Low alloy HRB400E steel without widmanstatten structure under direct rolling process

Abstract

The present application belongs to the HRB400E high-speed wire and high-speed bar rolling production technology field of steel metallurgical industry, and relates to a low alloy HRB400E steel without widmanstatten structure under direct rolling process, and chemical composition and mass percentage of the low alloy HRB400E steel without widmanstatten structure under direct rolling process are as follows: C: 0.18-0.25%, Si: ≤0.65%, Mn: ≤1.10%, P: ≤0.040%, S: ≤0.040%, N: ≤0.010%, O: ≤28ppm, and the balance is Fe and inevitable residual elements. The low alloy HRB400E steel without widmanstatten structure under direct rolling process in the present application is based on the direct rolling process, and a heating furnace is not needed, so that the energy consumption required for heating in the heating rolling process is saved, carbon dioxide zero emission is realized, low-consumption production is realized, the product organization is uniform pearlite and ferrite without widmanstatten structure, the organization is stable, the product performance is stable, the bar is good, and the problem that abnormal widmanstatten structure appears in the microstructure of HRB400E, mechanical properties are unstable, and the product is unqualified is effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of high-speed wire rod and high-speed bar rolling production technology of HRB400E steel in the iron and steel metallurgical industry, and relates to a low alloy HRB400E steel without Widmanstätten structure under direct rolling process. Background Technology

[0002] HRB400E accounts for over 80% of rebar products and is currently the mainstream product in the market, widely used in civil construction, bridges, high-speed rail, and urban rail transit. After years of development, advanced production technologies for HRB400E have become increasingly mature. Hot charging and hot delivery technology, continuous casting and rolling technology, endless rolling technology, low-temperature rolling technology, water cooling technology, high-speed steel loading technology, and slitting rolling technology have been successfully applied in many rebar manufacturers both domestically and internationally. Currently, traditional small-diameter HRB400E wire rods are mainly produced in China using high-speed bar and high-speed wire rod rolling methods.

[0003] Bar and wire rod manufacturers are increasingly stringent in controlling the production costs and product quality of HRB400E, striving to improve product quality while reducing production costs to enhance their competitiveness. Some companies, based on hot charging and hot delivery, are adopting a "full-line low-temperature rolling" process to reduce billet heating and rolling costs. Furthermore, they are controlling austenite grain size through low-temperature rolling, thereby reducing alloy costs through fine-grain strengthening.

[0004] However, while this type of low-temperature rolling process can reduce alloy costs in the production of HRB400E and effectively lower production costs, it also presents the following problems:

[0005] 1) The temperature difference between the head and tail of the rolled piece and the middle position is large, resulting in a large difference in the final microstructure, a large difference in mechanical properties, and poor product permeability;

[0006] 2) Low-temperature rolling throughout the entire line resulted in a significant increase in rolling power, which in turn increased the power consumption per ton of steel during rolling;

[0007] 3) Low-temperature rolling throughout the entire process increases wear on the rolling mill and rolls, leading to increased operating costs for the company;

[0008] 4) Due to the low-temperature rolling process throughout, although the austenite grain size was refined, the excessively low rolling temperature resulted in the formation of mixed-grain structures and some Widmanstätten structures (such as...). Figure 1 As shown in the figure, this type of organization leads to unstable mechanical properties of the final product.

[0009] To address the problems existing in the current industrial production of HRB400E using the direct rolling process, this invention provides a Widmanstätten-free low-alloy HRB400E steel for direct rolling. This Widmanstätten-free low-alloy HRB400E steel, based on a Widmanstätten structure control system and production method for low-alloy HRB400E using the direct rolling process, effectively solves the problem of abnormal Widmanstätten structure in the microstructure of HRB400E, which leads to unstable mechanical properties and product defects. It can improve the uniformity of the microstructure in high-speed wire rods and bars of HRB400E, reduce the Mn alloy content, lower alloy costs, and simultaneously improve the stability and rolling line operation rate of wire rod and bar production lines when producing HRB400E, reducing operating costs and improving economic efficiency. Summary of the Invention

[0010] In view of this, the purpose of the present invention is to provide a Widmanstätten-free low-alloy HRB400E steel under direct rolling process. This Widmanstätten-free low-alloy HRB400E steel is based on direct rolling process, and the product microstructure is uniform pearlite and ferrite without Widmanstätten structure, so as to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A Widmanstätten-free low-alloy HRB400E steel produced by direct rolling process. The chemical composition and mass percentage of the Widmanstätten-free low-alloy HRB400E steel produced by this direct rolling process are as follows: C: 0.18-0.25%, Si: ≤0.65%, Mn: ≤1.10%, P: ≤0.040%, S: ≤0.040%, N: ≤0.010%, O: ≤28ppm, with the balance being Fe and unavoidable residual elements.

[0013] Furthermore, the residual elements include Ti, Nb, and V.

[0014] Furthermore, the microstructure of the Widmanstätten-free low-alloy HRB400E steel produced by the direct rolling process is uniformly distributed ferrite + pearlite, with a pearlite ratio of ≥55%, a grain size grade of ≥10, and no Widmanstätten structure.

[0015] Furthermore, the Widmanstätten-free low-alloy HRB400E steel produced under the direct rolling process is based on the production of a high-speed wire rod production line under the direct rolling process;

[0016] The direct rolling process includes the following steps:

[0017] S1. Electromagnetic induction heating of continuous casting billet: An electromagnetic induction heating device is used to heat the continuous casting billet directly delivered from the continuous casting process.

[0018] S2. Roughing and intermediate rolling: The continuously cast billet after electromagnetic induction heating is subjected to roughing and intermediate rolling in sequence. The roughing and intermediate rolling mills adopt micro-tension control, and the pre-finishing mill adopts tension-free rolling. During rolling, the pass system of the roughing mill adopts box-box-variable ellipse-circle-ellipse-circle, and the pass system of the intermediate rolling mill is an ellipse-circle pass system.

[0019] S3. Pre-finishing mill rolling: The pre-finishing mill rolls are rolled after the intermediate mill and cooled by the pre-finishing water cooling box. The pre-finishing mill adopts tensionless rolling and the pass system of the pre-finishing mill is an elliptical-circular pass system.

[0020] S4. Finishing mill rolling: The rolled pieces that have been rolled by the pre-finishing mill and cooled by the water cooling box after pre-finishing are rolled by 2-8 passes of 45° top-crossing cantilever finishing mill. Micro-tension control is adopted between the finishing mills. The pass system of the finishing mill is an elliptical-circular pass system during rolling.

[0021] S5. Reduction Mill Rolling: The rolled workpiece, after being rolled by the finishing mill and cooled by the water cooling box after the finishing mill, is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is adopted between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of deformation per pass during the rolling process is 1.23 to 1.30. The rolled workpiece is a threaded wire rod. The running speed is 20m / s to 110m / s.

[0022] S6. Wire forming: After being rolled by the reducing mill and cooled by the water cooling box after the reducing mill, the rolled piece is fed into the wire forming machine by the pinch rolls. The wire forming temperature range of the rolled piece is 700℃~850℃.

[0023] S7. Air-cooled line cooling: The coils after being rolled into coils are cooled by air-cooled line control. The cooling rate of the rolled parts on the air-cooled line is 5℃ / s~30℃ / s, and the running speed of the air-cooled line roller is 0.15m / s~1.0m / s.

[0024] S8. Coil Collection: Coiled coils that have been cooled by the air-cooling line are collected at the coil collection station, cooled by the PF line, and then bundled and collected.

[0025] Furthermore, the production of Widmanstätten-free low-alloy HRB400E steel under the direct rolling process is based on a high-speed bar production line under the direct rolling process.

[0026] The direct rolling process includes the following steps:

[0027] S1. Electromagnetic induction heating of continuous casting billet: An electromagnetic induction heating device is used to heat the continuous casting billet directly delivered from the continuous casting process.

[0028] S2. Roughing and intermediate rolling mills: After electromagnetic induction heating, the continuously cast billet is rolled sequentially by roughing, intermediate rolling and pre-finishing mills. The roughing and intermediate rolling mills adopt micro-tension control. During rolling, the pass system of the roughing mill is box-box-variable ellipse-circle-ellipse-circle, and the pass system of the intermediate rolling mill and pre-finishing mill is ellipse-circle pass system.

[0029] S3. Pre-finishing mill rolling: The pre-finishing mill rolls are used to roll the workpieces that have been rolled by the intermediate mill and cooled by the water cooling box before pre-finishing. The pre-finishing mill adopts tensionless rolling and the roll pass system is an elliptical-circular roll pass system.

[0030] S4. Finishing mill rolling: The rolled pieces that have been rolled by the pre-finishing mill and cooled by the water cooling box after pre-finishing are rolled by 2-4 passes of 45° top-crossing cantilever finishing mill. Micro-tension control is used between the finishing mills. The roll pass system is an elliptical-circular roll pass system.

[0031] S5. Reduction Mill Rolling: The rolled piece after being rolled by the finishing mill and cooled by the water cooling box after the finishing mill is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is adopted between the two reduction mills. The rolling pass system is an elliptical-circular pass system. The average compression ratio of deformation per pass during the rolling process is 1.23 to 1.30. The rolled piece is a straight threaded bar. The running speed is 20m / s to 55m / s.

[0032] S6. Cooling bed: The rolled pieces after being deformed by the reducing mill are cooled by the water cooling box after the reducing mill. After being sheared by the double-length flying shear, they enter the cooling bed through the rotating hub for cooling. The temperature range of the upper cooling bed is 750℃~830℃, and the temperature range of the lower cooling bed is 250℃~350℃.

[0033] S7. Bundling and Collection: After the rolled pieces are cooled on the cooling bed, they are cut to length by cold shear and then counted, bundled and collected by a collection device.

[0034] Furthermore, the electromagnetic induction heating device has an electromagnetic induction heating temperature range of 50℃ to 200℃, and the temperature of the continuous casting billet after heating is 900℃ to 1000℃.

[0035] Furthermore, the average compression ratio of the pass deformation during the rolling process of the roughing mill and intermediate mill is 1.20 to 1.40. The rolling temperature of both the roughing mill and intermediate mill is within the complete recrystallization temperature range, which is 900℃ to 1000℃. The running speed of the rolled piece after rolling in the intermediate mill is 1m / s to 8m / s.

[0036] Furthermore, the average compression ratio of the deformation per pass during the pre-finishing mill rolling process is 1.15 to 1.33, the rolling temperature of the pre-finishing mill is in the complete recrystallization temperature range, which is 900℃ to 950℃, and the running speed of the rolled piece after the pre-finishing mill rolling is 3m / s to 25m / s.

[0037] Furthermore, the average compression ratio of the deformation per pass during the finishing mill rolling process is 1.18 to 1.26, the deformation temperature is 850℃ to 900℃, and the running speed of the rolled piece after finishing mill rolling is 10m / s to 80m / s.

[0038] Furthermore, the rolling temperature of the reducing mill is in the partial recrystallization or two-phase temperature range, and the initial rolling temperature range of the reducing mill is 750℃~850℃.

[0039] Furthermore, in the reducing mill rolling, the compression ratio of the last reducing mill stand is greater than or equal to the compression ratio of the penultimate reducing mill stand, and the average compression ratio per pass is ≥1.25; the rolling temperature of the corresponding mills before the pre-finishing mill, before the finishing mill, and before the reducing mill are all adjusted by water-cooled boxes, and the cooling capacity of a single water-cooled box is ≥150℃.

[0040] Furthermore, the electromagnetic induction heating device is equipped with a closed-loop temperature control system, and the temperature difference between the head and tail of the continuous casting billet after heating is ≤30℃.

[0041] Furthermore, the coiled products produced by the high-speed wire rod production line have a final nominal diameter of 6mm, 8mm, 10mm, 12mm and 14mm; the straight products produced by the high-speed bar production line have a final nominal diameter of 10mm, 12mm and 14mm.

[0042] The beneficial effects of this invention are as follows:

[0043] This invention provides a Widmanstätten-free low-alloy HRB400E steel produced by direct rolling. Based on the direct rolling process, it eliminates the need for a heating furnace, saving energy consumption required for the heating rolling process and achieving zero carbon dioxide emissions, thus realizing low-energy production. The product has a uniform microstructure of pearlite and ferrite, without Widmanstätten structure, resulting in stable microstructure, stable product performance, and good through-stretch properties. It effectively solves the problem of unstable mechanical properties and product defects caused by abnormal Widmanstätten structure in the microstructure of HRB400E. The product has low alloy cost, with approximately 20% lower Mn alloy content compared to conventional processes, resulting in lower production costs and stronger enterprise competitiveness.

[0044] Secondly, in the direct rolling process, an electromagnetic induction heating device is installed before the roughing mill. After heating, the temperature difference between the head and tail is ≤30℃, resulting in stable microstructure and properties at the head, tail, and middle positions of the final product. The product has good passability. The rolling temperature of the roughing mill, intermediate mill, and pre-finishing mill is controlled, resulting in relatively low rolling power and lower power consumption per ton of steel compared to low-temperature rolling, saving power costs and improving equipment stability and service life. Furthermore, a large reduction rolling is achieved through a two-stand reducing mill, ensuring uniform surface and core microstructure of the HRB400E product. Under this direct rolling process, the Widmanstätten-free low-alloy HRB400E steel can produce a wide range of low-alloy product specifications under low-cost process conditions. It can produce coils with nominal diameters of 6mm, 8mm, 10mm, 12mm, and 14mm for high-speed wire rod production lines and bars with nominal diameters of 10mm, 12mm, and 14mm for high-speed bar production lines.

[0045] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0046] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0047] Figure 1 The optical microstructure of HRB400E containing Widmanstätten structure in the prior art (background art);

[0048] Figure 2 This is a simplified diagram of the high-speed wire rod production process of Widmanstätten-free low-alloy HRB400E steel under the direct rolling process in this invention.

[0049] Figure 3 This is a simplified diagram of the high-speed bar production process of low-alloy HRB400E steel without Widmanstätten structure under the direct rolling process in this invention.

[0050] Figure 4 This is the temperature control curve for high-speed wire rod of Widmanstätten-free low-alloy HRB400E steel under the direct rolling process in this invention.

[0051] Figure 5 This is the temperature control curve of high-speed bar stock of low-alloy HRB400E steel without Widmanstätten structure under the direct rolling process in this invention.

[0052] Figure 6 This is the optical microstructure of the Widmanstätten-free low-alloy HRB400E steel produced by the direct rolling process in this invention.

[0053] Reference numerals: 1-Electromagnetic induction heating device; 2-Roughing mill; 3-First cutting flying shear; 4-Intermediate mill; 5-Pre-finishing mill pre-cooling box; 6-Second cutting flying shear; 7-Pre-finishing mill; 8-Pre-finishing mill post-cooling box; 9-Third cutting flying shear; 10-Finishing mill; 11-Finishing mill post-cooling box; 12-Fourth cutting flying shear; 13-Reducing mill; 14-Reducing mill post-cooling box; 15-Pinch roll; 16-Wire drawing machine; 17-Air cooling line; 18-Winding station; 19-Collecting device; 20-Cold shear; 21-Cooling bed; 22-Multiple length flying shear. Detailed Implementation

[0054] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0055] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0056] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0057] Please see Figures 2-6This is a Widmanstätten-free low-alloy HRB400E steel produced by direct rolling. The chemical composition and mass percentage of this Widmanstätten-free low-alloy HRB400E steel produced by direct rolling are as follows: C: 0.18~0.25%, Si: ≤0.65%, Mn: ≤1.10%, P: ≤0.040%, S: ≤0.040%, N: ≤0.010%, O: ≤28ppm, with the balance being Fe and unavoidable residual elements such as Ti, Nb, and V. The microstructure of this product is uniform pearlite and ferrite, without Widmanstätten structure. The matrix microstructure is uniformly distributed ferrite + pearlite, with a pearlite ratio ≥55% and a grain size grade ≥10.

[0058] The direct rolling process for Widmanstätten-free low-alloy HRB400E steel employs a direct rolling process that eliminates the need for a heating furnace. The direct rolling process includes electromagnetic induction heating of the continuously cast billet, rolling on the roughing mill, rolling on the intermediate mill, water cooling and recovery before pre-finishing rolling, rolling on the pre-finishing mill, water cooling and recovery after pre-finishing rolling, rolling on the finishing mill, water cooling and recovery after finishing rolling, rolling on the reducing mill, water cooling and recovery after reducing mill, wire coiling, air cooling line cooling, and coil collection. This direct rolling process employs an electromagnetic induction heating device before the roughing mill, ensuring a head-to-tail temperature difference of ≤30℃ after heating. Rolling is performed in the recrystallization zone of the roughing, intermediate, and pre-finishing mills, while the finishing mill uses a partial recrystallization temperature zone. The reducing mill uses a partial recrystallization zone or a two-phase zone low-temperature, high-pressure rolling process to ensure uniform surface and core microstructure of the HRB400E product. The product microstructure consists of uniform pearlite and ferrite, without Widmanstätten structure, exhibiting stable microstructure and performance. Under low-cost conditions, the production range of low-alloy products is wide. The produced rebar coils or straight bars exhibit high dimensional accuracy, excellent surface quality, and stable mechanical properties. To address the process differences between coils and straight bars of Widmanstätten-free low-alloy HRB400E steel produced using the direct rolling process, the following two process flows are derived:

[0059] 1) For high-speed wire rod production coil products, please refer to the following: Figure 2 and Figure 4 Its process flow is as follows Figure 2 As shown, the temperature control curve is as follows: Figure 5 As shown:

[0060] (1) Electromagnetic induction heating of continuous casting billet: Electromagnetic induction heating device 1 is used to heat the continuous casting billet directly sent from the continuous casting process. The electromagnetic induction heating temperature range is 50℃~200℃, and the temperature of the continuous casting billet after heating is 900℃~1000℃.

[0061] (2) Roughing and intermediate rolling mills: After electromagnetic induction heating, the continuous casting billet is rolled by roughing, intermediate rolling and pre-finishing mills in sequence. Roughing mill 2 and intermediate rolling mill 4 adopt micro-tension control. Loops are configured between pre-finishing mill 7 and tensionless rolling is adopted. During rolling, the pass system of the roughing mill is box-box-variable ellipse-circle-ellipse-circle, and the pass system of the intermediate rolling mill and pre-finishing mill is ellipse-circle pass system. The average compression ratio of deformation per pass during rolling is 1.20 to 1.40. The rolling temperature of the roughing and intermediate rolling mills is 900℃ to 1000℃. The running speed of the rolled piece after rolling by the intermediate rolling mill is 1m / s to 8m / s.

[0062] (3) Pre-finishing mill rolling: The workpieces that have been rolled by the intermediate mill 4 and cooled by the pre-finishing water cooling box 5 are rolled by the pre-finishing mill. Loops are configured between the pre-finishing mills, and tensionless rolling is adopted. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of deformation per pass during rolling is 1.15 to 1.33. The rolling temperature of the pre-finishing mill 7 is 900℃ to 950℃. The running speed of the workpieces after pre-finishing mill rolling is 3m / s to 25m / s.

[0063] (4) Finishing mill rolling: The rolled pieces that have been rolled by the pre-finishing mill and cooled by the water cooling box 8 after pre-finishing are rolled by the 45° top-crossing cantilever finishing mill in 2-8 passes. Micro-tension control is adopted between the finishing mills 10. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of deformation per pass during the rolling process is 1.18 to 1.26, and the deformation temperature is 850℃ to 900℃. The running speed of the rolled pieces after finishing mill 10 is 10m / s to 80m / s.

[0064] (5) Reduction mill rolling: The rolled piece after being rolled by the finishing mill 10 and cooled by the water cooling box 11 after the finishing mill is rolled by the two-pass 45° top-crossing cantilever reduction mill 13. Micro-tension control is adopted between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of the deformation per pass during the rolling process is 1.23 to 1.30, and the deformation temperature is 750℃ to 850℃. The rolled piece is a threaded wire rod, and the running speed is 20m / s to 110m / s.

[0065] (6) Wire forming: After being rolled by the reducing mill 13 and cooled by the water cooling box 14 after the reducing mill, the rolled piece is fed by the pinch roll 15 and then enters the wire forming machine 16 for wire forming. The wire forming temperature range of the rolled piece is 700℃~850℃.

[0066] (7) Air cooling line cooling: The coil after being rolled into a coil is cooled by air cooling line 17. The cooling rate of the rolled part on air cooling line 17 is 5℃ / s~30℃ / s, and the running speed of the air cooling line roller is 0.15m / s~1.0m / s.

[0067] (8) Coil collection: The coils cooled by the air-cooling line are collected by the coil collection station 18, cooled by the PF line, and then bundled and collected.

[0068] 2) For high-speed bar production of straight bar products, please refer to the following: Figure 3 and Figure 5 Its process flow is as follows Figure 3 As shown, its temperature control curve is as follows: Figure 5 As shown:

[0069] (1) Electromagnetic induction heating of continuous casting billet: Electromagnetic induction heating device 1 is used to heat the continuous casting billet directly sent from the continuous casting process. The electromagnetic induction heating temperature range is 50℃~200℃, and the temperature of the continuous casting billet after heating is 900℃~1000℃.

[0070] (2) Roughing and intermediate rolling mills: After electromagnetic induction heating, the continuous casting billet is rolled by roughing, intermediate rolling and pre-finishing mills in sequence. Roughing mill 2 and intermediate rolling mill 4 adopt micro-tension control. Loops are configured between pre-finishing mill 7 and tensionless rolling is adopted. During rolling, the pass system of the roughing mill is box-box-variable ellipse-circle-ellipse-circle, and the pass system of the intermediate rolling mill and pre-finishing mill is ellipse-circle pass system. The average compression ratio of deformation per pass during rolling is 1.20 to 1.40. The rolling temperature of the roughing and intermediate rolling mills is 900℃ to 1000℃. The running speed of the rolled piece after rolling in intermediate rolling mill 4 is 1m / s to 8m / s.

[0071] (3) Pre-finishing mill rolling: The workpieces that have been rolled by the intermediate mill 4 and cooled by the pre-finishing water cooling box 5 are rolled by the pre-finishing mill 7. Loops are configured between the pre-finishing mills 7, and tensionless rolling is adopted. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of deformation per pass during rolling is 1.15 to 1.33. The rolling temperature of the pre-finishing mill 7 is 900℃ to 950℃. The running speed of the workpieces after rolling by the pre-finishing mill 7 is 3m / s to 25m / s.

[0072] (4) Finishing mill rolling: The rolled piece after being rolled by the pre-finishing mill 7 and cooled by the water cooling box 8 after pre-finishing is rolled by the 45° top-crossing cantilever finishing mill 10 in 2-4 passes. Micro-tension control is adopted between the finishing mills 10. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of deformation per pass during the rolling process is 1.15 to 1.28, and the deformation temperature is 850℃ to 900℃. The running speed of the rolled piece after finishing mill rolling is 12m / s to 36m / s.

[0073] (5) Reduction mill rolling: The rolled piece after being rolled by the finishing mill 10 and cooled by the water cooling box 11 after the finishing mill is rolled by the two-pass 45° top-crossing cantilever reduction mill 13. Micro-tension control is adopted between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of the deformation per pass during the rolling process is 1.23 to 1.30, and the deformation temperature is 750℃ to 850℃. The rolled piece is a threaded straight bar with a running speed of 20m / s to 55m / s.

[0074] (6) Cooling on the cooling bed: The rolled piece after being rolled and deformed by the reducing mill 13 is cooled by the water cooling box 14 after the reducing mill. After being sheared by the double-length flying shear 22, it enters the cooling bed 21 through the rotating hub for cooling. The temperature range of the upper cooling bed is 750℃~830℃, and the temperature range of the lower cooling bed is 250℃~350℃.

[0075] (7) Bundling and collection: After the rolled pieces are cooled on the cooling bed, they are cut to length by the cold shear 20 and then counted, bundled and collected by the collection device 19.

[0076] The direct rolling process described in this application for low-alloy HRB400E steel without Widmanstätten structure eliminates the need for a heating furnace, saving energy consumption required for heating in the heating rolling process and achieving zero carbon dioxide emissions, thus realizing low-consumption production. An electromagnetic induction heating device is installed before the roughing mill, ensuring a temperature difference of ≤30℃ between the head and tail ends after heating. This results in stable microstructure and properties at the head, tail, and middle positions of the final product, and good product passability. The roughing mill, intermediate mill, and pre-finishing mill operate at high rolling temperatures with relatively low rolling power, resulting in lower power consumption per ton of steel compared to low-temperature rolling, saving electricity costs and improving equipment stability and service life. A two-stand reducing mill achieves high-reduction rolling, ensuring uniform surface and core microstructure of the HRB400E product. The product microstructure consists of uniform pearlite and ferrite, without Widmanstätten structure, exhibiting stable microstructure and product performance. Under low-cost process conditions, the low-alloy product can be produced in a wide range of specifications. The produced rebar coils or straight bars exhibit high dimensional accuracy, excellent surface quality, and stable mechanical properties.

[0077] Specifically, the nominal diameters of the high-speed wire rod production line products (coiled products) are 6mm, 8mm, 10mm, 12mm and 14mm, and the nominal diameters of the high-speed bar production line products (straight bar products) are 10mm, 12mm and 14mm.

[0078] Table 1. Chemical composition (mass fraction, %) of low alloy HRB400E in each embodiment.

[0079] Ingredients 1 0.22 0.40 0.85 0.030 0.030 0.0024 ≤0.25 98.47 Ingredient 2 0.23 0.35 0.95 0.030 0.030 0.0022 ≤0.25 98.41 Ingredient 3 0.22 0.43 1.05 0.030 0.030 0.0024 ≤0.25 98.24

[0080] Example 1

[0081] The chemical composition and mass percentage of the Φ6mm direct rolling process for non-Widmanstätten low-alloy HRB400E steel coil are shown in Component 1 of Table 1.

[0082] The specific production process of Widmanstätten-free low-alloy HRB400E steel coils under this direct rolling process is as follows:

[0083] (1) Electromagnetic induction heating of continuous casting billet: The continuous casting billet directly delivered from the continuous casting process is heated by an electromagnetic induction heating device. The size of the continuous casting billet is 165mm×165mm×12000mm. After heating, the temperature of the continuous casting billet is 950℃±30℃.

[0084] (2) Roughing mill rolling: The continuously cast billet after reheating in step (1) is rolled in six passes of roughing mill. The pass system during roughing mill rolling is box-box-variable ellipse-circle-ellipse-circle. The rolling temperature during rolling is 950℃±30℃. The average compression ratio of deformation per pass is 1.317. The diameter of the section of the rolled piece after roughing mill rolling is 79mm. The running speed of the rolled piece after roughing mill rolling is 0.55m / s.

[0085] (3) Intermediate mill rolling: The workpiece after rough rolling in step (2) and cutting by the first cutting head flying shear 3 is rolled in 6 passes in the intermediate mill. The pass system of the intermediate mill is elliptical-circular. The rolling temperature is 950℃±30℃. The average compression ratio of the deformation per pass is 1.325. The diameter of the workpiece section after intermediate mill rolling is 34mm. The running speed of the workpiece after intermediate mill rolling is 2.97m / s.

[0086] (4) Pre-finishing mill rolling: The workpiece after being rolled in step (3) and cut by the second cutting head flying shear for 6 passes is rolled in a 6-pass pre-finishing mill. The pass system of the pre-finishing mill is elliptical-circular. The rolling temperature during the rolling process is 930℃±30℃. The average compression ratio of the deformation per pass is 1.263. The diameter of the workpiece section after pre-finishing mill rolling is 16.9mm. The running speed of the workpiece after intermediate mill rolling is 12.01m / s.

[0087] (5) Finishing mill rolling: The rolled piece after being pre-finished by the finishing mill in step (4) and then cooled by the water cooling box 8 and the head and tail of the third cutting shear 9 is rolled by the finishing mill in 8 passes at 45° top-to-bottom cantilever. Micro-tension control is used between the finishing mills. The roll pass system is an elliptical-circular roll pass system. The rolling temperature is 870℃±30℃. The average compression ratio of the deformation per pass is 1.252. The cross-sectional diameter of the rolled piece after finishing mill rolling is 7.60mm. The running speed of the rolled piece after finishing mill rolling is 68.37m / s.

[0088] (6) Reduction mill rolling: The workpiece after being rolled by the finishing mill in step (5), cooled by the water cooling box 11 after the finishing mill, and cut by the fourth cutting head flying shear 12 is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is adopted between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The rolling temperature is 820℃±30℃. The average compression ratio of the deformation per pass is 1.268. The cross-sectional diameter of the workpiece after the reduction mill is 6.08mm. The running speed of the workpiece after the reduction mill is 110m / s.

[0089] (7) Wire forming: After being rolled by the reducing mill in step (6) and cooled by the reducing mill, the rolled piece is fed into the wire forming machine by the pinch rolls. The wire forming temperature range of the rolled piece is 780℃±30℃;

[0090] (8) Air cooling line cooling: The coil after being spun into a coil in step (7) is cooled by air cooling line control. The cooling rate of the rolled part on the air cooling line is 5℃ / s~30℃ / s, and the running speed of the air cooling line roller is 0.15m / s~1.0m / s. When it reaches the coil collection station, the temperature of the coil is 450℃±30℃.

[0091] (9) Roll collection: The coils cooled by the air-cooling line in step (8) are rolled up and then bundled after being cooled by the PF line.

[0092] Example 2

[0093] The chemical composition and mass percentage of the Φ10mm direct rolling process for low alloy HRB400E steel coils without Widmanstätten structure are shown in Component 1 of Table 1.

[0094] The specific production process of Widmanstätten-free low-alloy HRB400E steel coils under this direct rolling process is as follows:

[0095] (1) Electromagnetic induction heating of continuous casting billet: The continuous casting billet directly delivered from the continuous casting process is heated by an electromagnetic induction heating device. The size of the continuous casting billet is 165mm×165mm×12000mm. After heating, the temperature of the continuous casting billet is 950℃±30℃.

[0096] (2) Roughing mill rolling: The continuously cast billet after reheating in step (1) is rolled in six passes of roughing mill. The pass system during roughing mill rolling is box-box-variable ellipse-circle-ellipse-circle. The rolling temperature during rolling is 950℃±30℃. The average compression ratio of deformation per pass is 1.317. The cross-sectional diameter of the rolled piece after roughing mill rolling is 79mm. The running speed of the rolled piece after roughing mill rolling is 0.93m / s.

[0097] (3) Intermediate mill rolling: The workpiece after rough rolling in step (2) and head cutting is rolled in 6 passes in the intermediate mill. The pass system of the intermediate mill is elliptical-circular. The rolling temperature during the rolling process is 950℃±30℃. The average compression ratio of the deformation per pass is 1.306. The diameter of the workpiece section after intermediate mill rolling is 35.5mm. The running speed of the workpiece after intermediate mill rolling is 4.62m / s.

[0098] (4) Pre-finishing mill rolling: The workpiece after being rolled in step (3) and having its head and tail cut off is rolled in a 6-pass pre-finishing mill. The pass system of the pre-finishing mill is elliptical-circular. The rolling temperature during the rolling process is 930℃±30℃. The average compression ratio of the deformation per pass is 1.232. The diameter of the workpiece section after pre-finishing mill rolling is 19.0mm. The running speed of the workpiece after intermediate mill rolling is 16.13m / s.

[0099] (5) Finishing mill rolling: The workpiece after pre-finishing mill rolling in step (4) and controlled cooling and head and tail cutting is rolled in 4 passes of 45° top-crossing cantilever finishing mill. Micro-tension control is adopted between finishing mills. The roll pass system is elliptical-circular roll pass system. The rolling temperature is 870℃±30℃. The average compression ratio of deformation per pass is 1.229. The diameter of the workpiece section after finishing mill rolling is 12.37mm. The running speed of the workpiece after finishing mill rolling is 36.81m / s.

[0100] (6) Reduction mill rolling: The workpiece rolled by the finishing mill in step (5) and cooled by the finishing mill is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is used between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The rolling temperature is 820℃±30℃. The average compression ratio of the deformation per pass is 1.277. The diameter of the workpiece section after the reduction mill is 10.13mm. The running speed of the workpiece after the reduction mill is 60m / s.

[0101] (7) Wire forming: After being rolled by the reducing mill in step (6) and cooled by the reducing mill, the rolled piece is fed into the wire forming machine by the pinch rolls. The wire forming temperature range of the rolled piece is 780℃±30℃;

[0102] (8) Air cooling line cooling: The coil after being spun into a coil in step (7) is cooled by air cooling line control. The cooling rate of the rolled part on the air cooling line is 5℃ / s~30℃ / s, and the running speed of the air cooling line roller is 0.15m / s~1.0m / s. When it reaches the coil collection station, the temperature of the coil is 450℃±30℃.

[0103] (9) Roll collection: The coils cooled by the air-cooling line in step (8) are rolled up and then bundled after being cooled by the PF line.

[0104] Example 3

[0105] The chemical composition and mass percentage of the HRB400E low alloy steel coil without Widmanstätten structure produced by Φ14mm direct rolling process are shown in Component 2 of Table 1.

[0106] The specific process for producing high-speed coiled low-alloy HRB400E without Widmanstätten structure using this direct rolling technology is as follows:

[0107] (1) Electromagnetic induction heating of continuous casting billet: The continuous casting billet directly delivered from the continuous casting process is heated by an electromagnetic induction heating device. The size of the continuous casting billet is 165mm×165mm×12000mm. After heating, the temperature of the continuous casting billet is 950℃±30℃.

[0108] (2) Roughing mill rolling: The continuously cast billet after reheating in step (1) is rolled in six passes of roughing mill. The pass system during roughing mill rolling is box-box-variable ellipse-circle-ellipse-circle. The rolling temperature during rolling is 950℃±30℃. The average compression ratio of deformation per pass is 1.317. The diameter of the section of the rolled piece after roughing mill rolling is 79mm. The running speed of the rolled piece after roughing mill rolling is 1.23m / s.

[0109] (3) Intermediate rolling mill: The workpiece after rough rolling in step (2) and head cutting is rolled in an intermediate 6-pass rolling mill. The pass system of the intermediate rolling mill is elliptical-circular. The rolling temperature during the rolling process is 950℃±30℃. The average compression ratio of the deformation per pass is 1.306. The diameter of the workpiece section after rolling in the intermediate rolling mill is 35.5mm. The running speed of the workpiece after rolling in the intermediate rolling mill is 6.07m / s.

[0110] (4) Pre-finishing mill rolling: The workpiece after being rolled in step (3) and having its head and tail cut off is subjected to 4 passes of pre-finishing mill rolling. The pass system of the pre-finishing mill is elliptical-circular. The rolling temperature during the rolling process is 930℃±30℃. The average compression ratio of the deformation per pass is 1.257. The diameter of the workpiece section after pre-finishing mill rolling is 22.0mm. The running speed of the workpiece after intermediate mill rolling is 15.80m / s.

[0111] (5) Finishing mill rolling: The workpiece after pre-finishing mill rolling in step (4) and controlled cooling and head and tail cutting is rolled in two passes of 45° top-to-bottom cantilever finishing mill rolling. Micro-tension control is adopted between finishing mills. The roll pass system is an elliptical-circular roll pass system. The rolling temperature is 870℃±30℃. The average compression ratio of deformation per pass is 1.236. The cross-sectional diameter of the workpiece after finishing mill rolling is 17.50mm. The running speed of the workpiece after finishing mill rolling is 24.97m / s.

[0112] (6) Reduction mill rolling: The workpiece rolled by the finishing mill in step (5) and cooled by the finishing mill is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is used between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The rolling temperature is 820℃±30℃. The average compression ratio of the deformation per pass is 1.234. The diameter of the workpiece section after the reduction mill rolling is 14.19mm. The running speed of the workpiece after the reduction mill rolling is 38m / s.

[0113] (7) Wire forming: After being rolled by the reducing mill in step (6) and cooled by the reducing mill, the rolled piece is fed into the wire forming machine by the pinch rolls. The wire forming temperature range of the rolled piece is 780℃±30℃;

[0114] (8) Air cooling line cooling: The coil after being spun into a coil in step (7) is cooled by air cooling line control. The cooling rate of the rolled part on the air cooling line is 5℃ / s~30℃ / s, and the running speed of the air cooling line roller is 0.15m / s~1.0m / s. When it reaches the coil collection station, the temperature of the coil is 450℃±30℃.

[0115] (9) Roll collection: The coils cooled by the air-cooling line in step (8) are rolled up and then bundled after being cooled by the PF line.

[0116] Example 4

[0117] The chemical composition and mass percentage of the Φ10mm direct rolling process for the low-alloy HRB400E high-speed bar without Widmanstätten structure are shown in Component 1 of Table 1.

[0118] The specific production process of high-speed HRB400E low-alloy steel bars without Widmanstätten structure under this direct rolling process is as follows:

[0119] (1) Electromagnetic induction heating of continuous casting billet: The continuous casting billet directly delivered from the continuous casting process is heated by an electromagnetic induction heating device. The size of the continuous casting billet is 165mm×165mm×12000mm. After heating, the temperature of the continuous casting billet is 950℃±30℃.

[0120] (2) Roughing mill rolling: The continuously cast billet after reheating in step (1) is rolled in six passes of roughing mill. The pass system during roughing mill rolling is box-box-variable ellipse-circle-ellipse-circle. The rolling temperature during rolling is 950℃±30℃. The average compression ratio of deformation per pass is 1.338. The diameter of the section of the rolled piece after roughing mill rolling is 78.0mm. The running speed of the rolled piece after roughing mill rolling is 0.76m / s.

[0121] (3) Intermediate rolling mill: The workpiece after rough rolling in step (2) and head cutting is rolled in an intermediate 6-pass rolling mill. The pass system of the intermediate rolling mill is elliptical-circular. The rolling temperature during the rolling process is 950℃±30℃. The average compression ratio of the deformation per pass is 1.284. The diameter of the workpiece section after rolling in the intermediate rolling mill is 37.0mm. The running speed of the workpiece after rolling in the intermediate rolling mill is 3.37m / s.

[0122] (4) Pre-finishing mill rolling: The workpiece after being rolled in step (3) and having its head and tail cut off is rolled in a 6-pass pre-finishing mill. The pass system of the pre-finishing mill is elliptical-circular. The rolling temperature during the rolling process is 930℃±30℃. The average compression ratio of the deformation per pass is 1.241. The diameter of the workpiece section after pre-finishing mill rolling is 19.50mm. The running speed of the workpiece after intermediate mill rolling is 12.15m / s.

[0123] (5) Finishing mill rolling: The workpiece after pre-finishing mill rolling in step (4) and controlled cooling and head and tail cutting is rolled in 4 passes of 45° top-crossing cantilever finishing mill. Micro-tension control is adopted between finishing mills. The roll pass system is elliptical-circular roll pass system. The rolling temperature is 870℃±30℃. The average compression ratio of deformation per pass is 1.237. The diameter of the workpiece section after finishing mill rolling is 12.76mm. The running speed of the workpiece after finishing mill rolling is 28.38m / s.

[0124] (6) Reduction mill rolling: The workpiece rolled by the finishing mill in step (5) and cooled by the finishing mill is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is used between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The rolling temperature is 800℃±30℃. The average compression ratio of the deformation per pass is 1.26. The diameter of the workpiece section after the reduction mill is 10.13mm. The running speed of the workpiece after the reduction mill is 45m / s.

[0125] (7) Cooling on the cooling bed: The rolled piece after being deformed by the reducing mill in step (6) is cooled in a controlled manner. After being sheared by a high-speed flying shear, it enters the cooling bed through the rotating hub for cooling. The temperature range of the upper cooling bed is 750℃~830℃, and the temperature range of the lower cooling bed is 250℃~350℃.

[0126] (8) Bundling and collecting: After the rolled pieces cooled by the cooling bed in step (7) are cut to length, they are counted, bundled and collected.

[0127] Example 5

[0128] The chemical composition and mass percentage of the Φ14mm direct rolling process for the low alloy HRB400E high-speed bar without Widmanstätten structure are shown in Component 1 of Table 1.

[0129] The specific production process of high-speed HRB400E low-alloy steel bars without Widmanstätten structure under this direct rolling process is as follows:

[0130] (1) Electromagnetic induction heating of continuous casting billet: The continuous casting billet directly delivered from the continuous casting process is heated by an electromagnetic induction heating device. The size of the continuous casting billet is 165mm×165mm×12000mm. After heating, the temperature of the continuous casting billet is 950℃±30℃.

[0131] (2) Roughing mill rolling: The continuously cast billet after reheating in step (1) is rolled in six passes of roughing mill. The pass system during roughing mill rolling is box-box-variable ellipse-circle-ellipse-circle. The rolling temperature during rolling is 950℃±30℃. The average compression ratio of deformation per pass is 1.338. The diameter of the section of the rolled piece after roughing mill rolling is 78.0mm. The running speed of the rolled piece after roughing mill rolling is 0.99m / s.

[0132] (3) Intermediate rolling mill: The workpiece after rough rolling in step (2) and head cutting is rolled in an intermediate 6-pass rolling mill. The pass system of the intermediate rolling mill is elliptical-circular. The rolling temperature during the rolling process is 950℃±30℃. The average compression ratio of the deformation per pass is 1.284. The diameter of the workpiece section after rolling in the intermediate rolling mill is 37.0mm. The running speed of the workpiece after rolling in the intermediate rolling mill is 4.41m / s.

[0133] (4) Pre-finishing mill rolling: The workpiece after being rolled in step (3) and having its head and tail cut off is rolled in a 4-pass pre-finishing mill. The pass system of the pre-finishing mill is elliptical-circular. The rolling temperature during the rolling process is 930℃±30℃. The average compression ratio of the deformation per pass is 1.282. The diameter of the workpiece section after pre-finishing mill rolling is 22.50mm. The running speed of the workpiece after intermediate mill rolling is 11.92m / s.

[0134] (5) Finishing mill rolling: The workpiece after pre-finishing mill rolling in step (4) and controlled cooling and head and tail cutting is rolled in two passes of 45° top-crossing cantilever finishing mill rolling. Micro-tension control is adopted between finishing mills. The roll pass system is an elliptical-circular roll pass system. The rolling temperature is 870℃±30℃. The average compression ratio of deformation per pass is 1.236. The diameter of the workpiece section after finishing mill rolling is 18.2mm. The running speed of the workpiece after finishing mill rolling is 18.23m / s.

[0135] (6) Reduction mill rolling: The workpiece rolled by the finishing mill in step (5) and cooled by the finishing mill is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is used between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The rolling temperature is 800℃±30℃. The average compression ratio of the deformation per pass is 1.283. The diameter of the workpiece section after the reduction mill is 14.19mm. The running speed of the workpiece after the reduction mill is 30m / s.

[0136] (7) Cooling on the cooling bed: The rolled piece after being deformed by the reducing mill in step (6) is cooled in a controlled manner. After being sheared by a high-speed flying shear, it enters the cooling bed through the rotating hub for cooling. The temperature range of the upper cooling bed is 750℃~830℃, and the temperature range of the lower cooling bed is 250℃~350℃.

[0137] (8) Bundling and collecting: After the rolled pieces cooled by the cooling bed in step (7) are cut to length, they are counted, bundled and collected.

[0138] In summary, the mechanical properties of the Widmanstätten-free low-alloy HRB400E steel under the direct rolling process in the above five embodiments are shown in Table 2.

[0139] Table 2 Mechanical properties of low alloy HRB400E in each example

[0140]

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A low-alloy HRB400E steel without Widmanstätten structure under direct rolling process, characterized in that: The chemical composition and mass percentage of Widmanstätten-free low-alloy HRB400E steel under this direct rolling process are as follows: C: 0.18~0.25%, Si: ≤0.65%, Mn: ≤1.10%, P: ≤0.040%, S: ≤0.040%, N: ≤0.010%, O: ≤28ppm, with the balance being Fe and unavoidable residual elements; The residual elements include Ti, Nb, and V; The microstructure of the Widmanstätten-free low-alloy HRB400E steel under the direct rolling process is uniformly distributed ferrite + pearlite, with a pearlite ratio of ≥55%, a grain size grade of ≥10, and no Widmanstätten structure. The aforementioned direct rolling process for producing Widmanstätten-free low-alloy HRB400E steel is based on a high-speed wire rod production line or a high-speed bar production line under the direct rolling process. The direct rolling process based on the high-speed wire rod production line includes the following steps: S1. Electromagnetic induction heating of continuous casting billet: An electromagnetic induction heating device is used to heat the continuous casting billet directly delivered from the continuous casting process; the electromagnetic induction heating device is equipped with a closed-loop temperature control system, and the temperature difference between the head and tail of the continuous casting billet after heating is ≤30℃. S2. Roughing and intermediate rolling: The continuously cast billet after electromagnetic induction heating is subjected to roughing and intermediate rolling in sequence. The roughing and intermediate rolling mills adopt micro-tension control, and the pre-finishing mill adopts tension-free rolling. During rolling, the pass system of the roughing mill adopts box-box-variable ellipse-circle-ellipse-circle, and the pass system of the intermediate rolling mill is an ellipse-circle pass system. S3. Pre-finishing mill rolling: The pre-finishing mill rolls are rolled after the intermediate mill and cooled by the pre-finishing water cooling box. The pre-finishing mill adopts tensionless rolling and the pass system of the pre-finishing mill is an elliptical-circular pass system. S4. Finishing mill rolling: The rolled pieces that have been pre-finished and cooled by the water cooling box after pre-finishing are rolled in 2-8 passes of 45° top-crossing cantilever finishing mill. Micro-tension control is used between finishing mills. The pass system of the finishing mill is an elliptical-circular pass system during rolling. S5. Reduction Mill Rolling: The rolled workpiece after being rolled by the finishing mill and cooled by the water cooling box after the finishing mill is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is adopted between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of deformation per pass during the rolling process is 1.23 to 1.

30. The rolled workpiece is a threaded wire rod. The running speed is 20m / s to 110m / s. S6. Wire forming: After being rolled by the reducing mill and cooled by the water cooling box after the reducing mill, the rolled piece is fed into the wire forming machine by the pinch rolls. The wire forming temperature range of the rolled piece is 700℃~850℃. S7. Air-cooled line cooling: The coils after being rolled into coils are cooled by air-cooled line control. The cooling rate of the rolled parts on the air-cooled line is 5℃ / s~30℃ / s, and the running speed of the air-cooled line roller is 0.15m / s~1.0m / s. S8. Coil Collection: Coiled coils cooled by the air-cooling line are collected at the coiling station, cooled by the PF line, and then bundled and collected. The direct rolling process based on the high-speed bar production line includes the following steps: S1. Electromagnetic induction heating of continuous casting billet: An electromagnetic induction heating device is used to heat the continuous casting billet directly delivered from the continuous casting process; the electromagnetic induction heating device is equipped with a closed-loop temperature control system, and the temperature difference between the head and tail of the continuous casting billet after heating is ≤30℃. S2. Roughing and intermediate rolling mills: After electromagnetic induction heating, the continuously cast billet is rolled sequentially by roughing, intermediate rolling and pre-finishing mills. The roughing and intermediate rolling mills adopt micro-tension control. During rolling, the pass system of the roughing mill is box-box-variable ellipse-circle-ellipse-circle, and the pass system of the intermediate rolling mill and pre-finishing mill is ellipse-circle pass system. S3. Pre-finishing mill rolling: The pre-finishing mill rolls are used to roll the workpieces that have been rolled by the intermediate mill and cooled by the water cooling box before pre-finishing. The pre-finishing mill adopts tensionless rolling and the roll pass system is an elliptical-circular roll pass system. S4. Finishing mill rolling: The rolled pieces after pre-finishing mill rolling and controlled cooling in the water cooling box after pre-finishing are rolled in 2-4 passes of 45° top-crossing cantilever finishing mill. Micro-tension control is adopted between finishing mills. The roll pass system is an elliptical-circular roll pass system. S5. Reduction Mill Rolling: The rolled workpiece after being rolled by the finishing mill and cooled by the water cooling box after the finishing mill is rolled by a two-pass 45° top-crossing cantilever reduction mill. Micro-tension control is adopted between the two reduction mills. The roll pass system is an elliptical-circular roll pass system. The average compression ratio of deformation per pass during the rolling process is 1.23 to 1.

30. The rolled workpiece is a straight threaded bar. The running speed is 20m / s to 55m / s. S6. Cooling bed: The rolled pieces after being deformed by the reducing mill are cooled by the water cooling box after the reducing mill. After being sheared by the double-length flying shear, they enter the cooling bed through the rotating hub for cooling. The temperature range of the upper cooling bed is 750℃~830℃, and the temperature range of the lower cooling bed is 250℃~350℃. S7. Bundling and Collection: After the rolled pieces are cooled on the cooling bed, they are cut to length by cold shear and then counted, bundled and collected by a collection device.

2. The Widmanstätten-free low-alloy HRB400E steel produced by direct rolling process according to claim 1, characterized in that: The electromagnetic induction heating device has an electromagnetic induction heating temperature range of 50℃ to 200℃, and the temperature of the continuous casting billet after heating is 900℃ to 1000℃.

3. The Widmanstätten-free low-alloy HRB400E steel produced by direct rolling process according to claim 2, characterized in that: The average compression ratio of the pass deformation during the rolling process of the roughing mill and intermediate mill is 1.20 to 1.

40. The rolling temperature of both the roughing mill and intermediate mill is within the complete recrystallization temperature range, which is 900℃ to 1000℃. The running speed of the rolled piece after rolling in the intermediate mill is 1m / s to 8m / s.

4. The Widmanstätten-free low-alloy HRB400E steel produced by direct rolling process according to claim 3, characterized in that: During the pre-finishing mill rolling process, the average compression ratio of deformation per pass is 1.15 to 1.

33. The rolling temperature of the pre-finishing mill is in the complete recrystallization temperature range, which is 900℃ to 950℃. The running speed of the rolled piece after the pre-finishing mill rolling is 3m / s to 25m / s.

5. The Widmanstätten-free low-alloy HRB400E steel produced by direct rolling process according to claim 4, characterized in that: During the finishing mill rolling process, the average compression ratio of each pass is 1.18 to 1.26, the deformation temperature is 850℃ to 900℃, and the running speed of the rolled piece after finishing mill rolling is 10m / s to 80m / s.

6. The Widmanstätten-free low-alloy HRB400E steel produced by direct rolling process according to claim 5, characterized in that: The rolling temperature of the reducing mill is in the partial recrystallization or two-phase temperature range, and the initial rolling temperature range of the reducing mill is 750℃~850℃.

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