JP7594732B2 - Method for producing Zr-containing high Ni alloy ingot - Google Patents

Description

The present invention relates to a method for producing a Zr-containing high Ni alloy ingot in which Zr is uniformly distributed by an ESR process, and in particular to a method for producing a high Ni alloy ingot containing at least Al and Ti together with Zr.

In high-Ni alloys, which have excellent corrosion resistance and mechanical strength at high temperatures, the inclusion of Zr can further improve high-temperature strength. For such high-Ni alloys, the electroslag remelting (ESR) process can be used, in which an alloy ingot adjusted to a specified composition is obtained through refining by a metal-slag reaction between a consumable electrode and slag made by melting flux. However, since Zr is an active element with a high affinity for oxygen, it reacts with slag and is easily worn away, making it difficult to obtain a high-Ni alloy ingot with uniformly distributed Zr.

Here, a method is proposed in which, in the ESR process of Zr-containing high Ni alloys, _ZrO2 is added to the flux to control the metal-slag reaction and produce a high Ni alloy ingot with uniformly distributed Zr.

For example, Patent Document 1 discloses that in an ESR process for producing a relatively small Ni-based Cr-Mo-Fe alloy ingot containing Zr, about 100 mm in diameter, an appropriate amount of oxides of active components such as Si, Ti, and Al contained in the electrode components (target ingot components) together with ZrO ₂ is added to the flux composition (CaF ₂ -CaO system) so that the electrode components and the flux composition are in equilibrium. By adding ZrO ₂ to the flux composition, Zr remains in the obtained alloy ingot even in an ESR process using an _electrode that does not contain Zr. Specifically, it describes selectively adding 10 wt % or less of SiO ₂ , 5 to 25 wt % of TiO ₂ , and 5 to 30 wt % of Al _{2 O 3} to a flux containing CaF 2 and CaO with 5 to 25 wt % of ZrO 2.

Japanese Unexamined Patent Publication No. 63-216935

It is difficult to obtain a high-Ni alloy ingot with uniformly distributed Zr by the ESR process, but in particular, in large alloy ingots with a diameter of 300 mm or more, the loss of Zr at the bottom side tends to be large. In response to this, as described above, by adding a large amount of ZrO ₂ to the flux in the ESR process, a high-Ni alloy ingot with uniformly distributed Zr can be obtained to a certain extent. On the other hand, it has been pointed out that ZrO ₂ is expensive compared to the price of general slag materials such as _CaF 2 and CaO, and since most of the slag is removed, the utilization efficiency of the added Zr is low. Therefore, it was desired to optimize the amount of addition to the flux corresponding to the composition of the desired alloy ingot.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a high Ni alloy ingot in which Zr is uniformly distributed by controlling the metal-slag reaction while suppressing the amount of _ZrO2 added to the flux in the ESR process of a Zr-containing high Ni alloy.

The present invention has discovered that if a high Ni alloy ingot contains at least Al and Ti in addition to Zr, Zr can be uniformly distributed even in a large alloy ingot by performing a predetermined control while suppressing the amount of _ZrO2 added to the flux in the ESR process.

The manufacturing method according to the present invention is a method for manufacturing a high Ni alloy ingot containing at least Al and Ti together with Zr by utilizing an electroslag remelting (ESR) process, characterized in that the flux has a composition, in mass%, of _CaO : 10-40%, _ZrO2 : 0.01-2.0%, _Al2O3 : 10-40%, _TiO2 : 0.1-10%, MgO: 5% or less, _SiO2 : 3% or less, with the balance being _CaF2, and the composition of the flux and consumable electrode is adjusted so that Z, A, and T defined in the following formulas 1, 2, and 3 satisfy -1.0≦A-Z≦1.0 and 0.5≦T-Z≦2.5.

According to this feature, it is possible to produce a high Ni alloy ingot in which Zr is uniformly distributed while suppressing the amount of _ZrO2 added to the flux.

In the above-mentioned invention, the composition of the high Ni alloy ingot may be characterized as being mainly a Ni alloy containing 10 to 25% Cr and 5% or less Fe. This characteristic makes it possible to suppress iron oxide in the slag, stabilize the slag-metal reaction, and produce a high Ni alloy ingot with uniformly distributed Zr.

In the above invention, the consumable electrode may be characterized by having a composition, in mass percent, of Cr: 10-25%, Al: 1-5%, Ti: 1-4%, Zr: 0.01-0.1%, and the balance Ni. This characteristic makes it possible to stabilize the slag-metal reaction and produce a high-Ni alloy ingot with uniformly distributed Zr.

In the above invention, the composition of the consumable electrode may be characterized as containing Co: 25% or less, Mo: 5% or less, W: 3% or less, Fe: 5% or less, Nb: 3% or less, Mg: 0.1% or less, and B: 0.1% or less. This characteristic makes it possible to produce a high-Ni alloy ingot with uniformly distributed Zr without significantly affecting the slag-metal reaction.

The above-mentioned invention may be characterized in that the electrode has a diameter of 300 mm or more. With this characteristic, it is possible to produce a high-Ni alloy ingot with uniformly distributed Zr, even in the case of a large alloy ingot.

1 is a table showing the component composition of a consumable electrode used in a production test. 1 is a detailed view of some of the components of the consumable electrode. 1 is a table showing the composition of the flux in (a) mass % and (b) mole fraction. 1 is a table showing the Z value, A value, T value, and Zr analysis results of the obtained alloy ingot. FIG. 1 is a diagram showing the equilibrium between Z and A values. FIG. 1 is a balance diagram of Z and T values.

This section describes a method for producing high-Ni alloy ingots as one embodiment of the present invention.

The high Ni alloy ingot to be obtained has a composition containing at least Al and Ti together with Zr, and is produced by utilizing an electroslag remelting (ESR) process. The flux used in the ESR process has a composition, in mass %, of CaO: 10-40%, _ZrO2 : 0.01-2.0%, _Al2O3 : 10-40%, _TiO2 : 0.1-10%, MgO: 5% or less, _SiO2 : 3 _% or less, and the balance being _CaF2 .

The consumable electrode used in the ESR process and the above-mentioned flux have a composition in which the contents of Al, Ti, and Zr are adjusted as follows in order to control the slag-metal reaction. That is, in Z, A, and T defined in the following formulas 1, 2, and 3,
The value A minus the value Z (A-Z) is within the range of -1.0 to 1.0, and the value T minus the value Z (T-Z) is within the range of 0.5 to 2.5. In other words, -1.0≦(A-Z)≦1.0, and 0.5≦(T-Z)≦2.5.

The purpose of setting (A-Z) and (T-Z) within the above-mentioned ranges is to stabilize the following slag-metal reaction of Al and Ti with Zr.
4Al+3ZrO ₂ =2Al ₂ O ₃ +3Zr
Ti+ZrO ₂ =TiO ₂ +Zr

That is, by setting the values of (A-Z) and (T-Z) within a predetermined range, the slag-metal reaction is stabilized so as to maintain the equilibrium state with respect to Zr, and the ESR process proceeds. As a result, Zr can be stably present in both the metal and the slag, and a high-Ni alloy ingot containing a stable amount of Zr can be obtained. This makes it possible to distribute Zr uniformly, particularly in large alloy ingots, while suppressing the amount of _ZrO2 added to the flux.

Generally, only a part of Zr contained in the flux can be transferred to the alloy ingot, and the utilization efficiency is low. Therefore, when Zr is to be contained in the alloy ingot, the content of _ZrO2 in the flux is generally increased. For example, the above-mentioned Patent Document 1 specifies that the content of _ZrO2 in the flux is 5 to 25% by weight. In contrast, according to the above-mentioned method, even if the amount of _ZrO2 added is suppressed to 0.01 to 2.0% by mass, the equilibrium state in the slag-metal reaction can be stabilized, and Zr can be uniformly contained in the obtained alloy ingot.

It is also preferable that the resulting alloy ingot has a composition that contains mainly 10 to 25 mass% Cr and 5 mass% or less Fe. By reducing the Fe content, the iron oxide content in the slag can be suppressed and the ESR process can proceed. This makes it possible to stabilize the slag-metal reaction so as not to affect the equilibrium state regarding Zr, and to obtain an alloy ingot with a uniform distribution of Zr.

Furthermore, it is also preferable that the consumable electrode used in the ESR process has a composition, by mass percent, of Cr: 10-25%, Al: 1-5%, Ti: 1-4%, Zr: 0.01-0.1%, and the balance Ni. This also stabilizes the metal-slag reaction. In addition, the consumable electrode can have a composition that does not significantly affect the above-mentioned slag-metal reaction, which is Co: 25% or less, Mo: 5% or less, W: 3% or less, Fe: 5% or less, Nb: 3% or less, Mg: 0.1% or less, and B: 0.1% or less. Although Si, C, and N can be unavoidably contained, it is preferable to reduce their contents.

The manufacturing method of the high Ni alloy ingot described above can also be used to obtain large alloy ingots, as mentioned above. For example, even if the electrode diameter of the consumable electrode is 300 mm or more, it is possible to manufacture an alloy ingot with uniformly distributed Zr.

[Production testing]
Next, the results of a test carried out to produce a high Ni alloy ingot by the above-mentioned method will be described.

First, five consumable electrodes were prepared using a high-Ni alloy with a composition that included each component in the range shown in Figure 1. All of the electrodes used were large, with an electrode diameter of 300 mm or more.

In particular, Figure 2 divides the five consumable electrodes into comparative examples and examples 1 to 4, and shows the analytical values of the Al, Ti, Si, and Zr content for each.

Fluxes were prepared so as to have the component compositions ((a) mass%, (b) molar fraction) shown in the comparative example and examples 1 to 4 in Figure 3.

4 shows the above _- mentioned "Z", "A", and "T" values, as well as "A-Z" and "T-Z" values, regarding the relationship between _Al2O3 , _TiO2 , and _ZrO2 in the flux and Al, Ti, and Zr in the consumable electrodes. Then, ESR was performed using these consumable electrodes and fluxes, and alloy ingots were obtained for each of the comparative example and examples 1 to 4.

The results of the analysis of the Zr content in the alloy flakes cut from a position 100 mm from the bottom side of the obtained alloy ingot are also shown in mass % in the "ESR ingot Bot. [Zr]" column in the figure. The "change rate" is the percentage of the difference between the analytical value of the Zr content in the alloy flakes and the analytical value of the Zr content in the consumable electrode. In addition, the absolute value of the change rate of 10% or less is evaluated as good and marked with "◎", those between 10% and 30% or less are evaluated as acceptable and marked with "◯", and those over 30% are evaluated as unacceptable and marked with "X".

As a result, the comparative example was rated as "unacceptable," while examples 1 to 4 were rated as "good" or "passable." In other words, in examples 1 to 4, the change in the Zr content of the resulting alloy ingot relative to the consumable electrode was small, which is thought to have stabilized the equilibrium state in the slag-metal reaction. As a result, it is presumed that Zr was uniformly contained in the resulting alloy ingot.

Figure 5 shows the equilibrium diagram between the Z value and the A value. The straight line sloping upward to the right in the figure indicates A-Z = 1.0 at the top and A-Z = -1.0 at the bottom. The Z and A values of Examples 1 to 4 are plotted between these straight lines. In other words, (A-Z) was set within the range of -1.0 to 1.0.

Figure 6 also shows a diagram of the equilibrium between Z and T values. The straight line sloping upward to the right in the figure indicates T-Z = 2.5 at the top and T-Z = 0.5 at the bottom. The Z and T values of Examples 1 to 4 are plotted between these straight lines. In other words, (T-Z) was set within the range of 0.5 to 2.5.

In Examples 1 to 4, alloy ingots with uniformly distributed Zr could be produced, because the equilibrium state in the slag-metal reaction was stabilized. Based on Examples 1 to 4, the straight lines on the equilibrium diagram described above were determined as the range in which the metal-slag reaction can be stabilized. In other words, by setting the Z value, A value, and T value within the range between the straight lines described above, an alloy ingot with uniformly distributed Zr can be produced.

Although the representative embodiments of the present invention and modified examples based thereon have been described above, the present invention is not necessarily limited to these, and a person skilled in the art will be able to find various alternative embodiments and modified examples without departing from the spirit of the present invention or the scope of the appended claims.

Claims (1)

A method for producing a high Ni alloy ingot containing at least Al and Ti together with Zr by using an electroslag remelting (ESR) process to pass an electric current between a consumable electrode and a slag obtained by melting a flux , comprising:
The consumable electrode has an electrode diameter of 300 mm or more,
In mass percent,
Cr: 10-25%,
Al: 1 to 5%,
Ti: 1 to 4%,
Zr: 0.01 to 0.1%,
Co: 25% or less,
Mo: 5% or less,
W: 3% or less,
Fe: 5% or less,
Nb: 3% or less,
Mg: 0.1% or less,
B: 0.1% or less
The remainder of the composition is Ni and unavoidable impurities.
The flux comprises , in mass %,
CaO: 10-40%,
ZrO ₂ :0.01-2.0%,
Al ₂ O ₃ : 10-40%,
TiO ₂ :0.1-10%,
MgO: 5% or less,
_SiO2 : 3% or less,
The balance is _CaF2 ,
In the following formulas 1, 2, and 3, Z, A, and T are defined as follows:
A method for producing a Zr-containing high Ni alloy ingot, comprising adjusting the composition of the flux and the consumable electrode so that -1.0≦A−Z≦ 0 and 0.5≦T−Z≦2.5.

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