JPS626736A - Production of metallic ingot having uniform quality with decreased segregation - Google Patents

Abstract

PURPOSE:To make the quality of a steel ingot uniform and to prevent the defect thereof by removing part of the sensible heat and latent heat of solidification retrained by a molten steel and settling and depositing the molten steel in a semimolten state to the bottom of a casting mold. CONSTITUTION:Slag which is melted by heating in another place is preliminarily packed into the casting mold 4 installed on a molding board 5 and the molten steel 1b subjected to refining in a ladle 8 is poured through a tundish 7 or through a nozzle 3 directly inserted into the slag 2. Since the molten steel 1b is poured through the inside of the slag bath in this stage, the molten steel 1b directly contacts with the slag bath and the sensible heat and latent heat of solidification thereof are partly lost. Therefore the molten steel 1b settles in the slag bath and deposits in the form of a plate on the molding board 5. The molten steel is poured in the form of granular drops by the provision of an induction coil 12 to the outside circumference of the nozzle 3, etc. The quality over the entire part of the steel ingot is made uniform and the defect such as segregation and porosity is prevented by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a homogeneous metal lump with little segregation in a molten metal ingot forming method.

[Conventional technology]

Conventionally, thick steel plates have been produced using continuous casting slabs, but continuous casting slabs have problems such as a decrease in HIC resistance and low-temperature toughness in the product steel plate due to center segregation, and For the manufacture of steel plates, continuous casting slabs are unable to secure the required reduction ratio, so a method of using ingot making and blooming processes has been adopted.

However, in the production of flat steel ingots for extra-thick steel plates, the reverse ■
Casting defects such as segregation, macro-segregation, and cracks inevitably occur, which can lead to unfavorable quality results such as deterioration of the mechanical properties of product steel sheets and the appearance of false patterns.

Therefore, with the aim of drastically reducing the reverse black segregation in steel ingots, the production of flat steel ingots by the unidirectional solidification method has been carried out in various fields. The principle of this is to prevent the concentrated molten steel from being captured in a streak shape on the solidification front by making the floating direction of the solute-enriched molten steel the same as the advancing direction of the solidification interface.

However, the weak point of the unidirectional solidification method is that the conventional three-dimensional solidification is changed to one-dimensional solidification, so the heat removal rate is relatively low, resulting in coarse dendrites and pseudo-solidification due to component segregation between trees. Patterns tend to appear on the surface of the steel plate. Furthermore, even if you have a unidirectionally solidified steel ingot, inverted V segregation may appear in the steel ingot, and simply making the direction of solidification parallel to the direction of gravity will cause the solute-enriched molten steel to reach the solidification front. Another problem was that it was not possible to completely prevent the capture of

On the other hand, remelting methods such as ESR (electro slag remelting) and VAR (vacuum arbor remelting) are used to manufacture high alloy steels and Ti alloys, but these methods There are few problems with excellent quality, but when manufacturing large unit weight products such as extra-thick steel plates, the manufacturing equipment is expensive and the running costs associated with remelting are high, so the applicable products are expensive. It has no choice but to be limited to certain products, and the quantity to be covered is also limited by the capacity of manufacturing capacity.

Furthermore, for the production of high alloy pipe materials and rolls, CIP
methods (Cold Iso, 5tatic Press) and 0 spray methods (for example, British Patent No. 1353517, British Patent No. 15172A3) are applied, and these methods can also be scaled up in principle to produce large single-weight extra-thick steel plates. ii), is considered to be effective. However, the CIP method has a slight cost increase, and the 0-spray method has difficulties in scaling up the actual equipment.
It is difficult to apply this method to the production of extra-thick steel plates.

This type of extra-thick steel plate raw material steel ingot is supplied to the mold in the state of molten steel with superheat and latent heat of solidification, and solidification progresses through a cooling process over a long period of time. , micro-segregation, inverted-V segregation, macro-segregation,
Defects such as cracks and porosity occur. Therefore, in order to fundamentally eliminate these casting defects, it is necessary to eliminate the presence of a solid-liquid coexistence layer for a long time in the mold or the presence of a liquid layer adjacent to the solid-liquid coexistence layer. However, the steel ingot, which is a material for large unit weight and extremely thick steel plate, usually has a unit weight of about 20 to 100, and the latent heat of solidification is extremely large, not only due to the degree of superheating of the molten steel. Therefore, in order to remove these heat contents from molten steel, it is necessary to take a long time using normal methods. If most of the heat content of the molten steel can be removed from the molten steel and then fed into the mold, it is possible to essentially eliminate casting defects for the reasons mentioned above. Not only does the casting work disturb the production process, it is actually impossible to feed semi-molten steel that has lost its heat content in the ladle or tundish into the mold through the nozzle, and furthermore, it is impossible to feed semi-molten steel into the mold through the nozzle. It is not even possible to produce homogeneous semi-molten steel in a pot or tundish. It is known that a technology called rheocasting already exists and that it is possible to manufacture small ingots of low melting point metals, but it is difficult to manufacture small ingots of low melting point metals. Therefore, this method cannot be applied.

[Problem that the invention seeks to solve]

Under the above circumstances, the present invention is suitable for use as a material steel ingot for thick steel plates, especially extra-thick steel plates, and has no casting defects such as inverted V segregation or dents, and has a solidified structure that is homogeneous and dense throughout the entire steel ingot. It is an object of the present invention to provide a method for producing metal ingots, which is almost impossible to produce.

[Means for solving problems]

In the present invention, when molten steel is supplied to a mold, by removing part of the overt and latent heat of solidification due to the degree of superheating possessed by the molten steel, the molten steel in a semi-molten state is allowed to settle and accumulate at the bottom of the mold. The technical means is to facilitate directional solidification from the bottom, make it homogeneous and dense, and produce steel ingots free of micro and macro segregation.

[Effect] The configuration of the present invention will be explained in detail below along with its operation.

FIG. 1 is a block diagram showing an embodiment of the present invention. 15
A slag 2 (BaCQ2.Na
C1, etc. or oxide-based slag).
The refined molten steel 1b placed in the draw w48 is supplied through a tundishure or directly through a nozzle 3 inserted into the slag 2 in the mold, and is injected into the slag bath. The injected molten steel 1 exchanges heat with the slag bath by coming into direct contact with the slag bath, and loses some of the sensible heat and solidification heat due to the degree of heating of the molten steel, and settles in the slag bath to form a plate on a surface plate. It is deposited in the form of However, semi-molten molten steel deposited in a plate shape has an extremely small heat content until it completely solidifies, so it solidifies rapidly with a small amount of heat removed from the bottom of the steel ingot, resulting in a very fine and dense structure. present.

What is important here is the control of heat exchange between the molten steel supplied into the slag and the molten slag, which is governed by the physical properties of the molten slag, the slag temperature, the dimensions of the molten steel droplets supplied into the slag, etc.

According to the usual pouring method, molten steel is injected into the slag in the form of a continuous fluid, so the specific surface area of Cat becomes small, and heat exchange in the molten slag becomes insufficient, resulting in melting at the bottom of the mold. The liquid phase ratio of the steel in the molten state increases and solidifies, 1'i
Fine homogenization of the weave cannot be achieved.

Therefore, when supplying hot water into the lj type, a high frequency electromagnetic force is applied to the molten steel passing through the nozzle from the outer periphery of the nozzle through the induction coil 12, applying a pinch force to the molten steel flow, dividing the molten steel, dispersing the supplied hot water into the molten slag, and forming droplets. It is necessary to supply hot water in the form of droplets or dispersed by powerful ultrasonic waves.

Moreover, as the hot water supply progresses, the temperature of the molten slag increases due to the heat content of the molten steel, and its ability to extract heat from the molten steel decreases. Therefore, a thermocouple 13 was installed in the molten slag in the mold, and a thermometer 14 was installed.
Detects the slag temperature and controls it within a predetermined control range. The method is to add a predetermined amount of molten slag 2a held in the slug bot 11 at a predetermined temperature through the sliding gate IO and the nozzle 9 into the mold.

As the casting of molten metal progresses and the volume of molten steel increases,
When the molten slag level rises and reaches the upper end of the mold, the molten slag will flow from the mold into the mold, but this amount can be recovered and applied to the next use without causing any problems.

The solidification structure of the steel ingot that has been solidified by M-forming as described above is a plate-like layered structure in which molten steel grain droplets are spread out flat against the bottom of the steel ingot, and the inside of each layered structure is composed of fine granular crystals. Microsegregation is also extremely slight. Furthermore, fine porosity is sometimes found in the gaps in the layered structure, but the porosity calculated from the volume density is as small as 0.2% or less, and the steel ingot is heated prior to blooming or direct rolling. There is no problem because it is completely crimped by rolling at a reduction ratio of 2 without internal oxidation.

Further, according to the present invention, it is possible to perform complete oxidation-free casting of molten steel grain droplets despite the overcasting method.

〔Example〕

C=0.18% by weight, 5i=0.28fft amount%,
M n = 1.52% by weight, P = 0.019% by weight, S
50 kg of molten steel with weight = 0,007 μ% and A text = 0.040 weight% was melted in the atmosphere.

Then, three sand molds with an internal volume of 3.5 cm were preheated in a furnace at 850°C, and g-type A was heated with 22 pI of B a Cl 2 .
For mold B, BaCfL2 was added once and melted, and for mold C, for comparison, only preheating was performed without adding molten flux. Attach a refractory filter with a mesh hole of 5 mm diameter to the tip of the tanditshu nozzle and heat thoroughly.
15 kg of molten steel at a molten steel temperature of 1650° C. was cast into each mold via a tundish.

Each steel ingot was cut to examine the solidification structure, and xtlI
a Micro-segregation was investigated using a micro-analyzer.

The Am ingot consists of fine granular crystals over the entire area, and the B steel ingot has the same fine granular crystals as the A steel ingot up to 2/3 height from the bottom, and above that, there are 10 mm columnar crystals on the surface layer of the steel ingot and the inside thereof. Branched columnar crystals were observed. On the other hand, the C steel ingot had columnar crystals of about 15 mm around the entire circumference of the steel ingot and branched columnar crystals inside.

A micro-segregation investigation of each of the III and C steel ingots revealed that the A steel ingot had a maximum P microsegregation of 1.4 with respect to the molten steel composition, and the C steel ingot had a P microsegregation of <8.7. .

〔Effect of the invention〕

According to the present invention, a dense ingot that is homogeneous and free from segregation throughout the entire steel ingot can be produced as a material steel ingot for thick steel plates, especially extra-thick steel plates.
It was possible to obtain a steel ingot free of defects such as inverted V segregation, macro segregation, and pitting.

[Brief explanation of the drawing]

FIG. 1 is an embodiment diagram showing the configuration of the present invention. fa, lb... Molten steel, 2, 2a... Molten slag, 3
．． 3a... Nozzle, 4... Mold, 5... Surface plate, 6
゜6a...Sliding gate, 7...Tandish, 8...Ladle, 9...Nozzle, lO...Sliding gate, it...Slugbot, 12.
...Induction coil, 13...Thermocouple, 14...Thermometer. 15...Insulation sleeve

Claims (1)

[Claims] 1 In a method for forming molten metal ingots, a mold into which the molten metal is to be injected is filled in advance with molten slag having a lower melting point than the molten metal to be injected, and the metal is supplied into the mold through the molten slag layer. After releasing a part of the superheat and latent heat of solidification of the metal into the molten slag by heat exchange, the metal is deposited in a semi-molten state at the bottom of the mold,
A method for producing a homogeneous metal ingot with little segregation, characterized by facilitating unidirectional solidification from the bottom of a mold to form a metal ingot.