JPS6056469A - Production of longitudinally short casting ingot - Google Patents

Abstract

PURPOSE:To produce a longitudinally short steel ingot having less hydrogen blownholes and good quality at a high yield by interposing a molten slab having an adequate thickness in the head part of the cast molten metal, holding the same with a holding material and solidifying unidirectionally the same upward from the base part. CONSTITUTION:Molten slag 6 having >=3mm. thickness and a holding material 5 such as a heat insulating flux or the like having meltability for preventing the solidification from the head part of a molten metal and further carbonized chaff 7 are successively packed atop the molten metal 3 in a casting mold constituted to prevent cooling and solidifying of the molten metal 3 from the side wall as far as possible by adhereing a heat insulating material 4 such as ceramic fibers or the like to the inside circumferential wall of a casting mold 2 placed on a molding board 1. The unidirectional solidification upward from the base part is thus caused in the molten metal 3 to prevent generation of a defect such as segregation as well as to prevent the hydrogen generated from the material 4 and the material 5 from entering the inside of the molten metal 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing vertical and short steel ingots for manufacturing steel plates.

Normally, steel plates are manufactured by casting into a vertically elongated @-type with a regular or inverted conical shape, and then rolling the steel ingot in the longitudinal direction, except for those that are directly cast into slabs using the continuous casting method. be done. Therefore, regardless of bottom pouring or top pouring, cooling is mainly performed through the side walls of the mold, so defects such as segregation are unavoidable.

By the way, the horizontal short side (D) with respect to the height H) of the steel ingot
) Copper ingots with a ratio (H/D) of 1 or less (hereinafter referred to as vertical and short steel ingots) have become a bigger problem than before because solidification is substantially unidirectional from the bottom upwards. Many proposals have been made to achieve this kind of substantial unidirectional solidification, as it is expected that the internal quality of the steel ingot will be improved by improving the segregation and hollow defects that had previously occurred, and that the yield will also be improved. have been made by the present applicant (for example, Japanese Patent Publication No. 53-19290, Japanese Unexamined Patent Publication No. 57-228)
The reality is that there is still a lot of room for improvement. In particular, Samurai Publication No. 57-22864 proposes the use of a heat-insulating lid to reduce defects such as inverted V segregation and head (C) segregation. However, even with the method disclosed in the above publication, 5p of hydrogen was added to the cast vertically short steel ingot.
pm or more, and blowholes that are not crimped during the rolling process are likely to occur in the steel ingot, which inevitably causes problems in the production of extra-thick steel plates.

As a result of continuing research through basic experiments and actual operational tests regarding blowholes that are not crimped during the rolling process, the present inventors found that
Blowholes occur due to hydrogen gas generated by the amount of hydrocarbons contained in the heat insulating material and heat insulating material necessary for the production of directionally solidified steel ingots, and 4 to 7% of the hydrogen gas contained in the heat insulating material and heat insulating material.
It was confirmed that this is caused by hydrogen in water vapor due to moisture in
It has been found that when the hydrogen blowball index defined below is 2 or less, the properties of the slab are not particularly problematic.

Here, the hydrogen blowhole index is the number of hydrogen blowholes obtained by die checking and UST (ultrasonic flaw detection) on a sample of a steel ingot.

The method for producing a vertical and short steel ingot according to the present invention uses a mold whose inner peripheral wall is covered with a heat insulating material, and the head of the molten metal poured into the mold is kept warm using a heat insulating agent. Casting molten metal
! In a method in which the bottom surface is cooled and the solidification is unidirectionally solidified from the bottom surface upwards, a molten slag having a thickness of 3 mm or more is interposed between the molten metal head and the heat insulating agent. It is characterized by suppressing hydrogen intrusion into the interior.

Here, the thickness of the molten slag interposed between the molten metal head and the heat insulator was limited to 3 mm or more in order to suppress hydrogen intrusion into the steel, as is clear from Fig. 1. Up to mm, the hydrogen blowhole index is large;
This is because the hydrogen blowhole index becomes small and level off after reaching 3. Therefore, it is appropriate for the thickness of molten slag to be 3 or more to effectively inhibit/infiltrate hydrogen into steel. Note that as the 7 lacs for making the above molten slag, quicklime-based, soda ash-based, fluorite-based, etc. can be used, but the basicity (Ca
If O/) exceeds 1.5, the CaO content of 810° becomes large, which may cause hydrogen pickup by the slag itself, so it is desirable that /Sin, ' 5. T,0 (total carbon square) is necessary to promote flux slag formation, but 20
If it exceeds the chi, it will be an increase of melt fi (0), so 2=0
% or less is better.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for producing a vertically short steel ingot according to the present invention will be described in detail below with reference to the drawings.

Fig. 2 is a schematic cross-sectional view of a mold for explaining the method of the present invention. ) is the mold into which it is cast. (4) is a heat insulating material (hereinafter referred to as ceramic fiber) attached to the inner circumferential wall of the mold (2), and the molten metal due to cooling from the side walls of the mold (2). (3) The coagulation is prevented as much as possible. On the upper surface of the molten metal (3) is a molten slag (6), and further on the upper surface is a heat insulating agent (hereinafter referred to as an initial exothermic agent) (5) such as a molten heat insulating flux. Roasted rice hulls (7) are filled to keep the head of the molten metal warm and prevent solidification from the head of the molten metal, as well as to prevent hydrogen from penetrating into the molten metal.

〔Example〕

A molten pot having the composition shown in Table 1 was poured into a mold (2) shown in FIG. 2 at 1580°C. In the case of this example, the mold thickness is 30
The thickness of the ceramic fiber attached to the entire inner peripheral wall of the 0 mrl s mold is 7 omt+t, the moisture content of the ceramic fiber before attachment is 0.05%, and the casting height is 600 mm.
Electric, 700mm, 800 questions, 900m sleep 1000 rr
, m, 1100+m, and 1200+u+1. In this example, flux is applied to the molten field 1 during the molten steel injection process.
7 to 149 input per ton, and on top of that, 0 moisture content
．． 600 Kp of 9% initial exothermic agent (5) is added, and 150 Kp of dried roasted rice hulls are added to improve heat retention and prevent hydrogen from entering the molten metal (3).
) was completely insulated from the head and sides to prevent solidification, and unidirectional solidification was performed only from the bottom.

The ingredients of the rice cake are shown in Tables 2, 3, 4, and 5, respectively.

Table 1: Molten steel composition (%) Table 2: Mold internal dimensions (mm) Table 3: Initial heat generation heat insulating agent composition (1) Table 4: Ceramic fiber composition (1) and properties No. 5
Figure 1 shows the relationship between the molten slag thickness m→ during ingot making of the steel ingot produced by the method of the present invention and the hydrogen blowhole index of the product. This is the average value of data obtained for seven types of slabs with different filling heights.

As is clear from Figure 1, by interposing the molten slag, the blowholes caused by hydrogen are significantly improved, and this is especially noticeable when the molten slag has a thickness of 3 m or more, improving the core quality and internal quality of the brocade ingot. is obvious. In addition, the maximum value of hydrogen in the steel ingots was 2.5 ppm or less in all cases. This is due to the synergistic effect of the molten slag thickness being 3 mm or more and the moisture content in the ceramic fiber and the initial exothermic agent being 3 mm or less.

As is clear from the above examples, according to one method of the present invention, after casting a molten slag with a thickness of 3 mm or more into a vertically short steel ingot, it is interposed between the head of the molten metal and the initial exothermic agent (5), and the water is removed. If 3% or less of the initial heating agent and ceramic fiber are used, the hydrogen in the hydrogen gas and water vapor generated by the ceramic fiber (4) and the initial heating agent (5) will be suppressed from penetrating into the molten steel, and the copper ingot will be The hydrogen content in the field is reduced to 4 ppm or less, the occurrence of hydrogen blowholes is significantly reduced, the internal quality of the field mass is improved, and the yield is improved, resulting in extremely large effects.

[Brief explanation of the drawing]

FIG. 1 is a chart showing the relationship between molten slag thickness and hydrogen blowhole index, and FIG. 2 is a schematic cross-sectional view of a mold, etc. used in the method of the present invention. 1...Surface plate, 2...Room, 3...
... Molten metal, 4 ... Insulating material, 5 ... Heat retaining agent, 6 ... Molten slag, 7 ... Burnt rice husk. Applicant Sumitomo Metal Cormorant Industries Co., Ltd.

Claims (1)

[Claims] By using a mold whose inner peripheral wall is covered with a heat insulating material and keeping the head of the molten metal poured into the mold warm with a heat insulating agent, the molten metal in the mold is cooled from the bottom of the mold and solidified. In a method of unidirectional solidification substantially upward from the bottom part, a molten slag having a thickness of three or more layers is interposed between the molten metal head and the heat insulating agent to suppress hydrogen intrusion into the steel. :
q! A method for manufacturing a vertical and short can pit with f characteristics.