Method for using a hot metal dephosphorizing agent

Abstract

The application relates to the technical field of steel metallurgy, in particular to an application method of a hot metal dephosphorization agent, wherein argon, dephosphorization powder and iron powder with oxygen as a carrier gas are respectively applied to the hot metal at the bottom, top and wall of a furnace during the dephosphorization process until the dephosphorization is completed. The application has the beneficial effects that the temperature in the reaction process is stable and controllable, the dephosphorization agent can be quickly slagged, the temperature in the dephosphorization process has no significant fluctuation, the hot metal is not rephosphorized, the dephosphorization efficiency of the hot metal is improved, the dephosphorization effect is improved, the consumption of the dephosphorization agent is reduced, the dephosphorization rate is high, and the dephosphorization rate of the hot metal after the dephosphorization treatment is greater than 97.5%.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a method for applying a dephosphorizing agent to molten iron. Background Technology

[0002] Phosphorus is a segregating element that causes "cold brittleness" in steel. It cannot be removed in the blast furnace process and can only be removed during steelmaking. With users demanding higher phosphorus content in steel (≤0.01%, even ≤0.005%), and the continuously rising price of low-phosphorus iron ore, coupled with fierce competition among steel companies, steelmakers are being forced to use low-priced, high-phosphorus iron ore in blast furnace production, resulting in high-phosphorus molten iron. This necessitates metallurgists developing new process technologies for smelting ultra-low phosphorus steel using high-phosphorus molten iron.

[0003] The main factors affecting dephosphorization rate include dephosphorization thermodynamics, kinetics, and the selection of dephosphorizing agents. Ideal dephosphorization thermodynamic conditions include high alkalinity, high slag volume, high oxidizing power, and low temperature. However, actual production has shown that lower temperatures make lime slag formation difficult and result in a low slag formation rate. Therefore, ensuring small and appropriate temperature fluctuations during the dephosphorization process is extremely important. Ideal kinetic conditions are: 1) Rapid formation of slag with an appropriate w(FeO) / w(CaO) value in the furnace to improve LP (Liquidity Limit). 2) Formation of a large stirring intensity in the molten pool. Dephosphorizing agents mainly consist of oxidants, fixatives, and fluxes. Commonly used solid oxidants in steel plants include iron phosphorus, sintering dust, and iron concentrate powder. Among fixatives, CaO is the most commonly used, as it has a strong binding ability with phosphorus oxides but needs to be used in conjunction with fluxes. Soda-based dephosphorizing agents, represented by sodium carbonate, although having a low melting point and fluxing ability, easily corrode refractory materials.

[0004] In conclusion, to smelt ultra-low phosphorus steel from high-phosphorus molten iron, it is necessary to comprehensively consider the thermodynamics and kinetics of dephosphorization, as well as the combined effects of the selection of dephosphorizing agents on the dephosphorization reaction.

[0005] Chinese patent application CN116891921A, entitled "A dephosphorizing agent for molten iron and its dephosphorization method", proposes a method for pretreatment and dephosphorization of molten iron by adding a dephosphorizing agent made of lime, iron raw materials and flux powder to the molten iron ladle in batches. The disadvantage is that adding the dephosphorizing agent to the molten iron ladle in multiple batches will cause the temperature of the molten iron to drop continuously, resulting in poor lime slag formation and affecting the dephosphorization effect.

[0006] Chinese patent application CN107849625A discloses a "dephosphorizing agent, refining agent and dephosphorizing method for molten iron". It proposes to apply a dephosphorizing agent for molten iron containing 2-20% Al2O3, with the balance being calcium ferrite and impurities, and an Al2O3% / CaO% ratio of 0.04-0.5 to a converter. This will cause an increase in the consumption of calcium ferrite dephosphorizing agent, resulting in higher costs.

[0007] Chinese patent application CN102094100A discloses a "Dephosphorizing Agent for Molten Iron and its Application Method," which improves dephosphorization kinetics and ensures dephosphorization temperature by controlling the top-blown oxygen flow rate and the amount of dephosphorizing agent added, thereby increasing the dephosphorization rate and reducing slag consumption. Although this method reduces slag consumption, the dephosphorizing agent used contains a high CaO content of 75% to 85%, making its cost relatively high compared to conventional dephosphorizing agents. In addition, the oxygen consumption of this dephosphorization method is 1.5 to 5 times the weight of oxygen contained in the iron oxide in the dephosphorizing agent, which is also relatively high. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, this invention provides a method for applying a dephosphorizing agent to molten iron. Specifically for dephosphorizing high-phosphorus molten iron pretreatment, this method proposes applying argon, dephosphorizing powder, and iron powder with oxygen as a carrier gas to the molten iron at the furnace bottom, furnace top, and furnace wall respectively during the dephosphorization process until dephosphorization is complete. This method allows the dephosphorizing agent to quickly form slag, maintains minimal temperature fluctuations during the dephosphorization process, reduces dephosphorizing agent consumption, and achieves a high dephosphorization rate.

[0009] To achieve the above objectives, the present invention employs the following technical solution:

[0010] A method for applying a dephosphorizing agent to molten iron involves applying argon gas, dephosphorizing powder, and iron powder with oxygen as a carrier gas to the molten iron at the furnace bottom, furnace top, and furnace wall during the dephosphorization process until dephosphorization is complete. The method specifically includes the following steps:

[0011] 1) Pour molten iron into the furnace at a temperature of 1340–1380℃;

[0012] 2) Argon gas is blown into the molten pool from the bottom of the furnace to create disturbance in the molten pool. The argon gas flow rate increases in three stages.

[0013] 3) The dephosphorizing powder is blown in three batches from the top of the furnace. The three batches of dephosphorizing powder are added in three stages of argon flow rate change, with an interval t between each batch. The amount of dephosphorizing powder added decreases as a percentage of the total amount used.

[0014] 4) During the two intervals t between the addition of dephosphorization powder, iron powder is injected from the furnace wall into the molten pool using oxygen as the carrier gas.

[0015] 5) Dephosphorization ends 5-8 minutes after the third batch of dephosphorization powder is added.

[0016] Furthermore, the dephosphorization powder comprises converter dust, high-calcium fly ash, and fluorite powder; its composition by weight percentage is: converter dust: 10%–70%, high-calcium fly ash: 20%–80%, fluorite: 5%–10%.

[0017] Furthermore, the particle size of the converter dust is ≤45μm, and the particle size of the high-calcium fly ash and fluorite powder is ≤3mm.

[0018] Furthermore, the ratio of the dephosphorizing powder to the net weight of the molten iron is 7% to 10%.

[0019] Furthermore, in step 1), the molten iron has a Si content ≤ 0.15% and a P content ≥ 0.2%.

[0020] Furthermore, in step 2), the argon flow rate increases in three stages: the first stage argon flow rate is 0.2-0.35 L / min, the second stage argon flow rate is 0.4-0.55 L / min, and the third stage argon flow rate is 0.6-0.75 L / min.

[0021] Furthermore, the interval time t in step 2) is 5 to 10 minutes.

[0022] Furthermore, in step 3), the amount of dephosphorizing powder added is as follows: the first batch accounts for 50% to 60%, the second batch accounts for 30% to 38%, and the third batch is the remaining powder.

[0023] Furthermore, in step 4), the particle size of the injected iron powder is ≤120μm, and the amount of injected iron powder is: the amount of the first batch of injected iron powder is 20% to 30% of the amount of the first batch of injected dephosphorizing powder, and the amount of the second batch of injected iron powder is 5% to 15% of the amount of the second batch of injected dephosphorizing powder.

[0024] Furthermore, in step 4), the weight of oxygen is 0.5 to 1.2 times the weight of iron powder.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1) By adding iron powder with oxygen as the carrier gas to the molten iron during the interval between the addition of dephosphorizing powder, the oxidizing properties of the dephosphorizing agent are kept stable. At the same time, the reaction between the iron powder and oxygen at high temperature will release heat, ensuring that the temperature is stable and controllable during the reaction process, and also facilitating the rapid slag formation of the dephosphorizing agent.

[0027] 2) By incrementally controlling the bottom-blowing argon flow rate and adding dephosphorizing agent in a decreasing manner, the dephosphorizing agent can effectively exert its high-efficiency dephosphorization ability in the early stage of the reaction, and ensure that the molten iron does not return to phosphorus in the later stage of the reaction, thereby improving the dephosphorization efficiency and the dephosphorization effect.

[0028] 3) Select dephosphorizing agents made from dust collector ash, high-calcium fly ash, and fluorite powder. This will effectively utilize steelmaking by-products, improve their utilization rate, reduce dephosphorizing agent consumption, enhance dephosphorization efficiency, and reduce slag consumption.

[0029] 4) The dephosphorization rate of molten iron is greater than 97.5%. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below:

[0031] Example 1

[0032] The dephosphorization process is as follows:

[0033] 1) Molten iron with an initial P content of 0.206%, Si content of 0.144%, and C content of 4.13% was added into the furnace at a temperature of 1340℃ and a weight of 200kg.

[0034] 2) Argon gas is blown into the molten pool from the bottom of the furnace. The argon gas flow rate is controlled at 0.2 L / min in the first stage, 0.55 L / min in the second stage, and 0.6 L / min in the third stage.

[0035] 3) Dephosphorizing powder is blown in three batches from the top of the furnace. Based on a dephosphorizing powder to molten iron net weight ratio of 10%, the total amount of dephosphorizing powder added is 20 kg. The first batch of dephosphorizing powder, amounting to 50% of the total, is added at an argon flow rate of 0.2 L / min. The second batch, amounting to 38% of the total, is added at an argon flow rate of 0.55 L / min. The remaining 2.4 kg of dephosphorizing powder is added at an argon flow rate of 0.6 L / min. The time interval between the first and second batches is 5 min, and the time interval between the second and third batches is 10 min.

[0036] 4) During the interval between the two additions of dephosphorizing powder, iron powder is injected twice from the furnace wall upwards onto the molten pool using oxygen as the carrier gas. The first batch of injected iron powder is calculated as 20% of the first batch of dephosphorizing powder, which is 2 kg. The weight of the oxygen carrier gas is calculated as 0.5 times the weight of the iron powder, which is 1 kg, equivalent to a volume of 0.70 m³ under standard conditions. 3 The second batch of injected iron powder, calculated as 5% of the second batch of injected dephosphorization powder, amounts to 0.38 kg. The oxygen carrier gas, calculated as 0.5 times the weight of the iron powder, is 0.19 kg, equivalent to a volume of 0.14 m³ under standard conditions. 3 .

[0037] 5) Dephosphorization ends 8 minutes after the third batch of dephosphorization powder is added.

[0038] In this embodiment, the dephosphorizing agent is distributed in the following weight percentages: 70% dust collector ash, 20% high-calcium fly ash, 10% fluorite powder, with a dust collector ash particle size of 40.5 μm, high-calcium fly ash and fluorite powder particle sizes of 2.5 mm, and iron powder particle size of 116 μm.

[0039] Results: Samples were taken after dephosphorization treatment and tested. The phosphorus content of the molten iron after dephosphorization treatment was 0.0031%. According to the calculation of dephosphorization rate = (initial phosphorus content of molten iron - phosphorus content of molten iron after dephosphorization treatment) / initial phosphorus content of molten iron × 100%, the dephosphorization rate was 98.50%.

[0040] Example 2

[0041] The dephosphorization process is as follows:

[0042] 1) Molten iron with an initial P content of 0.251%, Si content of 0.115%, and C content of 4.25% was added into the furnace at a temperature of 1380℃ and a weight of 500kg.

[0043] 2) Argon gas is blown into the molten pool from the bottom of the furnace. The argon gas flow rate is controlled at 0.35 L / min in the first stage, 0.4 L / min in the second stage, and 0.75 L / min in the third stage.

[0044] 3) Dephosphorizing powder is blown in three batches from the top of the furnace. Based on a dephosphorizing powder to molten iron net weight ratio of 7%, the total amount of dephosphorizing powder added is 35 kg. The first batch of dephosphorizing powder, amounting to 60% of the total amount (21 kg), is added when the argon flow rate is 0.4 L / min. The second batch, amounting to 30% of the total amount (10.5 kg), is added when the argon flow rate is 0.75 L / min. The remaining 3.5 kg of dephosphorizing powder is added at a time interval of 10 min between the first and second batches, and 6 min between the second and third batches.

[0045] 4) During the interval between the two additions of dephosphorizing powder, iron powder is injected twice from the furnace wall upwards into the molten pool using oxygen as the carrier gas. The first batch of injected iron powder is calculated as 30% of the first batch of injected dephosphorizing powder, which is 6.3 kg. The weight of the oxygen carrier gas is calculated as 1.2 times the weight of the iron powder, which is 7.56 kg. The equivalent volume under standard conditions is 5.29 m³. 3 The second batch of injected iron powder, calculated as 15% of the second batch of injected dephosphorization powder, amounted to 1.575 kg. The oxygen carrier gas, calculated as 1.2 times the weight of the iron powder, amounted to 1.89 kg, which translates to a volume of 1.32 m³ under standard conditions. 3 .

[0046] 5) Dephosphorization ends 5 minutes after the third batch of dephosphorization powder is added.

[0047] In this embodiment, the dephosphorizing agent is distributed in the following weight percentages: 10% dust collector ash, 80% high-calcium fly ash, 10% fluorite powder, with a dust collector ash particle size of 44.5 μm, high-calcium fly ash and fluorite powder particle sizes of 2.0 mm, and iron powder particle size of 103 μm.

[0048] Results: Samples were taken after dephosphorization treatment and tested. The phosphorus content of the molten iron after dephosphorization treatment was 0.0039%. According to the calculation of dephosphorization rate = (initial phosphorus content of molten iron - phosphorus content of molten iron after dephosphorization treatment) / initial phosphorus content of molten iron × 100%, the dephosphorization rate was 98.45%.

[0049] Example 3

[0050] The dephosphorization process is as follows:

[0051] 1) Molten iron with an initial P content of 0.314%, Si content of 0.094%, and C content of 4.32% was added into the furnace at a temperature of 1364℃ and a weight of 500kg.

[0052] 2) Argon gas is blown into the molten pool from the bottom of the furnace. The argon gas flow rate is controlled at 0.26 L / min in the first stage, 0.47 L / min in the second stage, and 0.68 L / min in the third stage.

[0053] 3) Dephosphorizing powder is blown in three batches from the top of the furnace. Based on a dephosphorizing powder to molten iron net weight ratio of 8.5%, the total amount of dephosphorizing powder added is 42.5 kg. The first batch of dephosphorizing powder is added at an argon flow rate of 0.26 L / min, accounting for 55% of the total amount, which is 23.375 kg. The second batch of dephosphorizing powder is added at an argon flow rate of 0.47 L / min, accounting for 35% of the total amount, which is 14.875 kg. The remaining 4.25 kg of dephosphorizing powder is added at an argon flow rate of 0.68 L / min. The time interval between the first and second batches is 8 minutes, and the time interval between the second and third batches is 7 minutes.

[0054] 4) During the two intervals between the addition of dephosphorizing powder, iron powder is injected twice from the furnace wall upwards into the molten pool using oxygen as the carrier gas. The first batch of injected iron powder is calculated as 25% of the first batch of injected dephosphorizing powder, which is 5.84 kg. The weight of the oxygen carrier gas is calculated as 1.2 times the weight of the iron powder, which is 7.56 kg. The equivalent volume under standard conditions is 5.29 m³. 3 The second batch of injected iron powder, calculated as 10% of the second batch of injected dephosphorization powder, amounted to 1.488 kg. The oxygen carrier gas, calculated as 0.8 times the weight of the iron powder, amounted to 1.19 kg, which translates to a volume of 0.83 m³ under standard conditions. 3 .

[0055] 5) Dephosphorization ends 6.5 minutes after the third batch of dephosphorization powder is added.

[0056] In this embodiment, the dephosphorizing agent is distributed in the following weight percentages: 40% dust collector ash, 55% high-calcium fly ash, 5% fluorite powder, with a dust collector ash particle size of 40.5 μm, high-calcium fly ash and fluorite powder particle sizes of 1.5 mm, and iron powder particle size of 96 μm.

[0057] Results: Samples were taken after dephosphorization treatment and tested. The phosphorus content of the molten iron after dephosphorization treatment was 0.0072%. According to the calculation of dephosphorization rate = (initial phosphorus content of molten iron - phosphorus content of molten iron after dephosphorization treatment) / initial phosphorus content of molten iron × 100%, the dephosphorization rate was 97.71%.

[0058] The above description is only 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 concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for applying a dephosphorizing powder for molten iron, characterized in that, During the dephosphorization process, argon gas, dephosphorizing powder, and iron powder with oxygen as the carrier gas are applied to the molten iron at the furnace bottom, furnace top, and furnace wall respectively until dephosphorization is completed; specifically, it includes the following steps: 1) Pour molten iron into the furnace at a temperature of 1340–1380℃; 2) Argon gas is blown into the molten pool from the bottom of the furnace to create disturbance in the molten pool. The argon gas flow rate increases in three stages. 3) The dephosphorizing powder is blown in three batches from the top of the furnace. The three batches of dephosphorizing powder are added in three stages of argon flow rate change, with an interval t between each batch. The amount of dephosphorizing powder added decreases as a percentage of the total amount used. 4) During the two intervals t between the addition of dephosphorization powder, iron powder is injected from the furnace wall into the molten pool using oxygen as the carrier gas. 5) Dephosphorization ends 5-8 minutes after the third batch of dephosphorization powder is added.

2. The application method of the dephosphorizing powder for molten iron according to claim 1, characterized in that, The dephosphorization powder includes converter dust, high-calcium fly ash, and fluorite powder; its composition by weight percentage is: converter dust: 10%–70%, high-calcium fly ash: 20%–80%, and fluorite powder: 5%–10%.

3. The application method of the dephosphorizing powder for molten iron according to claim 2, characterized in that, The particle size of the converter dust is ≤45μm, and the particle size of the high-calcium fly ash and fluorite powder is ≤3mm.

4. The application method of the dephosphorizing powder for molten iron according to claim 1, characterized in that, In step 1), the molten iron has a Si content ≤ 0.15% and a P content ≥ 0.2%.

5. The application method of the dephosphorizing powder for molten iron according to claim 1, characterized in that, In step 2), the argon flow rate changes in three stages: the first stage argon flow rate is 0.2-0.35 L / min, the second stage argon flow rate is 0.4-0.55 L / min, and the third stage argon flow rate is 0.6-0.75 L / min.

6. The application method of the dephosphorizing powder for molten iron according to claim 1, characterized in that, The interval time for step 3) is t = 5 to 10 minutes.

7. The application method of the dephosphorizing powder for molten iron according to claim 1, characterized in that, The amount of dephosphorizing powder added in step 3) is as follows: the first batch accounts for 50% to 60%, the second batch accounts for 30% to 38%, and the third batch is the remaining amount of dephosphorizing powder.

8. The application method of the dephosphorizing powder for molten iron according to claim 1, characterized in that, In step 4), the particle size of the injected iron powder is ≤120μm, and the amount of injected iron powder is: 20% to 30% of the amount of the first batch of injected iron powder, and 5% to 15% of the amount of the second batch of injected iron powder.

9. The application method of the dephosphorizing powder for molten iron according to claim 1, characterized in that, In step 4), the weight of oxygen is 0.5 to 1.2 times the weight of iron powder.