JP2003293086A - Pearlitic rail having excellent wear resistance and ductility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the wear resistance and ductility of the head of a steel rail with a pearlitic structure used in a heavy load railway, and to improve the wear resistance and prevent the occurrence of cracking such as breakage in a rail used in a cold district by controlling the amount of C to be added, and further controlling the number of pearlite block grains with a grain size of 1 to 15 μm. <P>SOLUTION: In the steel rail with a pearlitic structure containing, by mass, 0.65 to 1.40% C, pearlite blocks with a grain size of 1 to 15 μm are present by ≥200 pieces per 0.2 mm<SP>2</SP>of the area to be examined at least in a part of the range to a depth of 10 mm with the surfaces of the corner parts and top part of the head as the starting points. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention improves the wear resistance required for rail heads of heavy-duty railways and, at the same time, controls the number of fine pearlite block grains in the rail heads to improve ductility. The present invention relates to a pearlite rail intended to improve and suppress rail breakage in cold regions.

[0002]

2. Description of the Related Art In overseas heavy-duty railways, the speed of trains and the weight of loaded trains have been increased as a means of increasing the efficiency of rail transportation. Such efficient rail transportation means that the rail usage environment becomes severe, and further improvement of the rail material has been required. Specifically, in the rail laid in the curved section, G. C. The wear on the (gauge / corner) part and the head side part increased rapidly, and it became a problem in terms of the service life of the rail.

From such a background, the development of a rail mainly aimed at the following improvement in wear resistance has been advanced. After rolling or after reheating, the rail head is heated from austenite temperature to 850 to 500 ℃ for 1 to 4 ℃ / sec.
A method for producing a high-strength rail of 130 kgf / mm ² (1274 MPa) or higher, which is accelerated cooling by means of Japanese Patent Laid-Open No. 57-198216. Using hyper-eutectoid steel (C: more than 0.85 to 1.20%),
A rail having excellent wear resistance with an increased cementite density in the lamella in the pearlite structure (Japanese Patent Laid-Open No. 14401/1996).
No. 6).

The characteristics of these rails are that steel containing eutectoid carbon (carbon content: 0.7 to 0.8%) or steel containing hypereutectoid carbon (carbon content: more than 0.85 to 1.20%). Is a high-strength rail exhibiting a fine pearlite structure, and its purpose is to reduce the lamella spacing in the pearlite structure, and further increase the density of the cementite phase in the pearlite lamella, and improve wear resistance. It was there.

However, since these high-strength rails have low toughness, there is a problem in that rail breakage is likely to occur due to defects such as rail head portions and low portions. Then, in order to solve such a problem, the present inventors developed the rail as shown below. Using eutectoid steel (C: 0.60 to 0.85%), the average block grain size of the pearlite structure was refined by rolling,
Rails with improved ductility and toughness (JP-A-8-10944)
No. 0). Using hyper-eutectoid steel (C: more than 0.85 to 1.20%),
A rail having a finer average block grain size of pearlite structure by rolling to improve ductility and toughness (Japanese Patent Laid-Open No. 8-109).
439). The characteristic of these rails was that the average block grain size of the pearlite structure was refined to improve wear resistance, ductility and toughness of the pearlite structure.

[0006]

The invention rails exhibiting the pearlite structure shown in the above-mentioned, by improving the ductility and toughness of the pearlite structure by refining the average block grain size of the pearlite structure, and breaking the rail. It is possible to reduce the occurrence of destruction such as. However, in cold regions where the temperature drops to below freezing, the rail has insufficient ductility and toughness, making it difficult to prevent rail breakage. In addition, in order to solve this problem, there is also a method of further reducing the average block grain size of the pearlite structure to improve the ductility and toughness of the rail, but the occurrence of fracture such as rail breakage in cold regions is sufficient. It was difficult to control.

From such a background, it is demanded to develop a rail which secures wear resistance in a rail head having a pearlite structure containing a high carbon content and at the same time prevents occurrence of breakage such as rail breakage in cold regions. Has become. That is, the present invention aims to improve the wear resistance required for a rail head for a heavy-duty railway, and particularly to prevent the occurrence of breakage such as rail breakage in cold regions.

[0008]

The present invention achieves the above object, and the gist thereof is as follows. (1) In a steel rail exhibiting a pearlite structure containing C: 0.65 to 1.40% by mass%, at least part of a range up to a depth of 10 mm from the head corner and the surface of the crown. A perlite rail having excellent wear resistance and ductility, characterized in that 200 or more perlite blocks having a particle size of 1 to 15 μm are present per 0.2 mm ^{2 of the} test area.

(2) C: 0.65 to 1.40 in mass%
%, Si: 0.05 to 2.00%, Mn: 0.05 to
In a steel rail exhibiting a pearlite structure containing 2.00%, the grain size is 1 to 1 in at least a part of the depth from the head corner portion and the top surface to a depth of 10 mm.
A pearlite rail with excellent wear resistance and ductility, characterized in that there are 200 or more 5 μm pearlite blocks per 0.2 mm ^{2 of the} test area.

(3) The pearlite system excellent in wear resistance and ductility, characterized in that the rails of (1) and (2) contain C: more than 0.85 to 1.40% in mass%. rail.

(4) The rails of (1) and (2) further contain, in mass%, one or more of the following components (1) to (5) selectively, with the balance being Fe and inevitable impurities. Perlite rail with excellent wear and ductility. Cr: 0.05-2.00%, Mo: 0.01-0.
50% 1 type or 2 types, V: 0.005-0.50%, Nb: 0.002-
0.050% of 1 type or 2 types, B: 0.0001 to 0.0050%, Co: 0.10 to 2.00%, Cu: 0.05 to 1.
00% 1 type or 2 types, Ni: 0.01 to 1.00%, Ti: 0.0050 to 0.0500%, Mg: 0.0
005-0.0200%, Ca: 0.0005-0.0
150% of 1 type or 2 types or more, Al: 0.0080 to 1.00%, Zr: 0.0001 to 0.2000%,

(5) With respect to the wear resistance and the ductility, the hardness is at least in the range of Hv300 to 500 at a depth of 20 mm from the surface of the head corner and the top surface of the steel rail. Excellent perlite rail.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The present inventors first organized the relationship between the occurrence of rail breakage and the mechanical properties of the pearlite structure. As a result, the load speed of the rail head caused by contact with the wheel is relatively slow, so the breakage phenomenon generated from the rail head is more ductile in the tensile test than in the impact test, which is a relatively fast load speed. It was confirmed that there is a good correlation with.

Next, the present inventors re-examined the relationship between the ductility and the block size of the pearlite structure in a steel rail having a high carbon content pearlite structure. As a result, when the average block grain size of the pearlite structure becomes finer, the ductility of the pearlite structure tends to improve, but in the region where the average pearlite block grain size is extremely fine, the average block grain size is simply It was confirmed that the ductility was not sufficiently improved even if the diameter was reduced.

Therefore, the present inventors examined the ductility controlling factor of the pearlite structure in the region where the average block grain size of the pearlite structure is fine. As a result, the ductility of the pearlite structure has a correlation with the number of fine pearlite block grains having a certain grain size, not the average block grain size. It has been found that the ductility of the pearlite structure is greatly improved by controlling the number of fine pearlite block grains having the above to a certain value or more.

As a result of the above, in a steel rail having a pearlite structure with a high carbon content, by controlling the number of fine pearlite block grains having a certain grain size in the rail head, the wear resistance of the rail head is improved. It was found that ductility is improved at the same time. That is, the present invention improves the wear resistance of the head of a heavy-duty railroad rail with high carbon content and, at the same time, controls the number of fine pearlite block grains having a certain grain size to achieve cold The purpose is to prevent the occurrence of damage such as rail breakage in the ground.

Next, the reasons for limitation of the present invention will be described in detail. (1) Definition of particle size and number of particles of pearlite First, the particle size of pearlite block that defines the number of particles is 1 to 1
The reason for defining the range of 5 μm will be described. This is because the pearlite block having a particle size of more than 15 μm does not significantly contribute to improving the ductility of the fine pearlite structure.
Further, the pearlite block having a particle size of less than 1 μm contributes to the improvement of ductility of the fine pearlite structure, but its contribution is small. Therefore, the particle size of the pearlite block that defines the number of particles is limited to the range of 1 to 15 μm.

Next, the number of grains of the pearlite block having a grain size of 1 to 15 μm is 200 per 0.2 mm ^{2 of the} test area.
Explain the reason for specifying more than one item. Test area 0.2mm
^{This is because if the} number of grains of the pearlite block having a grain size of 1 to 15 μm per ² is less than 200, the ductility of the fine pearlite structure cannot be improved. In addition, particle size 1 to 1
Although the upper limit is not set for the number of grains of the pearlite block having 5 μm, the upper limit is practically 1000 per 0.2 mm ^{2 of the} test area due to restrictions of rolling temperature during rail manufacturing and cooling conditions during heat treatment. Becomes

Next, the number of grains of the pearlite block having a grain size of 1 to 15 μm per test area of 0.2 mm ² is 20.
The reason why the region of 0 or more is limited to at least a part of the range up to the depth of 10 mm from the head corner and the surface of the crown will be described. The breakage generated from the rail head basically starts from the rail head surface. Therefore, in order to prevent rail breakage, it is necessary to increase the ductility of the rail head surface portion, that is, the number of grains of the pearlite block having a grain size of 1 to 15 μm. When the correlation between the ductility of the rail head surface and the rail head surface pearlite block was investigated by an experiment, the ductility of the rail head surface correlates with the pearlite block size ranging from the top surface to a depth of 10 mm. I found out that there is. Furthermore, as a result of investigating the correlation with the ductility of the rail head surface, if there is a region where the number of grains of the pearlite block having a grain size of 1 to 15 μm is 200 or more in at least a part of this region, the ductility of the rail head surface is It was confirmed that rail breakage could be suppressed as a result. This limitation is based on the above survey results.

Here, a method of measuring the pearlite block size will be described. The pearlite block is measured by the modified curling etch method, etch pit method,
Backscattered electron diffraction (EBSP) by SEM
ack-Scatter diffraction Pattern) method. Since the pearlite block size is minute in this measurement, it was difficult to confirm it by the modified curling etching method or the etch pit method. Therefore, the backscattered electron diffraction (EBSP) method was used.

The measurement conditions are described below. For the measurement, the particle size of the pearlite block was measured according to the procedure of, and the number of particles of the pearlite block having a particle size of 1 to 15 μm per 0.2 mm ^{2 of the} test area was counted. The measurement was performed at least two visual fields at each observation position, the number of particles was counted according to the following procedure, and the average value was used as the representative number of particles at the observation position. ● Measurement conditions of pearlite block SEM: High resolution scanning microscope Pretreatment for measurement: Machined surface 1 μm Diamond polishing → Electrolytic polishing Measurement field of view: 400 × 500 μm ² (Test area 0.2
mm ² ) SEM beam diameter: 30 nm Measurement step (interval): 0.1 to 0.9 μm Grain boundary recognition: At adjacent measurement points, a crystal orientation difference of 15 ° or more (large angle grain boundary) is recognized as a pearlite block grain boundary. It was Particle size measurement: After measuring the area of each pearlite block particle,
The pearlite block was assumed to be circular, the radius of each crystal grain was calculated, and then the diameter was calculated.

(2) Chemical composition of steel rail In claims 1 to 11, the reason why the chemical composition of the rail steel is limited to the above range will be described in detail. C is
It is an effective element that promotes pearlite transformation and secures wear resistance. When the C content is 0.65% or less, the hardness of the pearlite structure of the rail head cannot be secured, and further,
A pro-eutectoid ferrite structure is generated, wear resistance is reduced, and the service life of the rail is reduced. Further, when the amount of C exceeds 1.40%, the pro-eutectoid cementite structure is generated in the pearlite structure on the surface of the rail head or inside the head, and the density of the cementite phase in the pearlite structure is increased, so that the pearlite structure Ductility decreases. Therefore, the C content is 0.65 to 1.40.
Limited to%. In order to further improve the wear resistance, the density of the cementite phase in the pearlite structure is further increased to further improve the wear resistance.
It is desirable to make it super.

Si is an essential component as a deoxidizer.
It is also 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 pro-eutectoid cementite structure and improves the hardness and toughness of the rail. is there. But,
If it is less than 0.05%, the effect cannot be expected sufficiently, and no improvement in hardness or toughness is observed. Further, if it exceeds 2.00%, many surface defects are generated during hot rolling and the weldability is deteriorated due to the formation of oxides. Further, not only the pearlite structure itself becomes brittle and the ductility of the rail decreases, but also surface damage such as spalling occurs, and the service life of the rail decreases. Therefore, the Si amount is set to 0.05 to 2.0.
Limited to 0%.

Mn is an element that enhances the hardenability and makes the pearlite lamella spacing finer to secure the hardness of the pearlite structure and improve the wear resistance. However, if the content is less than 0.05%, the effect is small,
It becomes difficult to secure the wear resistance required for the rail. On the other hand, if it exceeds 2.00%, the hardenability is remarkably increased, a martensite structure harmful to wear resistance and toughness is easily generated, and segregation is promoted, so that a high carbon steel component system (C>
(0.85%), the proeutectoid cementite structure is generated in the pillar portion and the toughness of the rail is reduced. Therefore, Mn
The amount was limited to 0.05-2.00%.

Further, the rail manufactured with the above-mentioned component composition improves the wear resistance by strengthening the pearlite structure, prevents the toughness from decreasing by suppressing the formation of the pro-eutectoid cementite structure, and softens or embrittles the heat-affected zone of the weld zone. To improve the ductility and toughness of the pearlite structure, strengthen the pearlite structure and prevent the formation of pro-eutectoid cementite.
b, B, Co, Cu, Ni, Ti, Mg, Ca, Al,
The element of Zr can be added if necessary.

Here, Cr and Mo raise the equilibrium transformation point of pearlite and mainly secure the hardness of the pearlite structure by refining the pearlite lamella spacing.
V and Nb suppress the growth of austenite grains due to the carbides and nitrides generated during hot rolling and the subsequent cooling process, and further improve the ductility and hardness of the pearlite structure by precipitation hardening. In addition, carbides and nitrides are stably generated during reheating and softening of the heat affected zone of the welding joint is prevented. B reduces the cooling rate dependence of the pearlite transformation temperature and makes the hardness distribution of the rail head uniform. Co, Cu
Dissolves in ferrite in the pearlite structure to increase the hardness of the pearlite structure. Ni prevents embrittlement during hot rolling due to the addition of Cu, at the same time improves the hardness of pearlite steel, and further prevents softening of the heat affected zone of the welding joint. Ti makes the structure of the heat-affected zone finer and prevents the weld joint from becoming brittle. Mg and Ca serve to refine the austenite grains during rail rolling and, at the same time, promote the pearlite transformation and improve the ductility of the pearlite structure. Al shifts the eutectoid transformation temperature to a high temperature side and simultaneously shifts the eutectoid carbon concentration to a high carbon side, strengthens the pearlite structure and suppresses the formation of proeutectoid cementite, improves the wear resistance of the rail and reduces the toughness. Prevent. Zr suppresses the formation of a segregation zone at the center of the slab by increasing the equiaxed crystallization rate of the solidification structure by the ZrO ₂ inclusions becoming the solidification nuclei of high carbon rail steel, which is harmful to the toughness of the rail. The main purpose of addition is to suppress the formation of a disaggregated cementite structure.

The reasons for limiting each of these ingredients are as follows:
The details will be described below. Cr is an element that raises the equilibrium transformation point of pearlite and, as a result, makes the pearlite structure finer and contributes to higher hardness (strength), and at the same time strengthens the cementite phase and improves the hardness (strength) of the pearlite structure. However, if it is less than 0.05%, the effect is small and the effect of improving the hardness of the rail steel is not seen. Further, if added in excess of 2.00%, the hardenability increases, a large amount of martensite structure is generated, and the toughness of the rail decreases. Therefore, the amount of Cr is set to 0.05-2.
Limited to 00%.

Like Mo, Mo is an element that raises the equilibrium transformation point of pearlite and, as a result, contributes to higher hardness (strength) by making the pearlite structure finer and improves the hardness (strength) of the pearlite structure. However, if it is less than 0.01%, the effect is small, and the effect of improving the hardness of the rail steel cannot be seen at all. Further, if added in excess of 0.50%, the transformation rate of the pearlite structure is significantly reduced, and a martensite structure harmful to toughness is likely to be formed. Therefore, the amount of Mo added is 0.01 to 0.50.
Limited to%.

When V is heat-treated at a high temperature, V refines austenite grains due to the pinning effect of V carbide and V nitride, and further, V carbide produced in the cooling process after hot rolling, The precipitation hardening by V-nitride increases the hardness (strength) of the pearlite structure and
It is an element effective in improving ductility. Also, Ac1
In the heat-affected zone reheated to a temperature range below the point, it is an element effective for generating V carbides and V-nitrides in a relatively high temperature range and preventing softening of the weld joint heat-affected zone. However, if it is less than 0.005%, the effect cannot be sufficiently expected, and the hardness and ductility of the pearlite structure are not improved. Further, if added in excess of 0.500%, coarse V carbides and V nitrides are produced, and the toughness and internal fatigue damage resistance of the rail are reduced. Therefore, the V amount is 0.00
It was limited to 5 to 0.500%.

Like V, when Nb is heat-treated by heating it to a high temperature, Nb makes the austenite grains fine by the pinning effect of Nb carbide and Nb nitride, and further, in the cooling process after hot rolling. Nb carbide formed, Nb
It is an element effective for increasing the hardness (strength) of the pearlite structure and at the same time improving the ductility by precipitation hardening by nitride. In the heat-affected zone reheated to a temperature below the Ac1 point, Nb from low temperature to high temperature
It is an element effective in stably forming carbides and Nb nitrides and preventing softening of the heat affected zone of the welding joint. However, the effect cannot be expected if it is less than 0.002%, and no improvement in hardness or ductility of the pearlite structure is observed. Also, if added in excess of 0.050%, coarse N
Carbide of b and nitride of Nb are generated, and the toughness of the rail and the internal fatigue damage resistance are reduced. Therefore, the Nb amount is 0.0
It was limited to 02 to 0.050%.

B forms iron carbon boride and suppresses the formation of proeutectoid cementite, and at the same time, reduces the cooling rate dependency of the pearlite transformation temperature, makes the hardness distribution of the head uniform, and lowers the toughness of the rail. However, if the content is less than 0.0001%, the effect is not sufficient and no improvement is observed in the hardness distribution of the rail head. Further, when added in excess of 0.0050%, coarse iron carboride is generated, and ductility and toughness, and further, internal fatigue damage resistance is greatly reduced, so the B content is 0.0001.
It was limited to ~ 0.0050%.

Co dissolves in ferrite in the pearlite structure as a solid solution, and the solid solution strengthens the hardness (strength) of the pearlite structure.
Is an element that improves the ductility by increasing the transformation energy of pearlite to make the pearlite structure finer, but if it is less than 0.10%, its effect cannot be expected. Moreover, if added in excess of 2.00%, the ductility of the ferrite phase is significantly reduced,
Spalling damage occurs on the rolling surface, which reduces the surface damage resistance of the rail. Therefore, the Co amount is 0.10 to
Limited to 2.00%.

Cu dissolves in ferrite in the pearlite structure as a solid solution, and the solid solution strengthens the hardness (strength) of the pearlite structure.
Although it is an element that improves, the effect cannot be expected if it is less than 0.05%. If added in excess of 1.00%, martensite structure, which is harmful to toughness, is likely to be formed due to remarkable improvement in hardenability. Furthermore, the ductility of the ferrite phase is significantly reduced, and the ductility of the rail is reduced. Therefore, the amount of Cu is limited to 0.05 to 1.00%.

Ni is an element that prevents brittleness during hot rolling due to the addition of Cu, and at the same time increases the hardness (strength) of the pearlite steel by strengthening the solid solution in ferrite. Furthermore, in the heat-affected zone of welding, Ni ₃ Ti
Is an element that suppresses the softening due to precipitation strengthening by finely precipitating the intermetallic compound. However, if it is less than 0.01%, its effect is extremely small, and if it is added in excess of 1.00%, the ferrite phase of Ductility is significantly reduced, spalling damage occurs on the rolling surface, and surface damage resistance of the rail is reduced. Therefore, the amount of Ni is limited to 0.01 to 1.00%.

By utilizing the fact that Ti carbide and Ti nitride precipitated during reheating during welding do not dissolve in Ti, the structure of the heat-affected zone heated to the austenite region is miniaturized, and the weld joint is It is an effective component for preventing embrittlement of parts. However, if it is less than 0.0050%, its effect is small, and if it is added over 0.0500%, coarse Ti carbide and Ti nitride are generated, and the ductility and toughness of the rail, as well as the internal resistance The Ti content was limited to 0.0050 to 0.050% because the fatigue damage was significantly reduced.

Mg combines with O, S, Al or the like to form a fine oxide, and suppresses the grain growth of crystal grains during reheating during rail rolling, thereby making the austenite grains finer. , Is an element effective in improving the ductility of the pearlite structure. In addition, MgO and MgS finely disperse MnS, form a thin strip of Mn around MnS, and contribute to the formation of pearlite transformation. As a result, the pearlite block size is made finer, thereby reducing the ductility of the pearlite structure. Is an effective element to improve the. But,
If less than 0.0005%, the effect is weak and 0.0200.
%, Mg coarse oxide is generated, and the toughness of the rail and further the internal fatigue damage resistance are lowered. Therefore, the Mg content is limited to 0.0005 to 0.0200%.

Ca has a strong bonding force with S and forms a sulfide as CaS. Further, CaS finely disperses MnS and forms a Mn diluted zone around MnS, which causes the formation of pearlite transformation. It is an element that contributes and, as a result, reduces the size of the pearlite block to improve the ductility of the pearlite structure. But 0.0
If it is less than 005%, its effect is weak, and if it is added in excess of 0.0150%, coarse oxides of Ca are generated, and the toughness of the rail and further the internal fatigue damage resistance are reduced.
The amount of Ca was limited to 0.0005 to 0.0150%.

Al is an element that shifts the eutectoid transformation temperature to the high temperature side and simultaneously shifts the eutectoid carbon concentration to the high carbon side, and toughness is achieved by increasing the strength of the pearlite structure and suppressing the formation of the proeutectoid cementite structure. It is an element that prevents the decrease, but if it is 0.0080% or less, its effect is weak and 1.0
If it is added in excess of 0%, it becomes difficult to form a solid solution in steel, and coarse alumina inclusions that are the starting point of fatigue damage are generated, and the toughness of the rail and further the internal fatigue damage resistance are reduced. . Moreover, since an oxide is generated during welding and the weldability is significantly reduced, the Al content is 0.0080 to 1.00.
Limited to%.

Since Zr has a good lattice matching with γ-Fe in ZrO ₂ inclusions, γ-Fe becomes a solidification nucleus of high carbon rail steel which is a primary solidification crystal, and the equiaxed crystallization rate of the solidification structure is increased. By increasing the content, it is an element that suppresses the formation of a segregation zone at the center of the slab and suppresses the formation of a pro-eutectoid cementite structure harmful to the toughness of the rail. However, when the amount of Zr is 0.0001% or less, the number of ZrO ₂ -based inclusions is small, and the ZrO ₂ -based inclusions do not sufficiently function as a solidification nucleus. As a result, the effect of suppressing the formation of pro-eutectoid cementite structure decreases. Further, the Zr amount is 0.20
If it exceeds 00%, a large amount of coarse Zr-based inclusions are formed,
The toughness of the rail is reduced, and internal fatigue damage starting from coarse Zr-based inclusions is likely to occur, and the service life of the rail is reduced. Therefore, the Zr amount is 0.0001 to
It was limited to 0.2000%.

The rail steel composed of the above-described composition is melted in a commonly used melting furnace such as a converter or an electric furnace, and this molten steel is ingot-cast, ingot-casted or continuously cast, It is manufactured as a rail through hot rolling. Next, the rails that retain the high-temperature heat of this hot rolling or the rail heads that have been reheated to a high temperature for the purpose of heat treatment are subjected to accelerated cooling to form a pearlite structure with high hardness on the rail heads. It is possible to generate stably.

In the above manufacturing method, a pearlite block having a grain size of 1 to 15 μm is measured in an area of 0.2 mm ^{2 in} at least a part of a depth of 10 mm from the surface of the rail head corner and the surface of the crown. As a method of making 200 or more pieces per time, the temperature at the time of hot rolling is set as low as possible, and further accelerated cooling is performed as soon as possible after rolling to suppress austenite grain growth immediately after rolling, and to perform final rolling. It is desirable to perform accelerated cooling in a state in which the surface reduction rate is high and the high strain energy is accumulated in the austenite grains. Preferred hot rolling,
As the heat treatment conditions, the final rolling temperature is 980 ° C or lower, the final rolling surface reduction rate is 8% or higher, and the accelerated cooling rate is 800 to 550 ° C.
The interval is 3 ° C / sec or more.

When the rail is reheated for the purpose of heat treatment, the effect of strain energy cannot be used, so it is desirable to make the reheating temperature as low as possible and the accelerated cooling rate faster. As a preferable reheating heat treatment condition, the reheating temperature is 1000 ° C. or less, and the accelerated cooling rate is 800 ° C. to 550 ° C. and 5 ° C./sec or more.

(3) Hardness of Rail Head and Its Range The reason why the hardness in the depth range of 20 mm is limited to the range of Hv 300 to 500 from the head surface of the head corner portion and the top portion as a starting point will be described. . In this component system, if the hardness is less than Hv300, it becomes difficult to secure wear resistance when used in cold regions, and the service life of the rail decreases. Further, if the hardness exceeds Hv500, the wear resistance is remarkably improved, and fatigue damage is accumulated on the rolling surface, and the texture develops, resulting in rolling fatigue damage such as dark spot damage and surface damage resistance. Sex is greatly impaired. Therefore, the hardness of the pearlite structure is Hv30.
The range is limited to 0 to 500.

Next, the range of hardness Hv 300 to 500 is
The reason for limiting the depth to the range of 20 mm from the head surface of the head corner portion and the head top portion will be described.
When the length is less than 20 mm, considering the service life of the rail, the wear resistance required for the rail in the cold district is small as a required area, and it is difficult to secure a sufficient service life of the rail. Further, if the hardness Hv is in the range of 300 to 500 and the depth is 30 mm or more from the head surface of the head corner and the head top, the rail service life is further improved, which is more preferable.

Here, FIG. 1 shows a region where a pearlite structure having a hardness Hv of 300 to 500 and a name at the head cross-sectional surface position of the pearlite rail excellent in wear resistance and ductility of the present invention is required. In the rail head, 1 is the crown, 2
Is a head corner portion, and one of the head corner portions 2 is a gauge corner (GC) portion that mainly contacts the wheel. If the pearlite structure of this component system having a hardness of Hv 300 to 500 is arranged at least in the shaded area in the figure, the wear resistance of the rail can be secured. Therefore, it is desirable to arrange the pearlite structure whose hardness is controlled in the vicinity of the rail head surface where the wheel and the rail are mainly in contact with each other, and the other part may be a metal structure other than the pearlite structure.

The metal structure of the rail of the present invention is preferably a pearlite structure as described above. However, depending on the component system of the rail and the heat treatment manufacturing method, the proeutectoid ferrite structure, proeutectoid cementite structure, bainite structure or martensite structure may be mixed in the pearlite structure in the rail column part, head surface part, and head part. There is. However, even if a small amount of these structures is mixed, it does not have a great adverse effect on the wear resistance and ductility of the pearlite rail of the present invention.

[0047]

EXAMPLES Next, examples of the present invention will be described. Table 1 shows the chemical composition of the rail steel of the present invention, rolling and heat treatment conditions, head microstructure (5 mm below the head surface), grain size 1 to 15.
The number of particles of a pearlite block having a size of μm, the measurement position, and the hardness of the rail head (5 mm below the head surface) are shown. In addition, Table 1 also shows the amount of wear of the rail head material after the 700,000 times repetition in the Nishihara-type wear test under the forced cooling condition shown in FIG. 2 and the tensile test result. In FIG. 2, 3 is a rail test piece, 4 is a mating member, and 5 is a cooling nozzle.

Table 2 shows the chemical composition of the comparative rail steel, rolling and heat treatment conditions, head microstructure (5 mm below the head surface), grain number and measurement position of pearlite block having a grain diameter of 1 to 15 μm, rail head (head). The hardness is 5 mm below the surface. In addition, Table 1 also shows the amount of wear of the rail head material after the 700,000 times repetition in the Nishihara-type wear test under the forced cooling condition shown in FIG. 2 and the tensile test result.

The structure of the rail is as follows. -Rail steel of the present invention (12 pieces) Codes A to L Within the above composition range, at least a part of the range up to a depth of 10 mm from the head corner portion and the surface of the crown portion, a pearlite block having a particle size of 1 to 15 µm. Is the test area 0.2
Perlite rails with excellent wear resistance and ductility, characterized by the presence of 200 or more pieces per mm ² . -Comparative rail steel (10 pieces) Reference M-V Reference M-P: Comparative rail steel (4 pieces) in which the amounts of C, Si and Mn added are outside the above claims. Codes Q to V: Within the above component range, a pearlite block having a particle size of 1 to 15 μm is a test area of 0.2 mm ^{2 in} at least a part of a range from the head corner portion and the surface of the crown to a depth of 10 mm. Less than 200 comparative rail steels (6).

Now, the drawings in this specification will be described. FIG. 1 shows the names of the pearlite rails having excellent wear resistance and ductility according to the present invention at the head cross-section surface position and the areas where wear resistance is required. FIG. 2 shows an outline of the Nishihara abrasion tester. In the figure, 3 is a rail test piece, 4 is a mating member, and 5 is a cooling nozzle. Further, FIG. 3 illustrates the test piece sampling positions in the wear tests shown in Tables 1 and 2. FIG. 4 illustrates the test piece sampling positions in the tensile tests shown in Tables 1 and 2. Further, FIG. 5 shows the rail steel of the present invention shown in Table 1 (symbol:
(A to L) and the comparative rail steels (codes: MN) shown in Table 2 showing the relationship between the carbon content and the wear amount in the wear test results, and FIG. 6 shows the rail steel of the present invention shown in Table 1 (codes: A to L)
And the carbon content and the total elongation value in the tensile test results of the comparative rail steels (symbols: Q to V) shown in Table 2 are shown.

Various tests were conducted as follows. ・ Head wear test   Testing machine: Nishihara abrasion tester (see Fig. 2)   Test piece shape: Disc-shaped test piece (outer diameter: 30 mm, thickness: 8 mm)   Test piece sampling position: 2 mm below the rail head surface (see Fig. 3)   Test load: 686N (contact surface pressure 640MPa)   Slip rate: 20%   Counterpart material: Perlite steel (Hv380)   Atmosphere: In the air   Cooling: Forced cooling with compressed air (flow rate: 100 Nl / min)   Number of repetitions: 700,000 times

[0052] ・ Head tension test   Testing machine: Universal compact tensile testing machine   Test piece shape: Similar to JIS No. 4                   Parallel part length: 25 mm, parallel part diameter: 6 mm,                   Distance between elongation measurement scores: 21 mm   Test piece sampling position: 5 mm below the rail head surface (see Fig. 4)   Tensile speed: 10mm / min   Test temperature: Room temperature (20 ℃)

As shown in Tables 1 and 2, the rail steels of the present invention (symbols: A to L) have the addition amounts of C, Si and Mn as compared with the comparative rail steels (symbols of MP). By keeping the content within a certain range, a pro-eutectoid cementite structure, a pro-eutectoid ferrite structure, a martensite structure, etc. that adversely affect the wear resistance and ductility of the rail were not formed, and the surface damage resistance was good. In addition, as shown in FIG. 5, the rail steel of the present invention (symbols: A to L) is more wear resistant than the comparative rail steel (symbols: M to N) by keeping the carbon content within a certain range. Has improved. In particular, the rail steel of the present invention having a carbon content of more than 0.85% (symbols: E to L) has a higher wear resistance than the rail steel of the present invention having a carbon content of 0.85% or less (symbols: A to D). It has improved even more. Further, as shown in Tables 1 and 2, the rail steels of the present invention (reference numerals: A to L) are comparative rail steels (reference numeral:
Compared with Q to V), the ductility of the rail head is improved by controlling the number of pearlite blocks having a particle size of 1 to 15 μm, and the occurrence of breakage such as rail breakage in cold regions can be prevented. It has become possible.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

As described above, according to the present invention, it is possible to control the amount of C added, and further the number of pearlite blocks having a particle size of 1 to 15 μm in a pearlite steel rail used in heavy-duty railways. As a result, the wear resistance and ductility of the rail head can be improved, the wear resistance of the rail used in cold regions can be improved, and the occurrence of damage such as rail breakage can be prevented.

[Brief description of drawings]

FIG. 1 is a view showing a name and a region where wear resistance is required at a head cross-section surface position of a pearlite rail having excellent wear resistance and ductility according to the present invention.

FIG. 2 is a diagram showing an outline of a Nishihara-type abrasion tester.

FIG. 3 is a diagram showing the test piece sampling positions in the wear tests shown in Tables 1 and 2.

FIG. 4 is a view showing a test piece sampling position in the tensile tests shown in Tables 1 and 2.

5 is a diagram showing the relationship between the carbon content and the wear amount in the wear test results of the present invention rail steels (symbols: A to L) shown in Table 1 and the comparative rail steels (symbols: M to N) shown in Table 2. FIG. .

FIG. 6 shows the relationship between the carbon content and the total elongation value in the tensile test results of the present invention rail steels (symbols: A to L) shown in Table 1 and the comparative rail steels (symbols: Q to V) shown in Table 2. Fig.

[Explanation of symbols]

1: Top of the head 2: Head corner 3: Rail test piece 4: Counterpart material 5: Nozzle for cooling

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuya Iwano             No. 1-1 Tobata-cho, Tobata-ku, Kitakyushu, Fukuoka             Nippon Steel Co., Ltd., Yawata Works F-term (reference) 4K032 AA01 AA02 AA06 AA07 AA08                       AA09 AA10 AA11 AA12 AA14                       AA16 AA19 AA22 AA23 AA31                       AA32 AA35 AA36 AA39 BA00                       CB01 CB02 CC04 CD02 CF03

Claims (12)

[Claims] 1. A steel rail having a pearlite structure containing C: 0.65 to 1.40% in mass%, and at least one of a range up to a depth of 10 mm from a head corner portion and a top surface. A pearlite rail having excellent wear resistance and ductility, characterized in that there are 200 or more pearlite blocks having a particle size of 1 to 15 μm per 0.2 mm ^{2 of the} test area. 2. In mass%, C: 0.65 to 1.40%,
Si: 0.05 to 2.00%, Mn: 0.05 to 2.0
In a steel rail exhibiting a pearlite structure containing 0%, a depth of 10 from the corners of the head and the surface of the crown
Particle size 1 to 15 μm in at least part of the range up to mm
Perlite block is ² per 0.2 mm ² test area
A perlite rail with excellent wear resistance and ductility, characterized by the presence of at least 100 rails. 3. C: 0.85 to 1.40% in mass%
The pearlite rail having excellent wear resistance and ductility according to claim 1 or 2, further comprising: 4. In mass%, further Cr: 0.05-
The wear resistance according to any one of claims 1 to 3, wherein 2.00% and Mo: 0.01 to 0.50% are contained, and the balance is Fe and inevitable impurities. Perlite rail with excellent ductility. 5. In mass%, further, V: 0.005-
0.50%, Nb: 0.002-0.050% is contained, and the balance consists of Fe and unavoidable impurities, and wear resistance according to any one of claims 1 to 4, Perlite rail with excellent ductility. 6. In mass%, further, B: 0.0001-
The pearlite rail excellent in wear resistance and ductility according to any one of claims 1 to 5, characterized in that it contains 0.0050% and the balance is Fe and unavoidable impurities. 7. In mass%, further, Co: 0.10-
2.00%, Cu: 0.05 to 1.00% of 1 type or 2 types are contained, and the balance consists of Fe and inevitable impurities. Perlite rails with excellent wear resistance and ductility as described. 8. In mass%, further, Ni: 0.01-
The pearlite rail excellent in wear resistance and ductility according to any one of claims 1 to 7, characterized in that it contains 1.00% and the balance is Fe and inevitable impurities. 9. In mass%, Ti: 0.0050
~ 0.0500%, Mg: 0.0005-0.0200
%, Ca: 0.0005 to 0.0150% of 1 type or 2 types or more, and the balance consists of Fe and unavoidable impurities. Perlite rail with excellent wear resistance and ductility. 10. In mass%, further, Al: 0.008
The pearlite rail excellent in wear resistance and ductility according to any one of claims 1 to 9, characterized in that it contains 0 to 1.00% and the balance is Fe and inevitable impurities. 11. In mass%, further Zr: 0.000
The pearlite rail having excellent wear resistance and ductility according to any one of claims 1 to 10, wherein the pearlite rail contains 1 to 0.2000% and the balance is Fe and inevitable impurities. 12. The steel rail according to claim 1, wherein the head corner portion and the top surface are used as starting points.
Hardness in the range of at least 20 mm depth is Hv300 ~ 5
A perlite rail with excellent wear resistance and ductility, which is characterized by a range of 00.