A φ1000-1200 mm continuous casting protective slag and application thereof

Abstract

This invention provides a protective slag for continuous casting with a diameter of φ1000-1200mm and its application, relating to the field of steelmaking auxiliary materials technology. It comprises 4-8 parts fluorite, 3-10 parts cement clinker, 1-4 parts white alkali, 22-30 parts coke powder, 1-6 parts bentonite, 8-14 parts bauxite powder, 8-15 parts magnesium olivine powder, 32-42 parts blast furnace slag powder, and 2-3 parts binder. By increasing the carbon content, the temperature field difference at different parts of the large cross-section of the liquid surface is effectively alleviated, eliminating the shrinkage porosity in the middle of the continuously cast billet. By increasing the proportion of Al2O3 and MgO, the binary basicity of the prepared protective slag is reduced, the melting temperature is increased, and the crystallization temperature is increased. Combined with increasing the amount of coke powder added, not only can the melting rate be controlled, but also the three-layer structure of the protective slag in the crystallizer can be controlled, resulting in a suitable liquid slag layer thickness, a small sintered layer thickness, and no large slag streaks. The surface of the continuously cast billet shell is less prone to defects, and overall defects are fewer.

Description

Technical Field

[0001] This invention relates to the field of steelmaking auxiliary materials technology, and in particular to a protective slag for continuous casting with a diameter of φ1000-1200mm and its application. Background Technology

[0002] In existing technologies, medium carbon alloy steel continuously cast billets with a circular cross section of φ1000-1200mm are prone to surface longitudinal and transverse cracks, as well as subsurface microcracks, due to their large cross-section, low casting speed, long solidification time, and easily developed columnar crystal structure. Under the influence of casting stress, these continuously cast billets are prone to further expansion during subsequent stamping and forging processes, resulting in a decrease in yield and an increase in scrap rate. How to solve the above-mentioned defects of longitudinal and transverse cracks and subsurface microcracks in continuously cast billets has become a bottleneck problem in the metallurgical industry.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] One of the objectives of this invention is to provide a The protective slag used in continuous casting can eliminate the shrinkage porosity in the center of the continuously cast billet and make it less likely for defects to be generated on the surface of the billet shell. Overall, there are fewer defects, which solves at least one of the technical problems existing in the prior art.

[0005] The second objective of this invention is to provide a Application of continuous casting protective slag in the continuous casting of carbon alloy steel in φ1000~1200mm round billets.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] In a first aspect, the present invention provides a protective slag for continuous casting with a diameter of φ1000-1200mm. By weight, every 100 parts of raw materials of the protective slag include 4-8 parts of fluorite, 3-10 parts of cement clinker, 1-4 parts of white alkali, 22-30 parts of coke powder, 1-6 parts of bentonite, 8-14 parts of bauxite powder, 8-15 parts of magnesium olivine powder, 32-42 parts of blast furnace slag powder, and 2-3 parts of binder.

[0008] Furthermore, the chemical composition of the protective slag, by weight percentage, includes: 18-23% CaO, 21-25% SiO2, 12-17% Al2O3, 0.7-2.5% Na2O, 2-4% F-, 5.0-10.0% MgO, 0.3-2% Fe2O3, and 20-25% C, with the balance being volatile matter and unavoidable impurities.

[0009] Furthermore, the chemical composition of the protective slag, by weight percentage, includes: 19.5–21.5% CaO, 22.5–24.5% SiO2, 13.5–15.5% Al2O3, 0.7–2.5% Na2O, and 2.0–3.5% F. - It contains 6.0–9.0% MgO, 0.4–1.8% Fe2O3 and 21–24% C, with the balance being volatile matter and unavoidable impurities.

[0010] Furthermore, the chemical composition of the protective slag, by weight percentage, includes: 21.50% CaO, 23.57% SiO2, 14.06% Al2O3, 1.9% Na2O, and 2.05% F. - It contains 7.88% MgO, 0.9% Fe2O3 and 23.4% C, with the balance being volatile matter and unavoidable impurities.

[0011] Furthermore, the binary basicity of the protective slag is 0.8 to 1.0.

[0012] Furthermore, the melting point of the protective slag is 1250–1300°C.

[0013] Furthermore, the viscosity of the protective slag at 1300℃ is 1.3–2.5 Pa·s, and the crystallization rate is 20–30%.

[0014] Furthermore, the binder includes at least one of dextrin, starch, and carboxymethyl cellulose.

[0015] Secondly, the present invention also provides the application of a protective slag for continuous casting of φ1000-1200mm steel as described in any of the foregoing embodiments in the continuous casting of carbon alloy steel in φ1000-1200mm round billets.

[0016] Thirdly, the present invention also provides a continuous casting method for φ1000~1200mm, using the protective slag described in any of the foregoing embodiments, wherein... The casting speed for continuous casting is 0.10–0.20 m / min.

[0017] The protective slag provided by this invention is applied to the continuous casting production of medium-carbon alloy steel in round billets. Unlike conventional methods, it does not employ a protective slag with high basicity, high melting temperature, high crystallization temperature, and low viscosity to meet the requirements of conventional peritectic steel protective slags. Instead, based on the extremely low casting speed characteristic of this application scenario, it uses only coke powder as the carbon raw material for the protective slag. This serves to maintain the temperature and control the melting rate of the protective slag. By adding 22-30 parts of coke powder to increase the carbon content, it effectively alleviates the temperature field differences in different parts of the large cross-section of the liquid surface, which is beneficial to the feeding capacity in the middle of the large cross-section round billet. The shrinkage porosity in the middle of the continuously cast billet is eliminated; by increasing the amount of coke powder added, the dispersion ability of the coke powder and the ability to control the melting rate at high temperature are improved; at the same time, by adding 8-14 parts of bauxite and 8-15 parts of magnesium olivine powder, the proportion of Al2O3 and MgO is increased, which reduces the binary basicity of the prepared protective slag, increases the melting temperature and crystallization temperature, and also significantly increases the viscosity. Combined with increasing the amount of coke powder added, not only can the melting rate be controlled, but also the three-layer structure of the protective slag in the crystallizer can be controlled, so that the thickness of the liquid slag layer is appropriate, the thickness of the sintered layer is small, and there is no large slag strip phenomenon. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] The following is a detailed description of the protective slag for continuous casting with a diameter of φ1000~1200mm provided in this application and its application.

[0020] In a first aspect, the present invention provides a protective slag for continuous casting with a diameter of φ1000-1200mm. By weight, every 100 parts of raw materials of the protective slag include 4-8 parts of fluorite, 3-10 parts of cement clinker, 1-4 parts of white alkali, 22-30 parts of coke powder, 1-6 parts of bentonite, 8-14 parts of bauxite powder, 8-15 parts of magnesium olivine powder, 32-42 parts of blast furnace slag powder, and 2-3 parts of binder.

[0021] The amount of fluorite used can be, for example, but not limited to, 4 parts, 5 parts, 6 parts, 7 parts or 8 parts, or any other value within the range of 4 to 8 parts.

[0022] The amount of cement clinker can be, for example, but not limited to, 3, 4, 5, 6, 7, 8, 9 or 10 parts, or any other value within the range of 3 to 10 parts.

[0023] The amount of white alkali can be, for example, but not limited to, 1 part, 2 parts, 3 parts or 4 parts, or any other value within the range of 1 to 4 parts.

[0024] The amount of coke powder can be, for example, 22 parts, 23 parts, 24 parts, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts or 30 parts, or any other value in the range of 22 to 30 parts.

[0025] The amount of bentonite used can be, for example, but not limited to, 1 part, 2 parts, 3 parts, 4 parts, 5 parts or 6 parts, or any other value within the range of 1 to 6 parts.

[0026] The amount of bauxite powder used can be, for example, but not limited to, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts or 14 parts, or any other value within the range of 8 to 14 parts.

[0027] The amount of magnesium olivine powder can be, for example, but not limited to, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, or any other value in the range of 8 to 15 parts.

[0028] The amount of blast furnace slag powder can be, for example, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts or 42 parts, or any other value within the range of 32 to 42 parts.

[0029] The amount of adhesive used can be, for example, but not limited to, 2 or 3 parts, or any other value within the range of 2 to 3 parts.

[0030] The protective slag of this invention uses 22-30 parts of coke powder because, although the commonly used carbon black and graphite as carbon raw materials can control the melting rate of the protective slag, it cannot guarantee a high proportion of total carbon in the protective slag. This results in insufficient carbon combustion in the crystallizer. Adding 22-30 parts of coke powder can increase the proportion of total carbon. Carbon combustion has the effect of increasing heat, ensuring that the heat at the liquid surface in the crystallizer is not higher than the heat supplemented by carbon combustion, thus preventing the temperature in the middle of the crystallizer from dropping. This effectively alleviates the temperature field difference in different parts of the large cross-section of the liquid surface, which is beneficial to the feeding capacity in the middle of the large cross-section round billet and eliminates the shrinkage porosity in the middle of the continuously cast billet. By increasing the amount of coke powder... The addition of powder improves the dispersion ability of coke powder and the ability to control the melting rate at high temperatures. At the same time, by adding 8-14 parts of bauxite and 8-15 parts of magnesium olivine powder, the proportion of Al2O3 and MgO is increased, which reduces the binary basicity of the prepared protective slag, increases the melting temperature and crystallization temperature, and also significantly increases the viscosity. Using a protective slag with higher melting temperature, crystallization temperature and viscosity can control the amount of filling between the continuous casting billet shell and the crystallizer wall. Combined with increasing the amount of coke powder added, not only can the melting rate be controlled, but also the three-layer structure of the protective slag in the crystallizer can be controlled, so that the thickness of the liquid slag layer is appropriate, the thickness of the sintered layer is small, and there is no large slag streak phenomenon.

[0031] In a preferred embodiment, the chemical composition of the protective slag, by weight percentage, includes: 18-23% CaO, 21-25% SiO2, 12-17% Al2O3, 0.7-2.5% Na2O, and 2-4% F. - It contains 5.0–10.0% MgO, 0.3–2% Fe2O3, and 20–25% C, with the balance being volatile matter and unavoidable impurities.

[0032] By increasing the proportions of Al2O3 and MgO, the viscosity of the protective slag is increased. The combination of high viscosity and low casting speed results in a moderate slag film thickness. Al2O3 will produce calcium aluminum feldspar (2CaO.Al2O3.SiO2) crystals, and MgO will also produce calcium magnesium feldspar (Ca2MgSi2O7) crystals. This leads to uniform heat transfer, reduces the likelihood of defects on the surface of the continuously cast billet shell, and minimizes overall defects. The CaO content can be, for example, but not limited to, 18%, 19%, 20%, 21%, 22%, or 23%, or any other value within the range of 18% to 23%.

[0033] The SiO2 content can be, for example, but not limited to, 21%, 22%, 23%, 24% or 25%, or any other value in the range of 21% to 25%.

[0034] The content of Al2O3 can be, for example, but not limited to, 12%, 13%, 14%, 15%, 16% or 17%, or any other value in the range of 12% to 17%.

[0035] The Na2O content can be, for example, but not limited to, 0.7%, 1.0%, 1.5%, 2.0% or 2.5%, or any other value in the range of 0.7% to 2.5%.

[0036] F - The content can be, for example, but not limited to, 2%, 3% or 4%, or any other value in the range of 2% to 4%.

[0037] The MgO content can be, for example, but not limited to, 5%, 6%, 7%, 8%, 9% or 10%, or any other value in the range of 5.0% to 10.0%.

[0038] The Fe2O3 content can be, for example, but not limited to, 0.3%, 1%, 1.5% or 2%, or any other value in the range of 0.3% to 2%.

[0039] The content of C can be, for example, but not limited to, 20%, 21%, 22%, 23%, 24% or 25%, or any other value in the range of 20% to 25%.

[0040] It should be noted that, except for carbon, the chemical components of the protective slag need to be tested by acid dissolution. All carbonate substances will volatilize CO2 volatile substances, which are collectively referred to as volatile matter.

[0041] In a preferred embodiment, the chemical composition of the protective slag includes: 19.5–21.5% CaO, 22.5–24.5% SiO2, 13.5–15.5% Al2O3, 0.7–2.5% Na2O, and 2.0–3.5% F. - It contains 6.0–9.0% MgO, 0.4–1.8% Fe2O3 and 21–24% C, with the balance being volatile matter and unavoidable impurities.

[0042] In a preferred embodiment, the chemical composition of the protective slag includes: 21.50% CaO, 23.57% SiO2, 14.06% Al2O3, 1.9% Na2O, and 2.05% F. - It contains 7.88% MgO, 0.9% Fe2O3 and 23.4% C, with the balance being volatile matter and unavoidable impurities.

[0043] In a preferred embodiment, the binary basicity of the protective slag is 0.8 to 1.0.

[0044] In a preferred embodiment, the melting point of the protective slag is 1250–1300°C.

[0045] In a preferred embodiment, the protective slag has a viscosity of 1.3–2.5 Pa·s at 1300°C and a crystallization rate of 20–30%.

[0046] By selecting a binary basicity lower than that of conventional round billet protective slag, the proportion of Al2O3 and MgO is increased, thereby improving the melting point and viscosity of the protective slag. This allows for control of the thickness of the slag liquid layer and ensures a suitable three-layer structure for the overall protective slag. It also reduces the ability to precipitate gun crystals and minimizes the impact of excessive gun crystals on the crystallization ratio. This reduces the variation in protective slag performance, which is beneficial for the stability of heat transfer control. Appropriately increasing the crystallization rate of calcium aluminum feldspar and calcium magnesium feldspar, while maintaining a relatively stable crystallization rate, ensures good lubrication between the continuous casting billet shell and the crystallizer wall. At the same time, it also appropriately controls the heat transfer of the billet shell, ensuring the reliable surface quality of the continuous casting billet.

[0047] In a preferred embodiment, the adhesive comprises at least one of dextrin, starch, and carboxymethyl cellulose.

[0048] Based on the beneficial effects of the protective slag for φ1000~1200mm continuous casting provided by the present invention, in a second aspect, the present invention also provides the application of a protective slag for φ1000~1200mm continuous casting as described in any of the foregoing embodiments in the continuous casting of carbon alloy steel in φ1000~1200mm round billets.

[0049] Based on the beneficial effects of the protective slag for continuous casting with a diameter of φ1000-1200mm provided by the present invention, in a third aspect, the present invention also provides a continuous casting method for φ1000-1200mm, using the protective slag described in any of the foregoing embodiments. The casting speed for continuous casting is 0.10–0.20 m / min.

[0050] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0051] Example 1

[0052] This embodiment provides a protective slag for continuous casting with a diameter of φ1000~1200mm. By weight, its raw materials include: 4 parts fluorite, 6 parts cement clinker, 3 parts white alkali, 26 parts coke powder, 3 parts bentonite, 10 parts magnesium olivine powder, 10 parts bauxite powder, 36 parts blast furnace slag powder, and 2 parts starch.

[0053] The resulting protective slag contains the following chemical composition by mass percentage: 21.50% CaO, 23.57% SiO2, 14.06% Al2O3, 1.9% Na2O, and 2.05% F. -It contains 7.88% MgO, 0.9% Fe2O3 and 23.4% C, with the balance being volatile matter and unavoidable impurities.

[0054] The physical properties of this protective slag are: binary basicity (CaO / SiO2) of 0.92, melting temperature of 1258℃, viscosity of 1.9 Pa·s at 1300℃, and crystallization rate of 24%.

[0055] Example 2

[0056] The purity and fineness of the raw materials for the φ1000~1200mm continuous casting protective slag provided in this embodiment are the same as those in Example 1. The only difference is the amount of raw materials used.

[0057] By weight, its raw materials include 5 parts fluorite, 8 parts cement clinker, 4 parts white alkali, 24 parts coke powder, 1 part bentonite, 11 parts magnesium olivine powder, 13 parts bauxite powder, 32 parts blast furnace slag powder, and 2 parts carboxymethyl cellulose.

[0058] The resulting protective slag, by mass percentage, contains the following chemical components: 22.34% CaO, 22.78% SiO2, 16.66% Al2O3, 2.43% Na2O, and 2.45% F. - It contains 8.21% MgO, 0.9% Fe2O3 and 21.6% C, with the balance being volatile matter and unavoidable impurities.

[0059] The physical properties of this protective slag are: binary basicity (CaO / SiO2) of 0.98, melting temperature of 1245℃, viscosity of 2.45 Pa·s at 1300℃, and crystallization rate of 28%.

[0060] Example 3

[0061] The purity and fineness of the raw materials for the φ1000~1200mm continuous casting protective slag provided in this embodiment are the same as those in Example 1. The only difference is the amount of raw materials used.

[0062] By weight, its raw materials include 8 parts fluorite, 4 parts cement clinker, 1 part white alkali, 24 parts coke powder, 6 parts bentonite, 14 parts magnesium olivine powder, 8 parts bauxite powder, 33 parts blast furnace slag powder, and 2 parts dextrin.

[0063] The resulting protective slag, by mass percentage, contains the following chemical components: 21.05% CaO, 24.42% SiO2, 12.90% Al2O3, 0.71% Na2O, and 3.81% F. - It contains 9.32% MgO, 0.81% Fe2O3 and 21.7% C, with the balance being volatile matter and unavoidable impurities.

[0064] The physical properties of this protective slag are: binary basicity (CaO / SiO2) of 0.86, melting temperature of 1289℃, viscosity of 1.41 Pa·s at 1300℃, and crystallization rate of 21%.

[0065] Experimental Example 1: Effect of Different Coke Powder Addition Amounts on the Performance of Protective Slag

[0066] This experiment uses the protective slag prepared in Example 1 for testing, and sets up Comparative Example 1, Comparative Example 2 and Comparative Example 5.

[0067] Comparative Example 1:

[0068] The purity and fineness of the raw materials for the φ1000~1200mm continuous casting protective slag provided in this comparative example are the same as those in Example 1. The main difference is that the amount of coke powder is different, and the amount of blast furnace slag powder used is adjusted to make up for the difference.

[0069] The raw materials for this comparative example include: 4 parts fluorite, 6 parts cement clinker, 3 parts white alkali, 32 parts coke powder, 3 parts bentonite, 10 parts magnesium olivine powder, 10 parts bauxite powder, 30 parts blast furnace slag powder, and 2 parts starch.

[0070] The resulting protective slag contains the following chemical components by weight percentage: 17.89% CaO, 21.03% SiO2, 12.94% Al2O3, 1.94% Na2O, and 2.16% F. - It contains 7.21% MgO, 1.23% Fe2O3 and 30.6% C, with the balance being volatile matter and unavoidable impurities.

[0071] The physical properties of the protective slag in Comparative Example 1 are as follows: binary basicity (CaO / SiO2) 0.9, melting temperature 1312℃, viscosity at 1300℃ 2.53 Pa·s, and crystallization rate 16%.

[0072] Comparative Example 2:

[0073] The purity and fineness of the raw materials for the φ1000~1200mm continuous casting protective slag provided in this comparative example are the same as those in Example 1. The difference is that the amount of coke powder raw material is different, and the amount of blast furnace slag powder used is adjusted to make up for the difference.

[0074] The raw materials for this comparative example include: 4 parts fluorite, 6 parts cement clinker, 3 parts white alkali, 18 parts coke powder, 3 parts bentonite, 10 parts magnesium olivine powder, 10 parts bauxite powder, 44 parts blast furnace slag powder, and 2 parts starch.

[0075] The resulting protective slag contains the following chemical components by weight percentage: 24.51% CaO, 26.34% SiO2, 15.27% Al2O3, 1.94% Na2O, and 2.31% F.- It contains 8.67% MgO, 0.76% Fe2O3 and 16.2% C, with the balance being volatile matter and unavoidable impurities.

[0076] The physical properties of this protective slag are: binary basicity (CaO / SiO2) of 0.93, melting temperature of 1227℃, viscosity of 1.94 Pa·s at 1300℃, and crystallization rate of 35%.

[0077] Comparative Example 5

[0078] The purity and fineness of the raw materials for the φ1000~1200mm continuous casting protective slag provided in this comparative example are the same as those in Example 1. The difference is that the carbon source is a composite carbon source composed of carbon black and graphite, which replaces the coke powder in Example 1. The specific ratio of carbon black to graphite is 1:8.

[0079] The resulting protective slag contains the following chemical components by weight percentage: 18% CaO, 19.5% SiO2, 14.1% Al2O3, 1.9% Na2O, and 2.5% F. - It contains 7.7% MgO, 1.9% Fe2O3 and 23.5% C, with the balance being volatile matter and unavoidable impurities.

[0080] The physical properties of this protective slag are: binary basicity (CaO / SiO2) of 0.92, melting temperature of 1260℃, viscosity of 1.95 Pa·s at 1300℃, and crystallization rate of 25%.

[0081] The protective slags for continuous casting with a diameter of φ1000-1200mm prepared in Examples 1, 1, 2, and 5 were used as test slags and tested on a 1200mm round billet production line of a steel plant in China. The test slags for Example 1 were numbered XLY-1, for Comparative Example 1 XLY-4, for Comparative Example 2 XLY-5, and for Comparative Example 5 XLY-8. The test process parameters were: steel grade 14MnVNb, casting speed 0.15m / min. A total of 1T of protective slag was tested.

[0082] The specific results of the experiment are shown in Table 1.

[0083] Table 1. Test results of protective slag performance with different coke powder addition amounts

[0084]

[0085] As shown in Table 1, the protective slag provided in Example 1 of this invention has good spreadability and fluidity in the crystallizer. With the total slag layer controlled at 35-60mm, the liquid slag layer thickness is appropriate, the three-layer melting structure is obviously stable, and the production of six heats in a whole casting is stable. The pickled low-magnification surface of the billet produced in the test has clear and disordered vibration marks, and no defects such as pits, slag pits, or cracks. The microstructure distribution is uniform and reasonable, and all are qualified parts.

[0086] However, in Comparative Example 1, the amount of coke powder added was further increased, resulting in slow melting in the crystallizer, a reduced slag layer thickness, and a sintered layer thickness of 3-5 mm. This caused defects such as surface depressions, slag pits, and cracks on the billet, and even triggered continuous casting alarms, forcing the continuous casting to be interrupted and temporarily stopped, resulting in a high billet scrap rate. In Comparative Example 2, the amount of coke powder added was reduced, resulting in excessively fast melting in the crystallizer, a sintered layer thickness of 20-25 mm, severe slag agglomeration, and excessively large slag strips. This affected the uneven flow of slag and caused defects such as surface depressions, slag pits, and cracks on the billet, resulting in a high billet scrap rate and potentially triggering continuous casting alarms, affecting normal continuous casting operations. In Comparative Example 5, the coke powder was replaced with a composite carbon source of carbon black and graphite, resulting in a too slow melting rate. The slag could not meet the consumption requirements, and slag pits appeared on the surface of the billet.

[0087] Experimental Example 2: Effect of Different Magnesia-Olivine Powder Additions on the Performance of Protective Slag

[0088] This experimental example uses the protective slag prepared in Example 2 for testing, and sets up Comparative Example 3.

[0089] Comparative Example 3:

[0090] The purity and fineness of the raw materials for the φ1000~1200mm continuous casting protective slag provided in this comparative example are the same as those in Example 2. The main difference is that the amount of magnesium olivine powder raw material is different.

[0091] The raw materials for this comparative example include: 5 parts fluorite, 8 parts cement clinker, 4 parts white alkali, 24 parts coke powder, 1 part bentonite, 6 parts magnesium olivine powder, 13 parts bauxite powder, 37 parts blast furnace slag powder, and 2 parts carboxymethyl cellulose.

[0092] The resulting protective slag contains the following chemical components by weight percentage: 24.23% CaO, 22.16% SiO2, 17.39% Al2O3, 2.43% Na2O, and 2.41% F. - It contains 2.85% MgO, 0.7% Fe2O3, and 21.6% C, with the balance being volatile matter and unavoidable impurities.

[0093] The physical properties of this protective slag are: binary basicity (CaO / SiO2) of 1.08, melting temperature of 1235℃, viscosity of 1.19 Pa·s at 1300℃, and crystallization rate of 15%.

[0094] The protective slags for continuous casting with diameters of φ1000-1200mm prepared in Example 2 and Comparative Example 3 were used as test slags and tested on a 1200mm round billet production line of a steel plant in China. The test slags for Example 2 were numbered XLY-2 and the test slags for Comparative Example 3 were numbered XLY-6. The test process parameters were: steel grade 16MnVH, casting speed 0.15m / min. A total of 1T of protective slag was tested.

[0095] The specific results of the experiment are shown in Table 2.

[0096] Table 2. Test results of protective slag performance with different amounts of magnesium olivine powder.

[0097]

[0098] As shown in Table 2, the protective slag provided in Example 2 of this invention has good spreadability and fluidity in the crystallizer. With the total slag layer controlled at 35-60mm, the liquid slag layer thickness is appropriate. There are slight slag streaks and agglomeration in the crystallizer. The three-layer melting structure is clear. The production of the entire casting process is stable for 7 heats. The pickled low-magnification surface of the billet produced in the test has clear and disordered vibration marks, and there are no defects such as pits, slag pits, or cracks. All of them are qualified parts after testing.

[0099] However, in Comparative Example 3, the amount of magnesium olivine powder added was reduced, resulting in better spreadability and fluidity in the crystallizer, a thinner liquid slag layer, uneven lubrication during casting, excessively rapid heat transfer, unstable heat flow curve, and an uneven surface of the cast billet. After pickling, there were defects such as central depression and longitudinal cracks. Analysis showed that this was mainly due to the reduction of calcium magnesium feldspar, low crystallization rate, faster heat transfer of slag film, increased billet cracks, and increased scrap rate.

[0100] Experimental Example 3: Effect of Different Amounts of Bauxite Powder on the Performance of Protective Slag

[0101] This experimental example uses the protective slag prepared in Example 3 for testing, and sets up Comparative Example 4.

[0102] Comparative Example 4:

[0103] The purity and fineness of the raw materials for the φ1000~1200mm continuous casting protective slag provided in this comparative example are the same as those in Example 3. The main difference is that the amount of bauxite powder used is different.

[0104] The raw materials for this comparative example include: 8 parts fluorite, 4 parts cement clinker, 1 part white alkali, 24 parts coke powder, 6 parts bentonite, 14 parts magnesium olivine powder, 5 parts bauxite powder, 36 parts blast furnace slag powder, and 2 parts dextrin.

[0105] The resulting protective slag contains the following chemical components by weight percentage: 22.47% CaO, 25.23% SiO2, 10.07% Al2O3, 0.67% Na2O, and 3.76% F. - It contains 9.61% MgO, 0.58% Fe2O3 and 21.7% C, with the balance being volatile matter and unavoidable impurities.

[0106] The physical properties of this protective slag are: binary basicity (CaO / SiO2) of 0.88, melting temperature of 1299℃, viscosity of 1.26 Pa·s at 1300℃, and crystallization rate of 5%.

[0107] The protective slags for continuous casting with diameters of φ1000-1200mm prepared in Example 3 and Comparative Example 4 were used as test slags and tested on a 1200mm round billet production line in a steel plant in China. The test slags for Example 3 were numbered XLY-3 and the test slags for Comparative Example 4 were numbered XLY-7. The test process parameters were: steel grade 16MnVH, casting speed 0.15m / min. A total of 1T of protective slag was tested.

[0108] The specific results of the experiment are shown in Table 3.

[0109] Table 3. Effects of different bauxite powder addition amounts on the performance of protective slag.

[0110]

[0111] As shown in Table 3, the protective slag provided by Example 3 of the present invention has good spreadability and fluidity in the crystallizer, the liquid slag layer is slightly thin, there is no slag clump phenomenon in the crystallizer, the three-layer melting structure sintering layer is not obvious, the production of 6 heats in a whole casting is stable, the pickled low magnification billet surface of the produced billet has deep vibration marks and small slag pit defects, but no cracks. The microstructure distribution is reasonable after testing, and all are qualified parts.

[0112] However, in Comparative Example 4, the amount of bauxite powder added was reduced, which led to a significant increase in consumption during use due to the lower viscosity. This resulted in deeper vibration marks on the cast billet, more transverse cracks at the troughs, and a 20% increase in the quality of the cast billet and the grinding rate.

[0113] In summary, the protective slag provided by this invention is suitable for the continuous casting production of medium carbon alloy steel parts for φ1000~1200mm round billets. The raw material selection and performance index design are reasonable, which can play a good role in lubrication and heat transfer control during the continuous casting process of medium carbon alloy steel for φ1000~1200mm round billets. In addition, due to the increased amount of coke powder added to the slag, the phenomenon of non-organic shrinkage porosity in the center of the continuously cast billet is eliminated. The selection of a relatively high proportion of Al2O3 and MgO increases the melting point of the protective slag, and its slag surface melting reaction is normal. The viscosity of the protective slag is also increased, which makes the billet shell growth uniform and stable, the overall quality of the continuously cast billet stable, the production smooth, and no defective products appearing during billet inspection.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A protective slag for continuous casting with a diameter of φ1000~1200mm, characterized in that, By weight, each 100 parts of raw materials of the protective slag includes 4-8 parts of fluorite, 3-10 parts of cement clinker, 1-4 parts of white alkali, 22-30 parts of coke powder, 1-6 parts of bentonite, 8-14 parts of bauxite powder, 8-15 parts of magnesium olivine powder, 32-42 parts of blast furnace slag powder and 2-3 parts of binder. The chemical composition of the protective slag, by weight percentage, includes: 18–23% CaO, 21–25% SiO2, 12–17% Al2O3, 0.7–2.5% Na2O, and 2–4% F. - 5.0–10.0% MgO, 0.3–2% Fe2O3 and 20–25% C, with the balance being volatile matter and unavoidable impurities; The binary basicity of the protective slag is 0.8–1.0; The protective slag has a viscosity of 1.3 to 2.5 Pa·s at 1300°C and a crystallization rate of 20 to 30%.

2. The protective slag for continuous casting with a diameter of φ1000-1200mm as described in claim 1, characterized in that, The chemical composition of the protective slag, by weight percentage, includes: 19.5–21.5% CaO, 22.5–24.5% SiO2, 13.5–15.5% Al2O3, 0.7–2.5% Na2O, and 2.0–3.5% F. - It contains 6.0–9.0% MgO, 0.4–1.8% Fe2O3 and 21–24% C, with the balance being volatile matter and unavoidable impurities.

3. The protective slag for continuous casting with a diameter of φ1000-1200mm as described in claim 2, characterized in that, The chemical composition of the protective slag, by weight percentage, includes: 21.50% CaO, 23.57% SiO2, 14.06% Al2O3, 1.9% Na2O, and 2.05% F. - It contains 7.88% MgO, 0.9% Fe2O3 and 23.4% C, with the balance being volatile matter and unavoidable impurities.

4. The protective slag for continuous casting with a diameter of φ1000-1200mm as described in claim 1, characterized in that, The melting point of the protective slag is 1250–1300℃.

5. The protective slag for continuous casting with a diameter of φ1000-1200mm according to claim 1, characterized in that, The binder includes at least one of dextrin, starch, and carboxymethyl cellulose.

6. The application of the protective slag for continuous casting of φ1000~1200mm as described in any one of claims 1-5 in the continuous casting of carbon alloy steel in φ1000~1200mm round billets.

7. A continuous casting method for φ1000~1200mm, characterized in that, Using the protective slag described in any one of claims 1-5, the casting speed of the φ1000~1200mm continuous casting method is 0.10~0.20m / min.

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