A pre-coated steel sheet and a method for manufacturing the same

Abstract

The application relates to a precoated steel sheet and a preparation method thereof, the method comprising the following steps: heating and rolling a casting blank with a set chemical composition to obtain a hot-rolled sheet; first coiling the hot-rolled sheet and controlling the temperature of the first coiling to make part of TiC particles in the structure of the hot-rolled sheet precipitate, then pickling to obtain a pickling coil; continuously hot-dip galvanizing the pickling coil to obtain a precoated steel sheet; the continuously hot-dip galvanizing the pickling coil to obtain a precoated steel sheet comprises the following steps: annealing the pickling coil and controlling the temperature and time of the annealing to make TiC particles continuously precipitate in the structure of the pickling coil, then hot-dip galvanizing, and coating a coating in the post-processing section of the hot-dip galvanizing to obtain a precoated steel sheet. The application reduces a cold rolling process and a color coating process, greatly shortens a process, and the precoated steel sheet has good corrosion resistance and simultaneously has high strength and high plasticity.

Description

Technical Field

[0001] This application relates to the field of steel manufacturing technology, and in particular to a pre-coated steel plate and its preparation method. Background Technology

[0002] In traditional industries such as automobiles, home appliances, and construction, steel parts require painting after processing to achieve good appearance and durability. This process is prone to generating volatile substances during painting, causing environmental pollution; furthermore, the coating efficiency for individual parts is low. The development of color-coated steel sheets has largely avoided these problems, as parts formed directly from color-coated steel sheets no longer require painting.

[0003] However, the manufacturing process of color-coated steel sheets is complex and costly, requiring hot rolling, pickling, cold rolling annealing or hot-dip galvanizing, and then a separate color coating process. Furthermore, the highest strength grade currently available for color-coated steel sheets is 550 MPa, which is insufficient for higher strength requirements. Moreover, there are currently no publicly reported examples of coated steel sheets produced without a color coating process, and higher strength coated steel sheets remain to be developed. Summary of the Invention

[0004] This application provides a pre-coated steel plate and its preparation method to solve the following technical problem: providing a new method for preparing a pre-coated steel plate.

[0005] In a first aspect, this application provides a method for preparing a pre-coated steel plate, the method comprising:

[0006] A cast billet with a set chemical composition is heated and rolled to obtain a hot-rolled plate;

[0007] The hot-rolled plate is first wound up, and the temperature of the first winding is controlled so that some TiC particles are precipitated in the microstructure of the hot-rolled plate. Then, it is pickled to obtain pickled coil.

[0008] The pickled coil is continuously hot-dip galvanized to obtain a pre-coated steel sheet;

[0009] The process of continuously hot-dip galvanizing the pickled coil to obtain a pre-coated steel sheet includes:

[0010] The pickled coil is annealed, and the temperature and time of the annealing are controlled to allow TiC particles to continuously precipitate in the microstructure of the pickled coil. Then, hot-dip galvanizing is performed, and a coating is applied in the post-treatment section of the hot-dip galvanizing to obtain a pre-coated steel sheet.

[0011] Optionally, the temperature of the first winding is 530℃~630℃.

[0012] Optionally, the annealing temperature is 560℃~780℃, the annealing time is 10s~60s, and the annealing temperature and the annealing time satisfy the following relationship:

[0013] 185≤[t]+0.23[T]≤190

[0014] In the formula, [t] represents the annealing time, and [T] represents the annealing temperature.

[0015] Optionally, the coating process parameters include: the ratio of coating speed to strip running speed is ≥140%, and the coating thickness is 1.5μm to 4μm.

[0016] Optionally, the method further includes:

[0017] The pre-coated steel sheet is dried and cooled, and then a second coil is made to obtain the pre-coated steel sheet finished product; wherein, the drying temperature is 110℃~140℃, and the second coiling temperature is ≤40℃.

[0018] Optionally, the chemical composition of the plating solution in the hot-dip galvanizing process includes: Al, Mg, and Zn; wherein, by mass fraction,

[0019] The Al content is 5%–12%, and the Mg content is 1.5%–3.5%; and / or,

[0020] The coating thickness in the galvanized sheet is 20μm to 40μm.

[0021] Optionally, the heating temperature is 1200℃~1300℃; and / or,

[0022] The rolling process parameters include: initial rolling temperature of 1050℃~1150℃ and final rolling temperature of 830℃~950℃.

[0023] Optionally, the specified chemical composition includes:

[0024] C, Mn, Si, P, S, Als, N, Ti, Nb, and Fe; wherein, by mass fraction,

[0025] The C content is 0.06%–0.2%, the Mn content is 1.0%–2.5%, the Si content is 0.5%–2.0%, the P content is ≤0.03%, the S content is ≤0.02%, the Al content is 0.02%–0.07%, the N content is ≤0.003%, the Ti content is 0.07%–0.15%, and the Nb content is 0.01%–0.05%.

[0026] Secondly, this application provides a pre-coated steel plate prepared by the method described in the first aspect, the pre-coated steel plate comprising a steel substrate, a metal plating layer and a coating layer; wherein the metal plating layer is attached to at least a portion of the surface of the steel substrate, and the coating layer is adjacent to the metal plating layer.

[0027] Optionally, the mechanical properties of the pre-coated steel plate meet the following requirements: yield strength ≥700MPa, tensile strength ≥800MPa, and elongation after fracture ≥20%.

[0028] The technical solutions provided in this application have the following advantages compared with the prior art:

[0029] The method for preparing the pre-coated steel plate provided in this application includes: heating and rolling a billet with a set chemical composition to obtain a hot-rolled plate; first coiling the hot-rolled plate and controlling the temperature of the first coiling to precipitate some TiC particles in the microstructure of the hot-rolled plate, followed by pickling to obtain a pickled coil; continuously hot-dip galvanizing the pickled coil to obtain a pre-coated steel plate; the continuous hot-dip galvanizing of the pickled coil to obtain the pre-coated steel plate includes: annealing the pickled coil and controlling the annealing temperature and time to continuously precipitate TiC particles in the microstructure of the pickled coil, followed by hot-dip galvanizing, and applying a coating in the post-treatment section of the hot-dip galvanizing to obtain the pre-coated steel plate. Heating and rolling a billet with a set chemical composition can alter its microstructure. Hot-rolled plates are coiled, and the coiling temperature is controlled to ensure that precipitated particles remain fine and dispersed, preventing complete precipitation and the growth of the second phase. Sufficient precipitation of TiC particles gives the hot-rolled plate both high strength and high plasticity. Pickling provides a good surface condition for the coiled hot-rolled plate, allowing for annealing. Controlling the annealing temperature and time further promotes TiC particle precipitation and prevents excessive growth of the rolled precipitates, further improving the steel plate's plasticity and balancing its high strength and high plasticity. Hot-dip galvanizing and direct coating in the post-galvanizing stage reduce cold rolling and color coating processes, significantly shortening the process. This pre-coated steel plate exhibits good corrosion resistance while maintaining both high strength and high plasticity. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic flowchart illustrating a method for preparing a pre-coated steel plate according to some embodiments of this application;

[0033] Figure 2 This is a schematic diagram of the structure of a pre-coated steel plate provided according to some embodiments of this application;

[0034] Figure 3 The image shows a microscopic image of precipitated particles in a pre-coated steel plate according to Embodiment 1 of this application.

[0035] Figure 4 Images of a pre-coated steel plate after 300 hours of neutral salt spray testing according to Embodiment 1 of this application. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0038] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Here, A and B can be singular or plural.

[0039] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0040] Firstly, this application provides a method for preparing a pre-coated steel plate. Figure 1 For a flowchart illustrating a method for preparing a pre-coated steel plate according to some embodiments of this application, please refer to [link / reference]. Figure 1 The method includes:

[0041] S1. Heating and rolling a billet with a set chemical composition to obtain a hot-rolled plate;

[0042] In some embodiments, the specified chemical composition includes:

[0043] C, Mn, Si, P, S, Als, N, Ti, Nb, and Fe; wherein, by mass fraction,

[0044] The C content is 0.06%–0.2%, the Mn content is 1.0%–2.5%, the Si content is 0.5%–2.0%, the P content is ≤0.03%, the S content is ≤0.02%, the Al content is 0.02%–0.07%, the N content is ≤0.003%, the Ti content is 0.07%–0.15%, and the Nb content is 0.01%–0.05%.

[0045] In the embodiments of this application, carbon (C) is fundamental to improving the strength of steel. It can directly strengthen the matrix through solid solution strengthening, or it can form TiC and NbC precipitates with microalloying elements such as Nb and Ti in the steel to improve strength. However, as the carbon content increases, plasticity and weldability decrease. For example, the C content can be 0.06%, 0.09%, 0.08%, 0.1%, 0.15%, 0.2%, etc.

[0046] Manganese (Mn) not only reacts with sulfur (S) to form manganese sulfide, eliminating the brittleness of S, but the addition of Mn can also refine the grain size, improving the strength and toughness of the steel. However, Mn is easily oxidized, affecting the surface quality of the coating. Therefore, the Mn content should be controlled to eliminate the brittleness of S and improve the strength and toughness of the steel without affecting the surface quality of the coating. For example, the Mn content can be 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.5%, etc.

[0047] Silicon (Si) is a common steel strengthening element; an appropriate Si content can improve the strength of steel. However, Si easily forms oxides on the surface of steel plates, thus affecting the surface quality of the coating. For example, the Si content mentioned above can be 0.5%, 1.0%, 1.5%, 2.0%, etc.

[0048] Phosphorus (P) is mainly an impurity element that affects the plasticity of steel. For example, the P content mentioned above can be 0.03%, 0.02%, 0.015%, etc.

[0049] Sulfur (S) is an impurity element in steel, affecting its plasticity. Excessive S can also react with Ti and C to form coarse TiS or Ti4S4C2, affecting the steel's strength. For example, the S content could be 0.02%, 0.015%, or 0.01%.

[0050] Aluminum (Al) is a strong deoxidizer and can inhibit the formation of other oxides. For example, the content of Al can be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, etc.

[0051] Nitrogen (N) exists as a residual element in steel, which affects the steel's plasticity. The lower the content, the better. Moreover, N consumes Ti content, thereby reducing the amount of Ti that combines with C and reducing the amount of TiC formed, thus affecting strength. For example, the N content mentioned above can be 0.003%, 0.002%, 0.0015%, etc.

[0052] Titanium (Ti) can combine with carbon (C) in steel to form fine, dispersed TiC precipitates, resulting in a significant precipitation strengthening effect and thus improving the strength of the steel. For example, the Ti content can be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, etc.

[0053] Niobium (Nb) can refine grains and is another commonly used effective element for improving strength. A certain Nb content is also beneficial for improving welding performance. For example, the Nb content can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, etc.

[0054] In some embodiments, the heating temperature is 1200°C to 1300°C; and / or,

[0055] The rolling process parameters include: initial rolling temperature of 1050℃~1150℃ and final rolling temperature of 830℃~950℃.

[0056] In this embodiment, a specific heating temperature is used to ensure full austenitization of the steel billet and complete dissolution of coarse precipitates within the billet, allowing them to reprecipitate during subsequent rolling and cooling processes, thereby increasing the steel's strength. Simultaneously, this heating temperature prevents overheating and burning of the billet, inhibiting excessive grain growth. Limiting the initial and final rolling temperatures refines the grain structure of the heated billet. For example, the heating temperature can be 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, 1260℃, 1270℃, 1280℃, 1290℃, 1300℃, etc.; the initial rolling temperature can be 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, etc.; and the final rolling temperature can be 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, etc.

[0057] S2. The hot-rolled plate is first wound up, and the temperature of the first winding is controlled so that some TiC particles are precipitated in the microstructure of the hot-rolled plate. Then, it is pickled to obtain a pickled coil.

[0058] In some embodiments, the temperature of the first winding is 530°C to 630°C.

[0059] In this embodiment, a first coiling temperature is defined to control the size of the TiC precipitates. Higher coiling temperatures result in larger TiC particles and reduced precipitation strengthening effect. However, low-temperature coiling also inhibits TiC precipitation, both of which are detrimental to strength improvement. The unique feature of controlling the first coiling temperature is that by controlling the coiling temperature within a specific region below the "nose tip" temperature, only a portion of the Ti element is precipitated. Then, in the subsequent annealing stage, by adjusting the annealing temperature and strip running speed, the remaining Ti is allowed to fully disperse and precipitate, while avoiding excessive ripening and growth of the rolled precipitates. The resulting Ti precipitate particle size is smaller than that obtained through conventional techniques. Furthermore, this appropriate first coiling temperature ensures sufficient TiC precipitation in the microstructure to guarantee high steel strength while balancing high plasticity. For example, the first coiling temperature can be 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, etc.

[0060] S3. The pickled coil is continuously hot-dip galvanized to obtain a pre-coated steel sheet;

[0061] The process of continuously hot-dip galvanizing the pickled coil to obtain a pre-coated steel sheet includes:

[0062] The pickled coil is annealed, and the temperature and time of the annealing are controlled to allow TiC particles to continuously precipitate in the microstructure of the pickled coil. Then, hot-dip galvanizing is performed, and a coating is applied in the post-treatment section of the hot-dip galvanizing to obtain a pre-coated steel sheet.

[0063] In some embodiments, the annealing temperature is 560℃~780℃, the annealing time is 10s~60s, and the annealing temperature and the annealing time satisfy the following relationship:

[0064] 185≤[t]+0.23[T]≤190

[0065] In the formula, [t] represents the annealing time, and [T] represents the annealing temperature.

[0066] In this embodiment, the annealing process is key to achieving high strength and high plasticity. On one hand, annealing makes the hot-rolled microstructure more homogenized, eliminates some dislocations, and further increases the plasticity of the steel plate. This annealing process does not cause recrystallization, thus preventing a decrease in strength. This embodiment strictly controls the annealing temperature and time, ensuring that the annealing temperature T / ℃ is inversely proportional to the annealing time t / s, satisfying 185≤[t]-0.23[T]≤190. Higher annealing temperatures require shorter annealing times, and vice versa. This allows TiC particles to continuously precipitate during the low-temperature annealing process, while the particles already precipitated during rolling only undergo slight ripening. The resulting TiC particles have an average diameter of approximately 3 nm, which is about 20% smaller than the precipitated particles in microalloyed steel produced by traditional processes, thus achieving higher strength. However, excessively high annealing temperatures or long annealing times can lead to over-curing of the particles and reduced strength. Conversely, insufficient particle precipitation can also reduce strength if the annealing temperature or time is too low. For example, the annealing temperatures can be 560℃, 580℃, 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, 720℃, 740℃, 760℃, 780℃, etc., and the annealing times can be 10s, 20s, 30s, 40s, 50s, 60s, etc., and the value of [t]+0.23[T] can be 185, 186, 187, 188, 189, 190, etc. The above-mentioned annealing is continuous annealing. Specifically, the process parameters for continuous annealing include: heating zone temperature of 560–780℃, soaking zone temperature of 560–780℃, holding time of 10–60 seconds, and rapid cooling zone outlet temperature of 450℃–470℃. The annealing time corresponds to the holding time, and the annealing temperature corresponds to the soaking zone temperature. Maintaining a suitable soaking temperature during the annealing process can achieve synergistic control of plasticity and strength. Although plasticity increases with increasing annealing temperature, it must be considered in conjunction with strength. Within the above range, a better combined value of strength and plasticity can be achieved.

[0067] In some embodiments, the chemical composition of the plating bath in the hot-dip galvanizing process includes: Al, Mg, and Zn; wherein, by mass fraction,

[0068] The Al content is 5%–12%, and the Mg content is 1.5%–3.5%; and / or,

[0069] The coating thickness in the galvanized sheet is 20μm to 40μm.

[0070] In this embodiment, during the hot-dip galvanizing process, the plating solution is a zinc-aluminum-magnesium alloy. This coating composition exhibits a microstructure of "aluminum-rich phase + zinc-aluminum-magnesium ternary eutectic structure," and during corrosion, it displays corrosion characteristics of "few anodes, many cathodes, and in-phase galvanic couples," resulting in a high proportion of eutectic structure. The eutectic phase and the Al-rich phase form an in-phase corrosion galvanic couple, preventing local elemental deficiencies due to difficulties in lateral ion migration during longitudinal corrosion propagation, thus greatly improving corrosion resistance. For example, the Al content can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc., the Mg content can be 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, etc., and the coating thickness in the galvanized sheet can be 20μm, 25μm, 30μm, 35μm, 40μm, etc.

[0071] In some embodiments, the coating process parameters include: the ratio of coating speed to strip running speed (coating roller / strip speed ratio) is ≥140%, and the coating thickness is 1.5μm to 4μm.

[0072] In some embodiments, the method further includes:

[0073] The pre-coated steel sheet is dried and cooled, and then a second coil is made to obtain the pre-coated steel sheet finished product; wherein, the drying temperature is 110℃~140℃, and the second coiling temperature is ≤40℃.

[0074] In this embodiment, during the coating process, a dark-colored, organic, chromium-free, fingerprint-resistant coating is used on the surface. The color can be black, green, brown, red, or gray. A reverse coating process is employed to evenly coat the coating onto the steel strip. The ratio of coating speed to strip running speed is limited to ensure coating thickness. Hot air drying is then used, followed by cooling and winding. The winding temperature is limited to ensure the coating's corrosion resistance. Besides enhancing the color appearance, the surface coating also protects the zinc layer from corrosion. For example, the ratio of the coating speed to the strip running speed can be 140%, 142%, 144%, 146%, 148%, etc.; the coating thickness can be 1.5μm, 2.0μm, 2.2μm, 2.4μm, 2.6μm, 3.0μm, 3.2μm, 3.4μm, 3.6μm, 3.8μm, 4.0μm, etc.; the drying temperature can be 110℃, 120℃, 130℃, 140℃, etc.; the second winding temperature can be 40℃, 39℃, 38℃, 37℃, 36℃, 35℃, etc. Conventional post-processing can only form a transparent passivation film of about 1 micrometer, while the embodiments of this application realize the production of coated steel sheets with colored coatings in hot-dip galvanizing units.

[0075] The entire process of the aforementioned pre-coated steel sheet includes: the billet is heated, hot-rolled, laminar cooled, and coiled sequentially in a hot rolling mill to obtain a hot-rolled coil; the hot-rolled coil is uncoiled, pickled, and coiled in a continuous pickling mill to obtain a pickled coil; the pickled coil is cleaned, annealed, hot-dip galvanized, finished, coated, and coiled in a continuous hot-dip galvanizing mill to obtain a pre-coated steel coil; and the pre-coated steel coil is sheared to obtain the pre-coated steel sheet finished product.

[0076] Secondly, this application provides a pre-coated steel sheet prepared by the method described in the first aspect. Figure 2 This is a structural schematic diagram of a pre-coated steel plate provided according to some embodiments of this application; please refer to... Figure 2 The pre-coated steel plate includes a steel substrate, a metal plating layer, and a coating layer; wherein the metal plating layer is attached to at least a portion of the surface of the steel substrate, and the coating layer is adjacent to the metal plating layer.

[0077] In some embodiments, the mechanical properties of the pre-coated steel plate meet the following requirements: yield strength ≥ 700 MPa, tensile strength ≥ 800 MPa, and elongation after fracture ≥ 20%.

[0078] In this embodiment, the pre-coated steel plate comprises a steel substrate, a metal plating layer, and a surface coating. The pre-coated steel plate has a yield strength ≥700MPa, a tensile strength ≥800MPa, and an elongation after fracture ≥20%. The metal plating layer is a zinc-aluminum-magnesium plating layer, which ensures the steel substrate is not corroded; a neutral salt spray test shows that it takes more than 4000 hours to produce red rust. The surface coating is a chromium-free, fingerprint-resistant coating, which adds color while protecting the zinc layer from corrosion, preventing white rust formation for more than 300 hours. This pre-coated steel plate features high strength, high plasticity, high corrosion resistance, and a variety of colors.

[0079] The pre-coated steel plate is realized based on the above-described method for preparing pre-coated steel plates. The specific steps of the method for preparing pre-coated steel plates can be referred to the above embodiments. Since the pre-coated steel plate adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0080] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0081] This application provides a pre-coated steel sheet. Please refer to Table 1 for the chemical composition (wt%) of the steel substrate of the pre-coated steel sheet, Table 2 for the preparation process parameters of heating, rolling and annealing of the pre-coated steel sheet, and Table 3 for the process parameters of hot-dip galvanizing and coating of the pre-coated steel sheet.

[0082] Table 1. Chemical composition (wt%) of the steel substrate of pre-coated steel sheets

[0083]

[0084] Table 2. Preparation process parameters for heating, rolling, and annealing of pre-coated steel sheets.

[0085]

[0086] Table 3. Hot-dip galvanizing process parameters and coating process parameters for pre-coated steel sheets.

[0087]

[0088] Table 4 Mechanical properties and neutral salt spray test results of pre-coated steel plates

[0089] Serial Number Yield strength / MPa Tensile strength / MPa Elongation / % Time of white rust appearance / h Time of red rust appearance / h Example 1 725 879 21.9 442 5450 Example 2 758 888 22.3 481 5840 Example 3 805 896 20.5 480 6100 Comparative Example 1 652 746 22.5 350 2406 Comparative Example 2 694 773 23.5 220 3400 Comparative Example 3 690 789 13.0 72 3240 Comparative Example 4 603 738 23.5 430 5300

[0090] In summary, the above-mentioned method for preparing pre-coated steel plates achieves strict control over chemical elements, high strength through the combined effects of solid solution strengthening, precipitation strengthening, and grain refinement strengthening, resistance to red rust by controlling the alloy composition of the metal coating, and appearance protection and various aesthetic effects by controlling the color and thickness of the surface coating.

[0091] By moderately lowering the coiling temperature, the precipitated particles are kept fine and dispersed, preventing complete precipitation and the growth of the second phase. Further precipitation occurs during low-temperature annealing, further increasing strength and avoiding the strength reduction caused by aging. This also results in a more uniform microstructure and improved plasticity. Please refer to the method for maintaining a suitable homogenization temperature during the annealing process to achieve synergistic control of plasticity and strength. A reasonable coating process ensures the thickness of the surface coating, improving resistance to white rust.

[0092] It reduces the cold rolling and color coating processes, greatly shortening the process, and has good corrosion resistance. It achieves no red rust after 4000 hours of neutral salt spray testing and no white rust due to zinc layer corrosion after 300 hours of neutral salt spray testing.

[0093] For example, Figure 3 The image shows a microscopic image of precipitated particles in a pre-coated steel plate according to Embodiment 1 of this application; please refer to [link / reference]. Figure 3 This indicates the formation of fine, dispersed TiC precipitates within the microstructure. Figure 4 Images of a pre-coated steel plate after 300 hours of neutral salt spray testing according to Embodiment 1 of this application; please refer to... Figure 4 The result indicates that no white rust occurred after 300 hours, demonstrating that the pre-coated plate has good corrosion resistance.

[0094] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a pre-coated steel plate, characterized in that, The method includes: A cast billet with a set chemical composition is heated and rolled to obtain a hot-rolled plate; The hot-rolled plate is first wound up, and the temperature of the first winding is controlled so that some TiC particles are precipitated in the microstructure of the hot-rolled plate. Then, it is pickled to obtain pickled coil. The pickled coil is continuously hot-dip galvanized to obtain a pre-coated steel sheet; The process of continuously hot-dip galvanizing the pickled coil to obtain a pre-coated steel sheet includes: The pickled coil is annealed, and the temperature and time of the annealing are controlled so that TiC particles are continuously precipitated in the microstructure of the pickled coil. Then, hot-dip galvanizing is performed, and a coating is applied in the post-treatment section of the hot-dip galvanizing to obtain a pre-coated steel plate. The temperature of the first roll is 530℃~630℃; The annealing temperature is 560℃~780℃, the annealing time is 10s~60s, and the annealing temperature and annealing time satisfy the following relationship: 185≤[t]+0.23[T]≤190; In the formula, [t] represents the annealing time, and [T] represents the annealing temperature; The specified chemical composition includes: C, Mn, Si, P, S, Als, N, Ti, Nb, and Fe; wherein, by mass fraction, the content of C is 0.06%~0.2%, the content of Mn is 1.0%~2.5%, the content of Si is 0.5%~2.0%, the content of P is ≤0.03%, the content of S is ≤0.02%, the content of Als is 0.02%~0.07%, the content of N is ≤0.003%, the content of Ti is 0.07%~0.15%, and the content of Nb is 0.01%~0.05%.

2. The method according to claim 1, characterized in that, The coating process parameters include: the ratio of coating speed to strip running speed is ≥140%, and the coating thickness is 1.5μm~4μm.

3. The method according to claim 1, characterized in that, The method further includes: The pre-coated steel sheet is dried and cooled, and then a second coil is formed to obtain the finished pre-coated steel sheet; In the process, the drying temperature is 110℃~140℃, and the second winding temperature is ≤40℃.

4. The method according to claim 1, characterized in that, The chemical composition of the plating solution in the hot-dip galvanizing process includes: Al, Mg, and Zn; wherein, by mass fraction, The Al content is 5%~12%, and the Mg content is 1.5%~3.5%; and / or, The coating thickness in hot-dip galvanized steel sheets is 20μm~40μm.

5. The method according to claim 1, characterized in that, The heating temperature is 1200℃~1300℃; and / or, The rolling process parameters include: initial rolling temperature of 1050℃~1150℃ and final rolling temperature of 830℃~950℃.

6. A pre-coated steel plate prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The pre-coated steel plate includes a steel substrate, a metal coating, and a coating layer; wherein the metal coating is attached to at least a portion of the surface of the steel substrate, and the coating layer is adjacent to the metal coating.

7. The pre-coated steel plate according to claim 6, characterized in that, The mechanical properties of the pre-coated steel plate meet the following requirements: yield strength ≥ 700 MPa, tensile strength ≥ 800 MPa, and elongation after fracture ≥ 20%.

Images