JP2008173667A - Continuous casting method of steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method of steel, which method hardly causes the choke of a nozzle even when REM has been added into molten steel. <P>SOLUTION: In the continuous casting method of steel, molten steel 11 is poured into a casting mold 16 via one or more nozzles 13 to 15, and cast ingots 17 are continuously taken out from the lower portion of the casting mold 16. The molten steel 11 contains 0.0003 mass% or more of REM, and further is adjusted such that the ratio of the concentration of Al<SB>2</SB>O<SB>3</SB>to the concentration of REM-O in an inclusion satisfies the following condition, Al<SB>2</SB>O<SB>3</SB>/REM-O≥0.25, and further a refractory material 24 containing 10 mass% or more of CaO is arranged on at least one of the nozzles 13 to 15 in at least part of the internal surface to be brought into contact with the molten steel 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for continuous casting of steel. More specifically, the present invention relates to a method for continuously casting steel containing REM (rare earth element) without causing nozzle clogging or melting.

It is well known to add REM in steel as a means of improving the material properties of steel. For example, as disclosed in Patent Document 1, as a molten steel component, 0.01 mass% or less of C (carbon), 0.1 mass% or more and 7.0 mass% or less of Si (silicon), 0 1.00% by mass or more and 0.05% by mass or less REM for non-oriented electrical steel sheet containing Al (aluminum) and other elements of 1% by mass or more and 3.0% by mass or less In the case of adding (rare earth elements), the size, form and number of inclusions or precipitates such as REM oxide, REM sulfide, REM oxysulfide to be generated are controlled, and the growth of crystal grains is promoted to promote the growth of crystal grains. Attempts have been made to improve (iron loss).
Moreover, in patent document 2, 0.0020-0.010 mass% of REM which utilized that the formed REM oxysulfide suppresses the growth of the austenite grain at high temperature, and was excellent in the heat-affected zone to weld zone. An invention relating to a high-strength steel for welded structures having the following is disclosed.

On the other hand, in continuous casting of steel, alumina-graphite is resistant to heat shock (spalling) when receiving high-temperature molten steel as a refractory material for the molten steel supply nozzle and has little damage due to reaction with molten steel System (AG) refractories have been widely used in general. However, when a large amount of inclusions such as REM oxide, REM sulfide, and REM oxysulfide are generated due to the addition of REM, which is a strong deoxidation and strong desulfurization element, to the steel supply nozzle using an AG-based refractory. Since these inclusions are likely to adhere to the inner surface, nozzle clogging easily occurs, and in the worst case, the operation may be stopped.
Therefore, in Patent Document 3, when casting REM-added steel containing Al, at least the inner surface is an alumina-graphite (AG-based) refractory having an SiO ₂ content of less than 1 mass%, and the alumina content is 95 mass. % Or more of an alumina refractory, or a method using an immersion nozzle composed of refractories containing ZrO ₂ , CaO and C as basic components has been proposed.

Moreover, in patent document 3, in order to avoid the weldability deterioration and embrittlement phase precipitation of steel, reducing the oxygen potential of molten steel, Al content is 0.01 mass% or more and 0.5 mass% or less. As specific examples and comparative examples, the results when the Al content is 0.008, 0.05, 0.08 mass% are described (Tables 2, 5 in the specification, and Paragraphs 0017-20).
Furthermore, it is described that the deposit formed on the inner surface of the immersion nozzle is a REM oxide (oxide) generated by reducing the oxide in the immersion nozzle refractory by REM, and is stable oxide-based refractory. A ZrO ₂ —CaO—C (ZCG) refractory is described as a product.

International Publication No. 2004/099457 Pamphlet Japanese Patent Laid-Open No. 10-88276 JP 2003-342630 A

However, in the method described in Patent Document 3, since deoxidation is insufficient when the Al content is less than 0.1% by mass, the inner surface of the immersion nozzle includes REM oxide, oxysulfide, and the like. Even if a kimono is generated and casting of 40t scale molten steel as described in Patent Document 3 is possible, in casting of molten steel of 200t or more, for example, 350t scale, sufficient nozzle clogging during continuous casting of REM-added molten steel is sufficient. Could not be suppressed.

The present invention has been made in view of the problem of nozzle clogging when continuously casting REM-added molten steel as described above, and provides a steel continuous casting method in which nozzle clogging hardly occurs even when REM is added to molten steel. The purpose is to do.

In the continuous casting method of steel according to the present invention that meets the above-mentioned object, the molten steel is injected into the mold through one or more nozzles, and the slab is continuously drawn out from the lower part of the mold. wherein it comprises a molten steel is 0.0003 mass% or more REM (rare earth element), and, _Al 2 _{O 3} concentration in inclusions in the molten steel (mass%) and REM oxide concentration (wt%) ratio Al ₂ The O ₃ / REM oxide is adjusted to be 0.25 or more, and at least one of the nozzles is provided with a refractory containing 10% by mass or more of CaO on at least a part of the inner surface in contact with the molten steel. Yes.

In the present invention, “REM” means 15 elements from lanthanum (La) having an atomic number of 57 to lutesium (Lu) having an atomic number of 57, scandium (Sc) having an atomic number of 21 and yttrium having an atomic number of 39 ( Y) is a general term for 17 elements in total. The case where some or all of these are indicated is described as REM below.

For example, when 0.1% by mass or more of Al is contained in the molten steel, REM oxide (hereinafter referred to as “REM-O”) and REM sulfide (hereinafter referred to as “REM-S”) generated by addition of REM to the molten steel. A certain amount (up to about 30% by mass of the inclusions) of Al ₂ O ₃ is taken into inclusions mainly composed of REM oxysulfide (hereinafter referred to as “REM- (O, S)”). When the refractory contains 10% by mass or more of CaO, CaO reacts with the Al ₂ O ₃ incorporated in the inclusions on the surface of the refractory to generate low melting inclusions. Adherence of the inclusions and accompanying nozzle clogging are suppressed.
Here, REM-O contained in the inclusion forms a composite oxide with CaO contained in the refractory, but the composite oxide has a melting point higher than the molten steel temperature, and the inclusion adheres to the surface of the refractory. There is an action to promote that. For this reason, in addition to REM-O which is inevitably contained, REM-O and Al ₂ O ₃ are contained in the inclusion by a certain amount or more of Al ₂ O ₃ which suppresses inclusions from adhering to the refractory. It has been conceived that inclusions containing can be prevented from adhering to the refractory surface. Furthermore, the inventors of the present application made the ratio Al ₂ O ₃ / REM-O of the Al ₂ O ₃ concentration (% by mass) and the REM-O concentration (% by mass) in the inclusions to be 0.25 or more, The inventors have newly conceived that the above-described inclusion adhesion preventing effect can be obtained.

Here, the inclusion includes REM compounds such as 1) REM-O, 2) REM-S, 3) REM- (O, S), etc., but the above-mentioned ratio Al ₂ O ₃ / REM- The denominator REM-O of O includes, in addition to 1) REM-O, 3) an amount corresponding to the amount of REM-O in REM- (O, S). In other words, the REM oxide affects the adhesion of inclusions to the refractory regardless of the form.
In addition, in order to make the above-mentioned ratio Al ₂ O ₃ / REM-O to be 0.25 or more, the Al concentration (mass%), the REM concentration (mass%) in the molten steel, and the ratio Al concentration / REM of these mass% Adjust the density. For example, in a molten steel having a REM concentration of 0.0003 mass% or more, when the Al concentration in the molten steel is 0.1 mass% or more and the Al concentration exceeds 20 times the REM concentration, the ratio Al ₂ O ₃ / It was confirmed that REM-O could be controlled to 0.25 or more.

The aforementioned _{Al 2 O 3, REM-O} , REM- (O, S) weight% of the measurement method, such as can be measured using the EPMA (X-ray microanalyzer). The inclusions exposed on the polished surface of the sample solidified from the molten steel are irradiated with an electron beam and subjected to EPMA measurement, and the characteristic X-ray intensity is counted for each element. In calculating the composition ratio (mass%) of inclusions from the strength, a calibration curve for each element prepared from a sample whose mass% is known can be used. From the calculated mass% of each element, all metals excluding REM such as Al, Mg, and Si are assumed to be oxides such as Al ₂ O ₃ , and the remainder excluding O (oxygen) consumed by the oxides O and S in this form a compound with REM. Assuming that the REM compound is REM-O or REM-S, Al ₂ O ₃ mass% and REM-O mass% can be calculated from the above, and Al ₂ O ₃ / REM-O can be calculated.

In the continuous casting method of steel according to the present invention, the nozzle includes a first molten steel supply nozzle disposed between a ladle and a tundish, and a second used between the tundish and the mold. Any one of a molten steel supply nozzle, a flow rate adjusting nozzle disposed adjacent to the second molten steel supply nozzle, and a connection nozzle for connecting any one of these nozzles to the corresponding ladle or the tundish, respectively. It is preferable that
By using a refractory containing 10% by mass or more of CaO for at least one of the nozzles used for pouring molten steel into the mold, it is possible to prevent the nozzle from contacting the molten steel with the inner surface.

In the continuous casting method for steel according to the present invention, the refractory containing 10 mass% or more of CaO is preferably a refractory containing CaO and MgO as main components.
Since the refractory mainly composed of CaO and MgO is used, CaO in the refractory is consumed by the reaction, but the MgO particles remain on the contact surface with the molten steel and are concentrated, resulting in an MgO content of 50 % Or more MgO-rich barrier layer is formed. This barrier layer reduces infiltration of the molten steel into the refractory and improves the refractory resistance of the refractory, and CaO is supplied to the contact surface with the molten steel through the MgO particles of the barrier layer.

In the continuous casting method of steel according to the present invention, the refractory mainly composed of CaO and MgO has an MgO content of 20% by mass or more and 70% by mass or less, and the CaO content W1 and MgO The ratio W1 / W2 of the content rate W2 is preferably 0.33 or more and 3 or less.
The content ratio W1 / W2 between CaO, which has the ability to suppress inclusion adhesion but does not have the ability to improve the corrosion resistance, and MgO, which has the ability to improve the resistance to corrosion damage but has no ability to prevent inclusion adhesion, By adjusting the contents of both of them so as to be within the above range, both the formation of a sufficient MgO-rich barrier layer and the supply of a sufficient amount of CaO to the molten steel contact surface are ensured. Provided is a refractory for a nozzle that has both resistance to erosion and ability to prevent inclusions in steel.

In the continuous casting method of steel according to the present invention, the C content in the refractory mainly composed of CaO and MgO is preferably 0.1% by mass or more and 10% by mass or less.
By adjusting the content of C in the refractory so as to be within the above range, the thermal expansion strain of the refractory in contact with the molten steel is absorbed and relaxed, thereby improving the stability of the refractory as a structural body. It is possible to minimize deterioration due to oxidation and erosion while improving.

In the continuous casting method of steel according to the present invention, the molten steel is 0.001% by mass or more and 0.01% by mass or less C, 0.1% by mass or more and 7% by mass or less Si, 0.1% The slab contains Al of not less than 3% by mass and not more than 3% by mass, REM of not less than 0.0003% by mass and not more than 0.05% by mass, and the balance Fe and inevitable impurities. In particular, it is preferably used as a steel for non-oriented electrical steel sheets.

In the continuous casting method of steel according to claims 1 to 6, the ratio of REM content in molten steel, the ratio of Al ₂ O ₃ concentration and REM-O concentration in inclusions in molten steel, Al ₂ O ₃ / REM-O, In addition, by optimizing the content of CaO in the refractory used for the nozzle, the inclusion of inclusions in the steel on the inner surface of the nozzle during continuous casting of steel containing REM, and the resulting blockage of the nozzle are prevented. It becomes possible.
As a result, it becomes possible to stably carry out continuous casting of steel materials having material improvement effects such as magnetic properties in non-oriented electrical steel sheets by addition of REM on an industrial scale.

In particular, in the continuous casting method of steel according to claim 2, 10 masses of CaO is used for the first and second molten steel supply nozzles, flow rate adjustment nozzles, and connection nozzles that are used for pouring molten steel into the mold and are in contact with the inner surface of the molten steel. By using a refractory containing at least%, it becomes possible to stably perform continuous casting of REM-added steel while preventing clogging in a nozzle in a continuous casting apparatus in which the inner surface is in contact with molten steel.

In the continuous casting method for steel according to claim 3, by using a refractory mainly composed of CaO and MgO, an MgO-rich barrier layer excellent in melting resistance is formed on the surface of the refractory. Since CaO is supplied to the contact surface with the molten steel through the MgO particles of the layer, it is possible to improve both the erosion resistance characteristics of the refractory used for the nozzle and to continuously prevent inclusion adhesion.

In the continuous casting method for steel according to claim 4, since the MgO and CaO content is within a predetermined range, both the formation of a sufficient MgO-rich barrier layer and the supply of a sufficient amount of CaO to the molten steel contact surface are ensured. Is done. It becomes possible that the refractory used for the nozzle has both excellent resistance to erosion and the ability to prevent inclusions in steel.

6. The steel continuous casting method according to claim 5, wherein the content of C in the refractory is 0.1% by mass or more and 10% by mass or less, whereby the stability of the refractory used for the nozzle as a structure. It is possible to minimize deterioration due to oxidation and erosion while improving.

In the continuous casting method of steel of Claim 6, 0.001 mass% or more and 0.01 mass% or less C, 0.1 mass% or more and 7 mass% or less Si, 0.1 mass% The non-oriented electrical steel sheet is continuously casted with 3% by mass or less of Al, 0.0003% by mass or more of REM and 0.05% by mass or less of molten steel containing the remaining Fe and inevitable impurities. By using steel, it becomes possible to stably and continuously produce a non-oriented electrical steel sheet excellent in iron loss.

Subsequently, an embodiment of the present invention will be described to provide an understanding of the present invention.
Continuous casting of steel removes inclusions such as oxides that cause deterioration of steel strength, workability, fatigue resistance, etc. from the molten steel and has a certain shape so that it can be easily processed in the next rolling process. For the purpose of producing semi-finished products having
FIG. 1 shows a continuous casting machine 10 to which a steel continuous casting method according to an embodiment of the present invention is applied. Hereinafter, while explaining the continuous casting apparatus 10, the continuous casting method of steel which concerns on this Embodiment is demonstrated in detail.
The molten steel produced in the converter is injected directly or after a secondary refining process as necessary, into a ladle 12 located at the top of the continuous casting machine 10. In the ladle 12, since the inclusion which exists in the molten steel 11 floats, this is removed.

Next, the molten steel 11 is injected into a tundish 14 provided immediately below the ladle 12 via a first molten steel supply nozzle 13 which is an example of a nozzle. Since inclusions further float from the molten steel 11 stored in the tundish 14, the inclusions can be effectively removed from the molten steel 11 by removing the inclusions. Next, the molten steel 11 is injected into the uppermost part of the mold 16 through a second molten steel supply nozzle 15 which is an example of a nozzle. Since the mold 16 is made of copper having a high thermal conductivity and is always water-cooled, the molten steel 11 is rapidly cooled and starts to solidify. The slab 17 that has started solidification is continuously drawn out from the lower part of the mold 16 by the slab support roll 18 and further cooled by injection of cooling water or the like by the slab cooling device 19 to complete the solidification point (crater end). 20 completely solidifies. The completely solidified slab 17 is drawn from the continuous casting machine 10 by a slab drawing roll 21 and conveyed to a rolling process by a slab conveying roll 22.

Next, the ratio Al ₂ O ₃ / REM-O between the REM in molten steel 11 and the Al ₂ O ₃ concentration and the REM-O concentration in inclusions will be described.
When the content of REM in the molten steel is less than 0.0003 mass%, the improvement of material properties due to the addition of REM does not appear remarkably, and in the first place, there is a problem of blockage of the molten steel supply valve due to adhesion of inclusions. Does not occur. Therefore, the content of REM in the molten steel is 0.0003 mass% or more, preferably 0.001 mass% or more, more preferably 0.002 mass% or more. The upper limit of the REM content depends on the Al content in the molten steel and the composition of the refractory, so it is difficult to determine uniquely, but considering the increase in production cost due to the increase in Al content Then, it is 0.05 mass% or less, Preferably it is less than 0.03 mass%, More preferably, it is 0.01 mass% or less.

Ratio of Al ₂ O ₃ concentration and REM-O concentration in inclusions Al ₂ O ₃ / REM-O is 0.25 or more (that is, the inclusion is composed only of Al ₂ O ₃ and REM-O) In the case where the Al ₂ O ₃ concentration is 20% by mass or more), a stable nozzle blockage suppressing effect is obtained. The reason for this is that when the ratio Al ₂ O ₃ / REM-O of Al ₂ O ₃ concentration to REM-O concentration is 0.25 or more, CaO containing 10 mass% or more of Al ₂ O ₃ in the refractory. reacts with respect to form a low melting point composite oxides, in the case of concentration of _Al 2 _{O 3} and REM-O concentration ratio _Al 2 _O 3 / _REM-O inclusions of less than 0.25, the low This is because it is difficult to form a melting point composite oxide. In this case, in order to make the ratio 0.25 or more, the Al content in the molten steel is preferably 0.1 mass% or more. When the content of Al in the molten steel is less than 0.1% by mass, inclusions generated when REM is added to the molten steel contain almost no Al ₂ O _3, and thus refractory containing 10% by mass or more of CaO. Even if an object is arranged on the inner surface of the nozzle, the effect of preventing clogging due to the formation of low melting point inclusions does not appear. Therefore, the content of Al contained in the molten steel is 0.1% by mass or more, preferably 0.13% by mass or more. The upper limit of the preferable Al content is determined according to the use of the steel product. For example, when used as a steel for non-oriented electrical steel sheets, the upper limit is preferably 3% by mass from the viewpoint of production cost, and if it is a material to be welded, it is difficult to weld and continuously cast. From the above, the upper limit is preferably 0.5% by mass. In the present embodiment, the C content in the molten steel is 0.001% by mass or more and 0.01% by mass or less, and the Si content is 0.1% by mass or more and 7% by mass or less. And the remainder contains Fe and inevitable impurities.

The refractory 24 (see FIG. 2) disposed on the inner surface of the second molten steel supply nozzle 15 (same as the first molten steel supply nozzle 13) contains 10 mass% or more of CaO. When the content of CaO in the refractory is less than 10% by mass, the amount of CaO supplied to form the CaO—Al ₂ O ₃ low melting point compound (calcium aluminate) is insufficient, so the molten steel contact surface of the refractory In addition, inclusions and ingots including REM-O, REM- (O, S), REM-S, Al ₂ O _{3 and the} like accompanying them are likely to adhere. Therefore, the CaO content in the refractory is 10% by mass or more, preferably 15% by mass or more, and more preferably 20% by mass or more. On the other hand, if the CaO content exceeds 70% by mass, the thermal expansion coefficient of the refractory increases, so cracks are generated due to differences in the thermal expansion coefficient from other parts of the molten steel supply nozzle, and the life of the refractory Decreases. Accordingly, the CaO content in the refractory is preferably 70% by mass or less.

The refractory 24 containing 10% by mass or more of CaO is disposed on at least a part of the inner surface (molten steel contact surface) in contact with the molten steel of the second molten steel supply nozzle 15. Which position and range in the molten steel contact surface of the nozzle the refractory 24 is appropriately determined according to the composition, temperature, flow rate, and the like of the molten steel.
As shown in FIG. 2 (A), the arrangement position of the refractory 24 is the entire molten steel contact surface of the nozzle body 23, as shown in FIG. 2 (B), the molten metal surface 25 of the molten steel contact surface. The case where it arrange | positions only in the lower part, and the case where it arrange | positions only around the discharge outlet 26 among molten steel contact surfaces as shown in FIG.

In the present embodiment, the first molten steel supply nozzle 13 used between the ladle 12 and the tundish 14 and the second molten steel supply used between the tundish 14 and the mold 16 are used as nozzles. Although a refractory containing 10 mass% or more of CaO is disposed in the nozzle 15 (for example, an immersion nozzle, a long nozzle, etc.), a flow rate adjustment nozzle (not shown) disposed adjacent to the second molten steel supply nozzle 15 is further provided. (For example, a sliding nozzle, etc.) and any of the first and second molten steel supply nozzles 13 and 15 and the flow rate adjusting nozzle to the ladle 12 or the tundish 14 (that is, the first molten steel supply nozzle 13 is a ladle. 12, a connection nozzle (not shown) (for example, an upper nozzle, a lower nozzle, etc.) for connecting the second molten steel supply nozzle 15 and the flow rate adjustment nozzle to the tundish 14. Of nozzle etc., the composition of the molten steel, the temperature, and in one or more selected in accordance with the flow velocity, it is possible to place the refractory to at least a portion of molten steel contacting surface.

The refractory 24 is a refractory containing dolomite clinker, and mainly contains CaO and MgO. The MgO particles in the dolomite clinker form a MgO-rich barrier layer having an MgO content of 50% or more on the contact surface with the molten steel 11, thereby improving the erosion resistance of the refractory 24. Moreover, since CaO can be supplied to the contact surface with the molten steel 11 through the MgO particles, continuous inclusion adhesion prevention can be realized.

As the dolomite clinker, any dolomite clinker generally used as a raw material for dolomite refractories can be used. As an example of a component composition, what contains 57 mass% of CaO and 40 mass% of MgO is mentioned, for example. The dolomite clinker used as the refractory may be a dolomite clinker obtained by heat-treating natural dolomite, or a synthetic dolomite clinker prepared in an arbitrary composition using an artificial raw material.

The MgO content of the refractory 24 is 20% by mass or more and 70% by mass or less. When the content of MgO used in the refractory is less than 20% by mass, the MgO-rich barrier layer as described above is not sufficiently formed. Life is shortened.
When the MgO content exceeds 70% by mass, the amount of CaO supplied to the contact surface with the molten steel through the MgO particles of the MgO-rich barrier layer is insufficient, and inclusions tend to adhere to the refractory surface. .

The ratio W1 / W2 between the CaO content W1 and the MgO content W2 of the refractory 24 is 0.33 or more and 3 or less. When the ratio W1 / W2 is less than 0.33, W1 is 20% by mass or more. Even so, the CaO amount supplied to the contact surface with the molten steel is insufficient, and a sufficient adhesion preventing effect cannot be exhibited, and the amount of MgO is too large, so that spalling, cracking, etc. are likely to occur.
Further, when W1 / W2 exceeds 3, the amount of CaO supplied to the contact surface with the molten steel becomes excessive, so even if the content of MgO is 20% by mass or more, the MgO-rich layer serving as a protective layer is rich. Since the formation of the barrier layer is hindered, the erosion characteristics deteriorate. The ratio W1 / W2 is more preferably 0.90 or more and 2.6 or less.
The ratio W1 / W2 can be controlled not only by the content of MgO and CaO contained in the dolomite clinker used, but also by the amount of MgO clinker added separately.

Because the carbon contained in the refractory absorbs and relaxes the thermal expansion strain of the refractory in contact with the molten steel, the stability of the refractory as a structure is improved by adding carbon to the refractory. Can do. The content of carbon in the refractory 24 used in the present embodiment is 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 5% by mass or less. When the carbon content is less than 0.1% by mass, a sufficient effect cannot be obtained. When the carbon content exceeds 10% by mass, the carbon component is oxidized by oxygen in the molten steel or dissolved in the molten steel. Since melting loss becomes large, both are not preferable.

Next, examples carried out for confirming the effects of the present invention will be described.
A non-oriented electrical steel sheet whose magnetic properties (iron loss) are improved by the addition of REM is used as a cast steel grade, and a continuous casting machine (slab series) with a mold radius of 250 mm (thickness) x 1000 mm (width) and a radius of curvature of 10.5 m Using a casting machine (see FIG. 1), continuous casting was performed at a casting speed of 1 to 1.2 m / min. As the REM added to the molten steel, a misch metal containing La, Ce, Nd or the like as a main component was used.

Dolomite clinker was used as a refractory mainly composed of CaO and MgO. Main components other than CaO, MgO, and C are ZrO ₂ (over 0 to 5% by mass), SiC (over 0 to 3% by mass), SiO ₂ (over 0 to 1% by mass), and Fe (Over 0 and 0.1% by mass or less).
For comparison with dolomite clinker, ZCG (contains 55% by mass of ZrO ₂ and 1.2% by mass of SiC in addition to CaO and C. The balance is SiO ₂ , alumina and FeO) and alumina-graphite ( AG) refractories (almost alumina except C) were used. These refractories were arranged on the inner surface of the second molten steel supply nozzle (immersion nozzle) between the tundish and the mold in the manner as shown in FIGS.

In this embodiment, it is possible to perform continuous casting for all the molten steel supplied without causing the clogging of the molten steel supply nozzle in the middle of the process, “complete casting is possible”, inclusion adhesion and clogging, and refractory "Full casting is possible 2 times" that the casting can be performed twice continuously without replacing the molten steel supply nozzle due to melting, and complete casting is possible three or more times continuously without replacing the molten steel supply nozzle. This is defined as “possible three or more complete castings”.
A continuous casting test using molten steel 350 t as a charging unit is performed under the above conditions, and the test results are “350 t complete casting impossible”, “350 t complete casting possible”, “350 t full casting possible 2 times”, “350 t Was determined to be possible 3 times or more of complete casting. After the continuous casting test was completed or stopped, the presence or absence of inclusions on or clogged with the refractory in the molten steel supply nozzle, and the presence or absence of erosion were also examined.

A non-oriented electrical steel sheet was produced from a slab obtained by continuous casting according to a known method. Magnetic properties (iron loss: W15 / 50 (W / kg)) were evaluated as material properties of the non-oriented electrical steel sheet thus obtained, and the results were classified into normal values and higher values.

Various experimental conditions (REM and Al content in molten steel, ratio of Al ₂ O ₃ concentration to REM-O concentration in inclusions Al ₂ O ₃ / REM-O, refractory material, CaO, MgO, and Table 1 and Table 2 summarize the experimental conditions and results of the continuous casting tests (Examples 1 to 18 and Comparative Examples 1 to 11) conducted under the C content rate and the arrangement mode on the inner surface of the molten steel supply nozzle). Shown in

In Tables 1 and 2, “D” in the column of “refractory material” means dolomite, “ZCG” means ZCG (ZrO ₂ —CaO—C), and “AG” means alumina graphite.

In Tables 1 and 2, the symbol “◎” described in the column of “Number of continuous castings and nozzle state” is “350t complete casting is possible 3 times or more”, and “◯” is “350t complete casting 2”. “Turnable”, “Δ” means “350 t complete casting is possible”, and “x” means “350 t complete casting is not possible”.

Based on the results of these experiments, first, the content of REM in the molten steel component is examined.
Example 7 (REM content: 0.0003 mass%), Comparative Examples 1, 2, and 4 (REM content: 0.001%) having almost the same Al content (0.11 to 0.15% by mass). Comparison was made on the result of 0002 mass%.
As a result, the magnetic characteristic value (iron loss: W15 / 50) was “ordinary” for Comparative Examples 1, 2, and 4, whereas it was “high” for Example 7.

Moreover, in Comparative Example 1, 350 t continuous casting of molten steel having a REM content of 0.0002 mass% was performed using an alumina graphite refractory containing no CaO on the molten steel contact surface of the molten steel supply nozzle. . Although the result was “completely castable”, the nozzle tended to be clogged after the completion of the first 350 t continuous casting despite the low REM content.
As shown in Comparative Example 3 using the same refractory, when the content of REM was increased to 0.0031% by mass, the nozzle was clogged during the first 350t continuous casting, and the result was “cannot be completely cast. "Met.

From the above results, when the REM content is 0.0003 mass% or more, the iron loss (W15 / 50) of the non-oriented electrical steel sheet is improved, while the REM content exceeds 0.0002 mass%. And especially when using the refractory material which does not contain CaO, it turns out that the problem of the blockade of a molten steel supply nozzle becomes remarkable.

Next, the Al content in the molten steel is examined.
Comparative Example 6 and Example 17 are common in that the content of REM in molten steel is 0.0046% by mass and a refractory containing 10% by mass or more of CaO is used. In Comparative Example 6 in which the rate was 0.09% by mass, “350 t of complete casting was impossible”, whereas in Example 17 in which the Al content was 0.10% by mass, 350 t was cast. Although the nozzle was blocked, it was “350 t complete casting possible”.
Furthermore, when investigating the ratio _Al 2 _O 3 / _REM-O of the concentration of _Al 2 _{O 3} and REM-O concentration of inclusions in the steel at this time, whereas Comparative Example 6 was less than 0.25 Example 17 was 0.25 or more.
From these results, in order to prevent the inclusions from adhering to the molten steel supply nozzle, the Al concentration in the steel is controlled to an appropriate amount, and the ratio Al ₂ O ₃ concentration to REM-O concentration in the inclusions is Al. the ₂ O ₃ / REM-O it can be seen that it is necessary to be 0.25 or more.
In Comparative Examples 5 to 11, the REM content in the molten steel is 0.0003 mass% or more (0.0032 to 0.0151 mass%). In this case, the Al concentration is 0.1 mass%. above, and if the Al concentration does not exceed 20 times the REM concentration can not be 0.25 or more specific _Al 2 _O 3 / _REM-O of the concentration of _Al 2 _{O 3} and REM oxide concentration in inclusions It is shown that.

Next, the effect of the CaO content in the refractory is examined.
In Comparative Example 3 and Examples 14 and 18, the REM content in the molten steel is 0.0003 mass% or more (0.0031 to 0.0048 mass%), and the Al content in the molten steel is adjusted. (0.10 to 0.14% by mass), and the ratio of the Al ₂ O ₃ concentration to the REM-O concentration in the inclusion is common in that the ratio Al ₂ O ₃ / REM-O is 0.25 or more. The type of refractory used is different.
In Comparative Example 3 in which a refractory containing no CaO was used, the nozzle was clogged during the first continuous casting, and “350 tons cannot be completely cast”.

In Example 14 in which the CaO content in the refractory (dolomite) is 10% by mass, “350 t of complete casting is possible”, and inclusions tend to adhere to the nozzle after the completion of casting. . In Example 18 in which the content of CaO in the refractory (ZCG) was 19% by mass, although “350 t complete casting was possible”, the nozzle closed when 350 t was cast.
From the above, it can be seen that the CaO content of the refractory is preferably 10% by mass or more in order to prevent nozzle clogging during continuous casting. Moreover, it turns out that the refractory containing a dolomite has the inclusion prevention effect higher than ZCG, although the content rate of CaO was low.

The fact that the refractory containing dolomite is most preferable as the refractory used in the present invention is also apparent from the following examination results.
In Examples 17, 14, and 11, the REM content in the molten steel was 0.0003 mass% or more (0.0035 to 0.0046 mass%), and the Al content in the molten steel was adjusted (0. 10 to 0.19 mass%) to the ratio _Al 2 _O 3 / _REM-O of the concentration of _Al 2 _{O 3} and REM-O concentration in inclusions and 0.25 or more, the CaO in any 10 wt% Although the refractory material contained above is used, Example 17 differs in that a ZCG refractory material is used, and in Examples 14 and 11, a refractory material containing dolomite clinker is used.

In Example 17 using the ZCG refractory, although it was “350 t complete casting possible”, the molten steel supply nozzle was blocked when 350 t was cast. On the other hand, in Example 14 using the refractory containing dolomite, “350 t complete casting is possible”, but inclusions tend to adhere to the inner surface of the nozzle after casting, and the second time without nozzle replacement. It was judged that continuous casting of 350 tons was not possible. Similarly, in Example 11 using the refractory containing dolomite, the nozzle after completion of the second continuous casting tended to be clogged, but was “350t complete casting twice possible”.
From the above results, it is understood that the refractory containing dolomite clinker is the most preferable among the refractories containing 10 mass% or more of CaO as the material of the refractory.

Next, the content ratio (W1 / W2) of both in the refractory mainly composed of CaO and MgO is examined.
In Examples 2, 3, 4, 6, and 9, the REM content in the molten steel is 0.0003 mass% or more (0.0005 to 0.0038 mass%), and the Al content in the molten steel is adjusted. (0.14 to 0.25 wt%) to the ratio _Al 2 _O 3 / _REM-O of the concentration of _Al 2 _{O 3} and REM-O concentration in inclusions and 0.25 or more, the CaO 10 wt% It is an example using the refractory containing the dolomite clinker contained above. The content of the refractory is 45 to 65% by mass for CaO and 25 to 50% by mass for MgO, and the ratio W1 / W2 of the CaO content W1 and the MgO content W2 is 0.90 or more and 2.60. Within the following range.
In any case, complete casting of 350 t could be performed continuously twice, and after the second continuous end, the molten steel supply nozzle was not blocked and no erosion was observed. Therefore, in any case, it was determined that “350 t complete casting 3 times or more is possible”.

Next, the MgO content in the refractory is examined.
In all of Example 9, Example 8, and Example 13, the content of REM in the molten steel is 0.0003 mass% or more (0.0029 to 0.0038 mass%), and Al in the molten steel is adjusted (0 .17～0.25 wt%) that the ratio _Al 2 _O 3 / _REM-O of the concentration of _Al 2 _{O 3} and REM-O concentration in inclusions 0.25 or more, CaO 10% by mass or more ( 60 to 75% by mass) Although common in that a refractory containing a dolomite clinker, which is a refractory contained, is used in the order of Examples 9, 8, and 13, the content of MgO in the refractory is 25. It has decreased to 20% by mass, 20% by mass, and 15% by mass, and accordingly, the content of CaO and C (graphite) is changed.

As the amount of MgO decreased, the tendency of melting damage became more prominent, and in Example 9, “350 t complete casting was possible three times or more”, but in Example 8, the second continuous casting After completion of the nozzle, the tendency of the nozzle to be damaged was observed, so that “350t complete casting was possible twice” remained. In Example 13, the tendency of the nozzle to be damaged was already observed after the completion of the first continuous casting. It was possible to cast completely.
From the above results, the lower limit value of the content of MgO in the refractory is required to be 15% by mass or more, preferably 20% by mass, more preferably capable of performing 350t continuous casting at least once. Preferably it is 25 mass%.

In Example 3, Example 10, Example 11, and Example 14, the content of REM in the molten steel is 0.0003 mass% or more (0.0031 to 0.0043 mass%), Al in the molten steel. the content was adjusted (0.13 to 0.21 wt%) of the ratio _Al 2 _O 3 / _REM-O of the concentration of _Al 2 _{O 3} and REM-O concentration in inclusions and 0.25 or more, Although it is common in the point using the refractory containing the dolomite clinker containing 10 mass% or more of CaO, the MgO amount of the refractory is 50 mass%, 60 mass% in the order of Examples 3, 10, 11 and 14, It has increased to 70 mass% and 75 mass%, and accordingly, the CaO content is decreased.

As the amount of MgO increases, the tendency of adhesion of inclusions to the nozzle becomes noticeable. The results of casting in the order of Examples 3, 10, 11, and 14 are also “full casting of 350 t or more 3 times or more in Example 3. In Example 10, since the nozzle clogging tendency was slightly observed after the end of the second continuous casting, it became “350t complete casting twice possible”. Since the nozzle clogging tendency was observed after the end of the continuous casting of the second time, "350t complete casting was possible twice", and in Example 14, the tendency of the nozzle to be damaged was already observed after the end of the first continuous casting. 350 tons can be completely cast. "
From the above, the upper limit of the content of MgO in the refractory must be 75% by mass or less, preferably 70% by mass, and more preferably 60% by mass, which allows 350t of continuous casting to be performed at least once. %, More preferably 50% by mass.

Next, the ratio W1 / W2 between the CaO content W1 and the MgO content W2 in the refractory is examined.
In all of Example 9, Example 11, Example 14, Example 8, and Example 13, the content of REM in the molten steel is 0.0003 mass% or more (0.0029 to 0.0043 mass%), The content ratio of Al in the molten steel was adjusted (0.13 to 0.25% by mass), and the ratio of the Al ₂ O ₃ concentration to the REM-O concentration in the inclusions was set to 0. Al ₂ O ₃ / REM-O. 25 or more, and common in that a refractory containing a dolomite clinker containing 10% by mass or more (10 to 75% by mass) of CaO is used. The values of W1 / W2 are in the order of Examples 9, 11, and 14. It has decreased to 2.6, 0.33, and 0.13. In connection with this, the tendency of the nozzles to close up becomes strong, and in the order of the above-described embodiments, “350t complete casting is possible 3 times or more” (Example 9), “350t complete casting is possible 2 times” (Example 11). ), “350 t complete casting is possible” (Example 14), the number of times that continuous casting was possible without replacing the nozzles was reduced.
From the above results, it can be seen that W1 / W2 is preferably 0.33 or more.

Next, Examples 9, 8, and 13 are compared. The value of W1 / W2 increases to 2.6, 3.0, and 5.0 in the order of Examples 9, 8, and 13. Along with this, the tendency of the nozzle to melt becomes more prominent. In the order of the above-described examples, “350t complete casting is possible 3 times or more” (Example 9), “350t complete casting is possible 2 times” (Example 8). ), “350 t complete casting is possible” (Example 13), the number of continuous castings without changing the nozzle was reduced.
From the above results, it can be seen that W1 / W2 is preferably 3.0 or less.

From the above examination results, it is important to balance the content of CaO which has an effect of suppressing inclusion adhesion but easily causes melting damage and MgO which exhibits a barrier effect of melting damage but easily causes adhesion. It can be seen that W1 / W2 is preferably 0.33 or more and 3.0 or less.

Next, the content of C in the refractory is examined.
In Example 3, Example 2, Example 1, and Example 12, the content of REM in the molten steel is 0.0003 mass% or more (0.0032 to 0.0038 mass%), Al in the molten steel. the content was adjusted (0.13 to 0.21 wt%) of the ratio _Al 2 _O 3 / _REM-O of the concentration of _Al 2 _{O 3} and REM-O concentration in inclusions and 0.25 or more, Common in that a refractory containing dolomite clinker containing CaO of 10% by mass or more (40-50% by mass), CaO and MgO being approximately the same amount (0.90 ≦ W1 / W2 ≦ 1.11) is used. However, the content of C in the refractory increases in the order of Examples 3, 2, 1, and 12 to 1% by mass, 4% by mass, 10% by mass, and 20% by mass.

As the content of C increases, the tendency of the nozzle to melt is increased in the casting situation, and the casting results are in the order of Examples 3, 2, 1, 12 and in Examples 3 and 2, “350 tons of complete casting 3 times or more. However, in Example 1, since the nozzle was slightly damaged after the second continuous casting was completed, it became “350t complete casting twice possible”, and in Example 12, the first time Since the nozzle had already been melted after the end of continuous casting, “350 tons of complete casting was possible”.
In addition, although the experimental conditions differ in that CaO and MgO of the refractory are not substantially the same amount, as in Examples 9 and 10 in which the content of C is 5% by mass, 350 t of the refractory can be obtained without replacement of the molten steel supply nozzle. In some cases, complete casting could be performed twice or more in succession.
From the above, the upper limit of the C content in the refractory material needs to be 10% by mass or less, preferably 5% by mass, and more preferably 4% by mass, capable of performing at least one 350t continuous casting. It can be seen that it is.

Next, the case where the arrangement | positioning to the molten steel contact surface of the molten steel supply nozzle inner surface of the refractory containing 10 mass% or more of CaO differs is demonstrated based on Example 4, Example 15, and Example 16. FIG. In these examples, the same refractory (containing dolomite clinker, CaO content: 45 mass%, MgO content: 49 mass%, C content: 1 mass%) is used. As shown in FIG. 2 (A), the refractory on the inner surface of the nozzle is shown in FIG. 2 (B) in Example 15, and as shown in FIG. 2 (C) in Example 16. , Respectively.
In all of Examples 4, 15, and 16, the result of the continuous casting test was determined to be “350t complete casting 3 times or more possible”.
In any case, no clogging of the nozzle, which is a practical problem, was observed, and in these examples, no influence due to the difference in the arrangement of the refractories was observed.

The present invention is not limited to the above-described embodiment, and can be changed without changing the gist of the present invention. For example, some or all of the above-described embodiments and modifications are possible. The case where the continuous casting method for steel of the present invention is configured by combining the above is also included in the scope of the right of the present invention.
For example, the continuous casting machine used in the above embodiment may be a curved type as shown in FIG. 1, but it is of course possible to use a vertical bending type continuous casting machine.
Further, the refractory used in the embodiment is not limited to dolomite clinker, and any refractory having a CaO and MgO content W1, W2, or a ratio W1 / W2 within the above range may be used. it can.
Furthermore, the type of steel used for continuous casting is not limited to the steel for non-oriented electrical steel sheets exemplified in the examples, and the present invention is applicable to continuous casting of any steel whose material properties are improved by the addition of REM. It is.

As described above, the present invention can be used for continuous casting of steel such as steel for non-oriented electrical steel sheets to which REM is added in order to improve material properties, and the life of a molten steel supply nozzle is extended. It is useful for stable operation of continuous casting machines.

It is a schematic diagram of the continuous casting machine to which the continuous casting method of steel concerning one embodiment of the present invention is applied. (A)-(C) is explanatory drawing which shows the arrangement position of the refractory of the nozzle used for the continuous casting method of the steel, respectively.

Explanation of symbols

10: continuous casting machine, 11: molten steel, 12: ladle, 13: first molten steel supply nozzle, 14: tundish, 15: second molten steel supply nozzle, 16: mold, 17: slab, 18: casting Piece support roll, 19: Cast piece cooling device (spray), 20: Solidification completion point (crater end), 21: Cast piece drawing roll, 22: Cast piece transport roll, 23: Nozzle body, 24: Refractory, 25: Hot water surface, 26: Discharge port

Claims (6)

In a continuous casting method of steel, molten steel is injected into a mold through one or more nozzles, and a slab is continuously drawn out from the lower part of the mold.
Wherein it comprises a molten steel is 0.0003 mass% or more REM (rare earth element), and, _Al 2 _{O 3} concentration in inclusions in the molten steel (mass%) and REM oxide concentration (wt%) ratio Al ₂ The O ₃ / REM oxide is adjusted to be 0.25 or more, and at least one of the nozzles is provided with a refractory containing 10% by mass or more of CaO on at least a part of the inner surface in contact with the molten steel. A continuous casting method for steel, characterized by comprising: The continuous casting method of steel according to claim 1, wherein the nozzle is a first molten steel supply nozzle disposed between a ladle and a tundish, and a second used between the tundish and the mold. Any one of a molten steel supply nozzle, a flow rate adjusting nozzle disposed adjacent to the second molten steel supply nozzle, and a connection nozzle for connecting any one of these nozzles to the corresponding ladle or the tundish, respectively. A continuous casting method for steel characterized by the above. 3. The continuous casting method for steel according to claim 1, wherein the refractory includes CaO and MgO as main components. 4. 4. The continuous casting method for steel according to claim 3, wherein the refractory has an MgO content of 20% by mass or more and 70% by mass or less, and a ratio W1 / CaO content W1 and MgO content W2. W2 is 0.33 or more and 3 or less, The continuous casting method of steel characterized by the above-mentioned. 5. The steel continuous casting method according to claim 4, wherein the content of C in the refractory is 0.1 mass% or more and 10 mass% or less. In the continuous casting method of the steel according to any one of claims 1 to 5, the molten steel is 0.001 mass% or more and 0.01 mass% or less of C, 0.1 mass% or more and 7 Containing not more than mass% Si, not less than 0.1 mass% and not more than 3 mass% Al, not less than 0.0003 mass% and not more than 0.05 mass% REM, and the balance Fe and inevitable impurities, A continuous casting method for steel, wherein the slab is rolled and finally used as steel for non-oriented electrical steel sheets.

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