JPS60130448A - Ingot making device for flat steel ingot - Google Patents

Abstract

PURPOSE:To decrease segregation in the central part of a steel ingot by attaching the heat insulating materials for the inside surface of a casting mold only near the head part on the long side and up to the position shown by the specific equation on the short side. CONSTITUTION:A heat insulating material 6A is attached only near the head part of a long side 4A of a casting mold 4 having approximately 2 ratio of the length between the long side and the short side. A heat insulating material 6B is attached to the short side 4B up to such position where the relation between the height (h) of the material 4B at the base of the casting mold and the average thickness B of a steel ingot satisfies the equation 0<=h<=B. The cooling rate from the short side is limited by attaching the materials 6A and 6B in the above-mentioned way and therefore segregation is decreased and the discarding rate in the head part is decreased. The yield of the steel plate and the quality of the product thick steel plate are improved by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ingot making device for flat steel ingots, and more particularly to an ingot making device for large flat steel ingots made of extremely thick plates with extremely little segregation in the center.

Conventionally, large flat steel ingots for extremely thick plates are produced using a cast iron casting head and a surface plate by a top pouring method or a bottom pouring method as shown in FIG. The dimensional proportions of these large flat steel ingots are generally as follows.

Average thickness of the steel ingot: B Height: H Average width: W, then H/B = 1.5 to 3.0 WlB 2 The above dimensional ratio is generally selected, but the thickness B of the steel ingot is 'jIk is determined by the thickness of the finished product and the required reduction ratio during rolling, and the height, width, weight, etc. of the steel ingot are determined by various constraints in the factory, quality viewpoints, and order quantity, so there are no guarantees on quality. The reality is that it cannot be arbitrarily determined solely from the viewpoint of

Conventional methods for producing large flat steel ingots and the properties of steel ingots produced by these conventional methods will be explained with reference to FIGS. 1 and 2 when using the bottom pouring method. The mold 4 placed on the surface plate 2 is usually a wide mold with a long side 4A.
A heat insulating material 6 is pre-prepared on the inner surface near the head of the short side 4B of the mold.
(. When the molten steel 8 conveyed in a ladle is injected from the injection pipe 10, the molten steel 8 passes through the runner 12 formed inside the surface plate 2 and reaches the bottom of the mold 4. The molten steel 8 is injected into the mold 4 through the upstream sprue 14 provided therein. Molten steel 8 injected into the mold 4 starts to solidify from the bottom portion in contact with the surface plate 2 and the peripheral portion in contact with the mold 4.

When the molten steel 8 is poured into the mold 4, a surface coating heat insulating material 16 is placed on the surface of the molten steel to prevent oxidation of the surface of the molten steel 80 and keep it warm to facilitate the floating of inclusions and reduce segregation. .

In this case, if the length ratio of the long side 4A and the short side 4B of the mold 4 is about 2 and the heat removal status of the long side 4A and short side 4B is almost the same, the solidification at 1/2 height of the steel ingot will be As shown in FIG. 2, an elliptical final solidification region 18 remains in the center. The molten steel 8 contains various alloying elements and impurity elements in addition to Fe, and these elements gradually become concentrated toward the final solidification region 18 during solidification. This segregation tendency worsens as the thickness of the steel ingot increases, and in particular, as shown in Figure 2, when the long side ratio is about 2, solidification occurs in two thorny areas from the long side 4A and the short side 4B. As the disease progresses, the deterioration of the central area is further accelerated.

Therefore, products obtained from such conventional steel ingots have nonuniform mechanical properties, which often causes defects during welding, for example. Therefore, reducing segregation is important for improving the quality of finished steel products, and is especially important for large flat steel ingots.

In view of the current situation where quality requirements for extra-thick plates are becoming increasingly strict, the purpose of the present invention is to minimize the defects caused by the above-mentioned conventional techniques, and in particular to alleviate segregation in the center of the steel ingot and obtain a homogeneous steel ingot. The object of the present invention is to provide an ingot making device for flat steel ingots that is capable of producing flat steel ingots.

The gist of the present invention is as follows.

That is, in an ingot making device for flat steel ingots having a mold in which the ratio of the length of the long side to the short side is approximately 2, the mold is expressed on the inner surface from the head of the mold by the following relational expression. IV.
This is an ingot making device for flat steel ingots having the following characteristics.

0≦h≦B However, h: Height of the short side insulation material from the bottom of the mold B: Average thickness of the steel ingot In view of the above-mentioned current state of the prior art, the present inventors have determined that the long side ratio of the conventional mold is about 2. The progress of solidification when the heat insulating material 6 on the inner surface of the mold is attached only near the head is as follows.
As shown in the figure, solidification is first started from the bottom and the side walls in contact with the long side 4A and short side 4B, forming a solidified shell 8A,
As shown in Fig. 2, in each cross section, the solidified shell 8A grows two-dimensionally from the outside to the center, so the segregation of the final solidified zone 1B becomes worse and worse. In other words, we believed that the effect could be alleviated by approaching the short side 4B linearly, and as a result of repeated research into suppressing the cooling rate from the short side 4B, we completed the present invention.

Details and embodiments of the present invention will be described with reference to FIGS. 3, 4, and 5.

The present inventors installed a heat insulating material 6B on the inner surface of the short side 4B over the entire area from the head to the bottom in order to suppress the progress of solidification from the short side 4B, as shown in Figure 3 (BJ). Long side 4A
As for K, an agglomeration test was conducted using an agglomeration device with a heat insulating material 6A attached only near the head as before. Steel ingot 1 at this time
The progress of the coagulation line at the /2 height H is as schematically shown in FIG. In other words, in this case, the short side 4
It was found that the cooling rate from B was suppressed and the solidification progressed almost to a one-dimensional solidification form in the thickness direction. The final solidification zone 20 is more linear than the final solidification zone 18 according to the conventional method shown in FIG. 2, the positive segregation in the center is greatly improved, and the roughness in the center is also slightly alleviated.
Furthermore, the positive segregation of the head was also found to be smaller.

As a result, it became clear that not only the internal properties of the steel ingot were improved, but also the yield could be improved by reducing the amount of head cut off.

In the above experiment, the short side insulation material 6B was installed from the head to the lowest end of the bottom, but the lower end of the steel ingot is affected by the heat removal by the surface plate 2 and the effectiveness of installing the insulation material 6 is relatively small. Can be omitted. Accordingly, as a result of testing to determine how much height h from the surface plate 2 can be omitted, as shown in FIG. : Assuming the average thickness of the steel ingot, the effect of the present invention can be achieved by setting the upper limit of h to be the same as the average thickness B of the steel ingot, and setting the lower limit to 0, that is, the range up to the surface of the surface plate 2 at the lowest end of the mold. It turned out that there was almost no difference.

Therefore, in the range that satisfies the formula (1), 0≦h≦B...+IJ, the short side insulation material 6B
limited to installing.

As for the long side 4, it has been found that it is sufficient to attach the heat insulating material 6A only in the vicinity of the head as in the past in order to suppress coagulation in the vicinity of the head.

EXAMPLE A comparative test was conducted using a conventional apparatus and an ingot making apparatus according to the present invention using molds of the same size and shape and molten steel of the same composition. That is, as shown in Table 1, the conventional device uses the heat insulating material 6 only near the head on both the long side 4A and the short side 4B.
In the ingot making device according to the present invention, a heat insulating material 6B is installed over the entire area from the head to the bottom of the mold bottom on the short side 4B side, and a heat insulating material 6A is installed only near the head on the long side 4A side, similar to the conventional device. Ta. That is, the conditions for the comparative test are as shown in Table 1.

As a result of the above comparative test, it was found that the steel ingot produced by the apparatus of the present invention had significantly reduced segregation compared to the steel ingot produced by the conventional apparatus. For example, the distribution of C in the thickness direction at 1/2 height of each copper ingot is as shown in FIG. That is, in the case of the conventional device (I), the C concentration is 0.25% in the center.
In contrast to the 147% segregation of φ with respect to the C content of 0.17% in the molten steel component, in the case of the device ① of the present invention, the segregation was reduced to 0.2% in the center, and the C content in the molten steel component was 0.17%. 118%
It was found that the situation had been relaxed.

As is clear from the above embodiments, the ingot forming apparatus for flat steel ingots according to the present invention installs a heat insulating material over the entire inner surface of the short part of the mold or from the head to at least the same height as the average thickness of the steel ingot, and By providing heat insulating material only near the head on the inner surface of the side as before, the cooling rate from the short side is restricted and solidification is suppressed, thereby making the maximum Pt solidification region more one-dimensional than in the case of conventional equipment. As a result, we were able to achieve the following effects.

(a) Positive segregation at the center of the steel ingot could be significantly reduced, and the roughness at the center could be alleviated to some extent.

(b) Since positive segregation at the head of the steel ingot was also significantly reduced, the amount of head truncation was reduced and the yield of the steel ingot could be improved.

←1 As a result of (a) and (b), it has become possible to significantly improve the quality of finished extra-thick steel plates.

As mentioned above, the properties of extra-thick plate steel ingots were significantly improved by the ingot making device according to the present invention, but the effects of the present invention can be further improved by adding the following known means to the device according to the present invention. are self-evident and can be used together as appropriate.

(a) Heating the head of the steel ingot by energizing an electrode, etc.

(b) Use exothermic heat insulating material as the heat insulating material.

(C) The long side of the mold has an internal water cooling structure.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional bottom pouring agglomeration device. Figure #g2 shows the longitudinal progress of the steel ingot according to Figure 1.
2. Model iI in Sekisa? Top view, 3rd inning, (Junior shows the agglomeration device according to the present invention, C is a front sectional view, (3rd in)
BB of pronation, ii arrow side sectional view, Figure 4 is the 8th pronation,
A schematic cross-sectional view at 1/2 height showing the progress of solidification of the steel ingot according to (B), FIG. 6th
The figure is a diagram comparing the C distribution (1) from the surface of the steel ingot to the center in the example of the present invention with the C distribution (I) in the case of a conventional device. 2... Surface plate 4... Mold 4^... Long side 4B... Short side 6 (6A, 6B)... Insulation material 8... Molten steel 8A... a Inner shell 18...・Final solidification zone (conventional device t) 20...Final solidification zone (device of the present invention) Agent Patent attorney Takeo Nakaji (11) Figure 1 Figure 2

Claims (1)

[Claims] (1) In an ingot making device for flat steel ingots comprising a mold in which the ratio of the length of the long side to the short side is approximately 2, the mold has the following relational expression expressed from the head of the mold on the inner surface. 1. An ingot making apparatus for flat steel ingots, comprising: a short-side insulating material attached to a position where the ingot is formed, and a long-side insulating material attached only to the vicinity of the head of the mold. 0≦h≦B where h: Height of the short side insulation material from the bottom of the mold B: Average thickness of the steel ingot