JPH0722822B2 - Brazing method - Google Patents

Description

The present invention relates to a brazing method suitable for suppressing liquid metal brittleness.

"Prior Art" Conventionally, for example, a mass flowmeter as disclosed in JP-A-63-262526 is known. The structure is shown in FIGS. 2 and 3. In this mass flowmeter 1, the inlet portion 2a of the main body 2
The first straight pipe part 3 is connected to the outflow part 2b of the main body 2 and the second straight pipe part 4 is spaced apart in parallel to each other, and the tip ends of the straight pipe parts 3 and 4 are curved parts 3a and 4a. Connected to each other via the straight pipe section 3,4
The vibrator 5 is attached to the tip side of the
A pickup 6 for detecting vibration is provided on each of 3 and 4.

The mass flowmeter 1 having the configuration shown in FIG. 3 of FIG.
And, a fluid is caused to flow to the outlet of the main body 2 via the tip end side of the second straight pipe portion 4 and the second straight pipe portion 4, and at the same time, vibration is applied to the straight pipe portions 3 and 4 by the vibrator 5. This is a device that measures the flow rate by analyzing the Coriolis force generated by this vibration.

That is, according to this device, the straight pipe portions 3 and 4 have a fixed frequency determined by the spring constant of the pipe portion through which the fluid flows and the flowing fluid.
The vibration of the straight pipe part 3 and the straight pipe part 4 causes a time difference based on the action of the Coriolis force generated by this vibration, and this is detected as a signal of the time difference by the pickups 6 and 6 to detect the Coriolis force. The magnitude (the time difference) is proportional to the mass flow rate to obtain a signal proportional to the mass flow rate. By analyzing this signal, the flow rate can be accurately measured.

[Problems to be Solved by the Invention] By the way, when the present inventors manufacture and operate the mass flowmeter 1 having the above-described configuration, the straight pipe sections 3 and 4 made of Hastelloy alloy are used.
There was an accident in which a crack was generated in the portion joined to the stainless steel main body 2 and the straight pipe portions 3 and 4 were broken. It is considered that the cause of this accident is that the portion where the straight pipe portions 3 and 4 are joined to the main body 2 is brazed, and the joined portion becomes brittle during this brazing. And
Observation and analysis of the structure of the broken portion revealed that the metal in the broken portion had intergranular cracks.

Here, in general, when a solid metal under tensile stress is in contact with a liquid metal, the liquid metal locally penetrates along the grain boundaries of the solid metal and cracks along the grain boundaries of the solid metal. It is known to occur. This kind of phenomenon is conventionally known as liquid metal brittleness (solder brittleness), and it is a combination of a specific solid metal and a specific liquid metal, and it causes cracks only when stress is applied. is there.

Therefore, also in the mass flowmeter 1 having the above structure, brittleness occurs due to brazing around the brazed portions of the straight pipe portions 3 and 4,
It is thought that this is the reason why the straight pipe sections 3 and 4 suffered intergranular cracks and were broken.

It is known that the embrittlement phenomenon associated with brazing occurs in a combination of a specific metal and a brazing agent, but the generation mechanism thereof has not been clarified in detail at present.

As a measure against such solder brittleness, conventionally, heat treatment has been performed aiming at the removal of stress, and the type of brazing agent has been selected.

However, in the mass flowmeter 1 having the above structure, the straight pipe portion 3,
If heat treatment is performed on the brazed part of 4, the deformation of the heated part is unavoidable, and it is difficult to properly remove stress.

In addition, as the type of brazing agent, silver brazing, copper brazing, nickel brazing, phosphorous copper brazing, and gold brazing are generally used, and among these, gold brazing is known to be effective against solder brittleness. However, brazing wax has the drawback of being extremely expensive.

Further, copper braze and nickel braze have a high processing temperature of 1080 to 1200 ° C for the former and 875 to 1100 ° C for the latter, which causes deformation of the welded portion, and in addition to corrosion-resistant metal materials such as stainless steel and Hastelloy (registered trademark) alloys. There is a problem that causes deterioration of corrosion resistance. Also, phosphorus copper braze has a low processing temperature of 600 to 815 ° C, but since it is intended for copper-based materials, it is easy to form brittle intermetallic compounds when brazing iron-based or nickel-based alloys. There is.

Further, the processing temperature is as low as 600 to 800 ° C., and silver brazing used in many cases of brazing is also a material which is apt to cause solder brittleness, which is also unsuitable.

The present invention has been made to solve the above problems, and even when brazing a stressed member under stress, cracks due to intergranular cracks may occur in the brazed member. The purpose is to provide a brazing method that eliminates.

“Means for Solving the Problem” In order to solve the above-mentioned problems, the invention described in claim 1
In a method of brazing a nickel alloy member that is stressed by external stress, internal stress, thermal stress, etc. to another member, after forming a coating layer of nickel or an alloy containing nickel on the nickel alloy member Brazing with silver brazing is performed.

In order to solve the above-mentioned problems, the invention described in claim 2
The brazing method according to claim 1, wherein the nickel alloy member is a pipe member, and the coating layer is nickel plated or nickel alloy plated.

"Function" Since the member on which the coating layer of nickel or an alloy containing nickel such as a plating layer is formed is silver brazed, the coating layer on the surface of the member prevents the molten wax from entering the member structure. Therefore, the brazing material does not enter the crystal grain boundaries of the member, and solder embrittlement is prevented. Therefore, even if a member that is stressed by a stress such as a tensile stress is brazed, a crack does not occur in the brazed member, and the brazed portion does not break.

The present invention will be described in more detail below.

FIG. 1 is for explaining the process of one embodiment of the present invention. In the present invention, brazing is performed after forming a coating layer on one or both of two members A and B to be brazed by plating or the like. To do. In the present invention, brazing does not include joining with soft solder such as solder, but joining with hard solder such as silver solder.

Here, as an example of the members A and B to be brazed, the main body portion 2 of the straight pipe portions 3 and 4 of the mass flowmeter 1 having the structure described above with reference to FIGS. 2 and 3 is exemplified. You can Straight pipe section 3,4
Is a stainless steel (for example, SUS304, 316) Hastelloy alloy (for example, Hastelloy C-276) Ni alloy pipe such as Inconel, Incoloy, Nionel, Monel, and Chromimet, and the main body 2 for brazing these straight pipe portions 3 and 4 Is made of stainless steel (for example, SUS304).

The coating layer formed on the straight pipe portions 3 and 4 is preferably formed in a thickness range of 5 to 20 μm. If the thickness of the coating layer formed here is 5 μm or less, it is not preferable because it is not sufficient to prevent the molten brazing material from entering the member.
When the thickness is 20 μm or more, it is difficult to form the coating layer with the same thickness by plating or the like, and it is not economical, which is not preferable. The coating layer may be either a nickel single layer or an alloy layer containing nickel. The coating layer may be a plating layer, a thermal spray layer, a chemical vapor deposition film by CVD or the like, or a physical vapor deposition film by PVD or the like. Any layer may be used as long as it is a single layer structure, and the structure thereof may be either a single layer structure or a laminated structure.

When a plating layer is adopted as the coating layer, nickel plating is performed by using a known plating bath having a reducing agent such as hypophosphite, a borohydride compound or a hydrazine compound, and a straight pipe part 3 The plating layer can be formed by immersing 4, 4 or the main body 2 and applying a direct current or an alternating current. In order to adjust the thickness of the plating layer, the composition of the plating bath and the magnitude of the applied current may be adjusted appropriately.

In addition, when bathing the pipes 3 and 4, the TTC diagram (Time-Temperature) of the generally known Hastelloy C-276 is used.
As is clear from -Corosion-Diagram), Hastelloy C-276 as a base material tends to lose its original corrosion resistance when heated to 800 ° C or higher. Therefore, the melting temperature of the brazing agent used in the present invention is preferably 800 ° C. or lower. In this respect, ordinary silver solder is suitable because it has a melting point of 800 ° C. or lower. Although phosphorous copper braze is also known as a brazing filler having a low melting temperature, when this brazing agent is used in a Ni alloy or Fe alloy, Ni or Fe reacts with P at the brazing interface to form a brittle intermetallic compound. It is not suitable because it will do.

After the nickel plating layer is formed, silver brazing is performed on the inserted portions while the straight pipe portions 3 and 4 are inserted into the main body 2 by a commonly known brazing method. With this brazing,
Since the plating layer acts as a barrier layer for the straight pipe parts 3, 4 or the main body 2, the molten silver solder should enter the crystal grain boundaries of the metal structure of the straight pipe parts 3, 4 or the crystal grain boundaries of the main body 2. Disappears.

If silver brazing is performed after the nickel plating layer is formed as described above, the nickel plating layer prevents the molten silver braze from invading the crystal grain boundaries of the base metal. The brazing material will not enter, and the brazing material will not become brittle.

Therefore, even if stress is applied to the brazed portion, intergranular cracking does not occur in the brazed portion. For this reason, it is not necessary to select the brazing agent which has been conventionally used, and the brazing can be easily performed with the silver brazing agent.

When the member to be brazed is a non-magnetic material such as Hastelloy alloy or austenitic stainless steel, it can be brazed by the high frequency heating method, and in this case, the current efficiency can be improved. As a result, workability can be improved by brazing for a short time, and the heat input during brazing can be reduced, so that the corrosion resistance of the base material can be maintained.

However, if the brazing is performed by the above-mentioned method, solder brittleness does not occur, so that it is not necessary to perform the heat treatment that has been widely used in the past to remove stress after brazing, and the deformation of the brazed portion due to the heat treatment is eliminated. be able to.

[Example] A pipe made of Hastelloy C-276 having an outer diameter of 10 mm and an inner diameter of 9 mm, and a 2 mm-thick stainless steel plate (S
US304) and several were prepared. A nickel plating layer having a thickness of 20 μm was formed on each of the pipes by an electroplating method, and the pipes were brazed while being inserted into the holes of the stainless steel plates. As the brazing agent, silver brazing (BAg-7, 18, 24) and nickel brazing (BNi 6) were used separately. Also,
For comparison, brazing was performed using the same brazing agent without nickel plating. The above results are shown in Table 1,
Table 2 shows the compositions of the test waxes. The first
In the table, δ = 10.5 written in the column of bending indicates the case where a load of 10.5 kgf / mm ² is applied as bending stress, and δ
= 0 means that no bending stress is applied.

From Table 1, if the method of applying nickel plating and then brazing is carried out, without causing solder brittleness,
It has been found that any brazing agent can be brazed. In addition, in all the samples brazed after plating, no invasion of braze into the base metal was observed, and solder brittleness (liquid metal brittleness)
It is effective as a countermeasure.

On the other hand, when plating was not performed, all three types of silver brazing material became brittle and the base material was easily broken if stress was applied during the brazing operation. Although nickel brazing did not cause solder embrittlement, nickel brazing was not practically applicable because the melting (erosion) of the welded pipe was remarkable and the melting temperature of the brazing was higher than 800 ° C.

[Advantages of the Invention] As described above, according to the present invention, since a brazing member is coated with nickel or an alloy containing nickel and then silver brazing is performed, the crystal grain boundaries on the base metal side of the brazing member are The plating layer prevents the wax in the molten state from entering the inside. Therefore, since the molten brazing material does not enter, it is possible to prevent the brazed portion from becoming brittle.

Therefore, when using the method of the present invention, for example, when a straight pipe part made of Hastelloy of a mass flow meter is brazed to a stainless steel main body, even when vibration is applied to the straight pipe part and stress due to stress is applied, No cracks will occur in the brazed portion and the straight pipe will not be broken.

[Brief description of drawings]

FIG. 1 is a process diagram for explaining the method of the present invention, FIG. 2 is a perspective view of a mass flow meter, and FIG. 3 is a sectional view of the mass flow meter. 1 …… Mass flowmeter, 2 …… Main body, 2a …… Inlet, 2b ……
Outlet, 3,4 ... Straight pipe, 5 ... Vibrator, 6 ... Pickup.

Continuation of the front page (56) Reference JP-A-63-262526 (JP, A) JP-A-62-179866 (JP, A) JP-A-2-299772 (JP, A) JP-A-57-72770 (JP , A) JP-A-61-1469 (JP, A)

Claims (2)

[Claims] 1. A method of brazing a nickel alloy member, which is stressed by external stress, internal stress, thermal stress, etc., to another member, wherein the nickel alloy member comprises:
A brazing method, which comprises brazing with silver brazing after forming a coating layer of nickel or an alloy containing nickel. 2. The brazing method according to claim 1, wherein
The brazing method, wherein the nickel alloy member is a pipe member, and the coating layer is a nickel plating layer or a nickel alloy plating layer.