A method of manufacturing a construction steel by direct rolling process

Abstract

The application relates to the field of construction steel, in particular to a method for preparing construction steel through a straight rolling process. The method comprises the following steps: under the condition of setting a continuous casting machine pulling speed and setting a basic arc radius of the continuous casting machine, continuously casting molten steel to obtain a casting blank; under the condition of setting a shearing time, hydraulically shearing the casting blank, wherein the casting blank is in a heat preservation state; coarsely rolling the sheared casting blank with a set surface temperature, then medium-rolling and first cooling after rolling to obtain an intermediate blank; under the condition of setting a rolling temperature and setting a rolling deformation amount, finish-rolling the intermediate blank, then second cooling to obtain the construction steel. The application solves the technical problem that the production intensity such as Rel fluctuates greatly in the existing straight rolling process.

Description

Technical Field

[0001] This application relates to the field of construction steel, and more particularly to a method for preparing construction steel using a direct rolling process. Background Technology

[0002] The core of continuous casting direct rolling technology is to rapidly transport high-temperature castings to the rolling mill for rolling, minimizing heat loss in intermediate stages. Heating the billet accounts for over 80% of the energy consumption in the steel rolling process. Direct rolling eliminates blast furnace gas consumption, reduces billet oxidation and burn-off, and eliminates heating furnace maintenance costs. Simultaneously, it reduces emissions of pollutants such as SO2, NOx, and dust, resulting in significant economic and social benefits.

[0003] Currently, the direct rolling process without heating suffers from significant fluctuations in production strength, resulting in poor performance stability of the produced steel reinforcement. Summary of the Invention

[0004] This application provides a method for preparing construction steel using a direct rolling process to solve the technical problem of large fluctuations in production strength, such as Rel, in existing direct rolling processes.

[0005] In a first aspect, this application provides a method for preparing construction steel using a direct rolling process, the method comprising:

[0006] Under the conditions of setting the casting speed and the basic arc radius of the continuous casting machine, molten steel is continuously cast to obtain a billet.

[0007] Under a set shearing time, the billet is subjected to hydraulic shearing; wherein the billet is in a heat preservation state.

[0008] The cut billet with a set surface temperature is rough rolled, then intermediate rolled and cooled after rolling to obtain an intermediate billet;

[0009] Under the conditions of setting the rolling temperature and the rolling deformation, the intermediate billet is precision rolled and then subjected to a second cooling to obtain steel for construction.

[0010] Optionally, the continuous casting machine has a casting speed of 2.9 m / min to 4.0 m / min.

[0011] Optionally, the basic arc radius of the continuous casting machine is 7.0m-9.0m.

[0012] Optionally, the shearing time is 3s-10s.

[0013] Optionally, the surface temperature is 950℃-1000℃.

[0014] Optionally, the step of rough rolling the cut billet with a set surface temperature, followed by intermediate rolling and a first cooling, to obtain an intermediate billet includes:

[0015] The cut billet with a set surface temperature is rough rolled, then intermediate rolled and rolled, and then the billet is locally cooled, and the temperature difference between the head and tail of the billet is controlled to obtain an intermediate billet; wherein the temperature difference between the head and tail is <80℃.

[0016] Optionally, the rolling temperature is 850℃-1000℃.

[0017] Optionally, the rolling deformation is >40%.

[0018] Optionally, under the conditions of setting the rolling temperature and rolling deformation, the intermediate billet is precision rolled and then subjected to a second cooling to obtain construction steel, comprising:

[0019] Under the conditions of setting the rolling temperature and the amount of rolling deformation, the intermediate billet is precision rolled, and then the precision rolled intermediate billet is water-cooled under the condition of setting the first cooling rate.

[0020] Under the condition of setting a second cooling rate, the water-cooled intermediate billet is slowly cooled.

[0021] Optionally, the first cooling rate is ≥10℃ / s, and the second cooling rate is 0.05℃ / s-3℃ / s.

[0022] The technical solutions provided in this application have the following advantages compared with the prior art:

[0023] The method for preparing construction steel using direct rolling technology provided in this application reduces billet temperature loss by controlling the casting machine speed and hydraulic shearing time; ensures the stability of construction steel performance through rolling process design; and reduces fluctuations in construction steel performance and controls changes in the internal structure of the steel through cooling process design. This method solves the technical problem of large fluctuations in strength (Rel) during direct rolling production, effectively stabilizing the performance stability of construction steel reinforcement, while achieving heat-free production. It reduces billet oxidation loss by 1.0-1.5% per ton of steel compared to secondary heating; achieves zero emissions of NOx, SO2, particulate matter, and CO2, which is beneficial to environmental protection; and the energy consumption of the rolling process is less than 10 kgce / t, reducing carbon dioxide emissions by 75 kg per ton of steel. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic flowchart illustrating a method for preparing construction steel using a direct rolling process, provided as an embodiment of this application;

[0027] Figure 2 Microstructure of edge material for building steel prepared by direct rolling process, as provided in this application embodiment;

[0028] Figure 3 Microstructure of a steel core for building applications prepared by a direct rolling process, as provided in this application embodiment;

[0029] Figure 4 Microstructure of a direct rolling process for preparing construction steel, provided as a comparative example of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0032] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0034] Firstly, this application provides a method for preparing construction steel using a direct rolling process; please refer to [link to relevant documentation]. Figure 1 The method includes:

[0035] S1. Under the conditions of setting the continuous casting machine speed and setting the basic arc radius of the continuous casting machine, molten steel is continuously cast to obtain a billet.

[0036] S2. Under the condition of a set shearing time, the billet is subjected to hydraulic shearing; wherein the billet is in a heat preservation state;

[0037] S3. The cut billet with a set surface temperature is rough rolled, then intermediate rolled and cooled after rolling to obtain an intermediate billet.

[0038] S4. Under the conditions of setting the rolling temperature and setting the rolling deformation, the intermediate billet is precision rolled and then cooled a second time to obtain steel for construction.

[0039] In the embodiments of this application, the specific steps of the method for preparing construction steel by direct rolling process include: converter or electric furnace → (ladle refining) → continuous casting → continuous casting machine (150 cubic meters) → straightening machine → heat preservation roller conveyor → hydraulic shear → hot conveying roller conveyor → roughing mill → intermediate mill → graded cooling system → finishing mill → graded cooling system → cooling bed → warehousing.

[0040] By controlling the casting machine speed and hydraulic shearing time, the temperature loss of the cast billet is reduced; the rolling process is designed to ensure the stability of the performance of the steel for construction; and the cooling process is designed to reduce fluctuations in the performance of the steel for construction and control changes in the internal structure of the steel. Heated direct rolling requires two things: first, the continuous casting billet must be at a sufficiently high temperature after cutting; second, the cut continuous casting billet must be quickly transported to the rolling mill for rolling, with insulation measures taken when necessary. In this embodiment, the system includes: a pre-shearing insulation roller conveyor, a post-shearing insulation roller conveyor, and a transport insulation roller conveyor. The online insulation roller conveyor device for the continuous casting billet has an upper cover, rollers, and lower cover integrated into a single unit to achieve good insulation and heat replenishment effects, ensuring that the inlet temperature of the roughing mill is not lower than 950℃. The temperature drop of a 12m long continuous casting billet is 30℃-80℃. The high-speed transport insulation roller conveyor for direct rolling uses a high-speed insulation roller conveyor with a speed of 5.5m / s, resulting in a temperature drop of approximately 10℃-50℃ during transport. This method solves the technical problem of large fluctuations in production intensity (Rel) in existing direct rolling processes. It not only reduces production costs but also achieves stable performance and excellent quality in construction steel produced from continuously cast hot billets. Furthermore, it addresses the long-standing issue of relying on continuously cast billets cooled to room temperature and then heated in a furnace for further processing.

[0041] In some embodiments, the continuous casting machine has a casting speed of 2.9 m / min to 4.0 m / min.

[0042] In the embodiments of this application, the positive effects of controlling the casting speed of the continuous casting machine to be between 2.9 m / min and 4.0 m / min are: obtaining excellent billets that meet the conditions for direct rolling; excessively high casting speeds lead to steel leakage; excessively low casting speeds lead to excessive temperature drop, requiring subsequent temperature compensation and failing to achieve the effect of eliminating the need for heating. Specifically, the casting speed can be 2.9 m / min, 3.0 m / min, 3.3 m / min, 3.6 m / min, 3.9 m / min, etc.

[0043] In some embodiments, the basic arc radius of the continuous casting machine is 7.0m-9.0m.

[0044] The positive effects of controlling the basic arc radius of the continuous casting machine to 7.0m-9.0m include: ensuring the surface quality of the cast billet and achieving a surface temperature of no less than 1100℃ when exiting the straightening machine. Specifically, this radius can be 7.0m, 8.0m, 9.0m, etc.

[0045] In some implementations, the shearing time is 3s-10s.

[0046] The positive effects of controlling the shearing time to 3-10 seconds include: better control of temperature drop. If the time is too long, it can lead to excessive temperature drop; if the time is too short, it can result in poor shearing performance. Specifically, the shearing time can be 3s, 4s, 5s, 6s, 7s, 8s, 9s, 10s, etc.

[0047] In some embodiments, the surface temperature is 950°C-1000°C.

[0048] "Surface temperature" refers to the surface temperature of the rough-rolled billet. Controlling the surface temperature of the rough-rolled billet to 950℃-1000℃ has the following positive effects: on the one hand, it enables smooth rolling; on the other hand, it allows for low-temperature rolling, which is beneficial for subsequent compression ratio and performance improvement. If the temperature is too high, it can lead to performance discrepancies or large performance fluctuations in the later stages. If the temperature is too low, it can lead to excessive mill load and damage to the mill's lifespan. The core strain during rough rolling is higher than in traditional rolling, which helps control the amount of core deformation and improve the microstructure quality of the core. Specifically, this temperature can be 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃, etc. Preferably, the temperature is 950℃-960℃.

[0049] In some embodiments, the step of rough rolling the cut billet with a set surface temperature, followed by intermediate rolling and a first cooling, to obtain an intermediate billet includes:

[0050] The cut billet with a set surface temperature is rough rolled, then intermediate rolled and rolled, and then the billet is locally cooled, and the temperature difference between the head and tail of the billet is controlled to obtain an intermediate billet; wherein the temperature difference between the head and tail is <80℃.

[0051] The first cooling method is localized cooling, which is beneficial for controlling the temperature difference of the cast billet. Controlling the temperature difference between the beginning and end of the casting to <80℃ has the positive effect of reducing excessive performance fluctuations within the same billet. If this difference is too high, it can lead to excessive performance fluctuations, thus hindering cost control. Specifically, this temperature difference between the beginning and end can be 70℃, 75℃, 65℃, etc. The surface of the cast billet undergoes intermediate cooling, specifically cooling of the non-recrystallized zone, with a surface temperature drop of 200-400℃.

[0052] In some embodiments, the rolling temperature is 850°C-1000°C.

[0053] The positive effects of controlling the finishing rolling temperature to 850-1000℃ include: mitigating abnormal grain growth caused by recrystallization during finishing rolling, which can lead to excessively large grains; conversely, excessively high temperatures can result in excessively large grains or abnormal structures such as Widmanstätten structure. Specifically, this temperature can be 850℃, 880℃, 910℃, 940℃, 970℃, or 1000℃.

[0054] In some embodiments, the rolling deformation is >40%.

[0055] The positive effects of controlling the deformation amount in finishing rolling to >40% include: it helps to increase the core deformation amount in the rolling process, providing more nucleation points; if the deformation amount is too high, it will lead to excessive mill stress to some extent, and on the other hand, it will lead to improved material dimensional control. Specifically, this deformation amount can be 41%, 42%, 43%, etc.

[0056] In some embodiments, the step of finishing the intermediate billet under set rolling temperature and rolling deformation conditions, followed by a second cooling, to obtain construction steel includes:

[0057] Under the conditions of setting the rolling temperature and the amount of rolling deformation, the intermediate billet is precision rolled, and then the precision rolled intermediate billet is water-cooled under the condition of setting the first cooling rate.

[0058] Under the condition of setting a second cooling rate, the water-cooled intermediate billet is slowly cooled.

[0059] The positive effects of water cooling followed by slow cooling: ensuring the stability of the internal structure of structural steel. This slow cooling is carried out on a cooling bed, and the initial temperature of the slow cooling bed is controlled at 650-750℃. Its positive effects: it helps to retain more nucleation sites, providing the driving force for ferrite nucleation; if the temperature is too high, it will lead to a certain reduction in nucleation sites; if the temperature is too low, it will lead to a certain degree of abnormal microstructure transformation.

[0060] In some embodiments, the first cooling rate is ≥10℃ / s, and the second cooling rate is 0.05℃ / s-3℃ / s.

[0061] "First cooling rate" refers to the cooling rate of water cooling, while "first cooling rate" refers to the cooling rate of slow cooling.

[0062] The positive effects of controlling the cooling rate of water cooling to ≥10℃ / s include: controlling abnormal grain growth; if the cooling rate is too low, it can lead to abnormal grain growth to some extent. Specifically, the cooling rate of water cooling can be 10℃ / s, 11℃ / s, 12℃ / s, 13℃ / s, etc. The positive effects of controlling the cooling rate of slow cooling to 0.05-3℃ / s include: controlling the microstructure to transform into a ferrite + pearlite microstructure; if the cooling rate is too high, it can increase the risk of overcooling to some extent; if the cooling rate is too low, the cooling bed may be insufficient, resulting in incomplete microstructure transformation. Specifically, the cooling rate of water cooling can be 0.05℃ / s, 1℃ / s, 1.5℃ / s, 2℃ / s, 2.5℃ / s, 3.0℃ / s, etc.

[0063] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0064] Example 1:

[0065] A method for producing direct-rolled construction steel includes the following steps: smelting in a converter and refining outside the ladle, followed by continuous casting at a casting speed of 2.9 m / min. A hydraulic shear is used for the steel flame cutting, with a shearing time of 3 seconds to reduce temperature drop during the billet shearing process. The continuous casting machine has a basic arc radius of 8.0 mm, achieving a billet surface temperature of 1150℃ at the exit of the straightening machine. It employs pre-shearing heat-preserving roller conveyors, post-shearing heat-preserving roller conveyors, and transport heat-preserving roller conveyors. The online heat-preserving roller conveyor device for the continuous casting billet integrates the upper cover, rollers, and lower cover into a single unit, achieving an inlet temperature of 960℃ at the roughing mill; and a temperature drop of 50℃ for a 12m long continuous casting billet.

[0066] The rolling process includes roughing, intermediate rolling, and finishing rolling. The surface temperature of the initial billet in the roughing rolling process is 960℃, and the core strain during the roughing rolling process is higher than that in conventional rolling. Local cooling of the cast billet is adopted, and the temperature difference between the beginning and end is controlled at 50℃. The surface of the intermediate cooling is cooled in the non-recrystallized zone, with a surface temperature drop of 400℃. The finishing rolling temperature is 850℃, and the deformation is 41%. Cooling includes water cooling and slow cooling on a cooling bed. The cooling rate of the water cooling is 80℃ / s, and the starting temperature of the slow cooling on the cooling bed is 680℃, with a cooling rate of 3℃ / s.

[0067] The direct-rolled material produced using the embodiments of this application exhibits a higher penetration rate in the roughing stage compared to the transmission process, resulting in increased thermal strain in the core. This leads to a 3% increase in elongation of the hot-rolled material, a pearlite content of 39%, and a grain size of 9.5. The 400MPa grade achieves a Rel of over 430MPa, and the 500MPa grade achieves over 521MPa.

[0068] Example 2:

[0069] A method for producing direct-rolled construction steel includes the following steps: smelting in a converter and refining outside the ladle, followed by continuous casting at a casting speed of 4 m / min; a hydraulic shearing machine is used for steel flame cutting with a shearing time of 4 seconds to reduce the temperature drop during the billet shearing process. The continuous casting machine has a basic arc radius of 9.0 mm, achieving a billet surface temperature of 1150℃ at the exit of the straightening machine; pre-shearing heat-preserving roller conveyor, post-shearing heat-preserving roller conveyor, and transport heat-preserving roller conveyor are employed. The online heat-preserving roller conveyor device for the continuous casting billet integrates the upper cover, rollers, and lower cover into a single unit, achieving an inlet temperature of 970℃ at the roughing mill; and a temperature drop of 40℃ for a 12m long continuous casting billet.

[0070] The rolling process includes roughing, intermediate rolling and finishing rolling. The surface temperature of the unrolled billet in the roughing process is 965°C, and the core strain during the roughing process is higher than that in conventional rolling.

[0071] Local cooling of the cast billet is adopted, with the temperature difference between the beginning and end controlled at 45℃. The surface of the intermediate cooling zone is cooled to the non-recrystallized area, with a surface temperature drop of 350℃; the finishing rolling temperature is 890℃, and the deformation is 45%.

[0072] Cooling includes water cooling and slow cooling on a cooling bed. The water cooling rate is 110℃ / s, the starting temperature of the slow cooling on the cooling bed is 680℃, and the cooling rate of the slow cooling on the cooling bed is 2.5℃ / s.

[0073] The straight-rolled material produced using the embodiments of this application exhibits a higher penetration rate in the roughing stage compared to the transmission process, resulting in increased thermal strain in the core. This leads to a 4% increase in elongation of the hot-rolled material, a pearlite content of 39.5%, and a grain size of 10.0. The 400MPa grade yields a Rel of 450MPa; the 500MPa grade yields a Rel of 540MPa.

[0074] Example 3:

[0075] A method for producing direct-rolled construction steel includes the following steps: smelting in a converter and refining outside the ladle, followed by continuous casting at a casting speed of 3.5 m / min. A hydraulic shear is used for the steel flame cutting, with a shearing time of 5 seconds to reduce temperature drop during the billet shearing process. The continuous casting machine has a basic arc radius of 8.0 mm, achieving a billet surface temperature of 1150℃ at the exit of the straightening machine. It employs pre-shearing heat-preserving roller conveyors, post-shearing heat-preserving roller conveyors, and transport heat-preserving roller conveyors. The online heat-preserving roller conveyor device for the continuous casting billet integrates the upper cover, rollers, and lower cover into a single unit, achieving an inlet temperature of 955℃ at the roughing mill; and a temperature drop of 40℃ for a 12m long continuous casting billet.

[0076] The rolling process includes roughing, intermediate rolling, and finishing rolling. The surface temperature of the initial billet in the roughing rolling process is 965℃, and the core strain during the roughing rolling process is higher than that in conventional rolling. Local cooling of the cast billet is adopted, and the temperature difference between the beginning and end is controlled at 50℃. The surface of the intermediate cooling is cooled in the non-recrystallized zone, with a surface temperature drop of 350℃. The finishing rolling temperature is 900℃, and the deformation is 43%. Cooling includes water cooling and slow cooling on a cooling bed. The cooling rate of the water cooling is 150℃ / s, and the starting temperature of the slow cooling on the cooling bed is 700℃, with a cooling rate of 3℃ / s.

[0077] The straight-rolled material produced using the embodiments of this application exhibits a higher penetration rate in the roughing stage compared to the transmission process, resulting in increased thermal strain in the core. This leads to a 4.5% increase in elongation of the hot-rolled material, a pearlite content of 41%, and a grain size of 10.5. The 400MPa grade yields a Rel of 444MPa; the 500MPa grade yields a Rel of 541MPa.

[0078] Example 4:

[0079] A method for producing direct-rolled construction steel includes the following steps: smelting in a converter and refining outside the ladle, followed by continuous casting at a casting speed of 3.5 m / min. A hydraulic shear is used for the steel flame cutting, with a shearing time of 10 seconds to reduce temperature drop during the billet shearing process. The continuous casting machine has a basic arc radius of 7.0 mm, achieving a billet surface temperature of 1150℃ at the exit of the straightening machine. It employs pre-shearing heat-preserving roller conveyors, post-shearing heat-preserving roller conveyors, and transport heat-preserving roller conveyors. The online heat-preserving roller conveyor device for the continuous casting billet integrates the upper cover, rollers, and lower cover into a single unit, achieving an inlet temperature of 955℃ at the roughing mill; and a temperature drop of 40℃ for a 12m long continuous casting billet.

[0080] The rolling process includes roughing, intermediate rolling, and finishing rolling. The surface temperature of the initial billet in the roughing rolling process is 1000℃, and the core strain during the roughing rolling process is higher than that in conventional rolling. Local cooling of the cast billet is adopted, and the temperature difference between the head and tail is controlled at 75℃. The surface of the intermediate cooling is cooled in the non-recrystallized zone, with a surface temperature drop of 350℃. The finishing rolling temperature is 1000℃, and the deformation is 43%. Cooling includes water cooling and slow cooling on a cooling bed. The cooling rate of the water cooling is 10℃ / s, and the starting temperature of the slow cooling on the cooling bed is 750℃, with a cooling rate of 0.05℃ / s.

[0081] The direct-rolled material produced using the embodiments of this application exhibits a higher penetration rate in the roughing stage compared to the transmission process, resulting in increased thermal strain in the core. This leads to a 3% increase in elongation of the hot-rolled material, a pearlite content of 45%, and a grain size of 9. The 400MPa grade yields a Rel of 450MPa; the 500MPa grade yields a Rel of 560MPa.

[0082] Comparative Example 1:

[0083] A method for producing direct-rolled construction steel includes the following steps: smelting in a converter and refining outside the ladle, followed by continuous casting at a casting speed of 3.5 m / min; a hydraulic shearing machine is used for steel flame cutting, with a shearing time of 30 seconds to reduce the temperature drop during the billet shearing process. The continuous casting machine has a basic arc radius of 8 mm, achieving a billet surface temperature of 1000℃ at the exit of the straightening machine; and employs pre-shearing heat-preserving roller conveyors, post-shearing heat-preserving roller conveyors, and transport heat-preserving roller conveyors. The online heat-preserving roller conveyor device for the continuous casting billet integrates the upper cover, rollers, and lower cover into a single unit, achieving an inlet temperature of 850℃ at the roughing mill; and a temperature drop of 150℃ for a 12m long continuous casting billet.

[0084] Rolling includes roughing, intermediate rolling, and finishing. The surface temperature of the initial billet in the roughing process is 850℃. Local cooling of the cast billet is adopted, with the temperature difference between the beginning and end controlled at 150℃. The intermediate cooling is performed on the non-recrystallized zone, with a surface temperature drop of (100)℃. The finishing temperature is 900℃, and the deformation is 40%. Cooling includes water cooling and slow cooling on a cooling bed. The cooling rate of the water cooling is 100℃ / s, and the starting temperature of the slow cooling on the cooling bed is 650℃, with a cooling rate of 5℃ / s.

[0085] The direct-rolled material produced in this comparative model has a 5% increase in elongation and a pearlite content of 30%, with a grain size of (8). 400MPa grade Rel: 390MPa; 500MPa grade Rel: 480MPa.

[0086] like Figure 2 and Figure 3 As shown, the edge and core structures of the embodiment are ferrite + pearlite structures, and the structures are relatively uniform. Figure 4 For comparison, the presence of a certain amount of coarse Widmanstätten structure in the microstructure causes fluctuations in the performance of construction steel, resulting in a low performance qualification rate.

[0087] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing construction steel using a direct rolling process, characterized in that, The method includes: Under the conditions of setting the casting speed and the basic arc radius of the continuous casting machine, molten steel is continuously cast to obtain a billet. Under a set shearing time, the billet is subjected to hydraulic shearing; wherein the billet is in a heat preservation state. The cut billet with a set surface temperature is rough rolled, then intermediate rolled and cooled for the first time to obtain an intermediate billet; Under the conditions of setting the rolling temperature and setting the rolling deformation, the intermediate billet is precision rolled and then subjected to a second cooling to obtain steel for construction. The basic arc radius of the continuous casting machine is 7.0m-9.0m, the shearing time is 3s-10s, the surface temperature is 950℃-1000℃, and the rolling deformation is >40%. The second cooling includes: Under the condition that the first cooling rate is ≥10℃ / s, the intermediate billet after finishing rolling is water-cooled; The intermediate billet after water cooling is subjected to slow cooling under the condition that the second cooling rate is set to 0.05℃ / s-3℃ / s.

2. The method according to claim 1, characterized in that, The continuous casting machine has a casting speed of 2.9 m / min to 4.0 m / min.

3. The method according to claim 1, characterized in that, The process of rough rolling the cut billet with a set surface temperature, followed by intermediate rolling and a first cooling, to obtain an intermediate billet includes: The cut billet, after being cut to a set surface temperature, is subjected to rough rolling, followed by intermediate rolling and post-rolling finishing. The billet is partially cooled, and the temperature difference between the beginning and end of the billet is controlled to obtain an intermediate billet; wherein the temperature difference between the beginning and end is <80℃.

4. The method according to claim 1, characterized in that, The rolling temperature is 850℃-1000℃.

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