Crystallizer casting powder for continuous casting of wide and thick plate high-carbon steel and preparation method of crystallizer casting powder

Abstract

The invention relates to the technical field of steelmaking, and discloses crystallizer casting powder for continuous casting of wide and thick plate high-carbon steel, which comprises the following components in percentage by mass: 28.5 + / -5.0% of SiO2, 28.0 + / -5.0% of CaO, 4.0 + / -2.0% of Al2O3, 15.0 + / -3.0% of Na2O, 7.5 + / -3.0% of F, 4.0 + / -2.0% of MgO and the balance of inevitable impurities. The invention further provides a preparation method of the crystallizer casting powder for continuous casting of the wide and thick plate high-carbon steel. The casting powder disclosed by the invention is special casting powder with low melting point, low viscosity, weak crystallinity and high heat transfer capacity, so that the problems of poor lubrication, non-uniform heat transfer and crack control in the continuous casting process of high-carbon steel are solved, and the production stability and the casting blank quality are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, and in particular to a mold protection slag for continuous casting of wide and thick plate high carbon steel and a preparation method thereof. Background Art

[0002] During the continuous casting production of high-carbon steel, due to its high carbon content, its solidification shrinkage is small, resulting in a narrow gap between the crystallizer wall and the solidified billet shell. The liquid protective slag is difficult to fully penetrate, and the slag film formed is thin and uneven, thereby increasing the friction resistance of the billet, affecting the surface quality of the billet and increasing the risk of cracks. In addition, the high-temperature tensile strength of high-carbon steel is relatively low. Under the action of the static pressure of the molten steel, the billet shell is in close contact with the crystallizer wall. If the heat transfer capacity of the protective slag is insufficient, it is easy to cause uneven growth of the billet shell, and then cause steel leakage accidents. At present, traditional protective slag is mainly designed for low-carbon steel. Its high melting point and high viscosity characteristics make it difficult to adapt to the continuous casting needs of high-carbon steel. For example, high-viscosity protective slag has poor fluidity and cannot effectively fill narrow gaps, while high-melting point protective slag melts slowly, and the liquid slag layer is not thick enough, resulting in poor lubrication effect. While some companies have attempted to improve mold slag performance by adjusting alkalinity or adding fluxes (such as Na₂O and F content), issues persist, such as the difficulty in balancing melting rate and lubrication, and the conflict between heat transfer and crystallization performance. For example, while low-melting-point mold slag melts quickly, its low viscosity can lead to slag film loss. High heat transfer requirements necessitate a predominantly glassy mold slag, but the continuous casting process of high-carbon steel requires a certain crystallization rate to stabilize the slag film structure. Existing formulations struggle to simultaneously meet these requirements. Furthermore, the accumulation of impurities such as Al₂O₃ and MgO during continuous casting can alter mold slag properties, necessitating precise control of the composition range.

[0003] Therefore, there is a need in the prior art for improving the mold protection slag for continuous casting of wide and thick plate high carbon steel. Summary of the Invention

[0004] In view of this, the purpose of the embodiments of the present invention is to propose a crystallizer protective slag for continuous casting of wide and thick plates of high-carbon steel and a preparation method thereof, which is a special protective slag with low melting point, low viscosity, weak crystallinity and high heat transfer capacity, so as to solve the problems of poor lubrication, uneven heat transfer and crack control in the continuous casting process of high-carbon steel, thereby improving production stability and ingot quality.

[0005] Based on the above-mentioned purpose, an embodiment of the present invention provides a crystallizer protective slag for continuous casting of wide and thick plate high carbon steel, which includes, by mass percentage: SiO2: 28.5±5.0%, CaO: 28.0±5.0%, Al2O3: 4.0±2.0%, Na2O: 15.0±3.0%, F content: 7.5±3.0%, MgO: 4.0±2.0%, and the rest are unavoidable impurities.

[0006] In some embodiments, the mold flux has a basicity of 0.98±0.10, a melting temperature of 980±50° C., and a viscosity of 0.10±0.07 Pa·s at 1300° C.

[0007] Another aspect of the present invention provides a method for preparing mold powder for continuous casting of wide and thick plate high carbon steel, comprising the following steps: S1 weighs raw materials according to the ratio, and mixes SiO2, CaO, Al2O3, Na2O, CaF2, MgO and carbonaceous materials; S2: placing the mixed material in a ball mill for thorough grinding; S3 is added with a binder to be granulated, and after drying, the moisture content is controlled to ≤0.5% to obtain a finished protective slag. The protective slag includes, by mass percentage: SiO2: 28.5±5.0%, CaO: 28.0±5.0%, Al2O3: 4.0±2.0%, Na2O: 15.0±3.0%, F content: 7.5±3.0%, MgO: 4.0±2.0%, and the rest are unavoidable impurities.

[0008] In some embodiments, the method further comprises: a heat treatment step, heating the granulated protective slag to 600-800° C. at 5-10° C. / min under nitrogen protection, keeping the temperature for 1-2 hours, and then cooling with the furnace.

[0009] In some embodiments, in S2, the mixed material is placed in a ball mill and fully ground to a particle size of ≤2.0 mm.

[0010] In some embodiments, a graded grinding process is used during grinding, first coarse grinding to a particle size of 2.0-3.0 mm, then fine grinding to a particle size of ≤0.5 mm, and 0.1-0.3% of the total weight of the raw material zinc stearate is added as a grinding aid during fine grinding.

[0011] In some embodiments, the carbonaceous material is graphite or carbon black, and the added amount is 5.0±3.0% of the total mass.

[0012] In some embodiments, in S2, the ground mixture needs to pass through an 80-mesh sieve with a sieve residue rate of ≤5%.

[0013] In some embodiments, in S3, the binder is sodium carboxymethyl cellulose, and the added amount is 0.5% to 1.5% of the total mass of the mixture.

[0014] In some embodiments, the thickness of the liquid slag layer formed by the protective slag in the crystallizer is 8-15 mm, and the thickness of the slag film is 0.1-0.3 mm.

[0015] The present invention has at least the following beneficial technical effects: (1) Optimizing lubrication performance: By adjusting the SiO2 / CaO ratio and adding Na2O and F content, the melting point and viscosity are lowered to ensure that the liquid slag flows quickly into the narrow gap, forming a uniform slag film and reducing friction resistance; (2) Enhance heat transfer efficiency: Control the MgO and Al2O3 contents to ≤4%, combined with a low transition temperature (≤1100°C) design to inhibit crystal precipitation, reduce thermal resistance, and promote rapid and uniform growth of the shell; (3) Due to the lower melting temperature, faster melting rate and lower viscosity, the protective slag above the molten steel can be quickly melted into a liquid slag layer at a lower temperature and flow smoothly into the space between the crystallizer wall and the solidified billet shell, ensuring the lubrication effect on the billet, reducing the friction resistance between the billet and the crystallizer, improving the surface quality of the billet, and maintaining the smooth operation of the continuous casting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 This is a schematic diagram of an embodiment of a method for preparing mold protection slag for continuous casting of wide and thick plates of high carbon steel provided by the present invention. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the present invention pertains; the terms used in the specification herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention; for example, the directions or positions indicated by the terms "length", "width", "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the directions or positions shown in the accompanying drawings and are for ease of description only and should not be construed as limiting the present technical solution.

[0020] The terms "including," "having," and any variations thereof in the present specification, claims, and accompanying drawings are intended to cover non-exclusive inclusions. The terms "first," "second," and the like in the present specification, claims, and accompanying drawings are used to distinguish between different items, not to describe a particular order. "Multiple" means two or more, unless otherwise expressly specified.

[0021] Furthermore, references herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute a separate or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0022] Currently, wide and heavy plate high-carbon steel is a trend in continuous casting. Due to the relatively high carbon content, high-carbon steel grades experience relatively low solidification shrinkage, resulting in a narrow gap between the mold wall and the solidifying shell. This hinders the penetration of liquid mold slag above the molten steel. The resulting mold slag film is thin and uneven, increasing frictional resistance with the strand during casting, impairing lubrication, and causing uneven heat transfer. Furthermore, medium- and high-carbon steels have relatively good molten steel flowability, leading to close contact between the mold wall and the solidifying shell under the influence of ferrostatic pressure. Furthermore, they have low high-temperature tensile strength, poor toughness, and poor deformability. All of these factors increase the likelihood of cracks and breakouts during the continuous casting of medium- and high-carbon steel. To develop wide and heavy plate high-carbon steel (typically with a carbon mass fraction of 0.40% to 0.70% in the strand), and to reduce sticking breakout alarms, strand quality defects, and breakouts, a mold slag for wide and heavy plate high-carbon steel was developed.

[0023] The present invention provides a mold protection slag for continuous casting of wide and thick plate high carbon steel, which comprises, by mass percentage, the following: SiO2: 28.5±5.0%, CaO: 28.0±5.0%, Al2O3: 4.0±2.0%, Na2O: 15.0±3.0%, F content: 7.5±3.0%, MgO: 4.0±2.0%, and the rest are inevitable impurities.

[0024] Furthermore, the mold slag has a basicity of 0.98±0.10, a melting temperature of 980±50°C, and a viscosity of 0.10±0.07 Pa·s at 1300°C.

[0025] Another aspect of the present invention provides a method for preparing mold powder for continuous casting of wide and thick plate high carbon steel, comprising the following steps: S1 weighs raw materials according to the ratio, and mixes SiO2, CaO, Al2O3, Na2O, CaF2, MgO and carbonaceous materials; S2: placing the mixed material in a ball mill for thorough grinding; S3 is added with a binder to be granulated, and after drying, the moisture content is controlled to ≤0.5% to obtain a finished protective slag. The protective slag includes, by mass percentage: SiO2: 28.5±5.0%, CaO: 28.0±5.0%, Al2O3: 4.0±2.0%, Na2O: 15.0±3.0%, F content: 7.5±3.0%, MgO: 4.0±2.0%, and the rest are unavoidable impurities.

[0026] Furthermore, the method also includes: a heat treatment step, heating the granulated protective slag to 600-800°C at 5-10°C / min under nitrogen protection, keeping the temperature for 1-2 hours and then cooling it with the furnace.

[0027] Furthermore, in S2, the mixed material is placed in a ball mill and fully ground to a particle size of ≤2.0 mm.

[0028] Furthermore, a graded grinding process is adopted during grinding, first coarse grinding to a particle size of 2.0-3.0 mm, then fine grinding to a particle size of ≤0.5 mm, and 0.1-0.3% of the total weight of the raw materials is added as a grinding aid during fine grinding.

[0029] Furthermore, the carbonaceous material is graphite or carbon black, and the added amount is 5.0±3.0% of the total mass.

[0030] Furthermore, in S2, the ground mixture needs to pass through an 80-mesh sieve with a sieve residue rate of ≤5%.

[0031] Furthermore, in S3, the binder is sodium carboxymethyl cellulose, and the addition amount is 0.5% to 1.5% of the total mass of the mixture.

[0032] Furthermore, the thickness of the liquid slag layer formed by the protective slag in the crystallizer is 8~15mm, and the thickness of the slag film is 0.1~0.3mm.

[0033] The mold powder for continuous casting of thick and wide plate high-carbon steel prepared by the method of the present invention has the following characteristics: 1) a low melting temperature, a fast melting rate, and a low viscosity. Therefore, the mold powder above the molten steel can quickly melt into a liquid slag layer at a low temperature and smoothly flow into the space between the mold wall and the solidified shell, ensuring lubrication of the cast strand, reducing frictional resistance between the cast strand and the mold, improving the surface quality of the cast strand, and maintaining the smooth operation of the continuous casting process; 2) a low transition temperature and weaker crystallization ability. The low transition temperature means that the mold powder is less likely to precipitate crystals during the cooling process, resulting in a lower crystallization rate. Therefore, less heat is reflected and scattered at grain boundaries and lattice defects, which has a small effect on heat transfer and accelerates heat transfer; 3) it has good heat transfer ability. The mold powder with strong heat transfer ability can accelerate heat transfer from the molten steel in the mold in a short time, quickly forming a solidified shell of a certain thickness, and preventing steel leakage accidents. According to the analysis of molten steel composition and the current high carbon steel production status of other steel companies, the main physical and chemical indicators of high carbon steel protection slag for wide and thick plates are shown in Table 1 below: Table 1 Physical and chemical indicators of high carbon steel mold slag for wide and thick plates

[0034] The present invention will be further explained below with reference to specific embodiments.

[0035] Example 1 The composition of the protective slag (mass percentage) includes: SiO2: 23.5%; CaO: 23.0%; Al2O3: 2.0%; Na2O: 12.0%; F content: 4.5%; MgO: 2.0%; fixed carbon (Cf): 2.0%; other unavoidable impurities: balance.

[0036] The raw materials were mixed in a planetary mixer for 30 minutes; ground with a vibration mill to an average particle size of 1.8 mm; granulated with 0.5% sodium carboxymethyl cellulose aqueous solution; and dried at 80°C to a moisture content of 0.3%.

[0037] Performance indicators: Melting point: 930℃; Viscosity at 1300℃: 0.03Pa·s; Spreadability: 305cm²; Transition temperature: 1050℃.

[0038] The effect of casting the protective slag of Example 1 is as follows: When casting high carbon steel with a carbon content of 0.40%, the casting speed is 0.8m / min, the thickness of the liquid slag layer is 10mm, there are no cracks on the surface of the ingot, and no adhesion alarm.

[0039] Example 2 The protective slag composition (mass percentage) includes: SiO2: 28.5%; CaO: 28.0%; Al2O3: 4.0%; Na2O: 15.0%; F content: 7.5%; MgO: 4.0%; fixed carbon (Cf): 5.0%; other unavoidable impurities: balance.

[0040] 60% of the raw materials were melted at 1450°C and then water quenched for pre-melting treatment; mixed with the remaining raw materials and then ball-milled to 1.2 mm; spray granulation was performed with an inlet temperature of 200°C; and heat treatment was performed at 600°C for 1 hour.

[0041] Performance indicators: Melting point: 980℃; Viscosity at 1300℃: 0.10Pa•s; Spreadability: 350cm²; Transition temperature: 1000℃.

[0042] The effect of casting the mold slag of Example 2 is as follows: Casting carbon content 0.55% steel, casting speed 1.0m / min, slag film thickness 0.2mm, uniform heat transfer, shell growth deviation ≤3%.

[0043] Example 3 The protective slag composition (mass percentage) includes: SiO2: 33.5%; CaO: 33.0%; Al2O3: 6.0%; Na2O: 18.0%; F content: 10.5%; MgO: 6.0%; fixed carbon (Cf): 8.0%; other unavoidable impurities: balance.

[0044] The modified product was treated with nano-TiO2 at an addition amount of 1.0%; the product was graded and ground to D90 ≤ 0.8 mm; the product was granulated in a fluidized bed at a bed temperature of 150°C; and the product was heat treated at 750°C for 2 hours under nitrogen protection.

[0045] Performance indicators: Melting point: 1030℃; Viscosity at 1300℃: 0.17Pa•s; Spreadability: 380cm²; Transition temperature: 950℃.

[0046] The effect of casting the mold slag of Example 3 is as follows: Used for high carbon steel with a carbon content of 0.70%, with a pulling speed of 1.2m / min, a liquid slag layer thickness of 15mm, a 20% increase in high temperature plasticity, and no steel leakage accidents.

[0047] The lubrication mechanism optimization principle of the protective slag of the present invention is as follows: by controlling the alkalinity at 0.98±0.10 and adding 7.5±3.0% F content, the melting point (980±50°C) and viscosity (0.10±0.07 Pa·s) of the protective slag are significantly reduced; the low melting point property enables the protective slag to quickly form a liquid slag layer (8-15 mm in Example 2) at a lower temperature; the low viscosity ensures that the liquid slag can smoothly flow into narrow gaps to form a continuous and uniform slag film.

[0048] The heat transfer control mechanism of the mold slag of the present invention is as follows: controlling the MgO (4.0±2.0%) and Al2O3 (4.0±2.0%) contents to avoid excessive high-melting-point substances, and lowering the transition temperature (950-1050°C in Examples 1-3) through the synergistic effect of 15.0±3.0% Na2O and 7.5±3.0% F contents; the glassy microstructure (crystallization rate ≤30%) reduces the scattering of heat flux by grain boundaries, and the heat transfer coefficient is ≥1.5 W / (m·K). The crack suppression mechanism of the mold slag of the present invention: a fixed carbon content (5.0±3.0%) regulates the melting rate to ensure a stable liquid slag layer (15mm in Example 3); a uniform slag film thickness (0.1-0.3mm) reduces friction resistance fluctuations; optimized heat transfer enables uniform growth of the shell (deviation ≤3% in Example 2), reducing thermal stress concentration The mold slag of the present invention has the following mechanisms for preventing breakout: rapid formation of a primary shell (no adhesion alarm in Example 1); a stable liquid slag replenishment mechanism (spreadability ≥ 300 cm²); and a composition design that avoids the enrichment of impurities such as Al2O3 (total iron ≤ 5.0%).

[0049] The above are exemplary embodiments disclosed in the present invention, but it should be noted that various changes and modifications may be made without departing from the scope of the embodiments disclosed in the claims. The functions, steps and / or actions of the method claims according to the disclosed embodiments described herein do not need to be performed in any particular order. In addition, although the elements disclosed in the embodiments of the present invention may be described or required in individual form, they may also be understood as multiple unless expressly limited to the singular.

[0050] It should be understood that, as used herein, the singular forms "a" and "an" are intended to include the plural forms as well, unless the context clearly supports an exception. It should also be understood that, as used herein, "and / or" is intended to include any and all possible combinations of one or more of the associated listed items.

[0051] The serial numbers of the embodiments disclosed in the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0052] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to limit the scope of the disclosure of the present invention (including the claims) to these examples. Within the spirit of the present invention, the technical features of the above embodiments or different embodiments may be combined, and many other variations exist in different aspects of the above embodiments, which are not provided in detail for the sake of clarity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A mold powder for continuous casting of wide and thick plate high carbon steel, characterized in that: Calculated by mass percentage, it includes: SiO2: 28.5±5.0%, CaO: 28.0±5.0%, Al2O3: 4.0±2.0%, Na2O: 15.0±3.0%, F content: 7.5±3.0%, MgO: 4.0±2.0%, and the rest are unavoidable impurities.

2. The mold powder for continuous casting of thick plate high carbon steel according to claim 1, characterized in that: The protective slag has a basicity of 0.98±0.10, a melting temperature of 980±50° C., and a viscosity of 0.10±0.07 Pa·s at 1300° C.

3. A method for preparing mold powder for continuous casting of wide and thick plate high carbon steel, characterized in that: include: S1 weighs raw materials according to the ratio, and mixes SiO2, CaO, Al2O3, Na2O, CaF2, MgO and carbonaceous materials; S2: placing the mixed material in a ball mill for thorough grinding; S3 adds a binder to granulate, and controls the moisture content to ≤0.5% after drying to obtain a finished protective slag, wherein the protective slag comprises, by mass percentage: SiO2: 28.5±5.0%, CaO: 28.0±5.0%, Al2O3: 4.0±2.0%, Na2O: 15.0±3.0%, F content: 7.5±3.0%, MgO: 4.0±2.0%, and the rest are unavoidable impurities.

4. The method for preparing mold powder for continuous casting of thick plate high carbon steel according to claim 3, characterized in that: Also includes: In the heat treatment process, the granulated protective slag is heated to 600-800℃ at 5-10℃ / min under nitrogen protection, kept at this temperature for 1-2h and then cooled with the furnace.

5. The method for preparing mold powder for continuous casting of thick plate high carbon steel according to claim 3, characterized in that: In S2, the mixed material is placed in a ball mill and fully ground to a particle size of ≤2.0 mm.

6. The method for preparing mold powder for continuous casting of thick plate high carbon steel according to claim 5, characterized in that: The graded grinding process is adopted during grinding, first coarse grinding to a particle size of 2.0-3.0 mm, then fine grinding to a particle size of ≤0.5 mm, and 0.1-0.3% of the total weight of the raw materials is added as a grinding aid during fine grinding.

7. The method for preparing mold powder for continuous casting of thick plate high carbon steel according to claim 3, characterized in that: The carbonaceous material is graphite or carbon black, and the added amount is 5.0±3.0% of the total mass.

8. The method for preparing mold powder for continuous casting of thick plate high carbon steel according to claim 3, characterized in that: In S2, the ground mixture needs to pass through an 80-mesh sieve with a sieve residue rate of ≤5%.

9. The method for preparing mold powder for continuous casting of thick plate high carbon steel according to claim 3, characterized in that: In S3, the binder is sodium carboxymethyl cellulose, and the addition amount is 0.5% to 1.5% of the total mass of the mixture.

10. The method for preparing mold powder for continuous casting of thick plate high carbon steel according to claim 3, characterized in that: The thickness of the liquid slag layer formed by the protective slag in the crystallizer is 8-15 mm, and the thickness of the slag film is 0.1-0.3 mm.

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