Hot-rolled pickled plate and preparation method thereof

Abstract

This application relates to the technical field of steel production, and more particularly to a hot-rolled pickled steel plate and its preparation method. The chemical composition of the hot-rolled pickled steel plate includes: C, Si, Mn, Cr, Ti, Nb, B, Cu, and N; wherein the Nb content is 0.02-0.05% by weight, and the Cu content is 0.02-0.05% by weight. This application addresses the technical problem of poor hydrogen embrittlement resistance of existing hot-rolled pickled steel plates.

Description

Technical Field

[0001] The present application relates to the technical field of steel preparation, and in particular to a hot-rolled pickled plate and a preparation method thereof. Background Art

[0002] Automotive parts produced using hot stamping technology, due to their inherently high strength, can be thinned while still meeting performance requirements, ultimately achieving the goal of reducing vehicle weight. The use of high-strength steel is one of the primary solutions for promoting lightweight vehicles, and has therefore received significant attention in recent years from the manufacturing industry, particularly the automotive industry. 22MnB5 hot-rolled pickled steel, which undergoes heat treatment to form martensite, is used in door impact bars. This steel grade requires not only a certain degree of rigidity in the event of a side impact, but also the ability to absorb the impact energy of the collision, preventing the impact bar from breaking, which reduces crashworthiness, and preventing personal injury from sharp corners.

[0003] Currently, various components using ultra-high-strength steel pipes are susceptible to hydrogen embrittlement due to corrosion reactions in the atmospheric environment. This can lead to sudden and delayed failure during use. Metals of varying strengths respond to hydrogen embrittlement to varying degrees: it is less pronounced in medium- and low-strength ferritic steels, but is quite severe in high-strength martensitic steels, especially high-strength hot-formed steels. This phenomenon demonstrates a strong correlation between hydrogen embrittlement and the strength and microstructure of the metal. Summary of the Invention

[0004] The present application provides a hot-rolled pickled plate and a preparation method thereof, in order to solve the technical problem that the existing hot-rolled pickled plate has poor hydrogen embrittlement resistance.

[0005] In a first aspect, the present application provides a hot-rolled pickled plate, the chemical composition of which comprises:

[0006] C, Si, Mn, Cr, Ti, Nb, B, Cu and N; among them,

[0007] The content of Nb is 0.02-0.05 wt %, and the content of Cu is 0.02-0.05 wt %.

[0008] Optionally, in the chemical composition of the hot-rolled pickled plate, the C content is 0.22-0.25 weight%, the Si content is 0.25-0.3 weight%, the Mn content is 1.25-1.35 weight%, the Cr content is 0.2-0.25 weight%; the Ti content is 0.02-0.04 weight%; the B content is 0.002-0.003 weight%, and the N content is ≤50ppm.

[0009] In a second aspect, the present application provides a method for preparing a hot-rolled pickled plate, for preparing the hot-rolled pickled plate according to any embodiment of the first aspect, the method comprising:

[0010] Continuously casting the molten steel and controlling the process parameters of the continuous casting to obtain a cast billet;

[0011] The ingot is heated so that the heated ingot has a target temperature and the chemical composition of the surface iron oxide scale of the ingot has a target FeO content; wherein the heating includes: controlling the heating rate in stages and controlling the holding time of the soaking section;

[0012] The heated ingot is rolled in stages to obtain a hot-rolled plate;

[0013] Under a set cooling rate condition, laminar cooling is performed on the hot-rolled plate, and then coiling is performed while controlling the coiling temperature to obtain a hot-rolled coil;

[0014] The hot-rolled coil is immersed in water for cooling and then pickled to obtain a hot-rolled pickled plate.

[0015] Optionally, the process parameters of the continuous casting include: a billet drawing rate of 1.5-1.7 m / min, a straightening temperature of the straightening machine of

[0016] ≥950℃, electromagnetic stirring current is 120-160A.

[0017] Optionally, the target temperature is 1200-1230° C., and the target FeO content is ≥90 wt %.

[0018] Optionally, controlling the heating rate and the holding time of the soaking section in stages includes:

[0019] If the heating temperature is <1050°C, the heating rate is 5-10°C / min;

[0020] If the heating temperature is ≥1050°C, the heating rate is 8-12°C / min;

[0021] The holding time of the soaking section is ≤30 min.

[0022] Optionally, the heated ingot is rolled in stages to obtain a hot-rolled plate, comprising:

[0023] The heated ingot is subjected to rough rolling; wherein the R2 rough rolling mill adopts 1, 3, 4, and 5 passes for descaling;

[0024] The rough-rolled ingot is subjected to finish rolling to obtain a hot-rolled plate; wherein the outlet temperature of the finish rolling is 1030-1050° C., and double-pass descaling is started.

[0025] Optionally, the set cooling rate is 70-100°C / s, and the coiling temperature is 550-600°C.

[0026] Optionally, the hot-rolled coil is immersed in water and then pickled to obtain a hot-rolled pickled plate, comprising:

[0027] Under the condition of a set time, the hot-rolled coil is immersed in water for cooling; wherein the initial immersion temperature of the outer ring of the hot-rolled coil is controlled;

[0028] The hot-rolled coil after soaking is pickled, and the pickling rate is controlled to obtain a hot-rolled pickled plate.

[0029] Optionally, the setting time is 200-300 min, the initial immersion temperature of the outer ring of the hot-rolled coil is 350-400° C., and the pickling rate is 100-120 m / min.

[0030] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0031] The hot-rolled pickled plate provided in the embodiment of the present application has a larger hydrogen overvoltage, suppressed cathode reaction, reduced hydrogen intrusion, and improved delayed failure characteristics by adding Cu; the addition of Nb forms highly dispersed nano-scale NbC particles that act as effective hydrogen traps, playing a decisive role in resisting hydrogen embrittlement. At the same time, Nb alloying technology can significantly reduce the original austenite grain size and thus significantly increase the number of original austenite grain boundaries, reducing the hydrogen concentration on the unit grain boundary, thereby reducing the possibility of hydrogen atoms enriching to the critical fracture concentration. NbC, as a Covarigated gas cluster, can increase the slip activation energy, inhibit dislocation slip, and further reduce the occurrence of hydrogen embrittlement. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] Figure 1 A schematic flow chart of a method for preparing a hot-rolled pickled plate provided in an embodiment of the present application;

[0035] Figure 2This is a microscopic image of nano-precipitates formed after hot stamping after the addition of Nb element provided in the embodiment of the present application;

[0036] Figure 3 This is an image of the central segregation of C-Mn elements in the steel provided in the embodiment of the present application;

[0037] Figure 4 A microscopic image of the diffusion of Cu element in the primary iron sheet provided in the embodiment of the present application;

[0038] Figure 5 A microscopic image of the distribution of Cu elements in the iron sheet (white bright spots) provided in the embodiment of the present application;

[0039] Figure 6 A microscopic image of intergranular oxidation caused by high-temperature coiling provided in an embodiment of the present application;

[0040] Figure 7 This is a picture of hydrogen embrittlement evaluation using the bending method provided in the examples of this application. DETAILED DESCRIPTION

[0041] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0042] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0043] In this application, unless otherwise specified, the directional words used, such as "upper" and "lower", refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the present application specification, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" refers to one or more, and "plurality" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple.

[0044] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0045] In a first aspect, the present application provides a hot-rolled pickled plate, the chemical composition of which comprises:

[0046] C, Si, Mn, Cr, Ti, Nb, B, Cu and N; among them,

[0047] The content of Nb is 0.02-0.05 wt %, and the content of Cu is 0.02-0.05 wt %.

[0048] In the embodiments of the present application, the positive effect of controlling the Nb content to 0.02-0.05 wt% is: the formation of highly dispersed nano-scale NbC particles as effective hydrogen traps, which plays a decisive role in resisting hydrogen embrittlement. In terms of hydrogen capture capacity, NbC>TiC>VC. At the same time, Nb alloying technology can significantly reduce the original austenite grain size and thus significantly increase the number of original austenite grain boundaries, reduce the hydrogen concentration on the unit grain boundary, and thus reduce the possibility of hydrogen atoms enriched to the critical fracture concentration. NbC as a Coriolis gas cluster can increase the slip activation energy and inhibit dislocation slip, which can further reduce the occurrence of hydrogen embrittlement. Figure 2If the Nb content is too high, it will increase the production cost of the product to a certain extent. On the other hand, if too much Nb is added, it will easily cause large Nb to precipitate, reducing the hydrogen trapping ability. If the Nb content is too low, it will make it impossible to effectively achieve the effects of grain refinement and precipitation strengthening. Specifically, the Nb content can be 0.02% by weight, 0.03% by weight, 0.04% by weight, 0.05% by weight, etc.

[0049] Controlling the Cu content to 0.02-0.05% by weight has the following positive effects: The addition of Cu increases hydrogen overvoltage, suppresses cathodic reactions, reduces hydrogen intrusion, and improves delayed failure characteristics. If the Cu content is too high, hot brittle defects may occur on the hot-rolled sheet surface due to the liquefaction and precipitation of large amounts of Cu. If the Cu content is too low, it may not effectively inhibit hydrogen atom penetration. Specifically, the Cu content can be 0.02%, 0.03%, 0.04%, 0.05%, etc.

[0050] In some embodiments, in the chemical composition of the hot-rolled pickled plate, the C content is 0.22-0.25 weight%, the Si content is 0.25-0.3 weight%, the Mn content is 1.25-1.35 weight%, the Cr content is 0.2-0.25 weight%; the Ti content is 0.02-0.04 weight%; the B content is 0.002-0.003 weight%, and the N content is ≤50ppm.

[0051] The positive effect of controlling the C content to 0.22-0.25 wt% is to ensure the mechanical properties of the product and the strength grade of the product. Specifically, the C content can be 0.22 wt%, 0.23 wt%, 0.24 wt%, 0.25 wt%, etc.

[0052] The positive effect of controlling the Si content to 0.25-0.3 wt% is that the addition of Si reduces the amount of Cu-rich phase at the steel / iron sheet interface, which helps reduce surface hot brittleness sensitivity. At the same time, internal oxidation of Si helps reduce the penetration of Cu-rich phase. Specifically, the Si content can be 0.25 wt%, 0.26 wt%, 0.27 wt%, 0.28 wt%, 0.29 wt%, 0.3 wt%, etc.

[0053] The positive effect of controlling the Mn content to 1.25-1.35 wt% is to ensure the mechanical properties and strength grade of the product. Specifically, the Mn content can be 1.25 wt%, 1.30 wt%, 1.35 wt%, etc.

[0054] Controlling the Cr content to 0.2-0.25% by weight has the positive effects of improving the hardenability of the steel, promoting martensitic transformation during heat treatment, and ensuring the product strength of the steel. Specifically, the Cr content can be 0.021% by weight, 0.22% by weight, 0.23% by weight, 0.24% by weight, 0.25% by weight, etc.

[0055] Controlling the Ti content to 0.02-0.04% by weight and the N content to 50 ppm or less has the following positive effects: Titanium binds nitrogen more strongly than boron, and most free nitrogen is fixed by titanium, preferentially forming fine titanium nitride (nanometer-sized). This reduces the precipitation of coarse boron nitride (micrometer-sized) along grain boundaries, weakening the effect of boron nitride on grain boundaries, thereby improving the high-temperature plasticity of the continuous casting billet and making it less likely to crack during the straightening section of the casting. Specifically, the Ti content can be 0.02%, 0.03%, 0.04%, etc., and the N content can be 50 ppm, 49 ppm, 48 ppm, 47 ppm, etc.

[0056] The positive effects of controlling the B content to 0.002-0.003% by weight include: improving the hardenability of the steel, promoting martensitic transformation during heat treatment, and ensuring the product strength of the steel. Specifically, the B content can be 0.002%, 0.0025%, 0.003%, etc.

[0057] In the second aspect, the present application provides a method for preparing a hot-rolled pickled plate, see Figure 1 , for preparing the hot-rolled pickled plate according to any one of the embodiments of the first aspect, the method comprising:

[0058] S1, continuously casting molten steel and controlling process parameters of the continuous casting to obtain a cast billet;

[0059] S2. Heating the ingot so that the heated ingot reaches a target temperature and the chemical composition of the surface iron oxide scale of the ingot has a target FeO content; wherein the heating includes controlling the heating rate in stages and controlling the holding time of the soaking section;

[0060] S3, rolling the heated ingot in stages to obtain a hot-rolled plate;

[0061] S4. Under a set cooling rate, laminar cooling is performed on the hot-rolled plate, and then coiling is performed while controlling the coiling temperature to obtain a hot-rolled coil;

[0062] S5. Soaking the hot-rolled coil in water and then pickling it to obtain a hot-rolled pickled plate.

[0063] In the embodiments of the present application, the hydrogen embrittlement sensitivity is improved by adding Nb-Cu composite additions in the alloy design. At the same time, based on the characteristics of alloy element addition, the continuous casting-hot rolling-pickling optimization process route is designed to improve the product yield.

[0064] In some embodiments, the process parameters of the continuous casting include: a casting rate of 1.5-1.7 m / min, a straightening temperature of a straightening machine of ≥950° C., and an electromagnetic stirring current of 120-160A.

[0065] The effect of B addition on transverse cracking of slab corners was investigated. While Ti addition stabilizes N, high-temperature thermoplasticity testing of this steel revealed a decreasing trend in plasticity within the 750-850°C range, dropping below 70%. This temperature range was avoided during the straightening stage of the continuous casting process. To prevent the formation of large amounts of precipitates that embrittle grain boundaries, a weak cooling mode was used during the continuous casting process.

[0066] Controlling the drawing rate to 1.5-1.7 m / min and the straightening temperature of the drawing and leveling machine to ≥950°C has the positive effect of preventing the formation of large amounts of precipitates that embrittle grain boundaries. Specifically, the drawing rate can be 1.5 m / min, 1.6 m / min, 1.7 m / min, etc., and the straightening temperature can be 952°C, 954°C, 956°C, etc.

[0067] The positive effect of controlling the electromagnetic stirring current to 120-160A is to suppress the central segregation of C\Mn elements during continuous casting, such as Figure 3 Specifically, the electromagnetic stirring current can be 120A, 130A, 140A, 150A, 160A, etc.

[0068] In some embodiments, the target temperature is 1200-1230° C., and the target FeO content is ≥ 90 wt %.

[0069] The addition of Cu element can suppress the sensitivity of hydrogen embrittlement, but when Cu steel contains Cu element, it will cause hot brittleness, resulting in the presence of dispersed small warping on the surface of hot rolled strip. The solubility of Cu in FeO phase is very low, and the melting point of metallic Cu is 1083℃, so liquid Cu can easily migrate through FeO grain boundaries and matrix grain boundaries. Figure 4 As shown in Figure 2, research has shown that liquid Cu can migrate through FeO grain boundaries under heating conditions and then dissolve in Fe₃O₄. Increasing the FeO content in the primary iron scale helps reduce Cu enrichment at the interface. A weakly reducing atmosphere is used during the hot rolling heating process, with a λ value controlled between 0.8 and 1.0, where λ is the excess air coefficient.

[0070] The "target temperature" indicates the tapping temperature, and the "target FeO content" indicates the FeO content in the chemical composition of the surface oxide scale of the cast ingot. Controlling the tapping temperature to 1200-1230°C has the positive effect of ensuring that Nb-Ti precipitates formed during the continuous casting process dissolve back. Specifically, the tapping temperature can be 1200°C, 1210°C, 1220°C, 1230°C, etc. Furthermore, the heating time is 160-200 minutes.

[0071] Controlling the FeO content of the surface oxide scale of the cast ingot to ≥90 wt% has the following positive effects: firstly, the scale structure with a high FeO content is easier to descale, which greatly avoids scale indentation defects during hot rolling; secondly, the solubility of Cu in the FeO phase is very low. The melting point of metallic Cu is 1083°C, so liquid Cu easily migrates through FeO grain boundaries and matrix grain boundaries. Under high temperature conditions, Cu diffuses along the FeO grain boundaries to the scale surface and evaporates as Cu gas. This reduces the concentration of Cu at the scale / steel interface and avoids the occurrence of Cu brittle defects. See Figure 5 , ensuring that Cu diffuses in the iron sheet and reduces the enrichment of Cu elements at the interface. Specifically, the FeO content can be 90 weight %, 91 weight %, 92 weight %, 93 weight %, etc.

[0072] In some embodiments, the step of controlling the heating rate and the holding time of the soaking section in stages includes:

[0073] If the heating temperature is <1050°C, the heating rate is 5-10°C / min;

[0074] If the heating temperature is ≥1050°C, the heating rate is 8-12°C / min;

[0075] The holding time of the soaking section is ≤30 min.

[0076] When heating to a temperature <1050°C, the heating rate should be controlled at 5-10°C / min. This has the positive effect of ensuring thorough burnout and uniform internal and external temperatures during the low-temperature heating process. Furthermore, when the temperature is below the Cu liquefaction temperature, the heating rate can be slowed down to prevent Cu liquefaction and precipitation during the oxidation process. Specifically, when heating to a temperature <1050°C, the heating rate can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, etc.

[0077] The positive effect of controlling the heating rate to 8-12°C / min when the heating temperature is ≥1050°C is to increase the heating rate after reaching the melting point of Cu element, thereby reducing the Cu enrichment content and concentration in the surface layer. Specifically, when the heating temperature is ≥1050°C, the heating rate can be 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, etc.

[0078] The positive effect of controlling the soaking time in the soaking section to ≤ 30 minutes is to reduce the surface Cu enrichment content and concentration while ensuring the slab is burned through, thus avoiding the occurrence of Cu brittle defects. The soaking time can be 30 minutes, 28 minutes, 26 minutes, 24 minutes, etc.

[0079] In some embodiments, the step of rolling the heated ingot in stages to obtain a hot-rolled plate comprises:

[0080] The heated ingot is subjected to rough rolling; wherein the R2 rough rolling mill adopts 1, 3, 4, and 5 passes for descaling;

[0081] The rough-rolled ingot is subjected to finish rolling to obtain a hot-rolled plate; wherein the outlet temperature of the finish rolling is 1030-1050° C., and double-pass descaling is started.

[0082] During roughing, the R2 roughing mill utilizes 1, 3, 4, and 5 descaling passes, achieving positive results: Due to the high concentration of Cu and Si in the steel, the formation of fayalite, which causes sticky scale, is reduced. After the slab leaves the furnace, primary descaling is used to remove scale, maintaining a descaling pressure above 25 MPa. A 1+5 rolling pattern is employed. Due to the high concentration of Cu and Si in the steel, which can easily cause fayalite formation and cause sticky scale, R1 utilizes a single descaling pass. The roughing process temperature drop is between 150-170°C. Coil boxes are used after roughing to enhance descaling, and the intermediate slab thickness is controlled at 35-38 mm.

[0083] The positive effects of controlling the finishing rolling outlet temperature to 1030-1050°C and initiating double-pass descaling ensure the surface quality of the hot coil. During the finishing rolling process, descaling water is used between the F1 and F2 stands, with the water pressure controlled at 10-15 MPa. The rolling speed is controlled at 10-15 m / s, and the finished product thickness after finishing is 1.8-2.5 mm. The finishing rolling outlet temperature can be 1030°C, 1040°C, 1050°C, etc.

[0084] In some embodiments, the set cooling rate is 70-100°C / s, and the coiling temperature is 550-600°C.

[0085] like Figure 6As shown, since the steel contains a high content of Mn-Si elements, intergranular oxidation is prone to occur during the coiling process. In the embodiment of the present application, the above-mentioned laminar cooling adopts an ultra-fast cooling low-pressure mode, and the "set cooling rate" represents an ultra-fast cooling rate. The positive effect of controlling the cooling rate to 70-100℃ / s is to shorten the residence time of the strip in the two-phase region and avoid the formation of intergranular oxidation. The cooling rate can be 70℃ / s, 80℃ / s, 90℃ / s, 100℃ / s, etc., wherein the water pressure is 0.35MPa and the water flow is 100m 3 / h, up 80m 3 / h.

[0086] Controlling the coiling temperature to 550-600°C has the positive effect of lowering the strip coiling temperature and preventing the formation of intergranular oxidation during the coiling process. Specifically, the coiling temperature can be 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, etc. To ensure uniformity in performance between the head and tail, a head-to-tail U-shaped coiling process is adopted. The coiling temperature is increased by 30-40°C in the first 50m to ensure uniform Nb precipitation; the coiling temperature is increased by 30-50°C in the tail 150m.

[0087] In some embodiments, the hot-rolled coil is immersed in water and then pickled to obtain a hot-rolled pickled plate, comprising:

[0088] Under the condition of a set time, the hot-rolled coil is immersed in water for cooling; wherein the initial immersion temperature of the outer ring of the hot-rolled coil is controlled;

[0089] The hot-rolled coil after soaking is pickled, and the pickling rate is controlled to obtain a hot-rolled pickled plate.

[0090] In some embodiments, the setting time is 200-300 min, the initial immersion temperature of the outer ring of the hot-rolled coil is 350-400° C., and the pickling rate is 100-120 m / min.

[0091] The "set time" refers to the aforementioned immersion time. A positive effect of controlling the immersion time to 200-300 minutes is that after the coiling process completes the phase transformation, immersion in water shortens the time the middle portion of the strip remains in the high-temperature zone, preventing the formation of intergranular oxidation. Specifically, the immersion time can be 200 minutes, 250 minutes, 300 minutes, etc.

[0092] The positive effect of controlling the initial immersion temperature of the outer ring of the hot-rolled coil to 350-400°C is that after the phase transformation of the strip is completed, the time the middle part of the strip stays in the high-temperature zone is shortened, thus preventing the formation of intergranular oxidation. Specifically, this temperature can be 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, etc.

[0093] The positive effect of controlling the pickling rate to 100-120 m / min: Using a slower pickling rate ensures that the surface oxide layer is removed. Specifically, the pickling rate can be 100 m / min, 110 m / min, 120 m / min, etc. The pickling process also includes a tension-leveling process, which uses a two-bend-one-leveling process. The bending section insertion is controlled at 25-30 mm, the straightening section at 10-15 mm, and the elongation is set at 3-5%.

[0094] The preparation method of the hot-rolled pickled plate is implemented based on the hot-rolled pickled plate. The chemical dust composition of the hot-rolled pickled plate can be specifically referred to the above embodiment. Since the preparation method of the hot-rolled pickled plate adopts part or all of the technical solutions of the above embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiment, which will not be repeated here.

[0095] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0096] Table 1 Chemical composition of hot-rolled pickled plates (wt%)

[0097] Serial number C Si Mn Cr Nb Cu Ti N (ppm) Example 1 0.22 0.25 1.25 0.2 0.02 0.02 0.02 50 Example 2 0.25 0.3 1.35 0.25 0.05 0.05 0.04 48 Example 3 0.24 0.27 1.30 0.23 0.03 0.03 0.03 47 Comparative Example 1 0.23 0.15 1.5 0.15 0 0 0.04 45

[0098] Table 2 Preparation process parameters of hot-rolled pickled plates

[0099]

[0100]

[0101] Table 3 Hydrogen embrittlement evaluation results of hot-rolled pickled plates

[0102] Serial number Bending angle Hydrogen-induced delayed cracking time Example 1 80° No cracking after 500h Example 2 75° No cracking after 500h Example 3 70° Cracking after 1000h Comparative Example 1 50° Cracking after 210h

[0103] When high-end car companies certify the purchase of hot-formed steel, they require that the bending angle of the quenched hot-formed steel must exceed 60° and 65° before it can be purchased and used; at the same time, a three-point bending test of the hot-formed steel is carried out in a specified solution to ensure that hydrogen embrittlement fracture does not occur for a certain period of time (generally 300 hours). In the embodiment of this application, the bending angle of the steel is improved by solving the problems of center segregation, intergranular oxidation, and surface cracking, ensuring that there is no cracking when bending above 65°. At the same time, due to the characteristics of the steel with added alloy elements, such as Figure 7Hydrogen embrittlement evaluation using the four-point bending method revealed a significant improvement in the delayed hydrogen-induced cracking time and improved surface hydrogen-embrittlement fracture resistance. However, the comparative example, which did not employ the present embodiment, resulted in a lower bending angle for the steel plate, a shorter delayed hydrogen-induced cracking time, and poorer hydrogen-embrittlement fracture resistance.

[0104] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A hot-rolled pickled plate, characterized in that: The chemical composition of the hot-rolled pickled plate is as follows: C content is 0.22-0.25% by weight, Si content is 0.25-0.3% by weight, Mn content is 1.25-1.35% by weight, Cr content is 0.2-0.25% by weight, Ti content is 0.02-0.04% by weight, B content is 0.002-0.003% by weight, Nb content is 0.02-0.05% by weight, Cu content is 0.02-0.05% by weight, N content is ≤50ppm; the rest is Fe.

2. A method for preparing a hot-rolled pickled plate, characterized in that: For preparing the hot-rolled pickled plate according to claim 1, the method comprises: Continuously casting the molten steel and controlling the process parameters of the continuous casting to obtain a cast billet; The ingot is heated so that the heated ingot has a target temperature and the chemical composition of the surface iron oxide scale of the ingot has a target FeO content; wherein the heating includes: controlling the heating rate in stages and controlling the holding time of the soaking section; The heated ingot is rolled in stages to obtain a hot-rolled plate; Under a set cooling rate condition, laminar cooling is performed on the hot-rolled plate, and then coiling is performed while controlling the coiling temperature to obtain a hot-rolled coil; The hot-rolled coil is immersed in water for cooling and then pickled to obtain a hot-rolled pickled plate.

3. The method according to claim 2, characterized in that The process parameters of the continuous casting include: a casting rate of 1.5-1.7 m / min, a straightening temperature of a straightening machine of ≥950° C., and an electromagnetic stirring current of 120-160A.

4. The method according to claim 2, characterized in that The target temperature is 1200-1230° C., and the target FeO content is ≥90 wt %.

5. The method according to claim 2, characterized in that The stepwise control of the heating rate and the holding time of the soaking section include: If the heating temperature is <1050°C, the heating rate is 5-10°C / min; If the heating temperature is ≥1050°C, the heating rate is 8-12°C / min; The holding time of the soaking section is ≤30 min.

6. The method according to claim 2, characterized in that The heated ingot is rolled in stages to obtain a hot-rolled plate, comprising: The heated ingot is subjected to rough rolling; wherein the R2 rough rolling mill adopts 1, 3, 4, and 5 passes for descaling; The rough-rolled ingot is subjected to finish rolling to obtain a hot-rolled plate; wherein the outlet temperature of the finish rolling is 1030-1050° C., and double-pass descaling is started.

7. The method according to claim 2, characterized in that The set cooling rate is 70-100°C / s, and the coiling temperature is 550-600°C.

8. The method according to claim 2, characterized in that The hot-rolled coil is immersed in water and then pickled to obtain a hot-rolled pickled plate, comprising: Under the condition of a set time, the hot-rolled coil is immersed in water for cooling; wherein the initial immersion temperature of the outer ring of the hot-rolled coil is controlled; The hot-rolled coil after soaking is pickled, and the pickling rate is controlled to obtain a hot-rolled pickled plate.

9. The method according to claim 8, characterized in that The setting time is 200-300 minutes, the initial immersion temperature of the outer ring of the hot-rolled coil is 350-400° C., and the pickling rate is 100-120 m / min.

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