High-strength steel smelting method for improving purity of molten steel

Abstract

The invention discloses a high-strength steel smelting method for improving the purity of molten steel, which comprises the following steps: (1) carrying out composite desulfurization on lime and magnesium powder in a desulfurization station, and then removing slag to ensure that the sulfur in the back of a converter is less than 150ppm; (2) carrying out desulfurization on the LF by adopting lime and an aluminum deoxidizer until the desulfurization is 20-40ppm; (3) after the molten steel begins to circulate in the RH vacuum chamber, aluminum is added according to the predicted oxygen blowing amount, and oxygen blowing operation is carried out after aluminum adding is finished and stabilization is carried out; (4) 140 + / -10 m seamless pure calcium core-spun yarn is fed, and molten steel is statically stirred for 15-20 min after calcium treatment; (5) performing protective casting during continuous casting, and completely eradicating air suction; and (6) a strong secondary cooling water process is adopted for the thick plate continuous casting billet to accelerate dendritic crystal nucleation in the continuous casting billet, and when the solid-liquid phase rate of the continuous casting billet ranges from 0.2 to 1.0, the center segregation of the continuous casting billet is guaranteed under the heavy pressure of 12 mm. The method has the advantages of improving the purity of the molten steel and improving the center segregation of the continuous casting billet.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a high-strength steel smelting method for improving the purity of molten steel. Background Art

[0002] At present, aluminum deoxidation of steel is a commonly used refining method for low-sulfur molten steel in steelmaking. However, there are a large number of aluminum inclusions in the molten steel produced by this refining method. Inclusions are the main enrichment place of free gas. The inclusions and gases retained in the molten steel cause the increase of the total oxygen content of the molten steel, affecting the internal quality of the molten steel and reducing the performance of the steel plate. In particular, during the casting process of ultra-thick continuous casting billets, the slow growth of dendrites will also lead to severe center segregation, which greatly affects the quality of the steel plate. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that the existing refining method is prone to produce inclusions resulting in poor quality of steel plates, and to provide a high-strength steel smelting method for improving the purity of molten steel, which can effectively improve the purity of molten steel, improve the center segregation of continuous casting billets, and improve the quality of steel plates.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions: A high-strength steel smelting method for improving the purity of molten steel, wherein the weight percentage components of the high-strength steel include: C: 0.070-0.10%, Si 0.15-0.35%, Mn: 1.55-1.80%, P≤0.015%, S≤0.006%, Nb: 0.020-0.070%, Ti: 0.006-0.020%, Ca: 0.0005-0.0040%, Al: 0.025-0.070%, Cu: 0.10%, Ni: 0.20%, Cr: 0.10-0.30%, and the balance is Fe; the smelting method is carried out according to the following steps: (1) The desulfurization station uses lime and magnesium powder for composite desulfurization. After desulfurization, the slag is cleaned to ensure that the sulfur after the converter is less than 150ppm; (2) LF uses lime and aluminum deoxidizer for desulfurization operation, and desulfurization to 20-40ppm is sufficient, and no further deep desulfurization is required; (3) After the molten steel reaches the RH, it starts to circulate in the RH vacuum chamber and then adds aluminum according to the expected oxygen blowing amount, 100m 3 Add 100-120kg of aluminum particles into the oxygen. After the aluminum addition is completed and stabilized, lower the oxygen gun to 4.8-5.0m for oxygen blowing operation. The total oxygen blowing volume shall not exceed 100m 3 ; (4) After RH treatment, the molten steel is fed into a 140±10m seamless pure calcium cored wire. After calcium treatment, the molten steel is stirred for 15 to 20 minutes to fully float and remove large particle inclusions. (5) During continuous casting, protective casting should be done to prevent air inhalation and contamination of molten steel; (6) In the thick plate continuous casting process, a strong secondary cooling water process is used to accelerate the nucleation of dendrites in the continuous casting billet. When the solid-liquid phase ratio of the continuous casting billet is in the range of 0.2~1.0, a heavy pressure of 12 mm is applied to ensure the central segregation of the continuous casting billet.

[0005] Furthermore, in the weight percentage composition of the high-strength steel, the target value of the C content is 0.080%.

[0006] Furthermore, the high-strength steel has a Ceq of 0.37-0.45% and a Pcm of 0.15-0.20%.

[0007] Furthermore, the weight percentage composition of the high-strength steel includes: C: 0.082%, Si 0.24%, Mn: 1.75%, P: 0.013%, S: 0.005%, Nb: 0.035%, Ti: 0.016%, Ca: 0.0020%, Al: 0.045%, Cu: 0.10%, Ni: 0.20%, Cr: 0.20%, and the balance is Fe.

[0008] Furthermore, the weight percentage composition of the high-strength steel includes: C: 0.078%, Si 0.23%, Mn: 1.73%, P: 0.014%, S: 0.004%, Nb: 0.037%, Ti: 0.014%, Ca: 0.0019%, Al: 0.042%, Cu: 0.10%, Ni: 0.20%, Cr: 0.19%, and the balance is Fe.

[0009] Furthermore, in the step (3), the RH vacuum treatment time is 15 to 20 minutes, the vacuum degree is ≤3 mbar, no alloying operation is performed during the vacuum treatment, no deoxidizer is added, and calcium treatment is performed after the vacuum treatment.

[0010] Furthermore, in step (3), the RH aluminum supplement amount is 100-110 kg, and the RH oxygen blowing amount is 70-80 m 3 .

[0011] Furthermore, in the step (4), the feeding amount of seamless pure calcium cored wire is 140-150 m, and the static stirring time is 18-20 min.

[0012] The design principle of the present invention is: when the inclusions in the molten steel are solid inclusions, it is more conducive to the aggregation and growth of the inclusions and to the floating removal during the static stirring process. When the inclusions are in the form of CaS-Al2O3, the inclusions are more likely to form large-sized solid inclusions. When the molten steel is in a high-sulfur and low-oxygen environment, the sulfur is required to be greater than 12ppm and the oxygen is less than 12ppm. At this time, calcium treatment is more conducive to the formation of CaS-Al2O3 solid inclusions. Such solid inclusions are easy to aggregate, grow and float under the action of static stirring, reducing the number of large inclusions in the molten steel, and can improve the cleanliness of the molten steel. Based on the above research, the method of removing inclusions to improve the cleanliness of molten steel adopts a high-sulfur design, and blows in no more than 100m 3 After the vacuum treatment, 120m of seamless pure calcium cored wire is fed to form CaS-Al2O3 solid inclusions which are easier to remove, thus achieving the purpose of improving the purity of molten steel.

[0013] Compared with the prior art, the advantages of the present invention are: (1) The present invention adopts a low-oxygen and high-sulfur design, forms CaS-Al2O3 solid inclusions through a calcium treatment process, and fully floats during the static stirring process to improve the purity of the molten steel. A stronger secondary cooling water model and dynamic heavy pressure reduction technology are used to effectively improve the center segregation of the continuous casting billet; (2) The desulfurization station of the present invention uses lime and magnesium powder for mixed desulfurization, and the sulfur content of the converter steel is stabilized within 150ppm. The LF uses lime and aluminum for rapid desulfurization, and the sulfur content of the finished product is 20-50ppm. The product design meets the high sulfur requirements; (3) The aluminum particles added during RH in the present invention can ensure that the composition does not change during the RH vacuum treatment process. A small amount of oxygen blowing ensures that other alloying elements are not oxidized, but it plays a role in oxidizing and denaturing the calcium, magnesium, aluminum elements and inclusions in the molten steel and effectively removing them during the RH vacuum process, thereby reducing the overall number of inclusions in the molten steel, reducing the attachment environment of free oxygen in the molten steel, improving the purity of the molten steel, and reducing the total oxygen content of the molten steel; (4) The present invention feeds pure calcium cored wire after the RH treatment, which can improve the type of inclusions in the early stage, form CaS-Al2O3 solid inclusions, and float and remove large particle inclusions through long-term static stirring, thereby improving the removal rate of inclusions; (5) In the continuous casting production process of the present invention, the whole-process protection casting can isolate the air, eliminate the pollution of molten steel, and ensure the purity of molten steel in the early refining process. The secondary cooling water process and the dynamic heavy pressure process can make the thick specification continuous casting billet have better low-multiple quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The macrostructure of the continuous casting slab in Example 1 of the present invention is Figure 1 ; Figure 2 The macrostructure of the continuous casting slab in Example 1 of the present invention is Figure 2 ; Figure 3 The macrostructure of the continuous casting slab in Example 2 of the present invention Figure 1 ; Figure 4 The macrostructure of the continuous casting slab in Example 2 of the present invention Figure 2 . DETAILED DESCRIPTION Example 1

[0015] To make the present invention more clear, a high-strength steel smelting method for improving the purity of molten steel according to the present invention is further described below in conjunction with the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] In this embodiment, the weight percentage composition of the high-strength steel includes: C: 0.082%, Si 0.24%, Mn: 1.75%, P: 0.013%, S: 0.005%, Nb: 0.035%, Ti: 0.016%, Ca: 0.0020%, Al: 0.045%, Cu: 0.10%, Ni: 0.20%, Cr: 0.20%, and the balance is Fe.

[0017] The smelting method of the above-mentioned high-strength steel includes: (1) The desulfurization station uses lime and magnesium powder for composite desulfurization. After desulfurization, the slag is cleaned to ensure that the sulfur after the converter is less than 150ppm; (2) LF uses lime and aluminum deoxidizer for desulfurization operation, and desulfurization to 20-40ppm is sufficient, and no further deep desulfurization is required; (3) After the molten steel reaches the RH, it starts to circulate in the RH vacuum chamber and then adds aluminum according to the expected oxygen blowing amount, 100m 3 Add 100-120kg of aluminum particles into the oxygen. After the aluminum addition is completed and stabilized, lower the oxygen gun to 4.8-5.0 meters for oxygen blowing. The total oxygen blowing volume shall not exceed 100m 3 ; (4) After RH treatment, the molten steel is fed into 140±10 meters of seamless pure calcium cored wire. After calcium treatment, the molten steel is stirred for 15 to 20 minutes to fully float and remove large particle inclusions; (5) During continuous casting, protective casting should be done to prevent air inhalation and contamination of molten steel; (6) In the thick plate continuous casting process, a strong secondary cooling water process is used to accelerate the nucleation of dendrites in the continuous casting billet. When the solid-liquid ratio of the continuous casting billet is in the range of 0.2~1.0, a heavy pressure of 12 mm is used to ensure the central segregation of the continuous casting billet.

[0018] The smelting process and parameters of this embodiment are as follows:

[0019] The high-strength steel smelting of this embodiment is treated by calcium in a high-sulfur and low-oxygen environment after RH vacuum, and the harmful gases in the molten steel are significantly reduced, and the purity of the molten steel is improved; through the thick plate continuous casting secondary cooling water process and dynamic heavy pressure process, the low-multiple quality of the continuous casting billet is better, such as Figure 1 and 2 shown. Example 2

[0020] In this embodiment, the weight percentage composition of the high-strength steel includes: C: 0.078%, Si 0.23%, Mn: 1.73%, P: 0.014%, S: 0.004%, Nb: 0.037%, Ti: 0.014%, Ca: 0.0019%, Al: 0.042%, Cu: 0.10%, Ni: 0.20%, Cr: 0.19%, and the balance is Fe.

[0021] The smelting method of the above-mentioned high-strength steel includes: (1) The desulfurization station uses lime and magnesium powder for composite desulfurization. After desulfurization, the slag is cleaned to ensure that the sulfur after the converter is less than 150ppm; (2) LF uses lime and aluminum deoxidizer for desulfurization operation, and desulfurization to 20-40ppm is sufficient, and no further deep desulfurization is required; (3) After the molten steel reaches the RH, it starts to circulate in the RH vacuum chamber and then adds aluminum according to the expected oxygen blowing amount, 100m 3 Add 100-120kg of aluminum particles into the oxygen. After the aluminum addition is completed and stabilized, lower the oxygen gun to 4.8-5.0 meters for oxygen blowing. The total oxygen blowing volume shall not exceed 100m 3 ; (4) After RH treatment, the molten steel is fed into a 120±10 m seamless pure calcium cored wire. After calcium treatment, the molten steel is stirred for 15 to 20 min to fully float and remove large particle inclusions. (5) During continuous casting, protective casting should be done to prevent air inhalation and contamination of molten steel; (6) In the thick plate continuous casting process, a strong secondary cooling water process is used to accelerate the nucleation of dendrites in the continuous casting billet. When the solid-liquid ratio of the continuous casting billet is in the range of 0.2~1.0, a heavy pressure of 12 mm is used to ensure the central segregation of the continuous casting billet.

[0022] The smelting process and parameters of this embodiment are as follows:

[0023] The high-strength steel smelting of this embodiment is treated by calcium in a high-sulfur and low-oxygen environment after RH vacuum, and the harmful gases in the molten steel are significantly reduced, and the purity of the molten steel is improved; through the thick plate continuous casting secondary cooling water process and dynamic heavy pressure process, the low-multiple quality of the continuous casting billet is better, such as Figure 3 and 4 shown.

[0024] The high-strength steel smelted by the present invention is modified by calcium treatment of inclusions, and CaS-Al2O3 solid inclusions are easily generated, which float up and are removed during the static stirring process, and the purity of the molten steel is significantly improved; the continuous casting secondary cooling water process and the dynamic heavy pressure process improve the internal quality of the thick plate continuous casting billet, and the economic benefit is remarkable.

[0025] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A high-strength steel smelting method for improving the purity of molten steel, characterized in that: The weight percentage composition of the high-strength steel includes: C: 0.07-0.10%, Si 0.15-0.35%, Mn: 1.55-1.80%, P≤0.015%, S≤0.006%, Nb: 0.020-0.070%, Ti: 0.006-0.020%, Ca: 0.0005-0.0040%, Al: 0.025-0.070%, Cu≤0.10%, Ni≤0.20%, Cr: 0.10-0.30%, and the balance is Fe; the smelting method is carried out according to the following steps: (1) The desulfurization station uses lime and magnesium powder for composite desulfurization. After desulfurization, the slag is cleaned to ensure that the sulfur after the converter is less than 150ppm; (2) LF uses lime and aluminum deoxidizer for desulfurization operation, and desulfurization to 20-40ppm is sufficient, and no further deep desulfurization is required; (3) After the molten steel reaches the RH, it starts to circulate in the RH vacuum chamber and then adds aluminum according to the expected oxygen blowing amount, 100m 3 Add 100-120kg of aluminum granules into oxygen. After the addition of aluminum is completed and stabilized, lower the oxygen gun to 4.8-5.0m for oxygen blowing operation. The total oxygen blowing volume shall not exceed 100m 3 ; (4) After RH treatment, the molten steel is fed into a 140±10m seamless pure calcium cored wire. After calcium treatment, the molten steel is stirred for 15 to 20 minutes to fully float and remove large particle inclusions. (5) During continuous casting, protective casting should be done to prevent air inhalation and contamination of molten steel; (6) In the thick plate continuous casting process, a strong secondary cooling water process is used to accelerate the nucleation of dendrites in the continuous casting billet. When the solid-liquid phase ratio of the continuous casting billet is in the range of 0.2~1.0, a heavy pressure of 12 mm is applied to ensure the central segregation of the continuous casting billet.

2. The high-strength steel smelting method for improving the purity of molten steel according to claim 1, characterized in that: The high-strength steel has a Ceq of 0.37-0.45% and a Pcm of 0.15-0.20%.

3. The high-strength steel smelting method for improving the purity of molten steel according to claim 1 or 2, characterized in that: In the weight percentage composition of the high-strength steel, the target value of C content is 0.080%.

4. The high-strength steel smelting method for improving the purity of molten steel according to claim 1 or 2, characterized in that: The weight percentage composition of the high-strength steel includes: C: 0.082%, Si 0.24%, Mn: 1.75%, P: 0.013%, S: 0.005%, Nb: 0.035%, Ti: 0.016%, Ca: 0.0020%, Al: 0.045%, Cu: 0.10%, Ni: 0.20%, Cr: 0.20%, and the balance is Fe.

5. The high-strength steel smelting method for improving the purity of molten steel according to claim 1 or 2, characterized in that: The weight percentage composition of the high-strength steel includes: C: 0.078%, Si 0.23%, Mn: 1.73%, P: 0.014%, S: 0.004%, Nb: 0.037%, Ti: 0.014%, Ca: 0.0019%, Al: 0.042%, Cu: 0.10%, Ni: 0.20%, Cr: 0.19%, and the balance is Fe.

6. The high-strength steel smelting method for improving the purity of molten steel according to claim 1 or 2, characterized in that: In the step (3), the RH vacuum treatment time is 15 to 20 minutes, the vacuum degree is ≤3 mbar, no alloying operation is performed during the vacuum treatment, no deoxidizer is added, and calcium treatment is performed after the vacuum treatment.

7. The high-strength steel smelting method for improving the purity of molten steel according to claim 1 or 2, characterized in that: In step (3), the RH aluminum supplement amount is 100-110 kg, and the RH oxygen blowing amount is 70-80 m 3 .

8. The high-strength steel smelting method for improving the purity of molten steel according to claim 1 or 2, characterized in that: In the step (4), the feeding amount of seamless pure calcium cored wire is 140-150 m, and the static stirring time is 18-20 min.

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