JP6988323B2 - Gas shield arc Welding flux-cored wire 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 technical field related to welding, in order to improve the efficiency of welding work, gas shielded arc welding in a high current range using a solid wire for welding as a welding material has been conventionally performed. In high-current welding using a solid wire for welding, the amount of welding for each layer can be increased, so that the efficiency of welding can be improved.

However, high-current welding using a solid wire for welding has a problem that welding workability is poor, such as a large amount of spatter generated due to unstable arc and poor bead appearance and bead shape. Further, in high current welding using a solid wire for welding, since the spatter becomes large, it is difficult to remove the spatter adhering to the surface of the steel sheet, and there is a problem that the work efficiency is also poor. Especially in welding using 100% CO ₂ gas as a shield gas, the problem caused by the generation of spatter becomes serious. Since CO ₂ gas is inexpensive, it contributes to reduction of welding cost, but has a drawback that spatter is easily generated. Under such circumstances, it is desired to put into practical use a welding material capable of suppressing the amount of spatter generated even in gas shielded arc welding using _{CO 2 gas as a shield gas.}

As a means for solving these problems, an attempt has been made to develop a solid wire for gas shielded arc welding in which the amount of spatter generated is small. For example, in Patent Document 1, 0.005 to 0.50 g of molybdenum disulfide and 0.008 to 0.15 g of phospholipid are contained on the surface of the wire per 10 kg of wire, and the balance is a total of lubricants consisting of a liquid lubricating oil at room temperature. Since it has 0.5 to 2.5 g, it is said to have excellent welding workability such as good wire feeding property, small amount of spatter generation, less chip wear, and good arc stability. A technique for providing a copper-plated wire for carbon dioxide shielded arc welding is disclosed. Further, Patent Document 2 discloses a solid wire for welding, which is said to be able to reduce the amount of spatter generated by having an alkali metal impregnated portion impregnated with two or more kinds of alkali metals in the vicinity of the surface of the wire.

It is recognized that the solid wire by the above-mentioned technique has a reduced amount of spatter as compared with the conventional solid wire. However, the solid wire according to the above technique cannot reduce the spatter amount to the extent that it can be used for gas shielded arc welding _{using Ar-CO 2} mixed gas or CO _{2 gas as a shield gas.}

In recent years, for the purpose of further improving the efficiency of welding work, solid wires for gas shielded arc welding that meet the welding work conditions of large heat input and high interpass temperature have been developed, and their specific specifications have been developed. It is specified in JIS Z3312 YGW18. In such a solid wire for gas shielded arc welding, the maximum heat input is 40 kJ for high-strength steel having a tensile strength of 490 MPa as a condition that welding can be performed without deteriorating the strength and toughness of the weld metal. Welding conditions of / cm and maximum pass-to-pass temperature of 350 ° C are acceptable. Further, for high-strength steel having a tensile strength of 520 MPa class, welding construction conditions of a maximum heat input of 30 kJ / cm and a maximum interpass temperature of 250 ° C. are permitted.

As a solid wire for gas shielded arc welding corresponding to such welding construction conditions of large heat input and high interpass temperature, for example, as described in Patent Documents 3 to 5, the wire contains a large amount of Mo, Cr and the like. Things have been proposed. According to these solid wires, it is possible to secure the strength and toughness of the weld metal even under the welding construction conditions of large heat input and high interpass temperature.

However, even in the above-mentioned welding using the solid wire, there is a problem that the welding workability is poor, such as a large amount of spatter generated due to the unstable arc and a poor bead appearance and bead shape.

As a gas shielded arc welding wire with good welding workability while ensuring the strength and toughness of the weld metal under welding construction conditions with large heat input and high interpass temperature, for example, Patent Documents 6 and 7 describe large heat input. A flux-filled wire is disclosed in which good welding workability can be obtained and a weld metal having excellent mechanical performance can be obtained under welding construction conditions with a high interpass temperature.

However, although these flux-cored wires can reduce the amount of spatter generated relatively compared to the conventional high-current welding with solid wires for welding, they are still used for gas shielded arc welding using _{CO 2 gas as the shield gas.} However, the amount of spatter cannot be reduced to the extent possible. Further, in these flux-cored wires, since the amount of slag generated is large, there is a problem that welding defects such as slag entrainment are likely to occur.

In addition to the above-mentioned problems of improving welding efficiency and ensuring welding workability, in recent years, welding materials have been required to suppress solidification cracks. Solidification cracking is a type of high-temperature cracking (cracking that occurs at a high temperature such as in the solidification temperature range of the weld or immediately below it), and is generated when the weld metal opens without being able to withstand the shrinkage stress during solidification. It is a crack. In welding of wear-resistant steel, solidification cracks are likely to occur. Therefore, with the increase in demand for wear-resistant steel, there is a demand for a welding material capable of suppressing the occurrence of solidification crack even when applied to welding of a steel plate such as wear-resistant steel which is likely to cause solidification crack.

Further, it is also required for the welding material to suppress low temperature cracking. Low-temperature cracking is a general term for cracks that occur in the welded portion after the temperature of the welded portion drops to around room temperature after welding, and cracks under the bead and toe cracks belong to low-temperature cracking. The occurrence of low temperature cracks can be suppressed by preheating the welded portion before welding. For example, welding of wear-resistant steel used in construction machinery usually requires preheating at 50-200 ° C. However, the preheating process increases the time required for the welding work, and the work efficiency and the work cost are remarkably increased. Therefore, there is a need for a welding material that can omit or reduce the preheating step.

However, a welding material capable of suppressing low-temperature cracking and solidification cracking while ensuring high welding efficiency and welding workability has not been obtained. For example, Patent Document 8 discloses a flux-cored wire for gas shielded arc welding, which is said to be able to obtain a weld metal having excellent mechanical performance, in which the arc is stable and the amount of spatter generated is small even under high current welding conditions. ing. However, in Patent Document 8, no study is made regarding the suppression of low temperature cracking. According to the chemical composition of the flux-filled wire described in Patent Document 8, it is considered that the amount of diffusible hydrogen in the weld metal, which is a factor for generating low temperature cracks, cannot be reduced.

Japanese Unexamined Patent Publication No. 2006-95551 Japanese Unexamined Patent Publication No. 2009-255142 Japanese Unexamined Patent Publication No. 10-23387 Japanese Unexamined Patent Publication No. 11-90678 Japanese Unexamined Patent Publication No. 2001-287086 Japanese Unexamined Patent Publication No. 2005-279683 Japanese Unexamined Patent Publication No. 2011-25298 Japanese Unexamined Patent Publication No. 2016-20234

Therefore, the present invention has been devised to solve the above-mentioned problems, and is a weld metal having excellent welding workability, suppressing low temperature cracking and solidification cracking, and having appropriate tensile strength and toughness. It is an object of the present invention to provide a flux-cored wire for gas shielded arc welding and a method for manufacturing a welded joint.

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 in the steel outer skin, and is obtained by mass% with respect to the total mass of the flux-containing wire. As alloy components, C: 0.001 to 0.120%, Si: 0.40 to 1.60%, Mn: 1.50 to 2.50%, P: 0.030% or less, S: 0.030% Hereinafter, Cu: 0.05 to 0.50%, Ti: 0.04 to 0.30%, and Al: 0.200% or less are contained, and further, by mass% with respect to the total mass of the flux-filled wire. , Flude: Total F conversion value is more than 0.100% and 0.300% or less, Si oxide: SiO ₂ conversion value is 0.01 to 0.40%, and Na compound and K compound: Na conversion value and It contains 0.060 to 0.350% in total in terms of K, and the balance is composed of Fe and impurities in the form of any one or more of a steel outer skin, iron powder, and iron alloy powder.
(2) The flux-welded wire for gas shielded arc welding according to (1) above is the mass% of the total mass of the flux-welded wire, and Ni: 0% or more and less than 0.80% as the alloy component, Mo :. Further contains one or more selected from the group consisting of 0 to 0.50%, B: 0 to 0.0100%, Mg: 0 to 0.50%, and Sn: 0 to 0.40%, and contains C. The amount may be 0.001 to 0.080% .
(3) In the flux-cored wire for gas shielded arc welding according to (1) or (2) above, the mass% of the flux-cored wire with respect to the total mass is 0 to 0.300% in terms of Ca compound: Ca. May be.
(4) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (3) above, the steel outer skin is the weight% of the total mass of the steel outer skin, and the alloy component. Al: 0.003 to 0.200% may be contained.
(5) The flux-containing wire for gas shielded arc welding according to any one of (1) to (4) above is the mass% of the total mass of the flux-welded wire, and is 0 in terms of Zr compound: Zr conversion value. It may further contain ~ 0.30%.
(6) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (5) above, the steel outer skin may have a seamless shape.
(7) The flux-cored wire for gas shielded arc welding according to any one of (1) to (6) above is further provided with a feed lubricant on the outer surface of the steel outer skin, and the feed lubricant is further provided. The amount per 10 kg of the flux-cored wire may be 0.25 to 1.00 g.
(8) In the method for manufacturing a welded joint according to another aspect of the present invention, a steel plate is gas-shielded arc using the gas-shielded arc welding flux-containing wire according to any one of (1) to (7) above. Weld.

According to the present invention having the above-mentioned configuration, the arc stability, the appearance and shape of the bead are excellent, the amount of spatter generated is small, the amount of slag is small, welding defects can be prevented, and the welding workability is good, and low temperature cracking is prevented. The preheating process for this purpose can be reduced or omitted, solidification cracking is suppressed, and the tensile strength and toughness of the weld metal are sufficiently ensured and high even under welding construction conditions of large heat input and high interpass temperature. It is possible to provide a method for manufacturing a flux-filled wire for gas shielded arc welding and a welded joint capable of obtaining a high-quality weld metal.

The present inventors can suppress solidification cracking even in welding of a steel plate that easily causes solidification cracking such as wear-resistant steel, and use a gas that easily causes spatter such as _{CO 2 gas as a shield gas.} We have earnestly studied welding materials that can suppress the amount of spatter generated, suppress low-temperature cracking even when preheating is omitted or reduced, and can produce weld metals with sufficient mechanical properties. As a result, the following findings were obtained.

Regarding solidification cracks, the present inventors develop solidification cracks by reducing the C content of the welding material because C, which is transferred from the wear-resistant steel as the base material to the molten metal during welding, becomes a factor of solidification cracks. It was found that it can be suppressed. Specifically, by setting the content of C contained as an alloy component to 0.120% or less in terms of mass% with respect to the total mass of the flux-cored wire as a welding material, in welding of wear-resistant steel having a large carbon content. It was also found that solidification cracking can be suppressed. However, if the C content of the flux-cored wire is reduced, the tensile strength of the weld metal is reduced, and the strength balance between the base metal and the weld metal is lost. Therefore, as will be described later, it is necessary to preferably control alloying elements other than C to maintain the tensile strength of the weld metal.

Regarding the prevention of low temperature cracking, the present inventors have found that it is effective to include fluoride in the flux. Factors that cause low temperature cracking in HAZ during welding are the hardness of HAZ, the binding force of the joint, and the amount of diffusible hydrogen in the weld metal. The present inventors have a function that the flux in the flux reduces the amount of diffusible hydrogen of the weld metal, which is one of the factors causing low temperature cracking, and remarkably improves the low temperature crack resistance of the weld metal. It was found to have. The reason for this is not clear, but it is presumed that F and hydrogen (H) in the fluoride are combined during welding to form hydrogen fluoride (HF), and this HF is released to the outside of the weld metal. To. However, the fluoride in the flux increases the amount of spatter during welding.

Regarding ensuring welding workability, the present inventors set the amounts of fluorides, oxides, and some alloying elements, which are factors for increasing the amount of spatter, within the range in which the above-mentioned effect of reducing the amount of diffusible hydrogen can be ensured. It was found that the amount of spatter can be reduced to within the permissible range by reducing the amount as much as possible. Regarding the mechanical properties of the weld metal, the present inventors have found that it is possible to make up for the deficiency of C and secure toughness by utilizing elements such as Mn, Si, and Ti.

The flux-cored wire for gas shielded arc welding according to the embodiment of the present invention can be achieved by the synergistic effect of each component composition alone or coexisting based on the above-mentioned findings of the present inventors. The reasons for limiting the composition of each component are described. Unless otherwise specified, the content of each component composition shall be expressed in mass% with respect to the total mass of the flux-cored wire, and the description regarding the mass% shall be simply described as%.

The flux-containing wire according to the present embodiment includes a steel outer skin and a flux filled in the steel outer skin, and the "total mass of the flux-containing wire" is the mass of the steel outer skin and the mass of the flux. It is a total value. The components listed below are included as alloy components (ie, in a non-oxide or non-fluorinated state) in the flaked wire, even if they are contained in the steel hull, as plating on the surface of the steel hull. Also, it may be contained in the flux as a metal powder or an alloy powder. On the other hand, the components contained in the flux-cored wire as oxides or fluorides are contained in the flux.

First, the alloy component of the flux-cored wire will be described. The contents of C, Si, Mn, P, S, Cu, Ni, Mo, Ti, Al, B, and Mg described below are in the form of alloy components (ie, oxides, fluorides, or carbonates). It means the content of these elements present in the flux-filled wire as components that exist as elemental metals or alloys; P and S are also included in the alloy components for convenience). Unless otherwise specified, the numerical range of alloy components described below does not include the content of elements contained in the flux-cored wire in the form of oxides and fluorides.

[C: 0.001 to 0.120%]
When C is contained in the flux-cored wire as an alloying element, the strength of the weld metal is improved by solid solution strengthening. On the other hand, if the C content is excessive, the strength of the weld metal becomes excessively high and the toughness decreases. In addition, C increases the sensitivity to high-temperature cracking and acts as a factor that causes solidification cracking in particular. For example, even when the flux-cored wire according to the present embodiment is applied to welding of high carbon steel such as wear-resistant steel, in order to surely prevent the occurrence of solidification cracks, the C content of the flux-cored wire is set. It is necessary to suppress it to 0.120% or less. Therefore, the C content is 0.001 to 0.120%. When it is necessary to increase the strength of the weld metal, the lower limit of the C content may be 0.010% or 0.020%. On the other hand, when it is necessary to further ensure the prevention of solidification cracking, the upper limit of the C content may be 0.100% or 0.080%.

[Si: 0.40 to 1.60%]
Si is contained in the flux-filled wire in one or more embodiments selected from the group consisting of alloying elements, oxides, and fluorides, and when contained in the flux-filled wire as an alloy component, as a deoxidizing element of the weld metal. work. Furthermore, Si as an alloying element dissolves in the weld metal and also works as a strength improving element. Of the Si as an alloy component, the one that acts as a deoxidizing element _{is discharged to the outside of the weld metal as SiO 2,} etc., but in the flux-cored wire according to the present embodiment, an appropriate amount of Si is retained in the weld metal. Therefore, it is necessary to secure the strength of the weld metal.

In view of the above circumstances, the flux-cored wire according to the present embodiment has a Si content in the range of 0.40 to 1.60%. When Si is less than 0.40%, the amount of oxygen in the weld metal increases, and the hardenability of the weld metal is insufficient, so that the strength and toughness of the weld metal decrease. On the other hand, when Si exceeds 1.60%, the strength of the weld metal becomes excessively high, and the toughness cannot be stably obtained. Further, when Si exceeds 1.60%, the amount of generated slag increases and welding defects such as slag entrainment are likely to occur. The lower limit of the Si content may be 0.50% or 0.60%. The upper limit of the Si content may be 1.40% or 1.50%.

[Mn: 1.50 to 2.50%]
When Mn is contained in the flux-cored wire as an alloying element, it contributes to ensuring the toughness of the weld metal and improving the strength. If the Mn content is less than 1.50%, the strength and toughness of the weld metal will be insufficient. On the other hand, if the Mn content exceeds 2.50%, the toughness of the weld metal cannot be stably obtained. Further, when the Mn content exceeds 2.5%, the amount of generated slag increases, welding defects such as slag entrainment are likely to occur, and spatter also increases. Therefore, the Mn content is 1.50 to 2.50%. The lower limit of the Mn content may be 1.60% or 1.70%. Further, the upper limit of the Mn content may be 2.30% or 2.40%.

[P: 0.030% or less]
[S: 0.030% or less]
P and S impair the toughness of the weld metal and promote the occurrence of cracks in the weld metal, but have no advantageous effect. Therefore, the flux-cored wire according to the present embodiment does not need to contain P and S, and the lower limit of the content of P and S is 0%. However, P and S may be contained as impurities in the steel outer skin and the flux. P and S should be removed as much as possible, but the inclusion of 0.030% or less of P and 0.030% or less of S is acceptable. The upper limit of each of P and S may be 0.020% or 0.025%.

[Cu: 0.05 to 0.50%]
When Cu is contained in the flux-filled wire as an alloying element, it has a precipitation strengthening action and lowers the transformation temperature of the weld metal to make the structure of the weld metal finer and stabilize the toughness of the weld metal. If the Cu content is less than 0.05%, the toughness of the weld metal is insufficient. On the other hand, when the Cu content exceeds 0.50%, precipitation embrittlement occurs, the toughness of the weld metal is lowered, and high temperature cracking is likely to occur. Therefore, the Cu content is set to 0.05 to 0.50%. The lower limit of the Cu content may be 0.10% or 0.15%. Further, the upper limit of the Cu content may be 0.40% or 0.45%.

[Ti: 0.04 to 0.30%]
When Ti is contained in a flux-filled wire as an alloying element, it acts as a deoxidizer and forms a fine oxide of Ti in the weld metal, and this fine oxide refines the structure of the weld metal and welds it. Further improve the toughness of the metal. If the Ti content is less than 0.04%, the toughness of the weld metal is insufficient. On the other hand, when the Ti content exceeds 0.30%, the amount of solid solution Ti in the weld metal increases, and the toughness of the weld metal becomes insufficient. Further, when Ti exceeds 0.30%, the amount of slag generated during welding increases, and welding defects such as slag entrainment are likely to occur. Therefore, the Ti content is 0.04 to 0.30%. The lower limit of the Ti content may be 0.08% or 0.12%. Further, the upper limit of the Ti content may be 0.25% or 0.27%.

[Ni: 0% or more and less than 0.80%]
The content of Ni in the flux-cored wire according to the present embodiment is not essential, and therefore the lower limit of the content is 0%. However, Ni has the effect of increasing the toughness of the weld metal when it is contained in the flux-cored wire as an alloying element. Therefore, the lower limit of the Ni content may be 0.15% or 0.20%. On the other hand, the content of Ni of 0.80% or more causes an increase in cost. Therefore, the Ni content is preferably less than 0.80%. The upper limit of the Ni content may be 0.60% or 0.70%.

[Mo: 0 to 0.50%]
The content of Mo in the flux-cored wire according to the present embodiment is not essential, and therefore the lower limit of the content is 0%. However, when Mo is contained in the flux-cored wire as an alloying element, it enhances the hardenability of the weld metal and contributes to ensuring the tensile strength of the weld metal. Therefore, the lower limit of the Mo content may be 0.05% or 0.10%. On the other hand, Mo exceeding 0.50% may impair the toughness of the weld metal by excessively hardening the weld metal. Therefore, the upper limit of the Mo content is preferably 0.50%. The upper limit of the Mo content may be 0.40% or 0.45%.

[B: 0 to 0.0100%]
The content of B is not essential in the flux-cored wire according to the present embodiment, and therefore the lower limit of the content is 0%. However, when B is contained in the flux-cored wire as an alloying element, it enhances the hardenability of the weld metal and contributes to ensuring the tensile strength of the weld metal. Therefore, the lower limit of the B content may be 0.00009% or 0.00013%. On the other hand, B exceeding 0.0100% may impair the toughness of the weld metal by excessively hardening the weld metal. Therefore, the upper limit of the B content is preferably 0.0100%. The upper limit of the B content may be 0.0060% or 0.0080%.

[Al: 0.200% or less]
The inclusion of Al is not essential in the flux-cored wire according to the present embodiment. Therefore, the lower limit of the content is 0%. If the Al content exceeds 0.200%, the arc becomes unstable and the amount of spatter generated increases. Therefore, the Al content is 0.200% or less. However, since Al contained in a very small amount has an effect of improving the bead shape, the lower limit of the Al content may be 0.004% or 0.006%. The steel outer skin may contain 0.003 to 0.100% or 0.003 to 0.200% of Al in terms of mass% with respect to the total mass of the steel outer skin. Al contained in the steel outer skin has an effect of improving the bead shape.

[Mg: 0 to 0.50%]
The flux-cored wire according to this embodiment does not necessarily contain Mg. Therefore, the lower limit of the Mg content is 0%. However, when Mg is contained in the flux-filled wire as an alloying element, it has a deoxidizing effect, and in order to reduce the oxygen content of the weld metal and improve the toughness of the weld metal, it should be contained in an amount of 0.06% or more. Is desirable. Therefore, the lower limit of the Mg content may be 0.03% or 0.06%. On the other hand, when the Mg content exceeds 0.50%, the amount of generated slag increases and welding defects such as slag entrainment are likely to occur. Therefore, the upper limit of the Mg content is set to 0.50%. The upper limit of the Mg content may be 0.20% or 0.35%.

[Sn: 0 to 0.40%]
The content of Sn is not essential in the flux-cored wire according to the present embodiment, and therefore the lower limit of the content is 0%. However, since Sn has a function of improving the corrosion resistance of the weld metal, the lower limit of the Sn content may be 0.07%. On the other hand, if the Sn content exceeds 0.40%, liquid metal embrittlement cracking may occur. Therefore, the upper limit of the Sn content is set to 0.40%. The upper limit of the Sn content may be 0.35% or 0.30%.

Next, the compound component of the flux-cored wire will be described.

[Si oxide: 0.01 to 0.40% in terms of _{SiO 2]}
Further, Si is contained in the flux of the flux-cored wire as a Si oxide such as _{silica sand (SiO 2} ), zircon sand (ZrSiO ₄ ), sodium silicate (Na ₂ SiO ₃ ), and potassium silicate (K ₂ SiO _3). If this is the case, it has the function of increasing the viscosity of the molten slag to improve the slag encapsulation property, improving the familiarity of the bead toe, and improving the appearance and shape of the bead.

In view of the above circumstances, in the flux-cored wire according to the present embodiment, the amount of Si oxide is in the range of 0.01 to 0.40% in terms of _{SiO 2.} When the amount of Si oxide is _{less than 0.01% in terms of SiO 2} , the fit of the bead toe of the weld bead becomes poor, and the bead appearance and the bead shape become poor. When the amount of Si oxide _{exceeds 0.40% in terms of SiO 2} , the amount of slag generated during welding increases and welding defects such as slag entrainment are likely to occur. The lower limit of the Si oxide content may be 0.02% or 0.05% in terms _{of SiO 2.} The upper limit of the Si oxide content may be 0.35% or 0.30% in terms _{of SiO 2.}

Note that "SiO ₂ converted value of Si oxide in the flux-cored wire", in the case of Si contained in the Si oxide in the flux cored wire is considered that all of the SiO _2, the SiO ₂ flux cored It means the content in mass% with respect to the total mass of the wire. _{For the SiO 2} conversion value of the Si oxide in the flux-filled wire, the amount of Si constituting the Si oxide contained in the flux-filled wire is obtained, and 2.14 (= (28.1 + 16.0 × 2) / 28.1 and 28.1 are the atomic weights of Si, and 16.0 is the atomic weight of oxygen).

[Na compound and K compound: 0.060 to 0.350% in total of Na conversion value and K conversion value]
Na contained in the flux-cored wire as an oxide such as _{Na 2} O and Na ₂ SiO ₃ , and K contained in the flux-cored wire as an oxide such _{as K 2 O and K 2} SiO _{3 causes an arc.} It has the function of stabilizing and suppressing the amount of spatter. Further, when Na is contained as a fluoride such as NaF described later and K is _{contained as a fluoride such as K 2} SiF ₆ described later, it has a function of stabilizing an arc. In addition, Na fluoride and K fluoride also contribute to the reduction of the amount of diffusible hydrogen, which is understood as the effect of F described later. The Na compound and the K compound can be contained in the form of powders such as _{K 2} SiO ₃ , Na ₂ SiO ₃ , NaF, and K ₂ SiF _{6, which} are solid components of water glass composed of sodium silicate and potassium silicate.

In order to obtain the above effects, in the flux-cored wire according to the present embodiment, the total content (Na + K) of the Na compound and the K compound shall be 0.060% or more in total of the Na conversion value and the K conversion value. There is a need. On the other hand, when the total of the Na conversion value and the K conversion value exceeds 0.350%, the arc becomes too strong and the spatter amount increases. Further, when the total of the Na conversion value and the K conversion value exceeds 0.350%, the familiarity of the bead toe portion becomes poor, and the bead appearance and the bead shape become poor. Further, when the total of the Na conversion value and the K conversion value exceeds 0.350%, the amount of generated slag increases and welding defects such as slag entrainment are likely to occur. Therefore, the total value of the Na conversion value and the K conversion value is set to 0.350%. The lower limit of the total of the Na conversion value and the K conversion value may be 0.080% or 0.100%. Further, the upper limit of the total of the Na conversion value and the K conversion value may be 0.250% or 0.300%.

The "Na conversion value of the Na compound in the flux-cored wire" means the content of Na contained in the Na compound in the flux-cored wire in mass% with respect to the total mass of the flux-cored wire, and is "flux." The "K conversion value of the K compound in the flux-cored wire" means the content of K contained in the K compound in the flux-cored wire in mass% with respect to the total mass of the flux-cored wire. Similarly, the "F-converted value of the flux in the flux-cored wire" and the "Ca-converted value of the Ca compound in the flux-filled wire", which will be described later, are the same as those of the flux-cored wire of F contained in the flux-cored wire. The content in% by mass with respect to the total mass and the content in% by mass of Ca contained in the Ca compound in the flux-cored wire with respect to the total mass are shown.

[Fluoride: Total F conversion value is more than 0.100% and 0.300% or less]
F is _{contained in the flux-cored wire as a fluoride of CaF 2} , NaF, LiF, MgF ₂ , K ₂ SiF ₆ , K ₂ ZrF _6, Na ₃ AlF ₆ , AlF _3, etc., and the amount of diffusible hydrogen in the weld metal is reduced. It has the effect of reducing and preventing low temperature cracking. When the F content is 0.10% or less, low temperature cracking cannot be sufficiently suppressed. Further, NaF, Na ₃ AlF ₆ , AlF ₃ , K ₂ SiF ₆ , MgF _2, etc. also have a function as an arc stabilizer if the content is appropriate. On the other hand, fluoride has a function of increasing spatter, and particularly when the F content exceeds 0.300%, the arc becomes rough and unstable, and the spatter generation amount exceeds the allowable upper limit. Therefore, the F content is set to more than 0.100% and 0.300% or less. The lower limit of the F content may be 0.110% or 0.120%. The upper limit of the F content may be 0.250% or 0.270%.

[Ca compound: preferably 0 to 0.300% in terms of Ca]
Ca may be contained in the flux-cored wire as a fluoride or a Ca compound such as a Ca oxide as described above. However, the Ca compound is a compound that tends to increase the spatter amount in particular. It is preferable that the Ca compound is not contained in the flux-cored wire, and the lower limit of the content thereof is 0% in terms of Ca with respect to the total mass of the flux wire. However, the Ca compound may be mixed in the flux as an impurity. The Ca compound as an impurity is allowed to be contained up to about 0.300% in terms of Ca conversion with respect to the total mass of the flux wire. The upper limit of the content of the Ca compound may be 0.200% or 0.150% in terms of Ca conversion with respect to the total mass of the flux wire.

[Zr compound: 0 to 0.30% in terms of Zr]
The inclusion of the Zr compound in the flux-cored wire according to the present embodiment is not essential. Therefore, the lower limit of the content of the Zr compound is 0%. However, when the Zr compound is contained in the flux-cored wire, it has a deoxidizing effect, which reduces the amount of oxygen in the weld metal. Further, the Zr compound has an effect of improving the shape of the bead toe. Therefore, 0.06% or more of the Zr compound may be contained. On the other hand, when the content of the Zr compound exceeds 0.30%, the amount of generated slag increases and welding defects such as slag entrainment are likely to occur. Therefore, the upper limit of the content of the Zr compound is set to 0.30%. The upper limit of the content of the Zr compound may be 0.20% or 0.25%. Zr compound is contained as such ZrSiO ₄ and _K 2 ZrF _6.

The content of two or more of the fluoride, Si oxide, Na compound, K compound, Ca compound, and Zr compound, which are the components of the flux-filled wire according to the present embodiment, belongs to the compound. It shall be included in the content of each substance. For example, ZrSiO ₄ corresponds to a Zr compound and also corresponds to a Si oxide, but when ZrSiO ₄ is contained in a flux-filled wire, _{the content of ZrSiO 4 is} the content of the Zr compound (Zr conversion value) and. It shall be included in any of the Si oxide contents (SiO _{2 conversion value).} In other words, the portion of the ZrSiO ₄ content that Zr occupies is included in the Zr compound content (Zr conversion value), and the portion of the ZrSiO ₄ content that Si occupies is the Si oxide content (Zr-converted value). It is included in the SiO _{2 conversion value).} Similarly, when K ₂ ZrF ₆ is contained in the flux-cored wire, _{the content of K 2} ZrF _{6 is} the content of the Zr compound (Zr conversion value), the content of the K compound (K conversion value) and the fluoride. It shall be included in any of the contents (F conversion value).

[Remaining: Fe and impurities]
The balance of the components of the flux-cored wire for gas shielded arc welding according to this embodiment is Fe and impurities. Fe is contained in the flux-filled wire in the form of any one or more selected from the group consisting of a steel outer skin, iron powder for adjusting the filling rate, and iron alloy powder for controlling the amount of alloying elements. The type of iron powder is not particularly limited, but atomized iron powder is desirable in order to suppress an increase in the amount of oxygen in the weld metal. Impurities are components that are mixed in by various factors of the raw material or the manufacturing process when the flux-filled wire according to the present embodiment is industrially manufactured, and adversely affect the flux-filled wire according to the present embodiment. It means something that is acceptable to the extent that it does not exist. For example, Al, which can be contained as an impurity during steelmaking of a steel outer skin, is preferably small because it forms non-metal inclusions in the weld metal and reduces toughness as described above, but it is preferable with respect to the total mass of the flux-filled wire. If the mass% is 0.200% or less, it is acceptable. P and S reduce the toughness of the weld metal as described above, but are acceptable if they are 0.030% or less in mass% with respect to the total mass of the flux-cored wire. N impairs the toughness of the weld metal when it is contained in the weld metal as a solid-dissolved N, but it is permissible if it is 0.01% or less in mass% with respect to the total mass of the flux-filled wire.

In the flux-cored wire according to the present embodiment, the flux filling rate (ratio of the total mass of the flux to the total mass of the flux-filled wire) is not particularly limited, but is preferably 8 to 20% from the viewpoint of productivity.

The flux-cored wire according to the present embodiment is obtained by molding a steel outer skin into a pipe shape, filling the inside with flux, and then welding or crimping the seam of the steel outer skin. Therefore, the types of flux-cored wires include flux-cored wires, which have a seamless shape (so-called seamless shape) in the steel outer skin obtained by welding the seams of the molded steel outer skin, and seams in the steel outer skin. It can be roughly divided into a flux-cored wire having a seam on a steel outer skin that has not been welded.

In the flux-cored wire according to the present embodiment, any wire having any cross-sectional structure can be adopted. However, wires with seams on the steel hull are prone to low temperature cracking. This is because water may enter the flux-cored wire from the seam, and this water may serve as a hydrogen source to increase the amount of diffusible hydrogen in the weld metal. On the other hand, a wire with a seamless steel outer skin can be heat-treated for the purpose of reducing the total amount of hydrogen in the wire, and since there is no moisture absorption of the flux after production, the amount of diffusible hydrogen in the weld metal It is more preferable because it can reduce the amount of cracking and improve the resistance to low temperature cracking.

The flux-cored wire according to the present embodiment may further include a feed lubricant on the outer surface of the steel outer skin. The feed lubricant on the surface of the flux-cored wire improves the feedability of the flux-cored wire, especially in the case of semi-automatic welding, stabilizes the arc, reduces the amount of spatter, and prevents the occurrence of welding defects. .. The amount of the feed lubricant applied is not particularly limited, but is preferably 0.20 to 1.00 g per 10 kg of wire, for example. If the amount of the feed lubricant on the surface of the flux-cored wire is less than 0.20 g per 10 kg of the wire, the wire feedability may be poor, the arc may be unstable, and the amount of spatter generated may increase. Further, in this case, a slag entrainment defect may easily occur. On the other hand, if the amount of the lubricant on the surface of the flux-cored wire exceeds 1.00 g per 10 kg of wire, the flux-cored wire may slip at the feed roller portion, the arc may become unstable, and the amount of spatter generated may increase. be. Further, in this case, the amount of diffusible hydrogen in the weld metal may increase and low-temperature cracking may easily occur.

The feed lubricant may be animal or vegetable oil, mineral oil or synthetic oil. As animal and vegetable oils, palm oil, rapeseed oil, castor oil, pig oil, cow oil, fish oil and the like can be used, and as mineral oils, machine oil, turbine oil, spindle oil and the like can be used. As the synthetic oil, hydrocarbon-based, ester-based, polyglycol-based, polyphenol-based, silicone-based, and fluorocarbon-based oils can be used. Further, a sulfur-containing lubricating oil which is one or more of sulfur-containing fats and oils, sulfurized esters, sulfurized fatty acids or sulfurized olefins in one or more base oils of fats and oils or esters can also be used. The above-mentioned component specification of the flux-cored wire relates to the steel outer skin of the flux-cored wire and the flux, and does not include the component of the feed lubricant. Since the amount of the feed lubricant applied is very small with respect to the mass of the flux-cored wire, the feed lubricant has no substantial effect in defining the components of the flux-cored wire.

Next, a method for manufacturing a welded joint according to the present embodiment will be described. The method for manufacturing a welded joint according to the present embodiment is characterized by gas shielded arc welding using the flux-cored wire according to the above-described embodiment. The method for manufacturing a welded joint according to the present embodiment has good welding workability, can reduce or omit a preheating step for preventing low temperature cracking, suppresses solidification cracking, and further, the strength of the weld metal and the strength of the weld metal. Sufficient toughness can be ensured.

In the method for manufacturing a welded joint according to the present embodiment, the welding conditions are not particularly limited and can be appropriately selected from the usual range. For example, the type of shield gas is not particularly limited, _{and a mixed gas of Ar and CO 2} is effective, but when an inexpensive 100% CO ₂ gas is used, a remarkable effect is particularly exerted on the prior art. This is because the welding cost can be reduced while suppressing the amount of spatter within an allowable range. Further, the base material of the welded joint is not particularly limited, but when it is a steel material having a large amount of carbon and prone to solidification cracks such as wear-resistant steel, it exerts a remarkable effect on the prior art. This is because the method for manufacturing a welded joint according to the present embodiment can suppress solidification cracking more effectively than the conventional method.

Hereinafter, the effects of the present invention will be specifically described with reference to Examples.

Low carbon steel or ultra-low carbon steel (C: 0.001 to 0.08%) is used as the steel outer skin, and after forming into a U shape in the process of forming the steel outer skin, the seams of the steel outer skin are joined. Welded seamless wire (seamless wire) was formed and drawn, and a wire containing flux of various components shown in the table was prototyped. The Al content of the steel outer skin was 0.20% or less in mass% with respect to the total mass of the steel outer skin. The outer surface of the steel outer skin was coated with a feed lubricant so that the amount per 10 kg of flux-cored wire was 0.20 to 0.60 g. Iron powder (atomized iron powder) was appropriately added to the flux in order to adjust the filling rate. The wire diameter was 1.2 mm. In addition, a solid solid wire containing no flux was also prepared and evaluated in order to confirm the effect of the present invention. Solid wire was obtained by drawing and annealing a raw material having a predetermined chemical composition.

The "F-converted value" shown in the table is the F-converted value of the fluoride contained in the welding material, and "SiO _{2 " is the SiO 2-} converted value of the Si oxide contained in the welding material, which is "Na + K". Is the total value of the Na conversion value of the Na compound contained in the welding material and the K conversion value of the K compound, and "Ca" is the Ca conversion value of the Ca compound contained in the welding material, and is "Zr". Is a Zr conversion value of the Zr compound contained in the welding material. In addition, the content of the substance corresponding to 2 or more among the above-mentioned items was included in the value of each item to which the substance belongs. _{For example, the content of ZrSiO 4} corresponding to both the Zr compound and the Si oxide was included in both the Zr conversion value of the Zr compound and the SiO ₂ conversion value of the Si oxide. Numerical values outside the range specified in the present invention or values that do not meet the pass / fail criteria of the present invention are underlined. Further, a blank in the table relating to the content of the chemical component or compound means that the chemical component or compound is not intentionally added.

Using the prototype welding materials (wire with flux and solid wire) shown in the table, welding workability, measurement of the amount of spatter generated, presence of welding defects, and weld metal performance were investigated.

Weld metal performance was carried out by performing welding according to the weld metal test conditions shown in the table. A 6 m long conduit cable was used for wire feeding during welding. The specific evaluation method for each item is as follows.
The tensile strength was measured by collecting a No. A0 tensile test piece from a welded metal manufactured according to JIS Z3111 and performing a tensile test on it. A welding material from which a weld metal having a tensile strength of 490 MPa or more can be obtained was judged to be acceptable in terms of tensile strength.
The toughness of the weld metal was evaluated by collecting an impact test piece from the weld metal portion obtained by the above procedure and performing a Charpy impact test at 0 ° C. Welding materials that can obtain weld metal with absorbed energy of 60J or more in all tests and the average value of the average value of the three test results is 80J or more are judged to be acceptable in terms of low temperature toughness. did.

The crack resistance test for evaluating low temperature crack resistance and solidification crack resistance is a weld crack test shown in the table in accordance with JIS Z3158 using a wear resistant steel plate with a plate thickness of 50 mm specified in ABS500. A y-shaped weld crack test was carried out under the conditions. The test piece was tested at a test temperature of 5 degrees Celsius, without preheating, and 48 hours after welding, and the presence or absence of solidification cracks and low-temperature cracks in surface cracks and cross-section cracks (5 cross-sections) was investigated.

Further, the amount of spatter generated and the state of slag were evaluated by repeating bead-on-plate welding for 30 seconds × 5 times under the slag and spatter test conditions shown in the table using a copper collection box. Welding materials having a particle size of 1 mm or more and 0.30 g or less in terms of the amount of spatter generated per minute were judged to be good in terms of spatter suppression ability. In addition, welding materials that cause other welding workability defects such as slag entrainment, slag peeling failure, or arc instability due to an inappropriate amount of slag in the welded part are rejected with respect to slag, etc. Judgment was made and a statement to that effect was made in the "Bead" column.

Inventive examples A1 to A18, which are within the scope of the present invention, are welded metals having excellent welding workability (bead shape and spatter amount), suppressing low-temperature cracking and solidification cracking, and having appropriate tensile strength and toughness. Obtained. On the other hand, with respect to Comparative Examples B1 to B15, which are outside the scope of the present invention, one or more of the evaluation items were rejected, and the comprehensive evaluation was determined to be rejected.

Claims (8)

A flux-cored wire for gas shielded arc welding, comprising a steel outer skin and a flux filled in the steel outer skin.
C: 0.001 to 0.120% as an alloy component in mass% with respect to the total mass of the flux-cored wire.
Si: 0.40-1.60%,
Mn: 1.50 to 2.50%,
P: 0.030% or less,
S: 0.030% or less,
Cu: 0.05 to 0.50%,
It contains Ti: 0.04 to 0.30% and Al: 0.200% or less.
Further, by mass% of the total mass of the flux-cored wire,
Fluoride: Total F conversion value is more than 0.100% and 0.300% or less,
Si oxide: _{0.01 to 0.40% in terms of SiO 2} , and Na compound and K compound: 0.060 to 0.350% in total of Na conversion value and K conversion value.
A flux-filled wire for gas shielded arc welding, characterized in that the balance is composed of Fe and impurities in the form of any one or more of a steel outer skin, iron powder, and iron alloy powder. Ni: 0% or more and less than 0.80% as the alloy component in mass% with respect to the total mass of the flux-cored wire.
Mo: 0-0.50%,
B: 0-0.0100%,
Mg: 0 to 0.50% and Sn: 0 to 0.40%
Further comprise one or more selected from the group consisting of,
The flux-cored wire for gas shielded arc welding according to claim 1, wherein the C content is 0.001 to 0.080%. By mass% of the total mass of the flux-cored wire
Ca compound: 0 to 0.300% in terms of Ca
The flux-cored wire for gas shielded arc welding according to claim 1 or 2, wherein the wire is characterized by the above. One of claims 1 to 3, wherein the steel outer skin contains Al: 0.003 to 0.200% as the alloy component in mass% with respect to the total mass of the steel outer skin. Wire with flux for gas shielded arc welding as described in. By mass% of the total mass of the flux-cored wire
Zr compound: 0 to 0.30% in terms of Zr
The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 4, further comprising. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 5, wherein the steel outer skin has a seamless shape. The outer surface of the steel outer skin is further provided with a feed lubricant.
The flux for gas shielded arc welding according to any one of claims 1 to 6, wherein the amount of the feed lubricant per 10 kg of the flux-cored wire is 0.20 to 1.00 g. Wire. A method for manufacturing a welded joint, which comprises gas shielded arc welding of a steel sheet using the flux-cored wire for gas shielded arc welding according to any one of claims 1 to 7.