JPS6252021B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a nickel (Ni)-based superalloy, and in particular, by improving the method for refining molten nickel-based superalloy, the content of oxygen, nitrogen, and sulfur can be extremely reduced. The present invention relates to a method for producing a Ni-based superalloy. [Prior Art] Ni-based superalloys have excellent properties such as mechanical properties, heat resistance, and corrosion resistance, and have a wide range of uses as superheat-resistant alloys. In this Ni-based superalloy as well, as with normal alloys, if residual oxygen, nitrogen, and sulfur are present in large amounts, workability decreases, so it is important to sufficiently reduce residual oxygen, nitrogen, and sulfur. Regarding deoxidation and desulfurization during refining under vacuum or argon gas atmosphere, CaO (calcium oxide) content is described in JP-A-50-126511, JP-A-50-126516, and JP-A-52-58010, respectively. A deoxidizing and desulfurizing method is proposed, which is characterized by adding aluminum (Al) or its alloy to the molten metal in a vacuum or argon gas atmosphere using a melting furnace or ladle backed with a highly basic refractory. has been done. This principle is that CaO in the refractory is reduced by adding Al, and sulfur (S) and oxygen (O) in the molten metal are removed by the reduction product calcium (Ca). According to this method, containing Ni-based superalloy return material
Although it is possible to deoxidize and desulfurize a molten Ni-based superalloy to a certain extent, a method for manufacturing an alloy that enables more sufficient deoxidation and desulfurization is expected. Furthermore, addition of metallic calcium (Ca) has also been conventionally carried out as a deoxidizing and desulfurizing method for molten alloys. (For example, JP-A-50-128633, JP-A-56-
39364, etc.) However, Ca is present in the Ni-based superalloy molten metal in the melting tank supported by refractories with low CaO content.
When Ca is added, there are problems in that the Ca addition efficiency is low and the amount of oxides increases. Conventionally, C is added to the molten Ni-based alloy in a melting tank backed by zirconia refractory or spinel refractory in the first step to perform deoxidation and denitrification, and then There is also a refining method in which Al and Ti, or Al and Zr, etc. are added in two steps and treated in a vacuum, but desulfurization is hardly done in the first step and denitrification is insufficient, so Al, Ti, Zr, etc. combine with N and the denitrification effect becomes small. Furthermore, the yield of Al, Ti, and Zr is also low. In addition, the corrosion resistance of the furnace material is poor, and the amount of oxides present in the alloy increases. [Problems to be Solved by the Invention] As described above, the conventional methods cannot sufficiently reduce O, N, and S in the molten Ni-based superalloy. Additionally, the amount of nonmetallic inclusions attributable to refractories may increase. [Means for Solving the Problems] The present invention provides for adding 0.2% Al to a molten nickel-based superalloy in a vacuum or argon atmosphere in a melting furnace or ladle supported by a refractory containing 40% or more of CaO. After adding ~2% and deoxidizing, desulfurizing and denitrifying, C0.01~0.6%
O, N: At least one of them is 30 ppm or less, by adding and further denitrifying, and then adding at least one of Al, Ti, and Zr.
A method for producing a nickel-based superalloy with low contents of oxygen, sulfur and nitrogen, characterized in that the total amount of O and N is 100 ppm or less, S: 50 ppm or less (hereinafter referred to as
This may be called the first invention. ), and 0.5 to 1% Al is added to the molten nickel-based superalloy in a melting furnace or ladle backed by a refractory containing 40% or more CaO in a vacuum or argon atmosphere to perform deoxidation, desulfurization, and After denitrification, C0.01~0.6%
After that, at least one of Al, Ti, and Zr and Ca and/or Ca alloy are added, and then the temperature is maintained at 50°C or more higher than the temperature at the time of addition. Ca removal treatment, O, N: At least one of them is 30 ppm or less,
A method for producing a nickel-based superalloy (hereinafter sometimes referred to as the second invention), characterized in that the total amount of O and N is 100 ppm or less, S: 50 ppm or less, and Ca: 100 ppm or less. This is a summary. In this specification, % represents weight %. The configuration of the present invention will be explained in detail below. The alloy targeted by the method of the present invention is a Ni-based superalloy, but there are generally many types of Ni-based superalloys. An example is shown in Table 1. Note that the first
In addition to the table, TRWVIA, TWR−1900, MAR−
Examples include M412 and No.64BC.

【table】

[Table] In the present invention, Al is first added to a molten Ni-based superalloy in a vacuum or an argon atmosphere.
A part of this Al directly combines with O in the molten metal to perform deoxidation. In addition, another part of Al reacts with CaO on the surface of the refractory, resulting in 2Al + 3CaO → Al ₂ O ₃ + 3Ca, and Ca and Al ₂ O ₃ are generated. This Ca deoxidizes,
A desulfurization reaction results in CaO and CaS. On the other hand, when Al ₂ O ₃ has a large amount of O in the molten metal (for example, 70 ppm or more of O), C ₃ A is generated on the surface of the refractory due to the reaction Al ₂ O ₃ +3CaO→3CaO.Al ₂ O ₃ . Note that when O is low (for example, less than 70 ppm), this C ₃ A is hardly produced, and 12CaO・
It was observed that a composition mainly composed of 7Al ₂ O ₃ (hereinafter sometimes referred to as C ₁₂ A ₇ ) was formed. The C ₃ A produced in this way is, as is well known,
It has significantly higher desulfurization properties than C ₁₂ A ₇ (for example, "Tetsu to Hagane" Vol. 68 (1982), No. 6, P68). Therefore, the desulfurization of the molten metal becomes strong and sufficient. The generated active Ca also performs deoxidation and desulfurization. Further, after adding Al, the amount of N in the molten metal gradually decreases with the passage of time. This is because N also leaves the molten metal as Ca and the like evaporate (boil). The amount of Al added is 0.2 to 2%. If it is less than 0.2%, the deoxidation, denitrification, and desulfurization described above will be insufficient, and addition of more than 2% is unnecessary and may cause nitrification or change the alloy composition. It's inappropriate. The above deoxidation, denitrification, and desulfurization by adding Al may hereinafter be referred to as the first step. In the first aspect of the present invention, C is added after the first step. As a result, denitrification is further performed. (The reason is that the reducing effect of carbon in the molten metal on refractories under reduced pressure is very strong, and the following reaction generates CO gas. M _x O _y +yC→yC ₀ (↑) + xM This CO gas At the same time when leaving the molten metal
It is estimated that it will escape with _N2 gas. ) The amount of C added is 0.01 to 0.6%. If it is less than 0.01%, denitrification is insufficient, while 0.6%
If the amount is more than 1, the amount of C phase or carbide phase remaining in the alloy increases, which is not preferable. A particularly preferable amount of C added is about 0.02 to 0.2%. In the first invention, after adding C,
One or more of Al, Ti, and Zr are added. Then, final deoxidation, desulfurization, or denitrification is performed, and the contents of O, S, and N are further reduced. The preferred range for the amount of Al, Ti, and Zr added is 0.2
-2%, particularly preferably 0.5-1%. 0.2
If the amount is less than 2%, the deoxidation, desulfurization, and denitrification of the finish will be insufficient, and if it exceeds 2%, it will become a factor in fluctuations in the alloy composition and cause nitrification, which is undesirable. . In the second aspect of the present invention, C is added after the first step (first Al addition step), and then
At least one of Al, Ti, Zr and Ca and/or Ca
Add alloy. Deoxidation, desulfurization, and denitrification are performed by adding C,
Denitrification is more fully carried out by at least one of Al, Ti, and Zr and Ca and/or Ca alloy. (As Ca boils, nitrogen leaves the molten metal and denitrification occurs.) Also, high CaO refractories are used as the furnace material;
This refractory is extremely stable with respect to Ca and does not substantially react with added Ca. Therefore Ca
The above deoxidation, denitrification, and desulfurization reactions proceed satisfactorily.
Incidentally, in low CaO refractories, MgO refractories, etc., the furnace material reacts with Ca, resulting in a low Ca yield.
The effect of addition becomes smaller. In the second invention, at least one of Al, Ti, and Zr and Ca and/or Ca alloy are added, and after deoxidation, denitrification, and desulfurization reactions are performed, or after these reactions have progressed considerably. At this stage, the temperature of the molten metal is increased by 50℃ or more. By raising the molten metal temperature in this way, the N content can be further reduced and excess Ca can be removed.
can be removed by evaporation. Generally, when the temperature is raised to high temperature, the amount of refractory wear increases and the amount of oxides in the alloy increases, but high CaO refractories such as those of the present invention are extremely stable, and the amount of oxides hardly increases. Not only does it not eliminate the presence of inclusions, but it also has the effect of cleaning the molten metal by adsorbing the inclusions that are already present. In addition, when adding Ca alloy, Ca-Ni alloy etc. are suitable, but it is not limited to this. Ca
The and/or Ca alloy is added in the form of a powder, particulate, or wire, but it is preferably in the form of a wire because evaporation on the surface immediately after addition is reduced. In the method of the present invention, the supporting refractories used are calcia refractories (CaO), lalunite refractories (stabilized 2CaO・SiO ₂ ), melwinite refractories (3CaO・MgO・2SiO ₂ ), and CaO-enriched dolomite refractories. All of them contain 40% CaO.
It is a basic refractory containing the above. In the method of the present invention, the reason why the CaO content of the supporting refractory is limited to 40% or more is that the CaO content of less than 40%
For basic refractories containing
Because CaO is tightly bound to other oxides,
In basic refractories containing 40% or more CaO, the activity of CaO is low and is not reduced by aluminum.
This is because CaO has high activity and can be easily reduced by aluminum. In addition, refractories containing 40% or more of CaO include Al ₂ O ₃ and
It easily reacts with oxides such as HfO ₂ and therefore absorbs oxides in the molten metal, greatly reducing the amount of oxides present. In addition, refractories containing 40% or more of CaO are C,
It has high stability against Ti, Zr, etc., so it can be melted at high temperatures. According to the method of the present invention, the O, N, and S contents in the molten metal are finally set such that at least one of O and N is 30 ppm or less,
The total amount of O and N is 100 ppm or less, S: 50 ppm or less. Preferably, any of O, N, and S
30ppm or less. O and S become oxides and sulfides and affect the weldability, ductility, toughness, and forgeability of the alloy, but by keeping them within the above range, these properties become excellent. N causes defects on nitrides or pinholes and affects the heat resistance, high-temperature strength, toughness, and ductility of the alloy, but by keeping it in the above range, these properties become excellent. Incidentally, in the present invention, flux may be added. [Action] As mentioned above, metals such as Al, Ti, Zr, Ca and C
Deoxidation, denitrification, and desulfurization are performed by the action of .
Furthermore, the backing material with a high CaO content promotes the above reaction, absorbs oxides, and reduces the amount of oxides present. [Example] Examples will be described below. Example 1 (Method according to the first invention) Ni was melted in a supported high frequency induction melting furnace under a vacuum atmosphere of 1×10 ^-3 torr with a CaO refractory having the composition shown in Table 2. A molten metal with a Ni-Cr base composition was melted for the purpose of producing a base superalloy IN738 material (the main components are shown in Table 3).

【table】

【table】

[Table] While maintaining the temperature of this molten metal at 1500℃,
Al was added at a rate of 0.5% and held for 20 minutes. Next, carbon was added at a rate of 0.15% and held at 1650°C for 10 minutes, and then Al was added at a rate of 0.3% and held for 2 minutes. The nitrogen content, sulfur content, and oxygen content of this molten alloy were measured. The results are shown in Table 4. Comparative Example 1 An experiment was conducted in the same manner as in the Example except that the refractories in the Comparative Examples column of Table 2 were used. The results are shown in Table 4.

[Table] From Table 4, according to the method of the first invention, O,
It is clear that S and N can be sufficiently removed. Example 2, Comparative Example 2 (Method according to the second invention) In a high-frequency induction melting furnace supported by refractories in the Examples and Comparative Examples column of Table 2, the composition of Table 3 was melted.
The base composition of Ni super-alloy was melted in the same manner as in Example 1. The temperature of the molten metal is 1500℃. Next, 0.5% Al was added under an argon atmosphere and held for 10 minutes, and then C was added at a rate of 0.15% and held for 3 minutes. Furthermore, 0.2% Ca, Al and Ti
was added in 0.35% increments, and then the temperature of the molten metal was increased to 1650
The temperature was raised to ℃ and held for 10 minutes, and the oxygen content, nitrogen content, and sulfur content were measured. The results are shown in Table 5.

[Table] From Table 5, even by the method of the second invention,
It is clear that O, N, and S can be sufficiently removed. [Effects] As described above, according to the present invention, it is possible to perform extremely strong deoxidation, denitrification, and desulfurization of Ni-based superalloys, and the content of O, N, and S is extremely low, and the strength, heat resistance,
It is possible to produce alloys with outstanding properties such as toughness, ductility, weldability, and forgeability. Furthermore, there are almost no intervening oxides.

Claims (1)

[Scope of Claims] 1. 0.2 to 2% Al is added to a molten nickel-based superalloy in a melting furnace or ladle supported by a refractory containing 40% or more CaO in a vacuum or argon atmosphere, and desorption is performed. After acid, desulfurization and denitrification, C0.01~0.6%
O, N: At least one of them is 30 ppm or less, by adding and further denitrifying, and then adding at least one of Al, Ti, and Zr.
A method for producing a nickel-based superalloy with low contents of oxygen, sulfur, and nitrogen, characterized in that the total amount of O and N is 100 ppm or less, and S: 50 ppm or less. 2 Add 0.2 to 2% Al in a vacuum or argon atmosphere to the molten nickel-based superalloy in a melting furnace or ladle backed by a refractory containing 40% CaO or more, and perform deoxidation, desulfurization, and denitrification. After that, C0.01~0.6%
After that, at least one of Al, Ti, and Zr and Ca and/or Ca alloy are added, and then the temperature is maintained at 50°C or more higher than the temperature at the time of addition. Ca removal treatment, O, N: At least one of them is 30 ppm or less,
A method for producing a nickel-based superalloy, characterized in that the total amount of O and N is 100 ppm or less, S: 50 ppm or less, and Ca: 100 ppm or less.