A method for in-situ fluxing of a mould powder in a crystallizer

Abstract

The application belongs to the technical field of steel metallurgy, and particularly relates to a method for in-situ melting of a crystallizer inner protective slag, comprising: setting a heating device above a crystallizer in continuous casting production, in-situ heating the protective slag above molten steel in the crystallizer, improving the temperature of the protective slag, promoting the melting of the protective slag in the crystallizer, increasing the thickness of the liquid slag layer, controlling the excessive growth of the slag ring, eliminating the block-shaped fish and slag strips in the protective slag in the crystallizer, increasing the consumption of the protective slag, guaranteeing the smooth continuous casting, and improving the surface quality of the casting blank. The application utilizes laser spots generated by a laser to irradiate the slag surface of the protective slag in the crystallizer, heats the protective slag in the crystallizer, and discloses various working modes of laser heating of the protective slag according to various requirements of continuous casting production, realizes the purposes of rapid melting of the protective slag, control of the excessive growth of the slag ring, and ablation of high-melting-point refractory substances in the protective slag, guarantees the efficient operation of the continuous casting, and improves the surface quality of the casting blank.

Description

Technical Field

[0001] This application relates to the field of iron and steel metallurgy technology, specifically, to a method for in-situ fluxing of protective slag in a crystallizer. Background Technology

[0002] Continuous casting is a crucial process in steel production, vital to steel quality, yield, production efficiency, and the development of new steel grades. While significant progress has been made in continuous casting technology, various problems and challenges still frequently arise. For example, high-alumina steel, high-manganese steel, semi-peritectic steel, titanium- or rare-earth-containing steel, and high-alloy steel are particularly difficult to produce and have higher defect rates. High-speed continuous casting has not yet reached its ideal level. The crystallizer is the heart of the continuous casting machine, and the melting state of the protective slag within it is a key determinant of smooth casting operation. The thickness of the slag layer, the growth of the slag ring, and the rate at which the slag layer enters the gap between the billet shell and the copper plate in the crystallizer (i.e., slag consumption) are critical indicators of whether continuous casting proceeds smoothly.

[0003] In continuous casting production, the protective slag inside the crystallizer consists of three layers from top to bottom: a loose powdery layer, a relatively dense sintered layer, and a completely molten liquid slag layer. The melting of the protective slag mainly relies on the heat transfer from the molten steel to the protective slag and the heat release from the combustion of carbon in the protective slag. However, in production, due to factors such as low molten steel temperature, poor heat transfer of the protective slag, insufficient carbon content in the protective slag, high melting point of the protective slag, excessively fast continuous casting speed, and the reaction between the protective slag and molten steel to generate high-melting-point substances, problems often arise such as insufficient thickness of the liquid slag layer in contact with the molten steel, low temperature and high viscosity of the liquid slag layer, the presence of high-melting-point substances in the liquid slag layer, and excessive growth of the slag ring at the contact point between the liquid slag layer and the copper wall of the crystallizer. This results in the liquid protective slag in the liquid slag layer not being able to fully enter the space between the copper wall of the crystallizer and the solidified steel shell formed by the molten steel in the crystallizer. In some cases, some high-melting-point substances in the liquid slag layer may even block the channel between the liquid slag flowing into the copper wall and the steel shell. The steel shell and the copper wall of the crystallizer cannot be adequately lubricated, resulting in adhesion between the steel shell and the copper wall of the crystallizer, which in turn leads to sticking and leakage of steel.

[0004] Existing technologies primarily control the composition of the protective slag, particularly its basicity, the type and content of carbonaceous additives, and the type and content of flux, to ensure the melting temperature and rate of the protective slag. However, besides its lubricating function, the protective slag also needs to control heat transfer between the solidified billet shell and the copper plate of the crystallizer, and absorb inclusions in the steel. Controlling the composition of a protective slag that integrates multiple metallurgical functions is difficult, and it often cannot simultaneously satisfy all functions well, only achieving a trade-off between related functions. Other technologies promote the melting of the protective slag by controlling the casting temperature of the molten steel and the flow of molten steel in the crystallizer. However, the casting temperature of the molten steel has a significant impact on the internal and surface quality of the billet, and the flow of molten steel in the crystallizer must also consider factors such as the entrapment of the protective slag and the removal of inclusions, thus the control effect is also relatively limited.

[0005] Existing technologies include offline baking of the protective slag and increasing the temperature of the protective slag added to the crystallizer to promote melting of the protective slag after it is added to the crystallizer. Existing technology discloses a protective slag heating device and method for use in an automatic slag feeder, including a movable slag-carrying trolley. The trolley has a transformer installed inside its body, which is connected to an external power supply and control cabinet via a flexible cable. An induction heating component is installed on the upper part of the trolley, and the transformer is connected to this induction heating component. The induction heating component heats the flowing protective slag before it is fed into the crystallizer inlet. This method involves heating the protective slag outside the crystallizer before it enters the crystallizer, achieving goals such as "enhancing the melting capacity of the protective slag and rapidly forming sufficient liquid slag without producing excessive slag strands." However, the protective slag contains a large amount of low-melting-temperature flux. If this type of protective slag is heated offline or baked at a high temperature outside the crystallizer, it will cause premature combustion of carbon and agglomeration of the protective slag, affecting the uniform addition of the protective slag to the crystallizer and its heat preservation effect within the crystallizer. Therefore, the baking and heating temperatures must be controlled below the sintering temperature of the protective slag, and inert or reducing gas protection must be used to control the baking and heating process, as well as the contact combustion of the protective slag with air during injection into the crystallizer. Existing technologies have also disclosed offline heating and melting of the protective slag before pouring it into the crystallizer. However, this technology suffers from high heating temperatures, significant volatilization losses of fluxing substances in the protective slag during heating and melting, a large difference in composition between the protective slag added to the crystallizer and the protective slag melted in situ within the crystallizer, and the challenge of continuously, slowly, and uniformly pouring the melted protective slag into the crystallizer. Therefore, the technology of shifting and heating the protective slag outside the crystallizer has many problems. It is significantly different from the melting of the protective slag inside the crystallizer in the existing continuous casting production. The related technologies are difficult, have low heating efficiency, and are not effective.

[0006] Existing technology discloses an electromagnetic casting method that applies a high-frequency magnetic field within a continuous casting mold. The mold wall has longitudinal slits formed at predetermined intervals, and an electromagnetic coil is positioned around the outer periphery of the mold. Simultaneously, the immersion nozzle for supplying molten metal is constructed from a conductive material near its meniscus to inductively heat the mold powder. This method requires machining longitudinal slits in the mold wall, significantly shortening the mold's lifespan. Furthermore, deploying induction coils outside the mold to apply a high-frequency magnetic field to the crystallizer requires the magnetic field to penetrate the copper wall of the crystallizer, resulting in significant electromagnetic losses and limited heating efficiency. Additionally, this method necessitates improvements to the submerged entry nozzle material, ensuring that the portion of the nozzle in contact with the protective slag, particularly near the meniscus of the molten steel, is conductive. This allows the high-frequency magnetic field within the crystallizer to generate an induced current and heat in this contact area, thus heating the adjacent protective slag. This technology is slow, requires complex equipment, and has limited practical effectiveness. It cannot effectively enhance the fluxing of the protective slag, increase the thickness of the molten slag layer, or quickly control the development of the slag ring.

[0007] Existing technologies disclose irradiating mold powder into a continuous casting mold with microwaves to heat the mold powder. However, microwave radiation has a significant impact on the surrounding environment and workers, requiring sealed operation. But sealing the top of the crystallizer would affect operations such as adding protective slag inside the crystallizer. On the other hand, the microwaves mentioned in the prior art are electromagnetic waves. In modern continuous casting production, the crystallizer has a strong electromagnetic field due to the use of electromagnetic stirring, etc. The microwaves mentioned in the prior art would be affected by the electromagnetic field and the copper wall of the crystallizer. The distribution of electromagnetic waves in the crystallizer, i.e., the irradiation position, is difficult to control accurately, making it difficult to heat the protective slag efficiently and precisely. It can also easily cause the copper wall of the crystallizer to heat up. In actual production, it is very difficult to apply and has poor heating efficiency and effect.

[0008] Existing technology discloses a method of heating molten steel in the initial solidification zone by deploying an induction coil above the free liquid surface on the inner wall of the crystallizer, with the bottom of the coil 5mm-10mm away from the free liquid surface. The induction coil generates an alternating induced electromagnetic field to heat the molten steel in the initial solidification zone, thereby effectively controlling the growth of the meniscus solidification structure, improving the solidification structure, and reducing the probability of oscillation marks and other defects. This method is a heating method for the material inside the crystallizer, heating the molten steel in the initial solidification zone through an induced electromagnetic field, but it does not mention heating the protective slag inside the crystallizer. This method uses an electromagnetic field for heating, and it also suffers from the interaction between the induced electromagnetic field used and the electromagnetic field used for electromagnetic stirring in existing continuous casting crystallizers, as well as the copper wall of the crystallizer. Heating the molten steel in the initial solidification zone has a significant impact on the thickness and strength of the initial billet shell formed in the crystallizer, which not only affects existing continuous casting production but also heats the copper wall of the crystallizer, resulting in unstable heating effects and low efficiency.

[0009] Therefore, to avoid heating the copper wall of the crystallizer and affecting the electromagnetic field of stirring within the crystallizer in continuous casting production, it is crucial to employ non-electromagnetic field heating within the crystallizer, excluding electromagnetic induction heating, microwave heating, and electric heating. Simultaneously, considering the limited space within and near the crystallizer, placing the heating source within or near the crystallizer would hinder the observation and addition of the protective slag; therefore, the heating source needs to be positioned at a certain distance from the crystallizer.

[0010] In summary, there are still challenges in meeting the requirements of continuous casting production due to certain metallurgical properties or states of the protective slag. These include the rapid melting of protective slags with high basicity, high melting temperature, and high viscosity, as well as the rapid melting of protective slags in high-speed continuous casting and the rapid dissolution of high-melting-point substances generated by the reaction between molten steel and the protective slag. Furthermore, there are issues such as the limited space inside and near the crystallizer in continuous casting production, the presence of a strong electromagnetic stirring field within the crystallizer, and the strong interaction between the copper plate in the crystallizer and the electromagnetic field and microwaves within the crystallizer. Therefore, there is an urgent need to develop a rapid and efficient fluxing method for various protective slags, particularly an effective method for in-situ fluxing of protective slags within the crystallizer. This method should avoid obstructing observation of the protective slag within the crystallizer and the influence of electromagnetic fields, and should efficiently eliminate and dissolve the high-melting-point substances generated by the reaction between the protective slag and molten steel, as well as control the abnormal growth of the slag ring. Summary of the Invention

[0011] This study found that in actual continuous casting production, the protective slag in the crystallizer is mainly heated by the molten steel below it, causing a layer of liquid protective slag to form above the molten steel. This liquid protective slag moves downwards along the gap between the copper wall of the crystallizer and the solidified steel shell, playing a lubricating and heat transfer control role between the solidified billet shell and the copper wall of the crystallizer. In continuous casting production, a liquid protective slag layer thickness of 5.0-20 mm is generally required to ensure that the liquid protective slag can continuously enter the gap between the copper wall of the crystallizer and the solidified steel shell, preventing adhesion between the solidified steel shell and the copper wall, and ensuring smooth continuous casting production. In continuous casting production, when the protective slag melting is poor, the liquid slag layer thickness is insufficient, the slag ring is too developed, or the protective slag reacts with active elements in the molten steel to form slag strips, agglomerates, or other blocky high-melting-point substances, it is crucial to achieve in-situ heating of the protective slag within the crystallizer to increase its temperature and promote its melting. In particular, the inflow of liquid protective slag into the copper wall of the crystallizer and the solidified steel shell mainly occurs near the crystallizer wall. Slag rings also adhere to the copper wall of the crystallizer, and slag streaks often form near the copper wall as well. Heating the protective slag near the copper wall of the crystallizer promotes melting in this area, preferentially generating a large amount of liquid protective slag near the meniscus of the molten steel. This significantly increases the thickness of the liquid protective slag at this location, ensuring that the liquid protective slag flows smoothly into the gap between the copper wall and the solidified steel shell of the crystallizer, providing good lubrication. It also controls the development of slag rings in this area, eliminates the formation of slag streaks, and promotes the melting and elimination of high-melting-point refractory substances such as slag migrated from other areas, ensuring the smooth progress of continuous casting. Therefore, in-situ heating of the protective slag, especially the protective slag near the copper wall of the crystallizer, is particularly important for fluxing the process.

[0012] This application also found that the advantages of laser positioning (accurate, rapid heating, minimal or no impact on the observation and addition of protective slag by laser irradiation inside the crystallizer, long-distance heating, and the fact that laser is a light wave and has no effect on the electromagnetic field inside the crystallizer) can be fully utilized. By generating laser at a distance from the protective slag through a laser source and directly irradiating the protective slag, the protective slag can be heated, thereby realizing in-situ heating and melting of the protective slag inside the crystallizer in continuous casting production. Meanwhile, to minimize the impact of the heating system's footprint on the space surrounding the crystallizer, a fiber laser system is employed. This system includes a fiber laser, a fiber optic transmission system, and a heating end. The fiber laser is positioned away from the crystallizer to reduce its space and location requirements, while also avoiding the high-temperature environment near the crystallizer. The heating end, however, is positioned above the crystallizer to irradiate and heat the protective slag inside. To reduce the impact of the high-temperature environment within the crystallizer and its influence on metallurgical operations, the heating end is positioned 100mm-2000mm away from the protective slag, providing relatively distant irradiation. The laser beam generated by the fiber laser is transmitted to the heating end via the fiber optic transmission system, which then irradiates the surface of the protective slag within the crystallizer, achieving in-situ fluxing heating of the protective slag. Furthermore, considering the relatively large area of ​​the protective slag compared to a typical laser spot and the influence of the casting nozzle on laser irradiation, the crystallization process is optimized. Heating the entire protective slag in situ using a single laser spot is challenging. This application proposes several methods for arranging the heating ends, including using supports or robotic arms to hold the heating ends. By adjusting the size, position, and power of the laser beam generated by the heating ends to irradiate the protective slag surface, the protective slag can be heated uniformly or selectively. This can be achieved by fixing the position and angle of the heating ends to continuously heat the protective slag in the target area within the crystallizer, or by setting up multiple heating ends and splicing the laser spots irradiating the slag surface of the crystallizer to achieve complete irradiation and heating of the slag surface, or by rotating and moving the robotic arm to achieve reciprocating cumulative heating of the protective slag in the target area by moving the laser spot back and forth within the crystallizer. This promotes the melting of the protective slag within the crystallizer, increases the thickness of the liquid slag layer, controls excessive slag ring growth, eliminates blocky agglomerates and slag streaks in the protective slag within the crystallizer, increases the consumption of protective slag, ensures the smooth progress of continuous casting, and improves the surface quality of the cast billet.

[0013] Further research revealed that the thickness of the slag layer near the inner wall of the copper in the crystallizer is crucial to the smooth operation of continuous casting. A preferred method was proposed: using a control system and robotic arm to control the power density of the homogenized laser beam emitted from the heating end of the homogenized laser spot to heat the protective slag near the copper wall of the crystallizer. This method avoids the influence of the heating laser beam on the electromagnetic field and copper wall within the crystallizer, and also avoids occupying space within and near the crystallizer. It directly and precisely heats the protective slag within the crystallizer with high heating efficiency. It can efficiently heat the protective slag within the crystallizer, regulate its temperature and melting rate, and control the thickness of the slag layer. It can precisely control the temperature, melting, and slag layer thickness of the protective slag near the copper wall of the crystallizer, effectively controlling the development of the slag ring within the crystallizer, and controlling the formation of slag streaks and agglomerates in the protective slag, thus effectively ensuring the smooth operation of continuous casting production.

[0014] To address the aforementioned technical problems, this application provides a method for in-situ fluxing of protective slag within a crystallizer, comprising: setting up a heating device above the crystallizer in continuous casting production to in-situ heat the protective slag above the molten steel in the crystallizer, thereby increasing the temperature of the protective slag, promoting the melting of the protective slag within the crystallizer, increasing the thickness of the liquid slag layer, controlling excessive growth of the slag ring, eliminating blocky agglomerates and slag streaks in the protective slag within the crystallizer, increasing the consumption of protective slag, ensuring the smooth progress of continuous casting, and improving the surface quality of the cast billet.

[0015] As a preferred embodiment of the in-situ fluxing method for protective slag inside a crystallizer described in this application, the specific method of in-situ heating is as follows: a fiber laser system is used, the system including a fiber laser, a fiber transmission system and a heating end. The fiber laser is placed 5m-50m away from the crystallizer, and the heating end is placed 100mm-2000mm above the crystallizer and away from the protective slag inside the crystallizer. The fiber laser system generates a laser beam with a wavelength in the range of 600nm-12000nm. The fiber transmission system transmits the laser generated by the fiber laser to the heating end. The heating end irradiates the surface of the protective slag inside the crystallizer with the laser beam, thereby realizing in-situ fluxing heating of the protective slag inside the crystallizer.

[0016] As a preferred embodiment of the in-situ fluxing method for protective slag within a crystallizer described in this application, a laser collimator is used to collimate and shape the initial high-energy laser output from the laser through a reasonable design of the optical path within the fiber laser system, generating a uniformly distributed light spot with a uniform energy density. The energy transition zone of 10%-80% at the edge of the light spot is ≤5.0mm, that is, the length of the light spot area from the edge to where the energy density is less than 80% of the energy density at the center of the light spot is controlled to be ≤5.0mm. This achieves uniform heating of the area covered by the light spot, avoids excessively high local energy density of the light spot, which would cause the protective slag in the radiation area to heat up too much, leading to high-temperature vaporization of some easily vaporizable substances in the protective slag. The maximum temperature of the laser-heated slag surface is controlled to be ≤1500℃.

[0017] As a preferred embodiment of the in-situ fluxing method for protective slag within a crystallizer described in this application, the heating end is positioned above the continuous casting crystallizer via a support or robotic arm. The generated laser beam is perpendicular to the surface of the protective slag within the crystallizer or maintains an angle with the surface of the protective slag within the crystallizer. The position and angle of the heating end remain unchanged during the heating process, continuously heating the protective slag in the target heating area within the crystallizer. The laser power generated by the fiber laser system is greater than 1kW. The laser beam emitted by the heating end generates a laser spot on the surface of the protective slag within the crystallizer, and the protective slag at the laser spot is heated by the laser. For slab, square billet, and rectangular billet continuous casting machines, the laser spot generated by the heating end is set to be rectangular or rectangular, with its edge adjacent to the copper wall of the crystallizer parallel to the nearest copper wall of the crystallizer, to ensure that the protective slag within the crystallizer receives relatively uniform heating. For round billet continuous casting machines, the laser spot generated by the heating end can be set to be arc-shaped, semi-circular, crown-shaped, or arc-shaped, with its outer arc edge as far as possible. The laser spot can be parallel to the copper wall of the adjacent mold. For continuous casting of irregular billets, if the submerged entry nozzle is located at the center of the web, heating ends are set on both sides of the nozzle. The laser spot is set as a long strip or rectangular spot with the long side parallel to the web of the irregular billet, or a polygonal spot with each side parallel to the copper wall of the adjacent mold. For continuous casting of irregular billets, if the submerged entry nozzle is located at the center of the flanges on both sides of the web, heating ends are set above the center of the web and / or above the ends of the flanges on both sides, depending on the melting of the protective slag in the mold. The laser heating spot at the web is set as a rectangular spot with its long side parallel to the copper wall of the web of the adjacent irregular billet. The laser heating spot at the flange ends is a polygonal spot similar to the cross-sectional shape of the flange end or a parallelogram spot with a pair of sides parallel to the inner copper plate of the adjacent flange. The purpose of setting the spot shape is to promote the melting of the protective slag in the mold in a balanced and rapid manner, increase the thickness of the liquid slag layer, eliminate blocky agglomerates and slag strips in the protective slag in the mold, and control the excessive growth of the slag ring.

[0018] As a preferred embodiment of the in-situ fluxing method for protective slag within a crystallizer described in this application, the heating end is held by a support or a robotic arm. The size, position, and power of the laser beam generated by the heating end irradiating the protective slag surface are adjusted to uniformly or selectively heat the protective slag. Continuous heating of the target area of ​​the protective slag within the crystallizer is achieved by fixing the position and angle of the heating end, or by rotating and moving the robotic arm to achieve reciprocating cumulative heating of the target area of ​​the protective slag by moving the laser beam back and forth across the protective slag surface within the crystallizer. For uniform heating of the protective slag, the laser beam is set to have the same area and shape as the entire slag surface within the crystallizer, and the position and angle of the heating end are fixed, resulting in a uniform beam that covers and irradiates the entire heated slag surface within the crystallizer. Alternatively, the laser beam can be set smaller than the area of ​​the slag surface to be heated within the crystallizer, but by moving and rotating the position and angle of the heating end with the robotic arm, the resulting uniform beam scans and irradiates the entire slag surface within the crystallizer, achieving cumulative uniform heating of the entire slag surface within the crystallizer, meaning that all areas of the slag surface receive the same cumulative power of laser heating irradiation. Alternatively, several heating ends can be installed above the crystallizer. The laser heating spot generated by each heating end is smaller than the entire slag surface area. However, by reasonably arranging the position and angle of each heating end, the combination of homogenized light spots generated by each heating end can cover the entire slag surface inside the crystallizer. The selective heating of the protective slag involves setting the laser spot to be the same area and shape as the target slag surface to be heated within the crystallizer. The position and angle of the heating end are fixed, and the generated homogenized light spot covers and irradiates the target slag surface to be heated within the crystallizer. Alternatively, the laser spot can be set smaller than the area of ​​the target slag surface to be heated within the crystallizer. However, by moving and rotating the position and angle of the heating end with a robotic arm, the generated homogenized light spot repeatedly scans and irradiates the target slag surface to be heated within the crystallizer, achieving cumulative heating of the target slag surface. Or, several heating ends can be installed above the crystallizer. The laser heating spot generated by each heating end is smaller than the area of ​​the target slag surface to be heated. However, by reasonably arranging the position and angle of each heating end, the combination of homogenized light spots generated by each heating end can cover the entire target slag surface to be heated within the crystallizer.

[0019] As a preferred embodiment of the in-situ fluxing method for protective slag in the crystallizer described in this application, during continuous casting, the heating area and heating power of the laser spot are set at the heating end. The distance between the laser spot and the copper wall is controlled to be 0-150.0 mm, preferably controlled to be 0-5.0 mm. The size of the laser spot perpendicular to the copper wall of the crystallizer is 15.0-300.0 mm. The depth of the liquid slag layer near the copper wall in the crystallizer is preferably kept at 6.0-30.0 mm. Blocky agglomerates and refractory slag strips near the copper wall in the crystallizer are preferably eliminated. The shape and size of the protective slag ring in the crystallizer are preferably suitable for the smooth flow of continuous casting. The liquid slag near the copper wall of the crystallizer is preferably allowed to enter the gap between the solidified billet shell and the copper wall. The slag consumption in the continuous casting production of slabs is preferably greater than 0.2 kg / t steel.

[0020] As a preferred embodiment of the in-situ fluxing method for protective slag within a crystallizer described in this application, the growth of the slag ring within the crystallizer is adjusted by varying the distance between the laser spot and the copper plate of the crystallizer. Decreasing the distance between the laser spot and the copper plate wall inhibits slag ring growth, while increasing the distance promotes slag ring growth. The height of the slag ring is controlled to be 2.0-10 mm. Alternatively, the growth of the slag ring can be controlled by adjusting the power density of the laser spot. Higher power density results in a less developed slag ring, while lower power density leads to a more developed slag ring. The average power density of the laser spot is controlled to be 10-500 W / cm². 2 The power density of the laser spot is controlled by the control system by controlling the power of the fiber laser system.

[0021] As a preferred embodiment of the in-situ fluxing method of the protective slag in the crystallizer described in this application, the method is applicable to continuous casting of high-alumina steel with a protective slag basicity greater than 1.20, or / and aluminum content greater than 1.0% in the steel, or / and manganese content greater than 5.0% in the steel, or / and titanium content higher than 0.05% in stainless steel, or / and protective slag melting temperature greater than 1300℃, or / and casting speed greater than 1.5m / min.

[0022] As a preferred embodiment of the in-situ fluxing method for protective slag in a crystallizer described in this application, the laser spot is reciprocated across the protective slag surface within the crystallizer by rotating and moving a robotic arm, thereby achieving reciprocating cumulative heating of the protective slag in the target area. By controlling the robotic arm, the position and angle of the heating end of the homogenized laser spot are controlled, thereby controlling the laser spot to move and scan along / or parallel to the inner side of the copper wall of the crystallizer. The scanning speed of the spot on the slag surface is controlled to be 0.5-6.0 m / min, and the frequency of the laser spot irradiation heating of the target heating protective slag surface within the crystallizer is ≥1 s / min.

[0023] As a preferred embodiment of the in-situ fluxing method for protective slag in a crystallizer described in this application, a shielding cover needs to be installed around the heating end. Through water cooling of the shielding cover and air cooling inside the cover, the heating end is kept in a good temperature environment with a temperature of less than 80°C, ensuring its normal operation and long service life.

[0024] The beneficial effects of this application are as follows: This application provides a method for in-situ fluxing of protective slag within the crystallizer. In the continuous casting production of high-alumina steel, semi-peritectic steel, titanium- or rare-earth-containing steel, and high-alloy steel, the protective slag often melts poorly in the crystallizer due to factors such as high basicity of the protective slag, significant changes in the composition and properties of the protective slag reacting with the molten steel, and low molten steel temperature. This results in problems such as fish formation, well-developed slag rings, thin liquid slag layers, and low slag consumption. On the other hand, with the development of high-speed continuous casting, the amount of protective slag consumed per unit of steel produced by continuous casting has decreased, leading to insufficient lubrication in the crystallizer and making it easy for problems such as steel sticking and leakage to occur. To address these issues, this application employs a fiber laser system. The laser heating end of the fiber laser system is positioned 100mm-2000mm above the molded slag inside the mold, generating a laser beam with a wavelength in the range of 600nm-12000nm. This laser beam is then directed onto the surface of the molded slag inside the molded slag, achieving in-situ fluxing heating of the molded slag. By adjusting the size, position, and power of the laser beam irradiating the surface of the molded slag, the molded slag can be uniformly or selectively heated. This promotes melting of the molded slag within the molded slag, increases the thickness of the liquid slag layer, controls excessive slag ring growth, eliminates blocky agglomerates and slag streaks in the molded slag, increases the consumption of molded slag, and ensures smooth continuous casting. This application method fully utilizes the advantages of laser heating, such as high speed, easy adjustment of heating power, precise and controllable heating position, uniform heating spot power density, and long-distance laser irradiation. It precisely and rapidly heats the protective slag in the crystallizer in situ and adjusts the state of the protective slag in continuous casting production. This eliminates blocky agglomerates in the protective slag, controls the development of the slag ring, adjusts the viscosity, liquid slag layer thickness, and slag consumption of the protective slag, controls the depth of oscillation marks on the cast billet, avoids steel sticking accidents in continuous casting production, improves the surface quality of the cast billet, and ensures the continuous casting production of difficult-to-cast steel grades such as high-alumina steel, high-manganese steel, semi-peritectic steel, titanium- or rare-earth steel, and high-alloy steel, thus providing a smooth guarantee for high-speed continuous casting production.

[0025] Based on the behavior of adding, melting, and consuming protective slag in continuous casting production, and the functional requirements of protective slag for various steel grades, cross sections, and casting speeds, this application proposes a method for in-situ fluxing of protective slag within the crystallizer. This method utilizes a laser-generated laser spot to irradiate the surface of the protective slag within the crystallizer, heating it. Furthermore, it discloses various laser-heated protective slag working modes according to the requirements of different continuous casting production processes. This achieves the goals of rapidly fluxing the protective slag, controlling excessive slag ring growth, and dissolving high-melting-point refractory materials in the protective slag. This ensures efficient continuous casting operation, improves the surface quality of the cast billet, and guarantees smooth continuous casting production of difficult-to-cast steel grades such as high-alumina steel, high-manganese steel, semi-peritectic steel, and titanium- or rare-earth-containing steel. The beneficial effects of the technical solution provided in this application include at least the following: providing a new and flexible method for smooth production of high-speed continuous casting, high-alumina steel, high-manganese steel, semi-peritectic steel, titanium-containing and rare-earth stainless steel, and improving the surface quality of the billet; significantly increasing the melting rate of the protective slag in the crystallizer during the continuous casting growth process and increasing the depth of the liquid slag layer; providing effective means for controlling the growth of the protective slag ring in the crystallizer and dissolving high-melting-point substances such as slag bars and slag inclusions; and significantly reducing the risk of sticking and leakage, and reducing defects such as surface cracks and inclusions on the billet. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the technical solution in this application; Figure 2 This is a schematic diagram of the method for heating protective slag using multiple laser spots combined according to this application; Figure 3 This is a schematic diagram of the method for accumulating heating of protective slag using a moving laser spot, as described in this application.

[0028] Reference numerals: 1-Fiber laser, 2-Fiber optic transmission system, 3-Heating end, 4-Laser beam, 5-Laser spot, 6-Protective slag powder layer, 7-Protective sintering layer, 8-Protective slag liquid layer, 9-Solid slag film, 10-Liquid slag layer, 11-Bill shell, 12-Slag ring, 13-Molder, 14-Sprue, 15-Molder copper wall, 16-Protective slag surface, 17-Moving laser spot, 18-Moving direction.

[0029] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0030] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0031] This application provides a method for in-situ fluxing with protective slag within a crystallizer, comprising: Please see Figure 1 , Figure 1 This is a schematic diagram of the technical solution in this application. A heating end 3 of a fiber laser system is installed above the crystallizer 13 used in continuous casting. The system includes a fiber laser 1, a fiber optic transmission system 2, and a heating end 3. The fiber laser is positioned 5m-50m away from the crystallizer, and the heating end is positioned 100mm-2000mm above the crystallizer, a distance from the protective slag inside the crystallizer. The fiber laser system generates a laser beam 4 with a wavelength in the range of 600nm-12000nm. The fiber optic transmission system transmits the laser generated by the fiber laser to the heating end, which irradiates the surface 16 of the protective slag inside the crystallizer with the laser beam. This achieves in-situ fluxing heating of the protective slag inside the crystallizer, increases the temperature of the protective slag, promotes its melting, eliminates blocky agglomerates within the protective slag, controls the development of the protective slag ring, adjusts the thickness of the molten protective slag layer, ensures smooth continuous casting, and improves the surface quality of the cast billet. The billet and protective slag structure includes: protective slag powder layer 6, protective slag sintering layer 7, protective slag liquid layer 8, solid slag film 9, liquid slag layer 10, billet shell 11, and slag ring 12; Preferably, the heating end is located above the continuous casting crystallizer, and the laser beam can be perpendicular to the surface of the protective slag inside the crystallizer or at an angle to the surface of the protective slag inside the crystallizer; heating ends can be set on both sides of the immersion nozzle 14 inside the crystallizer, with the laser outlet of the heating end located 100mm-2000mm away from the protective slag inside the crystallizer, and the rated power of the heating end is greater than 5kW.

[0032] Preferably, for slab, square billet, and rectangular billet continuous casting machines, the laser spot 5 generated at the heating end can be set to be rectangular or rectangular, with its side length parallel to the adjacent copper wall of the crystallizer, to ensure that the protective slag in the crystallizer is heated more evenly; for round billet continuous casting machines, the laser spot generated at the heating end can be set to be a semi-circular, crown-shaped, or arc-shaped spot with its arc edge parallel to the copper wall of the crystallizer, or it can be set to be a rectangular, rectangular, or polygonal spot symmetrical on both sides of the sprue; for irregular billet continuous casting, if the submerged entry nozzle is located at the center of the web, heating ends can be set on both sides of the nozzle, and the laser spot can be set to be a long strip or rectangular spot with its long side parallel to the web of the irregular billet, or it can be a spot with each side parallel to the adjacent crystallizer. Polygonal laser spots on the copper wall; for continuous casting of irregular billets, such as when the submerged entry nozzle is located at the center of the flanges on both sides of the web, heating ends can be set above the center of the web or / and above the ends of the flanges on both sides, depending on the melting of the protective slag in the crystallizer. The laser heating spot at the web is set as a rectangular spot with the long side parallel to the web of the irregular billet, and the laser heating spot at the flange ends can be a polygonal spot similar to the cross-sectional shape of the flange end or a parallelogram spot with a pair of sides parallel to the inner copper plate of the adjacent flange. The purpose of setting the shape of the laser spot is to promote the melting of the protective slag in the crystallizer in a balanced and rapid manner, increase the thickness of the liquid slag layer, eliminate blocky agglomerates and slag strips in the protective slag in the crystallizer, and control the overproduction of slag rings.

[0033] Preferably, based on the continuous casting process, the heating area and heating power of the irradiation spot at the heating end are set to prioritize ensuring that the depth of the liquid slag layer in the crystallizer is 8-20mm, prioritize eliminating blocky agglomerates in the crystallizer, prioritize ensuring that the shape and size of the protective slag ring in the crystallizer are suitable for the smooth flow of continuous casting, and control the height of the slag ring, i.e. the distance from the top of the slag ring to the copper wall of the crystallizer, to be 2.0-20mm. Prioritize ensuring that the slag consumption in slab continuous casting production is greater than 0.2kg / t steel.

[0034] Preferably, for thin slag layers in continuous casting production, such as high-speed continuous casting and high-manganese steel continuous casting, a smaller laser spot can be used. This laser spot is positioned near the center line of the slag surface in the crystallizer, with its edge parallel to the adjacent copper wall of the crystallizer. The edge of the spot is further away from the adjacent copper wall, increasing the energy density of the laser spot and promoting the melting of the protective slag in the central region of the crystallizer. The melted protective slag then rapidly sinks to the bottom layer under gravity, increasing the depth of the slag layer. Simultaneously, the properties of the protective slag around the laser spot are maintained as much as possible, preserving the original melting pattern of the protective slag around the crystallizer and maintaining the original slag ring. Pattern formation and ablation: For excessive slag ring growth and excessive slag bars in the mold flux during continuous casting, a larger laser spot (approximately 2-10 mm) can be used to heat the copper wall of the mold flux near the mold flux, promoting the melting of slag bars and slag rings. For the presence of high-melting-point refractory substances such as lumpy agglomerates in the mold flux during continuous casting, a larger laser spot with higher power density can be used to promote the ablation of these substances and inhibit their precipitation and growth in the slag layer of the mold flux.

[0035] Preferably, through the rational design of the optical path within the fiber laser system, a laser collimator is applied to collimate and shape the initial high-energy laser output from the laser, generating a uniformly distributed beam with a uniform energy density. The energy transition zone at the edge of the beam (10%-80%) is ≤5.0mm, meaning the length of the beam area from the edge to the center (where the energy density is less than 80% of the center's energy density) is controlled to be ≤5.0mm. This ensures uniform heating of the beam area and avoids excessively high local energy density, which could lead to excessively high temperatures in the protective slag in the radiation area and cause high-temperature vaporization of some easily vaporizable substances in the protective slag. In principle, the maximum temperature of the slag surface heated by the laser is controlled to be ≤1500℃.

[0036] Preferably, when the mold flux exhibits numerous lumpy slag inclusions, a large number of slag strips, a well-developed slag ring, and a thin liquid slag layer, the power at the heating end can be increased to promote the melting of the mold flux, increase the thickness and temperature of the liquid slag layer, further promote the melting of lumpy slag inclusions and strips, and reduce the degree of slag ring development. After the slag inclusions and strips disappear, or the slag ring development is controlled, or the liquid slag layer thickness meets the standard, the power of laser heating can be gradually reduced until the thickness and temperature of the liquid slag layer are controlled to a level conducive to the smooth operation of current continuous casting production and a good slag consumption level. Furthermore, the growth of the slag ring within the mold can be adjusted by changing the distance between the laser spot and the copper plate of the mold. Decreasing the distance between the laser spot and the copper plate wall inhibits slag ring growth, while increasing the distance promotes slag ring growth. The average power density of the laser spot is controlled at 5-150 W / cm². 2 .

[0037] Preferably, the process involves adjusting the size, position, and power of the laser beam generated at the heating end to irradiate the protective slag surface, thereby uniformly or selectively heating the protective slag. Please refer to [link / reference]. Figure 2 , Figure 2 This is a schematic diagram of the method for heating protective slag using multiple laser spot combinations according to this application; the laser spot 5 is set to be the same as the area and shape of the entire slag surface inside the crystallizer for uniform heating of the protective slag, and the position and angle of the heating end are fixed, so that the generated uniform spot covers and irradiates the entire heated protective slag surface 16 inside the copper wall 15 of the crystallizer.

[0038] Please see Figure 3 , Figure 3 This is a schematic diagram of the method for cumulative heating of protective slag using a moving laser spot according to this application. The laser spot is set to be smaller than the area of ​​the slag surface to be heated in the crystallizer. However, by moving and rotating the position and angle of the heating end through a robotic arm, a uniform moving laser spot 17 is generated to reciprocate and scan the entire slag surface in the crystallizer. The moving direction 18 is controllable, so as to achieve cumulative uniform heating of the entire slag surface in the crystallizer, that is, each area of ​​the slag surface receives laser heating irradiation with the same cumulative power.

[0039] Preferably, by installing several heating ends above the crystallizer, the laser heating spot generated by each heating end is smaller than the entire slag surface area. However, by reasonably arranging the position and angle of each heating end, the combination of uniform light spots generated by each heating end covers the entire slag surface inside the crystallizer. The selective heating of the protective slag involves setting the laser spot to be the same area and shape as the target slag surface to be heated within the crystallizer, fixing the position and angle of the heating end, and generating a uniform light spot that covers and irradiates the target slag surface to be heated within the crystallizer. Alternatively, the laser spot can be set smaller than the area of ​​the target slag surface to be heated within the crystallizer, but by moving and rotating the position and angle of the heating end with a robotic arm, the generated uniform light spot repeatedly scans and irradiates the target slag surface to be heated within the crystallizer, achieving cumulative heating of the target slag surface. Or, by installing several heating ends above the crystallizer, the laser heating spot generated by each heating end is smaller than the area of ​​the target slag surface to be heated, but by reasonably arranging the position and angle of each heating end, the combination of uniform light spots generated by each heating end covers the entire target slag surface to be heated within the crystallizer.

[0040] Preferably, the method is applicable to continuous casting production of slabs, irregular billets, large square billets or rectangular billets with a continuous casting speed greater than 1.5 m / min, or / and a protective slag basicity greater than 1.20, or / and a high-alumina steel with an aluminum content greater than 1.0%, or / and a steel with a manganese content greater than 5.0%, or / and a stainless steel with a titanium content higher than 0.1%, or / and a protective slag melting temperature greater than 1300℃.

[0041] Preferably, the position of the heating end, the laser irradiation angle, and the size of the irradiation laser spot are reasonably set to avoid the laser directly irradiating the copper plates around the crystallizer and the immersion nozzle.

[0042] Preferably, in a method for in-situ fluxing of protective slag within a crystallizer, a shielding cover needs to be installed around the heating end. Through water cooling of the shielding cover and air cooling inside the cover, the heating end is kept in a good temperature environment (temperature less than 80°C), ensuring its normal operation and long service life.

[0043] The technical solution of this application will be further described below with reference to specific embodiments.

[0044] Example 1

[0045] A steel plant continuously casts slabs to produce SS400 steel. The slab cross-section is 250mm×2200mm, and the casting speed is 1.2m / min. This steel grade is highly susceptible to cracking. The basicity of the protective slag used in continuous casting is high, with a binary basicity of 1.65, and the melting temperature of the protective slag is 1310℃. At the same time, in order to control cracks and internal quality, the superheat of the molten steel is kept low, controlled at 10-20℃. During continuous casting, the melting rate of the protective slag in the crystallizer is slow, and the thickness of the liquid slag layer is 6-8mm.

[0046] Two fiber laser systems were installed on the continuous casting production platform. The fiber lasers were positioned 50m away from the crystallizer, with the heating ends positioned above the crystallizer and 2000mm away from the protective slag inside the crystallizer. The heating ends of the system were positioned above both sides of the immersion nozzle of the crystallizer. The laser wavelength generated by each heating end was 1064nm. The laser beam only irradiated the surface of the protective slag and did not irradiate the surface of the copper plate inside the crystallizer. The head of each heating end was 0.5m away from the surface of the protective slag, and the laser spot formed by the laser irradiating the slag surface was 900mm×100mm. Through the optimization of the optical system within the laser heating system, the collimation and shaping of the output laser beam were achieved, and the energy transition zone of 10%-80% at the edge of the spot was ≤4.0mm. The length direction of the generated laser spot was parallel to the copper plate on the wide side of the crystallizer, located near the center line of the slag surface inside the crystallizer, and 75mm away from the copper plates on both sides of the wide side of the crystallizer. The distance between the laser spots on both sides of the nozzle and the copper plates on the narrow side of the crystallizer was 100mm. The maximum temperature of the slag surface heated by laser is controlled to be ≤1500℃; the heating end is installed in a shielded steel cover, and the laser irradiates the surface of the billet through a narrow slit at the bottom of the shield. The shield is cooled by a water chiller, and the temperature inside the cover is controlled to be less than 40℃; the actual working power of the heating ends on both sides of the nozzle is set to 38kW, and the average power density of the laser spot is 42W / cm². 2The slag surface heating temperature reaches 1300℃, the thickness of the liquid slag layer of the protective slag increases to 15-17mm, the height of the slag ring is controlled within the range of 5.0-7.0mm, and the slag consumption of the protective slag reaches 0.4kg / t steel, ensuring smooth continuous casting.

[0047] Example 2

[0048] A steel plant produces high-alumina steel by continuous casting of slabs. The slab cross-section is 220mm×2200mm, and the casting speed is 1.2m / min. This steel grade is produced using non-reactive protective slag. The melting temperature of the protective slag is relatively high, reaching 1410℃. During continuous casting, the protective slag melts slowly in the crystallizer, and the thickness of the liquid slag layer is 5-6mm.

[0049] Two fiber laser systems were installed on the continuous casting production platform. The fiber lasers were positioned 50m away from the crystallizer, with the heating ends positioned above the crystallizer and 2000mm away from the protective slag inside the crystallizer. The heating ends of the system were positioned above both sides of the immersion nozzle of the crystallizer. The laser wavelength generated by each heating end was 1080nm. The laser beam only irradiated the surface of the protective slag and did not irradiate the surface of the copper plate inside the crystallizer. The head of each heating end was 0.6m away from the surface of the protective slag, and the laser spot generated on the surface of the protective slag of the crystallizer was 1000mm×60mm. Through optimization of the optical system within the laser heating system, collimation and shaping of the output laser beam were achieved, and the energy transition zone of 10%-80% at the edge of the spot was ≤4.0mm. The length direction of the generated laser spot was parallel to the wide copper plate of the crystallizer, located near the center line of the slag surface inside the crystallizer, and 80mm away from both sides of the copper plate on the wide side of the crystallizer. The distance between the laser spots on both sides of the nozzle and the narrow copper plate of the crystallizer was 50mm. The maximum temperature of the slag surface heated by laser is controlled to be ≤1500℃; the heating end is installed in a shielded steel cover, and the laser irradiates the surface of the billet through a narrow slit at the bottom of the shield. The shield is cooled by a water chiller, and the temperature inside the cover is controlled to be less than 42℃; the actual working power of the heating ends on both sides of the nozzle is set to 30kW, and the average power density of the laser spot is 50W / cm². 2 The protective slag surface heating temperature reached 1400℃, the thickness of the liquid slag layer of the protective slag increased to 10-12mm, the height of the slag ring around the copper wall of the crystallizer was controlled within the range of 5.0-8.0mm, and the slag consumption of the protective slag reached 0.38kg / t steel, ensuring the smooth operation of continuous casting.

[0050] Example 3

[0051] A steel plant produces low-carbon steel through continuous casting of slabs. The slab cross-section is 250mm×1580mm, and the casting speed is 3.0m / min. The continuous casting process uses a special protective slag with low melting temperature, low viscosity, and good lubricity for high casting speed. The melting temperature of the protective slag is 1112℃, and the viscosity of the protective slag at 1300℃ is 0.14Pa·s. During continuous casting, the melting rate of the protective slag in the crystallizer cannot meet the requirements of high casting speed, and the thickness of the liquid slag layer is 6-8mm, resulting in multiple leakage accidents.

[0052] Two fiber laser systems were installed on the continuous casting production platform. The fiber lasers were positioned 5m away from the crystallizer, with the heating ends placed 100mm above the crystallizer and 100mm away from the protective slag inside. The heating ends of the system were positioned above both sides of the immersion nozzle of the crystallizer. The laser wavelength generated by each heating end was 1060nm, and the laser beam only irradiated the surface of the protective slag, not the surface of the copper plate inside the crystallizer. The head of each heating end was 0.4m away from the surface of the protective slag, and the laser spot size was 650mm×100mm. Through optimization of the optical system within the laser heating system, collimation and shaping of the output laser beam were achieved, with the energy transition zone at the edge of the spot (10%-80%) ≤3.0mm. The length direction of the generated laser spot was parallel to the wide copper plate of the crystallizer, located near the center line of the slag surface inside the crystallizer, and 75mm away from both sides of the wide copper plate. The distance between the laser spots on both sides of the nozzle and the narrow copper plate of the crystallizer was 50mm. The maximum temperature of the slag surface heated by laser is controlled to be ≤1500℃; the heating end is installed in a shielded steel cover, and the laser irradiates the surface of the billet through a narrow slit at the bottom of the shield. The shield is cooled by a water chiller, and the temperature inside the cover is controlled to be less than 38℃; the actual working power of the heating ends on both sides of the nozzle is set to 50kW, and the average power density of the laser spot is 77W / cm². 2 The maximum temperature of the protective slag surface reached 1120℃, the thickness of the liquid slag layer of the protective slag increased to 10-14mm, the height of the slag ring was controlled at 4.0-6.0mm, and the slag consumption of the protective slag reached 0.32kg / t steel, ensuring smooth continuous casting.

[0053] Example 4

[0054] A steel plant was producing 321 stainless steel by continuous casting of slabs. The titanium content in the steel was 0.45%. The cross-section of the slab produced by continuous casting was 200mm×1280mm, the casting speed was 1.2m / min, and the basicity of the protective slag used in continuous casting was 0.92. During continuous casting, blocky slags appeared in the protective slag, and many slag inclusions and impurities appeared in the produced slabs and steel products. There were also several incidents of sticking and leakage of steel.

[0055] Two fiber laser systems were installed on the continuous casting production platform. The fiber lasers were positioned 5m away from the crystallizer, with the heating ends placed 100mm above the crystallizer and 100mm away from the protective slag inside. The heating ends of the system were positioned above both sides of the immersion nozzle of the crystallizer. The laser wavelength generated by each heating end was 1064nm, and the laser beam only irradiated the surface of the protective slag, not the surface of the copper plate inside the crystallizer. The head of each heating end was 0.5m away from the surface of the protective slag, and the laser spot size was 550mm×180mm. Through optimization of the optical system within the laser heating system, collimation and shaping of the output laser beam were achieved, with the energy transition zone at the edge of the spot (10%-80%) ≤1.0mm. The length direction of the generated laser spot was parallel to the wide copper plate of the crystallizer, and the distance between the side length of the laser spot and the nearest copper plate of the crystallizer was 10mm. The distance between the laser spot on both sides of the nozzle and the narrow copper plate of the crystallizer was also 10mm. The maximum temperature of the slag surface heated by laser is controlled to be ≤1500℃; the heating end is installed in a shielded steel cover, and the laser irradiates the surface of the billet through a narrow slit at the bottom of the shield. The shield is cooled by a water chiller, and the temperature inside the cover is controlled to be less than 40℃; the actual working power of the heating ends on both sides of the nozzle is set to 20kW, and the average power density of the laser spot is 20W / cm². 2 The maximum temperature of the protective slag surface is 1450℃, the thickness of the liquid slag layer is stable at 12-15mm, the height of the slag ring is controlled at 6.0-8.0mm, the fish in the protective slag disappears, and the slag consumption of the protective slag reaches 0.45kg / t steel, ensuring the smooth operation of continuous casting.

[0056] Example 5

[0057] A steel plant continuously cast 55C steel using irregularly shaped billets. This steel grade is crack-sensitive. The cross-section of the billets produced by continuous casting is 750mm×370mm×90mm, and the casting speed is 1.2m / min. During continuous casting, the nozzle is located at the center of the web, the basicity of the protective slag used is 1.32, and the melting temperature is 1280℃. During continuous casting, the slag layer is relatively thin, generally around 5-8mm thick, especially in the web area where the slag layer thickness is sometimes as low as 4mm. The produced irregularly shaped billets show many surface cracks, and there have been multiple incidents of sticking and leaking steel.

[0058] Two fiber laser systems were installed on the continuous casting production platform. The fiber lasers were positioned 25m away from the crystallizer, with the heating ends positioned above the crystallizer and 1000mm above the protective slag inside. The heating ends of the system were positioned above both sides of the crystallizer's immersion nozzle. Each heating end generated a laser wavelength of 1080nm, and the laser beam only irradiated the surface of the protective slag, not the surface of the copper plate inside the crystallizer. The head of each heating end was 0.5m away from the surface of the protective slag, and the laser spot size was 340mm × 60mm. The laser heating system... The optimization of the internal optical system has enabled collimation and shaping of the output laser beam, with the energy transition zone at the edge of the laser spot (10%-80%) ≤ 1.0 mm. Specifically, the length of the laser spot region from the edge to the center, where the energy density is less than 80% of the center energy density, is controlled to be ≤ 1.0 mm. The length direction of the generated laser spot is parallel to the copper plate of the crystallizer web, the distance between the laser spot and the copper wall is controlled to be 4.0 mm, and the dimension of the laser spot perpendicular to the copper wall of the crystallizer is 100.0 mm. Priority is given to ensuring that the depth of the liquid slag layer adjacent to the copper wall in the crystallizer is 15.0 mm. The maximum temperature of the slag surface heated by laser is controlled to be ≤1500℃; the heating end is installed in a shielded steel cover, and the laser irradiates the surface of the billet through a narrow slit at the bottom of the shield. The shield is cooled by a water chiller, and the temperature inside the cover is controlled to be less than 30℃; the actual working power of the heating ends on both sides of the nozzle is set to 15kW, and the average power density of the laser spot is 74W / cm². 2 The surface temperature of the protective slag reached a maximum of 1400℃, the thickness of the liquid slag layer was stable at 10-12mm, the height of the slag ring was controlled at 4.0-9.0mm, the slag consumption of the protective slag increased from 0.65kg / t to 0.8kg / t steel, the surface cracks of the produced irregular billets were controlled, and the accident of steel leakage due to crystallizer adhesion no longer occurred.

[0059] Example 6

[0060] A steel plant continuously casts large round billets to produce sub-peregrine steel. The cross-section of the billet produced by continuous casting is Ф1380mm, the casting speed is 0.1m / min, and high-basicity protective slag is used with a precision of 1.50. The melting temperature of the protective slag is 1332℃. During continuous casting, the melting rate of the protective slag in the crystallizer cannot meet the requirements of high casting speed. The thickness of the liquid slag layer is 6-8mm, and there are many cracks on the surface of the billet.

[0061] Fiber laser systems are installed on both sides of the immersion nozzle of the crystallizer. Each system includes a fiber laser, a fiber transmission system, and a laser heating end. The fiber laser is positioned 8.0m away from the crystallizer, and the heating end is mounted above the crystallizer via a support. Each laser heating end generates a laser with a wavelength of 1060nm, and the laser spot is an arc with an outer diameter of 1380mm, an inner diameter of 1180mm, and a length of 2010mm. Through optimization of the optical system within the fiber laser system, collimation and shaping of the output laser beam are achieved, with a 10%-80% energy transition zone at the edge of the spot ≤3.0mm. The position and angle of the laser heating end are set so that the long arc direction of the generated laser spot is aligned with the width of the crystallizer. The laser beams on both sides of the nozzle are parallel to the copper wall and 1mm away from the adjacent copper wall of the crystallizer. The laser beams on both sides of the nozzle align with each other, covering the protective slag within a 100mm radius of the copper wall inside the crystallizer. This ensures priority heating of the protective slag near the copper wall, and the laser beam only irradiates the surface of the protective slag, not the surface of the copper wall inside the crystallizer. The head of each laser heating end is 0.5m away from the surface of the protective slag. The laser heating end is installed in a shielded steel cover, and the laser beam irradiates the surface of the billet through the arc-shaped slit at the bottom of the shield. The shield is cooled by a water chiller, and the temperature inside the cover is controlled to be less than 38℃. The actual working power of the laser heaters on both sides of the nozzle is set to 30kW, and the average power density of the laser beam is 15W / cm². 2 The thickness of the liquid slag layer of the protective slag near the copper wall (0-50mm away from the copper wall) is increased to 10-15mm. The maximum temperature of the protective slag surface after being heated by laser is 1320℃. The height of the slag ring is controlled at 3.0-6.0mm. The slag consumption of the protective slag reaches 0.40kg / t steel, ensuring the smooth operation of continuous casting.

[0062] Example 7

[0063] A steel plant was producing high-alumina steel by continuous casting of slabs. The aluminum content of the steel was 2.58%. The cross-section of the slab produced by continuous casting was 200mm×2280mm, the casting speed was 1.2m / min, and the basicity of the protective slag used in continuous casting was 1.48. During continuous casting, a large number of slag streaks appeared in the protective slag, and the slag rings were relatively well-developed, with some slag rings having a thickness of more than 8mm. Many slag inclusions and impurities appeared in the produced slabs and steel products, and there were several incidents of sticking and leaking steel.

[0064] Two fiber laser systems are installed on each side of the immersion nozzle of the crystallizer. Each system includes a fiber laser, a fiber transmission system, and a laser heating end. The fiber laser is positioned 50.0m away from the crystallizer, and the heating end is mounted above the crystallizer via a support. Each laser heater generates a laser wavelength of 1064nm and a laser spot size of 550mm × 200mm. Through optimization of the optical system within the fiber laser system, collimation and shaping of the output laser beam are achieved, with a 10%-90% energy transition zone at the edge of the spot ≤1.0mm. The length direction of the generated laser spot is parallel to the wide copper plate of the crystallizer. Through optimized setting of the position and angle of the laser heating end, four laser beams are generated. The laser beams are arranged side-by-side on both sides of the protective slag surface at the crystallizer nozzle, covering the protective slag surface on both sides of the nozzle. The distance between the laser beam and the nearest copper plate in the crystallizer is 0 mm, and the distance between the laser beam and the narrow copper plate of the crystallizer on both sides of the nozzle is 1 mm. The laser beam only illuminates the surface of the protective slag and does not illuminate the surface of the copper plate inside the crystallizer. The head of each laser heater is 0.5 m away from the surface of the protective slag. The laser heating end is installed in a shielded steel cover, and the laser beam illuminates the surface of the billet through a narrow slit at the bottom of the shield. The shield is cooled by a water chiller, and the temperature inside the cover is controlled to be less than 40℃. The actual working power of the laser generated by each laser heating end is set to 22 kW, and the average power density of the laser beam is 20 W / cm². 2 The thickness of the liquid slag layer is stable at 12-15mm. The maximum temperature of the protective slag surface after laser heating is 1480℃. The slag strips in the protective slag disappear, and the thickness of the slag ring is controlled within the range of 3.0-6.0mm. The slag consumption of the protective slag reaches 0.45kg / t steel, ensuring the smooth operation of continuous casting.

[0065] Example 8

[0066] A steel plant was producing high-alumina steel by continuous casting of slabs. The aluminum content of the steel was 2.58%. The cross-section of the slab produced by continuous casting was 250mm×2250mm, the casting speed was 1.2m / min, and the basicity of the protective slag used in continuous casting was 1.48. During continuous casting, a large number of slag streaks appeared in the protective slag, and the slag rings were relatively well-developed, with some slag rings having a thickness of more than 10mm. Many slag inclusions and impurities appeared in the produced slabs and steel products, and there were several incidents of sticking and leaking steel.

[0067] One fiber laser system is installed on each side of the immersion nozzle of the crystallizer. Each system includes a fiber laser, a fiber transmission system, and a laser heating end. The fiber laser is positioned 50.0m away from the crystallizer, and the heating end is positioned above the crystallizer by a robotic arm. Each fiber laser system generates a laser wavelength of 1064nm and a laser spot size of 100mm × 100mm. Through optimization of the optical system within the fiber laser system, collimation and shaping of the output laser beam are achieved, with a 10%-90% energy transition zone at the edge of the laser spot ≤1.0mm. The generated laser spot has a pair of sides parallel to the wide copper plate of the crystallizer. The movement and rotation of the robotic arm are controlled by a program, and the generated laser spots are positioned along the copper wall inside the crystallizer on both sides of the nozzle. The laser beam moves laterally, with the distance between the laser spot and the adjacent copper plate of the crystallizer being 1 mm. The laser beam only irradiates the surface of the protective slag and does not irradiate the surface of the copper plate inside the crystallizer. The moving speed of the laser spot is 2.53 m / min, and the heating frequency of the protective slag near the copper wall around the crystallizer is 2.37 s / min. The head of each laser heating end is 0.5 m away from the surface of the protective slag. The laser heating end is installed in a shielded steel cover, and the laser irradiates the surface of the billet through a narrow slit at the bottom of the shield. The shield is cooled by a water chiller, and the temperature inside the cover is controlled to be less than 40℃. The actual working power of the laser generated by each laser heating end is set to 10 kW, and the actual working power of the laser heaters on both sides of the nozzle is set to 20 kW. The average power density of the laser spot is 100 W / cm². 2 The thickness of the liquid slag layer near the copper wall of the crystallizer is stable at 12-15mm. The highest temperature of the protective slag surface after laser heating is 1480℃. The slag strips in the protective slag near the copper wall of the crystallizer disappear. The thickness of the slag ring is controlled within 4.0-6.0mm. The slag consumption of the protective slag reaches 0.43kg / t steel, ensuring the smooth operation of continuous casting.

[0068] Based on the behavior of adding, melting, and consuming protective slag in continuous casting production, and the functional requirements of protective slag for various steel grades, cross sections, and casting speeds, this application proposes a method for in-situ fluxing of protective slag within the crystallizer. This method utilizes a laser-generated laser spot to irradiate the surface of the protective slag within the crystallizer, thereby heating the slag. Three laser-heated protective slag working modes are disclosed according to the requirements of various continuous casting production processes. These modes respectively achieve the goals of rapidly fluxing the protective slag, controlling excessive slag ring growth, and dissolving high-melting-point refractory materials in the protective slag. This ensures efficient continuous casting operation, improves the surface quality of the cast billet, and guarantees smooth continuous casting production of difficult-to-cast steel grades such as high-alumina steel, high-manganese steel, semi-peritectic steel, and titanium- or rare-earth-containing steel. The beneficial effects of the technical solution provided in this application include at least the following: providing a new and flexible method for the smooth operation and surface quality control of high-speed continuous casting production, high-alumina steel, high-manganese steel, semi-peritectic steel, and titanium- and rare-earth stainless steel. It can significantly improve the melting rate of the protective slag in the crystallizer during the continuous casting growth process and increase the depth of the liquid slag layer. At the same time, it provides an effective means for controlling the growth of the protective slag ring in the crystallizer and dissolving high-melting-point substances such as slag bars and slag inclusions. It can also significantly reduce the risk of sticking and leakage, and reduce defects such as surface cracks and inclusions on the billet.

[0069] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for in-situ fluxing of protective slag within a crystallizer, characterized in that, include: A heating device is installed above the crystallizer in continuous casting to heat the protective slag above the molten steel in the crystallizer in situ. This increases the temperature of the protective slag, promotes its melting in the crystallizer, increases the thickness of the liquid slag layer, controls excessive growth of the slag ring, eliminates blocky agglomerates and slag strips in the protective slag in the crystallizer, increases the consumption of protective slag, ensures the smooth progress of continuous casting, and improves the surface quality of the cast billet.

2. The method for in-situ fluxing of protective slag within a crystallizer according to claim 1, characterized in that, The specific method of in-situ heating is as follows: a fiber laser system is used, which includes a fiber laser, a fiber transmission system and a heating end. The heating end is placed above the crystallizer at a distance of 100mm-2000mm from the protective slag inside the crystallizer. The fiber transmission system transmits the laser generated by the fiber laser to the heating end, and the heating end irradiates the surface of the protective slag inside the crystallizer with the laser beam, thereby realizing in-situ fluxing heating of the protective slag inside the crystallizer.

3. The method for in-situ fluxing of protective slag within a crystallizer according to claim 2, characterized in that, By rationally designing the optical path within the fiber laser system and applying a laser collimator and shaper, the initial high-energy laser output from the laser is collimated and shaped to produce a uniformly distributed spot with a uniform energy density. The energy transition zone at the edge of the spot (10%-80%) is ≤5.0mm, and the maximum temperature of the laser-heated slag surface is controlled to be ≤1500℃.

4. The method for in-situ fluxing of protective slag in a crystallizer according to claim 3, characterized in that, The laser beam generated by the heating end is perpendicular to the surface of the protective slag inside the crystallizer or at an angle to the surface of the protective slag inside the crystallizer. The position and angle of the heating end remain unchanged during the heating process, and the protective slag in the target heating area inside the crystallizer is continuously heated.

5. The method for in-situ fluxing of protective slag within a crystallizer according to claim 3, characterized in that, The fiber laser system generates a laser power greater than 1kW. The laser beam emitted from the heating end generates a laser spot on the surface of the protective slag inside the crystallizer, and the protective slag at the laser spot is heated by the laser.

6. The method for in-situ fluxing of protective slag in a crystallizer according to claim 3, characterized in that, By adjusting the size, position, and power of the laser beam generated at the heating end to irradiate the protective slag surface, the protective slag can be uniformly or selectively heated; by fixing the position and angle of the heating end, continuous heating of the protective slag in the target area within the crystallizer can be achieved, or by the laser beam reciprocating on the protective slag surface within the crystallizer, reciprocating cumulative heating of the protective slag in the target area can be achieved.

7. The method for in-situ fluxing of protective slag within a crystallizer according to claim 3, characterized in that, During continuous casting, the heating area and heating power of the laser spot are set at the heating end. The distance between the laser spot and the copper wall is controlled to be 0-150.0mm, and the size of the laser spot perpendicular to the copper wall of the crystallizer is 15.0-300.0mm. This ensures that the depth of the liquid slag layer near the copper wall in the crystallizer is 6.0-30.0mm, eliminates blocky agglomerates and refractory slag strips near the copper wall in the crystallizer, ensures that the shape and size of the protective slag ring in the crystallizer are suitable for the smooth flow of continuous casting, ensures that the liquid slag near the copper wall of the crystallizer enters the gap between the solidified billet shell and the copper wall, and ensures that the slag consumption in slab continuous casting production is greater than 0.2kg / t steel.

8. The method for in-situ fluxing of protective slag in a crystallizer according to claim 3, characterized in that, The height of the slag ring is controlled at 2.0-10mm, and the average power density of the laser spot is controlled at 10-500W / cm². 2 .

9. A method for in-situ fluxing of protective slag within a crystallizer according to claim 3, characterized in that, This method is applicable to continuous casting of high-alumina steel with a basicity of slag greater than 1.20, or / and aluminum content greater than 1.0% in the steel, or / and manganese content greater than 5.0% in the steel, or / and titanium content higher than 0.05% in stainless steel, or / and slag melting temperature greater than 1300℃, or / and casting speed greater than 1.5m / min.

10. A method for in-situ fluxing of protective slag within a crystallizer according to claim 3, characterized in that, A shielding cover is installed around the heating end, and the temperature of the heating end is less than 80℃.

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