A method for reducing the wave fluctuation of the hardness of a hundred-meter steel rail

Abstract

The present application relates to the technical field of rail processing, and particularly relates to a method for reducing the hardness fluctuation of a 100-meter rail. The method comprises the following steps: after the rolling of the rail is completed, the rail is input to a heat treatment unit, the heat treatment device is started after the rail completely enters the heat treatment unit; the initial rolling end of the rail is cooled at a cooling rate of 4-6 DEG C / s; the middle part of the rail is cooled at a cooling rate of 3-5.5 DEG C / s; the final rolling end of the 100-meter rail is cooled at a cooling rate of 2-4.5 DEG C / s; and the heat treatment device is turned off after the heat treatment is completed. In the present application, the 100-meter rail is subjected to regionalized block cooling in the online heat treatment process, different cooling rates are matched based on the temperature difference of the rail, the hardness fluctuation of the 100-meter rail after production is greatly reduced, and the hardness fluctuation of the 100-meter rail is integrally reduced by combining heating and rolling control, so that the uniformity of the performance of the rail is improved.

Description

Technical Field

[0001] This invention relates to the field of rail processing technology, and in particular to a method for reducing the hardness fluctuation along the entire length of a 100-meter rail. Background Technology

[0002] 100-meter heat-treated rails effectively reduce the number of welding operations on the track, improving train stability and transportation efficiency. The rapid development of high-speed railways places higher demands on the overall service performance of rails. With increasing requirements for train safety, the overall performance of 100-meter rails before leaving the factory is subject to increasingly stringent constraints. my country's existing high-speed railways mainly use pearlitic hot-rolled and heat-treated rails. In the highly competitive market, manufacturers employ various technologies to improve the overall performance of pearlitic rails. Regarding reducing the hardness fluctuation along the entire length of 100-meter rails, online heat treatment is the most effective technological approach.

[0003] The hardness fluctuations along the entire length of a 100-meter steel rail before it leaves the factory can easily lead to uneven wear on the rail tread after it is installed on the track. The harder parts wear less, while the harder parts wear more. If the uneven wear becomes more concentrated, it will promote the formation of corrugation, increase the risk of the rail being removed from the track, reduce transportation efficiency, and even affect traffic safety.

[0004] Currently, the railway standard TB / T 3276~2012 clearly stipulates that the hardness variation range of a 100-meter heat-treated rail (the same rail) should not exceed 30HB. However, considering the service conditions of the rail lines, especially the harsh service conditions such as small-radius curves, the hardness fluctuation of the rail throughout the line exacerbates the abnormal wear of the rails and the abnormal contact light band caused by poor wheel-rail matching.

[0005] To address the issue of fluctuating hardness along the entire length of 100-meter steel rails during production, this invention proposes a method for reducing such fluctuations. Summary of the Invention

[0006] In order to solve the technical problems existing in the prior art, the present invention provides a method for reducing the hardness fluctuation of a 100-meter steel rail.

[0007] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0008] In a first aspect, in one embodiment of the present invention, a method for reducing the hardness fluctuation along the entire length of a 100-meter steel rail is provided, the method comprising:

[0009] After the rail rolling is completed, the rail is fed into the heat treatment unit. Once the rail has completely entered the heat treatment unit, the heat treatment device is started.

[0010] The initial rolling end of the rail is cooled at a cooling rate of 4–6℃ / s; the middle part of the rail is cooled at a cooling rate of 3–5.5℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 2–4.5℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0011] As a further aspect of the present invention, the initial rolling end of the rail is cooled at a cooling rate of 4.5 to 5.5°C / s; the middle part of the rail is cooled at a cooling rate of 4 to 5°C / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 3 to 4°C / s. After the heat treatment is completed, the heat treatment device is turned off.

[0012] As a further aspect of the present invention, the initial rolling end of the rail is cooled at a cooling rate of 5℃ / s; the middle part of the rail is cooled at a cooling rate of 4.5℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 3.5℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0013] As a further embodiment of the present invention, the initial rolling end is located at the 0-15m position of the rail head end; the intermediate part is located at the 15-85m position of the rail; and the final rolling end is located at the 85-100m position of the rail.

[0014] As a further aspect of the present invention, the rails are rolled in 15 passes to produce multiple profile rails with a weight of 50-75 kg / m, and the overall compression ratio of the rail head is between 8.5 and 14.2.

[0015] As a further aspect of the present invention, the billet before rail rolling is heated in a walking beam furnace for a total time of 170 to 350 minutes.

[0016] As a further aspect of the present invention, the heating furnace includes a preheating section, a heating section, and a soaking section, wherein the soaking section accounts for 22% to 30% of the total time spent in the furnace.

[0017] As a further aspect of the present invention, the rail head and bottom are cooled using the residual heat from the final rolling process, and the ratio of the cooling rate of the rail head to the cooling rate of the rail bottom is between 1.5 and 3.4.

[0018] As a further aspect of the present invention, the initial cooling temperature of the rail head is not lower than 700°C, and the final cooling temperature of the rail head is not lower than 460°C.

[0019] As a further aspect of the present invention, the chemical composition of the rail, by weight percentage, is: C: 0.65-1.20%, Mn: 0.5-1%, Si: 0.15-0.85%, Cr or V (at least one), Cr: 0.005-0.02% when Cr is present, V: 0.005-0.07% when V is present, P: ≤0.020%, S: ≤0.020%, with the remainder being Fe, residual elements, and general impurities.

[0020] The technical solution provided by this invention has the following beneficial effects: In the rail production process, this invention focuses on regional segmented cooling of 100-meter rails during the online heat treatment process. Based on the temperature difference along the entire length of the rail, different cooling rates are matched to different regions, which greatly reduces the hardness fluctuation after the production of 100-meter rails. At the same time, by combining heating and rolling control, the hardness fluctuation along the entire length of 100-meter rails is reduced in an integrated manner, and the uniformity of the performance along the entire length of the rail is improved.

[0021] These or other aspects of the invention will become more apparent from the following description of embodiments. It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. 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 embodiments can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram illustrating a method for reducing hardness fluctuations along the entire length of a 100-meter steel rail according to an embodiment of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0026] This invention provides a method for reducing the hardness fluctuation along the entire length of a 100-meter steel rail, the method comprising:

[0027] After the rail rolling is completed, the rail is fed into the heat treatment unit. Once the rail has completely entered the heat treatment unit, the heat treatment device is started.

[0028] The initial rolling end of the rail is cooled at a cooling rate of 4–6℃ / s; the middle part of the rail is cooled at a cooling rate of 3–5.5℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 2–4.5℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0029] In this embodiment of the invention, the heat treatment unit cools the rails using a blower.

[0030] In this embodiment of the invention, the method further includes: cooling the initial rolled end of the rail at a cooling rate of 4℃ / s, 4.5℃ / s, 5℃ / s, 5.5℃ / s, or 6℃ / s; cooling the middle part of the rail at a cooling rate of 3℃ / s, 4℃ / s, 4.5℃ / s, 5℃ / s, or 5.5℃ / s; cooling the final rolled end of the 100-meter rail at a cooling rate of 2℃ / s, 3℃ / s, 3.5℃ / s, 4℃ / s, or 4.5℃ / s; and after the heat treatment is completed, turning off the heat treatment device.

[0031] In this embodiment of the invention, the initial rolling end is located at the 0-15m position of the rail head; the intermediate part is located at the 15-85m position of the rail; and the final rolling end is located at the 85-100m position of the rail.

[0032] The rails mentioned are 100-meter rails.

[0033] In this embodiment of the invention, the rails are rolled in 15 passes to form multiple profile rails with a weight of 50-75 kg / m, and the overall compression ratio of the rail head is between 8.5 and 14.2.

[0034] In this embodiment of the invention, the billet before rail rolling is heated in a walking beam furnace for a total time of 170 to 350 minutes. The furnace includes a preheating section, a heating section, and a soaking section, wherein the soaking section accounts for 22% to 30% of the total time in the furnace.

[0035] In this embodiment of the invention, the rail head and bottom are cooled using the residual heat from the final rolling process, and the ratio of the cooling rate of the rail head to the cooling rate of the rail bottom is between 1.5 and 3.4.

[0036] In this embodiment of the invention, the initial cooling temperature of the rail head is not lower than 700°C, and the final cooling temperature of the rail head is not lower than 460°C.

[0037] In this embodiment of the invention, the chemical composition of the rail, by weight percentage, is: C: 0.65-1.20%, Mn: 0.5-1%, Si: 0.15-0.85%, Cr or V (at least one), Cr: 0.005-0.02% when Cr is present, V: 0.005-0.07% when V is present, P: ≤0.020%, S: ≤0.020%, with the remainder being Fe, residual elements, and general impurities.

[0038] This invention focuses on regionalized, segmented cooling of 100-meter sections of rail during the online heat treatment process in the rail production process. Based on the temperature differences along the entire length of the rail, different cooling rates are matched to different areas, which greatly reduces the hardness fluctuation of the 100-meter rail after production. At the same time, by combining heating and rolling control, the hardness fluctuation of the entire 100-meter rail is reduced in an integrated manner, thereby improving the uniformity of the rail's performance along its entire length.

[0039] Example 1

[0040] In this embodiment, the chemical composition of the rail, by weight percentage, is C: 0.71%, Mn: 0.96%, Si: 0.43%, Cr: 0.01%, V: 0.002%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0041] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0042] In this embodiment, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0043] In this embodiment, the initial rolling end of the rail is cooled at a cooling rate of 6℃ / s; the middle part of the rail is cooled at a cooling rate of 5.5℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 4.5℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0044] Example 2

[0045] In this embodiment, the chemical composition of the rail, by weight percentage, is C: 0.71%, Mn: 0.96%, Si: 0.43%, Cr: 0.01%, V: 0.002%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0046] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0047] In this embodiment, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0048] In this embodiment, the initial rolling end of the rail is cooled at a cooling rate of 5℃ / s; the middle part of the rail is cooled at a cooling rate of 4℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 3.5℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0049] Example 3

[0050] In this embodiment, the chemical composition of the rail, by weight percentage, is C: 0.71%, Mn: 0.96%, Si: 0.43%, Cr: 0.01%, V: 0.002%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0051] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0052] In this embodiment, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0053] In this embodiment, the initial rolling end of the rail is cooled at a cooling rate of 4℃ / s; the middle part of the rail is cooled at a cooling rate of 3℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 2℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0054] Example 4

[0055] In this embodiment, the chemical composition of the rail, by weight percentage, is C: 0.75%, Mn: 0.88%, Si: 0.66%, Cr: 0.01%, V: 0.05%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0056] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0057] In this embodiment, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0058] In this embodiment, the initial rolling end of the rail is cooled at a cooling rate of 6℃ / s; the middle part of the rail is cooled at a cooling rate of 5.5℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 4.5℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0059] Example 5

[0060] In this embodiment, the chemical composition of the rail, by weight percentage, is C: 0.75%, Mn: 0.88%, Si: 0.66%, Cr: 0.01%, V: 0.05%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0061] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0062] In this embodiment, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0063] In this embodiment, the initial rolling end of the rail is cooled at a cooling rate of 5℃ / s; the middle part of the rail is cooled at a cooling rate of 4℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 3.5℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0064] Example 6

[0065] In this embodiment, the chemical composition of the rail, by weight percentage, is C: 0.75%, Mn: 0.88%, Si: 0.66%, Cr: 0.01%, V: 0.05%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0066] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0067] In this embodiment, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0068] In this embodiment, the initial rolling end of the rail is cooled at a cooling rate of 4℃ / s; the middle part of the rail is cooled at a cooling rate of 3℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 2℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0069] Comparative Example 1

[0070] In this comparative example, the chemical composition of the rail, by weight percentage, is C: 0.71%, Mn: 0.96%, Si: 0.43%, Cr: 0.01%, V: 0.002%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0071] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0072] In the comparative example, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have fully entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0073] In the comparative example, the initial rolling end of the rail was cooled at a cooling rate of 7℃ / s; the middle part of the rail was cooled at a cooling rate of 6℃ / s; and the final rolling end of the 100-meter rail was cooled at a cooling rate of 5℃ / s. After the heat treatment was completed, the heat treatment device was turned off.

[0074] Comparative Example 2

[0075] In this comparative example, the chemical composition of the rail, by weight percentage, is C: 0.71%, Mn: 0.96%, Si: 0.43%, Cr: 0.01%, V: 0.002%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0076] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0077] In the comparative example, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have fully entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0078] In the comparative example, the initial rolling end of the rail was cooled at a cooling rate of 3.5℃ / s; the middle part of the rail was cooled at a cooling rate of 2.5℃ / s; and the final rolling end of the 100-meter rail was cooled at a cooling rate of 1.5℃ / s. After the heat treatment was completed, the heat treatment device was turned off.

[0079] Comparative Example 3

[0080] In this comparative example, the chemical composition of the rail, by weight percentage, is C: 0.71%, Mn: 0.96%, Si: 0.43%, Cr: 0.01%, V: 0.002%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0081] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0082] In the comparative example, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have fully entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0083] In the comparative example, the initial rolling end of the rail was cooled at a cooling rate of 4℃ / s; the middle part of the rail was cooled at a cooling rate of 4℃ / s; and the final rolling end of the 100-meter rail was cooled at a cooling rate of 4℃ / s. After the heat treatment was completed, the heat treatment device was turned off.

[0084] Comparative Example 4

[0085] In this comparative example, the chemical composition of the rail, by weight percentage, is C: 0.75%, Mn: 0.88%, Si: 0.66%, Cr: 0.01%, V: 0.05%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0086] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0087] In this comparative example, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0088] In this comparative example, the initial rolling end of the rail was cooled at a cooling rate of 7℃ / s; the middle part of the rail was cooled at a cooling rate of 6℃ / s; and the final rolling end of the 100-meter rail was cooled at a cooling rate of 5℃ / s. After the heat treatment was completed, the heat treatment device was turned off.

[0089] Comparative Example 5

[0090] In this comparative example, the chemical composition of the rail, by weight percentage, is C: 0.75%, Mn: 0.88%, Si: 0.66%, Cr: 0.01%, V: 0.05%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0091] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0092] In this comparative example, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0093] In this comparative example, the initial rolling end of the rail was cooled at a cooling rate of 3.5℃ / s; the middle part of the rail was cooled at a cooling rate of 2.5℃ / s; and the final rolling end of the 100-meter rail was cooled at a cooling rate of 1.5℃ / s. After the heat treatment was completed, the heat treatment device was turned off.

[0094] Comparative Example 6

[0095] In this embodiment, the chemical composition of the rail, by weight percentage, is C: 0.75%, Mn: 0.88%, Si: 0.66%, Cr: 0.01%, V: 0.05%, P: 0.012%, S: 0.007%, with the remainder being Fe, residual elements, and general impurities.

[0096] Molten steel meeting the above requirements for rail chemical composition is continuously cast into 410mm×320mm billets, heated in a walking beam furnace, and after complete austenitization, rolled online into 50-75kg / m rails with a rail head compression ratio of 8.5-14.2.

[0097] In this embodiment, for rails that meet the above requirements, the residual heat from the rolling process is used to start the heat treatment device after the hot-rolled rails have completely entered the heat treatment device, and the rail head and rail bottom are cooled respectively.

[0098] In this embodiment, the initial rolling end of the rail is cooled at a cooling rate of 4℃ / s; the middle part of the rail is cooled at a cooling rate of 4℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 4℃ / s. After the heat treatment is completed, the heat treatment device is turned off.

[0099] Performance testing

[0100] The rails treated in Examples 1-6 and Comparative Examples 1-6 were air-cooled to room temperature. Surface hardness samples were taken at the locations required by the TB / T2344-2012 standard, using a 10 / 3000 HBW test. One sample was taken from the beginning, middle, and end of the rails, with test points spaced 20 mm apart, and 5 points were tested on each sample. Fatigue crack propagation rate (da / dN) samples were taken according to the standard. Metallographic structure samples were taken 5 mm below the rail head tread. The examples and comparative examples used the same test locations and methods. The results are detailed in Tables 1-4.

[0101] Table 1. Hardness test results of the head end of the six embodiments and six comparative examples of the present invention.

[0102]

[0103] Table 2. Hardness test results of the center section of the six examples and six comparative examples of the present invention.

[0104]

[0105] Table 3. Results of tail end hardness testing in 6 sets of embodiments and 6 sets of comparative examples of the present invention.

[0106]

[0107]

[0108] Table 4 Comparison of comprehensive test results of 6 sets of embodiments and 6 sets of comparative examples of the present invention.

[0109]

[0110] This invention selects six sets of examples with different chemical compositions and different heat treatment cooling processes, along with corresponding comparative examples for comparison. In the examples, the regionalized block heat treatment cooling method used is the method described in this invention. The corresponding comparative examples are methods with upper and lower limits of cooling rate and without the regionalized block cooling process. The data comparison results of Examples 1 to 3 and Comparative Examples 1 to 2 show that, under this composition, as the cooling rate of each region increases, the surface hardness of the 100-meter rail gradually increases. When it exceeds the upper limit, martensite, bainite, and other abnormalities appear in each region of the rail, leading to a sharp increase in hardness. When it falls below the lower limit, the surface hardness of each region of the rail is lower than the design standard and does not meet the requirements. The same pattern exists for Examples 4 to 6 and Comparative Examples 4 to 5. The data comparison between Example 3 and Comparative Example 3 shows that the surface hardness difference of the 100-meter rail after applying the regionalized block cooling process is significantly lower than that without the process, the surface hardness fluctuation is smaller, the average P-lamellae difference in the 5mm below the rail head is smaller, the average fatigue crack propagation rate da / dN difference is smaller, and the overall performance is more uniform.

[0111] After adopting the method of reducing the hardness fluctuation of the entire length of 100-meter steel rail, the hardness fluctuation value of the entire length of 100-meter steel rail is ≤6HB, the hardness fluctuation is significantly reduced, the average pearlite lamellar spacing difference at 5mm below the rail head tread at various length positions of the 100-meter steel rail is smaller, and the crack propagation rate da / dN performance at various length positions of the 100-meter steel rail is more similar; thus greatly improving the uniformity of the hardness fluctuation and its comprehensive performance of the entire length of 100-meter steel rail.

[0112] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for reducing the hardness fluctuation along the entire length of a 100-meter steel rail, characterized in that, The method includes: The billet before rail rolling is heated in a walking beam furnace for a total time of 170–350 min. The furnace includes a preheating section, a heating section, and a soaking section, with the soaking section accounting for 22%–30% of the total time in the furnace. After complete austenitization, the rail is rolled online. The rail is rolled in 15 passes to produce multiple profile rails with a weight of 50–75 kg / m and a rail head compression ratio of 8.5–14.

2. After the rail rolling is completed, the rail is fed into the heat treatment unit. After the rail has completely entered the heat treatment unit, the heat treatment device is started. The rail head and bottom are cooled by the residual heat of the rail rolling. The ratio of the cooling rate of the rail head to the cooling rate of the rail bottom is between 1.5 and 3.

4. Regionalized, segmented cooling is implemented, with different cooling rates matched to different areas based on the temperature differences along the entire length of the rail. The initial rolling end of the rail is cooled at a rate of 5.5–6℃ / s; the middle section of the rail is cooled at a rate of 5–5.5℃ / s; and the final rolling end of the 100-meter rail is cooled at a rate of 2–4.5℃ / s; or The initial rolling end of the rail is cooled at a rate of 5–6℃ / s; the middle section of the rail is cooled at a rate of 4–5℃ / s; and the final rolling end of the 100-meter rail is cooled at a rate of 2–4℃ / s; or The initial rolling end of the rail is cooled at a cooling rate of 4-6℃ / s; the middle part of the rail is cooled at a cooling rate of 3-4℃ / s; and the final rolling end of the 100-meter rail is cooled at a cooling rate of 2-3℃ / s. After the heat treatment is completed, shut down the heat treatment equipment; The initial rolling end is located at the head end of the rail, from 0 to 15m; the intermediate part is located at the head end of the rail, from 15 to 85m; and the final rolling end is located at the head end of the rail, from 85 to 100m.

2. The method for reducing hardness fluctuation along a 100-meter length of steel rail as described in claim 1, characterized in that, The initial cooling temperature of the rail head shall not be lower than 700℃, and the final cooling temperature of the rail head shall not be lower than 460℃.

3. The method for reducing hardness fluctuation along a 100-meter steel rail as described in claim 1, characterized in that, The chemical composition of the rail, by weight percentage, is as follows: C: 0.65–1.20%, Mn: 0.5–1%, Si: 0.15–0.85%, Cr or V (at least one), Cr: 0.005–0.02% (when Cr is present), V: 0.005–0.07% (when V is present), P: ≤0.020%, S: ≤0.020%, with the remainder being Fe, residual elements, and general impurities.

Images