Method for manufacturing pearlitic steel rail having high surface hardness

Abstract

A method for manufacturing a pearlitic steel rail having high surface hardness, relating to the technical field of iron and steel smelting. The method comprises: feeding molten steel having undergone preliminary smelting into a ladle refining furnace, and adding an alloying element for deoxidization and alloying treatment to obtain refined molten steel, so as to further obtain a continuous casting billet; heating the continuous casting billet to a preset temperature by means of a heating furnace, and feeding the heated continuous casting billet into a rolling mill for multi-pass rolling comprising first-pass rolling and second-pass rolling, wherein during the first-pass rolling, the rolling speed is 5.0-7.5 s-1, and the rolling deformation should be 10-15%; after the first-pass rolling, the original austenite grain size is 85-115 μm; and the number of rolling passes is 9-13, and the total deformation is 85-95%; and gradually reducing the gap between rollers of the rolling mill to obtain steel rail blocks having desired specifications and shapes and performing on-line heat treatment and processing treatment on the steel rail blocks to obtain steel rails.

Description

Manufacturing method of pearlitic rail with high surface hardness

[0001] The present application claims priority to the Chinese patent application No. 202411060856.8, filed on August 2, 2024, and entitled "Manufacturing method of pearlitic rail with high surface hardness", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of steel smelting, more particularly to a manufacturing method of pearlitic rail with high surface hardness. BACKGROUND

[0003] In recent years, domestic and foreign rail production enterprises mainly use offline or online heat treatment to accelerate the cooling of the rail head, and combine with rolling process optimization to refine the pearlite structure of the rail head part, so as to obtain higher strength and hardness through grain refinement. The related patent technologies involved are as follows:

[0004] The prior art does not consider the key influence of the original austenite organization of the rail caused by the deformation of the rail continuous casting billet during the high temperature process at the initial stage of rail rolling on the performance of the rail, and does not consider the toughness of the rail, which has limited ability to improve the performance of the rail and insufficient consideration of the service safety of the rail.

[0005] The surface hardness of the prior art cannot reach more than 400HB, and the tensile strength cannot reach more than 1280MPa, which is difficult to be used as heavy load railway rail. At the same time, the online heat treatment process used by the prior art has low matching with the chemical composition, which cannot guarantee that the rail organization is full pearlite organization, and the abnormal organization such as martensite in the rail may cause serious safety accidents such as rail fracture during actual service of the rail.

[0006] The prior art cannot simultaneously achieve comprehensive improvement of tensile strength and elongation after fracture, and the steel rail manufacturing method of the prior art is complex, the product inspection method is difficult, and it is difficult to popularize and apply.

[0007] The prior art uses a high-carbon hypereutectoid composition system, which contains cementite in the microstructure, which will deteriorate the toughness and fatigue performance of the rail after distributing along the grain boundary. At the same time, the rail production method described in the prior art has limitations on the rolling compression ratio of the rail, and has many limitations on the parameters of each pass, which is complex and difficult to be applied on a large scale in actual production.

[0008] In the currently published patents related to improving the surface hardness of pearlitic rail, some patents improve the surface hardness of the rail by modifying some parameters in the production process of the rail, but none of them involves the control of the microstructure before the transformation of austenite microstructure in the high temperature stage, and they cannot improve the surface hardness of the rail from the basic principles of materials science and by using scientific methods. There is still a significant deficiency in improving the surface hardness of the rail. SUMMARY

[0009] Therefore, in one aspect, the present application provides a manufacturing method of a pearlitic rail with high surface hardness, comprising:

[0010] S1. feeding the molten steel after preliminary smelting into a ladle refining furnace, adding alloying elements for deoxidation and alloying treatment to obtain refined molten steel;

[0011] S2. treating the refined molten steel to obtain a continuous casting billet;

[0012] S3. heating the continuous casting billet to a preset temperature through a heating furnace, and feeding the heated continuous casting billet into a rolling mill for multi-pass rolling; the rolling includes first-pass rolling and second-pass rolling, wherein: when the first-pass rolling is performed, the rolling rate is 5.0-7.5 s -1 , and the rolling deformation amount should be 10-15%; after the first-pass rolling, the original austenite grain size is 85-115 μm; the rolling pass number is 9-13, and the total deformation amount is 85-95%; the required size and shape of the rail block are obtained by gradually reducing the roll gap of the rolling mill;

[0013] S4. performing online heat treatment and processing treatment on the rail block to obtain a rail.

[0014] In some embodiments, in step S3, the preset temperature for heating the continuous casting billet is 1150-1280℃, and the temperature is maintained for more than 45 min;

[0015] After the continuous casting billet is maintained at the temperature, the continuous casting billet is rolled into a rail block, and the rolling start temperature is 1150-1250℃.

[0016] In some embodiments, step S2 includes: feeding the refined molten steel into a vacuum circulation degassing device for vacuum treatment to obtain treated molten steel, and then continuously casting the treated molten steel through a continuous casting machine to form a continuous casting billet.

[0017] In some embodiments, in step S4, the online heat treatment includes heating, cooling, and temperature maintenance;

[0018] After the online heat treatment, the rail rolling is completed, the heating temperature is the rail top surface temperature between 675-815℃, the accelerated cooling is performed on the rail top surface and both sides of the rail head, and the cooling speed is 1.8-4.5℃ / s , and the accelerated cooling is stopped when the temperature is cooled to 495-575 DEG C, and the cooling is stopped at room temperature.

[0019] In some embodiments, in step S4, the cooling medium used in the online heat treatment is compressed air and / or water mist.

[0020] In some embodiments, in step S4, the processing treatment includes removing the surface scale and defects, and performing size finishing and surface treatment.

[0021] In some embodiments, the size of the continuous casting billet is: cross-sectional area 250mm*250mm-450mm*450mm, and the length is 5000mm-7000mm.

[0022] In some embodiments, the weight of the rolled rail per meter is 43-75kg.

[0023] In another aspect, the present application provides a heavy rail with high elongation after fracture prepared according to the method described above, the rail comprising the following components in mass fraction: C: 0.68-0.86%, Si: 0.15-0.70%, Mn: 0.50-1.25%, Cr: 0.05-0.30%, V: 0.01-0.10%, P≤0.030%, S≤0.025%, and the balance being Fe and impurities.

[0024] In some embodiments, the full cross-section microstructure of the rail is pearlite; the surface hardness of the rail top surface is in the range of 400-430HB according to Brinell hardness; the tensile strength of the rail is≥1280MPa, and the elongation after fracture is≥10%.

[0025] The present application has at least the following beneficial technical effects:

[0026] The present application provides a manufacturing method of a pearlitic rail with high surface hardness, the method comprising: feeding the molten steel after preliminary smelting into a ladle refining furnace, adding alloying elements for deoxidation and alloying treatment to obtain refined molten steel; treating the refined molten steel to obtain a continuous casting billet; heating the continuous casting billet to a preset temperature through a heating furnace, and feeding the heated continuous casting billet into a rolling mill for multi-pass rolling; the rolling includes first-pass rolling and second-pass rolling, wherein: when the first-pass rolling is performed, the rolling speed is 5.0-7.5s -1 , and the rolling deformation amount is 10-15%; after the first-pass rolling, the original austenite grain size is 85-115μm; the rolling pass number is 9-13, and the total deformation amount is 85-95%; the rail block with the required specification and shape is obtained by gradually reducing the roll gap of the rolling mill, and the rail is obtained by performing online heat treatment and processing treatment on the rail block.

[0027] The application adopts a method of controlling the chemical composition of the steel rail, rolling process and on-line heat treatment process, and the obtained pearlitic steel rail has high surface hardness without adding multiple micro-alloying elements, does not contain abnormal structures such as cementite and martensite in the microstructure which affect the service life of the steel rail, the surface hardness at the center of the rail top surface is in the range of 400-430 HB, and the wear resistance and service life of the steel rail on the heavy load line can be improved, thereby improving the overall transportation efficiency and safety of the heavy load railway. Meanwhile, the manufacturing method for improving the surface hardness of the pearlitic steel rail provided by the application is simple and easy to operate, and is conducive to popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, and are used together with the specific embodiments described below to explain the application, but do not constitute a limitation on the application. In the drawings:

[0029] Fig. 1 shows a flow chart of a manufacturing method of a pearlitic steel rail with high surface hardness according to an embodiment of the application;

[0030] Fig. 2 shows a component mass fraction diagram of the pearlitic steel rail with high surface hardness according to the application;

[0031] Fig. 3 shows a heat treatment process parameter diagram of the pearlitic steel rail with high surface hardness and the comparative example according to the application;

[0032] Fig. 4 shows a performance comparison diagram of the pearlitic steel rail with high surface hardness and the comparative example according to the application. DETAILED DESCRIPTION

[0033] The specific embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0034] In addition, the reference to "embodiments" in this text means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] Those skilled in the art will understand that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0036] In one aspect, the present application provides a manufacturing method of pearlitic rail with high surface hardness, referring to Fig. 1, which comprises:

[0037] S1. feeding the molten steel after primary smelting into a ladle refining furnace, adding alloying elements for deoxidization and alloying treatment to obtain refined molten steel;

[0038] S2. processing the refined molten steel to obtain a continuous casting billet;

[0039] S3. heating the continuous casting billet to a preset temperature through a heating furnace, and feeding the heated continuous casting billet into a rolling mill for multi-pass rolling; the rolling comprises first-pass rolling and second-pass rolling, wherein: when the first-pass rolling is performed, the rolling speed is 5.0-7.5 s -1 , the rolling deformation amount should be 10-15%; after the first-pass rolling, the original austenite grain size is 85-115 μm; the rolling pass number is 9-13, and the total deformation amount is 85-95%; the steel rail block with the required specification and shape is obtained by gradually reducing the roll gap of the rolling mill;

[0040] S4. performing online heat treatment and processing treatment on the steel rail block to obtain a steel rail.

[0041] The original austenite grain size of 85-115 μm means more interfaces and dislocations, thereby reducing the processing difficulty and improving the processing efficiency; these interfaces and dislocations can more effectively resist external stress, thereby improving the strength and toughness of the steel material. It can make the steel material form more fine microstructure, such as fine pearlite and bainite, in the subsequent cooling and transformation process, which helps to further improve the performance of the steel material, and also can reduce the number of defects in the steel material, such as cracks and inclusions, thereby improving the quality and reliability of the steel material.

[0042] Before the heating and rolling of the continuous casting billet, the method further comprises, in sequence: LF furnace refining, RH vacuum treatment, and continuous casting.

[0043] After the heating and rolling of the continuous casting billet, the method further comprises, in sequence: online heat treatment and processing.

[0044] The complete manufacturing process of the steel rail can be: using low-sulfur vanadium-containing molten steel, smelting by converter or electric furnace, LF refining, RH or VD vacuum treatment, protective continuous casting of bloom, heating of the bloom in a bloom heating furnace, high-pressure water descaling of the bloom before rolling, rolling by a universal rolling mill, on-line heat treatment of the steel rail, air cooling of the steel rail at room temperature in a walking beam cooling bed, flat-stand combined straightening, steel rail specification inspection, processing line treatment, surface inspection, and storage.

[0045] In some embodiments, in step S3, the preset temperature of the continuous casting billet heating is 1150-1280℃, and the temperature is maintained for more than 45 minutes.

[0046] After the continuous casting billet is maintained at the temperature, the continuous casting billet is rolled into a steel rail block, and the rolling start temperature is 1150-1250℃.

[0047] For the continuous casting billet heating temperature and the steel rail rolling start temperature, the steel rail rolling start temperature is in the range of 1150-1250℃, so as to ensure that the deformation resistance in the steel rail rolling process is minimum, and the original austenite grain size is appropriate, and the grain refinement effect is most obvious in the subsequent rolling process. Above this temperature, the continuous casting billet is always at high temperature in the rolling process, and it is difficult to obtain refined grains in the subsequent pearlite transformation; and below this temperature, the deformation resistance in the steel rail rolling process increases, resulting in that the multi-pass rolling cannot be smoothly performed.

[0048] For the continuous casting billet holding time, only when the holding time is more than 45 minutes at the heating temperature of 1150-1280℃, the center of the continuous casting billet with the size specified in the present application can reach the rolling required temperature, so as to ensure that the steel rail deformation resistance in the rolling process is minimum, and the steel rail full-section grain refinement effect is obvious.

[0049] By limiting the heating temperature, the microstructure transformation of the steel rail during heating can be accurately controlled, thereby obtaining the required hardness range. This hardness range not only meets the national standards, but also meets the performance requirements of the railway operation. Under appropriate heating temperature, the grain structure inside the steel rail will change, such as grain refinement and phase transformation, which helps to improve the mechanical properties and durability of the steel rail. Limiting the heating temperature can ensure that these microstructure changes are within a controllable range, thereby obtaining a steel rail with excellent performance. Operating within a stable heating temperature range can maintain the stability of the production process, reduce performance fluctuations and quality problems caused by temperature fluctuations. Excessive heating temperature may cause the steel rail to coarsen, degrade in performance, or even produce waste products. By limiting the heating temperature, the waste product rate can be reduced, and the production efficiency can be improved.

[0050] In some embodiments, step S2 includes: sending the refined molten steel into a vacuum circulating degassing device for vacuum treatment, obtaining treated molten steel, and then continuously casting the treated molten steel by a continuous casting machine to form a continuous casting billet.

[0051] Through LF refining and RH vacuum treatment, the chemical composition of the molten steel can be precisely controlled, harmful impurities and gases can be removed, and the purity and uniformity of the molten steel can be ensured, laying a solid foundation for the production of high-quality rails. During continuous casting, heating and rolling, through reasonable temperature control and deformation treatment, the internal microstructure of the rail can be optimized, making it more dense and uniform, thereby improving the mechanical properties and durability of the rail. The final hardness of the rail is in the range of 400-430 HB, which not only meets the national standard but also meets the requirements of rail hardness, wear resistance, fatigue resistance and other aspects for railway operation.

[0052] The continuous casting process realizes continuous pouring and solidification of the molten steel, greatly improving production efficiency and reducing production cycle. Each production link is carefully designed and strictly controlled to ensure the stability and consistency of the production process, reducing the scrap rate and substandard rate. Modern rail production lines generally use automated equipment and control systems, reducing manual intervention and improving production efficiency and product quality.

[0053] In some embodiments, in step S4, the online heat treatment includes heating, cooling and holding;

[0054] The online heat treatment process is as follows: after the rolling of the rail is completed, the heating temperature is between 675-815°C at the rail top surface, accelerated cooling is performed on the rail top surface and both sides of the rail head, the cooling speed is 1.8-4.5°C / s, and when the temperature cools to 495-575°C, the accelerated cooling is stopped, and the air cooling is performed to room temperature.

[0055] Online heat treatment technology can directly heat treat steel during rolling, eliminating the need for offline secondary heating. This not only reduces production steps, but also shortens production cycle, thereby improving overall production efficiency. This instant treatment method speeds up the production rhythm and improves the continuity and smoothness of the production line.

[0056] Online heat treatment technology can fully utilize the residual heat generated during rolling to heat treat the steel. This avoids energy waste and reduces energy consumption during production. Since the offline secondary heating process is eliminated, energy consumption due to reheating is also reduced. This is of great significance for reducing production costs and improving economic benefits.

[0057] In some embodiments, in step S4, compressed air and / or water mist are used as cooling media during online heat treatment.

[0058] Compressed air has a high flow rate and volume, which can quickly remove the heat from the surface of the steel, achieving rapid cooling. This is particularly important for heat treatment processes that require rapid quenching or controlled cooling rates. By designing the compressed air injection method and flow rate appropriately, uniform cooling of the steel surface can be achieved, avoiding excessive temperature gradients that can cause thermal stress and deformation.

[0059] Compressed air as a cooling medium does not contain harmful substances and does not pollute the environment and equipment. At the same time, compressed air can be recycled to reduce waste and reduce energy consumption. Compared with traditional water cooling or oil cooling methods, compressed air cooling does not require additional heating or cooling equipment, reducing energy consumption. In addition, compressed air cooling can also use waste heat from the production process for preheating, further improving energy efficiency.

[0060] By adjusting the flow rate, pressure, and injection angle of compressed air, the cooling speed and temperature distribution of the steel can be precisely controlled to meet different heat treatment requirements. The compressed air cooling system is relatively simple, reducing the complexity and maintenance difficulty of the equipment. At the same time, compressed air is not prone to scaling or clogging, reducing the workload of cleaning and maintenance.

[0061] Uniform and rapid cooling can reduce deformation and crack formation during heat treatment of the steel, improving the dimensional accuracy and surface quality of the product. By precisely controlling the cooling speed and time, the internal microstructure of the steel can be optimized, such as grain refinement, hardness improvement, etc., thereby improving the mechanical properties and durability of the product.

[0062] In some embodiments, in step S4, the processing treatment includes removing the surface scale and defects, performing size finishing, and surface treatment.

[0063] Through surface treatment, such as quenching, tempering, carburizing, nitriding, etc., the hardness and wear resistance of the steel rail can be significantly improved, enabling it to resist wear and impact during train operation, prolonging the service life. Spraying, sandblasting, etc. can improve the stress distribution state of the steel rail surface, reduce stress concentration, thereby improving the fatigue resistance of the steel rail and reducing the occurrence of cracks and fractures.

[0064] In some embodiments, the continuous casting billet has a size of 250mm x 250mm to 450mm x 450mm in cross-sectional area and a length of 5000mm to 7000mm.

[0065] After the size of the continuous casting billet is fixed, the equipment on the production line does not need to be frequently adjusted to adapt to different sizes of the steel billet, thereby reducing the time and labor cost of equipment adjustment. The fixed size of the continuous casting billet can maintain the continuity and stability of production, reducing production interruptions and downtime caused by size changes.

[0066] In some embodiments, the rolled steel rail has a weight of 43-75 kg per meter.

[0067] In another aspect, the present application provides a pearlitic steel rail with high surface hardness, which can be prepared by the method as described above, and comprises the following components by mass fraction: C: 0.68-0.86%, Si: 0.15-0.70%, Mn: 0.50-1.25%, Cr: 0.05-0.30%, V: 0.01-0.10%, P≤0.030%, S≤0.025%, and the balance of Fe and impurities.

[0068] C is the most important and cheapest element in the pearlitic steel rail, which can help the steel rail to obtain good comprehensive mechanical properties and promote pearlite transformation. When the content of C is less than 0.68%, the steel rail cannot have suitable hardness and wear resistance under the production process described in the present application. When the content of C is greater than 0.86%, the proportion of carbides in the steel rail is too high, which can cause high hardness points and uneven structure in the steel rail, and has an adverse effect on the safe use of the steel rail. Therefore, the content of C in the present application is limited to 0.68-0.86%.

[0069] The main role of Si in steel is to inhibit cementite formation and act as a solid solution strengthening element to improve the hardness of ferrite matrix and the strength and hardness of the steel. When the content of Si is less than 0.15%, the solid solution amount is low, which can not have obvious strengthening effect. When the content of Si is greater than 0.70%, the steel rail is prone to surface defects, and martensite abnormal structure can appear in the steel, which has an adverse effect on the safe use of the steel rail. Therefore, the content of Si in the present application is limited to 0.15-0.70%.

[0070] Mn can improve the hardenability of steel and is essential to increase the strength of ferrite and austenite in steel. When the content of Mn is less than 0.50%, it is difficult to increase the hardness of carbides and thus increase the strength of the steel. When the content of Mn is greater than 1.25%, it can coarsen the grain size and significantly reduce the toughness and plasticity of the steel. At the same time, Mn has a significant effect on the diffusion of C in steel, and abnormal structures such as bainite or martensite can be generated in the Mn segregation area, which can affect the welding performance of the steel rail. Therefore, the content of Mn in the present application is limited to 0.50-1.25%.

[0071] Cr as carbide forming element, with the carbon in the steel can form a variety of carbides, and Cr can evenly distribute the carbides in the steel, reduce the size of the carbide, improve the strength, hardness of the rail, improve the wear resistance of the rail. When the content of Cr <0.05%, the hardness and proportion of the formed carbide is low, which cannot play a strengthening role, when the content of Cr >0.30%, the hardenability of the rail is too high, which is easy to make the rail produce harmful bainite and martensite structure, which cannot guarantee the rail to be pearlite structure, and has adverse effects on the safe use of the rail. Therefore, the content of Cr in the application is limited to 0.05-0.30%.

[0072] V can form vanadium nitride containing Cr and other elements in the steel, which has precipitation strengthening effect. When the content of V <0.01%, it cannot form enough vanadium nitride in the steel, and the strengthening effect is insufficient, when the content of V >0.10%, too much vanadium nitride will be produced, which will increase the brittleness of the rail pearlite structure, and reduce the wear resistance of the rail, and increase the production cost. Therefore, the content of V in the application is limited to 0.01-0.10%

[0073] P and S are both impurity elements that cannot be completely removed in the rail. P will be segregated at the grain boundary of the rail structure, which will seriously reduce the toughness of the rail, and S is easy to form MnS inclusions in the steel, which is harmful to the wear resistance and contact fatigue resistance of the rail. Therefore, the content of P in the application should be controlled below 0.030%, and the content of S should be controlled below 0.030%.

[0074] In some embodiments, the microstructure of the rail is all pearlite, the surface hardness of the rail top surface is in the range of 400-430 HB calculated by Brinell hardness, the tensile strength of the rail is ≥1280 MPa, and the elongation after fracture is ≥10%.

[0075] High surface hardness means that the surface of the rail can resist wear and tear better, thereby prolonging its service life and reducing the cost of replacement and maintenance due to wear and tear. It helps to improve the fatigue resistance of the rail and reduce the cracking and breaking phenomenon caused by long-term bearing of the pressure and impact force of train operation. For heavy haul railway, high surface hardness rail can better withstand greater load and impact force, ensuring the safe operation of the railway line. High surface hardness rail can maintain good performance stability under different climate and environmental conditions, reducing performance degradation or damage caused by environmental changes.

[0076] In some embodiments, referring to FIG. 2, FIG. 3 and FIG. 4, the application will be described in detail by examples, but the scope of the application is not limited thereto.

[0077] The steels of Examples 1-3 and Comparative Examples 1-3 were selected from the following chemical compositions 1-3, and the specific chemical compositions are shown in FIG. 2. Except for the chemical compositions shown in FIG. 2, the balance was Fe and inevitable impurities.

[0078] The heat treatment process parameters of Examples 1-3 and Comparative Examples 1-3 are shown in FIG. 3, and the differences between the remaining processes of the examples and the comparative examples are negligible.

[0079] The tensile properties, surface hardness, microstructure, and original austenite grain size of Examples 1-3 and Comparative Examples 1-3 are shown in FIG. 4. According to GB / T 231.1 "Metallic Materials Brinell Hardness Test Part 1: Test Method", the Brinell hardness measurement method was used to measure the surface hardness of the rail and the average value was taken; according to GB / T 228.1 "Metallic Materials Tensile Test Part 1: Room Temperature Test Method", the tensile strength and elongation after fracture of the rail were measured; according to GB / T 13298-2015 "Metallic Microstructure Test Method", the original austenite grain size of the rail after the first rolling pass was measured.

[0080] By comparing the examples and the comparative examples, it can be seen that under the same chemical composition and smelting process, the different processes of rail heating and rolling have a significant impact on the microstructure and final performance of the rail. The rail obtained by using the method of the present application has a microstructure of pearlite, a rail top surface center surface hardness in the range of 400-430 HB, a tensile strength ≥ 1300 MPa, and an elongation after fracture > 11%. Compared with the comparative examples, the rail has higher and more stable hardness, higher tensile strength and elongation after fracture, and the rail product has higher wear resistance and service life.

[0081] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details in the above-described embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

[0082] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0083] In addition, various different embodiments of the present application can also be combined in any manner, as long as they do not deviate from the idea of the present application, and they should also be considered as disclosed by the present application.

Claims

1. A method of manufacturing a pearlitic rail having a high surface hardness, characterized by, The method comprises the following steps: S1. feeding the primary refined molten steel into a ladle refining furnace, adding alloying elements to perform deoxidation and alloying treatment, and obtaining refined molten steel; S2. processing the refined molten steel to obtain a continuous casting billet; S3. heating the continuous casting billet through a heating furnace to a preset temperature, and feeding the heated continuous casting billet into a rolling mill for multi-pass rolling; the rolling comprises a first-pass rolling and a second-pass rolling, wherein: when the first-pass rolling is performed, the rolling speed is 5.0-7.5 s -1 , and the rolling deformation amount should be 10-15%; after the first-pass rolling, the original austenite grain size is 85-115 μm; the rolling pass number is 9-13 passes, and the total deformation amount is 85-95%; the steel rail block with a required specification and shape is obtained by gradually reducing the roll gap of the rolling mill; S4. performing online heat treatment and processing treatment on the rail block to obtain a rail.

2. The manufacturing method according to claim 1, wherein in step S3, the preset temperature of the continuous casting billet is 1150-1280℃, and the temperature is maintained for more than 45 minutes; the continuous casting billet is rolled into a rail block at a rolling start temperature of 1150-1250℃. Step S2 comprises: feeding the refined molten steel into a vacuum circulating degassing device to perform vacuum treatment, obtaining treated molten steel, and then performing continuous casting by a continuous casting machine to form a continuous casting billet.

3. The production method according to claim 1, characterized by 4. The manufacturing method according to claim 1, wherein in step S4, the online heat treatment comprises heating, cooling and maintaining; the online heat treatment is performed after the rolling of the rail is completed, the heating temperature is a rail top surface temperature of 675-815℃, accelerated cooling is performed on the rail top surface and both sides of the rail head, the cooling speed is 1.8-4.5℃ / s, the accelerated cooling is stopped when the temperature is cooled to 495-575℃, and air cooling is performed to room temperature. In step S4, compressed air and / or water mist are used as the cooling medium during the online heat treatment. In step S4, the processing treatment comprises removing surface oxide scale and defects, performing size finishing and surface treatment.

5. The production method according to claim 1, characterized by The continuous casting billet has a cross-sectional area of 250mm×250mm-450mm×450mm and a length of 5000mm-7000mm.

6. The production method according to claim 1, characterized by The rail obtained by rolling has a weight of 43-75kg per meter.

7. The production method according to claim 1, characterized by The rail comprises the following components in mass fraction: C: 0.68-0.86%, Si: 0.15-0.70%, Mn: 0.50-1.25%, Cr: 0.05-0.30%, V: 0.01-0.10%, P≤0.030%, S≤0.025%, and the balance is Fe and impurities.

8. The production method according to claim 1, characterized by The rail has full cross-section microstructure of pearlite, a surface hardness of the rail top surface in the range of 400-430HB according to Brinell hardness, a tensile strength of ≥1280MPa, and an elongation after fracture of ≥10%.

9. A heavy rail having high post-break elongation prepared according to the method of any one of the preceding claims 1-8, characterized in that, ​ 10. The heavy haul rail with high post-break elongation according to claim 9, characterized in that, ​

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