Hot-rolled high-strength steel with uniform thickness and preparation method and application thereof

Abstract

The invention discloses a hot-rolled high-strength steel with uniform thickness. The hot-rolled high-strength steel is composed of the following elements in percentage by weight: C: 0.05%-0.10%, Si: 0.10%-0.60%, Mn: 1.20%-1.80%, Cr: 0.03%-0.20%, Nb: 0.03%-0.08%, Ti: 0.02%-0.05%, B: 0.001%-0.007%, Al: 0.010%-0.070%, P: ≤0.030%, S: ≤0.010%, N: ≤0.010%, and the rest is Fe and inevitable impurities. The invention can obtain the hot-rolled high-strength steel by controlling the composition and content of each element in the continuous casting billet and by controlling the hot rolling process parameters. The hot-rolled high-strength steel has the characteristics of uniform thickness and small thickness fluctuation.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-rolled high-strength steel production, and in particular relates to hot-rolled high-strength steel with uniform thickness, and a preparation method and application thereof. Background Art

[0002] Using high-strength steel for the manufacture of automotive structural parts is an important means to solve the problems of automobile weight reduction, energy saving, safety and environmental protection. In the production process of high-strength steel, the control of hot rolling temperature is required to be high, because the fluctuation of hot rolling temperature will lead to the fluctuation of high-strength steel performance, and the fluctuation of performance will affect the subsequent rolling process. For example, after acid rolling, the thickness difference between the head and the middle of high-strength steel is easy to be large, resulting in uneven thickness. It is difficult for the subsequent cold rolling manufacturer to control the thickness when rolling the hot-rolled substrate as raw material. When preparing parts, it is easy to cause insufficient precision of the parts, and sometimes even the mold will be stuck, resulting in interruption of production and processing, which needs to be repaired before it can continue, which greatly affects the production efficiency and yield rate.

[0003] The related art adopts the method of cutting off the part that does not meet the thickness standard after acid rolling to ensure that the thickness difference of the finished product is controllable. This method is relatively costly, has a low overall yield rate, and is prone to additional defects. Summary of the invention

[0004] An object of the present invention is to provide a hot-rolled high-strength steel with uniform thickness to solve at least one aspect of the problems and defects raised in the above-mentioned background technology.

[0005] The present invention also provides a method for preparing the hot-rolled high-strength steel with uniform thickness.

[0006] The present invention also provides application of the hot-rolled high-strength steel with uniform thickness.

[0007] The first aspect of the present invention provides a hot-rolled high-strength steel with uniform thickness, which is composed of the following elements in weight fractions: C: 0.05% to 0.10%, Si: 0.10% to 0.60%, Mn: 1.20% to 1.80%, Cr: 0.03% to 0.20%, Nb: 0.03% to 0.08%, Ti: 0.02% to 0.05%, B: 0.001% to 0.007%, Al: 0.01% to 0.07%, P: ≤0.030%, S: ≤0.010%, N: ≤0.010%, and the rest is Fe and unavoidable impurities.

[0008] According to a technical solution of a hot-rolled high-strength steel with uniform thickness according to the present invention, there are at least the following beneficial effects:

[0009] The present invention can enhance and improve the uniformity of the structure of hot-rolled high-strength steel by controlling the composition and content of each element in molten steel during smelting, so that the hardness, strength, toughness and other properties of the hot-rolled high-strength steel are more uniform, and the steel can more easily achieve uniform thickness during rolling, thereby reducing thickness fluctuations.

[0010] In the present invention, the C element is one of the main strengthening elements in the steel, and its content directly affects the strength and plasticity of the steel. Too low a content affects the strength, and too high a content can sharply deteriorate the formability and welding performance of the steel; the Si element can be dissolved in ferrite and austenite to improve the hardness and strength of the steel. Too high a Si element content can coarsen the ferrite grains, which may lead to uneven organization and make the thickness of the steel difficult to control; the Mn element can be dissolved with the Fe element to improve the strength of the steel, but too high a content can affect the plasticity and ultimately affect the control of the thickness of the steel; the Cr element can increase the hardenability and improve the strength and hardness of the steel in the rolled state; the Nb element in steel can improve the uniformity of the organization of hot-rolled high-strength steel, has the effect of refining the grains, and thus makes the cold-rolled high-strength strength more uniform, and is not prone to uneven thickness during the rolling process The Ti element has a good effect of fixing carbon. Titanium carbide has strong binding force and is stable. It also has the effect of preventing grain growth, which can make the steel structure uniform, but too much content will affect the hardenability; the B element can improve the hardenability of steel, and can make the entire cross-section of the steel part obtain uniform and consistent mechanical properties to reduce deformation and cracking. At the same time, uniform mechanical properties can reduce the thickness fluctuation of hot-rolled high-strength steel. Too high content will cause the steel to become brittle and affect the performance; the Al element has the effect of controlling the grain size in the steel, which can make the grain size in the structure uniform, and thus can fundamentally solve the problem of uneven thickness of hot-rolled high-strength steel, but too high content will make the toughness of hot-rolled high-strength steel lower at high temperature, causing subsequent processing difficulties; P element, S element and N element are harmful elements in steel and should be avoided as much as possible.

[0011] In some specific embodiments of the present invention, the Nb element content is controlled at 0.04% to 0.07%.

[0012] In the present invention, a large amount of Nb element will precipitate during the hot rolling process, which plays a role in refining the grains and making the hot-rolled high-strength steel structure more uniform. If the Nb element content is too low, the effect of refining the grains is not great and the uniformity of the structure of the hot-rolled high-strength steel cannot be improved. If the Nb element content is too high, it will cause abnormal fluctuations in the yield strength of the hot-rolled high-strength steel, thereby affecting the performance stability and uniformity and causing thickness fluctuations.

[0013] The second aspect of the present invention provides a method for preparing the above-mentioned hot-rolled high-strength steel, comprising the following steps: heating the continuous casting billet, first dephosphorization, rough rolling, second dephosphorization, finish rolling and coiling;

[0014] The heating consists of a first heating section, a second heating section and a soaking section.

[0015] According to a technical solution of a method for preparing hot-rolled high-strength steel with uniform thickness of the present invention, at least the following beneficial effects are achieved:

[0016] The present invention improves the quality problem of large fluctuation in thickness difference of hot-rolled high-strength steel plates by controlling hot rolling process parameters, improves the qualified rate of finished product thickness, and enables the continuous casting billet to reach a suitable rolling temperature and temperature difference of the end surface by different heating temperatures of the continuous casting billet, thereby ensuring the uniformity of the thickness of the hot-rolled high-strength steel.

[0017] The present invention removes the iron oxide scale on the surface of the hot-rolled high-strength steel plate through two dephosphorization processes, thereby avoiding the occurrence of large-area pressed iron oxide scale on the steel surface, which ultimately causes uneven thickness of the strip.

[0018] In some specific embodiments of the present invention, the temperature of the first heating section is 1100°C to 1220°C.

[0019] In some specific embodiments of the present invention, the temperature of the first heating section is 1160°C to 1220°C.

[0020] In some specific embodiments of the present invention, the temperature of the second heating section is 1160°C to 1240°C.

[0021] In some specific embodiments of the present invention, the temperature of the second heating section is 1200°C to 1240°C.

[0022] In some specific embodiments of the present invention, the temperature of the soaking section is 1160°C to 1220°C.

[0023] In some specific embodiments of the present invention, the temperature of the soaking section is 1200°C to 1220°C.

[0024] If the temperature of the soaking section in the present invention is too low, it will be difficult to fully soak the ingot, resulting in the subsequent rolling process being difficult to continue due to excessive deformation resistance. If the temperature of the soaking section is too high, it will cause serious oxidation on the steel surface and affect the surface quality of the strip.

[0025] In some specific embodiments of the present invention, the first dephosphorization pressure is 19 MPa to 24 MPa.

[0026] In some specific embodiments of the present invention, the first dephosphorization pressure is 21 MPa to 24 MPa.

[0027] If the dephosphorization pressure of the present invention is too small, the iron oxide scale cannot be effectively removed, thus affecting the quality of the steel strip; if the pressure is too large, defects are likely to occur in the steel strip, thus ultimately affecting the quality.

[0028] In some specific embodiments of the present invention, the pressure of the second dephosphorization is 19 MPa to 24 MPa.

[0029] In some specific embodiments of the present invention, the pressure of the second dephosphorization is 21 MPa to 23 MPa.

[0030] In some specific embodiments of the present invention, the coiling temperature is 460°C to 560°C.

[0031] A third aspect of the present invention provides the use of the hot-rolled high-strength steel in the preparation of automotive structural parts.

[0032] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0033] The present invention can obtain hot-rolled high-strength steel with uniform thickness and small thickness fluctuation range by controlling the composition and content of each element in the continuous casting billet and controlling the hot rolling process parameters. The present invention can effectively improve the thickness fluctuation of hot-rolled high-strength steel, improve the yield rate of hot-rolled high-strength steel coils, reduce the rework rate and cutting loss, and the preparation process is simple and reliable by reasonably optimizing the continuous casting billet heating process and reasonably selecting rough rolling, finishing rolling and coiling process parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0035] Figure 1 This is a thickness fluctuation diagram of the hot-rolled high-strength steel coil obtained in Example 1 of the present invention.

[0036] Figure 2 This is a thickness fluctuation diagram of the hot-rolled high-strength steel coil obtained in Example 2 of the present invention.

[0037] Figure 3 This is a thickness fluctuation diagram of the hot-rolled high-strength steel coil obtained in Comparative Example 1 of the present invention.

[0038] Figure 4 This is a thickness fluctuation diagram of the hot-rolled high-strength steel coil obtained in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0040] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0041] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0042] Specific embodiments of the present invention are described in detail below.

[0043] Example 1

[0044] This embodiment is a hot-rolled high-strength steel with uniform thickness, composed of the following elements in percentage by weight:

[0045] C: 0.08%, Si: 0.40%, Mn: 1.50%, Cr: 0.12%, Nb: 0.05%, Ti: 0.03%, B: 0.005%, Al: 0.04%, P: 0.01%, S: 0.004%, N: ≤ 0.002%, and the rest are Fe and unavoidable impurities.

[0046] The method for preparing hot-rolled high-strength steel with uniform thickness in this embodiment comprises the following steps:

[0047] The molten steel obtained by smelting the above components is continuously cast into a casting billet, and the obtained continuous casting billet is subjected to a heating process, with a temperature of 1190°C in the first heating section and a temperature of 1200°C in the second heating section, and then enters the soaking section, with a soaking temperature of 1220°C. The entire heating process takes 35 minutes, and then the first dephosphorization is carried out, with a dephosphorization pressure of 22Mpa, and 7 rough rolling passes after dephosphorization, and then the second dephosphorization is carried out, with a dephosphorization pressure of 22Mpa, and a temperature of 1100°C after dephosphorization, and 7 finishing mill rolling is carried out again, with a temperature of 900°C after rolling, and finally coiling is carried out, and ultra-fast cooling 3 headers are used during coiling, and the interval cooling mode is used for cooling in the first half of coiling, and the coiling temperature is 500°C, so as to obtain hot-rolled high-strength steel with uniform thickness. The thickness of the hot-rolled high-strength steel is measured to fluctuate within the range of 1.98mm to 2.04mm.

[0048] The thickness of the hot-rolled high-strength steel coil was measured. Figure 1 shown.

[0049] Example 2

[0050] This embodiment is a hot-rolled high-strength steel with uniform thickness, composed of the following elements in percentage by weight:

[0051] C: 0.06%, Si: 0.50%, Mn: 1.50%, Cr: 0.12%, Nb: 0.06%, Ti: 0.04%, B: 0.005%, Al: 0.04%, P: 0.02%, S: 0.007%, N: ≤ 0.003%, and the rest are Fe and unavoidable impurities.

[0052] The method for preparing hot-rolled high-strength steel with uniform thickness in this embodiment comprises the following steps:

[0053] The molten steel obtained by smelting the above components is continuously cast into a casting billet, and the obtained continuous casting billet is subjected to a heating process, with a temperature of 1180°C in the first heating section and a temperature of 1210°C in the second heating section, and then enters the soaking section, with a soaking temperature of 1220°C. The entire heating process takes 35 minutes, and then the first dephosphorization is carried out, with a dephosphorization pressure of 22Mpa, and 7 rough rolling passes after dephosphorization, and then the second dephosphorization is carried out, with a dephosphorization pressure of 22Mpa, and a temperature of 1120°C after dephosphorization, and 7 finishing mill rolling is carried out again, with a temperature of 910°C after rolling, and finally coiling is carried out, and ultra-fast cooling 3 headers are used during coiling, and the interval cooling mode is used for cooling in the first half of coiling, and the coiling temperature is 500°C, to obtain hot-rolled high-strength steel with uniform thickness. The thickness of the hot-rolled high-strength steel is measured to fluctuate within the range of 1.96mm to 2.03mm.

[0054] The thickness of the hot-rolled high-strength steel coil was measured. Figure 2 shown.

[0055] Comparative Example 1

[0056] This comparative example is a hot rolled high strength steel composed of the following elements in percentage by weight:

[0057] C: 0.08%, Si: 0.40%, Mn: 1.50%, Cr: 0.12%, Nb: 0.05%, Ti: 0.03%, B: 0.005%, Al: 0.04%, P: 0.01%, S: 0.004%, N: ≤ 0.002%, and the rest are Fe and unavoidable impurities.

[0058] The method for preparing hot-rolled high-strength steel in this embodiment comprises the following steps:

[0059] The molten steel obtained by smelting the above components is continuously cast into a casting billet, and the obtained continuous casting billet is subjected to a heating process, with a temperature of 1040°C in the first heating section and a temperature of 1150°C in the second heating section, and then enters the soaking section, with a soaking temperature of 1100°C. The entire heating process takes 40 minutes, and then the first dephosphorization is carried out, with a dephosphorization pressure of 25Mpa, and 7 rough rolling passes after dephosphorization, and then the second dephosphorization is carried out, with a dephosphorization pressure of 25Mpa, and a temperature of 1100°C after dephosphorization, and 7 finishing mill rolling is carried out again, with a temperature of 870°C after rolling, and finally coiling is carried out, and ultra-fast cooling 3 headers are used during coiling, and the interval cooling mode is used for cooling in the first half of coiling, and the coiling temperature is 450°C, to obtain hot-rolled high-strength steel. The thickness of the hot-rolled high-strength steel is measured to fluctuate within the range of 1.76mm to 2.11mm.

[0060] The thickness of the hot-rolled high-strength steel coil was measured. Figure 3 shown.

[0061] Comparative Example 2

[0062] This comparative example is a hot rolled high strength steel composed of the following elements in percentage by weight:

[0063] C: 0.08%, Si: 0.60%, Mn: 1.10%, Cr: 0.2%, Nb: 0.02%, Ti: 0.04%, B: 0.005%, Al: 0.04%, P: 0.03%, S: 0.007%, N: ≤ 0.01%, and the rest are Fe and unavoidable impurities.

[0064] The method for preparing hot-rolled high-strength steel in this embodiment comprises the following steps:

[0065] The molten steel obtained by smelting the above components is continuously cast into a casting billet, and the obtained continuous casting billet is subjected to a heating process, with a temperature of 1190°C in the first heating section and a temperature of 1200°C in the second heating section, and then enters the soaking section, with a soaking temperature of 1220°C. The entire heating process takes 35 minutes, and then the first dephosphorization is carried out, with a dephosphorization pressure of 22Mpa, and 7 rough rolling passes after dephosphorization, and then the second dephosphorization is carried out, with a dephosphorization pressure of 22Mpa, and a temperature of 1100°C after dephosphorization, and 7 finishing mill rolling is carried out again, with a temperature of 900°C after rolling, and finally coiling is carried out, and ultra-fast cooling 3 headers are used during coiling, and the interval cooling mode is used for cooling in the first half of coiling, and the coiling temperature is 500°C, so as to obtain hot-rolled high-strength steel with uniform thickness. The thickness of the hot-rolled high-strength steel is measured to fluctuate within the range of 1.43mm to 1.70mm.

[0066] The thickness of the hot-rolled high-strength steel coil was measured. Figure 4 shown.

[0067] The difference between Comparative Example 1 and Example 1 is that the preparation method of hot-rolled high-strength steel in Comparative Example 1 reduces the heating process, increases the dephosphorization pressure and reduces the coiling temperature. Figure 1 and Figure 3 It can be seen that the thickness of the hot-rolled high-strength steel obtained in Comparative Example 1 ranges from 1.76 mm to 2.11 mm, with a large fluctuation range. Under the same element composition, changing the preparation process of the hot-rolled high-strength steel has a greater impact on its thickness fluctuation. The main reason may be that some elements in the hot-rolled high-strength steel are not dissolved or precipitated under low heating temperature, affecting the performance uniformity of the hot-rolled high-strength steel, which is easy to cause defects after rolling, and further causes large fluctuations in the thickness of the hot-rolled high-strength steel.

[0068] The difference between Comparative Example 2 and Example 1 is that the composition elements of the hot-rolled high-strength steel in Comparative Example 2 are different. Under the same preparation method, the hot-rolled high-strength steels prepared with different chemical element compositions have greatly different organizations, which in turn affects the performance of the hot-rolled high-strength steel. Figure 1 and Figure 4 It can be seen that Comparative Example 2 reduces the content of Nb element, so that the thickness range of the hot-rolled high-strength steel prepared in Comparative Example 2 is 1.43 mm to 1.70 mm, with a large fluctuation range. The too low content of Nb element has little effect on the grain refinement of the hot-rolled high-strength steel organization, and cannot play a role in improving the uniformity of the organization of the hot-rolled high-strength steel, which leads to large thickness fluctuations.

[0069] In summary, the present invention can obtain hot-rolled high-strength steel with uniform thickness and small thickness fluctuation range by controlling the composition and content of each element in the continuous casting billet and controlling the hot rolling process parameters. The present invention can effectively improve the thickness fluctuation of hot-rolled high-strength steel, improve the yield rate of hot-rolled high-strength steel coils, and reduce the rework rate and cutting loss by reasonably optimizing the continuous casting billet heating process and reasonably selecting the rough rolling, finishing rolling and coiling process parameters, and the preparation process is simple and reliable.

[0070] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A hot-rolled high-strength steel with uniform thickness, characterized in that: Composed of the following elements in weight percentage: C: 0.05%~0.10%, Si: 0.10%~0.60%, Mn: 1.20%~ 1.80%, Cr: 0.03%~0.20%, Nb: 0.04%~0.08%, Ti: 0.02%~0.05%, B: 0.001%~0.007%, Al: 0.010%~0.070%, P: ≤0.030%, S: ≤0.010%, N: ≤0.010%, the rest is Fe and unavoidable impurities; When preparing hot-rolled high-strength steel, the continuous casting billet needs to be heated, and the heating consists of a first heating section, a second heating section and a soaking section; the temperature of the first heating section is 1100℃~1220℃; the temperature of the second heating section is 1160℃~1240℃; the temperature of the soaking section is 1160℃~1220℃.

2. The hot-rolled high-strength steel with uniform thickness according to claim 1, characterized in that: The Nb element content is controlled at 0.04% to 0.07%.

3. A method for preparing hot-rolled high-strength steel with uniform thickness as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: The continuous casting slab is subjected to heating, first descaling, rough rolling, second descaling, finish rolling and coiling; the heating comprises a first heating section, a second heating section and a soaking section.

4. The method for preparing hot-rolled high-strength steel with uniform thickness according to claim 3, characterized in that: The pressure of the first descaling is 19MPa~24MPa.

5. The method for preparing hot-rolled high-strength steel with uniform thickness according to claim 3, characterized in that: The pressure of the second descaling is 19MPa~24MPa.

6. The method for preparing hot-rolled high-strength steel with uniform thickness according to claim 3, characterized in that: The coiling temperature is 460°C to 560°C.

7. Use of the hot-rolled high-strength steel with uniform thickness as claimed in any one of claims 1 to 2 in the preparation of automobile structural parts.

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