KR100380745B1 - Flux applying to molten steel in tundish - Google Patents

Abstract

The present invention relates to a tundish flux used for preventing reoxidation of molten steel in a tundish and absorption of non-metallic inclusions in molten steel in a continuous casting industry. The object of the present invention is to utilize slag of a steelmaking process that is being discarded as industrial waste. It is to provide a good tundish flux with the overall characteristics such as the ability to absorb inclusions, preventing reoxidation of molten steel, and refractory erosion characteristics.

The present invention having this purpose is, by weight, aluminum dross: 7.5-12.5%, carbon content: 5-15%, light dolomite: 5-10%, chaff: 5-15% and the clean steel composition composed of the remaining steel slag The technical gist of the tundish flux for steel production is considered.

The tundish flux of the present invention has a basicity of about 4, (CaO / Al ₂ O ₃ ) of about 1.6, (FeO + MnO) content of less than about 2%, MgO and SiO ₂ content of about 10-12%, and flux Melting point is a very good flux with a property of about 1395 ° C.

Description

TFLISH APPLYING TO MOLTEN STEEL IN TUNDISH}

The present invention relates to a tundish flux used for preventing reoxidation of molten steel in the tundish and absorption of non-metallic inclusions in the molten steel in the continuous casting industry, and in particular, a tundish flux utilizing slag of the steelmaking process that is discarded as industrial waste. It is about.

In the continuous casting process, as shown in FIG. 1, the tundish 101 is placed between the ladle 100 and the mold 102, and molten steel is manufactured as a cast steel. Here, the tundish 101 serves as an intermediate container, and the upper portion of the tundish 101 is covered with a material 104 to protect the molten steel. Since the casting of steel has been switched from ingot casting to continuous casting, carbide chaff has been used as a material for protecting molten steel in tundish for quite a long time. Chaff has been termed a tundish protective material rather than a flux because it has only a simple function of preventing excessive reoxidation by the atmosphere and protecting molten steel from the cold air of the atmosphere.

The main component of the rice husk is SiO ₂ , and its melting point is about 1600 ° C. Therefore, it exists in the solid state at the tundish molten steel temperature (1540-1560 degreeC), and it turns out that it is not suitable for protecting molten steel from oxygen in air | atmosphere. In addition, in the case of casting of ultra low carbon steel having a very low carbon content, the present invention is using a painting chaff having a lower carbon content due to fear of pick-up of C by carbonized chaff.

Recently, with increasing interest in the manufacture of clean steel, there is a demand for the development of tundish fluxes with the ability to absorb the inclusions, in addition to the functions of simple thermal insulation and property prevention. This flux should be a material with good flowability and an appropriate CaO / Al ₂ O ₃ ratio and CaO / SiO ₂ ratio.

However, chaff has a high melting point as described above, and thus does not have the ability to absorb and remove floating inclusions. Rather, chaff is an undesirable substance that contaminates molten steel. This is because lower oxides such as FeO, MnO, and SiO ₂ act to reoxidize Al in the steel in an atmosphere in contact with molten steel.

In the face of this problem of chaff and the need to manufacture high-purity steel, various kinds of tundish fluxes have been developed and applied to the operation, and the types are largely divided into (1) basic tundish fluxes and (2). ) It can be divided into tundish flux using waste materials.

(1) Table 2 below lists the currently developed basic tundish flux.

TABLE 2

However, most of the tundish fluxes listed in Table 2 present significant problems in practical applications due to poor refractory erosion properties, low inclusion absorption, or high value.

(2) Meanwhile, tundish fluxes using waste materials have been developed and are now commercially available. A typical example is a tundish flux that recycles fly ash recovered from power plant stacks. This flux is cheaper than conventional rice hulls, but it is also the main composition of SiO ₂ , which has a high melting point and no absorption capacity for alumina inclusions.

As another example, a tundish flux utilizing a PI (powder injection) slag generated in a steelmaking process has been developed, but there are many problems in processing, handling and use. This flux is characterized by the addition of light dolomite to the PI slag. However, recovering only specific slag is a very cumbersome and difficult task in the steelmaking process. In addition, the oxidized fine iron generated in the recovery process has been found to act to reoxidize the steel after being put into the tundish. In addition, PI slag relies on production fluctuations of API materials whose orders change according to industry trends, resulting in unstable supply of basic materials. Therefore, in order to utilize the slag generated in the steelmaking process, a more convenient recovery method, a method of reducing fine iron mixed in the recovery, and a stable supply method must be secured.

Accordingly, the present invention utilizes the slag of the steelmaking process that is currently discarded as industrial waste, to provide a tundish flux having good overall characteristics such as absorption of inclusions in the steel, prevention of reoxidation of molten steel, refractory erosion characteristics and the like. have.

1 is a schematic diagram showing a ladle-tundish-mold of a playing process

2 is a graph evaluating the characteristics of the invention and the comparative material

Explanation of symbols on the main parts of the drawings

100 ... Ladle 101 ... Tundish

102 ... Mold 103 ... Submerged Entry Nozzle

104 ... Tundish Flux

105 ... long nozzle

The tundish flux of the present invention for achieving the above object, in weight percent, aluminum dross: 7.5-12.5%, carbon content: 5-15%, light dolomite: 5-10%, chaff: 5-15% and the rest It is made of steel slag.

Hereinafter, the present invention will be described in detail.

Recently, with the growing interest in environmental protection, the treatment of slag generated in the manufacturing process of steel has emerged as an important issue to be solved in the future. In particular, the slag generated in the steelmaking process has a high content of basic oxides such as MgO and CaO, and is considered to be unsuitable for landfill aggregates or cement raw materials.

Steel slag can be largely divided into converter slag, which accounts for the majority, and ladle slag, which is less than 10% of the total. Table 1 shows the chemical composition of the slag generated in the steelmaking process, the average composition of slag generated is 40-42% CaO, 9-10% SiO ₂ , 9-10% MgO, 4-6 Al ₂ O ₃ , 20% FeO + MnO.

TABLE 1

Such slag has sufficient quality as a good flux except that it contains a large amount of FeO and MnO. The present invention provides (b) aluminum dross, (c) carbon powder, (d) light dolomite and (a) in order to provide a flux having good characteristics while recycling the slag of the steelmaking process (a) as a tundish flux. d) We developed a composite tundish flux consisting of chaff, which is described in detail below.

(a) Steel slag

Steel slag has high quality flux as shown in Table 2, but it contains 20% FeO and MnO. When slag is used as a tundish flux, 60-70kg of oxygen and 130- It generates 150kg of Al ₂ O ₃ , which acts to reoxidize molten steel in tundish. Therefore, in order to suppress this, it is required to add a substance capable of reducing FeO and MnO in the slag, and the present invention adds the components described below for this purpose. The amount of steelmaking slag added is determined by the relative amounts of these components.

(b) aluminum dross

The aluminum dross is a waste that is oxidized and deposited as waste during the dissolution and processing of aluminum. The aluminum dross contains approximately 50% metallic aluminum, and thus may be used as a reducing agent for iron oxide and manganese oxide of steelmaking slag. However, in order to reduce all of FeO and MnO in steelmaking slag, it is preferable to add 7.5-12.5% of aluminum dross.

(c) carbon powder

The carbon powder is carbon powder (powder) generated during the processing of the electrode rod or the residue left during the coke manufacturing process.

When only aluminum dross is added to the steelmaking slag, the flux composition is changed to a slag composition containing 40-60% of alumina immediately after injection by aluminum oxidation at high temperature, and thus loses the ability to absorb inclusions. In the present invention, 5-15% carbon content is added to suppress this. The reason is that when the carbon content is added more than 15%, the amount of carbon mixed into the steel increases, and less than 5% has little effect on reducing lower oxides such as FeO and MnO.

In this way, the composition of the tungsten flux is composed of 35-50% CaO, 25-40% Al ₂ O ₃ , 5-7% MgO, 4-6% SiO ₂ , less than 3% (FeO + It can be derived from MnO) composition, so it is satisfactory to absorb inclusions and suppress reoxidation, but it is insufficient in terms of erosion ability.

To compensate for this, it is effective to increase SiO ₂ and MgO components by adding (d) small dolomite and (e) chaff.

(d) Light dolomite is a dolomite (dolomite) baked at a temperature within 1000 ℃ almost removed the carbonic acid component, the light dolomite is preferably added 5-10%, when less than 5% MgO in slag This is because the synergistic effect is small and the addition of more than 10% increases the slag melting point, resulting in inadequate composition of the composition, and a significant effect on the cost rise. It is preferable to use ore from which CO ₂ is sufficiently decomposed in advance so that the small borodolite has a C content of 1% or less. If the C content in the light dolomite exceeds this range, the CO ₂ generated during the decomposition of CaCO ₃ or MgCO ₃ may cause the steel to be reoxidized.

(e) Chaff is significant in terms of providing insulation by increasing volume and improving corrosion resistance. In this regard, it is desirable to add 5-15% of rice hull, which has a small effect on the increase of SiO ₂ content when it is less than 5% and an excessive increase of SiO ₂ content in steel when more than 15% is added. In addition to reducing the cost, the flux manufacturing cost is increased.

The particle size of the flux components of the present invention is preferably 20 mm or less in consideration of reactivity. On the other hand, when explaining the characteristics of the tundish flux of the present invention as described above, for example, the basicity is about 4, (CaO / Al ₂ O ₃ ) is about 1.6, (FeO + MnO) content is less than about 2% The MgO and SiO ₂ contents were about 10-12%, and the flux melting point was about 1395 ° C.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

The properties of the conventional tundish flux and the tundish flux of the present invention were evaluated and the results are shown in Table 1 below. The flux of the present invention was 20 mm or less in particle size, and the components thereof were blended with aluminum dross: 10 wt%, carbon content: 7 wt%, light dolomite: 7 wt%, rice husk: 7 wt%, and the remaining steel slag.

TABLE 3

As shown in Table 3, the tundish plus of the present invention was greatly improved than the conventional chaff flux in terms of cleanliness of the steel, and also no reoxidation of molten steel occurred and mild refractory erosion. Most notably, the price of tundish fluxes has been significantly reduced by one-fifth. On the other hand, the flux characteristics of the present invention are shown in FIG. 2 as compared with conventional materials, where flux C-L is the flux described in Table 2.

As described above, the present invention utilizes the slag of the steelmaking process, which is discarded as industrial waste, and is useful for providing a tundish flux having good overall characteristics such as absorption of inclusions in the steel, prevention of reoxidation of molten steel, and refractory erosion characteristics. It works.

Claims (3)

Tungsten flux for the manufacture of clean steel in weight percent, consisting of aluminum dross: 7.5-12.5%, carbon content: 5-15%, light dolomite: 5-10%, chaff: 5-15%, and the remaining steelmaking slag. The tungsten flux for producing clean steel according to claim 1, wherein the light dolomite has a carbon content of 1% or less. The tundish flux of claim 1, wherein the tundish flux has a particle size of 20 mm or less.