Continuous casting tundish covering agent for ultra-pure steel

Abstract

The invention discloses a continuous casting tundish covering agent for ultra-pure steel. The continuous casting tundish covering agent comprises the following active ingredients: 40-50 parts by mass of CaO; 5-10 parts by mass of a rare earth oxide; 3 to 5 parts by mass of MgO; 8 to 15 parts by mass of SiO2; 25 to 35 parts by mass of Al2O3; and 0-3 parts by mass of carbon powder. The continuous casting tundish covering agent is suitable for producing ultra-pure steel, has the comprehensive advantages of being good in spreadability, free of red emission and crusting in the molten steel pouring process, convenient to measure temperature and sample, high in inclusion adsorption capacity and invariant in the using process, and is low in corrosion to refractory materials, stable pouring of the ultra-pure steel can be achieved, and the service life of the continuous casting tundish covering agent is prolonged. And the inclusion content and the oxygen content in the steel are ensured to be in an extremely low range.

Description

Technical Field

[0001] The invention relates to a component, in particular to a continuous casting tundish covering agent. Background Art

[0002] The main function of the continuous casting tundish covering agent is to keep the molten steel warm during pouring and prevent it from contacting with the air. Its expected performance is: good spreadability, no reddening of the covering agent during the molten steel pouring process, convenient temperature measurement and sampling, strong ability to absorb inclusions, and no serious corrosion to refractory materials.

[0003] At present, the most widely used covering agent is magnesium covering agent, which has good spreadability and is easy to sample, and has no corrosion to refractory materials. However, due to its high melting point, once the temperature is measured and sampled during the pouring process, the temperature sampling port is prone to reddening, causing the molten steel to be exposed to the atmosphere and cause secondary oxidation of the molten steel, which is very unfavorable for smelting pure steel. It will also cause inclusions generated by secondary oxidation to block the water inlet of the crystallizer, thereby causing the pouring to shut down.

[0004] Based on this, for the pouring of pure steel, more steel companies began to use aluminum-calcium covering agents, which have the characteristics of good spreadability, strong adsorption capacity for inclusions, and not easy to turn red after sampling. However, aluminum-calcium covering agents also have disadvantages, and they are particularly prone to crusting. In order to solve this problem, one solution in the prior art is to add a layer of carbonized rice husk covering agent on the aluminum-calcium covering agent. For example, the Chinese patent document with publication number CN101758176B, publication date March 21, 2012, and titled "A double-layer tundish covering agent" also adopts this solution.

[0005] However, the SiO2 content in the carbonized rice husk covering agent is very high, and it is easy to continuously modify the underlying calcium aluminate covering agent components after addition, eventually causing the basicity of the calcium aluminate covering agent to drop below 2. For the smelting of aluminum-deoxidized ultra-pure steel, the decrease in the covering agent's basicity will cause the molten steel aluminum to react with the covering agent SiO2, thereby inducing secondary oxidation, which is very unfavorable for the smelting of ultra-pure steel, and will lead to an increase in the oxygen content of the steel, an increase in inclusions, an increased risk of nozzle blockage, and the occurrence of macroscopic inclusions. The molten steel often requires calcium treatment for stable pouring, and the steel defect rate also increases.

[0006] In order to solve the problem of denaturation of the bottom layer covering agent, a Chinese patent document with publication number CN103111592A, publication date May 22, 2013, and name "Tundish Covering Agent" provides a three-layer covering agent solution, in which a layer of magnesia-based hollow particle covering agent is added between the bottom aluminum-calcium covering agent and the upper high-SiO2 content covering agent. However, the addition of the magnesia covering agent cannot avoid the denaturation of the lower aluminum-calcium covering agent. Once the MgO content of the aluminum-calcium covering agent increases, it will harden and also affect the adsorption of inclusions.

[0007] Therefore, the covering agent in the prior art and its use inevitably have defects, which are disadvantageous to the continuous casting of ultra-clean steel. Summary of the invention

[0008] One of the purposes of the present invention is to provide a continuous casting tundish covering agent for ultra-clean steel, which is designed and developed based on the metallurgical solution density difference stratification principle and has the comprehensive advantages of good spreadability, no reddening of the covering agent during the molten steel pouring process, no crusting, convenient temperature measurement and sampling, strong ability to adsorb inclusions, and stability during use. It also has low corrosion to refractory materials, can achieve stable casting of ultra-clean steel, and ensure that the inclusion and oxygen content in the steel are within an extremely low range.

[0009] In order to achieve the above object, the present invention provides a continuous casting tundish covering agent for ultra-pure steel, the effective components of which include:

[0010] CaO: 40-50 parts by mass;

[0011] Rare earth oxide: 5-10 parts by mass;

[0012] MgO: 3-5 parts by mass;

[0013] SiO2: 8-15 parts by mass;

[0014] Al2O3: 25-35 parts by mass;

[0015] Carbon powder: 0 to 3 parts by mass.

[0016] Accordingly, the present invention also provides a continuous casting tundish covering agent for ultra-clean steel, wherein the effective components thereof are composed of the following items based on 100 parts by total mass:

[0017] CaO: 40-50 parts by mass;

[0018] Rare earth oxide: 5-10 parts by mass;

[0019] MgO: 3-5 parts by mass;

[0020] SiO2: 8-15 parts by mass;

[0021] Al2O3: 25-35 parts by mass;

[0022] Carbon powder: 0 to 3 parts by mass.

[0023] Compared with the existing aluminum-calcium covering agent, one of the important improvements of the present invention is that rare earth oxides are added and the SiO2 content is greatly increased, which is mainly used to increase the density of the covering agent and reduce the thermal conductivity of the covering agent.

[0024] The main function of increasing the density of the covering agent is that even if the carbonized rice husk covering agent is added on top, the density of this covering agent is much greater than the density of the molten carbonized rice husk, making it impossible for the molten layer of carbonized rice husk to penetrate into the lower layer of the covering layer formed by this covering agent, thereby playing a function close to the invariance of the molten steel covering agent.

[0025] The effect of reducing the thermal conductivity of the covering agent is that, in addition to further heat preservation, the covering agent can also prevent the surface of the covering agent from forming a crust during use, while the covering agent close to the molten steel is still in a completely liquid state to fully absorb inclusions. The principle is that the inventor has found through research that the principle of the crusting of conventional aluminum-calcium covering agents is that they have good thermal conductivity and low heat capacity, which easily leads to the formation of high-temperature sintering and precipitation of more high-melting-point CaOAl2O3 phases on the surface of the covering agent after it is put into use. This melting and then solidification precipitation of high-melting-point phases is the fundamental reason for the crusting of conventional calcium aluminate. Based on such research findings, the present invention greatly reduces the thermal conductivity of the covering agent by adjusting the covering agent composition, thereby achieving that the surface covering agent is always in a state without liquid phase precipitation, thereby solving the problem of crusting of the covering agent surface.

[0026] Although the continuous casting tundish covering agent described in the present invention increases the SiO2 content, the addition of rare earth oxides as basic oxides greatly reduces the SiO2 activity, thereby ensuring that when the covering agent comes into contact with molten steel during use, no reaction between the molten steel aluminum and the covering agent SiO2 occurs, thereby controlling the secondary oxidation of the molten steel.

[0027] In addition, the continuous casting tundish covering agent of the present invention can also selectively add carbon powder according to the steel type: for example, when casting low-carbon steel, no carbon powder can be added to its components; when casting medium-high carbon steel, an appropriate amount of carbon powder can be added to its components. The reason is that the pouring temperature of medium-carbon steel is relatively low, and there is no need to worry about the incompatibility of components caused by carbon addition. Adding carbon powder can further ensure that the surface of the covering agent does not form a crust, while the pouring temperature of low-carbon steel or ultra-low-carbon steel is high, so it is possible to ensure that the surface does not form a crust without adding carbon powder.

[0028] During continuous casting, the continuous casting tundish covering agent of the present invention may be used at the start of pouring, and the continuous casting tundish covering agent of the present invention may also be used when the continuous casting furnace is replenished.

[0029] In addition, for cost considerations, the continuous casting tundish covering agent of the present invention may be added at the start of pouring, and the carbonized rice husk covering agent may be added during the continuous pouring furnace.

[0030] Furthermore, in the continuous casting tundish covering agent of the present invention, the rare earth oxide includes at least one of La2O3 and Ce2O3.

[0031] Furthermore, the active ingredients of the continuous casting tundish covering agent of the present invention also include:

[0032] Na2O: 1 to 3 parts by mass;

[0033] CaF2: 1 to 2 parts by mass.

[0034] As a preferred embodiment of the present invention, the continuous casting tundish covering agent also includes appropriate amounts of Na2O and CaF2. The addition of these components can further ensure that the covering agent has good spreadability, and these trace additions basically do not cause corrosion to the magnesium refractory material of the tundish.

[0035] Furthermore, the melting point of the continuous casting tundish covering agent of the present invention is controlled to be 1390-1410°C.

[0036] Furthermore, the density of the continuous casting tundish covering agent of the present invention in the molten state is controlled to be 3 to 3.5 g / cm 3 .

[0037] Furthermore, the oxygen content in the continuous casting billet obtained by using the continuous casting tundish covering agent is lower than 10 ppm.

[0038] For spring steel and cold heading steel, the oxygen content can be controlled below 10 ppm by using the continuous casting tundish covering agent of the present invention.

[0039] Furthermore, the oxygen content of the continuously cast slab obtained by using the continuous casting tundish covering agent after rolling is lower than 4 ppm.

[0040] For bearing steel, the oxygen content can be stably controlled to be below 4 ppm by using the continuous casting tundish covering agent of the present invention.

[0041] The continuous casting billet obtained by using the continuous casting tundish covering agent has a Ds inclusion rating of 0.5 or below after rolling, and has no Class B inclusions and macro inclusions.

[0042] The continuous casting tundish covering agent of the present invention has the following advantages and beneficial effects:

[0043] The continuous casting tundish covering agent of the present invention does not emit redness or form a crust during the molten steel pouring process, and is convenient for temperature measurement and sampling.

[0044] The continuous casting tundish covering agent of the present invention has good spreadability.

[0045] The continuous casting tundish covering agent of the present invention does not corrode the tundish refractory material, and the covering agent does not change during use, and always maintains good absorption and secondary oxidation resistance, and can achieve stable casting of ultra-pure steel, ensuring that the inclusion and oxygen content in the steel are in an extremely low range. For example, the oxygen content of bearing steel is stably controlled to be below 4ppm; for spring steel and cold heading steel, the oxygen content is controlled to be below 10ppm.

[0046] The continuous casting slab obtained by using the continuous casting tundish covering agent has a Ds inclusion rating of 0.5 after rolling, and has no B-type inclusions and macro inclusions. DETAILED DESCRIPTION

[0047] The continuous casting tundish covering agent for ultra-clean steel described in the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0048] Example 1

[0049] The 150t electric furnace-LF-VD-bloom continuous casting process produces high carbon chromium bearing steel. After the refining of the bearing steel is completed, it is hoisted to the continuous casting station for casting. Before pouring, 50kg of covering agent is added to the tundish. The composition and parameters of the covering agent are shown in Table 1. During the casting process, after the steel liquid level is formed in the tundish, 150kg of the aforementioned covering agent is added. After each furnace of the continuous casting furnace is poured, 50kg of the aforementioned covering agent is added.

[0050] During the continuous casting process, the surface of the covering agent is a powdery covering agent that has not been sintered at high temperature. No reddening is seen during the continuous casting process. The covering agent is close to the molten steel and can fully absorb inclusions. The temperature measurement and sampling during the smelting process in the tundish can be conveniently carried out. After the temperature measurement and sampling, the temperature measurement and sampling covering agent mouth is automatically sutured to prevent secondary oxidation. After the pouring is completed, there is no obvious melting loss of the refractory in the tundish.

[0051] The oxygen content of the final casting billet bearing steel is 3.5ppm, the Ds inclusion rating is 0.5, and there are no B-type inclusions and macro inclusions. The use of this covering agent can ensure continuous casting of 7 or more continuous pours.

[0052] Example 2

[0053] 55SiCr spring steel is produced by the 150t electric furnace-LF-VD-bloom continuous casting process. After the spring steel is refined, it is hoisted to the continuous casting station for casting. 50kg of covering agent is added to the tundish before casting. The composition and parameters of the covering agent are shown in Table 1. During the casting process, after the steel liquid level is formed in the tundish, the composition is added as the aforementioned covering agent of 150kg. 50kg of carbonized rice husk covering agent is added after each continuous casting furnace is cast.

[0054] During the continuous casting process, the surface of the covering agent is a powdery covering agent that has not been sintered at high temperature. No reddening is seen during the continuous casting process. The covering agent is close to the molten steel and can fully absorb inclusions. The temperature measurement and sampling during the smelting process in the tundish can be conveniently carried out. After the temperature measurement and sampling, the temperature measurement and sampling covering agent mouth is automatically sutured to prevent secondary oxidation. After the pouring is completed, there is no obvious melting loss of the refractory in the tundish.

[0055] The oxygen content of the final cast spring steel is 9.5ppm, the Ds inclusion rating is 0.5, there is no B-type inclusion and macro inclusion, and the inclusion width is controlled to be less than 10μm. The use of this covering agent can ensure continuous casting of 7 continuous pours or more.

[0056] Example 3

[0057] 20K cold heading steel is produced in the 150t electric furnace-LF-VD-bloom continuous casting process. After the cold heading steel is refined, it is hoisted to the continuous casting station for casting. 50kg of covering agent is added to the tundish before casting. The composition and parameters of the covering agent are shown in Table 1. During the casting process, after the steel liquid level in the tundish is formed, the composition is added as the aforementioned covering agent of 150kg. 50kg of carbonized rice husk covering agent is added after each furnace of the continuous casting furnace is cast.

[0058] During the continuous casting process, the surface of the covering agent is a powdery covering agent that has not been sintered at high temperature. No reddening is seen during the continuous casting process. The covering agent is close to the molten steel and can fully absorb inclusions. The temperature measurement and sampling during the smelting process in the tundish can be conveniently carried out. After the temperature measurement and sampling, the temperature measurement and sampling covering agent mouth is automatically sutured to prevent secondary oxidation. After the pouring is completed, there is no obvious melting loss of the refractory material in the tundish.

[0059] The oxygen content of the final cold-forged steel in the ingot is 6ppm, the Ds inclusion rating is 0.5, and there are no B-type inclusions and macro inclusions. The use of this covering agent can ensure continuous casting of 7 or more continuous pours.

[0060] Example 4

[0061] The 150t electric furnace-LF-VD-bloom continuous casting process produces 55 series bearing steel. After the refining of the bearing steel is completed, it is hoisted to the continuous casting station for casting. Before pouring, 50kg of covering agent is added to the tundish. The composition and parameters of the covering agent are shown in Table 1. During the casting process, after the steel liquid level is formed in the tundish, the composition is added as the aforementioned covering agent of 150kg. After each continuous casting furnace is poured, 50kg of carbonized rice husk covering agent is added.

[0062] During the continuous casting process, the surface of the covering agent is a powdery covering agent that has not been sintered at high temperature. No reddening is seen during the continuous casting process. The covering agent is close to the molten steel and can fully absorb inclusions. The temperature measurement and sampling during the smelting process in the tundish can be conveniently carried out. After the temperature measurement and sampling, the temperature measurement and sampling covering agent mouth is automatically sutured to prevent secondary oxidation. After the pouring is completed, there is no obvious melting loss of the refractory in the tundish.

[0063] The oxygen content of the final casting billet bearing steel is 4.5ppm, the Ds inclusion rating is 0.5, and there are no B-type inclusions and macro inclusions. The use of this covering agent can ensure continuous casting of 7 or more continuous pours.

[0064] Example 5

[0065] The 150t electric furnace-LF-VD-bloom continuous casting process produces 65SiCrV spring steel. After the spring steel is refined, it is hoisted to the continuous casting station for casting. Before casting, 50kg of covering agent is added to the tundish. The composition and parameters of the covering agent are shown in Table 1. During the casting process, after the steel liquid level is formed in the tundish, the composition is added as the aforementioned covering agent of 150kg. After each continuous casting furnace is cast, 50kg of carbonized rice husk covering agent is added.

[0066] During the continuous casting process, the surface of the covering agent is a powdery covering agent that has not been sintered at high temperature. No reddening is seen during the continuous casting process. The covering agent is close to the molten steel and can fully absorb inclusions. The temperature measurement and sampling during the smelting process in the tundish can be conveniently carried out. After the temperature measurement and sampling, the temperature measurement and sampling covering agent mouth is automatically sutured to prevent secondary oxidation. After the pouring is completed, there is no obvious melting loss of the refractory in the tundish.

[0067] The oxygen content of the final cast spring steel is 8ppm, the Ds inclusion rating is 0, there is no B-type inclusion and macro inclusion, and the inclusion width is controlled to be less than 10μm. The use of this covering agent can ensure continuous casting of 7 continuous pours or more.

[0068] Example 6

[0069] SCM435 cold heading steel is produced by the 150t electric furnace-LF-VD-bloom continuous casting process. After the cold heading steel is refined, it is hoisted to the continuous casting station for casting. 50kg of covering agent is added to the tundish before casting. The composition and parameters of the covering agent are shown in Table 1. During the casting process, after the steel liquid level in the tundish is formed, the composition is added as the aforementioned covering agent of 150kg. 50kg of the covering agent is added after each continuous casting furnace is cast.

[0070] During the continuous casting process, the surface of the covering agent is a powdery covering agent that has not been sintered at high temperature. No reddening is seen during the continuous casting process. The covering agent is close to the molten steel and can fully absorb inclusions. The temperature measurement and sampling during the smelting process in the tundish can be conveniently carried out. After the temperature measurement and sampling, the temperature measurement and sampling covering agent mouth is automatically sutured to prevent secondary oxidation. After the pouring is completed, there is no obvious melting loss of the refractory material in the tundish.

[0071] The oxygen content of the final cold-forged steel in the ingot is 7ppm, the Ds inclusion rating is 0.5, and there are no B-type inclusions and macro inclusions. The use of this covering agent can ensure continuous casting of 8 or more continuous pours.

[0072] Table 1 lists the components and parameters of the continuous casting tundish covering agent of Examples 1-6 of the present invention.

[0073] Table 1.

[0074]

[0075] It can be seen from this that the continuous casting ladle covering agent of each embodiment of the present invention is suitable for the production of ultra-clean steel, has good spreadability, the covering agent does not turn red or form a crust during the molten steel pouring process, is convenient for temperature measurement and sampling, has a strong ability to adsorb inclusions, has the comprehensive advantages of no invariance during use, and has low corrosion to refractory materials, can achieve stable pouring of ultra-clean steel, and ensure that the inclusion and oxygen content in the steel are within an extremely low range.

[0076] It should be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with by those skilled in the art from the contents disclosed in the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A covering agent for continuous casting tundish of ultra-pure steel, characterized in that: Its active ingredients include: CaO: 40-50 parts by mass; Rare earth oxide: 5-10 parts by mass; MgO: 3-5 parts by mass; SiO2: 8-15 parts by mass; Al2O3: 25-35 parts by mass; Carbon powder: 0 to 3 parts by mass.

2. The continuous casting tundish covering agent according to claim 1, characterized in that: Its active ingredients consist of the following: CaO: 40-50 parts by mass; Rare earth oxide: 5-10 parts by mass; MgO: 3-5 parts by mass; SiO2: 8-15 parts by mass; Al2O3: 25-35 parts by mass; Carbon powder: 0 to 3 parts by mass.

3. The continuous casting tundish covering agent according to claim 1 or 2, characterized in that: The rare earth oxide includes at least one of La2O3 and Ce2O3.

4. The continuous casting tundish covering agent according to claim 1 or 2, characterized in that: Its active ingredients also include: Na2O: 1 to 3 parts by mass; CaF2: 1 to 2 parts by mass.

5. The continuous casting tundish covering agent according to claim 1 or 2, characterized in that: Its melting point is controlled at 1390~1410℃.

6. The continuous casting tundish covering agent according to claim 1 or 2, characterized in that: The density of the molten state is controlled to 3-3.5g / cm 3 .

7. The continuous casting tundish covering agent according to claim 1 or 2, characterized in that: The oxygen content in the continuous casting billet obtained by using the continuous casting tundish covering agent is lower than 10 ppm.

8. The continuous casting tundish covering agent according to claim 7, characterized in that: The oxygen content in the continuous casting billet obtained by using the continuous casting tundish covering agent is lower than 4ppm.

9. The continuous casting tundish covering agent according to claim 1 or 2, characterized in that: The continuous casting billet obtained by using the continuous casting tundish covering agent has a Ds inclusion rating of 0.5 or below after rolling, and has no Class B inclusions and macro inclusions.

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