JPS6058772B2 - Mold material for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting mold material that has extremely low electrical conductivity, can withstand high-temperature use, and has a long service life.

In continuous casting, the method of forcibly stirring the molten steel in the mold using an electromagnetic stirrer is as follows: 1. Reduction of blowholes during weakly deoxidized steel casting; 2. Reduction of nonmetallic inclusions under the surface layer of the slab; 3. It is effective in reducing center segregation of slabs, and is applied to many continuous casting machines.

However, conventionally, deoxidized copper or silver-containing copper, which has good thermal conductivity, has been used as a mold material for continuous casting.

Since copper has a low specific resistance, the magnetic flux inside it is attenuated greatly. Therefore, in order to produce a sufficient molten steel stirring effect, the necessary 10 to 50 cm/sec4, ←, + Must. Therefore, the present inventors conducted research to solve the above problems, and as a result,
The following findings were obtained.

1 For example, an electromagnetic stirring device for slab casting has a pair of coils 3 disposed facing each other close to the outer surfaces of a pair of long side copper plates 2 constituting a mold 1, as shown in a plan view in FIG. , the molten steel 4 in the mold 1 is stirred linearly (in the figure, the arrow 5 indicates the molten steel flow, and the arrow 6 indicates the short side copper plate constituting the mold 1).

The thickness of the long side copper plate 2 (same as the short side copper plate 6) is related to its size. For example, for a mold with a width of 1900, it is usually 2
A thickness of about 5 to 35 TwL is essential for problems such as deformation. Therefore, in order to stir the molten steel in the mold, magnetic force must be applied to the molten steel through the copper plate that makes up the mold. Attenuation of the generated magnetic flux occurs. The amount of attenuation of this magnetic flux is determined by the following formula,
xp (1 page m7) [Here, B: Magnetic flux density after attenuation iB(): Original magnetic flux density h: Mold (copper plate) thickness p: Specific resistance of mold material μ: Magnetic permeability of mold material (paramagnetic material In the case of 1.0) f: frequency].

Therefore, in order to perform electromagnetic stirring efficiently, it is better to use a material with a high specific resistance as the mold material. However, in mold materials, there is generally a proportional relationship between thermal conductivity and electrical conductivity, and when a mold material other than copper with high resistivity is used, deformation due to temperature rise of the mold, shell There are problems such as insufficient development of the shell and an increase in breakouts due to seizure between the shell and the mold material. For this reason, it is essential to use a copper-based alloy with high thermal conductivity as the mold material. 2. As can be seen from the above equation, the mold material properties necessary for electromagnetic stirring within the mold include low electrical conductivity, and the thickness of the mold material must be thin to prevent magnetic force from attenuating. It is necessary.

On the other hand, the mold is in contact with the hot shell during casting, and
Because heat is generated by magnetic force, thermal deformation and cracks are likely to occur. Mold deformation and cracking are related to material yield strength and elongation at the mold temperature during mold use, and thermal stress at this temperature. Therefore, we conducted many experiments on the relationship between the electrical conductivity of the mold material and the mold temperature, the relationship between the softening temperature of the mold material and the mold temperature, and the relationship between the high temperature strength of the mold material and the thermal stress inside the mold. Copper alloy with the following components: Cr: 0.2-1.0%, Zr: 0.1-0.3%, Al: 2.0-4.0%, Cu and unavoidable impurities: remainder, Copper alloy consisting of (more than 4% by weight) has low electrical conductivity, high high temperature strength, and high elongation, so when it is used in molds, it will not deform, crack, etc., and will last a long time. It can be used for a long time and has great strength, so if it is used as a mold, the thickness of the mold can be made thinner, which doubles the effect of electromagnetic stirring. It was found that it is optimal as a mold material.

In addition, the mold material having the above composition may be used, for example, after hot forging.
It is preferable to perform solution treatment at 60° C. and aging heat treatment at 500° C. with 2F1r or more, but it is not necessary to perform this. This invention was made based on the above findings, and is based on the above findings.
Chromium): 0.2 to 1.0%, Zr (zirconium): 0.1 to 0.3%, A1 (aluminum): 2.0 to 4.0%, Cu (copper) and inevitable impurities: remainder It is characterized in that it is a mold material for continuous casting consisting of (more than % by weight).

Next, the reason why the numerical values are limited as described above in this invention will be explained.

(1) Cr and Zr Cr and Zr act synergistically with each other to increase the heat resistance of Cu.

That is, Cr and Zr precipitation harden into the alloy (mold material) and increase its high temperature strength. However, the amounts of Cr and Zr added are 0.2% and 0.1%, respectively.
If the amount is less than 1, the above-mentioned effect cannot be obtained;
．． If it exceeds 0% or 0.3%, the mold material becomes brittle, so the amount of Cr added should be 0.2 to 1.0%.
%, and the amount of Zr added was determined to be 0.1 to 0.3%, respectively. (2) Al AI is added to 1. lower the electrical conductivity of the mold material, and 2. increase the elongation of the mold material (thus increasing the deformability of the mold material and reducing its hot brittleness). However, if the amount added is less than 2.0%, a sufficient addition effect cannot be obtained,
On the other hand, if it is added in excess of 4.0%, the thermal conductivity of the mold material decreases too much, which is undesirable because the cooling effect of the molten steel decreases and the temperature of the mold material itself increases too much.

Next, examples of the present invention will be described.

Conventional mold material made of silver-containing copper (Ag: 0.10% by weight)
, Cu and unavoidable impurities: remainder), and the mold material of the present invention (Cr: 0.0% by weight, Zr: 0.2% by weight, Al: 3.0% by weight).
Table 1 shows the properties (values at 300° C., excluding electrical conductivity) of heel weight (%) and unavoidable impurities (remaining).

From Table 1, it can be seen that the mold material of the present invention, compared to the conventional mold material,
It is clear that it has low electrical conductivity and is excellent in all of tensile strength, 0.2% proof stress, elongation, and hardness.

Therefore, since the mold material of the present invention has lower electrical conductivity than conventional mold materials, it is possible to reduce the attenuation of magnetic force (
The resistivity of the conventional mold material is 3.3×10-6 Ωm, whereas the resistivity of the mold material of the present invention is 15.4×10
-6 Ωm, and the magnetic flux density of the mold material of the present invention is 1.6 times that of the conventional mold material, so it is clear that electromagnetic stirring can be performed extremely efficiently by using the mold material of the present invention. . That is, in order to obtain the same stirring speed, the output of the coil may be 60% of that of the conventional coil, which is preferable in terms of mold structure. ) Also, the mold material of the present invention has a tensile strength of 0.2% at 300°C compared to the conventional mold material.
It is clear that since it is superior in yield strength, elongation, and hardness, it can be made thinner and can withstand higher temperatures than conventional mold materials. In addition, when the conventional mold material having the above-mentioned composition and the mold material of the present invention were applied to a mold without electromagnetic stirring and continuous casting was performed under the same conditions, it was found that the conventional mold material had a lifespan of 2.
500 times, whereas the mold material of the present invention has a lifespan of 43 times.
It was 00 times. As explained above, the present invention can provide a mold material for continuous casting that has a long service life and low electrical conductivity, so that electromagnetic stirring can be performed extremely efficiently.

[Brief explanation of drawings]

FIG. 1 is a plan view of an electromagnetic stirring device and a mold for slab casting. No. 1... Mold, 2... Long side copper plate, 3.
...Coil, 4... Molten steel, 5...
Arrow, 6...Short side copper plate.

Claims (1)

[Claims] 1 Cr: 0.2 to 1.0%, Zr: 0.1 to 0.3%, Al: 2.0 to 4.0%, and Cu and unavoidable impurities: the remainder (by weight %) for continuous casting.