JPH0651884B2 - Method for melting titanium-containing steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing titanium-containing steel. For example JIS
Although SUS 321 contains titanium, the titanium-containing steel in the present invention refers to carbon steel, alloy steel, and stainless steel containing titanium to the same extent as SUS 321.

[Prior Art] Titanium is an element having a strong affinity for oxygen and nitrogen. Therefore, when titanium is added to molten steel during the melting of titanium-containing steel, titanium is combined with oxygen and nitrogen in the molten steel to form TiO ₂ or TiN.
To generate. Oxygen content and nitrogen content of the molten steel is likely to vary, TiO ₂ Ya oxygen content and nitrogen content of the molten steel is fluctuated
If the amount of TiN produced fluctuates, the yield of titanium dissolved in molten steel becomes unstable. Therefore, there is a problem that the yield of titanium tends to become unstable in the production of titanium-containing steel.

In the production of titanium-containing steel, it was also formed in molten steel.
TiO ₂ and TiN adhere to the inner wall of the injection nozzle during casting,
There is a problem that the molten steel flow from the injection nozzle is throttled and, in an extreme case, the injection nozzle is blocked. JP-A-52-13381
No. 8 and JP-A-52-133827 show that in titanium-containing steel, if the titanium content and the aluminum content of the molten steel are controlled to a constant ratio, the clogging of the injection nozzle can be prevented. However, these publications do not describe means for stabilizing the yield of titanium. As mentioned above, the yield of titanium is unstable, and the yield of aluminum is also unstable.
Therefore, in these publications, titanium and aluminum whose yield is unstable and whose content easily fluctuates are controlled to a constant ratio, but it is necessary to stabilize the yield of titanium in order to obtain stable results. .

[Problems to be Solved by the Invention] The present invention provides a method for stabilizing the yield of titanium and controlling the Ti content of molten steel with high accuracy in the production of titanium-containing steel. The present invention further discloses a method for producing a titanium content in which the molten steel flow from the injection nozzle is not throttled or the injection nozzle is blocked during casting.

[Means for Solving the Problem] In the present invention, when the molten steel containing titanium is tapped into the ladle, the content of SiO ₂ in the slag in the ladle slagged is controlled to be 3% or less. To do.

The refining furnace in the present invention refers to an AOD furnace or a finishing refining furnace having the following functions of the AOD furnace. By controlling the SiO ₂ content of this slag, the titanium content of the molten steel in the ladle is desired with high accuracy. The content can be controlled. According to the knowledge of the inventor of the present invention, unless special measures are taken, titanium in molten steel is oxidized and reduced between the inside of the refining furnace and the inside of the ladle upon tapping, and the titanium content of the molten steel in the ladle is reduced. Is often lower than expected.

FIG. 2 is a result of an investigation conducted by the present inventor, and is a diagram showing the relationship between the SiO ₂ content of the tapping slag and the decrease in the titanium content of the molten steel during tapping. As can be seen in Fig. _2, the SiO _{2 of the} steel slag
If the content exceeds 3%, there is a large variation in the titanium reduction amount ΔTi at the time of tapping, and it is difficult to predict the titanium content of the molten steel after tapping. When the SiO ₂ content of the tapping slag is controlled to 3% or less, the titanium reduction amount ΔTi is always small, and the titanium content of the molten steel in the ladle does not become lower than expected. Therefore, by controlling the Ti content of the molten steel in the refining furnace before the ladle, the titanium content of the molten steel in the ladle can be controlled to a desired content with high accuracy.

In order to control the SiO ₂ content of the ladle slag to 3% or less, the present inventor used the following (1) to (4) together.

(1). Prior to the melting of titanium-containing steel, the present inventor previously removed slag having a high SiO ₂ content adhering to the inner wall of the refining furnace and the ladle. This removal was performed by melting and steeling the steel type reduced with aluminum as the previous charge. The slag with a high SiO ₂ content attached to the refining furnace and ladle is the Al ₂ O in the slag of this previous charge.
_A low melting point slag was formed and removed by ₃ .

(2). When melting the titanium-containing steel, the inventor set the Si content of the crude molten steel to be charged into the refining furnace to 0.3% or less. The Si content of the crude molten steel can be achieved, for example, by adjusting the Si of the molten steel in an electric furnace for obtaining the crude molten steel.

(3). As the slag forming agent to be added to the refining furnace, one having a limited SiO ₂ content was selected and used.

(4). Al was mainly used for the reduction of the molten steel in the refining furnace.

By the above means, the SiO ₂ content of the tap slag could be easily controlled to 3% or less.

In the present invention, as described above, the SiO _{2 of the} steelmaking slag from the refining furnace is
Is controlled to 3% or less to control the Ti content of the molten steel in the ladle with high accuracy, and the nitrogen content of the molten steel in the ladle [N]
(ppm) and titanium content [Ti] (%) are controlled within the range of formula (1).

7log [N] + 6log [Ti] ≦ 11.5 …… (1) By controlling this nitrogen content and titanium content, when casting molten steel in the ladle, from the ladle nozzle or the tundish nozzle in continuous casting, It is possible to prevent the molten steel flow from being throttled or from clogging these nozzles (hereinafter, abbreviated as nozzle clogging or the like). FIG. 1 is a result of an investigation conducted by the present inventor and is a diagram showing a relationship between nitrogen content and titanium content of molten steel in a ladle and nozzle clogging. As shown in Fig. 1, nozzle clogging occurs frequently in the range where the nitrogen content in the upper right is higher than the straight line 7log [N] + 6log [Ti] = 11.5, but the nitrogen content and titanium content can be calculated by the formula (1). When it is controlled within the range, there is no nozzle clogging. The reason why the nozzle clogging can be prevented by controlling the nitrogen content and the titanium content in this way is that in the titanium-containing molten steel in which the SiO ₂ content of the tapping slag is controlled to 3% or less, the clogging of the nozzle is mainly caused by TiN. It is thought that this is because it depends on the formation of

Since ordinary stainless steel, for example, JIS SUS 304 or SUS 321 molten steel has a high nitrogen solubility, the nitrogen content of the molten steel in the ladle becomes 200 ppm or more unless special measures are taken in melting.

Therefore, the present inventor used the following (1) and (2) together to control the nitrogen content of the molten steel in the ladle within the range of the formula (1), that is, the lower left range of the straight line in FIG.

(1) .The present inventor, when smelting titanium-containing steel, has a carbon content higher than usual, and charges 2.0% or more of crude molten steel into a smelting furnace to sufficiently perform a decarburization reaction in the smelting furnace. went. Although a large amount of CO gas was generated by this sufficient decarburization reaction, the nitrogen contained in the crude molten steel was removed from the molten steel by vigorous generation of CO gas, and molten steel with a low nitrogen content was obtained.

(2). Further, the present inventor filled the inside of the ladle receiving the molten steel containing titanium with argon gas, and tapped the molten steel containing titanium into the ladle filled with argon gas. When tapping molten titanium-containing steel in the atmosphere, the titanium-containing molten steel absorbs nitrogen gas during tapping, so the nitrogen content of the molten steel in the ladle is higher than the nitrogen content of the molten steel in the refining furnace, for example, 25 ppm. Get higher
By filling the inside of the ladle with argon gas, the increase in nitrogen content during tapping can be suppressed to about 10 ppm. The method of filling the inside of the ladle with argon gas can be achieved, for example, by the method described in Japanese Utility Model Publication No. 61-133541, that is, by covering the upper edge of the ladle with aluminum foil and blowing argon gas into the inside.

By the above means, the nitrogen content of the molten steel in the ladle can be reduced to the lower left range of the straight line in FIG. As described above, in the present invention, since the Ti content of the molten steel in the ladle can be controlled with high accuracy, it is possible to easily control the nitrogen content and the titanium content of the molten steel in the ladle within the range of formula (1). it can.

Incidentally, the titanium content of the target steel of the present invention, in (1)
[N] <200 ppm, 0.17% or more, and the upper limit is preferably about 0.5%.

[Example] SUS 321 was melted in an electric furnace having a capacity of 60 tons, refined by AOD and melted, and a continuous casting machine was used with a ladle sliding nozzle having an inner diameter of 50 mm and a tundish nozzle having an inner diameter of 30 mm. , 170mm round bloom.

Table 1 shows the outline of refining and casting. In Table 1, Comparative Examples Nos. 4, 5, and 6 had large fluctuations in titanium yield and clogged the tundish nozzle.
In o.1,2,3, the titanium yield was high and stable, and the tundish nozzle was not clogged.

[Advantages of the Invention] According to the present invention, when the titanium-containing steel is melted, the yield of Ti is improved and stabilized, and the Ti content of the molten steel can be controlled with high accuracy. Further, according to the present invention, it is possible to prevent nozzle clogging and the like, reduce casting accidents, and perform stable casting operations one after another.

[Brief description of drawings]

Fig. 1 shows the relationship between nitrogen content and titanium content of molten steel in ladle and nozzle clogging, and Fig. 2 shows SiO ₂ content of tap slag and Ti content of molten steel in tap steel. It is a figure which shows the relationship with the amount of decrease.

Claims (1)

[Claims] 1. In the production of titanium-containing steel, the content of SiO _{2 in the} steel slag from the refining furnace is 3% or less, and the nitrogen content [N] (ppm) and titanium content of the molten steel in the ladle [ Ti]
Melting method for titanium-containing steel, characterized by controlling (%) within the range of formula (1) 7log [N] + 6log [Ti] ≦ 11.5 …… (1)