Wire rod for forming molten metal and method for manufacturing welding products

Abstract

To provide a wire for molten metal formation excellent in arc stability in welding for a long time.SOLUTION: A wire for molten metal formation is made from Ti or a Ti alloy, has an oxygen condensed layer on the surface, and contains a metal compound having at least one metal selected from a group of alkali metal and alkali earth metal such that the alkali metal and / or the alkali earth metal is 0.002 to 0.050 mass% in total to the total mass of the wire. Cracks with which the metal compound is filled are formed on the surface, and the area ratio of the cracks is 4 to 25%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a wire rod for forming a molten metal made of a Ti-based material and a welded product having a weld formed using the same. [Background technology]

[0002] MIG welding (Metal Inert Gas Welding) is carried out by generating an arc between the welding wire fed from the welding equipment and the workpiece while they are surrounded by shielding gas, and then transferring and landing the molten droplets of the welding wire onto the workpiece, thereby continuously forming a bead.

[0003] The key to this is stabilizing the generated arc. If the generated arc is not stable, the formed bead will have constrictions and a large amount of spatter will be generated. The build-up will also be uneven. A bead with such a shape cannot be said to guarantee the reliability of the strength characteristics of the weld.

[0004] The use of oxygen-containing gas as a shielding gas is known as a method for stabilizing the arc, but when MIG welding wire made of Ti or Ti alloy is used, the use of oxygen-containing gas as a shielding gas not only oxidizes the bead surface but also reduces the ductility of the weld, so high-purity inert gases such as pure Ar gas are used as the shielding gas. However, the use of high-purity inert gas makes the cathode spot during arc discharge unstable.

[0005] Therefore, in welding wires made of Ti or Ti alloys, an oxide layer is formed on the surface of the welding wire to stabilize the cathode spot, and grooves are formed on the surface of the welding wire to hold metal compounds of alkali metals or alkaline earth metals inside the grooves, thereby improving feedability and arc stability (see, for example, the following patent document). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-136940 Summary of the Invention [Problem to be solved by the invention]

[0007] However, even when grooves are formed on the surface of the welding wire and metal compounds of alkali metals or alkaline earth metals are held inside the grooves, there is still a problem of arc instability during welding, which occurs when welding is performed for a long time, such as when there are many or long welds or when multiple welds are used.

[0008] SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a wire rod for forming molten metal which is excellent in arc stability during long-term welding, and a welded product using the same. [Means for solving the problem]

[0009] The present invention provides a wire rod for forming molten metal made of Ti or a Ti alloy, The wire has an oxygen-enriched layer on its surface and contains a metal compound having at least one metal selected from the group consisting of alkali metals and alkaline earth metals in an amount of 0.002 to 0.050 mass% in total of the alkali metal and / or alkaline earth metal relative to the total mass of the wire, Cracks filled with the metal compound are formed on the surface, and the area ratio of the cracks is 4 to 25%.

[0010] The oxygen in the oxygen-enriched layer stabilizes the generated arc and at the same time reduces the surface tension of the tip of the molten wire, making it easier for the generated droplets to detach from the tip of the wire. Furthermore, since the boiling points and ionization voltages of alkali metals and alkaline earth metals are lower than the melting point and ionization voltage of Ti, the alkali metals and alkaline earth metals exist as ionized metal vapor in the generated arc before the base metal (Ti or Ti alloy) melts due to the arc heat, thereby stabilizing the generated arc column. For this reason, in the present invention, a metal compound containing at least one metal selected from the group consisting of alkali metals and alkaline earth metals is contained in the wire so that the total amount of the alkali metal and / or alkaline earth metal is 0.002 to 0.050 mass% relative to the total mass of the wire.

[0011] The inventors have found that even in wires containing a predetermined amount of metal compounds, the arc becomes unstable during long-term welding due to uneven distribution of the metal compounds. The present invention was made based on this finding, and according to the present invention, by setting the area ratio of cracks formed on the surface of the wire to 4 to 25%, it is possible to maintain a predetermined amount of metal compounds in a uniformly distributed state on the surface of the wire (more specifically, within the cracks formed on the surface), thereby improving arc stability during long-term welding.

[0012] In the present invention, the crack propagation depth can be set to 20 μm or less. If the cracks formed on the surface are deeper than 20 μm, excessive amounts of metal compounds are retained in these deep cracks, which tends to cause variations in the distribution of the metal compounds as a whole. Therefore, it is desirable that the propagation depth of the cracks formed on the surface of the wire rod be set to 20 μm or less.

[0013] In addition, in the present invention, when the number of cracks present per predetermined length A μm in the longitudinal direction of the wire is defined as B, the distance between cracks obtained by A / B can be 15 μm or less, because if the distance between cracks in the longitudinal direction becomes excessively long, the arc may become unstable.

[0014] In the present invention, the boiling point of the metal can be set to 2000° C. or lower, and the metal compound can be a metal compound containing Ca.

[0015] In the present invention, the average oxygen concentration of the oxygen-enriched layer can be set to 1 to 40 mass %.

[0016] The welded product of the present invention is characterized in that it has welds welded using the above-mentioned wire rod for forming molten metal, and the total length of the welds is 300 mm or more. Since the above-mentioned wire rod for forming molten metal has excellent arc stability during long-term welding, it is possible to effectively suppress welding defects in welded products having welds with a total length of 300 mm or more. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is an explanatory diagram of a concentrated arc defined in the present invention. [Figure 2] 10 is a scanning electron microscope photograph of a cross section of a surface layer portion of a welding wire according to Example 24. [Figure 3] 10 is a scanning electron microscope photograph of the surface of the welding wire according to Example 24. [Figure 4] FIG. 2 is an explanatory diagram of the length between cracks defined in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The welding wire as the wire rod for forming molten metal according to this embodiment is made of Ti or a Ti alloy and has an oxygen-enriched layer on its surface. Furthermore, fine surface cracks, which are generated during the wiredrawing process described below, are distributed over the entire surface of the welding wire. These surface cracks are formed as fissures of a certain depth extending from the oxygen-enriched layer on the surface of the welding wire toward the inner layer of the base metal, and the cracks are filled with metal compounds, described below, including alkali metals and alkaline earth metals.

[0019] The oxygen-enriched layer and its average oxygen concentration are defined as follows: The cross section of the wire is mirror-polished, and the oxygen concentration distribution is analyzed by EPMA (Electron Probe Microanalysis). If the oxygen concentration at the center of the wire obtained by this analysis is defined as 1, the region where the oxygen concentration is 1.2 or higher (1.2 times or higher than the oxygen concentration at the center of the wire) is defined as the oxygen-enriched layer. The average oxygen concentration (at five measurement points) in the region where the oxygen concentration is 1.2 or higher is defined as the average oxygen concentration of the oxygen-enriched layer. If the oxygen concentration varies in the circumferential direction of the wire cross section, concentration measurement circles are set at various positions in the radial direction of the cross section, and the oxygen concentrations are averaged along each circle to determine the circumferentially averaged oxygen concentration distribution in the radial direction of the cross section. The region where the oxygen concentration is 1.2 times or higher than the oxygen concentration at the center of the wire is defined as the oxygen-enriched layer.

[0020] The thickness of the oxygen-enriched layer in the welding wire of this embodiment is preferably thicker than the natural oxide film that forms on the wire surface, which is typically 40 to 100 nm thick.

[0021] Moreover, the oxygen-enriched layer of the welding wire of the present embodiment satisfies the following relationship. That is, when the thickness of the oxygen-enriched layer is Tw and the diameter of the welding wire is Dw, the value of Tw / Dw is 0.3 × 10 -3 ~1×10 -1 and the average oxygen concentration of the oxygen-enriched layer is 1 mass % or more. By forming an oxygen-enriched layer having such a thickness and average oxygen concentration, it is possible to significantly improve the wire feedability through a conduit tube of a welding device, etc. Furthermore, it also improves the arc stability when performing arc welding or arc spraying.

[0022] Tw / Dw is 0.3×10 -3When Tw is less than 0.03% of Dw, or when the average oxygen concentration in the oxygen-enriched layer is less than 1 mass%, the feedability improvement effect becomes insufficient. In addition, the arc tends to become unstable, which is disadvantageous in forming a uniform weld bead or thermal spray layer. In addition, when Tw / Dw is 1×10 -1 (When Tw exceeds 10% of Dw, it takes an extremely long time to form the oxygen-enriched layer, and the effect is poor despite the difficulty of forming it. When used for welding, it may even cause adverse effects such as a decrease in the strength of the welded joint in a welded structure.)

[0023] The upper limit of the average oxygen concentration of the oxygen-enriched layer is described below. The average oxygen concentration of the oxygen-enriched layer is maximized when the entire layer is formed of titanium oxide, and this value is considered to be equal to the oxygen content calculated from the molecular formula of the formed oxide. For example, if the formed oxide is TiO2, the upper limit of the average oxygen concentration calculated from its stoichiometric oxygen content is 40.06 mass% (calculated assuming that the atomic weight of Ti is 47.88 and the atomic weight of oxygen is 16.0). Furthermore, Ti oxides with an even higher oxygen stoichiometry than TiO2 may be formed. For example, if Ti2O5 is formed, the upper limit of the average oxygen concentration is 45.52 mass%. Therefore, it is generally unlikely that the maximum average oxygen concentration of the oxygen-enriched layer will exceed 45.52 mass%. Therefore, it can be said that the maximum average oxygen concentration of the oxygen-enriched layer is 45.52 mass%. However, setting the average oxygen concentration of the oxygen-enriched layer to 45.52 mass% may result in adverse effects such as reduced ductility of the weld. Therefore, the average oxygen concentration in the oxygen-enriched layer is preferably set to 40 mass % or less.

[0024] In order to make the arc stabilization effect more pronounced, the ratio of the oxygen-enriched layer thickness Tw to the wire diameter Dw, Tw / Dw, should be set to 1×10 -3 ~1×10 -1In particular, when a thermal oxidation method or the like is employed to form an oxygen diffusion layer (a portion located inward from the outermost surface layer, which contains less oxygen than titanium oxide and is formed by oxygen diffusion into a metal phase mainly composed of Ti) in addition to a titanium oxide layer (similar to or thicker than a native oxide film having a thickness of about 40 to 100 nm) in the outermost surface layer, the thickness of the oxygen-enriched layer increases by the amount of the oxygen diffusion layer, making it more likely that Tw / Dw will fall within the above-mentioned desirable range.

[0025] When used as welding wire, if the oxygen-enriched layer becomes too thick or the average oxygen concentration becomes too high, problems may occur in that the strength of the welded joint in the resulting welded structure is impaired. Therefore, when used as welding wire, Tw / Dw is set to 1×10 -3 ~50×10 -3 It is more desirable to limit the Tw / Dw and the average oxygen concentration of the oxygen-enriched layer to 1 to 30 mass % (Tw is 5% of Dw). Also, when using it as a thermal spray wire, if it is desired to form a high-strength thermal spray layer with oxidation suppressed as much as possible using an inert gas such as argon as a spray medium, it may be desirable to limit Tw / Dw and the average oxygen concentration to the same ranges.

[0026] The welding wire of this example contains a metal compound having at least one metal selected from the group consisting of alkali metals and alkaline earth metals. Examples of alkali metals include Li, Na, K, Rb, and Cs, and examples of alkaline earth metals include Ca, Sr, and Ba. Alternatively, an appropriate metal may be selected from the alkali metals and an appropriate metal from the alkaline earth metals, and these compounds may be used together to contain both an alkali metal and an alkaline earth metal. Specifically, metal compounds such as carbonates are preferred as the metal compound. Sodium carbonate, potassium carbonate, and calcium carbonate are particularly preferred.

[0027] The metal compound of the present invention preferably contains, among the above-mentioned alkali metals or alkaline earth metals, a metal having a boiling point of 2000°C or less, and more preferably a metal having a boiling point of 600°C or more and 2000°C or less. In particular, it is preferable to contain one or more of K, Na, Ca, etc. Furthermore, it is more preferable to use a metal compound containing Ca.

[0028] All of these metals have lower boiling points and ionization voltages than Ti, the main component of the base metal. Because these metals are present in cracks on the surface of the welding wire, during MIG welding, before the base metal (Ti) melts due to the arc heat, these metals become ionized metal vapor and exist in the arc field. As a result, the generated arc becomes a concentrated arc and is stabilized.

[0029] A "concentrated arc" is defined as the following arc. It will be explained based on Figure 1. An arc is discharged through a wire with a diameter of D, and the boundary of the arc is visually observed. If the arc is so blurred that the boundary cannot be distinguished, it is not recognized as a concentrated arc, but is called a diffuse arc.

[0030] Then, imagine a truncated cone with its bottom located a diameter D below the lower end of the wire, and let θ be the angle between the side and bottom of this truncated cone. An arc with θ≧60° is called a concentrated arc. By making θ≧60°, droplets can always be formed. The welding wire of the present invention has the above-mentioned characteristics and can therefore be used in welding devices such as devices for performing MIG welding.

[0031] The total content of the alkali metals and / or alkaline earth metals is set to 0.002 to 0.050% by mass relative to the total mass of the welding wire. If the content of these metals is less than 0.002% by mass, the effects of these metals are not fully exerted, resulting in a low rate of concentrated arc generation and making it difficult to generate one droplet per pulse of current. As a result, the droplet at the tip of the wire and the molten pool in the base metal come into contact (short-circuit). The resulting increase in current releases the short circuit, resulting in spattering. Furthermore, if the total content of the alkali metals and / or alkaline earth metals is greater than 0.050% by mass, the arc force becomes too strong, causing spattering centered around the droplet during the transition to the weld zone, resulting in rough appearance not only of the bead but also of areas other than the weld zone.

[0032] In terms of realizing one droplet per one current pulse, the total content of alkali metals and / or alkaline earth metals is preferably 0.007 to 0.015 mass % with respect to the total mass of the welding wire.

[0033] In the welding wire of this embodiment, the shape of cracks formed on the surface of the welding wire and filled with a metal compound containing at least one metal selected from the group consisting of alkali metals and alkaline earth metals is specified. Specifically, the area ratio of the cracks, the propagation depth of the cracks, and the length between the cracks are specified. This is to distribute the metal compound uniformly on the surface of the welding wire.

[0034] The crack area ratio is the ratio of the crack area to the observed area of ​​the welding wire surface. In this example, the metal compounds are mainly held in a filled state inside the cracks formed on the surface of the welding wire. If the crack area ratio is too small, there will not be enough cracks to accommodate the required amount of metal compounds. If the crack area ratio is too large, there will be many cracks that are not filled with metal compounds. In either case, the distribution of the metal compounds will not be uniform, resulting in an unstable arc. For this reason, in this example, the crack area ratio is specified to be 4 to 25%. A more preferable area ratio is 7 to 20%.

[0035] The crack propagation depth is the depth of the crack from the surface of the welding wire toward the inner layer of the base metal, and in this example, the crack propagation depth is specified to be 20 μm or less. The upper limit of the propagation depth is specified because if an excessively deep crack exists, many of the metal compounds will fill these deep cracks, resulting in an uneven distribution of the metal compounds and, as a result, the arc may become unstable. A more preferable crack propagation depth is 15 μm or less.

[0036] The length between cracks is the length between cracks obtained by A / B, where B is the number of cracks present per predetermined length A μm in the longitudinal direction (wiredrawing direction) of the welding wire, and in this example, the length between cracks is specified to be 15 μm or less. The reason why an upper limit is specified for the length between cracks is that if the distance between cracks in the longitudinal direction is excessively long, the arc may become unstable. A more preferable length between cracks is 12 μm or less.

[0037] The welding wire of the present invention is mainly composed of Ti. In the present invention, "mainly composed of Ti" means that the component with the highest content in the wire is Ti, and preferably Ti accounts for 50 mass% or more. When a Ti alloy is used, various additive elements can be contained as minor components for the purpose of improving the strength or ductility of the resulting weld or thermal sprayed layer. Examples of usable additive elements and the range of desirable amounts are shown below.

[0038] (1) Al: 9% by mass or less Al stabilizes the α-phase, which is the low-temperature phase of Ti, and dissolves in the α-phase to strengthen it. However, if the Al content exceeds 9 mass%, a large amount of intermediate phases (intermetallic compounds) such as TiAl is formed, which leads to a decrease in toughness or ductility. On the other hand, to make the above effect significant, it is desirable to add 1 mass% or more, and more preferably, to add in the range of 2 to 8 mass%.

[0039] (2) At least one of N and O: 0.5% by mass or less in total N and O function as α-phase stabilizing and strengthening elements similar to Al, and the effect of adding O is particularly significant. However, if their total content exceeds 0.5 mass%, toughness or ductility is impaired. On the other hand, to make the above effect significant, it is desirable to add 0.03 mass% or more in total, and more desirably, a total addition range of 0.08 to 0.2 mass% is preferable. Note that the oxygen content here refers to the oxygen content of the inner layer portion other than the oxygen-enriched layer.

[0040] (3) One or more of V, Mo, Nb, and Ta: 45% by mass or less in total These elements are stabilizers of the β-phase, a high-temperature phase of Ti, and are effective in improving hot workability and increasing strength by improving heat treatability. However, these elements all have high specific gravity and high melting points, and excessive addition can impair the lightweight and high specific strength benefits inherent to Ti alloys, as well as raise the alloy melting point, making manufacturing by melting difficult. Therefore, the upper limit of the total addition amount is set at 45 mass%. On the other hand, to significantly enhance the above effects, it is desirable to add a total of 1 mass% or more. In addition, small amounts of Mo and Ta may be added to improve the corrosion resistance of the alloy.

[0041] (4) One or more of Cr, Fe, Ni, Mn, and Cu: 15% by mass or less in total These elements also have a β-phase stabilizing effect, and are effective in improving hot workability and increasing strength by improving heat treatability. However, all of these elements are prone to form intermediate phases with Ti (e.g., TiCr2, TiFe, Ti2Ni, TiMn, or Ti2Cu), and excessive addition can impair ductility and toughness, so the upper limit of the total addition amount is set at 15 mass%. On the other hand, to make the above effect significant, it is desirable to add a total of 0.5 mass% or more. In addition, a small amount of Ni may be added to improve the corrosion resistance of the alloy.

[0042] (5) At least one of Sn and Zr: 20% by mass or less in total These elements are known as neutral additives that strengthen both the α and β phases. However, excessive addition leads to saturation of the effect, so the upper limit of the total addition amount is set to 20 mass%. On the other hand, to make the above effect significant, it is desirable to add a total of 0.5 mass% or more.

[0043] (6)Si: 0.7% by mass or less It increases the creep resistance (creep rupture strength) of the alloy and has the effect of improving heat resistance. However, excessive addition can cause a decrease in creep rupture strength or ductility due to the formation of intermetallic compounds such as Ti5Si3, so the upper limit of the addition amount is set to 0.7 mass%. On the other hand, to make the above effect significant, it is desirable to add 0.03 mass% or more, and more desirably, to add in the range of 0.05 to 0.5 mass%.

[0044] (7) At least one of Pd and Ru: 0.5% by mass or less in total They have the effect of improving the corrosion resistance of alloys. However, since both are precious metals and expensive, the upper limit of the amount added is set at 0.5 mass %, taking into consideration the saturation of the effect. On the other hand, to make the above effect significant, it is desirable to add 0.02 mass % or more.

[0045] Specific examples of alloy compositions include the following (note that the composition is written with the main component element Ti at the beginning, and the subcomponent elements and their composition values, with the mass% unit omitted, connected by a hyphen (for example, a Ti-6 mass% Al-4 mass% V alloy is written as Ti-6Al-4V)).

[0046] [1] α type alloy: Ti-5Al-2.5Sn, Ti-5.5Al-3.5Sn-3Zr-1Nb-0.3Mo-0.3Si, Ti-2.5Cu

[0047] [2] Near-alpha alloy: Ti-6Al-2Sn-4Zr-2Mo-0.1Si, Ti-8Al-1Mo-1V, Ti-2.25Al-2Sn-4Zr-2Mo, Ti-6Al-2Sn-2Zr-2Mo-0.25Si, Ti-6Al-2 Nb-1Ta-0.8Mo, Ti-6Al-2Sn-1.5Zr-1Mo-0.35Bi-0.1Si, Ti-6Al-5Zr-0.5Mo-0.2Si, Ti-5Al-6Sn-2Zr-1Mo-0.25Si

[0048] [3]α+β type alloy: Ti-8Mn, Ti-3Al-2.5V, Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-7Al-4Mo, Ti-6Al-2Sn-4Zr-6Mo, Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.25Si, Ti-10V-2Fe-3Al, Ti-4Al-2Sn-4M o-0.2Si, Ti-4Al-4Sn-4Mo-0.2Si, Ti-2.25Al-11Sn-4Mo-0.2Si, Ti-5Al-2Zr-4Mo-4Cr, Ti-4.5Al-5Mo-1.5Cr, Ti-6Al-5Zr-4Mo-1Cu-0.2Si, Ti-5Al-2Cr-1Fe

[0049] [4] β-type alloy: Ti-13V-11Cr-3Al, Ti-8Mo-8V-2Fe-3Al, Ti-3Al-8V-6Cr-4Mo-4Zr, Ti-11.5Mo-6Zr-4.5Sn, Ti-11V-1 1Zr-2Al-2Sn, Ti-15Mo-5Zr, Ti-15Mo-5Zr-3Al, Ti-15V-3Cr-3Al-3Sn, Ti-22V-4Al, Ti-15V-6Cr-4Al

[0050] [5] Near-β alloy: Ti-10V-2Fe-3Al

[0051] [6] Corrosion-resistant alloy (can also be used for welding, but is particularly useful when forming a corrosion-resistant coating layer by thermal spraying) Ti-0.15Pd, Ti-0.3Mo-0.8Ni, Ti-5Ta

[0052] The welding wire of this embodiment is obtained by rolling an ingot of Ti or the above-mentioned Ti alloy into a coil, and then subjecting the rolled coil to an oxidation treatment to form an oxygen-enriched layer on the surface.

[0053] Specifically, in the welding wire of this embodiment, the oxygen-enriched layer can be formed by thermally oxidizing the Ti-based metal wire in an oxygen-containing atmosphere. The oxygen-containing atmosphere may be an oxygen-containing nitrogen atmosphere (including the air atmosphere), an oxygen-containing inert gas atmosphere, or a gas atmosphere containing an oxygen compound such as water vapor. In order to efficiently form an oxygen-enriched layer of sufficient thickness, an oxygen partial pressure of 5×10 3 ~15×10 3 It is preferable to use an oxygen-containing atmosphere of Pa. The treatment temperature is preferably set to, for example, 500 to 800°C.

[0054] At this stage, the coil wire in the thermal oxidation treatment state has no cracks on the surface consisting of the oxygen-enriched layer. Next, this coil wire is subjected to cold wire drawing to produce a wire of a predetermined diameter. At this time, cracks penetrate from the surface of the wire to the inside, and these cracks form in the surface layer of the wire.

[0055] The welding wire of the present embodiment is formed by filling the surface cracks with a metal compound containing at least one metal selected from alkali metals and alkaline earth metals. In this way, the welding wire of the present embodiment having an oxygen-enriched layer and a metal compound is manufactured.

[0056] The method of filling the cracks with the metal compounds is described below. For example, the metal compounds are mixed with a lubricant, and the lubricant is used during the cold wiredrawing process to generate surface cracks, which are then filled with the lubricant, resulting in the metal compounds being filled into the surface cracks. The amount of the metal compound filled can be adjusted, for example, by changing the mixing ratio of the metal compound to the lubricant, by changing the thickness of the oxygen-enriched layer, or by changing the area reduction rate during wire drawing.

[0057] Generally, lubricants are mixtures of calcium hydroxide, calcium stearate, etc., but if a carbonate of a specific metal is mixed with such a lubricant, the metal will be compounded with calcium and fill the surface cracks. Therefore, when filling a compound of a metal other than calcium, the wire rod should be washed after wiredrawing to remove the lubricant from the surface cracks, and then the wire rod should be passed through a wiredrawing machine with the specific metal compound and with a 0% reduction in area. Furthermore, when the lubricant itself contains the desired alkali metal or alkaline earth metal, the lubricant may be used for wire drawing. [Example]

[0058] Next, examples of the present invention will be described below. Here, a total of 31 types of welding wires for examples and comparative examples shown in Table 1 below were manufactured and various evaluations were carried out.

[0059] [Table 1]

[0060] 1. Manufacturing of welding wire A wire made of Ti or a Ti alloy was heat-treated in the atmosphere to form an oxide-enriched layer (embrittled phase) on its surface. In each of the examples and comparative examples, the temperature and / or time of the heat treatment process were changed to change the thickness and oxygen concentration of the oxide-enriched layer formed on the surface, thereby changing the form of cracks that would occur during the subsequent wiredrawing process. On the other hand, carbonate powders of alkali metals or alkaline earth metals shown in Table 1 were prepared. In addition, Koshin (a mixture of calcium hydroxide and calcium stearate, a trade name of Kyoeisha Chemical Co., Ltd.) was prepared as a lubricant. Using these carbonate powders and lubricants, cold wire drawing was performed to produce welding wires with a wire diameter (Dw) of 1.0 mm.

[0061] When a metal other than calcium was allowed to coexist alone with the oxygen-enriched layer, the drawn wire was first washed with Light Clean (detergent) to remove the calcium carbonate, and then the wire was passed through a wire drawing machine with a 0% area reduction rate and carbonate powder of the specified metal was used to fill the surface cracks. In Comparative Examples 2 and 3, which did not contain alkali metals or alkaline earth metals, the drawn wire was left in the state it had been washed in the same way.

[0062] 2. Evaluation For each of the obtained welding wires, the contents (mass%) of alkali metals and alkaline earth metals, the presence or absence of an oxygen-enriched layer, the crack propagation depth, the crack area ratio, the length between cracks, the arc stability, and the long-term arc stability were evaluated according to the following specifications.

[0063] <Alkali metal and alkaline earth metal content> The content (mass %) was evaluated by inductively coupled plasma emission spectroscopy.

[0064] <Presence or absence of oxygen-enriched layer> (1) The cross section of the wire is mirror-polished, and the polished surface is analyzed for the oxygen concentration distribution using EPMA. When the oxygen concentration at the center of the cross section is set to 1, the region where the oxygen concentration is 1.2 or more (1.2 times or more of the oxygen concentration at the center of the cross section) is defined as the oxygen-enriched layer. When the thickness of the oxygen-enriched layer is Tw and the diameter of the welding wire is Dw, the value of Tw / Dw is 0.3 × 10 -3 ~1×10 -1 (2) Furthermore, the average value of the oxygen concentration in the oxygen-enriched layer (measured at five measurement points) was calculated, and when this was taken as the average oxygen concentration in the oxygen-enriched layer, the average oxygen concentration was 1 mass% or more. If both of these requirements were met, the sample was deemed to have an "oxygen-enriched layer present," and if at least one of the requirements was not met, the sample was deemed to have no "oxygen-enriched layer."

[0065] <Crack propagation depth> The welding wire was cut parallel to the longitudinal direction, and the cut surface was mirror-finished. Ten randomly selected points on the cross section of the wire surface were then observed using a scanning electron microscope (SEM). The length of the deepest crack among the observed cracks was taken as the crack propagation depth. The magnification during observation was 2000 times, and the observation area per field of view was 2530 μm. 2 As an example, a scanning electron microscope photograph of a cross section of a surface layer portion of the welding wire according to Example 24 is shown in FIG.

[0066] <Crack area ratio> Ten randomly selected points on the wire surface of the welding wire were observed using an SEM. The total area of ​​cracks in the resulting 10 observation images (secondary electron images obtained from SEM observation) was calculated using WinROF (manufactured by Mitani Shoji Co., Ltd.). The total area of ​​cracks was then calculated by multiplying the total area of ​​the field of view (10 points) by the area per field of view (64550 μm 2 The area ratio of cracks was calculated by dividing the area ratio by the area ratio of cracks. The magnification during observation was 400 times. As an example, Fig. 3 shows a scanning electron microscope photograph of the surface of the welding wire according to Example 24.

[0067] <Length between cracks> Ten randomly selected points on the wire surface of the welding wire were observed using an SEM. A line equivalent to 150 μm in the wiredrawing direction was added to the center of each of the 10 observation images, and the total number of cracks intersecting with the added line was calculated (for example, in the observation image shown in Figure 4, 18 cracks intersect with the added white line). and Measurement length (10 locations x 150 μm) of Calculated total number of cracks The value obtained by dividing by 1 was taken as the length between cracks in the longitudinal direction of the welding wire. The magnification during observation was 400 times.

[0068] <Arc stability> Bead-on-plate welding was performed using each of the manufactured wires. MIG welding was performed under the conditions shown in Table 2 below. The weld length was 100 mm. The material to be welded in the bead-on-plate welding was a pure titanium plate of type 2 specified in JIS: H4600, measuring 1.5 mm thick, 50 mm wide, and 550 mm long. Arc stability was evaluated after welding was completed by measuring the amount of spatter deposits with a diameter of 1 mm or more per 100 mm of weld length. 0 to 1 spatter of 1 mm or more in diameter was marked "Good," and 2 or more spatters were marked "Poor."

[0069] <Long-term arc stability> Bead-on-plate welding was performed using each of the manufactured wires. MIG welding was performed three times under the conditions shown in Table 2 below. The weld length per weld was 500 mm. The material to be welded in the bead-on-plate welding was a pure titanium plate specified in JIS: H4600, measuring 1.5 mm thick, 50 mm wide, and 550 mm long. Long-term arc stability was evaluated based on the amount of spatter deposits with a diameter of 1 mm or more that occurred during three MIG welding runs. 0 to 1 spatter of 1 mm or more was marked "Good," 2 to 4 spatters were marked "Good," and 5 or more spatters were marked "Poor."

[0070] [Table 2]

[0071] The above evaluation results are all shown in Table 1. The evaluation results in Table 1 reveal the following. Comparative Example 1 is an example in which the area ratio of cracks exceeds the upper limit of 25% according to the present invention. In this Comparative Example 1, the arc stability was evaluated as "good", but the long-term arc stability was evaluated as "poor".

[0072] Comparative Example 2 did not contain a specified metal for enhancing arc stability, and was evaluated as "poor" for both arc stability and long-term arc stability. Comparative Example 3 is an example that does not contain a predetermined metal for improving arc stability and does not have a predetermined oxide-enriched layer. Similar to Comparative Example 2, Comparative Example 3 was also evaluated as "poor" for both arc stability and long-term arc stability.

[0073] In Comparative Example 4, the crack area ratio and the length between cracks were outside the ranges specified in the present invention, and the arc stability was evaluated as "good", but the long-term arc stability was evaluated as "poor". Comparative Example 5 is an example in which the area ratio of cracks exceeds the upper limit of 25% according to the present invention. In Comparative Example 5, the arc stability was evaluated as "good" as in Comparative Example 1, but the long-term arc stability was evaluated as "poor."

[0074] In Comparative Example 6, the crack propagation depth and crack area ratio were outside the ranges specified in the present invention, and the arc stability was evaluated as "good", but the long-term arc stability was evaluated as "poor". Comparative Example 7 is an example in which the Ca content exceeded the upper limit of 0.050% according to the present invention, and the arc stability and long-term arc stability were both evaluated as "poor."

[0075] As described above, in each of the comparative examples, at least the evaluation of long-term arc stability was unacceptable ("x").

[0076] In contrast, Examples 1 to 24, which had an oxygen-enriched layer and whose alkali metal and alkaline earth metal contents and crack area ratios were within the ranges specified in the present invention, were evaluated as passing ("Good" or "Good") in terms of long-term arc stability. Looking more specifically, in examples where the crack area ratio, crack propagation depth, and distance between cracks were all within the preferred ranges, i.e., examples where the crack area ratio was 7 to 20%, the crack propagation depth was 15 μm or less, and the distance between cracks was 12 μm or less (Examples 1 to 3, 5, 8, 16 to 20, and 24), the long-term arc stability was evaluated as "Good," and particularly good results were obtained.

[0077] Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiments and examples. In the above-described embodiments, the case where the wire for forming molten metal is used as a welding wire has been described in detail. However, since the wire for forming molten metal of the present invention also has arc stability and droplet transfer stability, it can also be used as a wire for thermal spraying in an arc thermal spraying method. Various modifications are possible within the scope of the present invention.

Claims

1. A wire for forming a molten metal made of Ti or a Ti alloy having a Ti content of 50 mass% or more, A surface analysis of the oxygen concentration of a mirror-polished cross section of the wire by EPMA is performed, and when the oxygen concentration at the center of the wire is taken as 1, an oxygen-enriched layer is formed on the surface of the wire such that the oxygen concentration is 1.2 or more, and the wire contains a metal compound having at least one metal selected from the group consisting of alkali metals and alkaline earth metals, such that the alkali metal and / or alkaline earth metal accounts for 0.002 to 0.050 mass% in total relative to the total mass of the wire; When the thickness of the oxygen-enriched layer is Tw and the wire diameter of the wire is Dw, the value of Tw / Dw is 0.3×10 −3 to 1×10 −1 , and the average oxygen concentration of the oxygen-enriched layer is 1 mass% or more, Cracks are formed on the surface into which the metal compound is filled, the area ratio of the cracks is 4 to 25%, the propagation depth of the cracks is 20 μm or less, and when the number of cracks present per predetermined length A μm in the longitudinal direction of the wire is B, the length between cracks obtained by A / B is 15 μm or less.

2. A wire for forming molten metal as described in claim 1, wherein the area ratio of the cracks is 7 to 20%, the propagation depth of the cracks is 15 μm or less, and the length between the cracks is 12 μm or less.

3. The Ti alloy is Al: 9% by mass or less One or more of V, Mo, Nb, and Ta: 45% by mass or less in total The wire for forming molten metal according to claim 1 or claim 2, comprising:

4. A wire for forming molten metal described in any one of claims 1 to 3, wherein the boiling points of the alkali metals and alkaline earth metals contained in the metal compounds are 2000°C or less.

5. The wire for forming molten metal according to any one of claims 1 to 4, wherein the metal compound is a metal compound containing Ca.

6. The wire for forming molten metal according to any one of claims 1 to 5, wherein the average oxygen concentration of the oxygen-enriched layer is 1 to 40 mass%.

7. A method for producing a welded product, comprising using the wire rod for forming molten metal according to any one of claims 1 to 6 to form a welded part having a total length of 300 mm or more by MIG welding.

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