A low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates and its preparation method

Abstract

The present application relates to a low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates and a preparation method, which belongs to the field of metallurgical technology. In terms of mass fraction, the chemical composition of the hot-dip galvanized IF steel includes: C≤0.003%, Si≤0.035%, 0.1%≤Mn≤0.3%, P≤0.02%, S≤0.015%, 0.03%≤Ti≤0.08%, 0.0001%≤B≤0.0008%, and matrix element Fe. By adding a small amount of B to the hot-dip galvanized IF steel to replace part of Ti, this not only reduces the amount of Ti to a certain extent, thereby reducing the production cost, but also reduces the secondary processing brittleness of the material and improves the deep drawing performance of the material. At the same time, the heating method of heating-saturating-fast cooling is adopted in the continuous annealing process, which omits the slow cooling link, improves the production efficiency, and achieves the purpose of reducing costs and increasing efficiency.

Description

Technical Field

[0001] The present application relates to the field of metallurgical technology, and in particular to a low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates and a preparation method thereof. Background Art

[0002] IF steel, or interstitial-free steel, is also called ultra-low carbon steel. IF steel is suitable for the preparation of stamping products due to its excellent properties such as low yield, high ductility, high deep drawing and no aging resistance. It is widely used in the automotive industry and other fields that require high-strength and high-ductility materials, reflecting its important position and development potential in modern industry. With the continuous development of the automotive industry, the requirements of automobiles for the performance of IF steel for automotive plates are constantly increasing, so the production technology of IF steel is constantly improving. The production of IF steel has relatively stringent requirements on the purity of molten steel, and the production process directly affects the quality of IF steel. In the future, IF steel will develop in the direction of higher strength, higher purity and better surface quality to meet the market demand for high-performance automotive steel plates.

[0003] Among the existing technologies, some technologies add relatively expensive alloy elements such as Nb and Ti, and the content is relatively high, which increases the manufacturing cost; some technologies use hood annealing or continuous annealing with a slow cooling stage, which affects the production efficiency; some technologies do not carry out galvanizing treatment, resulting in weak corrosion resistance of the strip, which is not conducive to the long-term service of the automobile; some technologies are only suitable for the production of steel strips of specific thickness, and the production specification capacity is limited. Summary of the invention

[0004] The present application provides a low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates and a preparation method thereof, in order to solve the following technical problem: how to prepare 320MPa grade hot-dip galvanized IF steel for automobile plates at low cost.

[0005] In the first aspect, an embodiment of the present application provides a low-cost 320MPa grade hot-dip galvanized IF steel for automotive plates. The chemical composition of the hot-dip galvanized IF steel includes, by mass fraction: C≤0.003%, Si≤0.035%, 0.1%≤Mn≤0.3%, P≤0.02%, S≤0.015%, 0.03%≤Ti≤0.08%, 0.0001%≤B≤0.0008%, and matrix element Fe.

[0006] Optionally, the thickness of the hot-dip galvanized IF steel is 0.35 mm to 3.0 mm.

[0007] Optionally, the hot-dip galvanized IF steel meets at least one of the following properties: 150≤R p0.2 ≤180MPa, 280≤R m ≤350MPa,r 90 ≥2.0, A80 ≥37%.

[0008] In a second aspect, the present application provides a method for preparing the low-cost 320MPa grade hot-dip galvanized IF steel for automobile sheet described in the first aspect, the method comprising:

[0009] Obtaining molten steel having the chemical composition;

[0010] Continuously casting the molten steel to obtain a continuously cast billet;

[0011] The continuous casting billet is sequentially heated, rolled and coiled to obtain a hot rolled coil;

[0012] Cold rolling the hot rolled coil to obtain a cold rolled coil;

[0013] The cold-rolled coil is subjected to continuous annealing and hot-dip galvanizing to obtain a galvanized steel strip;

[0014] The galvanized steel strip is flattened to obtain hot-dip galvanized IF steel.

[0015] Optionally, the continuous casting uses ultra-low carbon mold protection slag, the temperature of the molten steel during the continuous casting is 1550° C. to 1575° C., and the casting speed during the continuous casting is 1.0 m / min to 1.8 m / min.

[0016] Optionally, the heating temperature is 1150° C. to 1300° C., and the heating insulation time is 150 min to 250 min.

[0017] Optionally, the final rolling temperature is 880°C to 950°C, and the coiling temperature is 650°C to 750°C.

[0018] Optionally, the cold rolling equipment is a five-stand rolling mill, and when the thickness of the hot-rolled coil is 2.5 mm to 6.0 mm, the cold rolling reduction rate is 50% to 90%.

[0019] Optionally, the temperature of the soaking section of the continuous annealing is 750°C to 850°C, the temperature of the rapid cooling section of the continuous annealing is 440°C to 470°C, and the production speed of the continuous annealing is 100m / min to 170m / min.

[0020] Optionally, the dew point temperature of the hot-dip galvanizing treatment is -80°C to -20°C.

[0021] Optionally, the flattening elongation of the flattening treatment is 0.5% to 1.5%.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] The embodiment of the present application provides a low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates, and the chemical composition of the hot-dip galvanized IF steel includes, by mass fraction: C≤0.003%, Si≤0.035%, 0.1%≤Mn≤0.3%, P≤0.02%, S≤0.015%, 0.03%≤Ti≤0.08%, 0.0001%≤B≤0.0008%, and matrix element Fe. By adding a small amount of B to the hot-dip galvanized IF steel to replace part of Ti, this not only reduces the amount of Ti to a certain extent, thereby reducing the production cost, but also reduces the secondary processing brittleness of the material and improves the deep drawing performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] 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.

[0026] Figure 1 A schematic flow chart of a method for preparing a low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates provided in an embodiment of the present application;

[0027] Figure 2 The microstructure diagram provided in Example 1 of the present application;

[0028] Figure 3 This is a microstructure diagram provided for comparative example 1 of the present application. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] In this document, the terms including "including" and "including" mean "including but not limited to". Relational terms such as "first" and "second" are only used 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 multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, if the weight ratio of substance A, substance B and substance C is 1:2:3, then substance A, substance B and substance C should correspond to the proportional numbers in the proportional formula in the order of description, that is, the weight of substance A: the weight of substance B: the weight of substance C = 1:2:3.

[0032] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0033] In the first aspect, an embodiment of the present application provides a low-cost 320MPa grade hot-dip galvanized IF steel for automotive plates. The chemical composition of the hot-dip galvanized IF steel includes, by mass fraction: C≤0.003%, Si≤0.035%, 0.1%≤Mn≤0.3%, P≤0.02%, S≤0.015%, 0.03%≤Ti≤0.08%, 0.0001%≤B≤0.0008%, and matrix element Fe.

[0034] C plays a key role in balancing strength and plasticity in steel. Reasonable control of the mass fraction of C is the core link in steel design and production. The higher the mass fraction of C, the higher the strength and the worse the plasticity. High strength and low plasticity are not conducive to the deep drawing performance of IF steel. Therefore, the mass fraction of C is controlled to be ≤0.003% during production. For example, the mass fraction of C can be 0.001%, 0.0015%, 0.002%, 0.0025%, 0.003%, etc.

[0035] Si is one of the main solid solution strengthening elements. The addition of Si improves the strength of the steel matrix without sacrificing the ductility and r-value of the steel matrix. At the same time, Si is also a good deoxidizer, which can effectively remove oxygen from the steel and improve the purity of the molten steel. However, a Si mass fraction higher than 0.035% will reduce the plasticity and toughness of the steel, thereby affecting the deep drawing performance of IF steel. Therefore, the Si mass fraction is controlled to be ≤0.035%. Exemplarily, the Si mass fraction can be 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, etc.

[0036] Mn is also a solid solution strengthening element, which plays a role in enhancing strength in steel. At the same time, it can improve the hardenability of steel, and improve the processing performance and toughness of steel through desulfurization and deoxidation. However, the higher the mass fraction of Mn, the better. The mass fraction of Mn higher than 0.3% may reduce the ductility of steel and is not conducive to deep drawing. Therefore, the mass fraction of Mn in the embodiment of the present application is controlled at 0.1% to 0.3%. Exemplarily, the mass fraction of Mn can be 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, etc.

[0037] P has a high solid solubility in Fe and plays a strong solid solution strengthening role, which significantly improves the strength and hardness of steel. However, the increase in the mass fraction of P will significantly reduce the plasticity and toughness while improving the strength of the steel matrix, and deteriorate the deep drawing performance of the material. Therefore, the mass fraction of P is controlled to be ≤0.02% in the embodiment of the present application. For example, the mass fraction of P can be 0.004%, 0.008%, 0.012%, 0.016%, 0.02%, etc.

[0038] S usually forms sulfides in steel, which seriously affects the plasticity of the steel and increases its brittleness. In order to control costs and reduce the strict control of the refining process, the mass fraction of S needs to be limited. The embodiment of the present application controls the mass fraction of S to ≤0.015%. For example, the mass fraction of S can be 0.003%, 0.006%, 0.009%, 0.012%, 0.015%, etc.

[0039] Ti plays an important role in IF steel, mainly by forming stable compounds such as TiC and TiN to refine grains, thereby improving the strength, hardness and toughness of steel. However, the mass fraction of Ti should not be too high, on the one hand because the price of Ti is relatively high, and on the other hand because the strength and toughness of the steel matrix will decrease when the mass ratio of Ti to C exceeds 4. Therefore, the mass fraction of Ti in the embodiment of the present application is controlled at 0.03% to 0.08%. Exemplarily, the mass fraction of Ti can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, etc.

[0040] After B is added to IF steel, it can significantly improve the hardenability of the steel and improve the strength of the steel by forming a hardened layer during the quenching process. The addition of a small amount of B can replace part of Ti to achieve the effect of reducing costs, and can also reduce the secondary processing brittleness of the material and improve the deep drawing performance of the material. However, a mass fraction of B higher than 0.0008% may cause the brittleness of the steel to increase. Therefore, the mass fraction of B in the embodiment of the present application is controlled at 0.0001% to 0.0008%. Exemplarily, the mass fraction of B can be 0.0001%, 0.0002%, 0.0003%, 0.0004%, 0.0005%, 0.0006%, 0.0007%, 0.0008%, etc.

[0041] Fe is a matrix element. The specific content / content range of Fe can be obtained by the upper and lower limit formula of the component, that is:

[0042] The sum of the percentages of the contents of each component in a composition should be equal to 100%, and the content ranges of several components should meet the following conditions: the upper limit value of a component + the lower limit value of other components ≤ 100; the lower limit value of a component + the upper limit value of other components ≥ 100.

[0043] In some embodiments, the hot-dip galvanized IF steel has a thickness of 0.35 mm to 3.0 mm.

[0044] In some embodiments, the hot-dip galvanized IF steel meets at least one of the following properties: 150≤R p0.2 ≤180MPa, 280≤R m ≤350MPa,r 90 ≥2.0, A 80 ≥37%.

[0045] Hot dip galvanized IF steel is a high strength steel with good formability. Its mechanical properties usually include yield strength (R p0.2 ), tensile strength (R m ), plastic strain ratio (such as r 90 ) and elongation after fracture (such as A 80 ) and other key indicators.

[0046] Yield strength is the maximum stress that a material can withstand during the yield stage. For the hot-dip galvanized IF steel provided in the embodiment of the present application, the yield strength is between 150 MPa and 180 MPa, which can not only meet the strength requirements of the material, but also avoid the decrease in formability due to excessive strength. For example, R p0.2 It can be 150 MPa, 155 MPa, 160 MPa, 165 MPa, 170 MPa, 175 MPa, 180 MPa, etc.

[0047] Tensile strength is the maximum stress that a material can withstand during stretching. The tensile strength of the hot-dip galvanized IF steel provided in the present application embodiment is between 280MPa and 350MPa, which can meet the strength requirements of most application scenarios while maintaining good formability and toughness. m It can be 280 MPa, 290 MPa, 300 MPa, 310 MPa, 320 MPa, 330 MPa, 340 MPa, 350 MPa, etc.

[0048] Plastic strain ratio is an indicator to measure the ratio of the strain in the width direction to the strain in the thickness direction during the stretching process. 90 It refers to the ratio of the plastic strain in the width direction perpendicular to the stretching direction (i.e., 90-degree direction) to the plastic strain in the thickness direction during the stretching process. 90 The higher the value, the greater the strain in the width direction is relative to the strain in the thickness direction during the stretching process, that is, the material is less likely to become thinner in the thickness direction during the forming process, which is beneficial to improving the forming performance of the material and product quality. 90 The requirement of ≥2.0 indicates that hot-dip galvanized IF steel has good width-direction deformation capability during stretching, which helps the material maintain good shape stability and formability during stamping, stretching and other forming processes. 90 It can be ≥2.0, 2.1, 2.2, 2.3, 2.4, etc.

[0049] The elongation after fracture is an indicator to measure the plastic deformation ability of a material before it breaks during the stretching process. 80 It indicates the elongation after fracture of the sample with a gauge length of 80 mm. 80The requirement of ≥37% indicates that hot-dip galvanized IF steel has good plastic deformation capacity and can withstand large deformation without fracture during the tensile process. 80 It can be 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45% and so on.

[0050] In summary, the embodiment of the present application innovatively provides a low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates, which has the following advantages:

[0051] 1. Low cost: By optimizing the chemical composition and ratio, and improving the production process, the embodiment of the present application successfully achieves the goal of low-cost production of 320MPa grade hot-dip galvanized IF steel for automotive plates.

[0052] 2. High strength and toughness: Through optimized chemical composition and ratio, as well as optimized production process, the hot-dip galvanized IF steel has good toughness while ensuring high strength, meeting the requirements of automobile sheet manufacturing.

[0053] 3. Excellent deep drawing performance: The addition of element B and the optimization of the production process significantly improve the deep drawing performance of the material, making the hot-dip galvanized IF steel more suitable for the manufacture of automotive plates.

[0054] 4. Wide application: Due to its low cost and excellent performance, this hot-dip galvanized IF steel can be widely used in many fields such as automobile manufacturing and home appliance manufacturing, and has broad market prospects.

[0055] Therefore, the low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates provided in the embodiment of the present application achieves the goals of low cost, high strength, high toughness and excellent deep drawing performance by optimizing the chemical composition and ratio and improving the production process. This innovation not only reduces the production cost, but also improves the comprehensive performance of the material, providing strong technical support and economic benefits for the development of related industries such as automobile plate manufacturing.

[0056] Figure 1 A schematic flow chart of a method for preparing a low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates provided in an embodiment of the present application.

[0057] See also Figure 1 In a second aspect, the present application provides a method for preparing the low-cost 320MPa grade hot-dip galvanized IF steel for automobile sheet described in the first aspect, the method comprising:

[0058] S1, obtaining molten steel having the chemical composition;

[0059] In the embodiment of the present application, the KR desulfurization process is used for molten iron pretreatment, the molten iron is stirred by a stirring head, and a desulfurizer is added to remove the desulfurized slag. After KR desulfurization, S is controlled below 60ppm, and then the desulfurized molten iron and scrap steel are added to the converter according to a certain proportion, and the "full three removal" process of removing Si, removing P and removing C is used for steelmaking, and then RH refining treatment is performed to obtain molten steel with the chemical composition.

[0060] S2, continuously casting the molten steel to obtain a continuously cast billet;

[0061] In some embodiments, the continuous casting uses ultra-low carbon mold protection slag, the molten steel temperature of the continuous casting is 1550° C. to 1575° C., and the casting speed of the continuous casting is 1.0 m / min to 1.8 m / min.

[0062] Mold powder plays a vital role in continuous casting production, especially in the casting process of ultra-low carbon steel. The carbon content in ultra-low carbon mold powder is extremely low to reduce the effect of carbon addition on molten steel, which is crucial for the production of ultra-low carbon steel, because any additional carbon may change the chemical composition and properties of the steel. In addition, after melting, ultra-low carbon mold powder will form a liquid slag layer of a certain thickness, evenly covering the surface of the molten steel to isolate the molten steel from contact with the air and prevent secondary oxidation of the molten steel.

[0063] The temperature of the molten steel during continuous casting is one of the key factors affecting the quality of the continuous casting billet. A temperature higher than 1575°C may cause internal defects in the billet, such as cracks and bubbles; a temperature lower than 1550°C may affect the fluidity of the billet, resulting in difficulty in casting. For example, the temperature of the molten steel during continuous casting may be 1550°C, 1555°C, 1560°C, 1565°C, 1570°C, 1575°C, etc.

[0064] A continuous casting billet drawing speed faster than 1.8 m / min may cause surface defects of the billet, such as slag inclusions, cracks, etc. A billet drawing speed slower than 1.0 m / min may affect production efficiency and increase production costs. For example, the continuous casting billet drawing speed may be 1.0 m / min, 1.2 m / min, 1.4 m / min, 1.6 m / min, 1.8 m / min, etc.

[0065] S3, heating, rolling and coiling the continuous casting billet in sequence to obtain a hot rolled coil;

[0066] In some embodiments, the heating temperature is 1150° C. to 1300° C., and the heating insulation time is 150 min to 250 min.

[0067] Heating within this temperature range can ensure that the microstructure inside the steel is fully austenitized. Austenite is a kind of organizational form of steel at a higher temperature, with good plasticity and deformation ability. Sufficient austenitization helps to obtain a more uniform and stable organization in the subsequent rolling and annealing process, thereby improving the mechanical properties and surface quality of the steel. If the heating temperature is higher than 1300 ° C, overheating defects such as coarse grains and uneven organization may occur inside the steel. These defects will seriously affect the mechanical properties and surface quality of the steel. Therefore, limiting the heating temperature to the range of 1150 ° C to 1300 ° C can effectively avoid the occurrence of these overheating defects. Exemplarily, the heating temperature can be 1150 ° C, 1180 ° C, 1210 ° C, 1240 ° C, 1270 ° C, 1300 ° C, etc.

[0068] Appropriate holding time can promote the optimization of the microstructure inside the steel. By controlling the holding time, the size and shape of the grains inside the steel can be adjusted to obtain a more ideal organizational structure. This helps to improve the strength and toughness of the steel while maintaining good plasticity. Exemplarily, the holding time for heating can be 150min, 170min, 190min, 210min, 230min, 250min, etc.

[0069] In some embodiments, the final rolling temperature is 880°C to 950°C, and the coiling temperature is 650°C to 750°C.

[0070] In the final rolling temperature range of 880℃~950℃, the grain size of the steel will be refined, and the equiaxed grain ratio of the steel can be controlled, thereby obtaining a more uniform grain structure. This organizational feature helps to improve the strength and toughness of the steel, so that it meets the requirements of automotive plates for high strength and high toughness. Exemplarily, the final rolling temperature can be 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, etc.

[0071] In the coiling temperature range of 650℃~750℃, the hot rolled coil can form relatively fine grains during the cooling process, and the fine grains are helpful to improve the mechanical properties and processing properties of the steel. For example, the coiling temperature can be 650℃, 670℃, 690℃, 710℃, 730℃, 750℃, etc.

[0072] S4, cold rolling the hot rolled coil to obtain a cold rolled coil;

[0073] In some embodiments, the cold rolling equipment is a five-stand rolling mill, and when the thickness of the hot-rolled coil is 2.5 mm to 6.0 mm, the cold rolling reduction ratio is 50% to 90%.

[0074] The five-stand rolling mill is a multi-stand cold rolling equipment that can realize a continuous and efficient rolling process and greatly improve production efficiency. The rolling reduction rate refers to the ratio of the thickness change of the metal material before and after rolling to the thickness before rolling, usually expressed as a percentage. The rolling reduction rate is an important parameter in the cold rolling process and has a significant impact on the quality and performance of the product. By reasonably controlling the rolling reduction rate, cold-rolled products with the required thickness, shape and mechanical properties can be obtained. In the cold rolling process, the thickness of the hot-rolled coil is one of the important factors affecting the rolling reduction rate. When the thickness of the hot-rolled coil is large, in order to obtain the required thickness of the cold-rolled product, the rolling reduction rate needs to be increased; and when the thickness of the hot-rolled coil is small, the rolling reduction rate can be appropriately reduced. In the embodiment of the present application, when the thickness of the hot-rolled coil is 2.5mm~6.0mm, since the hot-rolled coil already has a certain thickness basis, the thickness requirement of the cold-rolled product can be achieved by a rolling reduction rate of 50%~90%. Illustratively, the rolling reduction ratio may be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

[0075] S5, performing continuous annealing and hot-dip galvanizing on the cold-rolled coil to obtain a galvanized steel strip;

[0076] In some embodiments, the temperature of the soaking section of the continuous annealing is 750°C to 850°C, the temperature of the rapid cooling section of the continuous annealing is 440°C to 470°C, the production speed of the continuous annealing is 100m / min to 170m / min, etc.

[0077] In the embodiment of the present application, the equipment for continuous annealing is a continuous annealing furnace. The continuous annealing furnace is a continuous heat treatment equipment, which is mainly composed of a feeding section, a heating section, a soaking section, a rapid cooling section and a discharging section. Its working principle is to feed the metal material into the furnace from the feeding port, and finally discharge it from the discharging port after a series of heating, soaking and rapid cooling processes. The continuous annealing furnace adopts a continuous production method, which can greatly improve production efficiency and reduce production costs. In the embodiment of the present application, the continuous annealing process adopts a heating method of heating-soaking-rapid cooling, which eliminates the slow cooling link, improves production efficiency, and achieves the purpose of reducing costs and increasing efficiency. When the steel reaches the target heating temperature, soaking is carried out. The soaking stage is conducive to uniform cold rolled coil structure and eliminating its internal residual stress. Exemplarily, the temperature of the soaking section can be 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, etc. After the soaking stage is completed, the rapid cooling stage begins. The temperature of the rapid cooling stage is 440°C to 470°C. Exemplarily, the temperature of the rapid cooling stage can be 440°C, 445°C, 450°C, 455°C, 460°C, 465°C, 470°C, etc.

[0078] The increase in the production speed of continuous annealing can significantly increase the processing volume per unit time, thereby improving production efficiency. In addition, the production speed also has a certain influence on the annealing quality. A production speed faster than 170m / min may lead to insufficient annealing, affecting the mechanical properties and surface quality of the material; while a production speed slower than 100m / min may increase production costs and energy consumption. Exemplarily, the production speed of continuous annealing can be 100m / min, 110m / min, 120m / min, 130m / min, 140m / min, 150m / min, 160m / min, 170m / min, etc.

[0079] In some embodiments, the dew point temperature of the hot dip galvanizing treatment is -80°C to -20°C.

[0080] Dew point temperature refers to the temperature at which water vapor in the air reaches a saturated state under a certain pressure. In the hot-dip galvanizing process, the dew point temperature reflects the dryness of the atmosphere in the furnace and has an important influence on the quality and performance of the galvanized layer. In the embodiments of the present application, a dew point temperature lower than -80°C may cause the atmosphere in the furnace to be too dry, affect the fluidity of the zinc liquid, and cause the galvanized layer to be uneven or insufficient in thickness; a dew point temperature higher than -20°C may cause oxidation of the steel surface, reduce the adhesion and corrosion resistance of the galvanized layer, and may also increase the moisture in the zinc liquid, resulting in the generation of zinc ash and zinc slag, and reducing the galvanizing efficiency. Exemplarily, the dew point temperature of the hot-dip galvanizing treatment can be -80°C, -70°C, -60°C, -50°C, -40°C, -30°C, -20°C, etc.

[0081] S6. Flatten the galvanized steel strip to obtain hot-dip galvanized IF steel.

[0082] In some embodiments, the flattening elongation of the flattening treatment is 0.5% to 1.5%.

[0083] Flattening elongation refers to the ratio of the increase in length of a metal material relative to its original length under the action of tensile force during the flattening process to its original length, usually expressed as a percentage. The size of the flattening elongation directly reflects the intensity of the flattening treatment and the degree of influence on the performance of the metal material. In the embodiment of the present application, a flattening elongation of 0.5% to 1.5% helps to improve the plate shape of the metal material, eliminate internal stress, and improve the surface quality and mechanical properties. Exemplarily, the flattening elongation can be 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, etc.

[0084] The product prepared by the method for preparing low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates is the above-mentioned low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates. Since the method for preparing low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates adopts part or all of the technical solutions of the embodiment of low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates, it at least has all the beneficial effects brought by the technical solutions of the embodiment of low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates, which are not repeated here one by one.

[0085] The present application is further described below in conjunction with specific embodiments. The experimental methods in the following embodiments that do not specify specific conditions are usually measured in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are measured in accordance with common international standards, conventional conditions, or conditions recommended by the manufacturer.

[0086] The chemical composition of molten steel is shown in Table 1.

[0087] Table 1 Chemical composition of molten steel of embodiment and comparative example (wt%)

[0088]

[0089]

[0090] Note: “-” means the element is not added.

[0091] Based on the chemical composition of the molten steel in the embodiment and the comparative example, this embodiment also provides a method for preparing low-cost 320MPa grade hot-dip galvanized IF steel for automobile plates, comprising the following steps:

[0092] Obtaining molten steel having the chemical composition;

[0093] Continuously casting the molten steel to obtain a continuously cast billet;

[0094] The continuous casting billet is sequentially heated, rolled and coiled to obtain a hot rolled coil;

[0095] Cold rolling the hot rolled coil to obtain a cold rolled coil;

[0096] The cold-rolled coil is subjected to continuous annealing and hot-dip galvanizing to obtain a galvanized steel strip;

[0097] The galvanized steel strip is flattened to obtain hot-dip galvanized IF steel. Please refer to Table 2 and Table 3 for the preparation process parameters.

[0098] Table 2 Preparation process parameters of examples and comparative examples

[0099]

[0100] Table 3 Preparation process parameters of examples and comparative examples

[0101]

[0102]

[0103] Table 4 Performance list of examples and comparative examples

[0104] Serial number Yield strength / MPa Tensile strength / MPa Elongation after break A80 / % <![CDATA[r 90 ]]> Example 1 169 302 42.0 2.25 Example 2 161 295 44.5 2.35 Example 3 167 300 44.0 2.38 Example 4 170 305 43.0 2.40 Example 5 158 291 45.0 2.42 Comparative Example 1 153 284 48.5 2.44 Comparative Example 2 153 284 48.5 2.57 Comparative Example 3 151 280 49.0 2.52

[0105] It can be seen from Tables 1 to 4 that the 320MPa grade hot-dip galvanized IF steel for automobile plates prepared in the embodiment has comparable strip performance to that of the original production line production process, but the production cost is lower, the production efficiency is higher, and the production process is better under the new composition, new production line, and new process.

[0106] Attached Figure 2-3 Detailed description:

[0107] Figure 2 The microstructure diagram provided in Example 1 of the present application; Figure 2 As shown, the structure is mainly composed of equiaxed ferrite grains.

[0108] Figure 3 The microstructure diagram provided for comparative example 1 of the present application; Figure 3 As shown, the structure is mainly composed of equiaxed ferrite grains.

[0109] pass Figure 2 and Figure 3 By comparison, it is found that there is no obvious difference in the microstructures of the embodiment and the comparative example, both of which are composed of ferrite, and the ferrite morphology is equiaxed and has comparable size.

[0110] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0111] The 320MPa grade hot-dip galvanized IF steel for automobile sheet provided by the embodiment of the present invention has excellent surface quality, high tensile strength and good deep drawing performance, 150≤R p0.2 ≤180MPa, 280≤R m ≤350MPa,r 90 ≥2.0, A 80 ≥37%, with the prospect of wide application.

[0112] The 320MPa grade hot-dip galvanized IF steel for automobile plates provided in the embodiment of the present invention adds element B, thereby suppressing the occurrence of secondary processing brittleness.

[0113] In the preparation method of 320MPa grade hot-dip galvanized IF steel for automobile plates provided in the embodiment of the present invention, the continuous annealing removes the slow cooling stage and increases the annealing speed, which not only achieves energy-saving and efficient production, but also conforms to the green and environmentally friendly production concept.

[0114] In the preparation method of 320MPa grade hot-dip galvanized IF steel for automobile plates provided in the embodiment of the present invention, the cold rolling production process is easy to implement and the production is easy to control, which is conducive to the production of stable and excellent performance of the strip steel.

[0115] The above description 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 the embodiments shown in the present application, but will conform to the widest range consistent with the principles and novel features applied for by the present application.

Claims

1. A low-cost 320MPa grade hot-dip galvanized IF steel for automobile sheet, wherein the chemical composition of the hot-dip galvanized IF steel comprises, by mass fraction: C≤0.003%, Si≤0.035%, 0.1%≤Mn≤0.3%, P≤0.02%, S≤0.015%, 0.03%≤Ti≤0.08%, 0.0001%≤B≤0.0008%, and matrix element Fe.

2. The hot-dip galvanized IF steel according to claim 1, characterized in that: The thickness of the hot-dip galvanized IF steel is 0.35 mm to 3.0 mm.

3. The hot-dip galvanized IF steel according to claim 1, characterized in that: The hot-dip galvanized IF steel meets at least one of the following properties: 150≤R p0.2 ≤180MPa, 280≤R m ≤350MPa,r 90 ≥2.0, A 80 ≥37%.

4. A method for preparing hot-dip galvanized IF steel according to any one of claims 1 to 3, characterized in that: The method comprises: Obtaining molten steel having the chemical composition; Continuously casting the molten steel to obtain a continuously cast billet; The continuous casting billet is sequentially heated, rolled and coiled to obtain a hot rolled coil; Cold rolling the hot rolled coil to obtain a cold rolled coil; The cold-rolled coil is subjected to continuous annealing and hot-dip galvanizing to obtain a galvanized steel strip; The galvanized steel strip is flattened to obtain hot-dip galvanized IF steel.

5. The method according to claim 4, characterized in that The continuous casting adopts ultra-low carbon mold protection slag, the temperature of the molten steel in the continuous casting is 1550° C. to 1575° C., and the casting speed in the continuous casting is 1.0 m / min to 1.8 m / min.

6. The method according to claim 4, characterized in that The heating temperature is 1150° C. to 1300° C., and the heating insulation time is 150 min to 250 min.

7. The method according to claim 4, characterized in that The final rolling temperature is 880°C to 950°C, and the coiling temperature is 650°C to 750°C.

8. The method according to claim 4, characterized in that The cold rolling equipment is a five-stand rolling mill. When the thickness of the hot-rolled coil is 2.5 mm to 6.0 mm, the cold rolling reduction rate is 50% to 90%.

9. The method according to claim 4, characterized in that The temperature of the soaking section of the continuous annealing is 750° C. to 850° C., the temperature of the rapid cooling section of the continuous annealing is 440° C. to 470° C., and the production speed of the continuous annealing is 100 m / min to 170 m / min.

10. The method according to claim 4, characterized in that The dew point temperature of the hot-dip galvanizing treatment is -80°C to -20°C; and / or, The flattening elongation of the flattening treatment is 0.5% to 1.5%.

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