Hot-rolled wire rod 30si2mn for prestressed steel bar and preparation method thereof

Abstract

The application discloses a hot-rolled wire rod 30Si2Mn for prestressed steel rods and a preparation method thereof. The hot-rolled wire rod comprises the following components in percentage by weight: C: 0.28%-0.33%, Si: 1.55%-1.70%, Mn: 0.65%-0.80%, P: <=0.020%, S: <=0.020%, Ni: <=0.20%, Cr: <=0.20%, Cu: <=0.20%, H <=0.0003%, and the balance of Fe and inevitable impurity elements. By designing the optimal component system, optimizing the controlled rolling and controlled cooling process, improving the mechanical properties of the wire rod, prolonging the wire rod online slow cooling time by taking process measures, releasing hydrogen and internal stress, controlling the hydrogen content below 3ppm, and achieving the section shrinkage rate above 50% after natural aging, hydrogen-induced delayed fracture of the prestressed steel rod is effectively avoided, and the safety of the construction engineering is improved.

Description

Technical Field

[0001] This invention relates to the fields of materials and metallurgy, and more specifically, to a hot-rolled wire rod 30Si2Mn for prestressed steel bars and its preparation method. Background Technology

[0002] 30MnSi hot-rolled wire rod is widely used in large-scale projects such as high-rise civil buildings, ports, and water conservancy projects due to its excellent strength-toughness ratio, low relaxation, weldability, and strong bond with concrete. It is the most commonly used product for manufacturing ordinary prestressed concrete steel bars. Since 30MnSi hot-rolled wire rod requires drawing, it needs appropriate strength, good plasticity, and good through-strength to ensure good drawing performance and stability. Therefore, high requirements are placed on the cooling process after rolling.

[0003] Patent document CN101245433A discloses a wire rod for prestressed concrete steel bars and its manufacturing process. The process involves a converter, LF ladle refining, continuous casting, and high-speed wire rod mill, with a delayed cooling process used during rolling. However, this delayed cooling process is primarily carried out on the air-cooled transport line. Due to the limited length of the insulation section on the air-cooled transport line, the slow cooling time is insufficient to release the hydrogen and internal stress in the wire rod, posing a potential risk of hydrogen-induced delayed fracture of the prestressed steel bars.

[0004] Patent document CN114101368A discloses a method for producing high-silicon prestressed steel bars. The controlled cooling process involves shutting down the insulation cover and fan of the Stellmore wire after coiling. This results in insufficient cooling time after coiling to release hydrogen and internal stress in the wire rod, posing a risk of hydrogen-induced delayed fracture in the prestressed steel bars. Furthermore, the existing production cost of 30MnSi prestressed concrete steel bars is high, and the overall pass rate is low. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a hot-rolled wire rod of 30Si2Mn for prestressed steel bars and its preparation method. By optimizing the controlled rolling and cooling process, the mechanical properties of the wire rod are improved. The residual heat of the wire rod is used to delay the slow cooling time of the wire rod after coiling, which is conducive to the release of hydrogen and internal stress, avoids delayed fracture of prestressed steel bars, improves the mechanical properties of the wire rod, reduces alloy costs, and enhances product competitiveness.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A hot-rolled wire rod 30Si2Mn for prestressed steel bars comprises the following components by weight percentage: C: 0.28%–0.33%, Si: 1.55%–1.70%, Mn: 0.65%–0.80%, P: ≤0.020%, S: ≤0.020%, Ni: ≤0.20%, Cr: ≤0.20%, Cu: ≤0.20%, H ≤0.0003%, with the balance being Fe and unavoidable impurity elements.

[0008] The present invention also discloses a method for preparing hot-rolled wire rod 30Si2Mn for prestressed steel bars as described above. The preparation method includes hot metal pretreatment, converter smelting, argon blowing at an argon station, LF refining, continuous casting process, heating process, rolling process and cooling process.

[0009] In the converter smelting process, the furnace charge includes molten iron pretreated by the aforementioned iron and scrap steel, with argon blowing throughout the process; the final composition of the converter is: C: 0.10% to 0.15%; deoxidizer, ferrosilicon, and ferrosilicon-manganese alloy are added for deoxidation and alloying when the steel is tapped to 1 / 4 to 3 / 4 of its capacity;

[0010] In the argon blowing process at the argon station, molten steel after being tapped from the converter smelting furnace is fed into the argon station for argon blowing treatment.

[0011] In the heating process, the billet that comes off the continuous casting line is sent into the heating furnace for heating;

[0012] In the rolling process, the heated billet is first subjected to high-pressure water descaling, and then sequentially undergoes rough rolling, intermediate rolling, pre-finish rolling, finish rolling, and wire drawing.

[0013] In the cooling process, after the wire is spun, 2 to 4 220,000m sections of the air-cooled transport line are opened. 3 The high-volume variable frequency fan provides rapid cooling, and the air volume is adjusted by frequency conversion (35Hz~50Hz). After the fan cools to 650℃~700℃, it enters the air-cooled transport line and is slowly cooled by the residual heat under the insulation cover. After exiting the insulation cover, the coiling and transporting are carried out by the standing coiling frame station, and the unloading station flips and unloads the coils onto the C-hook of the PF line for unwinding and cooling. An insulation channel is set up outside the PF transport line, and the wire is transported on the PF transport line inside the insulation channel.

[0014] Implementing the embodiments of the present invention will have the following beneficial effects:

[0015] (1) This invention improves the mechanical properties of wire rod by optimizing the controlled rolling and cooling process. After cooling by the fan, the residual heat of the wire rod is used for slow cooling through an insulation cover, a vertical core-winding frame transport line, and an external insulation channel on the PF transport line, extending the online slow cooling time of the wire rod. This effectively releases hydrogen and internal stress in the wire rod, and the hydrogen content can be controlled below 3ppm. The section shrinkage rate of the wire rod reaches more than 45%, and can reach more than 50% after natural aging. This can avoid hydrogen-induced delayed fracture of prestressed steel bars and improve the safety performance of construction projects.

[0016] (2) This invention can solve the problems of low temperature in the winter production environment of steel enterprises, long aging period of prestressed steel bars and long time of user capital occupation, shorten the natural aging period by more than 10 days and improve product competitiveness.

[0017] (3) The present invention uses a fan to quickly cool the wire after it is spun to improve its mechanical properties, which can reduce the cost of the alloy and save alloy resources.

[0018] (4) The present invention utilizes the production and promotion of high-strength prestressed steel bar wire rods, which is in line with the policies of low-carbon, energy-saving and emission-reduction development and has significant social benefits. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0020] I. Chemical composition and mechanical properties

[0021] This invention discloses a hot-rolled wire rod 30Si2Mn for prestressed steel bars, comprising the following components by weight percentage: C: 0.28%–0.33%, Si: 1.55%–1.70%, Mn: 0.65%–0.80%, P: ≤0.020%, S: ≤0.020%, Ni: ≤0.20%, Cr: ≤0.20%, Cu: ≤0.20%, H ≤0.0003%, with the balance being Fe and unavoidable impurity elements.

[0022] Specifically, carbon (C) has a significant impact on the mechanical properties of 30Si2Mn hot-rolled wire rod. To ensure good strength and toughness in steel bars, both strength and plasticity must be balanced; therefore, the C content is controlled between 0.28% and 0.33%. Si (Si) with a mass fraction of not less than 1.0% can effectively inhibit the propagation of microcracks in high-strength prestressed steel bars and improve their ability to prevent delayed fracture; therefore, the Si content is controlled between 1.55% and 1.70%. Mn (Mn) can improve the tensile strength of hot-rolled wire rod, while also improving plasticity and toughness, and eliminating hot brittleness. Therefore, the Mn content is controlled between 0.65% and 0.80%. P (P) and S (S) are harmful impurity elements in steel. P easily segregates in steel, significantly reducing plasticity and toughness and increasing brittleness. S easily causes hot brittleness in steel, reducing its ductility and toughness. Therefore, P ≤ 0.020% and S ≤ 0.020% in hot-rolled wire rod. Ni helps improve the toughness of weld metal and lowers the ductile-brittle transition temperature. Furthermore, Ni effectively prevents network cracking caused by the hot brittleness of Cu and significantly improves the corrosion resistance of steel and weld. Therefore, Ni ≤ 0.20%. When the Cu content is less than 0.5%, it improves weld strength through solid solution strengthening, lowers the initiation temperature of acicular ferrite, and increases the acicular ferrite content. Therefore, Cu ≤ 0.20%. The Cr content not only improves weld toughness but also forms dispersed carbides with carbon, increasing weld strength. Cr helps increase the acicular ferrite content, reduces proeutectoid ferrite, and refines ferrite grains, improving weld strength and toughness. Cr also helps maintain high weld performance after heat treatment. Therefore, Cr ≤ 0.20%. H is the main cause of delayed fracture in prestressed steel bars; H ≤ 0.0003% in hot-rolled wire rod.

[0023] The mechanical properties of the hot-rolled wire rod 30Si2Mn for prestressed steel bars of the present invention are as follows: tensile strength of hot-rolled wire rod is 680MPa~800MPa; reduction of area of ​​hot-rolled wire rod is ≥45%; elongation after fracture of hot-rolled wire rod is ≥20%.

[0024] Specifically, this invention involves extensive and repeated experimental research to further optimize the composition ratio of hot-rolled wire rod, selecting the optimal ratio range to achieve both improved quality and greater economic efficiency and convenience.

[0025] II. Production Process Technology

[0026] A method for preparing hot-rolled wire rod 30Si2Mn for prestressed steel bars as described in any embodiment of the present invention includes hot metal pretreatment, converter smelting, argon blowing at an argon station, LF refining, continuous casting process, heating process, rolling process, and cooling process.

[0027] Based on the above technical solution, the preparation method further includes:

[0028] S1. In the pretreatment of molten iron, the molten iron is desulfurized, and the S content of the molten iron after pre-desulfurization is ≤0.050%.

[0029] In one specific embodiment, the molten iron undergoes pre-treatment for desulfurization and slag removal before leaving the station. After pre-desulfurization, the molten iron has an S content of ≤0.050%. When the molten iron has an S content of ≤0.050%, desulfurization may not be performed.

[0030] S2. In converter smelting, the furnace charge includes molten iron pretreated as described above and scrap steel, with bottom blowing argon throughout the process; the final converter composition is: C: 0.10%–0.15%; deoxidizers, ferrosilicon, and ferrosilicon-manganese alloys are added for deoxidation and alloying when the steel is tapped 1 / 4 to 3 / 4 of the way through; the mass percentage of scrap steel is 10%–15%. Specifically, converter smelting adopts the "blast furnace molten iron + scrap steel" method, strictly controlling the amount of slag discharged during the tapping process to avoid the diffusion of harmful elements such as P and S from the slag into the molten steel during the refining process.

[0031] S3. In the argon blowing process at the argon station, molten steel after being tapped from the converter is fed into the argon station for argon blowing treatment. Specifically, the argon blowing at the argon station homogenizes the composition and temperature of the molten steel, promoting the flotation of inclusions.

[0032] In S4 and LF refining, the LF furnace arrival temperature is 1520-1540℃; the LF furnace cover must not leak water, and the platform material must be dry. It is strictly forbidden for the platform hopper alloy and carbon raiser storage areas to be damp; oxygen is determined during start-up and ladle change, and the oxygen value is <20ppm; calcium treatment is not required for continuous casting furnaces; soft argon blowing is ≥12min to ensure the argon blowing effect, of which medium blowing is performed for 5min first, followed by weak blowing; the LF furnace outlet temperature is 1543-1557℃.

[0033] S5. In the continuous casting process, electromagnetic stirring in the crystallizer and electromagnetic stirring at the end are adopted; the electromagnetic stirring current in the crystallizer is 280A, the frequency is 5Hz, and it operates in both forward and reverse directions; the electromagnetic stirring current at the end is 250A, the frequency is 8Hz, and it operates continuously; full-process protective casting is used; the working liquid level of molten steel in the tundish is controlled at ≥600mm, and the superheat is controlled at 20℃~35℃; medium-carbon protective slag is used in the crystallizer; the fluctuation of the liquid level in the crystallizer is controlled within ±5mm; the K value in the secondary cooling zone is 1.2; the casting speed is 2.4m / min; the cross-section of the continuously cast billet is 150mm×150mm; after cooling on the cooling bed, the continuously cast billet is slowly cooled in the slow cooling pit for at least 48 hours; the liquidus temperature is 1492℃. Specifically, by adopting full-process protective casting, electromagnetic stirring in the crystallizer and electromagnetic stirring at the end, and crystallizer liquid level control, the homogenization of the internal quality of the cast billet is improved.

[0034] S6. In the heating process, the billet that comes off the continuous casting line is sent into the heating furnace for heating.

[0035] S7. In the rolling process, the heated billet is first subjected to high-pressure water descaling treatment, and then successively undergoes rough rolling, intermediate rolling, pre-finish rolling, finish rolling, and wire drawing.

[0036] S8. In the cooling process, after the wire is spun out, it is rapidly cooled on the air-cooled transport line. After being cooled to 650℃~700℃ by the fan, it enters the air-cooled transport line insulation cover to use the residual heat for slow cooling. After exiting the insulation cover, the wire is collected and transported by the standing core winding frame station, and unwound at the unwinding station onto the C-shaped hook of the PF transport line for loose winding and cooling. An insulation channel is set outside the PF transport line, and the wire is transported on the PF transport line in the insulation channel and slow cooled online using the residual heat.

[0037] Specifically, this invention optimizes the controlled rolling and cooling process by using a vertical core-coiling frame for coiling, transportation, and online slow cooling via the PF line's insulation channel, and then utilizing the residual heat for online annealing of the wire rod. Compared to other steel companies, this extends the slow cooling time of the wire rod, which is beneficial for the release of hydrogen and internal stress. Furthermore, since the PF transport line suffers from problems such as rapid cooling at the coil ends and uneven cooling, this invention reduces the cooling rate by first transporting the coiled sections via a vertical core-coiling frame, which is more conducive to the slow cooling of prestressed steel bars and the release of hydrogen, avoiding excessively rapid cooling at the beginning and end. In addition, after being unloaded and re-coiled on the vertical core-coiling frame transport line, the coils enter the PF transport line's insulation channel for continued slow cooling using residual heat.

[0038] In one specific embodiment, step S3 further includes: the argon blowing time at the argon station is ≥5 min, and the temperature after treatment is 1543℃~1557℃.

[0039] In one specific embodiment, step S6 further includes: a preheating section at 830℃~930℃, a heating section at 1030℃~1130℃, a soaking section at 1090℃~1150℃, and a heating time of 1.5h~2.5h. Specifically, due to the high silicon content of 30Si2Mn, a low-temperature heating process is adopted to avoid excessively high heating temperatures and excessively long heating times, which could easily lead to the formation of iron oxide scale that is difficult to remove.

[0040] In one specific embodiment, step S7 further includes: since the iron oxide scale of high-silicon steel is difficult to remove, the high-pressure water descaling pressure is adjusted to ≥18MPa to ensure sufficient removal of the iron oxide scale from the billet surface. The initial rolling temperature is 950℃~1000℃. Low-temperature initial rolling helps to reduce the billet heating temperature and avoid the formation of Widmanstätten abnormal structure due to excessive heating temperature. After roughing, intermediate rolling, and pre-finishing rolling, the continuously cast square billet is cooled in a water tank. The water tank is cooled to a temperature of 860℃~900℃ for finish rolling. Lowering the finish rolling temperature helps to refine the grains and improve mechanical properties. After finish rolling, the billet is cooled in a water tank and homogenized. The coiling temperature is 860℃~900℃. The coiling temperature is 500℃~550℃.

[0041] In one specific embodiment, step S8 further includes: rapid cooling on the air-cooled conveyor line after spinning; cooling to 650℃~700℃ by the fan; then entering the air-cooled conveyor line insulation cover for slow cooling using residual heat; the number of insulation covers on the air-cooled conveyor line is ≥16; insulation covers No. 1 to No. 4 are opened, and insulation covers No. 5 to No. 16 are closed; the speed of the first section of the air-cooled roller conveyor is set to 0.25m / s, and the speed of other roller conveyors is increased by 3%~7%; the winding temperature at the winding station is 450℃~550℃; the temperature exiting the insulation channel is 150℃, and the temperature of the insulation channel is 60℃~80℃.

[0042] In one specific embodiment, step S8 further includes: setting the number of fans to be turned on according to the seasonal ambient temperature and different specifications; turning on 2 fans for 8mm specifications; turning on 3 to 4 large air volume variable frequency fans (35 to 50 Hz) for 10mm, 12mm, and 14mm specifications, and adjusting the air volume by frequency conversion; the insulation section is about 80m long; the number of vertical core frames is greater than 20; an insulation channel is set outside the vertical core frame unloading station to the PF transport line, with heating pipes inside; before changing the steel grade, the number of coils left in the insulation channel is greater than 20, using residual heat to reduce the temperature drop of the insulation channel.

[0043] By optimizing the above-mentioned process parameters, the hot-rolled wire rod produced by this invention has excellent mechanical properties. It can solve the problems of low temperature in the winter production environment of steel enterprises, long aging period of wire rod for prestressed steel bars, and long time of capital occupation for users. It can shorten the natural aging period by more than 10 days and improve product competitiveness.

[0044] The following are specific embodiments.

[0045] Example 1

[0046] I. Preparation of 30Si2Mn in this embodiment

[0047] Referring to the above process, a steel plant adopts hot metal pretreatment, converter smelting, argon blowing at the argon station, LF refining, and continuous casting of billets using a continuous casting machine (crystallizer electromagnetic stirring and end electromagnetic stirring, full-process protective casting; tundish molten steel working level control ≥600mm, crystallizer liquid level automatic control ±5mm, superheat ≤35℃). The steel rolling mill uses a high-speed wire rod walking beam furnace to heat continuously cast square billets. A high-pressure water descaling system (high-pressure descaling water pressure ≥18MPa) is used. The initial rolling temperature is 950℃~1000℃. The billets are rolled through a roughing mill, intermediate mill, and pre-finishing mill. The mills cut off the head and tail of the billets. Cooling water tanks control the temperature at the finishing mill, which is 860℃~900℃. Three cooling water tanks (with a uniform temperature section in the middle) provide cooling and uniform temperature. The wire drawing temperature is 860℃~900℃. After wire drawing, the billets are rapidly cooled to 650℃~700℃ by a fan before entering an insulation hood for slow cooling. After air cooling, the insulation hood is completely closed. The number of fans to be turned on is set according to the seasonal ambient temperature and specifications. The air volume is adjusted by frequency conversion (35-50Hz). Two fans are turned on for 8mm specifications, and three to four large-volume frequency conversion fans of 220,000 m3 / h are turned on for 10mm, 12mm, and 14mm specifications. The first section of the air-cooled roller conveyor is set at 0.25m / s, and the speed of other sections of the roller conveyor is 3% to 7%. The winding temperature is 500℃ to 550℃. After exiting the insulation cover, the winding enters the winding station and is wound by vertical core frame and transported by vertical core frame transport line. After unwinding and unloading, the winding enters the PF transport line. The PF transport line is equipped with an insulation channel with a temperature of about 60℃ to 80℃. In the insulation channel, the residual heat is used for slow cooling and online annealing treatment. The temperature of the winding exits the insulation channel is about 150℃.

[0048] The following are the test results of the products obtained by the casting method of this embodiment. Table 1 shows the chemical composition test results of this embodiment 1; Table 2 shows the low-magnification defect inspection results of the billet in this embodiment 1; Table 3 shows the specific process parameters of the heating temperature in this embodiment 1; Table 4 shows the controlled cooling process parameters of the air-cooled transport line in this embodiment 1; and Table 5 shows the mechanical property test results of the product in this embodiment 1.

[0049] Table 1. Results of chemical composition detection in Example 1

[0050]

[0051]

[0052] Table 2. Results of low-magnification defect inspection of the billet in Example 1 of this embodiment.

[0053]

[0054] Table 3. Specific process parameters for heating temperature in Example 1 of this embodiment.

[0055] Preheating section / ℃ Heating section / ℃ Heat soaking section / ℃ Furnace time / h 830～930 1030～1130 1090～1150 1.5～2.5

[0056] Table 4. Cooling process parameters for the air-cooled transport line in Example 1

[0057]

[0058] Table 5. Test results of the mechanical properties of the product in Example 1 of this embodiment.

[0059]

[0060] As shown in the table above, this invention, through designing an optimal composition system and optimizing the controlled rolling and cooling process, extends the slow cooling time of the coiled wire rod after coiling by using a vertical core with a transport line and a PF transport line insulation channel. Utilizing the residual heat of the wire rod for online annealing facilitates the release of hydrogen and internal stress. The hydrogen content in the section reduction rate can be controlled below 3 ppm, and the section reduction rate can exceed 45%, reaching over 50% after natural aging. This invention avoids hydrogen-induced delayed fracture of prestressed steel bars, ensuring the safety performance of construction projects. It also solves the problems of low operating temperatures in winter production environments for steel enterprises, long aging periods for prestressed steel bar wire rods, and prolonged capital tied up in user funds. It shortens the natural aging period of wire rods, improves product competitiveness, and aligns with the policies of low-carbon, energy-saving, emission-reduction, and waste-to-energy development, demonstrating significant social benefits.

[0061] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A hot-rolled wire rod of 30Si2Mn for prestressed steel bars, characterized in that, It comprises the following components by weight percentage: C: 0.28%–0.33%, Si: 1.55%–1.70%, Mn: 0.65%–0.80%, P: ≤0.020%, S: ≤0.020%, Ni: ≤0.20%, Cr: ≤0.20%, Cu: ≤0.20%, H ≤0.0003%, with the balance being Fe and unavoidable impurity elements.

2. The 30Si2Mn hot-rolled wire rod for prestressed steel bars according to claim 1, characterized in that, The tensile strength of the hot-rolled wire rod is 680MPa to 800MPa; The elongation after fracture of the hot-rolled wire rod is ≥20%; The section shrinkage rate of the hot-rolled wire rod is ≥45%.

3. A method for preparing hot-rolled wire rod 30Si2Mn for prestressed steel bars as described in any one of claims 1-2, characterized in that, The preparation method includes hot metal pretreatment, converter smelting, argon blowing at an argon station, LF refining, continuous casting process, heating process, rolling process, and cooling process. In the converter smelting process, the furnace charge includes molten iron pretreated by the aforementioned iron and scrap steel, with argon blowing throughout the process; the final composition of the converter is: C: 0.10% to 0.15%; deoxidizer, ferrosilicon, and ferrosilicon-manganese alloy are added for deoxidation and alloying when the steel is tapped to 1 / 4 to 3 / 4 of its capacity; In the argon blowing process at the argon station, molten steel after being tapped from the converter smelting furnace is fed into the argon station for argon blowing treatment. In the heating process, the billet that comes off the continuous casting line is sent into the heating furnace for heating; In the rolling process, the heated billet is first subjected to high-pressure water descaling, and then sequentially undergoes rough rolling, intermediate rolling, pre-finish rolling, finish rolling, and wire drawing. In the cooling process, after the yarn is spun, it is rapidly cooled on the air-cooled transport line. After being cooled to 650℃~700℃ by the fan, it enters the air-cooled transport line insulation cover to use the residual heat for slow cooling. After exiting the insulation cover, the coiling and transporting are carried out by the standing core frame station, and the unloading station flips and unloads the coil onto the C-type hook of the PF line for loose cooling. The PF transport line is equipped with an insulated channel, and the wire is transported on the PF transport line inside the insulated channel.

4. The preparation method according to claim 3, characterized in that, In the molten iron pretreatment, the molten iron is desulfurized, and the sulfur content of the molten iron after pre-desulfurization is ≤0.05%.

5. The preparation method according to claim 3, characterized in that, The argon blowing time at the argon station is ≥5 min, and the temperature after treatment is 1543℃~1557℃.

6. The preparation method according to claim 3, characterized in that, In the LF refining process, the LF furnace arrival temperature is 1520-1540℃; oxygen is constant during start-up and batch change, with a constant oxygen value of <20ppm; no calcium treatment is performed during continuous casting; soft argon blowing is ≥12min, including 5min of medium blowing followed by weak blowing; the LF furnace outlet temperature is 1543-1557℃. In the continuous casting process: electromagnetic stirring in the crystallizer and electromagnetic stirring at the end are adopted; the electromagnetic stirring current in the crystallizer is 280A, the frequency is 5Hz, and it can be rotated in both directions; the electromagnetic stirring current at the end is 250A, the frequency is 8Hz, and it is continuous; the entire process is protected during casting; the working liquid level of the molten steel in the tundish is controlled at ≥600mm, and the superheat is controlled at 20℃~35℃; medium carbon protective slag is used in the crystallizer; the fluctuation of the liquid level in the crystallizer is controlled within ±5mm; the K value in the secondary cooling zone is 1.2; the casting speed is 2.4m / min; the cross-section of the continuously cast square billet is 150mm×150mm; after cooling on the cooling bed, the continuously cast square billet is slowly cooled in the slow cooling pit for 48 hours; the liquidus temperature is 1492℃.

7. The preparation method according to claim 3, characterized in that, In the heating process, the preheating section is 830℃~930℃, the heating section is 1030℃~1130℃, the soaking section is 1090℃~1150℃, and the heating temperature is 1050~1100℃.

8. The preparation method according to claim 3, characterized in that, In the rolling process, high-pressure water descaling is performed with a descaling pressure ≥18MPa; the initial rolling temperature is 950℃~1000℃; the rolling mill passes through a roughing mill, intermediate mill, pre-finishing mill, cooling water tank, and finishing mill; the temperature entering the finishing mill is 860℃~900℃; after finishing, three sets of water tanks and a uniform temperature section are set up; the wire drawing temperature is 860℃~900℃.

9. The preparation method according to claim 3, characterized in that, In the cooling process, after spinning, the yarn is rapidly cooled on the air-cooled conveyor line. After being cooled to 650℃~700℃ by the fan, it enters the air-cooled conveyor line's insulation cover for slow cooling using residual heat. The number of insulation covers on the air-cooled conveyor line is ≥16. Insulation covers #1 to #4 are opened first, and insulation covers #5 to #16 are closed. The speed of the first section of the air-cooled roller conveyor is set to 0.25m / s, and the speed of other roller conveyors is increased by 3%~7%. The winding temperature at the winding station is 450℃~550℃. The temperature exiting the insulation channel is 150℃, and the temperature in the insulation channel is 60℃~80℃.

10. The preparation method according to claim 3, characterized in that, The air-cooled transport line operates 3 to 4 aircraft, totaling 220,000 m. 3 / h high-volume variable frequency fan; The number of vertical core frames is greater than 20; The vertical core frame station is connected to the PF transport line by an insulated channel with heating pipes inside; before changing the steel grade, the number of coils left in the insulated channel is greater than 20 coils.

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