Preparation method of low-carbon light-weight high-strength ferrite steel

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a preparation method of low-carbon light-weight high-strength high-hardness ferrite steel. The low-carbon light-weight high-strength high-hardness ferrite steel is obtained by carrying out two-phase region heat preservation treatment on to-be-treated steel, then carrying out rolling treatment, and then carrying out two-stage recrystallization heat treatment and continuous annealing treatment. A ferrite matrix and a multiphase structure of M / A island + kappa carbide are obtained based on tissue regulation and control, the strength and hardness of refined ferrite and M / A island are improved through online heat treatment, the M / A island and kappa carbide serve as an important way for regulating and controlling the toughness, the requirement for light weight of the steel is met in combination with component control, and the production cost is reduced. And the excellent comprehensive mechanical property of the light steel is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and more specifically relates to a preparation method of a low-carbon, light-weight and high-strength ferrite steel. Background Art

[0002] The steel for unmanned aerial vehicles needs to have characteristics such as high strength, high toughness, low density, and good processing performance, and is mainly applied to fuselage frames, engine components, and protective components, etc. With the continuous progress of materials science, the performance of ferrite light-weight steel has been continuously improved, and its application fields will also be further expanded. Therefore, light-weight steel is expected to be widely used in the field of steel for unmanned aerial vehicles.

[0003] Many research institutions at home and abroad have conducted extensive research on light-weight steel. In the prior art, the patent document with the publication number of CN108642403A proposes a 780MPa grade ultra-high strength Fe-Mn-Al-C series light-weight cast steel and its preparation method. The chemical composition mass percentage of this low-density cast steel is: 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%, and P ≤ 0.01%, S ≤ 0.01%, N ≤ 0.01%, and the rest are Fe and unavoidable impurities. At the same time, the weight percentage of Mn and Al satisfies 2.5% ≤ Mn / Al ≤ 3.0%; the weight percentage of Nb and V satisfies 0.10% ≤ Nb + V ≤ 0.20%.

[0004] The patent document with the publication number of CN 116288020 A proposes an Fe-Mn-Al-Ni-Mo-C high-strength austenitic low-density steel and its preparation method, belonging to the field of metallic materials. The chemical composition mass percentage of the steel is: 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 rest are Fe and unavoidable impurities. By adding a certain amount of Ni and a small amount of Mo and Nb, Ni-A1 type B2 phases and a small amount of nano-scale (NbMo)C that pin grain boundaries are formed. Using Mo to promote the precipitation of granular micron-scale and nano-scale B2 phase particles, and at the same time inhibiting the precipitation of k during aging, the strength and work hardening ability are improved, and excellent strength-ductility matching is obtained. The tensile strength reaches 1500 - 1700MPa, the elongation rate reaches more than 30%, and the density is 6.6 - 6.9g / cm 3 。

[0005] The invention patent with the publication number CN118957214A provides a lightweight and 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 structure of the steel plate of this invention is all ferrite. The yield strength of the steel plate is ≥500MPa, the tensile strength is ≥600MPa, and the elongation after fracture A 50 ≥20%, and the damping coefficient is ≥0.05. By adding Cu and Al elements, the damping performance of the steel is improved, and the precipitation strengthening effect of Cu element is used to improve the strength of the steel, so that the steel plate has good mechanical properties while having high damping performance; in addition, the combined addition of Al and Cu can also effectively improve the corrosion resistance of the steel.

[0006] The lightweighting of traditional lightweight steel usually requires reducing the alloy element content or the material density, but this will lead to a significant decrease in strength and hardness; while adding high-cost alloy elements (such as Ni, Mo, etc.) can improve strength, plasticity and toughness, it is difficult to achieve the lightweight goal, and the preparation cost is relatively high, and segregation occurs, resulting in performance deterioration. This invention prepares a ferritic lightweight steel with better performance by regulating the structure through composition design and mechanical metallurgy means. Summary of the Invention

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

[0008] To achieve the above purpose, this invention provides the following solutions:

[0009] One of the technical solutions of this invention: provides a preparation method of a low-carbon lightweight and high-strength ferritic steel, and the steps include:

[0010] Subject the steel to be treated to two-phase region heat preservation treatment, then carry out rolling treatment, and then carry out double-stage recrystallization heat treatment and continuous annealing treatment to obtain the low-carbon lightweight and high-strength ferritic steel.

[0011] Further, by mass percentage, except for 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%, and inevitable impurities.

[0012] Conventional ferritic-based low-density lightweight steel, with the alloy composition range as follows: the mass fraction of Mn is 2% - 12%, the mass fraction of Al is 3% - 7%, and the mass fraction of C is 0.05% - 0.5%. Moreover, after hot rolling and cold rolling processes, the microstructure of the conventional ferritic-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 is affected by the contents of Mn and Al, which has a greater impact on the mechanical properties of the steel. The present invention rationally designs the chemical compositions of the lightweight high-strength ferritic steel, regulates the relative addition amounts between some key elements, and combines the mechanical metallurgy of online hot processing to control the microstructure, thereby playing a key regulatory role of relevant elements in the strength and toughness of the steel of the present invention. Therefore, the optimal composition selected in the present invention is as described above.

[0013] Optionally, the mass percentage ratio of the chemical compositions of C, Si, Al, Mo, and Mn in the steel to be treated conforms to: 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 functions and content control principles, the present invention rationally designs the alloy composition of a high-strength, high-hardness, lightweight steel for unmanned aerial vehicles. By precisely controlling the contents of various alloying elements, on the premise of a relatively low alloying cost, the hardness and comprehensive properties of the steel are significantly improved: C, Si, Mn, V, Al, and Mo. On the basis of reasonably controlling the chemical composition ranges of each element, at the same time, through the regulation formula: 0.13 ≤ σ ≤ 2.3, σ = 0.5e (0.3Al-Mn) -0.25[4.2C - 1.2Si + 5V + 10lg(1 + Mo)], by precisely regulating the ratios of alloying elements such as carbon (C), silicon (Si), manganese (Mn), vanadium (V), aluminum (Al), and molybdenum (Mo), and clarifying the relative addition amounts between some key elements, the present invention realizes the precise regulation of the mechanical properties of the high-strength, high-hardness, lightweight steel for unmanned aerial vehicles. Among them, by controlling the parameter σ (an index reflecting the comprehensive content and ratio of alloying elements) between 0.13 and 2.3, it is ensured that while the steel reaches high hardness and high strength, problems such as a significant increase in alloy cost, complication of the preparation process, and composition segregation caused by too high a σ value are avoided; at the same time, adverse effects such as insufficient hardness, unreasonable tissue ratio, and decline in comprehensive mechanical properties caused by too low a σ value are prevented. Therefore, based on the design of lightweight and low-cost alloying elements and the design of M / A islands and κ-carbide structures at grain boundaries, the alloying 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 islands + κ-carbides, and under the premise of obtaining higher strength, better toughness is obtained.

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

[0016] Furthermore, the rolling treatment includes: hot rolling at the temperature of the two-phase region heat treatment, then cooling to a first preset temperature at a first cooling rate, performing a second rolling after holding, 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 holding time at the first preset temperature is 10 min.

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

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

[0023] The steel to be processed generates a ferrite matrix, partial M / A islands, and κ carbide structures after the two-phase region heat treatment and rolling treatment. Among them, if the temperature of the two-phase region heat treatment is higher than the temperature defined in the present invention, it will cause the grain size of the processed steel to be coarse. If the temperature of the two-phase region heat treatment is lower than the temperature defined in the present invention, it will cause uneven diffusion of internal elements in the processed steel, resulting in problems such as tissue segregation, which will further affect the service performance of the prepared lightweight steel. If the first preset temperature is lower than or higher than the temperature defined in the present invention, it is not conducive to the control of the grain size and the volume fraction of the duplex structure. Moreover, the first cooling rate can control the grain growth process during cooling. 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, holding for 10 - 30 s, then cooling to a third preset temperature at a third cooling rate, and holding for 30 - 60 min.

[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 double-stage recrystallization heat treatment, if the second preset temperature is too high, it will cause the grains to be coarse, reducing the material properties. If it is too low, the elements cannot be homogenized, and the activation energy required for recrystallization cannot be provided. Additionally, within the second preset temperature, the volume fractions of the two phases can be controlled; controlling the third preset temperature is beneficial for regulating the recrystallization size and the grain boundary area.

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

[0030] Optionally, the fourth cooling rate < 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 holding temperature, it will cause the precipitation of coarse κ-carbides and the grains to merge to form coarse grains. If it is lower than the fourth preset temperature, it will cause the uneven precipitation of κ-carbides, which 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] Technical solution two of the present invention: Provide a low-carbon lightweight high-strength ferritic steel prepared by the above preparation method.

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

[0036] Based on microstructure regulation, the present invention obtains a multiphase structure of a ferrite matrix and M / A islands + κ-carbides distributed at grain boundaries. Through online heat treatment, the refined ferrite and M / A islands increase the strength and hardness. The M / A islands and κ-carbides are important ways to regulate toughness. Combined with composition control, the lightweight requirement of the steel is solved, ensuring that the lightweight steel has good comprehensive mechanical properties.

[0037] By coupling regulation such as controlling the holding temperature, multi-stage hot working process, and cooling rate control, the present invention shortens the preparation process of the lightweight steel, avoids complex cold rolling processes, annealing processes, and aging processes, greatly shortens the heat treatment time, reduces the process production cost, improves the production efficiency, and is beneficial for the rapid and large-scale production of the lightweight steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

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

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

[0041] Figure 3 SEM image of the low-carbon lightweight high-strength ferrite steel prepared in Example 3. Detailed implementation manners

[0042] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation to the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0043] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation 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 related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0045] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the specification of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are also obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0046] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0047] It should be noted that the aspects not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

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

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

[0050] Example 1

[0051] The preparation steps of the low-carbon lightweight high-strength ferrite steel include:

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

[0053] S2. Keep the above-mentioned steel to be processed at 1100°C for 90 min, then perform hot rolling with a 50% deformation at 1100°C, then cool it to 1000°C at a cooling rate of 5°C / s and keep it for 10 min, then perform rolling with a 5% deformation, and finally cool it to 20°C at a cooling rate of 2°C / s;

[0054] S3. After step S2 is completed, heat it to 950°C at a heating rate of 10°C / s and keep it for 10 s, then cool it to 800°C at a cooling rate of 15°C / s and keep it for 30 min, then cool it to 450°C at a cooling rate of 8°C / s and keep it for 60 min, and finally cool it to 20°C at a cooling rate of 1°C / s to obtain the low-carbon lightweight high-strength ferrite steel.

[0055] Figure 1 SEM diagram of the low-carbon lightweight high-strength ferrite steel prepared in Example 1.

[0056] After testing, the microstructure of the low-carbon lightweight high-strength ferrite steel prepared in Example 1 is ferrite, M / A island and κ carbide microstructure, and the contents are 61%, 21% and 18% respectively. Among them, the ferrite grain size is 6 μm, the M / A island size is 5.4 μm, and the κ carbide size is 1.2 μm. The hardness of this low-carbon lightweight high-strength ferrite steel is 346 HV, the tensile strength is 780 MPa, the elongation is 13%, and the impact energy is 28 J.

[0057] Example 2

[0058] The preparation steps of the low-carbon lightweight high-strength ferrite steel include:

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

[0060] S2. Keep the above-mentioned steel to be processed at 1150 °C for 90 min, then perform hot rolling with a 60% reduction at 1150 °C, then cool it to 1050 °C at a cooling rate of 3 °C / s and keep it for 10 min, then perform rolling with a 7% reduction, and finally cool it to 25 °C at a cooling rate of 4 °C / s;

[0061] S3. After step S2 is completed, heat it to 980 °C at a heating rate of 18 °C / s and keep it for 10 s, then cool it to 900 °C at a cooling rate of 22 °C / s and keep it for 40 min, then cool it to 580 °C at a cooling rate of 5 °C / s and keep it for 90 min, and finally cool it to 25 °C at a cooling rate of 3 °C / s to obtain a low-carbon lightweight high-strength ferrite steel.

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

[0063] After testing, the structure of the low-carbon lightweight high-strength ferrite steel prepared in Example 2 is ferrite, M / A islands and κ-carbide structure, with contents of 66%, 23% and 11% respectively. Among them, the ferrite grain size is 10 μm, the M / A island size is 6 μm, and the κ-carbide size is 2 μm. The hardness of this low-carbon lightweight high-strength ferrite steel is 352 HV, the tensile strength is 792 MPa, the elongation is 10%, and the impact energy is 24 J.

[0064] Example 3

[0065] The preparation steps of the low-carbon lightweight high-strength ferrite steel include:

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

[0067] S2. Keep the above-mentioned steel to be processed at 1200 °C for 90 min, then perform hot rolling with a 70% reduction at 1200 °C, then cool it to 1100 °C at a cooling rate of 5 °C / s and keep it for 10 min, then perform rolling with a 10% reduction, and finally cool it to 30 °C at a cooling rate of 8 °C / s;

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

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

[0070] After testing, the microstructure of the low-carbon lightweight high-strength ferrite steel prepared in Example 3 is ferrite, M / A islands and κ-carbide microstructure, with contents of 69%, 21% and 10% respectively. Among them, the ferrite grain size is 13 μm, the M / A island size is 3 μm, and the κ-carbide size is 1.5 μm. The hardness of this low-carbon lightweight high-strength ferrite steel is 368 HV, the tensile strength is 812 MPa, the elongation is 8%, and the impact energy is 20 J.

[0071] Comparative Example 1

[0072] The preparation steps of the lightweight steel include:

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

[0074] S2. Keep the above-mentioned steel to be treated at 1250 °C for 90 min, then perform hot rolling with a 50% reduction at 1150 °C, then cool it to 1000 °C at a cooling rate of 5 °C / s and hold for 10 min, then perform rolling with a 5% reduction, and finally cool it to 20 °C at a cooling rate of 2 °C / s;

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

[0076] After testing, the microstructure of the lightweight steel prepared in Comparative Example 1 is ferrite, M / A islands and κ-carbide microstructure, with contents of 70%, 28% and 2% respectively. Among them, the ferrite grain size is 5.8 μm, the M / A island size is 6.5 μm, and the κ-carbide size is 2 μm. The hardness of this lightweight steel is 366 HV, the tensile strength is 810 MPa, the elongation is 7%, and the impact energy is 18 J.

[0077] Comparative Example 2

[0078] The preparation steps of the light steel include:

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

[0080] S2. Keep the above-mentioned steel to be processed at 1150°C for 90 min, then perform hot rolling with a deformation amount of 60% at 1150°C, then cool it to 1050°C at a cooling rate of 3°C / s and keep it for 10 min, then perform rolling with a deformation amount of 7%, and finally cool it to 25°C at a cooling rate of 4°C / s;

[0081] S3. After step S2 is completed, heat it to 1050°C at a heating rate of 18°C / s and keep it for 10 s, then cool it to 1000°C at a cooling rate of 22°C / s and keep it for 40 min, then cool it to 580°C at a cooling rate of 5°C / s and keep it for 90 min, and finally cool it to 25°C at a cooling rate of 3°C / s to obtain the light steel.

[0082] After testing, the microstructure of the light steel prepared in Comparative Example 2 is ferrite, M / A island and κ carbide microstructure, and the contents are 62%, 26% and 12% respectively. Among them, the ferrite grain size is 12 μm, the M / A island size is 7 μm, and the κ carbide size is 4.2 μm. The hardness of this light steel is 342 HV, the tensile strength is 762 MPa, the elongation is 11%, and the impact energy is 27 J.

[0083] Comparative Example 3

[0084] The preparation steps of the light steel include:

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

[0086] S2. Keep the above-mentioned steel to be processed at 1050°C for 90 min, then perform hot rolling with a deformation amount of 70% at 1050°C, then cool it to 950°C at a cooling rate of 5°C / s and keep it for 10 min, then perform rolling with a deformation amount of 10%, and finally cool it to 30°C at a cooling rate of 8°C / s;

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

[0088] After testing, the microstructure of the lightweight steel prepared in Comparative Example 3 is ferrite, M / A islands and κ-carbide microstructure, with contents of 69%, 17% and 14% respectively. Among them, the ferrite grain size is 15 μm, the M / A island size is 4.5 μm, and the κ-carbide size is 5.8 μm. The hardness of this lightweight steel is 326 HV, the tensile strength is 740 MPa, the elongation is 10%, and the impact energy is 20 J.

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

[0090] Compared with Example 1, the parameters in steps S2 and S3 of Comparative Example 1 have changed, resulting in an increase in the contents of ferrite and M / A islands and a decrease in κ-carbide, thereby increasing the strength and hardness, but significantly reducing the plasticity and toughness. Compared with Example 2, the second and third preset temperatures in steps S2 and S3 of Comparative Example 2 are higher, resulting in an increase in the content of M / A islands and κ-carbide and a decrease in ferrite. Moreover, this leads to an increase in the sizes of the above three phases. Although its plasticity and toughness increase slightly, the strength and hardness decrease significantly. Compared with Example 3, in Comparative Example 3, the rolling temperature in steps S2 and S3 is lower, the first preset temperature is lower, and the third preset temperature is higher. Finally, it results in an increase in the contents of ferrite, M / A islands and the size of κ-carbide. Its plasticity and toughness increase slightly, but the strength and hardness decrease significantly.

[0091] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0092] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will 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 two-stage recrystallization heat treatment and a continuous annealing treatment, so as to obtain the low-carbon, light-weight, high-strength ferrite steel; 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 inevitable impurities.

2. The preparation method according to claim 1, characterized in that 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, characterized in that: 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, characterized in that: The rolling treatment comprises: 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, performing a second rolling after heat preservation, and finally cooling to 20-30° C. at a second cooling rate.

5. The preparation method according to claim 4, characterized in that: The deformation amount of the hot rolling treatment is 50-70%; and / or, the first cooling rate is 1-5°C / s; and / or, the first preset temperature is 1000-1100°C; and / or, the insulation time at the first preset temperature is 10 minutes; and / or, the deformation amount of the second rolling is 5-10%; and / or, the second cooling rate is 1-5°C / s.

6. The preparation method according to claim 1, characterized in that: 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, cooling to a third preset temperature at a third cooling rate, and keeping the temperature for 30-60min.

7. The preparation method according to claim 6, characterized in that: 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.

8. The preparation method according to claim 1, characterized in that: 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.

9. The preparation method according to claim 8, characterized in that: 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.

10. Low-carbon, lightweight, high-strength ferritic steel obtained by the preparation method according to any one of claims 1 to 9.

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