590mpa grade hot dip galvanized dual phase steel and method of producing the same

Abstract

The present application belongs to the technical field of metallurgy, and particularly relates to a 590MPa grade hot-dip galvanizing dual-phase steel and a production method thereof. The chemical components of the steel are as follows in percentage by mass: C: 0.02%-0.06%, Si: 0.01%-0.03%, Mn: 0.90%-1.8%, P: 0.025% or less, S: 0.010% or less, Al: 0.005%-0.010%, Cr: 0.05%-0.30%, Mo: 0.05%-0.30%, O: 0.0060% or less, N: 0.010%-0.020%, and the rest is Fe and inevitable impurities. The present application has the advantages that: the component design of the present application adopts low-carbon-silicon-aluminum and high-nitrogen for synergistic regulation, and in the hot-rolling process, the premature precipitation of AlN particles in the hot-rolling process is effectively inhibited by controlling a lower coiling temperature, so that the nitrogen element is retained in a large amount in the hot-rolled plate in a solid solution state.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a 590MPa grade hot-dip galvanized duplex steel and its production method. Background Technology

[0002] Duplex steel, due to its advantages such as low yield strength, high initial work hardening rate, and good strength-ductility matching, is widely used in the automotive industry to achieve lightweighting and improve safety. Hot-dip galvanizing is an effective means to improve the corrosion resistance of steel. 590MPa grade hot-dip galvanized duplex steel is a typical grade of high-strength steel for automobiles. However, traditional duplex steel often adds a certain amount of silicon to ensure the austenite volume fraction. Silicon is prone to selective oxidation during continuous annealing, which severely deteriorates the wettability of the steel sheet for galvanizing, leading to poor coating adhesion, incomplete galvanizing, and other surface defects. To solve this problem, some existing technologies use methods such as reducing silicon content and adding other alloying elements, but it is often difficult to ensure both mechanical properties and excellent galvanized surface quality. Especially at the relatively low annealing temperature of the hot-dip galvanizing process, ensuring sufficient stability and volume fraction of austenite to ultimately obtain the target martensite content is a technical challenge in the production of high-performance hot-dip galvanized duplex steel.

[0003] In the prior art, patent application number CN202510248355.0 discloses a 590MPa grade hot-dip galvanized duplex steel, its preparation method, and its application. The chemical composition of the hot-dip galvanized duplex steel, by mass percentage, is: C: 0.07–0.09%, Si: 0.20–0.30%, Mn: 1.5–1.7%, Al: 0.02–0.05%, Cr: 0.30–0.40%, Nb: 0.015–0.025%, Ti: 0.015–0.025%, P≤0.015%, S≤0.015%, N≤0.008%, with the remainder being Fe and unavoidable impurities. Adding a high Si content is not conducive to obtaining good surface quality. Furthermore, using a higher galvanizing annealing temperature increases the austenite transformation amount during heating, and controlling the austenite transformation mode and amount during cooling increases the difficulty of control, easily leading to unstable mechanical properties.

[0004] Patent application number CN202411603977.2 discloses a low-cost 590MPa grade hot-dip galvanized duplex steel and its preparation method. The chemical composition, by mass percentage, includes: C: 0.06%–0.10%, Si: 0.30%–0.55%, Mn: 1.70%–2.00%, P≤0.018%, S≤0.007%, Als: 0.015%–0.070%, Cr: 0.15%–0.40%, N≤0.0055%, with the remainder being Fe and unavoidable impurities. In the hot-dip galvanizing process, the cold-rolled strip steel needs to be slowly cooled to 680℃–712℃. The high Si content in this duplex steel is detrimental to obtaining good surface quality, and controlling the austenite content before rapid cooling through slow cooling increases the difficulty of control and can easily lead to unstable mechanical properties.

[0005] Patent application CN202110283353.7 discloses a production method for 590MPa grade reinforced formable hot-dip galvanized duplex steel. The chemical composition, by mass fraction, is: C: 0.14–0.16%; Si: 0.08–0.13%; Mn: 1.7–1.9%; P: ≤0.012%; S: ≤0.065%; Al: 0.7–0.9%; Ti: 0.01–0.02%; N: ≤0.005%, with the remainder being Fe and unavoidable impurities. The slow cooling exit temperature during annealing is 690–710℃. The high C content in this duplex steel affects weldability, and the high Al content necessitates the use of high-alumina steel protective slag during continuous casting, increasing smelting difficulty and cost. Furthermore, controlling the austenite content before rapid cooling through slow cooling increases the difficulty of control and can easily lead to unstable mechanical properties. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a 590MPa grade hot-dip galvanized duplex steel and its production method that combines high strength, excellent galvanized surface quality, and good toughness. It adopts a "low carbon-low silicon-high nitrogen" composition design, combined with hot rolling and annealing processes, to ensure that the high strength of 590MPa is achieved while fundamentally avoiding galvanizing defects (such as incomplete galvanizing and poor adhesion) caused by surface oxidation of elements such as silicon and manganese, thus obtaining excellent galvanized surface quality.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A 590MPa grade hot-dip galvanized duplex steel, wherein the chemical composition of the steel, by mass percentage, is:

[0009] C: 0.02%~0.06%, Si: 0.01%~0.03%, Mn: 0.90%~1.8%, P≤0.025%, S≤0.010%, Al: 0.005%~0.010%, Cr: 0.05%~0.30%, Mo: 0.05%~0.30%, O≤0.0060%, N: 0.010%~0.020%, with the remainder being Fe and unavoidable impurities.

[0010] The metallographic structure of the steel includes ferrite, martensite and Mao islands, wherein the area fraction of ferrite is 79-85%, the area fraction of martensite is 12-16%, and the area fraction of Mao islands is 3-5%.

[0011] The steel has a yield strength of 360–400 MPa, a tensile strength of 620–675 MPa, and an elongation A. 80 The percentage is 27.0%–30.0%, the n value is 0.17–0.22, and the porosity is 55%–75%.

[0012] Considering production costs and overall performance, the chemical composition and main functions of the steel described in this invention are as follows:

[0013] C: Carbon (C) is a key austenite stabilizing element. It enhances strength through interstitial solid solution strengthening and works synergistically with nitrogen to ensure sufficient austenite formation during continuous annealing, which then transforms into martensite upon cooling. However, excessive C content can deteriorate weldability, toughness, and plasticity, and may promote carbide precipitation, affecting galvanizing quality. Therefore, this invention controls the C content to 0.02–0.06% to maintain good weldability and toughness while ensuring strength, and simultaneously optimizes austenite stability in conjunction with nitrogen.

[0014] Si: Si is commonly used for solid solution strengthening and inhibiting carbide precipitation. However, as a surface-active element, it easily accumulates on the surface during annealing, forming a SiO2 film that severely deteriorates zinc plating wettability and leads to plating defects. This invention uses an ultra-low Si content (0.01–0.03%) to fundamentally avoid surface oxidation problems. Furthermore, it works synergistically with nitrogen and aluminum to reduce Si segregation through AlN precipitation, thereby improving coating quality.

[0015] Mn: Mn is a major austenite stabilizing element that improves the hardenability of steel, promotes martensite formation, and thus enhances strength. However, Mn is prone to internal oxidation in the atmosphere of hot-dip galvanizing annealing furnaces, forming surface oxides that damage the coating adhesion. This invention controls the Mn content to be between 0.90% and 1.8%, and inhibits Mn surface segregation and oxidation by adding nitrogen to form Mn-N clusters or nitrides, thereby optimizing galvanizing performance while ensuring sufficient martensite volume fraction.

[0016] P: While phosphorus (P) provides some solid solution strengthening, it tends to segregate at grain boundaries, leading to decreased cold brittleness and toughness, and potentially affecting the surface quality of galvanized steel. Therefore, this invention strictly limits the P content to ≤0.025% to minimize its negative impact and ensure the toughness and formability of the steel.

[0017] S: S is a common impurity element that easily forms sulfide inclusions (such as MnS), which deteriorates the toughness, formability, and fatigue properties of steel, and affects the uniformity of the coating. This invention controls the S content to ≤0.010% to reduce the content of inclusions and ensure high purity and good coating adhesion.

[0018] Al: Al is mainly used for deoxidation and combines with nitrogen to form fine AlN particles, which precipitate during continuous annealing, pinning grain boundaries and refining grains. Simultaneously, it inhibits the surface segregation of Si and Mn, improving galvanizing performance. This invention controls the Al content to 0.005–0.010% to limit premature AlN precipitation during hot rolling, allowing nitrogen to function more effectively during annealing, thereby optimizing the microstructure, refining the austenite, and stabilizing the austenite.

[0019] Cr: Cr is an austenite stabilizing element that improves hardenability, inhibits the transformation of ferrite and pearlite, promotes martensite formation, and enhances corrosion resistance. This invention controls the Cr content to be between 0.05% and 0.30%, working synergistically with Mo to ensure stable austenite is obtained under hot-dip galvanizing cooling conditions, thereby improving strength and microstructure uniformity.

[0020] Mo: Mo is a strong carbide-forming element. In this invention, it mainly acts as an austenite stabilizing element, improving hardenability, delaying the transformation of bainite and proeutectoid ferrite, and ensuring that austenite directly transforms into martensite during cooling. This invention controls the Mo content to be between 0.05% and 0.30%, working synergistically with Cr and nitrogen to optimize the phase transformation path and ensure the strength and work hardening ability of the duplex steel.

[0021] O: O is an impurity element that easily forms oxide inclusions, reducing the toughness, fatigue performance, and surface quality of steel, and affecting the coating quality. This invention controls the O content to ≤0.0060% to minimize the impact of inclusions and ensure high purity and good zinc plating surface quality.

[0022] Nitrogen (N) is a core austenite stabilizing element. Through interstitial solid solution and synergy with carbon, it significantly reduces nitrogen (M). sThis invention improves the hardenability of austenite, ensuring sufficient martensite formation under low carbon and limited cooling rates. Simultaneously, N reacts with Al to form AlN particles, refining the grain size and suppressing surface segregation of Si and Mn, fundamentally improving galvanizing performance. Furthermore, N optimizes the phase transformation sequence, suppressing the transformation of proeutectoid ferrite and bainite, allowing austenite to directly transform into martensite, and enhancing martensite hardness through solid solution strengthening. The present invention controls the N content to be between 0.010% and 0.020% to fully utilize these effects while avoiding brittleness caused by excessive N.

[0023] A method for producing 590MPa grade hot-dip galvanized duplex steel includes the following steps: molten iron pretreatment, converter smelting, LF refining, continuous casting, slab heating, hot continuous rolling, laminar flow cooling and coiling, pickling and cold rolling, continuous annealing and hot-dip galvanizing, and finishing, wherein:

[0024] The aforementioned molten iron pretreatment involves using desulfurization powder and magnesium powder to desulfurize the molten iron to S≤0.015%, with slag thickness≤20mm and molten iron outlet temperature of 1240~1450℃;

[0025] The converter smelting process involves first adding refined scrap steel to an oxygen top and bottom blowing converter, then adding molten iron, with a tapping temperature of 1630–1670°C.

[0026] The LF refining process is as follows: slag thickness 50-100mm, net clearance 250-700mm, processing time ≥30min, and final oxygen content 300-600ppm.

[0027] The continuous casting process involves maintaining a constant casting speed, ranging from 1.0 to 1.6 m / min, and using light reduction, with a reduction amount of 3 to 8 mm.

[0028] Slab heating: The slab is heated in a walking beam furnace with an inlet temperature of 200-550℃ and an outlet temperature of 1200-1250℃, and the furnace time is 1-3 hours.

[0029] Hot continuous rolling: roughing rolling temperature ≥1050℃, finishing rolling temperature 880~920℃;

[0030] Laminar flow cooling and coiling: After final rolling, the hot-rolled steel strip is cooled to 550-600℃ at a laminar flow cooling rate of ≥60℃ / s, and then air-cooled to 500-550℃ for 3-6s before coiling.

[0031] Pickling and cold rolling: The hot-rolled steel strip is pickled to remove iron oxide scale, and then cold rolled with a reduction rate of 50% to 70%.

[0032] Continuous annealing and hot-dip galvanizing:

[0033] The preheating section heats the strip steel to 130-200℃ at a preheating rate of 2-6℃ / s.

[0034] The heating section heats the strip steel to 790–810℃ at a rate of 2–10℃ / s.

[0035] The soaking zone holds the strip at 790–810℃ for 60–150 seconds.

[0036] The slow cooling section cools the strip steel to 600-720℃, with a slow cooling rate of 1-15℃ / s;

[0037] The rapid cooling section cools the strip steel to 455-465℃, with a rapid cooling rate of 15-60℃ / s.

[0038] The equalization section holds the strip steel at 455–465℃ for 30–150 seconds.

[0039] The temperature of the zinc bath is 455-465℃, and the galvanizing time is 2-5 seconds;

[0040] Finishing:

[0041] The strip steel produced by continuous annealing and hot-dip galvanizing is finished with a finishing elongation of 0.6 to 1.8%.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] 1. This invention achieves fine-grain strengthening and enhances austenite stability by controlling the solid solution of nitrogen during hot rolling and the precipitation and interphase distribution of AlN during annealing, thus stably obtaining a sufficient amount of martensite and ensuring stable mechanical properties. Simultaneously, by regulating the distribution of nitrogen in martensite and ferrite, the material maintains continuous yield characteristics and possesses excellent coating and baking performance.

[0044] 2. In terms of composition design, this invention employs a synergistic regulation of low carbon, silicon, aluminum, and high nitrogen. During the hot rolling process, by controlling a lower coiling temperature, premature precipitation of AlN particles is effectively suppressed, allowing nitrogen to be retained in a large quantity in a solid solution state within the hot-rolled plate. On one hand, this significantly enhances the stability of austenite in the subsequent continuous annealing process, substantially reducing the martensite transformation temperature. Thus, even with low carbon content and limited cooling capacity in industrial production lines, a sufficient volume fraction of martensite can still be obtained after continuous annealing. On the other hand, compared to carbon, nitrogen, as an austenite stabilizer, has a smaller effect on raising the precipitation temperature of proeutectoid ferrite. Optimizing the phase transformation window before hot-dip galvanizing helps suppress the precipitation of proeutectoid ferrite, thereby laying the foundation for obtaining stable mechanical properties.

[0045] 3. During the heating and homogenization stages of continuous annealing, the dissolved nitrogen retained from the hot rolling stage undergoes dynamic precipitation with aluminum. The fine AlN particles effectively refine the austenite and subsequent ferrite / martensite grains by pinning grain boundaries, achieving grain refinement and improving material toughness. Furthermore, this pinning effect slows down the transformation kinetics from austenite to ferrite. Simultaneously, the dissolved nitrogen atoms themselves hinder cementite nucleation and growth, promoting more abundant carbon atom enrichment within the austenite. These two factors work synergistically to enhance the stability of austenite during the annealing cooling process, ensuring its complete transformation into martensite.

[0046] 4. During the final stage of annealing and subsequent cooling, nitrogen undergoes interphase distribution. Due to its strong solid solution strengthening tendency, it preferentially accumulates in the martensite phase that is about to transform, while the nitrogen content in the ferrite matrix is ​​extremely low. On the one hand, the low nitrogen content in the ferrite phase avoids the significant age hardening effect caused by nitrogen atoms, ensuring that the material can maintain continuous yield characteristics during subsequent coating and baking processes. On the other hand, the nitrogen enriched in the austenite / martensite phase plays a strong synergistic stabilizing role with carbon, which can obtain sufficient and highly stable austenite at a relatively low annealing temperature.

[0047] 5. This invention employs a low-silicon design to eliminate non-wetting oxides formed by silicon surface enrichment and oxidation at the source, thus avoiding galvanizing defects. Simultaneously, the added nitrogen interacts with manganese in the steel to form stable Mn-N clusters. This effectively inhibits the segregation and oxidation of manganese atoms on the steel strip surface during annealing, preventing the formation of surface oxides. The composition design, through the synergistic effect of nitrogen and manganese combined with the low-silicon design, ensures excellent hot-dip galvanized surface quality. Attached Figure Description

[0048] Figure 1 This is a metallographic diagram of Example 1. Detailed Implementation

[0049] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0050] Example:

[0051] The 590MPa grade hot-dip galvanized duplex steel, in this embodiment, has a microstructure comprising ferrite, martensite, and Mao islands, wherein the ferrite area fraction is 79-85%, the martensite area fraction is 12-16%, and the Mao island area fraction is 3-5%. The duplex steel in this embodiment has a yield strength of 360-400MPa, a tensile strength of 620-675MPa, and an elongation A... 80The content of ferrite was 27.0%–30.0%, the n value was 0.17–0.22, and the porosity was 55%–75%. In Example 1, the metallographic structure consisted of 82% ferrite + 14% martensite + 4% Mao islands. (See...) Figure 1 .

[0052] 590MPa grade hot-dip galvanized duplex steel and its production method, including molten iron pretreatment, converter smelting, LF refining, continuous casting, slab heating, hot continuous rolling, laminar flow cooling and coiling, pickling and cold rolling, continuous annealing and hot-dip galvanizing, and finishing.

[0053] The hot metal pretreatment parameters for each embodiment are shown in Table 1, the converter smelting parameters, LF refining parameters and continuous casting parameters are shown in Table 2, the chemical composition is shown in Table 3, the slab heating parameters, hot rolling parameters, laminar cooling and coiling parameters are shown in Table 4, the pickling and cold rolling parameters and continuous annealing parameters are shown in Table 5, the hot-dip galvanizing parameters and finishing parameters are shown in Table 6, and the metallographic structure test results of the finished steel plates for each embodiment are shown in Table 8.

[0054] Table 1. Pretreatment parameters of molten iron for each embodiment.

[0055]

[0056] Table 2 shows the converter smelting parameters, LF refining parameters, and continuous casting parameters for each embodiment.

[0057]

[0058] Table 3 Chemical composition (wt%) of each example.

[0059]

[0060] Table 4 shows the slab heating parameters, hot rolling parameters, laminar cooling and coiling parameters for each embodiment.

[0061]

[0062] Table 5 shows the pickling and cold rolling parameters and continuous annealing parameters for each embodiment.

[0063]

[0064] Table 6 shows the hot-dip galvanizing parameters and finishing parameters for each embodiment.

[0065]

[0066] Table 7 shows the test results of the mechanical properties of the finished steel plates in each embodiment.

[0067]

[0068] Table 8 shows the metallographic structure test results of the finished steel plates in each embodiment.

[0069]

[0070] This 590MPa grade hot-dip galvanized duplex steel, through a low-carbon, silicon-aluminum, and high-nitrogen composition design, combined with a hot-rolling low-temperature coiling process, lays the microstructural foundation for achieving high strength. This design effectively suppresses premature AlN precipitation during hot rolling, allowing nitrogen to remain in a solid solution state. During subsequent continuous annealing, the dissolved nitrogen and aluminum dynamically precipitate fine AlN particles, which not only pin grain boundaries and refine grains but also work synergistically with dissolved nitrogen atoms to enhance austenite stability, ensuring a sufficient amount of martensite.

[0071] During the annealing cooling process, nitrogen undergoes interphase distribution, preferentially enriching in the martensite phase, and synergistically exerts a strong stabilizing effect with carbon, enabling the formation of highly stable austenite at a relatively low annealing temperature; while the extremely low nitrogen content in the ferrite matrix avoids age hardening, ensuring that the material maintains continuous yield characteristics after baking.

[0072] Furthermore, the ultra-low silicon design fundamentally eliminates zinc plating defects caused by silicon surface oxidation, while nitrogen and manganese form Mn-N clusters, effectively inhibiting manganese surface segregation and oxidation. This synergistic design of composition and process ensures both high strength and excellent hot-dip galvanized surface quality.

Claims

1. A 590MPa grade hot-dip galvanized duplex steel, characterized in that, The chemical composition of the steel, expressed as a percentage by mass, is as follows: C: 0.02%~0.06%, Si: 0.01%~0.03%, Mn: 0.90%~1.8%, P≤0.025%, S≤0.010%, Al: 0.005%~0.010%, Cr: 0.05%~0.30%, Mo: 0.05%~0.30%, O≤0.0060%, N: 0.012%~0.020%, with the remainder being Fe and unavoidable impurities; The metallographic structure of the steel includes ferrite, martensite, and Mao islands, wherein the ferrite area fraction is 79-85%, the martensite area fraction is 12-16%, and the Mao island area fraction is 3-5%. The production method of the 590MPa grade hot-dip galvanized duplex steel includes the following steps: molten iron pretreatment, converter smelting, LF refining, continuous casting, slab heating, hot continuous rolling, laminar flow cooling and coiling, pickling and cold rolling, continuous annealing and hot-dip galvanizing, and finishing, wherein: Continuous casting: During the steel casting process, maintain a constant casting speed, ranging from 1.0 to 1.6 m / min, and use light reduction, with a reduction amount of 3 to 8 mm; Slab heating: The slab is heated in a walking beam furnace with an inlet temperature of 200-550℃ and an outlet temperature of 1200-1250℃, and the furnace time is 1-3 hours. Hot continuous rolling: roughing rolling temperature ≥1050℃, finishing rolling temperature 880~920℃; Laminar flow cooling and coiling: After final rolling, the hot-rolled steel strip is cooled to 550-600℃ at a laminar flow cooling rate of ≥64℃ / s, and then air-cooled to 500-550℃ for 3-6s before coiling. Pickling and cold rolling: The hot-rolled steel strip is pickled to remove iron oxide scale, and then cold rolled with a reduction rate of 50% to 70%. Continuous annealing and hot-dip galvanizing: The preheating section heats the strip steel to 130-200℃ at a preheating rate of 2-6℃ / s. The heating section heats the strip steel to 790–810℃ at a rate of 2–10℃ / s. The soaking zone holds the strip at 790–810℃ for 60–150 seconds. The slow cooling section cools the strip steel to 600-720℃, with a slow cooling rate of 1-15℃ / s; The rapid cooling section cools the strip steel to 455-465℃, with a rapid cooling rate of 15-60℃ / s. The equalization section holds the strip steel at 455–465℃ for 30–150 seconds. The temperature of the zinc bath is 455-465℃, and the galvanizing time is 2-5 seconds; Finishing: The strip steel produced by continuous annealing and hot-dip galvanizing is finished with a finishing elongation of 0.6 to 1.8%.

2. The 590MPa grade hot-dip galvanized duplex steel according to claim 1, characterized in that, The steel has a yield strength of 360–400 MPa, a tensile strength of 620–675 MPa, and an elongation A. 80 The percentage is 27.0%–30.0%, the n value is 0.17–0.22, and the porosity is 55%–75%.

3. A method for producing 590MPa grade hot-dip galvanized duplex steel as described in claim 1 or 2, characterized in that, Includes the following steps: Hot metal pretreatment, converter smelting, LF refining, continuous casting, slab heating, hot continuous rolling, laminar flow cooling and coiling, pickling and cold rolling, continuous annealing and hot-dip galvanizing, and finishing, among which: Continuous casting: During the steel casting process, maintain a constant casting speed, ranging from 1.0 to 1.6 m / min, and use light reduction, with a reduction amount of 3 to 8 mm; Slab heating: The slab is heated in a walking beam furnace with an inlet temperature of 200-550℃ and an outlet temperature of 1200-1250℃, and the furnace time is 1-3 hours. Hot continuous rolling: roughing rolling temperature ≥1050℃, finishing rolling temperature 880~920℃; Laminar flow cooling and coiling: After final rolling, the hot-rolled steel strip is cooled to 550-600℃ at a laminar flow cooling rate of ≥64℃ / s, and then air-cooled to 500-550℃ for 3-6s before coiling. Pickling and cold rolling: The hot-rolled steel strip is pickled to remove iron oxide scale, and then cold rolled with a reduction rate of 50% to 70%. Continuous annealing and hot-dip galvanizing: The preheating section heats the strip steel to 130-200℃ at a preheating rate of 2-6℃ / s. The heating section heats the strip steel to 790–810℃ at a rate of 2–10℃ / s. The soaking zone holds the strip at 790–810℃ for 60–150 seconds. The slow cooling section cools the strip steel to 600-720℃, with a slow cooling rate of 1-15℃ / s; The rapid cooling section cools the strip steel to 455-465℃, with a rapid cooling rate of 15-60℃ / s. The equalization section holds the strip steel at 455–465℃ for 30–150 seconds. The temperature of the zinc bath is 455-465℃, and the galvanizing time is 2-5 seconds; Finishing: The strip steel produced by continuous annealing and hot-dip galvanizing is finished with a finishing elongation of 0.6 to 1.8%.

4. The method for producing 590MPa grade hot-dip galvanized duplex steel according to claim 3, characterized in that, The aforementioned molten iron pretreatment involves using desulfurization powder and magnesium powder to desulfurize the molten iron to S≤0.015%, with slag thickness≤20mm and molten iron outlet temperature of 1240~1450℃; The converter smelting process involves first adding refined scrap steel to an oxygen top and bottom blowing converter, then adding molten iron, with a tapping temperature of 1630–1670°C. The LF refining process is as follows: slag thickness 50-100mm, net clearance 250-700mm, processing time ≥30min, and final oxygen content 300-600ppm.

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