JP5741314B2 - Immersion nozzle and continuous casting method of steel using the same - Google Patents

Description

  The present invention relates to an immersion nozzle suitable for manufacturing a relatively small slab and a continuous casting method of steel using the same.

  Continuous casting of steel is performed while supplying molten steel in a tundish into a mold of a continuous casting facility through an immersion nozzle. Molten steel is discharged into the mold from discharge holes formed in the lower end of the immersion nozzle. As shown in Patent Document 1, argon gas is conventionally supplied into the immersion nozzle. As shown in Patent Document 1, the immersion nozzle is usually cylindrical.

  The argon gas is supplied to the immersion nozzle for the purpose of preventing nozzle clogging due to alumina clusters or the like, supplying heat to the mold surface, and floating separation of inclusions in the mold. However, if the amount of argon gas blown in to increase these effects, a large amount of argon bubbles flow out into the mold and float with the molten steel. When a part of the slab is solidified while being caught in the solidified shell, a surface defect called a sliver is generated in the slab. In particular, when the bubble diameter of the argon gas entrained in the solidified shell exceeds 1 mm, it tends to cause sliver.

JP 2003-334638 A

  Accordingly, an object of the present invention is to solve the above-mentioned conventional problems and to provide a dipping nozzle capable of suppressing the occurrence of sliver due to argon gas blown into the dipping nozzle, and a steel continuous casting method using the dipping nozzle. It is.

The immersion nozzle of the present invention made to solve the above problems is an immersion nozzle for supplying molten steel into a mold having an electromagnetic brake in a continuous casting facility, and the immersion nozzle has a cylindrical shape. has a neck, a horizontal cross-sectional shape of rectangle, consists of a main body portion that long sides thereof are arranged such that the longitudinal direction of the flat line of the mold, the argon gas supplied to a position above the meniscus in said neck comprising a part, the main body is characterized in that the longitudinal direction of the nozzle inner diameter width before Sulfur butterfly square was not less than 100 mm.

  The inner diameter of the nozzle in the long side direction is preferably 120 mm or more, and the inner diameter of the nozzle in the long side direction is preferably 300 mm or less.

A steel continuous casting method of the present invention made to solve the above-mentioned problems is a steel continuous casting method using an immersion nozzle according to claim 1, wherein the main body portion is placed in a mold of a continuous casting equipment. And the argon gas is supplied to the internal space of the immersion nozzle from the argon gas supply unit, and the molten steel is supplied while an electromagnetic brake is applied to the discharge flow discharged from the immersion nozzle. is there.

  The immersion nozzle of the present invention has a flat cross-sectional shape in which the long side is located in the longitudinal direction of the mold and the inner diameter of the nozzle in the long side direction is 100 mm or more, and the discharge holes are formed at both ends in the longitudinal direction. ing. For this reason, unlike a conventional immersion nozzle having a circular cross section, it takes a certain time for molten steel to reach the discharge holes formed at both ends in the longitudinal direction from the center of the nozzle. In addition, in the present invention, an electromagnetic brake is applied in the vicinity of the discharge hole of the nozzle to generate an MHD counter flow in the direction opposite to the discharge flow, thereby braking the discharge flow and suppressing the flow velocity of the discharge flow.

  For this reason, as shown in the examples described later, the argon bubbles in the molten steel can sufficiently float while moving inside the flat immersion nozzle, and the amount of argon bubbles flowing out from the discharge holes into the mold can be reduced. . As a result, it is possible to suppress the occurrence of sliver due to the argon gas blown into the immersion nozzle.

It is the longitudinal cross-sectional view and horizontal sectional view which show embodiment of the immersion nozzle of this invention. It is sectional drawing of the side surface direction which shows embodiment of the immersion nozzle of this invention. It is sectional drawing which shows the use condition of the immersion nozzle of this invention. It is a top view which shows the use condition of the immersion nozzle of this invention. It is an expanded sectional view of a discharge hole part. It is a graph which shows the relationship between the nozzle inner diameter width and the bubble ratio which goes out in a mold.

Embodiments of the present invention will be described below.
1 and 2 are sectional views of the immersion nozzle of the present invention. The entire immersion nozzle 1 is made of a refractory material and includes a cylindrical neck portion 2 and a main body portion 3 which is flat and has a cross-sectional shape close to a rectangle. A highly corrosion-resistant layer 4 is formed on the outer peripheral surface of the main body 3 in the vicinity of a meniscus (molten liquid surface) that is relatively easily eroded. Further, an argon gas supply unit 5 is formed at a position above the meniscus.

  The argon gas supply unit 5 is formed by forming a porous layer on the inner peripheral surface of the neck 2 and supplies argon gas supplied from the outside to the upper space 7 rather than the meniscus in the neck 2. It is. The argon gas supplied to the upper space 7 is rolled into the falling molten steel flow and enters the molten steel, and functions as an argon bubble, such as floating separation of inclusions. Further, the entry of air into the immersion nozzle 1 is blocked to prevent the formation of alumina clusters and the like, and the nozzle is blocked.

  As shown in FIGS. 3 and 4, the immersion nozzle 1 is immersed in a horizontally long mold 6 for continuously casting a relatively small slab. The inner diameter of the mold 6 is, for example, 250 mm × 1630 mm. In this embodiment, a relatively small slab for IF steel is continuously cast. Since the immersion nozzle 1 of the present invention is immersed in the center of such a mold 6, the cross-sectional shape of the nozzle of the main body 3 is a flat shape in which the long side 8 is located in the longitudinal direction of the mold 6. ing. The outer diameter of the short side 9 is about 150 mm so that it can be immersed in the mold 6. The inner diameter of the main body 3 in the short side direction is about 50 mm. The discharge holes 10 are respectively formed in the short side 9 of the lower end portion of the immersion nozzle 1.

  In the immersion nozzle 1 of the present invention, the nozzle inner diameter width W in the long side direction is increased to 100 mm or more. Thus, by setting the nozzle inner diameter width W in the long side direction to 100 mm or more, the time required for the molten steel to reach the discharge holes 10 formed at both ends in the longitudinal direction from the center of the nozzle becomes longer than before, Argon bubbles can be floated on the surface. For this purpose, the inner diameter width W of the nozzle in the long side direction is preferably large, and more preferably 120 mm or more. However, if the nozzle inner diameter width W is too large, it is difficult to handle the submerged nozzle 1 on the site, and if it is too large, the influence of the discharge flow colliding with the short side of the mold increases, and the solid formation of the solidified shell thickness is hindered. Therefore, the thickness is preferably 300 mm or less.

  When continuous casting is performed using the immersion nozzle 1 of the present invention, argon gas is supplied from the argon gas supply unit 5 to the upper space 7 as shown in FIG. Continuous casting is performed while 11 is placed and the electromagnetic brake is applied. As a result, as shown in FIG. 5, an MHD counter flow in the opposite direction to the discharge flow is generated, the discharge flow is braked, and the flow rate of the discharge flow is suppressed.

  As a result, the argon bubbles that are about to flow into the mold 6 together with the discharge flow from the discharge hole 10 of the immersion nozzle 1 can be sufficiently floated, and the amount of argon bubbles flowing out from the discharge hole 10 into the mold 6 can be reduced. Therefore, according to the present invention, it is possible to suppress the occurrence of sliver while maintaining effects such as prevention of nozzle clogging by argon gas and floating separation of inclusions. In addition, the consumption of argon gas can be reduced. In addition, the supply flow rate of the argon gas from the supply unit 5 is set to a flow rate that secures the inside of the nozzle 7 at a positive pressure in consideration of the consumption amount in the molten steel and the balance of floating and recovery amount in the nozzle.

  The conditions necessary for obtaining the effect of the present invention described above are that the nozzle inner diameter width W of the immersion nozzle 1 is 100 mm or more and that an electromagnetic brake is applied to the discharge flow. FIG. 6 is a graph showing the relationship between the nozzle inner diameter width W and the ratio of bubbles that go out into the mold 6. Since the conventional immersion nozzle used for supplying molten steel to the mold 6 of the above size has a circular horizontal section and the nozzle inner diameter width W is 70 mm, when this conventional immersion nozzle is used, an argon bubble having a diameter of 1 mm is used. Assuming that the amount that goes out into the mold 6 is 100%, the value when the nozzle inner diameter width W is changed was obtained. In addition, since it is impossible to perform this measurement with an actual machine, the values in the graph of FIG. 6 are results obtained by calculation using a fluent, which is commercially available thermal / fluid analysis software. In this case, the casting speed Vc was 1.6 m / min.

  As shown in this graph, when the nozzle inner diameter width W, which was 70 mm in the prior art, is set to 100 mm, the ratio of bubbles that go out into the mold 6 is reduced to 80%, and to 120 mm, the ratio is reduced to 70%. Furthermore, if it is 170 mm, it will reduce to 50%. The inventor made a prototype flat nozzle having a nozzle inner diameter width of 170 mm and conducted a casting test using an actual machine. As a result, it was confirmed that the number of sliver defects was reduced to 50% or less of the conventional one.

  In addition, it is preferable to set the intensity | strength of an electromagnetic brake somewhat stronger than usual, for example, it is preferable to set it as 0.3-0.5T (Tesla).

  As described above, according to the present invention, argon bubbles in molten steel are sufficiently floated inside the immersion nozzle, and the amount of argon bubbles flowing out from the discharge holes into the mold is reduced, thereby suppressing sliver defects. It becomes possible.

  In addition, since the size of the discharge hole 10 is determined by the amount of molten steel to be supplied into the mold 6, it is not different from the conventional one. Further, the inner diameter width of the nozzle in the short side direction is not particularly important in the present invention, and may be a value determined from the mold size.

  In the above-described embodiment, the horizontal section of the main body 3 of the immersion nozzle 1 is substantially rectangular, but it may be oval. Further, it goes without saying that the present invention can be widely applied to the production of slabs that do not like the occurrence of surface defects other than IF steel.

DESCRIPTION OF SYMBOLS 1 Immersion nozzle 2 Neck part 3 Body part 4 High corrosion-resistant layer 5 Argon gas supply part 6 Mold 7 Upper space 8 Long side 9 Short side 10 Discharge hole 11 Electromagnetic coil

Claims (4)

In a continuous casting facility, an immersion nozzle for supplying molten steel into a mold equipped with an electromagnetic brake,
It said immersion nozzle of has a cylindrical neck portion, a horizontal cross-sectional shape of rectangle, consists of a main body portion that long sides thereof are arranged such that the longitudinal direction of the flat line of the mold,
An argon gas supply unit is provided at a position above the meniscus in the neck,
It said body portion, the immersion nozzle, characterized in that prior to the long side direction of the nozzle inner diameter width Sulfur butterfly square or more 100 mm.   The immersion nozzle according to claim 1, wherein the inner diameter of the nozzle in the long side direction is 120 mm or more.   The immersion nozzle according to claim 1 or 2, wherein the inner diameter width of the nozzle in the long side direction is 300 mm or less.   The steel continuous casting method using the immersion nozzle according to claim 1, wherein the main body is immersed in a mold of a continuous casting facility, and argon gas is supplied from the argon gas supply unit to an internal space of the immersion nozzle. In addition, a continuous casting method of steel, wherein molten steel is supplied while an electromagnetic brake is applied to a discharge flow discharged from the immersion nozzle.

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