U75v wear-resistant metro rail and production method thereof

Abstract

The application discloses a U75V wear-resistant subway rail and a production method thereof. The U75V wear-resistant subway rail is obtained by adjusting the contents of C, Si, Mn and V within a standard allowable range and performing narrow component range control, so that the tread hardness of the U75V wear-resistant subway rail can be obviously improved and reaches between 310 and 320 HB, the wear resistance of the U75V wear-resistant subway rail is good, and the U75V wear-resistant subway rail meets the requirements of TB / T2344-2020 '43kg / m~75kg / m Rail Order Technical Conditions'.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical engineering technology, specifically relating to a U75V wear-resistant subway rail and its production method. Background Technology

[0002] As an efficient and environmentally friendly urban rail transit system, subways play an indispensable role in alleviating road traffic congestion. Furthermore, the coordinated development of subways not only alleviates road traffic problems but also promotes the development of related industries, thus boosting urban economic growth.

[0003] Although my country's subway construction started relatively late, it has developed rapidly over the past few decades. With the accelerating pace of urbanization, my country's subway construction has entered a new peak phase. Subway trunk lines in cities such as Beijing, Shanghai, Guangzhou, Tianjin, Shenzhen, Dalian, Changchun, Wuhan, Nanjing, and Xi'an have been put into operation. According to the "2021 Ranking of Subway Operating Line Lengths in Major Chinese Cities" published by the China Urban Rail Transit Association, the length of China's subway operating lines has increased year by year. In 2021, the total length of China's subway operating lines reached 7253.7 kilometers, an increase of approximately 971 kilometers compared to 2020, representing a year-on-year growth of 15.5%. According to incomplete statistics, 33 cities nationwide are currently planning to build subways, and 28 cities have been approved to launch urban subway construction plans. Based on current plans, the total mileage is expected to reach 7000 kilometers by 2025.

[0004] However, with the gradual increase in subway passenger volume and train frequency, the wear and tear on subway rails is increasing, leading to a shorter rail lifespan and increased costs for users. This has drawn attention to the issue of rail wear. To reduce rail wear and extend rail lifespan, users require rail manufacturers to provide subway rails with excellent wear resistance. Undoubtedly, the chemical composition and tread hardness of the rails must meet the requirements of TB / T2344-2020 "Technical Conditions for Ordering Rails with a Strength of 43kg / m~75kg / m". Summary of the Invention

[0005] To address the problems existing in the prior art, one aspect of the present invention provides a U75V wear-resistant subway rail, the chemical composition of which, by mass percentage, is: C 0.77~0.80%, Si 0.72~0.75%, Mn 0.88~0.91%, V 0.07~0.10%, P and S total content ≤0.025%, the remainder being iron and unavoidable impurities;

[0006] The tread hardness of the U75V wear-resistant subway rail is ≥310 HB.

[0007] In some embodiments, the U75V wear-resistant subway rail has a yield strength ≥1060 MPa and an absorptivity (A) ≥10.5%.

[0008] In some embodiments, the tread hardness of the U75V wear-resistant subway rail is 311-318 HB.

[0009] In some embodiments, the yield strength of the U75V wear-resistant subway rail is 1060-1130 MPa, and A is 10.5-12.5%.

[0010] Another aspect of the present invention provides a method for producing U75V wear-resistant subway rails, which includes the following process steps:

[0011] 1) Iron pretreatment: The sulfur content in the molten iron is ≤0.011%, and the phosphorus content is ≤0.10%.

[0012] 2) Converter smelting: Strictly control the C content of the tapped steel to ≥0.08%, adopt aluminum-free deoxidation process, high-stretching and supplementary blowing at the end point, tapping temperature ≥1640℃, use SiCaBa as deoxidizer, add quicklime, silicon calcium barium and fluorite after tapping to modify the slag, ensure argon blowing effect during tapping, and avoid slag agglomeration when the molten steel is refined and placed in place.

[0013] 3) LF furnace refining: Desulfurization, composition fine-tuning and temperature increase are carried out according to the composition and temperature of the converter steel; the basicity and oxidizing properties of the LF furnace slag are strictly controlled. During LF refining, the slag basicity is controlled to be ≥2.3 and the off-site temperature is 1600-1620℃.

[0014] 4) VD vacuum degassing: Deep vacuum degassing time is 15-18 min, followed by soft blowing for 21-23 min. During the soft blowing process, the argon flow rate is stable, and the molten steel creeps without any exposed parts.

[0015] 5) Protective casting: To promote the flotation and removal of inclusions, an alkaline tundish covering agent is used, R=2.1±0.1; the tundish is operated in full to prolong the residence time of the molten steel, and the tundish liquid level is 605±5 mm.

[0016] 6) Large billet continuous casting: Low-alumina protective slag is used, weak cooling water is used in the secondary cooling section, constant casting speed is maintained throughout the process, casting speed is 0.60-0.70 m / min, electromagnetic stirring of the casting machine is turned on and light pressure is applied to ensure the quality of the billet;

[0017] 7) Steel billet heating: A walking beam furnace is used, with a total heating time of 160 minutes. The heating time and temperature of each section are as follows: Preheating section: 710±5℃, 25-35 min; Heating section 1: 930±5℃, 45-55 min; Heating section 2: 1200±5℃, 45-55 min; Soaking section: 1230±5℃, 25-35 min.

[0018] 8) Rolling: The billet undergoes one descaling with high pressure water -- billet opening BD1 -- billet opening BD2 -- high pressure water secondary descaling -- CCS universal rolling -- pre-bending -- cooling on a cooling bed -- straightening. The initial rolling temperature is 1100±10℃ and the final rolling temperature is 920±10℃.

[0019] In some embodiments, in process step (7), the heating time and heating temperature of each section are as follows: preheating section: 710℃, 30 min; heating section 1: 930℃, 50 min; heating section 2: 1200℃, 50 min; heat soaking section: 1230℃, 30 min.

[0020] The technical problem to be solved by the present invention is to provide a U75V subway rail that maximizes the surface hardness within the requirements of the TB / T2344-2020 standard "Technical Conditions for Ordering 43kg / m~75kg / m Rails". The U75V wear-resistant subway rail obtained by the present invention has a surface hardness of 310~320HB, thus having good wear resistance. Detailed Implementation

[0021] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0022] Example: A method for producing U75V subway rails with excellent wear resistance

[0023] 1) Iron pretreatment: The sulfur content in the molten iron is 0.011%, and the phosphorus content is 0.10%.

[0024] 2) Converter smelting: Strictly control the C content of the tapped steel to ≥0.08%, adopt the aluminum-free deoxidation process, high-stretching and supplementary blowing at the end point, tapping temperature of 1640℃, use SiCaBa as deoxidizer, add quicklime, silicon calcium barium and fluorite after tapping to modify the slag, ensure the argon blowing effect during tapping, and avoid the phenomenon of slag agglomeration when the molten steel is refined and placed in place.

[0025] 3) LF furnace refining: Desulfurization, composition fine-tuning and temperature increase are carried out according to the composition and temperature of the converter steel; the basicity and oxidizing properties of the LF furnace slag are strictly controlled. During LF refining, the basicity of the slag is controlled to be ≥2.3 and the temperature at the off-site is 1600℃.

[0026] 4) VD vacuum degassing: deep vacuum degassing time is 17 min, followed by soft blowing for 22 min. During the soft blowing process, the argon flow rate is stable, and the molten steel creeps without any exposed parts.

[0027] 5) Protective casting: To promote the removal of inclusions by floating, an alkaline tundish covering agent is used, with R=2.1; the tundish is operated in full to prolong the residence time of the molten steel, and the tundish liquid level is 605 mm.

[0028] 6) Large billet continuous casting: Low-alumina protective slag is used, and weak cooling water is supplied in the secondary cooling section. Constant casting speed of 0.65 m / min is maintained throughout the process. Electromagnetic stirring and light pressure are activated on the casting machine to ensure billet quality. The percentage mass content of chemical components in the molten steel supplied for continuous casting is shown in Table 1 below.

[0029] Table 1: Main Chemical Composition (%) of U75V Wear-Resistant Subway Rail

[0030]

[0031] 7) Steel billet heating: A walking beam furnace is used, with a total heating time of 160 minutes. The heating time and temperature of each section of the furnace are shown in Table 2.

[0032] Table 2: Heating Process for U75V Steel Billets

[0033]

[0034] 8) Rolling: The steel billet undergoes high-pressure water descaling (first stage) – billet opening (BD1) – billet opening (BD2) – high-pressure water descaling (second stage) – CCS universal rolling – pre-bending – cooling on a cooling bed – straightening – long-length processing – inspection – finished rail. The initial rolling temperature is 1100℃, and the final rolling temperature is 923℃. The mechanical properties of the U75V subway rails produced in each embodiment (each embodiment producing 65-75 heats) were tested, and the results are shown in Table 3 below.

[0035] Table 3: Test Results of Mechanical Properties of U75V Wear-Resistant Metro Rail

[0036]

[0037] As shown in Table 3 above, the U75V subway rail produced by this invention fully meets the requirements of TB / T2344-2020 "Technical Conditions for Ordering 43kg / m~75kg / m Rails" in terms of chemical composition and various mechanical properties. The hardness of the rail tread reaches 311 HB or above, exceeding the lower limit of the standard requirement of 31 HB and approaching the upper limit of the standard requirement. The wear resistance of the rail is greatly improved, which can well meet the needs of users.

[0038] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing U75V wear-resistant subway rails, comprising the following technological steps: 1) Iron pretreatment: The sulfur content in the molten iron is ≤0.011%, and the phosphorus content is ≤0.10%; 2) Converter smelting: Strictly control the C content of the tapped steel to ≥0.08%, adopt aluminum-free deoxidation process, high-stretching and supplementary blowing at the end point, tapping temperature ≥1640℃, use SiCaBa as deoxidizer, add quicklime, silicon calcium barium and fluorite after tapping to modify the slag, ensure argon blowing effect during tapping, and avoid slag agglomeration when the molten steel is refined and placed in place. 3) LF furnace refining: Desulfurization, composition fine-tuning and temperature increase are carried out according to the composition and temperature of the converter steel; the basicity and oxidizing properties of the LF furnace slag are strictly controlled. During LF refining, the slag basicity is controlled to be ≥2.3 and the off-site temperature is 1600-1620℃. 4) VD vacuum degassing: Deep vacuum degassing time is 15-18 min, followed by soft blowing for 21-23 min. During the soft blowing process, the argon flow rate is stable, and the molten steel creeps without any exposed parts. 5) Protective casting: To promote the flotation and removal of inclusions, an alkaline tundish covering agent is used, R=2.1±0.1; the tundish is operated in full to prolong the residence time of the molten steel, and the tundish liquid level is 605±5 mm. 6) Large billet continuous casting: Low-alumina protective slag is used, weak cooling water is used in the secondary cooling section, constant casting speed is maintained throughout the process, casting speed is 0.60-0.70 m / min, electromagnetic stirring of the casting machine is turned on and light pressure is applied to ensure the quality of the billet; 7) Steel billet heating: A walking beam furnace is used, with a total heating time of 160 minutes. The heating time and temperature of each section are as follows: Preheating section: 710±5℃, 25-35 min; Heating section 1: 930±5℃, 45-55 min; Heating section 2: 1200±5℃, 45-55 min; Soaking section: 1230±5℃, 25-35 min. 8) Rolling: The billet undergoes one descaling with high pressure water -- billet opening BD1 -- billet opening BD2 -- high pressure water secondary descaling -- CCS universal rolling -- pre-bending -- cooling on a cooling bed -- straightening. The initial rolling temperature is 1100±10℃ and the final rolling temperature is 920±10℃. The chemical composition of the U75V wear-resistant subway rail, by mass percentage, is: C 0.77~0.80%, Si 0.72~0.75%, Mn 0.88~0.91%, V 0.07~0.10%, P and S total content ≤0.025%, the remainder being iron and unavoidable impurities; The tread hardness of the U75V wear-resistant subway rail is ≥310 HB.

2. The production method according to claim 1, wherein in process step (7), the heating time and heating temperature of each section are as follows: preheating section: 710℃, 30 min; heating section 1: 930℃, 50 min; heating section 2: 1200℃, 50 min; heat soaking section: 1230℃, 30 min.

3. The production method according to claim 1, characterized in that, The U75V wear-resistant subway rail has a yield strength ≥1060 MPa and an absorptivity (A) ≥10.5%.

4. The production method according to claim 1, characterized in that, The surface hardness of the U75V wear-resistant subway rail is 311-318 HB.

5. The production method according to claim 1, characterized in that, The U75V wear-resistant subway rail has a yield strength of 1060-1130 MPa and an A value of 10.5-12.5%.

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