A low-fluorine slag system for electroslag remelting sulfur-containing steel and a method for producing sulfur-containing steel.

Abstract

This invention discloses a low-fluoride slag system for electroslag remelting sulfur-containing steel and a method for producing sulfur-containing steel, belonging to the field of special steel refining technology. The low-fluoride slag system for electroslag remelting sulfur-containing steel consists of the following components by mass percentage: CaF2: 20-32%, CaO: 5-15%, Al2O3: 25-35%, SiO2: 15-30%, Li2O: 0-5%, MgO: 0-3%, with the balance being unavoidable impurities, the total impurity content not exceeding 1%. This system minimizes desulfurization during electroslag remelting, reducing the decrease in cleanliness caused by the slag-steel reaction, and exhibits good crystallization properties to ensure effective control of heat transfer within the crystallizer during solidification. Simultaneously, due to the low calcium fluoride content of this invention's slag, the fluoride volatility is lower compared to traditional slags, significantly reducing fluoride pollution during the electroslag process.

Description

Technical Field

[0001] This invention belongs to the field of special steel refining technology, and discloses a low-fluorine slag system for electroslag remelting sulfur-containing steel and a method for producing sulfur-containing steel. Background Technology

[0002] Sulfur-containing steel possesses excellent machinability and cutting performance, and is mainly used in the precision instrument industry and the automotive industry, such as in internal combustion engine crankshafts. MnS inclusions in sulfur-containing free-cutting steel enter the tool / chip interface, acting as a lubricant and forming protective deposits on the tool, thus contributing to its excellent cutting performance. Traditional slag systems used in electroslag remelting are all high-basicity slags, and the desulfurization rate during electroslag remelting is typically no less than 60%, making these traditional slag systems unsuitable for producing sulfur-containing steel. Using acidic slags or slag systems containing a small amount of SiO2 is a feasible method for producing sulfur-containing steel through electroslag remelting. However, when using these slag systems for electroslag remelting to produce sulfur-containing steel, ensuring that the reaction between SiO2 in the slag and the molten steel does not lead to the burning off of other components in the molten steel and a reduction in the cleanliness of the molten steel, while avoiding or reducing sulfur burn-off, remains a challenge in industrial production. Furthermore, commercially available electroslag remelting slag systems all contain a high content of calcium fluoride (40wt%–70wt%). During the electroslag remelting process, the volatilization of fluorides (HF, SiF4, and AlF3, etc.) not only pollutes the environment, corrodes equipment, and endangers workers' health, but also causes continuous changes in slag composition, resulting in changes in slag-steel reaction and thus changes in steel composition.

[0003] Traditional slags, during electroslag remelting, generate large, blocky crystalline phases (11CaO·7Al2O3·CaF2 or xCaO·yAl2O3), which deteriorate the slag's crystallization, heat transfer, and lubrication properties. This leads to uneven heat transfer and insufficient lubrication, ultimately resulting in severe surface defects in the ingot, such as depressions and slag grooves. Fluoride volatilization also alters the slag's physicochemical properties (e.g., viscosity, solidification temperature), affecting the stability and refining efficiency of the electroslag process (including deoxidation, desulfurization, and inclusion removal), ultimately impacting product quality. Furthermore, green metallurgy has become an inevitable trend in the industry. During electroslag remelting, the slag's crystallization characteristics significantly influence the initial solidification of the molten metal in the crystallizer and the surface quality of the ingot. Generally, the melting point of the slag system should be approximately 100–200°C lower than that of the remelted alloy to ensure ingot formation and surface quality. The slag system should also have low viscosity at high temperatures to ensure good fluidity during smelting. Therefore, under the industry development trend of green metallurgy, in order to produce qualified electroslag remelted sulfur-containing steel, it is necessary to develop a low-fluorine slag system for electroslag remelting that can significantly reduce sulfur burn-off in steel, ensure good ingot surface quality, and has low reactivity, as well as its application method. Summary of the Invention

[0004] The purpose of this invention is to provide a low-fluoride slag system for electroslag remelting sulfur-containing steel and a method for producing sulfur-containing steel. This method minimizes the desulfurization capacity of the slag during electroslag remelting, reduces the decrease in cleanliness caused by the slag-steel reaction, and maintains good crystallization properties to ensure effective control of heat transfer within the crystallizer during solidification. Furthermore, because the slag of this invention has a low calcium fluoride content, its fluoride volatility is lower compared to traditional slags, significantly reducing fluoride contamination during the electroslag process. In addition, by adjusting the electroslag remelting process, it ensures a significant reduction in sulfur loss from the steel and guarantees good ingot surface quality.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] According to a first aspect of the present invention, a low-fluorine slag system for electroslag remelting sulfur-containing steel is provided, comprising the following components in mass percentage: CaF2: 20-32%, CaO: 5-15%, Al2O3: 25-35%, SiO2: 15-30%, Li2O: 0-5%, MgO: 0-3%, with the balance being unavoidable impurities, and the total impurity content not exceeding 1%.

[0007] Furthermore, the low-fluorine slag system is composed of the following components in weight percentage:

[0008] CaF2: 27%, CaO: 8%, Al2O3: 32%, SiO2: 28%, Li2O: 2.5%, MgO: 1.5%, with the balance being unavoidable impurities, and the total impurity content not exceeding 1%.

[0009] Furthermore, the low-fluorine slag system is composed of the following components in weight percentage:

[0010] CaF2: 28%, CaO: 8%, Al2O3: 30%, SiO2: 30%, Li2O: 1.0%, MgO: 2%, with the balance being unavoidable impurities, and the total impurity content not exceeding 1%.

[0011] Furthermore, the low-fluorine slag system is composed of the following components in weight percentage:

[0012] CaF2: 32%, CaO: 6%, Al2O3: 30%, SiO2: 29%, Li2O: 0.0%, MgO: 1%, the balance being unavoidable impurities, with the total impurity content not exceeding 1%.

[0013] Furthermore, the low-fluorine slag system is composed of the following components in weight percentage:

[0014] CaF2: 32%, CaO: 10%, Al2O3: 27%, SiO2: 30%, Li2O: 0.0%, MgO: 0%, the balance being unavoidable impurities, with the total impurity content not exceeding 1%.

[0015] It should be noted here that the Li2O content is only 0.0% when the CaF2 content is 32%.

[0016] Furthermore, the melting temperature of the slag system is 1150–1300℃; the crystallization temperature of the slag system is 1100–1250℃; the main crystalline phase of the slag system is Ca2Al2SiO7 with a crystallization rate of 70%–90%; the remaining crystalline phase is CaF2 with a crystallization rate of 5%–20%; and the viscosity of the slag system at 1600℃ is 0.05–0.10 Pa·s.

[0017] Furthermore, the slag raw material is crushed after being pre-melted at high temperature. The particle size of the crushed pre-melted slag is ≤10mm, of which particles with a size of 5-10mm account for more than 50% of the mass.

[0018] Furthermore, the slag system is used to produce electroslag steel with a sulfur content in the range of 0.020% to 0.150%.

[0019] According to a second aspect of the present invention, a method for producing sulfur-containing steel from a low-fluorine slag system for electroslag remelting sulfur-containing steel as described in any of the above aspects is provided, comprising the following steps:

[0020] S1 The low-fluorine pre-melted slag material is baked in a baking oven at 700-900°C for 8-12 hours.

[0021] In the electroslag remelting arc initiation stage (S2), a portion of the slag material baked in step S1 is continuously added to the crystallizer. 0.5% to 2% of the total slag amount of calcium sulfide is added to this portion of slag material added to the crystallizer in the early stage. In the initial stage of slag formation in electroslag remelting, after maintaining the power for 2 to 5 minutes, the electroslag remelting power is increased by 30% to 40%. During the subsequent slag formation period, the power is uniformly increased to the normal smelting power of electroslag remelting.

[0022] After the S3 electroslag remelting is completed, the ingot is demolded and cooled slowly using a heat insulation cover or sand pit for at least 3 hours to improve the uniformity of sulfur in the steel and obtain a sulfur-containing steel electroslag remelting ingot.

[0023] Furthermore, in S2, the electroslag remelting process does not use aluminum deoxidation; instead, it can use silicon-calcium or silicon-iron deoxidation.

[0024] Furthermore, in S2, the temperature difference between the inlet and outlet cooling water of the crystallizer is ≤6℃ during the electroslag remelting process; otherwise, the slag film inside the crystallizer will be too thick due to the excessive temperature difference, resulting in poor surface quality and numerous defects in the ingot.

[0025] Furthermore, in S2, the demolding time of the ingot after the electroslag remelting is one-third longer than the demolding time of similar ingots smelted with other slag systems (SiO2 content < 5%). Otherwise, the slag cap core will not be completely solidified, which will lead to slag flow and safety accidents during the demolding of the crystallizer.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. The low-fluorine slag of the present invention is suitable for use as slag in electroslag remelting of sulfur-containing steel, and its various physical and chemical properties and parameters, such as melting temperature, viscosity and crystallization temperature, are also applicable. Specifically: The present invention designs a melting temperature range of 1150–1300℃ to ensure easy arc initiation and slag formation during electroslag remelting, resulting in a smooth surface quality of sulfur-containing steel ingots without surface defects; the present invention designs a slag system crystallization temperature of 1100–1250℃, with the main crystalline phase being Ca2Al2SiO7 at a crystallization rate of 70%–90%, and the remaining crystalline phase being CaF2 at a crystallization rate of 5%–20%. These physicochemical properties ensure uniform heat transfer of the slag film within the electroslag remelting crystallizer, good heat transfer and lubrication performance within the crystallizer, and a smooth solidification process and solidification structure of the ingot, while also preventing cracks caused by thermal stress; the slag system in the present invention has a viscosity of 0.05–0.10 Pa·s at 1600℃, ensuring good fluidity of the slag during electroslag remelting, improving the refining effect on the molten steel, and providing lubrication for the initial solidified billet shell.

[0028] 2. The low-fluorine slag of the present invention solves the problem of severe sulfur loss in sulfur-containing steel during electroslag remelting. At the same time, the application of this slag system can greatly reduce the changes in steel composition caused by slag-steel reaction changes due to fluorine volatilization, as well as the environmental pollution, equipment corrosion and damage to human health caused by fluoride volatilization.

[0029] 3. The low-fluorine slag of this invention avoids the formation of large-particle blocky crystalline phases 11CaO·7Al2O3·CaF2 or xCaO·yAl2O3 in traditional slags. The crystalline mineral phase of the low-fluorine slag is mainly small-particle calcium aluminate phase (the crystalline phase of the slag system is mainly Ca2Al2SiO7, with a crystallinity of 70% to 90%, and the remaining crystalline phase is CaF2, with a crystallinity of 5% to 20%). The formation of this crystalline mineral phase is beneficial for fixing SiO2 in the slag, significantly reducing the slag-steel reaction involving SiO2, and solving the serious slag-steel reaction problem in the electroslag remelting process of high-SiO2 slag, thereby solving the problems of element loss in steel, secondary oxidation of molten steel, and reduced cleanliness. On the other hand, this slag system and its crystalline phase have stable heat transfer control in the crystallizer and have good lubrication and melting properties, resulting in good electroslag ingot solidification structure and surface quality.

[0030] 4. Similar to the traditional slag system used for electroslag remelting, the low-fluorine slag of the present invention has a lower melting temperature, which makes the electroslag ingot easier to solidify and form, and also effectively avoids surface defects of the electroslag ingot.

[0031] 5. During the electroslag remelting process, ensure that the temperature difference between the inlet and outlet cooling water of the crystallizer is ≤6℃ to avoid excessive slag film inside the crystallizer due to excessive temperature difference, resulting in poor surface quality and numerous defects in the ingot. The demolding time of the ingot after electroslag remelting should be one-third longer than that of similar ingots smelted with other slag systems (SiO2 content <5%) to avoid incomplete solidification of the slag cap core, which could lead to slag flow and safety accidents during crystallizer demolding. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0033] Figure 1 Scanning electron microscope (SEM) images of the crystalline phase and matrix according to the present invention are shown.

[0034] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0035] To better understand the preparation and effects of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The embodiments implemented based on the above technical solutions are some embodiments of the present invention, but are not limited to these embodiments.

[0036] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0037] Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0038] The purpose of this invention is to provide a low-fluorine slag system for electroslag remelting sulfur-containing steel and a method for producing sulfur-containing steel. This method minimizes the desulfurization capacity of the slag during electroslag remelting, reduces the decrease in cleanliness caused by the slag-steel reaction, and maintains good crystallization properties to ensure effective control of heat transfer within the crystallizer during solidification. Furthermore, because the slag of this invention has a low calcium fluoride content, its fluoride volatility is lower compared to traditional slags, significantly reducing fluoride pollution during the electroslag process.

[0039] The present invention provides a low-fluorine slag system for electroslag remelting sulfur-containing steel, which is composed of the following components in mass percentage: CaF2: 20-32%, CaO: 5-15%, Al2O3: 25-35%, SiO2: 15-30%, Li2O: 0-5%, MgO: 0-3%, with the balance being unavoidable impurities, and the total impurity content not exceeding 1%.

[0040] Preferably, the low-fluorine slag system can be composed of the following components in mass percentage: CaF2: 27%, CaO: 8%, Al2O3: 32%, SiO2: 28%, Li2O: 2.5%, MgO: 1.5%, with the balance being unavoidable impurities, and the total impurity content not exceeding 1%.

[0041] Preferably, the low-fluorine slag system can be composed of the following components in mass percentage: CaF2: 28%, CaO: 8%, Al2O3: 30%, SiO2: 30%, Li2O: 1.0%, MgO: 2%, with the balance being unavoidable impurities, and the total impurity content not exceeding 1%.

[0042] Preferably, the low-fluorine slag system can be composed of the following components in mass percentage: CaF2: 32%, CaO: 6%, Al2O3: 30%, SiO2: 29%, Li2O: 0.0%, MgO: 1%, with the balance being unavoidable impurities, and the total impurity content not exceeding 1%.

[0043] Preferably, the low-fluorine slag system can be composed of the following components in mass percentage: CaF2: 32%, CaO: 10%, Al2O3: 27%, SiO2: 30%, Li2O: 0.0%, MgO: 0%, with the balance being unavoidable impurities, and the total impurity content not exceeding 1%.

[0044] It should be noted here that the Li2O content is only 0.0% when the CaF2 content is 32%.

[0045] In addition, the slag composition of these groups can simultaneously significantly reduce or avoid sulfur burn-off during the electroslag remelting of sulfur-containing steel, significantly restore fluorides, react acidic slag with molten steel, and prevent secondary oxidation of molten steel, thus ensuring good solidification structure and surface quality of electroslag ingots and effectively avoiding surface defects of electroslag ingots.

[0046] The melting temperature of the slag system is 1150–1300℃; the crystallization temperature of the slag system is 1100–1250℃; and the viscosity of the slag system at 1600℃ is 0.05–0.10 Pa·s.

[0047] In addition, it should be noted that in the production of sulfur-containing steel using electroslag remelting, the physicochemical properties of the slag system will affect the quality of the steel ingot.

[0048] Melting temperature: The melting temperature of slag affects its viscosity, calorific value, and the efficiency of electroslag remelting arc initiation and slag formation. Excessively high or low melting temperatures are detrimental to electroslag remelting arc initiation and slag formation, and can easily lead to internal and surface defects in the ingot. This invention designs a melting temperature range of 1150–1300℃ to ensure easy electroslag remelting arc initiation and slag formation, resulting in a smooth surface quality and no surface defects in sulfur-containing steel ingots.

[0049] Crystallization temperature and crystallization rate: The crystallization temperature and crystalline phase of the slag affect the heat transfer and lubrication performance within the crystallizer, as well as the solidification process and solidification structure of the ingot. Excessively high crystallization temperature and crystallization rate reduce heat transfer and lubrication performance within the crystallizer, hindering ingot forming, solidification, and solidification structure refinement. Conversely, excessively low crystallization temperature and crystallization rate increase heat transfer efficiency within the crystallizer, potentially leading to distortion of the initial steel shell and inducing cracks. This invention designs the slag system with a crystallization temperature of 1100–1250℃, with the main crystalline phase being Ca2Al2SiO7 at a crystallization rate of 70%–90%, and the remaining phase being CaF2 at a crystallization rate of 5%–20%. These physicochemical properties ensure uniform heat transfer in the slag film within the electroslag remelting crystallizer, good heat transfer and lubrication performance within the crystallizer, and favorable solidification process and solidification structure of the ingot, while also preventing cracks caused by thermal stress.

[0050] Viscosity: The viscosity of slag has a significant impact on the fluidity of the slag and its refining effect on molten steel. Due to the electromagnetic stirring force, low-viscosity slag will have a strong stirring effect, thereby enhancing the fluidity of the slag, which is beneficial for uniform heat transfer within the slag pool, and also enhances the kinetics of the slag-steel reaction. Excessive slag viscosity is detrimental to the temperature uniformity of the slag pool, leading to uneven temperature distribution in the molten pool, which is unfavorable for the removal of inclusions from the molten steel and for the lubrication effect on the initial solidified billet shell during use. In this invention, the slag system has a viscosity of 0.05–0.10 Pa·s at 1600℃, ensuring good fluidity of the slag during electroslag remelting, enhancing its refining effect on the molten steel, and providing lubrication for the initial solidified billet shell.

[0051] The slag raw material is crushed after being pre-melted at high temperature. The particle size of the crushed pre-melted slag is ≤10mm, and the mass of particles with a size of 5-10mm accounts for more than 50%.

[0052] Among them, the slag system is used to produce electroslag steel with a sulfur content in the range of 0.020% to 0.150%.

[0053] The present invention also provides a method for producing sulfur-containing steel using a low-fluorine slag system for electroslag remelting of sulfur-containing steel, comprising the following steps:

[0054] S1 bakes the low-fluorine pre-melted slag material in a baking oven at 700-900℃ for 8-12 hours.

[0055] In the electroslag remelting arc ignition stage (S2), a portion of the slag material baked in step S1 is continuously added to the crystallizer. 0.5%–2% of the total slag weight of this portion of slag added to the crystallizer is then mixed with calcium sulfide. During the initial slag formation stage of electroslag remelting, the power is maintained for 2–5 minutes, after which the electroslag remelting power is increased by 30%–40%. During the subsequent slag formation period, the power is uniformly increased to the normal smelting power for electroslag remelting. Notably, aluminum deoxidation is not used in the electroslag remelting process; silicon-calcium or silicon-ferrosilicon deoxidation can be used instead.

[0056] In this application's technical solution, aluminum deoxidation cannot be used in the electroslag remelting process; instead, silicon-calcium or silicon-iron deoxidation can be used. Furthermore, the electroslag remelting process must ensure that the temperature difference between the inlet and outlet cooling water of the crystallizer is ≤6℃; otherwise, excessive temperature difference will result in an excessively thick slag film inside the crystallizer, leading to poor ingot surface quality and numerous defects.

[0057] Meanwhile, compared with the demolding time of similar ingots smelted by other slag systems (SiO2 content < 5%), the demolding time of the ingot after the electroslag remelting in this application needs to be extended by one-third. Otherwise, the slag cap core will not be completely solidified, which will lead to slag flow and safety accidents when the crystallizer is demolded.

[0058] After the S3 electroslag remelting is completed, the ingot is demolded and cooled slowly using an insulation cover or sand pit for at least 3 hours to improve the uniformity of sulfur in the steel.

[0059] Here, the novel slag system developed in this invention needs to contain 5-15% CaO to reduce the viscosity and melting temperature of the slag. Simultaneously, this CaO content range in the patented slag system is beneficial for adsorbing and dissolving inclusions in the steel. The 1-5% alkali metal oxide Li2O serves as an important fluxing agent for optimizing the physicochemical properties of the slag, replacing part of CaF2 to reduce fluoride volatilization and lowering the slag melting temperature and viscosity. Furthermore, the small amount of Li2O added can... The crystallization temperature, crystallization capacity, and crystalline phase of the slag are optimized to control heat transfer within the crystallizer. As a result, the slag has good lubrication and melting properties, leading to a good solidification structure and surface quality for electroslag ingots. The slag contains 25-35% Al2O3, which, in addition to having the same function as slag used in traditional electroslag remelting, will, in the slag system of this invention, avoid or significantly reduce the reaction between SiO2 in the slag and aluminum in the steel, thereby avoiding significant fluctuations in the aluminum content of the steel and secondary oxidation of the molten steel.

[0060] Example

[0061] Tables 1 and 2 show the chemical composition (weight percentage) of the consumable electrode and electroslag ingot for the examples and comparative examples. The slag was smelted according to the compositions shown in Table 1 for the examples and comparative examples via EAF→LF→VD→cast electrode→electroslag remelting. Table 1 shows the slag composition used in Example 1: CaF2: 32%, CaO: 10%, Al2O3: 27%, SiO2: 30%, Li2O: 0.0%, MgO: 0%, with the balance being unavoidable impurities, the total impurity content not exceeding 1%. Table 1 shows the slag composition used in Example 2: CaF2: 27%, CaO: 8%, Al2O3: 32%, SiO2: 28%, Li2O: 2.5%, MgO: 1.5%, with the balance being unavoidable impurities, the total impurity content not exceeding 1%. Table 1 shows the slag composition used in Comparative Example 1: 31% CaF2, 30% CaO, 33% Al2O3, 3% MgO, 1.5% SiO2.

[0062] Table 1. Chemical composition of steel before and after electroslag remelting (mass fraction, %)

[0063]

[0064] As shown in Table 1, the slag system and its application method of the present invention can solve the problem of sulfur burn-off in electroslag remelting of sulfur-containing crankshaft steel. The aluminum element burn-off caused by the slag-steel reaction is very small. At the same time, the new slag system can also significantly improve the cleanliness of the steel, and the oxygen content is comparable to that in steel produced by electroslag remelting using traditional slag systems.

[0065] According to the compositions shown in Table 2 for the examples and comparative examples, the slag was smelted in a vacuum induction furnace → electrode casting → electroslag remelting. The slag composition used in Example 3 of Table 2 is CaF2: 28%, CaO: 8%, Al2O3: 30%, SiO2: 30%, Li2O: 1.0%, MgO: 2%, with the balance being unavoidable impurities, the total impurity content not exceeding 1%. The slag composition used in Example 4 of Table 2 is CaF2: 32%, CaO: 6%, Al2O3: 30%, SiO2: 29%, Li2O: 0.0%, MgO: 1%, with the balance being unavoidable impurities, the total impurity content not exceeding 1%. The slag composition used in Comparative Example 2 of Table 2 is 58% CaF2, 20% CaO, 20% Al2O3, with the remainder being impurities.

[0066] Table 2 Chemical composition of steel before and after electroslag remelting (mass fraction, %)

[0067]

[0068] As shown in Table 2, the slag system and its application method of the present invention can significantly reduce the sulfur burn-off problem in electroslag remelting of sulfur-containing mold steel. The aluminum element burn-off caused by the slag-steel reaction is very small. At the same time, the new slag system can also significantly improve the cleanliness of the steel, and the oxygen content is comparable to that in steel produced by electroslag remelting using traditional slag systems.

[0069] like Figure 1 As shown, under the conditions of Example 2, the crystalline phase of the slag system is mainly Ca2Al2SiO7 with a crystallinity of about 85%, the remaining crystalline phase is CaF2 with a crystallinity of about 10%, and the rest is the matrix structure of the slag.

[0070] In summary, this invention provides a low-fluorine slag system for electroslag remelting sulfur-containing steel and its application method. The low-fluorine slag system can be used in the electroslag remelting production of sulfur-containing steel, such as free-cutting steel, sulfur-containing mold steel, sulfur-containing tool steel, and internal combustion engine crankshafts. This invention's low-fluorine slag system and its application method not only solve the problem of significant sulfur loss during electroslag remelting of sulfur-containing steel, achieving stable and uniform control of sulfur content, but also ensure good surface quality and solidification structure of the electroslag ingot. It also avoids elemental loss and reduced steel cleanliness caused by the reaction of SiO2 in the slag with steel components during the electroslag process, and significantly reduces environmental pollution, equipment corrosion, and harm to human health caused by the volatilization of fluorides in the slag during electroslag remelting.

[0071] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any modifications, substitutions and improvements made without departing from the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A low fluorine slag system for electroslag remelting of sulphur containing steel, characterized in that, Consist of the following components with mass percentage: CaF2: 20-32%, CaO: 5-15%, Al2O3: 25-35%, SiO2: 15-30%, Li2O: 0-5%, MgO: 0-3%, the rest is inevitable impurities, the total content of impurities is not more than 1%; The melting temperature of the slag system is 1150-1300 DEG C, the crystallization temperature of the slag system is 1100-1250 DEG C, and the viscosity of the slag system at 1600 DEG C is 0.05-0.10 Pa·s; The crystalline mineral phase of the low-fluorine slag is mainly small-grained calcium aluminate phase, the crystalline phase of the slag system is mainly Ca2Al2SiO7, the crystallization rate is 70-90%, and the remaining crystalline phase is CaF2, and the crystallization rate is 5-20%. The pre-melted slag is crushed after high-temperature pre-melting, and the particle size of the crushed pre-melted slag is ≤10 mm.

2. A low fluorine slag system for electroslag remelting of sulphur containing steel as claimed in claim 1, wherein, The mass percentage of the particles with a particle size of 5-10 mm after crushing of the pre-melted slag is more than 50%.

3. A low fluoride slag system for electroslag remelting of sulphur containing steel as claimed in claim 1, wherein, The slag system is used for producing an electroslag steel with a sulfur content in the range of 0.020% to 0.150%.

4. A process for producing sulphur containing steel using a low fluorine slag system for electroslag remelting of sulphur containing steel as claimed in any one of claims 1 to 3, wherein, The method comprises the following steps: S1 baking the pre-melted slag of the low-fluorine slag system in a baking furnace at 700-900 DEG C for 8-12 h; S2 during the arc starting stage of electroslag remelting, continuously adding a part of the baked slag of step S1 into the crystallizer, and adding 0.5-2% of calcium sulfide based on the total amount of the slag into the part of the slag added into the crystallizer in the early stage; after maintaining the power for 2-5 minutes in the initial stage of electroslag remelting, increasing the power by 30-40%, and uniformly increasing the power to the normal smelting power of electroslag remelting in the subsequent slag melting stage; S3 after the electroslag remelting is completed, demolding, and slowly cooling the electroslag ingot for more than 3 h to obtain a sulfur-containing steel electroslag remelted ingot.

5. The method of claim 4, wherein, In S2, silicon-calcium or silicon-iron deoxidation is selected for the electroslag remelting process.

6. The method of claim 4, wherein, In S2, the temperature difference between the inlet and outlet water temperatures of the cooling water of the crystallizer is ≤6 DEG C.

7. The method of claim 4, wherein, In S2, the demolding time of the ingot after the electroslag remelting is completed is prolonged by one-third of the demolding time of the ingot of similar type smelted by other slag systems with a SiO2 content of less than 5%.

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