High-modulus steel and preparation method thereof

Abstract

The invention relates to high-modulus steel and a preparation method thereof. The structure of the high-modulus steel comprises a ferrite matrix with the volume fraction being 86-88% and boronized particles with the volume fraction being 12-14%. The high-modulus steel has the characteristics of low density and high specific modulus, so that the requirements of steel for the fields of automobiles and the like with light weight and high rigidity requirements are met; according to the preparation method, by adopting a C-Cr-B component system and a high-temperature hot rolling-solution treatment mode process, the high-modulus steel with light boronized reinforced particles dispersed and distributed in a ferrite matrix is obtained; in the structure, boronized reinforced particles and a ferrite matrix form a coherent relationship, and the structure has strong binding capacity, so that the high modulus has good ductility and strength; and the high-temperature hot rolling process is adopted, continuous dynamic recrystallization can be achieved, stress concentration around boronized reinforced particles is restrained, the stress of the boronized reinforced particles and a ferrite matrix is evenly distributed, and therefore the machinability and the ductility of the high-modulus steel are improved.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a high-modulus steel and its preparation method. Background Technology

[0002] To meet stricter carbon dioxide emission regulations, the automotive industry needs more advanced lightweight high-strength steels. Lightweight high-strength steels have attracted significant attention due to their unique density-strength-stiffness synergistic characteristics. Their development requires reducing material density while maintaining sufficient stiffness (elastic modulus) to resist elastic deformation and high strength (yield strength) to prevent ductile failure. This presents a dual challenge to traditional alloy design theory. From a material physics perspective, elastic modulus, as a macroscopic manifestation of interatomic bonding forces, is primarily governed by electronic structure and crystal symmetry; while yield strength is related to dislocation movement resistance and can be optimized through microstructural control mechanisms such as grain boundary strengthening and precipitation phases. This fundamental difference leads to a common technical dilemma in lightweighting processes: "reducing modulus is easy, increasing strength is difficult."

[0003] In the early stages, many steel companies conducted research and development on low-density steel by adding the light element Al to reduce its density. However, due to the multi-scale influence of aluminum on the crystal structure and atomic bonding characteristics of steel, its elastic modulus generally decreased from 210 GPa to the 170-190 GPa range, while the increase in yield strength was limited by the solid solution softening effect caused by Al. Currently, lightweighting in manufacturing is mainly achieved by using ultra-high-strength steel and reducing its thickness. However, reducing thickness significantly reduces the stiffness of the material. Therefore, it has become extremely difficult to further reduce the weight of traditional steel while maintaining its stiffness. To solve this problem, developing steel materials with high specific stiffness has become particularly important.

[0004] Among these, developing steel-based high-modulus steel containing ceramic reinforcing phases is considered a highly promising solution. This type of high-modulus steel, by introducing a rigid and lightweight ceramic phase, can not only improve the specific strength and specific stiffness of the steel but also reduce its density, thus achieving weight reduction.

[0005] Currently, due to TiB2's very high elastic modulus, the Fe-Ti-B system concept is widely used in high-modulus steels. However, the Fe-Ti-B system requires rapid solidification technology for preparation, but the slow cooling rate of traditional casting processes leads to grain coarsening in the micrometer range, resulting in stress concentration during deformation and thus causing cracking.

[0006] In view of this, it is necessary to design a high-modulus steel and its preparation method to solve the above problems. Summary of the Invention

[0007] This application provides a high-modulus steel and its preparation method to solve the current automotive industry's need for steel grades that simultaneously meet the performance requirements of maintaining sufficient stiffness (elastic modulus) to resist elastic deformation and maintaining high strength (yield strength) to prevent plastic failure.

[0008] In a first aspect, this application provides a high-modulus steel, wherein the chemical composition of the high-modulus steel, by mass percentage, comprises: C: 0.08%-0.15%, Si: 0.1%-0.3%, Al: 0.03%-0.05%, Mn: 0.3%-1%, Cr: 18%-22%, B: 1.4%-1.6%, P≤0.01%, S≤0.01%, N: ≤0.004%, with the remainder being Fe and unavoidable impurities.

[0009] In some embodiments, the microstructure of the high-modulus steel comprises a ferrite matrix and boride particles; the volume fraction of the ferrite matrix is ​​86%-88%, and the volume fraction of the boride particles is 12%-14%.

[0010] In some embodiments, the high-modulus steel has a yield strength of 380 MPa-450 MPa, a tensile strength of 590 MPa-650 MPa, an elongation of 15%-18%, an elastic modulus of 220 GPa-230 GPa, and a density of 7.46 g / cm³. 3 -7.48g / cm 3 .

[0011] In some embodiments, the thickness of the high-modulus steel is 2.8 mm to 3.2 mm.

[0012] Secondly, this application provides a method for preparing the above-mentioned high-modulus steel, comprising the following steps:

[0013] Molten steel is provided, and the molten steel is smelted and continuously cast in sequence to obtain a slab;

[0014] The slab is hot-rolled to obtain a hot-rolled coil;

[0015] The hot-rolled coil is subjected to solution treatment and cooling treatment in sequence to obtain the high-modulus steel.

[0016] In some embodiments, during the tapping process, Si-Mn alloy is added to adjust the mass percentage content of Si in the molten steel to 0.1%-0.3%, C-Mn-Fe alloy is added to adjust the mass percentage content of Mn in the molten steel to 0.3%-1%, and CB-Fe alloy is added to adjust the mass percentage content of B in the molten steel to 1.4%-1.6%.

[0017] In the Si-Mn alloy, the mass percentage of Si is 65%-75%; in the C-Mn-Fe alloy, the mass percentage of C is 6.0%-8.0% and the mass percentage of Mn is 75%-85%; in the CB-Fe alloy, the mass percentage of C is 0.5%-2.0% and the mass percentage of B is 15%-25%.

[0018] In some embodiments, the smelting includes adding slag to molten steel during the tapping process. The slag includes quicklime and fluorite. The amount of quicklime added is 4 kg / ton of steel to 16 kg / ton of steel, and the amount of fluorite added is 4 kg / ton of steel to 8 kg / ton of steel. The particle size of the quicklime is 13 mm to 17 mm. The amount of slag discharged during tapping is ≤80 mm.

[0019] The process of adding the slag is as follows: the slag is added along with the steel flow at the beginning of the steel tapping process; the period of the beginning of the steel tapping process is: when the steel tapping amount accounts for 1 / 4 of the total steel tapping amount and before; all the slag is added before the steel tapping amount reaches 1 / 5 of the total steel tapping amount; the total steel tapping time is ≥4 minutes.

[0020] In some embodiments, the final target temperature of the smelting is 1660°C-1680°C; and / or,

[0021] The solution temperature is 850℃-1000℃, and the solution time is 0.5h-1h.

[0022] In some embodiments, the smelting includes adding an Al-Fe alloy to molten steel for deoxidation; the amount of Al-Fe alloy added is 3.5 kg / ton of steel to 4.5 kg / ton of steel; and the mass percentage of Al in the Al-Fe alloy is 40% to 60%.

[0023] In some embodiments, the hot rolling includes sequentially heating, roughing, finishing, cooling and coiling the slab; the heating temperature is 1150℃-1250℃; the finishing temperature is 920℃-1050℃; and the coiling temperature is 550℃-620℃.

[0024] The technical solutions provided in this application have the following advantages compared with the prior art:

[0025] The high-modulus steel provided in this application has the following composition: C: 0.08%-0.15%, Si: 0.1%-0.3%, Al: 0.03%-0.05%, Mn: 0.3%-1%, Cr: 18%-22%, B: 1.4%-1.6%, P≤0.01%, S≤0.01%, N: ≤0.004%. The microstructure of the high-modulus steel includes a ferrite matrix and boride particles; the volume fraction of the ferrite matrix is ​​86%-88%, and the volume fraction of the boride particles is 12%-14%. This gives the high-modulus steel the characteristics of low density and high specific modulus. The high-modulus steel has a yield strength of 380-450 MPa, a tensile strength of 590-650 MPa, an elongation of 15-18%, an elastic modulus of 220-230 GPa, and a density of 7.46 g / cm³. 3 -7.48g / cm 3 This satisfies the demand for lightweight and high-rigidity steel in fields such as automobiles. The method for preparing high-modulus steel provided in this application, through the use of a C-Cr-B composition system and a high-temperature hot rolling-solution treatment process, yields high-modulus steel with lightweight boronized reinforcing particles dispersed in a ferrite matrix; the boronized reinforcing particles (Fe...) in this microstructure... 1.1 Cr 0.9 B 0.9 The boronized reinforcing particles form a coherent relationship with the ferrite matrix, exhibiting strong bonding capabilities and resulting in good elongation and strength for high-modulus steel. Furthermore, the high-temperature hot rolling process enables continuous dynamic recrystallization, suppressing stress concentration around the boronized reinforcing particles and ensuring a uniform stress distribution between the particles and the ferrite matrix. This improves the later-stage workability and elongation of the high-modulus steel. Additionally, the addition of boronized reinforcing particles reduces the density of the high-modulus steel, thus reducing its weight.

[0026] Compared to existing technologies, while the Fe-Ti-B system concept is widely used in high-modulus steels (because TiB2 has a very high elastic modulus), its preparation requires rapid solidification technology. The slow cooling rate of traditional casting processes leads to grain coarsening within the micrometer range, resulting in stress concentration during deformation and thus inducing cracking. Although Fe in the Fe-Cr-B system... 1.1 Cr 0.9 B 0.9 While its elastic modulus is lower than that of high-modulus steels based on TiB2 in the Fe-Ti-B system, it reduces the tendency for particles to float and aggregate in the melt during solidification, thus simplifying the metallurgical process and alleviating the limitation of the critical solidification rate. Furthermore, Fe-Cr-B system-based high-modulus steels offer the possibility of achieving a wider range of microstructures and properties. Attached Figure Description

[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The microstructure of a high-modulus steel provided in this application is shown. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] Various embodiments of this application may exist in the form of a range. It should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application. Therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this application, it means including any referenced number (fraction or integer) within the indicated range. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application can be purchased commercially or prepared by existing methods. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in this application, the terms "comprising," "including," etc., mean "including but not limited to." In this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this application, "at least one" means one or more, and "more than one" means 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 represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple.

[0032] This application provides a high-modulus steel, the chemical composition of which, by mass percentage, comprises: C: 0.08%-0.15%, Si: 0.1%-0.3%, Al: 0.03%-0.05%, Mn: 0.3%-1%, Cr: 18%-22%, B: 1.4%-1.6%, P≤0.01%, S≤0.01%, N: ≤0.004%, with the remainder being Fe and unavoidable impurities.

[0033] This gives the high-modulus steel the characteristics of low density and high specific modulus, meeting the needs of steel used in fields such as automobiles that require lightweighting and high rigidity.

[0034] The design principles of each chemical element in this application are as follows:

[0035] Carbon (C): C is the most effective solid solution strengthening element and the most important element to ensure the strength of steel. High-modulus steel uses borides (M2B) as the reinforcing phase, and it is necessary to avoid C competing with B to form brittle Fe3C or M. 23 (C,B)6, reduce the volume fraction of boride; however, if the mass percentage of C is too low, it is difficult to achieve the required strength, and if the mass percentage of C is too high, it will deteriorate the weldability. Therefore, the mass percentage of C needs to be controlled within 0.08-0.15%.

[0036] Silicon (Si): Si is an important element for inhibiting cementite precipitation; however, excessive Si content can lead to the formation of oxides that deteriorate the surface quality of steel, while insufficient Si content makes it difficult to inhibit cementite precipitation. Al is a strong deoxidizer, preferentially combining with free oxygen in steel to form Al₂O₃. By consuming oxygen in the steel, Al reduces the reaction between Si and oxygen, thereby inhibiting the formation of excess SiO₂ and mitigating the deterioration of surface quality caused by Si. Al can also indirectly assist Si in inhibiting cementite precipitation by refining the steel grains. Therefore, it is necessary to control the Si content at 0.1%-0.3% and the Al content at 0.03%-0.05% to achieve proper control of the Si and Al content.

[0037] Manganese (Mn): Mn is a solid solution strengthening element and also an important element for stabilizing austenite. In high-Cr steel, Mn promotes the formation of δ-ferrite and reduces high-temperature rolling plasticity; Mn can also weaken the hot brittleness caused by S. However, if the mass percentage content of Mn is too high, it will cause Mn segregation and banded structure, deteriorating workability and weldability. Therefore, to maximize the formation of boronized reinforcing particles, improve the elastic modulus, and avoid casting / machining defects, while also balancing the liquidus temperature and preventing the precipitation of harmful phases, the mass percentage content of Mn needs to be controlled between 0.3% and 1%.

[0038] Chromium (Cr): Cr is an important element in this scheme. It combines with boron to form boronized reinforcing particles that enhance the elastic modulus of the steel. However, if the mass percentage of Cr is too low, the volume fraction of particles formed in the steel matrix will be low, failing to increase the elastic modulus of the steel. If the mass percentage of Cr is too high, it will adversely affect castability and machinability. Therefore, this scheme controls the mass percentage of Cr at 18%-22%.

[0039] Boron (B): B is also an important element in this scheme. It combines with Cr to form particles that enhance the elastic modulus of the steel. However, if the mass percentage of B is too low, the volume fraction of particles formed in the steel matrix will be low, failing to increase the elastic modulus of the steel. If the mass percentage of B is too high, it will cause grain boundary brittleness, which will adversely affect the castability and machinability of high-modulus steel. Therefore, this scheme controls the mass percentage of B at 1.4%-1.6%.

[0040] Phosphorus (P): P can significantly reduce the plasticity and toughness of steel, so its content should be kept as low as possible, and the mass percentage of P should be controlled at 0.01% or below.

[0041] Sulfur (S): S is a harmful impurity element in steel, which can cause hot brittleness, reduce the ductility and toughness of steel, and cause cracks during forging and rolling. Therefore, the mass percentage content of S must be controlled at 0.01% or below.

[0042] It is worth noting that the high modulus steel provided in this solution has a nitrogen content of ≤0.004% by mass.

[0043] Nitrogen (N): Like carbon (C), nitrogen is a solid-solution element. However, as the nitrogen content in steel increases, the stamping processability of the steel deteriorates. Furthermore, dissolved nitrogen is a major cause of aging in galvanized steel products, especially after leveling and strain aging, where nitrogen has a particularly significant impact. Therefore, nitrogen content should be kept as low as possible. This is because it is necessary to control the combination of nitrogen and boron (B) to avoid the poor processing performance and poor toughness of the steel produced by BN (nitrogen nitrogen). In this scheme, the mass percentage of nitrogen in the steel needs to be controlled at 0.004% or below.

[0044] As an optional implementation, in this embodiment of the application, the microstructure of the high-modulus steel includes a ferrite matrix and boride particles; the volume fraction of the ferrite matrix is ​​86%-88%, and the volume fraction of the boride particles is 12%-14%.

[0045] The boronized granular phase is a precipitated phase that can effectively pin dislocations during material deformation, thereby forming a concentrated deformation region around the particles. This region accumulates high strain energy due to dislocation aggregation, providing sufficient driving force for dynamic recrystallization and promoting continuous dynamic recrystallization. Through this series of effects, the granular phase and the surrounding matrix can achieve a uniform stress distribution, ultimately significantly improving the machinability of high-modulus steel.

[0046] As an optional implementation, in this embodiment of the application, the high-modulus steel has a yield strength of 380MPa-450MPa, a tensile strength of 590MPa-650MPa, an elongation of 15%-18%, an elastic modulus of 220GPa-230GPa, and a density of 7.46g / cm³. 3 -7.48g / cm 3 .

[0047] Thus, this high-modulus steel has the characteristics of low density and high specific modulus, which meets the needs of steel used in fields such as automobiles that require lightweighting and high rigidity.

[0048] As an optional implementation, in this embodiment of the application, the thickness of the high-modulus steel is 2.8mm-3.2mm.

[0049] Based on a general inventive concept, this application provides a method for preparing the above-mentioned high-modulus steel, comprising the following steps:

[0050] Step S1: Provide molten steel, and smelt and continuously cast the molten steel in sequence to obtain a slab;

[0051] Step S2: Hot-roll the slab to obtain a hot-rolled coil;

[0052] Step S3: The hot-rolled coil is subjected to solution treatment and cooling treatment in sequence to obtain the high-modulus steel.

[0053] The method for preparing high-modulus steel provided in this application, by employing a C-Cr-B composition system and a high-temperature hot rolling-solution treatment process, obtains high-modulus steel with lightweight boronized reinforcing particles dispersed in a ferrite matrix; the boronized reinforcing particles (Fe) in this microstructure 1.1 Cr 0.9 B 0.9 It forms a coherent relationship with the ferrite matrix, exhibiting strong bonding ability, thus enabling high-modulus steel to possess good elongation and strength. Furthermore, the high-temperature hot rolling process allows for continuous dynamic recrystallization, suppressing stress concentration around the particles and ensuring a uniform stress distribution between the particles and the matrix, thereby improving the workability and elongation of high-modulus steel. Additionally, the addition of lightweight particles reduces the density of high-modulus steel.

[0054] As an alternative implementation method, smelting can be carried out using a converter.

[0055] As an optional implementation, the cooling process includes water cooling; the cooling rate is 50℃ / s-70℃ / s.

[0056] As an optional implementation, in this embodiment of the application, during the steel tapping process, Si-Mn alloy is added to adjust the mass percentage content of Si in the molten steel to 0.1%-0.3%, C-Mn-Fe alloy is added to adjust the mass percentage content of Mn in the molten steel to 0.3%-1%, and CB-Fe alloy is added to adjust the mass percentage content of B in the molten steel to 1.4%-1.6%.

[0057] In the Si-Mn alloy, the mass percentage of Si is 65%-75%; in the C-Mn-Fe alloy, the mass percentage of C is 6.0%-8.0% and the mass percentage of Mn is 75%-85%; in the CB-Fe alloy, the mass percentage of C is 0.5%-2.0% and the mass percentage of B is 15%-25%.

[0058] In this way, precise control of alloying elements and synergistic elemental effects ensure the good performance of the high-modulus steel prepared subsequently.

[0059] In some embodiments of this application, the smelting includes adding slag to molten steel during the tapping process. The slag includes quicklime and fluorite. The amount of quicklime added is 4 kg / ton of steel to 16 kg / ton of steel, and the amount of fluorite added is 4 kg / ton of steel to 8 kg / ton of steel. The particle size of the quicklime is 13 mm to 17 mm, and the amount of slag discharged during tapping is ≤80 mm.

[0060] The process of adding the slag is as follows: the slag is added along with the steel flow at the beginning of the steel tapping process; the period of the beginning of the steel tapping process is: when the steel tapping amount accounts for 1 / 4 of the total steel tapping amount and before; all the slag is added before the steel tapping amount reaches 1 / 5 of the total steel tapping amount; the total steel tapping time is ≥4 minutes.

[0061] Thus, controlling the timing of slag addition can increase the deoxidation rate and inclusion removal rate, thereby improving the surface quality of the final high-modulus steel.

[0062] As an optional implementation, in this embodiment of the application, the final target temperature of the smelting is 1660℃-1680℃.

[0063] As an optional implementation, in this embodiment of the application, the solution temperature is 850℃-1000℃ and the solution time is 0.5h-1h.

[0064] By controlling the final temperature and the solution treatment process, the particles are dispersed and the grains are refined.

[0065] Solution treatment effectively improves the ductility of hot-rolled steel sheets, giving them superior formability during deformation. Specifically, if the solution temperature is below 850℃ or the holding time is less than 0.5 hours, the steel sheet cannot achieve complete solution treatment, weakening the treatment effect. Conversely, when the temperature exceeds 1000℃, the steel grains coarsen rapidly, impairing its deformation performance. Furthermore, keeping the holding time below 1 hour is also for economic reasons in production.

[0066] As an optional implementation, in this embodiment of the application, the smelting includes adding an Al-Fe alloy to molten steel for deoxidation; the amount of Al-Fe alloy added is 3.5 kg / ton of steel to 4.5 kg / ton of steel; and the mass percentage of Al in the Al-Fe alloy is 40% to 60%.

[0067] Thus, by adding Al-Fe alloy for quantitative deoxidation, the yield of B and the fixation rate of N are increased, and the content of boronized reinforcing particles is increased.

[0068] As an optional implementation, in this embodiment of the application, the hot rolling includes sequentially heating, roughing, finishing, cooling and coiling the slab; the heating temperature is 1150℃-1250℃; the finishing temperature is 920℃-1050℃; and the coiling temperature is 550℃-620℃.

[0069] If the slab heating temperature is below 1150℃, the nitrogen carbides cannot be completely dissolved, which will directly affect the strength and elongation of the steel. Conversely, if the heating temperature exceeds 1250℃, it will cause the steel plate grains to coarsen, thereby impairing its subsequent deformation ability. Therefore, the slab heating temperature should be controlled within the range of 1150℃-1250℃.

[0070] If the finishing temperature is below 920℃, coarse ferrite will be generated during hot rolling, which will affect the elongation properties of the steel produced subsequently. Conversely, if the temperature is above 1050℃, coarse austenite will be formed during hot rolling, which will adversely affect the strength of the steel produced subsequently. Therefore, the finishing temperature needs to be controlled between 920℃ and 1050℃.

[0071] While a coiling temperature below 550℃ can give the steel higher strength, it will lead to a decrease in its elongation. If the temperature is above 620℃, carbides will precipitate in the hot-rolled sheet, increasing the difficulty of subsequent processing. Therefore, the coiling temperature should be controlled within the range of 550℃-620℃.

[0072] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0073] Examples 1-3

[0074] Examples 1-3 each provide a method for preparing high-modulus steel, comprising the following steps:

[0075] Step S1: Provide molten steel, and smelt and continuously cast the molten steel in sequence to obtain a slab;

[0076] The chemical elements of each slab in Examples 1-3 are shown in Table 2;

[0077] During the tapping process, Si-Mn alloy is added to adjust the mass percentage content of Si in the molten steel to 0.1%-0.3%, C-Mn-Fe alloy is added to adjust the mass percentage content of Mn in the molten steel to 0.3%-1%, and CB-Fe alloy is added to adjust the mass percentage content of B in the molten steel to 1.4%-1.6%.

[0078] In the Si-Mn alloy, the mass percentage of Si is 65%-75%; in the C-Mn-Fe alloy, the mass percentage of C is 6.0%-8.0% and the mass percentage of Mn is 75%-85%; in the CB-Fe alloy, the mass percentage of C is 0.5%-2.0% and the mass percentage of B is 15%-25%.

[0079] The smelting process includes adding slag to molten steel during tapping. The slag includes quicklime and fluorite. The amount of quicklime added is 10 kg / ton of steel, and the amount of fluorite added is 6 kg / ton of steel. The particle size of the quicklime is 15 mm. The amount of slag discharged during tapping is ≤80 mm.

[0080] The process of adding the slag is as follows: the slag is added along with the steel flow at the beginning of the steel tapping process; all the slag is added before the steel tapping amount reaches 1 / 5 of the total steel tapping amount; the total steel tapping time is ≥4 min;

[0081] The final target temperature for the smelting process is 1660℃-1680℃;

[0082] The smelting process includes adding an Al-Fe alloy to molten steel for deoxidation; the amount of Al-Fe alloy added is 4 kg / t of steel; the mass percentage of Al in the Al-Fe alloy is 40%-60%;

[0083] Step S2: Hot-roll the slab to obtain a hot-rolled coil;

[0084] The hot rolling process includes sequentially heating, roughing, finishing, cooling, and coiling the slab; the heating temperature is 1150℃-1250℃; the finishing temperature is 920℃-1050℃; and the coiling temperature is 550℃-620℃.

[0085] Step S3: Solution treatment of the hot-rolled coil to obtain the target high-modulus steel;

[0086] The solution temperature is 850℃-1000℃, and the solution time is 0.5h-1h.

[0087] The chemical element content of the high-modulus steels prepared in Examples 1-3 is shown in Table 2. The specific process parameters for each step in Examples 1-3 are shown in Table 3.

[0088] Table 2. Mass percentage (%) of each chemical element in each slab (high modulus steel) of Examples 1-3 and Comparative Example 1.

[0089] serial number C / ％ Si / % Mn / % P / ％ S / ％ Cr / ％ B / ％ N / ％ Example 1 0.08 0.3 0.8 0.008 0.005 22 1.6 0.003 Example 2 0.1 0.25 0.3 0.005 0.008 21 1.5 0.0032 Example 3 0.13 0.17 0.6 0.009 0.007 19 1.45 0.0028 Example 4 0.15 0.1 1.0 0.006 0.009 18 1.4 0.0035 Comparative Example 1 0.11 1.0 2.3 0.006 0.003 0.025 0.002 0.003

[0090] Table 3. Specific parameters of each process in Examples 1-3 and Comparative Example 1.

[0091] Heating temperature / ℃ Finishing temperature of finishing rolling / ℃ Winding temperature / ℃ Solution temperature / h Solution time / h Hot-rolled coil thickness / mm Example 1 1150 920 550 850 2h 2.8 Example 2 1180 970 570 900 1.5h 3.0 Example 3 1210 1030 600 950 1.5h 3.1 Example 4 1250 1050 620 1000 1h 3.2 Comparative Example 1 1225 870 650 - - 3.0

[0092] Comparative Example 1

[0093] Comparative Example 1 provides a method for preparing modulus steel, comprising the following steps:

[0094] Step S1: Provide molten steel, and smelt and continuously cast the molten steel in sequence to obtain a slab;

[0095] The chemical elements of the slab are shown in Table 2;

[0096] During the tapping process, Si-Mn alloy is added to adjust the mass percentage content of Si in the molten steel to 1.0%, C-Mn-Fe alloy is added to adjust the mass percentage content of Mn in the molten steel to 2.3%, and CB-Fe alloy is added to adjust the mass percentage content of B in the molten steel to 0.002%.

[0097] The smelting process includes adding slag to molten steel during tapping. The slag includes quicklime and fluorite. The amount of quicklime added is 16,000 kg / ton of steel, and the amount of fluorite added is 4,000 kg / ton of steel. The particle size of the quicklime is 15 mm. The amount of slag discharged during tapping is ≤80 mm.

[0098] The process of adding the slag is as follows: the slag is added along with the steel flow at the beginning of the steel tapping process; all the slag is added before the steel tapping amount reaches 1 / 5 of the total steel tapping amount; the total steel tapping time is ≥4 min;

[0099] The final target temperature for the smelting process is 1660℃-1680℃;

[0100] The smelting process includes adding an Al-Fe alloy to molten steel for deoxidation; the amount of Al-Fe alloy added is 4 kg / t of steel.

[0101] Step S2: Hot-roll the slab to obtain a hot-rolled coil;

[0102] The hot rolling process includes sequentially heating, rough rolling, finish rolling, cooling, and coiling the slab; the heating temperature is 1225℃; the finish rolling temperature is 870℃; the coiling temperature is 650℃; and the target modulus steel is obtained after cooling.

[0103] The chemical element content of the modulus steel prepared in Comparative Example 1 is shown in Table 2.

[0104] Comparative Example 2

[0105] Comparative Example 2 provides a method for preparing modulus steel. The difference from Example 1 is that the solution treatment in step S3 is not performed. The remaining steps and process parameters are the same as in Example 1, and will not be repeated here.

[0106] The steels prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to microstructure analysis, and their mechanical properties were tested according to the national standard (GB / T 228.1-2010). The results are shown in Table 4. The properties of the steels prepared in Examples 1-4 and Comparative Examples 1-2 are shown in Table 5.

[0107] Table 4. Microstructure of the steels prepared in Examples 1-4 and Comparative Examples 1-2

[0108]

[0109] Table 5 shows the properties of the steels prepared in Examples 1-4 and Comparative Examples 1-2.

[0110]

[0111]

[0112] In addition, electron microscopy analysis was performed on the high-modulus steel in Example 1, and the results are as follows: Figure 1 As shown (the highlighted part is boride particles, and the matrix is ​​ferrite), the microstructure of high-modulus steel can be seen to consist of a ferrite matrix and boride particles.

[0113] As shown in Table 4, the high-modulus steels provided in Examples 1-4 have a yield strength of 380-450 MPa, a tensile strength of 590-650 MPa, an elongation of 15-18%, an elastic modulus of 220-230 GPa, and a density of 7.46-7.48 g / cm³. 3 This type of steel, characterized by low density and high specific modulus, better meets the needs of lightweight and high-rigidity steels used in fields such as automobiles.

[0114] The microstructure of the dual-phase steel provided in Comparative Example 1 consists of a soft ferrite matrix and a hard second-phase bainite. It has a yield strength of 320 MPa, a tensile strength of 590 MPa, an elongation of 13%, and an elastic modulus of 190 GPa. The elastic modulus, yield strength, and elongation are all lower than those of the high-modulus steel prepared by the method provided in this application. Moreover, the steel prepared in Comparative Example 1 has a higher density.

[0115] The steel prepared in Comparative Example 2, which did not undergo solution treatment, showed a lower amount of borides, resulting in poorer mechanical properties.

[0116] In summary, this invention provides a high-modulus steel with the following composition: C: 0.08%-0.15%, Si: 0.1%-0.3%, Al: 0.03%-0.05%, Mn: 0.3%-1%, Cr: 18%-22%, B: 1.4%-1.6%, P≤0.01%, S≤0.01%, N: ≤0.004%. The microstructure of the high-modulus steel comprises a ferrite matrix and boride particles; the volume fraction of the ferrite matrix is ​​86%-88%, and the volume fraction of the boride particles is 12%-14%. This results in a high-modulus steel with low density and high specific modulus. Specifically, the high-modulus steel has a yield strength of 380-450 MPa, a tensile strength of 590-650 MPa, an elongation of 15-18%, an elastic modulus of 220-230 GPa, and a density of 7.46-7.48 g / cm³. 3 This satisfies the demand for lightweight and high-rigidity steels in fields such as automobiles. The method for preparing high-modulus steel provided in this application, through the use of a C-Cr-B composition system and a high-temperature hot rolling-solution treatment process, obtains high-modulus steel with lightweight boronized reinforcing particles dispersed in a ferrite matrix; the boronized reinforcing particles (Fe...) in this microstructure... 1.1 Cr 0.9 B 0.9The boronized reinforcing particles form a coherent relationship with the ferrite matrix, exhibiting strong bonding capabilities and resulting in good elongation and strength for high-modulus steel. Furthermore, the high-temperature hot rolling process enables continuous dynamic recrystallization, suppressing stress concentration around the boronized reinforcing particles and ensuring a uniform stress distribution between the particles and the ferrite matrix. This improves the later-stage workability and elongation of the high-modulus steel. Additionally, the addition of boronized reinforcing particles reduces the density of the high-modulus steel, thus reducing its weight.

[0117] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this 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 this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A high-modulus steel, characterized in that, The chemical composition of the high-modulus steel, by mass percentage, comprises: C: 0.08%-0.15%, Si: 0.1%-0.3%, Al: 0.03%-0.05%, Mn: 0.3%-1%, Cr: 18%-22%, B: 1.4%-1.6%, P≤0.01%, S≤0.01%, N: ≤0.004%, with the remainder being Fe and unavoidable impurities.

2. The high-modulus steel according to claim 1, characterized in that, The microstructure of the high-modulus steel comprises a ferrite matrix and boride particles; the volume fraction of the ferrite matrix is ​​86%-88%, and the volume fraction of the boride particles is 12%-14%.

3. The high-modulus steel according to claim 2, characterized in that, The high-modulus steel has a yield strength of 380MPa-450MPa, a tensile strength of 590MPa-650MPa, an elongation of 15%-18%, an elastic modulus of 220GPa-230GPa, and a density of 7.46g / cm³. 3 -7.48g / cm 3 .

4. The high-modulus steel according to claim 3, characterized in that, The thickness of the high-modulus steel is 2.8mm-3.2mm.

5. A method for preparing high-modulus steel according to any one of claims 1 to 4, characterized in that, Includes the following steps: Molten steel is provided, and the molten steel is smelted and continuously cast in sequence to obtain a slab; The slab is hot-rolled to obtain a hot-rolled coil; The hot-rolled coil is subjected to solution treatment and cooling treatment in sequence to obtain the high-modulus steel.

6. The method for preparing high-modulus steel according to claim 5, characterized in that, During the tapping process, Si-Mn alloy is added to adjust the mass percentage content of Si in the molten steel to 0.1%-0.3%, C-Mn-Fe alloy is added to adjust the mass percentage content of Mn in the molten steel to 0.3%-1%, and CB-Fe alloy is added to adjust the mass percentage content of B in the molten steel to 1.4%-1.6%. In the Si-Mn alloy, the mass percentage of Si is 65%-75%; in the C-Mn-Fe alloy, the mass percentage of C is 6.0%-8.0% and the mass percentage of Mn is 75%-85%; in the CB-Fe alloy, the mass percentage of C is 0.5%-2.0% and the mass percentage of B is 15%-25%.

7. The method for preparing high-modulus steel according to claim 6, characterized in that, The smelting process includes adding slag to molten steel during tapping. The slag includes quicklime and fluorite. The amount of quicklime added is 4 kg / ton of steel to 16 kg / ton of steel. The amount of fluorite added is 4 kg / ton of steel to 8 kg / ton of steel. The particle size of quicklime is 13 mm to 17 mm. The amount of slag discharged during tapping is ≤80 mm. The process of adding the slag is as follows: the slag is added along with the steel flow at the beginning of the steel tapping process; the period of the beginning of the steel tapping process is: when the steel tapping amount accounts for 1 / 4 of the total steel tapping amount and before; all the slag is added before the steel tapping amount reaches 1 / 5 of the total steel tapping amount; the total steel tapping time is ≥4 minutes.

8. The method for preparing high-modulus steel according to claim 5, characterized in that, The target final temperature for the smelting process is 1660℃-1680℃; and / or, The solution temperature is 850℃-1000℃, and the solution time is 0.5h-1h.

9. The method for preparing high-modulus steel according to claim 6, characterized in that, The smelting process includes adding an Al-Fe alloy to molten steel for deoxidation; the amount of Al-Fe alloy added is 3.5 kg / ton of steel to 4.5 kg / ton of steel; the mass percentage of Al in the Al-Fe alloy is 40% to 60%.

10. The method for preparing high-modulus steel according to claim 6, characterized in that, The hot rolling process includes sequentially heating, roughing, finishing, cooling, and coiling the slab; the heating temperature is 1150℃-1250℃; the finishing temperature is 920℃-1050℃; and the coiling temperature is 550℃-620℃.

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