JP2691675B2 - Continuous casting method for scrap-based steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for industrially inexpensively continuously casting steel made from scrap as a raw material.

[0002]

2. Description of the Related Art Molten steel made from scrap is Cu,
Since elements such as Sn, which are called Trump elements, are included, there has been a problem that surface casting is likely to occur in a cast piece when casting is performed by a generally used continuous casting method. That is, since the liquid phase portion in which Cu and Sn are concentrated is formed in the austenite grain boundary during cooling of the slab and the grain boundary becomes fragile, surface cracks at the stage of the slab and surface defects during rolling tend to occur. Therefore, in the usual continuous casting of steel, the contents of these elements are regulated.

To solve this problem, Fe-Cu- shown in FIG.
Based on the Ni ternary phase diagram, a predetermined amount of Ni is added to steel containing Cu and Sn to fix Cu and Sn in the steel as an alloy of Ni-Cu-Sn to prevent the generation of surface flaws. Proposed. It is known that the addition of Ni can prevent the formation of a liquid phase in the γ grain boundary and prevent the brittle cracking of the grain boundary by making the composition of the austenite γ single phase region. Therefore, this is used. . However, Ni is also scarce in terms of resources and expensive, and if added directly to the molten steel, the manufacturing cost rises and it is not industrially feasible.

[0004]

SUMMARY OF THE INVENTION The present invention solves the problem of surface cracks during continuous casting of steel made from scrap, and provides a continuous casting method for steel with low production cost and high recovery efficiency.

[0005]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a direction in which a molten steel made from scrap containing a large amount of Cu and Sn as a trumb element is continuously cast in a direction that traverses the thickness of a slab in a continuous casting mold. The DC magnetic flux of is applied over the entire width,
With the static magnetic field band formed in the mold casting direction by the DC magnetic flux as a boundary, the molten steel is supplied to the lower side of the static magnetic field band through an immersion nozzle, and Ni is added to the upper side of the static magnetic field band. This is a continuous casting method for steel made from scrap, which is characterized by casting.

[0006]

FIG. 1 is a diagram schematically showing the continuous casting method of the present invention, in which a direct current magnetic flux in a direction traversing the thickness of a cast piece is applied in the continuous casting mold 1 over the entire width, and the direct current magnetic flux causes the mold to be cast. This is an example in which molten steel using scrap as a raw material is sequentially supplied to the lower side of the static magnetic field zone 3 formed in the casting direction, and the wire 6 containing Ni is supplied to the molten steel above the molten steel.

In this method, macroscopic convective mixing of molten steel above and below the static magnetic field zone 3 is prevented, and the amount of molten steel consumed above the static magnetic field zone 3, that is, the surface layer portion containing Ni as the cast slab 2 is drawn out. As molten metal 7, molten steel corresponding to the amount of movement to the lower side of the static magnetic field zone 3 is supplied from the lower side to the upper side of the static magnetic field zone 3.
Therefore, by adding Ni only to the molten steel on the upper side of the static magnetic field band 3, the total amount of Ni added can be significantly reduced, and the manufacturing cost can be reduced.

The amount of Ni added may be Ni ≧ Cu in the molten steel above the static magnetic field zone 3 based on FIG.
Considering the influence of Ni, Ni with Cu equivalent replaced by Cu equivalent
(%) ≧ Cu + 10Sn with the amount of Ni satisfying the static magnetic field band 3
It may be added to the upper side of.

That is, as schematically shown in FIG. 3 as the Ni concentration distribution in the cross section of the cast slab, Ni can be efficiently added only to the surface layer portion 7 containing Ni of the surface layer of the cast slab, and cracking can be prevented. , N in an amount corresponding to the thickness ratio of the surface layer portion 7 containing Ni.
The addition of i is sufficient, and the addition amount becomes approximately 1/5 or less as compared with the case where it is added to the entire molten steel, and the manufacturing cost is significantly reduced.

[0010]

EXAMPLE A molten steel made from the scrap shown in Table 1 was
As shown in FIG. 1, a dipping nozzle 4 is used to inject below the static magnetic field band 3, and at the same time, a wire 6 containing Ni is applied to the static magnetic field band 3.
Was added above.

[0011]

[Table 1]

The shape of the continuous casting mold 1 is 250 mm (thickness) × 1.
The casting speed was 200 m (width) and the casting speed was 1.0 m / min. The position of the static magnetic field band 3 is 45 from the meniscus 5 in the mold 1.
0 to 700 mm below, and the intensity of the DC magnetic flux was 0.5 Tesla. Further, the supply rate of the wire 6 containing Ni is such that the Ni concentration of the molten steel on the upper side of the static magnetic field zone 3 is 0.55% (> Cu +
It was adjusted so that 10Sn = 0.5%).

According to the present invention, when the wire 6 containing Ni was added to the upper side of the static magnetic field band 3, surface cracks caused by Cu and Sn were eliminated, but when the wire 6 containing Ni was not added, That is, surface cracks frequently occurred in the conventional ordinary continuous casting method.

Further, the Ni of the cast piece obtained by the method of the present invention is
The thickness of the surface layer portion including is about 20 mm, and the addition amount of Ni is ⅕ compared with the case where Ni is added to the entire slab.
Below, the manufacturing cost was greatly reduced.

[0015]

According to the present invention, it becomes possible to continuously and inexpensively cast steel made from scrap as a raw material.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a continuous casting method of the present invention.

FIG. 2 is a phase diagram of an Fe—Cu—Ni ternary system.

FIG. 3 is a diagram schematically showing a Ni concentration distribution in a cross section of a cast slab.

[Explanation of symbols]

 1 Continuous casting mold 2 Cast piece 3 Static magnetic field band 4 Immersion nozzle 5 Meniscus 6 Wire containing Ni 7 Surface layer portion containing Ni 8 Intermediate layer 9 Inner layer portion not containing Ni

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomohiro Furuta 1-1 Tobata-cho, Tobata-ku, Kitakyushu City Nippon Steel Corporation Yawata Works (56) Reference JP-A-3-243245 (JP, A)

Claims (1)

(57) [Claims] 1. When continuously casting molten steel made from scrap containing a large amount of Cu and Sn as a trumb element , a direct current magnetic flux in a direction traversing the thickness of a cast piece is continuously radiated in a continuous casting mold. The molten steel is supplied through the immersion nozzle to the lower side of the static magnetic field band with the static magnetic field band formed in the mold casting direction by the DC magnetic flux as a boundary, and Ni is added to the upper side of the static magnetic field band. A continuous casting method for steel made from scrap, characterized by casting while adding.