JPH08174270A - Coated arc electrode for ni-based high-cr alloy - Google Patents

Abstract

PURPOSE: To make it possible to obtain a weld metal and welded joint having an excellent high-temp. tension characteristic and weld crack resistance. CONSTITUTION: This coated arc electrode for a Ni-based high-Cr alloy is formed by using an alloy contg. specific ratios of C, Si, Mn, P, S, Cr, Mo, Cu, Wb, Al, Ti, Fe, Co, W, V, O and N and consisting of the balance Ni as a core wire and coating the circumference of this core wire with a coating material contg. specific ratios of metal carbonate, metal fluoride, oxide and further, consisting of an alloy agent, deoxidizing agent, slag forming agent and binder, exclusive of the materials described above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Ni such as Inconel 690 alloy (trade name of INCO, USA) used for high-temperature corrosion resistant equipment used at high temperatures of 300 to 350 ° C. represented by a pressurized water nuclear power plant. The present invention relates to a coated arc welding rod suitable for welding a base high Cr alloy, and more particularly to a coated arc welding rod capable of obtaining a weld metal having excellent high temperature tensile strength properties and weld crack resistance.

[0002]

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

[0003]

[Table 1]

When manufacturing a structure using this 690 alloy, it is common to involve covered arc welding, and in order to maintain the strength after welding by adding the alloy while melting the covered arc welding rod during welding. A lime type flux type covered arc welding rod is required to secure weld crack resistance. The American Society of Mechanical Engineers;
ASME) ASME Boiler and Pressure Vessel Regulations (ASME Boil
er and Pressure Vessel Code; ASMECod
(referred to as e) is used, and the chemical composition of the deposited metal is shown in Table 2.

[0005]

[Table 2]

As is clear from comparison with Table 1, the main composition of the coated arc welding rod is almost the same as that of the 690 alloy, but in order to prevent welding cracks, the coated arc welding rod is S.
The i, Mn, and P contents are particularly limited, and Nb is added to prevent deterioration of corrosion resistance. Besides this, ASM
Although not specified in E Code, it actually contains a deoxidizer added when manufacturing a coated arc welding rod and unavoidable impurities mixed in from the atmosphere, and the type and content thereof are analyzed by the inventors. According to the example 0: 0.08-0.15
%, N: 0.025%.

Since the Inconel 690 alloy is originally a material having a high Cr property, the welded portion of the structure welded using this covered arc welding rod is also sufficient in room temperature mechanical properties and weld crack resistance. It has excellent performance.

[0008]

However, there is a problem that the strength of the welded portion is insufficient when the above-mentioned equipment operating at a high temperature of 300 to 350 ° C. is used for a long time. That is, since the high temperature tensile strength of the weld metal and weld joint welded using the above Inconel 690 alloy and its covered arc welding rod is weaker than that of the base material, 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 to 500 N / mm.
^You can only get a low value of ² . Furthermore, since this Inconel 690 alloy-coated arc welding rod has an austenitic structure and is highly susceptible to welding cracks, it is necessary to sufficiently consider weld cracking resistance.

The present invention has been made in view of the above-mentioned state of the art, and its purpose is to weld a Ni-based high Cr alloy such as Inconel 690 alloy, which has excellent high temperature tensile properties and weld crack resistance, and It is intended to provide a covered arc welding rod capable of obtaining a welded joint.

[0010]

In order to achieve the above-mentioned object, the inventors of the present invention have made various studies on the material of the coated arc welding rod for Ni-base high Cr alloy, and as a result, have found that among the compositions of the Inconel 690 alloy coated arc welding rod. As for solid solution strengthening of austenite, it was found that the interstitial elements C and N contribute most to the strengthening. However, due to the excellent corrosion resistance, which is one of the characteristics of this Inconel 690 alloy-coated arc welding rod, the C content is 0.0
If added over 5%, the corrosion resistance deteriorates, so it is difficult to increase the C content and improve the high temperature tensile strength. Further, when only the amount of N is increased, welding defects are likely to occur, which is not preferable. Therefore, it has been found that the combined addition of W and V in addition to N can improve the high temperature strength without causing welding defects as described later.

Further, Mo, W, V, Ti and Al can be cited as the solid solution strengthening element of the γ matrix phase. However, in the composition of the Inconel 690 alloy-coated arc welding rod, Ti and Al act as deoxidizing agents, but are regulated in consideration of welding workability and weld crack resistance. Also,
Mo is limited in consideration of corrosion resistance, but considering the improvement of strength, it is desirable to design an alloy higher within the regulation range. In addition, although not specified in the ASME Code, W and V can be added as other elements in an amount of 0.5% or less, so W and V contents are increased within the range of 0.5% to strengthen the solid solution. It was found that the high temperature tensile strength was improved.

Next, since the Inconel 690 alloy-coated arc welding rod structure exhibits an austenite composition, it is highly susceptible to welding cracks, so that P, S, S which affect welding cracks are affected.
Weld susceptibility to weld cracking is secured by controlling the i and O contents to be low. In order to keep these elements low, it is necessary to consider the flux type of the core wire and the coated arc welding rod used. In general, there are two types of coated arc welding rods for Ni-based alloys: lime type welding rods containing limestone or fluorspar as the main component of the coating and lime titania type welding rods containing rutile as the main component of the coating, especially lime type welding. Inconel 6 because the rod has the effect of de-P / S-reduction, low Si and low O
By using this lime type welding rod for the 90 alloy-coated arc welding rod, the welding crack resistance is improved.

The present invention is based on the above findings and is based on ASME C
Add W and V within the specification of chemical composition of ode
It was completed by defining the content ranges of N and N and combining it with a coating material whose composition has been newly regulated. That is, in the present invention, C: 0.05% or less, Si: 0.75% or less, Mn: 2-5%, P: 0.
03% or less, S: 0.015% or less, Cr: 28 to 3
1.5%, Mo: 0.5% or less, Cu: 0.5% or less,
Nb: 1 to 2.5%, Al: 0.5% or less, Ti: 0.
5% or less, Fe: 7 to 12%, Co: 0.1% or less, maximum 2 types of W and V, 0.5% or less in total,
Further, as unavoidable impurities, O: 0.1% or less, N: 0.
An alloy containing 03 to 0.3% with the balance being Ni is used as a core wire, and one or two metal carbonates are used with respect to the total weight of the coating material.
1 or more: 20 to 50%, one or more metal fluorides: 20 to 50%, alloying agent: 3 to 20%, deoxidizing agent: 0.
2 to 5%, slag forming agent: 3 to 20%, and binder: 1 to
A coated arc welding rod for a Ni-based high Cr alloy, characterized in that a coating agent of 5% is coated around the core wire.

[0014]

The function of each component in the coated arc welding rod of the present invention and the reason for limiting the content thereof will be described below.

C is generally a solid solution strengthening element, and the tensile strength increases with an increase in the amount of C. On the other hand, an increase in the amount of C deteriorates the stress corrosion cracking resistance. % And 0.05% or less.

Si is effective in deoxidizing during welding. Further, as the amount of Si increases, the hot-crack susceptibility of the weld becomes higher. Therefore, by adopting a lime type welding rod, it is possible to impart high basicity to the slag and reduce Si in the weld metal. It was made to be Si. The amount of Si was set to more than 0% and 0.75% or less.

Mn is effective as a deoxidizing action and a desulfurizing action at the time of welding, and has an effect of fixing S which is harmful to high temperature cracking in welding and suppressing weld cracking property. To obtain this effect, 2% or more is preferable. However, if the amount of Mn added exceeds 5%,
The melting point of the slag decreases during welding, and the phenomenon of sticking to the bead surface occurs, making it easier to create welding defects.
It was set to 5%.

Cr is an essential element for improving the corrosion resistance,
28 in order to fully achieve the effect of stress corrosion cracking resistance
% Or more is required. On the other hand, if it exceeds 31.5%, the hot workability at the time of manufacturing the core wire is significantly deteriorated, so the Cr content is 2
It was 8 to 31.5%.

Mo dissolves in the matrix to improve the tensile strength. However, since an increase in the amount of Mo significantly deteriorates the hot workability during the production of the core wire, the amount of Mo exceeds 0% and is 0.5% or less. And However, if the tensile strength is taken into consideration, the amount of Mo is 0.
It is desirable to design the alloy to a higher value of about 0.4% within the range of 5% or less.

When Cu is heated to a high temperature, it finely disperses and precipitates in the matrix to increase the tensile strength. On the contrary, excessive addition increases the weld cracking susceptibility, so the Cu content exceeds 0% and is 0.5% or less. did.

Nb is a carbonitride forming element and improves the tensile strength, but if it is less than 1%, it has no effect.
% Is added, the weld cracking susceptibility is increased.
It was set to 2.5%.

Since Al is used as a deoxidizing agent when the core wire is melted, it is treated as an impurity. Further, it is considered that N in the weld metal is fixed as an N stabilizing element and contributes to the improvement of strength, but excessive addition causes slag during welding and deteriorates welding workability, so exceeds 0%. 0.5%
Below.

Ti, like Al, is used as a deoxidizer by utilizing its oxidizing power, and is therefore treated as an impurity. Further, Ti has a strong affinity with N and precipitates as TiN,
Al makes the structure finer and contributes to the improvement of tensile strength.
Similarly, excessive addition causes slag during welding and deteriorates welding workability, so Ti is set to more than 0% and 0.5% or less.

Fe is a high C such as Inconel 690 alloy.
Prevents or suppresses scale generation that occurs when the amount is r.
If it is less than 7%, the scale is significantly generated. Also,
If added in excess of 12%, the stress corrosion cracking property deteriorates. Therefore, Fe is set to 7 to 12%.

W and V are W and V within the range of 0.5% or less of other elements not specified in ASME Code.
Was added to improve the high temperature tensile strength.
W dissolves in the matrix to improve tensile strength,
If the amount of addition is large, the resistance to weld cracking deteriorates. Further, V substantially forms a solid solution in the matrix in the same manner as W and Mo to improve the tensile strength, but if it exceeds 0.5%, the ductility decreases. Therefore, W and V are set to a maximum of two types, and more than 0% and 0.5% or less in total.

When the Inconel 690 alloy is used for Co for a light water reactor, if Co contains a long half-life, activated Co circulates in the reactor system together with oxides and the like. However, it is better not to use Co because it increases the radioactivity level of the work environment during periodic inspections. 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. Considering this point, Co is set to 0.1% or less.

Since P is an unavoidable impurity and is an element which forms a eutectic (Ni-Ni ₃ P, etc.) having a low melting point with Ni and enhances the weld hot cracking susceptibility, the smaller the content, the better. Such restrictions lead to reduced economic efficiency. Further, by adopting a lime type welding rod, it was possible to give the slag a high basicity and reduce the P content by the deP effect. P is 0.03%
Below.

Since S is an unavoidable impurity and is an element which forms a eutectic (Ni-Ni ₃ S ₂ etc.) having a low melting point with Ni like P and enhances the weld hot cracking susceptibility, the content is S. The smaller the better, the better, but S was set to 0.015% or less.

O is an unavoidable impurity that intrudes from the atmosphere during melting of the core wire and collects in the form of an oxide in the crystal grain boundaries of the weld metal to weaken the high temperature strength of the crystal grain boundaries. Also, O
In order to increase the susceptibility to welding cracks, we adopted a lime type welding rod to reduce the O content. O is preferably 0.1% or less.

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

Next, the coating agent for the Ni-based coated arc welding rod will be described. As a coating agent used for a coated arc welding rod for Ni-based high Cr alloy (corresponding to an Inconel-based coated arc welding rod), a lime titania type flux type containing TiO ₂ , CaCO ₃ as a main component, CaCO ₃ , C
There is a lime type flux type containing aF ₂ as a main component. Generally, the lime type welding rod is characterized by good welding workability in all positions, but on the other hand, the stability of the arc and the reoccurrence of the arc are poor, so welding using a DC welding machine with a DC power source is not possible. Has been done. Also, CaC
As the main component is O ₃ coating agent, CaCO
₃ has the drawback that it decomposes and increases the C content of the deposited metal, degrading the corrosion resistance. In addition, since it has the effect of imparting basicity to the slag and reducing the contents of Si, P, and S of the deposited metal, it is possible to suppress the weld crack susceptibility to a low level.

Coated arc melting for Ni-based high Cr alloy of the present invention
The contact rod is a lime type welding rod,
CaCO so that it can be welded using a cheap AC welder₃, C
aF ₂Is the main component of lime type potassium titanate (TiK
₂O) is added to stabilize the arc and prevent re-arcing.
I am trying to improve. As a conventional product, a lime type welding rod
For DC only (AC breaks arc welding
No) and lime titania type welding rod for both direct and direct use
Have been. This lime titania type welding rod is in a downward position
Has a beautiful bead appearance, but is
The welding workability is slightly inferior because the bead appearance is convex.
Further, in the lime titania type welding rod, TiO₂, SiO
₂As the main component is P, S, Si, O
Weak crack susceptibility increases due to increased amount
There is.

In the present invention, the metal carbonate means CaC.
O _3, MnCO _3, BaCO ₃ refers to such, but they provide a basic slag none, P of the weld metal, S, S
Since it has the effect of suppressing i to a low level, it has good resistance to weld cracking. These metal carbonates decompose during welding to generate CO ₂ and shut off the molten metal from the atmosphere, lowering the partial pressures of H and N gases in the arc atmosphere, so that the total weight of the coating agent is 20% or more. It is necessary to add it, and if it is added in excess of 50%, the amount of gas generated becomes excessive, resulting in frequent pits. Furthermore, the melting point of slag rises, and the fluidity of slag deteriorates, resulting in sound welding. Since no bead was obtained, the metal carbonate content was set to 20 to 50%.

The metal fluoride referred to in the present invention means Ca
_{F 2, CeF 2, MgF 2} , BaF 2 refers to an the like, these are the effect of increasing the fluidity of the slag either, bead appearance is poor fluidity of the slag when the addition amount is less than 20% Deteriorates. On the other hand, if the addition amount exceeds 50%, the cylinder shape of the covered arc welding rod at the time of welding will be weakened, causing single melting and degrading the welding workability. Therefore, the metal fluoride was set to 20 to 50%.

The coating agent used for the coated arc welding rod of the present invention is 3-20% alloying agent, 0.2-5% deoxidizing agent, 3 in addition to the above metal carbonate, metal fluoride and oxide. ~ 20
% Slag-forming agent and 1-5% binder.

The alloying agents referred to here are Mn, Cr, Mo,
Most of these elements are contained in the core wire with one or more kinds of metal powder selected from W, V, Fe, Nb and CrN, but in order to supplement the components that are consumed by oxidation during welding. When the target components of the deposited metal are not satisfied, they are blended as an alloying agent to improve the mechanical properties of the deposited metal and to improve the corrosion resistance and crack resistance.

The deoxidizing agent is a simple metal such as Al, Ti or Si,
At least one of iron alloys such as Fe-Si and Fe-Al and Al-Mg is contained in a coating agent to improve blowhole resistance.

The slag-forming agent is TiO ₂ , SiO ₂ , T
1 selected from iK ₂ O, Cr ₂ O ₃ and Al ₂ O ₃
The slag covers the molten metal with one kind or two or more kinds of powders to prevent oxidation and nitridation by the atmosphere, and also aids the deoxidizing action and greatly affects the performance of the deposited metal and the welding workability. For example, if the content of the slag agent is small, the encapsulating property of the slag deteriorates and the arc becomes unstable. On the other hand, if the amount of the slag is too large, the fluidity of the slag deteriorates and the vertical weldability deteriorates. In particular, TiO ₂ and TiK ₂ O are effective for the stability of initial arc generation and rearc generation, which are the drawbacks of lime type welding rods. Further, SiO ₂ has an effect as a sliding agent at the time of coating, and becomes slag after welding. If the addition amount of these is less than 3%, arc breakage occurs and stable welding cannot be performed. On the other hand, if the addition amount exceeds 20%, the balance of high basicity, which is one of the features of the lime type welding rod, is lost, and the P, S and Si of the weld metal tend to increase,
Since the susceptibility to weld cracking is high, the amount of the slag-forming agent added is set to 3 to 20%.

The binder is a water glass consisting of an aqueous potassium silicate solution and an aqueous sodium silicate solution. Potassium silicate has a high hygroscopicity while having an effect on the stability of the arc. Further, sodium silicate is slightly inferior in arc stability, but is low in hygroscopicity. Utilizing the features of both, they are mixed and used as a binder. In the covered arc welding rod of the present invention, it is preferable to use sodium silicate as a main component particularly in consideration of hygroscopicity.

[0040]

The present invention will be described in more detail with reference to the following examples. A test piece was welded using a coated arc welding rod of the present invention in which a core wire having a different composition and a coating agent (flux) were combined and a coated arc welding rod of a comparative example whose composition was outside the scope of the present invention, and a room temperature tensile test was performed. A high temperature tensile test at 350 ° C., a T-type weld cracking test, and a C-type jig restraint butt welding cracking test were performed. As the base material, SUS304 of JIS G4304 (hot rolled stainless steel plate and steel strip) was used. Here, SUS304 is used as the base material because there are some places where SUS304 is used in the actual structure.
US304 has a larger content of P and S than Inconel 690 and is likely to cause weld cracking, which can be evaluated under severe conditions for cracking tests. In the tensile test of weld metal, overlay welding is performed on the entire surface of the base metal This is because there is no influence of the material because it is (according to JIS regulations).

The tensile test was carried out according to JIS Z3111 (method of tensile and impact test of deposited metal). S of test plate
US304 base metal groove surface and backing metal surface were two-layer buttered and welded as specified. Joint welding
No preheating, pass temperature 177 ℃ or less, welding current 140A
(Welding rod diameter 4 mm). From welding metal joints to JIS
Z3111 A2 (diameter of parallel part of test piece 6 mm)
After taking a tensile test piece by machining, JIS Z2
The tensile test was performed according to 241 (Metallic material tensile test method).

The T-type weld cracking test and the C-type jig restraint butt weld cracking test are performed according to JIS Z3153 and JIS, respectively.
It carried out according to Z3155. The shape of the sample used for the T-type weld cracking test is shown in FIG. 1, and the shape of the sample used for the C-type jig restraint butt welding cracking test is shown in FIG. Table 4 shows the compositions of the core wires used in the comparative examples and examples, and Table 5 shows the compositions of the coating agents (fluxes) used in the comparative examples and the examples.
Shown in In addition to the components shown in Table 5, an appropriate amount of sodium silicate as a binder was added to the coating agent.

The results of each test are shown in Table 6. Table 6 shows the tensile strength (σu), the elongation (EL) and the crack ratio (%) in the weld crack test of the deposited metal. The cracking rate is obtained by the following formula. Crack rate (%) = (crack length mm / weld bead length mm)
× 100 In Table 6, AC-1 is a commercially available welding rod for a Ni-based high Cr alloy, which is data to be used for comparison. First, as can be seen from the results of the T-shaped weld crack test, the crack resistance of RAC-2 to 15 using the materials within the composition range of the present invention as the core wire and using AD as the coating agent is AC-1. Is superior to the comparative example material. Further, the tensile strength (σu) in the high temperature tensile test at 350 ° C. is 497 MPa in the case of the commercially available welding rod, whereas it is RAC-2 to 15 of the present invention.
Was 534 to 560 MPa, and an improvement of 37 to 63 MPa was recognized. The results are summarized in Table 3, which shows that the high temperature strength can be increased without increasing the weld crack susceptibility.

[0044]

[Table 3]

Table 7 shows the effect of alloying elements on the characteristic values revealed by multiple regression analysis based on the above test results. In Table 7, ↑ indicates an improvement effect, ↓ indicates a reduction effect, and-indicates a state in which no remarkable effect is observed.

[0046]

[Table 4]

[0047]

[Table 5]

[0048]

[Table 6]

[0049]

[Table 7]

[0050]

EFFECT OF THE INVENTION Ni-based high Cr such as Inconel 690 alloy
The coated arc welding rod used for welding the alloy is ASME Co
Although the standard one was used for de, ASME Co
Although the de standardized material has good short-term tensile strength, it does not take into consideration the high-temperature strength of the welded portion, so the high-temperature tensile strength characteristics are not sufficient, and for example, the structure of structures such as pressurized water reactors When applied to the welding of members, it was unreliable to operate these devices at high temperature for a long time. As described above, the coated arc welding rod of the present invention is
It is based on the composition of the standard material of ME Code, but the high temperature tensile strength is improved by designing an alloy aiming at the upper limit within the standard composition range especially for the amount of Mo.
Next, the appropriate ranges of W and V elements not specified in ASME Code were clarified. Furthermore, by examining the residual amount of unavoidable impurities that are mixed in from the raw materials and auxiliary raw materials during melting, and by determining the allowable amount of N, which contributes to the improvement of high temperature tensile strength, the allowable amount is determined.
Compared to the high temperature tensile strength of the deposited metal at 350 ° C. of 500 N / mm ² when using the Code coated arc welding rod, the coated arc welding rod of the present invention has at least 540 N / mm ² or more under the same conditions. The high temperature tensile strength can be obtained, and as a result, great reliability can be imparted to the welding of the high temperature structure using the Inconel 690 alloy.

[Brief description of drawings]

FIG. 1 is a schematic view showing the shape of a sample used for a T-type weld cracking test.

FIG. 2 is a schematic view showing the shape of a sample used for a C-shaped jig restraint butt welding cracking test.

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[Procedure amendment]

[Submission date] February 16, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0046

[Correction method] Change

[Correction content]

[0046]

[Table 4]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0048

[Correction method] Change

[Correction content]

[0048]

[Table 6]

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masato Iida 1-1-1, Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Katsuji Danbayashi, Kobe-shi, Hyogo Prefecture 1-1-1, Wadasaki-cho, Ward Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Omae, 7800 Nakase, Hamakita-shi, Shizuoka Prefecture Japan Welding Rod Co., Ltd. Technical Research Institute (72) Inventor Tamao Takatsu 7800 Nakase, Hamakita City, Shizuoka Prefecture Japan Welding Rod Co., Ltd.

Claims (1)

[Claims] 1. C: 0.05% or less by weight%, Si:
0.75% or less, Mn: 2 to 5%, P: 0.03% or less, S: 0.015% or less, Cr: 28 to 31.5%,
Mo: 0.5% or less, Cu: 0.5% or less, Nb: 1 to
2.5%, Al: 0.5% or less, Ti: 0.5% or less,
Fe: 7 to 12%, Co: 0.1% or less, W and V at a maximum of two types, 0.5% or less in total, and O: 0.1% or less and N: 0 as unavoidable impurities. .03-0.
An alloy containing 3% and the balance being Ni is used as a core wire, and one kind or two or more kinds of metal carbonate based on the total weight of the coating material: 2
0-50%, one or more metal fluorides: 20-
50%, alloying agent: 3 to 20%, deoxidizing agent: 0.2 to 5%,
A coated arc welding rod for a Ni-base high Cr alloy, characterized in that a coating agent comprising a slag forming agent: 3 to 20% and a binder: 1 to 5% is coated around the core wire.