JP6953789B2 - Flux-cored wire for gas shielded arc welding and welding joint manufacturing method - Google Patents

Description

The present invention relates to a flux-cored wire for gas shielded arc welding and a method for manufacturing a welded joint.

Ferritic heat-resistant steels and austenitic heat-resistant steels are well known as high-temperature materials used for heat-resistant and pressure-resistant pipes in thermal power generation boilers and petrochemical refining equipment. Ferritic heat-resistant steel is characterized by containing several% to 12% of Cr and several% of Mo. Since the coefficient of thermal expansion is smaller and cheaper than that of austenitic heat-resistant steel, various ferrite-based heat-resistant steels are used in large quantities depending on the usage environment.

When these ferritic heat-resistant steels are used, they are generally assembled by welding to form a structure. At the time of welding, a welding material for ferritic heat-resistant steel, which has an alloy component similar to that of the base material ferrite-based heat-resistant steel and can form a similar structure, is widely used.

By the way, when welding is performed using these welding materials for ferritic heat-resistant steel, it is widely known that low-temperature welding cracking becomes a problem, for example, as described in Non-Patent Document 1. In order to prevent this, as shown in Non-Patent Document 1, work is taken to preheat the portion to be welded before welding.

Further, in Patent Document 1, in order to prevent low-temperature cracking of high Cr ferrite heat-resistant steel, preheating is performed at 150 to 300 ° C. regardless of welding methods such as shielded metal arc welding, TIG welding, and submerged arc welding. The specific method is shown. Further, in Patent Document 1, in order to prevent low-temperature cracking in welding, the welded portion is heated to a temperature of 150 to 300 ° C. per 25 mm of the base metal thickness before the welded portion is cooled to less than 300 ° C. after the completion of welding. It is stated that heat is required immediately after holding for minutes or more and 2 hours or less.

However, since the preheating operation shown in these documents heats the welded portion to a high temperature, the welding efficiency is significantly impaired and the welding cost is increased. Therefore, it is desired to omit the preheating work or lower the preheating temperature. In addition, it is desirable to omit the heat immediately after welding because it is necessary to heat and maintain the welded portion at a high temperature before the welded portion is cooled after welding.

Regarding the welding material that enables the omission of preheating and immediate heat, for example, Patent Document 2 states that the amount of alloying elements such as C is adjusted, and Cr and Mo are 0.8 to 1.5% and 0, respectively. TIG welding materials containing 4 to 1.2% have been proposed. However, the technique proposed here originally relates to a solid wire used for TIG welding in which low temperature cracking is less likely to be a problem, and cannot be applied to a flux-cored wire whose application range is expanding in recent years.

On the other hand, Patent Document 3 discloses a steel material for welding materials containing 0.1 to 10.0% of Co as an essential element and optionally 0.1 to 3.0% of Mo. In Patent Document 3, it is stated that preheating can be omitted by using a shielded metal arc welding material or a flux-cored wire manufactured by using the above-mentioned steel material for welding material in which Co is indispensable. Further, Patent Document 4 proposes a 490-780 MPa class high-tensile flux-cored wire having improved low-temperature cracking resistance by containing V in the outer skin or flux. However, the welding material proposed in Patent Document 3 is not preferable for industrial use in that it requires the inclusion of expensive Co. In Patent Document 4, no consideration is given to the strength of the weld metal at a high temperature.

Patent Document 5 discloses an epoch-making technique in which the amount of diffusible hydrogen contained in the weld metal is reduced and the low temperature crack resistance is improved by adding a fluoride mainly composed _{of CaF 2} to the flux-containing wire. doing. However, Patent Document 5 does not study the means for ensuring the high temperature strength of the weld metal.

As a result of investigating to solve the above-mentioned problems, the present inventors have managed the amount of flux in the flux in the flux-cored wire within an appropriate range to reduce the amount of diffusible hydrogen in the weld metal. It was found that the amount of reduction can be reduced, the preheating work can be simplified, and that the required high-temperature strength can be achieved at the same time by setting the alloy component of the entire wire within a predetermined range.

As a result, a welded joint having a welded portion having good high temperature strength and low temperature crack resistance was obtained. However, when the above-mentioned flux-cored wire is used for the welding work in which the shield gas is 100% CO _{2 gas, there is a problem that spatter occurs frequently and the workability is remarkably poor.} Since 100% CO ₂ shield gas is _{cheaper than Ar-CO 2} mixed shield gas, _{a flux-cored wire applicable to welding using 100% CO 2} shield gas can reduce the cost of welding work. can. Further, with respect to workability, the flux-cored wire is required to have excellent vertical weldability, specifically, to be able to suppress sagging of the molten portion when applied to vertical welding. A flux-cored wire having excellent vertical weldability can be used in a wide range of welding sites. However, according to the prior art, there has not been provided a welding material for ferritic heat-resistant steel having excellent low-temperature cracking resistance and high-temperature strength, which achieves both suppression of spatter generation amount and improvement of vertical weldability. rice field. In particular, the addition of fluoride, which is the technique for improving the low temperature cracking resistance of Patent Document 5 described above, has a drawback of increasing the amount of spatter generated.

Hyundai Welding Technology System <Volume 14> Welding of heat-resistant steel and heat-resistant materials, Sanpo Publishing Co., Ltd. (1980), P.M. 55-58

Japanese Unexamined Patent Publication No. 8-164481 Japanese Unexamined Patent Publication No. 2002-1579 Japanese Unexamined Patent Publication No. 2006-9070 Japanese Unexamined Patent Publication No. 8-257785 Japanese Unexamined Patent Publication No. 2015-27700

An object of the present invention is to provide a welded metal having excellent low temperature crack resistance and high temperature strength, a flux-containing wire having a small amount of spatter and excellent vertical weldability, and a method for manufacturing a welded joint. It is to be.

The gist of the present invention is as follows.

(1) The flux-containing wire for gas shielded arc welding according to one aspect of the present invention has a steel outer skin filled with flux, and the flux is converted into F with respect to the total mass of the flux-containing wire. A fluoride having a total value of 0.11% or more and less than 2.00%, and a total of 3.50% or more and less than 13.00% by mass% of the total mass of the flux-filled wire, Cr oxide and Ti oxidation. The flux-containing wire contains an oxide containing an substance and iron powder having a mass% of 0% or more and less than 10.0% based on the total mass of the flux-containing wire, and _{the content of CaF 2} contained in the fluoride is the flux-containing wire. The Ti oxide content is 2.50% or more and 8.50% by mass% of the total mass of the flux-welded wire in _{terms of TiO 2.} less than%, the content of Cr oxide is less than 10.00% 0.10% or more by mass% of the terms _{of Cr} 2 _{O 3} to the total mass of the flux cored wire, contained in the oxide The content of Ca oxide is 0% or more and less than 0.20% in terms of CaO equivalent with respect to the total mass of the flux-filled wire, and the fluoride and the chemical components excluding the oxide are the above. C: 0.003 to 0.150%, Si: 0.05 to 2.00%, Mn: 0.4 to 3.5%, P: 0.020% in terms of mass% of the total mass of the flux-containing wire. Hereinafter, S: 0.020% or less, Cr: 0.30 to 13.00%, and Mo: 0.10 to 2.50% are contained, and the balance is composed of Fe and impurities.
(2) In the flux-cored wire for gas shielded arc welding according to (1) above, the flux-cored wire and the chemical components excluding the oxide are further added to the total mass of the flux-welded wire. By mass%, instead of a part of Fe contained in the chemical component, V: 0.50% or less, Nb: 0.50% or less, Ti: 0.500% or less, and Ta: 0.50% or less. It may contain one or more selected from the group consisting of.
(3) In the gas-shielded arc welding flux-containing wire according to (1) or (2) above, the flux-containing wire further comprises the flux-containing wire and the chemical components other than the oxide. Cu: 1.00% or less, Ni: 1.0% or less, Co: 5.000% or less, and B: 0 in place of a part of Fe contained in the chemical component in mass% with respect to the total mass of It may contain one or more selected from the group consisting of .0200% or less.
(4) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (3) above, the flux-cored wire and the chemical components other than the oxide are further added. , W: 4.00% or less may be contained in place of a part of Fe contained in the chemical component in mass% with respect to the total mass of the flux-cored wire.
(5) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (4) above, the flux-cored wire and the chemical components other than the oxide are further added. , Ca: 0.500% or less, REM: 0.0100% or less, Mg: 0.80% or less in place of a part of Fe contained in the chemical component in mass% with respect to the total mass of the flux-cored wire. , And Al: 0.400% or less may be contained.
(6) The flux-containing wire for gas-shielded arc welding according to another aspect of the present invention is a flux-containing wire for gas-shielded arc welding in which a flux is filled inside a steel outer skin, and the flux is the flux. The total F conversion value with respect to the total mass of the welded wire is 0.11% or more and less than 2.00%, and the mass% with respect to the total mass of the flux-filled wire is 3.50% or more and less than 13.00% in total. Oxide containing Cr oxide and Ti oxide, iron powder of 0% or more and less than 10.0% in mass% with respect to the total mass of the flux-filled wire, and mass% with respect to the total mass of the flux-filled wire. _{The flux contains CaCO 3} , Na ₂ CO ₃ , and one or more carbonates selected from the group consisting of _{MgCO 3} , which are 2.00% or less in total, and the content of _{CaF 2 contained in the fluoride is the flux.} It is 0% or more and less than 1.00% in mass% with respect to the total mass of the welded wire, and the content of the Ti oxide is 2.50% or more in mass% in terms of _{TiO 2 with respect to the total mass of the flux-filled wire 8} less than .50%, the content of Cr oxide is at 10.00 less than% 0.10% or more by mass% of the terms _{of Cr} 2 _{O 3} to the total weight of the flux-cored wire, the oxide The content of the Ca oxide contained is 0% or more and less than 0.20% in terms of CaO equivalent with respect to the total mass of the flux-filled wire, and further, the fluoride, the oxide, and the carbonate are added. The chemical components to be excluded are C: 0.003 to 0.150%, Si: 0.05 to 2.00%, Mn: 0.4 to 3.5%, in mass% with respect to the total mass of the flux-filled wire. It contains P: 0.020% or less, S: 0.020% or less, Cr: 0.30 to 13.00%, and Mo: 0.10 to 2.50%, and the balance consists of Fe and impurities. ..
(7) In the flux-welded wire for gas shielded arc welding according to (6) above, the flux-containing wire further comprises the chemical components other than the fluoride, the oxide, and the carbonate of the flux-welded wire. V: 0.50% or less, Nb: 0.50% or less, Ti: 0.500% or less, and Ta: 0 in place of a part of Fe contained in the chemical component in mass% with respect to the total mass of It may contain one or more selected from the group consisting of .50% or less.
(8) In the flux-welded wire for gas shielded arc welding according to (6) or (7) above, the chemical component excluding the fluoride, the oxide, and the carbonate of the flux-welded wire is further contained. Cu: 1.00% or less, Ni: 1.0% or less, Co: 5.000% or less, in place of a part of Fe contained in the chemical component, in mass% with respect to the total mass of the flux-containing wire. And B: One or more selected from the group consisting of 0.0200% or less may be contained.
(9) The flux-cored wire for gas shielded arc welding according to any one of (6) to (8) above further excludes the flux, the oxide, and the carbonate of the flux-welded wire. The chemical component may contain W: 4.00% or less in place of a part of Fe contained in the chemical component in mass% with respect to the total mass of the flux-cored wire.
(10) The flux-containing wire for gas shielded arc welding according to any one of (6) to (9) above further excludes the fluoride, the oxide, and the carbonate of the flux-welded wire. The chemical component is Ca: 0.500% or less, REM: 0.0100% or less, Mg: 0, in place of a part of Fe contained in the chemical component, in mass% with respect to the total mass of the flux-filled wire. It may contain one or more selected from the group consisting of .80% or less and Al: 0.400% or less.
(11) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (10) above, the fluoride is CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , NaF, and K _2. It may be one or more selected from the group consisting of ZrF ₆ , and the X value calculated by Equation 1 may be 3.00% or less.
X = [Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ] + 1.5 x ([K ₂ ZrF ₆ ]) + 3.5 x ([CaF ₂ ]) ... (Equation 1)
However, the chemical formula in parentheses described in the formula 1 represents the content of the fluoride according to the chemical formula in mass% with respect to the total mass of the flux-cored wire, and the content of the fluoride not contained. Is considered to be 0%.
(12) In the flux-containing wire for gas shielded arc welding according to any one of (1) to (11) above, the oxide is the Cr oxide, the Ti oxide, and Fe oxide, Ba. One or more selected from the group consisting of oxides, Na oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, K oxides, and Ca oxides, and the Cr oxidation. Product, said Ti oxide, said Fe oxide, said Ba oxide, said Na oxide, said Si oxide, said Zr oxide, said Mg oxide, said Al oxide, said Mn oxide, said K oxidation things, and the total content of the Ca oxide, relative to the total weight of the flux-cored _{wire, Cr 2 O 3, TiO 2} , FeO, BaO, Na 2 O, SiO 2, ZrO 2, MgO, Al 2 The converted values of O ₃ , MnO ₂ , K ₂ O, and Ca O are 3.50% or more and less than 13.00%, and the V value calculated by Equation 2 is 5.00 or more and 27.00 or less. You may.
V = ([TiO ₂ ] + 1.2 × [SiO ₂ ] + 1.4 × [Al ₂ O ₃ ] + 1.5 × [ZrO ₂ ]) / (F) ^1/2 : Equation 2
However, regarding the chemical formulas in parentheses described in the above formula 2 , [TiO ₂ ] is the TiO ₂ conversion value of the Ti oxide, [SiO ₂ ] is the SiO ₂ conversion value of the Si oxide, and [Al ₂ O ₃ ]. _{Is the Al 2} O ₃ conversion value of the Al oxide , [ZrO ₂ ] is the ZrO ₂ conversion value, and represents the content of the flux-cored wire in mass% with respect to the total mass. Refers to the total of the F-converted values of the flux with respect to the total mass of the flux-cored wire, and the content of the oxide not contained is regarded as 0%.
(13) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (12) above, the steel outer skin may have a slit-like shape without gaps.
(14) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (12) above, the steel outer skin may have a slit-like gap.
(15) The flux-cored wire for gas shielded arc welding according to any one of (1) to (14) above may have perfluoropolyether oil on the surface of the steel outer skin.
(16) In the method for manufacturing a welded joint according to another aspect of the present invention, a steel material is welded using the flux-cored wire for gas shielded arc welding according to any one of (1) to (15) above. ..

INDUSTRIAL APPLICABILITY According to the present invention, a weld metal having excellent high-temperature strength can be obtained, low-temperature cracking resistance is excellent, the amount of spatter generated is small, and a flux-cored wire and a welded joint for gas shielded arc welding are excellent. Manufacturing method can be provided. In particular, the present invention has low temperature crack resistance even when applied to welding of ferritic heat-resistant steel used for members requiring high temperature strength and welding in which the shield gas is 100% CO _2. It is possible to provide a method for manufacturing a flux-filled wire for gas shielded arc welding and a welded joint, which are excellent, have less spatter generation, are excellent in vertical weldability, and can be welded with high welding efficiency.

It is a graph which shows the relationship between the X value and the spatter amount. It is a photograph of the cross section of (a) a wire made by butt-welding the edge surfaces, (b) a wire made by butt-butting the edge surfaces, and (c) a wire made by caulking the edge surfaces. It is a photograph exemplifying a welded part which is judged as "no dripping" in a general vertical welding workability evaluation test. It is a photograph exemplifying a welded portion which is judged as "there is sagging" in a general vertical welding workability evaluation test.

The present inventors conducted experiments by changing the amounts of various slag components in a flux-cored wire for gas shielded arc welding, which requires high-temperature strength. As a result, the present inventors can improve low-temperature cracking, which is a problem when a steel material is welded using a flux-cored wire containing 0.3 to 13.0% of Cr, and the shield gas can be used. We have found the types and amounts of flux and oxides that can suppress the amount of spatter generated even when used for welding, which is 100% CO _{2 gas.}

The present invention has been made as a result of the above studies. Hereinafter, the flux-cored wire according to the present embodiment will be described separately for the slag component and the alloy component. Unless otherwise specified, the content of the component in the description of the flux-cored wire represents mass% with respect to the total mass of the flux-cored wire.

The flux-cored wire for gas shielded arc welding according to the present embodiment has a steel outer skin and a flux wrapped in the steel outer skin. The flux filled inside the steel outer skin contains a slag component such as a fluoride, an oxide, and an optionally contained carbonate, and an alloy component such as a metal powder and an alloy powder. In addition, the flux may contain iron powder for adjusting the filling rate. First, the slag component inserted inside the steel outer skin of the wire will be described.

(Total F conversion value of fluoride with respect to the total mass of flux-cored wire: 0.11% or more and less than 2.00%)
(Type of fluoride: preferably one or more selected from the group consisting _{of CaF 2} , MgF ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF ₆₎
The flux-cored wire according to the present embodiment contains fluoride in an F-converted value (hereinafter, may be simply referred to as “F-converted value”) of 0.11% or more with respect to the total mass of the flux-cored wire. The F conversion value with respect to the total mass of the flux-cored wire indicates the amount of fluorine (F) contained in the fluoride in mass% with respect to the total mass of the flux-cored wire. _{For example, when CaF 2} of n% by mass with respect to the total mass of the flux-cored wire is contained in the flux-cored wire, _{the F conversion value of CaF 2} is obtained by the following formula A.
( _{F conversion value of CaF 2} ) = n × (19.00 × 2 / 78.08) ... (Equation A)
In the above formula A, "19.00" is the atomic weight of F, "2" is the number of F atoms contained in _{one CaF 2} , and "78.08" is the molecular weight of _{CaF 2.} Is. For _{fluorides other than CaF 2} , the F conversion value can be calculated in the same manner. When a plurality of types of fluorides are contained in the flux, the total value of the F-converted values of each fluoride is regarded as the F-converted value of the fluorides contained in the flux. The type of fluoride is not particularly limited, but may be one or more selected from the group consisting of _{, for example, CaF 2} , MgF ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF _6.

Fluoride can reduce the amount of diffusible hydrogen in the weld metal. If the total F conversion value of the fluoride is less than 0.11%, the amount of diffusible hydrogen in the weld metal can be stably reduced, and the low temperature crack resistance cannot be satisfied. In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the total F conversion value of the fluoride is 0.14%, 0.20%, 0.30%, 0.40%, or 0.50%. May be.

On the other hand, if the fluoride content is excessive, the amount of spatter during welding increases. Further, when the fluoride content is excessive, the arc force is increased and the molten metal is compressed, which may deteriorate the vertical weldability. Therefore, it is necessary that the total amount of the F-converted values of fluoride is less than 2.00%. The upper limit of the total amount of F-converted values of fluoride may be 1.95%, 1.90%, 1.70%, or 1.35%.

The reason why fluoride reduces the amount of diffusible hydrogen is not always clear, but it is either that the fluoride is decomposed by the welding arc and the generated fluorine is combined with hydrogen and diffused into the atmosphere as HF gas. It is believed that this is because hydrogen was fixed as HF in the weld metal as it was. Further, it is not always clear why the amount of spatter generated differs depending on the type of fluoride, but the present inventors have found that the metal element chemically bonded to the fluoride affects spatter generation for some reason. I'm guessing.

(CaF ₂ : 0% or more and less than 1.00% by mass with respect to the total mass of the flux-cored wire)
CaF ₂ causes more spatter in gas shielded arc welding using 100% CO ₂ gas than MgF ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF _6. Therefore, it is preferable that the flux-cored wire according to the present embodiment _{does not contain CaF 2. However, CaF 2} may be contained in the raw material of the flux. In that case, the CaF ₂ content is limited to less than 1.00%. If the CaF ₂ content is limited to less than 1.00%, the sputter amount will be within an acceptable range. In order to further reduce the amount of spatter generated, _{the upper limit of the CaF 2} content may be 0.75% or 0.50%. Since the flux cored wire according to the present embodiment does not require the CaF _2, the lower limit of the content of CaF ₂ is 0%.

(X value: preferably 3.00% or less)
As mentioned above _{, CaF 2} increases spatter in gas shielded arc welding in which the shield gas is 100% CO _{2 gas.} Furthermore, the present inventors have created a large number of 1.2 mmφ wires containing various fluorides, having no slit-like gaps in the steel outer skin, and having vegetable oil applied to the steel outer skin. The spatter characteristics were investigated. Welding current 280A, voltage 27V, welding speed 25cm / min, shield gas type 100% CO ₂ , shield gas flow rate 25l / min, and no preheating conditions in a copper collection box on a steel plate with a bead-on plate. Then, a weld bead was prepared for 1 minute using the various flux-cored wires described above. Spatter scattered in the box and spatter adhering to the steel sheet during the preparation of the weld bead were collected, and the total weight of those having a diameter of more than 1.0 mm was measured. As a result of multiple analysis of the data on the amount of spatter generated, the type of fluoride, and the content of each fluoride, the good value shown in FIG. 1 is between the X value calculated using Equation B and the amount of spatter generated. It was found to be correlated.
X = [Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ] + 1.5 x ([K ₂ ZrF ₆ ]) + 3.5 x ([CaF ₂ ]) ... (Formula B)
In the formula B, the chemical formula in parentheses represents the content of the compound (fluoride) according to the chemical formula in mass% with respect to the total mass of the flux-cored wire. The content of fluoride not contained in the flux is 0. By setting the X value defined by the formula B to 3.00% or less, the amount of sputtering when welding is performed under the above conditions can be further suppressed to 5.00 g / min or less, and various conditions can be obtained. It was found that the amount of spatter can be surely suppressed within a range where there is no problem even if welding is performed in. Therefore, in the flux-cored wire according to the present embodiment, the X value is preferably 3.00% or less. A more preferable upper limit of the X value is 2.80%, 2.50%, or 2.20%. In the flux-cored wire according to the present embodiment, it is not necessary to set the lower limit of the X value of the fluoride. This is because the lower limit of the fluoride content is defined by using the F conversion value described above.

(Total oxides: 3.50% or more and less than 13.00% of the total mass of the flux-cored wire)
(Types of oxides: Cr oxides and Ti oxides, and preferably Fe oxides, Ba oxides, Na oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, K One or more selected from the group consisting of oxides and Ca oxides)
The flux-cored wire according to the present embodiment contains an oxide. This oxide contains Cr oxide and Ti oxide, preferably Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide and K. It further comprises one or more selected from the group consisting of oxides and Ca oxides. The flux-cored wire according to the present embodiment contains 3.50% or more and less than 13.00% of these oxides in total.

The oxide can improve the shape of the weld bead. If the total oxide content is less than 3.50%, the shape of the weld bead may deteriorate. In order to further improve the shape of the weld bead, the lower limit of the total oxide content may be 3.80% or 4.00%. Further, when the total content of oxides is 13.00% or more, the toughness of the welded portion may be lowered. In order to improve the toughness of the welded portion, the upper limit of the total oxide content may be 12.00%, 11.50%, or 11.00%.

(Cr oxide content: 0.10% or more and less than 10.00% in terms of mass% of _{Cr 2} O _{3 with} respect to the total mass of the flux-cored wire)
In addition to the above-mentioned effects, the Cr oxide has an effect of suppressing spatter generation and improving welding workability. In the prior art, there is no example of a flux-cored wire using Cr oxide as a slag forming agent, and there is no example of examining the relationship between the amount of Cr oxide and the amount of spatter generated. As a result of an original experimental investigation, it was found that the amount of spatter generated can be suppressed by containing 0.10% or more of Cr oxide in mass% in terms of _{Cr 2} O _{3 in the flux.} Accordingly, the content of Cr oxides in the flux-cored wire according to the present embodiment, the total mass of the flux cored wire, is 0.10% or more by mass% of the terms of Cr ₂ O _3.

On the other hand, if the Cr oxide is excessive, the toughness of the welded portion may be impaired. This is because a part of the excess Cr oxide is not discharged as slag to the outside of the welded portion, but is dissolved as an alloying element in the welded portion, so that the Cr concentration of the welded portion is excessively increased. Is considered to be. Conventionally, it has been known that Cr oxide may cause embrittlement of welded parts. Therefore, the use of Cr oxide as a slag forming agent has been avoided in the prior art. On the other hand, when it is necessary to improve the Cr concentration of the welded portion, Cr has been added as an alloy component of metal powder, alloy powder, plating, or steel outer skin instead of oxide in the prior art. In the flux wire according to the present embodiment, the toughness of the welded portion is improved by other feature points, so that the Cr oxide content is the mass% in terms of _{Cr 2} O _{3 with respect to the total mass of the flux-cored wire.} Although it is permissible to make the content less than 10.00%, it is not preferable to contain more than 10.00%. The upper limit of the content of Cr oxides 9.50% by weight percent terms _{of Cr} 2 _{O 3} with respect to the total mass of the flux cored wire, 9.00%, 8.00%, or as 4.50% May be good.

The Cr oxide includes chromium (II) oxide: CrO, chromium (III) oxide: Cr ₂ O ₃ , chromium (IV) oxide: CrO ₂ , and chromium (VI) oxide: CrO ₃ . Since all of these have the same effect in the flux-cored wire according to the present embodiment, the type of Cr oxide is not particularly limited, and any one of these may be used alone or in combination. However, it is preferable that the most stable oxide, chromium (III) oxide: Cr ₂ O ₃ , is the main component of the Cr oxide. The content of Cr oxides described above, _Cr 2 _{O 3} in terms of value, i.e., at a content by mass percent of _Cr 2 _{O 3} when Cr contained in Cr oxides are all _Cr 2 _{O 3} be. Oxides other than Cr oxides, namely Ti oxides, Fe oxides, Ba oxides, Na oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, K oxides, and Similarly, the contents of each Ca oxide are also converted to _{TiO 2} , Cr ₂ O ₃ , FeO, BaO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , and K _{2 O.} May be. When an oxide of a metal other than these is contained in the flux-cored wire, the content thereof may be converted into the content of the most stable oxide of the metal.

(Ti oxide: 2.50% or more and less than 8.50% in terms of mass% of _{TIO 2 with} respect to the total mass of the flux-cored wire)
The flux of the flux-cored wire according to the present embodiment contains a Ti oxide of 2.50% or more and less than 8.50% in terms of mass% of _{the total mass of the flux-cored wire in terms of TiO 2.} Ti oxide mainly acts as a slag forming agent. Further, since the Ti oxide has a function of lowering the melting point of the slag and improving the viscosity of the molten slag, it suppresses the dripping of the molten slag and improves the vertical weldability. When vertical improvement welding is performed using a flux-cored wire having a Ti oxide content of less than 2.50%, the above-mentioned effects cannot be sufficiently obtained, so that vertical weldability cannot be ensured. Therefore, the lower limit of the content of Ti oxide is set to 2.50% in terms of mass% of _{TiO 2 with respect to the total mass of the flux-cored wire. The lower limit of the Ti oxide content in mass% in terms of TIO 2 with} respect to the total mass of the flux-cored wire is more preferably 2.70%, and in order to further improve the vertical weldability, 3. It may be 00%, 3.20%, 3.50%, or 4.00%.

_{On the other hand, a Ti oxide having a mass% of 8.50% or more in terms of TiO 2 with} respect to the total mass of the flux-cored wire excessively increases the amount of slag, and thus increases the defects of slag entrainment. Further, when the Ti oxide is excessive, the oxygen content of the weld metal becomes high and the toughness of the welded portion may be impaired. Therefore, the content of Ti oxide is set to less than 8.50% in terms of mass% of _{TiO 2 with} respect to the total mass of the flux-cored wire. The upper limit of the content of Ti oxide in mass% in terms of _{TIO 2 with} respect to the total mass of the flux-cored wire is more preferably 7.00%, and if necessary, 6.70% and 6.40. %, 6.20%, 6.00%, 5.90%, or 5.80%.

(Ca oxide: 0% or more and less than 0.20% in terms of mass% of CaO equivalent to the total mass of the flux-cored wire)
Ca oxide causes a lot of spatter in shielded arc welding using 100% CO _{2 gas.} When the flux-containing wire contains 0.20% or more of Ca oxide in terms of CaO equivalent to the total mass of the flux-containing wire, it becomes difficult to apply it to shielded arc welding using _{100% CO 2 gas.} .. Therefore, the content of Ca oxide is set to less than 0.20% in terms of mass% of CaO with respect to the total mass of the flux-cored wire. The upper limit of the Ca oxide content may be 0.10% in terms of mass% of CaO with respect to the total mass of the flux-cored wire. On the other hand, since Ca oxide is unnecessary for the flux-cored wire according to the present embodiment, the lower limit of the Ca oxide content is 0%.

Examples of the above-mentioned oxides, that is, Cr oxide, Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K. In addition to oxides and Ca oxides, oxides contained in binders used for granulating flux may be contained in the flux-containing wire. Therefore, the "total value of the oxide content" includes not only the total amount of these oxides but also the content of the oxide contained in the binder or the like used for granulating the flux.

(V value: preferably 5.00 or more and 27.00 or less)
In the flux wire according to the present embodiment, the V value calculated by the following formula C is preferably 5.00 or more and 27.00 or less.
V = ([TiO ₂ ] + 1.2 × [SiO ₂ ] + 1.4 × [Al ₂ O ₃ ] + 1.5 × [ZrO ₂ ]) / (F) ^1/2 …… Equation C
The compound corresponding to each chemical formula enclosed in square brackets in the above formula C indicates the content of each compound in mass% with respect to the total mass of the flux-cored wire, and corresponds to each oxide as described above. The content in the converted value is shown. F indicates the total content of fluoride in terms of F. Among the oxides, the present inventors have Ti oxide (TiO ₂ conversion value), Si oxide (SiO ₂ conversion value), Al oxide (Al ₂ O ₃ conversion value), and Zr oxide (ZrO ₂ conversion value). It was found that the relationship between the amount of value) and the amount of fluoride should be within an appropriate range. When welding is performed using a flux-cored wire in which the amount of Ti oxide, Si oxide, Al oxide, and Zr oxide is too large with respect to the amount of fluoride, that is, the V value is more than 27.00. The present inventors have found that slag entrainment is likely to occur because the amount of oxide-based slag having a high melting point increases. On the other hand, welding is performed using a flux-cored wire in which the amounts of Ti oxide, Si oxide, Al oxide, and Zr oxide are too small with respect to the amount of fluoride, that is, the V value is less than 5.00. In this case, the present inventors have found that the arc force is increased by the flux, the molten metal is compressed, and the bead shape is likely to be deteriorated and the vertical weldability is likely to be deteriorated. Therefore, the V value of the flux-cored wire according to the present embodiment is preferably 5.00 to 27.00. The lower limit of the V value is more preferably 7.00, 9.00, 10.00, 11.00, or 12.00. The upper limit of the V value is more preferably 25.00, 22.50, 20.00, 18.00, 16.00 or 15.00.

( _{Total content of one or more carbonates selected from the group consisting of CaCO 3} , Na ₂ CO ₃ , and MgCO ₃ :% by mass, preferably 2.00% or less, based on the total mass of the flux-filled wire)
The flux-cored wire according to this embodiment does not need to contain carbonate. Therefore, the lower limit of the carbonate content is 0%. However, it is preferable that the flux-containing wire according to the present embodiment further contains 2.00% or less of one or more carbonates selected from the group consisting of _{MgCO 3} , Na ₂ CO ₃ , and CaCO _{3 in total.} ..

Carbonate is ionized by an arc to generate _{CO 2 gas. The CO 2} gas generated from the carbonate lowers the partial pressure of hydrogen and reduces the amount of diffusible hydrogen in the weld metal. When a carbonate is contained in the flux-filled wire in order to obtain this effect, the total content of the carbonate is preferably more than 0% or 0.30% or more. In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the total carbonate content may be 0.10%, 0.50% or 1.00%. Further, if the total content of carbonates exceeds 2.00%, welding fume may be excessively generated. In order to avoid the generation of weld fume, the upper limit of the total carbonate content may be 1.80%, 1.50%, 1.30%, or 0.75%.

Next, the steel outer skin constituting the flux-cored wire according to the present embodiment, the alloy component and the metal deoxidizing component contained in the flux will be described. In the flux-containing wire according to the present embodiment, the alloy component and the metal deoxidizing component are components that do not constitute fluoride, oxide, and carbonate (chemical components excluding fluoride, oxide, and carbonate). Is. The alloy component may be contained in the flux in the form of a metal powder or an alloy powder, contained in a steel outer skin, or plated on a steel outer skin.

(C: 0.003 to 0.150%)
C is an essential additive element because it forms carbides, contributes to ensuring the high temperature strength of the weld metal, and is effective in obtaining bainite and martensite structures, and is in the range of 0.150% or less. It is contained in the flux-containing wire according to the present embodiment. When the C content of the alloy component exceeds 0.150%, the weld metal is excessively hardened, which is not preferable for the toughness of the weld metal. The upper limit of the C content may be 0.090%, 0.080%, or 0.070%. From the viewpoint of joint strength and decarburization cost during steel production, the lower limit of C content is set to 0.003%. The lower limit of the C content may be 0.015% or 0.020%.

(Si: 0.05 to 2.00%)
Si is a deoxidizing element. The flux-cored wire according to the present embodiment needs to contain 0.05% or more of Si in order to reduce the amount of O in the weld metal and improve the cleanliness. However, if Si is contained in excess of 2.00%, the creep ductility and toughness of the weld metal are lowered. Therefore, the Si content is set to 0.05 to 2.00%. Further, in order to stably secure the toughness of the weld metal, the lower limit of the Si content may be 0.10%, 0.20%, or 0.21%. The upper limit of the Si content may be 1.80%, 1.60% or 1.40%.

(Mn: 0.4 to 3.5%)
Mn is an element that secures the hardenability of the weld metal and enhances the strength, and is contained in the flux-containing wire according to the present embodiment in a range of 3.5% or less depending on the required strength of the weld metal. If Mn is contained in excess of 3.5%, the grain boundary embrittlement sensitivity of the weld metal increases and the toughness of the weld metal deteriorates. However, Mn also has the effect of immobilizing S as MnS and preventing the occurrence of high temperature cracks. In order to obtain this effect, it is desirable to set the lower limit of the Mn content to 0.4%. The lower limit of the Mn content may be 0.6%, 0.8%, 0.9%, or 1.0%. The upper limit of the Mn content may be 3.4%, 3.3%, or 3.2%.

(P: 0.020% or less)
Since P is an impurity element and inhibits the toughness of the weld metal, it is necessary to reduce it as much as possible. However, the P content is 0.020% or less within an allowable range of adverse effects on the toughness. The upper limit of P may be limited to 0.015% for further improvement of toughness.

(S: 0.020% or less)
S is also an impurity element, and if it is present in an excessive amount, both the toughness and ductility of the weld metal are deteriorated, so it is preferable to reduce it as much as possible. The S content shall be 0.020% or less within an acceptable range for adverse effects on the toughness and ductility of the weld metal. The upper limit of S may be limited to 0.010% in order to further improve the toughness of the weld metal.

(Cr: 0.30 to 13.00%)
Cr is an essential element for ensuring oxidation resistance and high-temperature corrosion resistance in heat-resistant steel, and for stably obtaining the bainite and martensite structures of the weld metal matrix. In order to obtain the effect, it is necessary to contain 0.30% or more. However, if Cr is excessively contained, the stability of the carbide is lowered due to the formation of a large amount of Cr carbide during use at a high temperature, the creep strength of the weld metal is lowered, and the toughness of the weld metal is also deteriorated. Therefore, the Cr content needs to be 13.000% or less. The desired range of Cr content is 0.50 to 12.50%, and the more desirable range is 1.00 to 12.00% or 2.15 to 11.00%.

(Mo: 0.10 to 2.50%)
Mo is an element that solid-solves and strengthens the weld metal matrix and contributes to the improvement of creep strength. In order to obtain this effect, the flux-cored wire according to the present embodiment needs to contain 0.10% or more of Mo. However, if Mo is contained in an amount of more than 2.50%, the effect is saturated and coarse carbides are generated, resulting in a decrease in the toughness of the weld metal. The desirable range of Mo content is 0.30 to 2.20%, and the more desirable range is 0.50 to 2.00%.

The flux-containing wire according to the present embodiment has V, Nb, Ti as an alloy component or a metal deoxidizing component, in addition to the above basic components, depending on the strength level of the steel material to be welded and the required degree of toughness of the welded portion. , Ta, Cu, Ni, Co, B, W, Ca, REM, Mg, and Al. Can be contained. However, even when these elements are not contained, the flux-cored wire according to the present embodiment can solve the problem, so the lower limit of the content of these elements is 0%.

(V: 0.50% or less, Nb: 0.50% or less, Ti: 0.500% or less, Ta: 0.50% or less)
The flux-cored wire according to the present embodiment is one or more selected from the group consisting of V: 0.50% or less, Nb: 0.50% or less, Ti: 0.500% or less, and Ta: 0.50% or less. May be optionally contained. All of these combine with carbon and nitrogen during use at high temperatures and precipitate as carbonitrides, which contributes to the creep strength of the weld metal. Therefore, even if the flux-filled wire according to the present embodiment contains these elements. good. However, if these elements are excessively contained, a large amount of the above-mentioned carbonitride is precipitated, which causes a decrease in the toughness of the weld metal. Therefore, when the flux-cored wire contains these elements, the upper limit of any of the elements is within the above range. The content of each of these elements is preferably 0.40% or less, more preferably 0.30% or less. Further, in order to stably obtain the effects of these elements, it is desirable to contain each of these elements in an amount of more than 0.015%, 0.02% or more, 0.03% or more, and further 0.04% or more.

(Cu: 1.00% or less, Ni: 1.0% or less, Co: 5.0000% or less, B: 0.0200% or less)
The flux-cored wire according to the present embodiment is one or more selected from the group consisting of Cu: 1.00% or less, Ni: 1.0% or less, Co: 5.0000% or less, and B: 0.0200% or less. May be contained. Since all of these are elements effective for enhancing the hardenability of the weld metal and obtaining a bainite structure or a martensite structure, the flux-filled wire according to the present embodiment may contain these elements. However, when these elements are excessively contained, the creep ductility of the weld metal is lowered. Therefore, when the flux-cored wire contains these elements, the upper limit is 1.00% for Cu, 1.0% for Ni, 5.000% for Co, and 0.0200% for B. Desirably, Cu and Ni are 0.80% or less, Co is 4.55000% or less, and B is 0.0180% or less. More preferably, Cu and Ni are 0.60% or less, Co is 4.00% or less, and B is 0.0150% or less. Further, in order to stably obtain these effects, it is desirable that Cu, Ni and Co are 0.1% or more, B is 0.0005% or more, and Cu, Ni and Co are 0.2. It is desirable that% or more and B be 0.001% or more.

(W: 4.0000% or less)
Since W is an element that solid-solves and strengthens the matrix of the weld metal and contributes to the improvement of creep strength, the flux-cored wire according to the present embodiment may contain W. However, when W is excessively contained, W produces a coarse intermetallic compound, which causes a decrease in the toughness of the weld metal. Therefore, when W is contained, the upper limit is 4.0000%. The W content is preferably 3.8000% or less, and more preferably 3.55000% or less. Further, in order to obtain a stable effect, it is desirable that W is contained in an amount of 0.1000% or more, more preferably 0.2000% or more.

(Mg: 0.80% or less, Ca: 0.500% or less, REM: 0.0100% or less, Al: 0.400% or less)
Mg is a strongly deoxidizing element, which reduces the amount of O in the weld metal and improves the ductility and toughness of the weld metal. When it is contained in order to obtain this effect, it is preferable to contain 0.10% or more of Mg. However, if the Mg content in the flux-cored wire exceeds 0.80%, Mg forms a coarse oxide in the weld metal, resulting in a non-negligible level of toughness reduction. Further, if the Mg content in the flux-cored wire exceeds 0.80%, the stability of the arc during welding deteriorates, which also causes the bead shape to deteriorate. Therefore, when Mg is contained, the content thereof is set to 0.80% or less.

Both Ca and REM are effective in improving the ductility and toughness of the weld metal by changing the structure of the sulfide in the weld metal and reducing the size of the sulfide and oxide in the weld metal. When it is contained in order to obtain the effect, the Ca content may be 0.100% or more, and the REM content may be 0.0020% or more. On the other hand, excessive content of Ca and REM causes coarsening of sulfides and oxides, resulting in deterioration of ductility and toughness of the weld metal. Further, if Ca and REM are excessively contained, there is a possibility that the shape of the weld bead is deteriorated and the weldability is deteriorated. Therefore, the upper limit of the Ca content is 0.500%, and the upper limit of the REM content is 0.0100%. The term "REM" refers to a total of 17 elements composed of Sc, Y and lanthanoids, and the above-mentioned "content of REM" means the total content of these 17 elements.

Al is a deoxidizing element, and like Si, it has the effect of reducing the amount of O in the weld metal and improving the cleanliness of the weld metal. When it is contained in order to exert its effect, it is preferable to contain 0.001% or more of Al. On the other hand, when Al is contained in excess of 0.400%, Al forms Al nitrides and Al oxides, and inhibits the toughness of the weld metal. Therefore, the Al content is set to 0.400% or less. Further, in order to sufficiently obtain the effect of improving the toughness of the weld metal, the lower limit of the Al content may be set to 0.004%, and the upper limit of the Al content may be set to suppress the formation of coarse oxides. , 0.200%, 0.100% or 0.080%.

The content of the elements contained as the above alloy component or metal deoxidizing component does not include the content when those elements are contained as a fluoride, an oxide, or a carbonate. Further, these elements do not necessarily have to be pure substances, and there is no problem even if they are contained in the form of an alloy such as Cu—Ni. Further, these elements may be contained in either the steel outer skin or the flux because the effect is the same regardless of whether they are contained in the steel outer skin or as a flux.

(Iron powder: 0% or more and less than 10.0%)
Iron powder (Fe powder) may be contained as necessary for adjusting the flux filling rate in the flux-cored wire or for improving the welding efficiency. However, since the surface layer of the iron powder is oxidized, if the flux contains an excessive amount of the iron powder, the oxygen content of the weld metal may be increased and the toughness may be lowered. Therefore, iron powder does not have to be contained. When iron powder is contained for adjusting the filling rate, the iron powder content is set to less than 10.0% in order to ensure the toughness of the weld metal. The upper limit of the iron powder content may be 5.0%, 3.0%, 2.0%, or 1.7%. On the other hand, since iron powder is not essential for solving the problem of the flux-cored wire according to the present embodiment, the lower limit of the iron powder content is 0%.

The above is the reason for limitation regarding the component composition of the flux-cored wire according to the present embodiment, but the other remaining components are Fe and impurities. Fe is contained in the iron powder described above, but as other Fe components, Fe in the steel outer skin and Fe in the alloy component added to the flux are contained in the flux-containing wire. The impurity is a component mixed by a raw material such as ore or scrap, or various factors in the manufacturing process when the flux and the steel outer skin are industrially manufactured, and is a wire containing flux according to the present embodiment. It means that it is acceptable as long as it does not adversely affect the characteristics of.

Subsequently, the form of the flux-cored wire will be described.
FIG. 2 shows the cut surface of the flux-cored wire. FIG. 2 (a) shows an example of a flux-cored wire made by butt-welding the edge surfaces, FIG. 2 (b) shows an example of a flux-cored wire made by butt-butting the edge surfaces, and FIG. 2 (c). An example of a flux-cored wire made by caulking the edge surface is shown below. As described above, the flux-cored wire includes a wire having no slit-shaped gap in the steel outer skin as shown in FIG. 2 (a) and a slit in the steel outer skin as shown in FIGS. 2 (b) and 2 (c). It can be roughly divided into wires having a similar gap. Any cross-sectional structure can be adopted for the flux-cored wire according to the present embodiment, but in order to suppress low-temperature cracking of the weld metal, a wire having no slit-shaped gap (also referred to as a seamless wire) should be used. Is preferable.

Hydrogen that invades the welded portion during welding diffuses into the weld metal and the steel material side, accumulates in the stress concentration portion, and causes low-temperature cracking. This hydrogen source includes moisture contained in the welding material, moisture mixed from the atmosphere, rust and scale adhering to the steel surface, and the like. Under welds where the cleanliness of the weld and the conditions of the gas shield are well controlled, the water hydrogen contained in the wire is the main source of diffusible hydrogen in the weld joint.

For this reason, it is desirable to use a steel outer skin as a pipe without slit-shaped gaps and suppress the invasion of hydrogen in the atmosphere from the steel outer skin into the flux from the time when the wire is manufactured until the time when it is used. When the steel outer skin is made of a tube having slit-shaped gaps (seam), moisture in the atmosphere easily invades into the flux through the slit-shaped gaps in the outer skin, so that hydrogen sources such as moisture do not enter. It cannot be prevented. If the steel crust has slits and has a long time to use after manufacture, it is desirable to vacuum package the entire wire or store it in a container that can keep the wire dry.

Further, in order to improve the feedability of the flux-cored wire, lubricating oil may be applied to the surface of the flux-cored wire. That is, the flux-cored wire according to the present embodiment may further be provided with lubricating oil on the surface of the steel outer skin. The lubricating oil applied to the surface of the wire is not particularly limited, and may be, for example, vegetable oil. In order to reduce diffusible hydrogen, the lubricating oil is preferably a hydrogen-free oil such as perfluoropolyether oil (PFPE).

The flux-cored wire according to the present embodiment can be manufactured by the same manufacturing process as the usual method for manufacturing a flux-cored wire. That is, first, a steel strip to be an exodermis and a flux in which a flux, an alloy component, an oxide, a carbonate and the like are blended so as to have a predetermined content are prepared. The steel strip is formed into an open pipe (U-shape) by a forming roll while being fed in the longitudinal direction to form a steel outer skin. During this molding, flux is supplied from the opening of the open tube. The opposing edge surfaces of the openings are butted and a slit-shaped gap is welded. The welding method is, for example, electric sewing welding, laser welding, TIG welding, or the like. A slit-shaped gapless tube obtained by welding is drawn and annealed during wire drawing or after the wire drawing process is completed to obtain a slit-shaped gapless wire having a desired wire diameter. Further, by not welding the slit-shaped gap after abutting the opposite edge surfaces of the openings, the steel outer skin is made into a pipe with a slit-shaped gap, and by drawing the wire, the slit-shaped gap is provided. Get the wire.

An example of a cross section obtained by cutting a wire having no slit-shaped gap welded by butt seam welding is shown in FIG. 2 (a). No weld marks are observed on this cross section unless it is polished and etched. Therefore, a wire having no slit-shaped gap as described above is sometimes called a seamless wire. For example, "Introduction to Welding and Joining Technology" (2008), edited by the Welding Society, Sanpo Publishing, p. In 111, a wire having no slit-shaped gap is described as a seamless type wire.

FIG. 2B shows an example of a wire in which the edge surfaces of the steel strips are butted, and FIG. 2C shows an example of a wire in which the edge surfaces of the steel strips are crimped. Even if the gaps are brazed after abutting as shown in FIG. 2 (b) or the gaps are brazed after crimping as shown in FIG. 2 (c), a wire without slit-shaped gaps is obtained. Will be brazed. Further, the wires of FIGS. 2B and 2C are wires having slit-shaped gaps when the gaps are not brazed.

The flux-cored wire according to this embodiment can be applied to any kind of steel material. For example, for gas shielded arc welding of ferrite heat-resistant steel containing Cr: 0.3 to 13% and Mo: 0.1 to 2.5% and having a plate thickness of 4 mm or more, the flux-containing wire according to the present embodiment is used. It can be used, but is not limited to this.

The flux-cored wire according to this embodiment can be applied to welding in which any kind of shield gas is used. In order to lower the oxygen content of the weld metal, suppress the amount of fume generation, and ensure the stability of the welding arc, the shield gas is, for example, a mixed gas of _{Ar and 3 to 20 vol% CO 2, Ar.} A mixed gas of 1 to 10 vol% O _{2 and 100% CO 2} gas can be used, but the present invention is not limited thereto. The flux-cored wire according to the present embodiment is less likely to generate spatter even when these shield gases are used. In particular, the flux-cored wire according to the present embodiment can suppress the amount of spatter generated even when _{100% CO 2 gas, which is prone to spatter according to the prior art, is used for welding as a shield gas.}

In the method for manufacturing a welded joint according to the present embodiment, a steel material is welded using the flux-cored wire for gas shielded arc welding according to the above-described embodiment. In the method for manufacturing a welded joint according to the present embodiment, preheating work for preventing low temperature cracking is unnecessary, or the preheating work can be remarkably reduced, and the amount of spatter generated can be reduced. As described above, the type of shield gas and the type of steel material used in the method for manufacturing a welded joint according to the present embodiment are not particularly limited. However, when the shield gas is 100% CO ₂ gas and the steel material is ferritic heat-resistant steel, the method for manufacturing the welded joint according to the present embodiment is remarkable as compared with the method for manufacturing the welded joint by the prior art. Since the amount of spatter generated can be reduced and the low temperature crack resistance can be remarkably improved, the welding workability can be improved. Further, in this case, the method for manufacturing a welded joint according to the present embodiment can improve the high temperature strength of the welded portion as compared with the method for manufacturing a welded joint according to the prior art.

Next, the feasibility and effect of the present invention will be described in more detail by way of examples.

While feeding the steel strip in the longitudinal direction, it is formed into an open tube by a forming roll, flux is supplied from the opening of the open tube during this forming, and the opposite edge surfaces of the opening are abutted and seam welded to form the steel strip. A flux-cored wire having a final wire diameter of φ1.2 mm was prototyped by using a seamless pipe and annealing during the wire drawing work of the pipe-made wire. In addition, a flux-cored wire having a wire diameter of φ1.2 mm was prototyped by drawing a seam-welded pipe without seam welding. The component compositions (flux composition and alloy component or metal deoxidizing component) of the prototyped flux-cored wire are shown in Table 1-1, Table 1-2, and Table 2. Numerical values outside the scope of the present invention are underlined. In addition, the components that were not added were left blank in the table. The alloy component or metal deoxidizing component was contained in the flux-filled wire in the form of a chemical component of a steel strip to be a steel outer skin or a metal powder or alloy component of a flux.

No. Only 2 was a seamed flux-cored wire with seams crimped and not brazed, as shown in FIG. 2 (C). Until just before the welding work, No. The entire flux-cored wire of 2 was vacuum-packed. In the other example, the steel outer skin was seam welded, and the steel outer skin was made into a seamless flux-cored wire. No. Only in 3, perfluoropolyether oil was applied to the surface of the flux-cored wire. Vegetable oil was applied to the other wires.

The low temperature crack resistance is determined by using a steel plate having a chemical composition (steel material component) shown in Table 4 and having a thickness of 20 mm, in accordance with JIS Z 3157 (U-shaped weld crack test method), at a temperature of 0 ° C. and a humidity of 60%. It was evaluated by a test under constant atmosphere control. Forty-eight hours after the test bead was created, the flux-filled wire applied to the sample (the wire whose U-shaped crack test result was "no crack") with no cracks on the surface and cross section of the weld was judged to pass the low temperature crack resistance. Was done. Welding heat input was 17 kJ / cm.

Furthermore, as a result of the welding low temperature crackability evaluation, the wires that passed the welding low temperature were welded on a steel plate with the same chemical composition as the steel plate used in the previous welding low temperature crackability test, with a thickness of 20 mm, a width of 150 mm, and a length of 200 mm. The lower limit preheating temperature at which cracks did not occur (preheating temperature shown in Table 3) was applied, and a fully welded metal was prepared by multi-layer overlay welding under the same welding method and welding conditions as described above.

The high temperature strength was evaluated by performing a creep rupture test on the obtained fully welded metal. For the examples of wire numbers 1 to 8 and 16 to 25, post-weld heat treatment (PWHT) of 740 ° C. × 1 hour, air cooling was applied to the whole weld metal, and for the examples of wire numbers 9 to 15 and 26 to 30. After applying post-weld heat treatment (PWHT) at 720 ° C for 1 hour and air cooling to the fully welded metal, a round bar creep breakage test piece with a parallel part diameter of 6 mm and a parallel part length of 30 mm was collected, and each welding material was prepared. A creep break test was conducted under stress conditions where the target breaking time of the base metal used at 550 ° C was about 1000 hours, and those exceeding 1000 hours were rated as "passed" in terms of high temperature strength (creep break test results). ..

Further, the Ti oxide, Si oxide, Mg oxide, Al oxide, Ca oxide, Zr oxide, and Cr oxide are TIO ₂ , SiO ₂ , MgO, Al ₂ O ₃ , CaO, and ZrO _{2, respectively.} , And Cr ₂ O ₃ .

The amount of spatter generated in each flux-cored wire was measured by the following means. Tested in a copper collection box on a steel plate with a bead-on plate under conditions of welding current 280 A, voltage 27 V, welding speed 25 cm / min, shield gas 100% CO ₂ (25 l / min), and no preheating. A weld bead was made for 1 minute using the flux-cored wire of interest. Spatter scattered in the box and spatter adhering to the steel sheet during the preparation of the weld bead were collected, and the total weight of those having a diameter of more than 1.0 mm was measured. The measurement results are shown in Table 3 in units of g / min. A flux-cored wire having a spatter generation amount of 5 g / min or less was accepted for spatter suppression performance (welding workability). A sample that satisfies all of the above test items is described as having a "comprehensive judgment" of "pass", and a sample that fails one or more of the above test items has a "comprehensive judgment" of "pass". It was stated that.
The vertical welding workability of each flux-cored wire was measured by the following means. Test target with bead-on plate welding on a steel plate under the conditions of welding current 200A, welding voltage 23V, welding speed 15cm / min, shield gas type 100% CO ₂ , shield gas flow rate 25L / min, and no preheating. A weld bead was prepared for 1 minute using the flux-cored wire. Those in which dripping did not occur when welding were accepted, and those in which dripping occurred were rejected. FIG. 3A is a photograph of the welded portion without sagging, and FIG. 3B is a photograph of the welded portion with sagging.

Table 3 shows the results of evaluating the low temperature crackability of welding. Wire numbers 1 to 8 and 16 to 25 were preheated at 100 ° C., and wire numbers 9 to 15 and 26 to 28 were tested at room temperature of 20 ° C. without preheating. bottom.

In addition, Table 3 shows the results of performing a creep test after performing multi-layer overlay welding to obtain a fully welded metal for the flux-filled wire with a wire number that passed as a result of welding low-temperature crackability evaluation. .. For examples of wire numbers that were not creep tested, the symbol "-" was added in the creep test results column. In addition, the numerical values of the amount of spatter generated that were outside the above-mentioned specified range are underlined.

The comparative example of the wire number 16 in which the amount of CaF ₂ was excessive was determined to be unacceptable because the amount of spatter generated was large and the welding workability was poor. The comparative example of the wire number 17 containing no Ti oxide was judged to be unacceptable because the vertical weldability was poor. The comparative example of the wire number 18 in which the amount of Cr oxide was insufficient was determined to be unacceptable because the amount of spatter generated was large and the welding workability was poor. The comparative example of the wire number 19 is a so-called metal wire, and the amount of fluoride, the amount of Ti oxide, the amount of Cr oxide, and the total amount of oxide are insufficient. In the comparative example of wire No. 19, the amount of spatter generated and the vertical workability were within the acceptable range because the amount of fluoride was small, but it was determined to be unacceptable because the low temperature cracking resistance was insufficient. The comparative example of the wire number 20 in which the amount of fluoride was excessive was judged to be unacceptable because the amount of spatter generated was large and the vertical weldability was also poor. The comparative example of the wire number 21 in which the amount of fluoride was insufficient was determined to be unacceptable because the low temperature cracking resistance was insufficient. The comparative example of the wire number 22 in which the amount of Ca oxide was excessive was determined to be unacceptable because the amount of spatter generated was large and the welding workability was poor. The comparative examples of wire numbers 23 and 28 having insufficient Mo content, the comparative examples of wire numbers 24 having an excessive Cr content, and the comparative examples of wire numbers 25 and 27 having insufficient Cr content have high high temperature strength. Due to the shortage, it was judged to be rejected. The comparative example of the wire number 26 having an excessive Ni content and a insufficient Cr content was determined to be unacceptable because the high temperature strength was insufficient.

On the other hand, in the examples of the present invention of wire numbers 1 to 15, it is possible to obtain a weld metal having excellent high-temperature strength, excellent low-temperature cracking resistance, a small amount of spatter, and a flux containing excellent vertical weldability. It was a wire. As described above, it can be seen that only the flux-cored wire satisfying the scope of the present invention can have the effect of reducing the preheating work, the welding workability, and the creep rupture strength of the weld metal.

INDUSTRIAL APPLICABILITY According to the present invention, a weld metal having excellent high-temperature strength can be obtained, low-temperature cracking resistance is excellent, the amount of spatter generated is small, and a flux-cored wire and a welded joint for gas shielded arc welding are excellent. Manufacturing method can be provided. In particular, the present invention has low temperature crack resistance even when applied to welding of ferritic heat-resistant steel used for members requiring high temperature strength and welding in which the shield gas is 100% CO _2. It is possible to provide a method for manufacturing a flux-containing wire for gas shielded arc welding and a welded joint, which are excellent, generate less spatter, and can be welded with high welding efficiency. Therefore, the present invention has high industrial applicability in the field of welding, particularly in the field of welding high-temperature materials used for heat-resistant and pressure-resistant pipes such as thermal power generation boilers and petrochemical refining equipment.

Claims (16)

A flux-cored wire for gas shielded arc welding in which the inside of a steel outer skin is filled with flux.
The flux is
Fluoride in which the total F conversion value with respect to the total mass of the flux-cored wire is 0.11% or more and less than 2.00%.
Oxides containing Cr oxide and Ti oxide, which are 3.50% or more and less than 13.00% in total in mass% with respect to the total mass of the flux-cored wire.
With iron powder of 0% or more and less than 10.0% in mass% with respect to the total mass of the flux-cored wire,
Including
_{The content of CaF 2} contained in the fluoride is 0% or more and less than 1.00% in mass% with respect to the total mass of the flux-cored wire.
The content of the Ti oxide is 2.50% or more and less than 8.50% in terms of mass% of TIO _{2 with} respect to the total mass of the flux-cored wire.
The content of the Cr oxide is 0.10% or more and less than 10.00% in terms of mass% of _{Cr 2} O _{3 with} respect to the total mass of the flux-cored wire.
The content of Ca oxide contained in the oxide is 0% or more and less than 0.20% in terms of mass% in terms of CaO with respect to the total mass of the flux-filled wire.
Further, the chemical components excluding the fluoride and the oxide are in mass% with respect to the total mass of the flux-cored wire.
C: 0.003 to 0.150%,
Si: 0.05 to 2.00%,
Mn: 0.4 to 3.5%,
P: 0.020% or less,
S: 0.020% or less,
Cr: 0.30 to 13.00%, and Mo: 0.10 to 2.50%,
A flux-cored wire for gas shielded arc welding, characterized in that the balance is composed of Fe and impurities. Further, the fluoride of the flux-filled wire and the chemical component excluding the oxide are mass% with respect to the total mass of the flux-filled wire, instead of a part of Fe contained in the chemical component.
V: 0.50% or less,
Nb: 0.50% or less,
The flux-cored wire for gas shielded arc welding according to claim 1, further comprising one or more selected from the group consisting of Ti: 0.500% or less and Ta: 0.50% or less. Further, the fluoride of the flux-filled wire and the chemical component excluding the oxide are mass% with respect to the total mass of the flux-filled wire, instead of a part of Fe contained in the chemical component.
Cu: 1.00% or less,
Ni: 1.0% or less,
The flux-cored wire for gas shielded arc welding according to claim 1 or 2, wherein it contains one or more selected from the group consisting of Co: 5.0000% or less and B: 0.0200% or less. Further, the fluoride of the flux-filled wire and the chemical component excluding the oxide are mass% with respect to the total mass of the flux-filled wire, instead of a part of Fe contained in the chemical component.
W: The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 3, which contains 4.0000% or less. Further, the fluoride of the flux-filled wire and the chemical component excluding the oxide are mass% with respect to the total mass of the flux-filled wire, instead of a part of Fe contained in the chemical component.
Ca: 0.500% or less,
REM: 0.0100% or less,
The gas shielded arc welding according to any one of claims 1 to 4, wherein it contains one or more selected from the group consisting of Mg: 0.80% or less and Al: 0.400% or less. For flux-cored wire. A flux-cored wire for gas shielded arc welding in which the inside of a steel outer skin is filled with flux.
The flux is
Fluoride in which the total F conversion value with respect to the total mass of the flux-cored wire is 0.11% or more and less than 2.00%.
Oxides containing Cr oxide and Ti oxide, which are 3.50% or more and less than 13.00% in total in mass% with respect to the total mass of the flux-cored wire.
With iron powder of 0% or more and less than 10.0% in mass% with respect to the total mass of the flux-cored wire,
Total 2.00% or less by mass% relative to the total weight of the flux-cored _wire, and CaCO _{3, Na} 2 CO 3, and one or more carbonates selected from the group consisting of MgCO _3,
Including
_{The content of CaF 2} contained in the fluoride is 0% or more and less than 1.00% in mass% with respect to the total mass of the flux-cored wire.
The content of the Ti oxide is 2.50% or more and less than 8.50% in terms of mass% of TIO _{2 with} respect to the total mass of the flux-cored wire.
The content of the Cr oxide is 0.10% or more and less than 10.00% in terms of mass% of _{Cr 2} O _{3 with} respect to the total mass of the flux-cored wire.
The content of Ca oxide contained in the oxide is 0% or more and less than 0.20% in terms of mass% in terms of CaO with respect to the total mass of the flux-filled wire.
Further, the chemical components excluding the fluoride, the oxide, and the carbonate are in mass% by mass with respect to the total mass of the flux-filled wire.
C: 0.003 to 0.150%,
Si: 0.05 to 2.00%,
Mn: 0.4 to 3.5%,
P: 0.020% or less,
S: 0.020% or less,
Cr: 0.30 to 13.00%, and Mo: 0.10 to 2.50%,
A flux-cored wire for gas shielded arc welding, characterized in that the balance is composed of Fe and impurities. Further, the chemical component excluding the fluoride, the oxide, and the carbonate of the flux-filled wire replaces a part of Fe contained in the chemical component in mass% with respect to the total mass of the flux-filled wire. hand,
V: 0.50% or less,
Nb: 0.50% or less,
The flux-cored wire for gas shielded arc welding according to claim 6, further comprising one or more selected from the group consisting of Ti: 0.500% or less and Ta: 0.50% or less. Further, the chemical component excluding the fluoride, the oxide, and the carbonate of the flux-filled wire replaces a part of Fe contained in the chemical component in mass% with respect to the total mass of the flux-filled wire. hand,
Cu: 1.00% or less,
Ni: 1.0% or less,
The flux-cored wire for gas shielded arc welding according to claim 6 or 7, wherein it contains one or more selected from the group consisting of Co: 5.0000% or less and B: 0.0200% or less. Further, the chemical component excluding the fluoride, the oxide, and the carbonate of the flux-filled wire replaces a part of Fe contained in the chemical component in mass% with respect to the total mass of the flux-filled wire. hand,
W: The flux-cored wire for gas shielded arc welding according to any one of claims 6 to 8, which contains 4.0000% or less. Further, the chemical component excluding the fluoride, the oxide, and the carbonate of the flux-filled wire replaces a part of Fe contained in the chemical component in mass% with respect to the total mass of the flux-filled wire. hand,
Ca: 0.500% or less,
REM: 0.0100% or less,
The gas shielded arc welding according to any one of claims 6 to 9, wherein it contains one or more selected from the group consisting of Mg: 0.80% or less and Al: 0.400% or less. For flux-cored wire. The fluoride is one or more selected from the group consisting of _{CaF 2} , MgF ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF _6.
The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 10, wherein the X value calculated by the formula 1 is 3.00% or less.
X = [Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ] + 1.5 x ([K ₂ ZrF ₆ ]) + 3.5 x ([CaF ₂ ]) ... (Equation 1)
However, the chemical formula in parentheses described in the formula 1 represents the content of the fluoride according to the chemical formula in mass% with respect to the total mass of the flux-cored wire, and the content of the fluoride not contained. Is considered to be 0%. The oxides are the Cr oxide, the Ti oxide, and Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide. One or more selected from the group consisting of substances and Ca oxides.
Cr oxide, Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, wherein K oxides, and the total content of the Ca oxide, relative to the total weight of the flux-cored _{wire, Cr 2 O 3, TiO 2} , FeO, BaO, Na 2 O, SiO 2, ZrO 2, MgO , Al ₂ O ₃ , MnO ₂ , K ₂ O, and Ca O, which are 3.50% or more and less than 13.00%, respectively.
The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 11, wherein the V value calculated by the formula 2 is 5.00 or more and 27.00 or less. V = ([TiO ₂ ] + 1.2 × [SiO ₂ ] + 1.4 × [Al ₂ O ₃ ] + 1.5 × [ZrO ₂ ]) / (F) ^1/2 : Equation 2
However, regarding the chemical formulas in parentheses described in the above formula 2 , [TiO ₂ ] is the TiO ₂ conversion value of the Ti oxide, [SiO ₂ ] is the SiO ₂ conversion value of the Si oxide, and [Al ₂ O ₃ ]. _{Is the Al 2} O ₃ conversion value of the Al oxide , [ZrO ₂ ] is the ZrO ₂ conversion value, and represents the content of the flux-cored wire in mass% with respect to the total mass. Refers to the total of the F-converted values of the flux with respect to the total mass of the flux-cored wire, and the content of the oxide not contained is regarded as 0%. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 12, wherein the steel outer skin has a slit-like shape without gaps. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 12, wherein the steel outer skin has a shape having a slit-shaped gap. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 14, wherein the surface of the steel outer skin has perfluoropolyether oil. A method for manufacturing a welded joint, which comprises welding a steel material using the flux-cored wire for gas shielded arc welding according to any one of claims 1 to 15.

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