Magnesium treatment method for reducing inclusions in molten steel in electric furnace smelting

Abstract

A magnesium treatment method for reducing inclusions in molten steel through electric furnace smelting comprises the key process steps that (1) electric arc furnace steelmaking is conducted, specifically, after the temperature of the molten steel reaches 1520-1620 DEG C, an AL-Mg alloy cored wire is fed into the molten steel through a wire feeding machine, the wire feeding speed is 2.0-3.5 m / s, and the feeding amount is 1.4-3.0 m / ton steel; the wire feeding angle is 80 DEG C or above, and the wire feeding position is in an area where molten steel flows violently; (2) magnesium treatment is conducted, specifically, the set molten steel components are analyzed, the aluminum content in the molten steel is adjusted, and for the steel type containing Ti + AL smaller than or equal to 0.04%, FeTi alloy with the total amount being 80% or less should be added before VD treatment; and (3) continuous casting: after magnesium treatment, the pulling speed is 0.7-3.0 m / min, and the superheat degree is 15-45 DEG C. The impact performance of the pipe prepared from the magnesium-treated continuous casting round pipe blank is improved by about 10%.

Description

Technical Field

[0001] The invention belongs to the technical field of electric furnace metallurgy and relates to a magnesium treatment method for reducing inclusions in molten steel during electric furnace smelting. Background Art

[0002] In the process of electric furnace smelting, inclusions in molten steel are one of the important factors affecting the quality of steel. Traditional deoxidation methods, such as calcium treatment, can effectively deoxidize, but the inclusions formed are large in size and not dispersed enough, affecting the mechanical properties and processing properties of steel. In recent years, studies have shown that the use of magnesium to treat molten steel can significantly reduce the size of inclusions and optimize their distribution, thereby improving the quality of steel. However, the existing magnesium treatment method still has some problems in practical applications and is rarely used in electric furnaces, such as wire feeding speed, feed amount, and control of molten steel composition after magnesium treatment, which need further optimization and improvement. Summary of the invention

[0003] The object of the present invention is to provide a magnesium treatment method for reducing inclusions in molten steel during electric furnace smelting, which can significantly reduce the number of inclusions in the molten steel and reduce the size of the inclusions, thereby improving the cleanliness and mechanical properties of the steel.

[0004] To achieve the above object, the present invention adopts the following technical solutions: The magnesium treatment method for reducing inclusions in molten steel during electric furnace smelting includes the following key process steps: electric arc furnace steelmaking → LF furnace → VD vacuum treatment → magnesium treatment → soft argon blowing → continuous casting: (1) Electric arc furnace smelting: When the temperature of the molten steel reaches 1520-1620°C, the AL-Mg alloy cored wire is fed into the molten steel through a wire feeder, with a wire feeding speed of 2.0-3.5 m / s and a feeding amount of 1.4-3.0 m / ton of steel; the wire feeding angle is above 80°, and the wire feeding position is in an area where the molten steel flows more violently; (2) Magnesium treatment: Analyze the set steel liquid composition and adjust the aluminum content in the steel liquid. For steel containing titanium Ti+AL≤0.04%, FeTi alloy within 80% of the total amount should be added before VD treatment; (3) Continuous casting: After magnesium treatment, the pulling speed is 0.7-3.0 m / min and the superheat is 15-45°C.

[0005] Beneficial effects of the present invention: The treatment method of the electric furnace smelting of the present invention can significantly reduce the number of inclusions in the molten steel and reduce the size of the inclusions, making the distribution of the inclusions more dispersed. At the same time, magnesium treatment can also promote the nucleation of the second phase, refine the grains, and improve the mechanical properties and processing properties of the steel. The impact properties of the pipe produced by the continuous casting round tube billet treated with magnesium are improved by about 10%. In addition, by accurately controlling the wire feeding parameters and the composition of the molten steel, the present invention also ensures the stability and safety of the magnesium treatment process. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 This is the metallographic image of inclusions at the 1 / 2 radius of the magnesium-treated billet in furnace C in Example 1.

[0007] Figure 2 This is the metallographic image of inclusions at 1 / 4 radius of the magnesium-treated billet in furnace C in Example 1.

[0008] Figure 3 This is the metallographic image of inclusions at 1 / 2 radius of the calcium-treated billet of furnace A in Example 1.

[0009] Figure 4 This is the metallographic image of inclusions at 1 / 4 radius of the calcium-treated billet in furnace A in Example 1.

[0010] Figure 5 This is the metallographic image of inclusions at 1 / 2 radius of the magnesium-treated billet in furnace 5 in Example 2.

[0011] Figure 6 This is the metallographic image of inclusions at 1 / 4 radius of the magnesium-treated billet in furnace 5 in Example 2.

[0012] Figure 7 This is the metallographic image of inclusions at 1 / 2 radius of the magnesium-treated billet in furnace 6 in Example 2.

[0013] Figure 8 This is the metallographic image of inclusions at 1 / 4 radius of the magnesium-treated billet in furnace 6 in Example 2.

[0014] Fig. 9 This is the metallographic image of inclusions at 1 / 2 radius of the calcium-treated billet of furnace 1 in Example 2.

[0015] Fig.10 This is the metallographic image of inclusions at 1 / 4 radius of the calcium-treated billet in furnace 1 in Example 2. DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with specific embodiments: Example 1

[0017] A magnesium treatment test of large tube billet 29Mn5 grade was carried out in a certain electric furnace steel plant. According to the method of the present invention, the wire feeding speed is controlled to be 3.4m / s, the feeding amount is 200 meters / furnace, the wire feeding angle is 85°, and FeTi alloy within 80% of the total amount is added before VD treatment. The test results show that the size of inclusions in the molten steel after magnesium treatment is significantly reduced, and the size of DS inclusions is reduced from about 14μm before treatment to about 7μm after treatment, and the number of inclusions is significantly reduced. At the same time, the mechanical properties and processing properties of the steel are improved.

[0018] The data of magnesium treatment after VD vacuum treatment in LF process are shown in Table 1.

[0019] The electron microscope analysis of inclusions in the C furnace magnesium treated billet is shown in Table 2.

[0020] The metallographic samples of the billets treated with magnesium in furnace C and calcium in furnace A were taken at 1 / 2 and 1 / 4 of the radius of the billet cross section for inclusion metallographic analysis. Figure 1~Figure 4 .from Figure 1 , Figure 2 It can be seen that no large inclusions were found in the metallographic observation of the 1 / 2 and 1 / 4 radius of the cross section of the blank. Random inclusions were found on the sample for electron microscopy detection. The composition of the inclusions showed that they were typical spinel and MgO inclusions formed after magnesium treatment. Figure 3 , Figure 4 It can be seen that large type B inclusions are observed on the metallographic structure at the 1 / 2 and 1 / 4 radius of the billet cross section, which will seriously affect the material properties and worsen the impact after subsequent thermal deformation.

[0021] Table 1 Data of magnesium treatment of molten steel in LF process in Example 1 .

[0022] Table 2 Typical inclusions detected by electron microscope in the blank of furnace C in Example 1 .

[0023] Table 3 Electron microscope inspection composition of inclusions in furnace A pipe in Example 1 (typical B-type inclusions) .

[0024] Table 4 Composition of inclusions detected by electron microscope in furnace C pipe in Example 1 (typical DS inclusions) .

[0025] Table 5 Heat treatment test data of magnesium-treated and calcium-treated pipes .

[0026] The inclusion detection data of hot rolled tube samples are shown in Tables 3 and 4. For the continuous casting round billets of furnace A (calcium treatment furnace) and furnace C (magnesium treatment furnace) of electric furnace smelting, after rolling production by tube rolling mill, samples of furnace A and furnace C were taken for analysis.

[0027] From Table 5, we can see that the tensile and hardness properties of the steel treated with calcium in furnace A and magnesium in furnace C are similar, but the impact properties of the steel treated with magnesium are about 5% to 10% higher than those treated with calcium. Example 2

[0028] A magnesium treatment test of 25CrMnMo grade was carried out in an electric furnace. According to the method of the present invention, the wire feeding speed is controlled to be 2.0m / s, the feeding amount is 200m / furnace (or 2.0m / ton of steel), and the wire feeding angle is 80°. The test results show that the number of Class B inclusions in the molten steel after magnesium treatment is significantly reduced, and the number of Class C inclusions increases, but the size of the inclusions is still small. In addition, by adjusting the heat treatment process parameters, the impact performance of the steel has been improved to a certain extent.

[0029] Typical inclusions in magnesium treated blanks: Figure 5~Figure 8 , metallographic detection of typical inclusions in calcium treated blanks Figure 9~Figure 10 Comparing the types, sizes and compositions of typical inclusions after calcium treatment and magnesium treatment, magnesium treatment can significantly reduce or eliminate type B inclusions compared with calcium treatment.

[0030] Table 6 Data of magnesium treatment of molten steel in LF process in Example 2 .

[0031] Table 7 Continuous casting process data table in Example 2 .

[0032] Table 8 Heat treatment test data of magnesium-treated and calcium-treated pipes in furnaces 5 and 6 .

[0033] Table 6 is the magnesium treatment data of molten steel in the LF process in Example 2; Table 7 is the continuous casting process data table in Example 2; Table 8 is the magnesium treatment pipe heat treatment test data table of Furnace 1, Furnace 5 and Furnace 6.

[0034] As can be seen from Table 8, the performance test data shows that magnesium treatment will not deteriorate the performance of the pipe, and the test performance data show that the tensile properties are similar. From the impact data, the impact performance of 25CrMnMo after magnesium treatment is improved by 12 to 19J compared with calcium treatment.

Claims

1. A magnesium treatment method for reducing inclusions in molten steel during electric furnace smelting. The process flow is electric arc furnace steelmaking → LF furnace → VD vacuum treatment → magnesium treatment → soft argon blowing → continuous casting. It is characterized by The key process steps include: (1) Electric arc furnace steelmaking: When the temperature of the molten steel reaches 1520-1620°C, the AL-Mg alloy cored wire is fed into the molten steel through a wire feeder, with a wire feeding speed of 2.0-3.5 m / s and a feeding amount of 1.4-3.0 m / ton of steel; the wire feeding angle is above 80°, and the wire feeding position is in an area where the molten steel flows more violently; (2) Magnesium treatment: Analyze the set steel liquid composition and adjust the aluminum content in the steel liquid. For steel containing titanium Ti+AL≤0.04%, FeTi alloy within 80% of the total amount should be added before VD treatment; (3) Continuous casting: After magnesium treatment, the pulling speed is 0.7-3.0 m / min and the superheat is 15-45°C.

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