Molten steel smelting method adopting fluoride-free refining slag in LF refining

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a molten steel smelting method adopting fluoride-free refining slag in LF (ladle furnace) refining, which comprises the following steps: taking a slag sample from the LF refining slag refined by fluorine-containing refining slag, analyzing the components of the slag sample, calculating the metallurgical properties including melting point and viscosity of the slag sample by using FactSage software, and calculating the content of the fluoride-free refining slag according to the calculation result. The composition of the fluoride-free refining slag system replacing the fluorine-containing refining slag is obtained through phase diagram calculation; obtaining the molten steel oxygen content and temperature at the converter smelting end point, and determining the amount of slag needing to be added according to the molten steel oxygen content and temperature at the converter smelting end point; lime and synthetic refining slag are added in the converter tapping process for slagging to achieve first modification; and in the LF refining process, residual lime and synthetic refining slag are added for slagging to realize secondary modification, a slag system is adjusted to a required fluoride-free refining slag system composition, and LF refining is realized by adopting molten steel of fluoride-free refining slag for smelting.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a method for smelting molten steel by using fluorine-free refining slag in LF refining. Background Art

[0002] LF furnace refining is required in the production process of some medium carbon steels. LF furnace refining is one of the main methods of refining outside the furnace. The key lies in the rapid production of reducing white slag. The purpose of LF slag making is desulfurization, deoxidation, improving alloy yield, and removing inclusions. Rapid slag making must also ensure that the slag has good fluidity, which is necessary for LF desulfurization, adsorption of inclusions and ensuring the quality of molten steel. Steel mills use calcium fluoride to reduce the melting point and viscosity of refined slag and improve the fluidity of slag. However, there are major problems with adding calcium fluoride to refined slag: (1) Slag containing CaF2 components corrodes the furnace lining quickly and reduces the life of the ladle; (2) CaF2 reacts with SiO2 in the slag and H2O brought in with the slag during the smelting process as follows: 2CaF2+SiO2=2CaO+SiF4, CaF2+2H2O=Ca 2+ +2OH - +2HF, the reaction generates SiF4 and HF gas, which will enter the air and pollute the atmosphere. At the same time, it will harm the health of operators if they inhale it. (3) As environmental protection measures become more stringent, the restrictions on the use of calcium fluoride will become more and more stringent. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a molten steel smelting method using fluorine-free refining slag in LF refining.

[0004] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0005] A method for smelting molten steel using fluorine-free refining slag in LF refining, comprising the following steps:

[0006] S1. Take slag samples from LF refined slag after refining with fluorine-containing refined slag, analyze the composition of the slag samples, use FactSage software to calculate the metallurgical properties of the slag samples including melting point and viscosity, and calculate the composition of the fluorine-free refined slag system that replaces the fluorine-containing refined slag through phase diagram according to the calculation results;

[0007] S2, obtaining the oxygen content and temperature of the molten steel at the end of converter smelting, and determining the amount of slag to be added according to the oxygen content and temperature of the molten steel at the end of converter smelting;

[0008] S3, adding lime and synthetic refined slag to make slag during the converter steelmaking process to achieve the first modification;

[0009] S4. During the LF refining process, the remaining lime and synthetic refining slag are added to make slag to achieve the second modification, and the slag system is adjusted to the required fluorine-free refining slag system composition, so as to achieve LF refining using fluorine-free refining slag for molten steel smelting.

[0010] As a preferred embodiment of the molten steel smelting method using fluorine-free refining slag for LF refining described in the present invention, wherein: in the step S2, the total slag amount m0 ​​to be added is determined according to the oxygen content of the molten steel at the converter end point and the steel output.

[0011] As a preferred embodiment of the molten steel smelting method using fluorine-free refining slag for LF refining of the present invention, in step S2, the relationship between the total slag amount m0 ​​and the oxygen content x of the molten steel at the converter end point and the steel output T is:

[0012] m0=[1.03%+(x-0.05)×0.1]×T

[0013] Wherein, m0 is the total slag amount, in kg; x is the oxygen content of molten steel at the end of the converter, in wt%, and T is the steel output, in t.

[0014] As a preferred embodiment of the molten steel smelting method using fluorine-free refining slag for LF refining described in the present invention, wherein: in the step S2, the amount of slag m1 to be added during the converter tapping process is determined according to the converter terminal molten steel temperature.

[0015] As a preferred embodiment of the molten steel smelting method using fluorine-free refining slag for LF refining of the present invention, in step S2, the relationship between the amount of slag m1 to be added during the converter tapping process and the converter terminal molten steel temperature t is:

[0016] m1=m0×[0.5+(t-1550)×0.16%]

[0017] Among them, m1 is the amount of slag that needs to be added during the steelmaking process of the converter, in kg; t is the final temperature of the molten steel in the converter, in ℃.

[0018] As a preferred embodiment of the LF refining method of molten steel using fluorine-free refining slag described in the present invention, in step S3, the amount of lime added and the amount of synthetic refining slag added are determined according to the amount of slag m1 required to be added during the converter steelmaking process and the composition of the fluorine-free refining slag system.

[0019] As a preferred embodiment of the molten steel smelting method using fluorine-free refining slag for LF refining described in the present invention, wherein: in the step S4, the amount of slag added during the LF refining process is m2=m0-m1, wherein m0 is the total slag amount.

[0020] As a preferred embodiment of the molten steel smelting method using fluorine-free refining slag in LF refining described in the present invention, wherein: in the step S4, the amount of lime added and the amount of synthetic refining slag added are determined according to the amount of slag m2 required to be added during the LF refining process and the composition of the fluorine-free refining slag system.

[0021] As a preferred embodiment of the molten steel smelting method using fluorine-free refining slag for LF refining described in the present invention, wherein: in the steps S3 and S4, the composition of the synthetic refining slag is: Al 30-40wt%, CaO 35-45wt%, Al2O3 15-20wt%, SiO2 10-15wt%.

[0022] As a preferred embodiment of the molten steel smelting method using fluorine-free refining slag for LF refining described in the present invention, wherein: in the steps S3 and S4, the fluorine-free refining slag system is a CaO-SiO2-Al2O3-MgO refining slag system.

[0023] The beneficial effects of the present invention are as follows:

[0024] The invention provides a method for smelting molten steel by using fluorine-free refining slag in LF refining, wherein slag samples are taken from LF refining slag refined by using fluorine-containing refining slag, the components of the slag samples are analyzed, the metallurgical properties of the slag samples including melting point and viscosity are calculated by using FactSage software, and the composition of the fluorine-free refining slag system replacing the fluorine-containing refining slag is obtained by phase diagram calculation according to the calculation results; the oxygen content and temperature of molten steel at the end point of converter smelting are obtained, and the amount of slag to be added is determined according to the oxygen content and temperature of molten steel at the end point of converter smelting; lime and synthetic refining slag are added to slag in the process of converter steel tapping to realize the first modification; the remaining lime and synthetic refining slag are added to slag in the process of LF refining to realize the second modification, and the slag system is adjusted to the required composition of the fluorine-free refining slag system, so as to realize smelting molten steel by using fluorine-free refining slag in LF refining. DETAILED DESCRIPTION

[0025] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. 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.

[0026] The main purpose of the present invention is to provide a molten steel smelting method using fluorine-free refining slag in LF refining, comprising the following steps:

[0027] S1. Take a slag sample from the LF refined slag after being refined with fluorine-containing refined slag, analyze the composition of the slag sample, use FactSage software to calculate the metallurgical properties of the slag sample including melting point and viscosity, and according to the calculation results, calculate the composition of the fluorine-free refined slag system that replaces the fluorine-containing refined slag through a phase diagram (a pseudo-quaternary phase diagram with a fixed magnesium oxide content, and find a suitable composition of the fluorine-free refined slag system by adjusting the magnesium oxide content);

[0028] S2, obtaining the oxygen content and temperature of the molten steel at the end of converter smelting, and determining the amount of slag to be added according to the oxygen content and temperature of the molten steel at the end of converter smelting;

[0029] S3. Adding lime and synthetic refined slag to slag during the converter steelmaking process to achieve the first modification; the refractory components in the lime and synthetic refined slag can slag in advance, prolonging the melting time, and can also quickly slag with the acidic oxides in the steel to form low-melting-point slag, which can play a certain desulfurization role;

[0030] S4. During the LF refining process, the remaining lime and synthetic refining slag are added to make slag for the second time, further optimizing the slag system composition, adjusting the slag system to the required fluorine-free refining slag system composition, ensuring the fluidity and desulfurization capacity of the slag, adsorbing and removing non-metallic inclusions in the molten steel, and realizing LF refining using fluorine-free refining slag for molten steel smelting.

[0031] Preferably, in step S2, the total amount of slag m0 to be added is determined according to the oxygen content of the molten steel at the converter end point and the steel output, and the relationship between the total amount of slag m0 and the oxygen content x of the molten steel at the converter end point and the steel output T is:

[0032] m0=[1.03%+(x-0.05)×0.1]×T

[0033] Wherein, m0 is the total slag amount, in kg; x is the oxygen content of molten steel at the end of the converter, in wt%, and T is the steel output, in t.

[0034] Preferably, in step S2, the amount of slag m1 to be added during the converter tapping process is determined according to the converter terminal molten steel temperature, and the relationship between the amount of slag m1 to be added during the converter tapping process and the converter terminal molten steel temperature t is:

[0035] m1=m0×[0.5+(t-1550)×0.16%]

[0036] Among them, m1 is the amount of slag that needs to be added during the steelmaking process of the converter, in kg; t is the final temperature of the molten steel in the converter, in ℃.

[0037] Preferably, in step S3, the amount of lime and the amount of synthetic refined slag added are determined according to the amount of slag m1 that needs to be added during the converter steelmaking process and the composition of the fluorine-free refined slag system.

[0038] Preferably, in step S4, the amount of slag added during LF refining is m2=m0-m1, wherein m0 is the total amount of slag.

[0039] Preferably, in step S4, the amount of lime and the amount of synthetic refined slag added are determined according to the amount of slag m2 required to be added in the LF refining process and the composition of the fluorine-free refined slag system.

[0040] Preferably, in steps S3 and S4, the synthetic refined slag has the following components: Al 30-40wt%, CaO 35-45wt%, Al2O3 15-20wt%, and SiO2 10-15wt%.

[0041] Preferably, in steps S3 and S4, the fluorine-free refined slag system is a CaO-SiO2-Al2O3-MgO refined slag system.

[0042] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0043] Example 1

[0044] This embodiment is a method for producing 45 steel in a steel plant using the present invention, comprising the following steps:

[0045] S1. FactSage calculated the composition (wt%) of the fluorine-free refined slag system as CaO: 55.02%, MgO: 6%, Al2O3%: 26.87%, SiO2: 10.91%, MnO+FeO=1%;

[0046] S2, the composition (wt%) of the final converter molten steel is C: 0.6927%, Si: 0.001%, Mn: 0.064%, P: 0.0431%, S: 0.030%, O: 0.0663%, the molten steel volume is 200t, and the tapping temperature is 1587°C. According to the oxygen content of the final converter molten steel and the tapping volume, the total slag volume m0 to be added is determined to be 2.39t, and according to the final converter molten steel temperature, the slag volume m1 to be added during the converter tapping process is determined to be 1.34t;

[0047] S3, according to the amount of slag m1 that needs to be added during the converter steel-making process and the composition of the fluorine-free refined slag system, the amount of lime added and the amount of synthetic refined slag added are determined to be 340 kg of lime and 1000 kg of synthetic refined slag, and the composition (wt%) of the synthetic refined slag is Al: 30%, CaO: 40%, Al2O3: 17%, SiO2: 13%. When the converter steel is 1 / 2 of the way out, the above slag is added to make slag to achieve the first modification;

[0048] S4. After the steel is tapped, the ladle is sent to the argon station for bottom blowing to make the inclusions grow and float up. After being treated in the argon station for 10 minutes, it enters the LF furnace for refining. Secondary slag making is carried out in the LF refining process. The slag making amount in this stage is m2=m0-m1=1.05t. The amount of lime added and the amount of synthetic refining slag added are determined to be 263kg lime and 787kg synthetic refining slag respectively according to the amount of slag m2 required to be added in the LF refining process and the composition of the fluorine-free refining slag system. Secondary slag making is carried out to adjust the slag composition to the fluorine-free refining slag system.

[0049] After LF refining uses fluorine-free refining slag system, the basicity of the slag system is 5.04, the calcium-aluminum ratio is 2.05, and the melting point is 1511℃. The number of inclusions in the refining process is counted. After LF makes white slag, 50mm 2 There are 94 inclusions in total, mainly Al2O3, and some magnesium-aluminum spinel and calcium-containing inclusions. The larger types of inclusions at this stage are mainly silicon-aluminum inclusions, as shown in Table 1; before LF bag hanging, there are 106 inclusions in total, mainly Al2O3.

[0050] Table 1

[0051] Inclusion Type Al-O Si-O Mg-Al-O Containing Ca <![CDATA[Number of inclusions (pieces / (50 mm 2 ))]]> 70 2 15 7 Average size of inclusions (μm) 4.05 4.07 3.96 4.74

[0052] Comparative Example 1

[0053] The difference from Example 1 is that a fluorine-containing slag system is used, and 2200 kg of active lime and 505 kg of fluorite (CaF2) are added as slag-making materials in the LF refining process. The refined slag is sampled and tested for analysis after making white slag and before hanging the bag. The composition (wt%) of the refined slag after making white slag by LF is CaO: 58.52%, MgO:

[0054] 2.70%, Al2O3%: 19.31%, SiO2: 13.86%, MnO: 0.30%, FeO: 2.99%, F:

[0055] 2.37%. The refined slag composition before LF ladle hanging is CaO: 58.63%, MgO: 2.19%, Al2O3%: 21.92%, SiO2: 13.66%, MnO: 0.12%, FeO: 0.55%, F: 2.96%. The melting point of slag is 1527℃.

[0056] After screening, the number of inclusions in the refining process was counted, and after LF made white slag, 50mm 2 There are 122 inclusions in total, mainly Al2O3, and some magnesium-aluminum spinel and calcium-containing inclusions, as shown in Table 2; before LF bag hanging, there are 123 inclusions in total, mainly Al2O3, with an increase in calcium-containing inclusions, and some large-sized calcium-magnesium-aluminum composite inclusions.

[0057] Table 2

[0058] Inclusion Type Al-O Si-O Mg-Al-O Containing Ca <![CDATA[Number of inclusions (pieces / (50 mm 2 ))]]> 85 2 19 16 Average size of inclusions (μm) 4.01 3.12 4.37 5.23

[0059] Example 2

[0060] This embodiment is a method for producing 45 steel in a steel plant using the present invention, comprising the following steps:

[0061] S1. FactSage calculated the composition (wt%) of the fluorine-free refined slag system as CaO: 54.87%, MgO: 5.5%, Al2O3%: 26.51%, SiO2: 12.12%, MnO+FeO=1%;

[0062] S2, the composition (wt%) of the final converter molten steel is C: 0.7276%, Si: 0.001%, Mn: 0.058%, P: 0.0431%, S: 0.030%, O: 0.0649%, and the molten steel volume is 210t. The tapping temperature is 1605℃. According to the oxygen content of the final converter molten steel and the tapping volume, the total amount of slag m0 to be added is 2.48t, and according to the final converter molten steel temperature, the amount of slag m1 to be added during the converter tapping process is determined to be 1.46t;

[0063] S3, according to the amount of slag m1 that needs to be added during the converter steelmaking process and the composition of the fluorine-free refined slag system, the amount of lime added and the amount of synthetic refined slag added are determined to be 365 kg of lime and 1095 kg of synthetic refined slag, respectively, and the composition (wt%) of the synthetic refined slag is Al: 30%, CaO: 40%, Al2O3: 17%, SiO2: 13%. When the converter steelmaking is 1 / 2, the above slag is added to make slag to realize the first modification;

[0064] S4. After the steel is tapped, the ladle is sent to the argon station for bottom blowing to make the inclusions grow and float up. After being treated in the argon station for 10 minutes, it enters the LF furnace for refining. Secondary slag making is carried out in the LF refining process. The slag making amount in this stage is m2=m0-m1=1.02t. The amount of lime added and the amount of synthetic refining slag added are determined to be 255kg lime and 765kg synthetic refining slag respectively according to the amount of slag m2 required to be added in the LF refining process and the composition of the fluorine-free refining slag system. Secondary slag making is carried out to adjust the slag composition to the fluorine-free refining slag system.

[0065] After LF refining uses fluorine-free refining slag system, the basicity of the slag system is 4.53, the calcium-aluminum ratio is 2.07, and the melting point is 1513℃. The number of inclusions in the refining process is counted. After LF makes white slag, 50mm 2There are 141 inclusions in total, mainly Al2O3, and some magnesium-aluminum spinel and calcium-containing inclusions. The larger types of inclusions at this stage are mainly silicon-aluminum inclusions, as shown in Table 3. Before LF bag hanging, there are 128 inclusions in total, mainly Al2O3.

[0066] Table 3

[0067] Inclusion Type Al-O Si-O Mg-Al-O Containing Ca <![CDATA[Inclusion count (pieces / (50 mm 2 ))]]> 83 8 32 18 Average size of inclusions (μm) 4.13 3.88 4.47 4.74

[0068] Comparative Example 2

[0069] The difference from Example 2 is that a fluorine-containing slag system is used, and 1980kg of active lime and 563kg of fluorite (CaF2) are added as slag-making materials in the LF refining process. The refined slag is sampled and tested for analysis after making white slag and before hanging the bag. The composition (wt%) of the refined slag after LF white slag making is CaO: 60.42%, MgO: 2.49%, Al2O3%: 20.14%, SiO2: 13.43%, MnO: 0.18%, FeO: 0.82%, F: 1.95%. The composition of the refined slag before LF hanging the bag is CaO: 59.35%, MgO: 2.75%, Al2O3%: 23.29%, SiO2: 11.34%, MnO: 0.08%, FeO: 0.44%, F: 2.01%. Its melting point is calculated to be 1518°C based on the obtained composition.

[0070] After screening, the number of inclusions in the refining process was counted. After LF made white slag, there were 149 inclusions, mainly Al2O3, as well as magnesium-aluminum spinel and calcium-containing inclusions, as shown in Table 4; before LF hanging bag, there were 134 inclusions, mainly Al2O3 and calcium-containing inclusions.

[0071] Table 4

[0072] Inclusion Type Al-O Si-O Mg-Al-O Containing Ca <![CDATA[Inclusion count (number / (50 mm 2 ))]]> 89 5 29 26 Average size of inclusions (μm) 4.22 3.68 4.19 5.73

[0073] It can be seen from the above embodiments and comparative examples that when fluorite is added in the traditional smelting process, it is widely used as a flux because fluorite can react with the oxides in the slag to generate low-melting-point compounds, thereby lowering the overall melting point and quickly slagging. However, the calcium fluoride in fluorite has a strong corrosive effect on refractory materials, causing the refractory bricks to be selectively corroded into a honeycomb structure, which is quickly destroyed, reducing the life of the furnace lining. At the same time, the corroded refractory enters the molten steel and pollutes the molten steel, affecting the purity of the molten steel. The use of calcium fluoride as a flux can also cause environmental problems. Toxic and harmful gases will be generated during the production process, polluting the environment and endangering the health of workers. The method of the present invention cancels the use of calcium fluoride. On the one hand, the use of fluorine-free refining slag improves the cleanliness of the molten steel and improves the quality of steel. On the other hand, fluorine-free smelting reduces the generation of toxic gases and has certain economic benefits.

[0074] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for smelting molten steel using fluorine-free refining slag in LF refining, characterized in that: The steps include: S1. Take slag samples from LF refined slag after refining with fluorine-containing refined slag, analyze the composition of the slag samples, use FactSage software to calculate the metallurgical properties of the slag samples including melting point and viscosity, and calculate the composition of the fluorine-free refined slag system that replaces the fluorine-containing refined slag through phase diagram according to the calculation results; S2, obtaining the oxygen content and temperature of the molten steel at the end of converter smelting, and determining the amount of slag to be added according to the oxygen content and temperature of the molten steel at the end of converter smelting; S3, adding lime and synthetic refined slag to make slag during the converter steelmaking process to achieve the first modification; S4. During the LF refining process, the remaining lime and synthetic refining slag are added to make slag to achieve the second modification, and the slag system is adjusted to the required fluorine-free refining slag system composition, so as to achieve LF refining using fluorine-free refining slag for molten steel smelting.

2. The method for smelting molten steel using fluorine-free refining slag in LF refining according to claim 1, characterized in that: In the step S2, the total amount of slag m0 to be added is determined according to the oxygen content of the molten steel at the end of the converter and the amount of steel discharged.

3. The method for smelting molten steel using fluorine-free refining slag in LF refining according to claim 2, characterized in that: In step S2, the relationship between the total slag amount m0, the oxygen content x of the molten steel at the converter end point, and the steel output T is: m0=[1.03%+(x-0.05)×0.1]×T Wherein, m0 is the total slag amount, in kg; x is the oxygen content of molten steel at the end of the converter, in wt%, and T is the steel output, in t.

4. The method for smelting molten steel using fluorine-free refining slag in LF refining according to claim 3, characterized in that: In the step S2, the amount of slag m1 that needs to be added during the converter tapping process is determined according to the final molten steel temperature of the converter.

5. The method for smelting molten steel using fluorine-free refining slag in LF refining according to claim 4, characterized in that: In step S2, the relationship between the amount of slag m1 that needs to be added during the converter tapping process and the final molten steel temperature t of the converter is: m1=m0×[0.5+(t-1550)×0.16%] Among them, m1 is the amount of slag that needs to be added during the steelmaking process of the converter, in kg; t is the final temperature of the molten steel in the converter, in ℃.

6. The method for smelting molten steel using fluorine-free refining slag in LF refining according to claim 5, characterized in that: In the step S3, the amount of lime and the amount of synthetic refined slag added are determined according to the amount of slag m1 that needs to be added during the converter tapping process and the composition of the fluorine-free refined slag system.

7. The method for smelting molten steel using fluorine-free refining slag in LF refining according to claim 4, characterized in that: In the step S4, the amount of slag added during the LF refining process is m2=m0-m1, wherein m0 is the total amount of slag.

8. The method for smelting molten steel using fluorine-free refining slag in LF refining according to claim 7, characterized in that: In the step S4, the amount of lime and the amount of synthetic refined slag to be added are determined according to the amount of slag m2 that needs to be added in the LF refining process and the composition of the fluorine-free refined slag system.

9. The method for smelting molten steel by using fluorine-free refining slag in LF refining according to claim 1, characterized in that: In the steps S3 and S4, the composition of the synthetic refined slag is: Al 30-40wt%, CaO 35-45wt%, Al2O3 15-20wt%, SiO2 10-15wt%.

10. The method for smelting molten steel by using fluorine-free refining slag in LF refining according to claim 1, characterized in that: In the steps S3 and S4, the fluorine-free refined slag system is a CaO-SiO2-Al2O3-MgO refined slag system.