A method for reducing the carbon increase when pouring molten steel from the first ladle into the tundish

Abstract

The present application provides a method for reducing the carbon increase amount when pouring molten steel from the first ladle into a tundish. When pouring molten steel from the first ladle into a new tundish, a low-carbon basic covering flux is used, and the carbon content of the low-carbon basic covering flux is 3% - 4%; after the pouring of the molten steel from the first ladle is completed, the subsequent pouring of the tundish uses a common basic covering flux, and the carbon content of the common basic covering flux is 18% - 20%; the use of the low-carbon content basic covering flux is effectively selected, and the addition timing and addition amount of the low-carbon basic covering flux during the pouring process of the first ladle are effectively standardized, so that the problem of the covering flux contaminating the molten steel is effectively controlled, and the carbon increase amount is controlled at 0.005% and below, which is reduced by about 83%, ensuring the composition quality of the molten steel and the performance stability of the rolled products. In addition, the operation of this method is simple, easy to track, and convenient to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of continuous casting of molten steel in tundishes, and particularly to a method for reducing the carbon increase amount when pouring the first ladle of molten steel into a tundish. Background Art

[0002] The tundish of a continuous caster is an intermediate link in the steelmaking production process, which has the functions of storing molten steel, stabilizing the flow, dividing the flow, equalizing the temperature, and removing inclusions, and is the connection point for the transition of molten steel from batch operation to continuous operation. When producing low-carbon steel, there is a phenomenon of carbon increase in the molten steel during the production of the continuous caster, especially when pouring the first ladle into a new tundish, the carbon increase phenomenon is very serious, often resulting in the chemical composition control exceeding the standard, and even being rejected, causing relatively large economic losses. Through follow-up research, it is found that the mold powder and the inner wall refractories of the tundish will also cause carbon increase, but they are not the main reasons, and it is not easy to control comprehensively. The main reason for carbon increase comes from the raw and auxiliary materials added to the tundish, namely carbonized rice husk and tundish covering agent. The contact area between the raw and auxiliary materials of the tundish and the molten steel is large, and the contact surface is relatively active, so the carbon in the raw and auxiliary materials is easily introduced into the molten steel.

[0003] During normal production, in order to prevent the molten steel in the tundish from being exposed to heat dissipation and secondary oxidation, and adsorb the inclusions in the molten steel, a certain amount of auxiliary materials need to be added to the tundish for each furnace. Generally, the main raw and auxiliary materials added to the tundish are carbonized rice husk and tundish covering agent. Previously, the carbonized rice husk and tundish covering agent have been replaced by the ordinary basic covering agent of the tundish. In the case of only using the ordinary basic covering agent, through tracking and calculation, the carbon increase amount in normal continuous casting heats is below 0.004%, and the increase is weak. However, for the first ladle poured into a new tundish, due to the high temperature, the liquid level in the tundish is too low, the molten steel is exposed, the liquid level fluctuates greatly, and a stable flow field is not formed, which makes the melting speed of the covering agent fast and the consumption large. Coupled with the poor timing of adding the covering agent, the possibility of the covering agent being involved in the molten steel by the vortex is greatly increased, resulting in a serious carbon increase phenomenon in the molten steel, generally reaching about 0.03%.

[0004] Using a carbon-free covering agent will not cause carbon increase in the molten steel, but in the middle and later stages of pouring, the covering agent will form a crust, which will not only make it difficult to add the covering agent, the continuous temperature measuring tube of the tundish is inaccurate (it will break severely in serious cases), but also lead to problems such as inclusions not being easy to float up in the production quality of molten steel.

[0005] Since the main reason for the carbon increase in the molten steel of the first ladle poured into a new tundish is the large consumption of the tundish covering agent and the large amount of the tundish covering agent involved due to the fluctuation of the tundish liquid level. The problems of covering agent consumption and involvement are comprehensive system problems and are difficult to avoid. Therefore, there is an urgent need for a process to reduce the influence of the carbon content of the molten steel in the first ladle during continuous casting in the tundish on the carbon increase of the first ladle of molten steel poured into a new tundish. Summary of the Invention

[0006] The object of the present invention is to provide a method for reducing the carbon increment when tapping molten steel from the first ladle into the tundish.

[0007] To solve the above technical problems, the technical solution proposed by the present invention is as follows:

[0008] A method for reducing the carbon increment when tapping molten steel from the first ladle into the tundish, when tapping molten steel from the first ladle into a new tundish, a low-carbon basic covering flux is used, and the carbon content of the low-carbon basic covering flux is 3% - 4%;

[0009] After the pouring of the molten steel from the first ladle is completed, the subsequent pouring of the tundish uses a common basic covering flux, and the carbon content of the common basic covering flux is 18% - 20%.

[0010] Preferably, the low-carbon basic covering flux comprises the following components in mass percentages: 17% - 18% of SiO2, 8.5% - 9.0% of Al2O3, 2.0% - 3.0% of MgO, 3.0% - 4.0% of C 固 , 26% - 27% of CaCO3, 0.60% - 0.70% of H2O, and the balance of CaO.

[0011] Preferably, the common basic covering flux comprises the following components in mass percentages: 21% - 22% of SiO2, 8.5% - 10% of Al2O3, 4% - 5% of MgO, 18% - 20% of C 固 , 18% - 19% of CaCO3, 0.4% - 0.5% of H2O, and the balance of CaO.

[0012] Preferably, when tapping molten steel from the first ladle into a new tundish, the low-carbon basic covering flux is added in three times, specifically as follows:

[0013] The first addition: when the molten steel depth in the tundish gradually increases to 400 mm, start adding 0.07 kg / t of molten steel of the low-carbon basic covering flux to each of the two sides separated by the middle steady-flow area of the tundish in the T-shaped tundish;

[0014] The second addition: when there are 80 tons of molten steel remaining in the first ladle, at this time, the molten steel liquid level height in the tundish is controlled at 500 mm, and start adding 0.07 - 0.13 kg / t of molten steel of the low-carbon basic covering flux to each of the two sides separated by the middle steady-flow area of the tundish in the T-shaped tundish;

[0015] Third addition: When there are 50 tons of molten steel remaining in the first ladle, the molten steel level in the tundish is controlled at 600 - 700 mm. Then, a low-carbon basic covering flux of 0.07 - 0.13 kg / t of molten steel is added to each of the two sides of the T-shaped tundish with the steady-flow zone in the middle of the tundish as the inner cavity partition. After the lower nozzle of the long nozzle of the first ladle is submerged below the molten steel surface, a low-carbon basic covering flux of 0.07 - 0.13 kg / t of molten steel is added to the steady-flow zone of the tundish.

[0016] Preferably, for heats with relatively high molten steel temperature, the low-carbon basic covering flux is added according to the lower limit, and the total addition amount of the low-carbon basic covering flux for the current heat does not exceed 1.00 kg / t of molten steel.

[0017] Preferably, during the process of changing the ladle, the basic covering flux of the tundish is not added first. After the ladle change is completed and the tundish liquid level is stable, the basic covering flux is added to the tundish to reduce the vortex generated by the liquid level agitation, which may cause the basic covering flux of the tundish to enter the molten steel and contaminate the molten steel.

[0018] The present application has achieved the following beneficial technical effects:

[0019] (1). In the present application, a basic covering flux with a low carbon content is used for the first ladle in the initial pouring of the new continuous casting tundish. This can not only reduce the carbon source for a large increase in carbon content in the molten steel but also avoid abnormal phenomena such as crust formation that occur when using a carbon-free covering flux alone, ensuring the ease of operation and production stability during the production process.

[0020] (2). According to the temperature and liquid level conditions of the molten steel in the first ladle during the initial pouring, the amount and timing of adding the basic covering flux to the first ladle of the tundish during the initial pouring are systematically described. This not only ensures the main functions of adsorbing inclusions, heat preservation, and preventing secondary oxidation after adding the basic covering flux to the tundish but also reduces the possibility of vortex entrainment of the molten steel after adding the basic covering flux due to high molten steel temperature and large tundish liquid level fluctuations, reducing the risk of carbon increase in the molten steel.

[0021] (3). This method effectively selects the covering fluxes for the first ladle in the initial pouring of the new tundish and the tundish during normal continuous casting heats, and optimizes the timing and amount of adding the basic covering flux for the first ladle in the initial pouring. As a result, the carbon increase in the molten steel of the first ladle in the tundish of the new pouring heat of the continuous caster is reduced, ensuring the stability of the molten steel quality.

[0022] (4) This application combines the characteristics of comprehensive system problems such as high temperature, low liquid level and large fluctuations in the first ladle during the initial casting, and a large amount of basic covering agent used. It effectively selects the use of a basic covering agent with a low carbon content, effectively standardizes the addition timing and addition amount of the low-carbon basic covering agent during the casting process of the first ladle, effectively controls the problem of the covering agent contaminating the molten steel, and controls the carbon addition amount within 0.005% or less, reducing it by about 83%. It ensures the composition quality of the molten steel and the performance stability of the rolled products. In addition, the operation of this method is simple, easy to track, and convenient to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a comparison of the effects of using a common basic covering agent and a low-carbon basic covering agent for the molten steel in the first ladle during the initial casting of the tundish Figure 1 (the left side of the dotted line in the figure is the common basic covering agent, and the right side of the dotted line is the low-carbon basic covering agent). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0025] This application provides a method for reducing the carbon addition amount when casting the molten steel in the first ladle of the tundish. When initially casting the molten steel in the first ladle of the new tundish, a low-carbon basic covering agent is used, and the carbon content of the low-carbon basic covering agent is 3%-4% (mass percentage);

[0026] After the casting of the molten steel in the first ladle is completed, a common basic covering agent is used for the subsequent casting of the tundish, and the carbon content of the common basic covering agent is 18%-20% (mass percentage).

[0027] In an embodiment of this application, the low-carbon basic covering agent contains the following components in mass percentage: 17%-18% of SiO2, 8.5%-9.0% of Al2O3, 2.0%-3.0% of MgO, 3.0%-4.0% of C 固 , 26%-27% of CaCO3, 0.60%-0.70% of H2O, and the balance is CaO.

[0028] In an embodiment of this application, the common basic covering agent contains the following components in mass percentage: 21%-22% of SiO2, 8.5%-10% of Al2O3, 4%-5% of MgO, 18%-20% of C 固, 18% - 19% CaCO3, 0.4% - 0.5% H2O, and the balance is CaO.

[0029] In an embodiment of the present application, when pouring the molten steel from the first ladle into the new tundish, the low-carbon basic covering flux is added in three times, with a total addition of 0.68 - 1.00 kg / t of molten steel, specifically as follows:

[0030] First addition: When the liquid depth of the molten steel in the tundish gradually increases to 400 mm, start adding 0.07 kg / t of molten steel of the low-carbon basic covering flux to each of the two sides separated by the stable flow area in the middle of the T-shaped tundish as the inner cavity partition.

[0031] Second addition: When there are 80 tons of molten steel remaining in the first ladle, at this time, the liquid level height of the molten steel in the tundish is controlled at 500 mm, and start adding 0.07 - 0.13 kg / t of molten steel of the low-carbon basic covering flux to each of the two sides separated by the stable flow area in the middle of the T-shaped tundish.

[0032] Third addition: When there are 50 tons of molten steel remaining in the first ladle, at this time, the liquid level height of the molten steel in the tundish is controlled between 600 mm - 700 mm, and start adding 0.07 - 0.13 kg / t of molten steel of the low-carbon basic covering flux to each of the two sides separated by the stable flow area in the middle of the T-shaped tundish. After the lower nozzle of the long nozzle of the first ladle is submerged below the steel liquid surface, add 0.07 - 0.13 kg / t of molten steel of the low-carbon basic covering flux into the stable flow area of the tundish.

[0033] In an embodiment of the present application, for the furnace with a relatively high molten steel temperature, the low-carbon basic covering flux is added according to the lower limit, and the total addition amount of the low-carbon basic covering flux for the current furnace does not exceed 1.00 kg / t of molten steel.

[0034] In an embodiment of the present application, during the process of changing the ladle, do not add the basic covering flux of the tundish first. Wait until the ladle change is completed and the liquid level of the tundish is stable, and then add the basic covering flux (including low-carbon basic covering flux and ordinary basic covering flux) to the tundish to reduce the vortex generated by the liquid level agitation, which may cause the basic covering flux of the tundish to enter the molten steel and contaminate the molten steel.

[0035] In the present application, a method for reducing the carbon increase when pouring the molten steel from the first ladle into the tundish. The pouring of the molten steel from the first ladle does not refer to the first ladle of molten steel in the tundish. Since the molten steel is continuously poured into the tundish, the molten steel in the tundish is continuous and uninterrupted. Therefore, there is no such thing as the first ladle, the second ladle, the third ladle, etc. in the tundish. Therefore, the above-mentioned pouring of the molten steel from the first ladle refers to the molten steel in the ladle upstream of the tundish. The ladle pours the molten steel into the tundish intermittently, and after pouring one ladle, it changes to the next ladle of molten steel.

[0036] The methods and devices not described in detail in the present invention are all prior arts and will not be elaborated herein.

[0037] To further understand the present invention, the following describes in detail a method for reducing the carbon increase amount when pouring molten steel from the first ladle into the tundish at the start of casting. The protection scope of the present invention is not limited by the following embodiments.

[0038] Example 1

[0039] A method for reducing the carbon increase amount when pouring molten steel from the first ladle into the tundish at the start of casting. When pouring molten steel from the first ladle into a new tundish, a low-carbon basic covering flux is used, and the carbon content of the low-carbon basic covering flux is 3%;

[0040] After the pouring of the molten steel from the first ladle is completed, the subsequent pouring in the tundish uses a common basic covering flux, and the carbon content of the common basic covering flux is 18%;

[0041] The low-carbon basic covering flux contains the following components in mass percentages: 17.1% of SiO2, 41.9% of CaO, 8.5% of Al2O3, 2.1% of MgO, 3.4% of C 固 , 26.35% of CaCO3, 0.65% of H2O;

[0042] The common basic covering flux contains the following components in mass percentages: 21.6% of SiO2, 26.7% of CaO, 8.9% of Al2O3, 4.1% of MgO, 19.5% of C 固 , 18.76% of CaCO3, 0.44% of H2O;

[0043] When pouring molten steel from the first ladle into a new tundish, the low-carbon basic covering flux is added in three times, specifically as follows:

[0044] The first addition: When the liquid depth of the molten steel in the tundish gradually increases to 400 mm, start adding 0.07 kg / t of molten steel of the low-carbon basic covering flux to both sides of the T-shaped tundish with the middle steady-flow area of the tundish as the inner cavity partition;

[0045] The second addition: When there are 80 tons of molten steel remaining in the first ladle, at this time, the liquid level height of the molten steel in the tundish is controlled at 500 mm, and start adding 0.09 kg / t of molten steel of the low-carbon basic covering flux to both sides of the T-shaped tundish with the middle steady-flow area of the tundish as the inner cavity partition;

[0046] Third addition: When there are 50 tons of molten steel remaining in the first ladle, the liquid level height of the molten steel in the tundish is controlled at 600 mm - 700 mm at this time. Start adding a low-carbon basic covering flux of 0.10 kg / t of molten steel to each side of the T-shaped tundish with the steady-flow area in the middle of the tundish as the inner cavity partition. After the lower nozzle of the long nozzle of the first ladle is submerged below the molten steel surface, add a low-carbon basic covering flux of 0.09 kg / t of molten steel to the steady-flow area of the tundish;

[0047] For the furnace with a relatively high molten steel temperature, the low-carbon basic covering flux is added according to the lower limit, and the total addition amount of the low-carbon basic covering flux for the current furnace does not exceed 1.00 kg / t of molten steel;

[0048] During the process of changing the ladle, do not add the basic covering flux of the tundish first. Wait until the ladle change is completed and the liquid level of the tundish is stable, and then add the basic covering flux to the tundish to reduce the vortex generated by the liquid level agitation, which may cause the basic covering flux of the tundish to enter the molten steel and contaminate the molten steel.

[0049] Table 1 Comparison of carbon content between the refined sample using the method of this application and the tundish sample when pouring the first ladle

[0050]

[0051] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for reducing the carbon increment when pouring molten steel from the first ladle into the tundish, characterized in that, When the first ladle of molten steel is poured into the new tundish, a low-carbon basic covering flux is used, and the carbon content of the low-carbon basic covering flux is 3% - 4%; After the pouring of the molten steel in the first ladle is completed, a common basic covering flux is used for the subsequent pouring of the tundish, and the carbon content of the common basic covering flux is 18% - 20%; The low-carbon basic covering agent contains the following components in mass percentages: 17% - 18% of SiO2, 8.5% - 9.0% of Al2O3, 2.0% - 3.0% of MgO, 3.0% - 4.0% of C 固 , 26% - 27% of CaCO3, 0.60% - 0.70% of H2O, and the balance of CaO; The ordinary basic covering agent contains components in the following mass percentages: 21% - 22% of SiO2, 8.5% - 10% of Al2O3, 4% - 5% of MgO, 18% - 20% of C 固 , 18% - 19% of CaCO3, 0.4% - 0.5% of H2O, and the balance of CaO; When the first ladle of molten steel is poured into the new tundish, the low-carbon basic covering flux is added in three times, specifically as follows: The first addition: When the liquid depth of the molten steel in the tundish gradually increases to 400 mm, start adding 0.07 kg / t of molten steel of the low-carbon basic covering flux to each of the two sides separated by the middle steady-flow area of the tundish in the T-shaped tundish; The second addition: When there are 80 tons of molten steel remaining in the first ladle, and at this time the liquid level height of the molten steel in the tundish is controlled at 500 mm, start adding 0.07 - 0.13 kg / t of molten steel of the low-carbon basic covering flux to each of the two sides separated by the middle steady-flow area of the tundish in the T-shaped tundish; The third addition: When there are 50 tons of molten steel remaining in the first ladle, and at this time the liquid level height of the molten steel in the tundish is controlled between 600 mm and 700 mm, start adding 0.07 - 0.13 kg / t of molten steel of the low-carbon basic covering flux to each of the two sides separated by the middle steady-flow area of the tundish in the T-shaped tundish. After the lower nozzle of the long nozzle of the first ladle is immersed below the steel liquid surface, add 0.07 - 0.13 kg / t of molten steel of the low-carbon basic covering flux to the steady-flow area of the tundish.

2. A method for reducing the carbon increase amount when pouring molten steel from the first ladle into the tundish as claimed in claim 1, characterized in that For the heats with relatively high molten steel temperature, the low-carbon basic covering flux is added according to the lower limit, and the total addition amount of the low-carbon basic covering flux for the current heat does not exceed 1.00 kg / t of molten steel.

3. A method for reducing the carbon increase during the initial pouring of molten steel from the first ladle into the tundish according to claim 1, characterized in that, During the process of changing the ladle, do not add the basic covering flux of the tundish first. Wait until the ladle change is completed and the liquid level of the tundish is stable, and then add the basic covering flux to the tundish to reduce the vortex generated by the liquid level agitation, which may cause the basic covering flux of the tundish to enter the molten steel and pollute the molten steel.

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