JPS6344464B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a mold additive for continuous casting of steel. That is, in continuous steel casting, the present invention adds powder or granules of additives to the surface of molten steel in the mold to keep the surface of the molten steel warm, prevent the surface of the molten steel from solidifying, and float the surface of the molten steel. It dissolves and absorbs nonmetallic inclusions. The present invention also relates to a surface protectant for continuous casting that achieves a lubricating effect by the slag film that flows between the mold and the solidified shell to obtain clean and good slabs. (Prior Art) Conventional molten steel surface protective agents used in continuous casting of molten steel prevent reoxidation of molten steel by air by completely covering the molten steel surface. By coating the surface of the molten steel, it prevents the occurrence of cracks. Molten slag enters between the mold and the slab and acts as a lubricant, so it must always be supplied in an appropriate amount. Therefore, it must have a melting rate that meets the consumption rate and provides an appropriate slag pool thickness. The molten slag layer should quickly absorb non-metallic inclusions floating from the steel without significantly changing the melting characteristics (physical properties such as melting point, viscosity, etc.) of the slag. The molten slag must have an appropriate melting point and viscosity to uniformly melt at the solidification temperature of the molten steel meniscus, flow into the gap between the mold and the solidification shell, and form a uniform slag film. The cast slag film provides complete lubrication of the mold and solidification shell. It is necessary to have properties such as reducing moisture absorption and preventing pinholes and blowholes from occurring due to absorbed moisture. Conventional powders are JP-A-50-22715, 50-
As with 1925, the purpose is only to prevent cracking due to the physical properties of the ingredients, but it does not include defects such as pinholes and blowholes due to moisture content in the hot water surface insulation agent, and it is difficult to recognize that it is sufficient. . Conventional surface protection agents used in continuous steel casting contain SiO ₂ 20-40wt%, calculated by chemical analysis.
CaO20~40wt%, _{Al2O3 1} ~10wt%, Na ⁺⁺ K ⁺ 3
~30wt%, F ^- 2~20wt%, and its raw materials include Portland cement, limestone, silica powder, silica powder, etc. as physical property modifiers, and fluorite and alkali metals as physical property modifiers. carbonate or
Fluorides or oxides in a molten state (for example, glass powder, etc.) with other metal oxides are used. At present, the hot water level protectant is prepared by adding 2 to 8 wt% of carbon powder as a melting rate regulator to the above composition and placing it in a plastic bag, paper bag, etc. to prevent moisture absorption. However, if the hot water surface protectant packaged in this way is damaged during transportation, or comes into contact with the atmosphere when used in an automatic dosing machine or when the bag is opened, it will absorb moisture from the atmosphere and cause the hot water surface to deteriorate. The amount of water in the protectant increases. When this moisture-absorbing surface protection agent is used, pinholes and blowholes occur frequently on the surface of the slab, and the molten or unmelted surface protection agent that is attached to or entangled in the slab may be deposited on the surface of the product after rolling. cause defects. (Object of the Invention) The present inventors conducted various studies in order to solve the problems with the hot water surface protective agent, and obtained the following knowledge regarding the hygroscopicity of the hot water surface protective agent. That is, it has been discovered that metal ions such as alkali metal carbonates, oxides, and fluorides in the hot water surface protective agent are significantly involved in moisture absorption. On the other hand, alkali metal ions are essential components in conventional hot water surface protective agents, and are used as raw materials in the form of carbonates and fluorides, and play a major role as physical property regulators of hot water surface protective agents. Therefore, in order to remove alkali metal ions, it is necessary to search for an alternative physical property modifier. Based on the above findings, the present invention has discovered a hot water surface protective agent that does not contain alkali metal ions and has a component system different from conventional ones. (Structure and operation of the invention) The present invention does not contain alkali metal ions, which were traditionally regarded as essential components, and suppresses the amount inevitably mixed in from other raw materials to 1% or less, thereby protecting the hot water surface. It greatly reduces the hygroscopicity of the agent, and can be used instead of alkali metal ions as a physical property adjusting agent for hot water surface protection agents.
This relates to a hot water surface protective agent containing MgO, AlF ₃ and B ₂ O ₃ . In continuous casting of steel, the casting speed is generally
0.2 to 2.0 m/min, and the required physical properties of the hot water surface protectant used at that time are viscosity of 0.5 to 10 poise,
Melting temperature is 900-1250℃. The physical properties can be broadly categorized based on the difference in casting speed: on the low speed side, high viscosity and high melting temperature, and on the high speed side, low viscosity and low melting temperature. For this reason, the basicity (CaO/SiO ₂ ) of the base material component must be in the range of 0.6 to 1.1, but as stated in the claims, by containing B ⁺ 0.1% or more, the basicity can be reduced to a high basicity of 1.3. , it becomes possible to maintain glass properties. In other words, within the scope of the claim, if the basicity exceeds 1.3, the glassiness will be lost, recrystallization will occur during solidification, the composition of the molten film will become non-uniform, and as a result, heat removal from the slab will become non-uniform, resulting in non-uniform casting. Causes surface defects on the pieces. Also, 0.6
If it is below, it becomes difficult to adjust the physical properties, especially the viscosity, and the required viscosity of 10 poise or less cannot be obtained. Therefore, the basicity (CaO/SiO ₂ ) needs to be in the range of 0.6 to 1.3. Therefore, satisfying the basicity of 0.6 to 1.3 and considering the relationship with other components, CaO25 to 40wt%, SiO ₂ 25
~40wt%. Al ₂ O ₃ is added as a base material component in the form of an oxide, but if it exceeds 10%, the viscosity and melting temperature will become extremely high, which will not meet the casting conditions, and precipitation of gehlenite will occur during use.
Troubles are more likely to occur during casting. Further, since 0.1% or more of impurities are inevitably mixed in from other raw materials, it is desirable to use Al ₂ O ₃ in an amount in the range of 0.1 to 10 wt%. F ^- has traditionally been used as an essential component of hot water surface protectants, and is added in the form of various fluorides such as CaF ₂ and MgF ₂ . When ^F- exceeds 15wt%,
Fluoride gasification occurs due to reaction with base metal components, causing defects such as pinholes in slabs.
^F- must be less than 15wt%. Also 3wt%
If it is less than that, the required physical properties cannot be obtained, and F ^- is required to be 3 to 15 wt%. MgO is added in the form of oxide, carbonate or fluoride. If it exceeds 20wt% due to MgO conversion, etc.,
It loses its glassiness, has a high melting point, and loses its function as a hot water surface protectant, so it is desirable to keep it below 20%.If it is below 1%, it will be difficult to adjust the physical properties with other substances. 1~20wt
Must be used within a range of %. AlF ₃ and B ⁺ are added instead of alkali metal ions to adjust physical properties. B ⁺ is 0.1wt%
It is difficult for it to work as a physical property modifier if it is less than 0.1%, so at least 0.1% or more is necessary.
When added at 20%, it loses its glass properties and becomes difficult to use as a physical property modifier. In other words, B ⁺ must be used within 0.1-20wt%. If AlF ₃ is added at a maximum of 20%, the maximum amount of Al ⁺ will cause a decrease in the absorption capacity of Al ₂ O ₃ in the steel, resulting in a decrease in the surface quality of the steel. be. Furthermore, if it is less than 0.1 wt%, it is difficult to function as a physical property modifier. Therefore, the amount of AlF ₃ used is 0.1
It needs to be ~20wt%. Also, AlF ₃ and B ⁺ are 2
If a combination of species is used, the above physical properties can be more easily achieved. In addition, as the raw material for obtaining the chemical composition of the converted value by the chemical analysis described above in the present invention, metal ion oxides, fluorides, and carbonates can be freely used as long as the range is satisfied. For example, Ca ²⁺ ,
CaO, CaF ₂ and MgO as Mg ²⁺ sources;
MgF ₂ , MgCO ₃ , etc. can be used depending on the purpose. In addition, from the viewpoint of hygroscopicity and uniformity, the raw materials are
It is preferable to perform firing or melting treatment, a mixture thereof, or heat treatment (calcination or melting) of the base material component, and then perform post-addition of AlF ₃ and B ⁺ . Also, if necessary, carbon powder of 10% or less may be used as a melting rate regulator. Its form is powder or granules. The effects of the present invention will be explained in more detail with reference to Examples below. (Examples and their effects) Table 1 shows the conventional product (a) in which the raw materials were melted, the raw material mixture product (b), and the product of the present invention, with the base material components SiO ₂ , CaO,
The product of the present invention is obtained by melting MgO and F and adding AlF ₃ afterward. (c) The base material components are melted in the same manner as c, and AlF ₃ ,
The product of the present invention to which B ⁺ was subsequently added is shown in (d). These etc.
The physical properties and chemical compositions of (a) to (d), the moisture absorption index measured by a moisture absorption meter, the casting conditions, and their evaluation are shown. Conventional product (a) contains 8.9wt% of alkali metal ions (Na ⁺ ).
The moisture absorption index was very high despite the melting process, and the evaluation showed that there were many pinholes and the product surface flaw occurrence index was high. Conventional product (b)
Although it contains the same alkali metal (Na ⁺ ) as (a), its evaluation showed that it had a higher moisture absorption index and a higher product surface flaw occurrence index than (a).
On the other hand, books

【table】

[Table] Both (c) and (d) of the invention products had extremely low hygroscopicity, fewer pinholes, and a significantly lower product surface flaw occurrence index. Furthermore, the product of the present invention has Al-
Despite being cast in K, approximately 5% of each
Although an increase in Al ₂ O ₃ was observed, no increase in viscosity during casting was observed when compared with conventional products, and it is recognized that it can sufficiently follow changes in casting speed during changes in operation. The effect is very good. As described above, the product of the present invention is a surface protectant for continuous casting of molten steel that is extremely useful for obtaining slabs of good quality.

Claims (1)

[Claims] 1 Powder or granules made by mixing raw materials, calcining, melting, or a mixture thereof, with a basicity (CaO/SiO ₂ ) of 0.6 to 1.3 and CaO25 to 40 wt%,
_SiO2 25~40wt%, F ^- 3~15wt%, _{Al2O3 0.1} ~
In the range of 10wt%, MgO1.0~20wt%,
Contains 0.1 to 20% of AlF ₃ , B ⁺ or a combination of the two, and 10% carbon powder as a melting rate regulator
A molten steel surface protection agent for continuous casting of molten steel with few surface defects, characterized by comprising the following: