Production method of large-size low-niobium HRB400E anti-seismic reinforcing steel

Abstract

The application discloses a production method of large-size low-niobium HRB400E anti-seismic reinforcing steel. The chemical components and the weight percentage are as follows: C: 0.22-0.25 Wt%, Si: 0.45-0.55 Wt%, Mn: 1.35-1.50 Wt%, Nb: 0.008-0.012 Wt%, P: <=0.040 Wt%, S: <=0.040 Wt%, and the balance is Fe and inevitable impurities. The large-size low-niobium HRB400E anti-seismic reinforcing steel is produced by the following process route: converter tapping, ladle argon blowing, continuous casting, step-by-step heating, rough and medium rolling, temperature control cooling before finish rolling, finish rolling, temperature control cooling after finish rolling, cold bed feeding and storage. The scientific component design and the reasonable controlled rolling and controlled cooling process are combined to obtain the large-size low-niobium HRB400E anti-seismic reinforcing steel, the performance of which fully meets the requirements of standard anti-seismic reinforcing steel.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and more specifically, to a method for producing large-diameter low-niobium HRB400E earthquake-resistant steel bars. Background Technology

[0002] Large-diameter HRB400E seismic steel bars are mainly used in railways, highways, high-rise buildings, etc. with heavy loads. They have better ductility than ordinary steel bars when subjected to severe deformation, which can effectively improve the structural stability of buildings and protect people's lives and property.

[0003] The production of large-size HRB400E seismic-resistant steel bars generally employs vanadium microalloying, niobium microalloying, vanadium-nitrogen microalloying, or niobium-vanadium microalloying technologies. However, vanadium microalloying and vanadium-nitrogen microalloying have relatively high alloying costs, and the vanadium content is generally greater than 0.03%. Niobium microalloyed HRB400E hot-rolled ribbed steel bars are prone to non-yielding phenomena, which reduces the performance of the steel bars. Furthermore, cracks often appear on the surface of niobium microalloyed steel continuous casting billets.

[0004] In view of the above problems, it is necessary to provide a production method for large-diameter low-niobium HRB400E seismic-resistant steel bars. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for producing large-size low-niobium HRB400E seismic-resistant steel bars.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] This invention provides a method for producing large-diameter low-niobium HRB400E seismic-resistant steel bars. The chemical composition and weight percentage of the large-diameter low-niobium HRB400E seismic-resistant steel bars are as follows: C: 0.22-0.25 wt%, Si: 0.45-0.55 wt%, Mn: 1.35-1.50 wt%, Nb: 0.008-0.012 wt%, P: ≤0.040 wt%, S: ≤0.040 wt%, with the balance being Fe and unavoidable impurities.

[0008] Large-size low-niobium HRB400E seismic-resistant steel bars are produced using the following method: converter tapping → ladle argon blowing → continuous casting → walking beam heating → roughing and intermediate rolling → pre-finishing temperature control cooling → finish rolling → post-finishing temperature control cooling → cooling bed → collection and storage; wherein, the billet obtained from continuous casting is loaded into the heating furnace for walking beam heating, the heating temperature of the first heating section is controlled at 1000~1100℃, the heating temperature of the second heating section is controlled at 1070~1170℃, the oxygen content in the first and second heating sections is ≤1%, the heating temperature of the soaking section is 1130~1170℃, the oxygen content in the soaking section is 5%~10%, and the furnace pressure of the heating furnace is controlled at 10Pa~30Pa, the total heating time of the billet in the heating furnace is 50~65min;

[0009] The matrix structure of the large-size low-niobium HRB400E seismic steel bars produced is: 54-62% ferrite + 38-46% pearlite, with no chilled layer in the macroscopic metallographic structure.

[0010] The present invention has the following beneficial effects:

[0011] This invention provides a method for producing large-diameter low-niobium HRB400E seismic-resistant steel bars. By controlling the content of each component in the large-diameter low-niobium HRB400E seismic-resistant steel bars and employing a high-temperature rapid heating method for the billet, heating the billet to approximately 1150°C, the pinning effect of niobium carbonitride at the austenite grain boundaries is fully utilized, preventing the growth of original austenite grains, refining the grains, shortening the billet's time in the furnace, improving rolling efficiency, saving energy and reducing consumption, and lowering production costs. Attached Figure Description

[0012] 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.

[0013] Figure 1 Macroscopic metallographic image of large-size low-niobium HRB400E seismic-resistant steel bars produced in an embodiment of the present invention;

[0014] Figure 2 The image shows the microstructure of large-diameter low-niobium HRB400E earthquake-resistant steel bars produced in an embodiment of the present invention. Detailed Implementation

[0015] 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.

[0016] The production of large-size HRB400E seismic-resistant steel bars generally employs vanadium microalloying, niobium microalloying, vanadium-nitrogen microalloying, or niobium-vanadium microalloying technologies. During the heating, controlled rolling, and controlled cooling processes, carbides, nitrides, or carbonitrides are generated in the steel bars, resulting in grain refinement or precipitation strengthening, thereby improving the strength and toughness of the steel bars. Research indicates that niobium is the most effective microalloying element for refining grains. Its refining effect is achieved by controlling the austenite grains during heat treatment and reheating processes. Furthermore, niobium has the characteristic of delaying recrystallization during the austenite deformation process in hot rolling, leading to grain refinement. However, cracks often appear on the surface of niobium microalloyed steel continuously cast billets. This is because the precipitation of niobium carbonitrides in the ferrite matrix or the accumulation of impurities at grain boundaries promotes crack formation. Niobium microalloyed steel is prone to mixed grains and indistinct yield points. Poor matching between controlled rolling and controlled cooling processes and niobium microalloying technology leads to unstable performance.

[0017] Through long-term practice, the inventors have proposed a production method for large-diameter low-niobium HRB400E seismic-resistant steel bars. This method employs scientific composition design, combined with a rationally controlled rolling and cooling process, allowing fine niobium nitrogen and carbides, as second-phase particles, to also play a precipitation strengthening role, thereby improving the tensile strength and yield strength of the steel bars. The produced low-niobium HRB400E seismic-resistant steel bars can effectively utilize the strengthening effect of niobium, avoiding problems such as billet cracking, lack of yield plateau in the steel bars, and reduced plasticity caused by excessive niobium content. This results in large-diameter low-niobium HRB400E seismic-resistant steel bars that meet all performance requirements.

[0018] The following is a detailed description of a production method for large-diameter low-niobium HRB400E seismic-resistant steel bars provided by an embodiment of the present invention.

[0019] The large-size low-niobium HRB400E seismic-resistant steel bars provided in this embodiment of the invention have the following chemical composition and weight percentage: C: 0.22-0.25 wt%, Si: 0.45-0.55 wt%, Mn: 1.35-1.50 wt%, Nb: 0.008-0.012 wt%, P: ≤0.040 wt%, S: ≤0.040 wt%, with the balance being Fe and unavoidable impurities.

[0020] The above embodiments of the present invention provide a large-size low-niobium HRB400E seismic-resistant steel bar, whose composition does not contain vanadium, titanium, chromium, or other strengthening elements, and the added niobium content is very low. This saves on alloy costs, alloy feeding time, and reduces the labor intensity of workers. Furthermore, it prevents excessive temperature drop in molten steel, thus saving energy. Compared with vanadium and titanium, niobium is the most effective in suppressing the growth tendency of austenite grains and the recrystallization of deformed austenite. Studies have shown that, under heat treatment conditions that only consider precipitation strengthening to produce the maximum strength increase, only 50% niobium is needed to achieve the same dispersion strengthening effect compared to vanadium, which can significantly reduce alloy costs.

[0021] Specifically, the functions of each component are as follows:

[0022] (1) C: Carbon content 0.22~0.25Wt%, carbon can dissolve into the matrix and play a solid solution strengthening role. At the same time, it can form more pearlite in steel and improve the strength of steel. The higher the carbon content, the higher the strength of the steel bar.

[0023] (2) Si: The silicon content is 0.45-0.55 wt%. Silicon can be dissolved in ferrite and austenite, and mainly improves the strength of steel bars through solid solution strengthening. Its role is second only to phosphorus, and stronger than elements such as manganese, chromium, tungsten, molybdenum and vanadium. It is also a deoxidizing element in steel. The maximum solubility of silicon in α-iron and γ-iron is 18.5% and 2.15% respectively, and it does not form carbides. Silicon is also an inexpensive element and a basic element to ensure the strength of steel bars. The higher the silicon content, the higher the strength of the steel bars. However, when the content is high, it is not good for the weldability of steel. Due to severe spatter during welding, the weld quality is damaged, and it is easy to cause cold brittleness. When Si>0.55%, the ductility of steel bars is poor, and it may cause cracking when bending.

[0024] (3) Mn: Manganese content 1.35~1.50 wt%. Manganese is a fundamental element for ensuring the strength of reinforcing bars and is one of the main alloying elements of threaded reinforcing bars. It is also a weak deoxidizer. Appropriate amounts of manganese can significantly improve the cold brittleness of steel and increase its yield strength and tensile strength. At the same time, it does not excessively reduce plasticity and impact toughness. Manganese can lower the austenite transformation temperature, refine ferrite grains and reduce the lamellar spacing of pearlite, which is beneficial to improving the strength and toughness of reinforcing bars. It can also strengthen ferrite through solid solution. As the Mn content increases, the strength of the steel also increases. However, when the manganese content is too high, there is a more obvious temper brittleness phenomenon, which will worsen the weldability of the steel and reduce its corrosion resistance.

[0025] (4) Nb: Niobium content 0.008~0.012Wt%. Niobium promotes bainite transformation, so as the niobium content increases, the bainite content increases. Studies have shown that when the bainite content is >10%, the steel bar has no yield plateau, its plasticity decreases, and it is detrimental to the seismic performance of the steel bar. The large-size low-niobium HRB400E seismic steel bar provided in this embodiment of the invention limits the niobium content to 0.008~0.012Wt%. Niobium cannot be dissolved in austenite. During the heating and rolling process of the billet, niobium forms niobium carbonitride with carbon and nitrogen, which segregates at the austenite grain boundaries, effectively inhibiting austenite recrystallization. As a second phase particle, it prevents austenite grain growth and plays a role in grain refinement, thereby improving the strength and toughness of the steel bar. The carbonitride precipitate phase of Nb pins dislocations and inhibits the recovery of austenite during heating and rolling, thereby refining the original austenite grains. The limiting effect of dissolved Nb on C diffusion and its dragging effect on the phase interface restricts ferrite nucleation and growth, thus delaying the γ→α transformation. The precipitation of niobium carbonitrides achieves good precipitation strengthening. The pinning of grain boundaries by carbonitrides and the dragging effect of dissolved Nb atoms on grain boundary movement inhibit the recrystallization of deformed austenite at high temperatures, creating conditions for rolling in the non-recrystallized region.

[0026] Meanwhile, this invention also provides a method for producing the above-mentioned large-size low-niobium HRB400E seismic-resistant steel bars, which uses niobium microalloying and controlled rolling and cooling processes to produce the steel bars.

[0027] The following process route is adopted: top and bottom blowing converter smelting → tapping → ladle argon blowing → 6-machine 6-strand 160mm×160mm square billet continuous casting → walking beam furnace heating → roughing rolling → intermediate rolling → pre-finishing rolling → pre-finishing rolling temperature-controlled cooling → finishing rolling → post-rolling temperature-controlled cooling → cooling bed → collection and warehousing. Specifically:

[0028] Converter smelting, argon blowing, and continuous casting include:

[0029] The smelting process is carried out in a conventional top and bottom combined oxygen converter. Argon is blown throughout the steel tapping process. When the steel is 1 / 4 tapped, silicon manganese, ferrosilicon, ferroniobium and carbon powder are added in sequence for deoxidation and alloying. After the steel ladle arrives at the argon blowing station, the alloy is fine-tuned. At the same time, argon is blown to make the composition and temperature uniform. The argon blowing time is ≥6min.

[0030] The rolling process includes:

[0031] (1) Large-diameter low-niobium HRB400E seismic-resistant steel bars cover Φ20~40mm, Φ20~22mm bi-cut rolling, and Φ25~40mm single-line rolling. The deformation rate and elongation coefficient of each pass are designed based on the temperature and speed of the rolled piece during hot rolling, with an elongation coefficient between 1.09 and 1.47 per pass. The rolling speed for Φ20mm low-niobium HRB400E seismic-resistant steel bars is 12.5m / s, with an elongation coefficient of 1.123~1.465; the rolling speed for Φ22mm low-niobium HRB400E seismic-resistant steel bars is 12m / s, with an elongation coefficient of 1.09~1.434; the rolling speed for Φ25mm low-niobium HRB400E seismic-resistant steel bars is 15m / s, with an elongation coefficient of 1.123~1.465; and the rolling speed for Φ28mm low-niobium HRB400E seismic-resistant steel bars is... The rolling speed for Φ32mm low-niobium HRB400E seismic-resistant steel bars is 13m / s, with an elongation coefficient of 1.16–1.434; the rolling speed for Φ36mm low-niobium HRB400E seismic-resistant steel bars is 6m / s, with an elongation coefficient of 1.123–1.465; and the rolling speed for Φ40mm low-niobium HRB400E seismic-resistant steel bars is 6m / s, with an elongation coefficient of 1.102–1.434. If the elongation coefficient is higher than the above coefficients, the workpiece deformation is greater, the rolling load is higher, the motor power is correspondingly increased, and the requirements for rolling equipment are more stringent. If the elongation coefficient is lower than the above coefficients, the workpiece deformation is smaller, the number of rolling passes increases accordingly, and the number of rolling equipment increases accordingly.

[0032] (2) Billet heating: First heating temperature: 1000~1100℃, second heating temperature: 1070~1170℃, soaking temperature: 1130~1170℃, total heating time: 50~65min. Since the niobium content in large-size low-niobium HRB400E seismic steel bars is not high, the heating rate can be unlimited. A high-temperature rapid heating method is adopted, raising the temperature of the first heating section of the furnace to 1000~1100℃ and the temperature of the second heating section to 1070~1170℃. After the billet enters the furnace, it can directly enter the high-temperature heating zone, and the outer layer of the billet can reach the required production temperature at the fastest heating speed. At the same time, the atmosphere inside the furnace in the first and second heating sections is controlled to be a high-temperature, low-oxygen atmosphere, with the oxygen content of the flue gas ≤1%, which can effectively prevent the rapid oxidation and burning of the billet. The soaking zone uses a furnace temperature of 1130–1170℃ to ensure that the core temperature of the billet quickly reaches the production requirements. The atmosphere inside the soaking zone is controlled to be a high-temperature oxygen-rich atmosphere, with the oxygen content of the flue gas controlled at 5%–10%. This can quickly oxidize the decarburized layer generated when the billet passes through the high-temperature heating zone, and it can be completely peeled off during rolling. The total heating time of the billet in the furnace is shortened to 50–65 minutes, and the furnace pressure is normally controlled within the range of 10Pa–30Pa to ensure a stable atmosphere inside the furnace, shorten the time the billet is in the furnace, and greatly improve production efficiency. If the temperature of the first heating section of the heating furnace is below 1000℃, or the temperature of the second heating section is below 1070℃, or the temperature of the soaking section is below 1130℃, the temperature of the second heating section or the soaking section cannot reach the predetermined temperature quickly, and the billet must be kept in the furnace for a longer period of time, increasing energy consumption. If the temperature of the first heating section of the heating furnace is above 1100℃, or the temperature of the second heating section is above 1170℃, or the temperature of the soaking section is above 1170℃, the billet will be kept in the high-temperature section for too long, resulting in increased oxidation and burning loss, and a decrease in metal yield.

[0033] (3) After the billet exits the heating furnace, it undergoes multiple primary and intermediate rolling passes. During this process, the temperature of the intermediate billet will rise, so temperature control and cooling are necessary. The temperature control device consists of two 6-meter-long water-cooling sections. The first water-cooling section has a water flow rate of 100-140 m³. 3 / h, pressure 1.8~2.2MPa, water flow rate of the second water inlet device 60~110m³ 3 The pressure is 1.8–2.2 MPa, ensuring a cooling rate of 8°C / s–14°C / s, thereby guaranteeing an entry temperature of 920–960°C for the finishing mill. Because this production line is an older type, the temperature control device for the finishing mill is a water-cooled device with limited length, making low-temperature rolling impossible. At the maximum cooling rate before entering the finishing mill, the entry temperature is 920°C. If the cooling rate is less than 8°C / s, the entry temperature will exceed 960°C. This will result in two problems: firstly, coarse austenite grains, reducing the yield strength of the steel reinforcement; secondly, to ensure the subsequent cooling bed temperature, the cooling rate before the cooling bed must be increased, leading to a chilled layer in the macroscopic metallographic structure, resulting in substandard steel reinforcement metallographic characteristics.

[0034] (4) After the intermediate billet undergoes multiple finishing rolling passes, the temperature continues to rise. Before the finished product is placed on the cooling bed, it continues to be cooled under controlled temperature. The temperature control device consists of six water-cooling devices, each 1.3 meters long. By opening the first, second, fifth, and sixth water-cooling devices, the water flow rate of the first and second water-cooling devices is 90-110 m³. 3 / h, pressure 1.8~2.5MPa, water flow rate of the fifth and sixth water inlet sections 30~60m³ 3 The cooling rate is maintained at 1.8–2.5 MPa per hour, with a guaranteed cooling rate of 4–10 °C / s and an upper cooling bed temperature of 880–920 °C. If the cooling rate exceeds 10 °C / s, the upper cooling bed temperature will be lower than 880 °C. This excessively high cooling rate will result in bainite formation during phase transformation. If the bainite content exceeds 10%, the plasticity of the steel reinforcement will decrease, and in severe cases, yield strength will be reduced, and a closed chilling layer will appear in the macroscopic metallographic structure, resulting in substandard metallographic properties. If the cooling rate is less than 4 °C / s, the upper cooling bed temperature will exceed 920 °C. A high upper cooling bed temperature leads to coarse grains in the steel reinforcement, reduced pearlite content, and decreased yield strength.

[0035] (5) After being placed on the cooling bed, the air cooling is carried out on the cooling bed for 450-500 seconds, and then the length is fixed and the bundle is tied.

[0036] Based on the aforementioned niobium microalloying and controlled rolling and cooling technology, the tensile strength R of HRB400E seismic steel bars with a specification of Φ20~40mm was achieved. m ≥610MPa, yield strength R eL ≥435MPa, maximum force total elongation A gt ≥13.5%, R 0 eL / R eL ≤1.21、R 0 m / R 0 eL Grain size ≥1.36, grain size ≥10.0, matrix structure is ferrite + pearlite, macroscopic metallographic structure has no chilled layer. Ferrite accounts for 54-62%, pearlite accounts for 38-46%.

[0037] As can be seen from the above, the embodiments of the present invention provide a production method for large-size low-niobium HRB400E seismic-resistant steel bars. The independently developed low-niobium microalloying and controlled rolling and cooling technology not only significantly improves rolling efficiency but also gives the product advantages in terms of quality. Specifically:

[0038] (1) This invention employs low-niobium microalloying and controlled rolling / cooling technology. By precisely controlling the process parameters of each stage of the HRB400E seismic-resistant steel reinforcement with diameters of Φ20–Φ40mm, the grain refinement and precipitation strengthening effects of niobium microalloying elements are achieved. The lower niobium content in the steel can prevent cracks from forming in the billet during continuous casting, solving the problem of cracks and the mismatch between strength and toughness in niobium-containing rebar billets. The tensile strength R of the HRB400E seismic-resistant steel reinforcement with diameters of Φ20–40mm is increased. m ≥610MPa, yield strength R eL ≥435MPa, maximum force total elongation A gt ≥13.5%, R 0 eL / R eL ≤1.21、R 0 m / R 0 eL Grain size ≥1.36, grain size ≥10.0, matrix structure is ferrite + pearlite, macroscopic metallographic structure has no chilled layer. Ferrite accounts for 54-62%, pearlite accounts for 38-46%.

[0039] (2) By adopting a high-temperature rapid heating method for the billet, the billet is heated to about 1150℃, which fully utilizes the pinning effect of niobium carbonitride at the austenite grain boundaries, prevents the growth of the original austenite grains, refines the grains, shortens the billet time in the furnace, improves rolling efficiency, saves energy and reduces consumption, and lowers production costs.

[0040] The present invention will be further described below with reference to embodiments.

[0041] Example 1

[0042] A large-size low-niobium HRB400E seismic-resistant steel bar has the following chemical composition and weight percentage: C: 0.23 wt%, Si: 0.51 wt%, Mn: 1.46 wt%, Nb: 0.012 wt%, P: 0.025 wt%, S: 0.028 wt%, with the balance being Fe and unavoidable impurities.

[0043] The above-mentioned production method for large-diameter low-niobium HRB400E seismic-resistant steel bars includes the following steps:

[0044] Converter smelting, argon blowing, and continuous casting include:

[0045] The smelting process is carried out in a conventional top and bottom combined oxygen converter. Argon is blown throughout the steel tapping process. When the steel is 1 / 4 tapped, silicon manganese, ferrosilicon, ferroniobium and carbon powder are added in sequence for deoxidation and alloying. After the steel ladle arrives at the argon blowing station, the alloy is fine-tuned. At the same time, argon is blown to make the composition and temperature uniform. The argon blowing time is ≥6min.

[0046] The rolling process includes:

[0047] (1) Specifications cover Φ20mm, rolling speed 12.5m / s, elongation coefficient 1.123~1.465.

[0048] (2) Heating of billet: First heating temperature: 1050℃, second heating temperature: 1150℃, soaking temperature: 1170℃, total heating time: 50min. Because the niobium content in large-size low-niobium HRB400E seismic-resistant steel bars is not high, the heating rate can be unlimited. A high-temperature rapid heating method is adopted, raising the temperature of the first heating section of the heating furnace to 1050℃ and the temperature of the second heating section to 1150℃. After the billet enters the furnace, it can directly enter the high-temperature heating zone. The outer layer of the billet can reach the temperature required for production at the fastest speed. At the same time, the atmosphere inside the furnace in the first and second heating sections is controlled as a high-temperature, low-oxygen atmosphere, with an oxygen content of 0.7% in the flue gas, which can effectively prevent the billet from rapid oxidation and burning. The soaking zone uses a furnace temperature of 1170℃ to ensure that the temperature of the billet core reaches the production requirement quickly. The atmosphere inside the soaking zone is controlled as a high-temperature, oxygen-rich atmosphere, with an oxygen content of 0.7% in the flue gas, which can quickly oxidize the decarburized layer generated when the billet passes through the high-temperature heating zone, and it can be completely peeled off during the rolling process. The total heating time of the billet in the furnace is shortened to 50 minutes, and the furnace pressure is normally controlled at 10Pa to ensure a stable atmosphere inside the furnace and shorten the time the billet is in the furnace.

[0049] (3) After the billet exits the heating furnace, it undergoes multiple primary and intermediate rolling passes. During this process, the temperature of the intermediate billet will rise, so temperature control and cooling are necessary. The temperature control device consists of two 6-meter-long water-cooling sections. The first water-cooling section has a water flow rate of 100m³. 3 / h, pressure 1.8MPa, water flow rate of the second water inlet device 60m³ / h 3 / h, pressure 1.8MPa, ensuring a cooling rate of 8℃ / s, thereby ensuring an entry temperature of 960℃ into the finishing mill.

[0050] (4) After the intermediate billet undergoes multiple finishing rolling passes, the temperature continues to rise. Before the finished product is placed on the cooling bed, it continues to be cooled under controlled temperature. The temperature control device consists of six water-cooling devices, each 1.3 meters long. By opening the first, second, fifth, and sixth water-cooling devices, the water flow rate of the first and second water-cooling devices is 90 m³ / s. 3 / h, pressure 1.8MPa, water flow rate of the fifth and sixth water inlet sections 30m³ / h 3 / h, pressure 1.8MPa, ensuring a cooling rate of 4℃ / s, and upper cooling bed temperature of 900℃.

[0051] (5) After being placed on the cooling bed, the air cooling is carried out on the cooling bed for 450 seconds, and then the length is fixed and the bundle is tied.

[0052] Example 2

[0053] A large-size low-niobium HRB400E seismic-resistant steel bar has the following chemical composition and weight percentage: C: 0.23 wt%, Si: 0.48 wt%, Mn: 1.44 wt%, Nb: 0.008 wt%, P: 0.031 wt%, S: 0.025 wt%, with the balance being Fe and unavoidable impurities.

[0054] The above-mentioned production method for large-diameter low-niobium HRB400E seismic-resistant steel bars includes the following steps:

[0055] Converter smelting, argon blowing, and continuous casting include:

[0056] The smelting process is carried out in a conventional top and bottom combined oxygen converter. Argon is blown throughout the steel tapping process. When the steel is 1 / 4 tapped, silicon manganese, ferrosilicon, ferroniobium and carbon powder are added in sequence for deoxidation and alloying. After the steel ladle arrives at the argon blowing station, the alloy is fine-tuned. At the same time, argon is blown to make the composition and temperature uniform. The argon blowing time is ≥6min.

[0057] The rolling process includes:

[0058] (1) Specifications cover Φ25mm, rolling speed 15m / s, elongation coefficient 1.123~1.465.

[0059] (2) Heating of billet: First heating temperature: 1060℃, second heating temperature: 1125℃, soaking temperature: 1143℃, total heating time: 58min. Because the niobium content in large-size low-niobium HRB400E seismic-resistant steel bars is not high, the heating rate can be unlimited. A high-temperature rapid heating method is adopted, raising the temperature of the first heating section of the heating furnace to 1060℃ and the temperature of the second heating section to 1125℃. After the billet enters the furnace, it can directly enter the high-temperature heating zone. The outer layer of the billet can reach the temperature required for production at the fastest speed. At the same time, the atmosphere inside the furnace in the first and second heating sections is controlled as a high-temperature, low-oxygen atmosphere, with an oxygen content of 0.8% in the flue gas, which can effectively prevent the billet from rapid oxidation and burning. The soaking zone uses a furnace temperature of 1143℃ to ensure that the temperature of the billet core reaches the production requirement quickly. The atmosphere inside the soaking zone is controlled as a high-temperature, oxygen-rich atmosphere, with an oxygen content of 8% in the flue gas, which can quickly oxidize the decarburized layer generated when the billet passes through the high-temperature heating zone, and it can be completely peeled off during rolling. The total heating time of the billet in the furnace is shortened to 58 minutes, and the furnace pressure is normally controlled at 20Pa to ensure a stable atmosphere inside the furnace and shorten the time the billet is in the furnace.

[0060] (3) After the billet exits the heating furnace, it undergoes multiple primary and intermediate rolling passes. During this process, the temperature of the intermediate billet will rise, so temperature control and cooling are necessary. The temperature control device consists of two 6-meter-long water-cooling sections. The first water-cooling section has a water flow rate of 110m³. 3 / h, pressure 1.9MPa, water flow rate of the second water inlet device 70m³ / h 3 / h, pressure 1.9MPa, ensuring a cooling rate of 10℃ / s, thereby ensuring an entry temperature of 945℃ into the finishing mill.

[0061] (4) After the intermediate billet undergoes multiple finishing rolling passes, the temperature continues to rise. Before the finished product is placed on the cooling bed, it continues to be cooled under controlled temperature. The temperature control device consists of six water-cooling devices, each 1.3 meters long. By opening the first, second, fifth, and sixth water-cooling devices, the water flow rate of the first and second water-cooling devices is 100 m³ / s. 3 / h, pressure 1.9MPa, water flow rate of the fifth and sixth water inlet sections 40m³ / h 3 / h, pressure 1.9MPa, ensuring a cooling rate of 7℃ / s, and upper cooling bed temperature of 890℃.

[0062] (5) After being placed on the cooling bed, the air cooling is carried out on the cooling bed for 470 seconds, and then the length is fixed and the bundle is tied.

[0063] Example 3

[0064] A large-size low-niobium HRB400E seismic-resistant steel bar has the following chemical composition and weight percentage: C: 0.24 wt%, Si: 0.52 wt%, Mn: 1.38 wt%, Nb: 0.011 wt%, P: 0.028 wt%, S: 0.027 wt%, with the balance being Fe and unavoidable impurities.

[0065] The above-mentioned production method for large-diameter low-niobium HRB400E seismic-resistant steel bars includes the following steps:

[0066] Converter smelting, argon blowing, and continuous casting include:

[0067] The smelting process is carried out in a conventional top and bottom combined oxygen converter. Argon is blown throughout the steel tapping process. When the steel is 1 / 4 tapped, silicon manganese, ferrosilicon, ferroniobium and carbon powder are added in sequence for deoxidation and alloying. After the steel ladle arrives at the argon blowing station, the alloy is fine-tuned. At the same time, argon is blown to make the composition and temperature uniform. The argon blowing time is ≥6min.

[0068] The rolling process includes:

[0069] (1) Specifications cover Φ32mm, rolling speed 9m / s, elongation coefficient 1.163~1.434.

[0070] (2) Heating of billet: First heating temperature: 1070℃, second heating temperature: 1140℃, soaking temperature: 1145℃, total heating time: 62min. Because the niobium content in large-size low-niobium HRB400E seismic-resistant steel bars is not high, the heating rate can be unlimited. A high-temperature rapid heating method is adopted, raising the temperature of the first heating section of the heating furnace to 1070℃ and the temperature of the second heating section to 1140℃. After the billet enters the furnace, it can directly enter the high-temperature heating zone. The outer layer of the billet can reach the temperature required for production at the fastest speed. At the same time, the atmosphere inside the furnace in the first and second heating sections is controlled as a high-temperature, low-oxygen atmosphere, with an oxygen content of 0.9% in the flue gas, which can effectively prevent the billet from rapid oxidation and burning. The soaking zone uses a furnace temperature of 1145℃ to ensure that the temperature of the billet core reaches the production requirement quickly. The atmosphere inside the soaking zone is controlled as a high-temperature, oxygen-rich atmosphere, with an oxygen content of 8% in the flue gas, which can quickly oxidize the decarburized layer generated when the billet passes through the high-temperature heating zone, and it can be completely peeled off during the rolling process. The total heating time of the billet in the furnace is shortened to 62 minutes, and the furnace pressure is normally controlled at 25Pa to ensure a stable atmosphere inside the furnace and shorten the time the billet is in the furnace.

[0071] (3) After the billet exits the heating furnace, it undergoes multiple primary and intermediate rolling passes. During this process, the temperature of the intermediate billet will rise, so temperature control and cooling are necessary. The temperature control device consists of two 6-meter-long water-cooling sections. The first water-cooling section has a water flow rate of 120m³. 3 / h, pressure 2.0MPa, water flow rate of the second water inlet device 90m³ / h 3 / h, pressure 2.1MPa, ensuring a cooling rate of 12℃ / s, thereby ensuring an entry temperature of 940℃ into the finishing mill.

[0072] (4) After the intermediate billet undergoes multiple finishing rolling passes, the temperature continues to rise. Before the finished product is placed on the cooling bed, it continues to be cooled under controlled temperature. The temperature control device consists of six water-cooling devices, each 1.3 meters long. By opening the first, second, fifth, and sixth water-cooling devices, the water flow rate of the first and second water-cooling devices is 100 m³ / s. 3 / h, pressure 2.3MPa, water flow rate of the fifth and sixth water inlet sections 50m³ / h 3 / h, pressure 2.2MPa, ensuring a cooling rate of 7℃ / s, and upper cooling bed temperature of 880℃.

[0073] (5) After being placed on the cooling bed, the air cooling is carried out on the cooling bed for 480 seconds, and then the length is fixed and the bundle is tied.

[0074] Example 4

[0075] A large-size low-niobium HRB400E seismic-resistant steel bar has the following chemical composition and weight percentage: C: 0.25 wt%, Si: 0.54 wt%, Mn: 1.48 wt%, Nb: 0.012 wt%, P: 0.034 wt%, S: 0.030 wt%, with the balance being Fe and unavoidable impurities.

[0076] The above-mentioned production method for large-diameter low-niobium HRB400E seismic-resistant steel bars includes the following steps:

[0077] Converter smelting, argon blowing, and continuous casting include:

[0078] The smelting process is carried out in a conventional top and bottom combined oxygen converter. Argon is blown throughout the steel tapping process. When the steel is 1 / 4 tapped, silicon manganese, ferrosilicon, ferroniobium and carbon powder are added in sequence for deoxidation and alloying. After the steel ladle arrives at the argon blowing station, the alloy is fine-tuned. At the same time, argon is blown to make the composition and temperature uniform. The argon blowing time is ≥6min.

[0079] The rolling process includes:

[0080] (1) Specifications cover Φ40mm, rolling speed 6m / s, elongation coefficient 1.102~1.434.

[0081] (2) Heating of billet: First heating temperature: 1080℃, second heating temperature: 1130℃, soaking temperature: 1155℃, total heating time: 65min. Because the niobium content in large-size low-niobium HRB400E seismic-resistant steel bars is not high, the heating rate can be unlimited. A high-temperature rapid heating method is adopted, raising the temperature of the first heating section of the heating furnace to 1080℃ and the temperature of the second heating section to 1130℃. After the billet enters the furnace, it can directly enter the high-temperature heating zone. The outer layer of the billet can reach the temperature required for production at the fastest speed. At the same time, the atmosphere inside the furnace in the first and second heating sections is controlled as a high-temperature, low-oxygen atmosphere, with an oxygen content of 0.9% in the flue gas, which can effectively prevent the billet from rapid oxidation and burning. The soaking zone uses a furnace temperature of 1155℃ to ensure that the temperature of the billet core reaches the production requirement quickly. The atmosphere inside the soaking zone is controlled as a high-temperature, oxygen-rich atmosphere, with an oxygen content of 8% in the flue gas, which can quickly oxidize the decarburized layer generated when the billet passes through the high-temperature heating zone, and it can be completely peeled off during the rolling process. The total heating time of the billet in the furnace is shortened to 65 minutes, and the furnace pressure is normally controlled at 28Pa to ensure a stable atmosphere inside the furnace and shorten the time the billet is in the furnace.

[0082] (3) After the billet exits the heating furnace, it undergoes multiple primary and intermediate rolling passes. During this process, the temperature of the intermediate billet will rise, so temperature control and cooling are necessary. The temperature control device consists of two 6-meter-long water-cooling sections. The first water-cooling section has a water flow rate of 140m³. 3 / h, pressure 2.1MPa, water flow rate of the second water inlet device 110m³ / h 3 / h, pressure 2.1MPa, ensuring a cooling rate of 14℃ / s, thereby ensuring an entry temperature of 920℃ into the finishing mill.

[0083] (4) After the intermediate billet undergoes multiple finishing rolling passes, the temperature continues to rise. Before the finished product is placed on the cooling bed, it continues to be cooled under controlled temperature. The temperature control device consists of six water-cooling devices, each 1.3 meters long. By opening the first, second, fifth, and sixth water-cooling devices, the water flow rate of the first and second water-cooling devices is 110 m³ / s.3 / h, pressure 2.4MPa, water flow rate of the fifth and sixth water inlet sections 55m³ / h 3 / h, pressure 2.2MPa, ensuring a cooling rate of 10℃ / s, and upper cooling bed temperature of 885℃.

[0084] (5) After being placed on the cooling bed, the air cooling is carried out on the cooling bed for 500 seconds, and then the length is fixed and the bundle is tied.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that the large-diameter low-niobium HRB400E seismic-resistant steel bar has a Nb content of 0.007Wt in its chemical composition.

[0087] Comparative Example 2

[0088] The difference from Example 1 is that in the temperature control step before entering the finishing mill, the water flow rate of the first water-passing device is 90m³. 3 / h, pressure 1.7MPa, water flow rate of the second water inlet device 50m³ / h 3 / h, pressure 1.7MPa, cooling rate 7℃ / s, and the temperature of the feed mill is 970℃.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that in the temperature control step before entering the finishing mill, the water flow rate of the first water-passing device is 145m³. 3 / h, pressure 2.3MPa, water flow rate of the second water inlet device 115m³ / h 3 / h, pressure 2.3MPa, cooling rate 15℃ / s, temperature of the feed into the finishing mill is 910℃.

[0091] Comparative Example 4

[0092] The difference from Example 1 is that, in the temperature control step before the upper cooling bed, the water volume of the first and second water inlet sections is 85m³. 3 / h, pressure 1.7MPa, water flow rate of the fifth and sixth water inlet sections 25m³ / h 3 / h, pressure 1.7MPa, cooling rate 3℃ / s, upper cooling bed temperature 925℃.

[0093] Comparative Example 5

[0094] The difference from Example 1 is that, in the temperature control step before the upper cooling bed, the water volume of the first and second water inlet sections is 115m³. 3 / h, pressure 2.6MPa, water flow rate of the fifth and sixth water inlet sections 65m³ / h 3 / h, pressure 2.6MPa, cooling rate 11℃ / s, upper cooling bed temperature 865℃.

[0095] Test Results

[0096] The macroscopic metallographic image of the large-diameter low-niobium HRB400E seismic-resistant steel bars produced in this embodiment of the invention is shown below. Figure 1 ,Depend on Figure 1 It can be seen that: the macroscopic metallographic structure shows no chilled layer; the microscopic metallographic image of the large-diameter low-niobium HRB400E seismic-resistant steel bar is shown below. Figure 2 ,Depend on Figure 2 It can be seen that the microstructure consists of ferrite and pearlite. As can be seen from the macro and micro metallographic images, the internal structure of the large-size low-niobium HRB400E seismic steel bar prepared in the embodiment of the present invention fully meets the requirements of standard seismic steel bars.

[0097] The test results of the reinforcing bars obtained in Examples 1-4 and Comparative Examples 1-5 are shown in the table below:

[0098]

[0099] As can be seen from the table above, the large-diameter low-niobium HRB400E seismic-resistant steel bars prepared in the embodiments of the present invention fully meet the standard requirements. When the chemical composition is different or the rolling process changes, the mechanical properties and microstructure of the steel bars are different. When the cooling rate is too high, the macroscopic metallographic structure of the steel bars has a chilled layer; when the cooling rate is too low, the mechanical properties of the steel bars decrease significantly.

[0100] In summary, this invention provides a method for producing large-diameter low-niobium HRB400E seismic-resistant steel bars. The chemical composition and weight percentage of these bars are as follows: C: 0.22–0.25 wt%, Si: 0.45–0.55 wt%, Mn: 1.35–1.50 wt%, Nb: 0.008–0.012 wt%, P: ≤0.040 wt%, S: ≤0.040 wt%, with the balance being Fe and unavoidable impurities. The process route is as follows: “Top and bottom blowing converter smelting → tapping → ladle argon blowing → 6-machine 6-strand 160mm×160mm square billet continuous casting → walking beam furnace heating → rough rolling → intermediate rolling → pre-finishing rolling → pre-finishing rolling temperature-controlled cooling → finishing rolling → post-rolling temperature-controlled cooling → cooling bed → collection and warehousing.” Compared with traditional vanadium microalloying, niobium microalloying, vanadium-nitrogen microalloying, or niobium-vanadium microalloying, the production method of large-size low-niobium HRB400E seismic-resistant steel bars provided in this invention adopts low-niobium microalloying and controlled rolling and cooling technology. By precisely controlling the process parameters of each process for HRB400E seismic-resistant steel bars with diameters of Φ20~Φ40mm, the grain refinement and precipitation strengthening effects of niobium microalloying elements are achieved, effectively solving the problems of cracks, indistinct yield plateaus, or insufficient mechanical properties in niobium-containing rebar billets. By adopting a high-temperature rapid heating method for the billet, the billet's time in the furnace is shortened, rolling efficiency is improved, and production costs are reduced.

[0101] 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 method for producing large-diameter low-niobium HRB400E seismic-resistant steel bars, characterized in that, The chemical composition and weight percentage of the large-size low-niobium HRB400E seismic steel bars are as follows: C: 0.22~0.25Wt%, Si: 0.45~0.55Wt%, Mn: 1.35~1.50Wt%, Nb: 0.008~0.012Wt%, P: ≤0.040Wt%, S: ≤0.040Wt, with the balance being Fe and unavoidable impurities; The large-size low-niobium HRB400E seismic-resistant steel bars are produced using the following method: converter tapping → ladle argon blowing → continuous casting → walking beam heating → roughing and intermediate rolling → pre-finishing temperature control cooling → finish rolling → post-finishing temperature control cooling → cooling bed → collection and storage; wherein, the billet obtained from continuous casting is loaded into a heating furnace for walking beam heating, the heating temperature of the first heating section is controlled at 1000~1100℃, the heating temperature of the second heating section is controlled at 1070~1170℃, the oxygen content in the first and second heating sections is ≤1%, the heating temperature of the soaking section is 1130~1170℃, the oxygen content in the soaking section is 5%~10%, and the furnace pressure of the heating furnace is controlled at 10Pa~30Pa, the total heating time of the billet in the heating furnace is 50~65min; The temperature control and cooling process before finishing rolling includes: the temperature control device uses two water purifiers, each 6 meters long. The water flow rate of the first water purifier is controlled at 100~140 m³ / h and the pressure at 1.8~2.2 MPa, while the water flow rate of the second water purifier is controlled at 60~110 m³ / h and the pressure at 1.8~2.2 MPa, ensuring a cooling rate of 8℃ / s~14℃ / s, so that the billet temperature entering the finishing mill is 920~960℃. The temperature control and cooling process after finishing rolling includes: the temperature control device uses 6 sections of water purifier, each 1.3 meters long, with the first, second, fifth, and sixth sections of the water purifier opened and the third and fourth sections closed. The water flow rate of the first and second sections of the water purifier is controlled at 90~110 m³ / h and the pressure at 1.8~2.5 MPa, while the water flow rate of the fifth and sixth sections of the water purifier is controlled at 30~60 m³ / h and the pressure at 1.8~2.5 MPa, ensuring a cooling rate of 4℃ / s~10℃ / s, so that the temperature of the billet on the cooling bed is 880~920℃. The matrix structure of the large-size low-niobium HRB400E seismic steel bars produced is 54~62% ferrite + 38~46% pearlite, with no chilled layer in the macroscopic metallographic structure.

2. The production method according to claim 1, characterized in that, The process of converter smelting, ladle argon blowing and continuous casting includes: smelting in a conventional top and bottom combined oxygen converter, argon blowing throughout the steel tapping process, adding ferrosilicon manganese, ferrosilicon, ferroniobium and carbon powder in sequence when 1 / 4 of the steel is tapped for deoxidation and alloying, fine-tuning of the alloy after the ladle arrives at the argon station, and blowing argon at the same time to make the composition and temperature uniform, with a blowing time of ≥6min.

3. The production method according to claim 1, characterized in that, The specifications of the large-diameter low-niobium HRB400E seismic-resistant steel bars cover Φ20~40mm. During the rolling process, Φ20~22mm is rolled in two sections, and Φ25~40mm is rolled in a single line.

4. The production method according to claim 3, characterized in that, The rolling speed and elongation coefficient of low-niobium HRB400E seismic-resistant steel bars with specifications of Φ20~22mm are set as follows: the rolling speed of low-niobium HRB400E seismic-resistant steel bars with specifications of Φ20mm is 12.5m / s, and the elongation coefficient is 1.123~1.465; the rolling speed of low-niobium HRB400E seismic-resistant steel bars with specifications of Φ22mm is 12m / s, and the elongation coefficient is 1.09~1.

434.

5. The production method according to claim 3, characterized in that, The rolling speed and elongation coefficient of low-niobium HRB400E seismic-resistant steel bars with specifications of Φ25~40mm are set as follows: Φ25mm low-niobium HRB400E seismic-resistant steel bars: rolling speed 15m / s, elongation coefficient 1.123~1.465; Φ28mm low-niobium HRB400E seismic-resistant steel bars: rolling speed 13m / s, elongation coefficient 1.16~1.434; Φ32mm low-niobium HRB400E seismic-resistant steel bars: rolling speed 9m / s, elongation coefficient 1.163~1.434; Φ36mm low-niobium HRB400E seismic-resistant steel bars: rolling speed 6m / s, elongation coefficient 1.123~1.465; Φ40mm low-niobium HRB400E seismic-resistant steel bars: rolling speed 6m / s, elongation coefficient 1.102~1.

434.

6. The production method according to claim 1, characterized in that, The process of placing the billet on the cooling bed includes: after the billet is placed on the cooling bed, it is air-cooled on the cooling bed for 450-500 seconds, and then it is cut to length and bundled.

7. The production method according to any one of claims 1-6, characterized in that, The tensile strength R of the large-size HRB400E seismic-resistant steel bars m ≥610MPa, yield strength R eL ≥435MPa, maximum force total elongation A gt ≥13.5%, R 0 eL / R eL ≤1.21、R 0 m / R 0 eL ≥1.

36.

8. The production method according to any one of claims 1-6, characterized in that, The large-size HRB400E seismic-resistant steel bars have a grain size of grade 10.0 or higher.

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