Preparation method of high-strength wear-resistant heavy-load railway rare earth steel rail

Abstract

This invention discloses a method for preparing high-strength, wear-resistant, heavy-duty railway rare-earth steel rails, comprising the following steps: hot metal pretreatment; converter smelting; LF furnace refining; VD vacuum degassing; continuous casting; rolling process; and heat treatment process. A gradient cooling heat treatment process is adopted, in which the rolled steel rail is fed into the heat treatment device at an incoming temperature of 750°C, first cooled to 610°C, and then further cooled to 538°C. By precisely controlling the cooling rate of each module, the formation of network cementite and martensite structures in the steel rail is avoided, and the final exit temperature of the steel rail is controlled at 500°C. This invention solves the problems of insufficient strength and poor wear resistance of existing heavy-duty steel rails through reasonable composition design and process optimization.

Description

Technical Field

[0001] This invention belongs to the field of railway rail technology, and particularly relates to a method for preparing high-strength, wear-resistant, heavy-duty rare earth steel rails for railways. Background Technology

[0002] With the increase in axle load and freight volume on heavy-haul railways, higher requirements are placed on the strength, wear resistance, and toughness of steel rails. Currently, the service life of rails on small-radius curves on heavy-haul lines such as the Datong-Qinhuangdao Railway is relatively short, and the highest tensile strength of existing pearlitic steel rails is only 1280 MPa, which is insufficient to meet the demands of heavy-haul transportation. Rare earth elements have the functions of purifying molten steel, refining grains, and improving wear resistance, and are a specialty resource of Baotou Steel. Developing high-strength wear-resistant steel rails based on rare earth microalloying is of great significance for extending the service life of rails and reducing the frequency of rail replacement.

[0003] Patent CN104480390A discloses a high-impact toughness rail and its production method, belonging to the field of rail material production technology. The technical problem solved by this invention is to provide a high-impact toughness rail. The high-impact toughness rail of this invention is a pearlitic rail with a lamellar spacing of 0.05–0.09 μm and an impact energy of 30–35 J at room temperature. The chemical composition of the rail is: C: 0.71–0.82%, Si: 0.25–0.45%, Mn: 0.75–1.05%, V: 0.03–0.15%, P: ≤0.030%, S: ≤0.035%, Al: ≤0.020%, with the balance being Fe and unavoidable impurities. The rail head U-shaped impact toughness manufactured using the method of this invention can reach over 30 J, and the tensile strength is greater than 1300 MPa. The rail has a good strength-toughness ratio, good rolling contact fatigue performance and wear resistance during use, and is suitable for railway rails in cold regions.

[0004] Patent CN107475616A discloses a high-strength and high-toughness pearlitic steel rail and its manufacturing method. Addressing the problem of uneven rail head cross-sectional properties and poor performance in existing pearlitic steel rail manufacturing techniques, this invention provides a manufacturing method for high-strength and high-toughness pearlitic steel rails, comprising the following steps: a) hot-rolling a steel billet into a rail at a final rolling temperature of 900–1000℃; b) utilizing the residual heat from final rolling, when the center temperature of the rail top surface is air-cooled to 800℃, spraying a cooling medium onto the top surface and both sides of the rail head, cooling to a center temperature of 750℃; c) spraying a cooling medium onto the top surface, both sides of the rail head, and both lower jaws of the rail head, cooling to a surface temperature ≤450℃, and then air-cooling to room temperature. This invention, by controlling the steel composition and employing a two-stage accelerated cooling method, produces steel with superior performance. The method is simple to operate, requires minimal equipment, and is suitable for widespread application.

[0005] Patent CN107675084A discloses a high-carbon, high-strength, and high-toughness pearlitic steel rail and its manufacturing method. Addressing the problem of uneven rail head cross-sectional properties and poor rail performance in existing technologies, this invention provides a manufacturing method for a high-carbon, high-strength, and high-toughness pearlitic steel rail, comprising the following steps: a) hot-rolling a steel billet into a rail at a final rolling temperature of 900–1000℃; b) when the center temperature of the rail top surface is air-cooled to 800–850℃, spraying a cooling medium onto the top surface, both sides of the rail head, and the lower jaws on both sides of the rail head, cooling to a center temperature of 480–530℃, and then air-cooling to room temperature. This invention, by controlling the steel composition and employing a two-stage accelerated cooling method, produces a high-carbon steel rail with higher strength and excellent toughness, suitable for heavy-haul railway applications. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing high-strength, wear-resistant, heavy-duty railway rare earth steel rails. Through reasonable composition design and process optimization, this method solves the problems of insufficient strength and poor wear resistance of existing heavy-duty steel rails.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for preparing high-strength, wear-resistant, heavy-duty rare-earth steel rails for railways, comprising the following steps:

[0009] Hot metal pretreatment: blast furnace hot metal with a temperature of 1300-1350℃ is selected, and its sulfur content is controlled at ≤0.030%. Pretreatment is carried out by injecting magnesium lime composite deoxidizer into the ladle to effectively reduce the sulfur content in the hot metal, provide high-quality raw materials for subsequent smelting, and ensure the purity of rail steel.

[0010] Converter smelting: 145-155t of pretreated molten iron and 14-16t of scrap steel are added to the converter. After smelting, the carbon content at tapping is controlled at 0.15-0.17%, and the tapping temperature is precisely controlled at 1600-1620℃. During the tapping process, quicklime and silicon-calcium-barium deoxidizer are added simultaneously to achieve preliminary deoxidation of the molten steel. At the same time, the slag is modified to ensure that the oxygen content and impurities in the molten steel are effectively controlled. The process parameters are strictly controlled throughout the smelting process to ensure the basic quality of the molten steel.

[0011] LF furnace refining: The molten steel after converter smelting is sent to the LF furnace for refining. During this process, 365-375 kg of high-carbon ferromanganese, 100-110 kg of high-carbon ferrochrome, and 38-42 kg of ferroniobium alloy are added to precisely adjust the chemical composition of the molten steel to meet the design requirements. During the refining process, the slag basicity is controlled at 2.0-2.2. The molten steel is heated to 1600±10℃ (preferably 1600℃) for 21 minutes using a heating device to further remove gases and inclusions from the molten steel, improve the uniformity and purity of the molten steel, and provide molten steel with stable composition for subsequent processes.

[0012] VD Vacuum Degassing: The refined molten steel enters the VD vacuum degassing device for deep vacuum degassing treatment. The deep vacuum is maintained for 15-20 minutes, followed by 12-16 minutes of soft blowing treatment. During the soft blowing process, the argon flow rate is kept stable to ensure that the molten steel moves smoothly without any exposed areas. After vacuum degassing, 15 kg of cerium-iron alloy is added to the molten steel to fully utilize the role of rare earth elements in purifying the molten steel and optimizing the morphology of inclusions. Finally, the VD descaling temperature is controlled at 1500-1560℃, which significantly reduces the gas content of the molten steel and further improves its purity.

[0013] Continuous casting process: A protective casting process is adopted, using low-alumina protective slag and alkaline covering agent to maintain the liquid level in the tundish above 700mm to avoid secondary oxidation of the molten steel; the billet size is designed to be 280mm×380mm, the casting speed is controlled at 0.61-0.63m / min during continuous casting, the superheat of the molten steel is maintained at 28-32℃, and electromagnetic stirring and light reduction technology of the casting machine are used to effectively reduce the center segregation and porosity defects of the billet, ensuring that the billet has a dense structure and uniform composition. After slow cooling for 48 hours, the billet is sent to the rail beam plant for subsequent processing.

[0014] Rolling process: The slowly cooled billet is fed into a heating furnace for heating for a total duration of 4-6 hours. The temperature in the soaking zone is set at 1200-1260℃ to ensure uniform heating of the billet and suppress carbon segregation. After heating, the billet is rolled, with strict control over the rolling rhythm and reduction. The final rolling temperature is 940-950℃, resulting in a good rolling microstructure for the rail and laying the foundation for subsequent heat treatment processes and performance improvement.

[0015] The heat treatment process adopts a gradient cooling heat treatment process. The rolled rail is fed into the heat treatment device at an incoming temperature of 750±10℃. It is first cooled at a temperature of 610±10℃ at a cooling rate of 4.5-5.5℃ / s, and then cooled again at a temperature of 538±10℃ at a cooling rate of 2.5-3.5℃ / s. Finally, the exit temperature of the rail is controlled at 500℃. (Preferredly, the heat treatment process adopts a gradient cooling heat treatment process. The rolled rail is fed into the heat treatment device at an incoming temperature of 750℃. It is first cooled at a temperature of 610℃ at a cooling rate of 5℃ / s, and then cooled again at a temperature of 538℃ at a cooling rate of 3℃ / s. Finally, the exit temperature of the rail is controlled at 500℃.)

[0016] Furthermore, the cerium-iron alloy has a Ce content of 10%.

[0017] Furthermore, after heat treatment, the rail microstructure becomes homogenized into pearlite with trace amounts of ferrite.

[0018] Furthermore, in the converter smelting process: 149.7t of pretreated molten iron and 15t of scrap steel are added to the converter. After smelting, the carbon content is controlled to be 0.16% when tapping the steel, and the tapping temperature is precisely controlled at 1610℃.

[0019] Furthermore, the LF furnace refining process involves sending the molten steel from the converter into the LF furnace for refining, during which 371 kg of high-carbon ferromanganese, 105 kg of high-carbon ferrochrome, and 40 kg of ferroniobium alloy are added to precisely adjust the chemical composition of the molten steel.

[0020] Furthermore, the VD vacuum degassing process involves a deep vacuum holding time of 18 minutes, followed by a soft blowing treatment for 14 minutes.

[0021] Furthermore, the casting speed was controlled at 0.62 m / min during the continuous casting process, and the superheat of the molten steel was maintained at 30°C.

[0022] Furthermore, the total heating time is controlled to be 5 hours, with the temperature of the soaking zone set at 1200~1260℃; finally, the rolling is completed at a final rolling temperature of 945℃.

[0023] Furthermore, the composition of the rail by mass percentage is as follows: C 0.92%-0.95%, Si 0.52%-0.60%, Mn 0.91%-0.95%, P ≤0.009%, S≤0.004%, Cr 0.16%-0.20%, Nb 0.017%-0.019%, Ni 0.15%-0.19%, Ce 0.001%-0.002%, with the remainder being Fe and impurities.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0025] The rail of this invention is based on C-Mn, with added Cr, Nb, Ni, and RE elements. Cr improves the hardness and wear resistance of the steel, Nb refines the grains and reduces overheating sensitivity, Ni improves toughness, and rare earth Ce purifies the molten steel and optimizes inclusion morphology. The manufacturing process employs hot metal pretreatment, converter smelting, LF refining, VD vacuum degassing, continuous casting, and precision heat treatment to ensure uniform chemical composition, dense microstructure, and compliance with performance standards. The rail of this invention has a tensile strength of 1371~1410MPa, a tread hardness of 392~411HB, and an elongation of 9~10%. Its wear resistance is superior to existing U78CrV rails, making it suitable for heavy-haul railway lines, and especially extending the service life of rails on small-radius curves.

[0026] Example (The composition of the rail by mass percentage is: C 0.94%, Si 0.56%, Mn 0.93%, P 0.009%, S 0.004%, Cr 0.179%, Nb 0.0167%, Ni 0.175%, Ce 0.0014%, with the remainder being Fe and impurities) The performance test results of the finished rail, after professional testing, show that the tensile strength reaches 1393MPa, the elongation is 11%, the average tread hardness is 395.6HB, and the fracture toughness is 29.3MPa·m¹ / ². All performance indicators meet the requirements of TB / T2344-2012 standard and are fully suitable for the stringent use requirements of heavy-haul railways, possessing excellent strength, wear resistance, and toughness. Detailed Implementation

[0027] A high-strength, wear-resistant, heavy-duty railway rare earth steel rail and its preparation method:

[0028] The rail of this invention is based on C-Mn, with added Cr, Nb, Ni, and RE elements. Cr improves the hardness and wear resistance of the steel, Nb refines the grain size and reduces overheating sensitivity, Ni improves toughness, and rare earth Ce purifies the molten steel and optimizes inclusion morphology. The manufacturing process employs hot metal pretreatment, converter smelting, LF refining, VD vacuum degassing, continuous casting, and precision heat treatment to ensure uniform chemical composition, dense microstructure, and compliance with performance standards. The rail of this invention has a tensile strength of 1371~1410MPa, a tread hardness of 392~411HB, and an elongation of 9~12%. Its wear resistance is superior to existing U78CrV rails, making it suitable for heavy-haul railway lines, and especially extending the service life of rails on small-radius curves.

[0029] Preparation process:

[0030] Hot metal pretreatment: blast furnace hot metal with a temperature of 1314℃ is selected, and its sulfur content is controlled at 0.021%. Pretreatment is carried out by injecting magnesium lime composite deoxidizer into the ladle, which effectively reduces the sulfur content in the hot metal, provides high-quality raw materials for subsequent smelting, and ensures the purity of rail steel.

[0031] Converter smelting: 149.7 tons of pretreated molten iron and 15 tons of scrap steel are added to the converter. After smelting, the carbon content at tapping is controlled to be 0.16%, and the tapping temperature is precisely controlled at 1610℃. During tapping, deoxidizers such as quicklime, silicon-calcium-barium oxide, etc., are added simultaneously to achieve preliminary deoxidation of the molten steel. At the same time, the slag is modified to ensure that the oxygen content and impurities in the molten steel are effectively controlled. The process parameters are strictly controlled throughout the smelting process to ensure the basic quality of the molten steel.

[0032] LF Furnace Refining: The molten steel after converter smelting is fed into the LF furnace for refining. During this process, 371 kg of high-carbon ferromanganese, 105 kg of high-carbon ferrochrome, and 40 kg of ferroniobium are added to precisely adjust the chemical composition of the molten steel to meet design requirements. The slag basicity is controlled at 2.1 during refining. The molten steel is heated for 21 minutes using a heating device to further remove gases and inclusions, improving the uniformity and purity of the molten steel and providing a stable composition for subsequent processes.

[0033] VD Vacuum Degassing: The refined molten steel enters the VD vacuum degassing unit for deep vacuum degassing treatment, which is maintained for 18 minutes, followed by 14 minutes of soft blowing. During soft blowing, the argon gas flow rate is kept stable to ensure smooth creeping of the molten steel without any exposed inclusions. After vacuum degassing, 15 kg of ferrocerium alloy (10% Ce content) is added to the molten steel to fully utilize the role of rare earth elements in purifying the molten steel and optimizing the morphology of inclusions. Ultimately, the VD degassing temperature is controlled at 1503℃, which significantly reduces the gas content of the molten steel and further improves its purity.

[0034] Continuous casting process: A protective casting process is adopted, using low-alumina protective slag and alkaline covering agent to maintain the tundish liquid level above 700mm to avoid secondary oxidation of the molten steel. The billet size is designed to be 280mm×380mm. During continuous casting, the casting speed is controlled at 0.62m / min, and the superheat of the molten steel is maintained at 30℃. At the same time, electromagnetic stirring and light reduction technology of the casting machine are used to effectively reduce defects such as center segregation and porosity of the billet, ensuring that the billet has a dense structure and uniform composition. After slow cooling for 48 hours, the billet is sent to the rail beam plant for subsequent processing.

[0035] Rolling process: The slowly cooled billet is fed into a heating furnace for heating for a total duration of 5 hours. The temperature in the soaking zone is set at 1200~1260℃ to ensure uniform heating of the billet and suppress carbon segregation. After heating, the billet is rolled, with strict control over the rolling rhythm and reduction. The final rolling temperature is 945℃, resulting in a good rolled structure for the rail and laying the foundation for subsequent heat treatment processes and performance improvement.

[0036] The heat treatment process employs a gradient cooling process. The rolled rails are fed into the heat treatment unit at an incoming temperature of 750℃. They are first cooled to 610℃ at a cooling rate of 5℃ / s, then further cooled to 538℃ at a cooling rate of 3℃ / s, finally exiting at 500℃. After this heat treatment process, the rail microstructure becomes homogenized, consisting of pearlite with trace amounts of ferrite, effectively improving the rail's strength and toughness.

[0037] The composition of the rails is determined by mass percentage: C 0.94%, Si 0.56%, Mn 0.93%, P 0.009%, S 0.004%, Cr 0.179%, Nb 0.0167%, Ni 0.175%, Ce 0.0014%, with the remainder being Fe and impurities.

[0038] The performance test results show that the finished rails have a tensile strength of 1393MPa, an elongation of 11%, an average tread hardness of 395.6HB, and a fracture toughness of 29.3MPa·m¹ / ². All performance indicators meet the requirements of the TB / T2344-2012 standard and are fully adapted to the stringent requirements of heavy-haul railways, possessing excellent strength, wear resistance, and toughness.

[0039] Performance of prototype rails

[0040]

[0041] Metallographic inclusion rating of rails

[0042]

[0043] The test results show that the level of inclusions in the steel meets the requirements of TB / T 2344.

[0044] According to the relevant methods of TB / T 2344 standard, samples were taken from the test rail to test the fracture toughness of the rail. The test used a three-point bending specimen with a thickness B=25mm and a width W=40mm. The test temperature was -20℃. The test results are shown in the table below.

[0045] Rail fracture toughness test results

[0046]

[0047] For the Kq values ​​in the table, according to K IC Criterion for determining whether K is valid IC :

[0048] 1) Criterion B ≥ 2.5 (K) Q / σy) 2 All 5 samples met the requirements.

[0049] 2) Regarding Pmax / P Q Five out of five samples had Pmax / P Q <1.10, therefore K Q = K IC .

[0050] The test results show that the fracture toughness K IC The minimum value is 26.9 MPa·m. 1 / 2 The average value is 29.3 MPa·m 1 / 2 The single minimum value specified in TB / T 2344 is greater than 26 MPa·m. 1 / 2 The average value is greater than 29 MPa·m 1 / 2 Requirements.

[0051] 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 method for preparing high-strength, wear-resistant, heavy-duty railway rare-earth steel rails, characterized in that: Includes the following steps: Hot metal pretreatment: blast furnace hot metal with a temperature of 1300-1350℃ is selected, and its sulfur content is controlled at ≤0.030%. Pretreatment is carried out by injecting magnesium lime composite deoxidizer into the ladle to effectively reduce the sulfur content in the hot metal, provide high-quality raw materials for subsequent smelting, and ensure the purity of rail steel. Converter smelting: 145-155t of pretreated molten iron and 14-16t of scrap steel are added to the converter. After smelting, the carbon content at tapping is controlled at 0.15-0.17%, and the tapping temperature is precisely controlled at 1600-1620℃. During the tapping process, quicklime and silicon-calcium-barium deoxidizer are added simultaneously to achieve preliminary deoxidation of the molten steel. At the same time, the slag is modified to ensure that the oxygen content and impurities in the molten steel are effectively controlled. The process parameters are strictly controlled throughout the smelting process to ensure the basic quality of the molten steel. LF furnace refining: The molten steel after converter smelting is sent to the LF furnace for refining. During this process, 365-375 kg of high-carbon ferromanganese, 100-110 kg of high-carbon ferrochrome, and 38-42 kg of ferroniobium alloy are added to precisely adjust the chemical composition of the molten steel to meet the design requirements. During the refining process, the slag basicity is controlled at 2.0-2.

2. The molten steel is heated to 1600±10℃ for 21 minutes using a heating device to further remove gases and inclusions from the molten steel, improve the uniformity and purity of the molten steel, and provide molten steel with stable composition for subsequent processes. VD Vacuum Degassing: The refined molten steel enters the VD vacuum degassing device for deep vacuum degassing treatment. The deep vacuum is maintained for 15-20 minutes, followed by 12-16 minutes of soft blowing treatment. During the soft blowing process, the argon flow rate is kept stable to ensure that the molten steel moves smoothly without any exposed areas. After vacuum degassing, 15 kg of cerium-iron alloy is added to the molten steel to fully utilize the role of rare earth elements in purifying the molten steel and optimizing the morphology of inclusions. Finally, the VD descaling temperature is controlled at 1500-1560℃, which significantly reduces the gas content of the molten steel and further improves its purity. Continuous casting process: A protective casting process is adopted, using low-alumina protective slag and alkaline covering agent to maintain the liquid level in the tundish above 700mm to avoid secondary oxidation of the molten steel; the billet size is designed to be 280mm×380mm, the casting speed is controlled at 0.61-0.63m / min during continuous casting, the superheat of the molten steel is maintained at 28-32℃, and electromagnetic stirring and light reduction technology of the casting machine are used to effectively reduce the center segregation and porosity defects of the billet, ensuring that the billet has a dense structure and uniform composition. After slow cooling for 48 hours, the billet is sent to the rail beam plant for subsequent processing. Rolling process: The slowly cooled billet is fed into a heating furnace for heating for a total duration of 4-6 hours. The temperature in the soaking zone is set at 1200-1260℃ to ensure uniform heating of the billet and suppress carbon segregation. After heating, the billet is rolled, with strict control over the rolling rhythm and reduction. The final rolling temperature is 940-950℃, resulting in a good rolling microstructure for the rail and laying the foundation for subsequent heat treatment processes and performance improvement. The heat treatment process adopts a gradient cooling heat treatment process. The rolled rail is fed into the heat treatment device at an incoming temperature of 750±10℃. It is first cooled at a temperature of 610±10℃ with a cooling rate of 4.5-5.5℃ / s, and then cooled at a temperature of 538±10℃ with a cooling rate of 2.5-3.5℃ / s. Finally, the exit temperature of the rail is controlled at 500℃. The composition of the rail by mass percentage is as follows: C 0.92%-0.95%, Si 0.52%-0.60%, Mn 0.91%-0.95%, P ≤0.009%, S≤0.004%, Cr 0.16%-0.20%, Nb 0.017%-0.019%, Ni 0.15%-0.19%, Ce 0.001%-0.002%, with the remainder being Fe and impurities.

2. The method for preparing high-strength, wear-resistant, heavy-duty rare-earth steel rails for railways according to claim 1, characterized in that: The cerium-iron alloy has a Ce content of 10%.

3. The method for preparing high-strength, wear-resistant, heavy-duty rare-earth steel rails for railways according to claim 1, characterized in that: After heat treatment, the rail microstructure becomes homogenized into pearlite with trace amounts of ferrite.

4. The method for preparing high-strength, wear-resistant, heavy-duty rare-earth steel rails for railways according to claim 1, characterized in that: The converter smelting process involves adding 149.7 tons of pretreated molten iron and 15 tons of scrap steel to the converter. After smelting, the carbon content at the tapping point is controlled to be 0.16%, and the tapping temperature is precisely controlled at 1610℃.

5. The method for preparing high-strength, wear-resistant, heavy-duty railway rare earth steel rails according to claim 1, characterized in that: The LF furnace refining process involves sending the molten steel from the converter to the LF furnace for refining. During this process, 371 kg of high-carbon ferromanganese, 105 kg of high-carbon ferrochrome, and 40 kg of ferroniobium alloy are added to precisely adjust the chemical composition of the molten steel.

6. The method for preparing high-strength, wear-resistant, heavy-duty rare-earth steel rails for railways according to claim 1, characterized in that: The VD vacuum degassing process involves maintaining a deep vacuum for 18 minutes, followed by a 14-minute soft blowing process.

7. The method for preparing high-strength, wear-resistant, heavy-duty railway rare earth steel rails according to claim 1, characterized in that: During continuous casting, the casting speed is controlled at 0.62 m / min, and the superheat of the molten steel is maintained at 30°C.

8. The method for preparing high-strength, wear-resistant, heavy-duty railway rare earth steel rails according to claim 1, characterized in that: The total heating time is controlled at 5 hours, with the temperature of the soaking zone set at 1200~1260℃; the final rolling is completed at a final rolling temperature of 945℃.

Images