JPS63224844A - Mold for horizontal continuous casting - Google Patents

Abstract

PURPOSE:To prevent witness crack developed on cast billet surface by arranging a cylindrical inserting material having thermal conductivity less than that of a mold body on the inner circumferential face of the mold body and specifying the relation between thickness and thermal conductivity of the inserting material. CONSTITUTION:The thermal conductivity of the inserting material 25 arranged on the inner circumferential face at upstream side of drawing direction in the mold body 20 is less than that of the mold body 20, to prevent solidified shell from becoming extremely thick. The inserting material 25 is to satisfy the condition in the inequality at the time of using (t) (cm) for this thickness and K (cal/cm.sec. deg.C) for this thermal conductivity at the using temp. The molten steel 1 in a tundish 16 is introduced to the mold 20 from the nozzle 13 through an intermediate ring 19. By this mold, the development of witness mark on the cast billet surface is prevented and the product yield is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to molds used in horizontal continuous casting equipment.

BACKGROUND ART A typical prior art is shown in FIG. Molten steel is stored in the tundish 1, and this molten steel is guided from the tundish/sill 2 through the intermediate ring 3 and from the break ring 4 to the mold 5. The mold 5 includes a mold body 6 made of a material such as copper, and a jacket 7 that cools the mold body 6 with water. The slab is designated by reference numeral 8.

In such horizontal continuous casting equipment, the slab 8 is moved in the drawing direction in order to prevent seizure between the slab 8 and the inner circumferential surface of the mold body 6, and to repair the solidified shell if it is torn off. It is being pulled out intermittently every 9 days. That is, the slab 8 is
The slab 8 is drawn and cast while repeating a cycle consisting of (,) one stop of drawing, or (I) a cycle consisting of one stop of drawing, one stop of pushing back, and one stop. The above-mentioned cycle is repeated several tens to hundreds of times per minute.

The break ring 4 connects the tundish 1 and the mold 5 together with the intermediate ring 3 to prevent leakage of steel and to fix the starting point of the steel in the mold body G. It is made of refractory materials such as ceramics. The mold body 6 of the mold 5 is made of copper or copper alloy and has a high efficiency, so that solidification of the molten steel progresses steadily during the stop or push-back period during the above-mentioned intermittent drawing.

Since the break ring 4 is also cooled by the mold body 6 at this time, the solidified shell indicated by reference numeral 10 in FIG. It becomes extremely thick at 10a. Therefore, at the corner 10a of this solidified shell 10,
This results in a joint developed in the direction perpendicular to the axis of the slab 8, and at this joint, not only the solidified m weave becomes discontinuous, but also a gap is created due to poor welding, resulting in cracks on the surface of the slab 8.

FIG. 8 is an enlarged cross-sectional view of the solidified structure of the solidified shell 10 of such a slab 8 at a portion indicated by section 2 in FIG. 7 near the seam. The surface of the slab 8 is indicated by reference numeral 1.
2. A surface crack that occurs at the joint of the solidified shell 10 is called a witness crack 13, and such a discontinuous solidified structure is called a witness mark 1.
I call it 4. Reference numeral 15 indicates a dendrite structure.

The witness cracks 13 are unlikely to disappear in subsequent processes such as rolling, and therefore it is necessary to scrape off the witness cracks 13 formed on the surface of the slab S. As a result, the yield of the slab 8 is poor, the manufacturing cost is high, and if you try to destroy the witness crack after rolling without scraping off the witness 1'' + scratch 13, the rolling process will be labor-intensive. It will take a while.

An object of the present invention is to provide a horizontal continuous casting mold that can prevent the occurrence of witness cracks formed on the surface of slabs.

Means for Solving Problem 7α The present invention provides a cylindrical insert made of a material having a lower thermal conductivity than the mold body on the inner peripheral surface of the mold body that cools the slab, at least on the upstream side in the drawing direction. When the thickness of this interpolation material is L (c + n) and the thermal conductivity at the operating temperature is k (cal/cm-8ee・℃), 2 < t/k < 1 5
This is a horizontal continuous casting mold characterized by (1).

Function According to the present invention, a cylindrical insert member is provided on the inner circumferential surface of the mold body at least on the upstream side in the drawing direction,
This insert is made of a material with a lower thermal conductivity than the mold body, so it prevents the molten metal from being excessively cooled, and is continuous with the insert on the upstream side in the drawing direction. When a break ring is provided in the insert, the break ring is prevented from being excessively cooled, and in this way, the portion of molten metal that contacts the inner circumferential surface of the insert and the end surface of the break ring is prevented from cooling excessively. In this case, it is possible to prevent the solidified shell from becoming extremely thick. Therefore, at such joints between the solidified shells, poor welding between the solidified shells and the molten metal is suppressed, and the occurrence of witness cracks is suppressed. Even when a break ring is not provided, the occurrence of witness cracks can be suppressed.

In particular, according to the present invention, the thickness of the interpolation material is t(eω),
When the thermal conductivity is k (caf/c+n-5ee ・℃), assuming that the insert is a flat plate and is in perfect contact with the mold body, its thermal resistance is expressed as t/, and this The value is selected to be greater than 2 and less than 15 as described above. t
When /k becomes 2 or less, the witness crack may not be resolved. When t/k is 15 or more, the cooling ability of the intercalating material is too low, and a solidified shell sufficient to withstand friction with the inner surface of the mold body during extraction is not formed.
It becomes difficult to cast at a practical speed.

Embodiment FIG. 1 is a cross-sectional view of one embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the section line ``---'' in FIG. The melt @ 17 in the tanditshu 16 is transferred to the tanditshu nozzle 18
from there through the intermediate ring 19 and into the mold 20. The mold 20 includes a mold body 21 made of resin and a jacket 22 that cools the mold body 21 with water. In the drawing direction 24, the slab 23 repeats a cycle consisting of drawing and stopping, or a cycle consisting of drawing, stopping, pushing back and stopping, and such a cycle is performed, for example, several tens to hundreds of times per minute. The slab 23
is intermittently drawn and manufactured into gr.

According to the present invention, a cylindrical insert member 25 is provided on the inner peripheral surface of the mold body 21 at least on the upstream side (left side in FIG. 1) in the drawing direction 2.1. This inner member 25+ has a first portion 25a that comes into contact with one intermediate ring, and a second portion 25 that has an inner diameter larger than the first g portion 25a. The inner peripheral surface of the second portion 251) is the mold body 21
It is continuous with the inner circumferential surface that contacts the slab 23. As in the case where a break ring is provided upstream of the insert member 25, the first portion 25a keeps the solidification start point of the molten steel constant, and further acts as a stopper for the solidified shell during pushback during intermittent drawing. Therefore, it has the effect of suppressing the tearing of the solidified shell. The intermediate ring 19 is made of zirconia ceramic or the like. The insert material 25 is boron nitride BN.
Alternatively, it is made of a refractory material such as zirconia Z+.02.

Axial length A of the insert material 25! 1 is, by any chance, an interpolation material 2
51] and the mold 21, the thickness of the solidified shell formed in the slab 23 will not be torn off when it is pulled out in the direction of the arrow 24. The length is selected to be, for example, about 3 ctn or more.

The length in the axial direction of the second portion 251 of the insert material 25! 2 is chosen as the following value. The slab 23 is pulled out in the pulling direction 2.A while repeating a cycle consisting of pulling out and stopping, or a cycle consisting of pulling out, stopping, pushing back, and stopping, as in the case of a double chain, and is pulled out to the above-mentioned length. 2 is the length by which the slab 23 is pulled out during each cycle;
In other words, it is selected to be longer than the one stroke. This length 12 is, for example, about 2.5 cm or more.

The shapes of the inner circumferential surfaces of the first portion 25a and the second portion 251 of the insert material 25 and the inner circumferential surface of the mold body 21 following them are uniformly formed in the direction of the rIJi line, and in this embodiment, It has a right cylindrical shape.

The experimental results of the present inventor are shown in Table f:tS1, and the experimental results conducted for comparison are shown in Table 2. Here, the thickness of the second portion 251) of the insert 25 is shown, and k is the thermal conductivity of the insert at around 500° C., which is considered to be the temperature of the insert during use.

In each of these experiments, the number of strokes in each cycle of intermittent drawing was 7 to 2511, and the number of cycles was 60 to 150 cycles per minute. According to experiments conducted by the inventor of the present invention, it has been confirmed that the depth of the witness mark formed on the slab 23 can generally be reduced by increasing the number of cycles per minute of intermittent drawing. .

(Margin below) Table 1 (Example) As a result of the experiment shown in Table 1, the cross section of the slab 23 is as shown in FIG. 3, and the witness mark 27 extending from the surface 2G of the slab 23 is , is inclined with respect to the axial direction (horizontal direction in FIG. 3) of the slab 23, and its radial length II is relatively shallow. However, there are cracks in slab 23.
There is no L. ,: the initial solidified shell formed in the inner seed material 25 does not have a deep end surface in the direction perpendicular to the axis;
and indicates that it is not overly cooled. Reference numeral 28 indicates a dendrite structure. In this manner, according to the present invention, the witness mark 27 is shallow;
Moreover, no cracks occurred.

On the other hand, in the above-mentioned Table 2, cracks occur in the first comparative example and the second comparative example, and the depth of the cracks is ++! 51
In the comparative example, the average is 0.7 mtt=, and in the second comparative example, the average is 0. Exn+n. f shown in Table 2:
In tS3 and the fourth comparative example, the solidified shell was torn off within the mold body 21, making it impossible to stably pull out the slab 23.

Therefore, from Tables 1 and 2, the thickness of the second portion 25f of the interpolation material 25 is set to j(c+o), and the thickness of the interpolation material 25
The thermal conductivity of the material is k(cai/am-see ・℃
), it can be seen that when t/k is less than 2, cracks occur on the surface of the slab 23, and when t/k is more than 15, the solidified shell is torn and cannot be pulled out stably.

FIG. 4 is a cross-sectional view of another embodiment of the invention.

Parts corresponding to those in the previous embodiment are given the same reference numerals.

In this example, what should be poured is 7 ml of tanditsu and 1 ml of water.
The inner peripheral surfaces of 8, intermediate ring 19, and mold body 21 are as follows:
A right cylindrical insert 29 is formed across the inner diameter and has a uniform inner diameter in the axial direction. Since the insert 29 extends over the tundish nozzle 18 and the intermediate ring 19, the solidified shell is prevented from entering the abutment surface 3o of the tundish nozzle 18 and the intermediate ring 19, thereby Tanditshu nozzle 18 and intermediate ring 19
and can be prevented from being damaged.

Furthermore, in this embodiment, since there is no step on the inner surface of the insert 29, the seam of the solidified shell becomes shallower, making it possible to more effectively prevent witness cracks.

Experimental results for the example shown in FIG. 4 are shown in Table 3, and for comparison, experimental results are shown in Table 4. Here, the thickness of the insert material 29 is shown, and k is the thermal conductivity of the insert material at around 500"C, which is considered to be the temperature of the insert material during use. In each of these experiments, the difference between intermittent drawing and One stroke in each cycle is 15 = 601 nm, and the number of cycles is 35 to 130 cycles per minute.

According to the experimental results shown in Table 3, no witness cracks were generated in the slab 23. On the other hand, in the fifth and sixth comparative examples in Table 4, a witness crack occurs, and in the fifth comparative example, the depth of the witness crack is 0.1 on average.
2"Im, and in the sixth comparative example, the average depth is 0.13+n
+n. In the seventh to tenth comparative examples, the mold body 2
The solidified shell was torn off within the insert material 29 where No. 1 was present, and stable extraction could not be performed. From the experimental results shown in Tables 3 and 4, L/
It can be seen that the value must be greater than 2 and less than 15.

FIG. 5 is an axial cross-sectional view of an insert 34 according to another embodiment of the present invention. This inner ψ material 34 is constructed by forming a plurality of (three in this embodiment) layers 31, 32, and 33 in the radial direction. The inner layer 31 is made of zirconia Z r O2 having excellent wear resistance, and the outer layers 32 and 33 are made of boron nitride BN or the like having high thermal conductivity and have a laminated structure. When the thickness of each layer 31 t 32 t 33, etc. is [i, their thermal conductivity is ki, and the number of layers 31, 32, 33, etc. is 11, according to the present invention, the following equation 1 holds true. Configure it as follows.

Note that if there is a void between each layer, the configuration is made so that the second equation holds true, including the value related to air.

As another embodiment of the present invention, depending on the baking strength 11 and wettability of the insert material to molten steel, the slab may be continuously pulled out to smoothly perform casting, instead of being pulled out intermittently.

It is also possible to cast other molten metals instead of molten steel.
Moreover, it is also possible to apply not only horizontal continuous casting but also other casting methods such as vertical continuous casting.

Effects As described above, according to the present invention, an insert material is provided on the inner peripheral surface of at least the upstream side in the drawing direction of the mold main body for cooling the slab, and the thickness of the insert material is set as l: (c + n). , when the thermal conductivity is k (caf/cm ・sec ・℃), L/ is selected to have a value greater than 2 and less than 15, so the cooling ability of the mold body becomes loose, and therefore Witness marks become shallower, and the occurrence of witness cracks can be suppressed.

As mentioned in connection with the prior art, this eliminates the need for surface preparation operations to remove cracks in the slab, thus improving product yield and shortening the process.
It becomes possible to realize cost reduction. Furthermore, according to the present invention, it is also possible to cast steel types that are highly susceptible to cracking.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention. ￥S2 figure is the first
A cross-sectional view taken from the section line ■-■ in the figure, Figure 3 is the slab 23
FIG. 4 is a cross-sectional view of an embodiment of the pond according to the present invention, FIG. 5 is a cross-sectional view perpendicular to the axis of interpolation +134 of still another embodiment of the present invention, and FIG. is a cross-sectional view of the prior art, FIG. It is an enlarged sectional view. 16... Tanditshu, 17... Molten steel, 18...
・S- dish nozzle, 19...intermediate ring, 20~・
・Mold, 21... Mold body, 22... Jacket, 23... Slab, 24... Pulling direction, 25
, 29゜34... Interpolation material agent Patent attorney Number of strokes Kei part 16 1 knee

Claims (1)

[Claims] A cylindrical insert made of a material having a lower thermal conductivity than the mold main body is provided on the inner circumferential surface of the mold main body that cools the slab at least on the upstream side in the drawing direction, and this inner peripheral material The thickness of the is t (cm), and the thermal conductivity at the operating temperature is k (
1. A mold for horizontal continuous casting, characterized in that 2<t/k<15 when cal/cm・sec・℃).