Method for producing a rail resistant to rail foot fracture and rail produced thereby

Abstract

The application discloses a preparation method of a rail with rail bottom fracture resistance and a rail prepared by the method. The method comprises the following steps: spraying a cooling medium on N regions of a rail bottom of a hot-rolled after-heat rail to accelerate cooling, the N regions are parallel to a length direction of the after-heat rail, N is an odd number, one region at a middle position of the rail bottom is a first region, each two regions on symmetrical positions on both sides of the first region are sequentially a second region, a third region,..., and an n-th region, wherein n=(N+1) / 2, the first region is accelerated and cooled at a first cooling rate, the second region, the third region,..., and the n-th region are accelerated and cooled at a second cooling rate, a third cooling rate,..., and an n-th cooling rate respectively. The prepared rail has good strength and toughness of the rail bottom, pearlite lamellas are refined, normal-temperature impact toughness is large, and a crack propagation rate is small, so that the rail bottom fracture resistance is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of rail manufacturing technology, and in particular to a method for manufacturing a rail resistant to bottom fracture and the rail manufactured therefrom. Background Technology

[0002] The development of high-speed, heavy-haul railways has placed higher demands on the overall service performance of rails. With increasing requirements for traffic safety, abnormal fatigue, excessive wear, and sudden fractures during rail service are now strictly limited. my country's existing passenger and freight mixed-transport railways and heavy-haul railways mainly use pearlitic steel rails. Current technologies generally employ microalloying and railhead heat treatment to improve the service performance of pearlitic steel rails.

[0003] However, due to the susceptibility of rail bases to corrosion under environmental influences, rust pits often form. Under the combined effects of tensile stress (temperature stress and residual stress) inside the rail and dynamic bending stress generated when the train passes over the rail, the rust pits at the rail base are prone to become stress concentration points and form crack initiation points. Therefore, insufficient toughness and fracture resistance of the rail material (especially the rail base) will cause cracks to propagate rapidly, eventually leading to rail fracture along the rail base, which seriously affects traffic safety.

[0004] Therefore, it is necessary to improve the fracture resistance of the rail base. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing rails resistant to rail base fracture. This method solves the problem in existing technologies where insufficient strength, toughness, and fracture resistance of the rail base lead to rail fracture along the rail base, severely impacting train safety.

[0006] On one hand, embodiments of the present invention disclose a method for preparing a rail resistant to bottom fracture, comprising the following steps:

[0007] Online cooling medium is sprayed onto N regions of the rail base of the hot-rolled residual heat rail to accelerate cooling. The N regions are parallel to the length direction of the residual heat rail, and the value of N is an odd number. A region at the middle position of the rail base is the first region. Extending from the first region to both ends of the rail base, with the first region as the center of symmetry, every two regions on both sides of the first region are successively the second region, the third region, ..., the nth region, where n = (N+1) / 2. The first region is accelerated cooling at a first cooling rate, and the second region, the third region, ..., the nth region are accelerated cooling at a second cooling rate, a third cooling rate, ..., the nth cooling rate, respectively.

[0008] According to one embodiment of the present invention, N rows of nozzles are arranged below N regions of the rail base. Cooling medium acts on the N regions of the rail base through the nozzles respectively. The first nozzle is located under the first region, and the cooling medium pressure of the first nozzle controls the first cooling rate of the cooling medium. The second nozzle is located under the second region, and the cooling medium pressure of the second nozzle controls the second cooling rate of the cooling medium. The third nozzle is located under the third region, and the cooling medium pressure of the third nozzle controls the third cooling rate of the cooling medium. ... The nth nozzle is located under the nth region, and the cooling medium pressure of the nth nozzle controls the nth cooling rate of the cooling medium.

[0009] According to one embodiment of the present invention, the value of N is 7, the first cooling rate is controlled at 1-5℃ / s, the second cooling rate is controlled at 1-3℃ / s, the third cooling rate is controlled at 1-2℃ / s, and the fourth cooling rate is controlled at 0.5-1.5℃ / s.

[0010] According to one embodiment of the present invention, the cooling medium pressure of the first nozzle is 4-10 kPa, the cooling medium pressure of the second nozzle is 3-8 kPa, the cooling medium pressure of the third nozzle is 2-6 kPa, and the cooling medium pressure of the fourth nozzle is 1-4 kPa.

[0011] According to one embodiment of the present invention, the waste heat rail is a rail or turnout rail rolled online from a steel billet to a strength of 50kg / m-75kg / m, with a final rolling temperature of 850-1100℃.

[0012] According to one embodiment of the present invention, the initial temperature of the rail base for accelerated cooling is controlled at 820-880°C, and the rail base is accelerated cooled to a temperature below 420-480°C and then air-cooled to room temperature.

[0013] According to one embodiment of the present invention, the cooling time for accelerated cooling of the rail bottom is controlled within 45-105 seconds.

[0014] According to one embodiment of the present invention, the composition of the steel billet, by mass percentage, includes: C: 0.50-0.90%, Mn: 0.35-1.00%, Si: 0.30-0.85%, Cr: 0.025-0.1%, V: 0.04-0.12%, P: ≤0.020%, S: ≤0.020%, with the remainder being Fe and unavoidable impurities.

[0015] According to one embodiment of the present invention, the cooling medium is a mixture of compressed air and quenching agent.

[0016] On the other hand, embodiments of the present invention also provide a rail resistant to bottom fracture prepared by any of the above methods, the composition of which, by mass percentage, includes: C: 0.50-0.90%, Mn: 0.35-1.00%, Si: 0.30-0.85%, Cr: 0.025-0.1%, V: 0.04-0.12%, P: ≤0.020%, S: ≤0.020%, with the remainder being Fe and unavoidable impurities.

[0017] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0018] The present invention provides a method for preparing rails resistant to bottom fracture. By focusing on regionalized and differentiated heat treatment of all parts of the rail bottom during the online heat treatment of the residual heat rail, the strength and toughness of the prepared rail bottom are improved, the pearlite lamellae of the rail bottom are refined, the spacing between the pearlite lamellae is in the range of 77-109 nm, the microstructure is more compact, the room temperature impact toughness is improved, and the crack propagation rate is significantly reduced, greatly improving the fracture resistance of the rail bottom. The prepared rails can be widely used in high-speed heavy-load lines, ensuring the driving safety of high-speed heavy-load lines. Attached Figure Description

[0019] 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.

[0020] Figure 1 A schematic diagram of the rail bottom region and nozzle arrangement in a method for preparing a rail resistant to bottom fracture, as disclosed in an embodiment of the present invention. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] On one hand, one embodiment of the present invention discloses a method for preparing a rail resistant to bottom fracture, comprising the following steps:

[0024] Online cooling medium is sprayed into N regions on the bottom of the hot-rolled residual heat rail to accelerate cooling. The N regions are parallel to the length of the residual heat rail, and N is an odd number. The region at the middle position of the rail bottom is the first region. Extending from the first region to both ends of the rail bottom, with the first region as the center of symmetry, every two regions on both sides of the first region are successively the second region, the third region, ..., the nth region, where n = (N+1) / 2. The first region is accelerated by the first cooling rate, and the second region, the third region, ..., the nth region are accelerated by the second cooling rate, the third cooling rate, ..., the nth region, respectively.

[0025] In some embodiments, N rows of nozzles are arranged below N regions on the rail base. Cooling medium acts on each of the N regions through these nozzles. A first nozzle is located under a first region, and the cooling medium pressure at the first nozzle controls a first cooling rate. A second nozzle is located under a second region, and the cooling medium pressure at the second nozzle controls a second cooling rate. A third nozzle is located under a third region, and the cooling medium pressure at the third nozzle controls a third cooling rate, and so on. An nth nozzle is located under an nth region, and the cooling medium pressure at the nth nozzle controls an nth cooling rate. In this embodiment, the cooling rate of the cooling medium is achieved by the pressure of the cooling medium at the nozzles.

[0026] like Figure 1 As shown, in some embodiments, the value of N is 7, that is, the rail base 100 is divided into 7 zones for cooling, where zone 4 is the first zone, zones 3 and 5 are the second zones, zones 2 and 6 are the third zones, and zones 1 and 7 are the fourth zones. The first cooling rate of the first zone is controlled at 1-5℃ / s, the second cooling rate of the second zone is controlled at 1-3℃ / s, the third cooling rate of the third zone is controlled at 1-2℃ / s, and the fourth cooling rate of the fourth zone is controlled at 0.5-1.5℃ / s.

[0027] In the above embodiments, different cooling rates are used for different regions. The thickness of the rail base varies depending on its location, resulting in inconsistent heat capacity and temperature field distribution after rolling. Regions 1 and 7 are the edge of the rail base, with thinner thickness and lower post-rolling temperatures. To achieve the goal of strengthening and toughening in these regions, a cooling rate below 0.5℃ / s has little effect, while a cooling rate above 1.5℃ / s easily leads to abnormal martensite and bainite structures, which do not meet the requirements for rail production. Therefore, the cooling rate in these regions is controlled between 0.5-1.5℃ / s. Regions 2 and 6 are the secondary edge of the rail base, with slightly thicker thickness than the edge and lower post-rolling temperatures. To achieve the goal of strengthening and toughening in these regions, a cooling rate below 1℃ / s has little effect, while a cooling rate above 2℃ / s easily leads to abnormal martensite and bainite structures. The martensite and bainite structures in this region do not meet the requirements for rail production, so the cooling rate in this region is controlled at 1-2℃ / s. Regions 3 and 5 are located near the middle of the rail base. To achieve the purpose of strengthening and toughening in this region, the strengthening and toughening effect is not obvious when the cooling rate is below 1℃ / s, and abnormal martensite and bainite structures are prone to appear when the cooling rate is above 3℃ / s, which does not meet the requirements for rail production. Therefore, the cooling rate in this region is controlled at 1-3℃ / s. Region 4 is located at the very center of the rail base, at the same position as the connection between the rail web and the rail base, and its thickness is the thickest part of the rail base. To achieve the purpose of strengthening and toughening in this region, the strengthening and toughening effect is not obvious when the cooling rate is below 1℃ / s, and abnormal martensite and bainite structures are prone to appear when the cooling rate is above 5℃ / s, which does not meet the requirements for rail production. Therefore, the cooling rate in this region is controlled at 1-5℃ / s.

[0028] In the above embodiment, seven rows of nozzles are arranged below seven regions of the rail base 100, and the first nozzle under the first region (attached) Figure 1 Nozzle 41) controls the first cooling rate by cooling medium pressure, and the second nozzle in the second region (attached) Figure 1 The cooling medium pressure of nozzles 31 and 51 controls the second cooling rate, and the third nozzle in the third region (attached) Figure 1 The cooling medium pressure of nozzles 21 and 61 controls the third cooling rate, and the fourth nozzle in the fourth region (attached) Figure 1 The cooling medium pressure of nozzles 11 and 71 controls the fourth cooling rate.

[0029] In some embodiments, the cooling medium pressure of the first nozzle is 4-10 kPa, the cooling medium pressure of the second nozzle is 3-8 kPa, the cooling medium pressure of the third nozzle is 2-6 kPa, and the cooling medium pressure of the fourth nozzle is 1-4 kPa. In this embodiment, for example, nozzles 11 and 71 correspond to rail bottom regions 1 and 7. Relying on the cooling medium pressure of these two nozzles of 1-4 kPa, a fourth cooling rate of 0.5-1.5℃ / s can be achieved. When the cooling medium pressure of the nozzle is less than 1 kPa, the cooling rate at the corresponding position will not reach 0.5℃ / s. When the cooling medium pressure of the nozzle is greater than 4 kPa, the cooling rate at the corresponding position will exceed 1.5℃ / s, which is prone to abnormal structure. The correspondence between the cooling medium pressure of the other nozzles and the rail bottom position and cooling rate is similar to the above.

[0030] In some embodiments, the steel billet for the waste heat rail is heated to 1220-1290°C in a walking beam furnace. The time required to maintain the temperature above 1220°C is controlled to be 25-65 minutes, accounting for 1 / 8 to 1 / 12 of the total heating time. In this embodiment, when the time above 1220°C is controlled to be less than 25 minutes, the steel billet is not fully heated or the alloy homogenization is poor. When the time above 1220°C is controlled to be more than 65 minutes, the rail billet is prone to overheating or excessive decarburization. Therefore, the time above 1220°C is controlled to be 25-65 minutes. When the time above 1220°C accounts for more than 1 / 8 of the total heating time, the steel billet is prone to overheating or excessive decarburization. When the time above 1220°C accounts for less than 1 / 12 of the total heating time, the steel billet is prone to underheating or poor alloy homogenization.

[0031] In some embodiments, the waste heat rail is a steel billet rolled online into a rail or turnout rail with a strength of 50kg / m-75kg / m, and a final rolling temperature of 850-1100℃.

[0032] In some embodiments, the initial temperature for accelerated cooling of the rail base is controlled at 820-880°C. After accelerated cooling to a temperature below 420-480°C, the rail base is air-cooled to room temperature. In this embodiment, accelerated cooling is stopped when the rail base temperature is below 420-480°C, allowing the rail to continue cooling to room temperature in the air. The finished rail is then obtained through processes such as horizontal and vertical composite straightening, flaw detection, and processing.

[0033] In some embodiments, the accelerated cooling time for the rail base is controlled within 45-105 seconds. In this embodiment, to achieve excellent strength and toughness and a fine pearlitic structure in the rail base, the phase transformation of the rail base needs to be completed at a suitable degree of supercooling. When the accelerated cooling time is below 45 seconds, at a constant cooling rate, the pearlitic structure of the rail base is relatively coarse, and the cooling effect is insufficient, failing to achieve the objective described in this invention. When the accelerated cooling time is above 105 seconds, due to the long cooling time, abnormal structures such as bainite and martensite will form in the rail base. Therefore, the accelerated cooling time is controlled within the range of 45-105 seconds.

[0034] In some embodiments, the composition of the steel billet, by mass percentage, includes: C: 0.50-0.90%, Mn: 0.35-1.00%, Si: 0.30-0.85%, Cr: 0.025-0.1%, V: 0.04-0.12%, P: ≤0.020%, S: ≤0.020%, with the remainder being Fe and unavoidable impurities.

[0035] In some embodiments, the cooling medium is a mixture of compressed air and a quenching agent. This helps to shorten the time required for accelerated cooling and improves process efficiency.

[0036] On the other hand, another embodiment of the present invention discloses a rail resistant to bottom fracture prepared by the method of any of the above embodiments, the composition of which, by mass percentage, includes: C: 0.50-0.90%, Mn: 0.35-1.00%, Si: 0.30-0.85%, Cr: 0.025-0.1%, V: 0.04-0.12%, P: ≤0.020%, S: ≤0.020%, with the remainder being Fe and unavoidable impurities.

[0037] The present invention will now be described in detail through specific embodiments.

[0038] This invention selected 17 sets of samples with the same chemical composition (see Table 1 below), the same quality specifications (all steel billets containing the above compositions were rolled into 60kg / m rails), the same furnace heating time, and the same rail bottom cooling time (see Table 2 below), but different rail bottom regional accelerated cooling control parameters (such as cooling rate) for comparison. Examples 1-6 adopted the preparation method disclosed in one embodiment of this invention, and the rail bottom regionalization and nozzle arrangement are shown in the attached figure. Figure 1As shown, Examples 1-6 differ only in the control parameters (such as cooling rate) for accelerated cooling of the rail base in different zones, as detailed in Table 3 below. Comparative Examples 1-11 have the same rail composition as those in this application, and the rail quality specifications, furnace heating time, and rail base cooling time are also the same. However, the rail bases of Comparative Examples 1-11 were not subjected to accelerated cooling, or the control parameters (such as cooling rate) for accelerated cooling of the rail base in different zones differed entirely or partially from the preparation method disclosed in the embodiments of this invention, as detailed in Table 4 below.

[0039] Table 1 Chemical composition of Examples 1-6 and Comparative Examples 1-11

[0040]

[0041] Table 2. Other control parameters for Examples 1-6 and Comparative Examples 1-11

[0042]

[0043] Table 3. Track Bottom Accelerated Cooling Control Parameters for Examples 1-6

[0044]

[0045]

[0046] Table 4 Comparative Examples 1-11 Rail Bottom Accelerated Cooling Control Parameters

[0047]

[0048] After the above-treated rails were air-cooled to room temperature, tensile strength test specimens, metallographic structure test specimens, fatigue crack propagation rate (da / dN) test specimens, and room temperature impact energy (Aku) test specimens were taken from locations 1 to 7 of the rail base according to the test requirements in TB / T2344-2012 standard. Examples 1-6 and Comparative Examples 1-11 used the same test locations and methods. For specific test results, please refer to Tables 5-8 below.

[0049] Table 5. Tensile strength of rail base in Examples 1-6 and Comparative Examples 1-11 (MPa)

[0050]

[0051] Table 6. Average pearlite lamellae / nm and microstructure of the rail base in Examples 1-6 and Comparative Examples 1-11

[0052]

[0053]

[0054] Note: In Table 6 above, pearlite is represented by "P" and martensite by "M".

[0055] Table 7. Fatigue crack propagation rate da / dN of rail base in Examples 1-6 and Comparative Examples 1-11

[0056]

[0057] Table 8. Room temperature impact energy (Aku / J) of rail base in Examples 1-6 and Comparative Examples 1-11

[0058]

[0059]

[0060] The comparative results listed in Tables 5-8 above show that, in Comparative Example 1, the rail base was not subjected to accelerated cooling, but the resulting rail base had low tensile strength, large pearlite lamellars, high fatigue crack propagation rate da / dN, and low room temperature impact energy Aku.

[0061] The comparison results listed in Tables 5-8 above show that the cooling rates of accelerated cooling of different regions of the rail base in Comparative Example 2 are all less than the minimum cooling rate in the preparation method disclosed in the embodiments of the present invention. However, the resulting rail base has low tensile strength, large pearlite lamellars, large fatigue crack propagation rate da / dN, and low room temperature impact energy Aku.

[0062] The comparison results listed in Tables 5-8 above show that the cooling rate of accelerated cooling of different regions of the rail base in Comparative Example 3 is greater than the maximum cooling rate in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the prepared rail base is high, abnormal martensite structure appears in the microstructure of different regions of the rail base, the fatigue crack propagation rate da / dN of the rail base is large, and the room temperature impact energy Aku of the rail base is small.

[0063] The comparison results listed in Tables 5-8 above show that the cooling rate of accelerated cooling of rail base regions 1 and 7 in Comparative Example 4 is greater than the maximum cooling rate of accelerated cooling of regions 1 and 7 in the preparation method disclosed in the embodiments of the present invention. The cooling rates of accelerated cooling of other regions fall within the range of cooling rates in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the obtained rail base is high, abnormal martensite structure appears in the microstructure of rail base regions 1 and 7, the fatigue crack propagation rate da / dN of rail base regions 1 and 7 is large, and the room temperature impact energy Aku of rail base regions 1 and 7 is small.

[0064] The comparative results listed in Tables 5-8 above show that the accelerated cooling rate of rail base regions 2 and 6 in Comparative Example 5 is greater than the maximum accelerated cooling rate of regions 2 and 6 in the preparation method disclosed in the embodiments of the present invention. The accelerated cooling rates of other regions fall within the range of cooling rates in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the obtained rail base is high, abnormal martensite structure appears in the microstructure of rail base regions 2 and 6, the fatigue crack propagation rate da / dN of rail base regions 2 and 6 is large, and the room temperature impact energy Aku of rail base regions 2 and 6 is small.

[0065] The comparison results listed in Tables 5-8 above show that the cooling rate of accelerated cooling of rail base regions 3 and 5 in Comparative Example 6 is greater than the maximum cooling rate of accelerated cooling of regions 3 and 5 in the preparation method disclosed in the embodiments of the present invention. The cooling rates of accelerated cooling of other regions fall within the range of cooling rates in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the obtained rail base is high, abnormal martensite structure appears in the microstructure of rail base regions 3 and 5, the fatigue crack propagation rate da / dN of rail base regions 3 and 5 is large, and the room temperature impact energy Aku of rail base regions 2 and 6 is small.

[0066] The comparison results listed in Tables 5-8 above show that the accelerated cooling rate of the rail base region 4 in Comparative Example 7 is greater than the maximum accelerated cooling rate of region 4 in the preparation method disclosed in the embodiments of the present invention. The accelerated cooling rates of other regions fall within the range of cooling rates in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the obtained rail base is high, abnormal martensite structure appears in the microstructure of the rail base region 4, the fatigue crack propagation rate da / dN of the rail base region 4 is large, and the room temperature impact energy Aku of the rail base region 4 is small.

[0067] The comparison results listed in Tables 5-8 above show that the cooling rate of accelerated cooling of rail base regions 1 and 7 in Comparative Example 8 is less than the minimum cooling rate of accelerated cooling of regions 1 and 7 in the preparation method disclosed in the embodiments of the present invention. The cooling rates of accelerated cooling of other regions fall within the range of cooling rates in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the obtained rail base is high, the pearlite lamellars in rail base regions 1 and 7 are large, the fatigue crack propagation rate da / dN in rail base regions 1 and 7 is large, and the room temperature impact energy Aku in rail base regions 1 and 7 is small.

[0068] The comparison results listed in Tables 5-8 above show that the cooling rate of accelerated cooling of rail base regions 2 and 6 in Comparative Example 9 is less than the accelerated cooling rate of regions 2 and 6 in the preparation method disclosed in the embodiments of the present invention. The cooling rates of accelerated cooling of other regions fall within the range of cooling rates in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the obtained rail base is high, the pearlite lamellars in rail base regions 2 and 6 are large, the fatigue crack propagation rate da / dN in rail base regions 2 and 6 is large, and the room temperature impact energy Aku in rail base regions 2 and 6 is small.

[0069] The comparison results listed in Tables 5-8 above show that the cooling rate of accelerated cooling of rail base regions 3 and 5 in Comparative Example 10 is less than the minimum cooling rate of accelerated cooling of regions 3 and 5 in the preparation method disclosed in the embodiments of the present invention. The cooling rates of accelerated cooling of other regions fall within the range of cooling rates in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the prepared rail base is high, the pearlite lamellars in rail base regions 3 and 5 are large, the fatigue crack propagation rate da / dN in rail base regions 3 and 5 is large, and the room temperature impact energy Aku in rail base regions 2 and 6 is small.

[0070] The comparison results listed in Tables 5-8 above show that the cooling rate of accelerated cooling of the rail base region 4 in Comparative Example 11 is less than the minimum cooling rate of accelerated cooling of region 4 in the preparation method disclosed in the embodiments of the present invention. The cooling rates of accelerated cooling of other regions fall within the range of cooling rates in the preparation method disclosed in the embodiments of the present invention. Although the tensile strength of the obtained rail base is high, the pearlite lamellars in the rail base region 4 are large, the fatigue crack propagation rate da / dN in the rail base region 4 is large, and the room temperature impact energy Aku in the rail base region 4 is small.

[0071] The data results in Tables 5-8 above show that, under the same chemical composition, smelting and rolling processes, the preparation method disclosed in the embodiments of this invention, which involves regional and differentiated heat treatment of the rail base, will have a significant impact on the final performance of the rail. Specifically, using the method of this invention, the metallographic structure of the rail base meets the standard (full pearlite structure), while the average pearlite lamellars are finer, the tensile strength of the rail base is better, the fatigue crack propagation rate da / dN of the rail base is significantly better than that of the comparative example, and the room temperature impact Aku of the rail base is significantly improved.

[0072] In summary, the method for preparing a rail resistant to bottom fracture disclosed in this invention improves the strength and toughness of the rail base by focusing on regionalized and differentiated heat treatment of all parts of the rail base during the online heat treatment of the residual heat rail. The pearlite lamellars of the rail base are refined, with the interlamellar spacing in the range of 77-109 nm, resulting in a denser microstructure, improved room temperature impact toughness, and a significantly reduced crack propagation rate. This greatly improves the fracture resistance of the rail base, and the prepared rail can be widely used in high-speed heavy-load lines, ensuring the safety of high-speed heavy-load lines.

[0073] 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.

[0074] 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.

[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 for preparing a rail resistant to bottom fracture, characterized in that, Includes the following steps: Online cooling medium is sprayed into seven areas on the bottom of the hot-rolled residual heat rail to accelerate cooling. These seven areas are parallel to the length of the residual heat rail. The area at the middle of the rail bottom is designated as the first area. Extending from the first area towards both ends of the rail bottom, with the first area as the center of symmetry, each pair of areas symmetrically positioned on either side of the first area is designated as the second, third, and fourth areas, respectively. The first area is accelerated cooling at a first cooling rate, while the second, third, and fourth areas are accelerated cooling at a second, third, and fourth cooling rates, respectively. The cooling rate is accelerated; the first cooling rate is controlled at 1-5℃ / s, the second cooling rate is controlled at 1-3℃ / s, the third cooling rate is controlled at 1-2℃ / s, and the fourth cooling rate is controlled at 0.5-1.5℃ / s. The composition of the rail, by mass percentage, includes: C: 0.50-0.90%, Mn: 0.35-1.00%, Si: 0.30-0.85%, Cr: 0.025-0.1%, V: 0.04-0.12%, P: ≤0.020%, S: ≤0.020%, with the remainder being Fe and unavoidable impurities.

2. The method for preparing a rail resistant to bottom fracture according to claim 1, characterized in that, Seven rows of nozzles are arranged below the seven regions of the rail base. The cooling medium acts on the seven regions of the rail base through the nozzles. The first nozzle is located under the first region, and the cooling medium pressure of the first nozzle controls the first cooling rate of the cooling medium. The second nozzle is located under the second region, and the cooling medium pressure of the second nozzle controls the second cooling rate of the cooling medium. The third nozzle is located under the third region, and the cooling medium pressure of the third nozzle controls the third cooling rate of the cooling medium. The fourth nozzle is located under the fourth region, and the cooling medium pressure of the fourth nozzle controls the fourth cooling rate of the cooling medium.

3. The method for preparing a rail resistant to bottom fracture according to claim 2, characterized in that, The cooling medium pressure of the first nozzle is 4-10 kPa, the cooling medium pressure of the second nozzle is 3-8 kPa, the cooling medium pressure of the third nozzle is 2-6 kPa, and the cooling medium pressure of the fourth nozzle is 1-4 kPa.

4. The method for preparing a rail resistant to bottom fracture according to claim 1, characterized in that, The waste heat rail is a steel rail rolled online from a steel billet to a strength of 50kg / m-75kg / m, with a final rolling temperature of 850-1100℃.

5. The method for preparing a rail resistant to bottom fracture according to claim 1, characterized in that, The initial temperature of the rail base for accelerated cooling is controlled at 820-880℃. After the rail base is accelerated cooled to 420-480℃, it is air-cooled to room temperature.

6. The method for preparing a rail resistant to bottom fracture according to claim 1, characterized in that, The cooling time for accelerated cooling of the rail base is controlled between 45 and 105 seconds.

7. The method for preparing a rail resistant to bottom fracture according to claim 1, characterized in that, The cooling medium is a mixture of compressed air and quenching agent.

8. A rail resistant to bottom fracture, prepared by the method according to any one of claims 1-7.

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