RU2631221C2 - Method of manufacture of annular moulded body - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: workpiece made of an alloy based on Ni, Co or Fe is subjected to forging to produce a disc-shaped body. By forming a through hole in this body, an annular intermediate body is obtained, which is then rolled. Forging includes at least two stages of hot forging. Each of the stages is performed if the deformation rate is not more than 0.5 s^-1. Absolute value εθ1 of deformation of the forged body in the circumferential direction is at least 0.3. Absolute value εh of deformation of the forged body in the height direction is at least 0.3. The relation εh /εθ1 between the absolute values of the deformation is 0.4-2.5.

EFFECT: possibility of manufacturing an annular moulded body having a thin crystalline homogeneous structure.

8 cl, 9 dwg, 2 tbl, 1 ex

Description

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing an annular molded body, which is used as a blank in the manufacture of an annular product, such as, for example, a turbine disk for aircraft engines.

Priority is claimed for the present invention in Japanese Patent Application No. 2013-069205, filed March 28, 2013 and incorporated herein by reference in its entirety.

State of the art

The turbine disk is an annular element having a through hole, and is designed for joint rotation with many turbine blades, which are located on its outer annular side.

The outer annular portion of the turbine disk is exposed to the products of combustion and reaches a high temperature of approximately 600-700 ° C, while the inner annular portion is maintained at a relatively low temperature and thus thermal stresses repeatedly occur during starting and stopping the engine. Accordingly, it is desirable that the turbine disks have excellent low-cycle fatigue characteristics. In addition, it is necessary that the turbine disks have high creep resistance, since centrifugal force is applied to the outer annular portion due to the rotation of the disks at high speed around the axis at high temperatures. In addition, it is required that the turbine disks have a high tensile strength and a high yield strength.

To ensure a sufficiently high mechanical strength, which must meet the various requirements described above, the ring shaped bodies used in turbine disks are made by forging a material having high heat resistance and consisting of a heat-resistant alloy (superalloy) based on Ni, and cutting the resulting ring forged body, as described, for example, in Patent documents 1 and 2. In particular, the deformation attached to the annular molded body and the crystalline grains of the material, correct it can be forged, resulting in increased tensile strength, fatigue strength, etc. As forging equipment, it is preferable to use a hydraulically controlled forging press capable of precisely controlling the forging speed, and it has been found that forging over the entire surface is preferable for simultaneously molding all the material in order to obtain a structure (crystalline grains) of an annular molded body, which is homogeneous around the circumference.

Meanwhile, in recent years, attempts have been made to increase the size of turbine disks in order to increase the power of aircraft engines. In the case of an increase in the size of the annular molded body due to an increase in the size of the turbine disks, a large hydraulic forging press with a capacity of several tens of thousands of tons is required (for example, see Non-Patent Document 1).

However, the above large hydraulic controlled forging presses are very expensive, and there are very few such presses around the world; accordingly, in the case of using such a large hydraulic forging press, the ability to supply ring shaped bodies can be limited, and the cost of manufacturing products will remain high. The tendency to use large turbine disks has recently reached such a high level that closed forging can be difficult even when using a large forging press with hydraulic control, which can cause problems with obtaining preferred mechanical characteristics in some areas of annular molded bodies to be forged, and ensuring uniformity of product structure.

On the other hand, instead of molding an annular molded body using a forging press, a method of molding an annular molded body by rolling can be used. In this case, equipment costs can be reduced, and the manufacture of large ring shaped bodies is simplified. However, usually the anisotropy of mechanical characteristics (strength characteristics) in products obtained by rolling is more likely than in the case of products obtained by forging on presses, and thus, rolling is not suitable for obtaining products, for example, turbine disks, which require isotropy of mechanical characteristics.

You can use the method in which the annular molded body is molded by a combination of forging press and rolling; however, in the case of using this method, a problem may arise consisting in the need for subsequent final forging after rolling to obtain the required uniform and fine structure, which makes the manufacturing processes more complicated and increases production costs.

To solve this problem, Patent Document 3 describes a method in which the forging process and the rolling process are used in combination, and hot forging is performed several times during the forging process, wherein the forged body is deformed in the circumferential direction εθ1, the forged body is deformed in the height direction εh and the strain ratio between the values of εh / εθ1 are adjusted to suitable values, which ensures the manufacture of an annular molded body having a fine crystalline structure with exceptional uniformity, with low cost.

Cited Documents

Patent documents

Patent Document 1 - JP 07-138719 A.

Patent Document 2 - JP 62-211333 A.

Patent Document 3 - JP 2011-255409 A.

Non-Patent Documents

Non-Patent Document 1 - “Year 2002 Research Report - Report Regarding Development of Innovative Members Using Ultra-Large Forging Press Machine”, (New Energy and Industrial Technology Development Organization, March 2003, pp. 10-11 and pp. 37-41) .

SUMMARY OF THE INVENTION

It should be noted that recently the production of high-power aircraft engines has increased, and thus the demand for large ring shaped bodies has also increased. As a result, a production method is required with which it is possible to continuously produce ring shaped bodies with a homogeneous structure in mass production.

The inventors of the present invention have studied the method for manufacturing ring shaped bodies described in Patent Document 3, and it has been found that, in fact, a ring shaped body can be obtained with fine crystalline grains and with the same grain size using hot forging, in which the forged body is deformed into circumferential direction εθ1, the deformation of the forged body in the height direction εh and the strain ratio between the values εh / εθ1 are adjusted to suitable values; however, in the production of large-sized ring-shaped bodies of large thickness, for example, the grain size of the ring-shaped bodies in some cases will not be uniform due to heterogeneous operating conditions, etc.

The present invention was developed taking into account the above circumstances, and the objective of the present invention is to provide a method of manufacturing an annular molded body for the production of annular molded bodies having exceptionally high mechanical strength, while ensuring the uniformity of their structure at low cost.

Solution

To solve these problems and the above problem, according to one aspect of the present invention, a method for manufacturing an annular molded body includes a step of forging an alloy preform to produce a forged body having a disk shape, and a rolling step of an annular intermediate body prepared by receiving a through hole in said forged body, to obtain an annular molded body, and this method is characterized in that the stage of forging includes at least two stages of hot forging. Moreover, each of the stages of hot forging is performed under such conditions that the strain rate is not more than 0.5 s ^-1 , the absolute value εθ1 of the deformation of the forged body in the circumferential direction is at least 0.3, the absolute value εh of the deformation of the forged body in the direction height is at least 0.3, and the ratio εh / εθ1 between the absolute values of the deformation is 0.4-2.5. According to the manufacturing method of the annular molded body of the present invention, the deformation rate in the forging step is not more than 0.5 s ⁻¹ . When the strain rate exceeds 0.5 s ⁻¹ , the temperature inside the forged body rises excessively due to the heat generated (ie, a phenomenon known as “heat generation”), which leads to the growth of crystalline grains inside the forged body. At the rolling stage after forging, the crystalline grains inside the forged body cannot be crushed, since sufficient deformation cannot be transmitted inside the forged body. According to the present invention, the strain rate is controlled in the range of 0.5 s ⁻¹ or less, and thus, the difference between the temperature on the surface of the forged body and the temperature inside the forged body during forging can be insignificant, which provides a more uniform structure. To more reliably ensure the above effects, the strain rate should preferably be not more than 0.15 s ⁻¹ .

The strain rate is determined by the following expression:

Expression 1

In the forging step, the absolute value of the strain in the circumferential direction εθ1 is set to at least 0.3, and thus, the amount of strain in the circumferential direction to be transmitted to the annular intermediate body in the rolling step can be relatively reduced. In addition, since the absolute value εh of the strain to be transmitted in the height direction is set to 0.3 or more, the strain which must be transmitted in the height direction and which is difficult to convey by rolling can be reliably transmitted to the required degree. Thus, the degree of processing at the rolling stage can be reduced, thereby eliminating the anisotropy of the strength properties of the annular molded body, and increasing isotropy, as a result of which a fine crystalline structure can be obtained in which sufficient uniformity is ensured.

The ratio εh / εθ1 means the equilibrium of the directions of deformation to be transmitted, and is an indicator of the regulation of changes in relative positions in the material before and after the process. At the next rolling step, the corresponding digital quantity inevitably becomes equal to “0” or close to “0” due to the manufacturing method and, therefore, it is very important to properly set the degree of deformation to be transmitted in the direction of height at the forging stage to eliminate anisotropy; however, if the ratio εh / εθ1 is less than 0.4, the effect may not be sufficient. On the other hand, if the ratio εh / εθ1 exceeds 2.5, the distribution of the strain to be transmitted in the direction of height may become excessive and the plastic flow may become unstable, resulting in deterioration of axial symmetry, which is essential to ensure uniformity of structure.

According to the present invention, the ratio εh / εθ1 between the absolute values of the deformation is adjusted so that it is in the range of 0.4-2.5, which stabilizes the plastic flow and provides axial symmetry in order to obtain a homogeneous structure.

According to the method for manufacturing the annular molded body of the present invention, at the rolling step, hot rolling can be performed so that the absolute value εθ2 of the strain transmitted to the annular molded body in the circumferential direction is at least 0.5 and, thus, the grain size in the product region an annular molded body may correspond to at least ASTM number 8 grain size.

In this case, at the rolling stage, by performing hot rolling, during which the deformation in the annular molded body in the circumferential direction is, in absolute value εθ2, 0.5 or more, crystalline grains in the region of the annular molded body product to be processed and machined for receiving the product, reliably crushed at least to grain size number 8 according to ASTM. Accordingly, the mechanical strength of an article made of an annular molded body can be increased.

The ASTM grain size number is believed to be determined according to ASTM ASTM E122.

Furthermore, in the method for manufacturing the annular molded body according to the present invention, the difference between the grain sizes in the product area in the section of the annular molded body in the direction including the axis of the annular molded body is within a ± 2 range according to ASTM grain size numbers.

In this case, due to the difference in grain sizes in the product area in the cross section of the annular molded body in the range of ± 2 according to ASTM grain size numbers, sufficient uniformity of the grain size of the annular molded body in the radial direction in the height direction is ensured.

Furthermore, in the method for manufacturing the annular molded body according to the present invention, the grain size of the forged body in the forging step can be adjusted to at least ASTM grain size 7.

In this case, due to the large amount of deformation transmitted during the forging step, as described above, the grain size of the forged body can be reduced to at least ASTM grain number 7. In this case, the structure of the annular molded body can be fine-grained, while the amount of deformation to be transmitted at the next rolling step will decrease.

Furthermore, by the method of manufacturing the annular molded body according to the present invention, the annular intermediate body can be obtained so that the T / H ratio between the thickness T of the annular intermediate body in the radial direction and the height H of the annular intermediate body in the axial direction is in the range of 0.6 -2.3, and the annular intermediate body can be processed to roll so that the difference between the grain sizes in several equivalent positions of the annular molded the body, evenly spaced around the circumference, was ± 1.5 according to ASTM grain size numbers.

In this case, by molding the annular intermediate bodies in such a way that the T / H ratio between the thickness T of the annular intermediate body in the radial direction and the height H of the annular intermediate body in the axial direction is in the range of 0.6-2.3, and rolling out of the annular of the intermediate body, the difference between the sizes of crystalline grains at several mutually equivalent positions of the annular intermediate bodies uniformly spaced around the circumference may be within ± 1.5 according to ASTM grain size numbers. In particular, in the annular molded body obtained by molding the annular intermediate body, uniformity of grain size in the circumferential direction can be ensured. In particular, it is known that during rolling, which is a local process, sequentially performed processes differ from the general case of partial forging and, therefore, the axial symmetry of the structure after molding is high and, therefore, the deviation of the characteristics of the material of the annular molded body in the circumferential direction is insignificant . In the present invention, by setting the above T / H ratio for the annular intermediate body before rolling in the above range according to this embodiment, it is possible to further improve the shape (roundness) of the annular molded body and improve the axial symmetry of the structure of the annular molded ring.

In other words, since the above T / H ratio is adjustable in the range of 0.6-2.3, rolling stability can be ensured, which is essential to ensure uniformity of structure. In particular, in the region in which the T / H ratio is lower than 0.6, the contact area between the two rolls used in the rolling process (the main roll and the rolling roll) and the material increases, and thus the degree of impact due to heat release processes relatively increases, which makes it difficult to ensure uniformity of the structure in the axial direction. On the contrary, with an increase in the T / H ratio, bending can occur more easily. In particular, in the region in which the T / H ratio is greater than 2.3, the above tendency increases and thus, it becomes more difficult to obtain a uniform structure in the circumferential direction.

According to the manufacturing method of the annular molded body according to the present invention, the alloy preform can be made of a Ni-based alloy. In this case, the forging step is preferably performed at a temperature of 950-1075 ° C., or the rolling step is preferably performed at a temperature of 900-1050 ° C.

Advantageous Effects Achieved in the Invention

According to the present invention, there is provided a method of manufacturing an annular molded body intended for the production of annular molded bodies having extremely high mechanical strength, while reliably ensuring uniformity of structure and low cost.

Brief Description of the Drawings

FIG. 1 is a top view of an embodiment of an annular molded body of the present invention;

FIG. 2 is a sectional view of the body in the direction of arrow XX in FIG. one;

FIG. 3 is a flow diagram of one embodiment of a method for manufacturing an annular molded body and a turbine disk of the present invention;

FIG. 4 is a sectional view of an annular intermediate body used in the manufacturing method of FIG. 3;

FIG. 5 is a perspective view illustrating the rolling performed by the manufacturing method of FIG. 3;

FIG. 6 is an explanatory view showing a rolling step using a rolling roll and an annular roll;

FIG. 7 is an explanatory view showing a rolling step using a rolling roll and an annular roll;

FIG. 8 is a graph showing the relationship between tensile strength and compression of samples of the annular molded body of the present invention;

FIG. 9 is a graph showing the relationship between yield strength and compression of samples of the annular molded body of the present invention.

Description of Embodiments

The following is a description of embodiments of the present invention with reference to the attached drawings. The annular molded body 10 of the present invention is used as a blank for molding turbine disks of aircraft engines.

As shown in FIG. 1 and 2, the annular molded body 10 has through holes and an annular shape about the O axis, and has a main body 11, an inner protrusion 12 that projects from the body 11 in a radial inner direction, and an outer protrusion 13 that protrudes from the body 11 in a radial outward direction.

The annular molded body 10 is formed of a heat-resistant Ni-based alloy (superalloy) having exceptional heat resistance, and in the present embodiment, the annular molded body 10 is formed of an Alloy 718 Ni-based alloy.

Alloy based on Ni Alloy 718 has a composition comprising 50.00-55.00% of the mass. Ni, 17.0-21.0% of the mass. Cr, 4.75-5.60% of the mass. Nb, 2.8-3.3% of the mass. Mo, 0.65-1.15% of the mass. Ti, 0.20-0.80% by weight. Al and 0.01-0.08% of the mass. C, the rest is Fe with inevitable impurities.

In the annular molded body 10, the grain size of the structure in the desired region (not shown) to be machined to produce a turbine disk (i.e., product) (hereinafter this area will be referred to as the "product area") corresponds to a grain size of at least number 8 according to ASTM. In addition, the virtual planes VS1, VS2 shown in FIG. 2 are cross-sections of an annular molded body 10 in a direction including an axis O of an annular molded body 10, i.e. the virtual planes VS1, VS2 occupy mutually equivalent positions determined by the uniform division of the annular molded body 10 in the circumferential direction. The annular molded body 10 provides a uniform structure, since the difference between the grain sizes in the structure of the product area in the cross section of the virtual plane VS1 (or VS2) is ± 2 according to ASTM grain size number. The difference in crystalline grain sizes in the mutually equivalent positions of the annular molded body 10 in the circumferential direction, i.e. the difference between the grain size in the virtual plane VS1 and the grain size in the virtual plane VS2 is ± 1.5 according to ASTM grain size number.

Next, with reference to FIG. 3-7, a description is given of a method for manufacturing an annular molded body 10 and a method for manufacturing a turbine disk.

Step S1 of melting and casting

First of all, molten metal of an alloy based on Ni Alloy 718 is prepared by smelting it. At this stage, the molten raw material is prepared in such a way that the content of its components corresponds to the above ranges for the alloy components based on Ni Alloy 718, and an ingot is obtained by vacuum induction melting (VIM). Further, this ingot is remelted by electroslag remelting (ESR) to re-produce the ingot. In addition, this ingot is subjected to vacuum arc remelting (VAR), and then hot forging is performed to obtain a cylindrical workpiece (alloy workpiece).

The cylindrical workpiece is molded so that, for example, it has a diameter of 7-12 inches (in particular, 165-315 mm). The structure of the obtained preform according to ASTM grain size numbers approximately corresponds to ASTM No. 6. By performing the above-described melting three times (triple melting), an extremely clean preform is obtained in which the segregation during solidification is negligible, while the solidification structure is controlled and only very minor inclusions are observed.

Step S2 forging

Next, the workpiece is forged so that the workpiece is compressed in the direction of the axis of the workpiece to obtain a forged body in the form of a disk.

At this step S2 of the forging, hot forging is performed at least twice, so that the absolute value εθ1 of the deformation of the forged body in the circumferential direction is 0.3 and higher, the absolute value εh of the deformation in the height direction is 0.3 and higher, and the ratio εh / εθ1 between the absolute values of the deformation was 0.4-2.5 in the state in which the workpiece was heated, for example, to a temperature of 950-1075 ° C.

The hot forging deformation rate in the forging step S2 is set to 0.5 s ⁻¹ or less.

In the present embodiment, the hot forging in the forging step S2 is carried out using a hydraulically controlled forging press device. The hydraulic forging press device is capable of adjusting the deformation rate in the above ranges with high accuracy by means of hydraulic control during forging.

It should be noted that in the present embodiment, the hot forging deformation rate in the forging step S2 is set to be 0.01 s ⁻¹ or more.

In addition, in the present embodiment, the absolute value εθ1 of the strain amount in the circumferential direction is set to 0.3 or more. The absolute value εh of the strain in the direction of height along the axis of the forging should be set to more than 0.3.

The height of the forged body is adjusted in step S2 of the forging, for example, to approximately 60-500 mm. By performing the forging step described above, the forged body acquires sufficient deformation, and the grain size of the forged body is ground to No. 7 according to ASTM or more according to ASTM grain numbers.

Step S3 of the manufacture of holes and intermediate rolling

Next, in the center of the obtained forged body using a water cutter, a through hole is made having a circular cross section. In addition, if necessary, after the formation of the through hole, an intermediate rolling of the ring is performed. By performing the hole manufacturing step S3 and the intermediate rolling, an annular intermediate body 20 is obtained.

In the present embodiment, the annular intermediate body 20 has a perpendicular to the circumference section of a substantially polygonal shape, as shown in FIG. 4, and includes a base portion 21 having a substantially perpendicular circumference of a substantially polygonal shape and an upper surface and a lower surface extending in a direction substantially perpendicular to the O axis; an inner protrusion 22 protruding radially inward from the base portion 21; and an outer protrusion 23 protruding radially outward from the base portion 21.

In particular, the height H of the annular intermediate body 20 (base portion 21) in the direction of the axis O is set in the range H = 60-500 mm. In addition, the annular intermediate body 20 is pressed in such a way that the T / H ratio between the radial thickness T, which is perpendicular to the axis O, and the height H described above is 0.6-2.3.

Step S4 Rolling

Next, the annular intermediate body 20 is subjected to rolling. The rolling is carried out, for example, at a temperature of 900-1050 ° C.

As shown in FIG. 5, in this embodiment, the rolling apparatus 30 includes a main roll 40 on the outer circumferential side of the annular intermediate body 20; a rolling roll 50 located in the inner circumferential side of the annular intermediate body 20; and a pair of axial rolls 31, 32 that are in contact with the end surfaces (in the present embodiment, with the upper surface and lower surface of the base portion 21) of the annular intermediate body 20 in the direction of the O axis.

The main roller 40 and the rolling roller 50 are arranged so that their axis of rotation are parallel to each other and are designed to grab and compress the annular intermediate body 20 from its inner circumferential side and the outer circumferential side and roll the annular intermediate body 20 with rotation around the circumference of the annular intermediate body twenty.

A pair of axial rolls 31, 32 is designed to capture and compress the annular intermediate body 20 in the direction of the axis O and to control the size of the annular intermediate body 20 in the height direction.

As shown in FIG. 6, a recess 41 is provided on the outer circumferential portion of the main roll 40, in which a portion of the intermediate body 20 can be located, and in this embodiment, the recess 41 has a depth sufficient to accommodate the outer protrusion 23, the base portion 21 and the outer circumferential portion of the inner protrusion 22 the annular intermediate body 20. In addition, on the bottom 41A of this recessed portion 41, a first molding groove 42 is formed to form the outer protrusion 13 of the annular molded body, and it extends radially into inside with respect to the main roll (to the right in Fig. 6). The first molding groove 42 has a depth equivalent to the height of the protrusion 13 to be molded.

On the other hand, a portion 51 is disposed in the outer circumferential portion of the rolling roll 50, which may engage with the main roll 40 inside the recess 41, and a second molding groove 52 is formed on the outer peripheral surface of the portion 51 to form the inner protrusion 12 of the annular molded body 10, and it extends radially inward with respect to the expansion roll 50 (left in FIG. 6). The second molding groove 52 has a depth equivalent to the height of the inner protrusion 12 to be molded.

The main roller 40 and the expansion roller 50 described above are brought closer together, as a result of which the annular intermediate body is gripped and compressed between the main roller 40 and the expansion roller 50. In particular, the main roller 40 and the expansion roller 50 are brought closer together In this case, the main roll 40 rotates around the axis of rotation of the main roll 40, as a result of which the annular intermediate body 20 rotates around the axis O due to the resistance of thorns arising between the annular intermediate body 20 and the main roll 40.

On the other hand, the expansion roll 50 can rotate around the axis of rotation of the expansion roll 50 and is driven by the friction resistance that arises between the annular intermediate body 20 and the expansion roll 50. The annular intermediate body 20 is plastically deformed when it fills the inner sides of the recess 41 and the first molding groove 42 of the main roll 40 and the inner side of the second molding groove 52 of the expansion roll 50, thereby forming an annular molding body 10. During this deformation The inner protrusion 12 of the annular molded body 10 is plastically deformed in the shape of the second molding groove 52. In addition, the outer protrusion 13 is plastically deformed in the shape of the first molding groove 42.

By performing the rolling in the above manner, the annular intermediate body 20 is plastically deformed so that it stretches in the circumferential direction, and its inner diameter and outer diameter increase, resulting in an annular molded body shown in FIG. 7.

At this rolling step S4, the absolute value εθ2 of the deformation of the annular molded body 10 in the circumferential direction is 0.5 or more. In particular, hot rolling is performed at least one or more times to obtain a total absolute value of the strain εθ2 in the range 0.5-1.3.

Heat treatment step S5 / machining step S6

The annular molded body 10, obtained in the manner described above, is subjected to adjustment of the properties by heat treatment and molding to the final form by cutting in order to obtain a turbine disk for aircraft engines.

According to the present embodiment of the method for manufacturing the annular molded body described above, in step S2 of the forging to obtain the forged body by forging the workpiece, the deformation rate is 0.5 s ⁻¹ or less, and thus, an excessive temperature increase inside the forged body can be prevented ( a phenomenon called “heat generation”), which may occur due to the heat generated. Accordingly, the difference between the temperature on the surface of the forged body and the temperature inside the forged body during forging can remain insignificant, and thus, the structure of the forged body can be aligned. In order to reliably provide these effects, it is preferable that the deformation rate in the forging step S2 is 0.15 s ⁻¹ or less.

In addition, due to the high value of 0.3 or more set as the absolute value εθ1 of the deformation in the circumferential direction in the forging step S2, the degree of deformation in the circumferential direction communicated to the annular intermediate body 20 in the rolling step S4 can be reduced. In addition, due to the high value of 0.3 or more specified as the absolute value εh of the strain in the height direction, such a degree of strain in the height direction that would otherwise be difficult to achieve could be sufficiently achieved in step S4 rolling out. Thus, the degree of processing in the rolling step S4 can be reduced, thereby eliminating the anisotropy of the strength properties of the annular molded body 10, while increasing the isotropy, as a result of which a fine crystalline structure can be obtained in which sufficient uniformity is achieved.

In addition, due to the high value of 0.4 or more specified as the ratio εh / εθ1 between the absolute strain value εθ1 in the circumferential direction and the absolute strain value εh in the height direction, a sufficient degree of deformation in the height direction can be ensured, as a result whereby uniformity of the structure can be ensured even if sufficient deformation in the height direction cannot be ensured in the subsequent rolling step S4. In addition, due to the fact that the ratio εh / εθ1 is 2.5 or less, the strain distribution in the height direction cannot be excessive, and thus the plastic flow becomes stable, as a result of which axial symmetry of the plastic flow can be ensured, which is essential to ensure uniformity of structure. Preferably, the ratio εh / εθ1 between the absolute values of the deformation is 0.6-2.1. Accordingly, the axial symmetry of the plastic flow can be improved, and thus, the uniformity of the structure can be more reliably ensured.

In addition, in this embodiment, due to the fact that the absolute value εθ1 of the strain value in the circumferential direction is 0.3 or more, and the absolute value εh of the strain value in the height direction along the axis of the forged body is 0.3 or more, in step S2 forging can prevent the growth of crystalline grains, which may occur due to the temperature increase inside the forged body as a result of heat generation.

In addition, since hot rolling is performed at the rolling stage, during which deformation with an absolute value εθ2 of 0.5 or more is provided in the ring shaped body 10 in the circumferential direction, the crystalline grains in the product region of the ring shaped body 10 are reliably crushed to at least the number 8 grain sizes according to ASTM. Accordingly, the mechanical strength of the article obtained from the annular molded body 10 is reliably increased. It should be noted that εθ2 should preferably be 1.3 or less. In addition, the grain size of the annular molded body 10 should preferably correspond to ASTM grain size number 8-13. Thus, the mechanical strength of the product obtained from the annular molded body 10 can be reliably increased.

Due to the difference in grain sizes in the product area in the cross-section in the direction including the axis of the annular molded body 10, which is ± 2 according to ASTM grain size numbers, sufficient uniformity of the grain size of the annular molded body 10 in the radial direction and in the direction heights.

In addition, due to the large amount of deformation at the forging stage, as described above, the grain size of the forged body can be reduced to at least ASTM grain size number 7. Thus, the structure of the annular molded body 10 can be crushed, while the amount of deformation in the subsequent rolling step is reduced.

In addition, since rolling is performed after molding the annular intermediate body 20, so that the T / H ratio between the radial thickness and the height H of the annular intermediate body 20 is 0.6-2.3, the difference between the grain sizes in mutually equivalent positions in the annular molded body 10 in the circumferential direction can be reduced within ± 1.5 according to ASTM grain size numbers. In other words, for the annular molded body 10 obtained by molding the annular intermediate body 20, a sufficiently high uniformity of grain sizes in the circumferential direction can be ensured.

In particular, it is known that during rolling, which is a local process, different processes are performed sequentially from ordinary partial forging, and thus, the axial symmetry of the structure after molding is high and, therefore, the deviation of the characteristics of the material of the annular molded body 10 in the circumferential direction is negligible. Accordingly, by selecting the above T / H ratio for the annular intermediate body 20 before rolling within the above range, as in this embodiment, the shape (roundness) of the annular molded body 10 can be further improved, and the axial symmetry of the ring structure can also be improved. molded body 10.

In other words, since the above T / H ratio is controlled in the range of 0.6-2.3, rolling stability can be achieved, which is essential to ensure uniformity of structure. In particular, in the region in which the T / H ratio is less than 0.6, the contact area along both rolls used in rolling (main roll 40 and rolling roll 50) and material increases, and thus, the degree of influence of heat release is relatively increased as a result of which it becomes more difficult to obtain uniformity of the structure in the circumferential direction. In contrast, when the T / H ratio increases, bending can occur more easily. In particular, in the region in which the T / H ratio is greater than 2.3, the above tendency increases and thus, it becomes more difficult to obtain a uniform structure in the circumferential direction.

As described above, according to the method of manufacturing an annular molded body, which is the present embodiment, it is possible to produce annular molded bodies in which the uniformity of the structure is reliably and at low costs, and the mechanical strength is sufficiently high.

The present invention is not limited to the above-described embodiment, and can also be implemented by various modifications and alternatives in a volume that does not go beyond the concept of the present invention.

For example, the shape of the annular molded body 10 and the annular intermediate body 20 is not limited to the presented embodiment, and the design can be modified as necessary, taking into account the shape of the manufactured annular product, such as a turbine disk.

The annular molded body 10 and the annular intermediate body 20 are made of an alloy based on Ni Alloy 718, as described above; however, the material of the annular molded body 10 and the annular intermediate body 20 is not limited to this, and the annular molded body 10 and the annular intermediate body 20 can be formed from other materials (e.g., Waspaloy (registered trademark) (United Technology Inc.), Alloy 720, Co-based alloys and Fe-based alloys).

In the above embodiment, the molten metal for the Ni Alloy-based alloy 718 is obtained by smelting, and the preform is obtained by casting, but the present invention is not limited to this. Alternatively, the preform can be obtained by molding the powder, and the resulting preform is then processed at the forging and rolling stage.

In addition, in an alternative embodiment, the preform can be made by double melting (VIM + ESR or VIM + VAR), instead of manufacturing the preform by triple melting.

The present embodiment includes the step of manufacturing an opening for forming a through hole in the center of the disk-shaped forged body using a water torch, but the present invention is not limited to this. Alternatively, a through hole may be obtained by another means that is not a water cutter. Furthermore, in an alternative embodiment, a through hole may be formed during forging, and thus, the step of manufacturing the hole may be skipped. As another option, the hole can be obtained during the forging step using a water torch or the like.

Furthermore, after molding the annular molded body 10 in the rolling step S4, as shown in FIG. 3. and before performing heat treatment step S5, as shown in FIG. 3, additional processes, such as partial forging, may be performed to shape or adjust the ring shaped body 10.

In this embodiment, mutually equivalent positions (virtual planes VS1, VS2) on the annular molded body 10, defined by the even division of the annular molded body 10 into halves in the circumferential direction, are used as reference positions to control the differences between the grain size on the virtual plane VS1 and grain size on the virtual plane VS2 within ± 1.5 according to ASTM grain size numbers; however, the number of virtual planes used for comparison is not limited to two. In other words, since the equivalence of the annular molded body 10 is fully ensured in the circumferential direction, the difference between the grain sizes in mutually equivalent positions determined by uniformly dividing the annular molded body 10 into three parts in the circumferential direction can also be controlled within ± 1.5 according to the numbers grain size according to ASTM, instead of determining the difference between grain sizes in mutually equivalent positions, determined by uniform separation of the ring th molded body 10 into two parts. The circumferential positions in the annular molded body 10 in which equivalent positions are mutually defined are not limited to the positions described above in this embodiment.

Examples

The following is a detailed description of the present invention with reference to examples. However, the present invention is not limited to the following examples.

Sample Preparation

First of all, molten metal was smelted for an alloy based on Ni Alloy 718. In particular, a melting raw material was prepared so as to satisfy the condition regarding the range of components of the alloy based on Ni Alloy 718 mentioned in the above embodiment. Triple melting of this molten metal was performed. In particular, to obtain a cylindrical billet with a diameter of 254 mm, vacuum induction melting (VIM), electroslag remelting (ESR) and vacuum arc remelting (VAR) were performed.

After that, the workpiece was processed at the forging stage to prepare a disk-shaped forged body. When forging, hot forging was performed twice with heating the workpiece to 1000 ° C.

The forging step was performed under the conditions shown in Table 1, with reference to the absolute value εθ1 of the deformation of the forged body in the circumferential direction, the absolute value εh of the deformation of the forged body in the height direction, the ratio εh / εθ1 between the absolute values of stress and the strain rate. After that, a through hole was formed in the center of the forged body with a water cutter to obtain an annular intermediate body 20. The annular intermediate body 20 was molded so that the T / H ratio between the thickness T and the height H corresponded to the value shown in table 1.

Then, the annular intermediate body 20 was rolled. When rolling, hot rolling was performed twice with heating of the annular intermediate body 20 to 1000 ° C. The rolling was performed so that the total sum of the absolute value εθ2 of the deformation in the circumferential direction in the annular molded body 10 satisfies the conditions shown in table 1, by performing double hot forging.

Then the annular molded body 10 was subjected to heat treatment. As a direct aging material, a material was prepared which underwent aging under the following conditions: 718 ° C / 8 hours + 621 ° C / 8 hours + air cooling (A.S.). As an aging material in the solution, a material was prepared that underwent aging under the following conditions: 718 ° C / 8 hours + cooling in air (A.S.) after treatment with the solution under the following conditions: 970 ° C / 1 hour + quenching in water (WQ) performed after rolling.

Grain size measurement

Using the prepared annular molded body 10, measurements were made and comparison of the maximum crystalline grains in the product areas within sections, including virtual planes VS1, VS2, as well as average grain sizes near the maximum crystalline grain. As the average grain size near the maximum crystalline grain, the average grain size was used at the detection site of the maximum crystalline grain (excluding the maximum crystalline grain). The results are shown in table 2.

High temperature tensile characterization test From the ring shaped bodies 10 prepared in the above manner for Example 1 of the present invention and Comparative Example 3, tensile tests were taken at locations located in the circumferential direction, the height direction and the radial direction from mutually equivalent locations including virtual planes VS1, VS2 shown in FIG. 1, and, accordingly, high temperature tensile tests were performed at 650 ° C. The tests were performed using small test pieces according to ASTM E8 with a diameter of parallel sections of 6.35 mm, and in accordance with ASTM E21, tensile strength, yield strength (yield strength 0.2%) and compression were measured. To check the deviations of the measured values in the circumferential direction, in the height direction and in the radial direction, the ratios in the height direction and in the radial direction were calculated, while the measured value in the circumferential direction was set as unit (100%). In FIG. 8 shows the correspondence between tensile strength and compression, and FIG. 9 shows the correspondence between yield strength and compression.

In comparative samples 1 and 2, in which the strain rate at the forging stage exceeds 0.5 s ⁻¹ , the difference between the maximum grain size and the average grain size near the maximum grain size was large, and it was found that the structure was not uniform. It was found that this is caused by local growth of crystalline grains inside the forged body due to an excessive increase in temperature inside the forged body, which is caused by the formation of heat (ie, a phenomenon known as “heat generation”).

In contrast, in samples 1-4 of the present invention, in which the strain rates at the forging step were 0.5 s ⁻¹ or less, the difference between the maximum grain size and the average grain size near the maximum grain size was small, and it was found that the structure was fairly homogeneous. It was found that fairly homogeneous structures were obtained due to the small difference between the surface temperature and the temperature inside the forged body during forging, which was provided by controlling the strain rate in the range of 0.5 s ^-1 or less. It should be noted that in examples 1, 2 and 4 of the present invention, in which strain rates were controlled in the range of 0.15 s ⁻¹ or less, the structures were more uniform.

As shown in FIG. 8 and 9, as a result of tests for determining tensile strength at high temperatures, it was found that sample 1 of the present invention had better characteristics compared to comparative sample 2, taking into account tensile strength, yield strength 0.2% and compression.

In particular, it was found that in sample 1 of the present invention, the isotropy of strength characteristics increased, and sample 1 of the present invention had a fine crystalline grain structure in which sufficient uniformity was ensured.

Industrial applicability

According to the method of manufacturing an annular molded body of the present invention, annular molded bodies can be manufactured in a stable manner and at low cost, in which uniformity of structure is ensured and the mechanical strength is sufficiently high. Accordingly, the method of manufacturing the annular molded body of the present invention can be suitably used in the manufacture of turbine disks and similar engine components for aircraft.

List of Reference Numbers

10 - ring shaped body

20 - annular intermediate body

H - the height of the annular intermediate body in the axial direction

O - axis

S2 - forging step

S4 - rolling stage

T is the thickness of the annular intermediate body in the radial direction

VS1 - virtual plane (equivalent position)

VS2 - virtual plane (equivalent position)

Claims (9)

1. A method of manufacturing an annular molded body, comprising the step of forging a workpiece from an alloy based on Ni, Co or Fe to obtain a forged body having a disk-like shape, and a rolling step of the annular intermediate body manufactured by molding a through hole in the forged body to obtain an annular molded body characterized in that the forging stage includes at least two stages of hot forging, wherein each of the stages of hot forging is performed subject to the following conditions: the strain rate is not more than 0.5 s ⁻¹ , the absolute value εθ1 of the deformation of the forged body in the circumferential direction is at least 0.3, the absolute value εh of the deformation of the forged body in the height direction is at least 0.3, and the ratio εh / εθ1 between the absolute values of the deformation is 0.4-2.5. 2. A method of manufacturing an annular molded body according to claim 1, characterized in that the difference between the grain sizes in the cross section of the annular molded body in the direction of the axis of the annular molded body is within a range of ± 2 according to ASTM grain size numbers. 3. A method of manufacturing an annular molded body according to claim 1 or 2, characterized in that at the forging stage, the grain size of the forged body corresponds to at least ASTM grain size number 7. 4. A method of manufacturing an annular molded body according to claim 1 or 2, characterized in that the annular intermediate body is formed in such a way that the T / H ratio between the thickness T of the annular intermediate body in the radial direction and the height H of the annular intermediate body in the axial direction is the range of 0.6-2.3, while the annular intermediate body is subjected to rolling so that the difference between the grain sizes in the equivalent positions of the annular molded body, evenly spaced in the circumferential direction and, is ± 1.5 according to ASTM grain size numbers. 5. A method of manufacturing an annular molded body according to claim 1 or 2, characterized in that at the rolling stage I carry out hot rolling so that the absolute value εθ2 of the deformation of the annular molded body in the circumferential direction transmitted to the annular molded body is 0.5-1 , 3. 6. A method of manufacturing an annular molded body according to claim 1 or 2, characterized in that the preform is made of an alloy based on Ni. 7. A method of manufacturing an annular molded body according to claim 6, characterized in that the forging stage is performed at a temperature of 950-1075 ° C. 8. A method of manufacturing an annular molded body according to claim 6, characterized in that the rolling step is performed at a temperature of 900-1050 ° C.

Images