JPS5937326B2 - High calcareous steel refining agent - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a high calcareous steel refining agent, more specifically a Ca0
-A7203-Relates to a steel refining agent containing CaF2 as a main component and having actions such as desulfurization and deoxidation.

In recent years, injection treatment in which powder or granular flux is blown in with high-pressure gas has become popular in steel refining, but injection treatment with lime-based granular refining agents has also gained attention in molten steel refining. Many suggestions have been made.

For example, in JP-A-54-131521, CaO: 30
~100%, CaF2+At203: 0-70, M
gO,5i02. A digestible lime-based molten steel refining agent is described, which is a non-crushable granular material formed by melting and solidifying Fe 2 oxides each having a composition of 10 or less.

This refining agent is made by melting raw materials such as lime, fluorite, and alumina in an electric furnace, dropping the molten metal, and blowing high-pressure gas onto it to form molten droplets, which are then rapidly solidified. Because it is a granular material that is spherical or nearly spherical and consists of microcrystals both on its surface and inside, it has excellent digestive resistance, but on the other hand, when lime is melted in an electric furnace, fluorite, alumina, etc. A large amount of fluxing agent is required, and CaO
It is difficult to make 70% or more, and there are disadvantages in terms of a decrease in refining effect due to a decrease in CaO and in terms of economy.

The present invention provides a high calcareous steel refining agent that maintains digestion resistance, enhances the refining effect, and is relatively inexpensive.

That is, the present invention provides at least 80 inches of CaO on a weight basis;
Contains At2031-14qb1CaF22.5-10 as a main component, MgO, 5i02. It is a steel refining agent with an unavoidable component such as Fe oxide of 4 or less, and is characterized by being a granular material in which CaF2 is fused to the surface layer such as CaO particles.

Hereinafter, the content of the present invention will be explained in detail.

As a refining agent for molten steel, it has a high basicity, that is, a high CaO content, and in order to prevent injection nozzle clogging accidents during blowing treatment, granules of 1rrtrrL or less are usually required, and moreover, it prevents hydrogen from being brought into the steel. Therefore, the CaO particles must be digestible.

The components of the refining agent of the present invention include at least 80% CaO as the main ingredient and 1 to 14% of A1203 as the slag adjustment aid.
%, and 2.5 to 10% of CaF2 as a fluxing agent that fuses to the surface of CaO particles to improve digestion resistance,
In addition, MgO, 5i02. Although Fe 2 oxide and the like are present, the content of these inevitable components is selected to be 4 or less.

If the CaO content is less than 80%, the activity for desulfurization and deoxidation reactions decreases, and the refining effect of the present invention decreases, which is not preferable.

At203 is used as a slagging adjustment aid, and if it is less than 1 part, the main slagging will not be sufficient, and the desulfurization and deoxidation reactions in molten steel will be rate-limited, so the refining effect of CaO will not be exhibited. If it exceeds this, CaO will be relatively reduced and the refining effect will be lowered, which is not preferable.

Next, if CaF2 is less than 2.5, it cannot be fused to each surface layer of the CaO particles, making it impossible to maintain digestion resistance.

Furthermore, when CaF2 exceeds a factor of 10, the activity of CaO decreases relatively, as in the case of At203, and the refining effect decreases.

Here, to further explain the state in which CaF2 fuses to the surface layer of CaO particles, when the basic raw material is heated, CaF2, which has the lowest melting point, melts on the surface of CaO particles,
If the heating time is long, the eutectic reaction of CaF2-'-CaO should proceed, but within a certain period of time, the CaO particles are fused to the surface, and when air-cooled as they are, they exhibit a fused and solidified state.

Since it is thought that the fusion effect of CaF2 is the same for At203 particles and CaO particles, it is preferable for At203 particles to be within the above range.

When observing the fused state of CaF2 on the surface of CaO particles using a scanning electron microscope, it was found that compared to those that were not fused, CaF2 covered the entire surface of the CaO particle in a molten state and solidified.
It was observed that the overall shape was round and smooth, and this is thought to be the reason why the digestion resistance was improved compared to those in which the CaO particles were not coated with CaF2.

Next, a method for producing the refining agent of the present invention will be explained.

CaO of limestone, quicklime, slaked lime, etc. adjusted to 1 m or less
A t203 source such as bauxite, alumina, etc., and a CaF2 source such as fluorite are blended so as to have the above-mentioned composition range, and this mixture is supplied to a rotary kiln,
Calcinate at a temperature of 0 to 1200°C and cool.

The obtained fired product has a nearly spherical shape that is almost the same as the particle size of the raw material before firing, and can be used as a refining agent without any means such as pulverization.

As described above, since the refining agent of the present invention is fired at a temperature far lower than the temperature at which it is melted in an electric furnace or the like, CaF2 melts and fuses to the surface layer of the CaO particles, but the CaO particles do not fuse together. It is characterized by the fact that it retains its original spherical or granular shape without changing, and since the CaO crystals inside the grains do not change, the highly active CaO is maintained as it is, which improves the refining effect. It is a characteristic.

The refining agent of the present invention explained above is Ca0-A/,03-
It is a refining agent mainly composed of CaF2, has a relatively high content of CaO, has a high CaO activity, and has an ASTM:
Digestion rate measured by the method specified for Cll0 is 0.1
('C/min) or less, and it is recognized that it is almost equivalent to CaO-based refining agents obtained by melting at high temperatures such as electric furnaces, and has a refining effect. There are some very remarkable things about this.

This is because the CaO crystals obtained by melting become microcrystals by rapid cooling and have excellent dispersion effects in molten steel, but on the other hand, because they are treated at high temperatures, the reaction activity of CaO such as slagging is reduced. It has the disadvantage of decreasing.

On the other hand, since the refining agent of the present invention is obtained by firing at a relatively low temperature, its reaction activities such as slagging, desulfurization, and deoxidation are limited.

In addition, all the units described in the specification are shown on a weight basis.

Next, the present invention will be explained in detail.

Example 1 80 parts by weight of calcium carbonate, 10 parts by weight of alumina for electrolysis (At20399 part) and 5 parts by weight of fluorite (CaF 285%), which had been adjusted to a particle size below the capacity of the powder, were mixed thoroughly and then fed to a CO gas-fired rotary kiln. 1000～
The refining agents shown in Table 1 were obtained by firing continuously at a temperature of 1200°C.

Next, when the refining agent was observed with an electron microscope, each particle was granulated into a nearly spherical shape, and as shown in Table 1, the particle size was the same as before firing, and the granules were separated by the firing. It was found that each particle was a homogenized fused product without any formation.

In addition, regarding the digestion resistance of this refining agent, ASTM: C11
When the digestion rate was measured using the method specified in 0.0, the average rate was 0.1 ('C/min) or less, which was almost the same as that obtained by electrofusion (commercial product).

Table 2 shows the results of adding the refining agent thus obtained to low-value molten steel, which had been high-frequency melted in an MgO crucible, along with argon gas in a weight ratio of 0.5, and treating for 10 minutes.

Furthermore, when the amount of hydrogen in the steel was determined, it was found that it was the same as before the treatment, and there was no hydrogen pick-up phenomenon due to the addition of the refining agent.

For comparison, the results of a similar experiment using a commercially available refining agent, so-called premelt flux, obtained by electrofusion are shown.

Claims (1)

[Claims] 1 At least 80% CaO by weight, At203
1-14%, CaF22.5-10% and MgO,S
It is a refining agent consisting of components of 4 or less unavoidable components such as iO2 and Fe oxide, and it also contains Ca on the surface of CaO particles.
A high calcareous steel refining agent consisting of granules with fused F2.