A continuous casting protective slag for high-aluminum peritectic steel and a method for using the same

Abstract

The application discloses a continuous casting protective slag for high-aluminum peritectic steel and a use method thereof. The A-type slag and B-type slag are combined, the surface longitudinal crack defects of the high-aluminum peritectic steel can be effectively controlled, the problem of the performance deterioration of the molten slag caused by the violent reaction of the high-aluminum peritectic steel with the slag can be overcome, the conflict problem of the performance requirement of the protective slag caused by the characteristics of the high-aluminum peritectic steel is reasonably avoided, the continuous casting process is ensured to be smooth, the occurrence rate of the breakout alarm is eliminated, and the surface quality of the casting blank is obviously improved, and the longitudinal crack defects are inhibited.

Description

Technical Field

[0001] This invention belongs to the field of auxiliary materials for continuous casting in steelmaking, specifically relating to a protective slag for continuous casting of high-alumina peritectic steel and its application method. Background Technology

[0002] Continuous casting flux is a functional auxiliary material used in steelmaking, applied to the surface of molten steel. It appears as a black powder or small granules. It possesses multiple functions, including heat insulation, preventing oxidation of the molten steel, absorbing inclusions, lubrication, and controlling heat transfer. It is the final process element in controlling the surface quality of the cast billet during steelmaking. To ensure these five functions, a liquid slag layer of a certain thickness must be formed between the molten steel and the solid flux when it is applied to the surface. This effectively prevents air from entering, accommodates more foreign inclusions, and provides sufficient liquid slag between the cast billet and the copper plate of the crystallizer, thus ensuring good lubrication and heat transfer control. If the flux performance is poor, and the liquid slag layer cannot be guaranteed to be thick enough or consumed sufficiently, it will cause surface defects such as inclusions and cracks in the cast billet. In severe cases, it can even cause excessive resistance during casting and lead to steel leakage. Therefore, flux is a crucial means to ensure the smooth operation of the continuous casting process and the surface quality of the cast billet.

[0003] Typically, protective slag is mainly composed of a binary system of CaO and SiO2, supplemented with fluxes such as CaF2, Na2O, and Li2O, as well as small amounts of components such as Al2O3, MgO, and MnO, and some unavoidable impurities (such as Fe2O3), to achieve suitable physicochemical properties and meet the aforementioned application requirements. However, since the melting point of protective slag is 400–500°C lower than that of molten steel, a certain amount of carbonaceous materials, such as carbon black and graphite, must be added to control the slow melting of the relatively low-melting-point protective slag on the surface of molten steel. Carbonaceous materials, due to their high melting point, can effectively prevent the aggregation of protective slag droplets, thereby controlling the melting rate of the protective slag; moreover, carbonaceous materials can be completely burned into gas, without polluting the protective slag, making them an inexpensive and practical skeletal material. In summary, protective slag is a mixture of various oxides and fluorides, mainly composed of CaO and SiO2 (the two together account for approximately 60–70%).

[0004] In the existing technology, there are mainly two types of protective slag: one is the protective slag used in peritectic steel smelting, and the other is the protective slag used in high-alumina steel smelting.

[0005] Peritectic steel refers to carbon steel with a carbon content ranging from 0.08% to 0.16%. During solidification, it undergoes a peritectic reaction, transforming from face-centered cubic ferrite to body-centered cubic austenite. This phase transformation is accompanied by significant volume shrinkage. In the continuous casting mold, the initial billet shell is highly susceptible to cracking due to uneven solidification and stress concentration at weak points. To address this, a high-basicity (CaO / SiO2) protective slag is used. By improving the crystallization properties of the protective slag, increasing the thickness of the solidified slag film, and increasing the thermal resistance of the slag film, a slow cooling effect is achieved in the mold, thereby promoting uniform billet shell growth and preventing stress concentration. Patents such as JP2017013082, JP2013078797, JP2013066913, and JP2012125826 all employ the design concept of high-basicity protective slag to address the longitudinal cracking problem of peritectic steel, requiring a basicity value higher than 1.0, and some even requiring a value above 1.6.

[0006] Aluminum possesses excellent deoxidizing, grain-refining, and corrosion-resistant properties, making it a common element in molten steel. It is also a highly reducing element. During the steel pouring process, aluminum comes into direct contact with the protective slag inside the crystallizer, inevitably undergoing the following redox reactions with the SiO2-dominant components of the slag:

[0007] 4[Al]+3(SiO2)=3[Si]+2(Al2O3) (1)

[0008] This reaction causes SiO2 in the protective slag to be reduced by aluminum in the molten steel, and the generated Al2O3 enters the protective slag again. The reduction of SiO2 leads to an increase in basicity, which deteriorates the glass transition effect of the protective slag, while the increase of Al2O3 causes a sharp increase in viscosity. Figure 1 The figure shows the reduction degree of SiO2 in the protective slag under different Al contents in molten steel. As can be seen from the figure, when the Al content in the steel exceeds 0.5%, the slag-steel reaction becomes quite severe, resulting in the reduction of about 1 / 3 of the SiO2. These changes in composition ultimately lead to severe modification of the protective slag, which in turn causes it to lose its proper metallurgical functions, which is very detrimental to the smooth operation of the continuous casting process and the improvement of the surface quality of the cast billet.

[0009] In response to the casting characteristics of high-alumina steel, the protective slag used is usually designed as an acidic slag, with an alkalinity of less than 0.7, as seen in patents JP2005152973, JP2010042421, CN201210259029.2, and CN201410641694.7. By adding a sufficient amount of SiO2, the alkalinity after the slag-steel reaction reaches equilibrium can be maintained within the normal range.

[0010] The two types of protective slags mentioned above employ completely different approaches depending on the characteristics of each steel grade: high-basicity slag for peritectic steel and low-basicity slag for high-alumina steel. However, with the continuous expansion of metallurgical technology, the role of aluminum in steel has become increasingly important, evolving from initial deoxidation and grain refinement to improving corrosion resistance, resistivity, and non-magnetic properties. The aluminum content in steel has also gradually increased from 0.02% to 0.5%, and even above 1%. Under such high aluminum content conditions, the presence of high-oxygen-potential oxides such as SiO2 in the protective slag is inevitably reduced. In this situation, to prevent slag degradation due to slag-steel reaction, only a low-reactivity protective slag design approach can be adopted. However, for high-alumina peritectic steel, low-basicity slag cannot achieve a slow cooling effect on the initial billet shell, and longitudinal cracking is a significant problem.

[0011] There has been no good solution for how to select protective slag for peritectic steel with an aluminum content of more than 0.5%. Even if a protective slag with a basicity of 1.1 to 1.2 is selected, the basicity of the slag and steel after reaction will reach more than 2.0, and the performance deterioration will still be relatively high. Due to the impact on lubrication function, steel leakage alarm accidents still occur frequently during continuous casting.

[0012] In view of the above, the present invention has developed a protective slag for high-alumina peritectic steel and its application method, which can prevent the deformation of the protective slag during the casting process and prevent longitudinal cracks in the cast billet, thereby meeting the actual production needs of high-alumina peritectic steel. Summary of the Invention

[0013] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a continuous casting protective slag for high-alumina peritectic steel and its application method. By employing a combination of type A and type B slag, this method not only effectively controls the unique surface longitudinal cracking defects of high-alumina peritectic steel but also overcomes the problem of slag performance deterioration caused by the intense slag-steel reaction in high-alumina peritectic steel. This rationally avoids the problem of conflicting requirements for protective slag performance due to the steel's characteristics, ensuring smooth continuous casting, eliminating the occurrence of steel leakage alarms, significantly improving the surface quality of the cast billet, and suppressing longitudinal cracking defects.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] The first aspect of the present invention provides a continuous casting protective slag for high-alumina peritectic steel, comprising type A slag and type B slag;

[0016] Both the Type A slag and the Type B slag include the following components by weight percentage: CaO and SiO2: 50-70%, Na2O: 5-12%, F: 7-10%, LiO: 0-2%, C: 2-4%, unavoidable metal oxides: 5-8%, and the balance being burn-off other than C.

[0017] The basicity of the type A slag is >1; the basicity of the type B slag is less than that of the type A slag.

[0018] Preferably, the type A slag comprises the following components by weight percentage: CaO and SiO2: 60-70%, Na2O: 5-10%, F: 7-10%, Li2O: 0-1%, C: 2-4%, unavoidable metal oxides: 5-8%, and the balance being burn-off other than C; and / or

[0019] The alkalinity of the type A slag is 1.1 to 1.4.

[0020] Preferably, the type B slag comprises the following components by weight percentage: CaO and SiO2: 50-60%, Na2O: 9-12%, F: 9-10%, Li2O: 1-2%, C: 3-4%, unavoidable metal oxides: 5-8%, and the balance being burn-off other than C; and / or

[0021] The basicity of the B-type slag is 0.5 to 0.9.

[0022] Preferably, the unavoidable metal oxides include Al2O3, MgO, MnO, and Fe2O3.

[0023] Preferably, the properties of the type A slag and the type B slag are as follows: melting point of 1000-1200℃, and viscosity of 0.07-0.15 Pa·s at 1300℃.

[0024] A second aspect of the present invention provides a method for using a continuous casting protective slag for peritectic steel, comprising the following steps:

[0025] S1, calculate the basicity of type A slag and type B slag, complete the preparation of type A slag and type B slag in the continuous casting protective slag for peritectic steel as described in the first aspect of the present invention, and determine the amount of type A slag used.

[0026] S2, In the initial stage of continuous casting, after the initial casting is completed using the initial casting slag, type A slag is first added to form a slag layer with crystallization effect on the surface of the molten steel; when the type A slag is used up, type B slag is continuously used.

[0027] Preferably, in step S1, the amount of type A slag used is calculated using the following formula:

[0028]

[0029] Wherein, G represents the amount of Type A slag used, in kg;

[0030] T represents the steel throughput, measured in t / min;

[0031] H represents the Al content of the steel grade, expressed in wt%.

[0032] Preferably, in step S1, the alkalinity of type A slag is calculated using the following formula:

[0033]

[0034] Among them, R A The alkalinity of type A slag is dimensionless.

[0035] H represents the Al content of the steel grade, expressed in wt%.

[0036] Preferably, in step S1, the alkalinity of type B slag is calculated using the following formula:

[0037]

[0038] Among them, R B The alkalinity of type B slag is dimensionless.

[0039] H represents the Al content of the steel grade, expressed in wt%.

[0040] The continuous casting protective slag for high-alumina peritectic steel and its application method provided by this invention have the following beneficial effects:

[0041] 1. The continuous casting protective slag for high-alumina peritectic steel and its application method of the present invention adopt a combination of type A slag and type B slag, which can not only effectively control the surface longitudinal crack defects unique to high-alumina peritectic steel, but also overcome the problem of slag performance deterioration caused by the intense reaction between the slag and steel in high-alumina peritectic steel. Thus, it reasonably avoids the problem of conflict between the performance requirements of protective slag due to the characteristics of high-alumina peritectic steel. It not only ensures the smooth operation of the continuous casting process and eliminates the occurrence rate of steel leakage alarm, but also significantly improves the surface quality of the billet and suppresses longitudinal crack defects.

[0042] 2. The continuous casting protective slag for high-alumina peritectic steel of the present invention and its application method, in the initial stage of continuous casting, after the initial casting is completed using the initial casting slag, firstly, type A slag with a basicity (CaO / SiO2) greater than 1 is added to preferentially form a slag layer with a certain crystallization ability on the surface of the molten steel. After flowing into the gap between the copper plate and the billet shell in the crystallizer, a crystalline solid slag film is formed, thereby achieving a slow cooling effect on the initial billet shell and preventing longitudinal crack defects. As the casting process proceeds, the slag-steel reaction will inevitably continue to occur, causing the basicity to rise continuously. When the basicity rises to a level sufficient to destroy the lubricating function of the slag, the use of type A slag is stopped. (The amount of Type A slag used can be calculated first to maintain the basicity of the slag), and then Type B slag is switched to be used. The basicity of Type B slag is lower than that of Type A slag. Its application quickly neutralizes the high basicity of the slag layer, thus suppressing the trend of slag performance deterioration. At the same time, the continuous use of Type B slag inhibits the continuous rise in basicity caused by slag-steel reaction. The basicity of the slag layer can be maintained within the normal allowable range (i.e., the basicity is maintained at around 1.5), thereby achieving stable casting of high-alumina peritectic steel. This not only eliminates the steel leakage alarm problem caused by poor lubrication of high basicity slag, but also solves the surface crack defects of the billet caused by low basicity slag. Attached Figure Description

[0043] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0044] Figure 1 A graph showing the relationship between the degree of SiO2 reduction in the protective slag and the aluminum content of the steel grade;

[0045] Figure 2 A flowchart illustrating the application method of continuous casting protective slag for peritectic steel. Detailed Implementation

[0046] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0047] The continuous casting protective slag for high-alumina peritectic steel provided by this invention includes type A slag and type B slag. Both type A slag and type B slag include the following components by weight percentage: CaO and SiO2: 50-70%, Na2O: 5-12%, F: 7-10%, Li2O: 0-2%, C: 2-4%, some unavoidable metal oxides such as Al2O3, MgO, MnO, and Fe2O3: 5-8%, with the balance being burn-off losses other than C (burn-off losses other than C include carbonate decomposition and trace amounts of moisture, etc.). The basicity of type A slag is >1, that is, CaO / SiO2 (mass ratio) >1; the basicity of type B slag is less than that of type A slag.

[0048] The aforementioned Type A and Type B slags are mainly composed of binary components of CaO and SiO2, with a content of 50-70%. The ratio of CaO / SiO2 is the basicity. A protective slag with a ratio greater than 1 is an alkaline slag, and a protective slag with a ratio less than 1 is an acidic slag. Type A slag is an alkaline slag, while Type B slag has a lower basicity than Type A slag. With the increase of Al content, Type B slag may even be an acidic slag. The basicity determines the crystallization ability of the protective slag.

[0049] Because alkaline slag is more likely to precipitate crystals such as lanceolite, feldspar, and nepheline, which are commonly found in protective slags, during solidification, it increases the thermal resistance of the slag film between the copper plate of the crystallizer and the solidified billet shell, reduces the heat transfer capacity, and achieves a slow cooling effect; acidic slag is difficult to precipitate crystals during solidification, and its solid phase is glassy, ​​with strong lubrication efficiency and low thermal resistance, which is conducive to the rapid solidification of the billet shell; therefore, the continuous casting protective slag for high-alumina peritectic steel of this invention needs to be used in combination with type A slag and type B slag.

[0050] Na₂O is a commonly used flux in protective slag, which can effectively reduce the melting point and viscosity of the slag. When the Na₂O content is below 5%, the melting point cannot be lowered to a suitable temperature range. In addition, the presence of Na₂O can also promote the precipitation of crystals such as sodium silicate (Na₂O·CaO·SiO₂) and nepheline (Na₂O·Al₂O₃·2SiO₂). When its content exceeds 12%, the amount of crystal precipitation is too large, and the melting point and viscosity tend to increase, which is not conducive to the lubrication of the slag on the billet. Therefore, in type A and type B slags, the Na₂O content is controlled between 5% and 12%.

[0051] Flame (F) is another common flux in protective slag, mainly used to reduce viscosity. It can also appropriately lower the melting point. In addition, F is an important component of gunpowder (3CaO·2SiO2·CaF2) in protective slag. Gunpowder is the most effective crystal for controlling slag film thermal resistance and adjusting the heat transfer capacity of the crystallizer. F is usually added in the form of CaF2 or NaF, and the Ca or Na it brings can be converted into oxides and included in the content of CaO and Na2O. When the F content is below 7%, the slag viscosity is difficult to reach the design value; when the F content is above 10%, the slag crystallization ability is too strong, which is detrimental to lubrication. Therefore, the F content should be controlled between 7% and 10%.

[0052] Li2O has the most significant effect in lowering the melting point and viscosity of protective slag, but it is expensive. Excessive addition will lead to a significant increase in the raw material cost of protective slag, which is not conducive to industrial application. Therefore, Li2O is usually used as an auxiliary fluxing agent and can be added appropriately when the melting point and viscosity are high. From a cost perspective, it should not exceed 2%.

[0053] In a specific embodiment, since the basicity of type A slag, i.e., CaO / SiO2 (mass ratio) > 1, type A slag includes the following components by weight percentage: CaO and SiO2: 60-70%, Na2O: 5-10%, F: 7-10%, Li2O: 0-1%, C: 2-4%, and unavoidable metal oxides: 5-8%; in a further preferred embodiment, the basicity of type A slag, i.e., the mass ratio of CaO to SiO2, is 1.1-1.4.

[0054] In a specific embodiment, since the basicity of type B slag is less than that of type A slag, type B slag includes the following components by weight percentage: CaO and SiO2: 50-60%, Na2O: 9-12%, F: 9-10%, Li2O: 1-2%, C: 3-4%, and unavoidable metal oxides: 5-8%.

[0055] In a specific embodiment, since the function of type B slag is to neutralize the alkalinity of the molten slag, type B slag should be acidic slag, that is, the alkalinity of type B slag, i.e., the mass ratio of CaO to SiO2, is <1; in a further preferred embodiment, the mass ratio of CaO to SiO2 is 0.5 to 0.9.

[0056] In specific embodiments, unavoidable metal oxides include Al2O3, MgO, MnO and Fe2O3; unavoidable metal oxides are components introduced by the raw materials.

[0057] The properties of the above-mentioned Type A slag and Type B slag are as follows: melting point of 1000-1200℃, and viscosity of 0.07-0.15 Pa·s at 1300℃.

[0058] Combination Figure 2 As shown, the method of using the above-mentioned continuous casting protective slag for high-alumina peritectic steel includes the following steps:

[0059] S1, calculate the basicity of type A slag and type B slag, complete the preparation of type A slag and type B slag in the continuous casting protective slag for high-alumina peritectic steel, and determine the amount of type A slag to be used.

[0060] Specifically, since the main components of both Type A slag and Type B slag are CaO and SiO2, a slag-steel reaction will occur during the casting process, namely 4[Al] + 3(SiO2) = 3[Si] + 2(Al2O3); therefore, the basicity of Type A slag and Type B slag and the amount of Type A slag used must be limited.

[0061] Since the amount of A-type slag used determines the control range of slag basicity, too little A-type slag will result in insufficient slag basicity, inadequate heat control of the slag film, excessive heat transfer in the crystallizer, and an increased risk of billet cracking. Too much A-type slag will lead to excessively high basicity in the slag, which can damage its lubrication function, causing slag performance deterioration, insufficient lubrication, and an increased likelihood of leakage alarms. Because slag basicity is difficult to measure quickly during continuous casting, the amount of A-type slag used must be determined in advance based on the continuous casting process. The amount of A-type slag used is related not only to the aluminum content in the steel but also to the continuous casting throughput, which is the weight of molten steel poured per unit time. The amount of A-type slag used is calculated using the following formula:

[0062]

[0063] Wherein, G represents the amount of Type A slag used, in kg;

[0064] T represents the steel throughput, measured in t / min;

[0065] H represents the Al content of the steel grade, expressed in wt%.

[0066] The amount of type A slag used can be calculated by rounding the above results to the nearest whole number.

[0067] Correspondingly, the basicity of Type A and Type B slag also depends on the Al content in the steel. The basicity of Type A and Type B slag can be calculated based on the aluminum content of the steel grade, thus completing the preparation of both types of slag. The basicity of Type A slag is calculated using the following formula:

[0068]

[0069] In the formula, R A The alkalinity of type A slag is dimensionless.

[0070] H represents the Al content of the steel grade, expressed in wt%.

[0071] The alkalinity of type B slag is calculated using the following formula:

[0072]

[0073] In the formula, R B The alkalinity of type B slag is dimensionless.

[0074] H represents the Al content of the steel grade, expressed in wt%.

[0075] Before specific use, the CaO and SiO2 contents of type A slag and type B slag can be further determined based on the alkalinity values ​​calculated above, thereby preparing the type A slag and type B slag to be used in this invention.

[0076] S2, In the initial stage of continuous casting, after the initial casting is completed using the initial casting slag, type A slag is first added to form a slag pool with a certain crystallization ability on the surface of the molten steel; when the type A slag is used up, type B slag is continuously used.

[0077] Specifically, in the initial stage of continuous casting, after the initial casting is completed using the initial casting slag, type A slag with a basicity >1 is first added to preferentially form a slag pool with a certain crystallization ability on the surface of the molten steel, thereby achieving a slow cooling effect on the initial billet shell and preventing longitudinal crack defects. As the casting process progresses, the slag-steel reaction inevitably continues, causing the basicity to rise continuously. Therefore, the amount of type A slag used is used according to the pre-calculated amount. When the type A slag is used up, a slag pool with a certain crystallization ability has formed on the surface of the molten steel. The process can then be switched to continuously using Type B slag, which has a lower basicity than Type A slag. The use of Type B slag quickly neutralizes the high basicity of the molten slag pool, thus suppressing the trend of slag performance deterioration. At the same time, the continuous use of Type B slag offsets the increase in basicity caused by the reaction between slag and steel, and the basicity of the molten slag can be maintained within the normal allowable range. This achieves stable casting of high-alumina peritectic steel, eliminating the steel leakage alarm problem caused by poor lubrication of high basicity slag, and also solving the surface crack defects of the billet caused by low basicity slag.

[0078] The following section provides a further description of the continuous casting protective slag for high-alumina peritectic steel and its application method, using specific examples.

[0079] Example 1

[0080] In this embodiment, a peritectic steel with an Al content of 0.5% and a C content of 0.08% is continuously cast from slabs, and the throughput of one flow of the casting machine is 3 t / min. First, the amount of type A slag used and the basicity of type A and type B slags are calculated, and type A and type B slags are prepared as shown in Table 1; the amount of type A slag used, G = 100 × 3 / (4.67 + 8.13 × 0.5 - 0.57 × 0.5^2) = 35 kg; the basicity of type A slag, R... A =1 / (0.67+0.17×0.5-0.02×0.5^2)=1.33; Basicity R of Type B slag B =1 / (0.7+0.94×0.5-0.1×0.5^2)=0.87; Then, after the pouring begins, after adding 15kg of initial pouring slag, use the type A slag shown in Table 1 first. The amount of type A slag used is 35kg. After about 20 minutes, when the type A slag is used up, start using type B slag continuously.

[0081] After adopting the above-mentioned protective slag for continuous casting of high-alumina peritectic steel and its application method, the entire continuous casting process was normal, with no steel leakage alarms and no longitudinal cracks on the surface of the billet.

[0082] Table 1

[0083]

[0084] Example 2

[0085] In this embodiment, a peritectic steel with an Al content of 0.8% and a C content of 0.10% is continuously cast from slabs, and the throughput of one flow on the casting machine is 2.5 t / min. First, the amount of type A slag used and the basicity of type A and type B slags are calculated, and type A and type B slags are prepared as shown in Table 1; the amount of type A slag used, G = 100 × 2.5 / (4.67 + 8.13 × 0.8 - 0.57 × 0.8^2) = 23 kg; the basicity R of type A slag... A =1 / (0.67+0.17×0.8-0.02×0.8^2)=1.26; Basicity R of Type B slag B =1 / (0.7+0.94×0.8-0.1×0.8^2)=0.72; Then, after the pouring begins, after adding 15kg of initial pouring slag, use type A slag as shown in Table 2, with a usage of 23kg. After about 20 minutes, when type A slag is used up, start using type B slag continuously.

[0086] After adopting the above-mentioned protective slag for continuous casting of high-alumina peritectic steel and its application method, the entire continuous casting process was normal, with no steel leakage alarms and no longitudinal cracks on the surface of the billet.

[0087] Table 2

[0088]

[0089] Example 3

[0090] In this embodiment, a peritectic steel with an Al content of 1.2% and a C content of 0.12% is continuously cast from slabs, and the throughput of one flow of the casting machine is 2.2 t / min. First, the amount of type A slag used and the basicity of type A and type B slags are calculated, and type A and type B slags are prepared as shown in Table 1; the amount of type A slag used, G = 100 × 2.2 / (4.67 + 8.13 × 1.2 - 0.57 × 1.2^2) = 16 kg; the basicity R of type A slag... A =1 / (0.67+0.17×1.2-0.02×1.2^2)=1.18; Basicity R of Type B slag B =1 / (0.7+0.94×1.2-0.1×1.2^2)=0.59. Then, after the pouring begins, after adding 15kg of initial pouring slag, use the type A slag shown in Table 3 first, with a usage amount G of 16kg. After about 20 minutes, when the type A slag is used up, start using type B slag continuously.

[0091] After adopting the above-mentioned protective slag for continuous casting of high-alumina peritectic steel and its application method, the entire continuous casting process was normal, with no steel leakage alarms and no longitudinal cracks on the surface of the billet.

[0092] Table 3

[0093]

[0094] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A continuous casting protective slag for peritectic steel, characterized in that, Including Type A slag and Type B slag; The type A slag comprises the following components by weight percentage: CaO and SiO2: 50-70%, Na2O: 5-12%, F: 7-10%, LiO: 0-2%, C: 2-4%, unavoidable metal oxides: 5-8%, and the balance being burn-off other than C. The type B slag comprises the following components by weight percentage: CaO and SiO2: 50-60%, Na2O: 9-12%, F: 9-10%, Li2O: 1-2%, C: 3-4%, unavoidable metal oxides: 5-8%, and the balance being burn-off other than C. The basicity of the type A slag is >1; the basicity of the type B slag is less than that of the type A slag, and is 0.5 to 0.

9.

2. The continuous casting protective slag for peritectic steel according to claim 1, characterized in that, The type A slag comprises the following components by weight percentage: CaO and SiO2: 60-70%, Na2O: 5-10%, F: 7-10%, Li2O: 0-1%, C: 2-4%, unavoidable metal oxides: 5-8%, with the balance being burn-off other than C; and / or The alkalinity of the type A slag is 1.1 to 1.

4.

3. The continuous casting protective slag for peritectic steel according to claim 1, characterized in that, The burn-off includes carbonate decomposition and trace amounts of moisture.

4. The continuous casting protective slag for peritectic steel according to claim 1, characterized in that, The unavoidable metal oxides include Al2O3, MgO, MnO, and Fe2O3.

5. The continuous casting protective slag for peritectic steel according to claim 1, characterized in that, The properties of the type A slag and the type B slag are as follows: melting point of 1000-1200℃, and viscosity of 0.07-0.15 Pa·s at 1300℃.

6. A method for using a continuous casting protective slag for peritectic steel, characterized in that, Includes the following steps: S1, calculate the basicity of type A slag and type B slag, complete the preparation of type A slag and type B slag in the continuous casting protective slag for peritectic steel as described in any one of claims 1 to 5, and determine the amount of type A slag used; S2, In the initial stage of continuous casting, after the initial casting is completed using the initial casting slag, type A slag is first added to form a slag layer with crystallization effect on the surface of the molten steel; when the type A slag is used up, type B slag is continuously used.

7. The method of using the continuous casting protective slag for peritectic steel according to claim 6, characterized in that, In step S1, the amount of type A slag used is calculated using the following formula: ； Wherein, G represents the amount of Type A slag used, in kg; T represents the steel throughput, measured in t / min; H represents the Al content of the steel grade, expressed in wt%.

8. The method of using the continuous casting protective slag for peritectic steel according to claim 6, characterized in that, In step S1, the alkalinity of type A slag is calculated using the following formula: ； in, The alkalinity of type A slag is dimensionless. H represents the Al content of the steel grade, expressed in wt%.

9. The method of using the continuous casting protective slag for peritectic steel according to claim 6, characterized in that, In step S1, the alkalinity of type B slag is calculated using the following formula: ； in, The alkalinity of type B slag is dimensionless. H represents the Al content of the steel grade, expressed in wt%.

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