High-strength corrosion-resistant rail and method for producing the same

Abstract

The application belongs to the technical field of steel and discloses a high-strength corrosion-resistant rail and a production method thereof.The high-strength corrosion-resistant rail comprises the following chemical components in percentage by mass: C: 0.60-0.75%, Si: 0.4-0.7%, Mn: 0.6-1.1%, Cr: 0.25% or more, Cu: 0.35% or more, Ni: 0.01-0.14%, Ti: 0.01-0.04%, P: less than 0.020%, S: less than 0.020%, and Cr+Cu: 0.6-1.5%, and the rest is Fe and inevitable impurities.The high-strength corrosion-resistant rail has a tensile strength of 1180 MPa or more, an elongation after fracture of 12% or more, a Brinell hardness of 330-390 HB on the rail top surface, and a relative corrosion resistance of 150% or more compared with U75V hot-rolled rails.The high-strength corrosion-resistant rail has good wear resistance and corrosion resistance, the production method is simple, has good operability, and has good popularization and application value.

Description

Technical Field

[0001] This invention belongs to the field of steel technology, specifically relating to a high-strength corrosion-resistant steel rail and its production method. Background Technology

[0002] my country's diverse climate and varying levels of industrial development create complex service environments for railway rails. These include industrial pollutants in the atmosphere, poor ventilation, prolonged darkness and dampness in tunnels, the hot and humid climate of southern and coastal areas, and the influence of marine atmospheres. Simultaneously, improvements in rail quality and enhanced railway maintenance measures have increased rail lifespan, leading to a growing proportion of rail failures caused by corrosion, which seriously threatens railway operational safety. Therefore, the industry is conducting research to improve the corrosion resistance of railway rails.

[0003] Currently, the hot-rolled corrosion-resistant steel rails used on railway lines in China have a strength grade of 980MPa, and their relative corrosion resistance compared to U75V hot-rolled steel rails meets the requirement of ≥130%. According to the "Rail Service Specification" (Q / CR 583-2017), to improve the service life of rails, higher-strength heat-treated rails are required for small-radius curves to enhance their wear resistance and fatigue resistance. The strength grades of existing corrosion-resistant steel rails are insufficient to meet the needs of railway operations, and their corrosion resistance can be further improved. Research on corrosion-resistant steel rails has been conducted both domestically and internationally, focusing on improving corrosion resistance; however, a rail product that combines high strength with high corrosion resistance has not yet been developed. To meet the needs of different railway operating conditions, there is an urgent need to develop a high-strength corrosion-resistant steel rail. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a high-strength corrosion-resistant steel rail and its production method. By rationally formulating the chemical composition of the steel rail and the production process, a steel rail with high tensile strength, high tread hardness and excellent corrosion resistance is obtained, which has good application value.

[0005] To solve the technical problem proposed in this invention, this invention provides a high-strength corrosion-resistant steel rail, the chemical composition of which, by mass percentage, includes: C: 0.60~0.75%, Si: 0.4~0.7%, Mn: 0.6~1.1%, Cr≥0.25%, Cu≥0.35%, Ni: 0.01~0.14%, Ti: 0.01~0.04%, P<0.020%, S<0.020%, and Cr+Cu: 0.6~1.5%, with the remainder being Fe and unavoidable impurities.

[0006] Preferably, the chemical composition of the high-strength corrosion-resistant steel rail, by mass percentage, includes: C: 0.62~0.70%, Si: 0.4~0.6%, Mn: 0.8~1.0%, Cr≥0.28%, Cu≥0.38%, Ni: 0.04~0.12%, Ti: 0.01~0.03%, P<0.020%, S<0.020%, and Cr+Cu: 0.7~1.4%, with the remainder being Fe and unavoidable impurities.

[0007] In the above scheme, the high-strength corrosion-resistant steel rail has a tensile strength ≥1180MPa, an elongation after fracture ≥12%, a Brinell hardness of 330~390HB on the top surface of the rail, and a relative corrosion resistance ≥150% compared with U75V hot-rolled steel rail.

[0008] In the above scheme, the microstructure of the high-strength corrosion-resistant steel rail is mainly pearlite, with the remainder being a small amount of ferrite.

[0009] This invention also provides a method for producing high-strength corrosion-resistant steel rails, comprising the following steps: 1) The molten steel is smelted in a converter, refined in an LF ladle furnace, and then treated with RH or VD vacuum before being cast into a billet; 2) The billet is fed into the heating furnace and heated in sequence through the heating section and the soaking section. The temperature of the heating section is 850~1060℃ and the temperature of the soaking section is 1150~1220℃. 3) Rolling is carried out at an initial rolling temperature of 1050~1120℃ and a final rolling temperature of 830~880℃.

[0010] 4) The rail head of the rolled rail is subjected to online accelerated cooling. The initial cooling temperature of the rail head tread is ≥700℃, the cooling rate is 0.2~1.5℃ / s, and the accelerated cooling is stopped when the rail head tread temperature drops to 560~660℃. Then, it is air-cooled to room temperature.

[0011] Preferably, in step 2), the temperature of the heating section is 880~1050℃, and the temperature of the heat spreader section is 1150~1210℃.

[0012] In the above scheme, the total heating time of the billet in the heating furnace is 100~160min, of which the soaking time is 30~60min.

[0013] Preferably, the total heating time of the billet in the heating furnace is 110~150 min, of which the soaking time is 35~55 min.

[0014] In the above scheme, the air-fuel ratio in the soaking section is controlled at 0.8~1.05 to maintain a weakly reducing atmosphere in the furnace.

[0015] Preferably, the air-fuel ratio in the heat spreader is controlled to be 0.82~1.04.

[0016] Preferably, the initial rolling temperature is 1060~1100℃ and the final rolling temperature is 840~870℃.

[0017] Preferably, the rail head tread temperature for online accelerated cooling is 710~780℃, the cooling rate is 0.4~1.4℃ / s, and accelerated cooling is stopped when the rail head tread temperature drops to 570~650℃.

[0018] In the above scheme, the rail head tread temperature refers to the surface temperature of the center part of the rail head tread.

[0019] The rationale behind the design of the chemical composition and production method of the rail in this invention is as follows: The carbon element designed into this steel has a high solid solubility with iron, which has a solid solution strengthening effect, improving the strength and hardness of the steel. Taking into account strength, toughness, corrosion resistance, and in combination with online heat treatment process, the medium carbon approach is adopted.

[0020] The main alloying elements Si and Mn added to this material are intended to improve the strength and phase transformation temperature of the rail. Si can reduce the austenite-ferrite transformation rate, thereby improving the steel's strength, elasticity, and tempering resistance. Mn expands the austenite phase region, increases the stability of the supercooled austenite, and significantly improves the steel's hardenability. However, due to the poor thermal conductivity of Si and Mn, and considering the weldability of the rail, their content should not be too high.

[0021] Adding chromium (Cr) can refine the grain structure of the rail, improving its strength, toughness, hardenability, and corrosion resistance. Adding copper (Cu) not only improves the rail's corrosion resistance but also hinders the decomposition of austenite into ferrite and pearlite, shifting the CCT curve to the lower right. This lowers the phase transformation initiation temperature of the steel at the same cooling rate, thus improving its hardenability. However, the simultaneous addition of both Cu and Cr significantly increases the hardenability of the steel. This can lead to the formation of bainite on the surface and martensite at the head-and-web junction during accelerated cooling after rolling at low cooling rates. Therefore, the combined addition of both elements needs to be limited to achieve a balance between improving rail strength and ensuring corrosion resistance without the formation of bainite and martensite.

[0022] The addition of Ni is primarily used to suppress the precipitation and diffusion of Cu along grain boundaries on the steel surface during heating, which can lead to cracking. Generally, the Ni / Cu ratio should be ≥1. Ni reduces the activity of Cu and inhibits its diffusion, effectively suppressing surface Cu precipitation. However, Ni alloys are relatively expensive, and a large addition significantly increases the alloy cost, reducing the product's applicability. Therefore, a low-Ni addition approach is adopted, combined with the heating process to control Cu precipitation on the rail surface.

[0023] Trace amounts of Ti can promote the formation of a dense rust layer and enhance atmospheric corrosion resistance. It can also refine grains and strengthen the steel through precipitation. However, when excessive Ti is added, it will form coarse TiN inclusions, which will worsen the toughness of the steel.

[0024] To suppress the precipitation and diffusion of Cu on the steel surface during the heating process, the heating time of the billet is strictly controlled. High-temperature rapid heating and segmented heating methods are adopted to quickly pass through the copper embrittlement sensitive zone of 1050~1150℃. The time and air-fuel ratio in the high-temperature soaking section are strictly controlled. The higher the air-fuel ratio, the higher the oxidizing atmosphere in the furnace, and the easier it is for Cu to be oxidized and precipitated.

[0025] To obtain good rail microstructure and properties, the addition of Cr and Cu alloying elements significantly improves the hardenability of the steel. The accelerated cooling after rolling adopts a lower cooling rate, and the austenite transformation termination temperature is used as the temperature to stop accelerated cooling to prevent the residual austenite from transforming into bainite or martensite in the subsequent cooling process, thus avoiding it becoming a source of fatigue during the use of the rail.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: To achieve a comprehensive improvement in both the strength and corrosion resistance of corrosion-resistant rails, this invention first rationally sets the composition of the rail, especially the content of alloying elements such as Cu, Cr, and Ni. Combined with the production process, particularly appropriate heating temperature, heating time, and heat treatment, this avoids surface cracking caused by copper precipitation and ensures that the microstructure does not produce undesirable structures such as bainite and martensite. This comprehensively improves the rail's tensile strength, tread hardness, and corrosion resistance. The resulting high-strength corrosion-resistant rail has a tensile strength ≥1180MPa, elongation after fracture ≥12%, and a Brinell hardness of 330~390HB on the rail top surface. Its relative corrosion resistance compared to U75V hot-rolled rails is ≥150%. This invention's high-strength corrosion-resistant rail exhibits excellent wear resistance and corrosion resistance. Its production method is simple, highly operable, and has significant potential for widespread application. Detailed Implementation

[0027] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0028] The chemical composition of the rails in the following examples is shown in Table 1, and the following production methods are adopted: 1) After converter smelting, LF refining, and RH vacuum treatment, the molten steel is cast into billets. Specifically, the basicity of the converter slag is controlled at 2.3~3.5. When about 1 / 4 of the molten steel has been tapped, alloys such as silicon, manganese, and vanadium, as well as carbon raisers, are added with the steel stream. When 3 / 4 of the molten steel has been tapped, all the alloys and carbon raisers are added. The LF furnace treatment time is >45min; the RH vacuum degree is ≤90Pa, and the pure vacuum treatment time is ≥16min. The casting process should be carried out under full protection to prevent contact with air. During casting, the tundish temperature superheat is controlled at 25~30℃, the billet pulling speed is 0.4~0.8m / min, and the cast billets are subjected to slow cooling treatment. 2) The billet is fed into the heating furnace and heated sequentially through a heating section and a soaking section. The temperature of the heating section is 850~1060℃, and the temperature of the soaking section is 1150~1220℃. The total heating time of the billet in the heating furnace is 100~160min, of which the soaking section time is 30~60min. The air-fuel ratio is controlled at 0.8~1.05 in the soaking section to maintain a weakly reducing atmosphere in the furnace. 3) Rail rolling: initial rolling temperature is 1050~1120℃, final rolling temperature is 830~880℃; 4) The rail head of the rolled rail is subjected to online accelerated cooling. The initial cooling temperature of the rail head tread is ≥700℃, the cooling rate is 0.2~1.5℃ / s, and the accelerated cooling is stopped when the rail head tread temperature drops to 560~660℃. Then, it is air-cooled to room temperature.

[0029] Table 1. Chemical composition (mass percentage) of each example and comparative example.

[0030] Table 2 Production process parameters for each embodiment and comparative example

[0031] Table 3 Production process parameters for each embodiment and comparative example (continued)

[0032] The tensile strength, tread Brinell hardness, and elongation after fracture of the rails obtained in the example were tested according to the method specified in TB / T 2344.1-2020 standard. The corrosion resistance of the obtained high-strength corrosion-resistant rails was characterized by the relative corrosion resistance in standard TJ / GW171-2021. The immersion test method was adopted, with a solution temperature of 45±2℃ and immersion in sodium bisulfite (NaHSO3). The test period was 96 hours, and there were 3 test groups. The average value of the relative corrosion resistance was taken. The relative corrosion resistance (I) was calculated using formula (1). The relative corrosion resistance results of the obtained high-strength corrosion-resistant rails and U75V hot-rolled rails are shown in Table 4.

[0033]

[0034] In the formula: I represents the average relative corrosivity; W0 represents the average corrosion weight loss rate of U75V hot-rolled steel rail, in g / (m³). 2 •h); W1 is the average corrosion weight loss rate of high-strength corrosion-resistant steel rails, in g / (m³). 2 ·h).

[0035] Table 4 Performance of each embodiment and comparative example

[0036] As can be seen from Tables 1 to 3, the tensile strength, elongation after fracture, tread Brinell hardness, and relative corrosion resistance compared to U75V hot-rolled rails in Examples 1-5 are well controlled. It can be seen that the high-strength corrosion-resistant rails produced using the method of this invention achieve a comprehensive improvement in both rail strength and corrosion resistance. Comparative Example 1 shows significantly improved corrosion resistance, with a relative corrosion resistance of only 126% compared to U75V hot-rolled rails, indicating no improvement in corrosion resistance. Comparative Example 2 shows the presence of a small amount of martensite, which is not permitted in rail standards, resulting in a reduced elongation. More importantly, this structure is prone to becoming a fatigue crack initiation point during rail use, increasing the risk of rail fracture.

[0037] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high-strength, corrosion-resistant steel rail, characterized in that, Its chemical composition by mass percentage includes: C: 0.60~0.75%, Si: 0.4~0.7%, Mn: 0.6~1.1%, Cr≥0.25%, Cu≥0.35%, Ni: 0.01~0.14%, Ti: 0.01~0.04%, P<0.020%, S<0.020%, and Cr+Cu: 0.6~1.5%, with the remainder being Fe and unavoidable impurities.

2. The high-strength corrosion-resistant steel rail according to claim 1, characterized in that, The chemical composition of the high-strength corrosion-resistant steel rail, by mass percentage, includes: C: 0.62~0.70%, Si: 0.4~0.6%, Mn: 0.8~1.0%, Cr≥0.28%, Cu≥0.38%, Ni: 0.04~0.12%, Ti: 0.01~0.03%, P<0.020%, S<0.020%, and Cr+Cu: 0.7~1.4%, with the remainder being Fe and unavoidable impurities.

3. The high-strength corrosion-resistant steel rail according to claim 1, characterized in that, The high-strength corrosion-resistant steel rail has a tensile strength ≥1180MPa, an elongation after fracture ≥12%, a Brinell hardness of 330~390HB on the top surface of the rail, and a relative corrosion resistance ≥150% compared to U75V hot-rolled steel rail.

4. The high-strength corrosion-resistant steel rail according to claim 1, characterized in that, The microstructure of the high-strength corrosion-resistant steel rail is mainly pearlite, with a small amount of ferrite remaining.

5. A method for producing high-strength corrosion-resistant steel rails as described in any one of claims 1 to 4, characterized in that, Includes the following steps: 1) The molten steel is smelted in a converter, refined in an LF ladle furnace, and then treated with RH or VD vacuum before being cast into billets; 2) The billet is fed into the heating furnace and heated in sequence through the heating section and the soaking section. The temperature of the heating section is 850~1060℃ and the temperature of the soaking section is 1150~1220℃. 3) Rolling is carried out at an initial rolling temperature of 1050~1120℃ and a final rolling temperature of 830~880℃. 4) The rail head of the rolled rail is subjected to online accelerated cooling. The initial cooling temperature of the rail head tread is ≥700℃, the cooling rate is 0.2~1.5℃ / s, and the accelerated cooling is stopped when the rail head tread temperature drops to 560~660℃. Then, it is air-cooled to room temperature.

6. The method for producing high-strength corrosion-resistant steel rails according to claim 5, characterized in that, The total heating time of the billet in the heating furnace is 100~160min, of which the soaking time is 30~60min; the air-fuel ratio is controlled at 0.8~1.05 in the soaking time.

7. The method for producing high-strength corrosion-resistant steel rails according to claim 5, characterized in that, The total heating time of the billet in the heating furnace is 110~150min, of which the soaking time is 35~55min; the air-fuel ratio is controlled at 0.82~1.04 in the soaking time.

8. The method for producing high-strength corrosion-resistant steel rails according to claim 5, characterized in that, The temperature of the heating section is 880~1050℃, and the temperature of the heat spreader section is 1150~1210℃.

9. The method for producing high-strength corrosion-resistant steel rails according to claim 5, characterized in that, The initial rolling temperature is 1060~1100℃, and the final rolling temperature is 840~870℃.

10. The method for producing high-strength corrosion-resistant steel rails according to claim 5, characterized in that, The online accelerated cooling of the rail head tread begins at a temperature of 710~780℃, with a cooling rate of 0.4~1.4℃ / s. Accelerated cooling stops when the rail head tread temperature drops to 570~650℃.

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