Low-cost 1500MPa-grade hot-rolled high-strength steel and preparation method thereof

Abstract

The invention provides low-cost 1500MPa-grade hot-rolled high-strength steel and a preparation method, and relates to the technical field of hot-rolled high-strength steel. The thickness of the low-cost 1500MPa-grade hot-rolled high-strength steel is 4-8mm, and the low-cost 1500MPa-grade hot-rolled high-strength steel comprises the following chemical components in percentage by mass: 0.20-0.24% of C, 2.4-2.8% of Mn, 1.4-1.8% of Al, 0.3-0.4% of Si, less than or equal to 0.01% of P, less than or equal to 0.01% of S and the balance of Fe and inevitable impurity elements. The preparation method comprises the steps of raw material weighing, continuous casting, heat treatment, hot rolling and critical annealing. According to the invention, by creatively selecting alloy elements and adjusting the content, combining hot rolling and critical annealing treatment and controlling the air cooling rate, the comprehensive properties such as strength, plasticity and impact resistance of the steel plate are synergistically improved; the method is high in resource utilization rate, low in production cost, short in process, easy to operate, high in efficiency and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] The invention relates to the technical field of hot-rolled high-strength steel, in particular to a low-cost 1500MPa grade hot-rolled high-strength steel. Background Art

[0002] In automobile manufacturing, hot-rolled high-strength steel can be used to manufacture important components such as door reinforcement plates, chassis crossbeams, protective armor, and railway body structures. It can effectively reduce the weight of the vehicle body, reduce energy consumption, and improve safety performance. At present, the hot-rolled high-strength steel used in large quantities in China is mainly 800MPa and below. In recent years, with the gradual strengthening of environmental pollution regulations, the application of hot-rolled high-strength steel in automobiles has become more and more extensive. For every 10% reduction in the total weight of the vehicle, energy economy can be improved by 4.9%, but it is accompanied by an increase in safety risks. Therefore, there are more and more studies on the commercial application of hot-rolled high-strength steel with a tensile strength of more than 1000 MPa.

[0003] Research shows that the main technical routes for hot-rolled high-strength steel include: 1) Precipitation strengthening type, the matrix structure is ferrite, and micro-alloying elements such as Nb, V, Ti, Mo, and Cu are added. This route has high alloy costs, and the further reduction of the size of the precipitate phase and the further increase of the number density face challenges. It is difficult for hot-rolled high-strength steel developed by improving precipitation strengthening to break through the bottleneck of 1000MPa and above. 2) Martensitic structure strengthening type, the matrix structure is full martensite or ferrite + martensite, but since this route generally does not perform tempering heat treatment, the plasticity of the steel is poor. 3) Traditional quenching and tempering heat treatment type, the matrix structure is martensitic tempering structure, and the process route is TMCP + quenching + tempering, which can improve the plasticity of martensitic steel, but the production process is complicated and requires matching heat treatment equipment, which is basically difficult to achieve on ordinary hot rolling production lines.

[0004] For example, Chinese patent CN109023091A discloses a hot-rolled ultra-high-strength steel plate with good forming performance and a preparation method thereof. The chemical composition of the steel has high carbon, aluminum and manganese contents, and a large amount of precious metal elements such as Nb, Ti, V, Mo are added. The alloy cost is high, and when the Ti content is high, TiN inclusions are easily formed, affecting the plasticity of the material; the low strength-plasticity product of the prepared material further proves that its strength and plasticity are not matched.

[0005] CN110578095A discloses a 1200MPa hot-rolled ultra-high strength steel plate and its preparation method. The alloy cost of the steel preparation process is high, and the phase transition temperature is low, resulting in poor precipitation strengthening effect of elements such as Ti and V, and low utilization rate of microalloying elements; and the yield strength is relatively high. Although the tensile strength exceeds 1200MPa, it does not reach the 1500MPa level, and the strength-plasticity product is also low, not exceeding 28GPa·%, so the strength and plasticity are not synergistically improved. The same is true for Chinese patents CN116571669A and CN114574760A. Although the tensile strength can reach the 1500MPa level, the strength-plasticity product is still very low, and does not exceed 28GPa·%; and the forging and spinning preparation methods adopted increase the production cost.

[0006] CN113215491A discloses a 1300MPa grade hot-rolled ultra-high strength steel plate and a preparation method thereof. The steel adopts the TMCP+direct quenching process, the tensile strength reaches 1300 MPa, the yield strength is relatively high, and the strength-plasticity product is low, indicating that the improvement of strength and plasticity is not matched. Although the microstructure is mainly martensitic structure, the plasticity is poor because no tempering treatment is performed.

[0007] Chinese patent CN115961128A discloses a 1500MPa grade pickling-free hot-formed steel and a preparation method thereof. The method prepares steel plates through the steps of desulfurized molten iron, smelting, refining outside the furnace, continuous casting, slab heating, hot rolling, finishing packaging, blanking, heating austenitization, and die stamping quenching. The strength-plasticity product of the prepared steel plates is also low. The strength and plasticity are improved, the elongation is reduced, the cost is high, and the efficiency is low.

[0008] In summary, how to control the microstructure of low alloy steel at low cost and high efficiency, so that it can obtain a multiphase structure with different mechanical responses during deformation, thereby further improving strength and elongation, is a technical problem that needs to be solved urgently. This is because it not only requires avoiding the addition of expensive alloy elements, but also requires omitting complex processing steps, and the processing process needs to be simple and easy to operate.

[0009] In summary, there is an urgent need to develop a hot-rolled high-strength steel with low alloy cost, high strength, good plasticity, suitable for industrial production lines and a preparation method thereof. Summary of the invention

[0010] In order to solve the technical problem that the strength and plasticity of hot-rolled high-strength steel in the prior art cannot be obtained through a low-cost, high-efficiency preparation method; therefore, the embodiment of the present invention provides a low-cost 1500MPa grade hot-rolled high-strength steel and a preparation method that can synergistically improve strength and plasticity and reduce yield strength ratio. The technical solution is as follows:

[0011] A low-cost 1500MPa hot-rolled high-strength steel, wherein the low-cost 1500MPa hot-rolled high-strength steel has a thickness of 4-8mm and a chemical composition of, by mass percentage, C 0.20-0.24%, Mn 2.4-2.8%, Al 1.4-1.8%, Si 0.3-0.4%, P≤0.01%, S≤0.01%, and the balance is Fe and unavoidable impurity elements.

[0012] Optionally, the metallographic composition of the low-cost 1500MPa grade hot-rolled high-strength steel is 82-87% lath-shaped bainitic ferrite structure + 5-10% a small amount of blocky martensite structure + 2-3% lamellar retained austenite structure + 4-5% island-shaped retained austenite structure.

[0013] Optionally, in the low-cost 1500MPa grade hot-rolled high-strength steel, the lath width of the bainitic ferrite structure is ≤1μm; the average size of the blocky martensite structure is ≤6μm; the lamellar thickness of the lamellar retained austenite structure is ≤1μm; and the average grain size of the island retained austenite structure is ≤3μm.

[0014] Optionally, the density of the low-cost 1500MPa grade hot-rolled high-strength steel is 7.5-7.6g / cm 3 , hardness is 490-520HV, tensile strength is not less than 1500MPa, yield strength is not less than 750MPa, yield strength ratio is 0.48-0.60, elongation is not less than 18%, strength-ductility product is not less than 28.798GPa·%, room temperature impact energy is not less than 39J, and -40℃ low temperature impact energy is not less than 30J.

[0015] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0016] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0017] S2, continuous casting: smelting the raw materials in S1 and continuously casting them to obtain high-strength steel slabs;

[0018] S3, heat treatment: heat treating the S2 high-strength steel slab to obtain a heat-treated high-strength steel slab;

[0019] S4, hot rolling: the high-strength steel slab after the S3 heat treatment is fully heated and then taken out of the furnace for hot rolling, and air-cooled to room temperature after the hot rolling to obtain a high-strength rolled plate;

[0020] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment and then air-cooled to room temperature to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0021] Optionally, the thickness of the S2 medium-high strength steel slab is 60-80 mm.

[0022] Optionally, the heating rate of the heat treatment in S3 is 5-9°C / min, the heat treatment temperature is 1170-1220°C, and the holding time is 15-30min.

[0023] Optionally, the starting rolling temperature of the hot rolling in S4 is 1060-1100°C, and after 8-10 rolling passes, the final rolling temperature is 860-900°C, the reduction in each pass is 10-30%, and the total reduction is 86-95%.

[0024] Optionally, the hot rolling in S4 is to control the rolling of the austenite recrystallization zone for 3-4 passes, the intermediate billet thickness is 12-18 mm, the rolling of the austenite non-recrystallization zone is 5-6 passes, and the finished steel thickness is 4-8 mm.

[0025] Optionally, the annealing temperature of the critical annealing treatment in S5 is 720-750° C., the holding time is 15-25 min, and the cooling rate of air cooling is -5~-10° C. / s.

[0026] Technical principle of the present invention:

[0027] The main alloying element selection mechanism in the steel of the present invention is as follows:

[0028] C is an important strengthening element in steel. The strength of bainite, martensite, retained austenite and other structures in steel is related to the carbon content. When the C content increases, the CCT curve can shift to the right, improve the stability of retained austenite, delay the transformation of pearlite, and increase the proportion of bainite ferrite structure. Therefore, the C content is controlled to 0.20-0.24%.

[0029] Mn has a strong effect on stabilizing austenite. 1% Mn content can reduce the Ms point by about 30 °C. Adding Mn to steel is conducive to retaining more residual austenite in the final microstructure. However, when the Mn content is too high, it is easy to cause casting segregation and affect the uniformity of the structure. Therefore, the Mn content is controlled to 2.5-2.8%.

[0030] Si can increase the activity of C during the phase transformation process, promote the diffusion of C from ferrite to retained austenite, purify ferrite, and enrich austenite with carbon, thereby improving the stability of retained austenite. At the same time, Si element inhibits the nucleation and precipitation of carbides, shifts the "C" curve of pearlite transformation to the right, and slows down the formation of pearlite. The Si content should not exceed 0.5%, otherwise it will affect the quality of the surface coating of the steel. Therefore, the Si content is controlled to 0.3-0.4%.

[0031] The Al element has a similar effect as Si in inhibiting the formation of cementite, and has no adverse effect on the quality of the surface coating of steel, and can replace or partially replace Si. At the same time, Al can reduce the austenite phase area in the steel, increase the Ac3 and Ms points, reduce the phase transformation driving force and shear resistance, and thus increase the Bs point. Therefore, the present invention controls the Al content to 1.4-1.8%.

[0032] P and S are inevitable impurity elements in steel, among which P is easy to be segregated at the grain boundary, and there is a large mismatch between P and Fe atomic lattices, so a high P content is easy to cause grain boundary embrittlement. S is easy to form long strip inclusions with Mn. Since the plasticity of the above-mentioned sulfide inclusions is quite different from that of the steel matrix, it will not deform with the subsequent hot working of the steel, which will cause the elastic modulus of the sulfide inclusions to be different from that of the steel matrix, and it is easy to become a crack diffusion source, resulting in a decrease in the ability of the steel to inhibit crack propagation. Therefore, the present invention controls the P content to ≤0.01% and the S content to ≤0.01%.

[0033] The process parameter selection mechanism of the present invention is as follows:

[0034] The main purpose of heating the ingot is to promote the solid solution of alloy elements. At the same time, if the heating temperature of the ingot is too high, it will easily lead to coarsening of the original austenite grains and reduce the plasticity of the material. Therefore, the heating temperature of the ingot is controlled to 1170-1220°C in the present invention.

[0035] The purpose of rolling in the austenite recrystallization zone is to achieve austenite structure refinement through recrystallization, improve the strength and plasticity of the material, and increase the rolling deformation, which is conducive to promoting sufficient deformation of the plate in the entire thickness direction and activating the austenite recrystallization process. Rolling in the austenite non-recrystallization zone promotes the flattening of austenite, provides more nucleation points for subsequent phase transformation, and thus refines the microstructure of the finished steel. Therefore, the present invention controls the thickness of the intermediate billet after rolling in the austenite recrystallization zone to be 18-24mm, and the thickness of the finished steel after rolling in the austenite non-recrystallization zone to be 4-8mm.

[0036] The CCT curve of the composition of the present invention calculated based on JMatPro software is shown in the attached figure. Figure 1As shown in the figure, it can be seen that when the cooling rate is -5~-20℃ / s, the cooling curve can directly pass through the bainite transformation temperature range, and the air cooling rate is -5~-10℃ / s. Therefore, the cooling process adopts air cooling to regulate the phase transformation process.

[0037] The purpose of critical annealing is to regulate the type and proportion of finished steel structure. For example, to make the distribution of bainitic ferrite more uniform, introduce high-density dislocations between laths, and improve strength. Promote the formation of residual austenite, which plays a role of strain hardening during deformation. Therefore, the critical annealing temperature is controlled to 720-750°C in the present invention. At the same time, in order to prevent grain coarsening and reduce the mechanical properties of the material, the holding time is controlled to 15-25min.

[0038] The organizational structure selection mechanism of the present invention:

[0039] The steel provided has good plasticity and impact resistance while having high strength. The reasons include: 1) Fine lath structure: Bainitic ferrite is composed of fine lath-like structures, which have high dislocation density. The fine lath structure helps to improve strength because dislocations are the main carriers of plastic deformation. High dislocation density means more obstacles hindering dislocation movement, thereby increasing tensile strength. 2) Phase interface strengthening: There are a large number of phase interfaces in the microstructure (for example, the interface between bainitic ferrite and retained austenite or other phases). These phase interfaces can play a strengthening role because they can effectively pin dislocations and prevent them from slipping, thereby improving the strength and toughness of the material. 3) The role of retained austenite: Retained austenite can undergo strain-induced martensitic phase transformation during tension. This phase transformation mechanism can absorb a large amount of deformation energy and delay crack propagation, thereby improving the ductility and toughness of the material. 4) Multi-directional slip system: The lath structure of bainitic ferrite provides multiple slip systems, allowing the material to slip in multiple directions during tension, thereby improving plastic deformation ability. This multi-directional slip system helps to improve the tensile ductility of the material. 5) Microstructure uniformity: The resulting steel has a relatively uniform microstructure, which helps to evenly disperse stress during the tensile process, thereby alleviating stress concentration, delaying the formation and expansion of cracks, and further improving the tensile properties of the material.

[0040] Therefore, the present invention adopts a low-carbon and low-alloy component design by comprehensively regulating the alloy composition and preparation process, without adding alloy elements such as Nb, V, Ti, Mo, and Cu; only hot rolling and critical annealing processes are used to prepare hot-rolled high-strength steel with a microstructure of lath-shaped bainitic ferrite, a small amount of blocky martensite, lamellar residual austenite, and island martensite / austenite. Compared with traditional hot-rolled high-strength steel, it has the advantages of low alloy cost and low production cost.

[0041] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0042] The above scheme, the present invention proposes a low-cost 1500MPa grade hot-rolled high-strength steel and a preparation method, which can solve the technical problem in the prior art that the strength and plasticity of hot-rolled high-strength steel cannot be obtained through a low-cost, high-efficiency preparation method.

[0043] The present invention adjusts the properties of the low-carbon low-alloy steel, such as the lath structure, dislocation density, and residual austenite, by selecting and adjusting the alloying elements and adjusting the contents, combining hot rolling and intercritical annealing treatments, and controlling the air cooling rate, so that the steel has high strength, high elongation, and high impact resistance, thereby avoiding the addition of expensive alloying elements and complicated heat treatment processes, having the advantages of low cost and high performance, and being suitable for large-scale industrial production.

[0044] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared by the present invention is 7.5-7.6g / cm 3 , hardness is 490-520HV, tensile strength is not less than 1500MPa, yield strength is not less than 750MPa, yield strength ratio is 0.48-0.60, elongation is not less than 18%, strength-ductility product is not less than 28.798GPa·%, room temperature impact energy is not less than 39J, and -40℃ low temperature impact energy is not less than 30J.

[0045] In summary, compared with other traditional methods, the method of the present invention creatively selects alloy elements and adjusts their contents, combines hot rolling and intercritical annealing treatments, and controls the air cooling rate. The fine lath structure of the bainitic ferrite structure, high dislocation density, phase interface strengthening, residual austenite effect, multi-directional slip system and microstructure uniformity work together to synergistically improve the comprehensive properties of the steel plate, such as strength, plasticity, and impact resistance. In addition, the method has high resource utilization, low production cost, short process, easy operation, high efficiency, and is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0047] Figure 1 It is a CCT curve diagram of the composition of a low-cost 1500MPa grade hot-rolled high-strength steel of the present invention calculated based on JMatPro software;

[0048] Figure 2 This is a SEM image of a low-cost 1500MPa grade hot-rolled high-strength steel according to Example 3 of the present invention;

[0049] Figure 3 This is an EBSD diagram of a low-cost 1500MPa grade hot-rolled high-strength steel according to Example 3 of the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0051] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0052] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same. "of", "corresponding" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same.

[0053] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0054] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0055] A low-cost 1500MPa hot-rolled high-strength steel, wherein the low-cost 1500MPa hot-rolled high-strength steel has a thickness of 4-8mm and a chemical composition of, by mass percentage, C 0.20-0.24%, Mn 2.4-2.8%, Al 1.4-1.8%, Si 0.3-0.4%, P≤0.01%, S≤0.01%, and the balance is Fe and unavoidable impurity elements.

[0056] In particular, the metallographic composition of the low-cost 1500 MPa grade hot-rolled high-strength steel is 82-87% lath-shaped bainitic ferrite structure + 5-10% small amount of blocky martensite structure + 2-3% lamellar retained austenite structure + 4-5% island-shaped retained austenite structure.

[0057] In particular, the lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel is ≤1μm; the average size of the blocky martensite structure is ≤6μm; the lamellar thickness of the lamellar retained austenite structure is ≤1μm; and the average grain size of the island retained austenite structure is ≤3μm.

[0058] In particular, the density of the low-cost 1500MPa grade hot-rolled high-strength steel is 7.5-7.6g / cm 3 , hardness is 490-520HV, tensile strength is not less than 1500MPa, yield strength is not less than 750MPa, yield strength ratio is 0.48-0.60, elongation is not less than 18%, strength-ductility product is not less than 28.798GPa·%, room temperature impact energy is not less than 39J, and -40℃ low temperature impact energy is not less than 30J.

[0059] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0060] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0061] S2, continuous casting: smelting the raw materials in S1 and continuously casting them to obtain high-strength steel slabs;

[0062] S3, heat treatment: heat treating the S2 high-strength steel slab to obtain a heat-treated high-strength steel slab;

[0063] S4, hot rolling: the high-strength steel slab after the S3 heat treatment is fully heated and then taken out of the furnace for hot rolling, and air-cooled to room temperature after the hot rolling to obtain a high-strength rolled plate;

[0064] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment and then air-cooled to room temperature to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0065] In particular, the thickness of the S2 medium and high strength steel slab is 60-80 mm.

[0066] In particular, the heating rate of the heat treatment in S3 is 5-9°C / min, the heat treatment temperature is 1170-1220°C, and the holding time is 15-30min.

[0067] In particular, the starting rolling temperature of hot rolling in S4 is 1060-1100°C, and after 8-10 rolling passes, the final rolling temperature is 860-900°C, the reduction in each pass is 10-30%, and the total reduction is 86-95%.

[0068] In particular, hot rolling in S4 is to control the rolling of the austenite recrystallization zone for 3-4 passes, the intermediate billet thickness is 12-18 mm, the rolling of the austenite non-recrystallization zone is 5-6 passes, and the finished steel thickness is 4-8 mm.

[0069] In particular, the annealing temperature of the critical annealing treatment in S5 is 720-750°C, the holding time is 15-25min, and the cooling rate of air cooling is -5~-10°C / s.

[0070] Example 1

[0071] A low-cost 1500 MPa grade hot-rolled high-strength steel. The low-cost 1500 MPa grade hot-rolled high-strength steel in this embodiment has a thickness of 4.3 mm, and has the following chemical compositions by mass percentage: C 0.20%, Mn 2.5%, Al 1.7%, Si 0.32%, P 0.01%, S0.008%, and the remainder is Fe and unavoidable impurity elements.

[0072] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0073] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0074] S2, continuous casting: S1 raw materials are smelted and continuously cast to obtain high-strength steel slabs; the thickness of the high-strength steel slabs is 62 mm;

[0075] S3, heat treatment: heat treatment is performed on the S2 high-strength steel slab, the heating rate of the heat treatment is 7°C / s, the heat treatment temperature is 1172°C, and the holding time is 18min, to obtain the high-strength steel slab after heat treatment;

[0076] S4, hot rolling: the high-strength steel slab after S3 heat treatment is fully heated and then taken out of the furnace for hot rolling. The starting rolling temperature of hot rolling is 1068°C, and after 8 passes of rolling, the final rolling temperature is 865°C, and the total reduction is 93%; after hot rolling, it is air-cooled to room temperature to obtain a high-strength rolled plate; wherein, hot rolling is controlled to roll 3 times in the austenite recrystallization zone, the intermediate billet thickness is 15mm, and the austenite non-recrystallization zone is rolled 5 times, and the finished steel thickness is 4.3mm;

[0077] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment, the annealing temperature of the critical annealing treatment is 725°C, and the holding time is 22 minutes; then it is air-cooled to room temperature at a cooling rate of -6°C / s to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0078] The metallographic composition of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 86% lath-shaped bainite ferrite structure + 6% small amount of blocky martensite structure + 3% lamellar retained austenite structure + 5% island-shaped retained austenite structure.

[0079] The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 0.9μm; the average size of the blocky martensite structure is 5.8μm; the lamellar thickness of the lamellar retained austenite structure is 1μm; and the average grain size of the island retained austenite structure is 2.8μm.

[0080] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 7.53g / cm 3 The hardness is 495HV, the tensile strength is 1522MPa, the yield strength is 750MPa, the yield strength ratio is 0.493, the elongation is 19.4%, the strength-ductility product is 29.527GPa·%, the room temperature impact energy is 40J, and the low temperature impact energy of -40℃ is 32J.

[0081] Example 2

[0082] A low-cost 1500 MPa grade hot-rolled high-strength steel. The low-cost 1500 MPa grade hot-rolled high-strength steel in this embodiment has a thickness of 5.7 mm, and the chemical composition is calculated by mass percentage as follows: C 0.21%, Mn 2.6%, Al 1.6%, Si 0.35%, P 0.008%, S 0.007%, and the balance is Fe and unavoidable impurity elements.

[0083] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0084] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0085] S2, continuous casting: S1 raw materials are smelted and continuously cast to obtain high-strength steel slabs; the thickness of the high-strength steel slabs is 73 mm;

[0086] S3, heat treatment: heat treatment is performed on the S2 high-strength steel slab, the heating rate of the heat treatment is 5°C / s, the heat treatment temperature is 1188°C, and the holding time is 22min, to obtain the heat-treated high-strength steel slab;

[0087] S4, hot rolling: the high-strength steel slab after S3 heat treatment is fully heated and then taken out of the furnace for hot rolling. The starting rolling temperature of hot rolling is 1082°C, and after 10 passes of rolling, the final rolling temperature is 884°C, and the total reduction is 92%; after hot rolling, it is air-cooled to room temperature to obtain a high-strength rolled plate; wherein, hot rolling is to control the austenite recrystallization zone rolling for 4 passes, the intermediate billet thickness is 17mm, the austenite non-recrystallization zone rolling is 6 passes, and the finished steel thickness is 5.7mm;

[0088] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment, the annealing temperature of the critical annealing treatment is 739°C, and the holding time is 16 minutes; then it is air-cooled to room temperature at a cooling rate of -8°C / s to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0089] The metallographic composition of the low-cost 1500 MPa grade hot-rolled high-strength steel prepared in this embodiment is 85% lath-shaped bainite ferrite structure + 8% small amount of blocky martensite structure + 3% lamellar retained austenite structure + 4% island-shaped retained austenite structure.

[0090] The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 0.8μm; the average size of the blocky martensite structure is 5.7μm; the lamellar thickness of the lamellar retained austenite structure is 0.9μm; and the average grain size of the island retained austenite structure is 2.8μm.

[0091] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 7.55g / cm 3 The hardness is 500HV, the tensile strength is 1534MPa, the yield strength is 762MPa, the yield strength ratio is 0.497, the elongation is 18.9%, the strength-ductility product is 28.993GPa·%, the room temperature impact energy is 40J, and the low temperature impact energy of -40℃ is 31J.

[0092] Example 3

[0093] A low-cost 1500 MPa grade hot-rolled high-strength steel. The low-cost 1500 MPa grade hot-rolled high-strength steel in this embodiment has a thickness of 4.8 mm, and has the following chemical compositions by mass percentage: C 0.24%, Mn 2.4%, Al 1.8%, Si 0.38%, P 0.009%, S 0.010%, and the remainder is Fe and unavoidable impurity elements.

[0094] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0095] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0096] S2, continuous casting: S1 raw materials are smelted and continuously cast to obtain high-strength steel slabs; the thickness of the high-strength steel slabs is 66 mm;

[0097] S3, heat treatment: heat treatment is performed on the S2 high-strength steel slab, the heating rate of the heat treatment is 8°C / s, the heat treatment temperature is 1200°C, and the holding time is 26 minutes to obtain the high-strength steel slab after heat treatment;

[0098] S4, hot rolling: the high-strength steel slab after S3 heat treatment is fully heated and then taken out of the furnace for hot rolling. The starting rolling temperature of hot rolling is 1098°C, and after 8 passes of rolling, the final rolling temperature is 898°C, and the total reduction is 93%; after hot rolling, it is air-cooled to room temperature to obtain a high-strength rolled plate; wherein, hot rolling is controlled to roll 3 times in the austenite recrystallization zone, the intermediate billet thickness is 12mm, and the austenite non-recrystallization zone is rolled 5 times, and the finished steel thickness is 4.8mm;

[0099] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment, the annealing temperature of the critical annealing treatment is 745°C, and the holding time is 24 minutes; then it is air-cooled to room temperature at a cooling rate of -9°C / s to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0100] like Figure 2 and 3 As shown, the metallographic composition of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 84% ​​lath-shaped bainitic ferrite structure + 9% small amount of blocky martensite structure + 3% lamellar retained austenite structure + 4% island-shaped retained austenite structure. It can be seen that the microstructure of this embodiment is mainly lath-shaped bainitic ferrite structure, and also contains a small amount of blocky martensite, lamellar retained austenite, and island-shaped martensite / austenite.

[0101] The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 0.7μm; the average size of the blocky martensite structure is 5.6μm; the lamellar thickness of the lamellar retained austenite structure is 0.7μm; and the average grain size of the island retained austenite structure is 2.6μm.

[0102] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 7.59g / cm 3 The hardness is 515HV, the tensile strength is 1547MPa, the yield strength is 7730MPa, the yield strength ratio is 0.500, the elongation is 18.5%, the strength-ductility product is 28.620GPa·%, the room temperature impact energy is 41J, and the low temperature impact energy of -40℃ is 32J.

[0103] Example 4

[0104] A low-cost 1500 MPa grade hot-rolled high-strength steel. The low-cost 1500 MPa grade hot-rolled high-strength steel in this embodiment has a thickness of 5.2 mm, and has the following chemical compositions by mass percentage: C 0.20%, Mn 2.7%, Al 1.4%, Si 0.36%, P 0.007%, S 0.009%, and the remainder is Fe and unavoidable impurity elements.

[0105] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0106] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0107] S2, continuous casting: smelting the raw materials of S1 and continuously casting to obtain high-strength steel slabs; the thickness of the high-strength steel slabs is 70 mm;

[0108] S3, heat treatment: heat treatment is performed on the S2 high-strength steel slab, the heating rate of the heat treatment is 9°C / s, the heat treatment temperature is 1192°C, and the holding time is 17min, to obtain the heat-treated high-strength steel slab;

[0109] S4, hot rolling: the high-strength steel slab after S3 heat treatment is fully heated and then taken out of the furnace for hot rolling. The starting rolling temperature of hot rolling is 1075°C, and after 9 passes of rolling, the final rolling temperature is 872°C, and the total reduction is 93%; after hot rolling, it is air-cooled to room temperature to obtain a high-strength rolled plate; wherein, hot rolling is controlled to roll 3 times in the austenite recrystallization zone, the intermediate billet thickness is 14mm, and the austenite non-recrystallization zone is rolled 6 times, and the finished steel thickness is 5.2mm;

[0110] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment, the annealing temperature of the critical annealing treatment is 730°C, and the holding time is 18 minutes; then it is air-cooled to room temperature at a cooling rate of -7°C / s to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0111] The metallographic composition of the low-cost 1500 MPa grade hot-rolled high-strength steel prepared in this embodiment is 86% lath-shaped bainitic ferrite structure + 7% small amount of blocky martensite structure + 3% lamellar retained austenite structure + 4% island-shaped retained austenite structure.

[0112] The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 0.9μm; the average size of the blocky martensite structure is 5.7μm; the lamellar thickness of the lamellar retained austenite structure is 0.9μm; and the average grain size of the island retained austenite structure is 2.6μm.

[0113] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 7.54g / cm 3 The hardness is 495HV, the tensile strength is 1528MPa, the yield strength is 755MPa, the yield strength ratio is 0.494, the elongation is 19.2%, the strength-ductility product is 29.338GPa·%, the room temperature impact energy is 39J, and the low temperature impact energy of -40℃ is 30J.

[0114] Example 5

[0115] A low-cost 1500 MPa grade hot-rolled high-strength steel. The low-cost 1500 MPa grade hot-rolled high-strength steel in this embodiment has a thickness of 6.6 mm, and has the following chemical compositions by mass percentage: C 0.21%, Mn 2.8%, Al 1.5%, Si 0.31%, P 0.010%, S 0.008%, and the remainder is Fe and unavoidable impurity elements.

[0116] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0117] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0118] S2, continuous casting: S1 raw materials are smelted and continuously cast to obtain high-strength steel slabs; the thickness of the high-strength steel slabs is 68 mm;

[0119] S3, heat treatment: heat treatment is performed on the S2 high-strength steel slab, the heating rate of the heat treatment is 6°C / s, the heat treatment temperature is 1215°C, and the holding time is 28min, to obtain the heat-treated high-strength steel slab;

[0120] S4, hot rolling: the high-strength steel slab after S3 heat treatment is fully heated and then taken out of the furnace for hot rolling. The starting rolling temperature of hot rolling is 1084°C, and after 9 passes of rolling, the final rolling temperature is 877°C, and the total reduction is 90%; after hot rolling, it is air-cooled to room temperature to obtain a high-strength rolled plate; wherein, hot rolling is to control the austenite recrystallization zone rolling for 4 passes, the intermediate billet thickness is 18mm, the austenite non-recrystallization zone rolling is 5 passes, and the finished steel thickness is 6.6mm;

[0121] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment, the annealing temperature of the critical annealing treatment is 735°C, and the holding time is 20 minutes; then it is air-cooled to room temperature at a cooling rate of -7°C / s to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0122] The metallographic composition of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 86% lath-shaped bainite ferrite structure + 8% small amount of blocky martensite structure + 2% lamellar retained austenite structure + 4% island-shaped retained austenite structure.

[0123] The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 0.8μm; the average size of the blocky martensite structure is 5.7μm; the lamellar thickness of the lamellar retained austenite structure is 0.9μm; and the average grain size of the island retained austenite structure is 2.7μm.

[0124] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 7.55g / cm 3 The hardness is 501HV, the tensile strength is 1531MPa, the yield strength is 759MPa, the yield strength ratio is 0.496, the elongation is 19.0%, the strength-ductility product is 29.089GPa·%, the room temperature impact energy is 40J, and the low temperature impact energy of -40℃ is 30J.

[0125] Example 6

[0126] A low-cost 1500 MPa grade hot-rolled high-strength steel. The low-cost 1500 MPa grade hot-rolled high-strength steel in this embodiment has a thickness of 7.1 mm, and has the following chemical compositions by mass percentage: C 0.23%, Mn 2.6%, Al 1.4%, Si 0.37%, P 0.009%, S 0.009%, and the remainder is Fe and unavoidable impurity elements.

[0127] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0128] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0129] S2, continuous casting: smelting the raw materials of S1 and continuously casting to obtain high-strength steel slabs; the thickness of the high-strength steel slabs is 75 mm;

[0130] S3, heat treatment: heat treatment is performed on the S2 high-strength steel slab, the heating rate of the heat treatment is 6°C / s, the heat treatment temperature is 1209°C, and the holding time is 20min, to obtain the high-strength steel slab after heat treatment;

[0131] S4, hot rolling: the high-strength steel slab after S3 heat treatment is fully heated and then taken out of the furnace for hot rolling. The starting rolling temperature of hot rolling is 1096°C, and after 9 passes of rolling, the final rolling temperature is 895°C, and the total reduction is 91%; after hot rolling, it is air-cooled to room temperature to obtain a high-strength rolled plate; wherein, hot rolling is to control the austenite recrystallization zone rolling for 4 passes, the intermediate billet thickness is 16mm, the austenite non-recrystallization zone rolling is 5 passes, and the finished steel thickness is 7.1mm;

[0132] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment, the annealing temperature of the critical annealing treatment is 734°C, and the holding time is 19 minutes; then it is air-cooled to room temperature at a cooling rate of -9°C / s to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0133] The metallographic composition of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 84% ​​lath-shaped bainitic ferrite structure + 10% small amount of blocky martensite structure + 2% lamellar retained austenite structure + 4% island-shaped retained austenite structure.

[0134] The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 0.7μm; the average size of the blocky martensite structure is 5.6μm; the lamellar thickness of the lamellar retained austenite structure is 0.8μm; and the average grain size of the island retained austenite structure is 2.7μm.

[0135] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 7.51g / cm 3 The hardness is 512HV, the tensile strength is 1540MPa, the yield strength is 768MPa, the yield strength ratio is 0.499, the elongation is 18.7%, the strength-ductility product is 28.798GPa·%, the room temperature impact energy is 41J, and the low temperature impact energy of -40℃ is 31J.

[0136] Comparative Example 1

[0137] A low-cost 1500MPa grade hot-rolled high-strength steel. The low-cost 1500MPa grade hot-rolled high-strength steel of this comparative example has a thickness of 7.5mm, and the chemical composition is calculated by mass percentage as follows: C 0.22%, Mn 2.6%, Al 1.5%, Si 0.36%, P 0.009%, S 0.009%, and the balance is Fe and unavoidable impurity elements.

[0138] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0139] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0140] S2, continuous casting: S1 raw materials are smelted and continuously cast to obtain high-strength steel slabs; the thickness of the high-strength steel slabs is 78 mm;

[0141] S3, heat treatment: heat treatment is performed on the S2 high-strength steel slab, the heating rate of the heat treatment is 6°C / s, the heat treatment temperature is 1190°C, and the holding time is 25min, to obtain the high-strength steel slab after heat treatment;

[0142] S4, hot rolling: the high-strength steel slab after S3 heat treatment is fully heated and then taken out of the furnace for hot rolling, the starting rolling temperature of hot rolling is 1080℃, and after 8 passes of rolling, the final rolling temperature is 879℃, and the total reduction is 90%; after the hot rolling is completed, it is air-cooled to room temperature to obtain a high-strength rolled plate; wherein, the hot rolling is to control the austenite recrystallization zone rolling for 3 passes, the intermediate billet thickness is 16mm, the austenite non-recrystallization zone rolling is 5 passes, and the finished steel thickness is 7.5mm;

[0143] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment, the annealing temperature of the critical annealing treatment is 728°C, and the holding time is 20 minutes; then it is water-cooled to room temperature at a cooling rate of -70°C / s to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0144] The metallographic composition of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this comparative example is 18% lath-shaped bainitic ferrite structure + 73% small amount of blocky martensite structure + 3% lamellar retained austenite structure + 6% island-shaped retained austenite structure.

[0145] The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 0.6μm; the average size of the blocky martensite structure is 5.5μm; the lamellar thickness of the lamellar retained austenite structure is 0.7μm; and the average grain size of the island retained austenite structure is 2.5μm.

[0146] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 7.57g / cm 3The hardness is 530HV, the tensile strength is 1603MPa, the yield strength is 1210MPa, the yield strength ratio is 0.755, the elongation is 14.8%, the strength-ductility product is 23.724GPa·%, the room temperature impact energy is 36J, and the low temperature impact energy of -40℃ is 27J.

[0147] Comparative Example 2

[0148] A low-cost 1500 MPa grade hot-rolled high-strength steel. The low-cost 1500 MPa grade hot-rolled high-strength steel in this embodiment has a thickness of 6.0 mm, and has the following chemical compositions by mass percentage: C 0.22%, Mn 2.5%, Al 1.5%, Si 0.33%, P 0.008%, S 0.008%, and the remainder is Fe and unavoidable impurity elements.

[0149] A method for preparing low-cost 1500MPa hot-rolled high-strength steel is provided. The method for preparing low-cost 1500MPa hot-rolled high-strength steel comprises the following steps:

[0150] S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials;

[0151] S2, continuous casting: S1 raw materials are smelted and continuously cast to obtain high-strength steel slabs; the thickness of the high-strength steel slabs is 72 mm;

[0152] S3, heat treatment: heat treatment is performed on the S2 high-strength steel slab, the heating rate of the heat treatment is 6°C / s, the heat treatment temperature is 1200°C, and the holding time is 21min, to obtain the heat-treated high-strength steel slab;

[0153] S4, hot rolling: the high-strength steel slab after S3 heat treatment is fully heated and then taken out of the furnace for hot rolling. The starting rolling temperature of hot rolling is 1090°C, and after 10 passes of rolling, the final rolling temperature is 890°C, and the total reduction is 92%; after hot rolling, it is air-cooled to room temperature to obtain a high-strength rolled plate; wherein, hot rolling is to control the austenite recrystallization zone rolling for 4 passes, the intermediate billet thickness is 15mm, the austenite non-recrystallization zone rolling is 6 passes, and the finished steel thickness is 6.0mm;

[0154] S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment, the annealing temperature of the critical annealing treatment is 800°C, and the holding time is 20 minutes; then it is air-cooled to room temperature at a cooling rate of -9°C / s to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

[0155] The metallographic composition of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 52% lath-shaped bainitic ferrite structure + 45% small amount of blocky martensite structure + 1% lamellar retained austenite structure + 2% island-shaped retained austenite structure.

[0156] The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 1.1μm; the average size of the blocky martensite structure is 6.2μm; the lamellar thickness of the lamellar retained austenite structure is 1.0μm; and the average grain size of the island retained austenite structure is 3.1μm.

[0157] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared in this embodiment is 7.52g / cm 3 The hardness is 521HV, the tensile strength is 1589MPa, the yield strength is 922MPa, the yield strength ratio is 0.580, the elongation is 15.1%, the strength-ductility product is 23.994GPa·%, the room temperature impact energy is 38J, and the low temperature impact energy of -40℃ is 30J.

[0158] In summary, after comparing the embodiment with the comparative example, it can be found that in comparative example 1, the water cooling rate is relatively large, which promotes the formation of more martensitic structures, and the yield strength and tensile strength are improved, but a large amount of hard and brittle martensitic structures significantly reduce the plasticity, which does not meet the requirements of the present invention. In addition, in comparative example 2, the critical zone annealing temperature is increased, the martensitic structure is significantly increased, and the grain size is increased. Although a certain strength value is maintained, the plasticity is reduced, which does not meet the requirements of the present invention. Therefore, this embodiment has ultra-high strength and good plastic matching, which is obtained under the combined action of fine and high dislocation density bainitic ferrite laths and martensitic structures, and a certain proportion of residual austenite.

[0159] The above scheme, the present invention proposes a low-cost 1500MPa grade hot-rolled high-strength steel and a preparation method, which can solve the technical problem in the prior art that the strength and plasticity of hot-rolled high-strength steel cannot be obtained through a low-cost, high-efficiency preparation method.

[0160] The present invention adjusts the properties of the low-carbon low-alloy steel, such as the lath structure, dislocation density, and residual austenite, by selecting and adjusting the alloying elements and adjusting the contents, combining hot rolling and intercritical annealing treatments, and controlling the air cooling rate, so that the steel has high strength, high elongation, and high impact resistance, thereby avoiding the addition of expensive alloying elements and complicated heat treatment processes, having the advantages of low cost and high performance, and being suitable for large-scale industrial production.

[0161] The density of the low-cost 1500MPa grade hot-rolled high-strength steel prepared by the present invention is 7.5-7.6g / cm 3, hardness is 490-520HV, tensile strength is not less than 1500MPa, yield strength is not less than 750MPa, yield strength ratio is 0.48-0.60, elongation is not less than 18%, strength-ductility product is not less than 28.798GPa·%, room temperature impact energy is not less than 39J, and -40℃ low temperature impact energy is not less than 30J.

[0162] In summary, compared with other traditional methods, the method of the present invention creatively selects alloy elements and adjusts their contents, combines hot rolling and intercritical annealing treatments, and controls the air cooling rate. The fine lath structure of the bainitic ferrite structure, high dislocation density, phase interface strengthening, residual austenite effect, multi-directional slip system and microstructure uniformity work together to synergistically improve the comprehensive properties of the steel plate, such as strength, plasticity, and impact resistance. In addition, the method has high resource utilization, low production cost, short process, easy operation, high efficiency, and is conducive to large-scale industrial production and promotion.

[0163] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0164] In the present invention, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0165] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0166] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A low-cost 1500MPa grade hot-rolled high-strength steel, characterized in that: The low-cost 1500MPa grade hot-rolled high-strength steel has a thickness of 4-8mm, and its chemical composition by mass percentage is: C 0.20-0.24%, Mn 2.4-2.8%, Al 1.4-1.8%, Si 0.3-0.4%, P≤0.01%, S≤0.01%, and the balance is Fe and unavoidable impurity elements.

2. The low-cost 1500MPa grade hot-rolled high-strength steel according to claim 1, characterized in that: The metallographic composition of the low-cost 1500MPa grade hot-rolled high-strength steel is 82-87% lath-shaped bainite ferrite structure + 5-10% small amount of blocky martensite structure + 2-3% lamellar retained austenite structure + 4-5% island-shaped retained austenite structure.

3. The low-cost 1500MPa grade hot-rolled high-strength steel according to claim 2, characterized in that: The lath width of the bainitic ferrite structure in the low-cost 1500MPa grade hot-rolled high-strength steel is ≤1μm; the average size of the blocky martensite structure is ≤6μm; the lamellar thickness of the lamellar retained austenite structure is ≤1μm; and the average grain size of the island retained austenite structure is ≤3μm.

4. The low-cost 1500MPa grade hot-rolled high-strength steel according to claim 1, characterized in that: The density of the low-cost 1500MPa grade hot-rolled high-strength steel is 7.5-7.6g / cm 3 , hardness is 490-520HV, tensile strength is not less than 1500MPa, yield strength is not less than 750MPa, yield strength ratio is 0.48-0.60, elongation is not less than 18%, strength-ductility product is not less than 28.798GPa·%, room temperature impact energy is not less than 39J, and -40℃ low temperature impact energy is not less than 30J.

5. A method for preparing low-cost 1500MPa grade hot-rolled high-strength steel according to claim 1, characterized in that: The method for preparing the low-cost 1500MPa grade hot-rolled high-strength steel comprises the following steps: S1. Raw material weighing: Use pure metals and intermediate alloys with a purity of 99.99% as raw materials, and accurately weigh and mix them according to the chemical composition ratio to obtain raw materials; S2, continuous casting: smelting the raw materials in S1 and continuously casting them to obtain high-strength steel slabs; S3, heat treatment: heat treating the S2 high-strength steel slab to obtain a heat-treated high-strength steel slab; S4, hot rolling: the high-strength steel slab after the S3 heat treatment is fully heated and then taken out of the furnace for hot rolling, and air-cooled to room temperature after the hot rolling to obtain a high-strength rolled plate; S5, critical annealing: The S4 high-strength rolled plate is subjected to critical annealing treatment and then air-cooled to room temperature to obtain a finished low-cost 1500MPa grade hot-rolled high-strength steel.

6. The method for preparing low-cost 1500MPa grade hot-rolled high-strength steel according to claim 5, characterized in that: The thickness of S2 medium and high strength steel slab is 60-80mm.

7. The method for preparing low-cost 1500MPa grade hot-rolled high-strength steel according to claim 5, characterized in that: The heating rate of the heat treatment in S3 is 5-9°C / min, the heat treatment temperature is 1170-1220°C, and the holding time is 15-30min.

8. The method for preparing low-cost 1500MPa grade hot-rolled high-strength steel according to claim 5, characterized in that: The starting rolling temperature of hot rolling in S4 is 1060-1100℃, and after 8-10 rolling passes, the final rolling temperature is 860-900℃, the reduction in each pass is 10-30%, and the total reduction is 86-95%.

9. The method for preparing low-cost 1500MPa grade hot-rolled high-strength steel according to claim 5, characterized in that: In S4, hot rolling is performed for 3-4 passes to control the austenite recrystallization zone, the intermediate billet thickness is 12-18 mm, and the austenite non-recrystallization zone is rolled for 5-6 passes, and the finished steel thickness is 4-8 mm.

10. The method for preparing low-cost 1500MPa grade hot-rolled high-strength steel according to claim 5, characterized in that: The annealing temperature of the critical annealing treatment in S5 is 720-750°C, the holding time is 15-25min, and the cooling rate of air cooling is -5~-10°C / s.

Images