Ultra-thin gauge high strength steel and method for producing ultra-thin gauge high strength steel based on discontinuous quenching line

Abstract

The application discloses a kind of ultra-thin gauge high-strength steel and the method for producing ultra-thin gauge high-strength steel based on non-continuous quenching line, comprising: providing molten steel, the converter smelting of molten steel, secondary refining and Si-Ca treatment in the secondary refining process, Si-Ca treatment process needs to be carried out soft blowing treatment to molten steel, Ca / S ratio in molten steel after Si-Ca treatment is 1.0~3.0, obtain the molten steel of high-strength steel;The continuous casting slab of high-strength steel molten steel is cast to obtain continuous casting slab;First heated slab is obtained by heating treatment to continuous casting slab;First heated slab is rolled to obtain finished rolling steel by rough rolling and finish rolling;Rough rolling temperature is 1060~1200 DEG C, and finish rolling finish rolling temperature is 860~900 DEG C;Finished rolling steel is obtained by laminar cooling to finished rolling steel, and cooling rate is 40~80 DEG C / s;Cold-rolled steel is obtained by pickling and cold rolling treatment to cooling steel;Cold-rolled steel is obtained by opening and quenching treatment to cold-rolled steel;Straightening and tempering treatment are carried out to quenched steel, and the ultra-thin gauge high-strength steel with thickness ≤3mm and yield strength ≥960MPa is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steelmaking, and particularly relates to an ultrathin high-strength steel and a method for producing the ultrathin high-strength steel based on a non-continuous quenching line. BACKGROUND

[0002] With the development of engineering machinery towards high-end, vehicle lightening and high-strength thinning are increasingly concerned by practitioners. The original high-strength steel of 700 MPa has been upgraded to 960 MPa, and the ultrathin high-strength steel with a thickness of less than or equal to 3 mm and a yield strength of greater than or equal to 960 MPa is mainly applied to the final section arm of a small crane, the final section arm of an aerial work platform and a truck-mounted crane, and plays an important role in the development of high-end and individualization of engineering machinery.

[0003] The high-strength steel product with a thickness of less than or equal to 3 mm and a yield strength of greater than or equal to 960 MPa is generally produced by a cold rolling process or on a continuous quenching line. The cold rolling process has a long production cycle, large product strength and large springback, and poor assembly precision in the forming process. Therefore, the continuous quenching line is the best choice, and the strip steel is uniformly stressed under the action of the tension roller, and the plate shape is well controlled, but the continuous quenching line can only produce a quenched plate with a thickness of less than or equal to 6 mm, and the annual output of the ultrathin high-strength steel with a thickness of less than or equal to 3 mm is small, and the economic benefits brought by the investment of several hundred million yuan in the construction of the production line are low. The existing non-continuous quenching line is used to produce the ultrathin high-strength steel, and the quenched roller cannot constrain the steel plate, that is, the strip steel specification has exceeded the design limit of the production line, so the plate shape of the ultrathin high-strength steel is poor, which restricts the development of the product. SUMMARY

[0004] The embodiment of the application provides an ultrathin high-strength steel and a method for producing the ultrathin high-strength steel based on a non-continuous quenching line, which can produce the high-strength steel product with a thickness of less than or equal to 3 mm and a yield strength of greater than or equal to 960 MPa by a simple preparation process based on the non-continuous quenching line.

[0005] In a first aspect, the application provides a method for producing an ultrathin high-strength steel based on a non-continuous quenching line, comprising:

[0006] The present application provides a method for preparing high-strength steel. The method comprises the following steps: providing molten steel, carrying out converter smelting, secondary refining and Si-Ca treatment during the secondary refining process on the molten steel, wherein the Si-Ca treatment is carried out by soft blowing treatment on the molten steel, the Ca / S ratio in the molten steel after the Si-Ca treatment is 1.0-3.0, and the molten steel of the high-strength steel is obtained; the molten steel of the high-strength steel is composed of the following chemical components in percentage by mass: C is 0.16wt.%-0.21wt.%, Si is less than 0.10wt.%, Mn is 1.60wt.%-1.90wt.%, P is less than or equal to 0.015wt.%, S is less than or equal to 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 is less than or equal to 0.004wt.%, Al is 0.010wt.%-0.060wt.%, and the rest is Fe and inevitable impurities; the above chemical components satisfy the following relationships simultaneously:

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

[0008] The molten steel of the high-strength steel is continuously cast to obtain a continuously cast slab;

[0009] The continuously cast slab is subjected to heating treatment to obtain a first heated slab;

[0010] The first heated slab is subjected to rough rolling and finish rolling in sequence to obtain a finish-rolled steel material; wherein the temperature of the rough rolling is 1060-1200℃, and the finish rolling temperature is 860-900℃;

[0011] The finish-rolled steel material is subjected to laminar cooling at a cooling rate of 40-80℃ / s to obtain a cooled steel material;

[0012] The cooled steel material is subjected to pickling and cold rolling treatment to obtain a cold-rolled steel material;

[0013] The cold-rolled steel material is subjected to opening flat and quenching treatment to obtain a quenched steel material;

[0014] The quenched steel material is subjected to straightening and tempering treatment to obtain an ultra-high-strength steel material with a thickness of less than or equal to 3mm and a yield strength of greater than or equal to 960MPa.

[0015] According to the embodiments of the first aspect of the present application, the soft blowing treatment on the molten steel during the Si-Ca treatment process comprises blowing argon to the molten steel between 5 minutes before the Si-Ca treatment and 8 minutes after the Si-Ca treatment.

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

[0017] According to the embodiment of the first aspect of the present application, the heating treatment of the continuous casting slab comprises that the heating temperature of the second heating section and the soaking section is 1160℃-1200℃.

[0018] According to the embodiment of the first aspect of the present application, the rough rolling and finish rolling of the first heated slab in sequence comprises that, in the process of rough rolling of the first heated slab, the phosphorus removal water pressure adopted between the rough rolling racks is 110bar-130bar.

[0019] According to the embodiment of the first aspect of the present application, the method for producing ultra-thin specification high-strength steel based on the discontinuous quenching line further comprises: coiling treatment of the cooled steel, the coiling temperature is 600℃-650℃, 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 comprises pickling using 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 liquid in the pickling tank is 60℃-90℃, and the pickling speed is 40m / min-70m / min.

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

[0022] According to the embodiment of the first aspect of the present application, the opening and quenching treatment of the cold rolled steel comprises: opening and rough straightening and opening and fine straightening of the cold rolled steel, the pressure of the opening and rough straightening is 6000KN-9000KN, the pressure of the opening and fine straightening is 15000KN-18000KN, and a straightened steel is obtained.

[0023] 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 amount ratio during quenching is 3:4, the cooling rate is 35℃ / s-50℃ / s, and a quenched steel is obtained.

[0024] According to the embodiment of the first aspect of the application, the straightening and tempering treatment of the quenched steel material comprises: rough straightening and fine straightening of the quenched steel material, the rough straightening pressure is 6000KN-9000KN, the fine straightening pressure is 15000KN-18000KN, to obtain the straightened steel strip with the straightened plate shape in the down buck state, and the unevenness is ≤6mm / m;

[0025] The straightened steel strip is subjected to tempering treatment, the heating temperature of the tempering treatment is 600±20℃, the holding time is 40±3 minutes, air cooling is performed, and the tempered steel material is obtained;

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

[0027] In the second aspect, the application provides an ultra-thin gauge high-strength steel, which is prepared based on the method for producing an ultra-thin gauge high-strength steel by a non-continuous quenching line; the ultra-thin gauge high-strength steel is composed of the following chemical components in mass percentage: C is 0.16wt.%-0.21wt.%, Si is <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.%, 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 inevitable impurities; the above chemical components satisfy 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 application, the steel plate of the ultra-thin gauge high-strength steel produced based on the non-continuous quenching line has an unevenness of ≤3mm / m and a thickness of ≤3mm, and the mechanical properties satisfy: the yield strength R eL ≥960MPa, the tensile strength R m ≥980MPa, and the elongation A≥12%; d=3a, 180° cold bending is qualified.

[0030] The embodiment of the present application is based on a method for producing an ultra-thin gauge high-strength steel by a non-continuous quenching line. The content of C and Mn in the ultra-thin gauge high-strength steel is increased, and the content of Si is reduced. The main reason is that, for the thin gauge high-strength steel, the normal purging gas flow cannot be used in the quenching process to prevent the steel plate from being blown into the gap between the rolls. When the content of Si in the steel is high, the water on the surface of the strip is blown clean and enters the tempering furnace, which will cause serious red rust on the surface. By increasing the content of C and Mn, not only the strength loss caused by the reduction of the content of Si can be avoided, but also the phenomenon of low strength caused by the decarburized layer on the surface of the strip during the quenching process of the high-strength steel can be avoided. By increasing the content of C and Mn to improve the solid solution strengthening effect of the steel plate and increasing the carbon content in the martensite to increase the strength, the strength of the ultra-thin gauge high-strength steel is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments of the present application will be briefly introduced. Those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0032] Figure 1 is an actual product diagram of an ultra-thin gauge high-strength steel prepared by the preparation method of the ultra-thin gauge steel produced by the non-continuous quenching line according to the embodiment of the present application.

[0033] Figure 2 is an actual product diagram of an ultra-thin gauge high-strength steel provided by Comparative Example 2.

[0034] Figure 3 is an actual product diagram of an ultra-thin gauge high-strength steel provided by 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 more clear and apparent, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, but not to limit the present application. The present application can be implemented without some of these specific details by those skilled in the art. The following description of the embodiments is only intended to provide a better understanding of the present application by showing examples of the present application.

[0036] It is to be noted that, in the present document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0037] To solve the problems in the prior art, the embodiment of the present application provides an ultra-thin gauge high-strength steel based on a non-continuous quenching line production and a preparation method thereof.

[0038] Firstly, the method for producing the ultra-thin gauge high-strength steel based on the non-continuous quenching line production provided by the embodiment of the present application is introduced. Figure 1 The flowchart of the method for producing the ultra-thin gauge high-strength steel based on the non-continuous quenching line production provided by the embodiment of the present application is shown.

[0039] As shown in the figure, the method for producing the ultra-thin gauge high-strength steel based on the non-continuous quenching line production comprises the following steps. Figure 1 The method for producing the ultra-thin gauge high-strength steel based on the non-continuous quenching line production comprises the following steps: providing molten steel, carrying out converter smelting, secondary refining and Si-Ca treatment in the secondary refining process on the molten steel, wherein the soft blowing treatment is needed during the Si-Ca treatment process, the Ca / S ratio in the molten steel after the Si-Ca treatment is 1.0-3.0, and the molten steel of the high-strength steel is obtained; the molten steel of the high-strength steel consists of the following chemical components in percentage by mass: C is 0.16wt.%-0.21wt.%, Si is less than 0.10wt.%, Mn is 1.60wt.%-1.90wt.%, P is less than or equal to 0.015wt.%, S is less than or equal to 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 is less than or equal to 0.00wt.4%, Als is 0.010wt.%-0.060wt.%, and the rest is Fe and inevitable impurities; the above chemical components satisfy the following relationships simultaneously:

[0040] 0.010wt.%-0.040wt.%, Mo is 0.30wt.%-0.50wt.%, B is 0.0010wt.%-0.0025wt.%, N is less than or equal to 0.00wt.4%, Als is 0.010wt.%-0.060wt.%, and the rest is Fe and inevitable impurities; the above chemical components satisfy the following relationships simultaneously:

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

[0042] casting the molten steel of the high-strength steel to obtain a continuous casting slab; heating the continuous casting slab to obtain a first heated slab; sequentially performing rough rolling and finish rolling on the first heated slab to obtain a finish-rolled steel material; wherein the temperature of the rough rolling is 1060-1200 ℃, and the finish rolling temperature is 860-900 ℃; performing laminar cooling on the finish-rolled steel material at a cooling rate of 40-80 ℃ / s to obtain a cooled steel material; performing pickling and cold rolling on the cooled steel material to obtain a cold-rolled steel material; performing flattening and quenching on the cold-rolled steel material to obtain a quenched steel material; performing straightening and tempering on the quenched steel material to obtain an ultra-thin high-strength steel with a thickness of ≤3 mm and a yield strength of ≥960 MPa.

[0043] The method for producing an ultra-thin high-strength steel based on a discontinuous quenching line in the embodiments of the present application increases the contents of C and Mn in the ultra-thin high-strength steel and reduces the content of Si. The main reason is that the steel plate of the ultra-thin high-strength steel is too thin, and thus normal purging airflow cannot be used in the quenching process to prevent the steel plate from being blown into the gap between the rolls. When the content of Si in the steel is relatively high, the water on the surface of the strip is blown clean and enters the tempering furnace, which can cause serious red rust on the surface. Increasing the contents of C and Mn can not only avoid the strength loss caused by the reduction of the content of Si, but also avoid the phenomenon of low strength caused by the decarburized layer on the surface of the strip during the quenching process of the high-strength steel. Increasing the contents of C and Mn can increase the solid solution strengthening effect of the steel plate and increase the carbon content in the martensite to increase the strength, thereby ensuring the strength of the ultra-thin high-strength steel.

[0044] It should be noted that the discontinuous quenching line refers to a normal quenching line, i.e., a production line in which the steel plates are quenched one by one or in blocks, and the method for producing an ultra-thin high-strength steel based on a discontinuous quenching line in 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 has unexpectedly found that the mechanical properties of the molten steel composition satisfying formula (1) meet the use requirements. When the value of 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 material. When the value of formula (1) is less than 800, the strength of the steel material cannot meet the target requirements.

[0047] In some embodiments of the present application, the Si-Ca treatment in the secondary refining process refers to adding Si-Ca wire into the molten steel in the secondary refining process to make the Ca content in the molten steel 20 ppm-30 ppm. The Si-Ca treatment of the molten steel in the secondary refining process 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 the ultra-thin gauge high-strength steel. The calcium content in the molten steel can be determined by the determination method of the composition content in the molten steel, and when the calcium content in the molten steel reaches 20 ppm-30 ppm, it can be considered that the Si-Ca treatment in the secondary refining process has been completed. Exemplarily, the calcium content in the molten steel reaches 22 ppm, 25 ppm, 27 ppm, 29 ppm, 30 ppm.

[0048] In some embodiments of the present application, the soft blowing treatment of the molten steel during the Si-Ca treatment process includes blowing argon to the molten steel between 5 minutes before the Si-Ca treatment and 8 minutes after the Si-Ca treatment, with the molten steel surface slightly stirring as the criterion.

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

[0050] In some embodiments of the present application, the heating treatment of the continuous casting slab includes making the heating temperature of the second heating section and the soaking section 1160℃-1200℃.

[0051] In some embodiments of the present application, the rough rolling and finish rolling of the first heated slab in sequence includes making the phosphorus removal water pressure between the rough rolling stands 110 bar-130 bar during the rough rolling of the first heated slab.

[0052] In some embodiments of the present application, the method for producing an ultra-thin gauge high-strength steel based on a non-continuous quenching line further includes: coiling the cooled steel material at a coiling temperature of 600℃-650℃ to obtain a coiled cooled steel material.

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

[0054] In the preparation method of the present application, the acid pickling treatment can remove the oxide scale on the surface of the cooled steel, which is beneficial to single stand rolling and the control of the plate shape in the subsequent quenching process. When the oxide scale exists on the surface of the steel, it will affect the temperature uniformity in the heating process. The ultra-thin high-strength steel is in the form of a strip and very thin, and uneven heating in the heating furnace will cause deformation of the plate shape and exacerbate the deformation in the quenching process. Therefore, it is necessary to perform acid pickling treatment on the cooled steel.

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

[0056] In the preparation method of the present application, the single stand rolling mill is used to perform cold rolling treatment on the cooled steel, which not only improves the flatness of the original plate shape, but also thins the steel plate. It is known that the hot rolling production line is difficult to control the plate shape when producing thin gauge hot-rolled coils, and different thickness specifications of steel plates are needed for transition, which will cause a large amount of non-required products. However, using single stand rolling can directly roll the 3mm hot-rolled raw material into 2mm thickness, reducing the production cost.

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

[0058] In the preparation method of the present application, the quenching treatment process adopts the strategy of using "small upper and large lower" cooling water for cooling, and the upper and lower water quantity ratio is 3:4, and the cooling rate is 35-50℃ / s. Because the cold-rolled steel for quenching treatment is in the form of a strip and very thin, it is necessary to use small upper and large lower cooling water, otherwise the cooling will be uneven and the cold-rolled steel will be severely deformed. Similarly, because the cold-rolled steel is very thin, if a larger cooling rate is used, the cold-rolled steel in the form of a strip is prone to deformation, and if a too low cooling rate is used, 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, the straightening and tempering treatment of the quenched steel material comprises: rough straightening and fine straightening of the quenched steel material, the rough straightening pressure is 6000KN-9000KN, the fine straightening pressure is 15000KN-18000KN, to obtain a straightened steel strip with a down-curved plate shape after straightening, and the unevenness is ≤6mm / m; the straightened steel strip is subjected to tempering treatment, the heating temperature of the tempering treatment is 600±20℃, the holding time is 40±3 minutes, air cooling is performed, to obtain a tempered steel material; the tempered steel material is subjected to secondary rough straightening and fine straightening, the rough straightening pressure is 4000KN-7000KN, the fine straightening pressure is 12000KN-15000KN, to obtain an ultra-high strength steel material.

[0060] In the preparation method of the present application, straightening treatment is adopted before and after tempering, which has different effects. The first straightening obtains a slightly down-curved plate shape, because the quenched steel material in strip form will shrink during air cooling after tempering, and the slightly down-curved original plate shape can offset the deformation caused by the shrinkage. The second straightening uniformly releases the internal stress of the steel plate and adjusts the final plate shape.

[0061] Therefore, the method for producing ultra-thin gauge high-strength steel based on the non-continuous quenching line of the present application adopts reasonable composition design, increases the C and Mn content, and reduces the Si content, to ensure that the material strength meets the performance requirements and improves the surface quality of the steel material. In addition, the present application adopts the pickling and single-stand rolling process, to obtain quenched raw materials with thickness specifications, plate shape and surface quality meeting the requirements. And the strategy of combining two straightening and tempering is adopted, to obtain ultra-thin gauge high-strength steel with good plate shape, and the unevenness of the plate shape is ≤3mm / m. After detection, the yield strength R eL ≥960MPa, the tensile strength R m ≥980MPa, the elongation A≥12%; d=3a, 180° cold bending is qualified. It is shown that the preparation method of the ultra-thin gauge steel based on the non-continuous quenching line of the present application, as a new manufacturing process, can produce the required ultra-thin gauge high-strength steel based on the non-continuous quenching line.

[0062] In a second aspect, the present application provides an ultra-thin gauge high-strength steel produced based on a non-continuous quenching line, which is prepared by a method for producing an ultra-thin gauge high-strength steel based on a non-continuous quenching line; the ultra-thin gauge high-strength steel is composed of the following chemical components in percentage by mass: C is 0.16wt.% to 0.21wt.%, Si is <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.% to 0.040wt.%, Ti is 0.010wt.% to 0.040wt.%, Mo is 0.30wt.% to 0.50wt.%, B is 0.0010wt.% to 0.0025wt.%, N is ≤0.004wt.%, Als is 0.010wt.% to 0.060wt.%, and the rest is Fe and inevitable impurities; the above chemical components satisfy the following relationships simultaneously:

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

[0064] In some embodiments of the present application, the mechanical properties of the ultra-thin gauge high-strength steel produced based on a non-continuous quenching line satisfy: the unevenness of the steel plate is ≤3mm / m, the thickness is ≤3mm, the yield strength R eL ≥960MPa, the tensile strength R m ≥980MPa, and the elongation A≥12%; d=3a, 180° cold bending is qualified.

[0065] The technical solution of the above components is adopted in the present application to prepare the ultra-thin gauge 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 and has the greatest influence on the yield strength and tensile strength of steel, and is an important element determining 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 a high-strength steel with a tensile strength of 980MPa, a certain carbon content must be ensured, but too high carbon content will affect the welding performance, so the C content in the present application is set to 0.16wt.% to 0.21wt.%.

[0066] Si: Si is a solid solution strengthening element, and there are many advantages of adding Si element in steel, but when Si≥0.10wt.%, it will generate iron oxide scale with strong adhesion on the surface of the strip steel, affecting the dephosphorization effect. Therefore, the Si content in the present application is set to <0.10wt.%.

[0067] Mn: Mn belongs to substitutional elements, which plays a role of solid solution strengthening; it can expand the austenite phase region, can reduce the critical quenching speed of steel, stabilize austenite, refine grains, and delay the transformation of austenite to pearlite. In order to ensure that the tensile strength is greater than or equal to 980 MPa, the content of Mn should be controlled to be greater than or equal to 1.60 wt.%, and if the content of Mn is too low, the undercooled austenite is not stable enough, and it is easy to transform into pearlite type organization when air cooling; if the content of Mn is too high, the alloy cost is affected, therefore, the content of Mn in the present application is set to 1.60 wt.% to 1.90 wt.%.

[0068] P and S: P and S are harmful inclusions in steel, which have a huge damaging effect on the forming performance, low temperature toughness, weldability and fatigue performance of the steel; in order to reduce the production cost and improve the product quality, the content of P is controlled to be less than or equal to 0.015 wt.% and the content of S is controlled to be less than or equal to 0.004 wt.%, so that the influence of P and S on the forming performance is reduced to a lower level.

[0069] Cr: Cr element can improve the hardenability of the steel, and reduce the adhesion of the iron oxide scale on the surface of the steel strip, reduce the powdering of the iron oxide scale on the surface of the steel plate, and improve the surface quality of the steel plate, therefore, the content of Cr in the present application is set to 0.20 wt.% to 0.50 wt.%.

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

[0071] Ti: Ti element has certain grain refinement and precipitation strengthening effect. A small amount of Ti can also improve the welding performance, therefore, the content of Ti in the present application is set to 0.010 wt.% to 0.040 wt.%.

[0072] Mo: Mo can refine the grain, improve the strength and the primary nature. Mo exists in the solid solution phase and the carbide phase in the steel, so the steel containing Mo has the effects of solid solution strengthening and carbide dispersion strengthening. Mo can make the C curve of the steel move to the right, significantly improve the hardenability of the steel, and improve the tempering stability of the steel. Mo can also improve the high-temperature brittleness of the alloyed and quenched steel, improve the toughness of the tempered sorbite, and in the high-temperature tempering, Mo2C is precipitated in situ on the dislocation and is coherent with the matrix, and is not easy to aggregate and grow, having a strong secondary hardening effect. Mo dissolves in ferrite, increases the self-diffusion activation energy of iron, and improves the recovery and recrystallization temperature of the steel. However, Mo is a noble metal element, so the Mo content is set to 0.30wt.% to 0.50wt.%.

[0073] B: B is an element in steel that has a strong quenching effect, and a small amount of B can greatly improve the hardenability of the steel, so the B content in the present application is set to 0.0010wt.% to 0.0025wt.%.

[0074] N: N is a harmful element in steel, and the N content is controlled at ≤0.004wt.% to reduce the risk of generating coarse TiN inclusions.

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

[0076] The technical solutions of the present application are further illustrated by specific examples and comparative examples.

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

[0078] A method for producing ultra-thin gauge high-strength steel based on non-continuous quenching line is provided, including providing the molten steel of examples 1-9 and comparative examples 1-3, carrying out converter smelting, secondary refining and adding silicon-calcium wire for Si-Ca treatment on the respective molten steel, controlling the Ca / S ratio in the molten steel to be 1.0 to 3.0 after Si-Ca treatment, and the calcium content in the molten steel reaches 25ppm, wherein argon blowing treatment is required during the Si-Ca treatment process to obtain the molten steel of high-strength steel; the molten steel obtained by examples 1-9 and comparative examples 1-3 is shown in table 1.

[0079] Table 1 Chemical composition and mass percentage content of the molten steel obtained by examples 1-9 and comparative examples 1-3

[0080]

[0081] The molten steel of the high-strength steel is continuously cast, electromagnetic stirring is used in the continuous casting process, the electromagnetic stirring uses a forward and reverse alternating stirring mode, the alternating time is 55s, the electromagnetic stirring current is 360A-380A, the electromagnetic stirring frequency is 15Hz-16Hz, and a continuously cast slab is obtained; the continuously cast slab is subjected to heating treatment, the heating temperature of the second heating section and the soaking section is 1160°C-1200°C, and a first heated slab is obtained; the first heated slab is sequentially subjected to rough rolling and finish rolling, and a finish rolled steel product is obtained; wherein the temperature of the rough rolling is 1060°C-1200°C, the phosphorus removal water pressure between the rough rolling stands is 120bar-125bar, and the finish rolling temperature is 860°C-900°C; the finish rolled steel product is subjected to laminar cooling, the cooling rate of the laminar cooling is shown in Table 2, and a cooled steel product is obtained; the cooled steel product is coiled and stacked, the coiling temperature is shown in Table 2, and a coiled cooled steel product is obtained; the coiled cooled steel product is subjected to pickling and cold rolling treatment, wherein the temperature of the pickling liquid in the 1#-3# pickling tanks is all 75°C, the cold rolling pass is 2-4 times, the front tension is 4-10KN / mm, the back tension is 11-16KN / mm, and a cold rolled steel product is obtained; the cold rolled steel product is subjected to opening and quenching treatment, including: the cold rolled steel product is subjected to opening rough straightening and opening finish straightening, the pressure of the opening rough straightening is 6000KN-9000KN, the pressure of the opening finish straightening is 15000KN-18000KN, and a straightened steel product is obtained; the straightened steel product is subjected to quenching treatment, the temperature of the quenching treatment is shown in Table 2, the holding time is 20±3 minutes, the upper and lower water amount ratio during quenching is 3:4, the cooling rate is shown in Table 2, and a quenched steel product is obtained; the quenched steel product is straightened and tempered, including: the quenched steel product is subjected to rough straightening and finish straightening, the rough straightening pressure is 6000KN-9000KN, the finish straightening pressure is 15000KN-18000KN, a straightened steel strip in which the straightened plate shape is in a downward buckling state is obtained, and the unevenness is ≤6mm / m; the straightened steel strip is subjected to tempering treatment, the heating temperature of the tempering treatment is shown in Table 2, the holding time is 40±3 minutes, air cooling is performed, and a tempered steel product is obtained; the tempered steel product is subjected to secondary rough straightening and finish straightening, the rough straightening pressure is 4000KN-7000KN, the finish straightening pressure is 12000KN-15000KN, and an ultra-thin gauge high-strength steel with a thickness ≤3mm and a yield strength ≥960MPa is obtained. The production process of the ultra-thin gauge high-strength steel of Examples 1-9 and Comparative Examples 1-3 is shown in Table 2:

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

[0083]

[0084]

[0085] Table 2 (Continued) shows the preparation process parameters of ultra-thin high-strength steels in 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 steels in Examples 1-9 and Comparative Examples 1-3

[0089]

[0090] Comparing Tables 1-3, it can be seen that the element content of Comparative Example 1 does not conform to the composition limit range of this application, nor does it conform to the relationship (1) of this application. Even though its preparation process is the same as that of this application, and the strength and flatness of the high-strength steel product prepared therefrom meet the requirements of this application, its bending performance is very poor and cannot meet the requirements of d=3a and 180° cold bending qualification. The element content of Comparative Example 2 basically conforms to the relationship (1) of this application, and the hot rolling process also conforms to 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 its heating in the quenching furnace is uneven, such as Figure 2 As shown, the steel plate was warped upon exiting the furnace; furthermore, the water-to-top ratio during quenching did not conform to the limits specified in this application, with a larger volume of water in the upper layer and an excessively high cooling rate, resulting in an average flatness of 7 mm / m for the steel plate, far exceeding the flatness of the ultra-thin high-strength steel of this application. Comparative Example 3's composition conformed to the element content limits specified in this application, but it was not pickled or rolled on a single stand, and the iron oxide scale on the steel plate surface severely affected its uniform heating, causing severe warping during heating. Although a smaller water-to-top ratio and a larger water-to-bottom ratio were used for cooling during quenching, and the cooling rate also met the limits specified in this application, it still could not compensate for the warping during heating, resulting in a very poor final plate shape with a flatness of 11 mm / m. Therefore, if at least one of the steel elements and their content, or the preparation process, is not within the limits specified in this application, high-strength steel produced based on a discontinuous quenching line is unlikely to meet the requirements for ultra-thin high-strength steel.

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

[0092] The embodiment of the present application is based on a method for producing ultra-thin high-strength steel by a non-continuous quenching line. The method adopts reasonable chemical composition ratio and a quenching and tempering process to ensure that the mechanical properties of the material meet the requirements. Through the processes of pickling and rolling by a single stand rolling mill, the method ensures that the steel has a good initial plate shape before quenching and that the surface of the steel plate is free of iron oxide scale, thereby ensuring uniform heating during the heating process. In addition, the method for producing ultra-thin high-strength steel by a non-continuous quenching line according to the embodiment of the present application ensures that the plate shape of the steel after quenching treatment is good by using a water ratio of small at the top and large at the bottom and a slow quenching speed. Through two straightening processes, the final unevenness of the steel plate meets 3mm / m. Thus, the good matching of the ultra-thin specification, high strength and plate shape of the steel is achieved.

[0093] The above is only a specific embodiment of the present application, and those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process described above can refer to the corresponding process in the foregoing method embodiment, which will not be described here. It should be understood that the protection scope of the present application is not limited thereto, and any person skilled in the art 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 covered within the protection scope of the present application.

Claims

1. A method for producing an ultra-thin gauge high-strength steel based on a non-continuous quenching line, characterized in that, The application relates to a method for preparing high-strength steel. The method comprises the following steps: providing molten steel, carrying out converter smelting, secondary refining and Si-Ca treatment in the secondary refining process, wherein the molten steel is subjected to soft blowing treatment during the Si-Ca treatment process, the Ca / S ratio in the molten steel after the Si-Ca treatment is 1.0-3.0, and the molten steel of the high-strength steel is obtained; the molten steel of the high-strength steel is composed of the following chemical components in percentage by mass: C is 0.16wt.%-0.21wt.%, Si is less than 0.10wt.%, Mn is 1.60wt.%-1.90wt.%, P is less than or equal to 0.015wt.%, S is less than or equal to 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 is less than or equal to 0.004wt.%, Al is 0.010wt.%-0.060wt.%, and the rest is Fe and inevitable impurities; the above chemical components satisfy the following relationship simultaneously: 800<=4370[wt.%C]+88[wt.%Si]+53[wt.%Mn]+22[wt.%Mo]-30[wt.%Cr]<=1000 (1); the molten steel of the high-strength steel is subjected to continuous casting, and a continuous casting slab is obtained; the continuous casting slab is subjected to heating treatment, and a first heated slab is obtained; the first heated slab is subjected to rough rolling and finish rolling in sequence, and a finish-rolled steel material is obtained; wherein the rough rolling temperature is 1060 DEG C-1200 DEG C, and the finish rolling final rolling temperature is 860 DEG C-900 DEG C; the finish-rolled steel material is subjected to laminar cooling, and the cooling rate is 40 DEG C / s-80 DEG C / s, and a cooled steel material is obtained; the cooled steel material is subjected to pickling and cold rolling treatment, and a cold-rolled steel material is obtained; the cold-rolled steel material is subjected to opening and quenching treatment, and a quenched steel material is obtained; the quenched steel material is subjected to straightening and tempering treatment, and an ultra-thin high-strength steel with a thickness of less than or equal to 3mm and a yield strength of more than or equal to 960MPa is obtained. The soft blowing treatment of the molten steel during the Si-Ca treatment process comprises blowing argon into the molten steel between 5 minutes before the Si-Ca treatment and 8 minutes after the Si-Ca treatment. The continuous casting of the molten steel of the high-strength steel comprises electromagnetic stirring of a crystallizer, the electromagnetic stirring adopts a forward and reverse alternating stirring mode, the alternating time is 50s-60s, the electromagnetic stirring current is 360A-480A, and the electromagnetic stirring frequency is 12Hz-20Hz, so as to obtain a continuous casting slab with a thickness of 210mm-230mm. At least one of the following requirements is met: The heating treatment of the continuous casting slab comprises that the heating temperature of a second heating section and a soaking section is 1160 DEG C-1200 DEG C; The rough rolling and finish rolling of the first heated slab in sequence comprises that, during the rough rolling of the first heated slab, the phosphorus removal water pressure adopted between rough rolling racks is 110bar-130bar. ​ ​ ​ 2. The method of claim 1, wherein, ​ 3. The method of claim 1, wherein, ​ 4. The method of claim 1, wherein, ​ ​ ​ 5. The method of claim 1, wherein, The preparation method of the ultra-thin gauge steel based on the non-continuous quenching line production further comprises: coiling the cooled steel material at a coiling temperature of 600-650 DEG C to obtain a coiled cooled steel material.

6. The method of claim 1, wherein, At least one of the following requirements is met: The pickling treatment of the cooled steel material comprises pickling in a pickling tank with an acid concentration of 70-120 g / L, 130-170 g / L or 170-210 g / L, the temperature of the acid in the pickling tank is 60-90 DEG C, and the pickling speed is 40-70 m / min; The cold rolling treatment of the cooled steel material comprises cold rolling the pickled cooled steel material using a single-stand rolling mill, the cold rolling pass is 2-4 passes, the single-pass reduction rate is ≤15%, the front tension is 4-10 KN / mm, the back tension is 11-16 KN / mm, and a cold-rolled steel material is obtained.

7. The method of claim 1, wherein, At least one of the following requirements is met: The opening and quenching treatment of the cold-rolled steel material comprises: opening and rough straightening and opening and fine straightening of the cold-rolled steel material, the rough straightening pressure is 6000-9000 KN, the fine straightening pressure is 15000-18000 KN, and a straightened steel material is obtained; The straightened steel material is quenched, the heating temperature of the quenching treatment is 900±20 DEG C, the holding time is 20±3 minutes, the upper-to-lower water ratio is 3:4 during quenching, the cooling rate is 35-50 DEG C / s, and a quenched steel material is obtained.

8. The method of claim 1, wherein, At least one of the following requirements is met: The straightening and tempering treatment of the quenched steel material comprises: rough straightening and fine straightening of the quenched steel material, the rough straightening pressure is 6000-9000 KN, the fine straightening pressure is 15000-18000 KN, a straightened steel strip with a down-curling plate shape is obtained, and the unevenness is ≤6 mm / m; The straightened steel strip is tempered, the heating temperature of the tempering treatment is 600±20 DEG C, the holding time is 40±3 minutes, air cooling is performed, and a tempered steel material is obtained; The tempered steel material is subjected to secondary rough straightening and fine straightening, the rough straightening pressure is 4000-7000 KN, the fine straightening pressure is 12000-15000 KN, and an ultra-thin gauge high-strength steel is obtained.

9. An ultra-thin gauge high-strength steel, characterized by, The ultra-thin gauge high-strength steel is prepared by the method for producing ultra-thin gauge high-strength steel based on non-continuous quenching lines according to any one of claims 1-8, and consists of the following chemical components in percentage by mass: C is 0.16wt.%-0.21wt.%, Si is <0.10wt.%, Mn is 1.60wt.%-1.90wt.%, P is ≤0.015wt.%, S is ≤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 is ≤0.004wt.%, Als is 0.010wt.%-0.060wt.%, and the rest is Fe and inevitable impurities; the above chemical components satisfy the following relationship at the same time: 800≤4370[%C]+88[%Si]+53[%Mn]+22[%Mo]-30[%Cr]≤1000 (1).

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

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