JP3026873B2 - Method for deoxidizing molten steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing microinclusions in molten steel during deoxidation with aluminum at the final stage of smelting in a steelmaking process.

[0002]

2. Description of the Related Art In a steelmaking process, after oxidizing and smelting is completed, dissolved oxygen in steel is removed by adding a deoxidizing agent. At this time, the reaction represented by the formula (1) generates a minute oxide by the deoxidation reaction and the subsequent reoxidation reaction, which is not removed and becomes a harmful inclusion, which causes a product defect.

XM + (y / 2) O ₂ → M _x O _y (1)

Conventionally, as a method of reducing minute inclusions in steel, various measures have been taken to remove nonmetallic inclusions generated by various factors by floating separation. In particular, in the case of aluminum deoxidation, the deoxidation product is finely dispersed, so that it is difficult to float and separate. As a countermeasure, in the deoxidation step, in order to extend the flotation time due to the aggregation and coalescence of minute inclusions, a steel removal deoxidation method in which aluminum is initially charged, and strong stirring in the RH treatment are used to float the inclusions. There are ways to promote There is also a method of providing various weirs in a continuous casting tundish to float inclusions.

However, even with these methods, it is difficult to float and separate minute inclusions of 5 μm or less from molten steel.
At present, cleaning has not been sufficiently achieved. On the other hand, as shown in JP-A-1-180466, the deoxidation product is converted into CaO by adding a deoxidizer Al and a conjugate and fusion of CaO and CaF ₂ during deoxidation.
Method in which harmless as the low melting point -al ₂ O ₃ compositions have been proposed.

[0006]

As described above, in the deoxidation step, fine alumina which is difficult to float is always generated. Further, even if Ca is added, the resulting CaO
-Al the ₂ O ₃ is due to the low deformability than Al ₂ O ₃ alone, there is a problem that tends to lead to product defects.
Therefore, there has been a demand for a means for converting the deoxidized product into Al ₂ O ₃ and sufficiently separating the product by flotation.

An object of the present invention is to provide a simple method for suppressing the generation of harmful fine inclusions which are difficult to float and separate when reducing inclusions in molten steel.

[0008]

The present inventors conducted various tests in order to solve the above-mentioned problems in the conventional method. The inventor has devised a deoxidation method for suppressing the formation of products. That is, this is a method for deoxidizing molten steel, which comprises using an aluminum-iron alloy having an aluminum content of 80% or less when deoxidizing molten steel with aluminum.

[0009]

The present inventors have considered the possibility of morphological control from the viewpoint of formation of easily floating alumina in the deoxidation reaction. Therefore, in crystal growth in an aqueous solution, the effect of supersaturation on the morphology was examined, focusing on the importance of supersaturation as a factor determining the morphology. That is, in a laboratory, pure aluminum and 90% aluminum-iron, 80% aluminum-iron, 4%
An aluminum production experiment was performed by a deoxidation reaction using a 5% aluminum-iron alloy. FIG. 2 and FIG. 3 are obtained by extracting alumina as a deoxidation product and observing it with a scanning electron microscope. FIG. 2 shows the case of deoxidation with pure aluminum, and FIG.
In the case of deoxidation with a 5% aluminum-iron alloy, as the amount of Al in the deoxidizer decreases and the degree of supersaturation decreases, a form that spreads in the lateral direction is formed. Was found.

Further, when these forming experiments are performed in a state where molten steel is flowing, that is, in a stirring bath, the form at the time of formation observed in the stationary bath is divided, but the characteristics of the form at the time of formation are maintained. As shown in FIG. 1, in deoxidation with pure aluminum, fine oxides of 1 to 5 μm are mainly used, whereas in deoxidation with ferromagnetic iron containing 80% or less of aluminum, oxidation is at least 5 μm or more. Found that only things were allowed.

That is, in the deoxidizing step, aluminum-
By deoxidizing with an iron alloy and reducing the degree of supersaturation during the formation of alumina, it has been found that large inclusions that can easily float and separate can be generated. As can be seen from FIG. 1, the effect can be seen even when the aluminum content of the alloy is 90%, but it is found that it is better to set the aluminum content to preferably 80% or less.

It is common practice to use ferroalloys alloyed with iron when adding elements in the steelmaking process. For example, Si or Mn is also added as a single metal such as metallic silicon or electrolytic manganese, but in many cases, ferrosilicon or ferromanganese is used. These are ferroalloys for facilitating dissolution in steel and for convenience in raw material production. As an extreme example, Mo and W have extremely high melting points and cannot be added as ferromolybdenum or ferrotungsten unless the melting point is lowered.

However, in the case where aluminum is added in the steel making process, a single piece of aluminum is conventionally used. This is because, unlike manganese and silicon, for example, aluminum is produced in large quantities as general-purpose ingot, and it is most convenient to use it as it is. It has been said that there is no particular problem even if aluminum is added alone. Here, it has been found that the present invention produces an excellent effect of reducing minute inclusions by alloying with iron.

[0014]

Next, an embodiment of the present invention will be described. Component C blown in a converter: 0.03-0.05%, Si: 0.
08 to 0.15%, Mn: 0.20 to 0.50%, P:
0.007 to 0.01%, S: 0.007 to 0.01%
First, in the RH treatment, 350 tons of molten steel was subjected to a vacuum decarburization treatment to adjust the carbon concentration to a predetermined value, and then Al or an Al-Fe alloy was charged to perform deoxidation. After the addition of the deoxidizing agent, the mixture was refluxed for 9 minutes. Thereafter, the slab slab having a thickness of 250 mm was produced by casting using a curved continuous caster. Immediately after deoxidation and at the time of 250 t injection into a tundish (capacity 50 t), slime extraction of inclusions was performed on samples taken therefrom.

Detailed conditions and results are shown in Table 1. In Examples of the present invention, the number of inclusions and the number of defects are reduced, and the effect is remarkable especially when the aluminum content in the alloy is 80% or less. You can see that there is.

[0016]

[Table 1]

[0017]

As has been described in detail above, the present invention uses at least 90% or less of Al-containing ferrous alloy as a deoxidizing agent to prevent the formation of minute inclusions of 5 μm or less which are difficult to float and separate. Since it can be reduced, inclusions are greatly reduced, and the industrial effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Al content in an Al—Fe alloy and the particle size of deoxidized alumina.

FIGS. 2A and 2B are photographs of a scanning electron microscope showing the morphology of alumina generated by a deoxidation reaction, where (a) is pure Al and (b) is 45% A
by l-Fe alloy

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C21C 7/04 C21C 7/06

Claims (1)

(57) [Claims] 1. In deoxidizing molten steel with aluminum,
Aluminum with an aluminum content of 80% or less
A method for deoxidizing molten steel, comprising using an iron alloy.