Flexible production method of low-alloy high-strength steel with yield strength of 420 / 460 MPa

Abstract

The invention relates to a flexible production method of low-alloy high-strength steel with yield strength of 420 / 460 MPa. The steel comprises the following chemical components: 0.12-0.16% of C, 0.12-0.16% of Si, 0.12-0.16% of Cr, 0.12-0.16% of Cr, 0.20%-0.3% of Si; mn: 1.2% to 1.5%; p is less than or equal to 0.02%; s < = 0.005%; 0.02% to 0.03% of Nb; 0.02% to 0.03% of V; 0.01%-0.03% of Als; the balance of Fe and impurities; the production process comprises the steps of converter smelting, LF refining, continuous casting, heating, rolling, controlled cooling after rolling and straightening. Through the coupling design of smelting, continuous casting, low-temperature heating, low-temperature rolling and controlled cooling processes, the comprehensive effect of fine grain strengthening, precipitation strengthening and phase change strengthening during rolling of the high-quality continuous casting billet is fully utilized, and flexible and efficient production of the low-alloy high-strength steel with the yield strength of 420 MPa and 460 MPa is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of low alloy high strength steel production, and in particular to a flexible and efficient production method for low alloy high strength steel with a yield strength of 420 MPa and 460 MPa. Background Art

[0002] Yield strength 420MPa and 460MPa low alloy high strength steel has good mechanical and welding properties and is widely used in machinery, construction, wind power, vehicles, ships, chemical equipment and other fields. It is a widely used variety of medium and thick plate products. With the changes in the market situation, the profitability of yield strength 420MPa and 460MPa low alloy high strength steel is getting lower and lower, and it is urgently needed to improve its profit-making ability through cost-reducing production.

[0003] At present, the main production mode of low-alloy high-strength steel with a thickness of 10 to 40 mm and a yield strength of 420 MPa or 460 MPa is controlled rolling and controlled cooling. In order to ensure the performance of the steel plate, it is usually required that the start temperature of the finishing rolling and the final rolling temperature be controlled within a narrow range, resulting in a slow pace of steel plate production and strict process requirements, which is not conducive to efficient production.

[0004] The Chinese invention patent with the authorization announcement number CN 112553437 B discloses "a method for controlling the yield strength fluctuation of 420MPa grade hot-dip galvanized high-strength steel", including steelmaking, continuous casting, heating of ingots, controlled rolling, controlled cooling, coiling, self-tempering slow cooling, pickling and galvanizing annealing processes, wherein the final rolling temperature of the controlled rolling process is 880±14℃; and the coiling temperature of the coiling process is 530±17℃. The cold-based hot-dip galvanized low-alloy high-strength steel of the present invention has a low yield strength ratio, good matching of strength and plasticity, stable coiling performance, an average yield strength ratio of 0.83, and a yield strength difference of ≤20MPa at the head, middle and end of the coil.

[0005] The Chinese invention patent with authorization announcement number CN 102400053 B discloses "a steel plate for building structure with a yield strength of 460 MPa and a manufacturing method thereof". The weight percentage of the chemical composition of the steel plate is: C 0.05% to 0.10%, Si 0.2% to 0.3%, Mn 1.40% to 1.60%, Nb 0.025% to 0.060%, Ti 0.015% to 0.030%, Als 0.015% to 0.045%, and also contains one of Cr 0.2% to 0.4%, Mo 0.10% to 0.30%, and B 0.0010% to 0.0020%, and the balance is Fe and unavoidable impurities. The impurity elements are controlled at P≤0.015%, S≤0.005%, [N]≤0.0040%, and [O]≤0.0020%. The manufacturing method is as follows: the billet heating temperature is 1180-1220°C, the first stage rolling temperature is 1040-1080°C, the final rolling temperature is 950-1000°C, and the second stage rolling starting temperature is 920-870°C; the final rolling temperature is controlled at 800-850°C, and the cumulative deformation amount of the second stage recrystallization zone rolling is greater than 60%; after hot rolling, it is kept warm for more than 15 seconds and then water-cooled, the water cooling starting temperature is 680-750°C, the cooling rate is 5-9°C / S, and the red-returning temperature is 450-620°C.

[0006] In addition, the designed compositions of steel plates of different thicknesses are usually different, which results in more steel tapping marks and affects production efficiency during smelting and continuous casting.

[0007] The present invention is optimized on the basis of the original Q420 grade steel composition, and obtains high-quality continuous casting billets through high-purity smelting and continuous casting process optimization, while reducing the heating temperature, ensuring that the second phase particles are fully dissolved back while reducing the original austenite grain size, and realizing the dispersion precipitation of the second phase particles through low-temperature large deformation rolling during rolling, and reducing the internal energy storage release by rapid cooling after rolling, and making full use of the effects of precipitation strengthening, fine grain strengthening and phase transformation strengthening, ensuring the flexible and efficient production of steel plates with a thickness of 10 to 40 mm and a yield strength of 420 MPa and 460 MPa, greatly improving the production efficiency of the steel plates while ensuring sufficient performance margin, greatly reducing the energy consumption of the heating furnace while improving the efficiency-creating ability of the low-alloy high-strength steel with a yield strength of 420 MPa and 460 MPa. Summary of the invention

[0008] The present invention provides a flexible production method for low-alloy high-strength steel with a yield strength of 420 / 460MPa. Through the coupled design of smelting, continuous casting, low-temperature heating, low-temperature rolling and controlled cooling processes, the comprehensive effects of fine grain strengthening, precipitation strengthening and phase transformation strengthening during rolling of high-quality continuous casting billets are fully utilized to achieve flexible and efficient production of steel plates.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A flexible production method for low-alloy high-strength steel with a yield strength of 420 / 460 MPa, wherein the chemical composition of the steel is C: 0.12%-0.16%; Si: 0.20%-0.3%; Mn: 1.2%-1.5%; P≤0.02%; S≤0.005%; Nb: 0.02%-0.03%; V: 0.02%-0.03%; Als: 0.01%-0.03%: the balance is Fe and unavoidable impurities; the finished steel plate is a steel plate with a yield strength of 420 MPa or a steel plate with a yield strength of 460 MPa; the production process includes converter smelting, LF refining, continuous casting, heating, rolling, controlled cooling after rolling and straightening, and specifically controls the following processes:

[0011] 1) Converter smelting and LF refining;

[0012] The smelting raw materials are pre-treated with molten iron, and the converter smelting adopts top and bottom double blowing to ensure that P ≤ 0.02% when the converter taps steel;

[0013] During the LF furnace refining process, white slag is made, aluminum iron is used for deoxidation to ensure that the oxygen content is less than 20ppm, and calcium is fed to modify the MnS inclusions to ensure that the soft blowing time is ≥8min; the total treatment time of LF refining is 35-50min, and S is ≤0.005% at the end of LF refining;

[0014] 2) Continuous casting;

[0015] The continuous casting superheat is controlled at 17-23℃, the electromagnetic stirring current intensity in the secondary cooling zone is 700-900A, and positive and reverse alternating stirring is adopted, and continuous stirring is 30-60s; the pulling speed is controlled at 1.05-1.15m / min, and the heavy pressure reduction process is adopted at the end of the solidification of the ingot, and the total pressure reduction is 15-20mm; the center segregation of the ingot is rated to C0.5 according to YB / T4003 "Continuous Casting Steel Slab Macrostructure Defect Rating Chart";

[0016] 3) heating;

[0017] After the ingot is off the production line, it is hot-charged and sent to the heating furnace for heating. The temperature entering the furnace is not less than 550℃, the temperature of the preheating section is 700~950℃, and the preheating time is 0.5~1h; the temperature of the heating section is 1210±20℃, and the heating time is 1~1.5h; the temperature of the soaking section is 1170±20℃, and the soaking time is 0.5~1h; the total time in the furnace is 2~4h; the temperature of the ingot when it is out of the furnace is 1150~1180℃, and the temperature difference between the surface and the core of the ingot does not exceed 25℃;

[0018] 4) rolling;

[0019] The continuous casting billet is rolled immediately after descaling, the rough rolling start temperature is 980-1030℃, the rough rolling widening stage is completed in 2-4 passes, the pass reduction rate is 8%-18%, the pass interval time is 4-10s, and the rolling rate is 0.8-1.2m / s; the rough rolling longitudinal rolling stage has a reduction rate of at least 23%-28%, a rolling speed of 0.5-1.0m / s, and a pass interval time of 10-15s; the rough rolling reduction rate of the remaining passes is 16%-23%, the rolling speed is 1.0-2.0m / s, and the pass interval time is 5-10s; the finishing rolling reduction rate of each pass is 10%-20%, the rolling speed is 2.5-3.3m / s, and the pass interval time is 3-8s;

[0020] 5) Cooling;

[0021] The steel plate is cooled immediately after rolling, and the cooling rate is 8-15°C / s. The red-return temperature of the yield strength 420MPa grade steel plate is 610-650°C, and the red-return temperature of the yield strength 460MPa grade steel plate is 570-610°C.

[0022] Furthermore, the continuous casting billet is descaled at least twice after leaving the heating furnace, and the descaling water pressure is 20-25 MPa.

[0023] Furthermore, for steel plates with a thickness of 10 mm ≤ ≤ 20 mm, a single-block controlled rolling method is adopted, the intermediate billet is not cooled to room temperature, and finishing rolling is carried out immediately after the rough rolling is completed; for steel plates with a thickness of 20 mm < ≤ 40 mm, a multi-block controlled rolling method is adopted, that is, single-frame cross rolling is carried out, after the rough rolling of the last steel plate in the rough rolling stage is completed, the first steel plate in the finishing rolling stage is immediately finished with finishing rolling, after the finish rolling of the first steel plate in the finishing rolling stage is completed, the second steel plate in the finishing rolling stage is immediately finished with finishing rolling, and so on until the finishing rolling of the last steel plate is completed.

[0024] Furthermore, the thickness of the ingot is 200-250 mm, the thickness of the intermediate ingot is 2-3 times the thickness of the finished steel plate, and the thickness of the finished steel plate is 10-40 mm.

[0025] Furthermore, the ferrite grain size of the finished steel plate is 9-11 levels.

[0026] Furthermore, the finished product performance of the yield strength 420MPa grade steel plate is: yield strength ≥420MPa, tensile strength 520~680MPa, elongation ≥19%, -20℃ Charpy impact energy ≥180J; the mechanical properties meet the requirements of Q420 level in GB / T1591 "Low Alloy High Strength Structural Steel" standard.

[0027] Furthermore, the finished product performance of the yield strength 460MPa grade steel plate is: yield strength ≥460MPa, tensile strength 540~720MPa, elongation ≥17%, -20℃ Charpy impact energy ≥150J; the mechanical properties meet the requirements of Q460 level in GB / T1591 "Low Alloy High Strength Structural Steel" standard.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Based on the original Q420 grade steel composition, high-quality continuous casting billets are obtained through smelting and continuous casting process optimization. At the same time, the heating temperature is reduced to ensure that the second phase particles are fully dissolved back while reducing the size of the original austenite grains. During rolling, the dispersion and precipitation of the second phase particles are achieved through low-temperature large deformation rolling. Rapid cooling after rolling reduces the release of internal energy storage, and fully utilizes the combined effects of precipitation strengthening, fine grain strengthening and phase transformation strengthening to ensure flexible and efficient production of steel plates with a thickness of 10 to 40 mm and a yield strength of 420 MPa and 460 MPa (the number of blocks per hour is increased by 1.6 blocks / h);

[0030] (2) No precious metal elements such as Ti, Cu, Cr, Mo, Ni and rare earth are added, and the alloy cost is extremely low, ensuring the product's ability to create effects.

[0031] (3) Under a lower alloy composition system, the performance of the original yield strength 420MPa grade steel plate can be guaranteed to meet the performance requirements of the yield strength 460MPa grade steel plate.

[0032] (4) The present invention does not limit the final rolling temperature of the steel plate, the production process is simple, and the process window is less restricted, which is conducive to the production of steel plates with complex nominal sizes. In addition, the first-time performance qualification rate after actual application is as high as over 99%.

[0033] (5) It effectively reduces the burning loss of the slab, improves the yield rate and obtains a high-quality steel plate surface.

[0034] (6) By adopting the low-temperature flexible rolling process, the molten steel (with the same composition) from the same casting or even the same furnace can produce a series of products with yield strength of 420MPa and 460MPa by adjusting the post-rolling cooling process parameters, which greatly improves the production efficiency of steelmaking. DETAILED DESCRIPTION

[0035] The present invention discloses a flexible production method for low-alloy high-strength steel with a yield strength of 420 / 460 MPa. The steel plate with a yield strength of 420 MPa or a yield strength of 460 MPa can be produced by using the same chemical composition. The chemical composition in the steel is as follows by weight percentage: C: 0.12% to 0.16%; Si: 0.20% to 0.3%; Mn: 1.2% to 1.5%; P≤0.02%; S≤0.005%; Nb: 0.02% to 0.03%; V: 0.02% to 0.03%; Als: 0.01% to 0.03%; the balance is Fe and unavoidable impurities.

[0036] The flexible and efficient production method of low alloy steel with a yield strength of 420-460 MPa described in the present invention comprises the following process steps: converter smelting - LF refining - continuous casting - heating - rolling - controlled cooling after rolling - straightening - cooling bed - shearing, etc., and specifically controls the following process:

[0037] 1) Converter smelting and LF refining;

[0038] The smelting raw materials are pretreated with molten iron, and the converter smelting adopts top and bottom double blowing to ensure that P ≤ 0.02% when the converter steel is tapped.

[0039] During the LF furnace refining process, white slag is made, aluminum iron is used for deoxidation to ensure that the oxygen content is less than 20ppm, and calcium is fed to modify MnS inclusions to ensure that the soft blowing time is ≥8min to promote the floating of inclusions; the total LF refining treatment time is 35-50min, and the LF outgoing station ensures that S is ≤0.005%;

[0040] 2) Continuous casting;

[0041] Low superheat and strong electromagnetic stirring technology are used to reduce central segregation. The superheat is controlled at 17-23°C, the electromagnetic stirring current intensity in the secondary cooling zone is 700-900A, and positive and reverse alternating stirring is adopted, and continuous stirring is 30-60s; the pulling speed is controlled at 1.05-1.15m / min, and the heavy pressure reduction process is adopted at the end of the solidification of the ingot. The heavy pressure reduction positions are preferably 10, 11 and 12 sections, and the total reduction is 15-20mm; the proportion of columnar crystals is minimized to the greatest extent, the density of the continuous casting ingot is improved, and the central segregation of the ingot is ensured to reach C0.5 level according to YB / T4003 "Continuous Casting Steel Slab Low-Magnification Structure Defect Rating Chart".

[0042] 3) heating;

[0043] After the continuous casting slab comes off the line, it is hot-charged and sent to a walking-beam heating furnace for heating. The temperature of the ingot entering the furnace is not less than 550°C. It passes through the preheating section, heating section and soaking section in sequence before being discharged from the furnace. The temperature range of the preheating section is 700-950°C, and the preheating time is 0.5-1h; the temperature range of the heating section is 1210±20°C, and the heating time is 1-1.5h; the temperature range of the soaking section is 1170±20°C, and the soaking time is 0.5-1h; the total time in the furnace is 2-4h; the temperature of the continuous casting slab when discharged from the furnace is 1150-1180°C, and the temperature difference between the surface and the core of the ingot is guaranteed not to exceed 25°C, which not only ensures the full solid solution of the micro-alloy elements, but also reduces the size of the original austenite grains.

[0044] After the continuous casting billet leaves the heating furnace, it shall be descaled at least twice with the descaling water pressure of 20-25MPa to ensure that no primary iron oxide scale remains on the surface of the steel plate.

[0045] 4) rolling;

[0046] The present invention adopts a controlled rolling production mode for steel plates with a thickness of 10 to 40 mm. Among them, a single-block controlled rolling strategy is adopted for steel plates with a thickness of 10 to 20 mm, and the intermediate billet is not cooled to a temperature, and finish rolling is performed immediately after the rough rolling is completed. A cross-rolling strategy, i.e., multi-block controlled rolling, is adopted for steel plates with a thickness of 20 to 40 mm. Since it is a single stand, after the rough rolling of the last steel plate in the rough rolling stage is completed during cross rolling, the first steel plate in the finish rolling stage is immediately finished with finish rolling, and after the finish rolling of the first steel plate in the finish rolling stage is completed, the second steel plate is immediately finished with finish rolling, and so on, until the finish rolling of the last steel plate is completed.

[0047] The continuous casting billet is rolled immediately after descaling, the rough rolling start temperature is 980-1030°C, the rough rolling widening stage is completed in 2-4 passes, the pass reduction rate is 8%-18%, the pass interval time is 4-10s, and the rolling rate is 0.8-1.2m / s; the rough rolling longitudinal rolling stage has a reduction rate of at least 23%-28%, a rolling speed of 0.5-1.0m / s, a pass interval time of 10-15s, and the reduction rate of the remaining rough rolling passes is 16%-23%, the rolling speed is 1.0-2.0m / s, and the pass interval time is 5-10s. The dynamic and static recrystallization ratios are respectively increased by low temperature and large reduction and appropriately increasing the pass interval time to ensure complete recrystallization in the rough rolling stage. The thickness of the intermediate billet is 2 to 3 times the thickness of the finished steel plate, the reduction rate of each finishing rolling pass is 10% to 20%, the rolling speed is 2.5 to 3.3 m / s, and the pass interval time is 3 to 8 s. The purpose is to increase the internal energy storage of the rolled steel plate and refine the grains through rapid and large reduction rolling; the present invention has no requirements for the finishing rolling temperature.

[0048] 5) Cooling;

[0049] After rolling, the steel plate quickly enters the cooling system for cooling, with a cooling rate of 8-15°C / s. The red-return temperature of Q420 grade steel plate is 610-650°C, and the red-return temperature of Q460 grade steel plate is 570-610°C. Rapid cooling reduces the release of internal energy stored in the steel plate after rolling, thereby refining the grain size, improving the elongation and -20°C low-temperature impact performance.

[0050] 6) Straightening, cooling bed and shearing, etc.;

[0051] After rapid cooling, the steel plate is straightened to ensure the plate shape. After straightening, it is cooled on a cooling bed. When the temperature of the steel plate is lower than 100℃, it is placed on the cooling bed for online shearing and finally stored.

[0052] In the present invention, the thickness of the continuous casting billet is 200-250 mm, the thickness of the finished steel plate is 10-40 mm, the ferrite grain size of the finished steel plate is in the range of 9-11, and the grains are uniform and fine.

[0053] When rolling by conventional process, the steel plate needs to be air-cooled to the start temperature of finishing rolling after rough rolling (usually takes 1 to 4 minutes), and laminar cooling is performed after rolling. The production method of the present invention is suitable for the production of steel plates with a thickness of 10-40 mm, wherein when rolling steel plates with a thickness of 10 to 20 mm, a single block controlled rolling mode is adopted but the intermediate billet is not cooled (because the controlled rolling mode of the fully automatic rolling mill will have two more passes than the hot rolling mode), and finishing rolling is performed immediately after the rough rolling is completed; when rolling steel plates with a thickness of 20 to 40 mm (excluding 20 mm), multiple steel plates are controlled and rolled at the same time, and when multiple controlled rolling is performed, the first steel plate in the finishing rolling stage is immediately finished after the rough rolling of the last steel plate, and the second steel plate in the finishing rolling stage is immediately finished after the finishing rolling of the first steel plate, and so on to ensure that the rolling mill does not stop, thereby improving the rolling efficiency.

[0054] The finished product performance of the 420MPa yield strength steel plate produced by the method of the present invention is: yield strength ≥420MPa, tensile strength 520-680MPa, elongation ≥19%, -20℃ Charpy impact energy ≥180J; the mechanical properties meet the Q420 level requirements of GB / T1591 "Low Alloy High Strength Structural Steel" standard.

[0055] The finished product performance of the 460MPa yield strength steel plate produced by the method of the present invention is: yield strength ≥460MPa, tensile strength 540-720MPa, elongation ≥17%, -20℃ Charpy impact energy ≥150J; the mechanical properties meet the Q460 level requirements of GB / T1591 "Low Alloy High Strength Structural Steel" standard.

[0056] In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with examples. The following examples are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the protection scope of the present invention.

[0057] [Example]

[0058] Table 1 shows the chemical composition of the steel in each embodiment, Table 2 shows the smelting and continuous casting process parameters of each embodiment, Table 3 shows the heating process parameters of each embodiment, Table 4 shows the rolling and cooling process parameters of each embodiment, and Table 5 shows the properties of the finished steel plates of each embodiment.

[0059] Table 1 Chemical composition of steel (wt%)

[0060] Example C Si Mn P S Nb V Als 1 0.156 0.25 1.48 0.016 0.0035 0.028 0.021 0.015 2 0.132 0.22 1.28 0.014 0.0038 0.025 0.023 0.025 3 0.142 0.25 1.40 0.012 0.0048 0.024 0.025 0.022 4 0.160 0.27 1.42 0.018 0.0046 0.021 0.028 0.023 5 0.126 0.23 1.36 0.018 0.0042 0.025 0.022 0.028 6 0.158 0.28 1.46 0.014 0.0036 0.027 0.026 0.019 7 0.131 0.25 1.22 0.016 0.0038 0.029 0.025 0.023 8 0.156 0.29 1.48 0.013 0.0043 0.028 0.028 0.021

[0061] Table 2 Steel smelting and continuous casting process parameters

[0062] Example 1 2 3 4 5 6 7 8 Phosphorus content of converter steel / wt% 0.016 0.014 0.012 0.018 0.018 0.014 0.016 0.013 Oxygen content in molten steel after LF refining / ppm 16 16 15 14 14 15 20 15 LF refining soft blowing time / min 8 10 9 11 12 10 13 9 LF refining total time / min 41 38 36 45 42 39 40 36 Electromagnetic stirring current intensity / A 800 800 800 800 800 800 800 800 Electromagnetic stirring time / s 30 45 40 45 35 50 55 48 Superheat / ℃ 21 17 22 22 23 18 18 22 Pulling speed m / min 1.12 1.08 1.05 1.15 1.05 1.08 1.10 1.15 Total pressure reduction at the end of solidification / mm 15 18 20 17 18 18 20 20 Continuous casting slab thickness / mm 236 234 233 235 233 223 231 232 Center segregation level of continuous casting slab C0.5 C0.5 C0.5 C0.5 C0.5 C0.5 C0.5 C0.5

[0063] Table 3 Billet heating process parameters

[0064]

[0065] Table 4 Steel plate rolling and cooling process parameters

[0066]

[0067]

[0068] Note: The first three passes in the table are the rough rolling and widening stages; the bold characters are the finishing rolling passes in each embodiment.

[0069] Table 5 Finished steel plate properties

[0070]

[0071] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A flexible production method for low alloy high strength steel with a yield strength of 420 / 460MPa. It is characterized in that The chemical composition of the steel is calculated by weight as follows: C: 0.12% ~ 0.16%; Si: 0.20% ~ 0.3%; Mn: 1.2% ~ 1.5%; P ≤ 0.02%; S ≤ 0.005%; Nb: 0.02% ~ 0.03%; V：0.02％～0.03％； Als: 0.01% to 0.03%: the balance is Fe and unavoidable impurities; The finished steel plate is a 420MPa yield strength steel plate or a 460MPa yield strength steel plate; the production process includes converter smelting, LF refining, continuous casting, heating, rolling, post-rolling controlled cooling and straightening, and the specific control process is as follows: 1) Converter smelting and LF refining; The smelting raw materials are pre-treated with molten iron, and the converter smelting adopts top and bottom double blowing to ensure that P ≤ 0.02% when the converter taps steel; During the LF furnace refining process, white slag is made, aluminum iron is used for deoxidation to ensure that the oxygen content is less than 20ppm, and calcium is fed to modify the MnS inclusions to ensure that the soft blowing time is ≥8min; the total treatment time of LF refining is 35-50min, and S is ≤0.005% at the end of LF refining; 2) Continuous casting; The continuous casting superheat is controlled at 17-23℃, the electromagnetic stirring current intensity in the secondary cooling zone is 700-900A, and positive and reverse alternating stirring is adopted, and continuous stirring is 30-60s; the pulling speed is controlled at 1.05-1.15m / min, and the heavy pressure reduction process is adopted at the end of the solidification of the ingot, and the total pressure reduction is 15-20mm; the center segregation of the ingot is rated to C0.5 according to YB / T4003 "Continuous Casting Steel Slab Macrostructure Defect Rating Chart"; 3) heating; After the ingot is off the production line, it is hot-charged and sent to the heating furnace for heating. The temperature entering the furnace is not less than 550℃, the temperature of the preheating section is 700~950℃, and the preheating time is 0.5~1h; the temperature of the heating section is 1210±20℃, and the heating time is 1~1.5h; the temperature of the soaking section is 1170±20℃, and the soaking time is 0.5~1h; the total time in the furnace is 2~4h; the temperature of the ingot when it is out of the furnace is 1150~1180℃, and the temperature difference between the surface and the core of the ingot does not exceed 25℃; 4) rolling; The continuous casting billet is rolled immediately after descaling, the rough rolling start temperature is 980-1030℃, the rough rolling widening stage is completed in 2-4 passes, the pass reduction rate is 8%-18%, the pass interval time is 4-10s, and the rolling rate is 0.8-1.2m / s; the rough rolling longitudinal rolling stage has a reduction rate of at least 23%-28%, a rolling speed of 0.5-1.0m / s, and a pass interval time of 10-15s; the rough rolling reduction rate of the remaining passes is 16%-23%, the rolling speed is 1.0-2.0m / s, and the pass interval time is 5-10s; the finishing rolling reduction rate of each pass is 10%-20%, the rolling speed is 2.5-3.3m / s, and the pass interval time is 3-8s; 5) Cooling; The steel plate is cooled immediately after rolling, and the cooling rate is 8-15°C / s. The red-return temperature of the yield strength 420MPa grade steel plate is 610-650°C, and the red-return temperature of the yield strength 460MPa grade steel plate is 570-610°C.

2. A flexible production method for low alloy high strength steel with a yield strength of 420 / 460 MPa according to claim 1, It is characterized in that The continuous casting billet is descaled at least twice after exiting the heating furnace, and the descaling water pressure is 20-25 MPa.

3. The flexible production method of low alloy high strength steel with a yield strength of 420 / 460 MPa according to claim 1, It is characterized in that For steel plates with a thickness of 10mm≤≤≤20mm, a single-block controlled rolling method is adopted, and the intermediate billet is not cooled to room temperature, and finishing rolling is carried out immediately after rough rolling. For steel plates with a thickness of 20mm<≤40mm, a multi-block controlled rolling method is adopted, that is, single-stand cross rolling is carried out, and after the rough rolling of the last steel plate in the rough rolling stage is completed, the first steel plate in the finishing rolling stage is immediately finished with finishing rolling, and after the finish rolling of the first steel plate in the finishing rolling stage is completed, the second steel plate in the finishing rolling stage is immediately finished with finishing rolling, and so on until the finishing rolling of the last steel plate is completed.

4. The flexible production method of low alloy high strength steel with a yield strength of 420 / 460 MPa according to claim 1, It is characterized in that The thickness of the ingot is 200-250 mm, the thickness of the intermediate ingot is 2-3 times the thickness of the finished steel plate, and the thickness of the finished steel plate is 10-40 mm.

5. The flexible production method of low alloy high strength steel with a yield strength of 420 / 460 MPa according to claim 1, It is characterized in that The ferrite grain size of the finished steel plate is 9 to 11 levels.

6. The flexible production method of low alloy high strength steel with a yield strength of 420 / 460 MPa according to claim 1, It is characterized in that The finished product performance of the yield strength 420MPa grade steel plate is: yield strength ≥420MPa, tensile strength 520~680MPa, elongation ≥19%, -20℃ Charpy impact energy ≥180J; the mechanical properties meet the requirements of Q420 grade in GB / T1591 "Low Alloy High Strength Structural Steel" standard.

7. The flexible production method of low alloy high strength steel with a yield strength of 420 / 460 MPa according to claim 1, It is characterized in that The finished product performance of the yield strength 460MPa grade steel plate is: yield strength ≥460MPa, tensile strength 540~720MPa, elongation ≥17%, -20℃ Charpy impact energy ≥150J; the mechanical properties meet the requirements of Q460 grade in GB / T1591 "Low Alloy High Strength Structural Steel" standard.

Images