JPS6284895A - Wire for mig arc welding for steel products for nuclear reactor and its production - Google Patents

Abstract

PURPOSE:To improve the toughness of a weld zone and to prevent embrittlement by neutron irradiation by incorporating specific weight % of various element such as C, Si and Cr into a wire and incorporating prescribed % of total B content and <10>B content as well as rare earth element therein. CONSTITUTION:0.05-0.15% C, 0.10-0.70% Si, 0.4-2.0% Mn, etc. are incorporated into the low-alloy steel wire for welding steel products for nuclear reactors in a pure inert or low active gas shielding atmosphere as the components of said wire and >=1 kinds among <=10.0% cr, <=1.5% Ni, <=2.5% Mo, and <=0.05% Ti are incorporated as additive elements therein. further the total B content is controlled to 0.0005-0.0050% and the <10>B to <=0.00004% and the rare earth element is incorporated into the wire at 0.02-0.30%. The toughness of the weld zone is improved by such component compsn. and the embrittlement by neutron irradiation is prevented by controlling the <10>B content.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a gas-shielded arc welding wire and a method for manufacturing the same, particularly for use in a neutron irradiation environment such as a nuclear reactor pressure vessel or related components. Concerning the wire used in MIG arc welding of steel materials and its manufacturing method, by adding B and rare earth elements to the wire, high toughness of the weld metal is ensured, while III
The present invention provides a narrow gap MIG arc welding wire that is effective in preventing neutron irradiation embrittlement by suppressing the B content.

(Prior art) A3
33 CCI steel, Cr-Mo steel, stainless steel, etc. are used, but MIG/
Arc welding is preferred, and due to the special circumstances of welding nuclear reactor steel materials, there is a need for welding materials, especially wires, that are effective in preventing neutron irradiation embrittlement of the weld metal.

Conventionally, in order to increase the toughness of weld metal, it has been effective to refine the weld metal structure, and generally a method of adding Ti or B to welding wire has been taken.

It is also known that addition of B is effective in improving high temperature tensile ductility and creep properties.

However, in the case of nuclear reactor related parts, the amount of B added is limited to a very small amount because the welded metal part is exposed to a neutron irradiation environment. The reason why B is not added is that when B is added, when the weld metal part is irradiated with thermal neutrons, 10B
(n, α)' This is because a Li nuclear reaction occurs, 10B collapses, and as a result, He gas is generated, and the He causes a decrease in ductility.

To reduce this Ie damage, that is, the embrittlement caused by neutron irradiation of B-containing metal materials, conventional methods have been proposed to reduce the amount of B as much as possible or to fix it with Ti, Nb, etc. No countermeasures were taken.

In addition, in the general MIG arc welding method, approximately 20χ of CO is added to the gauge gas as a shielding gas to stabilize the arc and prevent welding defects such as blowholes.
! Welding is performed by mixing gas (activated gas). However, this increases the amount of oxygen in the weld metal, and even if B is added, it becomes slag on the bead surface as oxidized inclusions, which not only reduces the effect of B addition but also reduces the In arc welding, there is a problem in that a large number of man-hours are required to remove the slag. In short, there were problems in that the yield of B was low and the "dispersion" was large, making it difficult to achieve the original purpose.

Against this background, the present inventors proposed a method for controlling the oxygen content in the weld metal to obtain high toughness, as disclosed in Japanese Patent Application Laid-Open Nos. 57-184586 and 1987-10493, etc. MIG Arc, which adds rare earth elements to the welding wire, stabilizes the arc even when welding in a low active gas shield atmosphere or a pure inert gas shield atmosphere, and improves the toughness of the weld metal. A welding method was proposed. However, although these methods were effective in improving toughness, they were completely ineffective against neutron irradiation embrittlement.

(Problems to be Solved by the Invention) As mentioned above, in the case of welded structural materials for nuclear reactors, if B is present in the weld metal, embrittlement due to neutron irradiation becomes a problem, but this is due to the presence of B in the natural world. for,'. There are two isotopic elements, B (approximately 20χ of the total daily amount) and JIB (approximately 80χ of the total daily amount), but only 10[1 of these can be transmuted into l0B(n,α)'Li by neutron irradiation. It is known that it is converted to He.

Note that IO[1 and IIB are considered to be completely similar in terms of metallurgical behavior and effects in weld metal. That is, since B is normally segregated at grain boundaries, it is considered that 10B is also unevenly distributed at grain boundaries. Therefore, by neutron irradiation,
The generated He gas reduces the bonding strength of grain boundaries, resulting in a reduction in the high-temperature tensile ductility of the weld metal.

Therefore, it can be seen that B, which is added for the purpose of making the structure finer and increasing its toughness, has the opposite effect in a neutron irradiation environment.

One way to deal with this is to suppress the amount of 10B, thereby reducing the deterioration in tensile ductility of the metal material due to neutron irradiation embrittlement. However, there are problems with MIG arc welding, such as the low-temperature toughness of the MIG arc welded metal,
Improvements in corrosion resistance properties are still required.

(Means for Solving the Problem) The present inventors have discovered that by adding rare earth elements to the wire, the oxygen content in the weld metal can be controlled, and the ratio of 11B [11B By adding a large amount of 11B, the m-weave is made finer and the toughness is increased, while at the same time the ratio of 11B is reduced [11B content is effective for preventing the decline in high temperature tensile ductility caused by neutron irradiation. The present invention provides an arc welding wire and a method for manufacturing the same.

First, it is a low alloy steel welding wire for welding nuclear reactor steel materials in a pure inert gas shield atmosphere or a low inert gas shield atmosphere, the wire having a C: 0.05~
0.15 w or less, Si: 0.10 to 0.70 kt
2Mn: 0.4-2.0 iyt%, P: <0
．． 02wt%, S: <0.02wL'A, and Cr: <10. OwtLNi:
<1.5 w or less, Mo: <2.5 11t
x4i: Contains one or more of <0.05 w or less, and further 0.0005 ev or less<(Io*l1)B≦0.
0050wt%, but +oBO amount is 0.00004
B that is less than or equal to wt%, and 0.02 to 0.30wtχ
MIG-arc welding wire for nuclear reactor steel containing rare earth elements with the remainder being mainly Fe and unavoidable impurities. An austenitic stainless steel welding wire for welding nuclear reactor steel materials in an ambient atmosphere, C: 0.01 to 0.08 wtχ.

St: 0.10-0.70 eat%, Mn:
1.0 to 2.5 w or less, Ni: 8 to 15 wt'%
, Cr: 17-25 w or less, Mo: ≦3.0
wt%, Ti:≦1.0wt%, P:≦0.03w or less, S:≦0.02w or less, and further Q
, 0005 ev or less <"""' B <0.005
0w or less, Rida LlOB (7) amount is 0.00004
B less than or equal to ntZ, and 0.02 to 0, 30@
It contains tχ of rare earth elements, and the remainder is mainly F.
MIG arc welding wire for nuclear reactor steel materials, which is an unavoidable impurity. Thirdly, in order to obtain the above wire, when melting steel, isotopes = JIB ratio (”
After adding a boron-containing raw material with B / ("B + IIB)) higher than the natural abundance ratio, B-removal refining is performed, followed by repeating the addition of a boron-containing raw material with a high IIB ratio several times to increase IIB content. Molten steel with a high ratio is melted, then rare earth elements and other necessary alloying elements are added to this molten steel and cast into steel slabs, which are then rolled and wire-drawn according to conventional methods to form wires of the final wire diameter. We propose a manufacturing method for MIG arc welding wire, which is characterized by the following.

In short, the present invention reduces I (IB) and enriches IIB by employing a welding wire added with a rare earth element. Because the oxygen content in the weld metal can be controlled to a low level during MIG arc welding,
It is a technology that reliably achieves high toughness, improves creep properties, and secures a weld metal with excellent high-temperature tensile ductility and embrittlement prevention even in a neutron irradiation environment.

The present invention is a wire used in a method of performing MIG arc welding in a pure inert gas shield atmosphere or a low inert gas shield atmosphere. It is possible to prevent the formation of slag, and it is possible to weld the next layer without slag removal work, so it is expected to improve work efficiency when welding thick materials with narrow grooves.

(Operation) The reason for limiting the composition of the wire according to the present invention will be described below.

■In the case of low alloy steel welding wire, C is 0 to improve hardenability and ensure tensile strength.
．． 0.05 wt% or more is required, but if it exceeds 0.15 w or less, the toughness will decrease significantly, so 0.05 to 0.1
It was limited to 5wtχ.

In order for Si to function effectively as a deoxidizing agent, it must be 0.
10 wt% or more is required. It is also effective in increasing strength, but if it exceeds 0.70 w or less, the stiffness deteriorates rapidly, so it is limited to 0.10 to 0.70 w or less.

When Mn is less than 0.4 wtχ, blowholes are generated due to insufficient deoxidation, and at the same time, the toughness is low; 2. Owt
If χ exceeds 0.4 to 2.0, the hardenability becomes too high and the toughness deteriorates. Limited to Ow or less.

Cr works effectively to improve high temperature characteristics, but 10. Ow
If added in excess of tχ, the hardenability will become too high,
Less than 10.0wt% due to deterioration of toughness and cracking.
Limited.

Ni is effective in improving low-temperature dust, but at 1.5 se
There is no need to add more than tχ, so 1.5 wt%
Limited to the following.

Mo is an effective element for increasing hardenability, but the
If it exceeds 2.5-w or less, the toughness will deteriorate.
It was limited to tz or less.

Ti is effective in improving the climate, but if it exceeds 0.05wtχ, it will deteriorate, so it was limited to 0.05wt% or less.

P has a negative effect on toughness, so the lower it is, the better; however, since it is difficult to form a film on steel, it is desirable to keep it at 0.02 wt% or less.

S is harmful to cracking, but Mn addition produces M'n S with a high melting point. However, the lower the content, the safer it is, so 0.02 wt% or less is desirable.

■In the case of austenitic stainless steel welding wire C is an effective element for improving high-temperature creep strength, but if it is less than 0.01wtχ, the high-temperature creep strength of the weld metal cannot be ensured, so the lower limit was set at 0.01wtz. Furthermore, if it is added in an amount exceeding 0.08 wtχ, an increase in high temperature creep strength can be expected, but this will cause hot cracking and deterioration of corrosion resistance due to a decrease in the amount of δ ferrite. Therefore, 0
．． It was limited to 01 to 0.08 wtχ.

Si must be 0.1 to maintain stable welding workability.
It is necessary to add 0wt% or more, but if it is added in excess of 0.70wtχ, it will promote welding hot cracking, so 0.10 to 0
．． It was limited to 70wtχ.

Mn is a deoxidizing element, and in order to obtain stable welding workability, 1. Ow or more is required. however,
Since it is an austenite-forming element, if it is added in excess of 2.5 wtχ, the amount of δ ferrite decreases, causing weld hot cracking. Therefore, it was limited to 1.0 to 2.5-[χ.

Ni is required in an amount of 8wt% or more to obtain high temperature creep resistance matrix toughness, but since it is an austenite-forming element, if it is added in excess of 15wtχ, the amount of δ ferrite will decrease, causing weld hot cracking. was limited to 8 to 15-tχ.

Cr is a ferrite-forming element and prevents welding hot cracking. In order to generate δ ferrite in the weld metal, 17 wt% or more is required. However, if it is contained in an excessive amount, it promotes the formation of intermetallic compounds such as Cr carbides and σ phase, and deteriorates the ductility of the weld metal.
% or less. Therefore, it was limited to 17-25-tχ.

Mo improves corrosion resistance, but 3. If the content exceeds Ow or less, the amount of δ ferrite becomes excessive and deteriorates the ductility of the weld metal, so the content is limited to 3 wt% or less.

Ti improves corrosion resistance, but 1. If added in excess of 0 w or less, ductility deteriorates, so it was limited to 1.0 i1t% or less.

It is better to lower P to promote welding hot cracking, but
Since it is difficult to form a film on steel, the content is preferably 0.03 wt% or less.

S is particularly harmful to weld cracking, so 0.0
The content is preferably 2 wt% or less.

Next, the basis for the amount of B added, which is the most important additive element in the wire of the present invention, will be described through experimental results as described below.

In other words, the experiment was conducted using 2 wires with a wire diameter of 1.2 nφ shown in Table 1.
! 4 Cr-IMo steel wire, using the symbol ~E,
MIG arc welding was performed on 2V4Cr-IMo steel with a plate thickness of 20 mm. Bevel shape: root width 12mm, bevel angle 2
A narrow gap of ゜ was used.

The welding conditions were 6-layer welding with 111 baths at 300A-24V-25cm/min in an atmosphere of Ar+5χCO□ gas shield with direct current positive polarity (wire (-)). The chemical compositions of the obtained weld metals are shown in Table 2-E'.

This means that wires and weld metals with the same alphabetic symbol correspond. (The same applies hereafter) Wires with symbols A to D had a very stable arc and no welding defects and showed good welding workability, but wires with symbol E had hot cracks in the weld metal.

After welding, a post-weld heat treatment was carried out at 690°C for 22 hours, and 2mV non-charpy impact test pieces were taken from the welded joints with symbols A' to D'. The amount of water required for improving toughness was determined. The results are shown in Table 3. In the case of the present invention, the objective was to increase the toughness, so the judgment was made stricter than the general standard.

That is, the absorbed energy vF at -65°C! -, @ were set to 5.5 kgf-t* or more, and the socal embrittlement index after step cooling according to the GH type was set to vTr4°+3ΔvTr4°<10°C.

From the results in Table 3, it is clear that when MIG arc welding is carried out in an atmosphere with a low active gas shield of ^r + 5% CO, sufficient refinement of the structure can be achieved when the amount of B added in the weld metal is less than 0,0005wtχ. However, at 0.0005 wt% or more, an improvement in toughness was obtained. That is, it was found that from the viewpoint of improving toughness, the amount of B added in the weld metal must be 0.0005 wt% or more. In addition, the B content in the weld metal is 0.0050wt.
It was found that if it exceeds χ, high temperature cracks occur, so it is necessary to regulate it below this value.

Next, when considering neutron irradiation embrittlement, the lower the 10B value, the safer it is, but since it cannot be reduced to Oppm, we investigated the criticality of the maximum allowable 10B amount as the next best measure.

Generally, tensile elongation at break is used as one of the indicators for evaluating the integrity of nuclear reactor structures. For example, a fast breeder reactor is designed on the premise that the material used is a ductile material, and a ductile material is required to have a tensile elongation at break of 10% or more.

Stigler et al. reported the relationship shown in Figure 1 between the tensile elongation at 700°C after irradiation of 5US304 steel and the amount of He produced in the steel.
TM-2019, Jan 196B) - The tensile test temperature of 700°C conducted by Stigler et al. is approximately 150°C compared to the typical maximum operating temperature of fast breeder reactor structures of 550°C.
expensive. Generally, the influence of He generation on tensile elongation at break becomes more pronounced at higher test temperatures. Therefore, it is safer to use FIG. 1 to determine the limit value of the amount of He produced to ensure tensile elongation at break even after irradiation. In addition, if one standard for material development is to ensure a tensile elongation at break of 20% or more after irradiation as a ductility condition with a margin to ensure the safety of the structural material, From Figure 1, the amount of He in the steel is 0.
It must be 1 app or less.

On the other hand, the amount of thermal neutrons that the reactor structure receives by the end of the reactor life is considered to be I Xl0tb . This value and the maximum operating temperature of fast breeder reactor 55
Based on the upper limit of 0.1 app+* for the amount of He in steel at 0°C, the allowable amount of 1°B in steel required to ensure a tensile elongation at break of 20% or more is approximately 0.4 ppm.
becomes. Therefore, one of the weld metals that should be improved is
It is important that the amount of 0B is also 0.4 pp+n or less.

The above has been described in the case of fast breeder reactors, but even in the case of light water reactors, where the environmental temperature in which the structural materials are used is low, regulating IIIB, which causes He generation, to 0.4 ppm or less is important for ensuring the safety of the materials in the reactor structure. It is useful for ensuring sex. In other words, in this case, the proportion of nuclear transmutation by I(IB(n, α)7Li in the alloy used as a nuclear reactor structure is relatively small compared to the amount of 1143 that does not undergo nuclear transmutation, so the B component is added. The deformation function of the structure is also maintained even when the temperature rises due to an abnormal increase in output due to an accident in a light water reactor.

Therefore, it is necessary to keep the amount of 111B in the weld metal at 0.4 ppm or less, and it is understood that the amount necessary for microstructural refinement is 5 ppm or more, and the appropriate amount is 50 ppm or less for preventing high temperature twisting.

Based on the experimental facts obtained so far, this regulation value is
In terms of the amount added in the wire, when MIG arc welding is performed in a pure inert gas shield atmosphere or a low active gas shield atmosphere, the yield of B amount is approximately 10%.
Since 0χ, the lower limit of the amount of B in the wire in this case is 0.0005%, the upper limit is 0.0050%, and +03
The amount must be 0.4 ppm or less. Here, when using B with a B composition ratio of 10B.2% and 1B-98χ, the upper limit of the amount of B added is 20 ppm.
The maximum B addition amount that does not cause hot cracking is 0,
The upper limit is 0.050 wt%.

In addition, the mechanism of the effect of suppressing the decrease in tensile ductility in item 3 is +
1B ratio [It is presumed that the presence of 11B suppresses aggregation and coarsening of the generated He.

Next, in order to investigate the effect of improving creep ductility by adding B, weld metals A", B", and C"DI shown in Table 1 were
After heat treatment at 690°C for 22 hours after welding, creep test pieces were taken by machining. A creep test was conducted under the conditions of a test temperature of 500° C. and an added stress of 25 kitf/mm 2 . The creep test results are shown in Figure 2.

The vertical axis in the figure shows the ratio when the rupture time of the weld metal (A") at a total daily dose (T - 8): 4 ppm is set to 1. The horizontal axis in the figure shows the ratio of T-B in the weld metal. As is clear from the figure, the creep rupture life ratio began to increase at T-8: 6 ppm or higher, and the effect was confirmed.
When the temperature exceeded pm, there was almost no change in the temperature and the temperature reached a saturated state.

Next, regarding the rare earth element content, in order to maintain stable MIG arc welding in a pure inert gas shield atmosphere or a low active gas shield atmosphere, it is necessary to add 0.02 wt% or more. is necessary. However, if added in too large a quantity, oxidized impurities will adversely affect toughness, so the upper limit is limited to 0.30 wt%.

Next, the above-mentioned wire manufacturing method according to the present invention will be specifically described. In other words, in order to manufacture welding wire containing IIIB, which is smaller than the abundance ratio in nature, sufficient B-removal refining (proceeds along with C removal) is required in the smelting process.
After performing this, B obtained by concentrating ++B is added, and if necessary, these smelting processes are repeated to achieve this.

In other words, a boron-containing raw material containing grain B at a natural abundance ratio (80.4%) or higher, such as F, is added to the molten steel (in the rough decarburization stage).
e-8 alloy, boron compounds (B*Oz), boric acid (HJOs)
), etc. are added and refined in a converter electric furnace, etc., and the de-B refining progresses with the de-C reaction. By repeating these operations several times, carbon steel with a high ttH content ratio and low Cr content can be produced.
- Molten Mo steel, ferritic high chromium steel, austenitic stainless steel, etc., and form ingots into steel slabs.

This steel billet is rolled according to a conventional method and then drawn into a welding wire.

(Example) 5-1 First, a method for manufacturing a welding wire used in this example will be described. During welding, the tapped steel component is in weight%, C: 0
．． 04%, Si: 0.35%, Mn: 1.6%, P:
0.02%, S: 0.01%, Ni: 10.5%, C
r: 20.0% and REM: 0.05%, melted in a converter, and then treated to remove B in a vacuum melting furnace to make the total daily amount 2 ppm (16Bii is 2 ppm x 0.
2-0.4 ppm), and then 50 ppII of Fe-B containing 98% of the total B of 119 was further added to the obtained molten steel.
+ was added and a steel ingot was made after B removal treatment. (10BI is 0.4
ppm + 50 ppm x 0.02 = 1.4 pl) m, that is, the ratio of 16 uil to the total daily amount is 1.4 ÷ 52 x
100 = 2.7χ) When analyzing the total daily amount, 2p
p- (the amount of 10B is 2 ppm x 0.027 = 0
．． 05 ppm), this steel ingot: In other words, a part of the raw steel ingot was remelted, and Fe-B in which 1B was 98% of the total B was added again in an amount to obtain a steel ingot with the composition shown in Table 4. Ta.

Here, 1 (IB was calculated from the all-day analysis values using the following formula.

+tIB amount-0, O5ppm+ (total B analysis value-2)p
pmxo, 02 Each steel ingot obtained by smelting as described above was forged.

The wire was drawn to produce a 1.2+n+φ MIG arc welding wire.

Next, regarding the wire GNK having the chemical composition shown in Table 4 obtained as described above, 5US30 with a plate thickness of 25mo+
A MIG arc welding test was conducted using four steel plates in a pure inert gas shield atmosphere with direct current reverse polarity (wire (+)). The conditions for welding are that the groove shape is a root groove width of 12IIIff+, a narrow groove angle of 2 degrees, and a groove width of 30 mm.
Six passes of welding were performed with one pass per layer under the conditions of 0A, 27V, and 22cm+/win. Table 4 also lists the chemical composition of the weld metal.

In addition to conducting a Charpy impact test on weld metal and an intergranular cracking test using sulfuric acid and copper sulfate, we also examined inventive examples and comparative examples based on conventional knowledge. Although the total daily amount of weld metal in wires G and H is sufficiently high, the toB amount is reduced to 0.
．． It is clear that the pH can be suppressed to 4 pph or less, which is within the regulation value determined by the present invention, and that neutron irradiation embrittlement can be prevented.

In addition, in wires G, H, and J, the weld metal
The absorbed energy at 6°C was also examined, and it fully satisfied the regulatory values, and no cracks were detected in the intergranular cracking test. Note that the weld metal of wire (3) had low absorbed energy, and intergranular cracking occurred. On the other hand, regarding wire K, hot cracking occurred in the weld metal.

-・” about 1.

(1) Inappropriateness of B in Wire Regarding Wire K, when a liquid penetration test of the weld metal was conducted, cracks believed to be caused by the high B content were found. Regarding wire I, weld metal 119
When a Charpy impact test was conducted at 6°C, the absorbed energy was below the regulation value. Furthermore, in the intergranular cracking test, cracks appeared that were thought to be caused by the low B content.

(2) Wire The amount of IIIB in the weld metal of +oH inert wire J, calculated from the total daily amount, exceeds 9.4 ppm, which exceeds the regulation value determined by the present invention.

(3) Wire REM 1゛Wire without REM addition (other components are C by weight%)
: 0.05%, Si: 0.36%, Mn: 1
．． 57%, P: 0.018%, S: 0.008%,
Ni: 10.2%, Cr: 20.2%, total B
: 20 ppm) and the steel plates used in the experiments shown in Table 4, MIG arc welding was performed with DC reverse polarity wire ○ in a pure inert gas shield atmosphere, but the arc crawled up the groove wall. , the tip of the wire would stick into the molten pool, making stable welding impossible.

(4) Shield gas set 1゛Using the wire H shown in Table 4 and a 5US304 steel plate with a plate thickness of 25 m, a test was carried out in a 100χAr shield atmosphere (pure inert gas shield)^r + 3% COt shield atmosphere (low MIG arc welding was carried out in a surrounding atmosphere (active gas shield) and ^r+20χCO□ shield (active gas shield). The absorbed energy of the weld metal was determined by Charpy impact test at 196℃, and the weld metal with pure inert gas shield was 17.3 kgf-m, the weld metal with low active gas shield was 12.1 kg f・m, and the absorbed energy was 12.1 kg f・m with active gas shield. The shield weld metal was 3.8 kgf-m, and if MIG arc welding was performed in an active gas shield atmosphere, which is generally used as a shield gas, the toughness deteriorated. Furthermore, when MIG arc welding is performed in an atmosphere surrounded by an active gas shield, the amount of slag produced increases significantly, and a large number of man-hours are required to remove the slag, especially in narrow gap welding of thick steel materials.

Example 2 1.2 tmφ of A333 CJ l steel shown in Table 1
Using wire F, MIG arc welding was performed on A333 C1l steel with a plate thickness of 50 mm. The groove shape is root part 4.
The 5R1 surface part had a narrow groove width of 11 ms and a groove depth of 45 m.

The welding conditions were 280^-24V-20cm/min in a low active gas shield atmosphere of Ar + 8% CO□, 1
MIG arc welding was performed with 11 passes of each layer and positive DC polarity.

The chemical composition of the weld metal is shown in Table 2, symbol F'. The amount of IIIB calculated from the total daily amount was 0.2 ppm, and it is clear that neutron irradiation embrittlement can be prevented.

After welding, post-weld heat treatment was performed at 590°C for 18 hours,
Weld metal was subjected to Charpy impact and impact tests. The results are shown in Table 5, and a weld metal with very good low-temperature toughness was obtained.

Table 5 Note that in this example, 2'ACr-
Although welding wires for IMo steel and A333 (11 steel) and 5LIS304 steel as stainless steel have been described, the present invention also applies to other materials such as 9Cr-Mo steel, stainless steel containing Nb, stainless steel containing Nb, Ni-based alloy (Inconel), etc. The same applies to other steel types.

(Effects of the Invention) As explained above, according to the present invention, it is possible to manufacture wires enriched with IIB and rare earth elements, and since such wires are used, pure inert gas shielding or low inert gas shielding atmosphere can be used. Among them, MIG arc welding can be performed stably and the oxygen content in the weld metal can be reduced, so the synergistic effect with B provides high toughness, high ductility, and excellent corrosion resistance. Furthermore, a welded joint can be obtained which advantageously prevents neutron irradiation embrittlement, thereby ensuring safety.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between tensile elongation at break and HeN, and Figure 2 is a graph showing the relationship between total daily amount and creep rupture life ratio.

Claims (1)

[Claims] 1. A low alloy steel welding wire for welding nuclear reactor steel materials in a pure inert gas shield atmosphere or a low active gas shield atmosphere, the wire having a C: 0.05 to 0.1
5wt%, Si: 0.10-0.70wt%, Mn: 0
．． 4-2.0wt%, P: 0.02wt%, S:≦0.
02wt%, and as an additive element, Cr≦10.0
wt%, Ni:≦1.5wt%, Mo:≦2.5wt%
, contains at least one type of Ti:≦0.05wt%, and further contains 0.0005wt%≦^(^1^0^+^1^1^)B
<0.005wt%, however, the amount of ^1^0B is 0.00
0.04 wt% or less, and 0.02 to 0.30
MIG for nuclear reactor steel containing wt% of rare earth elements and the balance being mainly Fe and unavoidable impurities.
Wire for arc welding. 2. An austenitic stainless steel welding wire for welding nuclear reactor steel materials in a pure inert gas shield atmosphere or a low inert gas shield atmosphere,
C: 0.01-0.08 wt%, Si: 0.10-0.
70wt%, Mn: 1.0~2.5wt%, Ni: 8~
15wt%, Cr: 17-25wt%, Mo:≦3.0
wt%, Ti:≦1.0wt%, P:<0.03wt%
, S: <0.02wt%, and further contains 0.0005
wt%≦^(^1^0^+^1^1^)B≦0.005
0wt%, but the amount of ^1^0B is 0.00004wt
% or less of B, and 0.02 to 0.30 wt% of rare earth elements, the remainder being mainly Fe and unavoidable impurities. 3. When melting steel, the ratio of isotope: ^1^1B [^1^1B/(^1^0B+
After adding a boron-containing raw material with a higher ratio of ^1^1B) than the natural abundance ratio, de-B refining is performed, followed by repeating the addition of a boron-containing raw material with a high ratio of ^1^1B several times. ^1 Molten steel with a high content ratio of B is melted, then rare earth elements and other necessary alloying elements are added to this molten steel and cast into steel billets.The steel billets are rolled and wire-drawn according to conventional methods to obtain the final wire diameter. A method for manufacturing a wire for MIG arc welding, characterized in that the wire is made into a wire.