JP7639422B2 - Manufacturing method of hot forged materials - Google Patents

Description

The present invention relates to a method for manufacturing hot forged materials.

For example, some aircraft engine parts and power generation parts are made by processing long bars into shaft shapes. To manufacture these, ingots adjusted to a specified composition are used to form billets or rough areas by hot forging, which are then hot forged into the final product shape. For example, Patent Document 1 (JP Patent Publication 6-238387) discloses an invention for a forging method of long steel material suitable for manufacturing long shafts for large aircraft engines, in which a bar having an upset end portion and a shaft portion, with a ratio L1/D of length L1 to outer diameter D of 1 to 3, is upset forged at an upset ratio of 1/2u or more at the upset end portion, reheated to a temperature below the recrystallization temperature, and the shaft portion is forged using a four-sided forging machine at a forging ratio of 2s or more to a length L2 of 2000 mm or more for the forged shaft portion.

Japanese Patent Application Publication No. 6-238387

According to the forging method for long steel materials described in the above-mentioned Patent Document 1, a forging material used in upset forging to form a flange is a cylindrical round bar. The forging material is heated to a predetermined temperature and inserted into a hole provided in a lower die for hot forging, and the part not restrained by the hole is pressed against the end face of the forging material by an upper die for hot forging to perform upset forging.
When a part of the material is hot forged, if the entire forging material to be hot forged is heated to a heating temperature, the parts that are not hot forged will also be heated at a high temperature. In particular, the heating temperature becomes high for hard-to-work materials such as Ni-based superalloys that are strengthened by precipitates such as γ' (gamma prime) phase.

However, by heating the entire forging material, there is a problem that bending defects occur in the forging material or the hot forged material after hot forging, and the hot forged material after hot forging is difficult to remove from the hole provided in the lower die for hot forging, which reduces productivity. Bending defects not only increase the machining cost, but also lead to defects in the product itself.
For example, even in the case of a round bar-shaped forging material, in a long stepped forging material with different diameters, such as a large diameter portion and a small diameter portion integrally formed, bending of the small diameter portion may occur if the forging material is placed horizontally in the heating process before hot forging. If this happens, it becomes difficult to insert the small diameter portion into the hole formed in the hot forging lower die in the next process of hot forging.
In addition, when the large diameter portion is pressed to perform hot forging while the small diameter portion is restrained by the hole formed in the lower die for hot forging, the small diameter portion may expand thermally and become difficult to insert into the hole, or after the large diameter portion is formed into a predetermined shape by hot forging, the large diameter portion and the cavity portion of the lower die are closely attached by the pressure of hot forging, so the lower end face side of the small diameter portion may be removed with a knockout pin. In this case, the small diameter portion may be deformed due to the impact of the knockout pin being applied to the small diameter portion. To prevent this, if the diameter of the small diameter portion and the diameter of the hole are similar, the space for deformation will be narrowed, but since the heated small diameter portion as described above undergoes thermal expansion, the diameter of the hole cannot be reduced excessively. Therefore, the temperature of the lower die for hot forging or the small diameter portion may be adjusted again before removal, which reduces productivity.
An object of the present invention is to provide a method for producing hot forged material that can increase productivity while suppressing bending of the forging material during heating in hot forging.

The present invention has been made in view of the above-mentioned problems.
That is, the present invention is a method for producing hot forged material by hot forging the large diameter portion of a rod-shaped forging material having a large diameter portion and a small diameter portion, wherein the small diameter portion of the forging material is inserted into a hole of a material holding jig having a hole for inserting the forging material, the large diameter portion is heated to a heating temperature to form a heated material, the heated material is removed from the material holding jig, and then the small diameter portion of the heated material is inserted into the hole of a hot forging lower die having a hole for inserting the heated material, and hot forging is performed in which the large diameter portion is pressed axially with a hot forging upper die to form a hot forged forging material.

According to the present invention, it is possible to suppress bending of the forging material when it is heated during hot forging, and further increase productivity.

1 is a schematic diagram of a stepped rod-shaped forging material and a heating jig for heating the forging material. 1 is a schematic cross-sectional view of a stepped rod-shaped forging material inserted into a through hole of a heating jig. 1 is a schematic cross-sectional view of a stepped rod-shaped forging material inserted into a blind hole in a heating jig. 1 is a schematic cross-sectional view of a large diameter portion of a heating material inserted into a lower die being hot forged by pressing with an upper die. FIG.

The present invention will be described in detail below. In the following, the term "heated material" refers to a material before being charged into a heating furnace, the term "heated material" refers to a material heated to a predetermined temperature in a heating furnace, and the term "hot forged material" refers to a material formed into a predetermined shape by a hot forging device.
In addition, the "hot forging" referred to in the present invention refers to a process in which the heated material is pressed by a lower die for hot forging (sometimes simply referred to as a "lower die") and an upper die for hot forging (sometimes simply referred to as an "upper die") to perform hot plastic processing.
<Forging material>
The forging material 1 used in the present invention is a stepped rod-shaped material having a large diameter portion 11 and a small diameter portion 12 as shown in FIG. 1. The forging material 1 is preferably shaped by radial forging using a four-sided forging machine, which repeatedly presses the rod-shaped material to be the forging material from four directions over its entire length while rotating it intermittently in the circumferential direction to elongate the entire length. Since the end face of the large diameter portion of the forging material is pressed by the upper die, it is preferable that the length of the forging material is three times or less than the diameter D of the large diameter portion so as not to cause buckling. In addition, the "large diameter" and "small diameter" in the present invention include not only a circle, but also a polygon having, for example, a hexagon or more. In the case of a polygon, the diameter D can be calculated from the circumscribing circle.
The material of the forging material used in the present invention is reinforced with precipitates such as the γ' (gamma prime) phase, which is suitable for aircraft engine parts and power generation parts, and is intended to be applied to Ni-base superalloys and maraging steels, which contain the most Ni.

<Material holding jig>
In the present invention, a material holding jig 2 as shown in Fig. 1 is used as a jig for heating the large diameter portion 11 of the forging material 1. The purpose of using the material holding jig 2 is to heat only the large diameter portion 11 as much as possible and to reduce the directly heated area of the small diameter portion 12, thereby suppressing thermal expansion of the small diameter portion and facilitating insertion and removal into and from the lower die.
The blank holding jig 2 shown in FIG. 1 has a plurality of holes 21 formed therein, into which the small diameter portion 12 of the forging blank 1 is inserted to expose the large diameter portion 11. The number of holes 21 formed in the blank holding jig 2 may be one, but it is preferable to provide two or more holes, since providing a plurality of holes allows multiple large diameter portions of the forging blank 1 to be heated simultaneously. The material of the blank holding jig may be any insulating material having a heat insulating effect, such as heat-resistant bricks or mortar. The diameter of the hole 21 formed in the blank holding jig 2 may be smaller than the diameter D of the large diameter portion 11 of the forging blank 1.
As shown in FIG. 1, when inserting the forging material 1 into the hole 21 of the material holding jig 2, it is preferable to insert it from the side, and the depth (length) of the hole is preferably deeper (longer) than the small diameter portion of the forging material. This structure is used because, for example, when the large diameter portions 11 of a plurality of forging materials 1 are to be heated simultaneously, even if there is some variation in the length of the small diameter portion 12 of the forging material 1, the large diameter portion 11 can be heated and the thermal expansion due to heating of the small diameter portion 12 can be suppressed. In addition, if the structure is used to insert from the side, the forging material can be easily inserted and removed with a manipulator, and productivity can be increased. Insertion and removal from above may require a crane, and it takes too much time from removal to the start of hot forging.

2 and 3 are schematic cross-sectional views of the small diameter portion 12 of the forging material 1 inserted into the material holding jig 2. The material holding jig 2 may be a through hole (hole 21) as shown in FIG. 2, or a non-through hole 21 having a bottom portion 22 as shown in FIG. 3. When the large diameter portion is heated, the temperature of the small diameter portion inevitably rises, and the non-through hole 21 having the bottom portion 22 as shown in FIG. 3 is more effective in suppressing the temperature rise of the small diameter portion. Therefore, in the present invention, it is preferable to use a material holding jig having a non-through hole 21 with a bottom portion 22.
In the present invention, the most preferable structure of the material holding jig is as follows.
A material holding jig for heating a large diameter portion of a rod-shaped forging material having a large diameter portion and a small diameter portion, the material holding jig having a side surface provided with a plurality of blind holes into which the small diameter portion of the forging material is inserted, the length of the holes being longer than the length of the small diameter portion.

<Large diameter portion heating process>
In the present invention, the small diameter portion 12 of the forging material 1 is inserted into the hole 21 provided in the material holding jig 2, and the large diameter portion 11 of the forging material 1 is heated to a heating temperature to become a heating material.
In order to partially heat the forging material 1 and heat the large diameter portion 12 to a predetermined heating temperature, for example, high-frequency heating or the like can be used, but in this case, heating is performed for each forging material. In addition, since it takes time to sufficiently heat the entire large diameter portion, it is preferable to select a method that can heat multiple forging materials at once. Therefore, in the present invention, when performing the heating process of the large diameter portion, it is preferable to select a method in which a material holding jig is installed in a heating furnace (not shown) in advance, and after the heating furnace is heated to a predetermined temperature, the small diameter portion 12 of the forging material 1 is inserted into a hole 21 provided in the material holding jig 2.
In the material holding jig 2 to be installed in the heating furnace, it is preferable to form a non-through hole 21 having a bottom portion 22 as shown in FIG. 3. For example, if the material of the forging material is a Ni-based super heat-resistant alloy, which is a difficult-to-process material, the heating temperature may be 850 to 1050°C. In this case, if a through hole (hole 21) as shown in FIG. 2 is formed, the temperature of the center of the small diameter portion is about 50 to 180°C lower than the temperature of the large diameter portion. In contrast, in the case of a structure in which a non-through hole 21 having a bottom portion 22 as shown in FIG. 3 is formed, the temperature is kept at 500°C or lower, which is 300°C or more lower than the temperature of the large diameter portion, and the thermal expansion of the small diameter portion can be reliably suppressed, and bending defects of the small diameter portion due to heating can be suppressed.

<Hot forging process>
In the large diameter portion heating process, the heating material heated to a predetermined temperature is removed from the material holding jig, and then the small diameter portion of the heating material is inserted into a hole provided in a lower die having a hole for inserting the heating material, and hot forging is performed in which the large diameter portion is pressed axially by an upper die to produce a hot forged material.
4 is a schematic cross-sectional view of the small diameter portion of the heating material 3, which is the forging material 1 heated to a predetermined temperature, being inserted into the hole 41 provided in the lower die 4. As described above, in the large diameter portion heating process, the thermal expansion of the small diameter portion is also suppressed by suppressing the temperature rise of the small diameter portion 12, so that the small diameter portion can be easily inserted into the hole 41 provided in the lower die 4.
In addition, since the heating material 3 according to the present invention has a stepped rod shape having a large diameter portion and a small diameter portion, the diameter of the large diameter portion of the heating material 3 is larger than the hole diameter of the hole 41 provided in the lower die 4, and the step of the stepped portion 31 of the large diameter portion is utilized to bring the step portion 31 into contact with the lower die (the step portion 31 is supported by the lower die), and the end face of the small diameter portion is suspended in the air without contacting the bottom of the lower die. Moreover, since the temperature of the small diameter portion is lower than that of the large diameter portion and thermal expansion is suppressed, for example, it is not necessary to excessively increase the gap between the diameter of the hole 41 provided in the lower die 3 and the diameter of the circumscribed circle of the small diameter portion 12. In addition, if the central axis of the heating material 3 and the hole 41 provided in the lower die 4 are aligned, it is also possible to make the small diameter portion of the heating material 3 inserted into the hole 41 of the lower die 4 non-contact with the inner peripheral surface of the hole 41.

As described above, the small diameter portion of the heating material 3 is inserted into the hole 41 provided in the lower die 4, the stepped portion 31 of the large diameter portion is brought into contact with the lower die 4 (the stepped portion 31 is supported by the edge of the hole 41 of the lower die 4), and the upper die 5 is lowered with the end face of the small diameter portion not in contact with the bottom of the lower die, and the large diameter portion of the heating material 3 is pressed in the axial direction to form the hot forged material 6. In addition, since the small diameter portion can be made not in contact with the bottom of the lower die 4, deformation such as bending of the small diameter portion can be suppressed when the large diameter portion 11 is pressed by the upper die. Even after being formed into the hot forged material 6, the thermal expansion of the small diameter portion remains suppressed, and the hot forged material 6 can be smoothly removed from the lower die 4.
According to the hot forging method of the present invention, the large diameter portion to be hot forged is heated preferentially and the temperature rise of the small diameter portion can be suppressed, so that bending of the small diameter portion during the heating process can be prevented. In addition, since the thermal expansion due to the temperature rise of the small diameter portion can be suppressed, the heating material can be smoothly inserted and removed from the lower die, so that the productivity can be improved.

Example 1
A stepped bar-shaped material of 18% Ni maraging steel (class 250) was prepared as a forging material to be formed into an aircraft engine part. The forging material was radially forged by a four-sided forging machine that repeatedly extends the entire length by pressing from four directions while rotating intermittently in the circumferential direction, and finished to a circumscribed circle of a large diameter portion of 180 to 205 mm, a length of the large diameter portion of 440 to 550 mm, a circumscribed circle of a small diameter portion of 118 to 139 mm, and a length of the small diameter portion of 1380 to 2150 mm.
The forged material was used to confirm the occurrence of bending failures during heating of the large diameter portion. The material holding jig used in the large diameter portion heating process had a through hole (hole 21) as shown in Figure 2 and a non-through hole 21 with a bottom portion 22 as shown in Figure 3. The one having the non-through hole 21 with the bottom portion 22 as shown in Figure 3 of the present invention is referred to as Example A of the present invention, and the one having the through hole (hole 21) as shown in Figure 2 is referred to as Example B of the present invention.

The diameter of the hole 21 of the blank holding jig 2 into which the small diameter portion 12 of the present invention A and B of the forging blank 1 is inserted is approximately 200 mm, the depth (length) of the hole 21 is approximately 2500 mm in the case of a non-through hole, and four holes were provided in the blank holding jig 2. The number of holes 21 in the blank holding jig 2 having through holes is also the same.
As shown in FIG. 1 , the material holding jig was installed in a heating furnace so that the forging material 1 could be inserted from the side when being inserted into the hole 21 of the material holding jig 2. The heating furnace was heated to a predetermined temperature and maintained at that temperature. The large diameter portion 11 of the forging material 1 was held by a manipulator in the hole 21 of the material holding jig 2, and the small diameter portion 12 was inserted into the hole 21 in sequence.
The heating temperature in the furnace for hot forging was set to about 900° C., and the large diameter portion 11 of the forging material 1 of the present invention A and the present invention B was selectively partially heated.
When the large diameter portion 11 was sufficiently heated, the temperature of the small diameter portion 12 near the center of its length was measured after extraction from the heating furnace. The results are shown in Table 1. The temperature was measured using a radiation thermometer. The temperatures shown in Table 1 are the measurement results of four pieces each, and the comparative example is the result of heating a material of the same shape in a furnace without using the heating jig of the present invention.

As shown in Table 1, the temperature of the small diameter portion of present invention A is 300°C or more lower than the temperature of the large diameter portion, and is suppressed to a temperature of 500°C or less. The temperature of the small diameter portion of present invention B is 60-180°C lower than the temperature of the large diameter portion, and is suppressed to a temperature of 800°C or less. Therefore, by applying the methods of present invention A and present invention B in particular, the effects of the present invention can be achieved. Furthermore, with present invention A, there was almost no bending of the small diameter portion after heating.

Example 2
Based on the results of Example 1 described above, hot forging was performed by applying the large diameter portion heating process applied to the present invention A and the present invention B. The material, shape, and dimensions of the forging material used and the material holding jig were the same as those shown in Example 1. The heating temperature for hot forging was set to approximately 900°C, and the forging material 1 of the present invention A and the present invention B was partially heated for 2 to 7 hours to selectively heat the large diameter portion 11. Next, after removing the heating material heated to approximately 900°C from the material holding jig, the small diameter portion of the heating material was inserted into the hole provided in the lower die having a hole for inserting the heating material, and hot forging was performed in which the large diameter portion was pressed axially by the upper die 5 to obtain a hot forged material.
As shown in FIG. 4, the hot forging was performed by inserting the small diameter portion of the heating material 3 into a hole 41 provided in the lower die 4. Since the heating material 3 is a stepped rod-shaped heating material 3 having a large diameter portion and a small diameter portion, the step of the stepped portion 31 of the large diameter portion is utilized, the step portion 31 is brought into contact with the lower die (the step portion 31 is supported by the lower die), and the end face of the small diameter portion is suspended in the air without contacting the bottom of the lower die. Furthermore, the central axes of the heating material 3 and the hole 41 provided in the lower die 4 are aligned, so that the small diameter portion of the heating material 3 inserted into the hole 41 of the lower die 4 is not in contact with the inner circumferential surface of the hole 41. In addition, in the large diameter portion heating process, the thermal expansion of the small diameter portion is also suppressed by suppressing the temperature rise of the small diameter portion 12, and the occurrence of bending is also suppressed, so that the small diameter portion can be easily inserted into the hole 41 provided in the lower die 4.
In addition, because the small diameter portion was not in contact with the bottom of the lower die 4, deformation such as bending of the small diameter portion was also suppressed when the large diameter portion 11 was pressed by the upper die. Even after being formed into the hot forged material 6, the thermal expansion of the small diameter portion remained suppressed, and the hot forged material 6 could be smoothly removed from the lower die 4.

More than 100 hot forged materials were produced by the above hot forging, and the defective rate due to bending was suppressed to 0% for invention A and to less than 1% for invention B.
From the above, according to the hot forging method of the present invention, the large diameter portion to be hot forged is heated preferentially, and the temperature rise in the small diameter portion can be suppressed, thereby preventing bending of the small diameter portion during the heating process. Furthermore, since thermal expansion due to the temperature rise in the small diameter portion can also be suppressed, the heating material can be smoothly inserted and removed from the lower die, thereby improving productivity.

Reference Signs List 1 Forging material 2 Material holding jig 3 Heated material 4 Lower die 5 Upper die 6 Hot forging material 11 Large diameter portion 12 Small diameter portion 21 Hole 31 Stepped portion of large diameter portion

Claims (1)

A method for producing a hot forged material, comprising hot forging a large diameter portion of a rod-shaped forging material having a large diameter portion and a small diameter portion,
A material holding jig having a hole into which the forging material is inserted is placed in advance in a heating furnace, and after the heating furnace is heated to a predetermined temperature, a small diameter portion of the forging material is inserted into the hole of the material holding jig , and the large diameter portion is heated to a heating temperature to form a heating material;
This method for producing hot forged material is characterized in that after the heated material is removed from the material holding jig, a small diameter portion of the heated material is inserted into a hole in a hot forging lower die having a hole for inserting the heated material, and hot forging is performed in which the large diameter portion is pressed axially by a hot forging upper die to produce a hot forged material.

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