JP2000144273A - Consumable electrode type re-melting method for super heat resistant alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method by which the development of spot-like segregation is prevented, cracks of a consumable electrode to cause inclusion of a non-metallic impurities are prevented, and a cast ingot free from any spot-like segregation or non-metallic impurities is stably manufactured in a consumable electrode type re-melting method of a super heat resistant alloy such as precipitation hardening type alloy. SOLUTION: In this consumable electrode type re-melting method of a super heat resistant alloy, a molten consumable electrode material is cast in a mold for columnar cast ingot, the ingot is drawn from the mold before a part from its outer diameter to the point of 1/3 of the diameter is solidified, charged in a furnace which is pre-heated at the temperature between the solid phase temperature and the temperature lower than the solid phase temperature by 500 deg.C, and held in the furnace for at least one hour to manufacture a consumable electrode for service.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a consumable electrode type remelting method for a super-heat-resistant alloy such as a precipitation hardening type.

[0002]

2. Description of the Related Art A super-heat-resistant alloy such as a precipitation hardening alloy is manufactured by melting and casting in a vacuum induction furnace or the like, and is used as a consumable electrode. The electroslag remelting method (hereinafter, referred to as "ESR"), vacuum arc. It is manufactured by melting and solidifying by a consumable electrode type remelting method such as a remelting method (hereinafter referred to as “VAR”). When a super heat-resistant alloy, particularly a precipitation hardening type, is produced by this production method, spot-like segregation may occur in the ingot, and in some cases, large nonmetallic inclusions may be contained. Forging an ingot containing this spot-like segregation or large non-metallic inclusions, there is a problem that cracks originating from the spot-like segregation and non-metallic inclusions may occur.

[0003] This spot-shaped segregation has cracks (formed during casting and remelting) inside the consumable electrode, so that the melting rate (M / R) becomes non-uniform during remelting (due to cracking). This is because heat conduction deteriorates, so that the part dissolving from the crack has a higher dissolution rate, and the part behind the crack has a lower dissolution rate.) The nonmetallic inclusions are presumed to be due to the fact that the consumable electrode is broken at the time of ESR melting and fragments are chipped off, and the fragments are solidified in a state involving slag.

The fact that the spot-like segregation is due to the non-uniform dissolution rate at the time of re-melting is that, when the ingot is cut in a portion where the dissolution rate becomes non-uniform, spot-shaped segregation occurs on the cross section. Confirmed by its existence. Also,
The cracks of the consumable electrode causing the non-metallic inclusions in the ESR are caused by a bursting sound of the consumable electrode exploding during remelting, a dissolution amount per hour of the consumable electrode, that is, a dissolution rate (M / R), When observing resistance, current, etc.,
It has been confirmed that the M / R suddenly increased and then became extremely small, and that the consumable electrode was cracked and chipped off due to changes in electric resistance and current.

[0005] As a method for preventing cracks of the consumable electrode causing entrainment of the non-metallic inclusions and stably producing an ingot having no abnormal structure, the consumable electrode is preheated before remelting. A method of dissolving a brittle Laves phase in a matrix is disclosed in JP-A-9-241767. However, even if the consumable electrode is preliminarily soaked and redissolved, the cracking cannot be sufficiently prevented, and the soaking heat treatment has a disadvantage that the consumable electrode needs to be maintained at a high temperature for a long time. . Further, even if the soaking treatment is performed, cracks generated during casting before the soaking treatment cannot be eliminated, so that spot-like segregation caused by the cracks cannot be prevented.

[0006]

SUMMARY OF THE INVENTION The present invention prevents the formation of spot-like segregation and causes entrapment of nonmetallic inclusions in a consumable electrode type remelting method of a super-heat-resistant alloy such as a precipitation hardening type. An object of the present invention is to provide a method for preventing cracks of a consumable electrode and stably producing an ingot without spot-like segregation and nonmetallic inclusions.

[0007]

Means for Solving the Problems In order to solve the above problems, the present inventor focused on casting at the time of producing a consumable electrode made of a super heat resistant alloy, and studied the cooling rate after casting. After casting the consumable electrode material, placing it in a furnace heated from a semi-solidified state, holding it for a certain period of time, and then cooling the furnace, we obtained the knowledge that the Laves phase decreased compared to ordinary cooled material, and obtained this finding. The present invention has been made based on the finding that the M / R at the time of re-dissolution of the consumable electrode manufactured as described above becomes uniform and no spot-like segregation occurs.

That is, in the consumable electrode type remelting method of a super-heat-resistant alloy such as a precipitation hardening type of the present invention, in the consumable electrode type re-melting method of a super-heat-resistant alloy, the melted consumable electrode material is cast into a cylindrical or conical shape. Cast into a lump mold and measure 1
Solidified to 1/3 of the diameter (solidifying from the outer periphery to the center to 1/3 of the diameter, solidifying from the entire periphery, 2% of the diameter on both sides
Before solidifying), the consumable electrode material is charged into a furnace which has been preheated to a temperature between the solid phase temperature and 500 ° C. lower than the solid phase temperature, After holding for 1 hour or more, cooling and using the electrode as a consumable electrode.

[0009]

Next, the present invention will be described in detail.
The present invention will be described with reference to FIG. 1. A super-heat-resistant alloy such as a precipitation hardening type is melted in a vacuum high-frequency furnace or the like, and cast into a cylindrical or conical ingot mold in a vacuum. /
3 is solidified (about 15 to 30 minutes after the completion of casting), and the die is cut out. The temperature between the solid phase temperature of the consumable electrode material and 500 ° C. lower than the solid phase temperature (for example, 810) ~ 9
00 ° C) in a held furnace for more than 1 hour, for example about 6
After holding for about 9 hours, the power of the furnace is then turned off and the furnace is cooled to room temperature (for example, at a cooling rate of about 4 to 10 ° C / hr) or cooled to about 400 to 600 ° C. This is a consumable electrode-type remelting method of a super heat-resistant alloy in which a product prepared by taking out and allowing it to cool by cooling is used as a consumable electrode.

In the consumable electrode type remelting method of the present invention, the super heat-resistant alloy is 0.10% or less, Si: 1.00% or less, Mn: 1.50% or less by weight (the same applies hereinafter). , N
i: 25.0-78.0%, Cr: 12.00-25.
0%, if necessary, Al + Ti: 1.3% or more, Nb
+ Ta: 5.8% or less and B: 0.01% or less, containing one or more kinds, and if necessary, Mo: 3.5.
% Or less, W: 3.5% or less, containing one or two kinds, and the balance is Fe and precipitation hardening type F or the like inevitable impurities.
e-Ni-Cr-based alloy, Cr: 18.0 to 21.0%,
Co: 2.0% or less, Fe: 5.0% or less, Ti: 1.
8 to 2.7%, AI: 0.5 to 1.8%, the balance being Ni and a precipitation hardening type Ni-Cr base alloy which is an unavoidable impurity, C: 0.030% or less, Ni: 53.6 to 54.9
%, Cr: 15.0 to 19.0%, Co: 12.0 to 1
8.5%, Mo: 3.0 to 6.0%, Al: 2.0 to
4.3%, Ti: 2.9-5.0%, B: 0.005-
0.030%, W: 1.5% or less, Zr: 0.05% or less, precipitation hardening type Ni—Cr─Co-based alloy, Co
Base alloy.

Specifically, JIS NCF718, NC
F750, NCF751 and NCF80A, A-28
6, Discaioy, V-57, Incoloy90
1, Nimonic80, InconelX750, U
dimet 500 to 710, Nivco, and the like.

The consumable electrode type remelting method in the consumable electrode type remelting method of the precipitation hardening type super-heat-resistant alloy of the present invention includes the above-mentioned ESR and VAR, and plasma arc remelting method. Further, the solid phase temperature of the above-mentioned material varies depending on its component composition, but is about 1250-1400 ° C., and the temperature 500 ° C. lower than the solid phase temperature is about 800-900 ° C.
It is about.

In the present invention, the mold is removed from the mold before solidification from the outer periphery to 1/3 of the diameter, and then the pre-heated solid is heated to a temperature between the solid phase temperature and 500 ° C. lower than the solid phase temperature. The mold was removed from the mold before one-third of its diameter was solidified, because the Laves phase of each part was cooled after casting and gradually cooled. As shown in FIG. 2, the area ratio of the Laves phase was gradually reduced as compared with that of the naturally cooled one, and one third of the diameter was solidified before solidification. This is because if the mold is cut out and then cooled slowly, the area ratio of the Laves phase can be reduced. As shown in FIG. 2, it is preferable that the mold be removed from the mold as soon as possible. However, since strength is required to perform the mold removal, specifically, a state in which the periphery is solidified by about 50 mm. It has been since.

[0014]

According to the present invention, the mold is removed from the mold before solidification to 1/3 of the diameter from the outer periphery (solidification to 2/3 of the diameter on both sides), and the consumable electrode is subjected to its solid phase temperature and solid phase temperature. More than 50
After holding for 1 hour or more, preferably for 4 hours or more, more preferably for 6 hours or more in a furnace maintained at a temperature between 0 ° C. lower and, for example, 810 to 900 ° C., the solution is cooled, Fluctuation in dissolution rate and dropout of the electrode can be suppressed or prevented. The reason for this is that when the treatment is performed as described above, the crystallization of the Laves phase, which is the embrittlement phase, is reduced, the cracks due to shrinkage during solidification of the consumable electrode, and the thermal stress are alleviated. The cracks inside the consumable electrode do not occur due to the thermal stress at the time of solidification of the consumable electrode and the thermal stress at the time of re-melting, which are the starting points of cracking. It is presumed that there is no).

[0015]

Next, an embodiment of a consumable electrode type remelting method for a super heat-resistant alloy according to the present invention will be described. Examples Consumable electrode materials (solid phase temperature 12
60 ° C.) in a vacuum high-frequency induction furnace, and poured the molten metal into a mold having a size of about φ380 mm × 2400 mm in vacuum, and removed the mold from the vacuum vessel about 1.8 minutes after the casting was completed. . At this time, the temperature of the top of the consumable electrode is 12
70 ° C. After that, about 1/7 of the diameter from the outer circumference solidifies (about 15 minutes after the casting is completed, the circumference solidifies about 50 mm), and then pushes out the consumable electrode from the mold (the surface temperature of the top of the consumable electrode is 980 ° C., Surface temperature 900
6 minutes later, the sample was placed in a furnace heated to 843 ° C. (the temperature of the top of the consumable electrode was 975 ° C. and the temperature of the bottom was 997 ° C.).

[0016]

[Table 1]

The temperature of the furnace rose to a maximum of 873 ° C. due to the high temperature of the consumable electrode.
When the temperature reached 3 ° C., the power of the furnace was turned off after 8.3 hours, and the furnace was cooled (6.5 ° C./hr). When the temperature reached 496 ° C. after 62.05 hours, it was carried out of the furnace and allowed to cool. The consumable electrode was melted and solidified by the VAR method to obtain an ingot having a diameter of 440 mm. During this re-dissolution, a variation in dissolution rate of about 5%
There were times. A section of the ingot where the M / R fluctuated was cut and its cross section was observed, but no spot-like segregation was observed.

Comparative Example As a comparative example, a consumable electrode material having the same composition as that of the above-described embodiment was melted in the same furnace, and the molten metal was poured into the same mold at the same temperature in a vacuum. A minute later, the mold was taken out of the vacuum vessel, and 90 minutes after the completion of casting, the consumable electrode was thrust up and taken out of the mold, and allowed to cool to room temperature.

This consumable electrode was subjected to V under the same conditions as in the above embodiment.
An ingot of almost the same size as that of the above example was obtained by the AR method. During this re-dissolution, the dissolution rate fluctuated by 20% or more six times. When one of the portions of the ingot where the M / R fluctuated was cut and the cross section thereof was observed, spot-like segregation was observed.

[0020]

According to the consumable electrode type remelting method for a super heat-resistant alloy of the present invention, the consumable electrode is not cracked during remelting and the ingot without spot-like segregation is stabilized by the above-mentioned structure. This has an excellent effect that it can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a relationship between a cooling temperature and a time after casting of a consumable electrode used in a consumable electrode type remelting method of a super heat resistant alloy of the present invention.

FIG. 2 is a graph showing the relationship between each part and the Laves phase area ratio of a consumable electrode made of a super-heat-resistant alloy, which was left to cool after casting and was gradually cooled.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22B 9/20

Claims (2)

[Claims] 1. In a consumable electrode type remelting method for a super heat-resistant alloy, a melted consumable electrode material is cast into a mold, and a die is cut before solidifying from the outer circumference to 1/3 of the diameter. Characterized in that it is charged into a furnace preheated to a temperature between the solidus temperature and 500 ° C lower than the solidus temperature, held for at least one hour, and used as a consumable electrode. Consumable electrode type remelting method for super heat resistant alloys. 2. The consumable electrode type remelting method for a super heat resistant alloy according to claim 1, wherein said super heat resistant alloy is a precipitation hardening type super heat resistant alloy.