KR20230082192A - Mold and method for mold - Google Patents

Abstract

The mold according to an embodiment of the present invention is formed on a body having an inner space in which molten steel is accommodated, a first coating layer formed on an inner wall surface of the body facing the inner space, and containing ceramic and metal, and formed on the first coating layer and carbon fiber ( and a second coating layer containing carbon fiber).
Therefore, according to the embodiments of the present invention, the thermal conductivity of the mold can be reduced. In addition, in a mold provided with a coating film having low thermal conductivity, it is possible to prevent the coating film from being damaged by heat. Thus, it is possible to prevent or suppress the surface of the solidification shell from becoming uneven or uneven due to shrinkage of the solidification shell due to supercooling. That is, the height of the surface of the solidification shell can be made even or flat by the mold having low thermal conductivity. Therefore, it is possible to prevent or suppress the occurrence of cracks on the surface of the cast steel due to contraction of the solidification shell.

Description

Mold and method for manufacturing mold {Mold and method for mold}

The present invention relates to a mold and a method for manufacturing the mold, and more particularly, to a mold and a method for manufacturing the mold capable of preventing or suppressing the occurrence of defects on the surface of a cast steel due to shrinkage of a solidification shell.

A continuous casting device is a device for injecting molten steel into a mold, solidifying it into a cast steel, and continuously drawing the cast steel from the mold. The mold is made of Cu (copper) with good thermal conductivity, and cooling water is circulated inside. Accordingly, when molten steel is injected into the mold, the molten steel is solidified by the mold in which cooling water is circulated. At this time, among the molten steel accommodated in the mold, the temperature of the molten steel in contact with the inner wall surface of the mold is the lowest. Therefore, the molten steel is solidified from the edge in contact with the inner wall surface of the mold, and the solidification shell begins to be formed. In addition, the thickness of the solidification shell becomes thick as it goes downward.

On the other hand, the mold has very high thermal conductivity, so that the molten steel in contact with the inner wall surface of the mold solidifies quickly. At this time, the solidification shell in contact with the inner wall surface of the mold is supercooled and shrinkage occurs accordingly. And, due to this solidification contraction, the surface height of the solidification shell toward the inner wall surface is not constant and non-uniform. That is, the surface of the solidification shell is not flat or flat, but is bumpy. In addition, the solidification shell may be torn due to excessive shrinkage of the solidification shell. Such non-uniformity and tearing of the surface of the solidification shell causes crack defects on the surface of the cast steel.

In order to prevent this problem, a coating film capable of lowering thermal conductivity was formed on the inner wall surface of the mold. At this time, the NiCo alloy was electroplated or sprayed to form a coating film. However, even if the coating film formed of the NiCo alloy is formed, the thermal conductivity of the mold is still high, and cracks are generated on the surface of the cast steel produced inside the mold.

Korean Patent Publication No. 10-2020-0036533

The present invention provides a mold provided with a coating film having excellent thermal shock resistance and low thermal conductivity, and a method for manufacturing the mold.

The present invention relates to a mold and a method for manufacturing the mold capable of preventing or suppressing damage to a coating film by heat.

A mold according to an embodiment of the present invention includes a main body having an internal space in which molten steel is accommodated; a first coating layer formed on an inner wall surface of the main body facing the inner space and containing ceramic and metal; and a second coating layer formed on the first coating layer and containing carbon fibers.

The thickness of the second coating layer may be 50 μm to 200 μm.

The first coating layer may have a thermal conductivity of 10 W/mK or less.

The ceramic of the first coating layer may include zirconia (ZrO ₂ ), and the metal may include Ni (nickel), Cr (chromium), Al (aluminum), and Y (yttrium).

The ceramic may include Yttria Stabilized Zirconia ( _YSZ ) in which Y ₂ O ₃ , SiO ₂ , TiO ₂ , and Fe ₂ O ₃ are mixed with the zirconia (ZrO 2 ).

The thickness of the first coating layer may be 0.5 mm to 1.5 mm.

A method for manufacturing a mold according to an embodiment of the present invention includes the steps of preparing a main body; forming a first coating layer having lower thermal conductivity than that of the body on the surface of the body; and forming a second coating layer including carbon fibers on the first coating layer.

The process of forming the first coating layer may include preparing a first raw material including ceramic; preparing a second raw material containing metal; preparing a first material by mixing the first raw material and the second raw material; and spraying the first material on the surface of the main body.

In preparing the first raw material, a raw material having a thermal conductivity of 3 W/mK or less may be prepared, and in preparing the second raw material, a raw material having a thermal conductivity of 15 W/mK or less may be included.

The first raw material may include Yttria Stabilized Zirconia (YSZ), and the second raw material may include Ni (nickel), Cr (chromium), Al (aluminum), and Y (yttrium).

In preparing the first raw material, Y ₂ O ₃ is 7 wt% to 8 wt%, SiO ₂ is 0.5 wt% to 1 wt%, TiO ₂ is 0.1 wt% to 0.3 wt%, Fe ₂ O ₃ is 0.1 wt% % to 0.3 wt%, ZrO ₂ is adjusted to be contained as the remaining balance, and in preparing the second raw material, Cr is 19 wt% to 22 wt% and Al is 9 wt% to 12 wt% , Y is adjusted to be more than 0 wt% and less than 2 wt%, and Ni is contained in the remaining balance.

In mixing the first raw material and the second raw material, the ratio of the content (A ₂ ) of the second raw material to the content (A ₁ ) of the first raw material is 1:2 to 2:1.

The process of forming the second coating layer may include heating the body on which the first coating layer is formed; spraying a second material containing C (carbon) onto the first coating layer; Adsorbing C (carbon) decomposed from the second material onto the surface of the first coating layer; and growing carbon fibers on the surface of the first coating layer by precipitating C (carbon) through a catalytic action of Ni (nickel) contained in the first coating layer.

According to the embodiments of the present invention, the thermal conductivity of the mold can be reduced. In addition, in a mold provided with a coating film having low thermal conductivity, it is possible to prevent the coating film from being damaged by heat. Thus, it is possible to prevent or suppress the surface of the solidification shell from becoming uneven or uneven due to shrinkage of the solidification shell due to supercooling. That is, the height of the surface of the solidification shell can be made even or flat by the mold having low thermal conductivity. Therefore, it is possible to prevent or suppress the occurrence of cracks on the surface of the cast steel due to contraction of the solidification shell.

1 is a schematic diagram of a casting apparatus including a mold according to an embodiment of the present invention.
2 is a three-dimensional view showing a mold according to an embodiment of the present invention.
Figure 3 is a cross-sectional view showing the cross-sectional shape of the mold by cutting the mold along the line AA' of FIG.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, only these embodiments will complete the disclosure of the present invention, and will fully cover the scope of the invention to those skilled in the art. It is provided to inform you. In order to explain the embodiments of the present invention, the drawings may be exaggerated, and the same reference numerals in the drawings refer to the same components.

1 is a schematic diagram of a casting apparatus including a mold according to an embodiment of the present invention.

Referring to FIG. 1, the casting apparatus includes a tundish 10 that receives molten steel M from a ladle and temporarily stores it, and a mold that receives molten steel M from the tundish 10 and initially solidifies it into a certain shape. 200, a nozzle 30 for supplying molten steel M of the tundish 10 to the mold 200, arranged in the casting direction from the lower side of the mold 200, and casting cast steel drawn from the mold 200 It may include a cooling table 40 for solidifying by spraying cooling water to the slab while guiding in the direction.

The molten steel M supplied to and solidified in the mold 200 according to the embodiment may be a type of molten steel that easily or a large amount of cracks occur due to solidification contraction of the solidification shell sh. For example, the molten steel M may be medium carbon steel containing 0.08 wt% to 0.17 wt% of carbon. Of course, the molten steel M is not limited to the above example, and molten steel of various types of steel may be applied.

2 is a three-dimensional view showing a mold according to an embodiment of the present invention. FIG. 3 is a cross-sectional view showing a cross-sectional shape of a mold by cutting the mold along the line A-A' of FIG. 2;

2 and 3, the mold 200 is formed on a body 210 having an inner space IS in which molten steel M can be accommodated and a surface of the body 210 facing the inner space IS. A coating film 220 may be included. In addition, the mold 200 may include a cooling water passage (not shown) provided buried inside the main body 210 so that the cooling water circulates.

The main body 210 may be made of metal or alloy, and may be provided with, for example, a material containing Cu (copper). The main body 210 includes an inner wall surface IF facing the inner space IS and an outer wall surface OF that is opposite to the inner wall surface IF and is exposed to the outside. And, as shown in FIG. 2 , the main body 210 may have, for example, a rectangular inner space IS.

Also, the main body 210 may include a plurality of walls. That is, the main body 210 is a pair of each extending in a first direction (X-axis direction) and spaced apart in a second direction (Y-axis direction) crossing or orthogonal to the first direction (X-axis direction). of the first wall 210a and each of them extends in a second direction (Y-axis direction) intersecting with the extension direction (X-axis direction) of the first wall 210a and is spaced apart in the first direction (X-axis direction) A pair of second walls 210b may be included.

The pair of first walls 210a and the pair of second walls 210b are interconnected. For example, one end of the pair of first walls 210a is connected to one end and the other end of the pair of second walls 210b, and one end to one end and the other end of the other second wall 210b. The other ends of the pair of first walls 210a are connected. Accordingly, an inner space IS surrounded by a pair of first walls 210a and a pair of second walls 210b is provided. In this case, the extension length of the first wall 210a in the first direction (X-axis direction) may be longer than the extension length of the second wall 210b in the second direction (Y-axis direction). Accordingly, the first wall 210a may be called a long side wall, and the second wall 210b may be called a short side wall.

The shape of the main body 210 is not limited to the above-described examples, and may be provided in various shapes having an internal space capable of accommodating the molten steel M. In addition, although it has been described above that the body 210 is composed of a pair of first walls 210a and a pair of second walls 210b, the body 210 may be provided as an integral wall. In the above example, the case where the extension lengths of the first wall 210a and the second wall 210b are different has been described, but it is not limited thereto and the extension lengths of the first wall 210a and the second wall 210b are the same. You may.

The coating film 220 is formed on the surface of the body 210 facing the inner space, that is, the inner wall surface IF. Thus, the coating film 220 is formed on the first coating film 220a formed on the inner wall surface IF of the pair of first walls 210a and the second coating film 220b formed on the inner wall surface IF of the second wall 210b. ) can be described as including.

Hereinafter, in describing the main body 210, for convenience of description, the first and second walls 210a and 210b will not be divided into descriptions but will be described as 'body 210'. Therefore, the main body 210 described below may describe at least one of the first wall 210a and the second wall 210b.

In addition, in describing the coating film 220, the first coating film 220a formed on the first wall 210a and the second coating film 220b formed on the second wall 210b are not separately described, and the 'coating film ( 220)'. Accordingly, the coating layer 220 to be described below may describe at least one of the first coating layer 220a and the second coating layer 220b.

Referring to FIG. 3, the coating film 220 is formed on the inner wall surface IF of the main body 210 facing the inner space IS and from the heat of the first coating layer 221 and the molten steel M having low thermal conductivity. A second coating layer 222 formed on the first coating layer 221 to protect the first coating layer 221 and including fibers F is included.

The first coating layer 221 is a layer that reduces heat transfer ability between the main body 210 and the molten steel M. That is, the first coating layer 221 reduces the speed at which the low temperature temperature of the main body 210 is transferred to the molten steel M when the temperature of the main body 210 maintained at a low temperature is transferred to the molten steel by the cooling water circulation. is the layer that In other words, when the molten steel M is cooled and solidified by the main body 210, the low-temperature thermal energy of the main body 210 reduces the transfer rate to the molten steel M, thereby solidifying the molten steel M. This is the layer that slows you down.

A material for forming the first coating layer 221 (hereinafter referred to as a first material) may include a first raw material and a second raw material different from the first raw material. Here, the first raw material may be a raw material having a low thermal conductivity of 3 W/mK or less (more than 0 W/mK), and the second raw material may be a raw material including a metal or an alloy.

The first raw material is a raw material that lowers the thermal conductivity of the first coating layer 221, and a ceramic raw material having a thermal conductivity of 3 W/mK or less (more than 0 W/mK) is used. More preferably, a ceramic raw material having a thermal conductivity of 2 W/mK or less (more than 0 W/mK) is used. For example, the first raw material may include ZrO ₂ (zirconia) and Y (yttrium). That is, the first raw material may include yttria stabilized zirconia (YSZ). More specifically, the first raw material may include ZrO ₂ , Y ₂ O ₃ , SiO ₂ , TiO ₂ , and Fe ₂ O ₃ . At this time, Y ₂ O ₃ is 7wt% to 8wt%, SiO ₂ is 0.5 wt% to 1 wt%, TiO ₂ is 0.1 wt% to 0.3 wt%, Fe ₂ O ₃ is contained at 0.1 wt% to 0.3 wt%, and , ZrO ₂ is contained in the remainder (90.4wt% to 96.3wt%), and may contain other unavoidable impurities. The first raw material, that is, Yttria Stabilized Zirconia (YSZ) has a low thermal conductivity of 1 W/mK or less.

The first raw material is not limited to the above-described examples, and various raw materials made of ceramic materials having low thermal conductivity of 3 W/mK or less may be used.

On the other hand, when the first coating layer 221 is formed using a material having a thermal conductivity as low as 3 W/mK or less, more specifically, a first raw material including yttria stabilized zirconia (YSZ) alone, the first coating layer 221 ) can be lowered to less than 3W/mK.

However, when only the first raw material is used as a material for forming the first coating layer 221, the thermal shock resistance of the first coating layer 221 is low. In this case, cracks or peeling due to the heat of the molten steel may easily occur in the first coating layer 221 . Therefore, a second raw material capable of improving thermal shock resistance is mixed with the first raw material.

The second raw material includes a metal or an alloy, and a material having a thermal conductivity of 15 W/mK or less (more than 0 W/mK), preferably 10 W/mK or less (more than 0 W/mK) is used. To this end, a metal alloy including Ni (nickel), Cr (chromium), Al (aluminum), and Y (yttrium), that is, a NiCrAlY alloy may be used as the second raw material. More specifically, the second raw material contains 19 wt% to 22 wt% of Cr, 9 wt% to 12 wt% of Al, more than 0 wt% of Y and less than or equal to 2 wt% of Ni, and the remainder of Ni (64 wt%). wt% to 71.9 wt%), and may contain other unavoidable impurities.

On the other hand, when the second raw material contains only Ni and Cr, the thermal conductivity of the second raw material is as high as about 70 W/mK. In addition, when the second raw material is mixed with the first raw material as it is, the thermal conductivity of the first coating layer 221 may be high to exceed 15 W/mK. And this increases the thermal conductivity of the mold 200 to cause shrinkage of the solidification shell (sh) due to supercooling, and accordingly, cracks may occur in the cast steel. Therefore, a second raw material containing Al and Y in Ni and Cr is used. At this time, Al is preferably contained in 9 wt% to 12 wt%, and Y is contained in more than 0 wt% and 2 wt%.

On the other hand, if the content of Al in the second raw material is less than 9 wt% or does not contain Y, the thermal conductivity may be high to exceed 15 W/mK. Conversely, when the Al content exceeds 12wt% or Y exceeds 2wt%, the thermal shock resistance of the first coating layer 221 may be reduced because the Ni and Cr content is reduced.

The first material is prepared by mixing the first raw material and the second raw material as described above. At this time, it is preferable that the ratio of the content of the second raw material (A ₂ ) to the content of the first raw material (A ₁ ) is 1: 2 to 2: 1 (A ₂ : A ₁ = 1: 2 to 2: 1) . In other words, it is preferable that the content ratio of the second raw material to the first raw material (A ₂ /A ₁ ) is 0.5 to 2. And when the first coating layer 221 is formed using a material prepared by mixing the first raw material and the second raw material, the thermal conductivity of the first coating layer 221 is 10 W / mK (exceeding 0 W / mK) or less, More preferably, it may be 4W/mK to 6W/mK.

On the other hand, when the ratio of the content of the second raw material to the first raw material (A ₂ /A ₁ ) is less than 0.5, the thermal shock resistance of the first coating layer 221 may be deteriorated because the content of the second raw material is small. Conversely, when the ratio of the content of the second raw material to the first raw material (A ₂ /A ₁ ) exceeds 2, the thermal conductivity may be increased because the content of the first raw material is small. Therefore, the content ratio of the second raw material to the first raw material (A ₂ /A ₁ ) is preferably set to 0.5 to 2.

In addition, the first material including the first and second raw materials as described above may be provided in a powder form including solid particles having a particle size of 10 μm to 50 μm.

The first coating layer 221 is formed by coating the first material on the inner wall surface IF of the body 210, and at this time, it may be formed by a thermal spraying method. That is, it may be formed by a spraying method in which flame or plasma is sprayed together while spraying the first material toward the inner wall surface IF of the main body 210 . At this time, the thickness (T ₁ ) of the first coating layer 221 is formed to 0.5mm to 1.5mm, preferably may be formed to 0.8mm to 1.2mm.

On the other hand, when the thickness (T ₁ ) of the first coating layer 221 is less than 0.5 mm, there is a problem in that the thickness is thin and the thermal conductivity is high. Conversely, when the thickness (T ₁ ) of the first coating layer 221 exceeds 1.5 mm, the bonding force with the main body 210 is weak and can be easily peeled off. Therefore, the first coating layer 221 is formed to a thickness of 0.5 mm to 1.5 mm.

The second coating layer 222 is formed to cover the first coating layer 221 on the opposite side of the body 210 . That is, it is formed on the surface of the first coating layer 221 facing the inner space (IS) and covers the first coating layer 221 so as not to be exposed to the inner space (IS) in which the molten steel (M) is accommodated. The second coating layer 222 serves to protect the first coating layer 221 from the heat of the molten steel M, thereby preventing the first coating layer 221 from being damaged by the heat of the molten steel M. That is, the second coating layer 222 protects the first coating layer 221 from being damaged by the heat of the molten steel M during casting in which the molten steel M is solidified inside the mold 200, so that the mold 200 prevent an increase in thermal conductivity. To this end, the second coating layer 222 needs to have thermal shock resistance capable of withstanding the heat of the molten steel M and has excellent bonding properties with the first coating layer 221 .

The second coating layer 222 may be provided to include fibers. More specifically, it may be prepared to include carbon fibers having a nano-sized diameter.

This second coating layer may be formed using a second material containing carbon (C). A method of forming the second coating layer 222 including carbon fibers (F) is described below. First, an inert gas, such as Ar gas, is supplied into the furnace to create a non-oxidizing atmosphere, and the inside temperature is heated to 300° C. to 400° C. After charging the main body 210 on which the first coating layer 221 is formed into the furnace, a second material (or source material) containing C (carbon) and H (hydrogen) is supplied. In this case, the second material may include, for example, C ₂ H ₂ (acetylene) and may be in the form of a gas. When the second material is supplied into the heated furnace, the second material is decomposed into C (carbon) and H (hydrogen). Then, the decomposed C (carbon) is adsorbed on the first coating layer 221, and at this time, C (carbon) is deposited on the surface of the first coating layer 221 by the catalytic action of Ni contained in the first coating layer 221. As is precipitated, carbon fibers (F) grow.

As the second coating layer 222 is formed by growing fibers F on the first coating layer 221 in this way, the second coating layer 222 and the first coating layer ( 221), the bonding strength between them is improved. That is, the fibers growing on the first coating layer 221 are physically bonded to the surface of the first coating layer 221, and thus the bonding strength between the first coating layer 221 and the second coating layer 222 is improved. In other words, the second coating layer 222 is strongly bonded to the first coating layer 221 .

In addition, since the second coating layer 222 includes fibers made of carbon, that is, carbon fibers, it has excellent thermal shock resistance. Accordingly, the second coating layer 222 can prevent cracking or peeling caused by the heat of the molten steel M. In addition, as cracks and peeling of the second coating layer 222 are prevented, exposure of the first coating layer 221 covered by the second coating layer 222 to molten steel can be prevented. Accordingly, it is possible to prevent cracks caused by the molten steel M from occurring in the first coating layer 221 or being separated from the main body 210 . In addition, it is possible to prevent the thermal conductivity of the mold 200 from being increased due to damage to the first coating layer 221 such as generation of cracks and peeling.

The second coating layer 222 has a thickness (T ₂ ) of 50 μm to 200 μm, preferably 100 μm to 150 μm.

On the other hand, when the thickness (T ₂ ) of the second coating layer 222 is less than 50 μm, the thermal shock resistance of the second coating layer 222 is lowered and may be damaged by the heat of the molten steel M. Conversely, when the thickness (T ₂ ) of the second coating layer 222 exceeds 200 μm, time and cost for forming the second coating layer 222 increase. Therefore, the second coating layer is formed to a thickness of 50 μm to 200 μm.

Hereinafter, the thermal conductivity and thermal shock resistance of the coating films according to the first to third experimental examples will be described.

Table 1 summarizes the composition of the coating film according to the first to third experimental examples and the coating film forming material.

division coating composition coating film forming material Example 1 1st coating layer First coating layer: NiB alloy Second Experimental Example 1st coating layer First coating layer: YSZ + NiCrAlY alloy Example 3 1st coating layer/2nd coating layer First coating layer: YSZ + NiCrAlY alloy
Second coating layer: containing carbon fiber

A specimen was prepared for the experiment, and coating films according to the first to third experimental examples were formed on the specimen. Here, the specimen is made of the same material as the main body of the mold, and may be provided with a material containing copper (Cu). In addition, a pipe through which cooling water can pass is buried inside the specimen, which is later used to evaluate thermal conductivity.

In the first and second experimental examples, a coating film was formed by forming one coating layer, that is, the first coating layer on the specimen. In the third experimental example, a coating film was formed by laminating a first coating layer and a second coating layer on a specimen.

The coating film according to the first experimental example, that is, the first coating layer is formed of an alloy (NiB alloy) containing Ni (nickel) and boron (B), formed to a thickness of 1 mm, and formed by an electroplating method.

The first coating layer of the coating film according to the second and third experimental examples was formed using the first material according to the previously described embodiment. That is, a first material was prepared by mixing a first raw material including stabilized zirconia (YSZ) and a second raw material including a NiCrAlY alloy, and the first material was thermally sprayed on the specimen to form a first coating layer. .

At this time, ZrO ₂ is 91.4 wt%, Y ₂ O ₃ is 7.5 wt%, SiO ₂ is 0.7 wt%, TiO ₂ is 0.2 wt%, Fe ₂ O ₃ is contained at 0.2 wt%, and stabilized zirconia in a powder state ( YSZ) was used as the first raw material. The second raw material includes an alloy including Ni, Cr, Al, and Y, that is, a NiCrAlY alloy. At this time, NiCrAlY alloy powder containing 67 wt% of Ni, 21 wt% of Cr, 11 wt% of Al, and 1 wt% of Y was used as the second raw material. And, the ratio of the content of the second raw material (A ₂ ) to the content of the first raw material (A ₁ ) was 1: 1 (A ₂ : A ₁ = 1 : 1).

The prepared first material was coated on the specimen by a thermal spraying method to form a first coating layer. At this time, a first coating layer having a thickness of 1 mm was formed by coating by a plasma spraying method in which a first material and plasma are sprayed together.

The second coating layer of the coating film according to the third experimental example was formed to include carbon fibers. The formation of the second coating layer will be described in more detail as follows. First, an inert gas, such as Ar gas, is supplied into the furnace to create a non-oxidizing atmosphere, and the inside temperature is heated to a temperature of 450°C. Then, after loading the specimen on which the first coating layer is formed into the furnace, a second material including C ₂ H ₂ (acetylene) is supplied. At this time, C (carbon) decomposed from the second material is adsorbed onto the first coating layer, and carbon fibers are grown on the first coating layer by the catalytic action of Ni contained in the first coating layer. In this way, by growing carbon fibers on the first coating layer for a predetermined time, a second coating layer having a thickness of 100 μm was formed.

Table 2 shows the temperature difference between the specimen and the coating film over time, and the minimum temperature difference and average temperature difference in order to evaluate the thermal conductivity according to the first to third experimental examples.

division Minimum temperature difference (℃) Average temperature difference (℃) Example 1 25.2 62.0 Second Experimental Example 145.6 147.3 Example 3 146.8 148.8

In order to evaluate the thermal conductivity, a thermocouple is installed to communicate with the inside of the pipe buried in the specimen. And, after heating the coating film to 600 ° C using a laser, and when it reaches 600 ° C, the temperature is measured for 15 minutes while circulating cooling water through the pipe. At this time, the temperature of the cooling water (hereinafter, the first temperature) circulating inside the specimen is measured using a thermocouple installed in the pipe, and the temperature of the coating film (the second temperature) is placed by placing a pyrometer disposed on the upper side of the coating film. ) is measured. Accordingly, each of the first temperature and the second temperature over time is measured. Then, the difference between the first temperature and the second temperature is calculated in real time for 15 minutes during which the temperature is measured. Accordingly, the temperature difference according to the lapse of time can be obtained.

These experiments were conducted for each of the first to third experimental examples. And in the first to third experimental examples, the minimum value and the average temperature difference among the temperature differences over time were summarized, which is shown in Table 2.

Referring to Table 2, the minimum temperature difference and the average temperature difference of the second and third experimental examples are larger than those of the first experimental example. From this, it can be seen that the thermal conductivity of the coating films of the second and third experimental examples is lower than that of the coating film of the first experimental example. In addition, it can be seen that when a coating film is formed using a first material containing a first material including yttria stabilized zirconia (YSZ) and a second material including a NiCrAlY alloy, thermal conductivity is reduced.

Also, when comparing the second and third experimental examples, the minimum temperature difference is similar and the average temperature difference is similar. From this, it can be seen that the second coating layer including carbon fibers has little effect on the thermal conductivity. That is, it can be seen that the thermal conductivity is not increased by the second coating layer formed on the first coating layer.

Table 3 summarizes the damage cycles of the coating films in order to evaluate the thermal shock resistance of the coating films of the first to third experimental examples.

For the experiment, the specimens on which the coating films according to the first to third experimental examples were formed were cut and processed into a horizontal length of 10 mm, a vertical length of 10 mm, and a thickness of 10 mm (10 mm * 10 mm * 10 mm). Then, heating and cooling were repeated a plurality of times for the specimens according to the first to third experimental examples. In heating the specimen, the specimen was loaded into an electric furnace heated at 700 ° C and maintained for 10 minutes, and then the specimen was taken out of the furnace and cooled at room temperature for 10 minutes. Here, heating for 10 minutes and then cooling for 10 minutes is regarded as one cycle. And this cycle was repeated a plurality of times, and each time the cycle was completed, whether or not damage such as cracks or peeling of the coating film was checked. And, the number of cycles in which the damage to the coating film occurred was summarized and shown in Table 3.

division coating film damage Example 1 400 times Second Experimental Example Episode 125 Example 3 400 times

Referring to Table 3, in the case of the second experimental example, the coating film was damaged at the 125th round, but in the case of the first experimental example and the third experimental example, the coating film was damaged at the 400th round. From this, it can be seen that the thermal shock resistance of the first and third experimental examples is superior to that of the second experimental example. In addition, it can be seen that the first experimental example and the third experimental example are similar in terms of thermal shock resistance. However, as described in Table 2, in the case of the first experimental example, the thermal conductivity is high and cannot be used as a coating film.

Next, comparing the second experimental example and the third experimental example, the third experimental example in which the second coating layer containing carbon fibers was formed on the first coating layer had a higher coating film damage than the second experimental example without it. That is, the third experimental example in which the second coating layer was formed on the first coating layer had better thermal shock resistance than the second experimental example in which the second coating layer was not formed. From this, it can be seen that the thermal shock resistance of the second coating layer is high. In addition, it can be seen that the first coating layer is prevented from being damaged by high heat by protecting the first coating layer having low thermal conductivity with the second coating layer having excellent thermal shock resistance.

As described above, the coating film 220 formed on the inner wall surface (IF) of the mold 200 is to prevent or reduce the occurrence of cracks on the surface of the cast steel due to excessive solidification shrinkage of the solidification shell (sh). The thermal conductivity needs to be low. In addition, since the coating film 220 is in contact with the molten steel M, the coating film 220 having low thermal conductivity must have excellent thermal shock resistance to the heat of the molten steel M. That is, when the thermal shock resistance of the coating film 220 is excellent, it is possible to prevent the coating film 220 having low thermal conductivity from being damaged by the heat of the molten steel M during casting, and accordingly, the mold 200 has low thermal conductivity. can keep

Therefore, taking the thermal conductivity evaluation of Table 2 and the thermal shock resistance evaluation of Table 3 together as described above, it is desirable to form a coating film like Experimental Example 3, which has low thermal conductivity and excellent thermal shock resistance, on the inner wall surface of the main body. Able to know. That is, the first coating layer 221 is formed by using a first material in which a first raw material containing yttria stabilized zirconia (YSZ) and a second raw material containing a NiCrAlY alloy are mixed, and the first coating layer 221 is formed on the first coating layer 221. It can be seen that it is preferable to form the coating film 220 by forming the second coating layer 222 containing carbon fibers (F) on the.

As such, the coating film 220 according to the embodiment includes a first coating layer 221 and a second coating layer 222 formed on the first coating layer 221 . In addition, the first coating layer 221 is formed of a material including yttria stabilized zirconia (YSZ) and a NiCrAlY alloy. In addition, the second coating layer 222 is formed on the first coating layer 221 to include carbon fibers (F). When the main body 210 having the coating film 220 having the first and second coating layers 221 and 222 is used as the mold 200, damage to the first coating layer 221 caused by the second coating layer 222 is prevented. As this is prevented, the molten steel can be solidified while maintaining low thermal conductivity by the first coating layer 221 .

Accordingly, it is possible to prevent or suppress the surface of the solidification shell sh from becoming flat or uneven and uneven due to excessive shrinkage of the solidification shell sh due to the high thermal conductivity of the main body 210 of the mold 200. . That is, the height of the surface of the solidification shell can be made even or flat by the mold having low thermal conductivity. Therefore, it is possible to prevent or suppress the occurrence of cracks on the surface of the cast steel due to contraction of the solidification shell.

200: mold 210: body
220: coating layer 221: first coating layer
222: second coating layer F: carbon fiber

Claims (13)

A main body having an inner space in which molten steel is accommodated;
a first coating layer formed on an inner wall surface of the main body facing the inner space and containing ceramic and metal; and
A mold including a second coating layer formed on the first coating layer and containing carbon fibers. The method of claim 1,
The mold having a thickness of the second coating layer is 50 μm to 200 μm. The method of claim 1,
The first coating layer has a thermal conductivity of 10 W / mK or less. The method of claim 3,
The ceramic of the first coating layer includes zirconia (ZrO ₂ ), and the metal includes Ni (nickel), Cr (chromium), Al (aluminum), and Y (yttrium). The method of claim 4,
The ceramic mold includes Yttria Stabilized Zirconia ( _YSZ ) in which Y ₂ O ₃ , SiO ₂ , TiO ₂ , and Fe ₂ O ₃ are mixed with the zirconia (ZrO 2 ). The method of claim 3,
The mold having a thickness of the first coating layer is 0.5 mm to 1.5 mm. The process of preparing the main body;
forming a first coating layer having lower thermal conductivity than that of the body on the surface of the body; and
Forming a second coating layer containing carbon fiber on the first coating layer; Method for manufacturing a mold comprising a. The method of claim 7,
The process of forming the first coating layer,
preparing a first raw material including ceramic;
preparing a second raw material containing metal;
preparing a first material by mixing the first raw material and the second raw material; and
A method of manufacturing a mold including spraying the first material on the surface of the main body. The method of claim 8,
In preparing the first raw material, it is prepared to contain a raw material having a thermal conductivity of 3 W / mK or less,
In preparing the second raw material, a method for manufacturing a mold prepared to contain a raw material having a thermal conductivity of 15 W / mK or less. The method of claim 9,
The first raw material includes stabilized zirconia (Yttria Stabilized Zirconia (YSZ)),
The second raw material is a method of manufacturing a mold including Ni (nickel), Cr (chromium), Al (aluminum), and Y (yttrium). The method of claim 10,
In preparing the first raw material, Y ₂ O ₃ is 7 wt% to 8 wt%, SiO ₂ is 0.5 wt% to 1 wt%, TiO ₂ is 0.1 wt% to 0.3 wt%, Fe ₂ O ₃ is 0.1 wt% % to 0.3 wt%, and ZrO ₂ is adjusted to be contained as the remaining balance,
In preparing the second raw material, Cr is 19 wt% to 22 wt%, Al is 9 wt% to 12 wt%, Y is more than 0 wt% and 2 wt% or less, and Ni is contained in the remaining balance. A method for manufacturing a mold to be made. According to any one of claims 8 to 11,
In mixing the first raw material and the second raw material, the mixing ratio of the content (A ₂ ) of the second raw material to the content (A ₁ ) of the first raw material is 1: 2 to 2: 1 Manufacturing method of the mold . According to claim 10 or claim 11,
The process of forming the second coating layer,
heating the body on which the first coating layer is formed;
spraying a second material containing C (carbon) onto the first coating layer;
Adsorbing C (carbon) decomposed from the second material onto the surface of the first coating layer; and
A process of growing carbon fibers on the surface of the first coating layer by precipitating C (carbon) through a catalytic action of Ni (nickel) contained in the first coating layer;

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