JP6358503B2 - Consumable electrode manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a consumable electrode used in secondary melting such as electroslag remelting or vacuum arc remelting, and in particular, to obtain a super heat resistant alloy having a specific component composition that easily precipitates grain boundary carbides. It is related with the manufacturing method of the consumable electrode for this.

  In general, super-heat-resistant alloys, which are high alloys, are prone to segregation during the melting and solidification process, and are compared by secondary melting such as electroslag remelting (ESR) or vacuum arc remelting (VAR). A homogeneous ingot is obtained. Here, the consumable electrode used for the secondary melting is suspended on the cooling mold and is continuously melted by resistance heating from the lower end thereof by flowing a large current. If such melting cannot be controlled so as to be stable and continuous, a homogeneous ingot cannot be obtained.

  For example, in Patent Document 1, in secondary melting of a super-heat-resistant alloy having a component composition containing Nb and / or Ti, an ingot that is unstable due to cracking of a consumable electrode and small pieces due to this cracking remain undissolved. Discloses a method of manufacturing a consumable electrode for preventing the residual electrode from remaining on the substrate. In Fe-Ni-Cr-based super heat-resistant alloys such as Inconel (registered trademark) 718, A286, and V57, it is known that Laves phases and carbides precipitate at crystal grain boundaries and embrittle them. . Also in the consumable electrode, particularly when the Laves phase is precipitated or crystallized at the crystal grain boundary, cracking is likely to occur during secondary melting starting from this. In other words, at the time of secondary melting, a large temperature gradient is generated at the tip of the consumable electrode, and therefore, a grain boundary crack occurs starting from a brittle grain boundary due to thermal stress, and if this propagates along the grain boundary, it becomes a large crack. It reaches. Therefore, in the production of the consumable electrode, soaking is performed at a temperature that is not higher than the melting point and that can dissolve the Laves phase.

Further, in Patent Document 2, in secondary melting of a super heat-resistant alloy having a composition containing Al and Ti, similarly to Patent Document 1, unstable melting resulting from cracking of a consumable electrode and dropping of the fragments into an ingot is performed. On the other hand, a method for producing a consumable electrode is disclosed in which heat treatment for solution of non-metallic inclusions is performed on the forged material, and then the structure is adjusted by oil cooling or water cooling. For super heat-resistant alloys such as Fe—Ni—Cr group, Ni—Cr group, Ni—Cr—Co group, or Co group containing a predetermined amount or more of Al + Ti, soaking (solution heat treatment) as disclosed in Patent Document 1 ) Alone is not sufficient to obtain a homogeneous ingot, forging the consumable electrode to improve toughness, and further adjusting the structure so that the hardness does not become too high by oil cooling or water cooling after heat treatment In particular, the precipitation of Ni ₃ (Al, Ti) should be prevented.

  Further, in Patent Document 3, in a γ ′ precipitation hardening type Ni-base superalloy such as Inconel (registered trademark) 718, in order to prevent partial loss of the consumable electrode, in a temperature range lower than the solution temperature. A method for manufacturing a consumable electrode is disclosed in which soaking treatment should be performed in an overaged state. The soaking process is performed for 10 hours or more in the γ ′ precipitation temperature range of 700 to 950 ° C., and the hardness is reduced as an overaged state, thereby reducing the embrittlement phase and preventing the partial loss of the consumable electrode. Yes.

JP-A-9-241767 JP 2000-109940 A JP 2009-97073 A

  By the way, with respect to a novel Ni-based superalloy for adjusting the balance between the precipitation amount of γ ′ and the hot workability by the contents of Nb, Al, and Ti, the same as in Inconel (registered trademark) 718 and the like described above. When trying to apply the manufacturing method, the consumable electrode is likely to be cracked particularly during secondary melting.

  The present invention has been made in view of the situation as described above, and an object thereof is to obtain a homogeneous ingot in secondary melting of a Ni-base superalloy having a predetermined component composition. The object is to provide a method for manufacturing a consumable electrode.

  The present inventors have at least mass%, Nb: 0.3% to less than 2.0%, Al: more than 3.00% to less than 6.50%, Ti: 0.20% to 2.49. Ni-based ultra-compact that contains less than 1%, Ti content is reduced while Al content is increased to ensure the same amount of precipitation of γ 'as before, achieving both hot forging processability and high-temperature strength characteristics. A heat-resistant alloy was developed. Here, when the cracking and missing of the consumable electrode during the secondary dissolution were investigated, it was observed that it was not caused by the precipitation of an intermetallic compound such as Laves phase like Inconel (registered trademark) 718. One of the causes is that such a Ni-based superalloy has been given a component composition design so as to suppress the precipitation of Laves phase, but the cause of cracking of the consumable electrode during secondary melting is mainly This is due to coarse carbides precipitated at the grain boundaries. That is, it is considered that the carbide precipitated in the primary melting is preferentially melted in the secondary melting, and cracks are generated and missing from this.

  Therefore, the manufacturing method of the consumable electrode according to the present invention is, in mass%, C: more than 0.001% to less than 0.100%, Cr: 11.0% to less than 19.0%, Co: 0.5% Or more to less than 22.0%, Fe: 0.5% or more to less than 10.0%, Si: less than 0.1%, Mo: more than 2.0% to less than 5.0%, W: 1.0% Excessive to less than 5.0%, Mo + 1 / 2W: 2.5% to less than 5.5%, S: 0.010% or less, Nb: 0.3% to less than 2.0%, Al: 3. More than 00% to less than 6.50%, Ti: 0.20% or more to less than 2.49%, balance Ni and inevitable impurities, and in atomic%, Ti / Al × 10: 0.2 or more Consumable electrode manufacturing method for providing a secondary melting ingot having a composition of less than 4.0 and Al + Ti + Nb: 8.5% to less than 13.0% A heat treatment step of furnace-cooling the primary melting bulk material having the above-described component composition at a cooling rate that suppresses precipitation of grain boundary carbides so as to have a hardness of 360 HV or less after heating to a temperature at which carbides can be dissolved. It is characterized by including.

  According to this invention, it is possible to manufacture a consumable electrode that suppresses the precipitation of carbides at grain boundaries and does not easily cause cracking or missing in secondary melting, that is, a consumable electrode for obtaining a homogeneous ingot by secondary melting. .

  In the above-described invention, the cooling rate may be 80 ° C./hr or less. According to this invention, the hardness of the consumable electrode can be reliably set to 360 HV or less, and precipitation of carbides at grain boundaries can be suppressed.

It is a flowchart of the manufacturing method by this invention. It is a figure which shows the component composition of the object alloy in the manufacturing method of this invention. It is the structure | tissue photograph after the heat processing of the object alloy in the manufacturing method of this invention. It is the structure | tissue photograph after the heat processing as a comparative example. It is a cross-sectional structure | tissue photograph as another comparative example.

  First, a method of manufacturing a consumable electrode according to one embodiment of the present invention will be described in detail along FIG. 1 with reference to FIG.

  Referring to FIG. 1 together with FIG. 2, first, Ti / Al × 10 = 0.2 or more and less than 4.0 in the range of the component composition shown in FIG. 2 and Al + Ti + Nb = 8.5%. In order to obtain a secondary melting ingot having a component composition satisfying the above range of less than 13.0%, an alloy primary melting bulk material having the same component composition is obtained (S1). Such a bulk material may be formed into a consumable electrode shape by casting, but may be subjected to processing such as forging as necessary. Here, the Example which each manufactured within the range of the component composition shown to the target value A and the target value B is shown.

  Next, the bulk material is subjected to heat treatment (S2). In this heat treatment, in order to dissolve the carbide, for example, it is heated to 1200 ° C. and held for 3 hours (S3), and then cooled in the furnace (S4). In the furnace cooling, the cooling rate is set to 80 ° C./hr or less, preferably 50 ° C./hr or less so as to suppress the precipitation of carbides on the grain boundaries. The consumable electrode obtained by such cooling can suppress the precipitation of carbides and can obtain a structure having a hardness of 360 HV or less.

  As described above, according to the consumable electrode in which the precipitation of carbide is suppressed, in the Ni-base superalloy having a specific component composition, cracking of the consumable electrode and its lack in secondary melting can be suppressed, and a homogeneous ingot can be obtained. You can get it.

  Next, the results of investigating the relationship between the heat treatment conditions and the precipitation state of carbides using the Ni-base superalloy having the component composition described above will be described with reference to FIGS.

  About the alloy of the component composition shown to the target value A of FIG. 2, several test pieces were created, the heat processing was changed, the heat processing was performed, and the microstructure was observed.

  As shown in FIG. 3, when air cooling (AC) is performed from isothermal holding at 1180 ° C. × 3 hr and 1200 ° C. × 3 hr, precipitation of carbides is observed at the grain boundaries. On the other hand, when cooling at 50 ° C./hr, imitating furnace cooling (FC), it can be seen that precipitation of carbides at the grain boundaries is suppressed as compared with the case of air cooling.

  In addition, the hardness was 385 HV and 396 HV in the order of isothermal holding at 1180 ° C. × 3 hr and 1200 ° C. × 3 hr, respectively, while the hardness was 385 HV and 396 HV in air cooling, and 349 HV in cooling at a cooling rate of 50 ° C./hr. The hardness was 319 HV. That is, the hardness is reduced by furnace cooling compared to air cooling, and is 360 HV or less.

  Here, precipitation of carbides at grain boundaries could be suppressed by air cooling at 50 ° C./hr, but it passed through the precipitation temperature region of γ ′ at a slower cooling rate than air cooling, and γ ′ was also precipitated. It is thought that there is. However, since the hardness at least at room temperature is low due to furnace cooling, it can be said that the amount of precipitated carbide is dominant in the hardness at room temperature.

  Furthermore, several additional tests were conducted, and it was confirmed that precipitation of carbides at grain boundaries could be suppressed in the same manner as described above by setting the cooling rate to 80 ° C./hr or less.

  Further, the alloy having the component composition indicated by the target value B in FIG. 2 was also tested, and it was confirmed that the precipitation of carbides at the grain boundaries could be similarly suppressed by setting the cooling rate to 80 ° C./hr or less.

  Furthermore, as shown in FIG. 4, as a comparative example, a test piece of Inconel (registered trademark) 718 was subjected to a heat treatment that was air-cooled after being kept isothermal at 1160 ° C. × 6.5 hr, and the structure was observed. Precipitation of carbides at the grain boundaries is hardly observed, and it can be seen that the behavior of the alloy having the component composition shown in FIG. 2 is different. That is, the alloy having the component composition shown in FIG. 2 causes grain boundary carbides to precipitate in the heat treatment in which air cooling is performed after heating and holding in the same manner as Inconel (registered trademark) 718, so that the furnace cooling is performed after solidifying the carbides. To suppress the precipitation of carbides.

  As shown in FIG. 5, as another comparative example, the microstructure of the lower end portion of the electrode when the secondary melting was performed on the consumable electrode obtained by air-cooling the alloy of FIG. 2 after heat treatment was investigated. The microstructure was obtained by interrupting secondary dissolution and observing the cross-sectional structure near the surface layer at the lower end of the consumable electrode. According to this, at the tip of the consumable electrode, it was observed that the vicinity of the grain boundary eluted preferentially during secondary dissolution. In other words, it is considered that the grain boundary carbide is preferentially melted, and starting from the elution part near the grain boundary, the grain boundary cracking occurs due to the thermal stress due to the temperature gradient during secondary melting, Propagation along the grain boundary is thought to lead to large cracks and missing electrodes. In the above-described embodiments, precipitation of grain boundary carbides that preferentially melt is suppressed, so that such elution near the grain boundary does not occur.

  In addition, the alloy made into object by this invention is the mass%, C: more than 0.001%-less than 0.100%, Cr: 11.0% or more-less than 19.0%, Co: 0.5% or more ~ 22.0%, Fe: 0.5% or more to less than 10.0%, Si: less than 0.1%, Mo: more than 2.0% to less than 5.0%, W: more than 1.0% -5.0% or less, Mo + 1 / 2W: 2.5% or more to less than 5.5%, S: 0.010% or less, Nb: 0.3% or more to less than 2.0%, Al: 3.00 More than% to less than 6.50%, Ti: 0.20% or more to less than 2.49%, balance Ni and inevitable impurities, and in atomic%, Ti / Al × 10: 0.2 or more to 4 Less than 0.0, Al + Ti + Nb: 8.5% or more and less than 13.0%. Such an alloy, for example, compared with Inconel (registered trademark) 718, increases the precipitation amount of γ ′ and improves the high-temperature mechanical strength at 700 ° C. or higher, while preventing an increase in the solid solution temperature of γ ′. It was developed in consideration of maintaining inter-workability.

  In addition, the above-described alloy targeted by the present invention is, as an optional additive element, in mass%, B: 0.0001% to less than 0.03%, Zr: 0.0001% to less than 0.1%, Mg: 0.0001% or more and less than 0.030%, Ca: 0.0001% or more and less than 0.030%, REM: 0.0001% or more and 0.200% or less. : Less than 0.020%, N: less than 0.020%.

  So far, representative examples and modified examples based on the examples have been described, but the present invention is not necessarily limited thereto. Those skilled in the art will recognize a variety of alternative embodiments without departing from the scope of the appended claims.

Claims (2)

% By mass
C: more than 0.001% to less than 0.100%,
Cr: 11.0% or more to less than 19.0%,
Co: 0.5% or more to less than 22.0%,
Fe: 0.5% to less than 10.0%,
Si: less than 0.1%,
Mo: more than 2.0% to less than 5.0%,
W: more than 1.0% to less than 5.0%,
Mo + 1 / 2W: 2.5% to less than 5.5%,
S: 0.010% or less,
Nb: 0.3% or more and less than 2.0%,
Al: more than 3.00% to less than 6.50%,
Ti: 0.20% or more to less than 2.49%,
It consists of the balance Ni and inevitable impurities, and in atomic%,
Ti / Al × 10: 0.2 or more and less than 4.0,
A method for producing a consumable electrode for providing a secondary dissolution ingot having a composition that satisfies Al + Ti + Nb: 8.5% to less than 13.0%,
The primary melting bulk material having the above component composition includes a heat treatment step of furnace cooling at a cooling rate in which precipitation of grain boundary carbides is suppressed so that the hardness is 360 HV or less after heating to a temperature at which carbides can be dissolved. A method for producing a consumable electrode.   The method for manufacturing a consumable electrode according to claim 1, wherein the cooling rate is 80 ° C./hr or less.