Seismic and weather-resistant steel plate for building structures with a yield strength of 550 MPa and method for producing the same

Abstract

The present invention relates to a seismic and weather-resistant steel plate for building structures of the V series 550 MPa grade and a manufacturing method thereof. The steel plate has the following components by mass%: C: 0.07 to 0.12%, Si: 0.35 to 0.45%, Mn: 1.30 to 1.40%, P ≤ 0.020%, S ≤ 0.008%, Cr: 0.60 to 0.70%, Ni: 0.25 to 0.35%, Cu: 0.30 to 0.40%, V: 0.08 to 0.12%, Als: 0.015 to 0.055%, N: 0.0200 to 0.0220%, with the balance being Fe and inevitable impurities. It is obtained by heating, rough rolling, finish rolling, laminar flow cooling, and coiling a slab containing the above components. The seismic and weather-resistant steel plate of the present invention is excellent in atmospheric corrosion resistance performance and seismic resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot continuous rolled strip, specifically relates to the technical field of earthquake-resistant and weather-resistant steel plates, and particularly relates to an earthquake-resistant and weather-resistant steel plate for V-type 550 MPa grade building structures and a manufacturing method thereof.

Background Art

[0002] Steel structure buildings have advantages such as light self-weight, high strength, convenient installation, short construction period, and high recycling rate, so the application of steel for building structures has been developing rapidly. Conventional steel for building structures such as carbon steel and low-alloy high-strength steel have poor corrosion resistance, are prone to corrosion, and greatly shorten the lifespan of steel structure buildings. Therefore, rust removal and painting are required during use, which not only increases the cost of steel structure buildings but also causes environmental pollution problems. Therefore, high-performance steel for building structures requires excellent atmospheric corrosion resistance. In addition, China is a region with frequent earthquakes, and there are 101 earthquake-prone areas (above magnitude 7) that require earthquake-resistant design, accounting for 32.5% of the total national area. Therefore, in order to achieve the goal of "not being damaged in minor earthquakes, being repairable in moderate earthquakes, and not collapsing in major earthquakes" for buildings, high-performance steel for building structures needs to further possess excellent earthquake resistance.

[0003] In "Structural Steel - Part 6: Technical Delivery Conditions for Steel for Seismic Resistant Building Structures" (GB / T 34560.6 - 2017), it is required that the yield ratio of steel for seismic resistant structures is ≤ 0.85. In the "Code for Seismic Design of Buildings" (GB 50011 - 2010), it is required that the yield ratio of steel for seismic resistant structures is ≤ 0.85, having a significant yield plateau, an elongation rate of ≥ 20%, and excellent impact toughness. The yield point elongation Ae (percentage yield point extension) is the percentage of the elongation of the extensometer gauge length from the start of yield to the start of uniform work hardening to the extensometer gauge length for a metallic material showing a significant yield phenomenon. The larger the Ae value, the longer the length of the yield plateau. Also, buildings during an earthquake mainly receive large strain loads due to alternating stresses, and in many cases, the number of alternations is 200 times or less. Thus, it can be seen that the process of damage and fracture of structural steel for buildings is very similar to high - strain low - cycle fatigue behavior. Therefore, in order to achieve excellent seismic resistance, structural steel for building structures needs to have not only excellent plasticity and toughness, but also a small yield ratio, a large Ae value, and excellent high - strain low - cycle fatigue performance.

[0004] In the inventions of Patent Documents 1 - 4, although building structural steel with a yield strength of 500 MPa or more and its manufacturing method are disclosed, only a low yield ratio can be achieved, excellent atmospheric corrosion resistance cannot be realized, and seismic resistance indicators such as the yield point elongation rate and high - strain low - cycle fatigue performance cannot be guaranteed either.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above technical problems, and provides a seismic and weather-resistant steel plate for V-series 550 MPa grade building structures and a manufacturing method thereof.

Means for Solving the Problems

[0007] The present invention adopts the following technical solutions.

[0008] In a V-series 550 MPa grade seismic and weather-resistant steel plate for building structures, which is one form of the present invention, the components are, by mass%, C: 0.07 to 0.12%, Si: 0.35 to 0.45%, Mn: 1.30 to 1.40%, P ≤ 0.020%, S ≤ 0.008%, Cr: 0.60 to 0.70%, Ni: 0.25 to 0.35%, Cu: 0.30 to 0.40%, V: 0.08 to 0.12%, Als: 0.015 to 0.055%, N: 0.0200 to 0.0220%, and the balance is Fe and unavoidable impurities.

[0009] Furthermore, the metallographic structure of the seismic and weather-resistant steel plate for building structures is polygonal ferrite and pearlite, and by volume%, ferrite is 75 to 80% and pearlite is 20 to 25%.

[0010] Furthermore, the atmospheric corrosion resistance index I of the seismic and weather-resistant steel plate for building structures is ≥ 6.5.

[0011] Furthermore, the seismic and weather-resistant steel plate for building structures has a yield strength of ≥ 550 MPa, a tensile strength of ≥ 600 MPa, an elongation after fracture of ≥ 20%, a yield ratio of ≤ 0.85, a yield point elongation of Ae ≥ 2.0%, D = 2a in the 180° bending test, and a collision energy KV2 of ≥ 70 J at -40 °C for a full-size V-notch.

[0012] Furthermore, the corrosion rate of the seismic and weather-resistant steel plate for building structures with respect to Q355B is ≤ 45%.

[0013] Furthermore, the fatigue life in the high-strain low-cycle fatigue test with a strain amplitude range of ±2% of the earthquake-resistant and weather-resistant steel plate for building structures is ≧200 cycles.

[0014] Furthermore, the thickness of the earthquake-resistant and weather-resistant steel plate for building structures is 6.0 to 16.0 mm.

[0015] The actions and mechanisms of each element and main process in the present invention are as follows.

[0016] Influence law of yield ratio: Grain refinement strengthening and dislocation strengthening can significantly increase the yield ratio because they make the amplification of the yield strength larger than that of the tensile strength. Precipitation strengthening has a slight influence on the yield ratio because it makes the amplification of the yield strength slightly larger than that of the tensile strength. Solid solution strengthening can decrease the yield ratio because it makes the amplification of the yield strength slightly smaller than that of the tensile strength.

[0017] Influence of yield point elongation rate: (1) Increasing the content of C and N interstitial atoms (self-interstitial) makes the yield phenomenon more pronounced, and increases the yield point elongation rate. The yield effect of mild steel is caused by dislocations being pinned by the Cottrell atmosphere formed by interstitial atoms C and N. Therefore, only when the stress is increased to a certain extent during deformation can the dislocations escape from the pinned state, at which time an upper yield point is formed on the tensile curve, and once the dislocations escape from the pinned state, they can continue to move even with a small stress, at which time a lower yield point is formed on the stress-strain curve. (2) When a structure with high dislocation density such as bainite or martensite appears in the microstructure, it reduces the yield point elongation rate. When the dislocation density in the crystal is high, the strengthening effect is large, and when force is applied, the interaction between dislocations becomes strong, the strain hardening action is prominent, the yield phenomenon becomes less pronounced, and the yield point elongation rate decreases. (3) The yield phenomenon becomes more pronounced when the crystal grains are refined, and the yield point elongation rate increases. The theory of polycrystalline cooperative deformation explains the remarkable improvement of the yield phenomenon by the refinement of the crystal grains. Unlike single crystals, polycrystals must maintain the harmony of deformation between crystal grains during the deformation process, and polycrystalline deformation requires five or more slip lines. Although ferrite with a body-centered cubic structure has five or more slip lines, when the crystal grains are large, the number of crystal grain orientations decreases, and the number of movable slip lines decreases accordingly, resulting in a low yield strength and slip occurring only in large crystal grains with favorable orientation. With an increase in stress, multiple slip and slip of other crystal grains are initiated in large crystal grains with favorable orientation, which causes the yield stage to end early and the work hardening stage to begin, thereby decreasing the elongation rate of the yield plateau. When the crystal grains are reduced, the number of crystal orientations increases significantly, and the number of movable slip lines also increases, resulting in the initial single slip occurring in more crystal grains. In addition, fine grains have higher yield strength and shear stress, and once the dislocation breaks free from the interstitial pinning state, the applied shear stress is much higher than the critical shear stress for dislocation initiation, so that single slips on more parallel slip planes can move in succession, forming nearly parallel slip bands and forming a macroscopically long yield plateau.Similarly, with the increase in stress, multiple slips do not preferentially occur in large grains with favorable orientations like in coarse-grained samples, but occur simultaneously in the majority of grains, so it does not enter the work hardening stage early.

[0018] In order to endow the product with comprehensive properties such as excellent seismic resistance and corrosion resistance, based on the influence laws of the yield ratio and the yield point elongation rate, the present invention limits the content of each element and the process parameters of the main processes.

[0019] Carbon: Carbon is an effective strengthening element in steel. It can dissolve in the matrix to play a role in solid solution strengthening, and can combine with V to form carbide precipitation particles to play a role in fine grain strengthening and precipitation strengthening. The improvement of the carbon content is beneficial to increasing the strength. At the same time, carbon can pin dislocations as an interstitial atom, making the yield phenomenon more prominent and increasing the Ae value. However, if the carbon content is too high, many coarse and brittle carbide particles will be generated in the steel, which is disadvantageous to the plasticity and toughness of the steel. Also, segregation bands are likely to occur in the center of the steel plate, which is disadvantageous to the bending performance and formability of the steel. At the same time, the welding carbon equivalent and the welding crack sensitivity index increase, which is disadvantageous to welding. Therefore, in the present invention, the content range of C is set to 0.07 - 0.12%.

[0020] Si: Silicon can dissolve in ferrite and austenite to increase the hardness and strength of the steel, refine the rust layer structure, and help reduce the overall corrosion rate of the steel. However, if the silicon content is too high, it will reduce the plasticity and toughness of the steel, make descaling difficult during rolling, and also lead to a decrease in welding performance. Therefore, in the present invention, the content range of Si is set to 0.35 - 0.45%.

[0021] Mn: Manganese is an important strengthening element. It has a strong solid solution strengthening effect, can significantly reduce the phase transition temperature of steel, and can refine the microstructure of steel. However, if the Mn content is too high, it is likely to cause cracks in the casting billet in the continuous casting process, lead to segregation of components in the core of the steel plate, and result in a decrease in the welding performance of the steel. Therefore, in the present invention, the Mn content range is set to 1.30 - 1.40%.

[0022] P and S: Phosphorus and sulfur have an adverse impact on the tissue performance of the steel plate. Phosphorus can effectively improve the atmospheric corrosion resistance of steel, but if the phosphorus content is too high, it will significantly reduce the plasticity and low-temperature toughness of the steel. Sulfur forms sulfides and intervenes to deteriorate the performance of the steel. Therefore, in the present invention, the P content range is set to ≤0.020%, and the S content range is set to ≤0.008%.

[0023] Cr: Chromium has a significant effect on improving the passivation ability of steel and helps to form a dense passivation film or protective rust layer on the surface of the steel. The enrichment of Cr in the rust layer can effectively improve the selective permeation characteristics of the rust layer against the corrosive medium. However, if the Cr content is too high, the manufacturing cost will increase. Therefore, in the present invention, the chromium element content range is set to 0.60 - 0.70%.

[0024] Ni: The addition of nickel to steel significantly improves the corrosion resistance of the steel. The nickel element and copper element form a Cu-rich phase containing Ni, and this Cu-rich phase remains in the outer oxide layer in the solid state, reducing the concentration of copper in the substrate and decreasing the chance of forming a liquid Cu-rich phase, thus avoiding the occurrence of high-temperature brittleness defects. Therefore, Ni / Cu in the steel is controlled to be ≥1 / 2. However, if the nickel content is too high, the adhesion of the oxide scale increases, and hot rolling defects are formed on the surface when the steel is pressed. Also, nickel is a noble metal, and if the nickel content is too high, the cost of the steel alloy will increase significantly. Therefore, in the present invention, the Ni content range is set to 0.25 - 0.35%.

[0025] Cu: The addition of copper to steel is advantageous for the formation of a dense and highly adhesive amorphous oxide (hydrocarbon-based oxide) protective layer on the surface of the steel, which has remarkable corrosion resistance. Also, copper forms poorly soluble sulfides with sulfur, offsetting the harmful effects of S on the corrosion resistance of the steel. However, since the melting point of copper is lower than the heating temperature of the steel slab, if the copper content is too high, the precipitated copper aggregates at the austenite grain boundaries in the liquid state, and after the precipitated copper reaches a certain amount, cracks are likely to occur during heating or hot rolling. Also, according to the calculation formula for the atmospheric corrosion resistance index I, if the copper content is either too high or too low, it will both reduce the calculated value of the atmospheric corrosion resistance index I. Therefore, in the present invention, the range of the Cu content is set to 0.30 - 0.40%.

[0026] V, N: The solid solution of vanadium elements in austenite can suppress static and dynamic recrystallization during the hot deformation process, expand the unrecrystallized region of austenite, increase the amount of strain in the unrecrystallized region during the finish rolling process, promote the transformation from austenite to ferrite, and refine the ferrite crystal grains. Also, vanadium combines with carbon and nitrogen to form fine carbonitrides, pinning the grain boundaries, delaying recrystallization, suppressing the growth of austenite crystal grains, and producing fine grain strengthening and precipitation strengthening effects, but increasing the yield ratio. The increase in the nitrogen element content in the steel is advantageous for the precipitation of the second phase of vanadium. However, if the nitrogen element content is too high, after fixing the vanadium element, there is still some remaining, and the remaining nitrogen elements pin the dislocations as interstitial atoms, making the yield phenomenon more prominent and increasing the Ae value. However, if the nitrogen content is too high, it will increase the aging tendency, low-temperature brittleness, and high-temperature brittleness of the steel, and impair the weldability and cold bendability of the steel. Therefore, in the present invention, the range of the V content is set to 0.08 - 0.12%, and the range of the N content is set to 0.0200 - 0.0220%.

[0027] Als: Adding aluminum to steel can play a role in deoxidation and improve the quality of steel. However, if the aluminum content is too high, nitrogen oxides are likely to precipitate at the austenite grain boundaries, resulting in cracks in the casting billet. Therefore, in the present invention, the content range of Als is set to 0.015 - 0.055%.

[0028] Another form of the present invention provides a method for manufacturing a seismic and weather-resistant steel plate for V-series 550 MPa grade building structures. The manufacturing method includes the steps of heating, rough rolling, finish rolling, laminar flow cooling, and coiling a slab containing the above components to obtain a seismic and weather-resistant steel plate for building structures.

[0029] Furthermore, in the heating process, the slab is heated in a regenerative heating furnace. Heating the slab serves to homogenize the casting structure and component segregation and dissolve alloying elements. However, if the heating temperature is too high and the heating time is too long, problems such as burning loss, overheating, and overburning will occur. Therefore, in the present invention, in the heating process, the heating temperature is set to 1180 - 1220 °C and the heating time is set to 180 - 400 min.

[0030] Furthermore, in the rough rolling process, rough rolling must achieve a sufficient amount of deformation to ensure the recrystallization of austenite, refine the austenite grain size, and prevent the occurrence of a mixed crystal structure. If the thickness of the intermediate billet is too large, the amount of deformation in rough rolling will be insufficient, increasing the load on finish rolling. If the thickness of the intermediate billet is too small, there is a risk that the amount of deformation in finish rolling will be insufficient. Therefore, in the present invention, in the rough rolling process, 6 passes of rough rolling are performed, and the amount of deformation per pass is ≧18%. When the thickness of the finished product is 6.0 - 10.0 mm, the thickness of the intermediate billet is 48 - 52 mm. When the thickness of the finished product is >10.0 - 16.0 mm, the thickness of the intermediate billet is 53 - 57 mm.

[0031] Furthermore, in the finish rolling process, the slabs on the mechanical frame in the last three passes after finish rolling are basically rolled in the unrecrystallized region of austenite. By adopting a large deformation rate, the recrystallized and somewhat refined austenite crystal grains are crushed and stretched, increasing the grain boundary area of austenite per unit volume. Additionally, a large number of deformation bands and high-density dislocations are generated within the crystal, enhancing the ferrite nucleation rate and resulting in a fine microstructure after phase transformation. If the finish rolling start temperature is too high, the amount of deformation in the unrecrystallized region of austenite during the finish rolling process will be insufficient, which is disadvantageous for microstructure refinement. If the finish rolling end temperature is too low, the difference from the start temperature will be too large, the cooling rate during the finish rolling process will be too fast, and there is a risk that some of the subsequent passes on the mechanical frame will be rolled in the two-phase region, resulting in inferior comprehensive product performance. If the finish rolling end temperature is too high, the amount of deformation in the unrecrystallized region will be insufficient, which is disadvantageous for the refinement of the final microstructure. Therefore, in the present invention, the finish rolling process performs seven passes of finish rolling, among which the reduction ratios of the mechanical frames in the last three passes are respectively ≥17%, ≥13%, and ≥10%, the finish rolling start temperature is ≤1030°C, and the finish rolling end temperature is 840 - 880°C.

[0032] In the laminar flow cooling process, adopting the front-stage cooling mode can achieve a large subcooling degree and refine the final microstructure. Adopting a relatively large cooling rate can achieve the effect of improving the banded structure in the core and is beneficial for the precipitation of fine and dispersed second phases, thus enhancing the effects of grain refinement strengthening and precipitation strengthening. However, if the cooling rate is too fast, it is easy to generate medium- and low-temperature microstructures such as bainite and martensite, resulting in a high yield ratio and a low yield point elongation rate. Therefore, in the present invention, the front-stage cooling mode is adopted, and the cooling rate is set at 40 - 80°C / s.

[0033] In the coiling process, if the coiling temperature is too low, the cooling rate during the cooling process will be too fast, which is likely to produce medium- and low-temperature structures such as bainite and martensite. As a result, the yield ratio increases and the yield point elongation decreases. If the coiling temperature is too high, the crystal grains and the particles of the second phase will become thicker, reducing the strength and toughness. Therefore, in the present invention, the coiling temperature is set to 650 - 690 °C.

Advantages of the Invention

[0034] The present invention has the following advantages compared with the prior art.

[0035] By adding a predetermined amount of elements such as Si, Cr, Ni, and Cu, the present invention realizes an atmospheric corrosion resistance index I ≥ 6.5, improves the atmospheric corrosion resistance of the product, and exerts the effects of fine grain strengthening and precipitation strengthening through the V-N microalloying method, endowing the product with excellent strength, plasticity, and toughness performance. At the same time, by controlling the rolling process and the cooling process, the tissue performance of the product is controlled. The obtained product has a uniform polygonal ferrite and pearlite metal structure, a low yield ratio, a high yield point elongation rate, and high high-strain low-cycle fatigue resistance. The steel for building structures manufactured by the components and the manufacturing method of the present invention has a yield strength ≥ 550 MPa, a tensile strength ≥ 600 MPa, an elongation after fracture ≥ 20%, a yield ratio ≤ 0.85, a yield point elongation Ae ≥ 2.0%, D = 2a in the 180° bending test, a collision energy KV2 of ≥ 70 J at -40 °C for a full-size V-notch, a corrosion rate ≤ 45% compared to Q355B, and a fatigue life ≥ 200 cycles during the high-strain low-cycle fatigue test with a strain amplitude range of ±2%, realizing excellent atmospheric corrosion resistance and seismic resistance.

[0036] For the above reasons, the present invention is widely applied in fields such as seismic-resistant and weather-resistant steel plates.

Brief Description of the Drawings

[0037] To more clearly illustrate the embodiments of the present invention or the technical means of the prior art, the drawings used in the following embodiments or descriptions of the prior art will be briefly described below. The following drawings relate to embodiments of the present invention, and it is obvious to those skilled in the art that other drawings can be obtained based on these drawings without creative labor.

[0038]

Figure 1

Modes for Carrying Out the Invention

[0039] As long as there is no conflict with each other, the features in the embodiments and examples of the present invention may be combined with each other. Hereinafter, the present invention will be described in detail in relation to the examples with reference to the drawings. In order to more clearly clarify the objectives, technical solutions and advantages of the embodiments of the present invention, hereinafter, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the drawings related to the embodiments of the present invention. Needless to say, the described embodiments are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is actually merely exemplary and does not limit the present invention and its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative labor shall be included in the protection scope of the present invention.

[0040] Hereinafter, to facilitate the understanding of the present invention, the present invention will be further described in relation to the examples and comparative examples.

[0041] The earthquake-resistant and weather-resistant steel plate for building structures of V series 550MPa grade according to the present invention has the following components by mass%: C: 0.07 - 0.12%, Si: 0.35 - 0.45%, Mn: 1.30 - 1.40%, P ≦ 0.020%, S ≦ 0.008%, Cr: 0.60 - 0.70%, Ni: 0.25 - 0.35%, Cu: 0.30 - 0.40%, V: 0.08 - 0.12%, Als: 0.015 - 0.055%, N: 0.0200 - 0.0220%, and the balance is Fe and inevitable impurities.

[0042] To further understand the present invention, examples using the components and manufacturing methods of the earthquake-resistant and weather-resistant steel plates for building structures described in the present invention in three sets are provided and will be described in comparison with two sets of comparative examples.

[0043] The atmospheric corrosion resistance index of the earthquake-resistant and weather-resistant steel plate for building structures is I = 26.01(%Cu) + 3.88(%Ni) + 1.20(%Cr) + 1.49(%Si) + 17.28(%P) - 7.29(%Cu)(%Ni) - 9.10(%Ni)(%P) - 33.39(%Cu) 2 is as follows.

[0044] The yield strength, tensile strength and elongation after fracture of the earthquake-resistant and weather-resistant steel plate for building structures are measured according to "Tensile testing of metallic materials - Part 1: Method of test at room temperature" (GB / T 228.1). The bending performance is measured according to "Bend test method for metallic materials" (GB / T 232). The impact performance is measured according to "Charpy impact test method for metallic materials" (GB / T 229). The corrosion resistance is measured for 72h according to "Periodic immersion corrosion test method for weathering steel for railways" (TB / T 2375). The high strain low cycle fatigue performance is measured according to "Fatigue testing of metallic materials - Axial strain control method". The strain amplitude range is ±2%, the strain ratio is R = -1, and the deformation speed is 2×10 -3 , the load is 3kN, and when the sample breaks or the stress value drops to 30% of the stable stress value, it is determined that the sample fails.

[0045] (Example 1) A seismic and weather-resistant steel plate for building structures of V series with a yield strength of 550 MPa, the chemical composition of which is shown in Table 1, and the balance being Fe and inevitable impurities.

[0046] A method for manufacturing a seismic and weather-resistant steel plate for building structures of V series with a yield strength of 550 MPa. According to the components, the slab is smelted by the conventional method, and the smelted slab is successively heated, roughly rolled, finish-rolled, laminar cooled and coiled for continuous processing. The specific processing process is as follows. The heating temperature is 1190 °C, the heating time is 220 min, rough rolling is carried out in 6 passes, the deformation amount per pass is ≥18%, the thickness of the intermediate billet is 51 mm, finish rolling is carried out in 7 passes, among which the rolling reduction rates of the mechanical frames of the latter 3 passes are ≥17%, ≥13%, ≥10% respectively, the start temperature of finish rolling is 1010 - 1020 °C, the end temperature of rolling is 850 - 860 °C, the front-stage cooling mode is adopted to cool to the target coiling temperature, the cooling rate is about 70 °C / s, and the coiling temperature is 650 - 660 °C. The metallographic structure is uniform polygonal ferrite and pearlite. As shown in Figure 1, the volume percentage of ferrite is 75% and the volume percentage of pearlite is 25%.

[0047] (Example 2) The seismic and weather-resistant steel plate for building structures of V series has the chemical composition shown in Table 1, and the balance being Fe and inevitable impurities.

[0048] The manufacturing method of a seismic and weather-resistant steel plate for building structures of V series with a yield strength of 550 MPa is to smelt the slab according to the components and by the conventional method, and then successively perform heating, rough rolling, finish rolling, laminar flow cooling, and coiling on the smelted slab for continuous processing. The specific processing process is as follows. The heating temperature is 1210 °C, the heating time is 250 min, 6 passes of rough rolling are performed, the deformation amount per pass is ≥ 18%, the thickness of the intermediate billet is 54 mm, 7 passes of finish rolling are performed, among which the rolling reduction ratios of the mechanical frames of the last 3 passes are ≥ 17%, ≥ 13%, and ≥ 10% respectively, the start rolling temperature of the finish rolling is 1010 - 1030 °C, the end rolling temperature is 860 - 870 °C, the front-stage cooling mode is adopted, cooled to the target coiling temperature, the cooling rate is about 65 °C / s, and the coiling temperature is 660 - 690 °C. The metallographic structure is uniform polygonal ferrite and pearlite, the volume percentage of ferrite is 78%, and the volume percentage of pearlite is 22%.

[0049] (Example 3) A seismic and weather-resistant steel plate for building structures of V series with a yield strength of 550 MPa, the chemical components are shown in Table 1, and the balance is Fe and unavoidable impurities.

[0050] The manufacturing method of a seismic and weather-resistant steel plate for building structures of V series with a yield strength of 550 MPa is to smelt the slab according to the components and by the conventional method, and then successively perform heating, rough rolling, finish rolling, laminar flow cooling and coiling on the smelted slab for continuous processing. The specific processing process is as follows. The heating temperature is 1185 °C, the heating time is 235 min, 6 passes of rough rolling are performed, the deformation amount per pass is ≥ 18%, the thickness of the intermediate billet is 56 mm, 7 passes of finish rolling are performed, among which the rolling reduction ratios of the mechanical frames of the last 3 passes are ≥ 17%, ≥ 13%, and ≥ 10% respectively, the start rolling temperature of the finish rolling is 1010 - 1030 °C, the end rolling temperature is 850 - 870 °C, the front-stage cooling mode is adopted, cooled to the target coiling temperature, the cooling rate is about 50 °C / s, and the coiling temperature is 670 - 680 °C. The metallographic structure is uniform polygonal ferrite and pearlite, the volume percentage of ferrite is 80%, and the volume percentage of pearlite is 20%.

[0051] (Comparative Example 1) Comparative Example 1 specifically refers to Example 2 in "Large-thickness Q500GJCD High-strength Steel Plate for Building Structures and Its Manufacturing Method" (Specification of Chinese Patent Application Publication No. 107385324).

[0052] It is a steel for building structures, and its chemical composition is shown in Table 1, with the balance being Fe and inevitable impurities.

[0053] It is a manufacturing method of steel for building structures. According to the components, the slab is smelted by the conventional method, and the smelted slab is heated, roughly rolled, finish-rolled, laminar cooled, and coiled in sequence by a wide-width thick plate rolling mill and then continuously processed. The specific process is as follows. The heating temperature is 1200 - 1220 °C, the heating time is 375 min. Rough rolling is carried out, the thickness at the temperature holding stage is 50 mm, and the starting temperature of finish rolling in the finish rolling mill is 900 °C after the temperature holding stage ends. Further, finish rolling is carried out, and the final rolling temperature is ≥ 796 °C. After rolling is completed, the rolled product is directly sent into the Acc equipment for water injection and rapid cooling. The cooling rate is 6 - 7 °C / s, and the final cooling temperature is 690 - 710 °C. Then, it is flattened by a hot straightening machine, sent to a cooling bed for natural cooling to 320 °C, then lowered from the cooling bed and stacked to be slowly cooled for 24 h.

[0054] (Comparative Example 2) Comparative Example 2 specifically refers to Example 2 in "High-strength Q500GJD Quenched and Tempered Steel Plate for Building Structures and Its Manufacturing Method" (Specification of Chinese Patent Application Publication No. 107604248).

[0055] It is a steel for building structures, and its chemical composition is shown in Table 1, with the balance being Fe and inevitable impurities.

[0056] A method for manufacturing steel for building structures, which includes smelting into slabs according to the components and by the conventional method, and then heating, rough rolling, finish rolling, laminar cooling and coiling the smelted slabs successively with a wide and thick plate rolling mill for continuous processing. The specific process is as follows. The heating temperature is 1180 - 1220 °C, and the heating time is 220 min. After rough rolling to a thickness of 65 mm, it is sent to the finish rolling mill for rolling. The finish rolling temperature is 795 °C. After rolling is completed, the rolled product is directly sent to the hot straightening machine for flattening, and then sent to the cooling bed for natural cooling. The qualified plates are transferred to the heat treatment process. Among them, the quenching temperature is 905 °C, and the residence time in the furnace is 25 min, followed by water cooling. The tempering temperature is 660 °C, and the residence time in the furnace is 27 min, and then air-cooled to room temperature.

[0057]

Table 1

[0058] The specific mechanical performance test results of the examples and comparative examples are shown in Table 2.

[0059]

Table 2

[0060] According to the manufacturing methods of 3 groups of examples and 2 groups of comparative examples, the chemical components in Table 1, and the performance test results of the examples and comparative examples in Table 2, in the examples, by adding a certain amount of elements such as Si, Cr, Ni, Cu, excellent atmospheric corrosion resistance is achieved. The V-N microalloying method exerts the effects of grain refinement and precipitation strengthening, endowing the product with excellent strength, plasticity and toughness. At the same time, by controlling the rolling process and the cooling control process, the tissue performance of the product is controlled. The obtained product has a relatively low yield ratio, high yield point elongation rate and high strain low cycle fatigue resistance. Therefore, the seismic-resistant and weather-resistant steel plate for building structures of V series 550 MPa grade and its manufacturing method disclosed in the present invention enable the product to have comprehensive performances such as excellent atmospheric corrosion resistance and seismic resistance, and have good application prospects.

[0061] Finally, the following should be noted. Each of the above embodiments is merely for explaining the technical solution of the present invention and does not limit the present invention. Although the present invention has been described in detail with reference to each of the above embodiments, those skilled in the art should understand that it is also possible to modify the technical solutions described in each of the above embodiments or perform equivalent replacements for some or all of their technical features. The essence of the corresponding technical solutions does not deviate from the scope of the technical solutions of each embodiment of the present invention due to these modifications or replacements.

[0062] (Addendum) (Addendum 1) The components are, by mass%, C: 0.07 - 0.12%, Si: 0.35 - 0.45%, Mn: 1.30 - 1.40%, P ≤ 0.020%, S ≤ 0.008%, Cr: 0.60 - 0.70%, Ni: 0.25 - 0.35%, Cu: 0.30 - 0.40%, V: 0.08 - 0.12%, Als: 0.015 - 0.055%, N: 0.0200 - 0.0220%, and the balance is Fe and unavoidable impurities. A seismic and weather-resistant steel plate for V-series 550 MPa-class building structures, characterized by the above.

[0063] (Addendum 2) The metallographic structure of the seismic and weather-resistant steel plate for building structures is polygonal ferrite and pearlite. By volume%, ferrite is 75 - 80% and pearlite is 20 - 25%. A seismic and weather-resistant steel plate for V-series 550 MPa-class building structures according to Addendum 1, characterized by the above.

[0064] (Addendum 3) The atmospheric corrosion resistance index I of the seismic and weather-resistant steel plate for building structures is ≥ 6.5. The yield strength of the seismic and weather-resistant steel plate for building structures is ≥ 550 MPa, the tensile strength is ≥ 600 MPa, the elongation after fracture is ≥ 20%, the yield ratio is ≤ 0.85, the yield point elongation Ae is ≥ 2.0%, D = 2a in the 180° bending test, and the impact energy KV2 at -40°C for the full-size V-notch is ≥ 70 J. The earthquake-resistant and weather-resistant steel plate for building structures of V series with 550 MPa grade according to Addendum 1, characterized by the following.

[0065] (Addendum 4) The corrosion rate of the earthquake-resistant and weather-resistant steel plate for building structures with respect to Q355B is ≤ 45%, and the fatigue life in the high-strain low-cycle fatigue test with a strain amplitude range of ±2% of the earthquake-resistant and weather-resistant steel plate for building structures is ≥ 200 cycles. The earthquake-resistant and weather-resistant steel plate for building structures of V series with 550 MPa grade according to Addendum 1, characterized by the following.

[0066] (Addendum 5) The thickness of the earthquake-resistant and weather-resistant steel plate for building structures is 6.0 - 16.0 mm. The earthquake-resistant and weather-resistant steel plate for building structures of V series with 550 MPa grade according to Addendum 1, characterized by the following.

[0067] (Addendum 6) A slab containing the components described in any one of Addenda 1 - 5 undergoes a heating process, rough rolling process, finish rolling process, laminar cooling process, and coiling process to obtain an earthquake-resistant and weather-resistant steel plate for building structures. The manufacturing method of the earthquake-resistant and weather-resistant steel plate for building structures of V series with 550 MPa grade, characterized by the following.

[0068] (Addendum 7) In the heating process, the heating temperature is 1180 - 1220 °C and the heating time is 180 - 400 min. The manufacturing method of the earthquake-resistant and weather-resistant steel plate for building structures of V series with 550 MPa grade according to Addendum 6, characterized by the following.

[0069] (Addendum 8) In the rough rolling process, when 6 - pass rough rolling is performed with a deformation amount per pass of ≥ 18% and the thickness of the finished product is 6.0 - 10.0 mm, the thickness of the intermediate billet is 48 - 52 mm; when the thickness of the finished product is > 10.0 - 16.0 mm, the thickness of the intermediate billet is 53 - 57 mm. In the finish rolling process, finish rolling is performed in 7 passes, among which the reduction ratios of the mechanical frames in the last 3 passes are respectively ≥17%, ≥13%, and ≥10%, the start rolling temperature of the finish rolling is ≤1030°C, and the finish rolling temperature is 840 - 880°C. A method for manufacturing a V-series 550 MPa grade earthquake-resistant and weather-resistant steel plate for building structures according to Supplementary Note 6, characterized by the above.

[0070] (Supplementary Note 9) In the laminar flow cooling process, the front-stage cooling mode is adopted, and the cooling rate is 40 - 80°C / s. A method for manufacturing a V-series 550 MPa grade earthquake-resistant and weather-resistant steel plate for building structures according to Supplementary Note 6, characterized by the above.

[0071] (Supplementary Note 10) In the coiling process, the coiling temperature is 650 - 690°C. A method for manufacturing a V-series 550 MPa grade earthquake-resistant and weather-resistant steel plate for building structures according to Supplementary Note 6, characterized by the above.

Claims

1. The components are, by mass%, C: 0.07 to 0.12%, Si: 0.35 to 0.45%, Mn: 1.30 to 1.40%, P ≤ 0.020%, S ≤ 0.008%, Cr: 0.60 to 0.70%, Ni: 0.25 to 0.35%, Cu: 0.30 to 0.40%, V: 0.08 to 0.12%, Als: 0.015 to 0.055%, N: 0.0200 to 0.0220%, and the balance is Fe and unavoidable impurities. A seismic and weather-resistant steel plate for building structures of V series with a strength of 550 MPa, characterized by the above.

2. The metallographic structure of the seismic and weather-resistant steel plate for building structures is polygonal ferrite and pearlite. By volume%, ferrite is 75 to 80% and pearlite is 20 to 25%. The seismic and weather-resistant steel plate for building structures of V series with a strength of 550 MPa according to Claim 1, characterized by the above.

3. The atmospheric corrosion resistance index I of the seismic and weather-resistant steel plate for building structures is ≥ 6.

5. The yield strength of the earthquake- and weather-resistant steel plate for building structures is ≥550 MPa, the tensile strength is ≥600 MPa, the elongation after fracture is ≥20%, the yield ratio is ≤0.85, the yield point elongation rate Ae is ≥2.0%, D = 2a in the 180° bending test, and the impact energy KV at -40°C of the full-size V-notch ２ is ≥70 J. The seismic and weather-resistant steel plate for building structures of V series with a strength of 550 MPa according to Claim 1, characterized by the above.

4. The corrosion rate of the seismic and weather-resistant steel plate for building structures with respect to Q355B is ≤ 45%, and the fatigue life in the high-strain low-cycle fatigue test with a strain amplitude range of ±2% of the seismic and weather-resistant steel plate for building structures is ≥ 200 cycles. The seismic and weather-resistant steel plate for building structures of V series with a strength of 550 MPa according to Claim 1, characterized by the above.

5. The thickness of the seismic and weather-resistant steel plate for building structures is 6.0 to 16.0 mm. The seismic and weather-resistant steel plate for building structures of V series with a strength of 550 MPa according to Claim 1, characterized by the above.

6. A slab containing the components according to any one of Claims 1 to 5 is subjected to a heating process, a rough rolling process, a finish rolling process, a laminar cooling process, and a coiling process to obtain a seismic and weather-resistant steel plate for building structures. A manufacturing method of a seismic and weather-resistant steel plate for building structures of V series with a strength of 550 MPa, characterized by the above.

7. In the heating process, the heating temperature is 1180 to 1220 °C and the heating time is 180 to 400 min. The manufacturing method of a seismic and weather-resistant steel plate for building structures of V series with a strength of 550 MPa according to Claim 6, characterized by the above.

8. In the rough rolling process, 6-pass rough rolling is performed. When the reduction per pass is ≥18% and the thickness of the finished product is 6.0 to 10.0 mm, the thickness of the intermediate billet is 48 to 52 mm. When the thickness of the finished product is >10.0 to 16.0 mm, the thickness of the intermediate billet is 53 to 57 mm. In the finish rolling process, 7-pass finish rolling is performed. Among them, the reduction ratios of the mechanical frames in the last 3 passes are ≥17%, ≥13%, and ≥10% respectively. The starting temperature of the finish rolling is ≤1030°C, and the ending temperature of the rolling is 840 to 880°C. A method for manufacturing a seismic and weather-resistant steel plate for V-series 550 MPa-class building structures according to claim 6, characterized in that.

9. In the laminar flow cooling process, the front-stage cooling mode is adopted, and the cooling rate is 40 to 80°C / s. A method for manufacturing a seismic and weather-resistant steel plate for V-series 550 MPa-class building structures according to claim 6, characterized in that.

10. In the coiling process, the coiling temperature is 650 to 690°C. A method for manufacturing a seismic and weather-resistant steel plate for V-series 550 MPa-class building structures according to claim 6, characterized in that.

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