JPH08174167A - Exothermic type molding powder for continuous casting - Google Patents

Abstract

PURPOSE: To improve the exothermic efficiency of an exothermic type molding powder for continuous casting and to decrease the generating rate of pin holes by previously mixing and sintering an exothermic material and a heating assist material and adding the mixture to a powder base material. CONSTITUTION: The exothermic material and heating assist material of the exothermic type powder raw material powder subjected to a design of mix in a prescribed range are mixed by using a mixer, such as V mixer. The powder mixture composed of the exothermic material and the heating assist material is then subjected to a sintering treatment to obtain a sintered compact. After this sintering treatment is continued down to room temp., the sintered compact is pulverized and the resulted powder is subjected to a grain size readjustment in such a manner that a grain size range of about 1 to 100μm is attained. The sintered compact powder subjected to this grain size readjustment is added to the powder base material and is mixed with equipment, such as mixer, by which the exothermic type powder is obtd. The state that the heating assist material and the metallic exothermic material to generate heat by combustion according to the reduction thereof exist extremely adjacently is obtd. by mixed sintering of the exothermic material and the heating assist material. The reaction of the exothermic material and the heating assist material is, therefore, effected efficiently even if the sintered compact powder is added to the powder base material and is uniformly mixed therewith.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a mold powder for continuous casting of steel.

[0002]

2. Description of the Related Art Mold powders for continuous casting of steel are classified into a mixed type and a premelt type according to components and a manufacturing method. The mixed type component is a calcareous raw material as a main raw material, a siliceous raw material added as necessary for basicity adjustment, further sodium carbonate, a freezing point such as fluorite, a flux raw material as a melting property adjusting material such as viscosity, And a carbonaceous raw material as a melting rate adjusting material. The pre-melt type includes a pre-melt type and a semi-pre-melt type in which all or a part of the components except the above carbonaceous raw material are melted and crushed. On the other hand, in terms of shape, there are a powder type in which powder raw materials are mixed and a granule type in which granulation is performed by various methods.

Mold powder for continuous casting (hereinafter, simply referred to as mold powder or powder) is added on the surface of molten steel injected into the mold, slag is formed on the surface of molten steel, and it is between the inner wall surface of the mold and the solidified shell. It is consumed while fulfilling the roles of lubrication, heat retention on the surface of molten steel in the mold, absorption of inclusions floating from the molten steel, and antioxidant on the surface of molten steel.

This powder has its dissolution rate, viscosity,
Since there are many control factors such as melting point, and the optimum powder differs depending on the steel type, casting speed, slab cross-sectional shape, etc., its selection is extremely important.

In order to reduce the occurrence rate of defects on the surface of the continuously cast slab, especially pinholes, the temperature of the molten steel surface in the mold is kept high and the bubbles and inclusions present in the molten steel in the mold rise up. Need to be easy.

Therefore, in order to improve the heat retention of the molten steel surface by the powder, Ca-Si, S
It has been directed to add a metal heating material such as i or Al to generate an exothermic reaction due to the oxidation thereof and supply heat to the surface of the molten steel.

The following methods have been proposed as a method for adding heat to the powder by adding a metal heating material to the powder.

Japanese Patent Laid-Open No. 2-220749 discloses Al ₂ O ₃
Inorganic powder -SiO ₂ -CaO-based, low-melting-adjusting material as _{Na 2 O, F, MgO,} Fe 2 O 3, B 2 O 3 and BaO of one or more, C and Ca-Si as a heat generating material
At least Ca-Si, the KMnO _4, Fe ₂ O ₃ and one or more MnO these heat generating material as improve combustion to generate heat (oxidizing agent), and powder was added to the culture are shown in.

Japanese Patent Laid-Open No. 3-226341 discloses a base material 20
~ 90 wt%, SiO ₂ 50 wt% or more siliceous raw material 0
10% by weight, 0 to 20% by weight of flux material, one or more exothermic materials of sodium carbonate, sodium hydrogen carbonate and sodium nitrate, 3 to 30% by weight, of reducing agents of silicon and silicon alloy 1 or 2
Powders containing from 3 to 30% by weight of the seeds and from 0 to 30% by weight of a flame suppressant consisting of iron oxide are shown.

In Japanese Patent Laid-Open No. 3-169467, a powder containing a slag base material, a flux, a viscosity modifier, carbon and the like is integrally sintered with a flux and Ca-Al alloy fine particles to form a powder. The Ca-Al alloy flux powder and the powder in which a heat generating material such as Ca-Si alloy powder or Al-Mg alloy powder are mixed are proposed.

[0011]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Based on the idea of the inventions of Japanese Patent Laid-Open No. 3-226341 and Japanese Patent Laid-Open No. 3-226341, a metal heat-generating material is added for the purpose of providing powder with heat-generating property in order to reduce defects in a cast piece. It is necessary to add an auxiliary combustion material for effective combustion. However, since these are mixed and added in a powder state, the probability that the auxiliary combustion material serving as an oxygen source and the metal heating material are present adjacent to each other due to other powder base materials is reduced, and therefore, such as inside the powder layer. There is a problem in the reaction efficiency in the region where the oxygen potential is low.

As disclosed in Japanese Unexamined Patent Publication No. 3-169467, by sintering a heat generating material and a flux, heat generated by oxidation of the heat generating material is prevented from radiating heat from molten steel, and a temperature drop is caused by melting of the flux component. In addition, the heat generated by the oxidation of the metal inside the powder layer is compensated for, and the temperature drop can be prevented. However, the powder according to the present invention is a front powder used only in the initial stage of casting, and its compounding ratio and components cannot be used as the powder for the constant casting portion.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a heat-generating mold powder capable of obtaining a slab with few pinholes in continuous casting of steel.

[0014]

The gist of the present invention resides in the following exothermic mold powder for continuous casting.

A powder for continuous casting of steel, comprising a powder base material, an exothermic material, and an auxiliary combustion material, which have been mixed and sintered in advance, and a mold powder for exothermic continuous casting.

The preferred powder bases are powders such as Portland cement, yellow phosphorus slag, wollastonite and synthetic calcium silicate.

Similarly, the heat generating material is one or more kinds of metal powders of calcium, silicon and aluminum or alloy powders thereof, or an alloy powder containing two or more kinds of silicon, calcium and aluminum.

Similarly, the combustion improver is Fe ₂ O ₃ , FeO, M
One or more of powders of nO, MnO ₂ and KMnO ₄ .

[0019]

The heat-generating powder of the present invention basically comprises a powder base material, a heat-generating material and an auxiliary combustion material. The heat-generating material and the auxiliary combustion material are premixed and sintered, and further pulverized to adjust the particle size. The applied product is added to the powder base material.

In addition to the above-mentioned three kinds of materials, the exothermic powder of the present invention further comprises a siliceous raw material as a basicity adjusting material, and sodium carbonate, borax, cryolite, fluorite, etc. as a melting characteristic adjusting material. Further, a carbonaceous raw material as a melting rate adjusting material is added in an amount of about 20 to 40% by mass, and a total of 10
There is no problem even if it is contained in the range of about 50%, 2-8%.

Desirable powder base materials are SiO ₂ , CaO and Al, which are the main components of the mold powder.
Powders of portland cement containing ₂ O ₃ , yellow phosphorus slag, wollastonite, synthetic calcium silicate and the like can be mentioned. The desirable particle size range of each powder base material is about 1 to 100 μm. Using these, the composition of the powder base material is% by mass, SiO ₂ : 30 to 40%, C
_{aO: 30~40%, Al 2 O} 3: 2~10%, Na 2
0: 5-15%, TF: 5-15%, basicity 0.8
It is good to be about 1.2. The desirable blending ratio range of the powder base material in the heat-generating powder is 90% by mass.
97%.

Desirable as the heat generating material is one or more metal powders of silicon, calcium and aluminum, or an alloy powder containing two or more kinds of silicon, calcium and aluminum. As alloy powder, Ca-Si, Al-Mg, Ca-Al
The alloy powder of can be mentioned. The desirable particle size range of the heat generating material is about 1 to 100 μm. It is preferable to use these and mix them so that the total of one kind or two kinds or more of metallic silicon, calcium and aluminum in the sintered body is in a range of about 30 to 80% by mass. The combination of silicon, calcium and aluminum is not particularly limited as long as they are contained in the sintered body in the form of a simple metal or an alloy within the above range.

Fe ₂ O ₃ ,
One or more of powders of FeO, MnO, MnO ₂ and KMnO ₄ . The desirable particle size range is about 1 to 100 μm. It is preferable to mix these in the sintered body in a range of about 20 to 70% by mass. These combinations are not particularly limited.

Among the exothermic powder raw material powders which are blended and designed in the above range, the exothermic material and the auxiliary combustion material are mixed using a mixing device such as a V mixer. Then, the mixed powder of the heat generating material and the auxiliary combustion material is sintered to obtain a sintered body. The sintering temperature range is 800 to 1100 ° C., and the sintering atmosphere is an inert atmosphere during processing and cooling to room temperature.

After the above-mentioned sintering, after cooling to room temperature, it is pulverized and the particle size is adjusted again so that the particle size is in the range of about 1 to 100 μm.

The sintered powder having the particle size re-adjusted is added to the above-mentioned powder base material and mixed with equipment such as a V mixer to obtain the exothermic powder of the present invention.

By mixing and sintering the above exothermic material and the auxiliary combustion material, it is possible to obtain a state in which the auxiliary combustion material and the metallic exothermic material which generates heat by combustion due to the reduction of the auxiliary combustion material are very adjacent to each other. Even if body powder is added to the powder base and mixed evenly,
The reaction between the heat generating material and the auxiliary combustion material in the mold powder is carried out efficiently, the heat of the mold powder can be effectively generated, the decrease of the molten steel surface temperature in the mold is prevented, and pinholes in the slab are generated. Can be suppressed.

[0028]

EXAMPLE A powder base material containing SiO ₂ , CaO and Al ₂ O ₃ as main components shown in Table 1 (particle size range: about 1 to 100 μm)
m), a sintered powder or a non-sintered powder (particle size range: about 1 to 100 μm) having the composition shown in Table 2 is added in an amount of 5 to 8% by mass with respect to the total mass of the mold powder to obtain an exothermic mold powder. Manufactured.

[0029]

[Table 1]

[0030]

[Table 2]

The sintered powders shown in Table 2 are raw material powders containing a heat generating material and an auxiliary combustion material (particle size range: about 1 to 100 μm), which are sintered in an inert atmosphere at 800 ° C. It was cooled to room temperature at room temperature, taken out, and pulverized to have a particle size range of about 1 to 100 μm. The non-sintered powder was used by mixing it with the powder base material in the same mixing ratio.

6 kinds of powders obtained and a bending radius of 10 m
Using a single-point straightening continuous casting machine, molten steel of stainless steel SUS304 having the chemical composition shown in Table 3 was cast at a speed of 0.8 m.
The width was 1280 mm and the slab had a thickness of 206 mm. The powder supply rate at this time was 0.95 for both cases.
kg / min.

[0033]

[Table 3]

Next, these slabs were hot-rolled to form hot-rolled coils having a thickness of 4.0 mm, and the defect rate of the slab, that is, pinhole occurrence rate, was evaluated by the maintenance rate of the hot-rolled coil represented by the following formula. 5% or less was considered good. The result is shown in FIG.

Maintenance rate (%) = (number of maintenance coils / total number of coils) × 100 FIG. 1 is a diagram showing the relationship between the maintenance rate of the coils and the type of mold powder used. As shown in Table 2 and FIG. 1, in Example 1, a Ca—Si alloy was used as the heat generating material, and Fe was used as the auxiliary combustion material.
_{In the case} of using ₂ O ₃ and adding it after sintering with an auxiliary combustion material, the result of the hot rolled coil was 5% or less, which is a good result.

In Example 2, silicon is used as the heat generating material and F is used as the combustion supporting material.
This is the case where e ₂ O ₃ is used after sintering with an auxiliary combustion material, and in this case as well, the result of the hot rolled coil was 5% or less, which is a good result.

Example 3 is a case where aluminum is used as the heat generating material and Fe ₂ O ₃ is used as the auxiliary combustion material.

In this case as well, good results were obtained with the maintenance ratio of the hot rolled coil being 5% or less.

Example 4 is a case where a Ca-Si alloy was used as a heat generating material and MnO ₂ was used as a combustion supporting material, which was previously sintered and used.
As for the result of the hot rolled coil, the maintenance ratio was 5% or less, and the good result was obtained as in the case of Example 1 using Fe ₂ O ₃ as the combustion improver.

Example 5 is a case in which silicon and aluminum are used together as the heat generating material and pre-sintered with Fe ₂ O _{3 which} is an auxiliary combustion material. Also in this case, as in the case of Examples 1 to 3, the result of the hot rolled coil was a good result that the maintenance ratio was 5% or less.

Example 6 is a case where a Ca-Si alloy and aluminum were used together as a heat generating material, and pre-sintered with Fe ₂ O ₃ which was an auxiliary combustion material. Also in this case, the result of the hot-rolled coil was a good result that the maintenance ratio was 5% or less.

In Comparative Example 1, a Ca-Si alloy was used as the heat generating material and Fe ₂ O ₃ was used as the combustion supporting material. However, since the addition was performed without sintering with the combustion supporting material, the heat generation efficiency decreased and the same heat generation was achieved. The maintenance ratio of the hot-rolled coil was increased as compared with Example 1 in which the material and the auxiliary material were used.

In Comparative Example 2, the heat generating material is silicon, and the combustion supporting material is F.
In the case where e ₂ O ₃ was used, the heat generation efficiency was lowered also in this case because the addition was made without sintering with the auxiliary combustion material, and the heat generation was lower than that in Example 2 using the same exothermic material and auxiliary combustion material. The maintenance rate of the rolled coil has increased.

Comparative Example 3 is a case where aluminum is used as the heat generating material and Fe ₂ O ₃ is used as the auxiliary combustion material. In this case as well, the addition of the auxiliary combustion material without sintering results in a decrease in the heat generation efficiency and the same heat generation. The maintenance ratio of the hot-rolled coil was increased as compared with Example 3 in which the material and the auxiliary material were used.

Comparative Example 4 is a case in which a Ca—Si alloy was used as the heat generating material and MnO ₂ was used as the combustion supporting material, and the same material as in Comparative Example 1 was used without sintering. Comparative Example 5 is a case in which silicon and aluminum are used together as the heat generating material, Fe ₂ O ₃ is used as the auxiliary combustion material, and sintering is not performed in advance. Comparative Example 6 uses Ca-as the heat generating material.
Using a Si alloy and aluminum together, the auxiliary material is Fe
₂ O ₃ and not sintered in advance. In all of these Comparative Examples 4 to 6, since the heat generating material and the auxiliary combustion material were used without sintering, the maintenance ratio of the hot rolled coil was increased.

[0046]

EFFECT OF THE INVENTION If the exothermic-type continuous casting mold powder of the present invention in which the exothermic material and the auxiliary combustion material are mixed and sintered in advance and added to the powder base material is used, the exothermic efficiency is improved and the pinhole of the slab is improved. The incidence can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a maintenance rate of a product coil and a type of mold powder used.

Claims (1)

[Claims] 1. A mold powder for continuous casting of exothermic type, which is a powder for continuous casting of steel, comprising a powder base material, a heating material and an auxiliary combustion material which are mixed and sintered in advance.