JP2018192518A - Flux-cored wire for gas shield arc welding, and manufacturing method of weld joint - Google Patents

Abstract

To provide a flux-cored wire and a manufacturing method of a weld joint, with which a weld metal can be obtained having excellent tensile strength, elongation, and low-temperature toughness, and with which welding workability is high and an amount of expensive alloy elements is reduced.SOLUTION: In a flux-cored wire for gas shield arc welding, the flux comprises: 0.21% or more of fluoride in total of an F conversion value; 0.30% or more but less than 3.50% of oxides; 0 to 3.50% of carbonates; 0% or more but less than 0.20% of CaO; 0% or more but less than 10.0% of iron powder; a spatter generation index X of 5.00% or less; less than 0.50% of CaF; 0.10% or more but less than 2.50% of Ti oxides; and 0 to 3.00% of MgCO, NaCO, and LiCOin a total value of their contents. Further, in the flux-cored wire, an alloy component and a metal deoxidizing component fall within a prescribed range.SELECTED DRAWING: Figure 2

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 purification process, hydrocarbon gas having a low carbon number is produced as a secondary. 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 building hydrocarbon gas carriers and above-ground tanks.

  The low carbon number hydrocarbon gas is maintained at about −100 ° C. or lower. Candidate 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. Ni-added steel is superior in terms of steel material cost and strength as compared to Al alloy and stainless steel, and further has good toughness even in a low temperature environment. In the construction of a hydrocarbon gas tank, good toughness in a low temperature environment at −100 ° C. or lower is also required for the weld metal to which this Ni-added steel is joined.

  In constructing a welded structure to be used in such a low temperature environment, various welding methods are applied. From the viewpoint of excellent work efficiency, gas shielded arc welding using a flux-cored wire is used. Is preferable. However, at present, there is no inexpensive flux-cored wire that can ensure the low temperature toughness of the weld metal for the joining of Ni-added steel. Due to the necessity of satisfying strict safety, Ni-based alloy welding materials containing 60 to 80% Ni are currently used.

Since the Ni-base alloy welding material contains a large amount of Ni, it is extremely expensive and easily generates hot cracks. Furthermore, since the Ni-based alloy welding material has a poor molten metal flow, 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, and therefore, the Ni-based alloy welding material also has a problem with respect to welding construction efficiency. Furthermore, it is common to use welding by using inexpensive 100% CO ₂ gas as a shield for tack welding, but the welding material of Patent Document 5 described later was used in combination with 100% CO ₂ gas. In this case, a large amount of spatter is generated. A large amount of spatter causes uneven coating after welding and generation of defects in subsequent welding.

  For such a current situation, for example, the following welding materials have been proposed as flux-cored wires for low-temperature steel.

In Patent Document 1, in order to obtain a weld metal having excellent toughness at −100 ° C., the main component is a metal fluoride in which the Ti oxide in the flux is reduced so that the amount of oxygen in the weld metal is reduced. A flux-cored wire is disclosed.
Patent Document 2 discloses a flux-cored wire in which metal fluoride is added to the flux to reduce the amount of oxygen, and Ni is added to improve toughness.
Patent Document 3 describes a flux that reduces the amount of weld metal oxygen by replacing the slag component in the flux from a Ti oxide system to a metal fluoride system, and improves the low temperature toughness by defining the ratio of fluoride to oxide. Cored wire is disclosed.
In Patent Document 4, in order to ensure a toughness of −40 ° C. in a weld metal having a strength of 780 MPa or more, the flux is replaced from a Ti oxide system to a metal fluoride system, and the amount of addition of Mo is defined.
Patent Document 5 discloses a pulse gas shielded arc welding method using a flux-cored wire in which the ratio of the content of fluoride and oxide is within a predetermined range and the content of Ceq is limited within the predetermined range. ing. Since the flux-cored wire described in Patent Document 5 contains a large amount of CaF ₂ , welding efficiency is significantly reduced by generating a large amount of spatter during 100% CO ₂ shield gas welding.
Non-Patent Document 1 discloses that the energy absorbed at −90 ° C. is about 100 J by using a flux-cored wire containing about 2% of Ni.
However, when the low temperature toughness is evaluated at −100 ° C. with respect to the weld metal obtained by welding using the flux-cored wire disclosed in these documents, the required level may not be reached.

JP 2010-064087 A Japanese Patent No. 3120912 JP-A-9-57488 Japanese Patent No. 5644984 JP 2008-246507 A

Kazuhiro Kojima et al. , OMAE99 / MAT-2102, “Development of Offshore Structure Steels and Welding Materials for Ultra Low Temperature Service 3-Welding Materials”.

  In view of such circumstances, the present invention provides a weld metal that is excellent in tensile strength, elongation, and toughness at −100 ° C., has high welding workability, and further reduces the amount of expensive alloy elements. It is an object of the present invention to provide a cored wire and a method for manufacturing a welded joint using the same.

The gist of the present invention is as follows.
(1) A flux-cored wire for gas shielded arc welding according to an aspect of the present invention includes a steel outer sheath and a flux filled in the steel outer sheath, and the flux is the entire flux-cored wire. 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 , where the total F converted value with respect to mass is 0.21% or more. Fe oxide, Ba, wherein the total content of one or more fluorides and the content of the flux-cored 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 oxide, Na oxide, Ti oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide Things and The total value of the content by mass% relative to the total weight of the flux cored wire is _{0~3.50%, MgCO 3, Na 2} CO 3, Li 2 CO 3, CaCO 3, K 2 CO 3, BaCO ₃ , one or two or more carbonates selected from the group consisting of FeCO ₃ and MnCO ₃ , and the content of CaO in the flux is expressed by mass% with respect to the total mass of the flux-cored wire. 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% by mass% with respect to the total mass of the flux-cored wire, and the formula (A) X value calculated using is 5.00% or less with respect to the total mass of the flux-cored wire, and the content of the CaF ₂ is a quality with respect to the total mass of the flux-cored wire. The content of the Ti oxide is less than 0.50% by mass%, and is 0.10% or more and less than 2.50% by mass% with respect to the total mass of the flux-cored wire, and the MgCO ₃ , Na ₂ CO _3, and the sum of the content of the _Li 2 CO ₃ is from 0 to 3.00% by mass% relative to the total weight of the flux-cored wire, further, the fluoride, the oxide, and the The chemical composition excluding carbonate is mass% with respect to the total mass of the flux-cored wire, C: 0.001% to 0.080%, Si: 0.001% to 0.800%, Mn: 0 10% to 1.50%, Al: 0.005% to 0.500%, Ni: 3.0% to 5.5%, Ti: 0.005% to 0.100%, Mg : 0.20% or more and 0.80% Lower, P: 0.030% or less, and, S: containing 0.030% or less, the balance being 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 ]) (A)
In addition, 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 fluoride not contained is 0. It is considered.
(2) The flux-cored wire for gas shielded arc welding described in (1) above may contain the carbonate in a total of 2.00% or less by mass% with respect to the total mass of the flux-cored wire. .
(3) The flux-cored wire for gas shielded arc welding according to (1) or (2) above is further in mass% with respect to the total mass of the flux-cored wire, and B: 0% or more and 0.0100% or less, You may contain 1 type, or 2 or more types selected from the group which consists of Cu: 0.5% or less and REM: 0.050% or less.
(4) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (3) above, the hardenability index α represented by the following formula (B) is 0.25% or more and 0.51. % Or less.
α = [C] + [Si] / 24 + [Mn] / 6 + ([Ni] + [Cu]) / 15 (B)
In addition, 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-cored wire. Represents.
(5) The flux-cored wire for gas shielded arc welding according to any one of (1) to (4) above has a hot crack susceptibility index β represented by the following formula (C) of 3.1 or less. Also good.
β = [Si] / 6 + [Mn] /1.5+ [Ni] / 3 + 200 × [B] (C)
In addition, 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-cored wire. Represents.
(6) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (5) above, the elongation index γ represented by the following formula (D) may be 1.8 or less. .
γ = [Mn] + [Mg] (D)
In addition, 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-cored 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 a gap.
(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 include perfluoropolyether oil on the surface of the steel outer shell.
(10) A method for manufacturing a welded joint according to another aspect of the present invention includes a step of welding a steel plate using the flux-cored wire for gas shielded arc welding according to any one of (1) to (9) above. Is provided.
(11) In the method for manufacturing a welded joint according to (10) above, in the main welding in the welding step, the shielding gas used in the tack welding in the welding step is 100% CO ₂ gas. 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, the Ni content is reduced to 5.5% by mass or less, which is the same as that of Ni-based low-temperature steel, so that it is excellent in welding construction efficiency in gas shielded arc welding and is an inexpensive flux-cored wire, By setting the alloy component in the flux-cored wire within a predetermined range and reducing the oxygen content of the weld metal, a weld metal excellent in tensile strength and low temperature toughness at −100 ° C. can be provided. Moreover, according to the present invention, the amount of spatter generated can be reduced even during 100% CO ₂ shield gas welding.

It is the figure showing the relationship between the spatter generation amount and the X value of the flux cored wire at the time of 100% CO ₂ shield gas welding for tack welding. It is sectional drawing of a flux cored wire. (A) is a flux-cored wire made by welding the edge surfaces, (b) is a flux-cored wire made by butting the edge surfaces, and (c) is a diagram showing a flux-cored wire made by crimping the edge surfaces. It is. It is a figure which shows the sampling position of the test piece based on JISZ3111-2005 concerning an Example and a comparative example.

(1) About low temperature toughness of weld metal The present inventors examined the flux cored wire which the low temperature toughness of a weld metal improves. Steel materials used in a low temperature environment, particularly weld metals formed by joining of Ni-based steel for low temperature use, are required to have a toughness (low temperature toughness) at −100 ° C. of 34 J or more. In order to ensure this low temperature toughness, the present inventors considered that it was necessary to (1-1) reduce the amount of oxygen in the weld metal and (1-2) refine the structure of the weld metal. . Furthermore, the present inventors considered that it is preferable to perform (1-3) suppression of grain boundary ferrite generation in the weld metal and (1-4) suppression of second phase generation in the weld metal. Note that (1-5) the amount of Ni in the weld metal also greatly affects the toughness. However, since the manufacturing cost increases when the Ni content of the flux-cored wire is increased, the present inventors minimize the Ni content and use the other means (1-1) to (1-4). Attempted to improve low temperature toughness.

(1-1) Reduction of oxygen content As means for reducing the oxygen content in the weld metal, fluoride components such as LiF, NaF, CaF ₂ , and MgF ₂ are contained in the flux-cored wire, Si, Mn, Ti And a deoxidizing element such as Al as a deoxidizing component (that is, in a form that does not constitute fluoride, oxide, and carbonate) in a flux-cored wire, and gas shielded arc welding using an inert gas It was thought to do. However, in gas shielded arc welding using inert gas, the arc becomes unstable, the penetration depth cannot be obtained sufficiently, and a sound weld metal without welding defects cannot be obtained. Therefore, the present inventors considered that it may be difficult to use as a means for reducing the amount of oxygen in the weld metal. Therefore, in the flux cored wire according to the present embodiment, the fluoride component and the metal deoxidation component are set within a predetermined range in order to reduce the amount of oxygen in the weld metal.

(1-2) Microstructural refinement As a means of microstructural refinement for ensuring low temperature toughness, the present inventors have developed Ti and Al compounds (mainly the formation nuclei of fine intragranular transformation structures). , Ti oxide and Al oxide). The Ti oxide and Al oxide finely dispersed in the weld metal can make the crystal grain size in the structure of the weld metal finer by increasing the number of crystal grains. In order to increase the number of Ti oxides and Al oxides contained in the weld metal, in the flux-cored wire according to this embodiment, the alloy Al content, the alloy Ti content, and the Ti oxide content are within a predetermined range. It is assumed to be inside. Since most of Ti oxide and Al oxide as slag components to be described later are discharged from the weld metal during welding and become slag, what are Ti oxide and Al oxide contained in the weld metal? Differentiated.

(1-3) Suppression of intergranular ferrite formation By means of the above (1-1) and (1-2), the low temperature toughness of the weld metal can be increased while sufficiently reducing the Ni content. However, it is possible to further improve the low temperature toughness by suppressing the formation of intergranular ferrite in the weld metal. In the weld metal after melting and solidification by welding, grain boundary ferrite is generated from the austenite structure when the temperature is lowered, 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 in order to suppress 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 means of the above (1-1) to (1-3), the low temperature toughness of the weld metal can be increased while sufficiently reducing the Ni content. However, it is possible to further improve the low temperature toughness by suppressing the formation of the second phase in the weld metal. 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)
In addition, 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-cored wire. .

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

(2) About the elongation and tensile strength of the weld metal The elongation of the weld metal tends to be inversely proportional to the hardness and tensile strength of the weld metal. Therefore, in the flux-cored wire according to the present embodiment, the amount of elements that enhance the hardenability such as C, Si, Mn, and Ni is reduced within a range in which the tensile strength required for the weld metal can be secured. Thus, the elongation of the weld metal is ensured. In addition, by increasing the hardenability of austenite grain boundaries by containing B, the amount of elements that enhance the hardenability such as C, Si, Mn, Ni can be suppressed, so the strength of the weld metal does not increase excessively. , Leading to securing toughness and elongation.

More preferably, in the flux cored wire according to the present embodiment, the elongation index γ defined by the following equation is set within a predetermined range.
γ = [Mn] + [Mg] (4)
In addition, 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-cored wire. .

  The inventors have found that there is a relatively strong correlation between the total amount of alloy components Mn and Mg contained in the flux-cored wire and the elongation of the weld metal. By managing the total content of Mn and Mg as the elongation index γ and making 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 with excellent low-temperature toughness, it is essential to reduce the oxygen content of the weld metal by adding fluoride to the flux-cored wire. is there. However, fluoride significantly increases the amount of spatter generated during welding. A large amount of spatter causes uneven coating after welding and generation of defects in subsequent welding.

The present inventors diligently studied a means for reducing the spatter amount while ensuring the low temperature toughness of the weld metal. As a result, the present inventors have found that the amount of sputtering varies depending on the fluoride species. Therefore, by quantitatively investigating the relationship between the type and amount of fluoride and the amount of spatter and conducting multiple regression analysis, there is a good linear relationship between the X value defined by the following formula and the amount of spatter. 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)
In addition, 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.

  Select the type of fluoride so that the X value is below the specified upper limit, and increase the total F converted value of the fluoride within that range, thereby improving the low temperature toughness of the weld metal while suppressing the amount of spatter The present inventors have found that this is possible. Therefore, in the flux-cored wire according to this embodiment, the type and amount of fluoride are defined by the sum of the X value and the F converted value.

  The inventors of the present invention have reached the present invention through the above-described examination process, and the necessary and preferred requirements will be sequentially described with respect to the present invention.

  The flux cored wire according to the present embodiment includes a steel outer sheath and a flux filled in the steel outer sheath. First, the component composition of the alloy component and the metal deoxidation component contained in the steel outer shell and the flux and the reason for the limitation will be described. In the flux-cored wire according to this embodiment, the alloy component and the metal deoxidation component are components that do not constitute fluoride, oxide, or carbonate. Accordingly, the content of elements constituting fluoride, metal oxide, or carbonate is not included in the alloy component and the metal deoxidation component. The alloy component and metal deoxidation component described below may be included in the flux in the form of metal powder or alloy powder, may be included as an alloy element in the steel outer shell, or may be plated on the steel outer shell. Content of each component shall mean the component content used as the sum total of the mass% of each component in the steel outer sheath and the flux with respect to the total mass of the wire.

(C: 0.001% to 0.080%)
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 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 high hardenability. Therefore, if the flux-cored wire contains C over 0.080%, the weld metal is extremely hardened. The toughness and elongation are greatly reduced, and hot cracks and cold cracks occur in the weld metal. In order to ensure toughness stably, the upper limit of the C content may be 0.070% or 0.060%.

(Si: 0.001% to 0.800%)
Si is an element necessary for improving the cleanliness of the weld metal and suppressing the occurrence of weld 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 easily segregates microscopically, and if more than 0.800% Si is contained in the flux-cored wire, the Si segregation part is significantly brittle. Will occur. Therefore, the upper limit of the Si content is 0.800%. Further, in order to stably secure the toughness of the weld metal, the upper limit of Si may be set to 0.600% or 0.550%.

(Mn: 0.10% to 1.50%)
Mn is an element necessary for improving the cleanliness of the weld metal and further degrading S and improving the toughness of the weld metal by forming MnS. In order to obtain the effect, it is necessary to contain 0.10% or more of Mn in the flux-cored wire. In order to further improve toughness, the lower limit of the Mn content may be 0.20%, 0.30%, or 0.40%. On the other hand, in a weld metal containing 3.0 to 5.5% Ni, Mn is easily segregated microscopically, and if Mn is added to the flux-cored wire in excess of 1.50%, significant embrittlement occurs in the Mn segregation part. Arise. In order to ensure 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% to 0.500%)
Al is a strong deoxidizer, and is an essential element for reducing Ti from Ti oxide, which is a slag agent, and ensuring fine Ti oxide effective for refinement of the microstructure of the weld metal. However, if the Al content in the flux-cored wire is less than 0.005%, the reduction effect of the slag Ti oxide by Al is insufficient, so it is not possible to secure fine Ti oxide in the weld metal that becomes the core of intragranular ferrite. . In this case, since the microstructure of the weld metal is not refined, the low temperature toughness of the weld metal is not improved. In order to further improve toughness, the lower limit of the Al content may be 0.030% or 0.040%. On the other hand, if more than 0.500% Al is contained in the flux-cored wire, the amount of Al oxide is greatly increased, and a large complex oxide of Al oxide and Ti oxide is formed in the weld metal. The As a result, the Ti oxide in the weld metal does not function as a nucleus of intragranular ferrite, and the microstructure of the weld metal is not refined, so that the toughness of the weld metal is reduced. In this case, the toughness of the weld metal also decreases due to an increase in the amount of Al nitride produced. Therefore, the upper limit of the Al content is 0.500%. Moreover, in order to ensure the toughness of a weld metal more stably, it is good also considering the upper limit of Al content as 0.200%, 0.100%, or 0.050%.

(Ni: 3.0% to 5.5%)
Ni is the only element that can improve its toughness regardless of the structure and components of the weld metal by solid solution toughening (the effect of increasing toughness by solid solution). 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 secure low temperature toughness more stably, the lower limit of the Ni content may be 3.1%, 3.2%, or 3.5%. On the other hand, when more than 5.5% Ni is contained in the flux-cored wire, the effect is saturated, the welding material cost increases, and hot cracking of the weld metal occurs. Therefore, the Ni content is 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 part of the metal Ti contained in the flux-cored wire is oxidized and slag-off, and the rest remains in the weld metal. 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 functions to improve 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. Ti forms a nitride prior to B to fix N in the high temperature region of the initial molten metal solidification process. Thereby, B does not form BN in the subsequent molten metal solidification process. That is, Ti is an essential component for segregating B as free B to the austenite grain boundary. This free B has the effect of improving the low-temperature toughness of the weld metal in synergy with the effect of refining the intragranular ferrite by the Ti oxide by suppressing the formation of coarse ferrite at the grain boundaries. For this effect, it is not sufficient to secure only the amount of Ti by reduction of the Ti oxide, and the above effect can be obtained only by containing metal Ti in the flux-cored wire. However, when the Ti content in the flux-cored wire is less than 0.005%, most of the metal Ti is oxidized and consumed, and sufficient Ti does not remain in forming TiN on the weld metal, so the above effect cannot be obtained sufficiently. Further, the refinement of the microstructure becomes insufficient, and the effect of improving toughness cannot be obtained. In order to further improve toughness, the lower limit of the Ti content may be 0.030% or 0.040%. Further, when Ti of more than 0.100% is contained in the flux-cored wire, the solid solution Ti is increased, the weld metal is excessively hardened, and the toughness is remarkably lowered. Therefore, the Ti content is 0.100% or less. Moreover, in order to ensure the toughness of a weld metal more stably, it is good also considering the upper limit of Ti content as 0.080% or 0.070%.

(P: 0.030% or less)
P is an impurity element and deteriorates the toughness of the weld metal, so 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 an allowable range of this adverse effect. In order to further improve the toughness of the weld metal, the upper limit of the P content may be 0.015%, 0.010%, 0.008%, or 0.006%.

(S: 0.030% or less)
Since S is an impurity element and significantly deteriorates the toughness of the weld metal, it is preferably reduced as much as possible. As a range in which an adverse effect on toughness is acceptable, the S content of the flux-cored wire is limited to 0.030% or less. In order to further improve the toughness of the weld metal, the upper limit of the S content may be 0.008%, 0.006%, 0.004%, or 0.003%.

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

  In addition to the basic component (essential element) described above as an alloy component or deoxidizing component, the flux-cored wire according to the present embodiment further includes B, Cu, depending on the strength level of the steel sheet to be welded or the degree of toughness required. In addition, 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 this embodiment, the lower limit value of the content of these selective elements is 0%. Regardless of whether or not the selected element is contained, if the content of the essential element in the flux-cored wire is within the specified range, the flux-cored wire is regarded as being within the range of the flux-cored wire according to the present embodiment. It is.

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

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

(REM: 0.050% or less)
REM is an element that can contribute to improving the toughness of the weld metal by reducing the size of sulfides and oxides in the weld metal, and thus may be added. However, if the flux-cored wire contains more than 0.050% of REM, spattering becomes intense and welding workability becomes poor. Moreover, in order to contribute to reduction of spatter and arc stability, 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 a lanthanoid, and the “content of REM” means the total content of these 17 elements. When lanthanoid is used as REM, REM is added industrially in the form of misch metal.

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

(Hot cracking susceptibility index β: 3.1 or less)
The alloy component contained in the flux-cored wire may easily cause hot cracking, and in order to suppress this, the hot cracking susceptibility index β represented by the following formula (3) is 3.1 or less. Furthermore, 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 hot cracking susceptibility, the amount of these elements is limited by the formula (3) in addition to the above-mentioned limitation while preventing hot cracking. It is preferable for obtaining the effect of each element.
β = [Si] / 6 + [Mn] /1.5+ [Ni] / 3 + 200 × [B] (3)
In addition, 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.

(Elongation 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 formula (4) is 1.8 or less. Since Mn and Mg are elements that have a particularly strong effect of hardening the weld metal and reducing the elongation, the amount of these elements may be limited by the formula (4) in addition to the above-mentioned limitation. It is preferable to obtain the effect of each element while ensuring the above.
γ = [Mn] + [Mg] (4)
In addition, 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.

  Then, the slag component inserted in the steel outer skin of a wire is demonstrated. The slag component described below is a fluoride, oxide, or carbonate, and is distinguished from the alloy component and metal deoxidation component described above.

(CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , LiF, NaF, K ₂ ZrF ₆ , BaF ₂ , and one or more fluorides selected from the group consisting of K ₂ SiF ₆ in flux (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 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 . A total of 0.21% or more fluoride is contained in terms of F with respect to the total mass of the flux-cored wire. The F-converted value with respect to the total mass of the flux-cored wire indicates the amount of fluorine (F) contained in the fluoride as a mass% with respect to the total mass of the flux-cored wire. For example, when n% of CaF ₂ is contained in the flux-cored wire in mass% with respect to the total mass of the flux-cored wire, the F-converted value of CaF ₂ is obtained by the following formula 5.
(F converted value of CaF ₂ ) = n × (19.00 × 2 / 78.08) (Formula 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 It is. For fluorides other than CaF ₂ , F conversion values can be calculated in the same manner. When a plurality of types of fluorides are included in the flux, the total value of F converted values of the respective fluorides is regarded as the F converted value of the fluorides included in the flux.

  The fluoride contained in the flux increases the low temperature toughness of the weld metal by reducing the oxygen content of 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 converted value of fluoride is less than 0.21%, the above-mentioned effects cannot be obtained, so that it is not possible to achieve simplification or omission of the weld metal having a preferable low temperature toughness and the preheating process. In order to further reduce the oxygen content and diffusible hydrogen content of the weld metal, the lower limit of the total F converted value may be 0.30%, 0.40%, or 0.50%.

  When the content of fluoride is excessive, the amount of spatter during welding increases. However, in the flux-cored wire according to this embodiment, it is not necessary to determine the upper limit value of the F-converted value of fluoride. This is because the inventors have found that the upper limit value of the fluoride content should be limited using a sputter 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% with respect to the total mass of the flux-cored wire)
Compared with MgF ₂ , Na ₃ AlF ₆ , LiF, NaF, K ₂ ZrF ₆ , BaF ₂ , and K ₂ SiF ₆ , CaF ₂ is sputtered in gas shielded arc welding using 100% CO ₂ gas. In order to generate in large quantities, it is preferable not to add to the flux-cored wire according to this embodiment. Therefore, the CaF ₂ content is limited to less than 0.50% in the flux-cored wire according to the present embodiment. If the CaF ₂ content is limited to less than 0.50%, the problem of sputtering can be ignored. In order to more reliably avoid the occurrence of spatter, the upper limit value of the CaF ₂ content may be set to 0.40% or 0.30%. The lower limit of CaF ₂ content of 0.10% or may be 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 gas shielded arc welding in which the shielding gas is 100% CO ₂ gas, CaF ₂ of the fluoride increases spatter. Furthermore, in order to investigate the relationship between the type of fluoride and the amount of spatter, the inventors of the present invention incorporated various types of fluoride so that there was no slit-like gap in the steel outer skin (vegetable oil was applied to the outer skin. ) A number of 1.2 mmφ wires were prepared. In a copper collection box, on a steel plate, with a bead-on plate, welding current 280A, voltage 27V, welding speed 30 cm / min, heat input 14.0 kJ / cm, shielding gas 100% CO ₂ , gas flow rate 25 l / min A weld bead was prepared for 1 minute using the above-mentioned various flux-cored wires under the conditions of no preheating. Spatter scattered in the box during the production of the weld bead and spatter adhering to the steel plate were collected, and the total weight of those having a diameter exceeding 1.0 mm was measured. As a result of multi-dimensional analysis of the spatter generation amount, the type of fluoride, and the content of each fluoride, a good value shown in FIG. 1 is obtained between the X value calculated using Equation 1 and the spatter generation amount. It was found that there was a correlation.
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 ]) (Formula 1)
In addition, 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 Formula 1, the chemical formula with 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 regarded as 0%. It was found that by increasing the X value defined by Equation 1 to 5.00% or less with respect to the total mass of the flux-cored wire, the amount of increase in sputtering was about 5.0 g / min or less in the above test. The flux-cored wire that can reduce the spatter generation amount to about 5.0 g / min or less in the above test provides good welding workability when used in welding in which the shielding gas is 100% CO ₂ gas. be able to. In the flux cored wire according to the present embodiment, it is not necessary to determine the lower limit value of the X value of fluoride. This is because the lower limit of the fluoride content is defined using the above-described F converted value.

  The reason why the fluoride contained in the flux-cored wire reduces the oxygen content of the weld metal is not necessarily clear, but the inventors have decomposed the fluoride in the molten pool and recombined it with the oxygen in the molten pool. I'm guessing, to surface. Further, although the reason why the amount of spatter generated varies depending on the type of fluoride is not necessarily clear, the present inventors have found that the element chemically bonded to fluorine affects the amount of spatter generated for some reason. I guess. The reason why the fluoride contained in the flux-cored wire reduces the amount of diffusible hydrogen in the weld metal is not necessarily clear, but the inventors have decomposed the fluoride by a welding arc and the generated fluorine is hydrogen. It is thought that it may be because it was combined with the hydrogen and dissipated into the atmosphere as HF gas, or hydrogen was fixed as HF in the weld metal as it was.

(One kind 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 The total content of the above or two or more oxides in mass% with respect to the total mass of the flux-cored 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. It is 1 type or 2 types or more selected from, and CaO mentioned later is not contained. In the present embodiment, “oxide excluding CaO” may be simply referred to as “oxide”.

  Oxides other than CaO have the effect of maintaining a good weld bead shape. When the total content of oxides excluding CaO is less than 0.30%, the shape of the weld bead may be deteriorated. In order to maintain the shape of the weld bead 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 oxygen content of the weld metal may be increased to lower the toughness of the weld metal. In order to improve the toughness of the 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, in addition to granulation of flux Oxides contained in the binder used may be contained in the flux-cored wire. In this case, the total value of the oxide content may be regarded as the total content of oxides contained in a binder or the like used for flux granulation. Each of Fe oxide, Ba oxide, Na oxide, Ti oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide includes, for example, FeO, BaO, and Na _2. O, TiO ₂ , SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , and K ₂ O may be used.

(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 oxide such as TiO ₂ contained in the flux is released to the outside of the weld metal as slag during welding. However, as described above, part of the Ti oxide in the flux of the flux-cored wire according to the present embodiment is once reduced by Al to become metal Ti, and then combined with oxygen in the weld metal to be welded. In the metal, it becomes a Ti oxide effective for refining the microstructure of the weld metal. Therefore, Ti oxide contributes to refinement of weld metal and improvement of low temperature toughness as a synergistic effect with Al as an alloy component. Further, the Ti oxide contributes to the improvement of the weld bead shape. Even when the total content of oxides excluding CaO is 0.30% or more and less than 3.50%, when 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, the lower limit value of the Ti oxide content needs to be 0.10%. In order to obtain a better weld bead shape by using Ti oxide as an arc stabilizer, the lower limit of the content of Ti oxide is 0.15%, 0.20%, 0.25%,. 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 to lower the toughness of the weld metal. Therefore, the content of Ti oxide needs to be less than 2.50%. In order to further improve the toughness of the weld metal, the upper limit of the Ti oxide content is 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:% by mass with respect to the total mass of the flux-cored wire, 0% or more and less than 0.20%)
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 shielding gas is 100% CO ₂ gas. Furthermore, since CaO changes to CaOH, which is a compound containing hydrogen when exposed to the atmosphere, it increases the diffusible hydrogen of the weld metal. Since CaO may be contained as an impurity in the flux material, it is necessary to select the flux 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 this embodiment, the lower limit value of the CaO content is 0%. The lower limit value of the CaO content may be 0.01%, 0.02%, or 0.05%.

(Of one or more carbonates 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 , (Total content in mass% with respect to the total mass of the flux-cored wire: 0 to 3.50%)
(Total value of content of MgCO ₃ , Na ₂ CO ₃ , and Li ₂ CO ₃ : 0 to 3.00% by mass% with respect to the total mass of the flux-cored wire)
The flux cored wire according to the present embodiment does not need to contain carbonate. Therefore, the lower limit of the total content of carbonate in the flux-cored wire according to this embodiment is 0%. However, the flux-cored 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 a total of 3.50% or less of one or more carbonates.

The carbonate is ionized by the arc and generates CO ₂ gas. The CO ₂ gas generated from the carbonate lowers the hydrogen partial pressure and reduces the amount of diffusible hydrogen in the weld metal. In order to obtain this effect, when carbonate is added to the flux-cored wire, 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 total lower limit of the carbonate content may be set to 0.50% or 1.00%. On the other hand, when the carbonate is excessive, the carbonate may be dissolved in the weld metal during welding, which may increase the carbon content and oxygen content of the weld metal. In this case, excessive hardening of the weld metal and low temperature toughness of the weld metal occur. In addition, when the carbonate content is excessive, the amount of welding fume generated becomes significant and the welding workability is deteriorated. In order to avoid these situations, the total content of carbonates needs to be 3.50% or less. In order to avoid welding fume generation, the upper limit of the total carbonate content is set to 3.00%, 2.50%, 2.00%, 1.50%, 1.00%, 0.50%, 0 .10%, 0.04%, 0.02%, or 0.01%.

The total content of MgCO ₃ , Na ₂ CO ₃ , and Li ₂ CO ₃ that may be contained in the above-described carbonate needs to be 0 to 3.00%. Even if the total content of carbonate is 0 to 3.50%, if the total content of MgCO ₃ , Na ₂ CO ₃ and Li ₂ CO ₃ is more than 3.00%, the weld bead It becomes easy to sag and welding workability deteriorates. In order to suppress sag 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 set to 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 over 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 filling rate of the flux 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 excessive iron powder, the oxygen content of the weld metal may be increased and the toughness may be lowered. Therefore, it is not necessary to contain iron powder. When iron powder is included 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 this embodiment, the lower limit of the iron powder content is 0%.

  Although the above is the reason for limitation regarding the component composition of the flux-cored wire according to the present embodiment, the other remaining components include Fe and impurities. The Fe component includes Fe in the steel outer shell, iron powder added in the flux, and Fe in the alloy component. Impurities are components that are mixed due to various factors in the manufacturing process, such as ore or scrap, when the flux-cored wire is manufactured industrially, and have an adverse effect on the flux-cored wire according to the present embodiment. It means that it is allowed in the range that does not give.

Subsequently, the form of the flux-cored wire will be described.
FIG. 2 shows a cut surface of the flux-cored wire. FIG. 2 (a) shows a flux-cored wire made by butting the edge surfaces and welding, FIG. 2 (b) shows a flux-cored wire made by joining 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 has a wire having no slit-like gap in the steel outer shell as shown in FIG. 2 (a), and a slit in the steel outer shell as shown in FIGS. 2 (b) and 2 (c). It can be roughly divided into wires having a gap in a shape. In the flux-cored wire according to the present embodiment, any cross-sectional structure can be adopted, but in order to suppress cold cracking of the weld metal, it is preferable to use a wire (seamless wire) having no slit-like gap. .

  Hydrogen entering the weld during welding diffuses in the weld metal and on the steel material side, accumulates in the stress concentration part, and causes cold cracking. This hydrogen source can increase moisture contained in the welding material, moisture mixed in from the atmosphere, rust and scale adhering to the steel surface, etc., but under the welding where the cleanliness of the weld and the gas shield conditions are sufficiently controlled. Then, hydrogen mainly contained in water in the wire becomes a main factor of diffusible hydrogen in the weld joint.

  For this reason, it is desirable that the steel outer shell is a tube having no slit-like gap, and that the penetration of hydrogen in the atmosphere from the steel outer shell to the flux is suppressed after the wire is manufactured and used. In the case of a pipe with a slit-like gap (seam) in the steel outer skin, moisture in the atmosphere easily enters the flux from the slit-like gap in the outer skin, and as it is, the intrusion of hydrogen sources such as moisture Therefore, when the period until use after production is long, it is desirable to vacuum-wrap the entire wire or store it in a container that can be kept dry.

  In addition, a lubricant can be applied to the surface of the wire in order to improve the wire feedability. As the lubricant applied to the surface of the wire, various kinds of materials such as vegetable oil can be used. However, in order to suppress cold cracking of the weld metal, hydrogen such as perfluoropolyether oil (PFPE oil) is used. Non-mineral oils are preferred.

  The flux cored wire according to the present embodiment can be manufactured by the same manufacturing process as that of a normal flux cored wire manufacturing method.

  That is, first, a steel strip as an outer skin and a flux containing alloy components, oxides, fluorides, carbonates and an arc stabilizer 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-shaped) with a forming roll to form a steel outer shell. During this forming, flux is supplied from the opening of the open tube, and the opposing edge surface of the opening is Weld the butt slit-shaped gap. As a welding method, electric seam welding, laser welding, or TIG welding is used. A slitless gap-free tube obtained by welding is drawn and annealed during or after the drawing process to obtain a slit-like gapless wire having a desired wire diameter. In addition, the slit-like gap is not welded and a tube having a slit-like gap is formed, and a wire having the slit-like gap is obtained by drawing the pipe.

A cross section obtained by cutting a wire having no slit-like gap made by butt seam welding looks like FIG. If this cross section is polished and etched, welding marks are observed, but if not etched, no welding marks are observed. Therefore, it may be called seamless as described above. For example, “New Edition Introduction to Welding and Joining Technology” edited by the Japan Welding Society (2008); Reference numeral 111 denotes 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 surface is caulked, but after the butting as shown in FIG. 2 (b), brazing or FIG. Even after brazing as in c), a wire having no slit-like gap can be obtained. In FIGS. 2B and 2C, the wire without brazing becomes a wire having a slit-like gap.

  Next, the manufacturing method of the welded joint according to this 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 flux-cored wire for gas shield arc welding according to the present embodiment. The application of the flux cored wire according to the present embodiment is not particularly limited. Therefore, even in the method for manufacturing a welded joint according to the present embodiment, the type of the base steel plate and the type of shield gas are not particularly limited. Since the method for manufacturing a welded joint according to this embodiment uses a flux-cored wire that reduces the amount of spatter and the amount of diffusible hydrogen in the weld metal, the workability is excellent. Further, in the method for manufacturing a welded joint according to the present embodiment, the alloy component and the metal deoxidation component are preferably adjusted, and a flux-cored wire containing fluoride that can reduce the oxygen content in the weld metal is used. It is possible to manufacture a welded joint including a weld metal including a weld metal excellent in thickness, elongation, and low temperature toughness.

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

In the welding method according to the present embodiment, the shielding gas used for tack welding is 100% CO ₂ gas, and the shielding gas used for main welding is pure Ar gas or pure He gas, and 2.5. It can be a mixed gas with ˜30.0 vol% O ₂ or 2.5-30.0 vol% CO ₂ . In this case, it is possible to reduce the welding cost without deteriorating the welding work environment due to the spatter, and therefore, further superiority over the prior art is shown. In addition, the welding conditions such as current and voltage may be those 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 is not limited as long as at least the portion forming the weld joint is plate-like, and the whole may not be a plate. Moreover, it is not limited to what is comprised from a separate steel plate, The butt-welding joint of what shape | molded one steel plate in predetermined shapes, such as a tubular shape, may be sufficient.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

While forming the steel strip of the chemical composition shown in Table 1 (mass% with respect to the total mass of the outer skin, the balance being iron and impurities) in the longitudinal direction, it is formed into an open tube by a forming roll, and from the opening of the open tube during this forming Flux is supplied, and the opposite edge surfaces of the opening are butt-seamed and welded to make seamless pipes (except for wires with “cage” written on the wire number), and the drawn wires are drawn. Annealing was performed in the middle of the work, and a flux-cored wire having a final wire diameter of φ1.2 mm was produced. The components of the wire thus obtained are shown in Tables 2-1 to 3-2. “Chemical component of wire alloy” means a metal or alloy component that does not form fluoride, oxide, or carbonate. The balance of the components of the entire wire is Fe and impurities. After the trial production, a lubricant was applied to the wire surface and subjected to welding described later. Tables 4-1 and 4-2 show the types of lubricants and the shielding gas types used in the main welding. Note that the shield gas for tack welding in all the inventive examples and the comparative examples was 100% CO ₂ . The unit of the composition of the shielding gas is vol%. In Tables 4-1 and 4-2, vegetable oil was applied to all the substances not described as PFPE oil. In addition, the wire with the notation “Caulking” in the wire number is a seamless tube that does not undergo seam welding, and is a flux-cored wire with a wire diameter of φ1.2 mm obtained by drawing it. 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 together with a root gap of 16 mm and a groove angle of 20 °, and welding is performed using the backing metal of the steel plate under the welding conditions shown in Table 4-1 and Table 4-2. did. On the groove face of the steel plate and the surface of the backing metal, buttering with two or more layers and a surfacing height of 3 mm or more was performed using a flux-cored wire to be tested, and a specimen was prepared. By this buttering, the components of the welding material are prevented from being diluted by the base material, and the characteristics of the welding material can be accurately evaluated.

  From the prepared specimen, A0 tensile test piece (round bar) (diameter = 10 mm) and Charpy test piece (2 mmV notch) in accordance with JIS Z3111 (2005) shown in FIG. 3 were collected as mechanical test pieces. Each mechanical property test was performed, and the tensile strength and total elongation of the weld metal and the Charpy absorbed 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 absorbed 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 280A, voltage 27V, welding speed 30 cm / min, heat input 14.0 kJ / cm, shielding gas type 100% CO ₂ , gas flow rate 25 l / A weld bead was prepared for 1 minute under the condition of no preheating. Spatters scattered in the box and spatters adhering to the steel plate were collected, and the weights of the sputters generated with a diameter exceeding 1.0 mm were measured. The results are shown in Tables 5-1 and 5-2 in units of g / min. A sample having a sputter generation amount of 5.0 g / min or less was accepted.

As shown in Tables 5-1 and 5-2, the wire numbers A1 to A10 as examples are excellent in the tensile strength, low-temperature toughness, and total elongation of the weld metal, and are also excellent in tack weldability. , Passed.
On the other hand, the wire numbers B1 to B9, which are comparative examples, do not satisfy the requirements defined in the present invention, and therefore satisfy one or more of the tensile strength, total elongation, low temperature toughness, and tack weldability of the weld metal. I was unable to do so, and I failed.

  According to the present invention, the Ni content is reduced to 5.0% by mass or less, which is the same as that of Ni-based low-temperature steel, so that it is excellent in welding construction efficiency in gas shielded arc welding and is an inexpensive flux-cored wire, By reducing the alloy components in the flux-cored wire and reducing the oxygen content of the weld metal, a weld metal having excellent low temperature toughness at −100 ° C. can be provided. Therefore, the present invention has high industrial applicability.

Claims (11)

A flux-cored wire for gas shield arc welding comprising a steel outer sheath and a flux filled in the steel outer shell,
The flux is
CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , LiF, NaF, K ₂ ZrF ₆ , BaF ₂ , and K ₂ SiF have a total F converted value with respect to the total mass of the flux-cored wire of 0.21% or more. One or more fluorides selected from the group consisting of ₆ ;
Fe oxide, Ba oxide, Na oxide, Ti oxide, Si oxidation, wherein the total content of the flux-cored wire in 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 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 ₃ , BaCO, wherein the total content of the flux-cored 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 ;
Including
The content of CaO in the flux is 0% or more and less than 0.20% by 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% by mass% with respect to the total mass of the flux-cored wire,
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% with respect to the total mass of the flux-cored wire,
The content of the Ti oxide is 0.10% or more and less than 2.50% by mass% with respect to the total mass of the flux-cored wire,
The total content of the MgCO ₃ , the Na ₂ CO ₃ , and the 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% with respect to the total mass of the flux-cored 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% to 0.500%,
Ni: 3.0% to 5.5%,
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 characterized by containing 0.030% or less and the balance being 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)
In addition, 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 fluoride not contained is 0. It is considered. 2. The flux-cored wire for gas shielded arc welding according to claim 1, wherein the carbonate is contained in a total of 2.00% by mass with respect to the total mass of the flux-cored wire. Furthermore, in mass% with respect to the total mass of the flux-cored wire,
B: 0.0100% or less,
It contains 1 type, or 2 or more types selected from the group which consists of Cu: 0.5% or less and REM: 0.050% or less, The gas shielded arc welding of Claim 1 or 2 characterized by the above-mentioned Flux-cored wire. Hardenability index (alpha) shown by following formula (2) is 0.25% or more and 0.51% or less, The flux containing for gas shielded arc welding of any one of Claims 1-3 characterized by the above-mentioned. Wire.
α = [C] + [Si] / 24 + [Mn] / 6 + ([Ni] + [Cu]) / 15 (2)
In addition, 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-cored wire. Represents. 5. The flux-cored wire for gas shielded arc welding according to claim 1, wherein a hot 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)
In addition, 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-cored wire. Represents. Elongation index (gamma) shown by following formula (4) is 1.8 or less, The flux cored wire for gas shielded arc welding of any one of Claims 1-5 characterized by the above-mentioned.
γ = [Mn] + [Mg] (4)
In addition, 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-cored wire. Represents.   The flux cored wire for gas shielded arc welding according to any one of claims 1 to 6, wherein the steel outer shell has a slit-shaped gap-free shape.   The flux cored wire for gas shielded arc welding according to any one of claims 1 to 6, wherein the steel outer shell has a shape having a slit-like gap.   The flux cored wire for gas shielded arc welding according to any one of claims 1 to 8, wherein perfluoropolyether oil is provided on a surface of the steel outer shell.   A method for manufacturing a welded joint, comprising a step of welding a steel plate using the flux-cored wire for gas shielded arc welding according to any one of claims 1 to 9. The shield gas used in tack welding in the welding step is 100% CO ₂ gas,
Production of a welded joint according to claim 10, wherein the welding is a process, shielding gas used in the present welding, characterized in that it is a mixed gas of CO ₂ of Ar and 2.5 to 30.0% by volume Method.