JPS6328869B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in calcareous refractories suitable for use in steelmaking refractories, particularly as linings for vacuum degassing and vacuum scouring equipment. Refractories used for melting and scouring molten metals (hereinafter referred to as molten metals) such as steel, iron-based, and nickel-based metals under vacuum must withstand high temperatures and resist the strong desulfurization of carbon, etc. during the vacuum scouring process. Basic refractories are widely used because they are physically and physically stable. Scouring in a vacuum or an inert gas atmosphere is effective in cleaning the molten metal, but is ineffective in desulfurization, and there is an urgent need to investigate the possibility of desulfurization in this atmosphere. Regarding deoxidation and desulfurization during scouring in vacuum or argon gas atmosphere, JP-A-50-126511, JP-A-Sho.
No. 50-126516 and JP-A No. 52-58010 disclose CaO40, which has a high calcium oxide (CaO) content.
Melting furnaces containing more than 60% and backed by basic refractories contain aluminum (Al) in the molten metal using a ladle and under vacuum or argon gas atmosphere.
or deoxidation characterized by adding an alloy thereof;
Desulfurization methods have been proposed. Based on this principle, by adding excessive Al, the
CaO is reduced, and the reduction product calcium (Ca) reduces sulfur (S) and oxygen (O) in the molten metal.
is supposed to be removed. However, this method requires that 0.06 to 20% or 0.005 to 0.06% of Al remain in the molten metal, and is considered to be a method applicable only to Al-containing alloys. In contrast, the present invention is based on the following points based on detailed research on the desulfurization ability of calcareous refractories. a The desulfurization reaction between the molten metal and the calcareous refractory occurs at the active calcium oxide (CaO) at the molten metal-refractory interface, as shown by equation (1). CaO+[S]=CaS[O] (1) Here, [ ] indicates a state dissolved in the molten metal. b Active CaO at the molten metal-refractory interface changes to calcium sulfide (CaS) over time, and [S]
inhibits reactivity with The above points a and b apply to the refractory after use, several mm from the inner surface that was in contact with the molten metal of the refractory.
This is also supported by the fact that sulfur (S) is detected at high concentrations within the range. c The desulfurization reaction shown by formula (1) is a reduction reaction of [S], and the molten metal needs to be reducible.
It is not necessarily necessary to contain excessive Al;
It is also sufficient to use a mildly deoxidized state using silicic acid, or deoxidized using carbon under vacuum. This is also proven in Examples 3 and 4, which will be described later. d CaS generated on the refractory surface is active CaO
This blocks direct contact with the molten metal and inhibits the desulfurization reaction. In order to continue this desulfurization reaction, it is necessary to remove this CaS. For example, it is necessary to remove the generated CaS by uniformly dissolving the lining refractory in an appropriate amount. This is clearly demonstrated by Examples 1 and 2, which will be described later. e At the contact point between the molten metal and the refractory, a boundary layer enriched with CaS generated by the desulfurization reaction shown in equation (1) and the eroded refractory is formed, reducing the desulfurization rate. Therefore, by stirring and holding the molten metal, desulfurization can be promoted by the movement of [S] and the floating separation of the welded refractories. This is clear from the results of Example 3, which used a low-frequency induction furnace with a large stirring effect, and Example 4, which used argon gas stirring. In order to realize the above principles, as a result of studying the material and scouring method of calcareous refractories, we found that CaO of 90% or more,
The desulfurization effect was completed by eroding a certain amount of a shaped refractory containing 1% or less of SiO ₂ , 5% or less of Fe ₂ O ₃ , and an alkali metal oxide as an erosion control agent. An object of the present invention is to provide a shaped refractory with excellent desulfurization properties. The present invention will be explained below with reference to Examples. Example 1 By blending electrolytic calcareous slinker, various sintered calcareous clinkers, and synthetic dolomite clinker, 50×50×
A 200mm brick was formed and fired, and a 50Kg high-frequency induction melting furnace was lined with magnesia mortar as a joint material, and the desulfurization properties of the bricks were compared. The melting material is JIS SUS420JI (0.2%C-0.4%Si-0.6%
Mn-13%Cr) steel, sulfur was added to check the desulfurization property.
A base material containing 0.05% was used. Melting was carried out under an argon gas atmosphere, and after melting, the temperature of the molten metal was maintained at 1600°C for 1 hour, the presence or absence of slag was observed, and sulfur analysis was conducted after casting. We also checked the weatherability of the refractories. Table 1 shows the component analysis values and dissolution status of the refractories used. Here, the desulfurization property is determined by the desulfurization rate = (1 - (% sulfur after casting)
Judging by base material sulfur%)) x 100%, ◎ is 50% or more,
○: 20-50%, △: 5-20%, ×: 5% or less.
Regarding the weatherability of the refractory lining, which powders and self-disintegrates during cooling after completion of melting, ◯ means almost no, △ means a little, and × means there is weathering.

[Table] From Table 1, the following can be determined. silicon oxide
In the case of lime refractories, SiO ₂ is empirically required to be about 1% or less to prevent weathering, which can be confirmed from these results. More than 90% of CaO is required for desulfurization. Fe ₂ O ₃ and Al ₂ O ₃ as mineralizers are limited because the higher the content, the less CaO there is.
As for Fe ₂ O ₃ , the increase in its content causes CaO
As the amount decreases, Fe ₂ O ₃ itself acts as an oxidizing agent for the molten metal and becomes a source of [O].
It needs to be as low as possible in order to transfer the reaction shown in equation (1) inward, and sample No. 3 and sample No. 4 in Table 1,
From the comparison of No. 5, 5% or less is required. It also appears that the generation of slag, that is, melting loss, is necessary for desulfurization. Example 2 Samples No. 1 and No. 3 shown in Table 1 were mixed with a small amount of sodium oxide Na ₂ O and potassium oxide K ₂ O, which are alkali metal oxides, as erosion amount adjusting agents. The bricks were each subjected to a melting test of 3 consecutive heats under the same conditions as in Example 1. FIG. 1 shows the relationship between the blending amount (weight) of the loss adjuster and the amount of loss per heat. Sample No. from this figure.
1 shows the amount of erosion loss per heat of 2.5 to 3 mm when no mixture is added, and it shows that the amount of erosion loss increases further in proportion to the blending ratio by adding the erosion amount regulator Na ₂ O. . In addition, sample No. 2 is approximately
The amount of erosion loss per 1 heat of 0.4 mm is shown, and it is shown that the amount of erosion loss is further increased approximately in proportion to the blending ratio by adding the erosion amount adjusting agent K ₂ O. This result suggests that it is possible to adjust the amount of erosion loss per heat to some extent by adjusting the content of mineralizer or MgO even when no erosion amount regulator is added. It has been shown that by adding an appropriate amount of an elution loss amount adjusting agent such as Na ₂ O or K ₂ O of 3% or less, the amount of elution loss per heat can be reliably adjusted over a wider range. Although FIG. 1 shows an example in which 0.2 to 2.3 of Na ₂ O or K ₂ O is added as an erosion amount adjusting agent, alkali metal oxides such as Li ₂ O have a similar effect. This result shows that the alkali metal oxide is effective as an agent for controlling the amount of erosion loss. Next, FIG. 2 shows the relationship between the desulfurization rate and the amount of erosion per heat. In this figure, the broken line corresponds to the broken line in FIG. 1, and the solid line represents the highest, lowest, and average desulfurization rates of the three heats for sample No. 3 + K ₂ O, and similarly for sample No. 1 + Na ₂ O. From this, the desulfurization rate is
It is strongly influenced by the amount of erosion per heat, and increases with the amount of erosion per heat up to about 4 mm, but above 4 mm, it reaches a saturation state and unnecessarily increases the loss of the lining. Furthermore, it can be seen that when sample No. 1 + Na ₂ O and sample No. 3 + K ₂ O have the same amount of erosion per heat, there is no significant difference in the desulfurization rate among the maximum, minimum, and average. The amount of corrosion loss per heat at which the desulfurization rate reaches saturation is thought to vary depending on the ratio of the amount of molten metal to the surface area of the refractory in contact with the molten metal, that is, the average depth of the molten metal. increases if . Furthermore, in this example, the amount of alkali metal oxide added was up to 2.3% by weight, but at least 3% by weight.
%, it is thought that the amount of erosion loss will increase in an extended line without any particularly large changes. Example 3 Component analysis values and characteristic values are shown in Table 2 A 6-ton low-frequency vacuum lined with two types of calcareous firebrick based on sample No. 1 used in Example 1 and a different type of sample No. 7 Continuous 20-heat melting was performed using an induction melting furnace. Table 3 shows the data for 12 heats. Eight heats not listed in this table were conducted for reproducibility tests on the same type of alloys as those listed in this table, and it was confirmed that there was sufficient reproducibility.

【table】

[Table] Table 3 shows C at the time of burn-through,
This is a summary of the SiAl content (weight)%, the material, and the increase/decrease in the S content during burn-through and after scouring. The following can be said from this table. Even if Al is Nil (not detected) at the time of melting, C, Si,
The presence of C, Si, etc. has a desulfurization effect, and the desulfurization rate is affected by the content of C, Si, etc. In other words, among No. 1 and No. 5 to 12, which contain 0.05% or more of C at the time of melting, except No. 12, which does not create a sufficient reducing atmosphere due to atmospheric dissolution.
Sufficiently low S content without adding Al,
It is desulfurized within the time until burn-through or during scouring. No. 12 has disadvantageous conditions because it dissolves in the atmosphere, but
A desulfurization rate of approximately 50% was obtained without adding Al until burn-through. Therefore, as mentioned above, if the molten metal contains a certain amount or more of carbon, sufficient desulfurization can be expected not only in an argon atmosphere, which is an inert gas, as shown in No. 11, but also in atmospheric dissolution. In addition, No. 2, No. 3, and No. 4, which had a C of 0.05% or less and a Si of 0.1% or less at the time of melting, were hardly desulfurized at the time of melting. Of these, No. 2 and No. 3 are after melting.
Added 0.01% Al, slightly desulfurized, but 50%
In order to expect the above desulfurization rate, the Al content of the molten metal would need to be 0.02% or more. Furthermore, at the time of melting, C is about 0.05% and Si is 0.1%.
No. 5 and No. 7 shown above have a sufficiently high desulfurization rate, and if a desulfurization rate of 50% or more is expected, about 0.1% or more of Si alone would be required. Furthermore, it appears that there is a difference in desulfurization resistance between the alloys, and No. 4 seems to have particularly good desulfurization resistance. The induction furnace used in this example, particularly the low-frequency induction furnace, has a stirring action, and the desulfurization promotion effect can be obtained through a good stirring action without using any special stirring means. Example 4 After removing the sludge, multiple types of molten steel melted in an electric arc furnace were tapped into a 20-ton ladle lined with calcareous refractory brick No. 7 shown in Table 2, and the ladle was heated for 12 to 16 minutes. Internal vacuum degassing treatment was performed. Pressure inside the vacuum chamber is 0.5~
The temperature was maintained at 5 Torr, and argon gas was blown into the ladle from the bottom using a porous plug to maintain stirring. Table 4 shows an example.

[Table] All steel types in this table have C0.05% or more and Si0.1
% or more are satisfied at the same time. In both cases, the Al analysis results at the time of tapping were Nil. From this table, the following can be said. No.1 without stirring by argon blowing,
Nos. 5 and 9 had poor desulfurization rates regardless of whether Al was added or not. Among these, Al was added.
The desulfurization rate of No. 9, which does not contain Al, is higher than the desulfurization rate of 11% and 8% for No. 1 and No. 5, which is 23%. This is Al0.03
This shows that the effect of a high C content is greater than the effect of %. No. 7 has a small argon injection amount of 3600Nl in total.
The desulfurization rate was 31%, which was insufficient. In addition, No. 10 with only argon stirring without adding Al,
No. 11 has a desulfurization rate of 62% and 60%, both good. Here, the effect of promoting desulfurization due to stirring by argon gas injection is clearly evident. In this example, the effect of adding 0.03% Al is masked by the presence of a certain amount or more of C and Si and cannot be found. In addition to the method of inert gas blowing shown in Example 4 and the stirring effect accompanying induction melting shown in Examples 1, 2, and 3, the stirring means may be the same as any other well-known stirring means. The effects can be expected. Furthermore, it is not necessary to be strong enough to reduce and generate Ca as a desulfurizing agent, and in addition to the detailed C, Si, and Al,
Known desulfurizing agents are also effective. As detailed above, the present invention can be summarized as follows. (1) Shaped refractories containing 90% or more of calcium oxide, 1% or less of silicon oxide, and 5% or less of iron oxide, and (2) Erosion control agent for alkali metal oxides such as K ₂ O, Na ₂ O, etc. (3) A molten metal containing at least one of C0.05% or more, Si0.1% or more, and Al0.01% or more is stirred and held in a container lined with a shaped refractory containing It is a refractory for desulfurization by melting away at a rate of 0.5 to 6.5 mm per heat. As described in detail above, the present invention is a refractory that can easily perform high-rate desulfurization especially under a vacuum or an inert gas atmosphere that is powerless against desulfurization.

[Brief explanation of the drawing]

Figure 1 is a graph showing the amount of erosion per heat of calcareous refractories containing alkali metal oxides, Figure 2
The figure is a graph showing the desulfurization rate versus the amount of erosion per heat. 〇: No. 1 sample + Na ₂ O, ×: No. 3 sample + K ₂ O.

Claims (1)

[Scope of Claims] A shaped refractory containing, in 1% by weight, 90% or more of calcium oxide, 1% or less of silicon oxide, 5% or less of iron oxide, and an alkali metal oxide as an erosion amount regulator, When molten metal is refined in a refractory-lined container, the amount of erosion per heat is 0.5~
A shaped refractory with excellent desulfurization properties characterized by its 6.5mm diameter. 2. A shaped refractory with excellent desulfurization properties according to claim 1, characterized in that the content of alkali metal oxides is 3% or less. 3 Alkali metal oxide is 2.3% or less,
A shaped refractory with excellent desulfurization properties according to claim 2, characterized in that the amount of erosion per heat can be adjusted to 0.5 to 6.5 mm.