High-performance low-alarm-rate turnout rail and production method thereof

Abstract

The invention belongs to the technical field of railway steel, and particularly discloses a high-performance low-alarm-rate turnout rail and a production method thereof. The method comprises the following steps that S1, a rectangular square billet is smelted and cast; s2, the smelted and cast rectangular square billet is heated and rolled, in the rolling process, the wide face of the rectangular square billet is rolled into a rail head, and the narrow face of the rectangular square billet is rolled into a rail waist; s3, rolling waste heat is used for online heat treatment; and S4, straightening and processing the turnout rail subjected to online heat treatment to obtain the high-performance low-alarm-rate turnout rail. According to the scheme, by means of the turn-over rolling technology, original casting blank narrow face rolling is changed into rail head rolling and wide face rolling is changed into rail waist rolling, the rail waist metal amount is increased, the rail waist deformation amount is increased, the rail waist density is improved, the rail waist non-metallic inclusion distribution rule is changed, and therefore the rail waist alarm rate is reduced.

Description

Technical Field

[0001] This invention belongs to the field of railway steel technology, specifically relating to a high-performance turnout rail with low alarm rate and its production method. Background Technology

[0002] Turnouts are a crucial component of railway transportation, their quality directly impacting train speed and safety. To meet the demands of my country's rapid railway development, the country has imported a complete set of forged turnout rails, which have been extensively installed on tracks. However, forged turnout rails suffer from poor quality stability, require extensive machining to maintain their shape, resulting in low production efficiency. Furthermore, the short lengths of forged rails necessitate multiple welds, and the weld quality and straightness fail to meet high-speed railway standards, making them unsuitable for my country's railway construction needs. Based on domestic and international track applications, producing turnout rails using rolling and in-line heat treatment with residual rolling heat can improve the quality and reliability of high-speed turnouts while significantly reducing costs, thus promoting the development of movable-point frog high-speed turnouts in my country.

[0003] The cross-section of the turnout rail is asymmetrical in both the horizontal and vertical directions, with varying lengths, widths, and thicknesses, resulting in a complex shape and significant manufacturing challenges. During heat treatment, the difference in cooling rates between the short and long ends of the turnout rail leads to uneven shrinkage, with deformation reaching 3-5 mm. Furthermore, controlling the microstructure and hardness is difficult. Offline heat treatment requires additional heating or complex controlled cooling equipment. In terms of microstructure control, the overall cooling rate is uncontrollable, easily leading to mixed crystals or residual stress.

[0004] Turnout rails, especially switch rails, are typically machined into extremely thin switch rails at the ends of the switching rails. To ensure the safety and durability of turnout rails, ultrasonic testing is required before the rails leave the factory, and only those that pass the testing can be shipped. Due to the relatively thick web of turnout rails (approximately 44mm, compared to only about 20mm for ordinary symmetrical rails), the web reduction is insufficient, making them highly susceptible to ultrasonic alarms caused by metallurgical defects such as inclusions, typically ranging from 1‰ to 3‰. This reduces the rail pass rate and degrades the service performance of the turnout rails on the track.

[0005] Therefore, the existing rolled ordinary carbon turnout rails are difficult to meet the development needs of heavy-haul lines at home and abroad, and there is an urgent need for a high-performance turnout rail with a low alarm rate and its production method. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention provides a high-performance, low-alarm-rate turnout rail and its manufacturing method, aiming to ensure the strength and toughness of the turnout rail while reducing the alarm rate of the rail web, thus meeting the requirements of high-performance internal structure and high straightness of railway dimensions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: According to a first aspect of the present invention, a method for producing high-performance turnout rails with low alarm rates is provided, comprising the following steps: S1: Smelting and casting rectangular billets; S2: The rectangular billet after smelting and casting is heated and rolled. During the rolling process, the wide side of the rectangular billet is rolled into a rail head and the narrow side of the rectangular billet is rolled into a rail web. S3: Utilizing residual heat from rolling for online heat treatment; S4: After straightening and processing the turnout rails that have undergone online heat treatment, high-performance turnout rails with low alarm rates are obtained.

[0008] According to some embodiments of the present invention, in step S1, the chemical composition of the rectangular billet, by weight percentage, includes: C: 0.60-0.82%, Si: 0.20-0.80%, Mn: 0.70-0.95%, P≤0.020%, S≤0.010%, V≤0.12%.

[0009] According to some embodiments of the present invention, in step S1, the molten steel is controlled to have hydrogen ≤1.4ppm, oxygen ≤10ppm, and nitrogen ≤45ppm during the smelting process.

[0010] According to some embodiments of the present invention, in step S1, the smelting process is controlled with a low sulfur content of 0.002-0.010%.

[0011] According to some embodiments of the present invention, in step S1, the smelting and casting process adopts protective casting throughout.

[0012] According to some embodiments of the present invention, in step S2, rolling is performed using a universal rolling mill, with an initial rolling temperature of 1100-1200℃ and a final rolling temperature of 900-950℃.

[0013] According to some embodiments of the present invention, in step S2, the rolling compression ratio during the rolling process is 9-13.

[0014] According to some embodiments of the present invention, in step S3, the forced cooling start temperature is 750-850℃, the forced cooling rate is 1.5-2.5℃ / s, and the forced cooling final cooling temperature is 500-600℃.

[0015] According to some embodiments of the present invention, in step S4, straightening is performed when the turnout rail after online heat treatment is cooled to below 60°C.

[0016] According to some embodiments of the present invention, in step S4, after straightening and before processing, an online ultrasonic test is performed.

[0017] According to a second aspect of the present invention, a high-performance turnout rail with a low alarm rate is provided, which is manufactured using the production method described in the first aspect of the present invention.

[0018] By adopting the above technical solution, the present invention has the following beneficial effects: The production method of high-performance, low-alarm-rate turnout rail provided by this invention uses a flipping rolling process, that is, changing the original narrow side of the cast billet to be rolled into the rail head and the wide side to be rolled into the rail web, to roll the wide side into the rail head and the narrow side into the rail web, thereby increasing the metal content of the rail web, increasing the deformation of the rail web, increasing the density of the rail web, and changing the distribution pattern of non-metallic inclusions in the rail web, thereby reducing the alarm rate of the rail web.

[0019] The turnout rails produced using the method of this invention have a web density between 0.945 and 0.955, a Class A non-metallic inclusion level ≤ 1.5, and a B+C+D+Ds level ≤ 0.5; an ultrasonic alarm rate ≤ 5‰; a tensile strength ≥ 1150 MPa, an elongation ≥ 10%, a tread hardness of 330-360 HB, and a hardness ≥ 32.0 HRC at the 6th point of the cross-section (30 mm from the surface); and a tensile strength ≥ 1240 MPa, an elongation ≥ 10%, a tread hardness of 360-400 HB, and a hardness ≥ 36.0 HRC at the 6th point of the cross-section (30 mm from the surface), with the microstructure being entirely fine pearlite. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart of the production method for high-performance, low-alarm-rate turnout rails provided by the present invention. Figure 2 A schematic diagram comparing the turnout rail rolling process provided by this invention with the original turnout rail rolling process; Figure 3 This is a diagram showing the test results of the rail web density of the turnout obtained in an embodiment of the present invention; Figure 4 The diagram shows the test results of the web density of the turnout rail obtained as a comparative example. Figure 5 This is a diagram showing the inspection results of non-metallic inclusions in turnout rails obtained according to an embodiment of the present invention. Figure 6 The image shows the inspection results of non-metallic inclusions in the turnout rail, obtained as a comparative example. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and accompanying drawings.

[0023] The first aspect of this invention provides a method for producing high-performance, low-alarm-rate turnout rails, such as... Figure 1 As shown, the method includes the following steps: S1: smelting and casting a rectangular billet; S2: heating and rolling the smelted and cast rectangular billet, during which the wide side of the rectangular billet is rolled into the rail head and the narrow side of the rectangular billet is rolled into the rail web; S3: using the residual heat of rolling for online heat treatment; S4: straightening and processing the turnout rail after online heat treatment to obtain a high-performance, low-alarm-rate turnout rail.

[0024] In the present invention, "rectangular billet" refers to a billet with a rectangular cross-section, "wide face of rectangular billet" refers to the surface of the billet perpendicular to the cross-section and corresponding to the long side of the rectangular cross-section, and "narrow face of rectangular billet" refers to the surface of the billet perpendicular to the cross-section and corresponding to the short side of the rectangular cross-section.

[0025] In the present invention, "rail head" refers to the upper region of the turnout rail that is in direct contact with the train wheels, "rail bottom" refers to the lower region where the turnout rail connects to the sleeper (or track slab), and "rail waist" refers to the middle connecting region where the turnout rail vertically connects the rail head and the rail bottom. The solution of this invention significantly improves the density of the turnout rail web by optimizing the rolling process, shortens the length of non-metallic inclusions in the rail web, and reduces the alarm rate of the turnout rail web, making it particularly suitable for the manufacture of turnout rails with high fatigue performance requirements.

[0026] Specifically, such as Figure 2 As shown, when rolling turnout rails using rectangular billets, the original turnout rail rolling process rolls the narrow side of the original cast billet into the rail head and the wide side into the rail web. This results in a smaller deformation and lower density of the rail web, and longer non-metallic inclusions in the rail web, which easily triggers ultrasonic alarms during ultrasonic testing, reducing the rail pass rate. The solution of this invention optimizes the rolling process, changing the original method of rolling the narrow side of the cast billet into the rail head and the wide side into the rail web to rolling the wide side into the rail head and the narrow side into the rail web. This increases the metal content of the rail web, improves the deformation and density of the rail web, and changes the distribution pattern of non-metallic inclusions in the rail web, thereby reducing the rail web alarm rate.

[0027] In some embodiments, in step S1, the chemical composition of the rectangular billet, by weight percentage, includes: C: 0.60-0.82%, Si: 0.20-0.80%, Mn: 0.70-0.95%, P≤0.020%, S≤0.010%, V≤0.12%. This composition helps ensure the strength and rigidity of the turnout rail while maintaining excellent toughness and plasticity.

[0028] In some embodiments, during step S1, the molten steel in the ladle is controlled to have hydrogen ≤1.4ppm, oxygen ≤10ppm, and nitrogen ≤45ppm. By controlling the hydrogen, oxygen, and nitrogen content in the molten steel, it is helpful to reduce hydrogen-induced cracking caused by high hydrogen, inclusion aggregation caused by high oxygen, and age embrittlement caused by high nitrogen, thereby reducing the ultrasonic alarm rate and improving the overall performance of the turnout rail.

[0029] In some embodiments, in step S1, the smelting process employs a low sulfur content control of 0.002-0.010%. Considering that sulfur exists in steel as sulfide inclusions, which adversely affect the steel's plasticity, toughness, weldability, fatigue performance, and corrosion resistance, the present invention helps to improve these properties of turnout rails by controlling the sulfur content.

[0030] In some embodiments, in step S1, protective casting is used throughout the smelting and casting process. This helps to suppress oxidation and reduce inclusions, thereby improving the purity of the billet; stabilize the casting process, ensuring the dimensional accuracy of the billet; and improve the mechanical properties of the billet.

[0031] In some embodiments, in step S2, the turnout rail is rolled and deformed using a universal rolling mill, with an initial rolling temperature of 1100-1200℃ and a final rolling temperature of 900-950℃. If the initial and final rolling temperatures are too low, the rolling deformation becomes more difficult, increasing the likelihood of cracking and a higher ultrasonic alarm rate. If the initial and final rolling temperatures are too high, the billet risks overheating or burning through, which also increases the ultrasonic alarm rate. The initial rolling temperature can typically, but is not limited to, be set to 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, or 1200℃. The final rolling temperature can typically, but is not limited to, be set to 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃.

[0032] In some embodiments, in step S2, the rolling compression ratio during rolling is 9-13. This rolling compression ratio helps to ensure the final turnout rail cross-sectional dimensions and microstructure refinement. A low rolling compression ratio results in insufficient microstructure refinement of the turnout rail, leading to a deterioration in both microstructure and ultrasonic alarm rate. An excessively high compression ratio increases rolling difficulty, which in turn increases the difficulty of metal deformation and raises the alarm rate. The rolling compression ratio can typically, but is not limited to, being set to 9, 10, 11, 12, or 13.

[0033] In some embodiments, in step S3, the forced cooling start-up temperature is 750-850℃, the forced cooling rate is 1.5-2.5℃ / s, and the forced cooling final cooling temperature is 500-600℃. If this forced cooling start-up temperature is too low, the difference between the forced cooling start-up temperature and the phase transformation temperature is too small, making it impossible to refine the microstructure using forced cooling and reducing strength and hardness; if the forced cooling temperature is too high, the grains are prone to coarsening, making it impossible to fully utilize grain refinement to improve strength and toughness. If this forced cooling rate is too low, it cannot improve strength and toughness; if the forced cooling rate is too high, it easily produces abnormal microstructures such as martensite. If this forced cooling final cooling temperature is too low, undercooled austenite will produce martensite; if the forced cooling final cooling temperature is too high, strength and toughness will be low. The forced cooling start-up temperature can typically, but not limitedly, be set to 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, or 850℃. The forced cooling rate can typically, but not limited to, be set to 1.5℃ / s, 1.6℃ / s, 1.7℃ / s, 1.8℃ / s, 1.9℃ / s, 2.0℃ / s, 2.1℃ / s, 2.2℃ / s, 2.3℃ / s, 2.4℃ / s, or 2.5℃ / s. The forced cooling final cooling temperature can typically, but not limited to, be set to 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃.

[0034] In some embodiments, step S3 includes: after rolling, the material is cooled to the forced cooling start temperature (i.e., 750-850°C) by natural air cooling, then cooled to the forced cooling final temperature (i.e., 500-600°C) by forced cooling rate (i.e., 1.5-2.5°C / s), and then naturally air cooled to room temperature.

[0035] In some embodiments, in step S4, straightening is performed when the turnout rail, after online heat treatment, cools to below 60°C. This helps to prevent the turnout rail from rebounding after straightening deformation.

[0036] In some embodiments, in step S4, after straightening and before processing, ultrasonic online testing is performed to ensure the quality of the turnout rail.

[0037] The second aspect of the present invention provides a high-performance turnout rail with a low alarm rate, which is manufactured using the production method described in the first aspect of the present invention.

[0038] The turnout rails produced using the method of this invention have a web density between 0.945 and 0.955, a Class A non-metallic inclusion level ≤ 1.5, and a B+C+D+Ds level ≤ 0.5; an ultrasonic alarm rate ≤ 5‰; H320 grade turnout rails have a tensile strength ≥ 1150 MPa, an elongation ≥ 10%, a tread hardness of 330-360 HB, and a hardness at the 6th point of the cross-section (30 mm from the surface) ≥ 32.0 HRC; H340 grade turnout rails have a tensile strength ≥ 1240 MPa, an elongation ≥ 10%, a tread hardness of 360-400 HB, and a hardness at the 6th point of the cross-section (30 mm from the surface) ≥ 36.0 HRC, and the microstructure is entirely fine pearlitic, making them particularly suitable for railway turnout rails.

[0039] The present invention will be further described below with reference to embodiments and comparative examples.

[0040] The turnout rails in the embodiments and comparative examples of this invention are cast with full protection, and their chemical composition is: 0.60-0.82% C, 0.20-0.80% Si, 0.70-0.95% Mn, ≤0.020% P, ≤0.010% S, and ≤0.12% V. Rectangular billets are used, heated in a walking beam furnace, and then rolled. The initial rolling temperature is 1100-1200℃, rolled using a universal rail rolling mill, with a rolling compression ratio of 9-13 and a final rolling temperature of 900-950℃. The embodiments and comparative examples of this invention employ different rolling and heat treatment processes, as shown in Table 1. In Table 1, "flipping rolling" refers to the rolling process of this application, which is to roll the wide side of the rectangular billet into the rail head and the narrow side of the rectangular billet into the rail web. "Normal rolling" refers to the original rolling process, which is to roll the narrow side of the rectangular billet into the rail head and the wide side of the rectangular billet into the rail web.

[0041] Table 1. Rolling and online heat treatment processes for examples and comparative models.

[0042] After being naturally cooled to room temperature, the rails are straightened, subjected to online ultrasonic testing, and sawed to produce high-performance, low-alarm-rate pearlitic turnout rails.

[0043] The turnout rails obtained in the examples and comparative examples were tested for tensile properties, cross-sectional hardness, tread hardness, and straightness according to the requirements of TB / T 3109 "Asymmetric Section Rails for Railways". The statistical data for tensile properties, cross-sectional hardness, and surface hardness are shown in Table 2. In addition, the turnout rails obtained in the examples and comparative examples were also tested for rail web density, ultrasonic alarm rate, and non-metallic inclusions; the results are shown in Table 3. Figure 3 and Figure 4 The figures shown are the test results of the rail web density of turnouts obtained from the embodiments of the present invention (specifically, Embodiment 1) and the comparative examples (specifically, Comparative Example 1). Figure 5and Figure 6 The figures shown are the inspection results of non-metallic inclusions in turnout rails obtained from the embodiments of the present invention (specifically, Embodiment 1) and the comparative examples (specifically, Comparative Example 1), respectively.

[0044] Table 2 Mechanical properties of turnout rails in the embodiments and comparative examples

[0045] Table 3. Results of rail web density and non-metallic inclusions in the examples and comparative cases.

[0046] Combining Table 2 and Table 3 Figure 3-6 It can be seen that the web density of the turnout rail produced using the scheme of this invention is between 0.945 and 0.955, the level of Class A non-metallic inclusions is ≤1.5, and the level of B+C+D+Ds is ≤0.5; the ultrasonic alarm rate is ≤5‰; the tensile strength of H320 grade turnout rail is ≥1150MPa, the elongation is ≥10%, the tread hardness is 330-360HB, and the hardness at the 6th point of the cross section (30mm from the surface) is ≥32.0HRC; the tensile strength of H340 grade turnout rail is ≥1240MPa, the elongation is ≥10%, the tread hardness is 360-400HB, and the hardness at the 6th point of the cross section (30mm from the surface) is ≥36.0HRC; the microstructure is entirely fine pearlite.

[0047] In summary, the turnout rail and its manufacturing method provided by this invention improve the strength and toughness of the turnout rail, while reducing the ultrasonic alarm rate and improving the operational safety of the turnout rail.

[0048] Although the method for producing turnout rails according to the present invention has been described in detail, those skilled in the art should understand that various modifications can be made to the present invention without departing from the spirit and scope thereof.

[0049] The above are exemplary embodiments disclosed in this invention. The order of the above embodiments is merely for description and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of this invention (including the claims) is limited to these examples. Various changes and modifications can be made without departing from the scope defined by the claims. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0050] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for producing high-performance, low-alarm-rate turnout rails, characterized in that, Includes the following steps: S1: Smelting and casting rectangular billets; S2: The rectangular billet after smelting and casting is heated and rolled. During the rolling process, the wide side of the rectangular billet is rolled into a rail head and the narrow side of the rectangular billet is rolled into a rail web. S3: Utilizing residual heat from rolling for online heat treatment; S4: After straightening and processing the turnout rails that have undergone online heat treatment, high-performance turnout rails with low alarm rates are obtained.

2. The method for producing high-performance, low-alarm-rate turnout rails according to claim 1, characterized in that, In step S1, the chemical composition of the rectangular billet, by weight percentage, includes: C: 0.60-0.82%, Si: 0.20-0.80%, Mn: 0.70-0.95%, P≤0.020%, S≤0.010%, V≤0.12%.

3. The method for producing high-performance, low-alarm-rate turnout rails according to claim 1, characterized in that, In step S1, during the smelting process, the molten steel is controlled to have hydrogen ≤1.4ppm, oxygen ≤10ppm, and nitrogen ≤45ppm.

4. The method for producing high-performance, low-alarm-rate turnout rails according to claim 1, characterized in that, In step S1, the smelting process is controlled with a low sulfur content of 0.002-0.010%.

5. The method for producing high-performance, low-alarm-rate turnout rails according to claim 1, characterized in that, In step S1, the entire smelting and casting process is carried out using protective casting.

6. The method for producing high-performance, low-alarm-rate turnout rails according to claim 1, characterized in that, In step S2, rolling is carried out using a universal rolling mill, with an initial rolling temperature of 1100-1200℃ and a final rolling temperature of 900-950℃.

7. The method for producing high-performance, low-alarm-rate turnout rails according to claim 6, characterized in that, In step S2, the rolling compression ratio during the rolling process is 9-13.

8. The method for producing high-performance, low-alarm-rate turnout rails according to claim 1, characterized in that, In step S3, the forced cooling start temperature is 750-850℃, the forced cooling rate is 1.5-2.5℃ / s, and the forced cooling final cooling temperature is 500-600℃.

9. The method for producing high-performance, low-alarm-rate turnout rails according to claim 1, characterized in that, In step S4, when the turnout rail after online heat treatment is cooled to below 60°C, it is straightened, and after straightening and before processing, ultrasonic online testing is performed.

10. A high-performance, low-alarm-rate turnout rail, characterized in that, It is produced by the production method described in any one of claims 1-9.

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