JP7370830B2 - Nickel-based alloy welding materials, welding materials for nuclear reactors, nuclear equipment and structures, and repair methods for nuclear equipment and structures - Google Patents

Description

Embodiments of the present invention relate to nickel-based alloy welding materials, welding materials for nuclear reactors, nuclear power equipment and structures, and methods for repairing nuclear power equipment and structures.

Conventionally, in boiling water reactor (BWR) plants, it has been reported that stress corrosion cracking (SCC) occurs in welded parts of reactor internal structures. Specifically, SCC occurred when a 182 alloy containing 14% by mass or more and 17% by mass or less of Cr, which is susceptible to SCC, was used as a welding material. In addition, 82 alloy contains 18% by mass or more and 22% by mass or less of Cr, and is a material with superior SCC resistance compared to 182 alloy, but damage cases have also been reported with this 82 alloy. ing.

Alloy 52, which is a 690 series alloy, is used as a welding material for welding parts in pressurized water reactor (PWR) plants, which have a more severe temperature environment than BWR plants. The 52 alloy contains 28% by mass or more and 31.5% by mass or less of Cr, and has a higher Cr content than the 82 alloy.

Generally, Cr is an element that improves the SCC resistance of the alloy. Therefore, when the proportion of Cr contained in the alloy increases, the SCC susceptibility of the alloy can be reduced.

Special Publication No. 2013-527805 Japanese Patent Application Publication No. 11-012669

Alloy 82, which has high SCC resistance, is mainly used as a welding material for BWR plants, but in situations where 82 alloy is damaged by SCC, it may be better than 82 alloy for BWR plants. It is necessary to use a welding material that has high SCC resistance.

Also, in PWR plants, 52 alloy, which has better SCC resistance than 82 alloy, is used. This is due to the high Cr content of 52 alloy, but on the other hand, welding with 52 alloy has a high Cr content of nearly 30%, so welding with 52 alloy causes hot cracking and reduced ductility compared to 182 alloy and 82 alloy. There is a problem that cracks are likely to occur during welding. Furthermore, 52 alloy has never been applied as a welding material for a BWR plant, and in order to use this 52 alloy for a BWR plant, it is necessary to establish welding conditions.

Therefore, an object of the embodiments of the present invention is to provide a nickel-based alloy welding material that has good SCC resistance and excellent weldability.

In order to achieve the above object, the nickel-based alloy welding material according to the present embodiment has, in mass %, Cr: more than 30.0% and 36.0% or less, C: 0.050% or less, Fe: 1 .00% or more and 3.00% or less, Si: 0.50% or less, Nb+Ta: 0.01% or more and 3.00% or less, Ti: 0.001% or more and 0.70% or less, Mn: 0 .10% or more and 3.50% or less, Cu: 0.5% or less, and the remainder consists of Ni and inevitable impurities, and S and P in the inevitable impurities are each 0.005% or less. , is characterized by.

Further, the nuclear reactor welding material according to this embodiment is characterized by using the above-mentioned nickel-based alloy welding material.

Furthermore, nuclear power equipment and structures according to the present embodiment are characterized by using the above-mentioned nickel-based alloy welding material.

Furthermore, the method for repairing nuclear power equipment and structures according to the present embodiment includes a material preparation step of preparing the above-mentioned nickel-based alloy welding material as a welding material for repair, and using the welding material to repair nuclear power equipment and structures. The present invention is characterized by comprising a repair step of repairing the structure.

According to the embodiments of the present invention, it is possible to provide a nickel-based alloy welding material that has good SCC resistance and excellent weldability.

1 is a comparison table showing chemical components of each of nickel-based alloy welding materials. It is a figure explaining specimen collection, (a) is a front view, (b) is a side view, and (c) is a top view. It is a figure which shows a CBB test jig, (a) is a front view, (b) is a side view. It is a table showing the results of the CBB test. It is a figure which shows the test piece shape used for an SCC crack growth test, (a) is a left view, (b) is a front view, and (c) is a right view. It is a graph showing the relationship between SCC crack growth rate and stress intensity factor for nickel-based alloy welding material C and 82 welding material according to the present example. FIG. 2 is a flow diagram showing the procedure of a repair method for nuclear equipment and structures. FIG. 2 is a partial elevational cross-sectional view conceptually showing a shroud support of a boiling water reactor. FIG. 2 is a partial elevational sectional view conceptually showing a control rod drive mechanism housing penetration portion of a boiling water reactor.

EMBODIMENT OF THE INVENTION Hereinafter, with reference to drawings, the nickel-based alloy welding material, the welding material for nuclear reactors, the nuclear power equipment and structures, and the repair method of nuclear power equipment and structures according to embodiments of the present invention will be described. Here, parts that are the same or similar to each other are given the same reference numerals, and overlapping explanations will be omitted.

The nickel-based alloy welding material in the first embodiment is composed of a nickel-based alloy having the chemical composition range shown below. In addition, in the following description, % representing a chemical composition represents mass % unless otherwise specified.

Nickel-based alloy welding materials include Cr (chromium): more than 30.0% and 36.0% or less, C (carbon): 0.050% or less, Fe (iron): 1.00% or more and 3.00%. % or less, Si (silicon): 0.50% or less, Nb (niobium) + Ta (tantalum): 3.00% or less, Ti (titanium): 0.70% or less, Mn (manganese): 0.10% or more and 3.50% or less, Cu (copper): 0.5% or less, and the remainder consists of Ni and inevitable impurities.

Further, the second embodiment further includes Mo (molybdenum): 2.00% or more and 5.00% or less as a nickel-based alloy welding material.

Further, in another embodiment, Zr (zirconium): 0.05% or less, B (boron): 0.05% or less, V (vanadium): 0. 5% or less, Al (aluminum): 0.5% or less, Co (cobalt): 0.12% or less.

Examples of unavoidable impurities in these nickel-based alloy welding materials include P (phosphorus) and S (sulfur). Unavoidable impurities are, for example, components contained in raw materials such as ore and scrap necessary for manufacturing the nickel-based alloy welding material, or components mixed in during the manufacturing process.

The nickel-based alloy welding material having the chemical composition range described above can be used as a welding material for a nuclear reactor for welding all the members constituting the reactor internals in the reactor pressure vessel of a BWR plant or a PWR plant. can. Here, the welding material for a nuclear reactor is a nickel-based alloy welding material made into a rod-like, wire-like, or powder-like form so that welding can actually be carried out.

For example, all of the members constituting the reactor internals may be welded using the nickel-based alloy welding material of this embodiment, or some of the members constituting the reactor internals may be welded using the nickel-based alloy welding material of this embodiment. Welding may be performed using alloy welding materials.

Next, the reasons for limiting each chemical composition range in the nickel-based alloy welding materials according to these embodiments will be explained.

(1) Cr
Cr is an essential element for increasing the SCC resistance, oxidation resistance, corrosion resistance, and mechanical strength of nickel-based alloy welding materials. Further, Cr is a constituent element of M ₂₃ C ₆ type carbide, which is a reinforcing phase. Generally, as the Cr content increases, corrosion resistance improves, but if the Cr content is too high, the price increases and mechanical strength decreases due to the precipitation of the harmful σ phase. , there is a concern that weldability may deteriorate.

The content of Cr is preferably about 26% or more, but in this embodiment, it is in the range of more than 30%. Further, as shown in the examples described later, confirmation was performed in a range up to 36.0%. As a result, it was confirmed that good results could be obtained even up to 36.0%.

As a result of the above, the content of Cr is set to be more than 30.0% and less than 36.0%.

(2)C
C is useful as a deoxidizer during dissolution and to increase mechanical strength. Further, C is a constituent element of M ₂₃ C ₆ type carbide, which is a reinforcing phase, and has the effect of ensuring the fluidity of the molten metal during casting. On the other hand, when the C content exceeds 0.050%, Cr deficiency occurs near the grain boundaries due to the precipitation of Cr carbides, resulting in a decrease in SCC resistance. In addition, ductility reduction cracking is more likely to occur. Therefore, the content of C is set to 0.050% or less. Further, if the C content is less than 0.001%, no effect of increasing mechanical strength can be expected, so it is preferably contained at 0.001% or more. However, if a sufficient strength improvement effect can be obtained by other additive elements, intentional addition may not be necessary.

(3) Fe
Fe is useful for increasing mechanical strength. If the Fe content is less than 1.00%, the mechanical strength will decrease. On the other hand, when the Fe content exceeds 3.00%, corrosion resistance decreases. Therefore, the Fe content is set to 1.00% or more and 3.00% or less.

(4) Si
Si is useful as a deoxidizing agent during melting and has the effect of improving the flow of molten metal during casting. As the Si content increases, nonmetallic inclusions are generated and the corrosion resistance decreases, so it is preferable that the Si content is low. When the Si content exceeds 0.50%, castability and mechanical strength decrease. Therefore, the content of Si is set to 0.50% or less. Further, if the Si content is less than 0.001%, no effect as a deoxidizer during dissolution can be expected, so it is preferably contained at 0.001% or more. However, if a sufficient deoxidizing effect during dissolution can be obtained by other additive elements, intentional addition may not be necessary.

(5) Nb+Ta
Nb and Ta suppress the generation of Cr carbides by forming carbides and improve SCC resistance. However, when the content of Nb and Ta increases, weld cracking becomes more likely to occur. For this reason, the content of Nb+Ta is set to 3.00% or less.

Further, if the content of Nb+Ta is less than 0.01%, no effect of suppressing the formation of Cr carbide can be expected, so it is preferable that the content is 0.01% or more. However, if a sufficient effect of suppressing Cr carbide formation can be obtained by other additive elements, intentional addition may not be necessary.

Here, "Nb+Ta" represents the total amount of Nb and Ta. It also means that either Nb or Ta may not be included, or both may be included, as long as the total amount is within the above range.

(6) Ti
By forming carbides, Ti suppresses the generation of Cr carbides and improves SCC resistance. When the Ti content exceeds 0.70%, weld cracking is likely to occur. Therefore, the Ti content is set to 0.70% or less. Moreover, 0.001% or more is preferable as the minimum amount at which the effect of suppressing Cr carbide generation can be expected. However, if a sufficient effect of suppressing Cr carbide formation can be obtained by other additive elements, intentional addition may not be necessary.

(7) Mn
Mn is an austenite stabilizing element, and combines with S (sulfur), which causes brittleness, to form MnS, which prevents brittleness and improves strength and melt flow. If the Mn content is less than 0.10%, the above effects cannot be obtained. On the other hand, when the Mn content exceeds 3.50%, nonmetallic inclusions with S and the like are likely to be formed, resulting in a decrease in corrosion resistance. Additionally, austenite stabilization increases weld cracking susceptibility. Therefore, the Mn content is set to 0.10% or more and 3.50% or less.

(8) Cu
Cu has the effect of increasing strength. However, if the amount added is too large, the weld cracking resistance will decrease, so the content of Cu is preferably 0.5% or less. Furthermore, the minimum content that can achieve the effect of increasing grain boundary strength is preferably 0.001% or more. However, if a sufficient strength improvement effect can be obtained by other additive elements, intentional addition may not be necessary.

(9)Mo
Mo increases strength and is effective against ductility-degrading cracking. However, if the amount added increases, a brittle phase is formed, so the Mo content is preferably 2.00% or more and 5.00% or less.

(10) Zr
Zr increases grain boundary strength and is effective against ductility reduction cracking. However, if the amount added is too large, weldability deteriorates, so the content of Zr is preferably 0.05% or less. In addition, the minimum amount for achieving the effect of suppressing ductility deterioration cracking is preferably 0.001% or more. However, if a sufficient effect of suppressing ductility reduction cracking can be obtained by other additive elements, intentional addition may not be necessary.

(11)B
B has the effect of increasing grain boundary strength. However, the content of B is preferably 0.05% or less. Furthermore, the minimum content that can achieve the effect of increasing grain boundary strength is preferably 0.01% or more. However, if a sufficient effect of improving grain boundary strength can be obtained by other additive elements, intentional addition may not be necessary.

(12)V
V has the effect of increasing strength. However, since ductility decreases if the amount added is too large, the content of V is preferably 0.5% or less. Furthermore, the minimum content that can provide the effect of increasing strength is preferably 0.01% or more. However, if a sufficient strength improvement effect can be obtained by other additive elements, intentional addition may not be necessary.

(13) Al
Al increases strength and has a deoxidizing effect. However, if the amount added is too large, welding workability will deteriorate due to slag generation, etc., so the content of Al is preferably 0.5% or less. In addition, the minimum content of 0.01% or more is preferable to increase the strength and obtain the deoxidizing effect. However, if sufficient strength improvement and deoxidation effects can be obtained by other additive elements, intentional addition may not be necessary.

(14) Co (cobalt)
Since the isotope ⁶⁰ Co of Co becomes a gamma ray source by decay, the content of Co when used in a nuclear reactor is preferably 0.12% or less.

(15) P and S
P and S are classified as inevitable impurities in the nickel-based alloy welding material in this embodiment. It is preferable that the content of these unavoidable impurities remaining in the nickel-based alloy welding material be as close to 0% as possible.

P causes grain boundary embrittlement and reduces corrosion resistance. Furthermore, due to the segregation of P, weld cracking becomes significantly more likely to occur. Therefore, it is preferable that the content of P is suppressed to 0.005% or less. Furthermore, when the S content is higher than 0.010%, S forms nonmetallic inclusions with Mn, reducing corrosion resistance. Therefore, it is more preferable that the S content is suppressed to 0.005% or less. When the contents of P and S are each 0.005% or less, solidification cracking is suppressed.

The nickel-based alloy welding material and nuclear reactor welding material according to the present embodiment described above have superior SCC resistance compared to alloys constituting existing BWR welding materials, such as 182 alloy and 82 alloy. In addition, it has good weldability. Therefore, by using the nickel-based alloy welding material of the embodiment as a welding material for welding reactor internals in a nuclear power plant, welding of reactor internals becomes easier, and welding of the reactor internals becomes easier. It can be expected to improve SCC resistance.

Hereinafter, specific examples of this embodiment will be described in detail with reference to the drawings and tables. Note that this embodiment is not limited to these examples.

(Step 1)
FIG. 1 is a comparison table showing the chemical components of each of the nickel-based alloy welding materials.
Four types of compositions, A, B, C, and D, are shown as nickel-based alloy welding materials.

In order to obtain each of the nickel-based alloy welding materials having these chemical compositions, necessary raw materials were melted in a vacuum induction melting furnace to produce ingots approximately 150 mm square x approximately 450 mm long. Thereafter, a forged product with a diameter of 60 mm x approximately 1000 mm was produced by forging, and the forged product was rolled into a diameter of 9.5 mm. Furthermore, after peeling the surface, a wire having a diameter of 1.2 mm was obtained by wire drawing. In this way, it was confirmed that four types of nickel-based alloy welding materials A, B, C, and D could be manufactured.

(Step 2)
FIG. 2 is a diagram illustrating specimen collection, in which (a) is a front view, (b) is a side view, and (c) is a plan view. A base portion 11 is formed into a flat plate shape on a flat plate 12a of the frame 12, and a built-up portion 10 is formed on the base portion 11. The frame 12 ensures rigidity so that the base member 11 does not deform. The base member 11 was made of 600 alloy. Three units were manufactured in this condition.

Using A, B, and C of the nickel-based alloy welding materials manufactured in step 1, heat input is 16 KJ/cm or less, base current is 180 A, and welding material feeding speed is applied to each base material part 11. By gas tungsten arc welding at a rate of 900 mm/min, a multilayer overlay portion 10 having a length L of 250 mm, a width W of 60 mm, and a height H of 50 mm was formed as shown in FIG.

As a result, it was confirmed that overlay welding could be performed without any problem with any of the welding materials made of nickel-based alloy welding materials A, B, and C, and that there were no harmful defects.

In addition, since the components other than Mo in the nickel-based alloy welding material D are the same as those in the nickel-based alloy welding material A, it is considered that welding can be performed under the same conditions as the welding material with the nickel-based alloy welding material A.

(Step 3)
Four test pieces 20 each having a width of 10 mm, a length of 50 mm, and a thickness of 2 mm were collected from each built-up portion 10 formed in step 2. A creviced bent beam (CBB) test described below was conducted on these test pieces.

FIG. 3 is a diagram showing a CBB test jig, in which (a) is a front view and (b) is a side view. Note that although the following description uses expressions in the vertical direction, it is used for convenience of explanation and is not meant to be limited to this.

As shown in FIG. 3, the CBB test jig 30 has an outer diameter of a substantially rectangular parallelepiped as a whole. The CBB test jig 30 includes an upper half 31 and a lower half 32 that vertically sandwich the test piece 20, and graphite wool 34 and two spacers to ensure a gap between the test piece 20 and the upper half 31. 35, and two bolts 33 for tightening the upper half 31 and lower half 32 together. The two spacers 35 are arranged so as to sandwich the graphite wool 34 between them.

The upper half part 31 is formed in a concave shape upward in the longitudinal direction, and the lower half part 32 is formed in a convex shape upward in the longitudinal direction so as to oppose the concave surface of the upper half part 31. The concave surface of the upper half part 31 and the convex surface of the lower half part 32 are each formed to have a radius of curvature of 100 mm.

The test piece 20 is sandwiched between an upper half 31 and a lower half 32 and tightened with bolts 33. At this time, a gap is secured between the test piece 20 and the upper half part 31 by the graphite wool 34 and the spacer 35, and a bending load is applied to the test piece 20 by the spacer 35 and the lower half part 32, and the upper surface A state in which a space for forming a corrosive environment is formed is ensured.

Based on the above test system, in order to evaluate stress corrosion cracking susceptibility in high-temperature water, a CBB test was conducted using test piece 20 using nickel-based alloy welding materials A, B, and C produced in step 2. I did it.

In the CBB test, the sample was immersed in high-temperature, high-pressure pure water at a temperature of 288° C. and a pressure of 7.8 MPa for 500 hours using an autoclave, and then the presence or absence of SCC generation was evaluated. The test was conducted on four test pieces 20 taken for each nickel-based alloy welding material.

FIG. 4 is a table showing the results of the CBB test, including a test piece using nickel-based alloy welding material A, a test piece using nickel-based alloy welding material B, and a test piece using nickel-based alloy welding material C. The number of cracks generated after each CBB test is shown.

As a result, no stress corrosion cracking was observed in all four test pieces using nickel-based alloy welding materials A, B, and C. In addition, since the amount of Cr, which affects corrosion resistance, in the nickel-based alloy welding material D is also equivalent to that in the nickel-based alloy welding material A, it is considered that the SCC resistance is excellent.

Furthermore, it has been reported that 182 alloy showed SCC susceptibility when a similar test was conducted ("Effect of processing on the SCC susceptibility of nickel-based weld metals in high temperature water", Materials and Environment 2005, A310 ).

(Step 4)
A CT (compact tension) test piece was taken from the built-up portion 10 of the nickel-based alloy welding material C formed in step 2, and an SCC crack growth test was conducted.

FIG. 5 is a diagram showing the shape of the test piece used in the SCC crack growth test, in which (a) is a left side view, (b) is a front view, and (c) is a right side view.

The CT test piece 40 has a cutout 42 formed at the center in the width direction of the base 41 from the end, and a tensile load is applied between the load application parts 43 and 44 . A stamp 45a is formed on the back surface 45 (right side in FIG. 5) of the base 41 at each divided portion.

The dimensions of each part of the CT test piece 40 are nominal values, and the thickness T is 12.7 mm, the width D is 30.48 mm, and the length H is 31.75 mm. It is a 0.5T CT test piece. . Further, the width W of the notch 42 is 1.6 mm.

After fatigue pre-cracking was introduced in the air at room temperature, pre-cracking was introduced in the environment using an autoclave at the following water quality. Thereafter, an SCC crack growth test was conducted under the following water quality and load conditions.

<Water quality conditions>
Temperature: 288℃
Pressure: 9MPa
Corrosion potential (ECP): 150mV _SHE or more <Load conditions>
Test load: 7.0kN
Target stress intensity factor K: approximately 32 to 34 MPa√m
The crack growth time under constant load was 562.9 hours, and the crack growth rate was determined by correcting the fracture surface after the test.

FIG. 6 is a graph showing the relationship between the SCC crack growth rate and the stress intensity factor for the nickel-based alloy welding materials C and 82 welding materials according to this example. Curve S is the average crack propagation rate curve of the proposed 82 alloy (TIG welding material) Report on load test). Further, point P is the test result for the present nickel-based alloy welding material C.

The crack growth rate in the case of the nickel-based alloy welding material C was 2.63×10 ⁻¹² (m/s) with a stress intensity factor K of 32.2 MPa√m. The crack growth rate da/dt at this time was less than about 1.23×10 ⁻¹² [m/s]. As shown in FIG. 6, the value of the crack growth rate da/dt in the case of the nickel-based alloy welding material C was shown to be sufficiently lower than that of the 82 alloy.

As shown above, according to the examples, it has been confirmed that it is possible to provide a nickel-based alloy welding material and a nuclear reactor welding material that have good SCC resistance and excellent weldability.

FIG. 7 is a flowchart showing the procedure of a method for repairing nuclear equipment and structures.
First, a nickel-based alloy welding material is prepared (step S01). Here, the nickel-based alloy welding material is the welding material shown in this embodiment.
Next, nuclear power equipment and structures are repaired using the nickel-based alloy welding material prepared in step S01 (step S02). As shown in the examples, by using a welding material with good SCC resistance and excellent weldability, highly reliable repairs of nuclear power equipment and structures can be performed.

FIG. 8 is a partial elevational sectional view conceptually showing a shroud support of a boiling water reactor. A shroud support 2 surrounding the reactor core on the radially outer side of the reactor core is supported from the reactor pressure vessel 1 via a shroud support 3 . The welded portion between the shroud support 3 and the reactor pressure vessel 1 is a dissimilar metal joint.
FIG. 9 is a partial elevational sectional view conceptually showing a penetration part of a control rod drive mechanism housing of a boiling water reactor. The welded portion for sealing the penetration portion of the control rod drive mechanism housing 5 that penetrates the reactor pressure vessel 1 from below is also a dissimilar material joint.
The nickel-based alloy welding material according to this embodiment can be applied to welding joints of such nuclear power equipment and structures. In addition to the dissimilar metal welds of the shroud support of boiling water reactors and the penetration part of the control rod drive mechanism housing, although not shown, welds of the nozzle holder of the pressure vessel upper cover of pressurized water reactors, or the welds of steam generators. It can be used for etc.
Furthermore, it can also be used in fields other than the nuclear power field, such as power plants and chemical plants that require high corrosion resistance, such as those in which nickel-based alloys are used, as well as marine ships and their structures.

[Other embodiments]
Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention.

Moreover, the features of each embodiment may be combined. Furthermore, these embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

DESCRIPTION OF SYMBOLS 1... Reactor pressure vessel, 2... Shroud, 3... Shroud support, 5... Control rod drive mechanism housing, 10... Overlay part, 11... Base material part, 12... Frame, 12a... Flat plate, 20... CBB test piece, 30... CBB test jig, 31... Upper half, 32... Lower half, 33... Bolt, 34... Graphite wool, 35... Spacer, 40... CT test piece, 41... Base, 42... Notch, 43, 44 ...Load application part, 45...back side, 45a...engraved

Claims (5)

In mass%, Cr: more than 30.0% and 36.0% or less, C: 0.050% or less, Fe: 1.00% or more and 3.00% or less, Si: 0.50% or less, Nb + Ta : 0.01% or more and 3.00% or less, Ti: 0.001% or more and 0.70% or less, Mn: 0.10% or more and 3.50% or less, Cu: 0.5% or less The remainder consists of Ni and unavoidable impurities,
S and P in the inevitable impurities are each 0.005% or less,
A nickel-based alloy welding material characterized by: The nickel-based alloy welding material according to claim 1, further comprising Mo in an amount of 2.00% or more and 5.00% or less in mass %. A welding material for a nuclear reactor, characterized in that the nickel-based alloy welding material according to claim 1 or 2 is used. Nuclear equipment and structures characterized by using the nickel-based alloy welding material according to claim 1 or 2 . a material preparation step of preparing the nickel-based alloy welding material according to claim 1 or claim 2 as a repair welding material;
a repair step of repairing nuclear equipment and structures using the welding material;
A method for repairing nuclear equipment and structures, comprising :

Images