JPH026037A - Method for continuously casting steel - Google Patents

Abstract

PURPOSE:To prevent uneven solidification in continuous casting for the specific steel by arranging notched parts having the specific size and arrangement at near meniscus of molten steel in a copper-made mold and specifying relation between casting velocity and oscillation cycle of the mold. CONSTITUTION:Grooves (the notched parts) 2 having 0.5-1.0mm depth and 0.3-1.0mm width are arranged on the surface of the copper-made mold 1 for continuous casting at near the meniscus of the molten steel in the mold. The grooves 2 are set at each 5-10mm interval as parallel with drawing direction of a cast slab. Further, the relation between the casting velocity (Vc) and the oscillation cycle of the mold (f) is made to satisfy the inequality I. Different kind of metal (Ni, Cr) or ceramic (BN, AlN, ZrO2) is filled up into the notched parts to the prescribed depth. By this method, the uneven solidification in the steel kind having hypo-peritectic solidification, such as 0.10-0.15% carbon content in the molten steel can be improved.

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 method.

[Prior Art] In recent years, a continuous casting process using a vertical or curved continuous casting machine has become essential for producing slabs. When attempting to manufacture slabs such as blooms and billets using such a continuous casting method, vertical cracks and horizontal cracks may occur on the surface of the slab. FIG. 19 is a graph showing the relationship between the carbon content of a slab and the surface crack index when the slab is cast using a conventional copper plate mold. 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 a steel type with the above carbon content solidifies, it undergoes a transformation process of L→δ+L→crystalline reaction (δ+L→γ)→δ+γ→γ.

Of these, the δ phase is body-centered cubic (bcc), and the γ phase is face-centered cubic (
fcc), and during the transformation from δ to γ, volume shrinks 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 solidification form, and the above stress is applied to the thin solidified shell. It is thought that cracks may occur in some parts. Conventionally, in order to prevent surface cracking of the above steel types, ■ trial and error mold powder was used.
Therefore, attempts were made to prevent surface cracking by changing the casting to a material with lower cracking susceptibility, and (2) reducing the amount of heat removed from the mold and performing slow casting.

[Problem to be solved by the invention] However, in order to prevent the occurrence of surface cracks, it is difficult to select a mold powder that satisfies all of the many casting conditions, and the time and cost are high. It takes.

■When low-speed casting is performed with reduced heat removal from the mold, it becomes difficult to synchronize with the hot rolling mill, making it impossible to perform direct hot rolling or hot charge rolling, which becomes an obstacle to labor-saving and energy-saving steel manufacturing processes. At the same time, there was a problem in that the yield of the product also decreased.

This invention has been made in view of the above circumstances, and is intended to prevent longitudinal cracking of the solidified shell in the initial stage of steel types with subperitectic coagulation with a carbon content of JL of 0.10 to 0.15%, and to prevent surface defects in the slab. The purpose is to provide a continuous casting method for

[Means for Solving the Problems] The method for continuous casting of steel of the present invention provides a method for continuously casting steel in the vicinity of the meniscus of molten steel in the mold on the surface of a copper continuous casting mold to a depth of 0.5 to 1.
．． Omm, width 0.3~1. Provide a notch of Omm,
The said notch is 5 to 10 m parallel to the direction of slab withdrawal.
They are arranged at intervals of m, and the relationship between the casting speed (Vc) during casting and the mold vibration period (f) satisfies the following formula.

10 > V c / f X 1000 However, Vc:
Casting speed (m/mm > f: mold vibration period (1/mix)) Furthermore, a dissimilar metal (N
i, Cr) or ceramic (BN, AJN, Zr
02) can also be filled to a depth where the thermal resistance ratio is 1.5 or more.

However, thermal resistance ratio: h=Rc/R.

RcU: Thermal resistance of the copper plate = Dcu/λcuRc: Thermal resistance of the dissimilar material embedded part = Dcu'/λcu+Dc/^Nikode, Dc,: Thickness of the copper plate of the mold (m>λcu: Thermal conductivity of the copper plate (Kcal) /m-H+”C) Dcu: Thickness from the bottom of the dissimilar material embedded part to the cooling water surface (m) Dc: Embedded thickness of the dissimilar material embedded part (m) λC: Thermal conductivity of the dissimilar material (Kcal/m・H+”C) [Function] The continuous steel casting method according to the present invention has a cutout portion parallel to the casting direction made on the surface of the mold and an oscillation mark perpendicular to the casting direction due to mold vibration. The cooling strength differs between the oscillation area and the non-oscillation area.In the notch area and the oscillation area, which are the weakly cooled areas, the initial shell solidification is slightly delayed.For this reason, a liquid phase remains at regular intervals, and this The liquid phase absorbs the strain caused by contraction and suppresses the initial bending of the solidified shell, preventing the mold from separating from the solidified shell locally.Therefore, heat is removed uniformly, and the thickness of the solidified shell grows uniformly. By carrying out the method 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, there will be no local areas where the solidified shell thickness is thin. Therefore, the shape of the cutout part is set to have a depth of 0.5 to 1.0 mm, a width of 0.5 to 1.0 mm, and a notch interval of 5 to 10 mm, so that stress does not concentrate at the - point. The reason why the casting speed (Vc) and the mold vibration period (f) during casting are limited as shown in the above equations is that the non-uniformity of the solidified shell thickness becomes large if the casting speed is otherwise determined.

[Example] Examples 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 due to thermal strain and transformation stress due to δ→γ transformation, and a gap is locally formed between the solidified shell and the mold wall, which causes the extraction process. A decrease in heat occurs and 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 average -solidification.

Based on this knowledge, in order to investigate the cause of the non-uniformity of the solidified shell thickness, we prepared a 100 mm x 360 mm immersed body (water-cooled flat plate = cooling water of the immersed body at a rate of 90 (1/mm)).
It is immersed in molten steel using an air cylinder from directly above a 00 kg melting furnace and held for a certain period of time to determine the unevenness of the solidified shell (solidified shell thickness non-uniformity is expressed as Δd/, &. Δd:
The thickness difference (d protrusion - d concavity) between adjacent asperities (p: distance between adjacent asperities) was investigated. FIG. 6 is a diagram showing a method for measuring solidified shell thickness non-uniformity. That is, the solidified shell 11 generated on the surface of the immersed body that is immersed in molten steel and held for a certain period of time.
Peel it from the immersed body, place it on a flat plate, and solidify the shell 11 thick between adjacent concavities and convexities (here, convexity is d2, concaveness is d+, ds).
The distance between adjacent asperities (ffl >
The value obtained by dividing the integral value of the ratio (Δd/ρ) between the distance between adjacent asperities (for example, ρl) by the number of measurements was taken as the average solidified shell thickness non-uniformity.

Average solidified shell thickness Average - degree - As for the experimental conditions, the carbon content in the molten steel and the surface texture of the immersed body were changed. The carbon content in molten steel is 0.01 to 0.
It was varied within a range of 50%.

At this time, Si: 0620%, Mn: 0.60%.

Pro, 015%, S: 0.010%.

So! ; IAJ2: kept almost constant at 0.10-0.30%.

FIG. 7 is a graph showing the relationship between the carbon content in molten steel and the average solidified shell thickness non-uniformity. Using a flat copper immersed body (thickness: 10 lffl), after immersing it for 8 to 9 seconds, the copper immersion body was pulled up and the average solidified shell thickness non-uniformity of the solidified shell formed on the surface of the copper immersion body was measured. did. The straight line portion indicates the variation in the average solidified shell thickness non-uniformity, and the mark . indicates the average value.

As is clear from this figure, when the carbon content in the molten steel is in the range of 0.10 to 0.15% at the same solidification time, the average degree of non-uniformity of the solidified shell is large, and a solidified shell with severe irregularities is formed. It shows.

In steel types in which the carbon content in the molten steel is in the range of 0.10 to 0.15%, a hexagonal pattern of irregularities is characteristically observed on the surface of the initial solidified shell (surface on the side of the immersed body). This tortoise-shell-like uneven pattern has a high center and groove-like depressions around the periphery.

In addition, in steel types that undergo hyperperitectic solidification with a carbon content of 0.15% or more, the surface of the solidified shell is immersed despite the δ → γ transformation, similar to steel types that undergo subperitectic solidification with a carbon content of 0.10 to 0.15%. No tortoiseshell-like uneven pattern is observed on the side of the 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 irregularities on the molten steel side of the initial solidified shell (distance between adjacent recesses and openings = mm), and the size of the irregularities on the immersed body side (tortoiseshell shape) of the initial solidified shell (equivalent circle diameter = mm).
) is a graph diagram showing the relationship between. The same immersion body as in FIG. 7 was used.

・The size of the irregularities on the side of the shell immersed body (marked) The distance between concavities and openings of the tortoise-concave pattern on the side of the solidified shell immersed body (lip) remains formed at the early stage of solidification and does not change with the solidification time, but O
The size of the unevenness on the molten steel side of the solidified shell (the distance between the protrusions 6 on the molten steel side of the solidified shell, &M) becomes larger as solidification progresses.

Figure 9 shows the type of groove 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).

There are three types of grooves: copper flat plate, copper vertical groove A, and copper vertical groove B. The vertical groove A has a vertical groove 13 on the surface of the immersion body 12, and the depth of the groove 13 is 0.5 mm. , 1 fortune is 0.5m +++, Ko 1
3 is 0.7 mm apart. Vertical groove B has a depth of 13 of 0.5 mm, a width of 0.5 mm, and an interval of 1.0 m between grooves 13.
It is m. As can be seen from this figure, the size of the hexagonal pattern on the side of the solidified shell immersed body is due to the detailed pattern on the surface of the immersed body 12.
When grooves were inserted, the size was about 10 to 15 m+n, which was the same as when the flat plate was not grooved. From these findings, in steel types that undergo subperitectic solidification with a large carbon content of 0.10 to 0.15%, when the initial solidification shell is formed, the solidification shell is bent due to thermal strain and transformation stress due to δ→γ transformation. Voids locally form between the solidified shell and the mold wall. This becomes a tortoise-like uneven pattern and is observed as R on the surface of the solidified shell immersed body.
Once this uneven pattern is formed, it remains forever. These voids cause a decrease in heat removal from the solidified shell and non-uniform growth of the solidified shell. Therefore, in order to suppress the uneven growth of the solidified shell of the above-mentioned steel types, the formation of a tortoise-shell pattern on the surface of the solidified shell on the side of the immersed body during initial solidification should be prevented or minimized, and the surface of the solidified shell and the solidified shell should be made as small as possible. It is sufficient to avoid forming a void between them. However, as shown in FIG. 9, even if dense vertical grooves with grooves 13 of 0.7 mm or 1.0 mm are formed on the immersed body 12, the size of the tortoiseshell pattern on the surface of the solidified shell immersed body will not change. Therefore, the inventors of the present invention attempted an experiment in which grooves were formed on the surface of the copper immersion body in a lattice pattern in order to allow non-uniform heat removal in an area smaller than the hexagonal uneven pattern. FIG. 10 is a graph showing the relationship between immersion time and average solidified shell thickness non-uniformity. In this figure, the * mark is an immersed flat copper plate with a thickness of 8 mm and a cooling water flow rate of 90 ρ/min, and the ○ mark is an immersed body with grid-like grooves on the surface of the copper plate, and the depth of the grooves is 0. .5mm, width is 0. ．． 5mm,
The grid spacing is 5 mm. The straight line portion indicates the variation in the average solidified shell thickness non-uniformity. As is clear from this figure, the average solidified shell non-uniformity of the immersed body with a grid-like pattern on the surface of the copper plate is smaller than that of the immersed body of a flat 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. The mark ○ is a dipping body of a flat copper plate, and the mark ・ is a dipping body with grid-like grooves on the surface of the copper plate, the depth of the grooves is 0.5 mm, the width is 0.5 mm,
The interval between the lattice grooves is 5 mm. The mark is an immersion body with grid grooves on the surface of a copper plate, the depth of the grooves is 0.5n+m, and the width is 0.
．． 5 mm, and the interval between the grating grooves is 10 IIlffi. As is clear from this figure, the presence of the lattice grooves results in slow cooling, 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 is reduced, so the surface cracking of the steel type mentioned above can be reduced and there is no need to reduce the casting speed since the cooling is not 1M.

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 thickness nonuniformity. The soaking time of the soaked body is 8-9
seconds, the depth of the groove is 0.5mm, the width is 0.5mm, and the interval of the grating groove is 0~30mm (0°5.1.0, 1.5.3
0 mm>. As is clear from this figure, by making the spacing between the lattice grooves smaller than the unevenness of the hexagonal pattern made of flat copper plates shown in Figure 9, it has a great effect on improving the non-uniformity of the average solidified shell thickness. . On the other hand, if it is too small, the processing will be complicated, and the overall heat removal will be reduced, resulting in slow cooling, making it impossible to secure the necessary casting speed.
A groove spacing of mm 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 non-uniformity of the average solidified shell thickness. The soaking time of the soaked body is 8 to 9
In seconds, the depth of the groove is 0.5 mm1, 0 mm, 1,
5m+++, width 0.5mm, 1.0mm.

1.5 mm, and the interval between the grating grooves is 5 mm. The cross-sectional shapes of the grating grooves are V-shaped, U-shaped, and square, as shown in Figure 13.
It is a kind.

As is clear from this figure, when the depth of the groove was 1.5 mm and the width was 1.5 ml11, the average solidified shell thickness nonuniformity was 061 or more, and insertion of molten steel was observed.

When the depth of the groove is 1.0 mm or less and the width is 1.0 mm or less, the average solidified shell thickness non-uniformity is improved regardless of the cross-sectional shape of the lattice groove.

(3) Influence of embedding foreign substances inside the groove Next, we investigated the degree of non-uniformity of the average solidified shell thickness when substances with different thermal conductivities were embedded in the groove.

Here, the ratio of local thermal resistance values in the body part and the groove part is h
It was evaluated as the degree of unripeness of the immersed body. FIG. 14 is an explanatory diagram showing the degree of unrestricted ripening of the immersed body.

The thermal resistance R6U of the copper flat plate portion of the immersed body 12 is Rou-dc
u/λ.

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-C) On the other hand, the thermal resistance R6 of the groove part filled with the substance 6 whose thermal conductivity differs from that of copper is Ro-dcu'/λcu+dc/ λ.

d'cu': Thickness from the bottom of the tube to the cooling water surface (m) d
, : Groove depth (m) λ. :Thermal conductivity of the embedded material (Kcal/m-Hr·'C) From this, the thermal resistance ratio is set as h=Rc/Rcu.

FIG. 15 is a graph showing the relationship between various embedded materials having different thermal conductivities and the non-uniformity of the average solidified shell thickness. The experimental conditions were that the groove depth was 0.5 mm, the width was 0.5 + nm, the grating width was 5 mm, the groove shape was V-shaped, and the thermal resistance ratio hG, t1.
．． 5. The embedding material 6 is metal (NL, Cr)-ceramic (BN, Zr02), and the immersion time of the immersion body is 8 to 9 seconds. As is clear from this figure, the buried material 6 is metal (Ni.

Cr) and ceramics (BN, Zr02) had improved effects on the average solidified shell thickness nonuniformity, and there was no difference depending on the filling material 6. Furthermore, there was no difference in the average solidified shell heterogeneity between the groove and the groove.

FIG. 16 is a graph showing the relationship between the thermal resistance ratio and the average solidified shell thickness non-uniformity. The experimental conditions were a groove depth of 0.5
mm, the width was 0.5 mm, the grid spacing was 5 mm, the shape was V-shaped, the filling material was Ni metal, 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 thickness 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+n+u or more.

(4) Range of lattice grooves As mentioned above, in order to prevent uneven solidification, it is necessary to prevent the formation of the hexagonal pattern that occurs on the surface of the immersed solidified shell. 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, if the uneven pattern on the molten steel side is not even formed on the immersed body side, the unevenness will occur at the beginning of solidification.
It does not form from the initial stage, resulting in uniform solidified shell growth. 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 range of the lattice grooves needs to be only directly below the meniscus at the initial stage of solidification, and the range is 60 m from the meniscus.
The range may be up to 300 mm, but considering fluctuations in the molten steel level, it is actually preferable to range up to about 300 mm from the top of the mold.

Next, the inventors thought that oscillation marks occur due to mold vibration in continuous casting, and that the horizontal grooves in the lattice grooves have already been provided, so we created a mold with only vertical grooves at 5 mm intervals on the copper plate. The interval between the oscillation marks is 5mm.
A casting test was conducted using a small continuous casting machine by adjusting the casting speed (Vc) and mold vibration period (f) so that the following results were obtained.

In FIG. 17, the depth of the groove was 0.5 mm, the width was 0.5 mm, the grid spacing was 5 mm, and the range of the vertical grooves was 300 mm from the upper end of the mold surface. Then, the casting speed (V
It is a graph figure which shows the relationship between the degree of non-uniformity of the average solidified shell thickness when a casting test was carried out by changing the mold vibration period (f) and the mold vibration period (f). When the value expressed by the casting speed (Vc) and the mold vibration period (f), Vc/f x 1000, was smaller than 10, the average solidified shell thickness non-uniformity became small. This V
c / f There is.

Therefore, in continuous casting using an actual machine, the mold only needs to have vertical grooves, and the horizontal grooves can be replaced by oscillation marks by changing the mold vibration cycle in accordance with the casting speed.

Figure 18 shows a mold with lattice grooves at 5 mm intervals and a mold with W grooves at 5 mm intervals, with the casting speed (Vc) and mold vibration period (f) adjusted.
The average solidified shell thickness nonuniformity was compared when oscillation marks were generated. There was no difference in the non-uniformity of the average solidified shell thickness between the two methods, and the non-uniformity of the average solidified shell thickness was significantly improved compared to the conventional method.

Table 1 shows molds with lattice grooves at 5mm intervals,
The mold machining cost in actual production was compared with a mold in which only vertical grooves were provided at 5 mm intervals. The mold processing cost for a mold with lattice grooves at 5 mm intervals is about 1.0% compared to a mold with only vertical grooves at 5 mm intervals.
The cost will increase five times.

Table 1 This calculation example is an example of the machining area of a 300 x 2000 mm mold.

This invention has been made based on the above findings.

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' of (a>. 1 is a mold, 2 is a 3 is the slit for cooling water, and the grooves 2 are arranged in a grid pattern. 4 is the molten steel surface of the mold, and 5 is the cooling surface of the mold, and the slit for cooling water is placed in this part. , the mold 1 is cooled.

(Example 1) Fig. 2 is a schematic diagram of the upper part of a mold according to an embodiment of the present invention, (a) is a front view, (b) is a sectional view taken along line AA' in (a), and (c) is an enlarged view of part 2 of the groove in (b). As shown in Figure 2, 50 to 30 mm from the upper end of the molten steel surface 4 side of the mold l.
A mold 1 with a volume of 0 ml11 has V-shaped grooves 2 with a depth of 0.5 mm and a width of 0.5 mm arranged parallel to the drawing direction at 10 mm intervals in a length range of 2000 mm in the width direction by 1000 m +++ from the center of the width. used.

A steel type with a carbon content of 0.10 to 0.15% was actually cast using this mold. At this time, change the mold vibration period according to the casting speed, and always keep the oscillation mark intervals at 8II.
I made it to be II11. 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 symbol indicates a conventional method, and the O symbol indicates an embodiment of the present invention. As is clear from this figure, this example has an improved slab surface cracking index compared to the conventional method, 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' of (a>, and (c ) is an enlarged view of the groove 2 part in (b).As shown in FIG.
00 mm, 2 in the width direction by 1000 mm from the center of the width.
000 mm length, 3.5 mm depth and 0.00 mm width.
5 mm square grooves 2 were arranged parallel to the drawing direction at 10 mm intervals, and Ni metal was used as the dissimilar metal 6 in the grooves 2. The depth of the Ni metal is 3.5 nu from the surface of the 19 mm copper mold 1 so that the thermal resistance ratio is 1.5.
It was set as n. Mold 1 has a length of 950 mm in the casting direction and a width of 2
The diameter of the cooling water slit 3 is 320 mm, the thickness is 40 mm, and the depth of the cooling water slit 3 is 21+ nm.

A steel type with a carbon content of 0.10 to 0.15% was actually cast using this mold. At this time, change the mold vibration period according to the casting speed, and keep the oscillation mark interval at 8 mm.
I made it so that 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 the conventional method, and the mark ○ indicates another embodiment of the present invention.

As is clear from this figure, the slab surface cracking index in this example is improved compared to the conventional method, and the slab surface cracking index is improved even during high-speed casting (< 1, 5 m/min or higher). . As a result, direct rolling becomes possible,
Productivity has also improved.

Here, we have explained the case of Ni as the dissimilar metal, but C
r, and ceramics (BN, AfflN.

Similar effects were obtained with Zr02).

[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) High-speed casting of the above steel types has become possible, and slab surface defects have been improved.

(3) Direct rolling became 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;
Figure 2 is a schematic diagram of the upper part of the mold according to an embodiment of the present invention, Figure 3 is a graph showing the relationship between slab surface crack index and casting speed according to an embodiment of the present invention, and Figure 4 is a diagram of the invention. FIG. 5 is a graph showing the relationship between the slab surface crack index and casting speed according to another embodiment of the present invention, and FIG. 6 is a diagram showing the solidified shell non-uniformity. A diagram showing the measurement method, Figure 7 is a graph showing the relationship between the carbon content in molten steel and the average degree of solidification shell heterogeneity, and Figure 8 is a graph showing the relationship between solidification time and the size of hexagonal irregularities. , Figure 9 is a graph showing the relationship between groove type and hexagonal pattern size, 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 solidified shell thickness and immersion. Figure 12 is a graph showing the relationship between the immersion time of the body, Figure 12 is a graph showing the relationship between the spacing of the lattice grooves and the average solidified shell heterogeneity, and Figure 13 is the relationship between the shape of the lattice grooves and the average solidified shell heterogeneity. FIG. 14 is an explanatory diagram showing the degree of unrestricted ripening of the immersed body. FIG. 15 is a graph diagram showing the relationship between various embedded materials with different thermal conductivities and the average degree of solidification shell heterogeneity. The figure is a graph showing the relationship between the thermal resistance ratio and the average solidified shell non-uniformity, and Figure 17 shows an example of the present invention when a casting test was conducted by changing the casting speed (Vc) and mold vibration period (f). Fig. 18 is a graph showing the relationship between average solidified shell thickness non-uniformity and Fig. 18 shows another embodiment of the present invention.
Figure 19 is a graph showing the relationship between the average solidified shell thickness non-uniformity when oscillation marks are generated, and Figure 19 is a graph showing the relationship between the carbon content and surface cracking index of a conventional molded copper plate. . 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.

Claims (2)

[Claims] (1) In copper continuous casting, a depth of 0.5 to 1.
．． Provide a notch with a width of 0 mm and a width of 0.3 to 1.0 mm,
The said notch is 5 to 10 m parallel to the direction of slab withdrawal.
Arranged at intervals of m, and casting speed (V_c) during casting
A continuous casting method for steel, characterized in that the relationship between and the mold vibration period (f) satisfies the following formula. 10>V_c/f×1000 However, V_c: Casting speed (m/min) f: Mold vibration period (1/min) (2) The steel according to claim 1, characterized in that the notch portion is filled with dissimilar metals (Ni, Cr) or ceramics (BN, AlN, ZrO_2) to a depth such that the heat resistance ratio is 1.5 or more. Continuous casting method. However, thermal resistance ratio: h=R_c/R_c_u R_c_u: Thermal resistance of the copper plate part=D_c_u/λ_c_u R_c: Thermal resistance of the dissimilar material embedded part=D_c_u_'/λ_c_u+D_c/λ_cwhere, D_c_u: Thickness of the copper plate of the mold (m ) λ_c_u: Thermal conductivity of 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・℃)
)