JPH0220645A - Mold for continuously casting steel - Google Patents

Abstract

PURPOSE:To prevent longitudinal crack of solidified shell at initial stage in kind of steel executing hypo-peritectic solidification having 0.10-0.15% carbon content by arranging the specific lattice-like grooves on mold surface positioning near meniscus of molten steel. CONSTITUTION:In the copper-made mold for continuous casting, on the mold surface positioning gear the meniscus of the molten steel in the mold, the lattice- like grooves having 0.5-1.0mm depth and 0.5-1.0mm width are arranged at 5-10mm interval between the grooves. By this method, cooling degrees at grooving part and non-grooving part fiffer and the initial solidification is a little delayed at the grooving part, which is weak cooling part. Therefore, the liquid phase is remained at every fixed intervals and absorbs strain at the time of shrinking, and bending of the solidified shell at the initial stage is restrained and the solidified shell is locally separated from the mold. Therefore, heat conduction is made uniform and the solidified shell thickness is made uniform. In this result, as the local thin part in the solidified shell layer is eliminated by developing the solidified shrinkage and transformation stress at the time of transforming delta gamma, the stress is not concentrated at one point.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to a method for preventing longitudinal cracking of the solidified shell in the initial stage of subperitectic solidifying steel with a carbon content of 0.10 to 0.15%. Concerning continuous casting molds.

[Prior Art] In recent years, continuous casting methods using vertical or curved continuous casting machines have become indispensable for producing slabs. When attempting to manufacture slabs such as blooms and billets using such continuous casting methods, vertical and horizontal cracks may occur on the surface of the slab. Figure 17 shows the results of casting using a conventional copper plate mold. FIG. 2 is a graph showing the relationship between the carbon content of the slab and the surface crack index. As is clear from this figure, many surface cracks occur in steel types that undergo subperitectic solidification and have a carbon content of 0.10 to 0.15%. The reason for this is that when steel with the above carbon content solidifies, it undergoes a transformation process of L→δ+L→peritectic reaction (δ+L→γ) →δ+γ→γ. Among these, the δ phase is body-centered cubic (bc
c), the γ phase has a face-centered cubic (fcc) crystal structure, and the δ
→During the γ transformation, volumetric contraction occurs due to this crystal structure difference, and a large transformation stress is generated. In addition, during this peritectic reaction of δ→γ, the liquid phase disappears, so there is nothing to absorb the strain caused by contraction, and the solidified shell itself assumes a non-uniform solidified form, and the stress is applied to the thin part of the solidified shell. It is thought that cracks will occur once the material is applied. Conventionally, in order to prevent surface cracking of the above steel types, the type of mold powder was selected through trial and error, and the type of mold powder was changed to one with low cracking susceptibility before casting, or the amount of heat extracted from the mold was reduced and low-speed casting was performed. It was intended to prevent cracking.

[Problem to be solved by the invention] However, when selecting a mold powder that suppresses the occurrence of surface cracking, it is difficult to select a mold powder that satisfies all of the many casting conditions, and it takes time and a large amount of money. .

In addition, when low-speed casting is performed to reduce the amount of heat removed from the mold, it is difficult to synchronize the continuous casting machine with the hot rolling machine for direct rolling (a method of flowing slabs from the continuous casting machine to the hot rolling machine). As a result, direct rolling and hot charge rolling become impossible, which poses a problem in that it becomes an obstacle to labor and energy saving in the integrated manufacturing process, and at the same time, the yield of the product decreases.

The present invention has been made in view of the above circumstances, and is intended to prevent the initial solidification shell coagulation of a steel with a carbon content of 0.10 to 0.15% that undergoes subperitectic solidification, thereby preventing surface defects in the slab. The purpose of this project is to provide a continuous casting mold for continuous casting.

[Means for Solving the Problems] In order to achieve the above object, the mold for continuous casting of steel of the present invention has a depth of 0.5 to 1.5 mm on the mold surface located near the meniscus of molten steel in the mold. 0mm, width 0.5-1.0mm
lattice-shaped grooves are provided, and the intervals between the lattice-shaped grooves are 5 to 10.
Let it be mm.

In addition, in order to obtain more preferable results, a metal dissimilar to the mold material copper, such as Ni or Cr, or a metal such as BN, A! A ceramic such as 2N or ZrO2 is filled to a depth where the thermal resistance ratio is 1.5 or more.

[Function] In the mold for continuous casting of steel according to the present invention, by providing a lattice-like groove on the surface of the mold, the strength of cooling is varied between the groove portion and the other portion, and the initial cooling temperature is lowered in the groove portion which is the weakly cooled portion. The solidification of the solidified shell is slightly delayed. For this reason, a liquid phase remains at regular intervals, and this liquid phase absorbs the strain caused by contraction, suppressing the initial bending of the solidified shell, and preventing the mold from separating from the solidified shell locally.Therefore, the amount of heat removed is reduced. becomes uniform,
Solidified shell thickness grows uniformly 0 By using the mold of the present invention, the initial solidified shell thickness is extremely uniform, so even if solidification shrinkage or transformation stress occurs during δ→γ transformation, localized Since there is no thin part of the solidified shell, −
The shape of the grid-like groove is 0.5 to 1.0 mm in depth and 0.5 to 1.0 + am in width so that stress does not concentrate at a point,
The reason why the wires are arranged in a lattice shape with intervals of 5 to 101 m is that the non-uniformity of the solidified shell thickness becomes large outside this range.

In addition, the reason why the lattice-shaped grooves are filled with dissimilar metals or ceramics is that if the grooves are simply provided, there is a risk that mold powder will enter the grooves during casting, disrupting the heat balance and causing cracks on the slab surface. This is because there is.

[Example] An embodiment of the present invention will be described below.

In steel types that undergo subperitectic solidification, when an initial solidified shell is formed, the solidified shell is bent by thermal strain and transformation stress due to δ→γ transformation, and a void is locally formed between the solidified shell and the mold wall, which causes local As a result, the solidified shell thickness grows non-uniformly. In the process leading up to the present invention, the present inventors have found that surface cracks occur where the thickness of the solidified shell is thin, and that surface cracks can be prevented by preventing uneven solidification.

Based on this knowledge, we conducted an experiment to investigate the cause of nonuniform solidified shell thickness. The experiment was carried out at 100mm
A 360 mm immersed body (water-cooled flat plate = cooling water of the immersed body is 904/min) is immersed in molten steel from directly above a 100 kg melting furnace using an air cylinder, held for a certain period of time, and the roughness of the solidified shell ('' a Solid shell heterogeneity expressed as Δd/l. Δd: Thickness difference between adjacent asperities d Convexity - d
Concavity, j: distance between adjacent concavities and convexities) was investigated. FIG. 6 is a diagram showing a method for measuring solidified shell non-uniformity.

Immediately, the solidified shell 11 generated on the surface of the immersed body was immersed in molten steel and held for a certain period of time. The solidified shell 11 generated on the surface of the immersed body was peeled off from the immersed body and placed on a flat plate. The concavity is dt, d3) and the distance between adjacent concavities and convexities (
! I), and calculate the integral value of the ratio (Δd/!2) between the difference in the thickness of the solidified shell 11 between adjacent asperities (for example, Δd=dz dt) and the distance between adjacent concave and convex portions (for example, ll1). The value divided by the number of measured pieces was taken as the average solidified shell heterogeneity.

Average solidified shell heterogeneity = Δd/ff1 = (Σld+
dt-11/! ;II)/n1 trout As the experimental conditions, the carbon content in the molten steel and the surface texture of the immersed body were changed. Carbon content in molten steel is 0.01~
It was varied within a range of 0.50%.

At this time Si: 0.20%, Mn: 0.60% P:0. O15% S: 0.010%.

5oJAjl: kept almost constant at 0.02-0.15%.

FIG. 7 is a graph showing the relationship between the carbon content in molten steel and the average degree of solidification shell heterogeneity. This figure shows a flat copper immersed body (thickness: 10 mm) that is immersed for 8 to 9 seconds, then pulled up and the average solidified shell non-uniformity of the solidified shell formed on the surface of the immersed body. This is the result. The straight line in the vertical direction indicates the variation in the average solidification shell heterogeneity, and the mark . indicates the average value.As is clear from this figure, at the same solidification time, the carbon content in the molten steel is 0.10.
When it is in the range of ~0.15%, the average degree of non-uniformity of the solidified shell is large, forming a solidified shell with severe irregularities. In the steel types mentioned above where the carbon content in the molten steel is in the range of 0.10 to 0.15%, the initial solidification shell surface (surface on the side of the immersed body) is characteristically
A tortoiseshell-like uneven pattern is observed. This tortoise-shell-like uneven pattern has a high center and groove-like depressions around the periphery. In addition, for steel types that undergo hyperperitectic solidification with a carbon content of 0.15 or more, 0.
Similar to steel types with subperitectic solidification of 10 to 0.15%, δ→γ
Despite the transformation, no tortoiseshell-like uneven pattern is observed on the surface of the solidified shell on the side of the immersed body. This is because in steel types that undergo hyperperitectic solidification, a liquid phase remains even during the δ→γ transformation, and the large transformation stress during the δ→γ transformation can be absorbed by the liquid phase portion.

Figure 8 shows the solidification time, the size of the unevenness on the molten steel side of the initial solidified shell (distance between adjacent depressions and openings = + nm), and the size of the unevenness on the immersed body side (tortoise shell) of the initial solidified shell (equivalent circle diameter = m).
It is a graph figure showing the relationship of (m). The same immersion body as in Section 7 was used.

・The size of the irregularities on the side of the shell immersed body (distance between concavities and openings of the tortoise-concave pattern on the side of the solidified shell immersed body =!; IP) remains formed at the early stage of solidification and does not change with the immersion time, but
The size of the unevenness on the solidified shell molten steel side marked O (distance between protrusions -5 on the solidified shell molten steel side - ρM) increases as solidification progresses.

Figure 9 shows the solidification time and the size of the tortoise-concave pattern on the solidified shell side (equivalent circle diameter = m
It is a graph figure showing the relationship of (m).

Three types of immersed bodies were used in this experiment: a flat copper plate, a copper plate with vertical grooves A, and a copper plate with vertical IBs. and groove 1
3 has a depth of 0.5 mm, a width of 0.5 mm, and an interval of 13.
It is 711m. The vertical groove B has a depth of 0.5 mm on the edge 13, a width of 0.5 mm, and an interval between the grooves 13 of 1.0++ m. As is clear from this figure, when the grooves 13 are densely arranged on the surface of the immersed body 12, the size of the hexagonal pattern on the side of the solidified shell immersed body is about 10~
The size was 15 mm. From these findings, for subperitectic solidifying steels with a carbon content of 0.10 to 0.15%,
When the initial solidified shell is formed, the solidified shell is bent due to thermal strain and transformation stress due to δ→γ transformation, and voids are locally created between the solidified shell and the mold wall. This becomes a tortoiseshell-like uneven pattern that can be observed on the surface of the solidified shell immersed body, and once this uneven pattern is formed, it remains forever thereafter. These voids cause a decrease in the amount of heat removed from the solidified shell and non-uniform growth of the solidified shell. Therefore, in order to suppress the non-uniformity of the solidified shell of the above-mentioned steel types, it is necessary to prevent the formation of the tortoise-shell-like uneven pattern on the surface of the solidified shell on the immersed body side during initial solidification, or to make it as small as possible so that it does not overlap with the surface of the immersed body 12. It is sufficient to prevent the formation of voids between the solidified shells. however,
As shown in FIG. 9, even if the intervals of the grooves 13 formed on the immersed body 12 are made denser by setting them to 0.7 mm or 1.0 mm, the size of the hexagonal uneven pattern on the surface of the solidified shell immersed body does not change. Therefore, the present inventors attempted an experiment in which grooves were formed on the surface of the copper immersion body in a lattice pattern so that heat could be removed unevenly in an area smaller than the hexagonal uneven pattern.

FIG. 10 is a graph showing the relationship between immersion time and average solidified shell non-uniformity. In this figure, the mark is thickness 8III
+, When using a copper flat plate immersion body with a cooling water volume of 90 (1/am), ○ indicates a grid-like groove on the surface of the copper plate, the groove depth is 0.5 mm, the width is 0.5 mm, The figure shows the case where an immersion body with grid grooves with a spacing of 5 mm is used.The straight line section shows the variation in the average solidified shell non-uniformity.As is clear from this figure, the immersion body with grid grooves on the surface of the copper plate is used. The average solidified shell non-uniformity is smaller in the solid copper plate than in the immersed copper plate, and the variation is also smaller.

FIG. 11 is a graph showing the relationship between the solidified shell thickness and the immersion time of the immersed body. O mark indicates when a copper flat plate immersion body is used; * mark indicates that a grid-like groove is formed on the surface of the copper plate, and the groove depth is 0.5 mm and the width is 0.5 n+a.

This is a case where an immersion body with a grid groove interval of 5 mm is used. In addition, the Mu mark has lattice grooves on the surface of the copper plate, and the depth of the grooves is 0.
．． This is a case where an immersion body with a diameter of 5 mm, a width of 0.5 mm, and a grid groove interval of 10 mm is used. As is clear from this figure,
Due to the presence of the lattice grooves, slow cooling occurs and the solidified shell thickness does not become thinner. Therefore, by using a mold with lattice grooves, the non-uniformity of the solidified shell thickness can be reduced, which can reduce the surface cracking of the steel types mentioned above, and since slow cooling is not required, there is no need to reduce the casting speed, so direct rolling is possible. can.

Next, we investigated the optimal conditions for lattice grooves to reduce surface cracks.

(1) Effect of lattice groove spacing FIG. 12 is a graph showing the relationship between lattice groove spacing and average solidified shell non-uniformity. In this figure, the immersion time of the immersed body is 8 to 9 seconds, the depth of the groove is 0.5 ml11, and the width is 0.5 m.
m, the spacing of the lattice grooves is o~3omffl (0, 5, 10,
These are the results when using immersed bodies (15, 30 mm). As can be clearly seen from this figure, by making the spacing between the lattice grooves smaller than the unevenness of the tortoise-shell pattern made of flat copper plates shown in Figure 8, a large effect was achieved in improving the average solidified shell non-uniformity. Demonstrate. On the other hand, if it is too small, the processing will be complicated, the overall heat removal will be reduced, and the cooling will be slow, making it impossible to secure the casting speed required for hot direct rolling.
A groove spacing of m is optimal.

(2) Effect of the shape of the lattice grooves FIG. 13 is a graph showing the relationship between the shape of the lattice grooves and the average solidified shell non-uniformity. In this figure, the immersion time of the immersed body is 8 to 9 seconds, and the groove depth is 0, 5 mm, and 1.0 m.
m, 1.5mm, groove width 0.5mm, 1.0mm
, 1.5 mm, and the results were obtained using an immersion body with a grid groove interval of 5 mm. There are three types of cross-sectional shapes of the lattice grooves: V-shape, U-shape, and square shape, as shown in Section 13.

As is clear from this figure, when the groove depth is 1.5 mm and the width is 1.5 mm, the average solidified shell non-uniformity is 0.
1 or more, and insertion of molten steel was observed. If the depth of the clearing is 1.0mm or less and the width is 1.0mm or less,
Regardless of the cross-sectional shape of the lattice grooves, the average solidified shell non-uniformity is improved in all cases.

(3) Influence of snow particles embedded in the grooves Next, we investigated the average solidification shell non-uniformity when materials with different thermal conductivities were embedded in the grooves. Here, the ratio of the local thermal resistance values in the body portion and the groove portion was defined as h, and was evaluated as the average minus ripening degree of the immersed body. Figure 14 shows the average of the immersed body.
It is an explanatory diagram showing the degree of ripening.

The thermal resistance Rcu of the copper flat plate portion of the immersion body 12 is Rcll=d
au/λ. 1 d cu: Thickness (m) λ of the copper flat plate portion of the immersed body. U=Thermal conductivity of the copper flat plate part of the immersed body (Kcal/m-Hr・℃) On the other hand, the thermal resistance R of the groove part in which a dissimilar metal or ceramic 6 having a different thermal conductivity than copper is embedded is R1,= dal
I′/λ. , +d6/λ.

dcu’: Thickness from the bottom of the groove to the cooling water surface (m) dc: Groove depth (m) ^C: Heat conduction of embedded material (Kcal/m-Hr・’C) From this, the thermal resistance ratio was set as h=Ro/Ro.

FIG. 15 is a graph showing the relationship between various embedded materials having different thermal conductivities and the average solidified shell non-uniformity. The experimental conditions were a groove width of 0.5 mm, a lattice groove interval of 5 mm, a V-shape, and the grooves were made of different metals or ceramics (Ni, Cr,
An immersed body in which BN and ZrO2)6 were embedded to give a thermal resistance ratio of 1.5 was used, and the immersion time of the immersed body was 8 to 9 seconds. As is clear from this figure, there is a difference in the amount of materials embedded in the grooves, namely metals (Ni, Cr) and ceramics (BN).
, Zr02), no difference in average solidified shell heterogeneity was observed.

FIG. 16 is a graph showing the relationship between the thermal resistance ratio and the average solidified shell non-uniformity. The experimental conditions were as follows: a width of 0.5 mm, a grid interval of 5 mm, a v-shape, an immersion body in which Ni was embedded as the dissimilar metal or ceramic, and the immersion time of the immersion body was 8 to 9 seconds. As is clear from this figure, when the thermal resistance ratio is 1.5 or more, the average solidified shell non-uniformity is improved. In order to maintain the thermal resistance ratio at 1.5 or more, when Ni is embedded in a 10 mm copper plate, it is necessary to ensure a depth of 1.8 mm or more.

(4) Location of providing lattice grooves As mentioned above, in order to prevent uneven solidification, it is necessary to avoid forming a hexagonal pattern on the surface of the solidified shell facing the immersion body. This is because, as shown in FIG. 8, a hexagonal pattern is formed on the side of the solidified shell immersed body in the initial stage of solidification, and the size of this pattern does not change as the solidified shell grows. On the other hand, the unevenness on the molten steel side has a size corresponding to the hexagonal uneven pattern on the surface of the solidified shell on the side of the immersed body at the initial stage of solidification, and the interval between them increases as the solidified shell grows. Therefore, the unevenness on the molten steel side will not be generated from the initial stage of solidification unless the uneven pattern on the immersed body side is formed, and will grow into a uniform solidified shell. In other words, if the formation of uneven patterns on the immersed body side is prevented at the initial stage of solidification, non-uniform growth can be completely prevented thereafter.

Therefore, in order to suppress unevenness, the lattice grooves only need to be located just below the meniscus of the molten steel at the early stage of solidification, and may be within a range of about 601!1 Ifi from the meniscus of the molten steel. 30mm from the top of the mold
It is preferable to provide it in a range up to around 0 mm.

FIG. 1 is a schematic diagram of the upper part of a mold according to an embodiment of the present invention.
(a) is a front view, and (b) is a sectional view taken along line AA in (a). 1 is a mold, 2 is a groove, 3 is a cooling water slit, and the grooves 2 are arranged in a grid pattern. 4 is the molten steel surface side of the mold, and 5 is a cooling surface of the mold, and since a cooling water slit is arranged on this surface, the mold 1 is cooled.

(Example 1) FIG. 2 is a schematic diagram of the upper part of a mold according to an example of the present invention, in which (a) is a front view, (b) is an AA sectional view of (a), and (c
) is an enlarged view of the groove portion in (b). As shown in FIG.
mm, 1001 mm from the center of the width to both ends
000, a total of 2000 mm). The grooves 2 were shaped like a square, and were arranged in a grid pattern with a depth of 0.5 mm, a width of 0.5 mm, and an interval of 10 mm.

Using this mold, the actual carbon content is 0.10-0.1
A 5% steel grade was cast. FIG. 3 is a graph showing the relationship between slab surface cracking index and casting speed according to an embodiment of the present invention. The Φ mark indicates ○ when using the conventional mold.
The marks are when a mold according to an embodiment of the present invention was used. As is clear from this figure, the slab surface cracking index of this example is improved compared to the conventional technology, and during high-speed casting (
1.5 m/min or more), the slab surface cracking index is improved.

(Example 2) FIG. 4 is a schematic diagram of the upper part of a mold according to another example of the present invention, in which (a) is a front view, (b) is a sectional view taken along line AA in (a),
(c) is an enlarged view of the groove in (b). As shown in FIG.
3001, too from the center of the width to both ends
It was set in a range of 2000+nm). Groove 2 is square and has a depth of 3.5 mm and a width of 0.5 mm.
, were arranged in a grid pattern with an interval of 10 mm. Furthermore, groove 2
Ni was filled in as a dissimilar metal 6. The Ni filling depth was set to have a thermal resistance ratio of 1.5, and was set to be 3.5 mm from the surface of the 19 mm copper mold 1. Mold 1 has a length of 950III in the casting direction! l, width 2320mm, thickness 4
0 mm, and the depth of the cooling water slit 3 is 21 mm.

Using this mold, the actual carbon content is 0.10-0.1
A 5% steel grade was cast. FIG. 5 is a graph showing the relationship between slab surface cracking index and casting speed according to another embodiment of the present invention.・The mark indicates when casting using conventional technology is used.
The O mark indicates the case where a mold of another embodiment of the present invention was used. As is clear from this figure, the slab surface cracking index of this example is improved compared to the conventional technology, and the slab surface cracking index is improved even during high-speed casting (1.5 m/mix or higher). .

The slab surface cracking index in this example is further improved than in Example 1, which uses a mold provided with only grooves. Considering the difference between the results of Example 1 and Example 2, if only grooves were provided, mold powder would enter the grooves due to the vibration of the mold during casting, lowering the thermal resistance ratio, and increasing the average solidified shell. It is considered that the degree of non-uniformity is lower than that when dissimilar metals or ceramics (Ni, Cr, BN, Zr02) are embedded.

In this way, in order to make the slab surface crack index a more preferable value, it is desirable to use a mold in which grooves are provided and dissimilar metals or ceramics are embedded in the grooves.

[Effects of the Invention] Since the present invention is configured as described above, (1) it improves the uneven solidification of steel types that undergo subperitectic solidification where the carbon content in the molten steel is 0.10 to 0.15%; be able to.

(2) The slab surface cracking index was improved. Furthermore, by filling the grid-like grooves with dissimilar metals or ceramics,
The slab surface cracking index is further improved.

(3) High-speed casting of this steel type is possible and direct rolling is possible, improving productivity.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the upper part of a mold according to an embodiment of the present invention, Fig. 2 is a schematic diagram of the upper part of a mold according to an embodiment of the present invention, and Fig. 3 is a schematic diagram of a slab surface crack according to an embodiment of the present invention. A graph showing the relationship between index and casting speed, FIG. 4 is a schematic diagram of the upper part of the mold according to another embodiment of the present invention, and FIG. 5 is a graph showing the slab surface crack index and casting speed according to another embodiment of the present invention. Fig. 6 is a graph showing the method of measuring solidified shell heterogeneity; Fig. 7 is a graph showing the relationship between the carbon content in molten steel and the average solidified shell heterogeneity; Fig. 8 The figure is a graph showing the relationship between coagulation time and the size of hexagonal irregularities.
The figure is a graph showing the relationship between the type of groove and the size of the hexagonal pattern, Figure 10 is a graph showing the relationship between immersion time and average solidified shell non-uniformity, and Figure 11 is a graph showing the relationship between the solidified shell thickness and the immersion of the immersed body. Figure 12 is a graph showing the relationship between lattice grooves and average solidified shell heterogeneity.
Figure 3 is a graph showing the relationship between the shape of the lattice grooves and the average degree of solidification shell non-uniformity, Figure 14 is an explanatory diagram showing the degree of unrestrictedness and unripeness of the immersed body, and Figure 15 shows various embedded materials with different thermal conductivities. Graph diagram showing the relationship between and the average solidified shell heterogeneity, 1st
FIG. 6 is a graph showing the relationship between the thermal resistance ratio and the average solidified shell non-uniformity, and FIG. 17 is a graph showing the relationship between the carbon content and surface cracking index of a conventional copper plate mold. DESCRIPTION OF SYMBOLS 1... Mold, 2... Groove, 3... Slit for cooling water, 4... Molten steel surface of the mold, 5... Cooling surface of the mold, 6...
...Dissimilar metals or ceramics.

Claims (2)

[Claims] (1) In a continuous casting mold made of copper, a depth of 0.5 to 1.
A mold for continuous casting of steel, characterized in that lattice-shaped grooves with a diameter of 0 mm and a width of 0.5 to 1.0 mm are provided, and the intervals between the lattice grooves are 5 to 10 mm. (2) The mold for continuous casting of steel according to claim 1, characterized in that the lattice-shaped grooves are filled with dissimilar metals or ceramics to a depth such that the heat resistance ratio h defined below is 1.5 or more. A mold for continuous casting of steel. Thermal resistance ratio: h = R_c/R_c_u R_c_u: Thermal resistance of the copper plate portion = D_c_u/λ_c_u R_c: Thermal resistance of the dissimilar material embedded portion = D_c_u'/
λ_c_u+D_c/λ_c where D_c_u: Thickness of the copper plate of the mold (m) λ_c_u: Thermal conductivity of the copper plate (Kcal/m・Hr・℃
) D_c_u′: Thickness from the bottom of the dissimilar material embedded part to the cooling water surface (m) D_c: Embedded thickness of the dissimilar material embedded part (m) λ_c: Thermal conductivity of the dissimilar material (Kcal/m・Hr・℃)
)