JP3409743B2 - Continuous casting method of round billet slab - 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 producing round billet slabs using a round billet continuous casting machine, and is particularly effective for suppressing the formation of white bands in the surface layer of round billets. The present invention relates to a continuous casting method for round billet slabs.

[0002]

2. Description of the Related Art For example, carbon steel tires for railway vehicles (JI
When manufacturing the S E 5401) forging material (hereinafter referred to as "wheel material") using a round billet continuous casting machine, the surface layer portion (surface to depth 3) of the round billet slab to be manufactured is used.
It is required to suppress the formation of white band at 0 mm).

The white band is a negative segregation zone formed on the surface of the billet. This is an electromagnetic stirrer inside the mold to stir molten steel during solidification so that the front surface of the solidification (the liquid at the solidification interface). This occurs because the liquid phase concentration on the solidification front side decreases due to the cleaning effect of the molten steel on the phase side), and as a result, the solute concentration on the solid phase side on the solidification front decreases according to the equilibrium distribution coefficient of the molten steel.

When the final product is used, the surface layer of the wheel material corresponds to the flange and rim contacting the rails of the carbon steel tire for railway vehicles, so that abrasion resistance and high strength are required. Since the white band described above impairs the hardenability of the steel material and the mechanical properties of the surface layer, the wheel material,
When manufacturing materials such as brake disc materials and crankshaft materials with severe mechanical strength specifications for the billet surface layer with a round billet continuous casting machine, it is possible to form a white band on the surface layer of the round billet slab. Need to be suppressed.

By the way, it is generally known that when electromagnetic stirring is applied to molten steel in a mold during continuous casting of a slab, the formation of equiaxed crystals inside the slab is significantly promoted by the flow of unsolidified molten steel. There is. Therefore, in order to improve the quality of the slab, the electromagnetic stirring technology has been conventionally applied.

For example, in Japanese Examined Patent Publication No. 62-47103, the installation position of the electromagnetic stirrer is set according to the solidified shell thickness of the slab and the mold shape, so that the equiaxed crystal zone can be efficiently generated by the electromagnetic stirring. A method of doing this is proposed. In addition, Japanese Patent Publication No. 63-48619 proposes a method of giving a good solidified structure by regulating the product of the magnetic flux density and the stirring time at the interface between the unsolidified portion and the solidified portion. Further, Japanese Patent Publication No. 63-58069 proposes a method of controlling the current of an electromagnetic stirrer so that negative segregation is always maintained at a target value. In addition, JP-A-53-45
No. 627 proposes a method of refining the solidified structure to improve the internal properties by adjusting the electromagnetic stirring position, magnetic flux density, and casting speed.

On the other hand, electromagnetic stirring may be applied for the purpose of intentionally forming a white band. For example, in Japanese Examined Patent Publication No. 7-16763, as a continuous casting method of a bloom / billet for a rod and wire, the molten steel in the mold is subjected to electromagnetic stirring to perform stirring while giving a stirring flow of 30 to 100 cm / sec. 10% or less of the surface layer portion is formed with a negative segregation zone in which the negative segregation degree of C and S is 0.93 or less, and the segregation degree of C and S is 1 in the core portion inside the surface layer portion. By forming a segregation zone of 1 or more,
A method of appropriately adjusting the C and S concentration distributions in a cast piece has been proposed.

However, as described above, the white band formed by excessively increasing the stirring force impairs the hardenability of the steel material and the mechanical properties of the surface layer portion, and therefore, in principle, it is unsolidified. It is desirable that electromagnetic stirring be applied to the molten steel to promote equiaxed crystallization of the solidified structure, but still not form a white band.

From the above viewpoint, in order to prevent the white band formed on the surface layer of the billet manufactured by the continuous casting machine, the stirring strength of the electromagnetic stirring is weakened, or
It is necessary to install the electromagnetic stirrer at a position that does not affect the surface layer portion, that is, at a position far from the meniscus position where the surface layer portion is completely solidified.

[0010]

However, in addition to improving the solidification structure, the electromagnetic stirring may be used for the purpose of heat compensation to the meniscus (acceleration and control of melting of mold powder, prevention of meniscus skinning). Many. From the viewpoint of heat compensation to the meniscus, it is desirable to set the installation position of the electromagnetic stirrer in the immediate vicinity of the meniscus. Case of installing an electromagnetic stirring device to the nearest meniscus, in order to white band is not formed, it is necessary you utmost weaken the strength of the electromagnetic stirring.

By the way, as a dipping nozzle used in a continuous casting machine for round billet slabs, it is general to use a cylindrical single-hole nozzle 1 as shown in FIG. Since the discharge flow from such a single-hole nozzle 1 is in the vertical direction, the action of supplying heat to the meniscus becomes weak. Therefore, melting and slag formation of the mold powder, which is the lubricant heat retaining agent on the meniscus, is delayed, and problems such as seizure breakout, powdery defects, and meniscus skinning are likely to occur. In order to solve this problem, therefore, in continuous casting of round billet slabs, electromagnetic stirring was applied to the molten steel in the mold so that the circumferential flow velocity of the molten steel exceeded 150 mm / sec. When electromagnetic stirring is applied to molten steel in a mold having a circular cross section, the molten steel receives rotational flow in the circumferential direction parallel to the mold cross section.

That is, in the conventional continuous casting of round billet slabs, consideration is given only to the promotion of equiaxed crystallization of the solidified structure and the heat supply to the meniscus, and the suppression of white band formation is completely considered. Was not done.

The present invention has been made in view of the problems that the above continuous casting method for round billet slabs has, and the round billet slabs made of materials whose quality of the billet surface layer such as wheel materials is required. When manufacturing the steel with a continuous casting machine, promotion of equiaxed crystallization of solidification structure, billet surface layer portion (surface to depth 30
(mm) white band formation prevention and proper powder melting control by supplying heat to the meniscus, all of which are intended to provide a continuous casting method for round billet slabs.

[0014]

In order to achieve the above object, the continuous casting method for round billet slabs according to the present invention has a maximum circumferential flow velocity of molten steel of 150 in a mold.
It is supposed that electromagnetic stirring is applied so as to be less than or equal to mm / sec. By doing so, in continuous casting of round billet slabs, white band formation can be suppressed while promoting equiaxed crystallization of the solidified structure and maintaining heat supply to the meniscus.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The continuous casting method for round billet slabs according to the first aspect of the present invention is a method for producing round billet slabs using a round billet continuous casting machine equipped with a mold having a circular cross section. The magnetic stirring is applied so that the maximum circumferential flow velocity of the molten steel in the mold is 150 mm / sec or less.

Further, the continuous casting method of round billet cast slab according to the second invention, Oite the continuous casting how the round billet slab according to a first aspect of the present invention described above, the nozzle side surface, a plurality of It uses an immersion nozzle having a discharge hole.

In the continuous casting method for round billet slabs according to the present invention, the maximum circumferential flow velocity of the molten steel in the mold is 150.
The reason for applying electromagnetic stirring such that it is less than or equal to mm / sec is based on the experimental results of the present inventors.

That is, the inventors of the present invention investigated the relationship between the segregation degree at the position 20 mm below the epidermis of the round billet and the maximum circumferential flow velocity of the molten steel in the mold. As a result, the segregation degree of the surface layer required as a wheel material, A value of 0.98 or more is satisfied when electromagnetic stirring is performed, as shown in FIG. 1, the maximum circumferential flow velocity in the mold is 150 mm / sec.
The following cases were found .

In the continuous casting method for round billet slabs according to the present invention, the immersion nozzle having a plurality of discharge holes on the side surface of the nozzle is used because a part of the discharge flow from the immersion nozzle is the inner wall of the mold. This is because they collide with and form an upward flow to the meniscus, which contributes to proper powder melting control by supplying heat to the meniscus .

If the immersion nozzle 2 used in the continuous casting method for round billet slabs according to the second aspect of the present invention has a plurality of discharge holes 2a on the side surface of the nozzle, for example, FIG.
Even if it has two discharge holes 2a as shown in (b), it has three discharge holes 2 as shown in FIG. 2 (c).
It may have a, or may have four ejection holes 2a as shown in FIG. 2 (d).

According to the above continuous casting method for round billet slabs according to the present invention, white band formation can be suppressed while promoting equiaxed crystallization of solidification structure and maintaining heat supply to the meniscus. .

[0022]

EXAMPLES The results of experiments conducted by the present inventors in order to confirm the effects of the continuous casting method for round billet slabs according to the present invention will be described below. Using a continuous casting mold having a circular cross section with a diameter of 360 mm, the casting speed was 1.0 m / min and the oscillation stroke was 6.0.
mm under the casting conditions shown in Table 1 below.
Round billet slabs for wheel materials specified in S E 5401 were continuously cast. Table 1 also shows the segregation degree at the position 20 mm under the epidermis of the billet (the segregation degree specification of the wheel material is 0.98 or more). In Table 1 , C and D are examples of the present invention corresponding to claim 2, B is an example of the present invention corresponding to claim 1, and E.
-H shows a comparative example.

[0023]

[Table 1]

(Example of the present invention )

B has a maximum flow velocity of 150 mm / se in the circumferential direction.
Since the magnetic stirring was performed at a temperature of c or less, the segregation degree of the surface layer portion is not a problem, but since the single-hole nozzle shown in FIG. 3 was used, some restriction due to insufficient meniscus temperature occurred. However, it did not affect the actual operation.

Both C and D have a maximum flow velocity of 150 m in the circumferential direction.
Since the electromagnetic stirring was carried out at m / sec or less, the segregation degree of the surface layer portion was within the specification of the wheel material without any problem. In addition, since the multi-hole nozzles shown in FIGS. 2C and 2B are used for both C and D, heat supply to the meniscus is secured, and restraint due to defective powder slag formation due to insufficient meniscus temperature ( No seizure on the mold) occurred and stable operation was possible.

(Comparative Example) Since E was not subjected to electromagnetic stirring, the segregation degree of the surface layer was within the specification of the wheel material, but the single-hole nozzle shown in FIG. 3 was used, and the meniscus temperature was insufficient. There was a problem in operation due to restraint (burning to the mold) due to poor powder slag formation.

F has a maximum circumferential flow velocity of 150 mm / se
Since the electromagnetic stirring exceeding c was performed, the segregation degree of the surface layer portion was not within the specifications of the wheel material, and a white band was formed on the billet surface layer portion. Although the single-hole nozzle shown in FIG. 3 was used, stable operation was possible without restraint by performing electromagnetic stirring with sufficient stirring strength.

G and H have a maximum circumferential flow velocity of 150 mm /
Since the electromagnetic stirring was performed for more than sec, the segregation degree of the surface layer portion was not within the specification of the wheel material, and a white band was formed on the billet surface layer portion.

[0030]

As described above, according to the method for continuously casting a round billet slab according to the present invention, white band formation is achieved while promoting the equiaxed crystallization of the solidification structure and maintaining the heat supply to the meniscus. It is possible to manufacture round billet slabs by suppressing as much as possible.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the maximum circumferential flow velocity of molten steel in a mold and the degree of segregation under the skin of a billet.

FIG. 2 is an explanatory view of an immersion nozzle used in the continuous casting method for round billet slabs according to the second aspect of the present invention, in which (a) is a longitudinal sectional view and (b) to (d) are cross-sections of discharge holes. In the plan view, (b) shows a hole with 2 holes, (c) shows a hole with 3 holes, and (d) shows a hole with 4 holes.

FIG. 3 is an explanatory diagram of a single-hole nozzle used in a conventional continuous casting method for round billet slabs.

[Explanation of symbols]

2 immersion nozzle 2a discharge hole

Continuation of the front page (56) Reference JP 58-3758 (JP, A) JP 4-220149 (JP, A) JP 61-135465 (JP, A) JP 11-188464 (JP , A) JP 58-77755 (JP, A) JP 49-128824 (JP, A) JP 58-5335 (JP, A) JP 63-188459 (JP, A) JP 2-263546 (JP, A) JP-A-1-180762 (JP, A) Actual development 1-151946 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22D 11/115 B22D 11/00 B22D 11/10 330

Claims (2)

(57) [Claims] 1. When manufacturing a round billet slab using a round billet continuous casting machine equipped with a mold having a circular cross section, the maximum circumferential flow velocity of molten steel in the mold is 150 mm / sec or less. Continuous casting method for round billet slabs, which is characterized by imparting different electromagnetic stirring. Wherein Oite the continuous casting how the round billet slab according to claim 1, the nozzle side surface, the continuous casting of round billet cast slab characterized by using an immersion nozzle having a plurality of discharge holes Method.