A hot-rolled steel rail with high yield strength ratio and its preparation method

Abstract

This invention belongs to the technical field of rail materials and discloses a hot-rolled rail with a high yield strength ratio and its preparation method. The method includes: subjecting the billet obtained by continuous casting to a five-stage step heating process; the first stage heating temperature is 500–750℃, and the heating time is ≥30 minutes; the second stage heating temperature is 750–950℃, and the heating time is ≥30 minutes; the third stage heating temperature is 950–1100℃, and the heating time is ≥30 minutes; the fourth stage heating temperature is 1100–1200℃, and the heating time is ≥30 minutes; the fifth stage heating temperature is... The temperature is 1200–1250℃, and the heating time is ≥30 minutes over a period of 60 minutes. The heated billet is then continuously and closely rolled into rails using a 7-stand rolling mill (BD1+BD2+UR1E1+UR2E2+UF, where UR1E1, UR2E2, and UF are closely spaced). The rails are then cooled to room temperature. The final rolling temperature at the rail head is 800–850℃, and the final rolling temperature at the rail base is 950–1000℃. During the rolling process, cooling medium is sprayed onto the rail head area. The cooled rails are then straightened. This invention effectively improves the yield strength ratio of rails.

Description

Technical Field

[0001] This invention relates to the field of rail material technology, specifically to a hot-rolled rail with a high yield strength ratio and its preparation method. Background Technology

[0002] As a critical track component directly bearing the weight of trains, rails are repeatedly subjected to train loading and impact during service. Elastic-plastic deformation occurs in the rail material approximately 8mm below the wheel contact surface. With increasing service time, this deformation gradually accumulates, creating a ratcheting effect. When the accumulated elastic-plastic deformation reaches the plastic stability limit, fine cracks will initiate inside the rail, eventually developing into fatigue damage and even rail fracture. For the widely used U71Mn and U75V hot-rolled rails, their low tensile strength and yield strength ratio of only about 0.5 make them prone to severe plastic deformation, fatigue cracks, and spalling during service.

[0003] Therefore, there is an urgent need for a hot-rolled rail with a high yield strength ratio. By increasing the yield strength of the rail, its elastic-plastic stability limit can be improved, thereby enhancing the rail's safe service performance. Summary of the Invention

[0004] The main objective of this invention is to provide a hot-rolled rail with a high yield strength ratio and a method for its preparation, so as to solve the problem of low yield strength ratio in existing rails.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] According to a first aspect of the present invention, a method for preparing a hot-rolled rail with a high yield strength ratio is provided, comprising the following steps:

[0007] S1. The billet obtained from continuous casting is subjected to a five-stage step heating process. The first stage heating temperature is 500–750℃, and the first stage heating time is ≥30 minutes; the second stage heating temperature is 750–950℃, and the second stage heating time is ≥30 minutes; the third stage heating temperature is 950–1100℃, and the third stage heating time is ≥30 minutes; the fourth stage heating temperature is 1100–1200℃, and the fourth stage heating time is ≥30 minutes; the fifth stage heating temperature is 1200–1250℃, and the fifth stage heating time is ≥60 minutes and ≥30 minutes.

[0008] S2, the billet heated by five-stage step heating is rolled into rails by a rolling mill and the rolled rails are cooled to room temperature. The final rolling temperature of the rail head is 800-850℃ and the final rolling temperature of the rail bottom is 950-1000℃. During the rolling process, cooling medium is sprayed into the rail head area.

[0009] S3, straightening the rails that have been cooled to room temperature.

[0010] According to some embodiments of the present invention, in step S1, 90 minutes ≥ first heating time ≥ 30 minutes, 90 minutes ≥ second heating time ≥ 30 minutes, 60 minutes ≥ third heating time ≥ 30 minutes, and 60 minutes ≥ fourth heating time ≥ 30 minutes.

[0011] According to some embodiments of the present invention, in step S2, the rolling mill is a seven-stand rolling mill, including a BD1 rolling mill, a BD2 rolling mill, an UR1E1 rolling mill composed of an UR1 rolling mill and an E1 rolling mill, an UR2E2 rolling mill composed of an UR2 rolling mill and an E2 rolling mill, and a UF rolling mill that perform rolling in sequence.

[0012] According to some embodiments of the present invention, the cooling medium sprayed on the rail head area during the rolling process includes: spraying the cooling medium on the rail head area during the rolling process using UR1E1 mill, UR2E2 mill, and UF mill.

[0013] According to some embodiments of the present invention, the cooling medium is high-pressure water mist.

[0014] According to some embodiments of the present invention, the chemical composition of the billet, by mass percentage, is: C: 0.65-0.80%, Si: 0.15-0.80%, Mn: 0.70-1.20%, V: ≤0.12%, P: ≤0.025%, S: ≤0.025%, Al: ≤0.004%, with the remainder being Fe and unavoidable impurities.

[0015] According to some embodiments of the present invention, in step S2, the rolled rail is naturally cooled to room temperature in air.

[0016] According to some embodiments of the present invention, in step S3, the rail cooled to room temperature is straightened using a horizontal-vertical composite straightening machine. The horizontal straightening machine of the horizontal-vertical composite straightening machine includes a first straightening roller, a second straightening roller, a third straightening roller, and a fourth straightening roller arranged sequentially in the horizontal direction in the direction of the rail head.

[0017] According to some embodiments of the present invention, the straightening reduction of the first straightening roller is 12-14 mm, the straightening reduction of the second straightening roller is 7-9 mm, the straightening reduction of the third straightening roller is 3-5 mm, and the straightening reduction of the fourth straightening roller is 0-2 mm.

[0018] According to a second aspect of the invention, a hot-rolled rail with a high yield strength ratio is provided, which is prepared using the method described in the first aspect of the invention.

[0019] By adopting the above technical solution, the present invention achieves the following technical effects:

[0020] In the method for preparing high yield strength ratio hot-rolled rails according to the present invention, by subjecting the billet obtained from continuous casting to five-stage step heating and controlling the heating temperature and time of each stage, the billet temperature can be gradually and stably increased, ensuring that the entire billet structure is fully austenitized, thus preparing for the subsequent rolling process. By using a rolling mill to roll the billet heated by the five-stage step heating and spraying cooling medium into the rail head area during the rolling process, the heat inside the rail head is consumed, while the rail bottom still retains a relatively high amount of heat. This reduces the heat difference caused by the larger volume of the rail head than the rail bottom, thereby improving the straightness of the rail before straightening caused by uneven thermal expansion and cooling rate during the subsequent cooling process. As a result, a low reduction in pressure can be used in the subsequent straightening process, solving the problem of a significant reduction in yield strength caused by straightening.

[0021] The method of this invention can effectively improve the yield strength ratio of rails, thereby increasing their elastic-plastic stability limit and achieving the goal of improving the safe service performance of rails. Specifically, rails prepared by the method of this invention, when sampled at the rail head arc in a room temperature air environment and subjected to tensile tests, exhibit a tensile strength ≥880MPa and a yield strength ratio ≥0.61. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic diagram illustrating a method for preparing a hot-rolled rail with a high yield strength ratio according to an embodiment of the present invention is shown.

[0024] Figure 2 A schematic diagram of a rolling mill unit according to an embodiment of the present invention is shown;

[0025] Figure 3 A schematic diagram of a horizontal straightening machine according to an embodiment of the present invention is shown;

[0026] Figure 4 The sampling area on the rail is shown in the tensile test according to an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0028] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0029] According to a first aspect of the present invention, a method for preparing a hot-rolled rail with a high yield strength ratio is provided. For example... Figure 1 As shown, the method includes the following steps:

[0030] S1. The billet obtained from continuous casting is subjected to a five-stage step heating process. The first stage heating temperature is 500–750℃, and the first stage heating time is ≥30 minutes; the second stage heating temperature is 750–950℃, and the second stage heating time is ≥30 minutes; the third stage heating temperature is 950–1100℃, and the third stage heating time is ≥30 minutes; the fourth stage heating temperature is 1100–1200℃, and the fourth stage heating time is ≥30 minutes; the fifth stage heating temperature is 1200–1250℃, and the fifth stage heating time is ≥60 minutes and ≥30 minutes.

[0031] S2, the billet heated by five-stage step heating is rolled into rails by a rolling mill and the rolled rails are cooled to room temperature. The final rolling temperature of the rail head is 800-850℃ and the final rolling temperature of the rail bottom is 950-1000℃. During the rolling process, cooling medium is sprayed into the rail head area.

[0032] S3, straightening the rails that have been cooled to room temperature.

[0033] In the method of this invention, by subjecting the billet obtained from continuous casting to five-stage step heating, and controlling the heating temperature and time of each stage, the billet temperature can gradually and steadily rise, ensuring that the entire billet microstructure is fully austenitized, preparing for the subsequent rolling process. The fifth stage heating time is limited to ≤60 minutes to avoid overheating defects caused by prolonged high-temperature heating. In the method of this invention, by using a rolling mill to roll the billet heated in five stages and spraying cooling medium into the rail head area during rolling, the heat inside the rail head is consumed, while the rail bottom retains a relatively high level of heat. This reduces the heat difference caused by the larger volume of the rail head than the rail bottom, thereby improving the straightness of the rail before straightening caused by uneven thermal expansion during subsequent cooling. This allows for a lower reduction in pressure during the subsequent straightening process, solving the problem of a significant decrease in yield strength caused by straightening.

[0034] In the method of this invention, to meet the needs of industrial production, the billet heating adopts a step-by-step heating method, with a final target heating temperature of 1200-1250℃. Since the billet cannot be directly placed in an atmosphere of 1200℃ at room temperature, excessive temperature differences may cause problems such as billet cracking. Therefore, the method of this invention adopts segmented step-by-step heating, with the temperature control range of each segment gradually narrowing to achieve precise heating with fluctuations within 50℃. This improves production operability and ensures accurate temperature control. Fewer than five heating segments would widen the temperature control range of each segment, affecting the accuracy of temperature control; more than five heating segments would increase the operational difficulty of temperature control and impose more restrictions on objective conditions such as the production site.

[0035] It should be noted that: the "Xth stage heating temperature" mentioned in this invention refers to the temperature control temperature of that stage, i.e., the ambient temperature of the heating furnace (the ambient temperature of each stage of the heating furnace is always maintained in a relatively stable state); the "Xth stage heating time" mentioned in this invention refers to the time the billet stays in that stage of the heating furnace, including the billet heating and holding time. For example: the first stage could be where the billet enters the heating furnace at a temperature of about 50°C, and the ambient temperature of the heating furnace is 500-750°C. Taking a heating time of 30 minutes as an example, the billet can be heated from 50°C to 500-750°C in about 20 minutes, and then held at a constant temperature for the remaining 10 minutes. Thus, the billet stays in that stage of the heating furnace for a total of 30 minutes.

[0036] Preferably, in step S1, 90 minutes ≥ first heating time ≥ 30 minutes, 90 minutes ≥ second heating time ≥ 30 minutes, 60 minutes ≥ third heating time ≥ 30 minutes, and 60 minutes ≥ fourth heating time ≥ 30 minutes.

[0037] refer to Figure 2In some embodiments, the rolling mill unit is a seven-stand mill, comprising, sequentially, a BD1 mill (first roughing mill), a BD2 mill (second roughing mill), an UR1E1 mill (first universal finishing and edge-rolling mill) composed of UR1 and E1 mills, an UR2E2 mill (second universal finishing and edge-rolling mill) composed of UR2 and E2 mills, and a UF mill (final mill). Each of the BD1, BD2, E1, and E2 mills includes a pair of horizontal rolls, while each of the UR1, UR2, and UF mills includes a pair of horizontal rolls and a pair of vertical rolls. These mills are arranged in a continuous, compact layout. The seven-stand mill is used to perform short-process rolling of the billet heated by a five-stage walking beam. During the rolling processes of the UR1E1, UR2E2, and UF mills, cooling media is sprayed onto the rail head area. Short-process rolling allows the rail to maintain a high temperature after BD1 and BD2 rolling for continuous, close rolling on three mills: UR1E1, UR2E2, and UF. During this process, cooling medium is sprayed onto the rail head area to dissipate internal heat, while the rail base retains a relatively high temperature. This reduces the heat difference caused by the larger volume of the rail head compared to the rail base, thereby improving the straightness of the rail before straightening caused by uneven thermal expansion during subsequent natural cooling. Preferably, the cooling medium is high-pressure water mist.

[0038] Preferably, in step S2, the rolled rail is allowed to cool naturally to room temperature in air.

[0039] Preferably, in some embodiments, in step S3, a horizontal-vertical composite straightening machine is used to straighten the rails cooled to room temperature. The horizontal-vertical composite straightening machine mainly consists of a horizontal straightening machine and a vertical straightening machine. The horizontal straightening machine is used to straighten the head and bottom of the rails, and the vertical straightening machine is used to straighten the sides of the rails. Figure 3 As shown, the horizontal straightening machine of the combined horizontal and vertical straightening machine includes a first straightening roller, a second straightening roller, a third straightening roller, and a fourth straightening roller arranged sequentially in the horizontal direction along the rail head. The straightening reduction of the first straightening roller is 12-14 mm, the second straightening roller is 7-9 mm, the third straightening roller is 3-5 mm, and the fourth straightening roller is 0-2 mm. Because the straightness of the rail is relatively high before straightening, a low reduction can be used, solving the problem of a significant decrease in yield strength caused by straightening.

[0040] In some embodiments, the chemical composition of the billet, by mass percentage, is: C: 0.65-0.80%, Si: 0.15-0.80%, Mn: 0.70-1.20%, V: ≤0.12%, P: ≤0.025%, S: ≤0.025%, Al: ≤0.004%, with the remainder being Fe and unavoidable impurities. By designing such a chemical composition, the yield strength ratio of hot-rolled rails can be further improved. In particular, by combining specific production processes with the chemical composition, the yield strength ratio of hot-rolled rails can be significantly improved.

[0041] The following explains why the content of the main chemical elements in the billet described in this invention is limited to the above-mentioned range.

[0042] Carbon (C) is the most important element for achieving a good balance of strength and toughness and overall mechanical properties in steel. Under the conditions of the rail manufacturing method described in this invention, when the carbon content is below 0.65%, the strengthening effect cannot be fully realized, leading to insufficient rail strength; when the carbon content is above 0.80%, the rail's toughness and plasticity decrease, and its fatigue resistance deteriorates. Therefore, this invention limits the carbon content to the range of 0.65-0.80%.

[0043] Silicon (Si) is typically dissolved in ferrite in steel, which can improve the material's strength and wear resistance. Under the rail manufacturing method described in this invention, when the silicon content is below 0.15%, the rail's strength and wear resistance cannot meet the requirements of railway line service. Furthermore, silicon is a crack-sensitive element in rail steel; a content above 0.80% can easily lead to fatigue cracks inside the rail. Therefore, this invention limits the silicon content to the range of 0.15-0.80%.

[0044] Manganese (Mn) plays a role in improving the hardenability of steel. Under the conditions of the rail preparation method described in this invention, when the manganese content is below 0.70%, the hardenability of the rail is insufficient, and the strength of the finished rail cannot meet the service requirements of the line; when the manganese content is above 1.20%, the hardenability of the rail is too strong, and heat treatment will cause abnormal structures such as martensite. Therefore, this invention limits the manganese content to the range of 0.70-1.20%.

[0045] Vanadium (V) in steel mainly reacts with carbon and nitrogen to form carbonitrides, which inhibit grain growth and improve the strength and toughness of rails. However, excessive vanadium content can affect weldability and reduce the plasticity of the rails. Therefore, this invention limits the vanadium content to ≤0.12%.

[0046] Phosphorus (P), sulfur (S), and aluminum (Al) are harmful elements in rail steel, causing hot brittleness and cold brittleness, and may also form inclusions, reducing the performance of the rail. Therefore, the content of these three elements is limited to a low range.

[0047] According to a second aspect of the invention, a hot-rolled rail with a high yield strength ratio is provided, which is prepared using the method described in the first aspect of the invention.

[0048] refer to Figure 4 Tensile tests can be performed on samples taken from the rail head arc to measure the tensile strength and yield strength of the rail material, thereby evaluating the yield-to-tensile ratio. In some embodiments, tensile tests are performed on samples taken from the rail head arc in a room temperature air environment, with a tensile strength ≥880MPa and a yield-to-tensile ratio ≥0.61.

[0049] This high yield strength ratio hot-rolled steel rail is suitable for lines with low axle loads, such as subways and passenger dedicated lines.

[0050] The present invention will now be described in detail through specific embodiments.

[0051] Example 1

[0052] The method for preparing hot-rolled rails with high yield strength ratio includes the following steps:

[0053] The first step involves subjecting the slab obtained from continuous casting to a five-stage step heating process: the first stage heating temperature is 500–750℃, and the heating time is 30 minutes; the second stage heating temperature is 750–950℃, and the heating time is 30 minutes; the third stage heating temperature is 950–1100℃, and the heating time is 30 minutes; the fourth stage heating temperature is 1100–1200℃, and the heating time is 30 minutes; the fifth stage heating temperature is 1200–1250℃, and the heating time is 30 minutes. The chemical composition of the slab, by mass percentage, is: C: 0.65%, Si: 0.15%, Mn: 0.70%, V: 0.12%, P: 0.025%, S: 0.025%, Al: 0.004%, with the remainder being Fe and unavoidable impurities.

[0054] The second step involves short-process rolling of the cast billet using a five-stage walking beam heating system. The mill layout is BD1+BD2+UR1E1, UR2E2, and UF (continuous and compact layout). During the rolling processes of UR1E1, UR2E2, and UF, high-pressure water mist is sprayed onto the rail head area. The final rolling temperature of the rail head is controlled at 800℃, and the final rolling temperature of the rail bottom is controlled at 950℃. The rail is then allowed to cool naturally to room temperature in the air.

[0055] The third step is to straighten the rails that have cooled to room temperature using a flat and vertical composite straightening machine. The vertical straightening reduction is as follows: 12mm for the first roller, 7mm for the second roller, 3mm for the third roller, and 0mm for the fourth roller.

[0056] The obtained hot-rolled steel rail was subjected to a tensile test at the rail head arc position in a room temperature air environment. The tensile strength was 894 MPa and the yield strength ratio was 0.61.

[0057] Example 2

[0058] The method for preparing hot-rolled rails with high yield strength ratio includes the following steps:

[0059] The first step involves subjecting the slab obtained from continuous casting to a five-stage step heating process: the first stage heating temperature is 500–750℃, and the heating time is 30 minutes; the second stage heating temperature is 750–950℃, and the heating time is 30 minutes; the third stage heating temperature is 950–1100℃, and the heating time is 30 minutes; the fourth stage heating temperature is 1100–1200℃, and the heating time is 30 minutes; the fifth stage heating temperature is 1200–1250℃, and the heating time is 60 minutes. The chemical composition of the slab, by mass percentage, is: C: 0.80%, Si: 0.80%, Mn: 1.20%, V: 0.10%, P: 0.020%, S: 0.020%, Al: 0.003%, with the remainder being Fe and unavoidable impurities.

[0060] The second step involves short-process rolling of the cast billet using a five-stage walking beam heating system. The mill layout is BD1+BD2+UR1E1, UR2E2, and UF (continuous and compact layout). During the rolling processes of UR1E1, UR2E2, and UF, high-pressure water mist is sprayed onto the rail head area. The final rolling temperature of the rail head is controlled at 850℃, and the final rolling temperature of the rail bottom is controlled at 1000℃. The rail is then allowed to cool naturally to room temperature in the air.

[0061] The third step is to straighten the rails that have cooled to room temperature using a combined flat and vertical straightening machine. The vertical straightening reduction is as follows: 14mm for the first roller, 9mm for the second roller, 5mm for the third roller, and 2mm for the fourth roller.

[0062] The obtained hot-rolled steel rail was subjected to a tensile test at the rail head arc position in a room temperature air environment. The tensile strength was 905 MPa and the yield strength ratio was 0.65.

[0063] Example 3

[0064] The method for preparing hot-rolled rails with high yield strength ratio includes the following steps:

[0065] The first step involves subjecting the slab obtained from continuous casting to a five-stage step heating process: the first stage heating temperature is 500–750℃, and the heating time is 30 minutes; the second stage heating temperature is 750–950℃, and the heating time is 30 minutes; the third stage heating temperature is 950–1100℃, and the heating time is 30 minutes; the fourth stage heating temperature is 1100–1200℃, and the heating time is 30 minutes; the fifth stage heating temperature is 1200–1250℃, and the heating time is 60 minutes. The chemical composition of the slab, by mass percentage, is: C: 0.72%, Si: 0.48%, Mn: 0.95%, V: 0.08%, P: 0.015%, S: 0.015%, Al: 0.002%, with the remainder being Fe and unavoidable impurities.

[0066] The second step involves short-process rolling of the cast billet using a five-stage walking beam heating system. The mill layout is BD1+BD2+UR1E1, UR2E2, and UF (continuous and compact layout). During the rolling processes of UR1E1, UR2E2, and UF, high-pressure water mist is sprayed onto the rail head area. The final rolling temperature of the rail head is controlled at 825℃, and the final rolling temperature of the rail bottom is controlled at 975℃. The rail is then allowed to cool naturally to room temperature in the air.

[0067] The third step is to straighten the rails that have cooled to room temperature using a flat and vertical composite straightening machine. The vertical straightening reduction is as follows: 13mm for the first roller, 8mm for the second roller, 4mm for the third roller, and 1mm for the fourth roller.

[0068] The obtained hot-rolled steel rail was subjected to a tensile test at the rail head arc position in a room temperature air environment. The tensile strength was 917 MPa and the yield strength ratio was 0.68.

[0069] Comparative Example 1

[0070] It is basically the same as Example 1, except that it does not use a five-stage step heating method, but uses a three-stage heating method to heat to 1250°C. The first stage heating temperature is 500-850°C and the heating time is 60 minutes; the second stage heating temperature is 850-1150°C and the heating time is 55 minutes; the third stage heating temperature is 1150-1250°C and the heating time is 45 minutes.

[0071] The obtained hot-rolled steel rail was subjected to tensile testing at the rail head arc position in a room temperature air environment. The tensile strength was 900 MPa and the yield strength ratio was 0.52.

[0072] Comparative Example 2

[0073] It is basically the same as Example 1, except that high-pressure water mist was not sprayed into the rail head area during the UR1E1, UR2E2, and UF rolling processes.

[0074] The obtained hot-rolled steel rail was subjected to a tensile test at the rail head arc position in a room temperature air environment. The tensile strength was 920 MPa and the yield strength ratio was 0.51.

[0075] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method of producing a hot-rolled rail having a high ratio of yield strength to tensile strength, characterised in that, The method comprises the following steps: S1, the cast blank obtained by smelting and continuous casting is subjected to five-stage step heating, the first-stage heating temperature is 500-750 DEG C, the first-stage heating time is greater than or equal to 30 minutes; the second-stage heating temperature is 750-950 DEG C, the second-stage heating time is greater than or equal to 30 minutes; the third-stage heating temperature is 950-1100 DEG C, the third-stage heating time is greater than or equal to 30 minutes; the fourth-stage heating temperature is 1100-1200 DEG C, the fourth-stage heating time is greater than or equal to 30 minutes; the fifth-stage heating temperature is 1200-1250 DEG C, the fifth-stage heating time is greater than or equal to 30 minutes and less than or equal to 60 minutes; S2, the cast blank subjected to the five-stage step heating is rolled into a steel rail by using a rolling mill set, and the rolled steel rail is naturally cooled to room temperature in air, the rail head finish rolling temperature of the steel rail is 800-850 DEG C, the rail bottom finish rolling temperature of the steel rail is 950-1000 DEG C, the rolling mill set is a seven-stand rolling mill, which comprises BD1 rolling mill, BD2 rolling mill, UR1E1 rolling mill composed of UR1 rolling mill and E1 rolling mill, UR2E2 rolling mill composed of UR2 rolling mill and E2 rolling mill, and UF rolling mill, which are sequentially arranged for rolling, and a cooling medium is sprayed to the rail head area during the rolling process by using the UR1E1 rolling mill, the UR2E2 rolling mill and the UF rolling mill; S3, the steel rail cooled to room temperature is straightened by using a flat-stand combined straightening machine, the horizontal straightening machine of the flat-stand combined straightening machine comprises first straightening roll, second straightening roll, third straightening roll and fourth straightening roll which are sequentially arranged in the horizontal direction at the direction of the rail head, the straightening reduction of the first straightening roll is 12-14 mm, the straightening reduction of the second straightening roll is 7-9 mm, the straightening reduction of the third straightening roll is 3-5 mm, and the straightening reduction of the fourth straightening roll is 0-2 mm.

2. The method of claim 1, wherein, In step S1, the first-stage heating time is greater than or equal to 30 minutes and less than or equal to 90 minutes, the second-stage heating time is greater than or equal to 30 minutes and less than or equal to 90 minutes, the third-stage heating time is greater than or equal to 30 minutes and less than or equal to 60 minutes, and the fourth-stage heating time is greater than or equal to 30 minutes and less than or equal to 60 minutes.

3. The method of claim 1, wherein, The cooling medium is high-pressure water mist.

4. The method of claim 1, wherein, The chemical composition of the cast blank, by mass percentage, is C: 0.65-0.80%, Si: 0.15-0.80%, Mn: 0.70-1.20%, V: ≤0.12%, P: ≤0.025%, S: ≤0.025%, Al: ≤0.004%, and the rest is Fe and inevitable impurities.

5. A hot-rolled steel rail with high yield ratio, which is prepared by the method according to any one of claims 1-4.

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