JP3111346B2 - Powder for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder for continuous casting for positively carburizing carbon in molten steel in a continuous casting mold.

[0002]

2. Description of the Related Art The present inventors have filed Japanese Patent Application No. 06-10436.
No. 5, in the continuous casting powder containing a predetermined alloy element is used, and at a position a fixed distance below the molten steel meniscus in the continuous casting mold, across the thickness of the slab, across the slab width direction While applying a DC magnetic field having a substantially uniform magnetic flux density distribution, inject molten steel of a certain composition, and among the upper and lower pools divided by the DC magnetic field band, through the above-mentioned continuous casting powder into the upper pool, alloy There has been proposed a method of producing a multilayer slab in which the concentration of alloy elements in the surface layer is higher than that in the inner layer by continuous casting while mixing elements.

[0003]

[Problems to be Solved by the Invention] Japanese Patent Application No. 06-1043
According to the method proposed in No. 65, it was possible to produce a multilayer cast slab in which the concentration of the alloying element in the surface layer was higher than that in the inner layer. It was different, but it was not disclosed.

[0004]

According to the present invention, there is provided a powder for continuous casting in which a sintered layer is not formed, wherein the weight ratio of carbon powder having a maximum particle size of 3 mm or less and a particle size of 100 μm or less is 20% or less. It is a powder for continuous casting characterized by adding a carbon powder adjusted so as to be as follows.

[0005]

The present invention will be described below with reference to FIG.

The carbon powder 13 added to the continuous casting powder 10 is diffused into the molten steel when the powder melts on the meniscus in the mold and comes into contact with the molten steel at the meniscus, and is mixed therewith. The carbon concentration of the upper molten steel pool 3 is adjusted to a predetermined value.

At this time, the inventors' experiments revealed that the particle size of the carbon powder 13 to be mixed into the powder 10 was very important, and found an optimum carbon particle size.

That is, when the carbon powder to be added is very small, the time taken for the mixed carbon powder to pass through the molten powder layer and reach the meniscus is prolonged, and most of the carbon powder stays in the molten powder layer. It will burn.

As a result, the amount of carbon diffused and mixed from the meniscus into the molten steel decreases. This tendency becomes remarkable when the weight% of the carbon powder having a particle diameter of 100 μm or less exceeds 20% (FIG. 2).

On the other hand, when the carbon particle size to be added is very large, problems such as partial melting failure of the powder and uneven flow into the mold / solidification shell gap are caused. Further, the non-uniformity of the thickness and the concentration distribution of the layer having a high carbon concentration in the molten steel in the vicinity of the meniscus is increased, and the non-uniformity of the thickness and the carbon concentration distribution of the layer having the high carbon concentration on the surface layer of the slab is enhanced. This tendency becomes remarkable when it exceeds 3 mm (FIG. 3).

Generally, in order to control the thickness of the molten layer of the powder, carbon pre-melted as an aggregate is used instead of fine carbon. In this case, a sintered layer tends to be formed.

If carbon powder is mixed into the powder forming the sintered layer during casting, the stable passage of the carbon powder mixed in the sintered layer is impeded, so that the carbon concentration in the molten steel near the meniscus is impaired. The thickness of the layer with high concentration and the non-uniformity of the concentration distribution are increased, and the thickness of the layer with high carbon concentration on the surface of the slab and the non-uniformity of the carbon concentration distribution are promoted, so that a sintered layer is formed during casting. It is not preferable to use powders that have a high viscosity.

Therefore, the carbon powder adjusted so that the particle size of the carbon powder to be added is 3 mm or less and the fine powder having a particle size of 100 μm or less is 20% by weight or less is mixed into a powder for continuous casting without forming a sintered layer. It is good to let.

There is no particular upper limit on the amount of carbon powder added to the powder, since it depends on how much the carbon concentration of the molten steel is to be increased.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a continuous casting process (FIGS. 4 to 6) in which a DC magnetic field 21 having a uniform magnetic flux density in the width direction can be applied 0.4 m below the meniscus, a width of 1.2 m,
Using the mold 1 having a thickness of 0.25 m, the medium carbon steel shown in Table 1 was cast at a casting speed of 1.6 m / min by the DC magnetic field 21.
In the braking zone 5 formed in the molten steel pool, the immersion nozzle 2
Was injected through. Solidified shell thickness d in this continuous casting machine
It is known that the growth rate of (m) is given by the equation (1), which indicates that the thickness of the surface layer is 10 mm.

[0016]

D = 0.02 × (L / Vc) ^1/2 (1)

Here, Vc indicates a casting speed (m / min), and L indicates a distance (m) from the meniscus.

The powder (A) for forming the sintered layer and the powder (B) for not forming the sintered layer were automatically supplied.

The used powder for continuous casting is classified into two types, one that forms a sintered layer (A) and one that does not form a sintered layer (B), and the maximum particle size of the carbon powder to be added is larger than 3 mm. (A), maximum particle size is 3 mm or less and 100 μm
Table 2 shows the relationship between the powder conditions and the vertical cracks on the surface of the slab, with the following weight ratios being classified into three types: a weight ratio of 20% or less (b), a weight ratio of 3 mm or less and 100 μm or less, and 20% or more (c). It was shown to.

The number of vertical cracks per slab of slab was examined by visual judgment, and the result was used as the index of occurrence of vertical cracks.

In addition, those having an index of occurrence of vertical cracks of 1% or less were regarded as good. Table 2 shows these results together with the operability.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

According to the present invention, the carbon concentration in the surface layer of a continuously cast slab can be stably increased by mixing carbon powder into powder and continuously adding the powder to the entire molten metal level from above the mold. be able to.

By using this method, a steel type which is liable to generate surface defects depending on the carbon concentration of the steel, for example, a medium carbon steel or a very low carbon steel (medium carbon steel; Ultra-low carbon steel; Inclusions on the surface of slabs, surface defects of cellular system and scale defects due to poor peeling of oxide scale), regardless of casting conditions, surface defects of products as well as slabs Can be easily avoided.

Further, by using the powder for continuous casting of the present invention, the carbon concentration of only the surface layer of the slab or the carbon concentration of the entire slab is increased in the continuous casting mold as described above. It is also possible to do.

[Brief description of the drawings]

FIG. 1 is a diagram showing a melting state of a powder for continuous casting added on a meniscus of a molten steel pool in a mold and a state in which carbon powder added in the powder is melted and mixed into molten steel.

FIG. 2 shows a particle diameter of 100 mixed into a powder for continuous casting.
It is a figure which shows the relationship between the weight ratio of carbon powder below [micrometer], and the carbon yield which shows how much with respect to the total addition amount of carbon powder contributed to the carbon concentration increase in molten steel.

FIG. 3 is a diagram showing the relationship between the maximum particle size of carbon powder mixed into powder for continuous casting and the variation in carbon concentration in the slab width direction.

FIG. 4 is a plan view showing a situation during casting in a continuous casting mold, schematically showing a casting situation viewed from above the mold.

FIG. 5 is a view showing a situation during casting in a continuous casting mold, and is a cross-sectional view schematically showing a structure in a vertical section in a continuous casting pool.

FIG. 6 is a diagram showing a situation during casting in a continuous casting mold, and is a cross-sectional view schematically showing a cross-sectional situation of a cast slab.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 immersion nozzle 3 upper molten steel pool 4 lower molten steel pool 5 braking zone (= transition zone between upper and lower molten steel pool) 6 surface layer of cast slab 7 inner layer of cast slab 8 transition zone of concentration 10 powder for continuous casting 11 Powder for continuous casting (powder layer) 12 Powder for continuous casting (melted layer) 13 Carbon powder 20 DC magnetic field generator 21 DC magnetic field

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-269559 (JP, A) JP-A-61-193756 (JP, A) JP-A-51-107234 (JP, A) JP-A-59-193 179258 (JP, A) JP-A-59-61558 (JP, A) JP-A-52-57029 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/108

Claims (1)

(57) [Claims] 1. A carbon powder having a maximum particle size of 3 mm or less and a carbon powder having a particle size of 100 μm or less adjusted to have a weight ratio of 20% or less in a powder for continuous casting without forming a sintered layer. A powder for continuous casting, characterized by having added thereto.