A continuous casting steel tundish covering agent modifier and its preparation and use method

Abstract

The present invention relates to a continuous casting tundish covering agent modifier and its preparation and use method. The composition of the modifier includes, by weight percentage: pure iron powder: 50% to 55%, aluminum powder: 3% to 5%, and pre-melted slag powder: 40% to 47%. The components of the pre-melted slag powder include, by weight percentage: CaO: 45% to 55%, SiO2: 35% to 45%, Na2O: 10.0% to 15.0%, and Al2O3 < 5%, Fe2O3 < 0.5%. Compared with the prior art, the beneficial effects of the present invention are: 1) the use of the modifier and method of the present invention can enable the covering agent to have the function of continuously absorbing inclusions in molten steel, thereby purifying the molten steel; 2) the present invention is simple, easy to make, low in cost, and easy to use.

Description

Technical Field

[0001] The invention belongs to the field of metallurgical technology, and particularly relates to a continuous steel casting tundish covering agent modifier and a preparation and use method thereof, which is suitable for modifying the covering agent in the tundish during the continuous steel casting process so that the covering agent has the function of continuously absorbing inclusions in the molten steel. Background Art

[0002] In the process of continuous steel casting, the molten steel needs to be covered in the tundish to keep it warm, isolate it from the air and absorb the inclusions in the molten steel. The first two are relatively easy to achieve, but the absorption of inclusions in the molten steel will cause the Al2O3-based inclusions in the molten steel to float up and melt into the molten layer of the covering agent, and the Al2O3 content in the molten layer of the covering agent will continue to increase, while it will drop significantly, causing the covering agent to lose its ability to absorb dissolved inclusions.

[0003] To this end, people have made many attempts, but none of them have any obvious effect. Therefore, a middle package covering agent or modifier that can continuously maintain the ability to adsorb inclusions is needed.

[0004] Patent "A Tundish Covering Agent and Its Use Method" (Application No.: 201911280453.3, Public Announcement No.: CN111001769A); discloses a tundish covering agent and its use method, wherein the mass percentage of each component of the covering agent is: CaO: 41-49%, Al2O3: 31-39%, SiO2 <6%, MgO <10%, C <0.5%, H2O <1%, and the remainder is unavoidable impurities; the ratio of the CaO to the SiO2 is 8-12. The application of the above-mentioned covering agent in production has good thermal insulation effect, and the smelting of ultra-low carbon steel can control carbon increase and absorb inclusions in molten steel. The invention of a tundish covering agent and its use method can only absorb inclusions in the molten steel in one or two tanks at the initial stage of continuous casting.

[0005] The patent "A covering agent for a heavy rail steel continuous casting tundish and a method for adding the same" (application number: 202210682383.X, public announcement number: CN115229139A); discloses a covering agent for a heavy rail steel continuous casting tundish and a method for adding the same. The initial covering agent includes (wt%): CaO: 37.0-47.0, BaCO3: 9.0-13.0, MgO: 8.0-12.0, Al2O3: 20.0-30.0, Na2CO3: 1.0-3.0, CaF2: 0.8-1.2, FeO+MnO: <1, C: 4.0-8.0, etc.; the modified covering agent includes (wt%): CaO: 55-65, BaO: 8-12, MgO: 4-6, Al2O3: 14-18, Na2O: 3-5, CaF2: 2.8-3.2, FeO+MnO: <1, etc.; the invention improves the purity of molten steel in the production process of heavy rail steel by adding the initial covering agent at the initial stage of casting and adding the modified covering agent in the middle stage of casting. The invention provides a heavy rail steel continuous casting tundish covering agent and a method for adding the same, wherein the modified covering agent cannot penetrate the solid slag layer and sintered layer of the initial covering agent, and thus cannot play a modifying role.

[0006] Therefore, the above-mentioned existing technologies are far from achieving the desired effect and cannot meet the needs well. Summary of the invention

[0007] The purpose of the present invention is to provide a continuous casting steel tundish covering agent modifier and its preparation and use method, so that the covering agent can have the function of continuously absorbing inclusions in molten steel, thereby purifying the molten steel.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A continuous casting steel tundish covering agent modifier, the composition of the modifier comprises, by weight percentage: pure iron powder: 50% to 55%, aluminum powder: 3% to 5%, pre-melted slag powder: 40% to 47%.

[0010] The components of the pre-melted slag powder include, by weight percentage: CaO: 45% to 55%, SiO2: 35% to 45%, Na2O: 10.0% to 15.0%, and Al2O3 < 5%, Fe2O3 < 0.5%.

[0011] The density of the pre-melted slag powder is 2.8×10 3 ~3.2×10 3 kg / m 3 .

[0012] The modifier is in the shape of a sphere with a diameter ranging from 3 to 8 mm.

[0013] The density of the modifier is: 4.50×103 ~5.55×10 3 kg / m 3 .

[0014] The role of pure iron powder: increase and adjust the density of the modifier, so that it can sink through the covering agent after falling on the surface of the covering agent and stay at the interface of the slag. The iron powder will melt into the molten steel. Because the total amount added is small and it is "gradually melted and released", the effect on the composition change of the molten steel is very small and can be ignored. The role of pre-melted slag: it can dilute the covering agent and reduce the content of Al2O3 to enhance the ability to adsorb Al2O3 inclusions. The role of aluminum powder: aluminum powder can reduce the iron oxide in the covering agent to reduce the oxidizing property of the covering agent.

[0015] A method for preparing a continuous steel casting tundish covering agent modifier, comprising:

[0016] 1) The pre-molten slag is crushed and ground into powder with a particle size range of 20 to 150 μm.

[0017] 2) Pure iron powder with a particle size range of 20 to 150 μm, aluminum powder with a particle size range of 20 to 150 μm and the pre-melted slag powder obtained in step 1) are fully mixed and pressed into small balls with a diameter range of 3 to 8 mm. The balls are vacuum-packed in bags.

[0018] A method for using a continuous casting steel tundish covering agent modifier, after adding the tundish covering agent during the continuous casting process, when the rate at which the covering agent absorbs Al2O3 inclusions in the molten steel decreases to below 50%, the modifier is sprinkled onto the surface of the covering agent, and the amount added is 1 / 10 to 1 / 5 of the amount of the covering agent used.

[0019] The modifier is added once or more times.

[0020] During the continuous casting process, after the covering agent is added to the tundish for a period of time, the Al2O3 inclusions in the molten steel are continuously absorbed by the liquid layer of the covering agent, resulting in a continuous increase in the Al2O3 content in its chemical composition, causing the melting point of the liquid layer to increase and become viscous, so that the ability to absorb Al2O3 inclusions in the molten steel becomes smaller and smaller, until this function is lost. The duration of this process is determined by the amount of Al2O3 inclusions in the cast steel. When the rate at which the covering agent absorbs Al2O3 inclusions in the molten steel decreases to below 50%, the ability of the covering agent to absorb Al2O3 inclusions in the molten steel becomes significantly smaller. At this time, the modifier is thrown onto the surface of the covering agent, and the amount added is 1 / 10 to 1 / 5 of the amount of the covering agent. After the modifier falls on the surface of the covering agent, since its density is significantly greater than the density of the covering agent (usually 2.3×10 3 kg / m 3The modifier is heated and melted by the molten steel, and the following processes occur: ① The pre-melted slag can dilute the covering agent and reduce the content of Al2O3 to enhance the ability to adsorb Al2O3 inclusions; ② The aluminum powder can reduce the iron oxide in the covering agent to reduce the oxidizing property of the covering agent, which is beneficial to improve the purity of the molten steel; ③ The iron powder melts into the molten steel. Because the total amount added is small and it is "gradually melted and released", the effect on the composition change of the molten steel is very small and can be ignored.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The use of the modifier and method of the present invention can enable the covering agent to have the function of continuously absorbing inclusions in the molten steel, thereby purifying the molten steel.

[0023] 2) The invention is simple, easy to manufacture, low in cost and convenient to use. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are further described below in conjunction with embodiments. The following embodiments are used to specifically illustrate the contents of the present invention. These embodiments are only general descriptions of the contents of the present invention and do not limit the contents of the present invention.

[0025] Embodiment 1:

[0026] The slab is continuously cast into ship plate steel AH32, with 6 castings in total, each casting is 260 tons.

[0027] 1. Prepare pre-melted slag with the following components: CaO: 48%, SiO2: 38%, Na2O: 13.2%, Al2O3: 0.5%, Fe2O3: 0.3%, crush and grind into powder with a particle size range of 20-100 μm. The density of the pre-melted slag powder is 3.2×10 3 kg / m 3 .

[0028] 2. Prepare pure iron powder and aluminum powder, with a particle size range of 20-100 μm. Mix pure iron powder, aluminum powder and pre-melted slag powder in the following ratio: pure iron powder: 50%, aluminum powder: 3%, pre-melted slag powder: 47%, and then press them into small balls with a diameter range of 3.5-4.5 mm and a density of 5.05×10 3 kg / m 3 . Vacuum pack the pellets into bags.

[0029] 3. During the continuous casting process, 150 kg of covering agent is added to the tundish. After 80 minutes (after casting 2 cans of steel), the rate at which the covering agent absorbs Al2O3 inclusions in the molten steel is reduced to less than 50%. The modifier is sprinkled in, and the amount of the modifier is 1 / 10 of the amount of the covering agent, that is, 15 kg.

[0030] 4. After 80 minutes (after casting 4 cans of steel), sprinkle the modifier in, the amount of which is 1 / 10 of the amount of covering agent, i.e. 15 kg.

[0031] 5. Casting is completed.

[0032] After inspection, the total oxygen content of AH32 continuous casting billet of ship plate steel was reduced from 0.0026% using the original tundish covering agent to 0.0017%. The modifying agent has a significant modifying effect on the tundish covering agent, and the ability to absorb inclusions in the molten steel is significantly improved.

[0033] Embodiment 2:

[0034] Billet continuous casting of automotive plate steel SPHC, a total of 3 castings, each tank is 180 tons.

[0035] 1. Prepare pre-melted slag, the composition is: CaO: 50%, SiO2: 37%, Na2O: 12.5%, Al2O3: 0.2%, Fe2O3: 0.3%, crushed and ground into powder, the particle size range is 30~90μm. The density of pre-melted slag powder is 2.8×10 3 kg / m 3 .

[0036] 2. Prepare pure iron powder and aluminum powder, the particle size range is 30 ~ 90μm. Pure iron powder, aluminum powder, pre-melted slag powder are fully mixed according to the following ratio: pure iron powder: 53%, aluminum powder: 4%, pre-melted slag powder: 43%, and then pressed into small balls. The diameter of the small balls ranges from 3.2 to 4.3 mm and the density is 5.25×10 3 kg / m 3 . Vacuum pack the pellets into bags.

[0037] 3. During the continuous casting process, 130 kg of covering agent is added to the middle bag. After 60 minutes (after casting 1.5 cans of steel), the modifier is sprinkled in. The amount of the modifier is 1 / 8 of the amount of covering agent, that is, 16.2 kg.

[0038] 4. Casting is completed.

[0039] After inspection, the total oxygen content of the continuous casting billet was reduced from 0.0023% using the original tundish covering agent to 0.0016%. The modifying agent has a significant modifying effect on the tundish covering agent, and the ability to absorb inclusions in the molten steel is significantly improved.

Claims

1. A continuous casting steel tundish covering agent modifier, characterized in that: The composition of the modifier includes, by weight percentage: pure iron powder: 50% to 55%, aluminum powder: 3% to 5%, pre-melted slag powder: 40% to 47%; The density of the modifier is: 4.50×10 3 ~5.55×10 3 kg / m 3 ; The method for preparing the continuous steel casting tundish covering agent modifier comprises: 1) crushing and grinding the pre-melted slag into powder with a particle size range of 20 to 150 μm; 2) Pure iron powder with a particle size range of 20 to 150 μm, aluminum powder with a particle size range of 20 to 150 μm and the pre-melted slag powder obtained in step 1) are fully mixed and pressed into small balls with a diameter range of 3 to 8 mm; The method for using the continuous casting steel tundish covering agent modifier is as follows: after adding the tundish covering agent during the continuous casting process, when the rate at which the covering agent absorbs Al2O3 inclusions in the molten steel drops below 50%, the modifier is sprinkled onto the surface of the covering agent, and the amount added is 1 / 10 to 1 / 5 of the amount of the covering agent used.

2. The continuous casting steel tundish covering agent modifier according to claim 1, characterized in that: The components of the pre-melted slag powder include, by weight percentage: CaO: 45% to 55%, SiO 2： 35%~45%, Na2O: 10.0%~15.0%, and Al2O3<5%, Fe2O3<0.5%.

3. The continuous casting steel tundish covering agent modifier according to claim 2, characterized in that: The density of the pre-melted slag powder is 2.8×10 3 ~3.2×10 3 kg / m 3 .

4. A method for preparing a continuous casting steel tundish covering agent modifier according to any one of claims 1 to 3, characterized in that: include: 1) crushing and grinding the pre-melted slag into powder with a particle size range of 20 to 150 μm; 2) Pure iron powder with a particle size range of 20 to 150 μm, aluminum powder with a particle size range of 20 to 150 μm and the pre-melted slag powder obtained in step 1) are fully mixed and pressed into small balls with a diameter range of 3 to 8 mm.

5. A method for using the continuous casting steel tundish covering agent modifier as claimed in any one of claims 1 to 3, characterized in that: After adding the tundish covering agent during the continuous casting process, when the rate at which the covering agent absorbs Al2O3 inclusions in the molten steel drops below 50%, a modifier is sprinkled onto the surface of the covering agent, and the amount added is 1 / 10 to 1 / 5 of the amount of the covering agent used.

6. A method for using the continuous casting steel tundish covering agent modifier as claimed in claim 5, characterized in that: The modifier is added once or more times.