Smelting method of high-grade ultralow-sulfur non-oriented silicon steel

Abstract

The invention discloses a smelting method of high-grade ultralow-sulfur non-oriented silicon steel. An RH furnace refining process is improved by reducing the oxidability of molten steel and steel slag and carrying out desulfurization in two stages; comprising the following steps: S1, low oxidability control of molten steel; and S2, a two-stage desulfurization process. According to the smelting method of the high-grade ultra-low-sulfur non-oriented silicon steel, the low oxidability of steel slag is guaranteed, the desulfurization efficiency is greatly improved, the desulfurization time is shortened while the desulfurization rate is increased, and batch production is guaranteed so that the production requirement can be met.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and particularly relates to a smelting method for high-grade ultra-low sulfur non-oriented silicon steel. Background Technology

[0002] Ultra-low sulfur steel refers to steel with a sulfur content of ≤0.003%. Non-oriented silicon steel is an indispensable low-carbon silicon-iron soft magnetic alloy for the power, electronics, and military industries. Summary of the Invention

[0003] To address the aforementioned technical problems, the purpose of this invention is to provide a method for smelting high-grade ultra-low sulfur non-oriented silicon steel to meet production needs.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for smelting high-grade ultra-low sulfur non-oriented silicon steel, comprising the following steps:

[0006] S1, Low Oxidation Control of Molten Steel

[0007] Controlling the low oxidation of molten steel involves two aspects: deoxidation of molten steel and deoxidation of steel slag.

[0008] (S1.1) Steel deoxidation process

[0009] Vacuum deoxidation of molten steel is divided into two stages. In the first stage, during the early stage of vacuum treatment in the RH furnace, the vacuum environment in the vacuum chamber is used to break the carbon-oxygen balance in the steel. The carbon elements in the steel react rapidly with oxygen to generate CO gas, which is then pumped away by the vacuum pump, reducing the oxygen content in the steel. In the second stage, aluminum particles are added at the end of the carbon-oxygen reaction to deoxidize the molten steel and aluminum alloying is carried out simultaneously to maintain the aluminum content in the steel at more than 0.10%, thus maintaining the strong reducing properties of the molten steel.

[0010] (S1.2) Process for reducing the oxidizing properties of steel slag

[0011] The first step is to add 190-210 kg of synthetic slag (preferably 200 kg) during the converter tapping process, and after tapping, add 80-280 kg of aluminum particles according to the final oxygen content to evenly distribute them on the surface of the molten steel slag to carry out the first modification of the molten steel slag, reducing the TFe content of the steel slag from 15-20% to 5-8%.

[0012] In the second step, during the deoxidation stage of molten steel in the RH furnace, a large amount of deoxidizing and alloying alloys enter the molten steel, the oxygen potential in the steel continuously decreases, and the steel slag is continuously reduced at the interface between the molten steel and the steel through diffusion reaction, further reducing the oxidizing power of the steel slag to 4-7%.

[0013] The third step involves adding 45-55 kg of aluminum granules (preferably 50 kg) evenly distributed on the top of the molten steel slag surface after the molten steel breaks through the void. The aluminum reacts with the oxygen in the slag to further reduce the oxidizing properties of the steel slag, thereby reducing the TFe content of the steel slag from 4-7% to 2-5%.

[0014] S2, two-stage desulfurization process

[0015] (S2.1) Vacuum desulfurizing agent desulfurization process

[0016] During the RH vacuum treatment process, the temperature of the alloyed molten steel is maintained within the range of 1565-1575℃. Taking advantage of the favorable desulfurization conditions created by the further reduction of slag oxidizability after the second step of the process described in S1, RH vacuum desulfurizer is added at a rate of 4.5-5.5 kg / ton of steel. The calcium oxide in the desulfurizer is melted to increase the basicity of the slag to 1.5-1.8.

[0017] Meanwhile, after the vacuum desulfurizing agent is added, the circulating argon gas is controlled at 170-190 Nm. 3 / h (preferably 180Nm) 3 / h); maintain a steel circulation rate of no less than 195t / min; accelerate the melting of the vacuum desulfurizing agent, promote the steel-slag interface reaction, and speed up the desulfurization reaction; ensure sufficient stirring time, while ensuring that the actual argon flow rate meets the requirements. The goal is to reduce the sulfur content of the molten steel from over 0.06% to 0.03%;

[0018] (S2.2) Calcium treatment desulfurization process

[0019] After recompression, calcium treatment is carried out using a high-calcium feed line, with an infeed rate of 50-200 m³ and a compressed air flow rate controlled to be less than 10 Nm³. 3 / h, after the third step of the process to reduce the oxidizability of steel slag described in S1, the oxidizability of steel slag is reduced to create favorable conditions for desulfurization; during calcium treatment, the sulfur element of the steel grade reacts rapidly with the steel slag in an environment of low oxidizability, high molten steel temperature, and high alkalinity, accompanied by a large amount of calcium vapor stirring, with the goal of further reducing the sulfur content in the steel and stabilizing it below 0.03%, without being affected by the "sulfur return" phenomenon during the quenching and casting process.

[0020] Furthermore, in step S1, carbon and aluminum from the molten steel are used for deoxidation, and the aluminum content is controlled to be above 0.10% to maintain a strong reducing atmosphere.

[0021] Furthermore, after the converter tapps, a modification method combining synthetic slag and aluminum particles is used to maintain the oxidizing index TFe of the steel slag below 8%.

[0022] Furthermore, through diffusion reaction, the oxygen content in steel slag is reduced to 4-7%.

[0023] Furthermore, aluminum particles are added after the void is broken for secondary modification, and the oxidation of the ex-situ steel slag is controlled to be 2-5%.

[0024] Furthermore, the vacuum desulfurizing agent is controlled at 180 Nm in the circulating argon gas. 3 Under the condition of / h, steel slag with extremely low oxidizability is added at a point of 5kg / t.

[0025] Furthermore, after secondary modification, 50-200m of high-calcium wire is fed in to prevent the molten steel from "re-sulfurizing".

[0026] Furthermore, the low oxidizing properties, high molten steel temperature, and high basicity specifically refer to: TFe content of 2-5%, displacement temperature range of 1565-1575℃, and basicity of 4.5-5.5.

[0027] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0028] The main problems in smelting this type of steel under existing technological conditions are as follows:

[0029] Under existing process conditions, if the target sulfur content requirement is to be achieved, the molten steel and steel slag have strong oxidizing properties, which is not conducive to producing a good desulfurization effect under vacuum conditions, and the desulfurization rate of vacuum desulfurizing agent is less than 10%.

[0030] In the existing process, the steel slag after vacuum treatment has a strong oxidizing property. During the calming process and the casting process, the high oxygen potential of the steel slag gradually transfers oxygen into the steel, causing secondary oxidation of the molten steel and further aggravating the "sulfurization" phenomenon.

[0031] Results of this invention:

[0032] Based on the actual on-site conditions of this ultra-low sulfur steel smelting, analysis shows that the final slag composition with RH high-efficiency deep desulfurization effect is as follows: the amount of vacuum desulfurizing agent added is controlled at 5 kg / t; the basicity of ladle slag is controlled at 3.5-4.5; and (TFe) is controlled within the range of 2-5%.

[0033] By improving the slag deoxidation process, the steel slag is modified twice, once after the converter tapping and once after RH vacuum treatment. This ensures low oxidizability of the steel slag, greatly improves desulfurization efficiency, and shortens the desulfurization time while increasing the desulfurization rate, thus ensuring mass production.

[0034] Using a large-circulation flow method during the vacuum addition of desulfurizing agent can accelerate the reaction of steel slag and speed up the diffusion reaction, providing kinetic conditions for efficient deep desulfurization. Detailed Implementation

[0035] A method for smelting high-grade ultra-low sulfur non-oriented silicon steel:

[0036] S1, Low Oxidation Control of Molten Steel

[0037] (S1.1) Steel deoxidation process

[0038] Vacuum deoxidation of molten steel is divided into two stages. In the first stage, during the early stage of vacuum treatment in the RH furnace, the vacuum environment inside the vacuum chamber disrupts the carbon-oxygen balance in the steel. The carbon in the steel reacts rapidly with oxygen to generate CO gas, which is then removed by the vacuum pump, reducing the oxygen content in the steel. In the second stage, aluminum particles are added at the end of the carbon-oxygen reaction to deoxidize the molten steel and simultaneously perform aluminum alloying to maintain the aluminum content in the steel above 0.10%, thus preserving the strong reducing properties of the molten steel.

[0039] (S1.2) Process for reducing the oxidizing properties of steel slag

[0040] The first step is to add 200 kg of synthetic slag during the converter tapping process, and after tapping, add 80-280 kg of aluminum particles according to the final oxygen content to evenly distribute them on the surface of the molten steel slag to carry out the first modification of the molten steel slag, reducing the TFe content of the steel slag from 15-20% to 5-8%.

[0041] In the second step, during the deoxidation stage of the RH furnace, a large amount of deoxidizing and alloying alloys enter the molten steel, the oxygen potential in the steel continuously decreases, and the steel slag is continuously reduced at the interface between the molten steel and the slag through diffusion reaction, further reducing the oxidizing power of the steel slag to 4-7%.

[0042] The third step involves adding 50 kg of aluminum granules after the molten steel breaks through the slag surface, distributing them evenly on top. The aluminum reacts with oxygen in the slag to further reduce the oxidizing properties of the steel slag, thereby lowering the TFe content from 4-7% to 2-5%.

[0043] S2, two-stage desulfurization process

[0044] (S2.1) Vacuum desulfurizing agent desulfurization process

[0045] During the RH vacuum treatment process, the temperature of the alloyed molten steel is maintained within the range of 1565-1575℃. RH vacuum desulfurizer is added at a rate of 5 kg / ton of steel. The calcium oxide in the desulfurizer dissolves and raises the basicity of the steel slag to 1.5-1.8. The circulating argon gas is controlled at 180 Nm. 3 / h. Maintain a molten steel circulation rate of no less than 195t / min. Ensure sufficient stirring time, and at the same time ensure that the actual argon gas flow rate meets the requirements.

[0046] (S2.2) Calcium treatment desulfurization process

[0047] After recompression, calcium treatment is carried out using a high-calcium feed line, with an infeed rate of 50-200 m³ and a compressed air flow rate controlled to be less than 10 Nm³. 3 / h, during calcium treatment, the sulfur element of the steel grade reacts rapidly with the steel slag under low oxidation (TFe content 2-5%), high steel temperature (absence temperature range 1565-1575℃), and high alkalinity (4.5-5.5) conditions, accompanied by a large amount of calcium vapor stirring.

[0048] Example 1

[0049] High-grade ultra-low sulfur non-oriented silicon steel was smelted using molten steel with a final sulfur content of 0.0064% in the converter as raw material. After RH treatment, the sulfur content was reduced to 0.003%. R=4.5, TFe=2.72%, CaO=45.23%, and the desulfurization rate was 53%.

[0050] After tapping from the converter, 153 kg of aluminum granules are added to the steel slag for the first modification. The RH process uses a dual deoxidation mode of carbon and aluminum in the molten steel, adding 1763 kg of aluminum granules to maintain the aluminum content in the steel at 0.55%. 1385 kg of vacuum desulfurizer is also added at a circulation flow rate of 180 Nm. 3 / h, after recompression, add 50kg of aluminum granules, and start at 10Nm. 3 / h bottom-blown argon-fed 75m high-calcium wire, finished product sulfur content 0.003%.

[0051] Example 2

[0052] High-grade ultra-low sulfur non-oriented silicon steel was smelted using molten steel with a final sulfur content of 0.0057% in the converter as raw material. After RH treatment, the sulfur content was reduced to 0.0026%. R=5.1, TFe=3.10%, CaO=51.18%, and the desulfurization rate was 54%.

[0053] After tapping from the converter, 170 kg of aluminum granules are added to the steel slag for the first modification. The RH process uses a dual deoxidation mode of carbon and aluminum in the molten steel, adding 1693 kg of aluminum granules to maintain the aluminum content in the steel at 0.53%. 1426 kg of vacuum desulfurizer is added at a circulation flow rate of 180 Nm. 3 / h, after recompression, add 50kg of aluminum granules, and start at 10Nm. 3 / h bottom-blown argon-fed 100m high-calcium wire, finished product sulfur content 0.0026%.

[0054] Example 3

[0055] High-grade ultra-low sulfur non-oriented silicon steel was smelted using molten steel with a final sulfur content of 0.0059% in the converter as raw material. After RH treatment, the sulfur content was reduced to 0.0027%. R = 5.1, TFe = 2.13%, CaO = 51.42%, and the desulfurization rate was 54%.

[0056] After tapping from the converter, 148 kg of aluminum granules are added to the steel slag for the first modification. The RH process uses a dual deoxidation mode of carbon and aluminum in the molten steel, adding 1708 kg of aluminum granules to maintain the aluminum content in the steel at 0.53%. 1436 kg of vacuum desulfurizer is added at a circulation flow rate of 180 Nm. 3 / h, after recompression, add 50kg of aluminum granules, and start at 10Nm. 3 / h bottom-blown argon-fed 120m high-calcium wire, finished product sulfur content 0.0027%.

[0057] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for smelting high-grade ultra-low sulfur non-oriented silicon steel, characterized by improving the RH furnace refining process by reducing the oxidizability of molten steel and slag and performing desulfurization in two stages; Its features include: Includes the following steps: S1, Low Oxidation Control of Molten Steel Controlling the low oxidation of molten steel involves two aspects: deoxidation of molten steel and deoxidation of steel slag. (S1.1) Steel deoxidation process Vacuum deoxidation of molten steel is divided into two stages. In the first stage, during the early stage of vacuum treatment in the RH furnace, the vacuum environment in the vacuum chamber is used to break the carbon-oxygen balance in the steel. The carbon elements in the steel react rapidly with oxygen to generate CO gas, which is then pumped away by the vacuum pump, reducing the oxygen content in the steel. In the second stage, aluminum particles are added at the end of the carbon-oxygen reaction to deoxidize the molten steel and aluminum alloying is carried out simultaneously to maintain the aluminum content in the steel at more than 0.10%, thus maintaining the strong reducing properties of the molten steel. (S1.2) Process for reducing the oxidizing properties of steel slag The first step is to add 190-210 kg of synthetic slag during the converter tapping process, and after tapping, add 80-280 kg of aluminum particles according to the final oxygen content to evenly distribute them on the surface of the molten steel slag to carry out the first modification of the molten steel slag, reducing the TFe content of the steel slag from 15-20% to 5-8%. In the second step, during the deoxidation stage of molten steel in the RH furnace, a large amount of deoxidizing and alloying alloys enter the molten steel, the oxygen potential in the steel continuously decreases, and the steel slag is continuously reduced at the interface between the molten steel and the steel through diffusion reaction, further reducing the oxidizing power of the steel slag to 4-7%. The third step is to add 45-55 kg of aluminum granules after the molten steel breaks through the void, and evenly distribute them on the top of the molten steel slag surface. The aluminum reacts with the oxygen in the slag to further reduce the oxidizing properties of the steel slag, thereby reducing the TFe content of the steel slag from 4-7% to 2-5%. S2, two-stage desulfurization process (S2.1) Vacuum desulfurizing agent desulfurization process During the RH vacuum treatment process, the temperature of the alloyed molten steel is maintained within the range of 1565-1575℃. Taking advantage of the favorable desulfurization conditions created by the further reduction of slag oxidizability after the second step of the process described in S1, RH vacuum desulfurizer is added at a rate of 4.5-5.5 kg / ton of steel. The calcium oxide in the desulfurizer is melted to increase the basicity of the slag to 1.5-1.

8. Meanwhile, after the vacuum desulfurizing agent is added, the circulating argon gas is controlled at 170-190 Nm. 3 / h; maintain the steel circulation rate at no less than 195t / min; accelerate the melting of the vacuum desulfurizing agent, promote the steel-slag interface reaction, and speed up the desulfurization reaction; ensure sufficient stirring time, and at the same time ensure that the actual argon flow rate meets the requirements; the goal is to reduce the sulfur content of the molten steel from more than 0.06% to 0.03%; (S2.2) Calcium treatment desulfurization process After recompression, calcium treatment is carried out using a high-calcium feed line, with an infeed rate of 50-200 m³ and a compressed air flow rate controlled to be less than 10 Nm³. 3 / h, after the third step of the process to reduce the oxidizability of steel slag described in S1, the oxidizability of steel slag is reduced to create favorable conditions for desulfurization; during calcium treatment, the sulfur element of the steel reacts rapidly with the steel slag in an environment of low oxidizability, high molten steel temperature, and high alkalinity, accompanied by a large amount of calcium vapor stirring, with the goal of further reducing the sulfur content in the steel and stabilizing it below 0.03%, without being affected by the "sulfur reversion" phenomenon during the quenching and casting process.

2. The smelting method for high-grade ultra-low sulfur non-oriented silicon steel according to claim 1, characterized in that: In step S1, carbon and aluminum from the molten steel are used for deoxidation, and the aluminum content is controlled to be above 0.10% to maintain a strong reducing atmosphere.

3. The smelting method for high-grade ultra-low sulfur non-oriented silicon steel according to claim 1, characterized in that: After the steel is tapped from the converter, a modification method combining synthetic slag and aluminum particles is used to maintain the oxidizing index TFe of the steel slag below 8%.

4. The smelting method for high-grade ultra-low sulfur non-oriented silicon steel according to claim 1, characterized in that: The oxygen content in steel slag is reduced to 4-7% through diffusion reaction.

5. The smelting method for high-grade ultra-low sulfur non-oriented silicon steel according to claim 1, characterized in that: After breaking the void, aluminum particles are added for secondary modification to control the oxidation of the ex-situ steel slag to 2-5%.

6. The smelting method for high-grade ultra-low sulfur non-oriented silicon steel according to claim 1, characterized in that: Vacuum desulfurizer is controlled at 180 Nm in circulating argon gas. 3 Under the condition of / h, steel slag with extremely low oxidizability is added at a point of 5kg / t.

7. The smelting method for high-grade ultra-low sulfur non-oriented silicon steel according to claim 1, characterized in that: After secondary modification, feed in 50-200m high-calcium wire to avoid "sulfurization" in molten steel.

8. The smelting method for high-grade ultra-low sulfur non-oriented silicon steel according to claim 1, characterized in that: The low oxidation, high molten steel temperature, and high basicity are specifically defined as follows: TFe content 2-5%, displacement temperature range 1565-1575℃, and basicity 4.5-5.5.