Pearlite rail

Abstract

A pearlite rail according to one embodiment of the present disclosure contains, in mass%, 0.65-1.20% of C, 0.05-2.00% of Si, 0.05-2.00% of Mn, 0.02-2.00% of Cr, 0.0020-0.0200% of N, 0.010-0.100% of V, 0% or more and less than 0.005% of Nb, 0% or more and less than 0.005% of Ti, and 0-0.100% of Mo or the like, with the balance being made up of Fe and impurities. With respect to the pearlite rail, the structure that has a depth of 25 mm starting from the outer contour surface of a head top part contains a pearlite structure in the area ratio of 95% or more, the hardness at the position of 25 mm depth from the surface of the head top part is at least HV350, and the number density per unit interface area of the nitride particles that contain V, have a particle diameter of 4 nm or more, and are present on the cementite interface of the pearlite structure at the position of 25 mm depth from the surface of the head top part is less than 1.0 × 1010 cm-2.

Description

TITLE OF INVENTION: PEARLITE RAIL TECHNICAL FIELD

[0001] The present disclosure relates to a pearlite rail intended to simultaneously improve wear resistance and ductility of the head in a rail used in a heavy load railway. BACKGROUND ART

[0002] In foreign heavy load railways, high integration of freight is promoted in order to improve efficiency of rail transportation. In particular, for steeply curved rails, the wear resistance of the G.C. portion (Gauge Corner portion) and the head side portion cannot be sufficiently secured. As a result, decrease in rail service life due to wear has become a problem. From such a background, it is required to develop a rail having wear resistance equal to or higher than that of a high-strength rail containing eutectoid carbon steel, which is being used.

[0003] In general, it is known that the higher the hardness of the rail, the better the wear resistance. However, actually, as described in Non Patent Document 1, it has been reported that the surface layer is work-hardened during use to increase hardness, thereby improving wear resistance. In addition, as described in Non Patent Document 2, it is shown that pearlite steel, which has excellent work hardening characteristics, is more excellent in wear resistance than martensite steel or bainite steel, which simply have high initial hardness. However, what kind of micro structure gives pearlite steel excellent wear resistance is not shown, and there are no sufficient guidelines for manufacturing rails. Patent Document 1 describes that carbonitride-generating elements such as Ti, V, Nb, or Mo are added in a certain amount to generate carbonitride precipitate particles thereof in the austenite phase so that the grain growth of austenite is inhibited during hot rolling to obtain fine grains, and thereby, the block size becomes finer after pearlitic transformation to improve ductility.

[0005] On the other hand, Patent Document 2 discloses a method in which W, V, Nb, or the like is added to precipitate a carbonitride in the ferrite phase after pearlitic transformation to strengthen the ferrite phase, thereby improving wear resistance. These two documents suggest that the same kind of elements are added to improve different properties of the rail.

[0006] In these documents, carbides are mainly used as precipitates in pearlite. On the other hand, Patent Document 3 describes that fine particles made of nitride are precipitated in ferrite to improve fatigue damage resistance and wear resistance. Patent Document 4 describes that fine particles made of nitride are precipitated in ferrite to improve fatigue damage resistance and delayed fracture resistance. In these documents, the particle size, the number density, and the component composition of nitride particles precipitated in ferrite are defined.

[0007] Patent Document 5 discloses a pearlite rail that is a steel rail including, in terms of mass%, C: 0.65 to 1.20%, Si: 0.05 to 2.00%, Mn: 0.05 to 2.00%, and Cr: 0.02 to 2.00%, and further including two or more of V, Nb, Ti, and Mo: each at least 0.005% or more and in an amount of V + Nb + Ti + Mo: 0.02 to 0.20%, and a balance including Fe and unavoidable impurities and having a head top hardness of at least 340 Hv, wherein the number density of carbonitride precipitate particles having a size of 10 nm or less in the ferrite phase is 5 x 1015 cm3 or less.

[0008] Patent Document 6 discloses a method for manufacturing a high toughness rail including rolling a steel containing 0.60 to 1.20% of C into a rail, wherein, in the finish rolling, continuous finish rolling is performed such that two or more passes of rolling are performed with a cross-sectional reduction rate of 5 to 30% per one pass between 850°C and 1000°C, and the interval between the rolling passes is 8 seconds or less, and subsequently, cooling is performed to 800 to 950°C at a cooling rate of 0.5 to 50 °C / s, followed by air cooling or accelerated cooling. Citation List Non Patent Document

[0009] Non Patent Document 1: Masaharu UEDA et al. “Influence of Hardness and Carbon Content on Rolling Contact Wear in Pearlitic Steels”, Tetsu-to-Hagane, Japan, The Iron and Steel Institute of Japan, 2001, Vol. 87, No. 4, P190-197 Non Patent Document 2: Masaharu UEDA et al. “Influence of Microstructure on Rolling Contact Wear in High Carbon Steels”, Tetsu-to-Hagane, Japan, The Iron and Steel Institute of Japan, 2004, Vol. 90, No. 12, P1023-1030 Patent Document

[0010] Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2010-1500 Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2007-51348 Patent Document 3: PCT International Publication No. WO 2020 / 054339 Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2020-70495 Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2015-158006 Patent Document 6: Japanese Unexamined Patent Application, First Publication No. 2001-234238 SUMMARY OF INVENTION Technical Problem

[0011] From such a background, there has been a demand for a pearlite rail used in a heavy load railway and whose head is excellent in hardness, wear resistance, and ductility; and a manufacturing method thereof. The utilization of nitride particles in recent years is also excellent from the viewpoint of removing unnecessary solid solution N having remained until now as impurities and from the viewpoint of rail hardening. However, the knowledge on the position where the nitride particles are precipitated in pearlite is not sufficient. The present disclosure has been made in view of the above-described problems, and an object thereof is to simultaneously improve the wear resistance and the ductility of the head top, which is required for a rail of a heavy load railway. Solution to Problem

[0012] The present inventors have conducted detailed metallographic studies on the surface hardness, internal hardness, and the rolling wear surface of a pearlite rail. As a result, the present inventors have found that, through an abrasion test, the pearlite lamella interval is narrowed in the contact surface region (miniaturization of pearlite lamella) and they are microcrystallized so that the hardness of the surface region is remarkably increased, and a larger increase in the hardness thereof means more excellent wear resistance. In the hardness increase due to lamella thinning and microcrystallization, the lamellar ferrite (ferrite phase) in pearlite, being soft and rich in ductility, is easily plastically deformed, and the pearlite structure constituted by lamellar cementite and lamellar ferrite is easily thinned and refined. This time, it has been found that an inhibiting factor therefor causes deterioration in wear resistance and occurrence of fatigue damage.

[0013] It has been found that, in a pearlite rail utilizing precipitate particles or clusters made of nitride, the lamella of a pearlite structure 1 mainly includes two precipitation positions of nitride particles as shown in FIG. 1: (1) the center portion of the lamellar ferrite 12; and (2) the interface of cementite 11 / ferrite 12 (hereinafter referred to as cementite interface 13). Nitride particles 22 distributed in the center portion of the ferrite 12 contribute to the hardening of the pearlite structure 1 through the hardening of the ferrite 12. On the other hand, nitride particles 21 precipitated on the cementite interface 13 hardly contribute to hardening. In addition, the nitride particles 21 precipitated on the cementite interface 13 are relatively large and, therefore, are not plastically deformed and decomposed even by repeatedly wearing the rail. For that reason, it has been found that the nitride particles 21 precipitated on the cementite interface 13 cause a decrease in the wear resistance and ductility of the rail. Accordingly, it has been revealed that a pearlite rail utilizing nitride needs decreasing the number of the nitride particles 21 on the cementite interface 13 and reducing the size thereof. On the other hand, the nitride particles 22 precipitated not on the cementite interface 13 but in the ferrite 12 strengthen the ferrite 12, thereby increasing the hardness of the rail itself. In particular, when distributed finely and at a high number density, the nitride particles 22 precipitated in the ferrite 12 can be utilized for hardening without decreasing wear resistance or ductility.

[0015] The present disclosure has been made based on the above new knowledge in order to solve the above problems, and the gist thereof is as follows.

[0016] (1) The pearlite rail according to an embodiment of the present disclosure includes, in terms of mass%, C: 0.65 to 1.20%, Si: 0.05 to 2.00%, Mn: 0.05 to 2.00%, Cr: 0.02 to 2.00%, N: 0.0020 to 0.0200%, V: 0.010 to 0.100%, Nb: 0% or more and less than 0.005%, Ti: 0% or more and less than 0.005%, Mo: 0 to 0.100%, B: 0 to 0.0050%, Co: 0 to 1.00%, Ni: 0 to 1.00%, Mg: 0 to 0.0200%, Ca: 0 to 0.0200%, Cu: 0 to 1.00%, REM: 0 to 0.0500%, Zr: 0 to 0.0200%, P: 0.025% or less, S: 0.025% or less, Al: 0 to 1.000%, O: 0.0040% or less, and a balance including Fe and impurities, wherein a microstructure in a range from a head outer surface to a depth of 25 mm includes a pearlite structure in an area fraction of 95% or more; hardness at a position having a depth of 25 mm from a surface of a head top is at least HV350; and on a cementite interface of the pearlite structure at the position having a depth of 25 mm from the surface of the head top, nitride particles containing V and having a particle size of 4 nm or more are present in a number density of less than 1.0 x 1010 cm2 per unit interface area. (2) Preferably, in the pearlite rail according to (1), in ferrite of the pearlite structure, nitride particles containing V, having a particle size of 0.5 to 4 nm, and separated from the cementite interface are present in a number density in a range of 4.0 x 1016 to 4.0 x 1017 cm3 per unit volume. (3) Preferably, the pearlite rail according to (1) or (2) further includes, in terms of mass%, one or more selected from the group consisting of: B: 0.0001 to 0.0050%, Co: 0.01 to 1.00%, Ni: 0.01 to 1.00%, Mg: 0.0005 to 0.0200%, Ca: 0.0005 to 0.0200%, Cu: more than 0% and 1.00% or less, REM: 0.0005 to 0.0500%, Zr: 0.0001 to 0.0200%, and Al: more than 0% and 1.000% or less. Advantageous Effects of Invention

[0017] According to the present disclosure, it is possible to provide a rail excellent in wear resistance and ductility in a steel rail having a pearlite structure. That is, the present disclosure presents a method for manufacturing a rail having improved wear resistance and ductility by suppressing wear resistance decrease due to nitride particles precipitated on the cementite / ferrite interface. BRIEF DESCRIPTION OF DRAWINGS

[0018] [FIG. 1] A schematic view showing a distribution of precipitated particles in a rail pearlite structure. [FIG. 2] A diagram showing the relationship between the number density of nitride particles on the cementite interface and wear amount. [FIG. 3] A drawing showing names in a rail head. [FIG. 4A] An example of a three-dimensional element map of Fe (iron) of a V-added rail. [FIG. 4B] An example of a three-dimensional element map of C (carbon) of a V- added rail. [FIG. 4C] An example of a three-dimensional element map of V (vanadium) detected with V2+ ions of a V-added rail. [FIG. 4D] An example of a three-dimensional element map of V (vanadium) detected with VN2+ ions of a V-added rail. [FIG. 5A] An example of a three-dimensional element map of C obtained by enlarging the box region X in FIG. 4D. [FIG. 5B] An example of a three-dimensional element map of V obtained by enlarging the box region X in FIG. 4D. [FIG. 5C] An example of a three-dimensional element map of Cr obtained by enlarging the box region X in FIG. 4D. [FIG. 5D] An example of a three-dimensional element map of Mn obtained by enlarging the box region X in FIG. 4D. DESCRIPTION OF EMBODIMENTS

[0019] The present inventors conducted rolling abrasion tests on pearlite steels different in their components and manufacturing methods in order to investigate what strongly affects the wear resistance in a pearlite rail utilizing nitride. Then, the present inventors observed the structure before the abrasion test and the abrasion structure after the abrasion test with a transmission electron microscope (TEM) to examine the relationship between the structural change and the wear resistance properties in detail. In addition, the present inventors examined the existence position, the number density, and the composition of fine nitride particles (including finer clusters) in a pearlite steel with a three-dimensional atom probe to investigate the relationship with pearlite rail wear resistance properties.

[0020] FIG. 1 is a view schematically showing the distribution state of precipitates and clusters of nitride in a pearlite structure 1 of a rail. In general, the pearlite lamella is constituted by an 80 to 200 nm-wide lamellar ferrite 12 and a 10 to 20 nm-wide lamellar cementite 11. The means for increasing the rail hardness under the same C amount is either to reduce the pearlite lamella interval (refinement strengthening) or to increase the hardness of the ferrite 12. Although a method of increasing the hardness of the cementite 11 is also conceivable, the hardness of the cementite 11 is already considerably high, and it is substantially difficult to intentionally further increase the hardness. In addition, when the hardness of the ferrite 12 is simply greatly increased, the rail surface is hardly plastically deformed during use such that an increase in hardness of the worn surface due to thinning and refinement of the pearlite lamella does not occur. On the other hand, it has been found that, when the ferrite 12 is hardened with very fine nitride particles, plastic deformation is not completely suppressed, and the fine nitride particles decompose during abrasion not to become a starting point of cracks and voids but to form solid solution atoms, dipoles of N with V or Cr, or the like and contribute to hardness and wear resistance.

[0021] Detailed structural observation revealed that the precipitation positions of the nitride particles are mainly at two positions: the cementite interface 13 (that is, the interface between the lamellar cementite 11 and the lamellar ferrite 12) position; and the center portion of the lamellar ferrite 12 separated from the cementite interface 13. Here, the center portion of the lamellar ferrite 12 refers to a region 5 nm or more away from the cementite interface 13. Among the cementite interface 13 and the center portion of the ferrite 12, it was considered that the nitride particles 22 distributed in the center portion of the ferrite 12 contribute to hardening, but the nitride particles 21 precipitated on the cementite interface 13 do not contribute to hardening. In addition, it was considered that, since nitride particles having a slightly large size are not deformed or decomposed by wear, strain is concentrated around the nitride particles, and the nitride particles serve as a starting point of voids or cracks, which causes deterioration in wear resistance, ductility, and the like. Therefore, it is necessary to reduce the size of the nitride particles 21 on the cementite interface 13 and to reduce the number density of large nitride particles. In addition, it was considered that the nitride particles 22 in the ferrite 12 can also be precipitated finely and at a high number density, thereby contributing to hardening without lowering ductility or wear resistance.

[0022] The present inventors devised chemical components, heat treatment, and the like to produce pearlite rails having initial pearlite hardness (strength) in a certain range but having different sizes and distribution states of nitride particles in the pearlite. From structural analysis and abrasion tests on these pearlite rails, the relationship between the nitride particle distribution and the wear resistance was examined. The wear resistance was quantitatively evaluated by using a Nishihara abrasion tester. In the abrasion test, wear amounts were compared at a contact surface pressure of 640 MPa, a slip ratio of 20%, and a repetition of 700,000.

[0023] FIG. 2 is a diagram showing, in each pearlite rail sample, (1) the relationship between the number density per unit interface area of nitride particles having a size of 4 nm or more observed on the cementite interface and the wear amount; and (2) the relationship between the number density per unit interface area of nitride particles having a size of 0.5 nm or more and less than 4 nm on the cementite interface and the wear amount in a rail sample containing no nitride particles having a size of 4 nm or more. Here, rail samples having a Vickers hardness of 380 to 400 Hv at a depth of 25 mm from the surface were used. The particle size and number density of the precipitated particles were examined with a three-dimensional atom probe.

[0024] According to the investigation results shown in FIG. 2, it is found that the wear amount increases when the number density of the nitride particles having a diameter of 4 nm or more on the cementite interface is higher than 1.0 x 1010 cm'2. When the number density of the nitride particles having a diameter of 4 nm or more on the cementite interface is less than 1.0 x 1010 cm2, the rail wear amount is not so much different from the case where substantially no precipitate is contained. When the number density of the nitride particles having a diameter of 0.5 nm or more and less than 4 nm is plotted in this figure, it is found that there is no correlation with the wear amount. This shows that relatively small nitride particles have a small influence on the decrease in wear resistance even when precipitated on the cementite interface.

[0025] When there are relatively large nitride particles on the cementite interface, not only the nitride particles do not contribute to improvement in rail hardness, but also strain accumulates at the particle positions on the cementite interface during the abrasion test so that voids and cracks are formed, which causes breakage. Therefore, when there are many relatively large nitride particles on the cementite interface, it is interpreted that the wear amount has increased. However, when the nitride particles are very fine, they will decompose during wear. Therefore, strain does not accumulate around the fine nitride particles, which does not lead to deterioration of wear resistance.

[0026] According to the above basic experiments, in order to improve the wear resistance in the pearlite rail steel in which nitride particles are utilized for hardening, it is desirable that the nitride particles on the cementite interface have a very small size or the number density of the large nitride particles is small on the cementite interface.

[0027] On the other hand, when nitride is precipitated in pearlite, the cementite interface serves as a preferential nucleation site. Accordingly, nitride precipitation on the cementite interface is more likely to occur than nitride precipitation in ferrite grains, which acts on hardening. Therefore, when nitride particles are precipitated in ferrite grains, it is difficult to completely suppress precipitation on the cementite interface. It is necessary to reduce the precipitation of nitride particles on the cementite interface by narrowing the range of manufacturing conditions such as components and working heat treatment.

[0028] The reason for the limited range of the pearlite rail according to the embodiment will be described below. Note that the head of the pearlite rail is usually worn during use due to contact with wheels. Therefore, the pearlite rail is required to have characteristics suitable for railway rails from the viewpoint of long life, not only at the surface of the head top but also at a depth of 25 mm from the head. In addition, at the surface of the pearlite rail, the pearlite lamella is more easily refined than at a depth of 25 mm, and the hardness is increased such that wear resistance is easily secured. The pearlite rail with suitable characteristics at a depth of 25 mm from the surface of the head top naturally also has suitable characteristics at the surface of the head top. In consideration of the above circumstances, in the pearlite rail according to the embodiment, the particle size and the number density of the nitride containing V and the hardness are limited at a depth of 25 mm from the surface of the head top. In addition, in the pearlite rail according to the embodiment, the amount of the pearlite structure is limited in a range from the head outer surface to the depth of 25 mm. (Nitride containing V) The pearlite rail according to the embodiment includes requirements on nitride particles containing V. The nitride particles containing V are nitride particles having a V content of 1 atom% or more. In general, the nitride is a crystal phase constituted by N and a metal element, and includes: nitrides containing one metal element such as VN, TiN, NbN, or CrN; and nitrides containing a plurality of metal elements such as (V, Cr)N and (Ti, V)N. The (V, Cr)N is a nitride in which V and Cr are mixed, and the (Ti, V)N is a nitride in which Ti and V are mixed. The elements in the parentheses are indicated in the order of having a larger number of atoms. In general, fine particles matching the ferrite matrix have a NaCl-type crystal structure. On the other hand, the carbide is a crystal phase in which N is replaced with C, and a small amount of N may be contained as the carbonitride. The nitride particles described in the present disclosure do not contain C. The term “do not contain” means being equal to or lower than the C solid solution concentration in the parent phase (ferrite phase) in which the nitride particles are present. A nitride can be precipitated finer than a carbide, which is often referred to as a cluster. In the present specification, such fine particles (0.5 to 4 nm) are also referred to as nitride particles.

[0030] (1) Particle size and number density of nitride containing V on cementite interface in pearlite structure at position having depth of 25 mm from head outer surface The number density of the nitride particles on the cementite interface hardly affects the strength of the ferrite phase. This is because the nitride particles on the cementite interface do not hinder the movement of dislocations within the ferrite. However, the nitride particles on the cementite interface affected the wear resistance. In particular, when the number density of the nitride particles having a size larger than a specific size on the cementite interface was increased, the wear resistance was deteriorated. This is because large nitride particles do not deform or do not decompose, so that strain accumulates therearound, which becomes a source of voids and cracks.

[0031] Therefore, in order to sufficiently maintain wear resistance, nitride particles containing V and having a particle size of 4 nm or more are present on the cementite interface in a number density of less than 1.0 x 1010 cm2 per unit interface area. The nitride particles having a small size on the cementite interface hardly affect the decrease in wear resistance. Therefore, the number density is not particularly limited as long as the nitride particles are smaller than 4 nm.

[0032] (2) Particle size and number density of nitride containing V in ferrite in pearlite structure at position having depth of 25 mm from head outer surface In the ferrite, the nitride particles containing V, having a particle size of 0.5 to 4 nm, and separated from the cementite interface are preferably contained in a number density in a range of 4.0 x 1016 to 4.0 x 1017 cm3 per unit volume. This is because the lamellar ferrite is strengthened to enhance rail hardness and improve wear resistance. When the particle size of the nitride containing V in the ferrite is within a range of 0.5 to 4 nm, the effect of strengthening the lamellar ferrite is obtained. Further, when the number density is within a range of 6.0 x 1016 to 5.0 x 1017 cm3, an even greater effect of strengthening the lamellar ferrite is obtained. More preferably, the number density of the nitride particles containing V and having a particle size of 0.5 to 4 nm in the ferrite is within a range of 8.0 x 1016 to 2.0 x 1017 cm3.

[0033] (3) Steel chemical components The component composition of the pearlite rail according to the embodiment may be limited for the following reasons. Note that “%” described below means “mass%” unless otherwise specified.

[0034] C: 0.65 to 1.20% C is an effective element that promotes pearlitic transformation and secures wear resistance. When the C amount is less than 0.65%, the minimum strength and wear resistance required for a rail cannot be maintained. When the C amount is more than 1.20%, a large amount of coarse pro-eutectoid cementite structure is formed, and wear resistance and ductility are deteriorated. Therefore, the C amount is limited to 0.65 to 1.20%. When the C amount is 0.70% or more, 0.80% or more, or 0.90% or more, the wear resistance is further improved, and the service life of the rail is further improved. The C amount may be 1.10% or less, 1.00% or less, or 0.95% or less.

[0035] Si: 0.05 to 2.00% Si is an essential component as a deoxidizing material. Si is an element that strengthens solid solution into the ferrite phase in the pearlite structure to improve the hardness (strength) of the rail head. Further, Si is an element that suppresses the formation of a pro-eutectoid cementite structure, suppresses a decrease in ductility, and suppresses a decrease in ductility in a hyper-eutectoid steel. However, when the Si amount is less than 0.05%, these effects cannot be sufficiently expected. When the Si amount is more than 2.00%, many surface defects are generated during hot rolling and oxides are formed such that weldability is deteriorated. Furthermore, when the Si amount is more than 2.00%, hardenability remarkably increases, and the martensite structure harmful to the wear resistance and the ductility of the rail is generated. Therefore, the Si amount is limited to 0.05 to 2.00%. The Si amount may be 0.10% or more, 0.20% or more, or 0.50% or more. The Si amount may be 1.80% or less, 1.60% or less, or 1.20% or less.

[0036] Mn: 0.05 to 2.00% Mn is an element that enhances hardenability and refines the pearlite lamella interval to secure the hardness of the pearlite structure and improve wear resistance. However, when the Mn amount is less than 0.05%, the effect is small, and it is difficult to secure the wear resistance required for a rail. When the Mn amount is more than 2.00%, hardenability is significantly increased, and the martensite structure harmful to wear resistance and ductility is likely to be generated. Therefore, the Mn amount is limited to 0.05 to 2.00%. The Mn amount may be 0.10% or more, 0.20% or more, or 0.50% or more. The Mn amount may be 1.80% or less, 1.60% or less, or 1.20% or less.

[0037] Cr: 0.02 to 2.00% Cr increases the equilibrium transformation temperature, and as a result, refines the ferrite structure and the pearlite structure to contribute to increasing the hardness. Furthermore, Cr is an element that forms a nitride together with V and improves the hardness (strength) of the pearlite structure by precipitation hardening. However, when the Cr amount is less than 0.02%, the effect is small, and the effect of improving the hardness of the rail steel is not observed. On the other hand, when the Cr amount is more than 2.00%, hardenability increases, a martensite structure is generated, spalling damage starting from the martensite structure occurs at the head corner or the head top, and the surface damage resistance decreases. Therefore, the Cr amount is limited to 0.02 to 2.00%. The Cr amount may be 0.10% or more, 0.20% or more, or 0.50% or more. The Cr amount may be 1.80% or less, 1.60% or less, or 1.20% or less.

[0038] V: 0.010 to 0.100% V is an important element in the steel according to the present disclosure. V suppresses austenite grain growth for refinement when the pearlite rail is manufactured. By cooling the rail in which the austenite grains are refined, fine pearlite is formed, and the wear resistance of the pearlite rail is improved. Further, V may be bonded to N atoms to become nuclei of nitride to form nitride particles or clusters. It is more preferable that a nitride containing V is precipitated in the ferrite because the nitride suppresses the movement of dislocations to contribute to increasing the hardness of the pearlite.

[0039] When the V amount is less than 0.010%, the effect cannot be sufficiently expected, and an increase in hardness and wear resistance improvement are not observed. On the other hand, when the V amount is excessive, large nitride particles are precipitated on the cementite interface. The coarse nitride on the cementite interface lowers plastic deformability and causes decrease in wear resistance. When the V amount is excessive, not V nitride but V carbide is likely to be generated. Therefore, the upper limit of the V amount is 0.100%. More preferably, the V amount is in a range of 0.020 to 0.050%. The V amount may be 0.015% or more, 0.020% or more, or 0.030% or more. The V amount may be 0.090% or less, 0.080% or less, or 0.070% or less.

[0040] N: 0.0020 to 0.0200% N becomes nuclei of a nitride together with V to form nitride particles. In general, about 0.0010% of N is contained in steel as an impurity. However, the N amount is preferably 0.0020% or more because nitride particles can be formed inside the ferrite. On the other hand, when the N amount is more than 0.0200%, the nitride particles become large and are also generated on the cementite interface. Therefore, the wear resistance is reduced. In addition, solute N remaining at a high concentration causes decrease in ductility itself. Therefore, the N amount is limited to 0.0020 to 0.0200%. The N amount may be 0.0025% or more, 0.0030% or more, or 0.0050% or more. The N amount may be 0.0180% or less, 0.0150% or less, or 0.0100% or less.

[0041] P: 0.025% or less P is an element that degrades the ductility of the rail steel. When the P amount is more than 0.025%, the influence cannot be ignored. Therefore, the P amount is 0.025% or less. The P amount may be 0.024% or less, 0.023% or less, or 0.022% or less. The lower limit of the P content is not particularly limited and may be 0%. On the other hand, from the viewpoint of reducing the refining cost, the P amount may be 0.010% or more, 0.011% or more, or 0.012% or more.

[0042] S: 0.025% or less S is an element that is present in the steel mainly in the form of inclusions (such as MnS) and causes embrittlement of the steel. In particular, when the S amount is more than 0.025%, the adverse effect on embrittlement cannot be ignored. Therefore, the S amount is 0.025% or less. The S amount may be 0.024% or less, 0.023% or less, or 0.022% or less. The lower limit of the S content is not particularly limited and may be 0%. On the other hand, from the viewpoint of reducing the refining cost, the S amount may be 0.008% or more, 0.009% or more, or 0.010% or more.

[0043] O: 0.0040% or less O is an impurity. The lower limit of the O content is not limited and may be 0.0001 % from the viewpoint of manufacturing cost. On the other hand, when the O amount is excessive, coarse oxide is generated and causes decrease in ductility and toughness of the steel. The O amount is preferably 0.0030% or less, and more preferably 0.0020% or less.

[0044] Nb: 0% or more and less than 0.005% Ti: 0% or more and less than 0.005% Mo: Oto 0.100% The rail manufactured with the component composition described above may contain one or more of Nb, Ti, and Mo in order to refine the pearlite structure. Nb, Ti, and Mo are elements effective in generating carbonitrides in a relatively high temperature range in the heat-affected zone reheated to a temperature range equal to or lower than the Acl point and preventing softening and embrittlement of the heat-affected zone of the weld joint. In particular, Mo is an element that not only generates carbonitrides but also increases the equilibrium transformation temperature, as with Cr, and as a result, refines the ferrite structure and the pearlite structure to contribute to higher hardness, and at the same time, reinforces the cementite phase to improve the hardness (strength) of the pearlite structure. However, these elements easily produce a large nitride, and thus unnecessarily consume N. Therefore, Nb is preferably less than 0.0050%. Ti is preferably less than 0.0050%. Mo is preferably 0.100% or less. Mo is more preferably 0.005% or less. Nb, Ti, and Mo may be 0.0040% or less, 0.0035% or less, or 0.0030% or less, respectively. It is not essential that Nb, Ti, and Mo are included in the rail according to the embodiment. Therefore, each of Nb, Ti, and Mo may be 0%.

[0045] The rail manufactured with the component composition described above may contain elements of B, Co, Ni, Mg, Ca, Al, and Cu as necessary for the purpose of refining the pearlite structure, increasing the strength, improving the ductility, preventing softening of the heat affected zone of the weld, controlling the cross-sectional hardness distribution inside the rail head, and the like. However, these elements are not necessarily included in the pearlite rail. The lower limit of the content of each of B, Co, Ni, Mg, Ca, Al, and Cu is 0%.

[0046] B: Oto 0.0050% B is an element that forms an iron carbide boride (Fe23(CB)6) at austenite grain boundaries, reduces the cooling rate dependency of the pearlitic transformation temperature by the effect of promoting pearlitic transformation, provides the rail with a hardness distribution more uniform from the head surface to the inside, and prolongs the life of the rail. When the B amount is 0.0001% or more, the effect can be sufficiently exhibited to improve the hardness distribution of the rail head. When the B amount is 0.0050% or less, generation of a coarse iron carbide boride can be suppressed to enhance ductility and toughness. Therefore, the B amount may be 0.0001 to 0.0050%. The B amount may be 0.0002% or more, 0.0003% or more, or 0.0005% or more. The B amount may be 0.0040% or less, 0.0020% or less, or 0.0010% or less.

[0047] Co: Oto 1.00% Co is an element that hardly acts on the solid solution strengthening and further refines the fine ferrite structure formed by contact with wheels at the worn surface of the rail head top to improve wear resistance. When the Co amount is 0.01% or more, the lamellar structure and the ferrite grain size are refined to exhibit the effect of improving wear resistance. When the Co amount is 2.00% or less, the ductility of the pearlite structure can be enhanced. In addition, when the Co amount is 1.00% or less, the alloying cost can be suppressed to enhance the economic efficiency. Therefore, the Co amount may be limited to 0.01 to 1.00%. The Co amount may be 0.02% or more, 0.05% or more, or 0.10% or more. The Co amount may be 0.80% or less, 0.50% or less, or 0.10% or less.

[0048] Ni: Oto 1.00% Ni improves ductility in the pearlite structure and suppresses decrease in ductility due to Co. At the same time, Ni is an element that strengthens the solid solution to increase the hardness (strength) of the rail. When the Ni amount is 0.01% or more, the effect can be sufficiently obtained. When the Ni amount is 1.00% or less, the ductility of the ferrite phase in the pearlite structure can be enhanced, and the wear resistance of the pearlite structure can be increased. Therefore, the Ni amount may be 0.01 to 1.00%. The Ni amount may be 0.02% or more, 0.05% or more, or 0.08% or more. The Ni amount may be 0.80% or less, 0.50% or less, or 0.10% or less.

[0049] Mg: 0 to 0.0200% Mg is an effective element that is bonded with O, S, or Al to form a fine oxide, suppresses the grain growth of crystal grains in reheating when the rail is rolled, refines the austenite grains, and improves the ductility of the ferrite structure and the pearlite structure. Furthermore, MgO and MgS, formed from Mg, finely disperse MnS to form a Mn dilute layer around MnS, thereby contributing to generating ferritic and pearlitic transformation. As a result, the size of the pearlite block is mainly refined. Therefore, Mg is an element effective for improving the ductility of the pearlite structure. When the Mg amount is 0.0005% or more, the effect can be sufficiently obtained. When the Mg amount is 0.0200% or less, the generation of coarse Mg oxides is suppressed, the toughness of the rail can be enhanced, and at the same time, fatigue damage starting from coarse precipitates can be suppressed. Therefore, the Mg amount may be limited to 0.0005 to 0.0200%. The Mg amount may be 0.0008% or more, 0.0010% or more, or 0.0012% or more. The Mg amount may be 0.0180% or less, 0.0100% or less, or 0.0030% or less.

[0050] Ca: 0 to 0.0200% Ca is an element that has a strong bonding force with S and forms CaS (sulfide). The CaS finely disperses MnS, relaxes stress concentration, and improves the internal fatigue damage resistance of the rail. When the Ca amount is 0.0005% or more, the effect can be sufficiently obtained. When the Ca amount is 0.0200% or less, the generation of coarse Ca oxides can be suppressed. In coarse Ca oxides, stress concentration, which generates a fatigue crack, is likely to occur. However, by suppressing the generation of coarse Ca oxides, the occurrence of fatigue cracks can be suppressed, and the internal fatigue damage resistance can be enhanced. Therefore, the Ca amount may be limited to 0.0005 to 0.0200%. The Ca amount may be 0.0008% or more, 0.0010% or more, or 0.0012% or more. The Ca amount may be 0.0180% or less, 0.0150% or less, or 0.0100% or less.

[0051] Al: Oto 1.000% Al has a deoxidizing effect. Al is an element that moves the eutectoid transformation temperature to the high temperature side and is an element that contributes to increasing the hardness (strength) of the pearlite structure. When the Al amount is 0.025% or more, the effect can be sufficiently obtained. When the Al amount is 1.000% or less, an Al solid solution in steel is easily made so that the number of coarse alumina based inclusions is reduced to enhance the toughness of the rail, and at the same time, the generation of fatigue damage from coarse precipitates can be prevented. Furthermore, when the Al amount is 1.000% or less, the generation of oxides in the weld can be prevented to remarkably enhance the weldability. Therefore, the Al amount may be limited to 0.025 to 1.000%. The Al amount may be more than 0%, 0.028% or more, 0.030% or more, or 0.035% or more. The Al amount may be 0.900% or less, 0.600% or less, or 0.400% or less.

[0052] Cu: Oto 1.00% Cu is an element that forms a solid solution or precipitates in the ferrite structure or the pearlite structure to improve the hardness (strength) of the pearlite structure through solid solution strengthening or precipitation strengthening. Since the Cu precipitation particles are soft, they do not adversely affect the wear resistance in a state of being precipitated in the ferrite phase. However, when the Cu content is high, the Cu solid solution amount also increases, and thus Cu lowers the wear resistance of the rail. On the other hand, from the viewpoint of reusing scrap of steel material, the rail is highly likely to contain Cu. Furthermore, Cu may be intentionally contained in the rail from the viewpoint of utilization as a solid solution strengthening element, surface damage resistance, and the like. In this sense, the Cu amount may be 1.00% or less. The Cu amount may be more than 0%, 0.01 % or more, 0.05% or more, or 0.010% or more. The Cu amount may be 0.20% or less, 0.10% or less, or 0.05% or less.

[0053] REM: 0 to 0.0500% REM is a deoxidizing / desulfurizing element, and generates a REM oxy sulfide (REM2O2S) that becomes generation nuclei of a Mn sulfide-based inclusion when REM is contained. The oxysulfide (REM2O2S) has a high melting point. Therefore, the oxysulfide suppresses stretching of the Mn sulfide-based inclusion after rolling. As a result, when REM is contained, MnS is finely dispersed, stress concentration is relaxed, and the internal fatigue damage resistance of the rail is improved. When the REM content is 0.0005% or more, the generation nuclei of the MnS-based sulfide are sufficiently formed, and the above-described effect is obtained. On the other hand, when the REM content is 0.0500% or less, excessive generation of the hard REM oxysulfide (REM2O2S) can be suppressed. In this case, generation of fatigue cracks due to stress concentration is suppressed, and the internal fatigue damage resistance is further improved. Therefore, when REM is contained in the rail, the REM content is preferably 0.0005 to 0.0500%. The lower limit of the REM content is more preferably 0.0010%, 0.0012%, or 0.0015%. The upper limit of the REM content is more preferably 0.0400%, 0.0300%, or 0.0100%.

[0054] REM is a rare earth metal from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The REM content is the total value of the contents of rare earth metal elements. When the total value of the contents is within the above range, the same effect can be obtained whether the rail contains one rare earth metal element or two or more thereof.

[0055] Zr: 0 to 0.0200% Zr is bonded with O to form a ZrO2-based inclusion. The ZrO2 inclusion and y-Fe have good lattice matching. Therefore, the ZrO2-based inclusion serves as solidification nuclei of a high carbon rail steel in which y-Fe is a solidification primary phase, increases the equiaxed crystal ratio of the solidification structure, and refines the solidification structure. As a result, MnS is finely dispersed, stress concentration is relaxed, and the internal fatigue damage resistance of the rail is improved. Furthermore, Zr suppresses the formation of a segregated zone at the central part of the cast piece, thereby suppressing the formation of a martensite structure in the segregated portion of the rail. When the Zr content is 0.0001% or more, the ZrO2-based inclusion is generated in such a number that sufficient action as solidification nuclei is exhibited. On the other hand, when the Zr content is 0.0200% or less, generation of a large amount of a coarse Zr-based inclusion is suppressed, fatigue cracks due to stress concentration are prevented, and the internal fatigue damage resistance of the rail can be further improved. Therefore, when Zr is contained, the Zr content is preferably 0.0001 to 0.0200%. The lower limit of the Zr content is more preferably 0.0005%, 0.0010%, or 0.0012%. The upper limit of the Zr content is more preferably 0.0100%, 0.0050%, or 0.0020%.

[0056] The balance of the chemical components of the rail steel is mainly Fe. In addition to the above components, the rail steel contains impurities.

[0057] (4) Area fraction of pearlite structure In the pearlite rail according to the embodiment, the microstructure in a range from the head outer surface to the depth of 25 mm (head front 3a) is mainly a pearlite structure. However, the microstructure in a range from the head outer surface of the pearlite rail to the depth of 25 mm is sometimes mixed with a trace amount of a proeutectoid ferrite structure, a pro-eutectoid cementite structure, a bainite structure, and a martensite structure in an area fraction of 5% or less. However, even when these structures are mixed, the wear resistance and the ductility of the rail head are not greatly affected. Therefore, the micro structure in a range from the head outer surface of the pearlite rail to the depth of 25 mm may be mixed with a trace amount, 5% or less, of a pro-eutectoid ferrite structure, a pro-eutectoid cementite structure, a bainite structure, and a martensite structure. In other words, in the pearlite rail according to the embodiment, the microstructure in a range from the head outer surface to the depth of 25 mm includes a pearlite structure in 95% or more thereof. In order to sufficiently secure wear resistance and ductility, the pearlite structure desirably occupies 98% or more of the range.

[0058] The meaning of the term “head outer surface” and other shapes of the pearlite rail will be described below. As shown in FIG. 3, a head 3 refers to the portion above the constricted portion at the center in the height direction of the pearlite rail in a crosssectional view of the pearlite rail. The head 3 includes a head top 31 and head corners 32 located at both ends of the head top 31. One of the head corners 32 is a gauge corner (G.C.) mainly in contact with wheels. In the head 3, the head outer surface refers to the total surface of: the surface of the head top 31 facing upward when the rail is upright; and the surface of the head corners 32. In the positional relationship between the head top 31 and the head corners 32, the head top 31 is located substantially at the center of the width direction of the rail head, and the head corners 32 are located at both ends of the head top 31.

[0059] The range from the surface of the head corners 32 and the head top 31 (head outer surface) to the depth of 25 mm is referred to as a head front (3a, hatched area). As shown in FIG. 6, in the head front 3a from the surface of the head corners 32 and the head top 31 (head outer surface) to the depth of 25 mm, a metallographic structure containing a pearlite structure having a predetermined hardness (a metallographic structure containing a pearlite structure in an area fraction of 95% or more) is arranged, which is necessary in order to improve the wear resistance and the internal fatigue damage resistance of the rail. 27

[0060] (5) Hardness at position having depth of 25 mm from surface of rail head top 31 The reason why the hardness at the position having a depth of 25 mm from the surface of the rail head top 31 is limited to at least 350 Hv will be described. In the component range, when the hardness at the position having a depth of 25 mm from the surface of the rail head top 31 is lower than 350 Hv, flaking damage due to plastic deformation occurs on the rolling surface of the rail head top 31. When the pearlite rail is used for heavy load railways and the hardness at the position having a depth of 25 mm from the surface of the rail head top 31 is lower than 350 Hv, securing wear resistance is difficult, and the rail service life is reduced. Therefore, the hardness at the position having a depth of 25 mm from the surface of the rail head top 31 is limited to at least 350 Hv. The hardness at the position having a depth of 25 mm from the surface of the rail head top 31 may be 360 HV or more, 380 HV or more, or 400 HV or more. In general, since the higher the hardness, the better the wear resistance, the upper limit of the hardness at the position is not particularly specified, and may be, for example, 600 HV or less, 550 HV or less, or 500 HV or less.

[0061] (Manufacturing method) The rail steel constituted by the component composition as described above is manufactured as a rail by melting steel in a commonly used melting furnace such as a converter or an electric furnace, subjecting the molten steel to the ingot-making / blooming method or the continuous casting method, and further performing hot rolling.

[0062] An example of the preferred method for manufacturing a rail in the present disclosure will be described. The manufacturing method makes it possible to obtain a pearlite rail in which the number density of the nitride particles having a particle size of 4 nm or more on the cementite interface is less than 1.0 x 1010 cm'2; the hardness of the head top is at least 350 Hv; and preferably, the number density of the nitride particles having a particle size of 0.5 to 4 nm in the ferrite is 4.0 x 1016 cm 3 or more. However, the example of the manufacturing method described below does not limit the method for manufacturing the pearlite rail according to the embodiment described above.

[0063] In order that the number density of the nitride precipitates having a size of 4 nm or more on the cementite interface in the ferrite is less than 1.0 x 1010 cm2, it is necessary to suppress the generation of nitride on the cementite interface. The nitride is likely to precipitate at a portion where solid solution V is present at a high concentration in the ferrite after pearlitic transformation. Since the nucleus of the nitride is VN, V is distributed from the cementite interface to the inner side of the cementite during pearlitic transformation to suppress the precipitation of the nitride on the cementite interface. This makes it possible to reduce the V solid solution concentration in the ferrite near the interface.

[0064] The means for distributing V to the inner side of the cementite is, for example, optimizing the cooling conditions. Since V has a small partition coefficient at high temperatures and diffuses slowly at low temperatures, V is less likely to be distributed to the inner side of the cementite. Therefore, a temperature therebetween is preferable, and it is necessary to search for an optimum cooling rate depending on the steel material components. When the pearlite rail is manufactured, it is preferable to realize an optimum temperature control.

[0065] In order that 4.0 x 1016 cm 3 or more of nitride particles having a particle size of 0.5 to 4 nm are precipitated in the ferrite, a sufficient amount of solid solution V is preferably left in the center portion of the lamellar ferrite after pearlitic transformation. It is necessary to perform them appropriately such that the lamellar ferrite width is not too narrow and the cooling rate is optimized not to excessively distribute V into the cementite.

[0066] The upper limit of the heating temperature is not particularly specified, but a liquid phase appears to destabilize the austenite phase at excessively high temperatures. Therefore, the upper limit of the temperature is substantially 1350°C. The lower limit of the heating temperature is preferably a high temperature of 1180°C or higher because it is necessary to once dissolve the nitride such as VN.

[0067] In order to perform pearlitic transformation from complete austenite, the rail head is in a temperature range of the Ari point or more immediately after rolling. When the rolled rail is once cooled and then reheated to manufacture the rail, the reheated rail head has a temperature of equal to or higher than the Acl point + 30°C. Preferably, a finish rolling is performed at 900 to 950°C.

[0068] The rail immediately after rolling or the rail cooled and reheated after rolling starts to be cooled preferably in a temperature range of 850 to 900°C. The time point at which the cooling is started is a time point at which spraying a cooling medium to the rail is started. That is, spraying a cooling medium to the rail head is started preferably when the rail head has a temperature in a temperature range of 850 to 900°C.

[0069] The cooling finishing temperature is preferably 790 to 820°C. The cooling finishing temperature is a time point at which spraying a cooling medium to the rail is finished. That is, spraying a cooling medium to the rail head is finished preferably when the rail head is in a temperature range of 790 to 820°C.

[0070] The cooling rate is preferably 20 to 50 °C / s. The cooling rate is a value obtained when the difference between the cooling start temperature (the temperature of the rail head at a time point at which spraying a cooling medium is started) and the cooling finishing temperature (the temperature of the rail head at a time point at which spraying a cooling medium is finished) is divided by the time during which a cooling medium is being sprayed. The temperature of the rail head is measured with a radiation thermometer. The position where the temperature is measured is the head outer surface of the rail.

[0071] By rapidly cooling the rail head under the above-described conditions, austenite grain growth is suppressed. When the cooling rate in the cooling immediately after hot rolling is too high, precipitation of carbonitride is completely suppressed on the high temperature side, and there is a possibility that the driving force increases for precipitating nitride on the cementite interface after pearlitic transformation. In this case, a nitride containing V is likely to precipitate on the cementite interface. In addition, it is technically difficult to realize a cooling rate higher than 50 °C / s. At a cooling rate lower than 20 °C / s, the effect of suppressing grain growth is small.

[0072] After the rapid cooling using a cooling medium, slow cooling is performed at 2 to 5 °C / s up to 740 to 780°C, which is the temperature range immediately before pearlitic transformation is started (cooling before controlled cooling). The time point at which the cooling before controlled cooling is started is a time point at which spraying a cooling medium is finished as described above. The time point at which the cooling before controlled cooling is finished is a time point at which the controlled cooling is started as described later. The cooling rate in the cooling before controlled cooling is a value obtained when the difference between the rail head temperature at the time point at which the cooling before controlled cooling is started and the rail head temperature at the finishing time point is divided by the time required for the cooling before controlled cooling. Through the cooling before controlled cooling, the pearlitic transformation temperature is slightly moved to the higher temperature side.

[0073] After the slow cooling as described above, the rail head is subjected to controlled cooling at preferably a cooling rate of 5 to 12 °C / s from the austenite temperature range to preferably 600 to 480°C. That is, the controlled cooling finishing temperature is within a range of 600 to 480°C. Preferably, the controlled cooling finishing temperature is 580 to 480°C. Thereby, a complete pearlite structure is obtained. The time point at which the controlled cooling is started is a time point at which spraying a cooling medium is started. The time point at which the controlled cooling is finished is a time point at which spraying a cooling medium is finished. The cooling rate in the controlled cooling is a value obtained when the difference between the rail head temperature at the time point at which the controlled cooling is started and the rail head temperature at the finishing time point is divided by the time required for the controlled cooling.

[0074] When the cooling rate of the controlled cooling is too high, the transformation temperature is significantly lowered. In this case, V solid solution atoms are not sufficiently distributed during pearlitic transformation, and the V solid solution concentration in the ferrite in the vicinity of the cementite interface is not reduced. Then, large nitrides are likely to be generated on the cementite interface after pearlitic transformation. When the cooling rate is too low or the finishing temperature is too high, pearlitic transformation proceeds on the higher temperature side, so that coarse pearlite is formed, and lamella refinement hardening is reduced.

[0075] Actually, since the precipitation driving force varies depending on the contents of V, Cr, and N, the correspondence with the preferred manufacturing method is not simple and changes. With the content ranges of V, Cr, and N in the embodiment, the manufacturing conditions as described above can be applied to suppress the precipitation and the enlargement of the nitride on the cementite interface. As for the controlled cooling method, for example, a predetermined cooling rate can be obtained by using air; a cooling medium mainly containing air and containing mist or the like; and a combination thereof.

[0076] The manufacturing method described here is an example and does not limit the pearlite rail having the microstructural characteristics described in claims, and even a pearlite rail having the same microstructure obtained by another manufacturing method belongs to the pearlite rail according to the embodiment. Examples

[0077] Next, embodiments of the present disclosure will be described. However, the conditions in Examples are merely one condition example adopted to confirm the enablement and effects of the present disclosure. The present disclosure is not limited to this one condition example. The present disclosure can adopt various conditions as long as the object thereof is achieved without departing from the gist thereof.

[0078] Tables 1A and IB show the chemical components of the tested rail steels. Tables 2A and 2B show the materials and the manufacturing conditions of the tested rail steels (Test No. 1 to 28) made of any of the steel types A to P disclosed in Tables 1A and IB. Tables 3A and 3B show the state of precipitates in the ferrite phase. Tables 4A and 4B show the characteristics of the rails and the results of the abrasion test. As the manufacturing conditions, the cooling rate in each temperature region is shown. As the characteristics of the rails, the head top hardness (Hv) (test load: 98 N) and the total elongation by a tensile test are shown. As the abrasion test, the wear amount (g) in the abrasion test of 700,000 times is shown. In the chemical components listed in Tables 1A and IB, the balance is iron and impurities. In Tables 1A and IB, the symbol described in the element content column means that the element attached with the symbol is not intentionally added to the pearlite rail. In Tables 1A and IB, “< 0.005” described in the element content column means less than 0.005 mass%.

[0079] The manufacturing conditions not described in the tables are as follows. For these steel rails, steel pieces for rail rolling obtained by component adjustment in a converter and then casting in the continuous casting method are heated at a heating temperature of 1250°C for 1 hour or more. After being heated and held, the steel was hot-rolled with a pass interval of 11 s. The steel was finish-rolled at 910°C at a cross-sectional reduction rate of 10% per pass.

[0080] The steel was rapidly cooled by water cooling or the like at a cooling rate of 20 to 50 °C / s from the hot rolling finishing temperature up to 900 to 800°C, then slowly cooled at 2 to 10 °C / s up to 760°C, and subsequently, subjected to controlled cooling at a cooling rate of 4 to 15 °C / s until the temperature of the rail head reached 610 to 450°C. The rail sample was subjected to characteristics evaluations by the following methods.

[0081] For rail head wear evaluation, the Nishihara abrasion test was performed. The test conditions are as follows. - Tester: Nishihara abrasion tester - Test piece shape: disk-shaped test piece (outer diameter: 30 mm, thickness: 8 mm) - Test piece collection position: 5 mm below rail head top surface - Test load: 684 N (contact surface pressure: 640 MPa) - Slip ratio: 20% - Counterpart material: pearlite steel (360 Hv) - Atmosphere: in the air - Cooling: Forced cooling by compressed air (flow rate: 100 Nl / min) - Number of repetitions: 700,000 The wear amount was determined as a decrease in the mass of the test piece after the test. When the wear amount was less than 1.00 g, the wear resistance was evaluated as good. Furthermore, when the wear amount was less than 0.80 g, the wear resistance was evaluated as excellent.

[0082] Further, a test piece was cut out from the rail head, and the total elongation was estimated from a tensile test. The conditions are shown.

[0083] - Tester: Universal small tensile tester - Test piece shape: JIS No. 4 similarity - Length of parallel part: 30 mm - Diameter of parallel part: 6 mm - Distance between elongation measurement scores: 25 mm - Test piece collection position: 5 mm below rail head top surface - Tensile speed: 10 mm / min - Test temperature: Normal temperature The tensile test was performed in accordance with JIS Z 2241:2011. When the total elongation value was 10.0% or more, it was determined as good.

[0084] The hardness of the head top was determined from Vickers hardness measurement using a load of 1 kg. The position was 25 mm below the head top surface. Since there is variation, the average value of the measurement results at the five points is shown in the table. When the value was 350 Hv or more, it was determined as good.

[0085] The pearlite fraction was examined by performing Nital etching on the polished sample surface. When a second phase other than the pearlite phase has an area fraction of more than 5%, the main second phase is described in the table. The measurement position for the pearlite fraction was in a range from the head outer surface to the depth of 25 mm. Specifically, samples were cut out from the cross section of each rail head, and each sample was polished with diamond, then subjected to a 3% Nital etching treatment, and then subjected to microstructure observation using an optical microscope (magnification 200), so that the pearlite fraction was measured. In the microstructure observation at a magnification of 200, the portion observed white is pro-eutectoid ferrite. Pro-eutectoid cementite can be determined as a different contrast along grain boundaries. Martensite and bainite can be determined from the lath structure. The other micro structure is pearlite in a block form, which is determined by the contrast changing depending on the lamella direction. When the micro structure is unclear, the pearlite lamella structure can be determined by high magnification observation with a scanning electron microscope (SEM). The measurement visual fields were arbitrary 10 visual fields at a depth of 2 mm from the head outer surface, and arbitrary 10 visual fields at a depth of 25 mm from the head outer surface. The average value of the area fraction of the pearlite structure in the arbitrary 10 visual fields at a depth of 2 mm from the head outer surface was defined as “surface layer pearlite fraction”, and the average value of the area fraction of the pearlite structure in the arbitrary 10 visual fields at a depth of 25 mm from the head outer surface was defined as “25 mm position pearlite fraction”. A rail in which both were 95 area% or more was determined as a rail whose microstructure in a range from the head outer surface to a depth of 25 mm includes a pearlite structure in an area fraction of 95% or more.

[0086] Precipitates in the pearlite structure at a position having a depth of 25 mm from the head outer surface were examined by three-dimensional atom probe observation with LEAP4000XHR manufactured by CAMECA. In the sample pearlite rail, out of the pearlite structure at a position having a depth of 25 mm from the head outer surface, a needle sample having a radius of curvature of 30 to 80 nm was prepared by focused ion beam (FIB) processing. With a three-dimensional atom probe, 20 million atoms were measured multiple times. From the data, a three-dimensional element map is obtained, for example, using IVAS software, which is three-dimensional construction software. V is detected as a V2+ ion having a peak at 25.5 Da and a VN2+ ion having a peak at 32.5 Da, in terms of mass-to-charge ratio. The VN2+ ion, which is an ion constituted by V and N, indicates that nitride particles containing V are present. The region where C is concentrated to 20 at% or more is a cementite lamella. The precipitates include two types: particles present on the 37 cementite interface; and particles distributed in the ferrite grains and separated from the cementite interface (see FIG. 1).

[0087] FIGS. 4A to 4D each show an example of a three-dimensional element map of the V-added rail. These are atom maps of Fe, C, and V in the same cuboid region having a height of 77 nm, a width of 78 mm, and a length of 232 nm. A dot represents one atom on the map. As for V, a map of V2+ ions and a map of VN2+ ions are shown. Since the VN2+ ion is an ion composed of a pair of N and V, the portion where dots indicating VN2+ ions are concentrated corresponds to the nitride particles containing V. In the C atom map, a lamellar cementite and a lamellar ferrite are shown. In the figure, the lamellar cementite is denoted as “CEMENTITE”, and the lamellar ferrite is denoted as “FERRITE”. In the VN2+ map, fine nitride particles are observed in the ferrite, and the slightly larger particle surrounded by a square box attached with a reference sign X is a nitride particle on the cementite interface.

[0088] FIGS. 5A to 5D each show a three-dimensional element map of the square box region X set in the VN2+ map of FIG. 4. The box has a cubic shape with a side of 10 nm. FIGS. 5A to 5D show atom maps of C, V, Cr, and Mn. Here, the V atom map is a combination of VN2+ and V2+. In the C atom map, the position of the interface between the cementite and the ferrite is indicated by a broken line. It is shown that a nitride particle containing V and Cr as components is in contact with the cementite, that is, present on the cementite interface. FIGS. 5A to 5D also show that C atoms are not contained in the nitride particle.

[0089] The type, the number density, and the size of the nitride particles on the cementite interface were estimated as follows. The number n of the nitride particles in contact with the cementite interface in the element map is determined, and the number n is divided by the total surface area S nm2 of the cementite in the visual field, so that the number density n / S nm'2 of the nitride particles per cementite interface area can be examined. When the lamellar cementite crosses the map, it is necessary to add both surfaces for the area. As shown in Tables 3A and 3B, the value may be multiplied by 1014 to convert the unit into -3 cm .

[0090] The type, the number density, and the size of the nitride particles in the ferrite were estimated as follows. For example, when 20 million atoms are measured, the value is divided by the detection rate (-0.38) of the device ion detector, the value is divided by the Fe atom density (-85 nm'3), and the value can be regarded as the measurement volume (nm3). The detection rate does not change depending on the number of atoms or the element type and is peculiar to the device. In order to determine the number density in the ferrite phase, when the cementite phase is included in the measurement visual field, the volume thereof is excluded to determine the measurement volume Vf (nm3) of the ferrite phase. When n precipitates are observed in the measurement volume, the number density thereof is determined as n / Vfnm 3. As shown in Tables 2A and 2B, the value may be multiplied by 1021 to convert the unit into cm'3.

[0091] In order to increase the accuracy, multiple measurements were made across the cementite lamella. For example, when the volume corresponding to 30 million atoms in the ferrite is measured and one precipitate is observed, the number density is about 1.0 x 1015 cm'3. When no precipitate is observed by such measurement, it is described as Therefore, when no precipitate is observed, the number density may be regarded as less than 1.0 x 1015 cm'3. For example, when the area of the cementite interface is 100 nm x 50 nm x 2 = 10000 nm2 in the 3D element map and one nitride particle is observed on the cementite interface, the number density is 1.0 x 1010 cm'2. When no precipitate is observed after such cementite is measured multiple times, it is indicated as in the table.

[0092] The composition of the precipitate particles was determined such that the constituent elements of the nitride particles and the number of atoms thereof were determined using a particle analysis program such as Maximum separation method included in IVAS software, which is three-dimensional construction software created by CAMECA. The composition of the precipitate particles may be determined by cutting a box directly in the 3D element map. The version of the IVAS software was 3.6.8. However, the version of the software does not affect the measurement results. The size of the precipitate particles was determined as a spherical equivalent diameter as follows. The number of constituent atoms other than nitrogen is determined by the above method. This is because current atom probes cannot correctly measure all nitrogen atoms. Assuming the stoichiometric composition, in the NaCl-type crystal structure, twice the number of constituent atoms such as V, Cr, and Mn other than nitrogen is equal to the number of constituent atoms including nitrogen of the nitride particles. Further, the value was divided by the ion detection rate of the atom probe (here, 0.38) to determine the actual number of constituent atoms / V. Finally, assuming a sphere having a diameter D, the particle diameter D is determined from the equation D = (6A7ti^)1 / 3, where the atomic density of the precipitates is Here, as the atomic density, a value of a = 113 nm'3 was used. Estimated thereby, the number density of the nitride particles containing V and having a particle size of 4 nm or more on the cementite interface and the number density of the nitride particles having a particle size of 0.5 to 4 nm in the ferrite are shown in Tables 3A and 3B.

[0093] [Table 1A] Steel type Chemical components (mass%) C Si Mn Cr N V Nb Ti Mo A 0.60 0.45 0.23 0.40 0.0032 0.015 <0.005 <0.005 <0.005 B 0.67 1.52 0.15 0.12 0.0015 0.040 <0.005 <0.005 <0.005 C 0.75 0.20 0.52 0.80 0.0035 0.008 <0.005 <0.005 <0.005 D 0.78 0.25 0.22 0.23 0.0025 0.050 <0.005 <0.005 0.065 E 0.86 0.55 0.28 0.34 0.0038 0.040 <0.005 <0.005 <0.005 F 0.95 0.32 1.32 0.60 0.0045 0.032 <0.005 <0.005 <0.005 G 1.02 0.20 0.40 0.74 0.0100 0.022 <0.005 <0.005 <0.005 H 1.15 0.06 1.75 0.10 0.205 0.032 <0.005 <0.005 <0.005 I 1.02 0.25 0.60 0.30 0.0032 0,110 <0.005 <0.005 <0.005 J 1,25 0.35 0.50 1.12 0.0023 0.074 <0.005 <0.005 <0.005 K 0.92 2,10 0.25 0.10 0.0024 0.040 <0.005 <0.005 <0.005 L 1.05 0.30 2,08 0.45 0.0022 0.023 <0.005 <0.005 <0.005 M 0.98 0.55 0.55 2,15 0.0040 0.090 <0.005 <0.005 <0.005 N 0.99 0.32 0.80 0.52 0.0031 0.080 0.051 <0.005 <0.005 0 0.95 0.28 0.34 0.33 0.0035 0.065 <0.005 0,021 <0.005 P 1.05 0.21 1.25 0.82 0.0042 0.040 <0.005 0,030 0.020 Q 0.79 0.38 0.28 0.28 0.0033 0.042 <0.005 <0.005 <0.005 R 0.78 0.29 0.19 0.32 0.0040 0.038 <0.005 <0.005 <0.005 S 0.83 0.50 0.40 0.35 0.0038 0.050 <0.005 <0.005 <0.005 T 0.92 0.38 0.37 0.48 0.0043 0.035 <0.005 <0.005 <0.005 U 1.02 0.28 0.42 0.62 0.0037 0.022 <0.005 <0.005 <0.005 V 0.83 0.50 0.40 0.35 0.0038 0.050 <0.005 <0.005 <0.005 W 0.92 0.38 0.37 0.48 0.0045 0.035 <0.005 <0.005 <0.005 X 1.02 0.28 0.42 0.62 0.0037 0.022 <0.005 <0.005 <0.005 5

[0094] [Table IB] Steel type Chemical components (mass%) B Co Ni Mg Ca Cu REM Zr P S Al 0 A - - - - - - - - 0.012 0.010 0.0020 0.0015 B - 0.32 - - 0.0008 - - - 0.012 0.008 0.8100 0.0009 C - - - - - - - - 0.013 0.012 0.0015 0.0013 D - - - - - - - - 0.012 0.010 0.0022 0.0013 E - - - - - - - - 0.012 0.011 0.0025 0.0021 F - - - - - - - - 0.012 0.012 0.0032 0.0015 G - - - - - 0.05 - - 0.012 0.010 0.0550 0.0018 H - - 0.25 - - - - 0.010 0.008 0.0018 0.0013 I 0.0032 - - - - - - - 0.012 0.011 0.0013 0.0028 J - - 0.28 - - - - - 0.012 0.010 0.0028 0.0013 K - - - - - - - - 0.012 0.013 0.0024 0.0008 L - - - - - 0.43 - - 0.014 0.009 0.0031 0.0018 M - - - - - - - - 0.012 0.011 0.0027 0.0013 N - - - - - - - - 0.012 0.010 0.0016 0.0019 0 - - - - - - - - 0.011 0.010 0.0018 0.0014 P - - - - - - - - 0.012 0.010 0.0021 0.0008 Q 0.0023 - - - - - - - 0.012 0.010 0.0016 0.0018 R - 0.48 - - - - - - 0.012 0.009 0.0080 0.0013 S - - 0.53 - - - - - 0.010 0.011 0.0023 0.0022 T - - - 0.003 - - - - 0.021 0.012 0.0610 0.0009 U - - - - 0.0015 - - - 0.018 0.010 0.0022 0.0014 V - - - - - 0.29 - - 0.011 0.011 0.0035 0.0015 W - - - - - - 0.0060 - 0.010 0.008 0.0017 0.0013 X - - - - - - - 0.0050 0.013 0.010 0.0021 0.0024

[0095] [Table 2A] Test No. Material Cooling immediately after hot rolling Cooling before controlled cooling Controlled cooling Steel type Cooling rate (900°C—»800°C) (°C / s) Cooling rate (800°C—»760°C) (°C / s) Cooling rate (°C / s) Finishing temperature (°C) 1 A 23 5 6 580 2 B 24 4 10 510 3 C 21 2 8 540 4 D 27 5 7 530 5 E 24 5 12 480 6 F 32 4 10 580 7 F 30 3 8 540 8 F 28 4 6 480 9 F 22 5 7 500 10 G 32 4 10 510 11 F 51 4 8 520 12 F 23 3 13 500 13 F 27 4 15 440 14 F 32 4 4 480 15 F 38 3 10 450 16 G 41 4 5 590 17 G 16 5 8 480 18 G 21 8 8 500

[0096] [Table 2B] Test No. Material Cooling immediately after hot rolling Cooling before controlled cooling Controlled cooling Steel type Cooling rate (900°C—»800°C) (°C / s) Cooling rate (800°C—»760°C) (°C / s) Cooling rate (°C / s) Finishing temperature (°C) 19 G 22 1 6 490 20 H 30 5 6 460 21 I 24 5 5 480 22 J 22 4 8 540 23 K 32 3 8 520 24 L 24 7 6 540 25 M 26 9 5 520 26 N 30 2 10 500 27 0 24 5 8 530 28 P 30 5 10 490 29 Q 25 5 8 530 30 R 27 4 10 510 31 S 33 4 9 580 32 T 29 3 8 550 33 U 27 4 7 530 34 V 25 5 11 490 35 W 32 3 12 570 36 X 31 4 10 550

[0097] [Table 3A] Test No. Precipitated particle composition Nitride particle precipitation state (25 mm position) Number density on cementite interface (x 1010 cm'2) Number density in ferrite (x 1016 cm'3) 1 (Cr, V) N 0.8 3.8 2 (V, Cr) N - - 3 - - - 4 (V, Cr) N 0.7 0.4 5 (V, Cr) N - 0.5 6 (V, Cr) N 0.8 0.8 7 (Cr, Mn, V) N 0.3 2.5 8 (V, Cr) N 0.5 11 9 (V, Cr) N 0.8 18 10 (Cr, Mn, V) N 0.5 3.0 11 (V, Cr) N 2,4 12 12 (V, Cr) N 4,5 2.0 13 (V, Cr) N 0.8 - 14 (V, Cr) N 1,2 0.5 15 (V, Cr) N 0.5 - 16 (V, Cr) N 2,1 - 17 (Cr, V) N 1.8 3.0 18 (Cr, V) N 1.0 0.2

[0098] [Table 3B] Test No. Precipitated particle composition Nitride particle precipitation state (25 mm position) Number density on cementite interface (x 1010 cm'2) Number density in ferrite (x 1016 cm'3) 19 (Cr, V) N 2,5 - 20 (Cr, V, Mn) N 4,0 12 21 VC - - 22 (Cr, V) N 1.8 9.0 23 - - - 24 - - - 25 (Cr, Mn, V) N 3.0 5.5 26 (V, Nb, Cr) N 2,1 8 27 (Ti, V) N 3.0 0.2 28 (V, Ti, Cr) N, (Ti, Mo) C 2,3 0.4 29 (V, Cr) N 0.7 3.2 30 (V, Cr) N - 0.5 31 (V, Cr) N 0.8 2.5 32 (V, Cr) N - 0.8 33 (Cr, Vr) N 0.7 5.0 34 (V, Cr) N 0.9 2.4 35 (V, Cr, Mn) N 0.8 1.0 36 (Cr, V) N 0.5 0.6 5

[0099] [Table 4A] Test No. Rail characteristics Wear resistance Remarks Microstructure Hardness at 25 mm position (Hv, 98 N) Total elongation (%) Wear amount (g, 700,000 times) 1 Pearlite + Pro-eutectoid ferrite 330 15.0 1,40 Comparative Example 2 Pearlite 340 14.2 1,32 Comparative Example 3 Pearlite 340 11.2 1.05 Comparative Example 4 Pearlite 360 11.0 1.00 Inventive Example 5 Pearlite 370 12.6 0.97 Inventive Example 6 Pearlite 380 11.6 0.95 Inventive Example 7 Pearlite 400 12.2 0.92 Inventive Example 8 Pearlite 410 12.0 0.80 Inventive Example 9 Pearlite 420 11.0 0.78 Inventive Example 10 Pearlite 430 10.9 0.95 Inventive Example 11 Pearlite 440 11.2 1.05 Comparative Example 12 Pearlite 410 9.0 1,02 Comparative Example 13 Pearlite + Bainite 390 10.5 1,15 Comparative Example 14 Pearlite 400 11.0 1,23 Comparative Example 15 Pearlite + Bainite 380 9.2 1,20 Comparative Example 16 Pearlite 400 12.0 1,18 Comparative Example 17 Pearlite 430 9.0 0.98 Comparative Example 18 Pearlite 410 11.5 1,25 Comparative Example

[0100] [Table 4B] Test No. Rail characteristics Wear resistance Remarks Microstructure Hardness at 25 mm position (Hv, 98 N) Total elongation (%) Wear amount (g, 700,000 times) 19 Pearlite 400 10.5 1,10 Comparative Example 20 Pearlite 430 8.5 0.90 Comparative Example 21 Pearlite 380 11.5 1,10 Comparative Example 22 Pearlite + Pro-eutectoid cementite 430 8.5 1,32 Comparative Example 23 Pearlite + Martensite 400 9.2 1,23 Comparative Example 24 Pearlite + Martensite 410 8.8 1,34 Comparative Example 25 Pearlite + Martensite 390 9.0 1,12 Comparative Example 26 Pearlite 420 9.8 1.03 Comparative Example 27 Pearlite 390 11.8 1,25 Comparative Example 28 Pearlite 410 9.0 1,13 Comparative Example 29 Pearlite 360 11.0 0.98 Inventive Example 30 Pearlite 370 12.5 0.94 Inventive Example 31 Pearlite 380 10.6 0.99 Inventive Example 32 Pearlite 390 12.2 0.92 Inventive Example 33 Pearlite 360 10.8 0.86 Inventive Example 34 Pearlite 370 12.2 0.92 Inventive Example 35 Pearlite 400 11.6 0.95 Inventive Example 36 Pearlite 380 12.0 0.90 Inventive Example

[0101] Test No. 1 (steel type A) was short of the C amount. In Test No. 1, the microstructure in a range from the head outer surface to the depth of 25 mm was mixed 5 with pro-eutectoid ferrite, and the area fraction of the pearlite structure was less than 95%. Test No. 1 was insufficient in hardness at a position having a depth of 25 mm from the surface of the head top and had insufficient wear resistance.

[0102] Test No. 2 (steel type B) was short of the N amount. Test No. 2 was insufficient 10 in hardness at a position having a depth of 25 mm from the surface of the head top, and wear resistance was impaired.

[0103] Test No. 3 (steel type C) was short of the V amount. Test No. 3 was insufficient in hardness at a position having a depth of 25 mm from the surface of the head top, and had insufficient wear resistance.

[0104] In Test No. 11, the cooling rate in the accelerated cooling immediately after the hot rolling was excessive. In Test No. 11, the number density of the nitride particles present on the cementite interface was excessive, and wear resistance was impaired.

[0105] In Test No. 12, the cooling rate in the controlled cooling was excessive. In Test No. 12, the number density of the nitride particles present on the cementite interface was excessive, and wear resistance and ductility were impaired.

[0106] In Test No. 13, the cooling rate in the controlled cooling was excessive. In Test No. 13, the micro structure in a range from the head outer surface to the depth of 25 mm was mixed with bainite, and the area fraction of the pearlite structure was less than 95%. In Test No. 13, wear resistance was impaired.

[0107] In Test No. 14, the cooling rate in the controlled cooling was insufficient. In Test No. 14, the number density of the nitride particles present on the cementite interface was excessive, and wear resistance was impaired.

[0108] In Test No. 15, the controlled cooling finishing temperature was too low. In Test No. 15, the micro structure in a range from the head outer surface to the depth of 25 mm was mixed with bainite, and the area fraction of the pearlite structure was less than 95%. In Test No. 15, wear resistance and ductility were impaired.

[0109] In Test No. 16, the controlled cooling finishing temperature was too high. In Test No. 16, the number density of the nitride particles present on the cementite interface was excessive, and wear resistance was impaired.

[0110] In Test No. 17, the cooling rate in the accelerated cooling immediately after the hot rolling was insufficient. In Test No. 17, the number density of the nitride particles present on the cementite interface was excessive, and ductility was impaired.

[0111] In Test No. 18, the cooling rate in the cooling before controlled cooling was excessive. In Test No. 18, the number density of the nitride particles present on the cementite interface was excessive, and wear resistance was impaired.

[0112] In Test No. 19, the cooling rate in the cooling before controlled cooling was insufficient. In Test No. 19, the number density of the nitride particles present on the cementite interface was excessive, and wear resistance was impaired.

[0113] Test No. 20 (steel type H) was excessive in the N amount. In Test No. 20, the number density of the nitride particles present on the cementite interface was excessive, and ductility was impaired.

[0114] Test No. 21 (steel type I) was excessive in the V amount. In Test No. 21, wear resistance was impaired. Test No. 22 (steel type J) was excessive in the C amount. In Test No. 22, the microstructure in a range from the head outer surface to the depth of 25 mm was mixed with pro-eutectoid cementite, and the area fraction of the pearlite structure was less than 95%. In Test No. 22, wear resistance and ductility were impaired.

[0116] Test No. 23 (steel type K) was excessive in the Si amount. Test No. 24 (steel type L) was excessive in the Mn amount. Test No. 25 (steel type M) was excessive in the Cr amount and the Mo amount. In Test No. 23 to 25, the micro structure in a range from the head outer surface to the depth of 25 mm was mixed with martensite, and the area fraction of the pearlite structure was less than 95%. In Test No. 23 to 25, wear resistance and ductility were impaired.

[0117] Test No. 26 (steel type N) was excessive in the Nb amount. In Test No. 26, the number density of the nitride particles present on the cementite interface was excessive, and ductility and wear resistance were impaired.

[0118] Test No. 27 (steel type O) was excessive in the Ti amount. In Test No. 27, the number density of the nitride particles present on the cementite interface was excessive, and wear resistance was impaired.

[0119] Test No. 28 (steel type P) was excessive in the Ti amount. In Test No. 28, the number density of the nitride particles present on the cementite interface was excessive, and ductility and wear resistance were impaired.

[0120] On the other hand, Test No. 4 to 10 and 29 to 36, which were appropriate in all of the chemical components, the hardness, the pearlite area fraction, and the state of nitride on the cementite interface, were excellent in both ductility and wear resistance. REFERENCE SIGNS LIST 5

[0121] 1        Pearlite structure 11      Cementite (lamellar cementite) 12      Ferrite (lamellar ferrite) 13      Cementite interface 10   21      Nitride particle present on cementite interface 22      Nitride particle in ferrite separated from cementite interface 3      Head 31     Head top 32     Head corner 15 3a Head front (in range from head outer surface to depth of 25 mm)

Claims

1. A pearlite rail comprising, in terms of mass%,C: 0.65 to 1.20%,Si: 0.05 to 2.00%,Mn: 0.05 to 2.00%,Cr: 0.02 to 2.00%,N: 0.0020 to 0.0200%,V: 0.010 to 0.100%,Nb: 0% or more and less than 0.005%,Ti: 0% or more and less than 0.005%,Mo: Oto 0.100%,B: Oto 0.0050%,Co: Oto 1.00%,Ni: Oto 1.00%,Mg: 0 to 0.0200%,Ca: 0 to 0.0200%,Cu: Oto 1.00%,REM: 0 to 0.0500%,Zr: 0 to 0.0200%,P: 0.025% or less,S: 0.025% or less,Al: Oto 1.000%,O: 0.0040% or less, anda balance including Fe and impurities, whereina micro structure in a range from a head outer surface to a depth of 25 mm includesa pearlite structure in an area fraction of 95% or more;hardness at a position having a depth of 25 mm from a surface of a head top is at least HV350; andon a cementite interface of the pearlite structure at the position having a depth of 25 mm from the surface of the head top, nitride particles containing V and having a particle size of 4 nm or more are present in a number density of less than 1.0 x 1010 cm 2 per unit interface area.

2. The pearlite rail according to claim 1, whereinin ferrite of the pearlite structure, nitride particles containing V, having a particle size of 0.5 to 4 nm, and separated from the cementite interface are present in a number density in a range of 4.0 x 1016 to 4.0 x 1017 cm 3 per unit volume.

3. The pearlite rail according to claim 1 or 2, further comprising, in terms of mass%, one or more selected from the group consisting of:B: 0.0001 to 0.0050%,Co: 0.01 to 1.00%,Ni: 0.01 to 1.00%,Mg: 0.0005 to 0.0200%,Ca: 0.0005 to 0.0200%,Cu: more than 0% and 1.00% or less,REM: 0.0005 to 0.0500%,Zr: 0.0001 to 0.0200%, andAl: more than 0% and 1.000% or less.

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