JP6891630B2 - 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.

In the gas refining process, low-carbon hydrocarbon gas is secondarily produced. This hydrocarbon gas is likely to be a raw material for petrochemical products. For this reason, in recent years, there has been an increasing demand for the construction of hydrocarbon gas carriers and ground tanks.

The low carbon number hydrocarbon gas is maintained at about −100 ° C. or lower. Candidates for tank structural members that can be used in a low temperature environment of about -100 ° C or lower include Ni-added steel, Al alloy, and stainless steel. Compared to Al alloys and stainless steels, Ni-added steels are superior in terms of steel cost and strength, and also have good toughness even in a low temperature environment. When constructing a hydrocarbon gas tank, the weld metal to which this Ni-added steel is joined is also required to have good toughness in a low temperature environment at -100 ° C or lower.

Various welding methods are applied in constructing a welded structure used in such a low temperature environment, but from the viewpoint of excellent work efficiency, gas shielded arc welding using a flux-cored wire is used. Is preferred. However, at present, there is no inexpensive flux-cored wire capable of ensuring the low temperature toughness of the weld metal for joining Ni-added steel. Due to the need to satisfy strict safety, Ni-based alloy welding materials containing 60-80% Ni are currently used.

Since the Ni-based alloy welding material contains a large amount of Ni, it is extremely expensive and easily cracks at high temperature. Further, since the Ni-based alloy welding material has a poor flow of molten metal, welding defects such as poor fusion are likely to occur. In order to prevent welding defects, welding using a Ni-based alloy welding material requires welding with a low heat input. Therefore, the Ni-based alloy welding material also has a problem in terms of welding efficiency. Further, in temporary welding, _{it is common to use inexpensive 100% CO 2} gas as a shield for welding, but the welding material of Patent Document 5 described later was used in combination with _{100% CO 2 gas.} In the case, a large amount of spatter is generated. A large amount of spatter causes uneven coating after welding and defect generation in subsequent welding.

In response to this situation, the following welding materials have been proposed as flux-cored wires for low-temperature steel, for example.

Patent Document 1 mainly contains metal fluoride in which the Ti oxide in the flux is reduced so that the amount of oxygen in the weld metal is reduced in order to obtain a weld metal having excellent toughness at −100 ° C. Flux-cored wires are disclosed.
Patent Document 2 discloses a flux-cored wire in which a metal fluoride is added to the flux to reduce the amount of oxygen, and at the same time, the toughness is improved by adding Ni.
Patent Document 3 describes a flux that reduces the amount of weld metal oxygen by replacing the slag component in the flux with a metal fluoride type and defines the ratio of fluoride to oxide to improve low temperature toughness. Fluoride is disclosed.
Patent Document 4 specifies the amount of Mo added by replacing the flux from a Ti oxide type with a metal fluoride type in order to secure toughness at −40 ° C. in a weld metal having a strength of 780 MPa or more.
Patent Document 5 discloses a pulse gas shielded arc welding method using a flux-cored wire in which the ratio of the contents of fluoride and oxide is within a predetermined range and the content of Ceq is limited within a predetermined range. ing. Since the flux-cored wire described in Patent Document 5 contains a large amount of CaF ₂ , the welding work efficiency is remarkably lowered due to the generation of a large amount of sputtering during 100% CO _{2 shield gas welding.}
Non-Patent Document 1 discloses that the absorbed energy at −90 ° C. becomes about 100 J by using a flux-cored wire containing about 2% of Ni.
However, when the low temperature toughness of the weld metal obtained by welding using the flux-cored wire disclosed in these documents is evaluated at −100 ° C., the required level may not be reached.

Japanese Unexamined Patent Publication No. 2010-064087 Japanese Patent No. 3120912 Japanese Unexamined Patent Publication No. 9-57488 Japanese Patent No. 5644984 Japanese Unexamined Patent Publication No. 2008-246507

Kazuhiro Kojima et al. , OMAE99 / MAT-2102, "Development of Offshore Temperature Steels and Welding Materials for Ultra Low Temperature Services 3-Welding Materials"

In view of such circumstances, the present invention provides a weld metal having excellent tensile strength, elongation, and toughness at -100 ° C., high welding workability, and a flux in which the amount of expensive alloying elements is reduced. An object of the present invention is to provide an insert wire and a method for manufacturing a welded joint using the wire.

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 includes a steel outer skin and a flux filled inside the steel outer skin, and the flux is the entire flux-containing wire. Select from the group consisting of _{CaF 2} , MgF ₂ , Na ₃ AlF ₆ , LiF, NaF, K ₂ ZrF ₆ , BaF ₂ , and K ₂ SiF ₆ , in which the total F conversion value with respect to the mass is 0.21% or more. Fe oxide, Ba, in which the total value of one or more fluorides to be formed and the content of the flux-filled wire in mass% with respect to the total mass is 0.30% or more and less than 3.50%. One or more oxidations selected from the group consisting of oxides, Na oxides, Ti oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, and K oxides. _{MgCO 3} , Na ₂ CO ₃ , Li ₂ CO ₃ , CaCO ₃ , K ₂ CO, the total content of the material and the flux-filled wire in% by mass with respect to the total mass is 0 to 3.50%. _3. Containing one or more carbonates selected from the group consisting of BaCO ₃ , FeCO ₃ and MnCO ₃ , the CaO content in the flux is relative to the total mass of the flux-filled wire. The mass% is 0% or more and less than 0.20%, and the content of iron powder in the flux is 0% or more and less than 10.0% in mass% with respect to the total mass of the flux-containing wire. The X value calculated using A) is 5.00% or less with respect to the total mass of the flux-filled wire, and the CaF ₂ content is 0 in mass% of the total mass of the flux-filled wire. .50% or more, and the content of the Ti oxide is 0.10% or more and less than 2.50% in mass% with respect to the total mass of the flux-filled wire, and the MgCO ₃ , the Na ₂ CO ₃ , and the like. And _{the total value of the content of Li 2} CO ₃ is 0 to 3.00% in mass% with respect to the total mass of the flux-filled wire, and further excludes the fluoride, the oxide, and the carbonate. The chemical composition is C: 0.001% or more and 0.080% or less, Si: 0.001% or more and 0.800% or less, Mn: 0.10% or more in mass% with respect to the total mass of the flux-filled wire. 1.50% or less, Al: 0.005% or more and 0.500% or less, Ni: 3.0% or more and 4.9% or less, Ti: 0 .005% or more and 0.100% or less, Mg: 0.20% or more and 0.80% or less, P: 0.030% or less, and S: 0.030% or less, and the balance is from Fe and impurities. Become.
X = [NaF] + [MgF ₂ ] + [Na ₃ AlF ₆ ] + 1.50 × ([K ₂ SiF ₆ ] + [K ₂ ZrF ₆ ] + [LiF] + [BaF ₂ ]) + 3.50 × ( [CaF ₂ ]) ・ ・ ・ (A)
The chemical formula with [] in the formula (A) represents the content of the fluoride according to each chemical formula in mass% with respect to the total mass of the flux-cored wire, and the content of the fluoride not contained is 0. Consider it as.
(2) The flux-cored wire for gas shielded arc welding according to (1) above may contain the carbonate in a total mass of 2.00% or less based on the total mass of the flux-cored wire. ..
(3) The flux-cored wire for gas shielded arc welding according to the above (1) or (2) further has a mass% of the total mass of the flux-welded wire, B: 0% or more and 0.0100% or less. It may contain one or more selected from the group consisting of Cu: 0.5% or less and REM: 0.050% or less.
(4) The flux-cored wire for gas shielded arc welding according to any one of (1) to (3) above has a hardenability index α of 0.25% or more and 0.51 represented by the following formula (B). It may be less than or equal to%.
α = [C] + [Si] / 24 + [Mn] / 6 + ([Ni] + [Cu]) / 15 ... (B)
The element with [] in the formula (B) is the content of the element contained in the chemical component excluding the fluoride, the oxide, and the carbonate in mass% with respect to the total mass of the flux-filled wire. Represents.
(5) The flux-cored wire for gas shielded arc welding according to any one of (1) to (4) above has a high temperature cracking susceptibility index β represented by the following formula (C) of 3.1 or less. May be good.
β = [Si] / 6 + [Mn] /1.5+ [Ni] /3+200 × [B] ... (C)
The element with [] in the formula (C) is the content of the element contained in the chemical component excluding the fluoride, the oxide, and the carbonate in mass% with respect to the total mass of the flux-filled wire. Represents.
(6) The flux-cored wire for gas shielded arc welding according to any one of (1) to (5) above may have an elongation index γ represented by the following formula (D) of 1.8 or less. ..
γ = [Mn] + [Mg] ... (D)
The element with [] in the formula (D) is the content of the element contained in the chemical component excluding the fluoride, the oxide, and the carbonate in mass% with respect to the total mass of the flux-filled wire. Represents.
(7) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (6) above, the steel outer skin may have a slit-like shape without gaps.
(8) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (6) above, the steel outer skin may have a slit-like gap.
(9) The flux-cored wire for gas shielded arc welding according to any one of (1) to (8) above may be provided with perfluoropolyether oil on the surface of the steel outer skin.
(10) The method for manufacturing a welded joint according to another aspect of the present invention is a step of welding a steel plate using the flux-containing wire for gas shielded arc welding according to any one of (1) to (9) above. To be equipped.
(11) In the method for manufacturing a welded joint according to (10) above, the shield gas used in the temporary welding in the welding step is 100% CO ₂ gas, and in the main welding in the welding step. The shield gas used may be a mixed gas of Ar and 2.5 to 30.0% by volume of CO _2.

According to the present invention, by reducing the Ni content to 5.5% by mass or less, which is equivalent to that of Ni-based low-temperature steel, welding work efficiency is excellent in gas shielded arc welding, and an inexpensive flux-containing wire can be obtained. By keeping the alloy component in the flux-containing wire within a predetermined range and reducing the amount of oxygen in the weld metal, it is possible to provide a weld metal having excellent tensile strength and low-temperature toughness at −100 ° C. Moreover, according to the present invention, the amount of spatter generated can be reduced even during _{100% CO 2 shield gas welding.}

It is a figure which showed the relationship between the amount of spatter generated and the X value of a flux-cored wire at the time of _{100% CO 2} shield gas welding for temporary welding. It is sectional drawing of the wire containing flux. (A) is a flux-cored wire made by butt-welding edge surfaces, (b) is a flux-cored wire made by butt-butting edge surfaces, and (c) is a flux-cored wire made by crimping edge surfaces. Is. It is a figure which shows the sampling position of the test piece which conformed to JIS Z3111-2005 which concerns on Example and comparative example.

(1) Low-temperature toughness of weld metal The present inventors have studied a flux-containing wire that improves the low-temperature toughness of weld metal. Steel materials used in a low temperature environment, particularly weld metals formed by joining Ni-based low temperature steels, are required to have a toughness at −100 ° C. (low temperature toughness) of 34 J or more. In order to ensure this low temperature toughness, the present inventors considered that it is necessary to (1-1) reduce the amount of oxygen in the weld metal and (1-2) finely granulate the structure of the weld metal. .. Furthermore, the present inventors considered that it is preferable to (1-3) suppress the formation of grain boundary ferrite in the weld metal and (1-4) suppress the formation of the second phase in the weld metal. The amount of Ni in the (1-5) weld metal also greatly affects the toughness. However, since the manufacturing cost increases when the Ni content of the flux-containing wire is increased, the present inventors minimize the Ni content and use other means (1-1) to (1-4). Attempts were made to improve low temperature toughness.

(1-1) Reduction of Oxygen Amount As a means for reducing the amount of oxygen in the weld metal, a _{fluoride component such as LiF, NaF, CaF 2} , and MgF ₂ is contained in the flux-filled wire, and Si, Mn, and Ti are used. , And deoxidizing elements such as Al as deoxidizing components (ie, in a form that does not constitute fluoride, oxides, and carbonates) in the fluxed wire, and gas shielded arc welding using an inert gas. Was considered to be done. However, in gas shielded arc welding using an inert gas, the arc becomes unstable, a sufficient penetration depth cannot be obtained, and a sound weld metal without welding defects cannot be obtained. Therefore, the present inventors have considered that it may be difficult to use it as a means for reducing the amount of oxygen in the weld metal. Therefore, in the flux-containing wire according to the present embodiment, the fluoride component and the metal deoxidizing component are set within a predetermined range in order to reduce the amount of oxygen in the weld metal.

(1-2) Tissue granulation As a tissue granulation means for ensuring low temperature toughness, the present inventors have stated that Ti and Al compounds (mainly, which are said to be the formation nuclei of fine intragranular transformation structures). , Ti oxide and Al oxide). By increasing the number of crystal grains of the Ti oxide and Al oxide finely dispersed in the welding metal, the crystal grain size in the structure of the welding metal can be made finer. In order to increase the number of Ti oxides and Al oxides contained in the weld metal, the alloy Al content, the alloy Ti content, and the Ti oxide content are within a predetermined range in the flux-containing wire according to the present embodiment. It is said to be inside. Most of the Ti oxides and Al oxides as slag components, which will be described later, are discharged from the weld metal during welding to form slag. Therefore, what are the Ti oxides and Al oxides contained in the weld metal? Distinguished.

(1-3) Suppression of grain boundary ferrite formation By the means of (1-1) and (1-2) above, the low temperature toughness of the weld metal can be increased while sufficiently reducing the Ni content. However, by suppressing the formation of grain boundary ferrite in the weld metal, it is possible to further improve the low temperature toughness. In the weld metal after melting and solidification by welding, grain boundary ferrite is generated from the austenite structure when the temperature drops, and this grain boundary ferrite may deteriorate the low temperature toughness of the weld metal. In order to improve the low temperature toughness, it is preferable to suppress the formation of grain boundary ferrite in the weld metal. The present inventors have found that it is effective to utilize B for suppressing the formation of grain boundary ferrite. By increasing the B content of the flux-cored wire, the hardenability of the austenite grain boundaries can be improved and the formation of grain boundary ferrite can be suppressed. Therefore, the flux-cored wire according to the present embodiment preferably further contains a predetermined amount of B.

(1-4) Suppression of Second Phase Generation By the means of (1-1) to (1-3) above, the low temperature toughness of the weld metal can be increased while sufficiently reducing the Ni content. However, by suppressing the formation of the second phase in the weld metal, it is possible to further improve the low temperature toughness. The second phase is MA (island martensite) or the like. The present inventors have found that the formation of the second phase is suppressed in the weld metal by setting the hardenability index α defined by the following formula within a predetermined range.
α = [C] + [Si] / 24 + [Mn] / 6 + ([Ni] + [Cu]) / 15 ... (2)
The element with [] in the formula (2) represents the content of the element contained in the chemical component excluding the fluoride, the oxide, and the carbonate in mass% with respect to the total mass of the flux-filled wire. ..

The formation of the second phase in the weld metal can be suppressed by keeping the hardenability of the weld metal within a suitable range. Further, by controlling α, the hardenability of the weld metal can be controlled. Since the present inventors have found a suitable numerical range of α that can suppress the formation of the second phase, α is preferably within a predetermined range in the flux-cored wire according to the present embodiment.

(2) Elongation and tensile strength of weld metal The elongation of weld metal tends to be inversely proportional to the hardness and tensile strength of the weld metal. Therefore, in the flux-containing wire according to the present embodiment, the amount of elements that enhance hardenability, such as C, Si, Mn, and Ni, should be reduced within a range in which the tensile strength required for the weld metal can be secured. Then, the elongation of the weld metal is secured. Further, by enhancing the hardenability of the austenite grain boundaries by containing B, the amount of elements that enhance the hardenability such as C, Si, Mn, and Ni can be suppressed, so that the strength of the weld metal does not increase excessively. , Leads to ensuring toughness and elongation.

More preferably, in the flux-cored wire according to the present embodiment, the elongation index γ defined by the following formula is within a predetermined range.
γ = [Mn] + [Mg] ... (4)
The element with [] in the formula (4) represents the content of the element contained in the chemical component excluding the fluoride, the oxide, and the carbonate in mass% with respect to the total mass of the flux-filled wire. ..

The present inventors have found that there is a relatively strong correlation between the total amount of Mn and Mg of the alloy components contained in the flux-filled wire and the elongation of the weld metal. By controlling the total content of Mn and Mg as the elongation index γ and keeping it within a predetermined range, the elongation of the weld metal can be further improved. Therefore, in the flux-cored wire according to the present embodiment, the elongation index γ is preferably within a predetermined range.

(3) Spatter amount during welding As described above, in order to obtain a weld metal having excellent low temperature toughness, it is essential to contain a fluoride in the flux-filled wire to reduce the oxygen content of the weld metal. is there. However, fluoride significantly increases the amount of spatter generated during welding. A large amount of spatter causes uneven coating after welding and defect generation in subsequent welding.

The present inventors have diligently studied means for reducing the amount of spatter while ensuring the low temperature toughness of the weld metal. As a result, the present inventors have found that the spatter amount changes depending on the fluoride species. Therefore, by quantitatively investigating the relationship between the type and amount of fluoride and the spatter amount and performing multiple regression analysis, there is a good linear relationship between the X value defined by the following formula and the spatter amount. The present inventors have found that.
X = [NaF] + [MgF ₂ ] + [Na ₃ AlF ₆ ] + 1.50 × ([K ₂ SiF ₆ ] + [K ₂ ZrF ₆ ] + [LiF] + [BaF ₂ ]) + 3.50 × ( [CaF ₂ ]) ・ ・ ・ (1)
The chemical formula with [] in the above formula (1) represents the content of fluoride according to each chemical formula in mass% with respect to the total mass of the flux-cored wire, and the content of fluoride not contained is regarded as 0.

By selecting the type of fluoride so that the X value falls below a predetermined upper limit and increasing the total F conversion value of fluoride within that range, the low temperature toughness of the weld metal is improved while suppressing the amount of spatter. The present inventors have found that this is possible. Therefore, in the flux-cored wire according to the present embodiment, the type and amount of fluoride are defined by the sum of the X value and the F conversion value.

The present inventors have arrived at the present invention through the above-mentioned examination process, and further describe necessary requirements and preferable requirements for the present invention.

The flux-cored wire according to the present embodiment includes a steel outer skin and a flux filled in the steel outer skin. First, the composition of the alloy component and the metal deoxidizing component contained in the steel outer skin and the flux and the reason for their limitation 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, or carbonate. Therefore, the content of the elements constituting the fluoride, metal oxide, or carbonate is not included in the alloy component and the metal deoxidizing component. The alloy component and the metal deoxidizing component described below may be contained in the flux in the form of a metal powder or an alloy powder, may be contained as an alloy element in the steel outer skin, or may be plated on the steel outer skin. The content of each component shall mean the component content which is the sum of the mass% of each component in the steel outer skin and the flux with respect to the total mass of the wire.

(C: 0.001% or more and 0.080% or less)
C is an element that improves the hardenability of the weld metal and promotes intragranular transformation, thereby ensuring the strength of the weld metal. In order to promote the intragranular transformation, it is necessary to contain 0.001% or more of C in the flux-cored wire. In order to improve the strength of the weld metal, the lower limit of the C content may be 0.005%, 0.008%, 0.010%, or 0.013%. On the other hand, a weld metal containing 3.0 to 5.5% Ni has a highly hardenable structure. Therefore, if the flux-containing wire contains more than 0.080% of C, the weld metal is extremely hardened. , Its toughness and elongation are greatly reduced, and high temperature cracks and low temperature cracks occur in the weld metal. In order to ensure stable toughness, the upper limit of the C content may be 0.070% or 0.060%.

(Si: 0.001% or more and 0.800% or less)
Si is an element necessary for improving the cleanliness of the weld metal and suppressing the occurrence of welding defects such as blow holes. In order to obtain these effects, the flux-cored wire needs to contain 0.001% or more of Si. In order to further prevent the occurrence of welding defects, the lower limit of Si may be set to 0.250% or 0.300%. On the other hand, in a weld metal containing 3.0 to 5.5% Ni, Si is easily microsegregated, and when Si of more than 0.800% is contained in a flux-cored wire, the Si segregated portion is significantly embrittled. Embrittlement occurs. Therefore, the upper limit of the Si content is set to 0.800%. Further, in order to stably secure the toughness of the weld metal, the upper limit of Si may be 0.600% or 0.550%.

(Mn: 0.10% or more and 1.50% or less)
Mn is an element necessary for improving the cleanliness of the weld metal and further forming MnS to detoxify S and improve the toughness of the weld metal. In order to obtain the effect, it is necessary to contain 0.10% or more of Mn in the flux-cored wire. The lower limit of the Mn content may be 0.20%, 0.30%, or 0.40% in order to further improve the toughness. On the other hand, in a weld metal containing 3.0 to 5.5% Ni, Mn is easily microsegregated, and when the flux-cored wire contains more than 1.50% of Mn, significant embrittlement occurs in the Mn segregated portion. Occurs. Further, in order to secure the toughness of the weld metal more stably, the upper limit of the Mn content may be 1.10%, 1.00%, or 0.95%.

(Al: 0.005% or more and 0.500% or less)
Al is a strong deoxidizer and is an essential element for reducing Ti from the Ti oxide which is a slag agent and securing a fine Ti oxide effective for microstructure micronization of the weld metal. However, if the Al content of the flux-containing wire is less than 0.005%, the reducing effect of the slag agent Ti oxide by Al is insufficient, so that the fine Ti oxide in the weld metal that is the core of the intragranular ferrite cannot be secured. .. In this case, since the microstructure of the weld metal is not atomized, the low temperature toughness of the weld metal is not improved. The lower limit of the Al content may be 0.030% or 0.040% in order to further improve the toughness. On the other hand, when more than 0.500% of Al is contained in the flux-filled wire, the amount of Al oxide is significantly increased, and a large composite oxide of Al oxide and Ti oxide is formed in the weld metal. To. As a result, the Ti oxide in the weld metal does not function as a nucleus of the intragranular ferrite, and the microstructure of the weld metal is not miniaturized, so that the toughness of the weld metal is lowered. Further, in this case, the toughness of the weld metal is also lowered by increasing the amount of Al nitride produced. Therefore, the upper limit of the Al content is set to 0.500%. Further, in order to secure the toughness of the weld metal more stably, the upper limit of the Al content may be 0.200%, 0.100%, or 0.050%.

(Ni: 3.0% or more and 5.5% or less)
Ni is the only element that can improve the toughness of the weld metal by solid solution toughness (the action of increasing toughness by solid solution) regardless of the structure and composition of the weld metal. In particular, Ni is an essential element in order to ensure the low temperature toughness of the weld metal at −100 ° C. In order to obtain this effect, it is necessary to contain 3.0% or more of Ni in the flux-cored wire. In order to ensure more stable low temperature toughness, the lower limit of the Ni content may be 3.1%, 3.2%, or 3.5%. On the other hand, if more than 5.5% of Ni is contained in the flux-cored wire, the effect is saturated, the cost of the welding material rises, and high-temperature cracking of the weld metal occurs. Therefore, the Ni content is set to 5.5% or less. The upper limit of the Ni content may be 5.3%, 5.2% or 5.0%.

(Ti: 0.005% or more and 0.100% or less)
Ti is a strong deoxidizer, and a part of the metal Ti contained in the flux-cored wire is oxidized and slag-off, and the rest remains in the weld metal. The Ti remaining in the weld metal forms fine Ti inclusions and acts as an intragranular transformation nucleus to refine the structure of the weld metal. Therefore, Ti has a function of improving the low temperature toughness of the weld metal. Further, when B is contained in the flux-cored wire, Ti has a function of promoting the effect of B. In the high temperature region of the initial molten metal solidification process, Ti forms a nitride before B to fix N. As a result, B does not form BN in the subsequent solidification process of the molten metal. That is, Ti is an essential component for segregating B into the austenite grain boundaries as free B. This Free B has an effect of improving the low temperature toughness of the weld metal in synergy with the effect of in-grain ferrite miniaturization by the Ti oxide by suppressing the formation of coarse ferrite at the grain boundary. This effect is not sufficient only by securing the amount of Ti by reducing the Ti oxide, and the above effect can be obtained only when the metal Ti is contained in the flux-cored wire. However, if the Ti content of the flux-containing wire is less than 0.005%, most of the metallic Ti is oxidatively consumed, and sufficient Ti is not retained to form TiN in the weld metal, so that the above effect cannot be sufficiently obtained. , The microstructure becomes insufficiently refined, and the toughness improving effect cannot be obtained. The lower limit of the Ti content may be 0.030% or 0.040% in order to further improve the toughness. Further, when more than 0.100% of Ti is contained in the flux-cored wire, the solid solution Ti increases, the weld metal is excessively hardened, and the toughness is remarkably lowered. Therefore, the Ti content is set to 0.100% or less. Further, in order to secure the toughness of the weld metal more stably, the upper limit of the Ti content may be 0.080% or 0.070%.

(P: 0.030% or less)
Since P is an impurity element and deteriorates the toughness of the weld metal, it is necessary to reduce it as much as possible. However, the P content of the flux-cored wire is limited to 0.030% or less as a range in which this adverse effect can be tolerated. The upper limit of the P content may be 0.015%, 0.010%, 0.008%, or 0.006% in order to further improve the toughness of the weld metal.

(S: 0.030% or less)
Since S is an impurity element and significantly deteriorates the toughness of the weld metal, it is preferable to reduce it as much as possible. The S content of the flux-cored wire is limited to 0.030% or less so that an adverse effect on toughness can be tolerated. The upper limit of the S content may be 0.008%, 0.006%, 0.004%, or 0.003% in order to further improve the toughness of the weld metal.

(Mg: 0.20% or more and 0.80% or less)
Mg is a strongly deoxidizing element, which is effective in reducing oxygen in the welding metal and improving the toughness of the welding metal. In order to obtain this effect, the Mg content in the flux-cored wire is set to 0.20% or more. The lower limit of the Mg content may be set to 0.25% or 0.30% in order to further improve the toughness of the weld metal. On the other hand, if more than 0.80% of Mg is contained in the flux-cored wire, the amount of spatter increases during welding and the welding workability deteriorates. In order to improve the welding workability, the upper limit of the Mg content may be 0.70%, 0.60%, or 0.50%.

The flux-containing wire according to the present embodiment has B, Cu as an alloy component or a deoxidizing component, in addition to the above-mentioned basic components (essential elements), depending on the strength level of the steel sheet to be welded or the degree of toughness required. And one or more of REM can be contained as a selective element. However, since these selective elements are not essential for solving the problem of the flux-cored wire according to the present embodiment, the lower limit of the content of these selective elements is 0%. If the content of the essential element in the flux-cored wire is within the above-mentioned specified range regardless of the presence or absence of the selected element, the flux-cored wire is considered to be within the range of the flux-cored wire according to the present embodiment. Is done.

(B: 0.0100% or less)
When an appropriate amount of B is contained in the weld metal via a flux-filled wire, it has the effect of combining with the solid solution N to form a BN and reducing the adverse effect of the solid solution N on the toughness of the weld metal, and welding. By enhancing the hardenability of the austenite grain boundaries in the metal, it has the effect of suppressing the formation of coarse grain boundary ferrites and ensuring low temperature toughness, so it may be added. However, when the flux-cored wire contains more than 0.0100% of B, B in the weld metal becomes excessive, and _{B compounds such as coarse BN and Fe 23} (C, B) ₆ are formed to reverse the toughness. Deteriorate. The upper limit of the B content may be 0.0080% or 0.0060% in order to further improve the toughness. In order to obtain the effect of B content more reliably, the lower limit of B content may be 0.0001%, 0.0002%, or 0.0010%.

(Cu: 0.5% or less)
Cu may be added to the plating on the outer skin surface of the wire and the flux because it may be contained as a simple substance or as an alloy and has an effect of improving the strength of the weld metal. When the flux-cored wire contains more than 0.5% Cu, the toughness of the weld metal is lowered. The upper limit of the Cu content may be 0.3%, 0.2%, or 0.1% in order to further improve the toughness of the weld metal. Regarding the Cu content, in addition to the amount contained in the outer skin itself or the flux, the amount is also included when the wire surface is copper-plated. In order to obtain the above-mentioned effect, the lower limit of the Cu content may be 0.01%.

(REM: 0.050% or less)
Since REM is an element that can reduce the size of sulfides and oxides in the weld metal and contribute to the improvement of the toughness of the weld metal, it may be added. However, if the flux-cored wire contains more than 0.050% of REM, spatter becomes intense and the welding workability becomes poor. Further, in order to contribute to the reduction of spatter and the stability of the arc, the upper limit of the REM content may be 0.030%, 0.020%, 0.010%, 0.005%, or 0.001%. .. 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. When lanthanoids are used as REMs, industrially, REMs are added in the form of mischmetal.

(Hardenability index α: 0.25% or more and 0.51% or less)
In order to increase the toughness of the weld metal, the alloy component or deoxidizing component (that is, fluoride, oxidation) so that the hardenability index α represented by the following equation (2) is 0.25% or more and 0.51% or less. It is preferable to adjust the content of (chemical components excluding substances and carbonates). When the hardenability index α is 0.25% or more, the formation of grain boundary ferrite that impairs the toughness of the weld metal can be further suppressed, which is preferable. On the other hand, when the hardenability index α is 0.51% or less, the formation of a second phase (for example, MA) that impairs the toughness of the weld metal can be further suppressed, and excessive hardening of the weld metal can be reliably prevented. It is preferable because it can be done.
α = [C] + [Si] / 24 + [Mn] / 6 + ([Ni] + [Cu]) / 15 ... (2)
The element with [] in the formula (2) represents the content of each element contained as an alloy component or a deoxidizing component in mass% with respect to the total mass of the flux-cored wire.

(High temperature crack susceptibility index β: 3.1 or less)
The alloy component contained in the flux-cored wire may easily cause high-temperature cracking, and in order to suppress this, the index β of the high-temperature cracking susceptibility represented by the following formula (3) should be 3.1 or less. In addition, it is preferable to adjust the content of the alloy component or the deoxidizing component. Since Si, Mn, Ni, and B are elements that particularly affect the sensitivity to high temperature cracking, limiting the amount of these elements by the formula (3) in addition to the above limitation prevents high temperature cracking. It is preferable to obtain the effect of each element.
β = [Si] / 6 + [Mn] /1.5+ [Ni] /3+200 × [B] ... (3)
The element with [] in the formula (3) represents the content of each element contained as an alloy component or a deoxidizing component in mass% with respect to the total mass of the flux-cored wire.

(Growth index γ: 1.8 or less)
In order to improve the elongation of the weld metal, it is preferable to adjust the content of the alloy component or the deoxidizing component so that the elongation index γ represented by the following equation (4) is 1.8 or less. Since Mn and Mg are elements having a particularly strong action of hardening the weld metal and reducing the elongation, the elongation of the weld metal can be limited by the formula (4) in addition to the above limitation. It is preferable to obtain the effect of each element while ensuring.
γ = [Mn] + [Mg] ... (4)
The element with [] in the formula (4) represents the content of each element contained as an alloy component or a deoxidizing component in mass% with respect to the total mass of the flux-cored wire.

Next, the slag component inserted into the steel outer skin of the wire will be described. The slag components described below are fluorides, oxides, or carbonates, which are distinct from the alloy components and metal deoxidizing components described above.

Fluxed one or more fluorides selected from the group consisting of (CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , LiF, NaF, K _{2 ZrF 6} , BaF ₂ , and K ₂ SiF _6). Total value of F conversion value with respect to the total mass of the wire: 0.21% or more)
In the flux-cored wire according to the present embodiment, one or more kinds selected from the group consisting of _{CaF 2} , MgF ₂ , Na ₃ AlF ₆ , LiF, NaF, K ₂ ZrF ₆ , BaF ₂ , and K ₂ SiF ₆ Fluoride is contained in a total of 0.21% or more in terms of F 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 calculated by the following equation 5.
( _{F conversion value of CaF 2} ) = n × (19.00 × 2 / 78.08) ... (Equation 5)
In the above formula 4, "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 flux contained in the flux enhances the low temperature toughness of the weld metal by reducing the amount of oxygen in the weld metal, and suppresses low temperature cracking in the weld metal by reducing the amount of diffusible hydrogen in the weld metal. If the total F conversion value of the fluoride is less than 0.21%, the above-mentioned effect cannot be obtained, so that the weld metal having preferable low temperature toughness and the simplification or omission of the preheating step cannot be achieved. In order to further reduce the amount of oxygen and the amount of diffusible hydrogen in the weld metal, the lower limit of the total F conversion value may be 0.30%, 0.40%, or 0.50%.

If the fluoride content is excessive, the amount of spatter during welding will increase. However, in the flux-cored wire according to the present embodiment, it is not necessary to set an upper limit value of the F conversion value of fluoride. This is because the present inventors have found that the upper limit of the fluoride content should be limited by using the spatter generation index X (X value) described later. The F-converted value of fluoride can be appropriately selected as long as the X value is within the range described below.

(CaF ₂ : less than 0.50% of the total mass of flux-cored wire)
CaF ₂ spatters in gas shielded arc welding using 100% CO ₂ gas compared to MgF ₂ , Na ₃ AlF ₆ , LiF, NaF, K ₂ ZrF ₆ , BaF ₂ and K ₂ SiF _6. Since it is generated in a large amount, it is preferable not to add it to the flux-cored wire according to the present embodiment. Therefore, the flux-cored wire according to the present embodiment _{limits the CaF 2} content to less than 0.50%. If the CaF ₂ content is limited to less than 0.50%, the problem of spatter can be ignored. In order to more reliably avoid the occurrence of spatter, _{the upper limit of the CaF 2} content may be 0.40% or 0.30%. Further, _{the lower limit of the CaF 2} content may be 0.10% or 0.00%.

(Spatter generation index X (X value): 5.00% or less with respect to the total mass of the flux-cored wire)
As described above, in gas shielded arc welding, particularly in gas shielded arc welding in which the shield gas is 100% CO ₂ gas, CaF ₂ among fluorides increases sputtering. Furthermore, in order to investigate the relationship between the type of fluoride and the amount of spatter, the present inventors contained various fluorides and applied vegetable oil to the outer skin without slit-like gaps in the steel outer skin. ) A large number of 1.2 mmφ wires were prepared. Welding current 280A, voltage 27V, welding speed 30cm / min, heat input 14.0kJ / cm, shield gas 100% CO ₂ , gas flow rate 25l / min, on a steel plate in a copper collection box. , And without preheating, weld beads were made for 1 minute using the various fluxed wires described above. The spatter scattered in the box and the spatter adhering to the steel plate 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 of 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 1 and the amount of spatter generated. It was found to be correlated.
X = [NaF] + [MgF ₂ ] + [Na ₃ AlF ₆ ] + 1.50 × ([K ₂ SiF ₆ ] + [K ₂ ZrF ₆ ] + [LiF] + [BaF ₂ ]) + 3.50 × ( [CaF ₂ ]) ... (Equation 1)
The chemical formula with [] in the formula (1) represents the content of the fluoride according to each chemical formula in mass% with respect to the total mass of the flux-cored wire, and the content of the fluoride not contained is regarded as 0.

In the formula 1, the chemical formula in parentheses indicates 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 the compound not contained in the flux-cored wire is considered to be 0%. By setting the X value defined in Equation 1 to 5.00% or less with respect to the total mass of the flux-cored wire, it was found that the amount of increase in spatter was about 5.0 g / min or less in the above test. The flux-cored wire, which can reduce the amount of spatter generated to about 5.0 g / min or less in the above test, provides good welding workability when used in welding in which _{the shield gas is 100% CO 2 gas.} be able to. 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.

The reason why the fluoride contained in the flux-filled wire reduces the amount of oxygen in the weld metal is not always clear, but we found that the fluoride was decomposed in the molten pool and recombinated with oxygen in the molten pool. I'm guessing that it's to surface. Further, the reason why the amount of spatter generated differs depending on the type of fluoride is not necessarily clear, but the present inventors have influenced the amount of spatter generated by the element chemically bonded to fluorine for some reason. I'm guessing that there is. It is not always clear why the fluoride contained in the flux-filled wire reduces the amount of diffusible hydrogen in the weld metal, but we found that the fluoride was decomposed by the welding arc and the generated fluorine was hydrogen. It is thought that it may be because it was combined with HF gas and diffused into the atmosphere as HF gas, or because hydrogen was fixed as HF in the weld metal as it was.

(One selected from the group consisting of Fe oxide, Ba oxide, Na oxide, Ti oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide. Total content of the above or two or more oxides in% by mass with respect to the total mass of the flux-filled wire: 0.30% or more and less than 3.50%)
The flux of the flux-cored wire according to the present embodiment contains a total of 0.30% or more and less than 3.50% of oxides. The type of this oxide is a group consisting of Fe oxide, Ba oxide, Na oxide, Ti oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide. One or more selected from, and CaO described later is not included. In the present embodiment, "oxide excluding CaO" may be simply referred to as "oxide".

Oxides other than CaO have the effect of maintaining the shape of the weld bead well. If the total content of oxides excluding CaO is less than 0.30%, the shape of the weld bead may deteriorate. In order to maintain the shape of the weld bead even better, the lower limit of the total amount of oxides excluding CaO may be 0.40%, 0.50%, 0.60%, or 0.70%. However, when the total amount of oxides excluding CaO is 3.50% or more, the amount of oxygen in the weld metal may be increased and the toughness of the weld metal may be lowered. To improve the toughness of weld metal, the upper limit of the total amount of oxides excluding CaO is 3.00%, 2.50%, 2.25%, 2.00%, 1.75%, 1.50%. , 1.25%, 1.00%, 0.90%, 0.80%, or 0.70%.

In addition to Fe oxide, Ba oxide, Na oxide, Ti oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide, for granulation of flux. Oxides contained in the binder used may be contained in the flux-filled wire. In this case, the total content of the oxides may be regarded as the total content of the oxides contained in the binder or the like used for granulating the flux. Fe oxides, Ba oxides, Na oxides, Ti oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, and K oxides are, for example, FeO, BaO, and Na _2. It may be O, TiO ₂ , SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , and K _{2 O.}

(Content of Ti oxide in mass% with respect to the total mass of the flux-cored wire: 0.10% or more and less than 2.50%)
_{Most of the Ti oxides such as TIO 2} contained in the flux are released to the outside of the weld metal as slag during welding. However, as described above, a part of the Ti oxide in the flux of the flux-containing wire according to the present embodiment is once reduced by Al to become metallic Ti, and then combined with oxygen in the weld metal for welding. Among metals, it is a Ti oxide that is effective for microstructure miniaturization of weld metals. Therefore, the Ti oxide contributes to the miniaturization of the weld metal and the improvement of low temperature toughness as a synergistic effect with Al as an alloy component. Furthermore, Ti oxide also contributes to the improvement of the weld bead shape. Even if the total content of oxides excluding CaO is 0.30% or more and less than 3.50%, if the Ti oxide contained in the oxides excluding CaO is less than 0.10%, the weld bead shape May get worse. In order to obtain these effects, it is necessary to set the lower limit of the content of Ti oxide to 0.10%. In order to obtain a better weld bead shape by using Ti oxide as an arc stabilizer, the lower limit of the Ti oxide content is set to 0.15%, 0.20%, 0.25%, 0. It may be 30%, 0.40%, or 0.45%. On the other hand, when the content of Ti oxide is 2.50% or more, the oxygen content of the weld metal may be increased and the toughness of the weld metal may be lowered. Therefore, the content of Ti oxide needs to be less than 2.50%. To further improve the toughness of the weld metal, the upper limit of the Ti oxide content was set to 2.40%, 2.20%, 2.00%, 1.80%, 1.50%, 1.25%. , 1.00%, 0.90%, 0.80%, 0.70%, 0.60%, or 0.50%.

(CaO: 0% or more and less than 0.20% in mass% of the total mass of the flux-cored wire)
CaO has properties different from those of other oxides, and when it is contained in an amount of 0.20% or more, a large amount of spatter is generated in gas shielded arc welding in _{which the shield gas is 100% CO 2 gas.} Furthermore, CaO changes to CaOH, which is a hydrogen-containing compound, when exposed to the atmosphere, thus increasing the diffusible hydrogen of the weld metal. Since CaO may be contained as an impurity in the flux raw material, it is necessary to select the flux raw material so that the CaO content is less than 0.20%. The CaO content is preferably 0.10% or less, or less than 0.10%. Since CaO is not required for the flux-cored wire according to the present embodiment, the lower limit of the CaO content is 0%. The lower limit of the CaO content may be 0.01%, 0.02%, or 0.05%.

(MgCO ₃ , Na ₂ CO ₃ , Li ₂ CO ₃ , CaCO ₃ , K ₂ CO ₃ , BaCO ₃ , FeCO ₃ , and MnCO _{3 of} one or more carbonates selected from the group. Total content in% by mass of flux-filled wire: 0-3.50%)
( _{Total value of MgCO 3} , Na ₂ CO ₃ , and Li ₂ CO ₃ contents: 0 to 3.00% by mass with respect to the total mass of the flux-cored wire)
The flux-cored wire according to this embodiment does not need to contain a carbonate. Therefore, the lower limit of the total content of carbonate in the flux-cored wire according to the present embodiment is 0%. However, the flux-containing wire according to the present embodiment is further selected from the group consisting of _{MgCO 3} , Na ₂ CO ₃ , Li ₂ CO ₃ , CaCO ₃ , K ₂ CO ₃ , BaCO ₃ , FeCO ₃ , and MnCO _3. It is preferable to contain 3.50% or less of one or more carbonates 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 carbonate is added to the flux-cored wire in order to obtain this effect, the total content of carbonate is preferably 0.30% or more. In order to further reduce the amount of hydrogen in the weld metal, the lower limit of the total content of carbonates may be 0.50% or 1.00%. On the other hand, if the amount of carbonate is excessive, the carbonate may dissolve in the weld metal during welding, increasing the amount of carbon and oxygen in the weld metal. In this case, the weld metal is excessively hardened and the low temperature toughness of the weld metal is lowered. Further, when the content of carbonate is excessive, the amount of welding fume generated becomes remarkable and the welding workability deteriorates. In order to avoid these situations, the total carbonate content needs to be 3.50% or less. To avoid the occurrence of welding fume, the upper limit of the total carbonate content is 3.00%, 2.50%, 2.00%, 1.50%, 1.00%, 0.50%, 0. .10%, 0.04%, 0.02%, or 0.01% may be used.

_{The total content of MgCO 3} , Na ₂ CO ₃ , and Li ₂ CO ₃ that may be contained in the above-mentioned carbonates needs to be 0 to 3.00%. Even if the total carbonate content is 0-3.50%, if the total content of MgCO ₃ , Na ₂ CO ₃ and Li ₂ CO ₃ is greater than 3.00%, the weld bead will be It becomes easy to hang down and welding workability deteriorates. In order to suppress the sagging of the weld bead, _{the upper limit of the total content of MgCO 3} , Na ₂ CO ₃ and Li ₂ CO ₃ may be 2.70%, 2.50%, or 2.00%. .. On the other hand, in order to further reduce the amount of hydrogen in the weld metal, the _{lower limit of the total content of MgCO 3} , Na ₂ CO ₃ and Li ₂ CO ₃ is more than 0.30%, 0.50%, 0.75. % Or 1.00%.

(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 include Fe and impurities. The Fe component includes Fe in the steel outer skin, iron powder added in the flux, and Fe in the alloy component. Impurities are components that are mixed in by raw materials such as ore or scrap, or various factors in the manufacturing process when industrially manufacturing a flux-filled wire, and adversely affect the flux-filled wire according to the present embodiment. Means what is allowed within the range that does not give.

Subsequently, the form of the flux-containing wire will be described.
FIG. 2 shows the cut surface of the flux-cored wire. FIG. 2 (a) shows a flux-cored wire made by butt-welding the edge surfaces, FIG. 2 (b) shows a flux-cored wire made by butt-butting the edge surfaces, and FIG. 2 (c) shows the edge surface. The flux-cored wire made by caulking is shown. 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, it is preferable to use a wire without slit-shaped gaps (seamless wire). ..

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 raises the moisture contained in the welding material, the moisture mixed from the atmosphere, the rust and scale adhering to the steel surface, etc., but under welding where the cleanliness of the weld and the conditions of the gas shield are sufficiently controlled. Then, hydrogen contained mainly in water in the wire is the main factor of diffusible hydrogen in the weld joint.

For this reason, it is desirable to use a tube with no slit-shaped gaps in the steel rind to suppress the invasion of hydrogen in the atmosphere from the steel rind into the flux between the time the wire is manufactured and the time it is used. When a pipe having a slit-shaped gap (seam) in the steel outer skin is used, moisture in the atmosphere easily invades into the flux through the slit-shaped gap in the outer skin, and as it is, invasion of a hydrogen source such as moisture. Therefore, if the period from manufacture to use is long, it is desirable to vacuum-pack the entire wire or store it in a container that can be kept dry.

Further, in order to improve the feeding property of the wire, a lubricant can be applied to the surface of the wire. As the lubricant applied to the wire surface, various kinds of lubricants such as vegetable oil can be used, but in order to suppress low temperature cracking of the weld metal, hydrogen such as perfluoropolyether oil (PFPE oil) is used. Minute-free oils are preferred.

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 alloy components, oxides, fluorides, carbonates and arc stabilizers are mixed so as to have a predetermined content are prepared. While feeding the steel strip in the longitudinal direction, it is formed into an open tube (U-shape) by a forming roll to form a steel outer skin, and during this forming, flux is supplied from the opening of the open tube to form the opposite edge surfaces of the openings. Weld the butt slit-shaped gap. As the welding method, electric stitch welding, laser welding, or TIG welding is used. 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, the slit-shaped gap is made into a pipe having a slit-shaped gap that is not welded, and the wire is drawn to obtain a wire having the slit-shaped gap.

A cross section of a wire formed by butt seam welding and having no slit-shaped gaps looks as shown in FIG. 2 (a). If this cross section is polished and etched, welding marks can be observed, but if it is not etched, no welding marks can be observed. Therefore, it is sometimes called seamless as described above. For example, "Introduction to Welding and Joining Technology" (2008), edited by the Welding Society, Sanpo Publishing, p. 111 is described as a seamless type.
FIG. 2 (b) shows an example in which the edge surfaces are butted, and FIG. 2 (c) shows an example in which the edge surfaces are crimped. Even if the wire is brazed after being crimped as in c), a wire having no slit-shaped gap can be obtained. Further, in FIGS. 2B and 2C, the wire as it is without brazing becomes a wire having a slit-shaped gap.

Next, the method for manufacturing the welded joint according to the present embodiment described above will be described. The method for manufacturing a welded joint according to the present embodiment includes a step of welding a steel plate using the above-described gas-shielded arc welding flux-containing wire according to the present embodiment. The use of the flux-cored wire according to the present embodiment is not particularly limited. Therefore, also in the method for manufacturing the welded joint according to the present embodiment, the type of the base steel plate and the type of the shield gas are not particularly limited. The method for manufacturing a welded joint according to the present embodiment is excellent in workability because it uses a flux-containing wire that reduces the amount of spatter and the amount of diffusible hydrogen in the weld metal. Further, in the method for manufacturing a welded joint according to the present embodiment, a flux-containing wire containing a fluoride in which the alloy component and the metal deoxidizing component are preferably adjusted and the amount of oxygen in the weld metal can be reduced is used, so that the tensile strength is strong. It is possible to manufacture a welded joint provided with a weld metal including a weld metal having excellent elongation, elongation, and low temperature toughness.

The welding method according to this embodiment can be applied to gas shielded arc welding of low temperature steel such as 3.5% Ni steel. In this case, it shows a further advantage over the prior art. While the mechanical properties of the weld metal can be maintained, a flux-cored wire having a reduced amount of alloying elements such as Ni, which is more expensive than the conventional flux-cored wire for welding low-temperature steel, is used. Such a welding method is excellent in economic efficiency.

Further, in the welding method according to the present embodiment, the shield gas used in the temporary welding is 100% CO ₂ gas, and the shield gas used in the main welding is pure Ar gas or pure He gas and 2.5. It can be a mixed gas with ~ 30.0% by volume O ₂ or 2.5 to 30.0% by volume CO _2. In this case, the welding cost can be reduced without deteriorating the welding work environment by spattering, which further shows an advantage over the prior art. Further, the welding conditions such as current and voltage may be the conditions normally used.

The shape of the welded joint to be manufactured is determined according to the application and is not particularly limited. It can be applied to welded joints that form grooves, such as ordinary butt joints, square joints, and T joints. Therefore, the shape of the steel plate to be welded may be as long as at least the portion forming the welded joint is plate-shaped, and the entire steel plate does not have to be a plate, and includes, for example, shaped steel. Further, the joint is not limited to one composed of separate steel plates, and may be a butt welded joint formed by molding one steel plate into a predetermined shape such as a tubular shape.

Next, an example of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is described in this one condition example. It is not limited. The present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

While feeding the steel strips of the chemical components shown in Table 1 (expressed as% by mass with respect to the total mass of the exodermis; the rest is iron and impurities) in the longitudinal direction, the steel strips are formed into an open tube by a forming roll, and during this forming, from the opening of the open tube Flux is supplied and the opposite edge surfaces of the openings are butt-seam welded to form a seamless pipe (excluding the wire with the notation "caulking" in the wire number), and the wire is drawn. Anneading was performed in the middle of the work, and a flux-containing wire having a final wire diameter of φ1.2 mm was prototyped. The components of the wire thus obtained are shown in Tables 2-1 to 3-2. "Chemical composition of an alloy of wire" means a metal component or alloy component that does not form fluoride, oxide, or carbonate. The rest of the components of the entire wire are Fe and impurities. After the trial production, a lubricant was applied to the surface of the wire and used for welding described later. Tables 4-1 and 4-2 show the types of lubricants and the types of shield gas used in the main welding. The shield gas for temporary welding in all the invention examples and the comparative examples was 100% CO ₂ . The unit of composition of the shield gas is vol%. Vegetable oils were applied to all the oils not described as PFPE oils in Tables 4-1 and 4-2. In addition, the wire with the notation "caulking" in the wire number is a seamless pipe that is not seam welded, and is a flux-cored wire with a wire diameter of φ1.2 mm obtained by drawing the wire. is there.

Using this flux-cored wire, the mechanical properties of the weld metal were evaluated in accordance with JIS Z3111 (2005). That is, steel plates having a thickness of 20 mm are butted against each other with a root gap of 16 mm and a groove angle of 20 °, and welding is performed using the backing metal of the steel plates under the welding conditions shown in Tables 4-1 and 4-2. did. A test piece was prepared by performing buttering on the groove surface of the steel sheet and the surface of the backing metal with two or more layers and a surplus height of 3 mm or more using a flux-cored wire to be tested. This buttering prevents the components of the welding material from being diluted by the base material, and the characteristics of the welding material can be accurately evaluated.

From the prepared test piece, A0 tensile test piece (round bar) (diameter = 10 mm) and Charpy test piece (2 mm V notch) conforming to JIS Z3111 (2005) shown in FIG. 3 were collected as mechanical test pieces. Then, each mechanical property test was carried out, and the tensile strength and total elongation of the weld metal and the Charpy absorption energy at −100 ° C. were measured. The measurement results of the obtained mechanical properties are shown in Table 5-1 and Table 5-2. The tensile strength was 450 MPa or more, the total elongation was 25% or more, and the Charpy absorption energy was 34 J or more.

The amount of spatter at the time of temporary attachment was measured as follows. In a copper collection box, on a steel plate with a bead-on plate, welding current 280 A, voltage 27 V, welding speed 30 cm / min, heat input 14.0 kJ / cm, shield gas type 100% CO ₂ , gas flow rate 25 l / A weld bead was prepared for 1 minute under the condition of minutes and no preheating. The spatter scattered in the box and the spatter adhering to the steel sheet were collected, and the weight of the spatter having a diameter of more than 1.0 mm was measured. The results are shown in Tables 5-1 and 5-2 in units of g / min. Samples with a spatter generation amount of 5.0 g / min or less were accepted.

As shown in Tables 5-1 and 5-2, the wire numbers A1 to A10 of Examples are excellent in tensile strength, low temperature toughness, and total elongation of the weld metal, and are also excellent in temporary weldability. , Was a pass.
On the other hand, since the wire numbers B1 to B9, which are comparative examples, do not satisfy the requirements specified in the present invention, they satisfy one or more of the tensile strength, total elongation, low temperature toughness, and temporary weldability of the weld metal. I couldn't, and I failed.

According to the present invention, by reducing the Ni content to 5.0% by mass or less, which is equivalent to that of Ni-based low-temperature steel, welding work efficiency is excellent in gas shielded arc welding, and an inexpensive flux-containing wire can be obtained. By reducing the alloy component in the flux-containing wire and reducing the amount of oxygen in the weld metal, it is possible to provide a weld metal having excellent low temperature toughness at −100 ° C. Therefore, the present invention has high industrial applicability.

Claims (11)

A flux-cored wire for gas shielded arc welding including a steel outer skin and a flux filled inside the steel outer skin.
The flux is
_{CaF 2} , MgF ₂ , Na ₃ AlF ₆ , LiF, NaF, K ₂ ZrF ₆ , BaF ₂ , and K ₂ SiF, which have a total F conversion value of 0.21% or more with respect to the total mass of the flux-cored wire. One or more fluorides selected from the group consisting of _{6 and}
Fe oxide, Ba oxide, Na oxide, Ti oxide, Si oxidation in which the total value of the content of the flux-containing wire in% by mass with respect to the total mass is 0.30% or more and less than 3.50%. One or more oxides selected from the group consisting of substances, Zr oxides, Mg oxides, Al oxides, Mn oxides, and K oxides, and
_{MgCO 3} , Na ₂ CO ₃ , Li ₂ CO ₃ , CaCO ₃ , K ₂ CO ₃ , BaCO, the total content of the flux-filled wire in mass% with respect to the total mass is 0 to 3.50%. _3. One or more carbonates selected from the group consisting of FeCO ₃ and MnCO _{3 and}
Including
The content of CaO in the flux is 0% or more and less than 0.20% in mass% with respect to the total mass of the flux-cored wire.
The content of iron powder in the flux is 0% or more and less than 10.0% in mass% with respect to the total mass of the flux-cored wire.
The X value calculated using the formula (1) is 5.00% or less with respect to the total mass of the flux-cored wire.
The CaF ₂ content is less than 0.50% by mass of the flux-cored wire with respect to the total mass.
The content of the Ti oxide is 0.10% or more and less than 2.50% in mass% with respect to the total mass of the flux-cored wire.
_{The total value of the contents of MgCO 3} , Na ₂ CO ₃ , and Li ₂ CO ₃ is 0 to 3.00% by mass with respect to the total mass of the flux-cored 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: 0.001% or more and 0.080% or less,
Si: 0.001% or more and 0.800% or less,
Mn: 0.10% or more and 1.50% or less,
Al: 0.005% or more and 0.500% or less,
Ni: 3.0% or more and 4.9% or less,
Ti: 0.005% or more and 0.100% or less,
Mg: 0.20% or more and 0.80% or less,
P: 0.030% or less, and
S: A flux-cored wire for gas shielded arc welding, which contains 0.030% or less and the balance is composed of Fe and impurities.
X = [NaF] + [MgF ₂ ] + [Na ₃ AlF ₆ ] + 1.50 × ([K ₂ SiF ₆ ] + [K ₂ ZrF ₆ ] + [LiF] + [BaF ₂ ]) + 3.50 × ( [CaF ₂ ]) ・ ・ ・ (1)
The chemical formula with [] in the formula (1) represents the content of the fluoride according to each chemical formula in mass% with respect to the total mass of the flux-cored wire, and the content of the fluoride not contained is 0. Consider it as. The flux-containing wire for gas shielded arc welding according to claim 1, wherein the carbonate is contained in a total of 2.00% or less in mass% with respect to the total mass of the flux-containing wire. Further, by mass% of the total mass of the flux-cored wire,
B: 0.0100% or less,
The gas shielded arc welding according to claim 1 or 2, wherein one or more selected from the group consisting of Cu: 0.5% or less and REM: 0.050% or less is contained. Flux-filled wire. The flux for gas shielded arc welding according to any one of claims 1 to 3, wherein the hardenability index α represented by the following formula (2) is 0.25% or more and 0.51% or less. Wire.
α = [C] + [Si] / 24 + [Mn] / 6 + ([Ni] + [Cu]) / 15 ... (2)
The element with [] in the formula (2) is the content of the element contained in the chemical component excluding the fluoride, the oxide, and the carbonate in mass% with respect to the total mass of the flux-filled wire. Represents. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 4, wherein the high-temperature cracking susceptibility index β represented by the following formula (3) is 3.1 or less. β = [Si] / 6 + [Mn] /1.5+ [Ni] /3+200 × [B] ... (3)
The element with [] in the formula (3) is the content of the element contained in the chemical component excluding the fluoride, the oxide, and the carbonate in mass% with respect to the total mass of the flux-filled wire. Represents. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 5, wherein the elongation index γ represented by the following formula (4) is 1.8 or less.
γ = [Mn] + [Mg] ... (4)
The element with [] in the formula (4) is the content of the element contained in the chemical component excluding the fluoride, the oxide, and the carbonate in mass% with respect to the total mass of the flux-filled wire. Represents. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 6, 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 6, 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 8, wherein the surface of the steel outer skin is provided with perfluoropolyether oil. A method for manufacturing a welded joint, comprising a step of welding a steel plate using the flux-containing wire for gas shielded arc welding according to any one of claims 1 to 9. The shield gas used in the temporary welding in the welding process is 100% CO ₂ gas.
The production of a welded joint according to claim 10, wherein the shield gas used in the main welding in the welding step _{is a mixed gas of Ar and 2.5 to 30.0% by volume of CO 2.} Method.

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