A 800MPa grade nano-precipitated high-strength steel and its preparation method

Abstract

The present application discloses an 800MPa-level nano-precipitated high-strength steel and a preparation method thereof. In terms of weight percentage, the components of the 800MPa-level nano-precipitated high-strength steel include: C, 0.050wt% to 0.090wt%; Mn, 1.60wt% to 2.0wt%; Si, 0.05wt% to 0.20wt%; Nb, 0.03wt% to 0.06wt%; V, 0.01wt% to 0.035wt%; T i, 0.09wt%~0.15wt%; Mo, 0.12wt%~0.25wt%; Cr, 0.02wt%~0.30wt%; S, 0wt%~0.008wt%; P, 0wt%~0.020wt%; the rest are Fe and inevitable impurity elements. The internal microstructure of the 800MPa-level nano-precipitated high-strength steel is mainly ferrite, and nano-scale precipitated particles are dispersed in the ferrite. The 800MPa-level nano-precipitated high-strength steel has good comprehensive mechanical properties, and has the advantages of high strength, good plasticity and good toughness, and is not easy to crack when the steel is formed.

Description

Technical Field

[0001] The present application belongs to the technical field of high-strength steel production, and specifically relates to an 800MPa-level nano-precipitation high-strength steel and a preparation method thereof. Background Art

[0002] At present, with the vigorous development of the automobile industry, the demand for high-strength automobile steel is also increasing. At the same time, as the country pays more and more attention to environmental protection and carbon reduction, the automobile industry has increased the application of lightweight. After advanced lightweight optimization design, high-strength steel plates for automobiles have certain special properties and can play a better safety performance. In some high-requirement automotive parts, such as fuel tank brackets and LNG tank brackets for commercial vehicles, they must have both high strength and high plasticity and good forming effect. Therefore, high-strength and plastic hot-rolled steel plates have become the mainstream of lightweight materials for automobiles for a period of time.

[0003] Quenched and tempered steel, as a type of steel widely used in the automotive industry, has high strength. Automotive parts made from quenched and tempered steel have good comprehensive mechanical properties.

[0004] However, there are still some disadvantages in tempered steel: first, the preparation process of quenched and tempered steel involves quenching and tempering, which is not easy to operate and consumes energy at high temperature for a long time; second, during the quenching process, the surface of the quenched and tempered steel is prone to quenching cracks and quenching deformation, poor surface quality and other problems. Therefore, this application uses a new preparation method to prepare a high-strength steel material that has high strength, plasticity, and toughness, and is not prone to cracks or deformation, and the preparation process is highly controllable and has low energy loss. Summary of the invention

[0005] In view of this, the embodiment of the present application provides an 800MPa-level nano-precipitated high-strength steel and a preparation method thereof, which can obtain a high-strength steel material that has high strength, plasticity, and toughness and is not prone to cracks or deformation. The preparation method is simple, has few steps, is easy to operate, and consumes little energy.

[0006] In a first aspect, an embodiment of the present application provides an 800MPa-level nano-precipitated high-strength steel. In terms of weight percentage, the components of the 800MPa-level nano-precipitated high-strength steel include: C, 0.050wt%~0.090wt%; Mn, 1.60wt%~2.0wt%; Si, 0.05wt%~0.20wt%; Nb, 0.03wt%~0.06wt%; V, 0.01wt%~0.035wt%; Ti, 0.09wt%~0.15wt%; Mo, 0.12wt%~0.25wt%; Cr, 0.02wt%~0.30wt%; S, 0wt%~0.008wt%; P, 0wt%~0.020wt%; the rest are Fe and unavoidable impurity elements.

[0007] The internal microstructure of 800MPa-level nano-precipitation high-strength steel is ferrite, in which nano-scale precipitated particles are dispersed.

[0008] According to one embodiment of the present application, the precipitated particles include a combination of one or more of Nb(C, N), V(C, N), TiC, and MoC.

[0009] According to one embodiment of the present application, in terms of percentage by number, the precipitated particles include 75% to 100% of precipitated particles having a particle size less than or equal to 10 nm and 0% to 25% of precipitated particles having a particle size greater than 10 nm.

[0010] According to one embodiment of the present application, the mechanical properties of 800MPa-level nano-precipitated high-strength steel include: yield strength greater than or equal to 700MPa, tensile strength greater than or equal to 800MPa, elongation after fracture greater than or equal to 18%, and hole expansion rate greater than or equal to 70%.

[0011] A second aspect of the embodiment of the present application provides a method for preparing 800MPa-level nano-precipitated high-strength steel, comprising:

[0012] The molten steel is cast by a continuous casting machine to obtain a continuous casting billet, wherein the molten steel components include, by weight percentage, C, 0.050wt%~0.090wt%; Mn, 1.60wt%~2.0wt%; Si, 0.05wt%~0.20wt%; Nb, 0.03wt%~0.06wt%; V, 0.01wt%~0.035wt%; Ti, 0.09wt%~0.15wt%; Mo, 0.12wt%~0.25wt%; Cr, 0.02wt%~0.30wt%; S, 0wt%~0.008wt%; P, 0wt%~0.020wt%; the rest are Fe and inevitable impurity elements;

[0013] Heating the continuous casting billet until the microalloying elements in the chemical elements are completely dissolved and exist in the form of compounds;

[0014] The heated continuous casting billet is subjected to rough rolling and finish rolling to obtain hot rolled steel, wherein the outlet temperature of the finish rolling is 850°C to 900°C, and the cumulative reduction rate of the non-recrystallized zone is controlled to be greater than or equal to 20%;

[0015] Laminar cooling of hot rolled steel, laminar cooling uses front-end centralized cooling and does not use ultra-fast cooling;

[0016] The hot rolled steel after laminar cooling is coiled to obtain 800MPa-level nano-precipitation high-strength steel, wherein the coiling temperature is 560°C~620°C, and the steel is naturally air-cooled to room temperature after coiling to obtain 800MPa-level nano-precipitation high-strength steel. The internal microstructure of the 800MPa-level nano-precipitation high-strength steel is ferrite, and nano-scale precipitated particles are dispersed in the ferrite.

[0017] According to one embodiment of the present application, in the heating step, the heating temperature of the continuous casting billet is controlled within a range of 1180°C to 1280°C.

[0018] According to one embodiment of the present application, in the heating step, the cumulative time of the continuous casting billet in the furnace is greater than or equal to 160 minutes, and the time in the soaking section is greater than or equal to 30 minutes.

[0019] According to one embodiment of the present application, in the step of rough rolling and finish rolling the heated continuous casting billet to obtain hot rolled steel, the outlet thickness of the rough rolling is less than or equal to 48 mm, and the start rolling temperature of the finish rolling is 1000°C~1100°C.

[0020] According to one embodiment of the present application, the step of rough rolling and finish rolling the heated continuous casting billet to obtain hot rolled steel includes a descaling operation.

[0021] According to one embodiment of the present application, the descaling operation includes:

[0022] After the heated continuous casting billet is taken out of the furnace and before the heated continuous casting billet is subjected to rough rolling, a high-pressure water rough descaling operation is performed to obtain a roughly descaled continuous casting billet;

[0023] Before the finish rolling of the continuous casting billet after rough rolling, the fine descaling operation is performed. In summary, the technical solution provided by the present application has the following beneficial effects:

[0024] (1) The present application relates to an 800MPa-level nano-precipitated high-strength steel, the internal microstructure of which is ferrite, and the steel components include microalloying elements Nb, V, Ti, Mo, and Cr. These microalloying elements will be dissolved and exist in the form of compounds during the heating process of preparing the steel. In the subsequent controlled rolling and controlled cooling process, a large amount of carbides or carbonitrides such as Nb (C, N), V (C, N), TiC, MoC, etc., will be dispersed and precipitated into the ferrite in the form of nano-scale particles, so as to improve the strength and plasticity of the steel, achieve better comprehensive mechanical properties, and have the advantages of high strength, good plasticity, and good toughness.

[0025] (2) The present application relates to a method for preparing 800MPa-level nano-precipitated high-strength steel, which is based on a hot rolling process and combines controlled rolling and controlled cooling, precipitation strengthening and fine grain strengthening to avoid cracking or deformation of the steel during the quenching and tempering process. The hot rolling process includes a step of heating the continuous casting billet, a step of rolling, a step of laminar cooling and a step of coiling: in combination with the microalloying elements in the steel components, the purpose of heating the continuous casting billet is to dissolve the microalloying elements and control the number and size of the precipitated particles through the controlled rolling and controlled cooling process, and precipitate a large amount of them in the ferrite to improve the strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly described below; obviously, the drawings described below only involve some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0027] Figure 1 A schematic flow chart of a method for preparing 800MPa-grade nano-precipitated high-strength steel provided in an embodiment of the present application;

[0028] Figure 2 A schematic flow chart of step S300 of the method for preparing 800MPa-level nano-precipitated high-strength steel provided in an embodiment of the present application;

[0029] Figure 3 A schematic flow chart of a method for preparing 800MPa-grade nano-precipitated high-strength steel provided in another embodiment of the present application;

[0030] Figure 4 This is an internal microstructure diagram of an 800MPa-grade nano-precipitated high-strength steel provided in Example 1 of the present application;

[0031] Figure 5 A schematic diagram of precipitation particles of an 800MPa-grade nano-precipitated high-strength steel provided in Example 1 of the present application;

[0032] Figure 6 An internal microstructure diagram of an 800MPa-grade nano-precipitated high-strength steel provided in Example 2 of the present application;

[0033] Figure 7 This is an energy spectrum diagram of precipitated particles of an 800MPa-grade nano-precipitated high-strength steel provided in Example 2 of the present application. DETAILED DESCRIPTION

[0034] In order to make the application purpose, technical solution and beneficial technical effect of the present application clearer, the present application is further described in detail in conjunction with the embodiments below. It should be understood that the embodiments described in this specification are only for explaining the present application, not for limiting the present application.

[0035] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unclearly recorded range; and any lower limit can be combined with other lower limits to form an unclearly recorded range, and any upper limit can be combined with any other upper limit to form an unclearly recorded range. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unclearly recorded range.

[0036] In the description of the present application, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number, and the “multiple” in “one or more” means two or more than two.

[0037] As the amount of steel used in high-strength automotive parts increases, and people have higher and higher requirements for the strength, plasticity and toughness of steel, steel with high strength, plasticity and toughness has become the mainstream of lightweight materials for vehicles. Existing quenched and tempered steel can meet the above requirements, but the preparation process of quenched and tempered steel inevitably includes quenching and high-temperature tempering. On the one hand, the quenching process and tempering process can make the steel have advantages such as high strength, excellent toughness, plasticity, cutting performance, etc., but on the other hand, it is easy to cause quenching cracks, quenching deformation, poor surface quality and other problems on the surface of the steel.

[0038] Through extensive research and practice, the applicant has found that by adopting hot rolling technology, combined with controlled rolling and controlled cooling, precipitation strengthening and fine grain strengthening, and adding a variety of microalloying elements, high-strength steel with good comprehensive properties can be obtained.

[0039] The embodiment of the present application provides an 800MPa-level nano-precipitated high-strength steel. In terms of weight percentage, the components of the 800MPa-level nano-precipitated high-strength steel include: C, 0.050wt%~0.090wt%; Mn, 1.60wt%~2.0wt%; Si, 0.05wt%~0.20wt%; Nb, 0.03wt%~0.06wt%; V, 0.01wt%~0.035wt%; Ti, 0.09wt%~0.15wt%; Mo, 0.12wt%~0.25wt%; Cr, 0.02wt%~0.30wt%; S, 0wt%~0.008wt%; P, 0wt%~0.020wt%; the rest are Fe and unavoidable impurity elements.

[0040] The internal microstructure of 800MPa-level nano-precipitation high-strength steel is ferrite, in which nano-scale precipitated particles are dispersed.

[0041] Metallographic analysis shows that the internal microstructure of the 800MPa-level nano-precipitated high-strength steel in this application is ferrite, followed by a small amount of carbide Fe3C. The carbide Fe3C is formed at high temperatures due to the strong binding force between the iron element (Fe) and the carbon element (C) in the steel. These carbides exist in the gaps of the ferrite in the form of dots, which plays a role in strengthening the ferrite.

[0042] In addition to iron (Fe) and carbon (C), the components of 800MPa-level nano-precipitated high-strength steel also include chemical elements such as Mn, Si, Nb, V, Ti, Mo, Cr, S, and P.

[0043] First, manganese (Mn) is dissolved in steel, which plays a role in solid solution strengthening of steel on the one hand, and desulfurization on the other hand, reducing the hot brittleness of steel. Silicon (Si) can be used as a deoxidizer on the one hand, and adding a proper amount can reduce the gas content in steel, and on the other hand, it can reduce iron loss on the other hand. Adding a proper amount of sulfur (S) can improve the surface finish of steel. Phosphorus (P) has the effect of promoting grain growth, increasing hardness, and reducing iron loss.

[0044] Pure ferrite has smooth grain boundaries, good plasticity and toughness, but insufficient strength and hardness. Microalloying elements Nb, V, Ti, Mo, and Cr will combine with carbon to form carbides, or combine with nitrogen sources in the air and molten steel to form nitrides or carbonitrides. These carbides, nitrides, or carbonitrides will precipitate in the form of nanometer-sized particles during the controlled rolling and controlled cooling process, forming second-phase precipitated particles in steel materials, which are randomly dispersed in the ferrite grains or on the grain boundaries, and play a role in hindering the growth of ferrite crystals, so as to strengthen ferrite and enhance the overall strength, hardness, and toughness of steel. In addition, the above-mentioned microalloying elements can play a role in fine grain strengthening and improve the plasticity and toughness of steel.

[0045] In some embodiments, in order to comprehensively improve the performance of high-strength steel, the weight percentage of niobium element (Nb) is 0.03wt%~0.06wt%. For example, the niobium element (Nb) is 0.035wt%, 0.04wt%, 0.045wt%, 0.05wt%, 0.055wt% or 0.06wt%. The weight percentage of niobium element (Nb) can also be any combination range of the above values.

[0046] In some embodiments, in order to comprehensively improve the performance of high-strength steel, the weight percentage of vanadium element (V) is 0.01wt%~0.035wt%. For example, the weight percentage of vanadium element (V) is 0.015wt%, 0.02wt%, 0.025wt% or 0.03wt%. The weight percentage of vanadium element (V) can also be any combination range of the above values.

[0047] In some embodiments, in order to comprehensively improve the performance of high-strength steel, the weight percentage of titanium element (Ti) is 0.09wt%~0.15wt%. For example, the titanium element (Ti) is 0.095wt%, 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, or 0.14wt%. The weight percentage of titanium element (Ti) can also be any combination range of the above values.

[0048] In some embodiments, in order to comprehensively improve the performance of high-strength steel, the weight percentage of molybdenum element (Mo) is 0.12wt%~0.25wt%. For example, the molybdenum element (Mo) is 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, 0.2wt%, 0.21wt%, 0.22wt%, 0.23wt% or 0.24wt%. The weight percentage of molybdenum element (Mo) can also be any combination range of the above values.

[0049] In some embodiments, in order to comprehensively improve the performance of high-strength steel, the weight percentage of chromium element (Cr) is 0.02wt%~0.30wt%. For example, the chromium element (Cr) is 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.15wt%, 0.2wt% or 0.25wt%. The weight percentage of chromium element (Cr) can also be any combination range of the above values.

[0050] In some embodiments, the precipitated particles include a combination of one or more of Nb(C, N), V(C, N), TiC, and MoC.

[0051] The precipitated particles are mainly Nb (C, N), V (C, N), TiC, MoC, and a small amount of Ti (C, N), Mo (C, N), Cr (C, N). These nano-scale precipitated particles are formed by heating carbonization or carbonitriding of microalloying elements Nb, V, Ti, Mo, Cr, and are dispersed in the grains or on the grain boundaries of ferrite. The overall strength, hardness and toughness of ferrite are enhanced through precipitation strengthening. At the same time, with the precipitation of precipitated particles, it also plays a role of grain refinement strengthening.

[0052] In some embodiments, the precipitated particles include, by number percentage, 75% to 100% of the precipitated particles having a particle size less than or equal to 10 nm and 0% to 25% of the precipitated particles having a particle size greater than 10 nm.

[0053] The smaller the particle size of the precipitated particles, the greater the contribution to increasing the strength of the steel. When the particle size of the precipitated particles is ≤10nm, when precipitated in the ferrite, it can improve the strength and toughness of the steel, and the more precipitated particles in this particle size range, the better. When the content of precipitated particles in this particle size range exceeds 75% of the total content of all precipitated particles, the strength of the steel can be greatly improved. However, when the particle size of the precipitated particles is greater than 50nm, it is equivalent to inclusions in the ferrite of the steel, which not only cannot improve the strength of the steel, but also destroys the continuity of the steel matrix and affects the various properties of the steel.

[0054] In some embodiments, the mechanical properties of 800MPa-level nano-precipitated high-strength steel include: yield strength greater than or equal to 700MPa, tensile strength greater than or equal to 800MPa, elongation after fracture greater than or equal to 18%, and hole expansion rate greater than or equal to 70%.

[0055] Figure 1 The following is a schematic diagram of a method for preparing 800MPa nano-precipitated high-strength steel according to an embodiment of the present application. Figure 1 As shown, a method for preparing 800MPa grade nano-precipitated high-strength steel comprises:

[0056] S100, molten steel is cast by a continuous casting machine to obtain a continuous casting billet, wherein the molten steel components include, by weight percentage, C, 0.050wt%~0.090wt%; Mn, 1.60wt%~2.0wt%; Si, 0.05wt%~0.20wt%; Nb, 0.03wt%~0.06wt%; V, 0.01wt%~0.035wt%; Ti, 0.09wt%~0.15wt%; Mo, 0.12wt%~0.25wt%; Cr, 0.02wt%~0.30wt%; S, 0wt%~0.008wt%; P, 0wt%~0.020wt%; the rest are Fe and unavoidable impurity elements;

[0057] S200, heating the continuous casting billet until the microalloying elements in the chemical elements are completely dissolved and exist in the form of compounds;

[0058] S300, rough rolling and finish rolling the heated continuous casting billet to obtain hot rolled steel, wherein the outlet temperature of the finish rolling is 850°C to 900°C, and the cumulative reduction rate of the non-recrystallized zone is greater than or equal to 20%;

[0059] S400, laminar cooling hot rolled steel, laminar cooling uses front section centralized cooling and does not use ultra-fast cooling;

[0060] S500, coiling the hot-rolled steel after laminar cooling to obtain 800MPa-level nano-precipitation high-strength steel, wherein the coiling temperature is 560°C-620°C, and the steel is naturally air-cooled to room temperature after coiling to obtain 800MPa-level nano-precipitation high-strength steel, wherein the internal microstructure of the 800MPa-level nano-precipitation high-strength steel is ferrite, and nano-scale precipitated particles are dispersed in the ferrite.

[0061] First, the continuous casting billet is heated in step S200. During the heating process, the micro-alloying elements in the chemical elements exist in the form of compounds, which can hinder the growth of austenite grains. Therefore, the heating temperature in step S200 can control the original grain size and the effect of solid solution of micro-alloying elements.

[0062] Secondly, step S300 performs rough rolling and finish rolling on the continuous casting billet, in which the outlet temperature of the finish rolling and the cumulative reduction rate not in the crystallization zone are precisely controlled. The outlet temperature of the finish rolling is controlled within the range of 850°C to 900°C. When rolling in the austenite non-recrystallization zone, with a large reduction, the grain boundary or deformation band of the deformed austenite is the ferrite nucleation site, thereby achieving the effect of grain refinement and improving strength. The greater the cumulative reduction rate not in the crystallization zone, the better the plasticity of the obtained steel. Combined with the temperature of this area, the control of the cumulative reduction rate can greatly improve the plasticity of the steel, and also play a role in controlling the continued growth of austenite grains, achieving the effect of grain refinement and strengthening.

[0063] Finally, the cooling mode of step S400 can improve the cooling effect and prevent cracks or deformation during steel forming. More importantly, as a precipitation strengthening method, it can promote the precipitation of a large number of precipitated particles in the gaps of ferrite, thereby greatly improving the strength of the steel.

[0064] In some embodiments, in step S200 of heating the continuous casting billet, the heating temperature of the continuous casting billet is controlled within a range of 1180°C to 1280°C.

[0065] As the heating temperature of step S200 increases and the heating time is prolonged, the microalloying elements in the chemical elements gradually dissolve to form precipitated particles. As the precipitated particles are formed and precipitated, the volume of the original austenite grains will gradually increase, which will reduce the impact toughness of the steel on the one hand, and hinder the growth and precipitation of the precipitated particles on the other hand, and easily lead to cracks in the later operation process, especially when the austenite grains are uneven in size, which is easy to reduce the structural strength of the steel and even cause brittle fracture. Therefore, the heating temperature of this step is controlled within the range of 1180℃~1280℃. On the one hand, the volume and content of the original austenite grains and carbonitrides in the continuous casting billet can be controlled, and the obtained austenite grains can be controlled within the range of about 40μm~60μm. On the other hand, it is ensured that the precipitated particles begin to form, which has a significant effect on improving the hardening effect of the steel.

[0066] In some embodiments, in step S200 of heating the continuous casting billet, the cumulative time of the continuous casting billet in the furnace is greater than or equal to 160 minutes, and the time in the soaking section is greater than or equal to 30 minutes.

[0067] In some embodiments, in the step of rough rolling and finish rolling the heated continuous casting billet to obtain hot rolled steel, the outlet thickness of the rough rolling is less than or equal to 48 mm, and the start rolling temperature of the finish rolling is 1000°C~1100°C.

[0068] This step controls the outlet thickness of rough rolling and the start rolling temperature of finishing rolling. The start rolling temperature of finishing rolling is controlled within the range of 1000℃~1100℃ to reduce burning loss, indirectly ensuring that the final rolling temperature of finishing rolling will not be too low, avoiding damage to the steel plate shape due to the final rolling temperature of finishing rolling being too low, and improving the performance of steel.

[0069] Figure 2 This is a schematic diagram of a specific process of step S300 of the method for preparing 800MPa grade nano-precipitated high-strength steel provided in the embodiment of the present application. Figure 2 As shown, step S300 specifically includes:

[0070] S310, performing rough rolling on the heated continuous casting billet to obtain rough rolled steel; wherein the outlet thickness of the rough rolled steel is less than or equal to 48 mm;

[0071] S320, performing finish rolling on the heated continuous casting billet to obtain hot rolled steel; wherein the start rolling temperature of the finish rolling is 1000°C to 1100°C, the outlet temperature of the finish rolling is 850°C to 900°C, and the cumulative reduction rate controlled in the non-recrystallized zone is greater than or equal to 20%.

[0072] In step S320, the cumulative reduction rate of the non-recrystallized zone is controlled to be ≥20%, which controls the continued growth of austenite grains, promotes grain refinement, and improves the strength of the steel. At the same time, the cumulative reduction rate is relatively large, which has a significant effect on improving the plasticity and toughness of the steel.

[0073] In some embodiments, in step S300 , the step of rough rolling and finish rolling the heated continuous casting billet to obtain hot rolled steel includes a descaling operation.

[0074] This step can reduce the probability of cracks in the steel, reduce the cold brittleness of the steel, and improve the plasticity and welding performance of the steel.

[0075] In some embodiments, the descaling operation includes:

[0076] S610, after the heated continuous casting billet is taken out of the furnace and before the heated continuous casting billet is subjected to rough rolling, a high-pressure water rough descaling operation is performed to obtain a roughly descaled continuous casting billet;

[0077] S620, before finishing rolling the continuous casting billet after rough rolling, finishing descaling operation is performed.

[0078] Figure 3 A schematic diagram of a process for preparing 800MPa grade nano-precipitated high-strength steel according to another embodiment of the present application. Figure 3 As shown, a method for preparing 800MPa grade nano-precipitated high-strength steel comprises:

[0079] S100, molten steel is cast by a continuous casting machine to obtain a continuous casting billet, wherein the molten steel components include, by weight percentage, C, 0.050wt%~0.090wt%; Mn, 1.60wt%~2.0wt%; Si, 0.05wt%~0.20wt%; Nb, 0.03wt%~0.06wt%; V, 0.01wt%~0.035wt%; Ti, 0.09wt%~0.15wt%; Mo, 0.12wt%~0.25wt%; Cr, 0.02wt%~0.30wt%; S, 0wt%~0.008wt%; P, 0wt%~0.020wt%; the rest are Fe and unavoidable impurity elements;

[0080] S200, heating the continuous casting billet until the microalloying elements in the chemical elements are completely dissolved and exist in the form of compounds;

[0081] S610, performing a high-pressure water rough descaling operation on the heated continuous casting billet to obtain a roughly descaled continuous casting billet;

[0082] S310, performing a rough rolling operation on the roughly descaled continuous casting billet to obtain a rough rolled steel; wherein the outlet thickness of the rough rolled steel is less than or equal to 48 mm;

[0083] S620, performing fine descaling operation on the rough rolled steel;

[0084] S320, performing a finish rolling operation on the rough-rolled steel after fine descaling to obtain hot-rolled steel; wherein the start rolling temperature of the finish rolling is 1000°C to 1100°C, the outlet temperature of the finish rolling is 850°C to 900°C, and the cumulative reduction rate of the non-recrystallized zone is greater than or equal to 20%;

[0085] S400, laminar cooling hot rolled steel, laminar cooling uses front section centralized cooling and does not use ultra-fast cooling;

[0086] S500, coiling the hot-rolled steel after laminar cooling to obtain 800MPa-level nano-precipitation high-strength steel, wherein the coiling temperature is 560°C-620°C, and the steel is naturally air-cooled to room temperature after coiling to obtain 800MPa-level nano-precipitation high-strength steel, wherein the internal microstructure of the 800MPa-level nano-precipitation high-strength steel is ferrite, and nano-scale precipitated particles are dispersed in the ferrite.

[0087] The above application content of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0088] Example

[0089] The following examples describe the disclosure of the present invention in more detail, and these examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available. Example 1

[0090] The invention discloses an 800MPa-level nano-precipitated high-strength steel, which comprises, by weight percentage, 0.0667wt% C, 1.8179wt% Mn, 0.1410wt% Si, 0.0543wt% Nb, 0.034wt% V, 0.1154wt% Ti, 0.1672wt% Mo, 0.0291% Cr, 0.0005wt% S, 0.0108wt% P, and the remainder is Fe and unavoidable impurity elements.

[0091] The preparation method of the 800MPa grade nano-precipitated high-strength steel is as follows:

[0092] S100, casting molten steel through a continuous casting machine to obtain a continuous casting billet, wherein the molten steel components include, by weight percentage, C, 0.0667wt%; Mn, 1.8179wt%; Si, 0.1410wt%; Nb, 0.0543wt%; V, 0.034wt%; Ti, 0.1154wt%; Mo, 0.1672%; Cr, 0.0291%; S, 0.0005wt%; P, 0.0108wt%; the rest are Fe and unavoidable impurity elements;

[0093] S200, heating the continuous casting billet in a heating furnace at a heating temperature of 1257° C. The continuous casting billet is in a soaking section for 32 minutes, and the cumulative furnace time of the continuous casting billet is 186 minutes, until the micro-alloying elements in the chemical elements are completely dissolved and exist in the form of compounds;

[0094] S610, performing a high-pressure water rough descaling operation on the heated continuous casting billet to obtain a roughly descaled continuous casting billet;

[0095] S310, sending the roughly descaled continuous casting billet to the rough rolling mill for five round trips to obtain rough rolled steel; wherein the rough rolling outlet thickness is 35 mm;

[0096] S620, performing fine descaling operation on the rough rolled steel;

[0097] S320, performing a finish rolling operation on the rough-rolled steel after fine descaling, sending it to a 7-stand finish rolling, and rolling out a hot-rolled steel with a finished thickness of 2.5 mm; wherein the start rolling temperature of the finish rolling is 1076° C., the cumulative reduction rate of the non-recrystallized zone is 22%, and the outlet temperature of the finish rolling is 876° C.;

[0098] S400, laminar cooling operation for hot-rolled steel, using front-end concentrated cooling mode; among them, ultra-fast cooling cannot be turned on;

[0099] S500, the hot rolled steel is coiled after cooling, the coiling temperature is 607°C, and then air-cooled to room temperature on the transport chain to obtain 800MPa-level nano-precipitated high-strength steel, and finally the 800MPa-level nano-precipitated high-strength steel is stored in a low-temperature pile for cooling. Example 2

[0100] The invention discloses an 800MPa-level nano-precipitated high-strength steel, which comprises, by weight percentage, 0.0596wt% C, 1.7447wt% Mn, 0.1735wt% Si, 0.0320wt% Nb, 0.022wt% V, 0.1450wt% Ti, 0.2242% Mo, 0.2492% Cr, 0.0010wt% S, 0.0146wt% P, and the remainder is Fe and unavoidable impurity elements.

[0101] The preparation method of the 800MPa grade nano-precipitated high-strength steel is as follows:

[0102] S100, casting molten steel through a continuous casting machine to obtain a continuous casting billet, wherein the molten steel components include, by weight percentage, C, 0.0596wt%; Mn, 1.7447wt%; Si, 0.1735wt%; Nb, 0.0320wt%; V, 0.022wt%; Ti, 0.1450wt%; Mo, 0.2242%; Cr, 0.2492%; S, 0.0010wt%; P, 0.0146wt%; the rest are Fe and unavoidable impurity elements;

[0103] S200, heating the continuous casting billet in a heating furnace at a heating temperature of 1245° C., the continuous casting billet being in a soaking section for 35 minutes, and the cumulative furnace time of the continuous casting billet being 206 minutes, until the micro-alloying elements in the chemical elements are completely dissolved and exist in the form of compounds;

[0104] S610, performing a high-pressure water rough descaling operation on the heated continuous casting billet to obtain a roughly descaled continuous casting billet;

[0105] S310, sending the rough descaled continuous casting billet to the rough rolling mill for 5 round trips to obtain rough rolled steel; wherein the rough rolling outlet thickness is 40 mm;

[0106] S620, performing fine descaling operation on the rough rolled steel;

[0107] S320, performing a finish rolling operation on the rough-rolled steel after fine descaling, sending it to a 7-stand finish rolling, and rolling out a hot-rolled steel with a finished thickness of 3.0 mm; wherein the start rolling temperature of the finish rolling is 1039° C., the cumulative reduction rate of the non-recrystallized zone is 21%, and the outlet temperature of the finish rolling is 879° C.;

[0108] S400, laminar cooling operation for hot-rolled steel, using front-end concentrated cooling mode; among them, ultra-fast cooling cannot be turned on;

[0109] S500, the hot-rolled steel is coiled after cooling, the coiling temperature is 589°C, and then air-cooled to room temperature on the transport chain to obtain 800MPa-level nano-precipitated high-strength steel, and finally the 800MPa-level nano-precipitated high-strength steel is stored in a low-temperature pile for cooling.

[0110] Test Section

[0111] The 800MPa grade nano-precipitated high-strength steel samples prepared in Example 1 and Example 2 with the same size specifications were tested under the same conditions. The test contents included internal microstructure detection and performance detection.

[0112] Internal microstructure inspection

[0113] Metallographic analysis was performed on the 800 MPa-level nano-precipitated high-strength steel samples prepared in Example 1 and Example 2 to observe the internal structure of the steel.

[0114] like Figure 4 As shown, the internal microstructure of the 800MPa grade nano-precipitated high-strength steel prepared in Example 1 is mainly ferrite, and a small amount of carbide Fe3C exists in the ferrite. Figure 5 As shown, there are a large number of nano-scale precipitated particles inside the 800MPa-level nano-precipitated high-strength steel, and the average size of the precipitated particles is 4.8nm, among which the precipitated particles with a particle size less than 10nm account for 83% of all precipitated particles.

[0115] like Figure 6 As shown in the figure, the internal microstructure of the 800MPa nano-precipitated high-strength steel prepared in Example 2 is mainly ferrite, in which there is a small amount of carbide Fe3C and a large number of nano-scale precipitated particles. The average size of the precipitated particles is 4.3nm, among which the precipitated particles with a particle size of less than 10nm account for 88% of all precipitated particles. Figure 7 As shown in the energy spectrum of precipitated particles, the precipitated particles in the 800MPa grade nano-precipitated high-strength steel are mainly VC, TiC and MoC.

[0116] Performance Testing

[0117] According to the first part of the tensile test of metallic materials in GB / T 228.1, the first part of the instrumented indentation test of metallic material hardness and material parameters in GB / T 21838.1, and the fourth part of the metal sheet forming properties and test methods in GB / T 15825.4, the mechanical properties of the 800MPa grade nano-precipitated high-strength steel provided in Examples 1 and 2 were longitudinally tested, and the test results are shown in Table 1.

[0118] Table 1 Performance test results of steel

[0119]

[0120] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for preparing 800MPa grade nano-precipitated high-strength steel, characterized in that: include: The molten steel is cast by a continuous casting machine to obtain a continuous casting billet, wherein the molten steel components are, by weight percentage, C, 0.050wt%~0.090wt%; Mn, 1.60wt%~2.0wt%; Si, 0.05wt%~0.20wt%; Nb, 0.03wt%~0.06wt%; V, 0.01wt%~0.035wt%; Ti, 0.09wt%~0.15wt%; Mo, 0.12wt%~0.25wt%; Cr, 0.02wt%~0.30wt%; S, 0wt%~0.008wt%; P, 0wt%~0.020wt%; the rest are Fe and unavoidable impurity elements; The continuous casting billet is heated until the microalloying elements in the chemical elements are completely dissolved and exist in the form of compounds; the heating temperature of the continuous casting billet is controlled within a range of 1180° C. to 1280° C., the cumulative time of the continuous casting billet in the furnace is greater than or equal to 160 minutes, and the time in the soaking section is greater than or equal to 30 minutes; The heated continuous casting billet is subjected to rough rolling and finish rolling to obtain hot rolled steel, wherein the outlet temperature of the finish rolling is 850° C. to 900° C., and the cumulative reduction rate of the non-recrystallized region is greater than or equal to 20% and less than or equal to 22%; laminar cooling of the hot rolled steel, wherein the laminar cooling adopts front-stage concentrated cooling and does not use ultra-fast cooling; The hot-rolled steel after laminar cooling is coiled, wherein the coiling temperature is 560° C. to 620° C., and the steel is naturally air-cooled to room temperature after coiling to obtain 800 MPa-level nano-precipitated high-strength steel, wherein the internal microstructure of the 800 MPa-level nano-precipitated high-strength steel is ferrite, and nano-scale precipitated particles are dispersed in the ferrite; The precipitated particles include Nb(C, N), V(C, N), TiC, and MoC.

2. The preparation method according to claim 1, characterized in that: In the step of rough rolling and finish rolling the heated continuous casting billet to obtain hot rolled steel, the outlet thickness of the rough rolling is less than or equal to 48 mm, and the start rolling temperature of the finish rolling is 1000° C. to 1100° C.

3. The preparation method according to claim 1, characterized in that: In terms of percentage by number, the precipitated particles include 75% to 100% of precipitated particles having a particle size less than or equal to 10 nm and 0% to 25% of precipitated particles having a particle size greater than 10 nm.

4. The preparation method according to claim 1, characterized in that: The mechanical properties of the 800MPa-level nano-precipitated high-strength steel include: yield strength greater than or equal to 700MPa, tensile strength greater than or equal to 800MPa, elongation after fracture greater than or equal to 18%, and hole expansion rate greater than or equal to 70%.

5. The preparation method according to claim 1, characterized in that: The step of rough rolling and finish rolling the heated continuous casting billet to obtain hot rolled steel includes a descaling operation.

6. The preparation method according to claim 5, characterized in that: The descaling operation comprises: After the heated continuous casting billet is taken out of the furnace and before the heated continuous casting billet is subjected to rough rolling, a high-pressure water rough descaling operation is performed to obtain a roughly descaled continuous casting billet; Before the finish rolling of the continuous casting slab after rough rolling, the finish descaling operation is carried out.

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