JPH07116792A - Method for preventing clogging of nozzle at the time of transfer-pouring molten alloy steel - Google Patents

Abstract

PURPOSE:To prevent the clogging of a nozzle by adjusting the adding quantity of Ca (Ca alloy) based on S concn. and O concn. dissolved in molten steel in a transferring vessel and vaporizing quantity of dissolved Ca in the molten steel so as to remain the dissolved Ca in the molten steel. CONSTITUTION:At the time of transferring the molten alloy steel from the transferring vessel to the other vessel through a nozzle, the adding quantity of Ca (Ca alloy) is adjusted so as to remain the dissolved Ca in the molten steel in the transferred vessel just before completing the transfer by this adjustment. At this time, in the molten alloy steel containing >=2wt% the total content of one or more kinds of components selected among Mo, V, Ti, Zr, Al and REM(rear earth element), the total Ca content satisfying the specific equation is contained. By this method, the clogging of the nozzle is prevented and the stable process production and a large quantity of production of the alloy steel can be obtd., and further, the development of breakout at the time of continuously casting is eliminated because the molten steel temp. is unnecessary to be high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly belongs to the field of steelmaking and casting of alloy steel, and proposes a method for preventing nozzle clogging when transferring molten alloy steel to another container through a nozzle.

Alloy steel is a steel that has hardenability, machinability, heat resistance,
For the purpose of imparting various special properties such as oxidation resistance, impact resistance, corrosion resistance, wear resistance, and invariability, various alloy components are added according to the purpose, and the high quality of steel these days Demand is increasing due to the increasing demand for steel and multi-purpose steel.

For example, from the viewpoint of reducing or preventing air pollution, for example, NOx and SOx in automobile exhaust gas are taken into consideration.
As a material for exhaust gas purifying metal honeycomb catalytic converters to reduce CO and CO, high Cr and high Al alloy steel with excellent heat resistance and oxidation resistance is drawing attention, and 20% Cr-5% Al steel seems to be mainly used. Is becoming. Further, in the above alloy steel, in order to further improve the oxidation resistance of the steel,
An appropriate amount of rare earth components (Ce, La, etc.) is also added.

As a method for producing an alloy steel containing such various alloy components in high concentration, an ingot making method is disclosed in Japanese Patent Laid-Open No.
No. 124345 (RE into mold in bottom casting method)
M addition method) and the continuous casting method is CAMP-ISIJ, Vo.15 (199
2) and P1294 respectively. And, in any of the above ingot making method and continuous casting method, in the case of mass production,
Add the necessary components to the molten steel in a container such as a transfer container to produce molten alloy steel with the desired component composition, and if necessary, use Al
Deoxidize with a deoxidizer such as.

Further, in the ingot making method, after pouring from a ladle directly into a mold through a nozzle, or from a ladle into a middle container through a nozzle, it is poured into the mold through a nozzle. Be ingot. On the other hand, in the continuous casting method, it is poured into a tundish from a ladle through a nozzle, is supplied from a tundish to a continuous casting mold through a dipping nozzle, and is continuously cast.

However, in any of the above cases,
There is a step of transferring molten alloy steel to another container through a nozzle, and the nozzle may be clogged at that step. The rate of occurrence is much higher in the case of molten alloy steel containing 2 wt% or more of the total content of one or more of Mo, V, Ti, Zr, Al and REM, compared with the case of ordinary steel. The damage due to such troubles was great, together with the expensive additive alloy components.

[0007] As a specific example, 2 Al is contained in molten steel.
If the content of Al is 2 wt% or more, even if the content of total oxygen in the molten steel is 20 wt ppm or less, and even if the molten steel is clean, which generally does not easily cause nozzle clogging,
Nozzle blockage often occurred and became a problem. Moreover, when the molten alloy steel contains a rare earth element (REM), there is a problem that the nozzle clogging is more likely to occur.

As described above, generally, when molten alloy steel is transferred from a transfer container to another container via a nozzle, there is a high risk of nozzle clogging as exemplified above, and this problem should be solved. Was urgent.

[0009]

2. Description of the Related Art As means for preventing nozzle clogging, for example, in JP-A-64-75621 (method of adding calcium to molten steel in ladle), aluminum is added to molten steel to obtain (FeO + MnO) in slag. Is disclosed to be 5% or less and calcium is added by a wire method.

In this disclosed example, aluminum reacts with slag [particularly, (FeO + MnO) in the slag exceeds 5%] to form Al ₂ O ₃ having a high melting point, which causes nozzle clogging. When calcium is added thereafter, CaO—Al ₂ O ₃ having a low melting point is formed, and nozzle clogging can be prevented, and an effective addition method of calcium is proposed.

However, the aforementioned Mo, V, Ti, Zr,
The total content of one or more of Al and REM is 2
In the case of molten alloy steel of wt% or more, the total oxygen content in the molten alloy steel is 20 wt ppm or less, which is clean molten steel, and (FeO + MnO) in the transfer container slag is 0.5 wt% or less, which is lower than the disclosed example. There is a problem that nozzle clogging occurs even when the number is very small.

[0012]

SUMMARY OF THE INVENTION The present invention has the above-mentioned problems, that is, an alloy containing 2 wt% or more of the total content of one or more of Mo, V, Ti, Zr, Al and REM. When transferring molten steel through a nozzle, (FeO +
(MnO) is as low as 0.5 wt% or less and the total oxygen content in molten alloy steel is as low as 20 wt ppm or less. .

[0013]

The summary of the present invention is as follows. When the molten alloy steel is transferred from the transfer container to another container through the nozzle, the amount of Ca or Ca alloy added is determined by the [S] concentration and [O] concentration dissolved in the molten steel in the transfer container and the molten steel. Adjust based on the amount of evaporation of [Ca] dissolved in it, and
The above-mentioned adjustment is a method for preventing nozzle clogging during molten alloy alloy steel transfer, in which dissolved Ca is left in the molten steel in the transfer container immediately before the completion of the transfer.

In the paragraph, the following formula (1) is satisfied for the molten alloy steel containing a total content of one or more components selected from Mo, V, Ti, Zr, Al and REM of 2 wt% or more. A method for preventing nozzle clogging at the time of molten alloy alloy transfer, which is characterized by containing a [Ca] Total amount. Note [Ca] Total ≧ 40/32 ・ [S] +40/16 ・ [O] + a _Ca・ tc + 3 (wt ppm) -------- (1) Here, [Ca] Total: Ca addition end Temporary total amount of Ca in molten steel in the transfer container (wt ppm) [S]: Dissolved [S] concentration in molten steel in the transfer container before addition of Ca (wt ppm) [O]: Transfer container before addition of Ca Dissolved [O] concentration in molten steel (wt ppm) a _Ca : In the transfusion container after addition of Ca Reduction rate of dissolved [Ca] in molten steel (wt ppm / min) tc: In the transfusion container after addition of Ca Time until completion of molten steel transfer (min)

[0015]

The background of the invention and its operation will be described below based on the experimental results. In order to elucidate the essential cause of nozzle clogging that occurs when the molten alloy steel is transferred through a nozzle, the inventors have made various changes in the composition of the alloy, and when transferring the molten steel through the nozzle. Conducting a wide range of molten steel transfer experiments in which the atmosphere in contact with the molten steel transfer flow of No. 1 was conducted, and in the above experiment, the phenomenon when nozzle blockage occurred was carefully observed, and the nozzle blockage was analyzed and investigated. We obtained the findings listed in.

When the molten alloy steel is transferred from the transfer container to another container through the nozzle, particularly Fe alloy among the alloy components in the molten steel is used.
A metal having a stronger affinity with oxygen is oxidized by oxygen in the atmosphere surrounding the nozzle, and an oxide of the metal is generated on the surface of the molten steel to be poured, and a film is formed.

The metal oxide coating increases the apparent viscosity of the molten steel for transfer pouring to cause stagnation of the pouring flow at the nozzle tip, and the oxide grows in a lump form from the stagnation part, Specifically, the nozzle is closed.

The phenomenon of the item (3) is more likely to occur when the liquidus temperature of the metal oxide is higher. The metal oxide is usually a composite oxide depending on the alloy component, but when the composite oxide forms a low melting point compound, nozzle clogging is less likely to occur. The lower the vapor pressure of the alloy component having a stronger affinity for oxygen than Fe, the more likely nozzle clogging will occur.

Regarding these findings, as a more specific example, when the molten steel containing 2 wt% or more of one or more of Al and REM in total is transferred through a nozzle, Al and REM are transferred to the tip of the nozzle. Oxidized by oxygen in the atmosphere near the pouring flow, the oxides of Al ₂ O ₃ and REM are formed on the surface of the pouring flow to form a film of these oxides. It was clearly observed that the viscosity was increased and the fluidity of the transfer stream was deteriorated, and as a result, the oxides of Al ₂ O ₃ and REM accumulated at the tip of the nozzle together with the base metal, leading to nozzle clogging.

Furthermore, the thickness of these oxide coatings ranges from 2 to
It was as thin as 30 μm, but it was also inferred that the greater the content of alloying components in the molten steel, the thicker the thickness, and the larger the apparent viscosity of the molten metal in the pouring flow. As one example of the experimental results, molten alloy steel in the composition range shown in Table 1 (superheat degree ΔT of molten steel in the transfer container: 70 to 90 ° C) was transferred from the transfer container to another container through a nozzle. FIG. 1 shows the results of the investigation on the presence or absence of nozzle blockage.

[0021]

[Table 1]

FIG. 1 is a graph showing the relationship between the total content of Mo, V, Ti, Zr, Al and REM and the presence or absence of nozzle clogging. As is clear from this figure, the total content of the above alloy components is It can be seen that at 2 wt% or more, nozzle clogging has occurred.

The degree of superheat (ΔT) of the molten steel to be transferred has a great influence on the nozzle clogging. The larger ΔT, the less likely the nozzle clogging will occur. However, if ΔT becomes large, there is a risk of breakout during continuous casting. Not only increases the life of the refractory in the molten steel refining vessel, but ΔT is 100 ° C.
The following is desirable.

As described above, according to the present invention, in order to prevent the clogging of the nozzle at the time of the molten alloy transfer, the molten steel has a high vapor pressure (low boiling point) and oxygen Dissolving [Ca] as a metal with a high affinity,
A large amount of Ca is evaporated from the transfer flow flowing out of the nozzle during the transfer of molten steel, and most of the oxygen in the atmosphere reacts with the evaporated Ca to oxidize the alloy components with a greater affinity for oxygen than Fe in molten steel. To prevent the formation of oxides of these alloy components near the tip of the nozzle.

In the above, dissolving [Ca] in the molten steel means that the flow of Ca vapor is transferred even if Ca vapor contacts and reacts with oxygen in the atmosphere near the nozzle tip to form CaO. Since it flows toward the outside of the flow, it is difficult to get caught in the transfer flow, and even if CaO is caught in the transfer flow, it reacts with Al ₂ O ₃ etc. in the molten steel to form a low melting point compound. Therefore, it has an advantageous effect on prevention of nozzle clogging.

Of the alloy components, the addition of REM to the molten steel is preferably carried out after adding Ca or a Ca alloy, whereby Ca fixes [S] and [O]. Therefore, generation of sulfides, oxides, oxysulfides, and the like of the above alloys that cause nozzle clogging is suppressed, which is advantageous in preventing nozzle clogging. In the case of pouring into a tundish or a mold through the immersion nozzle, the molten steel in the immersion nozzle is usually an unfilled flow, which is naturally effective for preventing nozzle clogging of the immersion nozzle.

Next, the appropriate amount of [Ca] Total added to the molten steel in order to prevent nozzle clogging was determined by the results of various experiments.
It has been found that it is sufficient to satisfy the following expression (1), which is determined by the [S] and [O] concentrations dissolved in molten steel and the decreasing rate of [Ca] dissolved. [Ca] Total ≧ 40/32 ・ [S] +40/16 ・ [O] + a _Ca・ tc + 3 (wt ppm) -------- (1) where [Ca] Total: At the end of Ca addition Total Ca content in molten steel in the transfer container (wt ppm) [S]: In the transfer container before addition of Ca Dissolved [S] concentration in the molten steel (wt ppm) [O]: In transfer container before addition of Ca Dissolved [O] concentration in molten steel (wt ppm) a _Ca : Decrease rate of dissolved [Ca] in molten steel (wt ppm / min) in Ca after addition of Ca tc: Molten steel in transfused container after addition of Ca It is not necessary to leave dissolved [Ca] in the molten steel after being transferred to the mold, which is the time (min) until the transfer is completed.

[0028]

【Example】

Example 1 The composition of the components shown in Table 2 in a ladle prepared by the converter-VOD method [O]: 5 wt ppm or less (measured with an oxygen probe).
20% Cr-5% Al alloy molten steel (La is added later) 100T, CaSi
The iron-coated wire containing (Ca: 55 wt%) was added at various addition amounts, and then La (REM) was added.

[0029]

[Table 2]

The amount of CaSi-containing wire added is a _Ca = 0.30-
0.43wt ppm / min (large when molten steel temperature is high), Tc = 70
The min was changed so that the [Ca] Total amount satisfying the above formula (1) (compliance example) and the insufficient [Ca] Total amount (comparative example). Here, in the case of the conforming example, [Ca] in the molten steel in the ladle immediately before the end of the transposition is 3 wt ppm or more, and in the case of the comparative example, it is less than 3 wt ppm. In the above, La
(FeO + MnO) in the slag after addition is 0.5 in each case.
It was less than wt%.

The final molten steels thus melted are transferred from the ladle to the tundish through an alumina ladle nozzle having a diameter of 70 mmφ and supplied from the tundish to a continuous casting mold for casting. Cast into pieces. At that time, the degree of superheat ΔTT _{/ D} of the molten steel in the tundish was changed in the range of 20 ° C to 120 ° C by adjusting the temperature of the molten steel in the ladle, and the presence or absence of clogging of the ladle nozzle was investigated. The survey results are summarized in FIGS.

FIG. 2 shows the melt in the molten steel in the ladle immediately before the end of the transfer.
A graph showing the relationship between the existing [Ca] concentration and the presence or absence of clogging of the ladle nozzle.
It is. Figure 2 shows the degree of superheat of molten steel in the tundish.
ΔT _{T / D}Divided into two, below 100 ℃ and above 100 ℃
I put it. As is clear from FIG._{T / D}Is 100 ° C
Dissolved in the molten steel in the ladle just before the end of the transfer
When [Ca] is 3 wtppm or more, nozzle clogging is prevented.
It has stopped.

FIG. 3 shows the superheat degree ΔT _{T / D of the} molten steel in the tundish and the complete pouring rate (transferred) with the dissolved [Ca] concentration in the molten steel (3 wt ppm or more and less than 3 wt ppm) as a parameter immediately before the end of the transposition. It is a graph showing the relationship between the injection weight / molten steel weight × 100). As is clear from FIG. 3, the concentration of dissolved [Ca] is 3 wt.
It has been shown that when the content is more than ppm, casting can be performed without causing nozzle clogging even if ΔT _{T / D} is lowered to 40 ° C. This indicates that the ladle molten steel temperature may be low, and is extremely effective in solving various problems such as breakout in continuous casting caused by the high temperature.

Example 2 Dissolved by the converter-VOD method [O]: 30% Cr-2% Mo alloy molten steel 90T having the composition shown in Table 3 in a ladle melted to 5 wt ppm or less, CaSi Wire as [Ca] Total
The superheat degree Δ of molten steel in the tundish was evaluated using the same ladle nozzle as in Example 1 for the additive (compliance example) satisfying the formula (1) and the additive-free one (comparative example).
The ladle was transferred from the ladle to the tundish so that T _{T / D} was 100 ° C., the tundish was supplied to the continuous casting mold to cast into a slab, and the ladle nozzle clogging rate during that time was investigated. In addition, (FeO + MnO) in the ladle slag is 0.5
It was less than wt%.

[0035]

[Table 3]

Here, the ladle nozzle clogging rate is (number of heats that could not be completely poured) ÷ (number of castings) × due to nozzle clogging.
Calculated as 100. As a result, the ladle nozzle clogging rate was 0% for the conforming example and 75% for the comparative example, indicating that the effect of adding an appropriate amount of [Ca] Total according to the present invention is remarkable.

[0037]

The present invention, when the molten alloy steel is transferred from the transfer container to another container through the nozzle, the addition amount of Ca or Ca alloy added to the molten alloy steel in the transfer container is [Ca] is left in the molten steel in the transfer container immediately before the end of the transfer, and the nozzle is adjusted by adjusting the [S] and [O] concentrations of According to the present invention, since it is possible to completely prevent the nozzle from being clogged, it becomes possible to perform stable process production and mass production of alloy steel, and without increasing the molten steel temperature. Since it is good, breakout does not occur during continuous casting.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the total content of Mo, V, Ti, Zr, Al and REM and the presence or absence of nozzle clogging.

[Fig. 2] Dissolution in molten steel [C
a] A graph showing the relationship between the concentration and the presence or absence of clogging of a transfer container nozzle.

[Fig. 3] Dissolved in molten steel [C
a] A graph showing the relationship between the degree of superheat ΔT _{T / D of} molten steel in a tundish and the complete pouring rate with concentration as a parameter.

Front page continuation (72) Inventor Saburo Moriwaki, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Inside the Chiba Steel Works, Kawasaki Steel Co., Ltd. Technology Research Division, Inc.

Claims (2)

[Claims] 1. When transferring molten alloy steel from a transfer container to another container through a nozzle, the additive amount of Ca or Ca alloy is [S] concentration and [S] dissolved in the molten steel in the transfer container and [ O] concentration and the evaporation amount of [Ca] dissolved in molten steel, and the above adjustment causes dissolved [Ca] to remain in the molten steel in the transfer container immediately before the end of transfer. Nozzle blockage prevention method when pouring molten alloy steel. 2. The molten alloy steel according to claim 1, wherein the total content of one or more components selected from Mo, V, Ti, Zr, Al and REM is 2 wt% or more, and the following formula (1 ) A method of preventing nozzle clogging at the time of molten alloy transfer, characterized by containing a [Ca] Total amount satisfying the above condition. Note [Ca] Total ≧ 40/32 ・ [S] +40/16 ・ [O] + a _Ca・ tc + 3 (wt ppm) -------- (1) Here, [Ca] Total: Ca addition end Temporary total amount of Ca in molten steel in the transfer container (wt ppm) [S]: Dissolved [S] concentration in molten steel in the transfer container before addition of Ca (wt ppm) [O]: Transfer container before addition of Ca Dissolved [O] concentration in molten steel (wt ppm) a _Ca : In the transfusion container after addition of Ca Reduction rate of dissolved [Ca] in molten steel (wt ppm / min) tc: In the transfusion container after addition of Ca Time until completion of molten steel transfer (min)