A hot-dip galvanizing dual-phase steel and a method for producing the same

Abstract

The application discloses a hot-dip galvanizing dual-phase steel and a preparation method thereof. The hot-dip galvanizing dual-phase steel comprises a dual-phase steel base material and a zinc plating layer plated on the surface of the dual-phase steel base material. The chemical composition of the dual-phase steel base material comprises the following components in percentage by mass: C: 0.06-0.15%, Si: 0.2-0.35%, Mn: 1.6-2.3%, Al: 0.02-0.05%, Cr: 0.1-0.2%, P: less than or equal to 0.015%, S: less than or equal to 0.015%, N: less than or equal to 0.008%, and the balance of Fe and inevitable impurities. The application can effectively reduce the production cost and obtain the hot-dip galvanizing dual-phase steel with stable mechanical properties and good surface quality by optimizing and adjusting the chemical composition and the production method of the dual-phase steel.

Description

Technical Field

[0001] This application relates to the field of iron and steel smelting technology, and more particularly to a hot-dip galvanized duplex steel and its production method. Background Technology

[0002] With the development of lightweight vehicles, users have increasingly higher requirements for corrosion resistance and safety performance, leading to a growing application of advanced high-strength steel in automobiles. Tin-plated duplex steel has become the preferred high-strength steel for automobiles due to its high strength, good corrosion resistance, and good formability.

[0003] Most existing galvanized duplex steels have low Si content and increase product strength by adding precious metal elements such as Nb and Mo. Nb and Mo are highly sensitive to temperature, and the high strength of hot-rolled substrates also poses a great challenge to the performance stability of products after pickling and galvanizing. Summary of the Invention

[0004] This application provides a hot-dip galvanized duplex steel and its production method, aiming to improve the performance stability of galvanized duplex steel products.

[0005] In a first aspect, embodiments of this application provide a hot-dip galvanized duplex steel, comprising a duplex steel substrate and a zinc coating applied to the surface of the duplex steel substrate. The chemical composition of the duplex steel substrate, by mass percentage, comprises: C: 0.06%–0.15%, Si: 0.2%–0.35%, Mn: 1.6%–2.3%, Al: 0.02%–0.05%, Cr: 0.1%–0.2%, P≤0.015%, S≤0.015%, N≤0.008%, with the balance being Fe and unavoidable impurities.

[0006] This application's embodiments, through the rational selection of chemical element composition and content, particularly by rationally controlling the content of C, Si, Mn, and Cr, achieve excellent mechanical properties (such as yield strength, tensile strength, and elongation) and improved product performance stability without adding precious metal elements such as Nb and Mo. Simultaneously, it effectively reduces the cost of hot-dip galvanized duplex steel. Specifically, this application's embodiments reduce the impact of C and Si content on galvanized weldability and surface quality by controlling the C and Si content within a reasonable range; furthermore, by adding a higher content of Mn, the hardenability and performance stability of the galvanized duplex steel are improved, reducing the requirements for post-galvanizing cooling capacity; and the addition of trace amounts of Cr reduces the critical cooling rate of the steel and improves hardenability and strength.

[0007] In some embodiments of this application, the chemical composition of the duplex steel substrate, by mass percentage, includes: C: 0.08%–0.12%, Si: 0.22%–0.3%, Mn: 1.8%–2.1%, Al: 0.02%–0.04%, Cr: 0.3%–0.2%, P≤0.014%, S≤0.014%, N≤0.008%, with the balance being Fe and unavoidable impurities.

[0008] More preferably, the chemical composition of the duplex steel substrate, by mass percentage, includes: C: 0.08%–0.1%, Si: 0.23%–0.38%, Mn: 1.8%–1.95%, Al: 0.02%–0.03%, Cr: 0.17%–0.2%, P≤0.012%, S≤0.012%, N≤0.006%, with the balance being Fe and unavoidable impurities.

[0009] In some embodiments of this application, the hot-dip galvanized duplex steel has a yield strength of 340–440 MPa, a tensile strength of 590–700 MPa, and an elongation of ≥22%.

[0010] According to embodiments of this application, without the need to add precious metal elements such as Nb and Mo, by rationally selecting the chemical element composition and content, especially by rationally controlling the content of C, Si, Mn, and Cr, and by optimizing the production process of hot-dip galvanized duplex steel, the desired crystal phase structure can be achieved, enabling the obtained hot-dip galvanized duplex steel to have excellent mechanical properties, especially a tensile strength of not less than 590 MPa, thereby providing 590 MPa grade low-cost hot-dip galvanized duplex steel.

[0011] Secondly, embodiments of this application provide a method for producing hot-dip galvanized duplex steel, the method comprising:

[0012] A continuously cast billet is provided, wherein the chemical composition of the continuously cast billet, by weight percentage, comprises: C: 0.06%–0.15%, Si: 0.2%–0.35%, Mn: 1.6%–2.3%, Al: 0.02%–0.05%, Cr: 0.1%–0.2%, P≤0.015%, S≤0.015%, N≤0.008%, with the balance being Fe and unavoidable impurities;

[0013] The continuously cast billet is heated and then hot-rolled and coiled. The coiling adopts a U-shaped coiling process, with the head and tail coiling temperature being 590-620℃ and the middle section coiling temperature being 540-580℃, to obtain a hot-rolled steel coil.

[0014] The hot-rolled steel coil is subjected to pickling, cold rolling, annealing, hot-dip galvanizing, and finishing treatment in sequence to obtain hot-dip galvanized duplex steel.

[0015] In some embodiments of this application, the U-shaped curling process specifically involves: the curling temperature of the head 20m and tail 20m being 590–620°C, and the curling temperature of the middle section being 540–580°C.

[0016] According to the embodiments of this application, a higher coiling temperature is beneficial for grain growth and improves formability, but it also leads to severe iron oxide scale on the steel plate surface, increasing the difficulty of pickling and affecting the quality of the steel plate. By adopting a U-shaped coiling process, under reasonable temperature control, the formation of surface iron oxide scale can be reduced while ensuring the strength performance of the steel plate, thus lowering the difficulty of pickling.

[0017] In some embodiments of this application, the temperature at which the continuously cast billet is heated is 1200–1280°C, and the heating time is 150–350 min.

[0018] In some embodiments of this application, the hot rolling includes roughing and finishing rolling performed sequentially, with the final finishing temperature being 880–920°C.

[0019] According to the embodiments of this application, when the hot rolling temperature is too high, the iron oxide scale is severe, pickling is difficult, and thus the surface quality of the steel plate is affected; when the temperature is too low, the material will mix crystals when entering the two-zone rolling, and snowflake defects will be generated during stamping, affecting the galvanized surface quality; the hot rolling final rolling temperature is adopted to roll at an austenitic zone temperature higher than Ar3, which can reduce the generation of iron oxide scale on the steel plate surface and control the generation of snowflakes during the stamping process, thereby improving the surface quality of hot-dip galvanized duplex steel.

[0020] In some embodiments of this application, the pickling temperature is ≥82°C and the acid concentration is ≥100g / L.

[0021] In some embodiments of this application, during the pickling process, when the thickness of the cold-rolled sheet is ≤1.5mm, the pickling speed is ≤220m / min; when the thickness of the cold-rolled sheet is >1.5mm, the pickling speed is ≤180mm / min.

[0022] In some embodiments of this application, the total cold rolling reduction rate is 52% to 70%.

[0023] According to the embodiments of this application, hot-rolled coils inevitably generate iron oxide scale. When the iron oxide scale is controllable, an unreasonable pickling process can lead to incomplete pickling of the surface iron oxide scale, resulting in oxide intrusion and over-pickling. Therefore, the pickling process parameters are controlled within the above range, and at the same time, appropriate cold rolling deformation is used to reduce the rolling difficulty while ensuring the pickling effect.

[0024] In some embodiments of this application, the annealing hot-dip galvanizing includes sequentially preheating, pre-oxidizing, heating, slow cooling, and rapid cooling of the steel coil before galvanizing. The preheating temperature is 560–660°C, the pre-oxidizing temperature is 580–680°C, the heating temperature is 760–780°C, the slow cooling temperature is 680–720°C, the rapid cooling section temperature is 450–470°C, the process speed is ≥60 m / min, and the oxygen content during pre-oxidation is controlled at 0.2%–2.0%.

[0025] According to the embodiments of this application, during the annealing hot-dip galvanizing stage, the external oxidation of alloying elements in the strip steel can be transformed into internal oxidation through pre-oxidation process control, ensuring the surface quality of galvanized products. However, if the oxygen content is too low during the pre-oxidation process, the alloying elements will undergo external oxidation, resulting in incomplete galvanization of the galvanized products. If the oxygen content is too high, over-oxidation will occur, and defects such as pitting will appear on the galvanized products. By reasonably controlling the oxygen content between 0.2% and 2.0%, the occurrence of external oxidation can be avoided as much as possible, thereby improving the surface quality of the products.

[0026] During the annealing and hot-dip galvanizing stage, a reasonable preheating temperature can ensure rapid heating to the two-phase region upon entering the heating section. A suitable heating temperature can ensure the production of a suitable amount of austenite in the annealing furnace. A slow cooling temperature can ensure that a small amount of austenite transforms into ferrite during cooling, which can both ensure the strength of the product and improve the stability of austenite. A rapid cooling temperature can ensure that the material passes through the bainite transformation zone quickly, ensuring that the austenite transforms into martensite after galvanizing.

[0027] In some embodiments of this application, the finishing elongation is 0.3% to 0.5%, and the finishing rolling force is 200t or more.

[0028] According to the embodiments of this application, by reasonably controlling the finishing parameters, the yield plateau of the steel plate can be effectively eliminated, tensile strain mark defects can be avoided during the stamping process, the plate shape can be improved, and the surface quality of galvanized steel can be enhanced.

[0029] In some embodiments of this application, the production method further includes tension straightening, specifically: tension straightening the galvanized steel sheet obtained after finishing, with a tension straightening elongation of 0.05% to 0.15%.

[0030] According to the embodiments of this application, by reasonably controlling the tension leveling process parameters, the plate shape can be effectively adjusted and optimized to avoid edge waviness and center waviness in the material. Attached Figure Description

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

[0032] Figure 1This is a metallographic image of hot-dip galvanized duplex steel provided in one embodiment of this application.

[0033] Figure 2 This is an appearance drawing of hot-dip galvanized duplex steel provided in one embodiment of this application. Detailed Implementation

[0034] The features and exemplary embodiments of various aspects of this application will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a comprehensive understanding of this application. However, it will be apparent to those skilled in the art that this application can be implemented without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of this application by illustrating examples. In the accompanying drawings and the following description, at least some well-known structures and techniques are not shown to avoid unnecessarily obscuring the application; and, for clarity, the dimensions of some structures may be exaggerated. Furthermore, the features, structures, or characteristics described below can be combined in any suitable manner in one or more embodiments.

[0035] 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. In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more. 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 additional identical elements in the process, method, article, or apparatus that includes said element.

[0036] To address the problems existing in the prior art, this application provides a hot-dip galvanized duplex steel and its production method. The hot-dip galvanized duplex steel provided in this application is described below.

[0037] A first aspect of this application provides a hot-dip galvanized duplex steel, comprising a duplex steel substrate and a zinc coating applied to the surface of the duplex steel substrate. The chemical composition of the duplex steel substrate, by mass percentage, includes: C: 0.06%–0.15%, Si: 0.2%–0.35%, Mn: 1.6%–2.3%, Al: 0.02%–0.05%, Cr: 0.1%–0.2%, P≤0.015%, S≤0.015%, N≤0.008%, with the balance being Fe and unavoidable impurities.

[0038] According to this application, galvanized duplex steel includes a duplex steel substrate and a galvanized layer coated on the surface of the duplex steel substrate. By optimizing the chemical composition of the duplex steel substrate, the performance stability of galvanized duplex steel is improved and its cost is reduced. The main chemical components of the duplex steel in this application are described in detail below.

[0039] The carbon content is controlled within the range of 0.06% to 0.15%. Carbon is an economical strengthening element in steel and a crucial component of duplex steel. The carbon content determines the strength, plasticity, and formability of the steel plate. Too low a carbon content reduces the stability of austenite and the hardenability of martensite; too high a carbon content reduces the plasticity and weldability of the duplex steel. The carbon content in this application is higher than that in existing technologies, which can reduce the addition of expensive alloying elements and lower costs while ensuring the strength of galvanized duplex steel.

[0040] In some embodiments, the C element content is further controlled at 0.08% to 0.12%, more preferably 0.08% to 0.1%.

[0041] The silicon (Si) content is controlled between 0.2% and 0.35%. Silicon can dissolve in ferrite and austenite to improve the strength of materials, and the strength increases with increasing silicon content. However, high silicon content can easily generate iron oxide scale that is difficult to pickle, which can also cause incomplete galvanizing after galvanizing and affect the surface quality of the steel plate. Controlling the Si content between 0.2% and 0.35% can improve the strength of the steel strip while controlling the formation of iron oxide scale, reducing the occurrence of incomplete galvanizing during the galvanizing process, and improving the surface quality of galvanized duplex steel.

[0042] In some embodiments, the content of Si element is further controlled at 0.22% to 0.3%, more preferably 0.23% to 0.28%.

[0043] The manganese (Mn) content is controlled between 1.6% and 2.3%. Manganese is a commonly used solid solution strengthening element in steel. Dual-phase steel typically contains at least 1.2% manganese to improve hardenability and ensure strength. Adding a certain amount of manganese allows it to combine with sulfur to form MnS, preventing hot brittleness and improving the steel's hot workability. Manganese also enhances austenite stability, shifting the C-curve to the right and reducing the critical cooling rate. However, excessive manganese content can lead to the formation of oxides that are difficult to pickle during hot rolling, and external oxidation during galvanizing annealing, resulting in large amounts of oxides and, in severe cases, incomplete galvanizing.

[0044] In some embodiments, the Mn content is further controlled at 1.8% to 2.1%, more preferably 1.8% to 1.95%.

[0045] The Cr content is controlled at 0.1% to 0.2%. Chromium can significantly delay the transformation of pearlite and bainite, thereby transforming austenite into martensite. Furthermore, chromium has a significant cost advantage over molybdenum and niobium, which can significantly reduce costs.

[0046] In some embodiments, the Cr content is further controlled at 0.13% to 0.2%, more preferably 0.17% to 0.2%.

[0047] The content of Al is controlled at 0.02% to 0.05%. Aluminum is added as a deoxidizer and can also form AlN pinned grain boundaries, which can refine the grains.

[0048] In some embodiments, the content of Al element is further controlled at 0.02% to 0.04%, more preferably 0.02% to 0.03%.

[0049] In some embodiments of this application, the yield strength of the galvanized duplex steel is 340-440 MPa, the tensile strength is 590-700 MPa, and the elongation is ≥22%.

[0050] In some embodiments of this application, the hot-dip galvanized duplex steel is a sheet material with a thickness of 0.7 to 2.3 mm.

[0051] An embodiment of the second aspect of this application provides a method for producing hot-dip galvanized duplex steel, comprising the following steps:

[0052] S10. Provide a continuously cast billet, wherein the chemical composition of the continuously cast billet by weight percentage includes: C: 0.06%~0.15%, Si: 0.2%~0.35%, Mn: 1.6%~2.3%, Al: 0.02%~0.05%, Cr: 0.1%~0.2%, P≤0.015%, S≤0.015%, N≤0.008%, with the balance being Fe and unavoidable impurities;

[0053] S20. After heating the continuously cast billet, it is hot rolled and coiled in sequence. The coiling adopts a U-shaped coiling process. The coiling temperature of the head and tail is 590-620℃, and the coiling temperature of the middle section is 540-580℃, to obtain hot-rolled steel coil.

[0054] S30. Hot-rolled steel coils are sequentially pickled, cold-rolled, annealed, hot-dip galvanized, and finished to obtain hot-dip galvanized duplex steel.

[0055] It should be noted that the continuously cast billets used in this application are produced according to existing technology. That is, the steelmaking processes before hot rolling are all based on existing technology, which involves batching, converter smelting, refining, and continuous casting according to the chemical composition design requirements of the steel grade in this application. Continuously cast billets can be produced by pouring molten steel into a mold for shaping.

[0056] In some embodiments of this application, the U-shaped coiling process specifically involves: coiling temperatures of 590–620°C for the head and tail 20m sections, and 540–580°C for the middle section. Higher coiling temperatures promote grain growth, reduce strength, and improve formability. However, annealing can lead to severe iron oxide scale buildup on the steel plate surface, making pickling difficult and affecting the steel plate quality. The U-shaped coiling process ensures stable performance throughout the coiling process, reduces the formation of surface iron oxide scale and the difficulty of pickling, and improves the surface quality of the galvanized product.

[0057] In some embodiments of this application, the temperature for heating the continuously cast billet is 1200–1280°C, and the heating time is 150–350 min.

[0058] In some embodiments of this application, hot rolling includes sequential roughing and finishing rolling, with the final finishing temperature being 880–920°C. The final finishing temperature is set at an austenitic temperature higher than that of Ar3. Excessive temperature results in severe iron oxide scale buildup, making pickling difficult and affecting the surface quality of the steel plate. Conversely, excessively low temperature during two-zone rolling can lead to mixed crystal formation in the material, causing snowflake-like defects during stamping and affecting the galvanized surface quality. Therefore, the final finishing temperature needs to be controlled between 880 and 920°C.

[0059] In some embodiments of this application, the pickling temperature is ≥82℃, and the acid concentration is ≥100g / L; when the cold-rolled sheet thickness is ≤1.5mm, the pickling speed is ≤220m / min; when the cold-rolled sheet thickness is >1.5mm, the pickling speed is ≤180mm / min. Hot-rolled coils inevitably generate iron oxide scale. Even when the iron oxide scale is controllable, the pickling process can lead to incomplete removal of the surface iron oxide scale, causing oxide intrusion and over-pickling. Therefore, controlling the pickling process requires controlling the pickling temperature to ≥82℃, the acid concentration to ≥100g / L, the pickling speed to ≤220m / min when the cold-rolled sheet thickness is ≤1.5mm, and the pickling speed to ≤180mm / min when the cold-rolled sheet thickness is >1.5mm. The acid solution is an aqueous solution of hydrochloric acid.

[0060] In some embodiments of this application, the total cold rolling reduction rate is 52% to 70%. The pickled steel sheet is cold rolled and coiled to obtain a cold-rolled coil. A larger amount of cold rolling deformation can reduce the recrystallization temperature and phase transformation temperature, but excessive deformation will increase the rolling difficulty. Therefore, the amount of cold rolling deformation needs to be controlled between 52% and 70%.

[0061] In some embodiments of this application, annealed hot-dip galvanizing includes preheating, pre-oxidizing, heating, slow cooling, and rapid cooling of the steel coil before galvanizing. The preheating temperature is 560–660°C, the pre-oxidizing temperature is 580–680°C, the heating temperature is 760–780°C, the slow cooling temperature is 680–720°C, the rapid cooling section temperature is 450–470°C, the process speed is ≥60 m / min, and the oxygen content during pre-oxidation is controlled at 0.2%–2.0%.

[0062] At this preheating temperature, the material can be rapidly heated to the two-phase region upon entering the heating section. A suitable heating temperature ensures the formation of an appropriate amount of austenite in the annealing furnace. The slow cooling temperature ensures that a small amount of austenite transforms into ferrite during cooling, which not only ensures the strength of the product but also improves the stability of the austenite. The rapid cooling temperature ensures that the material passes through the bainite transformation zone quickly, causing the austenite to transform into martensite after galvanizing. Therefore, it is necessary to control the preheating temperature to 560–660℃, the pre-oxidation temperature to 580–680℃, the heating temperature to 760–780℃, the slow cooling temperature to 680–720℃, the rapid cooling section temperature to 450–470℃, and the process speed to ≥60m / min. By controlling the pre-oxidation process, the external oxidation of alloying elements in the strip steel can be transformed into internal oxidation, thereby improving the surface quality of galvanized products. If the oxygen content is too low during the pre-oxidation process, the alloying elements will undergo external oxidation, resulting in incomplete galvanization of the galvanized products. If the oxygen content is too high, over-oxidation will occur, resulting in pitting on the galvanized products. Therefore, the oxygen content needs to be controlled between 0.2% and 2.0% during the pre-oxidation process.

[0063] In some embodiments of this application, the finishing elongation is 0.3% to 0.5%, and the finishing rolling force is above 200t. The purpose of finishing is to eliminate the yield plateau of the steel plate, avoid tensile strain mark defects during stamping, improve the plate shape, and enhance the surface quality of galvanization. Therefore, the finishing elongation needs to be controlled between 0.3% and 0.5%.

[0064] In some embodiments of this application, the production method of hot-dip galvanized duplex steel further includes tension straightening, specifically: the galvanized steel sheet obtained after finishing is tension straightened, with a tension straightening elongation of 0.05% to 0.15%. The purpose of tension straightening is to adjust and optimize the sheet shape, avoiding edge waviness and center waviness in the material. If the tension straightening elongation is too low, the sheet shape is poor; if the tension straightening elongation is too high, tension straightening marks are likely to appear. Therefore, the tension straightening elongation is controlled between 0.05% and 0.15%.

[0065] The following specific embodiments illustrate the present invention. It should be noted that the embodiments are only used to further illustrate the present invention and do not limit the scope of protection of the present invention. Non-essential modifications and adjustments made by others based on the present invention are still within the scope of protection of the present invention.

[0066] Examples 1-6

[0067] Based on the chemical composition of duplex steel shown in Table 1, hot-dip galvanized duplex steel was prepared according to the following method:

[0068] S10. Provide a continuously cast billet containing the chemical composition shown in Table 1;

[0069] S20. The 230mm thick continuous casting billet is heated in a heating furnace. The process parameters for the heating process are shown in Table 2.

[0070] S30. The heated continuous casting billet is hot rolled. Hot rolling includes rough rolling and finish rolling in sequence. Rough rolling includes rolling the heated continuous casting billet in 7 passes to obtain an intermediate billet with a thickness of 40 mm. Finish rolling includes rolling the intermediate billet in 7 passes and then using a U-shaped coiling process to coil it into a hot-rolled steel coil. The process parameters for hot rolling and coiling are shown in Table 2.

[0071] S40. After the hot-rolled steel coil is dephosphorized by tension leveling, it is pickled with hydrochloric acid. After pickling, it is cold-rolled in 5 stands to obtain a cold-hardened coil. The process parameters of pickling and cold rolling are shown in Table 3.

[0072] S50. The cold-hardened coil is annealed and hot-dip galvanized. The annealing and hot-dip galvanizing process includes preheating, pre-oxidation, heating, slow cooling and rapid cooling in sequence. After galvanizing in a zinc pot, it is smoothed and straightened. Finally, it is coiled and slit at the exit to obtain hot-dip galvanized steel coil. The process parameters of the annealing, hot-dip galvanizing, smoothing and straightening process are shown in Table 4.

[0073] Table 1:

[0074]

[0075] Table 2:

[0076]

[0077]

[0078] Table 3:

[0079] Cold rolling reduction rate / % Acid temperature / ℃ Acid concentration / g / L Pickling speed / m / min Example 1 70 82 140 220 Example 2 66 83 144 220 Example 3 57 83 157 215 Example 4 54 82 156 180 Example 5 53 82 167 174 Example 6 52 83 170 157

[0080] Table 4:

[0081]

[0082] The yield strength, tensile strength and elongation after fracture of the hot-dip galvanized duplex steels prepared in Examples 1-6 were tested according to GB / T 228.1-2021, and the results are shown in Table 5.

[0083] Table 5:

[0084]

[0085]

[0086] Combination Figure 1 In this embodiment, the microstructure of the hot-dip galvanized duplex steel is ferrite + martensite, with a uniform structure. Based on the data in Table 1, this embodiment adjusts the content of each component in the hot-dip galvanized duplex steel by adding low-cost metal elements such as Si and Mn, and trace amounts of Cr. This ensures good product performance while reducing the need for expensive elements such as Nb and Mo. Furthermore, the use of a U-shaped coiling process ensures stable performance throughout the coiling process, reduces the formation of surface oxide scale and the difficulty of pickling, and improves the surface quality of the galvanized product.

[0087] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A hot-dip galvanized duplex steel, characterized in that, It includes a duplex steel substrate and a zinc plating layer coated on the surface of the duplex steel substrate, wherein the chemical composition of the duplex steel substrate, by mass percentage, includes: C: 0.06%~0.15%, Si: 0.2%~0.35%, Mn: 1.6%~2.3%, Al: 0.02%~0.05%, Cr: 0.1%~0.2%, P≤0.015%, S≤0.015%, N≤0.008%, with the balance being Fe and unavoidable impurities; the microstructure of the hot-dip galvanized duplex steel is ferrite + martensite; The production method of the hot-dip galvanized duplex steel includes the following steps: Continuous casting billets are provided according to the above chemical composition; The continuously cast billet is heated and then hot-rolled and coiled in sequence. The coiling adopts a U-shaped coiling process, with the head and tail coiling temperature being 590~620℃ and the middle section coiling temperature being 540~580℃, to obtain hot-rolled steel coils. The hot-rolled steel coil is sequentially pickled, cold-rolled, annealed, hot-dip galvanized, and finished to obtain hot-dip galvanized duplex steel. The annealed hot-dip galvanizing process includes sequentially preheating, pre-oxidizing, heating, slow cooling, and rapid cooling of the steel coil before galvanizing. The preheating temperature is 560~660℃, the pre-oxidizing temperature is 580~680℃, the heating temperature is 760~780℃, the slow cooling temperature is 680~720℃, the rapid cooling section temperature is 450~470℃, the process speed is ≥60m / min, and the oxygen content is controlled at 0.2%~2.0% during pre-oxidation.

2. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The hot-dip galvanized duplex steel has a yield strength of 340~440MPa, a tensile strength of 590~700MPa, and an elongation of ≥22%.

3. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The U-shaped curling process specifically involves curling the head 20m and tail 20m at temperatures of 590~620℃, and the middle section at temperatures of 540~580℃.

4. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The continuous casting billet is heated at a temperature of 1200~1280℃ for a heating time of 150~350min.

5. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The hot rolling process includes roughing and finishing rolling performed sequentially, with the final finishing temperature being 880~920℃.

6. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The pickling temperature is ≥82℃, the acid concentration is ≥100g / L, and the pickling speed is ≤220m / min when the cold-rolled plate thickness is ≤1.5mm; the pickling speed is ≤180mm / min when the cold-rolled plate thickness is >1.5mm.

7. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The total cold rolling reduction rate is 52% to 70%.

8. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The finishing elongation is 0.3%~0.5%, and the finishing rolling force is above 200t.

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