CA2521820C - Welding wire - Google Patents

Abstract

The present invention provides a welding wire including Ti or a Ti alloy, wherein the welding wire has: an oxygen enriched layer on a surface thereof; and a metal compound having at least one metal selected from the group consisting of alkali metals and alkaline earth metals.

Description

WELDING WIRE
FXE~D 0~' THE TNVENTION
The present invention relates to a welding wire for use in the MIG welding of Ti-based material. More particularly, the present invention relates to a welding wire allowing the compatibility between stable arc and stable droplet transfer, and as a result, enabling the formation of the excellent bead shape. Further, when a welding wire of the present invention is used in a Ti thermal spraying, the stability of arc can also be achieved and then an excellent coating layer of the thermal spray can be obtained.
BACKGROUND OF THE INVENTTON
As for the welding of a member made of Ti or a Ti alloy, MIG welding (Metal Inert Gas Welding) that is more excellent in welding efficiency has received attention in place of TIG welding (Tungsten Inert Gas Welding). The MTG
welding is allowed to proceed in accordance with the following embodiment. Tn a condition that a welding wire made of Ti or a Ti alloy fed from a wire feeder and a base metal to be welded are surrounded by a shielding gas, an arc is generated between both. The droplets of the welding wire generated at this step are transferred and landed on the base metal to be welded, thereby to continuously farm beads.
The things that matter at this step are:
stabilization of the generated arc; and stable transfer and landing of droplets from the welding wire on the weld zone.
When the generated arc is not stable, or droplets axe not transferred to the weld zone with stability, for example, as shown in Fig. 7, constriction occurs in the formed bead, and the uniformly overlying state is not achieved. It is difficult to say that the bead in such a shape ensures the reliability of the strength characteristics at the weld zone.
incidentally, Ti is an active metal. Therefore, when an oxygen-containing gas is used as a shielding gas, not only the bead surface is oxidized, but also the reduction of ductility of the weld zone is caused. Such being the case, in general, a high purity inert gas such as a pure ~x gas is used as a shielding gas. However, the following fact is also known: when oxygen is contained in the shielding gas, the cathode spot upon arG generation is fixed on the base metal to be welded under the welding wire; as a result, arc is stabilized (see, Reference 1) This means as follows: oxygen is supplied to the field of the generated arc, so that the cathode spot is stabilized, and as a result, the generated arc is also stabilized. Based on such a fact, the following welding wires of Ti materials have been proposed (see, Reference 2y.
This welding wire is a welding wire configurEd as follows:
on the surface layer portion of a welding wire made of Ti or a Ti allay, an oxygen enriched layer with a higher oxygen concentration than that of the inward layer portion of the welding wire is formed. and the thickness of the oxygen enriched layer is larger than that of the very thin natural oxide film present on the surface of the welding wire.
This welding wire is manufactured in the following manner. fox example, a Ti material of a preferable composition is once rolled, and then, heat treated in an oxygen-containing atmosphere to foam a Ti oxide layer (oxygen enriched layer) thicker than the natural oxide film on the surface layEr portion. Then, the resulting welding wire is cold rolled to a prescribed wirE diameter. Then, this welding wire is used as a welding wire for MIG welding.
In consequence, oxygen is fed tv the field of the generated arc from the oxygen enriched layer even when an oxygen-containing gas is not used as a shielding gas. Therefore, the c~thvde spot is stabilized. As a result, a bead in a favorable shape is formed.

jReference 1] Proceedings of National Meeting of Japan Welding Society 65 (1999), 276 [Reference 2] J~ 2003-326389 A
However, according to the subsequent study on the welding wire of Reference 2, it has been proved that, when MIA welding is carried out with this welding wire, the following phenomenon occurs.
First, the cathode spot of the generated arc is situated at the position of the base metal to be welded under the welding wire as deduced, and stabilized without fluctuating. However, at the tip of the welding wire, there are generated two types of arcs: the concentrated arc in such a shape as shown in dig. $ (which is hereinafter referred to as a concentrated arc); and the diffused arc in such a shape as shown in Fig. 9 (which is hereinafter referred to as a diffused arc). The former arc has been Stabilized, and the latter arc has been unstable.
Then, when the former concentrated arc is generated, the tip of the welding wire is invariably released in the form of droplets, which transfer to the weld zone. Thus, the shape / outward appearance of the formed bead become favorable. However, when the latter diffused arc is generated, droplets may not be released from the welding wire tip. Even when droplets are released, the length of time required for the release is long. Therefore, the transfer time of the droplets to the weld zone is also long.
~s a result, the droplets cannot transfer to the weld zone during one pulsed current flow period, so that the next one pulsed current flow is carried out prior to the completion of transfer of the droplet.
Far this reason, the overlying state of the formed bead becomes ununiform, and constriction or the like may occur partially along the direction of welding. Further, a large amount of spatters are generated, resulting in the poor outward appearance of the bead. Such a phenomenon is conceivably generated due to the fact that the tip of the welding wire, i.e., the anode spot has been unstabilized.
An object of the invention is to provide a welding wire which solves such a problem, and whereby both of the cathode spot and the anode spot upon arc discharge are stabilized, and hence the arc is stabilized, and the transfer of droplets is also stabilized.
SUMMARY OF THE INVENTION
The present inventors have made eager investigation to examine the problem. As a result, it has been found that the foregoing objects Gan be achieved by the following welding wire. With this finding, the pxesent invention is accomplished.
The present invention is mainly directed to the following items:
(~.) ~ welding wire cpmpris~.ng Ti or a Ti alloy, wherein the welding wire has: an oxygen enriched layer on a surface thereof; and a metal compound ha~riz~g at least one metal selected from the group consisting of alkali metals and alkaline earth metals.
(2) The welding wire according to item (1), wherein the content of the metal compound is x.002 to 0.050 by weight based on the total weight of the welding wire.
(3) The welding wire according to item (1), wherein the welding wire has cracks an the surface, and the metal compound is present in the cracks.
(4) The welding wire according to item (1), wherein the boiling point of the metal is 2000°C or less.

(5) The welding wire according to item (1), wherein the metal compound is a metal compound containing Ca.

(6) The welding wire according to item (1), wherein the value of Tw/Dw is 0.3 x 10"3 to 1 x 10-1, wherein Tw represents the thickness of the oxygen enriched layer, and Dw represents the wire diameter of the welding wire, and wherein the average oxygen concentration of the oxygen enriched layer is not less than 1~ by weight.

(7) The welding wire accoxd~.ng to item (6), wherein the average oxygen concentration of the oxygen enriched layer is 1 to 40~ by weight_ (8) The welding wire according to item (1), wherein the surface roughness of the welding wire is 10 ~m or less in terms of the surface roughness expressed as Ry specified according to JIS B0601.

(9) The welding wire acaarding to item (6), wherein the ~ralue of Tw/Dw is 1 x 10'3 to 50 x IO-3, wherein Tw represents the thickness of the oxygen enriched layer, and Dw represents the wire diameter of the welding wire, and wherein the average oxygen concentration of the oxygen enriched layer is 1 to 30b by weight.
$RxEF DESCRIPTION OF THE DRAWINGS
Fig_1 is a micraphotoqraph of a surface of a welding wire of the present invention.
Fig. 2 is a cross-sectional microphotograph of a of a surface layex portion of a welding wire of the invention.
Fig. 3 is a microphotograph of a surface layer portion before wire drawing during manufacturing of a welding wire of the invention.
Fig. 4 is a correlation diagram between the ionization voltage and the boiling paint of each metal.

Fig. 5 is an explanatory diagram of the concentrated arc defined in the invention.
Fig. 6 is a photograph showing a bead formed by the use of a welding wixe of Experimental Example 6.
Fig. 7 is a photograph showing a bead in a defective shape.
Fig. 8 is a photograph showing an example of the concentrated arc.
Fig. 9 is a photograph showing an example of a diffused arc.

The foregoing effects are achieved by a welding wire comprising Ti or a Ti alloy, wherein the welding wire has:
an axygan enriched layer an a surface thereof; and a metal compound having at least one metal selected, from the group consisting of alkali metals and alkaline earth metals.
In the present invention, the term "welding wire"
has a meaning including a wire rod for thermal spraying (thermal spraying wire) as well as a wire rod for welding.
First, the surface micraphatograph and the cross sectional microphotograph of the surface layer portion of the welding wire of the invention are shown as Figs. 1 and 2, respectively. As apparent from Fig. 1, this welding wire is formed such that the surface is covered with an oxygen enriched layer, arid fine surface cracks generated in a wire drawing step described later are distributed over the surface of the entire welding wire. The foregoing surface cracks are, as shown in Pig. 2, formed as cracks with a depth from the oxygen enriched layer on the welding wire surface toward the inward layer portion of the base material. Then, in the cracks, the compound described later, including an alkali metal or an alkaline earth metal is packed.
In the invention, the oxygen enriched layer, and the average oxygen concentration thereof are defined as follows.
Namely, the cross section of the welding wire is mirror polished, and is subjected to area analysis by EPMA
(Electron Probe Micro Analysis) as to the oxygen concentration distribution. The oxygen concentration at the central part of the welding wire obtained by the analysis is taken as 1, and the region having an oxygen concentration of 1.2 or more (x. e., having an oxygen concentration of not less than i.2 times as large as that of the central part) is taken as an oxygen enriched layer.
~'urther, the average value (5 measuring points) of the oxygen concentration in a region with the oxygen concentration of 1.2 or more is taken as the average oxygen concentration of the oxygen enriched layer. Tncidentally, when the oxygen concentration varies along the circumferential direction of the welding wire cross section, concentration measuring circles are set at various position along the radius of the cross section, arid the oxygen concentrations axe averaged along the respective concentration measuring circles, thereby to determine the oxygen concentration distribution along the radius of the cross section, averaged along the cireumferential direction.
Then, the region having an oxygen concentration of not less than 1.2 times as large as that of the central part in the oxygen concentration distribution along the radius of the cross section is taken as the oxygen enriched layer.
The thickness of the oxygen enriched layer of the invention is preferably larger than that of the natural oxide film generated on the welding wire surface. The thickness of the natural oxide film is generally 40 to 100 nm.
Further, the oxygen enriched layer of the invention preferably satisfies the following ~celationship.
Namely, it is preferable that the value of Tw/Dw is 0.3 x 10-3 to 1 x 10°1, where Tw denotes the thickness of the oxygen enriched layer, and Dw denotes the wire diameter of the welding wire, and that the average oxygen concentration of the oxygen enriched layer is not less than fro by weight. By forming the oxygen enriched layer having such a thickness and average oxygen concentration, it is possible to largely improve the feedability of the welding wire via a conduit tube of a wire feeder. Further, the stability of the arc for carrying out axc welding or axc thermal spraying also becomes favorable.
When the Tw/Dw is less than 0.3 x 10-3 (Tw is 0.03 ofi Dw), ox the average oxygen concentration of the oxygen enriched layer is less than 1$ by weight, the feedability improving effect becomes insufficient. F~.irther, the arc becomes more likely to be unstabilized, resulting in a disadvantage for forming a uniform welding bead or spray deposit. When the Tw/Dw is 1 x 10-3 (Tw is 10$ of Dw) or more, a very lung time is required for the formation treatment of the oxygen enriched layer, and the effects are poor for the difficulty of the formation. When it is used for welding or the like, detrimental effects such as the reduction of the welded joint strength of the welding structure may be xather caused.
The upper limit value of the average oxygen concentration of the oxygen enriched layer is described below. The average oxygen concentration of the oxygen enriched layer becomes maximum when the entire oxygen enriched layer is farmed of titanium oxide. The value becomes conceivably equal to the oxygen content ratio calculated from the molecular formula of the oxide formed.
m For examp7.e, when the oxide to be formed is Ti02, the upper limit value of the average oxygen concentration calculated from the stoiohiometric oxygen content is 40.06ro by weight (calculated assuming that the atomic weight of Ti is 47.88 and the atomic weight of oxygen is 16.0). AlternativeJ.y, a Ti oxide haring a still higher oxygen stoichiometric ratio of oxygen than that of Ti02 may be formed. For example, when Tiz05 is formed, the upper lim~.t value of the average oxygen conGentratzon is 45.52 by weight. Therefore, it is generally unconceivable that the maximum value of the average oxygen concentration of the oxygen enriched layer exceeds 45.52 by weight. As a result, in the invention, it can be said that the maximum value of the average oxygen concentration of the oxygen enriched layer is 45.52% by weight. However, when the value of the average oxygen concentration of the oxygen enriched layer is set to 45.52$
by weight, adverse effects such as the deterioration of ductility of a welded joint may occur. Therefore, the average oxygen concentration of the oxygen enriched layer is preferably not zaore than 40~ by weight.
In order to make the arc stabilizing effECt more remarkable, the ratio 7.'w/Dw of the thickness of the oxygen enriched J.ayer Tw to the wire diameter Dw is preferably adausted in the range of 1 x 10-3 to 1 x 10-1. Particularly, when the oxygen diffused layer is formed in addition to the titanium oxide layer of the outermost surface layer portion (with a thickness equal to the thickness of about 40 to 100 nm of the natural oxide film, or larger), the thickness of the oxygen enriched layer increases by that of the oxygen diffused layer. Therefore, the possibility becomes higher that the Tw/~w falls within the foregoing preferable range.
The preferable upper limits of the xw/Dw value and the average oxygen concentration of the oxygen enriched layer vary between the case that the welding wire of the present invention is used as a wire rod for welding and the case that the welding wire is used as a wire rod for thermal spraying. When the welding wire of the present invention is used as a wire rod fox thermal spraying, the requirement in terms of strength may not be so stringent fox the spray deposzt as for the welded joint portion in many cases (of course there are some exceptions). For example, air may be used as a spraying medium tar molten metal. xn such a case. the oxygen concentration in the layer also inevitably increases because the molten Ti metal is deposited as a spray deposit while reacting with oxygen in the air. This is, however, sufficient for practical use, when high strength is not particularly required.
Furthermore, when the welding wire of the present invention is used as a wire rod for thermal spraying, in view of the fact that oxidation eventually proceeds in molten state, even an increase in the value of xw/pw and the average oxygen concentration of the oxygen enriched .layer to the upper limit values does not particularly cause any hindrance.
On the other hand, when used as a wire rod for welding, an excessively large thickness of the oxygen enriched layer or excessively high average oxygen concentration thereof may sometimes unfavorably cause degradation of the strength of a welded aoint of the resulting welding structure or the strength of the spray deposzt. Therefore, when used as a wire rod for welding, it is further preferable to restrict the Tw/Dw from 1.0 x 10-3 to 50 x 10-3 (Tw is 1 tv 5~ of I~w), and the average oxygen concentration of the oxygen enriched layer froze 1 to 30$ by we~.ght. When used as a wire rod for thermal spxaying, further when a high strength spray deposit is desired to be formed by uszx~g an inert gas such as argon as a spraying medium, and minimizing the oxidation, the fw/17w and the average oxygen concentration. may be preferably restricted within the same ranges.
The weld~.ng wire of the present invention contains Ti as a main component. Tn the invention, the woxding "containing Ti as a main component" means that the component having the highest content in the welding wire is Ti. Ti. is pxefexably contained in an amount of not less than 50b by weight. then a Ti alloy is adopted, aiming at the improvements of the strength or the ductility of the resulting weld zone or the spray deposit, and the like, various additive elements may be contained as sub-components. Examples of the adoptable additive element$
and the preferable xanges of amounts of these to be added are described below.
(1) Al: not more than 9% by weight A1 has functions of stabilizing the a phase which is a low temperature phase of Ti, and being solid solved in the a phase and strengthening it. However, when the content thereof exceeds 9% by weight, an inte~ctediate phase (intermetallic compound) of Ti3Al or the like is formed in a large amount, which leads to the inhibition of the toughness and the ductility. On the other hand, in order to make the foregoing effect remarkable, A1 is preferably added in an amount of nat less than 1% by weight, and more preferably added within a range of from 2 to 8% by weight.
(2) At least either of N and o: not more than 0.5% by weight in total N and O also function as the same ac phase stabilizing and strengthening elements as with A1.
particularly, the effect of addition of O is remarkable.
However, a total content of these exceeding 0.5% by weight leads to the inhibition of the toughness or the ductility.

On the other hand, in order to make the foregoing effect remarkable, the$e axe preferably added in a total amount of not leas than 0.03 by weight, and more preferably added within a range of from 0.08 to 0.2v by weight.
Incidentally, the oxygen content herein denotes the oxygen content of the inward layer portion other than the oxxgen enriched layer in any case.
(3y One, or two or more of V, Mo, Nb, and Ta: not more than 45b by weight in total All of these elements are stabilizing elements of the ~ phase which is a Ti high temperature phase, and effective in achieving the improvement of the hat workability and the higher strength through the improvement of the heat treatability. However, all of these elements are high in specific gravity and high in melting point.
Thus, excessive addition thereof nat only leads to the impairment of the effects of the light weight and the high specific strength, specific to Ti alloys. but also causes a difficulty in manufacturing by melting due to the increase in the alloy melting point. For this reason, the upper limit of the total amount of these to be added is set at 45~ by weight. On the other hand, in order to make the effect remarkable, these axe preferably added in a total amount of not less than 1~ by weight. Mo or Ta may be added in a small amount for improving the corrosion resistance of the alloy.
(4) One, or two or more of Cr, Fe, Ni, Mn, and Cu: not more than 15v by weight iz~ total These elements also have an effect of stabilizing the Ji phase, and are effective in achieving the improvement of the hot workability and the higher strength through the improvement of the heat treatability. However, any of these tends to form an intermediate phase (e. g., TiCrz, TiFe, Tiz Ni, TiMn, or Ti2Cu) between it and Ti, and excESSive addition thereof leads to degraded ductility and toughness. Therefore, the upper limit of the total amount of these to be added is set at 15ro by weight. On the other hand, in order to make the effect remarkable, these are preferably added in a total. amount of not ~.ess than 0.5~ by weight. Ni may be added in a small amount far improving the corrosion resistance of the alloy.
(5) At least either of Sn and Zr: not more than 20~ by weight in total These elements are known as neutral type additive elements fox strengthening both of the oc phase and the J3 phase. However, excessive addition thereof results xn saturation of the effect, so that the upper limit of the total amount of these to be added is set at 20~ by weight.
On the other hand, in order to make the effect remarkab~.e, these are preferably added in a total amount of not 3.ess 1?

than 0.5% by weight.
(6) Si: not more than 0,7$ by weight Si has effects of enhancing the creep resistance (creep rupture strength) of the alloy, and improving the heat resistance. However, an excessive addition thereof conversely causes the reduction of the creep rupture strength or the ductility due to the formation of an intermetallic compound such as Ti5Si3. Therefore, the upper limit of the amount of Si to be added is set at 0.7$ by weight. On the other hand, in order to make the effect remarkable, Si is preferably added in axe amount of not less than 0.03$ by weight, and more preferably added in an amount in the range of O.OS to 0.5$ by weight.
(7) At least either of Pd and Btu: not more than 0.5v by weight xn total These elements have an effect of improving the corrosion resistance of the alloy. However, the upper limit of the amount of these to be added is set at 0.5~ by weight in ~riew of the saturation of the effect, and the like, because all are noble metals and thus expensive. 0n the other hand, in order to make the effect remarkable, these are preferably added in an amount of not less than 0.02 key weight.
Specific examples of the alloy composition may incJ.ude the following ones (incidentally, tk~e composition is expressed as being headed by Ti, which is the main Component, followed by sub-components as being connected with hyphens together with the Composition numerals while omitting the unit of ~ Y~y weight ifor example, Ti-6b by weight A1-4~ by weight V alloy is simply expressed as Ti-6.F1.1-4V) ) , [1] a. type alloys:
Ti.-5A1-2.5Sn, Ti-5.5A1-3.5Sn-3Zr-1Nb-0.3Mo-0.3Si, and Ti-2.SCu [2] Near a type alloys:
Ti-6A1-2Sn-4Zr-2Mo-O.lSi, Ti-8A1-1Mo-1V, Ti-2.25A1-2Sn-42r-2Mo, Ti-6A1-2Sn-2Zr-2Mo-0.25Si, Ti-6A1-2Nb-1Ta-0.8Mo, Ti-6A1-25n-l.SZr-1Mo-0.35Hi~0_15i, xi-6A1-5Zr-0.5Mo-0.2Sz, and xi-5A1-6Sn-2Zr~lMo-0.25Si [ 3 ] a ~ (3-- type alloys Ti-8Mn, Ti-3A1-2.5V, Ti-6A1-9V, Ti-6A1-6V-2Sn, Ti~
7A1-4Mo, Ti-6A1-2Sn-~Zr--6Mo, Ti-6A.J.-2Sn-2Zr-2Mo-2Cr-0.25Si, Ti--lOV-2Fe-3A1, Ti-QAl-2Sn-4Mo-0.2Si, Ti-9A1-45n-4Mo-0.2Si, Ti-2.25A1-llSn-4Mo-0.2Si, Ti-5A1-2Zr-4Mo-4Cr, Ti-4.5,A1-SMo, l.SCr, Ti-6A1-5Zr-4Mo-1Cu-0.2Si, and Ti-5A1-2Cr-1Fe [4] J3 type alloys:
Ti-13V-llCr-3R1, Ti-8Mo-8V-2Fe-3A1, Ti-3A1--8V~6Cr-AMo-BZr, Ti-11.5MO-6Zr--4.5Sn, x~.-11V-l~,zr-2A1-2Sn, Ti-l5Mo-5Zr, Ti~l5Mo-5Zr-3A1, Ti-15V-3Cr-3A7.,3Sn, Ti-22V-4A1, and xi-J.5V-6Cr-9A1 (5] Near ~i type alloy:
Ti--10V-2Fe-3A1 (6] Corrosion resistant alloys (while available for welding, they are particularly useful when a corrosion resistant coating layer is desired to be formed by thermal spraying):
Ti-0,15pd, Ti-0.3Mo-0.$131, and Ti-5Ta The welding wire of the invention can be obtained by once rolling Ti or the Ti alloy ingot into a coil, then subjecting the rolled coil to an oxidation treatment, and thereby forming an oxygen enriched layer on the surface.
Specifically, in the welding wire of the invention, the oxygen enriched layer can be formed by subjecting a metal welding wire to a thermal. oxidation treatment in an oxygen-containing atmosphere. The usable oxygen-containing atmosphere is a gas atmosphere containing an oxygen compound such as an oxygen-containing nitrogen atmosphere (including an air atmospherey, or an oxygen-containing inert gas atmosphere, or in addition, water vapor. For forming the oxygen enriched layer having a necessary and sufficient thickness, it is preferable to use an oxygen-containing atmosphere having a partial pressure of oxygen of 5 x 103 to 15 x 10'3 Pa. Further, the treatment temperature is preferably set at,.for example, 500 to 800°C.
On the other hand, other than the thermal oxidation treatment, there is an adoptable method in which titanium oxide grains are embedded in the welding wire surface, or a titanium oxide layer is formed by a Vapor phase deposition process such as vapor deposition or sputtering, resulting in an oxygen enriched layer. Alternatively, the titanium oxide layer may be formed by a known sol~gel process. xhen, when the titanium oxide layer is formed according to any of these methods, it ~.s further preferable that the oxygen diffused layer is fiormed by a diffusion heat treatment.
Fig. 3 shows the cross sectional microphotograph of the a coil welding wire in the foregoing state. As apparent :~rvm Fig. 3, no crack is generated in the surface made of the oxygen enriched layer at this stage.
Subsequently, the coil welding wixe is subjected to a cold wire drawing processing, resulting in a welding wire with a preferable wire diameter. At this step, depending upon the magnitude of the surface reduction ratio, in the surface of the weld~.ng wixe, cracks are formed from the surface toward the inside of the welding wire as shown in Fig. 1, which are generated in the farm of a large number of surface cracks in the surface layer portion of the welding wire.
Incidentally, in the invention, the surface reduction ratio is defz.ned as the following equation:
Surface Reduction Ratio (%) (Cross sectional area of welding wire before wire drawing - Cross sectional area of welding wire after wire drawing) I (Cross sectional area of welding wire before wire drawing) x 100 Then, finally, in the surface cracks, a metal.
compound having at least one metal selected from alkali metals and alkal~.z~e earth metals is packed. thereby to form the welding wixe of the in~rention shown in Fig. 2.
In th~.s manner, the welding wixe of the invention having an oxygen enriched layer and a metal compound is manufactured.
As these metal compounds, metal. compounds such as carbonates are preferred. In particular, sodium carbpnate, potassium carbonate, and calcium carbonate are preferred.
The method for packing a metal compound in the cracks is described below. As the packing method, for example, mention may be made of the following method: any of these metal compounds is m~.xed in a lubricant, and wire drawing is carried out by the use of the lubricant for the cold wire drawing; as a result, surface cracks are generated, and at the same time, the lubricant is packed therein; rasultingxy, a metal compound is packed in the surface cracks.
The amount of the metal compound to be packed may be adjusted by, for example, changing the mixing ratio of the metal compound with the lubricant, changing the thickness of the oxygen enriched layer, or changing the surface reduction ratio in wire drawing.
Incidentally, the one including a compound such as Calcium hydroxide and calcium stearate is gezzerally used as the lubricant. To such a lubricant, for example, a carbonate of a prescribed metal i$ mixed, so that the whole of the metal is packed in the surface cracks with being combined with ca~.czwm.
Therefore, when a compound of a metal other than calcium is packed, the following procedure may be adopted.
The welding wire is once washed after wire drawing, thereby to remove the lubricant from the surface cracks. Then, by the use of a prescribed metal compound, the welding wire is passed through a wire drawing machine with a surface reduction xat~.o of When preferable alkali metals or alkaline earth metals are contained in the lubricant itself, wire drawing may be carried out by the use of the lubricant.
The weJ.ding wire of the i.zwention zs useful as a wire rod fox welding used in MzG welding of a Ti material.
Further, the welding wire of the invention also has the arc stability and the droplet transfer stability. Therefore, it can also be used as a wire rod for thermal spraying in an arc thermal spraying z~ethod.
Tn the invention, examples of the alkali, metals include Li, Na, K, Rb, and Cs, and examples of the alkaline earth metals include Ca, Sr, and Ba. further, an appropriate metal is selected from alkali metals, and another appropriate metal is also selected from alkaline earth metals, and the compounds thereof may be used together. Namely, the alkali metal and the alkaline earth metal may be contained together.
The metal compound of the invention preferably has a metal having a boiling point of 2000°C ar less, more preferably 600 to 2000°C, among the alkali metals or the alkaline earth metals. Particularly, it preferably has one or more of K, Na, Ca. E'urther, a metal compound containing Ca is fuxther preferably used.
xhe content of the metal compound is preferably set at 0.002 to 0.050 by weight based on the total weight of the welding wire.
This is for the following reason. When the content of the metal compound is less than 0.002 by weight, the effects of the metal compound are not sufficiently exerted.
Accordingly, the rate of ocGUrrence of the concentrated arc becomes small. As a result, ~t becomes difficult to attain the object of generating one droplet during one pulsed current flow period. This causes a difficulty in forming a good bead. when the content of the metal compound is larger than 0.050 by weight, the arc force becomes too strong. Thus, in the process of transfer of the droplet to the weld zone, the spattering phenomenon occurs centering on the droplet. As a result, outward roughness is generated certainly in the bead, but also i.n the sites other than the weld zone.
Further, in view of the implementation of one droplet during aria pulsed current flow period, the content of the metal compound is preferably 0.007 to 0.015% by weight based on the total weight of the welding wire.
A11 of these metals have lower boiling point and ionization potential than those of Ti which is the main component forming the base material. This is shown in Fig.
4. These metals are present in the cracks on the surface layer portion of the welding wire of the present invention.
Therefore, during MxG welding, prior to melting of the base material (xi) by the arc heat, these metals are present in the field of the arc in the form of ionized metal vapors.
For this reason, the generated arc becomes a concentrated arc, and stabilized.
Incidentally, the terra "concentrated arc" referred to xx~ the invention is defined as the following arc. This is described by reference to Fig. 5. A welding wire with a d~.ameter D is arc discharged, and the boundary portion of the arc is visually observed, The arc so blurred that the boundary portion cannot be identified is naturally not recognized as the concentrated arc, but referred to as a diffused arc.
Then, a truncated cane having a bottom face at a position lower than the lower end face of the welding wire by the diameter D of the welding wire is assumed. The arc in the case of 8 Z 60 °, where 9 denotes the angle formed between the $ide face and the bottom face of the truncated cone, is referred to as the concentrated arc. When it is set that B ~ 60 °, it is invariably possible to foam a droplet.
Since the welding wire of the invention has characteristics described abover it can be used for a wise feeder such as an apparatus for carrying out MIG welding.
The surface roughness of the welding wire surface of the invention is preferably 10 ~m or less in terms of the maximum height, which is referred to as Ry, from the viewpoint of improving the feedability of the welding wire in the wire feeder. Then, the oxygen enriched layer is farmed with the foregoing thicJmess and average oxygen concentration. This advantageously acts for obtaining the welding wire surface which has been adjusted in surface roughness to such a numerical value. The surface roughness of the welding wire is preferably set at 0.5 dun ar less in terms of the arithmetic average roughness Ra. Further, the lower limit values of the maximum height Ry and the arithmetic average roughnes$ Ra are riot particularly restricted, and are appropriately set in view of the tradeoff with the cost. Incidentally, the present inventors confirmed that ~y can be reduced to about 1.0 Eun, and that Ra to about 0.1 Vim. Incidentally, in this specification, the surface roughness denotes the one measured by the method specified in JIS: 80601 (ig~4).
In order to prevent the buckling of the welding wire in the wire feeder, the tensile strength of the welding wire is preferably 400 to 1500 MPa. When the tensile strength is less than 400 MPa, it becomes difficult to sufficiently prevent the buckling, When the tensile strength exceeds 1500 MPa, the flexibility of the welding wire is impaired, leading to deficiencies such as breakage and a difficulty in winding. The tensile strength of the welding wire can be controlled by, fox example, the adjustment of the surface reduction ratio of the cold working when the final stage of the wire drawing is carried out by cold working, or by the adju$tment of the annealing temperature and the time when annealing is subsequently carried out for strain removal. The tensile strength of the welding wire is more preferably 400 to 1200 Mfa.
EXAMPhES

The present invention is now illustrated in greater detail with reference to Examples and Comparative Examples, but it should be understood that the present invention is not to be construed as being limited thereto.
Experimental Examples 1 to 25 (1) Manufacture of welding wire Ti welding wire specified according to JTS H4670 (JIS Class 2, wire diameter 1.6 mm) was used for preparing Experimental Examples. Experimental Examples 1 to 22 each having a thick oxygen enriched layer were prepared by being subjected to a heat treatment in an air at a temperature of 750°C for 6 minutes to form an oxygen enriched layer on the surface. Experimental Examples 23 to 25 each having a thin oxygen enriched layer were prepared in the same manner as in Experimental Examples 1 to 2Z except that a temperature in a heat treatment was set at 450°C.
On the other hand, powders of carbonates of the alkali metals and the alkaline earth metals shown in Table 1 were prepared. As a lubricant, KOSHIN (a mixture of calcium hydroxide and calcium stearate, trade name, manufactured by KYOEISHA Chemical Co., Ltd.) was prepared.
By the use of the lubricant, a wire drawing processing was carried out cold, resulting in a welding wire with a wire diameter (Dw) of 1.0 mm. The surface reduction ratio at this step was 37.5.
When a metal other than calcium is allowed to be present alone with the oxygen enriched layer, the welding wire after wire drawing was once washed with LTGHT ChEAN
(detergent) to wash off KOS~rN. Then, the welding wire was passed through a wire drawing machine by the use of a powder of a prescribed metal carbonate with a surface rEduction ratio of 0~, so that the powder was packed in the surface cracks. Experimental Example 25 that does not have a metal with the oxygen enriched layer was prepared by merely being washed in the same manner as the above after wire drawing. Each resulting welding wire was measured for the metal content (~ by weight) of the metal compound, the thickness (Tw: dun) of the oxygen enriched layer, the tensile strength (MPa), the surface roughness, and the coefficient of dynamic friction according to the following specifications.
Metal content: It is analyzed by the inductively coupled plasma emission spectrometry.
Oxygen enriched layer: As described above, the cross section of the welding wire was mirror polished. The polished surface was subjected to area analysis on the oxygen concentration distribution by EPMA. The oxygen concentration at the cross section central part was taken as 1, and the region of the welding wire having an oxygen concentration of 1.2 or more (i.e., having an oxygen concentration of not less than 1.2 times as large as that of the central part) was taken as the oxygen enriched layer.
Average oxygen cpnGentration: As described above, the average value (5 measuring points) of the oxygen canGentxation in the oxygen enriched layer was determined, and it was taken as the average oxygen concentration of the oxygen enriched layer.
Thickness of the oxygen enriched layer: It was taken as the average value of the thickness of the oxygen enriched layer.
Tensile strength: A 100-mm long test piece was cut out Pram each welding wire, and pulled at a cross head speed of 1.0 mm/min by means of an Instron type tensile tester. Thus, a stress-strain curve was determined, and a maximum stress value was read as the tensile strength.
Surface Roughness: A roughness curve was determined with a method specified by JIS B0601 (1994), in accordance with an embodiment in which the assessment length was set along the longitudinal direction ofi the welding wire. The values of the maximum height Ry (gym) and the arithmetical average roughness Ra (~.un.) were respectively read therefrom.
Coefficient of dynamic friction: This was measured by using a 8owden~Leben-type friction tester. Specifically, a welding wire sample was set on a sample table, a steel material for pressing was stacked thereon from above, and the sample table was moved at a constant velocity while pressing the steel material by a weight with a given weight.
The frictional force at this step was detected by means of a strain gauge type load sensor.
The foregoing results are summarized and shown zn Table 1.

..
ca N N N N N N N N N N N N
E

O O O G O O O o o O O O

N ~ ~ 0 0 0 0 o d o o a o 0 a ~ r c~ ~ r- r ~ r ~ ~ r r v C
~ er d' ~r v d' ~r ~r ~ v er ~ 'a E
O

r r r ~ ~ ~ r r ~ r ,r t-C O G o 0 o O O O o c O

d .~
w Q

U

O O o O O c5 O O O C7 O o O
~ C O O O O t~ ~ p O O O o O O O 00 a0 CO do 00 00 O o0 O O O O O O o O p p O O p a0 c~ ao ao 00 00 cti o o ai atio0 c ~o c C O d O O O 4 O o o p O

N N N N CV N N N N N N N
C

.C
d ~~

C d C

N

d C
~

O t5 O O C 4 O O O O Q O

ao m ad co ~o o as ac ap ao 0 00 r o sn --, o ec~~ ~ ~n N ~ us o, o 4 0 ~ O ~ o 0 is ~C
~_ E
~

~ ~ Q O 0 r o Y Y p1 m 'C 0 N

a~ ~ o, o d ~

a '~ o o ~ ~ vi E .
~ .

.. _ ' o ~ ~ r, c -~ z Y ~ C1 U V? m o _ p v O
~

W ca is ~ Z V U

aW
~ o 0 0 O O a a"5 ~

O 0 ~; O v : o s- ~ ~ r r r r r s- r ~ r W
v . .~..w~ ~ W ~ ~.. ~ .~. ,~ _c0_c9 a- N of ~ u9 l0 i~ CD O r N
C G C C C ~C ~ ~ ~ C C C
~ r T

E a E E E E E E E E E E
N a '~ o. o_ o. a a a n a a c '~ ~ 'w 'w 'C c 'c 'C 'C w 'c 'C
E ~ E E E E E E ~ ~

o~ as of N ~ ro a~toa~ m N m a~
ev m t ~p ~ ca wt'~ca m w ~ i ~ ~ w 'u'~
'u5'u~ ~ tip u'~
t~

H

N N N N iV c~ C~ ~ N N N tV N

C? O O o C O G O C O C O O

O o O O O O O Q O O O O 4 r r t- ~ r r r .~-~~ r r r r d~ 'd' ~1'ef''d'd~ ~ ~d'~1 d' d~ ~

r r ~ c- r~ r r y~ ~ r ~ r O O O Q G Ci O O p O O O C

O O O O O O p O O G O O~ O
~ CO CD

op a0 0D 00 Cd ap a0 O Q 4 O O O O O, C, O ao c0 aD, a0 aD 00 CO 0C)a0 ~ 00 CJ iG O O O

O O O 4 4 C O 4 ~ C O O Q
N N N N N N N N N N N N N

M

r7 O O 8 O G7 O O O O O ao 00 ~

0D G7 api00 EO Ib a0 00 00 00 O O O

O C _O tt!p Q O t17 C o O C1 p O O G
r O r U V ~ m U U m V ~ ~, 0 ~ o N N ~ o o is eo id ~ Y

Q o O ~ Z V

0 0 o 0 0 , 0 Z Z Z ~ ~ ~ ~G

o o, o, o, o ca o, ~ o o o ~

r- r r e- r ~ r t- r r ~ w v-ca ~ ~ c~ to ,~ ~ ca is ~ c~ co Tn M ~ ~!7 tp i~ CO W O r ~ rs d' 47 g r c C ~ ~ C C ~ G ~E C
r- r r- A r N N N N N

Q7 W ~ m m 47 47 G~ G) 07 d N G?
~! ~1 d C~ ~ ~o _m G7 E'd ~ E~ d Q~
~ E E Ec E

Ea Eo. Eo.Ea ~ . E c . L a ~ m ~w ~m o ar3 ~a~. ~ ~a~ ~m o. o, o, E n a ~ ~ ~ ~m m' ~ ~
~ 4 s~. fl. W n n ~ ~ n 0.

uxr~uu u~ ~ 'u~~ u'~u~Wi ux t~~u'~~u~~
~

(2) MIG welding MIG weldings under the conditions shown in Table 2 were carried out using each welding wire shown in Table 1.
Tn these MIG weldings, Digital Pulse CPDP-350 (manufactured by l7A.xI~EN Corpoxatiox~) was used as a welding electric power source.
Tab~.e 2 Welding current 80 A

Arc voltage 18 V

Pulse peak current 320 A

Pulse peak time 1.2 ms Base current 30 A

Rise time 0.4 ms Fall time 0.8 ms Welding speed 600 mmlmin Shielding gas amount Pure Ar, 15 Umin After shielding gas Pure Ar, 40 Umin amount Back shielding gas amountPure Ar, 10 Umin Conduit Tube made of metal, length 1500 mm The f8edability of the welding wire during welding, the stability of the arc, and the amount of spatters generated were evaluated according to the following specifications. The shapE of the bead formed, and the tensile strength and the elong~.t~.on of the joint portion were evaluated according to the follow~.ng specifications.
Feedabi.lity of the welding wire: The case where no buckling of the wire had been generated during welding was rated as "TEA", and the case where the buckling of the wire had been generated was rated as "B".
Stab~.lity of arc: The state of the generated arc was photographed by means of a High Speed Camera System Model 1000 (one image / 1 ms; manufactured by Nao znc.), over 5 seconds after 2 seconds to 7 seconds from the start of welding. xhus, the stability of the arc was rated from the image.The case where the rate of occurrence of the concentrated arc had been 80~ or more was rated as "AA", the case of 65 to 60~ was rated as "A", and the case of lower than 65~ was rated as "B".
Amount of spatters generated: Amount of sputters generated was rated by an amount of sputters having a diameter of 1 mist or more, which were deposited on the base metal, with reference to a welding length of 100 mm. After the completion of welding, the state in which spatters had been deposited on the base metal to be welded was visually observed. The case where no spatter having a diameter of 1 mm or mare had been depos~.ted was rated as "AA", and the case where 1 to 10 spatters having the diameter range had been deposited was rated as "A", arid the case where 11 or more spatters having the diameter range had been deposited was rated as "8".
Bead shape: After welding, the bead was visually observed. The case where the width had been uniform and the outward appearance had been smooth was rated as ".~1.~1", az~d the case where irregularities of the width of the bead had been small was rated as "A", and the case where irregularities of the width of the bead had been large was rated as "g".
Tensile strength of the joint portion: xhe case of a measured value of 340 MPa or more was rated as "AA", and the case of a measuxed value equal to, or smaller than this was xated as "B".
The foregoing results are summarized and shown in Table 3.

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H

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N

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L

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G.
N

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m .3 O

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b N

td m m V, r .~ ~ .~~..~ .~ ~ ~ ~ r~ ~
C N f9 ~' Vii!~ ('~Gp ~7 ~ T' C c C c c ~ ~
~

N m ar p7 u~ m c c ~ c m ~ ~ ~ m ~ d m m N d~ m ~ m d m C ~ '~ '~ ~ C ~ 'C 'C
~ ~ ~ E ~ ~ E ~

o_~~.~ ~.~n.~a c.~~' o.~' ' ~ ~ ~
' ~

u~ ~ u ut u~ si u~ ts~
u !

m m H

x dd 4d ~d ~ ~ ~ ~ d ~ a ~t m dd ~ ~d ~ ~d ~ ~d ~ "~ ~ ~

N_ G
Q

E

d woc",~c~~~ c~u~ ~~ ,~r..~qo4~a~~go ~~r ~N ,f~c~~~ n"Wrs ~ ~ r C ~ C C r ~ ~ C ~ ~ c ,p r s- a~ r r- ~~ N N N N N N
d N 0~ v N m 1 d1 N N

N G1 m a7 m N dy ~ m A1 N m q 91 m N ~

. ' ' ' , _ ~

o.~~.~ ~~ ~ d .~am ~.~ ~ o.~ .~~~ ~ a~ v.~ i ' o ' ~ ' o w ' ~~ ~

~ixwu~ ,.,.,t'~ u~ ~w '~u)'~,~~~ ~ ~ ,~w ~ x ~,,, u'f ~u As apparent from Tables 1 and 3, when a welding wire of Experimental Example having an alkali metal or an alkaline earth metal is used, the arc is stabilized, and the bead shape becomes favorable in any case- Further, in Experimental Examples 1 to 20 in each of which the welding wire contains a metal compound in a proper amount, the effects are more excellent.
However, when the welding wire of Experimental Example 25 which does not have a metal compound at all, and in which the thickness of the oxygen enriched layer is small, is used, the generation of the concentrated arc is reduced, and the amount of spatters also increases, resulting in a degraded bead shape.
Incidentally, the photograph showing the shape of the bead formed by the use of the welding wire of Experimental Example 6 is shown in Fig. 6. As apparent from the drawing, use of this welding wire enables the formation of a bead with a uniform width and also in a uniformly overlying form, and good in both the outward appearance and the shape.
Experimental Examples 26 to 41 welding wires were manufactured in the same manner as in Experimental Examples 1 to 25, except that Ti alloy materials having constituents shown in Table 4 were used as the base materials and that the alkali metals and the alkaline eaxth metals were used according to the type and contents shown in Table 4.

H N N N N N CV N N N C~ CV
v O O o 9 O t7 O O O O O
~t 4J ~ ~ ~ o 4 O ~ O 6 O O O O o T t- T
_U
O ~ V' tt ~ '~ '~T '~l' eh st ~ V' V r T r' T r r Y"
O CJ C O O O C1 0 d 0 0 U o o Q 4~ ~ o q ~ i° °o r r r ..- t~ 1' r r m~
a0 try, o O o O 6 o a0 of 4 O o a0 aC ep 0J oo a0 o O a7 H X.
N tOV N ~ c~~ N COV N cOV N
e2 m a7 e0 o c7 O o O o ep a0 O
t'; O a0 00 aD ap a0 a0 o G CO
Q' O m m~~ oo~o_~__~o_°doc°o Q Q Q ~ O O ~ ø ~ O
O O ~ d ~ O Q 4 p d 4 c J.7 j< ~ ~ ~ SC ~ SG tj SC ~ SC
R
o~oooo,c?ooo,o r ~ r% r v- r~ ~ T
'v .....
N' N
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~r c~ '~ v~ a v 'Q > ? .
2 a.
, ~ ,o ~ ~ c m ~ ~ o ';~ ~ ~ ~ o o ~ ~ ';i o _, ~ ~ a~
N N ~ ~ ~ ~ ~ ~" ~ N
i E= (=
GN G~ ~~ .~.~N ~~ GN ~~j C~ C~ C~'~7 o~ m m d as as m ca as of m m as as m m m ~r m 'EC G ~ G ~ ~~ ~ ~ ~ ~ E ~ E ~ E' H

N N ht N t~
O o O Q

o O 4 O S5 r t- r ~C s~'V V_' V_' . .,..
r C o 0 o p h O m c0 c? O

alb G G OJ CD

N N N N N

O t4 OD 6 0 Q S? a! o7 N

4' o v $ ~ o O G o 0 0 v z m Y.

0 o c v o Y- Y e~ r ~

O
N r Y

C o N

N

n C
~t p, By the use of the welding Wires of Experimental Examples 26 to 41, MIG welding was carried out. The results are shown in Table 5.

C

o>

a' i n m g.

tit ~d ~ ~ a ~ d ~ Q

c om ~ ~ '~ ~d ~ ~ dd ~ dd dd a C

-a U

.~-_T

C_ 'O

'~

m a~

~G ~0 l~ ~ ~ ~ ,~ ,l~~ t~
i0 ~. W Of p r N CY!d- Ip ~ ~ C c ~ c C ~ e0 M
N N N N t"7t'7t'7 c0 91 ~ ~ ~ ~ ~ ~ ~ ~ N
m d1 d~ d~ o m m ~ ~ ~ ~ ~ d ~ .~ ~
W t~Q R ~ N ~ tie 1~0 '~ '~ ,~ ,~ '~ ,,u'~Is~ ,~ t'~au to ti5u1 w u~ u'~ t~

N

a Q ~ ~d a ~ ~ a a a C G C
M M

N a1 ~b ~ ~

~ Q ~ ~
~

Q. Q u'~wO. O.
~ i~~ U~ '~u'~
~i~ X

u U

Experimental Examples 42 to 53 Welding wires were manufactured in such a manner that the base material was made of JZS Class 2 as in the case of Example 1-24 and that the alkali metals and the alkaline earth metals were used according to the type and contents shown in Table 6.

l0 N N N N N N N N t~(h1 N N
~

V ~ O O O O Q G , O O O O Q
~ ~ O

C

> n > 5~ C7 ~1 C O O O O O t~ O O O
p ~

W .' r" r r r r r r ~ s-~r r r wr V
C

'ta tp CD to Sd t0 cD (D tp cp tD ~ cD
N
O

c r ~ ~r r ~- r r ~ r r ~ r-~ O O O O O O o o O Q C O

U
o a~
~
.., 0 0 0 0 0 0 0 ~ 0 0 0 0 h. A T~ 1r.i'-h~ 1'~1~ 1'.!~ t'.I~

D

M M c~! crfc~SM M M M M

cc m cc ca m co <o ~ cc v o H cc ..

~

_a .c .

~ ~? ~? 4 O O O O O O O Q Q
C

N N N N N N N N N N N N

L

O

a ~ ~~

x o o v o 0 0 o Q Q o a o r r r r r r r r T '~' Z- T

=A
C O O

GG

C 1." p Q O r ~? O O ~ ~ ~ O G
~ d "

N ~ d O O ~ o O G Q Q O O
~

~ ~ Y

m~ ~ Z V U m m Q o Y U
~ O o _ E""
to Y Y

L
~

_ m m s- ~~ ~- ~~ ~~ r r r r r r r C.~rC.~ W :.n9,rte..yr9 w .~..~~.rr~ +~rw ,p, ~ ~' ~' ~ ~ ~ 'a'u7 ~ ~ It7 C C C C C C C C

C C C c 41 C7 C~ d ~ m G1 ~ m a~ m d N N W 41 Q~ ~ G~ 07 07 p~ 4? a7 E E E aE E E E E ~ ~ E E
a. a a a 4 c~ a a a a a N _~ L 'c6'~ 'c 'c 'c '~ . ~ '~ '~5 E E E E E E E 'c E E E
E
' '~ ~ ~~ u~ ~~ ~~ ~~ u~ ~ ~ ~ a ~
' ~ ~ ~ ~

u~ u u , u , u u u u 3 The welding wires of Experimental.trxamples 42 to 53 was mounted in a thermal spray unit of a wire feeder, and fed to a welding gun to be thermally sprayed on the surface of an article to be processed. The feedability of the welding wire and the stability of the arc at this step were examined. The results ar~ shown, in Table 7.
Table 7 Evaluation Feedability ability of of welding arc wire Experimental Example AA AA

Experimental Example AA AA

Experimental Example AA RA

Experimental Example AA AA

Experimental Example AA AA

f=xperimental ExampleAA AA

Experimental Example AA AA

Experimental Example AA AA

Experimental Example AA AA

Experimental Example AA AA

Experimental F~campleAA A

Experimental Example AA A

The boiling point and the ionizat~.on potential of az~
alkali metal or an alkaline earth metal are lower than the melting point and the ionization potential of Ti, respectively. Therefore, prior to melting of the k~ase material (Ti ox Ti alloy) by the arc heat, the alkali metal or the alkaline earth metal is present in the forza of an ionized metal vapor in the field of the generated arc. For this reason, the generated arc column becomes stable, resulting in a concentrated arc. Further, the oxygen in the oxygen enriched layer also stabilize the generated arc, and at the same time, reduces the surface tension of the welding wire surface, so that generated droplets become more likely to be released from the welding wire tip.
These enable one droplet to transfer to the weld zone in one pulsed cuxxent flow period in MIG welding with reliability. As a result, the formation of the bead good in shape and outwaxd appearance becomes possible.
With the welding wixe of the present invention, the resulting arc becomes the concentrated arc, and one droplet transfer can be achieved during one pulsed current flow pexiod with reliability. Therefore, the shape and the outward appearance of the bead at the weld zone become excellent. This welding wire is useful as a wire rod for welding in MTG welding of a Ti material, or as a wire rod for thermal spraying at the time of Ti thermal spraying.
While the present invention has been described in detail arid with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
The present application is based on Japanese Patent Application No. 2004-300497 filed on October 14, 2004, and the contents thereof are incorporated herein by reference.

Claims (9)

1. A welding wire comprising Ti or a Ti alloy, wherein the welding wire has: an oxygen enriched layer on a surface thereof; and a metal compound having at least one metal selected from the group consisting of alkali metals and alkaline earth metals.

2. The welding wire according to claim 1, wherein the content of the metal compound is 0.002 to 0.050% by weight based on the total weight of the welding wire.

3. The welding wire according to claim 1, wherein the welding wire has cracks on the surface, and the metal compound is present in the cracks.

4. The welding wire according to claim 1, wherein the boiling point of the metal is 2000°C or less.

5, The welding wire according to claim 1, wherein the metal compound is a metal compound containing Ca.

6. The welding wire according to claim 1, wherein the value of Tw/Dw is 0.3 × 10 -3 to 1 × 10 -1, wherein Tw represents the thickness of the oxygen enriched layer, and Dw represents the wire diameter of the welding wire, and wherein the average oxygen concentration of the oxygen enriched layer is not less than 1% by weight.

7. The welding wire according to claim 6, wherein the average oxygen concentration of the oxygen enriched layer is 1 to 40% by weight.

8. The welding wire according to claim 1, wherein the surface roughness of the welding wire is µm or less in terms of the surface roughness expressed as Ry specified according to JIS B0601.

9. The welding wire according to claim 6, wherein the value of Tw/Dw is 1 × 10 -3 to 50 × 10 -3, wherein Tw represents the thickness of the oxygen enriched layer, and Dw represents the wire diameter of the welding wire, and wherein the average oxygen concentration of the oxygen enriched layer is 1 to 30% by weight.