JP2000212693A - High strength pearlitic rail excellent in toughness and ductility and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high strength pearlitic rail excellent in toughness and ductility in a cold district. SOLUTION: As to a high strength pearlitic rail excellent in toughness and ductility and its production, the rail has a compsn. contg., by weight, 0.55 to 1.20% C, 0.10 to 1.20% Si, 0.10 to 1.50% Mn, 0.002 to 0.035% S, 0.0004 to 0.02% Mg, and the balance Fe with inevitable impurities, and, at least the rail head part has a structure consisting substantially of pearlite in which Mg oxides having the size of 0.01 to 10 μm diameter are present by 500 to 100,000 in 1 mm2 in the optional cross-section in the pearlitic structure. By the addition of Mg into molten steel, fine Mg oxides are formed, and, by using the Mg oxides and MnS with the oxides as the nuclei, a high toughness rail satisfying Russian standards or the like can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength rail in which the pearlite structure of rail steel is refined to improve toughness and ductility, and to a method for producing the same.

[0002]

2. Description of the Related Art At present, railway transportation is being increased in load for improving transportation efficiency and speeding up for speeding transportation, and the requirements for rail characteristics are becoming stricter. Heavy load railways require more abrasion resistance and head internal fatigue damage resistance in sharply curved sections, and high-speed railways have a problem of increasing the rate of rail replacement mainly due to head surface damage in straight sections. . In addition to this, in the cold region railways, rail replacement due to the occurrence of rail cracks is concentrated in the winter season, and improving the toughness of the rail material has become a necessary issue for extending the rail life.

[0003] Heavy loading for improving transport efficiency promotes wear of the rail head, and the life of the rail has been shortened due to increased fatigue damage. In order to improve the shortening of rail life in heavy-duty railways, technical development of high-strength rail steel with excellent wear resistance has been actively conducted. As a result, almost high-strength rails have been used in curved sections.

On the other hand, along with the improvement of the wear resistance of the rail steel, a fatigue damage layer, which should be originally scraped off by the wear, remains on the rail head surface or the gauge corner (GC) surface against which the root of the wheel flange is pressed. Generation has begun to be observed. Furthermore, the improvement of the abrasion resistance of the rail steel reduces the stress concentration caused by the wheel load by the rail GC.
It was fixed to one point inside, and the fatigue damage from inside the rail GC was increased. In order to improve the head surface damage resistance and the internal fatigue damage resistance of such a rail, it is important to improve the toughness and ductility of the rail material.

The following methods can be considered as measures for improving the toughness and ductility of a high-strength rail. (1) A method in which, after ordinary rolling, a rail once cooled to room temperature is reheated at a low temperature and then acceleratedly cooled. (2) A method in which austenite grains are refined by controlled rolling and then the rail head is accelerated and cooled. (3) A method of reheating to a low temperature before controlled pearlite transformation after controlled rolling, and then accelerated cooling.

[0006]

In the above method (1), for example, as described in Japanese Patent Application Laid-Open No. 55-125321, reheating is performed to a low temperature of 850 ° C. or lower, which is lower than a normal heating temperature. However, it is intended to significantly improve toughness and ductility by reducing the size of austenite grains. However, when heating at a low temperature and deepening the heating to the inside of the rail head, it is necessary to reduce the amount of heat input and perform heating for a long time. This heat treatment impairs productivity and raises manufacturing costs. .

The method (2) is described in, for example,
-138427 and JP-A-52-138428.
As described in Japanese Patent Application Laid-Open Publication No. H10-107, an attempt is made to improve toughness and ductility by making austenite grains finer by controlled rolling. However, there are also problems from the viewpoint of the rolling mill's ability to require a large rolling force or the like, or the shape controllability in that the cross-sectional shape of the rail and the dimensional accuracy in the longitudinal direction cannot be easily obtained.

The method (3) is described in, for example,
No. 4371, after rolling at 5% or more at 800 ° C. or less, again at 750 to 900 ° C.
In this case, the austenite grains are refined by heating to improve toughness and ductility. But,
Since this method requires a heating furnace for reheating at a low temperature after rolling, it has problems such as workability, productivity, and production cost.

Methods for improving the toughness and ductility of rail steel include, for example, JP-A-8-104946 and JP-A-8-104946.
As described in JP-A-104947 and JP-A-8-109438, Mg is added as a deoxidizing element, and the number of MnS of 0.1 to 10 μm is 600 to 12,000 per 1 mm ^2. There is a high-strength pearlitic rail with excellent ductility, and this method has made it possible to produce a rail with excellent toughness and ductility. But,
In heavy-duty railways, further heavy load and higher speed are being studied, and further improvements in toughness and ductility properties have been demanded.

Therefore, the present inventors first studied in detail the formation of Mg oxide. As a result, when Mg is added as a deoxidizing element, a fine Mg oxide is generated, and when it is generated at the time of secondary deoxidation, an extremely fine Mg oxide is generated. As a result of examining in detail the effect of MnS generated using the Mg oxide as a nucleus, the above-mentioned JP-A-8-104946, JP-A-8-104947 and JP-A-8-1947 have been described.
In addition to the fact that MnS finely precipitated on the nucleus of the finely dispersed Mg oxide disclosed by the present applicant in JP-A-09438 suppresses the coarsening of austenite grains, the finely dispersed Mg oxide itself is It has been found that by suppressing the growth, the austenite grains are made finer, the transformation sites at the grain boundaries are increased, and the pearlite structure becomes finer.

Further, in addition to MnS, which is a nucleus of Mg oxide finely dispersed in austenite grains precipitated on the nucleus, serves as a pearlite transformation nucleus, and the finely dispersed Mg oxide itself also serves as a pearlite transformation nucleus. It has been found that a large number of transformations from the inside of the grains in addition to the transformations from the grains make the pearlite structure fine after the transformation.

By dispersing the Mg oxide generated during the deoxidation by the addition of Mg finely under certain conditions, the pearlite structure resulting from the austenite refinement is refined, and the Mg oxide is finely dispersed in the austenite grains. Mg oxide and M formed by using this Mg oxide as a nucleus
The inventors have found that a rail steel having excellent toughness and ductility can be obtained by a synergistic effect of refining the pearlite structure by intragranular transformation from nS, and completed the present invention.

[0013]

In order to achieve the above object, the present invention has the following features. That is,
(1) By weight%, C: 0.55 to 1.20%, Si: 0.10 to
1.20%, Mn: 0.10 to 1.50%, S:
0.002-0.035%, Mg: 0.0004-0.
02%, and further, if necessary, Al: 0.00%.
05-0.05%, Cr: 0.10-1.0%, N
i: 0.10 to 4.0%, Mo: 0.01 to
0.50%, Nb: 0.001 to 0.05%, B
: Containing 0.0001 to 0.0050% of one or more kinds, the balance being Fe and inevitable impurities, and at least the rail head has a diameter of 0.01 to 0.01 in an arbitrary cross section in the pearlite structure. M with a size of 10 μm
g A high-strength pearlite rail excellent in toughness and ductility, characterized by having a substantial pearlite structure in which 500 to 100,000 oxides are present in 1 mm ² . (2) After forming a slab consisting of the above components into a rail by hot rolling, the temperature is set to the austenite region temperature by hot rolling or heating after hot rolling, and at least the rail head is 700
The temperature is accelerated and cooled at a rate of 1 to 5 / sec between 500 ° C. and at least 5 mm of Mg oxide having a diameter of 0.01 to 10 μm in an arbitrary cross section of the pearlite structure in 1 mm ² . A high-strength pearlitic rail excellent in toughness and ductility, characterized by having a substantial pearlite structure having 500 to 100,000 pieces. (3) When casting a slab consisting of the above components,
Molten steel subjected to deoxidation treatment by adding at least Mg as a deoxidizing element, or molten steel formed by adding at least Mg as a secondary deoxidizing element to form secondary deoxidation of Mg oxide, or these two deoxidizing elements This is a method for producing a high-strength pearlitic rail having excellent toughness and ductility, characterized by using molten steel that has been subjected to both treatments.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. Next, the reasons for limiting the components of the rail steel will be described. C: C is an essential element for increasing the strength and forming the pearlite structure in the rail steel. If it is less than 0.55%, it is difficult to obtain the required high-strength pearlite structure.
If it exceeds 20%, not only will harmful pro-eutectoid cementite, which embrittles austenite grain boundaries, be generated, but also martensite will be generated in the heat treatment layer at the head of the rail and in the microsegregated portion of the welded part, significantly reducing the toughness ductility. 0.55-1.
Limited to 20%.

Si: Si not only contributes to high strength by solid solution strengthening in the ferrite phase in the pearlite structure, but also
There is a slight toughness and ductility improvement effect. If the content is less than 0.10%, the effect is small, and if it exceeds 1.20%, embrittlement is caused and weldability is reduced, so that 0.10 to 1.20%
Limited to.

Mn: Like C, Mn is an element that contributes to an increase in strength by lowering the pearlite transformation temperature and increasing hardenability. However, if it is less than 0.10%, the effect is small, and if it exceeds 1.50%, a martensitic structure is easily generated in the segregated portion.
%.

S: S is generally known as a harmful element, but in the present invention, MnS is formed by using an oxide in austenite as a nucleus to suppress austenite grain coarsening and MnS becomes a transformation nucleus of pearlite. The resulting pearlite structure is one of the important elements for miniaturization.
However, if it is less than 0.002%, a sufficient amount of MnS cannot be obtained, and if it exceeds 0.035%, coarse MnS
Begins to form, significantly reducing toughness and ductility,
It was limited to 0.002 to 0.035%.

Mg: Mg is an important constituent element of the present invention and contains a deoxidizing agent remaining in steelmaking. The Mg-based oxide and MnS precipitated by using this oxide as a nucleus have an effect of suppressing the growth of austenite grains by a pinning effect, and refine the pearlite structure after transformation. In addition to this effect, pearlite is generated from Mg oxide itself and MnS precipitated using the nucleus as a nucleus, and has a function of further refining the pearlite structure. As a result, it was possible to significantly improve the toughness and ductility of the rail steel. However, if it is less than 0.0004, there is almost no effect of suppressing austenite grain growth and the pearlite structure is not refined due to intragranular transformation, and if it exceeds 0.02%, coarse Mg
Oxide is generated and the toughness is significantly reduced.
It was limited to the range of 04 to 0.02%.

Further, in the present invention, in addition to the above components, one or more of Al, Cr, Ni, Mo, Nb, and B may be added as needed to improve the toughness of the ferrite ground and to improve the rail rolling. Therefore, high toughness can be obtained by reducing the size of austenite grains during heating or by reducing the size of austenite grains during controlled rolling, and thus the pearlite structure, and further increasing the pearlite structure by accelerated cooling in the cooling process. High toughness can be obtained simultaneously with strength. In addition, in the addition of the above components, Ni, Al, and Nb improve toughness, and Cr, Mo,
B is mainly intended to improve high strength and hardness at the same time as high toughness.

The reasons for limiting these chemical components will be described below. Al: Al contains a deoxidizing agent remaining during steelmaking. Al forms a composite oxide with Mg, suppresses austenite grain growth, and this Mg-Al composite oxide forms M
It becomes a nucleus of nS precipitation, and pearlite transformation is performed from these precipitates to make the structure fine. The effect of this composite precipitation is 0.0
005% or more is effective, and if it exceeds 0.05%, the Al oxide and the Mg-Al oxide are coarsened, and the toughness is lowered.
Limited to 05%.

Cr: Cr contributes to high strength by lowering the pearlite transformation temperature, and has the effect of strengthening the cementite phase in the pearlite structure. Therefore, from the viewpoint of preventing the weld joint from softening, 0.1% or more. Is effective. On the other hand, when the content exceeds 1.0%, bainite and martensite are formed not only at the element segregation portion at the time of forced cooling but also at the shoulder portion of the rail where the supercooling tendency is strong, resulting in a decrease in toughness. Therefore, the content is limited to 0.1% to 1.0% from the range where a certain contribution is expected to secure the strength and the toughness and ductility are not impaired.

Ni: Ni is a solid solution in ferrite and is an element effective for improving the toughness of ferrite.
When the content is less than 1%, the effect is extremely small.
Even if the content exceeds 0%, the effect is saturated. Therefore,
From the viewpoint of improving the toughness, the range is limited to 0.1 to 4.0%.

Mo: Mo is an element effective for improving the toughness because it suppresses the transformation rate of pearlite and refines the pearlite structure. Further, Mo prevents the induction of transformation at a high temperature in conjunction with the heat generated by the pearlite transformation of the surface layer inside the rail during accelerated cooling, and contributes to increasing the strength inside the rail to increase the strength. However, if the content is less than 0.01%, the above effect is small, and if the content exceeds 0.50%, the pearlite transformation rate is reduced, and bainite and martensite are generated in the pearlite structure, resulting in a decrease in toughness. Therefore, the range was limited to 0.01 to 0.50%.

Nb: By heating Nb at a low temperature during hot rolling, the carbonitride of Nb suppresses austenite grain growth and contributes to grain refinement. Further, austenite grains after hot rolling are refined by high-temperature heating / low-temperature finish rolling, and the pearlite structure obtained after accelerated cooling is refined. In order to obtain this effect, 0.01% or more is necessary. If it exceeds 0.05%, coarse Nb carbide, Nb nitride, and Nb carbonitride are formed, thereby lowering the toughness. Therefore, it was limited to the range of 0.01 to 0.05%.

B: B is an element that segregates at austenite grain boundaries even when added in a small amount, and significantly improves hardenability by delaying transformation. To get this effect,
0.0001% or more is required, and if it exceeds 0.0050%, carbonitride B is generated, and the toughness is significantly reduced. Therefore, the range is limited to 0.0001 to 0.0050%.

In order to reduce the toughness of the rail steel, P, which is an unavoidable element, is preferably reduced as much as possible to 0.03% or less.

The rail steel having the above-mentioned composition is subjected to smelting including deoxidation in a commonly used smelting furnace such as a converter or an electric furnace, or the smelting of the molten steel into an ingot By carrying out at least one of the secondary deoxidation of the Mg oxide when solidifying by the lump or the continuous casting method, and desirably both deoxidation treatments, it is possible to produce a finely dispersed Mg oxide. And a hot rolling method.

The pearlite generated from MnS in the austenite grains and also from the Mg oxide during cooling of the rail after hot rolling forms a fine pearlite structure together with the pearlite generated from the austenite grain boundaries.
As a result, a high-strength rail with excellent toughness can be manufactured as-rolled.

In the case where high strength of 1200 MPa or more is required together with high toughness, the steel sheet is reheated to the austenite region temperature after rolling is completed or for the purpose of heat treatment after once cooling to room temperature. 1-5 ° C / s
It is desirable to perform accelerated cooling with ec. In addition, since accelerated cooling causes pearlite transformation at a low temperature, the generation rate of pearlite transformation nuclei in rail steel is improved, and pearlite grains become fine. When the cooling rate during this accelerated cooling is less than 1 ° C./sec, the required strength cannot be obtained, and when it exceeds 5 ° C./sec, martensite is generated. Therefore, the cooling rate was limited to 1-5 ° C / sec. Such heating and cooling can be performed at least at the rail head.

As described above, accelerated cooling not only increases the strength, but also increases the austenite grain boundaries, Mg oxide and M
In the pearlite transformation from MnS with g oxide as a nucleus, transformation nuclei are increased to contribute to refinement of pearlite, and as a result, the toughness of the rail steel can be further improved. At this time, it is desirable to use a gas-liquid mixture such as air or mist as the cooling medium.

Next, the number of Mg oxides with a diameter of 0.01 to 10 μm in the pearlite structure of the rail steel
The reason why the number is limited to 500 to 100,000 in mm ² will be described. Mg oxide in the rail steel suppresses the grain growth of fine γ grains after processing by pinning, and makes the pearlite structure after transformation fine. In addition, the pearlite structure is refined and the toughness value is improved by performing pearlite transformation from Mg oxide in γ grains and MnS generated using the Mg oxide as a nucleus. At this time, an Mg oxide having an equivalent circle diameter (diameter) of less than 0.01 μm in an arbitrary cross section calculated from a cross sectional area of the Mg oxide in the cross section does not become a pearlite intragranular transformation nucleus. The size of the Mg oxide was limited to 0.001 to 10 μm because the starting point of the fracture would lower the toughness value. If the number is less than 500 in 1 mm ² , the effects of pinning and pearlite intragranular transformation are weak, and the effect of improving toughness cannot be obtained. If the number exceeds 100,000, the rail steel itself is contaminated and the toughness value is reduced. Therefore, the number of Mg oxides per 1 mm ² is limited to 500 to 100,000. Such a pearlite structure must be formed at least on the head of the rail.

[0032]

Next, an example of manufacturing a high-strength rail having high toughness manufactured according to the present invention will be described. Table 1 shows the chemical composition of the rail steel when Mg was added to the molten steel and when Mg was not added.

Table 2 shows the measurement results of the number of Mg oxides having a diameter of 0.001 to 10 μm in an arbitrary cross section present in the structure after cooling of the rail steel, the γ particle number of the sample quenched after processing, and The observation result of the presence or absence of perlite intragranular transformation is shown.

The particle size of the Mg oxide can be determined using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) at an arbitrary cross section at a magnification of 1,000 to 50,000 times. The area was determined and the diameter of a circle equal to this area was used. Further, Mg oxide in MnS is also S
Since the contrast is different in the images of EM and TEM, the particle size was calculated in the same manner as in the case of Mg oxide, with the portion having the different contrast as Mg oxide. The number of Mg oxides is determined by measuring the number of Mg oxides having a diameter of 0.01 to 10 μm in 20 visual fields, averaging the 20 visual fields according to a normal distribution, and calculating the average from the number in the area of one visual field to 1 mm ^2. The value converted to was used.

In the steel of the present invention which has been deoxidized by the addition of Mg, a predetermined amount of Mg oxide is finely dispersed, and the Mg oxide present in the grains and the M
It was confirmed that pearlite undergoes intragranular transformation from nS and the pearlite structure becomes fine.

Table 3 shows the tensile test strengths of the rail steels in which the cooling rate between 700 ° C. and 500 ° C. was changed in the range of 1 ° C./s to 5 ° C./s for each steel type in order to maintain the strength as it is as rolled. 4 shows the results of measuring the impact absorption energy at + 20 ° C. in the elongation and 2 mm U notch Charpy test.

In the tensile test, the diameter of the parallel portion was 6 mm and the length of the parallel portion was 30 mm, which was sampled from a depth of 10 mm inside the gauge corner of the rail head.
The test was performed on mm test pieces. As a result, the steel of the present invention was found to have sufficiently improved ductility due to the refinement of the pearlite structure as compared with the conventional steel. The impact test piece was taken from 1 mm below the rail head.

The test conditions are based on the Russian Γ oct standard, which specifies that the high strength
The impact-absorbing energy at 25 ° C. is required to be 25 J / cm ² or more, and the Mg-added steel of the present invention suppresses the growth of austenite fine grains after processing and changes the pearlite intragranular transformation from inside the austenite grains. Become an organization, all of which fully satisfy the Charpy absorbed energy specified in the Γoct standard.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

As described above, by controlling the size and number of Mg oxides by deoxidizing by adding Mg or the like, the pearlite structure in which austenite grains after processing become fine and transform from grain boundaries. Becomes finer,
In addition, the pearlite structure after the transformation is fine because the pearlite is transformed from the inside of the austenite grains from the Mg oxide present in the austenite grains and MnS generated from the Mg oxide as a nucleus. Further, the pearlite grains are refined even by accelerated cooling, and a shock absorption energy of 25 J / cm ² or more can be stably obtained. That is, the present invention can provide a high-strength pearlite rail excellent in toughness and ductility or a method for producing the same.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/54 C22C 38/54 (72) Inventor Kenichi Kamine 1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture No. F Term in Nippon Steel Corporation Yawata Works (reference) 4K013 AA00 BA08 BA14 EA18 FA02 4K042 AA04 BA01 BA02 CA02 CA06 CA08 CA09 CA10 DA04 DD05 DD06 DE05 DE06

Claims (8)

[Claims] C .: 0.55 to 1.20%, Si: 0.10 to 1.20%, Mn: 0.10 to 1.50%, S: 0.002 to 0. 035%, Mg: 0.0004-0.02%, the balance being Fe and unavoidable impurities,
At least the rail head has a substantial pearlite structure in which 500 to 100,000 Mg oxides having a diameter of 0.01 to 10 μm exist in 1 mm ² in an arbitrary cross section in the pearlite structure. High-strength pearlitic rail with excellent toughness and ductility. 2. C: 0.55 to 1.20%, Si: 0.10 to 1.20%, Mn: 0.10 to 1.50%, S: 0.002 to 0. 035%, Mg: 0.0004-0.02%, Al: 0.0005-0.05%, Cr: 0.10-1.0%, Ni: 0.10-4.0% , Mo: 0.01 to 0.50%, Nb: 0.001 to 0.05%, B: 0.0001 to 0.0050%, the balance being Fe and inevitable. It is made of impurities, and at least the rail head has a diameter of 0.01 to 1 at an arbitrary cross section in the pearlite structure.
Mg oxide having a size of 0 μm is 500 to 10 in 1 mm ^2.
A high-strength pearlitic rail excellent in toughness and ductility, characterized by having a substantial pearlite structure in which there are 000 rails. 3. C: 0.55 to 1.20%, Si: 0.10 to 1.20%, Mn: 0.10 to 1.50%, S: 0.002 to 0. A steel slab containing 035%, Mg: 0.0004-0.02%, and the balance consisting of Fe and unavoidable impurities is formed on a rail by hot rolling and then hot rolled or austenite by heating after hot rolling. 1 to 5 ° C / sec between 700 to 500 ° C at least at the rail head
At an accelerated cooling in at least the rail head, in any cross section in the pearlite structure having a diameter of 0.01 to 10μ
500-100 in 1 mm ² in size of the Mg oxides of m,
A method for producing a high-strength pearlite-based rail having excellent toughness and ductility, characterized by having a substantial pearlite structure having 000 pieces. 4. In% by weight, C: 0.55 to 1.20%, Si: 0.10 to 1.20%, Mn: 0.10 to 1.50%, S: 0.002 to 0. 035%, Mg: 0.0004-0.02%, Al: 0.0005-0.05%, Cr: 0.10-1.0%, Ni: 0.10-4.0% , Mo: 0.01 to 0.50%, Nb: 0.001 to 0.05%, B: 0.0001 to 0.0050%, the balance being Fe and inevitable. A steel slab made of impurities is formed into a rail by hot rolling, and then hot-rolled or heated after hot rolling to an austenite region temperature.
0 by accelerated cooling between ° C. at 1 to 5 ° C. / sec, at least the rail head, the diameter at any cross section of the pearlite structure in the magnitude of the oxide of Mg 0.01 to 10 [mu] m 1 mm ²
A method for producing a high-strength pearlite-based rail excellent in toughness and ductility, characterized by having a substantial pearlite structure in which 500 to 100,000 pieces are present. 5. A slab obtained by casting a molten steel produced by adding at least Mg as a deoxidizing element and performing a deoxidizing treatment, wherein C: 0.55 to 1.20 by weight%. %, Si: 0.10 to 1.20%, Mn: 0.10 to 1.50%, S: 0.002 to 0.035%, Mg: 0.0004 to 0.02%, with the balance being Is composed of Fe and unavoidable impurities,
After forming this steel slab into a rail by hot rolling, it is heated to austenite temperature by heating as it is or after hot rolling.
After accelerated cooling at 5 ° C./sec, at least the rail head has a diameter of 0.0 at an arbitrary cross section in the pearlite structure.
Mg oxides of 1~10μm magnitude is in 1 mm ² 500
A method for producing a high-strength pearlitic rail excellent in toughness and ductility, characterized in that it has a substantial pearlite structure having up to 100,000 pieces. 6. A slab obtained by casting a molten steel obtained by adding at least Mg as a deoxidizing element and performing a deoxidizing treatment, wherein C: 0.55 to 1.20 by weight%. %, Si: 0.10 to 1.20%, Mn: 0.10 to 1.50%, S: 0.002 to 0.035%, and Mg: 0.0004 to 0.02%. Al: 0.0005 to 0.05%, Cr: 0.10 to 1.0%, Ni: 0.10 to 4.0%, Mo: 0.01 to 0.50%, Nb: 0.001 to 0.05%, B: one or more of 0.0001 to 0.0050%, the balance being Fe and unavoidable impurities. After forming this steel slab into a rail by hot rolling, The temperature of the austenite zone is maintained by hot-rolling or by heating after hot-rolling.
Accelerated cooling at a rate of 1 to 5 ° C./sec between −500 ° C. and at least the rail head is made of Mg oxide having a diameter of 0.01 to 10 μm in an arbitrary cross section in a pearlite structure in 1 mm ² . A method for producing a high-strength pearlite-based rail having excellent toughness and ductility, characterized by having a substantial pearlite structure having 500 to 100,000 pieces. 7. M is added by adding at least Mg as a secondary deoxidizing element and generating Mg oxide by secondary deoxidizing.
g is finely dispersed, and is a slab obtained by casting molten steel. C: 0.55 to 1.20%, Si: 0.10 to 1.20%, Mn : 0.10 to 1.50%, S: 0.002 to 0.035%, Mg: 0.0004 to 0.02%, the balance being Fe and unavoidable impurities,
After forming this steel slab into a rail by hot rolling, it is heated to austenite temperature by heating as it is or after hot rolling.
After accelerated cooling at 5 ° C./sec, at least the rail head has a diameter of 0.0 at an arbitrary cross section in the pearlite structure.
Mg oxides of 1~10μm magnitude is in 1 mm ² 500
A method for producing a high-strength pearlitic rail excellent in toughness and ductility, characterized in that it has a substantial pearlite structure having up to 100,000 pieces. 8. M is added by adding at least Mg as a secondary deoxidizing element and generating Mg oxide by secondary deoxidizing.
g is finely dispersed, and is a slab obtained by casting molten steel. C: 0.55 to 1.20%, Si: 0.10 to 1.20%, Mn : 0.10 to 1.50%, S: 0.002 to 0.035%, Mg: 0.0004 to 0.02%, Al: 0.0005 to 0.05%, Cr: 0 0.10 to 1.0%, Ni: 0.10 to 4.0%, Mo: 0.01 to 0.50%, Nb: 0.001 to 0.05%, B: 0.0001 to 0.0050 % Or more, and the balance consists of Fe and inevitable impurities. This steel slab is formed into a rail by hot rolling and then hot-rolled or heated to an austenite zone temperature by heating after hot rolling. , At least 700 rail heads
Accelerated cooling at a rate of 1 to 5 ° C./sec between −500 ° C. and at least the rail head is made of Mg oxide having a diameter of 0.01 to 10 μm in an arbitrary cross section in a pearlite structure in 1 mm ² A method for producing a high-strength pearlite-based rail having excellent toughness and ductility, characterized by having a substantial pearlite structure having 500 to 100,000 pieces.