Method for controlling fine dispersion of inclusions in SWRH62A hard wire steel

Abstract

The invention discloses a method for controlling fine dispersion of inclusions in SWRH62A hard wire steel. The method specifically comprises the following steps: carrying out composite treatment on smelted molten steel by adopting CaO-MgO-Nb core-shell structure nano composite powder; the preparation method of the CaO-MgO-Nb core-shell structure nano composite powder comprises the following steps that nanoscale Nb particles and a dispersing agent are mixed and then added into absolute ethyl alcohol, and uniform Nb suspension liquid is formed through ultrasonic dispersion; dropwise adding a Ca < 2 + > and Mg < 2 + > mixed solution into the Nb suspension, and then adjusting the pH value to 9.5-10.5 by using ammonia water, so that the Ca (OH) 2-Mg (OH) 2 composite precipitate is uniformly coated on the surfaces of Nb particles to form a core-shell precursor; and carrying out centrifugal separation, washing and vacuum drying on the core-shell precursor, and then carrying out high-temperature calcination. By means of the method, the O content and the Al content in the hard wire steel can be controlled to be 30-40 ppm and 50-60 ppm respectively.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and particularly relates to a nano-scale core-shell structure calcium-magnesium-niobium composite processing method for hard wire steel. Background Art

[0002] In the steel industry, hard wire steel is primarily used to produce tire wire, prestressed steel wire, spring steel wire, galvanized steel wire, steel strand, and wire rope wire. In recent years, with the rapid development of my country's national economy and the continued construction of infrastructure, the demand for high-strength prestressed steel strand and wire has been increasing year by year.

[0003] Hard wire steel contains large, refractory inclusions during the smelting process, making it prone to cracking during rolling. Both magnesium and calcium treatments can deoxidize and desulfurize, thereby reducing inclusions and improving molten steel cleanliness. However, both treatments have different technical drawbacks. Calcium treatment requires strict control of dissolved calcium and acid-soluble aluminum levels. Improper control not only fails to purify the molten steel and resolve nozzle blockage, but can also exacerbate nodulation. MgAl2O4 inclusions generated during magnesium treatment can segregate, and if large, these inclusions can also affect steel quality.

[0004] There are also reports on the use of calcium-magnesium-niobium composite treatment to control the morphology of inclusions in steel and improve steel performance. However, after calcium, magnesium, and niobium nanoparticles are mechanically mixed and added to the molten steel at the same time, Ca and Mg will compete with Nb for dissolved oxygen and sulfur in the molten steel, causing Nb to be easily oxidized to form high-melting-point inclusions such as Nb2O3, which are difficult to float up and remove. This will also reduce the niobium recovery rate, requiring excessive addition to compensate for the loss. Summary of the Invention

[0005] The present invention aims to provide a method for controlling the fine dispersion of inclusions in SWRH62A hard wire steel, which can control the O content to 30-40ppm and the Al content to 50-60ppm; and more than 80% of the inclusions are within the range of 0-2μm in size.

[0006] To achieve the above object, the technical solution of the present invention is: A method for controlling the fine dispersion of inclusions in SWRH62A hard wire steel comprises: using CaO-MgO-Nb core-shell structure nanocomposite powder to composite the molten steel after smelting; wherein the preparation method of the CaO-MgO-Nb core-shell structure nanocomposite powder is as follows: mixing nano-sized Nb particles with a dispersant and adding them to anhydrous ethanol, and forming a uniform Nb suspension by ultrasonic dispersion; dropping CaO into the Nb suspension; 2+ and Mg 2+The mixed solution is then adjusted to a pH of 9.5-10.5 using ammonia water, so that the Ca(OH)2-Mg(OH)2 composite precipitate is evenly coated on the surface of the Nb particles to form a core-shell precursor; the core-shell precursor is centrifuged, washed and vacuum-dried, and then calcined at a high temperature to obtain.

[0007] Furthermore, the Ca 2+ and Mg 2+ Ca in mixed solution 2+ and Mg 2+ The total concentration of Ca is 0.3-0.7 mol / L, 2+ / Mg 2+ The molar ratio is 4:3-6:3.

[0008] Furthermore, the Ca 2+ and Mg 2+ The amount of mixed solution added is based on Ca 2+ and Mg 2+ The sum of the amounts of substances is calculated to be 5-10 times the amount of the nano-sized Nb particles.

[0009] Furthermore, the Ca 2+ and Mg 2+ The dropwise addition rate of the mixed solution is 0.5-1.5 mL / min, and the mixture is stirred and reacted for 1-3 hours after the addition is completed.

[0010] Furthermore, the Ca 2+ and Mg 2+ The mixed solution is a mixed solution of calcium nitrate and magnesium nitrate.

[0011] Furthermore, in the CaO-MgO-Nb core-shell structure of the present invention, the thickness of the CaO-MgO shell is 50-100 nm, and the Nb core accounts for 10%-30% of the mass of the composite powder.

[0012] Furthermore, the nano-scale Nb particles of the present invention have a particle size of 50-100 nm and a purity of ≥99.9%.

[0013] Furthermore, the dispersant of the present invention is polyvinyl pyrrolidone (PVP), and the amount used is 5%-15% of the mass of the nano-Nb particles.

[0014] Furthermore, the ultrasonic dispersion conditions of the present invention are: power 150-250W, time 20-40 minutes.

[0015] Furthermore, the concentration of the ammonia water of the present invention is 20-30%.

[0016] Furthermore, the centrifugal separation conditions of the present invention are: a rotation speed of 7000-9000 rpm, and a time of 8-12 minutes; the washing step includes: washing with deionized water 2-4 times, and then washing with anhydrous ethanol 1-2 times; the vacuum drying conditions are: a temperature of 50-70°C, a vacuum degree ≤0.1MPa, and a time of 10-14 hours; the high-temperature calcination temperature is 450-550°C, a heating rate of 3-7°C / min, and a holding time of 1.5-2.5 hours. After calcination, the powder is ground and passed through a 100-200 mesh sieve.

[0017] Furthermore, the specific operation of the composite treatment of the molten steel after melting described in the present invention is: placing the steel material in a corundum crucible, melting the steel material by vacuum induction melting, raising the furnace temperature to above 1600°C under argon conditions; adding aluminum alloy to deoxidize the molten steel after it is melted; and adding CaO-MgO-Nb core-shell structure nanocomposite powder after 5-10 minutes to perform calcium-magnesium-niobium composite treatment.

[0018] Furthermore, the calcium-magnesium-niobium composite treatment time of the present invention is 10-20 minutes.

[0019] Furthermore, after the magnesium-niobium composite treatment of the present invention, sampling is performed to detect elements, slag is removed and alloy is added to adjust the composition, the temperature is controlled at 1580-1620° C. for steel tapping, and LF / VD / VOD furnace refining is performed as needed.

[0020] Furthermore, the method of the present invention can control the O content in SWRH62A hard wire steel to 30-40 ppm and the Al content to 50-60 ppm; more than 80% of the inclusions in the obtained SWRH62A hard wire steel have a size within the range of 0-2 μm.

[0021] The inventive principle of the technical solution of the present invention is: This invention utilizes a core-shell structured nanoscale calcium-magnesium-niobium composite treatment, significantly improving element utilization through a gradient release mechanism. During the composite treatment, the outer calcium and magnesium layers react preferentially, rapidly capturing oxygen and sulfur in the molten steel to form low-melting-point composite inclusions, eliminating large Al2O3 inclusions. Once the oxygen and sulfur concentrations decrease, the Nb core is exposed and combines with carbon and nitrogen to form Nb(C,N). This improves niobium yield and inhibits austenite recrystallization. Furthermore, the core-shell structure enhances reactivity and increases the plasticity of the inclusions, making it easier to form a fine, dispersed distribution.

[0022] The present invention uses ammonia water to adjust the pH in the preparation process of CaO-MgO-Nb core-shell structure nanocomposite powder. Because ammonia water is a weak base, it slowly releases OH in the solution. -, which can avoid the rapid generation and agglomeration of Ca(OH)2 and Mg(OH)2 precipitates caused by excessive alkalinity in the local area, thereby ensuring that the composite precipitate is evenly coated on the surface of the Nb particles to form an ideal core-shell precursor structure. - High concentration and rapid release can easily lead to coarse precipitated particles and uneven coating, affecting the integrity of the core-shell structure and nano-scale dispersibility. In addition, the cation of ammonia is NH4 + In the subsequent centrifugal washing, vacuum drying and high temperature calcination process, NH4 + It will escape in the form of NH3 gas without introducing impure metal ions, ensuring the high purity of the composite powder and preventing impurities from affecting the steel liquid treatment effect.

[0023] The beneficial effects of the present invention are: The present invention uses nano-scale core-shell structured calcium-magnesium-niobium to perform a composite treatment on hard wire steel. Compared with calcium-magnesium-niobium with ordinary structure, the amount of calcium-magnesium-niobium used can be reduced; the problem of nodules at the tundish nozzle can be solved, and the lining can be effectively prevented from peeling and corroding the molten steel. In addition, the purification effect on the molten steel is more significant than that of single magnesium treatment or calcium treatment, and a purer, high-quality hard wire steel can be obtained.

[0024] The SWRH62A hard wire steel obtained by the method of the present invention is purer, and the O content can be controlled within 30-40 ppm, and the Al content can be controlled within 50-60 ppm; and more than 80% of the inclusions in the obtained SWRH62A hard wire steel have a size within the range of 0-2 μm. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention. Example 1

[0026] A method for controlling fine dispersion of inclusions in SWRH62A hard wire steel comprises the following steps: (1) Preparation of CaO-MgO-Nb core-shell structured nanocomposite powder Nano-Nb particles with a particle size of 500-100 nm and a purity of ≥99.9% and polyvinyl pyrrolidone are added to anhydrous ethanol at a solid-liquid ratio of 1:10, wherein the amount of polyvinyl pyrrolidone added is 10% of the mass of the nano-Nb particles; ultrasonic dispersion is carried out at a power of 150 W for 20 minutes to form a uniform Nb suspension.

[0027] Preparation of Ca2+ / Mg 2+ A mixed solution of calcium nitrate and magnesium nitrate with a molar ratio of 4:3 and a concentration of 0.3 mol / L; according to the amount of nano-sized Nb particles, the Ca 2+ and Mg 2+ The volume of the mixed solution was calculated based on the sum of the amounts of the nano-sized Nb particles, which was five times the amount of the nano-sized Nb particles. The Nb suspension was added dropwise at a rate of 0.5 mL / min under magnetic stirring (500 rpm). After the addition was complete, the pH was adjusted to 9.5 with 20% ammonia water. The reaction was stirred for 1 hour to form a Nb-Ca(OH)2-Mg(OH)2 core-shell precursor.

[0028] The precursor suspension was centrifuged at 7000 rpm for 8 minutes, the supernatant discarded, and the mixture was washed twice with deionized water and twice with anhydrous ethanol. The mixture was then transferred to a vacuum drying oven and dried at 50°C under a vacuum of ≤0.1 MPa for 10 hours. The dried powder was placed in a muffle furnace and heated to 450°C at a rate of 3°C / min. The temperature was maintained for 1.5 hours, calcined, and ground through a 100-mesh sieve to produce a core-shell composite powder with a shell thickness of 50 nm and a Nb core content of 10%.

[0029] (2) Calcium magnesium niobium composite treatment After the molten steel is melted, aluminum alloy is added for deoxidation; 5 minutes after the aluminum alloy is added, nano-scale core-shell structure CaO-MgO-Nb powder is added for calcium-magnesium-niobium composite treatment; 10 minutes later, a quartz tube is used to take out the sample after the alloy is added, and the taken out sample is placed in a sodium chloride solution for cooling to obtain the product.

[0030] The samples of this embodiment were analyzed, and the results were as follows: The O content in the sample is 38ppm, the Al content is 57ppm, and the inclusions are mainly CaO-MgO-Al2O3-Nb2O3 composite inclusions.

[0031] The sizes of microscopic inclusions in the samples are mainly concentrated in the range of 1-2μm, among which the inclusions in the range of 1-1.5μm account for 40.1%, the inclusions in the range of 1.5-2μm account for 42.8%, the inclusions in the range of 2-3μm account for 7.5%, the inclusions in the range of 3-4μm account for 5.9%, and the inclusions in the range of 4-5μm account for 1.1%; the average size is 1.71μm.

[0032] To visually describe the distribution of inclusions, we calculated the area percentage of inclusions at different locations within the steel matrix per unit area of the sample based on the two-dimensional coordinates of the inclusions on the sample surface and the area of each inclusion. The average inclusion area density of the sample in this example was 0.10%, and the maximum inclusion area density was 0.226%. The number of inclusions counted was 16. Example 2

[0033] A method for controlling fine dispersion of inclusions in SWRH62A hard wire steel comprises the following steps: (1) Preparation of CaO-MgO-Nb core-shell structured nanocomposite powder Nano-Nb particles with a particle size of 500-100 nm and a purity of ≥99.9% and polyvinyl pyrrolidone are added to anhydrous ethanol at a solid-liquid ratio of 1:10, wherein the amount of polyvinyl pyrrolidone added is 5% of the mass of the nano-Nb particles; ultrasonic dispersion is carried out at a power of 200 W for 30 minutes to form a uniform Nb suspension.

[0034] Preparation of Ca 2+ / Mg 2+ A mixed solution of calcium nitrate and magnesium nitrate with a molar ratio of 5:3 and a concentration of 0.5 mol / L; 2+ and Mg 2+ The volume of the mixed solution was calculated based on the sum of the amounts of the nano-sized Nb particles (7 times the amount of the nano-sized Nb particles). The Nb suspension was added dropwise at a rate of 1 mL / min under magnetic stirring (500 rpm). After the addition was complete, the pH was adjusted to 10 with 25% ammonia water. The reaction was stirred and continued for 2 hours to form a Nb-Ca(OH)2-Mg(OH)2 core-shell precursor.

[0035] The precursor suspension was centrifuged at 8000 rpm for 10 minutes, the supernatant discarded, and the suspension was washed three times with deionized water and once with anhydrous ethanol. The suspension was then transferred to a vacuum drying oven and dried at 60°C under a vacuum of ≤0.1 MPa for 12 hours. The dried powder was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min. The temperature was maintained for 2 hours. After calcination, the powder was ground through a 100-mesh sieve to produce a core-shell composite powder with a shell thickness of 70 nm and a Nb core content of 16%.

[0036] (2) Calcium magnesium niobium composite treatment After the molten steel is melted, aluminum alloy is added for deoxidation; 7 minutes after the aluminum alloy is added, nano-scale core-shell structure CaO-MgO-Nb powder is added for calcium-magnesium-niobium composite treatment; 15 minutes later, a quartz tube is used to take out the sample after the alloy is added; the taken out sample is placed in a sodium chloride solution for cooling to obtain the product.

[0037] The samples of this embodiment were analyzed, and the results were as follows: The O content in the sample is 36ppm, the Al content is 54ppm, and the inclusions are mainly CaO-MgO-Al2O3-Nb2O3 composite inclusions.

[0038] The sizes of microscopic inclusions in the samples are mainly concentrated in the range of 0-2μm, among which the inclusions in the range of 0-1μm account for 36.8%, the inclusions in the range of 1-1.5μm account for 25.6%, the inclusions in the range of 1.5-2μm account for 23.1%, the inclusions in the range of 2-3μm account for 8.5%, the inclusions in the range of 3-4μm account for 3.4%, and the inclusions in the range of 4-5μm account for 2.6%; the average size is 1.41μm.

[0039] The average area density of inclusions in the sample of this embodiment is 0.10%, and the maximum area density of inclusions is 0.18%; the number of inclusions counted is 14. Example 3

[0040] A method for controlling fine dispersion of inclusions in SWRH62A hard wire steel comprises the following steps: (1) Preparation of CaO-MgO-Nb core-shell structured nanocomposite powder Nano-Nb particles with a particle size of 500-100 nm and a purity of ≥99.9% and polyvinyl pyrrolidone are added to anhydrous ethanol at a solid-liquid ratio of 1:10, with the amount of polyvinyl pyrrolidone added being 15% of the mass of the nano-Nb particles; ultrasonic dispersion is performed at a power of 250 W for 40 minutes to form a uniform Nb suspension.

[0041] Preparation of Ca 2+ / Mg 2+ A mixed solution of calcium nitrate and magnesium nitrate with a molar ratio of 6:3 and a concentration of 0.5 mol / L; 2+ and Mg 2+ The volume of the mixed solution was calculated based on the sum of the molar masses, which was 10 times the mass of the nano-sized Nb particles. The Nb suspension was added dropwise at a rate of 1.5 mL / min under magnetic stirring (500 rpm). After the addition was complete, the pH was adjusted to 10.5 with 30% ammonia water. The reaction was stirred for 3 hours to form a Nb-Ca(OH)2-Mg(OH)2 core-shell precursor.

[0042] The precursor suspension was centrifuged at 9000 rpm for 12 minutes, the supernatant discarded, and the mixture was washed four times with deionized water and once with anhydrous ethanol. The mixture was then transferred to a vacuum drying oven and dried at 70°C under a vacuum of ≤0.1 MPa for 14 hours. The dried powder was placed in a muffle furnace and heated to 550°C at a rate of 7°C / min. The temperature was maintained for 2.5 hours, calcined, and ground through a 200-mesh sieve to produce a core-shell composite powder with a shell thickness of 100 nm and a Nb core content of 30%.

[0043] (2) Calcium magnesium niobium composite treatment After the molten steel is melted, aluminum alloy is added for deoxidation; 10 minutes after the aluminum alloy is added, nano-scale core-shell structure CaO-MgO-Nb powder is added for calcium-magnesium-niobium composite treatment; 20 minutes later, a quartz tube is used to take out the sample after the alloy is added; the taken out sample is placed in a sodium chloride solution for cooling to obtain the product.

[0044] The samples of this embodiment were analyzed, and the results were as follows: The O content in the sample is 32ppm, the Al content is 51ppm, and the inclusions are mainly CaO-MgO-Al2O3-Nb2O3 composite inclusions.

[0045] The sizes of microscopic inclusions in the samples are mainly concentrated in the range of 0-2μm, among which the inclusions in the range of 0-1μm account for 39.4%, the inclusions in the range of 1-1.5μm account for 28.3%, the inclusions in the range of 1.5-2μm account for 21.6%, the inclusions in the range of 2-3μm account for 6.2%, the inclusions in the range of 3-4μm account for 2.8%, and the inclusions in the range of 4-5μm account for 1.7%; the average size is 1.58μm.

[0046] The average area density of inclusions in the sample of this embodiment is 0.13%, the maximum area density of inclusions is 0.187%, and the number of inclusions counted is 16.

[0047] Comparative Example 1 The addition amount of Ca, Mg and Nb in this comparative example is 0, and the remaining experimental steps are consistent with those in Example 1.

[0048] The hard wire steel obtained in this comparative example has an O content of 82 ppm and an Al content of 130 ppm.

[0049] The size of microscopic inclusions in the hard wire steel of this comparative example is 0-2μm, mainly large-sized Al2O3 inclusions with irregular shapes, with a wide size distribution range, a minimum diameter of 0.9μm, and a maximum diameter greater than 10μm; the inclusion radius is 1-3μm, accounting for the highest proportion, at 72.16%, of which inclusions in the range of 1-1.5μm account for 22.16%, inclusions in the range of 1.5-2μm account for 25%, inclusions in the range of 2-3μm account for 25%, inclusions in the range of 3-4μm account for 14.77%, inclusions in the range of 4-5μm account for 3.41%, and inclusions larger than 5μm account for 9.09%; the maximum area density of inclusions reaches 1.4%.

[0050] The experimental results of various embodiments and comparative examples are summarized in Table 1.

[0051] Table 1 Experimental results of the embodiments and comparative examples

[0052] As shown in Table 1, the nanoscale core-shell calcium-magnesium-niobium composite treatment employed in the present invention effectively reduces the oxygen and aluminum contents in steel, as well as the number and size of inclusions. After calcium-magnesium-niobium composite treatment, the oxygen content of the molten steel remains low, and the average size and area density of inclusions are also relatively small. The average size of microscopic inclusions in the three samples is 1.57 μm, and the inclusion segregation areas are relatively small. This facilitates the fine and dispersed distribution of inclusions in the molten steel, achieving relatively ideal smelting results.

Claims

1. A method for controlling fine dispersion of inclusions in SWRH62A hard wire steel, characterized in that: The molten steel is composited with a CaO-MgO-Nb core-shell structure nanocomposite powder. The preparation method of the CaO-MgO-Nb core-shell structure nanocomposite powder is as follows: nano-sized Nb particles are mixed with a dispersant and then added to anhydrous ethanol to form a uniform Nb suspension by ultrasonic dispersion; CaO-MgO-Nb core-shell structure nanocomposite powder is added dropwise to the Nb suspension. 2+ and Mg 2+ The mixed solution is then adjusted to a pH of 9.5-10.5 using ammonia water, so that the Ca(OH)2-Mg(OH)2 composite precipitate is evenly coated on the surface of the Nb particles to form a core-shell precursor; the core-shell precursor is centrifuged, washed and vacuum-dried, and then calcined at a high temperature to obtain.

2. A method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The Ca 2+ and Mg 2+ Ca in mixed solution 2+ and Mg 2+ The total concentration of Ca is 0.3-0.7 mol / L, 2+ / Mg 2+ The molar ratio is 4:3-6:

3.

3. The method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The Ca 2+ and Mg 2+ The amount of mixed solution added is based on Ca 2+ and Mg 2+ The sum of the amounts of substances is calculated to be 5-10 times the amount of the nano-sized Nb particles.

4. The method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The Ca 2+ and Mg 2+ The dropwise addition rate of the mixed solution is 0.5-1.5 mL / min, and the mixture is stirred and reacted for 1-3 hours after the dropwise addition is completed.

5. The method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The Ca 2+ and Mg 2+ The mixed solution is a mixed solution of calcium nitrate and magnesium nitrate.

6. The method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The dispersant is polyvinyl pyrrolidone (PVP), and the amount used is 5%-15% of the mass of the nano Nb particles.

7. The method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The concentration of the ammonia water is 20-30%.

8. The method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The thickness of the CaO-MgO shell in the CaO-MgO-Nb core-shell structure is 50-100 nm, and the Nb core accounts for 10%-30% of the mass of the composite powder.

9. The method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The calcium-magnesium-niobium composite treatment time is 10-20 minutes.

10. The method for controlling fine dispersion of inclusions in SWRH62A hard wire steel according to claim 1, characterized in that: The method can control the O content in SWRH62A hard wire steel to 30-40 ppm and the Al content to 50-60 ppm; more than 80% of the inclusions in the obtained SWRH62A hard wire steel have a size within the range of 0-2 μm.

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