A steel sheet and a method for producing the same

Abstract

The application relates to the field of steel smelting, in particular to a steel plate and a production method thereof. The steel plate prepared by the production method of the application can meet the requirements of low residual stress, high toughness and high strength, and can be produced by reasonable component design, rolling process, straightening process and cutting process optimization, so that the problem of deformation in production caused by too large residual stress and insufficient impact energy of the steel plate can be avoided.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting, and specifically to a steel plate and its production method. Background Technology

[0002] Low residual stress and high toughness steel plates are important materials for industrial equipment manufacturing and engineering structures, widely used in various engineering machinery, shipbuilding, bridge structures, and other fields. With the increasing size of my country's machinery and equipment, the increasing tonnage of ships, and the increasing span of bridge structures, steel structures are continuously developing towards larger size, higher strength, and lighter weight. This has led to some structural components becoming increasingly narrower and longer. During the cutting and slitting process of these components, the presence of residual stress in the steel plate makes narrower and longer sections more prone to deformation. Deformed structural components require straightening or flattening before use, and some severely deformed components are scrapped. Severely deformed steel plates during the cutting and slitting process can even damage the cutting equipment, causing significant losses.

[0003] Patent CN 114231823 A describes the use of Thermomechanical Controlled Process (TMCP) rolling and post-rolling straightening to produce low residual stress Q355B steel plates with a single sheet residual stress ≤150MPa and a room temperature impact energy ≥34J. The carbon content is 0.19%–0.22%, and the manganese content is 1.35%–1.50%. While the high carbon content increases the steel plate strength, it also easily increases the residual stress. Secondly, the impact energy of the steel plates produced by this method only meets the B-grade requirement, with an impact energy of only 34J, which limits the applicable temperature range for the steel plates. Furthermore, the residual stress is relatively high, reaching 150MPa. Patent CN113604734 A describes the use of TMCP rolling and post-rolling offline tempering to produce ultra-thick, low residual stress forklift steel with a thickness of 60-100mm and a longitudinal V-shaped impact energy ≥150J at -5℃. Furthermore, it employs a TMCP rolling and offline tempering production method, which results in a long production cycle, complex processes, and high production costs, while also leading to significant residual stress in the steel plate. Therefore, current technology still lacks a steel plate with low residual stress and high impact energy to meet current industrial production needs and prevent deformation during production. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problem of deformation in production caused by high residual stress and low impact energy of steel plates in the prior art, thereby providing a steel plate and its production method.

[0005] Therefore, the present invention provides a method for producing steel plates, comprising the following steps:

[0006] S1: Molten iron is smelted in a converter, refined by LF, smelted in a vacuum, and continuously cast into a continuous casting billet. The continuous casting billet is then heated. The chemical composition and mass percentage of the continuous casting billet are as follows: C: 0.15-0.18%, Si: 0.10-0.20%, Mn: 1.10-1.30%, P: ≤0.020%, S: ≤0.006%, Nb: 0.010-0.020%, Ti: 0.010-0.020%, Al: 0.020-0.050%, with the remainder being Fe and unavoidable impurities.

[0007] S2: Rolling. When the thickness of the finished steel plate is <20mm, continuous rolling is performed. The initial rolling temperature is 1000℃~1100℃, and the final rolling temperature is 760℃~880℃. When the thickness of the finished steel plate is ≥20mm, the rolling includes a first-stage rolling and a second-stage rolling, with a waiting temperature between the first-stage rolling and the second-stage rolling. The initial rolling temperature of the first-stage rolling is 1000℃~1100℃, and the initial rolling temperature of the second-stage rolling is 860℃~940℃. The waiting temperature thickness is ≥2 times the thickness of the steel plate, and the final rolling temperature is 760℃~880℃. After rolling, the plate is air-cooled.

[0008] S3: Straightening: Straighten the steel plate at a temperature ≥650℃ (e.g., 650-750℃).

[0009] Furthermore, the sulfur content in the molten iron after converter smelting is ≤0.025%.

[0010] Furthermore, during the LF refining process, argon is blown at a rate of 300-900 L / min, the refining time for white slag is ≥20 min (e.g., 20-30 min), and the LF refining time is ≥40 min (e.g., 40-60 min).

[0011] Furthermore, the vacuum smelting time is ≥10 min (e.g., 10-20 min), the vacuum degree is ≤67 Pa (e.g., 20-67 Pa), and the soft blowing time is ≥8 min (e.g., 8-15 min).

[0012] Furthermore, the tundish temperature during the continuous casting process is 1527–1542℃.

[0013] Furthermore, the heating coefficient of the billet is ≥1 min / mm (e.g., 1.1-1.3 min / mm), the maximum heating temperature is ≤1250℃, and the soaking temperature is 1200℃~1230℃.

[0014] Furthermore, in the continuous casting process, for billets with a thickness of 220mm, when 2100mm ≥ slab width ≥ 1800mm, the casting speed is controlled at 1.25-1.35m / min; when 2400mm ≥ slab width > 2100mm, the casting speed is controlled at 1.15-1.25m / min; and when 2700mm ≥ slab width > 2400mm, the casting speed is controlled at 1.05-1.15m / min. For billets with a thickness of 320mm, when the slab width is 1800~2700mm, the casting speed is controlled at 0.60-0.70m / min.

[0015] Furthermore, step S3 is followed by a slitting step; preferably, the slitting method includes flame cutting, plasma cutting, or water jet cutting; preferably, the cutting speed is 0.4 m / min to 0.8 m / min.

[0016] Controlling the cutting speed to 0.4m / min to 0.8m / min can better reduce the residual stress in the steel plate.

[0017] The present invention also provides a steel plate, which is produced according to any of the steel plate production methods described above.

[0018] The present invention also provides a steel plate product, comprising the steel plate as described above, preferably further comprising a ship hull, bridge plate or equipment component (e.g., mechanical equipment, electrical equipment).

[0019] The technical solution of this invention has the following advantages:

[0020] 1. The present invention provides a method for producing steel plates, comprising the following steps: S1: molten iron is smelted in a converter, refined by LF, smelted in a vacuum, and continuously cast into a continuously cast billet, and then the continuously cast billet is heated. The chemical composition and mass percentage of the continuously cast billet are: C: 0.15-0.18%, Si: 0.10-0.20%, Mn: 1.10-1.30%, P: ≤0.020%, S: ≤0.006%, Nb: 0.010-0.020%, Ti: 0.010-0.020%, Al: 0.020-0.050%, with the remainder being Fe and unavoidable impurities; S2 S1: Rolling. When the thickness of the finished steel plate is <20mm, continuous rolling is performed. The initial rolling temperature is 1000℃~1100℃, and the final rolling temperature is 760℃~880℃. When the thickness of the finished steel plate is ≥20mm, the rolling includes a first-stage rolling and a second-stage rolling, with a waiting temperature between the first-stage rolling and the second-stage rolling. The initial rolling temperature of the first-stage rolling is 1000℃~1100℃, and the initial rolling temperature of the second-stage rolling is 860℃~940℃. The waiting temperature thickness is ≥2 times the thickness of the steel plate, and the final rolling temperature is 760℃~880℃. After rolling, the plate is air-cooled. S2: Straightening. The steel plate is straightened at a straightening temperature ≥650℃. In order to meet the requirements of low residual stress, high toughness and high strength, the steel plate prepared by the production method of this application can produce steel plates with low residual stress, high toughness and high strength through reasonable composition design and optimization of the above-mentioned rolling process and straightening process, thus avoiding the problem of deformation of steel plates during production due to excessive residual stress and insufficient impact energy.

[0021] 2. The billet heating coefficient provided by this invention is ≥1 min / mm, the maximum heating temperature is ≤1250℃, and the soaking temperature is 1200℃~1230℃. By reasonably controlling the heating coefficient and temperature of the billet, it is possible to ensure that the steel plate is heated more comprehensively and evenly, making the steel plate production process faster, more continuous, and more efficient. Detailed Implementation

[0022] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0023] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0024] Example

[0025] Examples 1-5 provide a series of methods for producing steel plates, including: smelting molten iron in a converter, refining it using an LF furnace, vacuum smelting it, and continuously casting it into a continuous casting billet; then heating, rolling, straightening, and cutting the billet into strips. The chemical composition and mass percentage of the continuous casting billet are shown in Table 1, with the remainder being Fe and unavoidable impurities. The production process is as follows:

[0026] Converter smelting: The sulfur content in the molten iron after converter smelting is 0.022%;

[0027] LF refining: Argon blowing is performed during the LF refining process. The argon flow rate and refining slag time are specified in each embodiment. 、 The total refining time for LF is shown in Table 2. The S content at the end of refining is 0.005%.

[0028] Vacuum smelting: The smelting vacuum degree is 65 Pa. The vacuum smelting time and soft blowing time are shown in Table 2.

[0029] Continuous casting: The tundish temperature, slab thickness, width and casting speed during continuous casting are shown in Table 2.

[0030] Billet heating: In each embodiment, the billet is heated to the maximum heating temperature and then held at a uniform heating temperature. The billet heating coefficient, maximum heating temperature and uniform heating temperature are shown in Table 2. This ensures that the billet is thoroughly heated and the temperature is uniform. Billet heating time = billet thickness × heating coefficient.

[0031] Rolling and straightening: The first stage rolling temperature (i.e., the rolling temperature in the table), the second stage rolling temperature (i.e., the second rolling temperature in the table), and the final rolling temperature of each embodiment are shown in Table 3. After rolling, the steel plate is air-cooled, transported to the straightening machine by roller conveyor, and then air-cooled to room temperature. No further straightening is performed at room temperature.

[0032] The straightening temperatures of steel plates are shown in Table 3.

[0033] Cutting and slitting: The steel plate is cut using flame cutting at a speed of 0.4 m / min.

[0034] Table 1 Chemical composition of continuously cast billets (wt%)

[0035]

[0036] Note: "-" indicates that the component does not exist.

[0037] Table 2 Process Parameters Table 1

[0038]

[0039] Table 3 Process Parameters Table 2

[0040]

[0041]

[0042] Note: "-" indicates that the operation does not exist.

[0043] Comparative Example 1

[0044] This comparative example provides a method for producing steel plates. The chemical composition and production process are basically the same as in Example 3, except that the second initial rolling temperature and the final rolling temperature are higher than the protection range of this application. Specific process parameters are shown in Table 3. After rolling, the steel plate is water-cooled to 620°C and then transported to a straightening machine for straightening. At this point, the steel plate temperature is 500°C. After straightening, the steel plate is then air-cooled to room temperature. The steel plate needs to be straightened again at room temperature.

[0045] Comparative Example 2

[0046] This comparative example provides a method for producing steel plates, the production process of which is the same as that of Example 3, the only difference being the chemical composition of the continuously cast billet, the specific chemical composition of which is shown in Table 1.

[0047] Comparative Example 3

[0048] This comparative example provides a method for producing steel plates, whose chemical composition and production process are basically the same as those in Example 3. The only difference is that a continuous rolling method without waiting for a specific temperature is adopted during the rolling process. The first rolling temperature and the final rolling temperature exceed the protection scope of this application. The specific process parameters are shown in Table 3.

[0049] Comparative Example 4

[0050] This comparative example provides a method for producing steel plates. The chemical composition and production process are basically the same as those in Example 3. The only difference is that the second rolling temperature and the final rolling temperature are lower than the protection range of this application during the rolling process. The specific process parameters are shown in Table 3.

[0051] Comparative Example 5

[0052] This comparative example provides a method for producing a steel plate with the same chemical composition and mass percentage as Example 3. The only difference is that the first rolling temperature is lower than the protection range of this application during the rolling process. The specific process parameters are shown in Table 3.

[0053] Experimental Example 1

[0054] The yield strength, tensile strength, and elongation of the steel plates prepared in each embodiment and comparative example were tested using the full-thickness plate tensile room temperature test method specified in GB / T 228.1-2021. The yield strength ratio is the ratio of yield strength to tensile strength. The yield strength ratios of each embodiment and comparative example were calculated based on the ratios of yield strength to tensile strength, as shown in Table 4.

[0055] The impact energy of each embodiment and comparative example at -40℃ was tested using the Charpy pendulum impact test method specified in GB / T229. The specific experimental results are shown in Table 4.

[0056] The maximum and minimum residual stresses of each embodiment and comparative example were tested using the blind hole test method, and the residual stress difference was calculated. The specific experimental results are shown in Table 5.

[0057] The unevenness and lateral curvature of the steel plates prepared in each embodiment and comparative example were tested using a ruler and string as specified in GB / 709. The specific experimental results are shown in Table 5.

[0058] Table 4 Mechanical Properties of Steel Plates

[0059]

[0060] Table 5 Residual stress, unevenness, and lateral curvature of steel plates

[0061]

[0062]

[0063] As can be seen from the results in Tables 4 and 5, compared with the comparative examples, Examples 1-5 of the present invention can significantly improve the elongation and impact energy of steel plates and reduce residual stress by precisely controlling the chemical composition and optimizing the rolling and straightening processes.

[0064] Comparative Example 4 reduced the second rolling temperature and the final rolling temperature. The yield strength, tensile strength, and -40°C impact energy of the steel plate prepared by it were different from those of the steel plate prepared in the embodiments of this application. The residual stress was also significantly higher than that of the steel plate prepared in this application, which affected the flatness and lateral curvature of the steel plate product and increased the degree of bending of the steel plate.

[0065] Comparative Example 5 reduced the first rolling temperature to prepare the steel plate, which significantly reduced the impact energy at -40℃ and significantly increased the residual stress of the steel plate, increasing the unevenness and lateral curvature of the steel plate products and aggravating the bending degree of the steel plate.

[0066] Therefore, it is evident that only by adopting the process conditions described in this application and rationally designing the steel plate composition, production temperature parameters, and process steps can the produced steel plate be guaranteed to possess excellent mechanical properties while simultaneously exhibiting low residual stress and high impact energy, thus meeting the needs of actual production. Changing any condition in the production process will significantly alter the performance of the produced steel plate, causing it to bend and deform. The steel plate produced using the process described in this application has a yield strength ≥385MPa, tensile strength ≥533MPa, elongation ≥29%, impact energy at -40℃ ≥126J, residual stress per sheet ≤36MPa, fluctuation range ≤14MPa, flatness after slitting ≤1.5mm / 1m, and lateral curvature ≤7.5mm / 10m. The steel plate prepared by this application possesses low residual stress while also exhibiting high toughness and high strength, solving the problem in existing technologies where low residual stress and high impact energy cannot be simultaneously achieved, leading to deformation during production.

[0067] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for producing steel plates, characterized in that, Includes the following steps: S1: Molten iron is smelted in a converter, refined by LF, smelted in a vacuum, and continuously cast into a continuous casting billet. The continuous casting billet is then heated. The chemical composition and mass percentage of the continuous casting billet are as follows: C: 0.15-0.18%, Si: 0.13-0.18%, Mn: 1.2-1.28%, P: ≤0.020%, S: ≤0.006%, Nb: 0.014-0.019%, Ti: 0.014-0.017%, Al: 0.03-0.038%, with the remainder being Fe and unavoidable impurities. S2: Rolling. When the thickness of the finished steel plate is <20mm, continuous rolling is performed. The initial rolling temperature is 1000℃~1100℃, and the final rolling temperature is 760℃~880℃. When the thickness of the finished steel plate is ≥20mm, the rolling includes a first-stage rolling and a second-stage rolling, with a waiting temperature between the first-stage rolling and the second-stage rolling. The initial rolling temperature of the first-stage rolling is 1000℃~1100℃, and the initial rolling temperature of the second-stage rolling is 860℃~940℃. The waiting temperature thickness is ≥2 times the thickness of the steel plate, and the final rolling temperature is 760℃~880℃. After rolling, the plate is air-cooled. S3: Straightening, straightening the steel plate at a temperature ≥650℃.

2. The method for producing steel plates according to claim 1, characterized in that, The sulfur content in the molten iron after converter smelting is ≤0.025%.

3. The method for producing steel plates according to claim 1 or 2, characterized in that, During the LF refining process, argon is blown at a rate of 300~900 L / min, the white residue refining time is ≥20 min, the LF refining time is ≥40 min, and the refining end S≤0.006%.

4. The method for producing steel plates according to claim 1 or 2, characterized in that, The vacuum smelting time is ≥10 min, the vacuum degree is ≤67 Pa, and the soft blowing time is ≥8 min.

5. The method for producing steel plates according to claim 1 or 2, characterized in that, The tundish temperature during continuous casting is 1527–1542℃.

6. The method for producing steel plates according to claim 1 or 2, characterized in that, The heating coefficient of the billet is ≥1min / mm, the maximum heating temperature is ≤1250℃, and the soaking temperature is 1200℃~1230℃.

7. The method for producing steel plates according to claim 1 or 2, characterized in that, In the continuous casting process, for billets with a thickness of 220mm, when 2100mm ≥ slab width ≥ 1800mm, the casting speed is controlled at 1.25-1.35m / min; when 2400mm ≥ slab width > 2100mm, the casting speed is controlled at 1.15-1.25m / min; when 2700mm ≥ slab width > 2400mm, the casting speed is controlled at 1.05-1.15m / min. For billets with a thickness of 320mm, when the slab width is 1800~2700mm, the casting speed is controlled at 0.60-0.70m / min.

8. The method for producing steel plates according to claim 1 or 2, characterized in that, Step S3 is followed by a step of cutting and slitting.

9. The method for producing steel plates according to claim 8, characterized in that, The cutting and slitting methods include flame cutting, plasma cutting, or water jet cutting.

10. The method for producing steel plates according to claim 8, characterized in that, The cutting speed is 0.4 m / min to 0.8 m / min.

11. A steel plate, characterized in that, It is produced by the steel plate production method according to any one of claims 1-10.

12. A steel plate product, characterized in that, The steel plate produced by the method of producing the steel plate according to any one of claims 1-10 or the steel plate according to claim 11.

13. The steel plate product according to claim 12, characterized in that, The steel plate products also include ship hulls, bridge plates, or equipment components.

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