Cold rolling method of strip steel and 780Mpa grade cold rolled duplex steel

Abstract

The present application discloses a cold rolling method for a steel strip and a 780Mpa grade cold-rolled dual-phase steel. The cold rolling method comprises providing a steel strip to be processed, pickling the steel strip to be processed; placing the pickled steel strip to be processed into a single-stand rolling mill, and rolling the steel strip to be processed back and forth in the single-stand rolling mill for n passes to prepare a 780Mpa grade cold-rolled dual-phase steel; wherein the reduction rate of each rolling pass is 6% to 25%, and the reduction rate of the i-th rolling pass is P i Less than the reduction rate P of the (i-1)th pass i‑1 , n and i are positive integers, 2≤i≤n. According to the cold rolling method of the embodiment of the present application, a 780 MPa grade cold-rolled dual-phase steel with a higher reduction rate and thinner thickness can be obtained by rolling.

Description

Technical Field

[0001] The present application belongs to the field of cold rolling technology, and in particular relates to a cold rolling method for strip steel and 780 MPa grade cold-rolled dual-phase steel. Background Art

[0002] 780Mpa-grade cold-rolled dual-phase steel (DP steel) boasts excellent mechanical properties, including a low yield-to-tensile ratio, good tensile strength, and high formability. It is widely used in the manufacture of automotive structural components such as anti-collision beams, reinforcement plates, bumpers, and wheels. However, 780Mpa-grade DP steel is currently typically cold-rolled using a tandem mill, with multiple mills arranged in series. The work roll diameter typically ranges from 360 to 440mm, and the rolling force is 15MN to 18MN. Due to the high rolling force, the reduction ratio is typically less than 50%. Summary of the Invention

[0003] The embodiments of the present application provide a cold rolling method for strip steel and 780 MPa grade cold-rolled dual-phase steel, which can be rolled to obtain 780 MPa grade cold-rolled dual-phase steel with a higher reduction rate and thinner thickness.

[0004] A first embodiment of the present application provides a cold rolling method for a steel strip, comprising:

[0005] Provide the steel strip to be processed and perform pickling on it;

[0006] The pickled steel strip is placed in a single-stand rolling mill, and the steel strip is rolled back and forth for n times in the single-stand rolling mill to produce 780 MPa grade cold-rolled dual-phase steel.

[0007] Among them, the reduction rate of each rolling pass is 6% to 25%, and the reduction rate of the i-th rolling pass is P i Less than the reduction rate P of the (i-1)th pass i-1 , n and i are positive integers, 2≤i≤n.

[0008] According to the implementation of the first aspect of the present application, the reduction rate satisfies the following conditions: P total =1-(1-P1)(1-P2)…(1-P n-1 )(1-P n ), where P total is the reduction ratio of 780Mpa grade cold-rolled dual-phase steel relative to the strip to be processed, P1 is the reduction ratio of the first rolling pass, 50%≤P total ≤70%, 17%≤P1≤25%.

[0009] According to any of the aforementioned embodiments of the first aspect of the present application, when a single-stand rolling mill performs the i-th pass rolling, the outlet tension T out(i) and inlet tension Tin(i) The tension difference is h i , the tension difference h of the single stand rolling mill for the (i-1)th pass (i-1) Greater than or equal to the tension difference h of the i-th rolling pass i .

[0010] According to any of the aforementioned embodiments of the first aspect of the present application, n is 5, the reduction rate P1 of the first rolling pass is 17% to 25%, and the entrance unit tension of the single-stand rolling mill is 40N / mm 2 ~65N / mm 2 , export unit tension is 150N / mm 2 ~200N / mm 2 The second pass rolling reduction rate P2 is 16% to 24%, and the entrance unit tension of the single stand rolling mill is 60N / mm 2 ~95N / mm 2 , export unit tension is 160N / mm 2 ~210N / mm 2 The third rolling reduction rate P3 is 15% to 23%, and the entrance unit tension of the single-stand rolling mill is 80N / mm 2 ~115N / mm 2 , export unit tension is 160N / mm 2 ~210N / mm 2 The fourth pass rolling reduction rate P4 is 14% to 22%, and the entrance unit tension of the single stand rolling mill is 95N / mm 2 ~130N / mm 2 , export unit tension is 170N / mm 2 ~220N / mm 2 The fifth rolling reduction rate P5 is 6% to 15%, and the entrance unit tension of the single-stand rolling mill is 80N / mm 2 ~115N / mm 2 , export unit tension is 90N / mm 2 ~145N / mm 2 .

[0011] According to any of the aforementioned embodiments of the first aspect of the present application, the rolling force F of the i-th pass of the single-stand rolling mill is i Less than or equal to the rolling force F of the (i-1)th pass of a single-stand rolling mill (i-1) .

[0012] According to any of the aforementioned embodiments of the first aspect of the present application, n is 5, the rolling force F1 of the first rolling pass of the single-stand rolling mill is 11MN~14MN, the rolling force F2 of the second rolling pass of the single-stand rolling mill is 10MN~13MN, the rolling force F3 of the third rolling pass of the single-stand rolling mill is 9MN~12MN, the rolling force F4 of the fourth rolling pass of the single-stand rolling mill is 9MN~12MN, and the rolling force F5 of the fifth rolling pass of the single-stand rolling mill is 8MN~11MN.

[0013] According to any of the aforementioned embodiments of the first aspect of the present application, the pickling tank is independently arranged with the single-stand rolling mill, the pickling tank includes a plurality of pickling sub-tanks, the strip to be processed passes through the plurality of pickling sub-tanks in sequence, the temperature of the pickling liquid in each pickling sub-tank is 75°C to 90°C, the concentration of hydrogen ions in the pickling liquid is 1.92mol / L to 5.48mol / L, and the moving speed of the strip to be processed in the pickling tank is 60-90m / min.

[0014] According to any of the aforementioned embodiments of the first aspect of the present application, the number of pickling sub-tanks is m, and the concentration of hydrogen ions in the pickling solution of the j-th pickling sub-tank is C j , C1 <C2≤…≤C m-1 <C m , m and j are positive integers, j∈{1, 2, 3…m}.

[0015] According to any of the foregoing embodiments of the first aspect of the present application, m is 5, C1 is the concentration of hydrogen ions in the pickling liquid of the first pickling sub-tank, 1.92 mol / L≤C1≤3.29 mol / L; C2 is the concentration of hydrogen ions in the pickling liquid of the second pickling sub-tank, 3.29 mol / L≤C2≤4.38 mol / L; C3 is the concentration of hydrogen ions in the pickling liquid of the third pickling sub-tank, 3.29 mol / L≤C3≤4.38 mol / L; C4 is the concentration of hydrogen ions in the pickling liquid of the fourth pickling sub-tank, 3.29 mol / L≤C4≤4.38 mol / L; C5 is the concentration of hydrogen ions in the pickling liquid of the fifth pickling sub-tank, 4.38 mol / L≤C5≤5.48 mol / L.

[0016] The second embodiment of the present application provides a 780 MPa grade cold-rolled dual-phase steel produced by the cold rolling method of any one of the first embodiment described above.

[0017] The cold rolling method of the strip steel of the embodiment of the present application provides a strip steel to be processed, pickles the strip steel to be processed, places the pickled strip steel to be processed into a single-stand rolling mill, and reciprocates the strip steel to be processed in the single-stand rolling mill for n passes, with a reduction rate of 6% to 25% for each pass, and a reduction rate P of the i-th pass. i Less than the reduction rate P of the (i-1)th pass i-1Compared with continuous rolling mills, the working rolls of single-stand rolling mills have smaller roll diameters and, under the same conditions, smaller rolling forces. Through multiple reciprocating rolling cycles, single-stand rolling mills can produce 780Mpa-grade cold-rolled duplex steel with a higher reduction rate and thinner thickness than continuous rolling mills. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions 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.

[0019] Figure 1 This is a schematic flow chart of a cold rolling method for strip steel according to an embodiment of the first aspect of the present application. DETAILED DESCRIPTION

[0020] 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 drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, not 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 merely to provide a better understanding of the present application by illustrating examples of the present application. In the drawings and the following description, at least some of the well-known structures and technologies are not shown in order to avoid unnecessary ambiguity in the present application; and, for clarity, the sizes of some structures may be exaggerated. In addition, the features, structures or characteristics described below may be combined in any suitable manner in one or more embodiments.

[0021] It should be noted that, in this document, unless otherwise specified, the meaning of "plurality" is more than two; the terms "upper", "lower", "left", "right", "inside", "outside", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific direction, be constructed and operate in a specific direction, and therefore should not be understood as limiting this application. In addition, relational terms such as first and second, etc. are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes 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 limitations, the elements defined by the sentence "including..." do not exclude the presence of other identical elements in the process, method, article or device that includes the elements.

[0022] The directional words appearing in the following description are all directions shown in the figures, and do not limit the specific structure of the embodiments of the present application. In the description of the present application, it should also be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected. It should be understood that when describing the structure of a component, when a layer or an area is referred to as being "above" or "above" another layer or another area, it can mean being directly above the other layer or another area, or that other layers or areas are included between it and the other layer or another area. Moreover, if the component is turned over, the layer or the area will be "below" or "below" the other layer or another area. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0023] Dual-phase steel (DP steel) boasts excellent mechanical properties, including a low yield-to-tensile ratio, good tensile strength, and high formability. It is widely used in the manufacture of automotive structural components such as anti-collision beams, reinforcement plates, bumpers, and wheels. 780 MPa-grade cold-rolled DP steel is particularly popular. However, 780 MPa-grade cold-rolled DP steel is currently typically produced using tandem mills, with multiple mills arranged in series. The work roll diameter typically ranges from 360 to 440 mm, and the rolling force is 15 to 18 MN. Due to the high rolling force, the reduction ratio is typically less than 50%, and the mill's high rolling speed capabilities are not fully utilized, resulting in low efficiency and hindering the mill's production capacity. In addition, since the pickling unit and the continuous rolling mill are connected in series, the pickling speed is relatively fast, generally 150-240m / min, and 780Mpa grade cold-rolled duplex steel generally requires the addition of alloy elements such as Cr and Mo, which makes the iron oxide scale more adherent, making it difficult to remove the iron oxide scale. Therefore, the surface quality after pickling is average, resulting in poor surface quality of the rolled 780Mpa grade cold-rolled duplex steel.

[0024] To solve the above problems, the embodiments of the present application provide a cold rolling method for strip steel and 780Mpa grade cold-rolled dual-phase steel, which can be rolled to obtain 780Mpa grade cold-rolled dual-phase steel with a higher reduction rate and thinner thickness. The embodiments provided in the present application will be introduced in detail in conjunction with the accompanying drawings.

[0025] Please refer to Figure 1 The first embodiment of the present application provides a cold rolling method for a steel strip, comprising:

[0026] S1. Provide the steel strip to be processed and pickle it.

[0027] S2. The pickled strip steel is placed in a single-stand rolling mill, and the strip steel is rolled back and forth for n times in the single-stand rolling mill to prepare 780 MPa grade cold-rolled dual-phase steel.

[0028] The reduction rate of each rolling pass is 6% to 25%, and the reduction rate of the i-th rolling pass is P i Less than the reduction rate P of the (i-1)th pass i-1 , n and i are positive integers, 2≤i≤n.

[0029] Duplex stainless steel is generally defined as steel composed of a ferrite and austenite phase structure, while duplex steel is defined as steel composed of a ferrite and martensite phase structure. Duplex steel is obtained by subjecting low-carbon steel or low-alloy high-strength steel to intercritical heat treatment or controlled rolling. Duplex steel is used to manufacture complex components that require cold stamping and deep drawing, and can also be used as pipeline steel, chains, cold-drawn steel wire, and prestressed steel bars. The method of this application is applied to the production of 780 MPa grade cold-rolled duplex steel.

[0030] The steel strip to be processed is hot-rolled. After hot rolling, a layer of iron oxide scale forms on the surface of the steel strip. Therefore, it needs to go through a pickling process to remove the surface oxide scale for the subsequent cold rolling process. During the pickling process, the steel strip to be processed is placed in a pickling tank and moved to complete the cleaning process.

[0031] The reduction ratio is the percentage of the reduction amount to the thickness of the steel strip before rolling. The reduction amount is the difference between the thickness of the steel strip before rolling and the thickness after rolling. In the cold rolling method provided in this application, the cold rolling process utilizes a single-stand rolling mill. Optionally, an 18-high single-stand rolling mill can be used for rolling. The working roll diameter of the 18-high single-stand mill is 140 mm to 170 mm, which is smaller than the working roll diameter of a continuous rolling mill and results in lower rolling forces. This is more conducive to achieving a large reduction ratio.

[0032] The strength of the strip is the lowest during the first rolling pass. As each pass is gradually reduced, the deformation resistance of the strip will gradually increase. Therefore, the reduction rate of the first pass is set to the maximum to reduce the difficulty of subsequent rolling passes. At the same time, as the number of rolling passes increases, the reduction rate should be gradually reduced. Multiple rolling of a single-stand rolling mill is achieved through reciprocating multiple rolling. For example, the first pass moves the strip in a first direction, then the second pass moves the strip in the opposite direction of the first direction, and the third pass rolls the strip again in the first direction, and so on, to complete the reciprocating multiple rolling.

[0033] The cold rolling method of the strip steel of the embodiment of the present application provides a strip steel to be processed, pickles the strip steel to be processed, places the pickled strip steel to be processed into a single-stand rolling mill, and reciprocates the strip steel to be processed in the single-stand rolling mill for n passes, with a reduction rate of 6% to 25% for each pass, and a reduction rate P of the i-th pass. i Less than the reduction rate P of the (i-1)th pass i-1 Compared with continuous rolling mills, the working rolls of single-stand rolling mills have smaller roll diameters and, under the same conditions, smaller rolling forces. Through multiple reciprocating rolling cycles, single-stand rolling mills can produce 780Mpa-grade cold-rolled duplex steel with a higher reduction rate and thinner thickness than continuous rolling mills.

[0034] In some optional embodiments, the reduction rate satisfies the following conditions: total =1-(1-P1)(1-P2)…(1-P n-1 )(1-P n ), where P total is the reduction ratio of 780Mpa grade cold-rolled dual-phase steel relative to the strip to be processed, P1 is the reduction ratio of the first rolling pass, 50%≤P total ≤70%, 17%≤P1≤25%. P total It is the total reduction rate, that is, the reduction rate of the final bidirectional steel relative to the strip to be processed after pickling.

[0035] In these alternative embodiments, the first rolling reduction is 17%≤P1≤25%, and the total rolling reduction is 50%≤P total ≤70%, and with a reduction ratio of 17% to 25%, the capacity of the single-stand rolling mill can be fully utilized while ensuring a large reduction ratio. A total reduction ratio of 50% to 70%, with a sufficiently large reduction ratio, enhances the deformation energy storage of the strip and increases the driving force for ferrite recrystallization. The yield strength and yield strength ratio of 780Mpa grade cold-rolled dual-phase steel are low, which is beneficial for subsequent processing.

[0036] In some optional embodiments, when a single-stand rolling mill performs the i-th pass rolling, the outlet tension T of the single-stand rolling mill is out(i) and inlet tension T in(i) The tension difference is h i , the tension difference h of the single stand rolling mill for the (i-1)th pass (i-1) Greater than or equal to the tension difference h of the i-th rolling pass i .

[0037] The entrance of a single-stand rolling mill is the port where the strip to be processed first enters the mill, and the exit of the single-stand rolling mill is the port where the strip to be processed last exits. Since the rolling of the strip to be processed by the single-stand rolling mill is reciprocating rolling, the entrance and exit of the single-stand rolling mill are relative. For example, the single-stand rolling mill includes a first port and a second port. During the first rolling pass, the strip to be processed moves from the first port to the second port. Therefore, the first port is the entrance of the single-stand rolling mill, and the second port is the exit of the single-stand rolling mill. During the second rolling pass, the strip to be processed moves from the second port to the first port. Therefore, at this time, the second port is the entrance of the single-stand rolling mill, and the first port is the exit of the single-stand rolling mill.

[0038] In these optional embodiments, as the number of rolling passes increases, the reduction rate should be gradually reduced. Accordingly, the rolling force of the single-stand rolling mill is also gradually reduced. Accordingly, the outlet tension T of the single-stand rolling mill is out(i) and inlet tension T in(i) The tension difference also decreases gradually.

[0039] In some optional embodiments, n is 5, the reduction ratio P1 of the first rolling pass is 17% to 25%, and the entrance unit tension of the single-stand rolling mill is 40N / mm 2 ~65N / mm 2 , export unit tension is 150N / mm 2 ~200N / mm 2 The second pass rolling reduction rate P2 is 16% to 24%, and the entrance unit tension of the single stand rolling mill is 60N / mm 2 ~95N / mm2 , export unit tension is 160N / mm 2 ~210N / mm 2 The third rolling reduction rate P3 is 15% to 23%, and the entrance unit tension of the single-stand rolling mill is 80N / mm 2 ~115N / mm 2 , export unit tension is 160N / mm 2 ~210N / mm 2 The fourth pass rolling reduction rate P4 is 14% to 22%, and the entrance unit tension of the single stand rolling mill is 95N / mm 2 ~130N / mm 2 , export unit tension is 170N / mm 2 ~220N / mm 2 The fifth rolling reduction rate P5 is 6% to 15%, and the entrance unit tension of the single-stand rolling mill is 80N / mm 2 ~115N / mm 2 , export unit tension is 90N / mm 2 ~145N / mm 2 .

[0040] In these optional embodiments, the steel strip undergoes five rolling passes to obtain 780 MPa grade cold-rolled dual-phase steel. The five-pass rolling process is beneficial for properly distributing the load and rolling force of the single-stand rolling mill, making rolling more stable and enabling a reduction ratio of 50% to 70%.

[0041] In some optional embodiments, the rolling force F of the i-th pass of the single-stand rolling mill is i Less than or equal to the rolling force F of the (i-1)th pass of a single-stand rolling mill (i-1) .

[0042] In these optional embodiments, as the rolling passes increase, the reduction rate of the single-stand rolling mill decreases gradually, but the deformation resistance also increases. Starting from the second pass, the rolling force of each pass is less than or equal to the rolling force of the previous pass.

[0043] For example, n is 5, the rolling force F1 of the first rolling pass of the single-stand rolling mill is 11MN~14MN, the rolling force F2 of the second rolling pass of the single-stand rolling mill is 10MN~13MN, the rolling force F3 of the third rolling pass of the single-stand rolling mill is 9MN~12MN, the rolling force F4 of the fourth rolling pass of the single-stand rolling mill is 9MN~12MN, and the rolling force F5 of the fifth rolling pass of the single-stand rolling mill is 8MN~11MN.

[0044] In some optional embodiments, the pickling tank is independently arranged with the single-stand rolling mill, and the pickling tank includes a plurality of pickling sub-tanks. The strip to be processed passes through the plurality of pickling sub-tanks in sequence. The temperature of the pickling liquid in each pickling sub-tank is 75°C to 90°C, the concentration of hydrogen ions in the pickling liquid is 1.92mol / L to 5.48mol / L, and the moving speed of the strip to be processed in the pickling tank is 60-90m / min.

[0045] The solute in the pickling solution can be HCl, H2SO4, HNO3, etc., and this application does not impose any restrictions. The concentration of hydrogen ions in the pickling solution determines the strength of the acidity of the pickling solution. The solute in the pickling solution is HCl, and the mass fraction of the solute in the pickling solution is 70g / L to 200g / L.

[0046] In these alternative embodiments, the pickling tank is independently located from the single-stand rolling mill, allowing for controlled pickling speed of the steel strip to be processed, ensuring sufficient pickling. Compared to the prior art, where the pickling tank and tandem mill are arranged in series, resulting in generally faster pickling speeds, this embodiment provides a more thorough pickling process, completely removing scale from the surface of the steel strip, thereby improving the surface quality of the resulting 780 MPa-grade cold-rolled duplex steel. Furthermore, when the pickling tank temperature is controlled between 75°C and 90°C, the hydrogen ion concentration in the pickling solution is between 1.92 mol / L and 5.48 mol / L, and the steel strip moves within the pickling tank at a speed of 60-90 m / min, the pickling effect on the steel strip is excellent.

[0047] In some optional embodiments, the number of pickling sub-tanks is m, and the concentration of hydrogen ions in the pickling solution of the jth pickling sub-tank is C j , C1 <C2≤…≤C m-1 <C m , m and j are positive integers, j∈{1, 2, 3…m}.

[0048] In these optional embodiments, the concentration of hydrogen ions in the pickling liquid of the last pickling sub-tank among the multiple pickling sub-tanks is the highest, so as to fully pickle the steel strip to be processed.

[0049] Exemplarily, the number of pickling sub-tanks is 5. C1 is the hydrogen ion concentration in the pickling solution of the first pickling sub-tank, 1.92 mol / L≤C1≤3.29 mol / L; C2 is the hydrogen ion concentration in the pickling solution of the second pickling sub-tank, 3.29 mol / L≤C2≤4.38 mol / L; C3 is the hydrogen ion concentration in the pickling solution of the third pickling sub-tank, 3.29 mol / L≤C3≤4.38 mol / L; C4 is the hydrogen ion concentration in the pickling solution of the fourth pickling sub-tank, 3.29 mol / L≤C4≤4.38 mol / L; and C5 is the hydrogen ion concentration in the pickling solution of the fifth pickling sub-tank, 4.38 mol / L≤C5≤5.48 mol / L. When the solvent of the pickling solution is HCl, the concentration of the pickling solution in the first pickling sub-tank is 70g / L~120g / L, the concentration of the pickling solution in the second pickling sub-tank is 120g / L~160g / L, the concentration of the pickling solution in the third pickling sub-tank is 120g / L~160g / L, the concentration of the pickling solution in the fourth pickling sub-tank is 120g / L~160g / L, and the concentration of the pickling solution in the fifth pickling sub-tank is 160g / L~200g / L.

[0050] In some optional embodiments, the surface roughness of the work rolls of a single-stand rolling mill is between 0.45 μm and 0.65 μm. The smaller the surface roughness of the work rolls, the smoother the surface finish. This reduces the coefficient of contact friction between the rolls and the processed strip in the contact deformation zone, facilitating lateral metal flow within the roll gap. This reduces transverse compressive stress within the processed strip at the exit of the single-stand rolling mill, thus improving diagonal waviness. However, it should be understood that the surface roughness of the work rolls should not be too small; otherwise, slippage may occur between the processed strip and the work rolls.

[0051] In some optional embodiments, the cold rolling method further comprises:

[0052] S3. Continuous annealing and tempering. Continuous annealing is a production method in which the strip passes continuously through an annealing furnace and is directly coiled without stopping. Continuous annealing eliminates work hardening and residual internal stresses, achieving microstructure and properties that meet customer processing requirements. Tempering eliminates diagonal ripples caused by rolling.

[0053] In order to further illustrate the cold rolling method provided by the present application, the following examples and comparative examples are provided.

[0054] Example 1:

[0055] During the S1 pickling process, the strip moved at a speed of 90 m / min. The solute in the pickling tank was HCl, and the temperature was 88°C. The hydrogen ion concentration of the pickling solution in the first pickling sub-tank was 3.01 mol / L, 3.84 mol / L in the second through fourth pickling sub-tanks, and 4.93 mol / L in the fifth pickling sub-tank. After pickling, no oxides remained in the strip.

[0056] In S2, the single-stand rolling mill rolls the strip to be processed in five passes. The entry thickness of the strip to be processed in the first pass is 1.8mm, the exit thickness is 1.36mm, the reduction rate is 24.4%, the unit tension at the entry is 54N / mm2, the unit tension at the exit is 175N / mm2, and the rolling force is 12.3MN; the exit thickness of the strip to be processed in the second pass is 1.04mm, the reduction rate is 23.5%, the unit tension at the entry is 84N / mm2, the unit tension at the exit is 182N / mm2, and the rolling force is 11.9MN; the exit thickness of the strip to be processed in the third pass is 0.82mm, the reduction rate is 21.2%, The unit tension at the inlet is 103 N / mm², the unit tension at the outlet is 191 N / mm², and the rolling force is 11.7 MN. The strip thickness at the fourth pass is 0.65 mm, the reduction is 20.7%, the unit tension at the inlet is 120 N / mm², the unit tension at the outlet is 211 N / mm², and the rolling force is 11.5 MN. The strip thickness at the fifth pass is 0.55 mm, the reduction is 14.1%, the unit tension at the inlet is 100 N / mm², the unit tension at the outlet is 142 N / mm², and the rolling force is 10.1 MN. The surface roughness of the work rolls of the single-stand mill is 0.6 μm.

[0057] In this embodiment, the rolling is stable, and the total reduction rate after rolling by a single-stand rolling mill is 69.4%, resulting in slight oblique ripples, which can be eliminated after leveling treatment.

[0058] Example 2:

[0059] During the S1 pickling process, the strip moved at a speed of 60 m / min. The solute in the pickling tank was HCl, and the temperature was 88°C. The hydrogen ion concentration of the pickling solution in the first pickling sub-tank was 3.15 mol / L, 4.11 mol / L in the second through fourth pickling sub-tanks, and 5.21 mol / L in the fifth pickling sub-tank. After pickling, no oxides remained in the strip.

[0060] In S2, the single-stand rolling mill rolls the strip to be processed for 5 passes. The entry thickness of the strip to be processed in the first pass is 4.3mm, the exit thickness is 3.474mm, the reduction rate is 19.2%, the unit tension at the entry is 42N / mm2, the unit tension at the exit is 179N / mm2, and the rolling force is 11.9MN; the exit thickness of the strip to be processed in the second pass is 2.944mm, the reduction rate is 15.3%, the unit tension at the entry is 71N / mm2, the unit tension at the exit is 194N / mm2, and the rolling force is 11.6MN; the exit thickness of the strip to be processed in the third pass is 2.518mm, the reduction rate is 14 0.5%, with an inlet unit tension of 95 N / mm², an outlet unit tension of 198 N / mm², and a rolling force of 10.8 MN. The fourth pass had an outlet thickness of 2.159 mm, a reduction of 14.3%, an inlet unit tension of 115 N / mm², an outlet unit tension of 209 N / mm², and a rolling force of 10.3 MN. The fifth pass had an outlet thickness of 2.0 mm, a reduction of 7.4%, an inlet unit tension of 91 N / mm², an outlet unit tension of 137 N / mm², and a rolling force of 9.3 MN. The surface roughness of the work rolls of the single-stand mill is 0.6 μm.

[0061] In this embodiment, the rolling is stable, and the total reduction rate after rolling by a single-stand rolling mill is 53.5%, resulting in slight oblique ripples, which can be eliminated after leveling treatment.

[0062] Comparative Example 1:

[0063] In S1, the strip was 3.1 mm thick and 1250 mm wide. During the pickling process, the strip traveled at a speed of 95 m / min, the pickling solution temperature was 88°C, the hydrogen ion concentration of the pickling solution in the first pickling sub-tank was 3.01 mol / L, the hydrogen ion concentration in the second through fourth pickling sub-tanks was 3.01 mol / L, and the hydrogen ion concentration in the fifth pickling sub-tank was 5.21 mol / L. The strip travel speed exceeded the upper limit, and the pickling solution concentrations in the second through fourth pickling sub-tanks were below the minimum. After pickling, residual oxides remained in the strip, requiring further pickling.

[0064] Comparative Example 2:

[0065] In S2, the single-stand rolling mill rolls the strip to be processed for 5 passes. The entry thickness of the strip to be processed in the first pass is 2.5mm, the exit thickness is 1.99mm, the reduction rate is 20.4%, the unit tension at the entry is 50N / mm2, the unit tension at the exit is 143N / mm2, and the rolling force is 12.1MN; the exit thickness of the strip to be processed in the second pass is 1.62mm, the reduction rate is 18.6%, the unit tension at the entry is 80N / mm2, the unit tension at the exit is 151N / mm2, and the rolling force is 11.8MN; the exit thickness of the strip to be processed in the third pass is 1.33mm, the reduction rate is 17.9 %, the unit tension at the entrance is 85N / mm2, the unit tension at the exit is 142N / mm2, and the rolling force is 11.1MN; the exit thickness of the strip to be processed at the 4th pass is 1.085mm, the reduction rate is 18.4%, the unit tension at the entrance is 94N / mm2, the unit tension at the exit is 143N / mm2, and the rolling force is 10.8MN; the exit thickness of the strip to be processed at the 5th pass is 1.0mm, the reduction rate is 7.8%, the unit tension at the entrance is 82N / mm2, the unit tension at the exit is 116N / mm2, and the rolling force is 9.98MN.

[0066] In this embodiment, the total reduction rate after rolling by a single-stand rolling mill is 60.0%, the reduction rate of each pass does not decrease successively, and the outlet unit tension from the first to the third pass is lower than the minimum value, after which the rear oblique ripples are serious and difficult to eliminate.

[0067] The second embodiment of the present application provides a 780 MPa grade cold-rolled dual-phase steel produced by the cold rolling method of any one of the first embodiment described above.

[0068] In some optional embodiments, the 780 MPa grade cold-rolled dual-phase steel has a thickness of 0.5 mm to 2.5 mm and a width of 900 mm to 1400 mm.

[0069] According to the embodiments of the present application as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to specific embodiments. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can make good use of the present application and the modifications based on the present application. It should be understood that the scope of protection 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 all be included in the scope of protection of the present application.

Claims

1. A cold rolling method for a steel strip, characterized in that: include: Providing a steel strip to be processed, and pickling the steel strip to be processed; The pickled steel strip is placed in a single-stand rolling mill, and the steel strip is rolled back and forth for n times in the single-stand rolling mill to produce 780 MPa grade cold-rolled dual-phase steel; Among them, the reduction rate of each rolling pass is 6% to 25%, and the reduction rate of the i-th rolling pass is P i Less than the reduction rate P of the (i-1)th pass i-1 , n and i are positive integers, 2≤i≤n, and the reduction rate satisfies the following conditions: P total =1-(1-P1)(1-P2)…(1-P n-1 )(1-P n ), where P total is the reduction ratio of the 780Mpa grade cold-rolled dual-phase steel relative to the strip steel to be processed, P1 is the reduction ratio of the first rolling pass, 50%≤P total ≤70%, 17%≤P1≤25%; When the single-stand rolling mill performs the i-th rolling, the outlet tension T out(i) and inlet tension T in(i) The tension difference is h i , the tension difference h of the single stand rolling mill for the (i-1)th pass (i-1) Greater than or equal to the tension difference h of the i-th rolling pass i ; The rolling force F of the single-stand rolling mill at the i-th pass i Less than or equal to the rolling force F of the (i-1)th pass of the single-stand rolling mill (i-1) ; The inlet of the single-stand rolling mill is the port where the strip to be processed first enters the single-stand rolling mill, and the outlet of the single-stand rolling mill is the port where the strip to be processed last exits; The single-stand rolling mill includes a first port and a second port. The strip to be processed moves from the first port to the second port during the 2j-1th pass. The first port is the inlet of the single-stand rolling mill, and the second port is the outlet of the single-stand rolling mill. j is a positive integer, and j≥1. In the 2jth pass, the steel strip to be processed is rolled along the second port toward the first port, the second port being the inlet of the single-stand rolling mill, and the first port being the outlet of the single-stand rolling mill; A pickling tank is independently provided with the single-stand rolling mill, the pickling tank comprising a plurality of pickling sub-tanks, the steel strip to be processed sequentially passing through the plurality of pickling sub-tanks, the temperature of the pickling solution in each of the pickling sub-tanks being 75° C. to 90° C., the concentration of hydrogen ions in the pickling solution being 1.92 mol / L to 5.48 mol / L, and the moving speed of the steel strip to be processed in the pickling tank being 60-90 m / min; The number of the pickling sub-tanks is m, and the concentration of hydrogen ions in the pickling solution of the j-th pickling sub-tank is C j , C1 <C2≤…≤C m-1 <C m , m and j are positive integers, j∈{1, 2, 3…m}.

2. The cold rolling method according to claim 1, characterized in that n is 5, The first rolling reduction rate P1 is 17% to 25%, and the entrance unit tension of the single-stand rolling mill is 40N / mm 2 ~65N / mm 2 , export unit tension is 150N / mm 2 ~200N / mm 2 ; The reduction rate P2 of the second rolling pass is 16% to 24%, and the entrance unit tension of the single-stand rolling mill is 60N / mm 2 ~95N / mm 2 , export unit tension is 160N / mm 2 ~210N / mm 2 ; The reduction rate P3 of the third rolling pass is 15% to 23%, and the entrance unit tension of the single-stand rolling mill is 80N / mm 2 ~115N / mm 2 , export unit tension is 160N / mm 2 ~210N / mm 2 ; The fourth rolling reduction rate P4 is 14% to 22%, and the inlet unit tension of the single-stand rolling mill is 95N / mm 2 ~130N / mm 2 , export unit tension is 170N / mm 2 ~220N / mm 2 ; The reduction ratio P5 of the fifth rolling pass is 6% to 15%, and the inlet unit tension of the single-stand rolling mill is 80N / mm 2 ~115N / mm 2 , export unit tension is 90N / mm 2 ~145N / mm 2 .

3. The cold rolling method according to claim 1, characterized in that n is 5, the rolling force F1 of the first rolling pass of the single-stand rolling mill is 11MN~14MN, the rolling force F2 of the second rolling pass of the single-stand rolling mill is 10MN~13MN, the rolling force F3 of the third rolling pass of the single-stand rolling mill is 9MN~12MN, the rolling force F4 of the fourth rolling pass of the single-stand rolling mill is 9MN~12MN, and the rolling force F5 of the fifth rolling pass of the single-stand rolling mill is 8MN~11MN.

4. The cold rolling method according to claim 1, characterized in that m is 5, C1 is the concentration of hydrogen ions in the pickling liquid of the first pickling sub-tank, 1.92 mol / L≤C1≤3.29 mol / L; C2 is the concentration of hydrogen ions in the pickling liquid of the second pickling sub-tank, 3.29 mol / L≤C2≤4.38 mol / L; C3 is the concentration of hydrogen ions in the pickling liquid of the third pickling sub-tank, 3.29 mol / L≤C3≤4.38 mol / L; C4 is the concentration of hydrogen ions in the pickling liquid of the fourth pickling sub-tank, 3.29 mol / L≤C4≤4.38 mol / L; C5 is the concentration of hydrogen ions in the pickling liquid of the fifth pickling sub-tank, 4.38 mol / L≤C5≤5.48 mol / L.

5. A 780Mpa grade cold-rolled dual-phase steel, characterized in that: The steel sheet is prepared by the cold rolling method according to any one of claims 1 to 4.

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