Manufacturing method for efficiently rolling high-surface-quality 355MPa-grade steel plate for engineering structure

Abstract

The invention discloses a manufacturing method for efficiently rolling a high-surface-quality 355MPa-grade steel plate for an engineering structure, and belongs to the field of metal processing. The manufacturing method comprises the steps of casting blank heating, rolling, controlled cooling, straightening (hot straightening) and air cooling to the room temperature. The steel plate can meet the performance requirements of the steel plate without subsequent controlled rolling, and meanwhile, the steel plate reaches the D-grade standard after shot blasting. And the remarkable effects of improving the production efficiency, improving the surface quality and reducing the production cost are achieved.

Description

Technical Field

[0001] The invention belongs to the field of metal processing, and in particular relates to a method for efficiently rolling a steel plate for engineering structure with high surface quality, thickness specification of 10-30 mm and yield strength of 355 MPa. Background Art

[0002] Faced with the challenging market conditions of the steel industry and increasingly stringent requirements from downstream users for steel plate surface quality, reducing manufacturing costs while ensuring product quality and maximizing production line capacity has become crucial. Currently, downstream users are gradually reducing the thickness of paint applied to steel plates after shot blasting to reduce manufacturing costs. This has led to increasingly stringent control of surface oxide scale on the raw steel plates (reaching Grade D standards, meaning no color difference or scale intrusion on the surface after shot blasting). At the same time, while ensuring production and equipment safety, the goal is to increase rolling line output per unit time (i.e., the number of blocks rolled per hour). Ultimately, this approach enables efficient production while maintaining surface quality while maximizing efficiency and minimizing consumption. In recent years, market competition has become increasingly prominent in 355MPa-grade medium and heavy plate grades (such as AH36 and Q355B). This type of steel is primarily based on carbon-manganese steel, with the addition of microalloying elements such as Al, Ti, and Nb, as well as high levels of Mn, to enhance the strength and toughness of the steel through solid solution strengthening, precipitation strengthening, and grain refinement. According to statistics, this strength grade of medium and heavy plate accounts for over 30% of annual production. Therefore, the production of medium and thick plate products, especially 355MPa grade steel plates, urgently needs to further optimize the production process, further reduce manufacturing costs (energy consumption, alloy costs) and improve surface quality on the current basis, so as to enhance the market competitiveness of products.

[0003] Currently, for 355MPa steel plates with a thickness of 10-30mm, a medium carbon (0.15%-0.25%) and medium Mn (1.15%-1.45%) composition is typically used to reduce alloy costs. This is coupled with a deep controlled rolling and controlled cooling process to minimize performance fluctuations associated with alloy cost reduction. However, these reduced alloy plates are typically produced using a multi-stage controlled rolling (TMCP) process, with final rolling temperatures typically at 800°C or lower. This lower temperature increases the deformation resistance of the rolled piece, thereby increasing mill load and making plate shape control more difficult. Furthermore, low-temperature rolling requires longer intermediate holding times, impacting rolling rhythm and production efficiency. Furthermore, improper control of process parameters such as billet furnace time, descaling mill pressure, intermediate billet holding time, temperature, descaling process, laminar cooling rate, and straightening temperature can directly lead to residual iron oxide scale, which is subsequently pressed into the steel plate and affects surface quality. Therefore, for 355MPa-grade engineering structural steel plates with high surface quality requirements, it is necessary to optimize their composition and process, so as to improve the rolling rhythm and ensure the performance and surface quality of the steel plates while controlling the alloy cost. This is a key issue that needs to be urgently solved in the mass production of economical 355MPa-grade medium and thick plates.

[0004] Compared with existing technologies: To date, little research has been conducted domestically or internationally on methods for improving the rolling cadence of steel plates with thicknesses of 10-30 mm and a yield strength of 355 MPa. Prior to the present invention, patent publication number CN 115537636 A disclosed a method for improving the rolling efficiency of A32-grade marine medium and heavy plate. This method employed a non-TMCP rolling process, controlling the billet heating regime to ensure that the final rolling temperature of the steel plate fell within a predetermined target range. However, its alloy composition was relatively high, and production thicknesses were primarily limited to 16 mm or less. Production processes for thicknesses above 20 mm were not addressed, and the surface quality requirements for the steel plates were not elaborated.

[0005] While the steel plate shape control methods disclosed in the aforementioned patent documents improve the rolling efficiency of some thickness specifications, they are not suitable for the efficient rolling, high surface quality, and engineering structural steel plates with thicknesses of 10-30 mm and a yield strength of 355 MPa. The technical solution provided by the present invention effectively overcomes these deficiencies and solves the problems of using continuous casting billets with a thickness of 250 mm or less. Through rational composition design and optimized heating, rolling, and cooling processes, it solves the problems of low rolling efficiency at rolling thicknesses of 10-30 mm due to low alloy content and the impact of iron oxide scale intrusion on surface quality. Summary of the Invention

[0006] The present invention aims to overcome the above-mentioned technical problems and deficiencies by providing a method for producing steel plates for engineering structures with high surface quality and high rolling efficiency, in thicknesses ranging from 10 to 30 mm and a yield strength of 355 MPa. This method eliminates the need for subsequent controlled rolling to meet performance requirements, while also achieving a Grade D standard after shot blasting (no color difference or iron scale intrusion on the surface after shot blasting). This method also addresses the issue of low alloy content in such steel plates, which requires controlling the final rolling temperature during the rolling process to maintain performance, impacting rolling efficiency, surface quality, and low first-pass yield.

[0007] To achieve the above object, the technical solution of the present invention is: The present invention provides a method for efficiently rolling a high-surface-quality 355 MPa-grade steel plate for engineering structures. The chemical composition of the steel plate comprises, by weight percentage, the following: C 0.15% to 0.20%, Si 0.25% to 0.35%, Mn 0.75% to 1.05%, Al 0.015% to 0.035%, P ≤ 0.035%, S ≤ 0.035%, and the balance being Fe and unavoidable impurities.

[0008] The functions of the main elements in the chemical composition of the steel plate of the present invention are as follows: C: The most economical and fundamental strengthening element in steel, it significantly increases steel strength through solid solution strengthening and precipitation strengthening. However, increasing C content negatively impacts steel's plasticity, toughness, and weldability. Therefore, the present invention sets the C content within a range of 0.15% to 0.20%.

[0009] Mn: It increases steel strength through solid solution strengthening, compensating for the loss of steel plate strength caused by reduced carbon content. It also lowers the γ-α transformation temperature, thereby refining ferrite grains, contributing to the production of fine low-temperature transformation products and improving their toughness. However, increasing the Mn content exacerbates centerline segregation in the continuously cast slab, hindering the improvement of low-temperature toughness in the steel plate. Furthermore, alloy cost considerations must be taken into account. Therefore, the Mn content in the present invention is designed to be within a range of 0.75% to 1.05%.

[0010] Si: Deoxidizes steel during steelmaking and improves matrix strength. However, excessive Si content and improper heating temperature control can produce a FeO / Fe₂SiO₄ eutectoid phase that "pins" the surface. Therefore, the Si content in this invention is set at 0.25% to 0.35%.

[0011] Al: Typically acts as a deoxidizer in steel and, if formed into AlN, also refines the structure. When Al content exceeds 0.035%, excessive aluminum oxide inclusions can reduce the cleanliness of the steel. Lower Al content results in inadequate deoxidation, so the lower limit for Al content is set at 0.015%.

[0012] P and S are unavoidable impurity elements in steel and should be as low as possible. However, due to smelting costs and process considerations, they cannot be kept indefinitely low. Therefore, the present invention sets the upper limits of P and S content at 0.020% and 0.015%, respectively.

[0013] The steel plate of the present invention has a thickness of 10-30 mm, is produced on a medium and thick plate reciprocating rolling mill using a continuous casting billet with a thickness of less than 250 mm, and uses water as a cooling medium.

[0014] The object of the present invention is achieved through the following technical solutions: The present invention provides a method for efficiently rolling a high-surface-quality 355MPa-grade steel plate for engineering structures, comprising heating the ingot → rolling → controlled cooling → straightening (hot straightening) → air cooling to room temperature; specifically comprising the following steps: 1) Billet heating: The billet is fed into a walking beam furnace for heating. The billet passes through the preheating section, heating section and soaking section in sequence before being taken out of the furnace. The temperature range of the preheating section is 400-600°C (to promote uniformity of the structure in the billet and promote full diffusion of elements), the temperature range of the heating section is 1210-1230°C, and the temperature range of the soaking section is 1100-1125°C. The total time in the furnace for the heating and soaking sections is controlled at 2.5-3.5 hours to ensure that the temperature difference between the upper and lower surfaces of the billet is within 15°C (the heating section uses a higher temperature for further The diffusion of elements Mn and C is promoted step by step, reducing the influence of their composition segregation on the organization and performance; at the same time, high temperature heating is provided in the heating section to ensure the temperature uniformity of each part of the ingot and improve the uniformity of metal flow in the horizontal and vertical directions on the surface of the steel plate; combined with the composition of the steel plate, the heating temperature of the ingot soaking section is lowered to reduce energy consumption, while avoiding excessive Si content and improper heating temperature control to produce FeO / Fe2SiO4 eutectic phase and "pin" the surface to affect the subsequent descaling effect, and also effectively inhibit the excessive growth of austenite grains and affect the performance of the steel plate).

[0015] 2) High-pressure water descaling and rolling: Before rolling, high-pressure water is used to descale the billet after it leaves the furnace for 1 to 1.5 minutes, and the descaling machine pressure is 20 to 25 MPa; the rolling mode of transverse and longitudinal rolling is adopted. In the transverse rolling stage, the reduction rate of each of the first two passes of rolling is greater than 20%, and the first pass of rolling is descaling by the rolling mill, the time is 0.3 to 0.6 minutes, and the pressure is 20 to 25 MPa. (The first two passes of rolling try to give full play to the capacity of the rolling mill, adopt a large reduction rate, promote the dynamic crystallization of austenite, refine the original austenite grains, and use high-pressure water descaling of the rolling mill to make the structure of the steel plate from the surface to the core uniform, improve the strength and toughness of the steel plate, and further remove the iron oxide scale on the surface of the billet); in the longitudinal rolling stage, the pressure of each of the first three passes of rolling is 20%. The reduction rate is greater than 25%, and only the first longitudinal rolling pass adopts full-length descaling, the time is 0.5-1min, and the pressure is 20-25MPa. No descaling is performed in other passes (a large reduction rate is used in the first three longitudinal rolling passes to further refine the austenite grains and improve the core structure. At the same time, a full-length descaling pass is taken before the start of longitudinal rolling to remove the iron oxide scale generated on the surface of the steel billet during the process of converting from horizontal rolling to longitudinal rolling. No descaling pass is added in the later stage of longitudinal rolling to ensure dense growth of all parts of the iron scale). In the later stage of rolling, due to the drop in temperature of the steel plate, the deformation resistance increases, and a small reduction rate rolling (less than 5%) is adopted in the last pass to flatten the shape of the steel plate and reduce the internal stress of the steel plate; the final rolling temperature of the steel plate is 860-900℃ (the final rolling temperature is controlled to reduce the formation of Fe2O3).

[0016] 3) Cooling control: laminar cooling is adopted, the cooling temperature range is 830-870℃, the final cooling temperature range is 530-600℃, the number of cooling manifolds opened is 3-6, and the water volume of a single manifold is 120-150m 3 / h, with the headers opened from back to front (in the direction of the rolling mill), and the cooling rate controlled at 10-15°C / s. (The cooling start temperature is controlled to ensure that the steel plate is austenitic when entering the water. During the cooling process, the cooling rate and final cooling temperature are controlled to suppress the formation of bainite and martensite on the steel plate surface and the amount of bainite in the core structure, thereby preventing bainite or martensite transformation on the surface and affecting the toughness of the steel plate. The number of header openings, water volume, and method are also controlled to ensure that the iron scale on the steel plate is further densified before cooling and does not break during the cooling process. The iron scale is primarily composed of FeO, supplemented by Fe3O4, with the mass percentages of 65%-80% and 35%-20%, respectively.)

[0017] 4) Straightening: The steel plate is hot straightened after controlled cooling.

[0018] 5) Air cool to room temperature.

[0019] Furthermore, in step 3), the cooling medium for laminar cooling is water.

[0020] Furthermore, in step 4), the hot straightening is performed in one pass, the position of the lead-in roller is -1.5mm to -3.1mm, the position of the lead-out roller is -2.1mm to -3.8mm, and the straightening force is between 2000KN and 3000KN (by setting appropriate roller gap and straightening force, it is ensured that the straightened steel plate is straight and has a good plate shape).

[0021] The above-mentioned composition and heating, rolling, and cooling process scheme overcomes the shortcomings of existing technologies and addresses the issues of low alloy content in such steel plates, which require controlling the final rolling temperature during the rolling process to ensure performance, affecting rolling efficiency, surface quality, and low first-pass pass rate of the plate shape. The resulting steel plates have the same performance as those produced using the existing TMCP process: flatness below 5mm / 2m, transverse tensile yield strength ≥355MPa, tensile strength between 490 and 570MPa, elongation ≥23%, transverse Charpy impact energy ≥100J at -20°C, and surface quality meeting Grade D standards. According to calculations, after optimizing the composition and process, the rolling rhythm of economical medium and thick plates with a yield strength of 355MPa and a thickness of 10-30mm has been significantly improved, and the average rolling time per plate has been reduced by 30-60 seconds, significantly improving production efficiency, surface quality, and reducing production costs.

[0022] Beneficial effects of the present invention: 1. Limit the temperature and time of the preheating section, heating section and soaking section of the billet to promote the homogenization of the structure of the billet and promote the full diffusion of elements. At the same time, a higher temperature is used in the heating section to further promote the diffusion of elements Mn and C, reducing the impact of their composition segregation on the structure and performance; at the same time, high temperature heating is provided in the heating section to ensure the temperature uniformity of all parts of the billet and improve the uniformity of the horizontal and vertical metal flow on the surface of the steel plate; based on the composition of the billet, by lowering the heating temperature of the soaking section of the billet, energy consumption is reduced, and at the same time, it is avoided that the Si content is too high and the heating temperature is too high, which will produce FeO / Fe2SiO4 eutectic phase and "pin" the surface to affect the subsequent descaling effect, and it also effectively inhibits the excessive growth of austenite grains to ensure the performance of the steel plate.

[0023] 2. The composition of the present invention is reasonable, the alloy addition amount is low, and the intermediate billet waiting time is eliminated, which greatly reduces the alloy cost and the high-temperature deformation resistance in the rough rolling and finishing rolling stages, is conducive to increasing the reduction per pass, and is conducive to ensuring the comprehensive performance of the super steel plate.

[0024] 3. By adopting the rolling mode of transverse and longitudinal rolling, adding the descaling process in the first pass of each stage, and using large reduction in the first two and three passes of each stage, the dynamic crystallization of austenite is promoted, the original austenite grains are refined, and the high-pressure water descaling of the rolling mill is used to make the microstructure distribution from the surface to the core of the steel plate uniform, thereby improving the strength and toughness of the steel plate and further removing the iron oxide scale on the surface of the ingot; at the same time, no descaling pass is added in the later stage of longitudinal rolling to ensure the dense growth of the iron scale in all parts, and a small reduction rate rolling (less than 5%) is adopted in the last pass to flatten the plate shape and reduce the internal stress of the steel plate; in addition, this rolling does not adopt the traditional TMCP process, eliminates the intermediate billet waiting temperature, and also improves the rolling efficiency, controls the final rolling temperature of the steel plate to 860-900℃, and reduces the probability of Fe2O3 formation.

[0025] 4. After rolling, the steel plate is cooled in a controlled manner. The cooling start temperature is controlled to ensure that the steel plate is in an austenitic state when entering the water. During the cooling process, the cooling rate and final cooling temperature are controlled to suppress the formation of bainite and martensite phases on the steel plate surface and the amount of bainite phase in the core structure. This prevents bainite or martensite phase transformation on the surface from affecting the toughness of the steel plate. At the same time, the number of manifold openings, water volume, and method are controlled to ensure that the iron scale on the steel plate surface is further densified before cooling and does not break during the cooling process. The iron scale is mainly composed of FeO and supplemented by Fe3O4, with the proportions of 65% to 80% and 35% to 20%, respectively.

[0026] 5. Use hot straightening, set the position and pressure of the lead-in and lead-out rollers to ensure that the straightened steel plate is straight and has a good shape.

[0027] 6. The above-mentioned composition and heating, rolling, and cooling process scheme overcomes the shortcomings of existing technologies and addresses the issues of low alloy content, such as the need to control the final rolling temperature during rolling to maintain performance, which impacts rolling efficiency, surface quality, and low first-pass pass rate of plate shape. The resulting steel plate has comparable performance to that produced using the existing TMCP process, with a flatness of less than 5mm / 2m, saving the cost of subsequent cold straightening. The plate exhibits a transverse tensile yield strength of ≥355MPa, a tensile strength between 490 and 570MPa, an elongation of ≥23%, a transverse Charpy impact energy of ≥100J at -20°C, and a surface quality that meets Grade D standards. Calculations show that the optimized composition and process significantly improve the rolling rhythm of economical medium and heavy plates with a yield strength of 355MPa and a thickness of 10-30mm, reducing the average rolling time per plate by 30-60 seconds. This significantly improves production efficiency, surface quality, and reduces production costs. DETAILED DESCRIPTION

[0028] The following examples are used to specifically illustrate the present invention. These examples are only general descriptions of the present invention and do not limit the present invention.

[0029] A method for efficiently rolling a high-surface-quality 355MPa-grade steel plate for engineering structures, wherein the chemical composition of the steel plate comprises, by weight percentage, the following: C 0.15% to 0.20%, Si 0.25% to 0.35%, Mn 0.75% to 1.05%, Al 0.015% to 0.035%, P ≤ 0.035%, S ≤ 0.035%, with the remainder being Fe and unavoidable impurities; the steel plate has a thickness of 10 to 30 mm and is produced on a medium-plate reciprocating rolling mill using ingots with a thickness of less than 250 mm, and the cooling medium is water; The preparation method comprises heating the ingot → rolling → controlled cooling → straightening (hot straightening) → air cooling to room temperature; specifically comprises the following steps: 1) Billet heating: The billet is fed into a walking beam furnace for heating. The billet 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 400-600°C (to promote uniformity of the structure in the billet and promote full diffusion of elements), the temperature range of the heating section is 1210-1230°C, and the temperature range of the soaking section is 1100-1125°C. The total time in the heating and soaking sections in the furnace is controlled at 2.5-3.5 hours to ensure that the temperature difference between the upper and lower surfaces of the billet is within 15°C.

[0030] 2) High-pressure water descaling and rolling: Before rolling, high-pressure water is used to descale the ingot after it is discharged from the furnace for 1 to 1.5 minutes, and the pressure of the descaling machine is 20 to 25 MPa; the rolling mode of transverse and longitudinal rolling is adopted. In the transverse rolling stage, the reduction rate of each of the first two rolling passes is greater than 20%, and the first rolling pass is descaled by the rolling mill, the time is 0.3 to 0.6 minutes, and the pressure is 20 to 25 MPa; in the longitudinal rolling stage, the reduction rate of each of the first three rolling passes is greater than 25%, and only the first longitudinal rolling pass adopts full-length descaling, the time is 0.5 to 1 minute, and the pressure is 20 to 25 MPa. No descaling is done in other passes, and the last pass adopts small reduction rate rolling (less than 5%); the finishing rolling temperature of the steel plate is 860 to 900 ° C.

[0031] 3) Cooling control: laminar cooling is adopted, the cooling temperature range is 830-870℃, the final cooling temperature range is 530-600℃, the number of cooling manifolds opened is 3-6, and the water volume of a single manifold is 120-150m 3 / h, the headers are opened from back to front (in the rolling mill direction), and the cooling rate is controlled at 10-15°C / s. The iron scale is mainly composed of FeO, supplemented by Fe3O4, with the mass percentages of the two being 65%-80% and 35%-20%, respectively.

[0032] 4) Hot straightening: The steel plate is hot straightened after controlled cooling (one-step straightening). The position of the lead-in roller is -1.5mm~-3.1mm, the position of the lead-out roller is -2.1mm~-3.8mm, and the straightening force is between 2000KN and 3000KN.

[0033] 5) Air cool to room temperature.

[0034] The steel plate has a thickness of 10-30 mm and is produced on a medium and thick plate reciprocating rolling mill using continuous casting billets with a thickness of less than 250 mm, with water as the cooling medium.

[0035] Examples 1-6 Table 1 shows the chemical composition of the steel of Example 1, Table 2 shows the heating system of the cast steel and the high-pressure water descaling process before continuous casting; Table 3 shows the rolling method of the steel of Example 1; Table 4 shows the cooling and steel straightening process of the steel of Example 1; Table 5 shows the dimensions, properties and straightness of the steel of Example 1 Table 1 Chemical composition of example steel (wt, %)

[0036] Note: Impurity elements in steel: P≤0.035%, S≤0.035%.

[0037] Table 2 Heating system of the cast steel and high-pressure water descaling process before continuous casting

[0038] Table 3 Rolling method of example steel

[0039] Table 4 Cooling and steel straightening process of example steel

[0040] Table 5 Dimensions, properties and straightness of the example steel

[0041] As can be seen, compared with the prior art, the present invention aims to overcome the aforementioned technical problems and deficiencies by providing a method for producing steel plates for engineering structures with high surface quality and high rolling efficiency, in thicknesses of 10-30 mm and a yield strength of 355 MPa. This method eliminates the need for subsequent controlled rolling to meet the required performance requirements, while also achieving a D-grade standard after shot blasting (no color difference or iron scale intrusion on the surface after shot blasting). This method addresses the issue of low alloy content in such steel plates, which, to maintain performance, require controlling the final rolling temperature during the rolling process, which affects rolling efficiency, surface quality, and plate shape, resulting in a low first-pass yield. Calculations show that after optimizing the composition and process, the rolling rhythm of economical medium and thick plates with a yield strength of 355 MPa and a thickness of 10-30 mm has been significantly improved, reducing the average rolling time per plate by 30-60 seconds. This significantly improves production efficiency, surface quality, and reduces production costs.

[0042] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for efficiently rolling high-surface-quality 355MPa-grade steel plates for engineering structures, characterized in that: The steps include: 1) Billet heating: The billet is fed into a walking beam furnace for heating. The billet passes through the preheating section, heating section, and soaking section in sequence before being discharged from the furnace. The temperature in the preheating section is 400-600°C, the temperature in the heating section is 1210-1230°C, and the temperature in the soaking section is 1100-1125°C. The total time in the heating and soaking sections is controlled within 2.5-3.5 hours to ensure that the temperature difference between the upper and lower surfaces of the billet is within 15°C. 2) High-pressure water descaling and rolling: Before rolling, high-pressure water is used to descale the cast billet after it leaves the furnace for 1 to 1.5 minutes, and the descaling machine pressure is 20 to 25 MPa. The rolling mode of transverse and longitudinal rolling is adopted. In the transverse rolling stage, the reduction rate of each of the first two rolling passes is greater than 20%, and the first rolling pass uses the rolling mill to descale, the time is 0.3 to 0.6 minutes, and the pressure is 20 to 25 MPa. In the longitudinal rolling stage, the reduction rate of each of the first three rolling passes is greater than 25%, and only the first longitudinal rolling pass uses full-length descaling, the time is 0.5 to 1 minute, and the pressure is 20 to 25 MPa. No descaling is performed in other passes, and the reduction rate of the last pass is less than 5%; the finishing rolling temperature of the steel plate is 860 to 900 ° C. 3) Cooling control: laminar cooling is adopted, the cooling start temperature is 830-870℃, the final cooling temperature is 530-600℃, the number of cooling control headers opened is 3-6 groups, and the water volume of a single header is 120-150m 3 / h, the rolling mill direction is forward, the header opening method is from back to front, and the cooling rate is controlled at 10~15℃ / s; 4) Straightening: Hot straightening is performed after the steel plate is cooled; 5) Air cool to room temperature; The iron scale on the surface of the steel plate is mainly composed of FeO and supplemented by Fe3O4. In terms of mass percentage, FeO accounts for 65% to 80% and Fe3O4 accounts for 35% to 20%.

2. The method for manufacturing a high-efficiency rolled high-surface-quality 355 MPa grade engineering structure steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by weight percentage, C 0.15% to 0.20%, Si 0.25% to 0.35%, Mn 0.75% to 1.05%, Al 0.015% to 0.035%, P≤0.035%, S≤0.035%, and the balance is Fe and unavoidable impurities.

3. The method for manufacturing high-efficiency rolled high-surface-quality 355 MPa grade engineering structure steel plate according to claim 1, characterized in that: The thickness of the steel plate is 10-30 mm.

4. The method for manufacturing high-efficiency rolled high-surface-quality 355 MPa grade engineering structure steel plate according to claim 1, characterized in that: The thickness of the cast slab is less than 250 mm.

5. The method for manufacturing high-efficiency rolled high-surface-quality 355 MPa grade engineering structure steel plate according to claim 1, characterized in that: The steel plate is obtained by rolling a cast billet in a medium and thick plate reciprocating rolling mill.

6. The method for manufacturing high-efficiency rolled high-surface-quality 355 MPa grade engineering structure steel plate according to claim 1, characterized in that: In step 3), the cooling medium for laminar cooling is water.

7. The method for manufacturing a high-efficiency rolled high-surface-quality 355 MPa grade engineering structure steel plate according to claim 1, characterized in that: In step 4), the hot straightening is a straightening process, the position of the lead-in roller is -1.5mm~-3.1mm, the position of the lead-out roller is -2.1mm~-3.8mm, and the straightening force is between 2000KN and 3000KN.

8. The method for manufacturing high-efficiency rolled high-surface-quality 355 MPa grade engineering structure steel plate according to claim 1, characterized in that: The transverse tensile yield strength of the steel plate is ≥355MPa, the tensile strength is between 490 and 570MPa, the elongation is ≥23%, the transverse Charpy impact energy at -20°C is ≥100J, the flatness is below 5mm / 2m, and the surface quality meets the D-level standard.

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