Construction steel bar containing trace niobium, vanadium and titanium elements and manufacturing method thereof

Abstract

The invention is based on the technical field of ferrous metallurgy, and particularly relates to a construction steel bar containing trace niobium, vanadium and titanium elements and a manufacturing method thereof. The construction steel bar comprises the following chemical elements in percentage by weight: 0.20-0.26% of C; 0.55 to 0.90 percent of Si; 0.5 to 1.0 percent of Mn; 0.01 to 0.04 part of Nb; 0.005% to 0.04% of V; 0.005% to 0.04% of Ti; p is less than or equal to 0.04%; s is less than or equal to 0.04%; and the carbon equivalent Ceq is less than or equal to 0.58. The invention further discloses a method for manufacturing the construction steel bar. Through combination of niobium, vanadium and titanium composite microalloying and controlled rolling and controlled cooling technologies, the HRB400 reinforcing steel bar with the performance meeting the requirements is produced under the low manganese content, the alloy raw material and manufacturing cost is reduced, and meanwhile it is guaranteed that the reinforcing steel bar has the good yield ratio and ductility.

Description

Technical Field

[0001] This invention is based on the field of iron and steel metallurgy technology, and specifically relates to a building steel bar containing trace amounts of niobium, vanadium, and titanium elements and its manufacturing method. Background Technology

[0002] As my country's construction industry rapidly develops towards green, energy-saving, and safe directions, higher requirements are being placed on the performance and cost of hot-rolled ribbed steel bars for construction. Increasing the strength grade of steel bars can reduce steel consumption, lower building weight, and simplify construction while ensuring safety, resulting in significant resource conservation and environmental protection benefits. Currently, the industry has widely adopted 400MPa and 500MPa grade high-strength earthquake-resistant steel bars and is actively developing even higher-grade products.

[0003] Achieving high-strength steel reinforcement mainly relies on microalloying and controlled rolling and cooling technologies. The addition of microalloying elements such as niobium (Nb), vanadium (V), and titanium (Ti) can effectively improve strength through grain refinement and precipitation strengthening. However, ensuring good plasticity, toughness, and seismic performance (usually measured by strength-to-yield ratio and total elongation at maximum force) while simultaneously increasing strength, and effectively controlling production costs, has always been a challenge in technological research and development.

[0004] In the existing technology, there are mainly the following technical routes, but each has its own limitations:

[0005] Vanadium-titanium (V-Ti) microalloying route: For example, patent CN111172459A discloses a high-strength, earthquake-resistant hot-rolled steel bar (HRB600E) with vanadium-titanium microalloying. This method uses a composite addition of V and Ti, combined with a nitrogen-enrichment process, to produce 600MPa grade steel bars. While this route achieves high strength, to meet performance requirements, the vanadium + titanium addition amount remains at 0.10–0.25%, and the Mn content is at least 0.10%. Furthermore, the high price of ferrovanadium alloys results in high raw material costs. Additionally, this approach still relies on a controlled cooling process after rolling, placing high demands on the stability of the production equipment.

[0006] Niobium-vanadium (Nb-V) composite microalloying routes, such as the technical solutions in patents CN116926432A and CN112609129A, involve 640MPa and 500MPa grade niobium-vanadium microalloyed steel bars, respectively. These routes utilize the strong grain-refining effect of niobium and the precipitation strengthening effect of vanadium to produce high-strength steel bars with excellent performance. However, to fully utilize the effects of niobium and vanadium, it is usually necessary to combine them with higher carbon (C) and manganese (Mn) contents and implement more stringent heating and rolling processes (such as higher heating temperatures). This not only increases the alloy cost but also poses challenges to the quality of continuously cast billets (such as the crack sensitivity of niobium-containing steel) and the control of the rolling process. Especially for large-scale steel bars, the core cooling rate is slow, and seismic resistance indicators such as strength-to-yield ratio are difficult to consistently meet standards.

[0007] Niobium-titanium (Nb-Ti) microalloying route: Patent CN110295326A discloses an HRB500E niobium-titanium microalloyed steel bar and its production process, primarily used for small-diameter steel bars. This route utilizes titanium to fix nitrogen, reducing the crack sensitivity of niobium. However, it still focuses on strength levels of 500 MPa and above, and does not address how to further reduce the cost of basic alloys such as manganese content while ensuring performance. The pre-water-piercing process also increases production complexity.

[0008] The existing steel reinforcement production technologies mentioned above generally face a common problem: while pursuing high strength, especially low cost (such as 400MPa grade), it is difficult to simultaneously achieve extremely high ductility and toughness, stable seismic performance, and simple and reliable production process.

[0009] Therefore, there is an urgent need in this field to develop a new microalloying composition system and a matching production process, aiming to stably produce steel bars for construction with ultra-high plasticity, excellent strength-to-yield ratio and uniform microstructure at a lower overall alloy cost. At the same time, the process should be simple, reliable and easy to implement on a large scale, so as to promote cost reduction, efficiency improvement and energy conservation and emission reduction in the construction industry. Summary of the Invention

[0010] The purpose of this invention is to provide a low-cost, high-performance building steel bar containing trace amounts of niobium, vanadium, and titanium, and its manufacturing method.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] In a first aspect, the present invention provides a building steel bar containing trace amounts of niobium, vanadium, and titanium elements. The chemical element composition and content of the building steel bar are as follows: C 0.20-0.26%; Si 0.55-0.90%; Mn 0.5-1.0%; Nb 0.01-0.04%; V 0.005-0.04%; Ti 0.005-0.04%; P ≤0.04%; S ≤0.04%; N 100-150ppm; the balance being Fe and other unavoidable elements, and the carbon equivalent Ceq ≤0.58.

[0013] In one specific embodiment of the present invention, the chemical element composition and content of the building steel reinforcement are as follows: C 0.22-0.24%; Si 0.6-0.8%; Mn 0.6-0.8%; Nb 0.015-0.025%; V 0.01-0.02%; Ti 0.01-0.02%; P ≤0.025%; S ≤0.025%; N 100-130ppm; the balance being Fe and other unavoidable elements, and the carbon equivalent Ceq ≤0.54.

[0014] In one specific embodiment of the present invention, the metallographic structure of the building steel reinforcement is ferrite + pearlite; the average grain size is grade 10.5.

[0015] In one specific embodiment of the present invention, the diameter φ of the building steel bar is 20mm, its yield strength is 400-455MPa, its tensile strength is 600-630MPa, its elongation is 24.5-26%, and its strength-to-yield ratio is 1.36-1.43.

[0016] Secondly, the present invention provides a method for manufacturing the above-mentioned building steel bars, comprising the following steps:

[0017] a. Converter smelting: Steel is smelted in an electric furnace at 1660~1680℃, and oxidants and alloys are added to the molten steel tapped from the converter to achieve ladle alloying; the alloys include silicon-manganese alloy, ferrosilicon alloy, ferrovanadium alloy and ferroniobium alloy.

[0018] b. Refining: Argon blowing is used to refine the molten steel alloyed in step a, and titanium-iron alloy is added for titanium microalloying.

[0019] c. Continuous casting: The molten steel refined in step b is continuously cast to obtain a continuously cast billet; a weak cooling regime is adopted in the secondary cooling zone, and the specific water content is controlled at 0.45-0.6 liters / kg of molten steel; the temperature of the continuously cast billet when passing through the straightening machine is >950℃.

[0020] d. Rolling: The continuously cast billet from step c is rolled to obtain building steel bars containing trace amounts of niobium, vanadium, and titanium. The temperature parameters during the rolling process are specifically controlled as follows: heating temperature 1160~1200℃; soaking temperature 1060~1120℃; temperature after the first stand 1000±50℃; finishing rolling temperature 830±30℃; and upper cooling bed temperature 800±30℃.

[0021] In one specific embodiment of the present invention, in step a, the steel is high-quality scrap steel; the ferrovanadium alloy is 50 ferrovanadium; the ferroniobium alloy is 60A ferroniobium; and the ferrotitanium alloy is 50 ferrotitanium.

[0022] In one specific embodiment of the present invention, step a, the endpoint of electric furnace smelting is C≥0.05%, P<0.015% and S<0.030% in the molten steel.

[0023] In one specific embodiment of the present invention, step a involves adding the alloy when the amount of steel tapped from the converter reaches 1 / 4, and completing the addition before the amount of steel tapped reaches 3 / 4.

[0024] In one specific embodiment of the present invention, in step b, the superheat of the molten steel in the argon blowing refining tundish is controlled to be 10-20°C; the argon blowing time for the argon blowing refining is >4 min.

[0025] In one specific embodiment of the present invention, step c, the continuous casting process adopts full-process protective casting; the casting speed of the continuous casting is 2.0 to 3.3 m / min.

[0026] The main functions of niobium-vanadium-titanium in high-strength low-alloy steel, as described in this invention, are grain refinement strengthening, precipitation strengthening, and phase transformation strengthening, with grain refinement being the dominant strengthening factor. The effective factors contributing to the strength and toughness of HRB400 steel bars include:

[0027] (1) During the solidification process of the billet, the small dispersed particles of VC, V(CN), NbC, Nb(CN), TiC, and Ti(CN) that precipitate in advance will help to form a fine equiaxed structure. This fine equiaxed structure is conducive to the formation of fine original austenite grains. Moreover, the small dispersed particles will inhibit the growth of austenite grains during the heating process.

[0028] (2) High-temperature precipitation inhibits the growth of austenite grains during deformation and recrystallization. This effect is very obvious. During the hot deformation process in the austenite region, according to the dissolution and precipitation law of V(CN), Nb(CN), and Ti(CN), the precipitation timing of V(CN), Nb(CN), and Ti(CN) can be controlled by controlling process parameters such as heating temperature, rolling start temperature, and rolling end temperature. The precipitation of V(CN), Nb(CN), and Ti(CN) in austenite is used to pin the grain boundaries, subgrain boundaries, displacement lines, and other defects in the austenite to delay the start time of austenite recrystallization and prevent secondary grain growth, thereby refining the austenite grains and further refining the ferrite grains, which strengthens the performance of steel bars.

[0029] The beneficial effects of this invention are:

[0030] 1. This invention combines niobium, vanadium, and titanium composite microalloying with controlled rolling and cooling technology to produce steel bars with satisfactory performance at a lower manganese content, reducing the cost of alloy raw materials and manufacturing, while ensuring that the steel bars have good strength-to-yield ratio and elongation.

[0031] 2. The alloy cost of the reinforcing steel in this invention is significantly reduced. Compared with traditional HRB400E reinforcing steel, only a small amount of niobium, titanium, and vanadium elements are needed to significantly improve the performance of the reinforcing steel, and the content of the alloying element Mn is greatly reduced by 0.4~0.5%.

[0032] 3. This invention uses three alloying elements, niobium, titanium, and vanadium, to enhance the performance of steel bars, resulting in more stable performance and smaller performance fluctuations.

[0033] 4. The continuous casting and rolling process designed for this steel bar chemical composition can ensure that the steel bar achieves the designed performance, and the quality of the manufactured steel bar fully meets the national standard requirements. Attached Figure Description

[0034] Figure 1 The image shows the metallographic structure of the steel bar prepared in Example 1 of this invention.

[0035] Figure 2 Photograph of the grain size of the steel bar prepared in Example 1 of this invention. Detailed Implementation

[0036] A type of steel reinforcement containing trace amounts of niobium, vanadium, and titanium has the following chemical element composition and content: C 0.20–0.26%; Si 0.55–0.90%; Mn 0.5–1.0%; Nb 0.01–0.04%; V 0.005–0.04%; Ti 0.005–0.04%; P ≤0.04%; S ≤0.04%; N 100–150 ppm; the balance being Fe and other unavoidable elements, and the carbon equivalent Ceq ≤0.58.

[0037] In some instances, the chemical element composition and content of the steel reinforcement bars are as follows: C 0.22–0.24%; Si 0.6–0.8%; Mn 0.6–0.8%; Nb 0.015–0.025%; V 0.01–0.02%; Ti 0.01–0.02%; P ≤0.025%; S≤0.025%; N 100–130 ppm; the balance being Fe and other unavoidable elements, and the carbon equivalent Ceq ≤0.54.

[0038] In some instances, the metallographic structure of the building steel reinforcement is ferrite + pearlite; the average grain size is grade 10.5.

[0039] In some instances, the reinforcing steel bars have a diameter φ of 20 mm, a yield strength of 400–455 MPa, a tensile strength of 600–630 MPa, an elongation of 24.5–26%, and a strength-to-yield ratio of 1.36–1.43.

[0040] A method for manufacturing the above-mentioned steel reinforcement containing trace amounts of niobium, vanadium, and titanium elements includes the following steps:

[0041] a. Converter smelting: Steel is smelted in an electric furnace at 1660~1680℃, and oxidants and alloys are added to the molten steel tapped from the converter to achieve ladle alloying; the alloys include silicon-manganese alloy, ferrosilicon alloy, ferrovanadium alloy and ferroniobium alloy.

[0042] b. Refining: Argon blowing is used to refine the molten steel alloyed in step a, and titanium-iron alloy is added for titanium microalloying.

[0043] c. Continuous casting: The molten steel refined in step b is continuously cast to obtain a continuously cast billet; a weak cooling regime is adopted in the secondary cooling zone, and the specific water content is controlled at 0.45-0.6 liters / kg of molten steel; the temperature of the continuously cast billet when passing through the straightening machine is >950℃.

[0044] d. Rolling: The continuously cast billet from step c is rolled to obtain building steel bars containing trace amounts of niobium, vanadium, and titanium. The temperature parameters during the rolling process are specifically controlled as follows: heating temperature is 1160~1200℃; soaking temperature is 1060~1120℃; temperature after the first stand is 1000±50℃; finishing rolling temperature is 830±30℃; and upper cooling bed temperature is 800±30℃.

[0045] In some examples, in step a, the steel is high-quality scrap steel; the ferrovanadium alloy is 50 ferrovanadium; the ferroniobium alloy is 60A ferroniobium; and the ferrotitanium alloy is 50 ferrotitanium. The high-quality scrap steel preferably has an S ≤ 0.030%. If the S in the scrap steel is > 0.030%, it needs to be mixed with scrap steel with S < 0.030% to ensure that the S in the electric arc furnace smelted steel is ≤ 0.030%.

[0046] The present invention controls the amount of water in the secondary cooling zone and the temperature of the straightening machine during the continuous casting process, which can prevent cracks from easily forming in the continuously cast billet due to the high stress during the solidification process of niobium-vanadium-titanium steel, and can avoid the low thermoplasticity zone of niobium-vanadium-titanium steel.

[0047] This invention achieves microalloying of niobium, vanadium, and titanium during converter smelting and refining, ensuring that the niobium, vanadium, and titanium are completely or mostly dissolved during the rolling heating of the billet and fully precipitated during hot rolling, which is beneficial for obtaining ferrite + pearlite microstructure in building steel bars. The rolling heating temperature ensures sufficient solid solution of niobium, vanadium, and titanium, preventing austenite grain coarsening. The upper cooling bed temperature avoids the appearance of surface tempering structures that are unacceptable to the market, and also avoids the generation of a large amount of bainite structure, which would cause the steel bars to reach their yield point.

[0048] In some instances, step a, the endpoint of electric furnace smelting, is that the molten steel has C ≥ 0.05%, P < 0.015%, and S < 0.030%.

[0049] In some instances, step a involves adding alloys when the steel output from the converter reaches 1 / 4 and completing the addition before the steel output reaches 3 / 4; the alloy addition sequence during converter smelting is: oxidant - deoxidizer - ferrosilicon - ferrosilicon - deoxidizer - 50 vanadium ferro and 60A niobium ferro.

[0050] In some cases, the amount of 50 vanadium ferrophosphate added is 0.1 to 0.45 kg / ton of molten steel, the amount of 60A niobium ferrophosphate added is 0.2 to 0.9 kg / ton of molten steel, and the amount of 50 titanium ferrophosphate added is 0.3 to 2.7 kg / ton of molten steel, thereby controlling the content of niobium, vanadium, and titanium in the reinforcing steel.

[0051] In some instances, in step b, the superheat of the molten steel in the argon blowing refining tundish is controlled to be 10–20°C; and the argon blowing time for the argon blowing refining is >4 min.

[0052] In some instances, step c involves continuous casting with full protective pouring; the casting speed is 2.0–3.3 m / min.

[0053] In this invention, niobium, vanadium, and titanium elements pin grain boundaries in the high-temperature austenite region through fine carbonitride compounds, strongly inhibiting grain growth and providing a large number of nucleation sites for subsequent phase transformation. Niobium, vanadium, and titanium form dispersed (Nb,V,Ti) (C,N) nano-precipitates, pinning austenite grain boundaries and achieving a grain size as fine as 10.5 grade. The ferrite proportion is increased to 76%, pearlite is reduced to 24%, the total grain boundary area increases, dislocation movement is hindered, yield strength is increased by more than 40 MPa, and impact toughness is improved by 30%. Therefore, the reinforcing steel of this invention combines the excellent plasticity and toughness of ferrite with the high strength of pearlite, while maintaining good weldability, achieving a synergistic improvement in strength, toughness, and seismic performance. Simultaneously, some vanadium elements precipitate during the phase transformation, producing a significant precipitation strengthening effect. The synergistic effect of the fine grain structure, precipitation strengthening, and phase transformation structure enables the reinforcing steel to achieve a perfect combination of high strength, high toughness, and a good yield strength ratio.

[0054] To further demonstrate the role of trace amounts of niobium, vanadium, and titanium elements in improving the strength-to-yield ratio and elongation of reinforcing steel bars in this invention, the following embodiments and comparative examples are provided:

[0055] Example 1

[0056] This embodiment provides a method for manufacturing φ20 HRB400E steel bars, including the following steps:

[0057] (1) Converter smelting: Scrap steel (S=0.030%) is smelted in an electric furnace at 1670℃. The final C content of the molten steel tapped from the converter is 0.05%, S content is 0.020%, and P content is 0.015%. During the tapping process, oxidants and alloys are added for alloying, and the amount of slag is strictly controlled during tapping. The order of adding oxidants and alloys is: deoxidizer-silicon manganese-silicon ferrosilicon-deoxidizer-50 vanadium ferro and 60A niobium ferro. The addition begins when the amount of steel tapped from the converter reaches 1 / 4 and is completed before 3 / 4 of the steel is tapped. Among them, the amount of 50 vanadium ferro is added is 0.25 kg / ton of molten steel, and the amount of 60A niobium ferro is added is 0.6 kg / ton of molten steel.

[0058] (2) LF furnace refining: The molten steel after alloying in the converter is refined by argon blowing in the LF furnace; wherein, the argon blowing is bottom blowing of the ladle, and the blowing time is 5 min; 50 ferrotitanium is added at the argon blowing station, and the addition amount is 1.8 kg / ton of molten steel;

[0059] (3) The refined steel from step b is continuously cast to obtain a continuously cast billet; wherein, a weak cooling regime is adopted in the secondary cooling zone during the continuous casting process, and the specific water volume in the secondary cooling zone is controlled at 0.55L / kg; the temperature of the continuously cast billet when passing through the straightening machine is 980℃; the superheat of the molten steel in the tundish is 15℃; the casting process adopts full-process protective pouring, and the casting speed is controlled at 2.7m / min;

[0060] (4) The continuously cast billet is rolled to obtain HRB400E steel bars with a diameter of φ20mm; wherein the rolling process temperature is controlled as follows: heating temperature is 1180℃, soaking temperature is 1090℃, temperature after 1 stand is 1000℃, finishing rolling temperature is 830℃, and upper cooling bed temperature is 800℃.

[0061] The chemical composition (mass percentage) of the HRB400E steel reinforcement in this embodiment was tested and found to be: C 0.20%; Si 0.60%; Mn 0.75%; Nb 0.03%; V 0.020%; Ti 0.015%; P 0.025%; S 0.025%; N 150ppm; and carbon equivalent of 0.53.

[0062] In this embodiment, the HRB400E steel bar has a yield strength of 448 MPa, a tensile strength of 615 MPa, an elongation of 25.4%, and a yield-to-tensile ratio of 1.37, all of which meet the national standard requirements.

[0063] The average grain size of the HRB400E steel reinforcement in this embodiment was determined according to GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals". The resulting average grain size photograph is attached. Figure 1 As shown.

[0064] The warp microstructure of the HRB400E steel bar in this embodiment was tested according to GB / T13298-2015 "Metal Fiber Structure Test Method". The metallographic images of the obtained microstructure are attached. Figure 2 As shown.

[0065] From the appendix Figure 1 , 2 It is evident that niobium, vanadium, and titanium elements form dispersed (Nb, V, Ti) and (C, N) nano-precipitates, pinning austenite grain boundaries and achieving a grain size as fine as 10.5 grade. The ferrite proportion increases to 76%, pearlite decreases to 24%, the total grain boundary area increases, dislocation movement is hindered, yield strength increases by over 40 MPa, and impact toughness increases by 30%. This combination of excellent ductility and toughness of ferrite and high strength of pearlite, while maintaining good weldability, achieves a synergistic improvement in strength, toughness, and seismic performance. Simultaneously, some vanadium elements precipitate during the phase transformation process, producing a significant precipitation strengthening effect. The synergistic effect of the fine grain structure, precipitation strengthening, and phase transformation structure enables the steel reinforcement to achieve high strength, high toughness, and a good yield strength ratio.

[0066] Example 2

[0067] This embodiment provides a method for manufacturing φ20 HRB400E steel bars, including the following steps:

[0068] (1) Converter smelting: Scrap steel (S=0.030%) is smelted in an electric furnace at 1680℃. The final C content of the molten steel tapped from the converter is 0.045%, S content is 0.025%, and P content is 0.017%. During the tapping process, oxidants and alloys are added for alloying, and the amount of slag is strictly controlled during tapping. The order of adding oxidants and alloys is: deoxidizer-silicon manganese-silicon ferrosilicon-deoxidizer-50 vanadium ferro and 60A niobium ferro. The addition begins when the amount of steel tapped from the converter reaches 1 / 4 and is completed before 3 / 4 of the steel is tapped. Among them, the amount of 50 vanadium ferro is added is 0.27 kg / ton of molten steel, and the amount of 60A niobium ferro is added is 0.56 kg / ton of molten steel.

[0069] (2) LF furnace refining: The molten steel after being smelted and alloyed in the converter is refined by argon blowing in the LF furnace; wherein, the argon blowing is bottom blowing of the ladle, and the blowing time is 6 minutes; 50 ferrotitanium is added at the argon blowing station, and the addition amount is 1.73 kg / ton of molten steel;

[0070] (3) The refined steel from step b is continuously cast to obtain a continuously cast billet; wherein, a weak cooling regime is adopted in the secondary cooling zone during the continuous casting process, and the specific water volume in the secondary cooling zone is controlled at 0.52L / kg; the temperature of the continuously cast billet when passing through the straightening machine is 988℃; the superheat of the molten steel in the tundish is 16℃; the casting process adopts full-process protective pouring, and the casting speed is controlled at 2.85m / min;

[0071] (4) The continuously cast billet is rolled to obtain HRB400E steel bars with a diameter of φ20mm; wherein the rolling process temperature is controlled as follows: heating temperature is 1188℃, soaking temperature is 1095℃, temperature after 1 stand is 1020℃, finishing rolling temperature is 830℃, and upper cooling bed temperature is 800℃.

[0072] The chemical composition (mass percentage) of the HRB400E steel reinforcement in this embodiment was tested and found to be: C 0.22%; Si 0.55%; Mn 0.70%; Nb 0.032%; V 0.022%; Ti 0.013%; P 0.020%; S 0.020%; N 110ppm; and carbon equivalent of 0.51.

[0073] In this embodiment, the HRB400E steel bar has a yield strength of 443 MPa, a tensile strength of 610 MPa, an elongation of 25.8%, and a yield-to-tensile ratio of 1.38, all of which meet the national standard requirements.

[0074] Example 3

[0075] This embodiment provides a method for manufacturing φ20 HRB400E steel bars, including the following steps:

[0076] (1) Converter smelting: Scrap steel (S=0.030%) is smelted in an electric furnace at 1665℃. The final C content of the molten steel tapped from the converter is 0.040%, S content is 0.018%, and P content is 0.016%. During the tapping process, oxidants and alloys are added for alloying, and the amount of slag is strictly controlled during tapping. The order of adding oxidants and alloys is: deoxidizer-silicon manganese-ferrosilicon-deoxidizer-50 vanadium iron and 60A niobium iron. The addition begins when the amount of steel tapped from the converter reaches 1 / 4 and is completed before 3 / 4 of the steel is tapped. Among them, the amount of 50 vanadium iron added is 0.23 kg / ton of molten steel, and the amount of 60A niobium iron added is 0.63 kg / ton of molten steel.

[0077] (2) LF furnace refining: The molten steel after being smelted and alloyed in the converter is refined by argon blowing in the LF furnace; wherein, the argon blowing is bottom blowing of the ladle, and the blowing time is 7 minutes; 50 ferrotitanium is added at the argon blowing station, and the addition amount is 1.88 kg / ton of molten steel;

[0078] (3) The refined steel from step b is continuously cast to obtain a continuously cast billet; wherein, a weak cooling regime is adopted in the secondary cooling zone during the continuous casting process, and the specific water volume in the secondary cooling zone is controlled at 0.50 L / kg; the temperature of the continuously cast billet when passing through the straightening machine is 975℃; the superheat of the molten steel in the tundish is 17℃; the casting process adopts full-process protective pouring, and the casting speed is controlled at 2.80 m / min;

[0079] (4) The continuously cast billet is rolled to obtain HRB400E steel bars with a diameter of φ20mm; wherein the rolling process temperature is controlled as follows: heating temperature is 1165℃, soaking temperature is 1086℃, temperature after 1 stand is 990℃, finishing rolling temperature is 825℃, and upper cooling bed temperature is 810℃.

[0080] The chemical composition (mass percentage) of the HRB400E steel reinforcement in this embodiment was tested and found to be: C 0.26%; Si 0.70%; Mn 0.85%; Nb 0.035%; V 0.023%; Ti 0.017%; P 0.021%; S 0.021%; N 130ppm; and carbon equivalent of 0.55.

[0081] In this embodiment, the HRB400E steel bar has a yield strength of 450MPa, a tensile strength of 628MPa, an elongation of 25.0%, and a yield-to-tensile ratio of 1.40, all of which meet the national standard requirements.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that 60A ferroniobium and 50 ferrotitanium are not added; only 50 ferrovanadium is added in the converter.

[0084] The properties of the φ20 steel bar prepared in this comparative example are as follows: yield strength of 415MPa, tensile strength of 590MPa, elongation of 18, and strength-to-yield ratio of 1.42.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that the specific water volume in the second cooling zone is controlled at 1.20 L / kg.

[0087] The properties of the φ20 steel bar prepared in this comparative example are as follows: yield strength of 420MPa, tensile strength of 600MPa, elongation of 19, and strength-to-yield ratio of 1.43.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 1 is that the temperature of the billet passing through the straightening machine is controlled at 940°C.

[0090] The properties of the φ20 steel bar prepared in this comparative example are as follows: yield strength of 405 MPa, tensile strength of 585 MPa, elongation of 18, and strength-to-yield ratio of 1.44.

[0091] Comparative Example 4

[0092] The difference between this comparative example and Example 1 is that 1.73 kg / ton of titanium-iron alloy was added during the converter smelting process.

[0093] Tests showed that the titanium yield in the φ20 steel bar of this comparative example was extremely low; this indicates that the titanium-iron alloy added during the converter smelting process did not have an alloying effect on the molten steel.

[0094] The properties of the steel bars obtained in this comparative example are: yield strength of 404 MPa, tensile strength of 580 MPa, elongation of 17, and strength-to-yield ratio of 1.44; they are almost indistinguishable from the properties of unalloyed steel bars produced by conventional processes.

Claims

1. A type of building steel reinforcement containing trace amounts of niobium, vanadium, and titanium, characterized in that, The chemical element composition and content of the steel reinforcement are as follows: C 0.20~0.26%; Si 0.55~0.90%; Mn 0.5~1.0%; Nb 0.01~0.04%; V 0.005~0.04%; Ti 0.005~0.04%; P ≤0.04%; S ≤0.04%; N 100~150ppm; the balance being Fe and other unavoidable elements, and the carbon equivalent Ceq≤0.

58.

2. The reinforcing steel bars for construction according to claim 1, characterized in that, The chemical element composition and content of the steel reinforcement are as follows: C 0.22~0.24%; Si 0.6~0.8%; Mn 0.6~0.8%; Nb 0.015~0.025%; V 0.01~0.02%; Ti 0.01~0.02%; P ≤0.025%; S ≤0.025%; N 100~130ppm; the balance being Fe and other unavoidable elements, and the carbon equivalent Ceq≤0.

54.

3. The reinforcing steel bars for construction according to claim 1 or 2, characterized in that, The metallographic structure of the building steel bars is ferrite + pearlite; the average grain size is grade 10.

5.

4. The reinforcing steel bars for construction according to claim 1 or 2, characterized in that, The steel reinforcement bars have a diameter φ of 20mm, a yield strength of 400-455MPa, a tensile strength of 600-630MPa, an elongation of 24.5-26%, and a strength-to-yield ratio of 1.36-1.

43.

5. A method for manufacturing the reinforcing steel bars according to any one of claims 1-4, characterized in that, Includes the following steps: a. Converter smelting: Steel is smelted in an electric furnace at 1660~1680℃, and oxidants and alloys are added to the molten steel tapped from the converter to achieve ladle alloying; the alloys include silicon-manganese alloy, ferrosilicon alloy, ferrovanadium alloy and ferroniobium alloy. b. Refining: Argon blowing is used to refine the molten steel alloyed in step a, and titanium-iron alloy is added for titanium microalloying. c. Continuous casting: The molten steel refined in step b is continuously cast to obtain a continuously cast billet; a weak cooling regime is adopted in the secondary cooling zone, and the specific water content is controlled at 0.45-0.6 liters / kg of molten steel; the temperature of the continuously cast billet when passing through the straightening machine is >950℃. d. Rolling: The continuously cast billet from step c is rolled to obtain building steel bars containing trace amounts of niobium, vanadium, and titanium. The temperature parameters during the rolling process are specifically controlled as follows: heating temperature is 1160~1200℃; soaking temperature is 1060~1120℃; temperature after the first stand is 1000±50℃; finishing rolling temperature is 830±30℃; and upper cooling bed temperature is 800±30℃.

6. The method according to claim 5, characterized in that: Step a, the steel is high-quality scrap steel; the ferrovanadium alloy is 50 ferrovanadium; the ferroniobium alloy is 60A ferroniobium; the ferrotitanium alloy is 50 ferrotitanium.

7. The method according to claim 5, characterized in that: Step a, the endpoint of electric furnace smelting is C ≥ 0.05%, P < 0.015%, and S < 0.030% in the molten steel.

8. The method according to claim 5, characterized in that: Step a: When the amount of steel tapped from the converter reaches 1 / 4, the alloy is added and the addition is completed before the amount of steel tapped reaches 3 / 4.

9. The method according to claim 5, characterized in that: In step b, the superheat of the molten steel in the tundish during argon blowing refining is controlled at 10-20°C; the argon blowing time during argon blowing refining is >4 min.

10. The method according to claim 5, characterized in that: Step c, the continuous casting process adopts full-process protective pouring; the casting speed of the continuous casting is 2.0 to 3.3 m / min.

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