JPH0985402A - Molding powder for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relieve the quantity of the heat removed from casting molds at the time of continuous casting and to prevent the longitudinal crack of a slab by adjusting the basicity and solidification temp. of molding powder prepd. by adding FeO, NiO and Fe2 O to a base material. SOLUTION: The powder to be used for continuous casting of molten steel having a carbon content of >=0.4mass% is formed of the powder which contains 1 to 10mass% one or >=2 kinds of the FeO, NiO and Cr2 O3 and having the basicity (CaO/SiO2 ) within a range of 0.7 to 1.1 and the solidification temp. within a range of 1000 to 1200 deg.C. As a result, the solidification shrinkage rate at the time the molten powder flowing between the slab and the casting molds is vitrified and solidified to a powder film is decreased and the removal of the heat of the slab from the casting molds is made uniform. Further, the radiation light in the powder film is absorbed and the heat extraction quantity is relieved by the effect of the FeO, NiO and Cr2 O3 . The base material consists of known SiO2 , CaO and Al2 O3 as forming components and the contents thereof are preferably specified to 70 to 80mass%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a mold powder for continuous casting of steel.

[0002]

2. Description of the Related Art Mold powder for continuous casting of steel (hereinafter referred to as powder) is mainly composed of calcareous raw material, and if necessary, siliceous raw material is added to adjust basicity, and further sodium carbonate, fluorite, etc. Freezing point, a flux material as a melting property adjusting material such as viscosity, and a mixed type consisting of a carbonaceous material as a melting rate adjusting material, a premelt obtained by melting and crushing all or part of the components excluding the carbonaceous material, There is a semi-premelt type. Also,
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.

Powder is added on the surface of molten steel injected into a mold (hereinafter, also referred to as a mold), slag is formed on the surface of the molten steel, the lubricating action between the inner wall surface of the mold and the solidified shell, the molten steel in the mold. It is consumed while playing a role of keeping the surface warm, absorbing inclusions floating from the molten steel, and preventing oxidation of the molten steel surface.

[0004] The powder has many control factors such as its melting rate, viscosity and melting point, and the optimum powder is different depending on the steel type, the casting speed, the cross-sectional shape of the slab, etc., so the selection is extremely important.

In order to reduce defects on the surface of the slab, especially cracks (longitudinal cracks) occurring in the casting direction of the slab, JP-A-3-
As described in Japanese Patent No. 210950, by adding a metal powder to the powder, the fluidity of the powder is improved by the heat generated by the oxidation reaction, and the powder is uniformly flown between the mold and the solidification shell, so that cracking due to uneven solidification occurs. There is a way to prevent.

Japanese Unexamined Patent Publication No. 3-198961 discloses that in powder
By containing ₁ to 7 mass% of ZrO ₂ or CeO ₂ , the crystallization rate is 50% or less, and the solidification temperature is 1200 ° C. or less,
It has been shown that restraint breakout can be prevented and vertical crack initiation is prevented.

Japanese Patent Laid-Open No. 1-306055 discloses that by preheating the powder to 700 to 900 ° C. before adding it to the surface of molten steel, the amount of heat removed from the surface of the slab is reduced, It has been shown that the fluidity is improved and evenly flows between the solidified shell and the mold to prevent the occurrence of vertical cracks.

[0008]

According to the idea disclosed in Japanese Patent Laid-Open No. 3-210950, a metal heat generating material is used as a powder in order to provide the continuously cast powder with heat generation for the purpose of reducing defects in the slab. Added. However, in this case, although the molten steel surface temperature rises, the exothermic powder does not retain heat, so that it becomes the same as the powder having no exothermic property after the end of exotherm. For this reason, the above-mentioned idea makes little contribution to the prevention of vertical cracks from the viewpoint of relaxing the amount of heat removed from the mold.

As shown in Japanese Patent Laid-Open No. 1-306055,
In the method of preheating the powder before adding it to the surface of the molten steel, the amount of heat removed from the surface of the molten steel is relaxed and the fluidity and inflowability of the powder are improved, as in the case of the above-mentioned JP-A-3-210950. But even with this method,
Similar to the above, from the viewpoint of relaxing heat removal from the mold, the contribution to preventing vertical cracking is small.

In the powder of Japanese Patent Laid-Open No. 3-198961, it is described that restraint breakout and vertical cracking are reduced, but radiant heat from a slab in a high temperature state is caused by reduction of crystallization rate. It is easily permeated, and the effect of alleviating heat removal from the surface of the slab cannot be expected.

As described above, the prior art has unsolved problems, and the prior art does not have the effect of reducing vertical cracks in a slab when continuously casting a steel type containing 0.4 mass% or more of carbon. .

An object of the present invention is to solve the above problems of the prior art and to provide a powder capable of obtaining a slab with less vertical cracks in continuous casting of steel.

[0013]

The gist of the present invention resides in the following powders.

A powder used for steel containing 0.4 mass% or more of carbon, which is one of FeO, NiO and Cr ₂ O ₃ .
1 to 10 mass% containing 1 or 2 or more species, basicity (CaO
/ SiO ₂ ) is 0.7-1.1, and the solidification temperature is 1000-1200 ℃.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The powder of the present invention mainly comprises a base material. Substrates are SiO ₂ , CaO and Al ₂ O
₃ is a main component, and examples of the raw material thereof include Portland cement, wollastonite, and synthetic calcium silicate. Desirable content of base material is 70-80mass
%. Further, there is no problem even if a basicity adjusting material, a melting property adjusting material and a melting rate adjusting material are contained in addition to the base material. The basicity adjusting material is a siliceous material such as silica sand, the melting property adjusting material is sodium carbonate, borax, cryolite and fluorite, and the melting rate adjusting material is a carbonaceous material such as coke powder.

The powder of the present invention contains 1 to 10 mass% of one or more of FeO, NiO and Cr ₂ O _{3 in} the above composition and has a basicity (CaO / SiO ₂ ).
0.7 to 1.1 and the solidification temperature is 1000 to 1200 ° C.

FeO is FeO and / or Fe ₂ O
Add in the form of ₃ . F when Fe ₂ O ₃ is used
Converted to eO and blended. NiO and Cr ₂ O ₃ are
These metal oxides are added as they are. FeO, Ni
For O and Cr ₂ O ₃ , 1 to 10 mass% of one or a mixture of two or more selected from these oxides is added.

The desirable range of particle size of the above oxide is 1 to 10
0 μm.

Further, the range of basicity (CaO / SiO ₂ ) is 0.7
~ 1.1, adjust the coagulation temperature range 1000 ~ 1200 ℃.

The basicity (CaO / SiO ₂ ) of the powder is 0.7-1.
By setting it to 1, it becomes possible to vitrify the molten powder flowing between the mold and the slab. This allows
Since the amount of solidification shrinkage when the molten powder solidifies to form a powder film is reduced, the heat removal of the slab by the mold becomes uniform. Further, the vitrified powder film described above is obtained by adding 1 to 10 mass% of one or more of FeO, NiO, and Cr ₂ O ₃ , which are oxides showing strong absorption in the wavelength region of radiant light. Radiant light is absorbed in
The amount of heat removed from the slab is reduced.

Therefore, the upper limit of the powder basicity is 1.1. If the upper limit of the powder basicity is exceeded, the powder flowing between the mold and the slab will not be vitrified, but all will be crystallized. The problem arises. On the other hand, the lower limit is 0.7
If it is less than this, it becomes difficult to control the physical properties of the powder, and similarly it becomes difficult to use it in operation.

When the content of the oxide is less than 1 mass%, the amount of absorption of the radiant light is not sufficient and the effect of relaxing the amount of heat removed from the cast piece cannot be obtained. On the other hand, if it exceeds 10 mass%, it becomes difficult to control the physical properties of the powder.

By thus uniformly removing heat from the mold and reducing the amount of heat removed from the slab, vertical cracking of the slab is achieved even in continuous casting of steel types having a high carbon content of 0.4 mass% or more. Occurrence of is suppressed low. The upper limit of the carbon content to which the powder of the present invention can be applied is about 0.8 mass%.

When the solidification temperature of the powder is less than 1000 ° C., problems such as excessive inflow of powder occur during operation. On the other hand, if the temperature exceeds 1200 ° C, the powder will be insufficiently melted, and similarly, a problem in operation will occur.

The powder of the present invention can be applied regardless of mixed type, premelt and semi-premelt type, and powder type and granule type.

[0026]

EXAMPLES As shown in Tables 1 and 2, SiO ₂ , C
A mixed powder type powder was produced by adding FeO, NiO, and Cr ₂ O ₃ to a powder base material containing aO and Al ₂ O ₃ as main components, respectively.

[0027]

[Table 1]

[0028]

[Table 2]

The casting test was carried out by using the continuous casting powders shown in Tables 1 and 2 and a single-point straightening type continuous casting machine with a bending radius of 10 m to cast molten steel having the chemical composition shown in Table 3 at a casting speed of 0.9 m / m.
It was a slab with a width of 1280 mm and a thickness of 206 mm.

[0030]

[Table 3]

Then, the occurrence rate of vertical cracking of the obtained slab was investigated. The vertical crack occurrence rate is a value represented by the following formula.
The results are shown in FIG.

Vertical crack occurrence rate (%) = (number of cast pieces having vertical cracks / total number of cast pieces) × 100 FIG. 1 is a diagram showing a comparison of vertical crack occurrence rates of cast pieces. A case where each powder is used will be described below with reference to FIG.

Comparative Example 1 is a case where FeO is contained in an amount of 0.5 mass%. However, since the content is small, the vertical crack occurrence rate is high.

In Example 1 and Example 2, FeO was contained in an amount of 1.0 mass% and 10 mass%, respectively, and the vertical crack occurrence rate was reduced.

In Comparative Example 2, FeO was contained in an amount of 12 mass%, but the physical properties of the powder were changed, and the vertical crack occurrence rate was high.

In Comparative Example 3, 0.7 mass% of NiO was contained, but the amount of heat removal by the powder could not be relaxed and the rate of occurrence of vertical cracking was high.

In Examples 3 and 4, NiO was added in an amount of 2 mass% and 9 mass%, respectively, and the vertical crack occurrence rate was low.

Comparative Example 4 is a case where NiO is contained in an amount of 11 mass%, but the physical properties of the powder are changed, so that the vertical crack occurrence rate is high.

In Comparative Example 5, 0.8 mass% of Cr ₂ O ₃ was contained, but the rate of occurrence of vertical cracks was high.

In Examples 5 and 6, Cr ₂ O ₃ was contained in an amount of 1.0 mass% and 10 mass%, respectively, and the incidence of vertical cracks was reduced.

In Comparative Example 6, 12 mass% of Cr ₂ O ₃ was contained, but the physical properties of the powder were changed, so that the vertical crack occurrence rate was high.

In Comparative Example 7, FeO is contained in an amount of 1.0 mass%, but the basicity of the powder is high, and the powder flowing between the mold and the cast piece is easily crystallized. For this reason,
The amount of solidification and shrinkage of the powder film increased, and the heat removal by the mold became non-uniform, resulting in a high vertical crack occurrence rate.

Comparative Example 8 is a case where the solidification temperature of the powder is 1250 ° C. and FeO is contained in an amount of 5 mass%. Since the solidification temperature of the powder was high, the incidence of vertical cracks was high.

[0044]

The powder of the present invention has a carbon content of 0.4 ma.
By using it for continuous casting of ss% or more steel grade, it is possible to reduce the vertical cracking occurrence rate of the slab.

[Brief description of drawings]

FIG. 1 is a diagram showing a comparison of vertical crack occurrence rates of cast slabs.

Claims (1)

[Claims] 1. A mold powder for continuous casting, which is used for steel containing 0.4 mass% or more of carbon, which comprises FeO and NiO.
1 to 10 mass of one or more of Cr ₂ O ₃ and Cr ₂ O ₃
%, A basicity (CaO / SiO ₂ ) of 0.7 to 1.1 and a solidification temperature of 1000 to 1200 ° C. A mold powder for continuous casting.