Patent Application
20220403493
The present invention relates to a method for producing a nickel-based alloy product or a titanium-based alloy product.
When a solution treatment is carried out on a disk-shaped metal material that has been formed into a predetermined shape by hot forging or the like and is made of a nickel-based alloy or titanium-based alloy, such as an aircraft engine member, various types of cooling media such as water, oil, and air (including a forced convection air flow generated by a blowing fan or the like) are used in the cooling process. In order to impart a high strength characteristic by a heat treatment, it is desirable that the material be cooled at a high cooling rate in the solution treatment. On the other hand, the generation of residual stress caused by an uneven temperature distribution in the material due to rapid cooling may subsequently cause shape distortion in machining performed to obtain the final product or the like, and may adversely affect the strength characteristic of the product, for example, a fatigue characteristic. Therefore, particularly for materials that are required to be given a high strength level and are solution-treated at a high temperature, the use of a cooling medium that gives an excessively high cooling rate, such as water and oil, tends to be avoided.
Furthermore, for the purpose of reducing residual stress, it is desirable that the entirety of the material be cooled as uniformly as possible in the cooling process of the material, and accordingly, for a material having a complex shape, there is a need to locally preferentially cool a thick portion, which is relatively difficult to cool. For example, the cooling rate of the entirety of the disk-shaped metal material is controlled by spraying a gas such as air from a plurality of high-pressure nozzles that are close to the site where the disk-shaped metal material is to be locally cooled, and a freely selected site of a material held in a heated state is thus rapidly cooled to achieve the desired cooling rate. In addition to air, a liquid refrigerant such as water may be sprayed along with the gas.
When air is blown by a fan or high-pressure air is sprayed from nozzles, it is difficult to increase the cooling rate to the desired range at the location to be cooled, since the density and specific heat of the air are low.
On the other hand, when a refrigerant such as water is sprayed simultaneously with a gas such as air, the refrigerant sprayed onto the workpiece has a certain dispersion, and there is a cooling effect due to latent heat of evaporation. Accordingly, it is difficult to strictly control a cooling site and cooling rate.
Furthermore, when a refrigerant such as water is sprayed simultaneously with a gas such as air, a large amount of vapor is generated, in addition to the dispersion of the refrigerant due to spraying, and this vapor also disperses. Accordingly, it is difficult to estimate the effect of the vapor at the position to be sprayed, and it is more difficult to locally control the cooling rate.
An object of the present invention is to provide a method for producing a nickel-based alloy product or a titanium-based alloy product, the method reliably enabling local cooling to perform effective cooling.
The present invention has been made in view of the problems described above.
The present invention is a method for producing a nickel-based alloy product or a titanium-based alloy product, including: a heating and holding step of heating and holding a hot working material of a nickel-based alloy or a titanium-based alloy after hot forging or hot ring rolling at a solution treatment temperature to obtain a material held in a heated state; and a cooling step of cooling the material held in a heated state to obtain a solution-treated material, in which the cooling step includes carrying out local cooling by contacting a cooling member with a part of a surface of the material held in a heated state.
It is preferable that the cooling member be worked into a shape in which a contact surface of the cooling member in contact with the part of the surface of the material held in a heated state matches the shape of the part to be locally cooled of the material held in a heated state.
It is preferable that the local cooling be carried out by contacting the cooling member with the part of the surface of the material held in a heated state at a surface pressure of at least 0.01 MPa.
According to the present invention, local cooling can be reliably achieved to carry out effective cooling even for a material to be treated having a complex shape, such as disk-shaped metal material.
First, in the present invention, it is preferable to work a hot working material of a nickel-based alloy or a titanium-based alloy after hot forging or hot ring rolling into a predetermined shape in advance to thereby obtain a material to be subjected to solution treatment.
Typical examples of hot forging include die forging. As used herein, “die forging” is forging that enables forming into a shape close to the final product by upper and lower dies. “Hot forging” includes isothermal forging, in which the forging temperature and the temperature of the metal die are almost the same temperature, and hot die forging, in which the die temperature is set lower than in iswothermal forging. In hot ring rolling, the height of a ring-shaped rolling material is pressed while expanding the diameter of the rolling material using a ring rolling mill having at least a main roll, a mandrel roll, and a pair of axial rolls to hot roll a ring-shaped rolling material. The hot working material as the object in the present invention is a material in which thickness changes as viewed on a cross section of the hot working material.
The hot working material formed into a predetermined shape by the hot working is worked into a predetermined shape in advance. The purpose of this working is, for example, to remove a relatively thick oxidized scale formed during the hot working or modify the contour of the surface of the hot working material by machining such as grinding, cutting, or blasting treatment, so that the contact state between a cooling member, which is described later, and a material held in a heated state when they are in contact can be managed to strictly control the state of cooling of the material held in a heated state due to heat transfer between the cooling member and the material held in a heated state.
In a case of carrying out the solution treatment in an oxidizing atmosphere such as in air, if the roughness of the machined surface is too great, the surface area increases, which may increase the amount of oxidized scale formed during heating and holding at the time of the solution treatment. As a result, the contact state between the cooling member and the material held in a heated state may be incomplete, and heat transfer to the cooling member may be inhibited by a thick oxidation scale. Therefore, it is desirable that the surface be a smooth surface having a standard finish or a finer level in terms of roughness (for example, preferably a surface roughness Ra of 5 to 13 μm).
As used herein, “nickel-based alloy” is an alloy for use in a high temperature region of 600° C. or higher, which is also referred to as a superalloy or heat-resistant superalloy, and is an alloy strengthened by a precipitation phase such as y′. Typical alloys include 718 alloys and Waspaloy alloys. In addition, 64Ti is an example of a typical titanium-based alloy.
The material to be subjected to solution treatment, which is obtained by machining the hot working material, is heated and held at a predetermined temperature to obtain a material held in a heated state. The heating temperature and holding time depend on the kind and size of the material, but for example, a temperature range of about 900 to 1200° C. and a time of about 0.5 to 6 hours are acceptable for a nickel-based alloy. For a titanium-based alloy, a temperature range of about 700 to 1000° C., and a time of about 0.5 to 6 hours are acceptable.
The material held in a heated state, which is heated and held at the above-described solution treatment temperature, is cooled to obtain a solution-treated material. Since the cooling step is the most characteristic step of the present invention, the cooling step will be described with reference to the drawings.
As shown in
This part where local cooling is preferentially carried out is a part where the flow of the sprayed gas is otherwise inhibited during the conventional cooling process in a solution treatment. In the present invention, it is possible to preferentially cool the predetermined site, due to the fact that the cooling member is in direct contact with the material held in a heated state. Specifically, the contact surface of the cooling member 1 is worked into a shape that matches the shape of the locally cooled part 12, where the local cooling of the material held in a heated state 11 is to be performed. For example, the cooling member 1 may have a single surface or a plurality of surfaces as the contact surface. The contact surface may be a flat surface such as a circle, an arc, a ring, a square, or a polygon; a curved surface such as an outer circumferential surface of a cylinder, an inner circumferential surface of a cylinder, an outer circumferential surface of a cone, an inner circumferential surface of a cone, or a combination thereof.
When contacting the cooling member with the material held in a heated state, a cooling capacity equal to or greater than that in local cooling technique using air can be achieved by controlling the contact surface pressure between the cooling member and the material held in a heated state such that the contact surface pressure is at least 0.01 MPa and is equal to or less than the high-temperature creep strength and high-temperature compression resistance of the material held in a heated state.
In view of increasing the cooling rate at the part of the material held in a heated state in contact with the cooling member, the contact surface pressure is preferably at least 0.05 MPa, more preferably at least 0.15 MPa, and further preferably at least 0.25 MPa. The upper limit of the contact surface pressure is not particularly limited, and it may be determined by taking into consideration, for example, the kind of the material held in a heated state, the treatment temperature, and the compressive yield strength. The calculated upper limit may be up to 50 MPa; however, in actual practice, up to 10 MPa is acceptable, up to 5 MPa is preferable, and up to 2 MPa is more preferable.
To adjust the contact surface pressure in this way, the weight of the cooling member itself may be changed, or a member for which weight can be changed, such as a weight different from the cooling member, may be placed on the cooling member, for example.
The center of the disk-like metal material as the material held in a heated state 11 shown in
The local cooling by the cooling member 1 may be effective until the temperature of the locally cooled part becomes equal to or less than a certain temperature. This temperature depends on the purpose for controlling the cooling rate of the material held in a heated state by the local cooling. For example, in the case of improving heterogeneity due to the precipitation behavior of the nickel alloy and the cooling temperature distribution of the material held in a heated state, the control of the cooling rate by local cooling functions sufficiently if the local cooling is effective until about 700° C. On the other hand, in the case of improving the heterogeneity of a strain distribution due to heat shrinkage during cooling of the material held in a heated state, the local cooling needs to be effective as far as a temperature range below 700° C. The contact cooling with the cooling member may be combined with normal cooling with a refrigerant such as air or water. When normal cooling and the contact cooling with the cooling member according to the present invention are combined, the material held in a heated state can be continuously locally cooled regardless of the heat capacity (volume) of the cooling member, which also gives the advantages of simplifying the structure and space-saving in cooling device design.
The cooling member will now be described in detail.
In the present invention, the cooling member functions as a so-called heat sink. Therefore, in view of the heat sink function, the heat flux during cooling can be controlled to some extent by adjusting, for example, the kind, size (volume), and shape of the cooling member, the surface roughness, and the surface pressure of the contact portion. In particular, by modifying the shape and volume of the cooling member and forecasting by calculation in advance how the cooling member will become hot due to contact with the material held in a heated state, the cooling rate can be controlled according to the temperature condition of the material held in a heated state during cooling. For example, in order to increase the cooling rate, a flow path for a cooling medium may be provided inside the cooling member, or a fin or the like may be provided in a part of the cooling member for air cooling. As a result, the cooling member can serve a function as a heat medium (conductor) that increases the heat transfer coefficient to the external cooling medium.
In addition, the material of the portion of the cooling member that contacts the material held in a heated state is required, for example, to have high thermal conductivity, to have a melting point that exceeds the solution treatment temperature, not to change or contaminate the material held in a heated state, and not to deform the material held in a heated state. Therefore, it is advisable to appropriately select the material from metal materials that satisfy these requirements. For superalloys (for example, Ni-based heat-resistant alloys and Co-based heat-resistant alloys) used for aircraft engine members, a material that is slightly inferior in high-temperature strength to the superalloy (that is, a material that is easily deformed so as to be in close contact) is desirable in view of improving the adhesion state when the cooling member is in contact with the material held in a heated state. From these viewpoints, preferable materials for the cooling member are, for example, pure Ni, a Ni-based alloy having a content of elements other than Ni of up to 10% by mass, and a Fe-based alloy.
The cooling member can be an assembly of two or more parts. As described above, for the portions of the cooling member that are to be in contact with the material held in a heated state, the material of the cooling member is required to have characteristics such that the materials of both are a suitable combination. On the other hand, for the portions that are not to be in direct contact with the material held in a heated state, a metal material that has excellent thermal conductivity and a large specific heat, such as an Al-based or Cu-based material, can be used, which serves as the portion that utilizes the heat capacity. In this case, the joining surface of the portion in direct contact with the material held in a heated state to the metal material having a high thermal conductivity may be a barrier to heat transfer. Accordingly, the joining surface should be designed such that the joining surface has a complex interface shape that can increase the contact area as much as possible and also such that different types of materials can be joined with a constant load. For example, instead of joining simple flat surfaces together, tapered cone-shaped joining surfaces are used, and the parts are firmly joined to each other with fastening parts such as bolts. In the case of welding, it is advisable to weld so that there are no voids, cracks, or the like. In particular, joining together the parts with fastening parts is economically efficient for the following reasons: the joining load can be controlled relatively strictly by the fastening torque, and detachability is good, so the parts can be replaced on a part-by-part basis.
It is also possible to sandwich an intermediate substance that improves heat transfer between the joining surfaces of the parts. This intermediate substance is not limited to a solid, and may be in the form of a gel or a clay. For example, a paste containing Ag, Al, or C can also be applied depending on the conditions of use.
In the working of the surface of the cooling member that is to be in contact with the material held in a heated state, extremely small protrusions can be formed on the surface of the cooling member, for example. Those protrusions are crushed at the time of contact with the high temperature material held in a heated state, thereby improving the close-contact state, which enables a highly close-contact state during contact with the cooling member.
According to this embodiment, the contact state between the material held in a heated state and the cooling member can be visually confirmed and managed by observing the deformed state of the protrusions after cooling.
Hereinafter, examples and comparative examples of the present invention will be described.
First, as the hot working material, a disk-shaped material to be subjected to solution treatment having a diameter of 220 mm and a thickness of 40 mm was obtained from a forged round bar of a nickel-based heat-resistant superalloy (718 alloy) having a diameter of 260 mm by machining involving saw cutting and turning. The surface on the side that was to be in contact with the cooling member 20, which will be described later, was finish to a standard finish level with a surface roughness Ra of 6.3 μm. Next, this material to be subjected to solution treatment was heated to a solution treatment temperature of 1120° C. and held at uniform heat for 70 to 100 minutes to obtain a material held in a heated state. Then, a cooling test for obtaining a solution-treated material was carried out by cooling this material held in a heated state with the cooling member. A schematic cross-section of the cooling test is shown in
As shown in
For the cooling test, the contact surface of the cooling member was worked into a shape matching the shape of the part to be locally cooled of the material held in a heated state. As shown in
In Examples 1 and 2, in which cooling was performed using the cooling member, cooling from 1100° C. to 700° C. after the start of cooling from 1120° C. at the center position of the material held in a heated state was achieved over a time of about 680 to 740 seconds, as shown in
In addition, as shown in
In the Comparative Example, in which the material held in a heated state was left to cool, the average cooling rate from 1100° C. to 700° C. was higher in order of the positions 60, 30, and 0 mm from the center of the material held in a heated state, as shown in
The part to be cooled of the material held in a heated state has a flat shape in this case; however, even if the part to be cooled has, for example, a curved shape or a complex shape, the above-mentioned effect can be obtained by working the contact surface of the cooling member into a shape that matches the shape of the part to be locally cooled of the material held in a heated state.
In the local cooling by contacting the cooling member according to the present invention as described above, modifying the shape of the contact portion of the cooling member enables selective cooling, compared to other cooling methods using a fluid such as air or water, and such selective cooling enables more precisely selecting and cooling a desired site of the material held in a heated state.
The cooling using the cooling member according to the present invention can be expected to be applied not only to Ni-based alloys and Ti-based alloys, but also to other alloys as well.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-215266 | Nov 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/043993 | 11/26/2020 | WO |
