JPS6320141A - Continuous casting method for thin slabs - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for continuously casting a thin slab of molten metal with a thickness of 50 mm or less than that of molten steel. This invention relates to a method for continuously casting thin slabs while preventing objects and scum from being caught up with belts and rolls and solidifying the surface of the molten metal.

(Prior Art) A continuous casting machine shown in FIGS. 2 and 3 is known as a continuous casting machine that directly produces thin slabs such as sheet bars with a thickness of 50 mm or less from molten steel.

The continuous casting machine for thin slabs shown in Fig. 2 is of a squeezing type, in which a pair of rollers move circularly through a plurality of guide rolls 3 while maintaining a gap to hold the molten steel or solidified shell over a predetermined distance. Metal belts 1 and 2 are arranged facing each other, and a casting space is formed by a pair of tapered short side molds 4.5 and the metal belt 1.2 that are in close contact with each metal belt 1.2. ing. Molten steel is injected into the casting space through an injection nozzle 6, and a thin slab 7 is pulled out from the bottom of the continuous thin slab caster.

Further, in the continuous thin slab casting machine shown in FIG. 3, a casting space is formed by a pair of rotating rolls 9 and a short side mold 4.5 that is in close contact with these rolls. Molten steel is injected into the casting space by an injection nozzle 6, and a thin slab 7 is pulled out from the bottom of the continuous thin slab caster.

(Problems to be Solved by the Invention) In the former belt-type thin slab continuous casting machine, cooling by the metal belt, which is cooled by a cooling pad 8 provided on the back of the metal belt, and radiation of the molten steel itself, There is a problem in that the molten steel surface 10 in the casting space is deprived of heat and solidifies.

In particular, when the surface of the molten steel near the injection nozzle solidifies, the risk of nozzle clogging increases. Furthermore, if the temperature of the molten steel in the mold decreases, it becomes impossible to pour the molten steel for a long time, and in particular, anchors are formed due to the skin on the molten metal surface, making it impossible to pull out the slab.

In addition, inclusions and scum generated by oxidation by oxygen in the atmosphere and most of the inclusions and scum floating up from the molten steel in the mold are caught in the metal belt, causing unevenness in the slab and This causes surface cracks. In order to prevent this, even if powder with a high rate of slag formation as described in JP-A No. 60-9559 is used, it cannot be converted into slag due to an increase in the casting speed, resulting in scum and unrefined particles. Molten powder gets caught up in the metal belt, causing problems such as slag chewing. When scum or unmelted powder gets caught up in the metal belt, the slab is cooled unevenly in the mold, resulting in insufficient cooling. It can also cause breakouts to occur at certain points.
It also causes cracks on the surface of the slab and unevenness on the slab.

The above-mentioned problems also occur in continuous thin slab casting machines in which a casting space is formed by a pair of rolls and a pair of short side molds.

(Means for Solving the Problems) The present invention provides a thin slab continuous casting machine in which a casting space is formed by a pair of rotating bodies arranged opposite to each other and a pair of short side molds adjacent to the rotating bodies. When continuously casting thin slabs,
Each of the above-mentioned problems has been solved by using a method for continuous casting of thin slabs, which is characterized by dividing the molten metal surface at least in the area where it contacts the rotating body or in the vicinity thereof with a heat insulating material, and adding powder to the inside of the molten metal surface. did.

Further, one embodiment of the present invention will be described in detail with reference to FIG. 1a. In the case shown in the figure, thin slabs are continuously cast using a belt-type continuous casting machine for thin slabs. At least the parts where the molten metal surface contacts the metal belts 1 and 2 are covered with heat insulators 12 made of refractories. In this method, a thin cast piece is continuously cast by covering it with powder and adding powder 11 inside it. In addition, in a method of continuously casting thin slabs using a thin slab continuous casting machine that uses a pair of rolls and a tapered short-side mold, the molten metal surface at least at the point where the molten metal surface contacts the rolls or in the vicinity is refractory. In this method, thin slabs are continuously cast by adding powder to the inside of the insulation body.

Furthermore, as shown in FIG. 1b, there is also a method of continuously casting thin slabs using a thin slab continuous casting machine that uses a pair of rolls 9 and a pair of short side molds 4.5 called side dams. The molten metal surface 10 is separated by a heat insulator 12 where it contacts the roll 9 or as shown in the same figure, and powder 11 is added to the inside of the molten metal surface 10 to form a thin slab 7. This is a continuous casting method.

The material of the heat insulating body 12 is preferably a single substance or a mixture of silica, SiO□, BN, 5iJ4, etc. to avoid damage by powder, but other fire-resistant materials can also be used, and the shape thereof is shown in Fig. 1a. It is best to make it into a frame shape as shown. Further, the heat insulator 12 is suspended at a predetermined height using a wire or the like before casting, and when the molten metal surface comes into contact with the heat insulator, powder is added to the inside of the heat insulator 12.

(Function) In the method of the present invention, the molten metal surface is separated by a heat insulating material at least at the point where the molten metal surface comes into contact with the rotating body, which is the long side surface of the mold, that is, the metal belt or roll, or in the vicinity thereof. It is possible to prevent floating inclusions, scum or unmelted powder from being caught in the metal belt or roll. Therefore, unevenness does not occur in the slab, the surface of the slab does not crack, and breakouts due to uneven cooling of the slab are also eliminated. Furthermore, since powder is added to the inside of the heat insulator, oxidation of the molten metal surface can be reduced, and since it has the effect of retaining heat, it is possible to pour the molten metal for a long time, making it possible to perform multiple casting.

(Example) C: 0.04 to 0.06% by weight, Si: 0.05
Weight% or less, Mn: 0.30 to 0.60% by weight, P
: 0.010-0.030% by weight, S: 0.0
10 to 0.030% by weight, to 7! :o, 03~0
．． 06% by weight, at a molten steel temperature of 1550-1565°C,
1-80 tons of molten steel per heat was poured into a belt-type continuous casting machine shown in Fig. 2, and a thin slab with a thickness of 30 mm and a width of 1200 mm was cast.

At that time, the conventional method using powder with the composition shown in Table 1 (hereinafter referred to as method A), the method of sealing with static gas without adding powder (hereinafter referred to as method B), the heat insulating method mainly composed of MgO By casting with the method of the present invention (hereinafter referred to as C method) using powders with the compositions shown in Table 1 for 62 heats, a) slag bite index, b) surface cracking index of slab, C)
Table 2 shows a comparison of the breakout index and d) casting trouble index associated with anchor formation.

As can be seen from Table 2, according to the method of the present invention, both the slag bite index and the surface cracking index of the slab were 115 or less for each of the conventional methods, and the yield of the slab was dramatically improved. The main reason for this is presumed to be that the unmelted powder was prevented from getting caught up in the metal belt due to the refractory insulation.

Moreover, the breakout index was 1712 or less for each conventional method. The main reason for this is thought to be that in the method of the present invention, the heat insulator prevents unmelted powder and scum from getting caught up in the metal belt, whereas in the conventional method, unmelted powder and scum are not caught up in the metal belt. As a result, the occurrence of non-uniform cooling and breakouts from insufficiently cooled areas has been drastically reduced.

Furthermore, in the method of the present invention, unlike the conventional method B, the occurrence of the inability to pull out the slab due to the formation of anchors due to the skinning of the molten metal surface is reduced.

(Effects of the Invention) As explained above, according to the method of the present invention, cracks on the surface of the slab and unevenness of the slab due to inclusion scum or unmelted powder being caught in the rotating body are eliminated, and the quality of the slab is improved. This improves performance, eliminates operational troubles such as breakouts, and enables multiple casting.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the inside of a mold of a belt-type continuous thin slab casting machine used in the method of the present invention, and FIG. 1b shows a pair of rolls and a pair of short piece molds used in the method of the present invention; That is, it is a cross-sectional view of a continuous thin slab casting machine composed of side dams, FIG. 2 is a diagram schematically showing a belt-type continuous thin slab casting machine used in the method of the present invention, and FIG. This is a continuous roll-type thin slab casting machine used in the invention method. 1.2...Metal belt 3...Guide roll 4.5
... Short side mold 6 ... Injection nozzle 7 ... Thin slab 8 ... Cooling pad 9 ... Roll
10... Hot water surface 11... Powder
12...Refractory heat insulator 13...Wire Figure 1a Figure 1b Figure 45 Hanjin mold

Claims (1)

[Claims] 1. When continuously casting thin slabs using a thin slab continuous casting machine in which a casting space is formed by a pair of rotating bodies arranged opposite to each other and a pair of short-side molds adjacent to the rotating bodies, at least the molten metal is A continuous casting method for thin slabs, characterized in that the molten metal surface at or near the point where the surface contacts a rotating body is separated by a heat insulator, and powder is added to the inside of the molten metal surface.