Low-temperature high-toughness corrosion-resistant aluminum hot flux suitable for corrosion-resistant steel rail and welding method thereof

Abstract

This invention discloses a low-temperature, high-toughness, corrosion-resistant aluminothermic welding flux suitable for corrosion-resistant steel rails. The raw material composition, by weight percentage, is: 17.7%-18.0% aluminum powder, 61.1%-62.3% iron oxide, 10.2%-11.2% cast iron shot, 1.24%-1.81% alloy additives, and the balance being iron filings, totaling 100%. The weight percentages of each component in the alloy additives in the aluminothermic welding flux are: Si 0.3%-0.5%, Mn 0.35%-0.45%, Cu 0.26%-0.36%, Co 0.25%-0.35%, and Ni 0.08%-0.15%. This invention, through improved formulation and welding process, increases the low-temperature fracture toughness of the welded joint at -20℃ by approximately 50%, preventing brittle fracture of the rail weld joint in cold regions, while maintaining its corrosion resistance and surface hardness.

Description

Technical Field

[0001] This invention relates to the field of rail welding technology, specifically to a low-temperature, high-toughness, corrosion-resistant aluminothermic welding flux suitable for corrosion-resistant rails and its welding method. Background Technology

[0002] Aluminothermic welding is a commonly used method for welding rails. Its advantages include portable equipment, no reliance on electricity, short welding time, and no need for longitudinal upsetting, making it suitable for rail replacement operations. The aluminothermic welding flux used in rail aluminothermic welding is typically composed of aluminum powder, iron oxide, and other alloying additives, as illustrated in Chinese patents CN102029486A, CN104625480A, and CN111590192A. During on-site welding, the aluminothermic welding flux is placed in a dedicated reaction crucible and ignited with a high-temperature match to initiate the aluminothermic reaction. During the reaction, iron oxide is reduced to iron, releasing a large amount of heat to melt the alloying additives and mix with the iron to form molten steel. Due to the high density of the molten steel, it settles at the bottom of the crucible, while the less dense slag floats to the top. The high-temperature molten steel melts the self-melting plug at the bottom of the crucible, flowing out and being poured into the cavity below, formed by the ends of the rail to be welded and a sand mold. The cavity shape is consistent with the rail profile. The cast molten steel fills the cavity as a filler metal, and after cooling, the two rail sections can be welded together.

[0003] Corrosion-resistant rails are a new type of rail developed in China in recent years. By adding alloying elements such as Cu, Cr, and Nb, the corrosion resistance and strength of the rails are significantly improved. Some research has been conducted in China on the aluminothermic welding of this new type of corrosion-resistant rail. For example, Chinese patent CN113894463B describes a corrosion-resistant aluminothermic welding flux and welding method suitable for U68CuCr rails. However, further promotion and application have revealed that while adding alloys can enhance the corrosion resistance of the aluminothermic weld joint, it has a significant negative impact on its toughness, especially in low-temperature areas at high latitudes and altitudes, such as the Sichuan-Tibet Railway currently under construction. More than 70% of the route is in tunnel environments. The high humidity inside tunnels is suitable for laying corrosion-resistant rails, but due to the high altitude and low temperature, the low-temperature toughness of the aluminothermic weld joint is poor, which may lead to brittle fracture during operation, seriously endangering operational safety. Therefore, this invention develops a low-temperature, high-toughness corrosion-resistant aluminothermic welding flux and its welding method suitable for corrosion-resistant rails. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a low-temperature, high-toughness, corrosion-resistant aluminothermic welding flux and its welding method suitable for corrosion-resistant rails, addressing the shortcomings of the existing technology. This invention, through improved formulation and welding process, increases the -20℃ low-temperature fracture toughness of the welded joint by approximately 50%, preventing brittle fracture of the rail weld joint in cold regions, while maintaining its corrosion resistance and surface hardness.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0006] A low-temperature, high-toughness, corrosion-resistant aluminothermic welding flux suitable for corrosion-resistant steel rails comprises aluminum powder, iron oxide, cast iron shot, iron filings, and alloy additives, wherein the alloy additives include Si, Mn, Cu, Co, and Ni.

[0007] Furthermore, the composition of the aluminothermic welding flux, calculated by weight percentage, is as follows: aluminum powder 17.7%-18.0%, iron oxide 61.1%-62.3%, cast iron shot 10.2%-11.2%, alloy additives 1.24%-1.81%, and the balance being iron filings, totaling 100%. The weight percentage of each component in the alloy additives in the aluminothermic welding flux is as follows: Si 0.3%-0.5%, Mn 0.35%-0.45%, Cu 0.26%-0.36%, Co 0.25%-0.35%, and Ni 0.08%-0.15%.

[0008] Furthermore, the carbon content of the cast iron shot is 3%-3.5%, and the carbon content of the iron filings is ≤0.1%.

[0009] Furthermore, the composition of the aluminothermic welding flux by weight percentage is as follows: 17.8% aluminum powder, 61.8% iron oxide, 10.4% cast iron shot, 0.4% Si, 0.45% Mn, 0.31% Cu, 0.30% Co, 0.12% Ni, and the remainder is iron filings.

[0010] Furthermore, the raw materials contain aluminum powder with a particle size of 25-40 mesh, iron oxide with a particle size of 20-50 mesh, cast iron shot with a particle size of 10-30 mesh, Si with a particle size of 10-80 mesh, Mn with a particle size of 10-80 mesh, Cu with a particle size of 10-80 mesh, Co with a particle size of 10-80 mesh, and Ni with a particle size of 10-80 mesh.

[0011] The method for welding corrosion-resistant steel rails using the aluminothermic flux of the present invention includes the following steps: (a) firstly, pre-treating the area of ​​the corrosion-resistant steel rail to be welded, and then preheating it for later use; (b) igniting the aluminothermic flux for welding; (c) during the cooling process of the joint, when the joint temperature cools to 900℃-940℃, quickly dismantling the aluminothermic welding equipment and removing the weld bead; after the treatment is completed, controlling the cooling rate by covering it with asbestos cloth, keeping the cooling rate below 0.5℃ / s; cooling to 550℃ and then continuing to cool to room temperature (i.e., cooling from 900℃-940℃ to 550℃). The cooling rate in the first stage is controlled within 0.5℃ / s. Covering with asbestos cloth is a simple and easy method, but other methods can also be used to control the cooling rate in this stage. After cooling to 550℃, the asbestos cloth can be removed to release the heat preservation and continue air cooling to room temperature. After the welding head cools to room temperature, the residue is removed and the head is repaired and polished. (d) The surface of the aluminothermic welding head and rail head is pre-treated by polishing with sandpaper of 400 grit or higher. Then, the surface of the aluminothermic welding head and rail head is finished by ultrasonic finishing equipment with an output power of 200-400W and an ultrasonic frequency of 24-32KHz.

[0012] Furthermore, the pretreatment in step (a) includes grinding and smoothing, cleaning residues or impurities, and aligning the rails. The preheating temperature is 850-900℃, and the preheating time is 5-10 minutes.

[0013] Improvements and mechanisms of the main components and processes in this invention:

[0014] Aluminum powder is an important component in the aluminothermic reaction, its main function being to reduce iron oxide, combine with oxygen to form aluminum oxide, and generate a large amount of heat. Compared to CN113894463B, this invention increases the aluminum powder content to 17.7%-18.0% and decreases the aluminum powder particle size to 25-40 mesh. The aim is to increase the intensity of the aluminothermic reaction, thereby increasing the temperature of the molten steel and resulting in a weld microstructure with larger grains in subsequent processes.

[0015] Iron oxide is another important component in the aluminothermic reaction. Its main function is to provide oxygen to participate in the reaction and be reduced by aluminum to iron to form molten steel. To achieve the goal of increasing the temperature of molten steel, the iron oxide content is reduced to 61.1%-62.3% (increasing the content of both aluminum powder and iron oxide can only increase the output of molten steel, but does not significantly increase the temperature of molten steel), and the particle size is reduced to 20-50 mesh to increase the intensity of the aluminothermic reaction.

[0016] The selection of alloy additives is one of the core aspects of this invention. In response to the technical problems to be solved by this invention, the adjustments of alloy additives in CN113894463B are mainly as follows: (1) Adding Si element. Si is a strong solid solution strengthening element with strong deoxidation ability. It can effectively reduce the gas content in the welding head, avoid the formation of pores and bubbles, and improve the performance of the welding head. At the same time, Si can improve the strength of the welding head. Since it is solid solution strengthening, it has no significant effect on the grain size. (2) Eliminating Cr and Nb, two alloys with extremely strong nucleation ability, to avoid excessive grain refinement. As a substitute, Ni and Co elements are added. Ni and Fe elements can be infinitely solid dissolved, which can play a role in refining the structure and improving strength and toughness. Co element can improve the corrosion resistance of steel, and at the same time, it can delay the precipitation and aggregation of other elements, reduce nucleation ability, and control grain size. (3) Since the addition of Si, Ni and other elements improves the strength of the welding head, the content of Mn element is reduced accordingly to avoid the strength being too high and exceeding that of the base material. (4) Since the elimination of Cr element reduces the corrosion resistance of steel, the content of Cu is increased accordingly to ensure the corrosion resistance of the welding head.

[0017] Furthermore, in conjunction with the aforementioned aluminothermic welding flux, this invention also improves the welding method by reducing the temperature range for disassembling the aluminothermic welding equipment to 900℃-940℃, extending the dwell time of the welding head in the high-temperature section, and obtaining a larger austenitic structure. After the welding head is processed, a step is added to control the cooling rate by covering it with asbestos cloth, etc., to prevent excessive cooling and overly fine grains, and to avoid the formation of harmful structures such as bainite and martensite. After cooling to 550℃, the asbestos cloth can be removed to release the heat preservation and continue air cooling to room temperature before subsequent slag removal and grinding. Then, the surface of the welding head is ultrasonically processed, which is also one of the core aspects of this invention. The principle of ultrasonic finishing is to convert ordinary alternating current into ultrasonic frequency electrical oscillations with a certain power output through an ultrasonic generator to provide vibration energy. A transducer then converts the electrical oscillations into mechanical vibrations. An amplitude transformer connected to the transducer amplifies the transducer's amplitude and concentrates the ultrasonic vibration energy to the tool head. The tool head impacts the metal surface at a frequency of tens of thousands of times per second, causing the subsurface grains to break down, achieving grain refinement near the surface. Combined with the aluminothermic welding flux described in this invention, the grain size of the weld head can be controlled within a suitable range of 6-7 grain size. Overall, the surface of the weld head forms a gradient grain effect with smaller outer grains and larger inner grains. Within an appropriate gradient range, this structure can significantly improve the low-temperature toughness of the material. The purpose of the improved flux and alloy composition and process adjustments in this invention is to control the weld head microstructure to a larger, suitable grain size while ensuring strength and corrosion resistance. This, combined with ultrasonic finishing, creates a gradient grain effect with smaller outer grains and larger inner grains near the surface, thereby increasing toughness. Conversely, if the grains of the welding head itself are fine enough, the gradient crystal effect will not be obvious after ultrasonic finishing, and the effect of increasing toughness will not be ideal.

[0018] Compared with existing aluminothermic welding fluxes, the beneficial effects of this invention are reflected in the following aspects: (1) By improving the formula and welding process, the low-temperature fracture toughness of the welded joint at -20℃ is increased by about 50%, preventing brittle fracture of the welded joint of the rail in cold regions, while not affecting its surface hardness; (2) The corrosion resistance of the welded joint of the corrosion-resistant rail is effectively maintained, comparable to CN113894463B, and the corrosion resistance of the welded joint of the existing conventional aluminothermic welding flux is improved by about 37%, effectively preventing selective corrosion of the welded joint and extending the service life of the rail; (3) The welding operation method is simple and meets the requirements of on-site construction. Attached Figure Description

[0019] Figure 1 A schematic diagram of the gradient grain effect on the rail head surface and a comparison diagram of the weld head grains in Example 1;

[0020] Figure 2 This is a schematic diagram showing the sampling locations of the immersion corrosion plate in the immersion experiment;

[0021] Figure 3 Potential dynamic polarization curves of U68CuCr steel rails welded using the aluminothermic welding flux of this invention and conventional aluminothermic welding flux. Detailed Implementation

[0022] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the following detailed description is provided in conjunction with specific embodiments.

[0023] Example 1

[0024] A low-temperature, high-toughness, corrosion-resistant aluminothermic welding flux, in its dry state, comprises the following raw material formula by weight percentage: 17.8% aluminum powder, 61.8% iron oxide, 10.4% cast iron shot, 0.4% Si, 0.45% Mn, 0.31% Cu, 0.30% Co, 0.12% Ni, and 8.42% iron filings. The particle size of the aluminum powder is 25-40 mesh, the iron oxide is 20-50 mesh, the cast iron shot is 10-30 mesh, the Si is 10-80 mesh, the Mn is 10-80 mesh, the Cu is 10-80 mesh, the Co is 10-80 mesh, and the Ni is 10-80 mesh. The above raw materials are uniformly mixed according to their weight percentages at room temperature and then sealed for storage.

[0025] In addition, a standard aluminothermic flux was prepared, with the following formula by weight percentage in the dry state: 16.5% aluminum powder, 63.5% iron oxide, 10% cast iron granules, 0.2% Si, 0.8% Mn, and 9% iron filings.

[0026] Welding experiments were conducted on the same batch of U68CuCr corrosion-resistant steel rails using the two aluminothermic welding fluxes mentioned above. The specific process is as follows: The adjacent ends of the two rails to be welded were ground flat and cleaned. After the rails were aligned, a sand mold and crucible support were installed, and the same weight of the two aluminothermic welding fluxes were placed into the crucible. The adjacent ends of the two rails to be welded were preheated at a temperature of 880℃ for 8 minutes. After preheating, the aluminothermic welding flux in the crucible was immediately ignited with a high-temperature match, and an aluminothermic reaction was carried out to generate molten steel. The high-temperature molten steel melted and flowed from the molten plug into the closed cavity formed by the sand mold and the end of the rail. After casting, the temperature of the joint was measured with a temperature gun. When the joint temperature dropped to 920℃, the tools were quickly removed and the nodules were pushed out. After processing, asbestos cloth was covered to control the cooling rate to within 0.5℃ / s. After cooling to 550℃, the joints were allowed to air cool naturally. After the two welded joints cooled to room temperature naturally, the residue was removed and the joints were repaired and ground.

[0027] In addition, a corrosion-resistant aluminothermic welding flux with the composition described in Example 1 of patent CN113894463B was prepared, and a section of U68CuCr corrosion-resistant steel rail was welded according to the welding method described in Example 1 of CN113894463B.

[0028] The welding head using the aluminothermic flux described in this embodiment was selected. The surface of the aluminothermic welding head rail was cleaned with 400-grit sandpaper, and then an ultrasonic finishing device was used to finish the surface of the aluminothermic welding head rail. The output power was 350W, the ultrasonic frequency was 28kHz, and the working time was 5 minutes. Welding heads using conventional aluminothermic flux did not undergo surface finishing. After treatment, samples were taken, and EBSD analysis was performed on the grains near the surface layer. A relatively obvious gradient grain effect was observed. Figure 1 .

[0029] Reference Figure 2 As shown in the method, corrosion samples (50×25×3mm) were taken from the three weld joints mentioned above and their corrosion resistance was tested. The results are shown in Table 1. Immersion test conditions: corrosive medium was 0.01mol / L sodium bisulfite solution, temperature 45℃, humidity 70%, infrared light irradiation.

[0030] Table 1 Comparison of perimeter immersion test results for different etched sheet samples

[0031]

[0032] As can be seen from the data in Table 1, the aluminothermic welding head obtained by using the corrosion-resistant aluminothermic welding flux and welding method provided by the present invention has a corrosion resistance performance that is about 37% higher than that of conventional aluminothermic welding heads, and is similar to the corrosion resistance effect of the flux described in CN113894463B.

[0033] Electrochemical experiments were conducted on 10×10×10mm samples taken from the center region of the weld seams of two types of aluminothermic weld joints obtained by welding with the flux described in this invention and conventional flux. The working electrode was a sample sealed with epoxy resin, the counter electrode (auxiliary electrode) was a platinum electrode, the reference electrode was a saturated calomel electrode, and the electrolyte was a 2.2% NaCl solution. Steady-state polarization-potential kinetic scanning was used to measure the potentiodynamic polarization curves. The initial scanning potential was set to -300mV relative open circuit potential, the termination potential to 300mV relative open circuit potential, and the scan rate to 0.5mV / s. The experimentally measured polarization curves are shown below. Figure 3 As shown, a comparison table of electrochemical experimental results is obtained after fitting the data.

[0034] Table 2 Comparison of Electrochemical Experiment Results for Different Weld Center Regions

[0035] The aluminothermic welding flux of the present invention Conventional aluminothermic flux Corrosion potential E(V) -0.57542 -0.64589 <![CDATA[Corrosion current density i corr (A / cm 2 )]]> <![CDATA[1.2403×10 -6 ]]> <![CDATA[1.1298×10 -5 ]]>

[0036] Depend on Figure 3As shown in Table 2, the corrosion potential of the weld head obtained using the aluminothermic flux provided by this invention is higher than that of conventional aluminothermic flux weld heads, and the corrosion current density is lower than that of conventional aluminothermic flux weld heads. Therefore, the corrosion-resistant aluminothermic weld head obtained by this invention is less prone to corrosion under the same conditions, has a lower corrosion rate, and exhibits stronger corrosion resistance.

[0037] Surface hardness samples were taken from the above three weld head locations for Vickers hardness testing; fracture toughness K was measured at the above weld head locations according to GB / T21143-2014. IC The fracture toughness of the specimens was tested at -20℃, and the results are shown in Table 3.

[0038] Table 3 Comparison of experimental results for hardness and fracture toughness of different welding heads

[0039]

[0040] As can be seen from Table 3, the aluminothermic welding head obtained by using the aluminothermic flux and welding method described in this invention has high surface hardness and low-temperature fracture toughness. The surface hardness is about 3.6% higher than that of existing aluminothermic flux welding heads, and there is no significant difference from the hardness of the welding head described in CN113894463B. The low-temperature fracture toughness at -20℃ is 49% higher than that of existing conventional aluminothermic flux welding heads and 42.5% higher than that of the welding head described in CN113894463B, which greatly improves the low-temperature toughness of the material.

[0041] Example 2

[0042] A corrosion-resistant aluminothermic welding flux, in its dry state, comprises the following raw material formula by weight percentage: 17.7% aluminum powder, 61.2% iron oxide, 10.3% cast iron shot, 0.32% Si, 0.36% Mn, 0.27% Cu, 0.26% Co, 0.08% Ni, and 9.51% iron filings. The aluminum powder has a particle size of 25-40 mesh, the iron oxide 20-50 mesh, the cast iron shot 10-30 mesh, the Si 10-80 mesh, the Mn 10-80 mesh, the Cu 10-80 mesh, the Co 10-80 mesh, and the Ni 10-80 mesh. The above raw materials are uniformly mixed according to their weight percentages at room temperature and then sealed for storage.

[0043] Referring to the welding method and ultrasonic surface finishing process described in Example 1, two sections of U68CuCr corrosion-resistant steel rails were welded using the aforementioned corrosion-resistant aluminothermic flux. Additionally, a section of U68CuCr corrosion-resistant steel rail was welded using the corrosion-resistant aluminothermic flux with the composition described in Example 1 of patent CN113894463B, following the welding method described in Example 1 of CN113894463B. Comparative tests were conducted on the corrosion resistance, hardness, and low-temperature toughness of the three types of weld heads.

[0044] Reference Figure 2 The method described above involved taking corrosion samples (50×25×3mm) from three weld joints and testing their corrosion resistance. The results are shown in Table 4. Immersion test conditions: corrosive medium was 0.01mol / L sodium bisulfite solution, temperature 45℃, humidity 70%, and infrared light irradiation.

[0045] Table 4 Comparison of perimeter immersion test results for different etched sheet samples

[0046]

[0047] As can be seen from the data in Table 4, the corrosion resistance of the aluminothermic welding head obtained by using the corrosion-resistant aluminothermic flux and welding method provided by the present invention is improved by about 34.74% compared with the conventional aluminothermic flux welding head, and slightly lower than that of the welding head described in CN113894463B.

[0048] Surface hardness samples were taken from the weld head area and subjected to Vickers hardness testing; fracture toughness K was measured at the aforementioned weld head area according to GB / T21143-2014. IC The fracture toughness of the specimens was tested at -20℃, and the results are shown in Table 5.

[0049] Table 5 Comparison of experimental results for hardness and fracture toughness of different welding heads

[0050]

[0051] As can be seen from Table 5, the aluminothermic welding head obtained by using the aluminothermic flux and welding method described in this invention has good surface hardness and low-temperature fracture toughness. The surface hardness is basically consistent with that of existing aluminothermic flux welding heads, and slightly lower than that of the welding head described in CN113894463B. However, the low-temperature fracture toughness at -20℃ is 49% higher than that of existing conventional aluminothermic flux welding heads, and 41.8% higher than that of the welding head described in CN113894463B.

[0052] Example 3

[0053] A corrosion-resistant aluminothermic welding flux, in its dry state, comprises the following raw material formula by weight percentage: 17.9% aluminum powder, 62.1% iron oxide, 11.0% cast iron pellets, 0.47% Si, 0.43% Mn, 0.35% Cu, 0.33% Co, 0.14% Ni, and 7.28% iron filings. The aluminum powder has a particle size of 25-40 mesh, the iron oxide 20-50 mesh, the cast iron pellets 10-30 mesh, the Si 10-80 mesh, the Mn 10-80 mesh, the Cu 10-80 mesh, the Co 10-80 mesh, and the Ni 10-80 mesh. The above raw materials are uniformly mixed according to their weight percentages at room temperature and then sealed for storage.

[0054] Referring to the welding method and ultrasonic surface finishing process described in Example 1, two sections of U68CuCr corrosion-resistant steel rails were welded using the aforementioned corrosion-resistant aluminothermic flux. Additionally, a section of U68CuCr corrosion-resistant steel rail was welded using the corrosion-resistant aluminothermic flux with the composition described in Example 1 of patent CN113894463B, following the welding method described in Example 1 of CN113894463B. Comparative tests were conducted on the corrosion resistance, hardness, and low-temperature toughness of the three types of weld heads.

[0055] Reference Figure 2 The method described above involved taking corrosion samples (50×25×3mm) from three weld joints and testing their corrosion resistance. The results are shown in Table 4. Immersion test conditions: corrosive medium was 0.01mol / L sodium bisulfite solution, temperature 45℃, humidity 70%, and infrared light irradiation.

[0056] Table 6 Comparison of perimeter immersion test results for different etched sheet samples

[0057]

[0058] As can be seen from the data in Table 6, the corrosion resistance of the aluminothermic welding head obtained by using the corrosion-resistant aluminothermic welding flux and welding method provided by the present invention is improved by about 37.1% compared with the conventional aluminothermic welding head, and is similar to the corrosion resistance effect of the flux described in CN113894463B.

[0059] Surface hardness samples were taken from the weld head area and subjected to Vickers hardness testing; fracture toughness K was measured at the above two weld head areas in accordance with GB / T21143-2014. IC The fracture toughness of the specimens was tested at -20℃, and the results are shown in Table 7.

[0060] Table 7 Comparison of Experimental Results of Hardness and Fracture Toughness of Different Weld Heads

[0061]

[0062] As can be seen from Table 7, the aluminothermic welding head obtained by using the aluminothermic flux and welding method described in this invention has higher surface hardness and low-temperature fracture toughness. The surface hardness is about 7.5% higher than that of existing aluminothermic flux welding heads and 5% higher than that of the welding head described in CN113894463B. The low-temperature fracture toughness at -20℃ is 42% higher than that of existing conventional aluminothermic flux welding heads and 35% higher than that of the welding head described in CN113894463B.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method of welding corrosion resistant rails by low temperature high toughness corrosion resistant aluminium thermit, characterized in that, First, the areas of the corrosion-resistant steel rail to be welded are pretreated and then preheated for later use. Then, the aluminothermic welding flux is ignited for welding. During the cooling process of the joint, when the joint temperature cools to 900℃-940℃, the aluminothermic welding equipment is quickly removed and the nodules are pushed out. After the treatment is completed, the cooling rate is controlled to within 0.5℃ / s. After cooling to 550℃, it is further air-cooled to room temperature. The residue is removed and the surface is repaired and polished. Then, the surface of the aluminothermic welding head and rail head is polished with sandpaper of 400 grit or higher for pretreatment. After that, the surface of the aluminothermic welding head and rail head is finished with ultrasonic finishing equipment. The process parameters of ultrasonic finishing are: output power 200-400W, ultrasonic frequency 24-32KHz. Finally, the rail head surface forms a gradient crystal effect with smaller outer and larger inner crystals. The low-temperature, high-toughness, corrosion-resistant aluminothermic welding flux is composed of the following raw materials by weight percentage: aluminum powder 17.7%-18.0%, iron oxide 61.1%-62.3%, cast iron shot 10.2%-11.2%, alloy additives 1.24%-1.81%, and the balance being iron filings, totaling 100%. The weight percentages of each component in the alloy additives in the aluminothermic welding flux are: Si 0.3%-0.5%, Mn 0.35%-0.45%, Cu 0.26%-0.36%, Co 0.25%-0.35%, and Ni 0.08%-0.15%. The aluminum powder has a particle size of 25-40 mesh.

2. The method for welding corrosion-resistant steel rails with low-temperature, high-toughness, and corrosion-resistant aluminothermic flux according to claim 1, characterized in that, The low-temperature, high-toughness, corrosion-resistant aluminothermic welding flux is composed of the following raw materials by weight percentage: 17.7%-17.9% aluminum powder, 61.2%-62.1% iron oxide, 10.3%-11.0% cast iron shot, 1.29%-1.72% alloy additives, and 7.28%-9.51% iron filings, totaling 100%.

3. The method for welding corrosion-resistant steel rails with low-temperature, high-toughness, and corrosion-resistant aluminothermic flux according to claim 1, characterized in that, The composition of the aluminothermic welding flux by weight percentage is as follows: 17.8% aluminum powder, 61.8% iron oxide, 10.4% cast iron shot, 0.4% Si, 0.45% Mn, 0.31% Cu, 0.30% Co, 0.12% Ni, and the remainder is iron filings.

4. The method for welding corrosion-resistant steel rails with low-temperature, high-toughness, and corrosion-resistant aluminothermic flux according to claim 1, characterized in that, The cast iron shot has a carbon content of 3%-3.5%, and the iron filings have a carbon content of ≤0.1%; the iron oxide has a particle size of 20-50 mesh, and the cast iron shot has a particle size of 10-30 mesh; the alloy additives are powders, with Si powder having a particle size of 10-80 mesh, Mn powder having a particle size of 10-80 mesh, Cu powder having a particle size of 10-80 mesh, Co powder having a particle size of 10-80 mesh, and Ni powder having a particle size of 10-80 mesh.

5. The method for welding corrosion-resistant steel rails with low-temperature, high-toughness, and corrosion-resistant aluminothermic flux according to claim 1, characterized in that, The pretreatment includes grinding and smoothing, cleaning residues or impurities, and alignment with the track. The preheating temperature is 850-900℃ and the preheating time is 5-10 minutes.

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