Pearlitic steel rail having tensile strength uniformly distributed in full cross-section, and production method therefor

Abstract

Disclosed in the present invention are a pearlitic steel rail having tensile strength uniformly distributed in the full cross-section, and a production method therefor. The method comprises: subjecting a rolled steel rail to an on-line heat treatment, the on-line heat treatment comprising: an accelerated cooling stage, wherein once the temperature of the top surface of the steel rail that has been subjected to finish rolling is between 680°C and 810°C, different portions of the steel rail are separately subjected to accelerated cooling until the temperature of the top surface of the rail is 480-590°C, the cooling rate of the top surface of the rail being 2.0-5.0°C / s, the cooling rate of the two sides of the rail head being 1.5-4.0°C / s, the cooling rate of the two sides of the upper portion of the rail web being 1.0-3.0°C / s, the cooling rate of the two sides of the middle portion of the rail web being 0.8-2.5°C / s, and the cooling rate of the center of the rail foot being 1.5-3.0°C / s; and an air cooling stage, wherein the steel rail that has undergone the accelerated cooling stage is air-cooled to room temperature. In the present invention, the pearlitic steel rail having tensile strength uniformly distributed in the full cross-section can be prepared without the need for adding a variety of microalloying elements, and the service performance of the steel rail is improved.

Description

Pearlite rail with uniform tensile strength distribution over the entire section and production method thereof Technical Field

[0001] The present invention relates to the technical field of rail production, and in particular to a pearlite rail with uniform tensile strength distribution over the entire cross section and a production method thereof. Background Art

[0002] As high-speed and heavy-haul railways develop in a more specialized direction, the existing railway network is also facing further upgrades and renovations, moving towards high speed and high efficiency, which places higher demands on rails. At the same time, due to the overall development of the railway network, the railway operating environment has gradually become more complex, resulting in the overall rail material being more susceptible to surface and shallow surface damage in various locations during transportation, storage, and service. Surface damage to the rails will have a negative impact on their service life and safety. Therefore, only by using rails with higher tensile strength across the entire section can the stability of the rails throughout their life cycle be guaranteed and the transportation efficiency of the railway be improved.

[0003] In recent years, domestic and foreign rail manufacturers have mainly adopted offline or online heat treatment to improve the hardness of rails. This method accelerates the cooling of the rail head, thereby refining the pearlite structure of the rail head and achieving higher strength and hardness by refining the grain size. The relevant patented technologies involved are as follows:

[0004] Patent CN116371908 "A Rolling Method for American Standard Medium-Strength Rails" discloses a rail with a tensile strength ≥1065MPa, a yield strength ≥723MPa, an elongation ≥10%, and a rail tread hardness ≥350HB after heat treatment. The chemical composition of the rail, calculated by mass percentage, includes: C: 0.70-0.85; Si: 0.30-0.57; Mn 0.9-1.18; P ≤ 0.020; S ≤ 0.020; Cr: 0.10-0.3; the remainder is Fe and unavoidable impurities. This rail has high internal hardness and tensile strength within the depth range of 0 to 25 mm, but the hardness difference between the rail waist and the rail bottom reaches 3 to 4 HRC. It can be seen that its tensile strength difference is also large, which makes it susceptible to external trauma and rail damage during use. At the same time, the large difference in tensile strength between the rail waist and the rail bottom may cause transverse cracks at this position after being subjected to external force, resulting in rail breakage and affecting the service safety of the rail.

[0005] Patent CN102220545 "High-carbon, high-strength heat-treated rail with excellent wear resistance and plasticity and its manufacturing method" discloses a high-carbon, high-strength heat-treated rail with excellent wear resistance and plasticity performance, with a rail head tensile strength ≥1330MPa, elongation ≥9%, rail head hardness ≥380HB, and a hardened layer depth of more than 25mm. Its chemical composition, by weight percentage, includes: C: 0.80% to 1.20%, Si: 0.20% to 1.20%, Mn: 0.20% to 1.60%, Cr: 0.15% to 1.20%, V: 0.01% to 0.20%, Ti: 0.002% to 0.050%, P≤0.030%, S≤0.030%, Al≤0.010%, N≤0.0100%, and the rest is Fe and unavoidable impurities. However, during the production process of this rail, only the rail head and rail bottom were strengthened by online heat treatment, and no strengthening measures were taken for the rail waist, which is most susceptible to damage by external forces.

[0006] Patent CN104060075 "Heat Treatment Method for Increasing the Depth of the Hardened Layer of Rails" discloses a heat treatment method for naturally cooling the rail after final rolling to a center temperature of 660-730°C on the rail head and tread, accelerating the cooling at a cooling rate of 1.5-3.5°C / s to a center temperature of 500-550°C on the rail head and tread, and then increasing the cooling rate by 1.0-2.0°C / s. When the center temperature of the rail head and tread drops below 450°C, the accelerated cooling is stopped and the rail is air-cooled to room temperature. This method can achieve a deep hardened layer of more than 25mm at the rail head, and the 25mm below the surface of the rail head has a hardness value equivalent to that of the rail head surface. In addition, the entire cross-section of the rail head is pearlite, which is beneficial to improving the service performance of the rail after continuous wear due to wheel-rail contact. However, the heat treatment method described in this patent only improves the hardness and tensile strength of the rail head, and does not take into account the simultaneous improvement of the hardness and tensile strength of the rail waist and rail bottom.

[0007] It can be seen that among the current patents related to improving the tensile strength of pearlite rails, some patents can improve the fillet on the rail head and the tensile strength of the rail top surface, but none of them involve uniformly improving the tensile strength of the rail waist and rail bottom. There are still obvious shortcomings in improving the actual service performance of the rails.

[0008] Summary of the Invention

[0009] The main purpose of the present invention is to provide a pearlite rail with uniform tensile strength distribution across the entire cross-section and a production method thereof, so as to solve the technical problem that the prior art fails to comprehensively improve the tensile strength of the rail.

[0010] According to one aspect of the present invention, a method for producing a pearlite rail having uniform tensile strength distribution across the entire cross-section is provided, comprising: performing an online heat treatment on the rolled rail, wherein the online heat treatment adopts a section-by-section accelerated cooling process, comprising:

[0011] Accelerated cooling stage: When the rail top surface temperature after final rolling is between 680 and 810°C, accelerated cooling is carried out in sections until the rail top surface temperature reaches 480-590°C; the cooling rate of the rail top surface is 2.0-5.0°C / s, the cooling rate of both sides of the rail head is 1.5-4.0°C / s, the cooling rate of both sides of the upper rail waist is 1.0-3.0°C / s, the cooling rate of both sides of the middle rail waist is 0.8-2.5°C / s, and the cooling rate of the center of the rail bottom is 1.5-3.0°C / s;

[0012] Air cooling stage: the rails that have undergone the accelerated cooling stage are air-cooled to room temperature.

[0013] According to one embodiment of the present invention, the cooling speed of the rail top surface, the cooling speed on both sides of the rail head, the cooling speed on both sides of the upper part of the rail waist, and the cooling speed on both sides of the middle part of the rail waist are reduced in sequence.

[0014] According to one embodiment of the present invention, during the accelerated cooling stage, when the rail top surface temperature of the rail after final rolling is between 740°C and 800°C, accelerated cooling is performed in sections until the rail top surface temperature is between 490°C and 560°C.

[0015] According to one embodiment of the present invention, during the accelerated cooling stage, the cooling rate of the rail top surface is 3.3-4.3°C / s, the cooling rate on both sides of the rail head is 2.9-3.7°C / s, the cooling rate on both sides of the upper rail waist is 2.4-3.0°C / s, the cooling rate on both sides of the middle rail waist is 1.5-2.1°C / s, and the cooling rate at the center of the rail bottom is 1.8-2.5°C / s.

[0016] According to one embodiment of the present invention, when performing the online heat treatment, the cooling medium used is water mist and / or compressed air.

[0017] According to one embodiment of the present invention, before performing the online heat treatment, the method further comprises: sequentially performing converter smelting, LF furnace refining, RH vacuum treatment, continuous casting, and rolling.

[0018] According to one embodiment of the present invention, the chemical composition of the steel rail is, by weight percentage, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: ≤0.025%, S: ≤0.020%, and the balance is Fe and unavoidable impurities.

[0019] According to another aspect of the present invention, a pearlite rail having uniform tensile strength distribution across its entire cross-section is provided. The rail has the following chemical composition, by weight percentage: C: 0.65-0.82%, Si: 0.10-0.60%, Mn: 0.65-1.25%, Cr: 0.05-0.25%, Mn+Cr: 0.75-1.50%, Mn / Cr: 7.0-10.0%, P: ≤0.030%, S: ≤0.025%, with the remainder being Fe and unavoidable impurities. The rail has a tensile strength of ≥1080 MPa at the fillet on the rail head, the center of the rail head, the center of the rail waist, and the center of the rail foot, with the difference being less than 80 MPa.

[0020] According to one embodiment of the present invention, the tensile strength of the rounded corners on the rail head of the steel rail is ≥1180 MPa, and the elongation is ≥10.0%; the hardness of the rail top surface is 350-390 HB; the tensile strength of the center of the rail head, the center of the rail waist, and the center of the rail bottom are all ≥1080 MPa, and the elongation is ≥10.0%.

[0021] According to one embodiment of the present invention, the chemical composition of the steel rail is, by weight percentage, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: ≤0.025%, S: ≤0.020%, and the balance is Fe and unavoidable impurities.

[0022] Through the technical solution of the present invention, pearlite rails with uniform tensile strength distribution across the entire cross-section can be prepared without adding multiple microalloying elements. This can improve the rails' ability to resist external damage during transportation, storage, and service, significantly reduce the negative impact of external damage on the rails' service performance, and extend the rails' service life and safety, thereby improving the overall transportation efficiency and safety of railways. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] FIG1 is a schematic diagram showing accelerated cooling and tensile strength testing of a rail with uniform tensile strength distribution over the entire cross section according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0026] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. Subsequent embodiments will not explain this one by one.

[0027] The present invention provides a method for producing a pearlite rail with uniform tensile strength distribution across the entire cross-section, comprising: performing an online heat treatment on the rolled rail, wherein the online heat treatment comprises:

[0028] Accelerated cooling stage: When the rail top surface temperature after final rolling is between 680 and 810°C, accelerated cooling is carried out in different parts until the rail top surface temperature reaches 480-590°C. The cooling rate of the rail top surface is 2.0-5.0°C / s, the cooling rate of both sides of the rail head is 1.5-4.0°C / s, the cooling rate of both sides of the upper rail waist is 1.0-3.0°C / s, the cooling rate of both sides of the middle rail waist is 0.8-2.5°C / s, and the cooling rate of the center of the rail bottom is 1.5-3.0°C / s. Figure 1 shows the accelerated cooling of various parts.

[0029] Air cooling stage: the rails that have undergone the accelerated cooling stage are air cooled to room temperature on a cooling bed.

[0030] The inventors of the present invention have found through extensive research that:

[0031] ① For the accelerated cooling stage: When the rail head and tread temperature is 680-810℃, in order to inhibit the precipitation of proeutectoid ferrite or proeutectoid cementite in the rail and obtain a rail with higher tensile strength, it is necessary to accelerate the cooling in the high temperature stage. At the same time, since the cross-sectional area of ​​the rail top is the largest, followed by the two sides of the rail head, the upper part of the rail waist and the center of the rail bottom, and the cross-sectional area of ​​the rail waist center is the smallest, it is necessary to control the accelerated cooling rate of different parts to be different so that the tensile strength of each part is more evenly distributed. The cooling rate of the rail top should be the largest, controlled in the range of 2.0-5.0℃ / s, while the cooling rates of the two sides of the rail head, the two sides of the upper part of the rail waist, and the two sides of the center of the rail waist decrease in sequence, controlled in the range of 1.5-4.0℃ / s, 1.0-3.0℃ / s, and 0.8-2.5℃ / s respectively. The cross-sectional area of ​​the center of the rail bottom is between the two sides of the rail head and the two sides of the upper part of the rail waist, and the cooling rate is controlled in the range of 1.5-3.0℃ / s.

[0032] ② Regarding the air cooling stage: After the rail is cooled to 480-590℃ in the accelerated cooling stage, the pearlite phase transformation has been completed in all parts of the rail. At this time, there is no obvious meaning in continuing the accelerated cooling. The rail can be air-cooled to room temperature for subsequent processing.

[0033] In some embodiments, during the accelerated cooling stage, when the rail top surface temperature of the rail after final rolling is between 740°C and 800°C, accelerated cooling is performed in sections until the rail top surface temperature is between 490°C and 560°C.

[0034] In some embodiments, during the accelerated cooling stage, the cooling rate of the rail top surface is 3.3-4.3°C / s, the cooling rate on both sides of the rail head is 2.9-3.7°C / s, the cooling rate on both sides of the upper rail waist is 2.4-3.0°C / s, the cooling rate on both sides of the middle rail waist is 1.5-2.1°C / s, and the cooling rate on the center of the rail bottom is 1.8-2.5°C / s.

[0035] In some embodiments, when performing the online heat treatment, the cooling medium used is water mist and / or compressed air.

[0036] In some embodiments, prior to performing the online heat treatment, the method further comprises sequentially performing converter smelting, LF furnace refining, RH vacuum treatment, continuous casting, and rolling. After the online heat treatment, the rails may be processed. In some embodiments, the complete rail production process may include: using low-sulfur, vanadium-containing molten steel, smelting in a converter or electric furnace, LF refining, RH or VD vacuum treatment, continuous casting of large square billets, heating in a billet heating furnace, high-pressure water descaling before billet rolling, rolling on a universal rolling mill, online heat treatment of the rails, room temperature air cooling on a walking beam cooling bed, horizontal and vertical composite straightening, rail specification inspection, processing on the processing line, surface inspection, and storage.

[0037] In some embodiments, the chemical composition of the steel rail is, by weight percentage, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: ≤0.025%, S: ≤0.020%, and the balance is Fe and unavoidable impurities.

[0038] The reasons for limiting the contents of the main chemical elements in the rails of the present invention are described in detail below.

[0039] Carbon is the most important and inexpensive element in pearlite rails, ensuring excellent overall mechanical properties and promoting pearlite transformation. When the carbon content is less than 0.65%, the production process described herein cannot guarantee the rail's appropriate hardness or resistance to external damage. When the carbon content is greater than 0.82%, the rail's strength is excessive, while its toughness and ductility are too low, resulting in an excessively high carbide content, which affects the rail's toughness and ductility, adversely affecting its safe use. Therefore, the carbon content in this invention is limited to 0.65-0.82%.

[0040] Si's primary function in steel is to inhibit cementite formation and, as a solid-solution strengthening element, increase the hardness of the ferrite matrix, improving the steel's strength and hardness. When the Si content is less than 0.10%, its solid solution content is too low, resulting in a less pronounced strengthening effect. When the Si content is greater than 0.60%, localized segregation is likely to occur, reducing the steel's toughness and ductility, adversely affecting the safe use of the rail. Therefore, the Si content in the present invention is limited to 0.10-0.60%.

[0041] Mn is essential for increasing the strength of ferrite and austenite in steel. When the Mn content is less than 0.65%, it fails to increase the hardness of carbides and, therefore, the strength of the steel. When the Mn content is greater than 1.25%, it coarsens the grain size, significantly reducing the toughness and ductility of the steel. Furthermore, Mn significantly affects the diffusion of carbon in steel, potentially creating abnormal structures such as bainite or martensite in Mn segregation areas, which in turn affects the weldability of the rail. Therefore, the Mn content in this invention is limited to 0.65-1.25%.

[0042] As a carbide-forming element, Cr forms a variety of carbides with carbon in steel. Cr also evens out the distribution of carbides in steel, reducing their size, increasing the rail's strength and hardness, and improving its wear resistance. When the Cr content is less than 0.05%, the hardness and proportion of the carbides formed are relatively low. When the Cr content is greater than 0.25%, the rail's hardenability is excessively high, which can lead to the formation of harmful bainite and martensite structures, making it impossible to maintain a pearlite structure, adversely affecting the rail's safe use. Therefore, the Cr content in the present invention is limited to 0.05-0.25%.

[0043] Because both Mn and Cr are strengthening elements that increase the hardness and hardenability of rails, their combined content needs to be limited to prevent the appearance of abnormal structures such as martensite in the rail microstructure and ensure that the finished rail performance meets the required specifications. When the Mn+Cr content is less than 0.75%, it is difficult to provide sufficient carbides, the strengthening effect is weak, and the rail hardness cannot be guaranteed to meet the design specifications. When the Mn+Cr content is greater than 1.45%, because both Mn and Cr can improve the hardenability of the rail, the risk of abnormal structures in the rail is greater. Therefore, the Mn+Cr content in the present invention is limited to 0.75-1.45%.

[0044] In rail steel, controlling the balance between Mn and Cr content is crucial for comprehensively regulating the rail's microstructure and hardness. Increasing the Mn content alone results in a more stable rail microstructure, but lowers internal hardness. Increasing the Cr content improves internal hardness, but is more susceptible to abnormal microstructure. When Mn / Cr is less than 7.0, the rail's high Cr content achieves higher hardness but carries a greater risk of abnormal microstructure. When Mn / Cr is greater than 10.0, the rail's high Mn content maintains a fully pearlite microstructure, but lowers internal hardness. Therefore, in the present invention, the Mn / Cr value is limited to 7.0 to 10.0.

[0045] Both phosphorus (P) and sulfur (S) are impurity elements that cannot be completely removed from rails. P will segregate at the grain boundaries of the rail structure, severely reducing the rail's toughness. S easily forms MnS inclusions in steel, which are detrimental to the rail's wear resistance and contact fatigue resistance. Therefore, the P content in this invention must be controlled below 0.030%, and the S content must be controlled below 0.030%.

[0046] The present invention also provides a pearlite rail with uniform tensile strength distribution across the entire cross-section. The rail is prepared using the above method. The chemical composition of the rail, measured in weight percentage, is as follows: C: 0.65-0.82%, Si: 0.10-0.60%, Mn: 0.65-1.25%, Cr: 0.05-0.25%, Mn+Cr: 0.75-1.50%, Mn / Cr: 7.0-10.0%, P: ≤0.030%, S: ≤0.025%, with the remainder being Fe and unavoidable impurities. The tensile strength of the rail head fillet, the center of the rail head, the center of the rail waist, and the center of the rail base of the rail is all ≥1080 MPa, and the difference is <80 MPa. Figure 1 shows a schematic diagram of tensile strength testing, where position ① is the tensile strength testing position for the fillet on the rail, position ② is the tensile strength testing position for the center of the rail head, position ③ is the tensile strength testing position for the center of the rail waist, and position ④ is the tensile strength testing position for the center of the rail bottom.

[0047] In some embodiments, the tensile strength of the rounded corners on the rail head is ≥1180 MPa, and the elongation is ≥10.0%; the hardness of the rail top surface is 350-390 HB; the tensile strength of the center of the rail head, the center of the rail waist, and the center of the rail bottom are all ≥1080 MPa, and the elongation is ≥10.0%.

[0048] In some embodiments, the chemical composition of the steel rail is, by weight percentage, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: ≤0.025%, S: ≤0.020%, and the balance is Fe and unavoidable impurities.

[0049] In summary, the present invention utilizes methods for controlling the chemical composition of rails and in-line heat treatment processes. The resulting pearlite rails exhibit uniformly distributed tensile strength across their entire cross-section, without the need for the addition of multiple microalloying elements. This improves the rails' resistance to external damage during transportation, storage, and service, significantly reducing the negative impact of external damage on their service performance. This increases the rails' service life and safety, thereby improving overall railway transportation efficiency and safety. Furthermore, the present invention provides a simple and easy-to-operate method for producing pearlite rails with uniform tensile strength across their entire cross-section, facilitating widespread application.

[0050] The following describes the specific embodiments.

[0051] Examples 1 to 3 and comparative examples 1 to 3 correspond to steel rails with chemical compositions numbered 1 to 3 below. The specific chemical compositions are shown in Table 1, with the remainder being Fe and unavoidable impurities.

[0052] Table 1: Rail chemical composition (wt%)

[0053] The heat treatment process parameters of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2. The differences in the smelting process and rolling process between the Examples and Comparative Examples are negligible.

[0054] Table 2: Heat treatment process parameters

[0055] The microstructure, tensile properties, and rail top surface hardness of Examples 1-3 and Comparative Examples 1-3 are shown in Table 3. The tensile strength measurement locations are shown in Figure 1: Location 1 is for testing the tensile strength of the rail fillet, Location 2 is for testing the tensile strength of the rail head center, Location 3 is for testing the tensile strength of the rail waist center, and Location 4 is for testing the tensile strength of the rail base center. Tensile specimens were taken at each location and tensile tests were performed in accordance with GB / T 228.1, "Tensile Tests on Metallic Materials - Part 1: Room Temperature Test Methods."

[0056] Table 3: Microstructure, rail top surface hardness and tensile properties

[0057] By comparing the examples and comparative examples, it can be seen that, under the same chemical composition and smelting process, the different heat treatment methods for the rolled rails in the examples of the present invention will have a significant impact on the final performance of the rails. The rail top surface hardness of the rails obtained by adopting the method of the present invention is in the range of 350 to 390 HB, and the tensile strength at the fillet on the rail head, the center of the rail head, the center of the rail waist, and the center of the rail bottom is relatively high, with a difference of less than 80 MPa and a uniform distribution. This can effectively reduce the wide-scale impact of surface and shallow surface damage on the service performance and safety of the rails. In contrast, in the comparative example, the tensile strength of the unheat-treated parts is significantly reduced, and these parts are susceptible to external damage during use, resulting in cracks and possible breakage of the rails.

[0058] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples. Within the spirit of the embodiments of the present invention, the technical features of the above embodiments or different embodiments may be combined, and there are many other variations of the different aspects of the embodiments of the present invention described above, which are not provided in detail for the sake of clarity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included within the scope of protection of the embodiments of the present invention.

Claims

1. A method for producing a pearlite rail with uniform tensile strength distribution over the entire cross section, characterized in that: include: The rolled rail is subjected to an online heat treatment, wherein the online heat treatment comprises: Accelerated cooling stage: when the rail top surface temperature after final rolling is between 680 and 810°C, accelerated cooling is carried out in different parts until the rail top surface temperature is between 480 and 590°C; among which, the cooling rate of the rail top surface is 2.0 to 5.0°C / s, the cooling rate of both sides of the rail head is 1.5 to 4.0°C / s, the cooling rate of both sides of the upper part of the rail waist is 1.0 to 3.0°C / s, the cooling rate of both sides of the middle part of the rail waist is 0.8 to 2.5°C / s, and the cooling rate of the center of the rail bottom is 1.5 to 3.0°C / s; Air cooling stage: the rails that have undergone the accelerated cooling stage are air cooled to room temperature.

2. The method according to claim 1, characterized in that The cooling rate of the rail top surface, the cooling rate on both sides of the rail head, the cooling rate on both sides of the upper part of the rail waist, and the cooling rate on both sides of the middle part of the rail waist decrease in sequence.

3. The method according to claim 1, characterized in that: In the accelerated cooling stage, when the rail top surface temperature of the steel rail after final rolling is between 740 and 800° C., accelerated cooling is performed in sections until the rail top surface temperature is between 490 and 560° C.

4. The method according to claim 1, characterized in that: During the accelerated cooling stage, the cooling rate of the rail top surface is 3.3-4.3°C / s, the cooling rate of both sides of the rail head is 2.9-3.7°C / s, the cooling rate of both sides of the upper rail waist is 2.4-3.0°C / s, the cooling rate of both sides of the middle rail waist is 1.5-2.1°C / s, and the cooling rate of the center of the rail bottom is 1.8-2.5°C / s.

5. The method according to claim 1, characterized in that When performing the online heat treatment, the cooling medium used is water mist and / or compressed air.

6. The method according to claim 1, characterized in that Before performing the online heat treatment, the method further comprises: sequentially performing converter smelting, LF furnace refining, RH vacuum treatment, continuous casting, and rolling.

7. The method according to claim 1, characterized in that The chemical composition of the rail is, in percentage by weight, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: ≤0.025%, S: ≤0.020%, and the remainder is Fe and unavoidable impurities.

8. A pearlite rail with uniform tensile strength distribution over the entire cross section, characterized in that: The chemical composition of the steel rail is, in weight percentage, C: 0.65-0.82%, Si: 0.10-0.60%, Mn: 0.65-1.25%, Cr: 0.05-0.25%, Mn+Cr: 0.75-1.50%, Mn / Cr: 7.0-10.0, P: ≤0.030%, S: ≤0.025%, and the remainder is Fe and unavoidable impurities; the tensile strength of the fillet on the rail head, the center of the rail head, the center of the rail waist, and the center of the rail bottom of the steel rail are all ≥1080MPa, and the difference is <80MPa.

9. The steel rail according to claim 8, characterized in that: The tensile strength of the rounded corners on the rail head is ≥1180MPa, and the elongation is ≥10.0%; the hardness of the rail top surface is 350-390HB; the tensile strength of the center of the rail head, the center of the rail waist, and the center of the rail bottom are all ≥1080MPa, and the elongation is ≥10.0%.

10. The steel rail according to claim 8, characterized in that: The chemical composition of the rail is, in percentage by weight, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: ≤0.025%, S: ≤0.020%, and the remainder is Fe and unavoidable impurities.

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