A zinc-aluminum-magnesium alloy plated high-strength steel and a method for manufacturing the same

Abstract

This invention provides a zinc-aluminum-magnesium alloy coated high-strength steel and its preparation method, belonging to the field of steel manufacturing technology. The zinc-aluminum-magnesium alloy coated high-strength steel includes a steel plate substrate and a zinc-aluminum-magnesium alloy coating on the surface of the steel plate substrate. The chemical composition of the steel plate substrate, by mass fraction, is: C: 0.03%–0.25%, Si: ≤0.18%, Mn: 0.5%–1.2%, P: ≤0.025%, S: ≤0.006%, Alt: 0.02%–0.06%, N: 0.002%–0.004%, Nb: 0.010%–0.025%, Ti: 0.015%–0.09%, with the remainder being Fe and impurities. This application achieves the preparation of zinc-aluminum-magnesium alloy coated high-strength steel of various specifications through a single substrate, a unified process flow design, and differentiated control of process parameters. This improves the performance stability of high-strength steel products of different thicknesses, significantly shortens production steps, and reduces production costs.

Description

Technical Field

[0001] This application relates to the field of steel manufacturing technology, and in particular to a zinc-aluminum-magnesium alloy coated high-strength steel and its preparation method. Background Technology

[0002] Currently, 450MPa high-strength steel with a thin 0.8–2.0mm hot-dip galvanized aluminum-magnesium alloy coating is mainly produced using a cold-rolling-hot-dip galvanizing process. Steel strips with a thickness of 2.0–6.0mm are supplied with base material from traditional hot continuous rolling lines, and the production of hot-dip galvanized high-strength steel is completed through pickling and continuous hot-dip galvanizing processes. Therefore, for producing high-strength steel with the same strength grade of zinc-aluminum-magnesium alloy coating of different thicknesses, existing technologies require matching steel plate base materials with different chemical compositions, resulting in complex production processes and high energy consumption and production costs. Summary of the Invention

[0003] This application provides a zinc-aluminum-magnesium alloy coated high-strength steel and its preparation method, in order to solve the technical problem that the existing technology requires matching steel plate substrates with different chemical compositions to prepare zinc-aluminum-magnesium alloy coated high-strength steel of the same strength level with different thicknesses, which leads to high production costs.

[0004] In a first aspect, this application provides a zinc-aluminum-magnesium alloy coated high-strength steel, which includes a steel plate substrate and a zinc-aluminum-magnesium alloy coating on the surface of the steel plate substrate.

[0005] The chemical composition of the steel plate substrate, by mass fraction, is as follows:

[0006] C: 0.03%–0.25%, Si: ≤0.18%, Mn: 0.5%–1.2%, P: ≤0.025%, S: ≤0.006%, Alt: 0.02%–0.06%, N: 0.002%–0.004%, Nb: 0.010%–0.025%, Ti: 0.015%–0.09%, with the remainder being Fe and impurities from the preparation of the steel plate substrate;

[0007] The thickness of the zinc-aluminum-magnesium alloy coated high-strength steel includes any one of the following specifications: 0.8 to 6.0 mm.

[0008] Furthermore, the C element content is 0.04% to 0.19% by mass fraction.

[0009] Furthermore, the Mn element content is 0.5% to 0.9% by mass fraction.

[0010] Furthermore, the metallographic structure of the steel plate substrate comprises 65-95% ferrite and 5-35% pearlite by volume fraction.

[0011] Further, by mass fraction, the composition of the zinc-aluminum-magnesium alloy coating is: Al: 1.0%–12.0%, Mg:

[0012] 1.0% to 3.0%, with the remainder being Zn and impurities from the preparation of the zinc-aluminum-magnesium alloy coating.

[0013] Furthermore, the high-strength steel with zinc-aluminum-magnesium alloy coating has a yield strength ≥450MPa, a tensile strength ≥510MPa, and an elongation after fracture (A80) ≥14%.

[0014] Secondly, this application provides a first-party

[0015] The method for preparing the zinc-aluminum-magnesium alloy coated high-strength steel described above includes:

[0016] A hot-rolled coil containing the same chemical composition as the steel plate substrate is obtained by using a multi-mode thin slab continuous casting and rolling production line process.

[0017] The hot-rolled coil is subjected to an acid plating production line process to obtain the zinc-aluminum-magnesium alloy coated high-strength steel.

[0018] The rolling modes used in the multi-mode thin slab continuous casting and rolling production line process include at least one of the following: single-slab rolling mode, semi-automatic headless rolling mode, and fully automatic headless rolling mode.

[0019] Furthermore, the process of using a multi-mode thin slab continuous casting and rolling production line to obtain hot-rolled coils containing the same chemical composition as the steel plate substrate specifically includes:

[0020] Molten steel containing the same chemical composition as the steel plate substrate is obtained;

[0021] The molten steel is smelted and continuously cast to obtain a continuously cast billet;

[0022] The continuously cast billet is heated to obtain a heated billet;

[0023] The heated billet is subjected to rough rolling, electromagnetic induction heating, finish rolling, laminar flow cooling, coiling and cooling to obtain a hot-rolled coil containing the same chemical composition as the steel plate substrate.

[0024] The continuously cast billet is heated in a roller-bottom tunnel soaking furnace, which includes a fixed section and a moving section, and is used to realize different rolling modes in the multi-mode thin slab continuous casting and rolling production line process.

[0025] Furthermore, different rolling modes are adopted according to the predetermined thickness d of the zinc-aluminum-magnesium alloy coated high-strength steel, specifically:

[0026] For diameters 0.8mm ≤ d < 2.5mm, a fully automatic headless rolling process is adopted.

[0027] For diameters of 2.5mm ≤ d < 4.0mm, a semi-automatic or fully automatic headless rolling process shall be adopted.

[0028] For diameters of 4.0mm ≤ d ≤ 6.0mm, a single-slab rolling mode is adopted.

[0029] Furthermore, in the hot-rolled coil acid plating production line process, different process parameters are adopted according to the predetermined thickness d of the zinc-aluminum-magnesium alloy coating on the high-strength steel, specifically:

[0030] For a diameter of 0.8mm ≤ d < 2.5mm, the process parameters for the hot-rolled coil acid plating production line include: target heat treatment temperature of 650~760℃ and rapid cooling outlet temperature of 430℃~470℃.

[0031] For a diameter of 2.5mm ≤ d < 4.0mm, the process parameters for the hot-rolled coil acid plating production line include: target heat homogenization temperature of 640~730℃ and rapid cooling outlet temperature of 420℃~470℃.

[0032] For hot-rolled coils with a diameter of 4.0mm≤d≤6.0mm, the process parameters for the acid plating production line include: target uniform heating temperature of 630~740℃ and rapid cooling outlet temperature of 410℃~470℃.

[0033] The technical solutions provided in this application have the following advantages compared with the prior art:

[0034] This application provides a zinc-aluminum-magnesium alloy coated high-strength steel and its preparation method. High-strength steel with zinc-aluminum-magnesium alloy coating of different specifications of 0.8-6.0 mm is prepared using a single-component substrate. Through the rational design of each component, the design of the same process flow, and the differentiated control of process parameters, the performance stability of high-strength steel products of different thicknesses is ensured, which greatly shortens the existing production process and reduces the production cost and subsequent recycling cost. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention 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.

[0037] Figure 1 A schematic flowchart illustrating a method for preparing a zinc-aluminum-magnesium alloy coated high-strength steel according to an embodiment of this application;

[0038] Figure 2This is a cross-sectional metallographic microstructure of a 1.0 mm zinc-aluminum-magnesium alloy coated high-strength steel obtained according to an embodiment of the present invention.

[0039] Figure 3 This is a cross-sectional metallographic microstructure of a 3.5mm zinc-aluminum-magnesium alloy coated high-strength steel obtained according to an embodiment of the present invention.

[0040] Figure 4 This is a cross-sectional metallographic microstructure of a 6.0 mm thick high-strength steel with a zinc-aluminum-magnesium alloy coating obtained according to an embodiment of the present invention.

[0041] Figure 5 This is a characterization diagram of the coating surface quality of a zinc-aluminum-magnesium alloy coated high-strength steel with a specification of 1.0 mm obtained in an embodiment of the present invention.

[0042] Figure 6 This is a characterization diagram of the coating surface quality of the zinc-aluminum-magnesium alloy coated high-strength steel with a specification of 3.5mm obtained in the embodiments of the present invention.

[0043] Figure 7 This is a characterization diagram of the coating surface quality of a 6.0mm zinc-aluminum-magnesium alloy coated high-strength steel obtained according to an embodiment of the present invention. Detailed Implementation

[0044] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0045] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0046] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0047] Currently, 0.8–2.0 mm thin-gauge hot-dip galvanized aluminum-magnesium coated 450 MPa high-strength steel is mainly produced using a cold-rolling-hot-dip galvanizing process, while 2.0–6.0 mm thick steel strips are supplied with base material from traditional hot continuous rolling lines, and the hot-dip galvanized high-strength steel is produced through pickling and continuous hot-dip galvanizing processes. If the thin and thick steel strips are matched with the same composition, the performance consistency of the finished products of different specifications is difficult to guarantee due to the different process routes, affecting the processing and use by downstream customers. If different specifications of steel plates are matched with different compositions, it increases the complexity of steel plate production, manufacturing, and recycling. In addition, the production process of the conventional cold-rolling-hot-dip galvanizing process for thin-gauge steel strips and the traditional hot continuous rolling process for supplying thick-gauge hot-dip galvanized substrates are both too long, resulting in high energy consumption and production costs.

[0048] The technical solution provided by the embodiments of the present invention is to solve the above-mentioned technical problems, and the general idea is as follows:

[0049] In a first aspect, this application provides a zinc-aluminum-magnesium alloy coated high-strength steel, which includes a steel plate substrate and a zinc-aluminum-magnesium alloy coating on the surface of the steel plate substrate.

[0050] The chemical composition of the steel plate substrate, by mass fraction, is as follows:

[0051] C: 0.03%–0.25%, Si: ≤0.18%, Mn: 0.5%–1.2%, P: ≤0.025%, S: ≤0.006%, Alt: 0.02%–0.06%, N: 0.002%–0.004%, Nb: 0.010%–0.025%, Ti: 0.015%–0.09%, with the remainder being Fe and impurities from the preparation of the steel plate substrate;

[0052] The thickness of the zinc-aluminum-magnesium alloy coated high-strength steel includes any one of the following specifications: 0.8 to 6.0 mm.

[0053] This application provides a zinc-aluminum-magnesium alloy coated high-strength steel and its preparation method. High-strength steel with zinc-aluminum-magnesium alloy coating of different specifications of 0.8-6.0 mm is prepared using a single-component substrate. Through the rational design of each component, the design of the same process flow, and the differentiated control of process parameters, the performance stability of high-strength steel products of different thicknesses is ensured, which greatly shortens the existing production process and reduces the production cost and subsequent recycling cost.

[0054] The roles and limitations of the main chemical elements in this application are as follows:

[0055] C: C is a commonly used strengthening element in steel. It is an interstitial solid solution atom that can significantly improve the strength of strip steel. To obtain a tensile strength of not less than 450 MPa, the C content must not be less than 0.03%. At the same time, to balance weldability and formability, the upper limit of the C content is no more than 0.25%. Therefore, the C content in this invention is controlled at 0.03% to 0.25%.

[0056] Si: Si is a strong solid solution strengthening element that can improve the strength of steel plates. However, Si is a key element that affects surface quality. Excessive Si content will lead to deterioration of the surface quality of hot-rolled coils, which in turn will affect the surface quality of the finished coating to a certain extent. In order to ensure good coating surface quality, the Si content in this invention is controlled at ≤0.18%.

[0057] Mn: Mn has a strong solid solution strengthening effect, and its content should not be too low. If it is too low, the mechanical properties will fluctuate greatly. The Mn content should not be lower than 0.5%. However, when the Mn content exceeds 1.2%, it is easy to cause Mn element segregation, resulting in a decrease in toughness and weldability. Therefore, the Mn content in this invention is controlled at 0.5% to 1.2%.

[0058] P: P tends to segregate at grain boundaries, leading to "cold brittleness" and poor weldability. Therefore, the P content in this invention is controlled to be ≤0.025%.

[0059] S: S is a harmful impurity element that easily combines with Mn to form coarse MnS inclusions, which deteriorates the low-temperature toughness of the steel plate. Therefore, the S content in this invention is controlled to be ≤0.006%.

[0060] Al: Al, as a deoxidizer, is added to steel and has a good deoxidation effect. It can also reduce the tendency for "cold brittleness" and improve impact toughness. The Al content should not be lower than 0.02%. However, when the Al content exceeds 0.6%, the alloy cost is high and the weldability deteriorates. Therefore, in this invention, the Alt (total aluminum content in steel) content is controlled at 0.02% to 0.06%.

[0061] Nitrogen (N): Generally, it is required to control the nitrogen (N) content in steel. Lower N content results in higher smelting costs. Higher N content easily combines with Ti to form coarse TiN precipitates, affecting the strengthening effect of Ti. Therefore, in this invention, the N content is controlled at 0.002%–0.004%.

[0062] Nitrogen (Nb): During hot rolling, Nb inhibits recrystallization and refines the original austenite grains, thereby refining the ferrite formed after austenite phase transformation. Grain refinement is beneficial for improving the strength and plasticity of strip steel. However, excessively high Nb content increases the rolling difficulty of thin-gauge steel strips due to their high hot strength, reduces the production stability of continuous casting and rolling lines, and significantly increases alloy costs. Therefore, the Nb content in this invention is controlled at 0.010%–0.025%.

[0063] Ti: During the heating and rolling process of slabs, Ti can refine grains and regulate the uniformity of microstructure. Additionally, during coiling and annealing / galvanizing, Ti precipitates as TiC, increasing the strength of the ferrite matrix. As an inexpensive alloying element, Ti can be added at a relatively high content to replace some of Nb and Mn in this invention. To obtain ideal mechanical properties without significantly increasing costs, the Ti content in this invention is controlled at 0.015%–0.09%.

[0064] In one embodiment of the present invention, the C element content is 0.04% to 0.19% by mass fraction.

[0065] In one embodiment of the present invention, the Mn element content is 0.5% to 0.9% by mass fraction.

[0066] As one embodiment of the present invention, the metallographic structure of the steel plate substrate comprises 65-95% ferrite and 5-35% pearlite by volume fraction.

[0067] In this application, the metallographic structure of the steel plate substrate includes 65-95% ferrite and 5-35% pearlite, which is beneficial to ensuring good processing performance and excellent low-temperature toughness of the strip steel.

[0068] As one embodiment of the present invention, the composition of the zinc-aluminum-magnesium alloy coating, by mass fraction, is: Al: 1.0% to 12.0%, Mg: 1.0% to 3.0%, with the remainder being Zn and impurities from the preparation of the zinc-aluminum-magnesium alloy coating.

[0069] In this application, the aluminum-silicon coating exhibits excellent corrosion resistance, which is beneficial for extending the service life of high-strength steel with zinc-aluminum-magnesium alloy coating.

[0070] As one embodiment of the present invention, the high-strength steel with zinc-aluminum-magnesium alloy coating has a yield strength ≥450MPa, a tensile strength ≥510MPa, and an elongation after fracture (A80) ≥14%.

[0071] The high-strength steel with zinc-aluminum-magnesium alloy coating in various specifications from 0.8 to 6.0 mm provided in this application has excellent performance, meeting the requirements of photovoltaic power stations for high mechanical performance stability, high corrosion resistance, and low cost of 450MPa grade high-strength steel in various thicknesses.

[0072] Secondly, this application provides a method for preparing the zinc-aluminum-magnesium alloy coated high-strength steel described in the first aspect, such as... Figure 1 As shown, the preparation method includes:

[0073] A hot-rolled coil containing the same chemical composition as the steel plate substrate is obtained by using a multi-mode thin slab continuous casting and rolling production line process.

[0074] The hot-rolled coil is subjected to an acid plating production line process to obtain the zinc-aluminum-magnesium alloy coated high-strength steel.

[0075] The rolling modes used in the multi-mode thin slab continuous casting and rolling production line process include at least one of the following: single-slab rolling mode, semi-automatic headless rolling mode, and fully automatic headless rolling mode.

[0076] In traditional production methods, different production schemes are used for steel plates of the same strength grade but different specifications: hot rolling for thicker specifications and cold rolling for thinner specifications. To achieve the same performance for steel plates of different specifications, the different processes and compositions result in variations in the performance stability of the products. Compared to these traditional processes, this application provides a method for preparing multi-specification zinc-aluminum-magnesium alloy coated high-strength steel through a single composition, a unified process flow design, and differentiated control of process parameters. This method, based on a multi-mode thin slab continuous casting and rolling production line and an acid plating production line, offers advantages such as a short process, low energy consumption, and environmental friendliness, reducing production costs and improving the performance stability of high-strength steel with thicknesses ranging from 0.8 to 6.0 mm.

[0077] As one embodiment of the present invention, the process of obtaining a hot-rolled coil containing the same chemical composition as the steel plate substrate using a multi-mode thin slab continuous casting and rolling production line specifically includes:

[0078] Molten steel containing the same chemical composition as the steel plate substrate is obtained;

[0079] The molten steel is smelted and continuously cast to obtain a continuously cast billet;

[0080] The continuously cast billet is heated to obtain a heated billet;

[0081] The heated billet is subjected to rough rolling, electromagnetic induction heating, finish rolling, laminar flow cooling, coiling and cooling to obtain a hot-rolled coil containing the same chemical composition as the steel plate substrate.

[0082] The continuously cast billet is heated in a roller-bottom tunnel soaking furnace, which includes a fixed section and a moving section, and is used to realize different rolling modes in the multi-mode thin slab continuous casting and rolling production line process.

[0083] The difference between the multi-mode thin slab continuous casting and rolling production line process used in this application and the conventional thin slab continuous casting and rolling production line is that: the multi-mode thin slab continuous casting and rolling production line is equipped with a roller hearth tunnel soaking furnace between the continuous casting machine outlet and the roughing mill. The roller hearth tunnel soaking furnace is used to heat the continuously cast billet. The roller hearth tunnel soaking furnace includes a fixed section and a moving section, thus having the function of removing steel slabs from the production line. It can realize multi-mode operation of single billet rolling mode, semi-automatic headless rolling mode or fully automatic headless rolling mode, thereby realizing the preparation of steel coils of different thicknesses.

[0084] The present invention uses a roller bottom tunnel heating furnace for the heating treatment, which has the following advantages: (1) It improves the temperature of the steel plate edges and corners, improves the uniformity of the temperature of the steel plate width, is conducive to the control of the steel plate shape, improves the uniformity of the steel plate performance, and eliminates edge defects of the steel plate; (2) It provides a buffer time for changing rollers during the heating process; (3) It can realize multi-mode rolling and provide galvanized substrates of various specifications from 0.8 to 6.0 mm.

[0085] In some specific embodiments, the continuous casting speed is 4.0–6.2 m / min; the thickness of the continuously cast billet is 110–123 mm; the length of the fixed section is 50–55 meters; the length of the moving section is 25–30 meters; the heating temperature of the continuously cast billet is 1150–1180°C; the roughing rolling process involves two passes, with an inlet temperature of 1150–1180°C and an outlet temperature of 950–970°C; the roughing billet is subjected to electromagnetic induction heating, with an outlet temperature of 1100–1220°C; two descaling processes are also performed before roughing and finishing rolling, mainly to remove iron oxide scale from the strip surface to ensure a substrate with good surface quality for hot-dip galvanizing; the finishing rolling process involves five passes with a total reduction rate of 75%–80%. The finishing rolling process parameters are related to the thickness of the hot-rolled coil and the rolling mode. After finishing rolling, the steel is cooled to the target temperature by laminar flow cooling before coiling. The working parameters for laminar flow cooling include: to improve performance consistency, laminar flow cooling adopts concentrated cooling in the front section, with the front section completing 70-90% of the cooling temperature drop; the working parameters for coiling include: determined according to the thickness d of the steel plate.

[0086] As one embodiment of the present invention, different rolling modes are adopted according to the predetermined thickness d of the zinc-aluminum-magnesium alloy coated high-strength steel, specifically:

[0087] For diameters 0.8mm ≤ d < 2.5mm, a fully automatic headless rolling process is adopted.

[0088] For diameters of 2.5mm ≤ d < 4.0mm, a semi-automatic or fully automatic headless rolling process shall be adopted.

[0089] For diameters of 4.0mm ≤ d ≤ 6.0mm, a single-slab rolling mode is adopted.

[0090] In this application, different rolling modes are adopted according to the predetermined thickness d of the zinc-aluminum-magnesium alloy coated high-strength steel. In some specific embodiments, when the thickness d is 0.8–2.5 mm, a fully automatic headless rolling mode is adopted, with an electromagnetic induction heating temperature of 1160–1220°C, a finishing rolling entry temperature of 1000–1050°C, a finishing rolling temperature of 820–850°C, and a coiling temperature of 590–620°C; when the thickness d is 2.5–4.0 mm, a semi-automatic headless rolling mode or the fully automatic headless rolling mode is adopted, with an electromagnetic induction heating temperature of 1140–1190°C, and a finishing rolling entry temperature of 980–1190°C. The rolling temperature is 030℃, the final rolling temperature is 820~850℃, and the coiling temperature is 580~610℃; when the thickness d is 4.0~6.0mm, a single-slab rolling mode is adopted, the electromagnetic induction heating temperature is 1100~1150℃, the entry temperature of the finishing roll is 960~1010℃, the final rolling temperature is 820~850℃, and the coiling temperature is 570~600℃; each temperature parameter should be as low as possible while ensuring the mechanical properties of the product, to reduce oxidation loss and avoid the incomplete removal of iron oxide scale due to temperature, which would affect the surface quality of the galvanized sheet.

[0091] As one embodiment of the present invention, in the hot-rolled coil acid plating production line process, different process parameters are adopted according to the predetermined thickness d of the zinc-aluminum-magnesium alloy coating on the high-strength steel, specifically:

[0092] For a diameter of 0.8mm ≤ d < 2.5mm, the process parameters for the hot-rolled coil acid plating production line include: target heat treatment temperature of 650~760℃ and rapid cooling outlet temperature of 430℃~470℃.

[0093] For a diameter of 2.5mm ≤ d < 4.0mm, the process parameters for the hot-rolled coil acid plating production line include: target heat homogenization temperature of 640~730℃ and rapid cooling outlet temperature of 420℃~470℃.

[0094] For hot-rolled coils with a diameter of 4.0mm≤d≤6.0mm, the process parameters for the acid plating production line include: target uniform heating temperature of 630~740℃ and rapid cooling outlet temperature of 410℃~470℃.

[0095] In this application, the process of obtaining the zinc-aluminum-magnesium alloy coated high-strength steel by using an acid plating production line for the hot-rolled coil specifically includes: the hot-rolled coil undergoes tension leveling to break scale and pickling to remove iron oxide scale, followed by online leveling and tension leveling to obtain a pickled strip with good shape and uniform surface structure; the pickled strip is then hot-dip galvanized, finished, and tension leveled to obtain zinc-aluminum-magnesium alloy coated high-strength steel with good surface quality. In some specific embodiments, in the pickling process, the hot-rolled coil is cooled before pickling. The running speed of the pickled strip is 80-300 m / min, the scale-breaking and tension leveling elongation is ≤1.8%, the pickling tank temperature is 60-100℃, the temperature of the last rinsing tank is 40-70℃, and the iron ion concentration is 80-120 g / L. After pickling, online leveling and tension leveling are performed, with the leveling elongation controlled at 0.6-1.6% and the tension leveling elongation at 0.5±0.2%. In the galvanizing process, the galvanized substrate is first rapidly heated to 230℃~250℃ for preheating, then heated to the target homogenization temperature at a heating rate of 8℃ / s~18℃ / s. The dew point in the furnace area is controlled at -40℃~-10℃, and the homogenization time is 40s~120s. Subsequently, it is rapidly cooled to the target temperature and placed in a zinc bath containing zinc, aluminum, and magnesium phosphate for hot-dip galvanizing. The zinc bath temperature is 420℃~470℃. After galvanizing, the finished elongation of the strip is 0.6%~1.2%, and the tensile elongation is 0.2±0.1%. The target homogenization temperature and the rapid cooling exit temperature are differentiated according to the strip thickness, specifically including:

[0096] When the thickness is 0.8–2.5 mm, the target uniform heating temperature is 650–760 °C, and the rapid cooling outlet temperature is 430 °C–470 °C; when the thickness is 2.5–4.0 mm, the target uniform heating temperature is 640–730 °C, and the rapid cooling outlet temperature is 420 °C–470 °C; when the thickness is 4.0–6.0 mm, the target uniform heating temperature is 630–740 °C, and the rapid cooling outlet temperature is 410 °C–470 °C.

[0097] The purpose of heat homogenization is twofold: firstly, to modify the surface under a specific atmosphere, improving the adhesion between the coating and the substrate and enhancing the surface quality of the coating; secondly, the heat homogenization temperature should not be too high or too low, as this can affect both the performance of the finished product and the surface quality of the coating, easily leading to defects such as incomplete coating, zinc stripping, and zinc flow marks. Because the latent heat of steel strips of different thicknesses varies, the entry temperature of steel strips into the hot-dip galvanizing bath must be differentiated to ensure a sufficiently stable hot-dip galvanizing reaction, thereby guaranteeing the surface quality and adhesion of the coating.

[0098] The present invention will be 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 invention. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0099] Examples 1-3 and Comparative Examples 1-2 provide a zinc-aluminum-magnesium alloy coated high-strength steel. The composition content of the steel plate substrate in each example is shown in Table 1, and the composition content of the coating is shown in Table 2.

[0100] Table 1. Chemical composition (wt.%) of the steel plate substrates in Examples 1-3 and Comparative Examples 1-2

[0101]

[0102]

[0103] Table 2. Chemical composition (wt.%) of the coatings in Examples 1-3 and Comparative Examples 1-2

[0104]

[0105] The preparation method of the zinc-aluminum-magnesium alloy coated high-strength steel provided in Examples 1-3 specifically includes:

[0106] After refining, molten steel is continuously cast and hot rolled to obtain hot-rolled coils of various thicknesses and specifications with the aforementioned chemical composition.

[0107] Hot-rolled coils undergo tension leveling to break up scale and pickling to remove iron oxide scale. They are then leveled and tensioned online to obtain pickled strips with good shape and uniform surface structure.

[0108] Pickled strip steel is hot-dip galvanized, bright-finished and tension-straightened to obtain high-strength steel with zinc-aluminum-magnesium alloy coating and good surface quality.

[0109] The continuous casting machine is equipped with a roller hearth tunnel soaking furnace between the continuous casting machine outlet and the roughing mill. This furnace includes a fixed section and a moving section, thus enabling the production of steel slabs. It can operate in multiple modes, including single-slab rolling, semi-automatic headless rolling, and fully automatic headless rolling, to produce steel coils of different thicknesses. The multi-mode thin slab continuous casting and rolling process includes: continuous casting to obtain a continuous casting billet, heat treatment of the billet, descaling before roughing, roughing, electromagnetic induction heating, descaling before finishing, finishing, laminar flow cooling, coiling, and cooling to obtain a hot-rolled coil.

[0110] The casting speed is 4.0 to 6.2 m / min, and the thickness of the continuous casting billet is 110 to 123 mm.

[0111] The heat treatment of the steel slab is carried out in a roller hearth tunnel soaking furnace, which includes a fixed section and a moving section. The fixed section is 50-55 meters long and the moving section is 25-30 meters long. The heat treatment temperature is 1150-1180℃.

[0112] The roughing process involves two passes, with an inlet temperature of 1150–1180℃ and an outlet temperature of 950–970℃.

[0113] The rough-rolled billet is heated by electromagnetic induction, with an exit temperature of 1100–1220℃;

[0114] The finishing rolling process uses 5 passes, with a total reduction rate of 75% to 80%.

[0115] The rolling mode is determined by the thickness of the hot-rolled coil. When the thickness is 0.8–2.5 mm, a fully automatic headless rolling mode is used, with an electromagnetic induction heating temperature of 1160–1220℃, a finishing rolling entry temperature of 1000–1050℃, a finishing rolling temperature of 820–850℃, and a coiling temperature of 590–620℃. When the thickness is 2.5–4.0 mm, a semi-automatic headless rolling mode or the fully automatic headless rolling mode is used, with electromagnetic induction heating... The heating temperature should be 1140~1190℃, the entry temperature for finishing rolling should be 980~1030℃, the final rolling temperature should be 820~850℃, and the coiling temperature should be 580~610℃; when the thickness is 4.0~6.0mm, a single-slab rolling mode is adopted, with an electromagnetic induction heating temperature of 1100~1150℃, an entry temperature for finishing rolling of 960~1010℃, a final rolling temperature of 820~850℃, and a coiling temperature of 570~600℃.

[0116] In the pickling process, the hot-rolled coil is cooled and then pickled. The running speed of the pickling strip is 80-300 m / min, the descaling elongation is ≤1.8%, the pickling tank temperature is 60-100℃, the temperature of the last rinsing tank is 40-70℃, and the iron ion concentration is 80-120 g / L. After pickling, online leveling and tension straightening are performed. The leveling elongation is controlled at 0.6-1.6%, and the tension straightening elongation is 0.5±0.2%.

[0117] In the galvanizing process, the galvanized substrate is first rapidly heated to 230℃~250℃ for preheating, then heated at a rate of 8℃ / s~18℃ / s to the target homogenization temperature. The dew point in the furnace area is controlled at -40℃~-10℃, and the homogenization time is 40s~120s. Subsequently, it is rapidly cooled to the target temperature and placed in a zinc bath containing zinc, aluminum, and magnesium phosphate for hot-dip galvanizing. The zinc bath temperature is 420℃~470℃. After galvanizing, the finished elongation of the strip is 0.6%~1.2%, and the tensile elongation is 0.2±0.1%. The target homogenization temperature and the rapid cooling exit temperature are controlled according to the strip thickness, specifically including:

[0118] When the thickness is 0.8–2.5 mm, the target uniform heating temperature is 650–760 °C, and the rapid cooling outlet temperature is 430 °C–470 °C; when the thickness is 2.5–4.0 mm, the target uniform heating temperature is 640–730 °C, and the rapid cooling outlet temperature is 420 °C–470 °C; when the thickness is 4.0–6.0 mm, the target uniform heating temperature is 630–740 °C, and the rapid cooling outlet temperature is 410 °C–470 °C.

[0119] The specific key process parameters for continuous casting, rolling, pickling, and galvanizing in Examples 1-3 are shown in Tables 3 and 4, respectively.

[0120] Table 3 Key process parameters for continuous casting and rolling in Examples 1-3

[0121]

[0122] Table 4 Key process parameters for pickling and hot-dip galvanizing in Examples 1-3

[0123]

[0124]

[0125] Comparative Examples 1 and 2 adopted a conventional hot-rolling-pickling-cold-rolling-hot-dip galvanizing process, with specific parameters as follows:

[0126] The continuously cast billet of the aforementioned composition was heated to 1250℃ and held for 1.8 hours. The inlet temperature for rough rolling was 1150℃, the inlet temperature for finish rolling was 1030℃, the final rolling temperature was 890℃, the coiling temperature was 580℃, and the thickness of the hot-rolled plate was 4.0mm. After pickling, the hot-rolled coil was cold-rolled to 1.0mm with a cold rolling reduction rate of 75%. The cold-rolled coil was annealed at a continuous annealing temperature of 760℃, and then cooled to 430℃ before being hot-dip galvanized in a zinc bath. The elongation after galvanizing was 1.0%.

[0127] Test results:

[0128] This example demonstrates the performance testing of the zinc-aluminum-magnesium alloy coated high-strength steels provided in Examples 1-3 and Comparative Examples 1-2. The test results are shown in Table 5.

[0129] Test standards and methods: The tensile strength and elongation after fracture (A80) were tested using a ZWICK / Roell 2100 tensile testing machine in accordance with GB / T228.1-2010 standard; the bending performance of the substrate and the adhesion of the coating were evaluated using the D=2.0a, 180° bending method.

[0130] Table 5 Mechanical properties of Examples 1-3 and Comparative Examples 1-2

[0131]

[0132] As shown in Examples 1-3, the tensile properties of hot-dip galvanized aluminum-magnesium coated high-strength steel with a yield strength of 450MPa obtained by the composition and preparation method of the present invention are as follows: yield strength ≥ 450MPa, tensile strength ≥ 510MPa, elongation after fracture (A80) ≥ 14%. It exhibits good 180° transverse bending performance, with no substrate cracking and no zinc peeling of the coating. Its comprehensive mechanical properties meet the requirements for steel used in photovoltaic power plants. The tensile properties of different specifications of strip steel show little difference, indicating good performance stability. Therefore, the springback amount during roll forming and high-frequency welded pipe forming of different specifications of strip steel can be accurately predicted, resulting in high yield and production efficiency.

[0133] As can be seen from Comparative Examples 1 and 2, to prepare thin-gauge steel strips with comparable mechanical properties using conventional cold rolling-hot-dip galvanizing processes, different chemical compositions must be used, resulting in higher alloy costs, energy consumption, and production costs.

[0134] In summary, this invention provides high-strength steel strips with zinc-aluminum-magnesium alloy coatings of various specifications ranging from 0.8 to 6.0 mm, along with their preparation methods, through rational composition design, consistent process flow design, and differentiated control of process parameters. The microstructure of the strips of different specifications is consistent (as shown in the attached figure). Figure 2-4 As shown; where, Figure 2 This is a cross-sectional metallographic microstructure image of a 1.0 mm thick high-strength steel with a zinc-aluminum-magnesium alloy coating obtained according to an embodiment of the present invention. Figure 3 This is a cross-sectional metallographic microstructure image of a 3.5mm zinc-aluminum-magnesium alloy coated high-strength steel obtained according to an embodiment of the present invention. Figure 4 The image shows a cross-sectional metallographic microstructure of a 6.0mm zinc-aluminum-magnesium alloy coated high-strength steel strip obtained according to an embodiment of the present invention. This ensures good performance consistency, and both thin and thick strips exhibit excellent coating surface quality (as shown in the attached image). Figure 5-7 As shown; where, Figure 5 This is a characterization image of the coating surface quality of a 1.0 mm zinc-aluminum-magnesium alloy coated high-strength steel obtained according to an embodiment of the present invention. Figure 6 This is a surface quality characterization image of the zinc-aluminum-magnesium alloy coated high-strength steel with a diameter of 3.5 mm obtained according to an embodiment of the present invention. Figure 7 This is a surface quality characterization diagram of the zinc-aluminum-magnesium alloy coated high-strength steel with a specification of 6.0 mm obtained in the embodiment of the present invention. It meets the requirements of photovoltaic power stations for high mechanical property stability, high corrosion resistance and low cost of 450MPa grade high-strength steel with various thicknesses. In addition, the method is based on a multi-mode thin slab continuous casting and rolling production line and an acid plating production line to prepare high-strength steel of various specifications from 0.8 to 6.0 mm under the same process flow, which has the advantages of short process, low energy consumption and green environmental protection.

[0135] It should be noted that, 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. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0136] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. 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 the invention. Therefore, the present invention 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 high-strength steel with a zinc-aluminum-magnesium alloy coating, characterized in that, The zinc-aluminum-magnesium alloy coated high-strength steel includes a steel plate substrate and a zinc-aluminum-magnesium alloy coating on the surface of the steel plate substrate. The chemical composition of the steel plate substrate, by mass fraction, is as follows: C: 0.03%–0.25%, Si: ≤0.18%, Mn: 0.5%–1.2%, P: ≤0.025%, S: ≤0.006%, Alt: 0.02%–0.06%, N: 0.002%–0.004%, Nb: 0.010%–0.025%, Ti: 0.015%–0.09%, with the remainder being Fe and impurities from the preparation of the steel plate substrate; The thickness of the zinc-aluminum-magnesium alloy coated high-strength steel includes any one of the following specifications: 0.8 to 6.0 mm. The metallographic structure of the steel plate substrate comprises 65-95% ferrite and 5-35% pearlite by volume fraction. The preparation method of the zinc-aluminum-magnesium alloy coated high-strength steel includes: A hot-rolled coil containing the same chemical composition as the steel plate substrate is obtained by using a multi-mode thin slab continuous casting and rolling production line process. The hot-rolled coil is subjected to an acid plating production line process to obtain the zinc-aluminum-magnesium alloy coated high-strength steel. The rolling mode adopted by the multi-mode thin slab continuous casting and rolling production line process includes at least one of the following: single slab rolling mode, semi-automatic headless rolling mode, and fully automatic headless rolling mode. The process of obtaining hot-rolled coils containing the same chemical composition as the steel plate substrate by using a multi-mode thin slab continuous casting and rolling production line specifically includes: Molten steel containing the same chemical composition as the steel plate substrate is obtained; The molten steel is smelted and continuously cast to obtain a continuously cast billet; The continuously cast billet is heated to obtain a heated billet; The heated billet is subjected to rough rolling, electromagnetic induction heating, finish rolling, laminar flow cooling, coiling and cooling to obtain a hot-rolled coil containing the same chemical composition as the steel plate substrate. The continuously cast billet is heated in a roller hearth tunnel soaking furnace, which includes a fixed section and a moving section, and is used to realize different rolling modes in the multi-mode thin slab continuous casting and rolling production line process. Different rolling modes are adopted according to the predetermined thickness d of the zinc-aluminum-magnesium alloy coated high-strength steel, specifically: For diameters 0.8mm ≤ d < 2.5mm, a fully automatic headless rolling process is adopted. For diameters of 2.5mm ≤ d < 4.0mm, a semi-automatic or fully automatic headless rolling process shall be adopted. For diameters 4.0mm ≤ d ≤ 6.0mm, a single-slab rolling process is adopted. In the hot-rolled coil acid plating production line process, different process parameters are adopted according to the predetermined thickness d of the zinc-aluminum-magnesium alloy coating on the high-strength steel, specifically: For a diameter of 0.8mm ≤ d < 2.5mm, the process parameters for the hot-rolled coil acid plating production line include: target heat treatment temperature of 650~760℃ and rapid cooling outlet temperature of 430℃~470℃. For a diameter of 2.5mm ≤ d < 4.0mm, the process parameters for the hot-rolled coil acid plating production line include: target heat homogenization temperature of 640~730℃ and rapid cooling outlet temperature of 420℃~470℃. For hot-rolled coils with a diameter of 4.0mm≤d≤6.0mm, the process parameters for the acid plating production line include: target uniform heating temperature of 630~740℃ and rapid cooling outlet temperature of 410℃~470℃.

2. The high-strength steel with zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that, The C element content is 0.04% to 0.19% by mass fraction.

3. The high-strength steel with zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that, The Mn element content is 0.5% to 0.9% by mass fraction.

4. The high-strength steel with zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that, The composition of the zinc-aluminum-magnesium alloy coating, by mass fraction, is: Al: 1.0%–12.0%, Mg: 1.0%–3.0%, with the remainder being Zn and impurities from the preparation of the zinc-aluminum-magnesium alloy coating.

5. The high-strength steel with zinc-aluminum-magnesium alloy coating according to any one of claims 1 to 4, characterized in that, The zinc-aluminum-magnesium alloy coated high-strength steel has a yield strength ≥450MPa, a tensile strength ≥510MPa, and an elongation after fracture (A80) ≥14%.

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