JPS5945068A - Cooling method in ingot making device with semi- continuous casting mold - Google Patents

Abstract

PURPOSE:To produce a large sized steel ingot having high quality in a high yield by solidifying a casting ingot drawn from a water cooled casting mold by spray cooling for the bottom end part, heat insulation for the top end part and natural cooling for the remaining intermediate part. CONSTITUTION:Molten metal 5 is injected from the nozzle 6 in a molten steel pan 4 into a water cooled casting mold 1 having copper plates 2 and while the melt level in the mold 1 is maintained constant, a bottom plate 3 inserted therein is lowered by means of a rack 7 and a pinion 8. A steel ingot 9 formed with a solidified shell by such lowering is drawn downward and further while the side faces are supported with grids 10, the ingot is forcibly cooled by the cooling water from sprays 11. When the ingot 9 attains a required length, the charging of the molten metal is stopped, and the lowering of the bottom plate 3 is stopped. The region of 1/2D-2D height upward from the bottom end of the ingot 9 wherein the diameter or the length on the short side thereof is designated as D is spray cooled from the initial period of casting until the solidification completes. The top surface thereof and the region of 1/6D-1/4D height from the top end thereof are insulated of heat with a heat insulating material 12, and the remaining intermediate part is allowed to cool, whereby the ingot is made.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a semi-continuous casting mold ingot-making device to cast large steel ingots, such as extremely thick flat steel ingots, which are difficult to cast with conventional continuous casting equipment due to their thickness. This invention relates to a method for cooling large steel ingots during production.

In the present invention, a large steel ingot has a thickness or a diameter of 1
] refers to those with fins of 5D0 or more and a height of about LD-10D.

In general, for final products with a thickness exceeding 150 mm, such as 6-oka ingots for thick plate cutting or large steel ingots for forging, a forging ratio of 3 or more is usually required for downstream ratios. The number of questions was extremely large, ranging from 500 to 3,000 questions, and it was extremely difficult to cast using conventional continuous casting equipment.

Therefore, the above-mentioned J: Eel large steel ingots had to be cast by the long-established ingot-forming method using casting molds.

In this way, one copper ingot produced by conventional ingot making has a lot of center porosity, and component imbalances within the steel ingot such as center segregation, V segregation, and head segregation can be avoided, and the quality and yield of 61111 ingots can be improved. There is a problem that the quality is inferior. Ma/ξ, there is a lot of manual work,
Maintenance was also difficult because a wide variety of molds were required.

On the other hand, as a method similar to the continuous Q casting method, a semi-continuous casting method disclosed in Japanese Patent Publication No. 56-464.57, for example, has been known. This semi-continuous casting method differs from continuous casting in that d4, only a predetermined product length is cast;
The process is repeated for each product.

The conventional semi-continuous casting method is a large 6'14
There is a lack of consideration for making 11j blocks, and large size ≦1.
It could not be applied to the production of bow mass.

The present invention is a product made of f114 ingots made by the traditional agglomeration method (IE).
With the aim of improving yield and simplifying manpower and maintenance management, quality is improved by cooling large steel ingots using the most appropriate cooling method using a semi-speed IQ mold ingot making machine, which is an improved semi-continuous casting method. The purpose is to produce large s+;+i blocks with excellent properties.

The gist of the present invention is that when manufacturing a large 611'l ingot by lowering the mold bottom plate while injecting melt into a water-cooled mold, the diameter or short side length of the steel ingot is Then, the 111th surface of the 7D to 2D 1j4J region upward from the lower end of the steel ingot is spray-cooled from the initial stage of casting until the completion of solidification, and the upper end surface of the steel ingot and the 111th surface extending downward from the upper end are spray-cooled. - A cooling method in a semi-continuous casting mold ingot making apparatus characterized by insulating the side surfaces of the D to LD height regions and cooling the remaining intermediate side surfaces.

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

Figures 1 and 2 are longitudinal cross-sectional views of a semi-continuous casting f1g type ingot making device for explaining the method of the present invention. Figure 1 shows the situation at the beginning of the injection of molten eggs, and Figure 2 fl'4 after stopping injection
The cooling status of one block is shown.

In Figures 1 and 2, l is a water-cooled mold, 2 is a copper plate, and 3
is the bottom plate, 4 is the melting ≦ (・11 pot, 5 is the bay outside jll, 6 is the nozzle, 7 is the rack, 8 is the binion, 9 is the 61J1 block, 1
0t is the grid, 11 is sub 1/-.

Ingots are made in the semi-continuous mold ingot making device as follows.

The water-cooled mold 1 has a structure similar to that of a mold for a continuous casting apparatus, with the upper and lower surfaces open and the inner surface made of a '41iil plate.

In the initial state of molten steel injection, the bottom plate 3 is inserted into the bottom of the mold 1 from below] 15, water cooling; 111 With the bottom of the mold 1 closed, the molten steel 61 and '45 in the molten steel ladle 4 are inserted into the nozzle 6. It is then injected into a water-cooled mold l. Next, the bottom plate 3 is lowered by the rack 7 and pinion 8 while keeping the molten liquid 1ii+''i in the water-cooled mold 1 at a substantially constant level.

As the bottom plate 3 descends, 4j, f solid shells are formed t
l+Ii mass 9 is pulled downwards from the water-cooled mold l, supported on its sides by steel grids IO, and grid 1
It is forcibly cooled by the cooling water from the spray 11 disposed in the gap of 0.

When the required steel ingot length is reached, the injection of molten steel is stopped, the bottom plate is lowered, and the molten steel tube 4 is removed. FIG. 2 shows this state, in which the lower part of the steel ingot 9 is continuously cooled by water, and the upper end is insulated by a heat insulating ring 12.

A method of cooling this copper ingot 9 will be explained using FIGS. 3 and 4.

Figure 1 shows the case of a steel ingot with a diameter of 21nm and a height of 3 m. Each figure (a) to (e) shows the right half of the longitudinal section at the center of the steel ingot, and A-E shows the surface cooling conditions. show. A is spray cooling, B is natural cooling, C is insulation, D is forced air cooling, E is heat retention (1
480°C). Further, 21 shows the solidification interface solo field after 5.3 hours, 22 shows the solidification interface profile just before solidification, and 23 r:j: solidification 11'''l crepe 1.

It is known that the internal quality of the jiifl lump, ie, center porosity -1■ segregation, inverted V segregation, etc., is relaxed to the extent that the solidification interface profile does not exhibit a sharp V-shape. FIG. 4 schematically shows this, and the l product Jfr is better in (b) II', jl than in (a).

Figure 3 (a) shows the case where the side surfaces are uniformly cooled and the bottom surface is spray-cooled, and the top surface is insulated by spray cooling.Even if the bottom surface is spray-cooled, the sharp V shape at the end of the center circle cannot be eliminated. Can not.

In (b), the side cooling in (a) is replaced with forced air cooling, but the sharp V-shape cannot be eliminated.

(C) is an alternative to (a) where the top surface is insulated: , L 48 Q°C. Although the solidification interface profile is considerably improved, it cannot be said to be sufficient in the end.

(d) is the same as (a) with the addition of a means for insulating the sides of the two-end open area. The V-shape is considerably relaxed. In I<e), the lower side of the 1j11 surface is water-cooled instead of the bottom surface water-cooled in (d), and the V-shape can be eliminated.

From Figures 3 and 4, in order to improve the l product (ti) of the steel ingot, the entire top surface of the gvti ingot must be heated by Ir, and the sides of the steel ingot must be insulated at the top, spray-cooled at the bottom, and cooled at the middle by air. It is known that it is best to keep the

As a result of examining this knowledge regarding various dimensions and height/diameter ratios for circular and rectangular cross sections, it was found that the following cooling method is the most ideal. Zunawaji, the diameter or short side length of the steel ingot is D, and the height is ID ~ 1. For large steel ingots at OD, the top surface of the steel ingot is heated, at least the area 1D to 2D from below the side surface of the steel ingot is spray-cooled, and the remaining middle area is allowed to cool. The water-cooled cooling section performs spray cooling even while the steel ingot is being lowered for casting. Therefore, the ejection position of the spray nozzle moves as the steel ingot descends.

The insulation area on the upper side of the steel ingot should be expanded from ↓D~yo-)4, since it would take a long time to complete solidification, which would be uneconomical, and if it was reduced, the effect of controlling the solidification profile would be significantly weakened, so it should be within this range. stipulated by.

In order to provide directionality to the cooling of the steel ingot, the spray cooling area on the lower side of the steel ingot must be at least ↓Dj2 above fiNi.
Spray cooling of an area exceeding 2D is limited to 2'I) to 2D because spray cooling of an area exceeding 2D may cause center porosity.

In other words, it is ideal to gradually expand the cooling area as the solidification interface within the spray cooling area rises. The intraclump coagulation can proceed in two directions from below. However, in order to judge the visual field, the crater in the unsolidified area must be
Need to detect the end. According to the knowledge obtained by the present inventors by detecting the crater end using ultrasonic waves or During cooling, solidification within the steel ingot progresses in an orderly manner from the bottom to the top.
-! If the spray cooling range exceeds 2, it will cause a crater.
There is a region above the end where solidification is completed before the crater end, creating large porosity.

From this point of view, t+ to obtain defect-free products
The rti mass lower spray area is limited to a range of 2D or less from the lower end.

In addition, in order to shorten the solidification time in the latter half of the cooling period according to the present invention, the crater end within the boundary of ηt' is detected, and the spray cooling area is expanded within a range of 1) above the end position. I can go.

Soufflé-cooling water M: density 0.005-0.1 l/
It is sufficient to install crl-rnin as a reference, and it is possible to realize cooling control from below the steel ingot.

Fig. 2 shows the cooling state after the injection of molten steel is stopped and after that, the spray cooling on the steel ingot 9 gradually moves downward as the bottom plate 3 descends, and from 11g to 11g of the 11 spray groups.
This shows a state in which only the llj group is spraying. During the casting of the steel ingot 9, of course, the sprayer 1lalllb+... spouts out cooling water as the steel ingot 9 moves, and the area within the range -ID~21) from the lower end of the steel ingot is outside the defined area. Cooling water spray will be stopped sequentially.

Reference numeral 12 in FIG. 2 indicates heat insulation removal, and after stopping the injection of molten steel, the water-cooled mold l shown in FIG. Although not shown in Figure 2, the upper surface of the steel ingot is also insulated. The insulating moon 12 in Fig. 2 is rod-shaped, but it may also be cap-shaped, which insulates the upper surface at the same time.As described above, by spray cooling the lower part of the aorta mass, insulating the upper end, and leaving the middle part to cool. , n! The unsolidified molten metal inside the lump d can be solidified from the bottom to the top one by one, and center porosity, V segregation, etc. are greatly improved.

When carrying out the method of the present invention, it is also possible to use means for further improving the quality of the steel ingot. For example, mainly in order to reduce individualization in the A1 part of the steel ingot, the unsolidified part of the curved head of the i;ri ingot is heated after the middle stage of the solidification process, and iron with a low impurity concentration such as pure iron is added to the unsolidified part. The impurities may be diluted by diluting the impurities.

For example, it is also effective to reduce center segregation and center porosity by adding &=; to the solidification process and using electromagnetic stirring of the unsolidified molten metal.

By the method of the present invention, it has become possible to cast large steel ingots with high quality and high yield using a semi-continuous casting mold ingot making device.

Example 1 Diameter 1. (A steel ingot with a length of 3 m and a height of 3.2 m was produced by cooling it using the apparatus shown in Fig. 1 and the controlled cooling shown in Fig. 5. In Fig. 5, A is the water density of 0.011/crI
・mln spray cooling, cooling area height 1.6nlX
B is for cooling, and C is for heat insulation.Insulated area Foil: The entire upper surface of the Ia mass and the side surface of the sail 32 m downward from the entire upper surface. The bottom surface is cooled by contact heat transfer with the bottom plate.

Molten steel has a liquidus temperature of 1517℃ and a common phase temperature of 1460℃.
, the injection temperature was 1560°C.

Figure 6 shows the above example with an average diameter of 1.6 m and a height of 3.2 m.
An example of the distribution of center volume If city in the frill ingot height direction when ingots are formed using a normal mold is shown. As seen in FIG. 6, the center voluntariness of the steel ingot produced by the method of the present invention was drastically reduced to a level above that of the conventional method.

Implementation 51] 2 #(4, Using the device shown in Figure 1, cross section 1,0771
X 2. Om, quotient 3. A copper ingot of Om was cast. Injection melt≦i, ra temperature is 1480°C, and drawing speed from the mold is 0.
2m for 1 minute, and after the start of drawing, the amount of cooling water from the spray, density 8
Spout cold water at A/m - + nin and draw it out while spraying an area of 1.5171 from the lower end of the side of the copper ingot in the J direction. rll up and down stop, if'! The two sides and the sides of the φ1" C1 area of Q, 277Z from the top downwards were covered with heat insulation, and the cooling was continued for 6 hours until the solidification process was completed. At this point, the unsolidified steel at the head of the steel ingot was heated, 50 U of pure iron was added, and the unsolidified molten steel was diluted to 17.

Comparison of the above II8 steel ingot with a steel ingot of the same size made by the conventional 11η ingot making method. The maximum porosity of the center axis "2" was 0.5 in the fl+4 block according to the conventional method, whereas it was 0.5 in the fl+4 block according to the conventional method, whereas it was 0.5 in the fl+4 block according to the conventional method, whereas it was ≦1. ``It was reduced to 002 in one block.

In addition, the truncation part of il・■11 lumps with positive segregation of 120% or more is one lump by the conventional method): L fl, ff lumps total 1
jjj'! The actual M1 of the present invention was
In the steel ingot according to one example, it was reduced to 15 East Lit%. Furthermore, it was confirmed that (1) segregation was alleviated in the copper ingots according to the examples of the present invention compared to the steel ingots made by the conventional method.

[Brief explanation of drawings]

g) Figures 1 and 2 are longitudinal cross-sectional views of essential parts of the semi-continuous casting mold ingot-making apparatus used in the implementation of the present invention, and Figure 3 is a steel ingot showing the evolution of the solidification line when external cooling conditions are extended. Fig. 4 is a schematic diagram of a longitudinal section of a steel ingot that qualitatively shows the relationship between the solidification profile and internal quality, and Fig. 5 is a schematic diagram of a longitudinal section at the center of the steel ingot without showing the external cooling conditions of the example. FIG. 6, which is a schematic diagram of a longitudinal section, is a graph illustrating the improvement in center porosity according to the embodiment. l...Water-cooled mold, 2...Copper plate, 3...Bottom plate, 4...
Molten steel pot, 5... Molten steel, 6... Nozzle, 7... Rack, 8... Binion, 9... Steel ingot, lo... Grid, ll... Spray 21.22... Solidification Interface 7゛ro-feel, 23...
Solidification shrinkage part A...spray cooling, B...cooling, C...insulation, D
・・Forced air cooling, E・・Heat retention. Fig. 1 Fig. 2 et al. Fig. 3 (a) (b) (c) Fig. 1 Fig. 5 (b) Fig. 6 Center porosity index

Claims (1)

[Claims] 1. When manufacturing a large steel ingot by lowering the mold bottom plate while pouring molten steel into a water-cooled mold, the diameter or short side length of the steel ingot is D, and the lower end of the steel ingot is More upwards - ID ~ 2D
The side surfaces of the height region are spray cooled from the initial stage of casting to the completion of solidification, and the upper end surface of the 6j:111 mass and the lower part from the upper end are 1D--! - A cooling method in a semi-continuous casting mold ingot making apparatus, characterized by insulating the side surface of the D height region 4 and cooling the remaining intermediate side surface.