JP2696464B2 - Alloy enrichment method for molten steel in continuous casting mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for enriching molten steel in a continuous casting mold.

[0002]

2. Description of the Related Art Generally, in continuous casting of steel, molten steel is continuously poured into a water-cooled mold whose top and bottom are open, and the casting is controlled at a predetermined drawing speed while controlling the amount of the molten steel. The molten steel surface of the continuous casting of steel comes in contact with a mold lubricant called a powder composed of components mainly composed of oxides such as SiO ₂ , CaO, and Al ₂ O _3. In order to improve the surface quality of the cast slab, it is important to inject the molten metal at a fixed surface level in order to improve the surface quality of the slab. When the powder is involved, the powder is a so-called non-metallic inclusion because the powder is an oxide mainly composed of the above components,
Since the strength, ductility, and machinability are significantly reduced, this is a major problem in quality. Furthermore, since the steel surface is the position where the steel starts to solidify first, turbulence in the metal surface directly induces surface irregularities and causes flaws.

[0003] From such a background, in order to control the molten metal level in the mold to a constant level, a molten metal level detecting means is provided, and the molten steel injection means such as a stopper or a sliding gate is controlled by this signal. It is no exaggeration to say that this control system is indispensable for satisfying quality in today's strict product quality.

[0004] As a means for detecting the molten metal level, there is, for example, one using eddy current. This consists of a magnetic field generating coil and a magnetic field detecting coil.An alternating current flows through the generating coil to generate eddy current in the molten steel, which is a conductor, and the position of the conductor is determined by the current induced in the detecting coil from the magnetic field generated by the eddy current. The measurement is based on the fact that the induced eddy current and magnetic field change depending on the distance from the conductor. In addition to this, there are methods of transmitting γ-rays, methods of estimating the level of the molten metal surface from temperature information by providing a thermocouple in a mold, and the like, but the eddy current formula is the most common in terms of danger of exposure and responsiveness. Became used.

[0005] In general, continuous casting is performed by pouring molten steel from a ladle into a mold through a pouring nozzle through an intermediate vessel called a tundish. At this time, since the components of the molten steel to be cast are adjusted in advance, it is possible to obtain a slab having uniform components with a high yield. In addition, it is most efficient to increase the ladle capacity in order to further improve the yield and to manufacture the ladle in a large lot, and to increase the capacity in Japan and overseas.

[0006]

However, in recent years, the product configuration has been diversified and high value-added products are not always large in market size, and are often in small lots. That is, it is a small lot multi-product type. Even in such a situation, there is an urgent need for efficient production, and production of high-performance steel at low cost is required. However, since the casting amount is determined by the capacity of the ladle, a great advantage can be enjoyed if components can be adjusted immediately before casting, that is, in a mold, for efficient production in a small lot. The inventors of the present invention have studied from the above viewpoints that the ladle molten steel can be used as a base molten steel to change the composition.

In order to achieve high functionality of steel materials, alloy components are often added, and the content is often about 0.1 to 2% by weight. Therefore, when manufacturing a slightly different component system, the alloy element may be added in a necessary casting amount after the base components are prepared. On the other hand, alloy components
There is a special steel containing 20% by weight. In this case, it is difficult to adjust the amount in the mold because the amount of addition is greatly different. However, even in high alloy steel, there are not a few elements to be added as trace elements. For example, C, Si, Mn, S, Pb, Ti,
B, Nb, Cr, V and the like.

As a method for adjusting the composition by adding a small amount of an alloy element, use of a tundish is considered. However, the tundish capacity is generally about several tens t, and the lot is relatively large. Further, since it takes time to adjust the components, compensating for the temperature drop during this time requires an increase in the temperature of the molten steel in the refining process and a heating device in a tundish. An increase in the temperature of the molten steel also causes an increase in the temperature in the preceding process, which promotes the consumption of refractories and increases costs. Further, the heating device causes an increase in equipment cost and power consumption, all of which increase costs. The cast slab cannot be used as a product due to inclusions, shrinkage cavities, etc. at the beginning and end of the casting, and the yield is generally extremely low.

[0009] On the other hand, the addition of the alloy in the mold is premised on stabilizing the charging, but the merit is extremely large since the sensible heat of the molten steel to be cooled is used.

As an alloy addition in a mold, Japanese Patent Publication No. Sho 55
As disclosed in Japanese Patent No. -14847, there is a method in which a wire containing an alloy component is charged into a mold. In this method, predetermined components are charged by controlling the mold size, the casting speed, and the wire charging speed. However, this does not mention the molten metal level detecting means and the electromagnetic stirring device, and does not sufficiently consider the characteristics of casting. That is,
The wire inserted for adjusting the alloy component greatly disturbs the molten metal level, giving a large disturbance to the molten metal level detecting means, and it is virtually impossible to achieve the constant molten metal level control. As described above, the slab quality is not guaranteed.

Japanese Patent Publication No. 63-6110 discloses a technique for changing the molten steel component in a mold and utilizing electromagnetic stirring in the mold.
There is one disclosed in Japanese Patent Publication No. 7 (1995). This is because a molten steel having a low concentration of some or all components with respect to a target slab composition is injected into a mold, and the molten steel injected into the mold is subjected to electromagnetic force at a flow rate of 0.2 to 2 m / sec. This is a continuous casting method of a sound slab having a sound surface in which an additive is added in a linear or band shape so as to obtain a target slab composition in a molten steel in a portion having a low stirring strength while providing forced stirring.

This is intended to change the composition of the molten steel in the mold. However, as described above, when the forced stirring is performed by the in-mold stirring device, the surface of the molten metal is disturbed, so that surface flaws are frequently generated and the soundness of the surface is not completely guaranteed. In particular, when the stirring flow rate exceeds 0.5 m / sec, the molten metal level fluctuates remarkably, leading to breakout as well as surface defects. On the other hand, if the speed is 0.5 m / sec or less, sufficient stirring cannot be obtained, and a uniform distribution of alloy elements cannot be guaranteed. Therefore, under stirring by the electromagnetic force of molten steel, the position where the linear or band-shaped additive is introduced is extremely important.

The present inventors have determined that the mold size is 247 mm × 3.
Using a mold having a molten steel stirrer, a vortex flow level controller and a mold having the same size of 162 mm x 162 mm, a cross section of 00 mm was used to investigate the influence including the size of the mold. As a result, when the wire feeding position was determined completely independently of the detection means and the stirring device, the level change was remarkable, and the level change before the wire feeding was about ± 2 mm with respect to the static level. It reached ± 6 to 10 mm at the same time as feeding. The level change speed of the molten metal was about 1 mm / sec before the wire was charged, and reached 4 mm / sec after the wire was charged. Of course, in the slab cast in such a situation, breakout (a facility accident in which the slab breaks and internal molten steel blows out) frequently occurred. Further, even when the breakout was not reached, many quality abnormalities such as powder biting and rough skin occurred on the slab surface. Therefore, it is indispensable to establish a technology to achieve both the wire feeding and the stable surface.

Next, as an applied technique for adding an alloy component to molten steel in a mold, there is production of a composite steel material, for example, disclosed in Japanese Patent Publication No. 4-16257. However, this does not show a technique for combining with a level detecting means or an electromagnetic stirrer which is substantially important for casting, and does not show a manufacturing method which is combined with a level detecting means and stirring in a mold.

According to the present invention, when a small lot product is manufactured by finely adjusting the alloy components having similar mother molten steel components to produce different small lot products, even if a wire is put into a mold, a large molten metal level does not change. And to provide a method for efficiently manufacturing at low cost while maintaining high quality.

[0016]

The gist of the present invention is as follows.

[0017] Casting is performed using a mold equipped with a molten steel stirring device by electromagnetic force and a molten metal level detection control means for automatically controlling the molten steel surface, and at the same time, a wire different from the molten steel component or the inside of the molten steel in the molten steel in the mold is formed. When a wire containing an alloy component is charged to change all or a part of the molten steel component in the mold, if the mold is a rectangle having a size of a (mm) × b (mm), along the inner wall of the mold , Let L (mm) be the distance from the molten metal level detecting means provided near the inner wall of the mold toward the upstream of the molten steel flow induced by the molten steel stirring device to the wire injection position near the inner wall of the mold. A method for enriching molten steel in a continuous casting mold, wherein the steel is put into a position satisfying the following conditions.

[0018]

## EQU3 ## 2 (a + b)> L ≧ 250 (mm)

Casting is performed using a mold equipped with a molten steel stirring device by electromagnetic force and a molten metal level detection control means for automatically controlling the molten steel surface, and at the same time, a wire different from the molten steel component or the inside of the molten steel in the molten steel in the mold is formed. When a wire containing an alloy component is charged to change all or a part of the molten steel component in the mold, if the mold is circular with a radius of r (mm), it is provided along the inner wall of the mold and near the inner wall of the mold. and the distance from the melt surface detection means to the wire loading position of the mold near the inner wall toward the upstream side of the flow of molten steel induced by solution steel stirrer L
(Mm), and a wire is charged into a position satisfying the following condition (4): A method for enriching molten steel in a continuous casting mold.

[0020]

## EQU4 ## 6.28r> L ≧ 250 (mm)

[0021]

The present invention will be described in detail with reference to the drawings.

FIG. 1 (a) is a schematic view of the addition of a wire in a mold in continuous casting, and FIGS. 1 (b) and 1 (c) are views of A in FIG. 1 (a).
FIG. 4B is a plan view of a mold showing a section A, in which FIG. 4B shows the relationship between the wire insertion position and the installation position of the molten metal level detecting means when the mold has a rectangular cross section, and FIG. here,
The wire feeding position and the position of
Both are near the inner wall of the mold.

The molten steel 2 is poured from the ladle 1 into the tundish 3 using the molten steel pouring device 1a, poured into the water-cooled mold 5 through the stopper 3a and the pouring nozzle 4, and cast as a slab in the casting direction 15. At this time, the molten steel 2 is given a forced flow by the molten steel stirring device 6 to form a molten steel flow 13. Further, the wire 9 is forcibly inserted into the mold 5,
Fluctuations 14 are inevitably generated at the wire feeding position and in the downstream stream, which causes the powder 10 to be caught. Further, even if no entanglement occurs, when the molten metal surface 7 comes into contact with the water-cooled mold 5 due to the molten metal surface turbulence 14, the molten steel and the mold 5 may seize and cause breakout. When the wire 9 is sufficiently mixed in the molten steel 12 in the mold, the entire solidified shell 11 becomes a material containing alloy elements uniformly. On the other hand, when the feeding speed of the wire 9 is increased, the wire 9 is melted in the deep region of the molten steel 12 in the mold, so that the solidified shell 11 already formed at the upper portion does not contain any alloying element, and is different from the deep molten steel 12. Component, and a composite material can be obtained.

In FIGS. 1 (b) and 1 (c), L is the distance from the molten metal level detecting means 8 to the upstream side with respect to the molten steel flow 13 caused by agitation, and to the wire 9 feeding position along the inner wall surface of the mold. . In the case of a mold having a rectangular cross section, as shown in FIG. 1 (b), assuming that the mold width a and the mold thickness b, 2 (a + b)> L
The wire 9 is put in a range satisfying ≧ 250 (mm). In the case of a mold having a circular cross section, as shown in FIG. 1 (c), assuming that the mold radius is r, 6.28r> L ≧ 2
The wire 9 is put in a range satisfying 50 (mm).

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment using the continuous casting machine shown in FIG. 1 will be described below.

C used was 0.05 to 0.1.
0 wt%, Si is 0.10 wt% or less, Mn is 0.68
1.02% by weight, P is 0.020% by weight or less, S is 0.025% by weight or less, and Al is 0.045% by weight or less.

The mold size is set to 247 mm × 300 mm and φ188 where the fluctuation of the molten metal level is most likely to occur and the operation is difficult.
mm. Therefore, a = 300 mm and b = 247
mm, r = 94 mm. 200 molten steel per channel
２270 t, and the average was 250 t. Casting continued as long as no breakout occurred at each test level.

As an alloying element, S was added into the mold to enrich the concentration to a target range of 0.2 ± 0.5% by weight.
S was used by being enclosed in a φ8 mm iron (0.17 wt% C steel) coated wire. The addition of S in the mold by the S-containing wire is performed by dissolving the molten steel in the mold at a depth of about 1 m from the molten metal by dissolving in the vicinity of the molten metal about 0.3 m from the molten metal and adding S to the entire molten steel in the mold. S was added to a part to carry out casting in which the solidified shell and the molten steel component in the mold were different. The melting depth of the wire can be easily changed by changing the feeding speed of the wire. Consider the heat content of the wire, such as the shape, melting point, S content of the wire, the melting point of the coating material and the amount of alloying element added into the mold, and the material balance, and select the wire according to the target concentration and wire melting position. it can.

The S-containing wire was guided by the guide device to the vicinity of the mold, and the horizontal deviation in the mold was within a circle of about 20 mm. The wire was wound in a coil shape and could be supplied continuously, and was fed mechanically by a feed roll or the like.

The molten steel in the mold was controlled by a stopper provided on the tundish, and the stopper was operated so as to keep the signal of the vortex type molten metal level detecting means in the mold constant. The material of the stopper is an MgO refractory, and the injection nozzle is an alumina graphite refractory.

FIG. 2 is an explanatory view showing the effect of the wire insertion position on the amount of fluctuation in the level of the level detecting means for the rectangular mold. The level change was observed and recorded based on continuous measurement analog data detected and measured by the level detector.

From the figure, it can be seen that if the wire input position is farther from the metal level detecting means or if the wire input position is located on the downstream side of the metal level detecting means, the level change amount decreases. Therefore, in order to avoid the disturbance caused by the insertion of the wire into the fluctuation amount of the molten metal level at the molten metal level detection position, the wire injection position is set to be 250 mm or more upstream of the molten metal level detecting means (L
≧ 250 mm) or downstream (2 (a + b)> L)
There is a need.

FIG. 3 is an explanatory diagram showing the effect of the wire feeding position on the incidence rate of slab surface flaws in a rectangular mold.
From the figure, it can be seen that the slab surface flaw is strongly affected by the wire feeding position as well as the molten metal level variation. Therefore, the same conditions as those for ensuring the stability of the molten metal surface are required for flaw prevention.

FIG. 4 is an explanatory diagram showing the effect of improving the breakout occurrence rate for a rectangular mold. The breakout occurrence rate was represented by the number of occurrences per 10,000 t of the casting amount from the total casting amount up to the breakout. Since the average is 250 t per channel, this corresponds to the occurrence rate per 40 channels.

It is known that breakout occurs due to turbulence in the molten metal level, and the incidence increases when the wire insertion position is brought closer to the molten metal level detecting means. This is also because the amount of molten steel is adjusted by the stopper based on the signal of the molten metal level detecting means, so that the steering tends to be unstable due to disturbance.
Therefore, in order to prevent a catastrophic operation trouble such as a breakout beforehand, it is necessary to carefully determine the wire insertion position. Also in this regard, it is essential that the wire input position is located at a distance of 250 mm or more downstream or upstream of the molten metal level detecting means.

FIG. 5 is an explanatory diagram showing the breakout occurrence rate when the shape of the mold is circular. Similarly, in the case where the mold is circular, it is necessary that the wire input position is L at a distance of 250 mm or more or downstream (6.28r> L ≧
250 mm).

As described above, in both the rectangular and circular continuous castings, the S content and the variation of the cast slab obtained after the casting are 0.21 ± 0.5% with respect to the target S concentration of 0.2 ± 0.5% by weight. 0.0
It was confirmed that the hit was accurate with a high accuracy of 2% by weight. In addition, even when a part of the molten steel in the mold is changed in composition, the above compositional ratio is cleared, and the thickness of the solidified shell at the outer peripheral portion where the alloy element is not enriched is 10 ± 1 mm with respect to the target of 10 ± 3 mm. .
A result of 5 mm was obtained.

[0038]

According to the present invention, when an alloy element is added to all or a part of molten steel in a mold by using a continuous casting machine equipped with a molten metal level detecting means and a molten steel stirring device by electromagnetic force in the mold, electromagnetic induction is caused by electromagnetic stirring. By taking the molten steel flow direction into consideration and setting the position of the molten metal level detecting means and the wire for adding the alloy element in the proper range according to the present invention, stable operation and improvement of surface quality can be achieved at the same time. Therefore, the production cost can be reduced by stable operation and high quality.

[Brief description of the drawings]

FIG. 1 is a view showing an apparatus for feeding a wire into a mold in continuous casting, (a) is a side view, (b) is a plan view of a rectangular mold, and (c) is a plan view of a circular mold. is there.

FIG. 2 is an explanatory diagram showing an influence of a wire feeding position on a molten metal level variation amount of a molten metal surface detecting means position in a rectangular mold.

FIG. 3 is an explanatory diagram showing the effect of the wire feeding position on the slab surface flaw occurrence rate for a rectangular mold.

FIG. 4 is an explanatory diagram showing an improvement effect of a breakout occurrence rate for a rectangular mold.

FIG. 5 is an explanatory diagram showing an improvement effect of a breakout occurrence rate for a circular mold.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ladle 1a molten steel pouring device 2 molten steel 3 tundish 3a stopper 4 pouring nozzle 5 water-cooled mold 6 molten steel stirring device 7 molten metal surface 8 molten metal surface detecting means 9 wire 10 powder 11 solidified shell 12 molten steel in molten metal 13 molten steel flow 14 molten metal surface 15 Casting direction L Distance from the molten metal level detecting means along the inner wall of the mold to the wire injection position toward the upstream side of the molten steel flow induced by the molten steel agitator a Slab width b Slab thickness r Slab radius

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Morio Hosaka 12 Nakamachi, Muroran, Hokkaido Nippon Steel Corporation Muroran Works (72) Inventor Masaru Abe 12 Nakamachi, Muroran, Hokkaido Nippon Steel Corporation Muroran Inside steelworks (56) References JP-A-57-75273 (JP, A)

Claims (2)

(57) [Claims] Casting is carried out using a mold provided with a molten steel stirring device by electromagnetic force and a molten metal level detection control means for automatically controlling a molten steel surface, and at the same time, a wire or a wire different from the molten steel component in the molten steel in the mold. When a wire containing an alloy component is introduced into the mold to change all or a part of the molten steel component in the mold, if the mold is a rectangle having a size of a (mm) × b (mm), the shape is changed along the inner wall of the mold. The distance from the molten metal level detecting means provided near the inner wall of the mold to the upstream of the molten steel flow induced by the molten steel stirring device to the wire injection position near the inner wall of the mold is defined as L (mm). A method for enriching an alloy of molten steel in a continuous casting mold, wherein the method is put into a position satisfying Equation 1. ## EQU1 ## 2 (a + b)> L ≧ 250 (mm) 2. Casting is performed using a molten steel stirring device by electromagnetic force and a mold equipped with a molten metal level detection control means for automatically controlling the molten steel surface, and at the same time, a wire or a wire different from the molten steel component in the molten steel in the mold. When a wire containing an alloy component is introduced into the mold to change all or a part of the molten steel component in the mold, if the mold has a circular shape with a radius of r (mm), along the mold inner wall, in the vicinity of the mold inner wall The distance from the molten metal level detecting means provided to the upstream of the molten steel flow induced by the molten steel stirring device to the wire injection position near the inner wall of the mold is represented by L.
(Mm), and a wire is charged into a position satisfying the following condition (2): A method for enriching molten steel in a continuous casting mold. ## EQU2 ## 6.28r> L ≧ 250 (mm)