A method for evaluating the matching of slag at the end of LF refining

Abstract

The present invention relates to the technical field of iron and steel metallurgy, and specifically to a method for evaluating the matching of molten steel and slag at the end of LF refining, which includes the following steps: obtaining the contents of Al and Si in molten steel and the contents of MgO and CaO in slag; determining the activities of each component in molten steel according to the Wagner equation; combining the molten steel-slag equilibrium principle and the slag coexistence theory to calculate the activities of each component in the CaO-SiO2-Al2O3-MgO quaternary slag system and the equilibrium oxygen content at the molten steel-slag interface; according to the activities of each component in the slag, combining the law of conservation of mass to calculate the mass fractions of Al2O3 and SiO2 in the slag that are in equilibrium with the contents of Al and Si in the molten steel, and comparing the theoretical contents of Al2O3 and SiO2 with the actual contents of Al2O3 and SiO2 in the slag to evaluate the matching degree of molten steel and slag. This method can be used to evaluate whether the slags at the end of refining of actual production steel grades reach an equilibrium relationship, trace the source of defects caused by the mismatch between molten steel and slag, reduce the production costs of enterprises, and point out the direction for improving the quality of steel.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for evaluating the matching of steel slag at the end of LF refining. Background Art

[0002] High-quality steel has more stringent requirements for cleanliness, precision, homogenization and refinement during the manufacturing process. Whether the cleanliness of steel materials meets the standards is one of the indicators for judging the quality and performance of steel materials. During the LF refining process, the physical and chemical reactions between the refining slag and the molten steel can play the role of deoxidation, desulfurization, inclusion modification and adsorption of inclusions, and this process can effectively improve the cleanliness of the molten steel. The chemical composition of the refining slag determines the melting temperature, viscosity, surface tension, alkalinity and low oxidizability of the refining slag and many other physical and chemical properties. The refining slag composition that matches the molten steel composition not only further promotes the deoxidation, desulfurization and adsorption of inclusions in the molten steel, but also effectively inhibits the secondary oxidation of the molten steel by SiO2 and other components in the slag. Therefore, evaluating the matching degree between steel slags at the end of LF refining plays an important role in the retrospective process of steel quality and properties that are unqualified due to cleanliness, and has guiding significance for the staff to add slag during the LF refining process.

[0003] After searching, the patent publication number is CN112501390A, which is a design method for a refining slag system for removing magnesia-alumina spinel inclusions. The design method includes establishing a magnesia-alumina spinel inclusion movement model, obtaining the relationship between the displacement of magnesia-alumina spinel inclusions and time, and judging the state of magnesia-alumina spinel inclusions; calculating the viscosity and interface characteristic conditions of the refining slag system that should be met for the removal of inclusions of different sizes; drawing a removal advantage zone map; obtaining the maximum size of unremoved inclusions in the steel according to the requirements of the steel grade, and selecting the target slag viscosity and surface tension coefficient according to the removal advantage zone map; calculating the first refining slag system component composition and the second refining slag system component composition according to the target slag viscosity and the surface tension coefficient, and taking their intersection to determine the target refining slag system component composition. This method is conducive to the design of refining slag used to remove magnesia-alumina spinel inclusions, with the aim of improving the cleanliness of molten steel. However, this method lacks consideration of the duration of inclusion movement at the steel-slag interface in actual industrial production. The longer the duration, the greater the probability that the inclusion will be drawn into the molten steel again, and the more difficult it is to remove the inclusion. Moreover, this method does not mention the matching of the molten steel composition and the refined slag composition, as well as the other properties of the refined slag, such as viscosity and melting temperature, and cannot guarantee the influence of the degree of slag interface reaction on deoxidation, desulfurization, and adjustment of molten steel composition.

[0004] Patent Publication No.: CN113761477A, ​​a method for constructing a slag viscosity prediction and composition control model. The method selects the slag composition range in advance, designs a quadratic regression orthogonal test scheme through the slag composition range, and obtains the mass fraction range of the slag composition. The slag viscosity value is tested using the rotating cylinder method, and the viscosity parameter equation is constructed using the Arrhenius equation in combination with the slag composition, a slag viscosity prediction model is constructed, and a viscosity isovalue diagram is drawn. Combined with the volatility of the slag, the slag is sampled for XRF composition analysis, the viscosity prediction model and isovalue diagram are corrected, and finally the effective control of the slag viscosity and composition is achieved. However, this method uses an empirical slag composition design, selects the slag composition in advance, and does not consider whether the molten steel composition matches the slag composition; secondly, this method only considers the slag viscosity problem, and multiple effective indicators such as slag oxidizability, melting temperature and alkalinity are not considered, and the effect is relatively single.

[0005] Patent Publication No.: CN108875285A, a method for designing the composition of molten steel refining slag. The method first establishes and solves the inclusion movement model at the steel-slag interface, and then quantitatively evaluates the influence of inclusion size, inclusion density, slag phase density, slag phase viscosity, molten steel density, molten steel viscosity, and the wettability of inclusions at the steel-slag interface on the movement and removal process of inclusions at the steel-slag interface, determines the slag phase viscosity range and slag phase composition range when the inclusions can be removed, and combines the target composition control requirements of inclusions in steel to determine the optimal refining slag composition range. This method can take into account the control of inclusion composition, reduce the number of inclusions, and predetermine the refining slag composition target required for the production of different steel grades, but it ignores the lateral force and lateral displacement of inclusions when considering the force analysis and displacement of inclusions, and the inclusions may be re-involved in the molten steel as time goes by after entering the slag layer, increasing the displacement parameter error.

[0006] In view of this, we propose a method for evaluating the matching of slag at the end of LF refining. The present invention determines the activity of components in molten steel according to the specific steel grade composition and Wagner equation, and then combines the slag equilibrium theory and slag coexistence theory to calculate the mass action concentration of each component in the slag, and then finds the theoretical equilibrium slag composition that best matches the steel grade composition. Based on the above classical theories, the theoretical slag composition that matches the molten steel composition is calculated, and the theoretical slag composition is used to evaluate whether the actual slag composition matches the molten steel composition. It has guiding significance for the adjustment of slag system composition in actual production and the addition amount of slag in the refining process, which is conducive to reducing the production cost of enterprises and improving the performance and quality of steel products. Summary of the invention

[0007] The purpose of the present invention is to provide a method for evaluating the matching of steel slag at the end of LF refining. According to the composition of a specific steel grade, based on the steel-slag equilibrium thermodynamic conditions, combined with the Wagner equation and the slag structure coexistence theory, a steel-slag equilibrium thermodynamic model is constructed to calculate the theoretical CaO-Al2O3-SiO2-MgO quaternary slag system slag composition that best matches the steel grade composition, aiming to clarify the problems existing in the production process and the direction of improvement, reduce the production cost of the enterprise, and improve the performance and quality of steel products.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A method for evaluating the matching of slag at the end of LF refining, comprising the following steps:

[0010] S1. Obtain the Al and Si contents in molten steel and the MgO and CaO contents in slag;

[0011] S2, according to the Al and Si contents in step S1, combined with the Wagner equation, calculate the Al and Si element activities in the molten steel;

[0012] S3, according to the Al and Si element activities in the molten steel in step S2, combined with the slag equilibrium principle and the slag coexistence theory, calculate the activity of each component in the slag and the equilibrium oxygen content at the slag interface;

[0013] S4. According to the component activities in the slag calculated in step S3 and in combination with the law of conservation of mass, the contents of Al2O3 and SiO2 in equilibrium with Al and Si in the molten steel are calculated, and the theoretical contents of Al2O3 and SiO2 are compared with the actual contents of Al2O3 and SiO2 in the slag to evaluate the matching degree of the slag.

[0014] Preferably, the reaction between aluminum, silicon and oxygen occurs simultaneously at the slag interface, as shown in the following formula:

[0015]

[0016] Among them, %Al and %Si are the Al and Si contents in molten steel, and %O is the equilibrium oxygen content at the slag interface. f Al , f Si is the activity coefficient of Al and Si elements, f O is the equilibrium oxygen activity at the slag interface, , is the mass action concentration of Al2O3 and SiO2, K Al , K Si It is the chemical reaction equilibrium constant of Al and Si elements in molten steel.

[0017] Preferably, in step S3, according to the slag equilibrium principle and slag coexistence theory, the equilibrium mole fraction of each structural unit is defined as the mass action concentration, and the expression is shown in (1):

[0018] (1) Where N i is the mass action concentration of the structural unit, n i is the equilibrium molar number of the component in the slag, is the total number of moles in the slag;

[0019] Combining the structural units, molar numbers and mass action concentrations in the slag, the following relationship (2) is obtained:

[0020]

[0021] N1—N 22 are the mass action concentrations of 22 molecules in the CaO-SiO2-Al2O3-MgO quaternary slag system, k1—k 18 They are the chemical reaction equilibrium constants of 18 complex molecular compounds in the CaO-SiO2-Al2O3-MgO quaternary slag system;

[0022] According to the law of conservation of mass, the sum of the mass action concentrations of all structural units is 1, and the following formula can be obtained: N1+N2+N3+...+N 20 +N 21 +N 22 =1(3).

[0023] Preferably, in step S3, the following equation can be formed by combining the Al and Si contents in the molten steel, relation (2), the chemical reaction equilibrium constant and the equilibrium oxygen content at the slag interface:

[0024] (4)

[0025] (5)

[0026] Wherein, %Al, %Si are the Al and Si contents in molten steel, %O is the equilibrium oxygen content at the slag interface; N3 is the mass action concentration of Al2O3, N4 is the mass action concentration of SiO2, and T is the absolute temperature;

[0027] Based on the above calculation results, the theoretical Al2O3 and SiO2 activities in the CaO-SiO2-Al2O3-MgO quaternary slag system under equilibrium state corresponding to the Al and Si contents in molten steel can be obtained.

[0028] Compared with the prior art, the method for evaluating the matching of slag at the end of LF refining is based on the given molten steel composition, combined with the Wagner equation, the slag equilibrium principle and the molecular-ion slag coexistence theory, to calculate the slag composition that is in equilibrium with the molten steel composition at the end of LF, and compare it with the actual slag composition to determine the matching degree of molten steel and slag at the end of refining. This method can be used to evaluate whether the slag at the end of refining of actual production steel grades reaches a balanced relationship, trace the source of defects caused by steel-slag mismatch, reduce enterprise production costs, and point out the direction for improving steel quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a comparison chart of theoretical Al2O3 and actual Al2O3 of slag at the end of refining of Example 1-62 of the present invention;

[0030] Figure 2 This is a comparison chart of the theoretical SiO2 and the actual SiO2 of the slag at the end of refining of Example 1-62 of the present invention;

[0031] Figure 3 This is a flow chart of the method for evaluating the matching degree of slag at the end of LF refining. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only 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 creative work are within the scope of protection of the present invention.

[0033] This embodiment provides a technical solution:

[0034] A method for evaluating the matching of slag at the end of LF refining, comprising the following steps:

[0035] S1. Obtain the Al and Si contents in molten steel and the MgO and CaO contents in slag. The reaction between aluminum, silicon and oxygen occurs simultaneously at the slag interface, as shown in the following formula:

[0036]

[0037] Among them: %Al, %Si are the Al and Si contents in molten steel, %O is the equilibrium oxygen content at the slag interface, f Al , f Si is the activity coefficient of Al and Si elements, f O is the equilibrium oxygen activity at the slag interface, , is the mass action concentration of Al2O3 and SiO2, K Al , K Si is the chemical reaction equilibrium constant of Al and Si elements in molten steel;

[0038] S2. Calculate the Al and Si element activities in molten steel according to the contents in step S1 and the Wagner equation. According to the existing phase diagram, there are 22 molecules in the CaO-SiO2-Al2O3-MgO quaternary slag system, namely CaO, SiO2, Al2O3, MgO, CaO·SiO2, 2CaO·SiO2, 3CaO·SiO2, CaO·Al2O3, CaO·2Al2O3, CaO·6Al2O3, 3CaO·Al2O3, 12CaO·7Al2 O3, MgO·SiO2, 2MgO·SiO2, MgO·Al2O3, CaO·MgO·SiO2, CaO·MgO·2SiO2, 2CaO·MgO·2SiO2, 3CaO·MgO·2SiO2, 2CaO·Al2O3·SiO2, CaO·Al2O3·2SiO2, 3Al2O3·2SiO2, combined with the Gibbs free energy calculation formula and the empirical formula, the calculation process of the chemical reaction equilibrium constants of the 18 complex molecular compounds in the above molecules is as follows:

[0039]

[0040] Where: R is the gas constant; T is the absolute temperature. The Gibbs free energy parameter in the above formula is obtained according to "Computational Thermodynamics of Metallurgical Melts and Solutions".

[0041] S3, according to the Al and Si element activities in the molten steel in step S2, combined with the slag equilibrium principle and the slag coexistence theory, calculate the activity of each component in the slag and the equilibrium oxygen content of the slag interface; according to the slag equilibrium principle and the slag coexistence theory, the equilibrium mole fraction of each structural unit is defined as the mass action concentration,

[0042] The expression is shown in (1):

[0043] (1)

[0044] Where N i is the mass action concentration of the structural unit, n i is the equilibrium molar number of the component in the slag, is the total number of moles in the slag;

[0045] Combining the structural units, molar numbers and mass action concentrations in the slag, the following relationship is obtained:

[0046]

[0047] N1—N 22 are the mass action concentrations of 22 molecules in the CaO-SiO2-Al2O3-MgO quaternary slag system, k1—k 18 They are the chemical reaction equilibrium constants of 18 complex molecular compounds in the CaO-SiO2-Al2O3-MgO quaternary slag system;

[0048] According to the law of conservation of mass, the sum of the mass action concentrations of all structural units is 1, and the following formula can be obtained: N1+N2+N3+...+N 20 +N 21 +N 22 =1 (3).

[0049] Combining the Al and Si contents in molten steel, equation (2), the chemical reaction equilibrium constant and the equilibrium oxygen content at the slag interface, the following equation can be formed:

[0050] (4)

[0051] (5)

[0052] Wherein, %Al, %Si are the Al and Si contents in molten steel, %O is the equilibrium oxygen content at the slag interface, N3 is the mass action concentration of Al2O3, N4 is the mass action concentration of SiO2, and T is the absolute temperature.

[0053] Based on the above calculation results, the theoretical Al2O3 and SiO2 activities in the CaO-SiO2-Al2O3-MgO quaternary slag system under equilibrium state corresponding to the Al and Si contents in molten steel can be obtained.

[0054] S4. According to the activity of the components in the slag calculated in step S3, combined with the law of conservation of mass, the contents of Al2O3 and SiO2 in equilibrium with Al and Si in the molten steel are calculated, and the theoretical contents of Al2O3 and SiO2 are compared with the contents of Al2O3 and SiO2 in the actual slag to evaluate the matching degree of the slag; the molar number of each component in 100g of slag is defined as ,Right now (6)

[0055] Combining formula (1) and (2),

[0056]

[0057] The above formula is based on EISENHÜTTENLEUTE, VD, ALLIBERT M, Slag Atlas, England: Woodhead Publishing Ltd, 1995.

[0058] Since the Al and Si contents in molten steel and the MgO and CaO contents in slag are known, the simultaneous equations (3), (4), (5), and (6) can be obtained: , we can further obtain The equilibrium mass fraction can be obtained by multiplying the corresponding molar mass by the value, as shown in equations (11) and (12):

[0059] (11)

[0060] (12)

[0061] According to the above calculation results, the theoretical Al2O3 and SiO2 contents in the CaO-SiO2-Al2O3-MgO quaternary slag system under equilibrium state can be obtained, and the theoretical Al2O3 and SiO2 contents can be compared with the Al2O3 and SiO2 contents in the actual slag to evaluate the matching degree of steel slag.

[0062] Table 1 shows the molten steel composition, actual slag composition, and theoretical slag composition parameters of Examples 1-34.

[0063]

[0064] Table 2 shows the molten steel composition, actual slag composition, and theoretical slag composition parameters of Examples 35-62.

[0065]

[0066] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for evaluating the matching of slag at the end of LF refining, characterized in that: The following steps are involved: S1. Obtain the Al and Si contents in molten steel and the MgO and CaO contents in slag; S2, according to the Al and Si contents in step S1, combined with the Wagner equation, calculate the Al and Si element activities in the molten steel; S3, according to the Al and Si element activities in the molten steel in step S2, combined with the slag equilibrium principle and the slag coexistence theory, calculate the mass action concentration of each component in the slag; then calculate the Al2O3 and SiO2 activities according to the mass action concentration of each component; According to the slag equilibrium principle and slag coexistence theory, the equilibrium mole fraction of each structural unit is defined as the mass action concentration, and the expression is shown in (1): Where N i is the mass action concentration of the structural unit, n i is the equilibrium molar number of the component in the slag, is the total number of moles in the slag; Combining the molar number and mass action concentration of each structural unit in the slag, the following relationship (2) is obtained: N1=N CaO N2=N MgO N1—N 22 are the mass action concentrations of 22 molecules in the CaO-SiO2-Al2O3-MgO quaternary slag system, k1—k 18 They are the chemical reaction equilibrium constants of 18 complex molecular compounds in the CaO-SiO2-Al2O3-MgO quaternary slag system; According to the law of conservation of mass, the sum of the mass action concentrations of all structural units is 1, and the following formula can be obtained: N1+N2+N3+...+N 20 +N 21 +N 22 =1 (3); S4. According to the component activities in the slag calculated in step S3 and in combination with the law of conservation of mass, the contents of Al2O3 and SiO2 in equilibrium with Al and Si in the molten steel are calculated, and the theoretical contents of Al2O3 and SiO2 are compared with the actual contents of Al2O3 and SiO2 in the slag to evaluate the matching degree of the slag.

2. The method for evaluating the matching of LF refining slag at the end of the refining process according to claim 1, characterized in that: The reaction between aluminum, silicon and oxygen occurs simultaneously at the slag interface, as shown in the following equation: Among them, %Al, %Si are the Al and Si contents in molten steel, %O is the equilibrium oxygen content at the slag interface, and f Al 、f Si is the activity coefficient of Al and Si elements, f O is the equilibrium oxygen activity at the slag interface, is the mass action concentration of Al2O3 and SiO2, K Al , K Si It is the chemical reaction equilibrium constant of Al and Si elements in molten steel.

3. The method for evaluating the matching of LF refining slag at the end of the refining process according to claim 1, characterized in that: In step S3, the following equation can be formed by combining the Al and Si contents in the molten steel, relation (2), the chemical reaction equilibrium constant and the equilibrium oxygen content at the slag interface: 2lg[%Al]+3lg[%O]-lgN3+64000 / T-20.57=0.99 (4) lg[%Si]+2lg[%O]-lgN4+30390 / T-11.58=0.646 (5) Wherein, %Al, %Si are the contents of Al and Si in molten steel, %O is the equilibrium oxygen content at the slag interface; N3 is the mass action concentration of Al2O3, N4 is the mass action concentration of SiO2, and T is the absolute temperature; Based on the above calculation results, the theoretical Al2O3 and SiO2 activities in the CaO-SiO2-Al2O3-MgO quaternary slag system under equilibrium state corresponding to the Al and Si contents in molten steel can be obtained.

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