Low-yield-ratio 460MPa-grade steel plate for building structure and preparation method of low-yield-ratio 460MPa-grade steel plate

Abstract

The invention provides a 460 MPa grade steel plate for a building structure. The 460 MPa grade steel plate comprises 0.13%-0.16% of C, 0.30%-0.50% of Si, 1.50%-1.70% of Mn, 0.038%-0.050% of Nb, 0.070%-0.080% of V, 0.010%-0.030% of Ti, 0.020%-0.050% of Al, CEV smaller than or equal to 0.45% and the balance Fe. The invention further provides a preparation method of the 460MPa-grade steel plate for the building structure. The thickness of the prepared steel plate ranges from 50 mm to 60 mm, the yield ratio is smaller than or equal to 0.80, the percentage elongation after fracture is larger than or equal to 18%, the core impact energy at the temperature of-40 DEG C is larger than or equal to 110 J, the Z-direction tensile section shrinkage rate is larger than or equal to 50%, the Z-direction tensile strength is larger than or equal to tensile strength * 90%, and a high-performance steel material can be provided for building of high-rise buildings, large-span steel structures, large meeting places and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of low alloy high strength steel, and in particular to a low yield ratio 460 MPa grade steel plate for building structures and a preparation method thereof. Background Art

[0002] In the building structure industry, there are strict requirements for the yield strength ratio of steel. If the yield strength ratio is too large, the material will soon reach the tensile limit after yielding, and then break, giving people very little time to react. At present, high-performance steel plates for building structures are developing in the direction of high strengthening. As the strength of the steel plate increases, the plastic toughness deteriorates, and the Z-direction performance also decreases, especially for thick steel plates above 50mm. Due to the small compression ratio, coarse grains in the core and many defects, its toughness and Z-direction performance are worse.

[0003] The Chinese patent with publication number CN101613828A discloses a low yield ratio steel plate for construction with a yield strength of 460MPa and a preparation method thereof, and the Chinese patent with publication number CN101323929 discloses a production method of a high-strength steel plate for thick high-rise building structures. The production of the above steel plates requires a strict heat treatment process, but the production cycle is relatively long and the cost is high. The Chinese patent with publication number CN114480969A provides a production method of Q460GJ, a super thick steel with high toughness and high Z-direction performance and a compression ratio of ≤4, but it adds more precious alloys such as Cr and Ni, and the performance stability of the water-cooled steel plate is poor.

[0004] Therefore, the development of a 460MPa-grade high-performance steel plate for building structures with low cost, low yield ratio, excellent Z-direction performance and high performance stability is of great significance to promoting the high-quality development of my country's steel structure industry. Summary of the invention

[0005] The technical problem solved by the present invention is to provide a method for preparing a low yield ratio 460MPa grade steel plate for building structure. The steel plate prepared by the preparation method provided in the present application has a low yield ratio, excellent Z-direction performance and high performance stability.

[0006] In view of this, the present application provides a low yield ratio 460MPa grade steel plate for building structures, which includes, by mass percentage: C: 0.13% ~ 0.16%, Si: 0.30% ~ 0.50%, Mn: 1.50% ~ 1.70%, Nb: 0.038% ~ 0.050%, V: 0.070% ~ 0.080%, Ti: 0.010% ~ 0.030%, Al: 0.020% ~ 0.050%, and CEV is controlled to be ≤ 0.45%, and the balance is Fe.

[0007] Preferably, it includes: C: 0.14% ~ 0.15%, Si: 0.32% ~ 0.45%, Mn: 1.59% ~ 1.68%, Nb: 0.041% ~ 0.048%, V: 0.074% ~ 0.078%, Ti: 0.013% ~ 0.026%, Al: 0.030% ~ 0.040%, and CEV is controlled to be ≤ 0.43%, and the balance is Fe.

[0008] The present application also provides a method for preparing the low yield ratio 460 MPa grade building structure steel plate, comprising the following steps:

[0009] S1) mixing the ingredients according to the composition ratio, casting the molten steel smelted and refined in a converter, and obtaining a continuous casting billet after cooling;

[0010] The converter smelting adopts a double slag deep dephosphorization process to make the molten steel P ≤ 0.008wt%;

[0011] The refining adopts LF+RH double refining method to make the molten steel P≤0.008wt%, S≤0.003wt%, As≤0.006wt%;

[0012] The casting is carried out under a protective atmosphere, the pulling speed is 0.95-1.05 m / min, and the superheat is ≤15°C;

[0013] S2) heating the continuous casting billet and performing rough rolling, and cooling the billet and performing finish rolling to obtain an initial steel plate;

[0014] The rough rolling is recrystallization rolling, and the reduction ratio of at least two passes is ≥16%;

[0015] The number of passes of the finishing rolling is ≤ 6, and the temperature of the last two passes is 790-810°C;

[0016] S3) slowly cooling the initial steel plate within 15 minutes, with the starting slow cooling temperature being ≥520° C. and the slow cooling time being ≥48 hours.

[0017] Preferably, in step S1), the cooling is to place the cast billet in a slow cooling pit at a temperature above 500°C for at least 48 hours to a temperature below 200°C.

[0018] Preferably, electromagnetic stirring is used during the casting process.

[0019] Preferably, in step S2), the continuous casting billet is charged into the furnace by cold charging, the heating temperature is 1170-1220° C., the time in the furnace is ≥200 min, and the soaking time is ≥50 min.

[0020] Preferably, in step S2), the thickness of the intermediate billet after rough rolling / the thickness of the initial steel plate=2.0, and the thickness fluctuation is within the range of ±3 mm.

[0021] Preferably, in step S2), the cooling temperature is 790-830°C.

[0022] Preferably, the rough rolling adopts a full longitudinal rolling mode, and the number of rough rolling passes is greater than or equal to 2 and less than or equal to 4.

[0023] Preferably, the steel plate has a thickness of 50 mm to 60 mm, a lower yield strength of 460 to 560 MPa, a tensile strength of 570 to 700 MPa, a yield strength ratio ≤ 0.80, an elongation after fracture ≥ 18%, a core impact energy at -40°C ≥ 110 J, a Z-direction tensile section shrinkage ≥ 50%, and a Z-direction tensile tensile strength ≥ tensile strength × 90%.

[0024] The present application provides a method for preparing a steel plate with a low yield ratio of 460MPa for building structures, which firstly performs batching and smelting according to the composition ratio, then casts the molten steel smelted and refined in a converter, and obtains a continuous casting billet after cooling, in which the relevant processes and parameters of converter smelting and refining are controlled; then the continuous casting billet is heated and rough rolled, and then fine rolled is performed after cooling to obtain an initial steel plate, in which the rough rolling and fine rolling are strictly controlled, and finally the obtained initial steel plate is slowly cooled; in the above-mentioned preparation process, the present application obtains a mixed structure of fine and uniformly distributed ferrite + pearlite through high-clean molten steel smelting technology, high-homogeneity ingot production technology and controlled rolling process control, so that the strength and toughness of the steel and the lamellar tearing resistance are excellent, the ratio of soft phase to hard phase in the structure is regulated, and a steel plate with a yield ratio of ≤0.80 is obtained, thereby improving the service safety of the steel plate; the steel plate after rolling is slowly cooled, which improves the stability of the steel plate performance and realizes the narrow range control of the steel plate performance.

[0025] At the same time, the low yield ratio 460MPa grade building structure steel plate provided in the present application adopts Nb+V+Ti micro-alloying composition design without adding precious alloys, thereby effectively reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a metallographic structure photograph of the steel plate at the 1 / 2 thickness position prepared in Example 1 of the present invention;

[0027] Figure 2 This is a metallographic structure photograph of the steel plate at 1 / 4 thickness prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0029] In view of the requirements of the prior art for 460MPa grade steel plates with low yield ratio, excellent Z-direction performance and stable performance, the present application provides a low yield ratio 460MPa grade steel plate for building structures and a preparation method thereof, which controls the alloy composition and preparation method of the steel plate, and the prepared steel plate is delivered in a controlled rolled state, eliminating the traditional post-rolling water cooling and heat treatment process, meeting the requirements of steel plate performance stability, low yield ratio, excellent Z-direction performance and stable performance, and shortens the production process, with excellent adaptability to industrial production. Specifically, an embodiment of the present invention discloses a low yield ratio 460MPa grade steel plate for building structures, which includes, by mass percentage: C: 0.13% to 0.16%, Si: 0.30% to 0.50%, Mn: 1.50% to 1.70%, Nb: 0.038% to 0.050%, V: 0.070% to 0.080%, Ti: 0.010% to 0.030%, Al: 0.020% to 0.050%, and CEV is controlled to be ≤0.45%, with the remainder being Fe.

[0030] In the low yield ratio 460MPa grade building structure steel plate provided in the present application, CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15, which represents the carbon equivalent, which is beneficial to ensure the strength and welding performance of the steel plate. If the CEV is too low, the strength cannot be guaranteed, and if the CEV is too high, the welding performance of the steel plate will deteriorate.

[0031] Specifically, the steel plate includes: C: 0.14% to 0.15%, Si: 0.32% to 0.45%, Mn: 1.59% to 1.68%, Nb: 0.041% to 0.048%, V: 0.074% to 0.078%, Ti: 0.013% to 0.026%, Al: 0.030% to 0.040%, and CEV is controlled to be ≤0.43%, and the balance is Fe; more specifically, the steel plate includes: C: 0.145%, Si: 0.34%, Mn: 1.59%, Nb: 0.041%, V: 0.074%, Ti: 0.013%, Al: 0.030%, and CEV is controlled to be 0.43%, and the balance is Fe.

[0032] The present application also provides a method for preparing a low yield ratio 460 MPa grade steel plate for building structures, comprising the following steps:

[0033] S1) mixing the ingredients according to the composition ratio, casting the molten steel smelted and refined in a converter, and obtaining a continuous casting billet after cooling;

[0034] The converter smelting adopts a double slag deep dephosphorization process to make the molten steel P ≤ 0.008wt%;

[0035] The refining adopts LF+RH double refining method to make the molten steel P≤0.008wt%, S≤0.003wt%, As≤0.006wt%;

[0036] The casting is carried out under a protective atmosphere, the pulling speed is 0.95-1.05 m / min, and the superheat is ≤15°C;

[0037] S2) heating the continuous casting billet and performing rough rolling, and cooling the billet and performing finish rolling to obtain an initial steel plate;

[0038] The rough rolling is recrystallization rolling, and the reduction ratio of at least two passes is ≥16%;

[0039] The number of passes of the finishing rolling is ≤ 6, and the temperature of the last two passes is 790-810°C;

[0040] S3) slowly cooling the initial steel plate after 15 minutes, with the starting slow cooling temperature being ≥520°C and the slow cooling time being ≥48h.

[0041] In the preparation method provided in the present application, firstly, the ingredients are prepared according to the proportion of the steel plate, and then the molten steel after converter smelting and refining is cast, and the continuous casting billet is obtained after cooling; the ingredients are added by raw materials familiar to those skilled in the art, and the converter smelting specifically adopts the double slag deep dephosphorization process, and the final slag basicity is controlled at 3.0-4.0, so that the end point P of the molten steel is ≤0.008%, and aluminum manganese iron is used for deoxidation, silicon manganese, metallic manganese, ferroniobium, and ferrovanadium are added when the steel is 20-40% tapped for alloying, and the above raw materials are added when the molten steel is 60-80%, and synthetic slag and pre-melted slag are added. The refining adopts LF+RH double refining method to reduce the N, O gas content and inclusion content, so that the molten steel P≤0.008%, S≤0.003%, As≤0.006%, reduce the content of impurity elements, and ensure the strength and toughness of the steel plate and the Z-direction performance. Among them, the LF refining is carried out with argon blowing and stirring throughout the whole process, and aluminum particles, calcium carbide and silicon carbide are used to adjust the slag. The top slag before leaving the station is white slag, and the retention time is ≥10min to reduce the S content; aluminum wire is used to adjust the Al composition to control the oxygen content of molten steel; titanium element is very easy to combine with oxygen, and titanium wire is used to adjust the titanium content to 0.010%~0.030%. Trace titanium can fix nitrogen in steel and promote the solid solution of niobium element to refine grains and improve strength and toughness; specifically, the titanium content in the titanium wire is 0.015~0.0 28%, more specifically, the titanium content in the titanium wire is 0.021-0.026%; RH refining ensures that the vacuum degree is ≤30Pa and the pure degassing time is ≥5min. After the RH refining is completed, 100-120m of nano high calcium wire is fed into each furnace to promote the refinement and spheroidization of inclusions through calcium treatment; specifically, the vacuum degree is 10-25Pa, the pure degassing time is 6-15min, more specifically, the vacuum degree is 13-20Pa, and the pure degassing time is 8-12min. The casting is protected throughout the entire process; the pulling speed is 0.95-1.05 m / min to ensure the stability of the casting process and prevent slag rolling. Specifically, the pulling speed is 0.98-1.0 m / min; the pouring temperature is lowered, and the superheat is controlled within 15°C, specifically the superheat is 8-12°C, to reduce the degree of segregation of the ingot and ensure the uniformity of the internal quality; electromagnetic stirring is preferably used during the casting process to disrupt the growth direction of columnar crystals and diffuse the equiaxed crystal area. The cooling is to put the refined ingot into a slow cooling pit at above 500°C for at least 48 hours to below 200°C, which can prevent the occurrence of defects such as cracks inside the continuous casting ingot; specifically, the ingot is slowly cooled at 550-600°C, and the slow cooling time is 56-60 hours.

[0042] The present application then heats the obtained continuous casting billet and performs rough rolling, and performs finish rolling after cooling to obtain an initial steel plate; the continuous casting billet is preferably charged into the furnace by cold charging, specifically heated in the furnace below 200°C; the heating temperature is 1170-1220°C, the furnace time is ≥200min, wherein the soaking time is ≥50min, specifically, the heating temperature is 1190-1200°C, the furnace time is 235-275°C, wherein the soaking time is 50-70min; to ensure that the continuous casting billet is heated evenly and the alloy elements therein are fully dissolved. The rough rolling adopts recrystallization rolling to reduce or even eliminate the widening pass, and the pass reduction rate of at least 2 passes (single pass thickness reduction / entry thickness) is ≥16% to improve the strength and toughness and Z-direction performance of the steel plate; specifically, the rough rolling adopts a full longitudinal rolling mode and 4 passes of rough rolling, and the reduction rate of the 3rd and 4th passes is ≥16%; more specifically, the reduction rate of the 3rd pass is 17.1-17.5%, and the reduction rate of the 4th pass is 17.8-18.1%. The intermediate billet thickness after rough rolling / initial steel plate thickness = 2.0, and the thickness fluctuation is within the range of ±3mm to ensure a reasonable distribution of rough rolling and finishing rolling reduction. The cooling temperature is 790-830°C, specifically, the cooling temperature is 811-820°C. The number of finishing passes is ≤6, specifically, the number of finishing passes is 5-6; the temperature of the last two finishing passes is 790-810°C, specifically, the temperature of the last two finishing passes is 800-805°C, so as to control the microstructure of the steel plate and ensure the strength, toughness and Z-direction performance of the steel plate. Air cooling after finishing rolling.

[0043] In this application, the initial steel plate after fine rolling is finally put into a slow cooling pit for slow cooling within 15 minutes, and the starting slow cooling temperature is ≥520°C, and the slow cooling time is ≥48h. Specifically, the starting slow cooling temperature is 550-560°C, and the slow cooling time is 60h-72h. After research, the applicant concluded that slow cooling of steel plates is the main way to reduce the hydrogen content in the initial steel plates; the residual hydrogen in the steel plates is easy to cause the formation of hydrogen-induced cracks, affecting the mechanical properties, Z-direction properties and flaw detection properties of the steel plates; the slow cooling temperature and time have a great influence on the slow cooling process, thereby affecting the performance of the steel plates; if the starting temperature of the slow cooling is too low, the hydrogen diffusion kinetic energy will be low and cannot overflow the surface of the steel plate, affecting the slow cooling effect; since the thickness of the steel plate of the present invention is 50-60mm, the hydrogen diffusion path of thick-gauge steel plates is far, and there must be enough slow cooling time to ensure the diffusion of hydrogen.

[0044] The present invention provides a low yield ratio 460MPa grade steel plate for building structure and a preparation method thereof. The steel plate adopts Nb+V+Ti microalloying composition design, does not need to add a large amount of precious alloys, effectively reduces production costs, and combines with a controlled rolling production process to avoid a traditional heat treatment process, shortening the production process; in the preparation process, through high-clean molten steel smelting technology, high-homogeneity ingot production technology and controlled rolling process control, a fine and uniformly distributed ferrite+pearlite mixed structure is obtained, so that the strength and toughness of the steel plate and the resistance to lamellar tearing are excellent, and at the same time, the ratio of soft phase and hard phase in the structure is scientifically regulated, and the yield ratio of the obtained steel plate is ≤0.80, which improves the service safety of the steel plate; further, the steel plate does not need water cooling after rolling, which improves the stability of the steel plate performance, and can achieve narrow range control of performance, such as yield strength Cpk>1.33, and excellent process capability. The experimental results show that the steel plate prepared in the present application has a thickness of 50mm to 60mm, a slab rolling compression ratio of ≤5 (the compression ratio is the ratio of the thickness of the continuous casting slab to the thickness of the steel plate. The thickness of the continuous casting slab of the present invention is 250mm, the thickness of the steel plate is 50-60mm, and the compression ratio is ≤5), a lower yield strength of 460 to 560MPa, a tensile strength of 570 to 700MPa, a yield strength ratio of ≤0.80, an elongation after fracture of ≥18%, a core impact energy at -40°C of ≥110J, a tensile section shrinkage in the Z direction of ≥50%, and a tensile tensile strength in the Z direction of ≥tensile strength×90%.

[0045] In order to further understand the present invention, the preparation method of the low yield ratio 460MPa grade building structure steel plate provided by the present invention is described in detail below in combination with the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0046] Example 1: 60mm thick Q460GJ steel

[0047] 1) Billet production

[0048] ① During the converter smelting process, the segregation, inclusions and gas content in the steel are strictly controlled to ensure the purity of the steel. Scrap steel is used, and no other scrap steel or slag steel shall be used. The amount of scrap steel added shall not exceed 8% of the total furnace load; double slag deep dephosphorization process is used for smelting, and the basicity of the final slag is controlled at R=3.3, so that early slag is achieved in the early stage, the slag is well deslaged during the process, and the final slag is fully dephosphorized, ensuring that the final phosphorus is ≤0.008%; aluminum-manganese iron is used for deoxidation, and aluminum-manganese iron is 2.5kg / t; low-carbon and low-phosphorus silicon-manganese, metallic manganese, ferroniobium and ferrovanadium are used for alloying; alloys are added during steelmaking, and the addition begins evenly when the molten steel reaches about 30%, and is completed when the molten steel reaches about 70%. The alloy is added to the impact zone of the steel flow, and 600kg of synthetic slag and 200kg of pre-melted slag are added;

[0049] ②LF+RH refining: LF refining is carried out with argon blowing and stirring at the bottom. Aluminum particles, calcium carbide and silicon carbide are used to adjust the slag. The top slag before leaving the station is white slag, which is kept for 13 minutes to reduce the S content. Aluminum wire is used to adjust the Al composition to control the oxygen content of molten steel. Titanium is very easy to combine with oxygen. In this stage, titanium wire is needed to adjust the titanium content to 0.021%. Trace titanium can fix nitrogen in steel and promote the solid solution of niobium to refine grains and improve strength and toughness. RH refining ensures a vacuum degree of 13Pa and a pure degassing time of 8 minutes. After RH refining, 120m of nano high calcium wire is fed to promote the refinement and spheroidization of inclusions through calcium treatment.

[0050] ③ Slab casting molten steel P≤0.008%, S≤0.003%, As≤0.006%; full protection casting is adopted, the crystallizer uses peritectic steel protection slag, and the tundish is covered with carbonized rice husk to prevent the molten steel from oxidation and remove the floating inclusions in the molten steel. The pulling speed is 1.0m / min, the superheat is controlled at 12℃ during casting, and electromagnetic stirring is used to disrupt the growth direction of columnar crystals and expand the equiaxed crystal area;

[0051] The continuous casting slab obtained by casting has a thickness of 250 mm, and the slab is slowly cooled in a slow cooling pit at 550°C for 56 hours;

[0052] 2) Controlled rolling

[0053] The ingot is heated in the furnace at a temperature below 200°C, the tapping temperature is 1200°C, the furnace time is 275 minutes, the soaking time is 50 minutes, and the ingot is descaled with high-pressure water after it is taken out of the furnace;

[0054] The rough rolling adopts the full longitudinal rolling mode without widening, with a total of 4 passes. The reduction rates of the 3rd and 4th passes are 17.1% and 18.2% respectively. The thickness of the intermediate billet after the rough rolling is 121mm. The intermediate billet is cooled by the intermediate billet cooling system. When it is cooled to 817℃, the finishing rolling stage begins. The finishing rolling is performed in 6 passes. The rolling temperatures of the last 2 passes of the finishing rolling are 805℃ and 803℃ respectively, thus obtaining a 60mm thick steel plate. Air cooling is performed after rolling.

[0055] 3) Slow cooling after rolling

[0056] The steel plate was put into the slow cooling pit for slow cooling within 15 minutes of rolling. The starting slow cooling temperature was 560°C and the slow cooling time was 72 hours to obtain 60mm thick Q460GJ steel.

[0057] Figure 1 This is a metallographic structure photograph of the steel plate prepared in this embodiment at the 1 / 2 thickness position. Figure 2 This is a metallographic structure photograph of the steel plate prepared in this embodiment at the 1 / 4 thickness position. It can be seen from the figure that the structure of the steel plate is ferrite + pearlite structure, and the grain size of the core structure is above level 8.

[0058] Example 2: 50mm thick Q460GJ steel

[0059] 1) Billet production

[0060] This embodiment and embodiment 1 are the same furnace, and the production process and chemical composition of the casting are consistent with those of embodiment 1;

[0061] The continuous casting slab obtained by casting has a thickness of 250 mm, and the slab is slowly cooled in a slow cooling pit at 550°C for 56 hours;

[0062] 2) Controlled rolling

[0063] The billet is charged into the furnace cold for heating, the tapping temperature is 1190℃, the time in the furnace is 235min, the soaking time is 50min, and the billet is descaled with high-pressure water after it is discharged from the furnace;

[0064] The rough rolling adopts the full longitudinal rolling mode without widening, with a total of 4 passes. The reduction rates of the 3rd and 4th passes are 17.5% and 17.8% respectively. The thickness of the intermediate billet after the rough rolling is 100mm; the finishing rolling stage begins after cooling to 811℃, with 6 passes of finishing rolling. The rolling temperatures of the last 2 passes of finishing rolling are 805℃ and 800℃ respectively, thus obtaining a 50mm thick steel plate; air cooling after rolling;

[0065] 3) Slow cooling after rolling

[0066] The steel plate was put into the slow cooling pit for slow cooling within 15 minutes of rolling. The starting slow cooling temperature was 550°C and the slow cooling time was 72 hours to obtain 50mm thick Q460GJ steel.

[0067] Comparative Example 1: 60mm thick Q460GJ steel

[0068] 1) Billet production

[0069] This comparative example is the same heat as Example 1, and the casting process and chemical composition are consistent with Example 1;

[0070] The continuous casting slab obtained by casting has a thickness of 250 mm, and the slab is slowly cooled in a slow cooling pit at 550°C for 56 hours;

[0071] 2) Controlled rolling

[0072] The billet is charged into the furnace cold for heating, the tapping temperature is 1200℃, the time in the furnace is 275min, the soaking time is 50min, and the billet is descaled with high-pressure water after it is discharged from the furnace;

[0073] The rough rolling passes are not strictly controlled, with a total of 6 passes, and the maximum pass reduction rate is 14.8%. The thickness of the intermediate billet after the rough rolling is 120mm; the finishing stage begins when it is cooled to 813℃, and the finishing rolling is 6 passes. The rolling temperatures of the last 2 passes of the finishing rolling are 801℃ and 798℃ respectively, thus obtaining a 60mm thick steel plate; air cooling after rolling;

[0074] 3) Slow cooling after rolling

[0075] The steel plate was put into the slow cooling pit for slow cooling within 15 minutes of rolling. The starting slow cooling temperature was 550°C and the slow cooling time was 72 hours to obtain 60mm thick Q460GJ steel.

[0076] Comparative Example 2: 60mm thick Q460GJ steel

[0077] 1) Billet production

[0078] This comparative example is the same heat as Example 1, and the casting process and chemical composition are consistent with Example 1;

[0079] The continuous casting slab obtained by casting has a thickness of 250 mm, and the slab is slowly cooled in a slow cooling pit at 550°C for 56 hours;

[0080] 2) Controlled rolling

[0081] The billet is charged into the furnace cold for heating, the tapping temperature is 1200℃, the time in the furnace is 275min, the soaking time is 50min, and the billet is descaled with high-pressure water after it is discharged from the furnace;

[0082] The rough rolling adopts the full longitudinal rolling mode without widening, with a total of 4 passes. The reduction rates of the 3rd and 4th passes are 17.5% and 18.1% respectively. The thickness of the intermediate billet after the rough rolling is 122mm; the finishing rolling stage begins after cooling to 814℃, with 6 passes of finishing rolling. The rolling temperatures of the last 2 passes of finishing rolling are 800℃ and 795℃ respectively, thus obtaining a 60mm thick steel plate; air cooling after rolling;

[0083] 3) Slow cooling after rolling

[0084] The steel plate starts to be slowly cooled at 450°C and the slow cooling time is 72h to obtain 60mm thick Q460GJ steel.

[0085] Table 1 is a table of smelting composition data of continuous casting billets of the embodiments and comparative examples, Table 2 is a table of tensile properties of steel plates prepared in the embodiments and comparative examples, Table 3 is a table of impact properties of steel plates prepared in the embodiments and comparative examples, Table 4 is a table of Z-direction properties of steel plates of the embodiments and comparative examples, and the test method adopts the national general method; specifically as follows:

[0086] Table 1: Composition control data of continuous casting slabs of embodiments and comparative examples Unit: wt%

[0087] Furnace No. C Si Mn P S Nb Ti V Als CEV H224-07142 0.145 0.34 1.59 0.008 0.003 0.041 0.013 0.074 0.030 0.43

[0088] Table 2 Tensile properties of steel plates prepared in Examples and Comparative Examples

[0089]

[0090] Table 3 Impact performance data of steel plates prepared in Examples and Comparative Examples

[0091]

[0092] Table 4 Z-axis performance data of steel plates prepared in the embodiments and comparative examples

[0093]

[0094] It can be seen from Table 2, Table 3 and Table 4 that, in Example 1 and Example 2, the lower yield strength is 460-560MPa, the tensile strength is 570-700MPa, the yield strength ratio is ≤0.80, the elongation after fracture is ≥18%, the core impact energy at -40°C is ≥110J, the Z-direction tensile section shrinkage is ≥50%, and the Z-direction tensile tensile strength is ≥tensile strength×90%; in Comparative Example 1, the rough rolling passes are not controlled, the rolling penetration effect cannot be fully exerted, the austenite grain crushing effect is poor, and the impact performance and Z-direction performance are significantly reduced; in Comparative Example 2, the slow cooling temperature is low at the beginning, resulting in low hydrogen diffusion kinetic energy and inability to overflow the steel plate surface, which easily generates stress concentration and becomes a cracking source, reduces the impact toughness, and the Z-direction section shrinkage and Z-direction tensile strength are also significantly reduced.

[0095] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0096] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A low yield strength ratio 460MPa grade steel plate for building structure, characterized in that: Calculated by mass percentage, it includes: C: 0.13%-0.16%, Si: 0.30%-0.50%, Mn: 1.50%-1.70%, Nb: 0.038%-0.050%, V: 0.070%-0.080%, Ti: 0.010%-0.030%, Al: 0.020%-0.050%, and CEV is controlled to be ≤0.45%, and the balance is Fe.

2. The steel plate for building structure according to claim 1, characterized in that: Including: C: 0.14% ~ 0.15%, Si: 0.32% ~ 0.45%, Mn: 1.59% ~ 1.68%, Nb: 0.041% ~ 0.048%, V: 0.074% ~ 0.078%, Ti: 0.013% ~ 0.026%, Al: 0.030% ~ 0.040%, and CEV is controlled to be ≤ 0.43%, and the balance is Fe.

3. The method for preparing the low yield ratio 460 MPa grade building structure steel plate according to claim 1 comprises the following steps: S1) mixing the ingredients according to the composition ratio, casting the molten steel smelted and refined in a converter, and obtaining a continuous casting billet after cooling; The converter smelting adopts a double slag deep dephosphorization process to make the molten steel P ≤ 0.008wt%; The refining adopts LF+RH double refining method to make the molten steel P≤0.008wt%, S≤0.003wt%, As≤0.006wt%; The casting is carried out under a protective atmosphere, the pulling speed is 0.95-1.05 m / min, and the superheat is ≤15°C; S2) heating the continuous casting billet and performing rough rolling, and cooling the billet and performing finish rolling to obtain an initial steel plate; The rough rolling is recrystallization rolling, and the reduction ratio of at least two passes is ≥16%; The number of passes of the finishing rolling is ≤ 6, and the temperature of the last two passes is 790-810°C; S3) slowly cooling the initial steel plate within 15 minutes, with the starting slow cooling temperature being ≥520° C. and the slow cooling time being ≥48 hours.

4. The preparation method according to claim 3, characterized in that: In step S1), the cooling is to place the cast billet in a slow cooling pit at a temperature above 500°C for at least 48 hours to below 200°C.

5. The preparation method according to claim 3, characterized in that: Electromagnetic stirring is used during the casting process.

6. The preparation method according to claim 3, characterized in that: In step S2), the continuous casting billet is charged into the furnace by cold charging, the heating temperature is 1170-1220°C, the time in the furnace is ≥200min, and the soaking time is ≥50min.

7. The preparation method according to claim 3, characterized in that: In step S2), the thickness of the intermediate billet after rough rolling / the thickness of the initial steel plate=2.0, and the thickness fluctuation is within the range of ±3 mm.

8. The preparation method according to claim 3, characterized in that: In step S2), the cooling temperature is 790-830°C.

9. The preparation method according to claim 3, characterized in that: The rough rolling adopts a full longitudinal rolling mode, and the rough rolling passes are greater than or equal to 2 passes and less than or equal to 4 passes.

10. The preparation method according to any one of claims 3 to 9, characterized in that: The steel plate has a thickness of 50 mm to 60 mm, a lower yield strength of 460 to 560 MPa, a tensile strength of 570 to 700 MPa, a yield strength ratio ≤ 0.80, an elongation after fracture ≥ 18%, a core impact energy at -40°C ≥ 110 J, a Z-direction tensile section shrinkage ≥ 50%, and a Z-direction tensile tensile strength ≥ tensile strength × 90%.

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