590mpa grade hot dip galvanized dual phase steel with different yield strengths and method for manufacturing the same

Abstract

The application provides a 590MPa grade hot-dip galvanizing dual-phase steel with different yield strengths and a preparation method thereof. The 590MPa grade hot-dip galvanizing dual-phase steel prepared by the preparation method comprises C: 0.06-0.14wt%, Si: 0.2-0.35wt%, Mn: 1.8-2.5wt%, Cr: 0.1-0.2wt%, and the rest is iron and inevitable impurities. The 590MPa grade hot-dip galvanizing dual-phase steel comprises two yield strength grades of 340-390MPa and 390-440MPa. The preparation method of the application controls annealing and finishing parameters, so that the 590MPa grade hot-dip galvanizing dual-phase steel with different yield strengths is prepared under the condition of the same components to meet different use requirements of different customers, and the technical problems of high production cost and poor effect in the related art are solved.

Description

Technical Field

[0001] This invention relates to the field of steel plate processing technology, and in particular to a 590MPa grade hot-dip galvanized duplex steel with different yield strengths and its preparation method. Background Technology

[0002] With the development of lightweight automobiles, the application ratio of high-strength steel in automobiles is increasing. Hot-dip galvanized duplex steel has become one of the important types of automotive parts due to its excellent corrosion resistance, low yield strength ratio, excellent ductility and easy processing and forming properties.

[0003] Because customers have different processing methods and uses, their performance requirements for products are also different. For example, stamping parts prefer lower yield strength to meet the processing requirements of stamping parts with higher depth requirements; while rolling parts prefer higher yield strength to provide better safety performance.

[0004] Currently, the production of duplex steel with different yield strengths is generally controlled by adjusting alloying elements or finishing elongation. However, the above process has technical problems such as high production cost and poor effect.

[0005] In summary, there is an urgent need for a 590MPa grade hot-dip galvanized duplex steel with different yield strengths and its preparation method to solve the problems existing in the related technologies. Summary of the Invention

[0006] The main objective of this invention is to provide a 590MPa grade hot-dip galvanized duplex steel with different yield strengths and its preparation method, so as to solve the technical problems of high production cost and poor effect in the production of duplex steel with different yield strengths by adjusting alloying elements or finishing elongation in related technologies.

[0007] To achieve the above objectives, the present invention provides a 590MPa grade hot-dip galvanized duplex steel with different yield strengths, the composition of which includes C: 0.06-0.14wt%; Si: 0.2-0.35wt%; Mn: 1.8-2.5wt%; Cr: 0.1-0.2wt%; the remainder being iron and unavoidable impurities;

[0008] The 590MPa grade hot-dip galvanized duplex steel includes two yield strength levels: 340-390MPa and 390-440MPa.

[0009] Preferably, the composition of the 590MPa grade hot-dip galvanized duplex steel includes C: 0.06-0.10wt%; Si: 0.2-0.25wt%; Mn: 2.0-2.5wt%; Cr: 0.1-0.2wt%; with the remainder being iron and unavoidable impurities.

[0010] The beneficial effects of this invention are that it provides 590MPa grade hot-dip galvanized duplex steel with two yield strength levels of 340-390MPa and 390-440MPa, with the same composition, to meet the different application needs of different customers (such as stamping and rolling).

[0011] The present invention also provides a preparation method for manufacturing the above-mentioned 590MPa grade hot-dip galvanized duplex steel, comprising: hot-dip galvanizing and annealing and finishing the pickled rolled steel strip according to the parameters corresponding to different yield strength levels to obtain 590MPa grade hot-dip galvanized duplex steel; the 590MPa grade hot-dip galvanized duplex steel includes two yield strength levels: 340-390MPa and 390-440MPa.

[0012] The composition of the pickled steel strip is the same as that of the above-mentioned 590MPa grade hot-dip galvanized duplex steel.

[0013] Preferably, the preparation process of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa includes:

[0014] The pickled and rolled steel strip is subjected to hot-dip galvanizing annealing, which includes sequential annealing and galvanizing. In the annealing step, the preheating temperature is 520–680℃, and the preheating time is 1–3 min; the heating temperature is 740–760℃, and the heating time is 2–5 min; the soaking temperature is 750–770℃, and the soaking time is 3–6 min; the slow cooling temperature is 690–710℃, the rapid cooling temperature is 450–460℃, and the rapid cooling rate is 25–30℃ / s; the temperature upon entering the zinc pot is 440–455℃.

[0015] The galvanized steel strip is then smoothed to obtain 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa. The elongation rate in the smoothing step is 0.2-0.4%.

[0016] Preferably, the annealing speed of the steel strip in the annealing step is 60-120 mpm.

[0017] Preferably, the metallographic structure of the 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa includes martensite, ferrite and pearlite, wherein the volume percentage of martensite is 20-22%, the volume percentage of ferrite is 73-77%, and the volume percentage of pearlite is 3-5%.

[0018] Preferably, the preparation process of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa includes:

[0019] The pickled and rolled steel strip is subjected to hot-dip galvanizing annealing, which includes sequential annealing and galvanizing. In the annealing step, the preheating temperature is 580–680℃, and the preheating time is 1–3 min; the heating temperature is 790–810℃, and the heating time is 2–5 min; the soaking temperature is 800–820℃, and the soaking time is 3–6 min; the slow cooling temperature is 650–670℃, the rapid cooling temperature is 450–460℃, and the rapid cooling rate is 15–20℃ / s; the temperature upon entering the zinc pot is 440–455℃.

[0020] The galvanized steel strip is then smoothed to obtain 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa. The elongation rate during the smoothing step is 0.4-0.6%.

[0021] Preferably, the annealing speed of the steel strip in the annealing step is 60-120 mpm.

[0022] Preferably, the metallographic structure of the 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa includes martensite, ferrite and pearlite, wherein the volume percentage of martensite is 23-26%, the volume percentage of ferrite is 70-73%, and the volume percentage of pearlite is 1-4%.

[0023] Preferably, the manufacturing steps of the pickled steel strip include sequentially desulfurizing molten iron, converter smelting, LF refining, continuous casting, hot rolling, and pickling to obtain pickled steel coils; wherein, the parameter conditions of some steps are as follows:

[0024] Converter smelting: tapped steel C≤0.070wt%, argon station C≤0.090wt%, tapping temperature>1650℃;

[0025] LF refining: C: 0.06~0.15wt%, Si: 0.2~0.35wt%, Mn: 1.6~2.5wt%, Cr: 0.10~0.20wt%;

[0026] Continuous casting: C: 0.06~0.15wt%, Si: 0.2~0.35wt%, Mn: 1.6~2.5wt%, Cr: 0.10~0.20wt%;

[0027] Hot rolling: furnace exit temperature 1150-1350℃; final rolling temperature 890±20℃; coiling temperature 580±20℃.

[0028] Pickling and rolling: reduction rate 50%–70%.

[0029] The beneficial effects of the present invention are as follows: the preparation method of the present invention, by controlling the annealing and finishing parameters, can prepare 590MPa grade hot-dip galvanized duplex steel with different yield strengths under the same composition to meet the different application needs of different customers. It solves the technical problems of high production cost and poor effect in the production of duplex steel with different yield strengths by adjusting alloying elements or finishing elongation in related technologies. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that all directional indicators (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicator will also change accordingly.

[0032] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0033] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0034] This invention provides a 590MPa grade hot-dip galvanized duplex steel with different yield strengths, the composition of which includes C: 0.06-0.14wt%; Si: 0.2-0.35wt%; Mn: 1.8-2.5wt%; Cr: 0.1-0.2wt%; the remainder being iron and unavoidable impurities;

[0035] The 590MPa grade hot-dip galvanized duplex steel includes two yield strength levels: 340-390MPa and 390-440MPa.

[0036] In some embodiments, the composition of the 590MPa grade hot-dip galvanized duplex steel includes C: 0.06-0.10wt%; Si: 0.2-0.25wt%; Mn: 2.0-2.5wt%; Cr: 0.1-0.2wt%; with the remainder being iron and unavoidable impurities.

[0037] This invention provides 590MPa grade hot-dip galvanized duplex steel with two yield strength levels of 340-390MPa and 390-440MPa, with the same composition, to meet the different application needs of different customers (such as stamping and rolling).

[0038] During their research, the inventors discovered that the elements and their corresponding contents in duplex steel have a significant impact on the yield strength and tensile strength of duplex steel, specifically:

[0039] C (carbon): Carbon plays a phase transformation strengthening role in the duplex steel of this application. As the carbon content in the steel increases, the yield strength and tensile strength of the duplex steel also increase, but the plasticity and toughness will also decrease. In this application, the inventors also found that too high carbon content will affect the iron-zinc reaction, resulting in an iron-zinc alloy layer that is too thick and thus the zinc layer has poor adhesion. Therefore, the carbon content used in this application is 0.06-0.14 wt%, and the more preferred carbon content is 0.06-0.10 wt%.

[0040] Silicon (Si): Silicon can increase the temperature of the transformation from supercooled austenite to ferrite. In solid cast iron, silicon is almost entirely dissolved in austenite and ferrite and does not enter carbides. Silicon atoms combine with iron atoms to form silicon-containing ferrite with strong covalent bonds, thereby promoting the precipitation of ferrite and increasing the enrichment of carbon in ferrite into austenite. Under the same cooling rate, more austenite is obtained, and the retained austenite will transform into martensite. Therefore, the silicon content used in this application is 0.2-0.35 wt%, and a further preferred silicon content is 0.2-0.25 wt%.

[0041] Manganese (Mn) in duplex steel expands the austenite region and delays the transformation of pearlite and bainite during the cooling process of supercooled austenite, thereby improving the hardenability of the steel and promoting the formation of martensite during rapid cooling after slow cooling. Similar to carbon, manganese reduces the amount of carbon used in duplex steel, increasing its yield strength and tensile strength while maintaining good plasticity and ductility. Therefore, the manganese content used in this application is 1.8-2.5 wt%, with a more preferred content of 2.0-2.5 wt%.

[0042] Cr (chromium): To reduce energy consumption and obtain martensitic structure at lower cooling rates, it is necessary to increase the alloying elements in steel to shift the transformation curves of pearlite and bainite to the right, so that the steel plate does not come into contact with the transformation curves of pearlite and bainite during cooling. Among the aforementioned elements, Mn can shift the CCT curve to the right, but excessive addition of manganese will result in poor platingability of duplex steel. Therefore, the addition of Cr in this application has the same effect, which is beneficial to reducing the cooling rate requirement, expanding the austenite region, and avoiding the sharp decrease in thermal conductivity and increase in the coefficient of linear expansion of steel due to excessive manganese content. This also avoids the formation of large internal stress during rapid heating or cooling of duplex steel and reduces the tendency to crack.

[0043] In addition, adding chromium to duplex steel can improve its tensile strength, yield strength, wear resistance, and corrosion resistance. Therefore, the chromium content used in this application is 0.1-0.2 wt%.

[0044] The present invention also provides a preparation method for manufacturing the above-mentioned 590MPa grade hot-dip galvanized duplex steel, comprising: hot-dip galvanizing and annealing and finishing the pickled rolled steel strip according to the parameters corresponding to different yield strength levels to obtain 590MPa grade hot-dip galvanized duplex steel; the 590MPa grade hot-dip galvanized duplex steel includes two yield strength levels: 340-390MPa and 390-440MPa.

[0045] The composition of the pickled steel strip is the same as that of the above-mentioned 590MPa grade hot-dip galvanized duplex steel.

[0046] The preparation method of this invention, by controlling the annealing and finishing parameters, can prepare 590MPa grade hot-dip galvanized duplex steel with different yield strengths under the same composition to meet the different application needs of different customers. It solves the technical problems in related technologies where adjusting alloying elements makes production casting more difficult and production costs higher; and that adjusting the finishing elongation has little effect on yield strength, resulting in less than ideal results.

[0047] In some embodiments, the preparation process of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa includes:

[0048] The pickled and rolled steel strip is subjected to hot-dip galvanizing annealing, which includes sequential annealing and galvanizing. In the annealing step, the preheating temperature is 520–680℃, and the preheating time is 1–3 min; the heating temperature is 740–760℃, and the heating time is 2–5 min; the soaking temperature is 750–770℃, and the soaking time is 3–6 min; the slow cooling temperature is 690–710℃, the rapid cooling temperature is 450–460℃, and the rapid cooling rate is 25–30℃ / s; the temperature upon entering the zinc pot is 440–455℃.

[0049] The galvanized steel strip is then smoothed to obtain 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa. The elongation rate in the smoothing step is 0.2-0.4%.

[0050] This application transforms the ferrite in the pickled and rolled steel coil into ferrite + austenite by annealing, and then transforms the austenite into martensite during the cooling process, finally obtaining a 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa, consisting of martensite + ferrite + a small amount of pearlite / bainite.

[0051] Specifically, by controlling the homogenization temperature to 750–770°C, a significant amount of ferrite in the pickled steel coil is transformed into austenite. During the subsequent slow cooling process, the selected cooling temperature is lower than that in related technologies, thus preventing secondary ferrite formation in some microstructures of the duplex steel, which would otherwise lead to a decrease in the yield strength of the duplex steel.

[0052] Subsequently, by setting a faster cooling rate, the austenite in the microstructure is transformed into martensite, effectively improving the yield strength of the duplex steel. The annealed duplex steel, combined with the selection of elongation range in the finishing process, results in a yield strength between 340-390 MPa, which can meet the requirements of some applications, such as stamping.

[0053] In some embodiments, the annealing speed of the steel strip in the annealing step is 60-120 mpm.

[0054] In some embodiments, the metallographic structure of the 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa includes martensite, ferrite and pearlite, wherein the volume percentage of martensite is 20-22%, the volume percentage of ferrite is 73-77%, and the volume percentage of pearlite is 3-5%.

[0055] In some embodiments, the preparation process of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa includes:

[0056] The pickled and rolled steel strip is subjected to hot-dip galvanizing annealing, which includes sequential annealing and galvanizing. In the annealing step, the preheating temperature is 580–680℃, and the preheating time is 1–3 min; the heating temperature is 790–810℃, and the heating time is 2–5 min; the soaking temperature is 800–820℃, and the soaking time is 3–6 min; the slow cooling temperature is 650–670℃, the rapid cooling temperature is 450–460℃, and the rapid cooling rate is 15–20℃ / s; the temperature upon entering the zinc pot is 440–455℃.

[0057] The galvanized steel strip is then smoothed to obtain 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa. The elongation rate during the smoothing step is 0.4-0.6%.

[0058] This application transforms the ferrite in the pickled and rolled steel coil into ferrite + austenite by annealing, and then transforms the austenite into martensite during the cooling process, finally obtaining a 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa, consisting of martensite + ferrite + a small amount of pearlite / bainite.

[0059] In particular, by controlling the homogenization temperature to 800–820℃ (which is higher than the homogenization temperature of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340–390MPa, resulting in a greater conversion of ferrite), more ferrite in the acid-rolled steel coil is converted into austenite. In the subsequent slow cooling process, the selected cooling temperature is lower than that in related technologies, thus avoiding the secondary formation of ferrite in some structures of the duplex steel, which would lead to a decrease in the yield strength of the duplex steel.

[0060] Subsequently, by setting a faster cooling rate, the austenite in the microstructure is transformed into martensite, effectively improving the yield strength of the duplex steel. The annealed duplex steel, combined with the selection of elongation range in the finishing process, results in a yield strength between 390-440 MPa, which can meet the requirements of some applications, such as rolling.

[0061] In some embodiments, the annealing speed of the steel strip in the annealing step is 60-120 mpm.

[0062] In some embodiments, the metallographic structure of the 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa includes martensite, ferrite and pearlite, wherein the volume percentage of martensite is 23-26%, the volume percentage of ferrite is 70-73%, and the volume percentage of pearlite is 1-4%.

[0063] In some embodiments, the manufacturing steps of the pickled steel strip include sequentially subjecting molten iron to desulfurization, converter smelting, LF refining, continuous casting, hot rolling, and pickling to obtain pickled steel coils; wherein, the parameter conditions for some steps are as follows:

[0064] Converter smelting: tapped steel C≤0.070wt%, argon station C≤0.090wt%, tapping temperature>1650℃;

[0065] LF refining: C: 0.06-0.15wt%, Si: 0.2-0.35wt%, Mn: 1.6-2.5wt%, Cr: 0.10-0.20wt%.

[0066] Continuous casting: C: 0.06~0.15wt%, Si: 0.2~0.35wt%, Mn: 1.6~2.5wt%, Cr: 0.10~0.20wt%.

[0067] Hot rolling: furnace exit temperature 1150-1350℃; final rolling temperature 890±20℃; coiling temperature 580±20℃.

[0068] Pickling and rolling: reduction rate 50%–70%.

[0069] This application controls the composition after each step in the preparation of pickled and rolled steel coils, so that the final pickled and rolled steel coils meet the preset composition range, thereby enabling the tensile strength of the duplex steel obtained from it to reach 590MPa. Furthermore, by combining the annealing and finishing steps, it is possible to prepare two 590MPa grade hot-dip galvanized duplex steels with different yield strengths without adjusting the composition ratio.

[0070] Example

[0071] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0072] Example 1

[0073] A method for preparing 590MPa grade hot-dip galvanized duplex steel with different yield strengths, comprising:

[0074] The molten iron is subjected to desulfurization, converter smelting, LF refining, continuous casting, hot rolling, pickling rolling, hot-dip galvanizing annealing, and finishing in sequence; the parameter conditions for some steps are as follows:

[0075] Converter smelting: tapped steel C≤0.070wt%, argon station C≤0.090wt%, tapping temperature 1700℃;

[0076] LF refining: C: 0.06wt%, Si: 0.35wt%, Mn: 2.5wt%, Cr: 0.10wt%;

[0077] Continuous casting: C: 0.06wt%, Si: 0.35wt%, Mn: 2.5wt%, Cr: 0.10wt%;

[0078] Hot rolling: furnace exit temperature 1300℃; final rolling temperature 900℃; coiling temperature 580℃;

[0079] Pickling and rolling: reduction rate 59%.

[0080] Hot-dip galvanizing annealing: The pickled and rolled steel strip is annealed and galvanized sequentially; in the annealing step, the preheating temperature is 680℃ and the preheating time is 2min; the heating temperature is 750℃ and the heating time is 3min; the soaking temperature is 750℃ and the soaking time is 6min; the slow cooling temperature is 710℃, the rapid cooling temperature is 460℃ and the rapid cooling rate is 25℃ / s; the annealing speed of the steel strip is 80mpm; the temperature of entering the zinc pot is 450℃.

[0081] Finishing: elongation 0.3%; to obtain hot-dip galvanized duplex steel, the composition of which includes C: 0.06wt%; Si: 0.35wt%; Mn: 2.5wt%; Cr: 0.1wt%; the remainder being iron and unavoidable impurities.

[0082] Examples 2-10 and Comparative Examples 1-10

[0083] The preparation processes of Examples 2-10 and Comparative Examples 1-10 are similar to those of Example 1. The difference lies in the chemical composition of the hot-dip galvanized duplex steel and the different process parameters of some steps. The differences in the chemical composition of the galvanized duplex steel are shown in Table 1, and the differences in the process parameters are shown in Table 2.

[0084] Table 1. Differences in the chemical composition of galvanized duplex steels in Examples 1-10 and Comparative Examples 1-10

[0085]

[0086]

[0087] Note: The remainder consists of iron and unavoidable impurities.

[0088] Table 2. Differences in process parameters between Examples 2-10 and Comparative Examples 1-10

[0089]

[0090] Performance tests were conducted on Examples 1-7 and Comparative Examples 1-7, including tensile tests and quantitative metallographic statistical tests. The test results are shown in Table 3.

[0091] Table 3 Performance Test Results

[0092] project Yield strength tensile strength Metallographic composition Example 1 362 619 21% martensite + 75% ferrite + 4% pearlite Example 2 369 623 21% martensite + 75% ferrite + 4% pearlite Example 3 357 614 20% martensite + 75% ferrite + 5% pearlite Example 4 378 628 22% martensite + 75% ferrite + 3% pearlite Example 5 428 669 26% martensite + 71% ferrite + 3% pearlite Example 6 417 654 25% martensite + 72% ferrite + 3% pearlite Example 7 402 648 24% martensite + 73% ferrite + 3% pearlite Comparative Example 1 304 527 15% martensite + 83% ferrite + 2% pearlite Comparative Example 2 339 573 18% martensite + 78% ferrite + 4% pearlite Comparative Example 3 320 577 16% martensite + 82% ferrite + 2% pearlite Comparative Example 4 347 578 20% martensite + 74% ferrite + 6% pearlite Comparative Example 5 317 549 17% martensite + 80% ferrite + 3% pearlite Comparative Example 6 305 548 14% martensite + 84% ferrite + 2% pearlite Comparative Example 7 302 519 12% martensite + 86% ferrite + 2% pearlite

[0093] As shown in Table 3, the duplex steels of Examples 1-7 have better performance than those of Comparative Examples 1-7. This demonstrates that the selection of chemical composition range and process parameter range in this invention has a significant effect on improving the performance of duplex steels. Without introducing new elements, it is possible to obtain 590MPa grade hot-dip galvanized duplex steels with yield strength of 340-390MPa and 590MPa grade hot-dip galvanized duplex steels with yield strength of 390-440MPa.

[0094] As can be seen from Examples 1-7 and Comparative Examples 1-7, the chemical composition of duplex steel and the process parameters in the smelting process of duplex steel have a significant impact on the performance of duplex steel. When the proportion of a certain element and / or the process parameters are higher or lower than the preferred range of this application, the yield strength and tensile strength of the obtained duplex steel decrease significantly, and the martensite content in the corresponding duplex steel also decreases significantly. For example, when the C content in Comparative Examples 2 and 6 is 0.2%, it will also affect the subsequent hot-dip galvanizing step, resulting in the zinc layer not being able to bond well with the surface of the duplex steel.

[0095] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing 590MPa grade hot-dip galvanized duplex steel with different yield strengths, characterized in that, Its composition includes C: 0.06-0.14wt%; Si: 0.2-0.35wt%; Mn: 1.8-2.5wt%; Cr: 0.1-0.2wt%; the remainder being iron and unavoidable impurities; The 590MPa grade hot-dip galvanized duplex steel includes two yield strength levels: 340-390MPa and 390-440MPa. The 590MPa grade hot-dip galvanized duplex steel includes: hot-dip galvanizing and annealing and finishing of pickled rolled steel strip according to parameters corresponding to different yield strength levels to obtain 590MPa grade hot-dip galvanized duplex steel; The composition of the pickled and rolled steel strip is the same as that of the 590MPa grade hot-dip galvanized duplex steel. The preparation process of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa includes: The pickled and rolled steel strip is subjected to hot-dip galvanizing annealing, which includes sequential annealing and galvanizing. In the annealing step, the preheating temperature is 520–680℃, and the preheating time is 1–3 min; the heating temperature is 740–760℃, and the heating time is 2–5 min; the soaking temperature is 750–770℃, and the soaking time is 3–6 min; the slow cooling temperature is 690–710℃, the rapid cooling temperature is 450–460℃, and the rapid cooling rate is 25–30℃ / s; the temperature upon entering the zinc pot is 440–455℃. The galvanized steel strip is then smoothed to obtain 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa. The elongation during the smoothing step is 0.2-0.4%. The preparation process of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa includes: The pickled and rolled steel strip is subjected to hot-dip galvanizing annealing, which includes sequential annealing and galvanizing. In the annealing step, the preheating temperature is 580–680℃, and the preheating time is 1–3 min; the heating temperature is 790–810℃, and the heating time is 2–5 min; the soaking temperature is 800–820℃, and the soaking time is 3–6 min; the slow cooling temperature is 650–670℃, the rapid cooling temperature is 450–460℃, and the rapid cooling rate is 15–20℃ / s; the temperature upon entering the zinc pot is 440–455℃. The galvanized steel strip is then smoothed to obtain 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa. The elongation rate in the smoothing step is 0.4-0.6%.

2. The method for preparing 590MPa grade hot-dip galvanized duplex steel with different yield strengths according to claim 1, characterized in that, The 590MPa grade hot-dip galvanized duplex steel composition includes C: 0.06-0.10wt%; Si: 0.2-0.25wt%; Mn: 2.0-2.5wt%; Cr: 0.1-0.2wt%; the remainder is iron and unavoidable impurities.

3. The method for preparing 590MPa grade hot-dip galvanized duplex steel with different yield strengths according to claim 1, characterized in that, In the preparation of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa, the annealing speed of the steel strip in the annealing step is 60-120mpm.

4. The method for preparing 590MPa grade hot-dip galvanized duplex steel with different yield strengths according to claim 1, characterized in that, The metallographic structure of the 590MPa grade hot-dip galvanized duplex steel with a yield strength of 340-390MPa includes martensite, ferrite and pearlite, wherein the volume percentage of martensite is 20-22%, the volume percentage of ferrite is 73-77%, and the volume percentage of pearlite is 3-5%.

5. The method for preparing 590MPa grade hot-dip galvanized duplex steel with different yield strengths according to claim 1, characterized in that, In the preparation of 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa, the annealing speed of the steel strip in the annealing step is 60-120mpm.

6. The method for preparing 590MPa grade hot-dip galvanized duplex steel with different yield strengths according to claim 1, characterized in that, The metallographic structure of the 590MPa grade hot-dip galvanized duplex steel with a yield strength of 390-440MPa includes martensite, ferrite and pearlite, wherein the volume percentage of martensite is 23-26%, the volume percentage of ferrite is 70-73%, and the volume percentage of pearlite is 1-4%.

7. The method for preparing 590MPa grade hot-dip galvanized duplex steel with different yield strengths according to claim 1, characterized in that, The manufacturing steps of the pickled and rolled steel strip include desulfurizing molten iron, converter smelting, LF refining, continuous casting, hot rolling, and pickling to obtain pickled and rolled steel coils; wherein the parameter conditions of some steps are as follows: Converter smelting: tapped steel C≤0.070wt%, argon station C≤0.090wt%, tapping temperature>1650℃; LF refining: C: 0.06~0.15wt%, Si: 0.2~0.35wt%, Mn: 1.6~2.5wt%, Cr: 0.10~0.20wt%; Continuous casting: C: 0.06~0.15wt%, Si: 0.2~0.35wt%, Mn: 1.6~2.5wt%, Cr: 0.10~0.20wt%; Hot rolling: furnace exit temperature 1150-1350℃; final rolling temperature 890±20℃; coiling temperature 580±20℃. Pickling and rolling: reduction rate 50% to 70%.

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