Solid wire for gas-shielded arc welding and method for manufacturing welded joint

Abstract

A solid wire for gas shielded arc welding according to one embodiment of the present disclosure contains, in mass % with respect to the total mass of the solid wire, 0.04 to 0.12% C, 0.13 to 0.28% Si, 1.4 to 2.3% Mg, 0.13 to 0.25% Ti, 0.001 to 0.050% Al, etc., where the following relationships are satisfied: Si × Mn ≤ 0.60; (Si + Mn / 5) / (Ti + Al) ≤ 4.0; 1.00 ≤ Si +0.5 × (Mn + Cr) +0.3 × Ni; 0.30 ≤ C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ≤ 0.55; and 0 ≤ Cr + Ni ≤ 3.00.

Description

[Technical Field]

[0001] The present disclosure relates to a solid wire for gas-shielded arc welding and a method for manufacturing a welded joint. This application claims priority based on Japanese Patent Application No. 2023-141138, filed on August 31, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Gas-shielded arc welding is widely used in various fields. For example, in the automotive field, gas-shielded arc welding is used to weld undercarriage components and the like. One example of a welding material for gas-shielded arc welding is solid wire. Solid wire is a wire that does not contain flux in the center of its cross section, and its cross section is solid. Various solid wires for gas-shielded arc welding have been proposed in the prior art.

[0003] Patent Document 1 discloses a gas-shielded arc welding wire containing, relative to the total mass of the wire, C: 0.01% by mass or more and 0.10% by mass or less, Si: 0.05% by mass or more and 0.55% by mass or less, Mn: 1.60% by mass or more and 2.40% by mass or less, Ti: 0.05% by mass or more and 0.25% by mass or less, Cu: 0.30% by mass or less, Al: 0.10% by mass or less, P: 0.025% by mass or less, S: 0.010% by mass or less, the balance being Fe and unavoidable impurities, wherein the Si content (mass %) relative to the total mass of the wire is [Si] and the Ti content (mass %) relative to the total mass of the wire is [Ti], and the relationship is 0.1≦[Ti] / [Si]≦3.0.

[0004] Patent Document 2 discloses an ultra-low silicon welding wire that has excellent porosity resistance and electrodeposition paintability and contains, by weight, C: 0.001 to 0.30%, Si: 0.15% or less, Mn: 0.50 to 3.00%, P: 0.030% or less, S: 0.030% or less, the balance being Fe and unavoidable impurities. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-45761 [Patent Document 2] Japanese Patent Application Publication No. 2019-81195 Summary of the Invention [Problem to be solved by the invention]

[0006] When gas-shielded arc welding is performed on steel members using a solid wire, the oxygen contained in the oxidizing gas in the shielding gas reacts with elements such as Si and Mn contained in the steel and wire, producing Si-Mn-based slag, primarily consisting of Si oxides and Mn oxides. As a result, a large amount of Si-Mn-based slag remains on the surface of the weld bead, which is the molten and solidified part.

[0007] Slag adhering to the bead of a welded joint can impair the electrodeposition paintability of the welded joint. The reason for this is that silicon oxide and manganese oxide, which are insulators, are not electrified during electrodeposition painting, preventing the paint from adhering to the entire surface of the weld.

[0008] Patent Documents 1 and 2 propose reducing the Si content as a means of improving electrodeposition paintability. Both documents disclose that slag formed by the combination of Si and oxygen during welding impairs the electrodeposition paintability of welded joints.

[0009] However, the present inventors have found that a solid wire with reduced Si content impairs welding workability, specifically, a solid wire with reduced Si content increases spatter and impairs gap weldability in lap welding.

[0010] Spatter is molten metal particles that fly off during arc welding. Spatter impairs welding workability. In addition, some of the spatter that flies into the welding work environment adheres to the surface of the welded joint, damaging the aesthetic appearance of the welded joint. Spatter that adheres to the surface of the welded joint can also become the starting point for fatigue cracks or the starting point for red rust due to poor electroplating. The process of removing spatter that has adhered to the welded joint increases the manufacturing cost of the welded joint.

[0011] Gap weldability refers to the ability to form a proper joint when welding multiple overlapping steel plates. In actual welding, gaps often occur between the steel plates at the weld due to variations in press quality and assembly accuracy. In lap fillet joints, which are commonly used in arc welding of thin steel plates, increasing the gap between the steel plates can easily cause the shape of the weld connecting the upper and lower plates to become distorted. Welds with a shape like that shown in Figure 3B may not achieve sufficient joint strength. When welding a plate assembly with a gap S between the upper and lower plates, a solid wire that cannot form weld metal 1 all the way to the top edge of the upper plate is evaluated as having poor gap weldability. When welding with a solid wire with poor gap weldability, as shown in Figure 3B, weld metal 1 may penetrate into the gap S between steel plate 2 or undercut A may occur in the lower plate (the steel plate 2, the surface of which is welded, below the paper). On the other hand, as shown in Figure 3A, when welding a plate assembly with a plate gap S between the upper and lower plates, a solid wire that melts the entire end face of the upper plate and produces a weld (weld joint) in which the weld metal 1 is formed up to the corners of the upper plate is evaluated as having high plate gap weldability.

[0012] In lap fillet arc welding using a solid wire with reduced Si content to improve electrodeposition paintability, the weld shape shown in Figure 3B is likely to be formed. Similar problems have also occurred in welding other than lap fillet welding.

[0013] Furthermore, increasing the amount of alloying elements contained in the solid wire increases the hardness of the alloy constituting the solid wire, which impairs the manufacturability of the solid wire. The solid wire is obtained by drawing a wire. The more alloying elements are added to the wire in order to increase the amount of alloying elements in the solid wire, the more difficult it becomes to draw the wire.

[0014] The industry has longed for a solid wire that can solve all of the above problems, but the prior art has not been able to fully meet this demand. Patent Document 1 addresses the problem of improving the spatter resistance of solid wire and the electrodeposition coatability of welded joints obtained using the solid wire. However, Patent Document 1 does not consider the gap weldability or manufacturability of solid wire. Patent Document 2 addresses the problem of improving the electrodeposition coatability of welded joints obtained using the solid wire. However, Patent Document 2 does not consider the spatter resistance, gap weldability, or manufacturability of solid wire.

[0015] An object of the present disclosure is to provide a solid wire for gas-shielded arc welding that can avoid welding defects in plate assemblies with large gaps, has excellent wire drawing processability during wire production, and is capable of producing a welded joint that is highly amenable to electrodeposition coating, and a method for producing a welded joint. [Means for solving the problem]

[0016] The gist of the present disclosure is as follows.

[0017] (1) A solid wire for gas-shielded arc welding according to one embodiment of the present disclosure has, in mass % relative to the total mass of the solid wire, C: 0.04 to 0.12%, Si: 0.13 to 0.28%, Mn: 1.4 to 2.3%, Ti: 0.13 to 0.25%, Al: 0.001 to 0.050%, Cr: 0 to 3.00%, Ni: 0 to 3.00%, P: 0.020% or less, S: 0.015% or less, N: 0.015% or less, and 0.0060% or less, Mo: 0-0.5%, B: 0-0.0100%, Cu: 0-0.50%, Nb: 0-0.30%, V: 0-0.5%, Zr: 0-0.20%, Mg: 0-0.050%, As: 0-0.020%, Sn: 0-0.100%, Sb: 0-0.10%, and the balance: iron and impurities, and the following formulas (i), (ii), (iii), (iv), and (v) are satisfied: Si×Mn≦0.60 (i) (Si+Mn / 5) / (Ti+Al)≦4.0···(ii) formula 1.00≦Si+0.5×(Mn+Cr)+0.3×Ni···(iii) formula 0.30≦C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≦0.55···(iv) formula 0≦Cr+Ni≦3.00···(v) formula Here, the element symbols in the formulas (i), (ii), (iii), (iv), and (v) represent the content of each element in mass % relative to the total mass of the solid wire. (2) Preferably, the solid wire for gas-shielded arc welding described in (1) above has, in mass % relative to the total mass of the solid wire, 0.16≦C×(5×Si+Mn)≦0.35···(vi) Formula Meet the following. (3) Preferably, the solid wire for gas-shielded arc welding according to (1) or (2) above contains, in mass % relative to the total mass of the solid wire, one or more selected from Al: 0.010 to 0.050%, Cr: 0.10 to 1.50%, Ni: 0.10 to 3.00%, and B: 0.0030 to 0.0100%. (4) Preferably, in the solid wire for gas-shielded arc welding according to any one of (1) to (3) above, the hardness measured at a cross section of the solid wire satisfies the following formulas (vii) and (viii): H2≧250...(vii) formula H2-H1≧40···(viii) formula Here, the symbol H1 in the formula (viii) is the Vickers hardness measured at a depth of 0.05 mm from the surface of the solid wire, and the symbol H2 in the formulas (vii) and (viii) is the average value of the Vickers hardness measured at depths of 0.25 mm and 0.35 mm from the surface. (5) Preferably, in the solid wire for gas-shielded arc welding according to any one of (1) to (4) above, the Si content is, in mass % relative to the total mass of the solid wire, 0.13 to 0.19%. (6) Preferably, in the solid wire for gas-shielded arc welding according to any one of (1) to (5) above, Cr is 0.15 to 3.00% by mass relative to the total mass of the solid wire. (7) Preferably, in the solid wire for gas-shielded arc welding according to any one of (1) to (5) above, Cr is, in mass % relative to the total mass of the solid wire, 0% or more and less than 0.50%. (8) Preferably, in the solid wire for gas-shielded arc welding according to any one of (1) to (7) above, Ni is contained in an amount of 0 to 0.45% by mass relative to the total mass of the solid wire. (9) Preferably, the solid wire for gas-shielded arc welding according to any one of (1) to (8) above has, in mass % relative to the total mass of the solid wire, 0.05≦Cr+Ni≦3.00...(ix) formula Meet the following. (10) Preferably, the solid wire for gas-shielded arc welding according to any one of the above (1) to (9) has a diameter of 0.8 to 1.4 mm.

[0018] (11) A method for manufacturing a welded joint according to another aspect of the present disclosure includes a step of gas-shielded arc welding steel plates using the solid wire for gas-shielded arc welding according to any one of (1) to (10) above. [Effects of the Invention]

[0019] According to the present disclosure, it is possible to provide a solid wire for gas-shielded arc welding that can avoid welding defects in plate assemblies with large gaps, has excellent wiredrawability during wire production, and is capable of producing a welded joint that is highly amenable to electrodeposition coating, and a method for producing a welded joint. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a graph showing the results of an experiment investigating the relationship between Si+0.5×(Mn+Cr)+0.3×Ni and gap weldability. [Figure 2] 10 is a graph showing the results of an experiment investigating the relationship between C×(5×Si+Mn) and the amount of sputtering. [Figure 3A] 1 is a cross-sectional view of an example of a weld obtained using a solid wire with high gap weldability. [Figure 3B] 1 is a cross-sectional view of an example of a weld obtained with a solid wire having poor gap weldability. [Figure 4] FIG. 2 is a schematic diagram showing a gap between steel plates for evaluating gap weldability. [Figure 5A] FIG. 1 is a schematic diagram showing the state of droplet transfer from the tip of a solid wire having poor droplet transfer characteristics. [Figure 5B] FIG. 1 is a schematic diagram showing the state of droplet transfer from the tip of a solid wire with high droplet transfer characteristics. [Figure 6] 1 is a graph showing examples of cross-sectional hardness of various welding wires. DETAILED DESCRIPTION OF THE INVENTION

[0021] First, the technical concept of the solid wire according to this embodiment will be described. In the following description, unless otherwise specified, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. However, when the numerical values ​​before and after "to" are followed by "greater than" or "less than," the numerical range does not include the numerical values ​​as the lower or upper limit.

[0022] (1. Electrodeposition paintability) The present inventors have conducted extensive research into measures to resolve the electrodeposition coating problem and have come to the following findings. (A) By minimizing the amount of Si in the solid wire and suppressing the generation of Si-based slag, it is possible to improve electrodeposition paintability. In systems with low Si content, the degree of deterioration of electrodeposition paintability due to Mn slag is small. (B) By controlling the Ti content of the solid wire within an appropriate range, conductive Ti-based slag is generated on the surface of the weld bead, improving electrodeposition paintability. (C) By controlling the Ti and Al contents of the solid wire within an appropriate range, the generation of insulating Si, Mn-based slag is suppressed, improving electrodeposition paintability.

[0023] Based on the above findings, the present inventors have found the following formulas (1) and (2). Si×Mn≦0.60···(1) formula (Si+Mn / 5) / (Ti+Al)≦4.0···(2) formula By controlling the alloying elements of the solid wire so that the formulas (1) and (2) are satisfied, the electrodeposition paintability of the welded joint can be improved.

[0024] On the other hand, solid wires that satisfy the above requirements have deteriorated gap weldability and increased spatter. Therefore, the present inventors have conducted extensive research into ways to improve electrodeposition coating properties while ensuring gap weldability and spatter resistance.

[0025] (2. Gap Weldability) The inventors prepared various lap fillet welded joints with a gap S and observed the welds. In a lap fillet welded joint with good gap weldability, as shown in Fig. 3A, the end surface of the steel sheet 2 on the upper side of the page melted and solidified, and weld metal 1 was formed up to the top edge of the end surface of the upper steel sheet 2, and was firmly connected to the weld metal 1. On the other hand, in a lap fillet welded joint with poor gap weldability, as shown in Fig. 3B, the end surface of the steel sheet 2 on the upper side of the page did not melt and solidify sufficiently, and it was thought that the strength required to connect the upper and lower steel sheets may be reduced.

[0026] The inventors considered that the heat input balance for melting the welding wire, along with the high-temperature physical properties of the weld metal, such as viscosity and surface tension, which are caused by the components of the molten metal, affects gap weldability. Focusing on this heat input balance, the inventors investigated the effect of the electrical resistance of the solid wire on the heat input balance.

[0027] During gas-shielded arc welding, the solid wire melts, and the molten metal moves from the tip of the solid wire to the steel sheet. The heat required to melt the solid wire comes from the resistance heating generated by the current flowing through the solid wire and the arc plasma generated between the solid wire and the steel sheet. Reducing the Si content of the solid wire reduces the electrical resistance of the solid wire, reducing the amount of resistance heat generated. As a result, the solid wire does not melt sufficiently. If the welding current is increased to ensure the heat required to melt the solid wire, the heat generated in the steel sheet and molten metal increases, causing the molten metal to become overheated. This is thought to promote burn-through at the weld.

[0028] Based on the above findings, the present inventors have found the following formula (3). 1.00≦Si+0.5×(Mn+Cr)+0.3×Ni···(3) formula The "Si + 0.5 × (Mn + Cr) + 0.3 × Ni" in formula (3) is an index of the electrical resistance of the solid wire. Mn, Cr, and Ni, like Si, increase the electrical resistance of steel. By controlling the alloy composition of the solid wire to satisfy formula (3), we aimed to promote resistance heating and melting of the solid wire during gas-shielded arc welding and prevent overheating of the molten metal.

[0029] FIG. 1 shows the results of an experiment conducted by the inventors regarding the effect of formula (3). The inventors performed gas-shielded arc welding under the same conditions using multiple solid wires with different compositions of Si+0.5×(Mn+Cr)+0.3×Ni. They then investigated the sheet gap (gap between steel sheets) that these solid wires could weld. Specifically, they performed lap fillet welding on a sheet assembly in which the gap between the steel sheets 2 gradually widens, as shown in FIG. 4, and determined the limit value of the sheet gap that would result in a good weld, as shown in FIG. 3A. Here, a "good weld" refers to a weld in which the weld metal 1 is formed all the way to the top edge of the upper sheet end.

[0030] Figure 1 is a graph with the horizontal axis representing the Si+0.5×(Mn+Cr)+0.3×Ni content of the solid wire and the vertical axis representing the upper limit of the welding gap (i.e., the upper limit of the gap at which a good weld joint can be obtained). As shown in Figure 1, it was found that good gap weldability can be ensured by using a solid wire with Si+0.5×(Mn+Cr)+0.3×Ni of 1.00% or more.

[0031] (3. Spatter resistance) Spatter reduction during welding can be achieved by optimizing welding conditions, such as increasing the welding voltage. However, increasing the welding voltage increases the welding heat input, which can lead to poor gap weldability and burn-through (holes) in the steel plate. For this reason, it is preferable to reduce spatter by improving the welding wire.

[0032] The inventors of the present invention have investigated the causes of spattering by observing the behavior of molten metal during gas-shielded arc welding using a high-speed camera. As a result, they found that droplet transfer becomes unstable when using a solid wire with reduced Si content to improve electrodeposition paintability. A droplet is a small particle of molten metal formed when the tip of the wire melts due to heat from an arc or other source. Droplet transfer is a phenomenon in which droplets pass through the arc generation area and transfer from the consumable electrode to the molten pool.

[0033] Generally, gas-shielded arc welding (GAW) for welding automotive parts and the like employs pulsed MAG welding, which periodically varies the welding current. In pulsed MAG welding, the ideal droplet transfer phenomenon is one in which droplets form at the tip of the solid wire when the welding current increases, and then separate from the tip of the solid wire when the welding current decreases. In other words, it is preferable that the droplet transfer cycle and the increase / decrease cycle of the welding current coincide.

[0034] However, the inventors have found that the lower the Si content of the solid wire, the more difficult it is for droplets to separate from the tip of the solid wire. When droplets are difficult to separate from the tip of the solid wire, the droplet transfer cycle and the welding current increase / decrease cycle do not match. The inventors have found that when these cycles are misaligned, spatter occurs.

[0035] Next, the inventors investigated methods for promoting droplet separation. They concluded that the surface tension and viscosity of droplets affect droplet separation characteristics. When using a solid wire with a reduced Si content to improve electrodeposition paintability, droplets 5 were observed to be constricted and elongated at the tip of the solid wire 4, as shown in Figure 5A, preventing droplet separation. It was hypothesized that the phenomenon shown in Figure 5A occurred when the Si content of droplets 5 was low, resulting in insufficient deoxidation, increasing the oxygen content of droplets 5 and reducing the surface tension of droplets 5.

[0036] If the Si content is increased to increase the surface tension of the droplets 5, the droplets 5 separate into spherical particles, as shown in Fig. 5B, improving the droplet transfer characteristics. However, the inventors' investigations have shown that in order to improve the separation characteristics of the droplets 5 solely through the Si content, it is necessary to add approximately 0.3 mass % of Si to the solid wire 4. This impairs the electrodeposition coatability.

[0037] Therefore, the inventors focused on viscosity, another factor affecting droplet separation characteristics. Specifically, by adding appropriate amounts of Si and Mn to the solid wire 4, they promoted deoxidation of the droplets 5, thereby increasing the surface tension of the droplets 5. Furthermore, by adding an appropriate amount of C to the solid wire 4, they reduced the viscosity of the droplets 5, thereby increasing the fluidity of the droplets. They attempted to promote stable droplet separation as shown in Figure 5B by utilizing the synergistic effect of these actions.

[0038] Based on the above findings, the present inventors have found the following formula (6). 0.16≦C×(5×Si+Mn)≦0.35···(6) formula "C × (5 × Si + Mn)" in equation (6) is an index of the viscosity of the droplets formed when the solid wire melts. C reduces the viscosity of the droplets. The larger (5 × Si + Mn), the more the deoxidation of the droplets is promoted and the greater the surface tension of the droplets. By controlling the chemical composition of the solid wire to satisfy equation (6) and by appropriately including C, Si, and Mn in the solid wire, droplet transfer can be stabilized and the amount of spatter generated can be reduced.

[0039] Figure 2 shows the results of an experiment conducted by the inventors regarding the effect of formula (6). The inventors performed gas-shielded arc welding under the same conditions using multiple solid wires with different C × (5 × Si + Mn). They then counted the number of spatter particles adhering to the surface of the steel sheet. Figure 2 is a graph in which the horizontal axis represents the C × (5 × Si + Mn) of the solid wire and the vertical axis represents the number of spatter particles adhering to the surface of the steel sheet. As shown in Figure 2, the amount of spatter was significantly reduced when a solid wire with C × (5 × Si + Mn) in the range of 0.16 to 0.35 was used.

[0040] (4. Manufacturability of solid wire) Solid wire with a reduced Si content to improve electrodeposition coatability must contain alloying elements to increase electrical resistance and reduce droplet viscosity. Furthermore, to reduce the electrical resistance of the slag, the solid wire must contain Ti. However, these alloying elements increase the hardness of the solid wire and the wire from which it is made. The greater the hardness of the wire, the more likely it is to break during wiredrawing.

[0041] Therefore, the present inventors decided to further control the chemical composition of the solid wire by the following formula (4). 0.30≦C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≦0.55···(4) formula The "C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14" in formula (4) is the carbon equivalent Ceq. The higher the Ceq of steel, the harder the steel becomes. Therefore, in the solid wire according to this embodiment, Ceq is set to 0.55 mass% or less. This makes the solid wire less susceptible to breakage during wire drawing, improving the manufacturability of the solid wire.

[0042] By satisfying the above-described formulas (1), (2), (3), and (4), a solid wire can be obtained that is easy to manufacture, can prevent welding defects in plate assemblies with large gaps, and can produce welded joints that are highly amenable to electrodeposition coating. Furthermore, by satisfying formula (6), the solid wire can have a spatter suppression effect.

[0043] Next, a specific embodiment of the solid wire according to the present embodiment will be described. Based on the above findings and various other circumstances, the inventors have determined the component composition of the solid wire for gas-shielded arc welding. The solid wire for gas-shielded arc welding according to the present embodiment achieves its effects by the individual component compositions and the synergistic effects of the coexistence of the individual component compositions. The reasons for limiting each component composition will be described below.

[0044] The contents of alloying elements described below are all in mass% relative to the total mass of the solid wire. When the solid wire has a plating layer such as copper plating, the mass% of the alloying elements relative to the total mass of the solid wire is calculated by dividing the mass of the alloying elements contained in the entire solid wire including the plating layer by the total mass of the solid wire including the plating layer. Hereinafter, mass% relative to the total mass of the solid wire will be simply referred to as "%". Furthermore, in this disclosure, the unit "mass%" for carbon equivalent Ceq will also be simply referred to as "%".

[0045] [C: 0.04-0.12%] C is an element that increases the strength of the weld metal. By setting the C content to 0.04% or more, the strength of the weld metal can be improved. In addition, C has the effect of reducing the viscosity of droplets formed by melting the solid wire. This stabilizes droplet transfer and suppresses the amount of spatter. By setting the C content to 0.04% or more, the above-mentioned effects can be obtained. Furthermore, it is preferable that the C content be 0.06% or more.

[0046] On the other hand, if the C content exceeds 0.12%, the raw wire hardens and the wire drawability of the wire deteriorates. Therefore, the C content is set to 0.12% or less. Furthermore, the C content is preferably set to 0.10% or less.

[0047] [Si: 0.13 to 0.28%] The silicon in solid wire is an element with a deoxidizing effect, and during gas-shielded arc welding, it combines with oxygen in the molten pool to form slag. When the molten pool solidifies and weld metal is formed, the slag is expelled from the weld metal. Therefore, silicon has the effect of reducing the oxygen content in the weld metal. Silicon is actively added to ordinary solid wires as a deoxidizing element.

[0048] However, slag containing Si as its main component has a high electrical resistance. Slag with a high electrical resistance prevents the coating from adhering to the weld metal or steel sheet during electrodeposition coating. Therefore, slag containing Si as its main component leads to poor electrodeposition coating of welded joints. From the viewpoint of improving electrodeposition coating properties, it is preferable to reduce the Si content of the molten pool. Therefore, the Si content of the solid wire is set to 0.28% or less. It is preferable to set the Si content to 0.25% or less, 0.22% or less, 0.20% or less, 0.19% or less, or 0.18% or less.

[0049] On the other hand, excessive reduction in the Si content of the solid wire results in insufficient electrical resistance of the solid wire. The lower the electrical resistance of the solid wire, the more difficult it is to melt the solid wire, resulting in poor gap weldability. Furthermore, excessive reduction in the Si content of the solid wire reduces the surface tension of droplets formed by melting the solid wire, destabilizing droplet transfer and increasing the amount of spatter. In the solid wire according to this embodiment, elements other than Si are used to satisfy formula (3) and, preferably, formula (6), thereby mitigating the adverse effects of reducing Si. However, if the Si content is below 0.13%, the above-mentioned adverse effects become significant. Therefore, the Si content of the solid wire is set to 0.13% or more. If necessary, the Si content may be set to 0.15% or more, 0.18% or more, or 0.20% or more.

[0050] [Mn: 1.4-2.3%] Like Si, Mn is also a deoxidizing element. Mn promotes deoxidation of the molten pool during arc welding. Furthermore, Mn also has the effect of improving the tensile strength of the weld metal. In addition, Mn promotes resistance heating of the solid wire, thereby improving gap weldability. Mn also has the effect of increasing the surface tension through its deoxidizing effect on the droplets, thereby stabilizing droplet transfer. Therefore, the Mn content of the solid wire is set to 1.4% or more. The Mn content is preferably 1.5% or more, 1.6% or more, 1.7% or more, or 1.8% or more.

[0051] On the other hand, if the Mn content is excessive, insulating Mn-based slag may be significantly generated on the surface of the weld metal, resulting in poor electrodeposition coating. Furthermore, if the Mn content is excessive, the wire material of the solid wire may become excessively hardened, which may impair the manufacturability of the solid wire. Therefore, the Mn content of the solid wire is 2.3% or less. The Mn content is preferably 2.2% or less, 2.1% or less, or 2.0% or less.

[0052] [Ti: 0.13 to 0.25%] During gas-shielded arc welding, Ti generates Ti-based slag, mainly composed of Ti oxides. Unlike Si-Mn-based slag, Ti-based slag is electrically conductive. Conductive Ti-based slag is less likely to cause electrodeposition coating defects. Therefore, Ti can improve the electrodeposition coating properties of solid wire. Ti also has the effect of suppressing the occurrence of blowholes. For these reasons, the Ti content of solid wire is set to 0.13% or more. The Ti content is preferably set to 0.15% or more, 0.18% or more, or 0.20% or more.

[0053] On the other hand, if the Ti content is excessive, Ti-based oxides are excessively formed, which may reduce the elongation of the weld metal. Therefore, the Ti content is set to 0.25% or less. The Ti content is preferably set to 0.24% or less, 0.23% or less, or 0.21% or less.

[0054] [Al: 0.001 to 0.050%] Al has a deoxidizing effect. By promoting deoxidation of the molten pool, Al improves the tensile strength of the weld metal. Furthermore, like Ti, Al reduces the amount of Si-Mn-based slag produced, improving electrodeposition paintability. Therefore, the Al content of the solid wire is 0.001% or more. The Al content is preferably 0.010% or more, 0.015% or more, or 0.018% or more.

[0055] On the other hand, if the Al content is excessive, excessive Al-based oxides are produced, resulting in reduced elongation of the weld metal. Furthermore, Al-based slag, like Si-based slag and Mn-based slag, is insulating. If significant amounts of Al-based slag are produced on the surface of the weld metal, this may result in poor electrodeposition coating. Therefore, the Al content of the solid wire is 0.050% or less. The Al content is preferably 0.030% or less, or 0.020% or less.

[0056] [0≦Cr+Ni≦3.00] Cr and Ni are not essential for solving the problems of the solid wire according to this embodiment. In the solid wire according to this embodiment, the lower limit of the Cr content is 0%, the lower limit of the Ni content is 0%, and the lower limit of the combined Cr and Ni content is also 0%.

[0057] On the other hand, Cr and Ni are elements that increase the electrical resistance of the solid wire and promote melting of the solid wire. Cr and Ni also function to improve the mechanical properties of the weld metal. Therefore, the solid wire preferably contains at least one of Cr and Ni. Preferably, both Cr and Ni are contained in the solid wire. When the total content of Cr and Ni is 0.05% or more, the above-mentioned effects can be obtained. Therefore, the total content of Cr and Ni is preferably 0.05% or more. It is more preferable that the total content of Cr and Ni is 0.10% or more, 0.15% or more, or 0.30% or more.

[0058] On the other hand, excessive Cr and Ni contents may reduce the elongation of the weld metal and cause cracks in the weld metal. Furthermore, excessive Cr and Ni contents may cause the wire rod, which is the material for the solid wire, to become excessively hard, which may impair the manufacturability of the solid wire. Therefore, the total content of Cr and Ni is set to 3.00% or less. The total content of Cr and Ni is preferably set to 2.50% or less, 2.00% or less, or 1.00% or less.

[0059] Therefore, the solid wire satisfies equation (5). 0≦Cr+Ni≦3.00···(5) formula Here, the element symbols in formula (5) represent the content of each element in mass% relative to the total mass of the solid wire. The values ​​on the left and right sides of formula (5) can be replaced with the above-mentioned preferred upper and lower limits of the total content of Cr and Ni. For example, instead of satisfying formula (5), the solid wire may satisfy formula (9). 0.05≦Cr+Ni≦3.00···(9) formula

[0060] [Cr: 0-3.00%] In addition to the total content of Cr and Ni being within the above range, the Cr content is set to 0 to 3.00%. The Cr content may be set to 0.05 to 1.50%. The Cr content is preferably 0.05% or more, 0.11% or more, 0.15% or more, or 0.20% or more. The Cr content is preferably 2.50% or less, 2.00% or less, 1.50% or less, 1.20% or less, 1.00% or less, 0.50% or less, less than 0.50%, 0.45% or less, or 0.40% or less.

[0061] [Ni: 0-3.00%] Furthermore, in addition to the total content of Cr and Ni being within the above range, the Ni content is set to 0 to 3.00%. The Ni content may be set to 0.05 to 3.00%. The Ni content is preferably 0.05% or more, 0.08% or more, 0.10% or more, or 0.20% or more. The Ni content is preferably 2.50% or less, 2.00% or less, 1.50% or less, 1.20% or less, 1.00% or less, 0.50% or less, 0.45% or less, or 0.40% or less.

[0062] [P:0.020% or less] P is an element that is generally present as an impurity in steel, and is also typically present as an impurity in solid wire for arc welding. Since P is one of the main elements that cause hot cracking in weld metal, it is desirable to minimize its content. If the P content exceeds 0.020%, hot cracking in the weld metal becomes significant. Therefore, the P content of solid wire is 0.020% or less. The P content is preferably 0.015% or less, 0.012% or less, or 0.010% or less.

[0063] P does not contribute to solving the problems of the present disclosure. Therefore, the P content of the solid wire may be 0%. However, in consideration of refining costs, the P content of the solid wire may be more than 0%. The P content may be 0.001% or more, 0.002% or more, or 0.005% or more.

[0064] [S:0.015% or less] Like P, S is an element that is generally mixed into steel as an impurity, and is also usually contained as an impurity in solid wire for arc welding. Therefore, the S content of the solid wire is 0.015% or less. The S content is preferably 0.012% or less, 0.010% or less, or 0.008% or less. The S content may be 0%, but may be greater than 0% or 0.001% or more in consideration of refining costs.

[0065] [N:0.006% or less] Nitrogen (N) is also an element commonly found as an impurity in steel, and is also commonly found as an impurity in solid wire for arc welding. Excessive N can reduce the toughness of the weld metal and cause porosity defects in the weld metal. Therefore, the N content of solid wire is set to 0.006% or less. The N content is preferably set to 0.005% or less, or 0.004% or less. The N content may be 0%, but considering refining costs, the N content may be set to more than 0% or 0.001% or more.

[0066] Mo, B, Cu, Nb, and V are not essential elements for solving the problems of the present disclosure. Therefore, the lower limit of the content of these elements is 0%. However, by adding one or more of these elements to the solid wire, the performance of the solid wire can be further improved.

[0067] [Mo: 0-0.5%] The Mo content of the solid wire may be 0%. However, since Mo improves the hardenability of the weld and improves the tensile strength, the Mo content of the solid wire may be set to 0.1% or more, 0.2%, or 0.3% or more, as necessary. On the other hand, to ensure the ductility of the weld, the Mo content of the solid wire is set to 0.5% or less. As necessary, the Mo content may be set to 0.4% or less, or 0.3% or less.

[0068] [B: 0 to 0.0100%] The B content of the solid wire may be 0%. However, since B improves the hardenability of the weld and improves the tensile strength, the B content of the solid wire may be set to 0.0010% or more, 0.0020% or more, or 0.0030% or more, as necessary. On the other hand, to ensure the ductility of the weld, the B content of the solid wire is set to 0.0100% or less. As necessary, the B content may be set to 0.0090% or less, or 0.0070% or less.

[0069] [Cu: 0-0.50%] The Cu content of the solid wire may be 0%. However, because the copper plating provided on the solid wire for arc welding has the effect of stabilizing wire feedability and current conduction, the Cu content of the solid wire may be set to 0.10% or more, 0.15% or more, or 0.18% or more, as needed. On the other hand, from the viewpoint of suppressing weld cracking, the Cu content of the solid wire is set to 0.50% or less. As needed, the Cu content may be set to 0.40% or less, or 0.30% or less.

[0070] [Nb: 0-0.30%] The Nb content of the solid wire may be 0%. However, since Nb has the effect of increasing the hardenability of the weld and improving the tensile strength, the Nb content of the solid wire may be set to 0.05%, 0.10% or more, or 0.12% or more, as necessary. On the other hand, from the viewpoint of ensuring the ductility of the weld, the Nb content of the solid wire is set to 0.30% or less. As necessary, the Nb content may be set to 0.25% or less, 0.20% or less, or 0.12% or less.

[0071] [V: 0 to 0.5%] The V content of the solid wire may be 0%. However, since V has the effect of increasing the hardenability of the weld and improving the tensile strength, the V content of the solid wire may be set to 0.05% or more, 0.1% or more, or 0.12% or more, as necessary. On the other hand, from the viewpoint of ensuring the ductility of the weld, the V content is set to 0.5% or less. As necessary, the V content may be set to 0.30% or less, or 0.20% or less.

[0072] (Zr: 0 to 0.20%) The Zr content of the solid wire may be 0%. However, because Zr has a deoxidizing effect that reduces the oxygen content in the weld metal and improves the toughness of the weld metal, the Zr content of the solid wire may be set to 0.01% or more, 0.05% or more, or 0.08% or more, as necessary. On the other hand, in order to suppress the formation of coarse inclusions (e.g., inclusions with an equivalent circle diameter of 5 μm or more), the upper limit of the Zr content is set to 0.20%. As necessary, the Zr content may be set to 0.18% or less, 0.15% or less, 0.10% or less, or 0.05% or less.

[0073] (Mg: 0 to 0.050%) The Mg content of the solid wire may be 0%. However, because Mg has a deoxidizing effect that reduces the oxygen content in the weld metal and improves the toughness of the weld metal, the Mg content of the solid wire may be set to 0.001% or more, 0.003% or more, or 0.005% or more, as necessary. On the other hand, because a reduced Mg content reduces the amount of slag produced and suppresses welding defects such as slag inclusion, the Mg content is set to 0.050% or less. As necessary, the Mg content may be set to 0.040% or less, 0.030% or less, 0.010% or less, or 0.008% or less.

[0074] (As: 0 to 0.020%) As is an element that is present as an impurity in steel and may also be present as an impurity in arc welding solid wire. Since As is one of the elements that segregates at grain boundaries during solidification of the weld metal and reduces the toughness of the weld metal, it is desirable to minimize its content. Therefore, the As content of the solid wire is 0.020% or less. The As content may be 0.015% or less, 0.012% or less, or 0.010% or less. On the other hand, from the viewpoint of reducing refining costs, the As content may be more than 0%, 0.001% or more, 0.005% or more, or 0.008% or more.

[0075] (Sn: 0 to 0.100%) The Sn content of the solid wire may be 0%. However, because Sn is an element that improves the corrosion resistance of the weld metal, the Sn content of the solid wire may be set to 0.001% or more, 0.005% or more, or 0.010% or more, as necessary. On the other hand, by reducing the Sn content of the wire, the occurrence of cracks in the weld metal is suppressed, so the Sn content is set to 0.100% or less. As necessary, the Sn content may be set to 0.080% or less, 0.050% or less, or 0.020% or less.

[0076] (Sb: 0 to 0.10%) The Sb content of the solid wire may be 0%. However, because Sb acts as a surface active element and has the effect of promoting the flow of molten metal and discharging impurity elements to the surface of the molten metal, the Sb content of the solid wire may be set to 0.001% or more, 0.005% or more, or 0.01% or more, as necessary. On the other hand, reducing the Sb content of the wire suppresses the occurrence of cracks in the weld metal, so the Sb content is set to 0.10% or less. As necessary, the Sb content may be set to 0.08% or less, 0.05% or less, or 0.02% or less.

[0077] The balance of the above-described components is iron (Fe) and impurities. The impurities refer to components contained in raw materials or components mixed in during the manufacturing process, and are contained in the solid wire within a range that does not adversely affect the solid wire.

[0078] The chemical composition of the solid wire according to this embodiment further satisfies the following formulas (1), (2), (3), and (4). Preferably, the chemical composition of the solid wire according to this embodiment also satisfies formula (6). Note that the element symbols in formulas (1), (2), (3), (4), and (6) represent the content of each element in mass % relative to the total mass of the solid wire.

[0079] (Si×Mn: 0.60 or less) As mentioned above, Si and Mn are elements that adversely affect electrodeposition coatability, but in a component system with a low Si content, the degree of deterioration of coatability due to Mn slag is small. Therefore, in the solid wire according to this embodiment, the contents of Si and Mn are set so as to satisfy the following formula (1). Si×Mn≦0.60···(1) formula

[0080] If the value of Si×Mn exceeds 0.60, insulating Si-based slag and Si-Mn-based slag will be significantly generated on the surface of the weld bead, which may result in poor electrodeposition coating. Therefore, Si×Mn is 0.60 or less. Si×Mn is preferably 0.55 or less, 0.50 or less, or 0.45 or less. The lower limit of Si×Mn is not particularly limited, but is, for example, 0.23 or more, 0.24 or more, or 0.25 or more.

[0081] ((Si+Mn / 5) / (Ti+Al):4.0 or less) As described above, Ti and Al are elements that can suppress the adverse effects of Si, Mn-based slag on electrodeposition coatability. Therefore, in the solid wire according to this embodiment, the contents of Si, Mn, Ti, and Al are set so as to satisfy the following formula (2): (Si+Mn / 5) / (Ti+Al)≦4.0···(2) formula

[0082] When the value of (Si+Mn / 5) / (Ti+Al) is 4.0 or less, the adverse effects of Si, Mn-based slag on electrodeposition coatability can be reliably suppressed, and excellent electrodeposition coatability can be obtained. The value of (Si+Mn / 5) / (Ti+Al) is preferably 3.5 or less, 3.0 or less, or 2.5 or less. There is no particular restriction on the lower limit of (Si+Mn / 5) / (Ti+Al), but for example, (Si+Mn / 5) / (Ti+Al) may be 1.3 or more, 1.5 or more, or 2.0 or more.

[0083] In addition, while the product of Si and Mn is used as an index in equation (1), the sum of Si and Mn / 5 is used as an index in equation (2). This is because the purpose of using Ti and Al is to reduce the absolute amount of Si-Mn slag.

[0084] (Si+0.5×(Mn+Cr)+0.3×Ni:1.00% or more) As mentioned above, Si + 0.5 × (Mn + Cr) + 0.3 × Ni is an index of the resistance value of the solid wire. If the resistance value of the solid wire is too low, the resistance heat generation of the solid wire will be small, making it difficult for the solid wire to melt. This will impair gap weldability. To improve gap weldability, the chemical composition of the solid wire is selected to satisfy the following formula (3). 1.00≦Si+0.5×(Mn+Cr)+0.3×Ni···(3) formula

[0085] The content of Si+0.5×(Mn+Cr)+0.3×Ni may be 1.10% or more, 1.20% or more, 1.30% or more, or 1.40% or more. The upper limit of Si+0.5×(Mn+Cr)+0.3×Ni is not particularly limited. From the viewpoint of ensuring the manufacturability of the solid wire, the content of Si+0.5×(Mn+Cr)+0.3×Ni may be 2.00% or less, 1.90% or less, 1.80% or less, or 1.60% or less.

[0086] (C×(5×Si+Mn): preferably 0.16 to 0.35) As mentioned above, C×(5×Si+Mn) is an index of the viscosity of the droplets formed when the solid wire melts. The larger C×(5×Si+Mn) is, the higher the surface tension of the droplets and the lower the viscosity, stabilizing the droplet transfer. This reduces spatter. Therefore, it is preferable that the chemical composition of the solid wire according to this embodiment be selected to satisfy the following formula (6): 0.16≦C×(5×Si+Mn)≦0.35···(6) formula

[0087] C×(5×Si+Mn) may be 0.18 or more, 0.19 or more, or 0.20 or more. On the other hand, if C×(5×Si+Mn) is excessive, the stability of droplet transfer decreases. Therefore, C×(5×Si+Mn) is preferably 0.35 or less. More preferably, C×(5×Si+Mn) is 0.30 or less, 0.25 or less, or 0.22 or less.

[0088] (Ceq: 0.30-0.55%) As described above, the carbon equivalent Ceq of the solid wire is C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14. By reducing Ceq, the hardness of the wire material used to make the solid wire decreases, improving the manufacturability of the solid wire. Therefore, the chemical components of the solid wire according to this embodiment are selected to satisfy the following formula (4): 0.30≦C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≦0.55···(4) formula

[0089] Ceq is preferably 0.55% or less, 0.50% or less, or 0.45% or less. On the other hand, from the viewpoint of improving the strength of the weld metal, Ceq is set to 0.30% or more. Ceq is preferably 0.32% or more, 0.35% or more, or 0.38% or more.

[0090] (H2≧250) (H2-H1≧40) The inventors have found that there is a correlation between the amount of spatter generated during welding and the mechanical properties of the solid wire. In order to reduce the amount of spatter generated, it is necessary to maintain a substantially constant wire feed speed. The wire feed speed is the length of the wire fed per unit time. Increasing the strength of the solid wire suppresses deformation of the solid wire. Reducing the amount of deformation of the solid wire suppresses friction of the solid wire within the wire cable. Reducing friction of the solid wire suppresses fluctuations in the wire feed speed. In other words, by increasing the strength of the wire, the wire feed speed can be maintained substantially constant, further suppressing the amount of spatter generated.

[0091] On the other hand, the inventors have also found that excessive hardening of the solid wire increases the amount of spatter generated. An excessively hardened solid wire accelerates wear of the electrode tip. Wear of the electrode tip causes the position of the power supply point to fluctuate. The power supply point is the contact point for supplying power by passing the solid wire through the electrode tip. Generally, the power supply point is located near the tip of the power supply tip. The fluctuation in the position of the power supply point increases the amount of spatter generated.

[0092] As a result of the above investigations, the inventors have found that increasing the hardness of the inside of the solid wire and softening the surface layer is extremely effective in suppressing spatter. Therefore, in the solid wire according to this embodiment, the hardness measured at the cross section of the solid wire preferably satisfies the following formulas (7) and (8). H2≧250···(7) formula H2-H1≧40···(8) formula

[0093] Here, the symbol H1 in equation (8) is the Vickers hardness measured at a depth of 0.05 mm from the surface of the solid wire. The symbol H2 in equations (7) and (8) is the average of the Vickers hardnesses measured at depths of 0.25 mm and 0.35 mm from the surface. The Vickers hardness is HV0.3 according to JIS Z2244-1:2024. HV0.3 is the Vickers hardness measured by a Vickers test with a test force of 2.942 N (300 gf). In addition, when a plating is applied to the surface of the solid wire, the surface of the solid wire refers to the interface between the plating and the substrate (the iron part of the substrate that corresponds to the unplated steel wire).

[0094] H2 represents the hardness of the inside of the solid wire. A solid wire that satisfies formula (7) has a sufficiently high hardness inside. Therefore, in welding using a solid wire that satisfies formula (7), the wire feed speed is stabilized and the amount of spatter generated is further suppressed.

[0095] H1 indicates the hardness of the surface layer of the solid wire. H2-H1 indicates the degree of softening of the surface layer of the solid wire. The larger H2-H1, the softer the surface layer of the solid wire. Therefore, in welding using a solid wire that satisfies equation (8), wear of the electrode tip is suppressed, and the amount of spatter generated is further suppressed. As described above, a solid wire that satisfies the formulas (7) and (8) is highly preferable because it further suppresses the amount of spatter generated. However, even a solid wire that does not satisfy the formulas (7) and (8) can suppress the amount of spatter generated to a practically necessary level, so it is not necessary to exclude solid wires that do not satisfy the formulas (7) and (8) from the solid wire according to this embodiment.

[0096] The solid wire satisfying the formulas (7) and (8) is, for example, (S1) a step of primarily drawing a wire rod having the same components as the solid wire according to the present embodiment to obtain a primarily drawn wire; (S2) annealing the primary drawn wire; (S3) a step of secondarily drawing the primarily drawn wire to obtain a solid wire; The resulting product is obtained by a manufacturing method comprising:

[0097] Annealing is carried out under the following conditions. Annealing temperature: 650~900℃ Annealing time: 10-30 min Annealing temperature (℃) and annealing time (min): 8400~25000℃·min Annealing atmosphere dew point: -10 to +10°C

[0098] The secondary wire drawing is carried out under the following conditions. Area ratio of secondary drawn wire to primary drawn wire: 10~30% That is, the cross-sectional area A1 of the primary drawn wire and the area ratio A2 of the secondary drawn wire satisfy the following formula. 0.10≦A2 / A1≦0.30

[0099] The following experiment was conducted to confirm the effect of controlling the hardness of solid wire. Solid wire was produced by cold-working a raw wire for primary wiredrawing, annealing it in an intermediate process, and then secondary wiredrawing. In the annealing process, the temperature was set to 750 to 900°C, and the annealing time was set to 20 to 30 minutes. Furthermore, in the annealing process, the dew point was controlled within the range of -10 to +10°C by adding water vapor or hydrogen gas to the nitrogen atmosphere. Note that, when producing Example A4, the atmospheric pressure was set to a reduced pressure of approximately 1000 Pa. Figure 6 shows examples of the cross-sectional hardness of various welding wires. The horizontal axis of Figure 6 represents the distance from the surface of the solid wire to the Vickers hardness measurement position. The vertical axis of Figure 6 represents the hardness of the solid wire at that measurement position (HV0.3 according to JIS Z2244-1:2024).

[0100] Examples A1 to A4 shown in the table below are produced by first drawing a 5.5 mm diameter raw wire having the composition of Example No. 1 shown in Table 2A to a 2.5 mm diameter, then annealing it under various conditions and processing it into a 1.2 mm diameter solid wire. In the production of Examples A1 to A4, the area ratio of the secondary drawn wire to the primary drawn wire was 23%.

[0101] [Table 1]

[0102] Example No. A1 was obtained by annealing the primarily drawn wire at an atmospheric dew point of -10°C, an annealing temperature of 600°C, and an annealing time of 10 minutes, followed by secondary drawing. Example No. A1 showed no surface softening and a high hardness distribution.

[0103] Example No. A2 was obtained by subjecting the primarily drawn wire to annealing at an atmospheric dew point of +5°C, an annealing temperature of 650°C, and an annealing time of 15 minutes, followed by secondary drawing. Example No. A2 has high hardness and a softened surface layer.

[0104] Example No. A3 was obtained by subjecting the primarily drawn wire to annealing at an atmospheric dew point of -7°C, an annealing temperature of 830°C, and an annealing time of 30 minutes, followed by secondary wire drawing. Compared to Example No. A2, Example No. A3 showed an increased degree of surface softening and a slight decrease in the hardness of the wire interior.

[0105] Sample No. A4 was obtained by subjecting the primarily drawn wire to annealing at an atmospheric dew point of -10°C, an annealing temperature of 900°C, and an annealing time of 30 minutes, followed by secondary drawing. Sample No. A4 showed no surface softening and a low hardness distribution.

[0106] The state of spatter adhesion during welding was investigated using these solid wires A1 to A4. As shown in Table 1, in welding tests using solid wires A1 and A4 that were not surface-softened, the number of spatter adhesions was somewhat high. In contrast, in welding tests using solid wires A2 and A3 that were surface-softened, the number of spatter adhesions was extremely low. Based on these evaluation results, the welding wire hardness standards for minimizing spatter adhesion were set to H2 ≥ 250 and H2 - H1 ≥ 40.

[0107] The chemical composition of the solid wire can be measured by a conventional method, for example, the content of each element in mass% relative to the total mass of the solid wire can be determined in accordance with JIS G 0321:2017 "Methods for analyzing steel products and their allowable variations."

[0108] The inventors determined the chemical composition of the solid wire by performing wet chemical analysis on the solid wire cut into lengths of about several millimeters. Therefore, the content of alloying elements in the present disclosure means the average content of alloying elements in the solid wire.

[0109] The diameter of the solid wire is not particularly limited, but is preferably within the range of 0.8 mm to 1.6 mm, for example. This further improves the manufacturability of the solid wire and the workability in arc welding. The diameter of the solid wire may be 0.9 mm or more, 1.0 mm or more, or 1.1 mm or more. The diameter of the solid wire may be 1.5 mm or less, 1.4 mm or less, or 1.3 mm or less.

[0110] Solid wire exists not only for gas-shielded arc welding but also for submerged arc welding (SAW). However, SAW wire has a large diameter, and manufacturers or users of welding wire can distinguish it from solid wire for gas-shielded arc welding by the wire diameter. Specifically, since the diameter of SAW wire is never less than 1.4 mm, manufacturers or users of welding wire can recognize any wire with a diameter of 1.4 mm or less as solid wire for gas-shielded arc welding. Furthermore, even for wire diameters greater than 1.4 mm, manufacturers or users of welding wire can easily determine whether it is SAW wire or solid wire for gas-shielded arc welding by the information on the packaging of the welding wire (the welding wire's standard name or standard number), as well as the welding material's standard name or welding material manufacturer's catalog.

[0111] The solid wire according to the present embodiment is preferably applied to gas-shielded arc welding of steel plates. For example, a method for manufacturing a welded joint including a step of gas-shielded arc welding steel plates using the solid wire for gas-shielded arc welding according to the present embodiment can suppress spatter, avoid welding defects in plate assemblies with large gaps, and manufacture a welded joint with high electrodeposition paintability. The method for manufacturing a welded joint according to the present embodiment is primarily intended for chassis parts of automobiles. The steel plate used as the welding base material is preferably a 440 MPa to 1180 MPa steel plate. The thickness of the steel plate used as the welding base material is preferably 1.0 mm to 3.5 mm. [Example]

[0112] The effects of one embodiment of the present disclosure will be explained in more detail using examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this example of conditions. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the present disclosure and the object of the present disclosure is achieved.

[0113] (Experiment 1) Solid wires with various chemical compositions were produced. The chemical compositions and calculated values ​​of these solid wires are shown in Tables 2A, 2B, 3A, 3B, 4A, and 4B. The content of alloying elements listed in Tables 2A to 3B is in mass %. The units of Ceq and "Si + 0.5 × (Mn + Cr) + 0.3 × Ni" listed in Tables 4A and 4B are also in mass %. The remainder of the chemical compositions listed in Tables 2A to 3B was iron and impurities. Numerical values ​​outside the range of this disclosure are underlined. Components that were not contained are left blank in the tables. The Cu in the solid wires originates from the Cu plating formed on the surface of the solid wires. Example 6 was a solid wire without Cu plating, so no Cu was contained.

[0114] The solid wire was manufactured as follows. Raw steel was vacuum melted and forged and rolled to produce a φ5.0 mm raw wire. The raw wire was then annealed and finish-drawn to a product diameter of 1.2 mm. Examples 6 and 17 were not copper-plated. The surfaces of the other wires were copper-plated. The solid wire after finish-drawing was wound into a 20 kg spool and used as a prototype. The annealing conditions for the primary wiredrawing (annealing temperature, annealing time, and annealing atmosphere) and the area ratio during the secondary wiredrawing were all the same as those for Example No. A3 in Table 1.

[0115] [Table 2A]

[0116] [Table 2B]

[0117] [Table 3A]

[0118] [Table 3B]

[0119] [Table 4A]

[0120] [Table 4B]

[0121] Using the prototype solid wire, lap fillet welding was performed on hot-rolled 440 MPa-class steel plates (plate thickness: 2.9 mm) and the gap weldability, amount of spatter adhesion to the steel plates, and electrodeposition coating defects were investigated. In all cases, lap fillet welding was performed using pulsed MAG welding with Ar + 20% CO2 shielding gas.

[0122] (Investigation of gap weldability) A taper test was conducted using a gap test piece with a gradually increasing gap between the steel plates 2, as shown in Figure 4. Lap fillet welding was performed on two overlapping 300 mm long test pieces with a 3 mm spacer sandwiched between one end of the other. The welding current was 260 A, the arc voltage was 28.5 V, and the welding speed was 100 cm / min. Welding was performed starting at a gap of 0 mm. After welding, the area where the upper sheet corner was molten, as shown in Figure 3A, was judged as good, while the area where the upper sheet corner was unmelted, as shown in Figure 3B, was judged as bad. The upper gap limit for welding was calculated and listed in the "Taper Test Results" column in Tables 5A and 5B. Half the steel plate thickness was used as the pass / fail criterion for gap weldability. In other words, a gap limit of 1.50 mm or greater was considered pass.

[0123] (Spatter deposition amount investigation) Bead-on-plate welding with a weld length of 120 mm was performed on a 150 mm x 50 mm steel plate specimen, and the number of spatter particles of 0.3 mm or larger adhering to the steel plate surface was counted. The welding current was 200 A, the arc voltage was 23.5 V, and the welding speed was 100 cm / min. A spatter count of 4 or less was evaluated as very good, 5 to 7 as good, and 8 or more as normal. The results were compared relative to each other, and the evaluation results are shown in the "Spatter Amount" column in Tables 5A and 5B.

[0124] (Measurement of the area ratio of electrodeposition coating defects) Welded test specimens prepared in a downward position were degreased, chemically treated, and then electrocoated to a thickness of 20 μm. The welding test specimens were manufactured under the following conditions: welding current 200 A, arc voltage 23.5 V, and welding speed 100 cm / min. The electrocoated weld bead was photographed, and the ratio of the area of ​​defective electrocoating to the total weld bead area was measured from the photographs. The bead length of the welded test specimens was 120 mm. The percentage of defective electrocoating was calculated for a 90 mm weld bead, excluding 15 mm at the start and end of the weld. The electrocoating was performed using a gray paint. This allowed for easy differentiation between the painted area and the defective electrocoating, which exposes reddish-brown or black slag. An area ratio of 5% or less of the defective electrocoating area was considered good, and this was marked "GOOD" in the "Defective Coating Area Ratio" column in Tables 5A and 5B. In cases where the coating was defective, the coating defect area rate is shown in the "Coating Defect Area Rate" column in Tables 5A and 5B.

[0125] Tables 5A and 5B also show the productivity of the solid wire. Productivity was evaluated by the presence or absence of wire breakage during finish drawing from an annealed φ5.0 mm raw wire to a φ1.2 mm, and the presence or absence of wire breakage is shown in the "Wire Breakage Presence / Absence" column in Tables 5A and 5B. During annealing, the raw wire was heated to 1200°C, and then the temperature history was controlled so that the cooling time from 800°C to 500°C was 300 seconds. As shown in Tables 5A and 5B, the solid wire composition of the present disclosure ensured stable productivity without breakage during wire drawing. On the other hand, wire breakage occurred in Comparative Examples 19, 20, and 27. In all examples, it is presumed that the hardening of the raw wire due to excessive Ceq was the cause of the breakage.

[0126] [Table 5A] [Table 5B]

[0127] In Example 18, the C content was inappropriate, and the formula (3), which is an index of gap weldability, was not satisfied. Example 18 failed in terms of gap weldability.

[0128] In Example 19, the C content was inappropriate and the formula (4), which is an index of productivity, was not satisfied. The wire of Example 19 broke during the manufacturing process.

[0129] In Example 20, the total content of Cr and Ni was inappropriate, and the formula (4), which is an index of productivity, was not satisfied. The wire of Example 20 broke during the manufacturing process.

[0130] Formula (3), which is an index of gap weldability, was not satisfied in Examples 21, 22, and 23. Examples 21, 22, and 23 failed in terms of gap weldability.

[0131] In Example 24, formula (2), which is an index of paintability, was not satisfied. Example 24 failed in terms of electrodeposition paintability.

[0132] The Si content was inappropriate in Example 25. Example 25 failed in terms of electrodeposition coatability.

[0133] In Example 26, the Mn content was inappropriate and the formulas (1) and (2), which are indicators of paintability, were not satisfied. Example 26 failed in terms of electrodeposition paintability.

[0134] In Example 27, the TI content was inappropriate, and the formula (2), which is an index of paintability, and the formula (4), which is an index of productivity, were not satisfied. The wire of Example 27 broke during the manufacturing process. Furthermore, Example 27 failed in terms of electrodeposition paintability.

[0135] On the other hand, in the case where the chemical composition was appropriate and formulas (1) to (4) were satisfied, productivity, gap weldability, and paintability were all good. In addition, in the case where formula (6), which is an index of the amount of spatter generated, was satisfied, the amount of spatter deposition was suppressed to an extremely low level.

[0136] (Experiment 2)

[0137] Various solid wires were manufactured by a manufacturing method including the steps of primarily drawing a wire rod to obtain a primarily drawn wire, annealing the primarily drawn wire, and secondarily drawing the primarily drawn wire to obtain a solid wire. When annealing the primarily drawn wire, the dew point of the annealing atmosphere was set within the range of -10 to +10°C. The solid wire compositions, annealing temperature, annealing time, and area ratio of the secondary drawn wire to the primary drawn wire were as shown in Table 6.

[0138] The solid wires were then measured for H1 (Vickers hardness measured at a depth of 0.05 mm from the surface) and H2 (the average value of Vickers hardness measured at depths of 0.25 mm and 0.35 mm from the surface). H2 and H2-H1 are shown in Table 6.

[0139] Furthermore, welding tests were carried out using these solid wires to investigate the amount of spatter deposited. The method for measuring the amount of spatter deposited was the same as in Experiment 1.

[0140] [Table 6]

[0141] In Example B2, the product of the annealing temperature and the annealing time was large. This resulted in a small H2 in Example B2. In the welding test of Example B2, the amount of spatter deposition was at the same level as that of conventional solid wire.

[0142] In Example B3, the product of the annealing temperature and the annealing time was small. This resulted in a small H2-H1 value for Example B3. In the welding test for Example B3, the amount of spatter deposition was at the same level as that of conventional solid wire.

[0143] In Example B7, the area ratio of the secondary drawn wire to the primary drawn wire was small, which resulted in a small H2-H1 in Example B7. In the welding test of Example B7, the amount of spatter adhesion was at the same level as that of conventional solid wire.

[0144] On the other hand, in the welding tests using solid wires in which H2 and H2-H1 were suitable, the amount of spatter deposition was significantly improved compared to conventional solid wires. [Explanation of symbols]

[0145] 1. Weld metal 2 steel plate 3 spacers 4 Solid Wire 5 droplets S plate gap A. Undercut

Claims

1. A solid wire for gas shielded arc welding, In mass % relative to the total mass of the solid wire, C: 0.04-0.12%, Si: 0.13-0.28%, Mn: 1.4-2.3%, Ti: 0.13 to 0.25%, Al: 0.001-0.050%, Cr: 0-3.00%, Ni: 0-3.00%, P: 0.020% or less, S: 0.015% or less, N: 0.0060% or less, Mo: 0-0.5%, B: 0 to 0.0100%, Cu: 0 to 0.50%, Nb: 0 to 0.30%, V: 0 to 0.5%, Zr: 0 to 0.20%, Mg: 0 to 0.050%, As: 0 to 0.020%, Sn: 0-0.100%, Sb: 0 to 0.10%, and The balance is iron and impurities. A solid wire for gas-shielded arc welding, characterized by satisfying the following formulas (1), (2), (3), (4), (5), and (6): Si×Mn≦0.60...Equation (1) (Si+Mn / 5) / (Ti+Al)≦4.0...Equation (2) 1.00≦Si+0.5×(Mn+Cr)+0.3×Ni...Equation (3) 0.30≦C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≦0.55...Equation (4) 0≦Cr+Ni≦3.00...Formula (5) 0.16≦C×(5×Si+Mn)≦0.35...Equation (6) Here, the element symbols in the formulas (1), (2), (3), (4), (5), and (6) represent the content of each element in mass % with respect to the total mass of the solid wire.

2. In mass % relative to the total mass of the solid wire, Al: 0.010-0.050%, Cr: 0.10-1.50%, Ni: 0.10 to 3.00%, and B: 0.0030-0.0100% 2. The solid wire for gas-shielded arc welding according to claim 1, further comprising at least one selected from the group consisting of:

3. 3. The solid wire for gas-shielded arc welding according to claim 1, wherein the hardness measured at a cross section of the solid wire satisfies the following formulas (7) and (8): H2≧250...Equation (7) H2-H1≧40...Formula (8) Here, the symbol H1 in the formula (8) is the Vickers hardness measured at a depth of 0.05 mm from the surface of the solid wire, and the symbol H2 in the formulas (7) and (8) is the average value of the Vickers hardness measured at depths of 0.25 mm and 0.35 mm from the surface.

4. In mass % relative to the total mass of the solid wire, Si: 0.13-0.19% 3. The solid wire for gas-shielded arc welding according to claim 1, wherein

5. In mass % relative to the total mass of the solid wire, Cr: 0.15-3.00% 3. The solid wire for gas-shielded arc welding according to claim 1, wherein

6. In mass % relative to the total mass of the solid wire, Cr: 0% or more and less than 0.50% 3. The solid wire for gas-shielded arc welding according to claim 1, wherein

7. In mass % relative to the total mass of the solid wire, Ni: 0-0.45% 3. The solid wire for gas-shielded arc welding according to claim 1, wherein

8. In mass % relative to the total mass of the solid wire, 0.05≦Cr+Ni≦3.00...Formula (9) 3. The solid wire for gas-shielded arc welding according to claim 1, wherein the above-mentioned condition is satisfied.

9. 3. The solid wire for gas-shielded arc welding according to claim 1, wherein the diameter of the solid wire is 0.8 to 1.4 mm.

10. A method for manufacturing a welded joint, comprising a step of gas-shielded arc welding steel plates using the solid wire for gas-shielded arc welding according to claim 1 or 2.

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