A low-cost 260MPa grade low-alloy high-strength steel and its preparation method

Abstract

The present application relates to a low-cost 260MPa-grade low-alloy high-strength steel and a preparation method, and belongs to the field of steel manufacturing technology. In terms of mass fraction, the chemical composition of the low-alloy high-strength steel includes: C: 0.07% to 0.11%, Si≤0.05%, Mn: 0.3% to 0.50%, P≤0.015%, S≤0.015%, Al: 0.020% to 0.060%, and matrix element Fe. The present application adopts a reasonable low-carbon component design, cancels the precious alloys of Nb and Ti, and reduces the alloy cost. At the same time, the heating method of heating-saturation-fast cooling is adopted in the continuous annealing process, which eliminates the slow cooling link and improves the production efficiency. On the basis of ensuring the excellent comprehensive performance of the product, the purpose of reducing costs and increasing efficiency is further achieved. In addition, after annealing, a large flat elongation mode is adopted to reduce the aging risk and improve the stamping quality. It is comprehensively realized that without adding precious alloy elements such as Nb and Ti, the strength requirements of 260MPa can still be achieved, and it can meet the supply requirements of multiple standards at home and abroad.

Description

Technical Field

[0001] The present application relates to the technical field of steel manufacturing, and in particular to a low-cost 260MPa grade low-alloy high-strength steel and a preparation method thereof. Background Art

[0002] Low-alloy high-strength steel is a type of steel that has its strength improved by adding trace alloying elements such as Nb and Ti to low-carbon steel. It has the characteristics of high yield strength and yield-to-strength ratio, good forming and welding properties, etc. It has higher yield strength than carbon structural steel and lower cost than advanced high-strength steels such as duplex steel. Therefore, it is highly favored by the market and is widely used in structural parts in the automotive, home appliance, construction and other industries.

[0003] In recent years, with the rise of domestic independent brand cars represented by new energy vehicles, competition in the automotive industry has been extremely fierce. Automakers have been competing for market share by cutting prices. Downstream vehicle manufacturers generally face greater price competition pressure, and the cost reduction pressure is then transmitted upward to parts and raw material suppliers, forcing steel mills to improve efficiency and reduce costs. Summary of the invention

[0004] The present application provides a low-cost 260MPa grade low-alloy high-strength steel and a preparation method thereof to solve the following technical problem: how to prepare 260MPa grade low-alloy high-strength steel at low cost.

[0005] In the first aspect, an embodiment of the present application provides a low-cost 260MPa grade low-alloy high-strength steel. The chemical composition of the low-alloy high-strength steel includes, by mass fraction: C: 0.07% to 0.11%, Si≤0.05%, Mn: 0.3% to 0.50%, P≤0.015%, S≤0.015%, Al: 0.020% to 0.060%, and matrix element Fe.

[0006] Optionally, the low-alloy high-strength steel satisfies at least one of the following properties: yield strength of 260MPa to 320MPa, tensile strength of 350MPa to 430MPa, elongation after fracture ≥28%, and work hardening index ≥0.15.

[0007] In a second aspect, an embodiment of the present application provides a method for preparing the low-cost 260 MPa grade low alloy high-strength steel described in the first aspect, the method comprising:

[0008] Obtaining a slab having the chemical composition;

[0009] The slab is sequentially heated, rolled, cooled and coiled to obtain a hot-rolled coil;

[0010] Cold rolling the hot rolled coil to obtain a cold rolled coil;

[0011] The cold rolled coil is subjected to continuous full annealing and hot dip galvanizing to obtain a galvanized steel strip;

[0012] The galvanized steel strip is flattened to obtain low-alloy high-strength steel.

[0013] Optionally, the heating temperature is 1150° C. to 1220° C., and the heating insulation time is ≥150 min.

[0014] Optionally, the final rolling temperature is 860°C to 900°C.

[0015] Optionally, the cooling adopts a front-stage centralized water cooling mode.

[0016] Optionally, the coiling temperature is 560°C to 600°C.

[0017] Optionally, the comprehensive reduction rate of the cold rolling is 70% to 85%.

[0018] Optionally, the continuous full annealing includes: a first stage heating, a second stage heating, soaking and rapid cooling.

[0019] Optionally, the terminal temperature of the first stage of heating is 450°C to 500°C, and the heating rate of the first stage of heating is 4°C / s to 7°C / s.

[0020] Optionally, the terminal temperature of the second stage heating is 750°C to 850°C, and the heating rate of the second stage heating is 2°C / s to 6°C / s.

[0021] Optionally, the temperature of the abatement is 750° C. to 850° C., and the insulation time of the abatement is 40s to 85s.

[0022] Optionally, the endpoint temperature of the rapid cooling is 440°C to 480°C, and the cooling rate of the rapid cooling is 6°C / s to 15°C / s.

[0023] Optionally, the flattening elongation of the flattening treatment is 1.7% to 2.0%.

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] The embodiment of the present application provides a low-cost 260MPa-grade low-alloy high-strength steel. The chemical composition of the low-alloy high-strength steel includes, by mass fraction: C: 0.07% to 0.11%, Si≤0.05%, Mn: 0.3% to 0.50%, P≤0.015%, S≤0.015%, Al: 0.020% to 0.060%, and matrix element Fe. In traditional low-alloy high-strength steels, micro-alloy elements such as Nb and Ti are often added to improve strength and toughness. However, these elements are expensive and increase production costs. The embodiment of the present application achieves the strength requirement of 260MPa level without adding precious alloy elements such as Nb and Ti by precisely controlling the mass fraction of conventional alloying elements such as C, Si, Mn, P, S, and Al, and optimizing their ratios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] 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.

[0028] Figure 1 A schematic flow chart of a method for preparing a low-cost 260MPa grade low-alloy high-strength steel provided in an embodiment 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 260MPa grade low-alloy high-strength steel. The chemical composition of the low-alloy high-strength steel includes, by mass fraction: C: 0.07% to 0.11%, Si≤0.05%, Mn: 0.3% to 0.50%, P≤0.015%, S≤0.015%, Al: 0.020% to 0.060%, and matrix element Fe.

[0034] C is the most important solid solution strengthening element. When the mass fraction of C is less than 0.07%, the solid solution strengthening ability is weak, which easily leads to insufficient material performance. However, when the mass fraction of C is higher than 0.11%, it will affect the welding performance and forming quality. For example, the mass fraction of C can be 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, etc.

[0035] Si is also one of the main solid solution strengthening elements, but it does not form carbides in steel, but dissolves in ferrite or austenite in the form of solid solution, which can reduce the austenite phase area. Increasing Si can improve the hardness, strength and high temperature fatigue strength of steel, but it will deteriorate the welding performance of steel, so the mass fraction of Si is controlled to be ≤0.05%. For example, the mass fraction of Si can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, etc.

[0036] Mn is also a solid solution strengthening element and a commonly used element for improving strength. Mn can expand the austenite region and form MnS with sulfur to prevent hot brittleness caused by sulfur, thereby improving the hot working properties of steel. Too little addition cannot guarantee the material properties; but Mn is prone to cause structural segregation. A mass fraction higher than 0.50% is prone to forming cracks, deteriorating the comprehensive properties of steel, and also affecting welding performance. For example, the mass fraction of Mn can be 0.3%, 0.35%, 0.40%, 0.45%, 0.5%, etc.

[0037] P also plays a role in solid solution strengthening, but while improving the strength, it causes a significant decrease in plasticity and impact toughness, and deteriorates the mechanical properties of the material. In the embodiment of the present application, the mass fraction of P is controlled to be ≤0.015%. For example, the mass fraction of P can be 0.003%, 0.005%, 0.007%, 0.009%, 0.011%, 0.013%, 0.015%, etc.

[0038] S comes from molten iron and steelmaking raw materials and is a harmful element. FeS formed in molten steel is prone to premature melting, resulting in cracking of the workpiece, while reducing the ductility and toughness of the steel. Exemplarily, the mass fraction of S can be 0.003%, 0.005%, 0.007%, 0.009%, 0.011%, 0.013%, 0.015%, etc.

[0039] Al is mainly used for deoxidation and alloying in steelmaking. When alloying elements are added to steel, they can refine the grains and fix nitrogen in the steel, thereby inhibiting the aging of low-carbon steel. For example, the mass fraction of Al can be 0.020%, 0.030%, 0.040%, 0.050%, 0.060%, etc.

[0040] 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:

[0041] 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.

[0042] In some embodiments, the low alloy high strength steel satisfies at least one of the following properties: yield strength of 260MPa to 320MPa, tensile strength of 350MPa to 430MPa, elongation after fracture ≥28%, and work hardening index ≥0.15.

[0043] Yield strength is an important indicator for measuring the material's ability to resist plastic deformation. In the embodiments of the present application, the yield strength of low-alloy high-strength steel ranges from 260 MPa to 320 MPa. The yield strength within this range ensures that the steel has sufficient rigidity and stability when subjected to external forces. For example, the yield strength may be 260 MPa, 270 MPa, 280 MPa, 290 MPa, 300 MPa, 310 MPa, 320 MPa, etc.

[0044] The tensile strength reflects the maximum stress that a material can withstand during the stretching process. In the embodiments of the present application, the tensile strength of the low-alloy high-strength steel is between 350MPa and 430MPa. The tensile strength within this range ensures that the steel is not easy to break when subjected to a tensile load and has excellent bearing capacity. For example, the tensile strength can be 350MPa, 360MPa, 370MPa, 380MPa, 390MPa, 400MPa, 410MPa, 420MPa, 430MPa, etc.

[0045] The elongation after fracture is an important indicator for measuring the plasticity of a material. In the embodiment of the present application, the elongation after fracture of the low-alloy high-strength steel is not less than 28%, which means that the steel can undergo greater plastic deformation before fracture, thereby improving its impact and seismic resistance. Exemplarily, the elongation after fracture can be 28%, 30%, 32%, 34%, 36%, 38%, 40%, etc.

[0046] The work hardening index reflects the ability of a material to harden during plastic deformation. In the embodiment of the present application, the work hardening index of low-alloy high-strength steel is not less than 0.15, which means that the steel can form a more uniform hardened layer during deformation, thereby improving its wear resistance and fatigue resistance. Exemplarily, the work hardening index can be 0.15, 0.155, 0.16, 0.165, 0.17, 0.175, 0.18, etc.

[0047] In summary, the embodiment of the present application innovatively provides a low-cost 260MPa grade low alloy high-strength steel, which has the following advantages:

[0048] 1. Low cost: By precisely controlling and optimizing the ratio of conventional alloy elements, the embodiment of the present application successfully achieves the strength requirement of 260 MPa without adding precious alloy elements such as Nb and Ti, significantly reducing the production cost.

[0049] 2. High strength and toughness: The optimized chemical composition and ratio ensure that the low-alloy high-strength steel has good toughness while ensuring high strength, meeting the needs of various application scenarios.

[0050] 3. Wide application: Due to its low cost and excellent performance, this low-alloy high-strength steel can be widely used in many fields such as construction, bridges, vehicles, machinery manufacturing, etc., and has broad market prospects.

[0051] Therefore, the low-cost 260MPa-grade low-alloy high-strength steel provided in the embodiment of the present application achieves the goal of achieving high strength requirements without adding precious alloy elements by precisely controlling and optimizing the ratio of conventional alloy elements. This innovation not only reduces production costs, but also maintains the excellent performance of steel, providing strong technical support and economic benefits for the development of related industries.

[0052] See also Figure 1 In a second aspect, the present application provides a method for preparing the low-cost 260MPa grade low-alloy high-strength steel described in the first aspect, the method comprising:

[0053] S1, obtaining a slab having the chemical composition;

[0054] In the embodiment of the present application, the molten iron is subjected to KR desulfurization, converter smelting, and then refined and continuously cast to obtain a slab with the chemical composition, which ensures the performance of the final product. KR desulfurization, namely KR (Kambara Reactor) desulfurization, is an important molten iron pretreatment desulfurization process.

[0055] S2, sequentially heating, rolling, cooling and coiling the slab to obtain a hot-rolled coil;

[0056] In some embodiments, the heating temperature is 1150° C. to 1220° C., and the heating insulation time is ≥150 min.

[0057] The heating temperature of 1150℃~1220℃ can ensure that the slab reaches the appropriate temperature before rolling, which is conducive to the plastic deformation of the slab, reduces defects such as cracking and deformation during rolling, and improves the rolling quality. In addition, heating within this temperature range can prevent the slab from overheating and overburning, and avoid the occurrence of coarse grains. Exemplarily, the heating temperature can be 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, etc.

[0058] During the heating process, the chemical composition inside the slab will gradually become evenly distributed as the temperature rises. A holding time of ≥150 min can ensure that the chemical composition inside the slab has enough time to diffuse and homogenize, thereby avoiding performance differences caused by uneven distribution of chemical composition. In addition, the length of the holding time has an important influence on the organizational structure of the steel. During a holding time of ≥150 min, the grains inside the steel can be fully grown and recrystallized, thereby optimizing the organizational structure, which helps to improve the strength and toughness of the steel, while reducing internal defects and improving overall performance. Exemplarily, the holding time for heating can be 150 min, 160 min, 170 min, 180 min, etc.

[0059] In some embodiments, the final rolling temperature of the rolling is 860°C to 900°C.

[0060] The final rolling temperature is one of the key factors affecting the internal structure of steel. Controlling the final rolling temperature within the range of 860°C to 900°C can ensure that the steel forms an ideal structure during the rolling process. For example, the final rolling temperature can be 860°C, 868°C, 876°C, 884°C, 892°C, 900°C, etc.

[0061] In some embodiments, the cooling adopts a front-stage centralized water cooling mode.

[0062] The front-end concentrated water cooling mode refers to the process of controlling the opening sequence and number of the manifold valves in the laminar cooling zone during the cooling of hot-rolled steel, so as to concentrate the rapid cooling area in the front of the laminar cooling zone to achieve uniform cooling and performance optimization of the steel. The main features of this mode are fast cooling speed, high cooling efficiency, and targeted cooling control for different parts of the steel. The front-end concentrated water cooling mode helps to refine the grains of steel and improve the strength and toughness of steel. Through rapid cooling, the transformation of austenite to pearlite can be suppressed and the formation of ferrite can be promoted, thereby obtaining a more uniform and fine structure. The front-end concentrated water cooling mode also helps to reduce defects such as cracks and inclusions generated in the hot rolling process of steel. Rapid cooling can suppress the formation and expansion of these defects, thereby improving the quality and reliability of steel.

[0063] In some embodiments, the coiling temperature is 560°C to 600°C.

[0064] Limiting the coiling temperature to 560°C to 600°C helps the steel to form a uniform and fine structure during the cooling process. This structure not only improves the strength and toughness of the steel, but also improves its processing performance and fatigue resistance. For example, the coiling temperature can be 560°C, 564°C, 568°C, 572°C, 576°C, 600°C, etc.

[0065] S3, cold rolling the hot rolled coil to obtain a cold rolled coil;

[0066] In some embodiments, the comprehensive reduction ratio of the cold rolling is 70% to 85%.

[0067] In the embodiment of the present application, the hot rolled coil is pickled and then cold rolled, and a large reduction design is adopted for the cold rolling to ensure that the interior of the cold rolled coil has sufficient recrystallization driving force, so as to promote the rapid equiaxed and homogenized grains in the strip steel under the short process annealing process. Exemplarily, the comprehensive reduction rate of cold rolling can be 70%, 73%, 76%, 79%, 82%, 85%, etc.

[0068] S4, performing continuous full annealing and hot-dip galvanizing on the cold-rolled coil to obtain a galvanized steel strip;

[0069] In some embodiments, the continuous full annealing includes: a first stage heating, a second stage heating, soaking and rapid cooling.

[0070] The traditional annealing process usually includes multiple heating and slow cooling processes, which is not only time-consuming but also energy-intensive. In the embodiment of the present application, a two-stage heating process without a slow cooling stage is adopted, which greatly improves the annealing rate and shortens the production cycle. In the embodiment of the present application, the continuous full annealing includes: the first stage heating, the second stage heating, the soaking and the rapid cooling process, and no slow cooling is performed after the soaking, and the rapid cooling terminal temperature is directly guaranteed.

[0071] In some embodiments, the terminal temperature of the first stage heating is 450° C. to 500° C., and the heating rate of the first stage heating is 4° C. / s to 7° C. / s.

[0072] In some embodiments, the end temperature of the second stage heating is 750° C. to 850° C., and the heating rate of the second stage heating is 2° C. / s to 6° C. / s.

[0073] Exemplarily, the end temperature of the first stage of heating can be 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, etc., and the heating rate of the first stage of heating can be 4.0°C / s, 5.0°C / s, 6.0°C / s, 7.0°C / s, etc.; the end temperature of the second stage of heating can be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, etc., and the heating rate of the second stage of heating can be 2.0°C / s, 3.0°C / s, 4.0°C / s, 5.0°C / s, 6.0°C / s, etc.

[0074] In some embodiments, the temperature of the abatement is 750° C. to 850° C., and the holding time of the abatement is 40 s to 85 s.

[0075] In the embodiment of the present application, the temperature of the aquaporization is 750℃~850℃, and the aquaporization holding time is 40s~85s, so as to fully eliminate the internal stress and residual stress in the cold-rolled coil, reduce the hardness of the cold-rolled coil, and stabilize the size of the cold-rolled coil. It can effectively eliminate the fibrous structure in the organization of the cold-rolled coil, refine the grains in the cold-rolled coil, and make the organization more uniform, thereby improving the strength and toughness of the cold-rolled coil and preventing deformation or cracking during use. Exemplarily, the aquaporization holding time can be 40s, 50s, 60s, 70s, 80s, 85s, etc.

[0076] In some embodiments, the endpoint temperature of the rapid cooling is 440° C. to 480° C., and the cooling rate of the rapid cooling is 6° C. / s to 15° C. / s.

[0077] In the embodiment of the present application, the heat-insulated steel strip is cooled to 440°C to 480°C at a cooling rate of 6°C / s to 15°C / s, and then galvanized. Controlling the endpoint temperature of rapid cooling to 440°C to 480°C can ensure the surface quality of the steel strip after hot-dip galvanizing. If the endpoint temperature of rapid cooling is higher or lower than this temperature range, it will lead to poor galvanizing, and defects such as missing plating, dezincification, and zinc flow lines are prone to occur. Exemplarily, the endpoint temperature of rapid cooling can be 440°C, 450°C, 460°C, 470°C, 480°C, etc.

[0078] S5. Flatten the galvanized steel strip to obtain low-alloy high-strength steel.

[0079] In some embodiments, the flattening elongation of the flattening treatment is 1.7% to 2.0%.

[0080] In the embodiment of the present application, the flattening treatment adopts a large elongation mode. Low-carbon steel is prone to aging. The large flattening elongation mode can improve the yield platform length before delivery, reduce the risk of aging, and avoid the occurrence of orange peel defects in stamping; secondly, it can improve the plate shape, thereby improving the forming performance. Exemplarily, the flattening elongation of the flattening treatment can be 1.7%, 1.75%, 1.8%, 1.85%, 1.9%, 1.95%, 2.0%, etc.

[0081] The 260MPa grade low alloy high strength steel provided in this application can meet the technical requirements of the HX260LAD+Z grade in the standard EN 10345 and the CR240LA grade in the standard VDA.

[0082] The product prepared by the method for preparing low-cost 260MPa-grade low-alloy high-strength steel is the above-mentioned low-cost 260MPa-grade low-alloy high-strength steel. Since the method for preparing low-cost 260MPa-grade low-alloy high-strength steel adopts part or all of the technical solutions of the low-cost 260MPa-grade low-alloy high-strength steel embodiment, it at least has all the beneficial effects brought by the technical solutions of the low-cost 260MPa-grade low-alloy high-strength steel embodiment, which will not be repeated here one by one.

[0083] 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.

[0084] The molten iron is subjected to KR desulfurization, converter smelting, refining and continuous casting to obtain a slab with high cleanliness. The chemical composition (wt%) of the slab is shown in Table 1.

[0085] Table 1 Chemical composition of slab (wt%), the rest is Fe and unavoidable impurities

[0086] Group C％ Si% Mn% P％ S％ Al％ Example 1 0.074 0.023 0.47 0.008 0.010 0.036 Example 2 0.096 0.019 0.41 0.008 0.009 0.038 Example 3 0.089 0.022 0.44 0.011 0.007 0.037 Example 4 0.090 0.025 0.41 0.009 0.011 0.034 Example 5 0.099 0.019 0.40 0.013 0.013 0.034 Example 6 0.088 0.015 0.39 0.010 0.010 0.040 Example 7 0.100 0.019 0.36 0.010 0.010 0.029 Example 8 0.095 0.019 0.40 0.010 0.010 0.029 Example 9 0.091 0.019 0.40 0.010 0.010 0.029 Example 10 0.110 0.023 0.33 0.006 0.008 0.035 Comparative Example 1 0.094 0.023 0.47 0.010 0.010 0.039 Comparative Example 2 0.05 0.04 0.25 0.011 0.009 0.040 Comparative Example 3 0.13 0.03 0.6 0.005 0.0010 0.028

[0087] Based on the chemical composition of the slabs in the embodiment and the comparative example, this embodiment also provides a method for preparing a low-cost 260 MPa grade low alloy high-strength steel, comprising the following steps:

[0088] Obtaining a slab having the chemical composition;

[0089] The slab is sequentially heated, rolled, cooled and coiled to obtain a hot-rolled coil;

[0090] Cold rolling the hot rolled coil to obtain a cold rolled coil;

[0091] The cold rolled coil is subjected to continuous full annealing and hot dip galvanizing to obtain a galvanized steel strip;

[0092] The galvanized steel strip is flattened to obtain low alloy high strength steel. Please refer to Table 2 and Table 3 for the preparation process parameters.

[0093] Table 2 Preparation process parameters of examples and comparative examples

[0094]

[0095] Table 3 Preparation process parameters of examples and comparative examples

[0096]

[0097]

[0098] Table 4 Performance list of embodiments and comparative examples

[0099] Group Yield strength / MPa Tensile strength / MPa Elongation after break / % Work hardening index Example 1 288 401 34.5 0.18 Example 2 291 401 36.5 0.18 Example 3 264 385 36 0.17 Example 4 287 388 38 0.18 Example 5 294 403 34.5 0.16 Example 6 273 387 38.5 0.16 Example 7 290 395 36.5 0.17 Example 8 283 393 36.5 0.17 Example 9 282 392 37.5 0.18 Example 10 287 394 34.5 0.16 Comparative Example 1 332 436 29.5 0.15 Comparative Example 2 249 356 36 0.18 Comparative Example 3 356 452 27 0.14

[0100] The mechanical properties of the embodiments and comparative examples are shown in Table 4. As shown in Tables 1 to 4, the 260MPa grade low alloy high strength steel prepared by the method provided by the embodiments of the present invention has a yield strength of 260MPa to 320MPa, a tensile strength of 350MPa to 430MPa, an elongation after fracture of ≥28%, and a work hardening index of ≥0.15. The technical requirements of the HX260LAD+Z grade in the standard EN 10345 and the CR240LA grade in the standard VDA can be met.

[0101] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0102] The low-cost 260MPa-grade low-alloy high-strength steel and preparation method provided in the embodiment of the present invention adopt a low-carbon cost system without adding Nb and Ti precious alloys, and at the same time match reasonable hot rolling and cold rolling processes. Annealing adopts a two-stage heating and no slow cooling stage process flow, which greatly improves the annealing rate and shortens the process. Compared with the existing process, it realizes the sharing of multiple standard grades with the same composition and process, achieves the purpose of low cost and efficient production, and meets the current market demand.

[0103] 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 260MPa grade low-alloy high-strength steel, wherein the chemical composition of the low-alloy high-strength steel comprises, by mass fraction: C： 0.07%~0.11%, Si≤0.05%, Mn: 0.3%~0.50%, P≤0.015%, S≤0.015%, Al: 0.020%~0.060%, and matrix element Fe.

2. The low alloy high strength steel according to claim 1, characterized in that: The low alloy high strength steel meets at least one of the following properties: yield strength of 260MPa to 320MPa, tensile strength of 350MPa to 430MPa, elongation after fracture ≥28%, and work hardening index ≥0.

15.

3. A method for preparing low alloy high strength steel according to any one of claims 1 to 2, characterized in that: The method comprises: Obtaining a slab having the chemical composition; The slab is sequentially heated, rolled, cooled 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 full annealing and hot dip galvanizing to obtain a galvanized steel strip; The galvanized steel strip is flattened to obtain low-alloy high-strength steel.

4. The method according to claim 3, characterized in that The heating temperature is 1150°C to 1220°C, and the heating insulation time is ≥150min; and / or, The final rolling temperature of the rolling is 860°C to 900°C; and / or, The cooling adopts a front-end centralized water cooling mode; and / or, The coiling temperature is 560°C to 600°C; and / or, The comprehensive reduction ratio of the cold rolling is 70% to 85%.

5. The method according to claim 3, characterized in that: The continuous full annealing includes: first stage heating, second stage heating, soaking and rapid cooling.

6. The method according to claim 3 or 5, characterized in that: The terminal temperature of the first stage heating is 450° C. to 500° C., and the heating rate of the first stage heating is 4° C. / s to 7° C. / s.

7. The method according to claim 3 or 5, characterized in that: The terminal temperature of the second stage heating is 750° C. to 850° C., and the heating rate of the second stage heating is 2° C. / s to 6° C. / s.

8. The method according to claim 3 or 5, characterized in that: The temperature of the abatement is 750° C. to 850° C., and the holding time of the abatement is 40s to 85s.

9. The method according to claim 3 or 5, characterized in that: The terminal temperature of the rapid cooling is 440°C to 480°C, and the cooling rate of the rapid cooling is 6°C / s to 15°C / s.

10. The method according to claim 3, characterized in that The flattening elongation of the flattening treatment is 1.7% to 2.0%.

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