JP2001003140A - High strength pearlitic rail excellent in toughness and ductility and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength pearlitic rail for a cold district having high strength and high ductility by adding Mg and Ti to molten steel and producing fine Mg oxides and Ti precipitates. SOLUTION: This rail has a compsn. contg., by mass, 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 0.001 to 0.05% Ti and furthermore contg., at need, one or >= two kinds among Al, Ni, Cu, Nb, Cr, Mo, V and B, and the balance Fe with inevitable impurities, in which rail, at least as to the rail head, in the optional cross-section in a pearlitic structure, Mg oxides of 0.01 to 10 μm diameter are present by 500 to 100000 pieces in 1 mm2, and also, Ti oxides, Ti nitrides, Ti carbides and Ti multiple precipitates thereof of 0.01 to 10 μm diameter are present by 500 to 120000 pieces in total in 1 mm2.

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 wear, remains on the surface of the rail head and the surface of the gauge corner (GC) 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]

The above method (1) includes:
For example, as described in Japanese Patent Application Laid-Open No. 55-125321, reheating to a low temperature of 850 ° C. or lower, which is lower than the normal heating temperature, and refining austenite grains greatly reduce toughness and ductility. They are trying to improve. 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 disclosed in, for example,
JP-A-2-138427 and JP-A-52-13842
As described in Japanese Patent Publication No. 8 (KOKAI) No. 8, the aim is to improve the 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 of (3) is described in, for example,
As described in Japanese Patent No. 4371, after rolling of 5% or more at 800 ° C. or less, 750 to 900
Austenite grains are refined by heating to
It is intended to improve toughness and ductility. However, this method requires a heating furnace for reheating at a low temperature after rolling, and thus has problems such as workability, productivity, and production cost.

Further, rails having improved toughness and ductility of rail steel are disclosed in, for example, JP-A-8-104946, JP-A-8-104947 and JP-A-8-1094.
As described in Japanese Patent Publication No. 38, No. 38
g of MnS of 0.1 to 10 μm is 1 mm ²
There are 600 to 12,000 high-strength pearlite-based rails with excellent toughness and ductility.

Further, Japanese Patent Application Laid-Open Nos. Hei 6-279927, Hei 6-279929 and Hei 8-333634.
As described in JP-A-9-227943 and JP-A-9-227943, Ti is added as a deoxidizing element,
The number of 15 μm MnS is 30 to 12.0 per mm ² .
There are 00 high-strength pearlitic rails having excellent toughness and ductility, and this method has enabled the production of rails having excellent toughness and ductility. However, further heavy load and higher speed are being studied in heavy load railways, and further improvements in toughness and ductility characteristics have been demanded.

[0011]

In order to achieve the above object, the present invention has the following features. (1) In mass%, 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%, Ti: 0.001 to 0.05%, the balance being Fe and unavoidable impurities,
At least the rail head has a substantially pearlite structure, and has an arbitrary cross section having a diameter of 0.01 to 10 μm.
g oxide having a size of 500 to 100,000 in 1 mm ² and a size of 0.01 to 10 μm in diameter,
i. A high-strength pearlitic rail excellent in toughness and ductility, characterized in that a total of 500 to 120,000 nitrides, Ti carbides, or these Ti composite precipitates are present in 1 mm ² .

(2) In mass%, Al: 0.0005 to 0.05%, Ni: 0.10 to 4.0%, Cu: 0.10 to 4.0%, Nb: 0.001 to The high-strength pearlitic rail according to the above (1), which comprises one or more of 0.05% by weight. (3) In mass%, Cr: 0.10 to 1.0%, Mo: 0.01 to 0.50%, V: 0.01 to 1.0%, B: 0.0001 to 0.0050 % Or more of the high-strength pearlite-based rails having excellent toughness and ductility according to the above (1) or (2).

(4) In mass%, C: 0.55 to 1.20%, Si: 0.10 to 1.20%, Mn: 0.10 to 1.50%, S: 0.002 to 0% 0.035%, Mg: 0.0004-0.02%, Ti: 0.001-0.05%, the balance being Fe and unavoidable impurities, a steel slab is formed on a rail by hot rolling. In the cooling process after hot rolling or in the cooling process after reheating after hot rolling to austenite temperature, at least the head of the rail is cooled at a cooling rate of 700 to 500 ° C. ~
By performing accelerated cooling at 5 ° C./sec, at least a rail head has a substantially pearlite structure, and Mg oxide having a diameter of 0.01 to 10 μm in an arbitrary cross section is 500 to 100,000 in 1 mm ^2. Pieces, and the diameter is 0.01 to
High strength excellent in toughness and ductility, characterized in that a total of 500 to 120,000 Ti oxides, Ti nitrides, Ti carbides or these Ti composite precipitates having a size of 10 μm are present in 1 mm ^2. Manufacturing method of perlite rail.

(5) In mass%, Al: 0.0005 to 0.05%, Ni: 0.10 to 4.0%, Cu: 0.10 to 4.0%, Nb: 0.001 to The method for producing a high-strength pearlite-based rail excellent in toughness and ductility according to the above (4), wherein one or more kinds of 0.05% are contained. (6) In mass%, Cr: 0.10 to 1.0%, Mo: 0.01 to 0.50%, V: 0.01 to 1.0%, B: 0.0001 to 0.0050 % Of one or more of the above-mentioned (4) or (5), the method for producing a high-strength pearlitic rail excellent in toughness and ductility.

(7) A steel slab obtained by adding at least Mg as a deoxidizing element or Ti in addition thereto to perform a deoxidizing treatment and casting a smelted molten steel. 4) The method for producing a high-strength pearlite rail excellent in toughness and ductility according to (5) or (6). (8) At least Mg as a secondary deoxidizing element, or Ti in addition thereto, and secondary deoxidizing generation of Mg oxide or Ti oxide in addition to Mg oxide or Mg oxide. (4), (5), (6), or (7), wherein a slab obtained by casting molten steel obtained by dispersing Ti oxide finely is used in addition to the above. A method for manufacturing a high-strength pearlite rail having excellent toughness and ductility.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The present inventors have studied in detail the generation of Ti-based precipitates in a slab to which Mg is added. As a result, in addition to the generation of fine Mg oxides due to the addition of Mg, Ti oxides, Ti nitrides, Ti carbides, and these Ti composite precipitates are finely generated, and these precipitates suppress grain growth. Thus, austenite grains are made finer than Mg addition alone, and particularly, by secondary deoxidation of Mg and Ti oxides, a remarkably large number of fine oxides are generated, and the number of transformation sites at austenite grain boundaries is increased. It was found that the pearlite structure after transformation was fine.

Further, as a result of a detailed study on the influence of MnS generated by using Mg oxide as a nucleus during the pearlite transformation, the above-mentioned JP-A-8-104946 and JP-A-8-104946 were disclosed.
As disclosed by the present applicant in JP-A-104947 and JP-A-8-109438, Mn in which Mg oxide finely dispersed in austenite grains is finely precipitated in nuclei.
In addition to S becoming a pearlite transformation site, Mn
It has been found that the precipitation of Ti nitrides, Ti carbides and these Ti composite precipitates on S makes pearlite remarkably easy to transform, resulting in an increase in the rate of transformation from within austenite grains and a fine pearlite structure. Was.

As described above, the Mg oxide generated during the deoxidation by the addition of Mg is finely dispersed under certain conditions.
By generating i-based precipitates, the pearlite structure resulting from austenite grain refinement is refined, and the Ti-based precipitates precipitated on MnS formed on the nuclei of Mg oxides finely dispersed in austenite grains are formed. Due to the synergistic effect of refinement of pearlite structure due to intragranular transformation,
The present inventors have found that a rail steel having excellent toughness and ductility can be obtained, and have completed the present invention.

Next, the reasons for limiting the components of the rail steel will be described. The content of the components is% by mass. 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 the content exceeds 20%, not only will harmful pro-eutectoid cementite which embrittles austenite grain boundaries be formed, but also martensite will be formed in the heat treatment layer at the head of the rail and in the micro segregated portion of the welded part, significantly reducing toughness and ductility. , 0.55-
Limited to 1.20%.

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 it 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: Similar to C, Mn is an element that contributes to high 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. However, in the present invention, MnS is generated by using an oxide in austenite as a nucleus to suppress austenite grain coarsening and MnS becomes a transformation nucleus of pearlite. This is one of the important elements for the refinement of the pearlite structure.
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. Mg-based oxide and MnS precipitated with this oxide as a nucleus are:
Each has an effect of suppressing the growth of austenite grains by the pinning effect and refines 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 M
g oxides are generated and the toughness is significantly reduced.
It was limited to the range of 004 to 0.02%.

Ti: Ti is an important constituent element of the present invention. The Ti-based precipitate, together with the Mg-based oxide and MnS precipitated by using this oxide as a nucleus, suppress the austenite grain growth due to the pinning effect, and refine the pearlite structure after transformation. Further, in addition to this effect, Ti nitride is formed on MnS in which finely generated Mg oxide is precipitated in the nucleus,
Austenite intragranular transformation is remarkably facilitated starting from Ti carbides and these composite inclusions, and the pearlite structure becomes fine. As a result, it was possible to significantly improve the toughness and ductility of the rail steel. However, when the content is less than 0.001%, there is almost no effect of suppressing austenite grain growth and the pearlite structure is finely refined due to intragranular transformation.
If it exceeds 0.005%, coarse Ti-based precipitates are formed and the toughness is significantly reduced.

Further, in the present invention, in addition to the above components, if necessary, Al, Ni, Cu, Nb, Cr, M
The addition of o, V, and B improves the toughness of the ferrite ground,
High toughness can be obtained by austenite grains during heating for rail rolling or by austenite grains being refined during controlled rolling, and further high strength and high toughness can be obtained by accelerated cooling in the cooling process. Can be. In addition, in the addition of the above components,
Al, Ni, Cu, Nb improve toughness, Cr, Mo,
V and B are intended to improve high strength and hardness at the same time as 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.
Since the oxide and the Mg-Al oxide are coarsened and lower the toughness, the content of Al is set to 0.0005 to 0.0005.
Limited to 0.05%.

Ni: Ni is a solid solution in ferrite and is an element effective for improving the toughness of ferrite. 0.
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%.

Cu: Cu, like Ni, is a solid solution in ferrite and is an element effective for improving the toughness of ferrite. When the content is less than 0.1%, the effect is extremely small, and when the content exceeds 4.0%, the effect is saturated. Therefore, from the viewpoint of improvement in toughness, 0.1 to 4.0%
Limited to the range.

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, 0.001% or more is required. If it exceeds 0.05%, coarse Nb carbide, Nb nitride, and Nb carbonitride are formed, and the toughness is reduced. Therefore, it was limited to the range of 0.001 to 0.05%.

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. The above content 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 range is limited to 0.1 to 1.0% as long as a certain contribution is expected to secure the strength and the toughness and ductility are not impaired.

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, it was limited to the range of 0.01 to 0.50%.

V: V is an element that precipitates in ferrite and is effective for improving the strength. If it is less than 0.01%, an increase in strength cannot be obtained, and if it exceeds 1%, coarse V carbides are formed and toughness is reduced. Therefore, 0.01 to 1.0
%.

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%. P, which is an unavoidable element, is desirably reduced as much as possible to lower the toughness of the rail steel, and is desirably 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 performing at least one of the secondary deoxidation and desirably both of the deoxidation of Mg when solidifying by the lump or the continuous casting method, a finely dispersed Mg oxide can be generated. The slab thus formed is formed on a rail by hot rolling. In the rail after hot rolling, in addition to pearlite generated from austenite grain boundaries during cooling, pearlite is also generated from MnS and Mg oxides in austenite grains to form a fine pearlite structure.
As a result, a high-strength rail with excellent toughness can be manufactured as-rolled.

Further, when high strength of 1200 MPa or more is required together with high toughness, the steel sheet is reheated to the austenite region temperature after the rolling is completed or for the purpose of heat treatment after once cooling to room temperature. 1-5
It is desirable to perform accelerated cooling at a rate of ° C./sec. 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. The cooling rate during this accelerated cooling is 1 ° C / sec.
When it is less than 5 ° C., the required strength cannot be obtained, and when it exceeds 5 ° C./sec, martensite is generated. Therefore, the cooling rate was limited to 1 to 5 ° C / sec.

As described above, accelerated cooling not only increases the strength but also increases the austenite grain boundary, 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 reason why the number of Mg oxides having a diameter of 0.01 to 10 μm in the pearlite structure of the rail steel is limited to 500 to 100,000 in an arbitrary cross section of 1 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. Further, 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, in an arbitrary cross section, the Mg oxide having a circle equivalent diameter (diameter) of less than 0.01 μm in the cross section calculated from the cross sectional area of the Mg oxide does not become a pearlite intragranular transformation nucleus, and has an If the size exceeds this, it becomes a starting point of fracture and lowers the toughness value. Therefore, the size of the Mg oxide is limited to 0.01 to 10 μm. 1mm 50 to ²
If the number is less than 0, the effects of pinning and pearlite intragranular transformation are weak, and the effect of improving toughness cannot be obtained. Also, 1
If the number exceeds 0.00000, 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.

Further, the reason why the number of Ti-based precipitates having a diameter of 0.01 to 10 μm in the pearlite structure of the rail steel is limited to 500 to 120,000 in an arbitrary cross section of 1 mm ² . The Ti-based precipitate in the rail steel is Mg
The growth of fine γ grains after processing is suppressed by pinning simultaneously with the system oxide, and the pearlite structure after transformation is made fine. Further, Ti-based precipitates are formed on MnS generated by using Mg oxide in γ grains as nuclei.
By performing pearlite transformation with i-type precipitates as nuclei, the pearlite structure becomes fine and the toughness value is improved.

At this time, in any cross section, the equivalent circle diameter (diameter) in the cross section calculated from the cross sectional area of the Ti-based precipitate
Is less than 0.01 μm and does not become a pearlite intragranular transformation nucleus. If the size exceeds 10 μm, it becomes a starting point of fracture and lowers the toughness value. It was limited to 01 to 10 μm. 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 120,000, 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 120,000.

[0041]

Next, an example of manufacturing a high-strength rail having high toughness and ductility manufactured according to the present invention will be described.
Table 1 shows the chemical composition of the rail steel when Mg and Ti were added to the molten steel and when they were not added. Table 2
Measurement results of the number of Mg oxides having a diameter of 0.01 to 10 μm in any cross section existing in the structure after cooling the rail steel,
The observation results of the γ particle number and the presence or absence of pearlite intragranular transformation of the sample quenched after processing are shown.

The particle size of the Mg oxide was determined by 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 adding Mg, a predetermined amount of Mg oxide is finely dispersed, and the Mg oxide present in the grains and the MnS generated using the Mg oxide as nuclei are used. It was confirmed that the pearlite was transgranularly transformed and the pearlite structure became fine.

Table 3 shows the tensile test strength of the rail steel 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 keep the strength as it is and as rolled. 2 shows the results of measuring the impact absorption energy at + 20 ° C. in the elongation and 2 mm U notch Charpy tests. The tensile test was performed on a test piece having a parallel part diameter of 6 mm and a parallel part length of 30 mm taken from a depth of 10 mm inside the rail head gauge corner.

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 oct standard,
The standard requires that the high-strength heat treated rail has an impact absorption energy at + 20 ° C. of 25 J / cm ² or more. The Mg-added steel of the present invention has a fine pearlite structure due to suppression of grain growth of austenite fine grains after processing and intra-pearlite transformation from inside austenite grains.
Charpy absorbed energy stipulated in the t standard is sufficiently satisfied.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

As described above, according to the present invention,
By controlling the size and number of Mg oxides by deoxidizing by adding Mg, etc., the austenite grains after processing become finer, the pearlite structure transformed from the grain boundaries becomes finer, and Existing Mg oxide and Mn generated using this Mg oxide as a nucleus
Since the pearlite is transformed from the inside of the austenite grains from S, the pearlite structure after the transformation becomes fine. 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, according to the present invention, a high-strength pearlite rail excellent in toughness and ductility can be manufactured.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/14 C22C 38/14 38/54 38/54 (72) Inventor Kenichi Kamine Hibata, Tobata-ku, Kitakyushu Town 1-1 Nippon Steel Corporation Yawata Works F-term (reference) 4K013 AA00 BA14 EA18 4K020 AA22 AC07 AC09 BB27 4K042 AA04 BA01 BA02 CA02 CA05 CA06 CA08 CA09 CA10 CA12 CA13 DA04 DA06 DB08 DD06 DE01 DE06

Claims (8)

[Claims] 1. Mass%, 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%, Ti: 0.001-0.05%, the balance being Fe and unavoidable impurities,
At least the rail head has a substantially pearlite structure, and has an arbitrary cross section having a diameter of 0.01 to 10 μm.
g oxide having a size of 500 to 100,000 in 1 mm ² and a size of 0.01 to 10 μm in diameter,
i. A high-strength pearlitic rail excellent in toughness and ductility, characterized in that a total of 500 to 120,000 nitrides, Ti carbides, or these Ti composite precipitates are present in 1 mm ² . 2. In mass%, Al: 0.0005 to 0.05%, Ni: 0.10 to 4.0%, Cu: 0.10 to 4.0%, Nb: 0.001 to 0% The high-strength pearlite-based rail excellent in toughness and ductility according to claim 1, which contains one or more of 0.05% by weight. 3. In mass%, Cr: 0.10 to 1.0%, Mo: 0.01 to 0.50%, V: 0.01 to 1.0%, B: 0.0001 to 0 The high-strength pearlitic rail according to claim 1 or 2, wherein the high-strength pearlitic rail has excellent toughness and ductility. 4. 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%, Ti: 0.001-0.05%, the balance being Fe and unavoidable impurities is formed on a rail by hot rolling, In the cooling process after hot rolling, or in the cooling process after setting the temperature to the austenitic region by reheating after hot rolling, at least the head of the rail is cooled at a cooling rate of 700 to 500 ° C in the temperature range of 1 to 500 ° C.
By performing accelerated cooling at 5 ° C./sec, at least a rail head has a substantially pearlite structure, and Mg oxide having a diameter of 0.01 to 10 μm in an arbitrary cross section is 500 to 100,000 in 1 mm ^2. Pieces, and the diameter is 0.01 to
High strength excellent in toughness and ductility, characterized in that a total of 500 to 120,000 Ti oxides, Ti nitrides, Ti carbides or these Ti composite precipitates having a size of 10 μm are present in 1 mm ^2. Manufacturing method of perlite rail. 5. In mass%, Al: 0.0005 to 0.05%, Ni: 0.10 to 4.0%, Cu: 0.10 to 4.0%, Nb: 0.001 to 0% 5. The method for producing a high-strength pearlite-based rail excellent in toughness and ductility according to claim 4, comprising one or more of 0.05% by weight. 6. In mass%, Cr: 0.10 to 1.0%, Mo: 0.01 to 0.50%, V: 0.01 to 1.0%, B: 0.0001 to 0 6. The method for producing a high-strength pearlite-based rail excellent in toughness and ductility according to claim 4 or 5, comprising one or more of .0050%. 7. A steel slab obtained by adding at least Mg as a deoxidizing element or Ti in addition thereto to perform a deoxidizing treatment and casting a smelted molten steel. 5. A method for producing a high-strength pearlite-based rail excellent in toughness and ductility according to claim 5, 5 or 6. 8. At least Mg as a secondary deoxidizing element, or Ti in addition thereto, and secondary deoxidation of Mg oxide or Ti oxide to form Mg oxide, 8. A steel slab obtained by casting a molten steel in which Ti oxides are finely dispersed and smelted is used in addition thereto, and has excellent toughness and ductility according to claim 4, 5, 6, or 7. Method of manufacturing high-strength pearlitic rail.