Highly formable hot-dip galvanized or hot-dip galvanized aluminum-magnesium plated duplex steel and its rapid heat treatment hot-dip galvanizing manufacturing method

Abstract

In the present invention, a highly formable hot-dip aluminum galvanized or hot-dip zinc aluminum magnesium plated dual-phase steel having a tensile strength of ≥ 590MPa and a rapid heat treatment hot-dip manufacturing method are provided, in which the mass percentages of the components of the steel are as follows: C: 0.045-0.12%, Si: 0.1-0.5%, Mn: 1.0-2.0%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02-0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr+Mo+Ti+Nb+V ≤ 0.5%, with the balance being Fe and other unavoidable impurities. The present invention uses rapid heat treatment to change the recovery of deformation structure during the annealing process, the recrystallization of ferrite, and the phase transformation process of austenite, increase the number of crystal nucleation points, shorten the grain growth time, and increase the heat treatment efficiency, while at the same time improving the strength and formability (n 90 value) and widen the performance range of the material.

Description

[Technical Field]

[0001] The present invention belongs to the field of rapid heat treatment of materials, and more particularly to highly formable molten aluminum zinc plated or molten zinc aluminum magnesium plated duplex steel (including molten aluminum zinc plated AZ products and molten zinc aluminum magnesium plated AM products) and a method for producing the same through rapid heat treatment and molten plating. [Background technology]

[0002] As public concern for energy conservation and material safety grows, many automobile manufacturers are using high-strength steel as automotive material. For example, materials used in automobile exhaust systems require high strength, high toughness, high corrosion resistance, and certain heat resistance properties. Meanwhile, materials for home appliances and buildings require high strength and thinness for substrate materials, and good corrosion resistance for coatings. Thus, in fields such as automobiles, home appliances, and buildings, the requirements for corrosion resistance, dent resistance, durability, large deformation impact strength, and safety of coatings and plated products are becoming increasingly stringent.

[0003] In the field of hot-dip galvanized high-strength steel for automobiles, hot-dip galvanized duplex steel is the most widely applied and has the greatest potential. Low-carbon, low-alloy hot-dip galvanized duplex steel has a low yield ratio, a high initial work hardening rate, and a good balance of strength and ductility, and is currently widely used as a high-strength, highly formable steel for press working in automobile structures.

[0004] However, as the demands for corrosion resistance in steel products become increasingly stringent, hot-dip pure zinc plating no longer meets these requirements, necessitating the development of new varieties with superior corrosion resistance coatings. Therefore, research into hot-dip aluminum zinc plating and hot-dip zinc-aluminum-magnesium plating coatings, which offer superior corrosion resistance, is becoming increasingly active. In response, hot-dip aluminum zinc plating and hot-dip zinc-aluminum-magnesium plating high-strength steel products are also emerging.

[0005] Currently, the main methods for hot-dip aluminum-zinc plated and hot-dip zinc-aluminum-magnesium plated duplex steels involve altering the microstructure and properties of the hot-dip plated duplex steel by adding alloying elements or by adjusting the soaking temperature, time, and cooling rate in the critical annealing process.

[0006] Chinese patent application CN201710994660.X discloses "550MPa grade structural hot-dip aluminum galvanized steel sheet and method for producing the same," whose chemical composition is C:0.02-0.07%, Si≦0.03%, Mn:0.15-0.30%, P≦0.020%, Si≦0.020%, Nb:0.015-0.030%, Als:0.020-0.070%, cold rolling is performed at a low cold rolling reduction ratio of 55-60%, yield strength is 550MPa or higher, tensile strength is 560MPa, and elongation is around 10%. The steel sheet according to this patent has the problem of low elongation and high yield strength ratio, which affects subsequent processing steps.

[0007] Chinese patent application CN102363857B discloses "Method for producing structural coated boards having a yield strength of 550 MPa," wherein Ti and Nb do not exceed 0.05% and 0.045%, and their yield strength Rp 0.2 The pressure reaches 550-600 MPa, and the tensile strength R m The pressure is 560-610 MPa, and the elongation rate after rupture is A 80 For materials with a thickness of ≥6% mm, the strengthening method is mainly based on low-temperature annealing. This method retains most of the non-recrystallized band structure, resulting in increased strength, but poor plasticity, which affects molding.

[0008] Chinese patent application CN100529141C discloses "Fully hardened aluminum-zinc plated steel sheet and method for producing the same." The steel sheet produced by this method has a yield strength of 600 MPa or more, a fracture elongation of ≤7%, and a total Ti and Nb content of 0.15%-0.100%. The annealing temperature is 630-710°C, and the fully hardened steel sheet is obtained by a low-temperature recovery annealing method. However, the elongation of the steel sheet product obtained by this method is too low to meet current workability requirements.

[0009] Chinese patent application CN201911161556.8 discloses "Hot-dip zinc-aluminum-magnesium plated high-strength steel, manufacturing method and application." The hot-dip zinc-aluminum-magnesium plated high-strength steel includes a base material and a zinc-aluminum-magnesium alloy coating on the surface of the base material. Based on the component design and control of the production process on top of the component design, a production method and core production technology are provided, with a CSP thin slab continuous casting and continuous rolling production line and a normal hot-dip galvanizing production line as core processes, comprising smelting, hot rolling, cold rolling, and annealing. The above hot-dip zinc-aluminum-magnesium plated high-strength steel has a yield strength exceeding 550 MPa and an elongation of >17%. Due to poor formability, it is only suitable for industries that require high corrosion resistance but not high formability, such as solar power mounting frames and road guardrails.

[0010] Chinese patent application CN106811686A discloses "High-strength zinc-aluminum-magnesium coated steel sheet with good surface quality and method for manufacturing the same." The chemical composition of the steel sheet includes C: 0.09-0.18%, Si: 0.40-1.60%, Mn: 0.80-2.10%, S: 0.001-0.008%, and may further contain Cr: 0.01-0.60%, and / or Mo: 0.01-0.30%. The chemical composition of the coating is Al: 1-14%, Mg: 1.0-5.0%, with the remainder being zinc and unavoidable impurities. Although this patent provides a method for producing high-strength zinc-aluminum-magnesium coated steel sheet, it is expensive, prone to surface quality problems due to its high Si content, has excessively high yield strength and low elongation, and affects subsequent processing and forming.

[0011] Chinese patent application CN104419867A discloses "1250MPa class ultra-high strength zinc-aluminum-magnesium coated steel sheet and method for producing the same," wherein the weight percentages of the chemical composition of the steel sheet are as follows: C: 0.15~0.35%, Si: 0.50~1.80%, Mn: 2.0~5.0%, Mn / Si is 2 or more, and the remainder is iron and unavoidable impurities; the weight percentages of the chemical composition of the coating are as follows: Al: 1~15%, Mg: 1~5%, Al / Mg ≥ 1, and the remainder is Zn and unavoidable impurities. The production method includes a smelting-continuous casting-hot continuous rolling-cold continuous rolling-continuous hot galvanizing process. The high corrosion-resistant, ultra-high-strength zinc-aluminum-magnesium coated steel sheet produced by this invention has a strength of 1250-1500 MPa, an elongation after fracture of 12-18%, and corrosion resistance more than four times that of ordinary galvanized sheets. The coating does not crack or peel even when bent at 180° 5a, meeting the needs for high corrosion resistance, high strength, and lightweight construction. Although this patent provides a method for producing high-strength zinc-aluminum-magnesium coated steel sheets, the high Si content makes surface quality issues likely, and the high C content results in poor weldability, affecting subsequent processing and forming.

[0012] As described above, current molten aluminum zinc-plated and molten zinc-aluminum magnesium-plated products are expensive, have poor surface quality, and suffer from subsequent processing and forming problems due to unsuitable strength or elongation formulations. At the same time, limited by the production equipment of companies, most relevant research has focused on heating strip steel at conventional heating equipment rates (5-20°C / s) to complete recrystallization and austenitization (Chinese Patent CN104988391A). In recent years, the development of rapid heating technologies such as transverse magnetic induction heating and new direct-fire heating has advanced the industrial application of rapid heat treatment processes. Cold-rolled strip steel can now achieve austenitization from room temperature in tens or even seconds, significantly shortening the length of the furnace heating phase and increasing system speed and production efficiency. At the same time, the very short recrystallization and austenitization processes enable more flexible and pliable microstructure design, resulting in improved material performance without changing the alloy composition or rolling process.

[0013] High-corrosion-resistant advanced high-strength steels, such as duplex steel, have broad application potential, and rapid heat treatment technology also has enormous development value. Therefore, the combination of these two inevitably provides more room for the development of duplex steel. [Overview of the project] [Problems that the invention aims to solve]

[0014] The object of the present invention is to provide a highly formable molten aluminum zinc plated or molten zinc aluminum magnesium plated duplex steel (including molten aluminum zinc plated AZ and molten zinc aluminum magnesium plated AM products) with a tensile strength of ≥590 MPa, and a rapid heat treatment molten plating manufacturing method. Rapid heating controls processes such as the recovery of the deformed base material during the annealing process, ferrite recrystallization, austenite phase transition, and grain growth, and finally, after the heat treatment is completed, a fine ferrite structure and a multi-morphological reinforcing phase structure are obtained, significantly increasing the strength of the material while simultaneously improving its toughness. The resulting duplex steel has a yield strength of ≥300 MPa, a tensile strength of ≥590 MPa, an elongation of ≥20%, a strength-ductility product of ≥15 GPa%, and a strain-hardening index of n 90 The value exceeds 0.20. [Means for solving the problem]

[0015] To achieve the above-mentioned objectives, the technical proposal of the present invention is: A highly formable hot-dip galvanized or hot-dip galvanized magnesium alloy duplex steel having a tensile strength of ≥590 MPa, wherein the mass percentage of its chemical composition is as follows: C: 0.045~0.12%, Si: 0.1~0.5%, Mn: 1.0~2.0%, P ≤0.02%, S ≤0.006%, Al: 0.02~0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, with Cr+Mo+Ti+Nb+V ≤0.5%, and the remainder being Fe and other unavoidable impurities. Preferably, this highly formable hot-dip galvanized or hot-dip galvanized magnesium alloy duplex steel has a yield strength of ≥300 MPa, a tensile strength of ≥590 MPa, an elongation of ≥20%, a strength-ductility product of ≥15 GPa%, and a strain-hardening index of n 90 The value is greater than 0.20; more preferably, the yield strength is 300 to 560 MPa, for example 300 to 400 MPa or 450 to 560 MPa, the tensile strength is 590 to 860 MPa, preferably 630 to 860 MPa, the elongation is 20 to 30%, and the strength-ductile product is 15 to 21 GPa%. Preferably, the C content is 0.045 to 0.105% or 0.05 to 0.12%. Preferably, the Si content is 0.1 to 0.4%. Preferably, the Mn content is 1.0% to 1.5% or 1.2 to 2.0%. Preferably, the duplex steel may contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.3%. Preferably, the metallographic structure of the duplex steel is a uniformly distributed duplex structure of ferrite and martensite, with an average grain size of 1 to 5 μm.

[0016] Preferably, the highly formable hot-dip aluminum-zinc plated or hot-dip zinc-aluminum-magnesium plated duplex steel with a tensile strength of ≥ 590 MPa is obtained by the following process: 1) Smelting and casting The smelting process is carried out according to the above chemical composition, and the slabs are cast into slabs; 2) Hot rolling, coiling The winding temperature should be 550-680°C. 3) Cold rolling The cold rolling reduction ratio shall be 40 - 85%; 4) Rapid heat treatment, hot dip aluminum - zinc plating or hot dip zinc - aluminum - magnesium plating The steel sheet after cold rolling is rapidly heated to 750 - 845°C, and the rapid heating can be one - stage or two - stage; When it is one - stage rapid heating, the heating rate is 15 - 500°C / s (for example, 50 - 500°C / s); When it is two - stage rapid heating, in the first stage, it is heated from room temperature to 550 - 650°C at a heating rate of 15 - 500°C / s, and in the second stage, it is heated from 550 - 650°C to 750 - 845°C at a heating rate of 30 - 500°C / s (for example, 50 - 500°C / s); Then soaking is carried out, soaking temperature: 750 - 845°C, soaking time: 10 - 60 s; After the soaking is completed, it is slowly cooled to 670 - 770°C at a cooling rate of 5 - 15°C / s, and then it is rapidly cooled to 580 - 600°C at a cooling rate of 50 - 200°C / s (for example, 50 - 150°C / s), and then immersed in a zinc pot for hot dip aluminum - zinc plating or hot dip zinc - aluminum - magnesium plating; After hot dip aluminum - zinc plating, it is rapidly cooled to room temperature at a cooling rate of 30 - 200°C / s (for example, 30 - 150°C / s) to obtain a hot dip aluminum - zinc plating AZ product; or After hot dip zinc - aluminum - magnesium plating, it is rapidly cooled to room temperature at a cooling rate of 10 - 300°C / s (for example, 30 - 180°C / s) to obtain a hot dip zinc - aluminum - magnesium plating AM product.

[0017] Preferably, the C content is 0.065 - 0.085% or 0.07 - 0.10%.

[0018] Preferably, the Si content is 0.15 - 0.25% or 0.1 - 0.4%. Preferably, the Mn content is 1.2% - 1.35% or 1.5 - 1.8%.

[0019] Preferably, the duplex steel may contain one or two of Cr, Mo, Ti, Nb, and V, and Cr+Mo+Ti+Nb+V ≤ 0.4% or ≤ 0.2%.

[0020] Preferably, the entire process of rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating according to step 4) takes 29 to 159 seconds, preferably 29 to 122 seconds.

[0021] Preferably, in step 2), the hot rolling completion temperature ≥ A r3 . Preferably, in step 2), the winding temperature is 580 to 650°C.

[0022] Preferably, in step 3), the cold rolling reduction ratio is 60 to 80%. Preferably, in step 4), when the rapid heating is a single-stage heating, the heating rate is 50 to 300°C / s.

[0023] Preferably, in step 4), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 15 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 50 to 300°C / s.

[0024] Preferably, in step 4), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 30 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 80 to 300°C / s.

[0025] Preferably, in step 4), after molten zinc-aluminum-magnesium plating, the product is rapidly cooled to room temperature at a cooling rate of 30 to 250°C / s to obtain a molten zinc-aluminum-magnesium plated AM product.

[0026] The metallographic structure of the duplex steel according to the present invention is a duplex structure of uniformly distributed ferrite and martensite, with an average grain size of 1 to 5 μm, for example, 1 to 3 μm.

[0027] In one embodiment, the highly formable hot-dip aluminum-zinc plated or hot-dip zinc-aluminum-magnesium plated duplex steel according to the present invention, having a tensile strength of ≥ 590 MPa, has the following mass percentages of chemical composition: C: 0.045~0.105%, Si: 0.1~0.4%, Mn: 1.0~1.5%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02~0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, with Cr+Mo+Ti+Nb+V ≤ 0.3%, the remainder being Fe and other unavoidable impurities. Preferably, the C content of this duplex steel is 0.065~0.085%; preferably, the Si content of this duplex steel is 0.15~0.25%; preferably, the Mn content of this duplex steel is 1.2%~1.35%. Preferably, this duplex steel may contain one or two of Cr, Mo, Ti, Nb, and V, and Cr+Mo+Ti+Nb+V ≤ 0.2%. Preferably, the metal structure of this duplex steel is a uniformly distributed duplex structure of ferrite and martensite, with an average grain size of 1 to 3 μm. Preferably, this duplex steel has a yield strength of 30 0 The strength is ~400 MPa, the tensile strength is 630~700 MPa, the elongation is 22~30%, the strength-ductile product is 15~20 GPa%, and the strain-hardening index n90 value is greater than 0.21; more preferably, this duplex steel has a yield strength of 304~398 MPa, a tensile strength of 630~698 MPa, an elongation of 22.3~29.4%, a strength-ductile product is 15.3~19.4 GPa%, and the strain-hardening index n90 value is greater than 0.21. Preferably, this duplex steel is obtained by the following process: a) Smelting, casting The smelting process is carried out according to the above chemical composition, and the slabs are cast into slabs; b) Hot rolling, coiling The winding temperature should be 550-680°C. c) Cold rolling The cold rolling reduction ratio should be 40-85%. d) Rapid heat treatment, hot-dip aluminum zinc plating or hot-dip galvanized aluminum magnesium plating The cold-rolled steel sheet is rapidly heated to 750-845°C, and this rapid heating is performed in one or two stages; When using a single-stage rapid heating system, the heating rate should be 15-500°C / s (for example, 50-500°C / s). In a two-stage rapid heating system, the first stage involves heating from room temperature to 550-650°C at a heating rate of 15-500°C / s, and the second stage involves heating from 550-650°C to 750-845°C at a heating rate of 30-500°C / s (for example, 50-500°C / s). Subsequently, soaking is performed at a temperature of 750-845°C for 10-60 seconds; after soaking, the material is slowly cooled to 670-770°C at a cooling rate of 5-15°C / s, then rapidly cooled to 580-600°C at a cooling rate of 50-200°C / s (e.g., 50-150°C / s), and finally immersed in a zinc furnace for molten aluminum zinc plating or molten zinc aluminum magnesium plating; After molten aluminum zinc plating, the product is cooled to room temperature at a cooling rate of 30-200°C / s to obtain a molten aluminum zinc plated AZ product; or, After hot-dip zinc-aluminum-magnesium plating, the product is cooled to room temperature at a cooling rate of 30-180°C / s to obtain a hot-dip zinc-aluminum-magnesium plated (AM) product.

[0028] Preferably, the entire process of rapid heat treatment in step d) and molten aluminum zinc plating or molten zinc aluminum magnesium plating takes 29 to 122 seconds.

[0029] Preferably, in step b), the hot rolling completion temperature ≥ A r3 . Preferably, in step b), the winding temperature is 580 to 650°C.

[0030] Preferably, in step c), the cold rolling reduction ratio is 60 to 80%. Preferably, in step d), when the rapid heating is a single-stage heating, the heating rate is 50 to 300°C / s.

[0031] Preferably, in step d), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 15 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 50 to 300°C / s.

[0032] Preferably, in step d), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 30 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 80 to 300°C / s.

[0033] In one embodiment, the highly formable hot-dip aluminum-zinc plated or hot-dip zinc-aluminum-magnesium plated duplex steel having a tensile strength of ≥ 590 MPa has the following mass percentage chemical composition: C: 0.05~0.12%, Si: 0.1~0.5%, Mn: 1.2~2.0%, P ≤ 0.015%, S ≤ 0.003%, Al: 0.02~0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, with Cr+Mo+Ti+Nb+V ≤ 0.5%, the remainder being Fe and other unavoidable impurities. Preferably, the C content of this duplex steel is 0.07~0.10%. Preferably, the Si content of this duplex steel is 0.1~0.4%. Preferably, the Mn content of this duplex steel is 1.5~1.8%. Preferably, the duplex steel may contain one or two of Cr, Mo, Ti, Nb, and V, and Cr+Mo+Ti+Nb+V≦0.4%. Preferably, the metal structure of this duplex steel is a uniformly distributed duplex structure of ferrite and martensite, with an average grain size of 1 to 5 μm. Preferably, this duplex steel has a yield strength of 470 to 560 MPa, a tensile strength of 780 to 860 MPa, an elongation of 20 to 25%, a strength-ductility product of 16 to 21 GPa%, and a strain-hardening index n 90Greater than 0.20; more preferably, this dual-phase steel has a yield strength of 476 - 556 MPa, a tensile strength of 786 - 852 MPa, an elongation of 20.1 - 24.8%, a strength-ductility product of 16.7 - 20.2 GPa%, and a strain hardening index n 90 Greater than 0.20. Preferably, this dual-phase steel is obtained by the following process: A) Smelting and casting Smelt according to the above chemical composition and cast into slabs; B) Hot rolling and coiling The coiling temperature is 550 - 680 °C; C) Cold rolling The cold rolling reduction is 40 - 85%; D) Rapid heat treatment, hot dip aluminum-zinc plating or hot dip zinc-aluminum-magnesium plating Rapidly heat the steel sheet after cold rolling to 750 - 845 °C, and the rapid heating is either one-stage or two-stage; When performing one-stage rapid heating, the heating rate is 15 - 500 °C / s (for example, 50 - 500 °C / s); When performing two-stage rapid heating, in the first stage, heat from room temperature to 550 - 650 °C at a heating rate of 15 - 500 °C / s, and in the second stage, heat from 550 - 650 °C to 750 - 845 °C at a heating rate of 30 - 500 °C / s (for example, 50 - 500 °C / s); Then perform soaking, soaking temperature: 750 - 845 °C, soaking time: 10 - 60 s; After the soaking is completed, slowly cool to 670 - 770 °C at a cooling rate of 5 - 15 °C / s, and then rapidly cool to 580 - 600 °C at a cooling rate of 50 - 200 °C / s (for example, 50 - 150 °C / s), and dip into a zinc pot for hot dip aluminum-zinc plating or hot dip zinc-aluminum-magnesium plating; After hot dip aluminum-zinc plating, rapidly cool to room temperature at a cooling rate of 30 - 150 °C / s to obtain a hot dip aluminum-zinc plating AZ product; or After hot dip zinc-aluminum-magnesium plating, rapidly cool to room temperature at a cooling rate of 10 - 300 °C / s to obtain a hot dip zinc-aluminum-magnesium plating AM product.

[0034] <Preferably, the entire process of rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating in step D) takes 29 to 159 seconds.

[0035] Preferably, in step B), the hot rolling completion temperature ≥ A r3 . Preferably, in step B), the winding temperature is 580 to 650°C.

[0036] Preferably, in step C), the cold rolling reduction ratio is 60 to 80%. Preferably, in step D), when the rapid heating is a single-stage heating, the heating rate is 50 to 300°C / s.

[0037] Preferably, in step D), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 15 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 50 to 300°C / s.

[0038] Preferably, in step D), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 30 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 80 to 300°C / s.

[0039] Preferably, in step D), after molten zinc-aluminum-magnesium plating, the product is rapidly cooled to room temperature at a cooling rate of 30 to 250°C / s to obtain a molten zinc-aluminum-magnesium plated AM product.

[0040] In the composition and process design of the steel of the present invention: C: Carbon is the most commonly used strengthening element in steel. Carbon increases the strength of steel and decreases its plasticity, but for forming steel, what is required is low yield strength, high and uniform elongation, and total elongation, so too high a carbon content is undesirable. Carbon content has a significant impact on the mechanical properties of steel. As the carbon content increases, the number of pearlites increases, so the strength and hardness of the steel increase significantly, but its plasticity and toughness decrease significantly. If the carbon content is too high, a clear network of carbides is formed in the steel, and the presence of network of carbides clearly reduces strength, plasticity, and toughness, so the strengthening effect of increasing the carbon content in the steel is significantly weakened, and the process performance of the steel deteriorates. Therefore, when strength can be guaranteed, the carbon content should be as low as possible.

[0041] For duplex steels, carbon primarily affects the volume fraction of austenite formed during the annealing process. During austenite formation, the diffusion of carbon within austenite or ferrite effectively controls the growth of austenite grains. As carbon content increases or the critical heating temperature rises, the volume fraction of austenite increases, and the martensite phase structure formed after cooling increases, thus increasing the material's strength. Therefore, it is necessary to comprehensively consider the material's strength-toughness composition and the increase in strength during the rapid annealing process. This invention limits the carbon content to within the range of 0.045-0.12%.

[0042] Manganese (Mn) forms a solid solution with iron, further increasing the strength and hardness of ferrite and austenite in carbon steel, and can impart relatively fine and high-strength pearlite to the steel during the cooling process after hot rolling. The pearlite content also increases with increasing Mn content. Manganese is also a carbide-forming element. Since manganese carbides can dissolve in cementite, they indirectly enhance the strength of pearlite. Manganese can also drastically increase the hardenability of steel, further increasing its strength.

[0043] For duplex steels, manganese is one of the elements that clearly influences the austenite formation kinetics during critical region annealing. Manganese primarily affects the process from austenite formation to its transformation into ferrite and subsequent growth, as well as the final equilibrium process between austenite and ferrite. Because the diffusion rate of manganese in austenite is much lower than that in ferrite, austenite grains controlled by manganese diffusion have a longer growth time, and a longer time for manganese to reach a uniform distribution within the austenite. When heating in the critical region, if the holding time is too short, manganese will not reach a uniform distribution within the austenite, and if the cooling rate is insufficient, a uniform island martensite structure cannot be obtained. Duplex steels produced by rapid heat treatment processes (e.g., water quenching continuous annealing production lines) generally have a high manganese content, and because they have a high manganese content immediately after austenite formation, the hardenability of island austenite is guaranteed, and after cooling, a uniform island martensite structure and uniform performance are obtained. Furthermore, manganese expands the γ phase region, A c1 and A c3 Because the temperature decreases, manganese-containing steel yields a higher martensite volume fraction than low-carbon steel under similar heat treatment conditions. However, when the manganese content is high, the crystal grains in the steel tend to coarseen, increasing the steel's overheat sensitivity. White spots are likely to occur in carbon steel when the cooling after molten casting and rolling is unsuitable. Considering these factors, the present invention sets the manganese content within the range of 1.0 to 2.0%.

[0044] Silicon (Si) forms solid solutions in ferrite or austenite, increasing the yield and tensile strength of steel. Furthermore, silicon increases the cold-work deformation and hardening rate of steel, making it a suitable element for alloy steels. Silicon exhibits a clear accumulation phenomenon at the crystal boundary cross-section of silicon-manganese steel. Segregation of silicon at the crystal boundary slows down the distribution of carbon and phosphorus in the crystal boundary cross-section, improving the brittle state of the crystal boundary. Silicon can increase the strength, hardness, and wear resistance of steel without significantly reducing its plasticity. Silicon has strong deoxidizing capabilities and is a commonly used deoxidizer in steelmaking. Silicon can also increase the flowability of molten steel. Therefore, silicon is generally included in steel. However, if the silicon content in steel is too high, its plasticity and toughness are significantly reduced.

[0045] For duplex steel, the main effect of silicon is to reduce the volume fraction of austenite when final equilibrium is reached under the conditions of a predetermined annealing time. Although silicon has no apparent effect on the growth rate of austenite, it has a clear effect on the manner and distribution of austenite formation. Therefore, this invention sets the silicon content within the range of 0.1 to 0.5%.

[0046] Cr: In steel, the main effect of chromium is to improve hardenability. Thus, after quenching and tempering, the steel has good overall mechanical properties. Chromium forms a continuous solid solution with iron, reducing the austenite phase region. Chromium forms numerous carbides with carbon, and its affinity for carbon is superior to that of iron and manganese. Chromium can form the intermetallic compound σ phase (FeCr) with iron. Chromium reduces the carbon concentration in pearlite and the intrinsic solubility of carbon in austenite. Chromium slows the decomposition rate of austenite, significantly improving the hardenability of steel. However, it also tends to increase the temper brittleness of steel. Chromium can increase the strength and hardness of steel. At the same time, the effect becomes more pronounced when other alloying elements are added. Cr increases the hardenability of steel during air cooling, thus negatively impacting the weldability of steel. However, if the chromium content is less than 0.3%, the negative impact on weldability is negligible. Above this content, cracks and defects such as impurities are more likely to occur during welding. When chromium (Cr) and other alloying elements are present simultaneously (e.g., together with V), the adverse effect of Cr on weldability is significantly reduced. For example, when elements such as Cr, Mo, and V are present simultaneously in steel, even if the Cr content reaches 1.7%, there is no significant adverse effect on the weldability of the steel. In this invention, chromium is a suitable and unnecessary additive element, and considering factors such as increased cost, it is preferable that the amount added is not excessive. In one embodiment, the Cr content is ≤0.35%.

[0047] Mo (molybdenum) can suppress the spontaneous diffusion of iron and the diffusion rates of other elements. Since the atomic radius of Mo is larger than that of α-Fe atoms, when Mo dissolves in an α-solid solution, intense lattice deformation occurs in the solution. Simultaneously, Mo increases the inter-lattice atomic bonding attractiveness, thus raising the recrystallization temperature of α-ferrite. The strengthening effect of Mo is evident in pearlite, ferritic, and martensitic steels, as well as high-alloy austenitic steels. The favorable effect of Mo in steel is related to its interaction with other alloying elements. Adding strong carbide-forming elements V, Nb, and Ti to steel further enhances the solid solution strengthening effect of Mo. This is because when strong carbide-forming elements combine with C to form stable carbides, the dissolution of Mo in the solid solution is further promoted, which is even more advantageous for increasing the thermal strength of the steel. Mo also increases the hardenability of steel, although its effect is not as significant as that of C and Cr. Mo suppresses the conversion of pearlite and accelerates the conversion of medium-temperature areas, so Mo-containing steel can form a certain number of bainite even at high cooling rates, and ferrite formation is also eliminated. This is one of the reasons why Mo has a favorable effect on the thermal strength of low-alloy heat-resistant steel. Mo can also significantly reduce the thermal brittleness of steel and decrease the spheroidization rate of pearlite. When the Mo content is 0.15% or less, it does not adversely affect the weldability of the steel. In this invention, molybdenum is a suitable and unnecessary additive element, and considering the increase in cost, it is best not to add too much. In one embodiment, the Mo content is ≤0.2%.

[0048] Microalloying elements Ti, Nb, V: By adding trace amounts of microalloying elements Nb, V, and Ti to steel, even when the carbon equivalent of the steel is low, the dispersed precipitation of mass points (size less than 5 nm) of the carbon and nitrides and the solid solution of Nb, V, and Ti refine the crystal grains, greatly increasing the strength and toughness of the steel, especially its low-temperature toughness, resulting in good weldability and usability. Nb, V, and Ti are carbide and nitride-forming elements, and these elements can satisfy these requirements even at relatively low concentrations. Nb, V, and Ti are strong carbide-forming elements, and at room temperature, in steel, the majority exist in the form of carbides, nitrides, and carbon nitrogenides, with some solid-solubilating in ferrite. The addition of Nb, V, and Ti inhibits the growth of austenite crystal grains and raises the coarsening temperature of the steel. The reason is that these carbonitrides, as dispersed particles, have a fixing effect on the austenite crystal boundaries, inhibiting the movement of austenite crystal boundaries, raising the austenite recrystallization temperature, and expanding the non-recrystallized area, thereby preventing the growth of austenite crystal grains. Adding small amounts of Nb, V, and Ti to steel can reduce the carbon equivalent content while simultaneously increasing strength and improving the weldability of the steel. On the other hand, it can fix impurities such as oxygen, nitrogen, and sulfur, improving the weldability of the steel. Furthermore, due to the effect of microparticle points (e.g., the insolubility of TiN at high temperatures), grain roughening in the heat-affected zone is prevented, toughness in the heat-affected zone is increased, and the weldability of the steel is improved. In this invention, microalloying elements are suitable and unnecessary additives, and considering the increase in cost, it is best not to add too much. In one embodiment, Ti content ≤ 0.04%. In one embodiment, Nb content ≤ 0.05%. In one embodiment, V content ≤ 0.05%.

[0049] This invention controls processes such as the recovery of the deformed structure, recrystallization, austenite phase transition, and grain growth in a continuous heat treatment process by using a rapid heat treatment process that includes rapid heating, short-term heat retention, and rapid cooling. During the cooling process, not only is the ferrite matrix phase formed, but gradient distributions of each reinforcing phase and its components are generated, ultimately resulting in a fine ferrite structure and a multi-morphological reinforcing phase structure. The material has a good strength-toughness composition, reduces alloy costs and the difficulty of manufacturing each process, and improves usability such as welding performance for steel grades of the same strength level.

[0050] The specific principle is as follows: Different heating rates are used at different temperature stages during the heating process. At low temperatures, mainly the recovery of the deformation structure occurs, so a relatively low heating rate is used to reduce energy consumption. At high temperatures, mainly the recrystallization of different phase structures and the growth of crystal grains occur, so a relatively high heating rate is used to shorten the residence time of the structure in the high-temperature range, thereby stopping the growth of crystal grains. By controlling the heating rate during the heating process, the recovery of the deformation structure and the recrystallization process of ferrite are suppressed, the recrystallization process and the austenite phase transition process overlap, the nucleation sites of recrystallized and austenite crystal grains are increased, and ultimately the crystal grains are refined. Short-time heat retention and rapid cooling shorten the crystal grain growth time during the soaking process, ensuring a fine and uniform distribution of crystal grain structure.

[0051] The present invention relates to a highly formable hot-dip galvanized aluminum plating with a tensile strength of ≥590 MPa. or The rapid heat treatment and hot-dip galvanizing method for producing molten zinc-aluminum-magnesium plated duplex steel includes the following steps: 1) Smelting and casting The smelting process is carried out according to the above chemical composition, and the slabs are cast into slabs; 2) Hot rolling, coiling The winding temperature should be 550-680°C. 3) Cold rolling The cold rolling reduction ratio is set to 40-85%, and after cold rolling, rolled hardened strip steel or steel plate is obtained; 4) Rapid heat treatment, hot-dip aluminum zinc plating, or hot-dip galvanized aluminum magnesium plating A) Rapid heating Cold-rolled steel strip or sheet is rapidly heated from room temperature to the endpoint temperature of the austenite-ferrite two-phase region, which is 750-845°C, and this rapid heating is performed in one or two stages; When using a single-stage rapid heating system, the heating rate should be 15-500°C / s (for example, 50-500°C / s). In a two-stage rapid heating system, the first stage involves heating from room temperature to 550-650°C at a heating rate of 15-500°C / s, and the second stage involves heating from 550-650°C to 750-845°C at a heating rate of 30-500°C / s (for example, 50-500°C / s). B) Soaking Soaking is performed at 750-845°C, which is the endpoint temperature of the austenite-ferrite two-phase region, with a soaking time of 10-60 seconds. C) cooling After the steel strip or sheet has been soaked, it is slowly cooled to 670-770°C at a cooling rate of 5-15°C / s; then rapidly cooled to 580-600°C at a cooling rate of 50-200°C / s (e.g., 50-150°C / s); D) Hot-dip aluminum zinc plating or hot-dip zinc-aluminum magnesium plating After rapid cooling to 580-600°C, the steel strip or sheet is immersed in a zinc oven to perform hot-dip aluminum-zinc plating or hot-dip zinc-aluminum-magnesium plating; E) After molten aluminum zinc plating, rapidly cool to room temperature at a cooling rate of 30-200°C / s (e.g., 30-150°C / s) to obtain molten aluminum zinc plated AZ products; or, After hot-dip zinc-aluminum-magnesium plating, the product is rapidly cooled to room temperature at a cooling rate of 10-300°C / s (30-180°C / s) to obtain a hot-dip zinc-aluminum-magnesium plated AM product.

[0052] Preferably, the entire process of the rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating takes 29 to 159 seconds, for example, 29 to 122 seconds.

[0053] Preferably, in one embodiment, the method is used to produce a duplex steel according to any one of the above embodiments, wherein the mass percentage of the chemical components is as follows: C: 0.045~0.105%, Si: 0.1~0.4%, Mn: 1.0~1.5%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02~0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.3%, with the remainder being Fe and other unavoidable impurities; however, after molten aluminum zinc plating, the product is cooled to room temperature at a cooling rate of 30~200°C / s to obtain a molten aluminum zinc plated AZ product, or after molten zinc aluminum magnesium plating, the product is cooled to room temperature at a cooling rate of 30~180°C / s to obtain a molten zinc aluminum magnesium plated AM product. Preferably, the entire process of rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating by this method takes 29 to 122 seconds.

[0054] Preferably, in one embodiment, the method is used to produce a duplex steel according to any one of the above embodiments, wherein the mass percentage of the chemical components is as follows: C: 0.05~0.12%, Si: 0.1~0.5%, Mn: 1.2~2.0%, P ≤ 0.015%, S ≤ 0.003%, Al: 0.02~0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.5%, with the remainder being Fe and other unavoidable impurities; however, after molten aluminum zinc plating, the product is rapidly cooled to room temperature at a cooling rate of 30~150°C / s to obtain a molten aluminum zinc plated AZ product, or after molten zinc aluminum magnesium plating, the product is rapidly cooled to room temperature at a cooling rate of 10~300°C / s to obtain a molten zinc aluminum magnesium plated AM product. Preferably, the entire process of rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating by this method takes 29 to 159 seconds.

[0055] Preferably, in step 2), the hot rolling completion temperature ≥ A r3 . Preferably, in step 2), the winding temperature is 580 to 650°C.

[0056] Preferably, in step 3), the cold rolling reduction ratio is 60 to 80%. Preferably, in step 4), when the rapid heating is a single-stage heating, the heating rate is 50 to 300°C / s.

[0057] Preferably, in step 4), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 15 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 50 to 300°C / s.

[0058] Preferably, in step 4), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 30 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 80 to 300°C / s.

[0059] Preferably, in step 4), the final temperature of the rapid heating is 770 to 830°C.

[0060] Preferably, in the soaking process of step 4), the steel strip or steel plate is heated to the endpoint temperature of the austenite-ferrite two-phase region, and then the temperature is kept constant to perform soaking.

[0061] Preferably, in the soaking process of step 4), the steel strip or steel plate is subjected to a small increase or decrease in temperature during the soaking time, with the temperature after the increase being 845°C or lower and the temperature after the decrease being 750°C or higher.

[0062] Preferably, the soaking time is 10 to 40 seconds. In the present invention, a rapid heat treatment hot-dip galvanizing method for producing 590 MPa class highly formable hot-dip aluminum zinc plated or hot-dip zinc aluminum magnesium plated duplex steel: 1. Control of heating rate The recrystallization kinetics of a continuous heating process can be quantitatively explained by a relationship that is affected by the heating rate. The functional relationship between the volume fraction of ferrite recrystallization and temperature T in a continuous heating process is as follows:

[0063]

number

[0064] However, X(T) is the volume fraction of ferrite recrystallization; n is the Avrami index, which is related to the phase transition mechanism and is generally in the range of 1 to 4, based on the decay period of the recrystallization nucleation rate; T is the heat treatment temperature; T star β is the recrystallization start temperature; β is the heating rate; b(T) is obtained by the following equation:

[0065]

number

[0066] As can be seen from the above equation and related experimental data, the recrystallization start temperature (T) increases with increasing heating rate. star ) and termination temperature (T fin Both ) increase. When the heating rate is 50°C / s or higher, the austenite phase transition and recrystallization process overlap, raising the recrystallization temperature to the two-phase region temperature, and if the heating rate is fast, the ferrite recrystallization temperature is high.

[0067] Conventional heat treatment processes involve slow heating, under which recovery, recrystallization, and grain growth occur sequentially in the deformed matrix. Subsequently, a phase transition from ferrite to austenite occurs, with the nucleation points for the austenite phase transition mainly located at the boundaries of the grown ferrite crystals, resulting in a low nucleation rate and a relatively coarse grain structure in the final product.

[0068] Under rapid heating conditions, a phase transition from ferrite to austenite occurs when the deformed matrix has not yet fully recovered, or when recrystallization is just completed and the crystal grains have not yet grown. When recrystallization is just completed, the crystal grains are fine and the area of ​​the crystal boundaries is large, so the nucleation rate is significantly increased and the austenite crystal grains are clearly refined. In particular, when the recrystallization of ferrite and the phase transition process of austenite overlap, a large number of crystal defects such as transitions remain in the ferrite crystal, providing a large number of nucleation sites for austenite, so austenite nucleates explosively and the austenite crystal grains are further refined. At the same time, the remaining high-density linear transition defects become pathways for rapid diffusion of carbon atoms, so austenite crystal grains are rapidly generated and grow, and the volume fraction of austenite increases.

[0069] During the rapid heating process, precise control of microstructure transformation, alloying element distribution, and the distribution of each phase component establishes a good foundation for the growth of the austenite structure and the distribution of each alloying component during the subsequent soaking process, as well as for the phase transition from austenite to martensite during the rapid cooling process. Ultimately, the microstructure of the final product is obtained, with refined crystal grains and a rational distribution of elements and each phase. Considering factors such as the effect of grain refinement by rapid heating, manufacturing cost, and manufacturability, the present invention uses a heating rate of 15 to 500°C / s during single-stage rapid heating and a heating rate of 30 to 500°C / s during two-stage rapid heating.

[0070] Within different temperature ranges, the effect of rapid heating on microstructural changes such as material recovery, recrystallization, and grain growth differs; therefore, the preferred heating rate for obtaining the most suitable microstructural control also differs within different heating temperature ranges: from 20°C to 550-650°C, the heating rate has the greatest effect on the recovery process, and the heating rate should be 15-500°C / s, more preferably 30-500°C / s; when the heating temperature is from 550-650°C to the austenitization temperature of 750-845°C, the heating rate has the greatest effect on the grain growth process, and the heating rate should be 50-500°C / s, more preferably 80-500°C / s.

[0071] 2. Control of the soaking temperature The soaking temperature is usually based on the carbon content, and in the duplex steel of the present invention, the carbon content is 0.045 to 0.12%, and the A of the steel of the present invention C1 and A C3 These are approximately 730°C and 870°C, respectively. The rapid heat treatment process of the present invention involves A C1 ~A C3 By heating and then soaking during the process, and by using rapid heating technology, a large number of transitions remain in the ferrite that has not been sufficiently recrystallized, providing a greater nucleation driving force for austenite transitions. As a result, the rapid heat treatment method of the present invention can obtain a larger amount of finer austenite structure compared to conventional continuous annealing processes.

[0072] Regarding the control of soaking temperature, the present invention proposes that the soaking temperature fluctuates within a certain range: that is, the temperature fluctuates during the soaking process, but the soaking temperature must always be kept within a certain range. The advantages are as follows: The process of rapidly raising and lowering the temperature within the temperature range of the two-phase region is, in practice, a process that increases the degree of superheating and supercooling for a rapid phase transition process. When both the range and rate of temperature fluctuations are sufficiently large, the repeated phase transitions from ferrite to austenite and from austenite to ferrite further refine the crystal grains, while simultaneously having a certain effect on carbide formation and the uniform distribution of alloying elements, ultimately resulting in a finer structure with uniformly distributed alloying elements.

[0073] Cold-rolled duplex steel contains a large amount of finely and uniformly distributed insoluble carbides. During the heating process, these carbides have a mechanical inhibitory effect on the growth of austenite grains, which is advantageous for refining the grain size of high-strength steel. However, if the soaking temperature is too high, the number of insoluble carbides decreases significantly, weakening this inhibitory effect, increasing the tendency for grain growth, and further reducing the strength of the steel. If there are too many insoluble carbides, aggregation occurs, leading to a non-uniform distribution of chemical components in certain areas. If the carbon content at these aggregation points is too high, localized overheating occurs. Ideally, a small amount of fine granular insoluble carbides should be uniformly distributed in the steel. This not only prevents abnormal growth of austenite grains but also increases the content of each alloying element in the base material, thus improving the mechanical properties of alloy steel, such as strength and toughness.

[0074] The selection of the soaking temperature aims to obtain finer, more uniform austenite grains, avoid coarsening of the austenite grains, and obtain a fine martensite structure after cooling. If the soaking temperature is too high, the austenite grains become coarse, and the resulting martensite structure after rapid cooling is also relatively coarse, resulting in poor mechanical properties of the steel. Furthermore, the number of retained austenites increases and the number of martensites decreases, reducing the hardness and wear resistance of the steel. If the soaking temperature is too low, there is insufficient carbon and alloying elements to dissolve in the austenite, resulting in an uneven concentration distribution of alloying elements in the austenite, significantly reducing the hardenability of the steel and negatively impacting its mechanical properties. The soaking temperature for hypoeutectoid steel should be Ac3 + 30~50°C. For ultra-high-strength steel, the presence of carbide-forming elements inhibits carbide changes, allowing the soaking temperature to be suitably increased. Considering the above factors comprehensively, in order to obtain a more ideal and rational final structure, the soaking temperature of this invention is set to 750 to 845°C.

[0075] 3. Control of soaking time The effect of soaking time is also based on the carbon and alloying element content in the steel. As the content increases, not only does the thermal conductivity of the steel decrease, but because alloying elements diffuse more slowly than carbon, they clearly delay the structural changes in the steel, and in this case, the holding time needs to be appropriately extended. Because this invention utilizes rapid heating, in the two-phase region, the material contains a large amount of residual transitions, providing a large number of nucleation sites for austenite formation, and providing pathways for rapid diffusion of carbon atoms, so austenite can be formed very quickly. If the soaking and holding time is short, the diffusion distance of carbon atoms is short, the carbon concentration gradient in the austenite becomes large, and the carbon content of the retained austenite that is finally retained is high. However, if the holding time is too short, the distribution of alloying elements in the steel becomes uneven, and austenitization becomes insufficient. If the holding time is too long, coarsening of the austenite crystal grains is likely to occur. The effect of the soaking time is also based on the carbon and alloying element content in the steel. As the content increases, not only does the thermal conductivity of the steel decrease, but because alloying elements diffuse more slowly than carbon, they clearly delay the structural changes in the steel, and in this case, the heating time needs to be appropriately extended. Therefore, the soaking time must be determined after comprehensively considering the soaking temperature, rapid cooling, and rapid heating processes, so that the ideal structure and elemental distribution can be obtained. Based on the above, the heating time in this invention is set to 10 to 60 seconds.

[0076] 4. Control of the rapid cooling rate In order to ultimately obtain a material structure with an ideal phase structure and a rational distribution of elements, the control of the rapid cooling process must be determined after comprehensively considering factors such as the transformation results of each structure and the diffusion distribution results of alloying elements during the preceding heating and soaking processes.

[0077] To obtain a sufficient martensitic strengthening phase, the cooling rate of the sample during quenching must exceed the critical cooling rate; otherwise, a martensitic structure cannot be obtained. The critical cooling rate is mainly related to the composition of the material. In this invention, the Si content is 0.1-0.5% and the Mn content is 1.0-2.0%. Because the content is relatively high, Si and Mn greatly enhance the hardenability of the duplex steel, lowering the critical cooling rate. At the same time, in order to ultimately obtain a reasonable distribution of each phase structure and alloying elements, the cooling rate must be determined after comprehensively considering the results of the microstructure transformation and alloy diffusion distribution during the heating and soaking processes. If the cooling rate is too low, a martensitic structure cannot be obtained, the strength will decrease, and the mechanical properties will not meet the requirements. However, if the cooling rate is too high, a large quenching stress (i.e., microstructure stress and thermal stress) will occur, and the sample will be prone to deformation and cracking. Therefore, the rapid cooling rate in this invention is set to 50-150°C / s.

[0078] With regard to high-strength hot-dip aluminum-zinc plated and hot-dip zinc-aluminum-magnesium plated products, the rapid heat treatment process reduces the residence time of the steel strip in the high-temperature furnace. As a result, the accumulation of alloying elements on the surface of the high-strength steel strip during the heat treatment process is significantly reduced, improving the plating properties of the high-strength hot-dip galvanized products. This is advantageous for reducing surface plating defects and improving corrosion resistance, and increases the yield of the finished product. Furthermore, the refinement of the product's crystal grains and the reduction in the alloy content of the material improve the processing and forming performance, such as hole expansion performance and bending performance, as well as user performance, such as welding performance, of the duplex steel products obtained using the technology of the present invention.

[0079] Rapid heat treatment process technology reduces heating and soaking times, shortens furnace length (by at least one-third compared to conventional continuous annealing furnaces), significantly reduces the number of furnace rolls, decreases the probability of surface defects occurring in the furnace, and thus significantly improves the surface quality of the product.

[0080] The present invention has the following advantages compared to the prior art: (1) The present invention suppresses the recovery of the deformed structure and the recrystallization process of ferrite during the heat treatment process by rapid heat treatment, overlaps the recrystallization process and the austenite phase transition process, increases the nucleation points of the recrystallized grains and austenite grains, and shortens the grain growth time. The metal structure of the resulting duplex steel is a duplex structure of ferrite and martensite with a uniform distribution. After rapid heat treatment, fine martensite is present in the structure in various forms such as lumps, stripes, and granules, and its distribution becomes more uniform, so that duplex steel products have a good strength-plastic balance.

[0081] (2) Compared to duplex galvanized steel obtained by the conventional continuous annealing hot-dip galvanizing method, the duplex steel obtained by the rapid heat treatment of the present invention has an average grain size of 1 to 5 μm, when the manufacturing conditions of the preceding process are unchanged, and exhibits a good crystal strengthening effect. Its yield strength is 300 to 560 MPa, its tensile strength is 590 to 860 MPa, its elongation is 20 to 30%, its strength-ductility product is 15 to 21 GPa%, and its strain hardening index is n 90 The value exceeds 0.20.

[0082] (3) In the low-carbon, low-alloy, highly formable low-carbon, low-alloy hot-dip galvanized duplex steel rapid heat treatment process according to the present invention, the time required for the entire heat treatment process can be shortened to 29 to 159 seconds, significantly reducing the time for the entire heat treatment process (the time for the conventional continuous annealing process is usually 300 to 480 seconds), resulting in a significant increase in production efficiency, a decrease in energy consumption, and a reduction in production costs.

[0083] (4) In terms of production costs and manufacturing difficulty, compared to conventional duplex steel and its heat treatment process, the rapid heat treatment method of the present invention shortens the length of the heating and soaking stages in a continuous hot-dip galvanizing annealing furnace (shortened by at least one-third compared to conventional continuous annealing furnaces), the time, and the total heat treatment process time, reducing energy consumption, significantly reducing the initial investment in furnace equipment, and significantly reducing production operating costs and equipment repair costs. Furthermore, by producing products with the same strength level through rapid heat treatment, the alloy content can be reduced, the production costs of the heat treatment and preceding processes are reduced, and the manufacturing difficulty of each process before heat treatment is lowered.

[0084] (5) Regarding product quality, compared to duplex steel obtained by conventional continuous annealing, the rapid heat treatment process technology reduces the heating and soaking time, shortens the furnace length, and significantly reduces the number of furnace rolls, thus reducing the probability of surface defects occurring in the furnace and significantly improving the surface quality of the product. For high-strength molten aluminum zinc plated and molten zinc aluminum magnesium plated products, the rapid heat treatment process reduces the residence time of the steel strip in the high-temperature furnace, so the amount of alloying elements accumulated on the surface of the high-strength steel strip during the heat treatment process is significantly reduced, which is advantageous for improving the plating properties of the product. This is advantageous for reducing surface plating leakage defects and improving corrosion resistance in high-strength molten aluminum zinc plated and molten zinc aluminum magnesium plated products, and the yield of the finished material is increased. Furthermore, due to the refinement of the crystal grains of the product and the reduction in the alloy content of the material, the processing and forming performance such as hole expansion performance and bending performance, as well as user performance such as welding performance, of the duplex steel products obtained by the technology of the present invention are also improved.

[0085] (6) Compared to hot-dip galvanized duplex steel obtained by conventional heat treatment, the hot-dip galvanized aluminum zinc plated and hot-dip galvanized aluminum magnesium plated duplex steel obtained by the technology of the present invention have improved user performance such as forming, welding, painting and corrosion resistance, and corrosion resistance is 3 to 8 times that of conventional GI duplex steel.

[0086] As described above, the highly formable hot-dip galvanized duplex steel obtained by the present invention has significant value for the healthy development of next-generation lightweight automobiles, trains, ships, airplanes and other transportation equipment, as well as the healthy development of advanced manufacturing industries. [Brief explanation of the drawing]

[0087] [Figure 1] Figure 1 is a microstructure diagram of a molten zinc-aluminum-magnesium plated duplex steel (AM) produced from test steel A of Example 1 of the present invention according to Example 1 (single-stage heating). [Figure 2]Figure 2 is a microstructure diagram of molten aluminum-zinc plated duplex steel (AZ) produced from test steel A of Example 1 of the present invention according to Example 1 (two-stage heating). [Figure 3] Figure 3 is a microstructure diagram of hot-dip galvanized duplex steel (AZ) produced from test steel A of Example 1 of the present invention according to conventional process 1. [Figure 4] Figure 4 is a microstructure diagram of the molten aluminum-zinc plated duplex steel (AZ) produced from test steel I of Example 1 according to Example 3 (two-stage heating) of the present invention. [Figure 5] Figure 5 is a microstructure diagram of the molten zinc-aluminum-magnesium plated duplex steel (AM) produced from test steel C of Example 1 of the present invention according to Example 15 (two-stage heating). [Figure 6] Figure 6 is a microstructure diagram of the molten aluminum-zinc plated duplex steel (AZ) produced from test steel D of Example 2 of the present invention according to Example 4 (single-stage heating). [Figure 7] Figure 7 is a microstructure diagram of hot-dip aluminum-zinc plated duplex steel (AZ) produced from test steel D of Example 2 of the present invention according to the conventional process 4. [Figure 8] Figure 8 is a microstructure diagram of molten aluminum-zinc plated duplex steel (AZ) produced from test steel N of Example 2 of the present invention according to Example 15 (two-stage heating). [Figure 9] Figure 9 is a microstructure diagram of a molten zinc-aluminum-magnesium plated duplex steel (AM) produced from test steel E of Example 2 of the present invention according to Example 17 (two-stage heating). [Modes for carrying out the invention]

[0088] The present invention will now be further described based on the examples and drawings. These examples are based on the technical proposal of the present invention and demonstrate detailed embodiments and specific operating procedures, but do not limit the scope of protection of the present invention.

[0089] In the examples, yield strength, tensile strength, and elongation were measured transversely on sample P7 according to "GB / T228.1-2010 Tensile Tests for Metallic Materials Part 1: Test Methods at Room Temperature". 90 The test was conducted according to "GB / T228.1-2010 Tensile Testing of Metallic Materials Part 1: Test Method at Room Temperature," and measurements were taken transversely on sample P7, according to "GBT5028-2008 Measurement Method for Tensile Strain Hardening Index (n-value) of Metallic Sheets and Strips." 90 Obtain a value. [Examples]

[0090] Example 1 The composition of the test steel in this embodiment is shown in Table 1, the specific parameters of the one-stage rapid heat treatment example and the conventional process in this embodiment are shown in Table 2, the specific parameters of the two-stage rapid heat treatment example and the conventional process in this embodiment are shown in Table 3, Table 4 shows the main properties of the duplex steel obtained by the one-stage heating example and the conventional process based on the composition of the test steel in this embodiment, and Table 5 shows the main properties of the duplex steel produced by the two-stage heating example and the conventional process based on the composition of the test steel in this embodiment.

[0091] As can be seen from Tables 1 to 5, the method of the present invention reduces the alloy content in the same level of steel, refines the crystal grains, and provides a material structure with improved strength and toughness. The duplex steel obtained by the method of the present invention has a yield strength of 304-398 MPa, a tensile strength of 630-698 MPa, an elongation of 22.3-29.4%, a strength-ductility product of 15.3-19.4 GPa%, and a strain hardening index of n 90 The value exceeds 0.21.

[0092] Figure 1 is a microstructure diagram of molten zinc-aluminum-magnesium plated duplex steel (AM) produced from test steel A of this embodiment according to Example 1 (single-stage heating) of the present invention; Figures 2 and 3 are microstructure diagrams (two-stage heating) obtained from typical component A steel via Example 1 and comparative conventional process Example 1; Figure 4 is a microstructure diagram of molten aluminum-zinc plated duplex steel (AZ) produced from steel I of this embodiment according to Example 3 (two-stage heating); and Figure 5 is a microstructure diagram of molten zinc-aluminum-magnesium plated duplex steel (AM) produced from steel C of this embodiment at the conventional heating rate (two-stage heating) in Example 15.

[0093] As can be seen from Figures 1 to 5, the microstructure of the material consists of ferrite, martensite, and small amounts of carbides. As shown in Figure 3, the characteristics of the microstructure treated with the conventional process are as follows: the crystal grains are coarse, a certain band-like structure is present, martensite and carbides are distributed in a network along the ferrite crystal boundaries, the ferrite crystal grains are relatively coarse, and the distribution of the two-phase structure of ferrite and martensite is non-uniform.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Table 3]

[0097] [Table 4]

[0098] [Table 5] [Examples]

[0099] Example 2 The composition of the test steel in this embodiment is shown in Table 6, the specific parameters of the one-stage rapid heat treatment embodiment and the conventional process in this embodiment are shown in Table 7, the specific parameters of the two-stage rapid heat treatment embodiment and the conventional process in this embodiment are shown in Table 8, Table 9 shows the main properties of the duplex steel obtained from the one-stage heating embodiment and the conventional process based on the composition of the test steel in this embodiment, and Table 10 shows the main properties of the duplex steel produced from the two-stage heating embodiment and the conventional process based on the composition of the test steel in this embodiment.

[0100] As can be seen from Tables 6 to 10, the method of the present invention reduces the alloy content in the same level of steel, refines the crystal grains, and provides a material structure with a suitable balance of strength and toughness. The duplex steel obtained by the method of the present invention has a yield strength of 476 to 556 MPa, a tensile strength of 786 to 852 MPa, an elongation of 20.1 to 24.8%, a strength-ductility product of 16.7 to 20.2 GPa%, and a strain hardening index of n 90 The value exceeds 0.20.

[0101] Figures 6 and 7 show the microstructure diagrams of molten aluminum zinc-plated duplex steel (AZ) obtained from test steel D of this embodiment via Example 4 and comparative conventional process example 4 (single-stage heating). Figure 8 shows the microstructure diagram of molten aluminum zinc-plated duplex steel (AZ) produced from test steel N of this embodiment by Example 15 (two-stage heating). Figure 9 shows the microstructure diagram of molten zinc-aluminum magnesium-plated duplex steel (AM) produced from test steel E of this embodiment by Example 17 (two-stage heating).

[0102] [Table 6]

[0103] [Table 7]

[0104] [Table 8]

[0105] [Table 9]

[0106] [Table 10]

[0107] The characteristics of the duplex steel structure obtained by processing with the present invention are as follows: the ferrite, martensite grain structure, and carbides are all very fine and uniformly distributed in the base material, which is very advantageous for increasing the strength and plasticity of the material. Therefore, in the method for producing duplex steel of the present invention, the grains are refined and the structure of each phase of the material is uniformly distributed in the base material, improving the structure of the material and enhancing its performance.

[0108] This invention modifies the conventional continuous annealing system through rapid heating and cooling processes, realizing a rapid heat treatment process. This significantly shortens the length of the furnace heating and soaking stages in conventional continuous annealing, increasing the production efficiency of the conventional continuous annealing system, reducing production costs and energy consumption, and improving the control capability of the surface quality of the steel strip by reducing the number of furnace rolls in the continuous annealing furnace, resulting in high-quality steel strip products. At the same time, by establishing a new type of continuous annealing system using rapid heat treatment process technology, it is possible to achieve objectives such as system miniaturization, easy modification of product specifications and varieties, and strong control capability. In terms of materials, the crystal grain of the steel strip is refined, the strength of the material is further increased, alloy costs and the difficulty of manufacturing processes before heat treatment are reduced, and the formability and user performance such as welding of the material are improved.

[0109] As described above, the present invention significantly advances continuous annealing process technology for cold-rolled steel strips through its rapid heat treatment process. Because the cold-rolled steel strip is completed from room temperature to the final austenitization process in just over ten seconds, or even just a few seconds in some cases, the length of the heating phase in the continuous annealing furnace is greatly reduced, making it easier to increase the speed and production efficiency of the continuous annealing system and significantly reducing the number of rolls in the furnace of the continuous annealing system. For rapid heat treatment production lines with a system speed of around 180 meters / minute, the number of rolls in the high-temperature furnace phase is reduced to 10 or less, and the surface quality of the steel strip is significantly improved. At the same time, the rapid heat treatment process method, in which the recrystallization and austenitization processes are completed in a very short time, provides a more flexible microstructure design method for high-strength steel, improving the material's microstructure and enhancing its performance without changing the conditions of the alloy composition and preceding processes such as the rolling process.

[0110] High-strength, advanced steels with highly corrosion-resistant coatings, such as duplex steel, have broad application potential, and rapid heat treatment technology also has enormous development value. Therefore, the combination of these two inevitably provides more room for the development and production of duplex steel.

Claims

1. A steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating with a tensile strength of ≥ 590 MPa, wherein the steel sheet is composed of a duplex steel sheet and the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating on the surface of the duplex steel sheet. The mass percentage of the chemical composition of the aforementioned duplex steel sheet is as follows: C: 0.045-0.12%, Si: 0.1-0.5%, Mn: 1.0-2.0%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02-0.055%, optionally containing one or two of Cr, Mo, Ti, Nb, and V, with Cr + Mo + Ti + Nb + V ≤ 0.5%, and the remainder being Fe and other unavoidable impurities. The steel sheet having the aforementioned highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of ≥300 MPa, tensile strength of ≥590 MPa, elongation of ≥20%, strength-ductility product of ≥15 GPa%, and strain-hardening index n ９０ The value is greater than 0.20; and The steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a metallographic structure of uniformly distributed ferrite and martensite, with an average grain size of 1 to 5 μm.

2. The C content is 0.045 to 0.105%; and / or The Si content is 0.15 to 0.25%; and / or The Mn content is 1.0% to 1.5%; and / or The aforementioned Cr+Mo+Ti+Nb+V ≤ 0.4%; and / or The steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 300 to 560 MPa, a tensile strength of 590 to 860 MPa, an elongation of 20 to 30%, and a strength-ductility product of 15 to 21 GPa%, as described in claim 1.

3. The C content is 0.05 to 0.12%; and / or The Si content is 0.1 to 0.4%; and / or The Mn content is 1.2 to 2.0%; and / or The aforementioned Cr+Mo+Ti+Nb+V ≤ 0.2%; and / or The steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 300 to 400 MPa, a tensile strength of 630 to 860 MPa, an elongation of 20 to 30%, and a strength-ductility product of 15 to 21 GPa%, as described in claim 2.

4. The C content is 0.065 to 0.085%; and / or The Mn content is 1.2% to 1.35%; and / or The steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 450 to 560 MPa, a tensile strength of 590 to 860 MPa, an elongation of 20 to 30%, and a strength-ductility product of 15 to 21 GPa%, as described in claim 2.

5. The C content is 0.07 to 0.10%; and / or The steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 2, wherein the Mn content is 1.5 to 1.8%.

6. The steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating with a tensile strength ≥ 590 MPa has the following mass percentage chemical composition: C: 0.045 to 0.105%, Si: 0.1 to 0.4%, Mn: 1.0 to 1.5%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02 to 0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.3%, with the remainder being Fe and other unavoidable impurities, as described in claim 1.

7. The duplex steel sheet has a carbon content of 0.065 to 0.085%; and / or Duplex steel sheets have a Si content of 0.15 to 0.25%; and / or Duplex steel sheets have a Mn content of 1.2% to 1.35%; and / or In duplex steel sheets, Cr + Mo + Ti + Nb + V ≤ 0.2%; and / or The steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has an average grain size of 1 to 3 μm; and / or The steel sheet having the aforementioned highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 300 to 400 MPa, a tensile strength of 630 to 700 MPa, an elongation of 22 to 30%, a strength-ductility product of 15 to 20 GPa%, and a strain-hardening index n ９０ A steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 6, wherein the value exceeds 0.

21.

8. The steel sheet having the aforementioned highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 304 to 398 MPa, a tensile strength of 630 to 698 MPa, an elongation of 22.3 to 29.4%, a strength-ductility product of 15.3 to 19.4 GPa%, and a strain-hardening index n ９０ A steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 7, wherein the value exceeds 0.

21.

9. The steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating with a tensile strength of ≥ 590 MPa, The mass percentage of the chemical composition of the duplex steel sheet is as follows: C: 0.05-0.12%, Si: 0.1-0.5%, Mn: 1.2-2.0%, P ≤ 0.015%, S ≤ 0.003%, Al: 0.02-0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.5%, with the remainder being Fe and other unavoidable impurities, the steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 1.

10. The duplex steel sheet has a carbon content of 0.07 to 0.10%; and / or Duplex steel sheets have a Si content of 0.1 to 0.4%; and / or Duplex steel sheets have a Mn content of 1.5 to 1.8%; and / or Cr + Mo + Ti + Nb + V ≤ 0.4%; and / or The steel sheet having the aforementioned highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 470 to 560 MPa, a tensile strength of 780 to 860 MPa, an elongation of 20 to 25%, a strength-ductility product of 16 to 21 GPa%, and a strain-hardening index n ９０ A steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 9, wherein the value exceeds 0.

20.

11. The steel sheet having the aforementioned highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 476 to 556 MPa, a tensile strength of 786 to 852 MPa, an elongation of 20.1 to 24.8%, a strength-ductility product of 16.7 to 20.2 GPa%, and a strain-hardening index n ９０ A steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 10, wherein the value exceeds 0.

20.

12. A method for producing a steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating with a tensile strength ≥ 590 MPa according to any one of claims 1 to 11, comprising the following steps: 1) Smelting and casting The chemical composition is described in any one of claims 1 to 7, 9, and 10, and the mixture is cast into a slab; 2) Hot rolling, coiling The winding temperature shall be 550 to 680°C; 3) Cold rolling The cold rolling reduction ratio is set to 40-85%, and after cold rolling, rolled hardened strip steel or steel plate is obtained; 4) Rapid heat treatment, hot-dip aluminum zinc plating, or hot-dip zinc aluminum magnesium plating A) Rapid heating Cold-rolled steel strip or sheet is rapidly heated from room temperature to the endpoint temperature of the austenite-ferrite two-phase region, which is 750 to 845°C, and the rapid heating is performed in one or two stages; When using a single-stage rapid heating system, the heating rate shall be 15 to 500°C / s; In a two-stage rapid heating system, the first stage involves heating from room temperature to 550-650°C at a heating rate of 15-500°C / s, and the second stage involves heating from 550-650°C to 750-845°C at a heating rate of 30-500°C / s. B) Soaking Soaking is performed at 750-845°C, which is the endpoint temperature of the austenite-ferrite two-phase region, with a soaking time of 10-60 seconds. C) cooling After the steel strip or sheet has been heated to a uniform temperature, it is slowly cooled to 670-770°C at a cooling rate of 5-15°C / s; then rapidly cooled to 580-600°C at a cooling rate of 50-200°C / s; D) Hot-dip aluminum zinc plating or hot-dip galvanized aluminum magnesium plating After rapid cooling to 580-600°C, the steel strip or steel plate is immersed in a zinc oven to perform hot-dip aluminum-zinc plating or hot-dip zinc-aluminum-magnesium plating; E) After molten aluminum zinc plating, the aluminum zinc product is rapidly cooled to room temperature at a cooling rate of 30 to 200°C / s; or, After molten zinc-aluminum-magnesium plating, the product is rapidly cooled to room temperature at a cooling rate of 10 to 300°C / s to obtain a zinc-aluminum-magnesium AM product.

13. The entire process of rapid heat treatment and molten aluminum zinc plating or molten zinc-aluminum magnesium plating according to step 4) takes 29 to 159 seconds; and / or In step 2), the hot rolling completion temperature ≥ A ｒ３ ; and / or In step 2), the winding temperature shall be 580 to 650°C; and / or In step 3), the cold rolling reduction ratio shall be 60 to 80%; and / or In step 4), when the rapid heating is a single-stage heating, the heating rate shall be 50 to 300°C / s; and / or In step 4), the rapid heating is a two-stage heating, where in the first stage the temperature is heated from room temperature to 550 to 650°C at a heating rate of 15 to 300°C / s, and in the second stage the temperature is heated from 550 to 650°C to 750 to 845°C at a heating rate of 50 to 300°C / s; and / or In step 4), the final temperature of the rapid heating shall be 770 to 830°C; and / or In the soaking process of step 4), the steel strip or sheet is heated to the endpoint temperature of the austenite-ferrite two-phase region, and then the temperature is kept constant to perform soaking; and / or In the soaking process of step 4), the steel strip or steel plate is subjected to a small increase or decrease in temperature during the soaking time, with the temperature after the increase being 845°C or lower and the temperature after the decrease being 750°C or higher; and / or The soaking time shall be 10 to 40 seconds; The method according to claim 12.

14. In step A), when single-stage rapid heating is used, the heating rate is 50 to 500°C / s; and / or In step A), when two-stage rapid heating is performed, in the first stage the rolled hardened strip steel or steel plate is heated from room temperature to 550 to 650°C at a heating rate of 15 to 500°C / s, and in the second stage it is heated from 550 to 650°C to 750 to 845°C at a heating rate of 50 to 500°C / s; and / or In step C), after soaking is complete, the steel strip or steel plate is slowly cooled to 670-770°C at a cooling rate of 5-15°C / s, and then rapidly cooled to 580-600°C at a cooling rate of 50-150°C / s; and / or In step E), after molten aluminum zinc plating, the steel plate is rapidly cooled to room temperature at a cooling rate of 30 to 150°C / s to obtain an aluminum zinc AZ product; and / or In step E), after molten zinc-aluminum-magnesium plating, the product is rapidly cooled to room temperature at a cooling rate of 30 to 180°C / s to obtain a zinc-aluminum-magnesium AM product. The method according to claim 12.

15. Step 4) The entire process of the rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating takes 29 to 122 seconds; and / or In step 4), the rapid heating is performed in two stages, where the steel strip or steel plate is heated from room temperature to 550 to 650°C in the first stage at a heating rate of 30 to 300°C / s, and then heated from 550 to 650°C to 750 to 845°C in the second stage at a heating rate of 80 to 300°C / s; In step 4), after molten zinc-aluminum-magnesium plating, the steel sheet is rapidly cooled to room temperature at a cooling rate of 30 to 250°C / s to obtain a zinc-aluminum-magnesium AM product; The method according to claim 13.

16. A method according to claim 12, The above method is as follows: (1) The steel strip or steel sheet has the following mass percentages of chemical composition: C: 0.045 to 0.105%, Si: 0.1 to 0.4%, Mn: 1.0 to 1.5%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02 to 0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.3%, with the remainder being Fe and other unavoidable impurities, provided that after molten aluminum zinc plating, it is cooled to room temperature at a cooling rate of 30 to 200°C / s to obtain an aluminum zinc AZ product, or after molten zinc aluminum magnesium plating, it is cooled to room temperature at a cooling rate of 30 to 180°C / s to obtain a zinc aluminum magnesium AM product; or The above method is as follows: (2) The steel strip or steel sheet has the following mass percentages of chemical composition: C: 0.05 to 0.12%, Si: 0.1 to 0.5%, Mn: 1.2 to 2.0%, P ≤ 0.015%, S ≤ 0.003%, Al: 0.02 to 0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.5%, with the remainder being Fe and other unavoidable impurities; provided that after molten aluminum zinc plating, it is rapidly cooled to room temperature at a cooling rate of 30 to 150°C / s to obtain an aluminum zinc AZ product, or after molten zinc aluminum magnesium plating, it is rapidly cooled to room temperature at a cooling rate of 10 to 300°C / s to obtain a zinc aluminum magnesium AM product.

17. The method according to claim 16, (1) In step 4), the entire process of the rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating takes 29 to 122 seconds; or (2) The method wherein the entire process of the rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating takes 29 to 159 seconds.

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