Production method of steel wire rod for manganese-silicon alloy high-strength prestressed steel bar

Abstract

The invention discloses a production method of a steel wire rod for a manganese-silicon alloy high-strength prestressed steel bar, and belongs to the technical field of steel and iron material production. According to the method, by optimizing chemical component design and matching rolling-cooling process parameters, a wire rod product with high strength, high toughness and excellent cold machining performance is obtained, and the method is suitable for machining and manufacturing prestressed steel bars in the fields of bridges, building pile foundations, nuclear power engineering and the like.

Description

Technical Field

[0001] This invention belongs to the field of steel material production technology, and in particular relates to a method for producing wire rods for high-strength prestressed steel bars made of manganese-silicon alloy. Background Technology

[0002] Prestressed steel bars, as core load-bearing components, are widely used in various large-scale engineering structures, and their performance directly determines the load-bearing capacity and service life of the project. With the increasing demands for lightweight, large-span, and durable structures in modern engineering, higher requirements are being placed on the strength grade, toughness indicators, and cold-working adaptability of wire rods used for prestressed steel bars. Currently, domestic prestressed steel bar wire rods mainly use carbon steel or low-alloy systems, achieving strength improvement by increasing carbon content, but this results in problems such as decreased toughness, easy cracking during cold working, and poor weldability. While systems strengthened with precious alloying elements such as chromium and nickel can improve overall performance, they significantly increase production costs and are highly resource-dependent.

[0003] Manganese-silicon alloys, as a classic strengthening system, offer advantages such as low cost and abundant alloy resources. They enhance material strength through the synergistic effects of solid solution strengthening, grain refinement strengthening, and precipitation strengthening. However, current manganese-silicon alloy wire rod production commonly suffers from problems such as unreasonable composition design, insufficient precision in rolling temperature control, and improper cooling rate matching. This results in poor wire rod microstructure uniformity, coarse grains, uneven pearlite lamellar spacing, Widmanstätten structure, and other defects, affecting the stability of subsequent cold drawing and twisting processes. Furthermore, the fatigue performance of the finished steel bars fails to meet the demands of high-strength applications. In addition, some production processes excessively increase the cooling rate in pursuit of strength, leading to excessively high surface hardness and internal stress concentration in the wire rods. This makes them prone to cracking during cold working, reducing production efficiency and product yield. Therefore, developing a compositionally optimized, process-controllable, and cost-effective method for producing high-strength prestressed steel bars using manganese-silicon alloy wire rods has become a pressing technical challenge for the industry. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing wire rods for high-strength prestressed steel bars made of manganese-silicon alloy, thereby solving the problem.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for producing wire rods for high-strength prestressed steel bars made of manganese-silicon alloy, comprising:

[0007] Converter smelting: A top-and-bottom blown converter is used for smelting, using high-quality scrap steel and pig iron as raw materials, and controlling the sulfur content of the molten iron to be ≤0.030%; during the smelting process, high-basicity slag R=3.0-3.5 is used, and the final temperature is controlled at 1520℃-1560℃ by oxygen blowing, with a final carbon content of 0.08%-0.12%; during tapping, bottom blowing of argon is used in the ladle, with the argon flow rate controlled at 15-25L / min. When 1 / 3 of the steel is tapped, silicon-manganese alloy and ferrosilicon alloy are added for deoxidation and alloying. In the later stage of tapping, ferrovanadium and ferrotitanium are added to adjust the alloy composition to ensure that the composition is uniform and meets the standards;

[0008] LF Refining: After tapping from the converter, the molten steel is sent to the LF refining furnace for refining treatment. The refining time is controlled at 40-60 minutes. In the initial stage of refining, strong argon stirring is used at a flow rate of 20-30 L / min to remove gas and inclusions from the molten steel. In the middle stage of refining, lime and fluorite are added to adjust the slag composition and maintain the slag in a white slag state. The temperature is controlled at 1530℃-1570℃. In the later stage of refining, weak argon stirring is used at a flow rate of 5-10 L / min to fine-tune the composition and homogenize the temperature, ensuring that the composition of the molten steel meets the design requirements. The purity of the molten steel is [O]≤20ppm and [H]≤2ppm.

[0009] Continuous casting: Refined molten steel is continuously cast using an arc-shaped continuous casting machine. Protective casting is employed during the process, with argon gas introduced into the crystallizer to prevent secondary oxidation. The crystallizer vibration frequency is controlled at 180-220 times / min, amplitude at 4-6mm, and casting speed at 1.2-1.6m / min. The secondary cooling zone uses mist cooling, with a cooling intensity controlled at 0.8-1.2L / kg to ensure uniform surface temperature of the billet and prevent cracking. After cutting, the billet undergoes slow cooling treatment at 600-700℃ for 4-6 hours to eliminate internal stress and improve the billet microstructure.

[0010] Heating: The continuously cast billet is fed into a walking beam furnace for heating. The heating process is divided into a preheating section, a heating section, and a soaking section. The temperature in the preheating section is 800-900℃, and the heating time is 1.5-2.0h. The temperature in the heating section is 1150-1250℃, and the heating time is 2.0-3.0h. The temperature in the soaking section is 1200-1230℃, and the soaking time is 1.0-1.5h.

[0011] Rolling: The heated billet is fed into the bar rolling production line for rolling. Rolling is divided into three stages: roughing, intermediate rolling, and finishing rolling. Continuous rolling is adopted, with speed matching between each stand to ensure tension-free rolling. The roughing stage uses 10-12 passes at a rolling temperature of 1100-1180℃, with a reduction of 30%-40% per pass, to gradually deform the billet and refine the grains. The intermediate rolling stage uses 8-10 passes at a rolling temperature of 950-1050℃, with a reduction of 25%-35% per pass, to further refine the grains and improve the uniformity of the microstructure. The finishing stage uses 6-8 passes at a rolling temperature of 850-950℃, with a reduction of 20%-30% per pass, and the final rolling temperature is controlled at 880-920℃.

[0012] Controlled cooling: The finished wire rod immediately enters an online controlled cooling device for controlled cooling, employing a two-stage cooling process of "water cooling + air cooling"; during the water cooling stage, the cooling water volume is controlled at 80-120 ml. 3 / h, cooling time 3-5s, rapidly reduce the surface temperature of the wire rod to 650-700℃, inhibiting grain growth during the pearlite transformation process; after water cooling, air cooling is performed for 10-15s, allowing the heat inside the wire rod to dissipate slowly, achieving uniform pearlite transformation and refining the interlamellar spacing of pearlite.

[0013] Winding and Inspection: After controlled cooling, the wire rod is spun into coils by a coil spinning machine. After the coils are naturally cooled to room temperature on a cooling bed, they are wound up and packaged.

[0014] The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.28%-0.35%, Si: 1.20%-1.60%, Mn: 1.40%-1.80%, P≤0.020%, S≤0.015%, Cr: 0.10%-0.30%, V: 0.06%-0.12%, Ti: 0.010%-0.030%, N: 0.008%-0.015%, with the balance being Fe and unavoidable impurities.

[0015] Furthermore, during the controlled cooling process, the temperature of the wire rod is monitored in real time using an infrared thermometer, and the cooling water volume is adjusted according to the temperature feedback to ensure that the cooling rate is stable at 5-10℃ / s, avoiding surface hardening due to excessively rapid cooling or coarse microstructure due to excessively slow cooling.

[0016] Furthermore, during the winding process, the winding tension is controlled at 15-25kN to avoid coil deformation or stress concentration.

[0017] Furthermore, the finished wire rods undergo visual inspection, dimensional measurement, mechanical property testing, and metallographic analysis to ensure that the wire rod surface is free of cracks, folds, and scabs, with a diameter tolerance ≤ ±0.3 mm, tensile strength ≥ 1000 MPa, yield strength ≥ 850 MPa, elongation after fracture ≥ 10%, and a metallographic structure of fine pearlite + a small amount of ferrite, with pearlite lamellar spacing ≤ 0.2 μm and grain size ≥ grade 8.

[0018] Furthermore, the chemical composition of the wire rod, by mass percentage, is as follows: C: 0.30%, Si: 1.35%, Mn: 1.55%, P: 0.015%, S: 0.010%, Cr: 0.20%, V: 0.08%, Ti: 0.020%, N: 0.012%, with the balance being Fe and unavoidable impurities.

[0019] Furthermore, the chemical composition of the wire rod, by mass percentage, is as follows: C: 0.32%, Si: 1.45%, Mn: 1.65%, P: 0.018%, S: 0.012%, Cr: 0.25%, V: 0.10%, Ti: 0.025%, N: 0.013%, with the balance being Fe and unavoidable impurities.

[0020] Furthermore, the chemical composition of the wire rod, by mass percentage, is as follows: C: 0.29%, Si: 1.30%, Mn: 1.50%, P: 0.016%, S: 0.009%, Cr: 0.15%, V: 0.07%, Ti: 0.018%, N: 0.011%, with the balance being Fe and unavoidable impurities.

[0021] The roles of each element are as follows: C is the core element to ensure the strength of the wire rod. It improves the hardness of pearlite through solid solution strengthening. The content is controlled at 0.28%-0.35%, which meets the high strength requirements and avoids the decrease in toughness and cold working cracking caused by excessive carbon content. Si is a strong deoxidizer. It also improves strength and corrosion resistance through solid solution strengthening. The content of 1.20%-1.60% can achieve a balance between strengthening effect and processing performance. Mn works synergistically with Si to refine the interlamellar spacing of pearlite and improve the uniformity of the structure. The content of 1.40%-1.80% can significantly improve strength and toughness. A small amount of Cr can improve hardenability, refine grains, and improve cold working performance. V forms nitride precipitates with Ti and N. It further improves strength through dispersion strengthening and inhibits austenite grain growth. The content of P and S impurities is strictly controlled to avoid the formation of brittle compounds and ensure the toughness and weldability of the wire rod.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] This invention optimizes the chemical composition of manganese-silicon alloy wire rods, rationally proportioning main alloying elements such as C, Si, and Mn with microalloying elements such as V, Ti, and N to achieve a synergistic effect of solid solution strengthening, grain refinement strengthening, and dispersion strengthening. This ensures high strength while also considering toughness and cold workability. An integrated production process is employed, encompassing converter smelting, LF refining, continuous casting, temperature-controlled rolling, and two-stage controlled cooling. Strict control over parameters such as temperature, time, and cooling rate at each stage effectively refines grain size and pearlite lamellar spacing, preventing defects such as Widmanstätten structure and improving the uniformity and purity of the wire rod structure. The production process eliminates the need for adding precious alloying elements such as chromium and nickel, reducing production costs by 10%-15%. Furthermore, the process is highly controllable and suitable for large-scale production.

[0024] The wire rod produced by this invention meets the following requirements: tensile strength ≥1000MPa, yield strength ≥850MPa, elongation after fracture ≥10%, and excellent cold working performance. After being processed into prestressed steel bars through cold drawing, heat treatment and other processes, its fatigue strength and corrosion resistance are significantly improved. It can be widely used in various large-scale engineering structures and has significant economic value and social benefits. Detailed Implementation

[0025] Example 1

[0026] The chemical composition of the wire rod in this embodiment, by mass percentage, is as follows: C: 0.30%, Si: 1.35%, Mn: 1.55%, P: 0.015%, S: 0.010%, Cr: 0.20%, V: 0.08%, Ti: 0.020%, N: 0.012%, with the balance being Fe and unavoidable impurities.

[0027] The production process steps are as follows:

[0028] Converter smelting: The sulfur content of the molten iron entering the furnace is 0.025%, the final temperature is 1540℃, the final carbon content is 0.10%, the argon flow rate at tapping is 20L / min, and silicon manganese alloy, ferrosilicon alloy, ferrovanadium and ferrotitanium are added according to the design ratio for alloying.

[0029] LF refining: Refining time 50 min, initial argon flow rate 25 L / min, intermediate temperature 1550℃, maintaining white slag state, later argon flow rate 8 L / min, after refining, molten steel [O] = 18 ppm, [H] = 1.8 ppm.

[0030] Continuous casting: crystallizer vibration frequency 200 times / min, amplitude 5mm, casting speed 1.4m / min, secondary cooling zone cooling intensity 1.0L / kg, billet size 150mm square billet, slow cooling temperature 650℃, holding time 5h.

[0031] Heating: Preheating section temperature 850℃, heating time 1.8h; heating section temperature 1200℃, heating time 2.5h; soaking section temperature 1210℃, soaking time 1.2h.

[0032] Rolling: Roughing 11 passes, rolling temperature 1150℃, reduction 35% / pass; Intermediate rolling 9 passes, rolling temperature 1000℃, reduction 30% / pass; Finishing rolling 7 passes, rolling temperature 900℃, reduction 25% / pass, final rolling temperature 900℃.

[0033] Cooling control: 100m³ of water-cooled water flow 3 / h, cooling time 4s, surface temperature drops to 680℃; air cooling time 12s, cooling rate 8℃ / s.

[0034] Winding and Inspection: Winding tension 20kN, finished wire diameter φ12mm, no surface defects, diameter tolerance ±0.2mm; tensile strength 1050MPa, yield strength 880MPa, elongation after fracture 12%; metallographic structure is fine pearlite + a small amount of ferrite, pearlite lamellar spacing 0.18μm, grain size grade 9.

[0035] Example 2

[0036] The chemical composition of the wire rod in this embodiment, by mass percentage, is as follows: C: 0.32%, Si: 1.45%, Mn: 1.65%, P: 0.018%, S: 0.012%, Cr: 0.25%, V: 0.10%, Ti: 0.025%, N: 0.013%, with the balance being Fe and unavoidable impurities.

[0037] In the production process, the continuous casting speed is 1.5 m / min, the cooling intensity in the secondary cooling zone is 1.1 L / kg, the heating zone temperature is 1220℃, the soaking zone temperature is 1220℃, the finishing rolling temperature is 910℃, and the cooling water volume is 110 m³ / kg. 3 The cooling rate is 9℃ / s, and the remaining process parameters are the same as in Example 1.

[0038] The finished wire rod has a tensile strength of 1080MPa, a yield strength of 900MPa, and an elongation after fracture of 11%. The metallographic structure is fine pearlite with a pearlite lamellar spacing of 0.16μm and a grain size of grade 9. All properties meet the processing requirements of high-strength prestressed steel bars.

[0039] Example 3

[0040] The chemical composition of the wire rod in this embodiment, by mass percentage, is as follows: C: 0.29%, Si: 1.30%, Mn: 1.50%, P: 0.016%, S: 0.009%, Cr: 0.15%, V: 0.07%, Ti: 0.018%, N: 0.011%, with the balance being Fe and unavoidable impurities.

[0041] In the production process, the continuous casting speed is 1.3 m / min, the cooling intensity in the secondary cooling zone is 0.9 L / kg, the heating zone temperature is 1180℃, the soaking zone temperature is 1200℃, the finishing rolling temperature is 890℃, and the cooling water volume is 90 m³ / kg. 3 The cooling rate is 7℃ / s, and the remaining process parameters are the same as in Example 1.

[0042] The finished wire rod has a tensile strength of 1030 MPa, a yield strength of 870 MPa, and an elongation after fracture of 13%. The metallographic structure consists of fine pearlite with a small amount of ferrite. The pearlite lamellar spacing is 0.19 μm, and the grain size is grade 8.5. No cracking occurs during cold working, and the processing performance is excellent.

[0043] 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 producing wire rod for high-strength prestressed steel bars based on manganese-silicon alloy, characterized in that, include: Converter smelting: A top-and-bottom blown converter is used for smelting, using high-quality scrap steel and pig iron as raw materials, and controlling the sulfur content of the molten iron to be ≤0.030%; during the smelting process, high-basicity slag R=3.0-3.5 is used, and the final temperature is controlled at 1520℃-1560℃ by oxygen blowing, with a final carbon content of 0.08%-0.12%; during tapping, bottom blowing of argon is used in the ladle, with the argon flow rate controlled at 15-25L / min. When 1 / 3 of the steel is tapped, silicon-manganese alloy and ferrosilicon alloy are added for deoxidation and alloying. In the later stage of tapping, ferrovanadium and ferrotitanium are added to adjust the alloy composition to ensure that the composition is uniform and meets the standards; LF Refining: After tapping from the converter, the molten steel is sent to the LF refining furnace for refining treatment. The refining time is controlled at 40-60 minutes. In the initial stage of refining, strong argon stirring is used at a flow rate of 20-30 L / min to remove gas and inclusions from the molten steel. In the middle stage of refining, lime and fluorite are added to adjust the slag composition and maintain the slag in a white slag state. The temperature is controlled at 1530℃-1570℃. In the later stage of refining, weak argon stirring is used at a flow rate of 5-10 L / min to fine-tune the composition and homogenize the temperature, ensuring that the composition of the molten steel meets the design requirements. The purity of the molten steel is [O]≤20ppm and [H]≤2ppm. Continuous casting: Refined molten steel is continuously cast using an arc-shaped continuous casting machine. Protective casting is employed during the process, with argon gas introduced into the crystallizer to prevent secondary oxidation. The crystallizer vibration frequency is controlled at 180-220 times / min, amplitude at 4-6mm, and casting speed at 1.2-1.6m / min. The secondary cooling zone uses mist cooling, with a cooling intensity controlled at 0.8-1.2L / kg to ensure uniform surface temperature of the billet and prevent cracking. After cutting, the billet undergoes slow cooling treatment at 600-700℃ for 4-6 hours to eliminate internal stress and improve the billet microstructure. Heating: The continuously cast billet is fed into a walking beam furnace for heating. The heating process is divided into a preheating section, a heating section, and a soaking section. The temperature in the preheating section is 800-900℃, and the heating time is 1.5-2.0h. The temperature in the heating section is 1150-1250℃, and the heating time is 2.0-3.0h. The temperature in the soaking section is 1200-1230℃, and the soaking time is 1.0-1.5h. Rolling: The heated billet is fed into the bar rolling production line for rolling. Rolling is divided into three stages: roughing, intermediate rolling, and finishing rolling. Continuous rolling is adopted, with speed matching between each stand to ensure tension-free rolling. The roughing stage uses 10-12 passes at a rolling temperature of 1100-1180℃, with a reduction of 30%-40% per pass, to gradually deform the billet and refine the grains. The intermediate rolling stage uses 8-10 passes at a rolling temperature of 950-1050℃, with a reduction of 25%-35% per pass, to further refine the grains and improve the uniformity of the microstructure. The finishing stage uses 6-8 passes at a rolling temperature of 850-950℃, with a reduction of 20%-30% per pass, and the final rolling temperature is controlled at 880-920℃. Controlled cooling: the wire rod after finishing rolling enters the online controlled cooling device immediately for controlled cooling, adopting two-stage cooling process of "water cooling + air cooling"; in the water cooling stage, the cooling water volume is controlled at 80-120 m 3 / h, the cooling time is 3-5 s, the surface temperature of the wire rod is rapidly reduced to 650-700 ℃, and the grain growth in the process of pearlite transformation is inhibited; after water cooling, air cooling is carried out, the air cooling time is 10-15 s, the internal heat of the wire rod is slowly dissipated, and uniform transformation of pearlite and refinement of pearlite interlamellar spacing are realized; Winding and Inspection: After controlled cooling, the wire rod is spun into coils by a coil spinning machine. After the coils are naturally cooled to room temperature on a cooling bed, they are wound up and packaged. The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.28%-0.35%, Si: 1.20%-1.60%, Mn: 1.40%-1.80%, P≤0.020%, S≤0.015%, Cr: 0.10%-0.30%, V: 0.06%-0.12%, Ti: 0.010%-0.030%, N: 0.008%-0.015%, with the balance being Fe and unavoidable impurities.

2. The method for producing wire rod for high-strength prestressed steel bars based on manganese-silicon alloy according to claim 1, characterized in that, During the controlled cooling process, the temperature of the wire rod is monitored in real time by an infrared thermometer. The cooling water volume is adjusted according to the temperature feedback to ensure that the cooling rate is stable at 5-10℃ / s, avoiding surface hardening due to excessive cooling or coarse microstructure due to excessive cooling.

3. The method for producing wire rod for high-strength prestressed steel bars based on manganese-silicon alloy according to claim 1, characterized in that, During the winding process, the winding tension should be controlled at 15-25kN to avoid coil deformation or stress concentration.

4. The method for producing wire rod for high-strength prestressed steel bars based on manganese-silicon alloy according to claim 1, characterized in that, Finished wire rods undergo visual inspection, dimensional measurement, mechanical property testing, and metallographic analysis to ensure that the wire rod surface is free of cracks, folds, and scabs, with a diameter tolerance ≤ ±0.3 mm, tensile strength ≥ 1000 MPa, yield strength ≥ 850 MPa, elongation after fracture ≥ 10%, and a metallographic structure of fine pearlite + a small amount of ferrite, with pearlite lamellar spacing ≤ 0.2 μm and grain size ≥ grade 8.

5. The method for producing wire rod for high-strength prestressed steel bars based on manganese-silicon alloy according to claim 1, characterized in that, The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.30%, Si: 1.35%, Mn: 1.55%, P: 0.015%, S: 0.010%, Cr: 0.20%, V: 0.08%, Ti: 0.020%, N: 0.012%, with the balance being Fe and unavoidable impurities.

6. The method for producing wire rod for high-strength prestressed steel bars based on manganese-silicon alloy according to claim 1, characterized in that, The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.32%, Si: 1.45%, Mn: 1.65%, P: 0.018%, S: 0.012%, Cr: 0.25%, V: 0.10%, Ti: 0.025%, N: 0.013%, with the balance being Fe and unavoidable impurities.

7. The method for producing wire rod for high-strength prestressed steel bars based on manganese-silicon alloy according to claim 1, characterized in that, The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.29%, Si: 1.30%, Mn: 1.50%, P: 0.016%, S: 0.009%, Cr: 0.15%, V: 0.07%, Ti: 0.018%, N: 0.011%, with the balance being Fe and unavoidable impurities.