The name of the invention: the molten steel surface heat retention agent and the molten steel surface heat insulation method
Technical field
[0001]
　The present invention, transferring the molten steel due to the ladle and continuous casting tundish, or when carrying out the refining process, on the surface of molten steel heat insulation agent to coat the surface of molten steel for the purpose of insulation and heat insulation or anti-air oxidation.
　The present application, to December 10, 2009, claiming priority based on Japanese Patent Application No. 2009-280205, filed in Japan, which is incorporated herein by reference.
Background technique
[0002]
　Conventionally, transfer the molten steel due to the continuous casting tundish or ladle, or when performing the refining process, coating the surface of the molten steel in the molten steel surface heat retaining agent, to prevent the heat dissipation and the outside air from entering from the molten steel there. As the molten steel surface heat retaining agent, SiO 2 baked rice mainly composed of the C are widely used. If you use the baked rice as molten steel surface heat retaining agent, SiO 2 reacts with Al in the molten steel Al 2 O 3 to produce a system inclusions, there is a problem that surface defects of the product is increased.
[0003]
　Therefore, SiO 2 as the low heat retaining agent having, as shown in Patent Document 1, the molten steel surface heat retaining agent of the MgO systems have been developed.
CITATION
Patent literature
[0004]
Chartered Document 1: Publication Kokoku No. 3-48152
Summary of the invention
Problems that the Invention is to Solve
[0005]
　However, the molten steel surface heat retaining agent composed mainly of MgO has a high melting point, since the working temperature is mainly solid phase, it is impossible to uniformly coat the surface of molten steel, by a reaction between ambient air and the molten steel surface, Al 2 O 3 inclusions of to produce.
[0006]
　The present invention is to solve the above problems, the components derived from the molten steel surface heat retaining agent, without the inclusion of the alumina is produced in the molten steel, and, faster melting rate in the molten steel surface, uniform molten steel surface and to provide a molten steel surface heat retaining agent that may be coated on.
Means for Solving the Problems
[0007]
　To solve the above problems, the present invention employs the following configurations and methods.
[0008]
(1) A first aspect of the present invention, there is provided a molten steel surface heat retaining agent disposed on molten steel surface with a predetermined molten steel surface temperature is lower than the molten steel surface temperature of the melting point, 50 wt% or more of low melting point material When the melting point is higher than the molten steel surface temperature, it contains a high-melting material is less than 50 wt%, as the average composition, and 10 to 60 wt% CaO, Al of 10 to 70 wt% 2 O 3 and 3, and ~ 30 wt% of MgO, 0 - 10 wt% SiO 2 and containing a total of 70 mass% or more, the CaO and the Al 2 O 3 and the ratio CaO / Al 2 O 3 is 0.5 to 2. 0, melting point is lower than the molten steel surface temperature more than 70 mass% are molten steel surface heat retaining agent is a powder having a particle size of 200 ~ 1000μm.
[0009]
(2) A second aspect of the present invention, the molten steel surface heat retaining agent according to the above (1), is disposed on the surface of molten steel so that the average melt layer thickness is in the range of 5 of 5 ~ 30 mm, the molten steel surface it is a warm way.
Effect of the invention
[0010]
　According to the configuration described in (1), the components of the molten steel surface heat retaining agent, without the inclusion of the alumina is produced in the molten steel, a uniform molten steel surface molten steel surface heat retaining agent is melted quickly coated on, it is possible to suppress the generation of the alumina-based inclusions caused by contact of the molten steel and the atmosphere.
[0011]
　According to the method described in the above (2), the molten steel surface heat retaining agent, quickly melted uniformly and reliably covers the molten steel surface, it is possible to prevent the occurrence of shelves fishing, the molten steel and the atmosphere it is possible to suppress the generation of the alumina-based inclusions due to the contact.
Brief description of the drawings
[0012]
[1] is the change amount of the total oxygen amount in the tundish outlet side of molten steel to the total amount of oxygen in the tundish inlet side molten steel at 1-2 pots in a row continuous casting.
[2] is an average number of surface defects due to oxide-based inclusions present in per one cold-rolled steel sheet coils obtained from billet produced in the continuous continuous casting 1-2 pot.
DESCRIPTION OF THE INVENTION
[0013]
　We, in order to uniformly coat the surface of molten steel in the molten steel surface heat retaining agent, was investigated a method for increasing the melting rate of the molten steel surface heat retaining agent. As a result, melting was produced low-melting material and the melting point of more than 50 wt% lower than the molten steel surface temperature by mixing the refractory material less than 50 wt% higher than the molten steel surface temperature is lower than the molten steel surface temperature of the melting point in the case of using the molten steel surface heat retaining agent, the melt is produced in the melt early molten steel surface heat retaining agent, we have discovered that it is possible to rapid melting of the molten steel surface heat retaining agent. It is described in detail below molten steel surface heat retaining agent according to the exemplary embodiment of the present invention based on the above discovery. Incidentally, the melting point of the molten steel surface heat insulator, a temperature starting the melt when raising the temperature of the material, in the case of a multi-component material is the melting point of the average composition corresponding to the solidus temperature.
[0014]
　Molten steel surface temperature, such as in continuous casting tundish and ladle is 1550 ℃ ~ 1650 ℃. Molten steel surface heat retaining agent in the liquid phase, in order to uniformly coat the surface of molten steel, Al due to the fact that molten steel surface is in contact with outside air 2 O 3 can be prevented the formation of inclusions of.
[0015]
　Low melting point material is initially generates a melt, by high melting point material is contacted with the melt, increase the melting rate of the high melting point material to promote diffusion into the melt in a refractory material there is an effect of. Incidentally, the proportion of the low melting point material is below 50 wt%, not the diffusion of the refractory material is sufficiently promoted, not increase the melting rate, followed by a state in which the high-melting-point material is not soluble long, and the ambient air of the molten steel surface cut-off is insufficient of. Therefore, the molten steel surface heat retaining agent according to the present embodiment, the proportion of the low melting point material is defined at least 50 wt%. For the upper limit, 90% by weight, may be 80 wt%, or 80 wt%.
[0016]
　Further, the molten steel surface heat retaining agent according to the present embodiment, by at least 70% by weight of the molten steel surface heat retaining agent powder having a particle size of 200 ~ 1000 .mu.m, together to quickly melt the low melting point material, a refractory material it can be quickly diffused into the melt in. More preferably, if you want to more than 70% by weight of the molten steel surface heat insulation agent and powder having a particle size of 300 ~ 900μm, if you want to more than 70% by weight of the molten steel surface heat insulation agent and powder having a particle size of 500 ~ 800μm further preferred. The particle size here is the dimension of the opening sieve, which is dimensioned to pass through the sieve of the predetermined mesh size. Further, the contact if more than 70 wt% is larger than the particle diameter 1000 microns, without the low melting point material melts rapidly, further, the diffusion rate into the melt in the refractory material is reduced, the molten steel surface outside air by, Al 2 O 3 based inclusions are produced. On the other hand, when more than 70% by weight of the molten steel surface heat retaining agent and particle size 200μm or less of the powder, the cost of finely the raw material becomes enormous. Further, the powder having a particle size of 200 ~ 1000 .mu.m is, the molten steel surface heat retaining agent 70 wt% less than the proportion only even if not accounted for, not sufficient generation quantity of the solution, also into the melt in a refractory material since the diffusion rate of is reduced, molten steel surface come into contact with the outside air.
　Molten steel surface heat retaining agent only needs to be placed in a bag in a state in which the low-melting-point material and the high melting point material has been mixed uniformly. The molten steel surface heat retaining agent of the state that have been queued in this bag, can be put into a bag for each molten steel surface. If the particle size of the low melting point material and the high melting point material is greatly different, for example, when the raw material and less than 200μm in 200 ~ 1000 .mu.m of the molten steel surface heat retaining agent according to the present embodiment, or a material of greater than 1000 .mu.m were mixed in bag , will be low-melting-point material and the high melting point material is unevenly distributed, if, when a high-melting-point raw material comes into contact with the first molten steel surface is rapidly melt is not produced in the molten steel surface, the molten steel surface and the outside air come into contact.
[0017]
　In the case where the melting point of the molten steel surface heat retaining agent (melting point in the average composition) is higher than the molten steel surface temperature, not lead to the molten steel surface heat insulation agent complete molten state, spreading resistance at the molten steel surface is deteriorated, molten steel surface but come into contact with the outside air. Therefore, the melting point of the molten steel surface heat retaining agent according to the present embodiment is set lower than the molten steel surface temperature.
[0018]
　If you use a completely melted molten steel surface heat retaining agent, erosion of refractory material, such as a ladle and tundish becomes a problem. Therefore, the molten steel surface heat retaining agent according to the present embodiment, by using a raw material containing magnesia (MgO) used in the coating material ladle or tundish, thereby preventing erosion of the tundish. When the amount of magnesia containing less than 3 wt%, the erosion rate of the coating material ladle and tundish faster, hinder the operation. On the other hand, if the amount of magnesia containing higher than 30% by mass, the melting point rises, it becomes impossible to uniformly coat the molten steel. Therefore, the molten steel surface heat retaining agent according to the present embodiment, defining the content of magnesia in the 3 to 30% by weight. More preferably, from 5 to 30 mass%, still more preferably 7 to 25 wt%.
[0019]
　Molten steel surface heat retaining agent according to the present embodiment, after mixing the composition (average composition) of 10 to 60 wt%, preferably from 15 to 55% by weight, still preferably 25 to 50 mass% of CaO 10 to 70 wt% , preferably 20 to 65 mass%, still preferably 40 to 60 mass% of Al 2 O 3 , 3 to 30 wt% MgO, 0 - 10 wt% or less of SiO 2 is a main component. However, CaO / Al 2 O 3 and = 0.5 to 2.0. This, CaO / Al 2 O 3 (melting point of the average composition) Melting point of the molten steel surface heat retaining agent in the range of = 0.5 to 2.0 is because is minimized. In addition, SiO occupied in the molten steel surface heat insulation agent 2 mass of is more than 10% by weight, by reaction with Al in the molten steel, Al 2 O 3 to produce a system inclusions, and surface defects of the product is increased put away. The content of MgO, are as described above. The term "a main component" refers to the case where corresponding components accounts for at least 70 wt% of the total. In the molten steel surface heat retaining agent according to the present embodiment, 80 wt% of the total sum of the components mentioned above, or may be 90 mass% or more.
[0020]
　As the low-melting point material described above, B melting point of less than molten steel surface temperature 2 O 3 , Li 2 O, Na 2 O, CaO-Al 2 O 3 , CaO-SiO 2 , SrO-SiO 2 , Al 2 O 3 MgO--CaO, Al 2 O 3 -CaO-SiO 2 , Al 2 O 3 -CaO-ZrO 2 , Al 2 O 3 -MgO-SiO 2 , CaF 2 may be a composite oxide such. As the composite oxide, it is possible to use quicklime and alumina that was ground after preliminary melting, or alumina cement was pulverized after quicklime and bauxite were pre-melted and solidified to any multi-component melt solid . As the high-melting-point material described above, MgO and prepared by calcining magnesite, DenToruhin MgO or,, CaO, Al 2 O 3 , SiO 2 , SrO, ZrO 2 , Al 2 O 3 -MgO, it is possible to use the CaO-MgO. The specific low-melting point material and the composition of the high melting material constituting the molten steel surface heat retaining agent, the low-melting material and the combination and blending ratio of the refractory raw material is shown as later examples.
[0021]
　As the molten steel surface heat insulation method is to place a molten steel surface heat insulating agent as described above, so that the average melting thickness is in the range of 5 of 5 ~ 30 mm in the molten steel surface. This is because when the average melt thickness is below 5mm is because blocking of the ambient air of the molten steel surface becomes insufficient. Further, when the average melt thickness exceeds 30mm, by an upper portion of the molten steel surface heat insulating agent which is a position away from the molten steel as a heat source is cooled, the ladle and tundish temperature is lower than the molten steel refractory to object surface, to adhere to the molten steel surface heat retaining agent is solidified, it is because she can is a gap between the molten steel and molten steel surface heat insulation agent. This is called a shelf fishing. When the shelf fishing occurs, since it is a gap between the molten steel and molten steel surface heat retaining agent, molten steel surface come into contact with the outside air. The molten steel surface heat retaining agent, the average melt thickness. 7 ~ 25 mm, or 9 may be disposed on the surface of molten steel to be in the range of ~ 20 mm.
Example
[0022]
　Next will be described the present invention based on examples, conditions in the examples are one condition example employed for confirming the workability and effects of the present invention, the present invention provides these conditions Example but it is not limited only to.
　The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of employing the combination of various conditions or conditions.
[0023]
　Molten steel hot metal pre-treatment of the first charge 280t, done converter decarburization, vacuum degassing process by RH, was melting the ultra-low carbon steel. This was prepared slab by a continuous casting method using a tundish capacity 60t. Casting was performed by continuously molten steel 15 charge fraction. Molten steel surface temperature was 1560 ~ 1580 ℃. Molten steel surface heat retaining agent of the present invention, or a comparative example, was used for the thermal insulation of the molten steel in the tundish from casting early. Molten steel surface heat retaining agent, examples, and 500kg for both tundish in Comparative Example was added per bag. A piece of the slab, the thickness 250mm, length 7000mm, a width of 1500mm. Slab is hot rolled commonly used, a thickness of 0.7mm through the cold rolling step, and the cold-rolled steel sheet in the width 1500 mm. In addition, it shows the data of the examples and comparative examples in Table 1 to Table 4. Was divided into convenience four tables of 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.
[0024]
[Table 1]

[0025]
[Table 2]

[0026]
[table 3]

[0027]
[Table 4]

[0028]
　Table 1 in 1 CaO-※ Al 2 O 3 is, CaO is 50 wt%, Al 2 O 3 is 50 wt%.
　In Table 1 of 2 CaO-※ SiO 2 is, CaO 55% by weight, CaO-SiO 2 is 45% by mass.
　Table 1 in 3 SrO-※ SiO 2 is, SrO is 50 wt%, SiO 2 is 50 mass%.
　Table 1 in 4 Al ※ 2 O 3 -CaO-MgO is, Al 2 O 3 is 50 wt%, CaO 45% by weight, MgO 5% by weight.
　Table 1 in 5 Al ※ 2 O 3 -CaO-SiO 2 is, Al 2 O 3 is 50 wt%, CaO is 45 wt%, SiO 2 is 5 wt%.
　Table 1 in. 6 Al ※ 2 O 3 -CaO-ZrO 2 is, Al 2 O 3 is 50 wt%, CaO is 45 wt%, ZrO 2 is 5 wt%.
　Table 1 in. 7 Al ※ 2 O 3 -MgO-SiO 2 is, Al 2 O 3 is 25 wt%, MgO 25 wt%, SiO 2 is 50 mass%.
　Table 2 in. 8 Al ※ 2 O 3 -MgO is, Al 2 O 3 75 wt%, MgO is 25 mass%.
　Table 2 in ※ 9 CaO-MgO is, CaO is 70 wt%, MgOs is 30% by mass.
　Table 4 in ※ 10 melted layer thickness, steel rod was immersed in molten steel, the thickness of the deposited molten steel surface heat retaining agent into a melted layer thickness.
　In Table 4 of ※ 11 ΔT. O is in the 1-2 pot continuous continuous casting, after the RH treatment to the total amount of oxygen (vacuum degassing after) in the molten steel, a variation in the total amount of oxygen in the tundish molten steel.
　Table 4 in ※. 12 defect number, the average number of surface defects due to oxide-based inclusions present in per one cold-rolled steel sheet coils obtained from billet produced in 1-2 pot successive continuous casting it is.
[0029]
　As shown in FIG. 1, in the embodiment, in the 1-2 pot continuous continuous casting, the total amount of oxygen in RH after treatment (after vacuum degassing treatment) molten steel, the total amount of oxygen in the tundish molten steel It has declined. This molten steel surface heat retaining agent, in order to uniformly coat the tundish surface to melt rapidly, along with the production of alumina-based inclusions caused by contact of the molten steel and the atmosphere is suppressed, alumina inclusions in molten steel floats on, because he is removed from the molten steel.
　Further, as shown in FIG. 2, in the embodiment, surface defects due to oxide-based inclusions present in per one cold-rolled steel sheet coils obtained from billet produced in 1-2 pot continuous casting average number has been greatly reduced compared to conventional comparative example. This also molten steel surface heat retaining agent, in order to uniformly coat the tundish surface to melt rapidly, since generation of the alumina-based inclusions caused by contact of the molten steel and the atmosphere is suppressed.
Industrial applicability
[0030]
　According to the present invention, the components derived from the molten steel surface heat retaining agent, without the inclusion of the alumina is produced in the molten steel, and, faster melting rate in the molten steel surface, to uniformly coat the surface of molten steel it is possible to provide a molten steel surface heat retaining agents that can.
The scope of the claims
[Claim 1]
　A molten steel surface heat retaining agent disposed on molten steel surface with a predetermined molten steel surface temperature,
　is lower than the molten steel surface temperature of the melting point, a low-melting material at least 50 wt%, is higher than the molten steel surface temperature of the melting point, 50 It contains a high-melting material is less than weight
　percent, and 10 to 60 wt% CaO, 10 - 70 wt% of Al 2 O 3 and 3 and to 30 mass% of MgO, 0 - 10% by weight of SiO 2 containing DOO total 70% by mass or more,
　the CaO and the Al 2 O 3 ratio CaO / Al of between 2 O 3 is from 0.5 to 2.0 and
　a melting point lower than the molten steel surface
　temperature, 70 wt% the above is the powder of particle size 200 ~ 1000 .mu.m
molten steel surface heat retaining agent, characterized in that.
[Claim 2]
　The molten steel surface heat retaining agent, is disposed on the surface of molten steel so that the average melt layer thickness is in the range of 5 of 5 ~ 30 mm of claim 1
molten steel surface heat insulation and wherein the.