Preparation method of green, low-cost and high-performance steel plate Q460GJC for building structure

Abstract

The invention discloses a preparation method of a green, low-cost and high-performance steel plate Q460GJC for a building structure, the steel plate is Q460GJC, the thickness range of the steel plate is 6-60mm, the steel plate comprises the following chemical components in percentage by mass: 0.12-0.17% of C, 0.30-0.50% of Si, 1.30-1.50% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.025-0.045% of V, 0.015-0.030% of Nb, 0.015-0.045% of Als and the balance of Fe and other impurity elements, molten steel is smelted through a 120-ton converter (BOF) and subjected to LF refining, and the molten steel is subjected to hot rolling, cold rolling and hot rolling to obtain the steel plate Through continuous casting, heating, two-stage controlled rolling, controlled cooling, slow cooling and other processes, the green, low-cost and high-performance steel plate for the building structure is obtained, wherein the steel plate is high in strength, low in yield ratio, qualified in ultrasonic flaw detection and excellent in toughness and welding performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and particularly relates to a preparation method of a green low-cost high-performance building structure steel plate Q460GJC. BACKGROUND

[0002] High-rise steel is used as a main application material for modern high-rise buildings, large-span bridges and large venues and other major projects, and its demand increases year by year. With the development of large projects such as bridges, large venues, terminal buildings and the like towards high strength and light weight, the development of high-strength high-rise steel is further promoted.

[0003] However, in the current period of severe challenges faced by the steel industry, domestic major steel plants are all reducing costs and increasing benefits. Therefore, the application discloses a green low-cost high-performance building structure steel plate and a preparation method thereof by reducing alloy content and adjusting production process parameters.

[0004] Before the application, a Chinese invention patent with patent application number 202310880787.4 discloses a smelting and rolling method of high-toughness high-rise steel Q420GJC. The steel adds alloy elements such as Nb, V, Ti, Mo, Ni, Cr and Cu, adopts a kr method desulfurization process for hot metal desulfurization treatment, adopts VD furnace degassing treatment, and is produced through a rough rolling, finish rolling and stacking treatment process. The cost is relatively high due to the addition of a large number of alloy elements.

[0005] A Chinese invention patent with patent application number 202210513942.4 discloses a production method of a high-rise building steel plate Q390GJC-N. The steel plate is produced by adopting a two-stage controlled rolling process + stacking and slow cooling process, and then is subjected to normalizing heat treatment to obtain a hot-rolled high-rise building steel plate with good strength and toughness, a low yield ratio and a grain size of 11-12 levels. The method adds Nb, V and Ti micro-alloy elements, and adopts controlled rolling + stacking and slow cooling + normalizing heat treatment, so the process is relatively complex and the production cost is relatively high.

[0006] A Chinese invention patent with patent application number 201210558637.3 discloses a new type of low-cost high-rise building Q345GJC / D steel plate and a production method thereof. The steel adopts V-Cr strengthening, and the chemical components include, by weight percentage, C 0.13-0.16%, Si 0.20-0.40%, Mn 0.90-1.10%, P≤0.020%, S≤0.015%, Als 0.015-0.030%, V 0.020-0.030%, and Cr 0.10-0.20%. The steel adopts a V and Cr composite adding mode, and the production cost is high.

[0007] The Chinese patent application No. 201210584936.4 discloses a production method of a low yield ratio high-rise building steel plate. The chemical composition of the steel plate includes, in percentage by weight, C 0.15-0.18%, Si 0.25-0.45%, Mn 1.4-1.8%, P≤0.02%, S≤0.004%, Nb 0.02-0.04%. The method adopts the way of adding micro-alloy element Nb, and the specific grade is not mentioned in the patent, but according to the strength described in the patent, it can be judged that it is Q345GJ steel. Adding Nb element in Q345GJ steel is easy to cause cost increase. SUMMARY

[0008] The application provides a preparation method of green low-cost high-performance building structure steel plate Q460GJC, and aims to provide a low-cost production process.

[0009] To this end, the application adopts the following technical scheme: A green low-cost high-performance building structure steel plate, the steel plate grade of which is Q460GJC, and the thickness of the steel plate ranges from 6 to 60 mm. The chemical composition of the steel plate includes, in percentage by mass, C: 0.12-0.17%, Si: 0.30-0.50%, Mn: 1.30-1.50%, P: ≤0.020%, S: ≤0.010%, V: 0.025-0.045%, Nb: 0.015-0.030%, Als: 0.015-0.045%, and the balance is Fe and other impurity elements.

[0010] The production process includes the following steps: 1) 120-ton converter (BOF) smelting: smelting molten iron into target composition molten steel, the number of point blowing is not more than 2 times, and slagging during tapping is avoided; the smelting time is 38-45 min; the molten steel temperature after tapping is 1630-1680℃; and the target composition control range of the molten steel after tapping is: C: ≤0.11%, P: ≤0.012%, S: ≤0.040%, Si: 0.25-0.45%, Mn: 1.30-1.50%; 2) BOF-LF furnace: the time from the molten steel tapping to the molten steel entering the LF furnace is controlled to be 9-13 min, and the temperature of the molten steel entering the LF furnace is not lower than 1550℃; 3) LF furnace refining: white slag smelting is adopted after the molten steel enters the LF furnace, the white slag holding time is ≥15 min, and desulfurization is performed; the smelting time is 45-55 min; vanadium iron is added according to the entering composition and the finished product composition after slagging, 6-9 bags of covering agent are added before exiting; the temperature of the molten steel when exiting the LF furnace is controlled to be 1575-1610℃; and the target composition control range of the molten steel after exiting the LF furnace is: P: ≤0.020%, S: ≤0.010%, V: 0.025-0.045%, Nb: 0.015-0.030%; Als: 0.015-0.045%; 4) continuous casting: adopting full-range non-oxidizing protection pouring, constant speed pouring, the casting speed is 1.2-1.5 m / min, the casting blank enters the slow cooling pit for slow cooling and heat preservation for 45-50 h, the element diffusion is realized by using the residual heat to reduce segregation and improve the flaw detection qualified rate of the steel plate; 5) heating: adopting three-stage heating mode of the walking beam type heating furnace to heat the blank, the first heating temperature is 1000-1100℃, the second heating temperature is 1180-1250℃, and the soaking heating temperature is 1180-1220℃; 6) rolling: adopting two-stage temperature waiting controlled rolling through the four-high reversible mill, the first stage rolling temperature is 1100-1150℃, the temperature waiting thickness is 2.3-3 times of the finished product thickness, the second stage rolling temperature is 840-870℃, the second stage final rolling temperature is 730-760℃, and the last pass reduction rate is not less than 10%; 7) controlled cooling: adopting air mist cooling, the cooling speed is 4-10℃ / s, the final cooling temperature is 630-670℃, and then air cooling is carried out, and it is required to ensure that the temperature of the steel plate after air cooling is within the required temperature range for stacking; 8) slow cooling of the steel plate: after the steel plate is cooled, the cooling speed is reduced by stacking, the stacking temperature T satisfies: 350℃ ≤ T ≤430℃, the slow cooling time t ≥15h.

[0011] The application adopts low-cost component design, reduces the contents of Mn and V on the basis of the original molten steel composition, fully utilizes the solid solution and precipitation strengthening of the micro-alloy elements Nb and V to improve the strength of the steel plate, especially the Nb element can significantly improve the austenite recrystallization termination temperature and expand the temperature range of the austenite non-recrystallization zone, laying a foundation for the controlled rolling two-stage rolling and low-temperature large reduction to refine the grains; at the same time, the re-rolling temperature, the final rolling temperature, the temperature waiting thickness and the final cooling temperature parameters of the product in the rolling process are adjusted to realize the improvement of the product strength, the addition amount of Mn and V elements is reduced, the strength is improved and the toughness is improved by adding trace Nb element and adopting "Nb+V" micro-alloying treatment, thereby reducing the production cost of the steel plate, and finally the various performance indexes of the produced high-strength building structure steel plate are: the yield strength is 470-495 MPa, the tensile strength is 595-607 MPa, the yield strength ratio is 0.79-0.82, the elongation is 21%-24%, the 0℃ impact energy is 129-270 J, and the various mechanical properties, ultrasonic flaw detection and other indexes all meet the provisions of the national standard "GB / T19879-2023 Building Structure Steel Plate". BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The near-surface metallurgical structure of the continuous casting slab of the steel plate of the present application is F+P, and the surface chilled crystal zone is equiaxed. Figure 2 The metallurgical structure of the finished product at the thickness of 1 / 4 after rolling of the continuous casting slab of the steel plate of the present application is F+P, which is equiaxed and has a grain size of 10. DETAILED DESCRIPTION

[0013] Comparative Example: Patent No. 202410839923.X discloses a production method of Q460GJ steel with a thickness of 80-150 mm, which includes smelting, refining, continuous casting, controlled rolling and controlled cooling, normalizing and tempering. The yield strength is ≥460 MPa, the tensile strength is ≥570 MPa, the elongation after fracture is ≥18%, the yield strength ratio is ≤0.83, and the impact energy at 0℃ is ≥47 J.

[0014] Patent No. 202110862168.3 discloses a low-cost and easy-to-weld normalized Q460GJ building steel plate and a manufacturing method thereof, which is produced by normalizing + controlled cooling process.

[0015] The controlled rolling and controlled cooling process is two-stage rolling, and the total compression ratio is ≥3 times. The rough rolling temperature is 1120-1160℃, the starting temperature of finish rolling is 820-860℃, the warm blank thickness is ≥2 times the finished product thickness, the final rolling temperature is 780-820℃, and the rolling is followed by laminar cooling. The entry water temperature is 760-800℃, the final cooling temperature is 550-650℃, and then air cooling is performed to room temperature. Subsequently, normalizing heat treatment is performed. The obtained Q460GJ steel has a yield strength of ≥475 MPa, a tensile strength of ≥643 MPa, an elongation of ≥20.5%, a yield strength ratio of ≤0.76, and a low-temperature impact value at -20℃ of ≥164 J.

[0016] Patent No. 201610034082.0 discloses a low-yield ratio Q460GJ building steel plate and a production method thereof. The rolling adopts two-stage controlled rolling. The rough rolling temperature is 1160-1200℃. The deformation amount of each pass is strictly controlled during finish rolling. The finish rolling starting temperature is ≤920℃, the starting thickness is 1.3-3.0 times the finished product thickness, there are at least two passes with a reduction of >20%, the last pass reduction is >10%, and the final rolling temperature is 840-860℃. The steel plate after rolling is subjected to controlled cooling, and the final cooling temperature is 660-680℃. The obtained Q460GJ steel has a yield strength of ≥460 MPa, a yield strength ratio of less than 0.81, and a longitudinal impact energy at -40℃ of greater than 34 J.

[0017] Patent application No. 201911074675.X discloses a production method of low yield ratio high toughness Q460GJ. The BOF-LF-RH production process path is adopted for smelting, hot charging and hot feeding are adopted, the furnace is charged above 600℃, the holding temperature is 1180℃-1220℃; two-stage rolling is adopted, the rough rolling opening temperature is ≥1000℃, the rolling is carried out to more than 1.5 times the target thickness, the last three passes cumulative reduction is ≥50%, the two-stage opening temperature is 780℃-820℃; after rolling, laminar flow cooling is directly adopted, the cooling speed is 5℃ / s-10℃ / s, and after cooling to 450℃-550℃, it is put into stack for slow cooling, and after slow cooling to room temperature, it is subjected to fire cutting process. The obtained Q460GJ steel has a yield strength of 480-560MPa, a tensile strength of 600-700MPa, an elongation of more than 20%, and a yield ratio of ≤0.8.

[0018] In the above patent, the production of Q460GJ steel adopts controlled rolling + heat treatment process to improve performance; part of the rapid cooling process is directly cooled to the stacking temperature after rolling for slow cooling. The present application simplifies the production process of Q460GJ steel, appropriately reduces the finish rolling temperature range, adopts gas mist cooling method after rolling to appropriately water cooling to ensure the controlled plate shape, at the same time, reduces the stacking temperature range, ensures the safety of on-site operation, and ensures the safety of equipment control.

[0019] The specific production method includes the following steps: 1) 120-ton converter (BOF) smelting: the molten iron is smelted into target composition liquid steel, the number of point blowing is 2 times, and the slag is avoided during tapping; the smelting time is 40 min; the liquid steel temperature after leaving the converter is 1657℃; the target composition control range of the liquid steel after leaving the converter is: C: 0.11%, P: 0.012%, S: 0.040%, Si: 0.35%, Mn: 1.40%.

[0020] 2) BOF-LF furnace: the time from the liquid steel leaving the converter to entering the LF furnace is controlled to be 10 min, and the temperature of the liquid steel entering the LF furnace is controlled to be 1595℃.

[0021] 3) LF furnace refining: white slag smelting is adopted after the liquid steel enters the LF furnace, the white slag holding time is 18 min, and desulfurization is carried out; the smelting time is 50 min; after slagging, vanadium iron is added according to the composition of the inlet and the composition of the finished product, 7 bags of covering agent are added before leaving the LF furnace; the temperature of the liquid steel after leaving the LF furnace is controlled to be 1590℃; the target composition control range of the liquid steel after leaving the LF furnace is: P: 0.020%, S: 0.010%, V: 0.030%, Nb: 0.020%, Als: 0.030%.

[0022] 4) Continuous casting: full-range non-oxidizing protection pouring, constant speed pouring, casting speed 1.1 m / min, billet into slow cooling pit stacking slow cooling for 48 h, using residual heat to diffuse elements to reduce segregation and improve steel plate detection qualified rate.

[0023] 5) Heating: heating furnace first plus section temperature 1050℃, second plus section temperature 1205℃, soaking section heating temperature 1185℃.

[0024] 6) Rolling: through four-roll reversible mill, two-stage temperature control rolling is adopted, wherein the first stage rolling temperature of Q460GJC steel plate with thickness 30mm and 40mm is 1108℃ and 1109℃ respectively, the temperature of 72 (2.4 times of finished product thickness) and 100mm (2.5 times of finished product thickness) is waited respectively, the second stage rolling temperature is 850℃ and 849℃ respectively, the second stage final rolling temperature is 747℃ and 750℃ respectively, 16 and 12 passes are adopted respectively to complete rolling, and the last pass reduction rate is 10% and 13% respectively.

[0025] 7) Controlled cooling: gas mist cooling is adopted, the cooling speed of Q460GJC steel plate with thickness 30mm and 40mm is 7℃ / s and 8℃ / s respectively, the final cooling temperature is 633℃ and 660℃ respectively, and then air cooling to the required temperature of stacking is carried out under the cooling bed.

[0026] 8) Steel plate slow cooling: after the steel plate is offline, the cooling speed is reduced by stacking, the stacking temperature of Q460GJC steel plate with thickness 30mm and 40mm is 390℃ and 405℃ respectively, and the stacking time is 20h. T

[0027] Actual production case: In a certain steel plant, through the above-mentioned 120 tons converter (BOF) smelting, LF refining, continuous casting and heating, two-stage temperature control rolling, controlled cooling and stacking slow cooling process, Q460GJC continuous casting slab with chemical composition as shown in Table 1 and Q460GJC high-rise building structure steel plate with high strength, low yield ratio, excellent elongation and impact performance as shown in Table 2 are obtained.

[0028] Table 1 Chemical composition of example Q460GJC continuous casting slab (%) Slab examples Steel grade C Si Mn P S V Nb Als CEV Example 1 Q460GJC 0.144 0.364 1.3990 0.013 0.005 0.0310 0.0260 0.032 0.393 Example 2 Q460GJC 0.142 0.356 1.4000 0.012 0.003 0.0290 0.0230 0.031 0.396 Example 3 Q460GJC 0.142 0.356 1.4170 0.012 0.003 0.0307 0.0210 0.032 0.399 Table 2 Mechanical properties of example Q460GJC steel plate In summary, the present application can continue to reduce the production cost on the prior art, by reducing the content of Mn and V elements, by micro "Nb+V" treatment, and by adjusting the second stage re-rolling temperature, final rolling temperature, temperature waiting thickness, final cooling temperature and steel plate stacking parameters in the rolling process, the comprehensive performance index of the steel plate is ensured to meet the requirements.​

[0029] Taking the Q460GJC steel plate with a thickness of 30 mm as an example, the second-stage rough rolling temperature is 850 ℃, which is 20 ℃ lower than that of the conventional process, so as to ensure that the second-stage rolling is completely in the austenite unrecrystallization temperature range, the single-pass low-temperature large reduction is used to maximize the dislocation density and the number of deformation bands in the deformed austenite grains, so as to ensure the hardening state of the austenite, significantly increase the nucleation rate of the subsequent ferrite phase change, and promote the grain boundary dispersion precipitation of Nb and V carbides through deformation induction, so as to further pin the grain boundary and prevent the migration of the grain boundary at a high temperature. The above mechanisms ensure the improvement of the yield strength through fine-grain strengthening and precipitation strengthening. The second-stage finish rolling temperature is 747 ℃, which is 20 ℃ lower than that of the conventional process, so as to be beneficial to avoiding the partial recovery and recrystallization of the deformed austenite and ferrite grains after rolling, and improving the tensile strength. The warm thickness is 72 mm (2.4 times of the finished product thickness), which is about 12 mm thicker than that of the conventional process, so as to increase the rolling amount in the austenite unrecrystallization zone, be beneficial to improving the morphology of the subsequent pearlite and ferrite, avoid the appearance of continuous banded structure, and refine the grain size, so as to ensure the good matching of the strength and toughness. The cooling rate is 7 ℃ / s, and the final cooling temperature is 633 ℃, which is 30 ℃ lower than that of the conventional process. The rapid cooling after rolling and the low final cooling temperature are beneficial to increasing the content of the pearlite, improving the yield and tensile strength, and promoting the dispersion precipitation of the elements Nb and V in the grains through rapid cooling, so as to further enhance the precipitation strengthening effect. In addition, the conventional process generally does not use the stacking and slow cooling process. The steel plate is stacked at 390 ℃, which is beneficial to improving the uniformity of the steel plate structure, eliminating the internal structure stress, enhancing the toughness, effectively improving the flaw detection qualified rate and the thickness direction performance, and meeting the production requirements of the high-strength Q460GJC product through the above process parameter adjustment and the micro “Nb+V” strengthening. In terms of cost, the low Mn, micro Nb and micro V elements are used to effectively reduce the raw material cost, and have an outstanding cost performance advantage.

Claims

1. A green, low-cost, high-performance steel plate for building structures, characterized in that: The chemical composition of the steel plate, calculated by mass percentage, includes: C: 0.12~0.17%, Si: 0.30~0.50%, Mn: 1.30~1.50%, P: ≤0.020%, S: ≤0.010%, V: 0.025~0.045%, Nb: 0.015~0.030%, Als: 0.015~0.045%, and the balance is Fe and other impurity elements.

2. The green, low-cost, high-performance steel plate for building structures according to claim 1, characterized in that: The thickness of the steel plate ranges from 6 to 60 mm.

3. The green, low-cost, high-performance steel plate for building structures according to claim 1, characterized in that: The grade of the steel plate is Q460GJC.

4. A method for producing a green, low-cost, high-performance steel plate for building structures according to any one of claims 1 to 3, characterized in that: The steps include: 1) BOF smelting: Molten iron is smelted into molten steel with target composition. The number of spot blowing is no more than 2 to avoid slag during tapping. The smelting time is 38-45 minutes. The temperature of the molten steel after the BOF is 1630-1680℃. The target composition control range of the BOF molten steel is: C: ≤0.11%, P: ≤0.012%, S: ≤0.040%, Si: 0.25~0.45%, Mn: 1.30~1.50%; 2) BOF → LF furnace: The time from molten steel leaving the converter to entering the LF furnace is controlled within 8-15 minutes, and the temperature of the molten steel when entering the LF furnace is not lower than 1550℃; 3) LF furnace refining: After the molten steel enters the LF furnace, it is smelted with white slag, with a holding time of ≥15 minutes and desulfurization; the smelting time is 45-55 minutes; after slag formation, ferrovanadium is added according to the incoming composition and finished product composition, and a covering agent is added before leaving the furnace; the temperature of the molten steel is controlled at 1575-1610℃ when leaving the LF furnace; the target composition control range of the molten steel leaving the LF furnace is: P: ≤0.020%, S: ≤0.010%, V: 0.025~0.045%, Nb: 0.015~0.030%; Als: 0.015~0.045%; 4) Continuous casting: Use non-oxidation protection casting throughout the process, constant casting speed, casting speed of 1.0-1.3m / min, the billet is stacked in a slow cooling pit for slow cooling and insulation for 45-50h, using the residual heat to diffuse the elements to reduce segregation and improve the flaw detection pass rate of the steel plate; 5) Heating: The slab is heated in a three-stage walking beam heating furnace. The temperature of the first heating stage is 1000-1100°C, the temperature of the second heating stage is 1180-1250°C, and the temperature of the soaking stage is 1180-1220°C. 6) Rolling: The rolling is carried out in two stages with temperature control by a four-roll reversing mill. The first stage rolling temperature is 1100-1150°C, the temperature-controlled thickness is 2.3-3 times the thickness of the finished product, the second stage rolling temperature is 840-870°C, the second stage finishing rolling temperature is 730-760°C, and the final reduction rate is not less than 10%; 7) Controlled cooling: Use mist cooling with a cooling rate of 4-10℃ / s and a final cooling temperature of 630-670℃, followed by air cooling. It is necessary to ensure that the temperature of the steel plate after air cooling is within the temperature range required for stacking; 8) Slow cooling of steel plates: After the steel plates come off the line, they are stacked to reduce the cooling rate and the stacking temperature T Must meet: 350℃≤ T ≤430℃, stack cooling time t ≥15h.

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