Preparation method of alloyed galvanized sheet and high-pressure gas purging device

Abstract

The invention relates to a preparation method of an alloyed galvanized plate and a high-pressure gas purging device, and belongs to the technical field of continuous strip steel hot dipping. The method comprises the following steps: obtaining a galvanized sheet; carrying out sectional alloying treatment on the galvanized plate to control the iron content of a plating layer of the galvanized plate so as to obtain an alloyed galvanized plate; wherein the sectional alloying treatment comprises alloying treatment of a heating section, a soaking section with a set temperature, a high-pressure gas purging section and a cooling section which are arranged in sequence. The weight of coated iron of the alloyed galvanized sheet prepared by the invention is 9.0-10.0%; the coating phase structure of the alloyed galvanized sheet comprises a granular delta phase and a layered columnar zeta phase, wherein the granular delta phase and the layered columnar zeta phase meet the following relation: [zeta] / ([zeta] + [delta]) is more than 5% and less than 15%; the maximum thickness lt of the Gamma + Gamma 1 phase layer of the plating layer of the alloyed galvanized sheet; and 1.0 [mu] m.

Description

Technical Field

[0001] The present application relates to the technical field of continuous strip hot-dip galvanizing, and particularly relates to a preparation method of an alloyed galvanized sheet and a high-pressure gas purging device. Background Art

[0002] An alloyed galvanized sheet (Galvannealed steel sheet, abbreviated as GA sheet) refers to a coated steel sheet with an iron-zinc layer obtained by performing alloying heat treatment on a galvanized sheet after it exits the zinc pot on the basis of a traditional hot-dip galvanizing (GI) production line. The Fe content in its coating is generally 7% - 15%, and it contains Zn-Fe alloy phases including Γ, Γ1, δ, and ζ phases. The hot-dip galvanized strip after coating alloying has good welding performance, coating performance, heat resistance, and corrosion resistance, and is widely used in automotive panels.

[0003] The requirements for the corrosion resistance of vehicle bodies increase year by year, and the proportion of galvanized automotive sheets used on vehicle bodies also increases year by year. Electro-galvanized sheets have relatively good surface quality, but the coating is thin and the corrosion resistance is relatively poor; pure hot-dip galvanized automotive sheets have sufficient coating thickness, but the weldability is relatively poor, and the coating is relatively soft, and the stone impact resistance and painting performance are relatively poor; alloyed hot-dip galvanized sheets have ideal corrosion resistance, welding performance, painting performance, and stone impact resistance due to their Fe-Zn phase coating, but also because of the relatively high iron content in the coating, it is difficult to control the coating phase structure, and the coating may have poor anti-powdering performance or poor formability, which is not conducive to sheet forming and may even damage the mold. Summary of the Invention

[0004] The present application provides a preparation method of an alloyed galvanized sheet and a high-pressure gas purging device to solve the following technical problems: how to improve the anti-powdering performance and formability of the coating of the alloyed galvanized sheet.

[0005] In a first aspect, an embodiment of the present application provides a preparation method of an alloyed galvanized sheet, the method comprising:

[0006] Obtaining a galvanized sheet;

[0007] Performing segmented alloying treatment on the galvanized sheet to control the iron content of the coating of the galvanized sheet, and obtaining an alloyed galvanized sheet; wherein, the segmented alloying treatment includes alloying treatment of a heating section, a soaking section with a set temperature, a high-pressure gas purging section, and a cooling section arranged in sequence.

[0008] Optionally, the temperature of the high-pressure gas in the high-pressure gas purging section is 300°C - 400°C.

[0009] Optionally, the flow rate of the high-pressure gas in the high-pressure gas purging section is ≥300m 3 / min.

[0010] Optionally, the set temperature is 460°C to 480°C.

[0011] Optionally, the time of the heating section is 1 s to 3 s, and the end temperature of the heating section is 500°C to 530°C.

[0012] Optionally, the running speed of the galvanized sheet is 70 m / min to 130 m / min; and / or,

[0013] the coating weight of the galvanized sheet is 40 g / m 2 to 55 g / m 2 , and the difference between the single-point maximum value and the single-point minimum value of the coating weight along the rolling direction and the transverse direction of the steel sheet is <7 g / m 2 .

[0014] Optionally, obtaining the galvanized sheet includes:

[0015] subjecting a substrate to hot-dip galvanizing to obtain a galvanized sheet; wherein, the process parameters of the hot-dip galvanizing include: the zinc pot temperature is 460°C to 470°C, the zinc liquid temperature in the zinc pot is 455°C to 465°C, and the aluminum weight in the zinc liquid is 0.128% to 0.135%.

[0016] Optionally, the method further includes:

[0017] skin-passing the alloyed galvanized sheet; wherein, the process parameters of the skin-pass rolling include: the surface roughness of the skin-pass roll is 1.0 μm to 1.2 μm, and the skin-pass elongation is 1.0% to 1.2%.

[0018] Optionally, the coating iron weight of the alloyed galvanized sheet is 9.0% to 10.0%;

[0019] the coating phase structure of the alloyed galvanized sheet includes granular δ phase and columnar ζ phase, and the granular δ phase and the columnar ζ phase satisfy the relationship: 5% < [ζ] / ([ζ] + [δ]) < 15%; wherein, [ζ] represents the volume percentage of ζ, and [δ] represents the volume percentage of δ;

[0020] the maximum thickness of the Γ + Γ1 phase layer of the coating of the alloyed galvanized sheet < 1.0 μm.

[0021] In a second aspect, an embodiment of the present application provides a high-pressure gas purging device for the high-pressure gas purging section of the method according to any one of the embodiments in the first aspect. The high-pressure gas purging device is composed of a plurality of nozzles arranged closely in the transverse direction. The width of the high-pressure gas purging device is the same as the width of the running channel of the galvanized sheet, and the high-pressure gas purging device faces the upper and lower surfaces of the galvanized sheet and is perpendicular to the surface of the galvanized sheet.

[0022] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0023] The method for preparing the alloyed galvanized sheet provided by the embodiment of the present application includes: obtaining a galvanized sheet; performing a segmented alloying treatment on the galvanized sheet to control the iron content in the coating of the galvanized sheet, thereby obtaining an alloyed galvanized sheet; wherein, the segmented alloying treatment includes an alloying treatment with a heating section, a soaking section with a set temperature, a high-pressure gas purging section, and a cooling section arranged in sequence. The galvanized layer of the galvanized sheet serves as the basis for subsequent alloying reactions; the galvanized sheet is subjected to an alloying treatment. Among them, the heating section can enable the galvanized layer and the substrate to reach the temperature conditions required for subsequent alloying reactions; the soaking section with a set temperature can cause the zinc in the galvanized layer to diffuse and chemically react with the iron in the substrate to form a zinc-iron alloy phase, and fully regulate the type, proportion, and distribution of the zinc-iron alloy phase, improving the anti-powdering performance and formability of the coating; a high-pressure gas purging section is added between the soaking section and the cooling section. The high-pressure gas purging section continuously ejects a high-pressure air flow to form an air flow wall, separating the soaking section from the cooling section, effectively avoiding heat loss in the soaking section, effectively controlling the iron content in the coating of the galvanized sheet, and thus greatly improving the controllability of the coating phase structure; the cooling section can further stabilize the phase structure of the coating, and at the same time, the bonding strength between the substrate and the coating is also enhanced; therefore, through the above alloying treatment, the formed zinc-iron alloy phase can have better stability and compactness, improving the anti-powdering performance of the coating of the alloyed galvanized sheet. At the same time, the coating phase structure also endows the coating itself with better plasticity and toughness, enabling it to withstand a greater amount of deformation during the forming process without damage, and improving the formability of the alloyed galvanized sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic flow chart of a method for preparing an alloyed galvanized sheet provided by an embodiment of the present application;

[0027] Figure 2 It is a schematic flow chart of the alloying of a method for preparing an alloyed galvanized sheet provided by an embodiment of the present application;

[0028] Figure 3The surface morphology of the coating of an alloying galvanized sheet provided by an embodiment of the present application;

[0029] Figure 4 The cross-sectional morphology of the coating of an alloying galvanized sheet provided by an embodiment of the present application. Specific embodiments

[0030] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0031] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single 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 that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0032] In the present application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing direction in the drawings. Additionally, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this document, "and / or" describes the associated relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Wherein A and B may be singular or plural.

[0033] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present application can be obtained through market purchases or can be prepared by existing methods.

[0034] In a first aspect, an embodiment of the present application provides a method for preparing an alloying galvanized sheet, Figure 1Schematic flow chart of a method for preparing an alloyed galvanized sheet provided by an embodiment of the present application; please refer to Figure 1 , the method includes:

[0035] S1. Obtain a galvanized sheet;

[0036] Obtain a galvanized sheet. The galvanized layer serves as the basis for subsequent alloying reactions and provides the necessary metal elements for forming an alloyed coating with specific properties. Obtaining the galvanized sheet and subsequent alloying are carried out continuously on a hot-dip galvanizing production line. An alloyed hot-dip galvanized sheet is produced by hot-dip galvanizing the substrate using a hot-dip galvanizing unit. In the embodiment of the present application, this alloyed galvanized sheet can be used for automotive panels. This alloyed galvanized sheet can be IF steel and can adopt a super-low carbon composition system with Nb-Ti composite. The steel is pure and no other alloying elements are added. The chemical composition of the substrate in terms of mass fraction may include: C: ≤0.003%; Si: <0.02%; Mn: 0.05% - 0.2%; P: <0.015; Alt: 0.2% - 0.5%; Nb: 0.005% - 0.02%; Ti: 0.01% - 0.04%.

[0037] Before step S1, it includes: heating the slab to 1200°C, holding for 2 hours, performing hot rolling, with the final rolling temperature of hot rolling being 910°C and the coiling temperature being 700°C; after the hot-rolled coil is naturally cooled, pickling and cold rolling are carried out, and the cold rolling reduction rate is 80%; then it enters the hot-dip galvanizing production line. After the strip is cleaned, annealing treatment is first carried out, with the annealing temperature at 830°C and the strip running speed being 90 m / min - 110 m / min.

[0038] In some embodiments, the obtaining of the galvanized sheet includes:

[0039] Subject the substrate to hot-dip galvanizing to obtain a galvanized sheet; wherein, the process parameters of the hot-dip galvanizing include: the zinc pot temperature is 460°C - 470°C, the zinc liquid temperature in the zinc pot is 455°C - 465°C, and the aluminum weight in the zinc liquid is 0.128% - 0.135%.

[0040] In the embodiments of the present application, hot-dip galvanizing means immersing a substrate into molten zinc liquid, so that a series of physical and chemical reactions occur between the surface of the substrate and the zinc liquid, thereby forming a zinc coating layer on the surface of the substrate. The control of the zinc pot temperature, the zinc liquid temperature in the zinc pot, and the aluminum weight of the zinc liquid promotes the control of the coating phase structure. The temperature of the substrate entering the zinc pot is controlled above the zinc liquid temperature in the zinc pot, which can be 460°C to 470°C. When the temperature entering the pot is too high and higher than 470°C, alloy phases may be produced in advance in the coating, which is not conducive to the control of the overall coating uniformity and increases the iron loss at the same time. When the temperature is too low and lower than 460°C, a zinc pot heater may be required to compensate for the heat loss taken away by the substrate from the zinc liquid, while intensifying the zinc liquid disturbance and easily generating zinc slag defects. The zinc liquid temperature in the zinc pot can be 455°C to 465°C, because when the zinc liquid temperature is too high and higher than 465°C, the reaction of Fe and Zn may be accelerated, easily forming a large amount of "explosion" structure, and the slag amount in the zinc pot increases, affecting the coating quality. The Al content of the zinc liquid can be 0.128% to 0.135%. When the Al content is low and lower than 0.128%, the interface layer between the raw material substrate and the coating is prone to rapid alloying and forming too much "explosion" structure, and the alloying process is not easy to control. When the Al content is too high and higher than 0.135%, a relatively thick Fe2Al5 blocking layer may be easily formed on the surface of the substrate, which will increase the difficulty of the alloying process, thus requiring a higher alloying temperature, also making the alloying process not easy to control, and easily causing over-alloying or under-alloying of the coating. When the coating is over-alloyed, the anti-powdering performance of the coating is poor, and when it is under-alloyed, there is more ζ phase on the surface of the coating, resulting in an increase in the friction coefficient of the coating and affecting the forming performance of the coating. Exemplarily, the zinc pot temperature can be 460°C, 462°C, 464°C, 466°C, 468°C, 470°C, etc.; the zinc liquid temperature in the zinc pot can be 455°C, 457°C, 459°C, 461°C, 463°C, 456°C, etc.; the aluminum weight of the zinc liquid can be 0.128%, 0.129%, 0.130%, 0.131%, 0.132%, 0.133%, 0.135%, 0.134%, etc.

[0041] In some embodiments, the running speed of the galvanized sheet is 70 m / min to 130 m / min; and / or,

[0042] the coating weight of the galvanized sheet is 40 g / m 2 ~55 g / m 2 and the difference between the single-point maximum value and the single-point minimum value of the coating weight along the rolling direction and the transverse direction of the steel sheet is <7 g / m 2 .

[0043] In the embodiments of the present application, the running speed of the galvanized sheet can be 70 m / min to 130 m / min. A reasonable running speed of the galvanized sheet matches the soaking section temperature of subsequent alloying. The running speed determines the alloying heat treatment time and the power of the heat treatment heating furnace. Under the same conditions, if the speed is too high and higher than 130 m / min, it may lead to insufficient alloying heat treatment time, easily resulting in uneven alloying and under-alloying; while if the speed is too low and lower than 70 m / min, it may easily lead to over-alloying, making the Г+Г1 phase layer in the coating too thick, thereby affecting the anti-chalking performance of the coating. Exemplarily, the running speed of the galvanized sheet can be 70 m / min, 80 m / min, 90 m / min, 100 m / min, 110 m / min, 120 m / min, 130 m / min, etc.

[0044] After the substrate is hot-dip galvanized in molten zinc, the coating thickness is controlled by an air knife. For the alloying coating used for automotive panels, the coating thickness can be 40 g / m 2 ~55 g / m 2 When the coating is too thin and lower than 40 g / m 2 , it is not conducive to corrosion resistance; when the coating is too thick and higher than 55 g / m 2 , it is not conducive to the anti-chalking performance of the coating, and chalking is likely to occur during the forming of the steel sheet. In order to accurately control the phase structure of the coating, it is also required that the coating weight of the alloying hot-dip galvanized steel sheet be controlled as evenly as possible, that is, the difference between the single-point maximum and minimum values of the coating weight along the rolling direction and the transverse direction of the steel sheet (hereinafter simply referred to as △h) can be less than 7 g / m 2 . Exemplarily, the coating weight of the galvanized sheet can be 40 g / m 2 , 42 g / m 2 , 44 g / m 2 , 46 g / m 2 , 48 g / m 2 , 50 g / m 2 , 52 g / m 2 , 54 g / m 2 , 55 g / m 2 , etc.; the difference between the single-point maximum and single-point minimum values of the coating weight along the rolling direction and the transverse direction of the steel sheet can be 6.5 g / m 2 , 6 g / m 2 , 5.8 g / m 2 , 5.5 g / m 2 , etc.

[0045] S2. Perform segmented alloying treatment on the galvanized sheet to control the iron content in the coating of the galvanized sheet and obtain an alloyed galvanized sheet; wherein, the segmented alloying treatment includes alloying treatment with a heating-up section, a soaking section with a set temperature, a high-pressure gas purging section, and a cooling section arranged in sequence.

[0046] The heating section can bring the galvanized layer and the substrate to the temperature conditions required for subsequent alloying reactions; the soaking section with a set temperature can cause the zinc in the galvanized layer to diffuse and chemically react with the iron in the substrate to form a zinc-iron alloy phase, and fully regulate the type, proportion, and distribution of the zinc-iron alloy phase, improving the anti-powdering performance and formability of the coating.

[0047] A high-pressure gas purging section is added between the soaking section and the cooling section. This section continuously ejects high-pressure airflows to form an air wall, effectively blocking the heat transfer between the soaking section and the cooling section. This enables the soaking section to maintain a relatively stable temperature, avoiding temperature fluctuations caused by heat loss, thereby ensuring the smooth progress of the alloying reaction and the stable formation of the zinc-iron alloy phase. By maintaining a stable high-temperature environment in the soaking section, the zinc-iron diffusion can proceed fully under set conditions, which is conducive to precisely controlling the iron content in the coating. The high-pressure airflows exert a certain pressure on the surface of the galvanized sheet, making the galvanized sheet more stable during operation, reducing the jitter and offset of the substrate, thereby improving the uniformity and stability of the coating. At the same time, the high-pressure airflows form a strong convection on the surface of the galvanized sheet, accelerating the heat transfer and exchange, making the temperature on the surface of the coating more uniform, reducing the internal stress concentration in the coating caused by temperature differences, thereby improving the quality and stability of the coating. By effectively controlling the heat transfer and atmosphere between the soaking section and the cooling section through the high-pressure gas purging section, the coating can be cooled and undergo phase structure transformation in a predetermined manner during the transition from the soaking section to the cooling section. This greatly improves the controllability of the coating phase structure, improves the anti-powdering performance and formability of the coating, and meets the requirements of different application fields. The high-pressure gas can be high-pressure air or high-pressure nitrogen.

[0048] Therefore, to ensure the quality of the alloyed coating, a high-pressure gas continuous purging section is added between the outlet of the alloying soaking section and the inlet of the cooling section to precisely control the phase structure of the alloyed coating, making it have excellent anti-powdering performance and formability. When using a hot-dip galvanizing unit to produce alloyed hot-dip galvanized sheets on a hot-dip galvanized substrate, after selecting the raw material substrate, Figure 2 is a schematic flow diagram of the alloying process of a method for preparing an alloyed galvanized sheet provided in an embodiment of the present application; please refer to Figure 2 , the annealed substrate strip steel is immersed in the molten zinc bath in the zinc pot through the furnace nose for hot-dip galvanizing, and then exits the zinc pot through the sink roll and the correction roll and the stabilizing roll above it. The zinc liquid on the surface of the substrate is quickly blown by an air knife in a molten state to obtain a set zinc layer thickness, and then the substrate enters the alloying furnace for heat treatment of coating alloying. Thermometers are provided at the outlets of the heating section and the soaking section of the alloying heat treatment to online detect the surface temperature of the substrate.

[0049] In some embodiments, the temperature of the high-pressure gas in the high-pressure gas purging section is 300°C to 400°C

[0050] In some embodiments, the flow rate of the high-pressure gas in the high-pressure gas purging section is ≥ 300 m 3 / min.

[0051] In the embodiments of the present application, a resistance heater is provided to heat the ejected air flow. The temperature of the high-pressure gas in the high-pressure gas purging section can be 300°C to 400°C, and the flow rate of the high-pressure gas in the high-pressure gas purging section can be ≥ 300 m 3 / min. The appropriately heated air flow and high-pressure gas flow have higher energy and activity, and can better perform heat exchange with the surface of the galvanized sheet. For the galvanized sheet after the soaking section, the heated air flow can, to a certain extent, slow down the cooling rate of the galvanized sheet, enabling the galvanized sheet to have a more suitable transition before entering the cooling section, and avoiding excessive stress generated inside the coating due to sudden temperature changes, thereby affecting the performance of the coating. Exemplarily, the temperature of the high-pressure gas flow can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, etc.

[0052] In some embodiments, the set temperature is 460°C to 480°C.

[0053] In the embodiments of the present application, the set temperature can be 460°C to 480°C, which can fully alloy the galvanized sheet. If the alloying temperature is too high and higher than 480°C, over-alloying will occur, and the content of Γ phase will increase rapidly, resulting in the deterioration of the anti-powdering performance of the coating. For general alloying hot-dip galvanizing production lines, since the alloying furnace is a vertical box structure as a whole and is directly connected to the cooling section, this will cause the "chimney effect" and the heat loss will be relatively fast. And the heating capacity of the resistance band in the soaking section of alloying is insufficient and only plays a heat preservation role. Therefore, it is necessary to increase the alloying induction heating power to increase the temperature of the alloying heating section. This will increase the difficulty of controlling the phase structure of the coating, and it is easy to form over-alloying or under-alloying, and it is not conducive to the control of the coating uniformity. Therefore, a high-pressure gas continuous purging section is added between the soaking section and the cooling section to effectively avoid the heat loss in the soaking section. At the same time, it not only improves the stability of the galvanized sheet but also improves the heat uniformity of the coating, greatly improving the controllability of the coating phase structure. Therefore, the set temperature in the soaking section and the high-pressure gas continuous purging section jointly control the coating phase structure, enabling the coating to have good anti-powdering performance and forming performance at the same time. Exemplarily, the set temperature can be 460°C, 465°C, 466°C, 468°C, 470°C, 471°C, 472°C, 473°C, 475°C, 480°C, etc.

[0054] In some embodiments, the time of the heating-up section is 1 s to 3 s, and the end temperature of the heating-up section is 500°C to 530°C.

[0055] In the embodiments of the present application, after the substrate forms a coating with a uniform thickness through air knife control, it enters an alloying furnace for alloying heat treatment. The alloying heat treatment process is preferably controlled by a process of high temperature first and then low temperature, and the time of the heating section can be 1 s to 3 s, and the end temperature of the heating section can be 500 °C to 530 °C. A fast heating speed can enable zinc and iron atoms to complete the diffusion and alloying process in a shorter time, thereby forming finer and more uniform zinc-iron alloy phase grains. This fine and uniform grain structure can effectively improve the strength and hardness of the coating, and at the same time can also improve the toughness and plasticity of the coating, so that the coating is not easily broken or peeled off when subjected to external forces, thereby improving the anti-powdering performance of the coating. The end temperature of the heating section is 500 °C to 530 °C, which provides the necessary starting conditions for the subsequent alloying reaction. Within this temperature range, the zinc in the galvanized layer and the iron atoms in the substrate have sufficient energy to overcome the lattice resistance between each other, thereby laying a good foundation for the alloying reaction carried out in the soaking section. Exemplarily, the time of this heating section can be 1 s, 2 s, 3 s, etc.; the end temperature of the heating section can be 500 °C, 510 °C, 512 °C, 514 °C, 516 °C, 518 °C, 520 °C, 530 °C, etc.

[0056] In some embodiments, the method further includes:

[0057] Skin-pass the alloyed galvanized sheet; wherein, the process parameters of the skin pass include: the surface roughness of the skin pass roll is 1.0 μm to 1.2 μm, and the skin pass elongation is 1.0% to 1.2%.

[0058] In the embodiments of the present application, skin pass rolling is performed on the alloyed galvanized sheet to improve the shape of the alloyed galvanized sheet, and requirements are put forward for the surface roughness of the skin pass roll and the skin pass elongation. Reasonably selecting the surface roughness of the skin pass roll and the skin pass elongation plays a key role in improving the coating forming performance and painting performance. Different from the pure galvanized sheet, the original surface roughness of the alloyed hot-dip galvanized coating is relatively large, generally above 2.0 μm. Therefore, a skin pass roll with a small roughness is required for skin pass rolling to reduce the roughness. Excessive or too small surface roughness of the coating is not conducive to the subsequent processing process. When the roughness is too small, not only the oil storage performance is poor, but also the coating adhesion to the steel plate during the subsequent painting process is insufficient, resulting in poor painting performance; when the roughness is relatively large, the surface friction coefficient of the coating will increase accordingly, affecting the material forming performance. The surface roughness of the skin pass roll can be 1.0 μm to 1.2 μm, and the skin pass elongation can be 1.0% to 1.2%. Combining with a reasonable alloy phase structure on the coating surface, the surface roughness of the galvanized sheet can be controlled to be 0.8 to 1.0 μm, and the friction coefficient value can be 0.13 to 0.14. The friction coefficient is measured by the flat plate sliding method, and the measurement conditions are: indenter pressure 3000 N, sliding speed 200 mm / min, and sliding distance 100 mm. At this time, a certain roughness value is retained on the coating surface, and a lower friction coefficient ensures the forming performance. Exemplarily, the surface roughness of the skin pass roll can be 1.0 μm, 1.12 μm, 1.14 μm, 1.15 μm, 1.17 μm, 1.18 μm, 1.2 μm, etc.; the skin pass elongation can be 1.0%, 1.12%, 1.14%, 1.16%, 1.18%, 1.2%, etc.

[0059] In some embodiments, the iron weight of the coating of the alloyed galvanized sheet is 9.0% to 10.0%;

[0060] The coating phase structure of the alloyed galvanized sheet includes granular δ phase and columnar ζ phase, and the granular δ phase and the columnar ζ phase satisfy the relationship: 5% < [ζ] / ([ζ] + [δ]) < 15%; where, [ζ] represents the volume percentage of ζ, and [δ] represents the volume percentage of δ;

[0061] The maximum thickness of the Γ + Γ1 phase layer of the coating of the alloyed galvanized sheet < 1.0 μm.

[0062] In the embodiments of the present application, the iron weight of the coating of the alloyed galvanized sheet can be 9.0% - 10.0%, and an ideal coating of Zn-Fe alloy phase containing Γ, Γ1, δ and ζ phases can be obtained. When the iron weight of the coating is lower than 9.5%, it may cause too much ζ phase to exist on the surface of the coating, resulting in an increase in the surface friction coefficient and being unfavorable for material forming; when the iron weight of the coating is higher than 10.5%, it may cause a decrease in the ζ phase content in the coating and an increase in the content of Γ+Γ1 phases. Even the maximum thickness of the Γ+Γ1 phase layer may be greater than 1 μm, which will increase the hardness and brittleness of the coating, thus resulting in a decrease in the anti-powdering performance. During forming, powdering is likely to occur, causing surface defects of parts and even damaging the mold.

[0063] The preparation method of the alloyed galvanized sheet provided by the embodiments of the present application has the following advantages:

[0064] 1. A high-pressure gas purging section is arranged between the soaking section and the cooling section. By continuously spraying high-pressure air flow to form an air flow wall, the soaking section and the cooling section are separated. This measure has multiple effects. It effectively avoids heat loss in the soaking section, ensures the temperature stability of the soaking section, and helps the stable progress of the alloying reaction; it also improves the stability of the substrate and the uniformity of the coating heated, and greatly enhances the controllability of the coating phase structure.

[0065] 2. Through the above alloying treatment process, the formed zinc-iron alloy phase has better stability and compactness, thereby improving the anti-powdering performance of the coating of the alloyed galvanized sheet, making it less likely to appear coating powdering during the use of the product. Due to the optimization of the coating phase structure after alloying treatment, the coating itself has better plasticity and toughness, can withstand a larger deformation amount during the forming process without damage, and thus improves the forming performance of the alloyed galvanized sheet, broadening the application range of the product in the field of processing and manufacturing.

[0066] In the second aspect, the embodiments of the present application provide a high-pressure gas purging device for the high-pressure gas purging section of the method described in any one of the embodiments of the first aspect. The high-pressure gas purging device is composed of a plurality of nozzles arranged closely horizontally. The width of the high-pressure gas purging device is the same as the width of the running channel of the galvanized sheet. The high-pressure gas purging device faces the upper and lower surfaces of the galvanized sheet and is perpendicular to the surface of the galvanized sheet.

[0067] In the embodiment of the present application, the high-pressure gas purging section is provided with multiple groups of high-pressure gas continuous purging devices facing the upper and lower surfaces of the galvanized sheet between the outlet of the alloying soaking section and the inlet of the cooling section. The high-pressure gas continuous purging device is composed of several nozzles arranged closely horizontally, so that the airflows ejected from the multiple nozzles can be superimposed and cooperate with each other. The closely arranged nozzles can form a continuous and uniform high-pressure airflow area on the surface of the galvanized sheet; continuously eject high-pressure airflow perpendicular to the surface of the galvanized sheet. When the airflow acts vertically on the surface of the galvanized sheet, it can more effectively blow away the impurities on the surface, and at the same time, a more effective airflow barrier can be formed between the soaking section and the cooling section, which can more efficiently cut off the heat, maintain the temperature difference between the soaking section and the cooling section, ensure the temperature stability of each stage in the preparation process of the alloying galvanized sheet, and further ensure the controllability of the coating phase structure; the width of the high-pressure gas continuous purging device is the same as the width of the galvanized sheet running channel, which ensures that the entire width direction of the galvanized sheet can be uniformly purged.

[0068] In the embodiment of the present application, the number of groups of the high-pressure gas continuous purging devices can be ≥2, and each group includes multiple nozzles arranged closely horizontally, and each group of devices is arranged in the order from top to bottom. When only one group of purging devices is set between the soaking section and the cooling section, there may be problems such as uneven airflow distribution and poor partition effect, resulting in the heat of the soaking section being transferred to the cooling section through local areas, affecting the cooling effect and the stability of the coating phase structure. By setting multiple groups of purging devices, the high-pressure airflows blown out by each group of devices are superimposed and supplemented with each other, and a more uniform, stable and effective airflow wall can be formed between the soaking section and the cooling section, more comprehensively and thoroughly preventing the heat of the soaking section from being transferred to the cooling section, better maintaining the temperature stability of the soaking section, and making the coating heat more evenly.

[0069] The following further elaborates the present application in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0070] A method for preparing an alloying galvanized sheet provided by an embodiment of the present application. Specifically, for the chemical composition of the substrate of the alloying galvanized sheet, please refer to Table 1, for the preparation process parameters of the alloying galvanized sheet, please refer to Table 2, and for the performance indicators of the alloying galvanized sheet, please refer to Table 3.

[0071] Table 1 Chemical composition (wt%) of the substrate of the alloying galvanized sheet, the rest is Fe and inevitable impurities

[0072] Serial number C Si Mn P Alt Nb Ti Example 1 0.003 0.010 0.095 0.010 0.045 0.010 0.021 Example 2 0.003 0.010 0.095 0.010 0.045 0.010 0.021 Example 3 0.003 0.010 0.095 0.010 0.045 0.010 0.021 Example 4 0.002 0.006 0.090 0.008 0.040 0.012 0.019 Example 5 0.002 0.006 0.090 0.008 0.040 0.012 0.019 Comparative example 1 0.003 0.012 0.090 0.010 0.042 0.009 0.020 Comparative example 2 0.003 0.012 0.090 0.010 0.042 0.009 0.020 Comparative example 3 0.003 0.012 0.090 0.010 0.042 0.009 0.020 Comparative example 4 0.002 0.007 0.010 0.008 0.042 0.012 0.020 Comparative example 5 0.002 0.007 0.010 0.008 0.042 0.012 0.020

[0073] Table 2 Preparation process parameters of the alloying galvanized sheet

[0074]

[0075]

[0076] Table 3 Performance indicators of alloyed galvanized sheets

[0077]

[0078]

[0079] *The powdering level here is the result of a 60° V-bend. The higher the level, the more severe the powdering and the poorer the anti-powdering performance of the corresponding coating

[0080] As can be seen from Table 3, in Examples 1 to 5, the Fe content in the coating is 9.5% - 10.0%, the ζ-phase content on the surface is 5% - 10%, the thickness of the Γ-phase layer is 0.6 - 0.8 μm, the roughness is 0.8 - 0.9 μm, the friction coefficient is 0.130 - 0.136, and the powdering level is below grade 3. In Comparative Examples 1 to 5, no high-pressure gas purging section was set, and the heat loss in the soaking section was fast, resulting in unstable temperature control, easy over-alloying or under-alloying. If under-alloyed, it would be classified as a surface defect and cause product downgrading. Therefore, the end temperature of the heating section was high, causing over-alloying and powdering during use. Therefore, compared with Comparative Examples 1 to 5, Examples 1 to 5 have a lower overall Fe content in the coating, stronger anti-powdering performance, and better formability. Exemplarily, Figure 3 is the surface morphology of the coating of an alloyed galvanized sheet provided by an embodiment of the present application; please refer to Figure 3 , indicating that the coating surface is relatively flat, with the δ-phase as the main body and containing a small amount of ζ-phase, which is beneficial to the formability and anti-powdering performance of the coating Figure 4 is the cross-sectional morphology of the coating of an alloyed galvanized sheet provided by an embodiment of the present application; please refer to Figure 4 , indicating that the thickness of the Γ + Γ1-phase layer of the coating is 0.8 μm, and the coating has good anti-powdering performance

[0081] One or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0082] (1) The alloyed hot-dip galvanized IF steel prepared in the embodiments of the present application has excellent anti-powdering performance and formability of the coating, and is very suitable for high-grade automotive panels;

[0083] (2) During the alloyed hot-dip galvanizing process, the temperatures in the heating section and the soaking section are more stable and controllable, so it is easier to obtain a suitable coating phase structure, which is beneficial to improving the overall formability and anti-powdering performance of the coating;

[0084] (3) The formation process of the alloyed coating is more stable, so that the overall coating of the strip steel is more uniform, improving the overall quality of the coating.

[0085] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing an alloyed galvanized sheet, the method comprising: Obtaining a galvanized sheet; Performing a segmented alloying treatment on the galvanized sheet to control the iron content in the coating of the galvanized sheet, thereby obtaining an alloyed galvanized sheet; wherein, the segmented alloying treatment includes an alloying treatment with a heating section, a soaking section with a set temperature, a high-pressure gas purging section, and a cooling section arranged in sequence.

2. The method according to claim 1, wherein The temperature of the high-pressure gas in the high-pressure gas purging section is 300°C to 400°C.

3. The method according to claim 1 or 2, characterized in that, The flow rate of the high-pressure gas in the high-pressure gas purging section is ≥ 300 m 3 / min.

4. The method according to claim 1, wherein The set temperature is 460°C to 480°C.

5. The method according to claim 1, characterized in that The time of the heating section is 1 s to 3 s, and the end temperature of the heating section is 500°C to 530°C.

6. The method according to claim 1, wherein The running speed of the galvanized sheet is 70 m / min to 130 m / min; and / or, The coating weight of the galvanized sheet is 40 g / m 2 ~55 g / m 2 , and the difference between the single-point maximum value and the single-point minimum value of the coating weight along the rolling direction and the transverse direction of the steel plate is <7 g / m 2 .

7. The method according to claim 1, characterized in that, The obtaining of the galvanized sheet includes: Performing hot-dip galvanizing on a substrate to obtain a galvanized sheet; wherein, the process parameters of the hot-dip galvanizing include: the zinc pot temperature is 460°C to 470°C, the zinc liquid temperature in the zinc pot is 455°C to 465°C, and the aluminum weight in the zinc liquid is 0.128% to 0.135%.

8. The method according to claim 1, characterized in that, The method further includes: Skin-passing the alloyed galvanized sheet; wherein, the process parameters of the skin-passing include: the surface roughness of the skin-pass roll is 1.0 μm to 1.2 μm, and the skin-pass elongation is 1.0% to 1.2%.

9. The method according to any one of claims 1 to 8, characterized in that The iron weight in the coating of the alloyed galvanized sheet is 9.0% to 10.0%; The coating phase structure of the alloyed galvanized sheet includes granular δ phase and columnar ζ phase, and the granular δ phase and the columnar ζ phase satisfy the relationship: 5% < [ζ] / ([ζ] + [δ]) < 15%; wherein, [ζ] represents the volume percentage of ζ, and [δ] represents the volume percentage of δ; The maximum thickness of the Γ + Γ1 phase layer in the coating of the alloyed galvanized sheet < 1.0 μm.

10. A high-pressure gas purging device for the high-pressure gas purging section of the method according to any one of claims 1 to 9, the high-pressure gas purging device is composed of a plurality of nozzles arranged closely in the transverse direction, the width of the high-pressure gas purging device is the same as the width of the running channel of the galvanized sheet, and the high-pressure gas purging device faces the upper and lower surfaces of the galvanized sheet and is perpendicular to the surface of the galvanized sheet.

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