A control method for removing inclusions by slag making in an acid intermediate frequency furnace

Abstract

The present invention discloses a control method for removing inclusions by slag making in an acid medium-frequency furnace, which includes: after all the materials are melted, first perform slagging treatment to basically clean up the slag formed by the impurities in the melted materials; increase the heating power of the medium-frequency furnace to heat the molten steel to 1400 °C; add sodium-silicate glass to the hump position of the molten steel in step 2, keep the power unchanged, and heat up to 1500 °C; stop heating, open the bottom blowing argon for argon blowing operation, and perform slagging treatment after argon calming. By using sodium-silicate glass to replace lime and fluorite for slag making, and cooperating with the argon blowing process and the calming time, the present invention can produce cleaner molten steel with lower inclusion content, providing technical support for expanding the smelting quality of acid medium-frequency furnaces.

Description

Technical Field

[0001] The present invention relates to the technical field of slag-making in medium-frequency furnace smelting, and particularly to a control method for removing inclusions by slag-making in an acidic medium-frequency furnace. Background Art

[0002] A medium-frequency furnace increases the frequency of the industrial-frequency current of 50 Hz of the variable-frequency power supply to a current of 150 - 200,000 Hz, and transmits this current to a circuit composed of an induction coil and a capacitor. The induction coil is a spiral coil wound with copper pipes, and the copper pipes are cooled by water. When the variable-frequency current passes through the induction coil, the metal charge in the crucible generates an induced current due to electromagnetic induction, and the charge is heated and melted by using the induced current. Medium-frequency induction electric furnaces are widely used in the smelting of non-ferrous metals and ferrous metals. However, with the increasing requirements for the quality of molten steel in products, the process of using the slag-making process to adsorb and remove inclusions in molten steel in medium-frequency furnaces has been gradually promoted. Currently, it is mainly for alkaline medium-frequency furnaces, and lime and fluorite can be used for slag-making to desulfurize and dephosphorize molten steel while removing some inclusions. However, for acidic medium-frequency furnaces, it is relatively special. Since the furnace lining is made of quartzite and the main content is SiO2, when using lime and fluorite, they first react with the furnace lining and erode the furnace lining, seriously affecting the furnace campaign life and not being suitable for long-term implementation. Currently, there are few patents on the control method for removing inclusions by the slag-making process in acidic medium-frequency furnaces.

[0003] Application No. 202011174076.8 discloses a slag-making process for smelting superalloys in a medium-frequency furnace. By using slag-making agents such as lime and fluorite to make slag on molten steel, desulfurization and dephosphorization of molten steel are carried out, and deoxidation of molten steel is carried out by using calcium-silicon alloy. This method mainly makes slag on molten steel by using lime and fluorite, which erodes the furnace lining of the acidic medium-frequency furnace to a great extent and seriously affects the furnace campaign life, and is applicable to the furnace lining of alkaline medium-frequency furnaces.

[0004] For the furnace lining of an acidic medium-frequency furnace, how to find a control method that can both meet slag-making to remove inclusions and not affect the furnace lining life has become a key technology for slag-making to remove inclusions in acidic medium-frequency furnaces. Summary of the Invention

[0005] In order to overcome the above problems existing in the prior art, the present invention proposes a control method for removing inclusions by slag-making in an acidic medium-frequency furnace.

[0006] The technical solution adopted by the present invention to solve its technical problems is: a control method for removing inclusions by slag-making in an acidic medium-frequency furnace, including the following steps:

[0007] A control method for removing inclusions by slag-making in an acidic medium-frequency furnace, including the following steps:

[0008] Step 1: First, add high-quality scrap steel accounting for 30% of the furnace capacity and melt it using a power of 1600 KW. After the scrap steel is melted, add industrial pure iron. After adding the industrial pure iron, add ferrosilicon and ferroboron. At this time, the melting power is increased to 3000 KW. After all the materials are melted, an initial layer of slag is formed, and the slag is fished out manually using a slag skimmer.

[0009] Step 2: Maintain a heating power of 3000 KW and heat the molten steel to 1400 °C.

[0010] Step 3: Add sodium silicate glass to the hump position of the molten steel in Step 2, keep the power unchanged, and raise the temperature to 1500 °C.

[0011] Step 4: Stop heating, open the bottom argon blowing for argon blowing operation, and perform slag removal treatment after argon calming.

[0012] For the above control method of removing inclusions by slag formation in an acid medium-frequency furnace, in Step 2, the power of the medium-frequency furnace is increased to 3500 KW for heating up.

[0013] For the above control method of removing inclusions by slag formation in an acid medium-frequency furnace, the sodium silicate glass in Step 3 includes the following weight percentages: SiO2: 70 - 75%, Na2O: 12 - 15%, CaO: 7 - 9%, MgO: 2 - 4%, Al2O3: 1 - 3%, K2O: < 1%.

[0014] For the above control method of removing inclusions by slag formation in an acid medium-frequency furnace, in Step 4, the argon blowing pressure is 0.2 MPa, and the argon calming time is 20 min to ensure that the inclusions float up sufficiently.

[0015] For the above control method of removing inclusions by slag formation in an acid medium-frequency furnace, the argon calming time in Step 4 is determined by the floating time of the inclusions. The calculation formula for the floating time of the inclusions is:

[0016]

[0017] Among them, θ represents the floating velocity of the inclusions, g represents the acceleration of gravity, ρ m represents the density of the inclusion particles, ρ i represents the density of the molten steel, r represents the diameter of the inclusions, η represents the dynamic viscosity of the molten steel, and k represents the shape factor coefficient.

[0018] For the above control method of removing inclusions by slag formation in an acid medium-frequency furnace, the mass of the sodium silicate glass added in Step 3 is 1 / 10 of the mass of the slag.

[0019] The beneficial effects of the present invention are as follows. By using sodium-silicate glass to replace lime and fluorite for slag making, and combining with the argon blowing process and the calming time, molten steel with lower and cleaner inclusion content can be produced, providing technical support for expanding the smelting quality of acid medium-frequency furnaces. Specific Embodiments

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below in conjunction with specific embodiments.

[0021] This embodiment discloses a control method for slag making and inclusion removal in an acid medium-frequency furnace with low cost and high efficiency.

[0022] Both this embodiment and the comparative example are implemented in our company's 15t medium-frequency furnace. First, high-quality scrap steel with a proportion of 30% of the furnace capacity is added, and melting is carried out using a power of 1600KW. After the scrap steel melts, industrial pure iron is added. After adding industrial pure iron, ferrosilicon and ferroboron are added. At this time, the melting power is increased to 3000KW. After all the materials are melted, an initial layer of slag is formed. The slag is fished out manually by a slag skimmer. The heating power of the medium-frequency furnace is increased to 3500KW. When the molten steel is heated to 1400°C, 5kg of sodium-silicate glass is weighed and added at the hump position of the molten steel. The temperature is raised to 1500°C while keeping the power unchanged. The power is turned off and bottom argon blowing is carried out. The argon blowing pressure is 0.2MPa. After argon blowing and calming for 20 minutes, slagging treatment is carried out to remove all the slag. After all the slag is removed, it is avoided that inclusions enter the next process along with the slag, improving the quality of molten steel.

[0023] Generally, the addition amount of sodium-silicate glass is about 1 / 10 of the slag quality. The slag quality is generally 50kg per furnace. Therefore, the addition amount of sodium-silicate glass in this embodiment is 5kg.

[0024] The component percentage of sodium-silicate glass for slag making in the acid medium-frequency furnace is as follows: SiO2: 70 - 75%, Na2O: 12 - 15%, CaO: 7 - 9%, MgO: 2 - 4%, Al2O3: 1 - 3%, K2O: <1%.

[0025] The process for slag making and inclusion removal in this patent is described in detail as follows:

[0026] The main component of sodium-silicate glass is SiO2, which avoids the erosion of the quartz sand furnace lining. Moreover, there are also some basic oxides in sodium-silicate glass, which can effectively increase the content of basic oxides in the local slag and improve the ability of the slag to adsorb inclusions.

[0027] After all the materials are melted, slagging treatment is carried out first to basically remove the slag formed by impurities in the melted materials. When the temperature rises to 1400°C, at this relatively high temperature, sodium-silicate glass is added to the molten steel hump at the middle position of the medium-frequency furnace. With the agitation of the molten steel by the magnetic field, inclusions in the molten steel can be fully adsorbed.

[0028] When the temperature rises to 1500°C, heating is stopped, and bottom argon blowing is started. Argon stirring is carried out under a pressure of 0.2 MPa. During the upward movement of argon bubbles, they collide with inclusions. Inclusion particles will be captured by the bubbles and adhere to the surface of the bubbles to form aggregates. When the bubbles reach the steel-slag interface, the bubbles burst, and the inclusions are released to the steel-slag interface and captured by the slag, achieving the effect of removing inclusions.

[0029] The required 20-minute calming time is mainly determined by the floating time of inclusions. Calculated according to Stokes' formula:

[0030]

[0031] Among them, θ represents the floating velocity of inclusions (m / s), g represents the acceleration due to gravity (m / s 2 ), ρ m represents the density of inclusion particles (kg / m 3 ), ρ i represents the density of molten steel (kg / m 3 ), r represents the diameter of inclusions (m), η represents the dynamic viscosity of molten steel (kg / m·s), and k represents the shape factor coefficient (1 - 5, taking 1 here)

[0032] The floating time of inclusions is 19.2 minutes. Therefore, the argon blowing and calming is set to 20 minutes. At this time, all inclusions have floated into the slag. At this time, slagging treatment is carried out to remove all the slag, avoiding the slag entering the next process.

[0033] Under the condition of ensuring that other conditions remain unchanged, through the slag-making process with sodium-silicate glass (example), compared with the process without sodium-silicate glass (control), the inclusion removal effect is shown in Table 1

[0034] Table 1 Number of inclusions (number / mm 2 )

[0035]

[0036] By using sodium-silicate glass to make slag, combined with argon blowing and calming processes, the number of inclusions is significantly reduced. The number of inclusions during steel tapping is reduced by 68.34%, effectively improving the quality of molten steel.

[0037] After the material is melted, sodium silicate glass is added to make slag when heated to 1400°C, argon blowing operation is carried out when the temperature is raised to 1500°C, slagging treatment is carried out after sufficient time of calming, all the furnace slag is removed, the number of inclusions is significantly reduced, the number of inclusions during steelmaking is reduced by 68.34%, and the quality of molten steel is effectively improved. The popularization of this process technology will effectively improve the application scenarios of acid medium-frequency furnaces and provide technical support for improving the quality of molten steel by slagging for acid furnace linings.

[0038] The above embodiments are only exemplary embodiments of the present invention and are not used to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements within the essence and protection scope of the present invention, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present invention.

Claims

1. A control method for removing inclusions from slag in an acidic medium frequency furnace, characterized in that: The steps include: Step 1: First, add 30% of the furnace capacity of high-quality scrap steel and use 1600kW power to melt it. After the scrap steel is melted, add industrial pure iron. After adding industrial pure iron, add ferrosilicon and ferroboron. At this time, the melting power is increased to 3000kW. After all the materials are melted, a layer of initial slag is formed. Use a slag scraper to manually salvage the slag; Step 2: Maintaining a heating power of 3000kW, heat the molten steel to 1400°C; Step 3: Add soda-silica glass to the hump of the molten steel in step 2, keep the power constant, and raise the temperature to 1500° C. The soda-silica glass comprises the following weight percentages: SiO2: 70-75%, Na2O: 12-15%, CaO: 7-9%, MgO: 2-4%, Al2O3: 1-3%, K2O: <1%; the mass of the soda-silica glass added is 1 / 10 of the mass of the slag; Step 4: stop heating, open the bottom argon blowing operation, and perform slag treatment after argon blowing and calming.

2. The control method for removing inclusions from slag in an acidic medium frequency furnace according to claim 1, characterized in that: In step 4, the argon blowing pressure is 0.2 MPa, and the argon blowing calming time is 20 minutes to ensure that the inclusions fully float up.

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