A production method for improving wear resistance of a channel rail for a tram

Abstract

The present application relates to the technical field of rail production process, in particular to a production method for improving wear resistance of channel rail for tram. After universal rolling, compressed air is applied to the channel rail for forced cooling in parts. In the first stage, supersonic air jet cooling is applied to the rail head tread, rail head running edge, rail head left side, rail lip and rail bottom to control the cooling speed of each part. In the second stage, supersonic air jet cooling is continuously applied to each part of the rail to control the cooling speed of each part. In the third stage, subsonic air jet cooling is applied to each part of the rail to control the cooling speed of each part, and then the rail is naturally cooled in air. The quenching effect of the channel rail tread and running edge is improved, the pearlite interlamellar spacing is refined, the rail strength and hardness are improved, and the channel rail has good wear resistance.

Description

Technical Field

[0001] This invention relates to the field of rail manufacturing technology, specifically a production method for improving the wear resistance of grooved rails used in trams. Background Technology

[0002] As an environmentally friendly and energy-saving mode of urban public transportation, trams play a vital role in modern urban development due to their advantages such as low construction costs, high safety, and low pollution. Compared to traditional buses, trams are electrically powered, significantly reducing exhaust emissions and contributing to improved urban air quality. Furthermore, because they enjoy independent right-of-way and operate on fixed tracks, the ride is smooth, offering high passenger comfort. Their flexible formations can adapt to varying passenger flow demands, effectively alleviating traffic congestion and holding strategic significance for improving urban public transportation efficiency and promoting sustainable urban development.

[0003] However, tram lines often need to follow existing roads and terrain, inevitably requiring the inclusion of small-radius curves. When vehicles pass through curves, they rely on the lateral force between the wheel and rail to provide centripetal force. The smaller the curve radius, the greater the lateral force, leading to increased wear on the rail head on the running side, which can easily cause damage such as side wear, peeling, and spalling, severely shortening the service life of the rails.

[0004] Channel rails are core components in tram systems, used to bear the weight of the tram and guide its direction of travel. Due to their asymmetrical cross-sectional structure and significant differences in metal distribution between the rail head, lip, and base, channel rails undergo more complex heat treatment processes than conventional rails. Currently, to improve the wear resistance of channel rails, differentiated cooling is often required for different parts. Improper process control can lead to uneven thermal stress distribution during quenching, causing rail bending, affecting heat treatment effectiveness, and potentially causing equipment collisions and endangering production safety. Some manufacturers use spray cooling to improve quenching strength, but this method requires strict cleanliness of the rail surface, and the nozzles are prone to clogging, resulting in poor cooling stability and controllability, and high maintenance costs. Furthermore, due to the asymmetrical cross-section and groove structure of channel rails, excessively rapid local cooling can easily form brittle structures such as martensite, impairing the overall performance of the rail and the yield rate of finished products. Therefore, there is an urgent need to develop an efficient and stable production process for channel rails that can effectively improve the quenching effect of the channel rail tread and the running edge, so that the produced channel rails have good wear resistance.

[0005] In the prior art, Chinese patent application CN202210889199.2 discloses "a channel rail and its preparation method," which improves straightness and fatigue resistance through induction heating and segmented cooling. However, the additional heating process leads to reduced production efficiency and increased costs, and its cooling rate is low (0.7-5℃ / s), resulting in limited improvement in wear resistance. Chinese patent application CN202310792997.8 discloses "a method for processing wear-resistant guard rails," which enhances local wear resistance by welding wear-resistant strips to the rail lip. Although the process is simple and the bond is strong, it does not improve the wear resistance of the rail head tread and the running edge. Furthermore, due to the involvement of CNC machining and welding, the process is time-consuming and costly, making large-scale promotion difficult. Chinese patent application CN201520075902.1 discloses "a locally reinforced and hardened channel rail," which involves creating machining grooves on the rail head and rail side guard rails and filling them with wear-resistant welding material to improve wear resistance and strength. However, this method involves complex groove machining, and the welding process easily introduces defects such as martensite and inclusions, affecting safety. It also suffers from high cost and limited applicability. Chinese patent application CN202110576248.2 discloses "A production method for improving the wear resistance of heat-treated rails," employing a seven-stage dynamic cooling process to treat the rail head of hot-rolled rails, aiming to improve wear resistance and toughness. However, this process has numerous control parameters, making production implementation difficult, and it is only designed for ordinary rails with symmetrical cross-sections, making it unsuitable for grooved rails with asymmetrical structures. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a production method for improving the wear resistance of channel steel rails used in trams, improving the quenching effect of the channel rail tread and running edge, refining the pearlite lamellar spacing, improving the strength and hardness of the rail, and giving the channel steel rail good wear resistance.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A production method for improving the wear resistance of channel steel rails for trams includes the following production process: vacuum smelting, continuous casting, billet heating, high-pressure water descaling, universal rolling of rails, online heat treatment, cooling bed cooling, straightening, flaw detection and inspection.

[0008] The online heat treatment process involves applying compressed air to the universally rolled channel steel rail for forced cooling in different sections. The cooling process is divided into the following three stages: Phase 1: Apply supersonic jet cooling to the rail head tread, rail head traveling edge, left side of the rail head, rail lip, and rail bottom, controlling the cooling rate of each part, so that the rail head tread cools from 730~800℃ to 580~620℃ at a cooling rate of 5~7℃ / s.

[0009] Second stage: Continue to apply supersonic air jet cooling to all parts of the rail, control the cooling rate of each part, and cool the rail head tread from 580~620℃ to 500~520℃ at a cooling rate of 4~5℃ / s.

[0010] The third stage involves applying subsonic air jets to various parts of the rail, controlling the cooling rate of each part, and cooling the rail head tread from 500-520℃ to 420-440℃ at a cooling rate of 1.5-2.5℃ / s. Subsequently, the rail is allowed to cool naturally in the air.

[0011] Furthermore, in the first cooling stage, the nozzle velocity of the supersonic jet cooling is 1.5~2 Ma.

[0012] Furthermore, in the first cooling stage, the cooling rate of the rail head running side is controlled to be 90% to 100% of the rail head tread cooling rate, the cooling rate of the left side of the rail head is 80% to 90% of the rail head tread cooling rate, the cooling rate of the rail lip is 70% to 80% of the rail head tread cooling rate, and the cooling rate of the rail base is 60% to 70% of the rail head tread cooling rate.

[0013] Furthermore, in the second cooling stage, the nozzle velocity of the supersonic jet cooling is 1~1.5 Ma.

[0014] Furthermore, in the second cooling stage, the cooling rate of the rail head running side is controlled to be the same as the cooling rate of the rail head tread, which is 4~5℃ / s; the cooling rate of the left side of the rail head is 80%~90% of the cooling rate of the rail head tread; and the cooling rate of the rail lip and rail bottom is 70%~80% of the cooling rate of the rail head tread.

[0015] Furthermore, in the third cooling stage, the nozzle velocity of the subsonic jet cooling is 0.3~0.6 Ma.

[0016] Furthermore, in the third cooling stage, the cooling rate of the rail head running side is controlled to be the same as that of the rail head tread, which is 1.5~2.5℃ / s; the cooling rate of the left side of the rail head is 80%~100% of the cooling rate of the rail head tread; the cooling rate of the rail lip is 60%~70% of the cooling rate of the rail head tread; and the cooling rate of the rail base is 70%~80% of the cooling rate of the rail head tread.

[0017] Furthermore, the channel rail obtained after the online heat treatment comprises the following components by weight percentage: C: 0.71%~0.80%, Si: 0.50%~0.80%, Mn: 0.75%~1.05%, V: 0.04%~0.12%, P≤0.030%, S≤0.025%, with the remainder being Fe and unavoidable impurities.

[0018] Furthermore, the online heat treatment is carried out in a dedicated online heat treatment unit, which is equipped with a nozzle group that can independently adjust the air pressure, air volume and angle, so as to spray air to cool the rail head tread, rail head traveling side, left side of rail head, rail lip and rail bottom of the channel rail respectively.

[0019] Furthermore, the channel rail obtained after the online heat treatment has a uniform and fine pearlitic microstructure at the rail head, which is allowed to contain a small amount of ferrite; its tensile strength reaches 1180~1320MPa, its elongation after fracture is not less than 10%, and the hardness of the rail head tread is controlled within the range of 365~400HBW.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention rapidly cools the rail head tread and the running edge with supersonic air jets in the first stage, increasing the undercooling degree of pearlite transformation and obtaining a pearlite structure with finer interlamellar spacing, higher strength and hardness, which directly and effectively improves the wear resistance of the most wear-prone areas of the rail.

[0021] 2. This invention effectively balances the thermal stress and phase transformation stress generated during heat treatment by applying differentiated cooling rate control to different parts of the asymmetrical cross-section of the channel rail, ensuring the straightness of the rail before, during and after treatment and avoiding deformation.

[0022] 3. The present invention achieves a uniform transition of hardness from the surface to the core through medium-speed cooling in the second stage, avoiding abrupt changes in performance; the third stage of subsonic slow cooling effectively prevents the surface "warming back" phenomenon caused by heat leakage from the core, ensuring the complete completion of pearlite transformation and the uniform and stable properties of the structure.

[0023] In summary, this invention improves the quenching effect of channel rails by combining supersonic and subsonic air jet cooling, effectively enhancing the strength and hardness of the rail head tread and running edge. This results in channel rails produced using this method exhibiting excellent wear resistance, meeting the technical requirements of the YB / T4653-2018 standard. Furthermore, this invention improves the wear resistance of channel rails, increases production efficiency, effectively extends their service life, enhances product competitiveness, and improves their operational safety, resulting in significant economic and social benefits. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing the cross-sectional shape of the channel rail and the names of its various parts.

[0025] Figure 2 This is a typical metallographic structure of the rail head of a grooved steel rail after online heat treatment. Detailed Implementation

[0026] This invention discloses a production method for improving the wear resistance of channel steel rails used in trams. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0027] A production method for improving the wear resistance of channel steel rails for trams includes the following production process: vacuum smelting, continuous casting, billet heating, high-pressure water descaling, universal rolling of rails, online heat treatment, cooling bed cooling, straightening, flaw detection and inspection.

[0028] This method mainly includes an online heat treatment process. After universal rolling, the channel rail enters the online heat treatment unit for accelerated cooling. Compressed air is applied to various parts of the rail for forced cooling. The cooling process is divided into three stages: The first stage involves the channel rails entering an online heat treatment unit for accelerated cooling. The rail temperature upon entering the unit is 730~800℃. The cooling method is supersonic jet cooling with a nozzle flow rate of 1.5~2Ma. The cooling rate of the rail head tread is 5~7℃ / s, the cooling rate of the rail head running side is 90%~100% of the rail head tread, the cooling rate of the left side of the rail head is 80%~90% of the rail head tread, the cooling rate of the rail lip is 70%~80% of the rail head tread, and the cooling rate of the rail bottom is 60%~70% of the rail head tread. When the rail head tread reaches 580~620℃, the second stage of cooling begins.

[0029] The second stage: The rails continue to be cooled by supersonic jet air, with a nozzle flow rate of 1~1.5 Ma, a cooling rate of 4~5℃ / s for the rail head tread and the running side, a cooling rate of 80%~90% for the left side of the rail head, and a cooling rate of 70%~80% for the rail lip and the rail bottom. When the rail head tread is cooled to 500~520℃, the third stage of cooling begins.

[0030] The third stage: The rails are cooled by subsonic jet air with a nozzle velocity of 0.3~0.6 Ma. The cooling rate of the rail tread and the running edge is 1.5~2.5℃ / s. The cooling rate of the left side of the rail head is 80%~100% of that of the rail head tread, the cooling rate of the rail lip is 60%~70% of that of the rail head tread, and the cooling rate of the rail base is 70%~80% of that of the rail head tread. When the rail head tread is cooled to 420~440℃, the rail is removed from the unit and allowed to cool naturally in the air.

[0031] A three-stage cooling system is employed. The primary purpose of the first stage is to increase the cooling rate of the rail tread and running edge by using supersonic jet cooling, ensuring sufficient time for the supercooled austenite to complete its pearlite transformation. This increases the degree of undercooling during pearlite transformation, thereby enhancing the driving force for the transformation of supercooled austenite into pearlite, resulting in a pearlitic microstructure with fine lamellar spacing. This improves the strength and hardness of the rail, thus enhancing the wear resistance of the rail surface. Simultaneously, the cooling rate of other parts is adjusted to ensure the straightness of the rail during heat treatment. The second stage... Based on the first stage, the cooling rate is appropriately reduced to allow the near-surface of the channel rail to cool at a faster rate, resulting in a uniform reduction in hardness from the surface to the core of the rail. This also prepares the rail for the third stage of cooling. The third stage uses subsonic jet cooling to continue applying a certain cooling rate to the surface of the channel rail, preventing backheating caused by the heat storage zone in the core, which would affect the heat treatment effect. At the same time, it evens out the temperature stress and phase transformation stress generated by the rapid cooling in the first two stages. When the temperature is cooled to 420~440℃, the pearlite transformation of the rail head and rail lip is completed, and the rail is removed from the online heat treatment unit.

[0032] In the embodiments and comparative examples of this invention, the channel rail grade is U75V, with the following chemical composition: C: 0.71%~0.80%, Si: 0.50%~0.80%, Mn: 0.75%~1.05%; V: 0.04%~0.12%; P≤0.030%; S≤0.025%, with the remainder being Fe and unavoidable impurities. The main heat treatment process parameters for the embodiments of this invention are shown in Tables 1, 2, and 3; the main heat treatment process parameters for the comparative examples of this invention are shown in Table 4; and the microstructure and properties of the embodiments and comparative examples of this invention are shown in Table 5.

[0033] Table 1. Main process parameters for heat treatment in embodiments of the present invention. Table 2 Main process parameters of heat treatment in the embodiments of the present invention (II) Table 3 Main process parameters of heat treatment in the embodiments of the present invention (III) Table 4 Main heat treatment process parameters of the comparative example of the present invention Table 5. Organization and performance of embodiments and comparative examples of the present invention As shown in Table 5, the channel rails obtained in Examples 1-6 have good performance indicators and microstructure. Compared with the channel rail in Comparative Example 1, the present invention improves the quenching effect of the channel rail by combining supersonic and subsonic air cooling, effectively improving the strength and hardness of the rail head tread and running edge. This results in the channel rail produced by this method having good wear resistance, and its performance meets the technical requirements of YB / T4653~2018 standard.

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A production method for improving the wear resistance of a channel section rail for a tram, the production process flow comprising: Vacuum smelting, continuous casting, billet heating, high-pressure water descaling, universal rolling of rails, online heat treatment, cooling bed cooling, straightening, flaw detection and inspection, characterized in that, The online heat treatment process involves applying compressed air to the universally rolled channel steel rail for forced cooling in different sections. The cooling process is divided into the following three stages: The first stage involves applying supersonic jet cooling to the rail head tread, rail head traveling edge, left side of the rail head, rail lip, and rail bottom, controlling the cooling rate of each part, so that the rail head tread cools from 730~800℃ to 580~620℃ at a cooling rate of 5~7℃ / s. Second stage: Continue to apply supersonic jet cooling to all parts of the rail, control the cooling rate of each part, and cool the rail head tread from 580~620℃ to 500~520℃ at a cooling rate of 4~5℃ / s. The third stage involves applying subsonic air jets to various parts of the rail, controlling the cooling rate of each part, and cooling the rail head tread from 500-520℃ to 420-440℃ at a cooling rate of 1.5-2.5℃ / s. Subsequently, the rail is allowed to cool naturally in the air.

2. The production method for improving the wear resistance of channel steel rails for trams according to claim 1, characterized in that, In the first cooling stage, the nozzle velocity of the supersonic jet cooling is 1.5~2 Ma.

3. A production method for improving the wear resistance of channel steel rails for trams according to claim 2, characterized in that, In the first cooling stage, the cooling rate of the rail head running side is controlled to be 90%~100% of the cooling rate of the rail head tread, the cooling rate of the left side of the rail head is 80%~90% of the cooling rate of the rail head tread, the cooling rate of the rail lip is 70%~80% of the cooling rate of the rail head tread, and the cooling rate of the rail base is 60%~70% of the cooling rate of the rail head tread.

4. The production method for improving the wear resistance of channel steel rails for trams according to claim 1, characterized in that, In the second cooling stage, the nozzle velocity of the supersonic jet cooling is 1~1.5 Ma.

5. A production method for improving the wear resistance of channel steel rails for trams according to claim 4, characterized in that, In the second cooling stage, the cooling rate of the rail head running side is controlled to be the same as that of the rail head tread, which is 4~5℃ / s; the cooling rate of the left side of the rail head is 80%~90% of the cooling rate of the rail head tread; and the cooling rate of the rail lip and rail bottom is 70%~80% of the cooling rate of the rail head tread.

6. A method for improving the wear resistance of channel steel rails for trams according to claim 1, characterized in that, In the third cooling stage, the nozzle velocity of the subsonic jet cooling is 0.3~0.6 Ma.

7. A method for improving the wear resistance of channel steel rails for trams according to claim 6, characterized in that, In the third cooling stage, the cooling rate of the rail head running side is the same as that of the rail head tread, which is 1.5~2.5℃ / s; the cooling rate of the left side of the rail head is 80%~100% of the cooling rate of the rail head tread; the cooling rate of the rail lip is 60%~70% of the cooling rate of the rail head tread; and the cooling rate of the rail base is 70%~80% of the cooling rate of the rail head tread.

8. The production method for improving the wear resistance of the channel section rail for tram according to claim 1, characterized in that, The channel rail obtained after the online heat treatment comprises the following components by weight percentage: C: 0.71%~0.80%, Si: 0.50%~0.80%, Mn: 0.75%~1.05%, V: 0.04%~0.12%, P≤0.030%, S≤0.025%, with the remainder being Fe and unavoidable impurities.

9. A production method for improving the wear resistance of channel steel rails for trams according to claim 1, characterized in that, The online heat treatment is carried out in a dedicated online heat treatment unit, which is equipped with a nozzle group that can independently adjust the air pressure, air volume and angle, so as to spray air to cool the rail head tread, rail head traveling side, left side of rail head, rail lip and rail bottom of the channel rail respectively.

10. A method for improving the wear resistance of channel steel rails for trams according to claim 1, characterized in that, The channel rail obtained after the online heat treatment has a uniform and fine pearlitic microstructure at the rail head, which is allowed to contain a small amount of ferrite; its tensile strength reaches 1180~1320MPa, its elongation after fracture is not less than 10%, and the hardness of the rail head tread is controlled within the range of 365~400HBW.

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