A method for producing a high-toughness hypereutectoid rail

Abstract

The application discloses a kind of high tough hypereutectoid rail preparation methods, comprising the following steps: (1) smelting casting;(2) heating and keeping warm;(3) control rolling process;(4) supercooling deformation;The mass percentage of the chemical composition of the hypereutectoid steel includes: C: 0.85%~1.10%, Si: 0.20%~0.45%, Mn: 0.60%~0.90%, V: 0.08%~0.15%, Cr: 0.30%~0.50%, P≤0.020%, S≤0.015%, the balance is Fe and inevitable impurities.The purpose of the present application is to provide a kind of high tough hypereutectoid rail preparation method, by component optimization and process innovation, realize no net cementite organization, ultrafine grain structure, while simplifying production process, reduce energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and in particular relates to a method for preparing high-strength and high-toughness hypereutectoid steel rails. Background Technology

[0002] Hypereutectoid steel, with a carbon content exceeding 0.77%, possesses high hardness and wear resistance, making it widely in demand for heavy-haul railway rails, cutting tools, and wear-resistant components. However, traditional hypereutectoid steels tend to form a network of cementite at room temperature, resulting in poor plasticity and toughness, and high brittleness, severely impacting their service safety and lifespan. Furthermore, existing manufacturing processes are often complex, requiring large strain deformation or prolonged heat treatment, leading to high energy consumption, low production efficiency, and difficulty in achieving a balanced strength and toughness. In the heavy-haul railway sector, traditional hypereutectoid steel rails can only withstand a single train's load of 80 tons, and suffer from severe wear, frequent replacements, and high maintenance costs. Meanwhile, foreign hypereutectoid steel rail technology has long monopolized the market, and domestic products lag behind in performance, failing to meet the stringent service requirements of heavy-haul railways with an annual transport capacity exceeding 500 million tons. Therefore, developing a simple, high-strength, and wear-resistant hypereutectoid steel and its manufacturing method is crucial for breaking the foreign technological monopoly and promoting the upgrading of domestic heavy-haul equipment. Summary of the Invention

[0003] To address the technical problems of insufficient toughness, complex preparation process, imbalance between strength and toughness, and need to improve wear resistance caused by the network cementite in existing hypereutectoid steels, the purpose of this invention is to provide a method for preparing high-strength and high-toughness hypereutectoid rails. Through composition optimization and process innovation, a network-free cementite structure and an ultra-fine grain structure are achieved, while simplifying the production process and reducing energy consumption.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for preparing high-strength and high-toughness hypereutectoid rails, comprising the following steps:

[0006] (1) Smelting and casting: The converter smelting + RH refining process is adopted to control the cleanliness of the molten steel. The P and S contents are ≤0.020% and 0.015% respectively, and the casting billet is obtained by casting.

[0007] (2) Heating and holding: Heat the billet to 1050℃~1150℃ and hold for 60~120min to allow vanadium to be fully dissolved and the original cementite to be dissolved;

[0008] (3) Controlled rolling process: rough rolling is first carried out at 1000℃~1050℃, and then finish rolling is carried out at 850℃~900℃, with a cumulative reduction rate ≥80% and the final rolling speed controlled at 5~8m / s;

[0009] (4) Overcooling deformation: After precision rolling, cool to 620℃~680℃ at a cooling rate of 30~60℃ / s, and plastic deformation of 1.6~2.0 at a strain rate of 0.01~0.1s⁻¹ within this temperature range; (5) Isothermal treatment: After deformation, isothermal hold at 580℃~630℃ for 20~40min, and then cool to room temperature at a cooling rate of 50~100℃ / s;

[0010] The chemical composition of the hypereutectoid steel by mass percentage includes: C: 0.85%~1.10%, Si: 0.20%~0.45%, Mn: 0.60%~0.90%, V: 0.08%~0.15%, Cr: 0.30%~0.50%, P≤0.020%, S≤0.015%, with the balance being Fe and unavoidable impurities.

[0011] Furthermore, the room temperature microstructure of the hypereutectoid steel is ultrafine pearlite + dispersed vanadium carbides, wherein the ferrite grain size is ≤0.8μm, the cementite grain size is ≤0.4μm, and no network cementite precipitation occurs.

[0012] Furthermore, the hypereutectoid steel has a tensile strength ≥1300MPa, a reduction of area ≥42%, and wear resistance that is more than 25% higher than that of traditional eutectoid steel.

[0013] Furthermore, the center segregation level of the billet described in step (1) is ≤1.5, and there are no shrinkage cavities or porosity defects inside.

[0014] Furthermore, in step (3), the roughing passes are 3 to 5, with a single pass reduction rate of 15% to 25%; the finishing passes are 6 to 8, with a single pass reduction rate of 8% to 15%.

[0015] Furthermore, the cooling rate in step (4) is precisely controlled by an online cooling control device to ensure that the austenite is supercooled to the A1~Arcm temperature range for deformation.

[0016] Furthermore, the chemical composition of the hypereutectoid steel by mass percentage includes: C: 0.92%, Si: 0.31%, Mn: 0.75%, V: 0.11%, Cr: 0.38%, P: 0.016%, S: 0.012%, with the balance being Fe and unavoidable impurities.

[0017] Furthermore, the chemical composition of the hypereutectoid steel by mass percentage includes: C: 1.05%, Si: 0.42%, Mn: 0.85%, V: 0.14%, Cr: 0.46%, P: 0.018%, S: 0.010%, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the hypereutectoid steel by mass percentage includes: C: 0.88%, Si: 0.25%, Mn: 0.68%, V: 0.09%, Cr: 0.33%, P: 0.015%, S: 0.013%, with the balance being Fe and unavoidable impurities.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] The hypereutectoid steel, at room temperature, has a microstructure of ultrafine pearlite and dispersed vanadium carbides, with ferrite grain size ≤0.8μm and cementite grain size ≤0.4μm, and no network cementite precipitation. Composition optimization design: Vanadium is innovatively added to the hypereutectoid steel, utilizing the vanadium carbides formed by vanadium and carbon to produce a dispersion strengthening effect. Simultaneously, chromium is used to refine the grains and improve hardenability. The carbon content is strictly controlled within the range of 0.85%~0.95% to ensure wear resistance while avoiding the precipitation of network cementite caused by excessive carbon.

[0021] 1. Excellent microstructure and properties: Through composition optimization and process control, the network cementite is completely eliminated, forming a composite microstructure of ultrafine pearlite and dispersed vanadium carbides. Both ferrite and cementite grains reach submicron levels, achieving a balanced match between strength and toughness. Tensile strength ≥1300MPa and reduction of area ≥42%. 2. Outstanding wear resistance: The synergistic effect of dispersed strengthening by vanadium carbides and the ultrafine microstructure improves the wear resistance of the material by more than 25% compared to traditional eutectoid steel, meeting the requirements of harsh wear conditions such as heavy-haul railways and extending service life by more than 30%. 3. Highly efficient and energy-saving process: The preparation process does not require prolonged spheroidizing annealing; the target microstructure can be obtained through supercooling deformation and short-time isothermal treatment. The production cycle is shortened by more than 40%, energy consumption is reduced by more than 30%, and it is easy to promote industrialization. 4. Wide range of applications: It can be used to manufacture heavy-duty railway rails, wear-resistant parts for engineering machinery, high-end cutting tools and other products. It is especially suitable for heavy-duty railway lines with a single train load of more than 100 tons, which can significantly reduce the frequency of rail replacement and reduce maintenance costs. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the grain size in Example 1;

[0024] Figure 2 This is a schematic diagram of the grain size in Example 2;

[0025] Figure 3 This is a schematic diagram of the grain size in Example 3. Detailed Implementation

[0026] Example 1

[0027] The high-strength and high-toughness hypereutectoid steel of this embodiment has the following chemical composition by mass fraction: C: 0.92%, Si: 0.31%, Mn: 0.75%, V: 0.11%, Cr: 0.38%, P: 0.016%, S: 0.012%, with the balance being Fe and unavoidable impurities.

[0028] Its preparation method includes the following steps:

[0029] Smelting and casting: The converter smelting + RH refining process is adopted, and the P content of the molten steel is controlled at 0.016% and the S content at 0.012%. The casting yields a 280mm×380mm billet with a center segregation grade of 1.2.

[0030] Heating and holding: The billet is sent into the heating furnace and heated to 1100℃, and held for 90 minutes;

[0031] Controlled rolling process: Four roughing passes are performed at 1020℃, with a single pass reduction rate of 18%~22% and a cumulative reduction rate of 82%; followed by seven finishing passes at 880℃, with a single pass reduction rate of 10%~14% and a final rolling speed of 6.5m / s.

[0032] Supercooling deformation: After precision rolling, the temperature is cooled to 650°C at a cooling rate of 45°C / s using an online controlled cooling device, and then deformed to a strain of 1.8 at a strain rate of 0.05s-¹.

[0033] Isothermal treatment: After deformation, the steel was held isothermally at 600℃ for 30 min, followed by cooling to room temperature at a rate of 80℃ / s. Testing revealed that the hypereutectoid steel prepared in this embodiment had a room temperature microstructure of ultrafine pearlite + dispersed vanadium carbides, with a ferrite grain size of 0.65 μm. Figure 1 The cementite particle size is 0.32μm, with no network cementite; the tensile strength is 1350MPa, the reduction of area is 45%, and the wear resistance is 28% higher than that of traditional eutectoid steel.

[0034] Example 2

[0035] The high-strength and high-toughness hypereutectoid steel of this embodiment has the following chemical composition by mass fraction: C: 1.05%, Si: 0.42%, Mn: 0.85%, V: 0.14%, Cr: 0.46%, P: 0.018%, S: 0.010%, with the balance being Fe and unavoidable impurities. Its preparation method includes the following steps: (1) Smelting and casting: using converter smelting + RH refining process, controlling the P content of molten steel to be 0.018% and the S content to be 0.010%, casting to obtain a 280mm×380mm billet, with a center segregation grade of 1.3 for the billet; (2) Heating and holding: sending the billet into a heating furnace, heating to 1130℃, and holding for 100min;

[0036] (2) Controlled rolling process: Five roughing passes are performed at 1040℃, with a single pass reduction rate of 16%~24% and a cumulative reduction rate of 85%; then eight finishing passes are performed at 890℃, with a single pass reduction rate of 9%~13% and a final rolling speed of 7.2m / s.

[0037] (3) Overcooling deformation: After finishing rolling, the temperature is cooled to 670°C at a cooling rate of 55°C / s by an online controlled cooling device, and deformed to a strain of 1.9 at a strain rate of 0.08s-¹.

[0038] (4) Isothermal treatment: After deformation, the steel was isothermally held at 620℃ for 25 min, and then cooled to room temperature at a cooling rate of 90℃ / s. Testing showed that the room temperature microstructure of the hypereutectoid steel prepared in this embodiment consisted of ultrafine pearlite + dispersed vanadium carbides, with a ferrite grain size of 0.72 μm. Figure 2 The cementite particle size is 0.38μm, with no network cementite; the tensile strength is 1420MPa, the reduction of area is 43%, and the wear resistance is 32% higher than that of traditional eutectoid steel.

[0039] Example 3

[0040] The high-strength and high-toughness hypereutectoid steel of this embodiment has the following chemical composition by mass fraction: C: 0.88%, Si: 0.25%, Mn: 0.68%, V: 0.09%, Cr: 0.33%, P: 0.015%, S: 0.013%, with the balance being Fe and unavoidable impurities. Its preparation method includes the following steps:

[0041] Smelting and casting: The converter smelting + RH refining process is adopted, and the P content of the molten steel is controlled at 0.015% and the S content at 0.013%. The casting yields a 280mm×380mm billet with a center segregation grade of 1.1.

[0042] Heating and holding: The billet is sent into the heating furnace and heated to 1080℃, and held for 75 minutes;

[0043] Controlled rolling process: Three roughing passes are performed at 1010℃, with a single pass reduction rate of 20%~25% and a cumulative reduction rate of 81%; followed by six finishing passes at 860℃, with a single pass reduction rate of 12%~15% and a final rolling speed of 5.8m / s.

[0044] Supercooling deformation: After precision rolling, the temperature is cooled to 630°C at a cooling rate of 35°C / s using an online controlled cooling device, and then deformed to a strain of 1.7 at a strain rate of 0.03s⁻¹.

[0045] Isothermal treatment: After deformation, the material is held at 590℃ for 35 minutes, and then cooled to room temperature at a cooling rate of 60℃ / s.

[0046] The hypereutectoid steel prepared in this embodiment has a room temperature microstructure of ultrafine pearlite + dispersed vanadium carbide, with ferrite grain size of 0.58 μm, cementite grain size of 0.29 μm, and no network cementite; tensile strength of 1320 MPa, reduction of area of ​​46%, and wear resistance improved by 26% compared with traditional eutectoid steel.

[0047] 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 and high-toughness hypereutectoid rails, characterized in that: Includes the following steps: (1) Smelting and casting: The converter smelting + RH refining process is adopted to control the cleanliness of the molten steel. The P and S contents are ≤0.020% and 0.015% respectively, and the casting billet is obtained by casting. (2) Heating and holding: Heat the billet to 1050℃~1150℃ and hold for 60~120min to allow vanadium to be fully dissolved and the original cementite to be dissolved; (3) Controlled rolling process: rough rolling is first carried out at 1000℃~1050℃, and then finish rolling is carried out at 850℃~900℃, with a cumulative reduction rate ≥80% and the final rolling speed controlled at 5~8m / s; (4) Overcooling deformation: After precision rolling, cool to 620℃~680℃ at a cooling rate of 30~60℃ / s, and plastic deformation of 1.6~2.0 at a strain rate of 0.01~0.1s⁻¹ within this temperature range; (5) Isothermal treatment: After deformation, isothermal hold at 580℃~630℃ for 20~40min, and then cool to room temperature at a cooling rate of 50~100℃ / s; The chemical composition of the hypereutectoid steel by mass percentage includes: C: 0.85%~1.10%, Si: 0.20%~0.45%, Mn: 0.60%~0.90%, V: 0.08%~0.15%, Cr: 0.30%~0.50%, P≤0.020%, S≤0.015%, with the balance being Fe and unavoidable impurities.

2. The method for preparing high-strength and high-toughness hypereutectoid rails according to claim 1, characterized in that: The room temperature microstructure of the hypereutectoid steel is ultrafine pearlite plus dispersed vanadium carbides, wherein the ferrite grain size is ≤0.8μm, the cementite grain size is ≤0.4μm, and no network cementite precipitation is observed.

3. The method for preparing high-strength and high-toughness hypereutectoid rails according to claim 1, characterized in that: The hypereutectoid steel has a tensile strength ≥1300MPa, a reduction of area ≥42%, and wear resistance that is more than 25% higher than that of traditional eutectoid steel.

4. The method for preparing high-strength and high-toughness hypereutectoid rails according to claim 1, characterized in that: The center segregation level of the billet described in step (1) is ≤1.5, and there are no shrinkage cavities or porosity defects inside.

5. The method for preparing high-strength and high-toughness hypereutectoid rails according to claim 1, characterized in that: In step (3), the roughing passes are 3 to 5, with a single pass reduction rate of 15% to 25%; the finishing passes are 6 to 8, with a single pass reduction rate of 8% to 15%.

6. The method for preparing high-strength and high-toughness hypereutectoid rails according to claim 1, characterized in that: The cooling rate in step (4) is precisely controlled by an online cooling control device to ensure that the austenite is supercooled to the A1~Arcm temperature range for deformation.

7. The method for preparing high-strength and high-toughness hypereutectoid rails according to claim 1, characterized in that: The chemical composition of the hypereutectoid steel by mass percentage includes: C: 0.92%, Si: 0.31%, Mn: 0.75%, V: 0.11%, Cr: 0.38%, P: 0.016%, S: 0.012%, with the balance being Fe and unavoidable impurities.

8. The method for preparing high-strength and high-toughness hypereutectoid rails according to claim 1, characterized in that: The chemical composition of the hypereutectoid steel by mass percentage includes: C: 1.05%, Si: 0.42%, Mn: 0.85%, V: 0.14%, Cr: 0.46%, P: 0.018%, S: 0.010%, with the balance being Fe and unavoidable impurities.

9. The method for preparing high-strength and high-toughness hypereutectoid rails according to claim 1, characterized in that: The chemical composition of the hypereutectoid steel by mass percentage includes: C: 0.88%, Si: 0.25%, Mn: 0.68%, V: 0.09%, Cr: 0.33%, P: 0.015%, S: 0.013%, balance being Fe and unavoidable impurities.

Images