A structural steel plate having a distinct yield plateau and a method of manufacture

Abstract

This application relates to a structural steel plate with a distinct yield plateau and its preparation method, belonging to the field of steel plate manufacturing technology. The chemical composition of the structural steel plate, by mass fraction, includes: C: 0.08%~0.18%, Si: 0.20%~0.40%, Mn: 1.00%~1.70%, P≤0.010%, S≤0.003%, Al: 0.020%~0.050%, Nb: 0.030%~0.110%, V: 0.050%~0.100%, Ti: 0.010%~0.030%, and the matrix element Fe. By optimizing the composition and process, without adding alloying elements such as Cu, Ni, Cr, and Mo, a large number of fine nanoscale Nb, V, and Ti precipitates are formed in the ferrite. These precipitates work synergistically through a dual mechanism: on the one hand, they strengthen the low dislocation density structure to improve the strength of the structural steel plate; on the other hand, they pin dislocations to induce a distinct yield plateau in the structural steel plate. By employing a specific high final cooling temperature process, the coiling or stacking cooling steps are eliminated, shortening the production process and expanding the production capacity of structural steel plate thickness specifications. Ultimately, this results in a significant reduction in alloy costs and an increase in production efficiency, forming a core technological advantage.

Description

Technical Field

[0001] This application relates to the field of steel plate manufacturing technology, and in particular to a structural steel plate with a distinct yield plateau and a method for its preparation. Background Technology

[0002] Structural steel plates are commonly used in steel structure buildings. Steel structure buildings, due to their high strength, durability, flexible design, and sustainability, are widely used in industrial, commercial, residential, and infrastructure sectors. The quality and performance of the structural steel plates directly determine the safety and seismic reliability of the steel structure. To meet seismic design requirements, GB50017-2017, the "Code for Design of Steel Structures," clearly stipulates that steel used for key seismic components must possess a low yield strength ratio, high plasticity, and a clear yield plateau (i.e., a continuous yield step on the tensile curve). With the rapid development of steel structures towards larger sizes and longer spans, the strength requirements for structural steel plates continue to upgrade, and 460MPa grade structural steel has been widely used. However, when the strength of steel plates is increased to above 460MPa, the steel plates are prone to exhibiting a lack of a yield plateau during tensile testing, making it difficult to meet the performance requirements of seismic codes for steel used in key components.

[0003] In existing technologies, to ensure the emergence of a yield plateau, expensive alloying elements such as Cu, Ni, Cr, and Mo are typically added, relying on complex processes such as multi-stage heat treatment (quenching + two-phase quenching + tempering) or controlled cooling after rolling. These methods not only significantly increase the cost of structural steel plates but also limit production efficiency due to the lengthy processes. Therefore, there is an urgent need to develop a new type of structural steel plate and its preparation method that eliminates the need for adding precious metal elements and simplifies the process, achieving a significant yield plateau and excellent seismic performance while ensuring high strength, thus overcoming the technical bottleneck in the seismic application of high-strength steel. Summary of the Invention

[0004] This application provides a structural steel plate with a distinct yield plateau and a method for its preparation, in order to solve the following technical problem: how to ensure that the structural steel plate has a distinct yield plateau while achieving high strength. In a first aspect, embodiments of this application provide a structural steel plate with a distinct yield plateau. The chemical composition of the structural steel plate, by mass fraction, includes: C: 0.08%~0.18%, Si: 0.20%~0.40%, Mn: 1.00%~1.70%, P≤0.010%, S≤0.003%, Al: 0.020%~0.050%, Nb: 0.030%~0.110%, V: 0.050%~0.100%, Ti: 0.010%~0.030%, and the matrix element Fe; The microstructure of the structural steel plate includes ferrite and pearlite.

[0005] Optionally, the volume fraction of ferrite is 80% to 90%, and the volume fraction of pearlite is 10% to 20%.

[0006] Optionally, the ferrite contains nanoscale Nb, V and Ti precipitates with a size ≤50 nm.

[0007] Optionally, the structural steel plate meets at least one of the following properties: yield strength ≥ 460 MPa, tensile strength ≥ 570 MPa, elongation after fracture ≥ 25%, yield-to-tensile ratio ≤ 0.85, and impact energy ≥ 120 J.

[0008] Secondly, embodiments of this application provide a method for preparing the structural steel plate described in the first aspect, the method comprising: A continuously cast billet with the following chemical composition was obtained: C: 0.08%~0.18%, Si: 0.20%~0.40%, Mn: 1.00%~1.70%, P≤0.010%, S≤0.003%, Al: 0.020%~0.050%, Nb: 0.030%~0.110%, V: 0.050%~0.100%, Ti: 0.010%~0.030%, and the matrix element Fe; The continuously cast billet is sequentially heated, rough rolled, finish rolled and water cooled to obtain structural steel plates with a thickness of 16mm to 80mm.

[0009] Optionally, the thickness of the continuously cast billet is 200mm~400mm, and the ratio of the thickness of the continuously cast billet to the thickness of the finished steel plate of the structural steel plate is ≥3.

[0010] Optionally, the heating temperature is 1120℃~1200℃, and the heating time is 200min~400min.

[0011] Optionally, the starting temperature of the rough rolling is 1000℃~1100℃, and the thickness of the intermediate billet after rough rolling is ≥2 times the thickness of the structural steel plate.

[0012] Optionally, the starting temperature of the finishing rolling is 880℃~980℃, and the ending temperature of the finishing rolling is 790℃~870℃.

[0013] Optionally, the initial temperature of the water cooling is 770℃~860℃, the cooling rate of the water cooling is 10℃ / s~30℃ / s, and the final cooling temperature of the water cooling is 600℃~700℃.

[0014] Optionally, the thickness of the structural steel plate is 16mm to 80mm.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a structural steel plate with a distinct yield plateau. The chemical composition of the structural steel plate, by mass fraction, includes: C: 0.08%~0.18%, Si: 0.20%~0.40%, Mn: 1.00%~1.70%, P≤0.010%, S≤0.003%, Al: 0.020%~0.050%, Nb: 0.030%~0.110%, V: 0.050%~0.100%, Ti: 0.010%~0.030%, and the matrix element Fe. The microstructure of the structural steel plate includes ferrite and pearlite. Through a precise "composition-process-microstructure" linkage design, a new balance is established between the strengthening mechanism and the plastic deformation mechanism. Specifically, its principle is reflected on two levels: In terms of composition design, 0.08wt%~0.18wt% C is used, while expensive elements such as Cu, Ni, Cr, and Mo are abandoned, and instead, Nb, V, and Ti are relied upon for microalloying. The core role of these elements, Nb, V, and Ti, is to precipitate a large number of nanoscale carbonitrides in the ferrite matrix during the subsequent controlled rolling and cooling process. On the one hand, these nanoprecipitates effectively pin dislocations through the Orovan mechanism, providing significant precipitation strengthening and thus contributing to high strength; on the other hand, these nanoprecipitates also act as pinning points that can be "broken free" by dislocations. During the tensile yielding stage, dislocations need to overcome the obstruction of these particles to begin sliding. This process requires additional energy, thus manifesting as a clear yield plateau on the stress-strain curve where stress does not increase but strain increases significantly. In terms of microstructure design, the microstructure is limited to ferrite and pearlite, which is a multiphase structure with a good balance of strength and toughness. Ferrite, as the soft phase, provides an excellent plasticity and toughness matrix and serves as the main carrier for nanoprecipitates; while an appropriate amount of pearlite, as the hard phase, further supplements the strength. This ferrite-based microstructure ensures that the structural steel plate has a low dislocation density initiation state, creating conditions for large-scale dislocation slip (i.e., the formation of a yield plateau).

[0016] In summary, by employing the synergistic principle of "nanoprecipitate strengthening + ferrite / pearlite multiphase structure", the goal of simultaneously achieving high strength and a significant yield plateau is achieved without a high yield strength ratio, fundamentally solving the technical challenge of achieving both high strength and excellent yield. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0019] Figure 1 A flowchart illustrating a structural steel plate with a distinct yield plateau and its preparation method, provided as an embodiment of this application; Figure 2 Microstructure of a structural steel plate with a distinct yield plateau provided in Embodiment 5 of this application; Figure 3 The morphology of Nb, V and Ti nanoprecipitates in the structural steel plate with a distinct yield plateau provided in Example 5 of this application; Figure 4 Energy dispersive spectral analysis of Nb, V and Ti precipitates in a structural steel plate with a distinct yield plateau provided in Embodiment 5 of this application; Figure 5 Tensile curve of a structural steel plate with a distinct yield plateau provided in Embodiment 5 of this application; Figure 6 Tensile curve of the steel plate with no obvious yield plateau provided for Comparative Example 1 of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges between 1 and 6 (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including" and "contains" used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship. "And / or" indicates that multiple situations can exist individually or simultaneously. Expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0022] In a first aspect, embodiments of this application provide a structural steel plate with a distinct yield plateau. The chemical composition of the structural steel plate, by mass fraction, includes: C: 0.08%~0.18%, Si: 0.20%~0.40%, Mn: 1.00%~1.70%, P≤0.010%, S≤0.003%, Al: 0.020%~0.050%, Nb: 0.030%~0.110%, V: 0.050%~0.100%, Ti: 0.010%~0.030%, and the matrix element Fe; The positive effects of limiting the C mass fraction to 0.08%~0.18%: C has a significant impact on the mechanical and weldability of structural steel plates. At the same temperature, increasing the C mass fraction increases the kinetic resistance to carbon atom migration during diffusion-controlled phase transformation, thereby inhibiting diffusion-type phase transformations such as ferrite and pearlite in structural steel plates. When the C mass fraction is too high, the growth mechanism of the diffusion-controlled lamellar precipitates in bainite phase transformation is further restricted, leading to the formation of martensite during cooling. By controlling the C mass fraction within an optimized range, a dual effect is achieved: on the one hand, it promotes appropriate diffusion-type phase transformation in structural steel plates, enabling the formation of the target ferrite-pearlite microstructure; on the other hand, it allows C to synergistically form nano-precipitates with added Nb, V, and Ti microalloying elements, effectively promoting a significant yield plateau in the tensile curve of the structural steel plate by pinning dislocations. For example, the C mass fraction can be 0.08%, 0.10%, 0.12%, 0.14%, 0.16%, 0.18%, etc.

[0023] The positive effects of limiting the Si mass fraction to 0.20%~0.40% are as follows: Si does not form carbides with C in steel and mainly exists in solid solution form. Si enhances the strength of structural steel plates through a solid solution strengthening mechanism, specifically through the interaction between Si atoms and the dislocation stress field, effectively hindering dislocation movement. Simultaneously, according to the formula for calculating weld crack sensitivity, an excessively high Si mass fraction will significantly deteriorate the weldability of structural steel plates. For example, the Si mass fraction can be 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, etc.

[0024] The positive effects of limiting the mass fraction of manganese (Mn) to 1.00%~1.70% include: As an austenite stabilizing element, Mn can expand the austenite phase region of steel. During cooling, Mn reduces the phase transformation driving force of steel through the solute dragging effect, inhibiting diffusion-type phase transformations such as ferrite and pearlite. By controlling the mass fraction of Mn and matching process parameters, it is possible to promote the formation of refined bainitic lath structures in steel, endowing structural steel plates with synergistic properties of high strength and high toughness. However, when the mass fraction of Mn is too high, Mn is prone to segregation during solidification, leading to a significant increase in the tendency for cracking in continuously cast billets and subsequent cooling stages. For example, the mass fraction of Mn can be 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, etc.

[0025] The positive effects of limiting the mass fraction of phosphorus (P) to ≤0.010%: P is an unavoidable harmful impurity element in steel. P is unevenly distributed in steel, concentrated at grain boundaries, affecting the grain boundary structure. Ultimately, P-rich grain boundaries and the affected grain boundary structure make steel prone to cold brittleness at low temperatures. For example, the mass fraction of P can be 0.002%, 0.004%, 0.006%, 0.008%, 0.010%, etc.

[0026] The positive effects of limiting the mass fraction of sulfur (S) to ≤0.003%: S is an unavoidable harmful impurity element in steel, which easily forms defects such as segregation and inclusions, thereby deteriorating the weldability and impact toughness of structural steel plates. For example, the mass fraction of S can be 0.001%, 0.002%, 0.003%, etc.

[0027] The positive effects of limiting the Al mass fraction to 0.020%~0.050% include: Al increases the driving force for phase transformation; Al interacts with N in steel to form fine and dispersed AlN precipitates, which can inhibit grain growth, thereby refining the grains and improving the toughness of structural steel plates at low temperatures. For example, the Al mass fraction can be 0.020%, 0.030%, 0.040%, 0.050%, etc.

[0028] The positive effects of limiting the Nb mass fraction to 0.030%~0.110% are as follows: After Nb is added to steel, it produces a dual effect by suppressing grain boundary migration during the recrystallization process in the austenite single-phase region: on the one hand, it increases the recrystallization temperature of austenite, significantly improving the rolling efficiency of the second stage in the two-stage controlled rolling process for structural steel plates; on the other hand, it refines the recrystallized austenite grain size, laying the foundation for the refinement of the final microstructure of the structural steel plate. Simultaneously, Nb combines with C and N to form MX-type carbonitrides. These nanoscale precipitates, which emerge during rolling cooling, effectively promote the formation of a distinct yield plateau in the tensile curve through pinning dislocation movement. For example, the Nb mass fraction can be 0.030%, 0.040%, 0.050%, 0.060%, 0.070%, 0.080%, 0.090%, 0.100%, 0.110%, etc.

[0029] The positive effects of limiting the mass fraction of V to 0.050%~0.100% are as follows: V is a grain-refining element. The dispersed precipitation of V(C,N) can significantly improve the strength of structural steel plates, while effectively pinning dislocations and promoting a significant yield plateau under tension. However, if the mass fraction of V is too high, it will reduce the toughness and weldability of the structural steel plate. For example, the mass fraction of V can be 0.050%, 0.060%, 0.070%, 0.080%, 0.090%, 0.100%, etc.

[0030] The positive effects of limiting the mass fraction of Ti to 0.010%~0.030% include: Ti acts as a ferrite stabilizing element, reducing the austenite phase region, and simultaneously optimizing the performance of structural steel plates through multiple effects: it combines with N to form high-temperature TiN particles, inhibiting austenite grain growth; it reacts with C and S to generate fine TiC or Ti carbides and sulfides, further refining the microstructure of the structural steel plate; in addition, Ti dissolved in austenite significantly improves the hardenability of the structural steel plate and enhances its transformation hardening ability, achieving synergistic regulation of microstructure and properties. For example, the mass fraction of Ti can be 0.010%, 0.020%, 0.030%, etc.

[0031] Fe is a matrix element, and the specific content / range of Fe can be obtained through the upper and lower limit formulas of the component, that is: The sum of the percentages of all components in a composition should equal 100%, and the content ranges of several components should meet the following conditions: the upper limit of a certain component + the lower limit of other components ≤ 100; the lower limit of a certain component + the upper limit of other components ≥ 100. Furthermore, the specific content of Fe is made up to 100% by the actual detected values ​​of the other chemical components mentioned above, together with any unlisted active elements and / or impurity elements, and Fe must constitute the absolute proportion as a matrix element.

[0032] The microstructure of the structural steel plate includes ferrite and pearlite.

[0033] Ferrite: A low-carbon body-centered cubic solid solution of carbon in α-Fe, exhibiting an equiaxed soft phase. Pearlite: A eutectoid structure composed of alternating lamellae of ferrite and cementite, providing strength support. Ferrite and pearlite work together to form the matrix structure of structural steel plates.

[0034] In some embodiments, the volume fraction of ferrite is 80% to 90%, and the volume fraction of pearlite is 10% to 20%.

[0035] By precisely controlling the volume fraction of ferrite in the microstructure to 80%–90% and the volume fraction of pearlite to 10%–20%, a multiphase microstructure is constructed, with ductile ferrite as the continuous matrix and pearlite as the dispersing unit, laying the structural foundation for achieving a low yield strength ratio and high plasticity. The high proportion of soft ferrite ensures excellent plasticity and toughness in the structural steel plate and provides an initial state of low dislocation density, a prerequisite for generating a significant yield plateau. An appropriate amount of hard pearlite acts as a second phase particle, supplementing strength by reasonably dispersing stress and preventing increased brittleness and yield strength ratio due to excessive pearlite volume fraction. For example, the volume fraction of ferrite can be 80%, 82%, 84%, 86%, 88%, 90%, etc.; the volume fraction of pearlite can be 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0036] In some embodiments, the ferrite contains nanoscale Nb, V, and Ti precipitates with a size ≤50 nm.

[0037] The role of Nb, V, and Ti precipitates is to enhance the strength of structural steel plates through the Orovan strengthening mechanism, while also acting as movable pinning points for dislocation slip, directly inducing a significant yield plateau. Nb, V, and Ti precipitates with a size ≤50 nm effectively hinder dislocation movement and significantly improve the strength of the ferrite matrix. For example, the sizes of Nb, V, and Ti precipitates can be 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, 50 nm, etc.

[0038] In some embodiments, the structural steel plate satisfies at least one of the following properties: yield strength ≥ 460 MPa, tensile strength ≥ 570 MPa, elongation after fracture ≥ 25%, yield-to-tensile ratio ≤ 0.85, and impact energy ≥ 120 J.

[0039] Yield strength: The minimum stress value at which a material begins to undergo permanent plastic deformation. A yield strength ≥ 460 MPa ensures that the structural steel plate has a sufficiently high resistance to initial deformation, which is the basis for meeting the design strength grade of high-strength steel structures (such as Q460 grade). This allows the structural steel plate to resist initial yielding under seismic loads and maintain structural integrity. Tensile strength: The maximum engineering stress that a material can withstand in a tensile test. A tensile strength ≥ 570 MPa gives the structural steel plate extremely high ultimate load-bearing capacity, providing a large plastic deformation reserve and overload safety margin after yielding and before fracture. It is the last line of defense against catastrophic brittle fracture of the structural steel plate due to accidental overload. Elongation after fracture: The percentage of permanent elongation of the gauge length after the specimen breaks relative to the original gauge length. An elongation after fracture ≥ 25% indicates that the structural steel plate possesses excellent plastic deformation capacity. When seismic energy is input, the structure can dissipate energy through the large deformation of the structural steel plate itself, avoiding brittle failure caused by stress concentration. This is key to achieving the seismic resistance concept of "cracking but not collapsing." Yield-to-tensile strength ratio: The ratio of yield strength to tensile strength. A yield-to-tensile strength ratio ≤ 0.85 is a core indicator for evaluating the seismic performance of steel plates. Impact energy: The ability of a material to resist brittle fracture under dynamic loads. An impact energy ≥ 120 J indicates excellent resistance to brittle fracture of the structural steel plate under low temperature or dynamic loads (such as seismic impact). For example, yield strength can be 460 MPa, 470 MPa, 480 MPa, 490 MPa, 500 MPa, etc.; tensile strength can be 570 MPa, 580 MPa, 590 MPa, 600 MPa, etc.; elongation after fracture can be 25%, 26%, 27%, 28%, 29%, 30%, etc.; yield-to-tensile strength ratio can be 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, etc.; impact energy can be 120 J, 122 J, 124 J, 126 J, 128 J, 130 J, etc.

[0040] Figure 1 This is a flowchart illustrating a structural steel plate with a distinct yield plateau and its preparation method, provided as an embodiment of this application.

[0041] Please see Figure 1 Secondly, this application provides a method for preparing the structural steel plate described in the first aspect, the method comprising: S1. A continuously cast billet with the following chemical composition is obtained: C: 0.08%~0.18%, Si: 0.20%~0.40%, Mn: 1.00%~1.70%, P≤0.010%, S≤0.003%, Al: 0.020%~0.050%, Nb: 0.030%~0.110%, V: 0.050%~0.100%, Ti: 0.010%~0.030%, and the matrix element Fe; S2. The continuously cast billet is sequentially heated, rough rolled, finish rolled and water cooled to obtain a structural steel plate with a thickness of 16mm~80mm.

[0042] In some embodiments, the thickness of the continuously cast billet is 200mm to 400mm, and the ratio of the thickness of the continuously cast billet to the thickness of the finished steel plate of the structural steel plate is ≥3.

[0043] The thickness of the continuously cast billet is between 200mm and 400mm, balancing the stability of the continuous casting process with the deformation space during rolling, providing a fundamental guarantee for the refinement of the microstructure of the structural steel plate. For example, the thickness of the continuously cast billet can be 200mm, 250mm, 300mm, 350mm, 400mm, etc. The ratio of the continuously cast billet thickness to the finished structural steel plate thickness is ≥3. Through critical plastic deformation, the internal defects of the continuously cast billet are forcibly welded together, and the grains of the structural steel plate are refined, providing necessary conditions for the control of nano-precipitates and high toughness. For example, the ratio of the continuously cast billet thickness to the finished structural steel plate thickness can be 3, 3.5, 4, etc.

[0044] In some embodiments, the heating temperature is 1120℃~1200℃, and the heating time is 200min~400min.

[0045] The heating temperature is between 1120℃ and 1200℃. Excessive heating temperature leads to excessive oxide scale formation on the surface of the continuously cast billet, exacerbating metal loss and wasting energy. Insufficient heating temperature fails to meet the thermodynamic conditions for austenite recrystallization, resulting in inadequate dynamic recrystallization of austenite during rolling and affecting the microstructure refinement of the structural steel plate. For example, heating temperatures can be 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, or 1200℃. The heating time is between 200min and 400min to ensure that the core temperature of the continuously cast billet is fully heated to the austenite recrystallization zone, achieving microstructure homogenization and solid solution diffusion of alloying elements. Simultaneously, it avoids underheating leading to rolling cracks or overheating causing grain coarsening, precisely balancing energy efficiency and process quality in the production process. For example, the heating time can be 200 min, 250 min, 300 min, 350 min, 400 min, etc.

[0046] In some embodiments, the starting temperature of the rough rolling is 1000℃~1100℃, and the thickness of the intermediate billet after rough rolling is ≥2 times the thickness of the structural steel plate.

[0047] The rough rolling starts at a temperature between 1000℃ and 1100℃. By activating the complete recrystallization mechanism within the structural steel plate, efficient grain refinement and deformation resistance optimization are achieved. For example, the starting temperature for rough rolling can be 1000℃, 1020℃, 1040℃, 1060℃, 1080℃, or 1100℃. The thickness of the intermediate slab after rough rolling is ≥2 times the thickness of the structural steel plate, providing critical deformation space for finish rolling. This forces grain breakage and regulates the precipitated phases within the structural steel plate, ensuring the core toughness and performance uniformity of the structural steel plate.

[0048] In some embodiments, the starting temperature of the finishing rolling is 880°C to 980°C, and the ending temperature of the finishing rolling is 790°C to 870°C.

[0049] The starting temperature for finishing rolling is between 880℃ and 980℃ to avoid the structural steel plate entering the partial recrystallization zone due to an excessively low starting temperature, which could result in oversized grains. For example, the starting temperature for finishing rolling can be 880℃, 900℃, 920℃, 940℃, 960℃, or 980℃. The ending temperature for finishing rolling is between 790℃ and 870℃ to avoid excessively high ending temperatures that could lead to grain growth in the subsequent structural steel plate. For example, the ending temperature for finishing rolling can be 790℃, 810℃, 830℃, 850℃, or 870℃.

[0050] In some embodiments, the initial temperature of the water cooling is 770°C to 860°C, the cooling rate of the water cooling is 10°C / s to 30°C / s, and the final cooling temperature of the water cooling is 600°C to 700°C.

[0051] The initial water cooling temperature is between 770℃ and 860℃ to lock the structural steel plate into a pure austenitic state, thus providing the necessary thermodynamic window for the controllable initiation of phase transformation. For example, the initial water cooling temperature can be 770℃, 790℃, 810℃, 830℃, or 850℃. The cooling rate is between 10℃ / s and 30℃ / s, suppressing the phase transformation coarsening process in the structural steel plate microstructure and achieving the precise formation of the target ferrite-pearlite microstructure. For example, the cooling rate can be 10℃ / s, 15℃ / s, 20℃ / s, 25℃ / s, or 30℃ / s. The final water cooling temperature is between 600℃ and 700℃, which, on the one hand, blocks the occurrence of non-target phase transformations in the structural steel plate, and on the other hand, simultaneously triggers the pinning effect of nano-precipitates on dislocation lines in the steel. For example, the final cooling temperature of water cooling can be 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, etc.

[0052] The product prepared by the method of preparing the structural steel plate is the aforementioned structural steel plate. Since the method of preparing the structural steel plate adopts some or all of the technical solutions of the embodiments of the structural steel plate, it has at least all the beneficial effects brought about by the technical solutions of the aforementioned embodiments, which will not be elaborated here.

[0053] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0054] The chemical composition (mass percentage / %) of the steels in the examples and comparative examples is shown in Table 1.

[0055] Table 1

[0056] Based on the steel chemical composition of the embodiments and comparative examples, this embodiment also provides a method for preparing a structural steel plate with a significant yield plateau, including the following steps: A continuously cast billet having the chemical composition described in Table 1 was obtained; The slab is sequentially heated, rough-rolled, finish-rolled, and water-cooled to obtain structural steel plates with a thickness of 16mm to 80mm. The process parameters are shown in Tables 2 and 3.

[0057] The process parameters for the examples and comparative examples are shown in Table 2.

[0058] Table 2

[0059] The process parameters for the examples and comparative examples are shown in Table 3.

[0060] Table 3

[0061] The mechanical properties of the embodiments and comparative examples are shown in Table 4.

[0062] Table 4

[0063] The data tables above provide a clear comparison of the differences between various embodiments and comparative examples. The following conclusions can be drawn: As can be seen from the data in Table 4, the structural steel plate provided in this application embodiment has a yield strength of 477MPa~511MPa, a tensile strength of 588MPa~625MPa, a yield-to-tensile ratio of 0.81~0.84, an elongation after fracture of 26%~32%, and an impact energy of 153J~283J.

[0064] Appendix Figures 2-6 Detailed explanation: Figure 2 Microstructure of a structural steel plate with a distinct yield plateau provided in Embodiment 5 of this application. According to Figure 2 It can be seen that the microstructure of this structural steel plate is mainly composed of uniform and fine ferrite (light-colored blocky grains), with a small amount of layered pearlite (dark-colored), and no brittle phases such as martensite and bainite. This confirms the precise control of the microstructure by the rolling and cooling processes in this application, as well as the microstructure basis for the significant yield plateau, low yield strength ratio, and high toughness of the structural steel plate.

[0065] Figure 3 The image shows the morphology of Nb, V, and Ti nanoprecipitates in a structural steel plate with a distinct yield plateau, as provided in Example 5 of this application. According to... Figure 3 It can be known that in structural steel plates, Nb, V and Ti composite nano-precipitates (size ≤50nm) are dispersed in the ferrite matrix.

[0066] Figure 4 Energy dispersive spectral analysis (EDS) diagrams of Nb, V, and Ti precipitates in a structural steel plate with a distinct yield plateau provided in Embodiment 5 of this application. According to... Figure 4 It can be known that in structural steel plates, the nano-precipitated phases are mainly composed of Nb, V and Ti.

[0067] Figure 5 Tensile curve of a structural steel plate with a distinct yield plateau provided in Embodiment 5 of this application. Figure 5 It can be seen that the tensile curve of the structural steel plate has a clear yield plateau, which reflects the performance characteristics of the structural steel plate, such as high strength, low yield strength ratio and high elongation.

[0068] Figure 6 Tensile curve of the structural steel plate with no obvious yield plateau provided in Comparative Example 1 of this application. Figure 6 It can be seen that the tensile curve of the structural steel plate in Comparative Example 1 has no obvious yield plateau, which confirms the performance degradation characteristics of the structural steel plate, which has a high yield strength ratio and low elongation due to excessive cooling rate.

[0069] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The present invention provides a structural steel plate with a distinct yield plateau, which has advantages such as low alloy addition, simplified production process, simple manufacturing process, and low overall cost. The manufactured structural steel plate has high strength, low yield strength ratio, high toughness, high plasticity and distinct yield plateau, which can fully meet the stringent requirements of steel structure buildings for the seismic performance of steel plates.

[0070] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A structural steel plate with a distinct yield plateau, characterized in that, The chemical composition of the structural steel plate, by mass fraction, includes: C: 0.08%~0.18%, Si: 0.20%~0.40%, Mn: 1.00%~1.70%, P≤0.010%, S≤0.003%, Al: 0.020%~0.050%, Nb: 0.030%~0.110%, V: 0.050%~0.100%, Ti: 0.010%~0.030%, and the matrix element Fe; The microstructure of the structural steel plate includes ferrite and pearlite.

2. The structural steel plate according to claim 1, characterized in that, The volume fraction of ferrite is 80% to 90%, and the volume fraction of pearlite is 10% to 20%.

3. The structural steel plate according to claim 1 or 2, characterized in that, The ferrite contains nanoscale Nb, V and Ti precipitates with a size ≤50 nm.

4. The structural steel plate according to claim 1, characterized in that, The structural steel plate meets at least one of the following properties: yield strength ≥ 460 MPa, tensile strength ≥ 570 MPa, elongation after fracture ≥ 25%, yield strength ratio ≤ 0.85, and impact energy ≥ 120 J.

5. A method for preparing a structural steel plate according to any one of claims 1 to 4, characterized in that, The method includes: A continuously cast billet having the chemical composition described in any one of claims 1 to 4 is obtained; The continuously cast billet is sequentially heated, rough rolled, finish rolled and water cooled to obtain structural steel plates with a thickness of 16mm to 80mm.

6. The method according to claim 5, characterized in that, The thickness of the continuously cast billet is 200mm~400mm, and the ratio of the thickness of the continuously cast billet to the thickness of the finished steel plate of the structural steel plate is ≥3.

7. The method according to claim 5, characterized in that, The heating temperature is 1120℃~1200℃, and the heating time is 200min~400min.

8. The method according to claim 5, characterized in that, The starting temperature of the rough rolling is 1000℃~1100℃, and the thickness of the intermediate billet after rough rolling is ≥2 times the thickness of the structural steel plate.

9. The method according to claim 5, characterized in that, The starting temperature of the finishing rolling is 880℃~980℃, and the ending temperature of the finishing rolling is 790℃~870℃.

10. The method according to claim 5, characterized in that, The initial temperature of the water cooling is 770℃~860℃, the cooling rate of the water cooling is 10℃ / s~30℃ / s, and the final cooling temperature of the water cooling is 600℃~700℃.

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