JPH02211950A - Method for pouring molten steel in continuous casting - Google Patents

Abstract

PURPOSE:To prevent the development of surface defect and internal defect in any cast slab width and casting velocity with one shape of a submerged nozzle by pouring while adjusting the pouring angle of the submerged nozzle set to bottom part of a tundish to the specific condition according to the casting rate. CONSTITUTION:At the time of setting the submerged nozzle 1 to the bottom part of the tundish 2, this is set as swingable thorough a swingable submerged nozzle fitting device 6. By this method, as this swinging angle theta can be adjusted to the suitable condition while matching to the casting condition, the development of the internal defect is prevented and the development of the surface defect can be restrained. Then, the relation between the casting condition and the suitable swinging angle has to satisfy the inequality I. As the molten steel flow can be adjusted to the optimum while matching to the casting condition, even if the casting condition varies, floating-up of inclusion is promoted and involution of powder can be prevented with one kind of the submerged nozzle.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for injecting molten steel from a tundish into a mold in continuous steel casting.

[Prior art]

As is well known, the continuous casting method involves charging molten steel into a tundish from a ladle, etc., and injecting the molten steel into a mold from a discharge port through an immersion nozzle attached to the tundish.
The slab is continuously pulled out from the bottom of the mold.

At this time, in order to promote the floating of inclusions that have entered the mold and prevent them from being captured by the solidified shell, the operating conditions of each continuous casting machine are set as shown in JP-A-62-137153. It is common to use an inverted Y2 hole type immersion nozzle with a shape suitable for.

[Problem to be solved by the invention]

In this technology, the width of the slab is wide and the meniscus flow rate increases as the casting speed increases, so the molten steel flow has a cleaning effect near the initial solidification, so surface defects due to inclusions are prevented. Although this can be suppressed, internal defects become worse because the molten powder present on the surface of the molten steel bath becomes easily caught up.

On the other hand, when the slab width is narrow and the casting speed is low, the meniscus flow rate is low, so powder entrainment does not occur, but the cleaning effect of the molten steel flow is weakened, and surface defects are more likely to occur.

Therefore, in order to prevent both internal defects and surface defects from occurring, it is important to use a submerged nozzle shape that is compatible with the cast slab width and casting speed.

However, in recent continuous casting, it is common practice to change the width of the slab to be cast during casting to match the ordered size, and at the same time to adjust the width of the slab to match the ordered size. The reality is that the casting speed is not constant due to matching constraints. In addition, in order to reduce casting costs and unsteady parts, it has been desired to be able to cast as long as possible with a single immersion nozzle, but from the above points of view, it has become difficult to cope with this with conventional technology. This is the reality.

The present invention solves the above-mentioned problems of the conventional technology, suppresses the occurrence of surface defects and internal defects at any slab width and casting speed with a single-shaped immersion nozzle, and stably yields defect-free slabs. Provided is a method for injecting molten steel that is well produced.

[Means to solve the problem]

The present invention is characterized in that when pouring molten steel into a mold, the pouring angle of a submerged nozzle placed at the bottom of the tundish is adjusted so as to satisfy the following formula (1) according to the casting flow rate. This is a method of injecting molten steel in casting.

-5×Q+20≦θ≦−5×Q+35 (1
) However, θ-swivel angle (deg,) Q=casting flow rate (ton/l1in) [Function] The present invention will be described in detail below based on the drawings.

FIG. 1 is a side sectional view of a submerged nozzle explaining the present invention in detail, FIGS. 2(a) and (b) are a side sectional view and a plan view showing an example of a rotatable submerged nozzle mounting device, and FIG. is a drawing explaining the action of the immersion nozzle, and (a+) to (dt
) is a plan view, (at) to (dt) are side sectional views, FIGS. 4(a) and (b) are drawings showing an example of the effects of the present invention, and FIG.
The figure is a diagram illustrating the appropriate turning angle of the immersion nozzle.

As a result of investigating the molten steel flow in the mold 4 of a continuous casting machine when using a general two-hole type immersion nozzle l, it was found that this flow is weak during narrow width low speed casting of less than 1300 mm and less than 1.6 m/win. It is not possible to prevent the inclusions from being captured in the part, and as a result, they become apparent as surface defects.
When wide-width high-speed casting of 6s/sin or more is performed, the
b2 As shown in Fig. 3-) and (+), as a result of the interaction of b' with the downward flow, the flow of molten steel in the mold is not necessarily bilaterally symmetrical, that is, it becomes an energetically stable drift state, so the mold Since the molten steel flow C is also formed between the immersion nozzle 4 and the immersion nozzle 1, and a cleaning effect is obtained, no surface defects occur.

In order to ensure the flow of molten steel between the mold and the immersion nozzle at narrow width and low speed, the immersion nozzle 1 is installed in a slightly rotated position compared to the conventional one, as shown in Figure 3 (c,) (c-). For example, technology can be found in the literature ``Tetsu to Hagane J VOI.

70 (1984) P81 and JP-A-58-7775
By applying the present technology introduced in Publication No. 4 and Japanese Patent Application Laid-Open No. 59-85351, a cleaning action by the molten steel flow C at the solidified shell interface can be obtained, so floating separation of inclusions can be promoted. , surface quality can be improved.

However, when this technology is applied to wide-width, high-speed casting, Figure 3 (
dt) and (dZ), the molten steel flow C between the immersed nozzle 1 and the mold 4 becomes too strong, and the incidence of immersed part defects increases.

In contrast, in the present invention, when installing the immersion fuzzle 1 at the bottom of the tundish 2 as shown in FIG.
By arranging the immersion nozzle in a rotatable manner via the rotatable immersion nozzle mounting device 6, the rotation angle θ can be adjusted according to the casting conditions.
can be adjusted to an appropriate state, so it is possible to suppress the occurrence of surface defects while preventing the occurrence of internal defects.

However, regarding the casting conditions and appropriate turning angle, the present inventors conducted various tests and found the following (1) as shown in Figure 5.
It was confirmed that the conditions of Eq.

−5×Q+20≦θf−5×Q+35・・・・・・(1
) However, θ = turning angle (deg,) Q = casting flow rate (ton/min) Details of the immersion nozzle mounting device 6 are shown in Figures 2 (a) and (b).
), first, the upper nozzle 17 is inserted into the interior of the tundish 2, and the fixing brick IO is fixed to the lower part thereof. Next, the immersion nozzle holder 1 has a rotating gear on its outer periphery.
Insert the immersion nozzle 1 into the frame 1 and hold it down.
2 and a presser bolt 14, it is installed so that the center is aligned directly under the fixing brick 10. A steel ball 13 is inserted between the immersion nozzle holder 11 and the presser frame 12 in order to minimize sliding resistance.

Next, an idle gear 15 is installed between the immersion nozzle holder 11 and the motor 16, and by driving the motor 16, the immersion nozzle 1 can be rotated even during casting, and the nozzle discharge port can be rotated. The orientation can be adjusted to the appropriate position. That is, as a result of this, the flow of molten steel can be optimally adjusted according to the casting conditions, so even if the casting conditions change, it is possible to promote the floating of inclusions and prevent the entrainment of powder using one type of immersion nozzle.

[Example-1] A slab with a casting width of 1200 inches and a thickness of 245 m was cast at a casting flow rate of 3.
When casting at ton/sin, the discharge hole diameter is 70 mmφ,
A two-hole submerged nozzle I with a downward discharge angle of 45" is attached to the bottom of the tundish 2 by a nozzle attachment device 6 that can be rotated as shown in FIGS. 1 and 2, and the rotation angle is set to 0@
After casting at four levels: , 5°, 10', and 15'', we investigated the incidence of surface defects and internal defects in the slab, and as shown in Figure 4(a), we found that when the turning angle is 7° or more, As a result, a high-quality slab with stable surface and internal defects was obtained.

[Example 2] Using the same equipment as in Example 1, a slab with a width of 1600 aa and a thickness of 245 a+s was cast at a flow rate of 5.65 ton/s.
When casting in, the turning angle is O@, 5°, 10@,
As a result of conducting the experiment at 15 degrees and four levels, and similarly examining the slab, as shown in the fourth (b), good quality was obtained at a turning angle of 5 degrees or less.

〔Effect of the invention〕

As explained above, by using the present invention, the flow of molten steel in the mold can be set to an ideal state according to the casting conditions. , it is possible to simultaneously prevent the occurrence of surface defects and internal defects, and to stably produce high-cleanliness steel with few inclusions at a high yield.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a submerged nozzle explaining the present invention in detail, FIGS. 2(a) and (b) are a side sectional view and a plan view showing an example of a rotatable submerged nozzle mounting device, and FIG. is a drawing explaining the action of the immersion nozzle, and (at) to (tL
) is a plan view, (ax) to (dt) are side sectional views, Fig. 4 (a) and (b) are drawings showing an example of the effects of the present invention, and Fig. 5 explains the appropriate turning angle of the immersion nozzle. This is a drawing. 1...Immersion nozzle, 2...Tandish, 3...
・Stopper, 4... Mold, 5... Slab, 6...
Rotatable immersion nozzle mounting device, 7...molten steel, 8...
- Molten powder, 9... Whirlpool, 10... Fixing plate brick, 11... Immersion nozzle receiver 11.12... Holding frame, 13... Steel ball, 14... Holding bolt, 1
5... Idle gear, 16... Drive motor, 1
7... Upper nozzle, a: upward reverse flow, b: downward flow, C
: Molten steel flow agent Patent attorney Masamitsu Akizawa and 1 other person Piece 1 figure Piece 2 figures (Q) Defects) i rate pilgrimage

Claims (1)

[Claims] A continuous method characterized in that when pouring molten steel into the mold, the injection angle of a submerged nozzle placed at the bottom of the tundish is adjusted so as to satisfy the following formula according to the casting flow rate. Method of injecting molten steel in casting. -5×Q+20≦θ≦-5×Q+35 However, θ=Turning angle (deg.) Q=Casting flow rate (ton/min)