JPH07106428B2 - Mold for continuous casting of metal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mold for continuous casting using a mold containing ceramic or cermet in the production of a metal material such as iron.

2. Description of the Related Art In the production of metal materials, so-called continuous casting, in which molten metal is continuously cast, has rapidly developed in terms of process saving and energy saving.

FIG. 3 shows an outline of horizontal continuous casting as an example of continuous casting. In the casting, the copper mold 1 and the tundish 5 are connected using a break ring 9, and the molten metal 6 is injected from the tundish 5 into the mold 1 for continuous casting. At this time, casting is performed while oscillating the casting mold 1 or the casting slab 7 for the purpose of improving lubrication of the solidified metal (cast slab) 7 and the casting mold 1. However, a slab cast by this method has a drawback that cold shut marks due to oscillation are generated in the surface layer of the slab, which causes defects. Then, measures such as cutting off the surface defects are taken.

Therefore, many proposals have been made in the past to prevent defects caused by the cold shut mark. As one of the methods, there is a method of using a ceramic or the like in a mold used for continuous casting and gently cooling the metal to prevent defects caused by cold shut marks.

For example, Japanese Unexamined Patent Publication (Kokai) No. 52-50929 discloses a mold containing a refractory and a graphite tube, and Japanese Unexamined Patent Publication (Kokai) No. 58-151939 discloses heat resistance / lubrication.
Corrosion resistant cermet conduit-It is disclosed that there is a possibility of steel production in the mould.

According to this method, Mitsubishi Steel Technical Review, Vol.19, No.1,2 (198
Cold shut marks are reduced as described in 5). However, the ceramic or cermet used for this has erosion resistance that can withstand erosion of molten metal, heat resistance that can withstand high temperatures, thermal shock resistance that can withstand rapid heating, etc.
Alternatively, many properties such as lubricity with a solidified metal (cast slab) and proper thermal conductivity for proper solidification of the metal are required. Such ceramics are described in Mitsubishi Steel Technical Report, Vol.19, No.1,2, (1985) mentioned above.
There are also BN, TiB ₂ , Si ₃ N _4, etc. and the cermet mentioned above.

However, these ceramics or cermets are used at high temperatures, for example above 1500 ° C for iron. Alternatively, there is a large temperature gradient in the ceramic or cermet because the inside is in contact with the molten metal and is heated to a high temperature, and the outside is in contact with the water-cooled copper plate. Furthermore, even if the preheating is sufficient at the start of casting, it is difficult to preheat to the molten metal temperature.
There is rapid heating when the molten metal first flows into the ceramic part. Due to these thermal shocks, the ceramic is cracked and damaged. Because of this, many new ceramics have been developed in recent years, but none have sufficiently satisfied the required erosion resistance, heat resistance, thermal shock resistance or lubricity, and appropriate thermal conductivity. .

Problems to be Solved by the Invention The present invention is for preventing slab surface defects, used in a mold containing ceramic or cermet, and improved thermal shock resistance without impairing erosion resistance of ceramic or cermet, It also provides a ceramic or cermet that ensures proper thermal conductivity.

Means for Solving the Problems The gist of the present invention is to provide a mold for continuous casting of metal containing ceramic or cermet, wherein the ceramic or cermet has a two-layer structure, and the inner layer material is a metal oxide. , 90% by volume or more of ceramic materials which are one or more of nitrides, carbides and borides,
Except for the ceramic material, the ceramic material is composed of pores or metal and has a thickness of 0.05 mm or more and 3 mm or less, and the outer layer material is one or more of metal oxides, nitrides, carbides and borides. It should occupy 35% by volume or more and 80% by volume or less, be composed of pores or metals other than ceramics, have a thickness of 0.3 mm or more and 10 mm or less, and have its inner layer material and its outer layer material integrally joined. In a mold for continuous casting of metal, which is characterized by

In order to prevent slab surface defects in continuous casting of metal, there has been proposed a method of incorporating ceramics or cermet in a copper mold as described above, and ceramics used for this has thermal shock resistance, erosion resistance, Ensuring properties such as lubricity and thermal conductivity is an important issue.

Therefore, as a result of studying this, the filling rate of oxides, nitrides, carbides or borides (also referred to as ceramic materials) of the metals that make up the ceramic is large in thermal shock resistance, erosion resistance, lubricity, and thermal conductivity. It was discovered that these characteristics can be ensured by properly controlling the filling rate of the ceramic material.

FIG. 1 shows an outline of a mold containing ceramic or cermet.

One end of the ceramic 2 contained in the copper mold 1 is inserted into the molten metal, and the other outer surface is in contact with a water-cooled copper plate for cooling. Then, the molten metal 6 flows in, is cooled, and the metal is solidified. Since the surface temperature of the slab is lowered in the area where the solidification is sufficiently performed on the mold outlet side, it is not always necessary to use ceramics or cermet, and carbon 3 with high lubricity or copper with high cooling power can be used. .

As for ceramics, if the filling rate of the ceramic material is increased and the porosity is decreased, the thermal conductivity is increased, the erosion resistance is increased, and the lubricity is improved. However, the thermal shock resistance is reduced.
On the contrary, if the filling rate of the ceramic material is lowered and the pores are enlarged, the thermal shock resistance is improved. However, the thermal conductivity, erosion resistance and lubricity are reduced.

Therefore, the ceramics contained in the mold have a two-layer structure, a material having high erosion resistance is used for the inner layer in contact with the metal, and a material having high thermal shock resistance is used for the outer layer to assist the thermal shock resistance of the inner layer. However, if only two layers are used, this effect is not exhibited, and the inner layer and the outer layer must be integrally joined. Moreover, its thickness is also regulated in order to ensure proper heat conduction.

From these facts, the inner layer material is composed of 90% by volume or more of a metal oxide, nitride, carbide or boride ceramic material, and other than the ceramic material is composed of pores or metal and has a thickness of 0.
It is necessary to make it between 05mm and 3mm. 9 ceramic materials
If the content of the pores or metals other than the ceramic material is less than 0% by volume and exceeds 10% by volume, the corrosion resistance of the ceramic is improved due to the penetration of the molten metal into the pores or the reaction between the molten metal and the metal in the ceramic. descend. A decrease in erosion resistance leads to a decrease in lubricity due to damage to ceramics, which causes breakout due to slab restraint.

The composition other than the ceramic material may be pores or one in which metal powder is dispersed in the pores. These have the function of releasing the thermal stress applied to the ceramics, and the larger the number, the better the thermal shock resistance. As described above, the erosion resistance decreases, so it is necessary to regulate the amount to be less than 10% by volume. As a preferred embodiment, there is a ceramic having a porosity of less than 10% by volume, which contains zirconia or a zirconia compound having excellent corrosion resistance and lubricity of molten metal.

Also, if the thickness of the ceramic is less than 0.05 mm, the damage is rapid and it is not practical. Furthermore, if the thickness of the ceramic exceeds 3 mm, the outer layer material must be thinned to ensure proper heat conduction. If the outer layer material is made thin, the thermal stress of the inner layer material cannot be absorbed, which causes cracking. Therefore, the thickness of the inner layer material must be 3 mm or less.

The outer layer material has the main purpose of absorbing the thermal stress of the inner layer material and preventing cracks from occurring.The ceramic material is composed of 35% by volume or more and 80% by volume or less, and is composed of pores or metals other than the ceramic material and has a thickness of It should be 0.3 mm or more and 10 mm or less.

When the ceramic material is less than 35% by volume and the porosity or the metal exceeds 65% by volume, the portion B inserted into the molten steel is easily corroded and damaged by the molten steel, which is not preferable. Further, when the porosity exceeds 65% by volume, the thermal conductivity is lowered, the outer layer material needs to be thinned, and the thermal stress of the inner layer material cannot be absorbed. On the other hand, if the metal content exceeds 65% by volume, the difference in thermal expansion from the inner layer material becomes too large, and conversely cracking tends to occur, which is not preferable. For this reason, the ceramic material of the outer layer must be 35% by volume or more. If the ceramic material of the outer layer exceeds 80% by volume, the thermal shock resistance deteriorates and cracks occur due to the relationship with the inner layer material. For this reason, the ceramic material of the outer layer material must be 80% by volume or less.

The thickness of the outer layer material is determined in terms of absorbing thermal stress of the inner layer material and ensuring proper heat conduction. When the thickness of the outer layer material is less than 0.3 mm, deformation due to thermal stress of the inner layer material cannot be absorbed and there is a risk of cracking, which is not preferable. On the other hand, if the thickness exceeds 10 mm, proper thermal conductivity cannot be secured and an economical structure cannot be obtained, which is not preferable. Further, since the cooling capacity is small, the temperature of the ceramic of the inner layer material rises, which causes deterioration of erosion resistance. Because of these, the thickness of the outer layer material is 0.3 mm or more, 10 mm
Must be:

As a preferred embodiment, there is a so-called cermet, which is a ceramic having high thermal conductivity, high thermal shock resistance, and anti-corrosion property, containing more than 20% by volume and less than 60% by volume of metal powder such as molybdenum or nickel. .

Further, as described above, simply stacking the inner layer material and the outer layer material causes slippage between the inner layer material and the outer layer material even if the inner layer material thermally expands, and the effect of preventing cracking of the inner layer material is not exhibited. For this reason, the inner layer material and the outer layer material must be joined together without slippage. As a joining method, there are a method of producing two layers at the time of ceramic production, and a method of producing each separately and then joining each.

In the production of ceramics, the raw materials of fine powder are blended with the intended formulation,
Then, it is molded and then baked and hardened. The method of molding is to put it in a mold and press it to solidify. Or there is a clay-like molding
Firing may be simply baking at a high temperature or pressing. When this is molded, it is molded into two layers and then baked and solidified to obtain two joined layers. Alternatively, they can be joined by stacking the respective ceramics and firing under pressure.

The present invention is particularly effective for horizontal continuous casting of metal such as iron.
It can also be used for horizontal continuous casting of other metals or vertical casting. Further, not only the method of inserting the ceramic or cermet into the molten metal as shown in FIG. 1, but also the break ring 9 or the like as shown in FIG. 2 is used to connect the tundish and the mold, and the ceramic or cermet is connected to the mold. It can also be applied to interior casting.

Furthermore, 3 layers or more of ceramic or cermet,
Alternatively, it is also applicable to casting in which a metal layer is provided on the outside of ceramic or cermet.

Examples Table 1 shows an outline of the examples.

The outline of the casting equipment used was the same as that shown in FIG. 3, and the mold shown in FIG. 1 was attached to this for casting.

Insert each ceramic or cermet shown in Table 1 into the mold, and attach a carbon pipe 3 having the same diameter as the ceramic and a length of 130 mm to the subsequent mold outlet side,
This was sandwiched between water-cooled steel molds.

As the metal, stainless steel having 0.04% carbon, 0.6% silicon, 1.4% manganese, 8% nickel and 18% chromium was cast. The temperature in the tundish was kept at 1490 to 1520 ℃ by medium frequency heating. The drawing length was 20 to 30 mm per cycle, and the casting speed was changed by changing the number of cycles (number of oscillations / minute).

The pores shown in Table 1 were obtained from the difference between the true density and the bulk density of ceramic or cermet.

Run Nos. 1 to 3 are comparative examples, and Run Nos. 4 to 6 are inventive examples.

In execution No. 1, a zirconia ceramic having a thickness of 3 mm and a porosity of 6% was used. At the time of casting 6 m, it was interrupted due to slab restraint. The slab after casting had cracks, which caused restraint.

Run No. 2 used 4 mm thick BN ceramics with a porosity of 12%. At the time of 12 m casting, it was suspended due to restraint. Used B
Since N-ceramic has a high porosity and is soft, cracking due to thermal shock was not observed, but it was severely damaged by wear and restrained, resulting in interruption.

In Run No. 3, a 2 mm thick, 13 vol% molabden-zirconia and a 4 mm thick, 62 vol% molybdenum-zirconia were integrally molded and then fired and joined. The porosities were 2% by volume and 3% by volume, respectively. During casting for about 1 m, the slab seized with the mold and was restrained and interrupted. No cracking of the ceramic was observed.

In Example No. 4, a zirconia ceramic having a thickness of 0.1 mm and a cermet containing 52% by volume of molybdenum in zirconia having a thickness of 0.5 mm were integrally molded. The porosities were 9% by volume and 3% by volume, respectively. After casting for about 90 m, good slabs without surface defects were obtained.

Implementation No. 5 is also an example of the present invention, 3 mm thick, 2% by volume molybdenum-
Zirconia, ZrB ₂ and BN and a 10 mm thick Si ₃ N ₄ + Al ₂ O ₃ ceramic were integrally molded. The porosities were 2% by volume and 23% by volume, respectively. It was possible to cast for about 40 m, no surface defects were observed, and good slabs were obtained.

In Run No. 6, 0.5 mm-thick TiN and 4 mm-thick 49% by volume nickel-zirconia were hot isostatically pressure-bonded at 1500 ° C. and 1500 atm, and sandwiched and cast in a steel mold. The porosities were 2% by volume and 3% by volume, respectively. About 85 m was cast, and the slab was good with no surface defects.

EFFECTS OF THE INVENTION According to the present invention, it is possible to prevent the occurrence of surface defects in continuously cast slabs of metal, extend the life of ceramics or cermets, improve the casting efficiency, improve the casting yield, reduce the maintenance cost, etc. It contributes to the development of industry.

[Brief description of drawings]

FIG. 1 and FIG. 2 are cross-sectional views showing the outline of a mold for continuous casting of metal containing ceramic or cermet. FIG. 3 is a sectional view showing an outline of equipment for continuous casting of metal. 1 ... Copper mold, 2 ... Interior ceramics, 3 ... Carbon ring, 4 ... Tundish connection nozzle, 5 ...
… Tundish, 6… Molten metal, 7… Solidified metal (cast slab), 8… Slab extraction device, 9… Break ring, A
…… Slab withdrawal direction, B …… Insert part in molten metal.

Claims (2)

[Claims] 1. A mold for continuous casting of metal containing ceramic or cermet, wherein the ceramic or cermet has a two-layer structure, and the inner layer material is a metal oxide.
90% by volume or more of ceramic material, which is one or more kinds of nitride, carbide, and boride, is composed of pores or metals other than ceramic material, and has a thickness of 0.05 mm or more, 3 m
m or less, and the outer layer material is a metal oxide, nitride,
A ceramic material, which is one or more kinds of carbides and borides, occupies 35% by volume or more and 80% by volume or less, and is composed of pores or metals other than the ceramic material and has a thickness of 0.3 mm or more and 10 mm or less, A mold for continuous casting of metal, wherein the inner layer material and the outer layer material are integrally joined. 2. The mold for continuous casting of metal according to claim 1, wherein a ceramic containing zirconia or a zirconia compound is used as the inner layer material and a cermet is used as the outer layer material.