Super large size high strength steel bar and its production method

Abstract

The application provides a super-large high-strength steel bar and a production method thereof. In the application, the super-large steel bar is designed in the following components: C, Si, Mn, Ni, Nb, V, Zr and N. The element component design is 0.5≤([Al]+4[Nb]) / [Si]≤1.1 and 0.86%≤([Zr]+[V]) / ([Si] / 10+[N])≤1.31%. The influence of each element on fine-grain strengthening and precipitation strengthening is comprehensively considered, the quantitative correlation of components, processes and structures is established, and a comprehensive steelmaking process is matched. The high-strength steel bar with a diameter of 36-50 mm is obtained by rolling under high-temperature rolling conditions. The steel bar can be produced by using common steelmaking equipment, without the need of modifying the existing production line, and the cost can be effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of alloy materials, and more specifically to an ultra-large specification high-strength steel bar and its production method. Background Technology

[0002] High-strength seismic-resistant steel bars combine high strength grade with high seismic performance (high strength-to-yield ratio and high total elongation at maximum force). The high-strength design of these bars can reduce reinforcement ratios, lower steel consumption, reduce resource and energy consumption, and lessen environmental burden. Seismic-resistant design of these bars can improve the earthquake resistance of buildings, reduce casualties and property damage caused by earthquakes, and help improve the reliability and safety level of key projects. However, the larger the steel bar specifications, the more difficult it is to increase its strength grade; the higher the strength of the steel bar, the more difficult it is to meet its plasticity and seismic resistance requirements. Summary of the Invention

[0003] The purpose of this invention is to provide an ultra-large specification high-strength steel bar and its production method.

[0004] This invention provides a method for producing ultra-large-sized high-strength steel bars. The chemical composition of the steel bars, by mass percentage, includes: C: 0.25~0.30%, Si: 0.3~0.45%, Mn: 1.5~1.80%, Ni: 0.1~0.2%, Zr: 0.01~0.03%, Nb: 0.025~0.040%, Al: 0.1~0.3%, V: 0.15~0.25%, N: 0.03~0.040%, with the balance being Fe and unavoidable impurities.

[0005] The chemical composition of the steel reinforcement also satisfies: 0.5≤([Al]+4[Nb]) / [Si]≤1.1, ([Zr]+[V]) / ([Si] / 10+[N]) is any one of the following values: 2.3, 2.5, 2.9, 3, 3.1, 3.2, 3.5, and 4. Wherein, the element symbol represents the mass percentage of the corresponding element; The production method includes the following steps: According to the above chemical composition ratio, the steel is smelted in a converter and then refined by LF to obtain molten steel. The molten steel is cast into a continuously cast billet through a continuous casting process; The continuously cast billet is heated and rolled to obtain steel bars. In the rolling process, the initial rolling temperature is controlled at 1130~1150℃ and the finishing rolling temperature is controlled at 1090~1130℃. The continuously cast billet is rolled into steel bars with a diameter range of 36~50mm. After finishing rolling, a feedback-type three-stage graded cooling is adopted, and the final rolling speed of the steel bars is controlled at 3.5~8.1m / s. After cooling, the microstructure of the steel bar consists of pearlite and ferrite, with the pearlite clusters ranging from 8 to 11 μm in size and accounting for 53 to 60% of the total. The ferrite clusters range from 4.3 to 4.9 μm in size. After cooling, the hardness of the steel reinforcement matrix at the center ranges from 307 to 318 HV5kg, and the hardness of the steel reinforcement matrix near the surface ranges from 312 to 325 HV5kg; the steel reinforcement has a yield strength ≥630MPa, a strength-to-yield ratio ≥1.25, an elongation after fracture A ≥16%, a total elongation at maximum force ≥9.0%, and no surface cracks after cold bending and reverse bending.

[0006] As a further improvement of the present invention, the converter smelting process specifically includes: The molten iron is transferred into a converter for oxygen blowing smelting. The charge is controlled at 108-115t, of which the amount of molten iron is controlled at ≥45t. At the end of smelting, the C content is controlled at ≤0.10% and the P content at ≤0.02%. The tapping temperature of the converter is controlled at 1620-1650℃. Silicon manganese alloy and lime are added during the process.

[0007] As a further improvement of the present invention, the LF refining process specifically includes: Transfer the molten steel from the converter to the LF station, and alternately cycle the bottom blowing argon and nitrogen for 5 minutes each. The bottom blowing flow rate of argon is controlled at 190~250L / min, and the bottom blowing flow rate of nitrogen is controlled at 110~160L / min. As a further improvement of the present invention, the LF refining process further includes: Add 5.5~6.7kg of lime and 1.6~2.4kg of fluorite to each ton of molten steel to adjust the white slag. After refining the white slag for 4 minutes, add niobium ferroalloy, vanadium ferroalloy, and silicon zirconium ferroalloy. Control the tapping temperature to 1555~1575℃.

[0008] As a further improvement of the present invention, the continuous casting process specifically includes: During continuous casting, the tundish temperature is controlled within the range of 1510~1550℃. Nitrogen is blown through the ladle with a long nozzle during the continuous casting process, and the flow rate is controlled within the range of 80~110L / min. An alkaline covering agent is used in the tundish, and the thickness of the liquid slag layer is controlled within the range of 8~10mm. The continuous casting yields a 150×150mm billet, with the casting speed controlled at 3.0~3.6m / min and the secondary cooling water volume controlled at 2.1~2.4L / kg.

[0009] As a further improvement of the present invention, the heating of the continuously cast billet specifically includes: The heating temperature range is controlled at 1240~1280℃, and the holding time range is controlled at 50~60min.

[0010] As a further improvement of the present invention, the feedback-type three-stage graded cooling specifically includes: The first stage involves aerosol cooling, with the terminal temperature controlled within the range of 1030~1070℃ and a cooling channel length of 8 meters; the second stage involves water spray cooling, with the terminal temperature controlled within the range of 960~1000℃ and a cooling channel length of 6 meters; the third stage involves aerosol cooling, with the terminal temperature controlled within the range of 910~950℃ and a cooling channel length of 4 meters.

[0011] As a further improvement of the present invention, the cooling process further includes: The temperature of the upper cooling bed is controlled at 890~930℃. After the upper cooling bed is placed, it is covered by an interval insulation cover with a spacing of 1.5 meters. The moving speed of the cooling bed is 2.0~2.5m / min.

[0012] The present invention also provides an ultra-large specification high-strength steel bar, which is manufactured by the above-mentioned ultra-large specification high-strength steel bar production method.

[0013] The present invention also provides an ultra-large specification high-strength steel bar, wherein the chemical composition of the steel bar, by mass percentage, comprises: C: 0.25~0.30%, Si: 0.3~0.45%, Mn: 1.5~1.80%, Ni: 0.1~0.2%, Zr: 0.01~0.03%, Nb: 0.025~0.040%, Al: 0.1~0.3%, V: 0.15~0.25%, N: 0.03~0.040%, with the balance being Fe and unavoidable impurities; The chemical composition of the steel reinforcement also satisfies: 0.5≤([Al]+4[Nb]) / [Si]≤1.1, ([Zr]+[V]) / ([Si] / 10+[N]) is any one of the following values: 2.3, 2.5, 2.9, 3, 3.1, 3.2, 3.5, and 4. Wherein, the element symbol represents the mass percentage of the corresponding element; The diameter of the reinforcing bar is in the range of 36~50mm; The hardness of the steel reinforcement matrix at the center ranges from 307 to 318 HV5kg, and the hardness of the steel reinforcement matrix near the surface ranges from 312 to 325 HV5kg; the steel reinforcement has a yield strength ≥630MPa, a strength-to-yield ratio ≥1.25, an elongation after fracture A ≥16%, a maximum force total elongation ≥9.0%, and no surface cracks after cold bending and reverse bending.

[0014] As a further improvement of the present invention, the microstructure of the steel bar is pearlite and ferrite, wherein the pearlite cluster size ranges from 8 to 11 μm, the pearlite content is 53 to 60%, and the ferrite size ranges from 4.3 to 4.9 μm.

[0015] The beneficial effects of this invention are as follows: In terms of composition design, the ultra-large specification steel bars of this invention are alloyed with C, Si, Mn, Ni, Nb, V, Zr, and N, and the element composition design adopts 0.5≤([Al]+4[Nb]) / [Si]≤1.1 and 0.86%≤([Zr]+[V]) / ([Si] / 10+[N])≤1.31%. Taking into account the influence of each element on fine grain strengthening and precipitation strengthening, a quantitative correlation between composition, process, and microstructure is established. With the support of a comprehensive steelmaking process, high-strength steel bars with a diameter of 36~50mm can be rolled under high-temperature rolling conditions. Moreover, they can be produced using ordinary steelmaking equipment without the need to modify existing production lines, which can effectively reduce costs. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the steps in the method for producing ultra-large-sized high-strength steel bars according to one embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0018] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0019] This embodiment provides an ultra-large specification high-strength steel bar and its production method. In terms of composition design, the ultra-large specification steel bar in this embodiment adopts C, Si, Mn, Ni, Nb, V, Zr, and N alloying, and adopts an element composition design of 0.5≤([Al]+4[Nb]) / [Si]≤1.1 and 0.86%≤([Zr]+[V]) / ([Si] / 10+[N])≤1.31%. Taking into account the influence of each element on fine grain strengthening and precipitation strengthening, a quantitative correlation between composition, process, and microstructure is established. With the support of a comprehensive steelmaking process, high-strength steel bars with a diameter of 36~50mm are rolled under high temperature rolling conditions. Moreover, it can be produced using ordinary steelmaking equipment without the need to modify existing production lines, which can effectively reduce costs.

[0020] In this embodiment, the chemical composition of the steel reinforcement, by mass percentage, includes: C: 0.25~0.30%, Si: 0.3~0.45%, Mn: 1.5~1.80%, Ni: 0.1~0.2%, Zr: 0.01~0.03%, Nb: 0.025~0.040%, Al: 0.1~0.3%, V: 0.15~0.25%, N: 0.03~0.040%, with the balance being Fe and unavoidable impurities.

[0021] The chemical composition of the reinforcing steel also meets the following requirements: 0.5≤([Al]+4[Nb]) / [Si]≤1.1, 0.86%≤([Zr]+[V]) / ([Si] / 10+[N])≤1.31%, Wherein, the element symbol represents the mass percentage of the corresponding element; The design of each component is explained below: C: As one of the important alloying elements in steel, carbon can be dissolved in steel, thereby effectively improving its yield strength and tensile strength, directly affecting the strength of the reinforcing steel. Furthermore, carbon can combine with vanadium and molybdenum in steel to form carbonitrides, increasing the yield strength and tensile strength of the matrix. When the carbon content is too high, it is detrimental to the plasticity of the reinforcing steel; therefore, in this embodiment, the carbon content is controlled within the range of 0.25~0.30%.

[0022] Si: Silicon is a deoxidizing element in steelmaking and can improve strength through solid solution strengthening. Furthermore, silicon promotes ferrite grain nucleation and coarsens ferrite grains; however, excessive silicon can impair the material's plasticity. Therefore, in this embodiment, the silicon content is controlled within the range of 0.3~0.45%.

[0023] Mn: Manganese and iron can form a solid solution, thereby increasing the hardness and strength of ferrite and austenite in steel. Simultaneously, manganese is a carbide-forming element, which can enter cementite and replace some iron atoms, thus increasing the strength of the steel. Furthermore, manganese in steel can lower the critical transformation temperature, thereby refining pearlite. However, excessively high manganese content will increase costs and is detrimental to the plasticity of steel bars. Therefore, in this embodiment, the manganese content is controlled within the range of 1.5~1.80%.

[0024] Nb and V: A major strengthening mechanism for reinforcing steel is the precipitation strengthening effect of carbides. The precipitates of microalloying elements niobium and vanadium exhibit good high-temperature stability, which beneficially improves the high-temperature strength of steel. Niobium, on the one hand, has a grain-refining strengthening effect; with appropriate process parameters, it can achieve second-phase strengthening, resulting in excellent overall strength and toughness. On the other hand, niobium can significantly enhance the strengthening effect of vanadium nitride precipitation. Vanadium, as a precipitation strengthening element, when added in appropriate amounts, can form V(C,N) dispersed in the steel. During rolling, nano-sized V(C,N) compounds precipitate, which can increase ferrite nucleation sites, thereby inhibiting ferrite grain growth and exhibiting a significant precipitation strengthening effect. While improving strength, it can effectively prevent the growth of austenite grains in the weld heat-affected zone, improving toughness. However, excessive addition can lead to an increase in the steel's susceptibility to weld cracking. Therefore, in this embodiment, the niobium content is controlled within the range of 0.025~0.040%, and the vanadium content is controlled within the range of 0.15~0.25%.

[0025] Ni: Nickel can lower the pearlite transformation temperature, thereby refining the pearlite and improving its strength while enhancing its low-temperature toughness. In this embodiment, the nickel content is controlled within the range of 0.1~0.2%.

[0026] Al: Adding aluminum to steel can improve the deoxidation ability of silicon and purify the molten steel. On the other hand, aluminum can refine the grains. However, aluminum is very easy to combine with oxygen, which increases the difficulty of casting. Therefore, in this embodiment, the aluminum content is controlled in the range of 0.1~0.3%.

[0027] Zr: Zirconium is a strong carbide-forming element. Adding a small amount of zirconium can play a role in degassing, purifying molten steel, refining grains, and precipitation strengthening. In this embodiment, the zirconium content is controlled in the range of 0.01~0.03%.

[0028] Nitrogen (N) can partially dissolve in iron, thus playing a role in solid solution strengthening and improving hardenability. More importantly, nitrogen can combine with alloying elements such as zirconium and vanadium to form nitride precipitation, which has a precipitation strengthening effect. If its content is too high, it can easily cause a decrease in the plasticity of steel. Therefore, in this embodiment, the nitrogen content is controlled in the range of 0.03~0.040%.

[0029] 0.5≤([Al]+4[Nb]) / [Si]≤1.1: If it is lower than the above range, it will result in larger ferrite size and higher ferrite ratio, which will prevent the fine grain strengthening and pearlite strengthening effects from being fully utilized. If it is higher than this range, it will cause alloy waste on the one hand, and on the other hand, the effect of improving the yield strength of the steel bar will be greater than the effect of improving the tensile strength, which is not conducive to the control of the strength-to-yield ratio.

[0030] 0.86%≤([Zr]+[V]) / ([Si] / 10+[N])≤1.31%: If it is higher than the above range, the precipitation of carbonitrides of alloying elements will be insufficient, and the strengthening effect will be limited. If it is lower than the range, the carbon and nitrogen content will be relatively high, which will lead to alloy waste and the residual nitrogen element may cause aging brittleness of steel bars, which is detrimental to the plasticity of steel bars.

[0031] like Figure 1 As shown, the production method of ultra-large high-strength steel bars includes the following steps: S1: According to the above chemical composition ratio, the steel liquid is obtained by smelting in a converter and refining in LF.

[0032] S2: The molten steel is cast into a continuously cast billet through a continuous casting process.

[0033] S3: The continuously cast billet is heated and rolled to obtain steel bars. In the rolling process, the initial rolling temperature is controlled at 1130~1150℃ and the finishing rolling temperature is controlled at 1090~1130℃. The continuously cast billet is rolled into steel bars with a diameter range of 36~50mm. After finishing rolling, a feedback three-stage graded cooling is adopted, and the final rolling speed of the steel bars is controlled at 3.5~8.1m / s.

[0034] S4: Cooling is performed. After cooling, the microstructure of the steel bar consists of pearlite and ferrite. The pearlite cluster size ranges from 8 to 11 μm, and the pearlite accounts for 53 to 60%. The ferrite size ranges from 4.3 to 4.9 μm.

[0035] After cooling, the hardness of the steel reinforcement matrix at the center ranges from 307 to 318 HV5kg, and the hardness of the steel reinforcement matrix near the surface ranges from 312 to 325 HV5kg; the steel reinforcement yield strength is ≥630MPa, the strength-to-yield ratio is ≥1.25, the elongation after fracture A is ≥16%, the total elongation at maximum force is ≥9.0%, and there are no cracks on the surface after cold bending and reverse bending.

[0036] In step S1, the converter smelting process specifically includes: The molten iron is transferred into a converter for oxygen blowing smelting. The charge is controlled at 108-115t, of which the amount of molten iron is controlled at ≥45t. At the end of smelting, the C content is controlled at ≤0.10% and the P content at ≤0.02%. The tapping temperature of the converter is controlled at 1620-1650℃. Silicon manganese alloy and lime are added during the process.

[0037] The LF refining process specifically includes: The molten steel from the converter is transferred to the LF station, and the bottom blowing argon and nitrogen are alternately circulated for 5 minutes each. The bottom blowing flow rate of argon is controlled at 190~250L / min, and the bottom blowing flow rate of nitrogen is controlled at 110~160L / min. 5.5~6.7kg of lime and 1.6~2.4kg of fluorite are added per ton of molten steel to adjust the white slag. After refining the white slag for 4 minutes, ferroniobium alloy, ferrovanadium alloy, and ferrosilicon-zirconium alloy are added. The tapping temperature is controlled at 1555~1575℃.

[0038] By alternately blowing argon and nitrogen into the bottom, the smelting process can be precisely controlled, effectively removing oxygen from the molten steel and helping to purify it. Furthermore, the blowing gas helps to fully mix the alloy in the molten steel and improves the uniform distribution of alloying elements.

[0039] In this embodiment, ferrosilicon alloy is not added; instead, ferrovanadium alloying is used, which can significantly reduce the cost of steel bars.

[0040] The continuous casting process specifically includes: The tundish temperature during continuous casting is controlled within the range of 1510~1550℃. Nitrogen blowing is carried out using a long nozzle in the ladle during the continuous casting process, with a flow rate controlled within the range of 80~110L / min. An alkaline covering agent is used in the tundish, and the thickness of the liquid slag layer is controlled within the range of 8~10mm. The continuous casting yields a billet with dimensions of 150×150mm. The casting speed is controlled within the range of 3.0~3.6m / min, and the secondary cooling water ratio is controlled within the range of 2.1~2.4L / kg.

[0041] Maintaining the tundish temperature at 1510~1550℃ ensures uniform temperature within the continuously cast billet, promoting a uniform distribution of elements. Nitrogen gas is introduced through the long nozzle of the ladle, facilitating nitriding of the steel and effectively reducing contact between the steel and oxygen in the air, preventing surface oxidation and improving surface quality.

[0042] In step S1, vanadium and nitrogen are alloyed by adding ferrovanadium and blowing nitrogen, which can effectively reduce the cost of steel bars, and the smelting process is simple and easy to operate.

[0043] In step S2, the continuously cast billet is heated, specifically including: The heating temperature range is controlled at 1240~1280℃, and the holding time range is controlled at 50~60min.

[0044] Maintaining a high homogenization temperature range ensures that alloying elements can fully dissolve in the matrix, promoting uniform distribution of alloying elements, improving the microstructure of the billet, making it more uniform, and enhancing the overall performance of the steel. Furthermore, a higher homogenization temperature and holding time can promote appropriate growth of the original austenite grains, improving the deformation capacity of the continuously cast billet and facilitating subsequent rolling.

[0045] In step S3, the initial rolling temperature is controlled at 1130~1150℃ and the finishing rolling temperature is controlled at 1090~1130℃. By using high initial rolling and finishing rolling temperatures, the rolling process is ensured to be rolled in the high-temperature recrystallization zone, resulting in higher deformation capacity of the steel. This can prevent insufficient strength-to-yield ratio caused by small grains, while reducing the burden on the rolling mill, comprehensively optimizing product performance and improving production efficiency.

[0046] After rolling, a feedback-based three-stage graded cooling process is performed, which specifically includes: The first stage involves aerosol cooling, with the terminal temperature controlled within the range of 1030~1070℃ and a cooling channel length of 8 meters; the second stage involves water spray cooling, with the terminal temperature controlled within the range of 960~1000℃ and a cooling channel length of 6 meters; the third stage involves aerosol cooling, with the terminal temperature controlled within the range of 910~950℃ and a cooling channel length of 4 meters.

[0047] In the first stage, the surface temperature of the steel billet is rapidly reduced by air mist cooling, which helps to form a uniform outer surface structure, while preventing overheating that could lead to grain growth. This also helps to adjust the primary structure of the steel bar and creates conditions for subsequent cooling processes.

[0048] In the second stage, water spray cooling can further control the cooling rate of the billet at a higher temperature, promoting grain refinement and uniformity of the structure. This cooling method helps to adjust the temperature distribution at the center and surface of the steel bar, optimize the grain structure, and improve the strength and toughness of the product.

[0049] In the third stage, aerosol cooling is mainly carried out at a lower temperature. The purpose is to continue to control the cooling rate, adjust the distribution of residual heat, and gradually reduce the temperature of the entire steel bar. Through this stage of cooling, the grain structure can be further optimized and the overall performance of the steel bar can be improved.

[0050] By designing a phased cooling process, the microstructure evolution of the steel billet can be effectively controlled.

[0051] In step S4, the cooling process specifically includes: controlling the temperature of the upper cooling bed to 890~930℃, passing through an interval-type heat preservation cover after the upper cooling bed is placed, with an interval distance of 1.5 meters between the heat preservation covers, and the cooling bed moving speed of 2.0~2.5m / min.

[0052] After cooling, the microstructure of the steel reinforcement consists of pearlite and ferrite. The pearlite clusters range in size from 8 to 11 μm, accounting for 53 to 60% of the total structure, while the ferrite clusters range in size from 4.3 to 4.9 μm. A suitable pearlite size helps improve the strength and hardness of the steel, and a pearlite content of 53 to 60% effectively leverages its strengthening effect.

[0053] The present invention also provides an ultra-large specification high-strength steel bar, which is manufactured using the above-mentioned ultra-large specification high-strength steel bar production method.

[0054] The present invention also provides an ultra-large specification high-strength steel bar, the chemical composition of which, by mass percentage, includes: C: 0.25~0.30%, Si: 0.3~0.45%, Mn: 1.5~1.80%, Ni: 0.1~0.2%, Zr: 0.01~0.03%, Nb: 0.025~0.040%, Al: 0.1~0.3%, V: 0.15~0.25%, N: 0.03~0.040%, with the balance being Fe and unavoidable impurities; The chemical composition of the reinforcing steel also meets the following requirements: 0.5≤([Al]+4[Nb]) / [Si]≤1.1, 0.86%≤([Zr]+[V]) / ([Si] / 10+[N])≤1.31%, Wherein, the element symbol represents the mass percentage of the corresponding element; The diameter of the reinforcing bars ranges from 36 to 50 mm; The hardness of the steel reinforcement matrix at the center ranges from 307 to 318 HV5kg, and the hardness of the steel reinforcement matrix near the surface ranges from 312 to 325 HV5kg; the yield strength of the steel reinforcement is ≥630MPa, the strength-to-yield ratio is ≥1.25, the elongation after fracture A is ≥16%, the total elongation at maximum force is ≥9.0%, and there are no cracks on the surface after cold bending and reverse bending.

[0055] The microstructure of the steel reinforcement consists of pearlite and ferrite, with pearlite clusters ranging from 8 to 11 μm in size and accounting for 53 to 60% of the total. The ferrite clusters range from 4.3 to 4.9 μm in size.

[0056] In summary, the ultra-large steel bars in this embodiment are alloyed with C, Si, Mn, Ni, Nb, V, Zr, and N, and the elemental composition is designed with 0.5 ≤ ([Al] + 4[Nb]) / [Si] ≤ 1.1 and 0.86% ≤ ([Zr] + [V]) / ([Si] / 10 + [N]) ≤ 1.31%. The influence of each element on fine grain strengthening and precipitation strengthening is comprehensively considered, and a quantitative correlation between composition, process, and microstructure is established. With the support of a comprehensive steelmaking process, high-strength steel bars with a diameter of 36~50mm can be rolled under high-temperature rolling conditions. Moreover, they can be produced using ordinary steelmaking equipment without the need to modify existing production lines, which can effectively reduce costs.

[0057] The following eight examples further illustrate specific embodiments of the present invention.

[0058] Examples 1 to 8 were all produced using the above-mentioned method for producing ultra-large-sized high-strength steel bars. Table 1 shows the chemical composition (wt%) of Examples 1 to 8, with the balance being Fe and unavoidable impurities.

[0059] Table 1 Chemical composition (wt, %) of Examples 1-8

[0060] Table 2 shows the mechanical properties of the steel bars in Examples 1-8. The yield strength of the steel bars is ≥630MPa, the strength-to-yield ratio is ≥1.25, the elongation after fracture (A) is ≥16%, the total elongation at maximum force is ≥9.0%, there are no surface cracks after cold bending and reverse bending, and the decrease in yield strength and tensile strength after 10 days of natural aging is ≤10MPa, which meets the comprehensive seismic requirements of ultra-large specification high-strength steel bars.

[0061] Table 2. Tissue and properties of Examples 1-8

[0062] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0063] The detailed descriptions listed above are merely specific descriptions of feasible implementations of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent implementations or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing ultra-large specification high-strength steel bars, characterized in that, The chemical composition of the steel reinforcement, by mass percentage, includes: C: 0.25~0.30%, Si: 0.3~0.45%, Mn: 1.5~1.80%, Ni: 0.1~0.2%, Zr: 0.01~0.03%, Nb: 0.025~0.040%, Al: 0.1~0.3%, V: 0.15~0.25%, N: 0.03~0.040%, with the balance being Fe and unavoidable impurities; The chemical composition of the steel reinforcement also satisfies: 0.5≤([Al]+4[Nb]) / [Si]≤1.1, ([Zr]+[V]) / ([Si] / 10+[N]) is any one of the following values: 2.3, 2.5, 2.9, 3, 3.1, 3.2, 3.5, and 4. Wherein, the element symbol represents the mass percentage of the corresponding element; The production method includes the following steps: According to the above chemical composition ratio, the steel is smelted in a converter and then refined in an LF refining process to obtain molten steel. The molten steel is cast into a continuously cast billet through a continuous casting process; The continuously cast billet is heated and rolled to obtain steel bars. In the rolling process, the initial rolling temperature is controlled at 1130~1150℃ and the finishing rolling temperature is controlled at 1090~1130℃. The continuously cast billet is rolled into steel bars with a diameter range of 36~50mm. After finishing rolling, a feedback-type three-stage graded cooling is adopted, and the final rolling speed of the steel bars is controlled at 3.5~8.1m / s. After cooling, the microstructure of the steel bar consists of pearlite and ferrite, with the pearlite cluster size ranging from 8 to 11 μm and the pearlite accounting for 53 to 60%, while the ferrite size ranges from 4.3 to 4.9 μm. After cooling, the hardness of the steel reinforcement matrix at the center ranges from 307 to 318 HV5kg, and the hardness of the steel reinforcement matrix near the surface ranges from 312 to 325 HV5kg; the steel reinforcement has a yield strength ≥630MPa, a strength-to-yield ratio ≥1.25, an elongation after fracture A ≥16%, a total elongation at maximum force ≥9.0%, and no surface cracks after cold bending and reverse bending.

2. The method for producing ultra-large specification high-strength steel bars according to claim 1, characterized in that, The converter smelting process specifically includes: The molten iron is transferred into a converter for oxygen blowing smelting. The charge is controlled at 108-115t, of which the amount of molten iron is controlled at ≥45t. At the end of smelting, the C content is controlled at ≤0.10% and the P content at ≤0.02%. The tapping temperature of the converter is controlled at 1620-1650℃. Silicon manganese alloy and lime are added during the process.

3. The method for producing ultra-large specification high-strength steel bars according to claim 1, characterized in that, The LF refining process specifically includes: The molten steel from the converter is transferred to the LF station, and the bottom blowing argon and nitrogen are alternately circulated for 5 minutes each. The bottom blowing flow rate of argon is controlled at 190~250L / min, and the bottom blowing flow rate of nitrogen is controlled at 110~160L / min.

4. The method for producing ultra-large specification high-strength steel bars according to claim 3, characterized in that, The LF refining process also includes: Add 5.5~6.7kg of lime and 1.6~2.4kg of fluorite to each ton of molten steel to adjust the white slag. After refining the white slag for 4 minutes, add niobium ferroalloy, vanadium ferroalloy, and silicon zirconium ferroalloy. Control the tapping temperature to 1555~1575℃.

5. The method for producing ultra-large specification high-strength steel bars according to claim 1, characterized in that, The continuous casting process specifically includes: During continuous casting, the tundish temperature is controlled within the range of 1510~1550℃. Nitrogen is blown through the ladle with a long nozzle during the continuous casting process, and the flow rate is controlled within the range of 80~110L / min. An alkaline covering agent is used in the tundish, and the thickness of the liquid slag layer is controlled within the range of 8~10mm. The continuous casting yields a 150×150mm continuous casting billet, with the casting speed controlled at 3.0~3.6m / min and the secondary cooling water volume controlled at 2.1~2.4L / kg.

6. The method for producing ultra-large specification high-strength steel bars according to claim 4, characterized in that, The heating of the continuously cast billet specifically includes: The heating temperature range is controlled at 1240~1280℃, and the holding time range is controlled at 50~60min.

7. The method for producing ultra-large specification high-strength steel bars according to claim 1, characterized in that, The feedback-based three-stage graded cooling system specifically includes: The first stage involves aerosol cooling, with the terminal temperature controlled within the range of 1030~1070℃ and a cooling channel length of 8 meters; the second stage involves water spray cooling, with the terminal temperature controlled within the range of 960~1000℃ and a cooling channel length of 6 meters; the third stage involves aerosol cooling, with the terminal temperature controlled within the range of 910~950℃ and a cooling channel length of 4 meters.

8. The method for producing ultra-large specification high-strength steel bars according to claim 1, characterized in that, The cooling process also includes: The temperature of the upper cooling bed is controlled at 890~930℃. After the upper cooling bed is in place, it is covered by an interval insulation cover with a spacing of 1.5 meters. The moving speed of the cooling bed is 2.0~2.5m / min.

9. A type of ultra-large specification high-strength steel bar, characterized in that, It is manufactured using the production method of ultra-large specification high-strength steel bars according to any one of claims 1 to 8.

10. A type of ultra-large specification high-strength steel bar, characterized in that, The chemical composition of the steel reinforcement, by mass percentage, includes: C: 0.25~0.30%, Si: 0.3~0.45%, Mn: 1.5~1.80%, Ni: 0.1~0.2%, Zr: 0.01~0.03%, Nb: 0.025~0.040%, Al: 0.1~0.3%, V: 0.15~0.25%, N: 0.03~0.040%, with the balance being Fe and unavoidable impurities; The chemical composition of the steel reinforcement also satisfies: 0.5≤([Al]+4[Nb]) / [Si]≤1.1, ([Zr]+[V]) / ([Si] / 10+[N]) is any one of the following values: 2.3, 2.5, 2.9, 3, 3.1, 3.2, 3.5, and 4. Wherein, the element symbol represents the mass percentage of the corresponding element; The diameter of the reinforcing bar is in the range of 36~50mm; The hardness of the steel reinforcement matrix at the center ranges from 307 to 318 HV5kg, and the hardness of the steel reinforcement matrix near the surface ranges from 312 to 325 HV5kg; the steel reinforcement has a yield strength ≥630MPa, a strength-to-yield ratio ≥1.25, an elongation after fracture A ≥16%, a maximum force total elongation ≥9.0%, and no surface cracks after cold bending and reverse bending.

11. The ultra-large specification high-strength steel bar according to claim 10, characterized in that, The microstructure of the steel reinforcement consists of pearlite and ferrite, with pearlite clusters ranging from 8 to 11 μm in size and accounting for 53 to 60% of the total. The ferrite clusters range from 4.3 to 4.9 μm in size.

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