A kind of protection slag and the control method of 210 square high carbon steel continuous casting billet surface slag groove

Abstract

The present application relates to a kind of control methods of protecting slag and 210 square high-carbon steel continuous casting billet surface slag groove, control method includes: before replacing crystallizer copper pipe, arc is carried out to the roll of enough;Crystallizer is vibrated and debugged, crystallizer uses sinusoidal vibration mode, the negative slip displacement amount of crystallizer vibration is set to 3-4mm, negative slip time is set to 0.12-0.18s, ensure that the vibration offset of crystallizer in X, Y, Z three directions is in the preset range;Enter continuous casting production link, add protecting slag, its binary basicity is set to 0.5-0.8, melting point is set to 960 ℃±30 ℃, viscosity is set to 0.20±0.05Pa·s, when the superheat of molten steel <20 ℃, set the pulling speed to 1.15m / min, when the superheat of molten steel is in 20-40 ℃ interval, set the pulling speed to 1.10m / min, when the superheat of molten steel >40 ℃, set the pulling speed to 1.05m / min.The present application can reduce or eliminate the detection rate of bearing steel, grinding ball steel and other high-carbon steel species continuous casting billet slag groove.

Description

Technical Field

[0001] This invention relates to a method for controlling protective slag and slag grooves on the surface of 210 cubic meter high carbon steel continuous casting billets, belonging to the field of metallurgy. Background Technology

[0002] Slag grooves on the surface of continuously cast billets refer to groove-like defects of a certain depth that appear on the surface of continuously cast billets along the casting direction. The main cause of their formation is the poor performance or improper use of the mold flux during the continuous casting process. For example, unsuitable melting characteristics of the mold flux, uneven melting, and insufficient melting of some high-melting-point substances can lead to problems. Furthermore, oxide inclusions in the molten steel rise to the slag surface but are difficult to absorb, leaving behind residues that accumulate during casting to form slag streaks. The presence of these streaks results in insufficient localized flow of liquid mold flux, causing premature cooling of the billet shell and the formation of depressions. The liquid slag further fills these depressions, forming a thicker slag film that hinders the recovery of the billet shell under static pressure, leaving behind the slag grooves. In addition, unreasonable vibration parameters of the mold and excessive fluctuations in the molten steel level can also contribute to the formation of slag grooves.

[0003] Application CN202510087443 discloses a production method for reducing slag grooves during the casting of spring steel billets. This patent, also invented by Huai Steel, is primarily applicable to spring steel with a carbon content of approximately 0.50%-0.90%, and its effectiveness is not significant for bearing steel GCr15 and ball steel SGI-2A with a carbon content ≥0.95%. However, in actual operation, slag grooves are particularly prone to occur during the continuous casting process of steel grades with a carbon content ≥0.95%. For bearing steel and ball steel with even higher carbon contents, the shrinkage during the initial solidification process is smaller, the liquidus temperature is lower, and secondary oxidation of the molten steel often more easily generates alumina inclusions. These inclusions are difficult to absorb, and all these factors lead to uneven melting of the protective slag, resulting in slag grooves.

[0004] To address the slag groove problem in high-carbon steel, application CN201911370062 proposed a protective slag for continuous casting molds used in medium and high carbon steels to solve the slag groove problem. However, actual production has revealed that the formation of slag grooves is not only related to the protective slag, but also has significant effects from other factors such as mold vibration, copper tube taper, and foot roller arc.

[0005] Therefore, it is necessary to propose a method for controlling slag grooves on the surface of continuous casting billets of high-carbon steel to ensure that the slag grooves of continuous casting billets of high-carbon steel grades such as bearing steel and grinding ball steel with a carbon content ≥0.95% have a low detection rate. Summary of the Invention

[0006] This invention provides a method for controlling protective slag and slag grooves on the surface of 210 cubic meter high carbon steel continuous casting billets, which can reduce or eliminate the detection rate of slag grooves on continuous casting billets of high carbon steel grades such as bearing steel and grinding ball steel with a carbon content ≥0.95%.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A protective slag, specifically designed for high-carbon steel, is provided for high-carbon steel with a carbon content ≥0.95%. The binary basicity of the protective slag is set to 0.5-0.8, the melting point is set to 960℃±30℃, and the viscosity is set to 0.20±0.05Pa·s.

[0009] A method for controlling slag grooves on the surface of a 210 cubic meter high-carbon steel continuous casting billet includes the following steps:

[0010] Step S1: Before replacing the copper tube of the crystallizer, the foot roller is calibrated.

[0011] Step S2: Vibration adjustment of the crystallizer. The crystallizer adopts sinusoidal vibration mode. The negative slip displacement of the crystallizer vibration is set to 3-4mm, and the negative slip time is set to 0.12-0.18s to ensure that the vibration offset of the crystallizer in the X, Y and Z axes is within the preset range.

[0012] Step S3: Enter the continuous casting production stage, add the protective slag, and set the casting speed to 1.15 m / min when the superheat of the molten steel is <20℃, set the casting speed to 1.10 m / min when the superheat of the molten steel is in the range of 20-40℃, and set the casting speed to 1.05 m / min when the superheat of the molten steel is >40℃.

[0013] Furthermore, in step S1, the foot rollers are calibrated to ensure that the positional error of each foot roller is ≤0.5mm;

[0014] Furthermore, in step S2, the vibration offset of the crystallizer in the X, Y, and Z axes is ≤0.1mm; the total taper of the crystallizer copper tube is set to 1%, and the taper at the meniscus inside the crystallizer copper tube is 2.0%-2.5%; the amplitude of the crystallizer is ±3mm, and the frequency is (100+70V)Hz, where V is the pulling speed.

[0015] Furthermore, in step S2, the flow rate of the primary cooling water in the crystallizer is set to 130 m³ / h. 3 / h, the temperature difference of the cold water is 5-6℃;

[0016] Furthermore, in step S3, the superheat range of molten steel is set to 20-35℃, and the drawing speed is 1.10m / min;

[0017] Furthermore, in step S3, the depth range of the slag line at the direct water inlet is set to 90-120mm; the electromagnetic stirring intensity of the crystallizer is set to the upper limit of the preset intensity, with the current set to 350A and the frequency to 2.5Hz.

[0018] Furthermore, the depth range of the slag line for the direct-flow water inlet is set to 90-100mm.

[0019] By employing the above technical solutions, the present invention has the following beneficial effects compared to the prior art:

[0020] 1. The protective slag provided by this invention is a special protective slag for high carbon steel. It has limited binary basicity, melting point and viscosity. It can melt rapidly on the surface of the billet and form a uniform and high-performance slag film. This slag film plays multiple important roles in the billet production process, such as lubrication, heat insulation and adsorption of inclusions. It can effectively prevent the protective slag from agglomerating or forming slag strips during the casting process, and is one of the key factors in reducing the possibility of slag groove formation.

[0021] 2. The method for controlling slag grooves on the surface of 210 cubic high carbon steel continuous casting billet provided by the present invention can closely control each link of the continuous casting billet production process, and can successfully control the detection rate of slag grooves on the surface of the continuous casting billet to below 1%, which greatly improves the surface quality of 210 cubic high carbon steel continuous casting billet. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Figure 1 This is a schematic diagram of the entire continuous casting process provided by the embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram obtained by providing a comparative scale for the entire continuous casting cycle. Detailed Implementation

[0025] The invention will now be described in further detail with reference to the accompanying drawings.

[0026] As described in the background section, current control methods for reducing the detection rate of slag troughs in steel grades with a carbon content of ≥0.95% are relatively simple, while the formation of slag troughs is related to multiple aspects such as equipment, continuous casting process, and protective slag.

[0027] The most important influencing factor in the entire control method is the protective slag. This application provides a protective slag specifically for high-carbon steel with a content ≥0.95%. The provided protective slag has a binary basicity set at 0.5-0.8, a melting point set at 960℃±30℃, and a viscosity set at 0.20±0.05 Pa·s. This protective slag ensures melting performance, with low viscosity, low basicity, and a low melting point, rapidly melting on the surface of the billet and forming a uniform and high-performance slag film. Regarding the addition of the protective slag, the principle of adding small amounts frequently must be strictly followed. The molten steel surface must not be exposed (bright surface), as this will cause the billet surface to lose the protection of the protective slag, leading to secondary oxidation of the molten steel or insufficient local lubrication causing leakage. Furthermore, an excessively thick protective slag layer should not be added, as this will affect the melting and penetration effect of the protective slag and may even produce slag streaks, further leading to slag grooves. In addition, special attention should be paid to timely removal of slag bars, because once slag bars are rolled into the surface of the billet, they are very likely to form slag grooves, which seriously affect the quality of the billet.

[0028] In the background art, bearing steel GCr15 is usually referred to as 210 square steel in actual working conditions. Therefore, the following is a method for controlling slag grooves on the surface of 210 square high-carbon steel continuous casting billets provided in this application, including the following steps:

[0029] Step S1, equipment preparation: Before each replacement of the crystallizer copper tubes, the foot rollers need to be aligned. The accuracy of the foot roller position directly affects the uniformity of support received by the billet during the initial solidification stage. If the foot roller position deviation is too large, uneven stress on the billet will easily lead to various surface defects in subsequent production processes, including slag grooves. Accurate alignment of the foot rollers lays a good foundation for the stable forming of the billet. Preferably, the positional error of each foot roller after alignment is ≤0.5mm.

[0030] Step S2: Before formal production, the crystallizer is vibrated to ensure that the vibration offset in the X, Y, and Z axes is ≤0.1mm. This vibration offset ensures that the protective slag flows evenly into the gap between the crystallizer wall and the billet, forming a uniform and effective slag film. This slag film acts as a "lubricant" and "heat insulation" for the billet, significantly reducing friction between the billet and the crystallizer wall and providing good heat insulation to prevent defects such as slag grooves from appearing on the billet surface due to uneven cooling or excessive friction.

[0031] Meanwhile, the crystallizer adopts a sinusoidal vibration mode, with a negative slip displacement of 3-4 mm and a negative slip time of 0.12-0.18 s. Based on the negative slip displacement and negative slip time, the crystallizer amplitude is set to ±3 mm, and the vibration frequency is (100+70V) Hz, where V is the casting speed. The sinusoidal vibration mode has less impact on the mechanism, which helps maintain the stability of the equipment, allowing the protective slag to spread evenly and melt smoothly on the surface of the molten steel. With the optimization of vibration parameters, it can further promote the penetration of the protective slag into the gap between the billet and the crystallizer wall, comprehensively improving lubrication conditions and reducing the probability of slag groove formation from the source.

[0032] The crystallizer in this application uses a high primary cooling intensity, with the primary cooling water being approximately 10%-20% higher than that of medium and low carbon steel. Preferably, the primary cooling water flow rate is set to 130 m³ / h. 3 / h, the temperature difference of the cooling water is 5-6℃. For the copper tubes used in the production of high-carbon steel, the taper at the meniscus needs special adjustment. Therefore, this application sets the total taper of the crystallizer copper tubes to 1%, and the taper at the meniscus inside the crystallizer copper tubes to 2.0%-2.5%. After reasonably setting the taper, the gap between the billet and the crystallizer wall is more reasonable in the early stage of solidification, creating favorable conditions for the smooth flow of protective slag into the gap at the meniscus. Good gap conditions help improve the lubrication and cooling of the billet surface, avoid stress concentration on the billet surface due to excessive taper, and effectively reduce the possibility of slag groove formation.

[0033] Step S3: Entering the continuous casting production stage, the protective slag described in this application for high-carbon steel with a content ≥0.95% is added. Superheat directly reflects the temperature state of the molten steel and has a decisive influence on the solidification process of the billet. The most important innovation in this stage is the coordinated control between casting speed and superheat. Specifically, when the superheat of the molten steel is <20℃, the casting speed is set to 1.15 m / min; when the superheat of the molten steel is in the range of 20-40℃, the casting speed is set to 1.10 m / min; and when the superheat of the molten steel is >40℃, the casting speed is set to 1.05 m / min. This strategy of adjusting the casting speed in real time according to the superheat ensures that the billet has a suitable solidification time and thickness in the crystallizer. If the casting speed is too fast when the superheat is high, the solidified layer on the surface of the billet will be too thin, making it highly susceptible to various adverse factors in the crystallizer and resulting in slag grooves.

[0034] Throughout the continuous casting process, the superheat of the molten steel should be controlled within the range of 20-35℃ as much as possible, and a constant casting speed of 1.10m / min should be achieved. Under these conditions, the solidification process of the molten steel is relatively stable, and the solidified layer on the surface of the billet can grow uniformly, providing a stable environment for the protective slag to play its full role and greatly reducing the probability of surface defects such as slag grooves.

[0035] It is also important to note that the submerged nozzle and electromagnetic agitator require corresponding controls. The depth of the submerged nozzle below the molten steel surface in the crystallizer should be controlled within the lower-middle range of a preset depth. The slag line depth of the straight-through nozzle should be controlled within the range of 90-120mm, preferably 90-100mm. For side-hole nozzles, the insertion depth can be appropriately increased to account for molten steel surface fluctuations. This optimizes the flow field of molten steel within the crystallizer, effectively reducing the scouring force of the molten steel on the crystallizer wall and surface. A stable and reasonable flow field is conducive to the stable existence and uniform distribution of the protective slag on the surface, avoiding the slag from being entrained in the molten steel or unevenly distributed due to turbulent flow, thereby reducing the risk of slag groove formation. The electromagnetic agitation intensity in the crystallizer should be set at the upper-middle limit of the preset intensity, preferably with a current of 350A and a frequency of 2.5Hz. Appropriate electromagnetic stirring can significantly improve the solidification structure of molten steel in the crystallizer, making the composition of molten steel more uniform. It can also promote the effective separation of protective slag from molten steel, improve the utilization rate of protective slag, enhance the film-forming effect of protective slag on the surface of the billet, and reduce the occurrence of slag grooves in all aspects.

[0036] The present application provides an embodiment and a comparative example to verify the feasibility of the present application.

[0037] Example:

[0038] Before replacing the copper tubes in the crystallizer, the foot rollers must be calibrated to ensure that the positional accuracy error of each roller is ≤0.5mm. Before production, the crystallizer vibration is checked to ensure that the vibration offset of the crystallizer in the X, Y, and Z axes is ≤0.1mm, and the actual inspection shows that it is around 0.05mm. The taper of the copper tube is optimized and appropriately reduced by 20-30%, with the taper at the inner meniscus of the crystallizer copper tube set to 2.0%-2.5%. The crystallizer uses sinusoidal vibration with an amplitude of ±3mm and a frequency of (100+70V)Hz, where V is the pulling speed. The primary cooling water flow rate is 130m³ / h. 3 The temperature difference between the cold water and the volumetric water is approximately 5.5℃ per hour; the casting speed is adjusted according to the superheat, with a superheat of 35℃ and a casting speed of 1.10 m / min; the insertion depth of the immersion nozzle is 95 mm; the electromagnetic stirring current of the crystallizer is 350 A, and the frequency is 2.5 Hz. A special protective slag made of high-carbon steel is used, with a binary basicity of 0.73, a melting point of 950℃, and a viscosity of 0.15 Pa·s. The slag addition operation should ensure frequent additions in small amounts, avoiding both a bright liquid surface and excessive addition; special attention should be paid to removing slag streaks. Figure 1 As shown, using this method, no slag channels were detected during the entire casting process.

[0039] Comparative example:

[0040] Before replacing the copper tubes in the crystallizer, the foot rollers were not specifically calibrated. The maximum vibration deviation of the crystallizer reached 0.15mm. Using the original crystallizer, the taper at the meniscus of the molten steel was approximately 3%. The vibration parameters were: frequency (70+90V) Hz, where V is the casting speed, amplitude ±2.4mm, and cooling water flow rate 130m³ / h. 3 The temperature difference between the cold water and the volumetric osmosis is approximately 5.5℃; the casting speed is adjusted according to the superheat, with a superheat of 35℃ and a casting speed of 1.10 m / min; the insertion depth of the immersion nozzle is 95 mm; the electromagnetic stirring current of the crystallizer is 350 A, and the frequency is 2.5 Hz. The basicity of the protective slag is 0.75, the melting point is 1010℃, and the viscosity is 0.17 Pa·s. Figure 2 As shown, the entire continuous casting furnace inspection revealed slag troughs ( Figure 2 Black-framed icon).

[0041] In summary, the method for controlling the protective slag and slag grooves on the surface of the 210 cubic meter high-carbon steel continuous casting billet provided in this application avoids slag grooves from damaging the integrity of the billet surface, improves the appearance quality of the billet, and reduces the difficulty of subsequent processing. At the same time, it prevents slag grooves from becoming stress concentration points, reducing the possibility of crack propagation during subsequent rolling, and further improving the performance and service life of the steel.

[0042] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0043] The meaning of "and / or" as used in this application includes situations where each exists alone or both exist simultaneously.

[0044] The term "connection" as used in this application can mean a direct connection between components or an indirect connection between components through other components.

[0045] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method of controlling surface notch of a 210 mm high carbon steel continuous casting billet, characterized by: The method comprises the following steps: S1. Before replacing the copper tube of the crystallizer, the arc of the foot roller is calibrated; Step S2, the crystallizer is subjected to vibration debugging, the crystallizer adopts a sinusoidal vibration mode, the negative stripping displacement amount of the crystallizer vibration is set to 3-4 mm, the negative stripping time is set to 0.12-0.18 s, and it is ensured that the vibration offset amount of the crystallizer in the X, Y and Z axes is within a preset range, all ≤0.1 mm; the total taper of the copper pipe of the crystallizer is set to 1%, and the taper at the meniscus of the copper pipe of the crystallizer is 2.0%-2.5%; the amplitude of the crystallizer is ±3 mm, the vibration frequency is (100+70V) Hz, V is the pulling speed, the flow of the cold water of the crystallizer is 130 m 3 / h, and the cold water temperature difference is 5-6℃; S3. In the continuous casting production process, the protective slag is added, the pulling speed is set to 1.15 m / min when the superheat of the molten steel is less than 20 DEG C, the pulling speed is set to 1.10 m / min when the superheat of the molten steel is in the range of 20-40 DEG C, and the pulling speed is set to 1.05 m / min when the superheat of the molten steel is greater than 40 DEG C; the depth range of the slag line of the straight-through water nozzle is set to 90-120 mm; the electromagnetic stirring intensity of the crystallizer is set to the upper limit of the preset intensity, the current is set to 350 A, and the frequency is set to 2.5 Hz; The binary basicity of the protective slag is set to 0.5-0.8, the melting point is set to 960 DEG C + / - 30 DEG C, and the viscosity is set to 0.20 + / - 0.05 Pa s.

2. The method of controlling the surface notch of a 210 mm high-carbon steel continuous casting billet according to claim 1, characterized by: In S1, the arc of the foot roller is calibrated to ensure that the position error of each foot roller is less than or equal to 0.5 mm.

3. The method of controlling the surface notch of a 210 mm high carbon steel continuous cast billet according to claim 1, characterized by: In S3, the superheat range of the molten steel is set to 20-35 DEG C, and the pulling speed is set to 1.10 m / min.

4. The method of controlling the surface notch of a 210 mm high carbon steel continuous cast billet according to claim 1, characterized by: The depth range of the slag line of the straight-through water nozzle is set to 90-100 mm.

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