JPS626606B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention deals with non-metallic inclusions in molten steel, especially fine particles.
This invention relates to a filter used to remove Al ₂ O ₃ based inclusions. Sulfur, phosphorus, oxygen, or nonmetallic inclusions remaining in molten steel adversely affect the workability and mechanical properties of steel. In recent years, the quality required for steel materials has become increasingly strict, and so-called clean steel with fewer impurities is in demand. Conventional methods for removing these impurities include adding CaO to hot metal and molten steel.
Desulfurization and dephosphorization treatments are carried out by adding refining agents (fluxes) such as CaF ₂ and Na ₂ CO ₃ . Regarding degassing of hydrogen, nitrogen, etc. in steel,
Treatment is performed using direct air degassing equipment such as RH type and DH type. Furthermore, deoxidation, that is, removal of nonmetallic inclusions, is also an important point in cleaning molten steel. especially
In the case of Al-deoxidized steel, Al ₂ O ₃ , which is a deoxidation product, is suspended in the molten steel, which causes deterioration in the quality of the slab. Normally, in the case of continuous casting, these non-metallic inclusions are floated and separated in a tundish and the molten steel is poured into a mold as clean molten steel. However, it is difficult to float and separate very fine Al ₂ O ₃ inclusions of 50μ or less from steel, and no appropriate removal technology has been established at present. The present inventors conducted various tests for removing nonmetallic inclusions, and as a result, they found an effective filter for removing these fine Al ₂ O ₃ inclusions. i.e. consisting of lime clinker alone or 50wt%
This calcareous filter is made of a basic material consisting of the above lime clinker and the remainder is magnesia clinker or dolomite clinker, and has a large number of molten steel passage holes. The present inventors have obtained the knowledge through various experiments that calcareous refractories that come into contact with molten steel tend to bond with Al ₂ O ₃ in the steel and easily absorb it. The present invention makes active use of this phenomenon, and allows the molten steel to pass through a large number of molten steel passing holes to increase the chance of contact, thereby absorbing and removing the Al ₂ O ₃ inclusions in the molten steel. This is a removal filter. Al ₂ O ₃ inclusions in contact with lime undergo the reaction x・CaO + yAl ₂ O ₃ = xCaO・yAl ₂ O ₃ to form, for example, 3CaO・Al ₂ O ₃ , 12CaO・
Calcium aluminates such as 7Al ₂ O ₃ are easily generated and absorbed into the calcareous filter. One of the characteristics that a filter for removing nonmetallic inclusions must have is that it must not itself become a source of inclusions due to reaction with molten steel.
In the case of acidic refractories, Al in the steel reacts with SiO ₂ , which is the main component of the refractory, to easily generate Al ₂ O ₃ according to the following formula. 4 Al + 3SiO ₂ = 2Al ₂ O ₃ + 3 Si On the other hand, the basic materials used in the present invention, especially lime CaO, itself has a high melting point of 2500°C or higher, and its dissociated oxygen pressure and vapor pressure are low, making it stable even in vacuum. It is the most stable refractory material even against molten steel. Needless to say, the larger the proportion of CaO in the composition of the filter, the less likely it is that it will become a source of inclusions, and the better the reactivity of Al ₂ O ₃ will be.
If the CaO clinker ratio is less than 50wt%
There is a risk that the reactivity with Al ₂ O ₃ will decrease and the effectiveness for removing inclusions will decrease. The present inventors further investigated the material of the filter and found that by adding 1 to 20 wt% of CaCl ₂ to lime or lime-magnesia (dolomite) material, Al ₂ O ₃ in molten steel could be more easily adsorbed. I found out. In other words, when using the filter of the present invention, depending on preheating or the temperature of molten steel,
Because it is heated above the melting point of CaCl ₂ (772°C), CaCl ₂ exists in a liquid phase. Therefore, it is considered that the absorbed Al ₂ O ₃ -based inclusions are easily moved into the inside of the filter and the absorption effect is increased.
The reason why the amount of CaCl ₂ added is 20 wt% or less is because if it exceeds the amount, the amount of liquid phase becomes too large and the strength in hot conditions decreases, resulting in increased wear due to molten steel. Figure 1 shows Al ₂ O ₃ when lime and lime-CaCl ₂ refractories are immersed in molten steel in a tundish.
It is a figure which shows the analysis example of the absorption of.

[Table] As shown in Figure 1, the CaO content is large and
It can be seen that the material to which CaCl ₂ is added has a greater ability to absorb Al ₂ O ₃ and is suitable as a filter material. The calcareous filter according to the invention is made within the scope of conventional calcareous refractory manufacturing techniques. For example, crushing lime clinker, magnesia clinker,
The particle size-adjusted product is kneaded with non-aqueous oil, microwave, etc. as a binder, cast into an appropriate shape, molded by vibration molding, pressure molding, or extrusion, and fired. Alternatively, if it contains CaCl ₂ , it is possible to heat the material to 772° C. or higher, where CaCl ₂ melts, and then hot-press and mold it into the shape of a filter in that temperature range. The filter for removing non-metallic inclusions according to the present invention can be used, for example, as a part of a long nozzle between a ladle and a tundish, or as a part of an immersion nozzle between a tundish and a mold. It is possible to use it in the form of moreover
It is also easy to install in a vacuum vessel during refining of RH, DH, etc. The shape of the filter is selected to suit the equipment or container in which it will be installed, but in order to increase the contact area with the molten steel, it is desirable that the molten steel passage holes have a small diameter and a large number. However, in order to remove nonmetallic inclusions without interfering with the passage of molten steel, the appropriate size of the passage hole is 5 to 100 mmφ. The cross-sectional area of the void through which molten steel passes is preferably at least 20% of the cross-section of the filter. As described above, in the calcareous filter according to the present invention, lime or lime-CaCl ₂ is mixed with Al ₂ O ₃ in molten steel.
This method takes advantage of the fact that calcium aluminate is easily generated when it comes into contact with inclusions, and is easily absorbed into the filter. Conventional filters for removing non-metallic inclusions simply adsorb Al ₂ O ₃ to the refractory. It is characterized by its extremely high absorption capacity, unlike those whose purpose is to remove it. Examples according to the present invention are shown below. Example 1 (Example of application to tundish) Installation situation: As shown in Fig. 2, filters 2 are installed in two places in tundish 1 for continuous casting. Filter material: 95% lime clinker +
Shape of filter: 20mmφ holes in the steel bath part, 100 holes per ^1m2 , thickness _100mm Pour 60t into a tundish from a ladle made in a converter and pass through two calcareous filters.
steel products were manufactured. Table 1 shows the composition of the molten steel in the ladle.

[Table] TO of steel after casting = 0.020% Al ₂ O ₃ inclusions (speculum inclusions of 30μ or more) = 2.0
pieces/ ^10cm2 , and as a comparative example, in the case of a tundish with a normal Al ₂ O ₃ weir, TO = 0.025% Al ₂ O ₃ inclusions (specular inclusions of 30μ or more) = 8.5
Al _{2 O 3} ^of the invention product compared to
The ability to remove system inclusions is remarkable. Example 2 (Application to immersion nozzle) A calcareous filter was installed at the tip of the immersion nozzle to allow molten steel from the tundish to pass through. Filter material: 100% lime clinker Filter shape: 200mmφ cylindrical filter with 150 10mmφ holes. When 60 tons of steel similar to Example 1 was passed through to investigate inclusions in the steel material, T.O = 0.023 Al ₂ O ₃ inclusions (speculum inclusions of 30μ or more) = 2.5
/10cm ² , and the effect is clearer than when no filter is used (comparison with Example 1).

[Brief explanation of the drawing]

Figure 1 is a diagram showing the analysis results of Al ₂ O ₃ absorption when lime and lime-CaCl ₂ refractories are immersed in molten steel in a tundish, and Figure 2 is a diagram showing embodiments in Examples. . 1: Tandem water, 2: Filter.

Claims (1)

[Scope of Claims] 1. A filter for removing non-metallic inclusions from molten steel, comprising lime clinker alone or 50 wt% or more of lime clinker with the remainder being dolomite clinker or magnesia clinker, and having a large number of molten steel passage holes. 2 Lime clinker alone or 50wt% or more of lime clinker with the balance being magnesia clinker or dolomite clinker, and 1 to 20wt%
% of calcium chloride, the filter for removing non-metallic inclusions from molten steel according to claim 1.