JPH01278944A - Heating mold for continuous casting - Google Patents

Abstract

PURPOSE:To obtain a heating mold having long service life whose stable operation can be executed, by arranging the specific refractory to the connecting part between upper heating part and lower cooling part. CONSTITUTION:The mold is constituted with three parts of the upper heating mold A, lower cooling mold C and the connecting part mold B. Particularly, the refractory B at the position connecting the heating mold A with the cooling mold C is necessary to consider on shock resistance, eroding resistance to molten steel, lubricating property, heat conductivity and electric conductivity for improving induction heating property. In order to achieve these purposes, the refractory connecting part B composing of 30-70wt. parts of boron nitride, 20-40wt. parts of one or more kinds among silicon nitride, aluminum nitride and sialon and 5-40wt. parts of one or more kinds of electric conductive ceramic, is arranged. Therefore, suitable heating and heat conductivity of the mold can be obtd. and by achieving the suitable initial solidification, the break-out can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a heatable mold for continuous casting.

[Prior art] Continuous casting equipment is mainly of the vertical type, vertical bending type, curved type, etc., and the molten steel injected into the mold from the tundish through the immersion nozzle continues downward from the meniscus in the mold. It is then cooled and solidified into slabs. The slab is pulled downward at a constant speed, but at this time, inside the mold,
In order to prevent the slab and mold from sticking to each other, the mold is vibrated and a flux of a specified viscosity is applied to the mold.
Lubrication between slabs is essential.

However, when the flux flows between the mold and the slab, it not only forms oscillation marks on the slab surface and deteriorates the surface quality, but also gets caught in the molten steel near the meniscus and forms an initial solidified shell. It is captured and becomes slab inclusions. The occurrence of these oscillation marks and slab inclusions is due to the fact that the melt surface and the initial solidification start point coincide in principle.

For this reason, the present applicant previously proposed in Japanese Patent Application No. 62-87009 a continuous casting technique using a mold having a heating function that separates the meniscus from the solidification start point and causes initial solidification to occur below the meniscus. In this continuous casting technology, the mold consists of an upper heating section and a lower cooling section, and an introduction tube for molten metal is placed all over the inner surface of the mold.The upper inner surface of the introduction tube is heated by induction heating, and the lower inner surface is heated by induction heating. By cooling, initial solidification occurs below the molten metal surface.

[Problems to be Solved by the Invention] As a result of various experiments, the present inventors have found that
It was found that No. 009 had the following problems. In other words, the properties required for a mold are mainly molten steel erosion resistance and induction heating properties in the heated part of the upper part of the mold, and molten steel erosion resistance, lubricity between the mold and the solidifying groin, and extraction properties near the initial solidification start point. In addition to thermal properties, induction heating properties are also required, and the cooling section is required to have lubricity and heat removal properties, and furthermore, it is a prerequisite that all parts have thermal shock resistance.

In this way, in the technology of the prior application, the mold requires different characteristics for each part, but in the molten metal introduction tube disclosed in the prior application, which has a poorly conductive single body or a molten metal introduction pipe with a poorly conductive upper part and a conductive lower part,
Not only is it difficult to carry out stable casting over a long period of time since the characteristics of 1:4 ratio cannot be obtained, but the use of an inlet pipe inevitably increases costs.

Therefore, based on elucidation of the necessary conditions for each part of the mold, the present inventors found an appropriate mold material in terms of molten steel corrosion resistance, lubricity, heat extraction property, induction heating property, and thermal shock resistance. By locating the mold near the initial solidification start point, it is possible to obtain an economical, long-life heating mold that is free from breakouts and the like.

[Means to solve the problem] The gist of the present invention is as follows.

In a continuous casting mold that has a heating section at the top and a cooling section at the bottom, and is configured to initially solidify below the meniscus existing in the heating section, nitriding is applied to the connection between the top heating section and the bottom cooling section. 30 to 70 parts by weight of boron, 20 to 20 parts by weight of one or more of silicon nitride, aluminum nitride, and sialon.
1. A heating mold for continuous casting, characterized in that a refractory joint is formed of 40 parts by weight and 5 to 40 parts by weight of one or more types of conductive ceramics.

The contents of the present invention will be explained in detail below.

The mold structure according to the present invention consists of three parts, and A shown in FIG. 1 is the upper heating mold, which must be heated by an induction coil G and must have corrosion resistance against molten steel and thermal shock resistance. be done. Therefore, it is desirable to use, for example, an alumina-graphite or zirconia-graphite material, which has been used as a submerged nozzle material in conventional continuous casting machines, for this part. The lower cooling mold shown in C requires heat dissipation, lubricity, and thermal shock resistance, so it is lined with a material such as graphite or boron nitride, or it is lined with a material such as boron nitride, fluorocarbon dispersion plating, or metal. Use a plated copper mold. Of course, it is also possible to use copper alone.

The refractory material B, which is the central part of the present invention and which connects the heating mold and the cooling mold, needs to take into consideration impact resistance, molten steel corrosion resistance, lubricity, heat extraction performance, and conductivity to improve induction heating performance. Therefore, as a result of researching various materials, the present inventors found that
30 to 70 parts by weight of hexagonal boron nitride, silicon nitride, aluminum nitride, 1f of Sialon! ! Or 2 or more types
We have found a connecting part material containing 0 to 40 parts by weight and 5 to 40 parts by weight of a conductive material such as titanium nitride or zirconium diboride.

In the above connection material, hexagonal boron nitride is blended for the purpose of imparting lubricity, thermal shock resistance, and heat removal properties, and if it is less than 30 parts by weight, the effect of addition is too small, resulting in cracks during pouring. In addition, if the amount exceeds 70 parts by weight, boron nitride is less corrosive to molten steel, resulting in melting damage due to the inability to obtain a lubricating effect, which causes seizure of the slab and this material. , cannot withstand long-term use.

Silicon nitride, aluminum nitride, and Sialon are added to supplement the corrosion resistance of boron nitride, and are 20 to 4
Add 0 parts by weight. In this case, if it is less than 20 parts by weight, the effect will be small, and if it exceeds 40 parts by weight, the thermal shock resistance will decrease and the problem of cracking will occur.

The conductive material is formulated to enable induction heating, but
It is desirable that the volume resistivity of the material is 102 Ω·-cm or less. The content of the conductive material may range from 5 to 40 parts by weight. If the amount is less than 5 parts by weight, it becomes difficult to control solidification in the mold due to decreased exothermic properties, and it becomes difficult to control the solidification start point. On the other hand, if it exceeds 40 parts by weight, the conductive materials such as titanium nitride and zirconium disulfide become excessive, leading to a decrease in lubricity and impact resistance.

In the figure, E indicates the solidified shell, F indicates the molten steel, H indicates the immersion nozzle, and ■ indicates the initial solidification point.

The contact surface of each mold can be made into a precision grinding surface by machining to prevent leakage of 9114.

The connecting part material in the composition range of the present invention has thermal shock resistance,
Lubricity, heat removal property, resistance? '8 Steel has excellent corrosion resistance, and furthermore, by adding a conductive material, it is possible to appropriately heat and remove heat from the mold, and by achieving appropriate initial solidification, breakout can be prevented.

[Example] Casting was carried out using a continuous casting machine shown in Fig. 1 at a mold size of φ180 and a casting speed of 1 to 2 m/min. Here, the high frequency output applied to the heating mold has a frequency of 1 kHz and an output of 150
The test was carried out at a constant kW. The upper heating mold was made of alumina-graphite, and the lower cooling mold was a nickel-plated copper mold. The experiments were conducted in nine ways as shown in Table 1, and Experiments No. 4 to No. 9 are comparative examples outside the scope of the present invention. Experiments No. 1 to 3 are included in the scope of the present invention, and were satisfactory in terms of crack generation, erosion, etc., and the mold life was 5 or more times in 120 minutes/casting. Ta. In Experiment Nos. 4.5 and 7.8, the mold life was short, 1 to 2 times, due to cracking and erosion of the mold material by molten steel. Also experiment N
o6 had a low boron nitride content of 25 parts by weight, but in this case, the lubricity was poor and the mold and slab were seized,
It fell into operational failure. In Experiment No. 9, the conductive material was reduced to 3 parts by weight, but in this case, the mold could not be heated, the molten steel was heated, and casting under the meniscus was not possible.

[Effects of the Invention] As described above, according to the heating mold of the present invention, a heating mold with a long life that can be stably operated can be obtained, and since the use of an introduction pipe is omitted, it is economical, etc. It is effective.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view of an example mold. A... Heating mold B... Connection mold C...
Cooling mold D... Lining E... Solidified shell
F... Molten steel G... 8 conductor coil Figure 1

Claims (1)

[Claims] 1. In a continuous casting mold that has a heating section in the upper part and a cooling section in the lower part, and is configured to initially solidify below the meniscus existing in the heating section, the connecting part between the upper heating part and the lower cooling part 30 to 70 parts by weight of boron nitride, silicon nitride,
2 types of aluminum nitride, sialon, or 2 or more types
1. A heating mold for continuous casting, characterized in that it is provided with a refractory joint part comprising 0 to 40 parts by weight and 5 to 40 parts by weight of one or more conductive ceramics.