EP3520916A1

EP3520916A1 - HOT EXTRUSION-MOLDING METHOD FOR Ni-BASED SUPER HEAT-RESISTANT ALLOY AND PRODUCTION METHOD FOR Ni-BASED SUPER HEAT-RESISTANT ALLOY EXTRUSION MATERIAL

Info

Publication number: EP3520916A1
Application number: EP17855498.6A
Authority: EP
Inventors: Remi MUKOSE; Gang Han
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2016-09-29
Filing date: 2017-08-23
Publication date: 2019-08-07
Also published as: US20200030863A1; EP3520916A4; WO2018061540A1; CN109789458A; JP6631896B2; JPWO2018061540A1

Abstract

Provided are: a hot extrusion-molding method for a precipitation strengthened-type Ni-based super heat-resistant alloy; and a production method for a Ni-based super heat-resistant alloy extrusion material. The hot extrusion-molding method is for a Ni-based super heat-resistant alloy, wherein: a billet has a component composition for a precipitation strengthened-type Ni-based super heat-resistant alloy which has a gamma prime phase equilibrium precipitation amount of 40 mol% or more at 700°C; a lubrication glass pad is installed between a die and the billet; and an adjustment is made such that the relationship between the outer diameter DB (mm) of the billet at the time of being inserted in a container and the inner diameter DC (mm) of the container satisfies the condition, (DC-DB): 2-8 mm, or an adjustment is made such that the relationship between the outer diameter DB' (mm) of the billet prior to being heated to a hot processing temperature and the inner diameter DC' (mm) of the container prior to being heated to a preheating temperature satisfies the condition, (DC'-DB'): 3-9 mm. The production method for a Ni-based super heat-resistant alloy extrusion material is performed using the hot extrusion-molding method mentioned above.

Description

TECHNICAL FIELD

The present invention relates to a method for hot-extruding a precipitation-strengthening type super heat-resistant Ni-based alloy, and a method for manufacturing an extruded material of the Ni-based alloy.

BACKGROUND ART

Extrusion-molding is a hot process including heating a billet at a hot-working temperature, inserting a billet heated at the hot-working temperature into a container, and applying a compressive force to the billet to extrude the billet through a hole of a dice to produce an extruded material.. FIG. 2 is a schematic view illustrating an example of a cross-sectional structure of an extruding apparatus. First, a billet 1 heated at a hot-working temperature is inserted into a container 2 In FIG. 2. Next, a compressive force is applied to the billet 1 inserted in the container 2 by a stem 4 via a dummy block 3. The applied compressive force causes the billet 1 to be extruded from a hole of a dice 5 located at the container 2 to produce an extruded material 6, so that the extruded material 6 has a cross-section having a shape of the hole of the dice 5.
Among various kinds of extrusion methods, so called "direct extrusion" is a basic method since a pressing machine is most simple. In the direct extrusion, a compressive force is applied to a billet from one end of a container into which the billet has been inserted and the billet is extruded from a dice hole at the other end of the container. In the direct extrusion, lubrication between the billet and the container is important. Thus, it has been proposed to coat a glass lubricant over a billet before the billet is inserted into a container ("lubricant-coating direct extrusion") (see Patent Literature 1). It has been also proposed, for improving lubrication between the billet and the dice, that a lubricating glass pad is attached between the billet and the dice ("glass lubricating extrusion") (see Patent Literature 2).

CITATION LIST

PATENT LITERATURE

PATENT LITERATURE 1: JP 06-269844 A
PATENT LITERATURE 2: JP 07-136710 A

SUMMARY OF INVENTION

In recent years, repairing or three-dimensional shaping of various kinds of heat-resistant components has been required and thus wires made of super heat-resistant Ni-based alloys have been demanded. Among the super heat-resistant Ni-based alloys, a precipitation strengthening type Ni-based alloy has excellent high-temperature strength. However, this type of the Ni-based alloy having a special composition has less hot-workability and thus it has been very difficult to produce a wire of the Ni-based alloy through extrusion.
An object of the present invention is to provide a method for hot-extruding a precipitation-strengthening type super heat-resistant Ni-based alloy, and a method for manufacturing an extruded material of the Ni-based alloy.
According to the present invention, provided is a method including: heating a billet at a hot-working temperature; inserting the billet heated at the hot-working temperature into a container; and applying a compressive force to the billet in the container to extrude the billet from a hole of a dice located at the container. The method is performed by direct extrusion. That is, the compressive force is applied to the billet from one end of the container, and the billet is extruded from the dice hole at the other end of the container. The method is performed by glass lubricating extrusion. That is, a lubricating glass pad is attached between the dice and the billet. The billet has a composition of a precipitation strengthening type Ni-based super heat-resistant alloy wherein an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol %. An outer diameter D_B (mm) of the billet and an inner diameter D_C (mm) of the container when the billet is inserted into the container are adjusted to satisfy a relationship: (D_C - D_B) = 2 to 8 mm. Alternatively, an outer diameter D_B' (mm) of the billet before heated at the hot-working temperature and an inner diameter D_C' (mm) of the container before heated at a preheating temperature are adjusted to satisfy a relationship: (D_C' - D_B') = 3 to 9 mm.
Preferably, the inner diameter D_C (mm) of the container is 60 to 180 mm. Preferably, the inner diameter D_C' (mm) of the container is 60 to 180 mm. In addition, it is preferable that the hot-working temperature is 1150 to 1180°C.
Also, provided is a method for manufacturing an extruded material made of a super heat-resistant Ni-based alloy, comprising: a first step of heating a billet of the Ni-based alloy at a hot-working temperature; and a second step of inserting the billet heated at the hot-working temperature into a container, and applying a compressive force to the billet from one end of the container to extrude the billet from a dice hole at the other end of the container, thereby producing an extruded material of the Ni-based alloy. The billet has a composition of a precipitation strengthening type super heat-resistant Ni-based alloy wherein an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol %. In the second step, a lubricating glass pad is attached between the dice and the billet, and an outer diameter D_B (mm) of the billet and an inner diameter D_C (mm) of the container when the billet is inserted into the container are adjusted to satisfy a relationship: (D_C - D_B) = 2 to 8 mm. Alternatively, an outer diameter D_B' (mm) of the billet before heated at the hot-working temperature and an inner diameter D_C' (mm) of the container before heated at a preheating temperature are adjusted to satisfy a relationship: (D_C' - D_B') = 3 to 9 mm..
Preferably, the inner diameter D_C (mm) of the container is adjusted to be 60 to 180 mm. Preferably, the inner diameter D_C' (mm) of the container is adjusted to be 60 to 180 mm. In addition, it is preferable that the hot-working temperature is 1150 to 1180°C.
According to the present invention, it is possible to extrude the precipitation strengthening type super heat-resistant Ni-based alloy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing an example of simulation result of a relationship of a difference "D_C - D_B (mm)" between an outer diameter D_B (mm) of a billet and an inner diameter D_C (mm) of a container when the billet is inserted into the container, with "a thickness (mm) of a lubricating film" formed between the container and the billet during the direct extrusion by glass lubrication.
FIG. 2 is a schematic view of a cross-sectional structure of an extruding apparatus, for the direct extrusion by glass lubrication.
FIG. 3 is a photograph, as a substitute for a diagram, showing an example of a surface of an extruded material manufactured by the method according to the present invention.
FIG. 4 is a photograph, as a substitute for a diagram, showing an example of a surface of an extruded material manufactured by a method according to a comparative example.

DESCRIPTION OF EMBODIMENTS

(1) The method according to the present invention includes performing "direct extrusion" including applying a compressive force to the billet from one end of a container to extrude the billet from a hole of a dice located at the other end of the container. In addition, the method is performed by glass lubricating extrusion including attaching a lubricating glass pad between the dice and the billet.
FIG. 2 illustrates an exemplary cross-sectional structure of an extruding apparatus for the direct extrusion by the glass lubrication. In FIG. 2, a compressive force is applied to a billet 1 inserted into a container 2, from one end of the container 2 and the billet 1 is extruded from a hole of a dice 5 located at the other end of the container 2. In a case of glass lubricating extrusion, a lubricating glass pad 7 is attached between the dice 5 and the billet 1 when the billet 1 is inserted in the container 2. The dice 5 may be set at the container 2 through a dice holder. In the case, the dice 5 in FIG. 2 includes the dice holder (not shown). Strictly speaking, when the extruding apparatus is in the state as shown in FIG. 2 (i.e., when the billet 1 is extruded from the hole of the dice 5 to some extent), the lubricating glass pad 7 is already molten. In the present invention, the molten lubricating glass pad 7 sufficiently penetrates between the billet 1 and the container 2. The molten lubricating glass pad 7 solidifies and adheres on a surface of an extruded material 6 extruded from the hole of the dice 5.
A typical known lubricating glass pad may be used in the method of the present invention. For example, a glass pad including any glass material molded with a binder may be used. For example, the lubricating glass pad 7 has a shape of a "disc" that substantially fits between the dice 5 and the billet 1 (therefore, also referred to as a glass disc). For example, the disc has "a hole" at a center of the disc, that corresponds to a position or a size of the dice hole. In some cases, a stack of a plurality of sheets of the lubricant glass pads 7 may be used. Such lubricating glass pad is effective for melting quickly and increasing fluidity of the molten lubricant to improving lubrication between the billet and the container, since the billet is made of the super heat-resistant Ni-based alloy and extruded at a high temperature.
The billet may be an ingot produced through casting of a molten metal. Alternatively, the ingot subjected to blooming, machining or heating as necessary may be used as the billet. The ingot may be a sintered material through powder metallurgy.
(2) In the method according to the present invention, the billet has a composition of a precipitation strengthening type Ni-based alloy wherein an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol %.

The precipitation strengthening type super heat-resistant Ni-based alloy has a structure composed of a gamma phase in which alloying elements are solid-solute in a Ni matrix, and gamma prime phase which is a precipitation strengthening phase of an intermetallic compound, typically represented as [Ni₃(TiAl)]. Usually, such a Ni-based alloy is hot-worked in a temperature range (for example, 900°C to 1200°C) between a solid solution temperature of the gamma prime phase (gamma prime solvus temperature) and a solidus temperature of the Ni-based alloy. If the Ni-based alloy includes a large amount of gamma prime phase, a deforming resistance increases and the hot-workability of the Ni-based alloy decreases as a whole in the hot working. Furthermore, when the hot working is hot extrusion with a high working ratio, the extruded material breaks for example, and it has been difficult to perform the hot working of the Ni-based alloy.
An amount of the gamma prime phase in the Ni-based alloy decreases as a temperature of the alloy (or a hot-working temperature) increases. Therefore, the hot-workability of the Ni-based alloy may be improved to some extent, by increasing the hot-working temperature. However, when the Ni-based alloy includes a large amount of the gamma prime phase, such as an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol %, even if the hot-working temperature is increased such as at a temperature close to the melting point, the gamma prime phase does not disappear from the alloy . Thus, the Ni-based alloy is particularly difficult to be hot-worked. In the method according to the present invention, the super heat-resistant Ni-based alloy which it has been difficult to perform the hot working is used as the billet and the billet is extruded.
The method according to the present invention makes it possible to extrude the Ni-based alloy including a large amount of gamma prime, which has been difficult to be hot-worked. Thus, it has higher utility as the Ni-based alloy includes a larger amount of gamma prime. From this view, an amount of precipitated gamma prime in equilibrium at 700°C in the billet is preferably not less than 50 mol%, more preferably 60 mol %. It is not particularly necessary to determine an upper limit thereof. However, about 75 mol% is practical for the upper limit.
The amount of precipitated gamma prime in equilibrium of the Ni-based alloy means an amount of gamma prime stably precipitated in a thermodynamic equilibrium state. The amount of precipitated gamma prime in equilibrium by "mol %" depends on a composition of the Ni-based alloy. This value by "mol%" can be obtained by analysis through a thermodynamic equilibrium calculation. This analysis can be conducted correctly and easily with use of various kinds of thermodynamic equilibrium calculation software.
The precipitation strengthening type super heat resistant Ni-based alloy, in which an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol%, has a basic composition, for example, including (by mass %, hereinafter "mass %" is simply referred to as "%") C: 0.001 to 0.25%, Cr: 8.0 to 22.0%, Mo: 2.0 to 7.0%, Al: 2.0 to 8.0%, Ti: 0.4 to 7.0%, and the balance of Ni and impurities. The alloy may further include one or more of Co: not more than 28.0%, W: not more than 6.0%, Nb: not more than 4.0%, Ta: not more than 3.0%, Fe: not more than 10.0%, V: not more than 1.2%, Hf: not more than 1.0%, B: not more than 0.300%, and Zr: not more than 0.30%. Examples of such an alloy include Alloy 713C, UDIMET720 (UDIMET is a registered trademark of Special Metals Corporation), and IN100.
With regard to the above composition, effects of each element are described below.

<C: 0.001 to 0.25%>

Carbon (C) effects to increase strength of grain boundaries of the Ni-based alloy. It also increases casting ability of the Ni-based alloy. When an amount of carbon increases, however, coarse eutectic carbides precipitate in a last solidification portion of the cast ingot. As the coarse carbides increase, hot-workability during the hot extrusion decreases. Accordingly, the carbon content is preferably 0.001 to 0.25%. More preferably, the carbon content is not more than 0.10%, further more preferably not more than 0.05%, and particularly preferably not more than 0.02%. Also, the carbon content is more preferably not less than 0.003%, further more preferably not less than 0.005%, and particularly preferably not less than 0.008%.

<Cr: 8.0 to 22.0%>

Chromium (Cr) improves oxidation resistance and corrosion resistance. However, excessive amount of Cr forms a brittle phase, such as a σ phase, to deteriorate strength and hot-workability. Therefore, the Cr content is preferably 8.0 to 22.0%. More preferably, the Cr content is not less than 9.0%, further more preferably not less 9.5%, and particularly preferably not less 10.0%. Also , the Cr content is more preferably not more than 18.0%, further more preferably not more than 16.0%, and particularly preferably not more than 14.0%.

<Mo: 2.0 to 7.0%>

Molybdenum (Mo) contributes to solid-solution strengthening of a matrix, and has an effect of improving high-temperature strength. However, excessive amount of Mo forms an intermetallic compound phase and deteriorates high-temperature strength. Therefore, the Mo content is preferably 2.0 to 7.0%. More preferably, the Mo content is not less than 2.5%, further more preferably not less than 3.0%. Also, the Mo content is more preferably not more than 6.0%, further more preferably not more than 5.5%, and particularly preferably not more than 5.0%.

<A1: 2.0 to 8.0%>

Aluminum (Al) forms the gamma prime phase and improves high-temperature strength. However, an excessive amount of Al deteriorates hot-workability and causes a material defect such as cracks during an extrusion process. Therefore, the Al content is preferably 2.0 to 8.0%. More preferably, the Al content is not less than 2.5%, further more preferably not less than 3.5%, and particularly preferably not less than 4.5%. Also, the Al content is more preferably not more than 7.5%, further more preferably not more than 7.0%, and particularly preferably not more than 6.5%.

<Ti: 0.4 to 7.0%>

Titanium (Ti), similar to Al, forms the gamma prime and increases high-temperature strength through forming the gamma prime. However, an excessive amount of Ti forms a harmful η (eta) phase and deteriorates hot-workability. Therefore, the Ti content is preferably 0.4 to 7.0%. More preferably, the Ti content is not less than 0.45%, and further more preferably not less than 0.5%. Also, the Ti content is more preferably not more than 5.0%, further more preferably not more than3.0%, and particularly preferably not more than 1.0%.
The balance, other than the elements described above, is nickel (Ni) as well as impurities. The Ni-based alloy may further include following elements as necessary.

<Co: not more than 28.0%>

Cobalt (Co) is an optional element that improves stability of the alloy structure, and can maintain hot-workability even if the alloy includes a large amount of strengthening element Ti. On the other hand, Co is expensive and thus increases a cost of the alloy. Therefore, even when the alloy include Co, the Co content is preferably up to 28.0%, more preferably up to 18.0%, further more preferably up to 16.0%, and particularly preferably up to 13.0%. If Co intentional addition is not needed (i.e. it is inevitable impurity in a raw material), the lower limit of Co is 0%. Furthermore, the Co content may be less than 1.0%.
In order to achieve the above effect of Co, the Co content is preferably not less than 1.0%, more preferably not less than 3.0%, further more preferably not less than 8.0%, and particularly preferably not less than 10.0%.

<W: not more than 6.0%>

Tungsten (W) is an optional element that contributes to solid-solution strengthening of a matrix, similar to Mo. However, excessive amount of W results in formation of a harmful intermetallic compound phase to decrease high-temperature strength. Therefore, even when the alloy includes W, the W content is preferably not more than 6.0%, more preferably not more than 5.5%, further more preferably not more than 5.0%, and particularly preferably not more than 4.5%. If W is not intentionally added (i.e. it is inevitable impurity in a raw material), the lower limit of W is 0%. Furthermore, the W content may be less than 1.0%, further less than 0.8%.
In order to achieve the above effect of W, the W content is preferably not less than 1.0%. Addition of both W and Mo is more effective in achieving the solid-solution strengthening. In the case where the alloy includes W in combination with Mo, the W content is preferably not less than 0.8%.

<Nb: not more than 4.0%>

Niobium (Nb) is an optional element that forms the gamma prime and increases high-temperature strength through forming the gamma prime, similar to Al and Ti. However, excessive amount of Nb results in formation of a harmful delta δ (delta) phase to deteriorate hot-workability. Therefore, even when the alloy includes Nb, the Nb content is preferably not more than 4.0%, more preferably not more than 3.5%, further more preferably not more than 3.0%, and particularly preferably not more than 2.5%. If Nb is not intentionally added (i.e. it is inevitable impurity in a raw material), the lower limit of Nb is 0%. Then, the Nb content is less than 0.5%.
In order to achieve the above effect of Nb, the Nb content is preferably not less than 0.5%, more preferably not less than 1.0%, further more preferably not less than 1.5%, and particularly preferably not less than 2.0%.

<Ta: not more than 3.0%>

Tantalum (Ta) is an optical element that forms the gamma prime and increases high-temperature strength through forming the gamma prime, similar to Al and Ti. However, excessive amount of Ta makes the gamma prime phase unstable and coarse at a high temperature. Furthermore, Ta forms a harmful η (eta) phase to deteriorate hot-workability. Therefore, even when the alloy includes Ta, the Ta content is preferably not more than 3.0%, more preferably not more than 2.5%, further more preferably not more than 2.0%, and particularly preferably not more than 1.5%. In addition, if Ta is not intentionally added (i.e. it is inevitable impurity in a raw material), the lower limit of Ta is 0%. Then, the Ta content is less than 0.3%.
In order to achieve the above effect of Ta, the Ta content is preferably not less than 0.3%, more preferably not less than 0.5%, further more preferably not less than 0.7%, and particularly preferably not less than 1.0%.

<Fe: not more than 10.0%>

Fe is an optional element that can be included in the alloy instead of expensive Ni or Co and is effective in reducing the cost. However, excessive amount of Fe forms a brittle phase such as a σ phase to deteriorate strength and hot-workability. Therefore, even when the alloy includes Fe, the Fe content is preferably not more than 10.0%, more preferably not more than 8.0%, further more preferably not more than 6.0%, and particularly preferably not more than 3.0%. If Fe is not intentionally added (i.e. it is inevitable impurity in a raw material), the lower limit of Fe is 0%. Then, the Fe content is less than 0.1%.
In order to achieve the above effect of Fe, an amount of Fe that is instituted of Ni or Co is preferably not less than 0.1%, more preferably not less than 0.4%, further more preferably not less than 0.6%, and particularly preferably not less than 0.8%.

<V: not more than 1.2%>

Vanadium (V) is an optical element that is effective for solid-solution strengthening of a matrix and generation of carbide to increase grain boundary strength. However, excessive amount of V results in formation of such phase that is unstable at a high temperature during a manufacturing process, and adversely affects the productivity and high-temperature dynamic performance. Therefore, even when the alloy includes V, the V content is preferably not more than 1.2%, more preferably not more than 1.0%, further more preferably not more than 0.8%, and particularly preferably not more than 0.7%. If V is not intentionally added (i.e. it is inevitable impurity in a raw material), the lower limit of V is 0%. Then, the V content is less than 0.1%.
In order to achieve the above effect of V, the V content is preferably not less than 0.1%, more preferably the V content 0.2%, further more preferably the V content 0.3%, and particularly preferably the V content 0.5%.

<Hf: not more than 1.0%>

Hafnium (Hf) is an optional element that is effective for improving oxidation resistance of the alloy and generation of carbide to increase grain boundary strength. However, excessive amount of Hf results in formation of oxide, and such a phase that is unstable at a high temperature during a manufacturing process, and adversely affects the productivity and high-temperature dynamic performance. Therefore, even when the alloy includes Hf, the Hf content is preferably not more than 1.0%, more preferably not more than 0.7%, further more preferably not more than 0.5%, and particularly preferably not more than 0.3%. If Hf is not intentionally added (i.e. it is inevitable impurity in a raw material), the lower limit of Hf is 0%. Then, the Hf content is less than 0.02%.
In order to achieve the above effect of Hf, the Hf content is preferably not less than 0.02%, more preferably not less than 0.05%, further more preferably not less than 0.1%, and particularly preferably not less than 0.15%.

<B: not more than 0.300%>

Boron (B) is an optional element that can strengthen grain boundaries and improve creep strength and ductility. However, excessive amount of B drastically decreases a melting point of the alloy and deteriorate hot strength and hot workability. Therefore, even when the alloy includes B, the B content is preferably not more than 0.300%, more preferably not more than 0.100%, further more preferably not more than 0.050%, and particularly preferably not more than 0.020%. If B is not intentionally added (i.e. it is inevitable impurity in a raw material), the lower limit of B is 0%. Then, the B content is less than 0.001%.
In order to achieve the above effect of B, the B content is preferably not less than 0.001%, more preferably not less than 0.003%, further more preferably not less than 0.005%, and particularly preferably not less than 0.007%.

<Zr: not more than 0.30%>

Zirconium (Zr) is an optional element that has an effect of improving grain boundary strength, similar to B. However, excessive amount of Zr drastically decreases a melting point of the alloy and decreases high-temperature strength and hot-workability. Therefore, even when the alloy includes Zr, the Zr content is preferably not more than 0.30%, more preferably not more than 0.25%, further more preferably not more than 0.20%, and particularly preferably not more than 0.15%. If Zr is not intentionally added (i.e. it is inevitable impurity in a raw material), the lower limit of Zr is 0%. Then, the Zr content is less than 0.001%.
In order to achieve the above effect of Zr, the Zr content is preferably not less than 0.001%, more preferably not less than 0.005%, further more preferably not less than 0.01%, and particularly preferably not less than 0.03%.
(3) In the method according to the present invention, an outer diameter D_B (mm) of the billet and an inner diameter D_C (mm) of the container when the billet is inserted into the container are adjusted to satisfy a relationship: (D_C - D_B) = 2 to 8 mm..
In the hot extrusion of the Ni-based alloy having the above special composition, there is an optimal relationship between the outer diameter D_B (mm) of the billet and the inner diameter D_C (mm) of the container when the billet is inserted into the container. In order to complete the hot extrusion of the Ni-based alloy without stopping or breaks of the material, it is important to adjust to effect the lubricating glass pad attached between the dice and the billet. The lubricating glass pad is heated and molten when the billet heated at the hot-working temperature is inserted into the container. The molten glass pad improves lubrication between the billet and the dice during the extrusion. In this case, when the molten glass can also permeate sufficiently between the billet and the container, it forms "a lubricating film" between the billet and the container and the lubrication therebetween can be improved. However, the Ni-based alloy is inferior in "wettability" to the molten glass as compared with a typical stainless steel or the like. Therefore, it is important to consider conditions on the extrusion or the like in order to permeate the molten glass sufficiently between the billet and the container, when the billet of the Ni-based alloy is hot extruded. The present inventors have found it effective to optimize a "clearance" between the billet and the container that directly relates to the permeation of the molten glass, in order to permeate it sufficiently to effect the permeation of the molten glass pad.
FIG. 1 is a graph showing an example of simulating result of a relationship between a value of "D_C - D_B (mm)" that is a difference between the outer diameter D_B (mm) of the billet and the inner diameter D_C (mm) of the container, and a "thickness of lubricating film (mm)" formed between the billet and the container during the hot extruding of the billet of the Ni-based alloy. Here, the thickness of the lubricating film is obtained at a part where the thickness of the lubricating film is at minimum in the billet. The results in FIG. 1 are obtained from calculation with the finite element analysis by a two-dimensional axis target model in which heat and deformation are linked . In the analysis, it was assumed that the billet 1 is an elastic-plastic body, the container 2 and a dummy block 3 are a rigid body, and the lubricating glass pad 7 is a rigid-plastic body. The stem 4 is not considered in the analysis model since the dummy block 3 is set to directly operate in the extruding direction. The calculation is performed with the finite element analysis software "FORGE Nxt ver1.0" of TRANSVALOR, assuming that the lubricating glass pad 7 is already completely molten by the contact with the billet 1.
FIG. 1 shows that, as the clearance (that is the value of "D_C - D_B (mm)") is reduced, the lubricating film having a sufficient thickness is formed between the billet and the container during the extrusion. For example, it is shown that the lubricating film has a thickness of more than 0.05 mm when the clearance is not more than 8 mm. It is considered to be due to faster flow of the molten glass pad. Thus, the lubrication between the billet and the container can be improved.
As the clearance becomes larger, the billet is easily deformed in the radial direction of the billet toward the inner wall of the container during the extrusion. In a part where the billet has deformed largely in the radial direction, a space between the billet and the container becomes partially narrower or closed during the extrusion and the flow of the molten glass pad is blocked, and thus the flow of the molten glass pad is interrupted. As a result, cracks may occur on a surface of the billet, and the extruded material may be broken, for example. Then, the extrusion cannot be completed.
However, too small clearance is not advantageous. If the clearance becomes too small, the flow of the molten glass pad may be blocked and the smooth flow thereof may be interrupted. Accordingly, for example in the case of FIG. 1, as the clearance is reduced from about 4 mm, the thickness of the lubricating film tends to become smaller. In FIG. 1, when the clearance is about 1 mm, even if the lubricating film maintains a thickness of about 0.05 mm, there is a possibility that the lubricating film is partially thin or broken.
In addition, if the clearance becomes too small, there is a possibility that a temperature of the billet may decrease not a little before the extrusion is started since the billet may contact with the inner wall of the container when the billet heated at the hot-working temperature is inserted into the container to prepare the extrusion. In particular, the Ni-based alloy more increases its deforming resistance as a temperature decrease, in comparison with typical general stainless steels or the like. Thus, the degree of decrease of the deforming resistance of the billet is more than a degree of the decrease of the temperature . Thus, completion of the extrusion is interrupted.
Accordingly , the outer diameter D_B (mm) of the billet and the inner diameter D_C (mm) of the container when the billet is inserted into the container are adjusted to satisfy a relationship: (D_C - D_B) = 2 to 8 mm. The value of (D_C - D_B) may be adjusted to, for example, 2 to 4 mm, or 4 to 8 mm as far as it is within the range of 2 to 8 mm. The value of (D_C - D_B) may be treated as an integer. For example, it may be rounded off to the nearest integer.
In general, the container of the extruding apparatus is a tubular shape, such as a cylindrical shape. Therefore, the billet has a pillar shape, such as a circular columnar shape. In this case, the (D_C - D_B) value can be adjusted in the parallel gap between an inner surface of the container and an outer peripheral surface of the billet.
The (D_C - D_B) value can be adjusted by adjusting the outer diameter of the billet, for example, specifically by adjusting the outer diameter of the billet before inserted into the container (that is, before the billet is heated at the hot-working temperature). The adjustment of the outer diameter of the billet can be performed by machining such as turning according to a composition or heating conditions of the billet in consideration of thermal expansion of the billet when heated at the hot-working temperature or the thermal expansion of the container when heated at a preheating temperature. Additionally, the outer diameter D_B' (mm) of the billet before heated at the hot-working temperature and the inner diameter D_C' (mm) of the container before heated at the preheating temperature may be adjusted such that a relationship therebetween satisfies (D_C' - D_B') = 3 to 9 mm, for example. The range may be 3 to 5 mm, or 5 to 9 mm for example,, as fat as it is within the range of 3 to 9 mm.
The (D_C' - D_B') value can be adjusted in the parallel gap between the inner surface of the container and the outer peripheral surface of the billet.
If the inner diameter of the container becomes too large, it is necessary to manufacture the billet with larger outer diameter in order to maintain the clearance with the inner diameter of the container. However, the billet with large outer diameter is difficult to handle to not small extent. Since it takes time and effort to handle the billet in inserting the billet heated at the hot-working temperature into the container, the temperature of the billet may decrease. Therefore, the inner diameter D_C (mm) of the container is preferably not larger than 180 mm. It is more preferable to be smaller such as not larger than 160 mm, not larger than 140 mm, not larger than 120 mm, or not larger than 100 mm.
On the contrary, if the inner diameter of the container becomes too small, it is necessary to decrease the diameter of the billet. As the diameter of the billet becomes smaller, the cooling rate of the heated billet itself becomes faster. For example, when the billet heated at the hot-working temperature is inserted into the container, the temperature of the billet may decrease drastically. Therefore, the inner diameter D_C (mm) of the container is preferably not smaller than 60 mm. It is more preferable to be larger such as not smaller than 70 mm, or not smaller than 80 mm.
Instead of setting the inner diameter D_C of the container as the above value, the inner diameter D_C' of the container before heated at the preheating temperature is preferably set to not larger than 180 mm. It is more preferable to be smaller such as not larger than 160 mm, not larger than 140 mm, not larger than 120 mm, or not larger than 100 mm. However, the inner diameter D_C' (mm) of the container is preferably not smaller than 60 mm. It is more preferable to be larger such as not smaller than 70 mm or not smaller than 80 mm.
For the billet having a composition of a precipitation strengthening type Ni-based alloy wherein an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol%, the hot-working temperature is preferably "1150 to 1180°C", more preferably not higher than 1170°C. The extrusion at such a high temperature contributes to maintaining the hot-workability of the billet of the Ni-based alloy. The extrusion at the high temperature is effective in promoting quick melting of the lubricating glass pad and facilitating flowing of the molten lubricating glass pad so as to improve the lubrication between the billet and the container.
According to the present invention, a glass lubricant may be applied to the peripheral surface of the billet when the billet heated at the hot-working temperature is inserted into the container
According to the present invention, an extruded material may have a cross section with a diameter of, for example, 10 to 130 mm. The diameter may be not more than 100 mm, not more than 60 mm, or not more than 30 mm. According to the present invention, an extrusion ratio in the extrusion (that is a ratio of a cross-sectional area of the billet / a cross-sectional area of the extruded material) may be, for example, not more than 70. The extrusion ratio may be not more than 40, not more than 30 , not more than 20, or not more than 10. However, the extrusion ratio may be not less than 2, not less than 4, or not less than 6.
The extruded material produced in this manner has a shape of a bar or a wire for example. The bar or wire may be is solid for example. The extruded material may be further hot-worked or cold-worked to produce a fine wire having a cross section with a diameter of 1 to 6 mm, furthermore a diameter of not more than 4 mm or not more than 3 mm.
According to the present invention, the billet may be configured such that a material to be molded (that is the precipitation strengthening type super heat-resistant Ni-based alloy) is housed in a vessel. In this case, the Ni-based alloy can also be hot extruded by setting the (D_C - D_B) value as described above or the (D_C' - D_B') value as described above.

EXAMPLES

A molten metal with a predetermined composition was prepared by vacuum melting and was cast to produce ingots. The ingots were subjected to machining and thus cylindrical billets A to E, corresponds to Alloy 713C, having a shape with a predetermined diameter and a length of 105 mm were manufactured. Diameters (D_B') of the billets A to E are: as follows.

billet A: 83 mm,
billet B: 82 mm,
billet C: 80 mm,
billet D: 76 mm, and
billet E: 72 mm

The composition of the billets A to E (i.e., ingots) is shown in Table 1. Since Co, W, Ta, V, and Hf are impurity elements, it satisfies Co ≤ 28.0%, W ≤ 6.0%, Ta ≤ 3.0%, V ≤ 1.2%, and Hf ≤ 1.0%.
An amount of gamma prime precipitated equilibrium at 700°C of the billets A to E was obtained with use of the thermodynamic equilibrium calculation software "JMatPro (Version 8.0.1, Sente Software Ltd.)". As a result of the calculating by inputting the contents of the elements in Table 1 into the software, the amount of gamma prime precipitated in equilibrium at 700°C was 70 mol %. The gamma prime solvus temperature of the billets A to E was 1180°C. [TABLE 1]

(mass%)

Billets A to E C Cr Mo Al Ti Nb Fe B Zr Ni*

0.017 12.0 4.5 5.9 0.6 2.0 1.1 0.009 0.090 balance

* including impurities
The billets A to E were heated at a hot-working temperature (first step). Each heated billet A to E was inserted into a cylindrical container of the extruding apparatus in FIG. 2 (JIS-SKD61, inner diameter before preheating (D_C') was 85 mm), and hot extruded under conditions in Table 2 to produce a solid extruded material (second step).
In the hot extrusion, the billets A to E were heated at the hot-working temperature of 1150°C before inserted into the container, and the container was also preheated at a temperature of 500°C. The heated billets A to E and the heated container forms following clearances (D_C - D_B) between the outer diameter D_B (mm) of the billets A to E and the inner diameter D_C (mm) of the container when the billets A to E were inserted into the container. The clearances were measured in the parallel part of the gap between the inner surface of the container and the outer peripheral surface of the billets A to E.

billet A: 1 mm,
billet B: 2 mm,
billet C: 4 mm,
billet D: 8 mm, and
billet E: 12 mm.

[TABLE 2]

Heating temperature (°C)	1150
Inner diameter of dice (mm)	27
Extrusion ratio	Billet A : 9.4
	Billet B : 9.2
	Billet C : 8.8
	Billet D : 7.9
	Billet E : 7.1
Stem speed (mm·s^-1)	16
Lubricating method	Glass pad

The hot extrusion was successfully conducted for each of the billets B to D. Substantial body of the billet B, C or D was extruded without breaks in the extruded material (having a cross section with a diameter of about 27 mm).
On the other hand, since the clearance was too small for the billet A, the billet contacted with the inner wall of the container when the billet was inserted into the container. Thus, it took time (so that the temperature of the billet decreased) and even starting of the hot extrusion was difficult. For the billet E, since the clearance was too large, it is supposed that smooth flow of the molten glass pad was interrupted. Thus, there was a sign of breaks. Therefore, the hot extrusion was stopped.
FIG. 3 shows an external appearance of the extruded material produced from the billet D (clearance: 8 mm) through the above hot extrusion. FIG. 4 shows an external appearance of the extruded material produced from the billet E (clearance: 12 mm). In FIGs. 3 and 4, the front end of the extruded material is shown on the right side (dice was on the left side). The adhered substance observed on a surface of the extruded material is a solidified lubricating glass .
On the surface of the extruded material in FIG. 3, the lubricating glass pad was adhered from the front end to the rear end of the extruded material. The surface was free from cracks or visible scratches, and exhibited an excellent surface state. This excellent surface state was similarly observed in the extruded material produced from the billet B (clearance: 2 mm) and the billet C (clearance: 4 mm).
On the other hand, on the surface of the extruded material in FIG. 4, the lubricating glass pad did not adhere ranging from the front end to the rear end of the extruded material. On the surface of the extruded material, a number of "constricted parts" were observed leading to breaks of the extruded material.

REFERENCE S LIST

1: billet
2: container
3: dummy block
4: stem
5: dice (including dice holder)
6: extruded material
7: lubricating glass pad

Claims

A method for hot-extruding a super heat-resistant Ni-based alloy, comprising:
heating a billet at a hot-working temperature;

inserting the billet heated at the hot-working temperature into a container; and

applying a compressive force to the billet in the container to extrude the billet from a hole of a dice located at the container,

wherein the method is performed by direct extrusion, in which the compressive force is applied to the billet from one end of the container and the billet is extruded from the dice hole at the other end of the container;

wherein the method is performed by glass lubricating extrusion, in which a lubricating glass pad is attached between the dice and the billet;

wherein the billet has a composition of a precipitation strengthening type super heat-resistant Ni-based alloy wherein an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol %; and

wherein an outer diameter D_B (mm) of the billet and an inner diameter D_C (mm) of the container when the billet is inserted into the container are adjusted to satisfy a relationship: (D_C - D_B) = 2 to 8 mm.
The method according to claim 1, wherein the inner diameter D_C (mm) is 60 to 180 mm.
A method for hot extruding a super heat-resistant Ni-based alloy, comprising:
heating a billet at a hot-working temperature;

inserting the billet heated at the hot-working temperature into a container; and

applying a compressive force to the billet in the container to extrude the billet from a hole of a dice located at the container,

wherein the method is performed by direct extrusion, in which the compressive force is applied to the billet from one end of the container and the billet is extruded from the dice hole at the other end of the container;

wherein the method is performed by glass lubricating extrusion, in which a lubricating glass pad is attached between the dice and the billet;

wherein the billet includes a composition of a precipitation strengthening type super heat-resistant Ni-based alloy wherein an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol%; and

wherein an outer diameter D_B' (mm) of the billet before heated at the hot-working temperature and an inner diameter D_C' (mm) of the container before heated at a preheating temperature are adjusted to satisfy a relationship: (D_C' - D_B') = 3 to 9 mm.
The method according to claim 3, wherein the inner diameter D_C' (mm) is 60 to 180 mm.
The method according to any one of claims 1 to 4, wherein the hot-working temperature is 1150 to 1180°C.
A method of manufacturing an extruded material of a super heat resistant Ni-based alloy, comprising:
a first step of heating a billet made of the Ni-based alloy at a hot-working temperature; and

a second step of inserting the heated billet into a container, and applying a compressive force to the billet from one end of the container to extrude the billet through a hole of a dice at the other end of the container, thereby producing the extruded material of the Ni-based alloy,

wherein the billet has a composition of a precipitation strengthening type super heat-resistant Ni-based alloy wherein an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol %; and

wherein the second step comprises
attaching a lubricating glass pad between the dice and the billet, and
adjusting an outer diameter D_B (mm) of the billet and an inner diameter D_C (mm) of the container when the billet is inserted into the container to satisfy a relationship: (D_C - D_B) = 2 to 8 mm.
The method according to claim 6, wherein the inner diameter D_C (mm) is adjusted to be 60 to 180 mm.
A method for manufacturing an extruded material made of a heat-resistant Ni-based super alloy, comprising:
a first step of heating a billet of the Ni-based alloy at a hot-working temperature; and

a second step of inserting the billet heated at the hot-working temperature into a container, and applying a compressive force to the billet from one end of the container to extrude the billet from a dice hole at the other end of the container, thereby producing an extruded material of the Ni-based alloy,

wherein the billet has a composition of a precipitation strengthening type super heat-resistant Ni-based alloy wherein an amount of precipitated gamma prime in equilibrium at 700°C is not less than 40 mol %; and

wherein the second step comprises
attaching a lubricating glass pad between the dice and the billet, and
adjusting an outer diameter D_B' (mm) of the billet before heated at the hot-working temperature and an inner diameter D_C' (mm) of the container before heated at a preheating temperature are adjusted to satisfy a relationship: (D_C' - D_B') = 3 to 9 mm.
The method according to claim 8, wherein the inner diameter D_C' (mm) of the container is adjusted to be 60 to 180 mm.
The method according to any one of claims 6 to 9, wherein the hot-working temperature is 1150 to 1180°C.