JP2014184484A - Method of forming thermostable alloy ring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a ring rolling raw material to be formed as a high-quality thermostable alloy ring.SOLUTION: For forming the ring rolling raw material, a ring rolling mill is used which includes: a main roll and a mandrel roll that are arranged opposite to the radial outer circumferential surface of the ring rolling raw material and the radial inner circumferential surface of the same, respectively; and an upper axial roll and a lower axial roll that are arranged opposite to the height-direction upper surface of the ring rolling raw material and the height-direction lower surface of the same, each of the axial rolls having a flat conical surface and a recessed part in the axial-direction end part of the axial roll. The ring rolling raw material is rolling-formed into a thermostable alloy ring by reducing a radial-direction interval between the main roll and the mandrel roll while heating the thermostable alloy raw material preformed in a ring shape to the recrystallization temperature or more. A cross-sectional shape 110 of the ring rolling raw material is a substantially symmetrical shape with respect to the center line dividing the height direction of the ring rolling raw material into two parts, and is formed in such a tapered shape that a height is reduced toward at least one of the inner diameter side and the outer diameter side of the center line. The tapered part forms a free space allowing for deformation of the ring rolling raw material in forming using the ring rolling mill, consequently abnormal heating in ring rolling is prevented.

Description

  The present invention relates to a heat-resistant alloy ring used in a high temperature environment, and to a method for forming a heat-resistant alloy ring.

As an example of an apparatus in which parts made of a heat-resistant alloy are frequently used, a gas turbine can be cited. The gas turbine generates power by arranging blade-shaped blades on the outer periphery of a ring-shaped turbine disk attached in multiple stages to a rotating shaft, and converting the axial fluid flow into rotational motion.
The air sucked from the front of the gas turbine is compressed by the subsequent multistage axial compression section, and then the high-temperature and high-pressure combustion is performed by burning the gas mixed with the fuel in the compressed air in the combustor placed after the gas turbine. Gas is generated. The combustion gas collides with a blade attached to the turbine disk while flowing in the axial direction in the flow path on the outer peripheral portion of the turbine disk, whereby the axial movement is converted into a rotational movement, and the turbine disk is rotated at a high speed. This rotational driving force acts to rotate continuously by rotating the turbine disk in the previous stage via the rotating shaft and compressing the air.

In recent years, improving the efficiency of gas turbines has become an important technical issue from the viewpoint of energy conservation. However, the higher the maximum temperature of the combustion gas handled, the higher the efficiency. Yes.
On the other hand, since the turbine disk and blade of a gas turbine are used by rotating at high speed, they receive a high load due to centrifugal force during operation. Further, since these turbine disks and blades are exposed to a high-temperature gas of 600 ° C. or higher or are used near the flow path of the high-temperature gas, it is indispensable to have high strength in a high-temperature environment. Further, when used in an operation pattern in which the start and stop of the gas turbine are intermittently generated, these components are repeatedly loaded, and the thermal stress generated during the temperature rise and cooling of the components also repeatedly acts.
Therefore, it is important to configure the gas turbine using parts having sufficient strength against the load and thermal stress that repeatedly act in this way.

  On the other hand, in order to increase the efficiency of the turbine, the size of a rotating body such as a turbine disk or blade tends to increase in size, so a high-quality heat-resistant alloy ring that can withstand higher centrifugal force is required. In order to meet these demands, austenitic stainless steel, titanium alloy, Ni-based alloy and the like are mainly used as heat resistant alloys having high strength in a high temperature environment in the gas turbine.

Among these heat-resistant alloys, it is known that Ni alloy (for example, 718 alloy) having excellent high temperature strength can improve fatigue strength by refining the metal crystal structure. Various techniques have been proposed so far for miniaturization techniques.
For example, as described in Patent Document 1, in order to refine the crystal structure, a method of precipitating particles that suppress the coarsening of crystal grains is an effective means. In addition, as described in Patent Document 2, a method of obtaining fine grains by mobilizing strain in a raw material during hot working to promote a miniaturization phenomenon has been proposed.
Regarding the heat-resistant alloy ring manufacturing method, among heat-resistant alloys, especially Ni-based materials are expensive compared to ordinary steel materials because they are mainly composed of rare metals, and near-net-shaped materials that are close to finished shapes as cutting materials. Near net forging which can reduce the amount of chips at the time of cutting and reduce the manufacturing cost is often used.

  Generally, hot forging is used for near net forging. As an example of the manufacturing process, first, a cylindrical billet is first formed into a disk by upsetting forging, then the center is perforated, and then predetermined by ring rolling. A hot forging process is used in which a ring having a diameter of 5 mm is formed and finally a cross-sectional shape is formed using a mold.

Japanese Patent Publication No. 7-42535 Japanese Examined Patent Publication No. 7-138719 JP 2011-56548 A

However, in ring rolling using the above-mentioned hot forging process, abnormally high temperature heat generation may occur depending on manufacturing conditions, which may cause quality deterioration. That is, in the case of a Ni-based alloy, for example, 718 alloy, when the temperature exceeds 1050 ° C., the particles that suppress the growth of crystal grains are dissolved in the base material, so that the growth of crystal grains is activated and a coarse grain structure is generated. For this reason, at the time of ring rolling, it is a very important technical problem to manufacture so that no abnormally high temperature generation point is generated in the Ni-based alloy.
Conventionally, a ring rolled material with a rectangular cross section is used as the ring rolled material, but when rolling this, it is easy to form a recess in the central part of the upper and lower surfaces, and in order to prevent this, rolling is performed while rolling down the axial roll in the vertical direction. There is a need to do. However, since the structure for rolling down in the vertical direction is a cantilever, it is general that the rolling force is about half that of the main roll. Therefore, in anticipation of the formation of a recess, a machining allowance is provided, so that not only the near net is insufficient, but the load required for rolling may increase.

  Further, in the forging process to the final die, when forming a complicated cross-sectional shape such as a turbine disk, it is difficult to apply uniform and optimal strain to the entire surface of the material by die forging. For this reason, depending on the forging target shape, there may be a dead zone in which distortion is hardly applied during forging. In such a case, in the dead zone, the phenomenon of refinement of the metal crystal structure due to strain mobilization is not sufficiently performed, and coarse grains that are a cause of quality deterioration frequently occur, which is a manufacturing problem. Become.

Therefore, when a die forging material is manufactured by ring rolling, it is an important technical problem to obtain a fine crystal structure in advance in the stage of ring rolling, which is a pre-process.
In light of these technical problems, the object of the present invention is to suppress an excessive temperature rise during ring rolling and to mobilize a uniform and optimal strain on the entire surface of the ring rolling material in a high temperature part such as a gas turbine. An object of the present invention is to provide a method for forming a ring made of a heat-resistant alloy as a material for a heat-resistant alloy rotating part to be used.

  The present invention includes a plurality of means for solving the above-described problems. For example, the ring rolling material forming method of the present invention comprises a heat-resistant alloy material preformed in a ring shape, and is recrystallized. A ring rolling mill comprising a main roll and a mandrel roll disposed opposite to the radially outer peripheral surface and the inner peripheral surface, and upper and lower axial rolls disposed opposite to the upper and lower surfaces in the height direction while being heated to a temperature higher than that. Is a method of forming a ring-rolled material that is rolled into a heat-resistant alloy ring by narrowing the radial distance between the main roll and the mandrel roll, and includes a flat conical surface and its axis as upper and lower axial rolls. An axial roll having a recess at the direction end is used, and the main roll and By reducing the radial distance between the rolls, the height of the ring-rolled material decreases in the height direction toward at least one of the inner diameter side and outer diameter side of the center line that bisects the height direction. In order to form a tapered shape, the ring rolled material is preformed, and then the upper and lower axial rolls are once separated from the upper and lower surfaces in the height direction of the ring rolled material, and the flat conical surface is the ring rolled. Heat resistance is achieved by further reducing the radial distance between the main roll and mandrel roll while moving the ring rolling material in the axial direction so as to face the upper and lower surfaces in the height direction of the material and maintaining the ring rolling material at the recrystallization temperature or higher. An alloy ring was rolled and formed.

By using the method for forming a ring-rolled material according to the present invention, it is possible to omit the man-hour for processing the cross-sectional shape of the ring-rolled material by a cutting process before ring-rolling, and a ring can be obtained in a short time. Moreover, since the amount of chips can be reduced by omitting the cutting process, the yield of the material can be improved.
That is, instead of cutting into a suitable material cross-sectional shape in the pre-ring process, the inner diameter side, which is likely to generate heat at the initial stage of rolling, is preformed into the shape of the ring rolled material of the present invention, so that ring rolling with less heat generation is performed. Thus, not only can a high-quality heat-resistant alloy ring be provided, but also a machining process is not required in the process before ring rolling, and the manufacturing time can be shortened.

  At that time, by selecting the rolling conditions such as the shape of the recesses formed in the upper and lower axial rolls, the initial heating temperature of the ring rolling material, the rolling force by each roll in the ring rolling mill, and the change speed sequence, the rolling time, etc. By making the temperature difference between the inner peripheral surface and the outer peripheral surface of the ring rolled material at the time of processing within 200 degrees, it is possible to perform rolling while maintaining the temperature in the ring cross section within a certain range, and the processing temperature becomes high. In addition to suppressing the generation of coarse particles due to excessively high temperature, it is possible to prevent the formation of a structure in which coarse particles and fine particles are mixed due to excessively low temperature, and a higher quality ring can be obtained. . Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

FIG. 1 is a schematic diagram showing an example of a ring rolled material. FIG. 2 is an example of a flowchart for explaining the manufacturing method of the first embodiment. FIG. 3 is a diagram illustrating a change in cross-sectional shape by the manufacturing method of the first embodiment. FIG. 4 is a schematic view showing an example of a ring rolling mill.

Hereinafter, examples will be described with reference to the drawings.
[Example 1]
As a ring rolling mill used in the present embodiment, for example, a structure as shown in FIG. 4 can be used.
That is, in this ring rolling mill, a main roll 106 that can be rotated at a predetermined rotational speed and a mandrel roll 105 that can be driven to rotate around an axis are disposed opposite to the radially outer peripheral surface and the inner peripheral surface of the ring rolled material 101, and the ring rolling is performed. Axial rolls 107 </ b> A and 107 </ b> B are provided so as to face the upper surface and the lower surface when viewed from the height direction of the material 101.
In order to reduce the misalignment of the ring rolled material 101 during rolling, a guide roll that can be driven and rotated on both sides of the main roll 106 is arranged, and rolling while supporting the outer peripheral portion of the ring rolled material 101 provides more stable rolling. Can do.

The main roll 106 has a cylindrical shape, and rotates the ring rolled material 101 by being driven while being in contact with the outer peripheral surface of the ring rolled material 101 during rolling.
A cylindrical roll is used as the mandrel roll 105, and the mandrel roll 105 has a structure that can freely rotate around the axis, and is disposed substantially parallel to the rotation axis of the main roll 106.
During rolling, rolling is performed in a state where the outer peripheral surface of the mandrel roll 105 is in contact with the inner peripheral surface of the ring rolled material 101, and the distance between the rolls sandwiched between the main roll 106 and the mandrel roll 105 is gradually increased during rolling. By narrowing the ring rolling material 101, the space between the radially inner peripheral surface and the outer peripheral surface of the ring rolled material 101 is pressed in the thickness direction.

The upper and lower axial rolls 107 </ b> A and 107 </ b> B have a conical shape having an apex angle of 20 to 45 °, and the front ends of the ring-rolled material 101 are substantially centered in order to adjust the height dimension of the ring-rolled material 101. Placed in.
In this embodiment, the axial rolls 107A and 107B are driven and rotated in accordance with the number of rotations of the ring rolling material 101 during rolling, but may be driven and rotated.

As a rolling procedure, the mandrel roll 105 is passed through the inner diameter hole of the ring rolled material 101 heated to a predetermined temperature, and the mandrel roll 105 is moved radially outward so that the distance between the main roll 106 and the mandrel roll 105 is gradually reduced. When the distance between the two rolls gradually matches the initial thickness of the ring rolled material 101, the ring rolled material 101 is rotated by the friction between the surface of the main roll 106 and the outer peripheral surface of the ring rolled material 101. Is granted. At this time, the mandrel roll 105 rotates following the rotation of the ring rolling material 101.
Thereafter, the mandrel roll 105 is gradually moved outward in the radial direction, and the interval between the main rolls 106 is gradually narrowed to reduce the thickness direction and continuously plastically deform along the circumferential direction of the ring rolled material 101. Will give.

In this embodiment, prior to the final rolling step, for example, the ring rolled material 101 is pre-formed into the shape 110 by the step shown in FIG. 2 and the cross-sectional shape shown in FIG. The rolling method is shown in the flowchart of FIG.
First, the rectangular ring rolling material 101 is heated in S1. Next, a rectangular ring rolling material is set in a rolling device in S2. After the positioning between the mandrel 105 and the main roll 106 is set to the rolling initial value in S3 and positioning is performed, the main roll 106 is rotated in S4 to start the rotation of the ring rolling material 101.

  Next, it positions so that the recessed part formed in the axial direction front end side of the axial roll 107 by S5 may correspond to the radial direction inner periphery and the outer peripheral corner | angular part of the ring rolling raw material 101. FIG. In this state, reduction is performed in the thickness direction in S6 to perform rolling of the 101 corners, for example, preforming into a form of the ring rolled material 101 as shown in FIG.

  In order to confirm the effect of the present embodiment, a change in cross-sectional shape was obtained using viscoplastic finite element analysis. In consideration of symmetry with respect to the center plane in the height direction of the ring rolled material 101, calculation was performed using a 1/2 model.

FIG. 3 shows a change in the cross-sectional shape obtained from the above analysis. Here, the analysis was performed with particular attention paid to the steps S5 and S6.
The initial gap between the axial roll recess and the material is defined as d0, and the axial pushing amount is defined as h0−H0 / d0k × 100%, and the cross-sectional shapes at the initial (0%), 50%, and 100% stages are extracted. .

  In the initial stage, as described above, first, the ring rolled material and the concave portion of the axial roll 107 are positioned at a position where they match. Thereafter, when the axial roll 107 is rolled down, the surface shape of the concave portion of the axial roll 107 is transferred to the corners of the ring-rolled material, and chamfered. Thereafter, the axial roll 107 is separated from the upper and lower surfaces of the ring rolled material 101, and the same rolling is performed by repositioning so that the flat conical surface of the axial roll 107 and the upper and lower surfaces of the ring rolled material 101 are in contact with each other. In the middle of rolling, rolling can be performed in a state where heat generation at the corners of the material is suppressed.

By carrying out the rolling method as described above, even when a conventional ring-rolled material having a rectangular cross section is used, by performing preforming of the corners at the initial stage, local heat generation in the rolled part is caused in the subsequent rolling. Therefore, a heat resistant alloy ring having a good internal structure can be manufactured. Moreover, the step of cutting the step of forming the tapered portion on the inner surface of the ring rolled material in advance is not necessary.
Further, the above rolling method utilizes the fact that the axial roll 107 can be reduced in the height direction, and even the rings having different thicknesses can be flexibly handled by positioning the axial roll 107.

Therefore, since it can be carried out without using the mandrel roll 105 and the main roll 106 provided with the conventional mold shape, not only the tool cost can be reduced, but also the number of man-hours for changing the mold of the mandrel roll 105 can be reduced. Can be shortened.
When the ring diameter of the rolling target is larger than the initial value, the material may flow again during rolling at the corners given in FIG. 3 (c). The diameter expansion may be continued after performing the steps b) and (c) and chamfering the corners again.

[Example 2]
A method for rolling the heat-resistant alloy ring of this example will be described.
In this embodiment, a Ni-base heat-resistant alloy excellent in high-temperature strength is used as a ring rolling material for a gas turbine disc having a diameter of 1000 or more. Hereinafter, as an example of a component of Ni-based heat resistant gold, i: 50 to 55%, Cr: 15 to 22%, Nb: 4.5 to 6.5%, Mo: 2.5 to 3.5%, Ti : Ni-alloy ring rolled material 101 having a component composition of 0.6 to 1.2%, Al: 0.2 to 0.8%, using the manufacturing method of the example, the heat-resistant alloy material is the final product When rolling into a ring, the composition and shape of the ring rolled material 101, the shape of the recess formed in the axial roll 107, the initial heating temperature of the ring rolled material 101, the rolling force of each roll in the ring rolling mill, and changes thereof By selecting rolling conditions such as speed sequence and reduction time, ring rolling is performed so that the temperature difference between the inner periphery and the outer periphery is within 200 ° C.

  That is, in order to prevent an unstable rolling state, it is effective to manage the temperature difference between the inner periphery and the outer periphery of the ring rolled material 101 in the rolling process of the ring rolled material 101. By setting the temperature within the range of 0 ° C., a stable state is maintained, and a heat-resistant ring having a good structure can be obtained.

  In the rolling conditions used in Example 1, since the main roll is larger than the mandrel roll, more attention is paid to the distortion on the inner and outer circumferences of the ring, and more distortion on the inner diameter side is introduced. Therefore, the inner diameter tends to generate heat. On the other hand, on the outer peripheral side, the heat of the material is transferred to the roll by contact with the main roll, so the outer peripheral portion tends to decrease in temperature. When ring rolling is performed, if the temperature of the outer peripheral portion decreases due to contact with the main roll or heat radiation to the outside air, the material from approximately 1/2 of the thickness to the outer peripheral portion may hinder the expansion of the ring itself. Act on. As a result, the inner diameter side material bears more rolling force from the mandrel roll, and heat generation increases.

  By using the manufacturing method of the above structure, the structure change during rolling can be produced stably, and a high-quality ring rolled material can be obtained. The ring outer circumference and inner circumference during ring rolling may be measured by measuring the surface temperature by using a non-contact thermometer.

100 Center axis of ring rolled material 105 Mandrel roll 106 Main roll 107A Upper axial roll 107B Lower axial roll 110 Height direction cross-sectional shape of ring rolled material

Claims (2)

A main roll and a mandrel roll, which are made of a heat-resistant alloy material preformed in a ring shape and are opposed to the radially outer peripheral surface and the inner peripheral surface in a state heated above the recrystallization temperature, and the upper surface in the height direction Using a ring rolling mill having upper and lower axial rolls arranged opposite to the lower surface, by narrowing the radial distance between the main roll and the mandrel roll, the ring rolling material is formed into a heat-resistant alloy ring by a rolling method. There,
As the upper and lower axial rolls, an axial roll having a flat conical surface and a concave portion at its axial end is used, and the concave portion is disposed opposite to the upper and lower surfaces in the height direction of the ring rolling material, while the main roll By narrowing the radial interval between the mandrel roll and the ring rolling material, the height of the cross-sectional shape in the height direction is increased toward at least one of the inner diameter side and the outer diameter side of the center line that bisects the height direction. A method of forming a ring-rolled material that forms a tapered shape with reduced thickness. By selecting the rolling conditions such as the shape of the recess, the initial heating temperature of the ring rolling material, the rolling force by each roll in the ring rolling mill, and the change speed sequence, the rolling time, etc., the ring rolling during the rolling step The method for forming a ring-rolled material according to claim 1, wherein a temperature difference between the inner peripheral surface and the outer peripheral surface of the raw material is within 200 degrees.

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