Pearlite rail with uniformly distributed tensile strength across full section and production method thereof

Abstract

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

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of rail production, and in particular to a pearlite rail with uniformly distributed tensile strength across full section and production method thereof. BACKGROUND

[0002] As high-speed railway and heavy-haul railway develop towards a more specialized direction, the existing railway network is also facing further upgrading and reconstruction, and developing towards directions of high speed and high efficiency, which puts higher requirements on rail. At the same time, due to the overall development of the railway network, the operating environment of the railway is gradually becoming more complex, resulting in the overall material of the rail also facing situations that are more likely to cause damage to the surface and shallow surface of the rail at various positions during transportation, storage and service, and surface damage on the rail will have a negative impact on its service life and safety. Therefore, only by using rail with higher tensile strength across full section can ensure the stability of the rail throughout its entire life cycle and improve the transportation efficiency of railway.

[0003] In recent years, in order to improve the hardness of the rail, domestic and foreign rail production enterprises have mainly adopted offline or online heat treatment methods to perform accelerated cooling on rail head of rail, so as to refine the pearlite structure of the rail head, and obtain higher strength and hardness by refining grain. The relevant patent technologies involved are as follows:

[0004] Patent CN116371908 "A rolling method of American-standard medium-strength rail " discloses a rail with a tensile strength >1065MPa, a yield strength >723MPa, an elongation >10%, and surface hardness of the rail is >350HB after heat treatment, it comprises the following chemical composition, by mass percent, C: 0.70-0.85; Si: 0.30-0.57; Mn: 0.9-1.18; P<0.020; S<0.020; Cr: 0.10-0.3; and the balance being Fe and inevitable impurities. The rail has high internal hardness and tensile strength within the depth range of 0-25 mm, but the hardness difference between its rail waist and rail base reaches 3-4 HRC, it can be seen that the tensile strength difference is also large, and it is easy to be affected by external injuries during use, resulting in rail damage. At the same time, the large difference in tensile strength between the rail waist and the rail base may cause transverse cracks at the position under external force, resulting in rail fracture and affecting the service safety of the rail.

[0005] Patent CN 102220545 "High-carbon and high-strength heat-treated rail with high wear resistance and plasticity and manufacturing method thereof' discloses a high-carbon and high-strength heat-treated rail with a tensile strength of a rail head >1330MPa, an elongation >9%, a surface hardness of the rail head >380HB, a depth of hardened layer of more than 25mm, and with excellent performance in terms of wear resistance and plasticity, it comprises the following chemical composition, by mass percent, C: 0.80%~1.20%, Si: 0.20%~1.20%, Mn: 0.20%~1.60%, Cr: 0.15%~1.20%, V: 0.01%~0.20%, Ti: 0.002%~0.050%, P<0.030%, S<0.030%, Al<0.010%, N<0.0100%, and the balance being Fe and inevitable impurities. However, during the production process of the rail, only the online heat treatment strengthening of the rail head and base was considered, and no strengthening measures were taken for the rail waist which is most susceptible to damage by external force.

[0006] Patent CN104060075 "Heat treatment method of improving depth of hardened layer of rail" discloses a heat treatment method of naturally cooling the rail after finish rolling until the center temperature of a rail head surface is 660-730 °C, accelerating cooling at a cooling rate of 1.5-3.5 °C / s until the center temperature of the rail head surface is 500-550 °C, and then increasing the cooling rate by 1.0-2.0°C / s, when the center temperature of the rail head surface drops below 450°C, stopping accelerated cooling and air cooling to room temperature, with the adoption of which, the deep hardened layer with the thickness of 25mm at the rail head part can be obtained, the position which is 25mm below the surface layer of the rail head has the hardness value equal to that of the surface layer of the rail head, and the whole section of the rail head is in a pearlite structure, which is beneficial for improving the service performance of the rail after being continuously worn due to wheel-rail contact. However, the heat treatment method described in the patent only focuses on improving the hardness and tensile strength of the rail head part of the rail, and does not take into account the simultaneous improvement of the hardness and tensile strength of the rail waist and rail base of the rail.

[0007] It can be seen that among the current patents related to improving the tensile strength of pearlite rail, some patents can improve the tensile strength of the upper rounded comer of the rail head and the running surface of the rail, but none of them involve uniform improvement of the tensile strength of the waist and rail base of the rail. There are still obvious deficiencies in improving the actual service performance of rail. SUMMARY

[0008] The main purpose of the present invention is to provide a pearlite rail with uniformly distributed tensile strength across full section and production method thereof, so as to solve the technical problem that the prior art fails to comprehensively improve the tensile strength of the rail.

[0009] According to one aspect of the present invention, a method for producing a pearlite rail with uniformly distributed tensile strength across full section is proposed, comprising: performing an online heat treatment on a rolled rail, wherein the online heat treatment adopts a process for accelerating cooling different parts, comprises: an accelerated cooling stage: when a temperature of a running surface of the rail after final rolling is between 680°C and 810°C, performing accelerated cooling to different parts until the temperature of the rail running surface is between 480°C and 590°C; wherein the rail running surface has a cooling rate of 2.0-5.0°C / s, both sides of a rail head has a cooling rate of 1.5-4.0°C / s, both sides of an upper part of a rail waist has a cooling rate of 1.0-3.0°C / s, both sides of a middle part of the rail waist has a cooling rate of 0.8-2.5°C / s, and center of a rail base has a cooling rate of 1.5-3.0°C / s; and an air cooling stage: air cooling the rail after the accelerated cooling stage to room temperature.

[0010] According to an embodiment of the present invention, the cooling rate of the rail running surface, the cooling rate of both sides of the rail head, the cooling rate of both sides of the upper part of the rail waist, and the cooling rate of both sides of the middle part of the rail waist decrease sequentially.

[0011] According to an embodiment of the present invention, in the accelerated cooling stage, when the temperature of the rail running surface of the rail after final rolling is between 740°C and 800°C, performing accelerated cooling to different parts until the temperature of the rail running surface is between 490 °C and 560°C.

[0012] According to an embodiment of the present invention, in the accelerated cooling stage, the cooling rate of the rail running surface is 3.3-4.3°C / s, the cooling rate of both sides of the rail head is 2.9-3.7°C / s, the cooling rate of both sides of the upper part of the rail waist is 2.4-3.0°C / s, the cooling rate of both sides of the middle part of the rail waist is 1.5-2.1 °C / s, and the cooling rate of the center of the rail base is 1.8-2.5°C / s.

[0013] According to an embodiment of the present invention, when performing the online heat treatment, cooling medium used is water mist and / or compressed air.

[0014] According to an embodiment of the present invention, before performing the online heat treatment, the method further comprises: sequentially performing converter smelting, LF furnace refining, RH vacuum treatment, continuous casting, and rolling.

[0015] According to an embodiment of the present invention, the rail comprises the following chemical composition, by mass percent, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: <0.025%, S: <0.020%, and the balance being Fe and inevitable impurities.

[0016] According to another aspect of the present invention, a pearlite rail with uniformly distributed tensile strength across full section is proposed, comprising: the following chemical composition, by mass percent, C: 0.65-0.82%, Si: 0.10-0.60%, Mn: 0.65-1.25%, Cr: 0.05-0.25%, Mn+Cr: 0.75-1.50%, Mn / Cr: 7.0-10.0, P: <0.030%, S: <0.025%, and the balance being Fe and inevitable impurities; an upper rounded comer of a rail head, a center part of the rail head, a center part of a rail waist, and a center part of a rail base of the rail all have tensile strength of >1080MPa, with a difference of <80MPa.

[0017] According to an embodiment of the present invention, the tensile strength of the upper rounded comer of the rail head of the rail is >1180MPa, the upper rounded corner of the rail head of the rail has an elongation of >10.0%; a rail running surface has a hardness of 350-390HB; and the tensile strength of the center part of the rail head, the center part of the rail waist, and the center part of the rail base are all >1080MPa, and the center part of the rail head, the center part of the rail waist, and the center part of the rail base have an elongation of^l0.0%.

[0018] According to an embodiment of the present invention, the rail comprises the following chemical composition, by mass percent, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: <0.025%, S: <0.020%, and the balance being Fe and inevitable impurities.

[0019] Through the technical solution of the present invention, a pearlite rail with uniformly distributed tensile strength across full section can be prepared without adding multiple micro-alloying elements. This can improve the ability of the rail to resist external force damage during transportation, storage and service, significantly reduce the negative impact of external damage on the service performance of the rail, improve the service life and safety of the rail, and thus improve the overall transportation efficiency and safety of railway. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly explain the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings needed in the description of the embodiments or the prior art. It is obvious that the drawings in the following description are only some embodiments of the present invention. Those skilled in the art can also obtain other drawings from these drawings without creative work.

[0021] Figure 1 shows a schematic diagram of accelerated cooling and tensile strength testing of a rail with uniformly distributed tensile strength across full section according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present invention more clear, embodiments of the present invention are further described in detail with reference to the attached drawings and specific embodiments.

[0023] It should be noted that all the expressions of "first" and "second" in the embodiments of the present invention are used to distinguish two entities or parameters with the same name but not the same. It can be seen that "first" and "second" are only for the convenience of expression, and should not be understood as limiting the embodiments of the present invention. This will not be explained in the subsequent embodiments.

[0024] The present invention proposes a method for producing a pearlite rail with uniformly distributed tensile strength across full section, comprising: performing an online heat treatment on a rolled rail, wherein the online heat treatment comprises: an accelerated cooling stage: when a temperature of a rail running surface of the rail after final rolling is between 680°C and 810°C, performing accelerated cooling to different parts until the temperature of the rail running surface is between 480 °C and 590°C; wherein the rail running surface has a cooling rate of 2.0-5.0°C / s, both sides of a rail head has a cooling rate of 1.5-4.0°C / s, both sides of an upper part of a rail waist 8 has a cooling rate of 1.0-3.0°C / s, both sides of a middle part of the rail waist has a cooling rate of 0.8-2.5 °C / s, and center of a rail base has a cooling rate of 1.5-3.0°C / s; figure 1 shows accelerated cooling of various parts; and an air cooling stage: air cooling the rail after the accelerated cooling stage to room temperature on a cooling bed.

[0025] The inventors of the present invention have found through extensive research that:

[0026] ©For the accelerated cooling stage: when the temperature of the running surface of rail head is 680-810°C, in order to suppress the precipitation of proeutectoid ferrite or proeutectoid cementite in the rail and obtain a rail with relatively high tensile strength, it is necessary to perform accelerated cooling on the rail in a high temperature stage. At the same time, since the cross-sectional area of the rail running surface is the largest, followed by the two sides of the rail head, the upper part of the rail waist and the center of the rail base, and the cross-sectional area of the center of the rail waist is the smallest, it is necessary to control the accelerated cooling rate of different parts to be different to make each part obtain a more uniformly distributed tensile strength. The cooling rate of the rail running surface should be the largest, which is controlled within the range of 2.0-5.0°C / s. While the cooling rate of two sides of the rail head, two sides of the upper part of the rail waist, and two sides of the center of the rail waist decrease sequentially, which are controlled within the range of 1.5-4.0°C / s, 1.0-3.0°C / s, and 0.8-2.5°C / s, respectively. The cross-sectional area of the center of the rail base is between that of the two sides of the rail head and that of the two sides of the upper part of the rail waist, and the cooling rate is controlled within the range of 1.5-3.0°C / s.

[0027] (2)For the air cooling stage: after cooling the rail to 480-590 °C in the accelerated cooling stage, the pearlite phase transformation has been completed in all parts of the rail. At this time, there is no obvious meaning to continue accelerated cooling, and the rail can be air-cooled to room temperature for subsequent processing.

[0028] In some embodiments, in the accelerated cooling stage, when the temperature of the rail running surface of the rail after final rolling is between 740°C and 800°C, accelerated cooling to different parts is performed until the temperature of the rail running surface is between 490°C and 560°C.

[0029] In some embodiments, in the accelerated cooling stage, the cooling rate of the rail running surface is 3.3-4.3°C / s, the cooling rate of both sides of the rail head is 2.9-3.7°C / s, the cooling rate of both sides of the upper part of the rail waist is 2.4-3.0°C / s, the cooling rate of both sides of the middle part of the rail waist is 1.5-2.1 °C / s, and the cooling rate of the center of the rail base is 1.8-2.5°C / s.

[0030] In some embodiments, when performing the online heat treatment, cooling medium used is water mist and / or compressed air.

[0031] In some embodiments, before performing the online heat treatment, the method further comprises: sequentially performing converter smelting, LF furnace refining, RH vacuum treatment, continuous casting, and rolling. After the online heat treatment, the rail can be processed. In some embodiments, the complete production process of the rail can include: using low sulfur vanadium containing molten steel, smelting in a converter or electric furnace, refining in a LF furnace, performing RH or VD vacuum treatment, performing large square bloom protective continuous casting, performing bloom heating in a heating furnace, performing high-pressure water descaling before bloom rolling, performing rolling in a universal rolling mill, performing online heat treatment of the rail, performing room temperature air cooling on a stepping cooling bed, performing horizontal and vertical composite straightening, performing rail specification inspection, treating in machining line, performing surface inspection and storage.

[0032] In some embodiments, the rail comprises the following chemical composition, by mass percent, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: <0.025%, S: <0.020%, and the balance being Fe and inevitable impurities.

[0033] The following provides a detailed explanation of the reasons for the limiting of the content of the main chemical elements in the rail described in the present invention.

[0034] C is the most important and cheapest element in pearlite rails to achieve good comprehensive mechanical properties and promote pearlite transformation. When the C content is less than 0.65%, under the production process of the present invention, it is impossible to ensure that the rail has appropriate strength and hardness, and the performance of resistance to external force damage of the rail cannot be guaranteed. When the C content is greater than 0.82%, under the production process of the present invention, the strength index of the rail is excessive and the toughness and plasticity are too low, and the proportion of carbides is too high, which affects the toughness and plasticity of the rail and has adverse effects on the safe use of the rail. Therefore, the carbon content in the present invention is limited to 0.65-0.82%.

[0035] The main function of Si in steel is to inhibit the formation of cementite and act as a solid solution strengthening element, improve the hardness of the ferrite matrix, and improve the strength and hardness of the steel. When the Si content is less than 0.10%, its solid solution amount is too low, resulting in an insignificant strengthening effect. When the Si content is greater than 0.60%, local segregation is prone to occur, which will reduce the toughness and plasticity of the steel and have adverse effects on the safe use of the rail. Therefore, the Si content in the present invention is limited to 0.10-0.60%.

[0036] Mn is essential for improving the strength of ferrite and austenite in steel. When the Mn content is less than 0.65%, it is difficult to achieve the effect of increasing the hardness of carbides and thus increasing the strength and hardness of steel. When the Mn content is greater than 1.25%, it will coarsen the grain size and significantly reduce the toughness and plasticity of the steel. At the same time, Mn has a significant impact on the diffusion of C in steel, and abnormal structures such as bainite or martensite may occur in the Mn segregation area, which also affects the welding performance of the rail. Therefore, the Mn content in the present invention is limited to 0.65-1.25%.

[0037] As a carbide-forming element, Cr can form various carbides with carbon in steel. At the same time, Cr can uniformly distribute carbides in steel, reduce the size of carbides, improve the strength and hardness of the rail, and improve the wear resistance of the rail. When the Cr content is less than 0.05%, the hardness and proportion of the formed carbides are relatively low. When the Cr content is greater than 0.25%, the hardenability of the rail is too high, which can easily lead to the production of harmful bainite and martensite structures in the rail, and cannot guarantee that the rail has a pearlite structure, which has adverse effects on the safe use of the rail. Therefore, the Cr content in the present invention is limited to 0.05-0.25%.

[0038] Since Mn and Cr are strengthening elements that increase the strength and hardness of the rail and improve the hardenability of the rail, it is necessary to limit their total content to control that abnormal structures such as martensite do not appear in the microstructure of the rail and ensure that the performance of finished rail meets the requirements. When the Mn+Cr content is less than 0.75%, it is difficult to provide sufficient carbides, the strengthening effect is weak, and it is impossible to ensure that the hardness of the rail meets the design indicators. When the Mn+Cr content is greater than 1.45%, since both Mn and Cr can improve the hardenability of the rail, there is a relatively high risk of abnormal structure in the rail. Therefore, the Mn+Cr content in the present invention is limited to 0.75-1.45%.

[0039] In rail steel, controlling the balance of Mn and Cr content is crucial for the comprehensive control of the structure and hardness of the rail. If only the Mn content is increased, the rail structure will be relatively stable, but the internal hardness will be low. If the Cr content is increased, the internal hardness of the rail can be improved, but abnormal structure is prone to occur. When Mn / Cr<7.0, the Cr content in the rail is relatively high, although a relatively high hardness can be achieved, the risk of appearing abnormal structure is relatively high. When Mn / Cr>10.0, the Mn content in the rail is relatively high, although the full pearlite structure can be maintained, the internal hardness is relatively low. Therefore, the Mn / Cr value in the present invention is limited to 7.0-10.0.

[0040] Both P and S are impurity elements that cannot be completely removed from the rail. P will be segregated at the grain boundaries of the rail microstructure, seriously reducing the toughness of the rail. S is prone to form MnS inclusions in steel, which is harmful to the wear resistance and contact fatigue resistance of the rail. Therefore, the P content in the present invention needs to be controlled below 0.030%; the S content needs to be controlled below 0.030%.

[0041] The present invention also proposes a pearlite rail with uniformly distributed tensile strength across full section, the rail comprises the following chemical composition, by mass percent, C: 0.65-0.82%, Si: 0.10-0.60%, Mn: 0.65-1.25%, Cr: 0.05-0.25%, Mn+Cr: 0.75-1.50%, Mn / Cr: 7.0-10.0, P: <0.030%, S: <0.025%, and the balance being Fe and inevitable impurities; an upper rounded corner of a rail head, a center part of the rail head, a center part of a rail waist, and a center part of a rail base of the rail all have tensile strength of >1080MPa, with a difference of <80MPa. Figure 1 shows a schematic diagram of tensile strength testing, wherein position © is the position for testing the tensile strength of the upper rounded corner on the rail, position @ is the position for testing the tensile strength of the center of the rail head, position (3) is the position for testing the tensile strength of the center of the rail waist, and position ©is the position for testing the tensile strength of the center of the rail base.

[0042] In some embodiments, the tensile strength of the upper rounded comer of the rail head of the rail is >1180MPa, the upper rounded comer of the rail head of the rail has an elongation of >10.0%; a rail mnning surface has a hardness of 350-390HB; the tensile strength of the center part of the rail head, the center part of the rail waist, and the center part of the rail base are all >1080MPa, and the center part of the rail head, the center part of the rail waist, and the center part of the rail base have an elongation of >10.0%.

[0043] In some embodiments, the rail comprises the following chemical composition, by mass percent, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: <0.025%, S: <0.020%, and the balance being Fe and inevitable impurities.

[0044] In summary, the present invention adopts a method of controlling the chemical composition of the rail and the online heat treatment process, and the obtained pearlite rail has uniformly distributed tensile strength across the full section without adding multiple micro-alloying elements. This can improve the ability of the rail to resist external force damage during transportation, storage and service, significantly reduce the negative impact of external damage on the service performance of the rail, improve the service life and safety of the rail, and thus improve the overall transportation efficiency and safety of railway. At the same time, the method for producing the pearlite rail with uniformly distributed tensile strength across full section proposed by the present invention is simple and easy to operate, and is conducive to promotion and application.

[0045] The following is a description based on specific embodiments.

[0046] Examples 1-3 and comparative examples 1-3 correspondingly select rails with the following chemical compositions numbered 1-3, the specific chemical compositions are shown in table 1, and the balance being Fe and inevitable impurities.

[0047] Table 1: rail chemical composition (wt%) Number C Si Mn Cr P S Mn+Cr Mn / Cr 1 0.73 0.48 1.01 0.12 0.023 0.004 1.13 8.42 2 0.79 0.53 1.19 0.17 0.018 0.009 1.36 7.00 3 0.77 0.59 1.10 0.14 0.013 0.012 1.24 7.86

[0048] The heat treatment process parameters for examples 1-3 and comparative examples 1-3 are shown in table 2. The differences between the smelting process and the rolling process of the examples and them of the comparative examples are negligible.

[0049] Table 2: heat treatment process parameters Number Accelerated cooling start temperature re Cooling rate of rail running surface / °C / s Cooling rate of both sides of rail head / °C / s Cooling rate of both sides of upper part of rail waist / °C / s Cooling rate of both sides of center of rail waist / °C / s Cooling rate of center of rail base / °C / s Accelerated cooling stop temperature re Example 1 798 4.21 3.65 2.98 2.05 2.45 554 Example 2 746 3.69 3.32 2.79 1.65 2.07 498 Example 3 765 3.37 2.95 2.48 1.57 1.86 519 Comparative example 1 739 4.08 4.08 / / / 529 Comparative example 2 765 3.86 3.75 / / 3.53 554 Comparative example 3 748 3.54 3.29 2.77 2.23 / 501

[0050] The microstructures, tensile properties and hardness of the rail runnning surface of examples 1-3 and comparative examples 1-3 are shown in table 3. Wherein, the positions for measuring tensile strength are shown in figure 1, position © is the position for testing the tensile strength of the upper rounded corner on the rail, position @ is the position for testing the tensile strength of the center of the rail head, position (3) is the position for testing the tensile strength of the center of the rail waist, and position ©is the position for testing the tensile strength of the center of the rail base. According to provisions of GB / T 228.1 "Metallic materials Tensile testing Part 1: Method of test at room temperature", tensile specimens are taken at various positions and subjected to tensile testing.

[0051] Table 3: microstructure, hardness of rail running surface and tensile properties Item Example 1 Example 2 Example 3 Compara tive exam ple 1 Compara tive exam ple 2 Compara tive exam ple 3 Microstructure Pearlite Pearlite Pearlite Pearlite Pearlite Pearlite hardness of rail running surface / HB 378 366 359 375 368 361 Upper rounded comer of rail head Tensile strength / MPa 1285 1256 1237 1276 1264 1233 Elongation / % 11.0 12.0 13.0 12.0 11.5 10.0 Center of rail head Tensile strength / MPa 1207 1178 1158 1183 1098 1074 Elongation / % 10.5 11.0 10.5 10.5 10.5 10.5 Center of rail waist Tensile strength / MPa 1213 1184 1171 987 973 1015 Elonga- 10.5 10.0 12.0 10.0 11.0 11.5 tion / % Center of rail Tensile strength / MPa 1225 1201 1209 963 1146 1026 base Elongation / % 11.5 10.5 11.5 10.5 10.0 12.0

[0052] By comparing the embodiments and the comparative examples, it can be seen that, under the same chemical composition and smelting process, the different heat treatment methods for the rolled rails in the embodiments described in the present invention will have a significant impact on the final performance of the rails. By adopting the method described in the present invention, the hardness of the rail running surface obtained is in the range of 350-390HB, and the tensile strength of the upper rounded comer of the rail head, the center of the rail head, the center of the rail waist, and the center of the rail base is relatively high, with a difference of less than 80MPa and a uniform distribution. This can effectively reduce the negative impact of damage to the surface and shallow surface of the rail on the service performance and safety of the rail. While in the comparative example, the tensile strength of the part that has not been heat treated is significantly reduced, and this position is easily damaged by external force during the use of the rail, resulting in cracks and then possible fracture of the rail.

[0053] Those skilled in the art should understand that the discussion of any of the above embodiments is only illustrative and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including claims) is limited to these examples; under the idea of the embodiments of the present invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention described above, which are not provided in details for simplicity. Therefore, any omission, modification, equivalent replacement, improvement, etc. made in the spirit and principle of the embodiments of the present invention shall be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for producing a pearlite rail with uniformly distributed tensile strength across full section, characterized by comprising: performing an online heat treatment on a rolled rail, wherein the online heat treatment comprises:an accelerated cooling stage: when a temperature of a rail running surface of the rail after final rolling is between 680°C and 810°C, performing accelerated cooling to different parts until the temperature of the rail running surface is between 480°C and 590°C; wherein the rail running surface has a cooling rate of 2.0-5.0°C / s, both sides of a rail head has a cooling rate of 1.5-4.0°C / s, both sides of an upper part of a rail waist has a cooling rate of 1.0-3.0°C / s, both sides of a middle part of the rail waist has a cooling rate ofO,8-2.5°C / s, and center of a rail base has a cooling rate of 1.5-3.0°C / s; andan air cooling stage: air cooling the rail after the accelerated cooling stage to room temperature.

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

3. The method according to claim 1, characterized in that in the accelerated cooling stage, when the temperature of the rail running surface of the rail after final rolling is between 740°C and 800°C, performing accelerated cooling to different parts until the temperature of the rail running surface is between 490 °C and 560 °C.

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

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

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

7. The method according to claim 1, characterized in that the rail comprises the following chemical composition, by mass percent, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: <0.025%, S: <0.020%, and the balance being Fe and inevitable impurities.

8. A pearlite rail with uniformly distributed tensile strength across full section, characterized by comprising the following chemical composition, by mass percent, C: 0.65-0.82%, Si: 0.10-0.60%, Mn: 0.65-1.25%, Cr: 0.05-0.25%, Mn+Cr: 0.75-1.50%, Mn / Cr: 7.0-10.0, P: <0.030%, S: <0.025%, and the balance being Fe and inevitable impurities; an upper rounded comer of a rail head, a center part of the rail head, acenter part of a rail waist, and a center part of a rail base of the rail all have tensile strength of >1080MPa, with a difference of <80MPa.

9. The rail according to claim 8, characterized in that the tensile strength of the upper rounded corner of the rail head of the rail is >1180MPa, the upper rounded comer of the rail head of the rail has an elongation of >10.0%; a rail running surface has a hardness of 350-390HB; and the tensile strength of the center part of the rail head, the center part of the rail waist, and the center part of the rail base are all >1080MPa, and the center part of the rail head, the center part of the rail waist, and the center part of the rail base have an elongation of >10.0%.

10. The rail according to claim 8, characterized in that the rail comprises the following chemical composition, by mass percent, C: 0.68-0.80%, Si: 0.25-0.60%, Mn: 0.75-1.20%, Cr: 0.05-0.20%, Mn+Cr: 0.85-1.45%, Mn / Cr: 7.5-10.0, P: <0.025%, S: <0.020%, and the balance being Fe and inevitable impurities.

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