JP2021169106A - Metal member joining method and joined body made of joined metal member - Google Patents

Abstract

To provide a technique that can further improve shape accuracy, in a joined body made of joined metal members formed of iron-based materials.SOLUTION: Two metal members 100 and 200 in which annular contact surfaces complementary to each other are formed are prepared. Power is distributed to a space between the two metal members 100 and 200 through a joined part while applying pressure to the joined part contacted with respective contact surfaces of the prepared two metal members 100 and 200, to join the two metal members 100 and 200 made of iron-based materials to each other. The power is distributed so that a temperature of the joining which the joined part reaches is below a temperature which is lower of melting points of the metal members forming the two metal members 100 and 200 respectively.SELECTED DRAWING: Figure 1

Description

The present invention relates to a joining technique for joining a metal member made of an iron-based material, and more particularly to a joining technique for airtightly joining a metal member.

Structures having a closed structure such as various containers and pipelines, such as fuel tanks for automobiles and piping for chemical equipment, are used in various fields of industry. Conventionally, such a structure has been formed by joining a plurality of metal members by a welding method (joining method) such as arc welding, but in the formed structure, the strength and airtightness of the welded portion It was not always easy to secure. Therefore, as a technique for ensuring the strength and airtightness of the welded portion, a ring projection having a predetermined shape is provided on one of a plurality of metal members forming a structure, and resistance welding is performed via the ring projection (ring projection). Welding) has been proposed (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-14290

However, when metal members are joined by ring projection welding as in Patent Document 1, the ring projection itself melts and flows, so that the relative positional relationship of the metal members changes before and after joining. Further, in a welding method such as arc welding, since the metal member and the welded material melt and flow at the welded portion, the relative positional relationship of the metal member cannot be stably maintained before and after joining. Therefore, depending on these conventional welding methods, the shape of the structure (joint) to which the metal members are joined varies, and it is difficult to obtain a joint with high shape accuracy.

An object of the present invention is to solve such a problem in a conventional joining method and to provide a technique for improving shape accuracy in a joined body formed by joining metal members made of an iron-based material.

Of the present invention, the invention according to claim 1 is a method of joining two metal members made of an iron-based material, wherein (a) the two metals having annular contact surfaces complementary to each other are formed. The step of preparing the members and (b) between the two metal members via the joints while applying pressure to the joints formed on the two metal members and in contact with the contact surfaces. A metal material that comprises a step of joining the two metal members at the joint portion by energization, and the joining temperature reached by the joint portion in the step (b), respectively. It is characterized in that the temperature is lower than the lower temperature of the melting point of.

The invention according to claim 2 further removes the oxide film formed on the contact surface of each of the two metal members prepared in the step (a) in the invention according to claim 1. It is characterized by having a process.

In the invention according to claim 3, in the invention according to claim 1 or 2, the two metal members are formed of austenitic stainless steel, and the bonding temperature is sharpened in the austenitic stainless steel. It is characterized in that it is set higher than the upper limit temperature at which

In the invention according to claim 4, in the invention according to claim 1 or 2, the two metal members are formed of austenitic stainless steel, and the joining temperature is the solution of the austenitic stainless steel. Is characterized in that it is set higher than the starting temperature.

The invention according to claim 5 is the invention according to claim 1 or 2, wherein the two metal members are formed of ferritic stainless steel, and the joining temperature is σ brittleness in the ferritic stainless steel. It is characterized in that it is set higher than the upper limit temperature at which is generated.

The invention according to claim 6 is a joined body in which the two metal members are joined, and is characterized in that they are joined by the joining method according to any one of claims 1 to 5.

According to the joining method according to claim 1, since the temperature of the joint portion is lower than the melting point of any of the two metal members at the time of joining, it is suppressed that the two metal members are melted at the joint portion, and the two metal members are formed. Deformation of the metal member is suppressed. Therefore, since the positional relationship between the two metal members can be maintained in substantially the same state before and after joining, it is possible to suppress variations in the shape of the obtained joined body and obtain a joined body with higher shape accuracy. It will be possible.

According to the joining method according to claim 2, since the oxide film formed on the contact surface is removed, the joining of the two metal members is promoted. Therefore, since the deformation of the two metal members is further suppressed, it is possible to obtain a bonded body having higher shape accuracy.

According to the joining method according to claim 3, since it is possible to suppress the occurrence of sensitization at the joint portion, it is possible to suppress the deterioration of the corrosion resistance against intergranular corrosion at the joint portion.

According to the joining method according to claim 4, solution-forming progresses at the joining portion, and the work-induced martensite generated when the contact surface is formed can be austenite, so that corrosion resistance to pitting corrosion at the joining portion can be achieved. Can be suppressed from decreasing.

According to the joining method according to claim 5, it is possible to suppress the occurrence of σ embrittlement at the joint portion, so that it is possible to suppress a decrease in the durability of the joint portion.

The present invention can be realized in various aspects. For example, it can be realized by a joining method, a method of manufacturing a container, a pipe, or the like using the joining method, and a joint, a container, a pipe, or the like manufactured by the joining method or the manufacturing method.

It is a process drawing which shows the joining process which joins two metal members as the 1st Embodiment of this invention. It is explanatory drawing which shows the state that the member to be joined is joined by energization. It is a metallographic structure photograph of the vicinity of the joint portion of the joint body obtained as an example of the first embodiment. It is a process drawing which shows a part of the joining process as the 2nd Embodiment of this invention. It is a metallographic structure photograph of the vicinity of the joint portion of the joint body obtained as an example of the second embodiment.

Hereinafter, a method for joining metal members according to the present invention and an embodiment of a joined body joined by the joining method will be described in detail with reference to the drawings.

<First Embodiment>
FIG. 1 is a process diagram showing a joining process for joining two metal members as the first embodiment of the present invention. In the joining step of the first embodiment, first, as shown in FIG. 1A, the two metal members to be joined (members to be joined) have a large diameter pipe 100 and an outer diameter larger than that of the large diameter pipe 100. Prepare a small diameter tube 200.

The large-diameter pipe 100 is a substantially cylindrical pipe material made of austenitic stainless steel (SUS304 or the like), and a mounting hole 190 for mounting the small-diameter pipe 200 is formed on the side surface thereof. The mounting hole 190 is a hole that penetrates the large-diameter pipe 100 from the outer peripheral side to the inner peripheral side, and is a taper hole 191 formed on the outer peripheral side (hereinafter, also simply referred to as the outer peripheral side) of the large-diameter pipe 100, and a taper hole. It is composed of parallel holes 192 formed on the inner peripheral side of 191 (hereinafter, also simply referred to as the inner peripheral side). In the example of FIG. 1, a mounting hole 190 composed of a tapered hole 191 and a parallel hole 192 is formed in the large diameter pipe 100, but the parallel hole is omitted and only the tapered hole is formed as a mounting hole in the large diameter pipe. It may be something to do.

The inner peripheral surface of the tapered hole 191 has a substantially truncated cone side surface shape (tapered shape), and the inner diameter thereof is formed so as to decrease from the outer peripheral side to the inner peripheral side. The parallel hole 192 is formed so that a substantially constant inner diameter is the same as the minimum inner diameter of the tapered hole 191, that is, the inner diameter of the inner peripheral side end of the tapered hole 191. Further, so-called counterbore processing is performed around the tapered hole 191 to form a horizontal plane F. That is, the mounting hole 190 composed of the tapered hole 191 and the parallel hole 192 is formed by perforating and counterboring the large-diameter pipe 100 which is a cylindrical raw pipe.

The small-diameter pipe 200 is a pipe material made of austenitic stainless steel like the large-diameter pipe 100, and has a cylindrical tubular portion 210 and a tapered portion 220 extending from one end of the tubular portion 210. The tapered portion 220 has an outer peripheral surface having a tapered shape, and is formed so that the outer diameter decreases toward the opposite direction (tip side) of the tubular portion 210. The small diameter pipe 200 having such a tapered portion 220 is usually formed by cutting one end of a cylindrical raw pipe. In the following description, for the small diameter pipe 200, the direction from the tubular portion 210 to the tapered portion 220 is also referred to as the front end side, and the direction from the tapered portion 220 toward the tubular portion 210 is also referred to as the rear end side.

The maximum outer diameter (outer diameter of the tubular portion 210) of the tapered portion 220 is larger than the maximum inner diameter (inner diameter of the outer peripheral side end) of the tapered hole 191 formed in the large diameter tube 100, and the minimum outer diameter is (Outer diameter of the tip side end) is formed so as to be smaller than the minimum inner diameter (inner diameter of the inner peripheral side end) of the tapered hole 191. Further, the taper portion 220 is formed so that its inclination is the same as the inclination of the taper hole 191 provided in the large diameter pipe 100. Here, the inclination of the tapered portion 220 and the tapered hole 191 is the inclination angle of the side surface of the truncated cone corresponding to the tapered shape of the outer peripheral surface and the inner peripheral surface thereof, that is, the angle formed by the axis and the side surface of the truncated cone. Is called.

As described above, in the example of FIG. 1, the tapered portion 220 provided in the small diameter pipe 200 has a maximum outer diameter larger than the maximum inner diameter of the tapered hole 191 and a minimum outer diameter of the minimum inner diameter of the tapered hole 191. It is formed to be smaller than the taper hole 191 and has the same inclination as the taper hole 191. Therefore, the tapered portion 220 provided in the small diameter pipe 200 and the tapered hole 191 provided in the large diameter pipe 100 have a shape that allows surface contact with each other. In the present invention and the present specification, the shapes that can come into surface contact with each other are also referred to as complementary shapes.

Further, as can be seen from the above description, both the inner peripheral surface of the tapered hole 191 and the outer peripheral surface of the tapered portion 220 are annular. Here, the fact that a certain portion is annular means that the portion has a shape that surrounds a certain region located inside the portion. Therefore, the inner peripheral surface of the tapered hole 191 and the outer peripheral surface of the tapered portion 220 are annular surfaces complementary to each other.

After preparing the large-diameter pipe 100 and the small-diameter pipe 200, the large-diameter pipe 100 and the small-diameter pipe 200 (that is, the members to be joined) are assembled as shown in FIG. 1 (b). Specifically, the tapered portion 220 provided on the tip end side of the small diameter pipe 200 is inserted into the mounting hole 190 from the outer peripheral side of the large diameter pipe 100. As a result, the tapered portion 220 provided in the small diameter pipe 200 and the tapered hole 191 of the mounting hole 190 formed in the large diameter pipe 100 are in surface contact with each other, that is, the outer peripheral surface of the tapered portion 220 and the tapered hole 191. The small-diameter pipe 200 is assembled to the large-diameter pipe 100 in a state of being in contact with the inner peripheral surface of the above. In this way, the outer peripheral surface of the tapered portion 220 and the inner peripheral surface of the tapered hole 191 are formed so as to come into contact with each other (contact with each other), and thus can also be called a contact surface.

As described above, since the taper hole 191 is counterbored and the horizontal plane F is formed, the tapered portion 220 of the small diameter pipe 200 and the tapered hole 191 of the large diameter pipe 100 are tapered. It is in a state of surface contact with a constant width (width in the vertical direction along the inclined surface) over the entire circumference of the hole 191 (that is, the entire circumference of the tapered portion 220). Further, when the tapered portion 220 of the small diameter pipe 200 and the tapered hole 191 of the large diameter pipe 100 are brought into surface contact as described above, the width of the surface contact portion between the two (the width in the vertical direction along the inclined surface) is tapered. The shape is adjusted so that the entire circumference of the hole 191 (that is, the entire circumference of the tapered portion 220) is 0.2 mm or more and 1.0 mm or less.

After assembling the members to be joined, the assembled members (large diameter pipe 100 and small diameter pipe 200) are connected to the power supply device 900 which is a current supply source (FIG. 1 (c)). Specifically, the large-diameter tube 100 is arranged on the first electrode body (lower electrode body) 910 connected to the power supply device 900, and the second electrode body (upper electrode body) connected to the power supply device 900 is arranged. Body) 920 is arranged on the rear end side of the small diameter tube 200 as shown by an arrow.

Generally, the electrical resistance (contact resistance) at the contact surface between two metal members is higher than the electrical resistance of the metal member itself. Therefore, when the two electrode bodies 910 and 920 are connected to the large diameter tube 100 and the small diameter tube 200, most of the electrical resistance between the two electrode bodies 910 and 920 has a large diameter with the lower electrode body 910. It is generated by the contact resistance between the tube 100, between the large diameter tube 100 and the small diameter tube 200, and between the small diameter tube 200 and the upper electrode body 920.

Of these contact resistances, if the contact resistance between the lower electrode body 910 and the large-diameter tube 100 and between the small-diameter tube 200 and the upper electrode body 920 becomes high, it is unnecessary for energization described later. There is a risk that the electrode bodies 910 and 920 and the members 100 and 200 to be joined will be fused together with the generation of a large amount of Joule heat and an increase in energy loss.

Therefore, in the first embodiment, as shown in FIG. 1 (c), a recess 919 having a shape complementary to the outer peripheral surface of the large-diameter tube 100 is formed on the upper portion of the lower electrode body 910 to be large. The area of the contact surface between the diameter tube 100 and the lower electrode body 910 is widened to reduce the contact resistance on the contact surface. Further, the upper electrode body 920 is formed with a flat surface portion 921 on the side in contact with the small diameter tube 200 to widen the area of the contact surface between the small diameter tube 200 and the upper electrode body 920, and the contact on the contact surface is widened. We are trying to reduce resistance.

Further, in the first embodiment, by forming the electrode bodies 910 and 920 with chromium copper having high electrical conductivity, the electric resistance of the electrode bodies 910 and 920 itself is further lowered, and the electrode bodies 910 and 920 are covered with the electrode bodies 910 and 920. The contact resistance between the joining members 100 and 200 is further reduced. The electrode body does not necessarily have to be made of chromium copper, and can be made of various metal materials. However, in order to reduce the electrical resistance of the electrode body itself and the contact resistance between the electrode body and the member to be joined, the electrode body is preferably formed of a copper alloy such as chromium copper.

After connecting the members 100 and 200 to be joined to the electrode bodies 910 and 920 in this way, as shown by the arrows in FIG. 1D, the power supply device while pushing down the upper electrode body 920 toward the lower electrode body 910. A current is output from 900 via the electrode bodies 910 and 920 to energize the members 100 and 200 to be joined.

The power supply device 900 has a function of outputting a pulsed current to a load (that is, members to be joined 100, 200) connected between two electrode bodies 910 and 920 according to preset energization conditions. There is. As the energization condition, the width of the current pulse (energization time) and the height of the current pulse (energization current) can be set.

As described above, since the contact resistance between the electrode bodies 910 and 920 and the members to be joined 100 and 200 is reduced, the electrical resistance between the two electrode bodies 910 and 920 is the large diameter tube 100 and the small diameter tube. Most of the contact resistance is between the 200 and the contact surface between the tapered portion 220 and the tapered hole 191. Therefore, when the members 100 and 200 to be joined are energized, Joule heat is mainly generated at the contact surface between the tapered portion 220 and the tapered hole 191 so that the contact surface is locally heated.

Then, the contact surface between the tapered portion 220 and the tapered hole 191 is locally heated by energization, and the upper electrode body 920 is pushed down toward the lower electrode body 910 to apply pressure to the contact surface. In, the large-diameter pipe 100 and the small-diameter pipe 200 are joined. As described above, the contact surface between the tapered portion 220 and the tapered hole 191 is a portion where the large-diameter pipe 100 and the small-diameter pipe 200 are joined, and thus can also be called a joint portion.

Further, in the first embodiment, the outer peripheral surface of the tapered portion 220 and the inner peripheral surface of the tapered hole 191, that is, the contact surfaces formed on the tapered portion 220 and the tapered hole 191 are annular. Therefore, since the joint portion between the tapered hole 191 and the tapered portion 220 is annular, the large diameter pipe 100 and the small diameter pipe 200 are airtightly joined. Here, airtightness means that the inner region and the outer region are not connected at the annular joint.

FIG. 2 is an explanatory view showing how the large-diameter pipe 100 and the small-diameter pipe 200 (members to be joined) are joined by energization. Note that FIG. 2 shows an enlarged view of the large-diameter pipe 100 and the small-diameter pipe 200 cut in a plane passing through the central axes of both of them.

As described above, the tapered hole 191 provided in the large-diameter pipe 100 and the tapered portion 220 provided in the small-diameter pipe 200 have a complementary shape. Therefore, as shown in FIG. 2A, when the large-diameter pipe 100 and the small-diameter pipe 200 are assembled, the tapered hole 191 and the tapered portion 220 are in surface contact at the joint portion CS.

In this state, by pushing down the small diameter pipe 200 toward the large diameter pipe 100 as shown by the white arrow in FIG. 2B, the tapered hole 191 and the tapered portion 220 are shown by the black arrow. Pressure is applied to the joint CS between and. Then, when energization is performed between the large-diameter pipe 100 and the small-diameter pipe 200 by the power supply device 900 according to the preset energization conditions, a current flows through the joint portion CS, and the joint portion CS is locally heated.

During energization, the heat generated at the joint CS is transferred to the peripheral region of the joint CS. When heat is transferred to the peripheral region of the joint portion CS in this way, the transferred heat may affect the material properties (corrosion resistance, mechanical properties, etc.) of the peripheral region. The peripheral region (heat-affected zone) of the joint portion CS affected by this heat expands as the energization time becomes longer. Therefore, in order to suppress heat transfer to the peripheral region of the joint portion CS and suppress expansion of the heat-affected zone, it is preferable that the energization time is sufficiently short with respect to the expansion speed of the heat-affected zone. Specifically, when the temperature of the welded portion rises to 900 to 1,000 ° C., the energization time (time Tp from the start of current flow to the peak) is preferably 1 ms or more and less than 100 ms. It is more preferably 5 ms or more and less than 50 ms, and particularly preferably 10 ms or more and less than 30 ms.

On the other hand, Joule heat generated by energization is concentrated in the joint CS. Therefore, even if the energization time is shortened as described above, the temperature of the joint CS is rapidly raised by sufficiently increasing the energization current. The temperature of the joint portion CS can be brought to a temperature suitable for joining (joining temperature). The energizing current is appropriately set by performing a simulation or the like based on the joining temperature, the energizing time, the area of the joint portion CS, the materials and shapes of the members 100 and 200 to be joined, and the like set in this way.

The bonding temperature, that is, the temperature reached at the bonding portion CS, is generally equal to or higher than the temperature at which bonding in the solid phase is possible (solid phase bonding temperature: thermodynamic temperature, which is about 0.5 times the melting point). Just do it. On the other hand, the upper limit of the joining temperature is set to the melting point of the metal material forming the members to be joined 100 and 200 (hereinafter, also referred to as the melting points of the members 100 and 200 to be joined). Therefore, in the first embodiment in which the members 100 and 200 to be joined are made of austenitic stainless steel, the joining temperature is set to be equal to or lower than the melting point (about 1400 ° C.) of the austenitic stainless steel.

In the first embodiment, the joining temperature is set to be equal to or lower than the melting point of the members 100 and 200 to be joined in this way. As shown in FIG. 2C, the large-diameter pipe 100 and the small-diameter pipe 200 are joined at the joint portion BR, and the large-diameter pipe 11 and the small-diameter pipe 12 are integrated into the joint body 10. Is obtained. Therefore, according to the first embodiment, the members 100 and 200 to be joined can be joined with sufficiently high strength in the joint portion CS.

Then, in the first embodiment, by setting the joining temperature to be equal to or lower than the melting point of the members 100 and 200 to be joined, the members 100 and 200 to be joined are joined to each other without melting. Therefore, it is suppressed that the members 100 and 200 to be joined are melted and deformed. Therefore, as shown in FIG. 2 (c), the positions of the large-diameter pipe 11 and the small-diameter pipe 12 in the joined body 10 obtained after joining. The relationship is maintained in substantially the same state as before joining. In this way, since the positional relationship of the members to be joined is maintained in substantially the same state before and after joining, it is possible to obtain a joined body 10 having higher shape accuracy.

Further, in the first embodiment, since the joining temperature is set to be equal to or lower than the melting point of the members to be joined 100 and 200, melting and resolidification of the members 100 and 200 to be joined do not occur in the joint portions CS and BR. Therefore, the coarsening of crystal grains and the segregation of additive elements and impurities due to the occurrence of re-solidification are suppressed, so that the ductility and toughness may decrease due to the coarsening in the region near the joint BR. , Changes in corrosion resistance and mechanical properties (material properties) due to segregation are suppressed.

As described above, the bonding temperature may be equal to or higher than the solid phase bonding temperature, but in the first embodiment, since the member to be bonded is made of austenitic stainless steel, the bonding temperature is austenitic stainless steel. It is preferable that the temperature is higher than the upper limit temperature at which sensitization occurs (sensitization temperature: about 800 ° C.). By setting the bonding temperature higher than the sensitization temperature in this way, it is possible to suppress the sensitization of the bonding portion BR and suppress the deterioration of the corrosion resistance to intergranular corrosion at the bonding portion BR.

Further, the bonding temperature is preferably higher than the temperature at which solidification (also referred to as solution) starts in austenitic stainless steel (solidification temperature: about 1100 ° C.). By setting the joining temperature higher than the solution temperature in this way, it is possible to austenite the work-induced martensite generated by machining or the like when forming the tapered hole 191 or the tapered portion 220. Therefore, it is possible to prevent the process-induced martensite from remaining in the joint BR and reducing the corrosion resistance to pitting corrosion (crevice corrosion) in the joint BR.

<Example of the first embodiment>
In order to confirm that the members to be joined can be joined by the joining step of the first embodiment, a joined body was prepared as an example, and the state of the joined portion in the obtained joined body was observed. Specifically, as a member to be joined, a large-diameter pipe having a tapered hole and a small-diameter pipe having a tapered portion are prepared from raw pipes having different diameters formed by SUS304, and as described above, the member to be joined. To obtain a bonded body. Then, a region including the joint was cut out from the obtained joint, and the metal structure of the joint was observed. In joining, the energizing time was set to 30 ms, and the energizing current was set so that the joining temperature was 900 ° C.

In observing the metallographic structure, a sample was prepared by cutting the joint on the surface passing through the central axes of both the large-diameter tube and the small-diameter tube, and the cut surface of the sample was polished. Then, after polishing the cut surface, the metal structure was exposed by immersing the sample in the etching solution. As the etching solution, a marble reagent (a mixed solution of 4 g of copper sulfate, 20 ml of hydrochloric acid and 20 ml of water) was used in order to reveal the metal structure of SUS304, which is an austenitic stainless steel.

In this way, the metal structure of the joint was observed by observing the sample in which the metal structure near the joint was exposed with an optical microscope. FIG. 3 is a photograph of the metallographic structure of the vicinity of the joint portion of the joint body obtained as an example of the first embodiment.

As can be seen from FIG. 3, in the embodiment of the first embodiment, the re-solidified portion (large-diameter pipe and small-diameter pipe) formed in the joint portion when the members to be joined (large-diameter pipe and small-diameter pipe) are melted and the melted portion is re-solidified. (Also called a nugget) was not formed. From this, it is considered that according to the joining method of the first embodiment, the melting of the member to be joined is suppressed, and the ductility and toughness are not lowered or the material properties are not changed due to the formation of the nugget.

In addition, it was confirmed that the large-diameter pipe and the small-diameter pipe were integrated on the outer peripheral side, although there was a gap on the inner peripheral side of the large-diameter pipe due to the machining error of the taper hole and the inclination of the tapered portion. did it. From this, it was confirmed that the large-diameter pipe and the small-diameter pipe can be airtightly joined by the joining method of the first embodiment.

On the other hand, as shown in FIG. 3, on the outer peripheral side of the large-diameter pipe, a protruding portion (burr) extending from the joint portion to the outer peripheral side was formed. Further, a forging stream line (fiber flow) was formed along the joint portion over substantially the entire area of the joint portion. Usually, such protrusions and streamlines are formed when the member to be joined is plastically deformed. From this, when the joint body of the example shown in FIG. 3 was prepared, the strength of the member to be joined in the vicinity of the joint portion decreased due to the temperature rise at the time of joining, and the joint portion and the region in the vicinity thereof were plastically deformed. it is conceivable that.

However, as shown in FIG. 3, the size of the protruding portion is sufficiently small, and the formation of the forged streamline is also limited to the region very close to the joint portion. From this, according to the joining method of the first embodiment, the positional relationship between the large-diameter pipe and the small-diameter pipe does not change significantly before and after the joining, and it is possible to obtain a joined body with higher shape accuracy. It was confirmed that it would be.

<Second Embodiment>
FIG. 4 is a process diagram showing a part of the joining process as the second embodiment of the present invention. The joining step of the second embodiment includes a step of removing the passivation film formed on the surfaces of the members 100 and 200 to be joined. Is different. Since the other points are the same as those of the first embodiment, the steps after the connection of the power supply device (FIG. 4 (d)) are not shown in FIG.

Also in the second embodiment, as shown in FIG. 4A, the same members 100 and 200 to be joined as in the first embodiment are prepared. Generally, on the surface of stainless steel, a passivation film (oxide film) is naturally formed by oxidizing chromium in the stainless steel by oxygen in the air. Therefore, a passivation film is naturally formed on the contact surfaces of the members 100 and 200 to be joined (the inner peripheral surface of the tapered hole 191 and the outer peripheral surface of the tapered portion 220) that come into contact with each other at the time of joining. However, the passivation film formed naturally in this way is not always uniform, and the thickness may be thicker than necessary.

Therefore, in the second embodiment, the prepared members 100 and 200 to be joined are pickled to temporarily remove the passivation film formed on the surfaces of the members 100 and 200 to be joined. Specifically, as shown in FIG. 4B, a cloth C containing an acid (acidic electrolytic solution or the like) is wound around an electrode 810, and a predetermined amount of electricity is applied to the electrode 810 by an electric applying device 800. While applying, lightly trace the inner peripheral surface of the tapered hole 191 and the outer peripheral surface of the tapered portion 220 with the cloth C wound around the electrode 810 (that is, the cloth C wound around the electrode 810 is brought into contact with those parts). When the member 100 or the member 200 to be joined is pickled in this way, another electrode 820 to which the cloth C is not wound is brought into contact with the member 100 or the member 200 to be joined. Further, as an acid for removing the passivation film formed on the surfaces of the members 100 and 200 to be joined, an acidic electrolytic solution (for example, Pika element #SUS Bright manufactured by Chemical Mountain Headquarters) can be preferably used. .. By applying such electricity, the passivation film formed on the inner peripheral surface of the tapered hole 191 and the outer peripheral surface of the tapered portion 220 is temporarily removed. As a result, the inner peripheral surface of the tapered hole 191 of the member 100a to be pickled and the outer peripheral surface of the tapered portion 220 of the member 200a to be joined are newly made extremely thin (about several nm) and uniform. A passivation film is formed.

By performing the pickling treatment in this way, the passivation coating formed on the inner peripheral surface of the tapered hole 191 of the member to be joined 100a and the contact surface of the outer peripheral surface of the tapered portion 220 of the member to be joined 200a becomes extremely thin. Moreover, since it becomes uniform, the joining is promoted at the joining portion where the contact surfaces are in contact with each other. Therefore, even if the energization time is shortened or the joining temperature is lowered, the joined members 100a and 200a (that is, the inner peripheral surface of the tapered hole 191 of the joined member 100a and the tapered portion 220 of the joined member 200a). (Outer peripheral surface) can be reliably joined. In this way, since the amount of heat input to the joint can be further reduced, the expansion of the heat-affected zone around the joint can be suppressed, and the material properties such as corrosion resistance and mechanical properties can be affected at the joint. It can be suppressed.

<Example of the second embodiment>
In order to confirm that the members to be joined can be joined by the joining step of the second embodiment, a joined body was prepared as an example, and the state of the joined portion in the obtained joined body was observed. Specifically, as in the embodiment of the first embodiment, a large-diameter pipe and a small-diameter pipe are prepared, and as described above, the passivation coating is removed and the members to be joined are joined to form a joined body. Obtained. Then, a sample was prepared in the same manner as in the examples of the first embodiment, and the metallographic structure of the joint was observed. In joining, the energizing time was set to 30 ms, which was the same as in the examples of the first embodiment. On the other hand, the energizing current was set so that the joining temperature was 850 ° C., which was lower than that of the embodiment of the first embodiment.

FIG. 5 is a photograph of the metallographic structure of the vicinity of the joint portion of the joint body obtained as an example of the second embodiment. As can be seen from FIG. 5, the nugget was not formed at the joint even in the embodiment of the second embodiment. From this, it is considered that the joining method of the second embodiment also suppresses the melting of the member to be joined, and the ductility and toughness are not lowered or the material properties are not changed due to the formation of the nugget. In addition, it was confirmed that the large-diameter pipe and the small-diameter pipe were integrated on the outer peripheral side of the large-diameter pipe. From this, it was confirmed that the large-diameter pipe and the small-diameter pipe can be airtightly joined by the joining method of the second embodiment.

Further, also in the embodiment of the second embodiment, the protruding portion is formed on the outer peripheral side of the large diameter pipe. However, in the embodiment of the second embodiment, although the forging line was formed at the joint, the region where the forging line was formed was smaller than that of the embodiment of the first embodiment shown in FIG. .. From this, in the embodiment of the second embodiment, by lowering the joining temperature as compared with the embodiment of the first embodiment, the region where the strength is lowered due to the temperature rise at the time of joining becomes smaller, and the plastic deformation can be suppressed. I found out. As described above, according to the joining method of the second embodiment, the plastic deformation of the member to be joined at the time of joining is suppressed, so that the change in the positional relationship between the large-diameter pipe and the small-diameter pipe before and after the joining is further suppressed. It was found that it is possible to obtain a bonded body with even higher shape accuracy.

<Modified example of the second embodiment>
In the second embodiment, the passivation film formed on the surface of the member to be joined is removed by the pickling treatment, but the passivation film is removed by the pickling treatment and the prepared member 100 to be joined. It is also possible to remove 200 by heating in a furnace having a reducing atmosphere such as hydrogen gas or carbon monoxide.

Further, in the second embodiment, the members to be joined 100a and 200a are assembled (FIG. 4 (c)) and connected to the power supply device 900 (FIG. 4 (d)), and the members to be joined 100a and 200a are connected. The passivation film is removed prior to energization (see FIG. 1D), but the passivation film can also be removed by energizing the member to be joined in a reducing atmosphere.

By doing so, the joint portion is heated, the passivation film formed on the contact surface of the member to be joined is removed, and the joint is performed in a state where the passivation film is not formed on the joint portion. Therefore, the joining of the members to be joined is promoted. Therefore, even if the energization time is further shortened or the joining temperature is lowered, the members to be joined can be reliably joined, so that the shape accuracy of the joined body is further improved and the heat-affected zone around the joined portion is expanded. Can be further suppressed, and the influence on material properties such as corrosion resistance and mechanical properties can be further suppressed.

<Modification example>
The present invention is not limited to each of the above embodiments, and can be implemented in various aspects without departing from the gist thereof. For example, the following modifications are also possible.

<Modification example 1>
In each of the above embodiments, the large-diameter pipe 100 and the small-diameter pipe 200 are provided with a tapered hole 191 and a tapered portion 220, respectively, and the inner peripheral surface of the tapered hole 191 and the outer peripheral surface (contact surface) of the tapered portion 220 are brought into contact with each other for joining. However, the contact surfaces formed on the two members to be joined may have shapes complementary to each other and may be formed in an annular shape. For example, two cylindrical pipe members having the same diameter may be joined at their end faces, or the first metal member provided with an annular flange may have a shape complementary to the flange. A second metal member having a formed mounting surface may be joined. Further, the contact surface does not necessarily have to be an annular shape or a tapered shape as long as it is an annular shape, and may be an elliptical frustum side surface shape or a quadrangular shape. Further, the contact surface does not have to be formed as a clear surface like the tapered hole 191 and the tapered portion 220 of each of the above embodiments, and may be formed at a corner portion as a micro shape.

<Modification 2>
In each of the above embodiments, the members 100 and 200 to be joined are made of austenite stainless steel, but the members to be joined are various types of ferritic stainless steel (SUS430, etc.) and martensitic stainless steel (SUS410, etc.). It can be made of stainless steel. Further, in general, the member to be joined may be made of any iron-based material (iron-based alloy and pure iron). Also in this case, it is preferable to remove the oxide film formed on the contact surface of the member to be joined, as in the second embodiment or a modification thereof, in that the joining of the member to be joined is promoted.

When the member to be joined is made of ferritic stainless steel, the joining temperature is higher than the upper limit temperature at which σ brittleness occurs (σ embrittlement temperature: about 800 ° C.) in ferritic stainless steel. Is preferable. By setting the joint temperature to be equal to or higher than the σ embrittlement temperature in this way, the occurrence of σ embrittlement at the joint portion is suppressed, so that it is possible to suppress a decrease in the durability of the joint portion.

When the member to be joined is made of tool steel or structural steel, the joining temperature is preferably equal to or higher than the temperature at which the transformation to austenite starts (Ac1 transformation point), and the transformation to austenite occurs. It is more preferable that the temperature is equal to or higher than the completion temperature (Ac3 transformation point). In this way, by setting the bonding temperature to the austenite transformation point (Ac1 transformation point or Ac3 transformation point) or higher, the bonding becomes stronger due to the change in the crystal structure when passing through the austenite transformation point, so that the bonding at the bonding portion becomes stronger. It is possible to increase the strength of the body.

<Modification example 3>
In each of the above embodiments, the members to be joined 100, 200 (100a, 200a) made of the same type of stainless steel (austenitic stainless steel) are joined, but the two members to be joined are made of different iron-based materials. It may be formed. Even in this case, by setting the joining temperature to be lower than the melting point of the two members to be joined, it is possible to prevent each member to be joined from melting at the joint. Therefore, the additive elements of each member to be joined are averaged in the molten portion, and the change in the alloy composition in the joint portion is suppressed. As described above, by suppressing the change in the alloy composition of each member to be joined at the joint portion, it is possible to suppress the change in the material properties of each member to be joined.

However, when the two members to be joined are made of different iron-based materials, thermal cycle fatigue may occur due to a difference in the coefficient of thermal expansion or the like, and the joint may be damaged. Therefore, it is preferable that the two members to be joined are made of the same type of iron-based material.

On the other hand, by forming the two members to be joined with different iron-based materials, each part of the joined body can be formed with a more appropriate material. For example, a tank made of austenitic stainless steel and a nozzle made of martensitic stainless steel may be joined to form a bonded body. In this case, it is easy to increase the capacity of the tank by forming the tank with austenitic stainless steel that can be easily drawn deeply, and high hardness is required by forming the nozzle with martensitic stainless steel. The nozzle can be formed more easily.

Further, the joining method according to the present invention includes not only joining two members to be joined of iron-based materials, but also joining of nickel-based alloys such as Inconel and Hastelloy, and joining of these nickel-based alloys and iron-based materials. Can also be used for. In addition, when the joining method according to the present invention is used for joining nickel-based alloys or joining those nickel-based alloys with iron-based materials, the ratio of nickel components in the nickel-based alloys is used. It is preferable that the content is 8.0% by mass or more and 20% by mass or less in terms of maintaining the bonding strength.

On the other hand, in the joining method according to the present invention, when the electric resistance of the two members to be joined is adjusted to 140 μΩ · cm or less and the thermal conductivity of the two members to be joined is adjusted to 30 Wm · k or less, a small amount of electric power is used. It is preferable because it enables joining with high strength. In addition, it is more preferable to adjust the electrical resistance of the two members to be joined to 120 μΩ · cm or less and the thermal conductivity of the two members to be joined to 20 Wm · k or less.

<Modification example 4>
In each of the above embodiments, the expansion of the heat-affected zone around the joint CS is suppressed by sufficiently shortening the energization time, but when the presence of the heat-affected zone in the joint does not matter, It is also possible to lengthen the energizing time. For example, when the obtained bonded body is heat-treated (solidification treatment, quenching, tempering, etc.) after bonding, or when the member to be bonded is formed of soft iron or the like, a heat-affected zone is present. However, since problems such as sensitization and embrittlement do not occur, the energization time can be lengthened.

Since the joining method of the present invention exerts an excellent effect as described above, it can be suitably used as a joining method for airtightly joining metal members made of various iron-based materials. Further, since the bonded body of the present invention exerts an excellent effect as described above, it can be suitably used as various mechanical parts requiring airtightness.

10 ... Joint body 11 ... Large diameter pipe 12 ... Small diameter pipe 100, 100a ... Large diameter pipe 190, 190a ... Mounting hole 191, 191a ... Tapered hole 192,192a ... Parallel hole 200, 200a ... Small diameter pipe 210, 210a ... Cylindrical Part 220, 220a ... Tapered part 900 ... Power supply device 910 ... Lower electrode body 919 ... Recessed part 920 ... Upper electrode body 921 ... Flat part BR ... Joint part CS ... Joint part F ... Horizontal plane

Claims (6)

It is a method of joining two metal members made of iron-based material.
(A) A step of preparing the two metal members having an annular contact surface formed complementary to each other, and a step of preparing the two metal members.
(B) The joint is formed by applying pressure to the joint formed in contact with the contact surface formed on each of the two metal members and energizing between the two metal members via the joint. The step of joining the two metal members in the part and
With
A joining method characterized in that the joining temperature reached by the joining portion in the step (b) is set to be lower than the melting point of the metal material forming the two metal members, respectively. The joining method according to claim 1, further
A step of removing an oxide film formed on the contact surface of each of the two metal members prepared in the step (a) is provided.
Joining method. The joining method according to claim 1 or 2.
The two metal members are made of austenitic stainless steel.
The joining temperature is set higher than the upper limit temperature at which sensitization occurs in the austenitic stainless steel.
Joining method. The joining method according to claim 1 or 2.
The two metal members are made of austenitic stainless steel.
The joining temperature is set higher than the temperature at which the solution of the austenitic stainless steel starts.
Joining method. The joining method according to claim 1 or 2.
The two metal members are made of ferritic stainless steel.
The joining temperature is set higher than the upper limit temperature at which σ brittleness occurs in the ferritic stainless steel.
Joining method. A joined body obtained by joining the two metal members by the joining method according to any one of claims 1 to 5.

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