JPH0751880A - Welding method - Google Patents

Abstract

PURPOSE:To provide a welding method so constituted that intergranular corrosion of a welded part between a fixed core and a sleeve is prevented. CONSTITUTION:A valve body 3 abutting upon a valve seat 2b is provided in a valve main body 2, when a plunger 6 is driven by a solenoid 7 the valve body 3 is separated from the valve seat 2b and fluid from an inflow path 2c flows into an outflow path 2d through the valve seat 2b. After the fixed core 9 inserted into the solenoid 7 is plated with nickel, it is welded to the sleeve 8. Since the welded part between the fixed core part 9 and the sleeve 8 is formed by two phase structure of a ferrite phase and a martensite phase by melting the nickel plate, the intergranular corrosion can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method, and more particularly, to a welding method for abutting and welding members made of magnetic stainless steel.

[0002]

2. Description of the Related Art For example, in a water pressure control unit for driving a control rod used in a nuclear power plant or the like, a cooling water feeding unit for cooling a seal portion of a control rod driving mechanism is provided separately from a pipe for scram operation. A pipe and a drive water supply pipe for supplying a predetermined amount of water to forcibly drive the control rod during a periodic inspection are provided.

A pilot type two-way solenoid valve is provided in the driving water feed pipe and is normally closed. On the other hand, the cooling water supply pipe is provided separately from the driving water supply pipe by bypassing it, and a fixed orifice is provided on the way to supply a small amount of cooling water to the seal part. It has become.

In such a pilot type two-way solenoid valve, the fixed iron core and the movable iron core are inserted into the center hole of the solenoid formed of a coil. The fixed iron core is inserted and fixed in the inner part of the tubular sleeve, and the movable iron core is slidably inserted in the sleeve. When the solenoid is excited, the fixed iron core is attracted to the position where it abuts on the fixed iron core.

Operation of the valve element of the pilot type two-way solenoid valve,
That is, the pilot portion that controls the valve opening and closing includes a movable iron core that opens and closes the pilot flow path of the valve body, a sleeve having a fixed iron core that serves as a guide for the movable iron core and magnetically attracts the movable iron core, and an electromagnetic coil of a magnetic force source. The movable iron core and the fixed iron core are made of ferritic stainless steel which is a magnetic material to form a magnetic circuit. The sleeve itself is made of austenitic stainless steel having corrosion resistance, pressure resistance and wear resistance.

Since high-pressure driving water is contained inside the sleeve, a pressure-proof sealing property is required. Therefore, conventionally,
The joint between the fixed core and the sleeve had a welded structure.

The above-mentioned ferritic stainless steel has excellent magnetic properties and is widely used as a magnetic circuit constituent member of a solenoid valve. However, it has a high heat-affecting effect, especially due to heat input during welding (HAZ). Part) has a property of being susceptible to coarsening of the metal structure, that is, sensitization. Therefore, in the welded structure of ferritic stainless steel, there is a possibility of occurrence of intergranular corrosion cracking (IGC) in an environment where a corrosive factor such as chlorine (Cl) in driving water exists.

[0008]

However, when welding the abutting portion of the fixed core and the sleeve, for example, electron beam welding or the like is used. When welding in this way, the irradiation position of the electron beam may slightly shift (about 0.2 to 0.3 mm) due to the mechanical accuracy of the welding device.

The material of one of the sleeves is made of non-magnetic stainless steel containing a large amount of nickel Ni (for example, 18Cr-8).
Ni-based stainless steel, etc.), where the electron beam irradiation position shifts to the sleeve side and a large amount of non-magnetic stainless steel is melted, the Ni content in the weld bead increases, so that the welded portion has a ferrite phase and a martensite phase. It has a phase structure and corrosion resistance does not decrease.

However, the material of the other fixed iron core is ferritic magnetic stainless steel containing a small amount of nickel Ni (for example, 13Cr or 18Cr magnetic stainless steel), and contrary to the above, electron beam irradiation. When the position is shifted to the fixed core side and a large amount of magnetic stainless steel is melted, the amount of Ni contained in the magnetic stainless steel is reduced, so that the welded part becomes a ferrite single-phase structure, and corrosion resistance may be reduced. . Further, in the welded portion of the fixed iron core, the heat-affected zone of magnetic stainless steel is sensitized by rapid heating and rapid cooling, which may reduce the corrosion resistance.

Moreover, manganese sulfide MnS, which is an inclusion in ferritic magnetic stainless steel, is melted and solidified due to the effect of welding heat, resulting in localized concentration of sulfa (a phenomenon in which the concentration increases). This may dissolve in the water inside and form a corrosive environment.

For this reason, there has been a problem that if the welding position at the abutting portion of the fixed core and the sleeve shifts to the fixed core side, corrosion may easily occur in the welded portion.

Therefore, an object of the present invention is to provide a welding method that solves the above problems.

[0014]

DISCLOSURE OF THE INVENTION The present invention is a welding method of abutting two members, at least one of which is made of magnetic stainless steel, and welding the abutted portions, wherein at least the abutted portions of the members made of magnetic stainless steel are joined together. After the nickel plating is applied, the abutting portions of the two members are welded.

[0015]

By welding the surface of at least a member made of magnetic stainless steel with nickel, when welding the abutting portions of the two members, the structure of the welded portion is the ferrite phase and martensite even if the welded portion shifts to the magnetic stainless steel side. And a decrease in corrosion resistance is prevented by forming a two-phase structure.

[0016]

1 to 3 show a pilot type two-way solenoid valve to which an embodiment of the welding method according to the present invention is applied.

In each figure, a pilot type two-way solenoid valve (hereinafter referred to as "solenoid valve") 1 supplies drive water to a cylinder (not shown) of a control rod drive mechanism that drives a control rod in nuclear power generation. It is an electromagnetic switching valve provided in the middle of the driving water feed pipe for checking the movement of the piston.

The solenoid valve 1 generally comprises a valve body 2, a valve body 3 inserted into a sliding hole 2a in the valve body 2, and a solenoid assembly 4 mounted on the valve body 2. . The valve body 2 has a valve seat 2b at the inner part of the sliding hole 2a, an inflow passage 2c for communicating the bottom portion with the sliding hole 2a, and an outflow passage 2d for communicating the bottom portion with the valve seat 2b.

Further, the valve body 2 is fixed to a bracket (not shown) of a water pressure control unit (not shown) by a bolt 5 and the driving water is slid through the inflow passage 2c into the sliding hole 2a.
Is supplied into the driving water supply pipe (not shown) from the valve seat 2b through the outflow passage 2d.

The valve body 3 has a seat member 3a that abuts on the valve seat 2b at the bottom and a seat surface 3b that abuts on the plunger (movable iron core) 6 of the solenoid assembly 4 at the top.
A first pilot hole 3c penetrating the center of the valve body 3 is opened at the bottom of the valve body 3 and at the center of the seat surface 3b.
A second pilot hole 3d is formed in the step portion below the seat surface 3b and the side surface of the valve body 3. An O-ring 3e is attached to the outer circumference of the valve body 3 to seal the gap with the sliding hole 2a.

The solenoid assembly 4 includes a solenoid 7 around which a coil is wound, a cover 8 for covering the solenoid 7, and a plunger 6 slidably provided in the solenoid 7.
It has a tubular sleeve 8 which is screwed to the valve body 2 and guides the plunger 6. A fixed iron core 9 is integrally fixed to the upper end of the sleeve 8.

As shown in FIG. 2, the flow rate adjusting mechanism 10 is attached to the side surface of the main body 2 and adjusts the flow rate by narrowing the flow passage area of the outflow passage 2d on the downstream side of the valve seat 2b. That is, the flow rate adjusting mechanism 10 includes the throttle valve body 11 slidably inserted in the throttle hole 2f intersecting the outflow passage 2d.
A holder 12 into which the valve body 11 is screwed in, an O-ring 13 for sealing between the valve body 11 and the hole 2f, a lock nut 14 screwed into a threaded portion of the valve body 11, and a screw of the holder 12 The cap 15 is screwed to the portion.

Therefore, when adjusting the flow rate, the cap 1
After removing 5 and loosening the lock nut 14, the end of the valve element 11 is rotated with a tool such as a spanner.

As shown in FIG. 3, on the surface of the fixed iron core 9,
The nickel plating layer 16 is formed. Sleeve 8
Is abutted against and integrally fixed to the stepped portion 9a of the fixed iron core 9 after the plating process. Since the outer periphery of the fixed iron core 9 is tapered, the tip portion 8a of the sleeve 8 is swaged inward.

The tip portion 8a of the sleeve 8 and the stepped portion 9a of the fixed iron core 9 are welded by, for example, an electron beam welding device (not shown). The gap 26 between the outer peripheral surface of the fixed iron core 9 and the inner peripheral surface of the sleeve 8 is filled with the driving water described above. Therefore, in the welded portion between the tip portion 8a of the sleeve 8 and the stepped portion 9a of the fixed iron core 9, the driving water that has entered the gap 26 comes into contact with the liquid from the inside.

It is not necessary to form the nickel plating layer 16 on the entire surface of the fixed iron core 9, and the nickel plating layer 16 is provided at least in the vicinity of the step 9a of the fixed iron core 9 with which the tip portion 8a of the sleeve 8 is butted. Just go. However, in this embodiment, nickel plating is applied to the entire surface of the fixed iron core 9 in order to simplify the work of the plating process.

Now, a process for welding the fixed iron core 9 and the sleeve 8 will be described with reference to FIG.

In FIG. 4, first, in step 1, the sleeve 8 is processed into a cylindrical shape. Since the sleeve 8 is made of austenitic stainless steel, it has excellent corrosion resistance. That is, the material of the sleeve 8 is a non-magnetic stainless steel containing a large amount of nickel Ni (for example, 18Cr-8Ni).
System stainless steel).

Next, in step 2, the fixed iron core 9 is processed into a predetermined shape. The material of the fixed iron core 9 is a ferritic magnetic stainless steel (for example, 13C) with a low nickel Ni content.
r-type or 18Cr-type stainless steel). Therefore, when welding, if the welding position shifts to the fixed iron core 9 side and a large amount of magnetic stainless steel is melted, the melting amount of Ni contained in the magnetic stainless steel decreases.

Therefore, in the next step 3, the fixed iron core 9 is dipped in the plating bath 17, and the fixed iron core 9 is plated with nickel. Therefore, the nickel plating layer 16 is formed on the front surface of the fixed iron core 9.
Is formed.

Then, in step 4, the tip portion of the sleeve 8 and the stepped portion 9a of the fixed iron core 9 are butted against each other, and the rotating roller 18 is pressed against this butted portion to crimp the tip portion 8a of the sleeve 8.

In step 5, the assembly 19 of the sleeve 8 and the fixed iron core 9 is mounted on the jig 21 provided in the vacuum chamber 20a of the electron beam welding apparatus 20.

In the next step 6, after the vacuum chamber 20a is evacuated, the abutting portion 22 (see FIG. 3) between the sleeve 8 and the fixed iron core 9 is automatically moved by the electron beam based on a program inputted in advance. Welded. The abutting portion 22 irradiated with the high-speed electron beam is heated to a high temperature and melted, and the welding beads 23 having a substantially triangular shape as shown in FIG.
Is formed. When the weld bead 23 is cooled, the abutting portion 22 of the sleeve 8 and the fixed iron core 9 is integrally joined, so that the triangular boundary line shown in FIG. 5 does not actually exist.

Then, in step 7, the sleeve 8 and the fixed iron core 9 are
After the burrs at the welded portions of and are polished by the polishing machine 24, the process proceeds to step 8 where the welded assembly of the sleeve 8 and the fixed iron core 9 is inserted into the through hole 7a of the solenoid 7 and the nut 2
It is fixed to the solenoid 7 by tightening 5 (see FIG. 1).

As described above, the fixed iron core 9 is made of nickel N.
Since it is made of ferritic magnetic stainless steel with a low i content (for example, 13Cr or 18Cr magnetic stainless steel), if the welding position shifts to the fixed core 9 side, nickel becomes insufficient and intergranular corrosion cracking occurs. It will be easier.
Further, in the welded portion of the fixed iron core 9, the heat-affected zone of magnetic stainless steel is sensitized by rapid heating and quenching, which reduces the corrosion resistance.

Moreover, manganese sulfide MnS, which is an inclusion in ferritic magnetic stainless steel, is melted and solidified due to the influence of welding heat, and local sulfur (sulfur S) is generated.
Thickening occurs.

However, in this embodiment, since the fixed iron core 9 is nickel-plated and the nickel plated layer 16 is formed on the surface of the fixed iron core 9, nickel is melted also in the welded portion on the fixed iron core 9 side. Become. As a result, the amount of molten nickel in the weld bead is increased even in the welded portion on the fixed iron core 9 side, so that the welded portion has a two-phase structure of a ferrite phase and a martensite phase, and corrosion resistance can be maintained.

Further, in high energy density welding such as electron beam welding, since the welding speed is high, the molten metal is not sufficiently agitated and mixed, but by forming the welded portion with the above two-phase structure, The impact can be reduced.

FIG. 6 shows the results of component analysis of the welded portion when the welding position was changed, and FIG. 7 shows an example of the components of the non-magnetic stainless steel used for the sleeve 8 and the magnetic stainless steel used for the fixed iron core 9. Is. In FIG. 6, each component S at three points (a, b, c) of the welding bead 23 is shown.
The change of i, Cr, and Ni is shown, and the A line shown by the broken line is the component change at the position of the above-mentioned three points (a, b, c), and the B line shown by the one-dot chain line is at three points (a, b 0.2 from the position of
This is the component change at the position displaced by mm, and the C line indicated by the solid line is the component change at the position displaced by 0.4 mm from the position of three points (a, b, c).

It can be seen from FIG. 6 that, in the welding process, if the welding position shifts to the magnetic stainless steel side of the fixed iron core 9, the amount of nickel in the weld bead 23, which is the welded portion, is significantly reduced. In the case of electron beam welding, the melting width of the welded portion is narrower than that in TIG welding and the like, so that the component fluctuation due to the displacement of the welding position becomes large, but this can also be reduced by melting the nickel plating layer 16.

FIG. 8 shows the results of the corrosion test according to the above deviations (lines A, B and C).

When the welding position is shifted to the side of the fixed iron core 9 and a large amount of the magnetic stainless steel side is melted, intergranular corrosion may occur through the welded portion, but the magnetic stainless steel and the non-magnetic stainless steel are combined. If almost the same amount is melted,
Alternatively, when a large amount of non-magnetic stainless steel was melted, corrosion did not occur in the welded portion.

Further, observing the structure of the welded portion, C
The structure of the welded portion, in which a large amount of magnetic stainless steel is melted, indicated by the line is a single phase of ferrite phase only.
At the welding position indicated by the line B, the structure has a two-phase structure in which the martensite phase is precipitated at the grain boundaries of the ferrite phase. The reason why the ferrite phase alone and the two-phase structure of the ferrite phase and the martensite phase are formed is due to the difference in the amount of nickel in the welded portion, as can be seen from the Schaeffler state diagram shown in FIG.

When the welded portion is a ferrite single phase, since the solid solubility of carbon in the ferrite phase is small, chromium carbide precipitates at the grain boundary of the ferrite phase during cooling of the welded portion, and a chromium deficient layer near the grain boundary. Is considered to be formed and become sensitive.

On the other hand, when a two-phase structure of a ferrite phase and a martensite phase is formed, it is considered that sensitization is unlikely to occur because the solid solubility of carbon in the martensite phase is large.

From the above reason, it is understood that intergranular corrosion of the welded portion can be prevented by increasing the nickel content so that the welded portion does not become a ferrite single phase. Therefore, in the present embodiment, the surface of the fixed iron core 9 made of magnetic stainless steel is plated with nickel to prevent the intergranular corrosion of the welded portion.

Although the amount of nickel contained in the nickel plating layer 16 varies depending on the amount of Cr, it is at least Ni 2% or more, preferably Ni in the plating step.
The plating thickness is set to be 4% or more.

As described above, the fixed iron core 9 is plated with nickel to form the nickel plated layer 16 on the surface of the fixed iron core 9, so that, for example, the welding position is on the fixed iron core 9 side.
Even if it deviates by 2 mm or 0.4 mm, the welded part can have a two-phase structure of a ferrite phase and a martensite phase. As a result, in the welded portion, intergranular corrosion did not occur even in the corrosion test by forming the two-phase structure of the ferrite phase and the martensite phase.

In the above embodiment, the pilot type two-way solenoid valve has been described as an example, but the present invention is not limited to this, and the present invention is not limited to this, as long as it is constructed such that the abutting portion of magnetic stainless steel and nonmagnetic stainless steel is welded. Of course, the invention can be applied.

Further, in the above embodiment, the welding was carried out by using the electron beam welding apparatus, but it is needless to say that welding is not limited to this and may be carried out by using, for example, a laser welding apparatus.

[0051]

As described above, the welding method according to the present invention is
When at least the surface of the member made of magnetic stainless steel is nickel-plated, when welding the abutting portions of the two members, the structure of the welded part after cooling is ferrite phase and martensite phase even if the welded part shifts to the magnetic stainless steel side. And a corrosion resistance can be maintained, intergranular corrosion of the welded portion can be prevented, and the reliability of the welded structure can be improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a pilot type two-way solenoid valve to which an embodiment of a welding method according to the present invention is applied.

FIG. 2 is a partial lateral cross-sectional view showing a flow rate adjusting mechanism of an outflow passage.

FIG. 3 is an enlarged vertical sectional view showing an enlarged welded portion.

FIG. 4 is a process drawing for explaining a process of welding a sleeve and a fixed iron core.

FIG. 5 is a vertical cross-sectional view for explaining a state in which a sleeve and a fixed iron core are welded to each other.

FIG. 6 is a diagram for explaining a component analysis result of a welded portion when a welding position is changed.

FIG. 7 is a diagram showing an example of components of non-magnetic stainless steel used for the sleeve 8 and magnetic stainless steel used for the fixed iron core 9.

FIG. 8 is a diagram showing results of a corrosion test.

FIG. 9 is a state diagram of Schaeffler.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solenoid valve 2 Valve body 3 Valve body 4 Solenoid assembly 8 Sleeve 9 Fixed iron core 20 Electron beam welding device 22 Butt portion 23 Weld bead

Claims (1)

[Claims] 1. A welding method of abutting two members, at least one of which is made of magnetic stainless steel, and welding the abutted portions, wherein after at least the abutted portions of the members made of magnetic stainless steel are plated with nickel, A welding method comprising welding the abutted portions of two members.