A method for preventing electrode breakage during smelting in a ladle refining furnace

Abstract

The application discloses a method for preventing electrode breakage in a ladle refining furnace smelting process, which adds circulating hot slag in the early stage of molten steel refining, utilizes the latent heat of the hot slag and the fluidity of the electric arc to maintain the stability of the electric arc in the early stage of slagging, adds cold slag batchwise in the middle stage of molten steel refining slagging, and increases the ladle bottom blowing flow, so as to prevent the cold material from caking after being added, reduce the existence time of the solid slag in the steel slag, and reduce the arc flow intensity to reduce the swing range of the graphite electrode in the slagging process. After the furnace slag is completely melted in the last stage of molten steel refining slagging, large arc flow and small bottom blowing operation are carried out, the electrode swing caused by the arc fluctuation of the ladle refining furnace in the smelting process is reduced, and thus the breakage probability of the graphite electrode in the refining process is reduced.

Description

A method for preventing electrode breakage during ladle refining furnace smelting. Technical Field

[0001] This invention relates to the field of metallurgical steelmaking technology, specifically to a method for preventing electrode breakage during the smelting process in a ladle refining furnace. Background Technology

[0002] A ladle refining furnace is an important metallurgical equipment that combines the functions of a steelmaking furnace for heating and refining. It is used to refine the molten steel melted in a primary furnace (electric arc furnace, open hearth furnace, converter) and can also regulate the temperature of the molten steel, provide process buffering, and meet the requirements of continuous casting and rolling.

[0003] The steel heating system in a ladle refining furnace mainly consists of a transformer, a high-voltage control system, water-cooled cables, conductive crossarms, electrode holders, and graphite electrodes. During heating, the electrical system controls the electrode current, voltage, and the distance between the graphite electrodes and the molten steel surface, generating a high-temperature electric arc between the graphite electrodes and the molten steel. Heat transfer between the electric arc, slag, and molten steel then heats the steel. During ladle furnace heating, the high-density current flowing through the electrodes causes them to heat up. Simultaneously, the electrodes are eroded and shortened by slag, molten steel, and the electric arc. When the graphite electrode length is worn down to a certain extent, it becomes impossible to form an electric arc between the graphite electrode and the molten steel, thus preventing heating. Therefore, it is necessary to continuously extend the electrodes during production to maintain the proper distance from the molten steel and ensure the electrode length can properly generate an arc for heating. Current electrode extension methods involve using boss-and-concave threads at both ends of each electrode segment, connecting the electrodes through thread locking. However, this method weakens the connection strength between the two electrode segments. At the same time, gaps will be generated at the connection. When high-energy current passes through these gaps, it will generate an electric arc, causing the connection to become hot and softened, resulting in a lower connection strength.

[0004] The stability of the electric arc during electrode heating is closely related to the resistance of the arc flow zone and the stability of the molten steel surface. The more stable the resistance of the arc flow zone and the molten steel surface, the more stable the arc and the smaller the electrode oscillation amplitude. During the heating of molten steel, after lumpy cold material is added to the ladle, it floats on the surface of the molten steel. When non-conductive lumpy slag floats into the arc region, it causes a sharp increase in the resistance between the electrode and the molten steel. The arc flow will deviate from the high-resistance region to the low-resistance region, which will cause the electrode to oscillate in the radial direction. In addition, the fluctuation of the molten steel surface caused by bottom blowing in the ladle will cause changes in the distance between the electrode and the molten steel, which will also cause the arc flow to oscillate and fluctuate. The amplitude of electrode oscillation is related to the current passing through the electrode and the size of the lumpy cold material, while the oscillation time is related to the time that the solid cold material exists in the steel slag. If there is significant and prolonged oscillation, the electrode may loosen or break at the threaded connection and fall off, causing an interruption in the heating process of the ladle furnace. If the graphite electrode that has fallen into the ladle is not removed in time, the carbon in the graphite electrode will continue to dissolve into the molten steel, causing the carbon content of the molten steel to exceed the standard. The molten steel cannot be returned to the converter for remelting, which will cause a huge impact on the production organization. Removing the electrode from the molten steel at around 1550℃ is a very dangerous operation and is very likely to cause a safety accident. Summary of the Invention

[0005] This invention provides a method to prevent electrode breakage during the smelting process of a ladle refining furnace. By adding circulating hot slag in the early stage of ladle refining and controlling the arc flow intensity and bottom blowing volume throughout the refining process, the arc flow during the refining process can be stabilized, thereby reducing the probability of graphite electrode breakage during refining.

[0006] This invention relates to a method for preventing electrode breakage during the smelting process in a ladle refining furnace, comprising the following steps:

[0007] Step 1: First, add the circulating hot slag into the ladle at the refining molten steel receiving position, then add molten steel. After the molten steel reaches the ladle heating position, smelting is carried out. The circulating hot slag refers to the final refining slag remaining in the ladle after the previous heat is poured during the smelting process in the ladle refining furnace.

[0008] Step 2: During the first 5 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 5-10 m³ / h. 3 / h, electrode arc current is 25000A, electrode arc voltage is 120V;

[0009] Step 3: Within 5-15 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 10-15 m³ / s. 3 / h, the electrode arc current is 15000A, the electrode arc voltage is 120V, the molten steel is heated, and active lime is added in batches during the heating process to form slag, and alloy is added to complete the alloying operation.

[0010] Step 4: After smelting for 15 minutes, adjust the bottom blowing flow rate of the ladle to 1-5 m³ / min. 3 The electrode arc current is 25000A and the electrode arc voltage is 120V per hour to heat the molten steel. After the molten steel reaches the set temperature, the electrode is lifted to end the molten steel heating operation.

[0011] Preferably, the temperature of the circulating hot slag in step one is 1450-1550℃, and it is composed of the following elements by weight percentage: CaO: 40-60%, SiO2: 10-30%, Al2O3: 10-15%, with the remainder being MgO and MnO.

[0012] Preferably, the amount of circulating hot slag used in step one is 4-5 kg / t of molten steel.

[0013] Preferably, in step three, the time interval between each batch of quicklime addition is more than 2 minutes, and the amount of quicklime added in each batch is 1-3 kg / t of molten steel.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. This invention introduces circulating hot slag in the early stage of steel refining instead of adding cold material. The latent heat of the hot slag and the high current of the electric arc are used to rapidly raise the temperature of the steel slag, avoiding interference caused by the simultaneous presence of cold material and high current in the early stage of smelting. This maintains the stability of the electric arc in the early stage of slag formation, and stabilizes the arc flow in the refining process by controlling the arc flow intensity and bottom blowing volume, reducing the occurrence of graphite electrode oscillation and breakage due to unstable arc flow during the heating process of the ladle furnace.

[0016] 2. In this invention, cold slag is added in batches during the middle stage of steel refining, and the bottom blowing flow rate of the ladle is increased to prevent the cold material from agglomerating after being added, thereby reducing the existence time of solid slag in the steel slag. At the same time, the arc flow intensity is reduced to reduce the oscillation amplitude of the graphite electrode during the slag formation process.

[0017] 3. In this invention, after the slag has completely melted at the end of the steel refining process, a large arc flow and small bottom blowing operation are performed. At this time, the liquid steel slag can form a stable resistance layer, and the high-intensity current will exist in a stable form, which will not easily cause the electrode to swing violently and will not cause the electrode to break.

[0018] 4. The method for preventing electrode breakage during the smelting process of a ladle refining furnace provided by the present invention effectively reduces electrode oscillation caused by arc fluctuations in the ladle refining furnace during the smelting process by coordinating the early, middle and late stages of smelting. This reduces the probability of graphite electrode breakage and electrode consumption caused by accidents during the refining process, saves production costs, and reduces the amount of scrap generated during the ladle furnace refining process and the operational risks of electrode retrieval. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments:

[0020] Example 1

[0021] Taking a 60t ladle furnace for producing HRB400 as an example, the implementation process of this invention is described below. The HRB400 refining cycle is 36 minutes, and the specific smelting steps are as follows:

[0022] Step 1: First, add the circulating hot slag to the ladle at the refining steel receiving position. The circulating hot slag refers to the final refining slag remaining in the ladle after the previous heat is poured during the ladle refining process. The circulating hot slag is composed of the following elements by weight percentage: CaO: 46%, SiO2: 29%, Al2O3: 15%, with the remainder being MgO and MnO. The amount of circulating hot slag used is 240 kg, and the temperature is 1480℃. Then, add the molten steel. After the molten steel reaches the ladle heating position, smelting will begin.

[0023] Step 2: During the first 5 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 5m³ / s. 3 / h, electrode arc current is 25000A, electrode arc voltage is 120V;

[0024] Step 3: Within 5-15 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 15m³. 3 The electrode arc current is 15000A and the electrode arc voltage is 120V, and the molten steel is heated twice. During the heating process, active lime is added in two batches to form slag. The first batch of active lime, 60kg, is added after 8 minutes of smelting, and the second batch of active lime, 100kg, is added after 12 minutes of smelting. After 6 minutes of smelting, alloying is started to complete the alloying operation. According to the target composition of the molten steel, 199.8kg of FeMn68Si18 and 48kg of FeSi75-A alloy are added to complete the alloying of the molten steel.

[0025] Step 4: After smelting for 15 minutes, adjust the bottom blowing flow rate of the ladle to 5m³ / min. 3 The electrode arc current is 25000A and the electrode arc voltage is 120V to heat the molten steel. After the molten steel temperature reaches 1590℃, the electrode is lifted to end the molten steel heating operation.

[0026] After the implementation of this method, the number of electrode breaks during the production process decreased from an average of 0.15 times per 10,000 tons to 0.03 times per 10,000 tons.

[0027] Example 2

[0028] Taking a 60t ladle furnace for producing R20 as an example, the implementation process of this invention is described below. The R20 refining cycle is 44 minutes, and the specific smelting steps are as follows:

[0029] Step 1: First, add the circulating hot slag to the ladle at the refining steel receiving position. The circulating hot slag refers to the final refining slag remaining in the ladle after the previous heat is poured during the ladle refining process. The circulating hot slag is composed of the following elements by weight percentage: CaO: 59%, SiO2: 28%, Al2O3: 13%, with the remainder being MgO and MnO. The amount of circulating hot slag used is 300 kg, and the temperature is 1500℃. Then, add the molten steel. After the molten steel reaches the ladle heating position, smelting will begin.

[0030] Step 2: During the first 5 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 10m³. 3 / h, electrode arc current is 25000A, electrode arc voltage is 120V;

[0031] Step 3: Within 5-15 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 15m³. 3 The electrode arc current is 15000A and the electrode arc voltage is 120V, and the molten steel is heated twice. During the heating process, active lime is added in two batches to form slag. At 8 minutes of smelting, the first batch of active lime (120kg) is added, and at 11 minutes of smelting, the second batch of active lime (60kg) is added. After 7 minutes of smelting, the alloy is added to complete the alloying operation. According to the target composition of the molten steel, 72kg of FeMn68Si18 and 66kg of FeSi75-A alloy are added to complete the alloying of the molten steel.

[0032] Step 4: After smelting for 15 minutes, adjust the bottom blowing flow rate of the ladle to 1 m³ / min. 3 The electrode arc current is 25000A and the electrode arc voltage is 120V to heat the molten steel. After the molten steel temperature reaches 1586℃, the electrode is lifted to end the molten steel heating operation.

[0033] After the implementation of this method, the number of electrode breaks during the production process decreased from an average of 0.14 times per 10,000 tons to 0.02 times per 10,000 tons.

[0034] Example 3

[0035] Taking a 60t ladle furnace producing 87B steel as an example, the implementation process of this invention is described below. The refining cycle for 87B is 57 minutes, and the specific smelting steps are as follows:

[0036] Step 1: First, add the circulating hot slag to the ladle at the refining steel receiving position. The circulating hot slag refers to the final refining slag remaining in the ladle after the previous heat is poured during the ladle refining process. The circulating hot slag is composed of the following elements by weight percentage: CaO: 60%, SiO2: 15%, Al2O3: 15%, with the remainder being MgO and MnO. The amount of circulating hot slag used is 300 kg, and the temperature is 1520℃. Then, add the molten steel. After the molten steel reaches the ladle heating position, smelting will begin.

[0037] Step 2: During the first 5 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 7m³ / h. 3 / h, electrode arc current is 25000A, electrode arc voltage is 120V;

[0038] Step 3: Within 5-15 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 12m³. 3 The electrode arc current is 15000A and the electrode arc voltage is 120V, and the molten steel is heated twice. During the heating process, active lime is added in two batches to form slag. The first batch of active lime, 180kg, is added after 8 minutes of smelting, and the second batch of active lime, 60kg, is added after 12 minutes of smelting. After 6 minutes of smelting, alloying is started to complete the alloying operation. According to the target composition of the molten steel, 126kg of FeMn68Si18 and 96kg of FeSi75-A alloy are added to complete the alloying of the molten steel.

[0039] Step 4: After smelting for 15 minutes, adjust the bottom blowing flow rate of the ladle to 3m³. 3 The electrode arc current is 25000A and the electrode arc voltage is 120V to heat the molten steel. After the molten steel temperature reaches 1560℃, the electrode is lifted to end the molten steel heating operation.

[0040] After the implementation of this method, the number of electrode breaks during the production process decreased from an average of 0.13 times per 10,000 tons to 0.01 times per 10,000 tons.

Claims

1. A method for preventing electrode breakage during the smelting process in a ladle refining furnace, characterized in that, Includes the following steps: Step 1: First, add the circulating hot slag to the ladle at the refining steel receiving position, then add molten steel. After the molten steel reaches the ladle heating position, smelting begins. The circulating hot slag refers to the final refining slag remaining in the ladle after the previous heat is poured during the ladle refining furnace smelting process. Step 2: During the first 5 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 5-10 m³ / h. 3 / h, electrode arc current is 25000A, electrode arc voltage is 120V; Step 3: Within 5-15 minutes of smelting, adjust the bottom blowing flow rate of the ladle to 10-15m³ / h. 3 / h, with an electrode arc current of 15000A and an electrode arc voltage of 120V, the molten steel is heated. During the heating process, active lime is added in batches to form slag, and alloys are added to complete the alloying operation; Step 4: After smelting for 15 minutes, the bottom blowing flow rate of the ladle is adjusted to 1-5m³ / h. 3 The electrode arc current is 25000A and the electrode arc voltage is 120V per hour to heat the molten steel. After the molten steel reaches the set temperature, the electrode is lifted to end the molten steel heating operation.

2. The method for preventing electrode breakage during ladle refining furnace smelting as described in claim 1, characterized in that: The temperature of the circulating hot slag in step one is 1450–1550°C, and it consists of the following elements by weight percentage. Composition: CaO: 40-60%, SiO2: 10-30%, Al2O3: 10-15%, the remainder being MgO and MnO.

3. The method for preventing electrode breakage during ladle refining furnace smelting as described in claim 2, characterized in that: The amount of circulating hot slag used in step one is 4-5 kg / t of molten steel.

4. The method for preventing electrode breakage during ladle refining furnace smelting as described in claim 1, characterized in that: In step three, the time interval between each batch of quicklime addition is more than 2 minutes, and the amount of quicklime added in each batch is 1-3 kg / t of molten steel.