Method for efficiently removing phosphorus from molten steel smelted by converter

Abstract

The invention belongs to the field of ferrous metallurgy, and relates to an efficient dephosphorization method for molten steel smelted by a converter, which adopts a'remaining slag + double slag 'dephosphorization process and specifically comprises the following steps: remaining slag in the converter in the last furnace and protecting the converter by splashing slag; adding a metal main material into the converter; desiliconizing and dephosphorizing in the earlier stage of converter smelting; desiliconizing, and removing slag after dephosphorization is finished; decarburization and dephosphorization in the middle and later stages of converter smelting; converter smelting end point control and tapping; wherein a BaO-containing material is added after the slag remaining of the previous converter is completed, and / or in the decarburization and dephosphorization stages in the middle and later periods of converter blowing. Based on the existing'residue and double residue 'smelting process, the BaO-containing material is added after the previous converter residue and / or the decarburization and dephosphorization stage in the middle and later periods of converter blowing, so that the dephosphorization effect of the converter steel slag is effectively improved.

Description

Technical Field

[0001] The invention belongs to the field of iron and steel metallurgy, discloses a method for efficiently removing phosphorus from molten steel in a converter, and particularly relates to a method for efficiently removing phosphorus by controlling the composition of steel slag in a converter "slag retention + double slag" process. Background Art

[0002] At present, the main steel production process in my country is sintering - blast furnace ironmaking - converter steelmaking - (refining) - continuous casting, which is a long process production process. The main methods of converter steelmaking dephosphorization are single slag method, double slag method, double connection method, and "slag retention + double slag" method. Among them, in order to recycle steel slag, the "slag retention + double slag" dephosphorization process has emerged; the process flow is: converter adding scrap steel and molten iron - converter early desiliconization and dephosphorization - converter removing early steel slag - converter blowing decarburization and heating - converter steelmaking - slag retention - slag splashing to protect the furnace. Because the "slag retention + double slag" process is carried out in the same converter, the heat loss of molten iron is small, and the heat of steel slag is recycled. Summary of the invention

[0003] The present invention aims to provide a method for efficiently removing phosphorus from molten steel in a converter, which can solve the problem of low phosphorus removal efficiency during the desiliconization and dephosphorization periods of the existing converter using the "slag retention + double slag" smelting process.

[0004] To achieve the above purpose, the technical solution of the present invention is as follows:

[0005] A method for efficiently removing phosphorus from molten steel in a converter, adopting a "slag retention + double slag" dephosphorization process, specifically comprising: retaining slag from the previous converter and protecting the converter with slag splashing; adding metal main materials to the converter; desiliconization and dephosphorization in the early stage of converter smelting; slag removal after the desiliconization and dephosphorization are completed; decarburization and dephosphorization in the middle and late stages of converter smelting; converter smelting endpoint control and steel tapping; wherein, BaO-containing materials are added after the slag retention in the previous converter is completed and / or during the decarburization and dephosphorization stages in the middle and late stages of converter blowing.

[0006] Furthermore, the BaO-containing material of the present invention is BaCO3.

[0007] Furthermore, the amount of BaO-containing material added in the present invention is 3-14.5 kg.

[0008] Furthermore, the main metal materials of the present invention are molten iron and scrap steel, wherein the weight percentage of the molten iron is 85%-95%, and the rest is scrap steel; the initial carbon content of the molten iron is 4.20%-4.60%, the initial silicon content is 0.10%-0.50%, and the molten iron temperature is ≥1250°C.

[0009] Furthermore, in the converter slag retaining and converter slag splashing protection stages of the previous heat of the present invention, the amount of converter slag retaining is 50%-90% of the weight of the slag at the end of steelmaking; when the silicon content of the next heat of molten iron is 0.10%, the amount of converter slag retaining is 90%; when the silicon content of the next heat of molten iron is 0.50%, the amount of converter slag retaining is 50%; the time for converter slag splashing protection is 3.0-5.0min.

[0010] Furthermore, in the desiliconization and dephosphorization stage of the converter smelting of the present invention, quicklime is added to the converter, and the amount of quicklime is determined by the silicon content of the molten iron, the calcium oxide content in the light-burned dolomite, the amount of slag and the alkalinity of the slag, and finally the binary alkalinity of the slag is 1.8-2.2; the oxygen supply in this stage accounts for 15%-25% of the total oxygen supply of this furnace smelting; the oxygen supply intensity is 3.0-3.4Nm 3 / (min·t steel); oxygen lance position control is: ignition lance position-low lance position-high lance position, the reference lance position is 1.6m, the high lance position is 1.7-1.8m, and the low lance position is 1.5-1.6m; slag temperature is 1350-1420℃; carbon content of molten iron after desiliconization and dephosphorization period is ≥3.50%.

[0011] Furthermore, in the present invention, slag is removed after desiliconization and dephosphorization, and the amount of slag removed is 50%-90% of the weight of the steel slag after desiliconization and dephosphorization.

[0012] Furthermore, in the decarburization and smelting endpoint control stages of the present invention, the oxygen supply accounts for 75%-85% of the total oxygen supply of the furnace; the oxygen supply intensity is 3.0-3.4Nm 3 / (min·t steel); oxygen lance position control is: reference lance position-high lance position-low lance position, the reference lance position is 1.6m, the high lance position is 1.9-2.0m, and the low lance position is 1.5-1.6m; slag binary basicity is 3.5-4.5; endpoint carbon content and endpoint temperature are determined according to the type of steel being smelted.

[0013] The inventive principle of the technical solution of the present invention is:

[0014] In the converter "slag retention + double slag" process of the present invention, after the last batch of converter slag retention is completed and / or in the decarburization and dephosphorization stage in the middle and late stages of converter blowing, BaO-containing materials are added for dephosphorization. On the one hand, the introduction of a new component BaO into the slag helps to reduce the melting point of the slag; on the other hand, Ba has similar properties to Ca and is an alkali metal, which will reduce the viscosity of the liquid phase of the slag and is beneficial to mass transfer; furthermore, the added BaO combines with phosphorus in the slag. According to thermodynamic calculations, BaO is more likely to combine with phosphorus to generate a more stable dephosphorization product Ba3(PO4)2. The formed dephosphorization product reacts with the solid phase 2CaO·SiO2 in the slag to form a solid solution, which reduces the content of phosphorus in the liquid phase of the slag, thereby accelerating the dephosphorization reaction.

[0015] The beneficial effects of the technical solution of the present invention are:

[0016] The present invention is based on the existing "slag retention + double slag" smelting process. After the slag retention of the previous furnace is completed and / or in the decarburization and dephosphorization stage in the middle and late stages of converter blowing, BaO is added to the steel slag in the converter desiliconization and dephosphorization period. The dephosphorization rate in the converter desiliconization and dephosphorization period is increased from 51.75% to 60.00% or more, which is increased by more than 15.9%, and the dephosphorization effect in the converter desiliconization and dephosphorization period is effectively improved. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described in detail below through embodiments.

[0018] Examples 1-12

[0019] IF steel was smelted using a 250-ton top and bottom combined blowing converter. Example 1 was used as a comparison without using this method. The smelting method thereof included the following steps:

[0020] (1) The stage of slag retention in the previous converter and slag splashing protection in the converter: the amount of slag retained in the previous converter is 50%-90% of the weight of the slag at the end of steel tapping; when the silicon content of the molten iron in the next heat is 0.10%, the amount of slag retained is 90% of the weight of the slag at the end of steel tapping; when the silicon content of the molten iron in the next heat is 0.50%, the amount of slag retained is 50% of the weight of the slag at the end of steel tapping; after the slag retention in the converter is completed, BaO-containing materials are added, and the BaO-containing materials are BaCO3; the time of slag splashing protection in the converter is 3.0-5.0 min; the silicon content of molten iron and the control parameters of slag retention in the previous converter and slag splashing protection in the converter in each embodiment are shown in Table 1.

[0021] Table 1 Silicon content of molten iron in each embodiment and control parameters of converter slag retention and converter slag splashing protection in the previous heat

[0022]

[0023] (2) Adding metal main materials into the converter: the metal main materials are molten iron and scrap steel, the weight percentage of the molten iron is 85%-95%, and the rest is scrap steel; the initial carbon content of the molten iron is 4.20%-4.60%, the initial silicon content is 0.10-0.50%, and the temperature of the molten iron is ≥1250° C. The main metal materials for converter smelting in each embodiment are shown in Table 2.

[0024] Table 2 Parameters of main metal materials and slag left in converter smelting of various embodiments

[0025]

[0026] (3) Desiliconization and dephosphorization in converter: Lime is added to the converter. The amount of lime is determined by the silicon content of the molten iron, the calcium oxide content in the light-burned dolomite, the amount of slag and the basicity of the slag, and the binary basicity of the slag is finally made 1.8-2.2; the oxygen supply in this stage accounts for 15%-25% of the total oxygen supply in this furnace; the oxygen supply intensity is 3.0-3.4Nm 3 / (min·t steel); oxygen lance position control is: base lance position - low lance position - high lance position, the base lance position is 1.6m, the high lance position is 1.7-1.8m, the low lance position is 1.5-1.6m; the slag temperature is 1350-1420℃; the carbon content of molten iron after the desiliconization and dephosphorization period is ≥3.50%; the slag removal amount is 50%-90% of the weight of the slag at the end of the desiliconization and dephosphorization stage of the converter smelting.

[0027] Table 3 Control parameters of desiliconization and dephosphorization in the early stage of converter smelting in various embodiments

[0028]

[0029] Table 4 Control parameters for early stage of converter smelting in various embodiments

[0030]

[0031]

[0032] (4) Decarburization and dephosphorization stage in the middle and late stages of converter smelting, the end of converter smelting and the steel-making stage: BaO-containing materials are added in the decarburization and dephosphorization stage in the middle and late stages of converter blowing; the oxygen supply accounts for 75%-85% of the total oxygen supply in this furnace smelting; the oxygen supply intensity is 3.0-3.4Nm 3 / (min·t steel); oxygen lance position control is: reference lance position-low lance position-high lance position, the reference lance position is 1.6m, the high lance position in this stage is 1.9-2.0m, and the low lance position in this stage is 1.5-1.6m; the amount of quicklime added is determined by the slag basicity, so that the slag binary basicity is 3.5-4.5; the end point carbon content and the end point temperature are determined according to the type of steel being smelted. The control parameters of the converter smelting decarburization period of each embodiment are shown in Table 5 and Table 6.

[0033] Table 5 Control parameters of converter smelting decarburization period in each embodiment

[0034]

[0035] Table 6 Converter smelting indexes and final molten steel control parameters of various embodiments

[0036]

[0037]

[0038] The present invention is based on the existing "slag retention + double slag" smelting process. After the slag retention of the previous furnace is completed and / or in the decarburization and dephosphorization stages in the middle and late stages of converter blowing, BaO-containing materials are added. The steel slag in the desiliconization and dephosphorization period of the converter contains BaO, which effectively improves the dephosphorization effect of the converter in the desiliconization and dephosphorization period. As in Examples 1-12, during the desiliconization and dephosphorization periods of the converter, when the BaO contents in the converter slag were 0%, 10.2%, 14.1%, 19.3%, 5.2%, 6.7%, 8.3%, 18.5%, 5.0%, 6.1%, 13.1% and 5.8%, the dephosphorization rates of the molten steel after the desiliconization and dephosphorization periods of the converter were 51.75%, 61.95%, 63.06%, 66.67%, 61.32%, 60.18%, 60.00%, 66.10%, 60.87%, 60.71%, 63.79% and 60.00%, respectively, and the dephosphorization rate was increased by more than 15.9%. In Example 1-12, during the desiliconization and dephosphorization period of the converter, the phosphorus content of the molten steel in the early stage of the converter is negatively correlated with the BaO content in the slag. The dephosphorization rate of the early steel slag increases with the increase of the BaO content in the slag, thereby achieving efficient removal of the phosphorus content in the early stage of the converter.

Claims

1. A method for efficient dephosphorization of molten steel in a converter, characterized in that: The "slag retention + double slag" dephosphorization process is adopted, which specifically includes: retaining slag from the previous converter and splashing slag to protect the converter; adding metal main materials to the converter; desiliconization and dephosphorization in the early stage of converter smelting; slag removal after desiliconization and dephosphorization are completed; decarburization and dephosphorization in the middle and late stages of converter smelting; converter smelting endpoint control and steel tapping; wherein, BaO-containing materials are added after the slag retention of the previous converter is completed and / or in the decarburization and dephosphorization stage in the middle and late stages of converter blowing.

2. The method for efficient dephosphorization of molten steel in converter according to claim 1, characterized in that: The BaO-containing material is BaCO3.

3. The method for efficient dephosphorization of molten steel in converter according to claim 1, characterized in that: The amount of the BaO-containing material added is 3-14.5 kg.

4. The method for efficient dephosphorization of molten steel in converter according to claim 1, characterized in that: The main metal materials are molten iron and scrap steel, the weight percentage of the molten iron is 85%-95%, and the rest is scrap steel; the initial carbon content of the molten iron is 4.20%-4.60%, the initial silicon content is 0.10%-0.50%, and the molten iron temperature is ≥1250°C.

5. The method for efficient dephosphorization of molten steel in converter according to claim 1, characterized in that: In the desiliconization and dephosphorization stage of the converter smelting, lime is added to the converter. The amount of lime is determined by the silicon content of the molten iron, the calcium oxide content in the light-burned dolomite, the amount of slag and the slag basicity, and the binary basicity of the slag is finally made 1.8-2.2; the oxygen supply in this stage accounts for 15%-25% of the total oxygen supply of this furnace smelting; the oxygen supply intensity is 3.0-3.4Nm 3 / (min·t steel); oxygen lance position control is: reference lance position-low lance position-high lance position; slag temperature is 1350-1420℃; carbon content of molten iron after desiliconization and dephosphorization period is ≥3.50%.

6. The method for efficient dephosphorization of molten steel in converter smelting according to claim 5, characterized in that: The reference gun position is 1.6m, the high gun position is 1.7-1.8m, and the low gun position is 1.5-1.6m.

7. The method for efficient dephosphorization of molten steel in converter smelting according to claim 1, characterized in that: In the slag removal stage after desiliconization and dephosphorization, the amount of slag removed is 50%-90% of the weight of the steel slag after the desiliconization and dephosphorization period.

8. The method for efficient dephosphorization of molten steel in converter smelting according to claim 1, characterized in that: During the decarburization and smelting endpoint control stage, the oxygen supply accounts for 75%-85% of the total oxygen supply of this furnace smelting; the oxygen supply intensity is 3.0-3.4Nm 3 / (min·t steel); oxygen lance position control is: reference lance position-high lance position-low lance position, the reference lance position is 1.6m, the high lance position is 1.9-2.0m, and the low lance position is 1.5-1.6m; The binary basicity of slag is 3.5-4.

5.

9. The method for efficient dephosphorization of molten steel in converter according to claim 1, characterized in that: In the converter slag retention stage, the amount of converter slag retention is 50%-90% of the weight of the slag at the end of steel tapping.

10. The method for efficient dephosphorization of molten steel in converter smelting according to claim 1, characterized in that: The time for the converter to protect the furnace by slag splashing is 3.0-5.0 minutes.

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