Steel rebar rolled by a direct rolling method without heating

Abstract

The application provides a kind of reinforcing bar rolled by heating-free straight rolling method, and the chemical composition of the reinforcing bar is as follows: C: 0.20-0.25wt%, Si: 0.40-0.55wt%, Mn: 1.10-1.25wt%, P: ≤0.045wt%, S: ≤0.045wt%, Nb: ≤0.004wt%, Ti: ≤0.007wt%, Alt: ≤0.006wt%, V: 0.02-0.03wt%, N: 0.005-0.011wt%. By the technical scheme of the application, the temperature difference between the head and tail of the reinforcing bar obtained by using the heating-free straight rolling process can be controlled within a reasonable range, and the problem of poor consistency of the head and tail strength caused by the excessive temperature difference between the head and tail can be eliminated.

Description

[0001] This invention is a divisional application, parent application number: 2022104713820, application date: April 28, 2022, invention title: A method for direct rolling of reinforcing bars without heating and reinforcing bars rolled by the method for direct rolling without heating. Technical Field

[0002] This invention relates to the field of steel production technology, and in particular to a steel bar rolled by a direct rolling method without heating. Background Technology

[0003] Direct rolling of billets without heating has become the current development direction of bar and wire rod production. In this process, the billet does not need to be reheated in a heating furnace and can be directly rolled into the rolling mill, thus improving efficiency and reducing production costs.

[0004] In the process of realizing this invention, the inventors discovered at least the following problems in the prior art:

[0005] Because directly rolled billets are not reheated in a furnace, the head of the billet is produced first in the continuous casting machine, followed by the tail. Therefore, the head of the billet has a lower temperature than the tail, resulting in high mechanical strength at the head and low strength at the tail of the rolled steel, thus affecting product quality stability. Therefore, controlling the temperature difference between the head and tail of the steel bar within a reasonable range during direct rolling of billets without reheating, thereby ensuring stable mechanical properties at both ends of the final product, is a problem that needs to be solved. Summary of the Invention

[0006] This invention provides a method for direct rolling of reinforcing bars without heating, in order to solve the problem of large differences in mechanical strength between the head and tail of finished reinforcing bars obtained by existing direct rolling methods without heating.

[0007] To achieve the above objectives, embodiments of the present invention provide a method for direct rolling of reinforcing bars without heating, comprising:

[0008] The process involves blast furnace iron smelting, iron smelting desulfurization pretreatment, converter steel smelting, billet continuous casting, hot rolling, and fixed-length shearing.

[0009] Among them, the billet heating process between billet continuous casting and hot rolling was eliminated;

[0010] In the continuous casting process of billets, the temperature difference between the head and tail of the billet is controlled between 20℃ and 40℃.

[0011] In the hot continuous rolling process, the temperature difference between the head and tail of the rolled piece is controlled between 20℃ and 30℃.

[0012] Furthermore, prior to the blast furnace iron smelting process, the following steps are also included:

[0013] The chemical composition and weight percentage of the reinforcing steel are determined as follows: C: 0.20~0.25Wt%, Si: 0.40~0.55Wt%, Mn: 1.10~1.25Wt%, P: ≤0.045Wt%, S: ≤0.045Wt%, Nb: ≤0.004Wt%, Ti: ≤0.007Wt%, Alt: ≤0.006Wt%, V: 0.02~0.03Wt%, N: 0.005~0.011Wt.

[0014] Furthermore, the chemical composition and weight percentage of the reinforcing steel are as follows: C: 0.23 wt%, Si: 0.50 wt%, Mn: 1.19 wt%, P: 0.030 wt%, S: 0.026 wt%, Nb: 0.002 wt%, Ti: 0.002 wt%, Alt: 0.0019 wt%, V: 0.026 wt%, N: 0.0075 wt%.

[0015] Furthermore, the temperature difference between the head and tail of the cast billet is controlled within 20℃ to 40℃, specifically including:

[0016] A billet length-cutting process is set up in the billet continuous casting process;

[0017] The billet cutting process is completed using hydraulic shears; the billet cutting process specifically includes:

[0018] A contact-type fixed-length device is installed on the billet feeding roller conveyor at a predetermined distance from the hydraulic shear;

[0019] When the head of the billet comes into contact with the contact-type length-fixing device, the contact-type length-fixing device outputs a shearing action signal to the control system.

[0020] The control system sends action commands to the hydraulic shears;

[0021] The hydraulic shears cut the casting billet according to the action command.

[0022] Furthermore, controlling the temperature difference between the head and tail of the cast billet to be between 20℃ and 40℃ also includes:

[0023] After the billet cutting process, a scale removal process, a measurement process, and a controlled cooling process for the billet are set up; among them...

[0024] In the oxide scale removal process, the oxide scale on the side of the billet is removed by a wire brush;

[0025] In the measurement process, the temperature of the side surface of the billet after removing the oxide scale is recorded at predetermined time intervals using a pyrometer, and a billet temperature curve is generated based on the measurement results. The billet temperature curve is used to reflect the temperature difference between different positions of the billet from the head to the tail.

[0026] The controlled cooling process of the billet is completed based on the billet temperature curve.

[0027] Furthermore, the controlled cooling process for the cast billet is completed based on the billet temperature profile, specifically including:

[0028] Based on the billet temperature profile, determine the starting position on the billet that is 20°C higher than the temperature at the head of the billet.

[0029] Water is sprayed onto the portion of the billet after the initial position by four billet cooling nozzles located at the upper left, lower left, lower right, and upper right positions on the outer side of the billet.

[0030] The water spray intensity of each billet cooling nozzle is adjusted in real time based on the billet temperature curve and the billet's moving speed.

[0031] Furthermore, the temperature difference between the head and tail of the rolled piece is controlled within 20℃ to 30℃, specifically including:

[0032] The hot continuous rolling process is sequentially set up with roughing, roughing controlled cooling, intermediate rolling, intermediate controlled cooling, finishing rolling, and finishing controlled cooling processes.

[0033] Temperature measurement is performed during the rough rolling process, and a first temperature curve is generated based on the measurement results.

[0034] The controlled cooling process in rough rolling specifically includes:

[0035] Water spray nozzles are installed on the outside of the rolled piece;

[0036] Select the starting position for water spraying on the rolled piece;

[0037] Water is sprayed onto the portion of the rolled piece after the initial water spraying position using a water nozzle.

[0038] The spray intensity of each water nozzle is adjusted in real time based on the first temperature curve.

[0039] Furthermore, controlling the temperature difference between the head and tail of the rolled piece to be between 20℃ and 30℃ also includes:

[0040] Temperature measurements are performed during the intermediate rolling process, and a second temperature profile is generated based on the measurement results.

[0041] The intermediate rolling controlled cooling process uses a water purifier to adjust the temperature of the rolled piece, and adjusts the controlled cooling intensity of the intermediate rolling controlled cooling process in real time according to the second temperature curve;

[0042] Temperature measurements are performed during the finishing rolling process, and a third temperature profile is generated based on the measurement results.

[0043] The finishing rolling controlled cooling process uses multi-stage coolers to adjust the temperature of the rolled piece, and adjusts the cooling intensity of the finishing rolling controlled cooling process in real time according to the third temperature curve.

[0044] Furthermore, after the controlled cooling process of finishing rolling, the following steps are also included:

[0045] Temperature measurement and controlled cooling processes after finishing rolling;

[0046] Among them, temperature measurement is carried out in the temperature measurement process after finishing rolling, and a fourth temperature curve is generated based on the measurement results;

[0047] The controlled cooling process after finishing rolling uses a multi-stage cooler to adjust the temperature of the rolled piece, and the cooling intensity of the controlled cooling process after finishing rolling is adjusted in real time according to the fourth temperature curve.

[0048] Furthermore, the process before finishing rolling also includes pre-finishing rolling and controlled cooling pre-finishing rolling.

[0049] Temperature measurement is performed during the pre-finishing rolling process, and a fifth temperature curve is generated based on the measurement results;

[0050] The pre-finishing rolling controlled cooling process uses multi-stage nozzles to adjust the temperature of the rolled piece, and adjusts the cooling intensity of the pre-finishing rolling controlled cooling process in real time according to the fifth temperature curve.

[0051] The present invention also provides a steel bar rolled by a direct rolling method without heating, wherein the chemical composition and weight percentage of the steel bar are: C: 0.20-0.25 wt%, Si: 0.40-0.55 wt%, Mn: 1.10-1.25 wt%, P: ≤0.045 wt%, S: ≤0.045 wt%, Nb: ≤0.004 wt%, Ti: ≤0.007 wt%, Alt: ≤0.006 wt%, V: 0.02-0.03 wt%, N: 0.005-0.011 wt%, using the direct rolling method for steel bars without heating described above.

[0052] Furthermore, the chemical composition and weight percentage of the reinforcing steel are as follows: C: 0.23 wt%, Si: 0.50 wt%, Mn: 1.19 wt%, P: 0.030 wt%, S: 0.026 wt%, Nb: 0.002 wt%, Ti: 0.002 wt%, Alt: 0.0019 wt%, V: 0.026 wt%, N: 0.0075 wt%.

[0053] Furthermore, the reinforcing steel is HRB400E seismic-resistant reinforcing steel.

[0054] Furthermore, the specifications of the reinforcing bars are φ12-40mm.

[0055] Furthermore, the steel bar has a specification of φ28mm.

[0056] Furthermore, the reinforcing bars are formed by rolling a cast billet with a cross-section of 165mm × 165mm and a length of 11m.

[0057] The above technical solution has the following beneficial effects:

[0058] In this invention, the temperature difference between the head and tail of the reinforcing bar is adjusted through multi-level temperature control methods: 1. A simple and reliable contact-type mechanical length-cutting device combined with hydraulic shears allows for rapid cutting of the billet, reducing waiting time and temperature drop; 2. By measuring the surface temperature of the billet and forming a temperature trend line, the water spray intensity of each billet cooling nozzle is adjusted in real time according to the temperature trend line, thereby cooling the rear section of the billet and keeping the temperature difference between the head and tail of the billet within a reasonable range before entering the rolling mill; 3. A multi-level cooling control device is established during the rolling process, especially in the roughing section where a unique type of water spray nozzle is designed. All cooling control processes use the measured temperature trend line as a reference, achieving real-time adjustment of the temperature control at different positions on the rolled piece, effectively reducing the temperature difference between the head and tail of the rolled piece. The adoption of these multiple technical means ensures that the strength difference between the head and tail of the final product is also controlled within a reasonable range, significantly improving product quality stability. Attached Figure Description

[0059] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 This is a flowchart of a method for direct rolling of reinforcing bars without heating according to an embodiment of the present invention;

[0061] Figure 2 This is a schematic diagram of the equipment used for removing oxide scale, measuring billet temperature, and controlling billet cooling in the billet continuous casting process of this invention.

[0062] Figure 3 This is a schematic diagram of the arrangement of the controlled cooling nozzles for the cast billet in an embodiment of the present invention;

[0063] Figure 4 This is a schematic diagram of the spray protection range of the controlled cooling nozzle for the billet in an embodiment of the present invention. Figure 2 (View A in the middle);

[0064] Figure 5 This is a schematic diagram of the nozzle structure of the billet controlled cooling nozzle in an embodiment of the present invention;

[0065] Figure 6 This is a schematic diagram of the contact-type length-fixing device in the billet continuous casting process of this invention.

[0066] Reference numerals: 1. Cast billet; 11. Corner; 2. Special heat insulation cover; 3. Billet feeding roller conveyor; 31. Side plate of billet feeding roller conveyor; 4. Cast billet controlled cooling nozzle; 41. Spray hole; 42. Rectangular water spray coverage area; 5. High temperature meter; 6. Control system; 7. Wire brush; 8. Contact-type length fixing device; 81. Long connecting rod; 82. Moving contact; 83. Length fixing device support; 84. Static contact; 85. Protective cover; 87. Return spring. Detailed Implementation

[0067] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] like Figure 1 As shown, this embodiment of the invention provides a method for direct rolling of reinforcing bars without heating, comprising: sequentially performing blast furnace molten iron smelting, molten iron desulfurization pretreatment, converter molten steel smelting, billet continuous casting, hot continuous rolling, and length shearing processes; wherein, the billet heating process between billet continuous casting and hot continuous rolling is eliminated; in the billet continuous casting process, the temperature difference between the head and tail of the billet is controlled between 20℃ and 40℃; in the hot continuous rolling process, the temperature difference between the head and tail of the rolled piece is controlled between 20℃ and 30℃.

[0069] In the direct rolling process without heating, since the billet does not need to be reheated in a furnace, the temperature at the tail end of the billet is significantly higher than that at the head end, and the temperature increases closer to the tail end. Consequently, in subsequent processes, the tail end temperature of the rolled piece will also be significantly higher than that at the head end, resulting in inconsistent strength between the head and tail ends of the finished product and causing quality problems. Therefore, to solve this problem, it is necessary to control the head-tail temperature difference of the billet and the rolled piece separately during the billet continuous casting and hot rolling stages. Analysis and actual measurements have confirmed that controlling the temperature difference between the head and tail ends of the billet within 20℃~40℃, and simultaneously controlling the temperature difference between the head and tail ends of the rolled piece within 20℃~30℃, can effectively ensure the quality of the final steel reinforcement product, making its head-tail strength more consistent.

[0070] This rolling method eliminates the need for a heating furnace; the billet is fed directly into the rolling mill via a feed roller conveyor, eliminating the need for the billet to be fed into a heating furnace. Furthermore, to minimize billet temperature drop, a fully enclosed multi-layered insulation cover is used throughout the entire process from the continuous casting machine to the rolling mill inlet. The outer layer of the insulation cover is a steel shell, the middle layer is high-temperature resistant insulation cotton, and the inner layer is a high-temperature resistant reflective material, thereby minimizing heat loss.

[0071] Furthermore, prior to the blast furnace iron smelting process, the following steps are also included:

[0072] The chemical composition and weight percentage of the reinforcing steel are determined as follows: C: 0.20~0.25Wt%, Si: 0.40~0.55Wt%, Mn: 1.10~1.25Wt%, P: ≤0.045Wt%, S: ≤0.045Wt%, Nb: ≤0.004Wt%, Ti: ≤0.007Wt%, Alt: ≤0.006Wt%, V: 0.02~0.03Wt%, N: 0.005~0.011Wt.

[0073] To achieve better results, this application features a special component design:

[0074] 1) Reduce the addition of alloying elements with low solubility after austenitization in steel at direct rolling temperatures, such as Nb, Ti, and Al. These alloying elements form nitrides and carbides in steel at direct rolling temperatures with high melting points, making them difficult to dissolve. Furthermore, these elements increase the recrystallization temperature of austenite in steel, inhibiting recrystallization and grain growth after recrystallization during rolling, resulting in significant grain refinement and strengthening effects under direct rolling conditions. Adding these elements will amplify the impact of temperature changes on steel properties, increasing the temperature difference between the head and tail of the rolled steel and affecting product quality stability.

[0075] 2) Add an appropriate amount of vanadium. At the direct rolling temperature, vanadium nitrides and carbides are almost completely dissolved in the austenite region, and mainly play a precipitation strengthening role in steel.

[0076] 3) Control the nitrogen element. Nitrogen can enhance the strengthening effect of vanadium and reduce costs. It can be added in the form of silicon nitride. See Table 1.

[0077] 4) Control the Si and Mn content. Si and Mn play a solid solution strengthening role, and the strengthening effect is less affected by the billet temperature. Si contributes more to tensile strength, while Mn contributes equally to tensile strength and yield strength. Due to the low rolling temperature and stronger fine grain strengthening effect in direct rolling, a certain amount of Si is required to ensure a qualified strength-to-yield ratio.

[0078] Furthermore, the chemical composition and weight percentage of the steel reinforcement are as follows: C: 0.23 wt%, Si: 0.50 wt%, Mn: 1.19 wt%, P: 0.030 wt%, S: 0.026 wt%, Nb: 0.002 wt%, Ti: 0.002 wt%, Alt: 0.0019 wt%, V: 0.026 wt%, N: 0.0075 wt%.

[0079] Experiments have confirmed that selecting the above-mentioned values ​​for the chemical composition of the material yields better implementation results.

[0080] Furthermore, controlling the temperature difference between the head and tail of the billet to be between 20℃ and 40℃ specifically includes: setting a billet length-fixing shearing process in the billet continuous casting process; the billet length-fixing shearing process is completed by hydraulic shears; the billet length-fixing shearing process specifically includes: setting a contact-type length-fixing device at a predetermined distance from the hydraulic shears on the billet feeding roller conveyor; when the head of the billet contacts the contact-type length-fixing device, the contact-type length-fixing device outputs a shearing action signal to the control system; the control system issues an action command to the hydraulic shears; the hydraulic shears cut the billet according to the action command.

[0081] The billet length is controlled in two ways: contact mechanical device control and infrared imaging control. Before the stepped billet exit is formed, a stopper rod flow control + infrared imaging method is used to form the stepped billet exit. Afterwards, all the heat insulation covers are closed, the drawing speed of each flow is controlled to be equal, and the contact mechanical device (i.e., contact length control device) is switched to control the shearing to the specified length. Using the stepped billet exit method ensures that the billet can enter the high-speed billet conveyor immediately after shearing, and enter the rolling mill at the fastest speed, reducing the temperature drop during waiting time.

[0082] Continuous casting machines use hydraulic shears to cut the billets. Hydraulic shears offer high cutting speeds, reducing billet waiting time and temperature drop. The structure of the contact-type length-keeping device 8 is as follows: Figure 6As shown, a mechanical contact-type length-fixing device 8 is installed at the billet length-fixing point (e.g., 10 or 11 meters from the hydraulic shear). The contact-type length-fixing device 8 is equipped with a horizontally arranged long connecting rod 81, the middle of which is hinged to the length-fixing device support 83, and can rotate with the hinge point as the center. One end of the long connecting rod 81 extends into the inner side of the billet feeding roller 3 through an opening on the side plate 31 of the billet feeding roller and is located on the running trajectory of the billet 1. The other end is provided with a moving contact 82, and a stationary contact 84 is fixedly installed above the moving contact 82. The stationary contact 84 is electrically connected to the signal receiving end of the external control system 6 through a wire. When the billet 1 runs on the billet feeding roller 3 to the position of the contact-type length-fixing device 8, one end of the long connecting rod 81 extending towards the inside of the billet feeding roller 3 is pressed down, while the other end is lifted in the opposite direction (simultaneously stretching the return spring 87), causing the moving contact 82 to contact the stationary contact 84, thereby sending an electrical signal to the control system 6 (computer or PLC, etc.). The control system 6 immediately sends a shearing signal to the hydraulic shear, which then cuts the billet 1. After being cut, the billet 1 is sent away by the billet feeding roller 3. Under the tension of the return spring 87, the contact-type length-fixing device 8 resets (i.e., the long connecting rod 81 returns to its initial horizontal state). When the next billet 1 passes by again, the long connecting rod 81 of the contact-type length-fixing device 8 is pressed down again, and the control system 6 sends a billet shearing signal once more. By repeating the above steps, continuous billet shearing operations can be achieved. In this device, to prevent scratching of the billet 1, several cylindrical guide wheels can be installed at the end of the long connecting rod 81 extending towards the inner side of the billet feeding roller 3. When in contact with the billet 1, the guide wheels can rotate as the billet 1 moves. Meanwhile, to prevent foreign objects from falling in and affecting use, a protective cover 85 can be arranged on the outside of the device. When adjustment or maintenance is required, the protective cover 85 can be lifted and removed from above. Furthermore, to ensure reliable contact and avoid poor contact, the stationary contact 84 can be made of a long, elastic sheet of metal.

[0083] To minimize heat loss, the insulation cover between the straightening machine and the hydraulic shear of the continuous casting machine is not perforated. Instead, a small hole with a diameter of 10mm is made in the upper part of the insulation cover after the hydraulic shear at the billet length setting position to facilitate observation of the billet's position.

[0084] Furthermore, controlling the temperature difference between the head and tail of the billet within 20℃ to 40℃ further includes: setting up a scale removal process, a billet measurement process, and a billet controlled cooling process after the length shearing process in the billet continuous casting process; wherein, in the scale removal process, the scale on the side of the billet is removed by a wire brush; in the billet measurement process, the temperature of the side surface of the billet after scale removal is recorded and measured at predetermined time intervals by a pyrometer, and a billet temperature curve is generated based on the measurement results, the billet temperature curve being used to reflect the temperature difference between different positions of the billet from head to tail; and the billet controlled cooling process is completed based on the billet temperature curve.

[0085] To control the temperature difference between the head and tail of the billet, this application employs a specially designed billet cooling nozzle to cool the higher-temperature sections at the rear of the billet, bringing their temperature closer to that of the head. To effectively control temperature changes, the water output of the nozzle needs to be quantified and controlled. Therefore, before using the billet cooling nozzle, the surface temperature of the billet is measured to obtain the actual temperature at each recording point. A temperature curve reflecting the temperature change trend at different locations on the billet is then plotted based on the actual temperatures at each recording point. This temperature curve is then input into the control system, which differentiates the treatment of each point on the billet according to the temperature curve. Higher-temperature areas receive a larger water output from the billet cooling nozzle, resulting in the greatest cooling effect, while lower-temperature areas receive a smaller water output. In this way, the temperature difference between the head and tail of the billet can be controlled between 20℃ and 40℃.

[0086] To avoid the impact of iron oxide scale on the accuracy of subsequent temperature measurements, the iron oxide scale on the surface of the billet should be removed before temperature measurement. The iron oxide scale removal device consists of a cylindrical wire brush 7 driven by a motor, rotating in the opposite direction to the movement of the billet 1. The cylindrical wire brush 7 is perpendicular to the ground and installed on the side of the billet feed roller 3 in front of the rolling mill. When the billet 1 passes through, the motor drives the wire brush 7 to rotate and remove the iron oxide scale from the surface of the billet 1.

[0087] After the iron oxide scale removal device, multiple temperature measurement points are set along the direction of the billet feeding roller 3. Each billet temperature measurement point is equipped with a high temperature meter 5 to measure the billet temperature. The billet temperature measurement point is located on the same horizontal line as the cylindrical wire brush 7. The high temperature meter 5 measures the temperature of the billet 1 after the iron oxide scale is removed and records the measurement value at a predetermined time interval (e.g., one number is recorded every 0.1 seconds). After the measurement value is transmitted to the control system 6 (e.g., computer), a trend line can be drawn based on the multiple measurement data. This trend line represents the temperature situation from the head to the tail of the billet 1.

[0088] like Figure 2 As shown, to meet the special requirements of oxide scale removal, billet temperature measurement, and billet cooling control processes, the insulation cover includes a dedicated insulation cover 2 for temperature measurement and cooling control. (The insulation layer structure of the insulation cover is no different from the aforementioned insulation cover or existing ordinary insulation covers, but it is called a dedicated insulation cover because it contains an oxide scale removal device, a temperature measuring point, and a temperature adjustment device.) This dedicated insulation cover 2 is located in front of the rolling mill. Along the conveying direction of the billet 1, the dedicated insulation cover 2 includes equipment used in three processes: an oxide scale removal device, a billet temperature measuring point, and a billet temperature adjustment device. The aforementioned oxide scale removal device is located within this dedicated insulation cover 2.

[0089] Furthermore, the step of completing the billet controlled cooling process based on the billet temperature curve specifically includes: determining a starting position on the billet that is 20°C higher than the temperature at the head of the billet based on the billet temperature curve; spraying water onto the portion of the billet after the starting position using billet controlled cooling nozzles located at four positions on the outer side of the billet: upper left, lower left, lower right, and upper right; and adjusting the water spray intensity of each nozzle in real time according to the billet temperature curve and the moving speed of the billet.

[0090] A temperature adjustment device is also installed in the special heat insulation cover 2 to complete the controlled cooling process. The length of the temperature adjustment device is approximately the same as that of the casting billet 1, such as... Figure 3 As shown, the temperature adjustment device mainly consists of multiple billet nozzles 4, which are arranged at the four corners of the special insulation cover 2 outside the billet feeding roller conveyor 3. Furthermore, it should be ensured that one billet nozzle 4 is arranged at each of the four corners of the same cross-section of the billet 1, that is, a total of four billet nozzles 4 in the upper left, upper right, lower left, and lower right sections of the same cross-section. The billet nozzles 4 should not be placed directly below the billet 1 to avoid clogging due to iron oxide scale falling from the billet 1, thus rendering them unusable. The billet nozzles 4 are evenly arranged along the length of the special insulation cover 2, forming four rows of billet nozzles. The spacing between the billet nozzles in the same row is configured so that the sprayed water can completely cover the surface of the billet 1. Since there are gaps between the lower rollers and on the sides of the billet feeding roller conveyor 3, the billet nozzles 4 located at the lower left and lower right can spray cooling water onto the sides and bottom of the billet 1.

[0091] Furthermore, the nozzle 41 of the billet nozzle 4 should not be a conventional round hole design, but rather a hollow rectangle (e.g., Figure 5 As shown), this is how it can be done. Figure 4 The water sprayed is arranged to form a rectangular water spray coverage area 42 (also called a rectangular annular water spray coverage area; the protection area of ​​ordinary round hole water outlets is circular or annular). Since the billet 1 is a square billet, and the billet nozzles 4 are arranged at the four corners inside the special insulation cover 2, the billet nozzles 4 are located on the diagonal lines connecting the square cross-section of the billet 1. Because the corners 11 of the billet 1 undergo two-dimensional heat transfer and have a rapid temperature drop, the water volume in the center of the water spray coverage area 42 from the billet nozzles 4 is small, while the water volume on both sides is large. This avoids excessive temperature drop at the corners 11 of the billet 1 and maintains the overall temperature uniformity of the billet 1.

[0092] When the head of billet 1 enters the rolling mill, water spraying begins to control the surface temperature. The temperature in the head area of ​​billet 1 is relatively low, so no water is sprayed. Based on the surface temperature trend curve of billet 1, the water volume of billet nozzle 4 is controlled by computer (control system 6). Water spraying begins to cool the billet 1 when the temperature rises by 20°C from the head to the rear. The greater the temperature rise, the greater the water spraying intensity, and the area of ​​water outlet moves with the movement of billet 1.

[0093] Furthermore, controlling the temperature difference between the head and tail of the rolled piece to be between 20°C and 30°C specifically includes: sequentially setting up roughing, roughing controlled cooling, intermediate rolling, intermediate controlled cooling, finishing rolling, and finishing controlled cooling processes in the hot continuous rolling process; wherein, temperature measurement is performed in the roughing process, and a first temperature curve is generated based on the measurement results; the roughing controlled cooling process specifically includes: setting water spray nozzles on the outside of the rolled piece; selecting a water spraying start position on the rolled piece; spraying water onto the portion of the rolled piece after the water spraying start position through the water spray nozzles; and adjusting the water spraying intensity of each water spray nozzle in real time according to the first temperature curve.

[0094] In order to control temperature changes reasonably, it is necessary to quantify and control the water output of each cooling device. Therefore, before cooling, similar to the aforementioned billet cooling method, the surface temperature of the rolled piece must be measured to obtain the actual temperature of each recording point. Based on the actual temperature of each recording point, a temperature curve reflecting the temperature change trend at different locations of the rolled piece is plotted. Then, the temperature curve is input into the control system, so that the control system treats each point on the rolled piece differently according to the temperature curve. The higher the temperature, the greater the cooling intensity and the largest temperature drop, while the correspondingly lower temperature has a smaller cooling intensity.

[0095] To this end, multiple temperature measurement points can be set along the direction of the billet feeding roller table. These temperature measurement points are distributed at corresponding positions in the roughing, intermediate rolling, pre-finishing, and finishing rolling processes. Each temperature measurement point is equipped with a pyrometer to measure the temperature and record the measured value at predetermined time intervals (e.g., one number is recorded every 0.1 seconds). After the measured values ​​are transmitted to the control system (e.g., a computer), a temperature curve can be plotted based on the multiple measured values. This temperature curve represents the current head-to-tail temperature difference of the rolled piece.

[0096] In the roughing rolling temperature control process, dedicated water spray nozzles are used as cooling devices. Multiple water spray nozzles are arranged at appropriate distances on the outside of the rolled piece. These nozzles are positioned at the four corners of the outer perimeter of the billet feeding roller table, and supports can be installed to fix the nozzles. Furthermore, it should be ensured that one water spray nozzle is placed at each of the four corners of the same cross-section of the rolled piece 1, i.e., four nozzles in total (upper left, upper right, lower left, and lower right) within the same cross-section. The nozzles should not be placed directly below the billet 1 to avoid clogging by impurities falling from the rolled piece 1. The water spray nozzles are evenly distributed along the length of the billet feeding roller table, forming four rows. The spacing between nozzles in the same row is configured such that the sprayed water completely covers the surface of the rolled piece 1. To control the temperature difference between 20℃ and 30℃, before water spraying for cooling, a position 20℃ higher than the head temperature of the rolled piece should be identified based on a pre-generated temperature curve as the starting point for water spraying. The portion after this starting point is then cooled.

[0097] Furthermore, controlling the temperature difference between the head and tail of the rolled piece to be between 20°C and 30°C further includes: performing temperature measurement in the intermediate rolling process and generating a second temperature curve based on the measurement results; using a water purifier to adjust the rolled piece temperature in the intermediate rolling controlled cooling process and adjusting the cooling intensity of the intermediate rolling controlled cooling process in real time according to the second temperature curve; performing temperature measurement in the finishing rolling process and generating a third temperature curve based on the measurement results; using a multi-stage cooler to adjust the rolled piece temperature in the finishing rolling controlled cooling process and adjusting the cooling intensity of the finishing rolling controlled cooling process in real time according to the third temperature curve.

[0098] In the remaining controlled cooling processes, even if other controlled cooling devices besides the aforementioned water spray nozzles are used, the controlled cooling amount should be adjusted according to the corresponding temperature curves. Temperature measuring points are set in the intermediate rolling mill stand and the finishing rolling mill stand, respectively, so that corresponding temperature curves are generated based on the temperature measuring results in the intermediate rolling and finishing rolling processes. The controlled cooling is then adjusted using the corresponding temperature curves in the subsequent intermediate rolling controlled cooling and finishing rolling controlled cooling processes.

[0099] Furthermore, after the finishing rolling controlled cooling process, the process further includes: post-finishing temperature measurement and post-finishing controlled cooling; wherein, in the post-finishing temperature measurement process, temperature measurement is performed, and a fourth temperature curve is generated based on the measurement results; the post-finishing controlled cooling process uses a multi-stage cooler to adjust the temperature of the rolled piece, and adjusts the cooling intensity of the post-finishing controlled cooling process in real time based on the fourth temperature curve.

[0100] In some rolling mill production lines, in addition to roughing, intermediate rolling and finishing rolling, a second cooling process is required after the finishing rolling cooling process (i.e., post-finishing cooling). At this time, temperature measurement is also required to generate a temperature curve, and then the post-finishing cooling process is carried out according to the temperature curve.

[0101] Furthermore, the process includes a pre-finishing rolling process and a pre-finishing rolling controlled cooling process before the finishing rolling process. In the pre-finishing rolling process, temperature measurement is performed, and a fifth temperature curve is generated based on the measurement results. The pre-finishing rolling controlled cooling process uses multi-stage nozzles to adjust the temperature of the rolled piece, and the controlled cooling intensity of the pre-finishing rolling controlled cooling process is adjusted in real time according to the fifth temperature curve.

[0102] In some rolling mill production lines, pre-finishing rolling is required between intermediate rolling and finishing rolling. At this time, temperature should be measured during the pre-finishing rolling process to generate a corresponding temperature curve. Then, the pre-finishing rolling controlled cooling process is carried out according to the temperature curve.

[0103] The following details the method for controlling the temperature difference between the head and tail of the rolled piece in this application:

[0104] 1. Rolling line design: to enable the rolling line to have a multi-level cooling control device during the rolling process.

[0105] Standard bar production line: 6 roughing mills + roughing mill cooling control device + 6 intermediate mills + intermediate mill cooling control device + 4 finishing mills + finishing mill cooling control device + recovery section + post-finishing temperature measurement device + 2 finishing mills + post-finishing cooling control device + recovery section + cooling bed (temperature measurement is performed after the 4th stand of the roughing, intermediate, and finishing mills, which provides time for the rolled piece to recover before temperature measurement, ensuring uniform surface temperature and avoiding uneven surface temperature and overcooling caused by the cooling control device, which would affect the accuracy of surface temperature measurement).

[0106] High-speed bar production line: 6 roughing mills + roughing mill cooling control device + 6 intermediate mills + intermediate mill cooling control device + 6 pre-finishing mills + pre-finishing mill cooling control device + 4 finishing mills + finishing mill cooling control device + recovery section + post-finishing temperature measurement device + 2 finishing mills + post-finishing cooling control device + recovery + cooling bed (temperature measurement is performed after the 4th stand of the roughing, intermediate, pre-finishing, and finishing mills, respectively, which can provide time for the rolled piece to recover before temperature measurement, uniform surface temperature, and avoid uneven surface temperature and overcooling of the rolled piece caused by the cooling control device).

[0107] High-speed wire rod production line: 6 roughing mills + roughing mill cooling control unit + 6 intermediate mills + intermediate mill cooling control unit + 6 pre-finishing mills + pre-finishing mill cooling control unit + recovery section + 8 finishing mills + finishing mill cooling control unit + recovery section + post-finishing temperature measurement unit + 2 slitting mills + post-finishing cooling control unit (temperature measurement is performed after the 4th stand of the roughing mill, intermediate mill, pre-finishing mill, and the 8th stand of the finishing mill, respectively, which can provide recovery time for the rolled piece before temperature measurement, uniform surface temperature, and avoid uneven surface temperature and overcooling of the rolled piece caused by the cooling control unit).

[0108] 2. Based on the temperatures obtained at various measurement points on the rolled piece, draw temperature trend lines at each measurement point. The controlled cooling process after each measurement point on the rolling line adjusts the rolled piece temperature according to the temperature trend lines to control the temperature difference between the head and tail of the rolled piece. Taking the surface temperature trend line of the rolled piece as a reference, water cooling begins at the point where the temperature is 20°C higher than the head of the rolled piece. The greater the temperature increase, the greater the water spray intensity.

[0109] 3. Different cooling devices are used in different positions: water nozzles are used in the roughing cooling process, water purifiers are used in the intermediate rolling cooling process, multi-stage nozzles are used in the pre-finishing cooling process, and multi-stage coolers are used in the finishing cooling process and the post-finishing cooling process.

[0110] In the roughing mill, controlled cooling is achieved using water spray nozzles. Because the rolled piece at the roughing mill exit is relatively large and its head may be bent, a cooling device (i.e., controlled cooling device) should be installed after the No. 1 flying shear. This cooling device consists of multiple sets of water spray nozzles. One water spray nozzle is placed at each of the four corners of the same cross-section of the rolled piece, resulting in four nozzles within the same cross-section. This prevents the nozzle directly below from becoming clogged by falling iron oxide scale from the cast billet, thus affecting its use. The water jets are rectangular, with the coverage area determined by ensuring that all four nozzles completely cover the surface of the rolled piece.

[0111] The intermediate rolling mill uses a water-cooling device: Since the size of the rolled piece at the exit of the intermediate rolling mill is also large, there may be problems such as bending at the head. Therefore, a cooling device (controlled cooling device) should be installed after the No. 2 flying shear. This cooling device uses the water-cooling device commonly used in bar rolling lines.

[0112] The pre-finishing mill, finishing mill, and post-finishing cooling all employ multi-stage cooling systems (graded cooling devices), with each location consisting of multiple small cooling devices that can individually control the water volume.

[0113] The following specific example illustrates the heat-free direct rolling method for reinforcing bars described in this application:

[0114] In a specific embodiment of the production of HRB400E steel bars, the chemical composition of the material is shown in the table below:

[0115] HRB400E ingredients (wt%)

[0116]

[0117] Table 1. HRB400E Material Composition Table

[0118] The steelmaking process in this embodiment is as follows:

[0119] The process route is as follows: blast furnace hot metal smelting → hot metal desulfurization pretreatment → converter steelmaking → billet continuous casting → hot continuous rolling → length shearing → inspection, packaging, and warehousing; the process characteristics of each stage are as follows:

[0120] Converter steelmaking: The sulfur content of the molten iron entering the furnace is 0.040 wt%; no alloys with high Nb, Ti, or Al content are added after the furnace.

[0121] The converter adopts a slag washing and desulfurization process: lime, synthetic slag and other slag-forming materials are added to the ladle before and during tapping to control the reasonable slag composition and fluidity, and to standardize the deoxidation process, temperature control and chlorination process to achieve the purpose of slag washing and desulfurization. (1) The basicity of the ladle top slag (CaO / SiO2) is 2.8. (2) Additional deoxidation materials are added during the tapping process to strengthen the deoxidation of molten steel and top slag. After tapping, deoxidation materials are added to the slag surface of the ladle. After tapping, the top slag (FeO) of the ladle is 1.7%. (3) The tapping temperature is increased by 15℃ compared with the conventional low-S heat. (4) The stirring intensity of the tapping process and the desulfurization process is increased. The strong argon blowing time after tapping is 6 minutes.

[0122] Billet continuous casting: Slag detection and control are employed in the ladle. The tundish pouring temperature is 1530℃. Ordinary covering agent and standard billet protective slag are used in the tundish. The single-strand casting speed is 3.6 m / min. Hydraulic shears are used to cut the billets, and a stepped exit method is adopted. The billet temperature at the shearing points is between 1000℃ and 1100℃, for example, 1020℃, 1050℃, and 1080℃. A fully water-cooled nozzle is used, and the specific water flow rate of the casting stream is 1.1 L / min.

[0123] like Figure 2 As shown, this rolling method eliminates the need for a heating furnace; the billet is directly fed into the rolling mill via the feeding roller conveyor 3, eliminating the need for the billet to be fed into the heating furnace via the feeding roller conveyor 3. For hot continuous rolling of bars: the billet is fed into the rolling mill via a direct feeding roller conveyor, using a high-speed motor. The length of the feeding roller conveyor 3 is within 200m, for example, 180 meters or 200 meters. The time from billet cutting to entering the rolling mill is 60 seconds.

[0124] The cross-section of the billet is 165mm×165mm and the length of the billet is 11m. Using the aforementioned method of controlling the temperature difference between the head and tail of the billet, the temperature curve generated after measurement shows that the temperature at 5m of the billet is 20℃ higher than that at the head, and the temperature at 10m is 55℃ higher than that at the head. Therefore, water cooling is started from 5m of the billet. The greater the temperature rise, the greater the water spray intensity, and finally the temperature difference between the head and tail of the billet is controlled to 28℃.

[0125] Before the billet enters the rolling mill, the temperature at the head of the billet is 890-910℃, and the temperature at the tail of the billet is 870-875℃. For example, the temperature at the head of the billet is 900℃, and the temperature at the tail of the billet is 873℃.

[0126] The production line is arranged as described in the aforementioned ordinary bar production line, namely: 6 roughing mill stands + roughing mill cooling control unit + 6 intermediate mill stands + intermediate mill cooling control unit + 4 finishing mill stands + finishing mill cooling control unit + recovery section + post-finishing temperature measuring device + 2 finishing mill stands + post-finishing cooling control unit + recovery section + cooling bed (temperature measuring is performed after the 4th stand of the roughing, intermediate, and finishing mills, respectively, to provide recovery time for the rolled piece before temperature measurement and to uniformly measure the surface temperature). The produced steel bars are 28mm in diameter, and the length of the finished rolled piece after cooling bed is 486m. The final temperature difference between the head and tail of the rolled piece is controlled at 25℃.

[0127] The final results are shown in the table below:

[0128]

[0129]

[0130] Table 2. Summary of Head and Tail Temperatures and Head and Tail Performance

[0131] During continuous hot rolling, the head temperature of the rolled piece is controlled at 890-910℃, and the tail temperature is controlled at 860-890℃. The difference in yield strength between the head and tail is less than or equal to 30 MPa, and the difference in elongation after fracture is less than or equal to 2%. For example:

[0132] The head temperature of the first rolled piece is 900℃, the yield strength of the head of the rolled piece is 440 MPa, and the elongation after fracture is 21%; the tail temperature is 880℃, the yield strength of the tail of the rolled piece is 455 MPa, and the elongation after fracture is 22%.

[0133] The head temperature of the second rolled piece is 905℃, the yield strength of the head of the rolled piece is 430 MPa, and the elongation after fracture is 20%; the tail temperature is 880℃, the yield strength of the tail of the rolled piece is 450 MPa, and the elongation after fracture is 21%.

[0134] The head temperature of the third rolled piece is 892℃, the yield strength of the head is 425 MPa, and the elongation after fracture is 23%; the tail temperature is 863℃, the yield strength of the tail is 455 MPa, and the elongation after fracture is 22%.

[0135] The fourth rolled piece has a head temperature of 910℃, a head yield strength of 435 MPa, and an elongation at break of 22%; the tail temperature is 890℃, the tail yield strength is 460 MPa, and the elongation at break is 20%. Compared with traditional cold billet reheating, this method saves 140 m³ of gas per ton of steel. 3 The above measures reduce the loss of iron oxide scale in the cast billet and increase the metal yield of rolled steel by 0.5% to 1.0%.

[0136] In the above detailed description, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features of the single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, wherein each claim stands alone as a preferred embodiment of the invention.

[0137] The disclosed embodiments have been described above to enable any person skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the spirit and scope of this disclosure. Therefore, this disclosure is not limited to the embodiments given herein, but is consistent with the broadest scope of the principles and novel features disclosed in this application.

[0138] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A type of reinforcing steel bar rolled by a direct rolling method without heating, characterized in that, The chemical composition and weight percentage of the reinforcing steel are as follows: C: 0.20~0.25Wt%, Si: 0.40~0.55Wt%, Mn: 1.10~1.25Wt%, P: ≤0.045Wt%, S: ≤0.045Wt%, Nb: ≤0.004Wt%, Ti: ≤0.007Wt%, Alt: ≤0.006Wt%, V: 0.02~0.03Wt%, N: 0.005~0.011Wt%. The reinforcing steel is produced by a direct rolling method without heating. The direct rolling method includes the following steps: blast furnace molten iron smelting, molten iron desulfurization pretreatment, converter molten steel smelting, billet continuous casting, hot continuous rolling, and fixed-length shearing. Among them, the billet heating process between billet continuous casting and hot rolling was eliminated; In the billet continuous casting process, the temperature difference between the head and tail of the billet is controlled between 20℃ and 40℃. In the hot continuous rolling process, the temperature difference between the head and tail of the rolled piece is controlled between 20°C and 30°C. Following the fixed-length shearing process, a descaling process, a measurement process, and a controlled cooling process for the cast billet are included; wherein... In the oxide scale removal process, the oxide scale on the side of the billet is removed by a wire brush; In the measurement process, the temperature of the side surface of the billet after descaling is measured at predetermined time intervals using a pyrometer, and a billet temperature curve is generated based on the measurement results. The billet temperature curve is used to reflect the temperature difference between different positions of the billet from the head to the tail. The controlled cooling process of the cast billet is completed according to the cast billet temperature curve. The step of controlling the cooling of the billet according to the billet temperature curve specifically includes: Based on the billet temperature curve, a starting position 20°C higher than the billet head temperature is determined on the billet. Water is sprayed onto the portion of the billet after the initial position by four billet cooling nozzles located at the upper left, lower left, lower right, and upper right positions on the outer side of the billet. The water spray intensity of each billet cooling nozzle is adjusted in real time according to the billet temperature curve and the billet moving speed; the shape of the spray holes on the billet cooling nozzle is a hollow rectangle. The head temperature of the rolled piece is controlled at 890-910℃, the tail temperature is controlled at 860-890℃, the difference in yield strength between the head and tail is less than or equal to 30 MPa, and the difference in elongation after fracture is less than or equal to 2%.

2. The reinforcing steel bar rolled by the heat-free direct rolling method as described in claim 1, characterized in that, The chemical composition and weight percentage of the reinforcing steel are as follows: C: 0.23 wt%, Si: 0.50 wt%, Mn: 1.19 wt%, P: 0.030 wt%, S: 0.026 wt%, Nb: 0.002 wt%, Ti: 0.002 wt%, Alt: 0.0019 wt%, V: 0.026 wt%, N: 0.0075 wt%.

3. The reinforcing steel bar rolled by the heat-free direct rolling method as described in claim 1, characterized in that, The steel bars are HRB400E seismic-resistant steel bars.

4. The reinforcing steel bar rolled by the heat-free direct rolling method as described in claim 1, characterized in that, The steel bars are φ12-40mm in size.

5. The reinforcing steel bar rolled by the heat-free direct rolling method as described in claim 1, characterized in that, The steel bar specification is 28mm, the length of the finished rolled product after being placed on the cooling bed is 486m, and the temperature difference between the head and tail of the rolled product is controlled at 25℃.

6. The reinforcing steel bar rolled by the non-heating direct rolling method as described in claim 1, characterized in that, The reinforcing bars are formed by rolling a cast billet with a cross-section of 165mm × 165mm and a length of 11m.

7. The reinforcing steel bar rolled by the heat-free direct rolling method as described in claim 1, characterized in that, Hot continuous rolling of bar stock: The billet is fed into the mill by a direct feeding roller. The length of the billet feeding roller (3) is within 200m. The time from cutting the billet to entering the mill is 60 seconds.

8. The reinforcing steel bar rolled by the heat-free direct rolling method as described in claim 1, characterized in that, Controlling the temperature difference between the head and tail of the cast billet to between 20℃ and 40℃ specifically includes: A billet length-cutting process is set in the billet continuous casting process; The billet cutting process is performed using hydraulic shears; the billet cutting process specifically includes: A contact-type length-fixing device is installed on the billet feeding roller conveyor at a predetermined distance from the hydraulic shear; When the head of the billet comes into contact with the contact-type length-fixing device, the contact-type length-fixing device outputs a shearing action signal to the control system. The control system sends action commands to the hydraulic shears; The hydraulic shears cut the casting billet according to the action command.

9. The reinforcing steel bar rolled by the heat-free direct rolling method as described in claim 1, characterized in that, Controlling the temperature difference between the head and tail of the rolled piece to be between 20°C and 30°C specifically includes: The hot continuous rolling process includes, in sequence, roughing, roughing controlled cooling, intermediate rolling, intermediate controlled cooling, finishing, and finishing controlled cooling processes. Temperature measurement is performed during the rough rolling process, and a first temperature curve is generated based on the measurement results. The controlled cooling process for rough rolling specifically includes: Water spray nozzles are installed on the outside of the rolled piece; Select the starting position for water spraying on the rolled piece; Water is sprayed onto the portion of the rolled piece after the initial water spraying position via the water nozzle; The spray intensity of each water nozzle is adjusted in real time based on the first temperature curve.

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