Cu-containing weather-resistant high-strength anti-seismic Korean standard steel bar and use thereof

Abstract

This invention belongs to the field of metallurgical technology, specifically relating to a high-strength, earthquake-resistant, and Cu-containing steel bar conforming to Korean standards, its preparation method, and its applications. The elemental composition of this steel bar, by mass percentage, is: C: 0.32%~0.37%, Si: 0.20%~0.30%, Mn: 1.65%~1.80%, P: 0.01%~0.02%, S: 0.01%~0.02%, V: 0.15%~0.16%, Nb: 0.015%~0.02%, Cu: 0.20%~0.25%, with the balance being Fe and unavoidable impurities. Through improvements in the elemental composition and technological advancements such as low superheat, weak secondary cooling water flow, and lower drawing speed, this steel bar achieves excellent compressive strength, yield strength, earthquake resistance, and corrosion resistance, making it suitable for use in environments with high earthquake resistance requirements or in corrosive conditions such as coastal areas.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a high-strength, earthquake-resistant, Cu-containing steel bar conforming to Korean standards and its applications. Background Technology

[0002] With the market's increasing demand for upgraded hot-rolled ribbed steel bars, some major projects have placed higher requirements on the seismic resistance and other properties of the steel bars. CN107974628A discloses a Korean standard SD500S.D10~D41 specification steel bar and its production method, which can meet the quality requirements of Korean standard KSD3504:2016 Bars for Reinforced Concrete. CN106756556A discloses a Korean standard SD400 ribbed threaded steel bar and its production method, achieving low-cost production of Korean standard SD400 ribbed threaded steel bars with qualified performance and excellent bending properties. However, the above-mentioned steel bars lack corrosion resistance and other disadvantages.

[0003] Therefore, developing high-strength, earthquake-resistant, and corrosion-resistant Korean standard steel bars will help meet the special performance requirements of steel bars in coastal areas and earthquake-prone regions. Summary of the Invention

[0004] To address the above problems, the purpose of this invention is to provide a high-strength, weather-resistant, earthquake-resistant steel bar containing Cu, conforming to Korean standards, and its applications.

[0005] A high-strength, weather-resistant, earthquake-resistant Korean standard steel bar containing Cu, wherein the elemental composition of the Korean standard steel bar, by mass percentage, is: C: 0.32%~0.37%, Si: 0.20%~0.30%, Mn: 1.65%~1.80%, P: 0.01%~0.02%, S: 0.01%~0.02%, V: 0.15%~0.16%, Nb: 0.015%~0.02%, Cu: 0.20%~0.25%, with the balance being Fe and unavoidable impurities.

[0006] Preferably, the elemental composition of the Korean standard steel bar is: C: 0.33%~0.37%, Si: 0.20%~0.30%, Mn: 1.70%~1.80%, P: 0.01%~0.02%, S: 0.01%~0.02%, V: 0.15%~0.16%, Nb: 0.017%~0.02%, Cu: 0.23%~0.25%, with the balance being Fe and unavoidable impurities.

[0007] In another aspect, the present invention provides a method for preparing the aforementioned Korean standard steel bars, specifically comprising the following steps:

[0008] Step S1 LF refining and alloying:

[0009] The ladle is placed in the refining position, where calcium carbide, calcium aluminate, lime, and iron oxide scale are added to the molten steel in the LF refining furnace. Nitrogen is used for blowing, with a nitrogen flow rate of 100~140 NL / min per ton of steel and a total nitrogen blowing time of 8~12 min. After fine-tuning the composition at the argon blowing station, the argon flow rate is 80 NL / min for strong argon blowing for 1.5~3 min. Then, the argon flow rate is adjusted to 40 NL / min for bottom blowing to weak blowing. High carbon ferrochrome is then fed in, and after adding carbonized rice husks, the argon flow rate is maintained at 20 NL / min for weak blowing for 5 min.

[0010] Aluminum cakes are then fed in for pre-deoxidation, gradually whitening the slag using a CaO-Al2O3-SiO2-MgO slag system. After refining the white slag and adjusting its composition, a slag-changing operation is performed to reduce the slag basicity R to below 1.15. Molten steel is obtained at a tap temperature of 1600℃.

[0011] Step S2: The molten steel obtained in step 1 is fed into a continuous casting machine for continuous casting to obtain a continuously cast steel billet;

[0012] S21: The molten steel after LF treatment is continuously cast. Protective casting is used throughout the continuous casting process, with the long nozzle and submerged nozzle argon-sealed to prevent secondary oxidation of the molten steel during casting. The long nozzle is inserted to a depth of 200~300mm to ensure a stable molten steel level.

[0013] S22: The production process adopts low superheat, weak secondary cooling water volume, and low casting speed. The overall superheat of continuous casting is 20℃~23℃, and the specific water volume is controlled at 0.25~0.29L / kg. According to the superheat of molten steel, the billet casting speed is controlled by the stopper rod of the tundish. The average casting speed is 2~3m / min, which fully ensures the surface quality of the continuous casting billet. The straightening temperature is controlled at 1050~1070℃.

[0014] Stirring was performed using an electromagnetic stirring device in the crystallizer and an electromagnetic stirring device at the end. The electromagnetic stirring parameters in the crystallizer were 3Hz frequency and 225A current; the electromagnetic stirring parameters at the end were 10Hz frequency and 300A current; the cooling water flow rate in the crystallizer was 2100~2300L / min; simultaneous secondary cooling was performed during continuous casting, with a specific water flow rate of 0.25~0.29L / Kg. Strong cooling was used to refine and control the dendritic structure of the billet, thereby improving low-magnification structures such as center segregation and center porosity, and controlling the center C segregation to ≤1.05.

[0015] By controlling the straightening temperature in step 2, the generation of cracks during the straightening stage can be reduced. Production verification showed that the continuously cast billet had no squarening or rhomboid deformation, the pickled surface had no cracks, and the entire surface of the low-magnification test piece was free of various crack defects.

[0016] Step S3: Inspect the continuously cast steel billet. After pickling, if the billet has no longitudinal cracks, transverse cracks, or corner cracks on the surface; and the central porosity, central segregation, and central shrinkage cavity are all ≤2.0 grade, then the billet is deemed qualified; otherwise, it is deemed unqualified.

[0017] Step S4: The qualified steel billet is sent into the heating furnace for heating. The temperature range of the heating furnace during the heating process is 1150℃~1250℃.

[0018] Step S5: Rolling is carried out using continuous rolling. The roughing temperature is set to 1050℃~1150℃, the intermediate rolling temperature to 1000℃~1100℃, and the finishing rolling temperature to 1050℃~1150℃ to obtain steel bars.

[0019] Step S6: Cool the steel bars on a cooling bed. The temperature range during the cooling process is 280℃~1070℃ to obtain the finished product.

[0020] The above-mentioned steel bars are suitable for use in coastal construction conditions, especially in coastal areas with high seismic resistance requirements.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) This invention breaks the current upper limit requirements for C and Mn content in steel, while controlling the upper limit of Si content. Through the niobium-vanadium composite microalloying strengthening process, the strength and toughness of the steel bar are improved by adding microalloys to improve the strength-to-yield ratio of the steel bar. Adding more than 0.20% copper element will increase the probability of cracks in the steel billet, but by scientifically and reasonably matching the proportion of each element, good weather resistance is still achieved. At the same time, cracks are well suppressed by setting and matching the superheat, drawing speed and water cooling parameters of each section.

[0023] (2) The prominent role of phosphorus (P) is to improve the atmospheric corrosion resistance of ordinary low-alloy steel, especially when used in combination with copper (Cu). The combination of 0.2% Cu and less than 0.040% P significantly improves weather resistance. However, increasing the Cu content increases the probability of cracks in the billet. In high-temperature castings, due to Fe oxidation, a Cu-rich phase forms under the FeO layer, which then forms a liquid phase that travels along the grain boundaries. This invention makes significant improvements in the preparation process, significantly improving the surface quality of continuously cast billets through production processes such as low superheat, weak secondary cooling water flow, and lower casting speed. Attached Figure Description

[0024] Figure 1 Macroscopic morphology of the sample from Example 1, obtained after 72 hours of accelerated corrosion;

[0025] Figure 2 Macroscopic morphology of Comparative Example 1 sample after 72 hours of accelerated corrosion. Detailed Implementation

[0026] The technical solutions and effects of the present invention will be shown and explained below with reference to specific embodiments, comparative examples, and accompanying drawings. These embodiments are only for illustrating the technical solutions of the present invention and are not intended to limit the scope of protection.

[0027] This invention provides a high-strength, weather-resistant, earthquake-resistant Korean standard steel bar containing Cu and its preparation method. The elemental composition of the Korean standard steel bar, by mass percentage, is: C: 0.32%~0.37%, Si: 0.20%~0.30%, Mn: 1.65%~1.80%, P: 0.01%~0.02%, S: 0.01%~0.02%, V: 0.15%~0.16%, Nb: 0.015%~0.02%, Cu: 0.20%~0.25%, with the balance being Fe and unavoidable impurities.

[0028] The preparation method of this Korean standard steel bar includes:

[0029] Step S1 LF refining and alloying:

[0030] The ladle is placed in the refining position, where calcium carbide, calcium aluminate, lime, and iron oxide scale are added to the molten steel in the LF refining furnace. Nitrogen is used for blowing, with a nitrogen flow rate of 100~140 NL / min per ton of steel (120 NL / min per ton of steel is used in the following specific examples and comparative examples), and a total nitrogen blowing time of 8~12 min (10 min in the following specific examples and comparative examples). After fine-tuning the composition at the argon blowing station, the argon flow rate is 80 NL / min for strong argon blowing for 1.5~3 min (2 min in the following specific examples and comparative examples). Then, the argon flow rate is adjusted to 40 NL / min for bottom blowing to weak blowing, and high-carbon ferrochrome (high-carbon ferrochrome contains 6.5% carbon, 51% chromium, <0.04% phosphorus, <0.03% sulfur, and the remainder is iron and unavoidable impurities) is fed in. After adding carbonized rice husks, the argon flow rate is maintained at 20 NL / min for weak blowing for 5 min.

[0031] Aluminum cakes are then fed in for pre-deoxidation, gradually whitening the slag using a CaO-Al2O3-SiO2-MgO slag system. After refining the white slag and adjusting its composition, a slag-changing operation is performed to reduce the slag basicity R to below 1.15. Molten steel is obtained at a tap temperature of 1600℃.

[0032] Step 1 enables deoxidation control throughout the refining process, keeping the oxygen content in the steel below 20 ppm to increase the nitrogen content and reduce the number of non-deformable inclusions. It also promotes sufficient plasticization of inclusions, resulting in low-melting-point deformable inclusions. Simultaneously, ensuring a sufficient soft-blowing time of ≥8 minutes allows inclusions to float to the surface. The adsorption and modification by the top slag not only effectively reduces the total number of inclusions but also yields finer inclusions; the size of inclusions in the finished steel bars is generally less than 30 μm.

[0033] Step S2: The molten steel obtained in step 1 is fed into a continuous casting machine for continuous casting to obtain a continuously cast steel billet;

[0034] S21: The molten steel after LF treatment is continuously cast. Protective casting is used throughout the continuous casting process, with the long nozzle and submerged nozzle argon-sealed to avoid secondary oxidation during the casting process. The insertion depth of the long nozzle is 200~300mm (270mm is used in the following specific embodiments and comparative examples) to ensure the stability of the molten steel level.

[0035] S22: The production process adopts low superheat, weak secondary cooling water volume, and low casting speed. The overall superheat of continuous casting is 20℃~23℃ (22±1℃ in the specific embodiments and comparative examples below), and the specific water volume is controlled at 0.25~0.29L / kg (0.26 L / kg in the specific embodiments and comparative examples below). According to the superheat of the molten steel, the billet casting speed is controlled by the stopper rod of the tundish, with an average casting speed of 2~3m / min (2.7m / min in the specific embodiments and comparative examples below), which fully ensures the surface quality of the continuous casting billet; the straightening temperature is controlled at 1050~1070℃ (1060±2℃ in the specific embodiments and comparative examples below).

[0036] Stirring was performed using an electromagnetic stirring device in the crystallizer and an electromagnetic stirring device at the end. The parameters for the electromagnetic stirring in the crystallizer were a frequency of 3Hz and a current of 225A; the parameters for the electromagnetic stirring at the end were a frequency of 10Hz and a current of 300A; the cooling water flow rate in the crystallizer was 2100~2300L / min (2200 L / min in the specific embodiments and comparative examples below); simultaneous secondary cooling was performed during continuous casting, with a specific water volume of 0.25~0.29L / Kg (0.26 L / kg in the specific embodiments and comparative examples below); strong cooling (i.e., controlling the temperature range of strong cooling of the billet surface in the continuous casting to 650℃~700℃) was used to refine the dendritic structure of the billet, so as to improve the low-magnification structure such as central segregation and central porosity of the billet, and control the central C segregation index to ≤1.05.

[0037] By controlling the straightening temperature in step 2, the generation of cracks during the straightening stage can be reduced. Production verification showed that the continuously cast billet had no squarening or rhomboid deformation, the pickled surface had no cracks, and the entire surface of the low-magnification test piece was free of various crack defects.

[0038] Step S3: Inspect the continuously cast steel billet. After pickling, if the billet has no longitudinal cracks, transverse cracks, or corner cracks on the surface; and the central porosity, central segregation, and central shrinkage cavity are all ≤2.0 grade, then the billet is deemed qualified; otherwise, it is deemed unqualified.

[0039] Step S4: The qualified steel billet is sent into the heating furnace for heating. The temperature range of the heating furnace during the heating process is 1150℃~1250℃ (in the following specific embodiments and comparative examples, the temperature of the heating furnace during the heating process is controlled at 1180±5℃).

[0040] Step S5: Rolling is performed using a continuous rolling method. The roughing temperature is set to 1050℃~1150℃, the intermediate rolling temperature to 1000℃~1100℃, and the finishing rolling temperature to 1050℃~1150℃ to obtain the reinforcing steel. In the following specific embodiments and comparative examples, the roughing temperature is 1100±5℃, the intermediate rolling temperature is 1050±5℃, and the finishing rolling temperature is 1120±5℃.

[0041] Step S6: Cool the steel bars on a cooling bed. The temperature range during the cooling process is 280℃~1070℃ to obtain the finished product. In the following specific embodiments and comparative examples, a three-stage cooling process is adopted: the first stage is cooling at 1000±20℃ for 4 hours, the second stage is cooling at 700±20℃ for 4 hours, and the third stage is cooling at 300±20℃ for 4 hours.

[0042] The above technical solutions, through the flow control method of stopper rod, ensure the insertion depth of the long nozzle, and use lower superheat, slower pulling speed, and appropriate secondary cooling water parameter configuration to control the cooling water volume of the crystallizer, can suppress the generation of cracks.

[0043] Example 1: A Cu-containing, weather-resistant, high-strength, earthquake-resistant Korean standard steel bar

[0044] This embodiment provides a high-strength, weather-resistant, earthquake-resistant Korean standard steel bar containing Cu, which contains, by mass percentage: C: 0.33%, Si: 0.20%, Mn: 1.65%, P: 0.01%, S: 0.01%, V: 0.15%, Nb: 0.015%, Cu: 0.20%, with the balance being Fe and unavoidable impurities.

[0045] Example 2: A Cu-containing, weather-resistant, high-strength, earthquake-resistant Korean standard steel bar

[0046] This embodiment provides a high-strength, weather-resistant, earthquake-resistant steel bar conforming to Korean standards containing Cu. By mass percentage, it contains: C: 0.35%, Si: 0.25%, Mn: 1.70%, P: 0.015%, S: 0.015%, V: 0.155%, Nb: 0.015%, Cu: 0.23%, with the balance being Fe and unavoidable impurities.

[0047] Example 3: A Cu-containing, weather-resistant, high-strength, earthquake-resistant Korean standard steel bar

[0048] This embodiment provides a high-strength, weather-resistant, earthquake-resistant steel bar conforming to Korean standards containing Cu. By mass percentage, it contains: C: 0.37%, Si: 0.30%, Mn: 1.80%, P: 0.02%, S: 0.02%, V: 0.16%, Nb: 0.02%, Cu: 0.25%, with the balance being Fe and unavoidable impurities.

[0049] The steel bars for Comparative Examples 1 and 2 were prepared below. The only difference between them and Example 1 is the elemental composition.

[0050] Comparative Example 1 steel bars contain, by mass percentage: C: 0.28%, Si: 0.70%, Mn: 1.50%, P: 0.035%, S: 0.03%, V: 0.16%, Nb: 0.02%, with the balance being Fe and unavoidable impurities.

[0051] Comparative Example 2 steel bars contain, by mass percentage: C: 0.28%, Si: 0.67%, Mn: 1.52%, P: 0.034%, S: 0.03%, V: 0.16%, Nb: 0.02%, with the balance being Fe and unavoidable impurities.

[0052] The steel reinforcement properties of Examples 1-3 and Comparative Examples 1 and 2 were subjected to routine tests, and the results are shown in Table 1. SD600S is the standard for seismic-resistant steel reinforcement, and HRB600 belongs to the Grade V steel reinforcement standard. The tensile strength and yield strength were determined according to GB / T28900-2022, and the strength-to-yield ratio (seismic performance) was calculated. As can be seen from Table 1, the tensile strength, yield strength, and seismic performance of the steel reinforcement in Examples 1-3 all meet the relevant standards and are far superior to the steel reinforcement in Comparative Examples 1 and 2.

[0053] Table 1 Comparison of Mechanical Properties and Seismic Performance

[0054]

[0055] The corrosion resistance of the reinforcing bars in Examples 1-3 and Comparative Examples 1 and 2 was tested (i.e., salt spray wet-dry cycle test). The corrosion resistance test conditions were: sodium chloride solution concentration 2%, solution temperature 45℃±2℃, pH 6.5~7.2, humidity in the salt spray chamber 70%RH±10%, each cycle 60 min, including a salt spray immersion time of 12 min±2 min, and a total test cycle of 72 h. The corrosion rate results are as follows:

[0056] Table 2 Statistical Table of Corrosion Resistance Immersion (72h) Test Data

[0057]

[0058] Figure 1 The steel reinforcement is from Example 1. Figure 2 For the steel reinforcement of Comparative Example 1, the rust layer on the surface of the steel reinforcement in the Example 1 is uniform and dense, while the rust layer on the surface of the steel reinforcement in the Comparative Example is loose and has a raised surface. The rust layer appears as spots / patches, indicating that the corrosion resistance of the steel reinforcement in the Example 1 is better than that of the steel reinforcement in the Comparative Example.

[0059] From Table 2 and Figure 1 , 2 It is evident that the corrosion rate of the steel bars in Examples 1-3 is much lower than that of the steel bars in Comparative Examples 1 and 2.

Claims

1. A Cu-containing weather-resistant high-strength anti-seismic Korean standard rebar, characterized by, The elemental composition of the Korean standard steel bars, by mass percentage, is as follows: C: 0.32%~0.37%, Si: 0.20%~0.30%, Mn: 1.65%~1.80%, P: 0.01%~0.02%, S: 0.01%~0.02%, V: 0.15%~0.16%, Nb: 0.015%~0.02%, Cu: 0.20%~0.25%, with the balance being Fe and unavoidable impurities; The preparation method of the Korean standard steel bars includes the following steps: Step S1 LF Refining and Alloying: After the steel ladle is placed in the refining station, calcium carbide, calcium aluminate, lime, and iron oxide scale are added. Nitrogen blowing is performed, and after fine-tuning the composition at the argon blowing station, argon is introduced. High-carbon ferrochrome is fed in, along with carbonized rice husks, and then aluminum cake is fed in for pre-deoxidation, causing the slag to gradually turn white. A CaO-Al2O3-SiO2-MgO slag system is used. After the white slag refining is completed and the composition is adjusted to the appropriate level, a slag-changing operation is performed to reduce the slag basicity R to below 1.

15. Molten steel is then obtained from the station. Step S2 Continuous casting: The molten steel obtained in step 1 is fed into a continuous casting machine for continuous casting to obtain a continuously cast steel billet; S21: Continuous casting of molten steel after LF treatment. Protective casting is used throughout the continuous casting process. Long nozzle and immersion nozzle are opened and argon-sealed. The insertion depth of the long nozzle is 200mm~300mm. S22: The production process adopts low superheat, weak secondary cooling water volume, and low casting speed. The overall superheat of continuous casting is 20℃~23℃, the specific water volume is controlled at 0.25L / kg~0.29L / kg, the average casting speed is 2m / min~3m / min, and the straightening temperature is controlled at 1050℃~1070℃. Stirring is carried out using an electromagnetic stirring device for the crystallizer and an electromagnetic stirring device at the end. The cooling water flow rate of the crystallizer is 2100~2300L / min. At the same time, secondary cooling is carried out in continuous casting, and the center C segregation is controlled to be ≤1.

05. Step S3 Inspection: Inspect the continuously cast steel billet. If, after pickling, the billet is free of longitudinal cracks, transverse cracks, and corner cracks, and the central porosity, central segregation, and central shrinkage cavity of the billet are all ≤2.0 grade, then the billet is deemed qualified; otherwise, it is deemed unqualified. Step S4 Heating: The qualified steel billet is sent into the heating furnace for heating. The temperature range of the heating furnace during the heating process is 1150℃~1250℃. Step S5 Rolling: Rolling is carried out using continuous rolling method, with roughing temperature of 1050℃~1150℃, intermediate rolling temperature of 1000℃~1100℃, and finishing rolling temperature of 1050℃~1150℃, to obtain steel bars; Step S6 Cooling: The steel bars are cooled on a cooling bed. The temperature range during the cooling process is 280℃~1070℃ to obtain the finished product.

2. The Cu-containing weather-resistant high-strength anti-seismic Korean standard reinforcement bar according to claim 1, characterized in that, The elemental composition of the Korean standard steel bars, by mass percentage, is as follows: C: 0.33%~0.37%, Si: 0.20%~0.30%, Mn: 1.70%~1.80%, P: 0.01%~0.02%, S: 0.01%~0.02%, V: 0.15%~0.16%, Nb: 0.017%~0.02%, Cu: 0.23%~0.25%, with the balance being Fe and unavoidable impurities.

3. The Cu-containing weather resistant high-strength anti-seismic Korean bar of claim 1, wherein the Cu-containing weather resistant high-strength anti-seismic Korean bar is a Korean bar having a yield strength of 550 MPa or more and a tensile strength of 700 MPa or more. In step S1, the nitrogen flow rate per ton of steel during nitrogen blowing is 100~140 NL / min, and the total nitrogen blowing time is 8~12 min.

4. The Cu-containing weather-resistant, high-strength, earthquake-resistant Korean standard steel bar as described in claim 1, characterized in that, In step S1, after fine-tuning the composition of the argon gas inlet station, the argon gas flow rate is 70~90 NL / min for strong argon blowing for 1.5~3 min, and then the argon gas flow rate is adjusted to 30~50 NL / min for bottom blowing to weak blowing; after adding carbonized rice husks, the argon gas flow rate is maintained at 10~25 NL / min for weak blowing for 3~7 min.

5. The Cu-containing weather resistant high-strength anti-seismic Korean bar of claim 1, wherein the Cu-containing weather resistant high-strength anti-seismic Korean bar is characterized by, In step S1, the temperature of the molten steel leaving the station is 1500℃~1700℃.

6. The Cu-containing weather resistant high-strength anti-seismic Korean bar of claim 1, wherein the Cu-containing weather resistant high-strength anti-seismic Korean bar is a Korean bar having a yield strength of 550 MPa or more and a tensile strength of 700 MPa or more. In step S22, the electromagnetic stirring parameters of the crystallizer are 1Hz~5Hz and 200A~300A; the electromagnetic stirring frequency at the end is 8Hz~12Hz and the current is 280A~320A; at the same time, the continuous casting secondary cooling has a specific water volume of 0.25~0.29L / Kg.

7. The use of the Cu-containing weather-resistant high-strength earthquake-resistant Korean standard steel bar as described in any one of claims 1 to 6 as earthquake-resistant steel bar.

8. The use of the Cu-containing weather-resistant, high-strength, earthquake-resistant Korean standard steel bar as described in any one of claims 1 to 6 as a corrosion-resistant steel bar for use in coastal working conditions.

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