Production method of wire rod for rare-earth high-silicon prestressed steel bar

Abstract

The invention discloses a production method of a wire rod for a rare-earth high-silicon prestressed steel bar, which is characterized by comprising the following steps of: 1) smelting and designing components; 2) a continuous casting process; and (3) a controlled rolling and controlled cooling process is carried out, specifically, a Stelmor controlled cooling line is adopted after finish rolling, and the cooling speed is controlled to be 5-15 DEG C / s by adjusting the air volume of a draught fan and the conveying speed. And after phase change is finished, air cooling is performed to reach the room temperature, a structure mainly comprising thin-sheet pearlite is obtained, a small amount of bainite is evenly distributed, and therefore the strength and toughness are balanced. The rare earth microalloying technology and the high-silicon component design are introduced, and the controlled rolling and controlled cooling technology is combined, so that the technical problem that high strength and high toughness are difficult to consider at the same time is solved, and a new technical path is provided for preparing high-end prestressed steel bars.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgical engineering, and particularly relates to a production method for wire rods used for rare earth high-silicon prestressed steel bars. Background Art

[0002] Performance requirements of prestressed steel bars:

[0003] Prestressed steel bars need to serve under high stress for a long time. Therefore, it is required that the material has high strength (tensile strength ≥ 1800 MPa), high toughness (elongation ≥ 7%), good fatigue resistance and corrosion resistance. The traditional process improves the strength by adding elements such as carbon, silicon, and manganese. However, a high silicon content (Si > 1.0%) will cause embrittlement of the material and reduce toughness. At the same time, the presence of inclusions in the steel is likely to cause cracks and affect the comprehensive performance of the material.

[0004] Limitations of the prior art:

[0005] High-silicon embrittlement problem: Although silicon can solid-solution strengthen the matrix, excessive silicon will promote the refinement of pearlite lamellae, increase grain boundary brittleness, and cause the material to be prone to fracture under low temperature or impact load.

[0006] Challenges of rare earth addition: Rare earth elements (RE) can improve the performance by purifying molten steel, refining grains, and improving the morphology of inclusions. However, the recovery rate of rare earth in the traditional process is low (usually < 30%), and the distribution is uneven, making it difficult to give full play to its role.

[0007] Insufficient process optimization space: The traditional rolling and cooling processes do not fully utilize the potential of composition design, resulting in an unsatisfactory match between strength and toughness, and the corrosion resistance is difficult to meet the requirements of harsh environments.

[0008] Deficiencies of existing solutions:

[0009] In the prior art, some studies have tried to improve toughness by reducing the silicon content or adding other alloying elements (such as vanadium and titanium), but this often sacrifices strength or increases costs. In addition, the instability of the rare earth treatment process also limits its application in industrial production. Therefore, developing a production method with coordinated optimization of composition and process is the key to improving the performance of prestressed steel bars. Summary of the Invention

[0010] The purpose of the present invention is to provide a production method for wire rods used for rare earth high-silicon prestressed steel bars, so as to solve the problems of imbalance between strength and toughness, low utilization rate of rare earth, and insufficient corrosion resistance in the prior art.

[0011] As a core material for infrastructure such as buildings, bridges, rail transit, and nuclear power plants, the properties of prestressed steel bars directly affect the safety and durability of structures. With the continuous improvement of the requirements for material strength, toughness, and corrosion resistance in modern engineering, traditional production processes are no longer able to meet the needs. By introducing rare earth microalloying technology and high-silicon composition design, combined with controlled rolling and controlled cooling processes, this invention solves the technical problem of difficulty in balancing high strength and high toughness, providing a new technical path for the preparation of high-end prestressed steel bars.

[0012] To solve the above technical problems, this invention adopts the following technical solutions:

[0013] A production method for wire rods used in rare earth high-silicon prestressed steel bars of this invention includes:

[0014] 1). Smelting and composition design

[0015] Chemical composition optimization:

[0016] Through thermodynamic calculations and experimental verification, the optimal mass percentage composition range of the molten steel is determined as follows:

[0017] C: 0.60 - 0.80%, Si: 1.20 - 1.80%, Mn: 0.50 - 0.80%, P: ≤0.020%, S: ≤0.010%, RE: 0.020 - 0.050%, and the balance is Fe and unavoidable impurities;

[0018] Smelting process:

[0019] Converter smelting is adopted, combined with LF refining and VD vacuum degassing to ensure the purity of the molten steel; rare earth alloys are added in the later stage of refining. The rare earth alloy wire is fed at a speed of 4 - 6 meters per minute in the later stage of refining, and electromagnetic stirring of 2 - 4 A is applied to improve the rare earth recovery rate and ensure its uniform distribution in the molten steel, increasing the rare earth recovery rate to 40 - 50%;

[0020] 2). Continuous casting process

[0021] Low superheat pouring: Control the superheat of the molten steel ≤25°C to reduce the columnar crystal zone of the billet, increase the proportion of equiaxed crystals, and improve the anisotropy of the material;

[0022] Electromagnetic stirring technology: Electromagnetic stirring is applied in the mold and secondary cooling zone to promote the flow of the molten steel, homogenize the composition, and refine the grains;

[0023] 3). Controlled rolling and controlled cooling process

[0024] Heating regime:

[0025] The billet is heated to 1150 - 1200°C and held for 2 - 3 hours to ensure the full dissolution of alloying elements while avoiding grain coarsening;

[0026] Rolling stage control:

[0027] Rough rolling: The temperature is ≥1000°C. The as-cast structure is broken by large reduction ratios to refine the grains.

[0028] Intermediate rolling: The temperature is 850 - 950°C. The grains are further refined to prepare for subsequent phase transformations.

[0029] Finish rolling: The temperature is 750 - 850°C. Rolling is carried out in the non-recrystallization zone of austenite to increase the dislocation density and improve the strength.

[0030] Controlled cooling process:

[0031] After finish rolling, the Stelmor controlled cooling line is adopted. By adjusting the air volume of the fan and the transportation speed, the cooling rate is controlled at 5 - 15°C / s. After the phase transformation is completed, it is air-cooled to room temperature to obtain a structure mainly composed of fine lamellar pearlite, with a small amount of bainite evenly distributed, thus balancing the strength and toughness.

[0032] Furthermore, the electromagnetic stirring current intensity applied in the mold and the secondary cooling zone is 2 - 4A.

[0033] Furthermore, the slab size: 150mm×150mm square billets are used to provide an appropriate reduction ratio for subsequent rolling.

[0034] Furthermore, the chemical composition of the wire rod by mass percentage is: C: 0.65%, Si: 1.40%, Mn: 0.60%, RE: 0.030%, P: 0.015%, S: 0.008%, and the balance is Fe and unavoidable impurities.

[0035] Furthermore, the chemical composition of the wire rod by mass percentage is: C: 0.70%, Si: 1.60%, Mn: 0.70%, RE: 0.040%, P: 0.012%, S: 0.006%, and the balance is Fe and unavoidable impurities.

[0036] Furthermore, the chemical composition of the wire rod by mass percentage is: C: 0.75%, Si: 1.80%, Mn: 0.50%, RE: 0.050%, P: 0.018%, S: 0.009%, and the balance is Fe and unavoidable impurities.

[0037] Furthermore, it specifically includes:

[0038] Smelting process:

[0039] After converter smelting, LF refining is carried out for 30 minutes, and VD vacuum degassing is carried out for 15 minutes.

[0040] In the later stage of refining, the RE-Si alloy wire is fed at a speed of 5m / min, and the rare earth recovery rate is 42%.

[0041] Continuous casting process:

[0042] Superheat 20°C, electromagnetic stirring current in the mold 3 A, weak cooling mode in the secondary cooling zone;

[0043] Rolling and controlled cooling:

[0044] Heating temperature 1180°C, holding for 2.5 hours;

[0045] Rough rolling temperature 1050°C, intermediate rolling temperature 900°C, finish rolling temperature 800°C;

[0046] After finish rolling, cool to 550°C at a speed of 10°C / s, and then air cool.

[0047] Furthermore, it specifically includes:

[0048] Smelting process:

[0049] After electric furnace smelting, LF refining for 40 minutes, VD vacuum degassing for 20 minutes;

[0050] The rare earth alloy is added in batches, and the recovery rate is 45%;

[0051] Continuous casting process:

[0052] Superheat 15°C, electromagnetic stirring current 4 A, good surface quality of the continuous casting billet;

[0053] Rolling and controlled cooling:

[0054] Heating temperature 1160°C, holding for 2 hours;

[0055] Rough rolling temperature 1020°C, intermediate rolling temperature 880°C, finish rolling temperature 780°C;

[0056] Controlled cooling speed 12°C / s, air cool after the phase transformation ends.

[0057] Furthermore, it specifically includes:

[0058] Smelting process:

[0059] After converter smelting, LF refining for 35 minutes, VD vacuum degassing for 18 minutes;

[0060] The rare earth alloy is quickly added in the later stage of refining, and the recovery rate is 48%;

[0061] Continuous casting process:

[0062] Superheat 25°C, electromagnetic stirring current 2 A, no obvious shrinkage cavity in the continuous casting billet;

[0063] Rolling and controlled cooling:

[0064] Heating temperature 1200°C, holding for 3 hours;

[0065] The rough rolling temperature is 1080°C, the intermediate rolling temperature is 950°C, and the finish rolling temperature is 850°C;

[0066] The controlled cooling rate is 8°C / s, and after cooling to 600°C, air cooling is adopted.

[0067] Principle of composition design:

[0068] Carbon (C): Carbon is the main element to strengthen the matrix, and it improves the strength by forming pearlite and bainite structures. However, too high carbon content will reduce the toughness, so it is controlled within the range of 0.60 - 0.80%, taking into account both strength and toughness.

[0069] Silicon (Si): Silicon improves the strength through solid solution strengthening, and at the same time inhibits the precipitation of cementite and refines the pearlite lamellae. In the present invention, the silicon content is increased to 1.20 - 1.80%, and the embrittlement problem is solved through subsequent process control.

[0070] Manganese (Mn): Manganese can lower the critical point of the steel, promote the formation of austenite, and at the same time combine with sulfur to form MnS inclusions, reducing the harmful effects of sulfur.

[0071] Rare earth (RE): Rare earth elements have a strong affinity with sulfur and oxygen, can form high-melting-point rare earth sulfides and oxides, reducing harmful inclusions in the steel; in addition, rare earth atoms segregate at grain boundaries, hinder dislocation movement, refine grains, and improve toughness.

[0072] Compared with the prior art, the beneficial technical effects of the present invention: Specific embodiments

[0073] Example 1

[0074] Chemical composition (mass percentage %): C: 0.65, Si: 1.40, Mn: 0.60, RE: 0.030, P: 0.015, S: 0.008, and the balance is Fe.

[0075] Smelting process:

[0076] After converter smelting, LF refining is carried out for 30 minutes, and VD vacuum degassing is carried out for 15 minutes.

[0077] In the later stage of refining, RE-Si alloy wire is fed at a speed of 5 m / min, and the rare earth recovery rate is 42%.

[0078] Continuous casting process:

[0079] The superheat is 20°C, the electromagnetic stirring current of the mold is 3 A, and a weak cooling mode is adopted in the secondary cooling zone.

[0080] Rolling and controlled cooling:

[0081] The heating temperature is 1180°C, and the holding time is 2.5 hours.

[0082] The rough rolling temperature is 1050°C, the intermediate rolling temperature is 900°C, and the finish rolling temperature is 800°C.

[0083] After finish rolling, it is cooled to 550°C at a speed of 10°C / s and then air-cooled.

[0084] Example 2

[0085] Chemical composition (mass percentage %):

[0086] C: 0.70, Si: 1.60, Mn: 0.70, RE: 0.040, P: 0.012, S: 0.006, the balance is Fe.

[0087] Smelting process:

[0088] After electric furnace smelting, LF refining is carried out for 40 minutes and VD vacuum degassing is carried out for 20 minutes.

[0089] The rare earth alloy is added in batches, and the recovery rate is 45%.

[0090] Continuous casting process:

[0091] The superheat is 15°C, the electromagnetic stirring current is 4A, and the surface quality of the billet is good.

[0092] Rolling and controlled cooling:

[0093] The heating temperature is 1160°C and the holding time is 2 hours.

[0094] The rough rolling temperature is 1020°C, the intermediate rolling temperature is 880°C, and the finish rolling temperature is 780°C.

[0095] The controlled cooling speed is 12°C / s, and it is air-cooled after the phase transformation ends.

[0096] Example 3

[0097] Chemical composition (mass percentage %):

[0098] C: 0.75, Si: 1.80, Mn: 0.50, RE: 0.050, P: 0.018, S: 0.009, the balance is Fe.

[0099] Smelting process:

[0100] After converter smelting, LF refining is carried out for 35 minutes and VD vacuum degassing is carried out for 18 minutes.

[0101] The rare earth alloy is quickly added in the later stage of refining, and the recovery rate is 48%.

[0102] Continuous casting process:

[0103] The superheat is 25°C, the electromagnetic stirring current is 2A, and there is no obvious shrinkage cavity in the billet.

[0104] Rolling and controlled cooling:

[0105] The heating temperature is 1200 °C and the holding time is 3 hours.

[0106] The rough rolling temperature is 1080 °C, the intermediate rolling temperature is 950 °C, and the finish rolling temperature is 850 °C.

[0107] The controlled cooling rate is 8 °C / s, and after cooling to 600 °C, it is air-cooled.

[0108] Comparative case:

[0109] The wire rod for prestressed steel bars produced by the traditional process has the following composition (mass %): C 0.70, Si 1.00, Mn 0.60, without RE element; the rolling heating temperature is 1100 °C, and after final rolling, it is air-cooled without controlled cooling.

[0110] Performance testing and benchmarking analysis:

[0111] 1. Mechanical property testing

[0112] Testing method: According to the standard of GB / T 228.1-2021, a tensile testing machine is used to test the tensile strength and elongation; the microhardness is measured by a hardness tester, and the yield ratio is calculated.

[0113] Testing results:

[0114] Performance indicators Example 1 Example 2 Example 3 Comparison case Tensile strength (MPa) 1850 1920 1880 1650 Elongation (%) 7.5 7.2 7.0 5.5 Yield ratio 0.92 0.93 0.91 0.88 Impact toughness (J) 45 42 40 30

[0115] The tensile strength of the example is increased by 12-16% compared with the comparative case, the elongation is increased by 30-36%, and the yield ratio is increased by 4-6%. This is because rare earths refine the grains, high silicon strengthens the matrix, and the controlled cooling process optimizes the pearlite lamellar structure, reducing the formation of brittle phases.

[0116] 2. Corrosion resistance testing

[0117] Testing method: Salt spray corrosion test (GB / T 10125-2021) is adopted, the testing time is 1000 hours, and the corrosion weight loss rate is evaluated.

[0118] Testing results:

[0119]

[0120]

[0121] The corrosion resistance of the example is significantly better than that of the comparative case. The main reasons include: rare earths purify the molten steel, reducing inclusions as corrosion sources; the high silicon content promotes the formation of a dense SiO2 film, hindering the intrusion of corrosive media.

[0122] Application Scenarios and Economic Benefits:

[0123] Application Areas:

[0124] The wire rods prepared by the present invention can be widely applied to fields with strict requirements for material properties, such as prestressed concrete pipe piles, bridge cables, and nuclear power plant containments, and are particularly suitable for use in corrosive environments such as humidity, saline-alkali, etc.

[0125] Economic Benefits:

[0126] The improvement in rare earth recovery rate reduces alloy consumption and lowers the cost by about 5 - 8%.

[0127] The high strength and high toughness of the wire rods reduce the amount of materials used in the project and improve the construction efficiency.

[0128] The enhanced corrosion resistance extends the service life of the structure and reduces the maintenance cost.

[0129] The embodiments described above are only used to describe the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A production method of wire rod for rare earth high-silicon prestressed steel bars, characterized in that, Including: 1). Smelting and composition design Chemical composition optimization: The mass percentage composition range is as follows: C: 0.60 - 0.80%, Si: 1.20 - 1.80%, Mn: 0.50 - 0.80%, P: ≤0.020%, S: ≤0.010%, RE: 0.020 - 0.050%, and the balance is Fe and unavoidable impurities; Smelting process: Converter smelting is adopted, combined with LF refining and VD vacuum degassing to ensure the purity of the molten steel; rare earth alloy is added in the later stage of refining. The rare earth alloy wire is fed at a speed of 4 - 6 m / min in the later stage of refining, and electromagnetic stirring of 2 - 4 A is applied to improve the rare earth recovery rate and ensure its uniform distribution in the molten steel, increasing the rare earth recovery rate to 40 - 50%; 2). Continuous casting process Low superheat pouring: Control the superheat of the molten steel ≤25°C; Electromagnetic stirring technology: Electromagnetic stirring is applied in the mold and secondary cooling zone to promote the flow of the molten steel, homogenize the composition, and refine the grains; 3). Controlled rolling and controlled cooling process Heating system: The slab is heated to 1150 - 1200°C and held for 2 - 3 hours; Rolling stage control: Rough rolling: The temperature ≥1000°C, and the as-cast structure is broken by large reduction to refine the grains; Medium rolling: The temperature is 850 - 950°C, further refining the grains to prepare for subsequent phase transformation; Finish rolling: The temperature is 750 - 850°C, rolling in the non-recrystallization zone of austenite to increase the dislocation density and improve the strength. Controlled cooling process: After finish rolling, the Stelmor controlled cooling line is adopted. By adjusting the air volume of the fan and the transportation speed, the cooling rate is controlled at 5 - 15°C / s. After the phase transformation is completed, it is air-cooled to room temperature to obtain a structure mainly composed of fine lamellar pearlite, with a small amount of bainite evenly distributed, thus balancing strength and toughness.

2. The production method of the wire rod for rare earth high-silicon prestressed steel bars according to claim 1, characterized in that, The electromagnetic stirring current intensity applied in the mold and secondary cooling zone is 2 - 4 A.

3. The production method of the wire rod for rare earth high-silicon prestressed steel bars according to claim 1, characterized in that, Slab size: 150mm×150mm square billets are adopted to provide a suitable reduction ratio for subsequent rolling.

4. The production method of the wire rod for rare earth high-silicon prestressed steel bars according to claim 1, characterized in that, The chemical composition of the wire rod in mass percentage is: C: 0.65%, Si: 1.40%, Mn: 0.60%, RE: 0.030%, P: 0.015%, S: 0.008%, and the balance is Fe and unavoidable impurities.

5. The production method of the wire rod for rare earth high-silicon prestressed steel bars according to claim 1, characterized in that, The chemical composition of the wire rod in mass percentage is: C: 0.70%, Si: 1.60%, Mn: 0.70%, RE: 0.040%, P: 0.012%, S: 0.006%, and the balance is Fe and unavoidable impurities.

6. The production method of the wire rod for rare earth high-silicon prestressed steel bars according to claim 1, characterized in that, The chemical composition of the wire rod in mass percentage is: C: 0.75%, Si: 1.80%, Mn: 0.50%, RE: 0.050%, P: 0.018%, S: 0.009%, and the balance is Fe and unavoidable impurities.

7. The production method of the wire rod for rare earth high-silicon prestressed steel bars according to claim 4, characterized in that, Specifically including: Smelting process: After converter smelting, LF refining for 30 minutes and VD vacuum degassing for 15 minutes; In the later stage of refining, RE-Si alloy wire is fed at a speed of 5 m / min, and the rare earth recovery rate is 42%; Continuous casting process: Superheat 20°C, electromagnetic stirring current in the mold is 3 A, and the secondary cooling zone adopts a weak cooling mode; Rolling and controlled cooling: Heating temperature 1180°C, holding for 2.5 hours; The rough rolling temperature is 1050°C, the intermediate rolling temperature is 900°C, and the finish rolling temperature is 800°C; After finish rolling, it is cooled to 550°C at a speed of 10°C / s and then air-cooled.

8. The production method of the wire rod for rare earth high-silicon prestressed steel bars according to claim 5, characterized in that, Specifically include: Smelting process: After electric furnace smelting, LF refining for 40 minutes and VD vacuum degassing for 20 minutes; The rare earth alloy is added in batches, and the recovery rate is 45%; Continuous casting process: The superheat is 15°C, the electromagnetic stirring current is 4A, and the surface quality of the billet is good; Rolling and controlled cooling: The heating temperature is 1160°C and the holding time is 2 hours; The rough rolling temperature is 1020°C, the intermediate rolling temperature is 880°C, and the finish rolling temperature is 780°C; The controlled cooling speed is 12°C / s, and it is air-cooled after the phase transformation ends.

9. The production method of the wire rod for rare earth high-silicon prestressed steel bars according to claim 6, characterized in that, Specifically include: Smelting process: After converter smelting, LF refining for 35 minutes and VD vacuum degassing for 18 minutes; The rare earth alloy is quickly added in the later stage of refining, and the recovery rate is 48%; Continuous casting process: The superheat is 25°C, the electromagnetic stirring current is 2A, and there is no obvious shrinkage cavity in the billet; Rolling and controlled cooling: The heating temperature is 1200°C and the holding time is 3 hours; The rough rolling temperature is 1080°C, the intermediate rolling temperature is 950°C, and the finish rolling temperature is 850°C; The controlled cooling speed is 8°C / s, and it is air-cooled after cooling to 600°C.

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