JPH0481248A - Mold for continuous casting and continuous casting method using this mold - Google Patents

Abstract

PURPOSE:To settle trouble on the operation and to produce a cast slab of steel or Ni base alloy without any surface defect on the cast slab by applying tapers on outer face of a ceramic maid and on inner face of a copper mold and executing shrinkage fit at the specific temp. to the fitting between these. CONSTITUTION:This invention relates to the mold for continuous casting directly connected with a tundish, and the copper mold and the ceramic mold inserted inl this are taper-fit and the shrinkage fit is executed to this fitting at the temp. TY=TCu-{(bCe/bCu).TCe+(1-bC<e>/bCu).TR} or higher. (wherein, TY: shrinkage fitting temp. (lower limit value), which does not develop slipping of the ceramic mold downward, bCu: coefficient of linear expansion of the copper mold, bCe: coefficient of linear expansion of the ceramic mold, TCu: copper mold temp. during casting, TCe: ceramic mold temp. during casting, TR: mold temp. at initial stage). Further, the continuous casting method related to this invention, continuously supplies molten metal from the tundish through a connecting ring.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a continuous cast slab of steel and Ni-based alloy suitable for producing small-lot continuous cast slabs without surface defects or small cross-section near net shave slabs. This invention relates to a casting mold and a continuous casting method using this mold.

(Prior Art) In the metal casting process, continuous casting has been attempted for the purpose of saving process and energy. However, when casting small cross-section slabs, continuous casting using a submerged nozzle clogs the nozzle, making casting impossible. Therefore, as shown in FIG. 5, a continuous casting method was devised in which the tundish 4 and the mold 1 were directly connected. This tanditshu-mold direct connection continuous casting method does not involve powder and produces clean slabs, and is suitable for producing small lots of continuously cast slabs. However, water-cooled copper mold (hereinafter simply referred to as "copper mold") 1
A solidified shell is generated at the contact point between the connecting ring 2 and the connecting ring 2, resulting in a slab defect called a pull-out mark M (see FIG. 6). Since this defect directly becomes a product defect, it is necessary to remove it. In addition, 3 in FIG. 5 and FIG. 6 is a molten metal supply refractory, and 5
6 is a molten metal, 6 is a slab, 7 is a slab drawing device, and 8 is a solidified shell.

As one of the measures to prevent the occurrence of pull-out marks in tanditshu-mold direct continuous casting, a method has been adopted in which a ceramic mold is inserted into a copper mold. For example, JP-A-52-50
No. 929 discloses that it is possible to cast steel using a mold with a refractory and graphite pipe inserted therein, and JP-A-58-151939 discloses that it is possible to cast steel using a heat-resistant, lubricating, and corrosion-resistant cermet conduit mold. . Furthermore, JP-A No. 64-27743 discloses a method of applying compressive stress to an inserted ceramic material by a method such as shrink fitting in order to improve the thermal shock resistance of ceramics; A method for manufacturing a ceramic mold inserted into a copper mold with excellent impact resistance and thermal stress resistance is described.

The reason for using ceramic molds is to ease cooling, and its effect is shown in Mitsubishi Steel Technical Report Vol. 1.19.
As described in Nα1.2 (1985), the pull-out marks are reduced.

(Problems to be Solved by the Invention) As mentioned above, in the continuous casting method of steel or Ni-based alloy in which the tundish and the mold are directly connected, in order to prevent surface defects of the slab, for example, as shown in FIG. It has been proposed to use a ceramic mold 1' inserted into the copper mold, but since the thermal expansion of the copper mold is larger than that of the ceramic mold, a gap is created between the copper ceramics, and the ceramic mold 1' is inserted into the copper mold. 1, and there is a risk that troubles such as a flashing in the tundish-mold connection part and a breakout from the tundish-mold connection part may occur as shown in FIG.

On the other hand, if the sinking of the ceramic mold 1' is mechanically prevented, such as by providing a step on the inner peripheral surface of the copper mold l and placing the ceramic mold 1' on this step, as shown in FIG. As a result, the solidification rate decreases, resulting in a solidified shell that either does not form or becomes extremely thin, making it impossible to draw the cast slab.

The present invention solves the above-mentioned operational troubles and is capable of manufacturing steel or Ni-based alloy slabs with no surface defects in the slab, and a continuous casting mold that is directly connected to the tanditshu mold, and a continuous casting mold using this mold. The purpose is to provide a continuous casting method.

(Means for solving the problem) In order to continuously cast slabs using a ceramic mold, it is necessary to simultaneously remove sensible heat and latent heat during solidification, and the ceramic mold must be inserted into a copper mold. At this time, in order to improve the contact between the ceramic mold and the backup copper mold, it is necessary to push the ceramic mold into the copper mold.Especially during casting, the copper mold expands and its inner diameter expands, so this is necessary. To maintain good contact, the ceramic mold must be held down at all times.

Based on these facts, the ceramic mold becomes as shown in FIG. 7, as described above.

However, since a copper mold has a larger thermal expansion than a ceramic mold, a gap is created between the copper and the ceramic during casting, and the ceramic mold sinks into the copper mold, creating a risk of flashing and breakout.

Therefore, in order to prevent the ceramic mold from sinking into the copper mold during casting, the inventors of the present invention should: (1) taper the outer surface of the ceramic mold and the inner surface of the copper mold, and insert the ceramic mold by fitting them together; They believed that it would be effective to apply shrink fitting to a copper mold to create a structure in which the ceramic mold would no longer deteriorate, and they established the following invention.

That is, the continuous casting mold according to the present invention is a continuous casting mold that is directly connected to a tundish, in which a copper mold and a ceramic mold inserted therein are tapered fitted, and this fitting is performed as follows: Ty = TCe −((bc, {(bCe/bCu)−T
R, ten (1-bo, /bo,) ・TR) However, TY
: Shrink fitting temperature that does not cause ceramic mold subsidence (
Lower limit value) t) Co: Coefficient of linear expansion of copper mold t) Ca: Coefficient of linear expansion of ceramic mold Tau: Copper mold temperature during casting TCa: Ceramic mold temperature during casting TRl: Shrink fitting at a temperature equal to or higher than the initial mold temperature This is a summary of what was done.

Further, the continuous casting method according to the present invention is characterized in that molten metal is continuously supplied to the continuous casting mold from a tundish via a connecting ring.

In the present invention, the reason why the shrink fitting temperature TY is set as shown in the above formula is as follows. That is, the ceramic mold sinkage amount S is expressed by the following equation.

×L...0 However, S: Ceramic mold sinkage amount (nun)bCu
: Linear expansion coefficient of copper mold (K-')bc*: Linear expansion coefficient of ceramic mold (K-') TCu: Upper temperature of copper mold (°C) TCuu: Lower temperature of copper mold (°C) TCa: Ceramic mold temperature (°C) TRl: Initial temperature (°C) R1: Upper ceramic mold outer surface radius (mm) R2: Lower ceramic mold outer surface radius (mm) L: Mold length (mm) In addition, T Cu, TCull , TCa measurement positions are as shown in FIG.

Here, T Cus TCuLI N Tc@ can be almost predicted from actual results and calculations depending on the thermal conductivity of the ceramic mold material. T Cu, T Cuu, and T. The relationship between , and thermal conductivity is shown in Figure 3. Figure 4 shows the ceramic mold sinkage amount S and copper mold upper temperature T by substituting the values in Table 1 below into the above equation 0 (when using a BN mold). , which shows the relationship between .

When shrink fitting is performed at 100°C (curve ■ in Figure 4)
, ceramic molds do not sink even when copper molds are heated to 185°C. Furthermore, when shrink fitting is performed at 200°C (curve ■ in Figure 4), the ceramic mold has a copper mold of 285
It will not sink even if the temperature rises. In other words, when using a BN mold, the temperature of TCu is 250°C, so if shrink fitting is performed at 165°C or higher, the ceramic mold will not sink.

Here, the curve ■ is S = 350 (1-4542/(Tcu-100+4
457) ) ... ■Curve ■ is 5=350 (1-4542/(TCe, -200+4
457) ) ・(Represented by iD. From the above formula, 85°C
The value is the difference between 4542 and 4457 in the above formulas 0 and 0, which is (bo, /be,)-'rca+ (
1-b, , /bo, )-TR. From the above, T.

Us 'rcuu % TCe is predicted from actual results and calculations, and TY=To, -((bc, /b,.)-TR, +(1b
It was found that the ceramic mold did not sink into the copper mold when shrink fitting was performed at a temperature of Cu/bo,) TR) or higher.

(Function) In the continuous casting mold according to the present invention, the outer surface of the ceramic mold and the inner surface of the copper mold are tapered, and the inner surface of the copper mold is inserted into the tapered surface. The amount of mold settling is reduced. Also, shrink fitting between a ceramic mold and a copper mold is easier if the mold is tapered.

In addition, since the mold of the present invention shrink-fits the copper mold and the ceramic mold, the ceramic mold will not sink due to the heat during casting.

(Example) The present invention will be described below based on an example shown in FIG.

FIG. 1 is a cross-sectional view of a main part showing the structure of a continuous casting mold according to the present invention, and 11 is a copper mold tapered so that the cross section of the inner surface on the side where the slab is pulled out has a small diameter, and 12 is a copper mold of this type. This is a ceramic mold with a taper on its outer surface that fits with the taper of the copper mold 11.

The copper mold 11 and the ceramic mold 12 are shrink-fitted at a temperature above a predetermined temperature, and the synergistic effect of this shrink-fitting and the taper prevents the ceramic mold 12 from sinking even with the heat of the molten metal during continuous casting.

Next, a case will be described in which the mold having the configuration shown in FIG. 1 is installed by the method shown in FIG. 7 and continuous casting is performed. For comparison, a case in which continuous casting was performed using a conventional mold will also be described.

The ceramic mold 12 has an inner diameter of 100 mm, the tapered one has an upper wall thickness of 15 mm, the lower wall thickness of 10 mm, and the non-tapered one has a wall thickness of 15 mm. The copper mold 11 has an inner diameter of 130 mmφ, and the tapered one has an upper wall thickness of 15 mm.
mm, lower wall thickness 20 mm, wall thickness 15 for those without taper
It is mm. The mold length was 350 m in both cases. The cast metal was 5t JS304 stainless steel, and the temperature of the molten metal in the tundish 4 was 40 to 50°C higher than the liquidus temperature. The casting speed was 1.0 m/min, and the drawing cycle was 60 cpm with intermittent drawing.

In Table 2 below, Indicate the conditions for implementation and the results. vinegar.

■ In the case of Comparative Example 1, since there was no taper, the temperature was 170°C (T
Even though shrink fitting was performed at Y=163°C), the ceramic mold sank, and molten steel leaked from the gap between the ceramic mold and the connecting ring. In the case of Comparative Example 2.3, since shrink fitting was not performed, (bo, /b,,)・T
o. Because a gap was created and cooling was no longer effective,
The shell thickness became thinner and the shell broke, resulting in a breakout (molten metal was discharged from the exit side of the mold). Further, in Comparative Example 3, the pullout resistance was large due to the presence of a gap between the upper part of the mold and the connecting ring, and the pullout was stopped. On the other hand, in the case of Comparative Example 4, 100°
Although the mold shrink fitting was performed at C, the temperature was TR (1
47°C), the ceramic mold sank and molten steel leaked from the gap between the ceramic mold and the connecting refractory.

On the other hand, in all of the examples of the present invention, the ceramic mold was inserted into the Cu mold using a taper, and the shrink fitting temperature was higher than TY, so the ceramic mold did not sink and a slab with good surface quality was inserted. , I was able to obtain it without any troubles such as breakouts.

(Effects of the Invention) As explained above, according to the present invention, small-lot continuously cast slabs of steel or Ni-based alloys or slabs with a small cross section can be continuously cast stably and trouble-free, reducing process steps and Energy conservation has made it possible to significantly reduce manufacturing costs.

[Brief explanation of drawings]

Figure 1 is a sectional view of the main part of the mold of the present invention, Figure 2 is an explanatory diagram of the measurement position when measuring the amount of sinkage of a ceramic mold, and Figure 3
Figure 1 shows the relationship between T Cus TCuu % 'ram and thermal conductivity. Figure 4 is a diagram showing the relationship between the sinking amount of the ceramic mold and the temperature at the top of the copper mold, Figure 5 is an illustration of the tanditshu-mold direct connection type continuous casting method, Figure 6 is an illustration of the drawing marks, and Figure 7 is an illustration of the copper mold. An explanatory view of a mold in which a ceramic mold is inserted into the mold, FIG. 8 is an explanatory view of problems in the case of FIG. 7, and FIG. 9 is an explanatory view showing another example of FIG. 7. 11 is a copper mold, 12 is a ceramic mold.

Claims (2)

[Claims] (1) A continuous casting mold that is directly connected to the tundish, in which the water-cooled copper mold and the ceramic mold inserted therein are tapered fitted, and this fitting is performed as follows: T_Y=T_C_u-{(b_C_e/b_C_u)・
T_C_e+(1-b_C_e/b_C_u)・T_R
}However, T_Y: Shrink fitting temperature (lower limit) at which the ceramic mold does not sink b_C_u: Coefficient of linear expansion of water-cooled copper mold b_C_e: Coefficient of linear expansion of ceramic mold T_C_u
: Water-cooled copper mold temperature during casting T_C_e: Ceramic mold temperature during casting T_R: Continuous casting mold characterized by being shrink-fitted at a temperature equal to or higher than the initial mold temperature. (2) A continuous casting method, characterized in that molten metal is continuously supplied to the continuous casting mold according to claim 1 from a tundish via a connecting ring.