Manufacturing method and rail for improving rail's resistance to low temperature fracture and contact fatigue damage

Abstract

The invention belongs to the field of rail manufacturing, and specifically discloses a manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rails and the rails obtained thereby. The method comprises the following steps: converter smelting, LF refining, RH vacuum treatment, billet continuous casting, billet cleaning and cooling, billet heating, rail rolling, online heat treatment and post-treatment, wherein: during the converter smelting process, bottom blowing of nitrogen is performed; after the RH vacuum treatment, iron-calcium wire feeding treatment is performed. Calculated by mass percentage, the chemical composition of the steel billet includes: C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 030-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30%, N: 0.007-0.030%, and the chemical composition of the steel billet also includes at least one of V, Nb, and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, and the rest is Fe and unavoidable impurities. The steel rail obtained by the method provided by the present invention has excellent comprehensive properties such as resistance to low-temperature fracture, resistance to contact fatigue, corrosion resistance and weldability.

Description

Technical Field

[0001] The invention belongs to the field of rail manufacturing, and in particular relates to a manufacturing method for improving the low-temperature fracture resistance and contact fatigue damage resistance of the rail and the rail obtained thereby. Background Art

[0002] Rails are one of the core components of the rail transit wheel-rail system. Their performance and quality directly affect the safety of train operation and the comfort of riding. With the construction of new rail transit projects and the ultimate pursuit of safety, comfort, efficiency and longevity in rail transit, the performance and quality of existing rails face new challenges. my country has a vast territory. With the development of the economy and society, my country's railways have been extended to various complex terrains such as high latitudes, plateaus, deserts, and mountains. There are more and more harsh service conditions such as low temperature, large temperature difference, and long and steep slopes, especially in plateau and mountainous areas, which put forward higher requirements on the rails' resistance to low-temperature fracture and contact fatigue.

[0003] For rails with pearlite structure, it is important and effective to improve low temperature toughness, reduce the carbon content of rail steel and refine the austenite grains of pearlite. However, the strength of the rail is significantly affected by reducing the carbon content. At present, the common method of grain refinement is to adopt low temperature large deformation process, or add Ti, Nb, V elements, and use the carbonitrides of these elements to precipitate and refine the grains. For low temperature large deformation, on the one hand, it will greatly increase the mill load during the rolling process and affect the safety and life of the equipment; on the other hand, it will increase the wear of the rollers and affect the surface quality and size of the rails. These factors will seriously reduce the production efficiency of the rails. For titanium, vanadium and niobium microalloying, adding titanium will easily form large particles of TiN hard inclusions, affecting the fatigue performance of the rails; adding niobium and vanadium, because the nitrogen content of rail steel is generally low, the precipitation of vanadium nitride and niobium nitride is small, the grain refinement is not obvious, and the grain size is uneven.

[0004] Patent document CN 114635072 A discloses a method for producing low-temperature resistant rails in high-cold areas, whose chemical composition is calculated by mass percentage: C: 0.67-0.69%, Si: 0.36-0.39%, Mn: 0.97-1.13%, P≤0.015%, S≤0.010%, and the rest is Fe and unavoidable impurities. This patent reduces the content of the C element, and at the same time reasonably designs the composition and adds the optimal Si and Mn alloy elements to the rails, and improves the tensile strength, elongation, tread hardness and other properties of the rails through conventional production processes. Under the existing composition system and process, this patent improves the performance of the rails by optimizing and adjusting some process parameters. Compared with the existing rails, the performance improvement is limited.

[0005] Patent document CN 112239831 A discloses a high-toughness high-cold railway rail and its production method, the weight percentage of alloy elements is: C: 0.40-0.65%, Si: 0.10-0.60%, Mn: 0.5-1.10%, Cr: 0.1-0.3%, P≤0.020%, S≤0.020%, V: 0.004-0.006%, the balance is iron and inevitable impurities. The patent reduces the C content, controls the content of harmful substances such as phosphorus, sulfur, hydrogen, oxygen, and nitrogen, improves the purity of steel, reduces inclusions, and uses the residual heat of rolling to accelerate cooling and refine the structure, thereby improving the low-temperature toughness index of the rail. In order to improve the low-temperature toughness, the patent reduces the C content to a lower level. Although Mn, Cr, and V strengthening elements are appropriately added, the strength improvement is limited, and it is impossible to take into account both high strength and high toughness. In addition, the levels of phosphorus, sulfur, hydrogen, oxygen, and nitrogen are not significantly improved compared with the existing process, and the effect on improving toughness is not obvious.

[0006] Patent document CN 109402520 A discloses a rare earth-containing low-temperature wear-resistant heat-treated rail and its preparation method. The weight percentage of alloying elements in its basic alloy system is: C: 0.63-0.69%; Si: 0.35-0.60%; Mn: 0.95-1.20%; P≤0.025%; S≤0.025%; RE alloy: 0.0002-0.001%; ​​the rest is Fe and unavoidable impurities. This patent optimizes the content of Si and Mn alloying elements by appropriately reducing the existing carbon content level of the rail, and further refines the grain size by adding rare earth elements, thereby improving the toughness and hardness index of the rail at the same time. Although the addition of rare earth elements can modify inclusions, the distribution of its inclusions is still uneven and large in size, and its grain size is uneven, and the effect of improving the toughness of the rail steel is unstable. Summary of the invention

[0007] In view of at least one of the problems that the low-temperature fracture resistance of existing rails is not significantly improved, the preparation cost is high, the efficiency is low, and the low-temperature fracture resistance and contact fatigue resistance cannot be taken into account at the same time, the present invention provides a manufacturing method for improving the low-temperature fracture resistance and contact fatigue damage resistance of rails and the rails obtained thereby, in order to further improve the low-temperature fracture resistance of the rails, reduce the preparation cost, improve the efficiency, and take into account the low-temperature fracture resistance and contact fatigue resistance at the same time.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] According to a first aspect of the present invention, a manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of a rail is provided, the manufacturing method comprising the following steps: converter smelting, LF refining, RH vacuum treatment, billet continuous casting, billet cleaning and cooling, billet heating, rail rolling, online heat treatment, and post-treatment, wherein, during the converter smelting process, bottom blowing of nitrogen is performed; after the RH vacuum treatment, an iron-calcium wire feeding treatment is performed; the chemical composition of the billet, calculated by mass percentage, comprises: C: 0.50-0.6 5%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 030-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30%, N: 0.007-0.030%, at least one of V, Nb and Ti, wherein when V is contained, the V is 0.02-0.15%, when Ti is contained, the Ti is 0.001-0.030%, when Nb is contained, the Nb is 0.01-0.08%, and the rest is Fe and unavoidable impurities.

[0010] According to one embodiment of the present invention, when nitrogen is blown at the bottom, the nitrogen flow rate is ≥1500NL / min.

[0011] According to one embodiment of the present invention, when nitrogen is blown at the bottom, the bottom blowing time of nitrogen is ≥10 min.

[0012] According to one embodiment of the present invention, the iron-calcium fed wire treatment is carried out under a protective atmosphere, and the iron-calcium fed wire is ≥ 600m.

[0013] According to one embodiment of the present invention, before the iron-calcium wire is treated, protective gas is used to blow away the protective slag on the surface of the molten steel, and the exposed size of the molten steel is 150mm*150mm-200mm*200mm.

[0014] According to one embodiment of the present invention, the steel billet is heated by a walking beam heating furnace, and the steel billet is heated at a temperature of 1150-1200°C.

[0015] According to one embodiment of the present invention, the rail rolling adopts universal rolling, including three processes of universal primary rolling, universal intermediate rolling and universal finishing rolling. The universal intermediate rolling temperature is 900-960°C, and the total deformation elongation coefficient is ≥1.80; the universal finishing rolling temperature is 850-900°C, and the deformation elongation coefficient is ≥1.12.

[0016] According to one embodiment of the present invention, the online heat treatment is carried out using the residual heat from rolling, and the rail top surface temperature is accelerated cooled from 730°C to 780°C at a rate of 4.0°C / s to 5.5°C / s for 42 to 52s, and then cooled to below 500°C at a rate of 1.0 to 2.0°C / s and then naturally cooled.

[0017] According to one embodiment of the present invention, the post-processing includes rail straightening, and the rail straightening is performed using a small deformation straightening process, and the total pressure reduction of the upper roller of the horizontal straightening machine is ≤40mm.

[0018] According to one embodiment of the present invention, universal medium rolling includes three passes, the rolling temperature of the first pass is 940-960°C, and the elongation coefficient is 1.15-1.20; the rolling temperature of the second pass is 920-935°C, and the elongation coefficient is 1.25-1.30; the rolling temperature of the third pass is 900-915°C, and the elongation coefficient is 1.20-1.25.

[0019] According to one embodiment of the present invention, the mass percentage of N in the steel billet is 0.015-0.030%.

[0020] According to one embodiment of the present invention, when V is contained in the steel billet, the mass percentage of V is 0.08-0.15%.

[0021] According to one embodiment of the present invention, the mass percentage of C in the steel billet is 0.60-0.65%.

[0022] According to one embodiment of the present invention, the sum of the mass percentages of Mn and Cr in the steel billet is ≥1.20%.

[0023] According to a second aspect of the present invention, there is provided a steel rail obtained by using the above-mentioned manufacturing method for improving the low-temperature fracture resistance and contact fatigue damage resistance of the steel rail.

[0024] By adopting the above technical solution, the present invention has the following beneficial effects:

[0025] The rails obtained by adopting the manufacturing method for improving the low-temperature fracture resistance and contact fatigue damage resistance of the rails described in the present invention have excellent comprehensive properties such as low-temperature fracture resistance, contact fatigue resistance, corrosion resistance and weldability, and can be applied to plateau mountain railways, high-speed railways, mixed passenger and freight railways, subways and other lines, thereby improving the service life of the rails. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] As required, specific embodiments of the present invention are disclosed in the present specification; however, it should be understood that the embodiments disclosed herein are merely examples of the present invention that can be implemented in multiple, alternative forms. In the following description, multiple operating parameters and components are described in multiple embodiments contemplated. These specific parameters and components are only used as examples in this specification and are not meant to be limiting.

[0028] According to a first aspect of the present invention, there is provided a manufacturing method for improving the low-temperature fracture resistance and contact fatigue damage resistance of a rail, the manufacturing method comprising the following steps: converter smelting, LF refining, RH vacuum treatment, billet continuous casting, billet cleaning and cooling, billet heating, rail rolling, online heat treatment and post-treatment. In which, during the converter smelting process, bottom blowing of nitrogen is carried out; after RH vacuum treatment, iron-calcium wire feeding treatment is carried out; the chemical composition of the steel billet, calculated by mass percentage, includes: C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 030-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30%, N: 0.007-0.030%, at least one of V, Nb and Ti, wherein when V is contained, V is 0.02-0.15%, when Ti is contained, Ti is 0.001-0.030%, when Nb is contained, Nb is 0.01-0.08%, and the rest is Fe and unavoidable impurities.

[0029] In some specific examples, the process flow of the manufacturing method is as follows: hot metal pretreatment - converter carburization smelting - aluminum-free deoxidation - in-ladle alloying - LF+RH refining - billet continuous casting - billet cleaning - billet heating - universal line rail rolling - online heat treatment - straightening - flaw detection - processing. In the present invention, unless otherwise specified, hot metal pretreatment, converter smelting or converter carburization smelting, aluminum-free deoxidation, in-ladle alloying, LF refining, RH vacuum treatment, billet continuous casting, billet cleaning, billet heating, rolling, online heat treatment, straightening, flaw detection, and processing related operations can all be conventional operations in the art.

[0030] In order to achieve the full precipitation of nitride particles such as nano-vanadium nitride, titanium nitride, and niobium nitride during the rolling process, the mass percentage of nitrogen in the rail steel needs to reach: 0.007%-0.030%, and bottom blowing of nitrogen is carried out during the molten steel smelting process to increase nitrogen. During the converter smelting process, the nitrogen flow rate is ≥1500NL / min. Preferably, the nitrogen flow rate is controlled to be 1500-2000NL / min, and the converter bottom blowing nitrogen time is ≥10min. Specifically, the nitrogen flow rate can be 1500NL / min, 1600NL / min, 1700NL / min, 1800NL / min, 1900NL / min, 2000NL / min, and the converter bottom blowing nitrogen time can be 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min, 20min.

[0031] Since the molten steel inevitably contains trace amounts of titanium (here it refers to residual elements, not elements added for alloying), the increase in nitrogen content increases the probability of titanium and nitrogen combining to form hard inclusions of titanium nitride. The presence of large particles of hard inclusions of titanium nitride will reduce the fatigue performance of the rail. Therefore, it is necessary to treat the molten steel with calcium, and then treat it with iron-calcium wire after RH vacuum treatment, with the iron-calcium wire ≥600m. Calcium treatment can avoid the formation of large particles of hard inclusions of titanium nitride. Titanium nitride is a hard and sharp particle. During the contact fatigue process of the rail, due to the large difference in performance between it and the rail matrix and its sharp shape, when its particles are large, during the contact fatigue process, the matrix near the titanium nitride particles is prone to stress concentration, fatigue cracks are generated, and they expand in long-term fatigue. After calcium treatment, titanium nitride changes from a single particle to a composite particle. While the hardness decreases, its shape also changes from sharp to blunt, making it less likely to produce stress concentration. In the present invention, the iron-calcium wire is a commercially available product, which contains 12-25% calcium and 3-6% silicon by mass percentage, and the balance is iron. Specifically, the length of the iron-calcium wire can be 600m, 620m, 640m, 660m, 680m, 700m, 720m.

[0032] Before the iron-calcium wire is fed, protective gas is used to blow away the protective slag on the surface of the molten steel. The exposed size of the molten steel is 150mm*150mm-200mm*200mm.

[0033] In the present invention, after the casting is formed, the billet is cooled to room temperature for surface treatment, and then heated in a walking beam heating furnace to be easy to be rolled and deformed. In order to make the rail easy to be rolled and deformed, the precipitation of vanadium nitride, niobium nitride, titanium nitride, etc. is coordinated, and suitable rolling waste heat is provided for the online heat treatment of the rail, and the billet soaking temperature is 1150-1200°C. Specifically, the billet soaking temperature can be 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C.

[0034] In the present invention, the rail is universally rolled, including three processes of universal primary rolling, universal intermediate rolling and universal finishing rolling. In order to achieve full precipitation of particles such as vanadium nitride, niobium nitride and titanium nitride, the universal intermediate rolling temperature is 900-960°C, the universal intermediate rolling total deformation extension coefficient (the ratio of the length of the rolled piece after rolling to the length of the rolled piece before rolling) is ≥1.80, the universal finishing rolling temperature is 850-900°C, and the universal finishing rolling deformation extension coefficient is ≥1.12. Specifically, the universal intermediate rolling temperature can be 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, the universal intermediate rolling total deformation extension coefficient can be 1.80, 1.90, 2.00, 2.10, and the universal finishing rolling temperature can be 850°C, 860°C, 870°C, 880°C, 890°C, 900°C.

[0035] In some embodiments, universal rolling is performed in 3 passes, the first pass has a rolling temperature of 940-960°C and an elongation coefficient of 1.15-1.20, the second pass has a rolling temperature of 920-935°C and an elongation coefficient of 1.25-1.30, and the third pass has a rolling temperature of 900-915°C and an elongation coefficient of 1.20-1.25. Specifically, the rolling temperature of the first pass can be 940℃, 945℃, 950℃, 955℃, and 960℃, and the elongation coefficient of the first pass can be 1.15, 1.16, 1.17, 1.18, 1.19, and 1.20; the rolling temperature of the second pass can be 920℃, 925℃, 930℃, and 935℃, and the elongation coefficient of the second pass can be 1.25, 1.26, 1.27, 1.28, 1.29, and 1.30; the rolling temperature of the third pass can be 900℃, 905℃, 910℃, and 915℃, and the elongation coefficient of the third pass can be 1.20, 1.21, 1.22, 1.23, 1.24, and 1.25.

[0036] After rolling, the rail is subjected to online heat treatment using the residual heat of rolling, which can refine the interlamellar spacing of the pearlite rail, and at the same time improve the strength and toughness of the rail, and improve the fatigue resistance of the rail. In the present invention, after the universal finish rolling of the rail, the residual heat of rolling is used for online heat treatment, and the rail top surface temperature is accelerated from 730℃ to 780℃ at a speed of 4.0℃ / s to 5.5℃ / s for 42 to 52s, and then cooled to below 500℃ at a speed of 1.0 to 2.0℃ / s, and then cooled naturally. Specifically, the rail top surface temperature can be 730°C, 740°C, 750°C, 760°C, 770°C, and 780°C, and the accelerated cooling rate can be 4.0°C / s, 4.1°C / s, 4.2°C / s, 4.3°C / s, 4.4°C / s, 4.5°C / s, 4.6°C / s, 4.7°C / s, 4.8°C / s, 4.9°C / s, 5.0°C / s, 5.1°C / s, 5.2°C / s, 5.3°C / s, 5.4°C / s. The accelerated cooling time can be 4s, 43s, 44s, 45s, 46s, 47s, 48s, 49s, 50s, 51s, 52s, and the slow cooling speed can be 1.0℃ / s, 1.1℃ / s, 1.2℃ / s, 1.3℃ / s, 1.4℃ / s, 1.5℃ / s, 1.6℃ / s, 1.7℃ / s, 1.8℃ / s, 1.9℃ / s, 2.0℃ / s.

[0037] The rail is straightened by a small deformation straightening process, and the total pressure reduction of the upper roller of the horizontal straightening machine is ≤40mm. Specifically, the total pressure reduction of the upper roller of the horizontal straightening machine can be 40mm, 39mm, 38mm, 37mm, 36mm, 35mm, and 34mm.

[0038] In order to achieve the technical purpose of the present invention, preferably, the mass percentage of N in the steel billet is 0.015-0.030%. In order to achieve the technical purpose of the present invention, preferably, when the chemical composition of the steel billet contains V, the mass percentage of V is 0.08-0.15%. In order to achieve the technical purpose of the present invention, preferably, the mass percentage of C in the steel billet is 0.60-0.65%. In order to achieve the technical purpose of the present invention, preferably, the sum of the mass percentages of Mn and Cr in the steel billet is ≥1.20%.

[0039] According to the second aspect of the present invention, a steel rail is provided by the manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of the steel rail. The chemical composition of the steel rail is calculated by mass percentage, C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 030-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30%, N: 0.007-0.030%, at least one of V, Nb, and Ti, wherein V is 0.02-0.15% when V is contained, Ti is 0.001-0.030% when Ti is contained, Nb is 0.01-0.08% when Nb is contained, and the rest is Fe and unavoidable impurities.

[0040] The method of the present invention uses a specific composition design in combination with the use of converter bottom blowing nitrogen and vanadium, niobium, titanium microalloying and controlled rolling technology to exert the precipitation strengthening and fine grain strengthening effects of nitrides such as vanadium nitride, niobium nitride and titanium nitride, reduce the carbon content of rail steel and significantly refine the original austenite grain size, and on this basis give full play to the role of alloy elements and heat treatment technology in synergistic cooperation to improve rail performance, thereby obtaining a rail with excellent low-temperature fracture resistance and excellent strong and tough mechanical properties. In addition, by modifying inclusions through calcium treatment, the problem of fatigue performance degradation caused by large-particle titanium nitride hard inclusions is avoided, and low-temperature fracture resistance and contact fatigue resistance are simultaneously taken into account, and good corrosion resistance is achieved. The steel rail steel matrix obtained by the manufacturing method of the present invention has nitride particles of vanadium nitride, niobium nitride, titanium nitride, etc. precipitated in a size of 0.5nm to 15nm, the original austenite grain size grade is ≥9.5, the tensile strength Rm of the rail is ≥1100MPa, the elongation after fracture A is ≥15%, the yield strength Rp0.2 is ≥750MPa, the hardness of the top surface of the rail head is 330 to 370HB, and the low-temperature fracture toughness KIC at -20℃ is ≥42MPa·m 0.5 、-40℃KIC≥40MPa·m 0.5, the corrosion resistance is ≥150% relative to U71Mn. The steel rail obtained by the manufacturing method of the present invention has excellent comprehensive properties such as resistance to low-temperature fracture, resistance to contact fatigue, corrosion resistance and weldability, and can be applied to plateau mountain railways, high-speed railways, passenger and freight mixed railways, subways and other lines, thereby increasing the service life of the steel rails.

[0041] The present invention is specifically described below through specific embodiments.

[0042] Example 1

[0043] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.63%, Si 0.56%, Mn 0.83%, Cr 0.36%, Cu 0.35%, Ni 0.17%, V 0.09%, N 0.0153%, Ti 0.009%, and the balance is Fe and other inevitable impurities.

[0044] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0045] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom. The nitrogen flow rate is 1600NL / min and the blowing time is 13min. After converter smelting, LF refining and vacuum treatment, 600m of iron-calcium wire is fed under protective atmosphere. The molten steel is continuously cast into large square billets using existing processes. The billets after cooling and cleaning are loaded into a step-beam heating furnace with a uniform heating temperature of 1180℃. After billet rolling and universal primary rolling, the billets are subjected to universal intermediate rolling. The universal intermediate rolling temperature is 900℃ and the total deformation elongation coefficient is 1.80. The first rolling temperature of the universal intermediate rolling is 948℃ and the elongation coefficient is 1.17, the second rolling temperature is 927℃ and the elongation coefficient is 1.28, and the third rolling temperature is 906℃ and the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 873℃. The universal finishing temperature is 850℃, and the deformation elongation coefficient is 1.12. The center temperature of the top surface of the rail is 730℃, and it enters the rail online heat treatment unit, where it is accelerated to cool at a speed of 4.4℃ / s for 50s, and then cooled to 496℃ at 1.3℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 38mm.

[0046] Example 2

[0047] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.60%, Si 0.47%, Mn 0.80%, Cr 0.48%, Cu 0.32%, Ni 0.15%, V 0.10%, N 0.0218%, Ti 0.008%, and the balance is Fe and other inevitable impurities.

[0048] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0049] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom. The nitrogen flow rate is 1800NL / min and the blowing time is 15min. After converter smelting, LF refining and vacuum treatment, 636m of iron-calcium wire is fed under protective atmosphere. The molten steel is continuously cast into large square billets using existing processes. The billets after cooling and cleaning are loaded into a step-beam heating furnace with a uniform heating temperature of 1173℃. After billet rolling and universal primary rolling, the billets are subjected to universal intermediate rolling. The universal intermediate rolling temperature is 920℃ and the total deformation elongation coefficient is 1.82. The first rolling temperature of the universal intermediate rolling is 953℃ and the elongation coefficient is 1.17, the second rolling temperature is 935℃ and the elongation coefficient is 1.28, and the third rolling temperature is 912℃ and the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 890℃. The universal finishing temperature is 870℃, and the deformation elongation coefficient is 1.15. The center temperature of the top surface of the rail is 780℃. It enters the rail online heat treatment unit and is accelerated to cool at a speed of 4.6℃ / s for 50s, and then cooled to 490℃ at 1.3℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 34mm.

[0050] Example 3

[0051] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.65%, Si 0.49%, Mn 0.72%, Cr 0.55%, Cu 0.31%, Ni 0.15%, V 0.08%, N 0.0194%, Ti 0.0010%, and the remainder is Fe and other inevitable impurities.

[0052] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0053] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown from the bottom. The nitrogen flow rate is 1750NL / min and the blowing time is 14min. After converter smelting, LF refining and vacuum treatment, the iron calcium wire is fed for 680m under protective atmosphere. The molten steel is continuously cast into large square billets using the existing process. The billet after cooling and cleaning is loaded into a step-beam heating furnace, and the heating furnace has an average heating temperature of 1162℃. After billet rolling and universal primary rolling, the billet is subjected to universal intermediate rolling. The universal intermediate rolling temperature is 940℃, and the total deformation elongation coefficient is 1.84. The first rolling temperature of the universal intermediate rolling is 943℃, the elongation coefficient is 1.17, the second rolling temperature is 921℃, the elongation coefficient is 1.28, and the third rolling temperature is 900℃, the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 861℃. The universal finishing temperature is 890℃, and the deformation elongation coefficient is 1.20. The center temperature of the top surface of the rail is 772℃. It enters the rail online heat treatment unit and is accelerated to cool at a speed of 4.2℃ / s for 50s, and then cooled to 486℃ at 1.3℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 36mm.

[0054] Example 4

[0055] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.63%, Si 0.76%, Mn 0.53%, Cr 0.75%, Cu 0.25%, Ni 0.13%, V 0.12%, N 0.0265%, Ti 0.007%, and the balance is Fe and other inevitable impurities.

[0056] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0057] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom. The nitrogen flow rate is 1800NL / min and the blowing time is 16min. After converter smelting, LF refining and vacuum treatment, 720m of iron-calcium wire is fed under protective atmosphere. The molten steel is continuously cast into large square billets using the existing process. The billet after cooling and cleaning is loaded into a step-beam heating furnace with a uniform heating temperature of 1175℃. After billet opening rolling and universal primary rolling, the billet is subjected to universal intermediate rolling. The universal intermediate rolling temperature is 960℃ and the total deformation elongation coefficient is 1.86. The first rolling temperature of the universal intermediate rolling is 942℃ and the elongation coefficient is 1.17, the second rolling temperature is 922℃ and the elongation coefficient is 1.28, and the third rolling temperature is 915℃ and the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 858℃. The universal finishing temperature is 900℃, and the deformation elongation coefficient is 1.23. The center temperature of the top surface of the rail is 761℃. It enters the rail online heat treatment unit and is accelerated to cool at a speed of 4.8℃ / s for 45s, and then cooled to 485℃ at 1.2℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 38mm.

[0058] Example 5

[0059] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.50%, Si 0.95%, Mn 0.35%, Cr 0.0.30%, Cu 0.20%, Ni 0.30%, V 0.02%, N 0.007%, Nb 0.01%, Ti 0.030%, and the balance is Fe and other inevitable impurities.

[0060] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0061] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom, with a nitrogen flow rate of 1600NL / min and a nitrogen blowing time of 13min. After converter smelting, LF refining and vacuum treatment, 600m of iron-calcium wire is fed under a protective atmosphere. The molten steel is continuously cast into large square billets using existing processes. The billets after cooling and cleaning are loaded into a step-beam heating furnace, and the heating furnace has an average heating temperature of 1180℃. After billet rolling and universal primary rolling, the billets are subjected to universal intermediate rolling. The universal intermediate rolling temperature is 910℃, and the total deformation elongation coefficient is 1.88. The first rolling temperature of the universal intermediate rolling is 948℃, the elongation coefficient is 1.17, the second rolling temperature is 927℃, the elongation coefficient is 1.28, and the third rolling temperature is 906℃, the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 873℃. The universal finishing temperature is 850℃, and the deformation elongation coefficient is 1.12. The center temperature of the top surface of the rail is 730℃, and it enters the rail online heat treatment unit, where it is accelerated to cool at a speed of 4.4℃ / s for 50s, and then cooled to 496℃ at 1.3℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 38mm.

[0062] Example 6

[0063] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.55%, Si 0.45%, Mn 0.85%, Cr 0.55%, Cu 0.55%, Ni 0.25%, Nb 0.08%, N 0.010%, Ti 0.001%, and the balance is Fe and other inevitable impurities.

[0064] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0065] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom. The nitrogen flow rate is 1800NL / min and the blowing time is 15min. After converter smelting, LF refining and vacuum treatment, 636m of iron-calcium wire is fed under protective atmosphere. The molten steel is continuously cast into large square billets using existing processes. The billets after cooling and cleaning are loaded into a step-beam heating furnace with a uniform heating temperature of 1173℃. After billet rolling and universal primary rolling, the billets are subjected to universal intermediate rolling. The universal intermediate rolling temperature is 920℃ and the total deformation elongation coefficient is 1.82. The first rolling temperature of the universal intermediate rolling is 953℃ and the elongation coefficient is 1.17, the second rolling temperature is 935℃ and the elongation coefficient is 1.28, and the third rolling temperature is 912℃ and the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 890℃. The universal finishing temperature is 870℃, and the deformation elongation coefficient is 1.15. The center temperature of the top surface of the rail is 780℃. It enters the rail online heat treatment unit and is accelerated to cool at a speed of 4.6℃ / s for 50s, and then cooled to 490℃ at 1.3℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 34mm.

[0066] Example 7

[0067] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.60%, Si 0.70%, Mn 0.70%, Cr 0.80%, Cu 0.40%, Ni 0.20%, Nb 0.04%, N 0.015%, and the balance is Fe and other inevitable impurities.

[0068] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0069] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown from the bottom. The nitrogen flow rate is 1750NL / min and the blowing time is 14min. After converter smelting, LF refining and vacuum treatment, the iron calcium wire is fed for 680m under protective atmosphere. The molten steel is continuously cast into large square billets using the existing process. The billet after cooling and cleaning is loaded into a step-beam heating furnace, and the heating furnace has an average heating temperature of 1162℃. After billet rolling and universal primary rolling, the billet is subjected to universal intermediate rolling. The universal intermediate rolling temperature is 940℃, and the total deformation elongation coefficient is 1.84. The first rolling temperature of the universal intermediate rolling is 943℃, the elongation coefficient is 1.17, the second rolling temperature is 921℃, the elongation coefficient is 1.28, and the third rolling temperature is 900℃, the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 861℃. The universal finishing temperature is 890℃, and the deformation elongation coefficient is 1.20. The center temperature of the top surface of the rail is 772℃. It enters the rail online heat treatment unit and is accelerated to cool at a speed of 4.2℃ / s for 50s, and then cooled to 486℃ at 1.3℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 36mm.

[0070] Example 8

[0071] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.65%, Si 0.85%, Mn 0.75%, Cr 0.60%, Cu 0.50%, Ni 0.15%, N 0.020%, Ti 0.015%, and the balance is Fe and other inevitable impurities.

[0072] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0073] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom. The nitrogen flow rate is 1800NL / min and the blowing time is 16min. After converter smelting, LF refining and vacuum treatment, 720m of iron-calcium wire is fed under protective atmosphere. The molten steel is continuously cast into large square billets using the existing process. The billet after cooling and cleaning is loaded into a step-beam heating furnace with a uniform heating temperature of 1175℃. After billet opening rolling and universal primary rolling, the billet is subjected to universal intermediate rolling. The universal intermediate rolling temperature is 960℃ and the total deformation elongation coefficient is 1.86. The first rolling temperature of the universal intermediate rolling is 942℃ and the elongation coefficient is 1.17, the second rolling temperature is 922℃ and the elongation coefficient is 1.28, and the third rolling temperature is 915℃ and the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 858℃. The universal finishing temperature is 900℃, and the deformation elongation coefficient is 1.23. The center temperature of the top surface of the rail is 761℃. It enters the rail online heat treatment unit and is accelerated to cool at a speed of 4.8℃ / s for 45s, and then cooled to 485℃ at 1.2℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 38mm.

[0074] Example 9

[0075] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.58%, Si 0.90%, Mn 0.80%, Cr 0.0.40%, Cu 0.25%, Ni 0.10%, V 0.15%, N 0.030%, and the balance is Fe and other inevitable impurities.

[0076] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0077] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom, with a nitrogen flow rate of 1600NL / min and a nitrogen blowing time of 13min. After converter smelting, LF refining and vacuum treatment, 600m of iron-calcium wire is fed under a protective atmosphere. The molten steel is continuously cast into large square billets using existing processes. The billets after cooling and cleaning are loaded into a step-beam heating furnace, and the heating furnace has an average heating temperature of 1180℃. After billet rolling and universal primary rolling, the billets are subjected to universal intermediate rolling. The universal intermediate rolling temperature is 910℃, and the total deformation elongation coefficient is 1.88. The first rolling temperature of the universal intermediate rolling is 948℃, the elongation coefficient is 1.17, the second rolling temperature is 927℃, the elongation coefficient is 1.28, and the third rolling temperature is 906℃, the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 873℃. The universal finishing temperature is 850℃, and the deformation elongation coefficient is 1.12. The center temperature of the top surface of the rail is 730℃, and it enters the rail online heat treatment unit, where it is accelerated to cool at a speed of 4.4℃ / s for 50s, and then cooled to 496℃ at 1.3℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 38mm.

[0078] Example 10

[0079] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C 0.62%, Si 0.60%, Mn 0.60%, Cr 0.45%, Cu 0.30%, Ni 0.27%, V 0.07%, N 0.025%, Ti 0.010%, and the balance is Fe and other inevitable impurities.

[0080] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0081] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom. The nitrogen flow rate is 1800NL / min and the blowing time is 15min. After converter smelting, LF refining and vacuum treatment, 636m of iron-calcium wire is fed under protective atmosphere. The molten steel is continuously cast into large square billets using existing processes. The billets after cooling and cleaning are loaded into a step-beam heating furnace with a uniform heating temperature of 1173℃. After billet rolling and universal primary rolling, the billets are subjected to universal intermediate rolling. The universal intermediate rolling temperature is 920℃ and the total deformation elongation coefficient is 1.82. The first rolling temperature of the universal intermediate rolling is 953℃ and the elongation coefficient is 1.17, the second rolling temperature is 935℃ and the elongation coefficient is 1.28, and the third rolling temperature is 912℃ and the elongation coefficient is 1.23. The universal finishing rolling becomes a rail, and the rail temperature after rolling is 890℃. The universal finishing temperature is 870℃, and the deformation elongation coefficient is 1.15. The center temperature of the top surface of the rail is 780℃. It enters the rail online heat treatment unit and is accelerated to cool at a speed of 4.6℃ / s for 50s, and then cooled to 490℃ at 1.3℃ / s before natural cooling. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 34mm.

[0082] Comparative Example 1

[0083] The chemical composition of the rail matrix of Comparative Example 1 is composed of the following elements in weight percentage: C 0.71%, Si 0.38%, Mn 1.10%, Cr 0.13%, V 0.01%, N 0.0043%, and the balance is Fe and other inevitable impurities. Comparative Example 1 is prepared by the existing method. The universal rolling method is used for rolling, and the universal final rolling temperature is 931°C. After rolling, the rolling waste heat is used for online heat treatment, and the rolling waste heat is accelerated to 548°C at a speed of 2.1°C / s, and then naturally cooled to room temperature in the air.

[0084] Comparative Example 2

[0085] The chemical composition of the rail matrix in Comparative Example 2 consists of the following elements in weight percentage: C 0.63%, Si 0.58%, Mn 0.81%, Cr 0.38%, Cu 0.34%, Ni 0.19%, V 0.08%, N 0.0043%, and the balance is Fe and other inevitable impurities. Comparative Example 1 is prepared by the existing method. The universal rolling method is used for rolling, and the universal final rolling temperature is 931°C. After rolling, the residual heat of rolling is used for online heat treatment, and the accelerated cooling is accelerated to 528°C at a speed of 2.8°C / s, and then naturally cooled to room temperature in the air.

[0086] Comparative Example 3

[0087] The chemical composition of the rail substrate in Comparative Example 3 consists of the following elements in weight percentage: C 0.77%, Si 0.61%, Mn 0.91%, Cr 0.02%, V 0.08%, N 0.0154%, and the balance is Fe and other inevitable impurities.

[0088] In this comparative example, the chemical composition of the steel billet and the rail substrate is consistent.

[0089] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown from the bottom. The nitrogen flow rate is 1600NL / min and the blowing time is 13min. After converter smelting, LF refining and vacuum treatment, 636m of iron-calcium wire is fed under protective atmosphere. The molten steel is continuously cast into large square billets using existing processes. The billets after cooling and cleaning are loaded into a step-beam heating furnace with a uniform heating temperature of 1185℃. After billet rolling and universal primary rolling, the billets are subjected to universal intermediate rolling. The first rolling temperature of universal intermediate rolling is 951℃ and the elongation coefficient is 1.18, the second rolling temperature is 931℃ and the elongation coefficient is 1.26, and the third rolling temperature is 911℃ and the elongation coefficient is 1.23. Universal finishing rolling becomes rails, and the temperature of the rails after rolling is 881℃. The rail top surface center temperature is 792℃, and then enters the rail online heat treatment unit, where it is cooled at a rate of 4.6℃ / s for 45s, and then cooled to 487℃ at 1.3℃ / s before being cooled naturally. The rail is straightened using a small deformation straightening process, and the total reduction of the upper roller of the horizontal straightening machine is 38mm.

[0090] Comparative Example 4

[0091] The chemical composition of the rail substrate in Comparative Example 4 consists of the following elements in weight percentage: C 0.61%, Si 0.52%, Mn 0.81%, Cr 0.45%, Cu 0.34%, Ni 0.18%, V 0.09%, N 0.0205%, Ti 0.005%, and the balance is Fe and other inevitable impurities.

[0092] In this comparative example, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0093] The molten iron from the blast furnace is poured into the converter. During the converter smelting process, nitrogen is blown at the bottom. The nitrogen flow rate is 1800NL / min and the blowing time is 15min. After converter smelting, LF refining and vacuum treatment, the existing process is used for continuous casting into large square billets. The billet after cooling and cleaning is loaded into a step-beam heating furnace, and the heating furnace is heated to 1169℃. After billet rolling and universal initial rolling, the billet is subjected to universal intermediate rolling. The first rolling temperature of universal intermediate rolling is 951℃ and the elongation coefficient is 1.17, the second rolling temperature is 932℃ and the elongation coefficient is 1.28, and the third rolling temperature is 910℃ and the elongation coefficient is 1.23. Universal finishing rolling becomes a rail, and the temperature of the rail after rolling is 887℃. The center temperature of the top surface of the rail is 791℃ and enters the rail online heat treatment unit, where it is accelerated to cool at a speed of 4.6℃ / s for 50s, and then cooled to 487℃ at 1.3℃ / s before cooling naturally. The rails are straightened using normal straightening technology, with the total depression of the upper roller of the horizontal straightening machine being 49 mm.

[0094] To illustrate the relevant performance of the rails prepared in the above embodiments of the present invention, the mechanical properties of the rails of the embodiments and comparative examples are tested below, wherein the room temperature metallographic structure is tested according to GB / T 13298 standard, the yield strength, tensile strength and elongation are tested according to GB / T 228.1 standard, and the Brinell hardness is tested according to GB / T 231.1 standard, and the specific data are shown in Table 1. The room temperature impact energy is tested according to GB / T 229 standard, the fracture toughness KIC of the rail is tested according to TB / T2344.1 and GB / T 4161, and the relative corrosion resistance of the rail is tested according to TB / T 2375-1993; the wear amount is tested on an MM-200 wear tester, the wear mode is dry grinding, the rotation speed is 200r / min, the total number of grinding revolutions is 100,000 revolutions, the test load is 980N, and the slip is 10%; the contact fatigue life test is carried out on a TIME 8123 rolling contact fatigue tester, and the test contact stress is 1200MPa and the slip is 1.0%, and the specific data are shown in Table 2.

[0095] Table 1 Microstructure and general mechanical properties of the embodiments and comparative examples

[0096]

[0097] It can be seen from Table 1 above that the rails prepared by the composition and process of the present invention have updated austenite grain size and pearlite interlamellar spacing, and thus have high strength and hardness while maintaining high elongation after fracture. Comparative Example 1 is a U71Mn carbon rail produced by the current conventional process, and its strength, hardness and elongation after fracture are all lower than the rail prepared by the present invention; Comparative Example 2 is a rail with the composition of the present invention, but still produced by the conventional nitrogen content and standard smelting process, and its strength and plasticity are slightly improved compared with the U71Mn rail, but compared with Examples 1-10, the elongation after fracture is much different; Comparative Example 3 is a rail produced by the smelting and rolling process of the present invention after alloying and improving the composition on the basis of U75V, although the strength, hardness and elongation after fracture are improved, due to the poor matching of the composition and the heat treatment process, its microstructure has martensite, which does not meet the standard requirements; Comparative Example 4 is a rail produced by the process of the present invention with chemical composition and nitrogen content controlled, and a finer austenite grain size and pearlite interlamellar spacing are obtained, but no calcium treatment is performed and a small deformation reduction straightening process is adopted, and the yield strength of the rail is low.

[0098] Table 2 Impact, fracture mechanics, wear, corrosion and contact fatigue properties of the embodiments and comparative examples

[0099]

[0100] It can be seen from Table 2 that the rails prepared by the composition and process of the present invention have good low-temperature impact performance and fracture toughness, and the wear test loss is lower than that of the U71Mn rail of Comparative Example 1, the relative corrosion resistance is greater than or equal to 147%, the contact fatigue life reaches more than 510,000 times, and the rotation bending fatigue limit is more than 486MPa. The rails of Comparative Examples 1-4 that are not produced by the composition and process of the present invention cannot have both good low-temperature performance and fatigue performance.

Claims

1. A manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rails, characterized in that: The following steps are involved: Converter smelting, LF refining, RH vacuum treatment, billet continuous casting, billet cleaning and cooling, billet heating, rail rolling, online heat treatment, post-treatment, including: During the converter smelting process, bottom blowing nitrogen is carried out, the bottom blowing nitrogen flow rate is ≥1500NL / min, and the bottom blowing nitrogen time is ≥10min; After RH vacuum treatment, the iron-calcium wire treatment is carried out. The iron-calcium wire treatment is carried out under a protective atmosphere. The iron-calcium wire feeding length is ≥ 600m. The rail rolling adopts universal rolling, including three processes: universal primary rolling, universal intermediate rolling and universal finishing rolling. The universal intermediate rolling temperature is 900-960℃, and the total deformation elongation coefficient is ≥1.80; the universal finishing rolling temperature is 850-900℃, and the deformation elongation coefficient is ≥1.12; Calculated in mass percentage, the chemical composition of the steel billet includes: C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 030-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30%, N: 0.007-0.030%, at least one of V, Nb and Ti, wherein when V is contained, V is 0.02-0.15%, when Ti is contained, Ti is 0.001-0.030%, when Nb is contained, Nb is 0.01-0.08%, and the rest is Fe and unavoidable impurities.

2. The manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rail according to claim 1, characterized in that: Before the iron-calcium wire is fed, protective gas is used to blow away the protective slag on the surface of the molten steel. The exposed size of the molten steel is 150mm*150mm-200mm*200mm.

3. The manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rail according to claim 1, characterized in that: The billet is heated in a walking beam heating furnace, and the billet soaking temperature is 1150~1200℃; The online heat treatment is carried out using the residual heat from rolling. The rail top surface temperature is accelerated from 730℃~780℃ at a rate of 4.0℃ / s~5.5℃ / s for 42~52s, and then cooled to below 500℃ at a rate of 1.0~2.0℃ / s and then cooled naturally. Post-processing includes rail straightening, which is carried out using a small deformation straightening process, with the total pressure reduction of the upper roller of the horizontal straightening machine ≤40mm.

4. The manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rail according to claim 1, characterized in that: Universal medium rolling includes three passes. The rolling temperature of the first pass is 940~960℃, and the elongation coefficient is 1.15~1.20; the rolling temperature of the second pass is 920~935℃, and the elongation coefficient is 1.25~1.30; the rolling temperature of the third pass is 900~915℃, and the elongation coefficient is 1.20~1.

25.

5. The manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rail according to claim 1, characterized in that: The mass percentage of C in the steel billet is 0.60-0.65%.

6. The manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rail according to claim 1, characterized in that: The mass percentage of N in the steel billet is 0.015-0.030%.

7. The manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rail according to claim 1, characterized in that: When V is contained in the steel billet, the mass percentage of V is 0.08-0.15%.

8. The manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rail according to claim 1, characterized in that: The sum of the mass percentages of Mn and Cr in the steel billet is ≥1.20%.

9. A steel rail obtained by using the manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of the steel rail according to any one of claims 1 to 8.

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