JPS6213515A - Lining construction of vacuum degassing device for steel making - Google Patents

Abstract

PURPOSE:To suppress the generation of oxide inclusions which are the cause for the defects of steel products by coating a coating material consisting of limestone, dolomite and binder on the surface of the lining refractories of a vacuum degassing device. CONSTITUTION:The coating material prepd. by adding 0.1-20 outer wt% binder to 100wt% 1 or 2 kinds of limestone and dolomite is coated to about 5-50mm thickness by spraying, etc. onto the surface of the lining refractories (magnesite- chrome brick, etc.) of the degassing device. >=1 kinds of inorg. compd. or inorg. salt (sodium hexamethaphosphate, potassium silicate, etc.) of an alkali metal, halogenide compd. (magnesium chloride, etc.) are used for the binder and the coating material is preferably preheated to about >=1,000 deg.C. The crystal size of the CaO and MgO formed from such coating material is about <=10mu and is not the cause for a defective steel product.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a lining structure for a vacuum degassing apparatus for steel manufacturing for storing clean steel.

Conventional technology The quality requirements for steel materials that can be used in civil engineering, architecture, ships, machinery, chemicals, electrical industries, etc. are becoming stricter. In the steel manufacturing industry, high-quality steel products are manufactured by desulfurizing hot metal using a pig iron mixer and removing impurities using a vacuum degassing device. However, 1) slag, 3) deoxidation products such as AJ3205, 3) reoxidation of molten steel, and oxide inclusions caused by damage to large objects, etc., deteriorate the quality of steel materials.

In order to deal with these, ') removing xD slag during slag cutting during converter tapping, 2) injecting inert gas into molten steel, and then flotation separation of deoxidized products using Synthetic 7lux 3) Preventing contact between the atmosphere and molten steel to prevent re-oxidation of molten steel, and μ) Using highly corrosion-resistant refractories to suppress damage to refractories.

Problem to be solved by the invention Inclusions generated due to damage to refractories are several tens of microns in size.
~ several hundred microns, making it the most difficult oxide inclusion to float and separate. That is, oxide inclusions with a size of 10 μm or less do not significantly affect the homogeneity of the steel material, and those with a size of several hundred μm or more float up due to the buoyancy of the molten steel and cause almost no problem. On the other hand, oxide inclusions of several tens of microns to several hundred microns are suspended in the molten steel and remain in the steel as they are. σ) Big 1! It is thought that ζ is due to the fact that the crystal grains of the refractory used are 30μ or more.

Among the oxide-based inclusions caused by refractories, 8102-based inclusions are soft (malleable) and therefore pose relatively no problem. Inclusions are hard (not malleable) and cause defects such as wire breakage and surface flaws.

In the steelmaking process after the converter, the ladle
206 yarn or FiZ r 8 + Oa type refractories are mainly used, and for continuous cast tundishes, MgO type coating materials are mainly used.

The lining of vacuum degassing equipment such as RH and D)1 type is as follows:
Magnetic resin bricks and alumina castables are used, and as hot repair materials, magnetic spraying materials and alumina press-fitting materials are used. That is, although the RH-PDH method is a means of improving the quality of steel materials, it also has the possibility of contaminating molten steel because it uses MgO, A12o6, and spinel-based refractories.

The object of the present invention is to coat a refractory lining of a degasser with a covering material made of limestone or dolomite to produce a steel that is completely clean.

Means for Solving the Problems The inventors have proposed a method of spraying, pouring, pressing, patching, etc. a coating material made of limestone and/or dolostone and a binder onto the lining refractory of a degasser. coated with 10
Use with or without preheating at temperatures above 00°C. 0 generated from this limestone or dolomite covering material
JIO6 or MgO has fine crystals of 10 μm or less and can prevent the generation of oxide-based inclusions of several tens to hundreds of μm.

The present invention is a type of limestone or dolostone, or
Inorganic compounds or inorganic salts of alkali metals or /% I: 0.1% by weight of one or more compounds
-20% by weight of the coating material added as a binder is sprayed, poured, or press-fitted onto the surface of the refractory lining of the degassing equipment, such as mag/chlorite brick or alumina castable.
Depends on the method of patching etc. ~! This method suppresses the generation of MgO, A#205, and spinel oxide inclusions of tens to hundreds of microns caused by mag-rear bricks and alumina castables by coating with a thickness of Om/m. .

If an alkali metal inorganic compound or inorganic salt or a halogenated compound is used as a binder for limestone or dolomite, it will not shrink even when used at high temperatures and sintering will be prevented. Therefore, OaO or MgO produced from limestone or dolomite has a fine crystal size of 10 μm or less and is active.

The limestone and dolomite used in the present invention are not particularly limited (but may be those commonly used in Japan. In addition, in terms of particle size, there is no problem with the particle size normally used for refractories.

The binder must be one or more inorganic compounds or salts of alkali metals or halogenated compounds. If other inorganic compounds are used, the firing shrinkage will be large (
Cracks and shedding are more likely to occur, and OaO, Mg
This is not preferable because O crystal growth occurs and the crystal diameter becomes larger than ioμ. In other words, inorganic compounds of alkali metals can be used as structures with firing shrinkage of about 0 to 2 when inorganic salts or halogenated compounds are used as binders, but when other binders are used If the product shrinks by 10% or more, cracks and falling off occur, making it impossible to use it as a covering material.

The amount of the binder added is within the range of 0.7-S-2oH mass %, and if it is less than O6/weight, the binding strength will be insufficient, and if it exceeds -0Xt, the corrosion resistance will deteriorate, which is not preferable. As the binder used, alkali phosphates such as sodium hexametaphosphate and potassium phosphate, alkali silicates such as No. 3 sodium silicate and potassium silicate, and halogenated compounds such as magnesium chloride, lucicum chloride, and sodium chloride can be used. .

It is applied on the cold or hot surface of large objects by methods such as spraying, pouring, press-fitting, and tucking to a thickness of 1 to 50 mm. If it is less than 51, the durability of the coating layer will be poor (the operating surface of the black brick or alumina castable will be exposed during use of the charge), which is undesirable (if it exceeds 7 smi, the coating will take too long). However, degassing reduces the internal volume of the snorkel, which is undesirable.

The coating material made of limestone or dolomite dissociates the 002 gas gold at temperatures below 1000°C, so it should be as much as possible.

It is desirable to preheat it to a temperature of C or higher before use. Examples will be described below.

Table 1 shows the quality and construction examples of limestone or dolomite covering materials. These coatings were applied to the snorkel portion of a Hg air degasser. The coating method uses spraying and/or press-fitting.The dry spraying method is used, and after each charge, it is applied to the inside and outside of the Exnorkel using an automatic spraying machine. It is suitable for cleaning and can be applied to the inner surface of the snorkel.

Table 2 shows a comparison of the inclusion index in the ladle after degassing when limestone or dolomite covering material is used and the ladle is not heated.
As a result, inclusions in rainbow steel were reduced when using rainbow, limestone, or dolomite covering materials, and the effect was recognized.

Table 2 Effect of comparative invention on inclusion index in molten steel after degassing The present invention provides the following effects.

l) If the crystal diameter of CjaO or MgO produced from limestone or dolomite is less than σlθμ, it will hardly cause defects in steel materials.

2) Active force (A#, which is a 1a01c rainbow deoxidized raw wave product,
051-Can be absorbed.

3) Active OaO can absorb S and P in steel.

Continued from page 1

Claims (2)

[Claims] (1) A lining structure for a vacuum degassing device for steel manufacturing, in which the surface of the inner lining refractory of the vacuum degassing device is coated with a coating material made of limestone and/or dolomite and a binder. (2) The binder contains one or more types of alkali metal inorganic compounds, inorganic salts, or halogenated compounds in an amount of 0.
A lining structure for a vacuum degassing device for steel manufacturing according to claim 1, wherein the lining structure is added in an amount of 1 to 20% by weight.