Production method for preventing casting nodulation of low-carbon low-silicon high-aluminum cold forging steel

Abstract

The invention belongs to the technical field of steel smelting, and particularly relates to a production method for preventing casting nodulation of low-carbon low-silicon high-aluminum cold forging steel. The low-carbon low-silicon high-aluminum cold forging steel is low in C and Si content in component control, the oxygen content is high in the converter tapping process, and a large number of high-melting-point inclusions are generated in the refining process through deoxidation; in addition, in component control, the Al content is high, and secondary oxidation is prone to occurring during continuous casting, so that Al2O3 inclusions are generated. Therefore, during continuous casting of the low-carbon low-silicon high-aluminum cold forging steel, nodulation fluctuation is easy to occur, so that the problem of cost loss caused by production casting stopping and fluctuating blank picking is caused. By controlling the key points such as converter tapping components, refining components, deoxidation slag protection in the refining process, continuous casting covering agent components and performance, continuous casting covering agent adding time and the like, the problem of casting nodulation of the low-carbon low-silicon high-aluminum cold forging steel is effectively solved, and the yield of a casting furnace and the casting blank quality are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and relates to a production method for preventing nodule formation during the initial casting of continuous casting low-carbon, low-silicon, high-alumina steel. Background Technology

[0002] Low-carbon, low-silicon cold-heading steel is formed by direct cold heading at room temperature and is used to produce screws, pins, nuts, and other products. Strict requirements are placed on the steel's composition and surface quality. Al (Al) is a key element in the composition of cold-heading steel, acting as a deoxidizer and influencing plasticity. A certain content in the steel is required to achieve a good deoxidation effect and improve plastic deformation during cold heading. Additionally, Si (Si) is also a deoxidizer and reduces plastic deformation capacity during cold heading. Therefore, for steel grades with large deformation at room temperature, the Si content must be controlled.

[0003] Therefore, in the production process of low-carbon, low-silicon cold heading steel, the Al content is controlled at a relatively high level while the Si content is controlled at a relatively low level. During deoxidation, a large amount of high-melting-point alumina inclusions are generated. Simultaneously, secondary Al oxidation is prone to occur during the initial casting of continuous casting, leading to fluctuations, nodule formation, and billet quality issues. Currently, regarding the initial casting problem of low-carbon, low-silicon, high-alumina cold heading steel, patent application CN201910763036.8, "A Method for Preventing Nodule Formation in Continuous Casting of High-Alumina Cold Heading Steel," proposes using low-alumina steel grades as a transition during the initial casting. However, if there are no production orders for low-alumina steel grades, a large amount of low-alumina steel used for the transition cannot be utilized, resulting in stagnant low-alumina steel inventory. Patent application CN202210306178.3, "Improving the Continuous Casting Process of Small Square Billets with Nodule Formation in Aluminum-Containing Steel," further supports this. CN202310972392.7 "A method to prevent nozzle formation during continuous casting of cold heading steel" and CN202410834704.2 "A method for direct casting of aluminum-containing cold heading steel" address the problem of nozzle formation during casting of aluminum-containing steel. They adopt measures such as refining to create white slag, composition control, cleaning the tundish during continuous casting, adding calcium line to the tundish, argon filling the tundish for protection, and adding a covering agent for protection. These measures can reduce the problem of secondary oxidation of Al during casting of aluminum-containing steel, but there are still some shortcomings. Adding calcium wire to the tundish can modify the alumina that has undergone secondary oxidation, but this modification also increases the amount of inclusions in the steel, affecting the cleanliness of the molten steel. Argon filling in the tundish can prevent secondary oxidation of the liquid surface, but the large amount of argon required increases the production cost. In addition, when the ladle is first started pouring, secondary oxidation inevitably occurs for a certain period of time as the molten steel flows from the ladle into the tundish. Adding a covering agent to isolate and control the liquid level in the tundish when it reaches a certain height can also be effective, but some secondary oxidation still exists before the covering agent is added.

[0004] For the production of low-carbon, low-silicon, high-aluminum steel, there is an urgent need for a production method that can ensure high cleanliness of the cast billets and stable casting process. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a production method for preventing nodule formation during the initial casting of low-carbon, low-silicon, high-alumina cold heading steel. While ensuring the stability of the initial casting of low-carbon, low-silicon, high-alumina cold heading steel, it can also ensure that the quality of the billet meets the requirements, thereby effectively avoiding production accidents and quality hazards caused by fluctuations in the initial casting.

[0006] The production method for low-carbon, low-silicon, high-aluminum cold heading steel with initial casting and nodule formation provided by this invention comprises the following steps: (1) The composition of the steel tapped from the converter is controlled as follows: C: 0.04~0.07%, Si≤0.02%, S≤0.010%, tapping temperature ≥1620℃. Alloy and slag are added when the steel is 1 / 3 of the total amount tapped. At the end of tapping, a double-barrel method is used to avoid slag discharge. After tapping, the molten steel is fed to the argon station to feed aluminum wire. After feeding the aluminum wire, the Al content in the steel is 0.050~0.070%.

[0007] (2) After the molten steel enters the LF, it is heated and the composition is finely adjusted using low-carbon ferromanganese. The refining cycle is controlled at 50~70min. In the first 20min of refining, aluminum particles and calcium carbide are used to deoxidize the slag surface and adjust the composition. In the middle 20~40min, calcium carbide is used to deoxidize the slag surface and maintain the slag. At the same time, lime, cryolite and fluorite are used to adjust the slag system. The refining slag requirements at the end of refining are CaO / SiO2: 9~15, CaO / Al2O3: 1.5~2, MnO+FeO≤1%.

[0008] (3) After refining, calcium treatment is carried out. The composition control requirements after calcium treatment are Ca / Al: 0.18~0.25, Ca / S>1, and soft blowing time ≥10min.

[0009] (4) The continuous casting adopts an internally installed immersion nozzle tundish. Before casting, the temperature inside the tundish is ≥1150℃. When the tundish is opened to the casting position, 100~150kg of low melting point covering agent is evenly added to the casting area and 20~40kg of low melting point covering agent is added to the impact area. After the covering agent is added, the long nozzle of the ladle is installed for casting.

[0010] (5) When the weight of molten steel in the tundish reaches 2 / 3, add 40 kg and 200 kg of low melting point covering agent to the impact zone and casting zone of the tundish respectively. After adding the covering agent, open the stopper rod to start casting in the tundish, and add carbonized rice husks to the tundish for heat preservation.

[0011] Furthermore, the converter's steel output is between 130 and 140 tons. The alloy added during steel tapping is low-carbon ferromanganese, and the slag material is lime and slag-reducing agent. At the end of steel tapping, the two baffles are a slag-blocking cone floating on the steel surface and a slag-blocking slide.

[0012] Furthermore, the low-melting-point covering agent has the following composition: CaO: 45~50%, SiO2≤3%, Al2O3: 40~45%, MgO≤1%, F: 2~8%, Na2O: 3~7%, MnO+FeO≤0.1%, melting point: 1380~1450℃, and particle size: 1.6~2.5mm.

[0013] In some embodiments of the present invention, the low-melting-point covering agent is composed of CaO: 46.4%, SiO2: 1.2%, Al2O3: 42.5%, MgO: 0.25~0.36%, F: 5.6%, Na2O: 4.2%, MnO+FeO: 0.05%, with a melting point of 1425℃ and a particle size of 1.7~1.8mm.

[0014] Furthermore, the weight of molten steel in the tundish when fully filled is between 40 and 50 tons.

[0015] Furthermore, the chemical composition of the low-carbon, low-silicon, high-aluminum cold heading steel, by weight percentage, is [C]: 0.04~0.10%, [Si]≤0.10%, [Mn]: 0.30~0.90%, [Al]≥0.020%, with the remainder being Fe and unavoidable impurities.

[0016] For the smelting process of low-carbon, low-silicon, and high-alumina steel, the C, Si, and S composition and tapping temperature are controlled during converter tapping to ensure good slag formation and rapid adjustment of composition to target values ​​in the slag added at tapping. Rapid deoxidation and composition adjustment are performed in the early refining stage; slag surface deoxidation and slag retention are carried out in the middle stage; and temperature and slag system are fine-tuned in the later stage to further ensure inclusion removal. Simultaneously, by controlling the amount of calcium treated, the calcium-aluminum ratio and calcium-sulfur ratio are maintained to prevent the formation of high-melting-point calcium sulfide and high-melting-point calcium aluminates, ensuring that inclusions are located in the low-melting-point region. When the final continuous casting begins, the tundish temperature is baked to the required level. A certain amount of low-melting-point covering agent is added to the tundish before casting begins. The low-melting-point covering agent has good melting and spreading properties, and it melts and spreads quickly on the surface of the molten steel after casting begins, isolating the alumina and spinel-like high-melting-point inclusions generated by secondary oxidation in the tundish during casting. In addition, when the liquid level in the tundish reaches a certain height, a certain amount of low-melting-point covering agent is added to form a second layer of protective slag. Finally, carbonized rice husks are added for insulation, further covering and insulating the molten steel surface in the tundish.

[0017] Compared to existing production processes, firstly, in the smelting of low-carbon, low-silicon, high-alumina steel, the converter and refining operations avoid the formation of high-melting-point calcium aluminates such as CaO·2Al2O3, CaO·6Al2O3, or Al2O3 due to improper Ca / Al control, or high-melting-point calcium aluminates such as CaS due to improper Ca / S control. This ensures that inclusions in the steel at the end of refining are in the low-melting-point calcium aluminate region, eliminating the need for transitioning with other low-alumina or similarly composed steel grades during continuous casting.

[0018] Secondly, the development of low-melting-point covering agents during initial casting involves controlling the composition and particle size of the covering agent, especially the SiO2 content. Higher SiO2 content is easily reduced by Al, leading to the formation of high-melting-point Al2O3. Due to the reduced SiO2 content, certain amounts of F and Na2O need to be added to adjust for the lower melting point of the covering agent. The MnO and FeO content in the covering agent must be strictly controlled. MnO and FeO directly provide oxygen upon contact with molten steel, reacting directly with Al and Si in the steel, resulting in the formation of high-melting-point Al2O3, severely contaminating the cleanliness of the molten steel. Simultaneously, the MgO content in the covering agent must be controlled to prevent reaction with Al and O in the molten steel to form spinel, which can lead to nodule formation during casting. Furthermore, controlling the particle size of the covering agent ensures rapid melting and spreading on the surface of the molten steel upon contact. However, existing processes often use covering agents with high SiO2, MnO, and FeO content, and poor particle size and melting point control result in slow melting and poor spreading.

[0019] Finally, during the start of continuous casting, a certain amount of low-melting-point covering agent is added to the tundish in advance. By controlling the particle size of the covering agent, it effectively spreads at the bottom of the tundish. After the molten steel enters the tundish, the covering agent melts rapidly and covers the surface of the molten steel, quickly isolating it from air. When the molten steel level in the tundish reaches a certain height, a second amount of low-melting-point covering agent is added to increase the sealing of the molten steel surface. At the same time, carbonized rice husks are added for insulation, ensuring that air is completely isolated from the moment the molten steel enters the tundish until it reaches the full liquid level for normal pouring. In existing processes, to prevent secondary oxidation or to modify oxidized inclusions during the start of continuous casting, argon is usually blown into the tundish in advance or a large amount of calcium wire is added to the tundish. Regarding the issue of argon blowing for atmosphere protection in the tundish, although it can eliminate a certain amount of oxygen in the tundish, there will inevitably be a short-term oxidation problem in the initial stage of molten steel entering the tundish. In addition, the layout, maintenance, and avoidance of argon blowing equipment will increase production costs. Regarding the addition of calcium wire in the tundish for inclusion modification, a large amount of high-melting-point alumina or spinel inclusions have already been generated in the tundish. Although these inclusions can be modified into low-melting-point calcium aluminates, the secondary oxidation and subsequent modification of inclusions will inevitably contaminate the molten steel. Even if the problem of nodule formation at the beginning of continuous casting is solved, the poor cleanliness of the molten steel will easily lead to excessive inclusions. Furthermore, when the calcium wire comes into contact with the molten steel, it generates a large amount of white smoke, causing significant environmental pollution.

[0020] In summary, the low-carbon, low-silicon, high-aluminum steel produced by this invention has stable continuous casting start-up, low production cost, and high billet cleanliness. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings, in which: Figure 1The distribution of ternary phase diagram of inclusions in the intermediate tundish in Example 1.

[0022] Figure 2 The distribution of ternary phase diagrams of inclusions in the intermediate tundish in Example 2.

[0023] Figure 3 To compare the distribution of ternary phase diagrams of inclusions in the intermediate tundish of Example 1.

[0024] Figure 4 To compare the distribution of ternary phase diagrams of inclusions in the intermediate tundish in Example 2.

[0025] Figure 5 To compare the distribution of ternary phase diagrams of inclusions in the intermediate tundish of Example 3.

[0026] Figure 6 To compare the distribution of ternary phase diagrams of inclusions in the intermediate tundish in Example 4.

[0027] Figure 7 To compare the distribution of ternary phase diagrams of inclusions in the intermediate tundish of Example 5.

[0028] Figure 8 To compare the distribution of ternary phase diagrams of inclusions in the intermediate tundish of Example 6.

[0029] Figure 9 To compare the distribution of ternary phase diagrams of inclusions in the intermediate tundish of Example 7. Detailed Implementation

[0030] The present invention will be further described in detail with reference to the embodiments.

[0031] Example 1

[0032] (1) The converter tapping rate is 135t, and the tapping composition is controlled as C: 0.05%, Si: 0.006%, S: 0.005%. The tapping temperature is 1635℃. When the tapping rate is 45t, 210kg of low-carbon ferromanganese, 600kg of lime, and 400kg of slag-reducing agent are added. At the end of tapping, slag-blocking cones and sliding plates are used to block slag. After tapping, the molten steel is fed to the argon station with 500m of aluminum wire. After feeding the aluminum wire, the Al content in the steel is 0.063%.

[0033] (2) When the molten steel reaches the LF, it is energized and heated. After heating for 5 minutes, 50 kg of aluminum granules and 100 kg of calcium carbide slag are added for deoxidation. After 10 minutes, 150 kg of low-carbon ferromanganese is added for composition adjustment. After 20 minutes, a sample is taken, and the composition is controlled as follows: [C]: 0.07%, [Si]: 0.04%, [Mn]: 0.45%, [Al]: 0.055%, S: 0.003%, P: 0.012%. Calcium carbide is added to the slag surface in small amounts multiple times for further deoxidation. At the same time, 80 kg of lime, 105 kg of cryolite, and 50 kg of fluorite are added to adjust the slag system. At the end of refining, the refining slag contains: CaO: 54.5%, SiO2: 4.8%, Al2O3: 34.4%, MgO: 4.2%, MnO: 0.06%, FeO: 0.61%. The CaO / SiO2 ratio is 11.4, the CaO / Al2O3 ratio is 1.6, and the MnO+FeO ratio is 0.67%.

[0034] (3) After refining, feed in 550m calcium wire. The final composition after calcium treatment is [C]: 0.08%, [Si]: 0.04%, [Mn]: 0.45%, [Al]: 0.046%, S: 0.003%, P: 0.011%, Ca: 0.009%. The control requirements are Ca / Al = 0.20 and Ca / S = 3. The soft blowing time is 13min. The product is then transferred to the continuous casting machine for casting.

[0035] (4) Continuous casting adopts an internally fitted immersion nozzle tundish. 42t of molten steel is poured into the tundish when it is full. The temperature inside the tundish before casting is 1186℃. The composition of the low-melting-point covering agent at the start of casting is CaO: 46.4%, SiO2: 1.2%, Al2O3: 42.5%, MgO: 0.25%, F: 5.6%, Na2O: 4.2%, MnO+FeO: 0.05%, melting point 1425℃, particle size 1.8mm. When the tundish is opened to the pouring position, 130kg of low-melting-point covering agent is evenly added to the pouring area, and 30kg of low-melting-point covering agent is added to the impact area. After the covering agent is added, the long nozzle of the ladle is installed for casting.

[0036] (5) When the weight of molten steel in the tundish reaches 28t, add 40kg and 200kg of low melting point covering agent to the impact zone and casting zone of the tundish respectively. After adding the covering agent, open the stopper rod to start casting in the tundish, and add carbonized rice husks to the tundish for heat preservation.

[0037] After the tundish was opened for casting, the stopper and liquid level were stable, and the casting process was normal. Samples were taken from the tundish for inclusion scanning analysis (e.g., Figure 1 (As shown), analysis area 50mm² 2 The inclusions are mainly distributed in the low melting point region, with a total of 252 inclusions and 0 spinel due to secondary oxidation.

[0038] Example 2

[0039] (1) The converter tapping rate is 138t, and the tapping composition is controlled as C: 0.04%, Si: 0.008%, S: 0.006%. The tapping temperature is 1640℃. When the tapping rate is 46t, 230kg of low-carbon ferromanganese, 600kg of lime, and 400kg of slag-reducing agent are added. At the end of tapping, slag-blocking cones and sliding plates are used to block slag. After tapping, the molten steel is fed to the argon station with 450m of aluminum wire. After feeding the aluminum wire, the Al content in the steel is 0.055%.

[0040] (2) When the molten steel reaches the LF, it is energized and heated. After heating for 8 minutes, 40 kg of aluminum granules and 120 kg of calcium carbide slag are added for deoxidation. After 13 minutes, 260 kg of low-carbon ferromanganese is added for composition adjustment. After 20 minutes, a sample is taken, and the composition is controlled as follows: [C]: 0.08%, [Si]: 0.05%, [Mn]: 0.63%, [Al]: 0.051%, S: 0.004%, P: 0.016%. Calcium carbide is added to the slag surface in small amounts multiple times for further deoxidation. At the same time, 70 kg of lime, 60 kg of cryolite, and 30 kg of fluorite are added for slag system adjustment. At the end of refining, the refining slag contains: CaO: 54.8%, SiO2: 5.1%, Al2O3: 34.9%, MgO: 3.3%, MnO: 0.08%, FeO: 0.52%. The CaO / SiO2 ratio is 10.7, the CaO / Al2O3 ratio is 1.6, and the MnO+FeO ratio is 0.60%.

[0041] (3) After refining, feed in 420m calcium wire. The final composition after calcium treatment is [C]: 0.08%, [Si]: 0.05%, [Mn]: 0.63%, [Al]: 0.043%, S: 0.003%, P: 0.016%, Ca: 0.0077%. The control requirements are Ca / Al = 0.18 and Ca / S = 2.5. The soft blowing time is 18min. The product is then transferred to the continuous casting machine for casting.

[0042] (4) Continuous casting adopts an internally fitted immersion nozzle tundish. 42t of molten steel is poured into the tundish when it is full. The temperature inside the tundish before casting is 1195℃. The composition of the low-melting-point covering agent at the start of casting is CaO: 46.4%, SiO2: 1.2%, Al2O3: 42.5%, MgO: 0.36%, F: 5.6%, Na2O: 4.2%, MnO+FeO: 0.05%, melting point 1425℃, particle size 1.7mm. When the tundish is opened to the pouring position, 140kg of low-melting-point covering agent is evenly added to the pouring area, and 40kg of low-melting-point covering agent is added to the impact area. After the covering agent is added, the long nozzle of the ladle is installed for casting.

[0043] (5) When the weight of molten steel in the tundish reaches 28t, add 40kg and 200kg of low melting point covering agent to the impact zone and casting zone of the tundish respectively. After adding the covering agent, open the stopper rod to start casting in the tundish, and add carbonized rice husks to the tundish for heat preservation.

[0044] After the tundish was opened for casting, the stopper and liquid level remained stable, and the casting process proceeded normally. Samples were taken from the tundish for inclusion scanning analysis (e.g., ...). Figure 2 (As shown), analysis area 50mm² 2 The inclusions are mainly distributed in the low melting point region, with a total of 226 inclusions, and the number of spinels caused by secondary oxidation is 0.

[0045] Comparative Example 1

[0046] In Example 1, the composition of the low-melting-point covering agent in step (4) during the initial pouring of the tundish is CaO: 46.4%, SiO2: 1.2%, Al2O3: 42.5%, MgO: 0.25%, F: 5.6%, Na2O: 4.2%, MnO+FeO: 0.05%, melting point 1425℃, particle size 1.8mm, which is adjusted to "the composition of the covering agent is CaO: 42.4%, SiO2: 5.9%, Al2O3: 41.8%, MgO: 0.29%, F: 5.7%, Na2O: 4.0%, MnO+FeO: 0.08%, melting point 1395℃, particle size 1.8mm", which increases the SiO2 content in the covering agent. The rest is the same as in Example 1.

[0047] After the tundish was opened for casting, the stopper rod showed a slight increase in height. Samples were taken from inside the tundish for inclusion scanning analysis (e.g., ...). Figure 3 (As shown), analysis area 50mm² 2 The inclusions are mainly distributed in the low melting point region, with a small number located outside the low melting point region. The total number of inclusions is 289, and the number of spinels caused by secondary oxidation is 25.

[0048] Comparative Example 2

[0049] In Example 1, the composition of the low-melting-point covering agent in step (4) during the initial pouring of the tundish is CaO: 46.4%, SiO2: 1.2%, Al2O3: 42.5%, MgO: 0.25%, F: 5.6%, Na2O: 4.2%, MnO+FeO: 0.05%, melting point 1425℃, particle size 1.8mm, is adjusted to "the composition of the covering agent is CaO: 42.2%, SiO2: 1.5%, Al2O3: 41.0%, MgO: 0.36%, F: 5.2%, Na2O: 4.3%, MnO+FeO: 2.0%, melting point 1381℃, particle size 1.8mm", that is, the MnO+FeO content in the covering agent is increased, and the rest is the same as in Example 1.

[0050] After the tundish was opened for casting, the stopper rod showed a significant rise. Samples were taken from inside the tundish for inclusion scanning analysis (e.g., ...). Figure 4 (As shown), analysis area 50mm² 2 The inclusions are mainly distributed in the low melting point region, with a small number located outside the low melting point region. The total number of inclusions is 243, and the number of spinels caused by secondary oxidation is 75.

[0051] Comparative Example 3

[0052] In Example 1, the composition of the low-melting-point covering agent in step (4) during the initial pouring of the tundish is CaO: 46.4%, SiO2: 1.2%, Al2O3: 42.5%, MgO: 0.25%, F: 5.6%, Na2O: 4.2%, MnO+FeO: 0.05%, melting point 1425℃, particle size 1.8mm, which is adjusted to "the composition of the covering agent is CaO: 42%, SiO2: 1.6%, Al2O3: 42.0%, MgO: 4.6%, F: 5.1%, Na2O: 4.6%, MnO+FeO: 0.09%, melting point 1385℃, particle size 1.8mm", which increases the MgO content in the covering agent. The rest is the same as in Example 1.

[0053] After the tundish was opened for casting, the stopper rod showed a significant rise. Samples were taken from inside the tundish for inclusion scanning analysis (e.g., ...). Figure 5 (As shown), analysis area 50mm² 2 The inclusions are located in the low melting point region, and some spinel is also generated. The total number of inclusions is 286, and the number of spinel caused by the covering agent and secondary oxidation of molten steel is 98.

[0054] Comparative Example 4

[0055] In Example 1, the low-melting-point covering agent before casting in step (4) is not added. In step (5), when the weight of molten steel reaches 28t, 330kg and 70kg of low-melting-point covering agent are added to the tundish casting area and impact area at one time, respectively. That is, the timing of adding the covering agent is adjusted. The rest is the same as in Example 1.

[0056] After the tundish was opened for casting, the stopper rod showed a significant rise. Samples were taken from inside the tundish for inclusion scanning analysis (e.g., ...). Figure 6 (As shown), analysis area 50mm² 2 Most of the inclusions are distributed outside the low melting point region, with a total of 450 inclusions, of which 72 are spinels caused by secondary oxidation.

[0057] Comparative Example 5

[0058] In Example 1, the low-melting-point covering agent before casting in step (4) is not added. When casting begins, 100m of calcium wire is added to the tundish. At the same time, when the weight of molten steel reaches 28t in step (5), 330kg and 70kg of low-melting-point covering agent are added to the casting area and impact area of ​​the tundish at one time. That is, the inclusions caused by secondary oxidation are modified in the tundish and the timing of adding the covering agent is adjusted. The rest is the same as in Example 1.

[0059] After the tundish was opened for casting, the stopper and liquid level remained stable, and the casting process proceeded normally. Samples were taken from the tundish for inclusion scanning analysis (e.g., ...). Figure 7 (As shown), analysis area 50mm² 2 The inclusions are mainly distributed in the low melting point region, with a total of 882 inclusions, and the number of spinels caused by secondary oxidation is 0.

[0060] Comparative Example 6

[0061] In Example 1, step (3) is modified as follows: "After refining, feed 450m of calcium wire. The final composition after calcium treatment is [C]: 0.08%, [Si]: 0.04%, [Mn]: 0.45%, [Al]: 0.046%, S: 0.003%, P: 0.011%, Ca: 0.009%. The control requirements are Ca / Al = 0.20 and Ca / S = 3. After soft blowing, transfer to continuous casting for casting in 13 minutes." to "After refining, feed 100m of calcium wire." The final composition of the calcium wire after calcium treatment is: [C]: 0.08%, [Si]: 0.04%, [Mn]: 0.45%, [Al]: 0.046%, S: 0.003%, P: 0.011%, Ca: 0.0016%. The control requirements are Ca / Al = 0.035 and Ca / S = 0.53. It is transferred to the continuous casting machine for initial casting after 13 minutes of soft blowing. This means that the Ca / Al and Ca / S ratios after calcium treatment at the end of refining have been adjusted; everything else is the same as in Example 1.

[0062] After the tundish was opened for casting, the stopper rod rose significantly. Samples were taken from inside the tundish for inclusion scanning analysis (e.g., ...). Figure 8 (As shown), analysis area 50mm² 2 The inclusions are located in the low melting point region, with a total of 291 inclusions, including 100 high melting point CaS inclusions.

[0063] Comparative Example 7

[0064] In Example 1, the particle size of the low melting point covering agent at the start of tundish casting is 1.8 mm in step (4) is adjusted to "the particle size of the low melting point covering agent at the start of tundish casting is less than 0.5 mm", that is, the covering agent is in powder form, and the rest is the same as in Example 1.

[0065] After the tundish casting process began, the covering agent was added prematurely. The covering agent showed significant clumping, causing it to clump together as it entered the tundish. This resulted in the covering agent remaining clumps on the surface of the molten steel, failing to effectively cover the molten steel and isolate it from air, causing the stopper rod to rise. Samples were taken from the tundish for inclusion scanning analysis (e.g., ...). Figure 9 (As shown), analysis area 50mm² 2 The inclusions are mainly distributed in the low melting point region, with a small number located outside the low melting point region. The total number of inclusions is 658, with 41 spinel and 286 high melting point calcium aluminate caused by secondary oxidation.

[0066] Table 1 shows the test results of non-metallic inclusions (rated according to GB / T 10561 Method A) in the rolled products of the examples and comparative billets.

[0067] Table 1. Results of non-metallic inclusion detection in rolled steel billets after Examples 1-3 and Comparative Examples 1-5

[0068] As shown in Table 1, in Comparative Example 1, increasing the SiO2 content in the covering agent causes Al in the steel to reduce the SiO2 in the covering agent, resulting in an increase in Class B inclusions. In Comparative Example 2, increasing the MnO+FeO content in the covering agent directly provides an oxygen source to the steel, leading to increased secondary oxidation and an increase in both Class B and DS inclusions. In Comparative Example 3, increasing the MgO content in the covering agent leads to increased secondary oxidation, causing the stopper rod to rise, resulting in an increase in both Class B and DS inclusions. In Comparative Example 4, adjusting the timing of covering agent addition—that is, the molten steel entering the tundish first and before the covering agent is added—is effective. Secondary oxidation of molten steel by oxygen in the air leads to an increase in DS inclusions in the steel. In Comparative Example 5, the addition of calcium wire in the tundish to modify the secondary oxidation products at the start of casting generates a large amount of DS inclusions, resulting in a significant deterioration in the cleanliness of the molten steel. In Comparative Example 6, the Ca / Al and Ca / S ratios in the steel were not properly controlled during the refining process, causing the stopper to rise significantly after casting and generating a large amount of Class A and DS inclusions. In Comparative Example 7, the particle size of the covering agent was not properly controlled, and the powdered covering agent added to the tundish in advance resulted in clumping, failing to effectively cover the molten steel and isolate it from the air, while also generating a large amount of Class D and DS inclusions.

[0069] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any skilled craftsmen...

[0070] Those skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this invention should still be covered by the claims of this invention.

Claims

1. A production method for preventing nodule formation during the initial casting of low-carbon, low-silicon, high-aluminum cold-heading steel, characterized in that, Includes the following steps: (1) The composition of the steel tapped from the converter is controlled as follows: C: 0.04~0.07%, Si≤0.02%, S≤0.010%, tapping temperature ≥1620℃, alloy and slag are added when the steel amount is 1 / 3, and the steel is tapped; after tapping, the molten steel is fed to the argon station to feed aluminum wire, and after feeding the aluminum wire, the Al in the steel is 0.050~0.070%; (2) After the molten steel enters the LF, it is heated and the composition is finely adjusted using low-carbon ferromanganese. The refining cycle is controlled within 50~70 min. The refining slag requirements at the end of refining are CaO / SiO2: 9~15, CaO / Al2O3: 1.5~2, MnO+FeO≤1%; (3) After refining, calcium treatment is carried out. The composition control requirements after calcium treatment are Ca / Al: 0.18~0.25, Ca / S>1, and soft blowing time ≥10min; (4) The continuous casting adopts an internally installed immersion nozzle tundish. Before casting, the temperature inside the tundish is ≥1150℃. Before casting, a low melting point covering agent is added to the tundish, and then the ladle long nozzle is installed for casting. (5) When the weight of molten steel in the tundish reaches 2 / 3, add low melting point covering agent to the tundish again. After adding the covering agent, open the stopper rod to start pouring in the tundish, and add carbonized rice husks to the tundish for heat preservation.

2. The production method for preventing nodule formation in low-carbon, low-silicon, high-alumina cold-heading steel according to claim 1, characterized in that: In step (1), the steel output of the converter is between 130 and 140 tons. The alloy added during steel output is low-carbon ferromanganese, and the slag material is lime and slag-forming agent.

3. The production method for preventing nodule formation in the initial casting of low-carbon, low-silicon, high-alumina cold-heading steel according to claim 1, characterized in that: In step (2), aluminum particles and calcium carbide are used to deoxidize the slag surface 20 minutes before the beginning of the refining cycle, and the composition is adjusted to the required level. Calcium carbide is used to deoxidize and retain the slag surface 20 to 40 minutes before the beginning of the refining cycle. Temperature is adjusted in the later part of the refining cycle, and lime, cryolite and fluorite are used to adjust the slag system.

4. The production method for preventing nodule formation in the initial casting of low-carbon, low-silicon, high-alumina cold-heading steel according to claim 1, characterized in that: The low-melting-point covering agent has the following composition: CaO: 45~50%, SiO2≤3%, Al2O3: 40~45%, MgO≤1%, F: 2~8%, Na2O: 3~7%, MnO+FeO≤0.1%, melting point: 1380~1450℃, and particle size: 1.6~2.5mm.

5. The production method for preventing nodule formation in the initial casting of low-carbon, low-silicon, high-alumina cold-heading steel according to claim 1, characterized in that: In step (4), 100-150 kg of low melting point covering agent is added to the casting zone of the tundish, and 20-40 kg of low melting point covering agent is added to the impact zone.

6. The production method for preventing nodule formation in low-carbon, low-silicon, high-alumina cold-heading steel according to claim 1, characterized in that: In step (5), 200 kg of low melting point covering agent is added to the casting zone of the intermediate ladle, and 40 kg of low melting point covering agent is added to the impact zone.

7. The production method for preventing nodule formation in the initial casting of low-carbon, low-silicon, high-alumina cold-heading steel according to claim 1, characterized in that: The weight of molten steel in the tundish mentioned in step (5) is between 40 and 50 tons when it is full.

8. The production method for preventing nodule formation in the initial casting of low-carbon, low-silicon, high-alumina cold-heading steel according to claim 1, characterized in that: The chemical composition of the low-carbon, low-silicon, high-aluminum cold heading steel, by weight percentage, is [C]: 0.04~0.10%, [Si]≤0.10%, [Mn]: 0.30~0.90%, [Al]≥0.020%, with the remainder being Fe and unavoidable impurities.

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