JP6671157B2 - Flux-cored wire for stainless steel welding, stainless steel welded joint, and method of manufacturing the same - Google Patents

Description

  The present invention relates to a welded structure used in an environment where seawater resistance, sea salt particle resistance is required, such as a ship, a marine structure, a bridge, and a seawater desalination apparatus, or a power generation facility, a chemical plant, or the like. Gas shielded arc welding of austenitic stainless steel and duplex stainless steel used in the assembly of welded structures used in various corrosive environments reduces the amount of oxygen in the weld metal while maintaining the same corrosion resistance as the base metal The present invention relates to a flux cored wire for welding stainless steel, which has ensured excellent toughness.

  Austenitic stainless steels such as SUS304 and duplex stainless steels such as SUS329J3L are used in ships, marine structures, bridges, seawater pumps, seawater desalination equipment, etc. due to their excellent corrosion resistance, strength and toughness. It is used in a wide range of fields as a corrosion-resistant material that can withstand severe corrosive environments requiring seawater resistance, sea salt particle resistance, and chloride resistance in various chemical plants and food production plants. Particularly, the duplex stainless steel is a stainless steel in which Cr, Ni, Mo, and N are main elements and the phase ratio between ferrite and austenite is adjusted to be about 50% by volume to ensure strength and corrosion resistance. In recent years, due to soaring Ni and Mo, a low-priced duplex stainless steel in which the amount of Ni and Mo has been reduced as much as possible (for example, Patent Document 1) has been developed, and is equivalent to austenitic stainless steel which is the mainstream of stainless steel. , While attracting attention as a stainless steel with low alloy cost and little price fluctuation.

  As a welding method for constructing these austenitic stainless steel and duplex stainless steel welded structures, gas shielded arc welding such as TIG welding and MIG welding, covered arc welding, submerged arc welding, and the like are applied. Among them, gas shielded arc welding using flux cored wire is more efficient and has better welding workability than gas shielded arc welding and covered arc welding using solid wire. The welding method uses a large amount of material. In addition, the corrosion resistance and tensile strength of the weld metal produced using these flux-cored wires are equivalent to those of the base metal.

  However, the impact characteristics of the weld metal obtained by gas-shielded arc welding using a commercially available flux-cored wire for stainless steel welding are quite low irrespective of the composition and structure, for example, a Charpy impact test at a temperature of 0 ° C. Thus, the absorbed energy is reduced to 以下 or less as compared with other welding methods, and insufficient toughness has been a problem (for example, Non-Patent Document 1). This is because the amount of oxygen contained in the weld metal obtained by gas shielded arc welding using a flux cored wire for stainless steel welding is extremely high, and the amount of oxygen in the case of covered arc welding is 0.04 to 0. On the other hand, in the case of welding using a flux-cored wire, it is 0.1 to 0.15%, which is twice or more. It is considered that the reason for this is that the differences in the temperature of the molten pool, the stirring state, the solid-liquid interface area, and the like affect the welding method. Further, even in gas metal arc welding using the same flux-cored wire, the amount of oxygen in the case of carbon steel is about 0.05 to 0.06%, which is about 1/3 in the case of stainless steel. This is because the oxygen activity coefficient decreases as Cr increases, and the oxygen activity coefficient of stainless steel containing about 20% of Cr decreases to about 1/10 of that of carbon steel containing no Cr. Therefore, it becomes difficult to remove oxygen, and a large amount of oxygen remains in the weld metal.

  As described above, it is a well-known fact that the gas shielded arc welding metal using the flux cored wire for stainless steel welding has an extremely high oxygen content and thus has low toughness.

  Patent Document 2 discloses a flux-cored wire for austenitic stainless steel welding with improved toughness of the weld metal, and Patent Document 3 discloses a flux-cored wire for duplex stainless steel welding with improved toughness of the weld metal. I have. However, all of these methods improve the toughness by making solidified crystal grains finer using TiN as a nucleus, and do not reduce the oxygen content of the weld metal. In order to reduce the amount of oxygen in the weld metal, it is effective to use pure Ar as a shield gas. However, in gas metal arc welding (MIG welding) of a pure Ar shield, the center of the wire remains undissolved. The molten state became unstable and welding was difficult. As a method for solving the problem, a coaxial multilayer wire (Patent Document 4) in which the outer skin and the center are made of metal materials having different melting points is reported. However, there is a problem that it is difficult to obtain good welding workability like a general flux-cored wire, and that the manufacturing cost is high. In addition, a number of patents for flux cored wires for welding stainless steel have been disclosed (eg, Patent Documents 5 and 6), but none of them has fundamentally improved toughness by reducing the amount of oxygen in the weld metal. Met.

International Publication No. WO 2002/027056 JP 2003-136280 A Japanese Patent No. 4531118 JP 2006-205204 A JP 2012-148298 A JP 2014-34051 A

Stainless Steel Flux-Coated Wire Guidebook: Japan Welding Association Welding Rod Section Technical Committee Edition (February 2008)

  SUMMARY OF THE INVENTION In view of the above-mentioned state of the art, the present invention provides a flux-cored wire used for gas-shielded arc welding of austenitic stainless steel and duplex stainless steel, austenitic stainless steel or duplex stainless steel on both or one of the base metals. With respect to a welded joint using, and a method of manufacturing the same, welding workability is good, while maintaining the tensile properties of the weld metal at the same level as the base metal properties, reducing the amount of oxygen contained in the weld metal, It is an object of the present invention to provide a flux-cored wire for stainless steel welding capable of ensuring the toughness of a weld metal, a welded joint having excellent toughness of a weld metal, and a method of manufacturing the same.

  The present inventors have conducted gas shielded arc welding using stainless steel flux-cored wires filled with various alloys and oxides to solve the above-mentioned problems, and determined the oxygen content and toughness of the formed weld metal. Investigated and examined in detail. As a result, it became clear that good toughness can be ensured when the oxygen content is 0.06% or less. In addition, in order to reduce the amount of oxygen, it was expected that the deoxidation reaction would be accelerated by controlling the oxide and alloy in the flux.

The present invention has been made as a result of further studies based on the above findings, and the gist thereof is as follows.
(1) In a flux-cored wire in which a flux containing an oxide and a fluorine compound is filled in an amount of 15 to 25% by mass with respect to the total mass of the wire, the oxidation is performed in a mass% with respect to the total mass of the wire. _{things, TiO 2: 1.0~3.5%, SiO} 2: 0.1~2.0%, CaO: 0.1~1.5%, and, _Al 2 _{O 3} and one ZrO ₂ Or 2 kinds: 0.1% or less in total, and the total of F-calculated values of the fluorine compound is 0.01 to 3.0%, and the oxide and the fluorine compound are 3.8 to 3.8% in total. containing 11.2%, _further, as a component other than _{TiO 2, SiO 2, CaO,} Al 2 O 3, ZrO 2 and the MgO of the fluorine compound, Si: 0.1~0.7%, Mn: 0. 3-5%, Al: 0.002-1.0%, Ti: 0.01-3 0%, Mg: 0.001-1.0%, C: 0.06% or less, Ni: 5-16%, and Cr: 16-27%, and Al + Ti + Mg: 0.5-3. Flux-cored wire for welding stainless steel, wherein 5% is satisfied and the balance is Fe and inevitable impurities.
(2) The flux-cored wire for welding stainless steel according to (1), wherein the oxide further contains 0.1 to 1.5% by mass of MgO based on the total mass of the wire.
(3) Further, one or more metal carbonates of CaCO ₃ , Na ₂ CO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ , and Li ₂ CO ₃ in total mass% with respect to the total mass of the wire. The flux-cored wire for stainless steel welding according to (1) or (2), which contains less than 0.6%.
(4) Further, Mo: 0.01 to 4.5%, Cu: 0.01 to 1.5%, W: 0.01 to 3.0%, Nb: 0. The flux-cored wire for welding stainless steel according to any one of (1) to (3), containing one or more selected from 01 to 1.0%.
(5) Flux for stainless steel welding according to any one of (1) to (4), further comprising N: 0.01 to 0.3% by mass% based on the total mass of the wire. Wire.
(6) Further, it is characterized in that it contains, in mass% based on the total mass of the wire, one or two of Na ₂ O and K ₂ O: 0.02 to 0.20% in total (1) to (1). 5) The flux-cored wire for stainless steel welding according to any one of 5).
(7) The stainless steel according to any one of (1) to (6), further containing 0.01 to 0.15% of the total amount of Bi in terms of mass% based on the total mass of the wire. Flux-cored wire for welding.
(8) The flux-cored wire for welding stainless steel according to any one of (1) to (7), wherein the outer skin has a slit-like shape without a gap.
(9) The flux-cored wire for welding stainless steel according to any one of (1) to (7), wherein the outer skin has a shape having a slit-shaped gap.
(10) Duplex stainless steel containing 0.1 to 11% of Ni by mass% and 18 to 27% of Cr and being two phases of ferrite and austenite and having a ferrite content of 30 to 70% by volume. A welded joint used for at least one of the plurality of base materials constituting the joint, wherein the amount of oxygen in the weld metal of the welded joint is 0.06% or less by mass%. Welded joint with excellent toughness of weld metal.
(11) A welded joint containing 5 to 21% by mass of Ni and 16 to 27% by mass of Cr, and using austenitic stainless steel for both or one of the base materials constituting the joint, A welded joint having excellent toughness of a welded metal, wherein the amount of oxygen in the welded metal of the welded joint is 0.06% or less by mass%.
(12) Using the flux-cored wire for stainless steel welding according to any one of (1) to (9), and mixing pure carbon dioxide gas or Ar with 3 to 30% by volume CO ₂ as a shielding gas. gas or, Ar and method for producing a welded joint which is characterized in that the gas shielded arc welding using a mixed gas of 0.2-10 vol _{O 2} (10) or (11).

  ADVANTAGE OF THE INVENTION According to the flux cored wire for stainless steel welding of this invention, in the welding of austenitic stainless steel and duplex stainless steel, the amount of oxygen contained in a weld metal can be reduced. Further, according to the stainless steel welded joint using austenitic stainless steel or duplex stainless steel for at least one of the plurality of base materials constituting the joint, the amount of oxygen contained in the weld metal is low. The toughness of metal can be greatly improved, and a welded joint having good toughness can be obtained.

(A) is an enlarged photograph of a cross section of the flux-cored wire of the embodiment of the present invention in which there is no slit-like gap in the outer skin, and (b) and (c) are other present inventions having a slit-like gap in the outer skin. It is an enlarged photograph of a section of a flux cored wire concerning an embodiment.

  First, the technical concept for reducing the oxygen content of the weld metal according to the present invention will be described.

In order to reduce oxygen, that is, to promote the deoxidation reaction, a method of increasing the amount of a deoxidizing element such as Si or Ti and a method of reducing the activity of a deoxidizing reaction product such as SiO ₂ or TiO ₂ are considered.
However, the former method of increasing the amount of the deoxidizing element reduces the activity coefficient of oxygen in the weld metal, as in the case of Cr described above with reference to Non-Patent Document 1, and thus the oxidation reaction of the deoxidizing element in the weld metal. Is less likely to occur, and as a result, there is a problem that it is difficult to remove oxygen from the weld metal. Thus, it is difficult to reduce the amount of oxygen in the weld metal simply by increasing the amount of the deoxidizing element.

  An effective method for reducing the activity of the deoxidation reaction product, which is the latter method, is to increase the basicity of the slag by increasing the number of basic compounds in the flux and decreasing the number of acidic compounds. By increasing the basicity of the slag, the oxidation reaction as a deoxidation reaction is promoted, and the generated oxide easily floats and is discharged as slag from the molten metal, and the amount of oxygen remaining in the weld metal is reduced.

By the way, oxides such as SiO ₂ and TiO ₂ are filled as flux components of the flux-cored wire for the purpose of improving slag encapsulation and slag removability and improving bead shape. Therefore, by increasing the basicity of the flux, the activity of the deoxidation reaction product is reduced to promote the oxidation reaction of the deoxidizing element, and as a result, the oxygen content of the weld metal is reduced.

  Hereinafter, the composition, manufacturing method, and the like of the flux-cored wire for stainless steel welding of the present invention will be described in detail. In the following description, “%” means “% by mass” unless otherwise specified, and the following component contents are the total amount (% by mass) contained in the outer sheath and the flux with respect to the total mass of the wire. .

[Oxide]
As described above, also in the present invention, at least one of TiO ₂ , SiO ₂ and CaO, and Al ₂ O ₃ and ZrO ₂ is used as an essential oxide. The content of these oxides is defined as follows from the viewpoint of the shape and encapsulation of the bead, the stability of the arc, and the like.

TiO _2: 1.0~3.5%
TiO ₂ forms a slag having good encapsulation property to improve the bead shape and stabilizes the arc. If it is less than 1.0%, the effect cannot be sufficiently obtained, the bead shape becomes convex, and the arc becomes unstable. If it exceeds 3.5%, the arc length becomes long, and the detachment of the droplet is hindered, resulting in frequent spattering. Therefore, its content is limited to 1.0 to 3.5%.

SiO ₂ : 0.1 to 2.0%
SiO ₂ adjusts the viscosity of the slag, and improves the encapsulability and peelability of the slag. If it is less than 0.1%, the slag peeling property is deteriorated, the viscosity is also increased, and the bead shape becomes unstable. If it exceeds 2.0%, the stability of the arc will be reduced, and the slag encapsulation will also be poor, resulting in poor bead appearance. Therefore, its content is limited to 0.1 to 2.0%.

CaO: 0.1-1.5%
CaO is also a basic compound, and is effective in increasing the basicity to reduce the activity of the deoxidized product and reducing the oxygen content of the weld metal. Since this effect is exhibited at 0.1% or more, the lower limit is set. However, if the content exceeds 1.5%, the arc becomes unstable, so the upper limit is set.

One or two of Al ₂ O ₃ and ZrO ₂ : 0.1% or less in total Al ₂ O ₃ and ZrO ₂ degrade the slag removability, so that the lower the possible, the better. Therefore, one or two of Al ₂ O ₃ and ZrO ₂ are limited to a total of 0.1% or less.

  In the present invention, if necessary, MgO may be further contained in the range of 0.1 to 1.5%. MgO is also a basic oxide, and is effective in increasing the basicity to reduce the activity of the deoxidized product and reducing the oxygen content of the weld metal. Since this effect is exerted at 0.1% or more, the content is made the lower limit when it is contained. If the content exceeds 1.5%, the arc becomes unstable, so the upper limit is set.

[Deoxidizing element]
In the present invention, in order to reduce the oxygen content of the weld metal, the content of a deoxidizing element as the following wire component is specified. The deoxidizing element may be a compound other than TiO ₂ , SiO ₂ , CaO, Al ₂ O ₃ , TiO ₂ , ZrO ₂ , MgO and a fluorine compound, a metal material including a single metal element, or a plurality of types of metal materials. It is added as a mixture of metal elements.

Si: 0.1 to 0.7%
Si acts as a deoxidizing element and reduces the amount of oxygen in the weld metal to obtain good ductility and toughness. Further, the viscosity of the slag is adjusted to improve the bead shape. If the content is less than 0.1%, the effect is not sufficient. On the other hand, if the content exceeds 0.7%, Si-based oxides are dispersed and precipitated as inclusions in the weld metal, and the ductility and toughness of the weld metal deteriorate. . Also, the bead shape becomes convex. Therefore, its content is limited to 0.1 to 0.7%.

Mn: 0.3-5%
Mn acts as a deoxidizing element, has the effect of reducing the oxygen content of the weld metal and improving the toughness, but if it is less than 0.3%, the effect is not sufficient. Mn is an austenite forming element, and in the case of a duplex stainless steel, is added in an amount of 0.3% or more so that the phase balance between the ferrite phase and the austenite phase is about 50% by volume. However, if it is added in excess of 5%, the droplets grow large, the amount of spatter generated increases, and a large amount of fume is generated. Therefore, its content is limited to 0.3 to 5%.

Al: 0.002 to 1.0%
Al is a deoxidizing element and has an effect of reducing the amount of oxygen and also has an effect of stabilizing the arc. However, if it is less than 0.002%, the effect is small. On the other hand, when a large amount is added, a large amount of Al-based oxide is generated, the toughness of the weld metal is deteriorated, and the arc becomes unstable. Therefore, the upper limit is 1.0%.

Ti: 0.01 to 3.0%
Although Ti acts as a deoxidizing element and reduces the amount of oxygen, this effect is exerted at 0.01% or more, so the lower limit is set. The lower limit is preferably 0.1%. More preferably, it is 0.2%. Further, TiO ₂ formed as a deoxidation product floats on the surface of the bead and turns into slag. However, since the melting point of TiO ₂ is relatively high, the difference in melting point between metal and slag increases to improve slag removability. There is also the effect of doing. However, if the addition exceeds 3.0%, the arc becomes unstable, so the upper limit is set. The upper limit is preferably 2.0%. More preferably, it is 1.6%.

Mg: 0.001-1.0%
Mg is a deoxidizing element and is effective in reducing the amount of oxygen, improves the timing of slag separation, and reduces the adhesion of a temper color. If it is less than 0.001, the effect is small. On the other hand, if it exceeds 1.0%, the viscosity of the slag increases, and the slag removability deteriorates. Therefore, its content is limited to 0.001 to 1.0%. The lower limit is preferably 0.005%. More preferably, it is 0.010%. The upper limit is preferably 0.7%. More preferably, it is 0.3%. Mg may be added as a flux component in the form of MgCO ₃ .

Al + Ti + Mg: 0.5-3.5%
Al, Ti, and Mg act as deoxidizing elements as described above, and each of them is effective in reducing the amount of oxygen in the weld metal, but its effect is further increased by being combined. Further, the composite oxide improves the melting point and viscosity of the slag and stabilizes the arc. If the total is less than 0.5%, the effect is small, and if it exceeds 3.5%, the arc becomes unstable and the slag peeling property is deteriorated. Therefore, the sum of the contents is limited to 0.5 to 3.5%. Preferably, it is 1.0 to 2.5%.

[Fluorine compound]
Total of F-converted values of fluorine compounds: 0.01 to 3.0%
Fluorine compounds are mainly basic compounds, which increase the basicity and reduce the activity of deoxidation products. In addition, it has the effect of reducing the amount of oxygen in the weld metal and improving the toughness in order to promote the slag floating separation of these deoxidized compounds from the molten metal. Further, the fluorine compound adjusts the melting point of the slag, thereby improving the slag encapsulation property and the slag releasability, and improving the bead shape. The fluorine compound, a metal fluoride, alkali metal fluorides, but using an alkaline-earth metal _{fluorides, CaF 2, BaF 2, MgF} 2, AlF 3, LiF, NaF, K 2 ZrF 6, K 2 SiF 6, Na ₃ AlF _{6 and the} like are effective, and when an alkali metal fluoride is used, arc stability is also improved. If the total of the F-values of one or more of the fluorine compounds is less than 0.01%, the effect is insufficient, and if it exceeds 3.0%, the fluidity of the slag becomes excessive and an arc is not generated. As a result, the melting point of the slag is remarkably reduced, and the bead shape becomes poor. Calculated in terms of F values, for example, in the case of CaF _2, the atomic weight 19.00 twice the value of F to divided by the molecular weight 78.08 of CaF _2, multiplied by the weight% of CaF ₂ with respect to the weld total mass of the wire And calculate.

Total of oxides and fluorine compounds: 3.8 to 11.2%
The oxide and the fluorine compound have respective effects as described above, but the total amount thereof affects the bead formation having a good encapsulation property and the amount of spatter generated. The bead forming effect with good encapsulation property can be obtained at 3.8% or more, but if it exceeds 11.2%, the droplets become entangled with the oxide and the droplet transfer state becomes unstable, and the amount of spatter generated Increase. Therefore, the total of the oxide and the fluorine compound is limited to 3.8 to 11.2% based on the total mass of the wire.

[Other basic wire components other than the above]
Next, in order to obtain other effects, the contents of the following components are specified.

C: 0.06% or less C is harmful to corrosion resistance, but must be contained to some extent from the viewpoint of strength. If the content is more than 0.06%, when as-welded and when reheated, it combines with Cr to precipitate Cr carbide, and the corrosion resistance is significantly deteriorated by a Cr-deficient layer formed in the vicinity thereof. Further, since the toughness and ductility of the weld metal are significantly reduced, the content is limited to 0.06% or less.

Ni: 5 to 16%
Ni: Ni is an austenite-forming element and stabilizes the austenite phase to improve the ductility and toughness of the weld metal. If the Ni content is less than 5%, the stability of the austenite phase is insufficient, and the toughness deteriorates. On the other hand, if it exceeds 16%, crystallization of the ferrite phase is suppressed, the amount of ferrite in the weld metal is reduced, and the tensile strength is reduced, and there is a risk that hot cracking may occur. Therefore, its content is limited to 5 to 16%.

Cr: 16-27%
Cr is a ferrite forming element and is effective in improving corrosion resistance. However, if the content is less than 16%, sufficient corrosion resistance cannot be obtained. On the other hand, when the content exceeds 27%, precipitation of Cr carbonitride increases, and the toughness and ductility of the weld metal deteriorate. Therefore, its content is limited to 16 to 27%.

  The balance other than the above-mentioned components and the like is Fe and inevitable impurities in the steel shell, and Fe and inevitable impurities in the flux.

Flux filling rate: 15 to 25%
If the flux filling rate inside the steel shell is less than 15% with respect to the total mass of the wire, the thickness of the steel shell becomes large, and the droplets are not smoothly separated and large spatters are generated when the droplets are separated. . On the other hand, when the flux filling rate exceeds 25%, disconnection is likely to occur during the production of the wire, resulting in poor productivity. Therefore, the flux filling rate is limited to 15 to 25% based on the total mass of the wire.

[Selective ingredients]
Although the above are the basic components of the flux-cored wire of the present invention, the following components can be selectively added. The following selective components may be added to the outer sheath of the wire as an alloy component, or may be added to the flux in the form of a single metal or a compound or mixture containing no oxygen other than impurities.

Mo: 0.01 to 4.5%
Mo is an element for improving corrosion resistance especially in a chloride environment, and can be added in an amount of 0.01% or more for improving corrosion resistance. However, when the content exceeds 4.5%, brittle intermetallic compounds such as a sigma phase are removed. When it is added because it is formed and the toughness of the weld metal is reduced, its content is limited to 0.01 to 4.5%.

Cu: 0.01 to 1.5%
Cu has a remarkable effect of increasing the strength and corrosion resistance, and can be added as an austenite-forming element for securing toughness of 0.01% or more. Since toughness deteriorates, when added, its content is made 0.01 to 1.5%.

W: 0.01 to 3.0%
W has a remarkable effect to enhance strength and corrosion resistance, and can be added in an amount of 0.01% or more. However, if added in excess of 3.0%, the toughness of the weld metal deteriorates. The content is set to 0.01 to 3.0%.

Nb: 0.01 to 1.0%
Nb is a stabilizing element, and forms NbC by combining with C before Cr combines with C to form Cr carbide, thereby suppressing the formation of Cr carbide and improving the intergranular corrosion resistance of the weld metal. Improve. If the content is less than 0.01%, the effect is insufficient. If the content exceeds 1.0%, the effect is not only saturated, but also high-temperature cracking tends to occur. The content is set to 0.01 to 1.0%.

N: 0.01-0.3%
N has the effect of stabilizing the austenite phase and increasing the strength of the weld metal as a solid solution strengthening element. Further, there is an effect of improving pitting corrosion resistance in a chloride environment. These effects are exhibited at 0.01% or more, and the lower limit is set. N is a strong austenite-forming element. In the case of duplex stainless steel, N is added in an amount of 0.01% or more so that the phase balance between the ferrite phase and the austenite phase is about 50% by volume. However, if it exceeds 0.3%, blowholes occur frequently and the defect resistance is reduced, and the composition is hardened and the toughness is reduced. Therefore, when added, the content is set to 0.01 to 0.3%. I do.

One or of the sum of Na ₂ O and _{K 2} O: 0.02 to 0.20%
Na ₂ O and K ₂ O stabilize the arc and suppress the generation of spatter. If the total of one or two of Na ₂ O and K ₂ O is less than 0.02, the effect of stabilizing the arc cannot be obtained. On the other hand, if it exceeds 0.20%, the amount of spatter generation increases. Therefore, to limit the total of one or two of Na ₂ O and _{K 2} O to 0.02 to 0.20 percent.

Bi: 0.01 to 0.15%
Bi is an element that improves the slag removability, and is the total of the Bi content (hereinafter referred to as “Bi-converted value”) contained in the Bi compound and the Bi content of Bi of the simple metal (hereinafter, “Bi”). Is less than 0.01%, the effect of improving the slag removability cannot be obtained. On the other hand, if the total amount of Bi conversion exceeds 0.15%, toughness deteriorates. Therefore, the total amount of Bi conversion is limited to 0.01 to 0.15%.

In the present invention, further CaCO ₃ if _{necessary, NaCO 3, BaCO 3, SrCO} 3, MgCO 3 and flux with one or a range of less than 0.6% of two or more metal carbonates in the total of LiCO ₃ May be contained. These metal carbonates have the effect of decomposing in the arc to generate CO ₂ gas, shielding the deposited metal from the atmosphere and lowering the hydrogen partial pressure in the arc atmosphere. In addition, it promotes separation of droplets, and is also effective in suppressing spatter. When a metal carbonate is used, it is preferable to contain the metal carbonate in a range of less than 0.6% in total with respect to the total mass of the wire in order to secure arc stability.

Subsequently, the form of the flux-cored wire will be described.
The flux-cored wire includes a wire having no slit-shaped gap in the outer skin as shown in FIG. 1A and a wire having a slit-shaped gap in the outer skin as shown in FIGS. 1B and 1C. Can be roughly classified. In the present invention, any cross-sectional structure can be adopted.

The flux-cored wire of the present invention can be manufactured by the same manufacturing steps as those of a normal flux-cored wire.
First, a steel strip such as a stainless steel strip serving as an outer skin is prepared, and a flux in which the above-mentioned components such as fluoride, alloy, oxide, and carbonate are blended so as to have a predetermined content is prepared. While feeding the steel strip in the longitudinal direction, it is formed into an open tube (U-shaped) by a forming roll to form an outer cover. During this forming, a flux is supplied from the opening of the open tube, and the facing edge surfaces of the opening are butt-slit. Weld the gap. As a welding method, electric resistance welding, laser welding, or TIG welding is used. A slit-shaped tube with no gap obtained by welding is drawn and annealed during drawing or after completion of the drawing step to obtain a slit-shaped wire with a desired wire diameter and no gap. Further, the slit-shaped gap is made into a tube having a slit-shaped gap without welding, and a wire having the slit-shaped gap is obtained by drawing the pipe.

  The steel sheath used for the flux-cored wire of the present invention is not particularly limited, but is preferably stainless steel from the viewpoint of reducing C. Further, the stainless steel strip may be any of austenitic, ferritic, and martensitic, or may be a multi-phase such as ferrite-austenite (two-phase).

  FIGS. 1A and 1B relate to a cut surface of a wire, wherein FIG. 1A shows a wire formed by butt welding of edge surfaces, FIG. 1B shows a wire formed by butt welding of edge surfaces, and FIG. It is a figure showing a wire. If the cut surface of FIG. 1A is polished and etched, welding marks are observed, but without etching, no welding marks are observed. For this reason, a wire having no slit-shaped gap formed by butt-welding and welding may be referred to as seamless. For example, “Introduction to New Welding and Joining Technology” edited by the Japan Welding Society (2008) Sangyo Publishing, p. 111 indicates a seamless type.

  Even if the edge surfaces are butted as shown in FIG. 1B or the edge surfaces are caulked as shown in FIG. 1C and brazed, a wire having no slit-shaped gap can be obtained. . Further, in FIGS. 1B and 1C, the wire that has not been brazed and has no slit is a wire having a slit-shaped gap.

Next, the stainless steel welded joint of the present invention will be described.
Welded joints include those obtained by welding the same material and those obtained by welding different materials. In the present invention, the use of a duplex stainless steel having a dual phase structure of ferrite and austenite at room temperature or an austenitic stainless steel is limited to at least one of a plurality of base materials constituting a welded joint.

  When using a duplex stainless steel, if the amount of ferrite is less than 30% by volume or more than 70% by volume, the corrosion resistance decreases, so the amount of ferrite is limited to 30 to 70% by volume. In order to obtain a two-phase structure of ferrite and austenite in which the amount of ferrite is 30 to 70% by volume at room temperature, the composition of the duplex stainless steel is Ni: 0.1 to 11% and Cr: 18 to 27%. It is necessary.

  When austenitic stainless steel having a single phase of austenitic stainless steel at room temperature is used, it is necessary that the composition of the austenitic stainless steel is 5 to 21% for Ni and 16 to 27% for Cr.

  In the present invention, the shapes of the above-described duplex stainless steel and austenitic stainless steel are not particularly limited, such as a plate, a pipe, and a wire. Further, since it is sufficient that the above-described duplex stainless steel or austenitic stainless steel is used for at least one base material of the plurality of base materials constituting the welded joint, a combination of base materials is Austenitic stainless steel, duplex stainless steel and austenitic stainless steel, duplex stainless steel and other metal materials, austenitic stainless steel and other metal materials. Other metal materials include, for example, carbon steel, but are not limited thereto.

  It is generally known that the impact characteristics of a weld metal obtained by gas-shielded arc welding using a flux-cored wire for welding stainless steel are considerably reduced. Therefore, the present inventors performed gas shielded arc welding using a stainless steel flux-cored wire filled with various alloying agents and slag agents, and investigated and examined in detail the oxygen content and toughness of the formed weld metal. . As a result, the toughness of the weld metal is unambiguously determined by the amount of oxygen in the weld metal, regardless of the type of alloy or slag added to the flux, regardless of the alloy composition other than the oxygen in the weld metal, or the amount of ferrite. It has been found that the toughness of the weld metal increases as the oxygen content decreases. And it has been found that good toughness can be ensured when the amount of oxygen in the weld metal is 0.06% or less. Therefore, in the welded joint of the present invention, the oxygen content in the weld metal is limited to the following.

Next, a method for manufacturing the above-described stainless steel welded joint will be described.
In manufacturing the stainless steel welded joint of the present invention, it is preferable to perform welding using the above-mentioned flux-cored wire. The flux-cored wire of the present invention can be used for various welding methods such as gas shielded arc welding, plasma welding, and submerged arc welding. In the following, it is manufactured by gas metal arc welding or TIG welding which is gas shielded arc welding. The case will be described.

As a shielding gas used in gas shielded arc welding, pure carbon dioxide gas, a mixed gas of Ar and CO ₂ , or a mixed gas of Ar and O ₂ is used in order to stabilize the arc and obtain a good penetration shape. Can be However, when the CO ₂ content of the mixed gas is less than 3% by volume or more than 30% by volume, or when the O ₂ content of the mixed gas is less than 0.2% by volume or more than 10% by volume since the stability of the arc is reduced, the ratio of Ar mixed gas, a mixed gas from 3 to 30 vol% for CO _2, in the case of _{O 2} was 0.2 to 10 vol% _{O 2.} By defining the type of the shielding gas in this way, stable welding is possible, and by defining the components contained in the shell and flux of the flux-cored wire used for welding as described above, It is possible to easily obtain a stainless steel welded joint in which the amount of oxygen is reduced to ensure excellent toughness.

  Hereinafter, the present invention will be described with reference to examples.

  [Welding action test of flux-cored wire] A stainless steel having a chemical composition shown in Table 1 was filled with a flux inside a steel sheath (W1, W2), and a composition and a flux filling rate shown in Tables 2-1 to 2-4. A flux-cored wire for welding was prototyped. Here, the “flux filling rate” means the ratio (% by mass) of the total components of the flux to the total mass of the wire.

  In Tables 2-1 to 2-4, "% by mass based on the total mass of the wire" is the total mass of the wire in the total amount of each element contained in the steel sheath and the flux when the steel sheath shown in Table 1 was filled with the flux. % By mass with respect to

In Tables 2-2 and 2-4, the "F-equivalent amount of fluoride" is the mass% of the total mass of the fluorine element contained in the fluorine compound as a component of the flux with respect to the total mass of the wire. The “Bi ₂ O ₃ equivalent amount of Bi ₂ O ₃ ” is a mass% of the total mass of the Bi element contained in Bi ₂ O ₃ as a flux component with respect to the total mass of the wire. In addition, the “total of Bi content” is the total amount of the “Bi ₂ O ₃ -converted amount of Bi” and the Bi content of Table 2-1 or Table 2-3.

"Oxide component and fluoride" in Tables 2-2 and 2-4 mean the total amount of the oxide component and the fluorine compound contained in the flux. This total amount is not calculated using the “fluoride F conversion value” in Tables 2-2 and 2-4, but is calculated using a fluorine compound. The sum of the amount of the “oxide component” and the “amount of fluoride converted to F” does not match.

  The prototype wire was a tube having no slit-like gap by welding the slit-like gap with the opposed edge surfaces of the opening, and having a wire diameter of 1.2 mm. In addition, only Example No. 13 was a tube having a slit-like gap that was not welded after being caulked as shown in FIG.

Next, a V groove having a groove angle of 60 ° and a root face of 0.5 mm was applied to various austenitic stainless steel sheets (B1, B2) and duplex stainless steel sheets (B3, B4) whose components are shown in Table 3. After being provided, the above-mentioned flux-cored wire was subjected to butt welding by gas metal arc welding to produce a welded joint. The welding conditions at this time were welding current: 250 A, arc voltage: 28 V, welding speed: 25 cm / min, and shielding gas: Ar + 20% CO ₂ .

  The welded joints obtained by welding were subjected to an oxygen content analysis of the weld metal and a Charpy impact test of the weld metal, respectively. In addition, the arc stability, slag removability, and bead shape during the production of the welded joint were evaluated. Tables 4-1 and 4-2 show the respective evaluation results. In addition, the Charpy absorbed energy of 4-1 and 4-2 was obtained by extracting a No. 4 Charpy test piece (2 mm V notch) Charpy test piece based on JIS Z3111 (2005) from the welded joint in a direction perpendicular to the welding direction. The Charpy impact test was performed at -20 ° C to determine the absorbed energy.

  In Table 4-1, wire no. In the invention examples 1 to 13, the component content and the flux filling rate are within the scope of the invention, the oxygen content of the weld metal is as small as about 0.05%, and the Charpy absorbed energy at -20 ° C is also 100 J. The above values are high. In addition, all have good arc stability, slag releasability, and bead shape, and show excellent welding workability.

On the other hand, wire No. 14 to 37 are comparative examples, and the evaluation results are shown in Table 2-1.
Wire No. In Comparative Example No. 14, since the Si content was lower than the range of the present invention, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Further, since the TiO ₂ content is lower than the range of the present invention, the arc becomes unstable, and the bead shape is convex.
Wire No. In Comparative Example No. 15, since the Si content was larger than the range of the present invention, the oxide was dispersed and precipitated in the weld metal, the oxygen content was high, and the Charpy absorbed energy was as low as 50 J or less. The bead shape is also convex.

Wire No. In Comparative Example No. 16, since the Mn content was lower than the range of the present invention, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Further, since the TiO ₂ content is larger than the range of the present invention, spatter occurs frequently and the arc becomes unstable.

  Wire No. In Comparative Example No. 17, although the Mn content was larger than the range of the present invention and the Charpy absorbed energy was high, spatter occurred frequently and the arc was unstable.

Wire No. In Comparative Example No. 18, since the Al content was lower than the range of the present invention, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Furthermore, since the SiO ₂ content is lower than the range of the present invention, the slag removability is poor.

  Wire No. In Comparative Example No. 19, since the Al content was larger than the range of the present invention, a large amount of oxide was precipitated in the weld metal, the oxygen amount was high, and the Charpy absorbed energy was as low as 50 J or less. The arc is also unstable.

Wire No. In Comparative Example No. 20, the Ti content was lower than the range of the present invention, so that the oxygen content of the weld metal was high and the Charpy absorbed energy was as low as about 50 J. Further, since the SiO ₂ content is larger than the range of the present invention, the arc becomes unstable, and the bead shape is deteriorated.

  Wire No. In Comparative Example No. 21, since the Mo content was larger than the range of the present invention, a sigma phase was precipitated and the Charpy absorbed energy was low. Further, since the Ti content is larger than the range of the present invention, the arc is unstable.

Wire No. In Comparative Example No. 22, since the Mg content was lower than the range of the present invention, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Furthermore, since the total content of Al ₂ O ₃ and ZrO ₂ is larger than the range of the present invention, the slag removability is deteriorated.

  Wire No. Comparative Example No. 23 has a low Charpy absorbed energy because the Cu content is larger than the range of the present invention. Further, since the Mg content is larger than the range of the present invention, the slag removability is deteriorated.

  Wire No. In Comparative Example 24, since the total content of Al + Ti + Mg was lower than the range of the present invention, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less.

  Wire No. Comparative Example No. 25 has a low Charpy absorbed energy because the W content is larger than the range of the present invention. Further, since the total content of Al + Ti + Mg is larger than the range of the present invention, the arc becomes unstable and the slag peeling property is also deteriorated.

  Wire No. In Comparative Example No. 26, since the CaO content was lower than the range of the present invention, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as about 50 J. Further, since the Nb content is larger than the range of the present invention, hot cracking occurs.

  Wire No. In Comparative Example No. 27, although the CaO content was higher than the range of the present invention and the Charpy absorbed energy was high, the arc was unstable.

  Wire No. Comparative Example No. 28 has a high oxygen content of the weld metal and a low Charpy absorbed energy of 50 J or less because the total of the F-converted values of the fluorine compounds is lower than the range of the present invention. Further, since the flux filling rate is lower than the range of the present invention, spatter frequently occurs and the arc becomes unstable.

  Wire No. In the comparative example of No. 29, since the total of the Bi conversion values of the metal Bi and the oxide Bi is larger than the range of the present invention, the oxygen content of the weld metal is high and the Charpy absorbed energy is as low as 50 J or less. Furthermore, since the total of the F-converted values of the fluorine compound is larger than the range of the present invention, the arc becomes unstable and the bead shape is also deteriorated.

  Wire No. Comparative Example No. 30 has a low Charpy absorbed energy because the C content is larger than the range of the present invention.

Wire No. Comparative Example No. 31 has low Charpy absorbed energy because the Ni content is lower than the range of the present invention. Furthermore, since the total content of Na ₂ O and K ₂ O is larger than the range of the present invention, spatters occur frequently and the arc becomes unstable.

  Wire No. In Comparative Example No. 32, hot cracking occurred because the Ni content was greater than the range of the present invention.

  Wire No. In Comparative Example No. 33, the Charpy absorbed energy was low because the Cr content was larger than the range of the present invention.

  Wire No. In the comparative example No. 34, since the N content was larger than the range of the present invention, the arc became unstable, and blowholes occurred frequently.

  Wire No. In Comparative Example No. 35, since the sum of the oxide component and the fluorine compound was lower than the range of the present invention, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Also, the bead shape has become worse.

  Wire No. In the comparative example No. 36, since the sum of the oxide component and the fluorine compound was larger than the range of the present invention, spatter frequently occurred and the arc became unstable.

  Wire No. In the comparative example of No. 37, since the flux filling rate was larger than the range of the present invention, disconnection occurred during wire production.

[Welding test with welding conditions and base metal]
Next, the influence of welding conditions and various combinations of base materials on welded joints was investigated.

  Flux was filled into the inside of the stainless steel skin (W1, W2) having the chemical composition shown in Table 1, and the composition and the flux filling rate shown in Tables 6-1 to 6-3 and Tables 7-1 to 7-3 were obtained. A flux-cored wire for welding stainless steel with a diameter of 1.2 mm was produced as a trial.

  Next, a V groove having a groove angle of 60 ° and a root face of 0.5 mm was provided for each of the steels B1 to B5 having the components shown in Table 5, and then gas metal was formed using the above flux-cored wire. Butt welding was performed by arc welding to produce a welded joint. As the shielding gas, pure carbon dioxide gas (G1), a mixed gas of Ar and carbon dioxide gas (G2, G4, G5) and a mixed gas of Ar and oxygen (G3, G6, G7) shown in Table 8 were used. Further, combinations of the welding wire, the type of the shielding gas, and the base material used are as shown in Tables 9-1 to 9-4. The welding conditions at this time were welding current: 250 A, arc voltage: 28 V, and welding speed: 25 cm / min.

  For the welded joints produced under the above welding conditions, an oxygen content analysis of the weld metal and a Charpy impact test of the weld metal were respectively performed. In addition, the arc stability, slag removability, and bead shape during the production of the welded joint were evaluated. Tables 9-1 to 9-4 show the respective evaluation results. In addition, the Charpy absorbed energy in Tables 9-1 to 9-4 is obtained by extracting a No. 4 Charpy test piece (2 mm V notch) Charpy test piece in accordance with JIS Z3111 (2005) from a direction perpendicular to the welding direction from the welded joint. , -20 ° C, and the absorption energy was determined.

(Example of the present invention)
In Table 9-1, the test numbers No. In the present invention examples 1 to 26, the component content and the flux filling rate are within the range of the present invention, the oxygen content of the weld metal is as small as about 0.05%, and the Charpy absorbed energy at -20 ° C is also 100 J. The above values are high. In addition, all have good arc stability, slag releasability, and bead shape, and show excellent welding workability.

(Comparative example)
On the other hand, in Tables 9-2 to 9-4, Test No. 27 to 82 are comparative examples.
No. In Comparative Example No. 27, since a flux having a composition in which the Si content was lower than the range of the present invention was used, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Further, since the TiO ₂ content of the flux is lower than the range of the present invention, the arc becomes unstable, and the bead shape is convex. On the other hand, No. In Comparative Example No. 28, since a flux having a Si content larger than the range of the present invention was used, an oxide was dispersed and precipitated in the weld metal, the oxygen content was high, and the Charpy absorbed energy was as low as 50 J or less. The bead shape is also convex.

No. In the comparative example No. 29, since the flux having a composition having a Mn content lower than the range of the present invention was used, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Further, since the TiO ₂ content is larger than the range of the present invention, spatter occurs frequently and the arc becomes unstable. On the other hand, No. In Comparative Example No. 30, a flux having a composition having a Mn content larger than the range of the present invention was used, and although the Charpy absorbed energy was high, spatter occurred frequently and the arc was unstable.

No. Comparative Example No. 31 has a high oxygen content of the weld metal and a low Charpy absorbed energy of 50 J or less, because a flux having a composition with an Al content lower than the range of the present invention was used. Furthermore, since the SiO ₂ content of the flux is lower than the range of the present invention, the slag removability is poor. On the other hand, No. In Comparative Example No. 32, since the Al content used a flux having a composition higher than the range of the present invention, a large amount of oxide was precipitated in the weld metal, the oxygen amount was high, and the Charpy absorbed energy was as low as 50 J or less. . The arc is also unstable.

No. Comparative Example No. 33 has a high oxygen content in the weld metal and a low Charpy absorbed energy of about 50 J because a flux having a composition with a Ti content lower than the range of the present invention was used. Further, since the content of SiO ₂ in the flux is larger than the range of the present invention, the arc becomes unstable and the bead shape is deteriorated. On the other hand, No. In Comparative Example No. 34, the arc was unstable because a flux having a composition having a Ti content larger than the range of the present invention was used. Further, since the Mo content in the flux is larger than the range of the present invention, a sigma phase is precipitated and the Charpy absorbed energy is low.

No. Comparative Example No. 35 has a high oxygen content of the weld metal and a low Charpy absorbed energy of 50 J or less, because a flux having a composition with a Mg content lower than the range of the present invention was used. Furthermore, since the total content of Al ₂ O ₃ and ZrO _{2 in} the flux is more than the range of the present invention, the slag removability is poor.

  No. In Comparative Example No. 36, the Charpy absorbed energy was low because a flux having a composition having a Cu content larger than the range of the present invention was used. Further, since the Mg content in the flux is larger than the range of the present invention, the slag removability is poor.

  No. In Comparative Example No. 37, since the total content of Al + Ti + Mg is lower than the range of the present invention, the oxygen content of the weld metal is high, and the Charpy absorbed energy is as low as 50 J or less. On the other hand, No. In Comparative Example No. 38, since a flux having a composition in which the total content of Al + Ti + Mg was larger than the range of the present invention was used, the arc became unstable, and the slag peeling property was also poor. Furthermore, since the W content in the flux is larger than the range of the present invention, the Charpy absorbed energy is low.

  No. Comparative Example No. 39 has a high oxygen content of the weld metal and a low Charpy absorbed energy of about 50 J because a flux having a CaO content lower than the range of the present invention was used. Further, since the Nb content in the flux is larger than the range of the present invention, hot cracking occurs. On the other hand, No. Comparative Example No. 40 was prepared using a flux having a composition having a CaO content larger than the range of the present invention, and although the Charpy absorbed energy was high, the arc was unstable.

  No. In the comparative example No. 41, since the flux having a composition in which the total of the F values of the fluorine compounds was lower than the range of the present invention was used, the oxygen content of the weld metal was high and the Charpy absorbed energy was as low as 50 J or less. Further, since the flux filling rate is lower than the range of the present invention, spatter occurs frequently and the arc becomes unstable. On the other hand, No. In the comparative example No. 42, the arc was unstable and the bead shape was poor because the total of the F-converted values of the fluorine compounds was larger than the range of the present invention. Further, the flux has a high oxygen content in the weld metal because the total of the Bi equivalent values of the metal Bi and the oxide Bi is larger than the range of the present invention. The Charpy absorbed energy of Comparative Example No. 42 is as low as 50 J or less.

  No. In Comparative Example No. 43, the Charpy absorbed energy was low because a flux having a composition in which the C content was larger than the range of the present invention was used.

No. In Comparative Example No. 44, the Charpy absorbed energy was low because a flux having a Ni content lower than the range of the present invention was used. Further, since the total content of Na ₂ O and K ₂ O is larger than the range of the present invention, spatter occurs frequently and the arc becomes unstable. On the other hand, No. In the comparative example of No. 45, a hot crack was generated because a flux having a Ni content larger than the range of the present invention was used. Also, since the MgO content of the flux is lower than the range of the present invention, the oxygen content of the weld metal is high, and the Charpy absorbed energy is as low as about 50J.

  No. In Comparative Example No. 46, the Charpy absorbed energy was low because a flux having a Cr content higher than the range of the present invention was used. Moreover, the MgO content of the flux is larger than the range of the present invention, and the arc is unstable.

  No. In the comparative example of No. 47, the arc became unstable and the number of blow holes occurred frequently because a flux having a composition in which the N content was larger than the range of the present invention was used.

  No. In Comparative Example No. 48, since a flux having a composition in which the sum of oxides and fluorides (hereinafter, referred to as “slag agent component”) was lower than the range of the present invention was used, the oxygen content of the weld metal was high, and the Charpy absorbed energy was high. Is also as low as 50 J or less. Also, the bead shape has become worse. Further, since the total of the metal carbonates of the flux is larger than the range of the present invention, the arc is unstable. On the other hand, No. In the comparative example of 49, since a flux having a composition in which the total of the slag agent components was larger than the range of the present invention was used, spatter occurred frequently and the arc became unstable.

  No. In Comparative Example No. 50, since the flux filling rate was larger than the range of the present invention, disconnection occurred during wire production.

No. In Comparative Examples 51 to 54, the composition of the flux-cored wire is within the range of the present invention, but the mixing ratio of the CO ₂ gas and the O ₂ gas of the mixed gas used as the shielding gas is outside the range of the present invention. , The arc is unstable.

No. Comparative Example No. 55 has a high oxygen content of the weld metal and a low Charpy absorbed energy of 50 J or less because a flux having a Si content lower than the range of the present invention was used. Further, since the TiO ₂ content of the flux is lower than the range of the present invention, the arc becomes unstable, and the bead shape is convex. On the other hand, No. In Comparative Example No. 56, since a flux having a composition having a Si content larger than the range of the present invention was used, an oxide was dispersed and precipitated in the weld metal, the oxygen content was high, and the Charpy absorbed energy was as low as 50 J or less. The bead shape is also convex.

No. In Comparative Example No. 57, since a flux having a composition having a Mn content lower than the range of the present invention was used, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Furthermore, since the TiO ₂ content of the flux is larger than the range of the present invention, spatter frequently occurs and the arc becomes unstable. On the other hand, No. The composition of the flux used in the preparation of Comparative Example No. 58 was such that the Mn content was greater than the range of the present invention and In the comparative example No. 58, although the Charpy absorbed energy was high, the spatter occurred frequently and the arc was unstable.

No. Comparative Example No. 59 has a high oxygen content in the weld metal and a low Charpy absorbed energy of 50 J or less, because a flux having a composition with an Al content lower than the range of the present invention was used. Furthermore, since the SiO ₂ content of the flux is lower than the range of the present invention, the slag removability is poor. On the other hand, No. In Comparative Example No. 60, since the Al content used a flux having a composition larger than the range of the present invention, a large amount of oxide was precipitated in the weld metal, the oxygen amount was high, and the Charpy absorbed energy was as low as 50 J or less. . The arc is also unstable.

No. Comparative Example No. 61 has a high oxygen content in the weld metal and a low Charpy absorbed energy of about 50 J because a flux having a composition with a Ti content lower than the range of the present invention was used. Further, since the SiO ₂ content of the flux is larger than the range of the present invention, the arc becomes unstable and the bead shape is also deteriorated. On the other hand, No. In Comparative Example 62, the arc was unstable because a flux having a composition in which the Ti content was greater than the range of the present invention was used. In addition, No. In Comparative Example No. 62, since a flux having a Mo content larger than the range of the present invention was used, a sigma phase was precipitated and the Charpy absorbed energy was low.

No. In the comparative example No. 63, the flux of the weld metal had a high oxygen content and the Charpy absorbed energy was as low as 50 J or less because the flux having a composition having a Mg content lower than the range of the present invention was used. Furthermore, since the total content of Al ₂ O ₃ and ZrO _{2 in} the flux is larger than the range of the present invention, the slag removability is deteriorated.

  No. Comparative Example No. 64 has a low Charpy absorbed energy because a flux having a composition having a Cu content larger than the range of the present invention was used. Furthermore, since the Mg content of the flux is larger than the range of the present invention, the slag removability is poor.

  No. In Comparative Example No. 65, a flux having a composition in which the total content of Al + Ti + Mg was lower than the range of the present invention was used. Therefore, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. On the other hand, No. In Comparative Example No. 66, the arc was unstable and the slag peeling property was poor because the flux having a composition in which the total content of Al + Ti + Mg was larger than the range of the present invention was used. Further, since the W content of the flux is larger than the range of the present invention, the Charpy absorbed energy is low.

  No. In Comparative Example No. 67, the flux of CaO content was lower than the range of the present invention, so the weld metal had a high oxygen content and a low Charpy absorbed energy of about 50 J. Furthermore, since the Nb content of the flux having the above composition is higher than the range of the present invention, hot cracking occurs. On the other hand, No. Comparative Example No. 68 was produced using a flux having a CaO content larger than the range of the present invention, and although the Charpy absorbed energy was high, the arc was unstable.

  No. Comparative Example No. 69 has a high oxygen content in the weld metal and a low Charpy absorbed energy of 50 J or less because a flux having a composition in which the total of the F values of the fluorine compounds in terms of F is lower than the range of the present invention was used. Further, since the flux filling rate is lower than the range of the present invention, spatter frequently occurs and the arc becomes unstable. On the other hand, No. In Comparative Example No. 70, the arc was unstable and the bead shape was poor because the flux having a composition in which the total of the F conversion values of the fluorine compounds was larger than the range of the present invention was used. In addition, No. The composition of the flux used in the production of Comparative Example No. 70 was such that the sum of the Bi-converted values of the metal Bi and the oxide Bi was larger than the range of the present invention, so that the oxygen content of the weld metal was high and the Charpy absorbed energy was 50 J or less And low.

  No. In Comparative Example 71, the Charpy absorbed energy was low because a flux having a composition having a C content larger than the range of the present invention was used.

No. In Comparative Example No. 72, the Charpy absorbed energy was low because a flux having a composition in which the Ni content was lower than the range of the present invention was used. Furthermore, since the total content of Na ₂ O and K ₂ O in the flux is larger than the range of the present invention, spatter occurs frequently and the arc becomes unstable. On the other hand, No. In the comparative example of No. 73, a hot crack was generated because a flux having a composition in which the Ni content was larger than the range of the present invention was used. Also, since the MgO content of the flux is lower than the range of the present invention, the oxygen content of the weld metal is high, and the Charpy absorbed energy is as low as about 50J.

  No. In Comparative Example No. 74, the Charpy absorbed energy was low due to the use of a flux having a composition having a Cr content larger than the range of the present invention. Further, the MgO content of the flux is more than the range of the present invention, and the arc is unstable.

  No. In Comparative Example No. 75, the arc became unstable and the number of blow holes occurred frequently because a flux having a composition in which the N content was larger than the range of the present invention was used.

  No. In Comparative Example No. 76, since the flux having a composition in which the total of the slag agent components was lower than the range of the present invention was used, the oxygen content of the weld metal was high, and the Charpy absorbed energy was as low as 50 J or less. Also, the bead shape has become worse. Further, since the total of the metal carbonates of the flux is larger than the range of the present invention, the arc is unstable. On the other hand, No. In the comparative example of No. 77, since the total of the slag agent components was larger than the range of the present invention, spatter frequently occurred and the arc became unstable.

  No. In Comparative Example No. 78, since the flux filling rate was larger than the range of the present invention, disconnection occurred during wire production.

No. In the comparative examples 79 to 82, the composition of the flux-cored wire is within the range of the present invention, but the mixing ratio of the CO ₂ gas and the O ₂ gas of the mixed gas used as the shielding gas is outside the range of the present invention. , The arc is unstable.

  From the results of the above examples, by applying a flux-cored wire for stainless steel welding and a shielding gas that satisfies the component content and the flux filling rate in the range of the present invention, the welding metal is maintained while maintaining excellent welding actionability. It has been found that a welded joint capable of reducing the amount of oxygen contained therein and significantly improving the toughness of a weld metal can be manufactured.

  Furthermore, by welding a flux-cored wire for stainless steel welding satisfying the component content and the flux filling rate within the range of the present invention under the conditions of the present invention, excellent welding action can be obtained even in various combinations of base materials. It has been found that it is possible to provide a stainless steel joint in which the amount of oxygen contained in the weld metal is reduced while maintaining the same, and the toughness of the weld metal is significantly improved.

  According to the present invention, in welding austenitic stainless steel and duplex stainless steel, the amount of oxygen contained in the weld metal is reduced while maintaining the tensile properties of the weld metal at the same level as the base metal properties, thereby reducing the weld metal Can be greatly improved, and a welded joint having good toughness can be obtained. Moreover, the present invention is also excellent in welding workability, and the application of the present invention greatly contributes to industrial development.

Claims (12)

A flux-cored wire in which a flux containing an oxide and a fluorine compound is filled inside the steel sheath in an amount of 15 to 25% by mass with respect to the total mass of the wire ,
In mass% based on the total mass of the wire,
The oxide contained in the flux ,
TiO _2: 1.0~3.5%,
SiO ₂ : 0.1 to 2.0%,
CaO: 0.1-1.5%,
MgO: 1.5% or less, and one or two kinds of Al ₂ O ₃ and ZrO ₂ : 0.1% or less in total,
The sum of the F-converted values of the fluorine compounds contained in the flux : 0.01 to 3.0%,
TiO _{2, SiO} 2, _CaO, contained 3.8 to 11.2% of _Al 2 O 3, ZrO ₂ and the MgO the fluorine compound in total,
Further, as a content of the wire component contained in the outer coat and the flux, excluding the oxide and the fluorine compound, the content is expressed as mass% with respect to the total mass of the wire.
Si: 0.1 to 0.7%,
Mn: 0.3-5%,
Al: 0.002 to 1.0%,
Ti: 0.01 to 3.0%,
Mg: 0.001 to 1.0%,
C: 0.06% or less,
Ni: 5 to 16%, and Cr: 16 to 27%,
And Al + Ti + Mg: 0.5 to 3.5% is satisfied;
The balance is a flux-cored wire for welding stainless steel, characterized by Fe and unavoidable impurities. As the oxide, in% by weight relative to total mass of the wire, M gO: Stainless steel welding flux cored wire according to claim 1, characterized in that it comprises 0.1 to 1.5%. Furthermore, one or more metal carbonates of CaCO ₃ , Na ₂ CO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ , and Li ₂ CO _{3 in} a mass% based on the total mass of the wire are added in a total amount of 0.6%. The flux-cored wire for stainless steel welding according to claim 1, wherein the flux-cored wire contains less than 10%. Furthermore, in mass% based on the total mass of the wire,
Mo: 0.01 to 4.5%,
Cu: 0.01-1.5%,
W: 0.01 to 3.0%,
Nb: 0.01 to 1.0%
The flux-cored wire for stainless steel welding according to any one of claims 1 to 3, further comprising one or more selected from the group consisting of: Furthermore, in mass% based on the total mass of the wire,
N: 0.01-0.3%
The flux-cored wire for welding stainless steel according to any one of claims 1 to 4, wherein the flux-cored wire comprises: Furthermore, in mass% based on the total mass of the wire,
One or of the sum of Na ₂ O and _{K 2} O: 0.02 to 0.20%
The flux-cored wire for welding stainless steel according to any one of claims 1 to 5, wherein the flux-cored wire comprises:   The stainless steel for welding according to any one of claims 1 to 6, further comprising a total of 0.01 to 0.15% of a Bi conversion amount in mass% based on the total mass of the wire. Flux-cored wire.   The flux-cored wire for welding stainless steel according to any one of claims 1 to 7, wherein the outer skin has a slit-like shape with no gap.   The flux-cored wire for welding stainless steel according to any one of claims 1 to 7, wherein the outer skin has a shape having a slit-shaped gap. In mass%,
Ni: 0.1 to 11%,
Cr: 18-27%
Containing
A welded joint using a duplex stainless steel having two phases of ferrite and austenite, and a ferrite content of 30 to 70% by volume, as at least one of a plurality of base materials constituting the joint,
The welded joint is obtained by performing gas shielded arc welding on the base material using the flux-cored wire for stainless steel welding according to any one of claims 1 to 9,
A welded joint characterized in that the amount of oxygen in the weld metal of the welded joint is 0.06% or less by mass%. In mass%,
Ni: 5 to 21%,
Cr: 16-27%
Containing
A welded joint using austenitic stainless steel for at least one base material of a plurality of base materials constituting the joint,
The weld metal of the weld joint is obtained by gas-shielding arc welding the base metal using the flux-cored wire for stainless steel welding according to any one of claims 1 to 9,
A gas shielded arc welded joint characterized in that the amount of oxygen in the weld metal of the welded joint is 0.06% or less by mass. A carbon dioxide gas or a mixed gas of Ar and 3 to 30% by volume CO ₂ , using the flux-cored wire for stainless steel welding according to any one of claims 1 to 9 and as a shielding gas, Alternatively, the production method of the welded joint according to claim 10 or 11, characterized in that the gas shielded arc welding using a gas mixture of Ar and 0.2 to 10 volume O _2.