Highly efficient arc-welding method

Abstract

To provide a highly efficient arc-welding method capable of performing good single-sided welding even with a single electrode on a plate thickness.SOLUTION: This highly efficient arc-welding method uses a flux-included wire filling a copper outer coat with fluxes, and performs welding using a shield gas. In the flux-included wire, the fluxes contain a slug forming agent which is made of a metal oxide by 0.40-1.20% with respect to the total mass of the wire. As a fluoride or an oxide containing an alkali metal, one containing a total of 0.05-0.50%b by mass in alkali metal conversion value is used. As the shield gas, a mixed gas of a carbon dioxide gas and an argon gas, which contains the carbon dioxide gas by 40-70% and the argon gas by 60-30% at a volume ratio, is used. Welding current is within the range of 400-580A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an arc welding method. [Background technology]

[0002] Conventionally, when arc welding is performed by butt welding from one side using gas-shielded arc welding, if the base material is thin, good weld beads can be formed on both the front and back surfaces in one pass. However, when the base material is thick, it is technically difficult to form a good weld bead in one pass, so multi-pass welding, in which welding is performed in several layers, is usually performed.

[0003] In multi-pass welding, not only does the welding time increase, but it also requires time and effort to remove the slag that forms on the bead surface after each pass, which significantly reduces productivity.

[0004] To address these issues, multi-electrode welding, which uses multiple wires simultaneously, has been performed. For example, Patent Document 1 listed below discloses three-electrode single-sided gas-shielded arc welding, which uses three electrodes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-52033 Summary of the Invention [Problem to be solved by the invention]

[0006] However, because multi-electrode welding requires large welding equipment, its application is limited to long-length welding in factories and it is not suitable for short-length welding performed by welders on-site. In addition, multi-electrode welding is prone to unstable welding due to mutual interference of the arcs between the electrodes.

[0007] The present invention has been made in view of the above problems, and has as its object to provide a highly efficient arc welding method that can perform good one-sided welding of thick plates even with a single electrode. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a high-efficiency arc welding method that uses a flux-cored wire in which flux is filled in a steel sheath and performs welding while using a shielding gas, characterized in that the flux used in the flux-cored wire contains 0.40 to 1.20% of a slag former made of a metal oxide relative to the total mass of the wire and 0.05 to 0.50 mass% in total of fluorides or oxides containing alkali metals, converted into alkali metals; the shielding gas used is a mixed gas of carbon dioxide gas and argon gas, containing 40 to 70% carbon dioxide gas and 60 to 30% argon gas by volume; and the welding current is in the range of 400 to 580 A. [Effects of the Invention]

[0009] According to the highly efficient arc welding method of the present invention, a deep arc hole can be stably maintained, thereby enabling good one-sided welding even for thick plates with a single electrode. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing arc welding according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a flux-cored wire according to an embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of a welding device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a graph for explaining an evaluation test relating to welding conditions according to an embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing a butted state of base materials according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011]

[0013] In general, in arc welding, a molten metal pool (molten pool) is formed by melting the wire and base metal, and a depression (hereinafter referred to as an "arc hole") is formed in the molten pool directly below the arc due to the arc pressure.

[0012] In this embodiment, by employing a flux-cored wire of a predetermined composition, a shielding gas of a predetermined composition, and predetermined welding conditions (welding current, etc.), a deep arc hole can be formed, and good one-sided welding can be achieved even for thick plates with a single electrode. Note that in this specification, the symbol "to" indicating a range of values ​​is used to mean that the values ​​before and after it are included as the lower limit or upper limit.

[0013] In arc welding, if the arc hole is deep, the arc can heat the base metal up to near the back surface, and a bead can be stably formed on the back surface. If the state in which this deep arc hole is formed can be stably maintained, good weld beads can be obtained on both the front and back surfaces, even with thick plates.

[0014] The arc hole is maintained by the balance between the crushing force caused by the hydrostatic pressure and surface tension of the molten metal and the arc pressure that resists it. As the plate thickness to be welded increases, the hydrostatic pressure of the molten metal increases, and the crushing force also increases, causing the arc hole to become unstable.

[0015] Furthermore, if the arc hole becomes deep, it becomes difficult to generate an arc throughout the entire arc hole, and the arc generation point becomes localized, disrupting the balance of forces and making the arc hole unstable.

[0016] In this way, when the formation of the arc hole becomes unstable, the heating condition on the back side of the base material becomes unstable, which causes the formation of the back bead to become irregular, or molten metal to flow ahead of the arc (metal leading), resulting in irregularities in the back bead, which in turn causes irregularities in the front bead.

[0017] On the other hand, even if an attempt is made to spread the arc by setting a high arc voltage and lengthening the arc length, with commonly used solid wires, the arc only spreads to the upper part of the groove during butt welding, and no arc is generated at the essential bottom of the groove.

[0018] Conversely, if the arc voltage is set low so that the arc occurs at the bottom of the groove, the arc will be concentrated at the bottom of the groove, and heating of the upper part of the groove will be neglected, resulting in a convex bead with a narrow fusion width and poor shape, and hot cracks due to poor penetration shape. Also, lowering the arc voltage will shorten the arc length, causing frequent short circuits and the problem of increased spatter.

[0019] Here, the state of gas-shielded arc welding in the groove during one-side butt welding using a single electrode is presumed to be as shown in the schematic diagram in Figure 1, based on observations using high-speed video. Figure 1 is a cross-sectional view seen from a direction perpendicular to the welding direction, and in Figure 1, the welding torch moves to the left.

[0020] In front of the arc (left side in Figure 1), the groove face melts, and the molten metal bridges within the groove, forming a molten metal wall in front of the arc. In addition, a pool of molten metal (molten pool) is formed behind the arc as the wire melts, and the arc pressure creates a deep depression (arc hole) in the molten pool directly below the arc.

[0021] The formation of these arc holes allows the arc to heat up to a position close to the back surface, resulting in stable formation of a back surface bead. If this state can be maintained stably, melting of the groove face, heating and melting of the back surface, and bead formation on the surface will proceed smoothly, resulting in a good weld bead.

[0022] Based on the above considerations, it was determined that stable formation of a deep arc hole is an essential condition for one-side butt welding of thick plates, and after extensive research into how to achieve this, it was discovered that this could only be achieved by welding at a large current using a combination of a flux-cored wire with a specific composition and a special shielding gas composition.

[0023] Next, we will first consider the flux components of a flux-cored wire to achieve stable and deep arc hole formation. In this embodiment, the flux components of a metal-based flux-cored wire (composite wire) are adjusted. The flux-cored wire (welding wire) 1 includes a core of flux 5 and a steel sheath 6 that surrounds the flux 5 (see FIG. 2).

[0024] In this embodiment, the flux-cored wire 1 has a wrap type structure with a seam in the outer sheath, but the outer sheath may be a seamless type with no seam, or the outer sheath surface of the flux-cored wire 1 may be further plated or the like.

[0025] In this embodiment, the steel skin 6 contains, relative to the total mass of the steel skin 6, 0.023 mass% C (carbon), 0.01 mass% Si (silicon), 0.14 mass% Mn (manganese), 0.008 mass% P (phosphorus), and 0.006 mass% S (sulfur), with the other components being Fe (iron), but also containing trace amounts of unavoidable impurities.

[0026] Regarding the size of the flux-cored wire 1, the outer diameter of the steel sheath 6 is φ1.6 mm. Of course, the size of the flux-cored wire 1 and the size and components of the steel sheath 6 can be changed as appropriate, and for example, the outer diameter may be φ1.4 mm.

[0027] Here, flux component evaluation test 1 was performed using bead-on-plate welding. As mentioned above, in order to simultaneously obtain good weld beads on both the front and back surfaces in one-pass welding with a groove, it is necessary to melt the groove surface across the entire plate thickness ahead of the arc (to prevent poor fusion defects) and to ensure stable metal retention behind the arc to prevent the molten metal from moving ahead (to form stable beads on both the front and back surfaces).

[0028] During bead-on-plate welding, there is no groove space in front of the arc, and welding progresses by melting the base material in front of it from the surface. The ability to melt the base material in the depth direction in front of the arc corresponds to the melting ability of the groove surface over the entire plate thickness in groove welding. Also, in bead-on-plate welding, the molten metal directly below the arc is depressed by the arc pressure, forming an arc hole, and the stable formation of this arc hole corresponds to the metal retention force of the arc in groove welding.

[0029] From this perspective, when evaluating the flux composition in bead-on-plate welding, not only the appearance of the weld bead was used as an evaluation index, but also the penetration depth and its shape as an index of the penetration ability in the plate thickness direction, and the fluctuations in the welding current and arc voltage as indexes of the stability of arc hole formation (metal holding power).

[0030] 3 is a schematic diagram showing the configuration of welding apparatus 10 according to this embodiment. Welding apparatus 10 is a consumable electrode gas-shielded arc welding apparatus, and includes welding power source 11, water cooling device 12, welding feeder 15, welding torch 16, and gas mixer 18. Welding power source 11 is a DC inverter power supply with a rated capacity of 600 A and a duty cycle of 100%.

[0031] The wire feeder 15 used in connection with the welding power source 11 had a maximum output of 15 m / min or more as the feed speed to ensure the deposition amount required for welding with a large current. A water-cooled welding torch 16 was used to enable continuous welding. In this evaluation test 1, the welding conditions were a welding current of 520 A, a welding voltage of 37 V, a welding speed of 20 cm / min, a base material with a plate thickness of 14 mm, and a torch angle of 0°.

[0032] The shielding gas was made by uniformly mixing commercially available carbon dioxide gas and argon gas at a predetermined ratio in a gas mixer 18 and spraying it onto the welded parts from a welding torch 16 at a flow rate of 25 L / min. In the flux component evaluation test 1, the shielding gas composition was set to 100% carbon dioxide gas to ensure a more stringent evaluation.

[0033] Hereinafter, specific examples A1 to 20 and comparative examples B1 to 5 regarding the components of the flux 5 of this embodiment are shown in Table 1. In Table 1, the component ratio of the flux 5 is shown as a percentage (mass %) of the mass ratio of each component to the total mass of the flux-cored wire 1.

[0034] [Table 1]

[0035] In Table 1, "FR" indicates the filling rate of the flux 5 in the flux-cored wire 1. The flux 5 in Example A and Comparative Example B contains a "metal," a "metal carbonate," a "slag former (alkali metal oxide)," a "fluoride," a "slag former (metal oxide)," and a "slag remover" in a predetermined component ratio (including 0 mass %).

[0036] In Example A and Comparative Example B, the metal powder contains, as the "metal," powders of iron (Fe), Mn (manganese), Mg (magnesium), Al (aluminum), Fe-Si alloy, Fe-Ti alloy, Fe-B alloy, Fe-Mn alloy, and Si-Mn alloy.

[0037] Furthermore, Example A and Comparative Example B contain CaCO3 (calcium carbonate) as the "metal carbonate" that is the gas generating agent. Examples of the metal carbonate that can be included include magnesium carbonate, dolomite, and the like.

[0038] Furthermore, Example A and Comparative Example B contain metal oxides, including alkali metal oxides, as slag formers. Examples of alkali metal oxide slag formers include Na2O·Al2O3·6SiO2 (soda feldspar) and KAlSiO3 (potassium feldspar). Examples of metal oxide slag formers include TiO2 (titanium oxide) and ZrO2 (zirconia). Examples of metal oxide slag formers include Fe2O3 (iron oxide).

[0039] Furthermore, Example A and Comparative Example B contain NaF2 (sodium fluoride), K2SiF6 (potassium silicofluoride), CaF2 (calcium fluoride), and Na3AlF6 (cryolite, sodium hexafluoroaluminate) as the "fluoride" gas generating agent. Examples of fluorides that can be included include potassium fluoride, aluminum fluoride, and magnesium fluoride. Furthermore, Example A and Comparative Example B contain Bi2O3 (bismuth oxide) as a slag remover.

[0040] Next, the evaluation results of Example A and Comparative Example B will be explained using Table 2. In this embodiment, arc welding was performed on Example A and Comparative Example B under CO2 gas shielding using 100% carbon dioxide gas as the shielding gas, and evaluations were made on "penetration," "bead appearance," "bead shape," "current and voltage stability," and their "overall evaluation" (all of which are shown in Table 2).

[0041] [Table 2]

[0042] Regarding Table 2, the evaluation of "penetration" and "bead shape" was performed by etching the cross section of the plate material that had been bead-on-plate welded using the flux-cored wire 1 of Example A and Comparative Example B, so that the penetration shape could be observed. The etched cross section image was then photographed and processed to determine the penetration depth (mm), bead width (mm), and weld height (mm), and the evaluation was performed based on these calculated values.

[0043] The "bead appearance" was evaluated by visually inspecting the bead condition of the bead-on-plate welded test piece after welding. The "current and voltage stability" evaluation results were evaluated by recording the current and voltage values ​​during welding on a data logger and calculating the standard deviation during each welding.

[0044] The evaluation results for "penetration" were "good (11.0 or more)" for Examples A1, 2, 4, 6-10, 12-17, and 19, "fair (10.0 to 10.9)" for Examples A3, 5, 11, 18, and 20 and Comparative Example B1, and "poor (9.9 or less)" for Comparative Examples B2 to B5.

[0045] The evaluation results for "bead shape (bead width)" were "Good (19.0 to 23.9)" for Examples A1 to A6, 8 to A16, 18 to A20 and Comparative Examples B1 and B3, "Fair (24.0 or more)" for Examples A7 and A17 and Comparative Example B4, and "Poor (18.9 or less)" for Comparative Examples B2 and B5.

[0046] The evaluation results for "bead shape (reinforcement height)" were "Good (6.0 or less)" for Examples A2 to A6, 8, 9, 13, 14, 19, and 20 and Comparative Examples B1, 3 to 5, "Fair (6.1 to 6.9)" for Examples A1, 7, 10 to 12, and 15 to 18, and "Poor (7.0 or more)" for Comparative Example B2.

[0047] The evaluation results for "bead appearance" were "good" for Examples A1, 3, 4, 6, 11, 14, 15, 17-20 and Comparative Examples B2, 3, and 5, "good" for Examples A2, 5, 7-10, 12, 13, and 16, "partially problematic" for Examples A2, 5, 7-10, 12, 13, and 16, and "poor" for Comparative Examples B1 and 4.

[0048] The evaluation results for "voltage stability" were "good (1.50 or less)" for Examples A2 to A6, 10 to A12, 14, 16 to A20 and Comparative Examples B1 and B3, "fair (1.51 to 1.69)" for Examples A1, 7 to A9, 13, and 15, and "poor (1.70 or more)" for Comparative Example B4.

[0049] The evaluation results for "current stability" were "Good (40.0 or less)" for Examples A3, 9, 11 to 20 and Comparative Examples B1 and 3, "Fair (40.1 to 59.9)" for Examples A1, 2, 4 to 8, and 10, and "Poor (60.0 or more)" for Comparative Example B4.

[0050] In order to comprehensively evaluate the evaluations of "Penetration," "Bead Appearance," "Bead Shape," and "Current and Voltage Stability" in Table 2, the overall evaluation results are shown in Table 2, with five or more "〇" marks being "◎," three to four "〇" marks being "〇," one to two "〇" marks being "△," and one or even one "×" mark being "×."

[0051] The evaluation results for "overall evaluation" were: Examples A3, 4, 6, 14, 19, and 20 were "A", Examples A1, 2, 5, 8, 9, 11 to 13, and 15 to 18 were "Good", Examples A7 and 10 were "Average", and Comparative Examples B1 to 5 were "Poor".

[0052] Next, based on the evaluation results of Example A and Comparative Example B, the characteristics of the numerical ranges of the flux components according to this embodiment will be explained in order with reference to Table 3. Table 3 lists the numerical values ​​of each Example A and Comparative Example B for the following numerical ranges (1) to (6).

[0053] [Table 3]

[0054] (1) Slag former consisting of metal oxide: 0.40 to 1.20 mass% The flux preferably contains 0.40 to 1.20 mass% of slag formers (Na2O·Al2O3·6SiO2, KAlSi3O8, TiO2, ZrO2) made of metal oxides including alkali metal oxides, relative to the total mass of the wire. All of Examples A1 to 20 satisfy the numerical range (1), but none of Comparative Examples B1 to 5 do so.

[0055] The arc generated from the tip of the wire melts the flux filled in the center along with the metal part of the wire sheath and moves to the bottom of the arc hole. At this time, in the shallow, recessed arc hole used in general welding, the molten slag is smoothly expelled to the rear of the molten pool, but in the deep arc hole used in deep penetration welding, the slag is not expelled smoothly and remains and accumulates.

[0056] Therefore, if the content of slag formers exceeds 1.20% by mass, the amount of slag that accumulates at the bottom of the arc hole increases, inhibiting arc generation and reducing penetration depth. Furthermore, if the content of slag formers increases, it becomes impossible to increase the content of metal powder. Furthermore, if the content of slag formers is less than 0.40% by mass, the amount of slag that covers the bead surface during welding decreases, resulting in an unstable bead appearance.

[0057] (2) Alkali metal equivalent value of fluorides or oxides containing alkali metals: 0.05 to 0.50 mass% The flux preferably contains 0.05 to 0.50 mass% of alkali metal-equivalent fluorides (NaF2, K2SiF6, Na3AlF6) or oxides (Na2O·Al2O3·6SiO2, KAlSi3O8) based on the total mass of the wire. It may contain only fluorides, only oxides, or both fluorides and oxides. All of Examples A1 to 20 satisfy the numerical range (2), but Comparative Example B5 does not.

[0058] Alkali metals such as Li, Na, and K are commonly used as arc stabilizers. In this embodiment, the addition of the alkali metal to the center of the wire allows the arc generated at the tip of the wire to spread over the entire inner wall of the arc hole, exerting arc pressure and stabilizing even a deep arc hole. If the alkali metal content is less than 0.05% by mass, the arc spread is small and the arc hole becomes unstable. On the other hand, if the alkali metal content exceeds 0.50% by mass, the arc hole is expanded too much, resulting in shallow welding penetration.

[0059] (3) Iron powder: 10.00% by mass or more The flux preferably contains 10.00 mass % or more of iron powder (Fe), which is a metal powder, relative to the total mass of the wire. All of Examples A1 to 20 satisfy the numerical range (3), but Comparative Examples B2 to 5 do not.

[0060] When welding in a groove, it is necessary to fill the groove with molten metal while melting the arc all the way to the bottom of the groove. Particularly in butt welding of thick plates like this, it is necessary to fill the groove with molten metal while simultaneously maintaining the stability of the arc generated in the groove. To achieve this, it is desirable to have an iron powder content of 10.00 mass% or more in the metal powder.

[0061] There are various types of iron powder, such as reduced iron powder and atomized iron powder, depending on the production method, but the type is not important. If the iron powder content is less than 10.00 mass%, not only will the arc become unstable and spatter increase, but the groove will not be able to be filled with molten metal, causing defects such as insufficient fusion and making it impossible to form a stable bead. (4) Fluoride as a gas generating agent: 0.19 to 1.00 mass% The flux preferably contains 0.19 to 1.00 mass% of fluorides (NaF2, K2SiF6, CaF2, Na3AlF6) as gas generating agents relative to the total mass of the wire. Examples A2 to A6, 8 to A10, 13 to A17, 19, and 20 satisfy the numerical range (4), but Comparative Examples B2 to B5 do not.

[0062] It was previously known that adding fluoride was effective in reducing hydrogen, which causes porosity defects and cold cracking, but this time it was added to the flux as a gas generating agent. By adding a gas generating agent made of fluoride to the flux, gas is generated from the fluoride filled in the center of the wire by the arc generated from the tip of the wire, and by increasing the internal pressure of the arc hole, it is possible to more reliably prevent the precursory phenomenon in the weld metal.

[0063] To achieve this effect, it is desirable to add 0.19% by mass or more of fluoride as a gas generating agent. Also, if the fluoride content as a gas generating agent exceeds 1.00% by mass, the arc hole will be too wide, resulting in shallow penetration and the generation of large spatter particles, which will make workability worse.

[0064] (5) Metal carbonate as a gas generating agent: 0.30 to 1.00 mass% The flux preferably contains 0.30 to 1.00 mass% of metal carbonate (CaCO3) as a gas generating agent relative to the total mass of the wire. Examples A3, 4, 6, 13, 14, 19, and 20 satisfy the numerical range (5), but Comparative Examples B2 to B5 do not.

[0065] Previous knowledge has shown that adding metal carbonates has the effect of reducing hydrogen in the weld metal, just like fluorides, and also has the effect of increasing the stability and concentration of the arc.However, this time, it was added to the flux as a gas generating agent, just like fluorides.

[0066] By adding a metal carbonate as a gas generating agent to the flux 5, carbon dioxide (CO2) gas is generated from the tip of the flux-cored wire 1, and the same effects as those of the above-mentioned fluoride gas generating agent are achieved.

[0067] To effectively obtain these effects, it is desirable to include 0.3 mass% or more of metal carbonate as a gas generating agent, but adding more than 1.00 mass% is not desirable because excessive CO2 gas is generated, which leads to poor penetration and bead appearance.

[0068] (6) Flux filling rate: 17.5 to 19.5 mass% The flux-cored wire preferably contains 17.5 to 19.5 mass % of flux relative to the total mass of the wire. All of Examples A1 to 20 satisfy the numerical range (6), but Comparative Examples B3 to 5 do not.

[0069] The flux filling rate of conventional general welding wire is 10 to 15 mass %, but in this embodiment, the flux filling rate is increased to achieve deep penetration and high welding strength. By increasing the flux filling rate, the cross-sectional area of ​​the steel sheath becomes smaller than that of conventional general welding wire, and the density of the current flowing only in the steel sheath becomes higher.

[0070] This increases the resistance heat generated at the protruding portion, causing the flux-cored wire to melt more quickly, increasing the amount of metal produced per unit time.

[0071] If the flux filling rate is less than 17.5 mass%, the penetration may be shallow and the bead may have a wavy appearance. If the flux filling rate is more than 19.5 mass%, problems may occur, such as the flux not being able to be stably filled into the steel sheath. Therefore, it is desirable to set the flux filling rate within the above numerical range (6).

[0072] Next, we will consider the welding conditions (welding current and arc voltage) required to achieve stable formation of deep arc holes. (7) Welding current: 400~580A FIG. 4 is a graph plotting combinations of welding conditions of welding current (horizontal axis) and arc voltage (vertical axis) in evaluation test 2 by butt welding regarding the composition of shielding gas and welding conditions.

[0073] Similar to Evaluation Test 1, Evaluation Test 2 was performed by bead-on-plate welding with a plate thickness of 14 mm, using the flux-cored wire of Example A2 and a mixed gas of 60% carbon dioxide and 40% argon gas as the shielding gas, while varying the welding conditions (welding current and arc voltage). In Figure 4, deep arc holes were stably formed under the welding conditions within the range surrounded by the parallelogram near the center.

[0074] When selecting welding conditions for groove welding, the cross-sectional area of ​​the groove (S cm 2 The welding current is set to obtain the amount of wire melting required to fill the groove space volume (S × V), which is determined by the welding speed (V cm / min) and the welding volume (S × V).

[0075] Therefore, although various values ​​of welding current can be set in principle, it was found that the welding current must be 400 A or more because a strong arc force is required to counter the large hydrostatic pressure of the molten metal when welding thick plates.

[0076] On the other hand, when the welding current value is increased and a welding wire with a wire diameter of 1.4φmm or 1.6φmm is fed at high speed, feeding tends to become unstable, the current value fluctuates greatly, and a stably formed molten pool cannot be achieved. Furthermore, problems occur such as an increase in the amount of spatter generated due to unstable wire plunge into the molten pool. In this embodiment, when the welding current is 580 A or higher, the problem of unstable wire feeding occurs. To solve these problems, the welding current needs to be set to 400 to 580 A.

[0077] (8) Arc voltage y V: 0.056x + 6.778 ≦ y ≦ 0.050x + 18.00, where x is the welding current. In order to stably form a deep arc hole when welding thick plates on one side, it is necessary to set the arc voltage appropriately for the set welding current. If the arc voltage is too low for the set welding current, the arc generation point will be localized at the bottom of the arc hole, making the arc hole unstable and causing a short circuit between the molten pool and the wire, resulting in the generation of a large amount of spatter.

[0078] On the other hand, if the arc voltage is too high, the arc will spread too much, resulting in shallow penetration and a flat bead shape with a wide bead width.When x is the welding current (A) and y is the arc voltage (V), it has been discovered that in order to stably form a deep arc hole, an arc voltage in the range of 0.056x + 6.778 ≦ y ≦ 0.050x + 18.00 is desirable for the above welding current range.

[0079] Next, we will consider the composition of the shielding gas to achieve stable formation of a deep arc hole. Here, evaluation test 3 regarding the shielding gas was performed using the above-mentioned welding device 10, with one-sided welding of base metals with a plate thickness of 14 mm, butt welding with a V groove of 36° and a root gap of 0 mm (see Figure 5).

[0080] With regard to the flux-cored wire, Example C1 used the flux component of Example A1, Examples C2 to C5 used the flux component of Example A2, Example C6 used the flux component of Example A6, Comparative Examples D1 to D5 used the flux component of Example A1, Comparative Example D6 used the flux component of Example A4, Comparative Example D7 used the flux component of Example A6, Comparative Example D8 used the flux component of Comparative Example B3, Comparative Example D9 used the flux component of Comparative Example B4, and Comparative Example 10 used the flux component of Comparative Example B6.

[0081] Regarding the composition of the shielding gas, in Examples C1 to C6 and Comparative Examples D1 to D10, the volume ratio [%] of carbon dioxide to argon gas was changed in 10% increments from 100:0 to 20:80, and the flow rate of the shielding gas was set to 25 to 30 L / min. Regarding the welding conditions, the welding current was set to 500 to 530 A, the arc voltage was set to 30 to 36.5 V, and the welding speed was set to 25 cm / min.

[0082] Table 4 shows specific examples C1 to C6 and comparative examples D1 to D10 regarding the shielding gas composition and welding conditions of this embodiment. [Table 4]

[0083] Next, the evaluation results of Example C and Comparative Example D will be explained using Table 4. In this evaluation test 3, evaluations were made on "Bead appearance (front bead)", "Bead appearance (reverse bead)", "Penetration shape", "Welding stability (arc voltage)", "Welding stability (welding current)", "Welding stability (number of short circuits)", and their "overall evaluation".

[0084] The "Bead appearance (front bead)" and "Bead appearance (reverse bead)" were evaluated by visually inspecting the state of the front and back beads of the butt-welded test pieces after welding. The "Penetration shape" was evaluated by etching the cross section of the welded test piece so that the penetration shape could be observed, and the cross-sectional shape and the presence or absence of defects were visually inspected.

[0085] "Welding stability (arc voltage)" and "welding stability (welding current)" were evaluated by recording the welding current and arc voltage values ​​during welding with a data logger and calculating the standard deviation during each welding. "Welding stability (number of short circuits)" was evaluated by recording the arc voltage values ​​during welding with a data logger and calculating the number of times the arc voltage fell below 25V.

[0086] The evaluation results for "Bead appearance (surface bead)" were "Good" for Examples C1 to 6 and Comparative Examples D1, 3, and 4, and "Poor" for Comparative Examples D2, 5 to 10. The evaluation results for "Bead appearance (reverse bead)" were "Good" for Examples C1 to 6 and Comparative Examples D2, 4 to 6, 8, and 9, "Good" for Comparative Examples D7 and 10, "Some problems" for Comparative Examples D1 and 3, and "Poor" for Comparative Examples D1 and 3.

[0087] The evaluation results for "melting shape" were "good (◯)" for Examples C1 to C6 and Comparative Examples D1, 2, 8, and 9, "partially problematic (△)" for Comparative Examples D3 and 6, and "poor (×)" for Comparative Examples D4, 5, 7, and 10.

[0088] The evaluation results for "welding stability (arc voltage)" were "Good (1.49 or less)" for Examples C2, 4 to 6 and Comparative Examples D3 to 5, 7, and 9, "Fair (1.50 to 1.59)" for Examples C1 and 3 and Comparative Examples D2 and 6, and "Poor (1.60 or more)" for Comparative Examples D1, 8, and 10.

[0089] The evaluation results for "welding stability (welding current)" were "Good (50.0 or less)" for Examples C2, 4, 5 and Comparative Examples D5, 7, 9, "Fair (50.1 to 69.9)" for Examples C1, 3, 6 and Comparative Examples D3, 4, 6, 8, and "Poor (70.0 or more)" for Comparative Examples D1, 2, 10.

[0090] The evaluation results for "welding stability (number of short circuits)" were "◯ (0)" for Examples C1 to C6 and Comparative Examples D3 to D5, D7, and D8, and "× (1 or more)" for Comparative Examples D1, D2, D6, D9, and D10.

[0091] In order to comprehensively evaluate the evaluation results in Table 4, the overall evaluation results are shown in Table 4, with "o" being "o" if there is only "o", "△" being "△" if there are 1 or 2 "△", and "X" being "X" if there are 3 or more "△" or at least 1 "X". The evaluation results for "overall evaluation" were "o" for Examples C2, 4, and 5, "△" for Examples C1, 3, and 6, and "X" for Comparative Examples B1 to 10.

[0092] Next, we will explain the characteristics of the shielding gas composition and the numerical ranges of the welding conditions (welding current and arc voltage) according to this embodiment based on the evaluation results (Table 4) of the above-mentioned Example C and Comparative Example D. In this evaluation test 3, the welding conditions of Example C satisfy the above-mentioned numerical range (7) for the welding current and numerical range (8) for the arc voltage.

[0093] (9) The shielding gas is a mixture of carbon dioxide and argon gas, with the volume ratio being 40-70% carbon dioxide and 60-30% argon. According to the results of the above overall evaluation, Example C, which used a mixed gas containing 40 to 70% carbon dioxide and 60 to 30% argon gas as a shielding gas and employed the flux-cored wire of Example A, received an overall evaluation of "△" or higher, while Comparative Example D, which used a mixed gas that did not satisfy the above numerical range (9) as a shielding gas and employed the flux-cored wire of Example A, received an overall evaluation of "×".

[0094] Therefore, the composition of the shielding gas is preferably a mixed gas containing 40 to 70% carbon dioxide gas and 60 to 30% argon gas by volume, based on the composition of the shielding gas in Example C. The mixed gas of carbon dioxide gas and argon gas also contains trace amounts of unavoidable impurities.

[0095] When the carbon dioxide gas mixture is 30% or less, the arc hole stability is excellent, but the arc spreads too much, resulting in shallow penetration. In addition, the penetration shape becomes thin and finger-like, and the thin penetration into the tip of the groove causes poor fusion. Also, when the carbon dioxide gas mixture is 80% or more, it is not possible to obtain an effective effect, and the arc hole becomes unstable, causing increased spatter and other problems similar to those with 100% carbon dioxide.

[0096] It should be noted that this effect was not observed with welding wires outside the component range of Example A according to this embodiment, and it was found that this excellent effect was only exhibited with the combination of the flux-cored wire according to this embodiment and the shielding gas composition.

[0097] (10) Welding torch angle: Reverse angle 10-30° In single-pass welding using ceramic backing materials, tilting the torch using the backstroke technique allows the molten metal to be held at the rear, making it easier to form a backstrip. Therefore, if the torch angle (backstroke angle) is less than 10°, the weld metal is more likely to undergo a front-end phenomenon, resulting in poor fusion or penetration. Furthermore, if the torch angle is more than 30°, the backstroke bead may become excessively thick and produce a large amount of spatter. For these reasons, it is desirable to move the welding torch using the backstroke technique at a tilt angle of 10 to 30°.

[0098] Next, evaluation test 4 on the welding time efficiency of Example E according to an embodiment of the present invention and Comparative Example F will be described with reference to Table 5. In this evaluation test 4, butt welding was performed while changing the base metal plate thickness (9 to 20 mm), groove shape (I-type, V-type), and root gap (0 to 5 mm) (see FIG. 5).

[0099] In Examples E1 to E4, a flux-cored wire with the same flux composition as in Example A2 was used, and a mixed gas of 60% carbon dioxide and 40% argon by volume was used as the shielding gas, with a shielding gas flow rate of 25 to 30 L / min. The welding current was 450 A, the arc voltage was 37 V, and the welding speed was adjusted to within the range of 20 to 30 cm / min, with the torch angle set to 10 to 30 degrees (sweep back angle) relative to the welding direction.

[0100] In Comparative Examples F1 to F4, a flux-cored wire with the same flux composition as Comparative Example B4 was used, the shielding gas was 100% carbon dioxide, and the shielding gas flow rate was 25 to 35 L / min. The welding current for the first layer was 180 A, the arc voltage was 27 V, and the welding speed was 15 cm / min, and the welding current for subsequent layers was 280 A, the arc voltage was 31 V, and the welding speed was adjusted within the range of 25 to 35 cm / min. Welding was performed with the torch angle set at 10 to 30 degrees (sweep back angle) relative to the welding direction, as in Example E.

[0101] [Table 5]

[0102] This welding method is a highly efficient welding method that can effectively achieve the benefits of deep penetration and high deposition not only in single-side single-pass welding but also in the first and second layers of multi-pass welding. To prove the high efficiency of the above embodiment compared to conventional technology, single-side butt welding was performed with plate thicknesses of 9 to 20 mm and groove conditions of an I groove or V groove 36°, and the welding operation time (including the time to remove slag during multi-pass welding) was measured under conditions that resulted in a good weld bead.

[0103] If each groove is filled with deposited metal during this construction time, the groove filling speed per unit time (cm 3 / min) was obtained, and the ratio of this to a comparative example of the same plate thickness was calculated as "time efficiency" to evaluate the high efficiency of the present invention. According to Table 5, Example E has a time efficiency 1.5 times or more that of Example F.

[0104] The above has described in detail an embodiment of the present invention. According to this embodiment, by employing a flux-cored wire of a predetermined composition, a shielding gas of a predetermined composition, and predetermined welding conditions (welding current, etc.), a deep arc hole can be stably formed, and good one-sided welding of thick plates can be achieved even with a single electrode.

[0105] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the present invention. For example, the shape and size of the flux-cored wire can be changed as appropriate.

[0106] Furthermore, in the above embodiment, butt welding is performed using a single electrode and one-sided welding, but the present invention can also be applied to double-sided welding. [Explanation of symbols]

[0107] 1 Flux-cored wire 5. Flux 6 Steel shell 10 Welding equipment 11 Welding power source 12 Water cooling system 15 Feeder 16 Welding Torch 18 Gas Mixer

Claims

1. A highly efficient arc welding method using a flux-cored wire with a steel outer sheath filled with flux and welding while using shielding gas, As the flux-cored wire, the flux is Contains 0.40 to 1.20% of a slag former consisting of a metal oxide; Use a material containing fluorides or oxides containing alkali metals in an amount of 0.05 to 0.50 mass% in total converted to alkali metals, As the shielding gas, a mixed gas of carbon dioxide gas and argon gas is used, the mixed gas containing 40 to 70% carbon dioxide gas and 60 to 30% argon gas by volume ratio, A highly efficient arc welding method characterized in that the welding current is in the range of 400 to 580A.

2. 2. The high-efficiency arc welding method according to claim 1, wherein the flux satisfies at least one of the following: a gas generating agent comprising a fluoride in an amount of 0.19 to 1.00 mass% relative to the total mass of the wire; and a gas generating agent comprising a metal carbonate in an amount of 0.30 to 1.00 mass% relative to the total mass of the wire.

3. When the welding current is x (A) and the arc voltage is y (V), 3. A highly efficient arc welding method according to claim 1, wherein the arc voltage y is in the range of 0.056x+6.778 or more and 0.050x+18.00 or less.

4. 3. A highly efficient arc welding method according to claim 1, wherein the welding torch is moved by a backward movement with an inclination angle of 10 to 30 degrees.

5. 3. A high-efficiency arc welding method according to claim 1, wherein the flux contains 10.00 mass % or more of iron powder, which is a metal powder, based on the total mass of the wire.

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