JPS6149751A - Mold for continuous casting - Google Patents

Abstract

PURPOSE:To provide a titled casting mold which improves the cooling on the short side faces of a billet, prevents longitudinal cracking and extends the life thereof by forming the short side faces of the casting mold in continuous casting into the arc-shaped taper surface of which the shape of the horizontal section is straight in the upper part and projects in the lower part. CONSTITUTION:The short side 2 faces of the casting mold are usually made into the opposed taper surfaces to prevent the generation of a gap on solidification of a molten metal and further the horizontal sectional shape is made into the straight shape in the upper part and into the calculated suitable arc shape in the lower part. The gap arising from the generation of the arc-shaped curve during the descending of the shells on the faces 2 on solidification is prevented, by which the cooling is improved and the longitudinal cracking of the billet is prevented. The uneven wear of the short side mold is prevented and the life thereof is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the shape of a PI type used for primary cooling of continuous HTh casting.

Conventional technology Type 9 is for primary cooling in conventional slab continuous PI machines.

The mainstream is an assembled mold consisting of a flat plate with internal water cooling on both the long and short sides.

In that case, as shown in Figure 734, the mold short side surfaces 2.2 require water to taper the mold short side surfaces 2.2 to narrow the mold short side surfaces 2.2 downward in the mold in accordance with the shrinkage of the slab. .

As the slab solidifies, the slab shrinks toward the lower end, so if the spacing between the opposing short sides of the mold is equal on the top and bottom, a gap will occur in the tHI between the short side of the mold and the slab. Become.

The gap acts as a thermal resistance, reducing the heat flux between the molten steel and the cooling water in the mold, resulting in an increase in temperature on the surface of the slab, increasing creep, and causing molten steel to flow from inside the short side of the slab. Bulging occurs due to static pressure.

When bulging occurs, the slab is deformed, and vertical cracks are likely to occur, especially at the corners where the bending moment is the greatest.In steel types with low ductility at high temperatures, such as high carbon steel (C≧1.0%), this may cause deformation during casting. This can lead to breakouts and cause large-scale operation-'JW failures. Therefore, for example, when the mold size is 250 x 300, the short side is 2 to 8 m on one side.
A commonly used method is to create a taper of approximately 1.5 m in diameter so that even if the slab solidifies and shrinks, no extreme gap will be created between the short side of the mold and the slab.

Problems to be Solved by the Invention However, in this method, the further down the mold, the stronger the part of the corner of the slab is due to the formation of an outer shell (hereinafter referred to as shell), which makes it difficult to contact the mold surface. This caused strong solid friction between the molds, resulting in uneven wear on the lower corners of the short sides of the mold, which was a major factor in shortening the life of the mold.

In addition, when casting high carbon steel containing (C)≧1.0%,
As solidification progresses, dents appear on the short sides of the slab. This will be explained with reference to FIG.

FIG. 5(a) is a cross-sectional view of an elevation during high carbon steel casting;
Fig. 5(b) shows the A-A end face of Fig. 5(a), and Fig. 5(c)
) is the B-B end face in Figure 5(a). In Figure 5, 1 is the long side of the mold, 2 is the short side of the mold, 3 is the nozzle, 4 is the solidified shell, 5 is the unsolidified part, and 6 is the gap. It is.

At the upper part of the short side of the mold in the height direction, the solidified R4 and the short side of the mold 2 are in close contact with each other, as shown in Figure 5(b), but at the bottom, as shown in Figure 5(C). A bulge occurs in the center of the solidified shell 4 due to solidification contraction.

Therefore, as long as a mold with a short side surface formed by a straight line in the width direction is used, no matter how large the taper is, a gap 6 will be created between the bulge of the slab and the short side surface of the mold. As a result, the surface temperature of the shell increases, and the shell is pressed against the short side of the mold by the static pressure of the molten steel, causing distortion in the shell due to the deformation of the slab. Vertical cracks occur on the short side of the piece. In addition, when the degree of vertical cracking is malignant, molten steel gushes out from the location where the vertical cracking occurs, and so-called breakout occurs frequently.

Japanese Patent Publication No. 54-421363 has been proposed as a solution to this problem. This technique makes the center of the short side of the mold convex, but M&
There is no consideration given to the height direction of j, and the cross section is uniformly the same from the upper end to the lower end in the height direction, and as explained in Figure 5(b) above, the casting It is inconvenient to make the short side of cast JJ1 convex because the solidification shrinkage of the piece is small.

In view of this, the present invention provides a larger bulge at the bottom of the short side of the mold to reduce uneven wear on the edge of the bottom of the mold on the short side and extend the life of the T4 type. The purpose is to extend the length and prevent vertical cracks and breakouts that occur on the short sides of slabs during casting of high carbon steel ([C]≧1.0%).

Means to solve problems This will be explained below with reference to the drawings.

A first embodiment of the shape of the n-type short side for continuous casting according to the present invention is shown below.
Figure ~': Shown in Figure JJ3.

The short side surface 2 of the mold shown in FIG. 1 has a rectangular plane at its upper end, but is characterized by a bulge at the center in the width direction as it approaches the lower end.

FIG. 2(a) is a side view, FIG. 2(b) is a front view, and FIG. 2(C) is a view of four sides of the lower end. FIG. 3 is an end surface of the section cut along the line CC in FIG. 2(a). When the bulge at the lower end is viewed from above, the inside of the mold forms an arc as shown in Figure 2 (C), and its radius is RZo.

d: Width of short side of mold (mm) δ. : Set so that the bulge (ffIIll) is at the lower end of the short side of the mold. At the same time, the horizontal cross-section of the range from the top to the bottom of the short side of the mold in contact with the slab is made to be a circular arc, and the radius R (am) of the circle is: X: Distance from the top of the mold (mm) Q: Set the length of the short side of the mold (am). Incidentally, the circular arc described above is a basic shape, and the present invention is also effective with shapes that approximate this, and these are also included in the present invention.

As a result, the surface of the n-type short side in contact with the slab can be configured with a smooth curved surface, and the depression that occurs between the short side of the slab and the surface of the short side of the mold due to shrinkage of the slab can be configured as a smooth curved surface. It becomes possible to suppress the gap, and it is possible to prevent the occurrence of vertical cracks on the short side of the corner that occur in high carbon steel ([C]≧1.0%). In addition, it is an OT function that prevents uneven wear of the lower edge portion of the short side of the mold, and significantly extends the life of the mold compared to a mold made of a conventional flat surface.

Effects of the Invention Figure 6 shows the effect of reducing vertical cracks that occur on the short sides of high carbon steel when the n-type according to the present invention is applied to high carbon steel slabs.
A comparison is shown with the case of using a conventional mold with flat short sides.

As is clear from the figure, the occurrence of vertical cracks on the short sides of the slab is significantly suppressed.

Furthermore, Fig. 7 shows the effect of extending the mold life when the mold according to the present invention is applied to stainless steel and high carbon steel slabs.
The lower end of both PJ5 and 9 molds is plated with Ni to a thickness of 2H on the surface in contact with the slab. Use until the Ni plating on the edges wears out and the copper plate is exposed.

The mold life was determined by the number of casting charges up to that point. As is clear from the figure, the life of the mold is longer than that of the conventional P by the present invention.
It can be seen that this is improved by about 50% compared to the 'i type.

[Brief explanation of drawings]

Figure 1 is a top view of the Pf type of the present invention, Figures 2 (a) and (b)
, and (C) are explanatory diagrams of the bulge of the mold of the present invention, FIG. 3 is an end view of the C-CVA cut section of FIG. 2(a), and FIG. 4 is an explanatory diagram of the conventional mold. A plan view, (b) is an elevational view, FIG. 5 is an explanatory diagram of the formation of depressions on the short side of the slab during casting, (a) is an elevational cross-sectional view, and (b) is an elevational view of A in (a).
-A line cut section end view; (C) is a B-B line cut section end view;
Figure 6 is a diagram comparing the occurrence rate of vertical cracking on the short side of the slab between a conventional mold and the mold of the present invention, and Figure 7 is a diagram comparing the life of the short side of the mold between the conventional mold and the mold of the present invention. . 1...n5 &, side surface, 2...mold short side surface, 3...
・Nozzle, 4... Solidified shell, 5... Unsolidified part, No. 6.
·gap.

Claims (1)

[Claims] 1. A mold for continuous casting, characterized in that, in a horizontal cross-sectional shape of a short side of the mold, the casting side has a substantially straight line at the top and a protruding arcuate bulge at the bottom.