Method for removing impurity elements of sulfur and oxygen in scrap steel electric furnace smelting

Abstract

The application provides a method for removing impurity elements sulfur and oxygen in scrap steel electric furnace smelting, which comprises the following steps: electric furnace smelting under the protection of refining protective slag, wherein, during smelting, desulfurization is firstly performed, and then deoxidation is performed to obtain a product, the smelting temperature is 1673-1923K; the refining slag is selected from CaO-Al2O3-SiO2-MgO system slag, CaO in the refining slag is 58-65wt%, SiO2 is 8.5-11wt%, and CaO / SiO2 is 5.8-6.4. The application removes the impurity element sulfur in scrap steel through the designed refining slag, improves the purity of scrap steel through the combined use of special amount and special type of deoxidizer A and deoxidizer B, and provides guarantee for realizing the recycling of scrap steel; the impurity elements sulfur and oxygen in scrap steel are effectively removed, the requirements of producing high-quality steel with impurity elements are met, and the recycling of scrap steel resources is realized.

Description

Technical Field

[0001] This patent relates to a method for removing impurity elements from steel, and more particularly to a method for removing sulfur and oxygen from scrap steel. Technical Background

[0002] In the past, scrap steel was mainly added to the traditional EAF production process, and then refined through processes such as RH and VD to bring the impurity elements in the molten steel to the required standards. However, with the wide availability of scrap steel sources, high transportation costs, and large scrap steel production in recent years, there is an urgent need to develop a convenient and flexible all-scrap steel production process. Steel parts that have been in service contain many impurity elements, including alloying elements added to steel grades for specific purposes and impurities introduced by the environment during service, especially impurity elements such as sulfur, oxygen, phosphorus, and hydrogen. These impurity elements have a particularly large impact on the performance of steel parts.

[0003] Patent CN201110354275.1 discloses a device and method for extracting impurity metal elements from preheated scrap steel in electric arc furnace steelmaking. The method involves using a horizontal conveyor preheating system to progressively heat fragmented scrap steel within a preheating channel. A certain amount of pulverized coal is injected into the preheating zone, causing the flue gas in the preheating channel to melt and separate mechanically mixed metals from the scrap steel under a reducing atmosphere and temperature control. These metals are then progressively collected as molten streams, converting harmful impurity metals into resources, while the scrap steel itself remains unmelted. The preheated scrap steel is then transported to the electric arc furnace. However, this patent does not address how to achieve rapid desulfurization and deoxidation.

[0004] Patent No. CN 114317884 A discloses a method for controlling the residual element content in all-scrap electric arc furnace smelting. The method includes: obtaining the residual element content of scrap steel raw materials; classifying the scrap steel raw materials based on the residual element content and a preset element removal difficulty level; calculating the addition amount of each type of scrap steel raw material based on a preset constraint function, wherein the constraint parameters of the constraint function include the residual element content of each type of scrap steel raw material and a preset upper limit threshold for the residual element content; and calculating smelting parameters based on the addition amount of each type of scrap steel raw material. This method attempts to solve the problem of controlling the residual element content in all-scrap electric arc furnace smelting. This patent does not address the selection of slag system and deoxidizer.

[0005] Patent No. CN201810934563.6 discloses a slag-forming method for all-scrap steel electric arc furnace smelting. The invention specifically includes the following steps: (1) charging scrap steel and lime into the electric arc furnace, and then supplying power to the furnace; (2) adding lime in batches after the molten pool is formed; (3) adding slag-forming materials to the furnace as needed based on the slag condition after the scrap steel is fully melted; (4) employing a large-volume slag flow operation during the oxidation period; and (5) controlling the slag flow based on the phosphorus content in the molten steel during the later oxidation stage. This invention effectively removes harmful impurities during the all-scrap steel smelting process, and can also improve the service life of the refractory bricks on the inner wall of the electric arc furnace, reducing operating costs. The slag system process used in this patent is mainly for dephosphorization.

[0006] Patent No. CN201710678453.3 discloses a clean and rapid smelting method for all-scrap steel electric arc furnaces. This invention, based on the smelting process of all-scrap steel electric arc furnaces, utilizes a spray gun embedded inside the refractory material on the side of the furnace bottom to spray different types of media at different smelting stages. In the carburizing and fluxing stage, carburizing of the molten pool accelerates melting and increases the carbon content of the molten pool. In the efficient dephosphorization and deep denitrification stages, the molten pool reaction is enhanced for efficient dephosphorization and deep denitrification, achieving clean and rapid smelting of all-scrap steel in an electric arc furnace. This patent primarily focuses on dephosphorization, carbon control, and nitrogen control.

[0007] Patent No. CN201710456056.1 discloses a method for producing clean steel through a dual-stage electric arc furnace using all-scrap steel. This method connects two electric arc furnaces in series: one is a dephosphorizing furnace, and the other is a decarburizing furnace. The dephosphorizing furnace melts the scrap steel, causing dephosphorization and carbonization. The decarburizing furnace performs deep dephosphorization, decarburization, degassing, and impurity removal on the molten steel. Simultaneously with the addition of scrap steel to the dephosphorizing furnace, carbon materials are added to the molten pool to lower the melting point of the scrap steel and the temperature of the molten pool, thereby increasing the carbon content of the molten steel. After the dephosphorization period, eccentric bottom tapping and steel retention are used to ensure slag-steel separation after the dephosphorization process. The molten steel is poured into the decarburizing furnace via a ladle, where slag formation and deep dephosphorization continue. The slag from the decarburizing furnace can be returned to the dephosphorizing furnace for reuse. During the decarburization period, oxygen is injected into the molten steel using the carbonization rate of the dephosphorizing furnace. The decarburization boiling process generates CO bubbles that can deeply remove [N], [H], and impurities from the molten steel, resulting in a high degree of cleanliness. This patent is primarily for dephosphorization, carbon control, and nitrogen control.

[0008] Patent No. CN201610030750.2 discloses a method for producing low-impurity steel from scrap steel. The method includes: 1) refining the steelmaking raw materials into molten steel in an electric arc furnace; 2) adding a purifying agent for impurity removal and refining; 3) tapping the steel and casting it to obtain steel products. The purifying agent, by weight, comprises: 0.5-1.4 parts quicklime, 0.9-1.5 parts lightly calcined dolomite, 0.6-1.0 parts calcium silicate powder, and 0.7-1.2 parts chromium nitride. This technology significantly reduces the impurity content of the refined steel, such as reducing the phosphorus (P) content to approximately 50 ppm and the sulfur (S) content to approximately 60-70 ppm.

[0009] The CaO-Al2O3-SiO2-MgO slag system has been used in LF refining processes. In their paper "Experimental Study on Desulfurization of Novel LF Deep Desulfurization Refining Slag", Peng Qichun et al. introduced that the desulfurization rate of the existing CaO-Al2O3-SiO2-MgO slag is about 70.12% (its composition is: 60.38%, SiO2 13.07%, Al2O3 18.77%, MgO 4.85%, Ash 2.93%). By introducing barium oxide, lithium oxide, boron oxide, and calcium fluoride, the sulfur content can be reduced to 11-14 ppm. However, its cost is extremely high, and the raw material it processes is not scrap steel.

[0010] Although technologies for producing qualified steel from 100% scrap have developed in recent years, most production methods rely on electric arc furnaces. While adding carbon to reduce the melting point of scrap and lower electricity consumption, the use of carbon inevitably has a detrimental environmental impact, making it counterproductive. Finally, qualified molten steel is obtained through scrap preheating and slag removal. Secondly, the high cost of electric arc furnaces restricts the production of scrap steel by small and medium-sized enterprises, hindering the widespread adoption of scrap steel recycling. Therefore, selecting easy-to-operate, flexible, convenient, and inexpensive electric arc furnaces to smelt 100% scrap steel, reducing carbon usage in the smelting process, and achieving a low-carbon, green, and environmentally friendly production process has become a hot topic in scrap steel recycling. The key technical challenge in electric arc furnace smelting of scrap steel is the rapid and efficient removal of impurities. Summary of the Invention

[0011] The purpose of this invention is to address the numerous problems existing in the technology for removing impurity elements in electric arc furnace (EAF) smelting of scrap steel, and to propose a method for removing sulfur and oxygen impurities in EAF smelting of scrap steel. This invention is based on the fact that high-basicity refining slag can achieve both sulfur and phosphorus removal, and the refining slag can also provide insulation, reducing heat diffusion in the molten steel and lowering power consumption. Secondly, scrap steel is easily oxidized during service, and the oxygen content in the steel is one of the key factors determining the quality of the steel. By selecting silicon and manganese deoxidation and aluminum and its alloys for enhanced deoxidation, the main impurity elements sulfur and oxygen in EAF smelting of scrap steel are effectively removed, ensuring the purity of the molten steel for subsequent alloying of specific steel grades. This invention features low EAF smelting cost, simple operation, and ease of implementation in the laboratory, effectively removing the main impurity elements sulfur and oxygen through refining slag desulfurization, silicon-manganese deoxidation, and aluminum-enhanced deoxidation methods.

[0012] This invention provides a method for removing sulfur and oxygen impurities from scrap steel in an electric arc furnace (EAF). The EAF smelting temperature must ensure both sufficient melting of the steel sample and a suitable optimal desulfurization temperature. The method optimizes the CaO activity at the refining slag smelting temperature, selecting a scrap steel EAF smelting temperature range of 1673-1923 K, preferably 1800-1850 K. Specifically, EAF smelting is carried out under the protection of refining protective slag. During smelting, desulfurization is performed first, followed by deoxidation to obtain the product. The smelting temperature is 1673-1923 K, preferably 1800-1850 K.

[0013] This invention provides a method for removing sulfur and oxygen impurities from scrap steel smelting in an electric arc furnace. The desulfurization refining slag is selected from a CaO-Al2O3-SiO2-MgO system. To ensure desulfurization efficiency, high basicity refining is used, and the activity of CaO in the refining slag is maintained at the smelting temperature. The main components and content range of the scrap steel electric arc furnace refining slag are selected as follows: CaO 58-65 wt%, SiO2 8.5-11 wt%, Al2O3 25-35 wt%, MgO ≤ 8.5 wt%; and CaO / SiO2 greater than or equal to 5.8. Preferably, it is 5.8-6.4, and more preferably 5.95-6.15. In this invention, such high basicity is used to ensure that sulfur in the molten steel is absorbed into the slag as much as possible, achieving a highly efficient sulfur removal effect. Too low basicity will result in poor desulfurization effect of the refining slag. This invention controls the basicity at 5.8-6.4 to ensure calcium activity in the refining slag, meaning that most of the slag remains in a molten state during the refining process, allowing sufficient calcium to combine with sulfur. Excessive basicity leads to weak steel slag activity and reduced effective calcium, consequently decreasing desulfurization capacity and efficiency. In existing technologies, the binary basicity is generally controlled at around 5. However, this invention has found that appropriately increasing the binary basicity to 5.8-6.4, preferably 5.95-6.15, when processing scrap steel, combined with subsequent deoxidation processes, significantly improves the desulfurization and deoxidation efficiency and depth of the product.

[0014] As a preferred embodiment, the present invention provides a method for removing sulfur and oxygen impurity elements from electric arc furnace smelting of scrap steel, wherein the refining slag from the electric arc furnace smelting of scrap steel comprises, by mass percentage, 59.8-60.2 wt% CaO, 29.8-10.2 wt% SiO, 24-26 wt% Al2O3, and 4-6 wt% MgO.

[0015] As a further preferred embodiment, the present invention provides a method for removing sulfur and oxygen impurities from scrap steel smelting in an electric arc furnace. The refining slag from the electric arc furnace smelting of scrap steel comprises, by mass percentage, 60 wt% CaO, 10 wt% SiO2, 25 wt% Al2O3, and 5 wt% MgO. Using this slag, when treating scrap steel with an average Mn content of 0.49 wt% (allowable distribution range 0.3-0.67 wt%), Si ≤ 0.30 wt%, C 0.42 wt%, P ≤ 0.0045 wt%, S < 350 ppm, O < 100 ppm, and the balance being Fe, by controlling the temperature at 1823 K and holding it at that temperature for 5 minutes or more during electric arc furnace smelting, the sulfur content in the molten steel can be reduced to below 18 ppm; that is, the desulfurization rate is greater than 94% (the highest desulfurization rate can reach 96.77%). It is far superior to the efficiency of existing technologies using composite slag desulfurization (desulfurization rate is about 80%-90%), such as the trial production and application of composite refining slag in the 70t electric furnace of Bagang Steel by Mu Baoan et al., Xinjiang Iron and Steel; and the highest desulfurization rate of 94.19% introduced by Peng Qichun et al. in the paper "Experimental Study on Desulfurization of New LF Deep Desulfurization Refining Slag".

[0016] In this invention, after adding desulfurized refining slag and reaching the smelting temperature, the temperature must be maintained for at least 10 minutes before adding the deoxidizer. The preferred order of adding the deoxidizer is to first add deoxidizer A and maintain the temperature for 10-30 minutes, followed by adding deoxidizer B. Deoxidizer A is selected from at least one of zero-valent silicon, ferrosilicon, zero-valent manganese, ferromanganese, and ferrosilicon. Deoxidizer B is selected from at least one of zero-valent aluminum, elemental titanium, and ferrotitanium.

[0017] This invention discloses a method for removing sulfur and oxygen impurities in electric arc furnace smelting of scrap steel. The method involves selecting a slag input rate of 5–30 kg / t for refining slag in the electric arc furnace smelting of scrap steel; preferably 18–22 kg / t, and more preferably 25 kg / t. This amount ensures that the refining slag components cover the surface of the molten steel to form a slag layer with a heat-insulating effect, and further enhances the removal efficiency of sulfur impurities.

[0018] This invention discloses a method for removing sulfur and oxygen impurities in electric arc furnace smelting of scrap steel. The selection of silicon and manganese deoxidizing elements takes into account burn-off. Therefore, when silicon and manganese or their ferroalloy combination are selected for deoxidation (i.e., when deoxidizer A is selected), deoxidizer A is added based on the upper limit of silicon and manganese requirements of the finished steel and an estimated burn-off of 15-25 wt%.

[0019] This invention discloses a method for removing sulfur and oxygen impurities in electric arc furnace smelting of scrap steel. The deoxidation time for deoxidizing agent A is selected to ensure sufficient removal of oxygen from the molten steel, with a deoxidation time range of 15-20 minutes. Furthermore, during the technical development process, it was discovered that under the refining slag system developed in this invention, with a 20% burn-off and steel grade requirement, adding deoxidizing agent A and holding the mixture at room temperature for approximately 15 minutes can reduce the oxygen content in the molten steel to 25-30 ppm.

[0020] Considering burn-off and inclusion dispersion, aluminum or its alloy combination is selected to strengthen deoxidation (i.e., when deoxidizer B is selected). The amount of aluminum used is based on the requirements of the finished steel, with a burn-off ratio of 65-75%.

[0021] In this invention, the calculation of aluminum particle addition based on 30% burn-off and the upper limit of aluminum content required by the steel grade of 0.06% means that, based on 30% burn-off, the actual amount of aluminum added is calculated as 70% of the original amount added, and the final aluminum mass fraction in the molten steel does not exceed 0.06%.

[0022] Preferably, in the method for removing sulfur and oxygen impurity elements in electric arc furnace smelting of scrap steel according to the present invention, the aluminum content in the steel grade does not exceed 0.06 wt%.

[0023] The selection of the deoxidation time for aluminum and its alloys is based on the requirement that oxygen, an impurity element, is fully removed from the molten steel. The deoxidation time range for scrap steel smelting in electric furnace is selected as 5 to 30 minutes, preferably 10 to 20 minutes.

[0024] Of course, in this invention, all deoxidizers must be added to the middle and below of the molten steel, preferably to the bottom. In industrial implementation, the deoxidizer is generally wrapped in high-purity iron sheet (99.999%), bound with wire, and then inserted into the middle to bottom section of the molten steel.

[0025] This invention discloses a method for removing sulfur and oxygen, impurity elements, from scrap steel in electric arc furnace smelting, which is applicable to the smelting of all scrap steel.

[0026] This invention discloses a method for removing sulfur and oxygen impurity elements from scrap steel smelting in an electric arc furnace. The scrap steel comprises, by mass percentage: Mn 0.30-0.67%, Si≤0.30%, C 0.4-0.44%, P≤0.0045%, S0.350ppm, O0.100ppm, with the balance being Fe.

[0027] Beneficial effects of the present invention

[0028] This invention is based on the use of electric arc furnaces for smelting scrap steel, which are easy to operate, inexpensive, flexible and convenient, thus greatly reducing the threshold for scrap steel smelting. Secondly, carbon is not used in the process of electric arc furnace smelting scrap steel. By directly heating the scrap steel with electricity, the environmental pressure caused by carbon emissions is alleviated, and the process of low-carbon, green and circular steel industry is promoted.

[0029] A highly efficient process for controlling sulfur and oxygen, the main impurity elements, in electric arc furnace (EAF) smelting of scrap steel has been developed. This invention effectively removes sulfur and oxygen, the main impurity elements, during the scrap steel EAF smelting process, improving the purity of molten steel produced by EAF smelting and promoting the industrial application of high-quality specific steel grades produced by EAF smelting; it also accelerates the realization of scrap steel recycling throughout society.

[0030] After optimization, this invention achieves a desulfurization rate of 96.77% within 10-45 minutes of smelting. Furthermore, the refining slag designed in this invention reduces the influence of slag particle size on the desulfurization effect to a negligible level. The desulfurization and deoxidation speed and depth of this invention are superior to existing similar products. Moreover, the slag system designed in this invention is the first time it has been used in electric arc furnaces for scrap steel treatment. Detailed Implementation

[0031] This example discloses a method for removing sulfur and oxygen, impurity elements, from scrap steel in electric arc furnace smelting. The method involves removing sulfur from scrap steel heated in the electric arc furnace using a designed high-basicity refining slag, followed by deoxidation of the molten steel using silicon and manganese, and finally, aluminum-enhanced deoxidation. This achieves effective control of impurity elements in scrap steel electric arc furnace smelting, thereby obtaining high-purity molten steel.

[0032] Example 1: A method for removing sulfur and oxygen, impurity elements, from scrap steel in electric arc furnace smelting, comprising the following steps:

[0033] (1) A high-alkalinity refining slag for scrap steel electric furnace smelting was designed. The laboratory analysis showed that the main components of the pure refining slag were CaO 60wt%, SiO2 10wt%, Al2O3 25wt%, and MgO 5wt%.

[0034] (2) The refining slag and scrap steel (average Mn content 0.49wt% (allowable distribution range 0.3-0.67wt%), Si≤0.30wt%, C 0.42wt%, P≤0.0045wt%, S 248ppm, balance Fe) were added together into the electric furnace crucible. The sulfur and oxygen contents in the scrap steel were 248ppm and 46ppm, respectively. The electric furnace smelting temperature of the scrap steel was set to 1823K and the sample was taken after holding for 5min. The sulfur content of the impurity element in the steel sample was analyzed by a carbon-sulfur analyzer and found to be 18ppm. The desulfurization rate was calculated to be 92.74%.

[0035] (3) Calculate the amount of 50SiFe alloy particles to be added based on a burn-off of 20% and the upper limit of silicon content of 0.03% required for steel grade. Wrap the 50SiFe alloy particles with high-purity iron sheet (99.999%) and bind the 50SiFe alloy particles with iron wire. Insert the wire-bound ferrosilicon alloy particles into the middle of the molten steel and keep it at the temperature for 10 minutes before taking a sample. The oxygen content of the impurity element in the steel sample was analyzed by a nitrogen, hydrogen and oxygen analyzer and found to be 32ppm.

[0036] (4) Calculate the amount of aluminum granules to be added based on a 70% burn-off and the upper limit of aluminum content of 0.06 wt% required for the steel grade. Wrap the aluminum granules with high-purity iron sheet (99.999%) and bind them with iron wire. Insert the wire-bound aluminum granules into the middle of the molten steel and keep it at that temperature for 5 minutes before taking a sample. The oxygen content of the steel sample was analyzed by a nitrogen, hydrogen, and oxygen analyzer and found to be 18 ppm. At this point, the sulfur content of the steel sample was analyzed by a carbon and sulfur analyzer and found to be 16 ppm. The desulfurization rate calculated at this point is 93.55%.

[0037] Example 2: A method for removing sulfur and oxygen, impurity elements, from scrap steel in electric arc furnace smelting, comprising the following steps:

[0038] (1) The high-alkalinity refining slag produced by electric arc furnace smelting of scrap steel was designed. The laboratory analysis showed that the main components of the pure refining slag were CaO 60%, SiO2 10%, Al2O3 25%, and MgO 5%.

[0039] (2) The refining slag and scrap steel (consistent with Example 1) were added together into the electric furnace crucible at a slag input rate of 20 kg / t. The sulfur and oxygen contents in the scrap steel were 248 ppm and 46 ppm, respectively. The electric furnace smelting temperature of the scrap steel was set to 1823 K and held for 10 min before sampling. The sulfur content of the impurity element in the steel sample was analyzed by a carbon-sulfur analyzer and found to be 15 ppm. The desulfurization rate calculated at this time was 93.95%.

[0040] (3) Calculate the amount of 50SiFe alloy particles to be added based on a burn-off of 20% and the upper limit of silicon content of 0.03% required for steel grade. Wrap the 50SiFe alloy particles with high-purity iron sheet (99.999%) and bind the 50SiFe alloy particles with iron wire. Insert the wire-bound ferrosilicon alloy particles into the middle of the molten steel and keep it at the temperature for 20 minutes before taking a sample. The oxygen content of the impurity element in the steel sample was analyzed by a nitrogen, hydrogen and oxygen analyzer and found to be 28ppm.

[0041] (4) Calculate the amount of aluminum granules to be added based on a 70% burn-off and the upper limit of aluminum content of 0.06% required for the steel grade. Wrap the aluminum granules with high-purity iron sheet (99.999%) and bind them with iron wire. Insert the wire-bound aluminum granules into the middle of the molten steel and hold for 10 minutes before sampling. The oxygen content of the steel sample was analyzed using a nitrogen, hydrogen, and oxygen analyzer and found to be 10 ppm. At this point, the sulfur content of the steel sample was analyzed using a carbon and sulfur analyzer and found to be 12 ppm. The calculated desulfurization rate at this point was 95.16%.

[0042] Example 3: A method for removing sulfur and oxygen, impurity elements, from scrap steel in electric arc furnace smelting, comprising the following steps:

[0043] (1) The high-alkalinity refining slag produced by electric arc furnace smelting of scrap steel was designed. The laboratory analysis showed that the main components of the pure refining slag were CaO 60%, SiO2 10%, Al2O3 25%, and MgO 5%.

[0044] (2) The refining slag and scrap steel (consistent with Example 1) were added together into the electric furnace crucible at a slag input rate of 20 kg / t. The sulfur and oxygen contents in the scrap steel were 248 ppm and 46 ppm, respectively. The electric furnace smelting temperature of the scrap steel was set to 1823 K and held for 15 min before sampling. The sulfur content of the impurity element in the steel sample was analyzed by a carbon-sulfur analyzer and found to be 10 ppm. The desulfurization rate calculated at this time was 95.97%.

[0045] (3) Calculate the amount of 50SiFe alloy particles to be added based on a burn-off of 20% and the upper limit of silicon content of 0.03% required for steel grade. Wrap the 50SiFe alloy particles with high-purity iron sheet (99.999%) and bind the 50SiFe alloy particles with iron wire. Insert the wire-bound ferrosilicon alloy particles into the middle of the molten steel, keep it at the temperature for 15 minutes and take a sample. The oxygen content of the impurity element in the steel sample is 25ppm according to the nitrogen, hydrogen and oxygen analyzer.

[0046] (4) Calculate the amount of aluminum granules to be added based on a 70% burn-off and the upper limit of aluminum content of 0.06% required for the steel grade. Wrap the aluminum granules with high-purity iron sheet (99.999%), bind the aluminum granules with iron wire, insert the wire-bound aluminum granules into the middle of the molten steel, keep it at that temperature for 10 minutes, and then take a sample. The oxygen content of the impurity element in the steel sample is 10 ppm according to the nitrogen, hydrogen, and oxygen analyzer. At this time, the sulfur content of the impurity element in the steel sample is 8 ppm according to the carbon and sulfur analyzer; the desulfurization rate calculated at this time is 96.77%.

[0047] During the exploration process, it was also found that when the heat preservation time in step (2) reached 20 min and 30 min, the desulfurization rate did not exceed 96%.

[0048] Comparative Example 1: A method for removing sulfur and oxygen, impurity elements, from scrap steel in an electric arc furnace, comprising the following steps:

[0049] (1) The high-alkalinity refining slag produced by electric arc furnace smelting of scrap steel was designed. The laboratory analysis showed that the main components of the pure refining slag were CaO 62%, SiO2 8%, Al2O3 25%, and MgO 5%.

[0050] (2) The refining slag was added to the electric furnace crucible at a rate of 20 kg / t and scrap steel (the composition of the scrap steel was the same as in Example 3). The sulfur and oxygen contents in the scrap steel were 248 ppm and 46 ppm, respectively. The electric furnace smelting temperature of the scrap steel was set to 1823 K and held for 15 min before sampling. The sulfur content of the impurity element in the steel sample was analyzed by a carbon-sulfur analyzer and found to be 136 ppm. The desulfurization rate was calculated to be 45.16%.

[0051] (3) Calculate the amount of 50SiFe alloy particles to be added based on a burn-off of 20% and the upper limit of silicon content of 0.03% required for steel grade. Wrap the 50SiFe alloy particles with high-purity iron sheet (99.999%) and bind the 50SiFe alloy particles with iron wire. Insert the wire-bound ferrosilicon alloy particles into the middle of the molten steel, keep it at the temperature for 15 minutes and take a sample. The oxygen content of the impurity element in the steel sample was analyzed by a nitrogen, hydrogen and oxygen analyzer and found to be 31ppm.

[0052] (4) Calculate the amount of aluminum granules to be added based on a 70% burn-off and the upper limit of aluminum content of 0.06% required for the steel grade. Wrap the aluminum granules in high-purity iron sheet (99.999%) and bind them with iron wire. Insert the wire-bound aluminum granules into the middle of the molten steel, hold for 10 minutes, and then take a sample. The oxygen content of the steel sample as an impurity element was analyzed by a nitrogen, hydrogen, and oxygen analyzer and found to be 15 ppm. At this time, the sulfur content of the steel sample as an impurity element was analyzed by a carbon and sulfur analyzer and found to be 125 ppm. The desulfurization rate calculated at this time was 49.60%.

[0053] Comparative Example 2: A method for removing sulfur and oxygen, impurity elements, from scrap steel in an electric arc furnace, comprising the following steps:

[0054] (1) The high-alkalinity refining slag produced by electric arc furnace smelting of scrap steel was designed. The laboratory analysis showed that the main components of the pure refining slag were CaO 55%, SiO2 15%, Al2O3 25%, and MgO 5%.

[0055] (2) The refining slag was added to the electric furnace crucible at a rate of 20 kg / t and scrap steel (Mn 0.49 wt%, Si ≤ 0.30%, C 0.67 wt%, P ≤ 0.0045%, balance Fe). The sulfur and oxygen contents in the scrap steel were 215 ppm and 36 ppm, respectively. The electric furnace smelting temperature for the scrap steel was set to 1823 K and the sample was taken after holding at that temperature for 15 min. The sulfur content of the impurity element in the steel sample was analyzed by a carbon-sulfur analyzer and found to be 198 ppm. The desulfurization rate was calculated to be 7.9%.

[0056] (3) Calculate the amount of 50SiFe alloy particles to be added based on a burn-off of 20% and the upper limit of silicon content of 0.03% required for steel grade. Wrap the 50SiFe alloy particles with high-purity iron sheet (99.999%) and bind the 50SiFe alloy particles with iron wire. Insert the wire-bound ferrosilicon alloy particles into the middle of the molten steel, keep it at the temperature for 15 minutes and take a sample. The oxygen content of the impurity element in the steel sample was analyzed by a nitrogen, hydrogen and oxygen analyzer and found to be 27ppm.

[0057] (4) Calculate the amount of aluminum granules to be added based on a 70% burn-off and the upper limit of aluminum content of 0.06% required for the steel grade. Wrap the aluminum granules with high-purity iron sheet (99.999%), bind them with iron wire, insert the wire-bound aluminum granules into the middle of the molten steel, hold for 10 minutes, and then take a sample. The oxygen content of the steel sample was analyzed by a nitrogen, hydrogen, and oxygen analyzer and found to be 22 ppm. At this time, the sulfur content of the steel sample was analyzed by a carbon and sulfur analyzer and found to be 186 ppm; the desulfurization rate calculated at this time was 13.4%.

[0058] Comparative Example 3: A method for removing sulfur and oxygen, impurity elements, from scrap steel in an electric arc furnace, comprising the following steps:

[0059] (1) The high-alkalinity refining slag produced by electric arc furnace smelting of scrap steel was designed. The laboratory analysis showed that the main components of the pure refining slag were CaO 60%, SiO2 10%, Al2O3 25%, and MgO 5%.

[0060] (2) The refining slag and scrap steel (consistent with Example 3) were added together into the electric furnace crucible at a slag input rate of 20 kg / t. The sulfur and oxygen contents in the scrap steel were 248 ppm and 46 ppm, respectively. The electric furnace smelting temperature of the scrap steel was set to 1823 K and held for 15 min before sampling. The sulfur content of the impurity element in the steel sample was analyzed by a carbon-sulfur analyzer and found to be 10 ppm. The desulfurization rate calculated at this time was 95.97%.

[0061] (3) Calculate the amount of 50SiFe alloy particles to be added based on a burn-off of 20% and the upper limit of silicon content of 0.03% required for steel grade. Wrap the 50SiFe alloy particles with high-purity iron sheet (99.999%) and bind the 50SiFe alloy particles with iron wire. Insert the wire-bound ferrosilicon alloy particles into the middle of the molten steel, keep it at the temperature for 15 minutes and take a sample. The oxygen content of the impurity element in the steel sample is 25ppm according to the nitrogen, hydrogen and oxygen analyzer.

[0062] (4) Calculate the amount of aluminum granules to be added based on a 70% burn-off and the upper limit of aluminum content of 3.57% required for the steel grade. Wrap the aluminum granules with high-purity iron sheet (99.999%) and bind them with iron wire. Insert the wire-bound aluminum granules into the middle of the molten steel, hold for 15 minutes, and then take a sample. The oxygen content of the steel sample as an impurity element was analyzed by a nitrogen, hydrogen, and oxygen analyzer and found to be 10 ppm. At this time, the sulfur content of the steel sample as an impurity element was analyzed by a carbon and sulfur analyzer and found to be 20 ppm. The calculated desulfurization rate at this time was 91.93%.

[0063] The above results indicate that impurity elements in scrap steel electric arc furnace smelting are effectively controlled, purity is improved, and the molten steel after the removal of impurity elements sulfur and oxygen meets the upper limit requirements for impurity elements in the production of specific steel grades.

[0064] This is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for removing sulfur and oxygen, impurity elements, from scrap steel in an electric arc furnace, characterized in that: Under the protection of refining slag, electric furnace smelting is carried out. During smelting, desulfurization is performed first, followed by deoxidation, to obtain the product. The smelting temperature is 1673-1923K. The refining slag is selected from the CaO-Al2O3-SiO2-MgO system slag, and the refining slag, by mass percentage, includes CaO 59.8-60.2wt%, SiO 29.8-10.2wt%, Al2O3 24-26wt%, and MgO 4-6wt%. After adding the refining slag and reaching the smelting temperature, it is necessary to hold the temperature for at least 10 minutes before adding the deoxidizer. The deoxidizer is added in the following order: first add deoxidizer A and hold for 10-30 minutes, then add deoxidizer B. Deoxidizer A is selected from at least one of zero-valent silicon, ferrosilicon, zero-valent manganese, ferromanganese, and ferrosilicon. Deoxidizer B is selected from at least one of zero-valent elemental aluminum, elemental titanium, and ferrotitanium. The range of slag input for electric arc furnace smelting of scrap steel is 18-22 kg / t. Based on the upper limit of silicon and manganese requirements for finished steel, and estimating a burn-off of 15-25 wt%, deoxidizer A is added; The dosage of deoxidizer B is based on the requirements of the finished steel, and is added at a loss of 65-75%; the deoxidation time range of deoxidizer B is 5-30 minutes. The scrap steel comprises, by mass percentage: Mn 0.30~0.67%, Si ≤ 0.30%, C 0.4-0.44%, P≤0.0045%, S less than 350ppm, O less than 100ppm, and the balance being Fe; In this steel grade, the aluminum content does not exceed 0.06 wt%.

2. The method for removing sulfur and oxygen impurity elements in electric arc furnace smelting of scrap steel according to claim 1, characterized in that: The deoxygenation time range of the deoxidizing agent A is 15~20 min.

3. The method for removing sulfur and oxygen impurity elements in electric arc furnace smelting of scrap steel according to claim 1, characterized in that: Based on the requirements of 20% burn-off and steel grade, after adding deoxidizer A and holding at temperature for 15 minutes, the oxygen content in the molten steel can be reduced to 25-30 ppm.

4. The method for removing sulfur and oxygen impurities in electric arc furnace smelting of scrap steel according to claim 1, characterized in that: The deoxygenation time range of deoxidizer B is 10-20 min.

5. The method for removing sulfur and oxygen impurity elements in electric arc furnace smelting of scrap steel according to claim 1, characterized in that: The scrap steel electric furnace smelting includes electric furnace smelting of all scrap steel.