JP3456311B2 - Continuous casting method of multilayer slab - 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 continuous casting of a slab, which is suitable for preventing surface cracking of the slab and also suitable for small-lot production of a wide variety of products. It proposes a continuous casting method for pieces.

The continuous casting method does not require slabbing, and
From the fact that it is suitable for mass production and has an excellent yield, such as economic efficiency and productivity, it is well established as a general process in steel casting.

In the process of development of the continuous casting method for steel, in recent years, the floating of inclusions in the molten metal in the mold is promoted, so that the vertical bending type continuous casting machine is often used instead of the full-curving type. Is becoming.

However, in the vertical bending type continuous casting machine, it is necessary to bend the solidified slab in the continuous casting machine and to correct the bending. At that time, in the case of steel which is sensitive to cracking susceptibility at high temperature, There is a problem that surface cracks occur on one side and many product defects occur, and such a steel is not suitable for casting in a vertical bending type continuous casting machine. Particularly, in the steel in which the amount of C that causes the peritectic reaction is in the range of 0.08 wt% to 0.17 wt%,
Surface cracking of the slab was very likely to occur, and almost no casting was possible.

Therefore, as one of the methods for preventing the surface cracks of the slab due to bending, a method of making only the surface layer portion of the slab a component composition having a low susceptibility to cracking at high temperature can be considered. On the other hand, it is known that in steel sheets and the like, when the alloy components such as C and B are concentrated only in the very surface layer, the hardness of the surface layer portion is increased and the mechanical properties such as bending characteristics are improved.

[0006]

2. Description of the Related Art As a casting method for casting a slab having different component compositions in the surface layer portion and the inner layer portion thereof, for example, Japanese Patent Publication No. 3-20295 (continuous casting method for composite metal materials) discloses Metal slab (composite slab) where the outer layer and the inner layer have different composition by supplying molten steel with two different composition from above and below the static magnetic field zone in the mold by two nozzles with different lengths A method of casting a metal material) has been proposed and disclosed.

However, in this method, two kinds of molten steel must be prepared at the refining stage of steel, which complicates the manufacturing process and causes a problem in workability and productivity. Since one kind of composite metal material is manufactured in a pan, there is a problem that it cannot be adapted to the needs of high-mix low-volume production which is a trend in recent years.

Further, in Japanese Patent Laid-Open No. 7-60408 (method for manufacturing a steel sheet for thin plate), the steel is divided by a DC magnetic field zone in a continuous casting mold. Layer metal slab is manufactured and the composition of molten steel for the outer layer to be injected into the upper pool is adjusted by adding molten steel for the inner layer to the ladle, surface tundish, surface nozzle or casting mold. A method has been proposed and disclosed in which an alloy component is added at one or more places in the upper pool, but the manufacturing process is unavoidably complicated because two nozzles and tundish are required. There is also a problem in workability, and there is no disclosure regarding means for adding alloy components to the pool in the nozzle or in the mold, and simply immersing or pouring the alloy will slow the melting rate and cause sufficient melting. Etc. can not be added efficiently synthetic component can be not or upper pool, there is a problem that a component adjustment becomes difficult.

[0009]

SUMMARY OF THE INVENTION The present invention is intended to advantageously solve the above-mentioned problems, and advantageously prevents surface cracking of a slab in casting in a vertical bending type continuous casting machine, and at the same time, steel material. Proposal of a continuous casting method for multi-layer slabs that improves various properties in the production process and is suitable for small-lot production of many types of products that can meet recent demands even in casting with a large-scale continuous casting machine and has excellent workability and productivity. The purpose is to

[0010]

The gist of the present invention is as follows.

For the molten metal supplied into the continuous casting mold,
When continuously casting a multi-layer slab in which alloy components are added and a segregation zone in which the alloy components are concentrated is formed in the surface layer of the slab, the tip of the rod-shaped additive containing the alloy components is dipped below the surface of the molten metal bath. Then, ultrasonic vibration is applied to the additive material to concentrate the alloy component of the additive material in the molten metal upper layer portion in the mold (first invention).

A continuous casting method (second invention) for a multi-layer cast product according to the first invention, wherein a DC magnetic field is applied to the upper layer of the molten metal in the mold in which the alloy components are concentrated.

The first or second alloy component is one selected from C, Ti, Nb, B or Zr or two or more selected from C, Ti, Nb, B, Zr or N.
A method for continuously casting a multi-layer cast product according to the invention (third invention).

The cross-sectional shape of the rod-shaped additive material may be circular, oval, rectangular, star-shaped, or any other shape.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the present invention is to prevent surface cracking of a slab in continuous casting of steel having a sensitive component composition which is susceptible to cracking at high temperatures, and to improve various properties of steel materials. For this reason, it is intended to cast a multi-layer slab having a segregation zone in which alloy components are concentrated only in the surface layer of the slab.
When casting a multi-layer slab, an alloy component to be concentrated by the molten metal in the mold is added to make it suitable for high-mix low-volume production, and when the alloy component is added, a rod-shaped additive containing the alloy component. The main point is to immerse the tip of the above under the surface of the molten metal bath and apply ultrasonic vibration to the additive.

That is, if the alloy components are simply dipped or poured into the molten metal, the dissolution rate into the molten metal is slow and the alloy cannot be sufficiently dissolved in the mold. By applying ultrasonic vibration to the containing rod-shaped additive material, vigorous stirring is caused in an extremely narrow area of the interface between the additive material and the molten metal to accelerate the reaction,
The melting of the additive can be rapidly advanced, and the alloy component of the additive can be concentrated in the upper layer of the molten metal in the mold. Thus, it is possible to easily cast a multi-layer slab having a segregation zone in which the alloy component of the additive is concentrated in the surface layer portion.

At this time, the amount of the alloy component dissolved can be changed by 1) the interfacial area between the molten steel and the rod-shaped additive material, and 2) the strength of ultrasonic vibration applied to the rod-shaped additive material, and so on. It is extremely easy to adjust the width of segregation zone of the surface layer of the cast slab and the concentration of alloy components by changing the immersion depth, the number and cross-sectional shape, and the strength of ultrasonic vibration. It becomes easy to cast multi-layer cast pieces with different segregation zone widths and alloy component concentrations from the same ladle and the same continuous casting machine.

In addition, since the present invention adds the alloy components in the mold as described above, a rod-shaped additive material having different alloy components is used for each strand of the continuous casting machine, or different alloy components are used during casting. It is also possible to cast a multi-layer slab having segregation zones of different alloy components from a series of the same ladle and the same continuous casting machine by replacing the rod-shaped additive with the above.

Therefore, even in continuous casting from the same ladle using a series of large continuous casting machines, it is possible to cast a multi-layer cast product having different segregation zones having different segregation zone widths, alloy components, concentrations, etc. It is possible to meet the recent needs of high-mix low-volume production.

Further, in the present invention, a DC magnetic field may be applied to the upper layer of the molten metal in the mold in order to suppress the flow of the upper layer of the molten metal in which the alloy component is concentrated. This is because the applied DC magnetic field suppresses the flow of molten steel immediately below the meniscus, and it is possible to more efficiently form a segregation zone in which the alloy components of the additive are concentrated in the surface layer, and the surface layer is extremely shallow. Because it becomes advantageous to form a segregation zone in the range.

Further, in the present invention, the alloy component to be concentrated in the surface layer of the slab is a machine for preventing surface cracks of the slab in the casting process and improving the hardness of the surface of the steel material manufactured from the slab. To improve the physical properties, C,
One of Ti, Nb, B or Zr or C, Ti, Nb,
It is preferable to use two or more of B, Zr or N.

Here, in the case of thickening two or more kinds of alloys, the rod-shaped additive material of each alloy component should be simultaneously immersed in the molten metal in the mold, and the rod-shaped additive material containing two or more kinds of alloys. May be immersed in the molten metal in the mold, and if it is desired to concentrate N, BN is used as a rod-shaped additive.
It is preferable to use a nitride such as.

As the alloy component to be concentrated in the surface layer of the cast slab, it is perfectly acceptable to use alloy components other than the above, such as Cr and Ni for improving the corrosion resistance.

[0024]

[Example] Al killed steel containing 0.12 wt% C: 230 ton melted in a converter was prepared in a ladle, and a continuous casting mold of a size of 230 mm x 1100 mm was prepared through a tundish and a dipping nozzle. Continuous supply, throughput: 4ton / min
With a casting speed of 2.0 m / min as a basic condition, 2 conforming examples and 3 comparative examples conforming to the present invention were cast into slabs under the following conditions.

Conformance Example 1 Two carbon rods having a diameter of 60 mm are used as rod-shaped additive materials,
As shown in Fig. 1, each of the carbon rods was immersed in molten steel at two places in the middle between the wall of the short side plate of the mold and the dipping nozzle from above, with a dipping depth of 100 mm.
Ultrasonic vibration of kHz, output: 3kW was applied, and both carbon rods were cast while descending at a speed of 10 mm / min.

Adaptation Example 2 DC magnetic field of magnetic flux density: 0.3 T, depth from meniscus: 340 m
Casting was carried out under the same conditions as in the conformity example 1 except that the molten steel in the mold was applied in the thickness direction over the range of m 2.

Comparative Example 1 Casting as it is. (Neither addition of additive material nor application of DC magnetic field)

Comparative Example 2 Casting carbon powder into molten steel in the mold for casting.

Comparative Example 3 A carbon rod was immersed in molten steel and cast in the same manner as in Comparative Example 1 except that ultrasonic vibration was not applied to the carbon rod.

Here, FIG. 1 is an explanatory view of a conforming example of the present invention. In this figure, 1 is a tundish, 2 is a dipping nozzle, 2'is a dipping nozzle discharge hole, 3 is a mold long side plate,
3'is a short side plate of a mold, 4 is an ultrasonic oscillator, 5 is a rod-shaped additive material, 6 is a DC electromagnetic coil, 7 is molten steel, 7'is molten steel in which the alloy component of the additive material is concentrated, and 8 is a solidified shell. Yes, 9 indicates the flow of molten steel 7. Then, ultrasonic vibration is applied to the rod-shaped additive material 5 by the ultrasonic oscillator 4, and a DC magnetic field is applied to the molten steel 7 ′ in which the alloy component of the additive material is concentrated by the DC electromagnetic coil 6 in the thickness direction.

For each of the slabs thus obtained, the carbon concentration in the thickness direction and the condition of surface cracking of the slab in the slab C cross section as shown in FIG. 2 were investigated.

FIG. 2 is an explanatory view showing the carbon concentration measuring position in the cross section of the slab C, and the carbon concentration was measured by a microanalyzer in the direction of the arrow in the drawing.

The results of these investigations will be described below in order. FIG. 3 is a graph showing the relationship between the distance from the upper surface of the slab and the carbon concentration, which is obtained in the first conformance example. As is clear from FIG. 3, the carbon concentration in the surface layer portion from the slab surface to 5 to 7 mm is concentrated to 0.18 wt%, while the carbon concentration in the inner layer portion is 0.12 wt% which is the same as that of the supplied molten steel. wt%
It turns out that

Next, conforming examples 1 and 2 and comparative example 1,
The average value of the carbon concentration in the surface layer portion up to 5 mm from the surface of each slab obtained by 2, 3 is C ₁ and ₁₀ mm from the slab surface
The average value of carbon concentration in the inner layer portion between 100 mm: C ₂ is shown together in Table 1.

[0035]

[Table 1]

As can be seen from Table 1, carbon is concentrated in the surface layer portion only in the slabs obtained in the conforming examples 1 and 2. It should be noted that these results show that the carbon is hardly dissolved in the molten steel even if the carbon powder is added (Comparative Example 2) or simply immersed in the carbon rod (Comparative Example 3). Further, in the adaptive example, it is shown that when a direct-current magnetic field is applied (adaptive example 2), carbon in the slab surface layer portion can be more effectively concentrated.

Further, FIG. 4 shows the result of visual inspection for surface cracks in the slab. FIG. 4 is a graph showing the number of surface cracks of each slab obtained in the conforming example 1 and the comparative example 3. As is clear from FIG. 4, the surface cracks of the slab of the conforming example are significantly reduced as compared with the comparative example.

[0038]

Industrial Applicability According to the present invention, when continuously casting a multi-layer cast product in which a segregation zone of the alloy component is formed in the surface layer of the cast product, the tip of the rod-shaped additive material containing the alloy component is immersed below the surface of the molten metal bath in the mold. Which imparts ultrasonic vibration to the additive,
According to the present invention, it is possible to prevent surface cracking of the slab during casting, improve the properties of the steel material obtained from the slab, and, even in casting by a large continuous casting machine, various types that can meet the needs of recent years. Easy production in small quantities,
It will also be excellent in productivity.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a conforming example of the present invention.

FIG. 2 is an explanatory diagram showing measurement positions of carbon concentration in a slab C cross section.

FIG. 3 is a graph showing the relationship between the distance from the upper surface of the slab and the carbon concentration, which was obtained in the first fitting example.

FIG. 4 is a graph showing the number of surface cracks of each slab obtained in the conforming example 1 and the comparative example 3.

[Explanation of symbols]

1 tundish 2 immersion nozzle 2'dipping nozzle discharge hole 3 Mold long side plate 3'mold short side plate 4 Ultrasonic oscillator 5 Rod-shaped additive material 6 DC electromagnetic coil 7 Molten steel Molten steel in which alloy component of 7'additive is concentrated 8 solidification shell 9 Flow of molten steel

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-224045 (JP, A) JP-A-7-145450 (JP, A) JP-A-7-51801 (JP, A) JP-A-7- 68348 (JP, A) JP-A-2-235557 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22D 11/00 B22D 11/108 B22D 11/11 B22D 11/115

Claims (3)

(57) [Claims] 1. A molten metal supplied into a mold for continuous casting,
When continuously casting a multi-layer slab, in which alloy components are added to form a segregation zone in which the alloy components are concentrated, the tip of the rod-shaped additive containing the alloy components is dipped below the surface of the molten metal. Then, ultrasonic vibration is applied to the additive material to concentrate the alloy component of the additive material in the upper layer portion of the molten metal in the mold. 2. The continuous casting method for a multi-layer cast product according to claim 1, wherein a direct current magnetic field is applied to the upper layer of the molten metal in the mold in which the alloy components are concentrated. 3. The alloy component is one kind selected from C, Ti, Nb, B or Zr or two or more kinds selected from C, Ti, Nb, B, Zr or N. Alternatively, the method for continuously casting a multi-layer cast product according to item 2.