A method for preparing low-carbon, lightweight and high-strength ferritic steel

Abstract

The present invention belongs to the technical field of iron and steel metallurgy, and more specifically relates to a method for preparing low-carbon, lightweight, high-strength, high-hardness ferritic steel. The present invention obtains low-carbon, lightweight, high-strength, high-hardness ferritic steel by subjecting the steel to be treated to a two-phase zone insulation treatment, followed by a rolling treatment, and then a double-stage recrystallization heat treatment and a continuous annealing treatment. The present invention obtains a multiphase structure of a ferrite matrix and M / A islands + κ carbides based on organizational regulation, and increases the strength and hardness of the refined ferrite and M / A islands through online heat treatment. M / A islands and κ carbides serve as important ways to regulate toughness. Combined with component control, they solve the demand for lightweight steel and ensure that lightweight steel has excellent comprehensive mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and more particularly relates to a method for preparing low-carbon, lightweight, high-strength ferritic steel. Background Art

[0002] Steel for drones requires high strength, high toughness, low density, and good processability. It is primarily used in fuselage frames, engine components, and protective elements. With the continuous advancement of materials science, the performance of ferritic lightweight steel continues to improve, further expanding its application areas. Therefore, lightweight steel is expected to find widespread application in the drone steel sector.

[0003] Numerous research institutions at home and abroad have conducted extensive research on lightweight steel. Among the prior art, patent publication CN108642403A proposes a 780 MPa ultra-high-strength Fe-Mn-Al-C lightweight cast steel and its preparation method. The chemical composition of this low-density cast steel is as follows: C: 0.80-1.30%, Mn: 15.00-20.00%, Al: 3.50-8.00%, Si: 0.05-0.25%, Cr: 0.5-1.5%, Cu: 0.01-0.06%, Mo: 0.30-0.80%, V: 0.05-0.20%, Nb: 0.01-0.10%, Ce: 0.005-0.025%, with P ≤ 0.01%, S ≤ 0.01%, and N ≤ 0.01%, with the remainder being Fe and unavoidable impurities. Meanwhile, the weight percentages of Mn and Al satisfy 2.5%≤Mn / Al≤3.0%; and the weight percentages of Nb and V satisfy 0.10%≤Nb+V≤0.20%.

[0004] Patent document CN 116288020 A proposes a Fe-Mn-Al-Ni-Mo-C high-strength austenitic low-density steel and its preparation method, belonging to the field of metal materials. The chemical composition of the steel is as follows: C 1.0-1.5wt%, Mn 20-30wt%, Al 7-10wt%, Ni 3.0-6.0wt%, Mo 0.5-1.5wt%, Nb 0.01-0.20wt%, and the remainder is Fe and unavoidable impurities. By adding a certain amount of Ni and a small amount of Mo and Nb, a Ni-A1-type B2 phase and a small amount of nanoscale (NbMo)C that pins the grain boundaries are formed. Mo promotes the precipitation of granular micron- and nanoscale B2 phase particles, while suppressing the precipitation of K during aging, thereby improving strength and work hardening ability and achieving an excellent strength-ductility match. The tensile strength is 1500-1700MPa, the elongation is more than 30%, and the density is 6.6-6.9g / cm 3 .

[0005] The invention patent with publication number CN118957214A provides a lightweight, high-strength cold-rolled ferritic steel plate and its manufacturing method. The chemical composition of the steel plate is C≤0.005%, Si≤0.05%, Cu:0.3%~0.8%, Al:5%~8%, S≤0.01%, P≤0.018%, and the balance is Fe and impurities. The steel plate structure of the invention is full ferrite, the yield strength of the steel plate is ≥500MPa, the tensile strength is ≥600MPa, and the elongation after fracture is A 50 ≥20%, damping coefficient ≥0.05. By adding Cu and Al elements to improve the damping properties of the steel, and utilizing the precipitation strengthening effect of Cu to increase the strength of the steel, the steel plate has both high damping properties and good mechanical properties. In addition, the combined addition of Al and Cu can also effectively improve the corrosion resistance of the steel.

[0006] Lightening traditional lightweight steel typically requires reducing alloying element content or material density, which results in a significant decrease in strength and hardness. Adding high-cost alloying elements (such as Ni and Mo) can improve strength and ductility, but this struggles to achieve both lightweighting goals, increases production costs, and can lead to segregation and deterioration in performance. This invention achieves superior performance by manipulating the microstructure of ferritic lightweight steel through compositional design and mechanical metallurgical methods. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for preparing low-carbon, lightweight, high-strength ferritic steel to solve the problems existing in the above-mentioned prior art.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] One of the technical solutions of the present invention is to provide a method for preparing low-carbon, lightweight, high-strength ferritic steel, comprising the following steps:

[0010] The steel to be treated is subjected to a two-phase region heat preservation treatment, followed by a rolling treatment, and then a double-stage recrystallization heat treatment and a continuous annealing treatment to obtain the low-carbon, lightweight, high-strength ferrite steel.

[0011] Furthermore, in terms of mass percentage, in addition to Fe, the components of the steel to be treated include: C 0.25-0.45%, Si 0.40-0.80%, Al 6.5-8.0%, Mo 0.15-0.25%, Mn 0.80-1.5% and V 0.01-0.05%, as well as unavoidable impurities.

[0012] Conventional ferrite-based low-density lightweight steel has an alloy composition range of: Mn mass fraction of 2% to 12%, Al mass fraction of 3% to 7%, and C mass fraction of 0.05% to 0.5%. Moreover, after hot rolling and cold rolling processes, the microstructure of conventional ferrite-based low-density lightweight steel presents a bimodal banded structure of δ-ferrite and austenite along the rolling direction. Among them, the phase structure of the austenite band will be affected by the Mn and Al content, which has a great influence on the mechanical properties of the steel. The present invention rationally designs the chemical components of lightweight high-strength ferrite steel, regulates the relative addition amounts of some key elements, and combines the mechanical metallurgical regulation of the organization by online hot processing, thereby playing a key regulatory role of the relevant elements on the strength and toughness of the steel of the present invention. Therefore, the optimal composition selected by the present invention is as described above.

[0013] Optionally, the chemical composition mass percentage ratio of C, Si, Al, Mo and Mn in the steel to be treated meets the following requirements: 0.13≤σ≤2.3, σ=0.5e (0.3Al-Mn) -0.25[4.2C-1.2Si+5V+10lg(1+Mo)].

[0014] Based on the consideration of the cost of alloying elements and the in-depth understanding of their role and content control principles, this paper rationally designs the alloy composition of a high-strength, high-hardness, lightweight steel for drones. By precisely controlling the content of each alloying element, the hardness and overall performance of the steel are significantly improved at a lower alloying cost: C, Si, Mn, V, Al, and Mo. On the basis of rationally controlling the chemical composition range of each element, and at the same time regulating the relationship: 0.13≤σ≤2.3, σ=0.5e (0.3Al-Mn) -0.25[4.2C-1.2Si+5V+10lg(1+Mo)], by precisely controlling the ratio of alloying elements such as carbon (C), silicon (Si), manganese (Mn), vanadium (V), aluminum (Al) and molybdenum (Mo), and clarifying the relative addition amounts of some key elements, the present invention achieves precise control of the mechanical properties of high-strength, high-hardness and lightweight steel for drones. Specifically, by controlling the parameter σ (an indicator reflecting the comprehensive content and ratio of alloying elements) between 0.13 and 2.3, it ensures that the steel achieves high hardness and high strength while avoiding problems such as a significant increase in alloy cost, complication of the preparation process, and composition segregation caused by excessively high σ values; at the same time, it prevents adverse effects such as insufficient hardness, unreasonable microstructure ratio, and decreased comprehensive mechanical properties caused by too low a σ value. Therefore, based on the lightweight and low-cost alloy element design and the M / A island and κ carbide structure design at the grain boundary, the alloy elements are controlled and the microstructure of the lightweight steel is regulated so that the microstructure of the lightweight steel is a multiphase structure of ferrite + M / A island + κ carbide, and better toughness is obtained while obtaining higher strength.

[0015] Furthermore, the temperature of the two-phase region insulation treatment is 1100-1200° C., and the time is 90 minutes.

[0016] Furthermore, the rolling process includes: hot rolling at the temperature of the two-phase region insulation treatment, then cooling to a first preset temperature at a first cooling rate, performing a second rolling after insulation, and finally cooling to 20-30°C at a second cooling rate.

[0017] Optionally, the deformation amount of the hot rolling treatment is 50-70%.

[0018] Optionally, the first cooling rate is 1-5°C / s.

[0019] Optionally, the first preset temperature is 1000-1100°C.

[0020] Optionally, the insulation time at the first preset temperature is 10 minutes.

[0021] Optionally, the deformation amount of the second rolling is 5-10%.

[0022] Optionally, the second cooling rate is 1-5°C / s.

[0023] After the steel to be treated undergoes two-phase heat preservation treatment and rolling treatment, a ferrite matrix, some M / A islands, and κ carbide structure are generated. If the temperature of the two-phase heat preservation treatment is higher than the temperature specified in the present invention, the grain size of the treated steel will be coarse. If the temperature of the two-phase heat preservation treatment is lower than the temperature specified in the present invention, it will cause uneven diffusion of elements inside the treated steel, resulting in structural segregation and other problems, thereby affecting the performance of the prepared lightweight steel. If the first preset temperature is lower or higher than the temperature specified in the present invention, it is not conducive to the control of grain size and volume fraction of the two-phase structure. Moreover, the first cooling rate can control the grain growth process during the cooling process. In addition, if the second cooling rate is higher than the above requirements, it will cause the material to crack.

[0024] Furthermore, the double-stage recrystallization heat treatment includes: heating to a second preset temperature at a heating rate of 5-30°C / s, keeping the temperature for 10-30s, and then cooling to a third preset temperature at a third cooling rate, and keeping the temperature for 30-60min.

[0025] Optionally, the second preset temperature is 950-1000°C.

[0026] Optionally, the third cooling rate is 15-35°C / s.

[0027] Optionally, the third preset temperature is 800-950°C.

[0028] During the dual-stage recrystallization heat treatment, if the second preset temperature is too high, the grains will be coarse and the material properties will be reduced. If it is too low, the elements will not be homogenized and the activation energy required for recrystallization will not be provided. Furthermore, within the second preset temperature, the volume fractions of the two phases can be controlled. Controlling the third preset temperature helps regulate the recrystallization size and grain boundary area.

[0029] Furthermore, the continuous annealing treatment includes: cooling to a fourth preset temperature at a fourth cooling rate and keeping the temperature for 60-120 minutes, and then cooling to 20-30° C. at a fifth cooling rate.

[0030] Optionally, the fourth cooling rate is less than 10°C / s.

[0031] Optionally, the fourth preset temperature is 450-700°C.

[0032] Optionally, the fifth cooling rate is 1-5°C / s.

[0033] If the fourth preset temperature is higher than the above-mentioned holding temperature, coarse κ carbide will precipitate and the grains will merge to form coarse grains. If it is lower than the fourth preset temperature, the κ carbide will precipitate unevenly and cannot precipitate along the ferrite grain boundaries. Moreover, the M / A island structure cannot be effectively obtained, which will result in insufficient strength and hardness of the obtained lightweight steel, affecting the use effect of the lightweight steel.

[0034] The second technical solution of the present invention is to provide a low-carbon, lightweight, high-strength ferritic steel produced by the above-mentioned preparation method.

[0035] The present invention discloses the following technical effects:

[0036] The present invention obtains a multiphase structure of a ferrite matrix and M / A islands + κ carbides distributed at the grain boundaries through microstructure control. The strength and hardness of the refined ferrite and M / A islands are increased through online heat treatment. M / A islands and κ carbides serve as important ways to control toughness. Combined with composition control, this solves the demand for lightweight steel and ensures that the lightweight steel has good comprehensive mechanical properties.

[0037] The present invention shortens the preparation process of lightweight steel by controlling the holding temperature, multi-stage thermal processing technology and cooling rate control, avoids complex cold rolling process, annealing process and aging process, greatly shortens the heat treatment time, reduces process production costs, improves production efficiency, and is conducive to the rapid and large-scale production of lightweight steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0039] Figure 1 This is the SEM image of the low-carbon, lightweight, high-strength ferritic steel prepared in Example 1.

[0040] Figure 2 This is the SEM image of the low-carbon, lightweight, high-strength ferritic steel prepared in Example 2.

[0041] Figure 3 This is the SEM image of the low-carbon, lightweight, high-strength ferritic steel prepared in Example 3. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0048] Unless otherwise specified, the "room temperature" and "normal temperature" involved in the specific embodiments of the present invention refer to 20-30°C.

[0049] The raw materials used in the present invention are all commercially available products, and the purchase channels do not affect the realization of the technical effects.

[0050] Example 1

[0051] The preparation steps of low carbon, lightweight and high strength ferritic steel include:

[0052] S1. Prepare steel to be treated, wherein the composition of the steel to be treated is, by mass percentage, C 0.28%, Mn 0.9%, Si 0.5%, Al 6.8%, Mo 0.18% and V 0.03%, with the balance being Fe and unavoidable impurities, and σ = 1.20;

[0053] S2, holding the steel at 1100°C for 90 minutes, then hot rolling at 1100°C with a deformation of 50%, then cooling to 1000°C at a cooling rate of 5°C / s and holding for 10 minutes, then rolling with a deformation of 5%, and finally cooling to 20°C at a cooling rate of 2°C / s;

[0054] After step S3 and step S2 are completed, the steel is heated to 950°C at a heating rate of 10°C / s and kept at this temperature for 10 seconds. Subsequently, the steel is cooled to 800°C at a cooling rate of 15°C / s and kept at this temperature for 30 minutes. The steel is then cooled to 450°C at a cooling rate of 8°C / s and kept at this temperature for 60 minutes. Finally, the steel is cooled to 20°C at a cooling rate of 1°C / s to obtain a low-carbon, lightweight, high-strength ferritic steel.

[0055] Figure 1 This is the SEM image of the low-carbon, lightweight, high-strength ferritic steel prepared in Example 1.

[0056] Testing revealed that the low-carbon, lightweight, high-strength ferritic steel produced in Example 1 consisted of ferrite, M / A islands, and kappa carbide, with contents of 61%, 21%, and 18%, respectively. The ferrite grain size was 6 μm, the M / A islands were 5.4 μm, and the kappa carbide was 1.2 μm. This low-carbon, lightweight, high-strength ferritic steel exhibited a hardness of 346 HV, a tensile strength of 780 MPa, an elongation of 13%, and an impact energy of 28 J.

[0057] Example 2

[0058] The preparation steps of low carbon, lightweight and high strength ferritic steel include:

[0059] S1. Prepare steel to be treated, wherein the composition of the steel to be treated is, by mass percentage, 0.32% C, 1.2% Mn, 0.6% Si, 7.2% Al, 0.20% Mo, and 0.02% V, with the balance being Fe and unavoidable impurities, and σ = 0.93;

[0060] S2, holding the steel at 1150° C. for 90 min, then hot rolling at 1150° C. with a deformation of 60%, then cooling to 1050° C. at a cooling rate of 3° C. / s and holding for 10 min, then rolling with a deformation of 7%, and finally cooling to 25° C. at a cooling rate of 4° C. / s;

[0061] After step S3 and step S2 are completed, the steel is heated to 980°C at a heating rate of 18°C / s and kept at this temperature for 10 seconds. Subsequently, the steel is cooled to 900°C at a cooling rate of 22°C / s and kept at this temperature for 40 minutes. The steel is then cooled to 580°C at a cooling rate of 5°C / s and kept at this temperature for 90 minutes. Finally, the steel is cooled to 25°C at a cooling rate of 3°C / s to obtain a low-carbon, lightweight, high-strength ferritic steel.

[0062] Figure 2 This is the SEM image of the low-carbon, lightweight, high-strength ferritic steel prepared in Example 2.

[0063] Testing revealed that the low-carbon, lightweight, high-strength ferritic steel produced in Example 2 consisted of ferrite, M / A islands, and κ carbide, with contents of 66%, 23%, and 11%, respectively. The ferrite grain size was 10 μm, the M / A islands were 6 μm, and the κ carbide was 2 μm. This low-carbon, lightweight, high-strength ferritic steel exhibited a hardness of 352 HV, a tensile strength of 792 MPa, an elongation of 10%, and an impact energy of 24 J.

[0064] Example 3

[0065] The preparation steps of low carbon, lightweight and high strength ferritic steel include:

[0066] S1. Prepare steel to be treated, wherein the composition of the steel to be treated is, by mass percentage, 0.42% C, 1.5% Mn, 0.8% Si, 7.8% Al, 0.25% Mo, and 0.05% V, with the balance being Fe and unavoidable impurities, and σ = 0.65;

[0067] S2, holding the steel at 1200° C. for 90 min, then hot rolling at 1200° C. with a deformation of 70%, then cooling to 1100° C. at a cooling rate of 5° C. / s and holding for 10 min, then rolling with a deformation of 10%, and finally cooling to 30° C. at a cooling rate of 8° C. / s;

[0068] S3. After step S2 is completed, heat to 1000°C at a heating rate of 25°C / s and keep warm for 25s, then cool to 950°C at a cooling rate of 30°C / s and keep warm for 60min, then cool to 670°C at a cooling rate of 2°C / s and keep warm for 100min, and finally cool to 30°C at a cooling rate of 1°C / s to obtain low-carbon, lightweight, high-strength ferritic steel.

[0069] Figure 3 This is the SEM image of the low-carbon, lightweight, high-strength ferritic steel prepared in Example 3.

[0070] Testing revealed that the low-carbon, lightweight, high-strength ferritic steel produced in Example 3 consisted of ferrite, M / A islands, and kappa carbide, with contents of 69%, 21%, and 10%, respectively. The ferrite grain size was 13 μm, the M / A islands were 3 μm, and the kappa carbide was 1.5 μm. This low-carbon, lightweight, high-strength ferritic steel exhibited a hardness of 368 HV, a tensile strength of 812 MPa, an elongation of 8%, and an impact energy of 20 J.

[0071] Comparative Example 1

[0072] The preparation steps of lightweight steel include:

[0073] S1. Prepare steel to be treated, wherein the composition of the steel to be treated is, by mass percentage, C 0.28%, Mn 0.9%, Si 0.5%, Al 6.8%, Mo 0.18% and V 0.03%, with the balance being Fe and unavoidable impurities, and σ = 1.20;

[0074] S2, holding the steel at 1250°C for 90 minutes, then hot rolling at 1150°C with a deformation of 50%, then cooling to 1000°C at a cooling rate of 5°C / s and holding for 10 minutes, then rolling with a deformation of 5%, and finally cooling to 20°C at a cooling rate of 2°C / s;

[0075] S3. After step S2 is completed, heat to 900°C at a heating rate of 10°C / s and keep warm for 10s, then cool to 750°C at a cooling rate of 15°C / s and keep warm for 30min, then cool to 400°C at a cooling rate of 8°C / s and keep warm for 60min, and finally cool to 20°C at a cooling rate of 1°C / s to obtain lightweight steel.

[0076] Testing revealed that the lightweight steel produced in Comparative Example 1 consisted of ferrite, M / A islands, and kappa carbide, with contents of 70%, 28%, and 2%, respectively. The ferrite grain size was 5.8 μm, the M / A islands were 6.5 μm, and the kappa carbide was 2 μm. This lightweight steel exhibited a hardness of 366 HV, a tensile strength of 810 MPa, an elongation of 7%, and an impact energy of 18 J.

[0077] Comparative Example 2

[0078] The preparation steps of lightweight steel include:

[0079] S1. Prepare steel to be treated, wherein the composition of the steel to be treated is, by mass percentage, 0.32% C, 1.2% Mn, 0.6% Si, 7.2% Al, 0.20% Mo, and 0.02% V, with the balance being Fe and unavoidable impurities, and σ = 0.93;

[0080] S2, holding the steel at 1150° C. for 90 min, then hot rolling at 1150° C. with a deformation of 60%, then cooling to 1050° C. at a cooling rate of 3° C. / s and holding for 10 min, then rolling with a deformation of 7%, and finally cooling to 25° C. at a cooling rate of 4° C. / s;

[0081] After step S3 and step S2 are completed, the steel is heated to 1050°C at a heating rate of 18°C / s and kept at this temperature for 10s, then cooled to 1000°C at a cooling rate of 22°C / s and kept at this temperature for 40min, then cooled to 580°C at a cooling rate of 5°C / s and kept at this temperature for 90min, and finally cooled to 25°C at a cooling rate of 3°C / s to obtain lightweight steel.

[0082] Testing revealed that the lightweight steel produced in Comparative Example 2 consisted of ferrite, M / A islands, and kappa carbide, with contents of 62%, 26%, and 12%, respectively. The ferrite grain size was 12 μm, the M / A islands were 7 μm, and the kappa carbide was 4.2 μm. This lightweight steel exhibited a hardness of 342 HV, a tensile strength of 762 MPa, an elongation of 11%, and an impact energy of 27 J.

[0083] Comparative Example 3

[0084] The preparation steps of lightweight steel include:

[0085] S1. Prepare steel to be treated, wherein the composition of the steel to be treated is, by mass percentage, 0.42% C, 1.5% Mn, 0.8% Si, 7.8% Al, 0.25% Mo, and 0.05% V, with the balance being Fe and unavoidable impurities, and σ = 0.65;

[0086] S2, holding the steel at 1050°C for 90 minutes, then hot rolling at 1050°C with a deformation of 70%, then cooling to 950°C at a cooling rate of 5°C / s and holding for 10 minutes, then rolling with a deformation of 10%, and finally cooling to 30°C at a cooling rate of 8°C / s;

[0087] S3. After step S2 is completed, heat to 1000°C at a heating rate of 25°C / s and keep warm for 25s, then cool to 950°C at a cooling rate of 30°C / s and keep warm for 60min, then cool to 850°C at a cooling rate of 2°C / s and keep warm for 100min, and finally cool to 30°C at a cooling rate of 1°C / s to obtain lightweight steel.

[0088] Testing revealed that the lightweight steel produced in Comparative Example 3 consisted of ferrite, M / A islands, and kappa carbide, with contents of 69%, 17%, and 14%, respectively. The ferrite grain size was 15 μm, the M / A islands were 4.5 μm, and the kappa carbide was 5.8 μm. This lightweight steel exhibited a hardness of 326 HV, a tensile strength of 740 MPa, an elongation of 10%, and an impact energy of 20 J.

[0089] Comparative Examples 1 to 3 of the present invention are solutions obtained by changing the relevant preparation process parameters of Examples 1 to 3. After testing, the performance parameters of Comparative Examples 1 to 3 have changed significantly after the preparation process parameters have been changed. Specifically:

[0090] Compared with Example 1, the parameters of Comparative Example 1 in steps S2 and S3 were changed, resulting in an increase in the ferrite and M / A island content and a decrease in κ carbide, thereby increasing strength and hardness, but significantly reducing plastic toughness. Compared with Example 2, the second and third preset temperatures in steps S2 and S3 of Comparative Example 2 were higher, resulting in an increase in the M / A island content and κ carbide, and a decrease in ferrite. Moreover, this resulted in an increase in the size of the above-mentioned three phases. Although its plastic toughness was slightly improved, its strength and hardness were significantly reduced. Compared with Example 3, the rolling temperature in steps S2 and S3 of Comparative Example 3 was lowered, the first preset temperature was lower, and the third preset temperature was higher, ultimately resulting in an increase in ferrite, M / A island content, and κ carbide size, and a slight increase in its plastic toughness, but a significant decrease in strength and hardness.

[0091] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0092] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one 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 invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing low-carbon, lightweight, high-strength ferritic steel, characterized in that the steps include: The steel to be treated is subjected to a two-phase region heat preservation treatment, followed by a rolling treatment, and then subjected to a double-stage recrystallization heat treatment and a continuous annealing treatment to obtain the low-carbon, lightweight, high-strength ferrite steel; In terms of mass percentage, in addition to Fe, the composition of the steel to be treated includes: C 0.25-0.45%, Si 0.40-0.80%, Al 6.5-8.0%, Mo 0.15-0.25%, Mn 0.80-1.5% and V 0.01-0.05%, as well as unavoidable impurities; The rolling process includes: hot rolling at the temperature of the two-phase region heat preservation treatment, then cooling to a first preset temperature at a first cooling rate, holding the temperature, and then performing a second rolling process, and finally cooling to 20-30° C. at a second cooling rate; The deformation amount of the hot rolling process is 50-70%; The first cooling rate is 1-5°C / s; The first preset temperature is 1000-1100°C; The holding time at the first preset temperature is 10 minutes; The deformation of the second rolling is 5-10%; The second cooling rate is 1-5°C / s.

2. The preparation method according to claim 1, wherein The chemical composition mass percentage ratio of C, Si, Al, Mo and Mn in the steel to be treated meets the following requirements: 0.13≤σ≤2.3, σ=0.5e (0.3Al-Mn) -0.25[4.2C-1.2Si+5V+10lg(1+Mo)].

3. The preparation method according to claim 1, wherein The temperature of the two-phase region heat preservation treatment is 1100-1200° C., and the time is 90 minutes.

4. The preparation method according to claim 1, wherein The dual-stage recrystallization heat treatment includes: heating to a second preset temperature at a heating rate of 5-30°C / s, keeping the temperature for 10-30s, and then cooling to a third preset temperature at a third cooling rate, and keeping the temperature for 30-60min.

5. The preparation method according to claim 4, wherein The second preset temperature is 950-1000°C; and / or, the third cooling rate is 15-35°C / s; and / or, the third preset temperature is 800-950°C.

6. The preparation method according to claim 1, wherein The continuous annealing treatment includes: cooling to a fourth preset temperature at a fourth cooling rate and keeping the temperature for 60-120 minutes, and then cooling to 20-30° C. at a fifth cooling rate.

7. The preparation method according to claim 6, wherein The fourth cooling rate is less than 10° C. / s; and / or the fourth preset temperature is 450-700° C.; and / or the fifth cooling rate is 1-5° C. / s.

8. Low-carbon, lightweight, high-strength ferritic steel produced by the production method according to any one of claims 1 to 7.

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