JPH0613431B2 - Refining refractory material and refining method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a calcia (CaO) -based refractory material for refining and a refining method using the same. For more details,
The present invention relates to the refractory material and refining method capable of simultaneously performing dephosphorization in addition to deoxidation and desulfurization.

[Prior Art] It is well known that the properties of an alloy can be significantly improved by reducing impurities, especially oxygen (O), sulfur (S), or phosphorus (P). For example, tempered brittleness and low temperature toughness of 9% Ni steel for cryogenic containers deteriorate even with low concentration of phosphorus. In addition, hydrogen-induced cracking (HIC) that occurs in a line pipe for transporting crude oil and natural gas containing H ₂ S originates from a stretched inclusion such as MnS and originates in bainite (B) or martensite (M). Grow along the quenched structure. Phosphorus in steel remarkably positively segregates in the macrosegregation portion of a steel ingot or continuous cast slag, and promotes the formation of a quenched structure in a thick plate. therefore,
In order to prevent the occurrence of HIC, it is necessary to reduce the phosphorus concentration below the critical value. Furthermore, the stress corrosion cracking (SCC) of austenitic stainless steel is promoted by phosphorus. In addition, phosphorus generally deteriorates high temperature ductility due to segregation at grain boundaries. Further, it is well known that various characteristics such as ductility and toughness deteriorate when the concentration of oxygen and sulfur in the molten alloy is high.

By the way, it is known that CaO-based refractory materials are thermodynamically stable even at high temperatures, and have an oxide absorbing action, a deoxidizing action, and a desulfurizing action by a so-called furnace wall slag reaction,
A method for deoxidizing and desulfurizing molten steel using this has been developed (for example, Japanese Patent Publication No. 54-849).

A method for dephosphorization using a CaO crucible to which CaF ₂ is added is also known (Tohoku University Institute for Materials Research, Common Facility Technology Laboratory Report No. 10, P. 49 to 50).

Conventionally, dephosphorization of molten iron has been performed using slag, and soda slag containing Na ₂ O · SiO ₂ or CaC ₂ has also been put to practical use (29th Honda Memorial Lecture, April 1, 1984). It is also known a method of using the CaO-CaF ₂ based flux or _{CaC 2} -CaF 2 system flux (Japanese Patent Publication No. 11099).

[Problems to be Solved by the Invention] According to the refining method known from Japanese Patent Publication No. 54-849, it is possible to perform strong deoxidation and desulfurization, but dephosphorization is hardly performed. Absent.

Further, the CaO-CaF ₂ type crucible or dephosphorization method dissolves iron whose surface has been oxidized in advance, and the applicable alloy species are limited. For alloy systems containing many oxidizing metal elements, It lacks versatility such as not being applicable.

On the other hand, the method of dephosphorization using slag has problems such as damage to the furnace wall due to contact between the slag and the furnace wall, entrainment of slag in molten metal or ingot, and generation of fume odor. Further, conventionally, the dephosphorization method using slag is carried out under an oxidizing atmosphere, but it is difficult to prevent the oxidation of the alloy, and if the processing is performed using a vacuum melting furnace, the slag is removed. There is a problem that slag treatment is difficult. [Means and Actions for Solving Problems] The refining refractory material of the present invention is characterized by containing CaC _{2 in an amount} of 50% by weight or less and the balance mainly CaO. To do.

Further, in the refining method of the present invention, the molten alloy is held under non-oxidizing property in a container having at least the inner surface made of the refractory material for refining, and the deoxidized material is contained in the molten alloy as necessary. It is characterized by that.

According to the present invention, dephosphorization can be performed simultaneously with deoxidation and desulfurization without using slag.

The present invention will be described in more detail below.

The refractory refractory material of the present invention contains CaC _{2 in an amount} of 50% by weight (hereinafter abbreviated as%) or less, and the balance mainly comprises CaO. The composition of the balance may consist essentially of CaO, or may contain CaF ₂ in an amount of 10% or less of the refractory material in addition to CaO.

In the refractory material for refining of the present invention, the content of CaC ₂ is 5
If it exceeds 0%, the handling difficulty increases and the corrosion resistance and fire resistance of the refractory material decrease. Also, CaC
_{When the} content of ₂ is less than 0.5%, the dephosphorization effect is reduced, so the blending range of CaC ₂ is 0.5 to
It is preferably 20%, especially 1 to 10%.

The CaC ₂ content in the refractory refractory material of the present invention means the content rate of CaC _{2 in} the entire refractory material, and may locally exceed 50%. For example, as described later, when a CaO-based raw material is molded and a carbon material is brought into contact with it to generate CaC ₂ , locally, the contact surface with the carbon material exceeds 50% of CaC ₂ However, such uneven distribution of CaO ₂ is acceptable as long as the properties as a refractory material are not impaired.

Further, the refining refractory material of the present invention can improve the dephosphorization effect when CaF ₂ is contained, which is extremely advantageous, but when the CaF ₂ is too much, the melting point of the refractory material decreases, It becomes impractical because high temperature melting becomes impossible. Therefore, the blending range of CaF ₂ is 10% or less of the refractory material, preferably 8% or less.

In addition to the refractory material for refining of the present invention, SiO ₂ , Al ₂
O ₃ , MgO, ZrO ₂ , Fe ₂ O ₃ , BaO, MnO
Metal oxides such as _2, fluoride such as MgF _2, Ca
One or more of chlorides such as Cl ₂ and MgCl ₂ or slag constituents such as CaCN may be contained. If the content of slag constituents becomes too large,
The CaO content in the refractory material becomes relatively small, and effective deoxidation and desulfurization action become difficult to occur, and the corrosion resistance and fire resistance of fire resistance may be reduced depending on the type of slag constituent material. For this reason, the slag component is a refractory material
The content is preferably 0% or less.

The raw material for CaO, which is the main oxide in the refractory material, is C
Various materials such as calcined aCO ₃ or Ca (OH) ₂ and electrofused calcia can be used. Electrofused calcia is suitable because it is dense. When the refractory material contains a slag constituent material, it is possible to use ralnite, melwinite, anorthite, dolomite, etc. together as a raw material for the CaO source.

In order to manufacture the refractory material of the present invention, for example, CaO particles, CaO ₂ powder, and if necessary, CaF ₂ powder and slag constituent material powder (or particles) are mixed at an appropriate ratio. In order to form an amorphous refractory material such as a stamp material, a non-aqueous binder (for example, ethanol in which calcium chloride is dissolved, pitch, tar, etc.) is added and used. Further, in order to obtain a standard refractory material, press molding may be performed with or without addition of these non-aqueous binders, and sintering may be performed as necessary.

Note that CaC ₂ is CaO when producing electrofused calcia.
Is relatively easily manufactured by arc heating and melting in the presence of C. The reaction between C and CaO is 1800
It occurs at a high temperature of ℃ or more, and CaC ₂ is easily obtained. From the above, it is possible to perform arc melting of CaO in the presence of C during the production of electrofused calcia, or
Also by raising the temperature of the mixture of C and C, Ca
A CaO-based refractory material containing C ₂ can be obtained.

Further, the CaO-based refractory material containing CaC ₂ can be obtained by firing the CaO-based compact in a state of being in contact with the carbon material. For example, if a CaO-based raw material is molded into a crucible shape, a carbon material is inserted inside the crucible and induction heating is performed, it is possible to perform sintering and CaC ₂ generation at the same time.

According to the refining method of the present invention, the molten alloy is held in a container having at least the inner surface made of this refractory material for refining, and a deoxidizing material is contained if necessary. This container may be a crucible like the refining refractory material described above, and the refining refractory material (either stable refractory material or amorphous refractory material may be attached to the inner surface). A refractory container may be used. In the case of a crucible, a CaO-based refractory composition in which only the inner surface is enriched with CaC ₂ may be used.

Further, in a CaO-based crucible or a refractory container lined with a CaO-based refractory material, CaC ₂ is formed by heating in the presence of C such as inserting a graphite rod into the inner surface of the crucible or the refractory container to form CaC ₂ on the inner surface portion. A material adapted to form a CaC ₂ enriched layer can also be suitably used.

To hold the molten alloy in this container, the molten metal melted by another melting device may be poured into this container, or all or part of the alloy raw material may be charged into the container. Alternatively, any method of heating and melting to form a molten metal may be used.

In the present invention, the molten alloy is held in the container under a non-oxidizing atmosphere. As the non-oxidizing atmosphere, vacuum or argon, nitrogen, or the like is preferably used as an inert gas.

In the present invention, it is possible to perform deoxidation by adding a deoxidizing material to this molten alloy. As the deoxidizing material, one or more of C, Al, Si, Ti, Zr, Hf, alkaline earth metals, B, rare earth elements (lanthanoid elements) and the like can be used. Among these deoxidizers, Al, Si, and Ti are particularly preferable. In addition, these deoxidizers may be added as a pure metal or an alloy.

In the refining method according to the present invention, it is preferable to add a sufficient amount of deoxidizing agent to carry out the deoxidizing reaction. Also,
It is preferable to select an addition amount such that the metal remaining in the molten metal does not deteriorate the properties of the obtained alloy. For example, when aluminum is added to the molten steel of carbon steel or alloy steel, the residual amount of aluminum in the molten steel is 0.0
It is preferable to set it to about 05 to 20%. In this case, when the residual aluminum amount is less than 0.005%, sufficient deoxidation and desulfurization are not performed, and when the residual aluminum amount exceeds 20%, the practicality of the obtained steel becomes poor.

In the present invention, the dephosphorization effect of the molten alloy is
It is estimated that the following reaction formula is used.

CaC ₂ → Ca + 2C 3Ca + 2P → Ca ₃ P ₂ Ca ₃ P ₂ + CaO → Ca ₃ P ₂ .CaO Further, when a deoxidizing material such as Al, Si, or Ti is added, for example, when Al is added, the following is performed. Deoxidation and desulfurization are performed by the reaction to complement the above dephosphorization reaction.

That is, the added Al is O in the molten metal and CaO in the furnace wall.
And reaction of the S in the melt (CaO + S → CaS + O ) by reacting with O produced, resulting 2Al + 30 → _Al 2 _{O 3.} Therefore, the _Al 2 _{O 3.} Further, Al in the molten metal reacts with CaO on the furnace wall to become 2Al + 3CaO → Al ₂ O ₃ + 3Ca (g), which also produces Al ₂ O ₃ . (In this case, the generated Ca has an action of promoting deoxidation, desulfurization, and dephosphorization by the following reaction.) Ca (g) + O → CaO Ca (g) + S → CaS 3Ca (g) + 2P → Ca ₃ P ₂ Al ₂ O ₃ reacts with CaO on the furnace wall as shown in the following equation, and 3C
active layer of aO · _Al 2 _{O 3} or 12CaO · _7Al 2 _{O 3} is formed on the furnace wall surface.

Al ₂ O ₃ + 3CaO → 3CaO.Al ₂ O ₃ 7Al ₂ O ₃ + 12CaO → 12CaO.7Al ₂ O ₃ The 12CaO.7Al ₂ O ₃ and 3CaO.Al ₂ O
₃ , especially 3CaO.Al ₂ O ₃ has high de-S-removing ability of the molten metal,
Good S removal progresses.

Thus, deoxidation by Al and active 3CaO.Al ₂ O ₃ and 12CaO.
Desulfurization is performed by 7Al ₂ O ₃ or CaO.

N in the molten metal is the reaction between Al and CaO and CaC.
_With the evaporation (boiling) of Ca or the like generated by the decomposition reaction of No. ₂ , the Ca is separated from the molten metal, and the amount of N in the molten metal is also reduced.

Further, CaO absorbs oxides, sulfides, phosphides, nitrides, etc. in the molten alloy, and the refining reaction also proceeds by this.

As described above, according to the present invention, in addition to the strong dephosphorization reaction, deoxidation, S, and N reactions are carried out, and the CaO furnace wall prevents contamination by impurities, and O, S, P, N contents are greatly reduced. Therefore, an extremely clean alloy can be obtained.

The refining method of the present invention is based on Fe-based, Co-based, Ni-based,
It can be applied to various alloys such as Cr-based, Mn-based, and Cu-based alloys.

Further, the means for heating the molten metal is optional,
If an induction heating device is used, its unique stirring action can be utilized, which is preferable.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded.

Using Example _{1 CaO-5% CaC 2 -3} % CaF crucible, O in the crucible, S, P content is respectively O0.03%, S0.0
Fe-30wt% Cr alloy 1 with 2% and P0.05%
It contains Kg and is at 1550 ° C under Ar1.0atm atmosphere.
It was melted by high frequency induction heating. Immediately after the melting, 0.5% of granular Al was added to the molten metal. FIG. 1 shows changes with time of O, S, and P in the molten alloy. From FIG. 1, it can be seen that the P concentration starts to decrease with the addition of Al after the start of melting and reaches 1/10 of the initial concentration in about 10 minutes. At the same time, a rapid decrease in O and S is also observed due to the addition of Al. In the drawings, O, S, and P are initial concentrations C _0.
It is shown as the ratio of the concentration C to.

[Effects of the Invention] As is clear from the above description, according to the present invention, dephosphorization, deoxidation, desulfurization and denitrification can be performed in one treatment step, and strong dephosphorization is performed. You can
Further, since there are no problems such as damage to the furnace wall, slag inclusion in the ingot, generation of fumes and odor, the refining operation is easy.

[Brief description of drawings]

 FIG. 1 is a graph showing the measurement results in Example 1.

Claims (4)

[Claims] 1. Containing 50% by weight or less of CaC ₂ and the balance C
Refining material for refining mainly composed of aO. 2. The balance mainly comprises CaO, and further CaF ₂
The refractory material for refining according to claim 1, wherein the refractory material contains 10% by weight or less of the whole. 3. CaC ₂ at least 50% by weight on the inner surface
A method for refining an alloy, characterized in that the molten alloy is held in a non-oxidizing atmosphere in a container containing the following, the remainder being a refractory material for refining mainly containing CaO. 4. At least the inner surface contains 50% by weight of CaC _2.
A molten alloy is held under a non-oxidizing atmosphere in a container containing the following, the balance of which is composed of refractory refractory material mainly composed of CaO, and the deoxidized material is contained in the molten metal. And alloy refining method.