Ultrahigh-strength steel plate with high r value and manufacturing method thereof

Abstract

The invention discloses a high-r-value ultrahigh-strength steel plate which comprises an upper surface layer, a middle layer and a lower surface layer in the thickness direction. Wherein the main body of the microstructure of the upper surface layer and the lower surface layer is ferrite, and the carbon content of each of the upper surface layer and the lower surface layer is less than or equal to 0.025%; the mass percentage contents of chemical elements in the upper surface layer and the lower surface layer respectively meet the following conditions: Ti-3. 42N-3.98C is greater than or equal to 0; the microstructure main body of the intermediate layer is at least one of tempered martensite and bainite. Correspondingly, the invention further discloses a manufacturing method of the high-r-value ultrahigh-strength steel plate. The steel plate disclosed by the invention has ultrahigh strength and also has a high r value, and the thickness of the ultrahigh-strength steel plate with the high r value is reduced slightly in the deformation process, so that better formability is realized in both global tensile deformation and local deformation.

Description

Technical Field

[0001] The present invention relates to a steel plate and a manufacturing method thereof, and in particular to a high-strength steel plate and a manufacturing method thereof. Background Art

[0002] The r value represents the ability of the steel plate to resist thinning during the deformation process of drawing. In high-formability deep-drawing steel plates with a tensile strength below 350MPa (such as interstitial-free steel), the r value is one of the important technical indicators. A high r value means that the steel plate has better drawing performance.

[0003] However, the existing high-strength steel plates are not used for deep drawing, and the r value of the steel plates and the performance represented by it are not paid attention to.

[0004] For example, the Chinese patent document with the publication number CN101768695A and the publication date of July 7, 2010, entitled "1000MPa Ti microalloyed ultrafine grain cold-rolled dual-phase steel and its preparation process", discloses that its chemical composition is: 0.03-0.2% C, 0.2-0.8% Si, 1.2-2.0% Mn, Ti: 0.03-0.15%, ≤0.02% P, S≤0.015, 0.02-0.15% Al, and the rest is Fe and unavoidable impurities. After hot rolling and cold rolling, annealing in the critical zone with a cooling rate of less than 50°C / s is performed to obtain a cold-rolled dual-phase steel with a strength of more than 980MPa. It can be seen that the high-strength steel does not pay attention to the r value of the steel plate.

[0005] For example, the Chinese patent document with publication number CN101363099A, publication date February 11, 2009, and titled "A cold-rolled dual-phase steel plate with a tensile strength of 1000 MPa and a preparation method thereof" discloses that C: 0.14-0.21%, Si: 0.4-0.9%, Mn: 1.5-2.1%, P: ≤0.02%, S≤0.01%, Nb: 0.001-0.05%, V: 0.001-0.02%, after hot rolling and cold rolling, it is kept at 760-820°C, the cooling rate is 40-50°C / s, and it is over-aged at 240-320°C for 180-300s. This high-strength steel does not pay attention to the r value of the steel plate.

[0006] Xiong Ziliu et al. introduced a dual-phase steel with a tensile strength of 980 MPa in "Forming Properties of High-Strength Dual-Phase Steel" (Metal Heat Treatment, Vol. 46, No. 5, 2021), but its r value is lower than 0.9.

[0007] Ge Delong et al. introduced 1000-1400MPa martensitic steels in "Maximum Bending Angle of 1000MPa Ultra-High Strength Martensitic Steel Based on Three-Point Bending" (Journal of Plasticity Engineering, Vol. 21, No. 4, 2014), whose r value is less than 0.7. Summary of the invention

[0008] One of the purposes of the present invention is to provide a high r-value ultra-high strength steel plate, which has ultra-high strength and high r-value at the same time. The high r-value ultra-high strength steel plate has a lighter thickness reduction during deformation, thereby showing better formability regardless of global tensile deformation or local deformation.

[0009] In the high r-value ultra-high strength steel plate described in the present invention, the r-value represents the ability of the steel plate to resist thinning during the deformation process of drawing. For a steel plate with a high r-value, the thickness of the steel plate is not easy to be thinned during the tensile deformation, so it is not easy to break. For an ultra-high strength steel plate, when it undergoes severe deformation locally, if the r-value is high, the thickness is not easy to be thinned locally, which can slow down the necking process, thus being beneficial to the formability of the steel plate.

[0010] In order to achieve the above-mentioned purpose, the present invention proposes a high r-value ultra-high strength steel plate, which includes an upper surface layer, an intermediate layer and a lower surface layer in the thickness direction; wherein the main body of the microstructure of the upper surface layer and the lower surface layer is ferrite, the carbon content of the upper surface layer and the lower surface layer is ≤0.025%, and the mass percentage of the chemical elements in the upper surface layer and the lower surface layer respectively satisfies: Ti-3.42N-3.98C≥0; the microstructure of the intermediate layer includes ferrite and tempered martensite.

[0011] One of the core points of the present invention is that a high r value is achieved by making the mass percentage of chemical elements in the upper and lower surface layers satisfy Ti-3.42N-3.98C≥0, and the carbon content of the upper and lower surface layers is ≤0.025%. At the same time, the high strength of the steel plate as a whole is mainly guaranteed by the organization of the middle layer.

[0012] Furthermore, in the high r-value ultra-high strength steel plate described in the present invention, the average grain diameter of the ferrite in the upper surface layer and the lower surface layer is ≤15 microns.

[0013] Furthermore, in the high r-value ultra-high strength steel plate of the present invention, the volume phase ratio of ferrite in the upper surface layer and the lower surface layer is ≥97%.

[0014] Furthermore, in the high r-value ultra-high strength steel plate of the present invention, the microstructure of the intermediate layer may also include bainite.

[0015] Furthermore, in the high r-value ultra-high strength steel plate of the present invention, no matter whether the intermediate layer contains bainite or not, the volume phase ratio of tempered martensite + bainite is ≥40%.

[0016] Furthermore, in the high r-value ultra-high strength steel plate described in the present invention, the ferrite of the upper surface layer and the lower surface layer contains carbides, and the types of the carbides are Ti(C, N) and Nb(C, N).

[0017] Furthermore, in the high r-value ultra-high strength steel plate described in the present invention, the thickness of the upper surface layer and the lower surface layer are respectively 100-200 microns.

[0018] Furthermore, in the high r-value ultra-high strength steel plate described in the present invention, the sum of the thickness of the upper surface layer and the lower surface layer does not exceed 40% of the total thickness of the steel plate.

[0019] Furthermore, the thickness of the high r-value ultra-high strength steel plate described in the present invention is 0.8-2.5 mm.

[0020] Furthermore, the high r-value ultra-high strength steel plate of the present invention contains Fe and inevitable impurity elements, and further contains the following chemical elements in the following mass percentages:

[0021] C: 0.08-0.20%; Si: 0.01-1.7%; Mn: 0.7-2.7%; Ti: 0.16-0.26%; Nb: 0.015-0.05%; Al: 0.02-0.06%; N≤0.005%.

[0022] Furthermore, in the high r-value ultra-high strength steel plate of the present invention, the mass percentage of each chemical element is:

[0023] C: 0.08-0.20%; Si: 0.01-1.7%; Mn: 0.7-2.7%; Ti: 0.16-0.26%; Nb: 0.015-0.05%; Al: 0.02-0.06%; N≤0.005%; the balance is Fe and unavoidable impurities.

[0024] In some embodiments, the design principles of the chemical elements of the high r-value ultra-high strength steel plate of the present invention are specifically as follows:

[0025] C: In the high r-value high-strength steel plate described in the present invention, C can improve the strength of the steel by affecting the hardness of martensite. If the carbon content in the steel is too low, the strength of the steel after quenching is low; and the higher the carbon content in the steel, the higher the strength of the steel after quenching. However, too high carbon is not conducive to obtaining a high r-value. Therefore, in the high r-value ultra-high strength steel plate described in the present invention, the C element content is controlled between 0.08-0.20%.

[0026] Si: In the high-r value high-strength steel plate of the present invention, Si can play the role of solid solution strengthening, inhibiting the precipitation of Fe3C, and promoting the formation of retained austenite. Based on this, the present invention controls the Si content to 0.01-1.7%.

[0027] Mn: Mn is the main element for improving the hardenability of steel. The content of Mn matches the cooling capacity of the cooling method used. When the content of Mn is too low, the steel plate cannot be hardened, and thus cannot obtain a high strength. If the content of Mn is too high, it is not good for the carbon equivalent. Therefore, in the high r-value ultra-high strength steel plate described in the present invention, the content of Mn element is controlled between 0.7-2.7%.

[0028] Ti: In the high r value high strength steel plate of the present invention, the content of Ti is closely related to the r value of the present invention. If the Ti content is too low, it is insufficient to fix all the C and N in the upper and lower surface layers, resulting in a low r value; if the Ti content is too high, Ti is excessive. Therefore, in the high r value ultra-high strength steel plate of the present invention, the Ti element is controlled between 0.16-0.26%.

[0029] Nb: In the high r value high strength steel plate of the present invention, Nb plays a role in assisting the fixation of C and N, forming Nb (C, N), and ensuring that C and N in the upper and lower surface regions are not in a solid solution state. Therefore, in the high r value ultra-high strength steel plate of the present invention, the Nb element is controlled between 0.015-0.05%.

[0030] Al: Its main function in the present invention is deoxidation during the smelting process, and its content range can be: 0.02-0.06%.

[0031] N: In the present invention, N is not conducive to forming a composition ratio of Ti-3.42N-3.98C ≥ 0 in the upper and lower surface layers, and is not conducive to forming a state without interstitial atoms locally, so it is necessary to control N ≤ 0.005%.

[0032] In the present invention, the inevitable impurities are mainly S and P. When the process conditions permit, it is desired that the content of S and P is as low as possible.

[0033] It can be understood that in the high-r value high-strength steel plate described in the present invention, the basic components are: C: 0.08-0.20%; Si: 0.01-1.7%; Mn: 0.7-2.7%. This basic component constitutes the basis of the strength of the steel plate, but a high r value cannot be obtained based on these basic components. In order to obtain a high r value, the steel plate described in the present invention also contains: Ti: 0.16-0.26%, Nb: 0.015-0.05, N≤0.005%.

[0034] Furthermore, in the high r-value ultra-high strength steel plate described in the present invention, the chemical elements also contain at least one of Cr, Mo, and B; wherein B≤0.005%, Cr+Mo≤0.5%.

[0035] In the appropriate amount of high r-value ultra-high strength steel plate described in the present invention, the alloy elements Cr, Mo, and B can effectively cooperate with manganese to improve the hardenability, so as to match the hardenability and rapid cooling capacity of the steel, so as to further avoid failure to harden or excessively high carbon equivalent.

[0036] Furthermore, the tensile strength of the high r value ultra-high strength steel plate of the present invention is ≥980MPa, and its r value is 90 ≥1.2, the microhardness of the upper and lower surface layers HV≤130, and the microhardness of the middle layer HV≥330.

[0037] Correspondingly, another object of the present invention is to provide a method for manufacturing a high r-value ultra-high strength steel plate, which can produce a high r-value ultra-high strength steel plate by optimizing the process.

[0038] In order to achieve the above object, the present invention also proposes a method for manufacturing a high r-value ultra-high strength steel plate as described above, comprising the steps of: smelting and casting; hot rolling; cold rolling after pickling; annealing; wherein the annealing step comprises:

[0039] High temperature humidification decarburization process: spray water vapor to humidify the annealing furnace, and at the same time control the steel plate heating temperature to 880-950℃ for 100-300s, and control the dew point in the annealing furnace to be above 0℃;

[0040] Ordinary slow cooling process: the steel plate is cooled from the high temperature and humidification temperature to between 730-770℃ at a cooling rate of 3-10℃ / s;

[0041] Quasi-static slow cooling process: the steel plate is slowly cooled from 730-770℃ to 680-720℃, the cooling temperature range is controlled at 40-60℃, the cooling rate is 0.03-0.1℃ / s, and the slow cooling process is ensured to last for more than 500s;

[0042] Rapid cooling process: The steel plate is rapidly cooled to below 300°C at a cooling rate of ≥50°C / s;

[0043] Over-aging process: the steel plate is tempered at 240-320℃ for 150-500s.

[0044] The process used in the manufacturing method of the present invention, especially the unique annealing process, is crucial for the ultra-high strength steel plate of the present invention to obtain a high r-value.

[0045] Among them, the decarburization method is to spray water vapor in the furnace for humidification, and the following reactions occur at high temperature to promote the decarburization reaction of the steel plate: C+H2O=CO+H2; C+2H2O=CO2+2H2. The heating temperature of the steel plate is between 880 and 950℃, and is maintained for 100-300s. The amount of humidified water is controlled according to the weight of the strip passing through the unit time and the thickness of the decarburization layer required to ensure that the dew point in the annealing furnace is above 0℃. The high-temperature humidification decarburization process makes the upper and lower surfaces of the steel plate become preliminary decarburization layers with a thickness of 100-200 microns respectively (that is, both the upper and lower surfaces are decarburization layers). In this process, if the heating temperature of the steel plate is too low, it will lead to insufficient decarburization, and if the heating temperature of the steel plate is too high, the grains will grow excessively. Therefore, in the high-temperature humidification decarburization process, the heating temperature of the steel plate is controlled to be 880-950℃, which is conducive to the decarburization reaction of the steel plate. The reason for selecting the dew point in the furnace to be above 0°C is that if the dew point in the furnace is low, the decarburization reaction of the steel plate will be slow, which is insufficient to obtain a decarburization layer of sufficient thickness.

[0046] After the above-mentioned high-temperature humidification decarburization process, the carbon content of the upper and lower surfaces of the steel plate is significantly reduced, which can be reduced to a level of ≤0.05%. At this time, the carbon content of the upper and lower surfaces of the steel plate is still too high, and the austenite is directly cooled and transformed into ferrite, and Fe3C will still precipitate. In order to further reduce the carbon content of the upper and lower surfaces of the steel plate, a quasi-static slow cooling process is further carried out below the Ac1 temperature of the iron-carbon phase diagram. In this quasi-static slow cooling process, the steel plate is slowly cooled from 730-770℃ to 680-720℃ at a rate of 0.03-0.1℃ / s. The temperature range of the entire slow cooling process is controlled at 40-60℃, and the duration is ≥500s. Within this temperature range, the upper and lower surfaces of the steel plate that has undergone preliminary decarburization are first subjected to austenite decomposition to form ferrite. During the slow cooling process, the carbon in the ferrite diffuses into the austenite in the high-carbon zone (middle layer) that has not undergone transformation, thereby further causing the carbon content of the upper and lower surfaces to decrease. If the slow cooling time is sufficient, the carbon content of the upper and lower surfaces can be reduced to a level close to that of industrial pure iron, so that the upper and lower surface areas of the invention steel meet Ti-3.42N-3.98C≥0.

[0047] In the manufacturing method of the present invention, slow cooling from 730-770°C to 680-720°C is crucial. After decarburization, the austenite decarburization content of the surface layer decreases, and Ac3 increases, so that the austenite→ferrite transformation occurs first in the process of slow cooling from 730-770°C to 680-720°C. When the local carbon content of the upper and lower surface layers of the steel plate of the present invention is reduced to ≤0.025%, the Ti, C, and N contents in the steel plate can meet the level of Ti-3.42N-3.98C≥0, thereby substantially forming a structure without interstitial atoms in the upper and lower surface layers, greatly improving the r value of the upper and lower surface layers, and further improving the r value of the steel plate as a whole.

[0048] After the slow cooling is completed, the steel plate is rapidly cooled to below 300°C at a cooling rate of ≥50°C / s, and tempered at 240-320°C for 150-500s. During the cooling process, the austenite in the middle layer is transformed into a martensite structure, and in some embodiments, a small amount of bainite and residual austenite structure may also be contained, thereby achieving ultra-high strength, such as a tensile strength of ≥980MPa.

[0049] The smelting, casting, hot rolling and cold rolling processes in the manufacturing method described in the present invention can all adopt conventional processes, and the present invention does not make any special improvements to these processes.

[0050] The high-r-value high-strength steel plate and the manufacturing method thereof of the present invention have the following advantages and beneficial effects compared with the prior art:

[0051] The present invention ensures ultra-high strength by controlling the organizational morphology of the middle layer, and at the same time achieves a high r value by controlling the mass percentage of chemical elements in the upper and lower surface layers to respectively satisfy Ti-3.42N-3.98C≥0, thereby achieving an ultra-high strength steel plate with a high r value.

[0052] From the perspective of composition design, the present invention can substantially achieve a solid solution state of interstitial atoms in the upper and lower surface layers by adding an appropriate amount of Ti and assisting with Nb to fix N and C, thereby greatly improving the r value of the surface layer, which in turn affects the r value of the entire steel plate, so that the r value of the 980MPa cold-rolled high-strength steel plate reaches above 1.2, thereby greatly reducing the thinning rate during the deformation process, thereby obtaining better formability.

[0053] From the perspective of manufacturing process, the high-r-value high-strength steel plate described in the present invention adopts a unique annealing process, undergoes a preliminary high-temperature humidification decarburization process and a long-term slow cooling austenite→ferrite transformation, so that the carbon content is redistributed, thereby reducing the carbon content of the upper and lower surface layers of the ultra-high-strength steel plate to below 0.025%. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The annealing process curve of the method for manufacturing a high-r-value high-strength steel plate according to one embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0055] The high r-value high-strength steel plate and the manufacturing method thereof described in the present invention will be further explained and illustrated below in conjunction with the drawings and specific embodiments of the specification. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0056] The high-r-value high-strength steel plates of Examples 1-6 and the comparative steel plates of Comparative Examples 1-2 were prepared by the following steps:

[0057] (1) Smelting: The molten iron is smelted in a converter and its composition is further optimized through a refining process;

[0058] (2) Continuously casting to obtain slabs, the composition contents of the slabs of various embodiments and comparative examples are shown in Table 1;

[0059] (3) Hot rolling: using conventional hot rolling process, for example, in some embodiments, the steel plate heating furnace temperature is controlled to be 1220-1280° C., the final rolling temperature is 870-930° C., and the coiling temperature is 570-630° C.;

[0060] (4) Cold rolling after pickling: In some embodiments, the cold rolling reduction rate is controlled to be 40-65%;

[0061] (5) Annealing Figure 1 The annealing process curve of the manufacturing method of the high-r-value high-strength steel plate according to the present invention in one embodiment is schematically shown, specifically comprising:

[0062] High temperature humidification decarburization process: spray water vapor to humidify the annealing furnace, and at the same time control the steel plate heating temperature to 880-950℃ for 100-300s, and control the dew point in the annealing furnace to be above 0℃;

[0063] Ordinary slow cooling process: the steel plate is cooled from the high temperature and humidification temperature to between 730-770℃ at a cooling rate of 3-10℃ / s;

[0064] Quasi-static slow cooling process: the steel plate is slowly cooled from 730-770℃ to 680-720℃, the cooling temperature range is controlled at 40-60℃, the cooling rate is 0.03-0.1℃ / s, and the slow cooling process is ensured to last for more than 500s;

[0065] Rapid cooling process: The steel plate is rapidly cooled to below 300°C at a cooling rate of ≥50°C / s;

[0066] Over-aging process: the steel plate is tempered at 240-320℃ for 150-500s.

[0067] The annealing process parameters of Examples 1-6 and Comparative Example 1 are listed in Table 2-1. Comparative Example 2 did not use the annealing process of the present invention, but used a conventional quenching + tempering process, and the specific process parameters of Comparative Example 2 are listed in Table 2-2.

[0068] Table 1 lists the mass percentages of the chemical elements in Examples 1-6 of the present invention and Comparative Examples 1-2.

[0069] Table 1. (wt%, the balance is Fe and other inevitable impurities except S, P, N)

[0070]

[0071]

[0072] Table 2-1 lists the specific process parameters of the annealing step of the high r-value high strength steel plates of Examples 1-6 and the comparative steel plates of Comparative Examples 1-2.

[0073] Table 2-1

[0074]

[0075] Table 2-2

[0076]

[0077] The steel plates of Examples 1-6 and Comparative Examples 1-2 were sampled, and the carbon content and other component contents of the upper and lower surfaces of the steel plates were detected using GDS (glow discharge spectrometer), and their microstructures were observed and detected using a metallographic microscope. The observation and detection results are listed in Table 3.

[0078] Table 3.

[0079]

[0080] Note: When the Ti-3.42N-3.98C value in the upper and lower surface layers is greater than 0, it means that there are no interstitial atoms in the upper and lower surface layers, and when the Ti-3.42N-3.98C value is less than 0, it means that there are interstitial atoms in the upper and lower surface layers. The two columns of data in the table represent the values ​​of the upper surface layer and the small surface layer respectively.

[0081] In order to verify the implementation effect of the present invention, the steel plates of Examples 1-6 and Comparative Examples 1-2 were sampled and their properties were tested, and the test results are listed in Table 4. Among them:

[0082] Mechanical properties test: tensile test is carried out along the direction perpendicular to the rolling direction of the steel plate. According to the JIS5# standard plate tensile test specimen with a gauge length of 50mm and a gauge area width of 25mm, the test is carried out on a tensile testing machine. During the test, the strength, elongation and r90 value data can be obtained. The value range of r90 value adopts the tensile strain range of 4-6%;

[0083] The hardness test uses a microhardness tester to test the HV hardness, with a loading load of 150g and a loading time of 15s.

[0084] Table 4 lists the relevant performance parameters of the high r-value high-strength steel plates of Examples 1-6 and the comparative steel plates of Comparative Examples 1-2.

[0085] Table 4.

[0086]

[0087] Note: The upper and lower surface hardness in the table has two columns of data representing the hardness values ​​of the upper surface and the lower surface respectively.

[0088] It can be seen from Table 4 that the tensile strength of the high-strength steel plates of Examples 1-6 of the present invention is ≥985MPa, and the r value r 90 ≥1.2, the microhardness of the upper and lower surface layers HV≤130, and the microhardness of the middle layer HV≥330, which shows that the high-strength steel plate described in the present invention can have both high strength and high formability.

[0089] The amount of Ti added in Comparative Example 1 does not satisfy the requirements of the present invention, and even if the process of the present invention is used, a high r value cannot be achieved.

[0090] Although Comparative Example 2 uses the ingredients of Example 2 of the present invention, it does not use the annealing process of the present invention, but uses a conventional quenching and tempering process, so a high r value cannot be obtained.

[0091] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0092] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A high r-value ultra-high strength steel plate, characterized in that: In the thickness direction, it includes an upper surface layer, an intermediate layer and a lower surface layer; the main body of the microstructure of the upper surface layer and the lower surface layer is ferrite, and the carbon content of the upper surface layer and the lower surface layer is ≤0.025%; the mass percentage of the chemical elements in the upper surface layer and the lower surface layer respectively satisfies: Ti-3.42N-3.98C≥0; the microstructure of the intermediate layer includes ferrite and tempered martensite.

2. The high r-value ultra-high strength steel plate according to claim 1, characterized in that: The average grain diameter of the ferrite in the upper surface layer and the lower surface layer is ≤15 microns.

3. The high r-value ultra-high strength steel plate according to claim 1, characterized in that: The volume ratio of ferrite in the upper surface layer and the lower surface layer is ≥97%.

4. The high r-value ultra-high strength steel plate according to claim 1, characterized in that: The microstructure of the intermediate layer also includes bainite.

5. The high r-value ultra-high strength steel plate according to claim 4, characterized in that: The volume phase ratio of tempered martensite+bainite in the intermediate layer is ≥40%.

6. The high r-value ultra-high strength steel plate according to claim 1, characterized in that: The ferrite of the upper surface layer and the lower surface layer contains carbides, and the types of the carbides are Ti(C, N) and Nb(C, N).

7. The high r-value ultra-high strength steel plate according to claim 1, characterized in that: The thickness of the upper surface layer and the lower surface layer are 100-200 microns respectively.

8. The high r-value ultra-high strength steel plate according to claim 1, characterized in that: Its thickness is 0.8-2.5mm.

9. The high r-value ultra-high strength steel sheet according to claim 1, containing Fe and inevitable impurity elements, characterized in that: It also contains the following chemical elements in the following mass percentages: C: 0.08-0.20%; Si: 0.01-1.7%; Mn: 0.7-2.7%; Ti: 0.16-0.26%; Nb: 0.015-0.05%; Al: 0.02-0.06%; N≤0.005%.

10. The high r-value ultra-high strength steel plate according to claim 9, characterized in that: The mass percentage of each chemical element is: C: 0.08-0.20%; Si: 0.01-1.7%; Mn: 0.7-2.7%; Ti: 0.16-0.26%; Nb: 0.015-0.05%; Al: 0.02-0.06%; N≤0.005%; the balance is Fe and unavoidable impurities.

11. The high r-value ultra-high strength steel plate according to claim 9 or 10, characterized in that: Its chemical elements also contain at least one of Cr, Mo and B; wherein B≤0.005%, Cr+Mo≤0.5%.

12. The high r-value ultra-high strength steel plate according to claim 1, characterized in that: Its tensile strength is ≥980MPa, and its r value is 90 ≥1.2, the microhardness of the upper and lower surface layers HV≤130, and the microhardness of the middle layer HV≥330.

13. A method for manufacturing a high r-value ultra-high strength steel plate according to any one of claims 1 to 12, characterized in that: The process includes the following steps: smelting and casting; hot rolling; cold rolling after pickling; annealing; The annealing step comprises: High temperature humidification decarburization process: spray water vapor to humidify the annealing furnace, and at the same time control the steel plate heating temperature to 880-950℃ for 100-300s, and control the dew point in the annealing furnace to be above 0℃; Ordinary slow cooling process: the steel plate is cooled from the high temperature and humidification temperature to between 730-770℃ at a cooling rate of 3-10℃ / s; Quasi-static slow cooling process: the steel plate is slowly cooled from 730-770℃ to 680-720℃, the cooling temperature range is controlled at 40-60℃, the cooling rate is 0.03-0.1℃ / s, and the slow cooling process is ensured to last for more than 500s; Rapid cooling process: The steel plate is rapidly cooled to below 300°C at a cooling rate of ≥50°C / s; Over-aging process: the steel plate is tempered at 240-320℃ for 150-500s.

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