Ultrathin-specification high-strength steel and method for producing ultrathin-specification high-strength steel based on discontinuous quenching line

Abstract

The invention discloses ultra-thin specification high-strength steel and a method for producing the ultra-thin specification high-strength steel based on a discontinuous quenching line, and the method comprises the steps that molten steel is provided, converter smelting and external refining are carried out on the molten steel, Si-Ca treatment is carried out in the external refining process, soft blowing treatment needs to be carried out on the molten steel in the Si-Ca treatment process, the Ca / S ratio in the molten steel obtained after Si-Ca treatment is 1.0-3.0, and the Ca / S ratio in the molten steel obtained after Si-Ca treatment is 1.0-3.0; molten steel of the high-strength steel is obtained; the molten steel of the high-strength steel is subjected to continuous casting to obtain a continuous casting slab; heating the continuous casting slab to obtain a first heated slab; performing rough rolling and finish rolling on the first heating plate blank to obtain finish rolled steel; the rough rolling temperature is 1060-1200 DEG C, and the finish rolling temperature is 860-900 DEG C; performing laminar cooling on the finish rolled steel to obtain cooled steel, wherein the cooling rate is 40-80 DEG C / s; performing acid pickling and cold rolling treatment on the cooled steel to obtain cold-rolled steel; performing flattening and quenching treatment on the cold-rolled steel to obtain quenched steel; and the quenched steel is straightened and tempered, and the ultra-thin high-strength steel with the thickness smaller than or equal to 3 mm and the yield strength larger than or equal to 960 MPa is obtained.

Description

Technical Field

[0001] The present application belongs to the technical field of steelmaking, and in particular relates to an ultra-thin high-strength steel and a method for producing the ultra-thin high-strength steel based on a discontinuous quenching line. Background Art

[0002] As construction machinery develops towards high-end, the lightweight and high-strength thinning of the whole vehicle are increasingly attracting the attention of practitioners. The high-strength steel originally used in the 700MPa grade has been partially upgraded to the 960MPa grade, among which the ultra-thin high-strength steel with a thickness of ≤3mm and a yield strength of ≥960MPa is mainly used in the end booms of small cranes, the end booms of aerial work platforms, and truck cranes, etc., which plays an important role in the high-end and personalized development of construction machinery.

[0003] High-strength steel products with a thickness of ≤3mm and a yield strength of ≥960MPa are generally produced by cold rolling or on a continuous quenching line. The cold rolling process has a long production cycle, high product strength and large springback, and poor assembly accuracy during the forming process. Therefore, the continuous quenching line is the best choice. The strip is evenly stressed under the action of the tension roller, and the plate shape is well controlled. However, the continuous quenching line can only produce thin quenched plates with a thickness of ≤6mm, and the annual output of ultra-thin specifications with a thickness of ≤3mm is relatively small, and the economic benefits of investing hundreds of millions of yuan to build this production line are low. When using the existing discontinuous quenching line to produce ultra-thin high-strength steel, the quenching roller can no longer constrain the steel plate, that is, the strip specifications have exceeded the design limit of the production line. Therefore, the plate shape of ultra-thin high-strength steel is poor, which restricts the development of this type of product. Summary of the invention

[0004] The embodiments of the present application provide an ultra-thin high-strength steel and a method for producing ultra-thin high-strength steel based on a discontinuous quenching line. Based on the discontinuous quenching line, a high-strength steel product with a thickness of ≤3 mm and a yield strength of ≥960 MPa that meets the requirements can be prepared through a simple preparation process.

[0005] In a first aspect, the present application provides a method for producing ultra-thin high-strength steel based on a discontinuous quenching line, comprising:

[0006] Molten steel is provided, and the molten steel is subjected to converter smelting, external refining, and Si-Ca treatment during the external refining process, wherein the molten steel needs to be subjected to soft blowing treatment during the Si-Ca treatment process, and the Ca / S ratio in the molten steel after the Si-Ca treatment is 1.0-3.0, thereby obtaining molten steel of high-strength steel; the molten steel of high-strength steel is composed of the following chemical components in terms of mass percentage: C is 0.16wt.%-0.21wt.%, Si is less than 0.10wt.%, Mn is 1.60wt.%-1.90wt.%, and P is less than or equal to 0.015wt. %, S≤0.004wt.%, Cr is 0.20wt.%~0.50wt.%, Nb is 0.020wt.%~0.040wt.%, Ti is 0.010wt.%~0.040wt.%, Mo is 0.30wt.%~0.50wt.%, B is 0.0010wt.%~0.0025wt.%, N≤0.004wt.%, Als is 0.010wt.%~0.060wt.%, and the rest is Fe and unavoidable impurities; the above chemical composition satisfies the following relationship at the same time:

[0007] 800≤4370[%C]+88[%Si]+53[%Mn]+22[%Mo]-30[%Cr]≤1000 (1);

[0008] Continuously casting high-strength steel molten steel to obtain a continuously cast slab;

[0009] Heating the continuous casting slab to obtain a first heated slab;

[0010] The first heated slab is subjected to rough rolling and finish rolling in sequence to obtain a finished steel product; wherein the rough rolling temperature is 1060° C. to 1200° C., and the finish rolling temperature is 860° C. to 900° C.;

[0011] The finished rolled steel is subjected to laminar cooling at a cooling rate of 40°C / s to 80°C / s to obtain a cooled steel;

[0012] The cooled steel is pickled and cold-rolled to obtain cold-rolled steel;

[0013] The cold-rolled steel is subjected to flattening and quenching treatment to obtain quenched steel;

[0014] The quenched steel is straightened and tempered to obtain ultra-high strength steel with a thickness of ≤3mm and a yield strength of ≥960MPa.

[0015] According to an embodiment of the first aspect of the present application, soft blowing treatment of molten steel during Si-Ca treatment includes blowing argon gas into the molten steel between 5 minutes before Si-Ca treatment and 8 minutes after Si-Ca treatment.

[0016] According to the embodiment of the first aspect of the present application, the continuous casting of molten high-strength steel includes electromagnetic stirring of the crystallizer, and the electromagnetic stirring adopts a forward and reverse alternating stirring mode, the alternating time is 50s to 60s, the electromagnetic stirring current is 360A to 480A, and the electromagnetic stirring frequency is 12Hz to 20Hz, so as to obtain a continuously cast slab with a thickness of 210mm to 230mm.

[0017] According to an embodiment of the first aspect of the present application, the heating treatment of the continuous casting slab includes setting the heating temperature of the second heating section and the soaking section to 1160°C to 1200°C.

[0018] According to an embodiment of the first aspect of the present application, sequentially rough rolling and finish rolling the first heated slab includes setting the dephosphorization water pressure between the rough rolling stands to 110 bar to 130 bar during the rough rolling of the first heated plate.

[0019] According to the embodiment of the first aspect of the present application, the method for producing ultra-thin high-strength steel based on a discontinuous quenching line also includes: coiling the cooled steel, the coiling temperature is 600°C to 650°C, and a coiled cooled steel is obtained.

[0020] According to the embodiment of the first aspect of the present application, the pickling treatment of the cooled steel includes pickling in a pickling tank with an acid concentration of 70g / L~120g / L, 130g / L~170g / L, and 170g / L~210g / L, the temperature of the acid in the pickling tank is 60℃~90℃, and the pickling speed is 40m / min~70m / min.

[0021] According to an embodiment of the first aspect of the present application, cold rolling treatment of cooled steel includes using a single-stand rolling mill to cold roll the cooled steel after pickling, the number of cold rolling passes is 2 to 4, the single-pass reduction rate is ≤15%, the front tension is 4KN / mm to 10KN / mm, and the rear tension is 11KN / mm to 16KN / mm, so as to obtain cold-rolled steel.

[0022] According to an embodiment of the first aspect of the present application, the cold-rolled steel is subjected to flattening and quenching treatment, comprising: flattening rough straightening and flattening fine straightening on the cold-rolled steel, the pressure of the flattening rough straightening is 6000KN to 9000KN, and the pressure of the flattening fine straightening is 15000KN to 18000KN, to obtain straightened steel;

[0023] The straightened steel is quenched at a heating temperature of 900±20°C, a holding time of 20±3 minutes, an upper and lower water volume ratio of 3:4 during quenching, and a cooling rate of 35°C / s to 50°C / s to obtain a quenched steel.

[0024] According to an embodiment of the first aspect of the present application, straightening and tempering the quenched steel includes: performing rough straightening and fine straightening on the quenched steel, the rough straightening pressure is 6000KN to 9000KN, the fine straightening pressure is 15000KN to 18000KN, and a straightened steel strip having a buckled plate shape after straightening and an unevenness of ≤6mm / m is obtained;

[0025] Tempering the straightened steel strip at a heating temperature of 600±20°C for a holding time of 40±3 minutes, followed by air cooling to obtain tempered steel;

[0026] The tempered steel is subjected to secondary rough straightening and fine straightening, with the rough straightening pressure being 4000KN to 7000KN and the fine straightening pressure being 12000KN to 15000KN, to obtain ultra-thin high-strength steel.

[0027] In a second aspect, the present application provides an ultra-thin specification high-strength steel, which is prepared by a method for producing ultra-thin specification high-strength steel based on a discontinuous quenching line; the ultra-thin specification high-strength steel is composed of the following chemical components in terms of mass percentage: C is 0.16wt.% to 0.21wt.%, Si is less than 0.10wt.%, Mn is 1.60wt.% to 1.90wt.%, P is ≤0.015wt.%, S is ≤0.004wt.%, Cr is 0.20wt.% to 0. 50wt.%, Nb is 0.020wt.%~0.040wt.%, Ti is 0.010wt.%~0.040wt.%, Mo is 0.30wt.%~0.50wt.%, B is 0.0010wt.%~0.0025wt.%, N≤0.004wt.%, Als is 0.010wt.%~0.060wt.%, and the rest is Fe and unavoidable impurities; the above chemical composition satisfies the following relationship at the same time:

[0028] 800≤4370[%C]+88[%Si]+53[%Mn]+22[%Mo]-30[%Cr]≤1000 (1).

[0029] According to the embodiment of the second aspect of the present application, the unevenness of the ultra-thin high-strength steel plate produced by the discontinuous quenching line is ≤3mm / m, the thickness is ≤3mm, and its mechanical properties meet the following requirements: yield strength R eL ≥960MPa, tensile strength R m ≥980MPa, elongation A≥12%; d=3a, 180° cold bending qualified.

[0030] The embodiment of the present application is based on a method for producing ultra-thin high-strength steel on a discontinuous quenching line, which increases the C and Mn contents and reduces the Si content in ultra-thin high-strength steel. The main reason is that the thin high-strength steel cannot use a normal purge airflow during the quenching process to prevent the steel plate from being blown into the roller gap because the steel plate is too thin. When the Si content in the steel is high, the water on the surface of the strip is not purged clean and enters the tempering furnace, which will cause severe red rust to form on its surface. Increasing the C and Mn contents can not only avoid the strength loss caused by the reduction in Si content, but also avoid the low strength phenomenon caused by the decarburization layer on the surface of the strip during the quenching process of high-strength steel. The solid solution strengthening effect of the steel plate is improved by increasing the C and Mn contents, and the strength is increased by increasing the carbon content in the martensite, thereby ensuring the strength of ultra-thin high-strength steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0032] Figure 1 This is an actual product picture of ultra-thin high-strength steel produced by the method for preparing ultra-thin steel produced by a discontinuous quenching line in an embodiment of the present application.

[0033] Figure 2 This is an actual product picture of the ultra-thin high-strength steel provided in Example 2.

[0034] Figure 3 This is an actual product picture of the ultra-thin high-strength steel provided in Example 5 of the present application. DETAILED DESCRIPTION

[0035] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0036] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0037] In order to solve the problems of the prior art, the embodiments of the present application provide an ultra-thin high-strength steel produced based on a discontinuous quenching line and a preparation method thereof.

[0038] The following first introduces the method for producing ultra-thin high-strength steel based on a discontinuous quenching line provided in an embodiment of the present application. Figure 1 A schematic flow chart of a method for producing ultra-thin high-strength steel based on a discontinuous quenching line provided in an embodiment of the present application is shown.

[0039] like Figure 1 As shown, the method for producing ultra-thin high-strength steel based on a discontinuous quenching line includes: providing molten steel, performing converter smelting, external refining and Si-Ca treatment on the molten steel during the external refining process, wherein the molten steel needs to be soft-blown during the Si-Ca treatment, and the Ca / S ratio in the molten steel after the Si-Ca treatment is 1.0-3.0, thereby obtaining molten steel of high-strength steel; in terms of mass percentage, the molten steel of high-strength steel is composed of the following chemical components: C is 0.16wt.%-0.21wt.%, Si is less than 0.10wt.%, Mn is 1.60wt.%-1.90wt.%, P≤0.015wt.%, S≤0.004wt.%, Cr is 0.20wt.%-0.50wt.%, Nb is 0.020wt.%-0.040wt.%, and Ti is

[0040] 0.010wt.%~0.040wt.%, Mo is 0.30wt.%~0.50wt.%, B is 0.0010wt.%~0.0025wt.%, N≤0.00wt.4%, Als is 0.010wt.%~0.060wt.%, and the rest is Fe and unavoidable impurities; the above chemical composition satisfies the following relationship at the same time:

[0041] 800≤4370[%C]+88[%Si]+53[%Mn]+22[%Mo]-30[%Cr]≤1000 (1);

[0042] The molten steel of high-strength steel is continuously cast to obtain a continuously cast slab; the continuously cast slab is heated to obtain a first heated slab; the first heated slab is subjected to rough rolling and finish rolling in sequence to obtain a finished rolled steel; wherein the rough rolling temperature is 1060°C to 1200°C, and the final rolling temperature of the finish rolling is 860°C to 900°C; the finished rolled steel is subjected to laminar cooling at a cooling rate of 40°C / s to 80°C / s to obtain a cooled steel; the cooled steel is pickled and cold rolled to obtain a cold rolled steel; the cold rolled steel is flattened and quenched to obtain a quenched steel; the quenched steel is straightened and tempered to obtain an ultra-thin specification high-strength steel with a thickness of ≤3mm and a yield strength of ≥960MPa.

[0043] The embodiment of the present application is based on a method for producing ultra-thin high-strength steel using a discontinuous quenching line, which increases the C and Mn contents and reduces the Si content in the ultra-thin high-strength steel. The main reason is that the steel plate of the ultra-thin high-strength steel is too thin, and a normal purge airflow cannot be used during the quenching process to prevent the steel plate from being blown into the roller gap. When the Si content in the steel is high, the water on the surface of the strip is not purged clean and enters the tempering furnace, which will cause severe red rust to form on its surface. Increasing the C and Mn contents can not only avoid the strength loss caused by the reduction in Si content, but also avoid the low strength phenomenon caused by the decarburization layer on the surface of the strip during the quenching process of high-strength steel. The solid solution strengthening effect of the steel plate is improved by increasing the C and Mn contents, and the strength is increased by increasing the carbon content in the martensite, thereby ensuring the strength of ultra-thin high-strength steel.

[0044] It should be noted that the discontinuous quenching line refers to an ordinary quenching line, that is, a production line for quenching steel plates one by one or one block at a time. The method of producing ultra-thin high-strength steel by a discontinuous quenching line of the present application is based on this production line.

[0045] In the preparation method of the present application, in formula (1), [%C] represents the mass content of carbon element; [%Si] represents the mass content of silicon element; [%Mn] represents the mass content of manganese element; [%Mo] represents the mass content of molybdenum element; and [%Cr] represents the mass content of chromium element.

[0046] Although the mechanism is not clear, the applicant unexpectedly found that the mechanical properties of the molten steel satisfying the formula (1) meet the use requirements. When the value of the formula (1) exceeds 1000, the strength exceeds the upper limit, and the carbon equivalent is too high, which affects the welding performance of the steel. When the value of the formula (1) is less than 800, the strength of the steel cannot meet the target requirements.

[0047] In some embodiments of the present application, Si-Ca treatment during refining outside the furnace refers to adding silicon-calcium wire to the molten steel during refining outside the furnace, so that the Ca content in the molten steel is 20ppm to 30ppm. Si-Ca treatment of molten steel during refining outside the furnace can improve the morphology of MnS inclusions in the molten steel, changing it from strip-shaped to spherical, thereby improving the cold forming performance of ultra-thin specification high-strength steel. The calcium content in the molten steel can be determined by the method for determining the component content in the molten steel. When the calcium content in the molten steel reaches 20ppm to 30ppm, the Si-Ca treatment during refining outside the furnace can be considered to be completed. Exemplarily, the calcium content in the molten steel reaches 22ppm, 25ppm, 27ppm, 29ppm, and 30ppm.

[0048] In some embodiments of the present application, soft blowing treatment of molten steel during Si-Ca treatment includes blowing argon gas into the molten steel between 5 minutes before Si-Ca treatment and 8 minutes after Si-Ca treatment, with the liquid level of the molten steel slightly flipping.

[0049] In some embodiments of the present application, continuous casting of molten high-strength steel includes electromagnetic stirring of the crystallizer, and the electromagnetic stirring adopts a forward and reverse alternating stirring mode, the alternating time is 50s to 60s, the electromagnetic stirring current is 360A to 480A, and the electromagnetic stirring frequency is 12Hz to 20Hz, so as to obtain a continuously cast slab with a thickness of 210mm to 230mm.

[0050] In some embodiments of the present application, the heating treatment of the continuous casting slab includes setting the heating temperature of the second heating section and the soaking section to 1160°C to 1200°C.

[0051] In some embodiments of the present application, sequentially rough rolling and finish rolling the first heated slab includes making the dephosphorization water pressure used between the rough rolling stands 110 bar to 130 bar during the rough rolling of the first heated slab.

[0052] In some embodiments of the present application, the method for producing ultra-thin high-strength steel based on a discontinuous quenching line also includes: coiling the cooled steel, with a coiling temperature of 600°C to 650°C to obtain a coiled cooled steel.

[0053] In some embodiments of the present application, the pickling treatment of the cooled steel includes pickling the cooled steel in a pickling tank with an acid concentration of 70g / L~120g / L, 130g / L~170g / L, or 170g / L~210g / L, the temperature of the acid in the pickling tank is 60°C~90°C, and the pickling speed is 40m / min~70m / min.

[0054] In the preparation method of the present application, pickling treatment is adopted to remove the iron oxide scale on the surface of the cooled steel, which is not only beneficial for single-stand rolling, but also more beneficial for the control of the plate shape during the subsequent quenching process. When there is iron oxide scale on the surface of the steel, it will affect its temperature uniformity during the heating process. However, since ultra-thin high-strength steel is in the form of a strip and is very thin, uneven heating in the heating furnace will cause its plate shape to deform, aggravating the deformation during the quenching process. Therefore, it is necessary to perform pickling treatment on the cooled steel.

[0055] In some embodiments of the present application, cold rolling the cooled steel includes using a single-stand rolling mill to cold roll the cooled steel after pickling, the cold rolling passes are 2 to 4 passes, the single pass reduction rate is ≤15%, the front tension is 4KN / mm to 10KN / mm, and the rear tension is 11KN / mm to 16KN / mm, so as to obtain cold-rolled steel.

[0056] In the preparation method of the present application, a single-stand rolling mill is used to cold-roll the cooled steel, which not only improves the flatness of the original plate shape, but also reduces the thickness of the steel plate. As is known to all, when a hot rolling production line produces thin-gauge hot-rolled coils, not only is the plate shape difficult to control, but also steel plates of different thickness specifications are required for transition, which will result in a large number of undesired products. By using a single-stand rolling mill, a 3mm hot-rolled raw material can be directly rolled into a thickness of 2mm, reducing production costs.

[0057] In some embodiments of the present application, the cold-rolled steel is subjected to flattening and quenching treatment, comprising: performing rough flattening straightening and fine flattening on the cold-rolled steel, the pressure of the rough flattening straightening is 6000KN~9000KN, and the pressure of the fine flattening straightening is 15000KN~18000KN, so as to obtain straightened steel; the straightened steel is subjected to quenching treatment, the heating temperature of the quenching treatment is 900±20℃, the holding time is 20±3 minutes, the upper and lower water volume ratio during quenching is 3:4, and the cooling rate is 35℃ / s~50℃ / s, so as to obtain quenched steel.

[0058] In the preparation method of the present application, the quenching process adopts a cooling strategy of "small on top and large on bottom" cooling water, and the ratio of the upper and lower water volume is 3:4, and the cooling rate is 35°C / s to 50°C / s. Because the cold-rolled steel to be quenched is in the form of a strip and its thickness is very thin, it is necessary to adopt a cooling water volume of small on top and large on the bottom, otherwise the cooling will be uneven and the cold-rolled steel will be severely deformed. Also because the cold-rolled steel is very thin, if a larger cooling rate is adopted, the cold-rolled steel in the form of a strip is easily deformed, and if a too low cooling rate is adopted, martensite cannot be obtained. Therefore, the quenching strategy of the present application can ensure that the plate shape and strength of the cold-rolled steel in the form of a strip are well matched.

[0059] In some embodiments of the present application, straightening and tempering the quenched steel include: performing rough straightening and fine straightening on the quenched steel, the rough straightening pressure is 6000KN~9000KN, and the fine straightening pressure is 15000KN~18000KN, so as to obtain a straightened steel strip with a plate shape in a buckled state after straightening, and the unevenness is ≤6mm / m; tempering the straightened steel strip, the heating temperature of the tempering treatment is 600±20℃, the insulation time is 40±3 minutes, and air cooling is performed to obtain tempered steel; performing secondary rough straightening and fine straightening on the tempered steel, the rough straightening pressure is 4000KN~7000KN, and the fine straightening pressure is 12000KN~15000KN, so as to obtain ultra-high strength steel.

[0060] In the preparation method of the present application, straightening treatment is performed before and after tempering, and each has its own role. The first straightening results in a slightly buckled plate shape, because the strip-shaped quenched steel will shrink during the air cooling process after tempering, and the slight buckling of the original plate shape can offset the deformation caused by the shrinkage process. The second straightening is used to even out the internal stress of the steel plate and adjust the final plate shape.

[0061] Therefore, the method of producing ultra-thin high-strength steel based on a discontinuous quenching line in this application adopts a reasonable composition design, by increasing the C and Mn content and reducing the Si content, to ensure that the material strength meets the performance requirements and improves the surface quality of the steel. In addition, this application adopts the process of pickling and single-stand rolling mill to obtain quenched raw materials that meet the requirements in thickness specifications, plate shape, and surface quality. And a strategy combining two straightening and quenching is adopted to obtain ultra-thin high-strength steel with good plate shape, and the unevenness of the plate shape is ≤3mm / m. After testing, the yield strength R eL ≥960MPa, tensile strength R m ≥980MPa, elongation A≥12%; d=3a, 180° cold bending qualified. Description The present application discloses a method for preparing ultra-thin steel produced by a discontinuous quenching line. As a new manufacturing process, ultra-thin high-strength steel that meets the requirements can be prepared by a discontinuous quenching line.

[0062] In the second aspect, the present application provides an ultra-thin specification high-strength steel produced based on a discontinuous quenching line, which is prepared by a method for producing ultra-thin specification high-strength steel based on a discontinuous quenching line; in terms of mass percentage, the ultra-thin specification high-strength steel is composed of the following chemical components: C is 0.16wt.%~0.21wt.%, Si<0.10wt.%, Mn is 1.60wt.%~1.90wt.%, P≤0.015wt.%, S≤0.004wt.%, Cr is 0.20 wt.%~0.50wt.%, Nb is 0.020wt.%~0.040wt.%, Ti is 0.010wt.%~0.040wt.%, Mo is 0.30wt.%~0.50wt.%, B is 0.0010wt.%~0.0025wt.%, N≤0.004wt.%, Als is 0.010wt.%~0.060wt.%, and the rest is Fe and unavoidable impurities; the above chemical composition satisfies the following relationship at the same time:

[0063] 800≤4370[%C]+88[%Si]+53[%Mn]+22[%Mo]-30[%Cr]≤1000 (1).

[0064] In some embodiments of the present application, the mechanical properties of ultra-thin high-strength steel produced by the discontinuous quenching line meet the following requirements: steel plate roughness ≤ 3 mm / m, thickness ≤ 3 mm, yield strength R eL ≥960MPa, tensile strength R m ≥980MPa, elongation A≥12%; d=3a, 180° cold bending qualified.

[0065] The present application adopts the technical solution of the above-mentioned composition to prepare ultra-thin specification high-strength steel for the following considerations: C: C, as an interstitial atom in steel, plays a very important role in improving the strength of steel, has the greatest impact on the yield strength and tensile strength of steel, and is an important element that determines the strength and hardness of materials. C can stabilize austenite and control the transformation amount of ferrite during laminar cooling air cooling. In order to obtain high-strength steel with a tensile strength of 980MPa, a certain carbon content must be guaranteed, but too high a carbon content will affect the welding performance, so the C content in this application is set to 0.16wt.%~0.21wt.%.

[0066] Si: Si is a solid solution strengthening element. Adding Si to steel has many advantages. However, when Si is ≥ 0.10wt.%, it will form strongly adherent iron oxide scale on the surface of the steel plate, affecting its dephosphorization effect. Therefore, the Si content in this application is set to < 0.10wt.%.

[0067] Mn: Mn is a substitutional element and plays a role in solid solution strengthening; it can expand the austenite phase region, reduce the critical quenching speed of steel, stabilize austenite, refine grains, and delay the transformation of austenite to pearlite. In order to ensure the tensile strength ≥ 980MPa, the Mn content should be controlled above 1.60wt.%, and if the Mn content is too low, the supercooled austenite is not stable enough and is easily transformed into a pearlite type structure during air cooling; if the Mn content is too high, it will affect the alloy cost, so the Mn content in this application is set to 1.60wt.% to 1.90wt.%.

[0068] P and S: P and S are harmful inclusions in steel, which have a great damaging effect on the steel's formability, low-temperature toughness, weldability and fatigue performance; this application controls the P content to ≤0.015wt.% and the S content to ≤0.004wt.%, in order to reduce production costs and improve product quality, so that the influence of P and S on the formability is reduced to a lower level.

[0069] Cr: The Cr element can improve the hardenability of steel, reduce the adhesion of the oxide scale on the surface of the strip steel, reduce the pulverization of the oxide scale on the surface of the steel plate, and improve the surface quality of the steel plate. Therefore, the Cr content in this application is set to 0.20wt.%~0.50wt.%.

[0070] Nb: Nb can hinder the recrystallization of austenite, precipitate NbC to refine ferrite grains, and improve strength and toughness. Nb can improve the tempering stability of steel and reduce the tempering brittleness of steel. In the solid solution state, Nb can effectively inhibit the transformation of austenite to ferrite, pearlite, and bainite, and improve the hardenability of steel plates. However, Nb is a precious metal element, so it is more appropriate to set the Nb content to 0.020wt.% to 0.040wt.%.

[0071] Ti: Ti element has certain fine grain strengthening and precipitation strengthening effects. A small amount of Ti can also improve welding performance. In this application, the fine grain strengthening and welding performance of Ti are mainly utilized, so the Ti content is set to 0.010wt.% to 0.040wt.%.

[0072] Mo: Mo can refine grains, improve strength and toughness. Mo exists in the solid solution phase and carbide phase in steel, so molybdenum-containing steel has both solid solution strengthening and carbide dispersion strengthening. Mo can shift the C curve of steel to the right, significantly improve the hardenability of steel, and improve the tempering stability of steel. Mo can also improve the high-temperature brittleness of alloy quenched and tempered steel, improve the toughness of tempered troostite, and precipitate Mo in situ during high-temperature tempering. 2C is in dislocation and maintains coherence with the matrix, is not easy to aggregate and grow, and has a strong secondary hardening effect. Mo dissolves in ferrite, increases the self-diffusion activation energy of iron, and increases the recovery and recrystallization temperature of steel. However, Mo is a precious metal element, so the Mo content is set to 0.30wt.%~0.50wt.%.

[0073] B: The B element has a strong hardenability effect in steel. A small amount of B can greatly improve the hardenability of steel. Therefore, the B content in this application is set to 0.0010wt.% to 0.0025wt.%.

[0074] N: N is a harmful element in steel. Controlling the N content to ≤0.004wt.% can reduce the risk of forming coarse TiN inclusions.

[0075] Als: Als has a deoxidizing effect in the steelmaking process and can improve the purity of molten steel. In addition, Als can fix N in steel and form stable compounds with N, effectively refining the grains. Therefore, the Als content in this application is set to 0.010wt.% to 0.060wt.%.

[0076] The technical solution of the present application is further illustrated below through specific embodiments and comparative examples.

[0077] Examples 1-9 and Comparative Examples 1-3

[0078] Provided are methods for producing ultra-thin high-strength steel based on a discontinuous quenching line, respectively, including providing molten steel of Examples 1-9 and Comparative Examples 1-3, subjecting the respective molten steels to converter smelting, off-furnace refining, and Si-Ca treatment by adding silicon-calcium wire, wherein the Ca / S ratio in the molten steel after Si-Ca treatment is controlled within the range of 1.0 to 3.0, and the calcium content in the molten steel reaches 25 ppm, wherein during the Si-Ca treatment, argon gas needs to be blown into the molten steel for soft blowing treatment to obtain molten steel of high-strength steel; the molten steels obtained in Examples 1-9 and Comparative Examples 1-3 are shown in Table 1.

[0079] Table 1 Chemical composition and mass percentage of molten steel obtained in Examples 1-9 and Comparative Examples 1-3

[0080]

[0081] The molten steel of high-strength steel is continuously cast, and electromagnetic stirring is adopted in the continuous casting process. The electromagnetic stirring adopts a forward and reverse alternating stirring mode, the alternating time is 55s, the electromagnetic stirring current is 360A-380A, and the electromagnetic stirring frequency is 15Hz-16Hz to obtain a continuously cast slab; the continuously cast slab is heated to make the heating temperature of the second heating section and the soaking section 1160℃-1200℃ to obtain a first heated slab; the first heated slab is subjected to rough rolling and finish rolling in sequence to obtain a finished rolled steel; wherein the rough rolling temperature is 1060℃-1200℃, and the rough rolling stand is The dephosphorization water pressure is 120 bar to 125 bar, and the final rolling temperature of the finishing rolling is 860 ℃ to 900 ℃; the finishing rolled steel is subjected to laminar cooling, and the cooling rate of the laminar cooling is shown in Table 2 to obtain the cooled steel; the cooled steel is coiled and stacked, and the coiling temperature is shown in Table 2 to obtain the coiled cooled steel; the coiled cooled steel is pickled and cold rolled, wherein the temperature of the pickling solution in the 1#-3# pickling tanks is 75 ℃, the number of cold rolling passes is 2 to 4 times, the front tension is 4 to 10 KN / mm, and the rear tension is 11 to 16 KN / mm to obtain the cold rolled steel; the cold rolled steel is The quenching and hardening treatment includes: rough straightening and fine straightening of the cold-rolled steel, the rough straightening pressure is 6000KN~9000KN, and the fine straightening pressure is 15000KN~18000KN, so as to obtain straightened steel; the straightened steel is quenched, the quenching temperature is shown in Table 2, the holding time is 20±3 minutes, the upper and lower water volume ratio is 3:4 during quenching, and the cooling rate is shown in Table 2, so as to obtain quenched steel; the quenched steel is straightened and tempered, including: rough straightening and fine straightening of the quenched steel, the rough straightening pressure is 6000KN~9 000KN, the fine straightening pressure is 15000KN~18000KN, and the straightening steel strip with a buckled plate shape after straightening is obtained, and the unevenness is ≤6mm / m; the straightening steel strip is tempered, the heating temperature of the tempering treatment is shown in Table 2, the holding time is 40±3 minutes, and air cooling is performed to obtain tempered steel; the tempered steel is subjected to secondary rough straightening and fine straightening, the rough straightening pressure is 4000KN~7000KN, and the fine straightening pressure is 12000KN~15000KN, and the ultra-thin specification high-strength steel with a thickness of ≤3mm and a yield strength of ≥960MPa is obtained. The production process of ultra-thin specification high-strength steel of Examples 1-9 and Comparative Examples 1-3 is described in Table 2:

[0082] Table 2 Preparation process parameters of ultra-thin high-strength steel of Examples 1-9 and Comparative Examples 1-3

[0083]

[0084]

[0085] Table 2 Preparation process parameters of ultra-thin high-strength steel of Examples 1-9 and Comparative Examples 1-3

[0086]

[0087] The high-strength steels of Examples 1-9 and Comparative Examples 1-3 were subjected to performance tests, and the test results are recorded in Table 3 below:

[0088] Table 3 Performance test results of high strength steel of Examples 1-9 and Comparative Examples 1-3

[0089]

[0090] Comparing Tables 1 to 3, it can be seen that the element content of Comparative Example 1 does not meet the composition limitation range of this application, nor does it meet the relationship (1) of this application. Even if its preparation process is the same as that of this application, and the strength and unevenness of the high-strength steel product prepared by it also meet the requirements of this application, the bending performance is very poor and cannot meet the requirements of d=3a and 180° cold bending. The content of each element in Comparative Example 2 basically meets the relationship (1) of this application, and the hot rolling process also meets the limitations of the preparation method of this application, but the pickling speed is too fast, the iron oxide scale on the surface of the steel plate is not completely removed, and it is heated unevenly in the quenching furnace, such as Figure 2 As shown, the steel plate was warped when it came out of the furnace; and the upper and lower water ratios during quenching did not meet the range specified in this application. The upper water volume was large, and the cooling rate was too high, resulting in an average unevenness of the steel plate of 7mm / m, which was much higher than the unevenness of the ultra-thin specification high-strength steel of this application. The composition of Comparative Example 3 meets the range specified in the element content of this application, but it was not pickled and single-stand rolled, and the iron oxide scale on the surface of the steel plate seriously affected its uniform heating, resulting in severe warping of the steel plate during the heating process. Although a water ratio of small upper and large lower was used for cooling during quenching, and the cooling rate also met the requirements of this application, it still could not compensate for the warping during the heating process, resulting in a poor final plate shape, and the unevenness of the steel plate reached 11mm / m. It can be seen that at least one of the steel elements and their content and the preparation process is not within the range specified in this application, and the high-strength steel produced based on the discontinuous quenching line is difficult to meet the requirements of ultra-thin specification high-strength steel.

[0091] As can be seen from the test results of the ultra-thin high-strength steel of Examples 1-9, the method for producing ultra-thin high-strength steel based on a discontinuous quenching line in the embodiment of the present application can produce a plate with a roughness of ≤3 mm / m, a thickness of ≤3 mm, and a yield strength R eL ≥960MPa, tensile strength R m ≥980MPa, elongation A≥12%; d=3a, 180° cold bending qualified ultra-thin specification high-strength steel. Figure 3 As shown, the ultra-thin high-strength steel of Example 5 of the present application has small unevenness and a smooth surface.

[0092] The method for producing ultra-thin high-strength steel based on a discontinuous quenching line in the embodiment of the present application adopts a reasonable chemical composition ratio and tempering process to ensure that the mechanical properties of the material meet the requirements. And through the process of pickling and single-stand rolling mill, it is ensured that the steel has a good initial plate shape before quenching, and there is no iron oxide scale on the surface of the steel plate, ensuring uniform heating during the heating process. In addition, the method for producing ultra-thin high-strength steel based on a discontinuous quenching line in the embodiment of the present application ensures that the plate shape of the steel after quenching is good through a water ratio of small top and large bottom and a slower quenching speed. And through two straightening processes, the final unevenness of the steel plate meets 3mm / m. Thereby achieving a good match between the ultra-thin specifications, high strength and plate shape of the steel.

[0093] The above is only a specific implementation method of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. It should be understood that the protection scope of the present application is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application.

Claims

1. A method for producing ultra-thin high-strength steel based on a discontinuous quenching line, characterized in that: include: Molten steel is provided, and the molten steel is subjected to converter smelting, external refining, and Si-Ca treatment during the external refining process, wherein the molten steel needs to be subjected to soft blowing treatment during the Si-Ca treatment process, and the Ca / S ratio in the molten steel after the Si-Ca treatment is 1.0-3.0, thereby obtaining molten steel of high-strength steel; the molten steel of high-strength steel is composed of the following chemical components in terms of mass percentage: C is 0.16wt.%-0.21wt.%, Si is less than 0.10wt.%, Mn is 1.60wt.%-1.90wt.%, and P is less than or equal to 0.015wt. %, S≤0.004wt.%, Cr is 0.20wt.%~0.50wt.%, Nb is 0.020wt.%~0.040wt.%, Ti is 0.010wt.%~0.040wt.%, Mo is 0.30wt.%~0.50wt.%, B is 0.0010wt.%~0.0025wt.%, N≤0.004wt.%, Als is 0.010wt.%~0.060wt.%, and the rest is Fe and unavoidable impurities; the above chemical composition satisfies the following relationship at the same time: 800≤4370[%C]+88[%Si]+53[%Mn]+22[%Mo]-30[%Cr]≤1000 (1); Continuously casting the molten steel of the high-strength steel to obtain a continuously cast slab; Heating the continuous casting slab to obtain a first heated slab; The first heated slab is subjected to rough rolling and finish rolling in sequence to obtain a finished steel product; wherein the rough rolling temperature is 1060° C. to 1200° C., and the finish rolling temperature is 860° C. to 900° C.; The finished rolled steel is subjected to laminar cooling at a cooling rate of 40°C / s to 80°C / s to obtain a cooled steel; The cooled steel is pickled and cold-rolled to obtain a cold-rolled steel; Performing flattening and quenching treatment on the cold-rolled steel to obtain quenched steel; The quenched steel is straightened and tempered to obtain ultra-thin high-strength steel with a thickness of ≤3 mm and a yield strength of ≥960 MPa.

2. The method according to claim 1, characterized in that During the Si-Ca treatment, the molten steel is subjected to a soft blowing treatment, including blowing argon gas to the molten steel between 5 minutes before the Si-Ca treatment and 8 minutes after the Si-Ca treatment.

3. The method according to claim 1, characterized in that The continuous casting of molten steel of high-strength steel includes electromagnetic stirring of the crystallizer, and the electromagnetic stirring adopts a forward and reverse alternating stirring mode, the alternating time is 50s to 60s, the electromagnetic stirring current is 360A to 480A, and the electromagnetic stirring frequency is 12Hz to 20Hz, so as to obtain a continuously cast slab with a thickness of 210mm to 230mm.

4. The method according to claim 1, characterized in that: At least one of the following requirements must be met: The heating treatment of the continuous casting slab includes setting the heating temperature of the second heating section and the soaking section to 1160° C. to 1200° C.; The sequentially rough rolling and finish rolling of the first heated slab includes making the dephosphorization water pressure used between the rough rolling stands be 110 bar to 130 bar during the rough rolling of the first heated slab.

5. The method according to claim 1, characterized in that The method for preparing ultra-thin steel produced by a discontinuous quenching line further includes: coiling the cooled steel at a coiling temperature of 600° C. to 650° C. to obtain a coiled cooled steel.

6. The method according to claim 1, characterized in that At least one of the following requirements must be met: The pickling treatment of the cooled steel material includes pickling in a pickling tank with an acid concentration of 70g / L to 120g / L, 130g / L to 170g / L, or 170g / L to 210g / L, wherein the temperature of the acid in the pickling tank is 60°C to 90°C, and the pickling speed is 40m / min to 70m / min; The cold rolling treatment of the cooled steel includes using a single-stand rolling mill to cold roll the cooled steel after pickling, the cold rolling passes are 2 to 4, the single pass reduction rate is ≤15%, the front tension is 4KN / mm to 10KN / mm, and the rear tension is 11KN / mm to 16KN / mm, so as to obtain cold-rolled steel.

7. The method according to claim 1, characterized in that At least one of the following requirements must be met: The step of performing the flattening and quenching treatment on the cold-rolled steel comprises: performing rough flattening and fine flattening on the cold-rolled steel, wherein the pressure of the rough flattening is 6000KN to 9000KN, and the pressure of the fine flattening is 15000KN to 18000KN, to obtain straightened steel; The straightened steel is quenched at a heating temperature of 900±20°C, a holding time of 20±3 minutes, an upper and lower water volume ratio of 3:4 during quenching, and a cooling rate of 35°C / s to 50°C / s to obtain a quenched steel.

8. The method according to claim 1, characterized in that At least one of the following requirements must be met: The straightening and tempering treatment of the quenched steel includes: performing rough straightening and fine straightening on the quenched steel, the rough straightening pressure is 6000KN-9000KN, the fine straightening pressure is 15000KN-18000KN, and the straightened steel strip is obtained in a buckled state after straightening, and the unevenness is ≤6mm / m; The straightened steel strip is tempered at a heating temperature of 600±20° C. for a holding time of 40±3 minutes, and air-cooled to obtain a tempered steel material; The tempered steel is subjected to secondary rough straightening and fine straightening, the rough straightening pressure is 4000KN-7000KN, and the fine straightening pressure is 12000KN-15000KN, so as to obtain ultra-thin high-strength steel.

9. An ultra-thin high-strength steel, characterized in that: The method for producing ultra-thin high-strength steel based on a discontinuous quenching line according to any one of claims 1 to 8 is prepared; in terms of mass percentage, the ultra-thin high-strength steel is composed of the following chemical components: C is 0.16wt.% to 0.21wt.%, Si is less than 0.10wt.%, Mn is 1.60wt.% to 1.90wt.%, P is ≤0.015wt.%, S is ≤0.004wt.%, Cr is 0.20wt.% to 0.5 0wt.%, Nb is 0.020wt.%~0.040wt.%, Ti is 0.010wt.%~0.040wt.%, Mo is 0.30wt.%~0.50wt.%, B is 0.0010wt.%~0.0025wt.%, N≤0.004wt.%, Als is 0.010wt.%~0.060wt.%, and the rest is Fe and unavoidable impurities; the above chemical composition satisfies the following relationship at the same time: 800≤4370[%C]+88[%Si]+53[%Mn]+22[%Mo]-30[%Cr]≤1000 (1).

10. The ultra-thin high-strength steel according to claim 9, characterized in that: The unevenness of the ultra-thin high-strength steel plate is ≤3mm / m, the thickness is ≤3mm, and the mechanical properties meet the following requirements: yield strength R eL ≥960MPa, tensile strength R m ≥980MPa, elongation A≥12%; d=3a, 180° cold bending qualified.

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