A medium-strength rail with high yield strength ratio and its manufacturing method

Abstract

This invention discloses a method for preparing medium-strength rails with a high yield strength ratio, comprising the following steps: subjecting the slab obtained from continuous casting to segmented step heating, wherein the heating temperature of each segment gradually increases and the heating time of each segment is ≥30 minutes; rolling the slab heated by segmented step heating using a rolling mill to produce a rail with residual heat, wherein the final rolling temperature of the rail head and rail base is controlled at 900–950°C; spraying a cooling medium on the final rolled rail head to accelerate the cooling rate and cooling it to 500–550°C; reheating the final rolled rail base to reduce the cooling rate and cooling it to 650–700°C; subsequently, allowing the rail to cool naturally in air to room temperature; and straightening the rail cooled to room temperature. Using this method, the yield strength ratio and tensile strength of the rail can be effectively improved, significantly enhancing the rail's plastic stability limit.

Description

Technical Field

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

[0002] As a critical track component directly bearing the load of trains, rails are repeatedly subjected to train loading and impact during service. At a depth of approximately 8mm below the wheel contact surface, the rail material undergoes elasto-plastic deformation. With increasing service time, this deformation gradually accumulates, creating a ratcheting effect. When the accumulated elasto-plastic deformation reaches the plastic stability limit, fine cracks will initiate inside the rail, eventually developing into rail fatigue damage and even rail fracture. This fatigue damage is particularly pronounced on lines with high axle loads and medium-strength rails.

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

[0004] To address the aforementioned technical problems, this invention proposes a medium-strength rail with a high yield strength ratio and a method for its preparation, which can solve the problem of significant fatigue damage of medium-strength rails when they are used on routes with high axle loads.

[0005] On one hand, embodiments of the present invention disclose a method for preparing a medium-strength rail with a high yield strength ratio, comprising the following steps:

[0006] The billet obtained by smelting and continuous casting is subjected to segmented step heating, wherein the heating temperature of each segment gradually increases and the heating time of each segment is ≥30 minutes.

[0007] The billet heated by segmented step heating is rolled into a rail with residual heat using a rolling mill. The final rolling temperature of the rail head and rail bottom is controlled at 900-950℃.

[0008] Cooling medium is sprayed onto the rail head after final rolling to accelerate the cooling rate and cool it to 500-550°C. The rail bottom after final rolling is reheated to reduce the cooling rate and cool it to 650-700°C. The rail is then allowed to cool naturally to room temperature in the air.

[0009] The rails, cooled to room temperature, are straightened.

[0010] According to one embodiment of the present invention, the segmented step heating is a five-segment step heating, wherein the heating temperature of the first segment is 500-750℃; the heating temperature of the second segment is 750-950℃; the heating temperature of the third segment is 950-1100℃; the heating temperature of the fourth segment is 1100-1200℃; and the heating temperature of the fifth segment is 1200-1250℃.

[0011] According to one embodiment of the present invention, the heating time range of each segment in the five-segment step heating process is as follows: 90 minutes ≥ first segment heating time ≥ 30 minutes; 90 minutes ≥ second segment heating time ≥ 30 minutes; 60 minutes ≥ third segment heating time ≥ 30 minutes; 60 minutes ≥ fourth segment heating time ≥ 30 minutes; 60 minutes ≥ fifth segment heating time ≥ 30 minutes.

[0012] According to one embodiment of the present invention, the cooling rate of the rail head after final rolling is 2 to 5 °C / s, and the cooling rate of the rail bottom after final rolling is 1 to 2.5 °C / s.

[0013] According to one embodiment of the present invention, the cooling medium is compressed air and / or water mist.

[0014] According to one embodiment of the present invention, based on the weight of the billet, the billet contains, by weight percentage: C: 0.72-0.82%, Si: 0.10-1.00%, Mn: 0.70-1.25%, Cr: 0.40-0.70%, P: ≤0.02%, S: ≤0.02%, Al: ≤0.005%, with the remainder being Fe and unavoidable impurities.

[0015] According to one embodiment of the present invention, 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.

[0016] According to one embodiment of the present invention, a rail cooled to room temperature is straightened using a horizontal-vertical composite straightening machine. The horizontal 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 one embodiment of the present invention, the horizontal straightening reduction of the first straightening roller is 13-15 mm, the horizontal straightening reduction of the second straightening roller is 8-10 mm, the horizontal straightening reduction of the third straightening roller is 4-6 mm, and the horizontal straightening reduction of the fourth straightening roller is 0-2 mm.

[0018] On the other hand, embodiments of the present invention also disclose a medium-strength rail with a high yield strength ratio, which is prepared using the method described in any one of the above embodiments.

[0019] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0020] The method for preparing high-yield-strength medium-strength rails provided by this invention involves segmented step heating of the billet obtained from continuous casting and controlling the heating time of each segment. This allows the billet temperature to gradually and steadily rise, ensuring full austenitization of the entire billet microstructure and preparing it for subsequent rolling processes. During rolling, the final rolling temperature of the rail head and bottom is controlled at 900–950°C to ensure that the microstructure of the rolled rail remains in an austenitic state, preparing it for subsequent heat treatment. During heat treatment, the steel with residual heat after rolling is... Compressed air is sprayed onto the rail head to accelerate the cooling rate and cool it to 500-550°C. The rail base of the rolled rail is heated to reduce the cooling rate and cool it to 650-700°C. Accelerating cooling at the rail head can refine the spacing between the rail head laminations, improve strength and toughness, and increase the yield strength ratio. Heating the rail base reduces its cooling rate, which can reduce the heat difference caused by the larger volume of the rail head than the rail base. This improves the straightness of the rail before straightening caused by uneven cooling rate during subsequent natural cooling, and also solves the problem of significant reduction in yield strength caused by straightening.

[0021] The method of this invention can effectively improve the yield strength ratio and tensile strength of rails, greatly improve the plastic stability limit of rails, and solve the problem of significant fatigue damage of medium-strength rails when they are used on routes with large axle loads. Rails prepared by the method of this invention, when subjected to tensile tests at the rail head arc in a room temperature air environment, have a tensile strength ≥1180MPa and a yield strength ratio ≥0.71. 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 This is a schematic flowchart of a method for preparing a medium-strength rail with a high yield strength ratio, as disclosed in an embodiment of the present invention.

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

[0025] Figure 3This is a schematic diagram of the horizontal straightening machine of the horizontal-vertical composite straightening machine according to an embodiment of the present invention;

[0026] Figure 4 The sampling area on the rail is the location for the tensile test in this embodiment of the 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] like Figure 1 As shown, according to a first aspect of the present invention, an embodiment of the present invention discloses a method for preparing a medium-strength rail with a high yield strength ratio, comprising the following steps:

[0030] S10, the billet obtained by smelting and continuous casting is subjected to segmented step heating, wherein the heating temperature of each segment gradually increases and the heating time of each segment is ≥30 minutes.

[0031] S20 is a steel rail with residual heat, which is rolled by a rolling mill using a segmented step heating billet. The final rolling temperature of the rail head and rail bottom is controlled at 900-950℃.

[0032] S30 involves spraying cooling medium onto the rail head after final rolling to accelerate the cooling rate and cool it to 500-550°C, and then reheating the rail bottom after final rolling to reduce the cooling rate and cool it to 650-700°C. The rail is then allowed to cool naturally to room temperature in the air.

[0033] S40 straightens the rails that have been cooled to room temperature.

[0034] The method for preparing high-yield-strength medium-strength rails provided by this invention involves segmented step heating of the billet obtained from continuous casting and controlling the heating time of each segment. This allows the billet temperature to gradually and steadily rise, ensuring full austenitization of the entire billet microstructure and preparing it for subsequent rolling processes. During rolling, the final rolling temperature of the rail head and bottom is controlled at 900–950°C to ensure that the microstructure of the rolled rail remains in an austenitic state, preparing it for subsequent heat treatment. During heat treatment, the rail, which retains residual heat after rolling, is... Compressed air is sprayed onto the rail head to accelerate the cooling rate and cool it to 500-550°C. The bottom of the rolled rail is then heated to reduce the cooling rate and cool it to 650-700°C. Accelerated cooling at the rail head can refine the spacing between the rail head laminations, improving strength and toughness, and increasing the yield strength ratio. Heating the bottom of the rail reduces its cooling rate, which can decrease the heat difference caused by the larger volume of the rail head than the bottom. This improves the straightness of the rail before straightening caused by uneven thermal expansion during subsequent natural cooling, and also solves the problem of a significant reduction in yield strength caused by straightening.

[0035] In some embodiments, the segmented step heating is a five-segment step heating, wherein the heating temperature of the first segment is 500-750°C; the heating temperature of the second segment is 750-950°C; the heating temperature of the third segment is 950-1100°C; the heating temperature of the fourth segment is 1100-1200°C; and the heating temperature of the fifth segment is 1200-1250°C.

[0036] 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. In this embodiment, a five-segment step-by-step heating method is used. If there are fewer than five heating segments, the temperature control range of each segment will expand, affecting the accuracy of temperature control; if there are more than five heating segments, the operational difficulty of temperature control will increase, and there will be more restrictions on objective conditions such as the production site.

[0037] It should be noted that: the "heating temperature of segment X" mentioned in this invention refers to the temperature control temperature of that segment, i.e., the ambient temperature of the heating furnace (the ambient temperature of each segment of the heating furnace is always maintained in a relatively stable state); the "heating time of each segment" mentioned in this invention refers to the time the billet stays in that segment of the heating furnace, including the billet heating and holding time. For example: the first segment 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 segment of the heating furnace for a total of 30 minutes.

[0038] In some embodiments, the heating time range for each stage in the five-stage step heating process is as follows: 90 minutes ≥ first stage heating time ≥ 30 minutes; 90 minutes ≥ second stage heating time ≥ 30 minutes; 60 minutes ≥ third stage heating time ≥ 30 minutes; 60 minutes ≥ fourth stage heating time ≥ 30 minutes; 60 minutes ≥ fifth stage heating time ≥ 30 minutes.

[0039] In some embodiments, the cooling rate of the rail head after final rolling is 2–5 °C / s, and the cooling rate of the rail base after final rolling is 1–2.5 °C / s. Accelerated cooling of the rail head can refine the interlayer spacing, improving strength and toughness, and increasing the yield strength ratio. Replenishing heat at the rail base reduces its cooling rate, minimizing the heat difference caused by the larger volume of the rail head compared to the rail base. This improves the straightness of the rail before straightening caused by uneven cooling rates during subsequent natural cooling, and also solves the problem of a significant reduction in yield strength caused by straightening.

[0040] In some embodiments, the cooling medium is compressed air and / or water mist.

[0041] In some embodiments, based on the weight of the billet, the billet contains, by weight percentage: C: 0.72-0.82%, Si: 0.10-1.00%, Mn: 0.70-1.25%, Cr: 0.40-0.70%, P: ≤0.02%, S: ≤0.02%, Al: ≤0.005%, 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.

[0042] 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.

[0043] 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 0.72% (by weight), the strengthening effect cannot be fully realized, leading to insufficient rail strength; when the carbon content is above 0.82%, the rail's toughness and plasticity decrease, and its fatigue resistance deteriorates. Therefore, this invention limits the carbon content to the range of 0.72% to 0.82%.

[0044] 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 0.10%, 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 1.00% can easily lead to fatigue cracks inside the rail. Therefore, this invention limits the silicon content to the range of 0.10% to 1.00%.

[0045] Manganese (Mn) plays a role in improving hardenability in 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 1.25%, the hardenability of the rail is too strong, and heat treatment will cause abnormal structures such as martensite. Therefore, this invention limits the silicon content to the range of 0.70% to 1.25%.

[0046] Chromium (Cr) also plays a role in improving hardenability in steel, and also has a certain antioxidant effect. It can improve the strength and corrosion resistance of steel. Under the conditions of the rail preparation method described in this invention, when the chromium content is below 0.40%, the rail strength is insufficient and cannot meet the service requirements of the line; when the chromium content is above 0.70%, the hardenability is too strong, abnormal structures are easily formed in the rail, and the plasticity of the rail is reduced. Therefore, this invention limits the chromium content range to 0.40%–0.70%.

[0047] 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.

[0048] In some embodiments, reference Figure 2 The rolling mill is a seven-stand mill, consisting of the BD1 mill (first roughing mill), the BD2 mill (second roughing mill), the UR1E1 mill (first universal finishing and edge-rolling mill) composed of the UR1 and E1 mills, the UR2E2 mill (second universal finishing and edge-rolling mill) composed of the UR2 and E2 mills, and the UF mill (final mill). The BD1, BD2, E1, and E2 mills each include a pair of horizontal rolls, while the UR1, UR2, and UF mills each include a pair of horizontal rolls and a pair of vertical rolls.

[0049] In some embodiments, rails cooled to room temperature are straightened using a horizontal-vertical composite straightening machine. The horizontal straightening unit 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 (e.g., [missing information]) arranged sequentially in a horizontal direction in the direction of the rail head. Figure 3 (As shown). 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 rail, while the vertical straightening machine is used to straighten both sides of the rail.

[0050] In some embodiments, the horizontal straightening reduction of the first straightening roll is 13–15 mm, the horizontal straightening reduction of the second straightening roll is 8–10 mm, the horizontal straightening reduction of the third straightening roll is 4–6 mm, and the horizontal straightening reduction of the fourth straightening roll is 0–2 mm. Since the rail has a high straightness before straightening, a low reduction is used, thus solving the problem of a significant decrease in yield strength caused by straightening.

[0051] According to a second aspect of the present invention, a medium-strength rail with a high yield strength ratio is provided, which is prepared using the method described in the first aspect of the present invention.

[0052] refer to Figure 4 A tensile test can be performed on a sample taken at the arc of the rail head to measure the tensile strength and yield strength of the rail material, and thus evaluate the yield-to-tensile ratio. In some embodiments, a tensile test is performed on a sample taken at the arc of the rail head in a room temperature air environment, with a tensile strength ≥1180MPa and a yield-to-tensile ratio ≥0.71.

[0053] This medium-strength rail with a high yield strength ratio can be used on lines with heavy axle loads, and the rail has minimal fatigue damage, greatly improving its safe service performance.

[0054] The present invention will be further described below with reference to specific embodiments.

[0055] Examples S1, S2, and S3 respectively prepared medium-strength steel rails according to the chemical composition range of the billet provided in the embodiments of the present invention and the preparation method provided in the embodiments of the present invention. Comparative Examples D1 and D2 were prepared as U75V heat-treated steel rails according to existing processes. The chemical composition of the billets of Examples S1, S2, and S3 and Comparative Examples D1 and D2 is shown in Table 1. The preparation process parameters of Examples S1, S2, and S3 and Comparative Examples D1 and D2 are shown in Tables 2, 3, and 4.

[0056] Table 1. Chemical composition (%) of the cast billets in the embodiments and comparative examples of the present invention.

[0057]

[0058] Table 2. Heating process parameters for the three embodiments and comparative examples of the present invention.

[0059]

[0060] Table 3. Heat treatment process parameters for rails in embodiments and comparative examples of the present invention.

[0061]

[0062] Table 4. Rail straightening process parameters of embodiments and comparative examples of the present invention.

[0063]

[0064] Samples were taken from the rail head arc position of the rails prepared in the above embodiments S1, S2 and S3 and comparative examples D1 and D2, and tensile tests were conducted to test the tensile strength and yield strength, and the yield strength ratio was calculated. The results are shown in Table 5.

[0065] Table 5. Tensile property data of rails in embodiments and comparative examples of the present invention.

[0066]

[0067]

[0068] A comparison of the data from Examples S1, S2, and S3 and Comparative Examples D1 and D2 in Table 5 reveals that, under the same testing conditions and methods, the tensile strength of the rails prepared by Examples S1, S2, and S3 of the present invention is essentially equivalent to that of Comparative Examples D1 and D2. The average tensile strength of the rails prepared by the three examples of the present invention is 1248 MPa, while the average tensile strength of the rails prepared by the two comparative examples is 1243 MPa. However, the average yield strength ratio of the rails prepared by the three examples of the present invention reaches 0.726, while the average yield strength ratio of the rails prepared by the two comparative examples is only 0.635. This demonstrates that the rails prepared by the method for preparing medium-strength rails provided by the embodiments of the present invention have a higher yield strength ratio.

[0069] In summary, the method for preparing medium-strength rails with high yield strength ratio provided by the embodiments of the present invention can effectively improve the yield strength ratio and tensile strength of the rails, greatly improve the plastic stability limit of the rails, and solve the problem of significant fatigue damage of medium-strength rails when they are used on routes with large axle loads. The rails prepared by the method of the present invention, when subjected to tensile tests at the rail head arc position in a room temperature air environment, have a tensile strength ≥1180MPa and a yield strength ratio ≥0.71.

[0070] It should be noted that the components or steps in the above embodiments can be interchanged, substituted, added, or deleted. Therefore, the combinations formed by these reasonable permutations and transformations should also fall within the protection scope of this invention, and the protection scope of this invention should not be limited to the above embodiments.

[0071] The above are exemplary embodiments disclosed in this invention. The order of the disclosed embodiments is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of this invention (including the claims) is limited to these examples. Various changes and modifications can be made without departing from the scope defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular.

[0072] 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 for preparing a medium-strength rail with a high yield strength ratio, characterized in that, Includes the following steps: The billet obtained from continuous casting is subjected to segmented step heating, wherein the heating temperature of each segment gradually increases and the heating time of each segment is ≥30 minutes; the segmented step heating is a five-segment step heating, wherein the heating temperature of the first segment is 500-750℃; the heating temperature of the second segment is 750-950℃; the heating temperature of the third segment is 950-1100℃; the heating temperature of the fourth segment is 1100-1200℃; and the heating temperature of the fifth segment is 1200-1250℃. The billet heated by segmented step heating is rolled into a rail with residual heat using a rolling mill. The final rolling temperature of the rail head and rail bottom is controlled at 900-950℃. Cooling medium is sprayed onto the rail head after final rolling to accelerate the cooling rate and cool it to 500-550°C. The rail bottom after final rolling is reheated to reduce the cooling rate and cool it to 650-700°C. The rail is then allowed to cool naturally to room temperature in the air. The cooling rate of the rail head after final rolling is 2-5°C / s, and the cooling rate of the rail bottom after final rolling is 1-2.5°C / s. Straighten the rails that have cooled to room temperature; Based on the weight of the cast billet, the cast billet contains, by weight percentage: C: 0.72-0.82%, Si: 0.10-1.00%, Mn: 0.70-1.25%, Cr: 0.40-0.70%, P: ≤0.02%, S: ≤0.02%, Al: ≤0.005%, with the remainder being Fe and unavoidable impurities.

2. The method for preparing a medium-strength rail with a high yield strength ratio according to claim 1, characterized in that, The heating time range for each segment in the five-segment step heating process is as follows: 90 minutes ≥ the heating time of the first segment ≥ 30 minutes; 90 minutes ≥ the heating time of the second segment ≥ 30 minutes; 60 minutes ≥ the heating time of the third segment ≥ 30 minutes; 60 minutes ≥ the heating time of the fourth segment ≥ 30 minutes; 60 minutes ≥ the heating time of the fifth segment ≥ 30 minutes.

3. The method for preparing a medium-strength rail with a high yield strength ratio according to claim 1, characterized in that, The cooling medium is compressed air and / or water mist.

4. The method for preparing a medium-strength rail with a high yield strength ratio according to claim 1, characterized in that, The rolling mill is a seven-stand rolling mill, including the BD1 rolling mill, the BD2 rolling mill, the UR1E1 rolling mill composed of the UR1 rolling mill and the E1 rolling mill, the UR2E2 rolling mill composed of the UR2 rolling mill and the E2 rolling mill, and the UF rolling mill, which perform rolling in sequence.

5. The method for preparing a medium-strength rail with a high yield strength ratio according to claim 1, characterized in that, The rails cooled to room temperature are straightened using a horizontal-vertical composite straightening machine. The horizontal 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.

6. The method for preparing a medium-strength rail with a high yield strength ratio according to claim 5, characterized in that, The horizontal straightening reduction of the first straightening roller is 13-15 mm, the horizontal straightening reduction of the second straightening roller is 8-10 mm, the horizontal straightening reduction of the third straightening roller is 4-6 mm, and the horizontal straightening reduction of the fourth straightening roller is 0-2 mm.

7. A medium-strength rail with a high yield strength ratio, which is manufactured using the method described in any one of claims 1-6.

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