Anti-seismic straight steel bar and preparation method and application thereof

Abstract

This invention discloses a seismic-resistant straight steel bar, its preparation method, and its application, relating to the field of steel production technology. It comprises the following elements by weight percentage: C: 0.26–0.28%, Si: 0.55–0.65%, Mn: 1.50–1.60%, S≤0.025%, P≤0.025%, V: 0.120–0.140%, N: 0.019–0.022%, Nb: 0.010–0.020%, with the balance being Fe and unavoidable impurities. By controlling the content of each alloying element in the steel bar within a narrow range, C, Si, and Mn exert solid solution strengthening effects, ensuring the yield strength of the steel bar. By controlling the content of microalloying elements such as V and Nb within the above range, the yield strength of the steel bar is improved, while the maximum value of the yield strength is limited. This results in a strength-to-yield ratio ≥1.25 for the steel bar with the above component content, exhibiting better seismic resistance.

Description

Technical Field

[0001] This invention relates to the field of steel production technology, and more specifically, to an earthquake-resistant straight steel bar, its preparation method, and its application. Background Technology

[0002] Hot-rolled ribbed steel bars are the primary reinforcing material in reinforced concrete structures, bearing tensile and compressive stresses and strains. They are widely used in various load-bearing processes such as welding, mechanical connections, bending, and straightening. Reducing steel consumption and lowering carbon emissions are current priorities for the steel industry.

[0003] Compared with ordinary 400MPa grade steel bars, high-strength seismic steel bars can not only greatly save steel bar usage for the same building structure, but also easily complete taller and larger span buildings. They also show significant progress in reducing steel bar processing and connection work, increasing the applicable building area, and improving the rationality, environmental protection and energy conservation of building structures.

[0004] However, high-strength seismic-resistant straight steel bars not only need to have high yield strength but also extremely high tensile strength, ensuring that the ratio of tensile strength to yield strength is ≥1.25. As the yield strength of seismic-resistant straight steel bars increases, to meet seismic performance requirements, the increase in tensile strength must exceed the increase in yield strength. Therefore, ensuring the required strength-to-yield ratio for seismic-resistant steel bars while maintaining high yield strength is a key technical challenge in the development of ultra-high-strength seismic-resistant steel bars.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a seismic-resistant straight steel bar, its preparation method and application, which can improve the yield strength of the steel bar while increasing its tensile strength, thus obtaining a straight steel bar with better seismic performance.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a seismic-resistant straight steel bar, comprising the following elements by weight percentage: C: 0.26-0.28%, Si: 0.55-0.65%, Mn: 1.50-1.60%, S≤0.025%, P≤0.025%, V: 0.120-0.140%, N: 0.019-0.022%, Nb: 0.010-0.020%, with the balance being Fe and unavoidable impurities.

[0009] In an optional implementation, V / N is 6.32 to 6.82.

[0010] In an optional embodiment, the steel bar has a yield strength ≥640MPa, tensile strength ≥800MPa, strength-to-yield ratio ≥1.25, elongation ≥14, and total elongation at maximum force ≥9.0.

[0011] Preferably, the yield strength of the steel bar is 645-660 MPa and the tensile strength is 810-840 MPa.

[0012] Preferably, the steel bars are Φ12mm~Φ25mm in size.

[0013] Secondly, the present invention provides a method for preparing earthquake-resistant straight steel bars as described in any of the foregoing embodiments, comprising continuously casting molten steel into a continuous casting billet, heating the continuous casting billet to obtain red steel, and rolling the red steel.

[0014] In an optional implementation, continuous casting includes casting molten steel using electromagnetic stirring and intermediate cooling.

[0015] Preferably, the superheat of the molten steel is 15-25℃, the billet pulling speed of the continuous casting billet is 2.5-2.7m / min, and the straightening temperature of the continuous casting billet is 980-1050℃.

[0016] Preferably, the electromagnetic stirring current is 300–400 A, and the frequency is 3–4 Hz; the cooling water flow rate of the crystallizer is 155–165 m³ / h. 3 / h, the specific water flow rate of secondary cooling water is 1.10~1.5L / Kg.

[0017] In an optional embodiment, the continuous casting billet heating includes sending the continuous casting billet to a heating furnace for heating, wherein the continuous casting billet is heated sequentially through a preheating section, a heating end, and a soaking section.

[0018] Preferably, the temperature of the continuously cast billet entering the heating furnace is 400-900℃, the temperature of the preheating section is 900-1100℃, the temperature of the heating section is 1160-1200℃, the temperature of the soaking section is 1170-1200℃, and the total heating time is 65-75 minutes.

[0019] Preferably, the heating gas includes any one of blast furnace gas, coke oven gas, or a mixture of the two.

[0020] Preferably, the calorific value of the heating gas is 5016–7524 KJ / m³. 3 .

[0021] Preferably, the heating furnace is an air-gas dual regenerative walking beam heating furnace.

[0022] In an optional embodiment, rolling includes sequentially roughing, intermediate rolling, and finishing rolling of the red steel.

[0023] Preferably, the initial rolling temperature of the red steel is ≥1050℃, and the temperature of the red steel during the rolling process is 1050~1100℃.

[0024] Preferably, the rolling process includes feeding the red steel into a six-stand alternating horizontal and vertical roughing mill for roughing, then shearing it with a No. 1 flying shear, feeding it into a six-stand alternating horizontal and vertical intermediate mill for intermediate rolling, and then shearing it with a No. 2 flying shear, feeding it into a six-stand alternating horizontal and vertical finishing mill for finishing.

[0025] In an optional embodiment, the molten steel is further subjected to converter smelting, argon blowing at an argon station, and LF refining before continuous casting.

[0026] Preferably, the feed components for converter smelting include at least one of molten iron, scrap steel, and pig iron; preferably, the amount of feed components added for converter smelting is 158-164t.

[0027] Preferably, the C content in the molten steel at the end of the converter smelting process is 0.06-0.12%, P ≤ 0.018%, and the tapping temperature of the molten steel is 1610-1640℃.

[0028] Preferably, during the tapping process, Si, Mn, V, N, and Nb elements are added to the molten steel in proportion; preferably, the tapping process is within the range of 1 / 3 to 3 / 4 of the molten steel has been tapped; preferably, the N element is added as a nitrogen-enhancing agent, and the amount of nitrogen-enhancing agent added is 1.2 × 10⁻⁶ of the weight of the molten steel. -3 ~1.4×10 -3 times.

[0029] Preferably, the argon blowing time at the argon station is ≥5 min, the molten steel temperature before argon blowing is 1570~1595℃, and the molten steel temperature after argon blowing is ≥1550℃.

[0030] Preferably, LF refining includes adding active lime to molten steel to form slag; preferably, the amount of active lime added is 400-500 kg / furnace, and the basicity of the molten steel during LF refining is 1.8-2.4.

[0031] Preferably, the refining slag produced by refining contains, by weight percentage, 35-45% CaO, 15-25% SiO2 and 8-13% MgO.

[0032] In an optional embodiment, the rolled red steel is further finished, including water cooling, multiple-length hot shearing, cooling bed straightening and slow cooling, and shearing.

[0033] Preferably, the opening degree of the water-cooled section is 1-5%.

[0034] Preferably, the temperature at which the rolled red steel is straightened and slowly cooled on the cooling bed is 980–1050°C.

[0035] Thirdly, the present invention provides an application of earthquake-resistant straight steel bars as described in any of the foregoing embodiments or earthquake-resistant straight steel bars prepared by any of the foregoing embodiments in the field of steel production.

[0036] The present invention has the following beneficial effects:

[0037] This invention provides a seismic-resistant straight steel bar, its preparation method, and its application. By controlling the content of each alloying element in the seismic-resistant straight steel bar through narrow composition, C, Si, and Mn can fully exert their solid solution strengthening effect, ensuring the yield strength of the steel bar. By controlling the content of microalloying elements such as V and Nb, their fine grain strengthening and precipitation strengthening effects can be fully exerted to improve the yield strength of the steel bar, while limiting the maximum value of the yield strength of the steel bar. This results in a strength-to-yield ratio ≥1.25 for steel bars with the above composition content, exhibiting better seismic resistance. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 Metallographic image of the seismic-resistant straight steel bar provided in Embodiment 1 of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0041] In a first aspect, the present invention provides a seismic-resistant straight steel bar, comprising the following elements by weight percentage: C: 0.26-0.28%, Si: 0.55-0.65%, Mn: 1.50-1.60%, S≤0.025%, P≤0.025%, V: 0.120-0.140%, N: 0.019-0.022%, Nb: 0.010-0.020%, with the balance being Fe and unavoidable impurities.

[0042] This invention controls the alloying elements such as C, Si, Mn, V, and Nb within a narrow range. C, Si, and Mn, as solid solution strengthening elements, fully exert their solid solution strengthening effect in steel bars, ensuring the yield strength of the steel bars. The addition of microalloying elements such as V and Nb can fully exert their grain refinement strengthening and precipitation strengthening effects, thereby improving the yield strength of steel bars. However, excessively high V content has a significant impact on the yield strength of steel bars. In order to prevent excessively high yield strength from leading to an unqualified strength-to-yield ratio and affecting the seismic performance of seismic steel bars, it is necessary to strictly control the amount of V.

[0043] In an optional embodiment, the V / N ratio is 6.32–6.82. The inventors have found that excessively high N content can affect the aging of reinforcing steel. While a high N content in reinforcing steel has almost no impact on the performance of freshly produced steel, its mechanical properties rapidly decrease with increasing storage time, affecting its safe use. By controlling the V / N ratio within the above range, an appropriate amount of N can promote the grain refinement and strengthening effect of V in the reinforcing steel. The combination of N and V can effectively refine the grains in the reinforcing steel.

[0044] In an optional implementation, the reinforcing steel has a yield strength ≥ 640 MPa, tensile strength ≥ 800 MPa, strength-to-yield ratio ≥ 1.25, elongation ≥ 14%, and total elongation at maximum force ≥ 9.0%. Compared to ordinary 400 MPa grade reinforcing steel, seismic-resistant reinforcing steel with a yield strength ≥ 640 MPa can save 45% of the steel usage for the same building structure, making the building structure more rational and achieving steel reduction.

[0045] Among them, the strength-to-yield ratio reflects the seismic performance of steel bars, and its calculation method is: strength-to-yield ratio = tensile strength / yield strength.

[0046] Preferably, in order to ensure that the strength-to-yield ratio of the steel bars is ≥1.25, the yield strength of the steel bars is 645-660 MPa and the tensile strength is 810-840 MPa.

[0047] Preferably, the steel bars have a diameter of Φ12mm to Φ25mm. By controlling the composition of the steel bars within the above range and controlling the steel bar specifications, the heating time of the steel bars in the heating furnace can be significantly reduced, thereby improving the production efficiency of the steel bars.

[0048] Secondly, the present invention provides a method for preparing earthquake-resistant straight steel bars as described in any of the foregoing embodiments, comprising continuously casting molten steel into a continuous casting billet, heating the continuous casting billet to obtain red steel, and rolling the red steel.

[0049] In an optional implementation, continuous casting includes casting molten steel using electromagnetic stirring and intermediate cooling.

[0050] Preferably, the superheat of the molten steel is 15-25℃, the billet pulling speed of the continuous casting billet is 2.5-2.7m / min, and the straightening temperature of the continuous casting billet is 980-1050℃.

[0051] During continuous casting, the superheat of molten steel is controlled within a low range, and the billet is drawn at a low speed. Electromagnetic stirring is maintained during the continuous casting process to prevent compositional segregation during the continuous casting of molten steel into billets, thus ensuring that steel bars with better performance are obtained during the rolling process.

[0052] Preferably, the electromagnetic stirring current is 300–400 A, and the frequency is 3–4 Hz; the cooling water flow rate of the crystallizer is 155–165 m³ / h. 3 / h, the specific water flow rate of secondary cooling water is 1.10~1.5L / Kg.

[0053] Preferably, the continuously cast billet obtained from continuous casting is cut and then transported to the steel rolling mill by a hot-rolling conveyor or a heated car.

[0054] In an optional embodiment, the continuous casting billet heating includes sending the continuous casting billet to a heating furnace for heating, wherein the continuous casting billet is heated sequentially through a preheating section, a heating end, and a soaking section.

[0055] Preferably, the temperature of the continuously cast billet entering the heating furnace is as follows: billet temperature upon entering the heating furnace is 400–900℃, preheating zone temperature is 900–1100℃, heating zone temperature is 1160–1200℃, soaking zone temperature is 1170–1200℃, and the total heating time is 65–75 minutes. By controlling the heating temperature of the continuously cast billet, the heating temperature of the billet at the beginning, middle, and end, as well as the core surface, is uniform within a short time, ensuring the solid solution of alloying elements such as V and Nb.

[0056] Furthermore, the applicant discovered that existing technologies typically achieve high-strength earthquake-resistant straight steel bars by increasing the content of microalloying elements such as niobium and vanadium. However, to ensure that these alloying elements can fully exert their effects, the rolling process requires a heating time of no less than 90 minutes, and the steel bars need at least five days of natural aging after production to meet the requirement that the ratio of tensile strength to yield strength is ≥1.25. This results in low efficiency in existing technologies. This application, through appropriate raw material ratios and process parameters, significantly reduces the total heating time of the earthquake-resistant steel bars, thereby improving production efficiency.

[0057] Preferably, the furnace exit temperature of the red steel is 1080-1100℃, which reduces the fluctuation of the properties of the finished steel bars at the head, middle and tail, and reduces the amount of trimming caused by the unstable mechanical properties of the head and tail of the steel bars.

[0058] Preferably, the heating gas includes any one of blast furnace gas, coke oven gas, or a mixture of the two.

[0059] Preferably, the calorific value of the heating gas is 5016–7524 KJ / m³. 3 .

[0060] Preferably, the heating furnace is an air-gas dual regenerative walking beam heating furnace.

[0061] During the heating process of continuously cast billets, in order to maintain a stable furnace temperature, it is necessary to adjust the flow rate of the furnace atmosphere. A dual-regenerative walking beam furnace using air and gas is employed, equipped with an intelligent combustion system. When the furnace atmosphere is below the lower temperature limit or above the upper temperature limit, the heating gas flow rate can be automatically adjusted to ensure the furnace temperature remains within the specified range. To further ensure a constant furnace temperature, both the furnace inlet and outlet doors have automatic opening functions. The doors open when the continuously cast billets enter and exit the furnace, and automatically close afterward.

[0062] In an optional embodiment, rolling includes sequentially roughing, intermediate rolling, and finishing rolling of the red steel.

[0063] Preferably, the initial rolling temperature of the red steel is ≥1050℃, and the temperature of the red steel during the rolling process is 1050~1100℃, so as to ensure V and Nb solid solution and refine the grain size of the steel reinforcement.

[0064] Preferably, the rolling process includes feeding the red steel into a six-stand alternating horizontal and vertical roughing mill for roughing, then shearing it with a No. 1 flying shear, feeding it into a six-stand alternating horizontal and vertical intermediate mill for intermediate rolling, and then shearing it with a No. 2 flying shear, feeding it into a six-stand alternating horizontal and vertical finishing mill for finishing.

[0065] In an optional embodiment, the molten steel is further subjected to converter smelting, argon blowing at an argon station, and LF refining before continuous casting.

[0066] Preferably, the feed components for converter smelting include at least one of molten iron, scrap steel, and pig iron; preferably, the amount of feed components added for converter smelting is 158-164t.

[0067] Preferably, nitrogen is blown into the bottom throughout the converter smelting process, and the consumption of molten iron is controlled according to the composition and temperature of the molten iron to ensure thermal balance.

[0068] Preferably, the C content in the molten steel at the end of the converter smelting process is 0.06-0.12%, P ≤ 0.018%, and the tapping temperature of the molten steel is 1610-1640℃.

[0069] Preferably, during the tapping process, Si, Mn, V, N and Nb elements are added to the molten steel in proportion; preferably, the tapping process is within the range of 1 / 3 to 3 / 4 of the molten steel has been tapped.

[0070] Preferably, the addition of Si, Mn, V, N and Nb elements to molten steel in proportion can be achieved by adding ferrosilicon, ferrosilicon, ferroniobium, vanadium nitrogen, carbon raiser and nitrogen raiser to molten steel.

[0071] Preferably, nitrogen is added as a nitrogen-enhancing agent. To ensure that nitrogen is fully incorporated into the molten steel, the amount of nitrogen-enhancing agent added is 1.2 × 10⁻⁶ of the weight of the molten steel. -3 ~1.4×10 -3 times.

[0072] Preferably, the argon blowing time at the argon station is ≥5 minutes to ensure effective air permeability of both permeable bricks. The molten steel temperature before argon blowing is 1570~1595℃, and the molten steel temperature after argon blowing is ≥1550℃.

[0073] Preferably, LF refining includes adding active lime to molten steel to form slag, thereby removing impurities from the molten steel and adjusting the content of various components in the molten steel.

[0074] Preferably, the amount of active lime added is 400-500 kg / furnace, and the basicity of the molten steel during LF refining is 1.8-2.4.

[0075] Preferably, the refining slag produced by refining contains, by weight percentage, 35-45% CaO, 15-25% SiO2 and 8-13% MgO.

[0076] After refining, the content of each component in the molten steel is tested, and the content of each component in the molten steel is fine-tuned to control it within the required range.

[0077] In an optional embodiment, the rolled red steel is further finished, including water cooling, multiple-length hot shearing, cooling bed straightening and slow cooling, and shearing.

[0078] Preferably, the opening degree of the water-cooled section is 1-5%.

[0079] Preferably, the temperature at which the rolled red steel is straightened and slowly cooled on the cooling bed is 980–1050°C.

[0080] Thirdly, the present invention provides an application of earthquake-resistant straight steel bars as described in any of the foregoing embodiments or earthquake-resistant straight steel bars prepared by any of the foregoing embodiments in the field of steel production.

[0081] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0082] Example 1

[0083] This embodiment provides a seismic-resistant straight steel bar with a specification of Φ12mm. The mass ratio of each component in the steel bar is as follows: C: 0.27%, Si: 0.60%, Mn: 1.54%, S: 0.025%, P: 0.025%, V: 0.130%, N: 0.0198%, Nb: 0.014%, with the balance being Fe and unavoidable impurities. The V / N ratio is 6.56.

[0084] This embodiment provides a seismic-resistant straight steel bar, the preparation method of which is as follows:

[0085] S1, Converter smelting

[0086] Molten iron and scrap steel are added to the converter. Taking a 130t top-and-bottom blowing converter as an example, a total of 159t of molten steel and scrap steel are added to each furnace. The consumption of molten iron is controlled according to the composition and temperature of the molten iron to ensure thermal balance. At the same time, nitrogen is blown from the bottom throughout the process.

[0087] The C content in the molten steel at the end of the smelting process is 0.08%, P is 0.015%, the tapping temperature of the molten steel is 1620℃, and a sliding plate is used to block slag.

[0088] During the steel tapping process, from when 1 / 3 of the molten steel has been tapped until 3 / 4 has been tapped, ferrosilicon, ferrosilicon, vanadium nitrogen, carbon raisers, and nitrogen raisers are added to the molten steel to control the proportions of C, Si, Mn, V, N, and Nb within the required range. The amount of nitrogen raiser added is 1.2 × 10⁻⁶ of the molten steel weight. -3 times.

[0089] S2, Argon blowing at the argon station

[0090] Argon blowing time at the argon station is 8 minutes to ensure effective air permeability of both permeable bricks. The molten steel temperature before argon blowing is 1586℃, and the molten steel temperature after argon blowing is 1560℃.

[0091] S3, LF Refining

[0092] Activated lime is added to the molten steel to form slag, with an addition rate of 450 kg / heat. The basicity of the molten steel during LF refining is 2.18. The refining slag produced by refining comprises, by weight percentage, 38% CaO, 22% SiO2, and 10% MgO.

[0093] After refining, the content of each component in the molten steel is tested and fine-tuned to control the mass ratio of each component in the steel bar as follows: C: 0.26-0.28%, Si: 0.55-0.65%, Mn: 1.50-1.60%, S≤0.025%, P≤0.025%, V: 0.120-0.140%, N: 0.019-0.022%, Nb: 0.010-0.020%, with the balance being Fe and unavoidable impurities.

[0094] S4, Continuous Casting

[0095] Continuous casting involves using electromagnetic stirring and intermediate cooling to continuously cast molten steel. The superheat of the molten steel is 15℃, the billet casting speed is 2.5–2.7 m / min, and the billet straightening temperature is 980–1050℃. The electromagnetic stirring current is 350 A, and the frequency is 4 Hz; the cooling water flow rate of the crystallizer is 159 m³ / min. 3 The secondary cooling water has a flow rate of 1.20 L / kg per hour. The continuously cast billets obtained from continuous casting are cut and then transported to the rolling mill via a hot-rolling conveyor.

[0096] S5, Heating

[0097] The continuously cast billet is sent to a heating furnace for heating, with the billet entering the furnace at a temperature of 810℃. The billet is then heated sequentially through a preheating section, a heating section, and a soaking section to obtain red-hot steel. The preheating section temperature is 950–980℃, the heating section temperature is 1180–1200℃, and the soaking section temperature is 1182–1195℃. The total heating time is 75 minutes, and the red-hot steel exits the furnace at a temperature of 1080–1100℃.

[0098] The heating furnace is an air-gas dual-regenerative walking beam furnace. The heating gas is a mixture of blast furnace gas and coke oven gas, with a calorific value of 5800 KJ / m³. 3 .

[0099] S6, Rolling

[0100] The red-hot steel is fed into a six-stand alternating horizontal and vertical roughing mill for roughing, then sheared by the No. 1 flying shear, and finally fed into a six-stand alternating horizontal and vertical intermediate mill for intermediate rolling. After shearing by the No. 2 flying shear, it is fed into a six-stand alternating horizontal and vertical finishing mill for finishing. The initial rolling temperature of the red-hot steel is 1080℃, and the temperature of the red-hot steel is controlled between 1050℃ and 1100℃ during the rolling process.

[0101] S7, Finishing

[0102] The rolled red steel undergoes water cooling, multiple-length hot shearing, straightening and slow cooling on a cooling bed, and shearing. The opening of the water cooling section is 2%. The temperature for straightening and slow cooling of the rolled red steel on the cooling bed is 980–1000℃.

[0103] Shearing involves cutting precision-rolled red steel into 9-meter or 12-meter length steel bars using two fixed-length shears spaced 9 meters apart. Finally, the length steel bars are bundled and packaged in fixed quantities to form the final product.

[0104] The seismic-resistant straight steel bars provided in this embodiment were tested and found to have a yield strength of 660 MPa, a tensile strength of 840 MPa, a strength-to-yield ratio of 1.27, an elongation of 18%, and a maximum force total elongation of 10.5%.

[0105] The microstructure of the seismic-resistant straight steel bars provided in this embodiment was observed, and the following results were obtained: Figure 1 The metallographic results shown are from Figure 1 It can be seen that the metallographic structure of the core and surface of the steel bar is uniform ferrite plus pearlite, which meets the national standard that the surface should not have tempered martensite structure.

[0106] Example 2

[0107] This embodiment provides a seismic-resistant straight steel bar with a specification of Φ20mm, and the preparation method is as follows:

[0108] S1, Converter smelting

[0109] Molten iron and scrap steel are added to the converter. Taking a 130t converter as an example, a total of 160t of molten steel and scrap steel are added to each furnace. The consumption of molten iron is controlled according to the composition and temperature of the molten iron to ensure thermal balance. At the same time, nitrogen is blown from the bottom throughout the process.

[0110] The C content in the molten steel at the end of the smelting process is 0.06%, P is 0.015%, the tapping temperature of the molten steel is 1630℃, and a sliding plate is used to block slag.

[0111] During the steel tapping process, from the point when 1 / 3 of the molten steel has been tapped until 3 / 4 has been tapped, ferrosilicon, ferrosilicon, vanadium nitrogen, carbon raisers, and nitrogen raisers are added to the molten steel to control the proportions of C, Si, Mn, V, N, and Nb within the required range. The amount of nitrogen raiser added is 1.25 × 10⁻⁶ of the molten steel weight. -3 times.

[0112] S2, Argon blowing at the argon station

[0113] Argon blowing time at the argon station is 10 minutes to ensure effective air permeability of both permeable bricks. The molten steel temperature before argon blowing is 1575℃, and the molten steel temperature after argon blowing is 1552℃.

[0114] S3, LF Refining

[0115] Activated lime is added to the molten steel to form slag, with an addition rate of 460 kg / furnace. The basicity of the molten steel during LF refining is 2.4. The refining slag produced by refining comprises, by weight percentage, 40% CaO, 20% SiO2, and 8% MgO.

[0116] After refining, the content of each component in the molten steel is tested and fine-tuned to control the mass ratio of each component in the steel bar as follows: C: 0.26-0.28%, Si: 0.55-0.65%, Mn: 1.50-1.60%, S≤0.025%, P≤0.025%, V: 0.120-0.140%, N: 0.019-0.022%, Nb: 0.010-0.020%, with the balance being Fe and unavoidable impurities.

[0117] S4, Continuous Casting

[0118] Continuous casting involves using electromagnetic stirring and intermediate cooling to continuously cast molten steel. The superheat of the molten steel is 20°C, the billet casting speed is 2.5–2.7 m / min, and the billet straightening temperature is 980–1050°C. The electromagnetic stirring current is 350 A, and the frequency is 4 Hz; the cooling water flow rate of the crystallizer is 160 m³ / min. 3 The secondary cooling water has a flow rate of 1.40 L / kg per hour. The continuously cast billets obtained from continuous casting are cut and then transported to the rolling mill via a hot-rolling conveyor.

[0119] S5, Heating

[0120] The continuously cast billet is sent to a heating furnace for heating. The billet enters the furnace at a temperature of 480℃. The billet then passes through a preheating section, a heating section, and a soaking section for heating to obtain red-hot steel. The preheating section temperature is 900–930℃, the heating section temperature is 1175–1198℃, and the soaking section temperature is 1178–1200℃. The total heating time is 68 minutes, and the red-hot steel exits the furnace at a temperature of 1080–1100℃.

[0121] The heating furnace is an air-gas dual-regenerative walking beam furnace. The heating gas is a mixture of blast furnace gas and coke oven gas, with a calorific value of 5200 KJ / m³. 3 .

[0122] S6, Rolling

[0123] The red-hot steel is fed into a six-stand alternating horizontal and vertical roughing mill for roughing, then sheared by the No. 1 flying shear, and finally fed into a six-stand alternating horizontal and vertical intermediate mill for intermediate rolling. After shearing by the No. 2 flying shear, it is fed into a six-stand alternating horizontal and vertical finishing mill for finishing. The initial rolling temperature of the red-hot steel is 1070℃, and the temperature of the red-hot steel is controlled between 1050℃ and 1100℃ during the rolling process.

[0124] S7, Finishing

[0125] The rolled red steel undergoes water cooling, multiple-length hot shearing, straightening and slow cooling on a cooling bed, and shearing. The opening of the water cooling section is 3%. The temperature for straightening and slow cooling of the rolled red steel on the cooling bed is 1000–1020℃.

[0126] Shearing involves cutting precision-rolled red steel into 9-meter or 12-meter length steel bars using two fixed-length shears spaced 9 meters apart. Finally, the length steel bars are bundled and packaged in fixed quantities to form the final product.

[0127] The seismic-resistant straight steel bars prepared by the above method were tested and found to have a yield strength of 650 MPa, a tensile strength of 820 MPa, a strength-to-yield ratio of 1.26, an elongation of 17.8, and a maximum force total elongation of 9.8.

[0128] Example 3

[0129] This embodiment provides a seismic-resistant straight steel bar with a specification of Φ22mm, and the preparation method is as follows:

[0130] S1, Converter smelting

[0131] Molten iron and scrap steel are added to the converter. Taking a 130t converter as an example, a total of 162t of molten steel and scrap steel are added to each furnace. The consumption of molten iron is controlled according to the composition and temperature of the molten iron to ensure thermal balance. At the same time, nitrogen is blown from the bottom throughout the process.

[0132] The C content in the molten steel at the end of the smelting process is 0.06%, P is 0.018%, the tapping temperature of the molten steel is 1630℃, and a sliding plate is used to block slag.

[0133] During the steel tapping process, from the point when 1 / 3 of the molten steel has been tapped until 3 / 4 has been tapped, ferrosilicon, ferrosilicon, vanadium nitrogen, carbon raisers, and nitrogen raisers are added to the molten steel to control the proportions of C, Si, Mn, V, N, and Nb within the required range. The amount of nitrogen raiser added is 1.32 × 10⁻⁶ of the molten steel weight. -3 times.

[0134] S2, Argon blowing at the argon station

[0135] Argon blowing time at the argon station is 15 minutes to ensure effective air permeability of both permeable bricks. The molten steel temperature before argon blowing is 1585℃, and the molten steel temperature after argon blowing is 1560℃.

[0136] S3, LF Refining

[0137] Activated lime is added to the molten steel to form slag, with an addition rate of 480 kg / heat. The basicity of the molten steel during LF refining is 2.04. The refining slag produced by refining comprises, by weight percentage, 41% CaO, 25% SiO2, and 10% MgO.

[0138] After refining, the content of each component in the molten steel is tested and fine-tuned to control the mass ratio of each component in the steel bar as follows: C: 0.26-0.28%, Si: 0.55-0.65%, Mn: 1.50-1.60%, S≤0.025%, P≤0.025%, V: 0.120-0.140%, N: 0.019-0.022%, Nb: 0.010-0.020%, with the balance being Fe and unavoidable impurities.

[0139] S4, Continuous Casting

[0140] Continuous casting involves using electromagnetic stirring and intermediate cooling to continuously cast molten steel. The superheat of the molten steel is 18℃, the billet casting speed is 2.5–2.7 m / min, and the billet straightening temperature is 980–1050℃. The electromagnetic stirring current is 380 A, and the frequency is 4 Hz; the cooling water flow rate of the crystallizer is 162 m³ / min. 3 The secondary cooling water volume is 1.5 L / kg. After being cut, the continuously cast billets obtained from continuous casting are transported to the steel rolling mill via a hot-rolling conveyor.

[0141] S5, Heating

[0142] The continuously cast billet is sent to a heating furnace for heating. The billet enters the furnace at a temperature of 800℃. The billet then passes through a preheating section, a heating section, and a soaking section for heating to obtain red-hot steel. The preheating section temperature is 980–1000℃, the heating section temperature is 1178–1195℃, and the soaking section temperature is 1180–1195℃. The total heating time is 70 minutes, and the red-hot steel exits the furnace at a temperature of 1080–1100℃.

[0143] The heating furnace is an air-gas dual-regenerative walking beam furnace. The heating gas is a mixture of blast furnace gas and coke oven gas, with a calorific value of 6000 KJ / m³. 3 .

[0144] S6, Rolling

[0145] The red-hot steel is fed into a six-stand alternating horizontal and vertical roughing mill for roughing, then sheared by the No. 1 flying shear, and finally fed into a six-stand alternating horizontal and vertical intermediate mill for intermediate rolling. After shearing by the No. 2 flying shear, it is fed into a six-stand alternating horizontal and vertical finishing mill for finishing. The initial rolling temperature of the red-hot steel is 1080℃, and the temperature of the red-hot steel is controlled between 1050℃ and 1100℃ during the rolling process.

[0146] S7, Finishing

[0147] The rolled red steel undergoes water cooling, multiple-length hot shearing, straightening and slow cooling on a cooling bed, and shearing. The opening of the water cooling section is 4%. The temperature for straightening and slow cooling of the rolled red steel on the cooling bed is 1020–1050℃.

[0148] Shearing involves cutting precision-rolled red steel into 9-meter or 12-meter length steel bars using two fixed-length shears spaced 9 meters apart. Finally, the length steel bars are bundled and packaged in fixed quantities to form the final product.

[0149] The seismic-resistant straight steel bars prepared by the above method were tested and found to have a yield strength of 650 MPa, a tensile strength of 825 MPa, a strength-to-yield ratio of 1.27, an elongation of 17, and a maximum total elongation of 10.2.

[0150] Comparative Example 1

[0151] This comparative example provides a seismic-resistant straight steel bar, whose preparation method is the same as that of Example 1, the only difference being the elemental composition of the steel bar, as follows: the mass ratio of each component in the steel bar is C: 0.27%, Si: 0.61%, Mn: 1.52%, S: 0.018%, P: 0.020%, V: 0.160%, N: 0.0210%, Nb: 0.018%, with the balance being Fe and unavoidable impurities. The V / N ratio is 7.62.

[0152] The seismic-resistant straight steel bars prepared by the above method were tested and found to have a yield strength of 670 MPa, a tensile strength of 820 MPa, a strength-to-yield ratio of 1.22, an elongation of 18, and a maximum total elongation of 8.5. The strength-to-yield ratio of the steel bars does not meet the seismic performance requirement of ≥1.25, and the elongation performance does not meet the requirement of ≥9.

[0153] Comparative Example 2

[0154] This comparative example provides a seismic-resistant straight steel bar, whose elemental composition is the same as that of Example 1, the only difference being the continuous casting process, as detailed below:

[0155] Continuous casting involves using electromagnetic stirring and intermediate cooling to continuously cast molten steel. The superheat of the molten steel is 15℃, the billet casting speed is 2.8–3.2 m / min, and the billet straightening temperature is 1000–1050℃. The electromagnetic stirring current is 400 A, and the frequency is 4 Hz; the cooling water flow rate of the crystallizer is 160 m³ / min. 3 The secondary cooling water has a flow rate of 1.60 L / kg per hour. The continuously cast billets obtained from continuous casting are cut and then transported to the rolling mill via a hot-rolling conveyor.

[0156] Due to the increased billet pulling speed, the specific water volume of the secondary cooling water needs to be increased simultaneously to ensure effective cooling of the reinforcing bars. However, testing revealed that the seismic-resistant straight reinforcing bars produced using the above method had a yield strength of 680 MPa, a tensile strength of 830 MPa, a strength-to-yield ratio of 1.25, an elongation of 13%, and a maximum force total elongation of 8.2%. The plasticity indicators of elongation and maximum force total elongation of the reinforcing bars still do not meet the standards.

[0157] Comparative Example 3

[0158] This comparative example provides a seismic-resistant straight steel bar, whose elemental composition is the same as that of Example 1, the only difference being the heating process, as detailed below:

[0159] The continuously cast billet is sent to a heating furnace for heating, with the billet entering the furnace at a temperature of 800℃. The billet is then sequentially heated through a preheating section, a heating section, and a soaking section to obtain red-hot steel. The preheating section temperature is 950–980℃, the heating section temperature is 1180–1200℃, and the soaking section temperature is 1182–1195℃. The total heating time is 85 minutes, and the red-hot steel exits the furnace at a temperature of 1080–1100℃.

[0160] The heating furnace is an air-gas dual-regenerative walking beam furnace. The heating gas is a mixture of blast furnace gas and coke oven gas, with a calorific value of 5800 KJ / m³. 3 .

[0161] The seismic-resistant straight steel bars prepared by the above method were tested and found to have a yield strength of 660 MPa, a tensile strength of 825 MPa, a strength-to-yield ratio of 1.25, an elongation of 19%, and a maximum force total elongation of 9.8%. Compared with Example 1, it can be seen that the yield strength and tensile strength did not change significantly after extending the heating time by 20 minutes.

[0162] Comparative Example 4

[0163] This comparative example provides a seismic-resistant straight steel bar, whose elemental composition is the same as that of Example 1, the only difference being the finishing process, as detailed below:

[0164] The rolled red steel undergoes water cooling, multiple-length hot shearing, straightening and slow cooling on a cooling bed, and shearing. The opening of the water cooling section is 20%. The temperature for straightening and slow cooling of the rolled red steel on the cooling bed is 900–940℃.

[0165] The seismic-resistant straight steel bars prepared by the above method were tested and found to have a yield strength of 680 MPa, a tensile strength of 830 MPa, a strength-to-yield ratio of 1.22, an elongation of 18%, and a maximum force total elongation of 8.8%. The plasticity indicators, elongation and maximum force total elongation, of the steel bars do not meet the standards.

[0166] In summary, this invention provides a seismic-resistant straight steel bar, its preparation method, and its application, which has at least the following advantages:

[0167] This invention controls the alloying elements such as C, Si, Mn, V, and Nb within a narrow range. C, Si, and Mn, as solid solution strengthening elements, fully exert their solid solution strengthening effect in steel bars, ensuring the yield strength of the steel bars. The addition of microalloying elements such as V and Nb can fully exert their grain refinement strengthening and precipitation strengthening effects, thereby improving the yield strength of steel bars. However, excessively high V content has a significant impact on the yield strength of steel bars. In order to prevent excessively high yield strength from leading to an unqualified strength-to-yield ratio and affecting the seismic performance of seismic steel bars, it is necessary to strictly control the amount of V.

[0168] The inventors discovered that excessive nitrogen (N) content can affect the aging of reinforcing steel. While a high N content in steel has almost no impact on the performance of freshly produced steel, its mechanical properties rapidly decline with increasing storage time, affecting its safe use. By controlling the V / N ratio within the aforementioned range, an appropriate amount of N can promote the grain refinement effect of V in the steel, and the combination of N and V can effectively refine the grains in the steel.

[0169] During continuous casting, the superheat of molten steel is controlled within a low range, and the billet is drawn at a low speed. Electromagnetic stirring is maintained during the continuous casting process to prevent compositional segregation during the continuous casting of molten steel into billets, thus ensuring that steel bars with better performance are obtained during the rolling process.

[0170] By controlling the heating temperature of the continuously cast billet, the heating temperature of the billet at the beginning, middle and end, and core surface is uniform in a shorter time, ensuring the solid solution of alloying elements such as V and Nb, and reducing the heating time, thus improving the production efficiency of steel bars.

[0171] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A type of earthquake-resistant straight steel bar, characterized in that, It includes the following elements by weight percentage: C: 0.26~0.28%, Si: 0.55~0.65%, Mn: 1.50~1.60%, S≤0.025%, P≤0.025%, V: 0.120~0.140%, N: 0.019~0.022%, Nb: 0.010~0.020%, with the balance being Fe and unavoidable impurities; V / N ratio is 6.32~6.82; The method for preparing the earthquake-resistant straight steel bar includes: continuously casting molten steel into a continuous casting billet, heating the continuous casting billet to obtain red steel, and rolling the red steel; The continuous casting process includes casting molten steel using electromagnetic stirring and intermediate cooling; the superheat of the molten steel is 15~25℃, the billet pulling speed is 2.5~2.7m / min, and the billet straightening temperature is 980~1050℃. The continuous casting billet heating includes sending the continuous casting billet to a heating furnace for heating. The continuous casting billet passes through a preheating section, a heating section, and a soaking section in sequence. The temperature of the continuous casting billet entering the heating furnace is 400~900℃, the temperature of the preheating section is 900~1100℃, the temperature of the heating section is 1160~1200℃, the temperature of the soaking section is 1170~1200℃, and the total heating time is 65~75min.

2. The seismic-resistant straight steel bar according to claim 1, characterized in that, The steel bars have a yield strength ≥640MPa, tensile strength ≥800MPa, strength-to-yield ratio ≥1.25, elongation ≥14, and total elongation at maximum force ≥9.

0.

3. The seismic-resistant straight steel bar according to claim 2, characterized in that, The yield strength of the steel bars is 645~660MPa, and the tensile strength is 810~840MPa.

4. The seismic-resistant straight steel bar according to claim 1, characterized in that, The specifications of the reinforcing bars are Φ12mm~Φ25mm.

5. The seismic-resistant straight steel bar according to claim 1, characterized in that, The current of electromagnetic stirring is 300-400 A, and the frequency is 3-4 Hz; the cooling water quantity of crystallizer is 155-165 m 3 / h, and the specific water quantity of secondary cooling water is 1.10-1.5 L / Kg.

6. The seismic-resistant straight steel bar according to claim 1, characterized in that, Heating gas includes any one of blast furnace gas, coke oven gas, or a mixture of the two.

7. The seismic-resistant straight steel bar according to claim 6, characterized in that, The calorific value of heating gas is 5016~7524 KJ / m³ 3 .

8. The seismic-resistant straight steel bar according to claim 1, characterized in that, The heating furnace is an air-gas dual-regenerative walking beam heating furnace.

9. The seismic-resistant straight steel bar according to claim 1, characterized in that, Rolling involves sequentially roughing, intermediate rolling, and finishing rolling of red steel.

10. The seismic-resistant straight steel bar according to claim 9, characterized in that, The initial rolling temperature of the red steel is ≥1050℃, and the temperature of the red steel during the rolling process is 1050~1100℃.

11. The seismic-resistant straight steel bar according to claim 9 or 10, characterized in that, The rolling process includes feeding the red steel into a six-stand alternating horizontal and vertical roughing mill for roughing, then shearing it with a No. 1 flying shear, feeding it into a six-stand alternating horizontal and vertical intermediate mill for intermediate rolling, and then shearing it with a No. 2 flying shear, feeding it into a six-stand alternating horizontal and vertical finishing mill for finishing.

12. The seismic-resistant straight steel bar according to claim 1, characterized in that, Before continuous casting, the molten steel also undergoes converter smelting, argon blowing at an argon station, and LF refining.

13. The seismic-resistant straight steel bar according to claim 12, characterized in that, The feed components for the converter smelting include at least one of molten iron, scrap steel, and pig iron.

14. The seismic-resistant straight steel bar according to claim 13, characterized in that, The amount of feed components added in the converter smelting is 158~164t.

15. The seismic-resistant straight steel bar according to claim 12, characterized in that, The C content in the molten steel at the end of the converter smelting process is 0.06~0.12%, P≤0.018%, and the tapping temperature of the molten steel is 1610~1640℃.

16. The seismic-resistant straight steel bar according to claim 15, characterized in that, During the tapping process of molten steel, from 1 / 3 to 3 / 4, Si, Mn, V, N, and Nb elements are added to the molten steel in a specific ratio. The added N element serves as a nitrogen-enhancing agent, and the amount of nitrogen-enhancing agent added is 1.2 × 10⁻⁶ of the molten steel's weight. -3 ~1.4×10 -3 times.

17. The seismic-resistant straight steel bar according to claim 12, characterized in that, The argon blowing time at the argon station is ≥5 minutes. The temperature of the molten steel before argon blowing is 1570~1595℃, and the temperature of the molten steel after argon blowing is ≥1550℃.

18. The seismic-resistant straight steel bar according to claim 12, characterized in that, LF refining includes adding active lime to molten steel to form slag; the amount of active lime added is 400~500 kg / furnace, and the basicity of the molten steel during LF refining is 1.8~2.

4.

19. The seismic-resistant straight steel bar according to claim 18, characterized in that, The refining slag produced by the refining process contains, by weight percentage, 35-45% CaO, 15-25% SiO2 and 8-13% MgO.

20. The seismic-resistant straight steel bar according to claim 1, characterized in that, It also includes finishing the rolled red steel, which includes water cooling, multiple-length hot shearing, cooling bed straightening and slow cooling, and shearing.

21. The seismic-resistant straight steel bar according to claim 20, characterized in that, The opening of the water-cooled section is 1-5%.

22. The seismic-resistant straight steel bar according to claim 20, characterized in that, The temperature at which the rolled red steel is straightened and slowly cooled on the cooling bed is 980~1050℃.

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