JP2803535B2 - Reduction smelting method in upper-bottom blowing converter - 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 refining and refining in an upper-bottom blowing converter, in particular, the concentration of Cr removed from P is 0.5 to 2.0%.
The present invention relates to a refining and refining method for reducing low-grade oxides such as FeO and MgO in slag, lowering slag viscosity and increasing steel cleanliness by adding Fe-Si alloy and aluminum by using molten iron.

[0002]

2. Description of the Related Art Bearing materials or gear materials are required to have high abrasion resistance so as not to cause cracking or abrasion of the materials since they are constantly subjected to friction between metals. In order to prevent the material from cracking due to such friction, it is important to regulate the amount, diameter, and form of the lower oxide that is the starting point of the crack. As for the amount of the lower oxide, the smaller the diameter, the smaller the diameter, and the form, the lower the melting point and the smaller the number of Al ₂ O ₃ type inclusions present in the thruster, the more resistant the material becomes. It is known that abrasion is improved.

[0003] As a refining method for improving the wear resistance of the above-mentioned materials, a method of refining low carbon steel having a blow-off C of 0.20% or less by a vertical blow converter is used.
A method in which Mn-containing substances are charged and blown using the molten hot metal, and powder or granular Fe-Si alloy is added after the end of oxygen blowing, and bottom blown gas is stirred to deoxidize and reduce ( Showa 5
2-238314) has been proposed.

[0004]

SUMMARY OF THE INVENTION The above-mentioned JP-A-52-23 is disclosed.
No. 8314 discloses a refining method that employs Fe-S in a converter.
Since the reduction product of the i-alloy is SiO ₂ , slag with poor inclusion absorption capacity is formed, which has a drawback that the contribution to improving the cleanliness of molten steel is small.

[0005] An object of the present invention is to provide a vertical blowing converter capable of reducing FeO and MgO in slag, which is an oxidation product, reducing the viscosity of slag by reducing FeO and MgO and achieving high purification of steel. It is to provide a reduction refining method.

[0006]

Means for Solving the Problems The present inventors have conducted various tests and studies to achieve the above object. As a result, by using Fe-Si alloy and Al as the reducing agent after the decarburization refining and setting the charging ratio of Si and Al reducing agent to 0.5 to 5.0, the viscosity of the slag as the oxidation product is increased. Lower,
Investigating that the ability to absorb inclusions in the slag at the interface between the slag and the steel is improved and that the molten steel can be highly purified,
The invention has been reached.

That is, according to the present invention, the C
In a method of reducing and refining clean steel having an r concentration of 0.5 to 2.0%, after removing de-P molten steel by oxygen blowing and decarburizing, an Fe-Si alloy and aluminum are used as reducing agents in Si / A
This is a refining and refining method in an upper-bottom blow converter, wherein the addition is carried out at a ratio of 0.5 to 5.0, and the mixture is reduced by vigorous stirring by blowing bottom gas.

[0008]

In the present invention, after the de-P steel is degassed by oxygen blowing, a Fe--Si alloy and aluminum are added as reducing agents at a Si / Al ratio of 0.5 to 5.0, and bottom blowing is performed. Since the gas is blown and strongly stirred for reduction, as shown in FIG. 4, Si and Al added to the steel undergo a reduction reaction with FeO and MnO in the slag generated by the decarburization refining according to the following reaction formula. 2FeO + Si → 2Fe + SiO ₂ , 3FeO + 2A
1 → 3Fe + Al ₂ O 3 2MnO + Si → 2Mn + SiO ₂ , 3MnO + 2A
l → 3Mn + Al ₂ O ₃ As a result, FeO, M called lower oxide in slag
While the concentration of nO decreases, the SiO ₂ and A
l ₂ O ₃ is absorbed into the slag by vigorous agitation by the bottom-blown gas, thereby improving the cleanliness of the steel. At that time, when the slag composition is located in the hatched portion in the CaO-Al ₂ O ₃ -SiO ₂ ternary phase diagram shown in FIG. 5, the slag melting point is low,
Since the viscosity is low, the ability to absorb inclusions at the interface between the steel and the slag is high, and it is possible to melt steel with high cleanliness.

In the present invention, the reason why the Si / Al ratio of the Fe—Si alloy and aluminum added as a reducing agent is 0.5 to 5.0 is that when the Si / Al ratio is less than 0.5, Al ₂ O ₃ The system increases, the SiO ₂ system decreases, and the slag composition becomes poor in the ability to absorb inclusions, and the total oxygen (T [O]) in the steel after tapping cannot be sufficiently reduced.
If it exceeds 5.0, on the contrary, the amount of SiO ₂ becomes too large, resulting in slag with poor inclusion absorption capacity, and it is not possible to sufficiently reduce the total oxygen (T [O]) in the steel after tapping. is there.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG.
After oxygen gas is blown upward at 00 Nm ³ / Hr and oxygen gas is blown from the bottom center nozzle 3 while blowing oxygen gas at a maximum of 5000 Nm ³ / Hr, Fe-Si alloy and Al are used as reducing agents, and Si / Al The ratio was added under the conditions shown in Table 1,
Ar gas is supplied from the bottom center nozzle 3 up to 4500 Nm ³ /
Hr, up to 800 Nm Ar gas from the bottom outer nozzle 4
^The bottom was blown with ³ / Hr, and the mixture was subjected to a reduction treatment for 6 minutes with strong stirring. Table 2 shows the chemical components of hot metal and molten steel before and after refining. After tapping each of the obtained molten steels, the molten steel was cast into a bloom by continuous casting, the total oxygen concentration in the bloom was measured, and the relationship between the Si / Al ratio and the total oxygen concentration in the steel was determined.
The result is shown in FIG. Moreover, the slag component after reduction treatment was measured to check the position of CaO-Al ₂ O ₃ -SiO ₂ ternary phase diagram in. The result is shown in FIG. In addition, 1 to 8 in FIGS. 1 to 8 are shown.

[0011]

[Table 1]

[0012]

[Table 2]

As shown in FIG. 2, reducing agents Si and A
l, that is, the test No. 1 in which the Si / Al ratio is 0.5 to 5.0. In the case of the method of the present invention of Nos. 2 to 4 and 6 to 8, the total oxygen (T [O]) in the steel was determined by the test No. Steels having lower cleanliness and better cleanliness than those of Comparative Examples 1 and 5 were obtained. This is because the slag component due to the Si / Al ratio of the reducing agent is C as shown in FIG.
present in the hatched portion of aO-Al ₂ O ₃ -SiO ₂ in the ternary system phase diagram, the melting point of the converter in the slag, the viscosity is low, because advantageous with respect to inclusions in the steel absorbed. This is shown in Test No.
The slag components of Comparative Examples 1 and 5 were CaO-Al shown in FIG.
From the fact that deviates from the shaded portions in ₂ O ₃ -SiO ₂ ternary phase diagram is clear.

[0014]

As described above, according to the method of the present invention, slag excellent in inclusion absorption capacity is formed in the converter,
It is possible to melt steel containing 0.5 to 2.0% of Cr having excellent cleanliness.

[Brief description of the drawings]

FIG. 1 is a sectional view of a converter used in an example.

FIG. 2 is a graph showing the relationship between the Si / Al ratio charged during reduction and bloom total oxygen (T [O]) in an example.

FIG. 3 shows test Nos. Is a CaO-Al ₂ O ₃ -SiO ₂ ternary phase diagram showing the location of 1-8 of the slag.

FIG. 4 is a schematic view of the process of the method of the present invention.

FIG. 5: CaO—Al ₂ showing preferred slag composition range
O ₃ is -SiO ₂ ternary phase diagram.

[Explanation of symbols]

 1 Converter 2 Oxygen lance 3 Bottom center nozzle 4 Bottom outer nozzle

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C21C 5/35 C21C 5/28 C21C 7/00 C21C 7/04

Claims (1)

(57) [Claims] 1. Cr concentration of 0.5 to 2.
In the method of reducing and refining 0% of steel, after removing the molten steel by oxygen blowing and decarburizing, a Fe-Si alloy and aluminum are added as reducing agents at a Si / Al ratio of 0.5 to 5.0. A reduction and refining method in an upper-bottom blow converter, wherein reduction is performed by vigorous stirring by blowing bottom gas.