KR100354314B1 - A method of measuring a crystallization ratio of the mold flux - Google Patents

Abstract

The method for measuring the crystallinity of the solvent includes preparing a sample, removing the carbon at 650 ° C, melting the carbon-depleted sample in a platinum container, and mounting the melted sample in a cooling water circulation system. Cooling at 15 ° C. in a platinum container, and observing the crystal state of the solidified slag to determine the ratio of the crystalline to the glassy layer.

Description

A method of measuring the crystallinity of a continuous casting solvent {A METHOD OF MEASURING A CRYSTALLIZATION RATIO OF THE MOLD FLUX}

The present invention relates to a test method for a solvent, that is, a mold flux used as an additive during continuous casting of steel, and more particularly, to a method for measuring the crystallinity of such a mold flux.

The crystallinity refers to the ratio of the crystalline phase to the total thickness of slag melted and solidified in the laboratory. CaO, F, etc. in the chemical composition increase the crystallinity, and MgO, Al ₂ O ₃ , B ₂ O ₃ and the like play a role of reducing the crystalline rate.

Continuous casting mold flux, which is injected and used in the mold during continuous casting of steel, is an additive that is generally used for the purpose of reducing oxide during metal melting, covering the surface of hot water to prevent oxidation, and promoting the removal of slag. It is mainly composed of SiO ₂ -CaF ₂ -Al ₂ O ₃ -Na ₂ OC, etc., as a major factor directly affecting the operation stability and cast surface quality in the process.

More specifically, the mold flux injected onto the molten steel in the mold shows three layers of unmelted layer, sintered layer, and molten slag layer by receiving the heat of molten steel.

1) It performs insulation function on molten steel surface and prevents solidification of molten steel.

-The protection of the mold flux is closely related to the carbon content in the components.

2) Prevention of Reoxidation of Molten Steel by Atmosphere.

3) Absorbs inclusions from the molten steel surface and fuses the inclusions to the molten surface to form and remove low melting point compounds.

It depends on the chemical composition of the mold flux.

4) Lubricating between the solidified slab contact and the mold.

It depends on the viscosity of the mold flux and the solidification temperature.

5) Heat transfer medium between the solidified slab contact and the mold

-It is closely related to the viscosity and solidification temperature of the mold flux.

The conditions for the mold flux used for continuous casting should not have a detrimental effect on the molten steel, should have a low impact on the refractory, and should be slag rapidly under the heat of the molten steel under an appropriate melting rate.

As described above, since the mold flux added during continuous casting of the steel has a great influence on the efficiency of the casting operation, it is a very important process to properly measure the crystallinity of the mold flux by measuring the exact crystallinity of the mold flux.

In particular, the surface defects (hereinafter referred to as cracks) occurring in medium carbon steels (C: 0.08 to 0.14) depend on the shape of the layer upon inflow of the mold flux slag, and its exact mechanism is only predictable. In the laboratory, there is a need for a method for measuring the crystalline rate of a mold flux by a simple method.

For the above reasons, in order to measure the crystalline rate of the mold flux, which is a continuous casting solvent, a means for predicting the ratio of the crystalline portion (heat reduction) and the amorphous portion (heat transfer increase) of the slag layer, which is a heat transfer medium, is needed.

An object of the present invention is to propose a method for accurately measuring the crystallinity of a product in order to improve the workability and surface quality by adjusting the lubrication and slag inflow rate of the steel during continuous casting of the steel.

In order to achieve the above object, the method for measuring the crystallinity of the solvent according to the present invention comprises the steps of preparing a sample, removing the carbon at 650 ℃ the sample, and melting the carbon-removed sample in a platinum container And cooling the molten sample in a platinum container mounted on a cooling water circulation device at 15 ° C. and observing the crystal state of the solidified slag to measure the ratio of crystalline and glassy layers.

According to such a method, it becomes possible to measure the exact crystallinity rate of a solvent, and to select the solvent most suitable for the characteristic of a target steel.

1 is a model diagram of an apparatus for measuring the crystalline rate of a continuous casting solvent.

Figure 2 is a model diagram of the slag state after measuring the crystalline rate of the continuous casting solvent.

3 is a graph showing the change in crystallinity with cooling temperature.

4 is a graph showing the relationship between the crystallinity of the solvent for continuous casting and the defects on the surface of the cast steel;

<Explanation of symbols for the main parts of the drawings>

10 ----- Sample 11 ----- Coolant Circulator

13 ----- Platinum container 15 ----- Slag

17 ----- Crystalline Layer 19 ----- Glassy Layer

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

1 is a schematic diagram of an apparatus for measuring the crystalline rate of a continuous casting solvent, wherein the crystalline rate of a mold flux is measured by the following method.

First, after preparing 30 grams of sample, the prepared sample is removed with carbon at 650 ° C. for about 5 hours, and the carbon-depleted sample is put in a platinum container and melted for 20 minutes. Thereafter, the molten sample 10 is placed in a platinum vessel 13 mounted on the cooling water circulator 11 and cooled at 15 ° C., and then the crystalline state of the solidified slag 15 is observed to determine the ratio between the crystalline and glassy layers, In other words, the crystallinity rate is measured.

Fig. 2 shows a model diagram of the slag state after measuring the crystallinity rate of the continuous casting solvent, in which reference numeral 15a denotes a crystalline layer and reference numeral 15b denotes a glassy layer.

3 is a graph showing the change in crystallinity according to the cooling temperature. From the figure, it can be seen that the crystallinity increases rapidly and the reliability of data is deteriorated when it is out of an appropriate temperature (15 ° C).

Table 1 shows the respective melting point, viscosity, and viscosity for the test article (QA, QB, QC, QD, QE) by adjusting the basicity, Al ₂ O ₃ , Na ₂ O, and F based on the medium carbon steel conventional (Q). The crystallinity rate was measured.

Existing product Test article Q QA QB QC QD QE Basicity (CaO / SiO ₂ ) 1.1 1.2 1.3 1.3 1.3 1.3 Al ₂ O ₃ (wt%) 7.6 8.4 4.7 3.6 4.0 3.3 Na ₂ O + K ₂ O (wt%) 9.0 6.0 7.6 4.6 5.5 4.3 Fluorine (F) (wt%) 5.6 5.9 7.9 7.6 5.2 4.4 Melting Point (℃) 1,154 1,146 1,102 1,145 1,130 1,168 Viscosity (1300 ℃, poise) 2.0 1.4 1.4 1.3 1.7 1.7 Crystallinity rate (%) 0.7 7.4 54.3 83.6 16.4 8.2

From Table 1, it can be seen that the crystallinity decreases as the alumina absorption of the mold flux decreases, but the decrease in width decreases as the fluorine content in the mold flux increases.

In addition, the slag layer is composed of amorphous of the mold side of the crystalline phase and the solidified cast steel contact portion side, the crystal phase is composed of a porous, and the material structure is made in the blood of coarse (Cuspidine, 3Cao.2SiO ₂ .CaF ₂₎ . The ratio of the crystalline phase and the amorphous state of the slag layer, i.e., the crystalline rate, has a significant effect on the heat transfer and a great influence on the surface quality of the slab.

These results are shown in Fig. 4 showing the relationship between the crystallinity of the continuous casting solvent and the defects on the surface of the cast steel. When the prepared specimens were tested by the field application, the specimen QC having a high crystallinity (83.6%) in the medium carbon steel was The surface defect index of cast steel was found to be very low.

Existing product Test article Q QA QB QC QD QE Cast Surface Defect Index 1.0 1.6 0.5 0.1 0.7 1.2

Steel grade ([C] wt%) Existing Product (Q) Test article (QC) Remarks 0.01 to 0.14 1.0 0.5 Casting speed: 1.0 to 1.2 m / min 0.08 to 0.090.15 to 0.29 1.0 0.4

Table 2 measures the cast defect index of existing and test specimens, and especially compares QC and Q with the same casting speed. As can be seen from the table, the higher the crystallinity of the specimen QC compared to the existing product in the slab surface defect index reduced by about 1/2, the more favorable the surface defect of the slab.

Although not shown in the drawings, the partial structure of the existing product and the test product was observed through an electron microscope, and it was found that crystalline at the part contacting the mold and vitreous at the slab contact part.

The crystallinity change according to the chemical composition of the mold flux is measured by applying basicity, F, Al ₂ O ₃ , B ₂ O ₃ , MgO, Li ₂ O to the existing products of medium carbon steel. As it increases, the crystallinity increases, and an increase in Al ₂ O ₃ , B ₂ O ₃ , MgO, Li ₂ O, and the like causes a decrease in the crystallinity.

The management of the optimum crystallinity is classified by steel type, and the classification is shown in Table 3.

Steel grade Proper crystalline rate (%) Slab Ultra Low Carbon Heavy Duty Weather Resistant Steel High Carbon Steel Sheet 035% or less 15% or less 05% or less Stainless Austenite Ferrite series Bloom Billet 35% or less 015% or less 15% or less Billet, Bloom, Beam blank, Round 0

<Example>

In the field test of the test product measured in the laboratory by the method of the present invention, the basicity (CaO / SiO ₂ ) 1.3, Al ₂ O ₃ 3.6%, Na ₂ O + K ₂ O 4.6% in medium carbon steel (C content: 0.08 ~ 0.14) , F 7.6% of a test product (crystallinity: 83.6%) was prepared. The existing product has a very low crystalline rate (0.7%), and there are many differences.When the defect index of the existing product is 1 in the field test, the test product is improved to 0.4, and the defect index of the cast steel is improved. The surface defects of the cast pieces are very advantageous.

As a result of repeated trials and errors to derive the proper crystallinity in medium-carbon steels, it is possible to develop products that meet the most basic requirements such as the consumption and lubrication capacity of the continuous casting mold flux. For example, the crystalline rate of medium-carbon steels is controlled below 35%.

By measuring and managing the accurate crystallinity of the mold flux corresponding to a specific steel and appropriately controlling the crystallinity of the moldflux, casting of the target steel can be efficiently performed.

Claims (3)

Preparing a sample; Removing carbon from the sample at 650 ° C .; Melting the carbon-depleted sample in a platinum container; Cooling the molten sample in a platinum container mounted on a cooling water circulation device at 15 ° C., Observing the crystallized state of the solidified slag and measuring the ratio of the crystalline and glassy layer, the crystallinity measurement method of the solvent. delete delete