A composite refining flux for molten iron and a method for using the same

Abstract

The present application relates to the technical field of metallurgy, and discloses a composite slagging agent for molten iron refining, which comprises a slagging agent TY1 and a slagging agent TY2, the slagging agent TY1 comprises CaF2, CaO, SiO2, P, S and H2O, the slagging agent TY2 comprises F, Na2O, Al2O3, SiO2, P, S and H2O, and the particle size of the slagging agent TY1 and the slagging agent TY2 is 5-50 mm.The composite slagging agent provided by the present application can completely replace traditional fluorite balls, TY1 and TY2 have a synergistic effect, the fluidity of the slag is greatly improved, the dephosphorization and desulfurization efficiency is significantly improved, the P and S impurity contents in the steel are effectively reduced, the purity of the molten steel is ensured, the requirements for high-quality steel smelting are met, the components of the composite slagging agent are clear and can be precisely controlled, the problem of fluctuation of the impurity content of natural fluorite is avoided, the physicochemical properties of the slag are stable, and the stability of the molten steel quality control is improved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a composite slag refining agent for molten iron and its application method. Background Technology

[0002] In steel smelting, the slag-forming and slag-refining operations in the semi-finished steel refining process of electric furnaces or converters are core steps to ensure the efficient conduct of metallurgical reactions such as dephosphorization and desulfurization. The performance of the slag-forming agent directly determines the physicochemical properties of the slag, the stability of the molten steel quality, and the smelting efficiency. Currently, fluorite (CaF2) or fluorite balls are commonly used in the industry as the core slag-forming agent. Although they have excellent fluxing and slag-forming effects, they have inherent defects that are difficult to avoid in industrial applications.

[0003] On the one hand, fluorite is a non-renewable strategic mineral resource, and long-term large-scale mining and application exacerbate the risk of resource depletion, which is inconsistent with the industry development trend of green and low-carbon smelting. On the other hand, the impurity content of natural fluorite fluctuates greatly, and harmful impurities such as SiO2, P, and S can easily cause uncontrolled slag composition, directly restricting the purity and quality stability of molten steel, and failing to meet the smelting requirements of high-end, high-quality steel. Although there is some research on low-fluorite and fluorite-free slagging agents in the industry, they generally suffer from problems such as insufficient slagging and fluxing effects, high smelting costs, and poor process adaptability, making it difficult to completely replace fluorite balls and hindering their stable promotion and application in large-scale industrial production.

[0004] Therefore, there is a need to improve composite slag refining agents in the existing technology. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a composite slag refining agent and its application method for molten iron, which takes into account the characteristics of efficient slag refining and precise controllable composition, while reducing smelting costs and improving steel quality, and is suitable for the needs of industrialized large-scale production.

[0006] Based on the above objectives, embodiments of the present invention provide a composite slagging agent for molten iron refining. The composite slagging agent includes slagging agent TY1 and slagging agent TY2. Slagging agent TY1 includes CaF2, CaO, SiO2, P, S, and H2O; slagging agent TY2 includes F, Na2O, Al2O3, SiO2, P, S, and H2O. The particle size of slagging agent TY1 and slagging agent TY2 is 5-50 mm.

[0007] In some embodiments, the slag-reducing agent TY1 contains, by mass percentage, 68.2-85% CaF2, 5-15% CaO, 10-15% SiO2, P≤0.30%, S≤0.50%, and H2O≤1.0%.

[0008] In some embodiments, the slag-reducing agent TY2 contains, by mass percentage, 40-60% F element, 15-25% Na2O content, 20-33% Al2O3 content, 3-5% SiO2 content, P≤0.10%, S≤0.15%, and H2O≤1.5%, and the F element is derived from at least one of sodium fluoroaluminate, sodium fluoride, and aluminum fluoride.

[0009] In some embodiments, the mass ratio of slag remover TY1 to slag remover TY2 is (1-1.5):1.

[0010] Another aspect of the present invention provides a method for using the composite slagging agent for molten iron refining as described above, comprising the following steps: S1 adds lime and slag-forming agent TY1 to the semi-steel molten steel according to the initial sulfur content. After stirring with inert gas, it is heated by electricity to form initial slag. After S2 reaches the target temperature, power supply is stopped. First, a carbon raiser is added, followed by a slag remover TY2 for slag breaking and refining.

[0011] In some implementations, in S1, the temperature for power-on heating is controlled at 1470-1500°C.

[0012] In some embodiments, in S1, the mass ratio of lime to slag-reducing agent TY1 is (3.5-4):1.

[0013] In some implementations, the target temperature in S2 is 1500-1530°C.

[0014] In some embodiments, in S2, the amount of carbon raiser added is 80~100kg.

[0015] In some embodiments, argon is used as the inert gas, the gas flow rate is controlled at 100~160NL / min during stirring, the stirring time is 4~6min, and the height of the molten iron surface fluctuation is controlled at 50~100mm during stirring.

[0016] The present invention has at least the following beneficial technical effects: (1) The composite slag agent provided by the present invention can completely replace traditional fluorite balls, get rid of dependence on non-renewable fluorite resources, reduce over-exploitation of resources, and fit the green and low-carbon development trend of the metallurgical industry.

[0017] (2) The synergistic effect of TY1 and TY2 significantly improves the fluidity of slag, significantly improves the dephosphorization and desulfurization efficiency, effectively reduces the content of P and S impurities in steel, ensures the purity of molten steel, and meets the requirements for high-quality steel smelting.

[0018] (3) The composite slag agent has a clear composition and can be precisely controlled, avoiding the problem of fluctuation in the content of natural fluorite impurities, stabilizing the physical and chemical properties of slag, and improving the stability of steel quality control.

[0019] (4) The method of precise temperature control and quantitative addition in stages is suitable for existing processes of electric furnace / converter semi-steel refining. It is simple to operate and easy to implement, and does not require major modification of production equipment. It can be promoted on a large scale in industry. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram illustrating an embodiment of the method of using the composite slag refining agent for molten iron provided by the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0023] The terms "comprising" and "having," and any variations thereof, used in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion; the terms "first," "second," etc., used in the specification, claims, and accompanying drawings are used to distinguish different objects, not to describe a particular order. "A plurality of" means two or more, unless otherwise explicitly specified.

[0024] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0025] The first aspect of this invention provides a composite slagging agent for molten iron refining. The composite slagging agent includes slagging agent TY1 and slagging agent TY2. Slagging agent TY1 includes CaF2, CaO, SiO2, P, S, and H2O; slagging agent TY2 includes F, Na2O, Al2O3, SiO2, P, S, and H2O. The particle size of slagging agent TY1 and slagging agent TY2 is 5-50 mm.

[0026] Furthermore, in slag-reducing agent TY1, TY1 is only a code, and by mass percentage, it includes: CaF2 content of 68.2-85%, CaO content of 5-15%, SiO2 content of 10-15%, P≤0.30%, S≤0.50%, and H2O≤1.0%.

[0027] Furthermore, in the slag-reducing agent TY2, TY2 is only a code, and by mass percentage, it includes: 40-60% F element content, 15-25% Na2O content, 20-33% Al2O3 content, 3-5% SiO2 content, P≤0.10%, S≤0.15%, H2O≤1.5%, and the F element is derived from at least one of sodium fluoroaluminate, sodium fluoride, and aluminum fluoride.

[0028] Furthermore, the mass ratio of slag remover TY1 to slag remover TY2 is (1-1.5):1.

[0029] This invention can replace traditional fluorite balls in the entire slag-forming and slag-refining process of electric arc furnace / converter semi-finished steel refining. It fundamentally solves the core pain points of traditional processes, which rely on non-renewable strategic mineral resources like fluorite and whose over-exploitation exacerbates resource depletion. It also avoids the environmental control risks associated with fluorite mining and use, perfectly aligning with the steel industry's policy orientation and industry trends towards green, low-carbon, and sustainable development. Simultaneously, by optimizing the particle size control of the slag-refining agent, it reduces smelting dust while maintaining reaction rate, further improving the environmental friendliness of the operation. Addressing the shortcomings of natural fluorite, such as high impurity content and large batch-to-batch composition fluctuations leading to uncontrolled slag composition and unstable steel quality, the composite slag-refining agent of this invention is prepared using precise manual batching. The core effective components can be quantitatively controlled, and harmful impurities such as P and S can be strictly limited. This avoids the inherent defects of natural fluorite from the raw material end, ensuring long-term stable slag physicochemical properties and significantly improving the batch stability of steel quality, providing a reliable guarantee for the large-scale stable production of high-end steel grades.

[0030] A second aspect of the present invention also provides a method for using a composite slagging agent for molten iron refining, comprising the following steps: S1 adds lime and slag-forming agent TY1 to the semi-steel molten steel according to the initial sulfur content. After stirring with inert gas, it is heated by electricity to form initial slag. After S2 reaches the target temperature, power supply is stopped. First, a carbon raiser is added, followed by a slag remover TY2 for slag breaking and refining.

[0031] Furthermore, in S1, the temperature for power-on heating is controlled at 1470-1500℃.

[0032] Furthermore, in S1, the mass ratio of lime to slag-reducing agent TY1 is (3.5~4):1. When the slag-reducing capacity is insufficient, slag-reducing agent TY1 can be added in appropriate amounts before slag breaking; slag-reducing agent TY2 can be added in appropriate amounts after slag breaking.

[0033] Furthermore, in S2, the target temperature is 1500-1530℃.

[0034] Furthermore, in S2, the amount of carbon raiser added is 80~100kg.

[0035] Furthermore, argon is used as the inert gas, and the gas flow rate is controlled at 100~160NL / min during stirring, the stirring time is 4~6min, and the height of the molten iron surface fluctuation is controlled at 50~100mm during stirring.

[0036] The slag-forming process in semi-finished steel refining is divided into two core stages: initial slag formation by heating and high-temperature slag breaking and refining. The slag state, metallurgical reaction requirements, and temperature windows of the two stages are completely different. Traditional fluorite balls adopt a "single component for the entire process" approach, which cannot simultaneously adapt to the thermodynamic requirements of both stages. However, this patent perfectly matches the thermodynamic requirements of the entire slag-forming process by precisely adding two components, TY1 and TY2, in stages.

[0037] 1. Initial slag formation stage: TY1 is precisely adapted to the thermodynamics of medium-temperature slag formation, rapidly constructing an efficient reaction system. The core problem during the heating stage (1470-1500℃) is that high-melting-point lime (CaO, melting point 2570℃) dissolves slowly and cannot quickly form initial slag with reasonable alkalinity and good fluidity, resulting in late start-up and low efficiency of dephosphorization and desulfurization reaction.

[0038] The present invention will be further explained below with reference to specific embodiments.

[0039] In the specific implementation process, those skilled in the art can determine the amount of lime and slag-reducing agent TYI, as well as the dosage of slag-reducing agent TYI, based on the initial S content of the molten iron. For details, please refer to Table 1.

[0040] Table 1 Dosage of lime and slag-reducing agents TYI and TY2

[0041] Example 1 (1) Preparation of slag-reducing agent Slag-reducing agent TY1 (particle size 10-30mm) has the following mass percentage values ​​for each component: CaF2 68.2%, CaO 14.0%, SiO2 13.5%, P 0.12%, S 0.20%, H2O 0.18%, with the balance being trace metallurgical-grade harmless impurities. All components are within the specified range.

[0042] Slag-reducing agent TY2 (particle size 10-30mm) has the following mass percentage values ​​for each component: F 42.0%, Na2O 20.0%, Al2O3 30.0%, SiO2 3.5%, P 0.05%, S 0.08%, H2O 0.37%, with the balance being trace metallurgical-grade harmless impurities. All components are within the specified range.

[0043] (2) How to use The test subject was semi-molten steel obtained from 30-ton electric furnace smelting, with an initial sulfur content ω(S) = 0.40%; Initial slag formation stage: Add 650 kg of lime and 165 kg of slag-forming agent TY1 to the molten iron, stir with argon gas for 5 min (gas flow rate 120 NL / min), and heat to 1480℃ by power supply to melt and form initial slag. Slag breaking and refining stage: After continuing to heat up to 1520℃, stop power supply, add 100kg of carbon raiser first, and then add 150kg of slag softener TY2 to complete the slag breaking and refining.

[0044] (3) Test results The slag fluidity index reached 1.8, the dephosphorization rate was 92%, the desulfurization rate was 88%, and the P content in the finished steel was 0.008% and the S content was 0.012%, which fully met the requirements for high-quality steel smelting.

[0045] Example 2 (1) Preparation of slag-reducing agent Slag-reducing agent TY1 (particle size 10-30mm) has the following mass percentage values ​​for each component: CaF2 72.0%, CaO 12.0%, SiO2 12.5%, P 0.10%, S 0.15%, H2O 0.25%, with the balance being trace metallurgical-grade harmless impurities. All components are within the specified range.

[0046] Slag-reducing agent TY2 (particle size 10-30mm) has the following mass percentage values ​​for each component: F 45.0%, Na2O 22.0%, Al2O3 26.0%, SiO2 3.2%, P 0.03%, S 0.06%, H2O 0.21%, with the balance being trace metallurgical-grade harmless impurities. All components are within the specified range.

[0047] (2) How to use The test subject was semi-molten steel obtained from 30-ton electric furnace smelting, with an initial sulfur content ω(S) = 0.53%; Initial slag formation stage: Add 950 kg of lime and 240 kg of slag-forming agent TY1 to the molten iron, stir with argon gas for 5 min (gas flow rate 120 NL / min), and heat to 1490℃ by power supply to melt and form initial slag. Slag breaking and refining stage: After continuing to heat up to 1530℃, stop power supply, add 100kg of carbon raiser first, and then add 160kg of slag softener TY2 to complete the slag breaking and refining.

[0048] (3) Test results The slag fluidity index reached 1.75, the dephosphorization rate was 90%, the desulfurization rate was 85%, and the P content in the finished steel was 0.009% and the S content was 0.016%, meeting the requirements for high-quality steel smelting under high-sulfur raw materials.

[0049] Example 3 (1) Preparation of slag-reducing agent Slag-reducing agent TY1 (particle size 10-30mm) has the following mass percentage values ​​for each component: CaF2 85%, CaO 15.0%, SiO2 14.8%, P 0.28%, S 0.45%, H2O 0.47%, with the balance being trace metallurgical-grade harmless impurities. All components are within the specified range.

[0050] Slag-reducing agent TY2 (particle size 10-30mm) has the following mass percentage values ​​for each component: F 40.0%, Na2O 16.0%, Al2O3 32.5%, SiO2 4.8%, P 0.09%, S 0.14%, H2O 0.47%, with the balance being trace metallurgical-grade harmless impurities. All components are within the specified range.

[0051] (2) How to use The test subject was semi-molten steel obtained from smelting in a 30-ton electric furnace, with an initial sulfur content ω(S) = 0.35%; Initial slag formation stage: Add 550 kg of lime and 140 kg of slag-forming agent TY1 to the molten iron, stir with argon gas for 5 min (gas flow rate 120 NL / min), and heat to 1470℃ by power supply to melt and form initial slag. Slag breaking and refining stage: After continuing to heat up to 1500℃, stop power supply, first add 100kg of carbon raiser, then add 140kg of slag softener TY2 to complete the slag breaking and refining.

[0052] (3) Test results The slag fluidity index reached 1.85, the dephosphorization rate was 93%, the desulfurization rate was 90%, and the P content in the finished steel was 0.007% and the S content was 0.010%, which fully met the smelting requirements of low-sulfur high-end steel and verified the technical feasibility of the component boundary value.

[0053] Comparative Example (1) Preparation of reference materials The steel smelting industry uses conventional fluorite spheres with a particle size of 10-30mm. The composition by mass percentage is: CaF2≥75%, SiO2≤15%, P≤0.30%, S≤0.50%, H2O≤1.0%. The impurity content is comparable to TY1 and TY2 in Example 1.

[0054] (2) How to use The test subject was exactly the same as in Example 1: 30 tons of molten steel with an initial sulfur content of ω(S) = 0.40%. The smelting process, temperature control, lime dosage, and carbon raiser dosage were exactly the same as in Example 1. The only difference was that the TY1+TY2 composite slag agent in Example 1 was replaced by 315 kg of traditional fluorite balls in equal mass.

[0055] (3) Test results The slag fluidity index is 1.5, the dephosphorization rate is 85%, the desulfurization rate is 80%, and the P content and S content in the finished steel are 0.012% and 0.018%, respectively. All metallurgical performance indicators are significantly lower than those of the embodiments of the present invention.

[0056] This invention, TY1, employs a ternary pre-matched system of CaO-SiO2-CaF2. The low melting point eutectic temperature of this system can be as low as 1100℃, far below the smelting temperature during the heating stage. After addition, it does not rely on the slow diffusion reaction of CaO and SiO2 in the furnace; it can rapidly melt to form a stable liquid phase molten pool, quickly encapsulating and wetting lime particles. This significantly reduces the dissolution activation energy of lime, shortening the complete dissolution time by more than 30%, and rapidly forming the optimal dephosphorization slag with a binary basicity of 2.5-3.5, allowing the dephosphorization reaction to start earlier and proceed efficiently throughout the entire process.

[0057] Traditional fluorite contains only CaF2, which needs to react randomly with CaO and SiO2 in the furnace to form a low-melting-point phase. The lime dissolves slowly, the initial slag formation is delayed, and local alkalinity fluctuations are prone to occur. It is impossible to stably maintain the optimal thermodynamic conditions for dephosphorization. Therefore, the dephosphorization efficiency is significantly lower than that of this invention.

[0058] High-temperature slag breaking and refining stage: TY2 is precisely adapted to the thermodynamics of high-temperature refining, continuously maintaining the optimal performance of the slag. The core problem in the slag breaking stage is that the initial slag gradually becomes "dry" as smelting progresses, the slag viscosity increases, the melting point rises, and mass transfer at the steel-slag interface is hindered; moreover, the CaF2 of traditional fluorite is easy to react with SiO2 at high temperatures to generate SiF4 gas volatilization, the fluxing effect decays rapidly, and the desulfurization efficiency drops significantly.

[0059] The present invention TY2 adopts a Na2O-Al2O3-SiO2-F multi-element stable system. The ternary eutectic temperature of this system is as low as 1060℃, and it still has extremely strong thermal stability at high temperatures, which is perfectly suited to the temperature window of the slag breaking stage. Strong network disruption effect: As a strong network modifier, Na₂O carries Na₂O. + It can quickly break the Si-O tetrahedral network structure in silicate slag, and its viscosity-reducing effect is similar to that of Ca. 2+ More than three times that of other processes, it can instantly solve the problem of slag "drying out"; High sulfur capacity enhancement effect: Na2O is a strong alkaline oxide that can significantly increase the sulfur capacity of slag. Compared with traditional fluorite, which can only improve fluidity, TY2 can simultaneously achieve "viscosity reduction + sulfur capacity enhancement", fundamentally strengthening the limits of desulfurization reaction from a thermodynamic perspective; Low volatility and stable fluxing: F in the system combines with Na and Al to form stable compounds such as sodium fluoride and sodium fluoroaluminate, avoiding the problem of volatilization caused by the reaction of traditional CaF2 with SiO2 at high temperature. The utilization rate of F element is increased by more than 40%, and it can continuously exert a fluxing effect throughout the process, stably maintaining the high fluidity of slag.

[0060] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0061] It should be understood that, as used herein, unless the context clearly supports an exception. It should also be understood that, as used herein, "and / or" means any and all possible combinations of one or more of the associated listed items.

[0062] The embodiment numbers disclosed in the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0063] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A composite slagging agent for molten iron refining, characterized in that, The composite slag-reducing agent includes slag-reducing agent TY1 and slag-reducing agent TY2. Slag-reducing agent TY1 includes CaF2, CaO, SiO2, P, S, and H2O; slag-reducing agent TY2 includes F, Na2O, Al2O3, SiO2, P, S, and H2O. The particle size of slag-reducing agent TY1 and slag-reducing agent TY2 is 5-50 mm.

2. The composite slagging agent for molten iron refining according to claim 1, characterized in that, The slag-reducing agent TY1 contains, by mass percentage, 68.2-85% CaF2, 5-15% CaO, 10-15% SiO2, P≤0.30%, S≤0.50%, and H2O≤1.0%.

3. The composite slagging agent for molten iron refining according to claim 1, characterized in that, The slag-reducing agent TY2 contains, by mass percentage, 40-60% F element, 15-25% Na2O element, 20-33% Al2O3 element, 3-5% SiO2 element, P≤0.10%, S≤0.15%, and H2O≤1.5%, and the F element is derived from at least one of sodium fluoroaluminate, sodium fluoride, and aluminum fluoride.

4. The composite slagging agent for molten iron refining according to claim 1, characterized in that, The mass ratio of slag remover TY1 to slag remover TY2 is (1-1.5):

1.

5. A method of using the composite slagging agent for molten iron refining according to any one of claims 1-4, characterized in that, include: S1 adds lime and slag-forming agent TY1 to the semi-steel molten steel according to the initial sulfur content. After stirring with inert gas, it is heated by electricity to form initial slag. After S2 reaches the target temperature, power supply is stopped. First, a carbon raiser is added, followed by a slag remover TY2 for slag breaking and refining.

6. The method of using the composite slagging agent for molten iron refining according to claim 5, characterized in that, In S1, the temperature for power transmission and heating is controlled at 1470-1500℃.

7. The method of using the composite slagging agent for molten iron refining according to claim 5, characterized in that, In S1, the mass ratio of lime to slag-reducing agent TY1 is (3.5-4):

1.

8. The method of using the composite slagging agent for molten iron refining according to claim 5, characterized in that, In S2, the target temperature is 1500-1530℃.

9. The method of using the composite slagging agent for molten iron refining according to claim 5, characterized in that, In S2, the amount of carbon raiser added is 80~100kg.

10. The method of using the composite slagging agent for molten iron refining according to claim 5, characterized in that, Argon is used as the inert gas. The gas flow rate is controlled at 100-160 NL / min during stirring, the stirring time is 4-6 min, and the height of the molten iron surface fluctuation is controlled at 50-100 mm during stirring.

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