Electroslag remelting atmosphere protection method and device

Abstract

A method and device for electroslag remelting in a gas atmosphere, the method comprising the following steps: 1) before the arc is introduced in the electroslag remelting, inert gas is filled into a sealed cover on a crystallizer until the oxygen content in the sealed cover is less than or equal to 50 ppm; 2) a ring-shaped air knife surrounding the consumable electrode is arranged above the surface of the slag pool near the crystallizer, and heated inert gas is introduced through the air knife to spray hot gas flow to the surface of the slag pool to form a hot inert gas cover layer with positive pressure on the surface of the slag pool; the temperature of the inert gas is 100-400 DEG C; 3) during the electroslag remelting, as the steel ingot grows and the surface of the slag pool rises, the ring-shaped air knife is controlled to rise at the same speed synchronously to maintain the hot gas flow directly covering the surface of the slag pool.

Description

Technical Field

[0001] This invention belongs to the field of special metallurgical processes, specifically relating to a method and apparatus for electroslag remelting atmosphere protection. Background Technology

[0002] With rapid economic development, the demand for energy is increasing. Thermal power generation is an important part of my country's energy mix. However, the environmental pollution problems caused by thermal power generation are increasingly conflicting with my country's ecological civilization construction and environmental protection concepts. Therefore, the demand for high-efficiency, low-emission, high-parameter thermal power units is becoming increasingly urgent. The higher the steam temperature and pressure parameters of coal-fired power generation, the lower the coal consumption and the less pollutant emissions, but the higher the performance requirements for materials. The P92 used in 600℃ ultra-supercritical units can no longer meet the requirements of higher parameter units; and to build ultra-supercritical units with parameters of 630℃ or higher, the high-temperature resistance of materials must reach 650℃.

[0003] G115 is a new type of martensitic heat-resistant steel (9Cr-3W-3CoVNbCuBN), specifically as shown in Chinese patent CN103045962B. This heat-resistant steel adopts a composite strengthening principle and contains multiple strengthening elements such as W, Co, Cu, B, and N. Its high-temperature long-term aging stability, high-temperature creep strength, and oxidation resistance are significantly higher than P92. It is suitable for long-term use under high-pressure conditions at temperatures below 650℃. Comparative studies have found that G115 has better creep strength and oxidation resistance at 650℃ than P92 at 600℃.

[0004] In G115, reactive elements such as B, Al, and Si are easily burned off, while nitrogen content tends to increase, and the burning-off pattern is unstable. This instability in the composition of the electroslag ingot can affect the production quality of subsequent processes and even lead to scrap. In existing electroslag remelting technologies, inert gases (such as argon) are typically used for protection to prevent oxygen from entering the slag pool and causing the burning off of reactive elements. A typical existing technology, such as the one disclosed in Chinese patent CN200410101591.8, employs a "sealed hood + oxygen partial pressure monitoring" method. This involves filling the entire chamber with room-temperature inert gas after evacuation and controlling the overall chamber pressure to achieve protection.

[0005] However, this traditional "whole-room cold charging" method has revealed the following significant drawbacks in actual production: 1. Significant cooling effect, impacting forming quality: The ambient temperature gas (approximately 25°C) directly contacts the high-temperature slag pool (approximately 1600°C). The huge temperature difference removes a large amount of heat from the slag surface, resulting in excessively thick slag skin or surface wrinkling on the crystallizer wall. This not only severely affects the surface quality of the steel ingot but also increases losses in subsequent peeling processes, reducing the yield.

[0006] 2. There are blind spots in protection and the purity is limited: In the large-volume sealed enclosure, it is difficult to completely replace the gas. Moreover, due to the strong thermal convection generated by the high temperature, simple pressure control cannot ensure that the key reaction zone on the surface of the slag pool is always in a high-purity atmosphere, which leads to insufficient control of active elements such as Ti and Al.

[0007] 3. Significant gas waste and high production costs: Existing technologies mostly use an open-circuit mode of "filling-emission", where a large amount of expensive argon gas is emitted after only one use, resulting in serious resource waste and increased cost per ton of steel. Summary of the Invention

[0008] The purpose of this invention is to provide a method and apparatus for protecting the atmosphere of electroslag remelting, which can provide hot gas protection, eliminate cold shock to the slag surface, improve the protection effect of inert gas atmosphere, make the burn-off of active elements of electroslag ingot stable and controllable, improve the surface quality of electroslag ingot, and improve production economy through waste gas recycling.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows: A method for electroslag remelting under protective atmosphere, comprising the following steps: 1) Before igniting the arc in electroslag remelting, inert gas is introduced into the sealing cover of the crystallizer until the oxygen content in the sealing cover is ≤50ppm; 2) An annular air knife is set above the surface of the consumable electrode near the slag pool of the crystallizer, and heated inert gas is introduced through it. Hot gas flow is sprayed onto the surface of the slag pool to form a hot inert gas covering layer with positive pressure on the surface of the slag pool; the temperature of the inert gas is 100~400℃. 3) During the electroslag remelting process, as the steel ingot grows and the slag pool surface rises, the annular air knife is controlled to rise synchronously at the same speed to always maintain the hot airflow directly covering the slag pool surface.

[0010] Preferably, during the remelting and feeding period, i.e. the end stage, the temperature of the inert gas is increased to 300~400℃ to slow down the solidification of the slag head by increasing the surface enthalpy of the slag pool.

[0011] Preferably, the height of the annular air knife from the surface of the crystallizer slag pool is 50-300 mm, and preferably, the initial position of the annular air knife is set at a distance of 50-300 mm from the arc-starting plate.

[0012] Preferably, during the electroslag remelting process, the fluorine-containing volatiles and waste gas generated by electroslag remelting inside the sealing cover are extracted through an exhaust port set at the top of the sealing cover, and after being filtered, defluorinated and reheated, they are sent to the annular air knife for recycling by a circulation pump.

[0013] In the design of the electroslag remelting atmosphere protection method of the present invention: This invention directly intervenes in the thermodynamic and kinetic equilibrium of the gas-slag-metal interface by changing the physical state of the atmosphere (temperature, flow state). The slag pool is not only a heat source and a site of chemical reaction, but also a "temperature controller" for the solidification process.

[0014] Traditional electroslag remelting atmospheres mostly use cold gas protection, that is, gas at or below room temperature is introduced. The slag pool surface has a drastic temperature difference, the slag surface "shells" or the viscosity increases suddenly, the slag skin is too thick and uneven, which hinders heat dissipation from the crystallizer wall, the solidification front is too deep, and the surface quality of the ingot is poor.

[0015] This invention is an innovative breakthrough. It uses hot gas and preheated (100~400℃) protective gas to reduce heat radiation loss from the slag surface, maintain high fluidity of the slag pool surface, and form a thin and uniform slag skin. The slag pool conducts heat uniformly, and the shallow and flat solidification front is conducive to excellent surface and internal crystallization of electroslag ingots.

[0016] Furthermore, this invention utilizes the viscosity and pressure difference of the gas to form a "covering" air curtain, rather than an "impact" jet. The main function of the airflow is to establish a slightly positive pressure zone; it "presses" onto the slag surface, rather than "blows" it away. This hot laminar flow causes minimal mechanical disturbance to the slag pool, ensuring a stable slag-metal interface and preventing molten slag from being entrained in the molten steel to form inclusions. It also reduces the probability of burn-off of reactive elements in the molten steel, improving the controllability of the electroslag ingot composition.

[0017] Fluorine-containing volatiles and waste gas generated by electroslag remelting are extracted through an exhaust port set at the top of the sealed cover. After filtration, defluorination and reheating, they are sent to the annular air knife for recycling through a circulating pump, which improves the economic efficiency of production.

[0018] The present invention also provides an electroslag remelting atmosphere protection device, comprising: A sealing cover is installed above the crystallizer; The annular air knife is fitted over the consumable electrode and located above the surface of the slag pool in the crystallizer; the annular air knife is equipped with a lifting device that moves synchronously with the consumable electrode; the annular air knife is connected to the air source through a connecting pipe. The gas heater has its outlet end connected to the inlet of the annular air knife via a connecting pipe, and the inlet end of the gas heater is connected to a gas source via a connecting pipe; preferably, the connecting pipe on the inlet side of the annular air knife is a high-temperature resistant flexible hose, and more preferably a high-temperature resistant telescopic flexible hose.

[0019] Preferably, it also includes a dust filter and a circulating pump connected in series via pipes; the inlet side of the dust filter is connected to an exhaust port located on the top of the sealing cover via a pipe; the outlet side pipe of the circulating pump is connected to the inlet side pipe of the gas heater, and the inlet of the gas heater is connected to the annular air knife via a pipe, forming a closed loop.

[0020] Preferably, the annular air knife is located 50-300 mm above the surface of the crystallizer slag pool and is connected to an external system through a high-temperature resistant telescopic pipe.

[0021] Preferably, the annular air knife is provided with a plurality of nozzles pointing towards the surface of the slag pool; preferably, the outlet angle of the nozzles forms an angle of 10 to 75° with the horizontal plane; more preferably, the nozzles are slit nozzles.

[0022] Preferably, the lifting device includes a lifting rod and a servo lifting drive mechanism; the lifting rod extends into the sealing cover; the annular air knife is disposed at the lower end of the lifting rod; preferably, a laser liquid level sensor is disposed on the annular air knife.

[0023] The annular air knife of this invention is not fixed on the furnace cover, but is sleeved on the outside of the consumable electrode and located above the surface of the slag pool of the crystallizer (e.g., 50-300 mm). It is equipped with a lifting device that moves up and down synchronously with the consumable electrode. It is connected to a gas heater through a high-temperature resistant hose (e.g., a telescopic hose, a corrugated pipe, etc.) so that the annular air knife sprays out hot inert gas, forming a hot inert gas covering layer with a certain positive pressure on the surface of the slag pool of the crystallizer.

[0024] The annular air knife has evenly distributed nozzles on its inner side, which can spray laminar inert gas to form a hot inert gas covering layer with a certain positive pressure on the surface of the crystallizer slag pool, like a "lid" directly pressing on the slag pool.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Improved surface quality: This invention uses preheated inert gas to spray onto the surface of the slag pool, which effectively reduces the heat radiation loss of the slag pool surface and eliminates the thermal impact of cold air on the slag pool. This reduces the thickness of the slag skin on the surface of the remelted ingot from the traditional 2-3mm to about 1mm, and the surface is smooth. Not only can the skin be peeled off without annealing, but it can even achieve peel-free forging.

[0026] 2. More precise composition control: Because the present invention uses close-range (e.g., 50~300mm) air curtain suppression, the oxygen partial pressure on the surface of the slag pool is extremely low, and the recovery rate of active elements such as Ti and Al can be stabilized at over 98%, which is better than the 95% recovery rate under traditional ambient gas protection.

[0027] 3. Energy saving and consumption reduction: This invention adopts a closed-loop gas circulation design, with a gas utilization rate exceeding 85%, significantly reducing production costs. Experimental data shows that argon gas consumption can be reduced from 5 m³ / ton to 0.8 m³ / ton. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of an embodiment of the hot atmosphere circulation protection device of the present invention. Detailed Implementation

[0029] The method for electroslag remelting atmosphere protection according to the present invention includes the following steps: 1) Before igniting the arc in electroslag remelting, inert gas is introduced into the sealing cover of the crystallizer until the oxygen content in the sealing cover is ≤50ppm; 2) An annular air knife is set above the surface of the consumable electrode near the slag pool of the crystallizer, and heated inert gas is introduced through it. Hot gas flow is sprayed onto the surface of the slag pool to form a hot inert gas covering layer with positive pressure on the surface of the slag pool; the temperature of the inert gas is 100~400℃. 3) During the electroslag remelting process, as the steel ingot grows and the slag pool surface rises, the annular air knife is controlled to rise synchronously at the same speed to always maintain the hot airflow directly covering the slag pool surface.

[0030] Preferably, during the remelting and feeding period, i.e. the end stage, the temperature of the inert gas is increased to 300~400℃ to slow down the solidification of the slag head by increasing the surface enthalpy of the slag pool.

[0031] Preferably, the height of the annular air knife from the surface of the crystallizer slag pool is 50~300mm.

[0032] Preferably, during the electroslag remelting process, the fluorine-containing volatiles and waste gas generated by electroslag remelting inside the sealing cover are extracted through an exhaust port set at the top of the sealing cover, and after being filtered, defluorinated and reheated, they are sent to the annular air knife for recycling by a circulation pump.

[0033] See Figure 1 The electroslag remelting atmosphere protection device of the present invention comprises: A sealing cover 1 is installed above the crystallizer 10; The annular air knife 2 is sleeved outside the consumable electrode 20 and located above the liquid surface of the slag pool 101 of the crystallizer 10; the annular air knife 2 is installed on a lifting device that synchronously raises and lowers the consumable electrode 20. The outlet end of the gas heater 3 is connected to the inlet of the annular air knife 2 via a connecting pipe, and the inlet end of the gas heater 3 is connected to the gas source via a connecting pipe; preferably, the connecting pipe on the inlet side of the annular air knife 2 is a high-temperature resistant flexible hose 6.

[0034] Preferably, it also includes a dust filter 4 and a circulation pump 5 connected in series via pipes; the inlet side of the dust filter 4 is connected to the exhaust port provided on the top of the sealing cover 1 via a pipe; the outlet side pipe of the circulation pump 5 is connected to the inlet side pipe of the gas heater 3, and the inlet of the gas heater 3 is connected to the annular air knife 2 via a pipe, forming a closed loop.

[0035] Preferably, the annular air knife 2 is located 50-300 mm above the surface of the slag pool in the crystallizer 10, and is connected to an external system through a high-temperature resistant telescopic pipe.

[0036] Preferably, the annular air knife 2 is provided with a plurality of nozzles pointing towards the surface of the slag pool; preferably, the outlet angle of the nozzles forms an angle of 10 to 75° with the horizontal plane; more preferably, the nozzles are slit nozzles.

[0037] Preferably, the lifting device includes a lifting rod 7 and a servo lifting drive mechanism; the lifting rod 7 extends into the sealing cover; the annular air knife 2 is disposed at the lower end of the lifting rod 7; preferably, a laser liquid level sensor 8 is provided on the annular air knife 2, and the servo lifting drive mechanism adjusts the position of the annular air knife 2 through the ranging feedback of the laser liquid level sensor 8.

[0038] Example The electroslag remelting atmosphere protection method of the present invention, for remelting G115 heat-resistant steel in a 20-ton electroslag furnace, includes the following steps: Preparation stage: After installing the electrodes, close the sealing cover; Start circulation: Turn on the circulation pump to replace the gas inside the crystallizer until the oxygen content inside the crystallizer is below 50 ppm; Hot state setting: Start the gas heater and set the gas heater temperature to 200℃; control the annular gas knife to descend to 100mm away from the arc-starting plate through the servo lifting mechanism and laser sensor; the preheated argon gas enters the annular hot gas knife through the high temperature resistant soft tube and is sprayed onto the slag pool surface through the nozzle at an angle of 10°~75°. Smelting process: Electroslag remelting begins with arc ignition and Ar gas is heated and ejected to cover the slag surface. During remelting, a laser level sensor continuously monitors the slag level in the crystallizer. For every 10mm rise in the slag level detected by the sensor, the servo control system drives the annular gas knife to rise synchronously by 10mm, maintaining a distance of approximately 100mm between the annular gas knife and the surface of the high-temperature slag pool. This dynamic tracking ensures that a high-temperature, pure laminar flow of argon gas constantly covers the most violently reacting slag-gold interface, preventing the slag pool and molten pool from reacting with air, which would lead to the loss of reactive elements and an increase in gas content. Waste gas treatment: The waste gas containing fluoride particles and a small amount of volatiles generated during the remelting process is discharged from the top of the sealed cover by the suction of the circulating pump. The waste gas first passes through a dust filter to remove harmful fluoride particles and dust, and then enters a gas heater to be heated to 100~400℃ before being sent back into the furnace for recycling.

[0039] The results of the electroslag ingot composition detection after adopting the method described in this invention are shown in Table 1.

[0040]

[0041] As shown in Table 1, the N content of the G115 electroslag ingot prepared by the method of this invention did not increase, which indirectly reflects that the airflow coverage formed by the hot Ar gas has a good protective effect on the slag-metal interface and eliminates the influence of air on the molten pool. The burn-off of active elements such as B, Al, and Si is controllable. The increase of B is 0.001, and the change rate of the electrode and standard deviation is 10%. The increase of Al is 0.002, and the change rate of the electrode and standard deviation is 22.22%. Si did not change, indicating that the composition variables of active elements are stable and controllable.

[0042] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for electroslag remelting atmosphere protection, characterized in that, Includes the following steps: 1) Before igniting the arc in electroslag remelting, inert gas is introduced into the sealing cover of the crystallizer until the oxygen content in the sealing cover is ≤50ppm; 2) An annular air knife is set above the surface of the consumable electrode near the slag pool of the crystallizer, and heated inert gas is introduced through it. Hot gas flow is sprayed onto the surface of the slag pool to form a hot inert gas covering layer with positive pressure on the surface of the slag pool; the temperature of the inert gas is 100~400℃. 3) During the electroslag remelting process, as the steel ingot grows and the slag pool surface rises, the annular air knife is controlled to rise synchronously at the same speed to always maintain the hot airflow directly covering the slag pool surface.

2. The method for electroslag remelting atmosphere protection as described in claim 1, characterized in that, During the remelting and feeding period, which is the final stage, the temperature of the inert gas is increased to 300~400℃.

3. The method for electroslag remelting atmosphere protection as described in claim 1, characterized in that, The annular air knife is 50-300 mm above the surface of the slag pool in the crystallizer.

4. The method for electroslag remelting atmosphere protection as described in claim 1, characterized in that, During the electroslag remelting process, the fluorine-containing volatiles and waste gas generated by electroslag remelting inside the sealed cover are extracted through the exhaust port set at the top of the sealed cover. After being filtered, defluorinated, and reheated, they are sent to the annular air knife for recycling through a circulation pump.

5. An electroslag remelting atmosphere protection device for the method as described in claim 1, characterized in that, include: A sealing cover is installed above the crystallizer; The annular air knife is fitted over the consumable electrode and located above the surface of the slag pool in the crystallizer. The annular air knife is mounted on a lifting device that moves up and down synchronously with the consumable electrode; The gas heater has its outlet end connected to the inlet of the annular air knife via a connecting pipe, and the inlet end of the gas heater is connected to a gas source via a connecting pipe; preferably, the connecting pipe on the inlet side of the annular air knife is a high-temperature resistant flexible hose, and more preferably a high-temperature resistant telescopic flexible hose.

6. The electroslag remelting atmosphere protection device as described in claim 5, characterized in that, It also includes a dust filter and a circulating pump connected in series via pipes; the inlet side of the dust filter is connected to the exhaust port on the top of the sealing cover via a pipe; the outlet side pipe of the circulating pump is connected to the inlet side pipe of the gas heater, and the inlet of the gas heater is connected to the annular air knife via a pipe, forming a closed loop.

7. The electroslag remelting atmosphere protection device as described in claim 5, characterized in that, The annular air knife is located 50-300 mm above the surface of the slag pool in the crystallizer. Preferably, the initial position of the annular air knife is set at a distance of 50-300 mm from the arc-starting plate.

8. The electroslag remelting atmosphere protection device as described in claim 5 or 7, characterized in that, The annular air knife is provided with a plurality of nozzles pointing towards the surface of the slag pool; preferably, the outlet angle of the nozzles forms an angle of 10 to 75° with the horizontal plane; more preferably, the nozzles are slit nozzles.

9. The electroslag remelting atmosphere protection device as described in claim 5, 7, or 8, characterized in that: The lifting device includes a lifting rod and a servo lifting drive mechanism; the annular air knife is located at the lower end of the lifting rod; preferably, a laser liquid level sensor is provided on the annular air knife.

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