Production method of microalloyed aseismic reinforcing steel bar

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a production method of a microalloyed anti-seismic reinforcing steel bar, which is characterized by comprising the steps of converter smelting, ladle furnace LF (ladle furnace) refining, square billet continuous casting and bar rolling line rolling adopting a controlled rolling and controlled cooling process.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and particularly relates to a production method of microalloyed earthquake-resistant steel bars. Background Art

[0002] With the rapid development of the construction industry, the demand for earthquake-resistant steel bars in engineering structures such as urban municipal and high-rise buildings is increasing. Under the background of the country's strong advocacy for energy conservation, emission reduction, environmental protection, and cost reduction, it is an important research and production direction to use suitable microalloying elements for substitution and achieve excellent mechanical properties.

[0003] Currently, domestic production of earthquake-resistant steel bars of the same grade adopts high-Mn element solid solution strengthening, combined with precious alloys V and Nb for microalloying. The alloy consumption is large and the production cost is high, which is not conducive to energy conservation, emission reduction, and cost reduction of manufacturing. Summary of the Invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a production method of microalloyed earthquake-resistant steel bars. The technical solution to solve the problem is to design the chemical composition of the steel through steelmaking, and then carry out smelting in a converter (electric furnace), refining in a ladle furnace (LF), continuous casting of square billets, and rolling in a bar rolling line using the controlled rolling and controlled cooling process. By adding Ti element alone and utilizing the fine grain strengthening and precipitation strengthening effects of Ti element, it is finally possible to partially replace the use of Mn element and completely replace V and Nb microalloying elements, obtaining straight earthquake-resistant steel bars with excellent performance, reducing production costs, and saving energy.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: A production method of microalloyed earthquake-resistant steel bars, characterized in that the chemical composition of the steel bars by weight percentage includes the following components: C: 0.20 - 0.24%, Si: 0.20 - 0.50%, Mn: 1.20 - 1.45%, P ≤ 0.025%, S ≤ 0.020%, Ti: 0.030 - 0.050%, Al: 0.015 - 0.035%, N ≤ 0.0060%, and the rest is Fe; The production method includes: smelting in a converter (electric furnace), refining in a ladle furnace (LF), continuous casting of square billets, and rolling in a bar rolling line using the controlled rolling and controlled cooling process. Specifically, it is the following steps: Step 1: Tapping from the converter (electric furnace), controlling the C ≥ 0.08%, P ≤ 0.020%, and end temperature ≥ 1620°C at the end of smelting. Use ferrosilicon for deoxidation. If the oxygen content at the end of the converter is relatively high, a small amount of ferraluminum or steel-cored aluminum can be appropriately added for deoxidation. For alloying, use silicomanganese iron. The alloy is added starting from 1 / 5 of the tapping time and added completely before 4 / 5 of the tapping time; Step 2: Ladle furnace LF refining. During LF refining in the ladle furnace, refining should be carried out under alkaline white slag. During smelting, first add aluminum wire (or aluminum pellets) for deep deoxidation, and the soft stirring time in the later stage should be ≥5 min; Step 3: Continuous casting of small billets. Electromagnetic stirring in the mold, and strong cooling is adopted for secondary cooling. The continuous casting speed is 2.5 - 2.8 m / min; Step 4: The bar rolling line is rolled by a horizontal - vertical alternating rolling mill, and earthquake - resistant steel bars are rolled using the controlled rolling and controlled cooling process.

[0006] Preferably, in Step 2, when ensuring that Al in the molten steel is 0.015 - 0.035%, then add ferrotitanium. The N content throughout the refining process should be ≤0.0060%, and the refining time in the ladle furnace should be ≥30 min.

[0007] Preferably, in Step 3, long - nozzle protected casting is adopted for continuous casting of billets. The electromagnetic stirring parameters in the mold are: current: 220 - 240 A, frequency: 4 - 6 Hz; secondary cooling: adopt a strong - cooling water meter (specific water volume is about 1.2 L / Kg); the cross - sectional size of the continuous casting billet produced is: 150 mm×150 mm.

[0008] Preferably, in Step 4, the controlled rolling and controlled cooling process is adopted for the bar rolling line: the heating furnace temperature is 1080 - 1130 °C, the residence time in the furnace is 40 - 70 min, the starting rolling temperature is 1030 ± 30 °C, the entry temperature of the finishing mill is 970 ± 30 °C, the temperature on the cooling bed is 920 ± 30 °C. After hot rolling, it is cooled naturally in the air and collected.

[0009] Preferably, through the above smelting and rolling processes, earthquake - resistant steel bars with performance, microstructure and other indicators all meeting the standards of 1499.2 - 2018 are finally obtained, and the production cost is greatly reduced.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention uses inexpensive Ti micro - alloying, utilizes the grain - refinement strengthening and precipitation strengthening effects of Ti element, partially replaces the use of Mn element, and completely replaces the use of precious alloys V and Nb elements. The performances of the products meet the requirements of GB / T 1499.2 - 2018 standard.

[0011] 2. The present invention greatly reduces the generation and removal of inclusions in steel and improves the alloy recovery rate of Ti element by optimizing the operation process of ladle furnace refining (LF).

[0012] 3. By using and adjusting the parameters of the controlled rolling and controlled cooling process for the bar rolling line, the rolling temperature of each key link of the bar rolling line is accurately and stably controlled, the grain - refinement strengthening and precipitation strengthening effects of Ti element in steel are improved, the use of other alloy elements is replaced, the production cost is reduced, and good economic benefits are achieved. Brief Description of the Drawings

[0014] Figure 1 This is the chemical composition table of the earthquake-resistant steel bars in Embodiments 1-3 of the present invention.

[0015] Figure 2 This is the mechanical property table of the earthquake-resistant steel bars in Embodiments 1-3 of the present invention. Detailed Description of the Invention

[0016] The technical solutions and effects of the present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0017] Embodiment 1 A production method of a microalloyed earthquake-resistant steel bar provided in this embodiment has a production process as follows: converter (electric furnace) → LF ladle refining furnace → small billet continuous caster → continuous casting billet with a cross-section of 150mm×150mm → bar rolling line rolling (using controlled rolling and controlled cooling process) → φ14mm earthquake-resistant steel bar.

[0018] The key control parameters are: (1) The ladle furnace refining (LF furnace) is smelted under alkaline white slag. First, deep deoxidation is carried out with aluminum, and the [Al] content in the molten steel is 0.021%. Then ferrotitanium is added. The soft stirring time before tapping is 6 min, the refining time is 32 min, and the [Ti] content in the steel is 0.035%; (2) The billet continuous casting adopts protective casting, and the chemical composition of the cast billet and the mass fraction of each component are shown in Table 1; (3) The rolling specification of the bar is φ14mm earthquake-resistant steel bar. The heating temperature in the heating process is 1095°C, and the time in the furnace is 45 min; in the rolling process: the starting rolling temperature is 1025°C, the finishing rolling inlet temperature is 970°C, and the temperature on the cooling bed is 930°C. The mechanical properties of the earthquake-resistant steel bars prepared in this embodiment are shown in Table 2.

[0019] Embodiment 2 A production method of a microalloyed earthquake-resistant steel bar provided in this embodiment has a production process as follows: converter (electric furnace) → LF ladle refining furnace → small billet continuous caster → continuous casting billet with a cross-section of 150mm×150mm → bar rolling line rolling (using controlled rolling and controlled cooling process) → φ20mm earthquake-resistant steel bar.

[0020] The key control parameters are as follows: (1) During the refining process in the ladle furnace (LF furnace), it is smelted under basic white slag. First, deep deoxidation is carried out with aluminum, and the content of [Al] in the molten steel is 0.026%. Then ferrotitanium is added. The soft stirring time before tapping is 6 min, the refining time is 33 min, and the content of [Ti] in the steel is 0.039%. (2) For the continuous casting of square billets, protective casting is adopted. The chemical composition of the cast billet and the mass fraction of each component are shown in Table 1. (3) The rolling specification of the bar is φ20mm anti-seismic steel bar. For the heating process, the heating temperature is 1110 °C and the residence time in the furnace is 49 min. For the rolling process: the starting rolling temperature is 1034 °C, the entry temperature of the finishing mill is 985 °C, and the temperature on the cooling bed is 948 °C. The mechanical properties of the anti-seismic steel bars prepared in this example are shown in Table 2.

[0021] Example 3 A production method of microalloyed anti-seismic steel bars provided in this example has a production process as follows: converter (electric furnace) → LF ladle refining furnace → small square billet continuous caster → continuous casting billet with a cross-section of 150mm×150mm → bar rolling line rolling (using controlled rolling and controlled cooling process) → φ28mm anti-seismic steel bar.

[0022] The key control parameters are as follows: (1) During the refining process in the ladle furnace (LF furnace), it is smelted under basic white slag. First, deep deoxidation is carried out with aluminum, and the content of [Al] in the molten steel is 0.028%. Then ferrotitanium is added. The soft stirring time before tapping is 7 min, the refining time is 33 min, and the content of [Ti] in the steel is 0.041%. (2) For the continuous casting of square billets, protective casting is adopted. The chemical composition of the cast billet and the mass fraction of each component are shown in Table 1. (3) The rolling specification of the bar is φ28mm anti-seismic steel bar. For the heating process: the heating temperature is 1115 °C and the residence time in the furnace is 54 min. For the rolling process: the starting rolling temperature is 1048 °C, the entry temperature of the finishing mill is 991 °C, and the temperature on the cooling bed is 954 °C. The mechanical properties of the anti-seismic steel bars prepared in this example are shown in Figure 2 .

[0023] The physical properties of the 400MPa grade anti-seismic steel bars with specifications of φ12 - φ32mm produced by using the process and flow described in the present invention are excellent and fully meet the requirements of the GB / T 1499.2 - 2018 standard.

[0024] The embodiments of the present invention have been shown and described. For those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for producing microalloyed earthquake-resistant steel bars, characterized in that: The chemical composition of the steel bar includes the following components by weight percentage: C: 0.20-0.24%, Si: 0.20-0.50%, Mn: 1.20-1.45%, P≤0.025%, S≤0.020%, Ti: 0.030-0.050%, Al: 0.015-0.035%, N≤0.0060%, and the rest is Fe; The production method comprises: converter smelting, ladle furnace LF refining, billet continuous casting and bar rolling line rolling using a controlled rolling and controlled cooling process, specifically the following steps: Step 1: tapping steel from a converter. The end point of the converter steelmaking process is controlled to be C ≥ 0.08%, P ≤ 0.020%, and the end point temperature ≥ 1620°C. Ferrosilicon is used for deoxidation. If the oxygen content at the end point of the converter is high, a small amount of ferroaluminum or steel core aluminum can be added for deoxidation. Ferrosilicon manganese is used for alloying. The alloy is added from 1 / 5 of the steel tapping to 4 / 5 of the steel tapping. Step 2: LF refining in ladle furnace. During LF refining in ladle furnace, refining should be carried out under alkaline white slag. During smelting, aluminum wire or aluminum particles are first added for deep deoxidation, and the soft stirring time in the later stage is ≥5min; Step 3: Continuous casting of small square billets, electromagnetic stirring of the crystallizer, strong cooling for secondary cooling, continuous casting speed: 2.5-2.8m / min; Step 4: The bar rolling line is a horizontal and vertical alternating rolling mill, and the earthquake-resistant steel bars are rolled using a controlled rolling and controlled cooling process.

2. The method for producing microalloyed earthquake-resistant steel bars according to claim 1, characterized in that: In the step 2, when Al content in molten steel is 0.015-0.035%, ferrotitanium is added, N is less than or equal to 0.0060% during the whole refining process, and the refining time in the ladle furnace is greater than or equal to 30 minutes.

3. The method for producing microalloyed earthquake-resistant steel bars according to claim 1, characterized in that: In the step three, the continuous casting of the square billet adopts long nozzle protection pouring, and the electromagnetic stirring parameters of the crystallizer are: current: 220-240A, frequency: 4-6Hz; secondary cooling: using a strong cooling water meter, the specific water volume is about 1.2L / Kg; the cross-sectional size of the continuous casting billet produced by continuous casting is: 150mm×150mm.

4. The method for producing microalloyed earthquake-resistant steel bars according to claim 1, characterized in that: In the step 4, the bar rolling line adopts a controlled rolling and controlled cooling process: heating furnace temperature 1080-1130°C, furnace time 40-70min, start rolling temperature 1030±30°C, finishing rolling inlet temperature 970±30°C, upper cooling bed temperature 920±30°C, natural air cooling and collection after hot rolling.

Images