Preparation method of low-cost 1000MPa-grade cold-rolled dual-phase steel plate

Abstract

The invention discloses a preparation method of a low-cost 1000MPa-grade cold-rolled dual-phase steel plate. The low-cost 1000MPa-grade cold-rolled dual-phase steel plate comprises the following components in percentage by weight: 0.16%-0.18% of C, 0.30%-0.40% of Si, 1.65%-1.80% of Mn, 0.20%-0.30% of Cr, 0.020%-0.040% of Ti, 0.0015%-0.003% of B, 0.030%-0.060% of Al, less than or equal to 0.015% of P, less than or equal to 0.010% of S and the balance of Fe and other inevitable impurities. Through low-cost component design and effective control of key process parameters of each process section, the tensile strength of the prepared cold-rolled dual-phase steel plate is larger than or equal to 980 MPa, the yield strength is 550-730 MPa, the A80 percentage elongation after fracture is larger than or equal to 10%, and the 1000 Mpa-grade cold-rolled dual-phase steel is produced through a low-cost gas cooling line while the comprehensive application performance is achieved.

Description

Technical Field

[0001] This invention relates to the fields of materials and metallurgy, and more specifically, to a method for preparing a low-cost 1000MPa grade cold-rolled duplex steel sheet. Background Technology

[0002] With the continuous development of lightweighting in automobiles, the increasing requirements for corrosion protection in car bodies, and the trend towards a low-carbon environment, the application of 1000MPa grade advanced high-strength steel products in automobile bodies is gradually increasing. Among them, dual-phase steel, complex-phase steel, and quenched fractional steel are the most mature and widely used. Dual-phase steel, in particular, consists of ferrite and a matrix of dispersed hard martensite. The hard martensite mainly plays a strengthening role, while the soft ferrite matrix contributes good elongation. This gives dual-phase steel characteristics such as a low yield strength ratio, high initial work hardening rate, and good strength-ductility balance, making it widely used in automotive structural components such as longitudinal beams, bumpers, and suspension systems, thus becoming an important automotive steel product.

[0003] However, due to the varying cooling methods used in continuous annealing production lines across different steel mills, each mill needs to employ different chemical composition systems to produce 1000MPa grade cold-rolled duplex steel products. This necessitates specialized design of the product alloy composition, and the process formulation must be matched to both the alloy design and the production line conditions. Furthermore, cost must be considered. Therefore, the demand for low-cost cold-rolled duplex steel products as automotive raw materials is extremely urgent.

[0004] In the past, the production of low-cost 1000MPa grade cold-rolled duplex steel products mainly involved high carbon and water-cooled production lines. This process required a large amount of unnecessary energy and often involved the addition of a large number of alloying elements, resulting in high alloy costs. Chinese patent CN117248158A discloses a low-cost, high-uniform-elongation 980MPa continuously annealed dual-phase steel and its preparation method. The alloy composition includes: C: 0.12%-0.17%, Si: 0.35%-0.60%, Mn: 1.90%-2.30%, P≤0.018%, S≤0.015%, N≤0.0060%, Cu: 0.020%-0.10%, Als: 0.02%-0.07%, N≤0.0060%, Cr: 0.35%-0.70%, Nb: 0.01%-0.03%, Ti: 0.01%-0.03%, B: 0.0010%-0.0050%, with the remainder being Fe and unavoidable impurities. This patent incorporates excessive amounts of the alloying element Cr, and also includes the expensive element Nb, significantly increasing the alloy cost. Chinese patent CN116043109A discloses a low-cost, high-hole-expansion-performance 980MPa grade hot-dip galvanized duplex steel and its preparation method. The alloy composition includes: C: 0.05%-0.12%, Si: 0.15%-0.40%, Mn: 2.10%-2.50%, P≤0.018%, S≤0.009%, Als: 0.010%-0.065%, N≤0.0065%, Cr: 0.25%-0.65%, Nb: 0.01%-0.03%, Ti: 0.005%-0.035%, B: 0.0010%-0.0050%, with the remainder being Fe and unavoidable impurities. The high Mn content in this patent tends to lower the martensitic transformation temperature, potentially negatively impacting weldability. Furthermore, the excessive Cr and the addition of expensive Nb significantly increase the alloy cost. Chinese Patent CN111455285A discloses a low-cost and easily produced cold-rolled duplex steel with a tensile strength of 980MPa and its production method. The steel contains the following chemical composition by mass percentage: C: 0.080%-0.095%, Si: 0.4%-0.6%, Mn: 2.1%-2.3%, Als: 0.06%-0.08%, Cr: 0.2%-0.4%, Nb: 0.03%-0.05%, Ti: 0.01%-0.02%, Ca: 0.0015%-0.0040%, P≤0.012%, S≤0.005%, N≤0.005%, with the balance being Fe and unavoidable impurities.Similarly, this patent has a high Mn content, which easily lowers the martensitic transformation temperature and has an adverse effect on weldability. Furthermore, the high Si content leads to an increase in iron oxide scale on the surface of the continuously cast billet, requiring an iron oxide scale removal process. Direct hot-rolling production is not possible, significantly increasing production costs. Additionally, the addition of expensive Nb to the alloy composition system greatly increases the alloy cost. Chinese patent CN112281062A discloses a 1000MPa grade low-cost hot-dip galvanized duplex steel and its preparation method. By weight percentage, the hot-dip galvanized duplex steel is composed of the following elements: C: 0.080-0.100%, Si: 0.35-0.55%, Mn: 2.40-2.60%, Cr: 0.45-0.55%, P≤0.015%, S≤0.008%, Al: 0.030-0.050%, with the balance being Fe and unavoidable inclusions. This patented technology has a high Mn content, which can lower the martensitic transformation temperature and negatively impact weldability. The excessive addition of Cr significantly increases the alloy cost. Furthermore, this technology falls under the category of hot-dip galvanized duplex steel. Chinese patent CN109913763A discloses a low-cost cold-rolled duplex steel with good cold-working properties (1000MPa grade) and its manufacturing method. The steel comprises the following chemical composition: C: 0.15-0.20, Mn: 1.20-1.70, Si: 0.20-0.50, Als: 0.40-0.80, 0.005≤P≤0.015, 0.0001≤S≤0.0010, Cr: 0.32-0.50, Nb: 0.010-0.05, Ca: 0.0005-0.0025, O≤0.002, 0.001≤N≤0.004, with the remainder being Fe and unavoidable impurities; and 0.50≤Si+Als≤0.80. This patent's high Al content easily leads to nozzle blockage, causing difficulties in continuous casting and potentially resulting in production accidents. Furthermore, the production cost is relatively high. Chinese patent CN105950998A discloses a 1000MPa grade low-carbon hot-dip galvanized duplex steel and its preparation method, composed of the following weight percentages: C: 0.07-0.10%, Si: 0.30-0.50%, Mn: 1.60-1.90%, Cr: 0.40-0.70%, Mo: 0.30-0.50%, Al: 0.02-0.05%, Ti: 0.030-0.050%, Nb: 0.020-0.040%, B: 0.0020-0.0030%, P≤0.012%, S≤0.002%, N≤0.0040%, with the balance being Fe and unavoidable impurities. This patent incorporates a large amount of Cr, and also adds expensive Nb and Mo elements to the alloy composition system, significantly increasing the alloy cost. Furthermore, this technology belongs to the field of hot-dip galvanized duplex steel.

[0005] Therefore, how to study a low-cost method for producing cold-rolled duplex steel sheets has become an urgent problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the aforementioned deficiencies in the existing technology and provide a low-cost method for preparing 1000MPa grade cold-rolled duplex steel sheets. Addressing market demand and the practicalities of gas-cooled production lines, this invention reduces the amount of alloying components added, significantly lowering costs. Simultaneously, by effectively controlling key process parameters at each stage, it ensures that the resulting cold-rolled duplex steel sheet has a tensile strength ≥980MPa and a yield strength of 550~730MPa. 80 Elongation after fracture ≥10%.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a low-cost 1000MPa grade cold-rolled duplex steel sheet, comprising the following components by weight percentage: C: 0.16%~0.18%, Si: 0.30%~0.40%, Mn: 1.65%~1.80%, Cr: 0.20%~0.30%, Ti: 0.020%~0.040%, B: 0.0015%~0.003%, Al: 0.030%~0.060%, P≤0.015%, S≤0.010%, with the balance being Fe and other unavoidable impurities; The method for preparing low-cost 1000MPa grade cold-rolled dual-phase steel sheet includes steelmaking process, hot rolling process, pickling process, continuous annealing process, and leveling process. The steelmaking process includes converter smelting, LF refining, RH refining, and continuous casting; the billet obtained by continuous casting is rolled by the hot rolling process through hot superheating charging. In the hot rolling process, heating, rough rolling, finish rolling, laminar flow cooling, and coiling are performed sequentially; wherein, the heating temperature is 1200~1250℃, the holding time is 2.5~3.5h, the cumulative rolling reduction rate in the austenitic region is ≥98%, the hot rolling thickness is 1.6~4.0mm, the final rolling temperature is 880~920℃, and the laminar flow cooling to the coiling temperature is 580~620℃; In the pickling and rolling process, after pickling, cold rolling is performed with a cold rolling reduction rate of 50% to 60% to obtain pickled and rolled strip steel. In the continuous annealing process, the pickled and rolled strip is continuously annealed at an annealing temperature of 840~860℃, a holding time of 110~220s, a slow cooling exit temperature of 710~730℃, a rapid cooling rate of 30~45℃ / s, a rapid cooling exit temperature of 250~290℃, an over-aging temperature of 220~290℃, and a final cooling temperature of 100~120℃. After exiting the furnace, the strip is leveled with a leveling elongation of 0.3%~0.6%. The finished steel coil is then obtained and air-cooled to room temperature to obtain the cold-rolled duplex steel sheet.

[0008] Optionally, the cold-rolled dual-phase steel sheet has a tensile strength ≥980MPa and a yield strength of 550~730MPa. 80 The elongation after fracture is ≥10%; the microstructure of the cold-rolled dual-phase steel sheet is ferrite and martensite.

[0009] Optionally, in the steelmaking process, converter smelting, LF refining and RH refining are carried out in sequence, and then a billet with a thickness of 230~240mm is prepared by continuous casting.

[0010] Optionally, in the hot rolling process, the coiling adopts a U-shaped coiling method, wherein the coiling temperature at both ends of the strip is controlled to be 100-150°C and 80-100°C higher than the coiling temperature in the middle of the strip, respectively, within a range of 40m from the head of the strip and 60m from the tail of the strip. Then, the temperature is reduced to the coiling temperature through temperature transition sections of 80m and 100m in length, respectively. After coiling, the strip is cooled by surrounding cooling.

[0011] Optionally, in the hot rolling process, the coiling temperature in the middle of the strip is 550~650℃.

[0012] Optionally, in the pickling process, the hot-rolled steel plate is pickled and then cold-rolled using a five-stand continuous rolling mill, with a cold-rolled thickness of 0.8 to 2.0 mm.

[0013] Implementing the embodiments of the present invention will have the following beneficial effects: This invention provides a low-cost method for preparing 1000MPa grade cold-rolled duplex steel sheets. Through a rational, economical, and low-cost composition design and effective control of key process parameters at each stage, compared with similar grade cold-rolled duplex steel products, this method employs a low-alloy cost design, omitting expensive alloying elements such as Mo and Nb. By controlling the addition and rational proportions of important alloying elements such as C, Si, Mn, Cr, and Ti, the production cost is not high. The resulting cold-rolled duplex steel sheet has a tensile strength ≥980MPa and a yield strength of 550~730MPa. 80With an elongation at break ≥10%, this invention enables the low-cost production of 1000MPa grade cold-rolled duplex steel using a gas-cooled line, achieving comprehensive performance. The chemical composition of the steel plate designed in this invention, while maintaining excellent microstructure and properties, strictly controls the content of alloying elements affecting the surface quality of the steel plate, facilitating large-scale continuous and stable production, and further improving production efficiency and reducing energy consumption costs. Attached Figure Description

[0014] Figure 1 The image shows the SEM microstructure of the cold-rolled duplex steel in Example 1 of this invention.

[0015] Figure 2 The image shows the SEM microstructure of the cold-rolled duplex steel in Example 2 of this invention. Detailed Implementation

[0016] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0017] This invention discloses a low-cost method for preparing 1000MPa grade cold-rolled dual-phase steel plates, including steelmaking process, hot rolling process, pickling process, continuous annealing process, and leveling process.

[0018] S1. The steelmaking process includes converter smelting, LF refining, RH refining and continuous casting; the billet obtained by continuous casting is rolled by hot rolling process through hot superheating charging.

[0019] In one specific embodiment, the steelmaking process involves sequentially using a converter for smelting, LF refining, and RH refining, followed by continuous casting to prepare a billet with a thickness of 230-240 mm.

[0020] S2. In the hot rolling process, heating, rough rolling, finish rolling, laminar cooling, and coiling are performed sequentially to obtain hot-rolled steel plates or hot-rolled steel strips. The heating temperature is 1200~1250℃, the holding time is 2.5~3.5h, the cumulative rolling reduction rate in the austenitic region is ≥98%, the hot-rolled thickness is 1.6~4.0mm, the final rolling temperature is 880~920℃, and the laminar cooling to coiling temperature is 580~620℃.

[0021] In one specific embodiment, during the hot rolling process, a U-shaped coiling method is used to improve the stability of the hot-rolled strip's continuous coiling performance. Specifically, the coiling temperature at both ends of the strip, within a range of 40m from the strip head and 60m from the strip tail, is controlled to be 100-150°C and 80-100°C higher than the coiling temperature in the middle of the strip, respectively. Subsequently, the temperature is reduced to the stated coiling temperature through temperature transition sections of 80m and 100m lengths, respectively. After coiling, to prevent excessively rapid cooling leading to increased strength and performance differences between the head, middle, and tail sections, the coil must be uncoiled and placed in a sheltered location as quickly as possible, and then surrounded by a hot coil (excluding the upper part of the coil).

[0022] In one specific embodiment, during the hot rolling process, the coiling temperature in the middle of the strip is 550–650°C.

[0023] Specifically, the hot rolling process control principle in this invention is as follows: To ensure the alloying elements in the billet dissolve fully and uniformly, the heating temperature is controlled at 1200~1250℃, and the holding time is 2.5~3.5h. Too low a heating temperature and holding time will result in the alloying elements not dissolving fully and uniformly, and the carbonitrides formed by microalloying elements not precipitating completely. Too high a heating temperature and holding time will lead to problems such as coarse microstructure and carbonitrides, as well as deterioration of the slab's thermoplasticity.

[0024] The final rolling temperature is controlled between 880 and 920℃. If the final rolling temperature is higher than 920℃, the steel plate will have a coarse structure, which will affect the performance of the finished product. If the final rolling temperature is lower than 880℃, rolling in the two-phase region will result in obvious banded structures in the structure, which will affect the uniformity of the steel plate structure.

[0025] The coiling temperature should be controlled between 580 and 620°C. If the coiling temperature is too low, the hard phase content in the microstructure will be high, the strength of the hot-rolled plate will be high, the cold rolling force will be large, which is not conducive to pickling and rolling production. If the coiling temperature is too high, the hot-rolled microstructure will have obvious banding, which will affect the stability of the finished product performance.

[0026] After hot-rolled steel coils are coiled, the significant difference in cooling rates between the inner and outer coils leads to severe performance differences at the head, middle, and tail of the coil, affecting the stability of cold rolling and finished product performance. To improve the overall performance stability of hot-rolled steel coils and reduce the performance differences at the head, middle, and tail, this invention employs a method of increasing the coiling temperature for a certain length at the head and tail (U-shaped coiling) and using surrounding cooling. This ensures that the temperature and cooling path at the head, middle, and tail of the strip are as similar as possible during the cooling process, thereby improving the performance differences at the head, middle, and tail of the hot-rolled steel coil.

[0027] S3. In the pickling and rolling process, after pickling, cold rolling is carried out with a cold rolling reduction rate of 50%~60% to obtain pickled and rolled strip steel.

[0028] In one specific embodiment, in the pickling and rolling process, after pickling, a five-stand continuous rolling mill is used for cold rolling, and the cold rolling thickness is 0.8 to 2.0 mm.

[0029] In the S4 continuous annealing process, the pickled and rolled strip is continuously annealed at an annealing temperature of 840~860℃, a holding time of 110~220s, a slow cooling exit temperature of 710~730℃, a rapid cooling rate of 30~45℃ / s, a rapid cooling exit temperature of 250~290℃, an over-aging temperature of 220~290℃, and a final cooling temperature of 100~120℃. After exiting the furnace, the strip is leveled with a leveling elongation of 0.3%~0.6%. The finished steel coil is then obtained and air-cooled to room temperature to obtain cold-rolled duplex steel sheet.

[0030] The present invention also discloses a low-cost 1000MPa grade cold-rolled dual-phase steel sheet prepared by the preparation method of any embodiment of the present invention, comprising the following components by weight percentage: C: 0.16%~0.18%, Si: 0.30%~0.40%, Mn: 1.65%~1.80%, Cr: 0.20%~0.30%, Ti: 0.020%~0.040%, B: 0.0015%~0.003%, Al: 0.030%~0.060%, P≤0.015%, S≤0.010%, with the balance being Fe and other unavoidable impurities.

[0031] In one specific embodiment, the tensile strength of the cold-rolled dual-phase steel sheet is ≥980MPa, and the yield strength is 550~730MPa. 80 Elongation after fracture ≥10%; the microstructure of cold-rolled dual-phase steel sheet is ferrite and martensite.

[0032] The following are specific embodiments. Example 1: The low-cost 1000MPa grade cold-rolled dual-phase steel sheet of this embodiment comprises the following components by weight percentage: C: 0.17%, Si: 0.32%, Mn: 1.74%, Cr: 0.28%, Ti: 0.033%, B: 0.0015%, Al: 0.052%, P: 0.013%, S: 0.003%, with the balance being Fe and other unavoidable impurities.

[0033] The low-cost gas cooling line method for producing 1000MPa grade cold-rolled duplex steel sheets in this embodiment includes the following steps: 1. Steelmaking process: After being smelted in a converter, refined by LF and RH, the molten steel with the chemical composition meeting the above requirements is continuously cast into a billet with a thickness of 230mm. The billet obtained by continuous casting is then rolled by hot rolling process through hot overheating charging.

[0034] 2. Hot Rolling Process: The process involves sequential heating, rough rolling, finish rolling, laminar cooling, and coiling to obtain hot-rolled steel sheets. The billet is heated to 1245℃ after entering the furnace and held for 3 hours. The cumulative rolling reduction in the austenitic region is ≥98%. The hot-rolled thickness is 4.0mm, the final rolling temperature is 898℃, and laminar cooling is performed to the target coiling temperature of 601℃. A U-shaped coiling method is used to improve the stability of the hot-rolled strip's continuous coiling performance. The coiling temperatures at both ends of the strip, 40m from the strip head and 60m from the strip tail, are increased by 100°C and 80°C respectively compared to the coiling temperature in the middle of the strip, reaching 701°C and 681°C respectively. The coiling temperature in the middle of the strip is 601℃. Subsequently, the temperature is reduced to the coiling temperature through temperature transition sections of 80m and 100m lengths.

[0035] 3. Cooling process after coiling: In order to prevent the steel coil from cooling too quickly, which would lead to an increase in strength and differences in performance between the head, middle and tail, the steel coil should be placed in a sheltered place in the shortest possible time after uncoiling, and surrounded by hot steel coil (excluding the top of the steel coil).

[0036] 4. Pickling process: The hot-rolled coil is dephosphorized, pickled, and then cold-rolled to 2.0mm using a five-stand continuous rolling mill with a cold rolling reduction rate of 50%. After coiling, a cold-hardened coil is obtained.

[0037] 5. Continuous annealing process: The pickled strip is heated to 856℃, held for about 188s, slow cooling ends at 711℃, rapid cooling rate is 33℃ / s, rapid cooling ends at 264℃, the end temperature of the over-aging section is 220℃, and the final cooling temperature is 120℃.

[0038] 6. Leveling process: Leveling elongation rate 0.3%. After coiling, air-cool to room temperature to obtain cold-rolled duplex steel sheet.

[0039] Example 2: The low-cost 1000MPa grade cold-rolled dual-phase steel sheet of this embodiment comprises the following components by weight percentage: C: 0.16%, Si: 0.35%, Mn: 1.75%, Cr: 0.26%, Ti: 0.030%, B: 0.0025%, Al: 0.048%, P: 0.015%, S: 0.003%, with the balance being Fe and other unavoidable impurities.

[0040] The low-cost gas cooling line method for producing 1000MPa grade cold-rolled duplex steel sheets in this embodiment includes the following steps: 1. Steelmaking process: After being smelted in a converter, refined by LF and RH, the molten steel with the chemical composition meeting the above requirements is continuously cast into a billet with a thickness of 230mm. The billet obtained by continuous casting is then rolled by hot rolling process through hot overheating charging.

[0041] 2. Hot Rolling Process: The process involves sequential heating, rough rolling, finish rolling, laminar cooling, and coiling to obtain hot-rolled steel sheets. The billet is heated to 1202℃ after entering the furnace and held for 3.2 hours. The cumulative rolling reduction in the austenitic region is ≥98%, the hot-rolled thickness is 2.4mm, the final rolling temperature is 895℃, and laminar cooling is performed to the target coiling temperature of 610℃. A U-shaped coiling method is used to improve the stability of the hot-rolled strip's continuous coiling performance. The coiling temperatures at both ends of the strip, 40m from the strip head and 60m from the strip tail, are increased by 100°C and 80°C respectively compared to the coiling temperature in the middle of the strip, reaching 710°C and 690°C respectively. The coiling temperature in the middle of the strip is 610℃. Subsequently, the temperature is reduced to the coiling temperature through temperature transition sections of 80m and 100m lengths.

[0042] 3. Cooling process after coiling: In order to prevent the steel coil from cooling too quickly, which would lead to an increase in strength and differences in performance between the head, middle and tail, the steel coil should be placed in a sheltered place in the shortest possible time after uncoiling, and surrounded by hot steel coil (excluding the top of the steel coil).

[0043] 4. Pickling process: The hot-rolled coil is dephosphorized, pickled, and then cold-rolled to 1.2mm using a five-stand continuous rolling mill with a cold rolling reduction rate of 50%. After coiling, a cold-hardened coil is obtained.

[0044] 5. Continuous annealing process: The pickled strip is heated to 843℃, held for about 160s, slow cooling ends at 720℃, rapid cooling rate is 42.8℃ / s, rapid cooling ends at 274℃, the end temperature of the over-aging section is 230℃, and the final cooling temperature is 120℃.

[0045] 6. Leveling process: Leveling elongation rate 0.4%. After coiling, it is air-cooled to room temperature to obtain cold-rolled duplex steel sheet.

[0046] Table 1 Mechanical properties of cold-rolled 980MPa grade duplex steel products from Examples 1-2

[0047] Figure 1 and Figure 2 By comparing the metallographic structures of Example 1 and Comparative Example 2, it can be seen from the two figures that both structures consist of ferrite and martensite.

[0048] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a low-cost 1000MPa grade cold-rolled dual-phase steel sheet, characterized in that, Cold-rolled duplex steel sheet comprises the following components by weight percentage: C: 0.16%~0.18%, Si: 0.30%~0.40%, Mn: 1.65%~1.80%, Cr: 0.20%~0.30%, Ti: 0.020%~0.040%, B: 0.0015%~0.003%, Al: 0.030%~0.060%, P≤0.015%, S≤0.010%, with the balance being Fe and other unavoidable impurities; The method for preparing low-cost 1000MPa grade cold-rolled dual-phase steel sheet includes steelmaking process, hot rolling process, pickling process, continuous annealing process, and leveling process. The steelmaking process includes converter smelting, LF refining, RH refining, and continuous casting; the billet obtained by continuous casting is rolled by the hot rolling process through hot superheating charging. In the hot rolling process, heating, rough rolling, finish rolling, laminar flow cooling, and coiling are performed sequentially; wherein, the heating temperature is 1200~1250℃, the holding time is 2.5~3.5h, the cumulative rolling reduction rate in the austenitic region is ≥98%, the hot rolling thickness is 1.6~4.0mm, the final rolling temperature is 880~920℃, and the laminar flow cooling to the coiling temperature is 580~620℃; In the pickling and rolling process, after pickling, cold rolling is performed with a cold rolling reduction rate of 50% to 60% to obtain pickled and rolled strip steel. In the continuous annealing process, the pickled and rolled strip is continuously annealed at an annealing temperature of 840~860℃, a holding time of 110~220s, a slow cooling exit temperature of 710~730℃, a rapid cooling rate of 30~45℃ / s, a rapid cooling exit temperature of 250~290℃, an over-aging temperature of 220~290℃, and a final cooling temperature of 100~120℃. After exiting the furnace, the strip is leveled with a leveling elongation of 0.3%~0.6%. The finished steel coil is then obtained and air-cooled to room temperature to obtain the cold-rolled duplex steel sheet.

2. The preparation method according to claim 1, characterized in that, The cold-rolled duplex steel sheet has a tensile strength ≥980MPa and a yield strength of 550~730MPa. 80 The elongation after fracture is ≥10%; the microstructure of the cold-rolled dual-phase steel sheet is ferrite and martensite.

3. The preparation method according to claim 1, characterized in that, In the steelmaking process, converter smelting, LF refining and RH refining are carried out in sequence, and then a billet with a thickness of 230~240mm is prepared by continuous casting.

4. The preparation method according to claim 1, characterized in that, In the hot rolling process, the coiling adopts a U-shaped coiling method. The coiling temperature at both ends of the strip is controlled to be 100-150°C and 80-100°C higher than the coiling temperature in the middle of the strip, respectively, within a range of 40m from the head and 60m from the tail of the strip. Then, the temperature is reduced to the coiling temperature through temperature transition sections of 80m and 100m in length, respectively. After coiling, the strip is cooled by surrounding cooling.

5. The preparation method according to claim 4, characterized in that, In the hot rolling process, the coiling temperature in the middle of the strip is 550~650℃.

6. The preparation method according to claim 1, characterized in that, In the pickling and rolling process, the hot-rolled steel plate is pickled and then cold-rolled using a five-stand continuous rolling mill, with a cold-rolled thickness of 0.8 to 2.0 mm.

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