A method for manufacturing a high-surface-quality 355mpa-grade engineering structural steel plate by efficient rolling

Abstract

The application discloses a manufacturing method of high-efficiency rolling of a 355MPa-grade engineering structure steel plate with high surface quality, and belongs to the field of metal processing.The manufacturing method comprises the following steps: casting blank heating, rolling, controlled cooling, straightening (hot straightening), and air cooling to room temperature.The steel plate does not need subsequent controlled rolling, and the performance requirements of the steel plate can be met, and the steel plate reaches D-grade standard after shot blasting, which has a remarkable effect on improving production efficiency, improving surface quality and reducing production cost.

Description

Technical Field

[0001] This invention belongs to the field of metal processing, and specifically relates to a method for manufacturing high-efficiency rolled steel plates for engineering structures with high surface quality, thickness specifications of 10-30mm, and yield strength of 355MPa. Background Technology

[0002] Faced with the severe market situation in 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 the paint applied to the steel plate surface after shot blasting to lower manufacturing costs. This has led to increasingly stringent requirements for controlling the iron oxide scale on the original steel plate surface (meeting the D-grade standard, meaning no color difference or iron scale indentation on the surface after shot blasting). Simultaneously, while ensuring production and equipment safety, increasing the output per unit time of the rolling line, i.e., the number of rolled pieces per hour, is essential to achieving high-efficiency production with maximum efficiency and minimum consumption while ensuring steel plate surface quality. This is especially true for medium and heavy plates of the 355MPa level (AH36, Q355B, etc.), where market competition has become increasingly apparent in recent years. This type of steel is mainly based on carbon-manganese steel, with the addition of microalloying elements such as Al, Ti, and Nb, which are carbon and nitride-forming elements, as well as a high content of Mn. Solid solution strengthening, precipitation strengthening, and grain refinement strengthening are used to improve the strength and toughness of the steel plate. Statistics show that medium and heavy plates of this strength level account for more than 30% of the annual production. Therefore, the production of medium and heavy plates, especially 355MPa grade steel plates, urgently needs to further optimize the production process, reduce manufacturing costs (energy consumption, alloy costs) and improve surface quality on the current basis, so as to enhance the market competitiveness of the products.

[0003] Currently, for 355MPa grade steel plates with a thickness of 10-30mm, a medium carbon (0.15%~0.25%) and medium Mn (1.15%~1.45%) composition design system is typically adopted to reduce alloy costs. Simultaneously, deep controlled rolling and controlled cooling processes are used to minimize performance fluctuations caused by reduced alloy costs. However, steel plates with reduced alloy content are usually produced using a multi-stage controlled rolling (TMCP) process, with final rolling temperatures of 800℃ or even lower. The lower temperatures increase the deformation resistance of the rolled piece, thereby increasing the load on the rolling mill and making plate shape control more difficult. Furthermore, low-temperature rolling requires a longer intermediate warming time, affecting rolling rhythm and production efficiency. In addition, improper control of processes such as billet time in the furnace, descaling machine pressure, intermediate billet warming time and temperature, descaling process, laminar cooling rate, and straightening temperature directly leads to residual iron oxide scale being pressed in, affecting the surface quality of the steel plate. Therefore, optimizing the composition and process of 355MPa grade engineering structural steel plates with high surface quality requirements is necessary. This is a key issue that needs to be addressed in the mass production of economical 355MPa grade medium and heavy plates, while controlling alloy costs, improving rolling speed, and ensuring steel plate performance and surface quality.

[0004] Compared with existing technologies:

[0005] To date, there has been very little research, both domestically and internationally, on methods to improve the rolling efficiency of steel plates with a thickness of 10-30mm and a yield strength of 355MPa. Prior to this invention, patent publication number CN 115537636 A disclosed a method for improving the rolling efficiency of A32 grade marine medium-thick plates. This method employs a non-TMCP rolling process, controlling the billet heating regime to ensure the final rolling temperature of the steel plate falls within a pre-set target range; however, it has a high alloy composition, and the production thickness is mainly below 16mm, without addressing the production process for thicknesses above 20mm, and it does not elaborate on the surface quality requirements of the steel plate.

[0006] While the steel plate shape control methods disclosed in the above patent documents improve the rolling efficiency of steel plates of certain thicknesses, they are not suitable for high-efficiency rolling, high-surface-quality engineering structural steel plates with a thickness of 10-30mm and a yield strength of 355MPa. The technical solution provided by this invention effectively overcomes these shortcomings. It solves the problems of low rolling efficiency for 10-30mm thickness steel plates and surface quality issues caused by low alloy content and the intrusion of iron oxide scale, which affect the rolling efficiency, when using continuously cast billets with a thickness of 250mm or less. Through reasonable composition design and optimized heating, rolling, and cooling processes, it addresses these issues. Summary of the Invention

[0007] The purpose of this invention is to overcome the aforementioned technical problems and deficiencies, and to provide a method for preparing engineering structural steel plates with high surface quality, high rolling efficiency, thickness specifications of 10-30mm, and yield strength of 355MPa. The steel plates do not require subsequent controlled rolling to meet the performance requirements, and after shot blasting, they meet the D-grade standard (the surface must not have color difference or indentation of iron scale after shot blasting). This solves the problems of low rolling efficiency, surface quality, and low first-pass yield of such steel plates due to their low alloy content, which necessitates controlling the final rolling temperature during rolling to ensure performance.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] This invention provides a method for manufacturing a high-efficiency rolled 355MPa grade engineering structural steel plate with high surface quality. The chemical composition of the steel plate, by weight percentage, includes: C 0.15%–0.20%, Si 0.25%–0.35%, Mn 0.75%–1.05%, Al 0.015%–0.035%, P≤0.035%, S≤0.035%, with the balance being Fe and unavoidable impurities.

[0010] The roles of the main elements in the chemical composition of the steel plate of this invention are as follows:

[0011] Carbon (C): The most economical and basic strengthening element in steel. It has a significant effect on improving the strength of steel through solid solution strengthening and precipitation strengthening. However, increasing the C content has a negative impact on the plasticity, toughness, and weldability of steel. Therefore, this invention sets the C content range to 0.15%–0.20%.

[0012] Mn: Mn strengthens steel through solid solution treatment, compensating for the strength loss caused by the reduced carbon content. Furthermore, it lowers the γ-α phase transformation temperature, refining ferrite grains and contributing to finer low-temperature transformation products, thus improving toughness. However, increasing the Mn content exacerbates center segregation in continuously cast billets, hindering the improvement of low-temperature toughness. Considering alloy cost, the Mn content range in this invention is designed to be 0.75%–1.05%.

[0013] Si plays a role in deoxidation and improving the strength of the matrix in steelmaking. However, excessive Si content and improper heating temperature control can lead to the formation of FeO / Fe2SiO4 eutectoid phases that "pin" the surface. Therefore, the Si content in this invention is set at 0.25% to 0.35%.

[0014] Al: Commonly used as a deoxidizer in steel, it can also refine the microstructure if it forms AlN. When the Al content exceeds 0.035%, excessive alumina inclusions will reduce the cleanliness of the steel. If the Al content is too low, deoxidation will be insufficient; therefore, the lower limit for Al content is set at 0.015%.

[0015] P and S are unavoidable impurity elements in steel, and their content should be as low as possible. However, due to considerations of smelting costs and processes, their content cannot be infinitely low. Therefore, this invention sets the upper limits for P and S content at 0.020% and 0.015%, respectively.

[0016] The steel plate of the present invention has a thickness of 10-30mm and is produced on a medium-thick plate reciprocating rolling mill using a continuous casting billet with a thickness of less than 250mm. The cooling medium is water.

[0017] The objective of this invention is achieved through the following technical solution:

[0018] This invention discloses a method for preparing high-efficiency rolled 355MPa grade engineering structural steel plates, comprising: billet heating → rolling → controlled cooling → straightening (hot straightening) → air cooling to room temperature; specifically including the following steps:

[0019] 1) Billet Heating: The billet is fed into a walking beam furnace for heating, passing through a preheating section, a heating section, and a soaking section before exiting the furnace. The preheating section has a temperature range of 400–600℃ (to promote homogenization of the billet's microstructure and facilitate element diffusion), the heating section has a temperature range of 1210–1230℃, and the soaking section has a temperature range of 1100–1125℃. The total time spent in the furnace during the heating and soaking sections is controlled to be 2.5–3.5 hours, ensuring the temperature difference between the upper and lower surfaces of the billet is within 15℃ (the heating section uses a higher temperature for further heating). This process promotes the diffusion of elements Mn and C, mitigating their impact on microstructure and properties due to component segregation. Simultaneously, the heating section provides high-temperature heating, ensuring temperature uniformity across all parts of the billet and improving the uniformity of transverse and longitudinal metal flow on the steel plate surface. Combined with the billet composition, reducing the heating temperature of the billet soaking section decreases energy consumption. It also prevents excessive Si content and improper heating temperature control from generating FeO / Fe2SiO4 eutectoid phases that "pin" the surface, affecting subsequent descaling. Furthermore, it effectively inhibits excessive austenite grain growth, which can negatively impact steel plate performance.

[0020] 2) High-pressure water descaling and rolling: Before rolling, the billet is descaled with high-pressure water for 1-1.5 minutes after exiting the furnace, with a descaling machine pressure of 20-25 MPa. A transverse and longitudinal rolling mode is adopted. In the transverse rolling stage, the reduction rate of each of the first two passes is greater than 20%, and the first pass utilizes the mill for descaling for 0.3-0.6 minutes at a pressure of 20-25 MPa. (The first two passes maximize the mill's capacity with a large reduction rate to promote dynamic austenite re-crystallization, refine the original austenite grains, and use high-pressure water descaling to ensure uniform microstructure distribution from the surface to the core of the steel plate, improving the strength and toughness of the steel plate, while further removing the iron oxide scale from the billet surface). In the longitudinal rolling stage, the pressure of each of the first three passes is greater than 20%. For a reduction rate greater than 25%, full-length descaling is used only in the first pass of longitudinal rolling, with a time of 0.5–1 min and a pressure of 20–25 MPa. Descaling is not performed in other passes. (The first three passes of longitudinal rolling use a high reduction rate to further refine the austenite grains and improve the core structure. At the same time, a full-length descaling pass is performed before the start of longitudinal rolling to remove the iron oxide scale generated on the surface of the billet during the transition from transverse rolling to longitudinal rolling. No additional descaling passes are added in the later stages of longitudinal rolling to ensure dense growth of the iron oxide scale in all parts.) Due to the temperature drop of the steel plate and the increase in deformation resistance in the later stages of rolling, a small reduction rate (less than 5%) is used 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℃ (to control the final rolling temperature to reduce the formation of Fe2O3).

[0021] 3) Controlled cooling: Laminar flow cooling is adopted, with an initial cooling temperature range of 830–870℃ and a final cooling temperature range of 530–600℃. The number of controlled cooling manifold groups is 3–6, and the water flow rate per manifold is 120–150 m³. 3 / h, the manifold opening method is from back to front (forward in the mill direction), and the cooling rate is controlled at 10~15℃ / s. (Control the opening cooling temperature to ensure that the microstructure of the steel plate is austenitic when it enters the water. During the cooling process, control the cooling rate and final cooling temperature to suppress the formation of bainite and martensite phases on the surface of the steel plate and the amount of bainite phase in the core microstructure, so as to avoid affecting the toughness of the steel plate due to bainite or martensite phase transformation on the surface; at the same time, control the number of manifold opening groups, water volume and method to ensure that the iron scale on the surface of the steel plate is further densified before cooling and does not break during the cooling process. The iron scale is mainly FeO and supplemented by Fe3O4, with the two proportions of 65%~80% and 35%~20% by mass percentage, respectively).

[0022] 4) Straightening: The steel plate is hot straightened after controlled cooling.

[0023] 5) Air cool to room temperature.

[0024] Furthermore, in step 3), the cooling medium for laminar flow cooling is water.

[0025] Furthermore, in step 4), the hot straightening is a single hot straightening process, with the inlet roller position at -1.5mm to -3.1mm and the outlet roller position at -2.1mm to -3.8mm. The straightening force is between 2000KN and 3000KN (by setting appropriate roller gaps and straightening force, the straightened steel plate is ensured to be straight and have a good shape).

[0026] By adopting the above-mentioned composition and heating, rolling, and cooling process scheme, the shortcomings of existing technologies are overcome. This solves the problems of low alloy content in this type of steel plate, which, in order to ensure performance, requires careful control of the final rolling temperature, resulting in low rolling efficiency, surface quality, and low first-pass yield. The final steel plate exhibits the same properties as that 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℃, and surface quality meeting Grade D standards. Calculations show that after composition and process optimization, the rolling rhythm of economical medium-thick plates with a yield strength of 355MPa (10-30mm thickness) is significantly improved, reducing the average rolling time per plate by 30-60 seconds. This has a significant effect on improving production efficiency, surface quality, and reducing production costs.

[0027] The beneficial effects of this invention are:

[0028] 1. The temperatures and times of the preheating, heating, and soaking zones of the billet are limited to promote the homogenization of the microstructure and facilitate the full diffusion of elements. At the same time, the heating zone uses a higher temperature to further promote the diffusion of Mn and C, reducing their impact on the microstructure and properties due to component segregation. The heating zone provides high-temperature heating to ensure temperature uniformity in all parts of the billet and improve the uniformity of transverse and longitudinal metal flow on the steel plate surface. In combination with the billet composition, the heating temperature of the soaking zone is reduced to decrease energy consumption. At the same time, it avoids the formation of FeO / Fe2SiO4 eutectoid phases due to excessive Si content and excessive heating temperature, which would "pin" the surface and affect the subsequent descaling effect. It also effectively inhibits the excessive growth of austenite grains and ensures the performance of the steel plate.

[0029] 2. The composition of this invention is reasonable, the amount of alloy added is low, and the intermediate billet waiting for heating is eliminated, which greatly reduces the alloy cost and the resistance to high-temperature deformation in the roughing and finishing rolling stages. This is conducive to increasing the reduction amount in each pass and ensuring the comprehensive performance of the super steel plate.

[0030] 3. By adopting a transverse and longitudinal rolling mode, adding a descaling process in the first pass of each stage, and using a large reduction in the first two and three passes of each stage, dynamic austenite re-crystallization is promoted, refining the original austenite grains. High-pressure water descaling in the rolling mill ensures uniform microstructure distribution from the surface to the core of the steel plate, improving the strength and toughness of the steel plate, while further removing iron oxide scale from the surface of the billet. No additional descaling passes are added in the later stages of longitudinal rolling to ensure dense growth of iron scale in all parts. A small reduction rate (less than 5%) is used in the final pass to flatten the shape of the steel plate and reduce internal stress. In addition, this rolling process does not use the traditional TMCP process, eliminating the intermediate billet warming process, which also improves rolling efficiency. The final rolling temperature of the steel plate is controlled at 860-900℃, reducing the probability of Fe2O3 formation.

[0031] 4. Controlled cooling is employed for the rolled steel plates. The initial cooling temperature is controlled to ensure the microstructure is austenitic when the steel plate enters the water. During cooling, 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 microstructure. This prevents bainite or martensitic phase transformations on the surface from affecting the steel plate's toughness. Simultaneously, the number of manifold openings, water volume, and method are controlled to ensure that the surface scale on the steel plate is further densified before cooling and does not break during the cooling process. The scale is primarily composed of FeO, with Fe3O4 as a secondary component, in proportions of 65%–80% and 35%–20%, respectively.

[0032] 5. Use hot straightening, set the position and pressure of the inlet and outlet rollers to ensure that the straightened steel plate is straight and has a good shape.

[0033] 6. By adopting the above-mentioned composition and heating, rolling, and cooling process scheme, the shortcomings of existing technologies are overcome. This solves the problems of low alloy content in this type of steel plate, which, in order to ensure performance, requires careful control of the final rolling temperature, resulting in low rolling efficiency, surface quality, and low first-pass yield. The final steel plate has the same performance as that produced using the existing TMCP process. The flatness of the steel plate is below 5mm / 2m, saving costs in subsequent cold straightening processes. The yield strength of the steel plate in the transverse tensile test is ≥355MPa, the tensile strength is between 490 and 570MPa, the elongation is ≥23%, the transverse Charpy impact energy at -20℃ is ≥100J, and the surface quality meets the D-grade standard. Calculations show that after composition and process optimization, the rolling rhythm of economical medium-thick plates with a yield strength of 355MPa (10-30mm thickness) is significantly improved, reducing the average rolling time per plate by 30-60 seconds. This has a significant effect on improving production efficiency, surface quality, and reducing production costs. Detailed Implementation

[0034] The following examples are used to illustrate the content of the present invention. These examples are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0035] A method for preparing high-efficiency rolled 355MPa grade engineering structural steel plates with high surface quality, wherein the chemical composition of the steel plate, by weight percentage, includes: C 0.15%–0.20%, Si 0.25%–0.35%, Mn 0.75%–1.05%, Al 0.015%–0.035%, P≤0.035%, S≤0.035%, with the balance being Fe and unavoidable impurities; the thickness of the steel plate is 10-30mm, and it is produced using a cast billet with a thickness of less than 250mm on a medium-thick plate reciprocating rolling mill, with water as the cooling medium;

[0036] The preparation method includes billet heating → rolling → controlled cooling → straightening (hot straightening) → air cooling to room temperature; specifically, it includes the following steps:

[0037] 1) Billet heating: The billet is sent into a walking beam furnace for heating. The billet passes through the preheating section, heating section and soaking section in sequence before exiting the furnace. The temperature range of the preheating section is 400-600℃ (to promote the homogenization of the microstructure in the billet and promote the full diffusion of elements), the temperature range of the heating section is 1210-1230℃, and the temperature range of the soaking section is 1100-1125℃. 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℃.

[0038] 2) High-pressure water descaling and rolling: Before rolling, the billet after exiting the furnace is descaled with high-pressure water for 1-1.5 minutes, with a descaling machine pressure of 20-25 MPa; a transverse and longitudinal rolling mode is adopted. In the transverse rolling stage, the reduction rate of each pass in the first two rolling passes is greater than 20%, and the first rolling pass uses the mill for descaling for 0.3-0.6 minutes at a pressure of 20-25 MPa; in the longitudinal rolling stage, the reduction rate of each pass in the first three rolling passes is greater than 25%, and only the first longitudinal rolling pass uses full-length descaling for 0.5-1 minutes at a pressure of 20-25 MPa. Other passes do not use descaling, and the last pass uses a small reduction rate (less than 5%); the final rolling temperature of the steel plate is 860-900℃.

[0039] 3) Controlled cooling: Laminar flow cooling is adopted, with an initial cooling temperature range of 830–870℃ and a final cooling temperature range of 530–600℃. The number of controlled cooling manifold groups is 3–6, and the water flow rate per manifold is 120–150 m³. 3 / h, the manifold opening method is from back to front (forward in the mill direction), and the cooling rate is controlled at 10~15℃ / s. The sheet metal is mainly FeO, supplemented by Fe3O4, with the proportions of the two by mass percentage being 65%~80% and 35%~20%, respectively.

[0040] 4) Hot straightening: After the steel plate is cooled, it is hot straightened (one-pass straightening). The position of the inlet roller is -1.5mm to -3.1mm, the position of the outlet roller is -2.1mm to -3.8mm, and the straightening force is between 2000KN and 3000KN.

[0041] 5) Air cool to room temperature.

[0042] The steel plate has a thickness of 10-30mm and is produced on a medium-thick plate reciprocating rolling mill using continuously cast billets with a thickness of less than 250mm. The cooling medium is water.

[0043] Examples 1-6

[0044] Table 1 shows the chemical composition of the steel in the examples; Table 2 shows the heating regime of the billet and the high-pressure water descaling process before rolling of the continuously cast billet; Table 3 shows the rolling method of the steel in the examples; Table 4 shows the cooling and straightening process of the steel in the examples; Table 5 shows the dimensions, properties and flatness of the steel in the examples.

[0045] Table 1 Chemical composition (wt, %) of the steel in the examples

[0046]

[0047] Note: Impurity elements in steel: P≤0.035%, S≤0.035%.

[0048] Table 2 Heating regime of steel billets and high-pressure water descaling process before rolling of continuously cast billets in the examples

[0049]

[0050] Table 3 Rolling method of steel in the examples

[0051]

[0052] Table 4. Cooling and straightening processes for steel in the examples.

[0053]

[0054] Table 5. Dimensions, properties, and flatness of the steel in the examples.

[0055]

[0056] Therefore, compared with the prior art, the purpose of this invention is to overcome the aforementioned technical problems and deficiencies, and to provide a method for producing engineering structural steel plates with high surface quality, high rolling efficiency, thickness specifications of 10-30mm, and yield strength of 355MPa. The steel plates do not require subsequent controlled rolling to meet the performance requirements, and after shot blasting, they meet the D-grade standard (the surface must not have color difference or indentation of iron scale after shot blasting). This solves the problems of low rolling efficiency, surface quality, and low first-pass yield of such steel plates due to their low alloy composition, which necessitates controlling the final rolling temperature during rolling to ensure performance. Calculations show that after optimizing the composition and process, the rolling rhythm of economical medium-thick plates with a yield strength of 355MPa and a thickness of 10-30mm is significantly improved, reducing the average rolling time per plate by 30-60 seconds, resulting in significant improvements in production efficiency, surface quality, and production costs.

[0057] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for manufacturing high-efficiency rolled 355MPa grade engineering structural steel plates, characterized in that, Includes 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 exiting the furnace. The temperature of the preheating section is 400-600℃, the temperature of the heating section is 1210-1230℃, and the temperature of the soaking section is 1100-1125℃. 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℃. 2) High-pressure water descaling and rolling: Before rolling, the billet after exiting the furnace is descaled with high-pressure water for 1-1.5 minutes, with a descaling machine pressure of 20-25 MPa; a transverse and longitudinal rolling mode is adopted. In the transverse rolling stage, the reduction rate of each pass in the first two rolling passes is greater than 20%, and the first rolling pass uses the rolling mill for descaling for 0.3-0.6 minutes at a pressure of 20-25 MPa; in the longitudinal rolling stage, the reduction rate of each pass in the first three rolling passes is greater than 25%, and only the first longitudinal rolling pass uses full-length descaling for 0.5-1 minute at a pressure of 20-25 MPa. Other passes do not descaling, and the reduction rate of the last pass is less than 5%; the final rolling temperature of the steel plate is 860-900℃; 3) Controlled cooling: Laminar flow cooling is adopted, with an initial cooling temperature of 830-870℃ and a final cooling temperature of 530-600℃. The number of controlled cooling manifold groups is 3-6, and the water flow rate per manifold is 120-150m³. 3 / h, the mill direction is forward, the manifold opening method is from back to front, and the cooling rate is controlled at 10~15℃ / s; 4) Straightening: The steel plate is hot-straightened after controlled cooling; 5) Air cool to room temperature; In step 3), the cooling medium for laminar flow cooling is water; In step 4), the hot straightening is a single straightening process, with the inlet roller position at -1.5mm to -3.1mm and the outlet roller position at -2.1mm to -3.8mm, and the straightening force between 2000KN and 3000KN. The chemical composition of the steel plate, by weight percentage, includes: C 0.15%–0.20%, Si 0.25%–0.35%, Mn 0.75%–1.05%, Al 0.015%–0.035%, P≤0.035%, S≤0.035%, with the balance being Fe and unavoidable impurities; The thickness of the steel plate is 10-30mm; The iron scale on the surface of the steel plate is mainly composed of FeO and supplemented by Fe3O4, with FeO accounting for 65% to 80% and Fe3O4 accounting for 35% to 20% by mass percentage. The steel plate has a transverse tensile yield strength ≥355MPa, a tensile strength between 490 and 570MPa, an elongation ≥23%, a transverse Charpy impact energy ≥100J at -20℃, a flatness below 5mm / 2m, and a surface quality that meets the D-grade standard. The D-grade standard means that there should be no color difference or iron sheet indentation on the surface after shot blasting.

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

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

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