JPS5886969A - Liquid drop casting method - Google Patents

Abstract

PURPOSE:To prevent the formation of a defect occuring in macro segregation, and to improve the quality of a steel ingot, by fractionized molten steel once to liquid drops, and stacking the granular drops cooled to an imperfectly solidified state in a mold. CONSTITUTION:The charging flow of molten steel 27 is fractionized to liquid drops of <=5mm. grain sizes by the liquid nitrogen or liquid argon sprayed from a nozzle 22 and is at the same time removed of heat. During dropping, the liquid drops cooled by convection and radiation heat transfer in the gaseous nitrogen or argon atmosphere maintained at a low temp. by the heat of evaporation and attain the imperfectly solidified state, wherein the surfaces are solidified and the inside are unsolidified. These liquid drops are stacked in a mold 24 to form a stacked ingot 28. Thus V segregation, inverse V segregation and segregation in the head part are eliminated at all, and the quality of the steel ingot is improved.

Description

Detailed Description of the Invention The present invention relates to a method of injecting molten steel into a #1 tank, more specifically, droplet casting in which molten steel is once turned into droplets, cooled to an incompletely solidified state, and nine droplets are accumulated in a mold. Regarding the law.

Steel casting is generally carried out by pouring molten steel in a ladle or tundish directly into a mold. In this method, the molten steel injected into the casting base is
As solidification occurs sequentially from i111 toward the center, it is unavoidable that macroscopic component segregation occurs, and V segregation and reverse V segregation occur in ingots, and center segregation occurs in CC (continuously manufactured) pieces. It is a well-known fact that internal cracks can be seen.

These defects reduce the quality of the steel ingot or require an extra tooth.

As a means to prevent the formation of defects caused by such macro-segregation and improve the quality of steel ingots, solidification after casting
A method of electromagnetically stirring residual molten steel at the base to reduce segregation (electromagnetic stirring method), iron is added to the molten steel flow during pouring! A method of adding a solidification nucleating agent, such as, and a low-temperature casting method have been proposed or put into practical use. However, the electromagnetic stirring method merely disperses the concentrated solute in the solidification core screen by stirring and changes the shape of the segregation zone, and therefore does not fundamentally eliminate segregation. In addition, with the method of adding a solidification nucleating agent, the number of inclusions increases due to the oxidation of the additive during addition, and the adjustment of the components is troublesome. There are still some supervisors left. On the other hand, regarding the low temperature casting method, there are also technical issues such as nozzle connection).
There is a world. 1 'Moreover, in either case, it does not change the method of sequentially solidifying the steel from the surface of the steel ingot, and thus fundamentally solves the problem of the occurrence of defects due to macro-segregation inherent to this method. I wasn't able to do it.

An object of the present invention is to provide a steel manufacturing method that can completely prevent macro segregation of ingots and CC slabs.

In this case, the present invention is characterized in that when molten steel is injected into a mold from a pile or a tundish, the molten steel flow is turned into droplets with a particle size of 6 mm or less by injection of liquefied inert gas, and the generated droplets are By the time 1 is solidified, only the surface is solidified, and the inside is unsolidified.
This is a method of casting molten steel that involves cooling it to an incompletely solidified state of 11% and collecting it in a mold in this state.

The method of the present invention is applicable to both ingot production and continuous casting.

According to the invention, a fluid jet of liquefied inert gas flows through the molten steel stream injected into the mold from a ladle or tandige! (Atomization) First, the liquid is atomized into droplets with a diameter of 5 mm or less. Liquid nitrogen or liquid argon is used as the liquefied inert gas.

Although the following explanation is limited to liquid N or liquid Ar, other liquefied inert gases can also be used as desired. The generated droplets are then cooled (by an appropriate cooling means) to form droplets in an incompletely solidified state where only the surface is solidified and the inside is not solidified, and in this state they are allowed to fall and accumulate in the mold. . Since the surface of each grain size has already solidified, there is no movement of components between grain droplets, so macroscopic segregation is completely prevented. Therefore, when an ingot is cast by the method of the present invention, not only V segregation and reverse segregation but also head segregation are reduced or virtually eliminated, which improves the quality of the steel ingot and also reduces the yield determined by feeder cutting. improves. Furthermore, when the method of the present invention is applied to a continuous casting method, center segregation of CC slabs is completely eliminated, internal cracks due to bulging are also eliminated, and quality can be significantly improved.

When manufacturing products such as eaves from ingots or CC slabs, there are forging and rolling processes, which are then pressurized.In particular, the quality of extra-thick steel plates is determined by the degree of pressurization (reduction ratio) K. In other words, defects such as macroscopic segregation are eliminated under pressure. According to Kenpo, this reduction rate (usually 1
15) is reduced to 1J.

This leads to a huge reduction in equipment costs (pressurization), which is a great benefit.

In the method of the present invention, the molten steel flow is liquid N, and the flow is liquid A.
The liquid is turned into droplets by the injection of r. Liquid N.

As will be described later, liquid Ar is advantageous in that it cools the droplets from the surface at the same time as they are formed into droplets, and the heat of vaporization eliminates the need for droplet separation means. Moreover, this N, and A
Both r are inert, and during a short period of time during falling, the particles MK
Without any substantial effect, these vaporized gases also serve as an anti-oxidation seal for the large surface area droplets.

The particle size of the generated droplets depends on many factors, including the type of liquid to be injected, its flow rate, the injection angle, and the flow diameter of the molten metal (molten steel fi) flowing into the injected liquid. The injection φ value that produces the desired droplet size can be determined experimentally.

When the particle size of the liquid exceeds 6s+a, solidification shrinkage pores are formed in each droplet, and when the solidification rate is large, the solidification shell on the grain surface also becomes strong, so that sufficient deformation within the mold does not occur. The voids between the droplets remain as fine pores in the lump stage. This will disappear with subsequent pressurization, but the same pressurizing force as conventional steel ingots with defects such as macroscopic component segregation is required.

Father, of course, don't rush the heat removal efficiency, the falling distance is 8r.
rL or more is required, making it impossible due to equipment considerations as a practical process. Therefore, the particle size of the droplets is limited by IFK to 5 cm or more. A preferred particle size range is about Q1 to zO■.

The generated droplets are cooled and solidified by the latent heat of vaporization of liquid Nt or liquid Ar, which removes heat from the surface at the same time as the droplets form. Also, during the subsequent fall into the mold, the vaporized N
In Kusumaku, Ar suppresses the rise of the electric plate in the surrounding atmosphere, improves heat removal efficiency, and performs cooling by convection and radiation heat transfer. Therefore, even without any special cooling means, only the surface of the grain solidifies. However, a cooling means may be separately provided in the falling dilute acid, that is, in the cooling bath, so that the solidification rate of the desired grain size can be easily obtained during the falling into the l# mold. In the method of the present invention, any cooling means can be used as long as it does not adversely affect the grain quality, but the same fluid as that used for forming droplets, that is, liquid N and liquid Ar, can be used as the cooling means. It is particularly preferable to directly cool down the falling grains by injection, or to cool them by suppressing the rise in ambient temperature by the heat of vaporization and improving heat removal efficiency.

In the present invention, the "incomplete solidification state" refers to the solidification rate IX
The above means a state of less than 100%.

However, the solidification rate referred to in Komu is the ratio of heat removal to latent heat of solidification.

The method of the invention will now be described in further detail with reference to one drawing.

Figure 1 shows a large steel ingot (i
L) and CC slab (b) schematically show oversolidified roots and defects that occur, where l is V segregation at the center of a large steel ingot, 2 is inverted V segregation (ghost), and 8 is V segregation at the center of a large steel ingot. In the segregation zone of the head, 4 is a central fold seen in the CC-piece, and 6 is an internal crack. Figures 9, 6, 7 and 8.9 show the positions of coagulation rods at each stage of the process. There are several factors that contribute to the generation mwt of these defects, but in any case, the fundamental cause is that the poured melt solidifies sequentially from the surface of the ingot. Because of these defects, the ingot is cut with a feeder to remove the head segregation zone, and the yield is reduced accordingly. ,
In order to avoid deterioration in the quality of the ingot, the pressure applied during the forging and rolling process from the ingot to the raw product (steel plate, steel bar) is increased to eliminate these defects. However, the degree of mitigation is not complete, and there is a large loss in both time and economic terms.

FIG. 2 schematically shows the method of the present invention, with 21
2 is a composting pot (or tundish), 22 is an annular injection nozzle for liquid Nut or liquid Ar, 28 cooling tanks, 24 is a mold, 26 is an exhaust gas plate, and 26 is a grain size collection plate. As shown in FIG. 2, in the method of the invention, the injected stream of melt@21 is injected from the nozzle 22 of liquid N! Or N is formed into droplets by jetting liquid Ar, and at the same time is heat removed by liquid N or Ar, and is further kept at a low temperature by the heat of vaporization while falling, or by convection or radiation heat transfer in an Ar gas atmosphere. Upon cooling, the surface is solidified and the inside is in an incompletely solidified state, which is accumulated in the am, and the accumulated mass 28
form. In the model Ill shown in Fig. 42, no separate cooling means is provided, and the amount of heat removed, that is, the solidification rate of the grain size, is determined by the injection flow rate of liquid N or AT and the falling distance IIm into the mold m.
! (In other words, the loss of the cooling tank) was finally completed. In this case, in order to obtain droplets of, for example, aitMI table 10V, a free fall distance of about 1-Jm or more is generally required.

To accelerate cooling and facilitate control of the solidification rate, the cooling tank 2BK can be provided with cooling means, preferably liquid N or AT injection.

Figure 8 schematically shows nine droplets produced by molten steel becoming droplets and islands; (a) shows the grain size during falling, and (b) shows the state of nine droplets accumulated in the mold. shows.

In the figure, A is the solidified shell and the mouth is the molten steel. As shown in the figure,
The droplet generated by the fluid jet loses its spherical shape due to surface tension, and the surface solidifies while falling, maintaining an almost spherical shape, but 11Il'! When the droplets are accumulated in i, they are deformed by their own weight and the weight of the particles accumulated above, and the gaps between the droplets disappear as shown in the ga(b) diagram. Solidification occurs from the surface within individual grains, as in the past, and in that sense, segregation occurs on a microscopic level. However, due to the presence of a solidified shell on the surface of each droplet, the flow of molten steel or the movement of components between the droplets and the grain size is prohibited, so there is no macroscopic component segregation. Also, the various defects described above due to such segregation do not occur. However, when the solidification rate reaches 100% and the droplets are completely solidified, there is almost no deformation of the droplets after accumulation, and voids are formed at the boundaries between the droplets, causing sag of large lumps. Since the condition resembles a so-called defect, it causes deterioration of mechanical properties. At the same time, the surface texture of the obtained steel ingot also deteriorates. Therefore, the solidification rate of the droplets on the collection surface into the mold must be less than 100%, with solidification rates in the range of about 6-40% being preferred.

When adopting a method of forming 1111wI4 into droplets during injection as in the present invention, since the surface area becomes large, it is of course essential to prevent oxidation. To use liquid N, t or Ar,
Nit or Ar gas, which is vaporized from this liquid, constitutes the surrounding atmosphere and also serves as an oxidation prevention agent.Therefore, the oxidation level of 11 degrees can be suppressed to the same level as in the ordinary over-pouring casting method.

From the molten steel having the composition shown in Table 11 given later in the Examples, 480×4
A 2 ton steel ingot with dimensions of 10 mm MIX 1810- was made. For comparison, molten steel with the same composition was υ
A 2-ton steel ingot of the same size was produced by casting.The manufacturing conditions for both are shown in Table 81I, and the properties of the obtained ingot are shown in Table 8. - In the method of the present invention, an amount of liquid N of 02'ld/T was used to form droplets and was injected from an annular nozzle. This corresponds to Q 12//min in terms of flow rate. The cooling of the droplets utilizes the amount of liquid N used to form them into droplets, and the latent heat required for this liquid N to vaporize and the sensible heat up to atmospheric temperature are equivalent to 86% of the latent heat of solidification of molten steel. .

The size of the droplets produced under the conditions shown in Part 2 was on average 08-4I, and the solidification rate of the droplets just before accumulation in the mold was about 8696 grains.

As can be seen from the results shown in Table 8, in the method of the present invention, the Go-axis crystallinity is significantly increased to more than twice that of the conventional method. There is almost no component segregation (S segregation) in the center of the steel ingot, and there is no macroscopic component segregation. In addition, inclusions due to molten steel oxidation, that is, the cleanliness, were suppressed to 1 fK, which is approximately the same as the normal casting method, by vaporizing to 9N and gas sealing.

Jlll1 Table # Steel composition (weight %) 1st 111 Manufacturing East case Hataori: ＠ shaped slit Oa C・Nislit injection hole oH gill m flow property table A simple diagram IIg#4 Figure 1 shows the ``conventional Large steel ingots manufactured using the normal casting method (
&) and CC slab (b), and Fig. 2 is a schematic cross-sectional view (partially perspective) showing the method of the present invention and an apparatus that can be used therein. Fig. 8) and Fig. 8 show the falling (a) and after accumulation (a) of molten steel generated due to dropletization and incomplete solidification by the method of the present invention.
It is a figure which shows typically the cross section of the droplet of b).

21 Tori @ (or Tandiji&) 22 Injection nozzle 28 Cooling tank 24 Patent attorney Akira Hirose, Patent attorney Hirose Akira -O 2 Drawing procedure amendment (voluntary) Commissioner of the Japan Patent Office Kazuo Wakasugi December 1982 28th 1, Display of the case 1982 Patent Application No. 162708 2, Title of the invention Droplet casting method 3, Relationship with the person making the amendment Patent applicant address 5-15 Kitahama, Higashi-ku, Osaka Name (211) Sumitomo Metal Industries Co., Ltd. 4, Agent address: 2-9 Kanda Tamachi, Chiyoda-ku, Tokyo 101
Nichichu Building Telephone (03) 254-7767 Explanation Column 6, Contents of Amendment (1) The scope of the claims will be amended as follows.

``When injecting molten steel into a mold from a ladle or tundish, the molten steel flow is turned into liquid 7L, and the liquid 11 is jetted to form droplets with a particle size of 5IIIl or less, and the resulting droplets are poured into the mold. A droplet casting method characterized by cooling to an incompletely solidified state where only the surface solidifies and the inside remains unsolidified before falling into the mold, and is collected in the mold in this state. ) "Liquefied inert gas" on page 3, page 10-11 and line 19 of the specification is corrected to "liquid argon or liquid nitrogen."

(3) In the following parts of the specification, "N2" is replaced with "nitrogen
I am corrected.

Page 5, lines 8.9 and 15, Page 6, lines 16 and 19, Page 7, line 9, Page 8, line 20, Page 9, lines 4, 5, 7, 12, and 18, Page 11, lines 8 and 9. , p. 12, lines 1.4.5 and 17, and the column of the method of the present invention (two places) in table 2, p. 13.

(4) rArJ in the following part of the specification is corrected to "argon".

5 page 9, lO and line 15, page 6 line 16 and 19, 7
Page line 9, page 8 line 20, page 9 4.5.7.13 and 1
Line 9, and lines 8 and 10 on page 11.

(5) Delete "As the liquefied inert gas...it can be used as desired" in lines 1-5 on page 4 of the specification.

(6) The following parts in the description are corrected as follows.

And Hill - Correction 1 - - Koshogo 11 4 12 Reverse segregation Reverse V segregation 9 15-16 In general
(Deleted) 9 16 More than 1113 Examples of Nature Example 113 15
0.27rrr/TO, 27nr/5te
el Ton14 5 Segregation rate Maximum segregation rate (7) Insert the following between lines 18 and 19 on page 5 of the statement box.

``In general, it is possible to turn a molten steel stream into droplets by gas injection, but the ability to cool the generated droplets is significantly inferior to that of liquid nitrogen or liquid argon, which can utilize the heat of vaporization. In order to solidify the surface before it is collected in the mold, an extremely large amount of gas is required compared to liquid nitrogen or liquid argon, and the cost is extremely high. It is extremely difficult to create practical equipment, droplet collection equipment, etc.” (8) Insert the following after “Kiru.” in the third line of page 6 of the specification box.

For example, when injecting liquid nitrogen, the amount of liquid nitrogen to be injected is 100 g per 111 kg of melt injected.
0g, liquid nitrogen pressure just before the injection nozzle is 5kg/cd
It is desirable that the liquid nitrogen be ejected from the nozzle at a speed of I N/see to 20 m/sec. j(9) Insert the following next to Table 3 on pages 1 and 4 of the specification box.

Example 2 A 2-ton steel ingot was manufactured in the same manner as in Example 1. However, the manufacturing conditions were as shown in Table 4 below. For comparison, a conventional method was also used. Note that in the method of the present invention, a collection plate was used to inject solidified metal into the CC mold. As a result of these castings, the ingots produced by the method of the present invention had no center segregation.

On the other hand, clear center segregation was observed in the ingots produced by the conventional method.

Claims (1)

[Claims] (1) When pouring molten steel into a mold from a ladle or tundish, the molten steel stream is turned into droplets with a particle size of υ6- or less by injection of liquefied inert gas, and the resulting droplets are... # A droplet casting method characterized by cooling to an incompletely solidified state where only the surface solidifies and the inside remains unsolidified before falling into the cutout, and is collected in the mold in this state.