A method for accelerating the desulfurization speed of a ladle furnace

Abstract

This invention discloses a method for accelerating the desulfurization speed of a ladle furnace, comprising the following steps: a) controlling the slag feeding from the converter to ensure that the slag layer thickness in the ladle furnace after tapping is <40mm, and adding hot slag to the ladle at the refining steel receiving position, with a hot slag dosage of 4-5kg / ton of steel; b) in the early stage of ladle furnace treatment, adjusting the arc current to 25000A and the voltage to 120V to rapidly heat the slag to above 1550℃; c) in the middle stage of ladle furnace treatment, adjusting the arc current to 20000A and the voltage to 120V, adding refining slag deoxidizer at a dosage of 1-5kg / ton of steel, adding lumpy limestone with a particle size controlled at 1-10mm, a CaO content ≥54% in the lumpy limestone, and a lumpy limestone dosage of 3-5kg / ton of steel; d) in the later stage of ladle furnace treatment, adjusting the arc current to 25000A and the voltage to 120V to control the slag temperature to >1600℃, and performing slag washing. This invention utilizes the exothermic reaction of Al in the refining deoxidizer to increase the slag temperature and improve the slag fluidity, thereby increasing the desulfurization rate in the ladle smelting process and saving production costs.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a method for accelerating the desulfurization rate of a ladle furnace. Background Technology

[0002] A ladle refining furnace is an important metallurgical device used to refine molten steel from primary furnaces (electric arc furnaces, open-hearth furnaces, converters), and to regulate the temperature of the molten steel, provide process buffering, and meet the requirements of continuous casting and rolling. During the smelting process, sulfur from iron ore and coke enters the steel along with the molten iron. Except for free-cutting steel, where sulfur is a beneficial alloying element, the presence of sulfur in most other steels is harmful. Increased sulfur content can cause hot brittleness in steel, reduce its ductility and toughness, make it prone to cracking during forging, and also reduce its corrosion resistance.

[0003] Currently, the main method used is to sprinkle lumpy active lime onto the surface of molten steel to achieve final desulfurization of the steel through mass transfer at the slag-steel interface. When lumpy limestone is added to the ladle furnace, it decomposes at high temperature to obtain lumpy active lime. During the desulfurization of the ladle furnace by lumpy active lime, the lumpy active lime and molten steel can undergo the following reactions:

[0004] CaO(s) + [S] = CaS(s) + [O];

[0005] CaO(s)+[Si]+1 / 2[S]=CaS(s)+l / 2Ca2SiO4,

[0006] Since lumpy quicklime cannot melt instantaneously, its dissolution always occurs on the surface in contact with high-temperature steel slag, proceeding from the surface inwards. This results in a typical three-layer structure on the surface of the lumpy quicklime: the outer layer is mainly composed of desulfurization product CaS, with a thickness of 10-50 μm; the middle layer is mainly composed of 2CaO·SiO2, with a thickness of approximately 10 μm; and the core is unreacted CaO. Because the melting points of the outer CaS layer and the middle 2CaO·SiO2 layer are very high, they are difficult to dissolve once formed on the surface of the lumpy quicklime. This hinders the further desulfurization reaction of the lumpy quicklime, slowing down the desulfurization rate of the molten steel and reducing the desulfurization efficiency of the ladle furnace. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for accelerating the desulfurization speed of a ladle furnace, thereby solving the problem that the active lime obtained after the lumpy limestone used as a desulfurizing agent is added to the ladle furnace and decomposes at high temperature affects the desulfurization speed.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for accelerating the desulfurization rate of a ladle furnace includes the following steps:

[0010] a. Control the slag discharge from the converter so that the slag layer thickness in the ladle furnace after tapping is <40mm. Add hot slag into the ladle at the refining molten steel receiving position. The amount of hot slag used is 4-5kg / ton of steel.

[0011] b. In the early stage of ladle furnace treatment, adjust the arc current to 25000A and the voltage to 120V to rapidly heat the slag to above 1550℃.

[0012] c. During the middle stage of ladle furnace treatment, adjust the arc current to 20000A, voltage to 120V, add refining slag deoxidizer, the amount of refining slag deoxidizer added is 1-5kg / ton of steel, add lumpy limestone, the particle size of the lumpy limestone is controlled at 1-10mm, the CaO content in the lumpy limestone is ≥54%, the amount of lumpy limestone used is 3-5kg / ton of steel, and adjust the slag to the target composition and temperature;

[0013] d. In the later stages of ladle furnace treatment, adjust the arc current to 25000A, voltage to 120V, control the slag temperature to >1600℃, and adjust the bottom blowing flow rate to 15-25m³ / h. 3 Wash the residue for 5-10 minutes per hour.

[0014] In step a, the hot slag composition is as follows: CaO 40-50%; Al2O3 40-50%; SiO2 <10%; FeO <1%, and the hot slag temperature is 1450-1500℃.

[0015] In step c, the composition of the refining slag deoxidizer is as follows: Al accounts for 25-35%, Al2O3 accounts for 55-65%, and the remaining components account for 5-10%. The above-mentioned materials are mixed evenly and then pressed into briquettes with a particle size of 30-50mm.

[0016] In step c, the target temperature of the refining slag is 1550-1600℃, and the target composition of the refining slag is: CaO 40-50%; Al2O3 40-50%; SiO2 <10%; FeO <1%.

[0017] Compared with the prior art, the beneficial effects of this invention are as follows: During the smelting process in a ladle refining furnace, circulating hot slag from the refining process is added. Utilizing the latent heat of the hot slag, the arc flow and bottom blowing of the ladle furnace are adjusted to rapidly raise the temperature of the steel slag to above 1550℃, providing heat assurance for the decomposition process of lumpy limestone. The addition of lumpy limestone to replace active lime as a desulfurizing agent in the refining process, and controlling the particle size of the lumpy limestone within the range of 1-10mm, allows the lumpy limestone to rapidly expand, decompose, and burst after being added to the high-temperature slag, increasing the contact area between the steel and slag. The CaO generated during decomposition will then dissolve uniformly in the slag. This method alters the reaction sequence from the surface to the interior during the desulfurization process of quicklime, avoiding the formation of high-melting-point desulfurization products such as CaS and 2CaO•SiO2. It reduces the existence time of particulate matter in the slag, accelerates slag formation, and adds refining deoxidizing slag to reduce the oxidizing properties of the molten slag, thereby increasing the sulfur capacity and distribution coefficient of the slag. By adjusting the composition of the ladle furnace, the slag melting point is controlled in the low-melting-point range. The exothermic reaction of Al in the refining deoxidizer is used to raise the slag temperature and increase the fluidity of the slag, thereby improving the desulfurization rate in the ladle smelting process, saving production costs, and maintaining stable and smooth production. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the invention.

[0019] Example 1:

[0020] The following uses a 60t ladle furnace producing HRB400 as an example to specifically introduce the implementation process and effects of this invention:

[0021] 1. The converter tapping adopts the slag-covering operation. After tapping, the slag layer thickness in the ladle furnace is 37mm. Circulating hot slag is added to the ladle at the refining molten steel receiving position. The hot slag usage is 4kg / ton of steel.

[0022] 2. After entering the refining steel treatment position, within the first 5 minutes of smelting, adjust the arc current to 25000A and the voltage to 120V to rapidly heat the slag to 1570℃.

[0023] 3. Within 5-10 minutes of smelting, adjust the arc current to 20000A and the voltage to 120V, add 1kg of refining slag deoxidizer, and add 3kg / ton of limestone after 9 minutes of smelting. Control the target composition of the ladle slag to CaO: 40%; Al2O3: 40%; SiO2: 7%; FeO+MnO: <1%, and the target slag temperature to 1580℃.

[0024] 4. After smelting for 10 minutes, adjust the arc current to 25000A, voltage to 120V, control the target slag temperature to 1620℃, and adjust the bottom blowing flow rate to 18m³ / min. 3 Slag washing is performed for 5 minutes per hour, and the composition is adjusted according to the requirements of the steel grade being smelted.

[0025] 5. After 17 minutes of smelting, the molten steel is transported to the pouring position to begin pouring.

[0026] The entire refining process took 25 minutes, and the sulfur content in the molten steel decreased from 0.050% when it entered the station to 0.023% before and after refining.

[0027] Example 2:

[0028] The following uses a 60t ladle furnace producing 87B steel as an example to specifically introduce the implementation process and effects of this invention:

[0029] 1. The converter tapping adopts the slag-covering operation. After tapping, the slag layer thickness in the ladle furnace is 33mm. Circulating hot slag is added to the ladle at the refining molten steel receiving position. The hot slag usage is 5kg / ton of steel.

[0030] 2. After entering the refining steel treatment position, adjust the arc current to 25000A and the voltage to 120V to rapidly heat the slag to 1560℃.

[0031] 3. After smelting for 5 minutes, adjust the arc current to 20000A and the voltage to 120V. Add 5kg of refining slag deoxidizer. After smelting for 8 minutes, add 5kg of lumpy limestone. Control the target composition of the ladle slag to CaO: 50%; Al2O3: 48%; SiO2: 9%; FeO+MnO: <1%, and the target slag temperature to 1580℃.

[0032] 4. After smelting for 10 minutes, adjust the arc current to 25000A, voltage to 120V, control the target slag temperature to 1600℃, and adjust the bottom blowing flow rate to 15m³ / min. 3 Slag washing is performed for 10 minutes per hour, and the composition is adjusted according to the requirements of the steel grade being smelted.

[0033] 5. After smelting for 35 minutes, lift the electrodes, stop heating, and transport the molten steel to the casting position to begin casting.

[0034] The entire refining process takes 50 minutes, and the sulfur content in the molten steel decreases from 0.035% when it enters the station to 0.005% before and after refining.

[0035] Example 3:

[0036] The following uses a 60t ladle furnace producing R20 steel as an example to specifically introduce the implementation process and effects of this invention:

[0037] 1. The converter tapping adopts the slag-covering operation. After tapping, the slag layer thickness in the ladle furnace is 32mm. Circulating hot slag is added to the ladle at the refining molten steel receiving position. The hot slag usage is 4.5kg / ton of steel.

[0038] 2. Enter the refining steel treatment position, adjust the arc current to 25000A and the voltage to 120V, and quickly heat the slag to 1550℃;

[0039] 3. After smelting for 4 minutes, adjust the arc current to 20000A and the voltage to 120V. Add the refining slag deoxidizer at a rate of 3kg / ton of steel. After smelting for 6 minutes, add lumpy limestone at a rate of 4kg / ton of steel. Control the target composition of the ladle slag to CaO: 45%; Al2O3: 45%; SiO2: 8%; FeO: <1%, and the target slag temperature to 1570℃.

[0040] 4. After smelting for 15 minutes, adjust the arc current to 25000A, voltage to 120V, control the target slag temperature to 1600℃, and adjust the bottom blowing flow rate to 25m³ / h. 3 Slag washing is performed for 8 minutes per hour, and the composition is adjusted according to the requirements of the steel grade being smelted.

[0041] 5. After smelting for 23 minutes, lift the electrodes, stop heating, and transport the molten steel to the casting position to begin casting.

[0042] The entire refining process took 35 minutes, and the sulfur content in the molten steel decreased from 0.041% when it entered the station to 0.013% before and after refining.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for accelerating the desulfurization rate of a ladle furnace, characterized in that: Includes the following steps: a. Control the slag discharge from the converter so that the slag layer thickness in the ladle furnace after tapping is <40mm. Add hot slag into the ladle at the refining molten steel receiving position. The amount of hot slag used is 4-5kg / ton of steel. b. In the early stage of ladle furnace treatment, adjust the arc current to 25000A and the voltage to 120V to rapidly heat the slag to above 1550℃. c. During the middle stage of ladle furnace treatment, adjust the arc current to 20000A, voltage to 120V, add refining slag deoxidizer, the amount of refining slag deoxidizer added is 1-5kg / ton of steel, add lumpy limestone, the particle size of the lumpy limestone is controlled at 1-10mm, the CaO content in the lumpy limestone is ≥54%, the amount of lumpy limestone used is 3-5kg / ton of steel, and adjust the slag to the target composition and temperature; d. At the end of the ladle treatment, adjust arc current 25000 A, voltage 120 V, control slag temperature > 1600 °C, adjust bottom blowing flow to 15-25 m 3 / h, conduct slag washing for 5-10 min.

2. The method for accelerating the desulfurization rate of a ladle furnace according to claim 1, characterized in that, In step a, the hot slag composition is as follows: CaO 40-50%; Al2O3 40-50%; SiO2 <10%; FeO <1%, and the hot slag temperature is 1450-1500℃.

3. The method for accelerating the desulfurization rate of a ladle furnace according to claim 1, characterized in that, In step c, the composition of the refining slag deoxidizer is as follows: Al accounts for 25-35%, Al2O3 accounts for 55-65%, and the remaining components account for 5-10%. After the above components are mixed evenly, they are pressed into briquettes with a particle size of 30-50mm.

4. The method for accelerating the desulfurization rate of a ladle furnace according to claim 1, characterized in that, In step c, the target temperature of the refining slag is 1550-1600℃, and the target composition of the refining slag is: CaO 40-50%; Al2O3 40-50%; SiO2 <10%; FeO <1%.