JP3170166B2 - Filler for Ni-base high Cr alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filler metal for welding a Ni-based high Cr alloy used in a pressurized water nuclear power plant operating at a high temperature, and more particularly to a high-temperature tensile strength characteristic and a weld crack resistance. The present invention relates to a filler metal for obtaining a weld metal having excellent properties.

[0002]

2. Description of the Related Art At present, Inconel 600 alloy having excellent corrosion resistance is used for a heat transfer tube of a steam generator of a pressurized water nuclear power plant operating at a high temperature of 300 to 350 ° C. Further, a newly developed Inconel 690 alloy has been started to be used as a heat transfer tube material in order to improve reliability.
Table 1 shows typical alloy compositions.

[0003]

[Table 1]

[0004] Manufacturing a structure using this 690 alloy usually involves welding. TIG welding or MIG welding is used as a welding method, and an alloy is added while melting during welding, and a filler metal for maintaining strength after welding and ensuring welding crack resistance is required. Regarding this filler metal, the American Society of Mechanica
l Engineers; ASME Boiler and Pressure Vessel Code;
ASME Code).
The chemical components are shown in Table 2.

[0005]

[Table 2]

As is apparent from comparison with Table 1, the main composition of the filler metal is almost the same as that of the 690 alloy, but the filler metal has a particularly low P and Cu content to prevent welding cracks. M is added to limit and prevent deterioration of corrosion resistance.
There are restrictions on o, Nb, Al, Ti and Al + Ti content. In addition, although not stipulated in the ASME Code, it actually contains a deoxidizing agent added when smelting a filler metal and unavoidable impurities mixed in from the atmosphere. According to the analysis example, Co:
0.05%, O: 0.004%, and N: 0.025%.

[0007] Since Inconel 690 alloy is originally a material having a high Cr property, the welded portion of a structure welded by TIG welding or MIG welding using this filler material also has room-temperature mechanical properties and weld crack resistance. It has sufficient performance in terms of properties.

[0008]

However, there is a problem that the strength of the welded portion is insufficient when the above-described equipment operating at a high temperature of 300 to 350 ° C. is used for a long time. That is, the high-temperature tensile strength of a weld metal or a welded joint formed by TIG welding or MIG welding using the above-mentioned Inconel 690 alloy and its filler material is weaker than that of the base metal, and the reliability of the high-temperature strength is not sufficient. For example, when a high temperature tensile test is performed on all the deposited metals at 350 ° C., the tensile strength is 480 N / m.
Only a low value of m ² can be obtained. Further, since the structure of the Inconel 690 alloy filler material has an austenitic structure and high weld cracking susceptibility, the weld crack resistance must be sufficiently considered.

The present invention has been made in view of the above-mentioned technical level, and has as its object the use of a welding metal which is used for welding Ni-based high Cr alloys such as Inconel 690 alloy and has excellent high-temperature tensile properties and weld crack resistance. An object of the present invention is to provide a filler material from which a welded joint can be obtained.

[0010]

In order to achieve the above object, the present inventors have conducted various studies on the material of a filler metal for a Ni-based high Cr alloy. As for solid solution strengthening, it was found that interstitial elements C and N contributed most to the strengthening. However, due to its excellent corrosion resistance, which is one of the features of this Inconel 690 alloy filler metal,
Since the amount of C is limited to a low level of 0.04% or less,
It is difficult to improve the high temperature tensile strength by increasing the content.
Further, when only the N amount is increased, welding defects are likely to occur, which is not preferable. For this reason, it was found that when W and V were added in addition to N, the high-temperature tensile strength could be improved without causing welding defects as described later.

Further, Mo, W, V, Ti and Al can be cited as solid solution strengthening elements for the γ matrix phase. However, in the composition of the Inconel 690 alloy filler metal, T
Although i and Al act as deoxidizing agents, they are regulated in consideration of welding workability. Mo is also restricted in consideration of corrosion resistance. In addition, although not stipulated in the ASME Code, W and V are 0.1 and 0.2 as other elements.
Since the addition of elements of 5% or less is permitted, the W and V
%, It was found that the solid solution strengthening improves the high temperature tensile strength.

In the present invention, C: 0.04% or less by weight%,
i: 0.1 to 0.5%, Mn: 0.2 to 1%, Cr: 2
8 to 31.5%, Mo: 0.5% or less, Cu: 0.3%
Hereinafter, Nb: 0.1% or less, Al: 0.5 to 1.1%,
Ti: 0.5 to 1%, Al + Ti: 1.5% or less, F
e: 7 to 11%, W and V at most 2 types, total 0.01
-0.5%, and Co:
0.1% or less, P: 0.02% or less, S: 0.015%
Hereinafter, a filler metal for a Ni-based high Cr alloy containing O: 0.1% or less and N: 0.03 to 0.3%, with the balance being Ni.

[0013]

The function of each component in the filler material of the present invention and the reason for limiting the content will be described below.

C is generally a solid solution strengthening element, and the tensile strength increases as the amount of C increases. On the other hand, an increase in the amount of C deteriorates the stress corrosion cracking resistance.
The amount was more than 0% and not more than 0.04%.

[0015] Si has a deoxidizing effect during welding, and it is necessary to add 0.1% or more to obtain the effect.
As the Si content increases, the welding hot cracking susceptibility increases. Therefore, the Si content is set to 0.1 to 0.5%.

Mn is effective as a deoxidizing action and a desulfurizing action at the time of welding, has an effect of fixing S harmful to welding hot cracking and suppressing welding cracking resistance. To enhance this effect, 0.2% Although it is necessary as described above, if the amount of Mn exceeds 1%, the flow of slag is deteriorated at the time of welding and welding workability is deteriorated. Therefore, Mn is set to 0.2 to 1%.

Cr is an essential element for improving corrosion resistance.
In order to fully enhance the effect of stress corrosion cracking resistance, 28
% Or more is required. On the other hand, if it exceeds 31.5%, the hot workability during the production of the filler metal is significantly deteriorated, so the Cr content was set to 28 to 31.5%.

Mo dissolves in the matrix to improve the tensile strength, but the increase in the amount of Mo significantly degrades the hot workability during the production of the filler metal.
% Or less. However, in consideration of the tensile strength, it is desirable to design the alloy to have a higher Mo content of about 0.4% within the range of 0.5% or less.

When Cu is heated to a high temperature, it is finely dispersed and precipitated in the matrix to increase the tensile strength. Conversely, excessive addition increases the susceptibility to weld cracking, so that the Cu content exceeds 0% and is not more than 0.3%. And

Nb is a carbonitride-forming element and improves the tensile strength. However, since an increase in the amount of Nb impairs wire workability,
The amount of b is more than 0% and 0.1% or less.

Al is used as a deoxidizing agent when smelting the filler metal, and also fixes N in the deposited metal as an N stabilizing element and contributes to an improvement in strength. % Or more is necessary, but excessive addition generates slag during welding and deteriorates welding workability.
5 to 1.1%.

Like Al, Ti is used as a deoxidizing agent by utilizing its oxidizing power, and also contributes to the improvement of hot workability in the production of filler metal. In addition, Ti has a strong affinity for N, and precipitates as TiN, refines the structure, and contributes to improvement in tensile strength.
% Or more is necessary, but like Al, excessive addition generates slag during welding and deteriorates welding workability, so Ti was set to 0.5 to 1%. Although the addition of Al + Ti is effective for the action as a deoxidizing agent, when the amount of Al + Ti increases, slag is generated during welding, and the welding workability is significantly deteriorated. Therefore, the amount of Al + Ti is more than 0% and 1.5% or less. And

Fe has a high C content such as Inconel 690 alloy.
Prevent or suppress the generation of scale that occurs when the amount is r.
If it is less than 7%, the scale is remarkably generated. Also,
Excessive addition exceeding 11% deteriorates stress corrosion cracking. Therefore, Fe was set to 7 to 11%.

W and V are W and V within a range of 0.5% or less of other elements not specified in ASME Code.
Was added to improve the high-temperature tensile strength.
W improves the tensile strength by dissolving in the matrix,
When the amount of addition increases, the susceptibility to weld cracking deteriorates. V forms a solid solution in the matrix in the same manner as W and Mo to improve the tensile strength. However, if it is less than 0.01% , the effect is not obtained, and if it exceeds 0.5%, the ductility decreases. Therefore, a maximum of two types of W and V, a total of 0.01
-0.5% .

When this Inconel 690 alloy is used for a pressurized water reactor, Co has a long half-life.
When Co is contained, it is preferable that Co is not present because activated Co circulates in the reactor system together with oxides and the like, and raises the radioactivity level of the working environment at the time of periodic inspection and the like. However, Co is originally contained in the Ni raw material at about 1 to 2%, and even if the purity of Ni is increased by refining, the Co content of the low CoNi raw material obtained industrially becomes about 0.1% or less. In consideration of this point, Co is set to 0.1% or less.

P is a eutectic of low melting point with Ni (Ni-Ni ₃ P
And the like, which enhance the susceptibility to welding hot cracking. Therefore, the smaller the content, the better. However, P is set to 0.02% or less because excessive restriction causes a reduction in economic efficiency.

S is an element that forms a low melting point eutectic with Ni (such as Ni—Ni ₃ S ₂ ) like P and increases the susceptibility to welding hot cracking. The smaller the content, the better. 015% or less.

O is an unavoidable impurity that invades from the atmosphere during the smelting of the filler metal, and gathers in the form of oxides at the crystal grain boundaries of the weld metal to weaken the high-temperature strength of the crystal grain boundaries. Also,
O enhances the weld cracking susceptibility, so it is desirable to make it 0.01% or less.

N is an unavoidable impurity like O.
It is important to define a limit for its content. However, N forms a nitride (such as TiN) with Ti or the like, and improves the tensile strength. Therefore, N is actively added. N contributes to the improvement of the tensile strength as the content increases, but the effect is small if it is less than 0.03%. However, since excessive addition causes the occurrence of welding defects such as blow holes, N is set to 0.03 to 0.03.
0.3%.

[0030]

The present invention will be described more specifically with reference to the following examples. A test piece was welded using a filler material of the present invention having a different composition and a filler material of a comparative example, which is a typical composition of a filler material conventionally used, and subjected to a room temperature tensile test and a 350 ° C. high temperature tensile test. , A T-type weld crack test and a C-type jig restraint butt weld crack test. JIS G4304 as base material
SUS304 (hot-rolled stainless steel sheet and steel strip) was used. Here, SUS304 was used as a base material because there was a place where SUS304 was used in an actual structure.
Since the S content is high, weld cracks are likely to occur, and it can be evaluated under severe conditions for crack tests. In the tensile test of the welded metal, overlay welding is performed on the entire surface of the base metal (according to JIS regulations), so the effect of the material is Because there is no.

The tensile test was carried out in accordance with JIS Z3111 (test method for tensile and impact of deposited metal). S of test plate
The US304 base material grooved surface and the backing metal surface used were two-layer buttering welded as specified. Joint welding is
The welding was performed by a TIG welding method at a welding current of 170 to 180 A, a welding voltage of 12 to 13 V, a welding speed of 85 mm / min, and an argon gas shield of 18 liter / min. A JIS Z3111 A2 (parallel portion of test piece having a diameter of 6 mm) tensile test piece was machined from this joint weld metal,
A tensile test was performed according to IS Z2241 (metallic material tensile test method).

The T-type welding crack test and the C-type jig restraint butt welding cracking test were conducted according to JIS Z3153 and JIS, respectively.
Performed according to Z3155. FIG. 1 is a schematic diagram showing a laminated state of a welded joint used in a normal temperature and high temperature tensile test,
FIG. 2 is a schematic diagram showing the shape of a sample used in a T-shaped welding crack test, and FIG. 3 is a schematic diagram showing the shape of a sample used in a C-shaped jig restraint butt welding crack test. Table 4 shows the compositions of the filler materials used in Comparative Examples and Examples.

Table 5 shows the results of each test. Table 5 shows the tensile strength (σu) in the tensile test of the deposited metal, 0.2%.
It shows proof stress (σy), elongation (EL), drawing (RA), and crack rate (%) in a weld crack test. The cracking rate was determined by the following equation. Crack rate (%) = (crack length mm / weld bead length mm)
× 100 From these results, those using the filler material of the present invention are particularly excellent in high-temperature tensile strength characteristics at 350 ° C. Table 3 summarizes the tendency from the results of each test, and shows that the high-temperature strength can be increased without increasing the weld cracking susceptibility.

[0034]

[Table 3]

Table 6 shows the effect of alloying elements on characteristic values clarified by multiple regression analysis based on these results. In Table 6, ↑ indicates an improvement effect, ↓ indicates a reduction effect, and-indicates a state in which no remarkable effect is observed.

[0036]

[Table 4]

[0037]

[Table 5]

[0038]

[Table 6]

[0039]

EFFECT OF THE INVENTION Ni-based high Cr such as Inconel 690 alloy
The filler metal used for welding the alloy was specified by ASME Code, but the standard material of ASME Code does not consider the high-temperature strength of the weld even if the short-term tensile strength is good. Therefore, the high-temperature tensile strength characteristics are not sufficient, and for example, when applied to welding of structural members such as pressurized water reactors, these devices lack reliability for long-time operation at high temperatures. Was. As described above, the filler metal of the present invention is based on the composition of the standard material of ASME Code. In particular, regarding the Mo amount, the alloy is designed with the aim of the upper limit within the range of the component of the standard. Make improvements and then ASME Code
The appropriate ranges of W and V elements not specified in the above were clarified. In addition, the remaining amount of unavoidable impurities mixed from raw materials and auxiliary materials at the time of smelting is examined, and among them, N which contributes to the improvement of high-temperature tensile strength is emphasized, and the allowable amount is determined. When the filler metal is used, the high temperature tensile strength of the deposited metal at 350 ° C. is 480 N / mm.
Compared to ² , the filler material of the present invention can provide a high-temperature tensile strength of at least 530 N / mm ² or more under the same conditions. As a result, great reliability can be imparted to welding of high-temperature structures using Inconel 690 alloy.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a laminated state of a welded joint used in a normal temperature and high temperature tensile test.

FIG. 2 is a schematic view showing the shape of a sample used in a T-shaped welding crack test.

FIG. 3 is a schematic view showing the shape of a sample used in a C-shaped jig restraint butt welding crack test.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ikuo Otake 1-1, Wadazakicho, Hyogo-ku, Kobe City, Hyogo Prefecture Inside Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Masaharu Takagishi Hyogo-ku, Kobe City, Hyogo Prefecture 1-1 1-1 Wadazakicho Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Takashi Omae 7800 Nakase, Nakase, Hamakita-shi, Shizuoka Japan Nippon Welding Rod Co., Ltd.Technical Laboratory (72) Inventor Tama Takatsu Male 7800 Nakase, Hamakita City, Shizuoka Prefecture Japan Welding Rod Co., Ltd. Technical Research Institute (56) References JP-A-8-174270 (JP, A) JP-A-62-10235 (JP, A) JP-A-48 JP-A-86750 (JP, A) JP-A-61-169192 (JP, A) JP-A-63-212091 (JP, A) JP-A-1-293992 (JP, A) JP-A-53-8303 2 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 35/30 REGISTRY (STN)

Claims (1)

(57) [Claims] 1. C: 0.04% or less by weight, Si:
0.1-0.5%, Mn: 0.2-1%, Cr: 28-
31.5%, Mo: 0.5% or less, Cu: 0.3% or less, Nb: 0.1% or less, Al: 0.5 to 1.1%, T
i: 0.5 to 1%, Al + Ti: 1.5% or less, Fe:
7-11%, W and V at most 2 types, total 0.01-
0.5%, and Co:
0.1% or less, P: 0.02% or less, S: 0.015%
Hereinafter, a filler metal for a Ni-based high Cr alloy containing O: 0.1% or less and N: 0.03 to 0.3%, with the balance being Ni.