JPH10102132A - Method of deoxidizing molten steel - Google Patents

Abstract

(57) [Problem] To provide a low-cost raw material and to produce steel with a high degree of cleanliness as conventionally, an object of the present invention is to use an inexpensive raw material for adjusting slag components. SOLUTION: In stirring molten steel in a state where the surface of the molten steel is covered with a slag component adjusting agent to deoxidize the molten steel, an input amount of Al from a component adjusting alloy is used as a component adjusting agent before the molten steel treatment. 5 g or less per ton, slag composition after molten steel treatment is CaO; 35-60% (% by weight,
Hereinafter the _{same), SiO 2; 30~55%,} Al 2 O 3; 6
10%, in other total of 15% of the oxide product the following, and, CaO / SiO _2; As will be from 1.30 to 1.70, quicklime before the molten steel processing, chamotte, calcium aluminate and soft One or more silica stones and one or more slag melting point depressants such as sodium fluoride or fluorite are added to the molten steel, and thereafter the molten steel is stirred. Acid method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for deoxidizing and refining molten steel for high-carbon steel wire or piano wire, SiCr spring steel, austenitic stainless steel spring material and the like.

[0002]

2. Description of the Related Art As is well known, in these steel materials, the form and size of nonmetallic inclusions have a significant effect on fatigue characteristics and die life. Further, in a high-carbon steel wire for an ultrafine wire, since the degree of cold working is high, nonmetallic inclusions cause disconnection during cold working. Non-metallic inclusions in the steel material after hot rolling and cold rolling of the slab have no adverse effect if the non-metallic inclusions are fine and stretched in the rolling direction, but coarse non-metallic inclusions remaining without stretching Significantly deteriorates fatigue characteristics and disconnection resistance. As this type of nonmetallic inclusions, there are various compositions, but inclusions having a high Al ₂ O ₃ content (simple A
l ₂ O ₃ and Al ₂ O ₃ -MgO-based inclusions) are extremely hard and lack stretchability, but have a low Al ₂ O ₃ content and a low CaO content.
-SiO ₂ -Al ₂ O ₃ -MnO-based inclusions are extremely good stretchability, critical molten steel deoxidation method for the favorable stretchability inclusions in producing these steels It is.

Conventionally, as a method for deoxidizing these steel materials, the input of Al is set to 5 g / ts or less, the surface of molten steel is covered with a slag containing CaO, and an inert gas and a synthetic flux are blown and stirred by a lance for blowing gas. A method for controlling the slag composition after the acid treatment has been proposed. By controlling the slag composition, it is possible to control the form of the nonmetallic inclusions.

However, this method can suppress the formation of hard non-metallic inclusions. However, synthetic slag used as a slag component regulator is obtained by adjusting the raw material → particle size, component adjustment → firing (homogenization) → grinding → particle size. , And are expensive slag component modifiers, and these steel materials were the main factors that resulted in high production costs.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts. In order to produce a steel having a high degree of cleanliness at a low level of production cost and a low level of production cost, it is inexpensive for adjusting slag components. It aims to utilize raw materials.

[0006]

Means for Solving the Problems The gist of the present invention is that the inclusion composition is C under strong stirring conditions such as an injection method.
Based on the finding that the aO-SiO ₂ -Al ₂ O ₃ system, a method of controlling the composition of inclusions to a low melting region by controlling the slag composition. Without using expensive calcined synthetic slag as a slag adjuster, even if inexpensive raw materials are used, if an appropriate amount of a slagging agent is blended, it is dissolved under strong stirring conditions by the injection method, and slag composition control after deoxidation Is possible,
Therefore, morphology control of nonmetallic inclusions can be performed.

The details will be described below.

[0008] The inclusion composition is strongly influenced by the slag composition on the surface of molten steel. In particular, it is governed by the contents of CaO / SiO ₂ and Al ₂ O ₃ ,
The composition changes very regularly due to secondary deoxidation. Therefore,
By controlling the CaO / SiO ₂ and Al ₂ O ₃ contents of the treated slag to appropriate values, it is possible to lower the melting point of inclusions. In the deoxidation method of the present invention, when the molten steel is stirred and deoxidized while the surface of the molten steel is covered with a slag containing CaO, the input amount of Al from the component adjusting alloy is set to 5 g or less per ton of molten steel. The adjustment CaO content of the slag components 35% to 60% (wt%, hereinafter the same), SiO ₂ content of 30 to 55% and CaO content and the ratio CaO / SiO ₂ of SiO ₂ content 1.30～ Adjust so as to be 1.70, and also adjust Al ₂ O ₃ to 6 to 10%. CaO
If / SiO ₂ is lower than this range, SiO ₂ -based hard inclusions are formed and affect the die life when using steel. Above this range the _{Al 2 O 3, MgO-Al} 2 O 3 based hard inclusions exacerbates the generated breakage resistance. In order to control the composition of the formed inclusions in a narrow range, the total of other oxide components is set to 15% or less. Although the slag composition strongly influences the inclusions due to the reaction between the molten steel and the slag, the time for the reaction, that is, the dissolution rate of the slag component modifier, affects the inclusion composition. In the conventional method, the particle size of the raw material is adjusted in advance so that the slag component modifier is quickly melted when added to the molten steel, blended with a target composition, fired, pulverized, sized, and homogenized. However, the production cost of the slag component modifier accounts for a large proportion of the production cost of these steel products, and in order to reduce the production cost of steel products, inexpensive raw materials were used as the slag component modifier. Quicklime for the adjustment of the raw material is mainly CaO content軟硅reduction, chamotte and calcium aluminate as a content of Al ₂ O ₃ for adjusting, fluorite or sodium fluoride as a slag formation accelerator for the adjustment SiO ₂ content Use A mixture of these is used as a slag regulator, but the dissolution rate is significantly slower than that of the conventional product because the homogenization treatment and the particle size adjustment are not performed. Therefore, even under the strong stirring condition, the composition of the formed inclusion is different from that of the conventional slag conditioner. Specifically, the CaO content of the slag covering the molten steel surface and the SiO2
_{2 The} content ratio CaO / SiO ₂ is controlled to be relatively high, and A
By controlling the l ₂ O ₃ content to be relatively high, the composition of the formed inclusions can be controlled in the low melting point region. The raw material must be inserted into the molten steel holding container before the injection treatment.

In addition, the raw material is added in a pot before tapping or during tapping, rather than on the molten steel after tapping is completed so as to melt as early as possible. It is desirable to add.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In a ladle treatment under a strong stirring condition, even if a raw material having a low homogeneity but an inexpensive raw material is used as a slag composition adjuster, the composition control accuracy of nonmetallic inclusions is equal to that of conventional materials. Things.

[0011]

EXAMPLE When molten steel 240 ton was put into a ladle, FeMn was 2.9 kg / ts and the Al content was 0.0
3% or less of FeSi was added to obtain the components before treatment described in Table 1. Raw materials having the compounding ratios shown in Table 2 (grade 3 in Table 3) were put on the molten steel surface after tapping was completed. At the time of molten steel treatment in the ladle, a powder mainly composed of CaO-CaF ₂ is blown from a lance together with a blow gas, and then Ar gas is blown to 1.0 Nm ^3.
/ Min was blown for 30 minutes and the slag was vigorously stirred.
The obtained molten steel was injected into a tundish through a long nozzle for preventing air oxidation, and further injected through an immersion nozzle into a continuous casting mold having a cross section of 300 mm x 500 mm to solidify. Tables 1 and 4 show the components after treatment and the final slag components of the molten steel of this example. It is clear that the final slag component is within the scope of the present invention. Further, the obtained bloom slab was heated to 1300 ° C.
hot rolled into a billet of mx 120 mm, and after cooling,
Heated to 100 ° C and hot rolled into a 5.5mm diameter wire rod,
Nonmetallic inclusions in rolled steel were investigated. The results are shown in FIG. As shown in the figure, the index of non-ductile inclusions was about the same as that of the conventional material, and the generation of hard inclusions was suppressed.

<Comparative Example 1> Raw materials were blended as shown in Table 2 and alloys for component adjustment and raw materials were added in the same manner as in Examples. The molten steel treatment in the ladle and the method of investigating nonmetallic inclusions were performed in the same manner as in the example. Table 4 shows the final slag components, and FIG. 1 shows the results of investigation of the non-ductile inclusion index. In this slag composition, Si
O ₂ -based inclusions are generated in large quantities.

<Comparative Example 2> The raw materials were blended as shown in Table 2 and alloys and raw materials for component adjustment were added in the same manner as in the examples. The molten steel treatment in the ladle and the method of investigating nonmetallic inclusions were performed in the same manner as in the example. Table 4 shows the final slag components, and FIG. 1 shows the results of investigation of the non-ductile inclusion index. In this slag composition, Al
_A large amount of ₂ O ₃ -based inclusions is generated.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

According to the present invention, a manufacturing process having a low manufacturing cost and a conventional level of nonmetallic inclusion control accuracy has been developed as shown in FIG.

[Brief description of the drawings]

FIG. 1 is a diagram comparing a conventional material with a material of the present invention and a comparative example in a non-ductile inclusion index.

FIG. 2 is a comparison diagram of a conventional material and a material of the present invention at a slag adjusting material original unit price.

Claims (3)

[Claims] 1. A method for mixing molten steel in a state where the surface of the molten steel is covered with a slag component modifier and deoxidizing the molten steel, wherein an input amount of Al from the alloy for component adjustment is 5 g or less per ton of molten steel. Slag composition after treatment is CaO; 35-60%
(% By weight, hereinafter the same), SiO ₂ ; 30 to 55%, Al
₂ O ₃ ; 6 to 10%, total of other oxide products is 1
5% or less, and, CaO / SiO _2; 1.30~1.
70, so that quicklime, chamotte,
One or more of calcium aluminate and soft silica and one or more of slag melting point depressant such as sodium fluoride or fluorite are added to molten steel, and then the molten steel is stirred. Method of deoxidizing molten steel. 2. The method for deoxidizing molten steel according to claim 1, wherein one or more of quick lime, chamotte, calcium aluminate, and soft silica are combined with a slag melting point depressant such as sodium fluoride or fluorite. A method for deoxidizing molten steel, comprising adding a seed or two or more kinds to a pot before tapping from a converter or during tapping. 3. The method for deoxidizing molten steel according to claim 1, wherein the molten steel is stirred by blowing an inert gas with an injection lance to agitate the molten steel.