KR20120080250A - Agent for maintaining surface temperature of molten steel and method for maintaining surface temperature of molten steel - Google Patents

Abstract

The present invention is a molten steel surface insulating agent disposed on a molten steel surface having a predetermined molten steel surface temperature, 50 mass% or more of a low melting point raw material having a melting point lower than the molten steel surface temperature, and 50 mass with a melting point higher than the molten steel surface temperature. It contains less than% high-melting-point raw material, total 10 to 60% by mass of CaO, 10 to 70% by mass of Al ₂ O ₃ , 3 to 30% by mass of MgO, and 0 to 10% by mass of SiO ₂ more than 70% by weight and contained, the CaO and Al ₂ O ₃ and the ratio of CaO / Al ₂ O ₃ is 0.5 to 2.0, a melting point of the molten steel surface is lower than the temperature of the powder of less than 70% by mass of the particle diameter of 200 to 1000㎛ It provides a phosphorus steel surface insulating agent.

Description

MAGNET FOR MAINTAINING SURFACE TEMPERATURE OF MOLTEN STEEL AND METHOD FOR MAINTAINING SURFACE TEMPERATURE OF MOLTEN STEEL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten steel surface heat insulating agent that coats a molten steel surface for the purpose of thermal insulation, thermal insulation, or air oxidation prevention when transferring or refining molten steel by ladle, continuous casting tundish or the like.

This application claims priority based on Japanese Patent Application No. 2009-280205 for which it applied to Japan on December 10, 2009, and uses the content here.

Conventionally, when molten steel is transferred or refined by continuous casting tundish, ladle, or the like, the molten steel surface is coated with a molten steel surface insulating agent to prevent heat dissipation from the molten steel and intrusion of outside air. As the molten steel surface insulating agent, the rice hulls burned mainly composed of SiO ₂ and C are widely used. When using the burned rice hulls as the insulating molten steel surface, SiO ₂ is generated, so the Al reacts with the Al ₂ O ₃ based inclusions of molten steel, there is a problem that the increase in surface defects of the product.

Therefore, as a heat insulating agent with little SiO ₂ , as disclosed in Patent Document 1, an MgO-based molten steel surface heat insulating agent has been developed.

Japanese Patent Publication Hei 3-48152

However, since the molten steel surface heat insulating agent mainly containing MgO has a high melting point and is mainly solid at the operating temperature, the molten steel surface cannot be uniformly coated, and the inclusion of Al ₂ O ₃ system is caused by the reaction between the outside and the molten steel surface. Is generated.

The present invention solves the above-mentioned problems, and the components derived from the molten steel surface warming agent prevent the formation of alumina inclusions in the molten steel, and the melt rate on the molten steel surface is high, so that the molten steel surface can be uniformly coated. An object of the present invention is to provide a molten steel surface insulating agent.

In order to solve the said subject, this invention adopts the following structures and methods.

(1) The 1st aspect of this invention is a molten steel surface heat insulating agent arrange | positioned on the molten steel surface which has a predetermined molten steel surface temperature, 50 mass% or more low melting-point raw material whose melting | fusing point is lower than the said molten steel surface temperature, and melting | fusing point are said containing a high, a refractory material is less than 50 mass% from the molten steel surface temperature, as the average composition, 10 to 60% by weight CaO and 10 to 70% by weight of Al ₂ O ₃ and from 3 to 30 wt% MgO and, 0 to contain 10% by weight of at least 70% by weight in total of SiO _2, and the CaO and the Al ₂ O for ₃ ratio CaO / Al ₂ O ₃ is 0.5 to 2.0, a melting point lower than the molten steel surface temperature, 70 mass% or more is molten steel surface heat insulating agent which is powder of particle size 200-1000 micrometers.

(2) The 2nd aspect of this invention is the molten steel surface heat insulation method which arrange | positions the said molten steel surface heat insulating agent as described in said (1) on the said molten steel surface so that average melt layer thickness may become 5-30 mm.

According to the configuration described in (1) above, alumina inclusions are not generated in the molten steel by the components of the molten steel surface warming agent, and the molten steel surface warming agent melts quickly to uniformly cover the molten steel surface, thereby allowing molten steel and the atmosphere. It becomes possible to suppress the generation of the alumina inclusions by the contact of.

According to the method described in (2) above, the molten steel surface warming agent melts quickly to uniformly and reliably coat the molten steel surface and prevents bridging from occurring. Therefore, the production of alumina inclusions due to the contact between molten steel and the atmosphere is prevented. It becomes possible to suppress it.

1 is a change amount of the total oxygen amount in the tundish outlet side molten steel with respect to the total amount of oxygen in the tundish inlet side molten steel in the 1-2 ladle in continuous casting.
FIG. 2 is an average number of surface defects due to oxide inclusions present in one cold rolled steel sheet coil obtained from a steel sheet manufactured in a 1-2 ladle of continuous casting. FIG.

The inventors examined a method for increasing the melting rate of the molten steel surface warming agent in order to uniformly cover the molten steel surface with the molten steel surface warming agent. As a result, a molten steel surface heat insulating agent having a melting point lower than the molten steel surface temperature produced by mixing a low melting point raw material having a melting point lower than the molten steel surface temperature and a high melting point raw material having a melting point lower than 50 mass% higher than the molten steel surface temperature. In the case of using, it was found that a melt was formed at the initial stage of melting of the molten steel surface warming agent, thereby enabling rapid melting of the molten steel surface warming agent. EMBODIMENT OF THE INVENTION Hereinafter, the molten steel surface heat insulating agent which concerns on embodiment of this invention based on the said discovery is demonstrated in detail. The melting point of the molten steel surface insulating material is a temperature at which melting starts when the temperature of the material is raised, and in the case of a multi-element material, it is a melting point at an average composition corresponding to the solidus temperature.

The molten steel surface temperature in the continuous casting tundish, ladle, etc. is 1550 degreeC-1650 degreeC. Molten steel surface of the insulating liquid is, it uniformly covers the molten steel surface, it is possible to prevent the generation of Al ₂ O ₃ based inclusions of molten steel surface due to the contact with outside air.

The low melting point raw material initially produces a melt, and the high melting point raw material is brought into contact with the melt to promote diffusion of the high melting point raw material into the melt, thereby increasing the melting rate of the high melting point raw material. When the ratio of the low melting point raw material is less than 50% by mass, the diffusion of the high melting point raw material is not sufficiently promoted, the melting rate does not increase, and the high melting point raw material is not dissolved for a long time. Blocking of becomes insufficient. For this reason, in the molten steel surface heat insulating agent which concerns on this embodiment, the ratio of a low melting-point raw material is prescribed | regulated to 50 mass% or more. About an upper limit, 90 mass%, 80 mass%, or 80 mass% may be sufficient.

Moreover, in the molten steel surface heat insulating agent which concerns on this embodiment, by making 70 mass% or more of molten steel surface warming agent into powder of 200-1000 micrometers of particle diameters, it melt | dissolves a low melting-point raw material rapidly, and makes a high melting-point raw material rapidly into the said liquid solution. Can spread. The case where 70 mass% or more of molten steel surface heat insulating agent is made into powder with a particle size of 300-900 micrometers is more preferable, and when 70 mass% or more of molten steel surface heat insulating agent is made into powder with a particle size of 500-800 micrometers, it is further more preferable. In addition, the particle diameter here is a dimension of the scale of a sieve, and is a dimension which can pass the sieve of the said predetermined scale dimension. In addition, greater than 70% by mass of the particle size of 1000μ, there being a low melting point material is quickly melted, and so that the diffusion rate of the melt into the melting point of the raw material decreases, since the molten steel surface in contact with ambient air, Al ₂ O ₃ based Inclusion of is produced. On the other hand, when 70 mass% or more of the molten steel surface heat insulating agent is made into powder with a particle diameter of 200 micrometers or less, the cost which refines a raw material will become enormous. In addition, even when the powder having a particle diameter of 200 to 1000 µm occupies only a proportion less than 70% by mass of the molten steel surface warming agent, the amount of generation of the solution is not sufficient, and the diffusion rate of the high melting point raw material into the melt is lowered. As a result, the molten steel surface comes into contact with outside air.

The molten steel surface heat insulating agent should just be put in the bag in the state in which the low-melting-point raw material and the high-melting-point raw material were mixed uniformly. The molten steel surface heat insulating agent of the state put into this bag can be thrown into the molten steel surface for every bag. When the particle size of the low melting point raw material and the high melting point raw material is greatly different, for example, when a raw material of 200 to 1000 µm and a raw material of less than 200 µm or more than 1000 µm of the molten steel surface heat insulating agent according to the present embodiment are mixed. When the low melting point raw material and the high melting point raw material are ubiquitous in the bag, and the high melting point raw material first comes into contact with the molten steel surface, for example, no melt is rapidly formed on the molten steel surface and the molten steel surface comes into contact with the outside air.

If the melting point (melting point in the average composition) of the molten steel surface warmer is higher than the molten steel surface temperature, the molten steel surface warming agent does not reach a complete molten state, and the diffusibility on the molten steel surface deteriorates, and the molten steel surface comes into contact with the outside air. Throw it away. For this reason, melting | fusing point of the molten steel surface heat insulating agent which concerns on this embodiment is set lower than molten steel surface temperature.

In the case of using a molten steel surface warming agent that is completely molten, melting loss of refractory materials such as ladle and tundish becomes a problem. Therefore, in the molten steel surface heat insulating agent which concerns on this embodiment, the melting loss of a tundish is prevented by using the raw material containing magnesia (MgO) used for the ladle or tundish coating material. When the amount of magnesia to contain is less than 3 mass%, the melting rate of the ladle or tundish coating material becomes high, and it causes trouble for operation. On the other hand, when the amount of magnesia to contain is higher than 30 mass%, since melting | fusing point rises, it becomes impossible to coat molten steel uniformly. Therefore, in the molten steel surface heat insulating agent which concerns on this embodiment, the content rate of magnesia is prescribed | regulated to 3-30 mass%. More preferably, it is 5-30 mass%, More preferably, it is 7-25 mass%.

The molten steel surface heat insulating agent which concerns on this embodiment is 10-60 mass% of composition (average composition) after mixing, Preferably it is 15-55 mass%, More preferably, 25-50 mass% CaO, 10-70 It is composed mainly of% by mass, preferably 20 to 65 mass%, more preferably from 40 to the Al ₂ O 60% by weight _3,3 to 30% by mass of MgO, SiO ₂ of not higher than 0 to 10% by mass. However, CaO / Al ₂ O ₃ = 0.5 to 2.0. This is because the melting point (melting point in the average composition) of the molten steel surface heat insulating agent becomes minimum in the range of CaO / Al ₂ O ₃ = 0.5 to 2.0. On the other hand, if the mass of SiO ₂ contributes to the molten steel surface insulating agent, more than 10% by mass, and by the reaction of Al in molten steel and generate the inclusions of Al ₂ O ₃ system becomes increasing surface defects of the product. The content of MgO is as described above. In addition, "it makes it a main component" points out when the corresponding component occupies 70 mass% or more of the whole. In the molten steel surface heat insulating agent which concerns on this embodiment, the total of the above-mentioned component may be 80 mass% or 90 mass% or more of the whole.

As the low melting point raw materials, the melting point is B ₂ O ₃ , Li ₂ O, Na ₂ O, CaO-Al ₂ O ₃ , CaO-SiO ₂ , SrO-SiO ₂ , Al ₂ O ₃ -CaO- Composite oxides such as MgO, Al ₂ O ₃ -CaO-SiO ₂ , Al ₂ O ₃ -CaO-ZrO ₂ , Al ₂ O ₃ -MgO-SiO ₂ , and CaF ₂ can be used. As this composite oxide, solids solidified with any polymorphic melt, such as preliminary melting of quicklime and alumina or ground, or alumina cement milled after preliminary melting of quicklime and bauxite, can be used. As the above-mentioned high melting point raw material, MgO produced by firing magnesite, MgO melted product, or CaO, Al ₂ O ₃ , SiO ₂ , SrO, ZrO ₂ , Al ₂ O ₃ -MgO, CaO-MgO can be used. Can be. In addition, the composition of the specific low melting-point raw material and the high melting-point raw material which comprise the molten steel surface heat insulating agent, the combination and the mixing | blending ratio of the low-melting-point raw material and the high melting-point raw material are shown as an Example later.

As a molten steel surface heat insulation method, the molten steel surface heat insulating agent demonstrated above is arrange | positioned on the molten steel surface so that average melt thickness may become in the range of 5-30 mm. This is because, when the average melt thickness is less than 5 mm, blocking of outside air on the molten steel surface is insufficient. In addition, when the average melt thickness is more than 30 mm, the upper part of the molten steel surface insulating agent located at a position spaced apart from the molten steel as a heat source is cooled, whereby the molten steel surface is insulated on the refractory surface of the ladle or tundish having a lower temperature than the molten steel. This is because I solidify and adhere, and there is a gap between the molten steel and the molten steel surface insulating agent. This is called bridging. If bridging occurs, a gap is formed between the molten steel and the molten steel surface insulating agent, and thus the molten steel surface comes into contact with the outside air. You may arrange | position a molten steel surface heat insulating agent on the molten steel surface so that average melt thickness may become in the range of 7-25 mm or 9-20 mm.

Example

Next, although this invention is demonstrated based on an Example, the conditions in an Example are one condition example employ | adopted in order to confirm the feasibility and effect of this invention, and this invention is not limited only to these example conditions. .

This invention can employ | adopt various conditions or a combination of conditions, as long as the objective of this invention is achieved without deviating from the summary of this invention.

One charge of 280 tons of molten steel was subjected to molten iron preliminary treatment, converter decarburization, and vacuum degassing treatment using RH to melt ultra-low carbon steel. This casting piece was produced by the continuous casting method using the tundish of 60-t capacity. Casting was performed continuously for 15 charges of molten steel. The molten steel surface temperature was 1560-1580 degreeC. The molten steel surface heat insulating agent of this invention or a comparative example was used for heat insulation of molten steel in a tundish from the beginning of casting. In the case of the Example and the comparative example, the molten steel surface heat insulating agent added 500 kg bag | bag with respect to a tundish. One casting piece is thickness 250mm, length 7000mm, width 1500mm. The cast piece was made into the cold rolled steel plate of thickness 0.7mm and width 1500mm through the hot rolling and cold rolling processes used normally. In addition, the data of an Example and a comparative example are shown to Tables 1-4. Although divided into four tables for the convenience of the layout, Table 2 is a continuation of Table 1, Table 3 is a continuation of Table 2, Table 4 is a continuation of Table 3.

Table 1 of ※ 1 CaO-Al ₂ O ₃ is, CaO is 50% by mass, the Al ₂ O ₃ 50% by weight.

Table 2 CaO-SiO ₂ is in the ※, CaO is a 55% by mass, CaO-SiO ₂ is 45 mass%.

Table 1 of ※ 3 SrO-SiO ₂ is, SrO is 50% by weight, SiO ₂ 50% by weight.

Table 1 of _{※ 4 Al 2 O 3 -CaO-} MgO is, the Al ₂ O ₃ is 50% by weight, CaO 45% by weight, MgO 5% by weight.

Table 1 of _{※ 5 Al 2 O 3 -CaO-} SiO 2 , is the Al ₂ O ₃ 50% by weight, CaO 45% by mass, SiO ₂ is 5% by mass.

Table 1 of _{※ 6 Al 2 O 3 -CaO-} ZrO 2 , is the Al ₂ O ₃ 50% by weight, CaO 45% by weight, ZrO ₂ is 5% by mass.

Table 1 of _{※ 7 Al 2 O 3 -MgO-} SiO 2 is a 25% by weight Al ₂ O _3, MgO 25% by weight, SiO ₂ 50% by weight.

Table 2 of ※ 8 Al ₂ O ₃ -MgO is, the Al ₂ O ₃ is 75 mass%, MgO of 25 mass%.

* 9 CaO-MgO in Table 2 has 70 mass% of CaO and 30 mass% of MgOs.

* 10 molten layer thickness of Table 4 immersed the iron rod in molten steel, and made the thickness of the molten steel surface heat insulating agent adhered as molten layer thickness.

* 11 ΔT.O in Table 4 is the amount of change in the total amount of oxygen in the tundish molten steel to the total amount of oxygen in the molten steel after the RH treatment (after the vacuum degassing treatment) in the 1-2 ladle of continuous casting.

* 12 defect generation number in Table 4 is the average number of surface defects by the oxide type interference | inclusion existing in one cold rolled sheet steel coil obtained from the steel piece manufactured by 1-2 ladle of continuous casting.

As shown in FIG. 1, in the Example, the total amount of oxygen in tundish molten steel is decreasing with respect to the total amount of oxygen in molten steel after RH treatment (after vacuum degassing treatment) in the 1-2 ladle of continuous casting. . This is because the molten steel surface warming agent melted rapidly and uniformly coated the tundish surface, so that the production of alumina inclusions due to the contact between the molten steel and the atmosphere was suppressed, and the alumina inclusions in the molten steel floated and removed from the molten steel. to be.

In addition, as shown in FIG. 2, in the Example, the average number of the surface defects by the oxide type interference | inclusion existing in per cold rolled sheet steel coil obtained from the steel slab manufactured by the 1-2 ladle of continuous casting is conventional. It is greatly reduced compared with the comparative example. This is also because molten steel surface heat insulating agent melted rapidly and uniformly coated the tundish surface, so that the production of alumina inclusions due to the contact between molten steel and the atmosphere was suppressed.

According to the present invention, the component derived from the molten steel surface heat insulating agent prevents the formation of alumina inclusions in the molten steel, the rapid melting rate on the molten steel surface, and the molten steel surface thermal insulation capable of uniformly covering the molten steel surface. Can offer

Claims (2)

A molten steel surface insulating agent disposed on the molten steel surface having a predetermined molten steel surface temperature,
It contains 50 mass% or more of low melting-point raw material which melting | fusing point is lower than the said molten steel surface temperature, and less than 50 mass% high melting-point raw material which is higher than the said molten steel surface temperature,
Of 10 to 60 mass% of CaO and containing 10 to 70% by weight of Al ₂ O ₃ and 3 to 30% by weight of MgO and 0 to 70% by weight in total of SiO ₂ of 10% by weight,
Wherein the CaO and Al ₂ O ₃ ratio of CaO / Al ₂ O ₃ is 0.5 to 2.0,
Melting point is lower than the molten steel surface temperature,
70 mass% or more is powder with a particle diameter of 200-1000 micrometers, The molten steel surface heat insulating agent characterized by the above-mentioned. The molten steel surface thermal insulation method of Claim 1 is arrange | positioned at the said molten steel surface so that average melt layer thickness may become 5-30 mm.

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