellent wear resistance using a rail broken in a low-temperature drop test. The cause of the significant decrease in toughness was clarified. As a result, it was confirmed that no inclusions existed at the origin of the fracture, and that the fracture progressed macroscopically from a region near the austenite grain boundary.

Next, the present inventors have observed the microstructure of the fracture starting point in detail. As a result, formation of a row of cementite (proeutectoid cementite) was recognized at the starting point along the prior austenite grain boundary. From the above results, it has been clarified that the cause of the significant decrease in the toughness of the pearlite-structured rail containing a high carbon content is mainly the formation of this row-shaped proeutectoid cementite.

Next, the present inventors clarified the relationship between the formation form of this row of pro-eutectoid cementite and the rail breakage, using a rail that broke in a low-temperature drop load test and a rail that did not break. As a result, in any cross section of the rail, the thickness (minor diameter) of pro-eutectoid cementite in a row
It is evident that fracture occurs on rails whose density exceeds a certain value, and by controlling the minor axis of proeutectoid cementite and its density within a certain range in any cross section, high carbon content It has been found that the toughness of a pearlite-structured rail containing iron can be stabilized, and high fracture resistance can be imparted to the rail.

From the above results, the present inventors have found that in a pearlite-structured rail containing a high carbon content, the minor axis of proeutectoid cementite and the density thereof are controlled within a certain range in an arbitrary cross section, whereby It has been found that the toughness can be stabilized and high fracture resistance can be imparted to the rail. That is, an object of the present invention is to provide a low-cost high-strength rail that simultaneously improves the fracture resistance and wear resistance required for heavy-load railways.

Next, the reasons for limitation of the present invention will be described in detail. First, FIG. 1 schematically shows an example of the microstructure of a wear-resistant pearlite-based rail of the present invention having excellent fracture resistance (rail steel of the present invention, code: I). In FIG. 1, the layered portions shown in white are the lamellar structure of the pearlite structure, and the row-like portions shown with diagonal lines are the proeutectoid cementite structure. In the rail steel of the present invention, the minor axis of the proeutectoid cementite indicates the shorter diameter of the elliptic proeutectoid cementite structure shown in FIG.

(1) The minor axis of pro-eutectoid cementite and the area occupied by any cross section: First, in the mixed structure of pearlite and pro-eutectoid cementite, the minor axis of pro-eutectoid cementite and the area occupied by any cross section are defined in the above-mentioned claims. The reason for the limitation will be described. If the maximum value of the minor axis of the proeutectoid cementite exceeds 500 nm, it will always be the starting point of destruction in a rail destruction test such as a low-temperature drop test, and the fracture resistance of the rail will be greatly reduced. It was limited to 500 nm or less.

If the area occupied by pro-eutectoid cementite exceeds 5% in an arbitrary cross section, even if the maximum value of the minor axis of each pro-eutectoid cementite is 500 nm or less, the pearlite structure as a base material becomes significantly embrittled, Since the fracture resistance of the rail is greatly reduced, the area occupied by proeutectoid cementite in an arbitrary cross section is limited to 5% or less.

Therefore, in order to improve the fracture resistance of the rail, the maximum value of the minor axis of proeutectoid cementite is 500 nm.
In addition, it is necessary to control the area occupied by proeutectoid cementite in an arbitrary cross section to 5% or less. In order to stably improve the fracture resistance in a mixed structure of pearlite and pro-eutectoid cementite, it is more desirable to control the area occupied by pro-eutectoid cementite in an arbitrary cross section to 3% or less.

For the measurement of the minor axis of proeutectoid cementite and its occupied area, steel is etched with a predetermined corrosive solution such as nital or picral, and these are observed with a scanning electron microscope or a transmission electron microscope. The major axis and minor axis of each proeutectoid cementite are measured. Further, the occupied area is obtained by performing elliptic approximation. Further, regarding the measurement of the minor axis of the proeutectoid cementite and the calculation of the occupied area, large variations occur depending on the visual field to be observed. Therefore, in order to obtain an average value, it is desirable to observe at least 20 visual fields in each steel and calculate the average value.

(2) Desirable range of mixed structure of pearlite and pro-eutectoid cementite: Next, the desired range of the mixed structure of pearlite and pro-eutectoid cementite is defined as the surface of the head at the corner and the top of the head. The reason why the depth is limited to the range of 20 mm starting from will be described. If the depth is less than 20 mm, the area of the destruction resistance and wear resistance required for the rail head is small, and sufficient destruction resistance and wear life improvement effect cannot be obtained. Also,
If the range exhibiting the mixed structure of the pearlite and pro-eutectoid cementite is 30 mm or more in depth from the head surface of the head corner and the crown, the effect of improving the fracture resistance and wear life is further increased, More desirable.

Here, FIG. 2 shows the name of the wear-resistant rail exhibiting a mixed structure of pearlite and pro-eutectoid cementite of the present invention at the head cross-sectional surface position, and the wear resistance and fracture resistance. Indicates an area where 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) part mainly in contact with wheels. If the mixed structure is arranged at least in the oblique line in the drawing, the wear life and the fracture resistance of the rail can be improved. Therefore, it is desirable that the mixed structure of pearlite and proeutectoid cementite be disposed near the surface of the rail head where the wheel and the rail are mainly in contact, and the other part is a structure other than the mixed structure of pearlite and proeutectoid cementite. There may be.

The metal structure of the rail of the present invention is preferably a mixed structure of pearlite and proeutectoid cementite as described above. For proeutectoid cementite,
As long as the formation is within the above-described range, the rail does not significantly affect the wear resistance, the fracture resistance, the surface damage resistance, and the like. Further, although there is no particular limitation on the pearlite, it is possible to maintain the wear resistance of the rail if it has a lamellar structure.

Further, depending on the rail heat treatment manufacturing method,
A bainite structure and a retained austenite structure may be mixed in a mixed structure of pearlite and proeutectoid cementite. However, even if a certain amount of these structures is mixed, it does not significantly affect the abrasion resistance, fracture resistance, surface damage resistance, etc. of the rail, and therefore, a mixed structure of pearlite and proeutectoid cementite is exhibited. The structure of the pearlite-based rail having excellent destructibility includes a slight mixture of a bainite structure and a retained austenite structure.

(3) Chemical composition of rail steel: Next, the reason why the chemical composition of the rail is limited to the above-described claims will be described. C is an effective element that promotes pearlite transformation and secures abrasion resistance. As a normal rail steel, a C content of 0.60 to 0.85% is added.
If the amount is less than 0.90%, the density of the cementite phase in the pearlite structure for improving the wear resistance cannot be ensured, and further, grain boundary ferrite, which is a starting point of fatigue damage, is formed inside the rail head. And rail life is shortened. If the C content exceeds 1.20%, coarse pro-eutectoid cementite is generated in the pearlite structure depending on the component system, and the toughness of the rail is greatly reduced, and the density of the cementite phase in the pearlite structure is increased. However, since the ductility required for the rail cannot be sufficiently secured, the C content is limited to 0.90 to 1.20%.

In the rail manufactured with the above composition, the ferrite on the wear surface is strengthened, the wear resistance is enhanced by promoting the generation of cementite, and the softening and embrittlement of the heat-affected zone of the weld are prevented. For the purpose, Si, Mn, Cr, Mo,
Elements of V, Nb, B, Co, Cu, Ni, Ti, Mg, and Ca are added as needed.

Here, Si secures the strength of the ferrite in the pearlite structure and suppresses the formation of proeutectoid cementite, thereby improving the wear resistance and the fracture resistance. Mn secures the strength of the pearlite structure by improving the quenchability and refines the pearlite lamella spacing, further suppresses the formation of the proeutectoid cementite structure, and improves the wear resistance and the fracture resistance. Cr and Mo raise the equilibrium transformation point of pearlite and mainly secure the strength of the pearlite structure by reducing the pearlite lamellar spacing to improve wear resistance. V and Nb are formed by carbides and nitrides generated during hot rolling and subsequent cooling processes.
The main purpose of addition is to suppress the growth of austenite grains, further increase the strength of the pearlite structure by precipitation hardening, and improve the wear resistance and ductility of the pearlite structure.

B forms iron carbide borides, suppresses the formation of proeutectoid cementite, further promotes pearlite transformation, and improves the fracture resistance and wear resistance of the rail.
Co and Cu aim to improve wear resistance mainly by solid solution strengthening of the base ferrite. Ni improves wear resistance mainly by solid solution strengthening of the base ferrite, and also increases softening resistance of the heat-affected zone during rail welding heat. Ti refines the structure of the heat-affected zone, which is heated to the austenite region during rail welding heat, and prevents the welding joint from becoming brittle. Mg, C
a is obtained by forming fine oxides and sulfides.
The main purpose of addition is to improve the ductility and toughness of the rail by finely dispersing nS and promoting the pearlite transformation and miniaturizing the pearlite block size.

Each of these components will be described in detail below. Si is an element that increases the hardness (strength) of the rail head by solid solution hardening to the ferrite phase in the pearlite structure, and at the same time, suppresses the formation of proeutectoid cementite and improves the fracture resistance of the rail. But,
If it is less than 0.10%, the effect cannot be sufficiently expected, and if it exceeds 1.00%, a large number of surface flaws are generated at the time of hot rolling, and weldability is reduced due to generation of oxides. Further, the pearlite structure is embrittled and the toughness of the rail is reduced, so that sufficient rail resistance cannot be imparted to the rail. Therefore, the amount of Si was limited to 0.10 to 1.00%.

Mn enhances the hardenability and reduces the pearlite lamella spacing, thereby securing the strength of the pearlite structure, improving the wear resistance, further suppressing the formation of the proeutectoid cementite structure, and Although it is an element that improves the fracture resistance, if its content is less than 0.10%, the effect is small, and it is difficult to secure the wear resistance and the fracture resistance required for the rail. On the other hand, if it exceeds 1.50%, hardenability is remarkably increased, and a martensitic structure harmful to toughness is easily formed, segregation is promoted, and coarse sedimentation harmful to rail toughness is caused at the segregated portion. Since a cementite structure is easily generated, the Mn content is limited to 0.10 to 1.50%.

Cr increases the pearlite equilibrium transformation point and reduces the pearlite lamellar spacing, thereby contributing to an increase in the strength of the pearlite structure and, at the same time, strengthening the cementite phase in the pearlite structure to improve wear resistance. However, if it is less than 0.05%, its effect is small, and if it is added in excess of 1.50%, a large amount of martensite structure is generated and the toughness of the rail is lowered, so that Cr The amount was limited to 0.05-1.50%.

Mo is an element that, like Cr, raises the equilibrium transformation point of pearlite and reduces the pearlite lamella spacing, thereby contributing to an increase in the strength of the pearlite structure and improving wear resistance. %, The effect is small, and excessive addition exceeding 0.20% promotes segregation, further reduces the pearlite transformation rate, generates a martensite structure in the segregated portion, and reduces the toughness of the rail. Therefore, the amount of Mo was limited to 0.01 to 0.20%.

Nb increases the strength by precipitation hardening by Nb carbide and Nb nitride generated in the cooling process during hot rolling,
Further, it is an element effective to refine the austenite grains by the action of suppressing the growth of crystal grains during the heat treatment of heating to a high temperature, thereby improving the ductility and toughness of the pearlite structure. Furthermore, in the heat affected zone of the rail welding, Nb carbide is generated during tempering and is an element that prevents softening due to precipitation strengthening. However, the effect cannot be expected if it is less than 0.002%, and an excessive amount exceeding 0.050%. No further effect can be expected even if it is added. Therefore, the amount of Nb was limited to 0.002 to 0.050%.

V, like Nb, increases the strength by precipitation hardening with V carbides and V nitrides, and further suppresses the growth of crystal grains during heat treatment for heating to a high temperature to reduce austenite grains. And is an element effective for improving the strength, ductility and toughness of the pearlite structure. Furthermore, in the heat affected zone of the rail welding, V carbide is generated during tempering and is an element that prevents softening by precipitation strengthening. However, if it is less than 0.01%, its effect cannot be expected sufficiently,
Even if added in excess of 0.50%, no further effect can be expected, so the V amount was limited to 0.01 to 0.50%.

B is an element that forms iron carbide boride, suppresses the formation of proeutectoid cementite, promotes pearlite transformation at the same time, and improves the fracture resistance and wear resistance of the rail. If the content is less than 0.0050%, coarse iron borides are formed and the ductility and toughness are greatly reduced. Limited to 0001 to 0.0050%.

Co is an element that forms a solid solution with ferrite in the pearlite structure and improves the wear resistance of the pearlite structure by solid solution strengthening, and further increases the transformation energy of the pearlite to make the pearlite structure fine. Is less than 0.10%, the effect cannot be expected, and even if excessive addition exceeding 2.00%, the effect reaches a saturation range.
The amount of Co was limited to 0.10 to 2.00%.

Cu is an element that forms a solid solution with ferrite in the pearlite structure and improves the wear resistance of the pearlite structure by solid solution strengthening, and its effect is 0.05 to 0.50%.
, And more than 0.50% tends to cause red-hot embrittlement.
Limited to 50%.

Ni is an element that improves the ductility and toughness of the pearlite steel and at the same time increases the strength of the pearlite steel by solid solution strengthening. Furthermore, in the heat affected zone, Ti
Intermetallic compound of Ni ₃ Ti composite is finely precipitated, is an element of suppressing the softening by precipitation strengthening, 0.05%
If it is less than 10%, the effect is extremely small, and even if an excessive addition exceeding 1.00% is performed, no further effect can be expected. Therefore, the amount of Ni was limited to 0.05 to 1.00%.

[0037] Titanium is used for the purpose of making use of the fact that Ti carbide and Ti nitride precipitated during reheating during welding do not dissolve.
It is an effective component for miniaturizing the structure of the heat-affected zone heated to the austenite region and preventing embrittlement of the weld joint. However, if the content is less than 0.0050%, the effect is small, and if it exceeds 0.0500%, coarse Ti
Since carbides and Ti nitrides are formed and become a starting point of fatigue damage during use of the rail and cracks are generated, the Ti content is reduced to 0.1%.
0050 to 0.050%.

Mg combines with O, S, Al or the like to form a fine oxide, suppresses the growth of crystal grains during reheating during rail rolling, and refines austenite grains. It 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 generated 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, forms a sulfide as CaS, and CaS finely disperses MnS, forms a dilute band of Mn around MnS, and contributes to the generation of pearlite transformation. As a result, by reducing the size of the pearlite block, it is an effective element for improving the ductility and toughness of the pearlite structure. 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 to 0.0150%.

The rail steel having the above-mentioned composition is melted in a commonly used melting furnace such as a converter or an electric furnace, and the molten steel is cast into an ingot-bulking method or a continuous casting method.
Further, it is manufactured as a rail through hot rolling. next,
By applying accelerated cooling to the rail that retains high-temperature heat after hot rolling, or to the rail head and bottom reheated to a high temperature for the purpose of heat treatment, and also to the entire rail, the shortage of proeutectoid cementite can be reduced. It is possible to stably produce a mixed structure of pearlite and proeutectoid cementite whose diameter and density are controlled within a certain range.

[0041]

Next, an embodiment of the present invention will be described. Table 1 shows the chemical composition, microstructure, and form of proeutectoid cementite of the rail steel of the present invention (the maximum value of the minor axis in any cross section,
Occupied area ratio). Table 1 also shows the wear amount, impact test result, and drop weight test result after repeated 700,000 times in the Nishihara abrasion test under the forced cooling condition shown in FIG.
In FIG. 3, 3 is a rail test piece, 4 is a mating material, and 5 is a cooling nozzle. Table 2 shows the chemical composition, microstructure, and form of proeutectoid cementite of the comparative rail steel (maximum minor axis in any cross section, occupied area ratio).

FIG. 4 shows the rail steel of the present invention shown in Table 1 and Table 2.
Comparative rail steel (eutectoid carbon-containing rail steel, code: M)
-O) in comparison between the amount of carbon and the amount of wear. FIG. 5 shows the rail steel of the present invention shown in Table 1 and the comparative rail steel shown in Table 2 (hypereutectoid carbon-containing rail steel, code: S to U).
5 is a comparison of the relationship between the occupied area ratio of proeutectoid cementite in an arbitrary cross section and the impact value.

The configuration of the rail is as follows. -Rail steel of the present invention (12) Symbols A to L Within the above component ranges, at least a part of the steel rail exhibits a mixed structure of pearlite and proeutectoid cementite, and in any cross section of the mixed structure, the proeutectoid cementite has Abrasion resistance excellent in fracture resistance, characterized in that the maximum value of the minor axis is 500 nm or less and the total area of proeutectoid cementite is 5% or less of the area of the mixed structure in the arbitrary cross section. Perlite rail. -Comparative rail steel (nine) Symbols M to O: Comparative rail steel (three) of eutectoid carbon-containing steel whose chemical components are out of the above-mentioned claims. Symbols P to R: Comparative rail steels (three) made of hypereutectoid carbon-containing steel whose chemical components are outside the above-mentioned claims. Symbols S to U: Comparative rail steel made of hypereutectoid carbon-containing steel in which the chemical composition is within the above-described claims and the form of proeutectoid cementite (maximum minor axis in any cross section, occupied area ratio) is out of the claims. (3).

The wear test conditions were as follows. Testing machine: Nishihara type abrasion tester Specimen shape: disk-shaped specimen (outer diameter: 30 mm, thickness: 8
mm) 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 of the impact test were as follows. Test piece: JIS No. 3 2mm U notch Charpy impact test piece Test temperature: Normal temperature (+ 20 ° C)

The conditions for the drop test were as follows. Tester: Drop weight tester Rail shape: 136 pounds (136 Lb) rail Specimen length: 1.5 m Distance between fulcrums: 1.0 m Supporting method: Test with head down (drop weight drop on bottom) Weight of falling weight: 1000kg Height of falling weight: 10m Test temperature: -60 ° C

As shown in FIG. 5, in the rail steel of the present invention, the amount of wear is reduced by increasing the carbon content as compared with the comparative rail steel, and the wear resistance is greatly improved. Further, as shown in FIG. 6, the rail steel of the present invention controls the occupied area ratio of proeutectoid cementite and the maximum value of the minor axis in an arbitrary cross section to reduce the impact value and break the rail in a drop weight test. It can prevent and prevent the rail from breaking.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

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

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an example of a microstructure of a wear-resistant pearlite-based rail excellent in fracture resistance according to the present invention.

FIG. 2 is a diagram showing names of cross-sectional surface positions of rail heads and regions where abrasion resistance and fracture resistance are required.

FIG. 3 is a schematic view of a Nishihara type abrasion tester.

FIG. 4 is a view comparing the relationship between the carbon content and the wear amount of the rail steel of the present invention and the comparative rail steel.

FIG. 5 is a view comparing the relationship between the occupied area ratio of proeutectoid cementite and the impact value in an arbitrary cross section of the rail steel of the present invention and the comparative rail steel.

[Explanation of Signs] 1: Head part 2: Head corner part 3: Rail test piece 4: Counterpart material 5: Cooling nozzle

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noriaki Onodera 1-1 Tobata-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Inside Yawata Works (72) Inventor Takuya Sato 1-1, Tobata-cho, Tobata-ku, Kitakyushu New Nippon Steel Corporation Yawata Works

Claims (10)

[Claims] 1. A steel rail containing C: 0.90 to 1.20% by mass, wherein at least a part of the rail exhibits a mixed structure of pearlite and proeutectoid cementite, and the mixed structure Wherein the maximum value of the minor axis of the proeutectoid cementite is 500 nm or less, and the total area of the proeutectoid cementite is 5% or less of the area of the mixed structure in the arbitrary cross section. Abrasion-resistant pearlitic rail with excellent destruction resistance. 2. A steel rail containing, by mass%, C: 0.90 to 1.20%, Si: 0.10 to 1.00%, and Mn: 0.10 to 1.50%, At least a part of the steel rail exhibits a mixed structure of pearlite and pro-eutectoid cementite, and in any cross section of the mixed structure, the maximum value of the minor axis of pro-eutectoid cementite is 500 nm or less, and the area of the pro-eutectoid cementite. Is 5% or less of the area of the mixed structure in the arbitrary cross section. 3. A steel rail containing, by mass%, C: 0.90 to 1.20%, Si: 0.10 to 1.00%, and Mn: 0.10 to 1.50%, 20 m depth from at least the rail head surface starting from the steel rail
The range of m presents a mixed structure of pearlite and proeutectoid cementite, and in any cross section of the mixed structure, the maximum value of the minor axis of proeutectoid cementite is 500 nm or less, and the total area of the proeutectoid cementite is An abrasion-resistant pearlite-based rail excellent in fracture resistance, wherein the area is 5% or less of the area of the mixed structure in the arbitrary cross section. 4. The method according to claim 1, further comprising one or more of Cr: 0.05 to 1.50% and Mo: 0.01 to 0.20% by mass%.
4. A wear-resistant pearlite-based rail excellent in fracture resistance according to any one of items 3 to 3. 5. The composition according to claim 1, further comprising one or two of Nb: 0.002 to 0.050% V: 0.01 to 0.50% by mass%.
5. The abrasion-resistant pearlite-based rail excellent in destruction resistance according to any one of items 4 to 4. 6. Abrasion resistance excellent in fracture resistance according to claim 1, further comprising B: 0.0001 to 0.0050% by mass%. Perlite rail. 7. The composition according to claim 1, further comprising one or more of Co: 0.10 to 2.00% and Cu: 0.05 to 0.50% by mass%.
7. A wear-resistant pearlite-based rail excellent in fracture resistance according to any one of items 6 to 6. 8. Abrasion resistance excellent in fracture resistance according to claim 1, further comprising Ni: 0.05 to 1.00% by mass. Perlite rail. 9. The method according to claim 1, further comprising: Ti: 0.0050 to 0.0500% by mass%. Wear perlite rail. 10. The method according to claim 1, further comprising one or more of Mg: 0.0010 to 0.0100% and Ca: 0.0010 to 0.0150% by mass%.
10. A wear-resistant pearlitic rail according to any one of claims 1 to 9, which is excellent in fracture resistance.