JPS62166052A - Casting mold for ingot making - Google Patents

Abstract

PURPOSE:To decrease the reverse V segregation, top segregation, hole type defects, etc. of a thin-walled steel ingot and to improve the yield thereof by forming a casting mold for a specified weight or about of the flat steel ingot into a specifically sized shape which is large in the wall thickness of the lower part and has a specified rate or below of an upwardly expanding taper. CONSTITUTION:The sized and shape of the casting mold for >=30t flat steel ingot are specified to the specific relations expressed by the equation I- equation IV, where M: the own weight of the casting mold, I: the own weight of the steel ingot, H: the height of the casting mold, D: the average thickness of the steel ingot, W: the average width of the steel ingot, D1: the distance between the top ends on the long side surfaces of the casting mold, D2: the distance between the top and bottom end thereof, d1: the wall thickness at the top end on the long side surface of the casting mold, d2: the wall thickness at the bottom end of said top surface. The steel ingot is made thin film if the casting mold is formed to such size relations. The wall thickness of the casting mold is made thinner toward the lower part and the upwardly expanding taper quantity is kept at <=2% by which the reverse V segregation and top segregation are decreased and the vertical distribution of C is made uniform. The hole type defects are decreased and the yield of the good steel ingot is improved. In addition, the cost of heating and rolling is decreased.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an ingot making mold, particularly an ingot making mold for making flat steel ingots of 30 or more, and is used in the field of making large flat steel ingots. .

[Conventional technology]

Conventionally, extra-thick steel plates with a product thickness exceeding 100m+a have been manufactured using flat steel ingots with a ratio of (steel ingot height)/(M ingot thickness) of 30 or more with a wide taper of about 25 to 35. It is normal to That is, the height can be increased to 3.5
It is common to roll a steel ingot with a thickness of more than 1 m.

In such a steel ingot, the solidification rate is slow due to the thick steel ingot, and at the same time, the solidification time is long, so reverse vB analysis occurs due to the former, and component segregation within the steel ingot, especially at the bottom and head, occurs. Component segregation increases.

Furthermore, since the steel ingot is thick, porosity defects are likely to occur in the shaft center, and in order to deal with this, the actual situation is that a wider taper than necessary is provided.

However, these steel ingots with a low height, thick thickness, and large taper require a large reduction ratio or forging ratio during rolling, resulting in a decrease in yield, resulting in increased heating costs, increased rolling quality, and a decrease in yield. This has become a big problem. In addition, in terms of quality, as mentioned above, satisfactory results have not been obtained in terms of reverse segregation and head segregation.

[Problem that the invention seeks to solve]

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and
An object of the present invention is to provide an ingot-forming mold that can reduce porosity defects, inverse Vs analysis, and head segregation of the above flat steel ingots, reduce costs in rolling, and improve yield.

[Means and operations for solving the problems] The gist of the present invention is as follows.

That is, 30, characterized in that it satisfies the following conditions:
This is an ingot making mold for flat steel ingots.

06100mm...(1) H/D≧50...
・…………(3) −D −D 2ip≦0,02 ………(4) W/D≧25 ・
・…………(5) M/I ≧1.2 ・・・…………
(6) However, M: Mold weight, I: fr1 ingot weight, H: Mold height D: Average thickness of steel ingot, W: Average width of steel ingot Dl: Distance between upper ends of mold long sides D: Lower end of mold long sides Distance between d: Thickness at the top of the long side of the mold d2: Thickness at the bottom of the long side of the mold The basic concept of the present invention is to make the steel ingot thinner in order to reduce inverted V scratches and hot rolling quality. , porosity defects were achieved by making the steel ingot thinner and the mold wall thickness thicker at the bottom, and head segregation was achieved by making the steel ingot thinner and keeping the upper wide taper amount below 20%. It is intended to reduce the

In the present invention, various conditions for the mold were investigated from the above viewpoint through experiments, and various conditions were set for the following reasons. In addition, since steel ingots with small weights pose fewer problems, in the present invention, the steel ingots are limited to 30 or more flat steel ingots.

In order to reduce the thickness and density of the inverted VWa line, it is desirable that the steel ingot be thinner, and if the average thickness D of the steel ingot exceeds 1000 mm, the inverted VWl line will become thicker and darker, even after normal heating and rolling processes. The number of questions was limited to 951,000 questions (1) in order to remain at a level that would pose a quality problem, but considering the rolling reduction ratio, approximately 600 to 800 mm is optimal.

In order to reduce the porosity defects in the shaft core, it is desirable to make the steel ingot thinner and taper the top wider, and the thickness should be an inverted V.
From the viewpoint of segregation, D≦10 Q Omm was restricted, and in order to make the upper wide taper as small as possible in consideration of head segregation, the mold wall thickness was increased at the bottom to increase the heat removal ability at the bottom. It was found that there was no effect on thick chi, so it was limited to.

According to conventional wisdom, head segregation is most dependent on the ratio H/D between the height H of the mold and the average thickness D of the steel ingot, and as this increases, the head segregation increases. In (
We focused on the fact that component segregation in the casting direction was small even though it was very large when expressed in H/D, and as a result of repeated experiments, we found that even if H/D is large, head segregation can be reduced by reducing the thickness D.
It has been found that this can be reduced by reducing the upper wide taper amount. For the same thickness D, head segregation increases as H/D increases, but from the results of experiments, it was found that the saturation value is reached at around 5, and in the present invention, H/D≧50... ...... limited to (3).

It was found that if it was limited to 1001 or less, combined with the condition of D≦100 mm, the head segregation could be suppressed to about 120% of the ladle value, so the upper wide taper amount was limited to .

If the width is too narrow relative to the thickness of the steel ingot, the final solidification will be linear, which is unfavorable in terms of porosity and center segregation. From the results of heat transfer analysis, it was found that W/D was required to be at least 2.5 in order for the final solidification to become planar, so it was limited to W/D≧25 (5).

Further, the ratio of the weight of the mold to the weight of the steel ingot represents the heat removal ability of the mold, and a value of about 1.0 is usually adopted. In the case of the present invention, M/T≧12 in order to increase the wall thickness of the lower part from the viewpoint of increasing the heat removal capacity of the lower part.
...... limited to (6).

In contrast to the above, the present invention reduces the thickness of the flat steel ingot of 30 mm or more, increases the height, and significantly changes the dimensions, resulting in excellent internal quality, significantly reducing rolling quality in the next process, and improving yield. We were able to.

Further, it is desirable to use a hot top in the ingot forming mold of the present invention in terms of quality, and it is particularly desirable to use it for high-grade steel.

〔Example〕

EXAMPLES A 40 ton flat steel ingot was cast from molten steel having the components shown in Table 1 using a mold that satisfied the conditions of the present invention and a conventional 40 ton typical shaped mold.

The dimensions of the molds of the embodiment of the present invention and the conventional example are shown in Fig. 1 (A), (B), (C) and Fig. 2 (A), respectively.
Shown in (B) and (C). In each case, (A) is a top surface view, (B) is a vertical sectional view, and (C) is a bottom plan view.

In addition, the relationship between these templates and the limiting conditions of the present invention will be explained in the second section.
Shown in the table.

Table 1 The internal quality of the steel ingots cast using these molds was investigated, and the porosity defect index in the axial core is shown in Figure 3, and the average number of inverse v segregation lines that intersect with the horizontal line in the longitudinal section of the steel ingot is shown in Figure 3. Table 3 shows the component segregation on the axis (10 mmφ drill sample) in Fig. 4.

Tables 2 and 3 From these results, it can be seen that in the examples of the present invention, both head segregation and inverted V segregation were significantly improved compared to the conventional example, and the number of porosity defects was also reduced by half.

〔Effect of the invention〕

As is clear from the above examples, the present invention is achieved by limiting the shape of the mold under conditions such as making the steel ingot thin, making the mold wall thicker at the bottom, and keeping the upper wide taper amount to 2% or less. 30 or more, it was possible to reduce inverted V-segregation, head segregation, porosity defects, etc. of flat steel ingots, reduce hot rolling costs in hot rolling, and improve yield.

[Brief Description of the Drawings] Figures 1 (A), (B), and (C) show the dimensions of the mold of the embodiment of the present invention, (Al is a top plan view, (B) is a vertical sectional view, (C ) is the bottom plan view, Figure 2 (A), (B), (C)
shows the mold dimensions of the conventional example, (A) is a top plan view, (B
) is a vertical sectional view, [C] is a bottom plan view, FIG. 3 is a diagram showing the porosity defect index at the core of the steel ingot in the embodiment of the present invention and the conventional example, and FIG. FIG. 3 is a diagram showing the distribution of C content in the core portion of the steel ingots of the example and the conventional example.

Claims (1)

[Claims] (1) An ingot making mold for flat steel ingots of 30 tons or more, which satisfies the following conditions. D≦100mm…………(1) (d_2-d_1)/H≧0.02…………(2) H/D≧5.0…………(3) [(D_1-D_2)/ (2H)]≦0.02…………
(4) W/D≧2.5…………(5) M/I≧1.2…………(6) where M: mold weight, I: steel ingot weight, H: mold height D: Average thickness of the steel ingot, W: Average width of the steel ingot D_1: Distance between the upper ends of the mold long sides D_2: Distance between the lower ends of the mold long sides d_1: Wall thickness of the upper end of the mold long sides d_2: Wall thickness of the lower end of the mold long sides thickness