Fluorine-free slag former, electric furnace slag system and electric furnace smelting process

Abstract

The invention relates to the technical field of steel smelting, in particular to a fluoride-free slag former, an electric furnace slag system and an electric furnace smelting process. The fluoride-free slag former comprises lime and a silicon-aluminum slag former, wherein the mass ratio of the lime to the silicon-aluminum slag former is (6-7): 1; the silicon-aluminum slag former comprises SiO2 with the mass fraction of 15%-30% and Al2O3 with the mass fraction of 70%-85%. The electric furnace slag system provided by the invention comprises the following components in percentage by mass: 8%-12% of SiO2, 4%-6% of Al2O3, 30%-40% of CaO and 30%-40% of FeO. The invention can solve the problems of poor environmental protection property and high steelmaking cost of the fluorine-containing slag former in the current electric furnace smelting.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, and in particular to a fluorine-free slag-forming agent, an electric furnace slag system and an electric furnace smelting process. Background Art

[0002] The process of electric furnace steelmaking is usually inseparable from fluorite. Fluorite is added to deslagging, accelerate the dissolution of limestone, improve the fluidity of steel slag, and enhance the steel-slag reaction ability. At the same time, fluorite contains SiO2 and S, which will generate low-melting point compounds after being added to the furnace, thereby improving the fluidity of the slag. In alkaline steelmaking furnaces, fluorite can ensure the alkalinity of the slag and dilute the slag at the same time. It is a commonly used steelmaking auxiliary material. During the reduction period, the fluoride ions in fluorite can also play a role in desulfurization.

[0003] Fluorite is mainly composed of calcium fluoride. Although it is effective as a slag-forming agent, excessive use will corrode the furnace lining and sometimes easily form serious foam slag, causing splashing. In addition, fluorite will produce gas at high temperatures, causing environmental pollution, and the fluorine element is harmful to human health. Based on this, developing a slag-forming agent that can replace fluorite is of great practical significance for reducing steelmaking costs and protecting the ecological environment. Summary of the invention

[0004] The invention aims to solve the problems of poor environmental protection and high steelmaking cost of the fluorine-containing slag-forming agent in the current electric furnace smelting.

[0005] As a first aspect, the present invention relates to a fluorine-free slag-forming agent, comprising lime and a silicon-aluminum slag-forming agent, wherein the mass ratio of the lime to the silicon-aluminum slag-forming agent is (6-7):1; the silicon-aluminum slag-forming agent comprises SiO2 with a mass fraction of 15%-30% and Al2O3 with a mass fraction of 70%-85%.

[0006] As a second aspect, the present invention relates to an electric furnace slag system, which is based on the above-mentioned fluorine-free slag-forming agent, and includes the following components in mass percentage: 8% to 12% SiO2, 4% to 6% Al2O3, 30% to 40% CaO and 30% to 40% FeO.

[0007] Optionally, the electric furnace slag system further includes a balance of metal oxides in a percentage of 10% to 15% by mass.

[0008] Optionally, the balance metal oxides include MgO, MnO and Cr2O3.

[0009] As a third aspect, the present invention relates to an electric furnace smelting process, which is based on the above-mentioned fluorine-free slag-making agent; the electric furnace smelting process comprises:

[0010] Pig iron, scrap steel and steel scraps are added to the electric furnace as the charge, and the charge is smelted by oxidation method;

[0011] Supply power to the electric furnace, blow oxygen to assist melting when the charge turns red, add fluorine-free slag-making agent to make slag once, and obtain the electric furnace slag system;

[0012] When the temperature of molten steel in the furnace is between 1580℃ and 1600℃, the furnace is turned over and slag is discharged;

[0013] Re-adding fluorine-free slagging agent for secondary slagging;

[0014] Steel is tapped when the molten steel temperature is between 1630°C and 1635°C.

[0015] Optionally, during the oxygen blowing to assist melting, the oxygen blowing pressure is not less than 0.5 MPa.

[0016] Optionally, the amount of the fluorine-free slag-forming agent added in the primary slag-forming is 4% to 4.5% of the weight of the charge.

[0017] Optionally, when the furnace is tilted and slag is discharged, the slag discharge amount is 80% to 85%.

[0018] Optionally, the amount of the fluorine-free slag-forming agent added in the secondary slag-forming is 2% to 3% of the weight of the charge.

[0019] Optionally, when pig iron, scrap steel and steel scraps are charged into the electric furnace as furnace charge, the mass percentage of pig iron is 25% to 30%.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In conventional slag-forming agents, the content of Al2O3 is generally around 1%, and the content of calcium fluoride can generally reach around 10%. In the fluorine-free slag-forming agent of the present invention, fluorite is not used, and the proportion of Al2O3 is increased accordingly. The use of Al2O3 to replace fluorite plays a role in reducing the melting point of electric furnace slag to below 1500°C, and at the same time, a certain proportion of CaO and SiO2 are combined. Among them, SiO2 is beneficial to lowering the melting point of slag, reducing the conductivity of slag, and reducing the burning loss of elements such as Al and Ti; Al2O3 can improve the resistivity and viscosity of the slag system, increase the high-temperature strength of solid slag, and reduce the high-temperature plasticity of the slag system, making up for the effect of reducing the use of CaF2 on the melting point of electric furnace slag; CaO is beneficial to ensure that the basicity of electric furnace slag is ≥2.5, and ensure the dephosphorization ability. The present invention forms a fluorine-free electric furnace slag system by mixing the above components in a certain proportion. During the electric furnace smelting process, the fluorine-free slag system has the same basicity change, dephosphorization ability and smelting time as the conventional fluorine-containing slag system electric furnace slag, and greatly reduces the smelting cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1It is a bar graph of the average values ​​of slag basicity in each embodiment and comparative example. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific implementation methods and are not intended to limit this application;

[0025] The term "including" and its variations used in this article are open inclusions, that is, "including but not limited to"; the term "based on" is "based at least in part on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first" and "second" mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, the meaning of "multiple" is two or more.

[0026] In the process of electric furnace smelting, slag-forming agent is a chemical additive used in the metal smelting process, which is mainly used to separate the molten metal from the oxide and remove impurities in the molten metal. The electric furnace slag system is a solid waste generated in the process of electric furnace metal smelting. Slag-forming agent can affect the formation speed of the electric furnace slag system, the fluidity of the slag, the oxidizability or reducibility of the slag, etc., thereby affecting the chemical reactions such as dephosphorization, desulfurization, and deoxidation in the smelting process.

[0027] Electric furnace slag plays an important role in electric furnace smelting. First, the electric furnace slag can prevent the metal from direct contact with the atmosphere, prevent oxidation and maintain the temperature of the molten pool. Secondly, the slag can absorb and dissolve impurities in the molten metal, such as harmful elements such as sulfur and phosphorus, as well as harmful gases such as hydrogen, oxygen and nitrogen, thereby improving the purity of the metal. In addition, the electric furnace slag can also control the direction and speed of chemical reactions during the smelting process. For example, adjusting the basicity of the slag can affect the effects of desulfurization and dephosphorization.

[0028] Slag basicity refers to the molar ratio of basic oxides (such as CaO) to acidic oxides (such as SiO2) in the slag. Basicity is a very important and practical parameter representing the composition of slag, which can determine the slag melting temperature, viscosity, desulfurization ability and other characteristics to a certain extent.

[0029] In general, an increase in slag basicity usually leads to an increase in melting temperature. This is because high-basicity slag contains more high-melting point compounds, such as dicalcium silicate (Ca2SiO4), which has a higher melting point and therefore requires a higher temperature to melt. As the basicity increases, the viscosity of the slag decreases. This is because the increase in basic oxides destroys the network structure of the slag, reducing the polymers in the slag and thus reducing the viscosity. In addition, the desulfurization ability of the slag is closely related to the basicity. High-basicity slag generally has a stronger desulfurization ability because the basic oxides can form stable compounds with sulfur, thereby removing sulfur from the molten iron. In order to achieve the best desulfurization effect, the basicity of the slag needs to be controlled within an appropriate range.

[0030] In order to solve the problems of poor environmental protection and high steelmaking cost of fluorine-containing slag system in current electric furnace smelting, the present invention provides a fluorine-free slag-forming agent, an electric furnace slag system and an electric furnace smelting process.

[0031] As a first aspect, the present invention relates to a fluorine-free slag-forming agent, which includes lime and a silicon-aluminum slag-forming agent, wherein the mass ratio of the lime to the silicon-aluminum slag-forming agent is (6-7):1, and the silicon-aluminum slag-forming agent includes SiO2 with a mass fraction of 15%-30% and Al2O3 with a mass fraction of 40%-50%.

[0032] In conventional slag-forming agents, the content of Al2O3 is generally around 1%, and the content of calcium fluoride can generally reach around 10%. In the fluorine-free slag-forming agent of the present invention, fluorite is not used, and the proportion of Al2O3 is increased accordingly. The use of Al2O3 to replace fluorite plays a role in reducing the melting point of electric furnace slag to below 1500°C, and at the same time, a certain proportion of CaO and SiO2 are combined. Among them, SiO2 is beneficial to lowering the melting point of slag, reducing the conductivity of slag, and reducing the burning loss of elements such as Al and Ti; Al2O3 can improve the resistivity and viscosity of the slag system, increase the high-temperature strength of solid slag, and reduce the high-temperature plasticity of the slag system, making up for the effect of reducing the use of CaF2 on the melting point of electric furnace slag; CaO is beneficial to ensure that the basicity of electric furnace slag is ≥2.5, and ensure the dephosphorization ability. The present invention forms a fluorine-free electric furnace slag system by mixing the above components in a certain proportion. During the electric furnace smelting process, the fluorine-free slag system has the same basicity change, dephosphorization ability and smelting time as the conventional fluorine-containing slag system electric furnace slag, and greatly reduces the smelting cost.

[0033] Based on the above-mentioned fluorine-free slag-forming agent, as a second aspect, an embodiment of the present invention also provides an electric furnace slag system, which is formed by the above-mentioned fluorine-free slag-forming agent through oxygen blowing and melting, and the electric furnace slag system includes the following components in mass percentage: 8% to 12% SiO2, 4% to 6% Al2O3, 30% to 40% CaO and 30% to 40% FeO.

[0034] After adding the fluorine-free slag-forming agent in the embodiment of the present invention to the smelting process and performing oxygen blowing to assist fluxing, an electric furnace slag system with stable content of each component is obtained, which can absorb harmful impurities such as sulfur and phosphorus in the molten steel, and remove non-metallic inclusions such as oxides and sulfides. By accurately obtaining the components of the electric furnace slag system, the efficiency and quality of the smelting process can be more accurately reflected.

[0035] The electric furnace slag system also includes 10% to 15% by mass of residual metal oxides, wherein the residual metal oxides include MgO, MnO and Cr2O3.

[0036] In the electric furnace slag system, there are other metal oxides to further improve the physical and chemical properties of the slag. For example, MgO can form a solidified film on the surface of the slag pool to reduce the oxygen absorption and heat loss of the slag pool; the melting of Cr2O3 will increase the viscosity of the slag, thereby reducing the diffusion of the slag into the castable, and improving the corrosion resistance and slag resistance of the castable; similar to FeO, MnO, as an alkaline oxide, can stabilize FeO and CaO, enhance the alkalinity of the slag, and reduce the melting temperature and viscosity of the slag. This makes the slag easier to flow, which helps to improve the efficiency and effect of the smelting process.

[0037] As a second aspect, the present invention also provides an electric furnace smelting process, which is based on the above-mentioned fluorine-free slag-making agent. The electric furnace smelting process comprises the following steps:

[0038] S1: Pig iron, scrap steel and steel chips are added to the electric furnace as charge, and the charge is smelted using the oxidation method.

[0039] Specifically, pig iron is an iron-carbon alloy with a carbon content greater than 2%; scrap steel refers to steel waste (such as trimmings, heads, etc.) that does not become products during the production process of a steel plant, as well as steel materials in equipment and components that are scrapped after use; steel scraps are debris generated during steel processing, usually free of impurities and oxides, and are divided into carbon steel scraps and alloy steel scraps. When pig iron, scrap steel and steel scraps are added to an electric furnace as a charge, the mass percentage of pig iron is 25% to 30%. In a specific embodiment, the ratio of pig iron, scrap steel and steel scraps is 3:5:2.

[0040] S2: supply power to the electric furnace, blow oxygen to assist melting when the charge is red hot, add fluorine-free slag-forming agent to perform primary slag-forming to obtain the electric furnace slag system.

[0041] Specifically, the amount of fluorine-free slag-making agent added in the primary slag-making is 4% to 4.5% of the weight of the charge, and the oxygen blowing pressure is not less than 0.5MPa when blowing oxygen to assist fluxing. During the primary slag-making period, attention should be paid to the slag-forming efficiency and the fluidity of the electric furnace slag, and lime or alumina powder can be appropriately added according to the viscosity of the electric furnace slag.

[0042] S3: When the temperature of the molten steel in the furnace is between 1580°C and 1600°C, the furnace is deslagging. Specifically, when the furnace is deslagging, the amount of slag discharged is 80% to 85%. When the temperature is appropriate, deslagging can reduce the erosion of the slag on the furnace lining, and because a large amount of slag accumulated in the furnace will deteriorate the permeability of the material column, deslagging is conducive to the smooth operation of the furnace.

[0043] S4: re-adding the fluorine-free slag-forming agent for secondary slag-forming. Specifically, the amount of the fluorine-free slag system added in the secondary slag-forming is 2% to 3% of the weight of the furnace charge.

[0044] S5: When the molten steel temperature is 1630 to 1635°C, steel is tapped.

[0045] The present invention applies the fluorine-free slag-forming agent to the electric furnace smelting process, and in the smelting process, after the fluorine-free slag-forming agent of the present invention is used for primary slag-forming, after the furnace is turned over and the slag is replaced by more than 80% of the slag, the fluorine-free slag-forming agent of the present invention is added again for secondary slag-forming, which can meet the process requirements of slag desulfurization and dephosphorization and improve the dephosphorization rate and desulfurization rate of the charge.

[0046] The present invention is described in detail below through specific examples and comparative examples:

[0047] Example 1

[0048] In the fluorine-free slag-forming agent of this embodiment, the mass ratio of lime to silicon-aluminum slag-forming agent is 6:1. In terms of mass fraction, the silicon-aluminum slag-forming agent includes 30% SiO2 and 70% Al2O3.

[0049] The fluorine-free slag-making agent in this embodiment is applied to the electric furnace smelting process, specifically including:

[0050] S1: Pig iron, scrap steel and steel scraps are added to the electric furnace as the charge, and the charge is smelted by oxidation method. The ratio of pig iron, scrap steel and steel scraps is 3:5:2.

[0051] S2: Power the electric furnace, blow oxygen to assist melting when the charge is red hot, spray carbon to make foamy slag, and add 4% fluorine-free slag-making agent to make slag once.

[0052] S3: When the temperature of molten steel in the furnace reaches 1590℃, the furnace is turned over and slag is discharged, and the slag discharge amount is 80%.

[0053] S4: re-adding the fluorine-free slag-forming agent to perform secondary slag-forming, wherein the amount of the fluorine-free slag-forming agent added is 2% of the weight of the charge.

[0054] S5: When the molten steel temperature reaches 1630°C, steel is tapped.

[0055] In the above electric furnace smelting process, the composition analysis of the electric furnace slag system in the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage was carried out. The results are shown in Table 1:

[0056] Table 1 Slag composition of the electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in Example 1

[0057]

[0058] Example 2

[0059] The difference between this embodiment and embodiment 1 is that in the fluorine-free slag-forming agent of this embodiment, the mass ratio of lime to silicon-aluminum slag-forming agent is 6.5:1, and the silicon-aluminum slag-forming agent includes 30% SiO2 and 70% Al2O3 in terms of mass fraction.

[0060] During the electric furnace smelting process, the composition analysis of the electric furnace slag system was carried out in the three stages of electric furnace slag replacement, slag replacement, and steel tapping, and the refining furnace steel tapping stage. The results are shown in Table 2:

[0061] Table 2 Slag composition of the electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in Example 2

[0062]

[0063] Example 3

[0064] The difference between this embodiment and embodiment 1 is that in the fluorine-free slag-forming agent of this embodiment, the mass ratio of lime to silicon-aluminum slag-forming agent is 7:1, and the silicon-aluminum slag-forming agent includes 28% SiO2 and 72% Al2O3 in terms of mass fraction.

[0065] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 3:

[0066] Table 3 Slag composition of the electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in Example 3

[0067]

[0068] Example 4

[0069] The difference between this embodiment and embodiment 1 is that in the fluorine-free slag-forming agent of this embodiment, the mass ratio of lime to silicon-aluminum slag-forming agent is 6:1, and the silicon-aluminum slag-forming agent includes 25% SiO2 and 75% Al2O3 in terms of mass fraction.

[0070] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 4:

[0071] Table 4 Slag composition before, after, and during the tapping and refining furnace tapping stages of the electric furnace in Example 4

[0072]

[0073] Example 5

[0074] The difference between this embodiment and embodiment 1 is that in the fluorine-free slag-forming agent of this embodiment, the mass ratio of lime to silicon-aluminum slag-forming agent is 6.5:1, and the silicon-aluminum slag-forming agent includes 20% SiO2 and 80% Al2O3 in terms of mass fraction.

[0075] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 5:

[0076] Table 5 Slag composition of the electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in Example 5

[0077]

[0078]

[0079] Example 6

[0080] The difference between this embodiment and embodiment 1 is that in the fluorine-free slag-forming agent of this embodiment, the mass ratio of lime to silicon-aluminum slag-forming agent is 7:1, and the silicon-aluminum slag-forming agent includes 15% SiO2 and 85% Al2O3 in terms of mass fraction.

[0081] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 6:

[0082] Table 6 Composition of slag samples before, after, and during the tapping and refining furnace tapping stages of the electric furnace in Example 6

[0083]

[0084] Example 7

[0085] The difference between this embodiment and embodiment 1 is that in step S2 of the electric furnace smelting process, 4.5% of fluorine-free slag-forming agent is added to perform primary slag-forming.

[0086] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 7:

[0087] Table 7 Composition of slag samples before, after, and during the tapping and refining furnace tapping stages of the electric furnace in Example 7

[0088]

[0089] Example 8

[0090] The difference between this embodiment and embodiment 1 is that in step S2 of the electric furnace smelting process, 4.3% of fluorine-free slag-forming agent is added to perform primary slag-forming.

[0091] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 8:

[0092] Table 8 Composition of slag samples before and after slag replacement, steel tapping and refining furnace steel tapping in Example 8

[0093]

[0094]

[0095] Example 9

[0096] The difference between this embodiment and embodiment 1 is that in step S2 of the electric furnace smelting process, 4.2% of fluorine-free slag-forming agent is added to perform primary slag-forming.

[0097] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 9:

[0098] Table 9 Composition of slag samples before, after, and during the tapping and refining furnace tapping stages of the electric furnace in Example 9

[0099]

[0100] Example 10

[0101] The difference between this embodiment and embodiment 1 is that in step S3 of the electric furnace smelting process, the slag discharge amount is 85%.

[0102] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 10:

[0103] Table 10 Slag composition of the electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in Example 10

[0104]

[0105]

[0106] Embodiment 11

[0107] The difference between this embodiment and embodiment 1 is that in step S4 of the electric furnace smelting process, during the secondary slag making, the amount of fluorine-free slag making agent added is 3% of the weight of the charge.

[0108] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 11:

[0109] Table 11 Slag composition of the electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in Example 11

[0110]

[0111] Example 12

[0112] The difference between this embodiment and embodiment 1 is that in step S4 of the electric furnace smelting process, during the secondary slag making, the added amount of the fluorine-free slag making agent is 2.5% of the weight of the charge.

[0113] In this embodiment, during the electric furnace smelting process, the composition analysis results of the electric furnace slag system at the three stages of electric furnace slag replacement, slag replacement, and steel tapping and the refining furnace steel tapping stage are shown in Table 12:

[0114] Table 12 Slag composition of the electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in Example 12

[0115]

[0116] Normally, the molten steel obtained by electric furnace smelting needs to be further refined in the refining furnace to further purify and optimize the composition of the molten steel, remove impurities and improve the quality of the steel. As shown in Table 1, in the slag samples at various stages of the electric furnace smelting process, the content of Al2O3 fluctuates between 4% and 6%, the content of SiO2 fluctuates between 9% and 12%, the content of CaO fluctuates between 30% and 40%, the content of FeO fluctuates between 30% and 40%, and the content of other metal oxides such as MgO fluctuates between 10% and 15%. Compared with the fluorine-free slag-making agent and the fluorine-containing slag-making agent, the Al2O3 content is significantly increased, and a small amount of electric furnace slag will be carried into the refining furnace when the electric furnace is tapped; but after comparison, there is no significant difference in the content of Al2O3 in the refining slag when the corresponding refining furnace is tapped, which shows that the composition of the slag sample when the refining furnace is tapped is not significantly affected by the electric furnace slag.

[0117] Comparative Example 1

[0118] The difference between this comparative example and Example 1 is that in the electric furnace smelting process, the slag-forming agent used for the primary slag-forming and the secondary slag-forming is a fluorine-containing slag-forming agent. Specifically, the fluorine-containing slag-forming agent includes the following components in mass percentage: 8% CaF2, 2% Al2O3, 11% SiO2, 35% CaO, 31% FeO, 4% MgO, 4% Cr2O3 and 5% MnO.

[0119] The composition analysis of the electric furnace before slag replacement, after slag replacement, and steel tapping, and the electric furnace at the steel tapping stage of the refining furnace, the results are shown in Table 13:

[0120] Table 13 Slag composition of electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in comparative example 1

[0121]

[0122] Comparative Example 2

[0123] The difference between this comparative example and Example 1 is that in the electric furnace smelting process, the slag-forming agents used for the primary slag-forming and the secondary slag-forming are both fluorine-containing slag-forming agents. Specifically, the fluorine-containing slag-forming agent includes the following components in mass percentage: 10% CaF2, 1% Al2O3, 10% SiO2, 36% CaO, 30% FeO, 3% MgO, 3% Cr2O3 and 7% MnO.

[0124] The composition analysis of the electric furnace slag system before, after and after slag replacement and steel tapping in the electric furnace and the steel tapping stage in the refining furnace is shown in Table 14:

[0125] Table 14 Slag composition of electric furnace before slag replacement, after slag replacement, steel tapping and refining furnace steel tapping in comparative example 2

[0126]

[0127]

[0128] It can be seen from Table 13 and Table 14 that in Comparative Examples 1 and 2, in the slag samples at various stages of the electric furnace smelting process, the component content of CaF2 fluctuates between 8% and 10%, the component content of Al2O3 fluctuates only between 0.5% and 1%, and the component content of SiO2 also decreases accordingly.

[0129] Since the slag basicity can determine its melting temperature, viscosity, desulfurization capacity, etc. to a certain extent, the average slag basicity of each embodiment and comparative example is statistically analyzed from Tables 1-12. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that the average basicity of each embodiment is 3.25, and the average basicity of each comparative example is 3.2. It can be seen that compared with the fluorine-containing slag system, the fluorine-free slag system in the present invention has little effect on the reduction of basicity, that is, the melting temperature, viscosity and desulfurization capacity of the electric furnace slag are achieved at normal levels without adding fluorine.

[0130] Furthermore, the molten steel in the electric furnace during steel tapping in Examples 1-12 and Comparative Examples 1 and 2 was sampled and chemically analyzed, and the element analysis results of the molten steel in the electric furnace during steel tapping in Examples 1-12 and Comparative Examples 1 and 2 were shown in Table 15:

[0131] Table 15 Elemental analysis of electric furnace molten steel during steel tapping in Examples 1-12 and Comparative Examples 1 and 2

[0132]

[0133]

[0134] It can be seen from Table 15 that the dephosphorization capacity of electric furnace slag using fluorine-free slag-forming agent and fluorine-containing slag-forming agent is equivalent, and has no obvious effect on the residual element content in molten steel.

[0135] Considering the influence of the slag ratio on the purity of molten steel, the UT flaw detection of the products in each embodiment is further analyzed:

[0136] Table 16 UT flaw detection of products in various embodiments

[0137]

[0138]

[0139] The products in Example 1 and Example 2 have passed the UT test before 12 heats of quenching and tempering, and passed the UT test after 3 heats of quenching and tempering, indicating that the slag system has no adverse effect on the quality of the steel products.

[0140] Furthermore, the embodiments and comparative examples were analyzed to compare the power consumption of the fluorine-containing slag system and the fluorine-free slag system. The results are shown in Table 17:

[0141] Table 17 Smelting schedule of each embodiment and comparative example

[0142]

[0143]

[0144] According to the previous smelting records of YB-70 steel, the average smelting time of the steel during the melting period is 70 minutes, the average smelting time during the oxidation period is 35.7 minutes, and the average total smelting time is 106 minutes. Therefore, the use of the fluorine-free slag-making agent in the embodiment of the present invention has no significant effect on the smelting time.

[0145] Finally, the economic benefits of the fluorine-free slag-forming agent in the present invention and the conventional fluorine-containing slag-forming agent in the production of different steel grades are calculated, and the calculation results are shown in Table 18:

[0146] Table 18 Economic accounting table

[0147]

[0148] In summary, compared with the fluorine-containing slag-forming agent, the electric furnace slag from the test furnace of fluorine-free slag-forming agent has the same dephosphorization capacity and smelting time, does not increase the consumption of electric furnace smelting electricity, saves nearly 9 yuan per ton of steel, and is expected to save more than 1.08 million yuan in total for the whole year.

[0149] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A fluorine-free slagging agent, characterized in that: It includes lime and a silicon-aluminum slag-forming agent, wherein the mass ratio of the lime to the silicon-aluminum slag-forming agent is (6-7): 1; The silicon-aluminum slag-forming agent comprises SiO2 with a mass fraction of 15%-30% and Al2O3 with a mass fraction of 70%-85%.

2. An electric furnace slag system, characterized in that: The electric furnace slag system is based on the fluorine-free slag-forming agent according to claim 1, and the electric furnace slag system includes the following components in mass percentage: 8% to 12% SiO2, 4% to 6% Al2O3, 30% to 40% CaO and 30% to 40% FeO.

3. The electric furnace slag system according to claim 2, characterized in that: The electric furnace slag system also includes a balance of metal oxides in a mass percentage of 10% to 15%.

4. The electric furnace slag system according to claim 3, characterized in that: The balance of metal oxides includes MgO, MnO and Cr2O3.

5. An electric furnace smelting process, characterized in that: The electric furnace smelting process is based on the fluorine-free slag-making agent according to claim 1; the electric furnace smelting process comprises: Pig iron, scrap steel and steel scraps are added to the electric furnace as the charge, and the charge is smelted by oxidation method; Supply power to the electric furnace, blow oxygen to assist melting when the charge turns red, add fluorine-free slag-making agent to make slag once, and obtain the electric furnace slag system; When the temperature of molten steel in the furnace is between 1580℃ and 1600℃, the furnace is turned over and slag is discharged; Re-adding fluorine-free slagging agent for secondary slagging; Steel is tapped when the molten steel temperature is between 1630°C and 1635°C.

6. The electric furnace smelting process according to claim 5, characterized in that: When blowing oxygen to assist melting, the oxygen blowing pressure is not less than 0.5 MPa.

7. The electric furnace smelting process according to claim 5, characterized in that: The addition amount of the fluorine-free slag system in the primary slag making is 4% to 4.5% of the weight of the charge.

8. The electric furnace smelting process according to claim 5, characterized in that: When the furnace is tilted and slag is discharged, the slag discharge amount is 80% to 85%.

9. The electric furnace smelting process according to claim 5, characterized in that: The addition amount of the fluorine-free slag system in the secondary slag making is 2% to 3% of the weight of the charge.

10. The electric furnace smelting process according to claim 5, characterized in that: When pig iron, scrap steel and steel chips are charged into an electric furnace as a charge, the mass percentage of pig iron is 25% to 30%.

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