JPH07216433A - Production of stainless steel for extra fine wire - Google Patents

Abstract

PURPOSE:To increase purity of stainless steel and to prevent wire breakage at drawing to extra fine wire by adjusting a concentration of Al and a basicity of molten slag to the specific values in refining stainless steel. CONSTITUTION:A stainless steel is produced from raw materials of steel scrap, Fe-Cr, etc., after decarburized/refined by adding Fe-Si as a reducer and CaO as a slag making agent into molten slag. The basicity of molten slag is adjusted to 1.2-1.8 and Cr2O3 in molten slag is reduced by Fe-Si so as to be recovered in stainless steel. Subsequently, this molten stainless steel is transferred to a ladle and the powdery flux containing CaO, CaF2 as essential components is blown therein with an inert gas such as Ar gas. Al content in the molten stainless steel is made to <=40ppm by significantly reducing non-metal inclusion, in particular, the quantity of Al2O3 with poor elongation, thus wire breakage at drawing to extra fine wire is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a stainless steel for extra fine wires, in which breakage during extra fine wire drawing is reduced.

[0002]

2. Description of the Related Art Ultrafine wire made of stainless steel or the like is finished to a desired wire diameter by wire drawing, but the wire diameter is 100 μmφ.
When the wire drawing is performed to a certain degree or less, the wire breakage easily occurs due to inclusions. Therefore, extremely high cleanliness is required for the ultrafine wire material. Therefore, in many cases, special melting methods such as a vacuum arc melting method, an electroslag melting method, and an electron beam melting method are applied to the production of a material for extra fine wires.

Among them, the electron beam melting method is capable of high cleanliness by evaporating and removing impurity elements by melting under an extremely high temperature and high vacuum, which is a characteristic of electron beam irradiation. You can get less material. However, when such a special dissolution method is applied, the manufacturing cost is very high, which is disadvantageous from the economical aspect. On the other hand, in an AOD furnace known as a general-purpose stainless steel refining furnace, so-called 2 slag is used in which slag that has once been generated after chromium reduction and desulfurization treatment is removed and CaO is added again to perform deoxidation / desulfurization treatment. There is a case where a material for extra fine wire is manufactured by adopting the method to achieve high cleanliness. This method is more economical than the special melting method, but it is difficult to sufficiently achieve high cleanliness, and thus it is difficult to sufficiently reduce the frequency of wire breakage during wire drawing.

On the other hand, a powder injection treatment method in which a highly basic powder such as CaO or CaF _{2 is} blown together with an inert gas into molten steel that has been tapped from a main refining furnace such as an AOD furnace. , For example Scan. J. Metal. 1 (19
72), p. Known by 103. According to this method, the deoxidation reaction and the desulfurization reaction proceed rapidly, so that high cleanliness can be achieved, but disconnection could not be sufficiently reduced only by high cleanliness.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a stainless steel for extra fine wires, in which breakage during wire drawing is reduced by softening the inclusions in a very small amount. To do.

[0006]

The present invention has been made to solve the above problems, and the gist thereof is to perform decarburization treatment by oxidative refining in a main refining furnace,
A reduction treatment for recovering the chromium oxidized by the decarburization treatment with an alloy containing silicon as a main component is performed, then steel is tapped from the main refining furnace into a ladle, and subsequently a powder injection treatment is performed in the ladle. In the refining of stainless steel, the concentration of [Al] in the molten steel discharged from the main refining furnace is 40 pp.
The composition of the slag, which is adjusted to m or less and is tapped together with the molten steel, has a CaO / SiO ₂ value of 1.2 to
The method for producing a stainless steel for extra fine wires, characterized in that the powder containing CaO and CaF ₂ as main components is blown together with an inert gas in the subsequent powder blowing treatment. It is in.

Next, the reasons for limitation in the present invention will be described. In FIG. 1, SUS316 stainless steel is subjected to decarburization treatment by oxidative refining in an AOD furnace, and reduction treatment for recovering chromium oxidized by the decarburization treatment with an alloy containing silicon as a main component is performed, followed by the main refining. Slag basicity before treatment when steel is taken out from the furnace into a ladle, and then CaO-40% CaF ₂ is blown with argon gas in the ladle at 5 kg / mol steel ton The relationship between (CaO / SiO ₂ ) and the number of inclusions having a size of 5 μm or more in a wire rod obtained by rolling the powder-blown material to 5.5 mmφ is shown. The [Al] concentration in the molten steel before the powder injection treatment was 4
The content of inclusions is 0 ppm or less, and the number of inclusions is a value obtained by measuring only oxide inclusions on a cross section of 300 mm ^{2 with an} optical microscope.

In FIG. 1, when the slag basicity (CaO / SiO ₂ ) before the powder blowing process is in the range of 1.2 to 1.8, the number of inclusions of 5 μm or more becomes extremely small.
In addition, FIG. 2 is the same as in FIG. 1, in the molten steel (Al] concentration before the treatment in which SUS316 stainless steel was blown, and the size of the raw material subjected to this blow treatment and rolled to 5.5 mmφ. It shows the relationship with the number of inclusions of 5 μm or more, in which the slag basicity (CaO
/ SiO ₂₎ is in the range of 1.2 to 1.8, inclusions number is a value determined in the same manner as in FIG. 1.

In FIG. 2, if the [Al] concentration in the molten steel before the blowing process is 40 ppm or less, the number of inclusions of 5 μm or more becomes extremely small. Fig. 3 shows the number of inclusions of 5 µm or more and the slag basicity (CaO /
The relationship between [Al] concentration in SiO ₂ ) and molten steel is shown. FIG. 4 shows a size of a wire rod having a wire diameter of 5.5 mm and a diameter of 5 μm, which is manufactured by blowing SUS316 stainless steel.
The relationship between the number of inclusions described above and the wire drawing amount per wire break when this wire is drawn into an ultrafine wire having a wire diameter of 50 μmφ is shown. Here, the wire extension per wire break is 50 kg
Wire drawing is performed on the above materials, and it is a value obtained by dividing the wire drawing amount at this time by the number of breaks.
It is an index showing that the wire drawability is good.

It can be seen from FIG. 4 that the wire drawability is remarkably improved when the number of inclusions having a size of 5 μm or more is set to 3 solids / cm ² or less. Therefore, the object of the present invention is to set the number of inclusions of 5 μm or more in the wire to 3 solids / cm ² or less. As can be seen from FIG. 3, the slag basicity (CaO / SiO ₂ ) before the powder injection treatment is in the range of 1.2 to 1.8, and the [Al] concentration in the molten steel is set to 40 ppm or less, and thus 5 μm or more. The number of inclusions is extremely reduced. Further, as can be seen from FIG. 4, when the number of inclusions of 5 μm or more is reduced, the wire drawing amount per wire breakage is greatly increased when this wire is drawn into an ultrafine wire with a wire diameter of 50 μmφ, and wire drawability is improved. To be done.

Therefore, the slag basicity (CaO / SiO ₂ ) before the powder injection treatment should be in the range of 1.2 to 1.8, and the [Al] concentration in the molten steel before the injection treatment should be 40 ppm or less. Thereby, the wire drawing workability can be greatly improved. The slag composition before the blowing treatment and the [Al] concentration control in the molten steel can be controlled by adjusting the amounts of auxiliary materials such as CaO and Al charged in the main refining furnace.

[0012]

[Function] CaO and CaF are produced by the ladle powder injection process.
By blowing a highly basic powder containing ₂ as a main component together with an inert gas, deoxidation proceeds and composition of inclusions changes due to the following two actions. By the reaction represented by the action (1), inclusions suspended in the molten steel are absorbed by the blown powder (CaO) and floated and separated.

(CaO) + (SiO ₂ ) → (CaO) · (SiO ₂ ) ... (1) Formula Action By injecting powder (CaO), the SiO ₂ activity in the slag-based inclusions is significantly increased. In order to reduce the amount, the reaction between silicon [Si] added for reduction in the main refining furnace and [O] in the molten steel is promoted, and deoxidation proceeds according to the formula (2).

Si + 2 O → (SiO ₂ ) (2) Formula (2) In order to promote the action of, it is necessary to use a highly basic powder containing CaO as a main component. It is desirable to increase the area of the reaction interface by refining the powder and increasing the blowing amount. Occurs in inclusions suspended in molten steel with the progress of deoxidation according to formula (2) (SiO ₂ ).
The concentration ratio increases, the (Al ₂ O ₃ ) concentration ratio decreases, and the composition of inclusions changes.
The composition of inclusions mainly composed of O ₂ can be controlled. CaO-SiO ₂
Since the main inclusions are easily stretched during rolling, they become fine after rolling. Therefore, it is possible to reduce the number of inclusions of 5 μm or more and improve the wire drawability.

Further, since the deoxidation is carried out by the Si deoxidation reaction of the formula (2), it is difficult to elongate during rolling (Al
₂ O ₃ ) is not generated (according to the formula (3) below). Therefore, the number of inclusions having a size of 5 μm or less in the rolled wire rod can be reduced and the wire drawability can be improved. In order to promote the action of 2 Al + 3 O → (Al ₂ O ₃ ) (3), the inert gas is blown into the molten steel to stir the molten steel and promote the agglomeration of inclusions. Therefore, it is necessary to quickly float and separate inclusions. Further, the inclusion of CaF ₂ in the powder contributes to the melting of the powder and accelerates the reaction of the formula (2).
And is important for promoting the agglomeration of inclusions.

In the present invention, chromium oxidized by decarburization is reduced by an alloy containing silicon as a main component,
The target is so-called silicon reduction. The reason is that when chromium oxide is reduced by aluminum, it is difficult to elongate during rolling due to the progress of the reaction of formula (3) (Al ₂ O
₃ ) is generated and the wire drawability of the wire is significantly deteriorated.

[0017]

EXAMPLE An example in which a SUS316 stainless steel ultrafine wire with a wire diameter of 50 μm is manufactured will be described. First, scrap and ferroalloy were melted in an electric furnace, decarburized in an AOD furnace, Fe-Si and CaO were added, and chromium reduction and desulfurization were performed. After that, it was tapped in a ladle.

In the ladle, powder having the amount and composition shown in Table 1 was blown as a carrier gas through a lance soaked in molten steel from above. The blowing rate is 500 l / min for argon gas and 50 kg / min for powder. The particle size of the powder is 250 μm or less. After the powder injection process in the ladle, a billet slab having a cross section of 150 mmφ was manufactured by continuous casting. This slab was rolled into a wire rod having a wire diameter of 5.5 mmφ, and the number of inclusions of 5 μm or more in the cross section was examined. Further, this wire was drawn into an ultrafine wire having a wire diameter of 50 μmφ, and then a wire drawing test was performed to evaluate the wire drawability.

In each of the examples of the present invention, the [O] and [Al] concentrations after the powder blowing process were low, the number of inclusions was small, and the (Al ₂ O ₃ ) concentration in the inclusions was also low. In addition, the wire drawing amount per cross section during wire drawing is 4.0 kg or more, which is a high value. On the other hand, the comparative example No.
Nos. 5 to 7 were low in the slag basicity before powder injection treatment or the [Al] concentration in the molten steel which did not satisfy the conditions of the present invention. Since neither oxygenation nor softening of inclusions can be achieved, the wire extension amount per wire break is as low as 2.7 kg or less, which is not a sufficient value.

[0020]

[Table 1]

[0021]

EFFECTS OF THE INVENTION According to the present invention, the frequency of wire breakage during wire drawing can be extremely reduced by producing a softened stainless steel with few inclusions. It is possible to manufacture the wire stably and economically.

[Brief description of drawings]

FIG. 1 Slag basicity (CaO / S before powder injection treatment)
iO ₂₎ and is a diagram showing the relationship between 5μm or more inclusions number of wire material.

FIG. 2 is a diagram showing a relationship between [Al] concentration in molten steel before powder injection treatment and the number of inclusions of 5 μm or more in a wire rod.

FIG. 3 Slag basicity (CaO / S before powder injection treatment)
iO ₂ ) and [Al] concentration in molten steel and 5 μm in wire rod
It is a figure which shows the relationship of the above-mentioned number of inclusions.

FIG. 4 is a diagram showing a relationship between the number of inclusions of 5 μm or more in a wire rod and the wire extension.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadanori Matsunami 3434 Shimada, Hitsu-shi, Yamaguchi Prefecture Nippon Steel Co., Ltd. Hikari Steel Works (72) Inventor Yuji Yoshimura 3434 Shimada, Hikari-shi, Yamaguchi Prefecture Made in Japan Inside the Kogaku Steel Works

Claims (1)

[Claims] 1. A decarburizing treatment by oxidative refining in a main smelting furnace, a reduction treatment for recovering chromium oxidized by the decarburizing treatment with an alloy containing silicon as a main component, and subsequently taken from the main smelting furnace. In the stainless steel refining in which steel is tapped into a ladle and subsequently powder is injected into the ladle, the [Al] concentration in molten steel tapped from the main refining furnace is adjusted to be 40 ppm or less. The composition of the slag tapped together with the molten steel is adjusted so that the value of CaO / SiO ₂ is 1.2 to 1.8, and CaO and CaF ₂ are the main components in the subsequent powder blowing process. A method for producing a stainless steel for extra fine wires, characterized in that the powder is blown together with an inert gas.