ES2550793T3 - Perlite rail that has superior abrasion resistance and excellent toughness - Google Patents

Abstract

A perlite rail having a steel composition comprising. in terms of mass percentage: C: from 0.65 to 1.20%; Yes: from 0.05 to 2.00%; Mn: from 0.05 to 2.00%; P <= 0.0150%; S <= 0.0100%; Ca: 0.0005% to 0.0200%; one or both of Mg: from 0.0005 to 0.0200% and Zr: from 0.0005 to 0.0100% and optionally one or more selected from Co: from 0.01% 1.00%, Cr: from 0.01 to 2.00%, Mo: 0.01 to 0.050%, V: 0.005 to 0.50%, Nb: 0.002 to 0.050%, B: 0.0001 to 0.0050%, Cu : 0.01 to 1.00%, Ni: 0.01 to 1.00%, Ti: 0.0050 to 0.0500%, Al: greater than 0.0100 to 1.00%, and N : from 0.0060 to 0.0200%, the rest being Fe and unavoidable impurities, in which an S / Ca ratio is in a range of 0.45 to 3.00 between a part of the rail head, in a part of the surface of the head that varies from the surfaces of the corner portions of the head and an upper part of the head to a depth of 10 mm or in a part that varies from the surfaces of the corner portions of the head and the upper part of the head to a depth of 20 mm, 95% or greater of a metallographic structure is a perlite structure, a hardness Hv of the perlite structure is in a range from 320 to 500, Mn sulfide-based inclusions having major lengths in a range of 10 to 100 µm are present in an amount per unit area in a range of 10 to 200 / mm2 in a cross-section taken from a part that varies from the surface of the head part of the rail to a depth of 3 mm to 10 mm along a longitudinal direction in the perlite structure, Mg oxides, Zr oxides and inclusions based on Mn sulfide having grain diameters in a range of 5 nm to 100 nm are present in an amount per unit area in a range of 500 to 50,000 / mm2 in a cross section taken from a part that varies from the surface of the surface part from the head of the rail to a depth of 3 mm to 10 mm in the perlite structure.

Description

Perlite rail that has superior abrasion resistance and excellent toughness

TECHNICAL FIELD The present invention relates to a perlite rail used for overseas freight railways in which both abrasion resistance (wear resistance) and toughness are improved in the head part.

PREVIOUS TECHNIQUE Along with economic development, a new development of natural resources, such as coal, is progressing

or similar. Specifically, mining has been launched in regions with a severe natural environment that until now had not been developed. Consequently, the environment of the tracks is becoming remarkably severe on freight railroads abroad used to transport natural resources. There is a demand for rails that have toughness or similar in regions with cold weather as well as greater wear resistance than ever. In such circumstances, there is a demand to develop rails that have greater wear resistance and greater toughness than those of the currently used high strength rails.

In general, it is known that the refining of a perlite structure, specifically, the refining of grain into an austenite structure that has yet to be transformed into perlite, or the refining of perlite blocks is effective in improving the toughness of a steel perlithic In order to achieve the refining of the grain in an austenite structure, during a hot rolling, the rolling temperature is decreased and the rolling reduction speed increases and additionally, a thermal treatment is implemented by reheating at low temperature after rolling in hot from the rails. In addition, to achieve the refining of a perlite structure, the transformation of perlite that starts inside the austenite grains is accelerated using transformation cores or the like.

However, in the manufacture of rails, from the point of view of assuring formability during hot rolling, there are limitations on a decrease in the rolling temperature and an increase in the speed of reducing rolling; and in this way, sufficient refining of the austenite grains could not be achieved. In addition, with respect to the transformation of perlite from within the austenite grains using transformation cores, there are problems while the amount of transformation cores is difficult to control, and the transformation of perlite from inside the grains is not is stable; and in this way a sufficient refining of the perlite structure cannot be achieved.

Due to these problems, a method has been applied to fundamentally improve the toughness of the rails that have a perlite structure in which reheating is performed at low temperature after hot rolling a rail, and then the transformation of perlite is performed by accelerated cooling such as to refine a perlite structure. However, recently, rails have been prepared that include a high carbon content to improve wear resistance; and therefore, there is a problem in that the thick carbides remain within the austenite grains during the low temperature preheating treatment described above, which reduces the ductility and toughness of a perlite structure after accelerated cooling. In addition, since this method includes overheating, there is another problem regarding economic efficiency, such as high manufacturing cost, low productivity or the like.

Accordingly, there is a demand to develop a method for manufacturing a high carbon steel rail that ensures formability during rolling and refining the perlite structure after hot rolling. To solve this problem, methods have been developed to manufacture a high carbon steel rail shown below. The main features of these methods for making a rail are that the fact that austenite grains in a high carbon steel are easily recrystallized at a relatively low temperature and even when a low speed of rolling reduction is used to refine the structure perlite As a result, fine grains with similar grain diameters are obtained by continuous rolling at a small rolling reduction rate; and in this way, the ductility and toughness of a perlitic steel is improved (for example, Patent Documents 1, 2 and 3).

Patent Document 1 describes that a rail having high ductility can be provided by making 3 or more continuous rolling passes with a predetermined time interval in the finishing laminate of a high carbon steel rail.

Patent Document 2 describes that a rail having superior wear resistance and high toughness can be provided by performing two or more continuous rolling passes with a predetermined time interval in the finishing laminate of a high carbon steel rail, and additionally performing accelerated cooling after continuous rolling.

Patent Document 3 describes that a rail having superior wear resistance and high toughness can be provided by cooling between the rolling passes in the finishing laminate of a high carbon steel rail and performing accelerated cooling after continuous rolling .

The technologies described by Patent Documents 1 to 3 can achieve the refining of the austenite structure at a certain level and present a slight improvement in the toughness due to the combination of temperature, the number of rolling passes and the time interval between the passes during continuous hot rolling. However, there is a problem in which these technologies have no effect with respect to the beginning of the fracture from the inclusions present within the steel; in this way the tenacity does not improve fundamentally.

Additionally, the grain growth rate of an austenite structure is fast in a high carbon steel. As a result, the grains of an austenite structure that have been refined by rolling grow after rolling; and therefore there is a problem in that the toughness of a heat treated rail does not improve even in the case of accelerated cooling.

Considering these circumstances, the addition of Ca, the reduction of oxygen content and the reduction of Al content have been studied to suppress the acceleration of typical rail inclusions, that is: MnS or Al2O3. The characteristics of these manufacturing methods are that the MnS is changed to CaS by adding Ca in the preliminary treatment of the hot metal in such a way that it becomes harmless and, additionally, the oxygen content is reduced as much as possible by adding deoxidation elements or applying a vacuum treatment such as to reduce the amount of inclusions in the molten steel, and the technologies of which they have been studied (for example, Patent Documents 4, 5 and 6).

The technology in Patent Document 4 describes a method for manufacturing a very clean, silicon and high carbon molten steel, in which the added amount of Ca is optimized to set the S as CaS; and in this way the amount of inclusions based on elongated MnS is reduced. In this technology, the S that is secreted and concentrated in a solidification process reacts with the Ca that it secretes and similarly concentrates or calcium silicate is generated in the molten steel; and in this way, the S is sequentially set as CaS. As a result, the generation of elongated MnS inclusions is suppressed.

The technology in Patent Document 5 describes a method for manufacturing a very clean and high carbon molten steel in which the amount of MnO inclusions is reduced; and in this way the amount of elongated MnS inclusions precipitated from MnO is reduced. In this technology, a steel is protected in a non-deoxidized or weakly deoxidized state after melting it in a furnace with refining atmosphere and then a vacuum treatment is performed at a vacuum degree of 1 Torr or less to make the content of Dissolved oxygen is in a range of 30 ppm or less. Next, Al and Si are added and then Mn is added. In this way, the number of secondary deoxidation products is reduced, which will become MnS crystallization nuclei that crystallize in the finally solidified portions, and the concentration of MnO in the oxides is reduced. In this way, the crystallization of MnS is suppressed.

The technology in Patent Document 6 describes a method for manufacturing a very clean and high carbon molten steel with reduced amounts of oxygen and Al in molten steel. In this technology, a rail having superior resistance to damage can be manufactured by limiting the total amount of oxygen based on the ratio between the total oxygen value in the oxide-based inclusions and the property of the damage. Additionally, the damage resistance of the rails can be further improved by limiting the amount of Al solubilized in the solid or the composition of the inclusions in a preferable range.

The technologies described above described in Patent Documents 4 to 6 control the configurations and amounts of inclusions based on MnS and Al generated in an efflorescence phase. However, the configuration of inclusions is altered during hot rolling in the rail rolling. In particular, the sulphide-based inclusions of Mn elongated in the longitudinal direction by rolling act as starting points of fracture in the rails; and therefore, there is a problem in which the resistance to damage or toughness of the rails cannot be stably improved in the case where only inclusions in the efflorescence phase are controlled.

In addition, the application of precipitates to suppress grain growth of an austenite structure after hot rolling has been studied. The characteristics of this manufacturing method are that alloy elements are added and the carbonitrides precipitate by dotting an austenite structure; and in this way the growth of grain is suppressed. Consequently, a heat treated structure is refined, and the toughness is improved (eg, Patent Document 7).

In the technology of Patent Document 7, V and Nb are added, and carbonitrides of V and Nb precipitate. Additionally, accelerated cooling is performed, depending on the added amounts of V and Nb, and the grain growth of the austenite structure after hot rolling is controlled; and in this way a perlite structure is refined and the tenacity of a rail is improved.

In the technology described in Patent Document 7, alloy elements are added and carbonitrides precipitate by dotting an austenite structure; and in this way the growth of grain is suppressed. However, the amount of carbonitrides generated from the alloy elements varies greatly depending on the

Laminating temperature and lamination reduction speed. As a result, a great variation occurs in the effects of suppressing the growth of grain and the thickening of the crystal grains occurs partially. Therefore, there is a problem in that the resistance to damage and the toughness of the rails cannot be stably improved by the carbonitrides of the alloy elements alone.

In addition, the technology described in Patent Document 7 only achieves the refining of an austenite structure. This technology has no effect on the damages due to inclusions based on elongated Mn sulfide in the longitudinal direction by rolling; and therefore there is a problem in that the resistance to damage and the toughness of the rails cannot be improved in a stable way.

Additionally, in the technologies described in Patent Documents 4 to 7, embrittlement occurs in a structure due to the alteration in the components of a steel, particularly the alteration of the components mixed therein as impurities. Therefore, there is a problem in that the resistance to damage and the toughness of the rails cannot be stably improved by controlling the inclusions due to the addition of alloy elements and the reduction of the oxygen content, and refining a structure of austenite due to the application of precipitates.

WO 2007 111 285 describes a perlite rail with excellent delayed fracture resistance.

From these circumstances, it has been desirable to provide a perlite rail having superior wear resistance and toughness in which both wear resistance and damage resistance of a perlite structure are improved.

DOCUMENTS OF THE PREVIOUS TECHNIQUE

Patent Documents

Patent Document 1: Japanese Unexamined Patent Publication No. H07-173530

Patent Document 2: Japanese Unexamined Patent Publication No. 2001-234238

Patent Document 3: Japanese Unexamined Patent Publication No. 2002-226915

Patent Document 4: Japanese Unexamined Patent Publication No. H05-171247

Patent Document 5: Japanese Unexamined Patent Publication No. H05-263121

Patent Document 6: Japanese Unexamined Patent Publication No. 2001-220651

Patent Document 7: Japanese Unexamined Patent Publication No. 2007-291413

EXHIBITION OF THE INVENTION

Problems to be solved by the Invention The present invention has been realized in consideration of the above problems, and the object of the present invention is to provide a perlite rail in which both wear resistance and toughness are improved in the head part, which is being particularly demanded as a rail for freight railroads in the Foreign.

Means to solve the problems The present invention, which is given in the claim, has the following characteristics.

A perlite rail according to the present invention consists of a steel comprising, in terms of mass percentage, C: from 0.65% to 1.20%, Si: from 0.05% to 2.00%, Mn: from 0.05% to 2.00%, P ≤ 0.0150%, S ≤ 0.0100%, Ca: from 0.0005% to 0.0200%, and Fe and inevitable impurities like the rest. In a part of the head of the rail, the part of the surface of the head that varies from the surfaces of the corner portions of the head and the top of the head to a depth of 10 mm has a perlite structure, and a hardness Hv of the perlite structure is in a range of 320 to 500. Mn sulfide-based inclusions having major lengths in a range of 10 to 100 µm are present in an amount per unit area in a range of 10 to 200 / mm2 in a cross section (a cross section parallel to the longitudinal direction of the rail) taken along a longitudinal direction in the perlite structure.

In this case, Hv refers to the Vickers hardness defined by JIS B7774.

In the perlite rail according to the present invention, the steel additionally includes, in terms of mass percentage, any one or both of Mg: from 0.0005 to 0.0200% and Zr: from 0.0005 to 0.010 0 %, and Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm in an amount per unit area in a range of 500 to 50,000 mm 2 may be present in a cross section (a cross section parallel to the rail width direction) in the perlite structure.

Steel may also include, in terms of mass percentage, one or more of the steel components described in the following points (1) to (9).

(one)

 Co: from 0.01% to 1.00%

(2)

 one or both of Cr: from 0.01% to 2.00% and Mo: from 0.01% to 0.50%

(3)

 one or both of V: from 0.005% to 0.50% and Nb: from 0.002% to 0.050%

(4)

 B: from 0.0001% to 0.0050%

(5)

 Cu: from 0.01% to 1.00%

(6)

 Ni: from 0.01% to 1.00%

(7)

 Ti: from 0.0050% to 0.0500%

(8)

 M: more than 0.0100% to 1.00%

(9)

 N: from 0.0060% to 0.0200%

Effects of the Invention In accordance with the present invention, the components, structure and hardness of a rail steel are controlled and, in addition, the contents of P and S are reduced, Ca is added and the number of sulfide-based inclusions is controlled. of Mn. In this way, the wear resistance and toughness of a perlite structure is improved; and, as a result, it is possible to improve the usable period of a rail, particularly for freight railroads abroad (freight railroads abroad). Additionally it is possible to further improve the toughness of the perlite structure by adding Mg and Zr and controlling the number of inclusions based on fine Mn sulphide and oxides based on Mg and Zr; and, as a result, it is possible to further improve the usable period.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view showing the nominal designations of the portions in a cross section (a cross section perpendicular to the longitudinal direction) of the rail steel according to the present invention. Figure 2 is a view showing the effects of the addition of Ca and the addition of Mg and Zr on the relationship between the amount of S and the impact value that are results obtained by melting steels in which the amount of S is altered , the amount of P is in a range of 0.0150% or less, the amount of carbon is 1.00% and Ca, Mg and Zr are added by performing a laboratory melting and rolling test that simulates equivalent rolling conditions for rails, and performing an impact test. Figure 3 is a view showing the observation zone of Mn sulfide-based inclusions in the rail steel according to the present embodiment. Figure 4 is a view showing the observation zone of Mn sulfide-based inclusions, Mg-based oxides and Zr oxides in the rail steel according to the present embodiment. Figure 5 is a view showing the area where samples are taken for the wear test. Figure 6 is a view showing the profile of the wear test. Figure 7 is a view showing the area where the samples are taken for the impact test. Figure 8 is a view showing the relationship between the amount of carbon and the amount of wear in the results of the wear test of the rail steels according to the present invention and the comparative rail steels (steels no. 48, 50 , 51, 52, 53, 64, 66 and 67). Figure 9 is a view showing the relationship between the amount of carbon and the impact value on the results of the impact test of the rail steels according to the present invention and the comparative rail steels (steels no. 49, 51 , 53, 65, 66 and 68). Figure 10 is a view showing the relationship between the amount of carbon and the impact value on the results of the impact test of the rail steels according to the present invention and the comparative rail steels (steels No. 54 to 63 and the rails with the added amounts of P, S and Ca outside the ranges of the present invention) Figure 11 is a view showing the relationship between the amount of carbon and the impact value on the results of the impact test of rail steels according to the present invention (steels no. 11 to 13, 18 to 20, 24 to 26, 29 to 31, 33 to 35, 36 to 38 and 45 to 47).

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, as embodiments for carrying out the present invention, perlite rails with superior wear resistance and toughness will be described in detail. In this case, the units of the alloy element contents are% mass and, hereinafter, will be expressed simply as%.

Figure 1 shows a cross section perpendicular to the longitudinal direction of the perlite rail having superior wear resistance and toughness in accordance with the present invention. A rail head part 3 includes an upper head part 1 and a corner head part 2 located at both ends of the upper head part 1. One of the corner portions 2 of the head is a corner calibration part (G.C.) that mainly comes into contact with the wheels.

A part that varies from the surfaces of the corner portions 2 of the head and the top part 1 to a depth of 10 mm is called part 3a of the surface of the head (area of the diagonal solid line). In addition, a part that varies from the surfaces of the corner portions 2 of the head and the top part 1 to a depth of 20 mm is given the reference number 3b (line area of

diagonal points).

First, the inventors of the present invention studied a system of steel components that had a bad effect on the toughness of the rails. A melt test and a hot rolling test were performed that simulated equivalent hot rolling conditions for rails on steels whose P and S contents were varied while using steels having a varied amount of carbon as the base; and, in this way, rail prototypes were manufactured. Then, the impact values of the prototypes were measured by an impact test, and the effects of the P and S contents on the impact values were studied.

As a result, with respect to perlitic steels that have Hv levels of 320 to 500, it was observed that the impact values improved in the event that the contents of both P and S were reduced to a certain level

or less.

In addition, as a result of studying the optimal contents of P and S, it was observed that the impact values improved greatly in the event that the contents of both P and S were reduced to a certain level or less.

Next, the inventors of the present invention attempted to clarify the dominant factors in the impact values to further improve the impact values of the rails. As a result, it was observed that the rails that had low impact values included many inclusions based on elongated Mn sulphide in the longitudinal direction by hot rolling and those inclusions acted as starting points of fracture.

Then, the inventors of the present invention clarified the mechanism of generating the sulfur-based inclusions of Mn elongated in the longitudinal direction. When rails are manufactured, an efflorescence is reheated at a temperature in a range of 1,200 ° C to 1,300 ° C, and the efflorescence is subjected to hot rolling. The inventors have investigated the relationship between hot rolling conditions and the MnS configuration. As a result, it was observed that, in the case that the rolling temperature was high or in the case that the rolling reduction speed was high during rolling, the plastic deformation of the soft Mn sulphide-based inclusions easily occurred; and thus, the sulfide-based inclusions of Mn easily lengthened in the longitudinal direction of the rails.

In view of these circumstances, the inventors of the present invention studied methods to suppress elongation of Mn sulfide-based inclusions. As a result of the fusion test and the hot rolling test, it was observed that inclusions based on Mn sulphide were generated from various kinds of oxides as nuclei. Additionally, as a result of investigating the hardness of the oxides and configurations of Mn sulfide-based inclusions, it was observed that elongation could be suppressed by hardening inclusions that acted as nuclei in Mn sulfide-based inclusions.

Additionally, the inventors of the present invention studied hard inclusions that acted as the nuclei of Mn sulfide based inclusions. As a result of performing a laboratory test using oxides with a high melting point, it was found that Ca, with a relatively high melting point, formed sulfides and oxides, and formed aggregates of CaO-CaS. In addition, the inventors have found that since CaS has a high consistency with Mn sulfide based inclusions, Mn sulfide based inclusions were efficiently generated in the aggregates of Ca oxides and sulfides (CaO-CaS).

In this case, consistency refers to a difference in the network constants (interatomic distance) in the crystalline planes in the crystalline structures of two metals. The smaller the difference, the greater the consistency. That is, two metals are considered to be easily joined.

Next, the inventors of the present invention performed a melt test and a hot rolling test using steels that included Ca to verify the above observation. As a result, it was observed that Mn sulfide-based inclusions generated from aggregates of Ca oxides and sulfides (CaO-CaS) that act as nuclei rarely lengthened after hot rolling; and consequently, the number of inclusions based on elongated Mn sulfide in the longitudinal direction decreased.

Additionally, as a result of performing an impact test using the steels, it was observed that, with respect to the steels in which Ca was added and the number of inclusions based on Mn sulfide was small, the appearance of fracture that it started from inclusions based on elongated Mn sulfide; and as a result the impact values improved.

In addition, to further suppress the elongation of Mn sulfide-based inclusions, the inventors of the present invention studied the relationship between the added amount of Ca and the added amount of S that made it possible for the oxides and sulfides to form aggregates by performing a test of Fusion and a hot rolling test. As a result, it was observed that an appropriate number of Ca sulfides was generated which were finally dispersed by controlling the ratio of the added amount of S and the added amount of Ca; and in

consequently, it was possible to further suppress the elongation of Mn sulfide based inclusions after hot rolling.

Additionally, in addition to suppressing the generation of elongated Mn sulfide-based inclusions that have a poor effect on toughness, the inventors of the present invention studied methods that suppressed grain growth of an austenite structure after hot rolling using inclusions. and oxides based on Mn sulfide. As a result of the melt test and the hot rolling test, it was found that it was necessary to finely disperse oxides and inclusions based on Mn sulphide of nanometric size instead of the alloy elements previously used, in an austenite structure as elements of dotted to stably suppress the grain growth of the austenite structure.

In view of these circumstances, the inventors of the present invention studied methods for finely dispersing oxides and inclusions based on Mn sulfide. As a result, it was observed that the oxides of Mn and Zr were not added, but dispersed fine and uniformly. Additionally, it was noted that since both Mg-based oxides and Zr oxides had a good consistency with Mn sulfide-based inclusions, Mn sulfide-based inclusions were also finely dispersed with fine oxides and nuclei. .

Next, the inventors of the present invention performed a hot rolling test using steels that included Mg and Zr. As a result, it was observed that the oxides of nanometric size and the sulphide-based inclusions of Mn dispersed finely, and the grain growth of the austenite structure after hot rolling could be suppressed. Additionally, as a result of performing an assay and an impact using these steels, it was observed that the impact values improved by refining a perlite structure in the steels including Mg and Zr.

The inventors of the present invention performed a fusion test of experimental steels by preparing steels that included carbon at a content of 1.00% and P at a content in the range of 0.0150% or less, adding various contents of S, and additionally adding Ca, Mg and Zr. Next, the inventors performed a laboratory rolling test that simulated equivalent rolling conditions for rails such as for making prototypes of rails. Then, the impact values of the prototypes were measured by an impact test and the effects of the amount of S and the effects of the addition of Ca, Mg and Zr on the impact values were studied. In this case, the hardness of the materials was adjusted to an Hv level of 400 controlling the heat treatment conditions.

Figure 2 shows the relationship between the amount of S (ppm) and the impact value. With respect to steels that included C at a content of 1.00% (● marks), it was observed that, in the event that the content of P was in the range of 0.0150% or less, the impact values improved if the P content was reduced to 0.0100% or less. In addition, from the results of steels that included Ca (■ marks), it was observed that the generation of elongated Mn sulfide-based inclusions was suppressed by the addition of Ca; and in this way the impact values improved. Additionally, from the results of the steels that included Ca, Mc, and Zr (Δ marks), it was observed that the oxides and inclusions based on Mn sulfide of nanometric size were finely dispersed by adding Mg and Zr together with Ca; and in this way the impact values improved significantly.

Based on the results of the study described above, the present invention has been completed with the characteristics described above. The features of the present invention will be described hereinafter.

(1) The reason why the chemical components of steels are limited:

The reason why the chemical components of steels are limited within the numerical ranges described above in the perlite rail according to the present invention will be described in detail. C is an effective element that accelerates the transformation of perlite and ensures wear resistance. In the event that the amount of C is less than 0.65%, in the present system of components, it is not possible to maintain a minimum level of resistance or wear resistance required for the rails. In addition, in the case that the amount of C exceeds 1.20%, a large amount of thick proeutectoid cementite structure is generated; and in this way the wear resistance or toughness is degraded. Therefore, the amount of C is limited to be in a range of 0.65% to 1.20%. In this case, it is preferable that the amount of C is in a range of 0.90% or greater to sufficiently ensure wear resistance.

Si is an essential element as a deoxidant material. In addition, Si is an element that increases the hardness (strength) of a head portion of a rail by strengthening in solid solution in the ferrite phase in a perlite structure. Additionally, Si is an element that suppresses the generation of proeutectoid cementite structures in hypereutectoid steels; and in this way, a decrease in toughness is suppressed. However, in the case that the amount of Si is less than 0.05%, it is not possible to sufficiently expect such effects. In addition, in the case that the amount of Si exceeds 2.00%, a number of defects is generated

Superficial during hot rolling and weldability degrades due to the generation of oxides. Additionally, the hardening capacity increases markedly, and a martensite structure is generated that is detrimental to the wear resistance and toughness of the rails. Therefore, the amount of Si is limited to being in a range of 0.05% to 2.00%. In this case, it is preferable that the amount of Si is in a range of 0.20% to 1.30% to ensure the hardening capacity and suppress the generation of the martensite structure that is detrimental to wear resistance or toughness .

Mn is an element that increases the hardening capacity and refines the lamellar spacing of the pearlite; and, in this way, the hardness of the perlite structure is ensured and the wear resistance is improved. However, in the case of the amount of Mn being less than 0.05%, such effects are small and it is difficult to ensure the wear resistance necessary for the rails. In addition, in the case that the amount of Mn exceeds 2.00%, the hardening capacity increases significantly and the martensite structure is easily generated, which is harmful for wear resistance or toughness. Therefore, the amount of Mn added is limited to being in a range of 0.05% to 2.00%. In this case, it is preferable that the amount of Mn is in a range of 0.40% to 1.30% to ensure the hardening capacity and suppress the generation of the martensite structure that is detrimental to wear resistance or toughness. .

P is an element inevitably included in steels. The amount of P has a relationship with the toughness and, if the amount of P increases, the perlite structure becomes brittle due to the fragility of the ferrite phases and it is easy for the brittle fracture to occur, that is, the fracture of the rail . Therefore, the amount of P is desirably small to improve the toughness. As a result of the experimental observation the relationship between the impact value and the amount of P it was observed that in the case that the amount of P was reduced to 0.0150% or less, the segregation of P was markedly reduced, and suppressed the fragility of the perlite structure that had a fracture starting point; and in this way the impact values improved greatly. From these results, the amount of P is limited to being in a range of 0.0150% or less. The lower limit of the amount of P is not specified; however, approximately 0.0020% is considered to be the lower limit of the amount of P when rails are actually manufactured in view of the ability to dephosphate in a refining process.

Meanwhile, a treatment to reduce the amount of P (reducing the amount of P) is not only accompanied by an increase in refining costs but also by productivity degradation. As a result, in consideration of economic efficiency, it is preferable that the amount of P is in a range of 0.0030% to 0.0100% to stably improve the impact values.

S is an element inevitably included in steels. The amount of S has a relationship with the toughness, and if the amount of S increases, the stress concentration occurs due to the thickening of MnS or the increase in the density of Mn; in this way it is easy for the fragile fracture to occur, that is, the damage to the rail. Therefore, the amount of S is desirably small to improve the toughness. As a result of experimentally observing the relationship between the impact value and the amount of S, it was observed that, if the amount of S was reduced to 0.0100% or less, the amount of Mn sulfide-based inclusions generated that they were the starting point of fracture, and additionally the fragility of the perlite structure was suppressed by the suppression of elongation of Mn sulfide-based inclusions or the refining of Mn sulfide-based inclusions due to Ca addiction, Zr or Mg. As a result, the impact value was greatly improved. From these results, the amount of S is limited to being in a range of 0.0100% or less. The lower limit of the amount of S is not specified; however, approximately 0.0010% is considered to be the lower limit of the amount of S when rails are actually manufactured in view of the sulfurization capacity in a refining process.

Meanwhile, a treatment to reduce the amount of S (reduction of the amount of S) is not only accompanied by an increase in refining costs but also by the degradation of productivity. As a result, in consideration of economic efficiency, it is preferable that the amount of S is in a range of 0.0060% or less to suppress the generation of sulphide inclusions based on elongated Mn and stably improve the impact values.

In addition, to further improve the impact values, it is preferable that the amount of S is in a range of 0.0020% to 0.0035% to stably generate fine Mn sulfide-based inclusions that dot the austenite structure and suppress the generation of inclusions based on elongated Mn sulfide.

Ca is a deoxidizing and desulfurizing element, and aggregates the calcium oxides and sulfides (CaO-CaS) that are generated by the addition of Ca. These aggregates act as nuclei for the generation of inclusions based on Mn sulfide; in this way the elongation of inclusions based on Mn sulfide after hot rolling is suppressed. Additionally, Mn sulfide-based inclusions of nanometric size are formed from these aggregates as cores (formed using the aggregates as cores). Ca is an element that has such functional effects. In the event that the amount of Ca is less than 0.0005%, such effects are small and the aggregates cannot act sufficiently as nuclei for the generation of inclusions based on Mn sulfide. In the event that the amount of Ca exceeds 0.0200% the amount of hard CaO

independent that does not act as the nuclei for sulfide-based inclusions of Mn increases depending on the amount of oxygen in a steel. As a result, the toughness of a rail steel is greatly degraded. Therefore, the amount of Ca is limited to being in a range of 0.0005% to 0.0200%.

Meanwhile, it is preferable that the amount of Ca is in a range of 0.0015% to 0.0150% to improve the impact values by stably suppressing the generation of elongated Mn sulfide-based inclusions and suppressing the generation in advance. of hard CaO that does not act as the nuclei for the sulphide-based inclusions of Mn and is detrimental to the toughness. In addition, to further improve the impact values, it is necessary to stably generate fine Mn sulfide-based inclusions that dot the austenite structure to suppress the thickening of the Mn sulfide-based inclusions. Therefore, it is more preferable that the amount of Ca is in a range of 0.0020% to 0.0080%.

As described above, S and Ca generate the aggregates of the oxides and sulfides (CaO-CaS). These aggregates act as nuclei for Mn sulfide-based inclusions; and therefore the aggregates greatly affect the elongation of inclusions based on Mn sulfide. Therefore, it is important to control the amount of S and the amount of Ca. In view of these circumstances, steels with varying amounts of S and Ca were subjected to fusion testing and a hot rolling test was performed. As a result, it was found that, in the event that the ratios of the amount of Ca to the amount of S (S / Ca) were within a specific range, an appropriate number of Ca acids and sulfides were generated and dispersed finely; and in this way, it was possible to further suppress the elongation of Mn sulfide based inclusions after hot rolling.

Specifically in the case that the S / Ca value is less than 0.45, the amount of independent hard CaO that does not act as nuclei for Mn sulfide-based inclusions slightly increases. As a result, there are cases in which the toughness of rail steels is degraded. In the event that the value of S / Ca exceeds 3.00, the number of sulphide aggregates (CaO-CaS) that act as nuclei for Mn sulfide-based inclusions is reduced; and in this way, the elongation of inclusions based on Mn sulfide is promoted. As a result, there are cases in which the toughness of rail steels is degraded. Therefore, it is preferable that the S / Ca ratio is in a range of 0.45 to 3.00.

The present invention preferably includes any or both or Mg and Zr.

Mg is a deoxidizing element that primarily binds with O to form a complex of fine oxides (MgO) and fine sulfides (MgS) of nanometric size. Mn sulfide-based inclusions of nanometric size are formed from complexes as nuclei (formed using complexes as nuclei). As a result, the growth of the grain of an austenite structure after hot rolling is suppressed; and, in this way, the structure of the rail steel is refined. As a result, it is possible to improve the toughness of a perlite structure. However, in the case that the amount of Mg is less than 0.005%, the amount generated of the complex oxides (MgO) and fine sulfides (MgS) is small; and thus the effect of suppressing the growth of grain of an austenite structure after hot rolling cannot be sufficiently obtained. In the event that the amount of Mg exceeds 0.0200%, thick oxides of Mg are generated; and in this way, the toughness of the rails is degraded and fatigue damage occurs simultaneously from the thick oxides. Therefore, the amount of Mg is limited to being in a range of 0.0005% to 0.0200%.

In this case, it is preferable that the amount of Mg is in a range of 0.0010% to 0.0050% to improve the impact values sufficiently ensuring the generated amount of fine oxides (MgO) that dot an austenite structure and generated amount of the complexes of the oxides (MgO) and sulfides (MgS) that form the Mn sulfide-based inclusions of a nanometric size and sufficiently suppress the generation of thick oxides that are detrimental to fatigue damage.

Zr is a deoxidizing element that is primarily bound to O such as to form fine oxides of nanometric size (ZrO2). These oxides disperse finely and uniformly and, additionally, Mn sulfide-based inclusions of nanometric size are formed from the oxides as nuclei (formed using the oxides as nuclei). As a result, grain growth of an austenite structure after hot rolling is suppressed; in this way, the structure of a rail steel is refined. As a result, it is possible to improve the toughness of a perlite structure. However, in the case that the amount of Zr is less than 0.0005%, the amount of fine oxides generated (ZrO2) is small; in this way the effect of suppressing the growth of grain of an austenite structure after hot rolling cannot be sufficiently obtained. In the event that the amount of Zr exceeds 0.0100%, thick oxides of Zr are generated; in this way, the toughness of the rails is degraded and, simultaneously, fatigue damage occurs from the thick precipitates. Therefore, the amount of Zr added is limited to being in a range of 0.0005% to 0.0100%.

Meanwhile, it is preferable that the amount of Mn is in a range of 0.0010% to 0.0050% to improve the impact values sufficiently ensuring the generated amount of fine oxides (ZrO2) that dot an austenite structure and the amount generated from oxides (ZrO2) that form inclusions based on Mn sulfide of nanometric size and sufficiently suppressing the generation of thick oxides that are detrimental to

fatigue damage.

If necessary, the rails manufactured in the component composition described above preferably include one or more elements selected from the group consisting of Co, Cr, Mo, V, Nb, B, Cu, Ni, Ti, Al and N for the purpose to improve the hardness (resistance) of a perlite structure or a proeutectoid ferrite structure, the improvement in toughness, the prevention of softening in the areas affected by thermal welding and the control of the hardness distribution in the cross section within of the head part of the rail.

Hereinafter, the main purposes and functional effects of the addition of the elements described above will be shown.

Co refines a lamellar structure on a contact surface with the laminate and decreases the diameter of ferrite grain; and in this way, the wear resistance of a perlite structure is increased. Cr and Mo increase the equilibrium transformation point and mainly refine the lamellar separation of perlite; and in this way, the hardness of a perlite structure is ensured. V and Nb generate carbides and nitrides in a hot rolling process and a subsequent cooling process; and, in this way, the growth of austenite grains is suppressed. Additionally, V and Nb precipitate and harden into a ferrite structure and a perlite structure; and in this way the toughness and hardness of a perlite structure are improved. In addition, V and Nb stably generate carbides and nitrides; in this way the softening of the welded joint of the heat affected areas is avoided.

B reduces the dependence of the perlite transformation temperature on the cooling rate; and in this way, the distribution of hardness in the head part of the rail becomes uniform. The Cu is solubilized in solid in a ferrite structure and in a ferrite phase in a perlite structure; and in this way the hardness of the perlite structure increases. Ni improves the hardness and toughness of a ferrite structure and a perlite structure and, simultaneously, Ni prevents softening of the heat-affected areas of a welded joint. The Ti refines the structure in the heat-affected areas welded and prevents the fragility of the heat-affected areas of a welded joint. Al raises the eutectoid transformation temperature to a higher temperature and increases the hardness of a perlite structure. N is segregated in the austenite grain boundaries; and in this way the transformation of perlite is accelerated. In addition, N refines the size of the perlite blocks and in this way the toughness is improved.

Hereinafter, the reason why the quantities of these components are limited will be described in detail.

Co is solubilized as a solid in a ferrite phase in a perlite structure. Theoretically, the fine ferrite structure formed by the contact with the wheels on the rolling contact surface of the rail head part is further refined; and as a result the wear resistance is improved. In the event that the amount of Co is less than 0.01%, refining of the ferrite structure is not achieved and, therefore, it is not possible to expect the effect of improving wear resistance. Furthermore, even if the amount of Co exceeds 1.00%, the effect described above is saturated; and, therefore, refining of the ferrite structure corresponding to the added amount of Co. is not achieved. In addition, an increase in the cost to add alloy elements degrades economic efficiency. Therefore, the amount of Co is limited to being in a range of 0.01% to 1.00%.

Cr increases the equilibrium transformation temperature and, consequently, Cr refines the ferrite structure and the perlite structure; and in this way, Cr contributes to an increase in hardness (resistance). At the same time, Cr reinforces the cementite phase and, in this way, the hardness (strength) of the perlite structure is improved. However, in the case that the amount of Cr is less than 0.01%, such an effect is small and the effect of improving the hardness of the rail steel is not observed at all. In the event that Cr is added excessively in an amount of more than 2.00%, the hardening capacity increases and martensite structure is generated. In this way, peeling damage from the martensite structure occurs in the corner portions of the head and the top of the head; and as a result, resistance to surface damage is degraded. Therefore, the amount of Cr is limited to being in a range of 0.01% to 2.00%.

The Mo, similar to Cr, increases the equilibrium transformation temperature and, consequently, the Mo refines the ferrite structure and the perlite structure and, in this way, the Mo contributes to an increase in hardness (resistance ). Therefore, Mo is an element that improves hardness (resistance). However, in the case that the amount of Mo is less than 0.01%, such an effect is small, and the effect of improving the hardness of the rail steels is not observed at all. In the event that the Mo is added excessively to an amount greater than 0.50%, the transformation rate is markedly degraded. In this way, peeling damage from the martensite structure occurs in the corner portions of the head and the top of the head; and as a result the resistance to surface damage is degraded. Therefore, the amount of Mo is limited to being in a range of 0.01% to 0.50%.

V refines the austenite grains due to the dotting effect of V carbides and V nitrides in the event that

a heat treatment is performed at high temperatures. Additionally, the V increases the hardness (strength) of the ferrite structure and the perlite structure due to precipitation hardening of the V carbides and V nitrides generated in the cooling process after hot rolling and, simultaneously, the V improves tenacity. The V is an effective element to obtain these effects. In addition, in the heat-affected portions that overheat at a temperature in a range of Ac1 or less, V is an effective element to prevent softening of the heat affected areas of the welded joint by generating V carbides and V nitrides. in a relatively high temperature range. However, in the case that the amount of V is less than 0.005%, such an effect cannot be expected sufficiently, and no improvement in the hardness and toughness of the ferrite structure and the perlite structure is observed. In the event that the amount of V exceeds 0.50%, the precipitation hardening of carbides and nitrides of V is excessive, and the toughness of the ferrite structure and the perlite structure is degraded. In this way, peeling damage occurs in the portions of the corner of the head and the top of the head; and as a result, resistance to surface damage is degraded. Therefore, the amount of V is limited to being in a range of 0.005% to 0.50%.

Nb, similar to V, refines austenitic grains due to the dotting effect of Nb carbides and Nb nitrides in the event that a heat treatment is carried out at high temperatures. Additionally, the Nb increases the hardness (strength) of the ferrite structure and the perlite structure due to precipitation hardening of Nb carbides and Nb nitrides generated in the cooling process after hot rolling and, simultaneously, the Nb Improves toughness Nb is an effective element to obtain these effects. In addition, in the portions affected by heat that overheat at a temperature in the range of Ac1 or less, Nb is an effective element to prevent softening of the heat affected areas of a welded joint by stably generating the carbides of Nb and Nb nitrides from a low temperature range to a high temperature range. However, in the case that the amount of Nb is less than 0.002%, such an effect cannot be expected, and the improvement in the hardness and toughness of the ferrite structure and the perlite structure is not observed. In the event that the amount of Nb exceeds 0.050%, the precipitation hardening of carbides and nitrides of Nb is excessive, and the toughness of the ferrite structure and the perlite structure is degraded. In this way, peeling damage occurs in the corner portions of the head and the top of the head; and as a result the resistance to surface damage is degraded. Therefore, the amount of Nb is limited to being in a range of 0.002% to 0.050%.

B forms iron borocarbons (Fe23 (CB) 6) at the austenite grain boundaries and B accelerates the transformation of perlite. This effect of accelerating the perlite transformation reduces the dependence of the perlite transformation temperature on the cooling rate; and in this way a more uniform distribution of hardness is achieved from the surface part of the head to the inner part of a rail. Therefore, it is possible to extend the usable period of the rail. In the event that the amount of B is less than 0.0001%, these effects are not sufficient and there is no improvement in the distribution of hardness in the head part of the rail. In the event that the amount of B exceeds 0.0050%, thick iron borocarbons are generated and in this way the toughness is degraded. Therefore, the amount of B is limited to being in a range of 0.0001% to 0.0050%.

Cu is an element that is solubilized as a solid in a ferrite structure and in a ferrite phase in a perlite structure, and Cu improves the hardness (strength) of a perlite structure due to solid solution reinforcement. In the event that the amount of Cu is less than 0.01%, these effects cannot be expected. In the event that the amount of Cu exceeds 1.00%, the structure of martensite, which is detrimental to the toughness, generates a marked improvement in the hardening capacity. In this way, peeling damage occurs in the corner portions of the head and the top of the head; and as a result the resistance to surface damage is degraded. Therefore, the amount of Cu is limited to being in a range of 0.01% to 1.00%.

Ni is an element that improves the toughness of a ferrite structure and a perlite structure and simultaneously, Ni increases the hardness (strength) by strengthening in solid solution. Additionally, Ni finely precipitates the Ni3Ti intermetallic compound, which is a complex compound with Ti, in the heat-affected areas of the weld; and softening by precipitation reinforcement is suppressed in this way. In the event that the amount of Ni is less than 0.01%, these effects are extremely small. In the event that the amount of Ni exceeds 1.00%, the tenacity of a ferrite structure and a perlite structure is markedly degraded. In this way peeling damage occurs in the corner portions of the head and the top of the head; and as a result, resistance to surface damage is degraded. Therefore, the amount of Ni is limited to being in a range of 0.01% to 1.00%.

Ti is an effective element that refines the structure of heat-affected areas that are heated to an austenite interval using the fact that Ti carbides and Ti nitrides, which precipitate during welding overheating, do not melt ; and in this way the Ti avoids the fragility of the welded joint portions. However, in the case that the amount of Ti is less than 0.0050%, these effects are small and in the case that the amount of Ti exceeds 0.0500%, thick carbides of Ti and nitrides of You; and in this way the tenacity of a rail is degraded. At the same time, fatigue damage occurs due to thick precipitates. Therefore, the amount of Ti is limited to being in a range of 0.0050% to 0.050%.

Al is an essential element as a deoxidizing material. In addition, Al is an element that raises the eutectoid transformation temperature to a higher temperature and Al contributes to an increase in the hardness (resistance) of a perlite structure. In the event that the amount of Al is 0.0100% or less, these effects are small. In the case that the amount of Al exceeds 1.00%, it is difficult to solubilize the Al solid in a steel; and in this way thick alumina based inclusions are generated. In this way the tenacity of a rail degrades and fatigue damage occurs simultaneously due to thick precipitates. Additionally, oxides are generated during welding; and in this way the weldability is markedly degraded. Therefore, the amount of Al is limited to being in a range of more than 0.0100% to 1.00%.

N is segregated in the austenite grain boundaries; in this way the N accelerates the ferrite transformation and the perlite transformation from the austenite grain limits. As a result, the size of the perlite blocks is mainly refined; In this way it is possible to improve the toughness. However, in the case that the amount of N is less than 0.0060%, these effects are small. In the event that the amount of N exceeds 0.0200%, it is difficult to solubilize the N solid in a steel. As a result, air bubbles are generated that act as starting points for fatigue damage; and thus fatigue damage occurs within the head part of the rail. Therefore, the amount of N is limited to being in a range of 0.0060% to 0.0200%.

(2) The reasons why the regions and the hardness of the perlite structure in the part of the surface of the head 3a of the rail are limited:

Next, the reasons why the part of the head surface 3a of a rail includes a perlite structure and the hardness Hv thereof is limited to being in a range of 320 to 500 will be described.

First, the reason why the hardness Hv of a perlite structure is limited to being in a range of 320 to 500 will be described.

In the present system of components, in case the hardness Hv of the perlite structure is less than 320, it is difficult to ensure the wear resistance of the part of the surface of the head 3a of the rail; and in this way, the usable period of the rail is reduced. In addition, peeling damage occurs on the contact surface with the laminate due to plastic deformation; and in this way, the resistance to surface damage on the surface part of the head 3a of the rail is greatly degraded. In addition, in the case that the hardness Hv of a perlite structure exceeds 500, the toughness of the perlite structure is greatly degraded; and in this way the damage resistance on the surface part of the head 3a of the rail is degraded. Therefore, the hardness Hv of the perlite structure is limited to being in a range of 320 to 500.

Next, the reason why a necessary interval to include a perlite structure having a hardness Hv in a range of 320 to 500 is limited to the part of the head surface 3a of a rail steel will be described.

In this case, the part of the surface of the head 3a of a rail refers to, as shown in Fig. 1, a part that varies from the surfaces of the corner portions of the head 2 and the upper part of head 1 to a depth of 10 mm (area of the diagonal solid line). If a perlite structure is provided having the components described above in the part of the surface of the head 3a, abrasion due to contact with the wheels is suppressed; and in this way the wear resistance of the rail is improved.

In addition, it is preferable to have a perlite structure having a hardness Hv in a range of 320 to 500 in a part 3b that varies from the surfaces of the corner portions of the head 2 and the top part of head 1 to a depth of 20 mm, that is, at least in the area of the diagonal dotted line in Fig. 1. In this way, wear resistance is further ensured even in the event of abrasion occurring in the deepest interior of the part of head of the rail due to contact with the wheels; and thus improves the usable period of the rails. Therefore, it is preferable to provide a perlite structure having a hardness Hv in a range of 320 to 500 at or near the surface proximities of the head portion of the rail 3 with which the wheels mainly come into contact, and other portions may have a metallographic structure different from the perlite structure.

Meanwhile, with respect to a method for obtaining a perlite structure having a hardness Hv in a range of 320 to 500 at or near the surface proximities of the head portion of rail 3, as described below, it is preferable to perform accelerated cooling on the head part of rail 3 that includes an austenite region in a high temperature state after hot rolling or reheating.

Between the head part of the rail 3 in the present invention, it is preferable that the metallographic structure in the surface part of the head 3a or in part 3b which varies up to a depth of 20 mm and that includes the surface part of head 3a consists of the perlite structure described above. However, depending on the component compositions of a rail and the conditions of the heat treatments and manufacturing methods and the cases in which the perlite structure is mixed in the proeutectoid ferrite structure, the

Proeutectoid cementite structure, bainite structure and martensite structure in a small amount, for example an area ratio of 5% or less. Even if the structures described above are contained at a content of 5% or less, these structures do not have a major adverse effect on the wear resistance and toughness of the head part of the rail 3. Therefore, the Perlite structure described above may include mixed structures with proeutectoid ferrite structure, proeutectoid cementite structure, bainite structure, martensite structure or the like in an area ratio of 5% or less.

In other words, between the head part of the rail 3 in the present invention, 95% or greater of the metallographic structure in the part of the surface of the head 3a or the part 3b which varies to a depth of 20 mm and which including the part of the surface of the head 3a it is necessary that it be a perlite structure, and it is preferable that 98% or greater of the metallographic structure in the head part is a perlite structure to sufficiently ensure wear resistance and the tenacity

Meanwhile, in the "microstructure" columns in Tables 1 and 2 below, the description of "small quantity" refers to a content of 5% or less, and structures other than a perlite structure without the description " small amount "means that the structures are included in an amount of more than 5% (outside the range of the present invention).

(3) The reason why the number (per unit area) of Mn sulfide-based inclusions that have a main axis (main lengths) in the range of 10 µm to 100 µm is limited:

The reason why, in the present invention, the length of the main axis (main length) of the sulfur-based inclusions of Mn in an arbitrary cross-section taken along the longitudinal direction, which are the subjects, will be described in detail of evaluation, is limited to be in a range of 10 µm to 100 µm.

As a result of the investigation of the main axis length of Mn sulfide-based inclusions and the actual damage performance of the real rails (damage state when the rails are actually used), in the present system of components, it was observed that the fracture of the rails occurred from the end portions of the sulphide-based inclusions of Mn in which stress concentration occurred. In view of these circumstances, the steels were tested in the molten state to include inclusions based on Mn sulfide having different lengths of the main axis, and a hot rolling test was performed. As a result, it was observed that there was a good relationship between the number of inclusions based on Mn sulphide that had lengths of the main axis in a range of 10 µm to 100 µm and the resistance to rail damage. Consequently, the length of the main axis of the sulfide-based inclusions of Mn eligible for evaluation subjects, taking these figures into account, is limited to a range of 10 µm to 100 µm.

Meanwhile, sulphide-based inclusions of Mn that have a length of the main axis in which stress concentration remarkably occur, have a large effect on damage resistance and sulphide-based inclusions of Mn that have a short length of Main shaft have a small effect on resistance to damage. However, in the steel according to the present invention, there is a small number of inclusions based on Mn sulphide having a length exceeding 100 µm that are not suitable for identifying the characteristics of the steels. And Mn sulfide-based inclusions that are less than 10 µm long have a small effect on damage resistance. Therefore, Mn sulfide-based inclusions having the lengths described above of the main axis (main lengths) are used as evaluation subjects.

Next, the reason why the number (per unit area) of Mn sulfide-based inclusions having major lengths in a range of 10 µm to 100 µm in an arbitrary cross-section taken along the line will be described in detail Longitudinal direction (a cross section parallel to the longitudinal direction of a rail) is limited to being in a range of 10 / mm2 to 200 / mm2.

In the event that the total number (per unit area) of inclusions based on Mn sulphide having main lengths in a range of 10 µm to 100 µm exceeds 200 / mm2, in the present system of components, the number of inclusions based in Mn sulfide it is excessive; and in this way, the possibility of rail damage increases due to the generation of stress concentration at or in the vicinity of inclusions. Even in terms of the mechanical characteristics of steel, it is not possible to improve the impact value. In the event that the total number (per unit area) of the sulphide-based inclusions of Mn having major lengths in a range of 10 µm to 100 µm is less than 10 / mm2, in the present system of components, the sites of entrapment that absorb the hydrogen that inevitably remains in the steel, are markedly reduced. In this way, the possibility of inducing hydrogen defects (hydrogen fragility) increases; and in this way the resistance to rail damage is affected. As a result, the total number (per unit area) of inclusions based on Mn sulfide having major lengths in a range of 10 µm to 100 µm is limited to being in a range of 10 / mm2 to 200 / mm2.

Meanwhile, in the present limitation, Mn sulfide based inclusions refer to both Mn sulfide based inclusions generated from calcium oxide and sulphide aggregates (CaO-CaS) and

nuclei and other inclusions based on Mn sulfide as evaluation subjects.

In addition, with respect to the number of inclusions based on Mn sulphide, a sample of a cross-section taken along the longitudinal direction of the head part of the rail 3 is taken, in which the damage of the rail is obvious as is shown in Fig. 3 and the measurement of sulfide-based inclusions is performed. The cross-section in the longitudinal direction of the rail of each of the samples taken is specularly polished, and Mn sulfide-based inclusions are investigated in an arbitrary cross-section with an optical microscope. Next, the number of inclusions that have the previously limited sizes is counted and calculated as the number per unit cross-sectional area. The typical value of each rail steel is obtained from the average value of the numbers per area of the unit cross-section of these 20 fields of vision. The zone (part) that will be used to investigate Nm sulfide-based inclusions is not particularly limited; however, it is preferable to observe a part that varies from the surface of the rail head part 3, which acts as the starting point of the damage, to a depth of 3 to 10 mm.

In addition, to stably improve the fracture resistance of a rail by further decreasing the effect of Mn sulfide based inclusions, which act as the starting points of the fracture and suppressing hydrogen suppression defects in advance, it is it is preferable to control the total number (per unit area) of the sulfide-based inclusions of Mn having major lengths in a range of 10 nm to 100 nm so that they are in a range of 20 / mm2 to 180 / mm2.

(4) The reason why the number (per unit area) of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm is limited:

In the present invention it is preferable that Mg-based oxides, Zr oxides and inclusions based on Mn sulphides having grain diameters in a range of 5 nm to 100 nm are present in an amount per unit area in a range of 500 / mm2 to 50,000 / mm2 in an arbitrary cross section.

The reason why the grain diameters of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions, which are the evaluation subjects, is limited to a range of 5 nm to 100 nm will be described in detail.

In the case that the grain diameters of the Mg-based oxides, Zr oxides and inclusions based on Mn sulfide are in a range of 5 nm to 100 nm, a sufficient dotting effect is obtained in the grain boundaries when They are generated in an austenite structure. In this way, it was observed that, without adversely affecting the damage resistance of a rail, consequently, a perlite structure was refined; and in this way the tenacity was improved reliably. Therefore, the grain diameters of the Mg-based oxides, Zr oxides and Mn sulfide-based inclusions eligible for the evaluation subjects are limited to being in a range of 5 nm to 100 nm.

Meanwhile, with respect to the dotting effect, the more inclusions that have fine grain diameters are present, the greater the effect. However, with respect to Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of less than 5 nm, it is extremely difficult to measure the number thereof. Furthermore, with respect to Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of more than 100 nm, the dotting effect described above cannot be obtained. Thus, Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having the grain diameters described above are used as evaluation subjects.

Next, with respect to the preferable configurations, the reason why the quantity (number) (per mm2) of Mn-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a grain diameter will be described in detail range of 5 nm to 100 nm in an arbitrary cross-section in the longitudinal direction is limited to being in a range of 500 to 50,000.

In the event that the total number (per unit area) of the oxides based on Mg, oxides of Zr and inclusions based on Mn sulfide having grain diameters in a range of 5 nm to 100 nm is less than 500 / mm2 , the dotting effect is not sufficiently obtained in an austenite structure after hot rolling. As a result, a perlite structure is thickened and the toughness of the rail is not improved. In the event that the total number (per unit area) of Mg-based oxides, Zr oxides and inclusions based on Mn sulphide having grain diameters in a range of 5 nm to 100 nm exceeds 50,000 / mm2, precipitation occurs excessively and a perlite structure becomes brittle; in this way, the toughness of the rail is degraded. Therefore the total number (per unit area) of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm is limited to being in a range of 500 / mm2 to 50,000 mm2.

Meanwhile, in the present limitation, Mg-based oxides and Zr oxides refer to oxides that partially include complex oxides such as Mn sulfide or the like. In addition, inclusions based on

Mn sulfide refers to inclusions generated from fine oxides such as Mg oxides, Zr oxides, Ca oxides or the like, as nuclei.

The grain diameter and the number of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions are observed and measured as follows. First, a thin film of an arbitrary cross-section shown in Figure 4 is taken, and the thin film is observed at a magnification of 50,000 to 500,000 using a transmission electron microscope. The grain diameter of the precipitates is obtained by measuring the area of each precipitate through observation and calculation of the diameter of a circle that has the same area as that of the precipitate.

The precipitates are observed at 20 display fields and the number of precipitates having diameters in a predetermined range of 5 nm to 100 nm is counted and the number per unit area is calculated from the counted number. The typical value of a rail steel is obtained from the average value of these 20 display fields. Meanwhile, the zone (part) to be used to investigate Mg-based oxides, Zr oxides and Mn sulfide-based inclusions is not particularly limited; however, it is preferable to observe a part that varies from the surface of the part of the head surface of the rail 3a to a depth of 3 mm to 10 mm, which requires toughness.

(5) Method for manufacturing the rail steel according to the present invention:

The method for manufacturing the rail steel according to the present invention includes the component composition described above and the microstructure is not particularly limited; however, in general, rail steel is manufactured by the following method. First, the melting is performed such as to obtain molten steel with a commonly used melting furnace, such as a converter furnace, an electric furnace or the like. Then, the molten steel is subjected to ingot preparation and a billet formation method or a continuous casting method such as for manufacturing a billet (a steel ingot) for rolling. Additionally, the billet is reheated to 1,200 ° C or higher, and then the billet is subjected to several hot rolling passes and molded on rails. Subsequently, heat treatments (reheating and cooling) are performed such as to make a rail.

In particular, in the hot metal stage, the general desulfurization and dephosphoration (dephosphorus and desulfurization treatment) is performed and additionally a sufficient desulfurization and dephosphoration is performed in a commonly used melting furnace, such as a converter furnace, an electric furnace or the like (dephosphorus and desulfurization treatment). Next, Ca is added to control Mn sulfide based inclusions. Additionally, according to the needs, Mg and Zr are added to finely disperse the oxides of nanometric size and inclusions based on Mn sulfide.

Details of the manufacturing conditions will be shown below.

In the hot metal stage, it is preferable to perform a general dephosphorus treatment and a desulfurization treatment in a careful manner to achieve the reduction of the amounts of P and S.

Regarding desulfurization, it is preferable to add CaO slowly and sufficiently in a ladle of hot metal (a stage prior to refining in a converter furnace) and eject CaS as slag.

Meanwhile, the addition of CaO is a method used in the case where S is reduced from a hot metal that has an extremely large amount of S. Unlike the addition of CaO-Si that is added to generate aggregates of oxides and Calcium sulfides (CaO-CaS) as described below, this method has no influence.

Regarding dephosphorus, it is preferable, when refining in a converter furnace, to eject slag in the middle of the refining to prevent the P from melting again from the slag including the P (P2O5 or the like) separated by dephosphorus.

Next, Ca is added as to control inclusions based on Mn sulfide.

It is preferable to add Ca in a refining process before casting. A preferable method of adding Ca is any of the addition of Ca alloy wires (Ca-Si alloy or similar) or Ca alloy ingots in a ladle or injecting a Ca alloy powder.

As the Ca alloy, a Ca-Si alloy (50Ca-50Si or similar), a Fe-Si-Ca alloy (Fe-30Si30Ca or similar) and a Ni-Ca alloy (90Ni-10Ca or similar) are used. ). Since the vapor pressure of Ca is high, if pure Ca is added, splashes occur in a molten steel or the slag on the surface of the molten steel is enveloped in the molten steel; and in this way the purity of molten steel is degraded. In addition, the rate of return becomes low. Consequently, the addition of a Ca alloy, for example a Ca-Si alloy, is widely performed. Compared to pure Ca, the activity of Ca is reduced in the alloy of Ca. Therefore,

in the case of adding the Ca alloy, the vaporization during the addition is relatively moderate and the yield rate also improves.

The lower the concentration of Ca in the alloy, the better the rate of return improves and the generation of splashes during addition is also suppressed. Therefore, the low concentration of Ca in the alloy is preferable. However, since elements other than Ca (Si or the like) are included in the case where the Ca concentration is low, it is necessary to carefully select the composition of the Ca alloy.

To avoid aggregation or segregation of aggregates of calcium oxides and sulfides (CaO-CaS), it is preferable to stir the molten steel by bubbling Ar or the like in the ladle after the addition of the Ca alloy such as to make that the concentration of Ca is uniform and float large inclusions. In the event that an amount of the molten steel is 200 t or greater, it is preferable to stir for about 5 minutes to 10 minutes. Excessive agitation causes the aggregation of inclusions; and in this way inclusions swell. Therefore, excessive agitation is not preferable.

From the point of view of ensuring the rate of Ca yield, it is advantageous to add a Ca alloy in the final stage of a refining process. Ca can be added to a trough in a casting process, rather than a refining process. It is necessary to adjust the rate of addition of a Ca alloy depending on the production during casting (the amount of laundry per hour). In this case, since the stirring of the molten steel after the addition of Ca is carried out inside the trough or a casting mold, the uniformity of the concentration of Ca is slightly worse than in the case of adding Ca in the ladle. Therefore, it is preferable to stir the molten steel during solidification by an electromagnetic force or the like to avoid aggregation or segregation of the aggregates of calcium oxides and sulphides (CaO-CaS) in the casting stage. In addition, it is preferable to optimize the shape of a casting nozzle to control the flow of molten steel during casting.

Additionally, to efficiently generate CaS having a high consistency with Mn sulfide-based inclusions, it is preferable to adjust the amount of oxygen in the molten steel such as to suppress the generation of an excessive amount of CaO. To adjust the amount of oxygen in advance, it is preferable to deoxidize the molten steel in advance by means of Al, Si or the like.

In addition, in order to finely disperse fine nanometer-size oxides and inclusions based on Mn sulfide, it is preferable to add pure metallic Mg, an Mg alloy (Fe-Si-Mg, Fe-Mn-Mg, Fe-Si-Mn- Mg and Si-Mg) or an alloy of Zr (Fe-Si-Zr, Fe-Mn-Mg-Zr and Fe-Si-Mn-Mg-Zr) in a high temperature molten steel ladle after a general refining or in a trough during laundry. Additionally, it is preferable to stir the molten steel during solidification by an electromagnetic force or the like to avoid aggregation or segregation in the casting stage. In addition, it is preferable to optimize the shape of a casting nozzle to control the flow of molten steel during casting.

In this case, although the order of addition of Ca, Mg and Zr is not clearly described, in a high carbon steel that includes a small amount of oxygen, it is preferable to add Ca which has a relatively weak oxidizing power at first, and then of adding Mg and Zr that have strong oxidizing powers to generate oxides of Ca, Mg and Zr with good efficiency.

In hot rolling, the temperature at which the final molding is performed is preferably in a range of 900 ° C to 1,000 ° C from the point of view of ensuring shape and material.

In addition, with respect to the heat treatment after hot rolling, it is preferable to perform accelerated cooling on a head portion of the rail 3 at high temperatures including austenite regions after hot rolling or reheating to obtain a perlite structure with a hardness Hv from 320 to 500 in the head part of rail 3. As the accelerated cooling method, performing heat treatment (and cooling) with a method described in Patent Document 8 (Japanese Unexamined Patent Application, Publication No. H08- 246100) or Patent Document 9 (Japanese Unexamined Patent Application, Publication No. H09-111352), it is possible to obtain a structure and hardness at predetermined intervals.

In this case, in order to carry out the thermal treatment with reheating after rolling the rail, it is preferable to heat the head part of the rail or the entire rail with a flame or by induction heating.

EXAMPLES Next, the examples of the present invention will be described.

Tables 1 to 6 show the chemical components of the rail steels tested. In this case, the rest consists of Faith and inevitable impurities. Rail steels having the component compositions shown in Tables 1 to 6 were manufactured as follows.

Dephosphoration and desulfurization were performed in a hot metal stage and, additionally, a

sufficient defosphration and desulfurization in a commonly used melting furnace, such as a converter furnace, an electric furnace or the like to obtain molten steel. Ca was added to the molten steel to control Mn sulfide-based inclusions, or Mg and Zr were additionally added to finely disperse the nanometer-sized oxides and Mn sulfide-based inclusions. Then, a steel ingot was manufactured

5 by a continuous casting method and hot rolling was performed on the steel ingot. Subsequently, a heat treatment was performed such as to manufacture a rail.

(a) The measurement of the number of inclusions based on Mn sulfide

Figure 3 shows an area in which inclusions based on Mn sulfide were observed in the rail steel. As shown in Figure 3, between the cross sections taken along the longitudinal direction of the

5 For rail steel obtained, a sample of a part that varied from the surface of the head part of the rail to a depth of 3 to 10 mm was cut including the part of the head surface 3a. Then, the number (per unit area) (inclusions / mm2) of inclusions based on Mn sulfide having main lengths (lengths of the main axes) in a range of 10 µm to 100 µm was obtained, by the method described above.

(b) The measurement of the number of inclusions based on Mn sulfide, Mg-based oxides and Zr oxides

Figure 4 shows an area in which inclusions based on Mn sulfide, Mg-based oxides and Zr oxides were observed in the rail steel.

15 As shown in Figure 4, between the cross sections of the rail steel obtained, a sample was cut from a part that varied from the surface of the rail head part to a depth of 3 to 10 mm including the part of the head surface 3a. Then, the number (per unit area) (inclusions / mm2) of the Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm, was obtained by method described above.

(c) The observation of the microstructure and the measurement of the hardness of the head surface part 3a

A sample of a part located at a depth of 4 mm from the surface of the head part of rail 3 was cut. Subsequently, a surface to be observed was polished, and then the surface was attacked with a fluid

25 attack of nital. The microstructure on the surface to be observed was observed using an optical microscope in accordance with JIS G 0551. In addition, according to JIS B7774, the Vickers Hv hardness of the cut sample was measured. In this case, Vickers hardness was measured while loading a hardness testing machine by diamond indentation on the sample at a load of 98 N (10 kfg). Vickers hardness is expressed as (Hv, 98 N) in the Tables.

30 The results obtained are shown in Tables 7 to 12. In this case, in the Tables, the 'material of the head part * 1' refers to a material in a part located at a depth of 4 mm from the surface of the head part of the rail 3.

(d) Wear test

Figure 5 shows an area from which a test sample was taken for the wear test, and the numerical values in the drawing show the dimensions (mm).

As shown in Figure 5, a disk-type test sample was cut from a part that included a head surface part 3a in the rail steel. Then, as shown in Figure 6, two opposite rotation axes were prepared, the disk-type test sample (rail test sample 4) was placed on one of the rotation axes, and an opposite material was arranged 5 on the other axis of rotation. The test sample for rail 4 and the opposite material 5 were contacted in a state where a predetermined load was applied to the test sample for rail 4. In that state, the two axes of rotation were rotated at a predetermined speed. while the test sample was cooling by supplying compressed air from a cooling nozzle 6. Then, after the rotation of the axes 700,000 times, the reduced amount (eroded amount) of the weight of the test sample of rail 4 was measured.

The conditions for the wear test are shown below.

Test machine: Nishihara type wear test machine (refer to Figure 6) Test sample shape: disc type test sample (external diameter: 30 mm, thickness: 8 mm) Area from which the test sample is taken: 2 mm below the surface of the head part of the rail (refer to Figure 5) Test load: 686 N (contact surface pressure 640 MPa) Slip Ratio: 20% Opposite material: perlithic steel (Hv 380) Atmosphere: in the atmosphere (air) Cooling: forced cooling by compressed air (flow rate: 100 Nl / min) Number of repetitions: 700,000

(e) Impact test of the head part

Figure 7 shows an area from which a test sample was taken for the impact test.

As shown in Figure 7, a test sample was cut along the direction of the rail width (cross section) in the cross section of the rail steel so that a part that included the part of the surface of 3rd head forms the bottom of a notch. Then, the test sample obtained was subjected to an impact test under the following conditions; and in this way the impact values (J / cm2) were measured.

Test machine: impact test machine Shape of the test sample: 2 mm U notch in JIS No. 3 Area from which the test sample is taken: 2 mm below the surface of the head part of the rail (refer to Figure 7) Test temperature: normal temperature (20 ºC)

The results obtained are shown in Tables 13 to 15. In this case, in the Tables, the "Wear test results * 2" refer to the results of the wear test described above, and the reduced amount (g) of the Test sample weight of rail 13 is expressed as the amount eroded. The "Impact test results * 3" refers to the results of the impact test described above of the head part and show the impact values (J / cm2). Meanwhile, a larger impact value (J / cm2) means a higher tenacity.

In the present evaluation, it was assessed that a case where an eroded amount was in the range of 1.5 g or less after 700,000 times of rotation had excellent wear resistance. Since the impact values measured at 20 ° C varied greatly with the amount of carbon in the steel, the criteria values that showed the relative merits of the characteristics were not established and the relative merits of the impact values between rail steels that had the same amount of carbon.

(1) Rails according to the present invention (47 rails), steels No. 1 to 47

5 Steels nº 3, 4, 7, 8, 11 to 14, 17 to 19, 21 to 25, 29, 30, 32 to 34, 36, 37, 43, 45 and 46: perlite rails that have wear resistance and Higher toughness of chemical compositions within the limited range described above of the present invention and in which the number of Mn sulfide-based inclusions having major lengths (lengths of main axes) in a range of 10 µm to 100 µm , the microstructure of the head part of the rail and the hardness are within the limited ranges of the present

10 invention.

Steels nº 1, 2, 5, 6, 9, 10, 15, 16, 20, 26 to 28, 31, 35, 38 to 42, 44 and 47: perlite rails that have superior wear resistance and toughness that have the chemical compositions within the limited range described above of the present invention and in which the number of inclusions based on Mn sulfide which

15 have main lengths (main axis lengths) in a range of 10 µm to 100 µm, the number of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions that have grain diameters in a 5 nm range at 100 nm, the microstructure of the rail head part and the hardness are within the limited ranges of the present invention.

20 (2) Comparative rails (21 rails), steels no. 48 to 68

Steels no. 48 to 53: rails whose amounts of C, Si and Mn are outside the ranges of the present invention.

Steels No. 54 to 55: rails whose amounts of P and S are outside the ranges of the present invention.

Steels No. 56 to 57: rails whose amount of Ca is outside the range of the present invention.

Steels No. 58 to 63: rails whose amounts of P, Si and Ca are outside the range of the present invention.

Steels No. 64 to 66: rails whose chemical composition is within the range of the present invention; however, the microstructure of the head part does not satisfy the characteristics described above of the present invention.

Steels No. 67 to 68: rails whose chemical compositions are within the range of the present invention; however, the hardness of the head part is outside the range described above of the present invention.

As shown in Tables 1 to 15, compared to comparative rail steels (steels no. 48 to 53),

5 Rail steels according to the present invention (steels # 1 to 47) include C, Si and Mn in contents within the limited ranges of the present invention. Therefore, it is possible to stably obtain a perlite structure having a hardness within a limited range of the present invention without generating an eutectoid ferrite structure, an eutectoid cementite structure and a martensite structure, which negatively affect the wear resistance and toughness.

In comparison with comparative rail steels (steels No. 64 to 68), the steels for rail according to the present invention (steels No. 1 to 47) include a perlite structure in the microstructure of the head part, and the Hardness of the perlite structure is within the limited range of the present invention. As a result, it is possible to improve the wear resistance and the toughness of the rail.

Figure 8 shows the results of the wear test of the rail steels according to the present invention (steels No. 1 to 47) and comparative rail steels (48, 50, 51, 52, 53, 64, 66 and 67 ).

In the event that C, Si and Mn are included in amounts within the limited range of the present invention,

20 prevents the generation of the eutectoid ferrite structure and the martensite structure, which negatively affect the wear resistance and, in addition, the hardness is within the limited range of the present invention. In this way, it is possible to greatly improve the wear resistance with any amount of carbon.

Figure 9 shows the results of the impact test of rail steels in accordance with the present invention (steels No. 1 to 47) and comparative rail steels (steels No. 49, 51, 53, 65, 66 and 68).

In the event that C, Si and Mn are included in amounts within the limited range of the present invention, the generation of the eutectoid cementite structure and the martensite structure, which negatively affect the toughness and, in addition, the Hardness is within the limited range of the present invention. From

30 this way, it is possible to greatly improve the toughness with any amount of carbon.

As shown in Figure 10, compared to comparative rail steels (steels no. 54 to 63), steels steels according to the present invention (steels no. 1 to 47) include P, S and Ca in center amounts of the limited ranges of the present invention. In this way, it is possible to greatly improve the toughness of

35 perlite rails with any amount of carbon.

Additionally, as shown in Figure 11, the rail steels according to the present invention (steels no. 11 to 13, 18 to 20, 24 to 26, 29 to 31, 33 to 35, 36 to 38 and 45 to 47 ) include Ca and, additionally, the added amount of Ca is optimized. In this way, Mn sulfide based inclusions are controlled so that

The number thereof is within a limited range of the present invention. As a result, it is possible to improve the toughness of the perlite rail. In addition, in the case that Mg and Zr are added, the oxides and inclusions based on Mn sulphide are finely dispersed so that the number of Mg-based oxides, Zr oxides and inclusions based on Mn sulfide is achieved in a range of 500 / mm2 to 50,000 / mm2. In this way it is possible to further improve the toughness of the perlite rail.

INDUSTRIAL APPLICABILITY The perlite rail according to the present invention has a wear resistance and toughness superior to those of a high strength rail of usual use. Therefore, the present invention can preferably be applied to rails used in an extremely severe derailment environment, such as freight rail rails

50 that transport mining natural resources from regions with severe natural environments.

Brief description of the symbols

1: top of head

2: part of the corner of the head

55 3: head part of the rail 3a: surface part of the head 3b: a part that varies from the surfaces of the corner portions of the head and an upper part of the head to a depth of 20 mm.

4: rail test sample

60 5: opposite material

6: cooling nozzle

Claims (1)

1. A perlite rail having a steel composition comprising. in terms of mass percentage: C: from 0.65 to 1.20%; 5 Si: from 0.05 to 2.00%; Mn: from 0.05 to 2.00%; P ≤ 0.0150%; S ≤ 0.0100%; Ca: 0.0005% to 0.0200%; 10 one or both of Mg: from 0.0005 to 0.0200% and Zr: from 0.0005 to 0.0100% and optionally one or more selected from Co: from 0.01% 1.00%, Cr: 0.01 to 2.00%, Mo: 0.01 to 0.050%, V: 0.005 to 0.50%, Nb: 0.002 to 0.050%, B: 0.0001 to 0.0050%, Cu: 0.01 to 1.00%, Ni: 0.01 to 1.00%, Ti: 0.0050 to 0.0500%, Al: greater than 0.0100 to 1.00%, and N: from 0.0060 to 0.0200%, the rest being inevitable Fees and impurities, 15 in which an S / Ca ratio is in a range of 0.45 to 3.00 between a part of the head of the rail, in a part of the surface of the head that varies from the surfaces of the corner portions of the head and an upper part of the head to a depth of 10 mm or a part that varies from the surfaces of the corner portions of the head and the upper part of the head to a depth of 20 mm, 95% or greater than a metallographic structure is a perlite structure, 20 a hardness Hv of the perlite structure is in a range of 320 to 500, the sulfide-based inclusions of Mn having major lengths in a range of 10 to 100 µm are present in an amount per unit area in a range of 10 at 200 / mm2 in a cross section taken from a part that varies from the surface of the head part of the rail to a depth of 3 mm to 10 mm along a longitudinal direction in the perlite structure, 25 Mg oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm are present in an amount per unit area in a range of 500 to 50,000 / mm2 in one section transverse taken from a part that varies from the surface of the part of the surface of the rail head to a depth of 3 mm to 10 mm in the perlite structure.