Refining slag for calcium-free treatment of aluminum killed steel LF refining process and application of refining slag

Abstract

The invention belongs to the technical field of ferrous metallurgy, particularly relates to refining slag for calcium-free treatment of an aluminum killed steel LF refining process and application of the refining slag, inhibits generation of MgO.Al2O3 inclusions in aluminum killed steel, solves the problems that in the prior art, a large number of large-size inclusions exist in steel and the castability of molten steel becomes poor, and improves the production efficiency by optimizing the alkalinity and components of the refining slag. And during calcium-free treatment, generation of MgO.Al2O3 inclusions in slag steel reaction is inhibited, nodulation of the MgO.Al2O3 inclusions on the inner wall of a tundish nozzle and the head of a stopper rod is reduced, and then the castability of molten steel is improved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a refined slag for calcium-free treatment in an LF refining process of aluminum-killed steel and application thereof. Background Art

[0002] With the development of iron and steel metallurgical industry technology and users' increasingly higher requirements for the quality and performance of steel products, clean steel smelting and inclusion control have become key issues in the steelmaking process. Aluminum-killed steel is widely used in automobile steel, pressure vessels, chemicals, construction and other industries due to its high plasticity, high low strength and cold rolling ductility. At present, the production process of aluminum-killed steel is mainly: converter steelmaking → LF refining → continuous casting. The refractory materials in the LF ladle furnace are mostly magnesium-carbon refractory materials, and high-basicity CaO-SiO2-Al2O3-MgO refining slag is mostly used during LF refining. This makes it inevitable that MgO·Al2O3 inclusions appear in the steel. Such inclusions have the characteristics of high melting point (2135℃), high hardness, sharp edges and corners, and are not easy to deform. They will seriously reduce the mechanical properties and corrosion resistance of steel products and cause surface defects of steel. In addition, MgO·Al2O3 inclusions tend to adhere to the inner wall of the immersion nozzle of the tundish and the plug rod head during the pouring of molten steel, and sinter with the refractory material to form nodules, which seriously affects the pouring process and continuous casting efficiency, and may even cause serious production accidents.

[0003] In the past, by feeding Ca wire into the ladle before LF refining (i.e., calcium treatment process), MgO·Al2O3 inclusions in molten steel can be effectively modified into CaO-Al2O3 (MgO) and liquid inclusions. However, this method has the disadvantages of difficult to accurately control the amount of Ca added, easy to cause molten steel pollution, and increase the cost per ton of steel, resulting in a large number of large-sized CaO-Al2O3 inclusions in the molten steel. For this reason, the calcium-free treatment process has been increasingly valued by steel companies in recent years. After adopting the calcium-free treatment process, the control of MgO·Al2O3 inclusions in steel has become a new contradiction to ensure smooth continuous casting, improve the cleanliness of molten steel, and improve the performance and quality of steel products. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a calcium-free refining slag for aluminum killed steel LF refining process and its application.

[0005] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0006] A refined slag for calcium-free treatment in LF refining process of aluminum-killed steel, comprising, by weight percentage, 64.25-65.25wt% CaO, 8.75-9.75wt% SiO2, 20±0.5wt% Al2O3, 6±0.5wt% MgO, and a basicity CaO / SiO2 of 6.7-7.3.

[0007] As a preferred solution of the calcium-free refining slag for the LF refining process of aluminum killed steel described in the present invention, the mass percentage of CaO in the refining slag is 64.75wt%.

[0008] As a preferred solution of the calcium-free refining slag for the LF refining process of aluminum-killed steel described in the present invention, the mass percentage of SiO2 in the refining slag is 9.25wt%.

[0009] As a preferred solution of the calcium-free refining slag for the LF refining process of aluminum-killed steel described in the present invention, the mass percentage of Al2O3 in the refining slag is 20wt%.

[0010] As a preferred solution of the refined slag for calcium-free treatment in the LF refining process of aluminum killed steel described in the present invention, the mass percentage of MgO in the refined slag is 6wt%.

[0011] As a preferred embodiment of the calcium-free refining slag for the LF refining process of aluminum-killed steel described in the present invention, the basicity CaO / SiO2 of the refining slag is 7.

[0012] To solve the above technical problem, according to another aspect of the present invention, the present invention provides the following technical solution:

[0013] A calcium-free treatment method for aluminum-killed steel LF refining process, in which 150-250kg / t 钢 The above-mentioned aluminum killed steel LF refining process does not require calcium treatment and uses refined slag to treat the molten steel.

[0014] As a preferred solution of the calcium-free treatment method for the LF refining process of aluminum-killed steel described in the present invention, the average size of MgO·Al2O3 inclusions in the molten steel after treatment is ≤2μm.

[0015] As a preferred embodiment of the calcium-free treatment method for aluminum-killed steel LF refining process described in the present invention, the area fraction of MgO·Al2O3 inclusions in the treated molten steel is ≤110μm 2 / mm 2 .

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention proposes a refined slag for calcium-free treatment in the LF refining process of aluminum killed steel and application thereof, which inhibits the generation of MgO·Al2O3 inclusions in the aluminum killed steel, overcomes the problems of a large number of large-sized inclusions in the steel and the deterioration of the castability of the molten steel in the prior art, and suppresses the generation of MgO·Al2O3 inclusions in the slag-steel reaction during the calcium-free treatment by optimizing the basicity and composition of the refined slag, reduces the nodules of MgO·Al2O3 inclusions on the inner wall of the tundish water inlet and the head of the plug rod, thereby improving the castability of the molten steel. DETAILED DESCRIPTION

[0018] 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.

[0019] The main purpose of the present invention is to propose a calcium-free refining slag for aluminum-killed steel LF refining process and its application, improve the composition and basicity of the refining slag, and have a lower basicity and lower Al2O3 content, so as to obtain a higher Al2O3 inclusion adsorption capacity, so as to reduce the transformation of Al2O3 inclusions in molten steel to MgO·Al2O3, and finally reduce MgO·Al2O3 inclusions in steel. The problem of controlling MgO·Al2O3 inclusions in steel after adopting the calcium-free treatment process becomes a new contradiction to ensure smooth continuous casting, improve the cleanliness of molten steel, and improve the performance and quality of steel products is solved.

[0020] According to one aspect of the present invention, the present invention provides the following technical solution:

[0021] A refined slag for calcium-free treatment in LF refining process of aluminum-killed steel, comprising, by weight percentage, 64.25-65.25wt% CaO, 8.75-9.75wt% SiO2, 20±0.5wt% Al2O3, 6±0.5wt% MgO, and a basicity CaO / SiO2 of 6.7-7.3.

[0022] Preferably, the mass percentage of CaO in the refined slag is 64.75wt%.

[0023] Preferably, the mass percentage of SiO2 in the refined slag is 9.25wt%.

[0024] Preferably, the mass percentage of Al2O3 in the refined slag is 20wt%.

[0025] Preferably, the mass percentage of MgO in the refined slag is 6wt%.

[0026] Preferably, the basicity CaO / SiO2 of the refined slag is 7.

[0027] According to another aspect of the present invention, the present invention provides the following technical solution:

[0028] A calcium-free treatment method for aluminum-killed steel LF refining process, in which 150-250kg / t 钢 The above-mentioned aluminum killed steel LF refining process free of calcium treatment using refined slag to treat molten steel, preferably, the amount of refined slag added in the aluminum killed steel LF refining process free of calcium treatment is 200kg / t 钢 .

[0029] Preferably, the average size of MgO·Al2O3 inclusions in the treated molten steel is ≤2 μm.

[0030] Preferably, the area fraction of MgO·Al2O3 inclusions in the treated molten steel is ≤110 μm 2 / mm 2 .

[0031] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0032] The composition of the following aluminum-killed steel liquid is Fe-0.065wt%Al-0.14wt%Mn-0.035wt%C. The refined slag is added and post-treated for 60 minutes to carry out slag-steel reaction. After the insulation time is over, sampling is carried out to obtain a steel ingot, and a 5mm×5mm thin steel sheet is taken from the steel ingot for inclusion analysis and statistics.

[0033] Example 1

[0034] A calcium-free treatment method for aluminum-killed steel LF refining process, in which 200kg / t 钢 The aluminum killed steel LF refining process calcium-free refining slag is treated; the aluminum killed steel LF refining process calcium-free refining slag, by weight percentage, has the following components: CaO 64.75wt%, SiO2 9.25wt%, Al2O320wt%, MgO 6wt%, and the basicity CaO / SiO2 is 7. The average size of MgO·Al2O3 inclusions in the treated molten steel is 1.68μm; the area fraction of MgO·Al2O3 inclusions in the treated molten steel is 104.49μm 2 / mm 2 .

[0035] Example 2

[0036] A calcium-free treatment method for aluminum-killed steel LF refining process, in which 200kg / t 钢The aluminum killed steel LF refining process calcium-free refining slag is treated; the aluminum killed steel LF refining process calcium-free refining slag, by weight percentage, has the following components: CaO 65.08wt%, SiO2 8.92wt%, Al2O3 20wt%, MgO 6wt%, and the basicity CaO / SiO2 is 7.3. The average size of MgO·Al2O3 inclusions in the treated molten steel is 1.72μm; the area fraction of MgO·Al2O3 inclusions in the treated molten steel is 105.41μm 2 / mm 2 .

[0037] Comparative Example 1

[0038] The difference from Example 1 is that the refined slag used has the following components, by weight percentage: CaO 58.7wt%, SiO2 5.3wt%, Al2O3 30wt%, MgO 6wt%, and the basicity CaO / SiO2 is 11.

[0039] The average size of MgO·Al2O3 inclusions in the treated molten steel is 2.53μm; the area fraction of MgO·Al2O3 inclusions in the treated molten steel is 166.63μm 2 / mm 2 .

[0040] Comparative Example 2

[0041] The difference from Example 1 is that the refined slag used has the following components, by weight percentage: CaO 48wt%, SiO2 16wt%, Al2O3 30wt%, MgO 6wt%, and the basicity CaO / SiO2 is 3.

[0042] The average size of MgO·Al2O3 inclusions in the treated molten steel is 2.59μm; the area fraction of MgO·Al2O3 inclusions in the treated molten steel is 148.93μm 2 / mm 2 .

[0043] It can be seen from Examples 1 and 2 of the present invention and Comparative Examples 1 and 2 that the present invention effectively achieves the reduction of the size of MgO·Al2O3 inclusions in aluminum killed steel by improving the refined slag composition and conducting slag-steel reaction tests. The test results show that when the basicity of the refined slag is 7, the Al2O3 content is 20wt%, and the MgO content is 6wt%, the inclusions in the steel are mainly MgO·Al2O3, and no large-sized CaO-Al2O3 inclusions are found. The average size of MgO·Al2O3 inclusions in the steel is significantly reduced compared with the existing process, from 2.59μm to 1.68μm. This effect effectively reduces the impact of MgO·Al2O3 inclusions in the steel on the performance of aluminum killed steel products. The present invention improves the composition of refined slag on the basis of the production process of aluminum-killed steel free of calcium treatment, and effectively reduces the area fraction of MgO·Al2O3 inclusions in aluminum-killed steel. The test results show that when the basicity of the refined slag is 7, the Al2O3 content is 20wt%, and the MgO content is 6wt%, the area fraction of MgO·Al2O3 inclusions in the steel is 104.49μm 2 / mm 2 , compared with the area fraction of MgO·Al2O3 inclusions in the steel using the existing refined slag composition in Comparative Example 1 of 166.63 μm 2 / mm 2 Compared with the above, it is reduced by 37.3%, indicating that the refined slag composition proposed by the present invention can effectively alleviate the nodule formation of MgO·Al2O3 inclusions in the steel on the inner wall of the nozzle and the head of the plug rod, thereby improving the castability of the molten steel.

[0044] 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 refined slag for calcium-free treatment in LF refining process of aluminum killed steel, characterized in that: Calculated by weight percentage, its composition is: CaO 64.25-65.25wt%, SiO2 8.75-9.75wt%, Al2O3 20±0.5wt%, MgO 6±0.5wt%, and the basicity CaO / SiO2 is 6.7-7.

3.

2. The refined slag for calcium-free treatment in LF refining process of aluminum killed steel according to claim 1, characterized in that: The mass percentage of CaO in the refined slag is 64.75wt%.

3. The refined slag for calcium-free treatment in LF refining process of aluminum killed steel according to claim 1, characterized in that: The mass percentage of SiO2 in the refined slag is 9.25wt%.

4. The refined slag for calcium-free treatment in LF refining process of aluminum killed steel according to claim 1, characterized in that: The mass percentage of Al2O3 in the refined slag is 20wt%.

5. The refined slag for calcium-free treatment in LF refining process of aluminum killed steel according to claim 1, characterized in that: The mass percentage of MgO in the refined slag is 6wt%.

6. The refined slag for calcium-free treatment in LF refining process of aluminum killed steel according to claim 1, characterized in that: The basicity of the refined slag is CaO / SiO27.

7. A calcium-free treatment method for aluminum-killed steel LF refining process, characterized in that: In the LF refining process, add 150-250kg / t 钢 The above-mentioned aluminum killed steel LF refining process does not require calcium treatment and uses refined slag to treat the molten steel.

8. The calcium-free treatment method for aluminum killed steel LF refining process according to claim 7, characterized in that: The average size of MgO·Al2O3 inclusions in the treated molten steel is ≤2μm.

9. The calcium-free treatment method for aluminum killed steel LF refining process according to claim 7, characterized in that: The area fraction of MgO·Al2O3 inclusions in the treated molten steel is ≤110μm 2 / mm 2 .