JPH04305340A - Casting mold for continuous casting and casting method by using the mold - Google Patents

Abstract

PURPOSE:To speedily and stably cast continuously cast billet of small lot or small section while effectively preventing the generation of the drawing mark and to reduce the manufacturing cost. CONSTITUTION:A water cooling casting mold 11 has a straight inner circumferential surface, at whose inner circumferential surface the step is set and a ceramic casting mold 12 is inserted in the above stepped part with shrinkage fitting. And the relation of the heat conductivity (a) and the length of casting mold L1 of the ceramics mold 12 is made to the next integrally in the case that the length of the copper casting mold 11 is L2. If a <=0.006 : (-3.05a+0.386) L2<=L1<=L2, if a>0.06:(-0.124a+0.221) L2<=L1<=L2, here L2<=1000 (mm).

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a continuous casting mold suitable for producing small-lot continuous casting slabs of steel and Ni-based alloys without surface defects, or small-section near-net-shape slabs, and this mold. This relates to a continuous casting method using.

0002

BACKGROUND OF THE INVENTION Continuous casting has been attempted in the metal casting process for the purpose of saving process and energy. but,
When casting small-section slabs, continuous casting using a submerged nozzle clogs the nozzle, making casting impossible. Therefore, as shown in FIG. 10, a continuous casting method was devised in which the tundish 4 and the mold 1 were directly connected.

[0003] This tundish-mold direct connection type continuous casting method does not involve powder and produces clean slabs, and is suitable for producing small lots of continuously cast slabs. However, a solidified shell is generated at the contact point between the water-cooled copper mold (hereinafter simply referred to as "copper mold") 1 and the connecting ring 2, and the pull-out mark M (
This results in a slab defect (see Fig. 11). Since this defect directly becomes a product defect, it is necessary to remove it. In addition, in FIGS. 10 and 11, 3 indicates a molten metal supply refractory, 5 indicates a molten metal, 6 indicates a slab, 7 indicates a slab drawing device, and 8 indicates a solidified shell.

[0004] As one measure to prevent the occurrence of pull-out marks in tundish-mold direct connection type continuous casting, a method has been adopted in which a ceramic mold is inserted into a copper mold. For example, JP-A-52-50929 discloses a mold with a refractory and graphite tube inserted therein, and JP-A-58-151,939 discloses a heat-resistant, lubricating, and corrosion-resistant cermet conduit mold that can be used to cast steel. It has been shown that there is. Furthermore, JP-A-64-277
Publication No. 43 describes 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, and JP-A-1-286967 discloses a method of applying compressive stress to an inserted ceramic material in order to improve the thermal shock resistance of ceramics. A method for manufacturing a ceramic mold that is inserted into a copper mold with excellent properties is described.

The reason for using a ceramic mold is to moderate cooling and generate a solidified shell within the ceramic mold, and this effect is described in Mitsubishi Steel Technical Report Vol. 1
9 No. 1.2 (1985), the pull-out marks are reduced.

[0006]

[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 mold 1 and to generate a solidified shell within the ceramic mold 1'. Here, the reason why the ceramic mold 1' is inserted into the copper mold 1 is that it is necessary to simultaneously remove sensible heat and latent heat during solidification.

However, in a conventional mold having a structure in which a ceramic mold 1' is inserted over the entire length of a copper mold 1 as shown in FIG. 13, (1) the cost of the ceramic mold 1' is high. ■ Ceramics generally have low thermal conductivity, so casting speeds cannot be increased. (2) As the copper mold 1 expands during casting, the ceramic mold 1' sinks. There are problems such as:

In order to solve the above problem, it is possible to shorten the length of the ceramic mold by providing a step on the inner peripheral surface of the copper mold 1 and placing the ceramic mold 1' on the step, as shown in FIG. Conceivable. Using this structure,
Not only can the cost of the ceramic mold 1' be reduced, but also the casting speed can be increased because the solidified shell can be reinforced by the copper mold 1 below the ceramic. Furthermore, the ceramic mold 1' does not sink into the copper mold 1.

However, in such a structure, (1) If the casting speed is too high, the position where the solidified shell is generated will fall, and the solidified shell will be generated at the contact point between the ceramic mold 1' and the copper mold 1 (indicated by A in FIG. 14). Since this connection step remains as it is as a product defect, it becomes necessary to cut and remove it. Therefore, if the length of the ceramic mold is too short, it becomes impossible to increase the casting speed compared to the mold having the structure shown in FIG. Also, if the casting speed is too low, the ceramic mold 1
A solidified shell is generated at the contact point between ' and the connecting ring 2 (indicated by B in FIG. 14), and cutting of the slab is still required. ■ Copper mold 1 has a larger thermal expansion than ceramic mold 1', so a gap is created between the copper and ceramics during casting, resulting in poor heat conduction and a slow solidification rate, making it difficult to increase the casting speed. become unable. There are problems such as:

[0010] Therefore, in order to deal with the above problems, it is necessary to clarify the relationship between the material (thermal conductivity) of the ceramic mold, its length, and casting speed, and to prevent gaps between copper and ceramics. From this viewpoint, the present applicant proposed the invention described in Japanese Patent Application No. 2-412494.

[0011] However, there are materials for ceramic molds that have the same thermal conductivity but different densities and specific heats, and subsequent research has revealed that considering only thermal conductivity is not sufficient.

By considering temperature conductivity instead of thermal conductivity, the present invention enables continuous casting of steel or Ni-based alloy using a mold directly connected to a tundish at high speed and without surface defects. The object of the present invention is to provide a continuous casting mold that enables casting of the present invention and reduction of mold material costs, and a continuous casting method using this mold.

[0013]

[Means for Solving the Problems] The present inventors have developed a mold having the structure shown in FIG. 14, in which a step is provided on the inner circumferential surface of a copper mold and a ceramic mold is placed on the step. ), its length and casting speed were varied to investigate whether or not pull-out marks were generated and whether a solidified shell thickness capable of withstanding pull-out could be secured. In addition, since the casting speed is greatly affected by the mold diameter and mold length, with a mold having the structure shown in Fig. 13, by variously changing the mold length L and mold diameter d, the solidified shell thickness becomes thinner and the slab can be drawn. The critical casting speed Vcma at which it disappears was investigated.

As a result, for various ceramic materials (temperature conductivity a), the ceramic mold length L1 (mm
) and copper mold length L2 (mm) (see Figure 14) ratio L1
/L2 and the ratio Vc/Vcma of the casting speed Vc and the critical casting speed Vcma of the mold with the structure shown in FIG. It was found that the critical casting speed VClim at which marklessness occurs increases.

The concept of the present invention will be described below using examples in which a Si3N4 mold, a BN mold, and a graphite mold are used as ceramic molds. Figures 2 to 4 are Figure 1, respectively.
3, the Si3N4 mold (a=0.0
48 m2/hr), BN mold (a=0.297)
, is the relationship between the mold length L, the mold diameter d, and the limit casting speed Vcma when a graphite mold (a=0.490) (a is the value at 0° C.) is used. According to this, it can be seen that in any mold, as the mold length becomes longer and as the mold diameter becomes smaller, the critical casting speed Vcma increases. In this way, each ceramic mold material (
temperature conductivity), mold diameter, and critical casting speed V at mold length
cma can be limited.

[0016] Figures 5 to 7 show the Si3N4 mold (a=0.048 m2/hr) and the BN mold (a=0
．． 297), graphite mold (a=0.490)
(However, a is the value at 0° C.) The relationship between L1/L2 and Vc/Vcma (hereinafter referred to as "casting speed ratio") during use is shown. Here, L1 /L2 = 1 means that the ceramic mold is inserted over the entire length of the copper mold, and L1 /L2 = 0 means that the ceramic mold is not inserted.

Line 2 in FIGS. 5 to 7 indicates the critical casting speed ratio Vcmax1/Vcma at which a solidified shell is formed at the joint between the ceramic mold and the copper mold. When the casting speed ratio is smaller than this line (■), a solidified shell is generated above the joint between the ceramic mold and the copper mold.

Line (2) in FIGS. 5 to 7 indicates the critical casting speed ratio Vcmin/Vcma at which a solidified shell is formed at the joint between the ceramic mold and the connecting refractory. When the casting speed ratio is larger than this line (■), a solidified shell is generated below the joint between the ceramic mold and the connecting refractory.

The line (■) in FIGS. 5 to 7 indicates the critical casting speed ratio Vcmax at which the solidified shell thickness becomes thinner and the slab cannot be pulled out.
2/Vcma. When the casting speed ratio is smaller than this line (2), the strength of the solidified shell is greater than the adhesion force to the ceramic, and stable casting can be performed without troubles such as breakouts. Furthermore, L1/L
When 2 = 0 (when no ceramic mold is used), pull-out marks are generated regardless of the casting speed ratio.

From the above, the area in which slabs without drawing marks can be cast without problems such as breakouts is shown in Figure 5.
It turned out that this was the area indicated by diagonal lines on the upper right side of FIG. Furthermore, in the case of Si3N4 mold, BN mold, and graphite mold, casting can be performed at a casting speed higher than the maximum casting speed when L1 /L2 = 1.
It was found that a region of 1/L2 (the region indicated by diagonal lines downward to the right in FIGS. 5 to 7, hereinafter referred to as "A region") exists.

FIG. 8 shows the relationship between the minimum value of L1 /L2 in region A of various ceramic mold materials and the temperature conductivity of ceramics, and the line ■ in FIG. 8 is expressed by the following equation 3. .

[0022]

[Math. 3] When a≦0.06: L1 /L2 = -3.05a+
If 0.386a>0.06: L1 /L2 = -0
．． 124 a+0.221 However, a: Temperature conductivity of ceramic mold (at0℃) (m2/hr) L1: Ceramic mold length (mm) L2: Copper mold length (mm)

On the other hand, in the mold having the structure shown in FIG. 14, a gap is created between the copper and the ceramics due to the difference in thermal expansion between the copper and the ceramics during casting, which deteriorates temperature conduction and reduces the solidification rate. become unable to raise it. Therefore, it has been found that the above-mentioned problem can be solved by performing shrink fitting between the ceramic mold and the copper mold at a temperature higher than the heating temperature of the copper mold during casting.

Therefore, the present inventors determined the temperature conductivity a (m2/hr) of ceramics and the copper mold heating temperature Tc during casting.
The relationship between u (°C) was investigated. The results are shown in FIG. Here, the copper mold temperature is expressed as a function of the temperature conductivity of ceramics as shown in Equation 4 below.

[0025]

[Formula 4] When a≦0.06: Tcu=2554.9a
+42.4a>0.06: Tcu=103.6
a+179.2

Based on the above facts, the present inventors have completed the present invention described below. That is,
The continuous casting mold according to the first aspect of the present invention is a water-cooled copper mold that is directly connected to a tundish and has a straight inner circumferential surface and a step on the inner circumferential surface. In addition to interpolation, the temperature conductivity a (m2/hr) of the ceramic mold and the ceramic mold length L1
(mm), the gist is that the following formula 5 is satisfied when the length of the copper mold is L2 (mm).

[0027]

[Math. 5] When a≦0.06: (-3.05a+0.386
) L2 ≦L1 ≦L2 If a>0.06: (
-0.124 a+0.221) L2 ≦L1 ≦L2
However, L2 ≦1000 (mm)

Furthermore, the continuous casting mold according to the second aspect of the present invention has a shrink-fitting temperature Ty( The gist of this is to conduct the test at a temperature of

[0029]

[Formula 6] When a≦0.06: Ty≧2554.9a+
42.4a>0.06: Ty≧103.6 a+
179.2

Further, the continuous casting method according to the present invention is characterized in that molten metal is continuously supplied from the tundish to the continuous casting mold according to the first or second aspect of the present invention via the connecting ring. It is.

[0031]

[Function] According to the continuous casting mold according to the present invention, the ceramic mold is inserted into the stepped portion of the copper mold and both molds are shrink-fitted, so that the ceramic mold does not sink during casting. Steel or Ni-based alloy can be cast continuously at high speed while effectively preventing the occurrence of pull-out marks, and the cost of ceramic molds can be reduced.

[0032]

[Embodiment] The present invention will be explained below based on an embodiment shown in FIG. FIG. 1 is a cross-sectional view of a main part showing the configuration of a continuous casting mold according to the present invention, in which 11 is a copper mold with a straight inner peripheral surface provided with a step, and 12 is a ceramic mold that fits into this copper mold 11. , and its outer peripheral surface is straight. The copper mold 11 and the ceramic mold 12 are shrink-fitted at a predetermined temperature or higher so that no gap is created between the copper and ceramics even by the heat of the molten metal during continuous casting.

Next, the mold having the configuration shown in FIG.
We will explain the case of installing and continuous casting using the method shown in . For comparison, a case where a mold having a structure in which a ceramic mold is inserted over the entire length of a copper mold is used, and a case where a ceramic mold is inserted into a copper mold without shrink fitting will also be described.

[0034] The inner diameter of the ceramic mold 12 is φ100.
~300 mm, and the wall thickness is 10 mm, and the upper end of the copper mold 11 has a wall thickness of 10 mm. Also, the length of the copper mold 11 is 20
The length of the ceramic mold 12 and the length from the upper end of the copper mold 11 to the step on the inner peripheral surface were varied. The cast metals were SUS304 stainless steel and Inconel 625, and the temperature of the molten metal in the tundish 4 was set 40 to 50°C higher than the liquidus temperature. The drawing cycle was 100 cpm with intermittent drawing, and the casting speed was varied depending on the material of the ceramic mold 12. Table 1 below shows the conditions during the implementation in the comparative example, Table 2 below shows the results in the comparative example, Table 3 below shows the conditions during the implementation in the example of the present invention, and Table 4 below shows the results. .

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

Comparative Examples 1 to 6 are cases in which casting was performed using a mold having a structure in which a ceramic mold was inserted over the entire length of the copper mold, but in all cases, the casting speed was lower than the limit casting speed Vcm.
Since the strength of the solidified shell was not sufficient,
Breakout occurred from the bottom of the mold.

[0040] In Comparative Examples 7 to 12, 19, and 20, the ceramic mold length was shorter than the minimum ceramic mold length in area A, and the casting speed was higher than the critical casting speed Vcma. A solidified shell was formed and pull-out marks were observed on the surface of the slab.

In Comparative Examples 13 to 18, the copper-ceramics mold was not shrink-fitted, so a gap was created between the copper and ceramics, resulting in poor heat conduction, and the casting speed was higher than the critical casting speed Vcma, resulting in solidification. The shell was not strong enough and broke out from the bottom of the mold.

On the other hand, in all of the examples of the present invention, slabs with good surface properties can be cast without trouble at a speed higher than the critical casting speed Vcma, and the cost of ceramic molds can be significantly reduced. Ta.

Comparative Examples 19 and 20 and Inventive Example 27 have different experimental results due to differences in temperature conductivity even though they have the same thermal conductivity.From these experimental results, it is clear that not only the thermal conductivity was taken into account, but also the temperature conductivity It turns out that it is necessary to take this into consideration.

[0044]

As explained above, according to the present invention, small-lot continuously cast slabs of steel or Ni-based alloys or slabs with small cross sections can be stably cast at high speed while effectively preventing the occurrence of pull-out marks. Continuous casting can be carried out, and manufacturing costs can be significantly reduced due to process and energy savings.

[Brief explanation of drawings]

FIG. 1 is a sectional view of essential parts of a mold according to the present invention.

FIG. 2 is a relationship diagram of the mold length, mold diameter, and limit casting speed when a Si3N4 mold is used as the ceramic mold in the mold having the structure shown in FIG. 13;

3 is a relationship diagram of the mold length, mold diameter, and limit casting speed when a BN mold is used as the ceramic mold in the mold having the structure shown in FIG. 13; FIG.

4 is a relationship diagram of the mold length, mold diameter, and limit casting speed when a graphite mold is used as the ceramic mold in the mold having the structure shown in FIG. 13; FIG.

[Fig. 5] L1/L2 when a Si3N4 mold is used as the ceramic mold in the mold having the structure shown in Fig. 13.
FIG.

6 is a diagram showing the relationship between L1/L2 and casting speed ratio when a BN mold is used as the ceramic mold in the mold having the structure shown in FIG. 13; FIG.

[Fig. 7] L1/L2 when a graphite mold is used as the ceramic mold in the mold having the structure shown in Fig. 13.
FIG.

FIG. 8 is a diagram showing the relationship between ceramic temperature conductivity and the minimum value of the ratio of ceramic mold length to copper mold length in region A determined from FIGS. 5 to 7. FIG.

FIG. 9 is a diagram showing the relationship between ceramic temperature conductivity and copper mold heating temperature during casting.

FIG. 10 is an explanatory diagram of a tundish-mold direct connection type continuous casting method.

FIG. 11 is an explanatory diagram of a pull-out mark.

FIG. 12 is an explanatory diagram of a mold in which a ceramic mold is inserted into a copper mold.

FIG. 13 is an explanatory view of a mold in which a ceramic mold is inserted over the entire length of a copper mold.

FIG. 14 is an explanatory view of a mold in which a step is provided on the inner peripheral surface of a copper mold, and a ceramic mold is placed on the step to shorten the length of the ceramic mold.

[Explanation of symbols]

11 Copper mold 12 Ceramics mold

Claims (3)

[Claims] 1. A ceramic mold is inserted by shrink fitting into the stepped portion of a water-cooled copper mold that is directly connected to a tundish and has a straight inner circumferential surface and a step on the inner circumferential surface. Temperature conductivity a(m2/
The relationship between hr) and ceramic mold length L1 (mm) is
A continuous casting mold, characterized in that it satisfies the following formula 1, where the length of the copper mold is L2 (mm). [Math. 1] When a≦0.06: (-3.05a+0.386
) L2 ≦L1 ≦L2 If a>0.06: (
-0.124 a+0.221) L2 ≦L1 ≦L2
However, L2 ≦1000 (mm) 2. The continuous casting mold according to claim 1, wherein the ceramic mold and the water-cooled copper mold are fitted at a shrink-fitting temperature Ty (° C.) that satisfies the following formula 2. [Math. 2] When a≦0.06: Ty≧2554.9a+
42.4a>0.06: Ty≧103.6 a+
179.2 3. A continuous casting method, characterized in that molten metal is continuously supplied to the continuous casting mold according to claim 1 or 2 from a tundish via a connecting ring.