TRACK AND METHOD FOR PRODUCING THE SAME

Abstract

Provided is a rail excellent in breakage resistance of a rail web. This rail has the composition containing C: 0.70-1.20% by mass, Si: 0.10-1.20% by mass, Mn: 0.10-1.80% by mass, P: 0.035% by mass or less, S: 0.020% by mass or less and Cr: 0.05-1.80% by mass with the balance being Fe and inevitable impurities. When the Vickers hardness at a depth of 0.5 mm from the surface of the rail web is measured in the range of ±17.5 mm above and below the central position of the rail height, the average of the Vickers hardness is Hv 280 or more and the standard deviation is 5 or less.

Description

1 / 29 TRACK AND METHOD FOR PRODUCING THE SAME TECHNICAL FIELD

[001] This disclosure relates to a rail and a method for producing it. BACKGROUND

[002] In heavy transport railways, built primarily to transport ore, the load applied to the axle of a freight car is much higher than in passenger cars, and the operating environments for rails are severe. Conventionally, steels having a pearlitic microstructure have been used primarily in such rails from the point of view of the importance of wear resistance.

[003] In recent years, the load weight of freight wagons has been further increased to improve rail transport efficiency. In addition, the number of wheels passing over the rails has increased due to the increased transport capacity.

[004] The passage of wheels applies repetitive bending stress to the outer track weave arranged in curved sections. As a result, the frequency of track replacement due to weave breakage has been increasing each year. Therefore, there is a growing demand for track steels with improved resistance to track weave fractures.

[005] In this context, several studies have focused on the track weave. For example, Patent Literature (PTL) 1 discloses a method in which the weave is rapidly cooled at a cooling rate of 15 °C / s or more, subsequently cooled to a temperature of 250 °C to 450 °C, and then cooled to the Ms point or lower when the bainite transformation reaches 30% or more to obtain a martensitic microstructure, thus forming the weave into a tempered martensite structure with high Petition 870250080624, dated 09 / 08 / 2025, pp. 73 / 109 2 / 29 tenacity.

[006] PTL 2 discloses a method for producing rails in which residual compressive stress is imparted by cooling the head to the upper neck or weave with high-pressure gas or gas containing water, thereby improving the fracture resistance of the rail fastening portion.

[007] PTL 3 discloses a rail with excellent resistance to rolling contact fatigue in the web, wherein the rail has a predetermined chemical composition, 90% or more by area of ​​the metallic structure of a cross-section of the rail web is a pearlitic microstructure, the minimum hardness of the rail column cross-section is Hv300 or more, and the difference between the maximum and minimum hardness of the rail column cross-section is Hv40 or less. LIST OF QUOTES Patent Literature

[008] PTL 1: JP S62-99438 A PTL 2: JP S59-47326 A PTL 3: WO 2020 / 189232. SUMMARY (Technical Problem)

[009] However, the conventional technologies above still have the following problems to be solved. The technology disclosed in PTL 1 requires maintaining the temperature until the bainite transformation begins, resulting in low production efficiency. The technology disclosed in PTL 2 places the highest priority on obtaining wear resistance / fatigue resistance by rolling contact at the head and thus does not necessarily provide the desired ability to inhibit crack growth in the weave. Depending on the production conditions, a Petition 870250080624, dated 08 / 09 / 2025, pp. 74 / 109 3 / 29 A martensitic microstructure susceptible to cracking can be generated. Furthermore, with regard to the technology described in PTL 3, the surface layer hardness can vary depending on the combination of ingredients and production conditions, and it is difficult to say that the fracture resistance of the weave is sufficient.

[010] To solve the problems described above in an advantageous way, the present disclosure aims to provide a rail with excellent resistance to rail weave fractures, together with a method for producing the same. (Solution to the Problem)

[011] In order to solve the above problem, rails with different C, Si, Mn and Cr contents were prepared and the hardness and three-point bending properties of the rail weave were intensively investigated. As a result, it was discovered that excellent fracture resistance can be obtained by ensuring that the hardness of the surface layer of the weave is equal to or greater than a certain value and by rigorously controlling the variation of hardness at the aforementioned position.

[012] This disclosure is based on the above findings and their main attributes are as follows.

[013] [1] A track comprising: a chemical composition containing (consisting of) C: 0.70% by mass to 1.20% by mass, Si: 0.10% by mass to 1.20% by mass, Mn: 0.10% by mass to 1.50% by mass, P: 0.035% by mass or less, S: 0.020% by mass or less, and Cr: 0.05% by mass to 1.80% by mass, with an equilibrium consisting of Fe and unavoidable impurities, wherein, when a Vickers hardness at a depth of 0.5 mm of Petition 870250080624, dated 08 / 09 / 2025, pp. 75 / 109 4 / 29 The surface of a rail weave is measured in a range of ±17.5 mm above and below a central rail height position, an average Vickers hardness value of Hv280 or higher with a standard deviation of 5 or less.

[014] [2] The rail, according to [1], in which the chemical composition additionally contains at least one selected from the group consisting of V: 0.30% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Nb: 0.05% by mass or less, Mo: 2.0% by mass or less, Al: 0.07% by mass or less, W: 1.0% by mass or less, Co: 1.0% by mass or less, B: 0.005% by mass or less, Ti: 0.05% by mass or less, Sb: 0.05% by mass or less, Mg: 0.01% by mass or less, Ca: 0.02% by mass or less, and Sn: 0.05% by mass or less.

[015] [3] A method for producing the rail according to [1] or [2], the method comprising: When producing a rail by hot rolling from a steel material having the chemical composition according to [1] or [2], the cooling after hot rolling is carried out so that an average cooling rate for the rail web is 0.4 °C / s to 5.0 °C / s from an initial cooling temperature of 750 °C or more to a stopping temperature of Petition 870250080624, dated 08 / 09 / 2025, pp. 76 / 109 5 / 29 cooling from 450 °C to 600 °C at each position between the central rail height position, a position 20 mm above the central rail height position, and a position 20 mm below the central rail height position, and such that a difference in the average cooling rate at each position is within 0.5 °C / s. (Beneficial Effect)

[016] According to the present disclosure, a rail with excellent resistance to rail web fractures, together with a method for producing the same, can be provided. The rail of the present disclosure contributes to extending the service life of rails for heavy transport railways and preventing railway accidents. The rail is therefore industrially beneficial. The method for producing a rail of the present disclosure enables the stable production of the rail of the present disclosure and is therefore industrially beneficial. BRIEF DESCRIPTION OF THE DRAWINGS

[017] In the attached figures: FIG. 1 is a cross-section of a rail; FIG. 2 is a diagram illustrating the position in which a test specimen for measuring the Vickers hardness of the rail weave is collected; FIG. 3 is a schematic diagram illustrating a method for cooling the rail weave; FIG. 4 is a diagram illustrating the positions at which specimens for a three-point bending test of the rail weave are collected; and FIG. 5 is a diagram illustrating the shape of a test specimen for a three-point bending test of the rail weave. DETAILED DESCRIPTION<Partes de Trilho> Petition 870250080624, dated 08 / 09 / 2025, pp. 77 / 109 6 / 29

[018] First, the designations of the various parts of the rail of the present disclosure are described with reference to the cross-sectional view of rail in FIG. 1. In rail 1 illustrated in FIG. 1, 11 indicates the rail head, 12 indicates the rail weave and 13 indicates the rail base. Hereafter, the rail head, the rail weave and the rail base are also referred to as the head, weave and base, respectively. <Composição Química de Trilho>

[019] The chemical composition of the rail steel according to this disclosure will be described below. In the following description, % denotes % by mass, unless otherwise specified. C: 0.70% to 1.20%

[020] C is an essential element to ensure the strength of the pearlitic microstructure, that is, fracture resistance. If the C content is less than 0.70%, it will be difficult to obtain excellent fracture resistance. If the C content exceeds 1.20%, a large amount of proeutectoid cementite is formed at the austenite grain boundaries during cooling after hot rolling, leading to a reduction in fracture resistance. Although proeutectoid cementite is also present when the C content is 1.20% or less, the amount produced is so small that its effect on fracture resistance is negligible. From this perspective, the C content is set in a range of 0.70% to 1.20%. The C content is preferably in a range of 0.70% to 0.89%. The C content is more preferably in a range of 0.70% to 0.85%. Yes: 0.10% to 1.20%

[021] In addition to its effect as a deoxidizer, Si is an element that contributes to strengthening the pearlitic microstructure, that is, improving fracture resistance, by increasing the equilibrium transformation temperature of pearlite and reducing lamellar spacing. From this perspective, the Petition 870250080624, dated 08 / 09 / 2025, pp. 78 / 109 7 / 29 The Si content needs to be 0.10% or more. However, if the Si content exceeds 1.20%, bainitic and martensitic microstructures are likely to occur in the surface layer, which promotes variation in hardness and results in reduced fracture resistance. Furthermore, weldability is also degraded due to the increase in Si oxides. In these perspectives, the Si content is established in a range of 0.10% to 1.20%. The Si content is preferably in a range of 0.15% to 1.10%. The Si content is more preferably in a range of 0.20% to 1.00%. Mn: 0.10% to 1.50%

[022] Mn is an element that contributes to strengthening the pearlitic microstructure, that is, improving fracture resistance, by lowering the pearlite transformation temperature and reducing lamellar spacing. If the Mn content is less than 0.10%, the effect is insufficient. On the other hand, if the Mn content exceeds 1.50%, bainitic and martensitic microstructures are likely to occur in the surface layer, which promotes variation in hardness and results in reduced fracture resistance. Furthermore, since Mn has the effect of moving the eutectic point to the lower C side, excessive Mn addition promotes the formation of proeutectoid cementite and leads to a reduction in fracture resistance. From these perspectives, the Mn content is established in a range of 0.10% to 1.50%. The Mn content is preferably in a range of 0.20% to 1.40%. The Mn content is most preferably in a range of 0.30% to 1.30%. P: 0.035% or less

[023] P in an amount exceeding 0.035% degrades fracture resistance and ductility. Therefore, the P content is set at 0.035% or less. The P content is preferably 0.020% or less. No specific lower limit is placed on the P content. The P content may be 0%, but Petition 870250080624, dated 08 / 09 / 2025, pp. 79 / 109 8 / 29 is generally more than 0% in industrial terms, and an excessive decrease in P content will increase refining costs. From an economic efficiency perspective, the P content is preferably 0.001% or higher. S: 0.020% or less

[024] S is an element present mainly in steel in the form of type A inclusions. When the S content exceeds 0.020% by mass, the amount of inclusions increases significantly and, at the same time, coarse inclusions are formed. As a result, fracture resistance and ductility deteriorate. Therefore, the S content is set at 0.020% or less. The S content is preferably 0.015% or less. The S content is more preferably 0.010% or less. No specific lower limit is placed on the S content. The S content can be 0%, but it is generally more than 0% in industrial terms, and an excessive decrease in the S content will increase refining costs. From an economic efficiency perspective, the S content is preferably 0.0005% or more. Cr: 0.05% to 1.80%

[025] Cr is an element that contributes to strengthening the pearlitic microstructure, i.e., improving fracture resistance, by increasing the equilibrium transformation temperature of pearlite and reducing lamellar spacing. If the Cr content is less than 0.05%, the effect is insufficient. On the other hand, if the Cr content exceeds 1.80%, the hardenability of the steel increases, and bainitic and martensitic microstructures are likely to occur in the surface layer, which promotes variation in hardness and results in reduced fracture resistance. From these perspectives, the Cr content is established in a range of 0.05% to 1.80%. The Cr content is preferably in a range of 0.10% to 1.60%. The Cr content is more preferably in a range of 0.15% to 1.40%. Petition 870250080624, dated 08 / 09 / 2025, pages 80 / 109 9 / 29

[026] In addition to the essential components mentioned above, the chemical composition of a rail used in this disclosure may optionally contain at least one selected from the group consisting of V: 0.30% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Nb: 0.05% by mass or less, Mo: 2.0% by mass or less, Al: 0.07% by mass or less, W: 1.0% by mass or less, Co: 1.0% by mass or less, B: 0.005% by mass or less, Ti: 0.05% by mass or less, Sb: 0.05% by mass or less, Mg: 0.01% by mass or less, Ca: 0.02% by mass or less, and Sn: 0.05% by mass or less.

[027] The reasons for the optional elements above are described below. V: 0.30% or less

[028] V is an element that forms carbonitrides in steel and disperses and precipitates in the matrix, thereby improving fracture resistance. If the V content exceeds 0.30%, fracture resistance and ductility deteriorate and the alloy cost, i.e., the cost of rail production, also increases. From these perspectives, the upper limit of the V content is preferably 0.30% in the case where the chemical composition contains V. The V content is preferably 0.001% or more from the perspective of expressing the fracture resistance improvement effect. The range of the V content is most preferably from 0.001% to 0.15%. Cu: 1.0% or less

[029] Cu is an element capable of further strengthening steel by strengthening it in solid solution, just like Cr. If the Cu content exceeds 1.0%, Cu cracking is likely to occur. Therefore, in cases where the chemical composition contains Cu, the Cu content is preferably 1.0% or less. The range of Cu content is more preferably from 0.001% to 0.5%. Petition 870250080624, dated 09 / 08 / 2025, pp. 81 / 109 10 / 29 Ni: 1.0% or less

[030] Ni is an element that can increase the strength of steel without deteriorating ductility. Furthermore, in the case where the chemical composition contains Cu, it is preferable to add Ni because Cu cracking can be suppressed by adding Ni in combination with Cu. However, if the Ni content exceeds 1.0% by mass, the hardenability of the steel increases further, the amount of martensite and bainite formed is increased, and the fracture resistance is reduced. From these perspectives, the Ni content is preferably 1.0% or less in the case where the chemical composition contains Ni. The range of Ni content is more preferably from 0.001% to 0.5%. Nb: 0.05% or less

[031] Nb is an element that combines with C in steel to precipitate as carbides during and after hot rolling to form the rail and acts effectively to refine the size of pearlite colonies. As a result, Nb greatly improves fracture resistance and wear resistance, rolling contact fatigue resistance and ductility, as well as contributing greatly to extending the service life of the rail. However, when the Nb content exceeds 0.05%, the property-enhancing effect is saturated and the effect does not increase as the content increases. From these perspectives, the upper limit of the Nb content is preferably 0.05% in the case where the chemical composition contains Nb. The Nb content is preferably 0.001% or more in order to obtain a sufficient effect with respect to extending the service life of the rail. The range of Nb content is more preferably from 0.001% to 0.03%. Mo: 2.0% or less

[032] Mo is an element capable of further strengthening steel by strengthening it in solid solution. Mo also has the effect of shifting the eutectic point to the high C side and thus has the effect of inhibiting cementite formation. Petition 870250080624, dated 08 / 09 / 2025, pages 82 / 109 11 / 29 proeutectoid. However, if the Mo content exceeds 2.0% by mass, the amount of bainite formed in the steel increases and fracture resistance is reduced. From these perspectives, the Mo content is preferably 2.0% or less in the case where the chemical composition contains Mo. From the perspective of high strength, the Mo content is preferably 0.001% or more. The range of Mo content is most preferably from 0.001% to 1.0%. Al: 0.07% or less

[033] Al is an element that can be added as a deoxidizer. If the Al content exceeds 0.07% by mass, a large number of oxide-based inclusions are formed in the steel due to the high bonding strength between Al and oxygen. As a result, the fracture resistance and ductility of the steel are reduced. Therefore, the Al content is preferably 0.07% or less in the case where the chemical composition contains Al. No lower limit is placed on the Al content, but the Al content is preferably 0.001% or more for deoxidation. The range of Al content is most preferably from 0.001% to 0.03%. W: 1.0% or less

[034] W is an element that precipitates as carbides during and after hot rolling to shape the steel into a rail shape and that improves the strength and fracture resistance of the rail through precipitation strengthening. If the W content exceeds 1.0%, martensite is formed in the steel. As a result, fracture resistance decreases. From these perspectives, the W content is preferably 1.0% or less in the case where the chemical composition contains W. No lower limit is placed on the W content, but the W content is preferably 0.001% or more in order to exert the effect of improving strength and fracture resistance. The range of W content is most preferably from 0.001% to 0.5%. Co: 1.0% or less Petition 870250080624, dated 08 / 09 / 2025, pages 83 / 109 12 / 29

[035] Co is an element that can increase the equilibrium transformation temperature of pearlite and reduce lamellar spacing, thereby further enhancing the strength of steel. Co also has the effect of suppressing the precipitation of proeutectoid cementite. If the Co content exceeds 1.0%, martensite forms in the steel. As a result, fracture resistance decreases. From these perspectives, the Co content is preferably 1.0% or less in the case where the chemical composition contains Co. No lower limit is placed on the Co content, but the Co content is preferably 0.001% or more to enhance strength. The range of Co content is most preferably from 0.001% to 0.5%. B: 0.005% or less

[036] B is an element that precipitates as nitrides in steel during and after hot rolling to shape the steel into a rail shape and improves the strength and fracture resistance of the steel through precipitation strengthening. If the B content exceeds 0.005%, martensite is formed and, as a result, fracture resistance decreases. From these perspectives, the B content is preferably 0.005% or less in the case where the chemical composition contains B. No lower limit is placed on the B content, but the B content is preferably 0.001% or more in order to exert the effect of improving strength and fracture resistance. The B content is most preferably from 0.001% to 0.003%. Ti: 0.05% or less

[037] Ti is an element that precipitates as carbides, nitrides, or carbonitrides in steel during and after hot rolling to shape the steel into a rail shape and that improves the strength and fracture resistance of the steel through precipitation strengthening. If the Ti content exceeds 0.05% by mass, coarse carbides, nitrides, or carbonitrides are formed. As Petition 870250080624, dated 09 / 08 / 2025, p. 84 / 109 13 / 29 result, fracture resistance decreases. From these perspectives, the Ti content is preferably 0.05% or less in the case where the chemical composition contains Ti. No lower limit is placed on the Ti content, but the Ti content is preferably 0.001% or more in order to exert the effect of improving strength and fracture resistance. The range of Ti content is most preferably from 0.001% to 0.03%. Sb: 0.05% or less

[038] Sb is an element that has a notable effect on preventing decarburization of steel during reheating of rail steel material in a heating furnace before hot rolling. If the Sb content exceeds 0.05%, fracture resistance and toughness will be negatively affected. Therefore, in the case where the chemical composition contains Sb, the Sb content is preferably 0.05% or less. No lower limit is placed on the Sb content, but the Sb content is preferably 0.001% or more in order to exert the effect of reducing the decarburized layer. The range of Sb content is most preferably from 0.001% to 0.03%. Mg: 0.01% or less

[039] Mg is an element that combines with oxygen to precipitate as MgO, thereby further enhancing strength. If the Mg content exceeds 0.01%, the increase in MgO negatively affects the fracture resistance and toughness of the steel. Therefore, in the case where the chemical composition contains Mg, the Mg content is preferably 0.01% or less. No lower limit is placed on the Mg content, but the Mg content is preferably 0.001% or more in order to exert the effect of improving strength. The range of Mg content is most preferably from 0.001% to 0.005%. Ca: 0.02% or less

[040] Ca is an element that combines with oxygen to precipitate as Petition 870250080624, dated 08 / 09 / 2025, pages 85 / 109 14 / 29 CaO, thus further enhancing strength. If the Ca content exceeds 0.02%, the increase in CaO negatively affects the fracture resistance and toughness of the steel. Therefore, in cases where the chemical composition contains Ca, the Ca content is preferably 0.02% or less. No lower limit is placed on the Ca content, but the Ca content is preferably 0.001% or more in order to exert the effect of improving strength. The range of Ca content is most preferably from 0.001% to 0.01%. Sn: 0.05% or less

[041] Sn is an element that has a notable effect in preventing decarburization of steel during reheating of rail steel material in a heating furnace before hot rolling. If the Sn content exceeds 0.05%, the ductility and toughness of the steel will be negatively affected. Therefore, in the case where the chemical composition contains Sn, the Sn content is preferably 0.05% or less. No lower limit is placed on the Sn content, but the Sn content is preferably 0.001% or more in order to exert the effect of reducing the decarburized layer. The range of Sn content is most preferably from 0.001% to 0.01%.

[042] In the chemical composition of the rail steel of the present disclosure, equilibrium, other than the essential and optional components above, consists of Fe and unavoidable impurities. As used in the present invention, examples of unavoidable impurities include N, O and the like. N contents of up to 0.008% and O contents of up to 0.004% are permitted. Impurities other than N and O may inevitably be mixed into the steel depending on the raw materials, materials, production facilities and other conditions. Raw materials include iron ore, reduced iron, scrap and the like. The above impurities are acceptable provided they do not interfere with the objective of the present disclosure. Impurities other than N and O include Pb, Zr, Bi, Zn, Se, As, Te, Tl, Cd, Hf, Ag, Hg, Petition 870250080624, dated 08 / 09 / 2025, pages 86 / 109 15 / 29 Ga, Ge, and REM. <Microestrutura de Trilho>

[043] The rail in this disclosure is a pearlitic rail, and the rail microstructure has 95% or more pearlite by area ratio. Residual microstructures other than pearlite are acceptable if the total area ratio is 5% or less, as fatigue crack propagation resistance is not significantly affected. Examples of residual microstructure include ferrite, proeutectoid cementite, bainite, and martensite. <Dureza Vickers>

[044] In the present disclosure, it is not sufficient that the chemical composition merely meets the above ranges. To obtain excellent fracture resistance in the rail weave, it is important to control the Vickers hardness Hv, at a depth of 0.5 mm from the rail weave surface, at a location within a range of 17.5 mm above and below the central rail height position (a total range of 35 mm), to be within a predetermined range. Specifically, the average Vickers hardness value at the aforementioned location is 280 or higher, and the standard deviation is 5 or less. From the perspective of achieving a stable improvement in fracture resistance, the average Vickers hardness at the aforementioned location is preferably Hv300 or higher, with a standard deviation of 4 or less.

[045] In FIG. 2, the rail height is expressed as the length A from the bottom of the base to the top of the head, and the central rail height position is the central rail height position A (position A / 2). The 17.5 mm range above and below the central rail height position (total range of 35 mm) is within the shaded area in FIG. 2. The Vickers hardness of the present disclosure can, for example, be measured with a pressing load of 98 N, at a depth of 0.5 mm from the surface of the corresponding location and in one step Petition 870250080624, dated 08 / 09 / 2025, pages 87 / 109 16 / 29 1 mm top-to-bottom rail clearance in the 17.5 mm range above and below the center rail height position (total range of 35 mm).

[046] The hardness in the 17.5 mm range above and below the center rail height position (total range of 35 mm) is set within a predetermined range for the following reasons.

[047] As mentioned above, the passage of the wheels applies repetitive bending stress to the outer track web of the rail arranged in curved sections. On the other hand, rolling marks or engravings are found within a range of 17.5 mm above and below the center of rail height on the rail web. We have found that when bending stress is applied, a portion of this rolling mark or engraving becomes a stress concentrator, and fracture occurs from this area. The present disclosure is based on this finding and controls the hardness in the range of 17.5 mm above and below the center of rail height on the rail web so that it is within a predetermined range.

[048] Thus, in addition to strengthening the pearlitic microstructure of the rail weave, the rigorous control of the variation in the hardness of the rail weave surface layer makes it possible to suppress stress concentration in locally softened areas, which significantly improves the fracture resistance of the rail weave. Excellent fracture resistance in the rail weave is a necessary property for rails in general and is also effective in increasing service life and preventing railway accidents for rails used in straight sections and rails that do not have rolling marks or engravings in the rail weave, for example. <Formato de trilho>

[049] The rail format of the present disclosure is not limited and may be the rail format described by JIS E 1101:2001, BS EN13674-1:2011, by Petition 870250080624, dated 08 / 09 / 2025, pages 88 / 109 17 / 29 American Railway Engineering and Maintenance-of-WayAssociation (AREMA) or similar. <Método para Produzir Trilho>

[050] A method for producing the rail of the present disclosure is now described. The rail of the present disclosure can be produced by sequentially applying the following treatments to a steel material having the chemical composition described above.

[051] The steel material used as a rail material has the chemical composition of the rail described above and can be produced by any method. In general, the steel material is preferably produced by ingot casting, particularly continuous casting. (1) Hot Rolling

[052] The steel material can be heated and then hot-rolled into the shape of a rail. (Heating Temperature)

[053] When heating steel material before hot rolling, the heating temperature is preferably 1350 °C or less. If the heating temperature exceeds 1350 °C, the steel material may partially melt due to excessive temperature increase, resulting in defects within the track. On the other hand, no lower limit is placed on the heating temperature, but the heating temperature is preferably 1150 °C or more to reduce resistance to deformation during rolling. (Lamination Finishing Temperature)

[054] Hot rolling is preferably carried out at a finishing rolling temperature of 850 °C or more. If the finishing rolling temperature is less than 850 °C, then the rolling is Petition 870250080624, dated 09 / 08 / 2025, pp. 89 / 109 18 / 29 performed in a low austenite temperature range, and processing expansion is introduced into the austenite crystal grains, which can lead to variations in the hardness of the pearlitic microstructure formed by accelerated cooling. Therefore, the finishing temperature for rolling is preferably 850 °C or higher. No upper limit is placed on the finishing temperature for rolling, but an extreme thickening of the austenite grain size will reduce fracture resistance and toughness. The finishing temperature for rolling is therefore preferably 1050 °C or lower. Here, the finishing temperature for rolling is the surface temperature of the central portion of the rail web on the entry side of the end mill and can be measured with a radiation thermometer.

[055] The other conditions for hot rolling are not limited. (2) Accelerated Cooling

[056] The rail can be obtained by cooling after hot rolling. During cooling, the rail web is subjected to accelerated cooling. At this time, the average cooling rate is controlled to be 0.4 °C / s 5.0 °C / s from an initial cooling temperature of 750 °C or more to a cooling stop temperature of 450 °C to 650 °C at each position between the central rail height position (position A / 2), a position 20 mm above the central rail height position (upper 20 mm position) and a position 20 mm below the central rail height position (lower 20 mm position), where the rail height is A, and the difference in the average cooling rate at these three positions is controlled to be within 0.5 °C / s.

[057] The accelerated cooling method is not limited and can be carried out, for example, by cooling using an online heat treatment plant. The cooling liquid is not limited and can be one or more Petition 870250080624, dated 08 / 09 / 2025, pages 90 / 109 19 / 29 selected from air, water spray, mist and similar methods, but air is the preferred option.

[058] In this accelerated cooling, if the average cooling rate at any central rail height position (position A / 2) or at positions 20 mm above and below the central rail height position (upper 20 mm position and lower 20 mm position) is less than 0.4 °C / s, then the lamellar spacing in the surface layer of the warp will become coarser, and proeutectoid cementite will also be more likely to form, resulting in a decrease in fracture resistance. Furthermore, increased cooling time at low temperatures can reduce productivity and increase rail production costs. Therefore, the average cooling rate at each of the three positions above is set at 0.4 °C / s or more. The average cooling rate is preferably 1.0 °C / s or more.On the other hand, if the average cooling rate at any of the three positions above exceeds 5.0 °C / s, bainitic and martensitic microstructures will form, decreasing fracture resistance. Therefore, each average cooling rate in the range above is set at 5.0 °C / s or less. The average cooling rate is preferably 4.0 °C / s or less.

[059] Furthermore, if the difference in the average cooling rate in the three positions mentioned above exceeds 0.5 °C / s, the variation in the hardness of the rail weave surface layer increases, making stress concentration in locally softened areas more likely during bending stress loading and thus decreasing fracture resistance. Therefore, the difference in the average cooling rate in the three positions above is within 0.5 °C / s. The difference in the average cooling rate is preferably 0.3 °C / s. The difference between the average cooling rate in the three positions is the difference between the highest average cooling rate and the lowest average cooling rate among the average cooling rates in the three positions. Petition 870250080624, dated 08 / 09 / 2025, pages 91 / 109 20 / 29

[060] The control of the average cooling rate in the central rail height position (position A / 2), the 20 mm upper position, and the 20 mm lower position is now described. With respect to heat flow, the upper and lower sides of position A / 2 are more susceptible than position A / 2 to heat radiation and heat conduction from the rail head and base, respectively. If the average cooling rate in the three positions, i.e., position A / 2, the 20 mm upper position, and the 20 mm lower position, is controlled within an appropriate range (0.4 °C / s to 5.0 °C / s), and the difference in the average cooling rate in the three positions is controlled within a certain range (within 0.5 °C / s), the average cooling rate in a range of 20 mm above and below position A / 2 (within a total range of 40 mm) is estimated to be appropriate and uniform.

[061] By properly enhancing accelerated cooling on the upper side of position A / 2 and on the lower side of position A / 2 relative to position A / 2, the difference in average cooling rates in the three positions above can be stably maintained within 0.5 °C / s.

[062] For example, the nozzles can be installed in three stages in the direction of height to discharge directly towards position A / 2, the upper side of position A / 2 and the lower side of position A / 2, respectively, and the amount of spray and the type of coolant in the three positions can be varied according to the temperature and shape of the rail. For example, as illustrated in FIG. 3, the air nozzles can be installed in three stages, with the highest injection volume set at the top 20 mm position, the second highest injection volume at the bottom 20 mm position and the lowest injection volume at position A / 2.

[063] In accelerated cooling, the temperatures used to determine the average cooling rate are representative of the temperatures Petition 870250080624, dated 08 / 09 / 2025, pages 92 / 109 21 / 29 of the surface temperature at position A / 2, 20 mm higher, and 20 mm lower. These can be measured with a radiation thermometer. Here, the initial cooling temperature is the rail weave surface temperature at the start of accelerated cooling, measured with a radiation thermometer, and the cooling stop temperature is the rail weave surface temperature after accelerated cooling has stopped (before heat recovery), measured with a radiation thermometer.

[064] In the production method of the present disclosure, it is important to cool the rail after hot rolling in order to satisfy the above set of conditions with respect to the rail web surface temperature and, if this set of conditions is satisfied, the method of cooling other parts of the rail (such as the rail head) is not limited. The rail head and base may be allowed to cool naturally or be subjected to accelerated cooling. (3) Other treatments

[065] After cooling, the rail material can be subjected to known treatments, such as cold roller straightening. EXAMPLES

[066] The present disclosure is described below in more detail by way of example, but the present disclosure is in no way limited to those examples and may be appropriately modified within a range consistent with the purpose of the present disclosure, all such modifications being included within the technical scope of the present disclosure.

[067] Steel materials having the chemical compositions illustrated in Table 1 were heated, subjected to hot rolling and subjected to accelerated cooling after hot rolling under the set of conditions illustrated in Table 2, to produce 60 kg of rail materials in Petition 870250080624, dated 08 / 09 / 2025, pages 93 / 109 22 / 29 in accordance with JIS E1101. The average cooling rate (°C / s) is obtained by converting the temperature change from the start to the end of cooling into a value per unit of time (seconds). After cooling was stopped, the rail materials were allowed to cool naturally.

[068] In the Examples, accelerated cooling of the rail weave was carried out using the air nozzles illustrated in FIG. 3, and the injected air content was changed as needed to vary the cooling rate. In the Comparative Example test No. 34, accelerated cooling was carried out using only one set of air nozzles installed at height A / 2 between the air nozzles illustrated in FIG. 3.

[069] At the initial and final points of accelerated cooling, surface temperatures at position A / 2, position 20 mm higher and position 20 mm lower were measured using a two-dimensional radiation thermometer capable of measuring the temperature distribution in the direction of the rail weave height, and the average cooling rate at these three positions was calculated. [Table 1] Petition 870250080624, dated 08 / 09 / 2025, pp. 94 / 109 23 / 29 Table 1 Observations Steel according to Chemical composition (% by mass) c CO Γϋ o _Q CO H CQ oo 1 60'0 CO o' | 0.91 | < 0.035 | 1 890'0 oo' | 0.82 I CD 00 _Q I 0.021 I 00 o^ o' I 0.22 | | 0.29 | o' CD CO o' DOI 0.29 | o' cn cn o' > | 0.04 I CM o' | 0.29 | o 00 CM θ' 1 08'0 LO O o' CM o' 0.24 o' Ln co o' 00 cn 00 oo' | 0.19 | | 0.36 I ld CD cn o' 0.77 0.42 cn cn o' 0.26 CO o' 0.79 o' cn o' I 0.30 II 0.22 | co LD o' 00 o' 0.24 CO | 0.003 1 | 0.005 | | 0.007 I | 900'0 1 | 0.004 1 | 0.005 | | 0.019 1 1 OTO'O I | 0.007 1 I 0.004 | | 0.003 | | 800'0 1 | 0.005 II 0.003 I | 0.004 1 1 900'0 I | 0.005 | | 0.003 1 I 0.004 | | 0.005 1 | 0.004 I | 0.003 1 I 0.005 II 0.003 I 1 900'0 I o CD o' | 0.005 | CL oo' 0.014 | 0.013 II oto'o CM O^ o' 0.018 | | OTO'O 0.013 | 1 600'0 0.014 | 0.034 | I uo'o | 600'0 | OTO'O | 0.012 1 0.018 | 0.013 | | ττοΌ I 0.012 | | 600'0 \ 0.016 I | ττοΌ CM O^ o' 0.015 | | OTO'O 1 600'0 0.018 | c 00 CO o' | 0.20 I | 0,58 I LO o' cn o LO o' CD o' cn CM o' CM cn o' 00 00 o' oo' cn o' co o' | 0.29 | oo co CM^ o' 0.16 LD CM o' cn co o' CD CM o' | 0.56 1 00 o' LD o' I 0.92 | CD CM o' | 0.39 | ÍÕ 1 917'0 CM O LO o' | ττ'ο CM^ o' Ch co UD o' CM cn o' | 0.50 1 0.26 | 0.35 | co o' | 0.19 I CD CM^ o' 0.34 I 0.82 | cn o' | 0.38 | I 0.20 I 0.51 | 0.36 I cn o' CM o' 0.59 0.43 0.47 | 0.20 | o oo o' LO 00 o' CM 00 o' 00 O 00 o' co o' ld o' 00 o' 06'0 00 o' o' co 00 o' oo o' Ln o' CO o' 08'0 oo o' ld o' o' o 00 o' Ln o' o' o' cn 00 o' CO 00 o' o' o' Steel No. τ—1 CM CO LO cd r- 00 σ» o CM CO LO CD 00 cn O CM CM CM CM CO CM CM LD CM CD CM CM, Petition 870250080624, dated 08 / 09 / 2025, pages 95 / 109 24 / 29 Observations Steel as per Comparative Steel Chemical composition (% by mass) c CO co oo' Ln oo' ro O |600'0| 00 o^ o' W) εοο'ο 600'0 _Q CO oo' H co oo' cn oo' CO 10.002 1 10.004 1 oo CM o' CM LO o' CD 00 o' < o _Q ZDO > o CO o' LT) CM o' CM CM o' o' o CD o' Ln Ln o' 1 06'0 0.24 co o' co o' Ln Ln o' o co o' co o' o cn co o' Ln CM CM o' co o' o co o' 00 o' 186 CO 0.005 | 0.007 | 0.004 | | 900'0 0.005 | ooooo 0.005 | 0.004 | | 900'0 0.007 | 0.005 | I 900'0 ooo 0.005 | co o^ o 0.003 | | 600'0 0.004 | 0.022 | 0.005 | oo CL I 0.012 I | 0.015 1 | 0.014 1 | 0.013 | | 0Τ0Ό I 1 0.012 1 | ττοΌ | | 0.014 1 | 0.013 I | 0.016 I 1 0.012 | 00 o^ o' | 0.015 1 I 0.013 I | ττοΌ | 1 0.012 | 00 o^ o' | οτο'ο | I 0.036 1 I 0.014 | I 0.019 I | 0.025 | c Σ LD o' CM o' σ» o' 1 0.20 1 00 o' o' CD o' CM o co o' 00 o' | ττΌ | I OZ'O I Ln o' CD 00 o' co cm o' | 09'0 | cN o ol [η 00 o' Ln CM CO co o' 1 66'0 I ίη | 0.56 I CM CD o' 00 CM o' CM O 0.72 | 0,40 1 CO CM o' 1 917'0 o CD o' Ln o' | 0t7'0 00 o' co CM o' Ln oo' 00 o Ó 00 CM o' o' 00 CD o' CD CM o' Ln o' CO Ln o' o 00 o' CO 00 o' LO o' S o' CM 00 o' o' 08'0 0.78 CM 00 o' 08'0 o' 00 o' 00 CD Ó CD CM CM o' 66'0 o' Ln o co 00 o' co o' oo' CM Steel no. 00 CM O CM o co CO CM CO co co co Ln co CD CO CO 00 co o co o CM CO Ln CD 00 o, Underlining indicates a value outside the applicable range. Petition 870250080624, dated 08 / 09 / 2025, pages 96 / 109 25 / 29 [Table 2] Table 2 Observations Example Investigation Results Three-point bending test*2 excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent Vickers Hardness Hv Standard Deviation CO CO CM CM LO CM ^1 LO CM CO CO CO vl CM CM CM CO CM LO CM CO CM ^1 CO CO Average LT) OO CO 378 384 412 O CO o LO CO 340 CM CO CO o LO MD CO CM 00 CM 374 MD σ CO 410 | 384 LO σ CO CO o LO 434 429 O 00 CO 448 | 436 MD CO LO CO 370 409 | 00 00 CO Production conditions Difference in average cooling rate [°C / s] CO o CM oo CO o CM o lo o CM o O o CO ooo CO oo CM oo CM o CO o CD oo CO oooo CO oo O o CO o CO o Average cooling rate [°C / s] Position 20 mm lower CM CO UD oo cm MD CO cm CM^ CO σ 'd·' O LO CO LO CO cm σ o cm σ o co 00 o co o lo CM cm CO o cm Position 20 mm higher LOCO LO lo o CO cm 00^ 00 cm O^ CO CM cm oo^ CM CO MD LO cm CM^ CO cm σ o lo co σ o LO CO 00 CO CM CO CO CO cm o cm Position A / 2 1 co UD o CM cm 00^ 00 cm CM^ σ o CO CO o CM cm CO CM cm 00 Cooling stop temperature [°C] 530 | OR UD LO or CM LO 540 | O MD LO 1,0517,650 | 590 | o LO 560 | 530 | o LO 530 | 550 | OR MD LO 520 | o 00 LO o MD | 610 1 O MD LO o MD o 00 LO 630 | o LO O LO LO o LO o O MD o 00 LO Initial cooling temperature [°C] O LO 00 o 00 O CO 00 oo 00 o 840 | 760 | o 00 O o 00 | 760 1 of 00 790 | 780 | OO 00 O 00 ooo 00 810 I 790 | o CM 00 o CO 00 O o 00 OO 00 o 00 O σ o 00 Rolling finish temperature [°C] o 00 00 o σ» o UD 00 920 | 870 | year 00,970 | 890 | or 00 910 | o LO 00 o σ 910 | 930 | OO σ 1,068,860 | or σ 00,920 | 900 | or σ 920 | 1 006 o CO σ O 00 00 920 | o σ o σ Access temperature [°C] 1250 | 1300 | 1 1 1250 | 1300 | 1250 | 1200 | | 1275 | 1300 | 1250 | 1225 | 1250 | 1 í1300 | | 1275 | 1250 | 1225 | 1250 | | 1275 1 1250 | 1225 | 1250 | 1275 | 1250 | 1300 | 1250 | 1 sm 1250 | Steel no. τ—1 CM CO LO MD 00 σ O CM CO LO MD 2 00 σ O CM CM CM CM CO CM CM LO CM MD CM CM 00 CM Test no. ^1 CM CO LO md r- 00 σ o ^-1 CM CO LO md 2 00 2 O CM CM CM CM CO CM CM LO CM MD CM CM 00 CM Petition 870250080624, dated 08 / 09 / 2025, pages 97 / 109 26 / 29 Observations Example Comparative Example Note: Underlining indicates a value outside the applicable range. Note 1: A indicates the track height (A / 2 corresponds to the central track height position). Note 2: Excellent: no parts fractured; poor: at least one part fractured. Research Results Three-point bending test*2 \ excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent EEEEEEEEEEEDDDDDD Vickers Hardness Hv Standard deviation cxl Ln ro rxl rxl rxl ro rxl rxl rxl σ>| rxl N rxl ool rxl 'tf tOl rxl N U2l Average 405 421 | 400 I 379 | 299 1 337 LO 00 ro 312 349 301 326 3 a 438 a | 449 | | 360 1 357 244 ^17 420 349 Production conditions | Difference in average cooling rate [°C / s] CN θ' o 17'0 | ro o rxl oo CN o' rxl o' 00^ CN o' o' rxl o' 1-0 θ' o' 17'0 | o' lo o' ro o' ro o' O^ o' rxl o' o' ro o' 3 Average cooling rate [°C / s] Position 20 mm lower O CN o O cx? lo ro rx? 00 o O rx? ro rx? o ex?LO o' co CN 1 4,1 | ro co 00^ cxl ex? lo o' I CV | I 0.4 I a LO Position 20 mm upper d ro ro 00 LO rx? σ» o' O ro LO σ LO rx? CM 00 o' ο ro or LO ro 1 2.0 1 LO ex? lo o' O^ a 00^ Position A / 2 1 CXl CN CN cxl ro LO LO rx? σι o' co LO σ LO rx? ro rx? 00 o' 00 ro ro 4.4 | 3.4 | CM 2.4 | lo o' I CV 0.4 | o Ln CXI ex? Cooling stop temperature [°C] 1 570 1 1 069 | | 550 I 1 570 1 | 530 1 1 550 1 | 560 1 1 590 | | 550 1 I 530 | | 580 | O cxl LO 1 500 1 I 640 | | 490 1 I 550 | | 500 | | 560 | I 550 | | 009 I o LO I 600 I | 500 | I 530 | Initial cooling temperature [°C] O o 00 1 ozz O o 00 o 00 O 00 750 1 o 00 780 | | 760 1 | ozz 790 | O σ o ro 00 oo 00 o LO 00 760 | 840 | 1 ozz 790 | oo 00 o 00 I 08Z 770 | 790 | Lamination finishing temperature [°C] 920 | 860 | | 006 930 | 890 | 860 1 910 | 900 | o 00 00 890 | 1 006 ο LD 00 940 1 900 | | 970 1 850 | 950 | 900 1 920 | o 00 00 | 006 900 | 920 | o 00 00 Heating temperature [°C] | 1250 1 | 1225 1 | 1175 | |1250 I | 1325 1 1 1250 1 | 1250 | 1 1 | 1250 1 I 1300 I | 1250 | 1 1225 1 1 1250 1 I 1250 | | 1300 1 I 1225 | | 1250 | | 1200 1 I 1300 I | 1250 1 III 1250 | | 1225 | 1 9ZZT I Steel no. σ> CXl O ro ro rxi ro ro ro ro ro LO ro LO ro CO 00 ro o ro 51 5l Si Si 51 Si si 51 Si Si LO ro 00 Test no. σ> CXl O ro ro rxi ro ro ro ro LO ro LO ro co 00 ro o ro ο 'tf rxl ro LO LO 00 σ o LO Ln cxl Ln Petition 870250080624, dated 08 / 09 / 2025, pages 98 / 109 27 / 29

[070] The resulting rails are pearlitic rails. Vickers hardness and three-point bending properties of the web were evaluated for each rail. Table 2 lists the test results. The details of each evaluation will be described below. <Dureza Vickers>

[071] After cutting the rail lead end following accelerated cooling, a portion of the rail weave, in a 20 mm strip above and below the central rail height position (position A / 2) illustrated in FIG. 2 (within a total range of 40 mm), was collected so as to include the rail weave on the rail weave surface and was used as a test specimen for Vickers hardness measurement. The test specimen was embedded in resin and mirror-polished, and the Vickers hardness at a depth of 0.5 mm from the rail weave surface was measured at 36 points in a 1 mm step from the top to the bottom of the rail under a load of 98 N in a 17.5 mm strip on each side in the vertical direction (total range of 35 mm) from the central rail height position (position A / 2). The mean and standard deviation were then calculated from each Vickers hardness obtained. <Propriedades de dobramento de três pontos>

[072] The specimens were collected from the rail weave from two locations, one position 17.5 mm above and one position 17.5 mm below the central rail height position (position A / 2), so as to include the rail weave surface, as illustrated in FIG. 4. Each specimen had the shape illustrated in FIG. 5, with a length L of 100 mm, a width H of 10 mm, and a thickness B of 10 mm. A notch was formed in the central L / 2 portion of the length L on the specimen surface, corresponding to the rail weave surface. The notch depth N was 0.5 mm, the notch width C was 1.0 mm, and the bottom of the notch had a radius of curvature R of 0.5 mm. Petition 870250080624, dated 08 / 09 / 2025, pages 99 / 109 28 / 29 mm.

[073] The specimen was placed with the notch facing down on supports with a support distance of 50 mm and a radius of curvature of 17 mm, and a bending dilation was applied on the opposite side of the notch using an indenter with a radius of curvature of 16 mm at a pressing speed of 0.1 mm / s. The specimens collected at the two locations above were tested and evaluated as having excellent resistance to rail weave fractures, if none of the specimens fractured at a displacement of 1.0 mm.

[074] As illustrated in Table 2, the test results for the rail materials (tests no. 1 to 39 in Table 2) of the Examples showed little variation in hardness in the surface layer of the rail weave, and all rail materials exhibited good three-point bending properties. On the other hand, the Comparative Examples (tests no. 40 to 52 in Table 2), for which the chemical composition of the rail material did not meet the set of conditions of this disclosure or for which a production method outside the scope of this disclosure was applied, fractured before reaching a predetermined displacement in the three-point bending test. INDUSTRIAL APPLICABILITY

[075] According to the present disclosure, a rail with excellent resistance to rail web fractures, together with a method for producing the same, can be provided. The rail of the present disclosure contributes to extending the service life of rails for heavy transport railways and preventing railway accidents. The rail is therefore industrially beneficial. The method for producing a rail of the present disclosure enables the stable production of the rail of the present disclosure and is therefore industrially beneficial. LIST OF REFERENCE SIGNS Petition 870250080624, dated 08 / 09 / 2025, pages 100 / 109 29 / 29 Rail Rail head (head) Rail pattern (weave) Rail base (base) Petition 870250080624, dated 08 / 09 / 2025, pages 101 / 109

Claims

1 / 2 CLAIMS 1. Rail, characterized in that it comprises: a chemical composition containing C: 0.70% by mass to 1.20% by mass, Si: 0.10% by mass to 1.20% by mass, Mn: 0.10% by mass to 1.50% by mass, P: 0.035% by mass or less, S: 0.020% by mass or less, and Cr: 0.05% by mass to 1.80% by mass, with an equilibrium consisting of Fe and unavoidable impurities, wherein, when a Vickers hardness at a depth of 0.5 mm from the surface of a rail weave is measured in a range of ±17.5 mm above and below a central rail height position, an average Vickers hardness value is Hv280 or more with a standard deviation of 5 or less.

2. Rail, according to claim 1, characterized in that the chemical composition further comprises at least one selected from the group consisting of V: ​​0.30% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Nb: 0.05% by mass or less, Mo: 2.0% by mass or less, Al: 0.07% by mass or less, W: 1.0% by mass or less, Co: 1.0% by mass or less, B: 0.005% by mass or less, Ti: 0.05% by mass or less, Petition 870250080624, dated 08 / 09 / 2025, p. 102 / 109 2 / 2 Sb: 0.05% by mass or less, Mg: 0.01% by mass or less, Ca: 0.02% by mass or less, and Sn: 0.05% by mass or less.

3. Method for producing the rail defined in claim 1 or 2, characterized in that it comprises: when producing a rail by hot rolling of a steel material having the chemical composition defined in claim 1 or 2, the cooling after hot rolling is carried out so that an average cooling rate for the rail web is from 0.4 °C / s to 5.0 °C / s from an initial cooling temperature of 750 °C or more to a cooling stop temperature of 450 °C to 650 °C at each position between the central rail height position, a position 20 mm above the central rail height position and a position 20 mm below the central rail height position, and so that a difference in the average cooling rate at each position is within 0.5 °C / s. Petition 870250080624, dated 08 / 09 / 2025, pp. 103 / 109

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