Dephosphorization method considering furnace hearth change in service period of electric furnace

Abstract

The invention relates to a dephosphorization method considering furnace hearth change in the service period of an electric furnace, and belongs to the technical field of electric furnace steelmaking processes. According to the method, the distribution mode and the adding amount of the oxide scales in the stock bin of the electric furnace are adjusted in a segmented mode, then the alkalinity of the electric furnace final slag in the front-middle-rear service cycle of the electric furnace is adjusted, side oxygen lance soft blowing and submerged arc electrode heating are combined, the slag forming capacity of the electric furnace in different service stages is improved, the stability of the electric furnace terminal molten steel dephosphorization rate is improved, and the dephosphorization effect is good. The content of phosphorus in the electric furnace is higher than 85%, the distribution ratio of phosphorus between steel and slag at the end point of the electric furnace is high and is within the range of 2.0-3.0, meanwhile, the electric furnace slag has good fluidity in the whole service cycle, and the requirement for smooth slag flowing of the electric furnace can be met when the slag flowing amount ratio exceeds 50%.

Description

Technical Field

[0001] The invention relates to the technical field of electric furnace steelmaking technology, and in particular to a dephosphorization method taking into account changes in the furnace during the service life of an electric furnace. Background Art

[0002] Electric arc furnace steelmaking mainly uses electric energy to generate a high-temperature arc between the electrode and the solid ferrous raw material, and mainly melts the solid charge in the molten pool through thermal radiation. The arc temperature is as high as 4000-6000℃. The temperature of the molten steel exceeds 2130℃. The main steel material for electric arc furnace steelmaking is scrap steel. Compared with the "long process" process, the coking, sintering and blast furnace ironmaking links are eliminated, and the energy consumption per ton of steel is only half of the long process steelmaking process, about 350kgce / t; the CO2 emission per ton of steel is only between 0.5 and 0.7t, the exhaust gas emission is reduced by 95%, the solid waste emission is reduced by 65%, and the wastewater emission is reduced by 33%, forming a "scrap steel-electric furnace short process" steelmaking method that corresponds to the "blast furnace-converter long process" with low energy consumption, multiple varieties, resource recycling, and environmental friendliness.

[0003] Dephosphorization is the eternal theme of steelmaking. The rapid development of the manufacturing industry and the fierce competition in the market have forced major steel production enterprises to continuously improve product quality and production efficiency. Various products have higher and higher requirements for harmful elements in steel, especially for phosphorus. Most steel grades require a phosphorus content of less than 0.020%, some require a phosphorus content of less than 0.010%, and some high-quality steels even require a phosphorus content of less than 0.006%. Lime is the main dephosphorization agent used in the steelmaking dephosphorization production process. It forms dicalcium silicate 2CaO·SiO2 (C2S) at steelmaking temperature and combines with tricalcium phosphate 3CaO·P2O5 (C3P) in the slag to form a stable phosphorus-containing solid solution 2CaO·SiO2-3CaO·P2O5 (C2S-C3P), so that the phosphorus in the molten iron enters the slag and exists stably, thereby achieving the purpose of dephosphorization of the molten iron. As the service time of the electric furnace increases, the volume of the furnace chamber will change significantly with the service life of the electric furnace, which will cause the height of the molten steel in the electric furnace to change, directly affecting the oxygen blowing, slag making and slag-steel interface dephosphorization reaction of the electric furnace. How to control the composition of the electric furnace slag to improve the slag forming ability of the electric furnace, ensure smooth slag flow during the electric furnace smelting process, and stabilize the dephosphorization rate of the molten steel at the end of the electric furnace is the focus of current electric furnace steelmaking dephosphorization. Summary of the invention

[0004] The object of the present invention is to overcome the shortcomings of the prior art and provide a dephosphorization method that takes into account the changes in the furnace during the service life of an electric furnace.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In a first aspect, the present invention provides a dephosphorization method taking into account changes in the furnace during the service life of an electric furnace, comprising the following steps:

[0007] (1) Preheating the iron oxide scale and lime added to the electric furnace;

[0008] (2) Determine the service stage of the electric furnace according to the age of the next furnace, and divide the service stage of the electric furnace into early, middle and late stages; and add iron oxide scale and lime in the following manner:

[0009] (2-1) Add 2-6 kg / ton of steel oxide scale to the silo of the electric furnace which is determined to be in the early stage of the service period of the electric furnace;

[0010] (2-2) Add 1-4 kg / ton of steel oxide scale to the silo of the electric furnace that is judged to be in the middle of its service period;

[0011] (2-3) No iron oxide scale is added to the silo of the electric furnace that is judged to be in the late stage of the service life of the electric furnace;

[0012] (3) During the melting process of scrap steel in an electric furnace, smelting is carried out by soft blowing of the side oxygen lance and heating of the submerged arc electrode.

[0013] The present invention adds iron oxide scale according to the changes in the volume and depth of the furnace during different service periods of the electric furnace, controls the amount of lime added by the amount of iron oxide scale added, and finally controls the T.Fe content and alkalinity of the final slag of the electric furnace, thereby achieving a relatively stable dephosphorization rate of molten steel at the end of the electric furnace, which is above 85%, and a high phosphorus distribution ratio between steel and slag at the end of the electric furnace, which is within the range of 2.0 to 3.0. At the same time, the electric furnace slag has good fluidity during the entire service period of the electric furnace, and the slag flow rate ratio exceeds 50%, meeting the requirements of fast and smooth slag flow of the electric furnace.

[0014] Preferably, the specific method of preheating in step (1) is: using the liquid electric furnace final slag of the previous electric furnace to preheat the iron oxide scale and lime.

[0015] Since the liquid final slag of the previous electric furnace has a relatively high temperature (>1600°C), the present invention fully utilizes the heat of the liquid final slag of the electric furnace to preheat the subsequent added auxiliary materials such as iron oxide scale and lime, and retains all the liquid final slag of the previous electric furnace in the furnace as a dephosphorization agent for the next batch, thereby meeting the requirements of fast and smooth slag flow in the electric furnace.

[0016] Preferably, the step (2) further comprises: adding 2-8 kg / ton of steel lime to the early, middle and late electric furnaces respectively before the scrap steel is melted.

[0017] Preferably, the step (2) further comprises: adding 2-4 kg / ton of lime before melting the scrap steel after the first slag flow in the electric furnace in the early, middle and late stages respectively.

[0018] Preferably, the step (2) further comprises: controlling the T.Fe content of the final slag of the electric furnace in the early stage of the electric furnace service to be within the range of 12% to 16%; or / and, controlling the T.Fe content of the final slag of the electric furnace in the middle stage of the electric furnace service to be within the range of 14% to 20%; or / and, controlling the T.Fe content of the final slag of the electric furnace in the late stage of the electric furnace service to be within the range of 16% to 24%.

[0019] Preferably, the step (2) further comprises: independently controlling the basicity of the final slag of the electric furnace in the early, middle and late service stages of the electric furnace within the range of 2.70 to 3.50.

[0020] In the early stage of the service cycle of the electric furnace (1-200 heats), due to the small volume of the electric furnace, the shallow depth of the molten pool, the low T.Fe content in the electric furnace slag, and the close distance between the oxygen lance and the steel liquid surface, 2-6 kg / ton of steel oxide scale is added through the silo to adjust the slag fluidity. At the same time, 2-8 kg / ton of steel lime is added before the scrap steel is melted and cleaned, and 2-4 kg / ton of steel lime is added after the first slag flow of the electric furnace. Finally, the T.Fe content of the electric furnace final slag is controlled in the range of 12% to 16%, and the basicity is in the range of 2.70 to 3.50, ensuring that the electric furnace slag is good in the early stage of the service cycle of the electric furnace and the dephosphorization rate of the molten steel is stable.

[0021] In the middle of the service life of the electric furnace (201-500 heats), the furnace of the electric furnace is larger than that of the previous period, the depth of the molten pool is deepened, and the distance between the oxygen lance and the steel liquid surface is increased. In order to promote the smooth slag flow of the electric furnace and improve the final dephosphorization rate of the electric furnace, 1-4 kg of iron oxide scale is added through the silo. At the same time, 2-8 kg of steel lime is added before the scrap steel is melted and cleaned, and 2-4 kg of steel lime is added after the first slag flow of the electric furnace. Finally, the T.Fe content of the final slag of the electric furnace is controlled in the range of 14% to 20%, and the basicity is in the range of 2.70 to 3.50, ensuring good slag flow of the electric furnace in the middle of the service life of the electric furnace and stable dephosphorization rate of molten steel.

[0022] In the later period of the service life of the electric furnace (501-800 heats), the furnace chamber of the electric furnace is significantly expanded compared with the earlier period, and the depth of the molten pool is significantly reduced. At this time, the T.Fe content in the electric furnace slag is usually above 20%, the oxygen lance is far away from the steel liquid surface, the molten pool is well blown, and no additional iron oxide scale is needed to ensure the fluidity of the final slag. In addition, 2-8 kg / ton of steel lime is added before the scrap steel is melted and cleaned, and 2-4 kg / ton of steel lime is added after the first slag flow of the electric furnace. Finally, the T.Fe content of the electric furnace final slag is controlled in the range of 16% to 24%, and the basicity is controlled in the range of 2.70 to 3.50, to ensure that the electric furnace slag is good in the later period of the service life of the electric furnace and the dephosphorization rate of the molten steel is stable.

[0023] Preferably, step (2) of the method further comprises determining the basicity of the final slag in the pre-, mid- and post-service period of the electric furnace, and the determination method is to calculate the basicity using the following formula:

[0024]

[0025]

[0026] In the above formulas [1]-[3], (%P2O5) is the mass fraction of phosphorus pentoxide in the final slag of the electric furnace, (%CaO) is the mass fraction of calcium oxide in the final slag of the electric furnace, (%SiO2) is the mass fraction of silicon dioxide in the final slag of the electric furnace, (%MgO) is the mass fraction of magnesium oxide in the final slag of the electric furnace, and (%T.Fe) is the mass fraction of total iron in the final slag of the electric furnace.

[0027] Preferably, the method for determining the service stage of the electric furnace according to the age of the electric furnace in step (2) is as follows:

[0028] (1) The furnace age of 1-200 years is considered as the early stage of the service life of the electric furnace;

[0029] (2) The furnaces with an age of 201-500 years are considered to be in the middle of the service life of the electric furnace;

[0030] (3) The furnaces with an age of 501-800 years are considered to be in the late stage of the service life of the electric furnace.

[0031] The "furnace age" mentioned in the present invention refers to the number of furnaces, that is, the number of times the electric furnace has been used.

[0032] Preferably, in step (3), the side oxygen lance blows oxygen weakly for 35 to 75 m 3 / t, single oxygen lance flow rate 500-3500Nm 3 The blowing time is 3 to 6 minutes; the power consumption of submerged arc electrode heating per ton of steel is 30 to 120 kW / t.

[0033] For each furnace smelting process, when the furnace blowing time is less than 3 minutes, the lime slag is not sufficient, the silicon and phosphorus in the molten iron compete for desiliconization, and the dephosphorization reaction has not yet begun. When the furnace blowing time is more than 20 minutes, the molten iron temperature is too high, which is not conducive to the dephosphorization reaction. At the same time, excessive oxygen blowing will increase the FeO content in the dephosphorization slag, resulting in higher iron loss.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention is based on the relatively high temperature (>1600°C) of the final slag of the previous furnace. First, it can better preheat the subsequent added iron oxide scale and auxiliary materials such as lime, which provides additional heat input for the melting of scrap steel in the electric furnace and reduces the submerged arc electrode heating time required for the melting of scrap steel. Secondly, by laying scrap steel at the bottom of the electric furnace, on the one hand, the scrap steel is preheated by the final slag left by the previous furnace, reducing the heat input required for the melting of scrap steel. On the other hand, by adding molten iron to the top, the stirring of the molten pool is strengthened, the dynamic conditions of the melting of scrap steel are improved, and the rapid melting of scrap steel in the early stage is promoted, and the time required for the electric furnace to reach the scrap steel melting state is shortened. Furthermore, combined with the change of the furnace volume during the pre-middle-post service period of the electric furnace, the amount of iron oxide scale added is adjusted in stages during the pre-middle-post service period of the electric furnace, and the basicity and T.Fe content of the final slag of the electric furnace are regulated to ensure smooth slag flow in the electric furnace during the entire smelting cycle and stabilize the dephosphorization rate of the molten steel at the end of the electric furnace. Finally, by combining side oxygen lance blowing and submerged arc electrode heating, the kinetic conditions of lime melting in the electric furnace are improved. At the same time, heat is input into the molten pool through the submerged arc electrode. On the basis of the residual heat of the slag in the electric furnace, the temperature of the electric furnace molten pool is rapidly increased, thereby accelerating the rapid slag formation of lime in the early stage.

[0036] The present invention has found through a large number of studies that in the electric furnace steelmaking process, in the early, middle and late stages of the electric furnace service, by adjusting the amount of additional iron oxide scale to control the amount of bottom lime, the requirements of electric furnace slag flow and good dephosphorization effect can be met at the same time.

[0037] In the early and middle batches of EAF smelting, the furnace is small and the molten pool is shallow, which can easily lead to hard blowing of the oxygen lance and poor slag removal effect. In order to speed up the melting of scrap steel and lime in the EAF, the amount of lime added needs to be reduced. At the same time, due to the short melting time of scrap steel in the EAF, the lime does not have time to melt completely. At this time, it is necessary to increase the FeO content in the slag to reduce the viscosity of the slag to ensure the smooth slag flow operation of the EAF.

[0038] In the later batches of EAF smelting, due to lining erosion, the furnace chamber becomes significantly larger than the previous and middle stages. At this time, the molten pool depth is low, oxygen soft blowing is easy to achieve, and the slag-melting effect is better. The amount of lime added can be increased. The FeO content in the molten slag of the later batches of EAF smelting is high, which can achieve better lime slag formation, which also reduces the difficulty of EAF slag flow operation.

[0039] The present invention adopts a suitable electric furnace distribution method and charging system, divides the electric furnace smelting period into the early stage, the middle stage and the late stage, and adjusts the amount of iron oxide scale added, thereby regulating the fluidity of the electric furnace final slag during the early-middle-late service period of the electric furnace. At the same time, combined with the soft blowing of the side oxygen gun and the heating of the submerged arc electrode, the rapid melting of lime is promoted, and the molten steel at the end of the electric furnace obtains a relatively stable and excellent dephosphorization rate. The dephosphorization rate of the molten steel at the end of the electric furnace is relatively stable during the entire service life of the electric furnace, which is above 85.0%. The phosphorus distribution ratio between steel and slag at the end of the electric furnace is relatively high, which is within the range of 2.0 to 3.0. At the same time, the electric furnace slag has good fluidity during the entire service life of the electric furnace, and the slag flow ratio exceeds 50%, which meets the requirements of fast and smooth slag flow of the electric furnace. DETAILED DESCRIPTION

[0040] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0041] This embodiment provides a dephosphorization method taking into account the changes in the furnace during the service life of the electric furnace, comprising the following steps:

[0042] (1) Preheating the scale and lime to be added to the electric furnace: After the steel is tapped at the end of the previous furnace, some molten steel is left in the furnace, and all the final slag is left for dephosphorization in the early stage of the next furnace;

[0043] (2) Scrap steel is placed at the bottom of the next electric furnace. The oxidized iron scale distribution method and addition amount are adjusted in stages during the service period of the electric furnace, the amount of lime added is controlled, and the T.Fe content and basicity of the final slag of the electric furnace are regulated:

[0044] The service stage of the electric furnace is determined according to the age of the electric furnace, and the service stage of the electric furnace is determined as early, middle and late stages; and iron oxide scale and lime are added in the following manner:

[0045] (2-1) Add 2-6 kg / ton of steel oxide scale to the silo of the electric furnace in the early stage of the service period, add 2-8 kg / ton of steel lime before the scrap steel is melted, and add 2-4 kg / ton of steel lime after the first slag flow of the electric furnace, and finally control the T.Fe content of the electric furnace final slag to be in the range of 12% to 16%, and the basicity to be in the range of 2.70 to 3.50;

[0046] (2-2) Add 1-4 kg / ton of steel scale to the silo of the electric furnace that is judged to be in the middle of its service period, add 2-8 kg / ton of steel lime before the scrap steel is melted, and add 2-4 kg / ton of steel lime after the first slag flow of the electric furnace, and finally control the T.Fe content of the final slag of the electric furnace to be in the range of 14% to 20%, and the basicity to be in the range of 2.70 to 3.50;

[0047] (2-3) No scale is added to the silo of the electric furnace that is judged to be in the late stage of service. 2-8 kg / ton of steel lime is added before the scrap steel is melted and 2-4 kg / ton of steel lime is added after the first slag flow of the electric furnace. The final T.Fe content of the electric furnace final slag is controlled to be in the range of 16% to 24%, and the basicity is in the range of 2.70 to 3.50;

[0048] (3) In the process of melting scrap steel in an electric furnace, before each furnace of scrap steel is completely melted, smelting is carried out by soft blowing of the side oxygen lance and heating of the submerged arc electrode, and then the oxygen blowing amount is increased until the end of smelting; the process is divided into 2-4 slag flows, and an appropriate amount of lime is added before the end to prevent phosphorus reversion.

[0049] Side oxygen lance weak blowing oxygen 35~75m 3 / t, single oxygen lance flow rate 500-3500Nm 3 The blowing time is 3 to 6 minutes; the power consumption of submerged arc electrode heating per ton of steel is 30 to 120 kW / t.

[0050] Preferably, step (2) of the method further comprises determining the basicity of the final slag in the pre-, mid- and post-service period of the electric furnace, and the determination method is to calculate the basicity using the following formula:

[0051]

[0052] In the above formulas [1]-[3], (%P2O5) is the mass fraction of phosphorus pentoxide in the final slag of the electric furnace, (%CaO) is the mass fraction of calcium oxide in the final slag of the electric furnace, (%SiO2) is the mass fraction of silicon dioxide in the final slag of the electric furnace, (%MgO) is the mass fraction of magnesium oxide in the final slag of the electric furnace, and (%T.Fe) is the mass fraction of total iron in the final slag of the electric furnace.

[0053] The method for determining the service stage of the electric furnace according to the age of the electric furnace in step (2) is as follows:

[0054] (1) The furnace age of 1-200 years is considered as the early stage of the service life of the electric furnace;

[0055] (2) The furnaces with an age of 201-500 years are considered to be in the middle of the service life of the electric furnace;

[0056] (3) The furnaces with an age of 501-800 years are considered to be in the late stage of the service life of the electric furnace.

[0057] The "furnace age" mentioned in the present invention refers to the number of furnaces, that is, the number of times the electric furnace has been used.

[0058] The distribution method of the embodiment and the comparative example, the chemical composition of the final slag of the electric furnace, the predicted value and calculated value of the phosphorus distribution ratio, the dephosphorization rate of the molten steel, the furnace age, the judgment of the service stage of the electric furnace, and the slag flow rate ratio are shown in Table 1. In the comparative example, except for the addition amount of iron oxide scale and the distribution method in the early, middle and late stages of the service of the electric furnace, the other operations are roughly the same as those of the embodiment.

[0059] Table 1: Charging method, chemical composition of final slag, dephosphorization rate of molten steel, furnace age, judgment of service stage of electric furnace and slag flow ratio

[0060]

[0061]

[0062] In Examples 1-15, the amount of scale added and the distribution method in the early, middle and late stages of the service of the electric furnace determined by the method of the present invention are operated and regulated, and the dephosphorization rate of the molten steel at the end of the electric furnace is relatively stable, all above 85.0%, and the phosphorus distribution ratio between steel and slag at the end of the electric furnace is relatively high, within the range of 2.0 to 3.0. At the same time, the electric furnace slag has good fluidity throughout the service cycle, and the slag flow rate ratio exceeds 50%, which can meet the requirements of smooth slag flow of the electric furnace, and the electric furnace has no obvious slag drying phenomenon during the entire service cycle. This method can simultaneously meet the requirements of stable dephosphorization rate of molten steel at the end of electric furnace steelmaking and smooth slag discharge of electric furnace slag.

[0063] In comparative example 1, 1.3 kg / ton of iron oxide scale was added to the hopper of the 122nd furnace (determined to be the early stage of the service of the electric furnace) in the service of the electric furnace. Industrial results show that lime slag is difficult, the viscosity of the electric furnace slag is high, the slag flow of the electric furnace is difficult, the dephosphorization rate of molten steel is low, which is 82.25%, lower than 85.00%, and the T.Fe content of the final slag is 10.76%.

[0064] In comparative example 2, 8.2 kg / ton of iron oxide scale was added to the hopper of the 155th furnace (determined to be the early stage of the service of the electric furnace) in the service of the electric furnace. Industrial results show that the limed slag is good and the viscosity of the electric furnace slag is moderate, but too much iron oxide scale added dilutes the activity of CaO in the slag, reduces the phosphorus enrichment capacity of the slag, and the dephosphorization rate of the molten steel is low, which is 78.97%, lower than 85.00%, and the T.Fe content of the final slag is 28.16%.

[0065] In comparative example 3, 0.5 kg / ton of iron oxide scale was added to the silo of the 316th furnace in service (determined to be in the middle of service of the furnace). Industrial results show that the lime slag is poor, the viscosity of the furnace slag is high, the furnace slag is difficult to flow, and the dephosphorization rate of molten steel is low, which is 84.78%, lower than 85.00%. The T.Fe content of the final slag is 12.80%.

[0066] In comparative example 4, 6.5 kg / ton of iron oxide scale was added to the silo of the 589th furnace (determined to be in the late service period of the furnace) in the service of the electric furnace. Industrial results show that the limed slag is good and the viscosity of the electric furnace slag is moderate, but too much iron oxide scale added dilutes the activity of CaO in the slag, reduces the phosphorus enrichment capacity of the slag, and the dephosphorization rate of the molten steel is low, which is 81.69%, lower than 85.00%, and the T.Fe content of the final slag is 26.56%.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A dephosphorization method taking into account the changes in the furnace during the service life of an electric furnace, characterized in that: The following steps are involved: (1) Preheating the iron oxide scale and lime added to the electric furnace; (2) Determine the service stage of the electric furnace according to the age of the next furnace, and divide the service stage of the electric furnace into early, middle and late stages; and add iron oxide scale and lime in the following manner: (2-1) Add 2-6 kg / ton of steel oxide scale to the silo of the electric furnace which is determined to be in the early stage of the service period of the electric furnace; (2-2) Add 1-4 kg / ton of steel oxide scale to the silo of the electric furnace that is judged to be in the middle of its service period; (2-3) No iron oxide scale is added to the silo of the electric furnace that is judged to be in the late stage of the service life of the electric furnace; (3) During the melting process of scrap steel in an electric furnace, smelting is carried out by soft blowing of the side oxygen lance and heating of the submerged arc electrode.

2. The dephosphorization method according to claim 1, characterized in that: The specific method of preheating in step (1) is: using the liquid electric furnace final slag of the previous electric furnace to preheat the iron oxide scale and lime.

3. The dephosphorization method according to claim 1, characterized in that: The step (2) further comprises: before the scrap steel is melted, 2 to 8 kg / ton of steel lime is added to the early electric furnace, the middle electric furnace and the late electric furnace respectively.

4. The dephosphorization method according to claim 1, characterized in that: The step (2) further comprises: adding 2-4 kg / ton of steel lime in the early, middle and late stages respectively after the first slag flow of the electric furnace.

5. The dephosphorization method according to claim 1, characterized in that: The step (2) further includes: controlling the T.Fe content of the electric furnace final slag of the early electric furnace within the range of 12% to 16%; or / and, controlling the T.Fe content of the electric furnace final slag of the middle electric furnace within the range of 14% to 20%; or / and, controlling the T.Fe content of the electric furnace final slag of the late electric furnace within the range of 16% to 24%.

6. The dephosphorization method according to claim 1, characterized in that: The step (2) further includes: independently controlling the basicity of the electric furnace final slag of the early electric furnace, the middle electric furnace, and the late electric furnace within the range of 2.70 to 3.

50.

7. The dephosphorization method according to claim 6, characterized in that: The method step (2) further comprises determining the basicity of the final slag in the pre-, mid- and post-service period of the electric furnace, wherein the basicity is calculated using the following formula: In the above formulas [1]-[3], (%P2O5) is the mass fraction of phosphorus pentoxide in the final slag of the electric furnace, (%CaO) is the mass fraction of calcium oxide in the final slag of the electric furnace, (%SiO2) is the mass fraction of silicon dioxide in the final slag of the electric furnace, (%MgO) is the mass fraction of magnesium oxide in the final slag of the electric furnace, and (%T.Fe) is the mass fraction of total iron in the final slag of the electric furnace.

8. The dephosphorization method according to claim 1, characterized in that: The method for determining the service stage of the electric furnace according to the age of the electric furnace in step (2) is as follows: (1) The furnace age of 1-200 years is considered as the early stage of the service life of the electric furnace; (2) The furnaces with an age of 201-500 years are considered to be in the middle of the service life of the electric furnace; (3) The furnaces with an age of 501-800 years are considered to be in the late stage of the service life of the electric furnace; The furnace age refers to the number of times the electric furnace has been used.

9. The dephosphorization method according to claim 1, characterized in that: In step (3), the side oxygen lance blows oxygen weakly for 35 to 75 m 3 / t, single oxygen lance flow rate 500-3500Nm 3 , the blowing time is 3 to 6 minutes; or / and, the submerged arc electrode heating power consumption per ton of steel is 30 to 120 kW / t.

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