Metal-based flux-cored wire and weld metal

Abstract

To provide a metal-based flux-cored wire that is able to obtain a satisfactory bead shape and a weld metal excellent in electrodeposition coatability and mechanical properties, and to provide a weld metal.SOLUTION: A metal-based flux-cored wire obtained by filling a steel outer-sheath with a flux contains, relative to the total mass of the wire, 90% or more Fe by mass, 0.04% or more and 0.12% or less C by mass, 0.05% or more and 0.70% or less Si by mass, 1.0% or more and 2.0% or less Mn by mass, 1.5% or more and 4.5% or less Ni by mass, 0.1% or more and 1.0% or less Mo by mass, and 0.10% or more and 0.40% or less Mo by mass. Cr is 0.6% or less by mass, and Cu is less than 0.5% by mass. The remainder includes unavoidable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a metallic flux-cored wire and a weld metal. [Background technology]

[0002] In the automotive field, efforts are being made to increase the strength of automotive parts made of high-tensile steel sheets of 780 MPa class or higher in order to reduce weight. Accordingly, welding wires used to weld high-tensile steel sheets are also required to have high strength. For example, Patent Document 1 discloses a solid wire for gas-shielded arc welding that can produce weld metal with high strength and excellent toughness when welding high-tensile steel sheets of 780 MPa class or higher. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5670305 Summary of the Invention [Problem to be solved by the invention]

[0004] When lap fillet arc welding of thin steel plates is performed using a solid wire such as that described in Patent Document 1, the spread of the base metal cathode spot (arc spread) is small, and the spread of heat on the base metal surface is limited, so the molten metal at the widthwise ends of the molten pool is rapidly cooled, which can result in a poor bead shape.It is known that poor bead toe shape reduces the resistance of automotive parts to repeated stresses, and improving the bead shape is also required from the perspective of improving fatigue properties.

[0005] Furthermore, automotive suspension components are exposed to corrosive environments due to moisture from the road surface and salt damage contained in snow-melting agents, resulting in localized thinning of steel sheets. A common method for protecting components from corrosive environments is to apply electrodeposition coating after arc welding. However, when electrodeposition coating is performed after welding, the electrodeposition coating film does not form on the welding slag, resulting in coating defects, which can cause corrosion to progress from these defects. Therefore, to further reduce the weight of components, a technology is needed that can ensure sufficient mechanical properties at the welded joint while preventing corrosion. However, Patent Document 1 does not consider electrodeposition coating properties. In particular, high-tensile steel sheets have a higher content of alloys such as Si and Mn than mild steel sheets, which increases the amount of slag generated during arc welding, making them more susceptible to coating defects.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a metal-based flux-cored wire and a weld metal that can obtain a good bead shape and can also obtain a weld metal that is excellent in electrodeposition coatability and mechanical properties. [Means for solving the problem]

[0007] As a result of extensive research into high-strength welding wires, the inventors have found that with metal-based flux-cored wires, the surface tension of the molten pool is reduced due to the influence of an oxygen source contained in the flux in lap fillet welding, making it easier to obtain a spread of the molten pool; and that the spread of the cathode spot in the base metal is greater than with solid wires, and the toe of the molten pool solidifies while being slowly cooled, making it possible to obtain a very smooth boundary with the base metal and a good bead shape.

[0008] On the other hand, compared to solid wire, metal-based flux-cored wires have a higher oxygen content in the weld metal, which increases the amount of slag generated, reducing electrodeposition coatability and degrading mechanical properties. The present inventors have found that by appropriately controlling the contents of C, Ni, Cr, and Mo, which are known to have low affinity for oxygen, in particular, it is possible to obtain a weld metal with a good balance of strength and toughness. Furthermore, the present inventors have found that by appropriately controlling the contents of Si, Mn, and Ti, the oxygen content in the weld metal can be controlled while allowing conductive slag to be the main component, thereby improving the electrodeposition coatability of the weld metal. As a result, even when metal-based flux-cored wires are used, electrodeposition coatability and mechanical properties can be improved. The present invention was made based on these findings.

[0009] The above object of the present invention is achieved by the following configuration [1] relating to a metal-based flux-cored wire.

[0010] [1] A metal-based flux-cored wire in which a steel sheath is filled with flux, For the total mass of the wire, Fe: 90% by mass or more, C: 0.04% by mass or more and 0.12% by mass or less, Si: 0.05% by mass or more and 0.70% by mass or less, Mn: 1.0 mass% or more and 2.0 mass% or less, Ni: 1.5% by mass or more and 4.5% by mass or less, Mo: 0.1% by mass or more and 1.0% by mass or less, and Ti: 0.10 mass% or more and 0.40 mass% or less, Cr: 0.6% by mass or less, Cu: less than 0.5% by mass, The remainder of the metal-based flux-cored wire is comprised of unavoidable impurities.

[0011] Furthermore, preferred embodiments of the present invention relating to the metal-based flux-cored wire relate to the following [2] to [4].

[0012] [2] Al: 0.05% by mass or less, P: 0.030% by mass or less, and The metal-based flux-cored wire according to [1], characterized in that S: 0.030 mass % or less.

[0013] [3] When the content of Si in the wire is [Si] in mass% relative to the total mass of the wire, and the content of Mn in the wire is [Mn] in mass% relative to the total mass of the wire, The metal-based flux-cored wire according to [1] or [2], characterized in that the value calculated by [Si] / [Mn] is 0.05 or more and 0.60 or less.

[0014] [4] The content of C in the wire is expressed as mass% relative to the total mass of the wire [C], The content of Si in the wire is expressed as mass% [Si] relative to the total mass of the wire, The content of Mn in the wire is expressed as [Mn] in mass% relative to the total mass of the wire, The content of Ni in the wire is expressed as [Ni] in mass% relative to the total mass of the wire, The content of Cr in the wire is expressed as mass% relative to the total mass of the wire [Cr], The content of Mo in the wire is expressed as [Mo] in mass% relative to the total mass of the wire, The content of Al in the wire is expressed as [Al] in mass% relative to the total mass of the wire, When the content of Ti in the wire is [Ti] in mass% relative to the total mass of the wire, [2] The metal-based flux-cored wire according to [2], characterized in that the value of A calculated by A = 1400 × [C] + 280 × [Si] + 150 × [Mn] + 55 × [Ni] + 110 × [Cr] + 280 × [Mo] + 20 × [Al] + 250 × [Ti] is 700 or more and 900 or less.

[0015] The above object of the present invention is also achieved by the following configuration [5] relating to the weld metal. The welded metal is characterized in that it is produced by gas shielded arc welding using the metal-based flux-containing wire according to any one of [1] to [4] of [5].

Effect of the Invention

[0016] According to the present invention, it is possible to provide a metal-based flux-containing wire and a welded metal capable of obtaining a good bead shape and a welded metal excellent in electrodeposition coating properties and mechanical properties.

Mode for Carrying Out the Invention

[0017] Hereinafter, the embodiments for carrying out the present invention will be described in detail. The present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention. First, the metal-based flux-containing wire according to the present embodiment will be described.

[0018] 〔Metal-based flux-containing wire〕 The metal-based flux-containing wire according to the present embodiment is one in which a flux is filled in a steel outer skin (hoop). Specifically, the metal-based flux-containing wire of the present embodiment is composed of a cylindrical steel outer skin and a flux filled inside the outer skin.

[0019] Hereinafter, the chemical components contained in the flux and the outer skin of the metal-based flux-containing wire according to the present embodiment will be described in detail, together with the reasons for addition and the reasons for numerical limitation. In the present embodiment, the content means mass% with respect to the total mass of the metal-based flux-containing wire (hereinafter, also simply referred to as "flux-containing wire" or "wire") unless otherwise specified. Further, each element contained in the flux-containing wire according to the present embodiment may be contained in either the steel outer skin (hereinafter, also simply referred to as "outer skin") or the flux, or may be contained in both the steel outer skin and the flux.

[0020] <Fe: 90 mass% or more> Fe is the main component of the wire according to this embodiment. Considering the content relationship of other components contained in the wire, the Fe content with respect to the total mass of the wire is 90% by mass or more, preferably 92% by mass or more, and more preferably 93% by mass or more.

[0021] <C: 0.04% by mass or more and 0.12% by mass or less> C is an element having the effect of enhancing the hardenability of the weld metal. When the C content is less than 0.04% by mass, the hardenability of the steel decreases, and the strength and toughness of the weld metal decrease. Therefore, the C content with respect to the total mass of the wire is 0.04% by mass or more, preferably 0.05% by mass or more, and more preferably 0.06% by mass or more. On the other hand, when the C content exceeds 0.12% by mass, the strength of the weld metal increases, and the ductility and toughness decrease. Also, when C is excessively contained in the wire, cold cracking is likely to occur. Therefore, the C content with respect to the total mass of the wire is 0.12% by mass or less, preferably 0.11% by mass or less, and more preferably 0.10% by mass or less.

[0022] <Si: 0.05% by mass or more and 0.70% by mass or less> Si is a strong deoxidizing element and has the effect of reducing the amount of oxygen in the weld metal and ensuring a better balance between the strength and toughness of the weld metal. Also, Si is an element that forms an amorphous slag with low conductivity. When the Si content is less than 0.05% by mass, the binding with oxygen in the weld metal is less, deoxidation is insufficient, porosity defects are likely to occur, and the tensile strength of the weld metal decreases. Therefore, the Si content with respect to the total mass of the wire is 0.05% by mass or more, preferably 0.07% by mass or more, and more preferably 0.10% by mass or more. On the one hand, if the Si content exceeds 0.70% by mass and Si is excessively contained in the wire, an amorphous slag with low conductivity is formed, resulting in a decrease in electrodeposition coating properties. Therefore, the Si content with respect to the total mass of the wire should be 0.70% by mass or less, more preferably 0.65% by mass or less, and even more preferably 0.60% by mass or less.

[0023] <Mn: 1.0% by mass or more and 2.0% by mass or less> Mn is an element that increases the hardenability of the weld metal and also has the effect of improving the electrodeposition coating properties by forming a composite oxide having conductivity together with Fe and Ti. If the Mn content is less than 1.0% by mass, the hardenability of the steel is insufficient, and the strength and toughness of the weld metal are insufficient. Also, it becomes difficult to form a composite oxide having conductivity, resulting in a decrease in electrodeposition coating properties. Therefore, the Mn content with respect to the total mass of the wire should be 1.0% by mass or more, more preferably 1.05% by mass or more, and even more preferably 1.10% by mass or more. On the other hand, if the Mn content exceeds 2.0% by mass, the strength of the weld metal increases, and the ductility and toughness of the weld metal decrease. Also, if Mn is excessively contained in the wire, cold cracking is likely to occur. Therefore, the Mn content with respect to the total mass of the wire should be 2.0% by mass or less, preferably 1.9% by mass or less, and more preferably 1.8% by mass or less.

[0024] <Ni: 1.5% by mass or more and 4.5% by mass or less> Ni is an element that increases the hardenability of the weld metal and also has the effect of strengthening the prior austenite grains and improving the low-temperature toughness. If the Ni content is less than 1.5% by mass, when trying to ensure stable toughness, the strength of the weld metal decreases. Therefore, the Ni content with respect to the total mass of the wire should be 1.5% by mass or more, preferably 1.6% by mass or more, and more preferably 1.7% by mass or more. On the one hand, if the Ni content exceeds 4.5% by mass and Ni is excessively contained in the wire, the cleavage transition temperature shifts to a lower temperature side, improving the low-temperature toughness, but the upper shelf energy decreases, and it is impossible to ensure the balance of the target mechanical properties. Therefore, the Ni content with respect to the total mass of the wire is 4.5% by mass or less, preferably 3.5% by mass or less, and more preferably 3.0% by mass or less.

[0025] <Mo: 0.1% by mass or more and 1.0% by mass or less> Mo is an element having an effect of increasing the hardenability of the weld metal. Also, compared with strong deoxidizing elements such as Si, Mn, Ti, and Al, Mo has a small affinity with oxygen, so it is also an element having an effect of reducing the slag amount. If the Mo content is less than 0.1% by mass, the hardenability of the steel decreases, and the strength and toughness of the weld metal are insufficient. Therefore, the Mo content with respect to the total mass of the wire is 0.1% by mass or more. Also, in order to ensure the strength and toughness of the weld metal while suppressing the slag generation amount, the Mo content with respect to the total mass of the wire is preferably 0.3% by mass or more. On the other hand, if the Mo content exceeds 1.0% by mass, the strength of the weld metal increases, and the ductility and toughness of the weld metal decrease. Therefore, the Mo content with respect to the total mass of the wire is 1.0% by mass or less. Also, in order to ensure a better balance between the strength and toughness of the weld metal, the Mo content with respect to the total mass of the wire is preferably 0.7% by mass or less.

[0026] <Ti: 0.10% by mass or more and 0.40% by mass or less> When Ti is contained in the wire, Ti-based oxides are formed. This Ti-based oxide has a high liquidus temperature and serves as a nucleus for the formation of complex oxides. Therefore, Ti is an element having an effect of improving the electrocoating property by forming a complex oxide having conductivity together with Mn and Fe. If the Ti content is less than 0.10% by mass, a conductive composite oxide with a Ti-based oxide as the core cannot be formed. Therefore, the Ti content with respect to the total mass of the wire should be 0.10% by mass or more. Also, in order to obtain a good balance between the slag generation amount and the generation amount of the conductive composite oxide, the Ti content with respect to the total mass of the wire is preferably 0.10% by mass or more, and more preferably 0.11% by mass or more. On the other hand, if the Ti content exceeds 0.40% by mass and Ti is excessively contained in the wire, the amount of slag increases, and the thickness of the slag increases, resulting in a decrease in electrodeposition coating properties. Therefore, the Ti content with respect to the total mass of the wire should be 0.40% by mass or less, preferably 0.35% by mass or less, and more preferably 0.30% by mass or less.

[0027] <Cr: 0.6% by mass or less> Cr is an element that has the effect of enhancing the hardenability of the weld metal. Also, compared with strong deoxidizing elements such as Si, Mn, Ti, and Al, Cr has a small affinity with oxygen, so it is also an element that has the effect of reducing the amount of slag. However, in the present embodiment, it is not always necessary to contain Cr in the wire, and it may be 0% by mass. In order to ensure the strength and toughness of the weld metal while suppressing the slag generation amount, the Cr content with respect to the total mass of the wire is preferably 0.01% by mass or more, and more preferably 0.03% by mass or more. On the other hand, when the Cr content with respect to the total mass of the wire exceeds 0.6% by mass, the strength of the weld metal increases too much, and the ductility and toughness of the weld metal decrease. Therefore, the Cr content with respect to the total mass of the wire should be 0.6% by mass or less. Also, considering the balance between the strength and toughness of the weld metal, the Cr content with respect to the total mass of the wire is preferably 0.5% by mass or less, and more preferably 0.4% by mass or less.

[0028] <Cu: less than 0.50% by mass> Since Cu is an element that reduces the toughness of the weld metal, in this embodiment, it is preferable to reduce the Cu content in the wire, and it may be 0% by mass. When the Cu content is 0.50% by mass or more, the grain boundaries of the weld metal become brittle, the toughness decreases, or cracks occur. Therefore, the Cu content with respect to the total mass of the wire is less than 0.50% by mass, preferably 0.45% by mass or less, and more preferably 0.40% by mass or less. When Cu plating is applied to the wire surface, the Cu contained in the plating is also included in the range of the Cu content defined in this embodiment, that is, less than 0.50% by mass.

[0029] Furthermore, in the flux-cored wire of this embodiment, the contents of Al, P, and S are preferably in the following ranges, respectively.

[0030] <Al: 0.05% by mass or less> Al is an element that forms Al-based oxides, increases the interfacial tension with the molten metal, and increases the fluidity of the slag. The spheroidized slag may follow the vicinity of the solid-liquid interface of the molten pool and increase the thickness of the slag. Therefore, in this embodiment, it is preferable to reduce the Al content in the wire, and it may be 0% by mass. When the Al content is 0.05% by mass or less, an increase in the thickness of the slag can be suppressed, and good electrodeposition coating properties can be ensured. Therefore, the Al content with respect to the total mass of the wire is preferably 0.05% by mass or less, more preferably 0.04% by mass or less, and even more preferably 0.03% by mass or less.

[0031] <P: 0.030% by mass or less> P is an impurity element and an element that affects the toughness of the weld metal. When the P content in the wire is 0.030% by mass or less, a decrease in the toughness of the weld metal can be suppressed. Therefore, the P content with respect to the total mass of the wire is preferably 0.030% by mass or less, more preferably 0.025% by mass or less, and even more preferably 0.020% by mass or less.

[0032] <S: 0.030 mass% or less> S has the function of reducing the surface tension of the molten metal, increasing the interfacial tension with the slag, and spheroidizing the slag. The slag spheroidized by the influence of S follows near the solid-liquid vicinity of the molten pool and may increase the thickness of the slag. When the S content in the wire is 0.030 mass% or less, an increase in the thickness of the slag can be suppressed, and good electrodeposition coating properties can be ensured. Therefore, the S content with respect to the total mass of the wire is preferably 0.030 mass% or less, more preferably 0.025 mass% or less, and still more preferably 0.020 mass% or less.

[0033] Furthermore, for the flux-containing wire of the present embodiment, the content ratio [Si] / [Mn] of Si and Mn represented by the following formula is preferably 0.05 or more and 0.60 or less.

[0034] <[Si] / [Mn]: 0.05 or more and 0.60 or less> Si and Mn are elements that have a high affinity with oxygen, deoxidize the oxygen in the weld metal, and strengthen the strength and toughness of the weld metal. The oxide of Si is an amorphous slag, which inhibits the electrodeposition coating properties, while the oxide of Mn forms a composite oxide with Fe and Ti, improving the electrodeposition coating properties. When the content of Si in the wire is [Si] in mass% with respect to the total mass of the wire, and the content of Mn in the wire is [Mn] in mass% with respect to the total mass of the wire, when the value calculated by [Si] / [Mn] is 0.05 or more, deoxidation in the weld metal becomes sufficient and the mechanical properties are improved. For this reason, the value calculated by [Si] / [Mn] is preferably 0.05 or more, more preferably 0.06 or more, and still more preferably 0.07 or more. Also, when the value calculated by [Si] / [Mn] is 0.60 or less, the electrodeposition coating properties are improved. For this reason, the value calculated by [Si] / [Mn] is preferably 0.60 or less, more preferably 0.55 or less, and still more preferably 0.50 or less.

[0035] Furthermore, in the flux-cored wire of this embodiment, it is preferable that the parameter A expressed by the following formula be 700 or more and 900 or less. A=1400×[C]+280×[Si]+150×[Mn]+55×[Ni]+110×[Cr]+280×[Mo]+20×[Al]+250×[Ti]

[0036] The parameter A is an index for maintaining a good balance between strength and toughness when high-tensile steel plates (steel plates of 780 MPa class or higher) are welded. When the value of A is 700 or higher, the strength of the weld metal is improved. When the value of A is 900 or lower, ductility and toughness can be ensured. Therefore, the value of A is preferably 700 or higher, more preferably 705 or higher, and even more preferably 710 or higher. Furthermore, the value of A is preferably 900 or lower, more preferably 895 or lower, and even more preferably 890 or lower.

[0037] In the above formula, [C] is the value of the C content in the wire expressed as mass% with respect to the total mass of the wire. [Si] is the value of the Si content in the wire expressed as mass% with respect to the total mass of the wire. [Mn] is the value of the Mn content in the wire expressed as mass% with respect to the total mass of the wire. [Ni] is the value of the Ni content in the wire expressed as mass% with respect to the total mass of the wire. [Cr] is the value of the Cr content in the wire expressed as mass% with respect to the total mass of the wire. [Mo] is the value of the Mo content in the wire expressed as mass% with respect to the total mass of the wire. [Al] is the value of the Al content in the wire expressed as mass% with respect to the total mass of the wire. [Ti] is the value of the Ti content in the wire expressed as mass% with respect to the total mass of the wire.

[0038] <Remainder> The remainder of the flux-cored wire of this embodiment contains unavoidable impurities. Examples of unavoidable impurities include O, N, As, Sb, Sn, Co, H, and Zn. The total amount of unavoidable impurities is preferably limited to 0.1% by mass or less, more preferably 0.05% by mass or less, based on the total mass of the wire. In addition to the above-described wire components, various metal components may be added in this embodiment as long as they do not impair the effects of the present invention. The type and amount of these metal components are not limited. For example, in order to improve strength while suppressing slag generation, the wire may contain Nb, V, B, W, Zr, N, etc., and the total amount of these metal components is preferably limited to 1.0% by mass or less, more preferably 0.5% by mass or less. Furthermore, the wire contains more O than solid wire due to the O contained in the flux.

[0039] In the flux-cored wire of the present embodiment, the total content of Fe, C, Si, Mn, Ni, Mo, Ti, Cr, and Cu is preferably 96 mass% or more, more preferably 97 mass% or more, even more preferably 98 mass% or more, and particularly preferably 99 mass% or more.

[0040] The flux-cored wire according to the present embodiment is a metal-based (metal-cored) wire, and preferably does not substantially contain a slag-forming agent such as SiO. The content of metal oxides relative to the total mass of the wire is preferably 1.0 mass% or less, and more preferably 0.5 mass% or less.

[0041] In this embodiment, the base material is not particularly limited, but since the deposited metal obtained by using the flux-cored wire according to this embodiment has excellent tensile strength and toughness, the flux-cored wire can be suitably used particularly for welding high-strength steel plates.

[0042] [Method of manufacturing flux-cored wire] The flux-cored wire according to this embodiment can be manufactured, for example, by the following method. First, a steel strip constituting the outer sheath is formed into a U-shaped open tube by a forming roll while being fed in the longitudinal direction. Next, a flux containing a predetermined amount of metal and alloy to achieve a predetermined chemical composition is filled into the open tube, and the tube is then processed to have a circular cross section. Thereafter, the wire is drawn by cold working, and a flux-cored wire having a desired wire diameter can be manufactured. Annealing may be performed during the cold working.

[0043] As described above, the wire according to this embodiment is a metal-based flux-cored wire, and therefore the manufacturing cost can be reduced compared to a solid wire. In this embodiment, the outer diameter of the wire is not particularly limited, but is preferably, for example, 0.9 mm or more and 1.6 mm or less. Furthermore, the outer sheath can be made seamless by welding or the like at the seam, and there are no limitations on the presence or absence of a seam in the outer sheath, the shape of the seam, or the cross-sectional shape. Note that solid wire for high-tensile steel plates tends to be difficult to draw due to its high strength, and therefore the manufacturing cost tends to be high. However, since the present embodiment is a metal-based flux-cored wire, it is easy to manufacture and the manufacturing cost can be kept relatively low.

[0044] <Flux filling rate: 8% by mass or more and 20% by mass or less> In the flux-cored wire according to the present embodiment, the flux filling rate, which is the mass of the flux relative to the total mass of the wire, is not particularly limited and can be set to any range as long as the contents of the components in the wire are within the above-mentioned ranges. In order to further improve the drawability and wire feedability of the wire, the flux filling rate is preferably set to, for example, 8 mass % or more and 20 mass % or less relative to the total mass of the wire.

[0045] Next, the weld metal according to this embodiment will be described.

[0046] [Weld metal] The weld metal according to this embodiment is produced by gas-shielded arc welding using the metal-based flux-cored wire according to this embodiment. In the gas-shielded arc welding method for obtaining the weld metal according to this embodiment, various welding conditions are not particularly limited except for the use of the flux-cored wire according to this embodiment, and general conditions for welding methods using metal-based flux-cored wires can be used for the type of base metal, welding voltage, welding current, welding position, etc. The shielding gas is also not limited, but is preferably 3-25% by volume Ar, balance CO.

[0047] In addition, although the welding position using the flux-cored wire according to the present embodiment is not particularly limited, the effect can be particularly obtained when welding by horizontal fillet welding. Furthermore, although the thickness of the steel sheath and the wire diameter (diameter) of the flux-cored wire according to the present embodiment are not particularly limited, they can be applied to wires with diameters specified in welding material standards such as AWS or JIS. [Example]

[0048] The effects of the present invention will be specifically explained below by giving examples of the present invention and comparative examples, but the present invention is not limited to these.

[0049] [Making wires] Flux-cored wires of the invention examples and comparative examples, each having a diameter of 1.2 mm, were prepared by filling a steel sheath with flux so that the wire contained various components shown in Tables 1 and 2. In addition, as a comparative example, a solid wire was prepared whose wire contained components were shown in Comparative Example 11 in Table 2.

[0050] [Weld metal evaluation] <Weld metal production by lap fillet welding> Using the obtained flux-cored wire and solid wire, lap fillet welding was carried out under the welding conditions shown in Table 3 below to form weld metal, and the amount of slag, bead shape and electrodeposition paintability were evaluated.

[0051] (amount of slag) The amount of slag generated during welding was confirmed. Specifically, for some wires, the bead after welding was photographed with a digital microscope, the slag on the bead was colored using image processing, and the percentage of the image occupied by slag was calculated as the slag area ratio, and the amount of slag was evaluated by this. The evaluation criteria for slag amount were as follows: a slag area ratio of 4.5% or less was evaluated as ◎ (excellent), and a slag area ratio of more than 4.5% was evaluated as ○ (good). In addition, the slag was visually confirmed based on the evaluation by measurement, and evaluated as ◎ or ○. Furthermore, samples without Ti addition in which amorphous slag consisting mainly of Si and Mn was generated were evaluated as △ (slightly poor), regardless of the amount of slag.

[0052] (Bead shape) The weld metal obtained was macro-sectioned, and the bead shape was evaluated by measuring the angle of the toe where the weld metal and the lower plate intersect. The evaluation criteria were based on the fact that the actual performance of current solid wire is such that the toe angle is 140° or less, so toe angles exceeding 140° were evaluated as ○ (good).

[0053] (Electrodeposition paintability) The resulting weld metal was subjected to cathodic electrodeposition coating, and the electrodeposition paintability was evaluated. The evaluation criteria for electrodeposition paintability were as follows: when a thin layer of slag spread over the weld metal and the electrodeposition paintability was good, it was rated as ◯ (good); when the slag on the weld metal aggregated and the electrodeposition paint was not applied, it was rated as × (poor).

[0054] [Evaluation of weld metal] <Preparation of deposited metal> Using the obtained flux-cored wire and solid wire, a weld metal was formed on a base material having a V-groove by gas-shielded arc welding under the conditions shown in Table 4 below, and the oxygen content was measured and the mechanical properties of the weld metal were evaluated.

[0055] (oxygen content) The oxygen content of the deposited metal obtained for some wires was measured. The amount of oxygen in the deposited metal affects bead shape and weld defects, so if the oxygen content is too low, the bead shape will be poor, and if the oxygen content is too high, welding defects and the like will occur. In this example, an oxygen content of more than 700 ppm or less than 350 ppm was evaluated as poor, an oxygen content of more than 650 ppm but not more than 700 ppm was evaluated as slightly poor, and an oxygen content of 350 ppm or more but not more than 650 ppm was evaluated as good.

[0056] <Mechanical property evaluation> The mechanical properties of the weld metal were measured in accordance with the "Tensile and impact test method for weld metal" specified in JIS Z 3111:2005. Tensile test pieces (A0 type) and impact test pieces (V-notch test pieces) were taken from the weld metal, and the tensile strength and Charpy absorbed energy were measured.

[0057] (tensile strength) A tensile test was carried out on each test piece at room temperature (approximately 20±2°C) to measure the tensile strength. As an evaluation standard for tensile strength, a tensile strength of 700 MPa or more was evaluated as good strength.

[0058] (Impact test) Each test piece was subjected to an impact test at a test temperature of -20°C, and the toughness was evaluated by measuring the Charpy absorbed energy (vE-20°C). As a criterion for evaluating toughness, a test piece was judged to have good toughness when the Charpy absorbed energy (vE-20°C) at -20°C was 50 J or more.

[0059] As an overall evaluation, wires that had an excellent amount of slag and all other evaluation results were good in the above various evaluation tests were judged as ⊚ (excellent), and wires that had good evaluation results were judged as ○ (good), and these wires were deemed to have passed. On the other hand, wires that had at least one evaluation result that was fair or poor were judged as × (poor), and were deemed to have failed. The evaluation results of the inventive examples and comparative examples are shown in Table 5 below.

[0060] [Table 1]

[0061] [Table 2]

[0062] [Table 3]

[0063] [Table 4]

[0064] [Table 5]

[0065] As shown in Tables 1, 2 and 5 above, in Invention Examples Nos. 1 to 10, the content of each chemical component in the wire was within the range specified by the present invention, and therefore a good bead shape was obtained, and a deposited metal with excellent electrodeposition coatability and mechanical properties was obtained.

[0066] On the other hand, in Comparative Examples No. 1 and No. 3, the Ni content in the wire was below the lower limit of the range specified in the present invention, and therefore Comparative Examples No. 1 and No. 3 had reduced tensile strength. In Comparative Example No. 2, the Ni content in the wire was below the lower limit of the range specified in the present invention, but the amount of slag increased due to the relationship with the Si content in the wire. In Comparative Examples 4 to 6, the Ni content and Ti content in the wire were below the lower limit of the range specified in the present invention, so the amount of slag increased and the electrodeposition coatability and tensile strength also decreased. In Comparative Examples 7 to 10, the Si content in the wire was below the lower limit of the range defined by the present invention, and therefore the tensile strength of the deposited metal was reduced. In Comparative Example No. 11, the solid wire was used, so the oxygen content in the deposited metal was low, and the bead shape was deteriorated.

Claims

1. A metal-based flux-cored wire having a steel outer sheath filled with flux, For the total mass of the wire, Fe: 90% by mass or more, C: 0.04% by mass or more and 0.12% by mass or less, Si: 0.05% by mass or more and 0.70% by mass or less, Mn: 1.0% by mass or more and 2.0% by mass or less, Ni: 1.5% by mass or more and 4.5% by mass or less, Mo: 0.1% by mass or more and 1.0% by mass or less, and Ti: 0.10% by mass or more and 0.40% by mass or less; Cr: 0.6% by mass or less, Cu: less than 0.5% by mass; The remainder of the metal-based flux-cored wire is comprised of unavoidable impurities.

2. Al: 0.05% by mass or less, P: 0.030% by mass or less, and 2. The metal-based flux-cored wire according to claim 1, wherein S is 0.030 mass % or less.

3. When the content of Si in the wire is [Si] in mass% with respect to the total mass of the wire, and the content of Mn in the wire is [Mn] in mass% with respect to the total mass of the wire, 2. The metal-based flux-cored wire according to claim 1, wherein a value calculated by [Si] / [Mn] is 0.05 or more and 0.60 or less.

4. The content of C in the wire is expressed as [C] in mass% relative to the total mass of the wire, The content of Si in the wire is expressed as [Si] in mass% relative to the total mass of the wire, The content of Mn in the wire is expressed as [Mn] in mass% relative to the total mass of the wire, The content of Ni in the wire is expressed as [Ni] in mass% relative to the total mass of the wire, The content of Cr in the wire is expressed as mass% relative to the total mass of the wire [Cr], The content of Mo in the wire is expressed as [Mo] in mass% relative to the total mass of the wire, The content of Al in the wire is expressed as [Al] in mass% relative to the total mass of the wire, When the content of Ti in the wire is expressed as [Ti] in mass% relative to the total mass of the wire, 3. The metal-based flux-cored wire according to claim 2, wherein the value of A calculated by A = 1400 × [C] + 280 × [Si] + 150 × [Mn] + 55 × [Ni] + 110 × [Cr] + 280 × [Mo] + 20 × [Al] + 250 × [Ti] is 700 or more and 900 or less.

5. A weld metal produced by gas-shielded arc welding using the metal-based flux-cored wire according to any one of claims 1 to 4.

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