High-toughness and low-yield-ratio Q690GJ steel plate for high-rise building and low-cost production method thereof

Abstract

The invention belongs to the technical field of production of high-strength steel plates for buildings, and particularly relates to a high-toughness low-yield-ratio Q690GJ steel plate for high-rise buildings and a low-cost production method thereof.The high-toughness low-yield-ratio Q690GJ steel plate is composed of, by mass, 0.12%-0.14% of C, 0.10%-0.30% of Si, 0.8%-1.2% of Mn, smaller than or equal to 0.015% of P, smaller than or equal to 0.0020% of S, 0.005%-0.020% of Ti, 0.010%-0.020% of Nb, smaller than or equal to 0.8% of Cr, 0.0008%-0.0020% of B, 0.015%-0.025% of Al, smaller than or equal to 0.0045% of N and the balance Fe and inevitable impurities; according to the steel plate, the yield strength is larger than or equal to 690 MPa, the tensile strength is larger than or equal to 770 MPa, the yield ratio is smaller than or equal to 0.85, the V-shaped notch impact energy at the temperature of-20 DEG C and-40 DEG C is larger than or equal to 180 J, the percentage elongation after fracture is larger than or equal to 22%, and the steel plate has the excellent comprehensive performance of being low in yield ratio, high in strength, high in elongation, high in low-temperature toughness and the like, is low in manufacturing cost and has good application prospects for high-rise, super high-rise and large-scale building steel structures.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-strength building steel plate production, in particular to a high-strength and high-toughness low-yield ratio Q690GJ steel plate for high-rise buildings and a low-cost production method thereof. BACKGROUND

[0002] Building steel is widely used in steel structure buildings such as high-rise buildings, stations, airports, and exhibition centers. With the rapid development of high-rise, super high-rise buildings, and large-scale building projects such as steel structure workshops, higher and higher requirements are put forward for the strength, seismic performance, and welding performance of building structure steel. Q690GJ, as a high-strength and high-performance building structure steel plate, is highly praised by the market due to its excellent high strength, high toughness, resistance to laminated tearing, good welding performance, easy construction of large-span and large-space building structures, short construction period, and lightweight and green materials.

[0003] Due to the limitations of material composition, microstructure, and process design principles, it is difficult to achieve the excellent matching of high strength and toughness and low yield ratio. Currently, there is no explicit mandatory requirement for yield ratio in the national standard GB / T 19879-2023, and there are few domestic factories that can mass-produce low-yield ratio Q690GJ steel. There are also few invention patents for yield strength 690MPa grade high-rise building steel plates reported.

[0004] For example, the invention patent with publication number CN 112813354 B discloses a 690MPa grade high-strength thick steel plate for high-rise buildings and a preparation method. In order to meet the excellent low-temperature toughness, 0.8% to 1.2% Ni is added in the composition design, which has a high cost. At the same time, the yield strength 690MPa grade high-rise building steel plate is produced by adopting quenching + high-temperature tempering process, which has a relatively complex process flow and high alloy cost.

[0005] The invention patent with publication number CN 118854185 A discloses an anti-seismic high-strength building Q690GJ steel plate. It uses 2.0% to 2.2% Mn instead of adding V element and uses a lower C content design to expand the austenite temperature range of the steel plate. The steel plate can obtain greater deformation in the rolling zone, and the grain becomes finer, so that the steel plate not only has high strength and high toughness, but also has the advantage of low cost. However, the high Mn content can cause serious segregation in the core of the steel plate, which is not conducive to the resistance to laminated tearing of the material, and the finer the grain, the higher the yield ratio, which is not conducive to the seismic performance.

[0006] The patent for invention with publication number CN 116640998 B discloses a high-rise building steel Q690GJ steel plate, Mo is added to improve the hardenability of the steel plate, and Nb, V and other micro-alloy elements are added to inhibit the growth of austenite grains, refine the grain size, and improve the strength of the steel plate. The alloy cost is relatively high, the process flow is long, the yield strength ratio control is difficult, the production cost is high, and it is not conducive to large-scale production and application at low cost.

[0007] The patent for invention with publication number CN 114570898 A discloses a production method of a low yield strength ratio low alloy high strength steel plate, which adopts TMCP process, and adds 0.3-0.5% Nb and 0.3-0.8% V to produce a low yield strength ratio Q690GJ building steel plate, and the alloy cost is too high.

[0008] In summary, how to reduce the yield strength ratio of the building steel plate with a yield strength of 690 MPa and above under the condition of low cost, improve the strength and toughness, and improve the resistance to lamellar tearing is the biggest problem to be solved in the production and application of the industry. SUMMARY

[0009] The purpose of the present application is to solve the problem that the existing production process of Q690GJ building steel plate cannot produce Q690GJ building steel plate with low cost, high toughness, low yield strength ratio and excellent resistance to lamellar tearing, and restrict the development of large building projects such as high-rise, super high-rise buildings and steel structure workshops, and to provide a high-strength and tough low-yield high-rise building Q690GJ steel plate and a low-cost production method thereof.

[0010] The high-strength and tough low-yield high-rise building Q690GJ steel plate of the present application is composed of the following mass percentage of elements: C: 0.12-0.14%, Si: 0.10-0.30%, Mn: 0.8-1.2%, P≤0.015%, S≤0.0020%, Ti: 0.005-0.020%, Nb: 0.010-0.020%, Cr≤0.8%, B: 0.0008-0.0020%, Als: 0.015-0.025%, N≤0.0045%, and the rest is Fe and unavoidable impurities.

[0011] The finished thickness specification of the steel plate produced by the present application is 16-50 mm.

[0012] The steel plate produced by the present application has a microstructure of ferrite + lath bainite + lath martensite, and the volume percentage of ferrite structure in the total microstructure is 8-18%.

[0013] The yield strength of the steel plate produced by the application is greater than or equal to 690 MPa, the tensile strength is greater than or equal to 770 MPa, the yield strength ratio is less than or equal to 0.85, the V-notch impact energy at -20 DEG C and -40 DEG C is greater than or equal to 180 J, and the elongation after fracture is greater than or equal to 22%.

[0014] The low-cost production method of the high-strength and high-toughness low-yield-ratio high-rise building Q690GJ steel plate of the application comprises: smelting-continuous casting-slab heating-rolling-laminar cooling-heat straightening-finishing-heat treatment-off line; wherein:

[0015] (1) smelting: smelting the steelmaking raw materials into molten steel, and the smelting comprises, in sequence, ironmaking, molten iron pretreatment, KR desulfurization, converter smelting, LF refining and RH refining; during smelting, the contents of alloy elements and P, S and N elements in the steel are ensured to be within the composition limit range;

[0016] (2) continuous casting: continuously casting the qualified molten steel to obtain a slab; the slab is composed of the following mass percentage elements: C: 0.12-0.14%, Si: 0.10-0.30%, Mn: 0.8-1.2%, P≤0.015%, S≤0.0020%, Ti: 0.005-0.020%, Nb: 0.010-0.020%, Cr≤0.8%, B: 0.0008-0.0020%, Als: 0.015-0.025%, N≤0.0045%, and the rest is Fe and inevitable impurities;

[0017] (3) slab heating: heating the slab to 1150-1250 DEG C, and ensuring the slab soaking time to be 45-65 min;

[0018] (4) rolling: adopting a two-stage rolling method, the rough rolling opening temperature is 1050 DEG C-1150 DEG C, the single pass reduction rate is greater than or equal to 13%, the core grain size is refined, and the resistance to lamellar tearing is improved; the finish rolling opening temperature is less than or equal to 960 DEG C, the final rolling temperature is 860 DEG C-930 DEG C, the total reduction of the last three passes of finish rolling is greater than or equal to 30%, and the grain size is further refined;

[0019] (5) controlled cooling: after rolling, the steel plate is subjected to segmented accelerated cooling, after the final pass rolling at 860-930 DEG C, the cooling speed is 4.8-13.6 DEG C / s to cool to 720-780 DEG C, and then the cooling speed is greater than or equal to 18.6 DEG C / s to cool to 280-420 DEG C;

[0020] (6) straightening: straightening the steel plate to reduce the plate shape defects caused by cooling, reduce the internal stress of the steel plate, and reduce the unevenness of the steel plate;

[0021] (7) cooling bed cooling: after straightening, the steel plate is naturally cooled on the cooling bed and then off line.

[0022] The component design principle of the present application is described as follows:

[0023] Carbon C: as the most basic strengthening element. C dissolves in steel to form interstitial solid solution, plays the role of solid solution strengthening, and forms carbide precipitation with strong carbide elements, which plays the role of precipitation strengthening. But too high C is not conducive to the ductility, toughness and crack stopping performance of the steel, and high carbon equivalent deteriorates the performance. In the process of bainite formation, carbon atoms need to be desorbed from ferrite (alpha phase) and diffuse into austenite through ferrite-austenite phase interface. When the carbon content increases, the amount of carbon that needs to diffuse during bainite formation increases, resulting in a decrease in diffusion speed and a decrease in bainite phase transition speed. Therefore, the C in the steel of the present application is controlled at 0.12% to 0.14%.

[0024] Manganese Mn: is the most basic alloying element of low alloy high strength steel, which improves the strength of the steel through solid solution strengthening to compensate for the loss of strength caused by the reduction of C content in the steel. Mn expands the element of the γ phase zone, which can reduce the γ→α phase transition temperature of the steel and increase the stability of austenite. When Mn is at a certain content, there is a clear separation of the upper and lower C curves on the supercooled austenite isothermal transformation curve, which helps to obtain bainite phase transition products. When the Mn content is too high, it is easy to produce segregation in the center of the thick steel plate, which reduces the low temperature toughness and the resistance to lamellar tearing of the center. Therefore, the Mn content in the steel of the present application is 0.8% to 1.20%.

[0025] Phosphorus P, sulfur S, nitrogen N: unavoidable harmful impurity elements in steel, which are easy to form defects such as segregation and inclusion, and deteriorate the welding performance, impact toughness and lamellar tearing resistance of the steel plate. Therefore, the production method of the steel of the present application adopts ultra-clean steel production technology to control P≤0.015%, S≤0.0020%, N≤0.0045%.

[0026] Niobium Nb: precipitates NbC or Nb(CN) fine precipitated particles, and fine TiC particles are induced to precipitate during rolling, which inhibits the growth of austenite grains, refines the grains, and improves the strength and toughness. However, if the Nb content is too high, the increase of yield strength is higher than the tensile strength due to grain refinement, which is not conducive to the control of low yield ratio, and the cost increases significantly. Therefore, the content is controlled at 0.010% to 0.020%.

[0027] Chromium Cr: Cr can slow down the decomposition rate of austenite, move the ferrite and pearlite transformation curve to the right on the supercooled austenite isothermal transformation curve, expand the cold speed range of bainite transformation, and significantly improve the hardenability of the steel. However, at the same time, Cr also increases the tendency of temper brittleness of the steel. In the present application, the Cr content is ≤0.8%.

[0028] Boron B, Titanium Ti: B mainly improves the hardenability of the steel and reduces the critical cooling rate of bainite and martensite transformation. It is generally considered that the effect is best when the content of B is less than 0.0020%. However, B can form brittle BN and Fe3(B,C), which deteriorates the mechanical properties. The premise for B to play a role is that it must be solid-solved in the steel. Adding a small amount of Ti can help to improve the hardenability effect of B by forming fine TiN, TiC or Ti(CN) precipitated particles with C and N. About 0.020% Ti can fix N below 60ppm in the steel. Therefore, in order to obtain good hardenability effect, the content of B is limited to 0.0008-0.0020% and the content of Ti is limited to 0.005%-0.020% in the present application.

[0029] Aluminum Al: Al is an important deoxidizer and nitrogen-fixing element. The mass percentage of Als in the present application is controlled at 0.015-0.025%.

[0030] The design principle of the process parameters of the production method of the high-strength and high-toughness low-yield ratio high-rise building Q690GJ steel of the present application is that:

[0031] In order to fully dissolve the micro-alloying elements and at the same time ensure a certain austenite grain size, the billet is heated to 1150-1250℃, and the soaking time of the billet is ensured to be 45-65min, which can ensure sufficient heating of the billet and inhibit excessive growth of the austenite grain;

[0032] Two-stage rolling method is adopted, the rough rolling opening temperature is 1050-1150℃, and the single pass reduction rate is ≥13%, which can effectively break the cast structure in the core and refine the austenite grain size in the core to improve the resistance to lamellar tearing; the finish rolling opening temperature is ≤960℃, and the final rolling temperature is 860-930℃, and the total reduction of the last three passes of finish rolling is ≥30%, which can further refine the grain size;

[0033] After rolling, the steel plate is cooled at a cooling rate of 4.8-13.6℃ / s to 720-780℃ after the final pass rolling at 860-930℃, and then cooled at a cooling rate of ≥18.6℃ / s to 280-420℃. In the time period from the front rolling to the cooling, a part of the austenite in the high-temperature state can be transformed into ferrite at the grain boundary. By controlling the front cooling rate, different proportions of ferrite can be obtained. When the remaining austenite is transformed into lath bainite + lath martensite in the rear rapid cooling, the yield ratio of the steel plate is controlled to be ≤0.85, and the high strength and high toughness of the steel plate are ensured.

[0034] The present application has the following beneficial effects:

[0035] 1.The high-toughness low-yield-ratio high-rise building Q690GJ steel plate and its low-cost production method, based on the C-Mn-Cr composition, without adding noble metals Mo and Ni, adding a certain amount of B element, and controlling 0.015≤Als≤0.025% and N content≤0.0045%, the alloy cost of high-strength building steel is reduced.

[0036] 2.The rolling and controlled cooling adopts segmented cooling, the proportion of the metallographic structure of lath bainite + lath martensite + ferrite is obtained by control, the yield strength of the steel plate is greater than 690MPa, the tensile strength is greater than 770MPa, the yield ratio is not higher than 0.85, at the same time, the V-type notch impact energy at-20℃ and-40℃ is greater than 180J, the elongation after fracture is greater than 22%, the steel plate has excellent comprehensive performance of low yield ratio, high strength, high elongation, high low-temperature toughness, and the performance of the steel plate is adjusted without increasing the heat treatment process, the manufacturing cost is low, and the steel plate has good application prospect for high-rise, super high-rise and large building steel structure buildings. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is the metallographic structure photo of the steel plate produced by the embodiment 4 of the present application, which is the quarter part of the thickness. DETAILED DESCRIPTION

[0038] In order to better explain the technical scheme of the present application, the technical scheme of the present application will be further described below in combination with specific embodiments, and the following embodiments are only exemplary to illustrate the technical scheme of the present application, and do not limit the present application in any form.

[0039] Table 1 below is the chemical composition value list (wt%) of the steel plate of each embodiment of the present application.

[0040] Table 2 below is the main process parameter value list of the rolling and cooling process of the steel plate of each embodiment of the present application.

[0041] Table 3 below is the main mechanical property test result list of the steel grade of each embodiment of the present application.

[0042] The low-cost production method of the high-toughness low-yield-ratio high-rise building Q690GJ steel plate of the present application comprises: smelting-continuous casting-slab heating-rolling-laminar cooling-heat straightening-finishing-heat treatment-off line; wherein:

[0043] (1) smelting: smelting the steelmaking raw materials into molten steel, the smelting includes ironmaking, molten iron pretreatment, KR desulfurization, converter smelting, LF refining and RH refining in sequence; during smelting, the content of P, S, N and other elements in the steel is treated to below the corresponding content, in order to ensure the control of inclusion generation and steel purification in the subsequent smelting process;

[0044] (2) continuous casting: the molten steel is subjected to continuous casting to obtain a slab; the chemical components and mass percentages of the chemical components of the slab are as follows: C: 0.12-0.14%, Si: 0.10-0.30%, Mn: 0.8-1.2%, P≤0.015%, S≤0.0020%, Ti: 0.005-0.020%, Nb: 0.010-0.020%, Cr≤0.8%, B: 0.0008-0.0020%, Als: 0.015-0.025%, N≤0.0045%, and the rest is Fe and inevitable impurities;

[0045] (3) slab heating: in order to fully dissolve micro-alloying elements and ensure a certain austenite grain size, the steel billet is heated to 1150-1250°C, and the steel billet soaking time is ensured to be 45-65 min, so as to ensure sufficient steel billet heating and inhibit excessive growth of austenite grains;

[0046] (4) rolling: a two-stage rolling method is adopted, the rough rolling opening temperature is 1050-1150°C, the single pass reduction rate is ≥13%, the core grain size is refined, and the resistance to lamellar tearing is improved; the finish rolling opening temperature is ≤960°C, the final rolling temperature is 860-930°C, and the total reduction of the last three passes of finish rolling is ≥30%;

[0047] (5) controlled cooling: after rolling, the steel plate is subjected to step cooling, after the final pass rolling at 860-940°C, the cooling speed is 4.8-13.6°C / s to cool to 720-780°C, and then the cooling speed is ≥18.6°C / s to cool to 280-420°C;

[0048] (6) straightening: the building steel plate is straightened to reduce the plate shape defects caused by cooling, reduce the internal stress of the steel plate, and reduce the unevenness of the steel plate;

[0049] (7) cooling bed cooling: after the steel plate is straightened, the steel plate is naturally cooled on the cooling bed and then discharged.

[0050] Table 1: Chemical composition value list of the steel plate of each embodiment of the present application (wt%)

[0051]

[0052] Table 2: Main process parameter value list of the rolling and cooling process of the steel plate of each embodiment of the present application

[0053]

[0054] Table 3: Main mechanical property result list of the steel plate of each embodiment of the present application

[0055]

[0056] As shown in Table 3, the high-rise building steel plates with thicknesses of 16-50 mm prepared in Examples 1-6 have yield strength ≥690 MPa, tensile strength ≥770 MPa, yield strength / tensile strength ratio ≤0.85, elongation after fracture ≥22%, V-notch impact energy at-20 ℃ and-40 ℃ are all greater than 180 J, and the yield strength, tensile strength and high toughness and plasticity have excellent matching.

[0057] Figure 1 Figure 1 is a microstructure photograph of the steel plate at a thickness of one quarter of the steel plate in Example 4. Figure 1 As shown in Figure 1, the microstructure of the steel plate is ferrite + lath bainite + lath martensite, and the proportion of ferrite is about 16%. In combination with the mechanical properties listed in Example 4, it can be seen that, by means of reasonable optimization of alloy element design and cooperation of rolling process control rolling and control cooling, the required microstructure is obtained, the required mechanical properties are achieved, excellent comprehensive properties of low yield strength ratio, high strength, high elongation and high low-temperature toughness are achieved, the manufacturing cost is low, and the steel plate is suitable for use in high-rise, super high-rise and large building steel structure buildings.

[0058] The above examples are merely specific examples of the present application for explaining the present application, and do not limit the present application in any form. Any non-substantial changes made by anyone according to the above content and form without departing from the protection scope of the claims of the present application should be considered to fall within the protection scope of the claims of the present application.

Claims

1. A high-strength, low-toughness, low-yield-strength ratio Q690GJ steel plate for high-rise buildings, characterized in that... The steel plate is composed of the following elements in the following mass percentages: C: 0.12–0.14%, Si: 0.10–0.30%, Mn: 0.8–1.2%, P ≤ 0.015%, S ≤ 0.0020%, Ti: 0.005–0.020%, Nb: 0.010–0.020%, Cr ≤ 0.8%, B: 0.0008–0.0020%, Als: 0.015–0.025%, N ≤ 0.0045%, with the remainder being Fe and unavoidable impurities.

2. The Q690GJ steel plate for high-strength, low-yield-strength ratio high-rise buildings according to claim 1, characterized in that: The finished thickness of the steel plate is 16-50 mm.

3. The Q690GJ steel plate for high-strength, low-yield-strength ratio high-rise buildings according to claim 1, characterized in that: The microstructure of the steel plate consists of ferrite, lath bainite, and lath martensite, with ferrite accounting for 8-18% of the total microstructure volume.

4. The Q690GJ steel plate for high-strength, low-yield-strength ratio high-rise buildings according to claim 1, characterized in that: The steel plate has a yield strength ≥690MPa, tensile strength ≥770MPa, yield-to-tensile ratio ≤0.85, V-notch impact energy ≥180J at -20℃ and -40℃, and elongation after fracture ≥22%.

5. A low-cost production method for Q690GJ steel plate for high-strength, low-yield-strength ratio high-rise buildings as described in any one of claims 1-4, comprising: The process involves smelting, continuous casting, slab heating, rolling, laminar flow cooling, hot straightening, finishing, heat treatment, and finishing. Its key feature is that after rolling, segmented accelerated cooling is employed. After the final rolling pass at 860–930℃, the steel plate is cooled to 720–780℃ at a cooling rate of 4.8–13.6℃ / s, and then further cooled to 280–420℃ at a cooling rate of ≥18.6℃ / s.

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