JP3124469B2 - Method for producing slabs with few inclusion defects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing molten steel of carbon steel by a continuous casting method, and more particularly to a method for producing a slab without inclusion defects.

[0002]

2. Description of the Related Art In recent years, defects in inclusions in cast slabs manufactured by a continuous casting method have been extremely reduced. This is the result of the technical improvement of the deoxidation method at the molten steel stage and the measures against various inclusions in continuous casting were effective (No. 126).
・ 127th Nishiyama Memorial Technical Lecture "High Purity Steel" Japan Iron and Steel Association. 1998). However, in the ladle changing section, when the amount of molten steel in the front ladle was reduced, the slag that had been on the molten steel flowed into the tundish through the nozzle below the ladle, and this became an inclusion in the molten steel. Become. Such inclusions caused by slag tend to elongate during rolling because their melting points are relatively low. If a long elongated inclusion is present in the steel material, cracks are likely to occur starting from the inclusion when performing a process of applying a tensile force in a direction perpendicular to that direction. In particular, in the case of a beverage can in which an organic film is stuck on the inside and processed, the influence is remarkable, and a collapse defect occurs.

Techniques for preventing such defects include:
When smelting steel, MgO is charged in a converter and M
A technique has been proposed in which gO is increased to prevent this slag from becoming a low-melting inclusion even when the slag is entrained in molten steel (Japanese Patent Application No. 6-090378). In addition, there is also proposed an invention in which a Mg alloy is added to molten steel through a gas injection lance together with an inert gas during secondary refining (Japanese Patent Application No. 6-131).
090380). However, such a technique is effective for detoxifying the inclusions of molten steel before continuous casting, but slag is introduced into the slag corresponding to the ladle exchange part in continuous casting by the aforementioned slag entrainment. Since the amount of system inclusions increases in large quantities, almost no effect can be expected. For this reason, the slab corresponding to the ladle changing section is treated not to be used for the beverage can, which is the original purpose, resulting in a large cost loss.

[0004]

DISCLOSURE OF THE INVENTION The present invention is to provide a continuous casting method by adding an appropriate amount of Mg during ladle replacement.
It is an object of the present invention to provide a method for producing a slab that produces harmless inclusions even when ladle slag flows into a tundish and has no inclusion defects.

[0005]

In order to achieve the above object, the present invention has the following features. When casting molten steel of carbon steel by the continuous casting method, a tube made by covering an alloy containing Mg with an iron coating material is provided on the shaft of the tundish stopper, and air-sealed at the upper end of the shaft. Through the ladle to the molten steel in the immersion nozzle.
A method for producing a raw material slab for a beverage can having few inclusion defects, wherein the slag is added only for a predetermined period before and after the change point . When casting molten steel of carbon steel by the continuous casting method, a wire made by covering an alloy containing Mg with an iron coating material is provided on the center axis of a rod-shaped refractory circular pipe dipped inside a tundish. Into the molten steel in the immersion nozzle through a tube
A method for producing a raw material slab for beverage cans having a small number of inclusion defects, wherein the material is added only for a predetermined period before and after the time of replacement . Before the ladle replacement point
During the later specified period, from 10t before the end of the injection of the front pot, from the rear pot
Characterized in that the injection is until 40 t after the start of injection.
The production of material slabs for beverage cans with few inclusion defects as described in
Construction method.

[0006] The range of components of the steel which is the subject of the present invention is as follows. C: 0.001 to 0.2% by weight, Mn: 0.1 to 0.5
% By weight, Si: 0.005 to 0.5% by weight, P: 0.0
01 to 0.05% by weight, S: 0.001 to 0.05% by weight, Al: 0.001 to 0.08% by weight, N: 0.00
0.05 to 0.005% by weight, and Ti, Nb, V, Cr, Mo, Cu, Ni, Zr,
One or more of B and Ca may be contained in an amount of 0.05% by weight or less.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors first investigated in detail the inclusions of a slab corresponding to the position at the time of ladle replacement in the continuous casting method, and found that the number of inclusions changed as shown in FIG. Was. That is, the inclusions in the slab are divided into alumina-based and non-alumina-based ones. Among them, the inclusions that are problematic as a material for beverage cans are non-alumina, and the change was investigated. The number of non-alumina-based materials increased remarkably during ladle replacement. Such non-alumina-based inclusions are caused by slag, and are classified into spherical inclusions and amorphous inclusions according to the form. Investigation of the composition of the inclusion revealed that CaO
-Al ₂ O ₃ -based inclusions having a melting point of about 1400 ° C. for spherical inclusions and about 1500 to 20 for amorphous inclusions
00 ° C.

When the melting point of the inclusions is about 1600 ° C. or less, since the inclusions are elongated during rolling, as described above, when performing a process of applying a tensile force in a direction perpendicular to the direction in which the inclusions extend, Cracks tend to occur starting from inclusions. In particular, in the case of a beverage can which is processed by sticking a resin film on the inner side, the effect is remarkable, and a broken body defect occurs. Therefore, it was found that it was necessary to minimize the number of low melting point inclusions between the spherical inclusions and the amorphous ones. As a method for this purpose, first of all, prevention of inflow of ladle slag can be considered, but for that purpose, special equipment needs to be provided in the ladle, and ladle slag is prevented from flowing in. Therefore, if you finish the ladle injection early,
The problem that molten steel remains in the ladle and the molten steel yield deteriorates is expected.

Therefore, the present inventors have conceived of increasing the melting point of inclusions by adding a strong deoxidizing element to the low-melting inclusions caused by slag. As a result of a thermodynamic study, an element that increases the melting point of CaO—Al ₂ O ₃ inclusions
Zr, Ca, and Al.
Has the effect of increasing the melting point with a small amount of addition, and has a very small amount of dissolution in molten steel, so that it is hardly affected by reoxidation. Therefore, Mg is suitable as an additive element.

Next, in order to confirm the results of the thermodynamic study and to determine the Mg concentration for obtaining the optimum effect, an experiment was conducted on the steels shown in Table 1 on a laboratory scale. FIG. 2 shows the effect of Mg concentration on the melting point of inclusions. As the Mg concentration increases, the MgO concentration in the inclusions increases, and the melting point also increases. The reason why the inclusion has a melting point of 1600 ° C. or more, which is a measure of difficulty in elongation during rolling, indicates that the Mg concentration is 5 ppm or more. Therefore, if Mg is added so as to have a concentration of 5 ppm or more, inclusions may be harmless to the broken body during can making. FIG. 3 shows the effect of the Mg concentration on the size of the inclusions. As the Mg concentration increases, the size of the inclusions becomes smaller. This is also an advantageous inclusion condition for a broken cylinder during can making. However, when the Mg concentration is increased, the particle size of the inclusions is increased. This is because the probability of aggregation and coalescence increases because the number of MgO-based inclusions increases. Therefore, an appropriate Mg concentration range is 5 ppm to 50 p.
pm.

[0011]

[Table 1]

Next, regarding the method of addition in an actual continuous casting machine, the Mg alloy is added to the molten steel only at the time of ladle replacement, so that addition to the tundish is desirable. However, even if the Mg alloy is directly added to a large tundish having a capacity of 40 to 80 t, it is difficult to make it uniform in molten steel. This is because there are various flows in the tundish, and the flows are not always uniform like a piston flow. As a method of adding an alloy in such a case, one of the present inventors has disclosed a technique in which an alloy wire is first added from the shaft of a tundish stopper and melted in molten steel in an immersion nozzle. Kaihei 6-299286). According to this method,
Since the alloy in a narrow space in the immersion nozzle is dissolved, it is possible to uniform mixing of the molten steel, the probability of contact with the CaO-Al ₂ O ₃ inclusions of slag caused contained in molten steel be very high , The melting point can be increased.

In addition, the timing of addition should be limited only to a position where slug-based inclusions become a problem from the viewpoint of minimizing the cost of Mg. In other words, the amount of molten steel in the ladle before the ladle replacement becomes very small, the timing at which the slag in the ladle flows into the molten steel in the tundish is the start of addition, and the timing after the ladle replacement. The time at which the molten steel injection into the pot is started and the influence of the slag that has flowed is eliminated is the addition end timing. We have:
Investigating these timings in detail,
The timing at which the slag started to flow was found to vary considerably and was found to be well before the end of the front pan. However, the initial inflow was slight, and it was found that the inflow that had a significant adverse effect on the inclusions was at a time when the molten steel amount of the ladle was about 10 t. On the other hand, variations were also observed in the period during which the inflowed slag had an adverse effect as inclusions, but the time at which the inclusions had no significant adverse effect was at the latest when the injection amount of the rear pan exceeded 40 t. understood. Therefore, the timing of adding Mg is preferably from 10 t before the end of the front pot to 40 t after the injection of the rear pot.

Next, the reason for defining the conditions of the present invention will be described. The target steel type may be any type of carbon steel. However, considering the steel composition range of the steel material actually used, the following composition range is obtained. Since C is an indispensable element for imparting the strength of steel, the lower limit is 0.001% by weight, and the upper limit is 0.2% by weight as the maximum amount of carbon used in the plate for processing. Also, Mn is necessary for obtaining strength and the lower limit is 0.1% by weight in order to exert its effect, and the upper limit is 0.5% by weight in consideration of workability. Although Si may not be required depending on the application, the lower limit is set to 0.
005% by weight, and the upper limit is 0.5% by weight in consideration of workability.

Since P is a harmful element to steel, its upper limit is preferably as low as 0.05% by weight, and is preferably as small as possible. However, considering the removal cost, the lower limit of 0.001% by weight is practical. Similarly, S often causes harm to the product characteristics, and is desirably as low as possible. However, considering the removal cost, the lower limit of 0.001% by weight is practical. The upper limit is 0.05% by weight to prevent cracking during continuous casting. Since Al is generally used as a deoxidizing element, it is in the range of 0.001 to 0.08% by weight.

[0016] Mg is an important element of the present invention, but in the present invention, it is added only to a specific part of the ladle replacement.
The average component need not be specified. here,
The appropriate Mg concentration in the slab portion corresponding to the ladle changing part position will be described. From the results of the above-described laboratory experiments, a concentration of 5 ppm or more is required in order to achieve a desired effect on inclusions. However, when the Mg concentration becomes very large, the size of the inclusions becomes large.
ppm. In an actual manufacturing process, the added elements are not necessarily included in the 100% molten steel. Therefore, it is necessary to add extra elements in consideration of the yield. Particularly, a metal having a very high vapor pressure such as Mg, when added to molten steel, causes a very low yield due to evaporation. Therefore, from many trials, an appropriate yield should be grasped so that the Mg concentration is in a desired value range. In addition, Ti, Nb, V, Cr, Mo, C
One, two or more of u, Ni, Zr, B, and Ca may be added in an amount of 0.
It may contain up to 05% by weight.

As a method of realizing this, as defined in the present invention, a rod-shaped refractory material circle formed by processing an Mg alloy into a wire and immersing it in a tundish stopper or a tundish of a continuous casting. It can be realized by a method of directly adding the molten steel in the immersion nozzle through a tube (tube) loaded in the tube.

The method of adding the Mg alloy wire of the present invention will be described below, particularly with reference to the addition method using a tundish stopper. FIG. 4 is a diagram showing an outline around a continuous casting machine in the addition method of the present embodiment. The molten steel in the ladle 1 is injected into the tundish 4 by the long nozzle 2, and the molten steel 3 in the tundish 4 is cast into the mold 7 by the immersion nozzle 6. The Mg alloy wire 9 of the present invention is supplied to the space 10 in the immersion nozzle 6 through a tube 12 provided through the center of the tundish stopper 5, where it is melted and added to the molten steel. Mg
Molten steel containing, in contact with inclusions of slag resulting suspended in the molten steel in the immersion nozzle becomes a high melting point of CaO-Al ₂ O ₃ -MgO based inclusions by reducing or aggregation coalescence, a mold Entrained in the solidification shell during solidification at Thus, in the present invention, the narrow space 1 of the immersion nozzle 6
In order to add the Mg alloy wire 9 to 0, compared to the conventional addition method in a tundish or a mold,
Better uniformity.

FIG. 5 shows an air seal mechanism of the present invention. In this figure, the tundish stopper 5
At the entrance of the wire 9 above the wire, the wire passes through the conducting portion 14 of the guide pipe 15 and is supplied from the distal end portion 17 of the tube. At the distal end of the tube is a threaded socket 16 of a guide pipe 15 which is fixed by this. The argon gas supplied to the inner tube is supplied from the inlet 13, and the inside of the tube becomes a non-oxidizing atmosphere. As this gas, other non-oxidizing gas can be used. The above-mentioned addition device can be changed in any way and can be appropriately selected depending on the continuous casting machine and its operation.

Next, the Mg alloy wire used will be described. Industrially available Mg alloys are Mg-Al alloy and Mg-Si alloy wires. This is covered with iron,
It is desirable that Mg be sufficiently immersed in molten steel before melting.

[0021]

EXAMPLE A carbon steel having the composition shown in Table 2 was continuously cast under the production conditions shown in Table 3, the number of inclusions in the obtained slab, the steel sheet obtained by rolling the slab, and the raw material We investigated the result of making a can. The investigation was performed under the manufacturing conditions shown in 1) below. The method for evaluating inclusions was as described in 2) below. Table 4 shows the results.
From the table, when the conditions in the case of the present invention are satisfied, good results were obtained with respect to the cylinder during can making.

[0022]

[Table 2]

1) Manufacturing conditions Manufacturing process: converter → RH → continuous casting → hot rolling → cold rolling →
Can making process Addition method of Mg: wire addition in a tundish stopper or wire addition in a refractory circular pipe immersed in molten steel in a tundish. Continuous casting: Vertical bending type continuous casting machine (vertical part 3m, bending radius 10.5m, slab continuous casting machine), slab size: width 18
00mm constant, thickness 280mm

[0024]

[Table 3]

2) Inclusion evaluation method Cast slab: A cast including the ladle replacement position and cast slabs before and after the ladder were inspected in total of three slabs. A sample was taken from the upper surface layer to a depth of 140 mm in a quarter of the slab width direction. After acid dissolution, slime extraction was performed, and the number, composition, and size of inclusions having a diameter of 37 μm or more were investigated. The results in the table are the average values of three sheets. Crash breakage: When the slab including the ladle replacement position and the slabs before and after the ladle, a total of three slabs, are hot-rolled, cold-rolled, cut out from the obtained steel plate, and canned. Investigate whether the material breaks or cracks. The results in the table were evaluated as x when the rate of occurrence in about 1 million cans using three cast pieces exceeded 50 ppm.

[0026]

[Table 4]

[0027]

As described above, according to the present invention, the number of harmful inclusions in the cast slab near the ladle changing section has been greatly reduced, and the number of crushing defects during can making has been drastically reduced. Therefore, according to the present invention, it is possible to manufacture a slab having few inclusion defects.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in the number of slab inclusions near a ladle changing section;

FIG. 2 is a diagram showing the effect of Mg concentration on the melting point of inclusions.

FIG. 3 is a diagram showing the effect of Mg concentration on the size of inclusions.

FIG. 4 is a diagram illustrating a method of adding Mg.

FIG. 5 is a diagram illustrating an air sealing mechanism of a typical Mg adding apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ladle 2 Long nozzle 3 Molten steel 4 Tundish 5 Tundish stopper 6 Immersion nozzle 7 Mold 8 Molten steel pool 9 Mg wire 10 Upper space 11 Meniscus 12 Tube 13 Ar intake 14 Conductive tube 15 Guide pipe 16 Socket with screw 17 Tube tip Department

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B22D 11/11 B22D 11/11 B C21C 7/00 C21C 7/00 A 7/04 7/04 R (56) References JP JP-A-7-62417 (JP, A) JP-A-54-31035 (JP, A) JP-A-6-299286 (JP, A) JP-A-4-147755 (JP, A) JP-A-5-131251 (JP JP-A-62-224461 (JP, A) JP-A-7-48616 (JP, A) JP-A-4-333359 (JP, A) JP-A-7-300613 (JP, A) 7-300611 (JP, A) JP-A-8-300111 (JP, A) JP-A-58-58966 (JP, A) WO 93/22085 (WO, A1) (58) Fields investigated (Int. Cl) . ^7, DB name) B22D 11/108 B22D 11/00 B22D 11/10 310 B22D 11/11 C21C 7/00 C21C 7/04

Claims (3)

(57) [Claims] When a molten steel of carbon steel is cast by a continuous casting method, a wire made by covering an alloy containing Mg with an iron coating material is provided on a shaft of a tundish stopper,
And through the tube air-sealed at the upper end of the shaft, the molten steel in the immersion nozzle, before and after the ladle replacement point
A method for producing a raw material slab for a beverage can having few inclusion defects, wherein the slab is added only for a predetermined period . 2. A rod-shaped refractory circular pipe in which a wire made by covering an alloy containing Mg with an iron covering material is immersed in a tundish when a molten steel of carbon steel is cast by a continuous casting method. provided at the center axis of, and through the air sealed tube axis upper end, into the molten steel in the immersion nozzle, a ladle
A method for producing a raw material slab for beverage cans having a small number of inclusion defects, wherein the material is added only for a predetermined period before and after the time of replacement . 3. The ladle before and after the ladle replacement time.
During the specified period, the filling of the back pot is started from 10 t before the end of the filling of the front pot.
2. The method according to claim 1, wherein the time is up to 40 tons after the start of entry.
Or 2 of the material slab for beverage can with few inclusion defects described in
Production method.