Method for producing high-quality IF steel with high N content and short process

Abstract

The invention relates to a method for producing high-quality IF steel with high N content in a short process, and belongs to the technical field of ferrous metallurgy. The method comprises the following steps: obtaining a casting blank with set chemical components; the casting blank is sequentially heated, rolled and curled, and a hot-rolled coil is obtained; the hot-rolled coil is subjected to cold rolling, and a cold hard coil is obtained; and the cold hard coil is continuously annealed, and the finished IF steel is obtained. By reasonably designing chemical components of the IF steel, increasing the tapping temperature, the finish rolling temperature and the coiling temperature in the hot rolling process and controlling textures generated in the cold rolling and annealing processes, the high gamma texture proportion and the high plastic strain ratio in the finished IF steel are achieved, and therefore the problem that the high-quality IF steel is difficult to produce due to the fact that the N content in electric furnace steelmaking is high is effectively solved.

Description

Technical Field

[0001] The present application relates to the technical field of iron and steel metallurgy, and in particular to a method for producing high-quality IF steel with a high nitrogen content and a short process. Background Art

[0002] Due to the high nitrogen content of scrap steel raw materials, the ionized air during the electric smelting process causes the steel liquid to absorb nitrogen, and the semi-closed structure of the electric furnace causes the steel liquid to absorb nitrogen when it comes into contact with the air, the N content in the molten steel of the electric furnace with a large scrap ratio is difficult to control below 30ppm. For IF (Interstitial Free Steel) steel without interstitial atoms, its composition is required to be very pure, with a carbon content of less than 50ppm and a nitrogen content of less than 30ppm, so that IF steel can obtain excellent formability and surface quality. The high N content caused by the short process of the electric furnace itself makes it impossible for the N element to precipitate completely, and the residual N element is dissolved in the Fe matrix, resulting in the inability to obtain IF steel by conventional rolling methods. At the same time, the r value of the annealed or galvanized finished product of its high N content product is reduced to below 2.5, affecting normal use. Traditional adjustment methods will lead to defects such as inclusions, uneven iron scale or poor forming performance. Therefore, the production of high-N and high-quality IF steel by short process technology has become an industry problem.

[0003] In order to solve the problem of high nitrogen content in electric furnace steelmaking, Beijing University of Science and Technology proposed a method to reduce the nitrogen content in steel to obtain low-nitrogen steel in the electric furnace steelmaking process. Shandong Iron and Steel Co., Ltd. proposed a nitrogen control method for the entire process of electric furnace steelmaking, and through various control methods, it ensured that the average nitrogen content of the steel grade was reduced to 40-50ppm. However, through existing means, it is still difficult to stably control the nitrogen content of electric furnace molten steel to below 30ppm at a low cost or simple process, reaching the level of conventional converter steelmaking. Therefore, it is necessary to solve the technical problem of solid solution of excess N elements from other ways to achieve the production of high-N and high-quality IF steel with a short process. Summary of the invention

[0004] The present application provides a method for producing high-quality IF steel with a high N content and a short process, so as to solve the following technical problem: how to produce high-quality IF steel with a higher N content.

[0005] The present application provides a method for producing high-quality IF steel with a high nitrogen content and a short process, the method comprising: Obtaining a casting billet with a set chemical composition; The ingot is sequentially heated, rolled and coiled to obtain a hot rolled coil; Cold rolling the hot rolled coil to obtain a chilled coil; The chilled coil is continuously annealed to obtain finished IF steel.

[0006] Optionally, the set chemical composition includes, by mass fraction: C≤0.0020%, Si≤0.030%, Mn:≤0.2%, N: 0.003%~0.008%, Al: 0.060%~0.12%, Ti: 0.030%~0.100%, V: 0.001%~0.050%, Nb: 0.001%~0.030%.

[0007] Optionally, the thickness of the ingot is 220 mm to 250 mm, the heated furnace-out temperature is 1100° C. to 1250° C., and the heating furnace time is 100 min to 180 min.

[0008] Optionally, the final rolling temperature is 850°C to 950°C, and the coiling temperature is 680°C to 730°C.

[0009] Optionally, the cold rolling adopts an acid rolling combined unit, and the total reduction rate of the cold rolling is 80% to 90%.

[0010] Optionally, the microstructure of the chilled coil includes a second γ texture and an α texture, the α texture forms a lamellar structure, the lamellar spacing of the lamellar structure is 5 μm to 15 μm, and the area percentage of the second γ texture is >30%.

[0011] Optionally, the soaking temperature of the annealing is 790° C. to 820° C., and the strip speed of the annealing is 220 mpm to 280 mpm.

[0012] Optionally, the microstructure of the finished IF steel satisfies at least one of the following: an average grain size of 18 μm to 30 μm, a grain size of level 7 to 8, and an area percentage of the first γ texture > 60%.

[0013] Optionally, the finished IF steel meets at least one of the following properties: yield strength of 145MPa to 200MPa, tensile strength of 290MPa to 320MPa, elongation ≥44%, plastic strain ratio ≥2.5, and work hardening index ≥0.23.

[0014] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art: The present application provides a method for producing high-quality IF steel with a high nitrogen content in a short process, the method comprising: obtaining a cast billet with a set chemical composition; heating, rolling and curling the cast billet in sequence to obtain a hot-rolled coil; cold-rolling the hot-rolled coil to obtain a chilled coil; and continuously annealing the chilled coil to obtain a finished IF steel. By rationally designing the chemical composition of IF steel, adding alloy elements that can form stable compounds with nitrogen to fix nitrogen; increasing the furnace discharge temperature, final rolling temperature and coiling temperature during hot rolling, promoting the full growth and precipitation of alloy nitrides during the hot rolling stage, and reducing their adverse effects on product performance in subsequent processing; by controlling the texture during cold rolling and annealing, optimizing the crystal orientation of the steel plate, increasing the nucleation points of the γ texture (i.e., favorable deep drawing texture), promoting the rapid growth of the nucleation grains, and achieving a high γ texture ratio and a high plastic strain ratio, thereby effectively solving the problem that it is difficult to produce high-quality IF steel with a high nitrogen content in electric furnace steelmaking. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0017] Figure 1 A schematic diagram of a process for producing high-quality IF steel with a high nitrogen content and a short process provided in an embodiment of the present application; Figure 2 The ODF diagram of the IF steel provided in Example 1 of the present application; Figure 3 This is the XRD spectrum of the hot-rolled sample of IF steel provided in Example 4 of the present application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0019] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the 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., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0020] In this document, the terms including "including" and "including" mean "including but not limited to". Relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "plurality" 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 all mean: a, b, c, ab (i.e. a and b), ac, bc, or abc, where a, b, and c can be single or plural. Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0021] This application provides a method for producing high-quality IF steel with high N content in a short process, see Figure 1 , the method comprising: S1, obtaining a casting billet with a set chemical composition; In some embodiments, the set chemical composition includes, by mass fraction: C≤0.0020%, Si≤0.030%, Mn:≤0.2%, N: 0.0030%~0.008%, Al: 0.060%~0.12%, Ti: 0.030%~0.100%, V: 0.001%~0.050%, Nb: 0.001%~0.030%.

[0022] This application uses scrap steel, cast iron blocks, sponge iron and molten iron as raw materials for electric furnace smelting. The purpose of the configuration of cast iron blocks, sponge iron and molten iron is to reduce the amount of nitrogen absorbed during the electric furnace smelting process, and at the same time, with refining, the nitrogen content of the steel output meets 0.0030% to 0.008%. The proportion of scrap steel in the raw materials is 70% to 80%. This proportion of scrap steel will not introduce too many residual elements, thereby having a great impact on the performance of this product. At the same time, it responds to the national "dual carbon" policy and achieves a significant reduction in carbon emissions from products. The molten steel enters the continuous casting system to cast a 220mm-250mm thick ingot, ensuring that the composition of the ingot meets C≤0.0020%, Si≤0.030%, Mn:≤0.2%, N:0.003%-0.008%, Al:0.060%-0.12%, Ti:0.030%-0.100%, V:0.001%-0.050%, Nb:0.001%-0.030%. Among them, when the N content is low, the Al / N ratio is about 20. As the N content increases, the Al / N ratio gradually decreases to 15, and the proportion of other alloy elements is increased to achieve the purpose of complete N solidification.

[0023] The positive effect of limiting the C content to ≤ 0.0020% is that a lower C content helps reduce the number of interstitial atoms in the steel, which can easily cause lattice distortion in the steel and affect the mechanical properties and processing properties of the steel. By strictly controlling the C content, the purity of the steel can be significantly improved, the content of harmful elements can be reduced, and the overall quality of the steel can be improved to ensure that the steel produced is IF steel. For example, the C content can be 0.0004%, 0.0008%, 0.0012%, 0.0016%, 0.0020%, etc.

[0024] Positive effects of limiting the Si content to ≤0.030%: Si is a commonly used alloying element, which can cause a solid solution strengthening effect in steel and increase the strength of the steel. However, in the preparation of IF steel, a Si content higher than 0.030% may weaken other favorable properties of the steel, such as deep drawing performance and ductility. By limiting the Si content to a lower level (≤0.030%), the solid solution strengthening effect caused by Si can be reduced, making the steel easier to plastically deform and improving the formability of the steel. Exemplarily, the Si content can be 0.005%, 0.010%, 0.015%, 0.020%, 0.025%, 0.030%, etc.

[0025] Positive effects of limiting the content of Mn to ≤ 0.2%: Mn is an effective solid solution strengthening element. Mn is added to ensure that IF steel has a certain strength. By limiting the content of Mn, the strength of IF steel can be controlled not to exceed the upper limit and sufficient tensile deformation capacity can be maintained. For example, the content of Mn can be 0.14%, 0.145%, 0.15%, 0.155%, 0.16%, etc.

[0026] The positive effect of limiting the N content to 0.0030% to 0.008% is that due to the influence of raw materials and electric furnace technology, the steelmaking process needs to reduce the N content as much as possible, so the upper limit of the N content is controlled to 0.008%, and the process limits the N content to be unable to be lower than 0.0030%. For example, the N content can be 0.0030%, 0.0040%, 0.0050%, 0.0060%, 0.0070%, 0.008%, etc.

[0027] The positive effect of limiting the Al content to 0.060% to 0.12% is that in addition to traditional alloying elements such as Nb, V, and Ti, Al can also form a large-sized AlN precipitate phase with the N element, ensuring that a relatively pure ferrite matrix is ​​obtained when the N element is increased in the short process. For example, the Al content can be 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, etc.

[0028] The positive effect of limiting the Ti content to 0.030% to 0.100% is: the interstitial atoms such as C and N are reduced by Ti treatment, so that the r value of the product is greatly improved. Since the N content in the molten iron in the short process is relatively high, the Ti content needs to be controlled above 0.030%, and Ti combines with N to form TiN particles with sharp corners, which can easily lead to stress concentration during the stamping process. Therefore, the Ti content needs to be controlled not higher than 0.100% to prevent excessive TiN precipitation from affecting the forming properties of the material. Exemplarily, the Ti content can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, etc.

[0029] The positive effect of limiting the V content to 0.001% to 0.050% is that vanadium is a strong carbonitride-forming element in steel, and can form fine VN (vanadium nitride) and VC (vanadium carbide) particles. For example, the V content can be 0.001%, 0.010%, 0.015%, 0.020%, 0.025%, 0.030%, 0.035%, 0.040%, 0.045%, 0.050%, etc.

[0030] The positive effect of limiting the Nb content to 0.001% to 0.030% is: adding alloying elements above the lower limit of the composition first combines with C and N to form a large particle precipitation phase to prevent the fine dispersed precipitation from having an adverse effect on the finished product texture, thereby affecting the r value. The addition content of alloying elements is not higher than the upper limit to ensure that the yield and tensile strength of the product are not greatly increased due to solid solution strengthening or precipitation strengthening, affecting the forming performance during stamping. Exemplarily, the Nb content can be 0.001%, 0.005%, 0.010%, 0.015%, 0.020%, 0.025%, 0.030%, etc.

[0031] In some embodiments, the thickness of the ingot is 220 mm to 250 mm.

[0032] S2, heating, rolling and coiling the ingot in sequence to obtain a hot rolled coil; This step can ensure that the alloy elements can fully fix N, and that precipitates such as AlN, Nb(CN), and VN have sufficient energy and time to grow to form large spherical precipitates. This can, on the one hand, eliminate the pinning effect of N elements as interstitial atoms on dislocations and their influence on the active slip system during the cold rolling process, thereby optimizing the microstructure of the cold-hardened product. On the other hand, coarse precipitates are beneficial to the optimization of the annealing microstructure and the improvement of the performance of the finished product.

[0033] In some embodiments, the heating furnace temperature is 1100° C. to 1250° C., and the heating furnace time is 100 min to 180 min.

[0034] The positive effect of limiting the heating furnace temperature to 1100℃~1250℃: This temperature range can effectively ensure that the ingot is evenly and fully heated throughout the heating process. The high temperature enables the internal structure of the ingot to be fully austenitized, eliminates or reduces the stress and defects inside the ingot, and provides a good foundation for the subsequent rolling process. In addition, this temperature range can significantly improve the plasticity and toughness of the ingot, reduce the deformation resistance during the rolling process, make the rolling process smoother, reduce the fluctuation of the rolling force, and thus improve the production efficiency and product quality of the rolling mill. Exemplarily, the furnace temperature can be 1100℃, 1125℃, 1150℃, 1175℃, 1200℃, 1225℃, 1250℃, etc.

[0035] The positive effects of limiting the heating time in the furnace to 100 minutes to 180 minutes are: ensuring the uniformity of the temperature of the ingot, facilitating the uniform distribution of elements and structures inside the ingot, and ensuring the stability of hot rolling. For example, the time in the furnace can be 100 minutes, 120 minutes, 140 minutes, 160 minutes, 180 minutes, etc.

[0036] In some embodiments, the final rolling temperature is 850°C to 950°C, and the coiling temperature is 680°C to 730°C.

[0037] The positive effect of limiting the final rolling temperature of rolling to 850℃~950℃: For IF steel, the final rolling temperature within this range can ensure rolling in the austenite single-phase region. This is conducive to obtaining a uniform ferrite structure and improving the mechanical properties and formability of the steel. A final rolling temperature below 850℃ may cause the steel to enter the non-single-phase region, increase the difficulty of rolling, and may produce undesirable structures, such as mixed structures or banded structures, affecting the performance of the steel. In addition, final rolling within this temperature range can ensure that the hot-rolled structure has fine grains, which is conducive to improving the uniformity of deformation of the finished product. Exemplarily, the final rolling temperature can be 850℃, 870℃, 890℃, 910℃, 930℃, 950℃, etc.

[0038] The positive effect of limiting the coiling temperature to 680°C to 730°C is to ensure the growth of precipitates and deep drawing performance. For example, the coiling temperature can be 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, etc.

[0039] S3, cold rolling the hot rolled coil to obtain a chilled coil; In some embodiments, the cold rolling adopts an acid rolling combined unit, and the total reduction rate of the cold rolling is 80% to 90%.

[0040] The pickling and cold rolling combined unit is an efficient and continuous steel production equipment, which combines the two processes of pickling and cold rolling in one unit, realizing the continuous pickling and rolling of hot-rolled steel coils. The pickling and cold rolling combined unit first performs pickling treatment before cold rolling, which can effectively remove the oxide scale and rust on the surface of the hot-rolled coil, reduce the roll surface contamination during the cold rolling process, and thus improve the surface quality of the chilled coil.

[0041] The positive effect of limiting the total cold rolling reduction rate to 80% to 90% is that the cold-hardened product has a higher γ texture ratio by controlling the cold rolling reduction rate. For example, the total cold rolling reduction rate can be 80%, 82%, 84%, 86%, 88%, 90%, etc.

[0042] In some embodiments, the microstructure of the chilled coil includes a second γ texture and an α texture, the α texture forms a lamellar structure, the lamellar spacing of the lamellar structure is 5 μm to 15 μm, and the area percentage of the second γ texture is >30%.

[0043] By controlling the higher γ texture ratio in the cold hardened product, the γ texture that is beneficial to deep drawing can be rapidly nucleated in large quantities at an early stage during the annealing process. By controlling the size and morphology of the precipitated phase, a spherical large-particle precipitated phase is obtained, so that the grain boundary migration of the γ texture grains is not hindered during the growth process, and other oriented grains can be quickly engulfed. Exemplarily, the area percentage of the second γ texture can be 30%, 31%, 32%, 33%, 34%, 35%, etc.

[0044] S4, continuously annealing the chilled coil to obtain finished IF steel; In some embodiments, the soaking temperature of the annealing is 790° C. to 820° C., and the strip speed of the annealing may be 220 mpm to 280 mpm.

[0045] The annealing temperature and belt speed are controlled so that the γ texture that is beneficial to deep drawing can be rapidly nucleated in large quantities at an early stage during the annealing process. The annealing temperature and belt speed will also affect the size and morphology of the precipitated phase, and obtain a spherical large-particle precipitated phase, so that the grain boundary migration during the growth of the γ texture grains is not hindered, and other oriented grains can be quickly engulfed, and finally a short-process high-N high-formability IF steel product is formed. Exemplarily, the annealing soaking temperature can be 790°C, 795°C, 800°C, 805°C, 810°C, 815°C, 820°C, etc.; the annealing strip speed can be 220mpm, 230mpm, 240mpm, 250mpm, 260mpm, 270mpm, 280mpm, etc.

[0046] IF steel, the full name of which is Interstitial-Free Steel, is interstitial-free steel, sometimes also called ultra-low carbon steel. This steel has excellent deep drawing properties and is widely used in the automotive industry and other fields.

[0047] In some embodiments, the microstructure of the finished IF steel satisfies at least one of the following conditions: an average grain size of 18 μm to 30 μm, a grain size of level 7 to 8, and an area percentage of the first γ texture > 60%.

[0048] Grain size is an important parameter in microstructure, which directly affects the strength and toughness of steel. Within this range, the grain size of IF steel is moderate, which ensures sufficient strength and maintains good toughness. Exemplarily, the average grain size can be 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, etc.

[0049] Grain size is another way to express grain size, usually compared through standard graphs. In the grain size range of 7 to 8, it means that the grains are relatively small and uniform. This uniform fine-grained structure helps to improve the mechanical properties of steel, especially fatigue resistance and toughness. Exemplarily, the grain size can be 7, 8, etc.

[0050] γ texture (favorable deep drawing texture) is a favorable texture type in IF steel, which is crucial to improving the deep drawing performance of steel. When the first γ texture area percentage is >60%, IF steel generally exhibits excellent deep drawing performance, including high plastic strain ratio and low plane anisotropy. Exemplarily, the γ texture area percentage can be 60%, 61%, 62%, 63%, 64%, 65%, etc.

[0051] In some embodiments, the finished IF steel meets at least one of the following properties: yield strength of 145MPa to 200MPa, tensile strength of 290MPa to 320MPa, elongation ≥44%, plastic strain ratio ≥2.5, and work hardening index ≥0.23.

[0052] Yield strength is the stress required for a material to begin to undergo significant plastic deformation. In this application, the yield strength ranges from 145 MPa to 200 MPa. This means that when stress is applied to such a material, it needs to reach a stress of at least 145 MPa (but not more than 200 MPa) before it begins to undergo significant plastic deformation. Exemplarily, the yield strength may be 145 MPa, 155 MPa, 165 MPa, 175 MPa, 185 MPa, 195 MPa, 200 MPa, etc.

[0053] Tensile strength is the maximum stress that a material can withstand before breaking. In this application, the range of tensile strength is 290MPa to 320MPa. This means that in a tensile test, the maximum stress that this material can withstand is a value between 290MPa and 320MPa, exceeding this value, and the material will break. Exemplarily, the tensile strength can be 290MPa, 295MPa, 300MPa, 305MPa, 310MPa, 315MPa, 320MPa, etc.

[0054] Elongation, elongation refers to the ratio of the increase in length of a specimen when it is stretched to break to the original length, usually expressed as a percentage. It reflects the ability of a material to undergo plastic deformation during stretching. For example, the elongation can be 44%, 45%, 46%, 47%, 48%, 49%, 50%, etc.

[0055] The plastic strain ratio is the ratio of the strain in the width direction to the strain in the thickness direction of the metal sheet during the stretching process. Usually, when the strip specimen is stretched on a tensile testing machine to produce a tensile deformation of 20%, the ratio of the strains in these two directions is defined as the plastic strain ratio. The plastic strain ratio reflects the ability of the metal sheet to resist thinning or thickening when subjected to tension or pressure. When the sheet is formed, the larger the plastic strain ratio, the greater the tensile strength, the smaller the deformation resistance, and the more favorable it is for forming. Especially in the drawing process, materials with a large plastic strain ratio can better resist concentrated instability and wrinkling, thereby improving the drawing performance of the sheet. Exemplarily, the plastic strain ratio can be 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, etc.

[0056] The work hardening index, also known as the hardening index in English, is an important parameter for evaluating the performance of metal materials in plastic deformation. This index is one of the important indicators for evaluating the forming performance of sheet metal, which reflects the strengthening ability of sheet metal deformation and the ability to resist instability. In addition, the work hardening index has a significant effect on the forming limit curve of the sheet metal. The larger the work hardening index, the higher the forming limit curve of the material, indicating that the material can withstand greater strain without damage during plastic deformation. Exemplarily, the work hardening index can be 0.23, 0.24, etc.

[0057] The present application is further described below in conjunction with specific examples. The experimental methods in the following examples that do not specify specific conditions are usually measured according to industry standards; if there are no corresponding industry standards, they are carried out according to common international standards, conventional conditions, or conditions recommended by the manufacturer.

[0058] After smelting in an electric furnace, the chemical composition of the ingot is shown in Table 1.

[0059] Table 1 Chemical composition of ingot (wt %) Based on the chemical composition of the ingot of the embodiment, this embodiment also provides a method for producing high-quality IF steel with a high nitrogen content and a short process, comprising the following steps: Obtaining a casting billet with a set chemical composition; The ingot is sequentially heated, rolled and coiled to obtain a hot rolled coil; Cold rolling the hot rolled coil to obtain a chilled coil; The cold hardened coil is continuously annealed to obtain a finished IF steel. The process parameters for preparing the IF steel are shown in Table 2, and the mechanical properties of the IF steel are shown in Table 3.

[0060] Table 2 Process parameters for preparation of IF steel Table 3 Mechanical properties of IF steel It can be seen from Examples 1 to 4 that the chemical composition and main process parameters of the examples are all within the required range of the present invention, the yield strength is 145 MPa to 200 MPa, the tensile strength is 290 MPa to 320 MPa, the elongation is ≥44%, the plastic strain ratio is ≥2.5, and the work hardening index is ≥0.23.

[0061] Attached Figure 2~3 Detailed description: Figure 2 This is the ODF diagram of the IF steel provided in Example 1 of the present application. As can be seen from the figure, the IF steel produced according to the process described in the present application has an extremely strong γ fiber texture, accounting for 67.8%, showing excellent isotropy and deep drawing performance.

[0062] Figure 3 The xrd spectrum of the hot-rolled sample of IF steel provided in Example 4 of the present application shows that, in addition to the relatively strong peaks, the IF steel produced according to the process described in the present application also has several weak nitride peaks caused by the addition of alloying elements, indicating that the addition of alloying elements such as Ti, V, Nb, and Al plays a good role in fixing nitrogen.

[0063] One or more technical solutions in the embodiments of the present application also have at least the following technical effects or advantages: (1) The raw materials for electric furnace smelting contain 70% to 80% scrap steel. A large scrap steel ratio saves raw material costs.

[0064] (2) The use of electric furnace short-process steelmaking is in line with the country's low-carbon route and development strategy.

[0065] (3) The performance of the IF steel product produced according to the process described in this application can reach the performance level of existing converter steel products, with the advantages of high performance, high cost performance, low carbon emissions, etc., and is more energy-saving and environmentally friendly than conventional converter steel IF steel.

[0066] The above is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features applied for by the present application.

Claims

1. A method for producing high-quality IF steel with a high nitrogen content and a short process, characterized in that: The method comprises: Obtaining a casting billet with a set chemical composition; The ingot is sequentially heated, rolled and coiled to obtain a hot rolled coil; Cold rolling the hot rolled coil to obtain a chilled coil; The chilled coil is continuously annealed to obtain finished IF steel.

2. The method according to claim 1, characterized in that In terms of mass fraction, the set chemical composition includes: C≤0.0020%, Si≤0.030%, Mn:≤0.2%, N: 0.003%~0.008%, Al: 0.060%~0.12%, Ti: 0.030%~0.100%, V: 0.001%~0.050%, Nb: 0.001%~0.030%.

3. The method according to claim 1, characterized in that The thickness of the ingot is 220 mm to 250 mm, the temperature of the heated furnace is 1100° C. to 1250° C., and the heating time in the furnace is 100 min to 180 min.

4. The method according to claim 1, characterized in that: The final rolling temperature is 850°C to 950°C, and the coiling temperature is 680°C to 730°C.

5. The method according to claim 1, characterized in that The cold rolling adopts an acid rolling combined unit, and the total reduction rate of the cold rolling is 80% to 90%.

6. The method according to claim 1, characterized in that The microstructure of the cold-hardened coil includes a second γ texture and an α texture, the α texture forms a lamellar structure, the lamellar spacing of the lamellar structure is 5 μm to 15 μm, and the area percentage of the second γ texture is greater than 30%.

7. The method according to claim 1, characterized in that The annealing soaking temperature is 790° C. to 820° C., and the annealing strip speed is 220 mpm to 280 mpm.

8. The method according to claim 1, characterized in that The microstructure of the finished IF steel satisfies at least one of the following: an average grain size of 18 μm to 30 μm, a grain size of level 7 to 8, and an area percentage of the first γ texture>60%.

9. The method according to claim 1, characterized in that: The finished IF steel meets at least one of the following properties: yield strength of 145MPa to 200MPa, tensile strength of 290MPa to 320MPa, elongation ≥44%, plastic strain ratio ≥2.5, and work hardening index ≥0.23.

Images