Production process for improving the conductivity of U75V rail for subway

Abstract

The application discloses a production process for improving the conductivity of U75V steel rails for subways, which comprises the following steps: a smelting process, wherein vacuum smelting is adopted to realize non-aluminum deoxidization and alloying, and the whole smelting process is protected in a vacuum; a rolling process; and a heat treatment process, wherein the U75V steel rail is heated to 200 DEG C and kept for 40 minutes, and then air-cooled to room temperature; the chemical composition of the U75V steel rail is as follows: C 0.71-0.75%, Si 0.50-0.60%, Mn 0.75-0.85%, Cr 0.00-0.15%, Cu 0.10-0.15%, Ni 0.00-0.10%, V≤0.03%, P≤0.015%, S≤0.010%, and the rest is Fe and impurities. The application aims to obtain a steel rail with good strength, toughness and low resistivity, so that the steel rail can be applied to complex underground subway traffic facilities, and the traffic danger index caused by the stray current of the subway steel rail is reduced.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and in particular relates to a production process for improving the conductivity of U75V steel rails used in subways. Background Technology

[0002] Subways, a mode of transportation that emerged with economic development and the rise of metropolises to meet the daily travel needs of urban residents, play a crucial role in subway systems. During operation, stray currents leaking through the rails can cause electrochemical corrosion of the subway system's metal structure. This corrosion severely impacts the safe operation of the subway and people's normal travel. In my country, most subway construction has lagged behind urban development and infrastructure. As a result, stray currents from older underground pipelines and reinforcing steel will inevitably cause severe corrosion damage during the later stages of subway construction and operation.

[0003] Due to various reasons, such as cost-saving measures during subway construction leading to the absence of actual stray current protection devices or the lack of designated installation locations; the inability of some subway systems' online stray current monitoring systems to comprehensively monitor actual stray current leakage; and the short lifespan and poor effectiveness of some protective devices, the hazards of stray currents in subways remain severe. To meet the needs of the subway rail market and prevent electrochemical corrosion of surrounding buildings from causing fractures and collapses, it is essential to develop subway rails with low resistance, high tensile strength, and high tread hardness.

[0004] However, most subway construction procurement standards in my country are based on the rail material specifications in the industry standard TB / T2344. While patent CN106978567 B discloses a material for preventing stray currents, this material is not included in the industry standard and its production involves heat treatment, increasing production costs. Therefore, given the current demand for high-strength, low-resistance rails for subways, the development of this patented, high-performance, low-resistance U75V rail is of significant production and economic importance. Summary of the Invention

[0005] The purpose of this invention is to provide a production process for improving the conductivity of U75V steel rails used in subways. Based on Ohm's law and the electric power theorem, and combined with the actual working conditions of subways, the process reduces the resistance of the rail material, thereby reducing stray currents and lowering the rail potential. This results in steel rails with good strength, toughness, and low resistivity, making them suitable for use in subway transportation facilities with complex underground conditions. This reduces the risk of stray currents from subway rails to traffic and minimizes electrochemical corrosion of underground structures.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses a manufacturing process for improving the conductivity of U75V steel rails used in subways, comprising:

[0008] Smelting process: smelting in a 25kg medium-frequency vacuum induction furnace → heating steel ingots in an electric induction heating furnace → rolling in a pilot-scale small rolling mill → air cooling; vacuum smelting adopts aluminum-free deoxidation alloying, and the entire smelting process is protected by vacuum.

[0009] Rolling process: 25kg cylindrical steel ingot → heating → rolling on a pilot-scale small rolling mill → air cooling → heat treatment; the steel ingot heating and holding temperature is 1230℃; the furnace exit temperature is not lower than 1100℃, the rolling temperature is 950℃-1050℃, and the final rolling temperature is 890℃-950℃; the heat treatment process is: heating to 200℃ and holding for 40 minutes, then air cooling to room temperature;

[0010] The chemical composition of the U75V steel rail by mass percentage is as follows: C 0.71-0.75%; Si 0.50-0.60%; Mn 0.75-0.85%; Cr 0.00-0.15%; Cu 0.10-0.15%; Ni 0.00-0.10%; V≤0.03%; P≤0.015%; S≤0.010%; the remainder is Fe and impurities, with a total mass fraction of 100%.

[0011] Furthermore, the chemical composition of the U75V rail by mass percentage is as follows: C 0.72%; Si 0.52%; Mn 0.78%; Cr 0.12%; Cu 0.11%; Ni 0.08%; P 0.012%; S 0.004%; the remainder is Fe and impurities, with a total mass fraction of 100%.

[0012] Furthermore, the chemical composition of the U75V rail by mass percentage is as follows: C 0.73%; Si 0.50%; Mn 0.79%; Cr 0.13%; Cu 0.10%; Ni 0.09%; P 0.010%; S 0.006%; the remainder is Fe and impurities, with a total mass fraction of 100%.

[0013] Furthermore, the chemical composition of the U75V rail by mass percentage is as follows: C 0.71%; Si 0.52%; Mn 0.77%; Cr 0.13%; Cu 0.12%; Ni 0.07%; P 0.010%; S 0.002%; the remainder is Fe and impurities, with a total mass fraction of 100%.

[0014] Furthermore, the chemical composition of the U75V rail by mass percentage is as follows: C 0.72%; Si 0.53%; Mn 0.78%; Cr 0.11%; Cu 0.11%; Ni 0.08%; P 0.009%; S 0.007%; the remainder is Fe and impurities, with a total mass fraction of 100%.

[0015] Furthermore, the chemical composition of the U75V steel rail by mass percentage is as follows: C 0.73%; Si 0.53%; Mn 0.76%; Cr 0.11%; Cu 0.13%; Ni 0.06%; P 0.012%; S 0.002%; the remainder is Fe and impurities, with a total mass fraction of 100%.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0017] This invention reduces the resistivity of rails by decreasing the levels of C, P, and S elements, and improves the strength and hardness of rails by adding alloying elements such as Cu and Cr. Further heat treatment of the rolled material samples results in a more uniform internal structure and eliminates post-rolling cooling stress, thereby improving the tensile strength, hardness, toughness, and electrical conductivity of the rail material. Rail materials produced using this method exhibit low resistivity while maintaining good tensile strength and tread hardness. The low-resistivity U75V subway rail material of this invention features a unique alloy design, making it suitable for large-scale production and possessing significant potential for widespread application. Detailed Implementation

[0018] A manufacturing process to improve the conductivity of U75V steel rails used in subways:

[0019] The steel smelting process is as follows: The pilot-scale steel smelting process involves: smelting in a 25kg medium-frequency vacuum induction furnace → heating the steel ingot in an induction heating furnace → rolling in a pilot-scale small rolling mill → air cooling. Vacuum smelting employs aluminum-free deoxidation alloying. The chemical compositions of each embodiment are shown in Table 1.

[0020] Table 1. Components of each embodiment (mass percentage / %)

[0021] Example C Si Mn P S Cr Cu Ni Example 1 0.72 0.52 0.78 0.012 0.004 0.12 0.11 0.08 Example 2 0.73 0.50 0.79 0.010 0.006 0.13 0.10 0.09 Example 3 0.71 0.52 0.77 0.010 0.002 0.13 0.12 0.07 Example 4 0.72 0.53 0.78 0.009 0.007 0.11 0.11 0.08 Example 5 0.73 0.53 0.76 0.012 0.002 0.11 0.13 0.06 U75V standard 0.71-0.80 0.50-0.80 0.75-1.05 ≤0.025 ≤0.025 ≤0.15 ≤0.15 ≤0.10

[0022] The rolling process is as follows: The pilot-scale experimental process for the rail material is as follows: 25kg cylindrical steel ingot → heating → rolling on a pilot-scale small rolling mill → air cooling → heat treatment simulation experiment. The ingot heating and holding temperature is 1230℃; the furnace exit temperature is not lower than 1100℃, the rolling temperature is 950℃-1050℃, and the final rolling temperature is 890℃-950℃. The heat treatment experiment for the rail was conducted considering the electrical conductivity, internal structure of the material, and the effect of the cooling process. The heat treatment process is: heating to 200℃ and holding for 40 minutes, followed by air cooling to room temperature.

[0023] Steel specimen performance: Tensile specimens were prepared with a diameter d0 = 10 mm and a gauge length Lo = 5 do. Tread surface hardness was measured by randomly sampling five points on the rolled material, performing Brinell hardness tests, and calculating the average value. The test temperature was 20℃ ± 5℃. Resistivity was measured using a multimeter. The experimental specimen dimensions were 60 cm × 15 cm × 20 cm (length × width × thickness), and the measured values ​​were converted to per kilometer.

[0024] Resistance values ​​of a 60 kg / m rail. The experimental results are shown in Table 2.

[0025] Table 2 Mechanical properties of each embodiment

[0026] Example <![CDATA[Tensile strength σ b (MPa)]]> Elongation δ (%) Average Brinell hardness (HB) Rail resistance value per kilometer (60 kg / m) / mΩ Example 1 993 12.7 294 32.7 Example 2 1015 12.5 297 33.1 Example 3 1005 13.5 287 34.2 Example 4 1012 11.4 292 33.2 Example 5 999 12.7 289 34.1 U75V standard ≥980 ≥10 ≥280

[0027] As can be seen from Table 2, each embodiment has good strength, hardness and mechanical properties. The rails produced by it meet the technical requirements of U75V standard composition, and the material has good conductivity, which reduces corrosion caused by stray current in the line.

[0028] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A manufacturing process for improving the conductivity of U75V steel rails used in subways, characterized in that, include: Smelting process: smelting in a 25kg medium-frequency vacuum induction furnace → heating steel ingots in an electric induction heating furnace → rolling in a pilot-scale small rolling mill → air cooling; vacuum smelting adopts aluminum-free deoxidation alloying, and the entire smelting process is under vacuum protection; Rolling process: 25kg cylindrical steel ingot → heating → rolling on a pilot-scale small rolling mill → air cooling → heat treatment; the steel ingot heating and holding temperature is 1230℃; the furnace exit temperature is not lower than 1100℃, the rolling temperature is 950℃-1050℃, and the final rolling temperature is 890℃-950℃; the heat treatment process is: heating to 200℃ and holding for 40 minutes, then air cooling to room temperature; The chemical composition of the U75V steel rail by mass percentage is as follows: C 0.71-0.75%; Si 0.50-0.60%; Mn 0.75-0.85%; Cr 0.00-0.15%; Cu 0.10-0.15%; Ni 0.00-0.10%; V≤0.03%; P≤0.015%; S≤0.010%; the remainder is Fe and impurities, with a total mass fraction of 100%.

2. The production process for improving the conductivity of U75V steel rails for subway use according to claim 1, characterized in that, The chemical composition of the U75V steel rail by mass percentage is as follows: C 0.72%; Si 0.52%; Mn 0.78%; Cr 0.12%; Cu 0.11%; Ni 0.08%; P 0.012%; S 0.004%; the remainder is Fe and impurities, with a total mass fraction of 100%.

3. The production process for improving the conductivity of U75V steel rails for subway use according to claim 1, characterized in that, The chemical composition of the U75V steel rail by mass percentage is as follows: C 0.73%; Si 0.50%; Mn 0.79%; Cr 0.13%; Cu 0.10%; Ni 0.09%; P 0.010%; S 0.006%; the remainder is Fe and impurities, with a total mass fraction of 100%.

4. The manufacturing process for improving the conductivity of U75V steel rails for subway use according to claim 1, characterized in that, The chemical composition of the U75V steel rail by mass percentage is as follows: C 0.71%; Si 0.52%; Mn 0.77%; Cr 0.13%; Cu 0.12%; Ni 0.07%; P 0.010%; S 0.002%; the remainder is Fe and impurities, with a total mass fraction of 100%.

5. The production process for improving the conductivity of U75V steel rails for subway use according to claim 1, characterized in that, The chemical composition of the U75V steel rail by mass percentage is as follows: C 0.72%; Si 0.53%; Mn 0.78%; Cr 0.11%; Cu 0.11%; Ni 0.08%; P 0.009%; S 0.007%; the remainder is Fe and impurities, with a total mass fraction of 100%.

6. The production process for improving the conductivity of U75V steel rails for subway use according to claim 1, characterized in that, The chemical composition of the U75V steel rail by mass percentage is as follows: C 0.73%; Si 0.53%; Mn 0.76%; Cr 0.11%; Cu 0.13%; Ni 0.06%; P 0.012%; S 0.002%; the remainder is Fe and impurities, with a total mass fraction of 100%.