Low-alloy high-strength cold rolled steel and preparation method thereof

Abstract

The invention discloses low-alloy high-strength cold rolled steel and a preparation method thereof. The low-alloy high-strength cold-rolled steel comprises the following components in percentage by mass: 0.03 to 0.07 weight percent of C, less than or equal to 0.05 weight percent of Si, 0.08 to 0.2 weight percent of Mn, less than or equal to 0.02 weight percent of P, 0.02 to 0.03 weight percent of Nb, 0.02 to 0.05 weight percent of Als, less than or equal to 0.007 weight percent of N, less than or equal to 0.01 weight percent of S and the balance of Fe. And the balance of Fe and inevitable trace elements. According to the low-alloy high-strength cold-rolled steel, the design that low-carbon steel components and a trace amount of Nb alloy are added is utilized, the high-strength performance can be kept under the thin specification (0.6-1.0 mm), a common material or a thick-specification material is replaced, and the advantage of remarkably reducing the cost is achieved.

Description

Technical Field

[0001] The present application belongs to the technical field of steel smelting, and in particular relates to a low-alloy high-strength cold-rolled steel and a preparation method thereof. Background Art

[0002] With the increasing development of social production, logistics and transportation have developed rapidly. Van transportation has developed rapidly due to its many convenient advantages. However, the sharp increase in the number of commercial vehicles has put great pressure on road resources and environmental protection. In order to solve the problems of safety accidents caused by vehicle overloading and excessive emissions, the country has gradually restricted vehicle loads in recent years.

[0003] In order to increase the strength of steel used in vehicles and reduce the thickness of steel plates to make the car lighter, existing technologies mostly use new composite materials or even lightweight alloy materials to replace the original ordinary steel materials to achieve the purpose of weight reduction, resulting in soaring costs and generally lower durability than steel materials. Summary of the invention

[0004] The embodiment of the present application provides a low-alloy high-strength cold-rolled steel and a preparation method thereof. The low-alloy high-strength cold-rolled steel of the present application utilizes a low-carbon steel component plus a trace amount of Nb alloy design to maintain high-strength performance in thin specifications (0.6 to 1.0 mm) to replace ordinary materials or thick specifications materials, and has a significant cost reduction advantage.

[0005] In the first aspect, a low-alloy high-strength cold-rolled steel comprises, in terms of mass percentage, the following components: C: 0.03wt%~0.07wt%, Si: ≤0.05wt%, Mn: 0.08wt%~0.2wt%, P: ≤0.02wt%, Nb: 0.02wt%~0.03wt%, Als: 0.02wt%~0.05wt%, N: ≤0.007wt%, S≤0.01wt%; and the remainder of Fe and unavoidable trace elements.

[0006] In a first possible implementation, the trace elements include, in terms of mass percentage, As≤0.03wt%, Sn≤0.03wt%.

[0007] In combination with the above possible implementations, the metallographic structure of the low alloy high strength cold rolled steel includes ferrite and carbide; and / or, the second phase precipitated particles of the low alloy high strength cold rolled steel include one or more of niobium carbonitride compounds, niobium carbide, and niobium nitride.

[0008] In combination with the above possible implementation methods, the low alloy high strength cold rolled steel meets one or more of the following conditions (1) to (3): (1) the yield strength of the low alloy high strength cold rolled steel is ≥700 MPa;

[0009] (2) The tensile strength of the low alloy high strength cold rolled steel is ≥700 MPa; (3) The elongation of the low alloy high strength cold rolled steel is ≥5%, preferably ≥10%.

[0010] In the second aspect, a method for preparing low-alloy high-strength cold-rolled steel comprises: smelting converter steel liquid; performing LF refining on the converter steel liquid to obtain LF refined steel liquid, wherein the LF refined steel liquid contains the components of the first aspect; performing continuous casting on the LF refined steel liquid to obtain a slab; then performing hot rolling on the slab to obtain a hot-rolled steel plate; performing cold rolling on the hot-rolled steel plate to obtain a cold-rolled steel plate; and annealing the cold-rolled steel plate to obtain an annealed steel plate.

[0011] In a first possible implementation, in the step of smelting converter steel, C≤0.045wt%, P≤0.017wt%, S≤0.06% in the converter steel, the liquidus of the converter steel is 1520℃~1530℃, and the converter tapping temperature is>1600℃; and / or, in the step of smelting converter steel, P≤0.15wt%, S≤0.06wt% in the raw iron.

[0012] In combination with the above possible implementation methods, the steps of continuously casting LF refined molten steel to obtain slabs and hot-rolling the slabs to obtain hot-rolled steel plates both adopt CSP process; and / or, in the step of continuously casting LF refined molten steel, the slab pulling speed is ≥3.6m / min, the thickness of the slab is 50mm~90mm, and the slab furnace outlet temperature is 1080℃~1200℃; and / or, in the step of hot-rolling the slabs to obtain hot-rolled steel plates, the final rolling temperature is 890℃~930℃, the coiling temperature is 590℃~650℃, and preferably, the coiling temperature is 600℃~650℃; and / or, the tensile strength of the hot-rolled steel plate is ≥350MPa, the yield strength is ≥300MPa, and the elongation is ≥20%.

[0013] In combination with the above possible implementations, the hot rolled steel plate is subjected to straightening and pickling before cold rolling; and / or the total reduction ratio of the cold rolling is 60% to 75%.

[0014] In combination with the above possible implementation methods, the annealing step of the cold-rolled steel sheet adopts an incomplete recrystallization annealing process, and the incomplete recrystallization annealing process includes: heating the cold-rolled steel sheet in a bell furnace to above the recrystallization temperature, and then annealing below the Ac1 temperature to eliminate cold rolling work hardening and internal stress to obtain the required structure and performance; preferably, heating to the recrystallization temperature, a free heating method is adopted below 400°C, a segmented controlled heating rate is adopted from above 400°C to the intermediate temperature and the temperature is kept for a predetermined time, and a controlled heating method is adopted from the intermediate temperature to the hot spot temperature (i.e., annealing temperature), the heating time is 2h, and the temperature is kept at the hot spot temperature for 9h to 12h, wherein the hot spot temperature is 520°C to 580°C; water cooling is started after cooling with a heating hood for 2h, and the water cooling temperature is ≤450°C; the steel plate furnace temperature is ≤90°C; more preferably, the hot spot temperature is 530°C to 560°C.

[0015] In combination with the above possible implementations, the preparation method may further include flattening the annealed steel plate, wherein the flattening is performed using a constant rolling force method, and the rolling force is 2000KN to 4000KN.

[0016] Compared with the prior art, the present application has at least the following beneficial effects: the low-alloy high-strength cold-rolled steel of the present application is designed by adding a trace amount of Nb alloy to a low-carbon steel component, combined with a thin slab continuous casting and rolling process, pickling and cold rolling once, and a hood furnace low-temperature annealing process for heat treatment. It can maintain a yield strength of more than 700MPa in thin specifications (0.6-1.0mm) to replace ordinary materials or thick specifications. It has a significant cost reduction advantage and meets the steel needs of van compartments, container bodies, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 1 is a metallographic diagram of a low alloy high strength cold rolled steel according to an embodiment of the present application.

[0019] Figure 2 This is a physical picture of a truck compartment side panel obtained using the low-alloy high-strength cold-rolled steel of the present application.

[0020] Figure 3 This is a physical picture of a container corrugated board obtained using the low-alloy high-strength cold-rolled steel of the present application. DETAILED DESCRIPTION

[0021] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0022] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unclearly recorded range; and any lower limit can be combined with other lower limits to form an unclearly recorded range, and any upper limit can be combined with any other upper limit to form an unclearly recorded range. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unclearly recorded range.

[0023] The above-mentioned inventive content of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates an exemplary embodiment. In many places throughout the application, guidance is provided by a series of embodiments, which can be used in various combinations. In each example, the enumeration is only a representative group and should not be interpreted as exhaustive. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0024] With the increasing development of social production, logistics and transportation have developed rapidly. Van transportation has developed rapidly due to its many convenient advantages. However, the sharp increase in the number of commercial vehicles has put great pressure on road resources and environmental protection. In order to solve the problems of safety accidents caused by vehicle overloading and excessive emissions, the country has gradually restricted vehicle loads in recent years.

[0025] In order to increase the strength of steel used in vehicles and reduce the thickness of steel plates to make the car lighter, existing technologies mostly use new composite materials or even lightweight alloy materials to replace the original ordinary steel materials to achieve the purpose of weight reduction, resulting in soaring costs and generally lower durability than steel materials.

[0026] In view of the above problems, the embodiments of the present application provide a low-alloy high-strength cold-rolled steel and a preparation method thereof. The low-alloy high-strength cold-rolled steel of the present application utilizes a low-carbon steel component plus a trace amount of Nb alloy design to maintain high-strength performance in thin specifications (0.6 to 1.0 mm), thereby replacing ordinary materials or thick specifications materials, and has a significant cost reduction advantage.

[0027] In the first aspect, a low-alloy high-strength cold-rolled steel comprises, in terms of mass percentage, the following components: C: 0.03wt%~0.07wt%, Si: ≤0.05wt%, Mn: 0.08wt%~0.2wt%, P: ≤0.02wt%, Nb: 0.02wt%~0.03wt%, Als: 0.02wt%~0.05wt%, N: ≤0.007wt%, S≤0.01wt%; and the remainder of Fe and unavoidable trace elements.

[0028] The inventors found that by using a low-carbon steel component plus a trace amount of Nb alloy design, combined with a thin slab continuous casting and rolling process, pickling cold rolling once and a bell-type furnace low-temperature annealing process for heat treatment, it is possible to maintain a yield strength of more than 700MPa in thin specifications (0.6-1.0mm) to replace ordinary materials or thick specifications. The advantages have significant cost reduction advantages, such as Figure 2 and Figure 3 As shown, it can meet the steel needs of van carriages, container bodies, etc.

[0029] In some specific embodiments, the trace elements include, by weight percentage: As≤0.03wt%, Sn≤0.03wt%.

[0030] In some specific embodiments, Figure 1 As shown, the metallographic structure of the low alloy high strength cold rolled steel includes ferrite and carbide; and / or, the second phase precipitation particles of the low alloy high strength cold rolled steel include one or more of niobium carbonitride compounds (Nb(C, N)), niobium carbide (NbC), and niobium nitride (NbN).

[0031] In some specific embodiments, the low alloy high strength cold rolled steel satisfies one or more of the following conditions (1) to (3): (1) the yield strength of the low alloy high strength cold rolled steel is ≥700 MPa, for example, it can be 700 MPa, 720 MPa, 750 MPa, 780 MPa, 800 MPa, 850 MPa, or any combination range of the above values; (2) the tensile strength of the low alloy high strength cold rolled steel is ≥700 MPa, for example, it can be 700 MPa, 720 MPa, 750 MPa, 780 MPa, 800 MPa, 850 MPa, or any combination range of the above values; (3) the elongation of the low alloy high strength cold rolled steel is ≥5%, preferably ≥10%, for example, it can be 10%, 10.5%, 11%, 11.5%, 12%, 13%, 15%, or any combination range of the above values.

[0032] In the second aspect, a method for preparing low-alloy high-strength cold-rolled steel comprises: smelting converter steel liquid; performing LF refining on the converter steel liquid to obtain LF refined steel liquid, wherein the LF refined steel liquid contains the components of the first aspect; performing continuous casting on the LF refined steel liquid to obtain a slab; then performing hot rolling on the slab to obtain a hot-rolled steel plate; performing cold rolling on the hot-rolled steel plate to obtain a cold-rolled steel plate; and annealing the cold-rolled steel plate to obtain an annealed steel plate.

[0033] In some specific embodiments, in the step of smelting converter steel, C≤0.045wt%, P≤0.017wt%, S≤0.06% in the converter steel, the liquidus of the converter steel is 1520℃~1530℃, for example, it can be 1520℃, 1523℃, 1525℃, 1528℃, 1530℃, or any combination of the above values, and the converter tapping temperature is greater than 1600℃, for example, it can be 1601℃, 1610℃, 1620℃ , 1650℃, 1680℃, 1700℃, 1800℃, or any combination range of the above values; and / or, in the step of smelting converter molten steel, P≤0.15wt%, S≤0.06wt% in the raw molten iron, when S>0.06wt%, it enters the desulfurization station for desulfurization, and the outlet molten iron S≤0.03wt%, the residual elements in the outlet molten iron are required to be As≤0.02wt%, Sn≤0.03wt%, and it is not allowed to use recycled molten steel to smelt this product.

[0034] In some specific embodiments, the step of continuously casting the LF refined steel liquid to obtain a slab and the step of hot rolling the slab to obtain a hot-rolled steel plate both adopt the CSP process; and / or, in the step of continuously casting the LF refined steel liquid, the slab pulling speed is ≥3.6 m / min, for example, it can be 3.6 m / min, 3.8 m / min, 4 m / min, 4.2 m / min, 4.5 m / min, 4.8 m / min, 5 m / min, or any combination range of the above values, and the thickness of the slab is 50 mm to 90 mm, for example, It can be 50mm, 55mm, 60mm, 65mm, 70mm, 75mm, 80mm, 85mm, 90mm, or any combination range of the above values, the furnace temperature of the slab is 1080℃~1200℃, for example, it can be 1080℃, 1090℃, 1100℃, 1120℃, 1150℃, 1180℃, 1200℃, or any combination range of the above values; and / or, in the step of hot-rolling the slab to obtain the hot-rolled steel plate, the final rolling temperature is 890℃~930℃, for example, 890°C, 895°C, 900°C, 905°C, 910°C, 915°C, 920°C, 925°C, 930°C, or any combination range of the above values, the coiling temperature is 590°C to 650°C, for example, it can be 590°C, 595°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, or any combination range of the above values, preferably, the coiling temperature is 600°C to 650°C; and / or the tensile strength of the hot rolled steel plate is ≥350MPa, for example, it can be 350MPa, 380MPa, 400MPa, 420MPa, 450MPa, 500MPa, or any combination range of the above values, the yield strength ≥300MPa, for example, it can be 300MPa, 320MPa, 350MPa, 380MPa, 400MPa, 420MPa, 450MPa, 500MPa, or any combination range of the above values, the elongation ≥20%, for example, it can be 20%, 22%, 25%, 28%, 30%, 35%, or any combination range of the above values.

[0035] In some specific embodiments, the hot-rolled steel plate is subjected to tension straightening and pickling before cold rolling; and / or the total reduction ratio of cold rolling is 60% to 75%, for example, it can be 60%, 62%, 65%, 68%, 70%, 75%, or any combination range of the above values.

[0036] In some specific embodiments, the annealing step of the cold-rolled steel sheet adopts an incomplete recrystallization annealing process, and the incomplete recrystallization annealing process includes: heating the cold-rolled steel sheet in a bell furnace to above the recrystallization temperature, and then annealing below the Ac1 temperature to eliminate the cold rolling work hardening and internal stress to obtain the desired structure and performance; preferably, heating to the recrystallization temperature, a free heating method is adopted below 400°C, a segmented controlled heating rate is adopted from above 400°C to the intermediate temperature and the temperature is kept for a predetermined time, and a controlled heating method is adopted from the intermediate temperature to the hot spot temperature (i.e., the annealing temperature), and the heating time is 1h to 3h, for example, it can be 1h, 1.2h, 1.5h, 2h, 2.5h, 3h, or any combination range of the above values, and the hot spot temperature is kept for 9h to 12h, for example, it can be It is 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, or any combination range of the above numerical values, wherein the hot spot temperature is 520℃~580℃, for example, it can be 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, or any combination range of the above numerical values; water cooling starts after 2h~6h of cooling time with heating hood, for example, it can be 2h, 3h, 4h, 5h, 6h, or any combination range of the above numerical values, and the water cooling temperature is ≤450℃, for example, it can be 450℃, 440℃, 430℃, 420℃, 410℃, 400℃, 390℃, or any combination range of the above numerical values; the steel plate furnace temperature is ≤90℃; more preferably, the hot spot temperature is 530℃~560℃.

[0037] In the above specific implementation manner, the cold-rolled steel sheet undergoes incomplete recrystallization annealing to form relatively fine ferrite grains, thereby improving the poor plasticity of the material in a cold hard state. At the same time, low-temperature annealing can partially retain the deformed grains in the microstructure, so there are a large number of dislocations in the organization. Dislocation strengthening further improves the strength. Subsequent production using a flat constant rolling force mode ensures that the strip obtains good plate shape and surface quality.

[0038] In some specific embodiments, the preparation method may further include flattening the annealed steel plate, wherein the flattening is performed using a constant rolling force method, and the rolling force is 2000KN to 4000KN, for example, 2000KN, 2200KN, 2500KN, 2800KN, 3000KN, 3200KN, 3500KN, 3800KN, 4000KN, or any combination range of the above values.

[0039] In addition, the term "and / or" in this article is only a description of the association relationship between the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0040] It should be understood that in the embodiment of the present application, "B corresponding to A" means that B is associated with A, and B can be determined according to A. However, it should also be understood that determining B according to A does not mean determining B only according to A, and B can also be determined according to A and / or other information.

[0041] Example 1

[0042] A low-alloy high-strength cold-rolled steel is prepared by the following method:

[0043] Smelting converter steel, where the raw material iron water: P≤0.150wt%, S≤0.06wt%, if the iron water S>0.06wt%, then enter the desulfurization station for desulfurization, the exit S≤0.03wt%, the iron water residual elements require As≤0.02wt%, Sn≤0.03wt%, it is not allowed to use the recycled steel water to smelt this product. In the converter iron water, C≤0.045wt%, P≤0.017wt%, S≤0.06%, the liquidus of the converter steel water is 1530℃.

[0044] The above-mentioned converter steel liquid is subjected to LF refining to obtain LF refined steel liquid, which contains: C: 0.0524wt%, Si: 0.0258wt%, Mn: 0.1449wt%, P: 0.0122wt%, S: 0.0034wt%, Als: 0.0252wt%, Nb: 0.0223wt%, N: 0.0053wt%, and the remainder of iron and inevitable trace elements.

[0045] The LF refined steel liquid is CSP casted with low carbon steel protection slag to obtain slab. The LF refined steel liquid can be mixed with low carbon steel grades such as SPHC, the slab pulling speed is ≥3.6m / min, the middle package composition is C: 0.03wt%~0.07wt%, Si: ≤0.05wt%, Mn: 0.08wt%~0.20wt%, P: ≤0.02wt%, S: ≤0.01%, N: ≤0.007%, the thickness of the slab is 50mm~90mm, and the slab out of the furnace temperature is 1080℃~1200℃.

[0046] The slab obtained above is subjected to hot continuous rolling in a CSP continuous rolling mill to obtain a hot rolled steel plate, wherein the final rolling temperature is 893° C. and the coiling temperature is 592° C. Through hot rolling, controlled rolling and controlled cold rolling, the hot rolled steel plate is ensured to have a tensile strength of ≥350MPa, a yield strength of ≥300MPa, and an elongation of ≥20%.

[0047] The hot-rolled steel plate obtained above is put into the straightening machine to improve the shape of the hot-rolled raw material plate through bending and stretching deformation, and the surface oxide scale is broken to improve the subsequent pickling speed and pickling quality. Then, online continuous rapid pickling is carried out to remove impurities such as oxides, oil stains, rust, etc. on the surface of the strip steel to improve product quality.

[0048] The hot-rolled steel sheet after pickling is subjected to cold tandem rolling to obtain a cold-rolled steel sheet, wherein the cold tandem rolling is a six-roller five-stand tandem rolling with a total reduction ratio of 65.5%.

[0049] The cold-rolled steel sheet obtained above is annealed in a bell furnace to obtain an annealed steel sheet. The incomplete recrystallization annealing process is adopted to heat the steel coil in a bell furnace to a temperature above the recrystallization temperature and below the Ac1 temperature for annealing to eliminate the cold rolling work hardening and internal stress and obtain the desired structure and performance. The specific process is as follows:

[0050] The temperature below 400℃ is raised freely. The temperature above 400℃ is raised in stages and kept warm for a certain period of time. From the middle temperature to the hotspot temperature (520℃), the temperature is raised in a controlled manner for 2 hours and kept warm at the hotspot temperature for 9 to 12 hours. The cooling time with the heating cover is 2 hours. The water cooling temperature is ≤450℃. The temperature of the steel coil out of the furnace is ≤90℃.

[0051] The annealed steel plate obtained above was flattened in a constant rolling force mode with a rolling force of 3500 KN, with good export plate shape as the control principle, and finally a low-alloy high-strength cold-rolled steel plate with a thickness of 0.9 mm was obtained.

[0052] Embodiment 2-6

[0053] The low alloy high strength cold rolled steel of Examples 2-6 differs from that of Example 1 in that the components are the same but the contents are different and the preparation conditions are different. The specific component contents and preparation conditions are shown in Tables 1 and 2.

[0054] Comparative Example 1

[0055] The steel of Comparative Example 1 differs from that of Example 1 in that the steel does not contain Nb and the preparation conditions are different. The specific component contents and preparation conditions are shown in Tables 1 and 2.

[0056] Table 1 Main element components of low alloy cold rolled steels of Examples 1-6 and steel of Comparative Example 1

[0057]

[0058] Table 2 Preparation condition parameters of low alloy cold rolled steel of Examples 1-6 and steel of Comparative Example 1

[0059]

[0060]

[0061] The low alloy high strength cold rolled steel obtained in Examples 1-6 was tested by the test method in GB / T 228.1-2021, and the test results are shown in Table 3.

[0062] Table 3 Performance data of low alloy cold rolled steel of Examples 1-6 and steel of Comparative Example 1

[0063]

[0064] Compared with the low alloy cold rolled steel of comparative example 1, the performance of the low alloy high strength cold rolled steels of Examples 1-6, which meet the conditions of the present application in terms of chemical composition and production process, all meet the performance requirements of yield strength ≥700 MPa and elongation ≥5%, and the steel performance can be regulated by controlling the coiling temperature and annealing temperature. For example, when the coiling temperature and annealing temperature are lower (Example 1), the finished product performance strength is relatively high and the elongation is lower; when the annealing temperature is relatively high (Example 2), a higher elongation can be achieved while meeting the standard performance strength.

[0065] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A low alloy high strength cold rolled steel, characterized in that: Measured by mass percentage, the components of the low alloy high strength cold rolled steel include: C: 0.03wt%~0.07wt%, Si: ≤0.05wt%, Mn: 0.08wt%~0.2wt%, P: ≤0.02wt%, Nb: 0.02wt%~0.03wt%, Als: 0.02wt%~0.05wt%, N: ≤0.007wt%, S≤0.01wt%; and the remainder of Fe and inevitable trace elements.

2. The low alloy high strength cold rolled steel according to claim 1, characterized in that: In terms of mass percentage, the trace elements include: As≤0.03wt%, Sn≤0.03wt%.

3. The low alloy high strength cold rolled steel according to claim 1 or 2, characterized in that: The metallographic structure of the low-alloy high-strength cold-rolled steel includes ferrite and carbide; And / or, the second phase precipitated particles of the low alloy high strength cold rolled steel include one or more of niobium carbonitride compounds, niobium carbide, and niobium nitride.

4. The low alloy high strength cold rolled steel according to claim 1 or 2, characterized in that: The low alloy high strength cold rolled steel meets one or more of the following conditions (1) to (3): (1) The yield strength of the low alloy high strength cold rolled steel is ≥700 MPa; (2) The tensile strength of the low alloy high strength cold rolled steel is ≥700 MPa; (3) The elongation of the low alloy high strength cold rolled steel is ≥5%, preferably ≥10%.

5. A method for preparing low-alloy high-strength cold-rolled steel, characterized in that: include: Smelting converter steel; Performing LF refining on the converter molten steel to obtain LF refined molten steel, wherein the LF refined molten steel contains the components according to any one of claims 1 to 4; Continuously casting LF refined molten steel to obtain slabs; Hot-rolling the slab to obtain a hot-rolled steel plate; Performing continuous cold rolling on the hot-rolled steel sheet to obtain a cold-rolled steel sheet; The cold-rolled steel sheet is annealed to obtain an annealed steel sheet.

6. The preparation method according to claim 5, characterized in that: In the step of smelting converter steel, C≤0.045wt%, P≤0.017wt%, S≤0.06% in the converter steel, the liquidus of the converter steel is 1520°C to 1530°C, and the converter tapping temperature is greater than 1600°C; And / or, in the step of smelting converter molten steel, P≤0.15wt% and S≤0.06wt% in the raw molten iron.

7. The preparation method according to claim 5, characterized in that: The steps of continuously casting the LF refined steel liquid to obtain a slab and hot-rolling the slab to obtain a hot-rolled steel plate both adopt the CSP process; And / or, in the step of continuously casting the LF refined molten steel, the slab pulling speed is ≥3.6 m / min, the slab thickness is 50 mm to 90 mm, and the slab furnace temperature is 1080° C. to 1200° C.; And / or, in the step of hot-rolling the slab to obtain the hot-rolled steel plate, the final rolling temperature is 890°C to 930°C, the coiling temperature is 590°C to 650°C, and preferably, the coiling temperature is 600°C to 650°C; And / or, the hot-rolled steel plate has a tensile strength of ≥350 MPa, a yield strength of ≥300 MPa, and an elongation of ≥20%.

8. The preparation method according to claim 5, characterized in that: The hot rolled steel plate is subjected to straightening and pickling before cold continuous rolling; And / or, the total reduction ratio of the cold rolling is 60% to 75%.

9. The preparation method according to claim 5, characterized in that: The step of annealing the cold-rolled steel sheet adopts an incomplete recrystallization annealing process, and the incomplete recrystallization annealing process includes: heating the cold-rolled steel sheet in a bell-type furnace to a temperature above the recrystallization temperature, and then annealing below the Ac1 temperature to eliminate cold rolling work hardening and internal stress to obtain the required structure and performance; Preferably, when heated to the recrystallization temperature, a free heating method is used below 400°C, a segmented heating rate is used from 400°C to the intermediate temperature and the temperature is kept for a predetermined time, a controlled heating method is used from the intermediate temperature to the hot spot temperature, the heating time is 1h to 3h, and the temperature is kept at the hot spot temperature for 9h to 12h, wherein the hot spot temperature is 520°C to 580°C; water cooling is started after cooling with a heating hood for 2h to 6h, and the water cooling temperature is ≤450°C; the temperature of the steel plate out of the furnace is ≤90°C; More preferably, the hot spot temperature is 530°C to 560°C.

10. The preparation method according to claim 5, characterized in that: The method further comprises flattening the annealed steel plate, wherein the flattening is performed using a constant rolling force method, and the rolling force is 2000KN to 4000KN.

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