Device and method for improving purity of LF refined molten steel

Abstract

The invention relates to a device and method for improving the purity of LF refined molten steel, and belongs to the technical field of refining processes in the metallurgical industry. According to the technical scheme, the device comprises a steel ladle (6), an argon metal hose (8), a slit type air brick (9), an argon top lance (11) and an argon pipeline (12), the argon top lance (11) is arranged above the steel ladle (6), and the argon top lance (11) is connected with the argon pipeline (12); two slit type air bricks (9) are arranged at the ladle bottom of the steel ladle (6), brick core slits of the two slit type air bricks (9) are respectively connected with the argon metal hose (8), and the argon top lance (11) is located between the two slit type air bricks (9); and a spray head of the argon top lance (11) adopts a four-hole argon spray head. The method has the beneficial effects that the main body flowing direction of the molten steel in the steel ladle can be changed, collision polymerization and floating of the inclusions are facilitated, and therefore the inclusions in the molten steel can be efficiently removed in the steel ladle refining process.

Description

Technical Field

[0001] The invention relates to a device and a method for improving the purity of LF refined molten steel, belonging to the technical field of refining process in the metallurgical industry. Background Art

[0002] In recent years, the requirements for steel quality and performance in the construction, military, machinery manufacturing and other industries have been increasing, and the refining technology outside the furnace is increasingly valued by many manufacturers. Generally speaking, if an enterprise needs to smelt pure steel or ultra-pure steel, it can choose the refining technology outside the furnace as the necessary technical support. By introducing the new refining technology outside the furnace, the enterprise should be able to ensure the realization of good steelmaking process effects, speed up the processing of molten steel, and ensure the economic benefits of the enterprise itself.

[0003] The essence of off-furnace refining technology is to improve the chemical and thermal conditions in steel smelting operations, thereby significantly improving steel smelting efficiency and smelting speed. In the production process, off-furnace refining plays a connecting role between steelmaking and continuous casting processes, simplifies the production process, improves production efficiency, and reduces production costs. The widespread use of off-furnace refining has enabled companies to control the existing refining reaction process at any time and ensure that intelligent means are used throughout the entire smelting reaction process.

[0004] The most widely used stirring method for off-furnace refining is argon stirring in the ladle. According to the characteristics of the steel grade, the corresponding refining slag system is selected. At present, the ternary refining slag system is usually used. The use of argon stirring can accelerate the material transfer between steel and slag, accelerate the circulation speed of molten steel, improve the process of deoxidation and desulfurization, improve the kinetic reaction conditions of molten steel, remove non-metallic impurities, and improve the purity of molten steel, especially for alumina type inclusions. However, at present, argon blowing in the ladle mainly adopts the method of blowing argon at the bottom of the ladle. The argon bubbles blown at the bottom of the ladle will directly float vertically after entering the molten steel. The vertical floating of the argon bubbles drives the molten steel in the ladle to flow mainly in the longitudinal direction. This way of molten steel flow will cause a "circulation blind area" to appear at the bottom of the ladle near the wall and far away from the argon eye, which slows down the downward circulation speed of the longitudinal circulation, slows down the effect of collision polymerization and growth of inclusions, and the stirring power is not strong enough, so the efficiency of removing inclusions by blowing argon at the bottom of the ladle is low. Summary of the invention

[0005] The purpose of the present invention is to provide a device and method for improving the purity of LF refined molten steel, which can change the main flow direction of molten steel in the ladle, which is conducive to the collision, aggregation and floating of inclusions, so that inclusions in the molten steel can be efficiently removed during the ladle refining process, solving the problems existing in the background technology.

[0006] The technical solution of the present invention is: A device for improving the purity of LF refined molten steel comprises a ladle, an argon metal hose, a slit-type air-permeable brick, an argon top gun and an argon pipeline. An argon top gun is arranged above the ladle and is connected to the argon pipeline; two slit-type air-permeable bricks are arranged at the bottom of the ladle, the brick core slits of the two slit-type air-permeable bricks are respectively connected to the argon metal hose, and the argon top gun is located between the two slit-type air-permeable bricks.

[0007] The distance between the nozzle of the argon top gun and the slag liquid level in the ladle is 0.5-0.8m.

[0008] The nozzle of the argon top gun adopts a four-hole argon nozzle.

[0009] The angle between the center line of the two slit-type air-permeable bricks and the horizontal line of the ladle is 15°~35°.

[0010] A method for improving the purity of LF refined molten steel, using the device for improving the purity of LF refined molten steel as defined above, the refined smelting slag adopts a quaternary slag system composed of CaO, SiO2, A12O3 and MgO, and the quaternary slag system contains: 600-800kg of lime, 200-300kg of fluorite, 20-40kg of aluminum wire segments, and 20-30kg of magnesia.

[0011] The mass percentage of CaF2 in the fluorite is greater than or equal to 75%.

[0012] The bottom blowing argon gas flow rate is 80~230NL / min, and the outlet pressure is 0.33~0.38MPa. The top blowing argon gas flow rate is 200~330NL / min, and the outlet pressure is 0.35~0.42MPa.

[0013] The beneficial effects of the present invention are: (1) Compared with the traditional ladle bottom blowing argon process, the longitudinal descent rate of molten steel is increased, and transverse vortex is also generated. The average velocity of molten steel flowing in the ladle is much greater than the average velocity of molten steel in the traditional ladle bottom blowing argon process. Moreover, the proportion of "circulation blind area" when the molten steel in the ladle forms transverse vortex is smaller than that of the traditional ladle bottom blowing argon process, which is more conducive to driving more inclusions to float and be removed; (2) The top blowing of argon in the ladle increases the longitudinal circulation velocity. Due to the increase in the amount of top blowing, the slag surging intensity increases, the contact surface of the steel-slag interface increases, the inclusions float up and fully dissolve in the refining slag, which is more conducive to the floating removal of inclusions; (3) Since the amount of argon gas blown from top and bottom to form the swirl is much greater than that from bottom blowing, the number of argon bubbles blown from bottom increases, thereby increasing the probability of inclusion collision formation; (4) Due to the addition of argon blowing from the top gun, the argon gas blown out from the four-hole nozzle of the top gun generates a certain lateral velocity at the slag interface, so that the argon bubbles enter the slag interface at the corresponding lateral velocity, move farther in the ladle, stay longer in the molten steel, and the argon bubbles are more dispersed in the ladle, increasing the probability of argon bubbles capturing inclusions; (5) Compared with the traditional ternary refining slag system, under the action of top blowing, the inclusions in the quaternary slag system will move with the lateral swirl, and the probability of inclusions colliding, aggregating and growing will increase. At the same time, the optimization of the refining slag system increases the adsorption capacity and sulfur capacity of the quaternary slag system, which can make the inclusions exist stably in the slag, thereby improving the purity of the molten steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structure of the present invention; Figure 2 It is a schematic diagram of the angle between the air-permeable brick, the top gun and the horizontal reference line of the present invention; In the figure: 1-display screen, 2-control rotary knob, 3-control box, 4-winch, 5-furnace cover, 6-ladle, 7-quick connector, 8-argon metal hose, 9-slit air brick, 10-molten steel, 11-argon top gun, 12-argon pipeline; 13-bottom blowing eye of ladle. DETAILED DESCRIPTION

[0015] The present invention will be further described below by way of examples with reference to the accompanying drawings.

[0016] See attached Figure 1-2 , a device for improving the purity of LF refined molten steel, comprising a ladle 6, an argon metal hose 8, a slit-type air-permeable brick 9, an argon top gun 11 and an argon pipeline 12. An argon top gun 11 is arranged above the ladle 6, and the argon top gun 11 is connected to the argon pipeline 12; two slit-type air-permeable bricks 9 are arranged at the bottom of the ladle 6, and the brick core slits of the two slit-type air-permeable bricks 9 are respectively connected to the argon metal hose 8, and the argon top gun 11 is located in the middle of the two slit-type air-permeable bricks 9.

[0017] A method for improving the purity of LF refined molten steel, wherein the refined smelting slag adopts a quaternary slag system composed of CaO, SiO2, A12O3 and MgO, wherein the quaternary slag system comprises: 600-800kg of lime, 200-300kg of fluorite, 20-40kg of aluminum wire segment, 20-30kg of magnesia, wherein the mass percentage of CaF2 in the fluorite is greater than or equal to 75%; the bottom blowing argon gas flow rate is 80-230NL / min, the outlet pressure is 0.33-0.38MPa, the top blowing argon gas flow rate is 200-330NL / min, and the outlet pressure is 0.35-0.42MPa. Example

[0018] See attached Figure 1-2 The nozzle of the argon top gun 11 adopts a four-hole argon nozzle. When the ladle 6 is in the LF furnace refining position, the external argon pipe is connected to the ladle quick connector 7 through a quick connector, and the argon enters the molten steel 10 through the slit-type air-permeable brick 9 to realize the internal circulation of the molten steel 10; when the refining is in the top and bottom double blowing process, the adjustment knob 2 on the control box 3 controls the start of the winch 4, so that the argon top gun 11 is raised and lowered, so that the top gun reaches the specified position, that is, the top gun descends to a position where the nozzle is 0.5~0.8m away from the slag liquid surface, and the top gun nozzle is located between the two argon eyes. The argon flow rate is adjusted by the argon control knob 2, and the argon flow rate data is displayed on the display 1. The argon metal hose 12 is connected to the argon top gun. In the process of top and bottom double blowing, in order to effectively prevent the splashing of slag and facilitate observation, the top blowing furnace cover 5 must be buckled.

[0019] After the ladle enters the refining station, the quaternary slag system is selected for slag making. After the ladle enters the LF refining position, slag making agent is added to the molten steel 10 in three times, 200kg of lime and 100kg of fluorite are added each time, and a total of 600kg of lime and 300kg of fluorite are added. After the slag is molten after 400s of power supply, 30kg of aluminum wire segments are added to the molten steel 10 to adjust the refining slag system to a low melting point position, reduce the CaO activity and the refining slag viscosity, and add 20kg of magnesia.

[0020] Correct use of top gun and determination of bottom blowing and top blowing argon flow rate: 150t ladle is used for molten steel smelting in the refining operation area. Two slit air bricks 9 are installed at both ends of the same height circumference diameter of the bottom of the ladle at the hot repair 1# ladle turner. The installation angle of the two slit air bricks 9 is 25° with the horizontal diameter of the ladle. According to the on-site ladle parameters and the physical and chemical parameters of molten steel and argon, a simulation model is established based on Fluent software, and the refining bottom blowing argon flow setting value is calculated to be 180NL / min, the outlet pressure is 0.35MPa, and the top gun argon flow setting value is 300NL / min, and the outlet pressure is 0.39MPa.

[0021] Ladle top and bottom combined blowing argon refining: When the ladle leaves the refining station for soft blowing outside the station, the bottom blowing argon flow rate is set to 180NL / min. After the ladle enters the pretreatment position, the top and bottom combined blowing is carried out together. The top gun is lowered until the top gun nozzle is 0.5~0.8m away from the slag liquid surface, then the argon is turned on, the flow rate is modulated to 300NL / min, and the argon blowing time is 8min. After the blowing time is met, the top and bottom blowing argon are turned off, and the top gun is raised to the specified position.

[0022] Sampling analysis and testing: After the blowing is completed, samples are taken from the molten steel for oxygen content analysis and inclusion inspection. At this time, the total oxygen content in the molten steel is 10ppm, and the DS inclusion rating is between 0 and 0.7.

[0023] Comparative Example Ladle double-hole bottom blowing argon refining When the ladle leaves the refining station for soft blowing outside the station, the bottom blowing argon flow rate is set to 180NL / min and the argon blowing time is 8min.

[0024] After the ladle enters the refining station, the traditional ternary slag system is selected for slag making. After the ladle enters the LF refining position, slag making agent is added to the molten steel 10 in three times, 200kg of lime and 100kg of fluorite are added each time, and a total of slag making agent (600kg of lime and 300kg of fluorite) is added. After the slag is removed after 400s of power supply, 30kg of aluminum wire segments are added to the molten steel 10 to adjust the refining slag system to a low melting point position, reduce the CaO activity and the viscosity of the refining slag.

[0025] Sampling analysis and testing: After the blowing is completed, samples are taken from the molten steel for oxygen content analysis and inclusion detection. At this time, the total oxygen content in the molten steel is 30ppm, and the DS inclusion rating is between 0.7 and 1.6.

[0026] The total oxygen content in the molten steel can reflect the amount of inclusions, and the number of DS inclusions can reflect the distribution of inclusion sizes. From the above comparison, it can be seen that the method provided in this patent can reduce the total oxygen content by more than one time, significantly reduce the large particle inclusions in the molten steel, and more effectively remove the inclusions.

Claims

1. A device for improving the purity of LF refined molten steel, characterized in that: The invention comprises a ladle (6), an argon metal hose (8), a slit-type air-permeable brick (9), an argon top gun (11) and an argon pipeline (12). An argon top gun (11) is arranged above the ladle (6), and the argon top gun (11) is connected to the argon pipeline (12). Two slit-type air-permeable bricks (9) are arranged at the bottom of the ladle (6), and the brick core slits of the two slit-type air-permeable bricks (9) are respectively connected to the argon metal hose (8), and the argon top gun (11) is located between the two slit-type air-permeable bricks (9).

2. The device for improving the purity of LF refined molten steel according to claim 1, characterized in that: The distance between the nozzle of the argon top gun (11) and the slag liquid surface in the ladle (6) is 0.5-0.8 m.

3. A device for improving the purity of LF refined molten steel according to claim 2, characterized in that: The nozzle of the argon top gun (11) adopts a four-hole argon nozzle.

4. The device for improving the purity of LF refined molten steel according to claim 1, characterized in that: The angle between the center line of the two slit-type air-permeable bricks (9) and the horizontal line of the ladle (6) is 15° to 35°.

5. A method for improving the purity of LF refined molten steel, characterized in that: A device for improving the purity of LF refined molten steel as defined in claims 1-3 is used, and the refined smelting slag adopts a quaternary slag system composed of CaO, SiO2, A12O3 and MgO, and the quaternary slag system contains: 600-800kg of lime, 200-300kg of fluorite, 20-40kg of aluminum wire segments, and 20-30kg of magnesia.

6. A method for improving the purity of LF refined molten steel according to claim 5, characterized in that: The mass percentage of CaF2 in the fluorite is greater than or equal to 75%.

7. A method for improving the purity of LF refined molten steel according to claim 5, characterized in that: The bottom blowing argon gas flow rate is 80~230NL / min, and the outlet pressure is 0.33~0.38MPa. The top blowing argon gas flow rate is 200~330NL / min, and the outlet pressure is 0.35~0.42MPa.

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