High-strength steel with ultrahigh elongation and method for manufacturing the same

Abstract

The present application relates to the technical field of automobile steel, and particularly relates to a high-strength steel with ultrahigh elongation and a preparation method thereof.The high-strength steel with ultrahigh elongation provided by the present application comprises the following components in percentage by mass: C 0.20%-0.25%, Mn 5.0%-7.5%, Al 1.5%-2.5%, P<=0.015%, S<=0.005%, Nb<=0.04%, and the balance of Fe and inevitable impurities.The high-strength steel with ultrahigh elongation provided by the present application can improve the elongation while ensuring high strength;the volume content of residual austenite in the high-strength steel is 15%-25%, so that the high-strength steel has excellent elongation;the tensile strength of the high-strength steel is >980MPa, the yield strength is 650-800MPa, and the elongation is >25%;the high-strength steel is suitable for automobile structural parts with complex drawing forming, and can meet the requirements of automobile lightweight and safety.

Description

Technical Field

[0001] This invention relates to the field of automotive steel technology, and in particular to a high-strength steel with ultra-high elongation and its preparation method. Background Technology

[0002] With increasingly stringent requirements for lightweighting and safety in automobiles, the application of high-strength steel in vehicle bodies continues to rise. Among them, DP steel, due to its excellent comprehensive performance and mature manufacturing process, is currently widely used in body reinforcement components. However, the elongation of traditional 980MPa grade DP steel is generally less than 13%, which makes it difficult to meet the stamping requirements of parts with complex shapes.

[0003] Third-generation high-strength steels, represented by QP steel, offer significantly improved elongation and formability compared to DP steel, leading to their widespread application in complex parts. However, with the continued development of lightweighting and the increasingly integrated design of vehicle body structural components, higher demands are being placed on the formability of third-generation high-strength steels. Therefore, further improving the formability of third-generation high-strength steels has become a key technical challenge that the industry urgently needs to overcome.

[0004] Currently, Zr microalloying, precise control of C, Si, and Mn content, combined with controlled rolling and cooling production processes, has improved the elongation of high-strength steel. However, its tensile strength and other performance indicators remain relatively low, limiting its application in vehicle bodies. Based on medium-manganese steel, a high-strength steel with both high strength and high elongation has been prepared by optimizing the continuous annealing process. However, the continuous annealing process has strict requirements on parameters such as heating rate, holding time, and cooling rate, making process control complex. Ti-Zr-Nb composite microalloying and controlled rolling and cooling technologies have improved the material's formability and solved the common technical challenge of controlling the size and quantity of liquid-precipitated TiN in Ti microalloyed high-strength steel. However, the addition of multiple microalloying elements increases material costs, which also limits its widespread application in vehicle bodies.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a high-strength steel with ultra-high elongation, which significantly improves elongation while ensuring high strength.

[0007] The second objective of this invention is to provide a method for preparing high-strength steel with ultra-high elongation.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a high-strength steel with ultra-high elongation, comprising the following components by mass percentage: C 0.20%~0.25%, Mn 5.0%~7.5%, Al 1.5%~2.5%, P≤0.015%, S≤0.005%, Nb≤0.04%, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, the high-strength steel with ultra-high elongation comprises, by mass percentage, the following components: C 0.20%~0.22%, Mn 5.5%~7.0%, Al 1.7%~2.2%, P≤0.015%, S≤0.005%, Nb 0.01%~0.03%, balance Fe and unavoidable impurities.

[0010] Furthermore, the microstructure of the high-strength steel with ultra-high elongation includes lath tempered martensite and retained austenite.

[0011] Furthermore, it includes at least one of the following features (1) to (3); (1) The volume percentage of lath tempered martensite in the high-strength steel with ultra-high elongation is 75%~85%, and the volume percentage of retained austenite is 15%~25%; (2) The lath width of the lath tempered martensite is ≤0.6μm; (3) The width of the lath of the retained austenite is ≤0.3μm.

[0012] Furthermore, the high-strength steel with ultra-high elongation has a tensile strength > 980 MPa and a yield strength of 650~800 MPa.

[0013] Furthermore, the elongation of the high-strength steel with ultra-high elongation is >25%.

[0014] The present invention also provides a method for preparing high-strength steel with ultra-high elongation as described above, comprising the following steps: S1. Molten steel is successively smelted and continuously cast and rolled into thin slabs to obtain hot-rolled coils; S2. The hot-rolled coil is pickled to obtain cold-hardened strip steel; or, the hot-rolled coil is pickled and cold-rolled in sequence to obtain cold-hardened strip steel. S3. After the cold-hardened strip steel is annealed, the high-strength steel with ultra-high elongation is obtained.

[0015] Further, in step S1, the thin slab continuous casting and rolling includes: sequentially heating, rough rolling, finish rolling and coiling; wherein, the temperature of coiling is ≤200℃.

[0016] Furthermore, in step S2, the reduction in cold rolling is ≤20%.

[0017] Furthermore, in step S3, the annealing treatment is carried out at a homogenization temperature of 690~720℃ for 10~20min.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The high-strength steel of this invention, characterized by ultra-high elongation, optimizes the microstructure and phase ratio by adjusting the composition and content of each component, thereby significantly improving elongation while maintaining high strength. The retained austenite volume content in the high-strength steel is 15%~25%, contributing to its excellent elongation. The high-strength steel exhibits a tensile strength >980MPa, a yield strength of 650~800MPa, and an elongation >25%. Furthermore, it does not contain expensive alloying elements such as Mo, reducing its cost. It is suitable for complex drawn automotive structural parts and meets the requirements for lightweighting and safety in automobiles.

[0019] The present invention provides a method for preparing high-strength steel with ultra-high elongation by using thin slab continuous casting and rolling, which shortens the production process and helps reduce costs and energy consumption; it also eliminates the need for large deformation cold rolling, significantly reducing process costs and making it more economical and competitive in the market; and the use of appropriate coiling and annealing treatments helps to improve elongation while ensuring the strength of high-strength steel. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a microstructure diagram of the high-strength steel with ultra-high elongation in Embodiment 1 of the present invention.

[0022] Figure 2 This is a comparison chart of the tensile curves of the high-strength steel with ultra-high elongation in Example 1 of the present invention and the third-generation high-strength steel in Comparative Example 13. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0024] In some embodiments of the present invention, a high-strength steel with ultra-high elongation is provided, comprising the following components by mass percentage: C 0.20%~0.25%, Mn 5.0%~7.5%, Al 1.5%~2.5%, P≤0.015%, S≤0.005%, Nb≤0.04%, with the balance being Fe and unavoidable impurities.

[0025] In different implementations, the mass percentages of each component in high-strength steel with ultra-high elongation can be as follows: The mass percentage of C can be 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, or any value between any two of these. The mass percentage of Mn can be 5.0%, 5.2%, 5.4%, 5.6%, 5.8%, 6.0%, 6.2%, 6.4%, 6.6%, 6.8%, 7.0%, 7.2%, 7.4%, 7.5%, and any value between any two of these. The mass percentage of Al can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, and any value between any two of these. The mass percentage of P can be 0%, 0.005%, 0.01%, 0.015%, or any value between any two of these. The mass percentage of S can be 0%, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, or any value between any two of these. The mass percentage of Nb can be 0%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, and any value between any two of these.

[0026] The high-strength steel of the present invention has an ultra-high elongation rate. By adjusting the composition and content of each component, the elongation rate is significantly improved while ensuring high strength. Moreover, no expensive alloying elements such as Mo are added to the high-strength steel, which reduces the cost of the high-strength steel. It is suitable for complex drawn automotive structural parts and can meet the requirements of automotive lightweighting and safety.

[0027] In the high-strength steel with ultra-high elongation of this invention, excessively high carbon content results in high strength but low elongation; excessively low carbon content leads to decreased tensile strength. Excessively high manganese (Mn) content results in high tensile strength but low elongation; excessively low manganese content also leads to decreased tensile strength. Excessively high al content increases the proportion of soft phase in the microstructure, reducing tensile strength; excessively low al content lowers the phase transformation point of the sample, resulting in a higher proportion of hard phase in the microstructure under relevant annealing processes and a decrease in the content of retained austenite, thus increasing tensile strength and decreasing elongation. Excessively low nitrogen (Nb) content also significantly reduces the allowance for high-strength tensile strength.

[0028] To further improve the performance of high-strength steel with ultra-high elongation, this invention optimizes the content of each component in the high-strength steel with ultra-high elongation, resulting in superior performance. In some preferred embodiments of this invention, the high-strength steel with ultra-high elongation comprises the following components by mass percentage: C 0.20%~0.22%, Mn 5.5%~7.0%, Al 1.7%~2.2%, P≤0.015%, S≤0.005%, Nb 0.01%~0.03%, balance Fe and unavoidable impurities.

[0029] In some embodiments of the present invention, the microstructure of high-strength steel with ultra-high elongation includes lath tempered martensite and retained austenite.

[0030] In some embodiments of the present invention, the volume percentage of lath tempered martensite in high-strength steel with ultra-high elongation is 75% to 85%. Typically, but not limitingly, the volume percentage of lath tempered martensite in high-strength steel with ultra-high elongation can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, and any value between any two of these.

[0031] In some embodiments of the present invention, the volume percentage of retained austenite in high-strength steel with ultra-high elongation is 15% to 25%; typically, but not limitingly, for example, the volume percentage of retained austenite in high-strength steel with ultra-high elongation can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, and any value between any two thereof.

[0032] In some embodiments of the present invention, the lath width of the lath tempered martensite is ≤0.6μm.

[0033] In some embodiments of the present invention, the width of the residual austenite laths is ≤0.3μm.

[0034] In some embodiments of the present invention, the high-strength steel with ultra-high elongation has a tensile strength > 980 MPa and a yield strength of 650~800 MPa; preferably, the high-strength steel with ultra-high elongation has a tensile strength of 1000~1100 MPa. The testing standard is GB / T 228.1-2021.

[0035] In some embodiments of the present invention, the elongation of the high-strength steel with ultra-high elongation is >25%; preferably, the elongation of the high-strength steel with ultra-high elongation is 26%~30%; the elongation is within a gauge length of 80mm (A). 80 The elongation rate of ( ). The test standard is GB / T 228.1-2021.

[0036] The high-strength steel of this invention has an ultra-high elongation rate and a tensile strength of over 980 MPa, with a gauge length of 80 mm (A). 80 The elongation is greater than 25%, which is more than 50% higher (relative value) than the existing 980MPa grade third-generation high-strength steel. The main reason for the high elongation is that the microstructure of the high-strength steel contains a high content of retained austenite, with a volume percentage between 15% and 25%. During deformation, it can continuously generate a phase transformation induced plasticity effect (i.e., TRIP effect), thereby effectively delaying the occurrence of necking and improving the elongation and formability of the high-strength steel.

[0037] In some embodiments of the present invention, a method for preparing high-strength steel with ultra-high elongation is also provided, comprising the following steps: S1. Molten steel is successively smelted and continuously cast and rolled into thin slabs to obtain hot-rolled coils; S2. After pickling, hot-rolled coils are used to obtain cold-hardened strip steel; or, hot-rolled coils are used to obtain cold-hardened strip steel after pickling and cold rolling in sequence. S3, after annealing, cold-hardened strip steel is used to obtain high-strength steel with ultra-high elongation.

[0038] In some embodiments of the present invention, step S1, the continuous casting and rolling of thin slab includes: sequentially heating, rough rolling, finish rolling and coiling; wherein, the coiling temperature is ≤200℃; preferably, the coiling temperature is 150~200℃.

[0039] The present invention provides a method for preparing high-strength steel with ultra-high elongation. By optimizing the microstructure and phase ratio of the high-strength steel, a high volume fraction (15%~25%) of residual austenite can be obtained, thereby giving the high-strength steel excellent elongation, which is suitable for complex drawn automotive structural parts.

[0040] Step S1 of this invention involves smelting and hot rolling. Molten steel is smelted in a converter and then hot-rolled coils are produced using a thin slab continuous casting and rolling process. After surface defects are removed from the cast slab obtained from the smelting, it enters a tunnel furnace for heating, and then undergoes rough rolling and finish rolling before being coiled at a temperature ≤200℃. The thin slab continuous casting and rolling process shortens the production process, which helps reduce costs and energy consumption. The microstructure obtained by coiling at ≤200℃ is martensite, and annealing the martensitic structure further facilitates obtaining higher elongation.

[0041] In some embodiments of the present invention, in step S2, the reduction in cold rolling is ≤20%.

[0042] Step S2 of this invention is pickling, or step S2 is pickling and cold rolling, that is, the hot-rolled coil obtained in step S1 is pickled to remove the iron oxide scale on the surface. After pickling, cold rolling is not performed or is performed with a cold rolling reduction of ≤20%. The cold rolling reduction of ≤20% is to avoid obvious edge cracks or strip breakage; in addition, not cold rolling or using a small reduction in cold rolling helps to reduce costs. This invention eliminates the need for large deformation cold rolling treatment, significantly reducing process costs and making it more economical and competitive in the market.

[0043] In some embodiments of the present invention, in step S3, the homogenization temperature of the annealing treatment is 690~720°C, and the homogenization time is 10~20 min; typically, but not limitingly, for example, in step S3, the homogenization temperature of the annealing treatment can be 690°C, 700°C, 710°C, 720°C, and any value between any two of them; the homogenization time of the annealing treatment can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, and any value between any two of them.

[0044] In step S3 of this invention, the annealing process is carried out in a continuous annealing furnace with a homogenization temperature of 690~720℃ and a homogenization time of 10~20min. If the homogenization temperature is below 690℃, the tensile strength decreases, and the retained austenite content is low and highly stable, resulting in a low elongation. If the homogenization temperature is too high, the retained austenite becomes less stable, resulting in high tensile strength but low elongation. If the homogenization temperature is too long, the tensile strength decreases. If the homogenization time is too short, the retained austenite content becomes too low, significantly reducing the elongation.

[0045] In some embodiments of the present invention, step S3, after annealing, further includes rapid cooling and aging in sequence; preferably, the rapid cooling rate is 30~50℃ / s, the rapid cooling temperature is 170~180℃, the aging temperature is 170~180℃, and the aging time is 40~60min.

[0046] The following detailed description of the high-strength steel with ultra-high elongation and its preparation method according to the present invention will be provided in conjunction with several specific embodiments. The embodiments of the present invention mainly focus on the specific chemical composition and process conditions determined for the development of automotive steel sheets, but the principles of the present invention are also applicable to medium and heavy plates, profiles, and bars and wires.

[0047] Examples 1-4 The preparation method of the high-strength steel with ultra-high elongation provided in Examples 1-4 includes the following steps: S1. After the molten steel is smelted in a converter, a billet is obtained. After the billet is produced, the surface defects are removed by a machine and then it is heated in a tunnel heating furnace. After being rolled in sequence through rough rolling and finish rolling, it is coiled to obtain a hot-rolled coil. The composition and mass percentage of the hot-rolled coils in Examples 1-4, as well as the winding temperature (CT), are shown in Table 1.

[0048] Table 1

[0049] S2. Pickling the hot-rolled coil to remove the iron oxide scale on the surface, and then either not cold-rolling or cold-rolling with a cold rolling reduction of no more than 20%, to obtain cold-hardened strip steel.

[0050] S3. The cold-hardened strip steel is annealed at a homogenization temperature of 700℃ for 15 minutes. Then it is rapidly cooled at a rate of 30-50℃ / s at a temperature of 170℃. Finally, it is aged at a temperature of 170℃ for 50 minutes to obtain high-strength steel with ultra-high elongation.

[0051] Example 5 The preparation method of the high-strength steel with ultra-high elongation provided in this embodiment is the same as that in Embodiment 1, except that the homogenization temperature of the annealing treatment in step S3 is 720°C.

[0052] Comparative Examples 1-8 The preparation method of the high-strength steel provided in Comparative Examples 1-8 includes the following steps: S1. After the molten steel is smelted in a converter, a billet is obtained. After the billet is produced, the surface defects are removed by a machine and then it is heated in a tunnel heating furnace. After being rolled in sequence through rough rolling and finish rolling, it is coiled to obtain a hot-rolled coil. The composition and mass percentage of the hot-rolled coils in Comparative Examples 1 to 8, as well as the winding temperature (CT), are shown in Table 2.

[0053] Table 2

[0054] S2. Pickling the hot-rolled coil to remove the iron oxide scale on the surface, and then either not cold-rolling or cold-rolling with a cold rolling reduction of no more than 20%, to obtain cold-hardened strip steel.

[0055] S3. Cold-hardened strip steel is annealed; then rapidly cooled at a rate of 30~50℃ / s, followed by aging; to obtain high-strength steel with ultra-high elongation. The annealing temperatures, annealing times, rapid cooling temperatures, aging temperatures, and aging times for Comparative Examples 1 to 8 are shown in Table 3.

[0056] Table 3

[0057] Comparative Examples 9-12 The high-strength steels provided in Comparative Examples 9-12 were prepared using the same method as in Example 1, except that the soaking temperature and soaking time for the annealing treatment were different in step S3. The soaking temperature, soaking time, rapid cooling temperature, aging temperature, and aging time for the annealing treatments of Comparative Examples 9-12 are shown in Table 4.

[0058] Table 4

[0059] Comparative Example 13 The comparative example provided is the conventional third-generation high-strength steel DH980.

[0060] Test case Scanning electron microscopy (SEM) was performed on the high-strength steel with ultra-high elongation from Example 1, and its microstructure morphology is as follows: Figure 1 As shown.

[0061] from Figure 1It can be seen that the microstructure of the high-strength steel with ultra-high elongation in Example 1 consists of lath-shaped tempered martensite and retained austenite.

[0062] The properties of the high-strength steels in Examples 1-5 and Comparative Examples 1-13 were tested according to GB / T 228.1-2021, and the results are shown in Table 5. A comparison of the tensile curves of the high-strength steel with ultra-high elongation in Example 1 (the high-plasticity high-strength steel of this invention) and the conventional third-generation high-strength steel DH980 (conventional third-generation high-strength steel) in Comparative Example 13 is shown below. Figure 2 As shown.

[0063] The retained austenite content is the volume percentage of retained austenite in high-strength steel.

[0064] Table 5

[0065] As shown in Table 5, comparing Example 1 with Comparative Examples 1-8, it can be seen that Comparative Example 1, due to its coiling temperature of 520℃, resulted in a lower elongation of the high-strength steel after annealing. Comparative Example 2, with its high C content, exhibited high strength but low elongation. Comparative Example 3, with its low C content, resulted in a decrease in the tensile strength of the high-strength steel. Comparative Example 4, with its low Al content, resulted in a lower phase transformation point, a higher proportion of hard phase in the microstructure under the relevant annealing process, and a decrease in the content of retained austenite, leading to an increase in tensile strength but an elongation below 25%. Comparative Example 5, with its high Al content, resulted in an increase in the proportion of soft phase in the microstructure, leading to a decrease in tensile strength. Comparative Example 6, with its low Mn content, resulted in low tensile strength. Comparative Example 7, with its high Mn content, resulted in a higher tensile strength but an elongation below 25%. Comparative Example 8, with its excessively low Nb content, also showed a significant decrease in the allowance of tensile strength.

[0066] A comparison of Examples 1-5 and Comparative Examples 9-12 shows that Examples 1-5, due to their reasonable annealing conditions, enable the high-strength steel to possess both excellent strength and elongation.

[0067] The low homogenization temperature of Comparative Example 9 resulted in a high-strength steel with a tensile strength below 980 MPa. Simultaneously, the low content and high stability of retained austenite led to a lower elongation. The high homogenization temperature of Comparative Example 10 resulted in lower stability of retained austenite, thus leading to higher tensile strength and higher A... 80 The content was below 25%. The soaking temperature of Comparative Example 11 was too long, resulting in a tensile strength below 980 MPa. The soaking time of Comparative Example 12 was too short, resulting in a low residual austenite content, which led to A... 80 Significantly lower than 25%.

[0068] from Figure 2It can be seen that the high-strength steel with ultra-high elongation of the present invention has a tensile strength of over 980MPa and an elongation of over 25%, which is more than 50% (relative value) higher than the existing 980MPa grade third-generation high-strength steel.

[0069] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A high-strength steel with ultra-high elongation, characterized in that, By weight percentage, it includes the following ingredients: C 0.20%~0.25%, Mn 5.0%~7.5%, Al 1.5%~2.5%, P≤0.015%, S≤0.005%, Nb≤0.04%, with the balance being Fe and unavoidable impurities.

2. The high-strength steel with ultra-high elongation according to claim 1, characterized in that, By weight percentage, it includes the following ingredients: C 0.20%~0.22%, Mn 5.5%~7.0%, Al 1.7%~2.2%, P≤0.015%, S≤0.005%, Nb 0.01%~0.03%, balance Fe and unavoidable impurities.

3. The high-strength steel with ultra-high elongation according to claim 1, characterized in that, The microstructure of the high-strength steel with ultra-high elongation includes lath tempered martensite and retained austenite.

4. The high-strength steel with ultra-high elongation according to claim 3, characterized in that, Includes at least one of the following features (1) to (3); (1) The volume percentage of lath tempered martensite in the high-strength steel with ultra-high elongation is 75%~85%, and the volume percentage of retained austenite is 15%~25%; (2) The lath width of the lath tempered martensite is ≤0.6μm; (3) The width of the lath of the retained austenite is ≤0.3μm.

5. The high-strength steel with ultra-high elongation according to claim 4, characterized in that, The high-strength steel with ultra-high elongation has a tensile strength >980MPa and a yield strength of 650~800MPa.

6. The high-strength steel with ultra-high elongation according to claim 5, characterized in that, The elongation of the high-strength steel with ultra-high elongation is >25%.

7. The method for preparing high-strength steel with ultra-high elongation as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Molten steel is successively smelted and continuously cast and rolled into thin slabs to obtain hot-rolled coils; S2. The hot-rolled coil is pickled to obtain cold-hardened strip steel; or, the hot-rolled coil is pickled and cold-rolled in sequence to obtain cold-hardened strip steel. S3. After the cold-hardened strip steel is annealed, the high-strength steel with ultra-high elongation is obtained.

8. The method for preparing high-strength steel with ultra-high elongation according to claim 7, characterized in that, In step S1, the thin slab continuous casting and rolling includes: heating, rough rolling, finish rolling and coiling in sequence; wherein the temperature of coiling is ≤200℃.

9. The method for preparing high-strength steel with ultra-high elongation according to claim 7, characterized in that, In step S2, the reduction in cold rolling is ≤20%.

10. The method for preparing high-strength steel with ultra-high elongation according to claim 7, characterized in that, In step S3, the annealing temperature is 690~720℃ and the annealing time is 10~20min.

Images