JP2581824B2 - Method for producing metal article and unidirectional solidification mold used for the method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel method for producing a unidirectionally solidified metal article and a unidirectionally solidified mold used therefor.

[Conventional technology]

Since a single crystal of a metal article has no grain boundaries, it is known to exhibit excellent characteristics not found in conventional ordinary cast products. One example is a single crystal of a Ni-based superalloy. Ni-base superalloys have excellent high-temperature properties, especially high-temperature creep strength, and have already been used as moving blades for aircraft jet engines.

Another example is a corrosion-resistant alloy such as stainless steel. Austenitic stainless steel and duplex stainless steel composed of ferrite and austenite are materials having high resistance to stress corrosion cracking. However, in order to further enhance stress corrosion cracking resistance, as disclosed in JP-A-62-180038, It is in a situation where a single crystal is to be used.

Most of the above single crystals are disclosed in JP-A-53-51102,
It is manufactured by the unidirectional solidification method described in JP-A-2-43777 and JP-A-60-44168. In this method, a mold is drawn downward from a heated furnace and gradually solidified upward from a lower end.

The rotor blades used in aviation jet engines have a length of 10
The cross-sectional area of the shank is about 10 cm ² at the cm level,
In addition, the projecting dimension of the platform that protrudes in the lateral direction of the main body is small, so that the whole is small, and a single crystal can be produced by unidirectionally solidifying a wing-shaped casting by the above method. In addition, materials with excellent corrosion resistance, such as stainless steel, have a single crystal shape of a simple round bar or flat plate,
When actually used, it is machined into a shape such as a bolt or a hook. Therefore, it was possible to produce a single crystal by unidirectionally solidifying the corrosion resistant alloy by the above method.

[Problems to be solved by the invention]

However, the above prior art does not consider a large article having a cross-sectional area of 15 cm ² or more, or an article having a portion that protrudes largely in the lateral direction with respect to the progress of solidification, and an article having a portion that protrudes greatly in the lateral direction. However, even when directional solidification is performed in the same manner as in the prior art, the entire casting cannot be single-crystallized. The reason is considered as follows. If there is a part that protrudes largely in the lateral direction, even if unidirectional solidification is performed, in the part that protrudes in the lateral direction, solidification also starts from the outer peripheral portion of the casting. Since the portion solidified from the outer peripheral portion is solidified irrespective of the casting main body, it has a crystal orientation different from that of the casting main body.
Therefore, when the solidification proceeds further and both crystals collide,
The surface becomes a crystal grain boundary, and a single crystal cannot be obtained.

For the above-mentioned reasons, it has not been possible to make a metal article such as a jig or a bolt having a portion protruding largely in the lateral direction entirely into a single crystal structure.

An object of the present invention is to provide a method for producing a single crystal metal article having excellent tensile strength, creep strength, or fatigue resistance to heat and stress, and a unidirectional solidification mold used for the production.

[Means for solving the problem]

The present invention provides a metal article having a different cross-sectional area in a cross section perpendicular to the solidification direction, particularly a cross-sectional area of 15 cm, by a manufacturing method described below and by using a unidirectional solidification mold.
^In a metal article in which a portion having a cross-sectional area larger than the cross-sectional area is integrally formed with at least two portions, at least the matrix structure of the metal article is a single crystal, and the portion having the large cross-sectional area is smaller than that. A solidified metal article can be obtained after the cross-sectional area.

The protruding taper angle of the portion having the large cross-sectional area is
10 degrees or less, the protrusion distance is 1 cm or more, the metal article is a Ni-based alloy or an austenitic steel containing Ni as a main component, and the γ phase is a single crystal, or a ferrite or austenitic steel. Preferably, the ferrite or austenite phase of the matrix is a single crystal.

The present invention relates to a bolt having a screw portion and a head, wherein the bolt is made of a Ni-based alloy or stainless steel, and is solidified in one direction from the screw portion toward the head, and the γ phase is a single crystal. Can be obtained.

The present invention provides a main mold in which a first mold is integrally formed with a second mold having a cross-sectional area larger than a cross-sectional area perpendicular to the solidification direction of the first mold; 2
And a bypass mold provided separately from the main mold in communication with the mold.

The present invention provides a main mold in which a second mold having a cross-sectional area larger than a cross-sectional area perpendicular to the solidification direction of the first mold is integrally formed in a first mold, A bypass mold communicating with a second mold and having a bypass mold separately provided for the main mold, placing the main mold and the bypass mold in a heating furnace and injecting a molten metal into the main mold and the bypass mold; Then, while the main mold and the bypass mold are heated and held in the heating furnace, the molten metal is gradually pulled out of the heating furnace and the molten metal is removed from the first mold by a second method.
A method of manufacturing a metal article, characterized by unidirectional solidification toward a mold.

[Action]

In the manufacturing method according to the present invention, since the casting body and the mold provided with a separate bypass are used to unidirectionally solidify together, the crystal orientation of the casting body and the cross-sectional area solidified through the bypass rapidly increase the projection portion. The crystal orientation matches, and the whole including the protrusions becomes a single crystal.

The high-strength metal article according to the present invention has a large complex shape having projections having a cross-sectional area larger than 15 cm ^{2 in} a portion having a cross-sectional area of 15 cm ² or more. The austenitic steel used in the present invention has higher strength than that in which a grain boundary exists.
≦ 0.15, Si ≦ 1.0, Mn ≦ 2.0, Cr: 15-25, Ni: 18-30, balance is
Fe, especially C <0.08, Si ≦ 1.0, Mn ≦ 2.0, C
r: 16 to 18.5, Ni: 9 to 15, Mo: 1 to 3 are good. Ferrite + austenitic steel is expressed in weight%, C ≦ 0.15, Si ≦ 1.0, Mn ≦ 2.
0, Cr: 15 to 25, Ni: 4 to 12, the balance being Fe.
The C content is preferably 0.001 to 0.02%.

The present invention adds Ti, Nb, Al, Zr, V, Ta, and W to these steels by 2% each.
Hereinafter, Mg and rare earth elements can be contained in an amount of 0.2% or less. For Ni-base superalloys, C0 to 0.16%, Si0 to 0.5% by weight
%, Mn0 ~ 1.4%, Cr5 ~ 30%, Co0 ~ 30%, Mo0 ~ 15%, W0 ~ 15
%, Ti + Al 1-10%, and the balance Ni. In addition, N
Each of b, Zr, V, Ta, and Hf can contain 5% or less, and Mg can contain a rare earth element of 0.2% or less.

The present invention relates to a method of melting and solidifying an austenitic, ferritic, or austenitic-ferritic stainless steel from one direction, or a homogenizing heat-treated austenitic or ferritic stainless steel having a single crystal structure. It is achieved by manufacturing components.
In this case, in the case of the stainless steel, melting is performed at a temperature of 1500 to
At 1650 ° C, vacuum of 3 × 10 ^-3 Torr or less or in an inert gas atmosphere, solidification from one direction is set in a mold heating furnace on a water-cooled chill, and the mold is heated to 1500-1650 ° C. After the molten stainless steel is cast into a mold at 1500-1650 ° C. and held for several minutes, the mold is gradually pulled out of the mold heating furnace. The atmosphere at this time is a vacuum of 2 × 10 ⁻³ Torr or less or in an inert gas, and the solidification speed is 1 to 50 cm / h. The subsequent homogenization treatment is performed at 1200-1350 ° C at least once, for example, 13 minutes.
It is carried out by a method of holding at 00 ° C. for 5 hours, then at 1100 ° C. for 1 hour in an argon gas atmosphere, and then quenching with water. After casting, the bypass portion is cut from the casting body.

〔Example〕

Example 1 FIG. 1 shows an M40 single crystal bolt made of an alloy having the composition (% by weight) shown in Table 1, and FIG. 2 shows an outline of a method of manufacturing the bolt using a mold of the present invention. It is shown.

In FIG. 2, first, a mold 2 according to the present invention is fixed on a water-cooled copper chill 1, which is set in a mold heater 3, and the mold 2 is heated to a temperature equal to or higher than the melting point of the cast alloy. Next, the melted alloy is cast into a mold 2, and then the water-cooled copper chill 1 is pulled downward and solidified in one direction. When unidirectionally solidified, many crystals are initially generated in the starter 4 at the lower end of the mold 2, but the selector 5 that rotates at 360 ° C. is squeezed into one crystal in the process of solidification to become a single crystal. Further, a large single crystal is formed in the enlarged portion 6 and solidification proceeds to the bolt screw portion 7 and the bolt head 8 of the casting. Table 2 shows the casting conditions. The selector 5 is obtained by bending or spiraling.

In the main mold 2, the portion forming the screw thread was directed downward, and the entire bolt was inclined by 15 ° with respect to the vertical axis. Then, the bottom end of the bolt head 8 and the position 20 mm below the bolt are
The connection was made with a 4 mm bypass mold 9.

Bypass 9 different from the mold part of the mold forming the casting body
The mounting position may be any position as long as it is above the selector 5 in the selector method, and above the seed crystal and below the position of the bolt head in the seeding method, but it is necessary to remove the bypass part after casting the single crystal. Therefore, the position of the casting main body above the selector 5 or the seed crystal, that is, the position of the enlarged portion 6 below the bolt screw portion 7 in FIG.

In the conventional method, another crystal is generated when the shape is enlarged at the bolt head 8, and a bolt-shaped single crystal cannot be manufactured. However, the bolt-shaped single crystal can be easily manufactured by the method of the present invention. did it.

The bolts obtained in this embodiment are used as bolts used for an upper lattice plate and a core support plate of a light water reactor.

In this embodiment, the screws are machined. It is preferable to perform annealing after processing.

Example 2 An eyebolt used for a light water reactor core support plate shown in FIG. 3 was cast by the same unidirectional solidification method as in Example 1. The casting conditions and alloy composition are the same as in Tables 1 and 2 of Example 1.

Four bypasses 9 are provided at 90 ° intervals between the enlarged portion 10 of the eyebolt and the enlarged portion 6 from the selector 5 to the eyebolt body 11. The shape of the bypass is a line with a diameter of 3 mm.

According to the method of the present invention, a single crystal was obtained without polycrystallization in the enlarged eyebolt portion 10.

The number of bypass molds 9 is preferably two or more, but usually about four is preferable in order to solidify from four sides. In this case, one body may be used, but in this case, as shown in the first embodiment, the main body is slightly tilted toward the side where the bypass mold is provided. It is necessary to connect to the lowermost part of the enlarged portion 10.

Example 3 6.5% Cr-4.3% Mo-7.3% W by weight as Ni-based alloy
A 10 mm thick T-shaped planar article was cast using -5.1% Al-7.3% Ta balance Ni. Conventionally, since a single crystal was not grown in the portion that protruded in the lateral direction, it was necessary to provide a taper angle 13 in the enlarged portion 12 as shown in FIG. FIG. 5 shows the relationship between the taper angle θ when the solidification rate is set to 10 cm / h and the distance of the overhang portion where the single crystal grows. When the taper angle θ is within about 10 °, the overhang distance in the lateral direction is small. If it is 1 cm or more, single crystals cannot be grown. By unidirectionally solidifying such a T-shaped casting 14 using the mold 2 shown in FIG. 6 under the same conditions as in Table 2,
A single crystal could be grown without giving a taper angle. A specific example of such a product is a jet engine blade shown in FIG. 7, which solidifies in one direction from the wing portion 15 and provides a bypass mold for the platform 16 to provide a wing portion of the platform 16. A single crystal blade can be produced by solidifying simultaneously from the side and the outside, and then solidifying into a shank 7 and a dovetail 8.

Example 4 By weight, C 0.08% or less, Cr 14-20%, Fe 10% or less, Al 0.4
As an example of an alloy having an alloy composition of 1.0% to 1.0%, Ti2 to 3%, Nb 0.5 to 1.5%, and the balance Ni, C0.02%, Cr15.6%, Fe
A bolt used in a reactor core was manufactured by the method shown in Example 1 consisting of 8.0%, 2.5% of Ti, 0.8% of Al, 1.0% of Nb, 0.3% of Cu and the balance of Ni. The structure as cast has a large eutectic γ '
Although a phase is formed, this is carried out at 1,200 to 1,350 ° C × 2 to 10
h to form a single crystal gamma phase, then 650-750
By aging at ℃, fine γ 'phase was precipitated and strengthened. The one according to the present example is excellent in stress corrosion cracking resistance, has a 0.2% proof stress of 70 kg / mm ² or more, and has an elongation of 20% or more.

In the present embodiment, the screw is formed by machining, but it is preferable to obtain the screw by casting, since no residual stress is formed on the surface. After processing, it is preferable to perform annealing.

〔The invention's effect〕

According to the present invention, the crystal orientation of the overhang portion in the transverse direction to the solidification progress direction can be made the same as the crystal orientation of the casting body, so that a large single crystal metal article can be efficiently manufactured. it can.

Further, the unidirectionally solidified metal article obtained by the present invention can be used for high-strength bolts and the like, and has improved strength.

Further, according to the method for manufacturing a cast product according to the present invention, it is easy to single crystallize a member having a complicated shape which cannot be manufactured by the conventional casting method. In that case, the casting material is iron, cobalt,
All dissolvable materials such as stainless steel, aluminum and copper can be applied.

[Brief description of the drawings]

FIG. 1 is a plan view of a single crystal bolt according to the present invention, FIG. 2 is a sectional view of a mold showing a method of manufacturing the bolt of FIG. 1, and FIG. FIG. 4, FIG. 4 is a front view of a T-shaped metal article, FIG. 5 is a view showing the relationship between the tapered surface, overhang distance, and crystal structure, and FIG. 6 is a mold showing a method of casting the T-shaped metal article. FIG. 7 is a perspective view of a jet engine blade. 2 Main mold, 8 Bolt head, 9 Bypass mold, 10 Eyebolt enlargement.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshi Saito 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratory, Ltd. In the laboratory (56) References JP-A-62-180029 (JP, A) JP-A-62-180037 (JP, A) JP-A-62-180038 (JP, A) JP-A-59-85360 (JP, A) JP-A-59-207895 (JP, A) JP-A-59-54695 (JP, A)

Claims (2)

(57) [Claims] 1. A main mold in which a first mold is integrally formed with a second mold having a cross-sectional area larger than a cross-sectional area perpendicular to the solidification direction of the first mold; and the first mold. And a bypass mold which is provided separately from the main mold in communication with the second mold.The main mold and the bypass mold are set in a heating furnace, and the molten metal of the metal is poured into the main mold and the bypass mold. The molten metal is poured into the first mold by gradually pouring the main mold and the bypass mold from the heating furnace while heating and holding the main mold and the bypass mold in the heating furnace.
A method for producing a metal article, comprising: unidirectionally solidifying from a first mold toward a second mold. 2. A main mold comprising a first mold integrally formed with a second mold having a cross-sectional area larger than a cross-sectional area perpendicular to the solidification direction of the first mold; and the first mold. A unidirectional solidification mold, comprising: a bypass mold communicating with the second mold and separately provided with respect to the main mold.