Nitrogen control method for converter smelting of low-carbon molten iron

Abstract

The invention relates to a nitrogen control method for smelting low-carbon molten iron by a converter. The method comprises the following steps: adding light scrap steel; active lime and dolomite are adopted as slag making materials; low-lance-position small-flow blowing is adopted; argon is blown in the whole bottom blowing process; the final temperature is greater than or equal to 1660 DEG C, and the final oxygen value ranges from 200 ppm to 500 ppm; alloying after tapping for a set time; alloy is added, and bottom argon blowing of the molten steel tank is started; after the alloy is added, the modifier is added into the molten steel tank through the blanking elephant trunk; and slag-stopping tapping is adopted after tapping is finished. The method has the advantages that the low-carbon abnormal molten iron is smelted by adding the light steel scrap and the converter, and early-stage melting of the steel scrap and denitrification reaction can be well promoted by adopting the light steel scrap, increasing the molten iron ratio and other measures; active lime and dolomite are adopted as slag making materials, when blowing begins, the lime is added at a time, the remaining dolomite is added when slag is active, the dolomite is added in batches for slag making, continuous CO2 bubble generation in the furnace can be promoted, and denitrification reaction is further promoted.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, and in particular to a method for controlling nitrogen in converter smelting low-carbon molten iron. Background Art

[0002] Nitrogen in steel exists in the form of nitrides. With the advancement of science and technology, customers' pursuit of steel performance continues to improve, and molten steel control is gradually developing in the direction of purification. The presence of nitrogen in steel reduces the toughness and plasticity of steel. With high nitrogen content, steel is prone to strain aging, aging precipitation hardening or aging brittleness, causing blue brittleness and cold brittleness of steel, affecting the deep drawing performance, welding performance and hot working performance of steel. Therefore, under normal circumstances, the presence of nitrogen is harmful and should be reduced as much as possible. The carbon content in normal molten iron ranges from 4.0% to 4.9%. When the blast furnace is abnormal, the carbon content in molten iron will be reduced to about 3.5%. In the smelting of low-carbon molten iron, due to the low carbon content brought in, the CO produced during the converter smelting process will be sharply reduced. According to the denitrification principle of the converter, the denitrification effect will be significantly worse, and the nitrogen content at the converter end will reach 30-60ppm, which is very easy to cause the nitrogen content of the finished product to exceed the standard and affect the performance of the steel. Summary of the invention

[0003] The purpose of the present invention is to provide a method for controlling nitrogen in low-carbon molten iron in a converter, which reduces the nitrogen content at the converter end point through a reasonable slag making process and an oxygen supply process.

[0004] To achieve the above object, the present invention is implemented through the following technical solutions:

[0005] A method for controlling nitrogen in converter smelting low-carbon molten iron, specifically comprising the following steps:

[0006] S1. Add light scrap steel and smelt low-carbon abnormal molten iron in converter, with molten iron ratio ≥92%;

[0007] S2, slag making materials are activated lime and dolomite;

[0008] S3, adopt low gun position and small flow blowing;

[0009] S4, argon blowing during the whole bottom blowing process;

[0010] S5, the end point temperature is ≥1660℃, the end point oxygen value range is 200~500ppm, and re-blowing is strictly prohibited at the end point;

[0011] S6, the steel is alloyed after the set time, and the deoxidized aluminum is prepared on the top of the alloy;

[0012] S7. Add alloy according to the requirements of steel grade and start blowing argon gas from the bottom of the molten steel tank;

[0013] S8. After the alloy is added, the modifier is added into the molten steel tank through the feed chute. The modifier is lime.

[0014] S9. After steel tapping is completed, slag blocking is adopted.

[0015] In S2, the consumption of lime is between 15 and 30 kg / t, and the consumption of dolomite is between 10 and 15 kg / t. The adding process is as follows:

[0016] At the beginning of blowing, lime is added all at once, and dolomite is added at 2 / 3 of the total amount;

[0017] The remaining dolomite is added when the slag is active, in batches, with the amount added in each batch ≤0.5 tons.

[0018] In S3, the oxygen supply intensity of the oxygen lance ranges from 2.6 to 3.0 Nm 3 / min.t, the oxygen gun position is controlled between 1.8 and 2.5m, and the carbon pulling gun position is ≥2 minutes.

[0019] In S4, the argon flow rate range is 8~10Nm 3 / min.

[0020] In S7, the argon flow rate range is 60~90Nm 3 / h, argon blowing time ≥ 3 minutes.

[0021] In S8, the lime range is 2 to 3 kg / t.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Add light scrap steel and use the converter to smelt low-carbon abnormal molten iron. By using light scrap steel and increasing the molten iron ratio, the early melting of scrap steel and the denitrification reaction can be promoted;

[0024] 2. The slag-making materials are activated lime and dolomite. At the beginning of blowing, lime is added all at once, and the remaining dolomite is added when the slag is active. By adding dolomite in batches to slag-making, continuous CO 2 The generation of bubbles further promotes the denitrification reaction;

[0025] 3. In converter smelting of low-carbon hot metal (carbon content less than 3.9%), nitrogen-controlled operation effectively avoids high nitrogen accidents;

[0026] 4. The converter smelts low-carbon molten iron (carbon content less than 3.9%), avoiding abnormal molten iron to pig iron operation, simplifying the process flow and reducing production costs;

[0027] 5. After the alloy is added, it is added into the tank through the material discharge chute. The modifier is lime. By adding the modifier into the molten steel tank, it can effectively cover the surface of the molten steel to avoid nitrogen absorption after steel tapping;

[0028] 6. Use slag blocking at the end of steel tapping to avoid impurities being brought into the molten steel, causing nitrogen increase, phosphorus return, and increased inclusions in the molten steel. DETAILED DESCRIPTION

[0029] The present invention is described in detail below, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0030] A method for controlling nitrogen in converter smelting low-carbon molten iron, specifically comprising the following steps:

[0031] S1. Add light scrap steel, and it is strictly forbidden to add heavy scrap steel. The converter is used to smelt low-carbon abnormal molten iron, and the molten iron ratio is ≥92% to reduce the nitrogen content brought in; among them, low-carbon abnormal molten iron is molten iron with a carbon content of ≤3.9%.

[0032] S2, slag making materials are activated lime and dolomite;

[0033] The consumption of lime is between 15 and 30 kg / t, and the consumption of dolomite is between 10 and 15 kg / t. The adding process is as follows:

[0034] At the beginning of blowing, lime is added all at once, and dolomite is added at 2 / 3 of the total amount;

[0035] The remaining dolomite is added in batches according to the state of the slag. It should be added when the slag is active to increase the bubbles generated in the molten pool and promote the discharge of nitrogen content. It is added in batches, with the amount added in each batch ≤0.5 tons.

[0036] S3, adopt low lance position and small flow blowing, the oxygen supply intensity of the oxygen lance ranges from 2.6 to 3.0 Nm 3 / min.t, the oxygen lance position is controlled between 1.8 and 2.5m, and the carbon pulling lance position is ≥2 minutes, which is used for low final slag oxidation and high desulfurization efficiency.

[0037] S4: Bottom blowing is carried out with argon throughout the whole process, and the argon flow rate range is 8-10Nm3 / min.

[0038] S5, the end point temperature is ≥1660℃, the end point oxygen value range is 200~500ppm, and re-blowing is strictly prohibited at the end point;

[0039] S6, alloying starts 2 minutes after steel tapping begins, and deoxidized aluminum is placed on top of the alloy;

[0040] S7. Add alloy according to the requirements of steel grade, open the bottom of the steel tank to blow argon, and the argon flow rate range is 60~90Nm 3 / h, argon blowing time ≥ 3 minutes.

[0041] S8. After the alloy is added, the modifier is added into the molten steel tank through the feed chute. The modifier is lime; lime 2-3 kg / t;

[0042] S9. At the end of steel tapping, slag blocking is adopted to prevent slag from falling into the molten steel.

[0043] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0044] [Example 1]

[0045] A method for controlling nitrogen in converter smelting low-carbon molten iron, using a 260-ton converter to smelt grade A steel plate, with the carbon content of the molten iron entering the furnace being 3.5%, specifically comprising the following steps:

[0046] Step S1, adopting molten iron + scrap steel smelting, the amount of molten iron is 265 tons, the scrap steel is 15 tons, and the scrap steel material type is light and thin material.

[0047] Step S2, at the beginning of blowing, 4 tons of lime are added into the furnace at one time, 2 tons of dolomite are added, and the remaining dolomite is added in batches, each batch is ≤ 0.5 tons, and the timing of adding is based on the state of the slag. When the slag is active, it is used to reduce the formation of FeO in the slag and create favorable conditions for desulfurization.

[0048] Step S3: Smelting adopts low lance position and small flow blowing, and the oxygen supply intensity of the oxygen lance is 2.8Nm 3 / min.t, the oxygen gun position is controlled at 1.8~2.5m, and the carbon pulling gun position is required to be ≥2 minutes.

[0049] Step S4: endpoint temperature 1662° C., endpoint oxygen value 350 ppm, endpoint nitrogen content 20 ppm.

[0050] Step S5: Blow argon throughout the bottom blowing process, with an argon flow rate of 8 to 10 Nm 3 / min.

[0051] Step S6: alloying the steel structure 2 minutes after it is tapped, and adding alloys according to the requirements of the steel grade.

[0052] Step S7: After the alloy is added, it is added into the tank through the discharge chute, and 0.6 tons of lime is used for modification.

[0053] Step S8: Add alloy and start blowing argon from the bottom of the molten steel tank, with an argon flow rate of 60-90 Nm 3 / h, argon blowing time ≥ 3 minutes.

[0054] The sulfur content of the argon station can reach 0.009%

[0055] Step S9: After steel tapping is completed, slag blocking operation is performed to prevent molten steel from slag falling.

[0056] Step S10: The molten steel is directly treated in an argon station or a CAS refining furnace, and is poured into a casting machine after the composition and temperature meet the requirements.

[0057] The invention adds light scrap steel and smelts low-carbon abnormal molten iron in a converter. By adopting light scrap steel and improving the molten iron ratio and other measures, the early melting of scrap steel and the denitrification reaction can be better promoted. The slag-making material adopts active lime and dolomite. At the beginning of blowing, the lime is added at one time, and the remaining dolomite is added when the slag is active. By adding dolomite in batches to slag-making, the continuous CO in the furnace can be promoted. 2 The generation of bubbles further promotes the denitrification reaction; the converter smelts low-carbon molten iron (carbon content less than 3.9%), and effectively avoids high nitrogen accidents through nitrogen control operations; the converter smelts low-carbon molten iron (carbon content less than 3.9%), avoids abnormal molten iron to pig iron operations, simplifies the process flow, and reduces production costs; after the alloy is added, it is added to the tank through the discharge chute, and the modifier is lime. By adding the modifier into the molten steel tank, it can effectively cover the surface of the molten steel to avoid nitrogen absorption after tapping; slag blocking is used at the end of tapping to avoid impurities from being brought into the molten steel, causing nitrogen increase, phosphorus return, and increased inclusions in the molten steel.

Claims

1. A method for controlling nitrogen in converter smelting low-carbon molten iron, characterized in that: The specific steps include: S1. Add light scrap steel and smelt low-carbon abnormal molten iron in converter, with molten iron ratio ≥92%; S2, slag making materials are activated lime and dolomite; S3, adopt low gun position and small flow blowing; S4, bottom blowing with argon throughout the whole process; S5, the end point temperature is ≥1660℃, the end point oxygen value range is 200~500ppm, and re-blowing is strictly prohibited at the end point; S6, the steel is alloyed after the set time, and the deoxidized aluminum is prepared on the top of the alloy; S7, add alloy and start blowing argon gas from the bottom of the molten steel tank; S8. After the alloy is added, the modifier is added into the molten steel tank through the feed chute. The modifier is lime. S9. After steel tapping is completed, slag blocking is adopted.

2. The method for controlling nitrogen in converter smelting low-carbon molten iron according to claim 1, characterized in that: In S2, the consumption of lime is between 15 and 30 kg / t, and the consumption of dolomite is between 10 and 15 kg / t. The adding process is as follows: At the beginning of blowing, lime is added all at once, and dolomite is added at 2 / 3 of the total amount; The remaining dolomite is added when the slag is active, in batches, with the amount added in each batch ≤0.5 tons.

3. The method for controlling nitrogen in converter smelting low-carbon molten iron according to claim 1, characterized in that: In S3, the oxygen supply intensity of the oxygen lance ranges from 2.6 to 3.0 Nm 3 / min.t, the oxygen gun position is controlled between 1.8 and 2.5m, and the carbon pulling gun position is ≥2 minutes.

4. The method for controlling nitrogen in converter smelting low-carbon molten iron according to claim 1, characterized in that: In S4, the argon flow rate range is 8~10Nm 3 / min.

5. The method for controlling nitrogen in converter smelting low-carbon molten iron according to claim 1, characterized in that: In S7, the argon flow rate range is 60~90Nm 3 / h, argon blowing time ≥ 3 minutes.

6. The method for controlling nitrogen in converter smelting low-carbon molten iron according to claim 1, characterized in that: In S8, the lime range is 2-3 kg / t.