JPH11151581A - Joining method for steel material and manufacture of metallic mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joining method for a steel material, a method of obtaining a satisfactory joining state free from void while dimensional precision and mechanical characteristic are maintained, and to provide a metallic mold using such joining method as well as the manufacture of the mold. SOLUTION: The joining surfaces of a plurally divided steel member are abutted on each other, with a first heat treatment 51 performed in which this steel member is raised in temperature and held to an austenite area temperature. Then, after cooled, the steel member is put through a second heat treatment 52 in which the member is raised and held in a temperature lower than the austenite area temperature. The first and the second heat treatment are desirably performed in a low pressure atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for joining a plurality of divided steel materials.

[0002]

2. Description of the Related Art For example, in a die for hot extrusion, a die for hot die casting, and a die for hot pressing, it is necessary to provide a cooling water passage or the like inside the die. If the cooling water passages and the like have a complicated shape that is bent inside, it is difficult to provide the cooling water passages and the like by cutting and using a block-shaped lump of steel material. It is. Therefore, there was a limit to the cooling of the mold. For this reason, the inventor focused on manufacturing a mold having the cooling water passage and the like by subjecting a plurality of divided steel materials to predetermined processing in advance, and laminating and joining them.

[0003] As a joining method of the steel material, for example, a joining method by brazing, a liquid phase diffusion joining method in which a low melting point material is interposed and diffused in the joining surface of the steel material, and a joining surface of the steel material is directly contacted. Solid-phase diffusion bonding method, etc. Among these joining methods, when manufacturing the above-mentioned mold for hot working, a solid-phase diffusion joining method (hereinafter simply referred to as a diffusion joining method) is often used from the viewpoint of heat resistance and the like.

[0004]

However, there are the following problems in the method of joining steel materials using the above-mentioned conventional diffusion joining method. That is, when a steel material is diffusion-bonded, voids often remain at the bonding interface, and it is very difficult to completely eliminate the voids. In addition, when voids remain at the joint interface, cracks may occur in the joint at an early stage due to repeated use of the joined steel materials at high temperatures.

On the other hand, as a measure for eliminating the above-mentioned voids, measures have been taken such as increasing the pressure during diffusion bonding, or maintaining the temperature for a long time at a high temperature to further promote the diffusion of atoms. However, when the pressing force is increased, there is a problem that the deformation of the steel material is increased and the dimensional accuracy is reduced. In addition, holding at a high temperature for a long time leads to coarsening of crystal grains, which does not satisfy the mechanical properties required for steel materials.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and a method of joining steel materials capable of obtaining a good joining state with almost no voids while maintaining dimensional accuracy and mechanical properties. An object of the present invention is to provide a mold using a joining method and a method of manufacturing the mold.

[0007]

According to a first aspect of the present invention, a first heat treatment is performed in which a plurality of divided steel members are brought into contact with each other, and the steel members are heated to an austenite region temperature and maintained. After the cooling, the steel member is subjected to a second heat treatment for raising and maintaining the temperature of the steel member at a temperature lower than the austenite region temperature.

The most remarkable point in the present invention is that two heat treatments, a first heat treatment and a second heat treatment, are performed in the specific temperature range.

The contact between the joining surfaces of the steel materials can be performed only by the pressing force of the steel materials by their own weight. In addition, external pressure can be applied as needed. In this case, the pressure applied to the contact surface is 0.1 to 5 kgf / mm ^2.
It is preferred that If it is less than 0.1 kgf / mm ² , there is a problem that the first and second steps of joining described later cannot be sufficiently advanced. On the other hand, 5kg
If f / mm ² is exceeded, there is a problem that the deformation of the steel material becomes large and the dimensional accuracy deteriorates.

The first heat treatment is a heat treatment for raising and maintaining the temperature in the austenite region. Here, the austenite region temperature is a temperature range in which the steel material has a uniform austenite structure. For example, when the steel material is a hypoeutectoid steel refers to so-called A ₃ transformation point or higher and A ₄ temperature region below the transformation point.

The holding time after the temperature is raised in the first heat treatment is preferably 0.1 to 5 hours. If the time is less than 0.1 hour, there is a problem that a first bonding step described later cannot be sufficiently advanced. on the other hand,
If the time exceeds 5 hours, there is a problem that the crystal grains become coarse.

The second heat treatment is a heat treatment in which the temperature is raised to and maintained at a temperature lower than the austenite region temperature. Here, the temperature lower than the austenite region temperature refers to a temperature at which the steel material does not have an austenitic structure due to the temperature rise. For example, when the steel material is hypoeutectoid steel, the temperature is lower than the so-called A ₃ transformation point. In addition,
The temperature for the second heat treatment is preferably set to a temperature or higher in order to promote atomic diffusion.

[0013] The holding time after the temperature is raised in the second heat treatment is preferably 0.5 to 10 hours. 0.5
If the time is less than the time, there is a problem that the second step of bonding described later cannot be sufficiently advanced. On the other hand, if it exceeds 10 hours, there is a problem that the crystal grains become coarse.

As the above-mentioned steel material, various iron-based metal materials such as various special steels such as carbon steel and alloy steel for tools can be applied.

Next, the operation of the present invention will be described. In the present invention, the first heat treatment is performed in a state where the joining surfaces of the plurality of steel materials are in contact with each other. As a result, the steel material to be joined is diffusion-joined at the joining surface, and the first step of joining is performed. However, at this point,
A large number of voids remain.

Next, the second heat treatment is performed. Thereby, as shown in the example of the embodiment, almost all voids disappear,
The second step of bonding is performed in which the crystal at the bonding interface has an intricate shape. By the completion of the second step, the boundary of the joining surface disappears, and the joining is performed very firmly.

As described above, according to the present invention, by performing the above-described two-stage heat treatment, a sound bonding state with almost no voids can be easily obtained. In addition, the first heat treatment and the second heat treatment do not need to particularly increase the pressing force and the temperature retention time as compared with the conventional diffusion bonding method. Therefore, the joined steel material can achieve the above-mentioned sound joining state without deteriorating its mechanical properties and dimensional accuracy.

Therefore, according to the present invention, the dimensional accuracy,
It is possible to provide a method for joining steel materials, in which a good joining state with almost no voids can be obtained while maintaining mechanical properties.

Next, as in the second aspect of the present invention, the first
The heat treatment and the second heat treatment are preferably performed in a reduced-pressure atmosphere. As a result, oxidation of the steel material can be prevented, and a more sound joining state can be obtained.
In this case, the pressure reduction is 1 × 10 ⁻² to 1 × 10 ⁻⁷ To.
It is preferable to perform the process at a vacuum of rr. 1 × 10 ^-2 T
If it is less than orr has a problem that the effect due to a reduced pressure atmosphere of the can not be sufficiently exhibited, whereas, 1 × 10 ^-7
When the pressure exceeds Torr, there are problems such as an increase in processing time and an increase in equipment cost.

Also, as in the third aspect of the present invention, the first
Preferably, the heat treatment is performed as a quenching treatment, and the second heat treatment is also performed as a tempering treatment. As a result, the steel material after joining can be a tough material having a quenched and tempered structure without newly performing heat treatment.

Further, as in the fourth aspect of the present invention, the second
After the heat treatment, a third heat treatment of quenching / tempering, annealing, and normalizing may be performed. In this case, regardless of the above-described heat treatment for bonding, an optimum heat treatment can be performed under a free temperature condition or the like.

Further, the above excellent method for joining steel materials can be applied to a method for manufacturing a mold. That is, claim 5
In the method of manufacturing a mold by joining a plurality of divided mold members as in the invention of the third aspect, the joining of the mold members is performed by the joining method according to any one of claims 1 to 4. There is a mold manufacturing method characterized by the following.

In this case, as a mold, for example,
There are various dies such as a hot extrusion die, a hot die casting die, and a hot press die. Further, as the mold member, a member which has been processed in advance for a cooling water passage or the like which is difficult to perform post-processing can be used. In this case, since the joining method of steel materials is used for joining the mold members, a mold having a sound joining state as described above can be obtained with excellent mechanical properties and dimensional accuracy.

The following inventions are available as molds obtained by this excellent manufacturing method. That is, in a mold formed by joining a plurality of divided mold members as in the invention of claim 6, the joining of the mold members is performed by the joining according to any one of claims 1 to 4. There is a mold that is performed by a method. Since this mold has the above-described sound joining state, it is possible to suppress the occurrence of cracks and the like from the joining portion due to repeated use, and to exhibit extremely excellent durability.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 A method for joining steel materials according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, a mold 1 according to the present embodiment includes mold members 2 and 3 made of a steel material divided into two parts.
Is a mold formed by bonding

In joining the mold members 2 and 3, first, the joining surfaces 20 and 30 of the mold members 2 and 3 are brought into contact with each other. Next, as shown in FIG. 2, a first heat treatment 51 for raising and holding the abutted mold members 2 and 3 to the austenite region temperature is performed. Next, after cooling, a second heat treatment 52 for raising and maintaining the temperature of the mold members 2 and 3 at a temperature lower than the austenite region temperature is performed.

Hereinafter, this will be described in detail. As shown in FIG. 1A, the mold 1 manufactured in the present embodiment is
Is a mold that incorporates. As shown in FIG. 1B, since the cooling water passage 5 is bent in a U-shape, the cooling water passage 5 cannot be provided by drilling or the like in a block-shaped piece of steel material.

For this reason, in this embodiment, as shown in FIG. 1B, a groove 25 for the cooling water passage 5 is provided in advance on the bottom surface of one mold member 2. And the other mold member 3
The mold 1 having the cooling water passage 5 is provided by contacting and joining with the mold. As the mold members 2 and 3 in this example, a hot alloy tool steel (JIS standard SKD61) containing Cr, W, Mo, and V was used.

Next, the contact between the mold members 2 and 3 is as follows.
The test was performed by applying a pressure of ² kgf / mm ² . Next, the contacted mold members 2 and 3 were placed in a heat treatment furnace, and a first heat treatment and a second heat treatment were performed. The first heat treatment and the second heat treatment were performed in a reduced pressure atmosphere in which the inside of the heat treatment furnace was reduced to a degree of vacuum of the order of 10 ⁻⁵ Torr.

First, as shown in FIG. 2, the first heat treatment 51 was performed by raising the temperature of the austenite region (γ region) of the mold members 2 and 3 to 1050 ° C. (T ₁ ) and holding it for 3 hours. . The lower limit temperature T of the γ region in this example
₀ is about 1010 ° C. Next, after cooling, a second heat treatment 52 was performed. The second heat treatment 52 was performed by raising the temperature to 900 ° C. (T ₂ ) slightly lower than T _{0 and} maintaining the temperature for 4 hours.

The mold 1 manufactured through such a series of steps can be manufactured without sacrificing mechanical properties and dimensional accuracy.
A sound joint was obtained. Therefore, even when the mold 1 was repeatedly used at a high temperature, it was possible to avoid the early cracking of the joining portion, and showed extremely excellent durability.

Embodiment 2 In this embodiment, the excellent jointability in Embodiment 1 is quantitatively evaluated, and a test piece is used to clarify the soundness of the joint by observing the structure of the joint. Was done. As the test piece, a steel material made of SKD61 having a diameter of 80 mm and a length of 300 mm was used. The surface roughness of the joint surface of the test piece was 3.2S.

In this example, in addition to the two examples E1 and E2 in which the test pieces were joined by the joining method of the present invention,
For comparison, Comparative Examples C1 to C4 in which test pieces were bonded by a conventional diffusion bonding method were performed. Table 1 shows the bonding conditions and the like of each example.

[0034]

[Table 1]

As shown in Table 1, Examples E1 and E2
The test piece is brought into contact with a pressure of 1-2 kgf / mm ² ,
A first heat treatment 51 and a second heat treatment 52 similar to the pattern shown in FIG. That is, in Example E1, the first heat treatment at 1050 ° C. × 3 hours and the second heat treatment at 900 ° C. × 4 hours were performed. The cooling rate after the first heat treatment was 5 ° C./min, and the cooling rate after the second heat treatment was 1 ° C./m.
in. The atmosphere for the heat treatment was a reduced pressure atmosphere having a degree of vacuum of 1 × 10 ⁻⁵ Torr.

In Example E2, at 1050 ° C.
A first heat treatment of × 2 hours and a second heat treatment of 850 ° C. × 4 hours were performed. The cooling rate and heat treatment atmosphere after each heat treatment were the same as in Example E1. In Example E2, quenching and tempering were further performed as a third heat treatment. The quenching conditions were a quenching temperature of 1050 ° C. and N ₂ gas cooling.
50 ° C, air cooling.

In Comparative Example C1, only the heat treatment was performed at 900 ° C. for 3 hours, as shown in the heat treatment pattern 53 shown in FIG. Further, Comparative Examples C2 and C3 are all Comparative Examples C
The holding time of 3 hours for one heat treatment was extended to 6 hours and 9 hours, respectively. Comparative Example C4
Is obtained by changing the heat treatment of Comparative Example C1 to 1030 ° C. × 3 hours. In each comparative example, the contact conditions, the cooling rate, and the heat treatment atmosphere were the same as those in Examples E1 and E2.

Next, Examples E1 and E2 and Comparative Examples C1 to C1
A test for measuring the shear strength was performed on C4. The test method conformed to the method shown in JIS-G0601. Table 1 shows the measurement results. As known from Table 1,
Embodiments E1 and E2 which are examples using the joining method of the present invention
Is compared with Comparative Examples C1 to C4 using the conventional joining method,
As a result, the joining strength was remarkably high.

Further, from the results of Comparative Examples C1 to C3, it is also understood that the mere extension of the heat treatment time cannot improve the bonding strength. Also, from the results of Comparative Example C4, it can be seen that excellent bonding strength cannot be obtained even if only the first heat treatment in the present invention is performed.

Next, the residual ratio of voids (void ratio) at the joint of each sample was measured. The measurement of the void ratio was performed by observing the bonded interface with an optical metallographic microscope and measuring the ratio of non-bonded portions and vacancies observed in a visual field of 50 magnification. Table 1 shows the results. As can be seen from Table 1, Examples E1 and E2 resulted in a significantly lower void ratio than Comparative Examples C1 to C4. The results also show that the void fraction has a large effect on the shear strength. In addition, it can be seen from the results of Comparative Examples C1 to C3 that voids cannot be reduced simply by extending the heat treatment time.

Next, Examples E1 and E2 and Comparative Examples C4 and C
For each of No. 5, the metal structure of the joint was observed. Here, in Comparative Example C5, the same sample as Comparative Example C4 was subjected to quenching and tempering. The quenching and tempering conditions were the same as in Example E2. Drawing-substitute photographs showing the metal structure of the joint are shown in FIGS. Each is a photomicrograph at a magnification of 150 times.

FIG. 4 shows the metal structure of the joint in Example E1. As can be seen from the figure, the interface at the joint almost disappeared. From this, it can be seen that the joint of Example E1 is very sound and excellent. Further, the metal structure of Example E1 was a tempered structure. This is because the second heat treatment was a process also serving as a tempering process. The hardness of the sample is H _B 1
70.

FIG. 5 shows the metal structure of the joint in Example E2. As can be seen from the figure, the interface at the joint was hardly known, and the crystal had a structure in which the crystal crossed the interface and became intricate. From this, it is understood that an excellent joint can be obtained even when the quenching / tempering treatment is performed after performing the joining method of the present invention. Example E2
Had a quenched and tempered structure. The hardness HRC of the sample was 53.

FIG. 6 shows the metal structure of the joint in Comparative Example C4. As can be seen from the figure, the interface at the joint remained very clearly. In addition, accumulation of carbides was observed near the interface. From this, it was found that an excellent joint cannot be obtained only by the same heat treatment as the first heat treatment. Further, the metal structure of Comparative Example C4 was a quenched structure. The hardness HRC of the sample was 50.

FIG. 7 shows the metal structure of the joint in Comparative Example C5. As can be seen from the figure, also in this case, the interface at the joint remained very clearly. From this, it is understood that even if the quenching / tempering treatment is performed after the same heat treatment as the first heat treatment, the joint is not improved. Further, the metal structure of Comparative Example C5 was a quenched / tempered structure. The hardness HRC of the sample was 48.

From the results of the above tests, it can be seen that the method for joining steel materials of the present invention is extremely effective as a means for obtaining a very excellent sound joint. Therefore, by using the joining method of the present invention, a product formed by joining a mold and other steel materials can be made more excellent in durability and the like than before.

[Brief description of the drawings]

FIG. 1A is a front view of a mold according to a first embodiment,
(B) A bottom view of the upper metal member.

FIG. 2 is an explanatory diagram showing patterns of a first heat treatment and a second heat treatment in the first embodiment.

FIG. 3 is an explanatory view showing a heat treatment pattern of a comparative example in the second embodiment.

FIG. 4 is a drawing-substitute photograph (magnification: 150 ×) showing the metal structure of the joint of Example E1 in Embodiment 2.

FIG. 5 is a photograph (magnification: 150 ×) showing a metallographic structure of a joint portion of Example E2 in Embodiment 2;

FIG. 6 is a drawing substitute photograph (magnification: 150 ×) showing the metal structure of the joint of Comparative Example C4 in Embodiment 2.

FIG. 7 is a drawing substitute photograph (magnification: 150 ×) showing the metal structure of the joint of Comparative Example C5 in Embodiment 2.

[Explanation of symbols]

 1. . . Mold, 2,3. . . Mold member, 51. . . First heat treatment, 52. . . Second heat treatment,

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroki Takagi 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Nobuhiko Nagai 1-1-1, Showa-machi, Kariya-shi, Aichi Prefecture (72) Inventor Shigeyoshi Hashimoto 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture, Denso Corporation (72) The inventor Minoru Yamamoto, 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture, Denso Corporation (72) Masao Hisada 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO Corporation (72) Inventor Makoto Manabe 8-21 Nisone, Kokura-Minami-ku, Kitakyushu-city Inside Tobata Corporation

Claims (6)

[Claims] 1. A first heat treatment for bringing the joint surfaces of a plurality of divided steel members into contact with each other, heating and holding the steel members to an austenite region temperature, and then cooling the steel members to austenite. A method for joining steel materials, comprising performing a second heat treatment for raising and maintaining a temperature lower than a region temperature. 2. The method according to claim 1, wherein the first heat treatment and the second heat treatment are performed in a reduced pressure atmosphere. 3. The method according to claim 1, wherein the first heat treatment is performed as a quenching treatment, and the second heat treatment is performed as a tempering treatment. 4. The method for joining steel materials according to claim 1, wherein a third heat treatment of quenching / tempering, annealing, and normalizing is performed after the second heat treatment. 5. A method of manufacturing a mold by joining a plurality of divided mold members, wherein the joining of the mold members is performed by the joining method according to any one of claims 1 to 4. A method for manufacturing a mold, characterized in that: 6. A mold formed by joining a plurality of divided mold members, wherein said mold members are joined together.
A die, which is performed by the joining method according to any one of the above.