JPH08225820A - Production of high carbon silicon killed steel - Google Patents

Abstract

PURPOSE: To reduce the inclusion in steel, and to improve workability by dropping the melting point of the residual inclusions (to improve the ductility), by receiving the refined killed steel in a ladle, and blowing the flux together with an inert gas to achieve the secondary refining. CONSTITUTION: When or after the molten steel having the composition consisting of, by mass, 0.5-1.0% C, 0.1-2.0% Si, 0.2-1.0% Mn, <=1.0% Cr, <=0.5% Y, <=0.020% P, <=0.020% S, <=0.005% AI, and the balance substantially Fe is tapped, the slag, in the ladle is removed, and new flux is added to adjust CaO/SiO2 in the slag to be 0.8-2.0. Then, Al of <=50g/T is added to achieve the deoxidation adjustment, and the flux containing CaO is blown together with the inert gas in the secondary refining. Alternatively, the basicity of the slag is adjusted by blowing the flux in the secondary refining, and after attaining CaO/SiO2 of 0.8-2.0 and Al2 O3 of 20%, the molten steel is stirred to promote the inclusions to be afloat.

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 high carbon Si killed steel, and more particularly, to reduce the amount of inclusions produced during the melting of high carbon Si killed steel and the amount of inclusions remaining in the steel. High carbon Si with low melting point and excellent workability
It relates to a method for producing killed steel.

[0002]

2. Description of the Related Art Conventionally, high carbon Si killed steels used for tire cords, valve springs, etc. have been found to reduce the inclusions and inclusions in the steel which cause wire breakage and cutting damage due to severe processing and usage conditions. Is required to have a low melting point (ductility).

In response to such a demand, for example, Japanese Patent Publication No.
No. 35243 discloses CaO-containing flux and C
Although a method of reducing inclusions (decrease in total oxygen content) by blowing in a, REM, etc. has been proposed, this method is effective in reducing total oxygen, but carryover slag from the converter It is difficult to control the composition of inclusions due to the influence of.

Further, in Japanese Patent Laid-Open No. 3-173713, the slag composition at the time of secondary refining is CaO / SiO ₂ = 0.
A method of lowering the melting point of inclusions in steel has been proposed by controlling it to 5 to 0.9. However, when low basicity slag is used, the deoxidizing power of slag and the adsorption capability of inclusions are low, and inclusions are included. There is a limit to the absolute number reduction, and total oxygen reduction cannot be expected.

As described above, it has been difficult to reduce the total oxygen in Si-killed steel and lower the melting point of inclusions by the conventional method.

Japanese Patent Laid-Open No. 4-272119 proposes a method of controlling the slag composition after tapping steel to make inclusions harmless, but the target steel is Si-A.
It is a 1-killed steel, and the effect of reducing oxygen in Si-killed steel has not been recognized.

[0007]

This invention is a high carbon S
In i-killed steel, when the total oxygen is reduced, the composition of inclusions becomes non-ductile, and when the composition of inclusions is controlled to be in the ductile region, total oxygen cannot be reduced. In order to increase the ductility of residual inclusions and prevent wire breakage and cutting damage during processing and use of high carbon Si killed steel, the amount of inclusions generated during melting of high carbon Si killed steel and the steel are reduced. An attempt is made to propose a method for producing a high carbon Si killed steel capable of easily achieving a low melting point of residual inclusions therein.

[0008]

The present invention provides C0.5-
1.0 mass%, Si 0.1-2.0 mass%, Mn 0.2
~ 1.0 mass%, Cr≤1.5 mass%, V≤0.5 mass%, P≤0.020 mass%, S≤0.020 mass%, A
1 ≦ 0.005 mass%, Al is added to molten steel consisting of balance Fe and unavoidable impurities in a range of 50 g / T or less, and then CaO / SiO _{2 of} slag is 0.8 to
After adjusting to 2.0 and performing deoxidation, a CaO-containing flux is blown together with an inert gas (first invention), and Al in the same molten steel as above in a range of 50 g / T or less. After the addition, the CaO-containing flux was blown into the molten steel together with the inert gas, and the slag composition was changed to CaO / SiO ₂ =
It is characterized by adjusting to 0.8 to 2.0 and Al ₂ O ₃ ≦ 20 mass% and performing molten steel stirring (second invention).

[0009]

First, the reasons for limiting the components contained in the high carbon Si killed steel, which is the object of the present invention, will be described below. C: 0.5 to 1.0% by mass C is an element necessary to secure the strength, but if the content is increased, C tends to segregate, so that center segregation of C occurs and in the wire drawing step or the like. 0.5% by mass easily breaks
If it is less than 1.0%, the amount of segregation of C is reduced, but it is difficult to obtain high strength. On the other hand, if it exceeds 1.0% by mass, the workability is deteriorated. did.

[0010] Si: 0.1 to 2.0 but mass% Si is a deoxidizing element, the effect is small is less than 0.1 wt%, on the other hand, more than 2.0 wt%, the fine inclusions of SiO ₂ system The content is limited to 0.1 to 2.0 mass% because it causes the generation of substances.

Mn: 0.2 to 1.0% by mass Mn is effective in securing strength, but less than 0.2% by mass has little effect, and more than 1.0% by mass causes poor workability. It was set to 0.2 to 1.0 mass%.

Cr: 1.5% by mass or less Cr is effective for securing the strength, but excessive addition thereof causes precipitation of carbides and lowers the strength, so the content is set to 1.5% by mass or less.

V: 0.5% by mass or less V is as effective as Cr in ensuring strength, but excessive addition causes precipitation of carbides and lowers strength.
It was set to not more than mass%.

In addition to the above-mentioned essential components, the contents of P, S and Al contained as impurities are regulated for the following reason. P: 0.020 mass% or less Since P is an element that lowers the toughness and ductility of steel similarly to S and is more likely to segregate, it is necessary to regulate to 0.020 mass% or less.

S: 0.020% by mass or less Since S is an element which lowers the toughness and ductility of steel similarly to P and is easily segregated, it is necessary to regulate S to 0.020% by mass or less.

Al: 0.005% by mass or less When Al is contained in an amount of more than 0.005% by mass, Al ₂
Since O ₃ and MgO-Al ₂ O ₃ to generate a lot of non-ductile inclusions such, cause breakage in the drawing step, also non-ductile inclusions, these worsen the die life,
It is preferable that the Al content be as low as possible.
It is regulated to 005 mass% or less.

Further, the higher the Si content of the steel, the greater the amount of trace Al mixed from the ferroalloy and the more likely it is that Al ₂ O ₃ -based non-ductile inclusions will be generated. It is necessary to reduce the amount of Al to 50 g / T or less.

In the first invention, the CaO / SiO ₂ content of the slag in the ladle after tapping is adjusted to 0.8 to 2.0.
This is because the composition of the inclusions is controlled to a low melting point composition, and the production amount of SiO ₂ increases as the Si content becomes higher. Therefore, it is possible to stabilize by increasing the CaO content and selecting CaO / SiO ₂ according to the steel type. And an inclusion having a uniform composition is obtained. Here, the reason why CaO / SiO ₂ is limited to the range of 0.8 to 2.0 is that when it is less than 0.8, deoxidation by slag is insufficient and the total oxygen amount in the steel increases, while This is because if it exceeds 0, large inclusions increase and the cleanliness of the steel deteriorates. Add CaO / SiO _{2 of the} slag in the ladle to 0.8-2.
The method of adjusting to 0 is to remove slag and add flux.

To reduce the total oxygen, it is effective to add strong deoxidizing elements such as Ca and Al. However, when deoxidizing with an alloy, non-ductile inclusions, which are deoxidizing products, are present in the steel. Are very likely to remain in the steel and are unsuitable for the production of steel grades where the presence of non-ductile inclusions poses a problem.

Therefore, as a method of reducing inclusions, a flux blowing method that promotes floating of inclusions can be adopted. As blowing flux, CaO-CaF
_{There are 2} types, CaO-SiO ₂ type, etc., but the CaO-CaF ₂ type is superior in reducing total oxygen. Also, Ca
The amount of F ₂ is preferably 15% or more in order to promote the slag formation of the flux.

In the second invention, in order to reduce oxygen and non-metallic inclusions in the molten steel for cleaning the Si killed steel, a CaO-containing flux is blown into the molten steel together with an inert gas in the secondary refining to form a slag composition. adjust. The CaO-containing flux blown into the molten steel together with the inert gas during the secondary refining immediately melts in the molten steel after being blown, and in the process of floating in the molten steel, inclusions are trapped, dissolved and enlarged while the molten steel separates. .

Next, slag refining is carried out by stirring the molten steel in order to make the residual inclusions in the steel ductile and further reduce the number thereof when the flux is blown. At this time, the ductility of inclusions proceeds due to the interfacial reaction between the slag-molten steel and inclusions,
In the composition range of the Si killed steel which is the target steel of the present invention, the slag composition is the same as that in the first invention when the molten steel is stirred, as in the first invention.
O / SiO ₂ is 0.8 to 2.0, and Al ₂ O ₃ ≦
By setting the content to 20%, ductility of inclusions is possible. Here, CaO / SiO ₂ is set to 0.8 to 2.0 for the same reason as in the first invention. Further, since _{the Al} 2 _{O 3} based non ductile inclusions which content is due to dissociation of greater than 20%, the _Al 2 _{O 3} of _Al 2 _{O 3} in the slag increases, _Al 2 _{O 3} ≦ This invention It was set to 20%.

As the blowing flux, there are CaO-CaF ₂ system, CaO-SiO ₂ system and the like as in the first invention, but CaO-CaF ₂ system is superior in reducing total oxygen. Further, the amount of CaF ₂ is preferably 15% or more in order to promote the slag formation of the flux.

[0024]

1 is a block diagram showing a process for producing a high carbon Si killed steel according to the present invention, wherein (A) corresponds to claim 1 (first invention) of the present invention and (B) the same. It corresponds to the item 2 (second invention).

That is, in the first invention, the slag in the ladle is removed during or after tapping the converter, and flux is added to the ladle so that CaO / SiO _{2 of the} slag is adjusted to 0.8 to 2.0. adjust. After that, deoxidation is adjusted and Ca is added in the secondary refining.
The O-containing flux is blown into the ladle together with the inert gas to promote the floating of inclusions.

In the second invention, the CaO-containing flux is blown into the ladle together with the inert gas as the first step in the secondary refining, and the slag composition is CaO / SiO ₂ = 0.
Adjusted to 8 to 2.0 and Al ₂ O ₃ ≦ 20%, slag refining by molten steel agitation was carried out as the second step, and ductility of residual inclusions in steel during flux injection and further reduction of the number Measure

Next, claim 1 (first invention) of the present invention,
Examples corresponding to claim 2 (second invention) are shown below as Example 1 and Example 2, respectively. Example 1 The steel types shown in Table 1 were treated with the process shown in FIG. 1 (A) by changing CaO / SiO _{2 of the} slag in the ladle variously.
In this embodiment, CaO-CaF ₂ series flux was used, but the flux is not limited to this. Table 2 shows the molten steel composition after the flux injection, and Table 3 shows the slag in the ladle, CaO / SiO ₂ after the secondary refining, the total oxygen content, and the number of non-ductile inclusions.

From the results shown in Table 3, it can be seen that the present invention can simultaneously achieve the reduction of total oxygen and the ductility of the composition of inclusions, and the effect of reducing the number of inclusions is greater than that of the conventional method.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

Example 2 Molten steel having the components shown in Table 4 was used for the slag composition (CaO / Si in the secondary refining process in the process shown in FIG. 1B).
O ₂ and Al ₂ O ₃ ) were variously processed. The flux used was the same as that used in Example 1. Table 5 shows the molten steel composition after the flux injection in this example, and Table 6 shows the CaO / SiO ₂ content, the total oxygen content, and the number of non-ductile inclusions after the secondary refining.

From the results shown in Table 6, it can be seen that the reduction of total oxygen and the ductility of the composition of inclusions can be achieved at the same time in this embodiment, and the effect of reducing the number of inclusions is great.

[0034]

[Table 4]

[0035]

[Table 5]

[0036]

[Table 6]

[0037]

As described above, according to the method of claim 1 of the present invention, the control of the composition of inclusions from the time of tapping and the deoxidizing effect by the flux injection are not compatible with each treatment. Reduction of total oxygen and ductility of inclusion composition can be easily achieved, and the cleanliness of Si-killed steel can be significantly improved. Similarly, according to the method of claim 2, since the effect of reducing the number of non-ductile inclusions is great, it is possible to manufacture a Si-killed steel having high cleanliness.

[Brief description of drawings]

FIG. 1 is a block diagram showing a manufacturing process of high carbon Si killed steel according to the present invention, wherein (A) is a claim of the present invention.
Process (B) is a process corresponding to claim 2.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C22C 38/04 C22C 38/04 38/24 38/24 (72) Inventor Masamichi Suzuki Ogurakita, Kitakyushu City No. 1 Konomicho, Ward Sumitomo Metal Industry Co., Ltd. Kokura Works

Claims (2)

[Claims] 1. C0.5-1.0 mass%, Si0.1
2.0 mass%, Mn 0.2 to 1.0 mass%, Cr ≦ 1.
5% by mass, V ≦ 0.5% by mass, P ≦ 0.020% by mass,
A molten steel containing S ≦ 0.020 mass% and Al ≦ 0.005 mass% with the balance Fe and unavoidable impurities, A
1 in the range of 50 g / T or less, and then C of slag
A method for producing a high carbon Si killed steel, which comprises adjusting aO / SiO ₂ to 0.8 to 2.0, performing deoxidation, and then blowing a CaO-containing flux together with an inert gas. 2. C0.5-1.0 mass%, Si0.1
2.0 mass%, Mn 0.2 to 1.0 mass%, Cr ≦ 1.
5% by mass, V ≦ 0.5% by mass, P ≦ 0.020% by mass,
A molten steel containing S ≦ 0.020 mass% and Al ≦ 0.005 mass% with the balance Fe and unavoidable impurities, A
1 is added in a range of 50 g / T or less, and then Ca is added to the molten steel.
The O-containing flux was blown together with the inert gas, and the slag composition was CaO / SiO ₂ = 0.8 to 2.0, Al ₂ O ₃ ≦
A method for producing high carbon Si killed steel, which comprises adjusting the content to 20 mass% and stirring the molten steel.