Production process for improving conductivity of U71Mn steel rail for subway

Abstract

The invention discloses a production process for improving the electric conductivity of a U71Mn steel rail for a subway. The production process comprises the following steps: a smelting process: smelting in a 25kg medium-frequency vacuum induction furnace, heating a steel ingot in an electric induction heating furnace, rolling in a pilot-scale small rolling mill, and cooling in air; aluminum-free deoxidation alloying is adopted in the smelting process, the deep vacuum degree in the whole process is smaller than or equal to 0.06 KPa, the deep vacuum time is larger than or equal to 15 min, and 0.0010-0.0040% of rare earth alloy is added; the rolling process comprises the following steps: heating a 25kg cylindrical steel ingot, and rolling by a pilot-scale small rolling mill; the heating and heat preservation temperature of the steel ingot is 1230 DEG C; the tapping temperature is not lower than 1100 DEG C, the rolling temperature is 950-1050 DEG C, and the finish rolling temperature is 890-950 DEG C. According to the production process for improving the conductivity of the U71Mn steel rail for the subway, the resistance of a steel rail material is reduced according to the Ohm law and the electric power theorem in combination with the actual working condition of the subway, so that stray current is reduced, and the potential of the steel rail is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a production process for improving the conductivity of U71Mn rails for subways. Background Art

[0002] Subway is a mode of transportation that was born with the economic development and the emergence of metropolises to meet the daily travel needs of urban residents. At present, the rails used in most urban subways in my country are made of U71Mn material, which is mainly composed of C-Si-Mn elements. In order to meet the standard performance, the content of elements such as C and Si in the steel is usually increased. Subway trains are mainly driven by electric traction locomotives. As the main circuit equipment for traction power operation, the steel rails have low conductivity, resulting in stray currents leaking through the steel rails, which can cause electrochemical corrosion of the metal structure of the subway system itself. The corrosion caused by stray currents seriously affects the safe operation of the subway and people's normal travel.

[0003] Most of the subway construction in my country is not synchronized with urban construction and lags behind urban construction facilities. When the subway is completed and put into operation, the stray current will inevitably cause serious corrosion damage to the underground pipeline steel, steel bars, etc. that are very old. In order to meet the needs of the subway rail market and prevent the electrochemical corrosion of buildings around the underground track from causing fracture and collapse accidents, it is very necessary to develop subway rails with low resistance, high tensile strength and tread hardness. According to statistics, the domestic and international markets for subway rails are growing steadily every year, and the market demand is constantly increasing. Therefore, the development of low-resistance rails with excellent performance has very important production and economic significance. Summary of the invention

[0004] The purpose of the present invention is to provide a production process for improving the conductivity of U71Mn rails for subways. According to Ohm's law and the electric power theorem and in combination with actual subway working conditions, the resistance of the rail material is reduced to prevent stray current and reduce the rail potential. By using the characteristics of Baosteel's own ore and unique rail production equipment, the U71Mn rail material is smelted and rolled through pilot tests to obtain rails with good strength, toughness and low resistivity, so that it can be applied to subway transportation facilities with complex underground working conditions, reduce the risk index of subway rail stray current to traffic, and reduce electrochemical corrosion to underground building facilities.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention discloses a production process for improving the conductivity of U71Mn rails for subways, comprising:

[0007] Smelting production process: 25kg medium frequency vacuum induction furnace smelting → electric induction heating furnace heating steel ingot → pilot small rolling mill rolling → air cooling; smelting adopts aluminum-free deoxidation alloying, the whole process deep vacuum degree ≤ 0.06KPa, deep vacuum time ≥ 15min, rare earth alloy addition is 0.0010 ~ 0.0040%;

[0008] The rolling process is: 25kg cylindrical steel ingot → heating → rolling on a pilot small rolling mill; the heating and insulation temperature of the steel ingot is 1230°C; the furnace temperature is not less than 1100°C, the rolling temperature is 950°C~1050°C, and the final rolling temperature is 890°C~950°C.

[0009] Furthermore, the chemical composition of the U71Mn rail is as follows: C 0.60-0.80%, Si 0.15-0.58%, Mn 0.70-1.20%, Cr≤0.15%, Cu≤0.15%, P≤0.025%, S≤0.025%, RE 0.0010-0.0030%, and the rest is Fe, with a total mass fraction of 100%.

[0010] Furthermore, the chemical composition of the U71Mn rail is as follows: C 0.65%, Si 0.24%, Mn 1.15%, Cr 0.124%, Cu 0.104%, P 0.012%, S 0.004%, RE 0.0013%, and the rest is Fe, with a total mass fraction of 100%.

[0011] Furthermore, the chemical composition of the U71Mn rail is as follows: C 0.67%, Si 0.20%, Mn 1.13%, Cr 0.125%, Cu 0.125%, P 0.010%, S 0.0060%, RE 0.0012%, and the rest is Fe, with a total mass fraction of 100%.

[0012] Furthermore, the chemical composition of the U71Mn rail is as follows: C 0.65%, Si 0.19%, Mn 1.18%, Cr 0.130%, Cu 0.141%, P 0.014%, S 0.0020%, RE 0.0010%, and the rest is Fe, with a total mass fraction of 100%.

[0013] Furthermore, the chemical composition of the U71Mn rail is as follows: C 0.62%, Si 0.16%, Mn 1.10%, Cr 0.140%, Cu 0.135%, P 0.015%, S 0.0070%, RE 0.0013%, and the rest is Fe, with a total mass fraction of 100%.

[0014] Furthermore, the chemical composition of the U71Mn rail is as follows: C 0.64%, Si 0.19%, Mn 1.12%, Cr 0.142%, Cu 0.144%, P 0.014%, S 0.0020%, RE 0.0010%, and the rest is Fe, with a total mass fraction of 100%.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are:

[0016] After hot rolling, the tensile strength is ≥880MPa, the elongation is ≥10%, and the rail tread hardness is ≥260HB.

[0017] Compared with similar rails, the material of the present invention has a lower C content. According to relevant studies, the chemical composition element in steel has the greatest influence on the resistance of steel, and C is the most important. Reducing the C content can reduce the resistivity of the material to the greatest extent. Therefore, the present invention reduces the C content appropriately while ensuring the performance of the rail. Mn expands the austenite phase region, increases the stability of the supercooled austenite of steel, and significantly improves the hardenability of steel. The invention of low Si content is innovative in that it can reduce the resistance of the material; because the Si content is significantly correlated with the resistivity.

[0018] The present invention utilizes the provisions of the Cr and Cu residual elements in the standard. These two elements have good electrical conductivity. The addition mainly improves the electrical conductivity of the U71Mn rail. In addition, the RE resource characteristics of Baosteel are fully utilized. The addition of rare earths has the function of controlling the morphology of sulfides in the smelting process, forming rare earth oxysulfides and reducing the formation of other metal sulfide compounds. This new sulfide compound does not deform or is very small during the rolling process, so that the grains in the steel are refined. In addition, rare earths can improve the oxidation resistance and corrosion resistance of steel. DETAILED DESCRIPTION

[0019] A production process for improving the conductivity of U71Mn rails for subways, comprising:

[0020] The smelting production process of steel is: smelting in a 25kg medium frequency vacuum induction furnace → heating the steel ingot in an electric induction heating furnace → rolling in a pilot small rolling mill → air cooling; smelting adopts aluminum-free deoxidation alloying, the deep vacuum degree of the whole process is ≤0.06KPa, the deep vacuum time is ≥15min, and the rare earth alloy addition is 0.0030%. The chemical composition of each example is shown in Table 1.

[0021] Table 1 Composition of each example (mass percentage / %)

[0022]

[0023] The rolling process is as follows: the pilot test research process of the rail material is as follows: 25kg cylindrical steel ingot → heating → rolling with a pilot small rolling mill → air cooling. The steel ingot heating and insulation temperature is 1230℃; the furnace temperature is not less than 1100℃, the rolling temperature is 950℃~1050℃, and the final rolling temperature is 890℃~950℃.

[0024] Performance of steel samples after rolling: The tensile specimens were processed according to TB / T2344, with a diameter of d0 = 10.0 mm and a gauge length of Lo = 5do. The tread hardness was randomly sampled on the plate, with a specimen length of 250 mm, and the top surface of the rail head was ground off by 0.5 mm. There were 5 test points, and the Brinell hardness test was performed to calculate the average value. The test temperature was 20°C ± 5°C. The experimental results are shown in Table 2.

[0025] Table 2 Mechanical properties of each example

[0026]

[0027]

[0028] It can be seen from Table 2 that each example has good strength, hardness and mechanical properties. The rails produced by them meet the technical requirements, and the material has good electrical conductivity, which reduces the corrosion caused by line stray current.

[0029] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A production process for improving the conductivity of U71Mn rails for subways, characterized in that: include: Smelting production process: 25kg medium frequency vacuum induction furnace smelting → electric induction heating furnace heating steel ingot → pilot small rolling mill rolling → air cooling; smelting adopts aluminum-free deoxidation alloying, the whole process deep vacuum degree ≤ 0.06KPa, deep vacuum time ≥ 15min, rare earth alloy addition is 0.0010 ~ 0.0040%; The rolling process is: 25kg cylindrical steel ingot → heating → rolling on a pilot small rolling mill; the heating and insulation temperature of the steel ingot is 1230°C; the furnace temperature is not less than 1100°C, the rolling temperature is 950°C~1050°C, and the final rolling temperature is 890°C~950°C.

2. The process for improving the conductivity of U71Mn rails for subways according to claim 1, characterized in that: The chemical composition of the U71Mn rail is as follows: C 0.60-0.80%, Si 0.15-0.58%, Mn 0.70-1.20%, Cr≤0.15%, Cu≤0.15%, P≤0.025%, S≤0.025%, RE 0.0010-0.0030%, and the rest is Fe, with a total mass fraction of 100%.

3. The process for improving the conductivity of U71Mn rails for subways according to claim 2, characterized in that: The chemical composition of the U71Mn rail is as follows: C 0.65%, Si 0.24%, Mn 1.15%, Cr 0.124%, Cu 0.104%, P 0.012%, S 0.004%, RE 0.0013%, and the rest is Fe, with a total mass fraction of 100%.

4. The process for improving the conductivity of U71Mn rails for subways according to claim 2, characterized in that: The chemical composition of the U71Mn rail is as follows: C 0.67%, Si 0.20%, Mn 1.13%, Cr 0.125%, Cu 0.125%, P 0.010%, S 0.0060%, RE 0.0012%, and the rest is Fe, with a total mass fraction of 100%.

5. The process for improving the conductivity of U71Mn rails for subways according to claim 2, characterized in that: The chemical composition of the U71Mn rail is as follows: C 0.65%, Si 0.19%, Mn 1.18%, Cr 0.130%, Cu 0.141%, P 0.014%, S 0.0020%, RE 0.0010%, and the rest is Fe, with a total mass fraction of 100%.

6. The process for improving the conductivity of U71Mn rails for subways according to claim 2, characterized in that: The chemical composition of the U71Mn rail is as follows: C 0.62%, Si 0.16%, Mn 1.10%, Cr 0.140%, Cu 0.135%, P 0.015%, S 0.0070%, RE 0.0013%, and the rest is Fe, with a total mass fraction of 100%.

7. The process for improving the conductivity of U71Mn rails for subways according to claim 2, characterized in that: The chemical composition of the U71Mn rail is as follows: C 0.64%, Si 0.19%, Mn 1.12%, Cr 0.142%, Cu 0.144%, P 0.014%, S 0.0020%, RE 0.0010%, and the rest is Fe, with a total mass fraction of 100%.

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